U.S. patent application number 10/005830 was filed with the patent office on 2003-03-20 for photodegradation-resistant electrodepositable coating compositions and processes related thereto.
Invention is credited to Anderton, Christian A., Eswarakrishnan, Venkatachalam, Karabin, Richard F., Kollah, Raphael O., McCollum, Gregory J., Poole, James E., Scott, Mattew S., Webster, Geoffrey R. JR., Zawacky, Steven R., Zwack, Robert R..
Application Number | 20030054193 10/005830 |
Document ID | / |
Family ID | 27357965 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030054193 |
Kind Code |
A1 |
McCollum, Gregory J. ; et
al. |
March 20, 2003 |
Photodegradation-resistant electrodepositable coating compositions
and processes related thereto
Abstract
The invention provides a process for coating a substrate
including electrodepositing an electrodepositable composition on
the substrate, heating the coated substrate to cure the coating
thereon, applying over the cured electrodeposited coating one or
more pigment-containing coating compositions and/or one or more
pigment-free coating compositions to form a top coat thereover, and
heating the coated substrate to cure the top coat. The
elecrodepositable composition is formed from an ungelled cationic
salt group-containing resin where the salt groups are formed from
pendant and/or terminal amino groups, and an at least partially
blocked aliphatic polyisocyanate curing agent. Also provided is a
photodegradation resistant multi-layer composite coating of a
primer layer formed from the electrodepositable composition and a
top coat thereover, where the composite coating exhibits
substantially no interlayer delamination upon concentrated solar
spectral irradiance exposure equivalent to two years outdoor
weathering. The invention further provides improved processes for
electrophoretically coating a substrate.
Inventors: |
McCollum, Gregory J.;
(Gibsonia, PA) ; Anderton, Christian A.;
(Cranberry Twp., PA) ; Eswarakrishnan, Venkatachalam;
(Allison Park, PA) ; Karabin, Richard F.; (Ruffs
Dale, PA) ; Kollah, Raphael O.; (Pittsburgh, PA)
; Poole, James E.; (Gibsonia, PA) ; Scott, Mattew
S.; (Pittsburgh, PA) ; Webster, Geoffrey R. JR.;
(Gibsonia, PA) ; Zawacky, Steven R.; (Pittsburgh,
PA) ; Zwack, Robert R.; (Allison Park, PA) |
Correspondence
Address: |
PPG Industries, Inc.
One PPG Place
Pittsburgh
PA
15272
US
|
Family ID: |
27357965 |
Appl. No.: |
10/005830 |
Filed: |
November 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60266577 |
Feb 5, 2001 |
|
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60266576 |
Feb 5, 2001 |
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Current U.S.
Class: |
428/626 ;
204/486; 204/487 |
Current CPC
Class: |
C09D 5/4488 20130101;
B05D 7/52 20130101; C09D 5/4434 20130101; B05D 1/007 20130101; B05D
7/546 20130101; Y10T 428/12569 20150115; B05D 7/56 20130101; C09D
5/4473 20130101 |
Class at
Publication: |
428/626 ;
204/486; 204/487 |
International
Class: |
C25D 013/00 |
Claims
Therefore, we claim:
1. In a process for coating an electroconductive substrate
comprising the following steps: (a) electrophoretically depositing
on the substrate a curable electrodepositable coating composition
to form an electrodeposited coating over at least a portion of the
substrate, the electrodepositable coating composition comprising a
resinous phase dispersed in an aqueous medium, said resinous phase
comprising: (1) one or more ungelled active hydrogen-containing,
cationic amine salt group-containing resins which are
electrodepositable on a cathode, and (2) one or more at least
partially blocked aliphatic polyisocyanate curing agents; (b)
heating the coated substrate to a temperature and for a time
sufficient to cure the electrodeposited coating on the substrate;
(c) applying directly to the cured electrodeposited coating one or
more pigment-containing coating compositions and/or one or more
pigment-free coating compositions to form a top coat over at least
a portion of the cured electrodeposited coating; (d) heating the
coated substrate of step (c) to a temperature and for a time
sufficient to cure the top coat, the cured top coat having at least
0.1 percent light transmission measured at 400 nanometers, the
improvement comprising the presence in the curable
electrodepositable coating composition of one or more cationic
amine salt group-containing resins wherein the amine salt groups
are derived from pendant and/or terminal amino groups having the
following structures (I) or (II):--NHR (I) 9wherein the R groups
represent H or C.sub.1 to C.sub.18 alkyl; R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 are the same or different, and each
independently represents H or C.sub.1 to C.sub.4 alkyl; and X and Y
can be the same or different, and each independently represents a
hydroxyl group or an amino group.
2. The process of claim 1, wherein the cured top coat has from 0.1
to 50 percent light transmission measured at 400 nanometers.
3. The process of claim 1, wherein the cationic amine salt groups
of resin (1) are derived from one or more pendant amino groups
having the structure (II), such that when the electrodepositable
coating composition is electrodeposited and cured, at least two
electron-withdrawing groups are bonded in the beta-position
relative to substantially all of the nitrogen atoms
4. The process of claim 1, wherein at least three
electron-withdrawing groups are bonded in the beta-position
relative to substantially all of the nitrogen atoms
5. The process of claim 1, wherein the electron-withdrawing groups
are selected from an ester group, a urea group, a urethane group,
and combinations thereof.
6. The process of claim 1, wherein the active hydrogen-containing,
cationic amine salt group-containing resin (1) comprises a polymer
selected from at least one of a polyepoxide polymer, an acrylic
polymer, a polyurethane polymer, a polyester polymer, mixtures
thereof and copolymers thereof.
7. The process of claim 1, wherein the resin (1) comprises a
polyepoxide polymer.
8. The process of claim 1, wherein the resin (1) comprises a
polyepoxide polymer and an acrylic polymer.
9. The process of claim 8, wherein the polyepoxide polymer is
present in the electrodepositable coating composition in an amount
ranging from 10 to 90 weight percent, based on total weight of
resin solids present in the electrodepositable coating
composition.
10. The process of claim 1, wherein the resin (1) comprises
cationic amine salt groups derived from at least one compound
selected from ammonia, methylamine, diethanolamine,
diisopropanolamine, N-hydroxyethyl ethylene diamine,
diethylenetriamine, and mixtures thereof.
11. The process of claim 1, wherein the resin (1) is present in the
electrodepositable coating composition in an amount ranging from 20
to 80 weight percent, based on total combined weight of resin
solids of the resin (1) and the curing agent (2) present in the
electrodepositable coating composition.
12. The process of claim 1, wherein the curing agent (2) comprises
at least one at least partially blocked polyisocyanate selected
from 1,6-hexamethylene diisocyanate, isophorone diisocyanate,
bis-(isocyanatocyclohexyl)methane, polymeric 1,6-hexamethylene
diisocyanate, trimerized isophorone diisocyanate, norbornane
diisocyanate and mixtures thereof.
13. The process of claim 12, wherein the curing agent (2) comprises
one or more fully blocked polyisocyanates.
14. The process of claim 12, wherein the curing agent (2) comprises
a fully blocked polyisocyanate selected from a polymeric
1,6-hexamethylene diisocyanate, isophorone diisocyanate, and
mixtures thereof.
15. The process of claim 1, wherein the polyisocyanate curing agent
(2) is at least partially blocked with at least one blocking agent
selected from a 1,2-alkane diol, a 1,3-alkane diol, a benzylic
alcohol, an allylic alcohol, caprolactam, a dialkylamine, and
mixtures thereof.
16. The process of claim 15, wherein the polyisocyanate curing
agent (2) is at least partially blocked with at least one
1,2-alkane diol having three or more carbon atoms.
17. The process of claim 15, wherein the polyisocyanate curing
agent (2) is at least partially blocked with at least one blocking
agent selected from a 1,2-alkane diol having more than three carbon
atoms, and a benzylic alcohol, and mixtures thereof.
18. The process of claim 17, wherein the polyisocyanate curing
agent (2) is at least partially blocked with 1,2-butanediol, benzyl
alcohol, and mixtures thereof.
19. The process of claim 1, wherein the polyisocyanate curing agent
(2) is present in the electrodepositable coating composition in an
amount ranging from 20 to 80 weight percent, based on total
combined weight of resin solids of the resin (1) and the curing
agent (2) present in the electrodepositable coating
composition.
20. The process of claim 1, wherein the coated substrate of step
(a) is heated to a temperature ranging from 250.degree. to
400.degree. F. (121.1.degree. to 204.4.degree. C.).
21. The process of claim 1, wherein the electrodepositable coating
composition is free of lead compounds.
22. The process of claim 1, wherein the coated substrate of step
(a) is heated to a temperature of 360.degree. F. (180.degree. C.)
or less for a time sufficient to cure the electrodeposited coating
on the substrate.
23. The process of claim 1, wherein the coated substrate of step
(a) is heated in an atmosphere having 5 parts per million or less
of NO.sub.x to a temperature and for a time sufficient to cure the
electrodeposited coating on the substrate
24. The process of claim 23, wherein the coated substrate of step
(a) is heated in an atmosphere having 1 part per million or less of
NO.sub.x to a temperature and for a time sufficient to cure the
electrodeposited coating on the substrate
25. The process of claim 1, wherein the electrodepositable coating
composition further comprises at least one source of a metal
selected from rare earth metals, yttrium, and mixtures thereof,
present in an amount of 0.005 to 5 percent by weight metal, based
on total weight of resin solids present in the composition.
26. A process for forming photodegradation-resistant multi-layer
coating on an electroconductive substrate comprising the following
steps: (a) electrophoretically depositing on the substrate a
curable electrodepositable coating composition to form an
electrodeposited coating over at least a portion of the substrate,
the electrodepositable coating composition comprising a resinous
phase dispersed in an aqueous medium, said resinous phase
comprising: (1) one or more ungelled cationic polymers which are
electrodepositable on a cathode, and (2) one or more at least
partially blocked aliphatic polyisocyanate curing agents; (b)
heating the coated substrate in an atmosphere having 5 parts per
million or less of NO.sub.x to a temperature and for a time
sufficient to cure the electrodeposited coating on the substrate;
(c) applying directly to the cured electrodeposited coating one or
more pigment-containing coating compositions and/or one or more
pigment-free coating compositions to form a top coat over at least
a portion of the cured electrodeposited coating; and (d) heating
the coated substrate of step (c) to a temperature and for a time
sufficient to cure the top coat, the cured top coat having at least
0.1 percent light transmission measured at 400 nanometers.
27. The process of claim 26, wherein the cationic polymer comprises
cationic amine salt groups.
28. The process of claim 27, wherein the cationic amine salt groups
are derived from pendant and/or terminal groups having the
structure (I) or (II): 10wherein the R groups represent H or
C.sub.1 to C.sub.18 alkyl; R.sup.1, R .sup.2, R.sup.3, and R.sup.4
are the same or different, and each independently represents H or
C.sub.1 to C.sub.4 alkyl; and X and Y can be the same or different,
and each independently represents a hydroxyl group or an amino
group.
29. The process of claim 27, wherein the cationic amine salt groups
are derived from one or more pendant amino groups having the
structure (II), such that when the electrodepositable coating
composition is electrodeposited and cured, at least two
electron-withdrawing groups are bonded in the beta-position
relative to substantially all of the nitrogen atoms.
30. The process of claim 29, wherein the electron-withdrawing
groups are selected from an ester group, a urea group, a urethane
group, and combinations thereof.
31. The process of claim 26, wherein the top coat has from 0.1 to
50 percent light transmission as measured at 400 nanometers.
32. The process of claim 26 wherein the polymer (1) is selected
from at least one of a polyepoxide polymer, an acrylic polymer, a
polyurethane polymer, a polyester polymer, copolymers thereof, and
mixtures thereof.
33. The process of claim 32, wherein the polymer (1) comprises a
polyepoxide polymer.
34. The process of claim 32, wherein the polymer (1) comprises a
polyepoxide polymer, an acrylic polymer, and mixtures thereof.
35. The process of claim 34, wherein the polyepoxide polymer is
present in the electrodepositable coating composition in an amount
ranging from 10 to 90 weight percent, based on total weight of
resin solids present in the electrodepositable coating
composition.
36. The process of claim 26, wherein the polymer (1) comprises
cationic amine salt groups derived from at least one compound
selected from ammonia, methylamine, diethanolamine,
diisopropanolamine, N-hydroxyethyl ethylenediamine,
diethylenetriamine, and mixtures thereof.
37. The process of claim 26, wherein the polymer (1) is present in
the electrodepositable coating composition in an amount ranging
from 20 to 80 weight percent, based on total combined weight of
resin solids of the resin (1) and the curing agent (2) present in
the electrodepositable coating composition.
38. The process of claim 26, wherein the curing agent (2) is
selected from 1,6-hexamethylene diisocyanate, isophorone
diisocyanate, bis-(isocyanatocyclohexyl)methane, polymeric
1,6-hexamethylene diisocyanate, trimerized isophorone diisocyanate,
norbornane diisocyanate, and mixtures thereof.
39. The process of claim 26, wherein the curing agent (2) comprises
one or more fully blocked polyisocyanates.
40. The process of claim 39, wherein the curing agent (2) comprises
at least one fully blocked polyisocyanate selected from polymeric
1,6-hexamethylene diisocyanate, isophorone diisocyanate, and
mixtures thereof.
41. The process of claim 26, wherein the polyisocyanate curing
agent (2) is at least partially blocked with at least one blocking
agent selected from a 1,2-alkane diol, a 1,3-alkane diol, a
benzylic alcohol, an allylic alcohol, caprolactam, a dialkylamine,
and mixtures thereof.
42. The process of claim 41, wherein the polyisocyanate curing
agent (2) is at least partially blocked with at least one
1,2-alkane diol having three or more carbon atoms.
43. The process of claim 41, wherein the polyisocyanate curing
agent (2) is at least partially blocked with at least one blocking
agent selected from a 1,2-alkane diol having more than three carbon
atoms, a benzylic alcohol, and mixtures thereof.
44. The process of claim 43, wherein the polyisocyanate curing
agent (2) is at least partially blocked with a blocking agent
selected from 1,2-butanediol, benzyl alcohol, and mixtures
thereof.
45. The process of claim 26, wherein the polyisocyanate curing
agent (2) is present in the electrodepositable coating composition
in an amount ranging from 20 to 80 weight percent, based on total
combined weight of resin solids of the resin (1) and the curing
agent (2) present in the electrodepositable coating
composition.
46. The process of claim 26, wherein the coated substrate of step
(a) is heated to a temperature ranging from 250.degree. to
400.degree. F. (121.1.degree. to 204.4.degree. C.).
47. The process of claim 46, wherein the coated substrate of step
(a) is heated to a temperature of 360.degree. F. (180.degree. C.)
or less for a time sufficient to cure the electrodeposited coating
on the substrate.
48. The process of claim 26, wherein the electrodepositable coating
composition is free of lead compounds.
49. The process of claim 26, wherein the electrodepositable coating
composition further comprises at least one source of metal selected
from rare earth metals, yttrium, and mixtures thereof, present in
an amount of 0.005 to 5 percent by weight metal, based on the total
weight of resin solids in the electrodepositable composition.
50. A process for forming a photodegradation-resistant multi-layer
coating on an electrically conductive substrate comprising the
following steps: (a) electrophoretically depositing on the
substrate an aqueous, curable electrodepositable coating
composition to form an electrodeposited coating over at least a
portion of the substrate, the substrate serving as a cathode in an
electrical circuit comprising the cathode and an anode, the cathode
and the anode being immersed in the aqueous electrodepositable
coating composition, wherein electric current is passed between the
cathode and the anode to cause the coating to be electrodeposited
over at least a portion of the substrate, the electrodepositable
coating composition comprising a resinous phase dispersed in an
aqueous medium, said resinous phase comprising: (1) one or more
ungelled cationic amine salt group-containing polyepoxide resins
which are electrodepositable on a cathode, and (2) one or more at
least partially blocked aliphatic polyisocyanate curing agents; (b)
heating the coated substrate at a temperature and for a time
sufficient to cure the electrodeposited coating on the substrate;
(c) applying directly to the cured electrodeposited coating one or
more pigment-containing coating compositions and/or one or more
pigment-free coating compositions to form a top coat over at least
a portion of the cured electrodeposited coating; and (d) heating
the coated substrate of step (c) to a temperature and for a time
sufficient to cure the top coat, the cured top coat having at least
0.1 percent light transmission as measured at 400 nanometers,
wherein the improvement comprises the inclusion in the circuit of a
non-ferrous anode.
51. The process of claim 50, wherein the aqueous electrodepositable
coating composition is in the form of an electrodeposition bath
comprising less than 10 parts per million soluble iron.
52. The process of claim 50, wherein the coated substrate of step
(a) is heated in an atmosphere having 5 parts per million or less
of NOx.
53. The process of claim 52, wherein the coated substrate of step
(a) is heated in an atmosphere having 1 part per million or less of
NOx.
54. The process of claim 50, wherein the cured electrodeposited
coating of step (b) comprises less than 10 parts per million
soluble iron.
55. The process of claim 50, wherein the curable electrodepositable
coating composition further comprises a material selected from at
least one of a hindered amine light stabilizer, an antioxidant, an
ultraviolet light absorber, and mixtures thereof.
56. In a process for coating an electroconductive substrate
comprising the following steps: (a) electrophoretically depositing
on the substrate a curable electrodepositable coating composition
to form an electrodeposited coating over at least a portion of the
substrate, the electrodepositable coating composition comprising a
resinous phase dispersed in an aqueous medium, said resinous phase
comprising: (1) one or more ungelled active hydrogen-containing,
cationic amine salt group-containing resins which are
electrodepositable on a cathode, said resins selected from at least
one of an acrylic polymer, a polyepoxide polymer, and mixtures
thereof, and (2) one or more aliphatic polyisocyanate curing agents
at least partially blocked with one or more blocking agents
selected from a 1,2-alkane diol having at least three carbon atoms,
a benzylic alcohol, and mixtures thereof; (b) heating the coated
substrate to a temperature ranging from 250.degree. to 400.degree.
F. (121.1.degree. to 204.4.degree. C.) for a time sufficient to
cure the electrodeposited coating on the substrate; (c) applying
directly to the cured electrodeposited coating one or more
pigment-containing coating compositions and/or one or more
pigment-free coating compositions to form a top coat over at least
a portion of the cured electrodeposited coating; (d) heating the
coated substrate of step (c) to a temperature and for a time
sufficient to cure the top coat, the cured top coat having 0.1 to
50 percent light transmission as measured at 400 nanometers
wavelength, the improvement comprising the presence in the curable
electrodepositable composition of cationic amine salt groups which
are derived from one or more pendant and/or terminal amino groups
having the following structure (II): 11wherein R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 are the same or different, and each
independently represents H or C.sub.1 to C.sub.4 alkyl; and X and Y
are the same or different, and each independently represents a
hydroxyl group or an amino group, characterized such that when the
electrodepositable coating composition is electrodeposited and
cured, at least two electron-withdrawing groups are bonded in the
beta-position relative to substantially all of the nitrogen atoms,
said electron-withdrawing groups selected from an ester group, a
urea group, a urethane group, and combinations thereof.
57. A photodegradation-resistant multi-layer composite coating
comprising: a cured primer coating layer over at least a portion of
an electroconductive substrate, and a cured top coat layer over at
least a portion of the cured primer coating layer, the primer
coating layer being formed from a curable electrodepositable
coating composition comprising a resinous phase dispersed in an
aqueous medium, said resinous phase comprising: (1) one or more
active ungelled hydrogen-containing, cationic amine salt
group-containing resins which are electrodepositable on a cathode,
and (2) one or more at least partially blocked aliphatic
polyisocyanate curing agents, wherein the cationic amine salt
groups are derived from pendant and/or terminal amino groups having
the following structures (I) or (I): 12 wherein the R groups
represent H or C.sub.1 to C.sub.18 alkyl; R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 are the same or different, and each
independently represents H or C.sub.1 to C.sub.4 alkyl; and X and Y
can be the same or different, and each independently represents a
hydroxyl group or an amino group, the top coat layer being formed
from one or more pigment-containing coating compositions and/or one
or more pigment-free coating compositions, characterized in that
the multi-layer composite coating exhibits substantially no
interlayer delamination between the cured primer coating layer and
the cured top coat layer upon concentrated solar spectral
irradiance exposure equivalent to two years outdoor weathering when
the top coat layer has at least 80 percent light transmission as
measured at 400 nanometers.
58. The multi-layer composite coating of claim 57, wherein the
active hydrogen-containing, cationic amine salt group-containing
resin (1) comprises a polymer selected from a polyepoxide polymer,
an acrylic polymer, a polyurethane polymer, a polyester polymer,
copolymers thereof, and mixtures thereof.
59. The multi-layer composite coating of claim 58, wherein the
resin (1) comprises a polyepoxide polymer.
60. The multi-layer composite coating of claim 58, wherein the
resin (1) comprises a polymer selected from at least one of a
polyepoxide polymer, an acrylic polymer, and mixtures thereof.
61. The multi-layer composite coating of claim 60, wherein the
polyepoxide polymer is present in the electrodepositable coating
composition in an amount ranging from 10 to 90 weight percent or
more, based on total weight of resin solids present in the
electrodepositable coating composition.
62. The multi-layer composite coating of claim 57, wherein the
cured top coat has from 0.1 to 50 percent light transmission
measured at 400 nanometers.
63. The multi-layer composite coating of claim 57, wherein the
cationic amine salt groups of resin (1) are derived from one or
more pendant amino groups having the structure (II), such that when
the electrodepositable coating composition is electrodeposited and
cured, at least two electron-withdrawing groups are bonded in the
beta-position relative to substantially all of the nitrogen
atoms.
64. The multi-layer composite coating of claim 63, wherein the
electron-withdrawing groups are selected from an ester group, a
urea group, a urethane group, and combinations thereof.
65. The multi-layer composite coating of claim 57, wherein the
resin (1) comprises cationic amine salt groups derived from at
least one compound selected from ammonia, methylamine,
diethanolamine, diisopropanolamine, N-hydroxyethyl ethylenediamine,
diethylenetriamine, and mixtures thereof.
66. The multi-layer composite coating of claim 57, wherein the
resin (1) is present in the electrodepositable coating composition
in an amount ranging from 20 to 80 weight percent, based on total
combined weight of resin solids of the resin (1) and the curing
agent (2) present in the electrodepositable coating
composition.
67. The multi-layer composite coating claim 66, wherein the curing
agent (2) comprises at least one at least partially blocked
polyisocyanate selected from 1,6-hexamethylene diisocyanate,
isophorone diisocyanate, bis-(isocyanatocyclohexyl)methane,
polymeric 1,6-hexamethylene diisocyanate, trimerized isophorone
diisocyanate, norbornane diisocyanate, and mixtures thereof.
68. The multi-layer composite coating of claim 66, wherein the
curing agent (2) comprises one or more fully blocked
polyisocyanates.
69. The multi-layer composite coating of claim 68, wherein the
curing agent (2) comprises a fully blocked polyisocyanate selected
from polymeric 1,6-hexamethylene diisocyanate, isophorone
diisocyanate, and mixtures thereof.
70. The multi-layer composite coating of claim 57, wherein the
polyisocyanate curing agent (2) is at least partially blocked with
at least one blocking agent selected from a 1,2-alkanediol, a
1,3-alkanediol, a benzylic alcohol, an allylic alcohol,
dialkylamine, and mixtures thereof.
71. The multi-layer composite coating of claim 70, wherein the
polyisocyanate curing agent (2) is at least partially blocked with
at least one 1,2-alkanediol having three or more carbon atoms.
72. The multi-layer composite coating of claim 70, wherein the
polyisocyanate curing agent (2) is at least partially blocked with
at least one blocking agent selected from a 1,2-alkanediol having
more than three carbon atoms, a benzylic alcohol, and mixtures
thereof.
73. The multi-layer composite coating of claim 72, wherein the
polyisocyanate curing agent (2) is at least partially blocked with
a blocking agent selected from 1,2-butanediol, benzyl alcohol, and
mixtures thereof.
74. The multi-layer composite coating of claim 57, wherein the
polyisocyanate curing agent (2) is present in the
electrodepositable coating composition in an amount ranging from 20
to 80 weight percent, based on total combined weight of resin
solids of the resin (1) and the curing agent (2) present in the
electrodepositable coating composition.
75. The multi-layer composite coating of claim 57, wherein the
electrodepositable coating composition is free of lead
compounds.
76. The multi-layer composite coating of claim 57, wherein the
electrodepositable coating composition further comprises at least
one source of metal selected from rare earth metals, yttrium, and
mixtures thereof, present in an amount of 0.005 to 5 percent by
weight metal, based on the total weight of resin solids in the
electrodepositable coating composition.
77. The multi-layer composite coating of claim 57, wherein the
primer coating layer is cured in an atmosphere having 5 parts per
million of NO.sub.x or less.
78. The multi-layer composite coating of claim 57, wherein the
primer coating layer is cured in an atmosphere having 1 part per
million of NO.sub.x or less.
79. A photodegradation-resistant multi-layer composite coating
comprising: a cured primer coating layer over at least a portion of
an electroconductive substrate, and a cured top coat layer over at
least a portion of the cured primer layer, the primer coating layer
being formed from a curable electrodepositable coating composition
comprising a resinous phase dispersed in an aqueous medium, said
resinous phase comprising: (1) one or more active
hydrogen-containing, cationic amine salt group-containing resins
which are electrodepositable on a cathode, said resin selected from
an acrylic polymer, a polyepoxide polymer, and mixtures thereof;
and (2) one or more aliphatic polyisocyanate curing agents at least
partially blocked with a blocking agent selected from a 1,2-alkane
diol having more than three carbon atoms, a benzylic alcohol, and
mixtures thereof, wherein the cationic amine salt groups of the
resin (1) are derived from pendant and/or terminal amino groups
having the following structures (I) or (II): 13 wherein the R
groups represent H or C.sub.1 to C.sub.18 alkyl; R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 are the same or different, and each
independently represents H or C.sub.1 to C.sub.4 alkyl; and X and Y
are the same or different, and each independently represents a
hydroxyl group or an amino group, the top coat layer being formed
from one or more pigment-containing coating compositions and/or one
or more pigment-free coating compositions, characterized in that
the multi-layer composite coating exhibits substantially no
interlayer delamination between the cured primer coating layer and
the cured top coat layer upon concentrated solar spectral
irradiance exposure equivalent to two years outdoor weathering when
the top coat layer has at least 80 percent light transmission as
measured at 400 nanometers.
80. A process for coating a metal substrate comprising the
following steps: (a) electrophoretically depositing on the
substrate a curable, electrodepositable coating composition
comprising the following components: (1) an active
hydrogen-containing, cationic salt group-containing resin
electrodepositable on a cathode; and (2) an at least partially
blocked polyisocyanate curing agent, wherein the cationic salt
group-containing resin of component (1) is derived from a
polyglycidyl ether of a polyhydric phenol essentially free of
aliphatic carbon atoms to which are bonded more than one aromatic
group, and wherein the curing agent of component (2) is essentially
free of isocyanato groups or blocked isocyanato groups to which are
bonded aromatic groups; (b) heating the substrate to a temperature
of 250.degree. F. to 400.degree. F. (121.1.degree. C. to
204.4.degree. C.) for a time sufficient to effect cure of the
electrodepositable composition; (c) applying directly to the
electrodepositable composition one or more pigmented-containing top
coating compositions and/or one or more pigment-free top coating
compositions; and (d) heating the coated substrate to a temperature
and for a time sufficient to effect cure of the pigment-containing
and/or pigment-free top coating compositions.
81. The process of claim 80, wherein the metal substrate is
selected from steel coated with a zinc-rich or iron phosphide-rich
organic coating; stainless steel; steel surface-treated with zinc
metal, zinc compounds or zinc alloys; aluminum; copper; magnesium;
magnesium alloys; zinc-aluminum alloys and combinations
thereof.
82. The process of claim 81, wherein the metal substrate comprises
more than one metal.
83. The process of claim 80, wherein the cationic salt groups in
the resin of component (1) are amine salt groups.
84. The process of claim 83, wherein the cationic salt groups are
derived from an amine containing a nitrogen atom to which is bonded
at least one substituted alkyl group having a hetero atom in a
beta- position relative to the nitrogen atom.
85. The process of claim 84, wherein the amine salt groups are
derived from a compound selected from diethanolamine,
aminopropyldiethanolamine, N-methylethanolamine,
aminopropylmorpholine, N-(2-aminoethyl)-morpholine,
diethylenetriamine, diethylenetriamine bisketimine, and mixtures
thereof.
86. The process of claim 83, wherein the amine salt groups are
derived from basic nitrogen groups neutralized with an acid
selected from the group consisting of formic acid, acetic acid,
lactic acid, phosphoric acid, sulfamic acid, dimethylolpropionic
acid, and mixtures thereof.
87. The process of claim 80, wherein the polyhydric phenol is
selected from the group consisting of resorcinol, hydroquinone,
catechol, and mixtures thereof.
88. The process of claim 87, wherein the polyhydric phenol is
selected from resorcinol, catechol, and mixtures thereof.
89. The process of claim 87, wherein the resin of component (1)
comprises at least 16 percent by weight, based on the total weight
of the resin solids, of a functional group having the following
structure: 14
90. The process of claim 80, wherein the electrodepositable coating
composition further comprises at least one source of a metal
selected from rare earth metals, yttrium, and mixtures thereof,
present in an amount of 0.005 to 5 percent by weight metal, based
on the total weight of resin solids in the electrodepositable
coating composition.
91. The process of claim 90, wherein the metal comprises
yttrium.
92. The process of claim 80, wherein the electrodepositable coating
composition further comprises a hindered amine light stabilizer,
present in an amount of 0.1 to 2 percent by weight, based on the
total weight of resin solids in the electrodepositable coating
composition.
93. The process of claim 80, wherein the cationic salt
group-containing resin of component (1) in the electrodepositable
coating composition is present in an amount of 20 to 80 percent by
weight based on the total combined weight of resin solids of (1)
and (2).
94. The process of claim 80, wherein the curing agent of component
(2) in the electrodepositable coating composition is present in an
amount of 20 to 80 percent by weight based on the total combined
weight of resin solids (1) and (2).
95. The process of claim 80, wherein the electrodepositable coating
composition is substantially free of lead.
96. A process for coating a metal substrate comprising the
following steps: (a) optionally forming a metal object from the
substrate; (b) optionally cleaning the substrate with an alkaline
and/or acidic cleaner; (c) optionally pretreating the substrate
with a solution selected from the group consisting of a metal
phosphate solution, an aqueous solution containing at least one
Group IIIB or IVB metal, an organophosphate solution, an
organophosphonate solution, and combinations thereof; (d)
optionally rinsing the substrate with water; (e)
electrophoretically depositing on the substrate a curable,
electrodepositable coating composition comprising the following
components: (1) an active hydrogen-containing, cationic salt
group-containing resin electrodepositable on a cathode; and (2) an
at least partially blocked polyisocyanate curing agent, wherein the
cationic salt group-containing resin of component (1) is derived
from a polyglycidyl ether of a polyhydric phenol essentially free
of aliphatic carbon atoms to which are bonded more than one
aromatic group, and wherein the curing agent of component (2) is
essentially free of isocyanato groups or blocked isocyanato groups
to which are bonded aromatic groups; (f) heating the substrate to a
temperature of 250.degree. F. to 400.degree. F. (121.1.degree. C.
to 204.4.degree. C.) for a time sufficient to effect cure of the
electrodepositable composition; (g) applying directly to the
electrodepositable composition one or more pigment-containing top
coating compositions and/or one or more pigment-free top coating
compositions; and (h) heating the coated substrate to a temperature
and for a time sufficient to effect cure of the pigment-containing
and/or pigment-free coating compositions.
97. The process of claim 96, wherein the substrate is cold rolled
steel and wherein the substrate is pretreated as in step (c).
98. A curable, electrodepositable coating composition comprising
the following components: (a) an active hydrogen-containing,
cationic salt group-containing resin electrodepositable on a
cathode; and (b) an at least partially blocked polyisocyanate
curing agent, wherein the cationic salt group-containing resin of
component (a) is derived from a polyglycidyl ether of a polyhydric
phenol essentially free of aliphatic carbon atoms to which are
bonded more than one aromatic group, wherein the curing agent of
component (b) is essentially free of isocyanato groups or blocked
isocyanato groups to which are bonded aromatic groups, and wherein
when the electrodepositable coating composition is applied to a
zinc substrate and cured, then subjected to corrosion testing in
accordance with ASTM B117 and/or GM standard 9540P, Method B, the
electrodepositable coating composition will have no more scribe
corrosion than exhibited by control compositions containing
aromatic isocyanates and/or Bisphenol A based aromatic
polyepoxides, and wherein when the electrodepositable coating
composition is topcoated with a transparent coating composition
having greater than 50% transmission of 400 nm wave length
ultraviolet region energy, the electrodepositable coating
composition will endure at least 1500 hours xenon arc accelerated
weathering as per SAE J1960 without substantial degradation
thereof.
99. The coating composition of claim 98, wherein the cationic salt
groups are amine salt groups.
100. The coating composition of claim 99, wherein the cationic salt
groups are derived from an amine containing a nitrogen atom to
which is bonded at least one substituted alkyl group having a
hetero atom in a beta-position relative to the nitrogen atom.
101. The coating composition of claim 100, wherein the amine salt
groups are derived from a compound selected from diethanolamine,
aminopropyldiethanolamine, N-methylethanolamine,
aminopropylmorpholine, N-(2-aminoethyl)-morpholine,
diethylenetriamine, diethylenetriamine bisketimine, and mixtures
thereof.
102. The coating composition of claim 99, wherein the amine salt
groups are derived from basic nitrogen groups neutralized with an
acid selected from the group consisting of formic acid, acetic
acid, lactic acid, phosphoric acid, sulfamic acid,
dimethylolpropionic acid, and mixtures thereof.
103. The coating composition of claim 98, wherein the polyhydric
phenol is selected from the group consisting of resorcinol,
hydroquinone, catechol, and mixtures thereof.
104. The coating composition of claim 103, wherein the polyhydric
phenol is selected from resorcinol, catechol, and mixtures
thereof.
105. The coating composition of claim 103, wherein the cationic
salt group-containing resin of component (a) comprises at least 16
percent by weight, based on the total weight of the resin solids of
a functional group having the following structure: 15
106. The coating composition of claim 98, further comprising at
least one source of a metal selected from rare earth metals
yttrium, and mixtures thereof, present in an amount of 0.005 to 5
percent by weight metal, based on the total weight of resin solids
in the coating composition.
107. The coating composition of claim 106, wherein the metal
comprises yttrium.
108. The coating composition of claim 98, further comprising a
hindered amine light stabilizer, present in an amount of 0.1 to 2
percent by weight, based on the total weight of resin solids in the
electrodepositable coating composition.
109. The coating composition of claim 98, wherein the cationic salt
group-containing resin of component (a) is present in an amount of
20 to 80 percent by weight based on the total combined weight of
resin solids of (a) and (b).
110. The coating composition of claim 98, wherein the curing agent
of component (b) is present in an amount of 20 to 80 percent by
weight based on the total combined weight of resin solids of (a)
and (b).
111. The coating composition of claim 98, wherein the composition
is substantially free of lead.
112. A process for coating a metal substrate comprising the
following steps: (a) electrophoretically depositing on the
substrate a curable, electrodepositable coating composition
essentially free of heavy metals and comprising the following
components: (1) an active hydrogen-containing, cationic salt
group-containing polymer electrodepositable on a cathode and
derived from a polymer selected from the group consisting of an
acrylic polymer, a polyester polymer, a polyurethane polymer, and
mixtures thereof; (2) an at least partially blocked polyisocyanate
curing agent and (3) at least one source of a metal selected from
rare earth metals, yttrium, and mixtures thereof, present in an
amount of 0.005 to 5 percent by weight metal, based on the total
weight of polymer solids in the electrodepositable coating
composition., (b) heating the substrate to a temperature of 250 to
400.degree. F. (121.1 to 204.4.degree. C.) for a time sufficient to
effect cure of the electrodepositable composition.
113. The process of claim 112, wherein the metal of component (3)
is yttrium.
114. A process for coating a metal substrate comprising the
following steps: (a) optionally forming a metal object from the
substrate; (b) optionally cleaning the substrate with an alkaline
and/or acidic cleaner; (c) optionally pretreating the substrate
with a solution substantially free of heavy metals and selected
from the group consisting of a metal phosphate solution, an aqueous
solution containing at least one Group IIIB or IVB metal, an
organophosphate solution, an organophosphonate solution, and
combinations thereof; (d) optionally rinsing the substrate with
water; (e) electrophoretically depositing on the substrate a
curable, electrodepositable coating composition free of heavy
metals and comprising: (1) an active hydrogen-containing, cationic
salt group-containing polymer electrodepositable on a cathode and
derived from a polymer selected from the group consisting of
acrylic, polyester, polyurethane, and mixtures thereof; (2) an at
least partially capped polyisocyanate curing agent essentially free
of isocyanato groups or capped isocyanato groups to which are
bonded aromatic groups; and (3) at least one source of a metal
selected from rare earth metals, yttrium, and mixtures thereof,
present in an amount of 0.005 to 5 percent by weight metal, based
on the total weight of polymer solids in the electrodepositable
coating composition, wherein the polymer is essentially free of
aliphatic carbon atoms to which are bonded more than one aromatic
group; and (f) heating the substrate to a temperature of 250 to
400.degree. F. (121.1 to 204.4.degree. C.) for a time sufficient to
effect cure of the electrodepositable composition.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority from U.S.
Provisional Applications No. 60/266,577 and No. 60/266,576, both
filed Feb. 5, 2001.
FIELD OF THE INVENTION
[0002] The present invention is directed to an electrodepositable
primer composition and a process for coating an electroconductive
substrate using the composition. More particularly, the present
invention is directed to multilayer composite coatings comprising a
photodegradation-resistant electrodepositable primer composition
and a top coat thereover, and to a process for forming such a
composite coating on the substrate.
BACKGROUND OF THE INVENTION
[0003] Electrodeposition as a coating application method involves
deposition of a film-forming composition onto a conductive
substrate under the influence of an applied electrical potential.
Electrodeposition has become increasingly important in the coatings
industry because, by comparison with non-electrophoretic coating
means, electrodeposition offers increased paint utilization,
improved corrosion protection and low environmental
contamination.
[0004] Initially, electrodeposition was conducted with the
workpiece to be coated serving as the anode. This was familiarly
referred to as anionic electrodeposition. However, in 1972 cationic
electrodeposition was introduced commercially and has continued to
gain in popularity. Today, cationic electrodeposition is by far the
prevalent method of electrodeposition. For example, a cationic
primer coating is applied by electrodeposition to more that 80
percent of all motor vehicles produced throughout the world.
[0005] Electrodepositable primer coating compositions, particularly
those used in the automotive industry, typically are
corrosion-resistant epoxy-based compositions crosslinked with
aromatic isocyanates. If exposed to ultraviolet energy, such as
sunlight, such compositions can undergo photodegradation. In some
applications, a primer-surfacer is spray-applied directly to the
cured electrodeposited coating prior to application of one or more
top coats. The primer-surfacer can provide a variety of properties
to the coating system, including protection of the electrodeposited
coating from photodegradation. Alternatively, one or more top coats
can be applied directly to the cured electrodeposited coating and
in such instances, the top coat(s) are formulated such that the top
coat provides sufficient protection to prevent photodegradation of
the electrodeposited primer coating. If the top coat(s) do not
provide sufficient protection, photodegradation of the
electrodeposited primer coating can result in delamination of the
subsequently applied top coats from the cured electrodeposited
primer coatings producing catastrophic failure of the cured coating
system.
[0006] For example, if one or more top coats are sufficiently
opaque to ultraviolet light transmission, such as by a high
concentration of pigment and/or light absorbing compounds, little
or no ultraviolet light can penetrate through the top coat(s) to
the electrodeposited primer coating to cause photodegradation.
However, if a thin top coat and/or a top coat which is not
ultraviolet light absorbing is applied to the cured
electrodeposited primer coating, ultraviolet light can pass through
the top coat(s) resulting in photodegradation of the cured
electrodeposited primer coating. Such a problem is likely to occur
when a top coat is lightly pigmented with metal flake pigments
which tend to allow transmission of visible and/or ultraviolet
light to the previously applied and cured electrodeposited primer
coating.
[0007] A variety of approaches are known to avoid photodegradation
of the cured electrodeposited coatings. As mentioned above, top
coats can be formulated to have a high concentration of pigments
which provide ultraviolet light opacity. Further, top coat
formulations can include additives to prevent or diminish the
transmission of ultraviolet light such as ultraviolet light
absorbers ("UVAS") and/or hindered amine light stabilizers ("HALS")
which can be used in combination with anti-oxidants, for example,
phenolic antioxidants.
[0008] Other factors can exacerbate the photosensitivity of an
epoxy-based primer, thereby contributing to delamination of a
subsequently applied top coat from the primer coating. Such factors
include, but are not limited to, the use of aromatic isocyanate
crosslinkers, and overbake of the electrodeposited primer coating
at excessive times and/or temperatures.
[0009] U.S. Pat. No. 4,755,418 discloses a method of preventing the
yellowing of the outermost coating of a multicoat coating system.
The method comprises initially depositing onto a conductive
substrate by cathodic electrodeposition a primer coating of at
least one layer of an amine-epoxy resin adduct and a cross-linking
agent; curing the primer to a hard, durable film; depositing a
second coating onto the primer layer comprising at least one layer
of a pigmented basecoat; depositing a third outermost coating onto
the second coating comprising at least one layer of a clear top
coat; and simultaneously curing the basecoat and the clear top
coat. The electrodepositable primer coating composition contains a
blocked polyisocyanate cross-linking agent selected from aliphatic
polyisocyanates of at least six carbon atoms, the isocyanurates of
aliphatic polyisocyanates, aromatic polyisoycanates having a
molecular weight greater than 174, and the isocyanurates of
aromatic diisocyanates having a molecular weight greater than
174.
[0010] U.S. Pat. No. 5,205,916 discloses electrodepositable primer
compositions containing an aqueous dispersion of an epoxy-based
ionic resin and an anitoxidant additive comprising a combination of
a phenolic antioxidant and a sulfur-containing antioxidant. Such
additives are disclosed as providing reduced overbake yellowing of
the subsequently applied top coats as well as preventing intercoat
delamination of these top coats upon exterior exposure.
[0011] U.S. Pat. No. 5,260,135 discloses photodegradation-resistant
electrodepositable compositions comprising an epoxy-based ionic
resin, a hindered amine light stabilizer present at levels of about
1 percent, and a phenolic anitoxidant. Although effective for
improving the resistance of the electrodeposited coating to
photodegradation, the effect can vary somewhat due to the
volatilization of the HALS present at the surface upon thermal
curing of the composition. In some instances, the inclusion of HALS
in electrodepositable coating compositions can provide only a
marginal improvement for photodegradation resistance of the cured
electrodeposited coating because the HALS can migrate into the
subsequently applied top coating layers. Moreover, due to
environmental and toxicity concerns, it is desirable to avoid the
use of phenolic compounds such as the phenolic antioxidant
mentioned above.
[0012] Although the aforementioned references disclose
photodegradation resistant coating systems which can provide many
advantages, each of the respective coating system disclosed therein
can have one or more deficiencies, including excessive cost,
toxicity issues, or marginal effectiveness. Accordingly, there
remains a need in the coatings industry for a cost effective
electrodepositable primer composition which retards
photodegradation and delamination of subsequently applied top coats
independent of the top coat composition(s).
SUMMARY OF THE INVENTION
[0013] In one embodiment, the present invention is directed to an
improved process for coating an electroconductive substrate. The
process comprises (a) electrophoretically depositing on the
substrate a curable electrodepositable coating composition to form
an electrodeposited coating over at least a portion of the
substrate; (b) heating the coated substrate to a temperature and
for a time sufficient to cure the electrodeposited coating on the
substrate; (c) applying directly to the cured electrodeposited
coating one or more pigment-containing coating compositions and/or
one or more pigment-free coating compositions to form a top coat
over at least a portion of the cured electrodeposited coating; (d)
heating the coated substrate of step (c) to a temperature and for a
time sufficient to cure the top coat, the cured top coat having at
least 0.1 percent light transmission measured at 400 nanometers.
The electrodepositable coating composition comprises a resinous
phase dispersed in an aqueous medium, the resinous phase
comprising: (1) one or more ungelled, active hydrogen-containing,
cationic amine salt group-containing resins which are
electrodepositable on a cathode, and (2) one or more at least
partially blocked aliphatic polyisocyanate curing agents. The
improvement comprises the presence in the curable
electrodepositable coating composition of one or more cationic
amine salt group-containing resins, wherein the amine salt groups
are derived from pendant and/or terminal amine groups having the
following structures (I) or (II):
--NHR (I)
[0014] or 1
[0015] wherein R represents H or C.sub.1 to C.sub.18 alkyl;
R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are the same or different,
and each independently represents H or C.sub.1 to C.sub.4 alkyl;
and X and Y can be the same or different, and each independently
represents a hydroxyl group or an amino group.
[0016] The present invention is further directed to a process for
forming a photodegradation-resistant multi-layer coating an
electroconductive substrate. The process comprises (a)
electrophoretically depositing on the substrate a curable
electrodepositable coating composition to form an electrodeposited
coating over at least a portion of the substrate; (b) heating the
coated substrate in an atmosphere having 5 parts per million or
less of NO.sub.x to a temperature and for a time sufficient to cure
the electrodeposited coating on the substrate; (c) applying
directly to the cured electrodeposited coating one or more
pigment-containing coating compositions and/or one or more
pigment-free coating compositions to form a top coat over at least
a portion of the cured electrodeposited coating; and (d) heating
the coated substrate of step (c) to a temperature and for a time
sufficient to cure the top coat, the cured top coat having at least
0.1 percent light transmission measured at 400 nanometers. The
electrodepositable coating composition comprises a resinous phase
dispersed in an aqueous medium, the resinous phase comprising (1)
one or more cationic polymers which are electrodepositable on a
cathode, and (2) one or more at least partially blocked aliphatic
polyisocyanate curing agents.
[0017] In another embodiment, the present invention provides a
process for forming a photodegradation-resistant multi-layer
coating on an electrically conductive substrate comprising (a)
electrophoretically depositing on the substrate an aqueous, curable
electrodepositable coating composition as described above to form
an electrodeposited coating over at least a portion of the
substrate, the substrate serving as a cathode in an electrical
circuit comprising the cathode and an anode, the cathode and the
anode being immersed in the aqueous electrodepositable coating
composition, wherein electric current is passed between the cathode
and the anode to cause the coating to be electrodeposited over at
least a portion of the substrate; (b) heating the coated substrate
at a temperature and for a time sufficient to cure the
electrodeposited coating on the substrate; (c) applying directly to
the cured electrodeposited coating one or more pigment-containing
coating compositions and/or one or more pigment-free coating
compositions to form a top coat over at least a portion of the
cured electrodeposited coating; and (d) heating the coated
substrate of step (c) to a temperature and for a time sufficient to
cure the top coat, the cured top coat having at least 0.1 percent
light transmission as measured at 400 nanometers. The improvement
comprises the inclusion in the circuit of a non-ferrous anode.
[0018] In a further embodiment, the present invention is directed
to an improved process for coating an electroconductive substrate
comprising: (a) electrophoretically depositing on the substrate a
curable electrodepositable coating composition to form an
electrodeposited coating over at least a portion of the substrate;
(b) heating the coated substrate to a temperature ranging from
250.degree. to 400.degree. F. (121.1.degree. to 204.4.degree. C.)
for a time sufficient to cure the electrodeposited coating on the
substrate; (c) applying directly to the cured electrodeposited
coating one or more pigment-containing coating compositions and/or
one or more pigment-free coating compositions to form a top coat
over at least a portion of the cured electrodeposited coating; and
(d) heating the coated substrate of step (c) to a temperature and
for a time sufficient to cure the top coat, the cured top coat
having 0.1 to 50 percent light transmission as measured at 400
nanometers wavelength. The electrodepositable coating composition
comprises a resinous phase dispersed in an aqueous medium, said
resinous phase comprising (1) one or more active
hydrogen-containing, cationic amine salt group-containing resins
which are electrodepositable on a cathode, said resins selected
from at least one of an acrylic polymer, a polyepoxide polymer, and
mixtures thereof, and (2) one or more aliphatic polyisocyanate
curing agents at least partially blocked with one or more blocking
agents selected from a 1,2-alkane diol having at least three carbon
atoms, a benzylic alcohol, and mixtures thereof. The improvement
comprises the presence in the curable electrodepositable
composition of a resin having cationic amine salt groups which are
derived from one or more pendant and/or terminal amino groups
having the structure (II) above, where R.sup.1, R.sup.2, R.sup.3,
R.sup.4, X and Y are as described above for that structure. The
process is characterized in that when the electrodepositable
coating composition is electrodeposited and cured, at least two
electron-withdrawing groups are bonded in the beta-position
relative to substantially all of the amine nitrogen atoms.
[0019] The present invention is also directed to a
photodegradation-resist- ant multi-layer composite coating
comprising a cured primer coating layer over at least a portion of
an electroconductive substrate, and a cured top coat layer over at
least a portion of the cured primer coating layer. The primer
coating layer is formed from a curable electrodepositable coating
composition comprising a resinous phase dispersed in an aqueous
medium, said resinous phase comprising (1) one or more active
hydrogen-containing, cationic amine salt group-containing resins
which are electrodepositable on a cathode, and (2) one or more at
least partially blocked aliphatic polyisocyanate curing agents. The
cationic salt groups of the resin (1) are derived from one or more
pendant and/or terminal amino groups having the structure (I) or
(II) above, where R, R.sup.1, R.sup.2, R.sup.3, R.sup.4, X and Y
are as described above for that structure. The top coat layer is
formed from one or more pigment-containing coating compositions
and/or one or more pigment-free coating compositions. The
multi-layer composite coating is characterized in that it exhibits
substantially no interlayer delamination between the cured
electrodeposited primer coating layer and the cured top coat layer
upon concentrated solar spectral irradiance exposure equivalent to
two years outdoor weathering when the top coat layer has at least
80 percent light transmission as measured at 400 nanometers.
[0020] In one embodiment, the present invention provides a
photodegradation-resistant multi-layer composite coating comprising
a cured primer coating layer over at least a portion of an
electroconductive substrate, and a cured top coat layer over at
least a portion of the cured primer layer. The primer coating layer
is formed from a curable electrodepositable coating composition
comprising a resinous phase dispersed in an aqueous medium, the
resinous phase comprising (1) one or more active
hydrogen-containing, cationic amine salt group-containing resins
which are electrodepositable on a cathode, the resin being selected
from an acrylic polymer, a polyepoxide polymer, and mixtures
thereof; and (2) one or more aliphatic polyisocyanate curing agents
at least partially blocked with a blocking agent selected from a
1,2-alkane diol having more than three carbon atoms, a benzylic
alcohol, and mixtures thereof. The resin (1) comprises cationic
amine salt groups which are derived from one or more pendant and/or
terminal amino groups having the structure (I) or (11) above, where
R, R.sup.1, R.sup.2, R.sup.3, R.sup.4, X and Y are as described
above for that structure. The top coat layer is formed from one or
more pigment-containing coating compositions and/or one or more
pigment-free coating compositions. The multi-layer composite
coating is characterized in that it exhibits substantially no
interlayer delamination between the cured primer coating layer and
the cured top coat layer upon concentrated solar spectral
irradiance exposure equivalent to two years outdoor weathering when
the top coat layer has at least 80 percent light transmission as
measured at 400 nanometers.
[0021] In an alternative embodiment, the present invention is
directed to a process for coating a metal substrate comprising the
following steps: (a) electrophoretically depositing on the
substrate a curable, electrodepositable coating composition; (b)
heating the substrate to a temperature of 250.degree. F. to
400.degree. F. (121.1.degree. C. to 204.4.degree. C.) for a time
sufficient to effect cure of the electrodepositable composition;
(c) applying directly to the cured electrodepositable composition
one or more pigment-containing coating compositions and/or one or
more pigment-free top coating compositions to form a top coat
thereover; and (d) heating the coated substrate to a temperature
and for a time sufficient to effect cure of the one or more
pigment-containing coating compositions and/or one or more
pigment-free coating compositions.
[0022] Also provided is a curable, electrodepositable coating
composition used in the above alternative process, comprising (1)
an active hydrogen-containing, cationic salt group-containing resin
electrodepositable on a cathode, derived from a polyglycidyl ether
of a polyhydric phenol that is essentially free of aliphatic carbon
atoms to which are bonded more than one aromatic group; and (2) an
at least partially blocked polyisocyanate curing agent essentially
free of isocyanato groups or blocked isocyanato groups to which are
bonded aromatic groups. This composition, when applied to a
substrate and properly cured, then subjected to corrosion testing,
such as a standard ASTM B117 salt spray test or a cyclic test such
as GM Engineering Standard 9540P, Method B, will have no more
scribe corrosion than exhibited by suitable controls containing
aromatic isocyanates and/or Bisphenol A based aromatic
polyepoxides. When top coated with a transparent base coat and/or
clear coat composition having greater than 50% light transmission
measured at 400 nanometers wave length, it will endure at least
1500 hours xenon arc accelerated weathering as per SAE J1960
without substantial degradation.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Other than in the operating examples, or where otherwise
indicated, all numbers expressing quantities of ingredients,
reaction conditions and so forth used in the specification and
claims are to be understood as being modified in all instances by
the term "about." Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the following specification
and attached claims are approximations that may vary depending upon
the desired properties sought to be obtained by the present
invention. At the very least, and not as an attempt to limit the
application of the doctrine of equivalents to the scope of the
claims, each numerical parameter should at least be construed in
light of the number of reported significant digits and by applying
ordinary rounding techniques.
[0024] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical values, however,
inherently contain certain errors necessarily resulting from the
standard deviation found in their respective testing
measurements.
[0025] Also, it should be understood that any numerical range
recited herein is intended to include all sub-ranges subsumed
therein. For example, a range of 1" to 10" is intended to include
all sub-ranges between and including the recited minimum value of 1
and the recited maximum value of 10, that is, having a minimum
value equal to or greater than 1 and a maximum value of equal to or
less than 10.
[0026] As mentioned above, in one embodiment, the present invention
is directed to an improved process for coating an electroconductive
substrate. The process comprises (a) electrophoretically depositing
on the substrate a curable electrodepositable coating composition
to form an electrodeposited coating over at least a portion of the
substrate; (b) heating the coated substrate to a temperature and
for a time sufficient to cure the electrodeposited coating on the
substrate; (c) applying directly to the cured electrodeposited
coating one or more pigment-containing coating compositions and/or
one or more pigment-free coating compositions to form a top coat
over at least a portion of the cured electrodeposited coating; (d)
heating the coated substrate of step (c) to a temperature and for a
time sufficient to cure the top coat, the cured top coat having at
least 0.1 percent light transmission measured at 400 nanometers.
The electrodepositable coating composition comprises a resinous
phase dispersed in an aqueous medium, the resinous phase
comprising: (1) one or more ungelled, active hydrogen-containing,
cationic amine salt group-containing resins which are
electrodepositable on a cathode, and (2) one or more at least
partially blocked aliphatic polyisocyanate curing agents. The amine
salt groups of the cationic resin (1) are derived from pendant
and/or terminal amine groups having the following structures (I) or
(II): 2
[0027] wherein R represents H or C.sub.1 to C.sub.18 alkyl;
R.sup.1, R.sup.2 R.sup.3, and R.sup.4 are the same or different,
and each independently represents H or C.sup.1 to C.sub.4 alkyl;
and X and Y can be the same or different, and each independently
represents a hydroxyl group or an amino group.
[0028] In the processes of the present invention, the curable
electrodepositable coating composition can be electrophoretically
deposited onto at least a portion of any of a variety of
electroconductive substrates, including various metallic
substrates. Suitable metallic substrates can include ferrous metals
and non-ferrous metals. Suitable ferrous metals include iron,
steel, and alloys thereof. Non-limiting examples of useful steel
materials include cold-rolled steel, galvanized (i.e., zinc coated)
steel, electrogalvanized steel, stainless steel, pickled steel,
GALVANNEAL.RTM., GALVALUME.RTM., AND GALVAN.RTM. zinc-aluminum
alloys coated upon steel, and combinations thereof. Useful
non-ferrous metals include conductive carbon coated materials,
aluminum, copper, zinc, magnesium and alloys thereof. Cold rolled
steel also is suitable when pretreated with a solution such as a
metal phosphate solution, an aqueous solution containing at least
one Group IIIB or IVB metal, an organophosphate solution, an
organophosphonate solution and combinations of the above as are
discussed below. Combinations or composites of ferrous and
non-ferrous metals can also be used.
[0029] The electrodepositable coating compositions of the present
invention can be applied to either bare metal or pretreated metal
substrates. By "bare metal" is meant a virgin metal substrate that
has not been treated with a pretreatment composition such as
conventional phosphating solutions, heavy metal rinses and the
like. Additionally, for purposes of the present invention, "bare
metal" substrates can include a cut edge of a substrate that is
otherwise treated and/or coated over the non-edge surfaces of the
substrate.
[0030] Before any treatment or application of any coating
composition, the substrate optionally may be formed into an object
of manufacture. A combination of more than one metal substrate can
be assembled together to form such an object of manufacture.
[0031] Also, it should be understood that as used herein, an
electrodepositable composition or coating formed "over" at least a
portion of a "substrate" refers to a composition formed directly on
at least a portion of the substrate surface, as well as a
composition or coating formed over any coating or pretreatment
material which was previously applied to at least a portion of the
substrate.
[0032] That is, the "substrate" upon which the coating composition
is electrodeposited can comprise any electroconductive substrates
including those described above to which one or more pretreatment
and/or primer coatings have been previously applied For example,
the "substrate" can comprise a metallic substrate and a weldable
primer coating over at least a portion of the substrate surface.
The electrodepositable coating composition described above is then
electrodeposited and cured over at least a portion thereof. One or
more top coating compositions as described in detail below are
subsequently applied over at least a portion of the cured
electrodeposited coating.
[0033] For example, the substrate can comprise any of the foregoing
electroconductive substrates and a pre-treatment composition
applied over at least a portion of the substrate, the pretreatment
composition comprising a solution that contains one or more Group
IIIB or IVB element-containing compounds, or mixtures thereof,
solubilized or dispersed in a carrier medium, typically an aqueous
medium. The Group IIIB and IVB elements are defined by the CAS
Periodic Table of the Elements as shown, for example, in the
Handbook of Chemistry and Physics, (60th Ed. 1980). Transition
metal compounds and rare earth metal compounds typically are
compounds of zirconium, titanium, hafnium, yttrium and cerium and
mixtures thereof. Typical zirconium compounds may be selected from
hexafluorozirconic acid, alkali metal and ammonium salts thereof,
ammonium zirconium carbonate, zirconyl nitrate, zirconium
carboxylates and zirconium hydroxy carboxylates such as
hydrofluorozirconic acid, zirconium acetate, zirconium oxalate,
ammonium zirconium glycolate, ammonium zirconium lactate, ammonium
zirconium citrate, and mixtures thereof.
[0034] The pretreatment composition carrier also can contain a
film-forming resin, for example, the reaction products of one or
more alkanolamines and an epoxy-functional material containing at
least two epoxy groups, such as those disclosed in U.S. Pat. No.
5,653,823. Other suitable resins include water soluble and water
dispersible polyacrylic acids such as those as disclosed in U.S.
Pat. Nos. 3,912,548 and 5,328,525; phenol-formaldehyde resins as
described in U.S. Pat. No. 5,662,746, incorporated herein by
reference; water soluble polyamides such as those disclosed in WO
95/33869; copolymers of maleic or acrylic acid with allyl ether as
described in Canadian patent application 2,087,352; and water
soluble and dispersible resins including epoxy resins, aminoplasts,
phenol-formaldehyde resins, tannins, and polyvinyl phenols as
discussed in U.S. Pat. No. 5,449,415.
[0035] Further, non-ferrous or ferrous substrates can be pretreated
with a non-insulating layer of organophosphates or
organophosphonates such as those described in U.S. Pat. Nos
5,294,265 and 5,306,526. Such organophosphate or organophosphonate
pretreatments are available commercially from PPG Industries, Inc.
under the trade name NUPAL.RTM.. Application to the substrate of a
non-conductive coating, such as NUPAL, typically is followed by the
step of rinsing the substrate with deionized water prior to the
coalescing of the coating. This ensures that the layer of the
non-conductive coating is sufficiently thin to be non-insulating,
i.e., sufficiently thin such that the non-conductive coating does
not interfere with electroconductivity of the substrate, allowing
subsequent electrodeposition of a electrodepositable coating
composition. The pretreatment coating composition can further
comprise surfactants that function as aids to improve wetting of
the substrate. Generally, the surfactant materials are present in
an amount of less than about 2 weight percent on a basis of total
weight of the pretreatment coating composition. Other optional
materials in the carrier medium include defoamers and substrate
wetting agents.
[0036] Due to environmental concerns, the pretreatment coating
composition can be free of chromium-containing materials, i.e., the
composition contains less than about 2 weight percent of
chromium-containing materials (expressed as CrO.sub.3), typically
less than about 0.05 weight percent of chromium-containing
materials.
[0037] In a typical pre-treatment process before depositing the
pre-treatment composition upon the surface of the metal substrate,
it is usual practice to remove foreign matter from the metal
surface by thoroughly cleaning and degreasing the surface. The
surface of the metal substrate can be cleaned by physical or
chemical means, such as by mechanically abrading the surface or
cleaning/degreasing with commercially available alkaline or acidic
cleaning agents which are well know to those skilled in the art,
such as sodium metasilicate and sodium hydroxide. A non-limiting
example of a suitable cleaning agent is CHEMKLEEN.RTM. 163, an
alkaline-based cleaner commercially available from PPG Pretreatment
and Specialty Products of Troy, Mich. Acidic cleaners also can be
used. Following the cleaning step, the metal substrate is usually
rinsed with water in order to remove any residue. The metal
substrate can be air-dried using an air knife, by flashing off the
water by brief exposure of the substrate to a high temperature or
by passing the substrate between squeegee rolls. The pretreatment
coating composition can be deposited upon at least a portion of the
outer surface of the metal substrate. Preferably, the entire outer
surface of the metal substrate is treated with the pretreatment
composition. The thickness of the pretreatment film can vary, but
is generally less than about 1 micrometer, preferably ranges from
about 1 to about 500 nanometers, and more preferably ranges from
about 10 to about 300 nanometers.
[0038] The pretreatment coating composition is applied to the
surface of the metal substrate by any conventional application
technique, such as by spraying, immersion or roll coating in a
batch or continuous process. The temperature of the pretreatment
coating composition at application is typically about 10.degree. C.
to about 85.degree. C., and preferably about 15.degree. C. to about
60.degree. C. The pH of the pretreatment coating composition at
application generally ranges from 2.0 to 5.5, and typically from
3.5 to 5.5. The pH of the medium may be adjusted using mineral
acids such as hydrofluoric acid, fluoroboric acid, phosphoric acid,
and the like, including mixtures thereof; organic acids such as
lactic acid, acetic acid, citric acid, sulfamic acid, or mixtures
thereof; and water soluble or water dispersible bases such as
sodium hydroxide, ammonium hydroxide, ammonia, or amines such as
triethylamine, methylethyl amine, or mixtures thereof.
[0039] Continuous processes typically are used in the coil coating
industry and also for mill application. The pretreatment coating
composition can be applied by any of these conventional processes.
For example, in the coil industry, the substrate typically is
cleaned and rinsed and then contacted with the pretreatment coating
composition by roll coating with a chemical coater. The treated
strip is then dried by heating, painted and baked by conventional
coil coating processes.
[0040] Mill application of the pretreatment composition can be by
immersion, spray or roll coating applied to the freshly
manufactured metal strip. Excess pretreatment composition is
typically removed by wringer rolls. After the pretreatment
composition has been applied to the metal surface, the metal can be
rinsed with deionized water and dried at room temperature or at
elevated temperatures to remove excess moisture from the treated
substrate surface and cure any curable coating components to form
the pretreatment coating. Alternatively, the treated substrate can
be heated to a temperature ranging from 65.degree. C. to
125.degree. C. for 2 to 30 seconds to produce a coated substrate
having a dried residue of the pretreatment coating composition
thereon. If the substrate is already heated from the hot melt
production process, no post application heating of the treated
substrate is required to facilitate drying. The temperature and
time for drying the coating will depend upon such variables as the
percentage of solids in the coating, components of the coating
composition and type of substrate.
[0041] The film coverage of the residue of the pretreatment
composition generally ranges from 1 to 10,000 milligrams per square
meter (mg/m.sup.2), and usually from 10 to 400 mg/M.sup.2.
[0042] A layer of a weldable primer also can be applied to the
substrate, whether or not the substrate has been pretreated. A
typical weldable primer is BONAZINC.RTM., a zinc-rich mill applied
organic film-forming composition, which is commercially available
from PPG Industries, Inc., Pittsburgh, Pa. BONAZINC can be applied
to a thickness of at least 1 micrometer and typically to a
thickness of 3 to 4 micrometers. Other weldable primers, such as
iron phosphide-rich primers, are commercially available.
[0043] The electrodeposition process of the present invention
typically involves immersing the electroconductive substrate into
an electrodeposition bath of an aqueous electrodepositable
composition, the substrate serving as a cathode in an electrical
circuit comprising the cathode and an anode. Sufficient electrical
current is applied between the electrodes to deposit a
substantially continuous, adherent film of the electrodepositable
coating composition onto at least a portion of the surface of the
electroconductive substrate. Electrodeposition is usually carried
out at a constant voltage in the range of from 1 volt to several
thousand volts, typically between 50 and 500 volts. Current density
is usually between 1.0 ampere and 15 amperes per square foot (10.8
to 161.5 amperes per square meter) and tends to decrease quickly
during the electrodeposition process, indicating formation of a
continuous, self-insulating film.
[0044] Any of a variety of electrodepositable coating compositions
can be used in the processes of the present invention. In a
particular embodiment of the present invention, the
electrodepositable coating composition comprises a resinous phase
dispersed in an aqueous medium, the resinous phase comprising (1)
one or more ungelled, cationic resins or polymers, typically an
active hydrogen group-containing, cationic amine salt
group-containing polymer, which are electrodepositable on a
cathode; and (2) one or more at least partially blocked aliphatic
polyisocyanate curing agents.
[0045] Cationic polymers suitable for use in the electrodepositable
coating compositions, typically as the main film-forming polymer,
can include any of a number of cationic polymers well known in the
art so long as the polymers are "water dispersible," i.e., adapted
to be solubilized, dispersed or emulsified in water. Such polymers
comprise cationic functional groups to impart a positive
charge.
[0046] By "ungelled" is meant the resins are substantially free of
crosslinking and have an intrinsic viscosity when dissolved in a
suitable solvent, as determined, for example, in accordance with
ASTM-D1795 or ASTM-D4243. The intrinsic viscosity of the reaction
product is an indication of its molecular weight. A gelled reaction
product, on the other hand, since it is of essentially infinitely
high molecular weight, will have an intrinsic viscosity too high to
measure. As used herein, a reaction product that is "substantially
free of crosslinking" refers to a reaction product that has a
weight average molecular weight (Mw), as determined by gel
permeation chromatography, of less than 1,000,000.
[0047] Also, as used herein, the term "polymer" is meant to refer
to oligomers and both homopolymers and copolymers. Unless stated
otherwise, as used in the specification and the claims, molecular
weights are number average molecular weights for polymeric
materials indicated as "Mn" and obtained by gel permeation
chromatography using polystyrene standards in an art-recognized
manner.
[0048] Suitable examples of such cationic film-forming resins can
include active hydrogen-containing, cationic polymers selected from
one or more of a polyepoxide polymer, an acrylic polymer, a
polyurethane polymer, a polyester polymer, mixtures thereof, and
copolymers thereof, for example a polyester-polyurethane polymer.
Typically, the resin (1) comprises a polyepoxide polymer, or a
mixture of a polyepoxide polymer and an acrylic polymer. As
aforementioned, the polymers which are suitable for use as the
cationic resin (1), comprise active hydrogens as curing reaction
sites. The term "active hydrogen" refers to those groups which are
reactive with isocyanates as determined by the Zerewitnoff test as
is described in the JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol.
49, page 3181 (1927). In one embodiment of the present invention,
the active hydrogens are derived from hydroxyl groups, primary
amine groups and/or secondary amine groups.
[0049] Any of a variety of polyepoxides known in the related art
can be used to form the cationic resin (1). Examples of
polyepoxides which are suitable for this purpose include those
having a 1,2-epoxy equivalency greater than one, and typically two;
that is, polyepoxides that have on average two epoxide groups per
molecule. Such polyepoxide polymers can include the polyglycidyl
ethers of cyclic polyols, for example polyhydric phenols, such as
Bisphenol A. These polyepoxides can be prepared by etherifiction of
polyhydric phenols with an epihalohydrin or dihalohydrin such as
epichlorohydrin or dichlorohydrin in the presence of alkali.
Nonlimiting examples of suitable polyhydric phenols include
2,2-bis-(4-hydroxyphenyl)propane, 1,1-bis-(4-hydroxyphenyl)ethane,
2-metyl-1,1-bis-(4-hydroxyphenyl)propane,
2,2-(4-hydroxy-3-tertiarybutylp- henyl)propane, and
bis-(2-hydroxynaphthyl)methane
[0050] Besides polyhydric phenols, other cyclic polyols can be used
to prepare the polyglycidyl ethers of cyclic polyol derivatives
Examples of such cyclic polyols include alicyclic polyols, such as
cycloaliphatic polyols, for example 1,2-cyclohexanediol,
1,4-cyclohexanediol, 1,2-bis-(hydroxymethyl)cyclohexane,
1,3-bis-(hydroxymethyl)cyclohexane and hydrogenated bisphenol
A.
[0051] The polyepoxides can be chain-extended with a polyether or a
polyester polyol. Examples of suitable polyether polyols and
conditions for chain extension are disclosed in U.S. Pat. No.
4,468,307. Examples of polyester polyols for chain extension are
disclosed in U.S. Pat. No. 4,148,772.
[0052] Other suitable polyepoxides can be produced similarly from
novolak resins or similar polyphenols. Such polyepoxide resins are
described in U.S. Pat. Nos. 3,663,389; 3,984,299; 3,947,338; and
3,947,339. Additional polyepoxide resins which are suitable for use
in forming the cationic resin (1) include those described in U.S.
Pat. Nos. 4,755,418, 5,948,229 and 6,017,432.
[0053] Suitable acrylic polymers from which the active
hydrogen-containing, cationic salt group-containing polymer may be
derived can include copolymers of one or more alkyl esters of
acrylic acid or methacrylic acid, optionally together with one or
more other polymerizable ethylenically unsaturated monomers.
Suitable alkyl esters of acrylic acid or methacrylic acid include
methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl
acrylate, butyl acrylate, and 2-ethyl hexyl acrylate. Suitable
other copolymerizable ethylenically unsaturated monomers include
nitrites such acrylonitrile and methacrylonitrile, vinyl and
vinylidene halides such as vinyl chloride and vinylidene fluoride
and vinyl esters such as vinyl acetate. Acid and anhydride
functional ethylenically unsaturated monomers such as acrylic acid,
methacrylic acid or anhydride, itaconic acid, maleic acid or
anhydride, or fumaric acid may be used. Amide functional monomers
including, acrylamide, methacrylamide, and N-alkyl substituted
(meth)acrylamides are also suitable. Vinyl aromatic compounds such
as styrene and vinyl toluene can be used so long as
photodegradation resistance of the polymer and the resulting
electrodeposited coating is not compromised.
[0054] Functional groups such as hydroxyl and amino groups can be
incorporated into the acrylic polymer by using functional monomers
such as hydroxyalkyl acrylates and methacrylates or aminoalkyl
acrylates and methacrylates. Epoxide functional groups (for
conversion to cationic salt groups) may be incorporated into the
acrylic polymer by using functional monomers such as glycidyl
acrylate and methacrylate, 3,4-epoxycyclohexylmethyl(meth)acrylate,
2-(3,4-epoxycyclohexyl)ethyl(met- h)acrylate, or allyl glycidyl
ether. Alternatively, epoxide functional groups may be incorporated
into the acrylic polymer by reacting carboxyl groups on the acrylic
polymer with an epihalohydrin or dihalohydrin such as
epichlorohydrin or dichlorohydrin. The acrylic polymer can be
prepared by traditional free radical initiated polymerization
techniques, such as solution or emulsion polymerization, as known
in the art using suitable catalysts which include organic peroxides
and azo type compounds and optionally chain transfer agents such as
alpha-methyl styrene dimer and tertiary dodecyl mercaptan.
Additional acrylic polymers which are suitable for forming the
active hydrogen-containing, cationic amine salt group-containing
resin (1) which is used in the electrodepositable compositions of
the present invention include, those resins described in U.S. Pat.
Nos. 3,455,806 and 3,928,157.
[0055] Besides the above-described polyepoxide and acrylic
polymers, the active hydrogen-containing, cationic salt
group-containing polymer can be derived from a polyester. Such
polyesters can be prepared in a known manner by condensation of
polyhydric alcohols and polycarboxylic acids. Suitable polyhydric
alcohols include, for example, ethylene glycol, propylene glycol,
butylene glycol, 1,6-hexylene glycol, neopentyl glycol, diethylene
glycol, glycerol, trimethylol propane, and pentaerythritol.
Examples of suitable polycarboxylic acids used to prepare the
polyester include succinic acid, adipic acid, azelaic acid, sebacic
acid, maleic acid, fumaric acid, phthalic acid, tetrahydrophthalic
acid, hexahydrophthalic acid, and trimellitic acid. Besides the
polycarboxylic acids mentioned above, functional equivalents of the
acids such as anhydrides where they exist or lower alkyl esters of
the acids such as the methyl esters may be used.
[0056] The polyesters contain a portion of free hydroxyl groups
(resulting from the use of excess polyhydric alcohol and/or higher
polyols during preparation of the polyester) which are available
for cure reactions. Epoxide functional groups may be incorporated
into the polyester by reacting carboxyl groups on the polyester
with an epihalohydrin or dihalohydrin such as epichlorohydrin or
dichlorohydrin.
[0057] Amino groups can be incorporated into the polyester polymer
by reacting epoxy functional groups of the polymer with a hydroxyl
containing tertiary amine, for example, N,N-dialkylalkanolamines
and N-alkyidialkanolamines. Specific examples of suitable tertiary
amines include those N-alkyl dialkanolamines disclosed in U. S.
Pat. No. 5,483,012, at column 3, lines 49-63. Suitable polyesters
for use in the process of the present invention include those
disclosed in U. S. Pat. No. 3,928,157.
[0058] Polyurethanes can also be used as the polymer from which the
active hydrogen-containing, cationic salt group-containing resin
can be derived. Among the polyurethanes which can be used are
polymeric polyols which are prepared by reacting polyester polyols
or acrylic polyols such as those mentioned above with a
polyisocyanate such that the OH/NCO equivalent ratio is greater
than 1:1 so that free hydroxyl groups are present in the product.
Smaller polyhydric alcohols such as those disclosed above for use
in the preparation of the polyester may also be used in place of or
in combination with the polymeric polyols.
[0059] Additional examples of polyurethane polymers suitable for
forming the active hydrogen-containing, cationic amine salt
group-containing resin (1) include the polyurethane, polyurea, and
poly(urethane-urea) polymers prepared by reacting polyether polyols
and/or polyether polyamines with polyisocyanates. Such polyurethane
polymers are described in U.S. Pat. No. 6,248,225.
[0060] Hydroxyl functional tertiary amines such as
N,N-dialkylalkanolamine- s and N-alkyl dialkanolamines may be used
in combination with the other polyols in the preparation of the
polyurethane. Examples of suitable tertiary amines include those
N-alkyl dialkanolamines disclosed in U.S. Pat. No. 5,483,012 at
column 3, lines 49-63.
[0061] Epoxide functional groups may be incorporated into the
polyurethane by methods well known in the art. For example, epoxide
groups can be incorporated by reacting hydroxyl groups on the
polyurethane with an epihalohydrin or dihalohydrin such as
epichlorohydrin or dichlorohydrin in the presence of alkali.
[0062] Mixtures of the polymers described above also can
advantageously be used. In one embodiment of the present invention
the cationic resion (1) comprises a mixture of a cationic
polyepoxide polymer and a cationic acrylic polymer. Where such
mixtures are used, the polyepoxide polymer can be present in the
electrodepositable coating compositions in an amount ranging from
10 to 90, typically 20 to 80 weight percent, based on total weight
of resin solids present in the composition.
[0063] The polymers used in the electrodepositable coating
composition of the present invention can have number average
molecular weights (Mn) ranging from 1000 to 20,000, often from 1000
to 8000, and typically from 1000 to 5000, depending on the type of
resin used, as determined by gel permeation chromatography using a
polystyrene standard.
[0064] The active hydrogen-containing resin (1) comprises cationic
amine salt groups which are derived from pendant and/or terminal
amino groups. By "terminal and/or pendant" is meant that primary
and/or secondary amino groups are present as a substituent which is
pendant from or in the terminal position of the polymeric backbone,
or, alternatively, is an end-group substituent of a group which is
pendant and/or terminal from the polymer backbone. In other words,
the amino groups from which the cationic amine salt groups are
derived are not within the polymeric backbone.
[0065] The pendant and/or terminal amino groups can have the
following structures (I) or (II): 3
[0066] wherein R represents H or C.sub.1 to C.sub.18 alkyl;
R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are the same or different,
and each independently represents H or C.sub.1 to C.sub.4 alkyl;
and X and Y can be the same or different, and each independently
represents a hydroxyl group or an amino group.
[0067] By "alkyl" is meant alkyl and aralkyl, cyclic or acyclic,
linear or branched monovalent hydrocarbon groups. The alkyl groups
can be unsubstituted or substituted with one or more heteroaoms,
for example, non-carbon, non-hydrogen atoms such as one or more
oxygen, nitrogen or sulfur atoms.
[0068] The pendant and/or terminal amino groups represented by
structures (I) and (II) above can be derived from a compound
selected from the group consisting of ammonia, methylamine,
diethanolamine, diisopropanolamine, N-hydroxyethyl ethylenediamine,
diethylenetriamine, and mixtures thereof. One or more of these
compounds is reacted with one or more of the above described
polymers, for example, a polyepoxide polymer, where the epoxy
groups are ring-opened via reaction with a polyamine, thereby
providing terminal amino groups and secondary hydroxyl groups.
[0069] In one particular embodiment of the invention, the cationic
salt group-containing polymer contains amine salt groups which are
derived from one or more pendant and/or terminal amino groups
having the structure (II) above, such that when the
electrodepositable coating composition is electrodeposited and
cured, at least two electron-withdrawing groups (as described in
detail below) are bonded in the beta-position relative to
substantially all of the nitrogen atoms present in the cured
electrodeposited coating. In a further embodiment of the invention,
when the electrodepositable coating composition is electrodeposited
and cured, three electron-withdrawing groups are bonded in the
beta-position relative to substantially all of the nitrogen atoms
present in the cured electrodeposited coating. By "substantially
all" of the nitrogen atoms present in the cured electrodeposited
coating is meant at least 65 percent, and typically 90 percent, of
all nitrogen atoms present in the cured electrodeposited coating
which are derived from the amine used to form the cationic amine
salt groups.
[0070] As discussed below, the electron-withdrawing groups to which
reference is made herein are formed by the reaction of the
polyisocyanate curing agent (2) with the pendant and/or terminal
hydroxyl and/or amino groups represented by X and Y in structure
(II) which are bonded in the beta-position relative to the nitrogen
atom depicted in this structure. The amount of free or unbound
amine nitrogen present in a cured free film of the
electrodepositable composition can be determined as follows. The
cured free coating film can be cryogenically milled and dissolved
with acetic acid then titrated potentiometrically with acetous
perchloric acid to determine the total base content of the sample.
The primary amine content of the sample can be determined by
reaction of the primary amine with salicylaldehyde to form an
untitratable azomethine. Any unreacted secondary and tertiary amine
then can be determined by potentiometric titration with perchloric
acid. The difference between the total basicity and this titration
represents the primary amine. The tertiary amine content of the
sample can be determined by potentiometric titration with
perchloric acid after reaction of the primary and secondary amine
with acetic anhydride to form the corresponding amides.
[0071] In one embodiment of the present invention, the terminal
amino groups have the structure (II) where both X and Y comprise
primary amino groups, e.g., the amino group is derived from
diethylenetriamine. It should be understood that in this instance,
prior to reaction with the polymer, the primary amino groups can be
blocked, for example, by reaction with a ketone such as methyl
ethyl ketone, to form the diketimine. Such ketimines are those
described in U.S. Pat. No. 4,104,147, column 6, line 23 to column
7, line 23. The ketimine groups can decompose upon dispersing the
amine-epoxy reaction product in water, thereby providing free
primary amine groups as curing reaction sites.
[0072] Minor amounts (e.g., an amount which would represent less
than or equal to 5 percent of total amine nitrogen present in the
composition) of amines such as mono, di, and trialkylamines and
mixed aryl-alkyl amines which do not contain hydroxyl groups, or
amines substituted with groups other than hydroxyl provided that
the inclusion of such amines does not negatively affect the
photodegradation resistance of the cured electrodeposited coating.
Specific examples include monoethanolamine, N-methylethanolamine,
ethylamine, methylethylamine, triethylamine, N-benzyldimethylamine,
dicocoamine and N,N-dimethylcyclohexylamine.
[0073] The reaction of the above-described amines with epoxide
groups on the polymer takes place upon mixing of the amine and
polymer. The amine may be added to the polymer or vice versa. The
reaction can be conducted neat or in the presence of a suitable
solvent such as methyl isobutyl ketone, xylene, or
1-methoxy-2-propanol. The reaction is generally exothermic and
cooling may be desired. However, heating to a moderate temperature
of about 50.degree. C. to 150.degree. C. may be done to hasten the
reaction.
[0074] The active hydrogen-containing, cationic salt
group-containing polymer used in the electrodepositable composition
is prepared from components selected so as to maximize the
photodegradation resistance of the polymer and the resulting cure
electrodeposited composition. Though not intending to be bound by
any theory, it is believed that photodegradation resistance (i.e.,
resistance to visible and ultraviolet degradation) of the cured
electrodeposited coating can be correlated with the location and
nature of nitrogen-containing cationic groups used for dispersion
of the active hydrogen-containing, cationic amine salt
group-containing resin.
[0075] For purposes of the present invention, the amines from which
the pendant and/or terminal amino groups are derived comprise
primary and/or secondary amine groups such that the active
hydrogens of said amines will be consumed by reaction with the at
least partially blocked aliphatic polyisocyanate curing agent (2)
to form urea groups or linkages during the curing reaction. The
urea groups formed during the curing reaction appear to have no
significant negative influence on photodegradation resistance of
the cured electrodeposited coating where the subsequently applied
top coat has at least 0.1 percent light transmission as measured at
400 nanometers.
[0076] In one embodiment of the present invention, a polyepoxide
polymer can be "defunctionalized" with an excess of ammonia,
yielding a polymer comprising one or more of the following
structural units (III). Cationic salt groups subsequently can be
formed by admixing such a polymer with a suitable solubilizing acid
to promote dispersion in water. 4
[0077] In an alternative embodiment of the present invention, the
cationic polymer (1) can comprise a polyepoxide polymer having
pendant and/or terminal amino groups comprising primary amine
groups from which cationic amine salts can be formed. Such a
polymer can be prepared, for example, by reacting diethylene
triamine bis-ketamine with an epoxy group containing polymer,
followed by hydrolysis to decompose the ketimine. Such a polymer
can comprise one or more of the following structural units (IV):
5
[0078] It was surprising to find that, despite the presence of the
tertiary nitrogen in this structural unit, electrodeposited
compositions comprising such polymers exhibit improved
photodegradation resistance. Without intending to be bound by
theory, it is believed that this is due to the formation during the
cure reaction with the polyisocyanate curing agent of two strong
electron-withdrawing groups (in this case, urea groups) bonded in
the beta-position relative to the tertiary nitrogen.
[0079] Likewise, it was found that polymers comprising other
structural units having isocyanate-reactive groups in the
beta-position relative to the nitrogen atom also can exhibit
similar photodegradation resistance. Such polymers can comprise,
for example, the following structural units (V) and (VI): 6
[0080] Upon reaction of polymers having one or more of the
structural units (VI) with the polyisocyanate curing agent (2),
electron-withdrawing urethane groups are formed at the
beta-position relative to the tertiary nitrogen atoms which are
derived from the pendant and/or terminal amino groups. Likewise,
upon reaction of polymers having one or more of the structural
units (V) with the polyisocyanate curing agent (2),
electron-withdrawing urethane and urea groups are formed at the
beta-position relative to the tertiary nitrogen atoms derived from
the pendant and/or terminal amino groups.
[0081] As used herein, in the specification and in the claims, by
"electron-withdrawing group" is meant a group (e.g., a urethane or
urea group) that tends to draw electrons or electronegative charge
from the amine nitrogen atom, thereby rendering the amine nitrogen
less basic. Such electron-withdrawing groups can be derived from
the reaction of the polyisocyanate curing agent (2) with the
hydroxyl and/or amino groups, represented by X and Y in structure
(II) above, which are pendant and/or terminal from the resin (1).
Moreover, it should be understood that for purposes of the present
invention, the urethane groups derived from the reaction of the
polyisocyanate curing agent and the hydroxyl groups along the
polymer backbone, and/or the secondary hydroxyl groups which are
formed upon the ring opening of an epoxy group, are not intended to
be within the meaning of the term "electron-withdrawing
group(s)".
[0082] It has been found that polymers comprising primarily
structural units such as structural units (VII) and/or (VIII)
below, where R represents an unsubstituted alkyl group, exhibit
significantly poorer photodegradation resistance as compared to
those polymers discussed immediately above. Without intending to be
bound by theory, it is believed that the poorer photodegradation
resistance of such polymers comprising primarily structural units
(VII) and/or (VIII) can be attributed to the fact that the basic
nitrogens are present in the backbone of the polymer (and are not
pendant and/or terminal with respect to the polymer backbone)
and/or do not react with the polyisocyanate curing agent to
generate two electron-withdrawing groups in the beta-position
relative to the basic amine group. 7
[0083] It can be inferred by those skilled in the art from the
generally poorer cure response of cationic epoxies containing a
preponderance of structural units (VII) and (VIII), that the
hydroxyl groups beta to phenoxy groups on the backbone of (VII) and
near the end of structural unit (VIII) do not effectively
participate in cure, i.e. they are not completely converted to
electron-withdrawing urethane groups during the curing step. Also,
it should here be noted that the degree of consumption of basic
nitrogen by reaction with the polyisocyanate curing agent can be
measured by titration of the cryogenically ground
electrodepositable composition after the curing step as described
above.
[0084] If desired, a minor amount of the polymer(s) having the
structural units (VII) and/or (VIII) can be included in the
electrodepositable coating compositions of the present invention,
provided that such polymers are not present in an amount sufficient
to negatively affect photodegradation resistance of the cured
electrodeposited coating.
[0085] The active hydrogen-containing, terminal amino
group-containing polymer is rendered cationic and water dispersible
by at least partial neutralization with an acid. Suitable acids
include organic and inorganic acids such as formic acid, acetic
acid, lactic acid, phosphoric acid, dimethylolpropionic acid, and
sulfamic acid. Mixtures of acids can be used. The extent of
neutralization varies with the particular reaction product
involved. However, sufficient acid should be used to disperse the
electrodepositable composition in water. Typically, the amount of
acid used provides at least 30 percent of the total theoretical
neutralization. Excess acid may also be used beyond the amount
required for 100 percent total theoretical neutralization.
[0086] The extent of cationic salt group formation should be such
that when the polymer is mixed with an aqueous medium and the other
ingredients, a stable dispersion of the electrodepositable
composition will form. By "stable dispersion" is meant one that
does not settle or is easily redispersible if some settling occurs.
Moreover, the dispersion should be of sufficient cationic character
that the dispersed particles will migrate toward and electrodeposit
on a cathode when an electrical potential is set up between an
anode and a cathode immersed in the aqueous dispersion.
[0087] Generally, the cationic polymer is ungelled and contains
from about 0.1 to 3.0, preferably from about 0.1 to 0.7
millequivalents of cationic salt group per gram of polymer
solids.
[0088] The active hydrogens associated with the cationic polymer
include any active hydrogens which are reactive with isocyanates
within the temperature range of about 93.degree. C. to 204.degree.
C., preferably about 121.degree. C. to 177.degree. C. Typically,
the active hydrogens are selected from the group consisting of
hydroxyl and primary and secondary amino, including mixed groups
such as hydroxyl and primary amino Preferably, the polymer will
have an active hydrogen content of about 1.7 to 10 millequivalents,
more preferably about 2.0 to 5 millequivalents of active hydrogen
per gram of polymer solids.
[0089] The cationic salt group-containing polymer can be present in
the electrodepositable composition used in the processes of the
present invention in an amount ranging from 20 to 80 percent, often
from 30 to 75 percent by weight, and typically from 50 to 70
percent by weight based on the total combined weight of resin
solids of the cationic salt group-containing polymer and the curing
agent.
[0090] As mentioned above, the resinous phase of the
electrodepositable coating composition further comprises (2) a
curing agent adapted to react with the active hydrogen groups of
the cationic electrodepositable resin (1) described immediately
above. In one embodiment of the present invention, the curing agent
(2) comprises one or more at least partially blocked aliphatic
polyisocyanates. In this embodiment, a minor amount (i.e. less than
10, preferably less than 5 weight percent of total resin solids of
the curing agent present in the composition) of aromatic
polyisocyanate can be included, provided that the aromatic
polyisocyanate is not present in an amount sufficient to
deleteriously affect the photodegradation resistance of the cured
electrodeposited composition.
[0091] The curing agents employed in cationic electrodeposition
compositions of the present invention typically are blocked
aliphatic polyisocyanates. The aliphatic polyisocyanates can be
fully blocked as described in U.S. Pat. No. 3,984,299 column 1
lines 1 to 68, column 2 and column 3 lines 1 to 15, or partially
blocked and reacted with the polymer backbone as described in U.S.
Pat. No. 3,947,338 column 2 lines 65 to 68, column 3 and column 4
lines 1 to 30. By "blocked" is meant that the isocyanate groups
have been reacted with a compound such that the resultant blocked
isocyanate group is stable to active hydrogens at ambient
temperature but reactive with active hydrogens in the film forming
polymer at elevated temperatures usually between 90.degree. C. and
200.degree. C. In one embodiment of the present invention, the
polyisocyanate curing agent is a fully blocked polyisocyanate with
substantially no free isocyanate groups.
[0092] Diisocyanates typically are used, although higher
polyisocyanates can be used in lieu of or in combination with
diisocyanates. Examples of aliphatic polyisocyanates suitable for
use as curing agents include cycloaliphatic and araliphatic
polyisocyanates such as 1,6-hexamethylene diisocyanate, isophorone
diisocyanate, bis-(isocyanatocyclohexyl)methane, polymeric
1,6-hexamethylene diisocyanate, trimerized isophorone diisocyanate,
norbornane diisocyanate and mixtures thereof. In a particular
embodiment of the present invention, the curing agent (2) comprises
a fully blocked polyisocyanate selected from a polymeric
1,6-hexamethylene diisocyanate, isophorone diisocyanate, and
mixtures thereof. In another embodiment of the present invention
the polyisocyanate curing agent comprises a fully blocked trimer of
hexamethylene diisocyanate available as Desmodur N3300.RTM. from
Bayer Corporation.
[0093] In one embodiment of the present invention, the
polyisocyanate curing agent (2) is at least partially blocked with
at least one blocking agent selected from a 1,2-alkane diol, for
example 1,2-propanediol, a 1,3-alkane diol, for example
1,3-butanediol, a benzylic alcohol, for example, benzyl alcohol, an
allylic alcohol, for example, allyl alcohol, caprolactam, a
dialkylamine, for example dibutylamine, and mixtures thereof. In a
further embodiment of the present invention, the polyisocyanate
curing agent (2) is at least partially blocked with at least one
1,2-alkane diol having three or more carbon atoms, for example
1,2-butanediol.
[0094] If desired, the blocking agent can further comprise minor
amounts of other well known blocking agents such as aliphatic,
cycloaliphatic, or aromatic alkyl monoalcohol or phenolic compound,
including, for example, lower aliphatic alcohols such as methanol,
ethanol, and n-butanol; cycloaliphatic alcohols such as
cyclohexanol; aromatic-alkyl alcohols such as phenyl carbinol and
methylphenyl carbinol; and phenolic compounds such as phenol itself
and substituted phenols wherein the substituents do not affect
coating operations, such as cresol and nitrophenol. Glycol ethers
and glycol amines may also be used as blocking agents. Suitable
glycol ethers include ethylene glycol butyl ether, diethylene
glycol butyl ether, ethylene glycol methyl ether and propylene
glycol methyl ether. Other suitable blocking agents include oximes
such as methyl ethyl ketoxime, acetone oxime and cyclohexanone
oxime. As mentioned above, these conventional blocking agents can
be used in minor amounts provided that they are not present in
amounts sufficient to deleteriously affect photodegradation
resistance of the cured electrodeposited coating.
[0095] The at least partially blocked polyisocyanate curing agent
(2) can be present in the electrodepositable composition used in
the processes of the present invention in an amount ranging from 80
to 20 percent, often from 75 to 30, and typically from 70 to 50
percent by weight, based on the total combined weight of resin
solids of the cationic salt group-containing polymer (1) and the
curing agent (2).
[0096] As mentioned above, the present invention also is directed
to an "alternative process" for coating any of the metal substrates
described in detail above comprising: (a) electrophoretically
depositing on at least a portion of the substrate a curable,
electrodepositable coating composition described below; (b) heating
the substrate to a temperature of 250.degree. F. to 400.degree. F.
(121.1.degree. C. to 204.4.degree. C.) for a time sufficient to
effect cure of the electrodepositable composition; (c) applying
directly to the electrodepositable composition one or more
pigment-containing coating compositions and/or one or more
pigment-free coating compositions to form a top coat thereover; and
(d) heating the coated substrate to a temperature and for a time
sufficient to effect cure of the top coating composition(s).
[0097] This "alternative process" can include one or more optional
steps, as outlined below: (a) optionally forming a metal object
from the substrate; (b) optionally cleaning the substrate with an
alkaline and/or acidic cleaner such as any of those described
above; (c) optionally pretreating the substrate with a solution
selected from the group consisting of a metal phosphate solution,
an aqueous solution containing at least one Group IIIB or IVB
metal, an organophosphate solution, an organophosphonate solution,
and combinations thereof, suitable examples of which are described
above; (d) optionally rinsing the substrate with water; (e)
electrophoretically depositing on the substrate the curable,
electrodepositable coating composition described below; (f) heating
the substrate to a temperature ranging from 250.degree. F. to
400.degree. F. (121.1.degree. C. to 204.4.degree. C.) for a time
sufficient to effect cure of the electrodepositable composition;
(g) applying directly to the electrodepositable composition one or
more pigment-containing coating compositions and/or one or more
pigment-free coating compositions to form a top coat thereover: and
(h) heating the coated substrate to a temperature and for a time
sufficient to effect cure of the top coating composition(s).
[0098] Note that the order of the alternative process steps (a)
through (h) can be altered with the same results and without
departing from the scope of the invention. Also, additional water
rinsing steps can be added as necessary.
[0099] Also provided is a curable, electrodepositable coating
composition used in the above "alternative process". This
composition comprises: (1) an active hydrogen-containing, cationic
salt group-containing resin electrodepositable on a cathode,
derived from a polyglycidyl ether of a polyhydric phenol that is
essentially free of aliphatic carbon atoms to which are bonded more
than one aromatic group; and (2) an at least partially blocked
polyisocyanate curing agent essentially free of isocyanato groups
or blocked isocyanato groups to which are bonded aromatic
groups.
[0100] The curable electrodepositable coating composition for use
in the "alternative processes" of the present invention typically
comprises an amine salt group-containing resin (1) in conjunction
with an at least partially blocked polyisocyanate curing agent (2).
In a particular embodiment, this composition comprises a cationic
polyepoxide resin which comprises a chain-extended polyglycidyl
ether of a polyhydric phenol having cationic salt groups and active
hydrogen groups selected from aliphatic hydroxyl and primary and
secondary amino groups.
[0101] Such a chain-extended polyepoxide can be prepared by
reacting together the polyepoxide and a polyhydroxyl or
polycarboxyl group-containing material neat, or in the presence of
an inert organic solvent such as a ketone, including methyl
isobutyl ketone and methyl amyl ketone, aromatic solvents such as
toluene and xylene, and glycol ethers such as the dimethyl ether of
diethylene glycol. The reaction usually is conducted at a
temperature ranging from 80.degree. C. to 160.degree. C. for 30 to
180 minutes, until an epoxy group-containing resinous reaction
product is obtained. In general, the epoxide equivalent weight of
such polyepoxides will range from 100 to 2000, typically from 180
to 500. The epoxy compounds may be saturated or unsaturated, cyclic
or acyclic, aliphatic, alicyclic, aromatic or heterocyclic. They
may contain substituents such as halogen, hydroxyl, and ether
groups.
[0102] Examples of polyepoxides suitable for use in the alternative
compositions are those having a 1,2-epoxy equivalency greater than
one and preferably about two; that is, polyepoxides that have on
average two epoxide groups per molecule. Suitable polyepoxides are
polyglycidyl ethers of polyhydric phenols that are essentially free
of aliphatic carbon atoms to which are bonded more than one
aromatic group. In one alternative embodiment, such polyepoxides
comprise polyglycidyl ethers of polyhydric phenols selected from
the group consisting of resorcinol, hydroquinone, catechol, and
mixtures thereof. In another embodiment, these polyepoxides
comprise polyglycidyl ethers of polyhydric phenols selected from
resorcinol, catechol and mixtures thereof. These polyglycidyl
ethers of polyhydric phenols can be produced by etherification of
polyhydric phenols with an epihalohydrin or dihalohydrin such as
epichiorohydrin or dichlorohydrin in the presence of alkali.
[0103] In the electrodepositable compositions for use in the
alternative processes of the present invention, the cationic salt
group-containing resin comprises at least 16 percent by weight,
typically least 30 percent by weight, based on the total weight of
resin solids, of a functional group having the following structure:
8
[0104] Examples of polyhydroxyl group-containing materials used to
chain extend or increase the molecular weight of the polyepoxide
(i.e., through hydroxyl-epoxy reaction) include any of the
polyhydric phenols listed above. Other polyols can also be used in
chain extension. Examples of cyclic polyols include alicyclic
polyols, particularly cycloaliphatic polyols such as
1,2-cyclohexane diol, 1,4-cyclohexane diol,
2,2-bis(4-hydroxycyclohexyl)propane,
1,1-bis(4-hydroxycyclohexyl)ethane,
2-methyl-1,1-bis(4-hydroxycyclohexyl)propane,
2,2-bis(4-hydroxy-3-tertiar- ybutylcyclohexyl)propane,
1,3-bis(hydroxymethyl)cyclohexane and
1,2-bis(hydroxymethyl)cyclohexane. Examples of aliphatic polyols
include, inter alia, trimethylpentanediol and neopentyl glycol.
Polymeric polyols suitable for chain extension include polyester
polyols such as those described in U.S. Pat. No. 4,148,772; and
urethane diols such as those described in U.S. Pat. No. 4,931,157,
with the proviso that the polyols described in these patents should
be essentially free of aliphatic carbon atoms to which are bonded
more than one aromatic group. Mixtures of alcoholic hydroxyl
group-containing materials and phenolic hydroxyl group-containing
materials may also be used.
[0105] The equivalent ratio of reactants; i.e., epoxy:polyhydroxyl
group-containing material during chain extension typically is from
1.00:0.75 to 1.00:2.00. The chain extension of such polyepoxides
can also be performed using a polycarboxylic acid material, most
often a dicarboxylic acid. Useful dicarboxylic acids include acids
having the general formula: HOOC--R--COOH, where R is a divalent
moiety that is substantially unreactive with the polyepoxide. R can
be a straight chained or a branched alkylene or alkylidene moiety
normally containing from 2 to 42 carbon atoms. Some examples of
suitable dicarboxylic acids include cyclohexanedicarboxylic acid,
which is preferred, adipic acid, 3,3-dimethylpentanedioic acid,
benzenedicarboxylic acid, phenylenediethanoic acid,
naphthalenedicarboxylic acid, pimelic acid, suberic acid, azelaic
acid, sebacic acid and the like. It should be understood that
dicarboxylic acids of the above general formula where R is a moiety
of less than 4 carbon atoms can include, for example, oxalic acid,
malonic acid, succinic acid, and glutaric acid, but these acids are
less preferred. Additional suitable dicarboxylic acids include
substantially saturated acyclic, aliphatic dimer acids formed by
the dimerization reaction of fatty acids having from 4 to 22 carbon
atoms and a terminal carboxyl group (forming dimer acids having
from 8 to 44 carbon atoms). Dimer acids are well known in the art
and are commercially available from Emery Industries, Inc. under
the name EMPOL.RTM.. Dicarboxylic acids can be formed as reaction
products of anhydrides and diols or diamines at reaction conditions
and techniques known to those skilled in the art for the particular
reactants. Diols can include polytetramethylene glycols,
polycaprolactones, polypropylene glycols, polyethylene glycols, and
the like. Suitable anhydrides include maleic, phthalic,
hexahydrophthalic, tetrahydrophthalic and the like. Additionally,
dicarboxylic acids formed by the reaction of an anhydride and a
diamine can be used. Dicarboxylic acids formed by the reaction of a
polyoxyalkylenediamine such as polyoxypropylenediamine,
commercially available from Huntsman Chemical Company under the
name JEFFAMINE.RTM.), with an anhydride like those listed above can
be used.
[0106] Typically, the amount of dicarboxylic acid used to chain
extend the polyepoxide is sufficient to provide from 0.05 to 0.6,
often from 0.2 to 0.4 acid groups per epoxide group. This reaction
normally is carried out at between 80.degree. C. and 175.degree.
C.
[0107] Materials having mixed hydroxyl and carboxyl functionality,
such as 2-hydroxypivalic acid, are also suitable for use as chain
extending agents. Materials having mixed hydroxyl/amino and
amino/carboxyl functionality may also be used, some of which are
further described below.
[0108] The chain-extended polyepoxides can have number average
molecular weights ranging from 1000 to 3000, typically from 1700 to
2600. Epoxy group-containing acrylic polymers can also be used. One
particular suitable polyepoxide is a cycloaliphatic diepoxide
available as EPON X1510.RTM. from Shell Oil and Chemical Company,
chain extended with a material selected from resorcinol, catechol
and mixtures thereof.
[0109] Any of the previously described acrylic, polyester,
polyurethane and polyepoxide resins also can be used in conjunction
with the polyepoxides described immediately above (i.e., those used
in the alternative compositions).
[0110] As mentioned above, the compositions used in the alternative
processes of the present invention comprise a resin, such as the
polyepoxides described immediately above, having cationic salt
groups. The cationic salt groups can be incorporated into the resin
by reacting the epoxy group-containing resinous reaction product
prepared as described above with a material capable of forming
cationic salt groups. Such a material is reactive with epoxy groups
and can be acidified before, during, or after reaction with the
epoxy groups to form cationic salt groups. Examples of suitable
materials include amines such as primary or secondary amines which
can be acidified after reaction with the epoxy groups to form amine
salt groups, or tertiary amines which can be acidified prior to
reaction with the epoxy groups and which after reaction with the
epoxy groups form quaternary ammonium salt groups. Examples of
other suitable materials include sulfides, which can be mixed with
acid prior to reaction with the epoxy groups and form ternary
sulfonium salt groups upon subsequent reaction with the epoxy
groups.
[0111] When amines are used to form cationic salt groups,
monoamines, typically hydroxyl-containing amines, are employed.
Polyamines may be used but are not recommended because of a
tendency to gel the resin.
[0112] In one embodiment of the invention, the cationic salt
group-containing resin (used in the alternative electrodepositable
compositions) contains amine salt groups which are derived from an
amine containing a nitrogen atom to which is bonded at least one,
preferably two, alkyl groups having a hetero atom in a
beta-position relative to the nitrogen atom. A hetero atom is a
non-carbon or non-hydrogen atom, typically oxygen, nitrogen, or
sulfur.
[0113] Hydroxyl-containing amines, when used for this purpose, can
impart the resin with amine groups comprising a nitrogen atom to
which is bonded at least one alkyl group having a hetero atom in a
beta-position relative to the nitrogen atom. Examples of
hydroxyl-containing amines are alkanolamines, dialkanolamines,
alkyl alkanolamines, and aralkyl alkanolamines containing from 1 to
18 carbon atoms, typically from 1 to 6 carbon atoms in each of the
alkanol, alkyl and aryl groups. Specific examples include
ethanolamine, N-methylethanolamine, diethanolamine,
N-phenylethanolamine, N,N-dimethylethanolamine,
N-methyidiethanolamine, and N-(2-hydroxyethyl)-piperazine. In one
particular alternative embodiment of the present invention amines
are selected from the group consisting of diethylenetriamine,
diethylenetriamine bisketimine, aminopropyldiethanolamine,
aminopropylmorpholine, N-(2-aminoethyl)-morpho- line, and mixtures
thereof.
[0114] Minor amounts of amines such as mono, di, and trialkylamines
and mixed aryl-alkyl amines which do not contain hydroxyl groups,
or amines substituted with groups other than hydroxyl which do not
negatively affect the reaction between the amine and the epoxy also
can be used, Specific examples include ethylamine,
methylethylamine, triethylamine, N-benzyldimethylamine, dicocoamine
and N,N-dimethylcyclohexylamine.
[0115] Mixtures of the above mentioned amines also may be used.
Note that for purposes of this alternative embodiment of the
invention, all of the amines mentioned above as suitable for use as
cationic salt group formers may also be used to chain extend the
polyepoxide prior to salt group formation.
[0116] The reaction of a primary and/or secondary amine with the
polyepoxide takes place upon mixing of the amine and polyepoxide.
The amine may be added to the polyepoxide or vice versa. The
reaction can be conducted neat, or in the presence of, a suitable
solvent such as methyl isobutyl ketone, xylene, or
1-methoxy-2-propanol. The reaction is generally exothermic and
cooling may be desired. However, heating to a moderate temperature
of about 50.degree. C. to 150.degree. C. may be done to hasten the
reaction.
[0117] The reaction product of the primary and/or secondary amine
and the polyepoxide is made cationic and water dispersible by at
least partial neutralization with an acid. Suitable acids include
any of the organic and inorganic neutralizing acids mentioned
above. The extent of neutralization varies with the particular
reaction product involved, However, sufficient acid should be used
to disperse the electrodepositable composition in water. Typically,
the amount of acid used provides at least 20 percent of all of the
total theoretical neutralization. Excess acid also may be used
beyond the amount required for 100 percent total theoretical
neutralization.
[0118] In the reaction of a tertiary amine with a polyepoxide, the
tertiary amine can be prereacted with the neutralizing acid to form
the amine salt and then the amine salt reacted with the polyepoxide
to form a quaternary salt group-containing resin. The reaction is
conducted by mixing the amine salt with the polyepoxide in water.
Typically the water is present in an amount ranging from about 1.75
to about 20 percent by weight based on total reaction mixture
solids.
[0119] In forming the quaternary ammonium salt group-containing
resin, the reaction temperature can be varied from the lowest
temperature at which the reaction will proceed, generally at or
slightly above room temperature, to a maximum temperature of about
100.degree. C. (at atmospheric pressure). At higher pressures,
higher reaction temperatures may be used. Preferably the reaction
temperature is in the range of about 60.degree. C. to 100.degree.
C. Solvents such as a sterically hindered ester, ether, or
sterically hindered ketone may be used, but their use is not
necessary.
[0120] In addition to the primary, secondary, and tertiary amines
disclosed above, a portion of the amine that is reacted with the
polyepoxide can be a ketimine of a polyamine, such as those
described above.
[0121] In addition to resins containing amine salts and quaternary
ammonium salt groups, cationic resins containing ternary sulfonium
groups may be used in forming the cationic polyepoxide used in this
alternative embodiment. Examples of these resins and their method
of preparation are described in U.S. Pat. Nos. 3,793,278 to DeBona
and U.S. Pat. No. 3,959,106 to Bosso et al., incorporated herein by
reference.
[0122] Generally, the cationic resin is ungelled and contains from
about 0.1 to 3.0, preferably from about 0.1 to 0.7 millequivalents
of cationic salt group per gram of resin solids. Typically, the
polyepoxide will have an active hydrogen content of 1.7 to 10
millequivalents, and often 2.0 to 5 millequivalents of active
hydrogen per gram of resin solids.
[0123] The cationic salt group-containing resin can be present in
the alternative composition of the present invention in an amount
ranging from 20 to 80 percent, often 30 to 75 percent by weight,
and typically 40 to 70 percent by weight based on the total
combined weight of resin solids of the cationic salt
group-containing resin (1) and the curing agent (2).
[0124] The polyisocyanate curing agent used in the alternative
compositions of the present invention can be at least partially
blocked, and typically is a fully blocked polyisocyanate with
substantially no free isocyanate groups. The polyisocyanate can be
an aliphatic or an aromatic polyisocyanate, or a mixture of the
two, however, the curing agent is essentially free of isocyanato
groups or blocked isocyanato groups to which are bonded aromatic
groups. That is, for purposes of the alternative compositions, any
aromatic groups present in the curing agent are not directly bonded
to the isocyanato groups. Diisocyanates are most often employed,
although higher polyisocyanates can be used in lieu of or in
combination with diisocyanates.
[0125] Examples of suitable aliphatic diisocyanates include any of
the previously described aliphatic polyisocyanates. Examples of
suitable aralkyl diisocyanates are meta-xylylene diisocyanate and
.alpha. .alpha. .alpha.' .alpha.' tetramethylmeta-xylylene
diisocyanate. A preferred polyisocyanate is a fully blocked trimer
of hexamethylene diisocyanate available as DESMODUR N3300 from
Bayer Corporation.
[0126] Isocyanate prepolymers, for example, reaction products of
polyisocyanates with polyols such as neopentyl glycol and
trimethylol propane or with polymeric polyols such as
polycaprolactone diols and triols (NCO/OH equivalent ratio greater
than one) can also be used.
[0127] For purposes of the alternative embodiment of the present
invention, any suitable aliphatic, cycloaliphatic, or aromatic
alkyl monoalcohol or phenolic compound may be used as a capping
agent for the polyisocyanate including, for example, lower
aliphatic alcohols such as methanol, ethanol, and n-butanol;
cycloaliphatic alcohols such as cyclohexanol; aromatic-alkyl
alcohols such as phenyl carbinol and methylphenyl carbinol; and
phenolic compounds such as phenol itself and substituted phenols
wherein the substituents do not affect coating operations, such as
cresol and nitrophenol. Glycol ethers may also be used as capping
agents. Suitable glycol ethers include ethylene glycol butyl ether,
diethylene glycol butyl ether, ethylene glycol methyl ether and
propylene glycol methyl ether. Diethylene glycol butyl ether is
preferred among the glycol ethers.
[0128] Other suitable capping agents include oximes such as methyl
ethyl ketoxime, acetone oxime and cyclohexanone oxime, lactams such
as epsilon-caprolactam, and secondary amines such as dibutyl
amine.
[0129] The polyisocyanate curing agent can be present in the
alternative composition of the present invention in an amount of 20
to 80 percent, usually 30 to 75 percent by weight, typically 50 to
70 percent by weight based on the total combined weight of resin
solids of the cationic salt group-containing resin (1) and the
curing agent (2).
[0130] This compositions of the alternative embodiment of the
present invention, when applied to a substrate and properly cured,
then subjected to corrosion testing such as a standard ASTM B117
salt spray test or a cyclic test such as GM Engineering Standard
9540P, Method B, will have no more scribe corrosion than exhibited
by suitable controls containing aromatic isocyanates and/or
Bisphenol A based aromatic polyepoxides. When top coated with a
transparent base coat and/or clear coat composition having greater
than 50% light transmission measured at 400 nanometers wave length,
it will endure at least 1500 hours xenon arc accelerated weathering
as per SAE J1960 without substantial degradation. Any of the
previously described electrodepositable coating compositions can
further comprise at least one source of a metal selected from rare
earth metals, yttrium, bismuth, zirconium, tungsten, and mixtures
thereof. The at least one source of metal typically is present in
the electrodepositable composition in an amount of 0.005 to 5
percent by weight metal, based on the total weight of resin solids
in the coating composition. Yttrium typically is employed.
[0131] Both soluble and insoluble yttrium compounds may serve as
the source of yttrium in the electrodepositable composition used in
the process of the present invention. Examples of yttrium sources
suitable for use in the electrodepositable composition are soluble
organic and inorganic yttrium salts such as yttrium acetate,
yttrium chloride, yttrium formate, yttrium carbonate, yttrium
sulfamate, yttrium lactate and yttrium nitrate. When the yttrium is
to be added to the composition as an aqueous solution, yttrium
nitrate, a readily available yttrium compound, is a preferred
yttrium source Other suitable yttrium compounds are organic and
inorganic yttrium compounds such as yttrium oxide, yttrium bromide,
yttrium hydroxide, yttrium molybdate, yttrium sulfate, yttrium
silicate, and yttrium oxalate. Organoyttrium complexes and yttrium
metal can also be used. When the yttrium is to be incorporated into
the composition as a component in a pigment paste, yttrium oxide is
the preferred source of yttrium.
[0132] Suitable rare earth metal compounds include soluble,
insoluble, organic, and inorganic salts of rare earth metals, such
as acetates, oxalates, formates, lactates, oxides, hydroxides,
molybdates, etc., of the rare earth metals.
[0133] There are various methods by which the yttrium, bismuth,
zirconium, tungsten, or rare earth metal compound can be
incorporated into any of the electrodepositable compositions used
in any of the processes of the present invention. A soluble
compound may be added "neat," that is, added directly to the
composition without prior blending or reacting with other
components. Alternatively, a soluble compound can be added to the
predispersed clear polymer feed which may include the cationic
polymer, the curing agent and/or any other non-pigmented component.
Preferably, a soluble compound is added "neat". Insoluble compounds
and/or metal pigments, on the other hand, are preferably
pre-blended with a pigment paste component prior to the
incorporation of the paste to the electrodepositable
composition.
[0134] Any of the above described electrodepositable compositions
used in any of the processes of the present invention can contain
yttrium, bismuth, zirconium, tungsten, or a rare earth metal as the
sole corrosion inhibiting inorganic component or can be
supplemented with other corrosion inhibiting inorganic or organic
components such as calcium. In one embodiment of the present
invention, the electrodepositable coating composition used in the
processes and photodegradation resistant coatings and multi-layer
composite coatings of the present invention is substantially free
of heavy metals such as lead.
[0135] Any of the previously described electrodepositable
compositions of the present invention can further comprise a
hindered amine light stabilizer for added UV degradation
resistance, but it is not required Such hindered amine light
stabilizers include those disclosed in U.S. Pat. No. 5,260,135.
When used, these materials can be present in the electrodepositable
composition in an amount of 0.1 to 2 percent by weight, based on
the total weight of polymer solids in the electrodepositable
composition.
[0136] The compositions when used as an electrodeposition bath in
any of the previously described processes of the present invention
have a polymer solids content usually within the range of about 5
to 25 percent by weight based on total weight of the
electrodeposition bath.
[0137] Besides water, the aqueous medium of the electrodeposition
bath may contain a coalescing solvent. Useful coalescing solvents
include hydrocarbons, alcohols, esters, ethers and ketones. The
preferred coalescing solvents include alcohols, polyols and
ketones. Specific coalescing solvents include isopropanol, butanol,
2-ethylhexanol, isophorone, 2-methoxypentanone, ethylene and
propylene glycol and the monoethyl, monobutyl and monohexyl ethers
of ethylene glycol. The amount of coalescing solvent is generally
between about 0.01 and 25 percent and when used, preferably from
about 0.05 to about 5 percent by weight based on total weight of
the aqueous medium.
[0138] As mentioned above, a pigment composition and other optional
additives such as surfactants, wetting agents or catalyst can be
included in the electrodeposition bath. The pigment composition may
be of the conventional type comprising inorganic pigments, for
example, iron oxides, china clay, carbon black, coal dust, titanium
dioxide, talc, barium sulfate, as well as organic color pigments
such as phthalocyanine green and the like. The pigment content of
the dispersion is usually expressed as a pigment-to-polymer ratio.
In the practice of the invention, when pigment is employed, the
pigment-to-polymer ratio is usually within the range of about 0.02
to 1:1. The other additives mentioned above are usually in the
dispersion in amounts of about 0.01 to 3 percent by weight based on
weight of polymer solids.
[0139] All of the electrodepositable coating compositions of the
present invention are in the form of an aqueous dispersion. The
term "dispersion" is believed to be a two-phase transparent,
translucent or opaque resinous system in which the resin is in the
dispersed phase and the water is in the continuous phase. The
average particle size of the resinous phase is generally less than
1.0, usually less than 0.5 microns, and typically less than 0.15
micron.
[0140] The concentration of the resinous phase in the aqueous
medium is at least 1 and usually from 2 to 60 percent by weight
based on total weight of the aqueous dispersion. When the
compositions of the present invention are in the form of resin
concentrates, they generally have a resin solids content of 20 to
60 percent by weight based on weight of the aqueous dispersion.
[0141] The previously described curable electrodepositable coating
compositions of the present invention typically are supplied as two
components: (1) a clear resin feed, which includes, generally,
active hydrogen-containing, cationic polymer, i.e., the main
film-forming polymer, the at least partially blocked polyisocyanate
curing agent, and any additional water-dispersible, non-pigmented
components; and (2) a pigment paste (described above), which,
generally, includes one or more pigments, a water-dispersible grind
resin which can be the same or different from the main-film forming
polymer, and, optionally, additives such as catalysts, and wetting
or dispersing aids. An electrodeposition bath is prepared by
dispersing components (1) and (2) in an aqueous medium which
comprises water and, usually, coalescing solvents. Alternatively,
the electrodepositable compositions of the present invention can be
supplied as one component compositions.
[0142] Generally, as aforementioned, in the process of
electrodeposition, the metal substrate being coated, serving as a
cathode, and an electrically conductive anode are placed in contact
with the cationic electrodepositable composition. Upon passage of
an electric current between the cathode and the anode while they
are in contact with the electrodepositable composition, an adherent
film of the electrodepositable composition will deposit in a
substantially continuous manner on the electroconductive
substrate.
[0143] In one embodiment, the present invention is directed to an
improved process for forming a photodegradation-resistant
multi-layer coating on an electrically conductive substrate
comprising (a) electrophoretically depositing on the substrate any
of the aqueous, curable electrodepositable coating compositions
described above to form an electrodeposited coating over at least a
portion of the substrate, the substrate serving as a cathode in an
electrical circuit comprising the cathode and an anode, the cathode
and the anode being immersed in the aqueous electrodepositable
coating composition, wherein electric current is passed between the
cathode and the anode to cause the coating to be electrodeposited
over at least a portion of the substrate: (b) heating the coated
substrate at a temperature and for a time sufficient to cure the
electrodeposited coating on the substrate; (c) applying directly to
the cured electrodeposited coating one or more pigment-containing
coating compositions and/or one or more pigment-free coating
compositions to form a top coat over at least a portion of the
cured electrodeposited coating; and (d) heating the coated
substrate of step (c) to a temperature and for a time sufficient to
cure the top coat, the cured top coat having at least 0.1 percent
light transmission as measured at 400 nanometers. The improvement
comprises the inclusion in the circuit of a non-ferrous anode, for
example, anodes comprised of ruthenium oxide and carbon rods.
[0144] In most conventional cationic electrodeposition bath
systems, the anode(s) are comprised of a ferrous material, for
example, stainless steel. A typical cationic bath has an acidic pH
ranging from 4.0 to 7.0, and often from 5.0 to 6.0. However, in a
typical electrodeposition bath system, the anolyte (i.e., the bath
solution in the immediate area of the anode) can have a pH as low
as 3.0 or less due to the concentration of acid at or near the
anode. At these strongly acidic pH ranges, the ferrous anode can
degrade, thereby releasing soluble iron into the bath. By "soluble
iron" is meant Fe.sup.+2 or Fe.sup.+3 ions derived from iron salts
which are at least partially soluble in water. During the
electrodeposition process, the soluble iron is electrodeposited
along with the resinous binder and is present in the cured
electrodeposited coating. It has been found that the presence of
iron in soluble form can contribute to interlayer delamination of
subsequently applied top coat layers from the cured
electrodeposited coating layer upon weathering exposure. In view of
the foregoing, it is desirable that the electrodepositable coating
composition of the present invention, when in the form of an
electrodeposition bath, comprises less than 10 parts per million,
typically less than 1 part per million of soluble iron. This can be
accomplished by the inclusion in the circuit of a non-ferrous
anode.
[0145] Once the above-described electrodepositable coating
composition is electrodeposited over at least a portion of the
electroconductive substrate, the coated substrate is heated to a
temperature and for a time sufficient to cure the electrodeposited
coating on the substrate. The coated substrate can be heated to a
temperature ranging from 250.degree. to 450.degree. F.
(121.1.degree. to 232.2.degree. C.), often from 250.degree. to
400.degree. F. (121.1.degree. to 204.4.degree. C.), and typically
from 300.degree. to 360.degree. (148.9.degree. to 180.degree. C.).
The curing time can be dependent upon the curing temperature as
well as other variables, for example, film thickness of the
electrodeposited coating, level and type of catalyst present in the
composition and the like. For purposes of the present invention,
all that is necessary is that the time be sufficient to effect cure
of the electrodeposited coating on the substrate. For example, the
curing time can range from 10 minutes to 60 minutes, and typically
from 10 to 30 minutes. In one embodiment of the present invention,
the coated substrate is heated to a temperature of 360.degree. F.
(180.degree. C.) or less for a time sufficient to effect cure of
the electrodeposited coating on the substrate. The thickness of the
resultant cured electrodeposited coating usually ranges from 15 to
50 microns.
[0146] As used herein, the term "cure" as used in connection with a
composition, e.g., "a cured composition" shall mean that any
crosslinkable components of the composition are at least partially
crosslinked. In certain embodiments of the present invention, the
crosslink density of the crosslinkable components, i.e., the degree
of crosslinking, ranges from 5% to 100% of complete crosslinking.
In other embodiments, the crosslink density ranges from 35% to 85%
of full crosslinking. In other embodiments, the-crosslink density
ranges from 50% to 85% of full crosslinking. One skilled in the art
will understand that the presence and degree of crosslinking, i.e.,
the crosslink density, can be determined by a variety of methods,
such as dynamic mechanical thermal analysis (DMTA) using a TA
Instruments DMA 2980 DMTA analyzer conducted under nitrogen. This
method determines the glass transition temperature and crosslink
density of free films of coatings or polymers. These physical
properties of a cured material are related to the structure of the
crosslinked network. For purposes of the present invention, a cured
composition, when subjected to double rubs with a cloth soaked in
acetone, will endure at least 100 double rubs before noticeable
degradation (marring) of the coating occurs.
[0147] In another embodiment, the present invention is directed to
a process wherein any of the above-described electrodepositable
coating compositions can be electrophoretically applied to an
electroconductive substrate as in step (a), and heated in an
atmosphere having 5 parts per million or less, typically 1 part per
million or less, of nitrogen oxides (NO.sub.x) to a temperature and
for a time sufficient to cure the electrodeposited coating on the
substrate as described above. The presence of NO.sub.x in the
curing ovens can create an oxidizing atmosphere which can result in
interlayer delamination between the cured electrodeposited coating
and any subsequently applied top coats upon weathering
exposure.
[0148] Nitrogen oxides can be formed during combustion of a
hydrocarbon fuel, such as natural gas used to fuel gas-fired ovens.
Nitrogen oxides form as a result of two oxidation mechanisms: (1)
reaction of nitrogen in the combustion air with excess oxygen
(referred to as thermal NO.sub.x) and (2) reaction of nitrogen that
is chemically bound in the fuel (referred to as fuel NO.sub.x). In
addition, minor amounts of NO.sub.x are formed through complex
interaction of molecular nitrogen with hydrocarbons in the early
phase of the flame front (referred to as prompt NO.sub.x). The
quantity of NO.sub.x created when a fuel burns depends primarily on
temperature, time, and turbulence variables. That is, flame
temperature and the residence time of the fuel/air mixture, along
with the nitrogen content of the fuel and the quantity of excess
air used for combustion determine the NO.sub.x levels present in
the curing oven atmosphere. By delaying the mixing of fuel and air,
low NO.sub.x burners can reduce combustion temperatures, minimize
initial turbulence, and retard the formation of NO.sub.x in the
curing oven to levels of less than 5 parts per million
NO.sub.x.
[0149] Once the electrodeposited coating is cured on the substrate
as in any of the processes of the present invention, one or more
pigment-containing coating compositions and/or one or more
pigment-free coating compositions are applied directly to the cured
electrodeposited coating.
[0150] The use of a primer or primer-surfacer is unnecessary
because of the improved photodegradation resistance afforded by the
various compositions used in any of the processes of the present
invention. Suitable top coats (including base coats, clear coats,
pigmented monocoats, and color-plus-clear composite compositions)
include any of a variety of top coats known in the art, and each
independently may be waterborne, solventborne,in solid particulate
form, i.e., a powder coating composition, or in the form of a
powder slurry. The top coat typically includes a film-forming
polymer, crosslinking material and, if a colored base coat or
monocoat, one or more pigments.
[0151] Non-limiting examples of suitable base coat compositions
include waterborne base coats such as are disclosed in U.S. Pat.
Nos. 4,403,003; 4,147,679; and 5,071,904. Suitable clear coat
compositions include those disclosed in U.S. Pat. Nos. 4,650,718;
5,814,410; 5,891,981; and WO 98/14379.
[0152] The top coat compositions can be applied by conventional
means including brushing, dipping, flow coating, spraying and the
like, but they are most often applied by spraying. The usual spray
techniques and equipment for air spraying and electrostatic
spraying and either manual or automatic methods can be used.
[0153] After application of each top coat to the substrate, a film
is formed on the surface of the substrate by driving water out of
the film by heating or by an air-drying period. Typically, the
thickness of a pigmented base coat ranges from about 0.1 to about 5
mils (about 2.54 to about 127 microns), and preferably about 0.4 to
about 1.5 mils (about 10.16 to about 38.1 microns). The thickness
of a clear coat usually ranges from about 0.5 to about 5 mils
(about 12.7 to about 127 microns), preferably about 1.0 to about 3
mils (about 25.4 to about 76.2 microns).
[0154] The heating will preferably be only for a short period of
time and will be sufficient to ensure that any subsequently applied
top coating can be applied without any dissolution occurring at the
coating interfaces. Suitable drying conditions will depend on the
particular top coat composition and on the ambient humidity (if the
top coat composition is waterborne), but in general a drying time
of from about 1 to 5 minutes at a temperature of about 80.degree.
F. to 250.degree. F. (20.degree. C. to 121.degree. C.) is used.
Usually between coats, the previously applied coat is flashed, that
is, exposed to ambient conditions for about 1 to 20 minutes.
[0155] After application of the top coat composition(s), the coated
substrate is then heated to a temperature and for a period of time
sufficient to effect cure of the coating layer(s). In the curing
operation, solvents are driven off and the film-forming materials
of the top coats are each crosslinked. The heating or curing
operation is usually carried out at a temperature in the range of
from 160.degree. F. to 350.degree. F. (71.degree. C. to 177.degree.
C.) but if needed, lower or higher temperatures may be used as
necessary to activate crosslinking mechanisms. Cure is as defined
as above.
[0156] For purposes of the present invention, the percent light
transmission is determined by measuring light transmission of free
cured top coat films ranging from 1.9 to 2.2 mils (48.26 to 55.88
micrometers) film thicknesses using a Perkin-Elmer Lambda 9
scanning spectrophotometer with a 150 millimeter Lap Sphere
integrating sphere. Data is collected using Perkin-Elmer UV WinLab
software in accordance with ASTM E903, Standard Test Method for
Solar Absorbance, Reflectance, and Transmittance of Materials Using
Integrating Spheres.
[0157] In one embodiment, the present invention is directed to a
photodegradation resistant multi-layer composite coating comprising
a cured primer coating layer over at least a portion of an
electroconductive substrate, and a cured top coat layer over at
least a portion of the cured primer layer. The primer coating layer
is formed from any of the curable electrodepositable coating
compositions described in detail above.
[0158] The top coat layer can be formed from one or more
pigment-containing coating compositions and/or one or more
pigment-free coating compositions as described above and is
characterized in that the multi-layer composite coating exhibits
substantially no interlayer delamination between the cured primer
coating layer and the cured top coat layer upon concentrated solar
spectral irradiance exposure equivalent to two years outdoor
weathering when the top coat layer has at least 80 percent light
transmission as measured at 400 nanometers. Any of the
above-described top coating compositions can be used to form the
top coat layers of the photodegradation multi-layer composite
coating, provided that when cured, the top coat layer has at least
80 percent light transmission as measured at 400 nanometers
wavelength. Also, it should be obvious that the improved
photodegradation resistance can be observed upon such concentrated
solar spectral irradiance only if the cured electrodeposited primer
coating has acceptable initial adhesion to the substrate, and the
cured multi-layer composite coating exhibits acceptable initial
interlayer adhesion. This is because the adhesion failure in such
instances is obviously due to factors other than photodegradation
of the cured electrodeposited coating. As used herein, in the
specification and in the claims, "concentrated solar irradiance
exposure" equivalent to two years outdoor weathering is intended to
mean accelerated exposure testing conducted in accordance with SAE
J1961 which specifies ASTM G90-98, Standard Practice for Performing
Accelerated Outdoor Weathering of Non metallic Materials Using
Concentrated Natural Sunlight, Cycle 3, which utilizes fresnel
solar concentrators using the EMMAQUA-NTW.RTM. (Equatorial Mount
with Mirrors for Acceleration, with Water-nighttime wetting) test
method, available through ATLAS Weathering Services Group, DSET
Laboratories of Phoenix, Ariz. The accelerated exposure testing is
conducted for a period of time and under conditions which correlate
to two years outdoor weather exposure (as described in detail
below). This method includes the use of a fresnel-reflecting system
which employs ten flat first-surface mirrors to concentrate natural
sun light onto coated test panel surfaces mounted on a target
board. The high quality first-surface mirrors uniformly focus
sunlight onto the test panel surfaces at an intensity of
approximately eight times that of global daylight and approximately
five times the global radiation in the ultraviolet spectrum. Test
panels are sprayed with pure deionized water at pre-determined,
regular intervals.
[0159] Testing parameters are governed by ISO 877,
Plastics--Methods of Exposure to Direct Weathering, to Weathering
Using Glass-filtered Daylight, and to Intensified Weathering by
Daylight Using Fresnel Mirrors, and ASTM G90. EMMAQUA exposures are
correlated to equivalent "yeah" of average desert (central Arizona)
or subtropical (south Florida) total ultraviolet real-time
exposure. (See correlation table below.) For example, see
correlation data presented in Bauer, D. R., "Chemical Approaches
for Evaluating Automotive Materials and Test Methods," presented at
the Advanced Symposium on Automotive Materials Testing, Scottsdale,
Ariz., 1993; Bauer, D. R., Paputa Peck, M. C., and Carter, R. O.,
"Evaluation of Accelerated Weathering Tests for a
Polyester-Urethane Coating Using Photoacoustic Infrared
Spectroscopy," Journal of Coatings Technology, December 1987, Vol.
59, No. 755, pg. 103-109; Higgins, Dr. Richard J., "Powder
Coatings, Focus on Usage Trends," Metal Architecture, September
1991, Vol. 7, No. 9, pg. 56-60 (FIG. 2); Keller, D. M., "Testing to
Failure of Paint on Plastics," presented at the Advanced Coatings
Technology Conference, Chicago, Ill., 1992, pg. 133-144; Wineburg,
J. P., "Automotive Coatings and Stabilizers," presented at the
Advanced Symposium on Automotive Materials Testing, Scottsdale,
Ariz., 1993; and Zerlaut, G. A. and Robbins, J. S., "Accelerated
Outdoor Exposure Testing of Coil Coatings by the EMMAQUA.RTM. Test
Method," presented at the Advanced Coatings Technology Seminar,
Detroit, Mich., 1991 (Table 4).
[0160] For purposes of the present invention, the concentrated
solar spectral irradiance exposure correlates to two years south
Florida at 450 outdoor exposure.
[0161] As was previously discussed, the transmission of visible
and/or ultraviolet radiation through the cured topcoating layer(s)
to the cured electrodeposited coating is known to cause
photodegradation of the electrodeposited coating at the
electrocoating/topcoating interface which can result in interlayer
delamination of the topcoat layer from the electrocoat layer.
Therefore, to ensure that the topcoat layer(s) have at least 80
percent light transmission measured at 400 nanometers wavelength,
two clear (i.e., unpigmented) top coat layers are typically formed
over the electrodeposited primer layer. For purposes of testing,
the two clear top coat layers are formed from a first or base coat
layer which is substantially free of pigment, followed by
subsequent application of second or clear coat layer which is also
substantially free of pigment.
[0162] Metal substrates coated by the processes of the present
invention demonstrate excellent corrosion resistance as determined
by salt spray and/or other cyclic corrosion resistance testing and
excellent resistance to photodegradation. When topcoated with a
basecoat and/or clearcoat system having at least 0.1 percent light
transmission as measured at 400 nanometers wave length, the
resulting multi-layer composite coating exhibits substantially no
interlayer delamination or adhesion loss between the cured
electrodeposited coating and the subsequently applied top coating
layers as determined in accordance with ASTM-3359-97, method B.
Further, the multi-layer composite coating of the present invention
exhibits substantially no interlayer delamination or adhesion loss
between the cured electrodeposited coating and the subsequently
applied top coating layers upon concentrated solar spectral
irradiance exposure equivalent to two years outdoor weathering when
the top coating layer(s) have at least 80 percent light
transmission as measured at 400 nanometers wavelength.
[0163] Illustrating the invention are the following examples that
are not to be considered as limiting the invention to their
details. All parts and percentages in the examples, as well as
throughout the specification, are by weight unless otherwise
indicated.
EXAMPLE A
[0164] This example describes the preparation of a cationic amine
salt group-containing acrylic resin having a blocked aliphatic
polyisocyante curing agent mixed with the polymer. The resin was
used as a component in the electrodepositable coating composition
of Example 1 below. The cationic acrylic polymer was prepared as
described below from the following ingredients:
1 INGREDIENTS PARTS BY WEIGHT DOWANOL PNB.sup.1 84.48 DOWANOL
PM.sup.2 108.58 Methylisobutyl ketone 27.60 TINUVIN .RTM.
1130.sup.3 20.40 Ethyl Acrylate 456.00 Styrene 84.00 Hydroxypropyl
methacrylate 180.00 Methyl methacrylate 336.00 Glycidyl
methacrylate 144.00 t-Dodecyl mercaptan 12.00 VAZO-67.sup.4 30.01
DOWANOL PNB 38.40 DOWANOL PM 19.20 Methylisobutyl ketone 15.36
LUPERSOL-75M.sup.5 24.00 DOWANOL PNB 19.20 DOWANOL PM 9.60
Methylisobutyl ketone 113.30 Diethanolamine 80.64 Ketimine.sup.6
72.00 Crosslinker.sup.7 787.34 Sulfamic acid 77.28 Deionized Water
5537.58 .sup.1N-Butoxypropanol solvent available from Dow Chemical.
.sup.2Propylene glycol monomethyl ether solvent available from Dow
Chemical. .sup.3Ultraviolet light stabilizer, commercially
available from CIBA-GEIGY Corp. .sup.4A radical initiator,
available from DuPont Specialty Chemicals. .sup.5Reacting
diethylenetriamine and methylisobutyl ketone (72.69% solids in
methylisobutyl ketone). .sup.6Crosslinker prepared by reacting one
equivalent of isocyanurated hexmethylene diisocyanate with one mole
of dibutylamine according to a procedure described in U.S. Pat. No.
4,576,979, Preparation of Component (B), Table 1.
[0165] The epoxy equivalent weight of the monomer mixture as
measured by titration with perchloric acid was found to be 1212.
The first four ingredients were charged into a suitably equipped
reaction vessel under a nitrogen atmosphere and heated to a
temperature of 100.degree. C. at which time the next ten
ingredients were added to the vessel over a period of 2.5 hours.
When the addition was complete, the reaction mixture was held for
an additional 30 minutes at a temperature ranging between
1150.degree. to 120.degree. C. The reaction mixture then was
maintained at a temperature of 120.degree. C. during addition of
the next three ingredients which were added over a period of 10 to
15 minutes, and the temperature was maintained for 30 minutes. The
reaction mixture was cooled to room temperature then diluted with
the final charge of methylisobutyl ketone. A sample, which was
diluted with Dowanol PM at a ratio of polymer to solvent of 2:1,
had a Gardner-Holt bubble viscosity of T-U.
[0166] The reaction mixture was heated to 90.degree. C. under a
nitrogen blanket at which time diethanolamine was added and this
mixture was maintained at a temperature of 90.degree. C. for one
hour. The ketimine was then added followed by and the resultant
reaction mixture was maintained at 90.degree. C. for an additional
one-hour period. The crosslinker was added and the reaction mixture
was maintained at 90.degree. C. for 20 minutes. A polymer sample
was found to have a Gardner-Holt bubble viscosity of R. The last
two ingredients were mixed separately and heated to a temperature
of 50.degree. C. To this, 94% of the polymer was added under
agitation to produce a dispersion of the organic polymer in an
aqueous medium having a weight solids of 25 percent. Final
distillation to remove methylisobutyl ketone yielded a dispersion
having 30.88 percent solids by weight.
EXAMPLE B
[0167] This example describes the preparation of a cationic amine
salt group-containing polyepoxide resin having a blocked aliphatic
polyisocyanate curing agent mixed with the polymer. The resin was
used as a component in the electrodepositable coating composition
of Example 2 below. The cationic polyepoxide resin was prepared as
described below from the following ingredients:
2 INGREDIENTS PARTS BY WEIGHT EPON 880.sup.1 614.68 Bisphenol
A-ethylene oxide adduct.sup.2 125.00 Bisphenol A 265.42
Methylisobutyl ketone 20.51 Ethyltriphenylphosphonium iodide 0.6
Bisphenol A-ethylene oxide adduct 125.00 Methylisobutyl ketone
21.11 Crosslinker.sup.3 891.13 Diketimine.sup.4 57.01
Methylethanolamine 48.68 .sup.1Diglycidyl ether of bisphenol A
having an epoxy equivalent weight of 188, available from Resolution
Performance Products. .sup.2Reaction product prepared from
bisphenol A and ethylene oxide at a molar ratio of 1:6 (100%
solids). .sup.3Prepared by reacting 3 equivalents of DESMODUR N
3300 (polyfunctional hexamethylene diisocyanate available from
Bayer Corp.) with 3 equivalents of caprolactam, using dibutyltin
dilaurate as catalyst (85% solids in methylisobutyl ketone).
.sup.4Reaction product of diethylenetriamine and methylisobutyl
ketone (73% solids in methylisobutyl ketone).
[0168] The first four ingredients were added to a suitably equipped
reaction vessel and heated under nitrogen atmosphere to a
temperature of 125.degree. C. Ethyltriphenylphosphonium iodide was
added and the reaction mixture was allowed to exotherm to a
temperature of 145.degree. C. That temperature was maintained for a
period of 2 hours at which time the second charge of bisphenol
A-ethylene oxide adduct was added and an epoxy equivalent was
obtained. The second charge of methylisobutyl ketone, crosslinker,
diketimine and methylethanolamine were added sequentially. The
resulting reaction mixture was allowed to exotherm and a
temperature of 122.degree. C. was established and maintained for a
period of one hour. An aqueous dispersion was prepared by adding
1900 parts by weight of the reaction mixture to a mixture of 39.44
parts by weight sulfamic acid and 1255 parts by weight deionized
water. To this mixture was added 17.1 parts by weight of a 30%
solution of rosin acid in butylcarbitol formal. The dispersion was
diluted with 1437 parts by weight deionized water (water added in
two stages), then vacuum stripped to remove organic solvent. The
resultant product had a solids content of 38.84 percent (1 hour at
110.degree. C.).
EXAMPLE C
[0169] This example describes the preparation of a cationic amine
salt group-containing polyepoxide resin having a blocked aliphatic
polyisocyanate curing agent mixed with the polymer. The resin was
used in the electrodepositable coating composition of Example 3
below. The cationic polyepoxide resin was prepared as described
below from the following ingredients:
3 INGREDIENTS PARTS BY WEIGHT EPON 880 614.68 Bisphenol A-ethylene
oxide adduct of Example B 125.00 Bisphenol A 265.42 Methylisobutyl
ketone 20.51 Ethyltriphenylphosphonium iodide 0.6 Bisphenol
A-ethylene oxide adduct of Example B 125.00 Methylisobutyl ketone
22.46 Crosslinker of Example B 905.58 Diethanolamine 68.05
Diketimine of Example B 57.01
[0170] The first four ingredients were charged to a suitably
equipped reaction vessel and heated under a nitrogen atmosphere to
a temperature of 125.degree.. Ethyltriphenylphosphonium iodide was
then added and the reaction mixture was allowed to exotherm to a
temperature of 145.degree. C. The reaction mixture was maintained
at that temperature for a period of 2 hours at which time the
second charge of bisphenol A-ethylene oxide adduct was added and an
epoxy equivalent was obtained. The second charge of methylisobutyl
ketone, crosslinker, and diethanolamine then were added
sequentially. The resulting reaction mixture was allowed to
exotherm and a temperature of 122.degree. C. was established. This
reaction mixture was maintained at this temperature for a period of
30 minutes at which time the diketimine was added and the resulting
reaction mixture was maintained at 122.degree. C. for 30 additional
minutes. An aqueous dispersion was prepared by adding 1900 parts by
weight of the reaction mixture to a mixture of 38.81 parts by
weight sulfamic acid and 1255 parts by weight of deionized water.
To this mixture was added 17.1 parts by weight of a 30% solution of
rosin acid in butylcarbitol formal. The mixture was diluted with
1437 parts by weight deionized water (water added in two stages),
then vacuum stripped to remove organic solvent. The resultant
product had a solids content of 37.3 percent (1 hour at 110.degree.
C.).
EXAMPLE D
[0171] This example describes the preparation of a cationic amine
salt group-containing polyepoxide resin having a blocked aliphatic
polyisocyanate curing agent mixed with the polymer. The cationic
resin is used as a component in the electrodepositable coating
composition of Example 4 below. The cationic resin was prepared in
two steps as described below.
EXAMPLE D-1
[0172] This example describes the preparation of a blocked
aliphatic polyisocyanate curing agent used in the
electrodepositable coating compositions of the present invention.
The blocked polyisocyanate was prepared as follows.
4 INGREDIENTS PARTS BY WEIGHT DESMODUR .RTM. N-3300.sup.1 1600.0
Methylisobutyl ketone 137.3 Dibutyltin dilaurate 3.0 Caprolactam
340.2 Caprolactam 340.2 Caprolactam 340.2 Methylisobutyl ketone
873.2 .sup.1A hexamethylene diisocyanate trimer, having an NCO
equivalent weight of 194, available from the Bayer Corporation
[0173] The first three ingredients were charged to a
suitably-equipped vessel under a nitrogen atmosphere. The mixture
was heated to 105.degree. C. Upon attaining this temperature, the
first portion of caprolactam was added. After an initial exotherm,
the reaction mixture was cooled to a temperature of 105.degree. C.,
at which time the second portion was added. The reaction mixture
was then permitted to exotherm, and the temperature was again
adjusted to a temperature of 105.degree. C. Upon attaining this
temperature, the third portion of caprolactam was added and the
reaction mixture was again permitted to exotherm. The temperature
then was adjusted to 105.degree. C. and the reaction mixture was
held at that temperature for 3 hours. The reaction mixture was
monitored by infrared spectroscopy for the disappearance of NCO.
Upon disappearance of the NCO peak, the methylisobutyl ketone was
added slowly and the reaction mixture was mixed until homogeneous.
The final reaction product had a solids content of 69.6 percent
(one hour at 111.degree. C.).
EXAMPLE D-2
[0174] The following example describes the preparation of a
cationic amine salt-group-containing polyepoxide resin having the
blocked polyisocyanate crosslinker of Example D-1 mixed with the
resin. The cationic resin was prepared as follows.
5 INGREDIENTS PARTS BY WEIGHT EPON 880 973.1 Bisphenol A 375.3
MAZON .RTM. 1651.sup.1 104.7 TETRONIC .RTM. 150R1.sup.2 0.5
Diethanolamine 56.3 1-Amino-3-N,N-di(2-hydroxyethyl)amino 153.8
propane.sup.3 Crosslinker of Example D-1 2036.5 Deionized water
851.7 Sulfamic acid 28.6 30% Gum rosin solution in MAZON .RTM. 1651
13.6 Deionized water 950.6 Deionized water 1600 .sup.1The formal of
2-(2-butoxyethoxy) ethanol, commercially available from BASF
Corporation. .sup.2An alkoxylated diamine surfactant, available
from BASF Surfactants. .sup.3Available from Air Products and
Chemicals, Inc.
[0175] The first four ingredients were charged to a suitably
equipped vessel, and, under a nitrogen atmosphere, heated to
70.degree. C. and held at that temperature for a period of 15
minutes. At that point, the two amines were added. The reaction
mixture was permitted to exotherm, after which the temperature was
adjusted to 140.degree. C. The reaction mixture was held at that
temperature for a period of 2 hours, at which time the crosslinker
was added, and the reaction mixture was adjusted to a temperature
of 120.degree. C. An aqueous dispersion was prepared by dispersing
1600 grams of the resultant reaction mixture in a solution prepared
from the eighth and ninth ingredients. The gum rosin solution was
added to the dispersion followed by the addition of deionized
water. The resulting dispersion was diluted with an additional
quantity of deionized water and heated to a temperature ranging
from 60.degree. to 65.degree. C. Organic solvent was removed under
reduced pressure to yield an aqueous dispersion having a
non-volatile solids content of 26.8% (one hour at 110.degree.
C.).
EXAMPLE E
[0176] This example describes the preparation of a cationic amine
salt group-containing acrylic resin having a blocked aliphatic
polyisocyanate curing agent mixed with the polymer. The resin was
used as a component in the electrodepositable coating composition
of Example 5 below. The cationic acrylic resin was prepared from
the following ingredients:
6 INGREDIENTS PARTS BY WEIGHT DOWANOL PNB 122.5 DOWANOL .RTM. PM
157.44 Methylisobutyl ketone 40.02 TINUVIN .RTM. 1130 29.58 Ethyl
acrylate 661.20 Styrene 121.80 Hydroxypropyl methacrylate 261.00
Methyl methacrylate 487.20 Glycidyl methacrylate 208.80 t-Dodecyl
mercaptan 17.40 VAZO-67 43.51 DOWANOL PNB 55.68 DOWANOL PM 27.84
Methylisobutyl ketone 22.27 LUPERSOL-75M 34.80 DOWANOL PNB 27.84
DOWANOL PM 13.92 Methylisobutyl ketone 164.29 Diethanolamine 116.93
Ketimine of Example A 104.40 Crosslinker of Example A 1141.64
Sulfamic acid 112.06 Deionized water 8029.49
[0177] The epoxy equivalent weight of the monomer mixture as
measured by titration with perchloric acid was found to be 1212,
meeting the specification range of 1195-1263. The first four
ingredients were charged into a suitably equipped reaction vessel
under a nitrogen atmosphere and heated to a temperature of
100.degree. C. The next ten ingredients were added to the vessel
over a period of 2.5 hours, and upon completion of the addition,
the reaction mixture was maintained at a temperature ranging
between 115.degree. C. and 120.degree. C. for a period of 30
minutes. The reaction mixture was heated to a temperature of
120.degree. C. at which time the next three ingredients were added
over a period of 10 to 5 minutes, and that temperature was
maintained for a period of 30 minutes. The reaction mixture then
was cooled to room temperature, and a viscosity sample was drawn.
The reaction mixture was then diluted with the final charge of
methylisobutyl ketone. The viscosity sample was diluted with
DOWANOL PM at a ratio of resin to solvent of 2:1. The sample was
found to have a Gardner-Holt bubble viscosity of T-U.
[0178] The reaction mixture then was heated to a temperature of
90.degree. C. under a nitrogen blanket, at which time
diethanolamine was added, and the resulting reaction mixture was
maintained for one hour at a temperature of 90.degree. C. The
ketimine then was added, and the reaction temperature again
maintained at 90.degree. C. for one hour. The crosslinker then was
added followed by a 20-minute hold period. A viscosity sample was
found to have a Gardner-Holt bubble viscosity of Q+. The last two
ingredients were separately mixed and heated to a temperature of
52.degree. C., at which time 94% of the reaction mixture prepared
as described immediately above was added under agitation to produce
a dispersion of the organic resin in an aqueous medium having a
solids content of 25 percent (one hour at 110.degree. C.). The
dispersion was distilled under vacuum to remove organic solvent,
yielding a final product having a solids content of 32.23 percent
(one hour at 110.degree. C.)
EXAMPLE F
[0179] This example describes the preparation of a cationic amine
salt group-containing polyepoxide resin having a blocked aliphatic
polyisocyanate curing agent mixed with the polymer. The cationic
polyepoxide resin was used as a component in the electrodepositable
coating composition of Example 5 below. The cationic polyepoxide
resin was prepared from the following ingredients:
7 INGREDIENTS PARTS BY WEIGHT EPON 880 614.68 Bisphenol A-ethylene
oxide adduct of Example B 125 Bisphenol-A 265.42 Methylisobutyl
ketone 20.51 Ethyltriphenylphosphonium iodide 0.6 Bisphenol
A-ethylene oxide adduct of Example B 125 Methyl isobutyl ketone
1.64 Crosslinker.sup.1 877.11 Diketimine of Example B 57.01
Methylethanolamine 48.68 .sup.1Blocked polyisocyanate prepared by
reacting 1 equivalent of DESMODUR N 3300 (a polyfunctional
hexamethylene diisocyanate, available from Bayer Corporation) with
1 equivalent of 1,2-butanediol using dibutyltin dilaurate as a
catalyst (80% solids in methylsobutyl ketone).
[0180] The first four ingredients were added to a suitably equipped
reaction vessel and heated under a nitrogen atmosphere to a
temperature of 125.degree. C. Ethyltriphenylphosphonium iodide was
added and the reaction mixture was allowed to exotherm to a
temperature of 145.degree. C. The reaction mixture was maintained
at that temperature for a period of 2 hours at which time the
second charge of bisphenol A-ethylene oxide adduct was added and an
epoxy equivalent was obtained. The second charge of methylisobutyl
ketone, the crosslinker, diketimine and methylethanolamine then
were added to the reaction mixture sequentially. The reaction
mixture was allowed to exotherm and a temperature of 122.degree. C.
was established and maintained for a period of one hour. An aqueous
dispersion was prepared by adding 1900 parts by weight of the
reaction mixture prepared as described immediately above to a
mixture of 47.69 parts of sulfamic acid and 1220 parts of deionized
water. To this mixture was added 16.87 parts of a 30 percent
solution of rosin acid in butylcarbitol formal. The dispersion was
further diluted with 1425 parts by weight of deionized water (added
in two stages). The dispersion was vacuum stripped to remove
organic solvent yielding a final product having a solids content of
45.72 percent (one hour at 110.degree. C.).
EXAMPLE G
[0181] This example describes the preparation of a cationic amine
salt group-containing acrylic resin having a blocked aliphatic
polyisocyanate curing agent mixed with the polymer. The cationic
acrylic resin was used as a component in the electrodepositable
coating composition of Example 6 below. The cationic acrylic resin
was prepared as described below from the following ingredients:
8 INGREDIENTS PARTS BY WEIGHT Methylpropyl ketone 274.78 TINUVIN
.RTM. 1130 27.85 Ethyl acrylate 605.23 Styrene 463.25 Hydroxypropyl
methacrylate 149.45 Methyl methacrylate 52.30 Glycidyl methacrylate
224.18 t-Dodecyl mercaptan 14.93 VAZO-67 37.34 DOWANOL PNB 47.83
DOWANOL PM 23.90 Methylisobutyl ketone 19.38 LUPERSOl-75M 29.95
DOWANOL PNB 23.90 Methylisobutyl ketone 11.95 Diethanolamine 134.16
Ketimine of Example A 109.68 Crosslinker.sup.1 1973.42 Sulfamic
acid 89.45 Deionized water 9033.12 .sup.1Blocked polyisocyanate
curing agent prepared by reacting 10 equivalents of isophorone
diisocyanate with 1 equivalent of trimethylol propane, 3
equivalents of bisphenol A-ethylene oxide polyol (prepared at a
bisphenol A to ethylene oxide molar ratio of 1:6 (100% solids), and
6 equivalents of primary hydroxyl from butylene glycol.
[0182] The first two ingredients were charged into a suitably
equipped reaction vessel under a nitrogen atmosphere and heated to
a temperature of 101.degree. C. The next ten ingredients were added
to the reaction vessel over a period of 2.5 hours. When the
addition was complete, the reaction mixture was maintained at a
temperature ranging between 103.degree. C. and 108.degree. C. for a
period of 30 minutes. The reaction mixture then was heated to a
temperature of 120.degree. C. at which time the next three
ingredients were added over a period of 10 to 15 minutes and
maintained at a temperature of 120.degree. C. for a period of 30
minutes. The reaction mixture then was cooled to room temperature
and viscosity sample was drawn. The sample was diluted with DOWANOL
PM at a resin to solvent ratio of 2:1 and was found to have a
Gardner-Holt bubble viscosity of K-L. The reaction mixture then was
heated to a temperature of 110.degree. C. under a nitrogen blanket,
at which time diethanolamine was added, and the reaction mixture
was maintained at a temperature of 110.degree. C. for a period of
one hour. The ketimine then was added followed by another one-hour
hold period, and the crosslinker then was added followed by an
additional 20-minute hold period. A viscosity sample then was drawn
and measured to have a Gardner-Holt bubble viscosity of T-U. The
last two ingredients were mixed separately and heated to a
temperature of 50.degree. C. An aqueous dispersion was prepared by
adding under agitation 95% of the resin prepared as described
immediately above. This dispersion had a solids content of 25
percent by weight. Organic solvent was removed by distillation to
yield a final product having a solids content of 28.6 percent by
weight (one hour at 110.degree. C.).
EXAMPLE H
[0183] This example describes the preparation of a cationic amine
salt group-containing polyepoxide resin having a blocked aliphatic
polyisocynate curing agent mixed with the polymer. The cationic
polyepoxide resin was used as a component in the electrodepositable
coating composition of Example 6 below. The cationic polyepoxide
resin was prepared from the following ingredients:
9 INGREDIENTS PARTS BY WEIGHT Epon 880 448.71 Bisphenol A-ethylene
oxide ratio) of Example B 91.25 Bisphenol A 193.76 Methylisobutyl
ketone 6.95 Ethyltriphenylphosphonium iodide 0.44 Bisphenol
A-ethylene oxide adduct of Example B 91.25 Methylisobutyl ketone
4.55 Crosslinker.sup.1 833.59 Methylisobutyl ketone 18.33
Diethanolamine 42.99 Diketimine of Example B 65.71 Epon 880 (85%
solution in methylisobutyl 18.96 ketone) TINUVIN .RTM. 123.sup.2
16.12 .sup.1Blocked polyisocyanate curing agent prepared by adding
10 equivalents of DESMODUR N 3300 (a polyfunctional aliphatic
isocyanate resin based on hexamethylene diisocyanate available from
Bayer Corp.) to a mixture of 5 equivalents of 1,2-butanediol and 5
equivalents of benzyl alcohol, using dibutyl tin dilaurate as a
catalyst (87% solids in methylisobutyl ketone). .sup.2A hindered
amine light stabilizer, available from Ciba-Geigy Corp.
[0184] The first four ingredients were charged to a suitably
equipped reaction vessel and heated under a nitrogen atmosphere to
a temperature of 125.degree. C. Ethyl triphenylphosphonium iodide
then was added and the reaction mixture was allowed to exotherm to
a temperature of 145.degree. C. The reaction mixture was held at
that temperature for a period of 2 hours, at which time the second
charge of bisphenol A-ethylene oxide adduct was added and an epoxy
equivalent was obtained. The second charge of methylisobutyl
ketone, crosslinker, methylisobutyl ketone, and diethanolamine then
were added sequentially. The reaction mixture was allowed to
exotherm and a temperature of 122.degree. C. was established. The
reaction mixture was maintained at that temperature for a period of
30 minutes at which time the diketimine was added, and the reaction
temperature was maintained at 122.degree. C. for an additional one
hour period. To this reaction mixture was added EPON 880 (85%
solution in methylisobutyl ketone) and the reaction mixture was
held at 1 22.degree. C. for 30 minutes. TINUVIN 123 then was added
and the temperature was maintained at 122.degree. C. for 30
minutes. An aqueous dispersion was prepared by adding 1500 parts by
weight of the reaction mixture prepared as described immediately
above to a mixture of 29.71 parts of sulfamic acid and 971 parts of
deionized water. The dispersion was diluted with 1119 parts by
weight of deionized water (added in two stages) and the resulting
dispersion was vacuum stripped to remove organic solvent. The final
product had content of 39.58 percent (one hour at 110.degree.).
EXAMPLE I
[0185] This example describes the preparation of a cationic
polyepoxide resin having the blocked aliphatic crosslinker mixed
with the polyepoxide polymer. The polyepoxide resin was used as a
component in the electrodepositable coating compositions of Example
7 below. The cationic polyepoxide resin was prepared as described
below from the following ingredients:
10 INGREDIENTS PARTS BY WEIGHT EPON 880 89.7 Co-resin.sup.1 18.3
Bisphenol-A 38.7 Methyl isobutyl ketone 1.4 Ethyltriphenyl
phosphonium iodide 0.088 Co-resin.sup.1 18.3 Methyl isobutyl ketone
2 Crosslinker.sup.2 139 Methyl isobutyl ketone 4.5 Diethanolamine
10 Diketimine.sup.3 8.3 EPON 880 (85% solution in MIBK) 3.48
TINUVIN 123 2.95 .sup.1Bisphenol A-ethylene oxide adduct (1/6 molar
ratio) available from BASF Corporation. .sup.2Prepared by adding 10
equivalents of a polyfunctional aliphatic isocyanate resin based on
hexamethylene diisocyanate (DESMODUR N 3300, available from Bayer
corporation) to a mixture of 5 equivalents of 1,2-butanediol and 5
equivalents of benzyl alcohol using dibutyl tin dilaurate as a
catalyst. The crosslinker is 87% solids in methyl isobutyl ketone.
.sup.3Derived from diethylenetriamine and methyl isobutyl ketone
(73% solids in methyl isobutyl ketone).
[0186] The EPON 828, initial charge of bisphenol A-ethylene oxide
adduct, bisphenol A, and the initial charge of methyl isobutyl
ketone were charged into a suitably equipped reaction vessel and
heated under a nitrogen atmosphere to a temperature of 125.degree.
C. Ethyl triphenyl phosphonium iodide then was added and the
reaction mixture allowed to exotherm to a temperature of about
145.degree. C. The reaction was held at 145.degree. C. for 2 hours,
the second charge of bisphenol A-ethylene oxide adduct was added,
and an epoxy equivalent was obtained. The second charge of methyl
isobutyl ketone, crosslinker, methyl isobutyl ketone and
diethanolamine were added sequentially. The mixture was allowed to
exotherm and then a temperature of 122.degree. C. was established.
The reaction mixture was maintained at a temperature of 122.degree.
C. for 30 minutes and the diketimine was added This reaction
mixture was maintained at a temperature of 122.degree. C. for one
hour, at which time EPON 880 in methyl isobutyl ketone was added
and the mixture was held for 30 minutes at 122.degree. C. TINUVIN
123 then was added and the temperature was maintained at
122.degree. C. for 30 minutes. The reaction mixture (330 parts) was
dispersed in aqueous medium by adding it to a mixture of 9.2 parts
of sulfamic acid and 225.7 parts of deionized water. To this was
added 4.7 parts of surfactant (a 50/50 mixture of SURFYNOL 104 and
the N-hydroxyethyl imidazoline of coconut fatty acid neutralized to
75% total theoretical neutralization with acetic acid) available
from Air Products and Chemicals, Inc., and 2.95 parts of a 30%
solution of rosin acid in butylcarbitol formal. The dispersion was
further diluted with 117.8 parts of deionized water and 127.1 parts
of deionized water in separate additions. The resultant dispersion
was vacuum stripped to remove organic solvent yielding a dispersion
having a solids content of 40.62 percent.
EXAMPLE J
[0187] This example describes the preparation of a cationic acrylic
resin used in the electrodepositable coating composition of Example
7 below. The acrylic resin was prepared as described below from the
following ingredients:
11 INGREDIENTS PARTS BY WEIGHT Methyl propyl ketone 274.78 TINUVIN
.RTM. 1130 27.85 Ethyl acrylate 605.23 Styrene 463.25 Hydroxypropyl
methacrylate 149.45 Methyl methacrylate 52.3 Glycidyl methacrylate
224.18 t-Dodecyl mercaptan 14.93 VAZO-67 37.34 PROPASOL B 47.83
DOWANOL PM 23.9 Methyl isobutyl ketone 19.38 LUPERSOL-75M 29.95
PROPASOL B 23.9 Methyl isobutyl ketone 4.78 Diethanolamine 134.16
Ketimine of Example I 109.68 Crosslinker.sup.1 1255.88 Sulfamic
acid 88.51 Deionized Water 7771.22 .sup.1Crosslinker is prepared by
reacting one equivalent of isocyanurated hexmethylene diisocyanate
with one mole of dibutylamine according to a procedure described in
U.S. Pat. No. 4,576,979.
[0188] The first two ingredients were charged into a suitable
equipped reaction vessel under a nitrogen atmosphere and heated to
a temperature of 100.degree. C. The next ten ingredients were fed
into the vessel over a period of 2.5 hours. When the feed was
complete, the reaction mixture was maintained for an additional 30
minutes at a temperature between 115.degree. C. and 120.degree. C.
At the end of the hold period, the reaction vessel was heated to
120.degree. C. and the next three ingredients were added over a
period of 10 to 15 minutes, followed by a 30-minutes hold period.
The reaction mixture was cooled to room temperature then sampled
for bubble viscosity measurement. The sample was diluted with
Dowanol PM at a 2:1 resin:Dowanol PM had a viscosity of K. The next
day, the reaction mixture was heated to 110.degree. C. under a
nitrogen blanket. To this, diethanolamine was added followed by a
one hour hold at 110.degree. C. The diketimine was then added
followed by another one hour hold. Finally, the crosslinker was
added followed by a 20- minute hold. A sample was taken after the
hold for viscosity measurement and the sample was found to have a
Gardner-Holt bubble viscosity of Z. The last two ingredients were
mixed and heated to 52.degree. C. then 94% of the resin was added
under agitation to produce a dispersion of the organic resin in an
aqueous medium at 25% solids by weight. Final distillation to
remove methyl isobutyl ketone gave a dispersion at 23.9% solids
(one hour at 110.degree. C.).
Electrodepositable Coating Compositions
EXAMPLE 1
[0189] This example describes the preparation of an
electrodepositable coating composition of the present invention
based on the cationic acrylic resin of Example A. The coating
composition was prepared from a mixture of the following
ingredients:
12 INGREDIENTS PARTS BY WEIGHT Cationic resin of Example A 2283.5
Pigment paste.sup.1 170.1 Catalyst paste.sup.2 22.0 Deionized water
1324.4 .sup.1The pigment paste was prepared by sequentially adding
the ingredients listed below under high shear agitation. When the
ingredients were thoroughly blended, the paste was transferred to a
vertical sand mill and ground to a Hegman value of about 7.25.
[0190]
13 INGREDIENTS PARTS BY WEIGHT Cationic grind resin.sup.a 3268.0
Ti-Pure R-900.sup.b 5940.0 CSX-333.sup.c 60.0 Deionized water 732.0
.sup.aPrepared as described in U.S. Pat. No. 4,715,898, Example 4,
except that the ethylene glycol monobutyl ether was replaced with a
mixture of propylene glycol butyl ether and propylene glycol methyl
ether (solids content of 31%). .sup.bTitanium dioxide pigment
available from E. I. Dupont de Nemours & Co. .sup.cCarbon black
beads available from Cabot Corp. .sup.2The catalyst paste was
prepared by sequentially adding the ingredients listed below under
high shear agitation. When the ingredients were thoroughly blended,
the paste was transferred to a vertical sand mill and ground to a
Hegman value of about 7.25.
[0191]
14 INGREDIENTS PARTS BY WEIGHT Cationic grind resin.sup.a 527.7
n-butoxypropanol 6.9 FASCAT 4201.sup.b 312.0 Deionized water 59.8
.sup.aPrepared as described in U.S. Pat. No. 4,715,898, Example 4,
except that the ethylene glycol monobutyl ether was replaced with a
mixture of butylcarbitol formal and propylene glycol butyl ether,
and 2% by weight ICOMEEN T surfactant was added (solids content of
31%). .sup.bDibutyltin oxide catalyst, commercially available from
Atofina Chemicals.
[0192] The electrodepositable coating composition in the form of an
electrodeposition bath was prepared by adding 300 parts of the
deionized water to the cationic resin under agitation. The pigment
paste and catalyst paste were separately mixed under agitation and
diluted with 300 parts of the deionized water. The paste admixture
then was blended with the diluted resin under agitation. The
remainder of the deionized water was then added under agitation.
Final bath solids were 22 weight percent, with a pigment to resin
ratio of 0.15:1.0. The bath was mixed under mild agitation for
about two hours. Twenty percent of the total paint weight was
removed by ultrafiltration and replaced with deionized water.
EXAMPLE 2
[0193] This example describes the preparation of an
electrodepositable coating composition of the present invention
based on the cationic polyepoxide resin of Example B. The coating
composition was prepared from a mixture of the following
ingredients:
15 INGREDIENTS PARTS BY WEIGHT Cationic resin of Example B 1395.2
Co-resin.sup.1 98.7 Pigment paste.sup.2 140.8 Catalyst paste.sup.3
18.0 Deionized water 2147.3 .sup.1Prepared as follows: 639.65 g of
DER 732 (diglycidyl ether of polypropylene glycol available from
Dow Chemical Co.) and 156.27 g of bisphenol A were charged to a
suitable reaction vessel and heated to 130.degree. C. until the
epoxy equivalent weight of the reaction mixture was 1230. The
reaction mixture was then cooled to 100.degree. C. at which time
71.63 g MAZON 1652 (butyl diethylene glycol formal available from
BASF Corp.) was added followed by the # addition of 164.92 g of
JEFFAMINE D400 (liquid epoxy resin available from Resolution
Performance Products). The mixture was held at 90.degree. to
95.degree. for 4 hours at which time a sample diluted with methoxy
propanol (10 g resin and 8.7 g methoxy propanol) had a Gardner-Holt
bubble viscosity of K. A mixture of 19 g EPON 828 AND 3.07 g of
MAZON 1651 was then added and the mixture was maintained at a
temperature of 90.degree. to 95.degree. c. for 80 minutes at which
time a sample diluted with methoxy # propanol (10 g resin and 8.7 g
methoxy propanol) had a Gardner-Holt bubble viscosity of P-Q. Of
this mixture, 896.26 g was poured into a solution of 34.83 g
sulfamic acid and 1065.19 g deionized water and 58.20 g MONAZOLINE
T (a N-hydroxyethyl imidazoline of tall oil fatty acid available
from Mona Industries, Inc.) with agitation to form a viscous
aqueous dispersion. After mixing for 30 minutes, 586.99 g deionized
water were added under agitation. # The final aqueous dispersion
had a measured solids content of 35% (one hour at 110.degree. C.).
.sup.2The pigment paste was prepared by sequentially adding the
ingredients listed below under high shear agitation. When the
ingredients were thoroughly blended, the paste was transferred to a
vertical sand mill and ground to a Hegman value of about 7.25.
[0194]
16 INGREDIENTS PARTS BY WEIGHT Cationic grind resin.sup.a 2158.3
Ti-Pure R-900 3564.0 CSX-333 36.0 Deionized water 241.7
.sup.aPrepared as described in Example F of U.S. Pat. No.
5,130,004, except that ethylene glycol monobutyl ether was replaced
with a mixture of propylene glycol butyl ether and propylene glycol
methyl ether (solids content 31%). .sup.3The catalyst paste was
prepared by sequentially adding the ingredients listed below under
high shear agitation. When the ingredients were thoroughly blended,
the paste was transferred to a vertical sand mill and ground to a
Hegman value of about 7.25.
[0195]
17 INGREDIENTS PARTS BY WEIGHT Cationic grind resin.sup.a 527.7
n-butoxypropanol 6.9 Dibutyltin oxide 312.0 Deionized water 59.8
.sup.aPrepared as described in Example 4 of U.S. Pat. No. 4,715,898
except that the ethylene glycol monobutyl ether was replaced with a
mixture of butylcarbitol formal and propylene glycol butyl ether,
and with the addition of 2% by weight on solids of ICOMEEN T, a
surfactant available from BASF Corp.
[0196] The electrodepositable coating composition in the form of an
electrodeposition bath was prepared by first diluting the co-resin
with 300 parts of the deionized water under agitation. The cationic
resin was then added under agitation. The pigment paste and
catalyst paste were separately mixed under agitation and diluted
with 300 parts of the deionized water. The paste admixture then was
blended with the diluted resin admixture under agitation. The
remainder of the deionized water was then added under agitation.
Final bath solids were eighteen weight percent, with a pigment to
resin ratio of 0.15:1.0. The bath was mixed under mild agitation
for about two hours. Thirty percent of the total paint weight was
removed by ultrafiltration and replaced with deionized water.
EXAMPLE 3
[0197] This example describes the preparation of an
electrodepositable coating composition of the present invention
based on the cationic polyepoxide resin of Example C. The coating
composition was prepared from a mixture of the following
ingredients:
18 INGREDIENTS PARTS BY WEIGHT Cationic resin of Example C 1451.3
Co-resin.sup.1 115.2 Pigment paste of Example 2 140.8 Catalyst
paste of Example 2 18.0 Deionized water 2074.7 .sup.1Prepared as
follows: 639.65 g of DER 732, 156.27 g of bisphenol A, and 10.97 g
ethylene glycol monobutyl ether were charged to a suitable reaction
vessel and heated to a temperature of 103.degree. C. 1.5 g of
benzyldimethylamine were then added and the reaction mixture was
held at 135.degree. C. until the epoxy equivalent weight of the
reaction mixture was 1250, at which time 52.7 g of ethyleneglycol
monobutyl ether were added and the reaction mixture # was cooled to
100.degree., at which time 164.92 g JEFFAMIN D400 were added. The
mixture was held at 95.degree. C. for a period of 4 hours at which
time a sample diluted with methoxy propanol (10 g resin and 8.7 g
methoxy propanol) had a Gardner-Holt bubble viscosity of K. A
mixture of 19.38 g EPON 828 and 3.07 g of ethylene glycol monobutyl
ether were then added and the # mixture was held at 95.degree. C.
for 80 minutes at which time a sample diluted with methoxy propanol
(10 g resin and 8.7 g solvent) had a Gardner-Holt bubble viscosity
of P-Q. Of this reaction mixture, 889.49 g were then poured into a
mixture of 29.07 lactic acid (88% solution) and 929.18 g deionized
water with agitation to form a viscous aqueous dispersion. After
mixing for 30 minutes, 1009.15 g deionized water were added under
agitation. The # final aqueous dispersion had a measured solids
content of 30% (one hour at 110.degree.).
[0198] The electrodepositable coating composition in the form of an
electrodeposition bath was prepared by first diluting the co-resin
with 300 parts of the deionized water under agitation. The cationic
resin was then added under agitation. The pigment paste and
catalyst paste were separately mixed under agitation and diluted
with 300 parts of the deionized water. The paste admixture then was
blended with the diluted resin admixture under agitation. The
remainder of the deionized water was then added under agitation.
Final bath solids were eighteen weight percent, with a pigment to
resin ratio of 0.15:1.0. The bath was mixed under mild agitation
for about two hours. Thirty percent of the total paint weight was
removed by ultrafiltration and replaced with deionized water.
EXAMPLE 4
[0199] This example describes the preparation of an
electrodepositable coating composition of the present invention
based on the cationic polyepoxide resin of Example D. The coating
composition was prepared from a mixture of the following
ingredients:
19 INGREDIENTS PARTS BY WEIGHT Cationic resin of Example D 2251.83
Co-resin.sup.1 132.18 Pigment paste of Example 2 154.17 Catalyst
paste.sup.2 21.31 Deionized water 1240.51 Diethylene glycol Hexyl
ether 45.00 .sup.1Prepared from the reaction product of 639.65 g of
DER. 732 (a diglycidyl ether of polypropylene glycol available from
Dow Chemical Co.), 156.27 g of bisphenol A, and 10.97 g of ethylene
glycol monobutyl ether were charged to a suitably equipped reaction
vessel and heated to a temperature of 130.degree. C. 1.5 g of
benzyldimethyl amine was then added and the reaction mixture was
held at a temperature of 135.degree. C. until the epoxy equivalent
weight of the # reaction mixture was 1250. 52.7 g of ethylene
glycol monobutyl was added and the reaction mixture was then cooled
to a temperature of 100.degree. C., at which time 164.92 g of
JEFFAMINE D400 (a polyoxypropylene diamine available from Huntsman
Corp.) was then added. The reaction mixture was held at a
temperature of 95.degree. C. for 4 hours at which time a sample
diluted with methoxy propanol (10 g resin and 8.7 g methoxy
propanol) had a Gardner-Holt viscosity of "K". A mixture of 19.38 g
EPON 828 # (a liquid epoxy resin available from Resolution
Performance Products) and 3.07 g of ethylene # glycol monobutyl
ether was then added and the mixture was held at 95.degree. C. for
80 minutes at which time a sample diluted with methoxy propanol (10
g resin + 8.7 g methoxy propanol) had a Gardner-Holt viscosity of
"P-Q". 889.49 g of the reaction mixture was then poured into a
mixture of 17.05 g acetic acid and 941.2 g deionized water with
agitation to form a viscous aqueous dispersion. After mixing for 30
minutes, 923.87 g deionized water was # added and mixed until well
blended. The final aqueous dispersion had a solids content of 30%
(one hour at 110.degree. C.). .sup.2Prepared by sequentially adding
the ingredients listed below under high shear agitation. When the
ingredients were thoroughly blended, the paste was transferred to a
vertical sand mill and ground to a Hegman value of about 7.25.
[0200]
20 INGREDIENTS Parts by Weight Cationic grind resin.sup.a 208.07
Deionized water 269.63 Dibutyltin Oxide 293.18 Deionized water
171.28 .sup.aPrepared as described in U.S. Pat. No. 4,007,154,
Example II.
[0201] The electrodepositable coating composition, in the form of
an electrodeposition bath was prepared by adding each of the above
ingredients sequentially under agitation. The resulting
electrodeposition bath had a solids content of 20 percent based on
total weight of the bath, a pH of 5.54, and a conductivity of 1395
micro-Siemans as measured using an ACCUMET pH/conductivity meter,
available from Fisher Scientific, Inc.
EXAMPLE 5
[0202] This example describes the preparation of three
electrodepositable coating compositions of the present invention
comprising the cationic acrylic resin of Example E and the cationic
polyepoxide resin of Example F. Comparative Example 5A describes
the preparation an electrodeposition bath containing no soluble
iron, Example 5B describes the preparation of an electrodeposition
bath containing 15 parts per million of soluble iron, and Example
5C describes the preparation of an electrodeposition bath
containing 30 parts per million of soluble iron. Each of the
electrodepositable compositions were prepared as described below
from a mixture of the following ingredients.
21 EXAMPLE 5A* EXAMPLE 5B EXAMPLE 5C (Parts (Parts (Parts
INGREDIENTS by Weight) by Weight) by Weight) Cationic resin of
1314.8 1314.8 1314.8 of Example E Cationic resin 580.5 580.5 580.5
of Example F Co-resin of 47.6 47.6 47.6 Example 2 Pigment paste of
170.1 170.1 170.1 Example 1 Catalyst paste of 22.0 22.0 22.0
Example 1 Deionized 1665.0 1665.0 1665.0 water Iron (II) -- 0.187
0.374 acetate.sup.4 *Comparative example.
[0203] Each of the above electrodepositable coating compositions
was prepared in the form of an electrodeposition bath as follows.
The cationic resin of Example F and the co-resin were blended under
agitation as 300 parts of deionized water were slowly added to the
admixture. The admixture was then added to the Cationic resin of
Example E. The pigment paste and the catalyst paste were mixed
separately and diluted with 300 parts of deionized water, then
blended with the resin admixture. The remainder of the deionized
water was then added to this admixture under agitation. The
composition was mixed under mild agitation for about two hours.
Final bath solids were about 22 percent by weight, with a pigment
to resin ratio of 0.15:1.0. Twenty percent of the total bath weight
was removed by ultrafiltration and replaced with deionized water.
Iron (II) acetate was added under agitation to the compositions of
Examples 5B and 5C.
EXAMPLE 6
[0204] This example describes the preparation of an
electrodepositable coating composition of the present invention
based on the cationic acrylic resin of Example G and the cationic
polyepoxide resin of Example H. The coating composition was
prepared from a mixture of the following ingredients:
22 INGREDIENTS PARTS BY WEIGHT Cationic resin of Example G 1447.7
Cationic resin of Example H 697.3 E6251.sup.1 237.5 Catalyst paste
of Example 1 6.6 Deionized water 1410.9 .sup.1Pigment paste
commercially available from PPG Industries, Inc.
[0205] The electrodepositable coating composition was prepared in
the form of an electrodeposition bath as follows. To the cationic
resin of Example G was added 300 parts of deionized water under
agitation, then the cationic resin of Example H is added. The
pigment paste and the catalyst paste were separately mixed under
agitation and diluted with 300 parts of deionized water. The paste
admixture then was added under agitation to the resin admixture,
followed by addition of the remainder of the deionized water. The
composition was blended under mild agitation for about two hours.
Final bath solids were about 22 percent, with a pigment to resin
ratio of 0.15:1.0. Twenty percent of the total bath weight was
removed by ultrafiltration and replaced with deionized water.
[0206] Test Panel Preparation
[0207] Each of the electrodepositable coating compositions of
Examples 1 through 5, and a comparative conventional
electrodepositable composition, prepared as described in U.S. Pat.
No. 5,389,219, Example 2, was electrodeposited onto 4".times.12"
zinc-phosphated galvanized steel test panels commercially available
from ACT Laboratories, Inc. as APR23834(B) (E60 EZG 60G, two-sided
with C700 C18 phosphate and rinse). Each of the compositions was
electrodeposited on the aforementioned substrates under conditions
necessary to form a substantially continuous film having a film
thickness of approximately 1 mil (25.4 micrometers) on the
substrate. The electrocoated test panels were thermally cured as
follows: one set was cured at 360.degree. C. for 30 minutes in an
electric oven; one set was cured at 395.degree. C. for 60 minutes
in an electric oven; and one set was cured at 395.degree. C. for 60
minutes in a gas-fired oven.
[0208] The test panels were then top coated with a solvent-based
unpigmented base/clear top coat system which was designed to permit
80 percent light transmission measured at 400 nanometers
wavelength. The base coat composition is as follows:
23 INGREDIENTS Parts by Weight Methyl ethyl ketone 94.1 Xylene
280.4 Diisobutyl ketone 490.7 Amyl alcohol 80.7 TINUVIN 328.sup.1
60.5 Microgel.sup.2 458.1 RESIMENE 755.sup.3 1008.3 Polyester
resin.sup.4 100.8 Acrylic resin.sup.5 1038.1 Methanol 121.1
Catalyst.sup.6 67.2 .sup.1Ultraviolet light absorber available from
Ciba Specialty Chemicals. .sup.2Prepared as described in U.S. Pat.
No. 4,147,688, Example II. .sup.3Melamine-formaldehyde crosslinker
available from Solutia, Inc. .sup.4Condensation reaction product of
a C.sub.36 dibasic acid (59.1% of reactant solids) and neopentyl
glycol (16.9% of reactant solids), cyclohexane dimethanol (17.5% of
reactant solids), and trimethylol propane (6.5% of reactant
solids)(100% total solids). .sup.5Hydroxy functional acrylic resin
(18.5% n-butyl methacrylate/40 hydroxypropyl acrylate/0.5% methyl
methacrylate/20% styrene/19% n-butyl acrylate/2% acrylic acid),
68.8% solids in a mixture of acetone, Aromatic 100 and amyl
acetate. .sup.6Diisopropylamine neutralized dodecylbenzene sulfonic
acid.
[0209] The base coat composition was spray applied to each of the
electrocoated test panels to yield a base coat dry film thickness
of about 0.35 mils (8.89 micrometers). The applied base coat was
given a one minute flash period. A solvent-based clear coat, DCT
1002B (available from PPG Industries, Inc.) then was spray-applied
to the base coat to give a dry clear coat film thickness of 1.6 to
1.8 mils (40.64 to 15.72 micrometers). The test panels were then
thermally cured at a temperature of 250.degree. F. (121.1.degree.
C.) for 30 minutes.
[0210] Light transmission of the base coat/clear coat system was
determined using cured free films applied at the dry film thickness
described above using a Perkin-Elmer Lambda 9 scanning
spectrophotometer with a 150 millimeter Lab Sphere integrating
sphere. Data collection was accomplished with Perkin-Elmer UV
WinLab software in accordance with ASTM E903.
[0211] Photodegradation resistance was evaluated as described above
in accordance with ASTM G90-98 using EMMAQUA NTW.RTM., available
through Atlas Weather Services, Inc., DSET Laboratories of Phoenix,
Ariz. The test panels were cooled by forced air convection to limit
the increase in surface temperatures of the specimens to 10.degree.
C. above the maximum surface temperature when identically mounted
specimens are exposed to direct sunlight at normal incidence at the
same time and location without concentration. Exposure is reported
as the total integrated UV radiation ranging between wavelengths of
295 and 385 nonometers.
[0212] Two panels sets from each of the three curing schemes
discussed above (2".times.5.5" panels) were tested using the above
method. For one panel set ("set 1"), half of each panel was masked
with aluminum foil at an exposure of 145 MJ/m.sup.2. The test
panels of set 1 were removed from exposure and evaluated for
photodelamination resistance after an exposure of 290 MJ/m.sup.2.
Half of each panel of the second set ("set 2") was masked with
aluminum foil at an exposure of 435 MJ/m.sup.2. Set 2 was removed
from exposure for evaluation after an exposure of 580 MJ/m.sup.2.
Total integrated UV radiation ranged between wavelengths of 295 and
385 nanometers.
[0213] As previously discussed, the weathering exposure testing
done in accordance with this method has been correlated with south
Florida exposure at 45.degree. south. Exposure correlation is as
follows:
24 Equivalent Florida Exposure Energies Exposure (MJ/m.sup.2)
(40.degree. South) 145 6 months 290 12 months 435 18 months 5880 24
months
[0214] Photodegradation resistance of the cured electrodeposited
coating was evalutated by crosshatch adhesion testing of the
exposed test panels at each of the aforementioned exposure
energies. Adhesion testing was conducted after each of the test
panels had been exposed for 16 hours at 100% relative humidity at
100.degree. F. Cross-hatch adhesion testing was done in accordance
with ASTM D3359-97, using a rating scale ranging from 0 to 10,
where 10+best, and using a 2 millimeter crosshatch tool (Model
PA-2056, available from BYK Gardner).
[0215] Adhesion results are reported below in Tables 1 and 2
below.
25TABLE 1 ADHESION TEST RESULTS 145 290 435 580 Example Cure
Initial Post NJ/m.sup.2 Post NJ/m.sup.2 Post NJ/m.sup.2 Post
NJ/m.sup.2 Post # Conditions Adhesion Humidity Adhesion Humidity
Adhesion Humidity Adhesion Humidity Adhesion Humidity 1 30' @
350.degree. F. E 8 TI 9 TI 8 TI 9 TI 9 TI 9 TM 9 TM B 7 TM 10 5 TM
60' @ 385.degree. F. E 6 TI 4 TI 9 TI 6 TI 9 TI 6 TM 10 8 TI 9 TI 6
TM 60' @ 385.degree. F. G 8 TI 6 TI 10 8 TI 10 8 TI 9 TI B 8 TI 10
8 TM 2 30' @ 360.degree. F. E 10 10 10 10 10 10 10 B 10 10 10 60' @
395.degree. F. E 10 10 10 10 10 10 10 B 10 10 10 60' @ 395.degree.
F. G 10 10 10 3 TI 10 0 TI 3 B TI 3 TI 4 TI 0 TI 3 30' @
360.degree. F. E 10 10 10 10 10 10 10 B 10 10 10 60' @ 395.degree.
F. E 10 10 10 10 10 10 10 B 10 10 10 60' @ 395.degree. F. G 10 10
10 10 10 0 TI 0 TI 0 TI 5 TI 0 TI 4 30' @ 360.degree. F. E 10 10 10
10 10 10 9 B TI 5 TI 8 TI 0 TI 60' @ 395.degree. F. E 10 10 10 10
10 10 6 TI B 4 TI 6 TI 0 TI 60' @ 395.degree. F. G 10 10 1 TI 0 TI
0 TI 0 TI 0 TI B 0 TI 1 TI 0 TI ED5070.sup.1 30' @ 340.degree. F. E
9 9 10 10 0 TI 0 TI 2 TI 0 TI 0 TI 0 TI (Compar- 60' @ 375.degree.
F. E 9 9 10 0 TI 0 TI 0 TI 1 TI 0 TI 0 TI 0 TI ative) 60' @
375.degree. F. G 10 10 0 TI 0 TI 0 TI 0 TI 0 TI 0 TI 0 TI 0 TI
.sup.1Cationic electrodeposition primer available from PPG
Industries, Inc. Failure, is considered to be a rating of less than
7 with a failure mode of TI. Codes: B = Blushing of Clear Coat TI =
Intercoat failure at Electrocoat/Basecoat interface TM = Adhesion
failure at the Electrocoat/Metal interface G = Gas Oven E =
Electric Oven
[0216]
26TABLE 2 ADHESION TEST RESULTS 145 290 435 580 Example Cure
Initial Post NJ/m.sup.2 Post NJ/m.sup.2 Post NJ/m.sup.2 Post
NJ/m.sup.2 Post # Conditions Adhesion Humidity Adhesion Humidity
Adhesion Humidity Adhesion Humidity Adhesion Humidity 5A* 30' @
350.degree. F. E 10 10 10 10 10 10 9.5 B 10 10 10 60' @ 385.degree.
F. E 10 10 10 10 10 10 9 B 10 10 10 60' @ 385.degree. F. G 10 10 10
10 10 10 10 B 10 10 10 5B 30' @ 350.degree. F. E 10 10 10 10 10 10
10 B 10 10 10 60' @ 385.degree. F. E 10 10 10 10 10 10 10 B 9 10 8
TM 60' @ 385.degree. F. G 10 8 TI 10 10 10 10 9 B 6 TI 10 9 5C 30'
@ 350.degree. F. E 10 10 10 10 10 10 9 B 10 10 10 60' @ 385.degree.
F. E 10 9 TI 10 10 10 10 10 10 10 10 60' @ 385.degree. F. G 9 TI 8
TI 10 10 10 10 8 B TI 5 TI 9 TI 6 TI *Comparative Example. Codes: B
= Blushing of Clear Coat TI = Intercoat failure at
Electrocoat/Basecoat interface TM = Adhesion failure at the
Electrocoat/Metal interface G = Gas Oven E = Electric Oven
EXAMPLE K
[0217] This example describes the preparation of a cationic
polyepoxide resin having a blocked polyisocyanate curing agent
mixed with the polymer. The cationic resin was used as a component
in the electrodepositable composition of Example 7 below. The
cationic polyepoxide resin was prepared as described below from the
following ingredients:
27 INGREDIENTS PARTS BY WEIGHT EPON 880 89.7 Co-resin.sup.1 18.3
Bisphenol-A 38.7 Methyl isobutyl ketone 1.4 Ethyltriphenyl
phosphonium iodide 0.088 Co-resin.sup.1 18.3 Methyl isobutyl ketone
2 Crosslinker of Example 1 139 Methyl isobutyl ketone 4.5
Diethanolamine 10 Diketimine.sup.2 8.3 EPON 880 (85% solution in
MIBK) 3.48 TINUVIN 123 2.95 .sup.1Bisphenol A-ethylene oxide adduct
(1/6 molar ratio). .sup.2Diketimine is derived from
diethylenetriamine and methyl isobutyl ketone (73% solids in methyl
isobutyl ketone).
[0218] The EPON 828, initial charge of the co-resin, bisphenol A
and the initial charge of methyl isobutyl ketone were charged to a
suitably equipped reaction vessel and heated under a nitrogen
atmosphere to a temperature of 125.degree. C. Ethyl triphenyl
phosphonium iodide then was added and the reaction mixture allowed
to exotherm to about 145.degree. C. The reaction was held at that
temperature for 2 hours and the second charge of co-resin was added
and an epoxy equivalent was obtained. The second charge of methyl
isobutyl ketone, crosslinker, methyl isobutyl ketone, and
diethanolamine were added sequentially. The reaction mixture was
allowed to exotherm and a temperature of 122.degree. C. was
established. The reaction mixture was held at 122.degree. C. for 30
minutes and diketimine was added and the mixture held at
122.degree. C. for one hour. EPON 880 (85% solution in methyl
isobutyl ketone) was added and the mixture was held for 30 minutes
at 122.degree. C. TINUVIN 123 then was added and the temperature
was maintained at 122.degree. C. for 30 minutes. The reaction
mixture (330 parts) was dispersed in aqueous medium by adding it to
a mixture of 9.2 parts of sulfamic acid and 225.7 parts of
deionized water. To this was added 4.7 parts of surfactant (50/50
mixture of SURFYNOL 104 and the N-hydroxyethyl imidzoline of
coconut fatty acid, neutralized to 75% total theoretical
neutralization with acetic, 63.5% solids in ethylene glycol
monobutyl ether) available from Air Products and Chemical, Inc. and
95 parts of a 30% solution of rosin acid in butylcarbitol formal.
The dispersion was further diluted with 117.8 parts of deionized
water and 127.1 parts of deionized water added in two stages. The
dispersion was vacuum stripped to remove organic solvent yielding a
dispersion having a solids content of 40.6 percent (one hour at
110.degree. C.).
EXAMPLE L
[0219] This example describes the preparation of a cationic acrylic
resin having a blocked polyisocyanate curing agent mixed with the
polymer. The cationic resin was used as a component in the
electrodepositable coating composition of Example 7. The acrylic
resin was prepared as described below from the following
ingredients:
28 INGREDIENTS PARTS BY WEIGHT Methyl propyl ketone 274.78 TINUVIN
.RTM. 1130 27.85 Ethyl acrylate 605.23 Styrene 463.25 Hydroxypropyl
methacrylate 149.45 Methyl methacrylate 52.3 Glycidyl methacrylate
224.18 t-Dodecyl mercaptan 14.93 VAZO-67 37.34 PROPASOL B 47.83
DOWANOL PM 23.9 Methyl isobutyl ketone 19.38 LUPERSOL-75M 29.95
PROPASOL B 23.9 Methyl isobutyl ketone 4.78 Diethanolamine 134.16
Diketimine of Example I 109.68 Crosslinker.sup.1 1255.88 Sulfamic
acid 88.51 Deionized water 7771.22 .sup.1Prepared by reacting one
equivalent of isocyanurated hexmethylene diisocyanate with one mole
of dibutylamine according to a procedure described in U.S. Pat. No.
4,576,979.
[0220] The first two ingredients were charged into a suitably
equipped reaction vessel under a nitrogen atmosphere and heated to
a temperature of 100.degree. C. The next ten ingredients were fed
into the vessel over a period of 2.5 hours. When the addition was
complete, the reaction mixture was held for an additional 30
minutes at a temperature between 115.degree. C. and 120.degree. C.
The reaction mixture was heated to a temperature of 120.degree. C.
at which time the next three ingredients were added over a period
of 10 to 15 minutes followed by a 30-minute hold period. The
reaction mixture was cooled to room temperature then sampled for
viscosity measurement. The sample which was diluted with DOWANOL PM
at a 2:1 ratio of resin to solvent had a Gardner-Holt bubble
viscosity of K. The reaction mixture was heated to a temperature of
110.degree. C. under a nitrogen blanket, at which time
diethanolamine was added and the temperature was maintained for one
hour at 110.degree. C. The diketimine was then added followed by
another one-hour hold period. The crosslinker then was added
followed by a 20-minute hold period. A sample then was drawn for
viscosity measurement. This sample was found to have a Gardner-Holt
bubble viscosity of Z. The last two ingredients were mixed
separately and heated to a temperature of 52.degree. C. then 94% of
the resin was added under agitation to produce a dispersion of the
organic resin in an aqueous medium having 25% solids content by
weight. Final distillation to remove methyl isobutyl ketone yielded
a dispersion having a solids content of 23.9% (one hour at
110.degree. C.).
EXAMPLE 7
[0221] This example describes the preparation of ten
electrodepositable coating compositions in the form of
electrodeposition baths, each comprising one of a variety of rare
earth metals. The electrodeposition baths were prepared as
described below.
29 INGREDIENTS PARTS BY WEIGHT Cationic resin of Example K 3220.25
Cationic resin of Example L 8205.58 Pigment paste.sup.1 1124.88
Catalyst paste of Example 1 31.18 Deionized water 5418.11
.sup.1E6251, commercially available from PPG Industries, Inc.
[0222] The electrodepositable coating composition in the form of an
electrodeposition bath was prepared by adding 800 parts of the
deionized water to the cationic resin of Example K under agitation.
The cationic resin of Example L was then added to the admixture.
The pigment paste and catalyst paste were mixed separately under
agitation and diluted with 500 parts of the deionized water, then
blended into the reduced resin admixture under agitation. The
remainder of the deionized water was then added under agitation.
Final bath solids were about 22%, with a pigment to resin ratio of
0.15:1.0. The bath was allowed to agitate for two hours. Twenty
percent of the total bath weight was removed by ultrafiltration and
replaced with deionized water.
EXAMPLES 7A TO 7J
[0223] The following Examples 7A through 7I describe the
preparation of electrodepositable coating compositions in the form
of electrodeposition baths, each containing a rare earth element in
accordance with the present invention. Comparative Example 7J
describes the preparation of an electrodeposition bath comprising
no rare earth element. The electrodepositable coating compositions
were prepared as described below from the following
ingredients.
30 INGREDIENTS PARTS BY WEIGHT EXAMPLE 7A Electrodepositable
composition of Example 7 1600.0 Dysprosium nitrate.sup.1 2.0
Deionized water 97.1 .sup.1Commercially available from Alfa Aesar.
EXAMPLE 7B Electrodepositable composition of Example 7 1600.0
Erbium nitrate.sup.1 2.0 Deionized water 98.0 .sup.1Commercially
available from Alfa Aesar. EXAMPLE 7C Electrodepositable
composition of Example 7 1600.0 Europium nitrate.sup.1 2.2
Deionized water 97.8 .sup.1Commercially available from Alfa Aesar.
EXAMPLE 7D Electrodepositable composition of Example 7 1600.0
Gadolinium acetate.sup.1 1.6 Deionized water 98.4
.sup.1Commercially available from Alfa Aesar. EXAMPLE 7E
Electrodepositable composition of Example 7 1600.0 Holmium
nitrate.sup.1 2.0 Deionized water 98.0 .sup.1Commercially available
from Alfa Aesar. EXAMPLE 7F Electrodepositable composition of
Example 7 1600.0 Lutetium nitrate.sup.1 1.6 Deionized water 98.6
.sup.1Commercially available from Alfa Aesar. EXAMPLE 7G
Electrodepositable composition of Example 7 1600.0 Neodymium
acetate.sup.1 1.7 Deionized water 98.3 .sup.1Commercially available
from Aldrich Chemical Company, Inc. EXAMPLE 7H Electrodepositable
composition of Example 7 1600.0 Praseodymium Nitrate.sup.1 2.2
Deionized water 97.8 .sup.1Commercially available from Acros
Organics. EXAMPLE 7I Electrodepositable composition of Example 7
1600.0 Samarium acetate.sup.1 1.6 Deionized water 98.4
.sup.1Commercially available from Aldrich Chemical Company, Inc.
COMPARATIVE EXAMPLE 7J Electrodepositable composition of Example 7
1600.0 Deionized water 100.0
[0224] Each of the electrodepositable coating compositions of
Examples 7A through 7I were prepared by first diluting the
respective rare earth materials with the deionized water and then
adding the mixture under agitation to the composition of Example 7.
The composition of Comparative Example 7J was prepared by adding
the deionized water to the electrodepositable composition of
Example 7. Each composition was then allowed to agitate for least
two hours.
[0225] Electrocoating Procedure:
[0226] Each of the electrodepositable coating compositions of
Examples 7A to 7J above were electrodeposited onto phosphated cold
rolled steel panels, commercially available from ACT Laboratories
(phosphate treatment commercially available from PPG Industries,
Inc., as Chemfos700, followed with a deionized water rinse.)
Conditions for cationic electrodeposition were 2 minutes at
90.degree. F. at voltages required to yield a cured film thickness
of 1.0 to 1.1 mils (25.4 micrometers). The coated substrates were
cured in an electric oven at 360.degree. F. for 30 minutes.
[0227] Testing Procedure
[0228] Each of the coated steel test panels was single-scribed,
cutting through the coating to the metal substrate, in an "I"
pattern. The test panels were then subjected to cyclic corrosion
testing in accordance with GM 9511P Standard. Test panels were
evaluated for "scribe creep" corrosion and visual appearance.
Scribe creep is reported in millimeters of corrosion as a total
scribe width. Test results are reported in the following TABLE
3.
31 TABLE 3 Example # Rare earth metal Scribe Creep* (mm) 7A Dy 4 7B
Er 7 7C Eu 4 7D Gd 3.5 7E Ho 3.5 7F Lu 4.5 7G Nd 6 7H Pr 6 7I Sm 6
7J** -- 9 *Average scribe creep following 20 cycles GM 9511P.
**Comparative example.
[0229] The data presented above in Table 3 illustrate that the
inclusion of a rare earth metal in an electrodepositable coating
composition of the present invention provides improved scribe creep
corrosion resistance over an analogous composition which does not
contain a rare earth metal.
[0230] Alternative Embodiments of the Invention
EXAMPLE M
[0231] This example describes the preparation of a cationic resin
in accordance with an alternative embodiment of the present
invention. The cationic resin was prepared as described below.
[0232] Into a 3000 ml, 4-neck, round-bottom flask was charged 576.7
g (4.727 equivalents) of resorcinol diglycidyl ether having an EEW
of 122 (available as Erisys RDGE from CVC Specialty Chemicals, Inc.
of Maple Shade, N.J.), 188.2 g (3.765 equivalents) of resorcinol,
and 169.5 g of 1-butoxy-2-propanol. The flask was fitted with a
stir paddle with bearing, a thermocouple probe, a heating mantle, a
gas fitting, and a water-cooled condenser. Under a nitrogen
blanket, the flask contents were heated to a temperature of
105.degree. C. and held at that temperature for 10 minutes, at
which time 0.6 g of ethyltriphenylphosphonium iodide was added. The
reaction mixture was allowed to exotherm, then the reaction mixture
was adjusted to 160.degree. C. and that temperature was maintained
for 105 minutes. The reaction mixture was then cooled to
100.degree. C. At this time was added 58.3 g (0.1155 mole) of an
approximately 71% solution of the diketimine (formed from
diethylenetriamine and excess methyl isobutyl ketone,such that the
amine equivalent weight of the diketimine solution was 125), and
49.7 g (0,662 equivalents) of N-methylethanolamine. The reaction
mixture was adjusted to 140.degree. C. and maintained at that
temperature for at least 1.5 hours, then cooled to 80.degree. C.
Upon achieving that temperature, 745.9 g of crosslinker.sup.1 and
11.0 g of SURFYNOL 104 (surfactant available from Air Products and
Chemicals Inc.) were added, and the reaction mixture was mixed for
15 minutes. Of this mixture, 1500 g was added to a solution of 54.8
g (0.564 equivalents) of sulfamic acid in 781.2 g of deionized
water. At least 20 minutes later, a total of 1335 g of additional
deionized water was added. The resulting dispersion was diluted
with an additional kilogram of deionized water, warmed to a
temperature of 60.degree. to 65.degree. C., and solvent was
co-distilled under reduced pressure to yield a dispersion which was
found to be 46.6% non-volatile (one hour at 110.degree. C.). .sup.1
Crosslinker prepared as follows. Into a 5000 ml, 4-neck,
round-bottom flask was charged 1136.2 g (8.788 equivalents) of
dibutylamine and 86.4 g of methyl isobutyl ketone. The flask was
then fitted with a stir paddle with bearing, a thermocouple probe,
a gas fitting, a water-cooled condenser, a heating mantle, and an
addition funnel. The addition funnel was charged with 1716.9 g
(8.850 equivalents) of an hexamethylene diisocyanate trimer with an
NCO equivalent weight of 194 (available as DESMODUR N-3300 from the
Bayer Corporation) and 343.4 g of methyl isobutyl ketone and mixed
to form a uniform solution. To the dibutylamine solution under a
nitrogen blanket was added the isocyanurate solution, beginning at
ambient temperature and the addition was continued at such a rate
as to keep the reaction temperature below 80.degree. C. At the
completion of the addition, the funnel was rinsed with 73.8 g of
methyl isobutyl ketone and the reaction was held at 80.degree. C.
until an infrared spectrum of the reaction mixture revealed no more
than a negligible NCO peak. At that point, the product was cooled.
The resultant crosslinker had a solids content (one-hour at
110.degree. C.) of 85.1%.
EXAMPLE N
[0233] This example describes the preparation of a cationic resin
in accordance with an alternative embodiment of the present
invention. The cationic resin was prepared as described below.
[0234] Into a 3000 ml, 4-neck, round-bottom flask was charged 617.9
g (5.327 equivalents) of resorcinol diglycidyl ether with an EEW of
116 (as used in Example M), 214.0 g (3.891 equivalents) of
resorcinol, and 184.3 g of 1-butoxy-2-propanol. The flask was then
equipped with a stir paddle with bearing, a thermocouple probe, a
heating mantle, a gas fitting, and a water-cooled condenser. Under
a nitrogen blanket, this reaction mixture was heated to a
temperature of 105.degree. C. To the reaction mixture was added 0.7
g of ethyltriphenylphosphonium iodide, and the mixture was held at
105.degree. C. for 10 minutes. The temperature was then increased
to 160.degree. C., and the reaction mixture was maintained at that
temperature for 105 minutes, at which time the reaction mixture was
cooled to a temperature of 100.degree. C. and sampled to find that
the epoxy equivalent weight ("EEW") was 875 based on solids. 63.4 g
(0.169 mole) of the diketimine (as described in Example M above),
and 54.1 g (0.720 equivalents) of N-methylethanolamine then were
added to the reaction mixture, and the temperature was increased to
140.degree. C. The temperature was maintained at 140.degree. C. for
80 minutes and the EEW was found to be 33,000 on solids. This
material was cooled to 80.degree. C. at which time 653.7 g of
crosslinker.sup.1 and 12.0 g of SURFYNOL104 were added and the
reaction mixture was blended for 15 minutes. Of this product, 1500
g was poured into a solution of 59.6 g (0.614 equivalents) of
sulfamic acid in 759.9 g of deionized water, and the mixture was
blended for at least 20 minutes, at which time 1325 g of additional
deionized water was added. This dispersion was further diluted with
a kilogram of deionized water and warmed to a temperature of
60.degree. to 65.degree. C., whereupon the solvent was co-distilled
under reduced pressure to yield a dispersion having a solids
content of 32.7% (one hour at 110.degree. C.). .sup.1 Crosslinker
prepared as follows. Into a 5000 ml, 4-neck, round-bottom flask was
charged 630.3 g (4.886 equivalents) of dibutylamine and 210.1 g of
methyl isobutyl ketone. The flask was then fitted with a stir
paddle with bearing, a thermocouple probe, a gas fitting, a
water-cooled condenser, a heating mantle, and an addition funnel.
The addition funnel was charged with 645.0 g (4.886 equivalents) of
a methylene diphenyl diisocyanate ("MDI") having an NCO equivalent
weight of 132 (available as PAPI.RTM. 2940 from Dow Chemical
Company). To the stirred dibutylamine solution under a nitrogen
blanket, beginning at ambient temperature, was added the MDI at
such a rate as to keep the temperature under 70.degree. C. When the
addition was completed, the funnel was rinsed with 14.7 g of methyl
isobutyl ketone and the reaction mixture was adjusted to 70.degree.
C. The temperature was maintained at 70.degree. C. until an
infrared spectrum of a sample of the reaction mixture indicated no
more than a negligible NCO peak. The reaction mixture was cooled.
The resultant crosslinker was found to have a solids content of
85.9% (one-hour at 110.degree. C.).
EXAMPLE O
[0235] This example describes the preparation of a cationic resin
in accordance with an alternative embodiment of the present
invention. The cationic resin was prepared as described below.
[0236] Into a 5000 ml, 4-neck, round-bottom flask was charged 955.6
9 (4.550 equivalents) of a saturated epoxy having an EEW of 210
(available as EPONEX 1510 from Shell Oil and Chemical Company),
182.8 g (3.324 equivalents) of resorcinol, and 157.5 g of
1-butoxy-2-propanol. The flask was then fitted with a stir paddle
with bearing, a thermocouple probe, a gas fitting, a water-cooled
condenser, and a heating mantle. Under a nitrogen blanket, the
mixture was heated to 105.degree. C., at which time 0.6 g of
ethyltriphenylphosphonium iodide was added, and heating was
continued to attain a temperature of 160.degree. C. The reaction
mixture maintained at 160.degree. C. for a period of 105 minutes,
then cooled to 100.degree. C. The EEW was determined to be 1244
based on solids. At that point, 54.2 g (0.144 mole) of the ketimine
(as described in Example M above) and 46.2 g (0.615 equivalents) of
N-methylethanolamine were added, and the temperature was adjusted
to 140.degree. C. This temperature was maintained for 1.5 hours,
whereupon the EEW was found to be infinite. The reaction mixture
was cooled to 80.degree. C. and 693 g of crosslinker (as described
in Example M above) and 10.2 g of SURFYNOL 104 were added and the
reaction mixture was blended to homogeneity over a period of 15
minutes. Of this material, 1500 g was poured into a solution of
43.6 g (0.449 equivalents) of sulfamic acid in 872.1 g of deionized
water, This mixture was blended under agitation for a period of 20
minutes at which time 1081 g of deionized water were added. This
dispersion was then diluted with a kilogram of deionized water,
warmed to a temperature of 60.degree. to 65.degree. C., and exposed
to reduced pressure to co-distill the solvent, resulting in a
dispersion having a solids content of 43.3% (one hour at
110.degree. C.).
EXAMPLE P
[0237] This example describes the preparation of a cationic epoxy
resin for use in the alternative electrodepositions of the present
invention. The cationic resin was prepared as described below.
[0238] Into a 3000 ml, 4-neck, round-bottom flask was charged 920.8
g (4.898 equivalents) of a bisphenol A diglycidyl ether resin
having an epoxy equivalent of 188 (EPON 880, available from Shell
Oil and Chemical Company), 196.7 g (3.576 equivalents) of
resorcinol, and 169.5 g of 1-butoxy-2-propanol. The flask was then
fitted with a paddle stirrer with bearing, a thermocouple probe, a
gas fitting, a water-cooled condenser, and a heating mantle. Under
a nitrogen blanket, the mixture was heated to a temperature of
105.degree. C., 0.6 g of ethyltriphenylphosphonium iodide was
added, and heating was continued to a temperature of 160.degree. C.
The temperature was held at 160.degree. C. for a period of 105
minutes, then cooled to 100.degree. C. at which time it was
determined that the EEW based on solids was 1118. 58.3 g (0.155
mole) of the diketimine (as described in Example M above), and 49.7
g (0.662 equivalent) of N-methylethanolamine were added, and the
reaction mixture was heated to 140.degree. C. and held at that
temperature for six hours. The EEW based on solids was determined
to be 9757 after two hours. The reaction mixture was then cooled to
80.degree. C. and 745.9 g of crosslinker (as described in Example M
above), and 11.0 g of SURFYNOL 104 were added and mixed for 15
minutes. Of this material, 1500 g was poured into a solution of
45.8 g (0.472 equivalent) of sulfamic acid in 854.3 g of deionized
water. The reaction mixture was mixed for 20 minutes and 1372 g of
deionized water were added. The dispersion was further diluted with
a kilogram of deionized water, heated to a temperature of
60.degree. C. to 65.degree. C. and subjected to co-distillation
under reduced pressure to remove the organic solvent. The final,
dispersion had a solids content of 37.8% (one hour at 110.degree.
C.).
EXAMPLE Q
[0239] This example describes the preparation of a cationic epoxy
resin used as a component in the electrodepositable coating
compositions of the alternative embodiment of the present
invention, The cationic resin was prepared as described below.
[0240] Into a 5000 ml, 4-neck, round-bottom flask was charged 656.7
g (3.127 equivalents) of a saturated epoxy with EEW of 210
(available as EPONEX 1510 from Shell Oil and Chemical Company),
108.2 g (1.967 equivalents) of resorcinol, and 169.5 g of
1-butoxy-2-propanol. The flask was then fitted with a stir paddle
with bearing, a thermocouple probe, a gas fitting, a water-cooled
condenser, and a heating mantle. Under a nitrogen blanket, the
mixture was heated to 105.degree. C., at which time 0.6 g of
ethyltriphenylphosphonium iodide was added, and heating was
continued to attain a temperature of 160.degree. C. The reaction
mixture was maintained at 160.degree. C. for a period of 105
minutes, cooled to 100.degree. C., and the EEW was determined to be
877 based on solids. 58.3 g (0.156 mole) of the diketimine (as
described in Example M above) and 49.7 g (0.662 equivalent) of
N-methylethanolamine were added, and the temperature was adjusted
to 140.degree. C. This temperature was maintained for 1.5 hours,
whereupon the EEW was found to be infinite. The reaction mixture
then was cooled to 80.degree. C. and 745.9 g of crosslinker
(prepared as described in Example M above) and 11 g of SURFYNOL 104
were added and mixed to homogeneity over a period of 15 minutes. Of
this material, 1500 g was poured into a solution of 54.8 g (0.564
equivalent) of sulfamic acid in 781.2 g of deionized water.
[0241] The reaction mixture was blended for 20 minutes and a total
of 1045 g of deionized water was added. This dispersion was then
diluted with a kilogram of deionized water, warmed to a temperature
of 60.degree. C. to 65.degree. C., and co-distilled under reduced
pressure to remove organic solvent. The final dispersion had a
solids content of 48.0% (one hour at 110.degree. C.).
EXAMPLE R
[0242] This example describes the preparation of a cationic epoxy
resin used as a component in the electrodepositable coating
compositions of the alternative embodiment of the present
invention. The cationic resin was prepared as described below.
[0243] Into a 3000 ml, 4-neck, round-bottom flask was charged 642.1
g (3.415 equivalents) of a bisphenol A diglycidyl ether resin
having an epoxy equivalent of 188 (EPON 880, available from Shell
Oil and Chemical Company), 122.7 g (2.231 equivalents) of
resorcinol, and 169.5 g of 1-butoxy-2-propanol. The flask was then
fitted with a paddle stirrer with bearing, a thermocouple probe, a
gas fitting, a water-cooled condenser, and a heating mantle. Under
a nitrogen blanket, the mixture was heated to 105.degree. C., 0.6 g
of ethyltriphenylphosphonium iodide was added, and heating was
continued to reach a temperature of 160.degree. C. The temperature
was held at 160.degree. C. for a period of 105 minutes, then cooled
to 100.degree. C. at which time it was determined that the EEW
based on solids was 735. 58.3 g (0.155 mole) of diketimine (as
described in Example M above) and 49.8 g (0.662 equivalent) of
N-methylethanolamine were added, and the reaction mixture was
heated to 140.degree. C. and held at that temperature for six
hours. The EEW based on solids was determined to be 9071 after 1.5
hours. The reaction mixture was then cooled to 80.degree. C. and
746.1 g of crosslinker (described in Example M above) and 11.0 g of
SURFYNOL 104 were added and mixed for 15 minutes. Of this material,
1500 g was poured into a solution of 54.8 g (0.565 equivalent) of
sulfamic acid in 781.2 g of deionized water. The reaction mixture
was blended for 20 minutes at which time 1335 g of deionized water
was added. The dispersion was further diluted with a kilogram of
deionized water, heated to a temperature of 60.degree. C. to
65.degree. C. and co-distilled under reduced pressure to remove
organic solvent. The final dispersion had a solids content of 42.0%
(one hour at 110.degree. C.).
EXAMPLE S
[0244] This example describes the preparation of a cationic epoxy
resin used in the electrodepositable coating compositions of the
alternative embodiment of the present invention. The cationic resin
was prepared as described below.
[0245] Into a 3000 ml, 4-neck, round-bottom flask was charged 568.2
g (4.898 equivalents) of resorcinol diglycidyl ether having an EEW
of 116, 196.7 g (3.576 equivalents) of catechol, and 169.5 g of
1-butoxy-2-propanol. The flask was fitted with a stir paddle with
bearing, a thermocouple probe, a heating mantle, a gas fitting, and
a water-cooled condenser. Under a nitrogen blanket, the flask
contents were heated to a temperature of 105.degree. C. and that
temperature was maintained for 10 minutes at which time 0.6 g of
ethyltriphenylphosphoniu- m iodide was added. The reaction mixture
was allowed to exotherm, then the reaction temperature was adjusted
to 160.degree. C. and held for a period of 105 minutes. The
reaction mixture was then cooled to 100.degree. C. at which time,
the EEW based on solids was found to be 754. To this was added 58.3
g (0.155 mole) of diketimine (described in Example M above) and
49.7 g (0.662 equivalent) of N-methylethanolamine. The reaction
temperature was adjusted to 140.degree. C. and held for one hour,
whereupon the EEW based on solids was found to be 29,750. The
reaction mixture was then cooled to 80.degree. C. At that
temperature, 745.9 g of crosslinker (prepared as described in
Example M above) and 11.0 g of SURFYNOL104 were added, and the
reaction mixture was mixed for 15 minutes. Of this mixture, 1500 g
was added to a solution of 54.8 g (0.564 equivalents) of sulfamic
acid in 781.2 g of deionized water. The mixture was agitated for 20
minutes at which time 1335 g of deionized water was added. The
resulting dispersion was diluted with a kilogram of deionized
water, warmed to a temperature of 60.degree. C. to 65.degree. C.,
and solvent was co-distilled under reduced pressure to yield a
dispersion having a solids content of 38.3% (one hour at
110.degree. C.).
EXAMPLE T
[0246] This example describes the preparation of a cationic epoxy
resin used in the electrodepositable coating compositions of the
alternative embodiment of the present invention. The cationic resin
was prepared as described below.
[0247] Into a 3000 ml, 4-neck, round-bottom flask was charged 568.2
g (4.898 equivalents) of resorcinol diglycidyl ether having an EEW
of 116, 196.7 g (3.576 equivalents) of hydroquinone, and 169.5 g of
1-butoxy-2-propanol. The flask was fitted with a stir paddle with
bearing, a thermocouple probe, a heating mantle, a gas fitting, and
a water-cooled condenser. Under a nitrogen blanket, the flask
contents were heated to 105.degree. C. and held at that temperature
for 10 minutes, at which time 0.6 g of ethyltriphenylphosphonium
iodide was added. The reaction mixture was allowed to exotherm,
then the reaction mixture was adjusted to 160.degree. C. and held
at that temperature for a period of 105 minutes. The reaction
mixture was then cooled to 100.degree. C. at which time the EEW
based on solids was found to be 695. To the reaction mixture then
was added 58.3 g (0.155 mole) of diketimine (prepared as described
above in Example M) and 49.7 g (0.662 equivalent) of
N-methylethanolamine. The reaction mixture temperature was adjusted
to 140.degree. C. and that temperature maintained for at least 2.5
hours, then cooled to 80.degree. C. At that temperature, 745.9 g of
crosslinker (prepared as described in Example M above) and 11.0 g
of SURFYNOL 104 were added, and the agitation was continued for 15
minutes. Of this mixture, 1500 g was added to a solution of 54.8 g
(0.564 equivalent) of sulfamic acid in 781.2 g of deionized water.
The reaction mixture was blended for 20 minutes and 1335 g of
additional deionized water was added. The resulting dispersion was
diluted with one kilogram of deionized water, warmed to a
temperature of 60.degree. to 65.degree. C., and solvent was
co-distilled under reduced pressure to yield a dispersion having a
solids content of 39.9% (one hour at 110.degree. C.).
EXAMPLE 8 THROUGH 15
[0248] The following Examples 8-15 describe the preparation of
electrodepositable coating compositions (in the form of
electrodeposition baths) in accordance with the alternative
embodiment of the present invention. The electrodepositable coating
compositions comprise the cationic resins of Examples M through
T.
EXAMPLE 8
[0249] This example describes the preparation of an
electrodepositable coating composition of the alternative
embodiment of the present invention. The electrodeposition bath was
prepared as described below from the following ingredients.
32 Parts by Weight Parts Solids by Weight INGREDIENTS (grams)
(grams) Cationic resin of Example M 1514.2 705.6 Pigment
paste.sup.1 166.5 118.8 Catalyst paste.sup.2 22.0 11.7 Deionized
water 2097.3 -- INGREDIENTS Parts by Weight Parts Solids Grind
resin.sup.a 1612.9 500.0 Carbon black pigment.sup.b 30.0 30.0
Titanium dioxide pigment.sup.c 2970.0 2970.0 Deionized water 387.1
-- .sup.1A pigment paste was prepared from a mixture of the
following ingredients by processing in a sand-mill to a Hegman
value of 7. .sup.aPrepared as described in U.S. Pat. No. 5,130,004,
Example F, except that the ethylene glycol monobutyl ether was
replaced with a mixture of propylene glycol butyl ether and
propylene glycol methyl ether, having a solids content of 31.0%.
.sup.bCSX-333, available from Cabot Corp. as Raven 410.
.sup.cAvailable from Kerr-McGee Corp. as Tronox CR-800E. .sup.2A
catalyst paste was prepared from the following ingredients by
forming an admixture and processing in a sand-milled to a Hegman
value of 7.
[0250]
33 INGREDIENTS Parts by Weight Parts Solids Grind vehicle.sup.a
407.7 126.4 Dibutyltin oxide.sup.b 191.6 191.6 Deionized water 0.7
-- .sup.aPrepared as described in U.S. Pat. No. 5,130,004, Example
F, except that the ethylene glycol monobutyl ether was replaced
with a mixture of propylene glycol butyl ether and propylene glycol
methyl ether, having a solids content of 31.0%. .sup.bAvailable
from Atofina Chemicals as Fascat 4201.
[0251] The resulting electrodeposition bath solids was content for
each of the baths was 22% and the pigment to binder ratio was
0.15:1.0. Twenty percent by weight of each bath composition was
removed by ultrafiltration, and replaced with deionized water.
EXAMPLES 9 THROUGH 15
[0252] Electrodepositable coating compositions of Examples 9
through 15, in the form of electrodeposition baths, were prepared
exactly as in Example 8 above except that the amounts of cationic
resins of Example N through T, respectively, were adjusted to
produce 705.6 parts of solids and the amounts of deionized water
were accordingly adjusted to produce 3800 parts by weight of
electrodeposition bath for each example.
TESTING PROCEDURES
[0253] Each of the electrodepositable coating compositions of the
alternative embodiment of the present invention (Examples 8-15)
were electrodeposited onto various test substrates under conditions
sufficient to provide an electrodeposited film thickness of about 1
mil (25.4 micrometers), The various substrates, curing conditions,
and test methods used to evaluate for corrosion resistance and
photodegradation resistance are as described in the following Table
4. It should be noted that for Xenon Arc Weatherometer testing, the
cured electrocoated test panels were subsequently coated with the
unpigmented base coat/clear coat system (providing 80% light
transmission at 400 nanometers) which was described above with
reference to Examples 1-5.
34TABLE 4 CORROSION RESISTANCE AND DURABILITY Weather- 20 day 20 GM
Cycle B, mm Total Scribe Creep.sup.2 Ometer Saltspray.sup.1
Electrogalvazined hours Scribe Creep Steel Substrate Steel
Zinc-Iron Alloy Xenon Arc to failure (mm) (Chemfos C700 (Chemfos
C700 (Chemfos C700 WeatherOMeter.sup.7 (10 = (6 rating Test Bare
Bare Phosphate, Phosphate, Phosphate, best) or less) Example Steel
Steel Deionized Deionized Deionized Steel (Chemfos C700 Phosphate,
# Cure Conditions Substrate.sup.3 Substrate.sup.3 Water
Rinse).sup.4 Water Rinse).sup.5 Water Rinse).sup.6 Deionized Water
Rinse).sup.4 8 60' @ 385.degree. F. 9.5 29 5 1 1 10 no failure @
3759 hr. 8 30' @ 350.degree. F. 8.5 12 5 1 1 10 no failure @ 3759
hr. 8 30' @ 325.degree. F. 9 12 7 1 1 9.5 no failure @ 3759 hr. 9
60' @ 385.degree. F. 4.5 10 2 2 1 0 1500 hr. 9 30' @ 350.degree. F.
4.5 10 3 2 1 0 1000 hr. 9 30' @ 325.degree. F. 6 7 3 2 1 0 1000 hr.
10 60' @ 385.degree. F. 15 13 4 2 1 6 3759 hr. 10 30' @ 350.degree.
F. 12.5 7 5 1 1 8 no failure @ 3759 hr. 10 30' @ 325.degree. F. 12
8 7 1 1 8.5 no failure @ 3759 hr. 11 60' @ 385.degree. F. 2 9 4 1 1
0 2500 hr. 11 30' @ 350.degree. F. 6 14 3 1 1 0 3200 hr. 11 30' @
325.degree. F. 4.5 Total 4 1 1 0 3200 hr. delamination 12 60' @
385.degree. F. Total Total 8 1 2 7.5 no failure @ delamination
delamination 3759 hr. 12 30' @ 350.degree. F. 17.5 Total 5 2 2 8 no
failure @ delamination 3759 hr. 12 30' @ 325.degree. F. 20 9 8 2 2
8.5 no failure @ 3759 hr. 13 60' @ 385.degree. F. 11 Total 6 2 3 9
no failure @ delamination 3759 hr. 13 30' @ 350.degree. F. 8 Total
6 1 2 8 no failure @ delamination 3759 hr. 13 30' @ 325.degree. F.
11 17 5 1 2 8 no failure @ 3759 hr. 14 60' @ 385.degree. F. 7.5 14
3 1 1 10 no failure @ 3759 hr. 14 30' @ 350.degree. F. 5 12 4 1 1
10 no failure @ 3759 hr. 14 30' @ 325.degree. F. 5.5 12 5 2 1 10 no
failure @ 3759 hr. 15 60' @ 385.degree. F. 11 12 4 1 1 9 no failure
@ 3759 hr. 15 30' @ 350.degree. F. 10 10 4 1 1 7 no failure @ 3759
hr. 15 30' @ 325.degree. F. 11.5 7 5 1 1 9 no failure @ 3759 hr.
.sup.1According to ASTM B117. .sup.2According to General Motors
Engineering Standard 9540P, Method B. .sup.3Available from Advanced
Coating Technologies, Inc. as APR28110. .sup.4Available from
Advanced Coating Technologies, Inc. as APR28630. .sup.5Available
from Advanced Coating Technologies, Inc. as APR31611.
.sup.6Available from Advanced Coating Technologies, Inc. as
APR32457. .sup.7Tested according to ASTMJ1960, using an Atlas Model
Ci65XWA WeatherOMeter using Type S borosilicate inner and outer
filters .sup.83759 hr. exposure under clear basecoat/clearcoat with
80% transmission @ 400 nm, A 2 mm, 6 teeth cross-cutting tool
(Byk-Gardner Model PA-2056) was used according to ASTM D3359-97,
except that a 1 to 10 rating system was employed
[0254] Example 8 versus 9 is a comparison of aliphatic versus
aromatic isocyanate. The data in Table 4 illustrate that aliphatic
isocyanate provides improved durability over aromatic isocyanate
however, aliphatic isocyanates are poorer for corrosion resistance
on steel substrates.
[0255] Examples 8 versus 10 versus 11 represent a comparison of
resorcinol diglycidyl ether to saturated epoxy to aromatic
bisphenol A epoxy extended with equal amounts of resorcinol. The
data of Table 4 illustrate that resorcinol diglycidyl ether
provides improved durability over the saturated epoxy analog which
gives better durability than the composition comprising bisphenol
A. Aromatic bisphenol A epoxy however, gave the best corrosion
resistance over steel substrates.
[0256] Examples 8 versus 12 versus 13 represents a comparison of
resorcinol diglycidyl ether to saturated epoxy to aromatic
bisphenol A epoxy extended with resorcinol, using amounts
permitting comparison at equal levels of crosslinker. The data in
Table 4 illustrate that the resorcinol diglycidyl ether provides
improved durability over either the saturated or the aromatic
bisphenol A epoxy. Also resorcinol has the best overall corrosion
resistance.
[0257] Examples 8 versus 14 versus 15 represents a comparison of
resorcinol-to catechol- and hydroquinone-extended resorcinol
diglycidyl ether. The data presented in Table 4 illustrate that
each of these compositions gave good durability and corrosion
resistance, with the catechol version being slightly improved in
both categories.
[0258] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications which are within the spirit and scope of the
invention, as defined by the appended claims.
* * * * *