U.S. patent application number 09/855370 was filed with the patent office on 2001-10-18 for thermosetting compositions containing carboxylic acid functional polymers prepared by atom transfer radical polymerization.
Invention is credited to Barkac, Karen A., Coca, Simion, Franks, James R., Humbert, Kurt A., Lamers, Paul H., Martin, Roxalana L., O'Dwyer, James B., Olson, Kurt G., White, Daniela.
Application Number | 20010031829 09/855370 |
Document ID | / |
Family ID | 26794916 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010031829 |
Kind Code |
A1 |
Barkac, Karen A. ; et
al. |
October 18, 2001 |
Thermosetting compositions containing carboxylic acid functional
polymers prepared by atom transfer radical polymerization
Abstract
A thermosetting composition comprising a co-reactable solid,
particulate mixture of (a) polycarboxylic acid functional polymer,
and (b) epoxide functional crosslinking agent having at least two
epoxide groups, e.g., triglycidyl isocyanurate (TGIC), is
described. The polycarboxylic acid functional polymer is prepared
by atom transfer radical polymerization and has well defined
polymer chain architecture and polydispersity index of less than
2.0. The thermosetting compositions of the present invention have
utility as powder coatings compositions.
Inventors: |
Barkac, Karen A.;
(Murrysville, PA) ; Coca, Simion; (Pittsburgh,
PA) ; Franks, James R.; (Gibsonia, PA) ;
Humbert, Kurt A.; (Bethel Park, PA) ; Lamers, Paul
H.; (Allison Park, PA) ; Martin, Roxalana L.;
(Pittsburgh, PA) ; O'Dwyer, James B.; (Valencia,
PA) ; Olson, Kurt G.; (Gibsonia, PA) ; White,
Daniela; (Pittsburgh, PA) |
Correspondence
Address: |
PPG INDUSTRIES, INC.
One PPG Place
Pittsburgh
PA
15272
US
|
Family ID: |
26794916 |
Appl. No.: |
09/855370 |
Filed: |
May 15, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09855370 |
May 15, 2001 |
|
|
|
09375017 |
Aug 16, 1999 |
|
|
|
6265489 |
|
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60098603 |
Aug 31, 1998 |
|
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Current U.S.
Class: |
525/119 |
Current CPC
Class: |
C09D 133/02 20130101;
C08L 63/00 20130101; C09D 133/064 20130101; C09D 133/02 20130101;
C08L 2666/14 20130101; C09D 133/064 20130101; C08L 2666/14
20130101 |
Class at
Publication: |
525/119 |
International
Class: |
C08F 008/00 |
Claims
We claim:
1. A thermosetting composition comprising a co-reactable solid,
particulate mixture of: (a) polycarboxylic acid functional polymer
prepared by atom transfer radical polymerization initiated in the
presence of an initiator having at least one radically transferable
group, and in which said polymer contains at least one of the
following polymer chain structures:
--[(M).sub.p--(G).sub.q].sub.x--and
--[(G).sub.q--(M).sub.p].sub.x--wherein M is a residue, that is
free of carboxylic acid functionality, of at least one
ethylenically unsaturated radically polymerizable monomer; G is a
residue, that has carboxylic acid functionality, of at least one
ethylenically unsaturated radically polymerizable monomer; p and q
represent average numbers of residues occurring in a block of
residues in each polymer chain structure; and p, q and x are each
individually selected for each structure such that said
polycarboxylic acid functional polymer has a number average
molecular weight of at least 250; and (b) epoxide functional
crosslinking agent having at least two epoxide groups.
2. The composition of claim 1 wherein said polycarboxylic acid
functional polymer is selected from the group consisting of linear
polymers, branched polymers, hyperbranched polymers, star polymers,
graft polymers and mixtures thereof.
3. The composition of claim 1 wherein said polycarboxylic acid
functional polymer has a number average molecular weight of from
500 to 16,000, and a polydispersity index of less than 2.0.
4. The composition of claim 1 wherein said initiator is selected
from the group consisting of linear or branched aliphatic
compounds, cycloaliphatic compounds, aromatic compounds, polycyclic
aromatic compounds, heterocyclic compounds, sulfonyl compounds,
sulfenyl compounds, esters of carboxylic acids, polymeric compounds
and mixtures thereof, each having at least one radically
transferable halide.
5. The composition of claim 4 wherein said initiator is selected
from the group consisting of halomethane, methylenedihalide,
haloform, carbon tetrahalide, 1-halo-2,3-epoxypropane,
p-methanesulfonyl halide, p-toluenesulfonyl halide, methanesulfenyl
halide, p-toluenesulfenyl halide, 1-phenylethyl halide,
C.sub.1-C.sub.6-alkyl ester of 2-halo-C.sub.1-C.sub.6-carboxylic
acid, p-halomethylstyrene, mono-hexakis
(.alpha.-halo-C.sub.1-C.sub.6-alkyl)benzene,
diethyl-2-halo-2-methyl malonate, ethyl 2-bromoisobutyrate and
mixtures thereof.
6. The composition of claim 1 wherein said polycarboxylic acid
functional polymer has a carboxylic acid equivalent weight of from
100 to 10,000 grams/equivalent.
7. The composition of claim 1 wherein M is derived from at least
one of vinyl monomers, allylic monomers and olefins.
8. The composition of claim 7 wherein M is derived from at least
one of alkyl (meth)acrylates having from 1 to 20 carbon atoms in
the alkyl group, vinyl aromatic monomers, vinyl halides, vinyl
esters of carboxylic acids and olefins.
9. The composition of claim 1 wherein G is derived from: alkyl
(meth)acrylate, which after polymerization is hydrolyzed; or at
least one hydroxy functional ethylenically unsaturated radically
polymerizable monomer, which after polymerization is post-reacted
with a cyclic anhydride.
10. The composition of claim 9 wherein G is derived from:
C.sub.1-C.sub.4 alkyl (meth)acrylate, which after polymerization is
hydrolyzed; or at least one of hydroxyethyl (meth)acrylate and
hydroxypropyl (meth)acrylate, which after polymerization is
post-reacted with a cyclic anhydride.
11. The composition of claim 1 wherein said polycarboxylic acid
functional polymer (a) has at least one of the following polymer
chain structures:
.phi.--[[(M).sub.p--(G).sub.q].sub.x(M).sub.r--T].sub.z and
.phi.--[[(G).sub.q--(M).sub.p].sub.x--(G).sub.s--T].sub.z wherein
.phi. is or is derived from the residue of said initiator free of
said radically transferable group; T is or is derived from said
radically transferable group of said initiator; x is independently
from 1 to 100 for each structure; p and q are each independently
within the range of 0 to 100 for each x-segment and for each
structure, the sum of p and q being at least 1 for each x-segment,
and q being at least 1 for at least one x-segment; r and s are each
independently for each structure within the range of 0 to 100; z is
independently for each structure at least 1; and said
polycarboxylic acid functional polymer has a polydispersity index
of less than 2.0.
12. The composition of claim 11 wherein said polycarboxylic acid
functional polymer has a number average molecular weight of from
500 to 16,000, and a polydispersity index of less than 1.8.
13. The composition of claim 11 wherein p is independently selected
for each structure within the range of 1 to 20; and q is
independently selected for each structure within in the range of 1
to 20.
14. The composition of claim 11 wherein x is independently selected
for each structure within the range of 1 to 50.
15. The composition of claim 11 wherein T is halide.
16. The composition of claim 15 wherein T is derived from a
dehalogenation post-reaction.
17. The composition of claim 16 wherein said dehalogenation
post-reaction comprises contacting a precursor of said
polycarboxylic acid functional polymer that is substantially free
of carboxylic acid functionality with a limited radically
polymerizable ethylenically unsaturated compound.
18. The composition of claim 17 wherein said limited radically
polymerizable ethylenically unsaturated compound is selected from
the group consisting of 1,1-dimethylethylene, 1,1-diphenylethylene,
isopropenyl acetate, alpha-methyl styrene, 1,1-dialkoxy olefin and
combinations thereof.
19. The composition of claim 1 wherein said epoxide functional
crosslinking agent (b) is selected from the group consisting of
epoxide functional polyesters, epoxide functional polymers prepared
by conventional free radical polymerization methods, epoxide
functional polyethers, epoxide functional isocyanurates and
mixtures thereof.
20. The composition of claim 19 wherein said epoxide functional
crosslinking agent (b) is tris(2,3-epoxypropyl) isocyanurate.
21. The composition of claim 1 wherein the equivalent ratio of
carboxylic acid equivalents in said polycarboxylic acid functional
polymer (a) to epoxy equivalents in said epoxide functional
crosslinking agent (b) is within the range of 0.7:1 to 2:1.
22. The composition of claim 1 wherein said polycarboxylic acid
functional polymer (a) is present in said thermosetting composition
in an amount of from 50 to 98 percent by weight, based on total
resin solids weight, and said epoxide functional crosslinking agent
(b) is present in said thermosetting composition in an amount of
from 2 to 50 percent by weight, based on total resin solids
weight.
23. The composition of claim 1 further comprising polycarboxylic
acid functional polyester.
24. The composition of claim 23 wherein said polycarboxylic acid
functional polyester has a carboxylic acid equivalent weight of
from 290 grams/equivalent to 3,000 grams/equivalent, and is present
in said composition in an amount of from 1 percent by weight to 40
percent by weight, based on the total weight of resin solids.
25. A method of coating a substrate comprising: (a) applying to
said substrate a thermosetting composition; (b) coalescing said
thermosetting composition to form a substantially continuous film;
and (c) curing said thermosetting composition, wherein said
thermosetting composition comprises a co-reactable solid,
particulate mixture of: (i) polycarboxylic acid functional polymer
prepared by atom transfer radical polymerization initiated in the
presence of an initiator having at least one radically transferable
group, and in which said polymer contains at least one of the
following polymer chain structures:
--[(M).sub.p--(G).sub.q].sub.x--and
--[(G).sub.q--(M).sub.p].sub.x--where- in M is a residue, that is
free of carboxylic acid functionality, of at least one
ethylenically unsaturated radically polymerizable monomer; G is a
residue, that has carboxylic acid functionality, of at least one
ethylenically unsaturated radically polymerizable monomer; p and q
represent average numbers of residues occurring in a block of
residues in each polymer chain structure; and p, q and x are each
individually selected for each structure such that said
polycarboxylic acid functional polymer has a number average
molecular weight of at least 250; and (ii) epoxide functional
crosslinking agent having at least two epoxide groups.
26. The method of claim 25 wherein said polycarboxylic acid
functional polymer is selected from the group consisting of linear
polymers, branched polymers, hyperbranched polymers, star polymers,
graft polymers and mixtures thereof.
27. The method of claim 25 wherein said polycarboxylic acid
functional polymer has a number average molecular weight of from
500 to 16,000, and a polydispersity index of less than 2.0.
28. The method of claim 25 wherein said initiator is selected from
the group consisting of linear or branched aliphatic compounds,
cycloaliphatic compounds, aromatic compounds, polycyclic aromatic
compounds, heterocyclic compounds, sulfonyl compounds, sulfenyl
compounds, esters of carboxylic acids, polymeric compounds and
mixtures thereof, each having at least one radically transferable
halide.
29. The method of claim 28 wherein said initiator is selected from
the group consisting of halomethane, methylenedihalide, haloform,
carbon tetrahalide, 1-halo-2,3-epoxypropane, p-methanesulfonyl
halide, p-toluenesulfonyl halide, methanesulfenyl halide,
p-toluenesulfenyl halide, 1-phenylethyl halide,
C.sub.1-C.sub.6-alkyl ester of 2-halo-C.sub.1-C.sub.6-carboxylic
acid, p-halomethylstyrene,
mono-hexakis(.alpha.-halo-C.sub.1-C.sub.6-alkyl)benzene,
diethyl-2-halo-2-methyl malonate, ethyl 2-bromoisobutyrate and
mixtures thereof.
30. The method of claim 25 wherein said polycarboxylic acid
functional polymer has a carboxylic acid equivalent weight of from
100 to 10,000 grams/equivalent.
31. The method of claim 25 wherein M is derived from at least one
of vinyl monomers, allylic monomers and olefins.
32. The method of claim 31 wherein M is derived from at least one
of alkyl (meth)acrylates having from 1 to 20 carbon atoms in the
alkyl group, vinyl aromatic monomers, vinyl halides, vinyl esters
of carboxylic acids and olefins.
33. The method of claim 25 wherein G is derived from: alkyl
(meth)acrylate, which after polymerization is hydrolyzed; or at
least one hydroxy functional ethylenically unsaturated radically
polymerizable monomer, which after polymerization is post-reacted
with a cyclic anhydride.
34. The method of claim 33 wherein G is derived from:
C.sub.1-C.sub.4 alkyl (meth)acrylate, which after polymerization is
hydrolyzed; or at least one of hydroxyethyl (meth)acrylate and
hydroxypropyl (meth)acrylate, which after polymerization is
post-reacted with a cyclic anhydride.
35. The method of claim 25 wherein said polycarboxylic acid
functional polymer (i) has at least one of the following polymer
chain structures:
.phi.--[[(M).sub.p--(G).sub.q].sub.x(M).sub.r--T].sub.z and
.phi.--[[(G).sub.q--(M).sub.p].sub.x--(G).sub.s--T].sub.z wherein
.phi. is or is derived from the residue of said initiator free of
said radically transferable group; T is or is derived from said
radically transferable group of said initiator; x is independently
from 1 to 100 for each structure; p and q are each independently
within the range of 0 to 100 for each x-segment and for each
structure, the sum of p and q being at least 1 for each x-segment,
and q being at least 1 for at least one x-segment; r and s are each
independently for each structure within the range of 0 to 100; z is
independently for each structure at least 1; and said
polycarboxylic acid functional polymer has a polydispersity index
of less than 2.0.
36. The method of claim 35 wherein said polycarboxylic acid
functional polymer has a number average molecular weight of from
500 to 16,000, and a polydispersity index of less than 1.8.
37. The method of claim 35 wherein p is independently selected for
each structure within the range of 1 to 20; and q is independently
selected for each structure within in the range of 1 to 20.
38. The method of claim 35 wherein x is independently selected for
each structure within the range of 1 to 50.
39. The method of claim 33 wherein T is halide.
40. The method of claim 39 wherein T is derived from a
dehalogenation post-reaction.
41. The method of claim 40 wherein said dehalogenation
post-reaction comprises contacting a precursor of said
polycarboxylic acid functional polymer that is substantially free
of carboxylic acid functionality with a limited radically
polymerizable ethylenically unsaturated compound.
42. The method of claim 41 wherein said limited radically
polymerizable ethylenically unsaturated compound is selected from
the group consisting of 1,1-dimethylethylene, 1,1-diphenylethylene,
isopropenyl acetate, alpha-methyl styrene, 1,1-dialkoxy olefin and
combinations thereof.
43. The method of claim 25 wherein said epoxide functional
crosslinking agent (ii) is selected from the group consisting of
epoxide functional polyesters, epoxide functional polymers prepared
by conventional free radical polymerization methods, epoxide
functional polyethers, epoxide functional isocyanurates and
mixtures thereof.
44. The method of claim 43 wherein said epoxide functional
crosslinking agent (ii) is tris(2,3-epoxypropyl) isocyanurate.
45. The method of claim 25 wherein the equivalent ratio of
carboxylic acid equivalents in said polycarboxylic acid functional
polymer (i) to epoxy equivalents in said epoxide functional
crosslinking agent (ii) is within the range of 0.7:1 to 2:1.
46. The method of claim 25 wherein said polycarboxylic acid
functional polymer (i) is present in said thermosetting composition
in an amount of from 50 to 98 percent by weight, based on total
resin solids weight, and said epoxide functional crosslinking agent
(ii) is present in said thermosetting composition in an amount of
from 2 to 50 percent by weight, based on total resin solids
weight.
47. The method of claim 25 further comprising polycarboxylic acid
functional polyester.
48. The method of claim 47 wherein said polycarboxylic acid
functional polyester has a carboxylic acid equivalent weight of
from 290 grams/equivalent to 3,000 grams/equivalent, and is present
in said composition in an amount of from 1 percent by weight to 40
percent by weight, based on the total weight of resin solids.
49. A substrate coated by the method of claim 25.
50. A substrate coated by the method of claim 35.
51. A multi-component composite coating composition comprising: (a)
a base coat deposited from a pigmented film-forming composition;
and (b) a transparent top coat applied over said base coat, wherein
said transparent top coat is deposited from a clear film-forming
thermosetting composition comprising a co-reactable solid,
particulate mixture of: (i) polycarboxylic acid functional polymer
prepared by atom transfer radical polymerization initiated in the
presence of an initiator having at least one radically transferable
group, and in which said polymer contains at least one of the
following polymer chain structures:
--[(M).sub.p--(G).sub.q].sub.x--and
--[(G).sub.q--(M).sub.p].sub.x--where- in M is a residue, that is
free of carboxylic acid functionality, of at least one
ethylenically unsaturated radically polymerizable monomer; G is a
residue, that has carboxylic acid functionality, of at least one
ethylenically unsaturated radically polymerizable monomer; p and q
represent average numbers of residues occurring in a block of
residues in each polymer chain structure; and p, q and x are each
individually selected for each structure such that said
polycarboxylic acid functional polymer has a number average
molecular weight of at least 250; and (ii) epoxide functional
crosslinking agent having at least tow epoxide groups.
52. The multi-component composite coating composition of claim 51
wherein said polycarboxylic acid functional polymer is selected
from the group consisting of linear polymers, branched polymers,
hyperbranched polymers, star polymers, graft polymers and mixtures
thereof.
53. The multi-component composite coating composition of claim 51
wherein said polycarboxylic acid functional polymer has a number
average molecular weight of from 500 to 16,000, and a
polydispersity index of less than 2.0.
54. The multi-component composite coating composition of claim 51
wherein said initiator is selected from the group consisting of
linear or branched aliphatic compounds, cycloaliphatic compounds,
aromatic compounds, polycyclic aromatic compounds, heterocyclic
compounds, sulfonyl compounds, sulfenyl compounds, esters of
carboxylic acids, polymeric compounds and mixtures thereof, each
having at least one radically transferable halide.
55. The multi-component composite coating composition of claim 54
wherein said initiator is selected from the group consisting of
halomethane, methylenedihalide, haloform, carbon tetrahalide,
1-halo-2,3-epoxypropane, p-methanesulfonyl halide,
p-toluenesulfonyl halide, methanesulfenyl halide, p-toluenesulfenyl
halide, 1-phenylethyl halide, C.sub.1-C.sub.6-alkyl ester of
2-halo-C.sub.1-C.sub.6-carboxylic acid, p-halomethylstyrene,
mono-hexakis (.alpha.-halo-C.sub.1-C.sub.6-alkyl)ben- zene,
diethyl-2-halo-2-methyl malonate, ethyl 2-bromoisobutyrate and
mixtures thereof.
56. The multi-component composite coating composition of claim 51
wherein said polycarboxylic acid functional polymer has a
carboxylic acid equivalent weight of from 100 to 10,000
grams/equivalent.
57. The multi-component composite coating composition of claim 51
wherein M is derived from at least one of vinyl monomers, allylic
monomers and olefins.
58. The multi-component composite coating composition of claim 57,
wherein M is derived from at least one of alkyl (meth)acrylates
having from 1 to 20 carbon atoms in the alkyl group, vinyl aromatic
monomers, vinyl halides, vinyl esters of carboxylic acids and
olefins.
59. The multi-component composite coating composition of claim 51
wherein G is derived from: alkyl (meth)acrylate, which after
polymerization is hydrolyzed; or at least one hydroxy functional
ethylenically unsaturated radically polymerizable monomer, which
after polymerization is post-reacted with a cyclic anhydride.
60. The multi-component composite coating composition of claim 59
wherein G is derived from: C.sub.1-C.sub.4 alkyl (meth)acrylate,
which after polymerization is hydrolyzed; or at least one of
hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate, which
after polymerization is post-reacted with a cyclic anhydride.
61. The multi-component composite coating composition of claim 51
wherein said polycarboxylic acid functional polymer (a) has at
least one of the following polymer chain structures:
.phi.--[[(M).sub.p--(G).sub.q].sub.x(- M).sub.r--T].sub.z and
.phi.--[[(G).sub.q--(M).sub.p].sub.x--(G).sub.s--T]- .sub.z wherein
.phi. is or is derived from the residue of said initiator free of
said radically transferable group; T is or is derived from said
radically transferable group of said initiator; x is independently
from 1 to 100 for each structure; p and q are each independently
within the range of 0 to 100 for each x-segment and for each
structure, the sum of p and q being at least 1 for each x-segment,
and q being at least 1 for at least one x-segment; r and s are each
independently for each structure within the range of 0 to 100; z is
independently for each structure at least 1; and said
polycarboxylic acid functional polymer has a polydispersity index
of less than 2.0.
62. The multi-component composite coating composition of claim 61
wherein said polycarboxylic acid functional polymer has a number
average molecular weight of from 500 to 16,000, and a
polydispersity index of less than 1.8.
63. The multi-component composite coating composition of claim 61
wherein p is independently selected for each structure within the
range of 1 to 20; and q is independently selected for each
structure within in the range of 1 to 20.
64. The multi-component composite coating composition of claim 61
wherein x is independently selected for each structure within the
range of 1 to 50.
65. The multi-component composite coating composition of claim 61
wherein T is halide.
66. The multi-component composite coating composition of claim 65
wherein T is derived from a dehalogenation post-reaction.
67. The multi-component composite coating composition of claim 66
wherein said dehalogenation post-reaction comprises contacting a
precursor of said polycarboxylic acid functional polymer that is
substantially free of carboxylic acid functionality with a limited
radically polymerizable ethylenically unsaturated compound.
68. The multi-component composite coating composition of claim 67
wherein said limited radically polymerizable ethylenically
unsaturated compound is selected from the group consisting of
1,1-dimethylethylene, 1,1-diphenylethylene, isopropenyl acetate,
alpha-methyl styrene, 1,1-dialkoxy olefin and combinations
thereof.
69. The multi-component composite coating composition of claim 51
wherein said epoxide functional crosslinking agent (b) is selected
from the group consisting of epoxide functional polyesters, epoxide
functional polymers prepared by conventional free radical
polymerization methods, epoxide functional polyethers, epoxide
functional isocyanurates and mixtures thereof.
70. The multi-component composite coating composition of claim 69
wherein said epoxide functional crosslinking agent (b) is
tris(2,3-epoxypropyl) isocyanurate.
71. The multi-component composite coating composition of claim 51
wherein the equivalent ratio of carboxylic acid equivalents in said
polycarboxylic acid functional polymer (a) to epoxy equivalents in
said epoxide functional crosslinking agent (b) is within the range
of 0.7:1 to 2:1.
72. The multi-component composite coating composition of claim 51
wherein said polycarboxylic acid functional polymer (a) is present
in said thermosetting composition in an amount of from 50 to 98
percent by weight, based on total resin solids weight, and said
epoxide functional crosslinking agent (b) is present in said
thermosetting composition in an amount of from 2 to 50 percent by
weight, based on total resin solids weight.
73. The multi-component composite coating composition of claim 51
further comprising polycarboxylic acid functional polyester.
74. The multi-component composite coating composition of claim 73
wherein said polycarboxylic acid functional polyester has a
carboxylic acid equivalent weight of from 290 grams/equivalent to
3,000 grams/equivalent, and is present in said composition in an
amount of from 1 percent by weight to 40 percent by weight, based
on the total weight of resin solids.
75. A substrate having said multi-component composite coating
composition of claim 51 deposited thereon.
76. A substrate having said multi-component composite coating
composition of claim 61 deposited thereon.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/098603, filed Aug. 31, 1998, which is
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to thermosetting compositions
of one or more carboxylic acid functional polymers and an epoxide
functional crosslinking agent, such as tris(2,3-epoxypropyl)
isocyanurate. The carboxylic acid functional polymer is prepared by
atom transfer radical polymerization, and has well defined polymer
chain structure, molecular weight and molecular weight
distribution. The present invention also relates to methods of
coating a substrate, and substrates coated by such methods.
BACKGROUND OF THE INVENTION
[0003] Reducing the environmental impact of coatings compositions,
in particular that associated with emissions into the air of
volatile organics during their use, has been an area of ongoing
investigation and development in recent years. Accordingly,
interest in powder coatings has been increasing due, in part, to
their inherently low volatile organic content (VOC), which
significantly reduces air emissions during the application process.
While both thermoplastic and thermoset powder coatings compositions
are commercially available, thermoset powder coatings are typically
more desirable because of their superior physical properties, e.g.,
hardness and solvent resistance.
[0004] Low VOC coatings are particularly desirable in a number of
applications, e.g., the automotive original equipment manufacture
(OEM), industrial and appliance markets, due to the relatively
large volume of coatings that are used. However, in addition to the
requirement of low VOC levels, many manufactures have strict
performance requirements of the coatings that are used. Examples of
such requirements include, good exterior durability, solvent
resistance, and excellent gloss and appearance. While liquid
topcoats can provide such properties, they have the undesirable
draw back of higher VOC levels relative to powder coatings, which
have essentially zero VOC levels.
[0005] Powder coatings based on carboxylic acid functional polymers
cured with epoxide functional crosslinkers, such as
tris(2,3-epoxypropyl) isocyanurate, ("epoxy cured powder coatings")
are known and have been developed for use in a number of
applications, such as industrial and automotive OEM topcoats. The
epoxide functional crosslinker tris(2,3-epoxypropyl) isocyanurate
is also commonly referred to as triglycidyl isocyanurate (TGIC).
Such epoxy cured powder coatings, in which the crosslinking agent
is TGIC, are described in, for example, U.S. Pat. Nos. 3,935,138,
4,242,253, 4,605,710, 4,910,287, 5,264,529 and 5,684,067. However,
their use has been limited due to deficiencies in, for example,
flow, appearance and storage stability. The binder of epoxy cured
powder coatings compositions typically comprises polyester and/or
acrylic polymers having carboxylic acid functionality. The
carboxylic acid functional polymers used in such epoxy cured powder
coatings compositions are typically prepared by standard, i.e.,
non-living, radical polymerization methods, which provide little
control over molecular weight, molecular weight distribution and
polymer chain structure.
[0006] The physical properties, e.g., glass transition temperature
(Tg) and melt viscosity, of a given polymer can be directly related
to its molecular weight. Higher molecular weights are typically
associated with, for example, higher Tg values and melt
viscosities. The physical properties of a polymer having a broad
molecular weight distribution, e.g., having a polydispersity index
(PDI) in excess of 2.0 or 2.5, can be characterized as an average
of the individual physical properties of and indeterminate
interactions between the various polymeric species that comprise
it. As such, the physical properties of polymers having broad
molecular weight distributions can be variable and hard to
control.
[0007] The polymer chain structure, or architecture, of a copolymer
can be described as the sequence of monomer residues along the
polymer back bone or chain. For example, a carboxylic acid
functional copolymer prepared by standard radical polymerization
techniques will contain a mixture of polymer molecules having
varying individual carboxylic acid equivalent weights. Some of
these polymer molecules can actually be free of carboxylic acid
functionality. In a thermosetting composition, the formation of a
three dimensional crosslinked network is dependent upon the
functional equivalent weight as well as the architecture of the
individual polymer molecules that comprise it. Polymer molecules
having little or no reactive functionality (or having functional
groups that are unlikely to participate in crosslinking reactions
due to their location along the polymer chain) will contribute
little or nothing to the formation of the three dimensional
crosslink network, resulting in less than desirable physical
properties of the finally formed polymerizate, e.g., a cured or
thermoset coating.
[0008] The continued development of new and improved epoxy cured
powder coatings compositions having essentially zero VOC levels and
a combination of favorable performance properties is desirable. In
particular, it would be desirable to develop epoxy cured powder
coatings compositions that comprise carboxylic acid functional
polymers having well defined molecular weights and polymer chain
structure, and narrow molecular weight distributions, e.g., PDI
values less than 2.5. Controlling the architecture and
polydispersity of the carboxylic acid functional polymer is
desirable in that it enables one to achieve higher Tg's and lower
melt viscosities than comparable carboxylic acid functional
polymers prepared by conventional processes, resulting in
thermosetting particulate compositions which are resistant to
caking and have improved physical properties.
[0009] International patent publication WO 97/18247 and U.S. Pat.
Nos. 5,763,548 and 5,789,487 describe a radical polymerization
process referred to as atom transfer radical polymerization (ATRP).
The ATRP process is described as being a living radical
polymerization that results in the formation of (co)polymers having
predictable molecular weight and molecular weight distribution. The
ATRP process is also described as providing highly uniform products
having controlled structure (i.e., controllable topology,
composition, etc.). The '548 and '487 patents and WO 97/18247
patent publication also describe (co)polymers prepared by ATRP,
which are useful in a wide variety of applications, for example,
with paints and coatings.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention there is provided,
a thermosetting composition comprising a co-reactable solid,
particulate mixture of:
[0011] (a) polycarboxylic acid functional polymer prepared by atom
transfer radical polymerization initiated in the presence of an
initiator having at least one radically transferable group, and in
which said polymer contains at least one of the following polymer
chain structures I and II:
--[(M).sub.p--(G).sub.q].sub.x-- I
and
--[(G).sub.q--(M).sub.p].sub.x-- II
[0012] wherein M is a residue, that is free of carboxylic acid
functionality, of at least one ethylenically unsaturated radically
polymerizable monomer; G is a residue, that has carboxylic acid
functionality, of at least one ethylenically unsaturated radically
polymerizable monomer; p and q represent average numbers of
residues occurring in a block of residues in each polymer chain
structure; and p, q and x are each individually selected for each
structure such that said polycarboxylic acid functional polymer has
a number average molecular weight of at least 250; and
[0013] (b) epoxide functional crosslinking agent having at least
two epoxide groups.
[0014] In accordance with the present invention, there is also
provided a method of coating a substrate with the above described
thermosetting composition.
[0015] There is further provided, in accordance with the present
invention, a multi-component composite coating composition
comprising a base coat deposited from a pigmented film-forming
composition, and a transparent top coat applied over the base coat.
The transparent top coat comprises the above described
thermosetting composition.
[0016] 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 modified in all instances by the
term "about."
[0017] As used herein, the term "polymer" is meant to refer to both
homopolymers, i.e., polymers made from a single monomer species,
and copolymers, i.e., polymers made from two or more monomer
species.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Thermosetting compositions in accordance with the present
invention, comprise one or more polycarboxylic acid functional
polymers. As used herein and in the claims, by "polycarboxylic acid
functional polymer" and like terms is meant a polymer having two or
more carboxylic acid groups in terminal and/or pendent positions
that are capable of reacting and forming covalent bonds with
compounds containing epoxide (or oxirane) groups.
[0019] The carboxylic acid functional polymer of the present
invention is prepared by atom transfer radical polymerization
(ATRP). The ATRP method is described as a "living polymerization,"
i.e., a chain-growth polymerization that propagates with
essentially no chain transfer and essentially no chain termination.
The molecular weight of a polymer prepared by ATRP can be
controlled by the stoichiometry of the reactants, i.e., the initial
concentration of monomer(s) and initiator(s). In addition, ATRP
also provides polymers having characteristics including, for
example, narrow molecular weight distributions, e.g., PDI values
less than 2.5, and well defined polymer chain structure, e.g.,
block copolymers and alternating copolymers.
[0020] The ATRP process can be described generally as comprising:
polymerizing one or more radically polymerizable monomers in the
presence of an initiation system; forming a polymer; and isolating
the formed polymer. The initiation system comprises: an initiator
having a radically transferable atom or group; a transition metal
compound, i.e., a catalyst, which participates in a reversible
redox cycle with the initiator; and a ligand, which coordinates
with the transition metal compound. The ATRP process is described
in further detail in international patent publication WO 97/18247
and U.S. Pat. Nos. 5,763,548 and 5,789,487.
[0021] In preparing carboxylic acid functional polymers of the
present invention, the initiator may be selected from the group
consisting of linear or branched aliphatic compounds,
cycloaliphatic compounds, aromatic compounds, polycyclic aromatic
compounds, heterocyclic compounds, sulfonyl compounds, sulfenyl
compounds, esters of carboxylic acids, polymeric compounds and
mixtures thereof, each having at least one radically transferable
group, which is typically a halo group. The initiator may also be
substituted with functional groups, e.g., oxyranyl groups, such as
glycidyl groups. Additional useful initiators and the various
radically transferable groups that may be associated with them are
described on pages 42 through 45 of international patent
publication WO 97/18247.
[0022] Polymeric compounds (including oligomeric compounds) having
radically transferable groups may be used as initiators, and are
herein referred to as "macroinitiators." Examples of
macroinitiators include, but are not limited to, polystyrene
prepared by cationic polymerization and having a terminal halide,
e.g., chloride, and a polymer of 2-(2-bromopropionoxy) ethyl
acrylate and one or more alkyl (meth)acrylates, e.g., butyl
acrylate, prepared by conventional non-living radical
polymerization. Macroinitiators can be used in the ATRP process to
prepare graft polymers, such as grafted block copolymers and comb
copolymers. A further discussion of macroinitiators is found on
pages 31 through 38 of international patent publication WO
98/01480.
[0023] Preferably, the initiator may be selected from the group
consisting of halomethane, methylenedihalide, haloform, carbon
tetrahalide, 1-halo-2,3-epoxypropane, methanesulfonyl halide,
p-toluenesulfonyl halide, methanesulfenyl halide, p-toluenesulfenyl
halide, 1-phenylethyl halide, C.sub.1-C.sub.6-alkyl ester of
2-halo-C.sub.1-C.sub.6-carboxylic acid, p-halomethylstyrene,
mono-hexakis(a-halo-C.sub.1-C.sub.6-alkyl)benz- ene,
diethyl-2-halo-2-methyl malonate, ethyl 2-bromoisobutyrate and
mixtures thereof. A particularly preferred initiator is
diethyl-2-bromo-2-methyl malonate.
[0024] Catalysts that may be used in preparing carboxylic acid
functional polymers of the present invention, include any
transition metal compound that can participate in a redox cycle
with the initiator and the growing polymer chain. It is preferred
that the transition metal compound not form direct carbon-metal
bonds with the polymer chain. Transition metal catalysts useful in
the present invention may be represented by the following general
formula III,
TM.sup.n+X.sub.n III
[0025] wherein TM is the transition metal, n is the formal charge
on the transition metal having a value of from 0 to 7, and X is a
counterion or covalently bonded component. Examples of the
transition metal (TM) include, but are not limited to, Cu, Fe, Au,
Ag, Hg, Pd, Pt, Co, Mn, Ru, Mo, Nb and Zn. Examples of X include,
but are not limited to, halogen, hydroxy, oxygen,
C.sub.1-C.sub.6-alkoxy, cyano, cyanato, thiocyanato and azido. A
preferred transition metal is Cu(I) and X is preferably halogen,
e.g., chloride. Accordingly, a preferred class of transition metal
catalysts are the copper halides, e.g., Cu(I)Cl. It is also
preferred that the transition metal catalyst contain a small
amount, e.g., 1 mole percent, of a redox conjugate, for example,
Cu(II)Cl.sub.2 when Cu(I)Cl is used. Additional catalysts useful in
preparing the carboxylic acid functional polymers of the present
invention are described on pages 45 and 46 of international patent
publication WO 97/18247. Redox conjugates are described on pages 27
through 33 of international patent publication WO 97/18247.
[0026] Ligands that may be used in preparing carboxylic acid
functional polymers of the present invention, include, but are not
limited to compounds having one or more nitrogen, oxygen,
phosphorus and/or sulfur atoms, which can coordinate to the
transition metal catalyst compound, e.g., through sigma and/or pi
bonds. Classes of useful ligands, include but are not limited to:
unsubstituted and substituted pyridines and bipyridines;
porphyrins; cryptands; crown ethers; e.g., 18-crown-6; polyamines,
e.g., ethylenediamine; glycols, e.g., alkylene glycols, such as
ethylene glycol; carbon monoxide; and coordinating monomers, e.g.,
styrene, acrylonitrile and hydroxyalkyl (meth)acrylates. A
preferred class of ligands are the substituted bipyridines, e.g.,
4,4'-dialkylbipyridyls. Additional ligands that may be used in
preparing the carboxylic acid functional polymers of the present
invention are described on pages 46 through 53 of international
patent publication WO 97/18247.
[0027] In preparing the carboxylic acid functional polymers of the
present invention the amounts and relative proportions of
initiator, transition metal compound and ligand are those for which
ATRP is most effectively performed. The amount of initiator used
can vary widely and is typically present in the reaction medium in
a concentration of from 10.sup.-4 moles/liter (M) to 3 M, for
example, from 10.sup.-3 M to 10.sup.-1 M. As the molecular weight
of the carboxylic acid functional polymer can be directly related
to the relative concentrations of initiator and monomer(s), the
molar ratio of initiator to monomer is an important factor in
polymer preparation. The molar ratio of initiator to monomer is
typically within the range of 10.sup.-4:1 to 0.5:1, for example,
10.sup.-3:1 to 5.times.10.sup.-2: 1.
[0028] In preparing the carboxylic acid functional polymers of the
present invention, the molar ratio of transition metal compound to
initiator is typically in the range of 10.sup.-4:1 to 10:1, for
example, 0.1:1 to 5:1. The molar ratio of ligand to transition
metal compound is typically within the range of 0.1:1 to 100:1, for
example, 0.2:1 to 10:1.
[0029] Carboxylic acid functional polymers useful in the
thermosetting compositions of the present invention may be prepared
in the absence of solvent, i.e., by means of a bulk polymerization
process. Generally, the carboxylic acid functional polymer is
prepared in the presence of a solvent, typically water and/or an
organic solvent. Classes of useful organic solvents include, but
are not limited to, esters of carboxylic acids, ethers, cyclic
ethers, C.sub.5-C.sub.10 alkanes, C.sub.5-C.sub.8 cycloalkanes,
aromatic hydrocarbon solvents, halogenated hydrocarbon solvents,
amides, nitriles, sulfoxides, sulfones and mixtures thereof.
Supercritical solvents, such as CO.sub.2, C.sub.1-C.sub.4 alkanes
and fluorocarbons, may also be employed. A preferred class of
solvents are the aromatic hydrocarbon solvents, particularly
preferred examples of which are xylene, and mixed aromatic solvents
such as those commercially available from Exxon Chemical America
under the trademark SOLVESSO. Additional solvents are described in
further detail on pages 53 through 56 of international patent
publication WO 97/18247.
[0030] Due to the possible deactivation of some ATRP catalysts,
e.g., copper, in the presence of carboxylic acid groups, the above
described ATRP process is generally performed in the substantial
absence of carboxylic acid functionality. Accordingly, the
carboxylic acid functional polymer used in the composition of the
present invention is typically prepared in two stages. The first
stage involves the ATRP preparation of a precursor of the
polycarboxylic acid functional polymer that is substantially free
of carboxylic acid functionality ("precursor polymer"). In the
second stage, the precursor polymer is converted to the
polycarboxylic acid functional polymer of the composition of the
present invention.
[0031] The conversion of the precursor polymer to the
polycarboxylic acid functional polymer is accomplished using
methods known to those of ordinary skill in the art. Such known
methods of conversion include, but are not limited to: (a)
hydrolyzing residues of alkyl (meth)acrylate monomers, e.g.,
t-butyl methacrylate, present in the backbone of the precursor
polymer; and (b) reacting residues of hydroxy functional
ethylenically unsaturated radically polymerizable monomers present
in the backbone of the precursor polymer with cyclic anhydrides,
e.g., succinic anhydride.
[0032] The precursor polymer of the carboxylic acid functional
polymer is typically prepared at a reaction temperature within the
range of 25.degree. C. to 140.degree. C., e.g., from 50.degree. C.
to 100.degree. C., and a pressure within the range of 1 to 100
atmospheres, usually at ambient pressure. The atom transfer radical
polymerization is typically completed in less than 24 hours, e.g.,
between 1 and 8 hours.
[0033] When the carboxylic acid functional polymer is prepared in
the presence of a solvent, the solvent is removed after the polymer
has been formed, by appropriate means as are known to those of
ordinary skill in the art, e.g., vacuum distillation.
Alternatively, the polymer may be precipitated out of the solvent,
filtered, washed and dried according to known methods. After
removal of, or separation from, the solvent, the carboxylic acid
functional polymer typically has a solids (as measured by placing a
1 gram sample in a 110.degree. C. oven for 60 minutes) of at least
95 percent, and preferably at least 98 percent, by weight based on
total polymer weight.
[0034] Prior to use in the thermosetting compositions of the
present invention, the ATRP transition metal catalyst and its
associated ligand are typically separated or removed from the
carboxylic acid functional polymer. The ATRP catalyst is preferably
removed prior to conversion of the precursor polymer to the
carboxylic acid functional polymer. Removal of the ATRP catalyst is
achieved using known methods, including, for example, adding a
catalyst binding agent to the a mixture of the precursor polymer,
solvent and catalyst, followed by filtering. Examples of suitable
catalyst binding agents include, for example, alumina, silica, clay
or a combination thereof. A mixture of the precursor polymer,
solvent and ATRP catalyst may be passed through a bed of catalyst
binding agent. Alternatively, the ATRP catalyst may be oxidized in
situ and retained in the precursor polymer.
[0035] The carboxylic acid functional polymer may be selected from
the group consisting of linear polymers, branched polymers,
hyperbranched polymers, star polymers, graft polymers and mixtures
thereof. The form, or gross architecture, of the polymer can be
controlled by the choice of initiator and monomers used in its
preparation. Linear carboxylic acid functional polymers may be
prepared by using initiators having one or two radically
transferable groups, e.g., diethyl-2-halo-2-methyl malonate and
.alpha.,.alpha.'-dichloroxylene. Branched carboxylic acid
functional polymers may be prepared by using branching monomers,
i.e., monomers containing radically transferable groups or more
than one ethylenically unsaturated radically polymerizable group,
e.g., 2-(2-bromopropionoxy)eth- yl acrylate, p-chloromethylstyrene
and diethyleneglycol bis(methacrylate). Hyperbranched carboxylic
acid functional polymers may be prepared by increasing the amount
of branching monomer used.
[0036] Star carboxylic acid functional polymers may be prepared
using initiators having three or more radically transferable
groups, e.g., hexakis(bromomethyl)benzene. As is known to those of
ordinary skill in the art, star polymers may be prepared by
core-arm or arm-core methods. In the core-arm method, the star
polymer is prepared by polymerizing monomers in the presence of the
polyfunctional initiator, e.g., hexakis(bromomethyl)benzene.
Polymer chains, or arms, of similar composition and architecture
grow out from the initiator core, in the core-arm method.
[0037] In the arm-core method, the arms are prepared separately
from the core and optionally may have different compositions,
architecture, molecular weight and PDI's. The arms may have
different carboxylic acid equivalent weights, and some may have no
carboxylic acid functionality. After the preparation of the arms,
they are attached to the core. For example, the arms may be
prepared as precursor polymers by ATRP using glycidyl functional
initiators. These arms are then attached to a core having three or
more active hydrogen groups that are reactive with epoxides, e.g.,
carboxylic acid or hydroxyl groups. Finally, the precursor polymer
arms of the formed star polymer are converted to carboxylic acid
functional arms, as discussed previously herein. The core can be a
molecule, such as citric acid, or a core-arm star polymer prepared
by ATRP and having terminal reactive hydrogen containing groups,
e.g., carboxylic acid, thiol or hydroxyl groups.
[0038] An example of a core prepared by ATRP methods that can be
used as a core in an ATRP arm-core star polymer is described as
follows. In the first stage, 6 moles of methyl methacrylate are
polymerized in the presence of one mole of
1,3,5-tris(bromomethyl)benzene. In the second stage 3 moles of
2-hydroxyethyl methacrylate are fed to the reaction mixture. The
core having terminal residues of 2-hydroxyethyl methacrylate is
isolated and then in the third stage reacted with a cyclic
anhydride, such as succinic anhydride. In the next stage, three
precursor polymer arms of varying or equivalent composition and at
least one of which has been prepared by ATRP, are connected to the
carboxylic acid terminated core by reaction between the carboxylic
acid groups of the core and reactive functionality in the arms,
e.g., epoxide groups. The attached precursor polymer arms of the
star polymer are then converted to carboxylic acid functional
arms.
[0039] Carboxylic acid functional polymers in the form of graft
polymers may be prepared using a macroinitiator, as previously
described herein. Graft, branched, hyperbranched and star polymers
are described in further detail on pages 79 through 91 of
international patent publication WO 97/18247.
[0040] The polydispersity index (PDI) of carboxylic acid functional
polymers useful in the present invention, is typically less than
2.5, more typically less than 2.0, and preferably less than 1.8,
for example, 1.5. As used herein, and in the claims,
"polydispersity index" is determined from the following equation:
(weight average molecular weight (Mw)/number average molecular
weight (Mn)). A monodisperse polymer has a PDI of 1.0. Further, as
used herein, Mn and Mw are determined from gel permeation
chromatography using polystyrene standards.
[0041] General polymer chain structures I and II together or
separately represent one or more structures that comprise the
polymer chain, or back bone, architecture of the carboxylic acid
functional polymer. Subscripts p and q of general polymer chain
structures I and II represent average numbers of residues occurring
in the M and G blocks of residues respectively. Subscript x
represents the number of segments of M and G blocks, i.e.,
x-segments. Subscripts p and q may each be the same or different
for each x-segment. The following are presented for the purpose of
illustrating the various polymer architectures that are represented
by general polymer chain structures I and II.
[0042] Homoblock Polymer Architecture:
[0043] When x is 1, p is 0 and q is 5, general polymer chain
structure I represents a homoblock of 5 G residues, as more
specifically depicted by the following general formula IV.
--(G)--(G)--(G)--(G)--(G)-- IV
[0044] Diblock Copolymer Architecture:
[0045] When x is 1, p is 5 and q is 5, general polymer chain
structure I represents a diblock of 5 M residues and 5 G residues
as more specifically depicted by the following general formula
V.
--(M)--(M)--(M)--(M)--(M)--(G)--(G)--(G)--(G)--(G)-- V
[0046] Alternating Copolymer Architecture:
[0047] When x is greater than 1, for example, 5, and p and q are
each 1 for each x-segment, polymer chain structure I represents an
alternating block of M and G residues, as more specifically
depicted by the following general formula VI.
--(M)--(G)--(M)--(G)--(M)--(G)--(M)--(G)--(M)--(G)-- VI
[0048] Gradient Copolymer Architecture:
[0049] When x is greater than 1, for example, 3, and p and q are
each independently within the range of, for example, 1 to 3, for
each x-segment, polymer chain structure I represents a gradient
block of M and G residues, as more specifically depicted by the
following general formula VII.
--(M)--(M)--(M)--(G)--(M)--(M)--(G)--(G)--(M)--(G)--(G)--(G)--
VII
[0050] Gradient copolymers can be prepared from two or more
monomers by ATRP methods, and are generally described as having
architecture that changes gradually and in a systematic and
predictable manner along the polymer backbone. Gradient copolymers
can be prepared by ATRP methods by (a) varying the ratio of
monomers fed to the reaction medium during the course of the
polymerization, (b) using a monomer feed containing monomers having
different rates of polymerization, or (c) a combination of (a) and
(b). Gradient copolymers are described in further detail on pages
72 through 78 of international patent publication WO 97/18247.
[0051] With further reference to general polymer chain structures I
and II, M represents one or more types of residues that are free of
carboxylic acid functionality, and p represents the average total
number of M residues occurring per block of M residues (M-block)
within an x-segment. The --(M).sub.p-- portion of general
structures I and II represents (1) a homoblock of a single type of
M residue, (2) an alternating block of two types of M residues, (3)
a polyblock of two or more types of M residues, or (4) a gradient
block of two or more types of M residues.
[0052] For purposes of illustration, when the M-block is prepared
from, for example, 10 moles of methyl methacrylate, the
--(M).sub.p-- portion of structures I and II represents a homoblock
of 10 residues of methyl methacrylate. In the case where the
M-block is prepared from, for example, 5 moles of methyl
methacrylate and 5 moles of butyl methacrylate, the --(M).sub.p--
portion of general structures I and II represents, depending on the
conditions of preparation, as is known to one of ordinary skill in
the art: (a) a diblock of 5 residues of methyl methacrylate and 5
residues of butyl methacrylate having a total of 10 residues (i.e.,
p =10); (b) a diblock of 5 residues of butyl methacrylate and 5
residues of methyl methacrylate having a total of 10 residues; (c)
an alternating block of methyl methacrylate and butyl methacrylate
residues beginning with either a residue of methyl methacrylate or
a residue of butyl methacrylate, and having a total of 10 residues;
or (d) a gradient block of methyl methacrylate and butyl
methacrylate residues beginning with either residues of methyl
methacrylate or residues of butyl methacrylate having a total of 10
residues.
[0053] Also, with reference to general polymer chain structures I
and II, G represents one or more types of residues that have
carboxylic acid functionality, and q represents the average total
number of G residues occurring per block of G residues (G-block).
Accordingly, the --(G).sub.q-- portions of polymer chain structures
I and II may be described in a manner similar to that of the
--(M).sub.p-- portions provided above.
[0054] Residue M of general polymer chain structures I and II is
derived from at least one ethylenically unsaturated radically
polymerizable monomer. As used herein and in the claims,
"ethylenically unsaturated radically polymerizable monomer" and
like terms are meant to include vinyl monomers, allylic monomers,
olefins and other ethylenically unsaturated monomers that are
radically polymerizable.
[0055] Classes of vinyl monomers from which M may be derived
include, but are not limited to, (meth)acrylates, vinyl aromatic
monomers, vinyl halides and vinyl esters of carboxylic acids. As
used herein and in the claims, by "(meth)acrylate" and like terms
is meant both methacrylates and acrylates. Preferably, residue M is
derived from at least one of alkyl (meth)acrylates having from 1 to
20 carbon atoms in the alkyl group. Specific examples of alkyl
(meth)acrylates having from 1 to 20 carbon atoms in the alkyl group
from which residue M may be derived include, but are not limited
to, methyl (meth)acrylate, ethyl (meth)acrylate, propyl
(meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate,
isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl
(meth)acrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate,
cyclohexyl (meth)acrylate and 3,3,5-trimethylcyclohexyl
(meth)acrylate.
[0056] Residue M may also be selected from monomers having more
than one (meth)acrylate group, for example, (meth)acrylic anhydride
and diethyleneglycol bis((meth)acrylate). Residue M may also be
selected from alkyl (meth)acrylates containing radically
transferable groups, which can act as branching monomers, for
example, 2-(2-bromopropionoxy)ethyl acrylate.
[0057] Specific examples of vinyl aromatic monomers from which M
may be derived include, but are not limited to, styrene,
p-chloromethylstyrene, divinyl benzene, vinyl naphthalene and
divinyl naphthalene. Vinyl halides from which M may be derived
include, but are not limited to, vinyl chloride and vinylidene
fluoride. Vinyl esters of carboxylic acids from which M may be
derived include, but are not limited to, vinyl acetate, vinyl
butyrate, vinyl 3,4-dimethoxybenzoate and vinyl benzoate.
[0058] As used herein and in the claims, by "olefin" and like terms
is meant unsaturated aliphatic hydrocarbons having one or more
double bonds, such as obtained by cracking petroleum fractions.
Specific examples of olefins from which M may be derived include,
but are not limited to, propylene, 1-butene, 1,3-butadiene,
isobutylene and diisobutylene.
[0059] As used herein and in the claims, by "allylic monomer(s)" is
meant monomers containing substituted and/or unsubstituted allylic
functionality, i.e., one or more radicals represented by the
following general formula VIII,
H.sub.2C.dbd.C (R.sub.4)--CH.sub.2-- VIII
[0060] wherein R.sub.4 is hydrogen, halogen or a C.sub.1 to C.sub.4
alkyl group. Most commonly, R.sub.4 is hydrogen or methyl and
consequently general formula VIII represents the unsubstituted
(meth)allyl radical. Examples of allylic monomers include, but are
not limited to: (meth)allyl alcohol; (meth)allyl ethers, such as
methyl (meth)allyl ether; allyl esters of carboxylic acids, such as
(meth)allyl acetate, (meth)allyl butyrate, (meth)allyl
3,4-dimethoxybenzoate and (meth)allyl benzoate.
[0061] Other ethylenically unsaturated radically polymerizable
monomers from which M may be derived include, but are not limited
to: cyclic anhydrides, e.g., maleic anhydride,
1-cyclopentene-1,2-dicarboxylic anhydride and itaconic anhydride;
esters of acids that are unsaturated but do not have
.alpha.,.beta.-ethylenic unsaturation, e.g., methyl ester of
undecylenic acid; and diesters of ethylenically unsaturated dibasic
acids, e.g., diethyl maleate.
[0062] Residue G of general polymer chain structures I and II is
typically derived from: alkyl (meth)acrylate, which after
polymerization is hydrolyzed; or at least one hydroxy functional
ethylenically unsaturated radically polymerizable monomer, which
after polymerization is post-reacted with a cyclic anhydride.
Examples of classes of suitable hydroxy functional ethylenically
unsaturated radically polymerizable monomers from which residue G
may be derived include, but are not limited to: vinyl esters such
as vinyl acetate, which are hydrolyzed to residues of vinyl alcohol
after polymerization; allylic esters such as allyl acetate, which
are hydrolyzed to residues of allyl alcohol after polymerization;
allylic functional monomer that also have hydroxy functionality,
e.g., allyl alcohol and 2-allylphenol; vinyl aromatic monomers
having hydroxy functionality, e.g., 2-ethenyl-5-methyl phenol,
2-ethenyl-6-methyl phenol and 4-ethenyl-3-methyl phenol; and
hydroxy functional (meth)acrylates such as hydroxyalkyl
(meth)acrylates, e.g., hydroxyethyl (meth)acrylate and
hydroxypropyl (meth)acrylate.
[0063] The cyclic anhydride is selected from those which can react
with residues of the hydroxy functional ethylenically unsaturated
radically polymerizable monomers in the precursor polymer backbone,
thereby attaching carboxylic acid groups thereto. Examples of
suitable cyclic anhydrides include, but are not limited to,
succinic anhydride, maleic anhydride, glutaric anhydride, adipic
anhydride and pimelic anhydride.
[0064] In a preferred embodiment of the present invention, residue
G is derived from: C.sub.1-C.sub.4 alkyl (meth)acrylate, e.g.,
t-butyl methacrylate, which after polymerization is hydrolyzed; or
at least one of hydroxyethyl (meth)acrylate and hydroxypropyl
(meth)acrylate, which after polymerization is post-reacted with a
cyclic anhydride, e.g., succinic anhydride.
[0065] Residue G may also be derived from other monomers which can
be converted or further reacted with other compounds to provide
acid functionality after completion of the ATRP polymerization
process. Examples of such other monomers from which residue G may
be derived include, but are not limited to: acrylonitrile, the
nitrile portion of which can be hydrolyzed to a carboxylic acid
group after polymerization; isocyanate functional monomers, e.g.,
3-isopropenyl-.alpha.,.alpha.-dimet- hylbenzyl isocyanate [chemical
abstracts (CAS) registry number 2094-99-7], which can be reacted
after polymerization with compounds containing both carboxylic acid
and hydroxyl functionality, e.g., 12-hydroxystearic acid and lactic
acid; and maleic anhydride, which after polymerization can be
either hydrolyzed to form carboxylic acid groups or reacted with a
monofunctional alcohol in the presence of acid catalyst to form
ester and carboxylic acid groups.
[0066] The choice of monomers from which each of residues M and G
are selected is interrelated, i.e., the choice of monomers from
which G is derived limits the choice of monomers from which M is
derived. When residue G is derived from hydroxy functional
ethylenically unsaturated radically polymerizable monomer(s), which
after polymerization are post-reacted with a cyclic anhydride,
residue M is typically not derived from such monomer(s). Also, when
residue G is derived from one or more alkyl (meth)acrylates, which
after polymerization are hydrolyzed, residue M is typically not
derived from such monomers.
[0067] Subscripts p and q represent average number of residues
occurring in a block of residues in each polymer structure.
Typically, p and q each independently have a value of 0 or more,
preferably at least 1, and more preferably at least 5 for each of
general polymer structures I and II. Also, subscripts p and q each
independently have a value of typically less than 100, preferably
less than 20, and more preferably less than 15 for each of general
polymer structures I and II. The values of subscripts p and q may
range between any combination of these values, inclusive of the
recited values. Moreover, the sum of p and q is at least 1 within
an x-segment and q is at least 1 within at least one x-segment in
the polymer.
[0068] Subscript x of general polymer structures I and II typically
has a value of at least 1. Also, subscript x typically has a value
of less than 100, preferably less than 50, and more preferably less
than 10. The value of subscript x may range between any combination
of these values, inclusive of the recited values. If more than one
of the structures I and/or II occur in the polymer molecule, x may
have different -values for each structure (as may p and q),
allowing for a variety of polymer architectures such as gradient
copolymers.
[0069] The polycarboxylic acid functional polymer of the present
invention may be further described as having at least one of the
following general polymer chain structures IX and X:
.phi.--[[(M).sub.p--(G).sub.q].sub.x(M).sub.r--T].sub.z IX
and
.phi.--[[(G).sub.q--(M).sub.p].sub.x--(G).sub.s--T].sub.z X
[0070] wherein p, q, x, M and G have the same meanings as
previously described herein. The subscripts r and s represent
average numbers of residues occurring in the respective blocks of M
and G residues. The --(M).sub.r-- and --(G).sub.s-- portions of
general formulas IX and X have meanings similar to those as
previously described herein with regard to portions --(M).sub.p--
and --(G).sub.q-- General polymer chain structures IX and X can
represent the polymer itself or, alternatively, each of the
structures can comprise a terminal segment of the polymer. For
example, where z is 1, the structures IX and X can represent a
linear polymer, prepared by ATRP using an initiator having 1
radically transferable group. Where z is 2, the structures IX and X
can represent a linear "leg" extending from the residue of an
initiator having 2 radically transferable groups. Alternatively,
where z is greater than 2, the structures IX and X can each
represent an "arm" of a star polymer prepared by ATRP, using an
initiator having more than 2 radically transferable groups.
[0071] Symbol .phi. of general formulas IX and X is or is derived
from the residue of the initiator used in the ATRP preparation of
the polymer, and is free of the radically transferable group of the
initiator. For example, when the carboxylic acid functional polymer
is initiated in the presence of benzyl bromide, the symbol .phi.,
more specifically .phi.-, is the benzyl residue, 1
[0072] The symbol .phi. may also be derived from the residue of the
initiator. For example, when the carboxylic acid functional polymer
is initiated using epichlorohydrin the symbol .phi., more 2
[0073] specifically .phi.-, is the 2,3-epoxy-propyl residue, The
2,3-epoxy-propyl residue can then be converted to, for example, a
2,3-dihydroxypropyl residue.
[0074] In general formulas IX and X, subscript z is equal to the
number of carboxylic acid functional polymer chains that are
attached to .phi.. Subscript z is at least 1 and may have a wide
range of values. In the case of comb or graft polymers, wherein
.phi. is a macroinitiator having several pendent radically
transferable groups, z can have a value in excess of 10, for
example 50, 100 or 1000. Typically, z is less than 10, preferably
less than 6 and more preferably less than 5. In a preferred
embodiment of the present invention, z is 1 or 2.
[0075] Symbol T of general formulas IX and X is or is derived from
the radically transferable group of the initiator. For example,
when the carboxylic acid functional polymer is prepared in the
presence of diethyl-2-bromo-2-methyl malonate, T may be the
radically transferable bromo group.
[0076] The radically transferable group may optionally be (a)
removed or (b) chemically converted to another moiety. In either of
(a) or (b), the symbol T is considered herein to be derived from
the radically transferable group of the initiator. The radically
transferable group may be removed by substitution with a
nucleophilic compound, e.g., an alkali metal alkoxylate. However,
in the present invention, it is desirable that the method by which
the radically transferable group is either removed or chemically
converted, also be relatively mild, i.e., not appreciably affecting
or damaging the polymer backbone.
[0077] In a preferred embodiment of the present invention, when the
radically transferable group is a halogen, the halogen can be
removed by means of a mild dehalogenation reaction. The reaction is
typically performed as a post-reaction after the precursor polymer
has been formed, i.e., prior to conversion of the precursor polymer
to the polycarboxylic acid functional polymer, and in the presence
of at least an ATRP catalyst. Preferably, the dehalogenation
post-reaction is performed in the presence of both an ATRP catalyst
and its associated ligand.
[0078] The mild dehalogenation reaction is performed by contacting
the halogen terminated precursor of the carboxylic acid functional
polymer of the present invention that is substantially free of
carboxylic acid functionality with one or more ethylenically
unsaturated compounds, which are not readily radically
polymerizable under at least a portion of the spectrum of
conditions under which atom transfer radical polymerizations are
performed, hereinafter referred to as "limited radically
polymerizable ethylenically unsaturated compounds" (LRPEU
compound(s)). As used herein, by "halogen terminated" and similar
terms is meant to be inclusive also of pendent halogens, e.g., as
would be present in branched, comb and star polymers.
[0079] Not intending to be bound by any theory, it is believed,
based on the evidence at hand, that the reaction between the
halogen terminated precursor polymer and one or more LRPEU
compounds results in (1) removal of the terminal halogen group, and
(2) the addition of at least one carbon-carbon double bond where
the terminal carbon-halogen bond is broken. The dehalogenation
reaction is typically conducted at a temperature in the range of
0.degree. C. to 200.degree. C., e.g., from 0.degree. C. to
160.degree. C., a pressure in the range of 0.1 to 100 atmospheres,
e.g., from 0.1 to 50 atmospheres. The reaction is also typically
performed in less than 24 hours, e.g., between 1 and 8 hours. While
the LRPEU compound may be added in less than a stoichiometric
amount, it is preferably added in at least a stoichiometric amount
relative to the moles of terminal halogen present in the precursor
polymer. When added in excess of a stoichiometric amount, the LRPEU
compound is typically present in an amount of no greater than 5
mole percent, e.g., 1 to 3 mole percent, in excess of the total
moles of terminal halogen.
[0080] Limited radically polymerizable ethylenically unsaturated
compounds useful for dehalogenating the precursor polymer of the
carboxylic acid functional polymer of the composition of the
present invention, under mild conditions, include those represented
by the following general formula XI. 3
[0081] In general formula XI, R.sub.1 and R.sub.2 can be the same
or different organic groups such as: alkyl groups having from 1 to
4 carbon atoms; aryl groups; alkoxy groups; ester groups; alkyl
sulfur groups; acyloxy groups; and nitrogen-containing alkyl groups
where at least one of the R.sub.1 and R.sub.2 groups is an organo
group while the other can be an organo group or hydrogen. For
instance when one of R.sub.1 or R.sub.2 is an alkyl group, the
other can be an alkyl, aryl, acyloxy, alkoxy, arenes,
sulfur-containing alkyl group, or nitrogen-containing alkyl and/or
nitrogen-containing aryl groups. The R.sub.3 groups can be the same
or different groups selected from hydrogen or lower alkyl selected
such that the reaction between the terminal halogen of the polymer
and the LRPEU compound is not prevented. Also an R.sub.3 group can
be joined to the R.sub.1 and/or the R.sub.2 groups to form a cyclic
compound.
[0082] It is preferred that the LRPEU compound be free of halogen
groups. Examples of suitable LRPEU compounds include, but are not
limited to, 1,1-dimethylethylene, 1,1-diphenylethylene, isopropenyl
acetate, alpha-methyl styrene, 1,1-dialkoxy olefin and mixtures
thereof. Additional examples include dimethyl itaconate and
diisobutene (2,4,4-trimethyl-1-pentene).
[0083] For purposes of illustration, the reaction between halogen
terminated precursor polymer and LRPEU compound, e.g., alpha-methyl
styrene, is summarized in the following general scheme 1. 4
[0084] In general scheme 1, P--X represents the halogen terminated
precursor polymer, which is later converted to the polycarboxylic
acid functional polymer of the composition of the present
invention, as described previously herein.
[0085] For each of general polymer structures IX and X, the
subscripts r and s each independently have a value of 0 or more.
Subscripts r and s each independently have a value of typically
less than 100, preferably less than 50, and more preferably less
than 10, for each of general polymer structures IX and X. The
values of r and s may each range between any combination of these
values, inclusive of the recited values.
[0086] The carboxylic acid functional polymer typically has a
carboxylic acid equivalent weight of at least 100 grams/equivalent,
and preferably at least 200 grams/equivalent. The carboxylic acid
equivalent weight of the polymer is also typically less than 10,000
grams/equivalent, preferably less than 5,000 grams/equivalent, and
more preferably less than 1,000 grams/equivalent. The carboxylic
acid equivalent weight of the carboxylic acid functional polymer
may range between any combination of these values, inclusive of the
recited values.
[0087] The number average molecular weight (Mn) of the carboxylic
acid functional polymer is typically at least 250, more typically
at least 500, preferably at least 1,000, and more preferably at
least 2,000. The carboxylic acid functional polymer also typically
has a Mn of less than 16,000, preferably less than 10,000, and more
preferably less than 5,000. The Mn of the carboxylic acid
functional polymer may range between any combination of these
values, inclusive of the recited values.
[0088] The carboxylic acid functional polymer may be used in the
thermosetting composition of the present invention as a resinous
binder or as an additive with a separate resinous binder, which may
be prepared by ATRP or by conventional polymerization methods. When
used as an additive, the carboxylic acid functional polymer as
described herein typically has low functionality, e.g., it may be
monofunctional, and a correspondingly high equivalent weight.
[0089] The carboxylic acid functional polymer (a) is typically
present in the thermosetting composition of the present invention
in an amount of at least 50 percent by weight, preferably at least
70 percent by weight, and more preferably at least 80 percent by
weight, based on total weight of resin solids of the thermosetting
composition. The thermosetting composition also typically contains
carboxylic acid functional polymer present in an amount of less
than 98 percent by weight, preferably less than 95 by weight, and
more preferably less than 90 percent by weight, based on total
weight of resin solids of the thermosetting composition. The
carboxylic acid functional polymer may be present in the
thermosetting composition of the present invention in an amount
ranging between any combination of these values, inclusive of the
recited values.
[0090] The thermosetting composition of the present invention may
optionally further comprise a polycarboxylic acid functional
polyester. Polycarboxylic acid functional polyesters useful in the
composition of the present invention typically have an average of
at least two carboxylic acid groups per polyester molecule.
Polyesters having carboxylic acid functionality may be prepared by
art-recognized methods, which include reacting carboxylic acids (or
their anhydrides) having acid functionalities of at least 2, and
polyols having hydroxy functionalities of at least 2. As is known
to those of ordinary skill in the art, the molar equivalents ratio
of carboxylic acid groups to hydroxy groups of the reactants is
selected such that the resulting polyester has carboxylic acid
functionality and the desired molecular weight.
[0091] Examples of multifunctional carboxylic acids useful in
preparing the polycarboxylic acid functional polyester include, but
are not limited to, benzene-1,2,4-tricarboxylic acid, phthalic
acid, tetrahydrophthalic acid, hexahydrophthalic acid,
endobicyclo-2,2,1,5-heptyne-2,3-dicarboxyli- c acid,
tetrachlorophthalic acid, cyclohexanedioic acid, succinic acid,
isophthalic acid, terephthalic acid, azelaic acid, maleic acid,
trimesic acid, 3,6-dichlorophthalic acid, adipic acid, sebacic
acid, and like multifunctional carboxylic acids. Examples of
polyols useful in preparing the polycarboxylic acid functional
polyester include, but are not limited to, glycerin,
trimethylolpropane, trimethylolethane,
trishydroxyethylisocyanurate, pentaerythritol, ethylene glycol,
propylene glycol, trimethylene glycol, 1,3-, 1,2- and
1,4-butanediols, heptanediol, hexanediol, octanediol,
2,2-bis(4-cyclohexanol)propane, neopentyl glycol,
2,2,3-trimethylpentane-1,3-diol, 1,4-dimethylolcyclohexane,
2,2,4-trimethylpentane diol, and like polyols.
[0092] Polycarboxylic acid functional polyesters useful in the
present invention typically have an Mn within the range of from
1,000 to 10,000, e.g., from 2,000 to 7,000. The acid equivalent
weight of the carboxylic acid functional polyester is typically
within the range of from 290 grams/equivalent to 3,000
grams/equivalent, e.g., from 500 to 2,000 grams/equivalent. When
present in the thermosetting composition of the present invention,
the polycarboxylic acid functional polyester is typically present
in an amount of from 1 percent to 40 percent by weight, based on
the total weight of resin solids, e.g., from 5 percent to 35
percent by weight, based on the total weight of resin solids.
[0093] The thermosetting composition comprises also one or more
epoxide functional crosslinking agents having at least two epoxide
groups. The epoxide functional crosslinking agent (b) is not
prepared by ATRP methods, and is preferably solid at room
temperature. Classes of epoxide functional crosslinking agents
useful in the composition of the present invention include, but are
not limited to, epoxide functional polyesters, epoxide functional
polymers prepared by conventional free radical polymerization
methods, epoxide functional polyethers, epoxide functional
isocyanurates and mixtures thereof.
[0094] Epoxide functional polyesters useful in the present
invention may be prepared by art-recognized methods. For example,
the hydroxyl groups of a hydroxy functional polyester may be
reacted with 1-halo-2,3-epoxy propane, e.g., epichlorohydrin, to
form the epoxide functional polyester. Polyesters having hydroxy
functionality may be prepared by traditional methods, which include
reacting polyols having hydroxy functionalities of at least 2, and
carboxylic acids (or their anhydrides) having acid functionalities
of at least 2. As is known to those of ordinary skill in the art,
the molar equivalents ratio of hydroxy groups to carboxylic acid
groups of the reactants is selected such that the resulting
polyester has hydroxy functionality and the desired molecular
weight. Examples of multifunctional carboxylic acids and polyols
useful in preparing the hydroxy functional polyester precursor of
the epoxide functional polyester include, but are not limited to,
those recited previously herein with regard to the optional
polycarboxylic acid functional polyester.
[0095] The Mn of epoxide functional polyesters useful in the
present invention is typically within the range of 1,000 to 10,000,
e.g., from 2,000 to 7,000. The equivalent weight of the epoxide
functional polyester is typically within the range of 290 to 3,000
grams/equivalent, e.g., 500 to 2,000 grams/equivalent.
[0096] Epoxide functional polymers prepared by conventional free
radical polymerization methods that may be used as the epoxide
functional crosslinking agent in the composition of the present
invention are not prepared by ATRP. These epoxide functional
polymer crosslinking agents are typically prepared by
copolymerizing epoxide functional ethylenically unsaturated
radically polymerizable monomer(s), typically a glycidyl functional
(meth)acrylate, such as glycidyl (meth)acrylate, with ethylenically
unsaturated radically polymerizable monomer(s) free of epoxide
functionality, e.g., alkyl (meth)acrylates. Typically, the epoxide
functional polymer prepared by conventional free radical
polymerization methods is an epoxide functional acrylic
polymer.
[0097] The conventional radical polymerization methods by which the
epoxide functional polymer crosslinking agent is prepared typically
involve the use of free radical initiators, such as organic
peroxides and azo type compounds. Optionally, chain transfer agents
may also be used, e.g., alpha-methyl styrene dimer and tertiary
dodecyl mercaptan.
[0098] Examples of ethylenically unsaturated radically
polymerizable monomers that may be used in the preparation of the
epoxide functional polymer crosslinking agent include, but are not
limited to, glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl
(meth)acrylate, 2-(3,4-epoxycyclohexyl)ethyl (meth)acrylate and
allyl glycidyl ether. Ethylenically unsaturated radically
polymerizable monomer(s) free of epoxide functionality that may be
used to prepare the epoxide functional polymer crosslinking agent
include those recited previously herein with regard to the M and G
residues of the polycarboxylic acid functional polymer prepared by
ATRP.
[0099] The Mn of the epoxide functional polymer crosslinking agent
prepared by conventional free radical polymerization methods is
typically less than 10,000, e.g., between 1,000 and 5,000, and
preferably between 1,000 and 2,500. The epoxide functional polymer
crosslinking agent usually contains from 3 to 6 moles of epoxide
functional ethylenically unsaturated monomer per kilogram of
epoxide functional polymer crosslinking agent, e.g., between 3.1
and 5.1 moles of epoxide functional monomer per kilograms of
epoxide functional polymer crosslinking agent.
[0100] Epoxide functional polyether crosslinking agents useful in
the present invention may be prepared by art-recognized methods.
For example, polyols having two or more hydroxy groups and
polyepoxides having two or more epoxide groups are reacted in
proportions such that the resulting polyether has epoxide
functionality, as is known to those of ordinary skill in the art.
The polyols and polyepoxides used in the preparation of the epoxide
functional polyether may be selected from, for example, aliphatic,
cycloaliphatic and aromatic polyols and polyepoxides, and mixtures
thereof. Specific examples of polyols include those recited
previously herein. Polyepoxides useful in preparing the epoxide
functional polyether include those resulting from the reaction of a
polyol and epichlorohydrin, as is known to those skilled in the
art. In a preferred embodiment of the present invention, the
epoxide functional polyether is prepared from
4,4'-isopropylidenediphenol and the diglycidyl ether of
4,4'-isopropylidenediphenol. An example of a commercially available
epoxide functional polyether useful in the present invention is
EPON.RTM. Resin 2002 from Shell Chemical Company.
[0101] The epoxide functional polyether crosslinking agent
typically has a Mn of less than 10,000, e.g., between 1,000 and
7,000. The epoxide equivalent weight of the epoxide functional
polyether crosslinking agent is typically less than 2,000
grams/equivalent, e.g., between 300 and 1,000 grams/equivalent.
[0102] Epoxide functional isocyanurates are known and may be
prepared by art-recognized methods. A preferred epoxide functional
isocyanurate is tris(2,3-epoxypropyl) isocyanurate.
[0103] The epoxide functional crosslinking agent (b) is typically
present in the thermosetting composition of the present invention
in an amount of at least 2 percent by weight, preferably at least 5
percent by weight, and more preferably at least 10 percent by
weight, based on total weight of resin solids of the thermosetting
composition. The thermosetting composition also typically contains
epoxide functional crosslinking agent present in an amount of less
than 50 percent by weight, preferably less than 30 by weight, and
more preferably less than 20 percent by weight, based on total
weight of resin solids of the thermosetting composition. The
epoxide functional crosslinking agent may be present in the
thermosetting composition of the present invention in an amount
ranging between any combination of these values, inclusive of the
recited values.
[0104] To achieve a suitable level of cure with the thermosetting
composition of the present invention, the equivalent ratio of
carboxylic acid equivalents is the polycarboxylic acid functional
polymer (a) to epoxide equivalents in the epoxide functional
crosslinking agent (b) is typically from 0.7:1 to 2:1, e.g., from
0.8:1 to 1.3:1. The above recited ranges of ratios are meant to
also be inclusive of the carboxylic acid equivalents associated
with any polycarboxylic acid functional polyester(s) that may
optionally be present in the composition.
[0105] The thermosetting composition of the present invention may
also include pigments and fillers. Examples of pigments include,
but are not limited to, inorganic pigments, e.g., titanium dioxide
and iron oxides, organic pigments, e.g., phthalocyanines,
anthraquinones, quinacridones and thioindigos, and carbon blacks.
Examples of fillers include, but are not limited to, silica, e.g.,
precipitated silicas, clay, and barium sulfate. When used in the
composition of the present invention, pigments and fillers are
typically present in amounts of from 0.1 percent to 70 percent by
weight, based on the total weight of the thermosetting
composition.
[0106] The thermosetting composition of the present invention may
optionally contain additives such as waxes for flow and wetting,
flow control agents, e.g., poly(2-ethylhexyl)acrylate, degassing
additives such as benzoin, adjuvant resin to modify and optimize
coating properties, antioxidants and ultraviolet (UV) light
absorbers. Examples of useful antioxidants and UV light absorbers
include those available commercially from Ciba-Geigy under the
trademarks IRGANOX and TINUVIN. These optional additives, when
used, are typically present in amounts up to 20 percent by weight,
based on total weight of the thermosetting composition.
[0107] The thermosetting composition of the present invention is
typically prepared by first dry blending the carboxylic acid
functional polymer, the epoxide functional crosslinking agent and
additives, such as flow control agents, decassing agents,
antioxidants and UV absorbing agents, in a blender, e.g., a Henshel
blade blender. The blender is operated for a period of time
sufficient to result in a homogenous dry blend of the materials
charged thereto. The homogenous dry blend is then melt blended in
an extruder, e.g., a twin screw co-rotating extruder, operated
within a temperature range of 80.degree. C. to 140.degree. C.,
e.g., from 100.degree. C. to 125.degree. C. The extrudate of the
thermosetting composition of the present invention is cooled and,
when used as a powder coating composition, is typically milled to
an average particle size of from, for example, 15 to 30
microns.
[0108] In accordance with the present invention there is also
provided, a method of coating a substrate comprising:
[0109] (a) applying to said substrate a thermosetting
composition;
[0110] (b) coalescing said thermosetting composition to form a
substantially continuous film; and
[0111] (c) curing said thermosetting composition by the application
of heat, wherein said thermosetting composition comprises a
co-reactable solid, particulate mixture as previously described
herein.
[0112] The thermosetting composition of the present invention may
be applied to the substrate by any appropriate means that are known
to those of ordinary skill in the art. Generally, the thermosetting
composition is in the form of a dry powder and is applied by spray
application. Alternatively, the powder can be slurried in a liquid
medium such as water, and spray applied. Where the language
"co-reactable solid, particulate mixture" is used in the
specification and claims, the thermosetting composition can be in
dry powder form or in the form of a slurry.
[0113] When the substrate is electrically conductive, the
thermosetting composition is typically electrostatically applied.
Electrostatic spray application generally involves drawing the
thermosetting composition from a fluidized bed and propelling it
through a corona field. The particles of the thermosetting
composition become charged as they pass through the corona field
and are attracted to and deposited upon the electrically conductive
substrate, which is grounded. As the charged particles begin to
build up, the substrate becomes insulated, thus limiting further
particle deposition. This insulating phenomenon typically limits
the film build of the deposited composition to a maximum of 3 to 6
mils (75 to 150 microns).
[0114] Alternatively, when the substrate is not electrically
conductive, for example as is the case with many plastic
substrates, the substrate is typically preheated prior to
application of the thermosetting composition. The preheated
temperature of the substrate is equal to or greater than that of
the melting point of the thermosetting composition, but less than
its cure temperature. With spray application over preheated
substrates, film builds of the thermosetting composition in excess
of 6 mils (150 microns) can be achieved, e.g., 10 to 20 mils (254
to 508 microns). Substrates that may be coated by the method of the
present invention include, for example, ferrous substrates,
aluminum substrates, plastic substrates, e.g., sheet molding
compound based plastics, and wood.
[0115] After application to the substrate, the thermosetting
composition is then coalesced to form a substantially continuous
film. Coalescing of the applied composition is generally achieved
through the application of heat at a temperature equal to or
greater than that of the melting point of the composition, but less
than its cure temperature. In the case of preheated substrates, the
application and coalescing steps can be achieved in essentially one
step.
[0116] The coalesced thermosetting composition is next cured by the
application of heat. As used herein and in the claims, by "cured"
is meant a three dimensional crosslink network formed by covalent
bond formation, e.g., between the epoxide groups of the
crosslinking agent and the carboxylic acid groups of the polymer.
The temperature at which the thermosetting composition of the
present invention is cured is variable and depends in part on the
amount of time during which curing is conducted. Typically, the
thermosetting composition is cured at a temperature within the
range of 149.degree. C. to 204.degree. C., e.g., from 1540 C to
177.degree. C., for a period of 20 to 60 minutes.
[0117] In accordance with the present invention there is further
provided, a multi-component composite coating composition
comprising:
[0118] (a) a base coat deposited from a pigmented film-forming
composition; and
[0119] (b) a transparent top coat applied over said base coat,
wherein said transparent top coat is deposited from a clear
film-forming thermosetting composition comprising a co-reactable
solid, particulate mixture as previously described herein. The
multi-component composite coating composition as described herein
is commonly referred to as a color-plus-clear coating
composition.
[0120] The pigmented film-forming composition from which the base
coat is deposited can be any of the compositions useful in coatings
applications, particularly automotive applications in which
color-plus-clear coating compositions are extensively used.
Pigmented film-forming compositions conventionally comprise a
resinous binder and a pigment to act as a colorant. Particularly
useful resinous binders are acrylic polymers, polyesters including
alkyds, and polyurethanes.
[0121] The resinous binders for the pigmented film-forming base
coat composition can be organic solvent-based materials such as
those described in U.S. Pat. No. 4,220,679, note column 2 line 24
through column 4, line 40. Also, water-based coating compositions
such as those described in U.S. Pat. Nos. 4,403,003, 4,147,679 and
5,071,904 can be used as the binder in the pigmented film-forming
composition.
[0122] The pigmented film-forming base coat composition is colored
and may also contain metallic pigments. Examples of suitable
pigments can be found in U.S. Pat. Nos. 4,220,679, 4,403,003,
4,147,679 and 5,071,904.
[0123] Ingredients that may be optionally present in the pigmented
film-forming base coat composition are those which are well known
in the art of formulating surface coatings and include surfactants,
flow control agents, thixotropic agents, fillers, anti-gassing
agents, organic co-solvents, catalysts, and other customary
auxiliaries. Examples of these optional materials and suitable
amounts are described in the aforementioned U.S. Pat. Nos.
4,220,679, 4,403,003, 4,147,769 and 5,071,904.
[0124] The pigmented film-forming base coat composition can be
applied to the substrate by any of the conventional coating
techniques such as brushing, spraying, dipping or flowing, but are
most often applied by spraying. The usual spray techniques and
equipment for air spraying, airless spray and electrostatic
spraying employing either manual or automatic methods can be used.
The pigmented film-forming composition is applied in an amount
sufficient to provide a base coat having a film thickness typically
of 0.1 to 5 mils (2.5 to 125 microns) and preferably 0.1 to 2 mils
(2.5 to 50 microns).
[0125] After deposition of the pigmented film-forming base coat
composition on to the substrate, and prior to application of the
transparent top coat, the base coat can be cured or alternatively
dried. In drying the deposited base coat, organic solvent and/or
water, is driven out of the base coat film by heating or the
passage of air over its surface. Suitable drying conditions will
depend on the particular base coat composition used and on the
ambient humidity in the case of certain water-based compositions.
In general, drying of the deposited base coat is performed over a
period of from 1 to 15 minutes and at a temperature of 21.degree.
C. to 93.degree. C.
[0126] The transparent top coat is applied over the deposited base
coat by any of the methods by which powder coatings are known to be
applied. Preferably the transparent top coat is applied by
electrostatic spray application, as described previously herein.
When the transparent top coat is applied over a deposited base coat
that has been dried, the two coatings can be co-cured to form the
multi-component composite coating composition of the present
invention. Both the base coat and top coat are heated together to
conjointly cure the two layers. Typically, curing conditions of
149.degree. C. to 204.degree. C. for a period of 20 to 30 minutes
are employed. The transparent top coat typically has a thickness
within the range of 0.5 to 6 mils (13 to 150 microns), e.g., from 1
to 3 mils (25 to 75 microns).
[0127] The present invention is more particularly described in the
following examples, which are intended to be illustrative only,
since numerous modifications and variations therein will be
apparent to those skilled in the art. Unless otherwise specified,
all parts and percentages are by weight.
Synthesis Examples A and B
[0128] Synthesis Examples A and B describe the preparation of
carboxylic acid functional acrylic polymers that are used in the
powder coating compositions of Examples 1 and 2. The carboxylic
acid functional polymer of Example A is a comparative polymer
prepared by non-living radical polymerization. The carboxylic acid
functional polymer of Example B is representative of a polymer
useful in the thermosetting coating compositions of the present
invention. The physical properties of the polymers of Examples A
and B are summarized in Table 1.
[0129] In synthesis Examples A and B, the following monomer
abbreviations are used: methyl methacrylate (MMA); n-butyl
methacrylate (n-BMA); tertiary-butyl methacrylate (t-BMA); and
methacrylic acid (MAA).
EXAMPLE A
[0130] A comparative carboxylic acid functional polymer was
prepared by standard, i.e., non-controlled or non-living, radical
polymerization from the ingredients enumerated in Table A.
1 TABLE A Ingredients Parts by weight Charge 1 toluene 350
initiator (a) 40 Charge 2 MMA 100 n-BMA 350 MAA 50 (a)
2,2'-azobis(2-methylbutanenitrile) initiator, obtained commercially
from E.I. du Pont de Nemours and Company.
[0131] Charge 1 was heated to reflux temperature (at about
115.degree. C.) at atmospheric pressure under a nitrogen blanket in
a 2 liter round bottom flask equipped with a rotary blade agitator,
reflux condenser, thermometer and heating mantle coupled together
in a feed-back loop through a temperature controller, nitrogen
inlet port, and two addition ports. After holding Charge 1 for 30
minutes at reflux, Charge 2 was added over a period of 1 hour. With
the completion of the addition of Charge 2, the contents of the
flask were held at reflux for an additional 3 hours. The contents
of the flask were then vacuum stripped. While still molten, the
stripped contents of the flask were transferred to a suitable
shallow open container and allowed to cool to room temperature and
harden. The solidified resin was then broken into smaller pieces,
which were transferred to a suitable closed container for
storage.
EXAMPLE B
[0132] A carboxylic acid functional polymer useful in the
thermosetting compositions of the present invention was prepared by
atom transfer radical polymerization from the ingredients listed in
Table B.
2 TABLE B Ingredients Parts by weight toluene 350 copper(II)
bromide (b) 2.0 copper powder (c) 2.2 2,2'-bypyridyl 7.4
diethyl-2-bromo-2-methylmalonate 50.6 MMA 100 n-BMA 350 t-BMA 83
(b) The copper(II) bromide was in the form of flakes and was
obtained from Aldrich Chemical Company. (c) The copper powder had
an average particle size of 25 microns, a density of 1
gram/cm.sup.3, and was obtained commercially from OMG Americas.
[0133] The ingredients were all added to a 2 liter 4-necked flask
equipped with a motor driven stainless steel stir blade, water
cooled condenser, and a heating mantle and thermometer connected
through a temperature feed-back control device. The contents of the
flask were heated to and held at 85.degree. C. for 4 hours. The
contents of the flask were then cooled, filtered and the solvent
was removed by means of vacuum stripping. To the stripped resin was
added 350 ml of dioxane, and a 3 times molar excess (relative to
the moles of t-BMA) of HCl (1 Molar in water). The resin, dioxane,
HCl and water mixture was refluxed in a suitable round bottom flask
for 4 hours. The contents of the flask were then cooled to room
temperature and the pH was neutralized by the addition of sodium
carbonate. The neutralized contents of the flask were filtered, and
the water and dioxane were removed by vacuum distillation in a
suitable flask. While still molten, the stripped contents of the
flask were transferred to a suitable shallow open container and
allowed to cool to room temperature and harden. The solidified
resin was then broken into smaller pieces, which were transferred
to a suitable closed container for storage.
3TABLE 1 Physical Data of the Polymers of Synthesis Examples A and
B Example A Example B Mn (d) 3100 2840 Mw (d) 6045 3550 PDI (e)
1.95 1.25 Tg onset (.degree. C.) (f) 28.3 39.9 Tg midpoint
(.degree. C.) (f) 45.4 54.8 Tg endpoint (.degree. C.) (f) 62.3 69.6
Melt Viscosity 572 112 at 180.degree. C. (poise) (g) Acid
Equivalent 896 925 Weight (h) Percent Weight Solids 99.8 99.9 (i)
(d) The molecular weight data was obtained by means of gel
permeation chromatography using polystyrene standards. The
abbreviations are summarized as follows: number average molecular
weight (Mn); and weight average molecular weight (Mw). (e)
Polydispersity index (PDI) = (Mw/Mn). (f) Glass transition
temperature (Tg) onset, midpoint and endpoint values were
determined by means of differential scanning calorimetry (DSC). The
polymer samples underwent a stress release cycle followed by
heating at a rate of 10.degree. C./minute. (g) Melt viscosity at
180.degree. C. was determined using a Brookfield CAP 2000 High
Temperature Viscometer. (h) Acid equivalent weight was determined
by titration with potassium hydroxide, and is shown in units of
grams of resin / equivalent of acid. (i) Percent weight solids,
based on total weight was determined from 0.2 gram samples at
110.degree. C. / 1 hour.
Powder Coating Composition Examples 1 and 2
[0134] Powder coating Example 2 is representative of a
thermosetting coating composition according to the present
invention, while powder coating Example 1 is a comparative
thermosetting coating composition example. The powder coating
compositions were prepared from the ingredients enumerated in Table
2.
4TABLE 2 Powder Coating Compositions Ingredient Example 1 Example 2
Polymer of 9 0 Example A Polymer of 0 9 Example B
triglycidylisocyanurate 1 1 crosslinker (j) Flow Control Agent (k)
0.3 0.3 Benzoin 0.1 0.1 (j) triglycidylisocyanurate (TGIC)
crosslinker, commercially available from ACETO Agricultural
Chemical Corporation. (k) TROY 570 flow control agent, commercially
available from Troy Corporation.
[0135] The ingredients listed in Table 2 were melt mixed by hand
using a spatula on a hot plate at a temperature of 175.degree. C.
(347.degree. F.). The melt-mixed compositions were then coarsely
ground by hand using a mortar and pestle. The course particulate
thermosetting coating compositions of Examples 1 and 2 were found
to have 175.degree. C. (347.degree. F.) melt viscosities of 36
poise and 23 poise respectively. The melt viscosities were
determined using a temperature controlled cone and plate viscometer
manufactured by Research Equipment (London) Ltd. These results show
that a thermosetting coating composition according to the present
invention, i.e., Example 2, has a lower melt viscosity than that of
a comparative thermosetting coating composition, i.e., Example
1.
[0136] The present invention has been described with reference to
specific details of particular embodiments thereof. It is not
intended that such details be regarded as limitations upon the
scope of the invention except insofar as and to the extent that
they are included in the accompanying claims.
* * * * *