U.S. patent application number 13/323926 was filed with the patent office on 2013-06-13 for resin based post rinse for improved throwpower of electrodepositable coating compositions on pretreated metal substrates.
This patent application is currently assigned to PPG Industries Ohio, Inc.. The applicant listed for this patent is Richard F. Karabin, Michael J. Pawlik, Steven D. Perrine, Nathan J. Silvernail. Invention is credited to Richard F. Karabin, Michael J. Pawlik, Steven D. Perrine, Nathan J. Silvernail.
Application Number | 20130146460 13/323926 |
Document ID | / |
Family ID | 47040835 |
Filed Date | 2013-06-13 |
United States Patent
Application |
20130146460 |
Kind Code |
A1 |
Silvernail; Nathan J. ; et
al. |
June 13, 2013 |
RESIN BASED POST RINSE FOR IMPROVED THROWPOWER OF
ELECTRODEPOSITABLE COATING COMPOSITIONS ON PRETREATED METAL
SUBSTRATES
Abstract
Disclosed are methods for treating metal substrates, including
ferrous substrates, such as cold rolled steel and electrogalvanized
steel. The methods include (a) contacting the substrate with a
pretreatment composition including a group IIIB or IVB metal and an
electropositive metal, (b) contacting the substrate with a post
rinse composition and (c) electrophoretically depositing an
electrodepositable coating composition to the substrate, wherein
the post rinse composition improves the throwpower of the
subsequently applied electrodepositable coating composition. The
present invention also relates to coated substrates produced
thereby.
Inventors: |
Silvernail; Nathan J.;
(Allison Park, PA) ; Perrine; Steven D.; (Allison
Park, PA) ; Pawlik; Michael J.; (Glenshaw, PA)
; Karabin; Richard F.; (Ruffs Dale, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Silvernail; Nathan J.
Perrine; Steven D.
Pawlik; Michael J.
Karabin; Richard F. |
Allison Park
Allison Park
Glenshaw
Ruffs Dale |
PA
PA
PA
PA |
US
US
US
US |
|
|
Assignee: |
PPG Industries Ohio, Inc.
Cleveland
OH
|
Family ID: |
47040835 |
Appl. No.: |
13/323926 |
Filed: |
December 13, 2011 |
Current U.S.
Class: |
204/486 |
Current CPC
Class: |
C25D 13/04 20130101;
C25D 13/20 20130101; C23C 28/00 20130101 |
Class at
Publication: |
204/486 |
International
Class: |
C25D 13/20 20060101
C25D013/20 |
Goverment Interests
[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with Government support under
Contract No. W15QKN-07-C-0048 awarded by the ARDEC. The United
States Government may have certain rights in this invention.
Claims
1. A method for coating a substrate comprising: (a) contacting the
substrate with a pretreatment solution comprising a group IIIB
metal and/or a group IVB metal and an electropositive metal; (b)
contacting the substrate with an anionic resin-based post rinse
composition comprising an anionic resin; and (c)
electrophoretically depositing a cationic electrodepositable
coating composition onto the substrate.
2. The method of claim 1, wherein said cationic resin comprises a
phosphitized epoxy resin.
3. The method of claim 1, wherein step (a) occurs before step (b)
and wherein step (b) occurs before step (c).
4. The method of claim 1, wherein said group IIIB metal and/or a
group IVB metal comprises zirconium.
5. The method of claim 1, wherein the throwpower of the cationic
electrodepositable coating composition is increased by at least 6%
compared to the throwpower of said cationic electrodepositable
coating composition applied to the substrate without step (b).
6. The method of claim 1, wherein said group IIIB metal and/or
group IVB metal comprises a group IIIB metal compound and/or a
group IVB metal compound.
7. The method of claim 6, wherein said group IVB metal compound
comprises a zirconium compound
8. The method of claim 1, wherein step (b) comprises: immersing the
substrate in a bath comprising the anionic resin-based post rinse
composition; removing the substrate from said bath; and rinsing the
substrate with water.
9. The method of claim 1, wherein step (b) comprises: spraying the
substrate with the anionic resin-based post rinse composition; and
drying the anionic resin-based post rinse composition onto the
substrate prior to step (c).
10. A substrate coated according to the method of claim 1.
11. A method for coating a substrate comprising: (a) contacting the
substrate with a pretreatment solution comprising a group IIIB
and/or a group IVB metal and an electropositive metal; (b)
contacting the substrate with an cationic resin-based post rinse
composition comprising a cationic resin; and (c)
electrophoretically depositing an anionic electrodepositable
coating composition onto the substrate.
12. The method of claim 11, wherein said cationic resin comprises a
trisaminoepoxy resin.
13. The method of claim 11, wherein step (a) occurs before step (b)
and wherein step (b) occurs before step (c).
14. The method of claim 11, wherein said group IVB metal comprises
zirconium.
15. The method of claim 11, wherein said group IIIB metal and/or
group IVB metal comprises a group IIIB metal compound and/or a
group IVB metal compound.
16. The method of claim 15, wherein said group IVB metal compound
comprises a zirconium compound
17. The method of claim 11, wherein step (b) comprises: immersing
the substrate in a bath comprising the cationic resin-based post
rinse composition; removing the substrate from said bath; and
rinsing the substrate with water.
18. The method of claim 11, wherein the throwpower of the anionic
electrodepositable coating composition is increased by at least 6%
compared to the throwpower of said anionic electrodepositable
coating composition applied to the substrate without step (b).
19. The method of claim 11, wherein said cationic resin comprises
an amine adduct of an epoxy resin.
20. A coated substrate coated according to the method of claim 11.
Description
FIELD OF THE INVENTION
[0003] The present invention relates to methods for coating a metal
substrate, including ferrous substrates, such as cold rolled steel
and electrogalvanized steel. The present invention also relates to
coated metal substrates.
BACKGROUND INFORMATION
[0004] The use of protective coatings on metal substrates for
improved corrosion resistance and paint adhesion is common
Conventional techniques for coating such substrates include
techniques that involve pretreating the metal substrate with a
phosphate conversion coating and chrome-containing rinses. The use
of such phosphate and/or chromate-containing compositions, however,
imparts environmental and health concerns. As a result,
chromate-free and/or phosphate-free pretreatment compositions have
been developed. Such compositions are generally based on chemical
mixtures that in some way react with the substrate surface and bind
to it to form a protective layer. For example, pretreatment
compositions based on a group IIIB or IVB metal compound have
recently become more prevalent.
[0005] After pretreating the substrates with pretreatment
compositions, it is also common to subsequently contact the
pretreated substrates with an electrodepositable coating
composition. Both cationic and anionic electrodepositions are used
commercially, with cationic being more prevalent in applications
desiring a high level of corrosion protection. As with all
electrodepositable coating compositions, it is highly desirable to
increase their respective throwpowers to allow the
electrodepositable coating compositions to be deposited in recessed
areas of the pretreated substrates without otherwise adversely
affecting the performance characteristics of the coated
substrates.
SUMMARY OF THE INVENTION
[0006] In certain respects, the present invention is directed to a
method for treating a metal substrate comprising: (a) contacting
the substrate with a pretreatment solution comprising a group IIIB
and/or IVB metal and an electropositive metal; (b) contacting the
substrate with an anionic resin-based post rinse composition; and
(c) electrophoretically depositing a cationic electrodepositable
coating composition onto the substrate.
[0007] In still other respects, the present invention is directed
to methods for treating a metal substrate comprising contacting the
substrate (a) contacting the substrate with a pretreatment solution
comprising a group IIIB and/or IVB metal and an electropositive
metal; (b) contacting the substrate with an cationic resin-based
post rinse composition; and (c) electrophoretically depositing an
anionic electrodepositable coating composition onto the
substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0008] For purposes of the following detailed description, it is to
be understood that the invention may assume various alternative
variations and step sequences, except where expressly specified to
the contrary. Moreover, other than in any operating examples, or
where otherwise indicated, all numbers expressing, for example,
quantities of ingredients used in the specification and claims are
to be understood as being modified in all instances by the term
"about". Accordingly, unless indicated to the contrary, the
numerical parameters set forth in the following specification and
attached claims are approximations that may vary depending upon the
desired properties to be obtained by the present invention. At the
very least, and not as an attempt to limit the application of the
doctrine of equivalents to the scope of the claims, each numerical
parameter should at least be construed in light of the number of
reported significant digits and by applying ordinary rounding
techniques.
[0009] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical value, however,
inherently contains certain errors necessarily resulting from the
standard variation found in their respective testing
measurements.
[0010] Also, it should be understood that any numerical range
recited herein is intended to include all sub-ranges subsumed
therein. For example, a range of "1 to 10" is intended to include
all sub-ranges between (and including) the recited minimum value of
1 and the recited maximum value of 10, that is, having a minimum
value equal to or greater than 1 and a maximum value of equal to or
less than 10.
[0011] In this application, the use of the singular includes the
plural and plural encompasses singular, unless specifically stated
otherwise. In addition, in this application, the use of "or" means
"and/or" unless specifically stated otherwise, even though "and/or"
may be explicitly used in certain instances.
[0012] As previously mentioned, certain embodiments of the present
invention are directed to methods for treating a metal substrate.
Suitable metal substrates for use in the present invention include
those that are often used in the assembly of automotive bodies,
automotive parts, and other articles, such as small metal parts,
including fasteners, i.e., nuts, bolts, screws, pins, nails, clips,
buttons, and the like. Specific examples of suitable metal
substrates include, but are not limited to, cold rolled steel, hot
rolled steel, steel coated with zinc metal, zinc compounds, or zinc
alloys, such as electrogalvanized steel, hot-dipped galvanized
steel, galvanealed steel, and steel plated with zinc alloy. Also,
aluminum alloys, aluminum plated steel and aluminum alloy plated
steel substrates may be used. Other suitable non-ferrous metals
include copper and magnesium, as well as alloys of these materials.
Moreover, the bare metal substrate being coating by the methods of
the present invention may be a cut edge of a substrate that is
otherwise treated and/or coated over the rest of its surface. The
metal substrate coated in accordance with the methods of the
present invention may be in the form of, for example, a sheet of
metal or a fabricated part.
[0013] The substrate to be treated in accordance with the methods
of the present invention may first be cleaned to remove grease,
dirt, or other extraneous matter. This is often done by employing
mild or strong alkaline cleaners, such as are commercially
available and conventionally used in metal pretreatment processes.
Examples of alkaline cleaners suitable for use in the present
invention include Chemkleen 163, Chemkleen 177, and Chemkleen
490MX, each of which are commercially available from PPG
Industries, Inc. Such cleaners are often followed and/or preceded
by a water rinse.
[0014] As previously indicated, certain embodiments of the present
invention are directed to methods treating a metal substrate that
comprise contacting the metal substrate with a pretreatment
composition comprising a group IIIB and/or IVB metal. As used
herein, the term "pretreatment composition" refers to a composition
that upon contact with the substrate reacts with and chemically
alters the substrate surface and binds to it to form a protective
layer.
[0015] Often, the pretreatment composition comprises a carrier,
often an aqueous medium, so that the composition is in the form of
a solution or dispersion of a group IIIB or IVB metal compound in
the carrier. In these embodiments, the solution or dispersion may
be brought into contact with the substrate by any of a variety of
known techniques, such as dipping or immersion, spraying,
intermittent spraying, dipping followed by spraying, spraying
followed by dipping, brushing, or roll-coating. In certain
embodiments, the solution or dispersion when applied to the metal
substrate is at a temperature ranging from 60 to 150.degree. F. (15
to 65.degree. C.). The contact time is often from 10 seconds to
five minutes, such as 30 seconds to 2 minutes.
[0016] As used herein, the term "group IIIB and/or IVB metal"
refers to an element that is in group IIIB or group IVB of the CAS
Periodic Table of the Elements as is shown, for example, in the
Handbook of Chemistry and Physics, 63.sup.rd edition (1983). Where
applicable, the metal themselves may be used. In certain
embodiments, a group IIIB and/or IVB metal compound is used. As
used herein, the term "group IIIB and/or IVB metal compound" refers
to compounds that include at least one element that is in group
IIIB or group IVB of the CAS Periodic Table of the Elements.
[0017] In certain embodiments, the group IIIB and/or IVB metal
compound used in the pretreatment composition is a compound of
zirconium, titanium, hafnium, yttrium, cerium, or a mixture
thereof. Suitable compounds of zirconium include, but are not
limited to, hexafluorozirconic acid, alkali metal and ammonium
salts thereof, ammonium zirconium carbonate, zirconyl nitrate,
zirconium carboxylates and zirconium hydroxy carboxylates, such as
hydrofluorozirconic acid, zirconium acetate, zirconium oxalate,
ammonium zirconium glycolate, ammonium zirconium lactate, ammonium
zirconium citrate, and mixtures thereof. Suitable compounds of
titanium include, but are not limited to, fluorotitanic acid and
its salts. A suitable compound of hafnium includes, but is not
limited to, hafnium nitrate. A suitable compound of yttrium
includes, but is not limited to, yttrium nitrate. A suitable
compound of cerium includes, but is not limited to, cerous
nitrate.
[0018] In certain embodiments, the group IIIB and/or IVB metal
compound is present in the pretreatment composition in an amount of
at least 10 ppm metal, such as at least 100 ppm metal, or, in some
cases, at least 150 ppm metal. In certain embodiments, the group
IIIB and/or IVB metal compound is present in the pretreatment
composition in an amount of no more than 5000 ppm metal, such as no
more than 300 ppm metal, or, in some cases, no more than 250 ppm
metal. The amount of group IIIB and/or IVB metal in the
pretreatment composition can range between any combination of the
recited values inclusive of the recited values.
[0019] In certain embodiments, the pretreatment composition also
comprises an electropositive metal. As used herein, the term
"electropositive metal" refers to metals that are more
electropositive than the metal substrate. This means that, for
purposes of the present invention, the term "electropositive metal"
encompasses metals that are less easily oxidized than the metal of
the metal substrate. As will be appreciated by those skilled in the
art, the tendency of a metal to be oxidized is called the oxidation
potential, is expressed in volts, and is measured relative to a
standard hydrogen electrode, which is arbitrarily assigned an
oxidation potential of zero. The oxidation potential for several
elements is set forth in the table below. An element is less easily
oxidized than another element if it has a voltage value, E*, in the
following table, that is greater than the element to which it is
being compared.
TABLE-US-00001 Element Half-cell reaction Voltage, E* Potassium
K.sup.+ + e .fwdarw. K -2.93 Calcium Ca.sup.2+ + 2e .fwdarw. Ca
-2.87 Sodium Na.sup.+ + e .fwdarw. Na -2.71 Magnesium Mg.sup.2+ +
2e .fwdarw. Mg -2.37 Aluminum Al.sup.3+ + 3e .fwdarw. Al -1.66 Zinc
Zn.sup.2+ + 2e .fwdarw. Zn -0.76 Iron Fe.sup.2+ + 2e .fwdarw. Fe
-0.44 Nickel Ni.sup.2+ + 2e .fwdarw. Ni -0.25 Tin Sn.sup.2+ + 2e
.fwdarw. Sn -0.14 Lead Pb.sup.2+ + 2e .fwdarw. Pb -0.13 Hydrogen
2H.sup.+ + 2e .fwdarw. H.sub.2 -0.00 Copper Cu.sup.2+ + 2e .fwdarw.
Cu 0.34 Mercury Hg.sub.2.sup.2+ + 2e .fwdarw. 2Hg 0.79 Silver
Ag.sup.+ + e .fwdarw. Ag 0.80 Gold Au.sup.3+ + 3e .fwdarw. Au
1.50
[0020] Thus, as will be apparent, when the metal substrate
comprises one of the materials listed earlier, such as cold rolled
steel, hot rolled steel, steel coated with zinc metal, zinc
compounds, or zinc alloys, hot-dipped galvanized steel, galvanealed
steel, steel plated with zinc alloy, aluminum alloys, aluminum
plated steel, aluminum alloy plated steel, magnesium and magnesium
alloys, suitable electropositive metals for deposition thereon in
accordance with the present invention include, for example, nickel,
copper, silver, and gold, as well mixtures thereof.
[0021] In certain embodiments, the source of electropositive metal
in the pretreatment composition is a water soluble metal salt. In
certain embodiments of the present invention, the water soluble
metal salt is a water soluble copper compound. Specific examples of
water soluble copper compounds, which are suitable for use in the
present invention include, but are not limited to, copper cyanide,
copper potassium cyanide, copper sulfate, copper nitrate, copper
pyrophosphate, copper thiocyanate, disodium copper
ethylenediaminetetraacetate tetrahydrate, copper bromide, copper
oxide, copper hydroxide, copper chloride, copper fluoride, copper
gluconate, copper citrate, copper lauroyl sarcosinate, copper
formate, copper acetate, copper propionate, copper butyrate, copper
lactate, copper oxalate, copper phytate, copper tartarate, copper
malate, copper succinate, copper malonate, copper maleate, copper
benzoate, copper salicylate, copper aspartate, copper glutamate,
copper fumarate, copper glycerophosphate, sodium copper
chlorophyllin, copper fluorosilicate, copper fluoroborate and
copper iodate, as well as copper salts of carboxylic acids in the
homologous series formic acid to decanoic acid, copper salts of
polybasic acids in the series oxalic acid to suberic acid, and
copper salts of hydroxycarboxylic acids, including glycolic,
lactic, tartaric, malic and citric acids.
[0022] When copper ions supplied from such a water-soluble copper
compound are precipitated as an impurity in the form of copper
sulfate, copper oxide, etc., it may be preferable to add a
complexing agent that suppresses the precipitation of copper ions,
thus stabilizing them as a copper complex in the solution.
[0023] In certain embodiments, the copper compound is added as a
copper complex salt such as K.sub.3Cu(CN).sub.4 or Cu-EDTA, which
can be present stably in the composition on its own, but it is also
possible to form a copper complex that can be present stably in the
composition by combining a complexing agent with a compound that is
difficultly soluble on its own. Examples thereof include a copper
cyanide complex formed by a combination of CuCN and KCN or a
combination of CuSCN and KSCN or KCN, and a Cu-EDTA complex formed
by a combination of CuSO.sub.4 and EDTA.2Na.
[0024] With regard to the complexing agent, a compound that can
form a complex with copper ions can be used; examples thereof
include inorganic compounds, such as cyanide compounds and
thiocyanate compounds, and polycarboxylic acids, and specific
examples thereof include ethylenediaminetetraacetic acid, salts of
ethylenediaminetetraacetic acid, such as dihydrogen disodium
ethylenediaminetetraacetate dihydrate, aminocarboxylic acids, such
as nitrilotriacetic acid and iminodiacetic acid, oxycarboxylic
acids, such as citric acid and tartaric acid, succinic acid, oxalic
acid, ethylenediaminetetramethylenephosphonic acid, and
glycine.
[0025] In certain embodiments, the electropositive metal, such as
copper, is included in the pretreatment compositions in an amount
of at least 1 ppm, such as at least 5 ppm, or in some cases, at
least 10 ppm of total metal (measured as elemental metal). In
certain embodiments, the electropositive metal is included in such
pretreatment compositions in an amount of no more than 500 ppm,
such as no more than 100 ppm, or in some cases, no more than 50 ppm
of total metal (measured as elemental metal). The amount of
electropositive metal in the pretreatment composition can range
between any combination of the recited values inclusive of the
recited values.
[0026] In some embodiments, the pretreatment composition may be a
silane or a non-crystalline phosphate, such as iron phosphate,
containing pretreatment composition. Suitable silane containing
pretreatment compositions include, but are not limited to, certain
commercially available products, such as Silquest A-1100 Silane,
which is described in the Examples herein and which is commercially
available from Momentive Performance Materials. Suitable
non-crystalline phosphate containing pretreatment composition
include pretreatment composition that comprise, iron phosphate,
manganese phosphate, calcium phosphate, magnesium phosphate, cobalt
phosphate, or an organophosphate and/or organophosphonate, such as
is disclosed in U.S. Pat. Nos. 5,294,265 at col. 1, line 53 to col.
3, line 12 and 5,306,526 at col. 1, line 46 to col. 3, line 8, the
cited portions of which being incorporated herein by reference.
Suitable non-crystalline phosphate containing pretreatment
compositions are commercially available, such as Chemfos.RTM. 158
and Chemfos.RTM. 51, which are iron phosphate pretreatment
compositions commercially available from PPG Industries, Inc.
[0027] In certain embodiments, the pretreatment composition
comprises a resinous binder. Suitable resins include reaction
products of one or more alkanolamines and an epoxy-functional
material containing at least two epoxy groups, such as those
disclosed in U.S. Pat. No. 5,653,823. In some cases, such resins
contain beta hydroxy ester, imide, or sulfide functionality,
incorporated by using dimethylolpropionic acid, phthalimide, or
mercaptoglycerine as an additional reactant in the preparation of
the resin. Alternatively, the reaction product is that of the
diglycidyl ether of Bisphenol A (commercially available from Shell
Chemical Company as EPON 880), dimethylol propionic acid, and
diethanolamine in a 0.6 to 5.0:0.05 to 5.5:1 mole ratio. Other
suitable resinous binders include water soluble and water
dispersible polyacrylic acids as disclosed in U.S. Pat. Nos.
3,912,548 and 5,328,525; phenol formaldehyde resins as described in
U.S. Pat. Nos. 5,662,746; water soluble polyamides such as those
disclosed in WO 95/33869; copolymers of maleic or acrylic acid with
allyl ether as described in Canadian patent application 2,087,352;
and water soluble and dispersible resins including epoxy resins,
aminoplasts, phenol-formaldehyde resins, tannins, and polyvinyl
phenols as discussed in U.S. Pat. No. 5,449,415.
[0028] In these embodiments of the present invention, the resinous
binder is present in the pretreatment composition in an amount of
0.005 percent to 30 percent by weight, such as 0.5 to 3 percent by
weight, based on the total weight of the ingredients in the
composition.
[0029] In other embodiments, however, the pretreatment composition
is substantially free or, in some cases, completely free of any
resinous binder. As used herein, the term "substantially free",
when used with reference to the absence of resinous binder in the
pretreatment composition, means that any resinous binder is present
in the pretreatment composition in an amount of less than 0.005
percent by weight. As used herein, the term "completely free" means
that there is no resinous binder in the pretreatment composition at
all.
[0030] The pretreatment composition may optionally contain other
materials, such as nonionic surfactants and auxiliaries
conventionally used in the art of pretreatment. In an aqueous
medium, water dispersible organic solvents, for example, alcohols
with up to about 8 carbon atoms, such as methanol, isopropanol, and
the like, may be present; or glycol ethers such as the monoalkyl
ethers of ethylene glycol, diethylene glycol, or propylene glycol,
and the like. When present, water dispersible organic solvents are
typically used in amounts up to about ten percent by volume, based
on the total volume of aqueous medium.
[0031] Other optional materials include surfactants that function
as defoamers or substrate wetting agents, such as those materials
and amounts described earlier with respect to the plating
solution.
[0032] In certain embodiments, the pretreatment composition also
comprises a reaction accelerator, such as nitrite ions, nitro-group
containing compounds, hydroxylamine sulfate, persulfate ions,
sulfite ions, hyposulfite ions, peroxides, iron (III) ions, citric
acid iron compounds, bromate ions, perchlorinate ions, chlorate
ions, chlorite ions as well as ascorbic acid, citric acid, tartaric
acid, malonic acid, succinic acid and salts thereof. Specific
examples of suitable materials and their amounts are described in
United States Patent Application Publication No. 2004/0163736 A1at
[0032] to [0041], the cited portion of which being incorporated
herein by reference.
[0033] In certain embodiments, the pretreatment composition also
comprises a filler, such as a siliceous filler. Non-limiting
examples of suitable fillers include silica, mica, montmorillonite,
kaolinite, asbestos, talc, diatomaceous earth, vermiculite, natural
and synthetic zeolites, cement, calcium silicate, aluminum
silicate, sodium aluminum silicate, aluminum polysilicate, alumina
silica gels, and glass particles. In addition to the siliceous
fillers other finely divided particulate substantially
water-insoluble fillers may also be employed. Examples of such
optional fillers include carbon black, charcoal, graphite, titanium
oxide, iron oxide, copper oxide, zinc oxide, antimony oxide,
zirconia, magnesia, alumina, molybdenum disulfide, zinc sulfide,
barium sulfate, strontium sulfate, calcium carbonate, and magnesium
carbonate.
[0034] As indicated, in certain embodiments, the pretreatment
composition is substantially or, in some cases, completely free of
chromate and/or heavy metal phosphate. As used herein, the term
"substantially free" when used in reference to the absence of
chromate and/or heavy metal phosphate, such as zinc phosphate, in
the pretreatment composition means that these substances are not
present in the composition to such an extent that they cause a
burden on the environment. That is, they are not substantially used
and the formation of sludge, such as zinc phosphate, formed in the
case of using a treating agent based on zinc phosphate, is
eliminated.
[0035] Moreover, in certain embodiments, the pretreatment
composition is substantially free, or, in some cases, completely
free of any organic materials. As used herein, the term
"substantially free", when used with reference to the absence of
organic materials in the composition, means that any organic
materials are present in the composition, if at all, as an
incidental impurity. In other words, the presence of any organic
material does not affect the properties of the composition. As used
herein, the term "completely free" means that there is no organic
material in the composition at all.
[0036] In certain embodiments, the film coverage of the residue of
the pretreatment coating composition generally ranges from 1 to
1000 milligrams per square meter (mg/m.sup.2), such as 10 to 400
mg/m.sup.2. The thickness of the pretreatment coating can vary, but
it is generally very thin, often having a thickness of less than 1
micrometer, in some cases it is from 1 to 500 nanometers, and, in
yet other cases, it is 10 to 300 nanometers.
[0037] Following contact with the pretreatment solution, the
substrate may be rinsed with water and dried.
[0038] Next, after the pretreatment step, the substrate is
contacted with a resin-based post-rinse solution. It has been
surprisingly discovered that the use of a post-rinse, in
conjunction with the use of an electropositive metal such as copper
in the pretreatment solution, increases the throwpower of
subsequently applied electrodeposition coatings as compared with
the application of the electrodeposition coatings applied to the
substrate in the absence of the post-rinse.
[0039] As defined herein, the ability for an electrodepositable
coating composition to coat interior recesses of a substrate, at a
given temperature and voltage, is called "throwpower". A higher
"throwpower" means that the electrodepositable coating composition
is further "thrown" into the recesses of a recessed substrate.
Higher throwpower therefore is synonymous with greater surface
coverage on hard to reach recessed areas of a substrate.
[0040] Moreover, the use of a post-rinse, as described in the
previous paragraphs in conjunction with the use of an
electropositive metal such as copper in the pretreatment solution,
does not adversely affect the corrosion resistance of the formed
panels.
[0041] In the context of the present invention, throwpower was
evaluated by placing two 4''.times.12'' pretreated and post-rinsed
panels on either side of a 4 mm shim and clamping them together.
The shimmed panels were then immersed 27 cm into the electrocoat
bath (either a cationic or anionic electrodepositable coating
composition bath) and coated to a predetermined thickness.
Throwpower readings were recorded as a percentage by measuring the
distance (in cm) from the bottom of the back side of the panels to
the point where no coating was deposited and dividing that number
by 27 cm.
[0042] In certain embodiments utilizing a resin based post rinse,
the throwpower for the immersion applied electrodepositable coating
composition increased at least 6% as compared to the throwpower of
the same electrodepositable coating composition applied to the
substrate under the same coating conditions in the absence of the
post rinse step.
[0043] The type of resin-based post rinse utilized is dependent
upon the type of electrodepositable coating composition that is
subsequently applied to the treated substrate. For pretreated
substrates to be coated with a cationically applied
electrodeposition coating, the resin-based post-rinse composition
is anionic in nature (i.e.
[0044] an "anionic resin-based post rinse composition").
Conversely, for pretreated substrates to be coated with an
anionically applied electrodeposition coating, the resin-based
post-rinse composition is cationic in nature (i.e. a "cationic
resin-based post rinse composition").
[0045] In certain embodiments, the resin-based post rinse solution
is formed by dissolving a respective cationic or an anionic resin
in water. In certain of these embodiments, the resin solids of the
resin-based post rinse solution is from 0.1 to 10%.
[0046] In certain embodiments, the pH of the anionic resin-based
post rinse solution is from 1 to 10, such as from 1 to 7.
[0047] In certain embodiments, the pH of the cationic resin-based
post rinse solution is from 6 to14.
[0048] In certain embodiments, the cationic or anionic resin-based
post rinse composition is applied to the pretreated panel by
immersing the pretreated panel into the composition for a
predetermined period of time, such as, for example, 1 minute,
removing the panel, rinsing with deionized water, and drying the
panel prior to application of an anionic electrodepositable coating
composition.
[0049] In certain other embodiments, the cationic resin-based post
rinse composition is applied to the pretreated panel via a
dry-in-place application. In these embodiments, the composition is
sprayed onto the panel and dried without a rinsing step prior to
application of a cationic electrodepositable coating
composition.
[0050] In another exemplary embodiment, the anionic resin-based
post rinse composition comprises a phosphitized epoxy resin
composition. Exemplary water-based phosphitized epoxy resins that
may be utilized include Nupal.RTM. 435 F and Nupal 510.RTM. R, both
commercially available from PPG Industries, Inc.
[0051] In certain of these embodiments, the water-based
phosphitized epoxy composition has a pH adjusted between 3 and 7.
In certain other embodiments, the resin content of the water-based
phosphitized epoxy composition is from about 0.1 to 10% resin
solids.
[0052] In one exemplary embodiment, the cationic resin-based post
rinse composition comprises an epoxy-functional material that is
reacted with either an alkanolamine, or a mixture of alkanolamines.
In certain embodiments, primary or secondary alkanolamines, or
mixtures thereof are used. Tertiary alkanolamines or mixtures
thereof are also suitable, but the reaction conditions differ when
these materials are used. Consequently, tertiary alkanolamines are
not typically mixed with primary or secondary alkanolamines.
[0053] In certain embodiments, the alkanolamines have alkanol
groups containing fewer than about 20 carbon atoms, such as fewer
than about 10 carbon atoms. Examples of suitable alkanolamines
include methyl ethanolamine, ethylethanolamine, diethanolamine,
methylisopropanolamine, ethylisopropanolamine, diisopropanolamine,
monoethanolamine, and diisopropanolamine and the like.
[0054] In certain embodiments, the tertiary alkanolamines that may
be used contain two methyl groups. An example of suitable material
is dimethylethanolamine.
[0055] In certain embodiments, the epoxy-functional material and
the alkanolamines are reacted in a equivalent ratio of from about
5:1 to about 1:4, such as from about 2:1 to about 1:2.
[0056] The epoxy-functional material and the alkanolamines can be
co-reacted by any of the methods well known to those skilled in the
art of polymer synthesis, including solution, emulsion, suspension
or dispersion polymerization techniques. In the simplest cases, the
alkanolamine is added to the epoxy-functional material at a
controlled rate, and they are simply heated together, usually with
some diluent, at a controlled temperature. In certain embodiments,
the reaction is conducted under a nitrogen blanket or another
procedure known to those skilled in the art for reducing the
presence of oxygen during the reaction.
[0057] The diluent serves to reduce the viscosity of the reaction
mixture. Exemplary diluents are water-dispersible organic solvents.
Examples include alcohols with up to about eight carbon atoms, such
as methanol or isopropanol, and the like; or glycol ethers such as
the monoalkyl ethers of ethylene glycol, diethylene glycol, or
propylene glycol, and the like. Water is also a suitable
diluent.
[0058] Other suitable diluents include nonreactive oligomeric or
polymeric materials with a viscosity ranging from about 20
centipoise to about 1,000 centipoise, as measured with a Brookfield
viscometer at about 72.degree. F.; and a glass transition
temperature lower than about 35.degree. C., as measured by any of
the common thermal analytical methods well known by those skilled
in the art. Examples include plasticizers such as tributyl
phosphate, dibutyl maleate, butyl benzyl phthalate, and the like
known to those skilled in the art; and silane compounds such as
vinyl trimethoxy silane, gamma-methacryloxypropyl trimethoxy
silane, and the like known to those skilled in the art. Mixtures of
any of these alternative diluents, water, or organic solvents are
suitable as well.
[0059] If a tertiary alkanolamine is used, a quaternary ammonium
compound is formed. In this case, it is the usual practice to add
all the raw materials to the reaction vessel at once and heat them
together, usually with some diluent, at a controlled temperature.
Typically, some acid is present, which serves to ensure that a
quaternary ammonium salt is formed instead of a quaternary ammonium
oxide. Examples of suitable acids are carboxylic acids such as
lactic acid, citric acid, adipic acid, and the like. Acetic acid is
preferred. The quaternary ammonium salts are preferred because
these are more easily dispersed in water, and because they produce
an aqueous dispersion with a pH in or near the desired range. If,
instead, a quaternary ammonium oxide is prepared, it can later be
converted to a quaternary ammonium salt with the addition of
acid.
[0060] The molecular weight of epoxy-functional material that is
reacted with either an alkanolamine is limited only by its
dispersibility in the other materials comprising the non-chrome
post-rinse composition. The dispersibility is determined, in part,
by the nature of the epoxy-functional material, the nature of the
alkanolamine, and the equivalent ratio in which the two are
reacted. Typically, the epoxy-functional material that is reacted
with either an alkanolamine has a number-average molecular weight
of up to about 1500, as measured by gel permeation chromatography
using polystyrene as a standard.
[0061] Optionally, the epoxy-functional material that is reacted
with either an alkanolamine can be neutralized to promote good
dispersion in an aqueous medium. Typically, this is accomplished by
adding some acid. Examples of suitable neutralizing acids include
lactic acid, phosphoric, acetic acid, and the like known to those
skilled in the art.
[0062] The epoxy-functional material that is reacted with either an
alkanolamine is present in the cationic post-rinse composition at a
level of at least about 100 ppm, such as from about 400 ppm to
about 1400 ppm, the concentration based on the solid weight of the
epoxy-functional material that is reacted with either an
alkanolamine on the total weight of the cationic post-rinse
composition.
[0063] In a related embodiment, the cationic resin-based post rinse
comprises an amine adduct of Epon.RTM. 828 that may be formed as
the reaction product of diethanolamine and Epon.RTM. 828, and in
certain embodiments may be made in accordance with the method
disclosed in Example 1 of U.S. Pat. No. 5,653,823 (without the
subsequent preparation with 5% fluorozirconic acid).
[0064] In one exemplary embodiment, the cationic resin-based post
rinse composition comprises a trisaminoepoxy compound.
[0065] In certain embodiments of the methods of the present
invention, after the substrate is contacted with the pretreatment
composition and the resin-based post rinse, it is then contacted
with an electrodepositable coating composition. The
electrodepositable coating compositions are either cationic, when
the post-rinse is an anionic resin-based post rinse as described
above, or anionic, when the post-rinse is a cationic resin-based
post rinse. In either case, the electrodepositable coating
composition comprises a film-forming resin.
[0066] As used herein, the term "film-forming resin" refers to
resins that can form a self-supporting continuous film on at least
a horizontal surface of a substrate upon removal of any diluents or
carriers present in the composition or upon curing at ambient or
elevated temperature. Conventional film-forming resins that may be
used include, without limitation, those typically used in
automotive OEM coating compositions, automotive refinish coating
compositions, industrial coating compositions, architectural
coating compositions, coil coating compositions, and aerospace
coating compositions, among others.
[0067] In certain embodiments, the coating composition comprises a
thermosetting film-forming resin. As used herein, the term
"thermosetting" refers to resins that "set" irreversibly upon
curing or crosslinking, wherein the polymer chains of the polymeric
components are joined together by covalent bonds. This property is
usually associated with a cross-linking reaction of the composition
constituents often induced, for example, by heat or radiation.
Curing or crosslinking reactions also may be carried out under
ambient conditions. Once cured or crosslinked, a thermosetting
resin will not melt upon the application of heat and is insoluble
in solvents. In other embodiments, the coating composition
comprises a thermoplastic film-forming resin. As used herein, the
term "thermoplastic" refers to resins that comprise polymeric
components that are not joined by covalent bonds and thereby can
undergo liquid flow upon heating and are soluble in solvents.
[0068] As previously indicated, in certain embodiments, the
substrate is contacted with a coating composition comprising a
film-forming resin by an electrocoating step wherein an
electrodepositable composition is deposited onto the metal
substrate by electrodeposition. In the process of
electrodeposition, the metal substrate being treated, serving as an
electrode, and an electrically conductive counter electrode are
placed in contact with an ionic, electrodepositable composition.
Upon passage of an electric current between the electrode and
counter electrode while they are in contact with the
electrodepositable composition, an adherent film of the
electrodepositable composition will deposit in a substantially
continuous manner on the metal substrate.
[0069] Electrodeposition is usually carried out at a constant
voltage in the range of from 1 volt to several thousand volts,
typically between 50 and 500 volts. Current density is usually
between 1.0 ampere and 15 amperes per square foot (10.8 to 161.5
amperes per square meter) and tends to decrease quickly during the
electrodeposition process, indicating formation of a continuous
self-insulating film.
[0070] The electrodepositable composition utilized in certain
embodiments of the present invention often comprises a resinous
phase dispersed in an aqueous medium wherein the resinous phase
comprises: (a) an active hydrogen group-containing ionic
electrodepositable resin, and (b) a curing agent having functional
groups reactive with the active hydrogen groups of (a).
[0071] In certain embodiments, the electrodepositable compositions
utilized in certain embodiments of the present invention contain,
as a main film-forming polymer, an active hydrogen-containing
ionic, often cationic, electrodepositable resin. A wide variety of
electrodepositable film-forming resins are known and can be used in
the present invention so long as the polymers are "water
dispersible," i.e., adapted to be solubilized, dispersed or
emulsified in water. The water dispersible polymer is ionic in
nature, that is, the polymer will contain anionic functional groups
to impart a negative charge or, as is often preferred, cationic
functional groups to impart a positive charge.
[0072] Examples of film-forming resins suitable for use in anionic
electrodepositable compositions are base-solubilized, carboxylic
acid containing polymers, such as the reaction product or adduct of
a drying oil or semi-drying fatty acid ester with a dicarboxylic
acid or anhydride; and the reaction product of a fatty acid ester,
unsaturated acid or anhydride and any additional unsaturated
modifying materials which are further reacted with polyol. Also
suitable are the at least partially neutralized interpolymers of
hydroxy-alkyl esters of unsaturated carboxylic acids, unsaturated
carboxylic acid and at least one other ethylenically unsaturated
monomer. Still another suitable electrodepositable film-forming
resin comprises an alkyd-aminoplast vehicle, i.e., a vehicle
containing an alkyd resin and an amine-aldehyde resin. Yet another
anionic electrodepositable resin composition comprises mixed esters
of a resinous polyol, such as is described in U.S. Pat. No.
3,749,657 at col. 9, lines 1 to 75 and col. 10, lines 1 to 13, the
cited portion of which being incorporated herein by reference.
Other acid functional polymers can also be used, such as
phosphatized polyepoxide or phosphatized acrylic polymers as are
known to those skilled in the art.
[0073] As aforementioned, it is often desirable that the active
hydrogen-containing ionic electrodepositable resin (a) is cationic
and capable of deposition on a cathode. Examples of such cationic
film-forming resins include amine salt group-containing resins,
such as the acid-solubilized reaction products of polyepoxides and
primary or secondary amines, such as those described in U.S. Pat.
Nos. 3,663,389; 3,984,299; 3,947,338; and 3,947,339. Often, these
amine salt group-containing resins are used in combination with a
blocked isocyanate curing agent. The isocyanate can be fully
blocked, as described in U.S. Pat. No. 3,984,299, or the isocyanate
can be partially blocked and reacted with the resin backbone, such
as is described in U.S. Pat. No. 3,947,338. Also, one-component
compositions as described in U.S. Pat. No. 4,134,866 and DE-OS No.
2,707,405 can be used as the film-forming resin. Besides the
epoxy-amine reaction products, film-forming resins can also be
selected from cationic acrylic resins, such as those described in
U.S. Pat. Nos. 3,455,806 and 3,928,157.
[0074] Besides amine salt group-containing resins, quaternary
ammonium salt group-containing resins can also be employed, such as
those formed from reacting an organic polyepoxide with a tertiary
amine salt as described in U.S. Pat. Nos. 3,962,165; 3,975,346; and
4,001,101. Examples of other cationic resins are ternary sulfonium
salt group-containing resins and quaternary phosphonium salt-group
containing resins, such as those described in U.S. Pat. Nos.
3,793,278 and 3,984,922, respectively. Also, film-forming resins
which cure via transesterification, such as described in European
Application No. 12463 can be used. Further, cationic compositions
prepared from Mannich bases, such as described in U.S. Pat. No.
4,134,932, can be used.
[0075] In certain embodiments, the resins present in the
electrodepositable composition are positively charged resins which
contain primary and/or secondary amine groups, such as described in
U.S. Pat. Nos. 3,663,389; 3,947,339; and 4,116,900. In U.S. Pat.
No. 3,947,339, a polyketimine derivative of a polyamine, such as
diethylenetriamine or triethylenetetraamine, is reacted with a
polyepoxide. When the reaction product is neutralized with acid and
dispersed in water, free primary amine groups are generated. Also,
equivalent products are formed when polyepoxide is reacted with
excess polyamines, such as diethylenetriamine and
triethylenetetraamine, and the excess polyamine vacuum stripped
from the reaction mixture, as described in U.S. Pat. Nos. 3,663,389
and 4,116,900.
[0076] In certain embodiments, the active hydrogen-containing ionic
electrodepositable resin is present in the electrodepositable
composition in an amount of 1 to 60 percent by weight, such as 5 to
25 percent by weight, based on total weight of the
electrodeposition bath.
[0077] As indicated, the resinous phase of the electrodepositable
composition often further comprises a curing agent adapted to react
with the active hydrogen groups of the ionic electrodepositable
resin. For example, both blocked organic polyisocyanate and
aminoplast curing agents are suitable for use in the present
invention, although blocked isocyanates are often preferred for
cathodic electrodeposition.
[0078] Aminoplast resins, which are often the preferred curing
agent for anionic electrodeposition, are the condensation products
of amines or amides with aldehydes. Examples of suitable amine or
amides are melamine, benzoguanamine, urea and similar compounds.
Generally, the aldehyde employed is formaldehyde, although products
can be made from other aldehydes, such as acetaldehyde and
furfural. The condensation products contain methylol groups or
similar alkylol groups depending on the particular aldehyde
employed. Often, these methylol groups are etherified by reaction
with an alcohol, such as a monohydric alcohol containing from 1 to
4 carbon atoms, such as methanol, ethanol, isopropanol, and
n-butanol. Aminoplast resins are commercially available from
American Cyanamid Co. under the trademark CYMEL and from Monsanto
Chemical Co. under the trademark RESIMENE.
[0079] The aminoplast curing agents are often utilized in
conjunction with the active hydrogen containing anionic
electrodepositable resin in amounts ranging from 5 percent to 60
percent by weight, such as from 20 percent to 40 percent by weight,
the percentages based on the total weight of the resin solids in
the electrodepositable composition.
[0080] As indicated, blocked organic polyisocyanates are often used
as the curing agent in cathodic electrodeposition compositions. The
polyisocyanates can be fully blocked as described in U.S. Pat. No.
3,984,299 at col. 1, lines 1 to 68, col. 2, and col. 3, lines 1 to
15, or partially blocked and reacted with the polymer backbone as
described in U.S. Pat. No. 3,947,338 at col. 2, lines 65 to 68,
col. 3, and col. 4 lines 1 to 30, the cited portions of which being
incorporated herein by reference. By "blocked" is meant that the
isocyanate groups have been reacted with a compound so that the
resultant blocked isocyanate group is stable to active hydrogens at
ambient temperature but reactive with active hydrogens in the film
forming polymer at elevated temperatures usually between 90.degree.
C. and 200.degree. C.
[0081] Suitable polyisocyanates include aromatic and aliphatic
polyisocyanates, including cycloaliphatic polyisocyanates and
representative examples include diphenylmethane-4,4'-diisocyanate
(MDI), 2,4- or 2,6-toluene diisocyanate (TDI), including mixtures
thereof, p-phenylene diisocyanate, tetramethylene and hexamethylene
diisocyanates, dicyclohexylmethane-4,4'-diisocyanate, isophorone
diisocyanate, mixtures of phenylmethane-4,4'-diisocyanate and
polymethylene polyphenylisocyanate. Higher polyisocyanates, such as
triisocyanates can be used. An example would include
triphenylmethane-4,4',4''-triisocyanate. Isocyanate ( )-prepolymers
with polyols such as neopentyl glycol and trimethylolpropane and
with polymeric polyols such as polycaprolactone diols and triols
(NCO/OH equivalent ratio greater than 1) can also be used.
[0082] The polyisocyanate curing agents are typically utilized in
conjunction with the active hydrogen containing cationic
electrodepositable resin in amounts ranging from 5 percent to 60
percent by weight, such as from 20 percent to 50 percent by weight,
the percentages based on the total weight of the resin solids of
the electrodepositable composition.
[0083] In certain embodiments, the coating composition comprising a
film-forming resin also comprises yttrium. In certain embodiments,
yttrium is present in such compositions in an amount from 10 to
10,000 ppm, such as not more than 5,000 ppm, and, in some cases,
not more than 1,000 ppm, of total yttrium (measured as elemental
yttrium).
[0084] Both soluble and insoluble yttrium compounds may serve as
the source of yttrium. Examples of yttrium sources suitable for use
in lead-free electrodepositable coating compositions are soluble
organic and inorganic yttrium salts such as yttrium acetate,
yttrium chloride, yttrium formate, yttrium carbonate, yttrium
sulfamate, yttrium lactate and yttrium nitrate. When the yttrium is
to be added to an electrocoat bath as an aqueous solution, yttrium
nitrate, a readily available yttrium compound, is a preferred
yttrium source. Other yttrium compounds suitable for use in
electrodepositable compositions are organic and inorganic yttrium
compounds such as yttrium oxide, yttrium bromide, yttrium
hydroxide, yttrium molybdate, yttrium sulfate, yttrium silicate,
and yttrium oxalate. Organoyttrium complexes and yttrium metal can
also be used. When the yttrium is to be incorporated into an
electrocoat bath as a component in the pigment paste, yttrium oxide
is often the preferred source of yttrium.
[0085] The electrodepositable compositions described herein are in
the form of an aqueous dispersion. The term "dispersion" is
believed to be a two-phase transparent, translucent or opaque
resinous system in which the resin is in the dispersed phase and
the water is in the continuous phase. The average particle size of
the resinous phase is generally less than 1.0 and usually less than
0.5 microns, often less than 0.15 micron.
[0086] The concentration of the resinous phase in the aqueous
medium is often at least 1 percent by weight, such as from 2 to 60
percent by weight, based on total weight of the aqueous dispersion.
When such compositions are in the form of resin concentrates, they
generally have a resin solids content of 20 to 60 percent by weight
based on weight of the aqueous dispersion.
[0087] The electrodepositable compositions described herein are
often supplied as two components: (1) a clear resin feed, which
includes generally the active hydrogen-containing ionic
electrodepositable resin, i.e., the main film-forming polymer, the
curing agent, and any additional water-dispersible, non-pigmented
components; and (2) a pigment paste, which generally includes one
or more pigments, a water-dispersible grind resin which can be the
same or different from the main-film forming polymer, and,
optionally, additives such as wetting or dispersing aids.
Electrodeposition bath components (1) and (2) are dispersed in an
aqueous medium which comprises water and, usually, coalescing
solvents.
[0088] As aforementioned, besides water, the aqueous medium may
contain a coalescing solvent. Useful coalescing solvents are often
hydrocarbons, alcohols, esters, ethers and ketones. The preferred
coalescing solvents are often alcohols, polyols and ketones.
Specific coalescing solvents include isopropanol, butanol,
2-ethylhexanol, isophorone, 2-methoxypentanone, ethylene and
propylene glycol and the monoethyl monobutyl and monohexyl ethers
of ethylene glycol. The amount of coalescing solvent is generally
between 0.01 and 25 percent, such as from 0.05 to 5 percent by
weight based on total weight of the aqueous medium.
[0089] In addition, a colorant and, if desired, various additives
such as surfactants, wetting agents or catalyst can be included in
the coating composition comprising a film-forming resin. As used
herein, the term "colorant" means any substance that imparts color
and/or other opacity and/or other visual effect to the composition.
The colorant can be added to the composition in any suitable form,
such as discrete particles, dispersions, solutions and/or flakes. A
single colorant or a mixture of two or more colorants can be
used.
[0090] Example colorants include pigments, dyes and tints, such as
those used in the paint industry and/or listed in the Dry Color
Manufacturers Association (DCMA), as well as special effect
compositions. A colorant may include, for example, a finely divided
solid powder that is insoluble but wettable under the conditions of
use. A colorant can be organic or inorganic and can be agglomerated
or non-agglomerated. Colorants can be incorporated by use of a
grind vehicle, such as an acrylic grind vehicle, the use of which
will be familiar to one skilled in the art.
[0091] Example pigments and/or pigment compositions include, but
are not limited to, carbazole dioxazine crude pigment, azo,
monoazo, disazo, naphthol AS, salt type (lakes), benzimidazolone,
condensation, metal complex, isoindolinone, isoindoline and
polycyclic phthalocyanine, quinacridone, perylene, perinone,
diketopyrrolo pyrrole, thioindigo, anthraquinone, indanthrone,
anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone,
dioxazine, triarylcarbonium, quinophthalone pigments, diketo
pyrrolo pyrrole red ("DPPBO red"), titanium dioxide, carbon black
and mixtures thereof. The terms "pigment" and "colored filler" can
be used interchangeably.
[0092] Example dyes include, but are not limited to, those that are
solvent and/or aqueous based such as pthalo green or blue, iron
oxide, bismuth vanadate, anthraquinone, perylene, aluminum and
quinacridone.
[0093] Example tints include, but are not limited to, pigments
dispersed in water-based or water miscible carriers such as
AQUA-CHEM 896 commercially available from Degussa, Inc., CHARISMA
COLORANTS and MAXITONER INDUSTRIAL COLORANTS commercially available
from Accurate Dispersions division of Eastman Chemical, Inc.
[0094] As noted above, the colorant can be in the form of a
dispersion including, but not limited to, a nanoparticle
dispersion. Nanoparticle dispersions can include one or more highly
dispersed nanoparticle colorants and/or colorant particles that
produce a desired visible color and/or opacity and/or visual
effect. Nanoparticle dispersions can include colorants such as
pigments or dyes having a particle size of less than 150 nm, such
as less than 70 nm, or less than 30 nm. Nanoparticles can be
produced by milling stock organic or inorganic pigments with
grinding media having a particle size of less than 0.5 mm Example
nanoparticle dispersions and methods for making them are identified
in U.S. Pat. No. 6,875,800 B2, which is incorporated herein by
reference. Nanoparticle dispersions can also be produced by
crystallization, precipitation, gas phase condensation, and
chemical attrition (i.e., partial dissolution). In order to
minimize re-agglomeration of nanoparticles within the coating, a
dispersion of resin-coated nanoparticles can be used. As used
herein, a "dispersion of resin-coated nanoparticles" refers to a
continuous phase in which is dispersed discreet "composite
microparticles" that comprise a nanoparticle and a resin coating on
the nanoparticle. Example dispersions of resin-coated nanoparticles
and methods for making them are identified in United States Patent
Application Publication 2005-0287348 A1, filed Jun. 24, 2004, U.S.
Provisional Application No. 60/482,167 filed Jun. 24, 2003, and
U.S. patent application Ser. No. 11/337,062, filed Jan. 20, 2006,
which is also incorporated herein by reference.
[0095] Example special effect compositions that may be used include
pigments and/or compositions that produce one or more appearance
effects such as reflectance, pearlescence, metallic sheen,
phosphorescence, fluorescence, photochromism, photosensitivity,
thermochromism, goniochromism and/or color-change. Additional
special effect compositions can provide other perceptible
properties, such as opacity or texture. In certain embodiments,
special effect compositions can produce a color shift, such that
the color of the coating changes when the coating is viewed at
different angles. Example color effect compositions are identified
in U.S. Pat. No. 6,894,086, incorporated herein by reference.
Additional color effect compositions can include transparent coated
mica and/or synthetic mica, coated silica, coated alumina, a
transparent liquid crystal pigment, a liquid crystal coating,
and/or any composition wherein interference results from a
refractive index differential within the material and not because
of the refractive index differential between the surface of the
material and the air.
[0096] In certain embodiments, a photosensitive composition and/or
photochromic composition, which reversibly alters its color when
exposed to one or more light sources, can be used in the present
invention. Photochromic and/or photosensitive compositions can be
activated by exposure to radiation of a specified wavelength. When
the composition becomes excited, the molecular structure is changed
and the altered structure exhibits a new color that is different
from the original color of the composition. When the exposure to
radiation is removed, the photochromic and/or photosensitive
composition can return to a state of rest, in which the original
color of the composition returns. In certain embodiments, the
photochromic and/or photosensitive composition can be colorless in
a non-excited state and exhibit a color in an excited state. Full
color-change can appear within milliseconds to several minutes,
such as from 20 seconds to 60 seconds. Example photochromic and/or
photosensitive compositions include photochromic dyes.
[0097] In certain embodiments, the photosensitive composition
and/or photochromic composition can be associated with and/or at
least partially bound to, such as by covalent bonding, a polymer
and/or polymeric materials of a polymerizable component. In
contrast to some coatings in which the photosensitive composition
may migrate out of the coating and crystallize into the substrate,
the photosensitive composition and/or photochromic composition
associated with and/or at least partially bound to a polymer and/or
polymerizable component in accordance with certain embodiments of
the present invention, have minimal migration out of the coating.
Example photosensitive compositions and/or photochromic
compositions and methods for making them are identified in U.S.
application Ser. No. 10/892,919 filed Jul. 16, 2004, incorporated
herein by reference.
[0098] In general, the colorant can be present in the coating
composition in any amount sufficient to impart the desired visual
and/or color effect. The colorant may comprise from 1 to 65 weight
percent, such as from 3 to 40 weight percent or 5 to 35 weight
percent, with weight percent based on the total weight of the
compositions.
[0099] After deposition, the coating is often heated to cure the
deposited composition. The heating or curing operation is often
carried out at a temperature in the range of from 120 to
250.degree. C., such as from 120 to 190.degree. C. for a period of
time ranging from 10 to 60 minutes. In certain embodiments, the
thickness of the resultant film is from 10 to 50 microns.
[0100] As will be appreciated by the foregoing description, the
present invention is directed to methods for coating a metal
substrate comprising: (a) contacting the substrate with a
pretreatment composition comprising a group IIIB metal and/or a
group IVB metal, (b) contacting the substrate with a resin-based
post rinse composition that comprises either an anionic or cationic
resin-based post rinse composition, (c) electrophoretically
depositing either an anionic or cationic electrodepositable coating
composition onto the substrate, wherein an anionic
electrodepositable coating composition is utilized in conjunction
with the cationic resin-based post rinse composition and wherein a
cationic electrodepositable coating composition is utilized in
conjunction with the anionic resin-based post rinse
composition.
[0101] In certain embodiments, the three steps (a), (b) and (c) are
done sequentially without any intervening steps or processes. In
certain other embodiments, one or more intervening steps or
processes may occur between any of steps (a), (b) and/or (c).
[0102] In certain embodiments, step (b) occurs immediately after
step (a), and in certain other embodiments step (c) occurs
immediately after step (b) and/or after step (a). In still other
embodiments, step (c) occurs immediately after step (b) which
itself occurs immediately after step (a).
[0103] These methods of the present invention do not include
depositing a zinc phosphate or chromate-containing coating on the
substrate.
[0104] As has been indicated throughout the foregoing description,
the methods and coated substrates of the present invention, in
certain embodiments, do not include the deposition of a heavy metal
phosphate, such as zinc phosphate, or a chromate. As a result, the
environmental drawbacks associated with such materials is avoided.
Nevertheless, the methods of the present invention have been shown
to provide coated substrates that are, in at least some cases,
resistant to corrosion at a level comparable to, in some cases even
superior to (as illustrated in the Examples), methods wherein such
materials are used. This is a surprising and unexpected discovery
of the present invention and satisfies a long felt need in the art.
In addition, the methods of the present invention have been shown
to avoid the discoloration of subsequently applied coatings, such
as certain non-black electrodeposited coatings.
[0105] Illustrating the invention are the following examples that
are not to be considered as limiting the invention to their
details. All parts and percentages in the examples, as well as
throughout the specification, are by weight unless otherwise
indicated.
Example 1
[0106] Coating compositions were prepared as follows: [0107]
Cleaner 1: Chemkleen 166 HP/171ALF, alkaline cleaner, commercially
available from PPG Industries, Inc. [0108] Pretreatment 1: CHEMFOS
700/CHEMSEAL 59, immersion applied tricationic Zn phosphate and
sealer, commercially available from PPG Industries, Inc. [0109]
Pretreatment 2: ZIRCOBOND.RTM., immersion applied zirconium
pretreatment, commercially available from PPG Industries, Inc.
[0110] Post Rinse 1: Resin containing post rinse zirconium
pretreatment based on a phosphatized (anionic) epoxy polymer in an
aqueous solution is prepared by dissolving 2% (w/w) Nupal.RTM. 510R
(commercially available from PPG Industries, Inc.) in 5 gal of
H.sub.2O, with a pH=3. [0111] Post Rinse 2: Resin containing post
rinse zirconium pretreatment based on a phosphatized (anionic)
epoxy polymer in an aqueous solution is prepared by dissolving 2%
(w/w) Nupal.RTM.435F (commercially available from PPG Industries,
Inc.) in 5 gal of H.sub.2O, with a pH=3. [0112] Post Rinse 3: Resin
containing post rinse zirconium pretreatment based on an amine
adduct of EPON 828 (cationic) polymer in an aqueous solution
prepared by dissolving 2% (w/w) amine adduct of EPON 828 in 5 gal
of H.sub.2O, with a pH=10.4. [0113] Post Rinse 4: Resin containing
dry-in-place coating for a zirconium pretreatment based on a
phosphatized (anionic) epoxy polymer in an aqueous solution
prepared by dissolving 0.1% (w/w) Nupal.RTM. 510R (commercially
available from PPG Industries, Inc.) in 5 gal of H.sub.2O, with a
pH=4. [0114] Post Rinse 5: Deionized water post rinse. [0115] Paint
1: ED6060CZ, a cathodic electrocoat commercially available from PPG
Industries. [0116] Paint 2: AEROCRON CF, an anionic electrocoat
commercially available from PPG Industries.
Example 1
Evaluation of Throwpower of Anionic or Cationic Electrodepositable
Coating Composition for Various Pretreatment/Post Rinse Systems
[0117] In this example, Post Rinses 1-5 were evaluated to determine
the throwpower of subsequently applied anionic or cationic
electrodepositable coatings.
[0118] In this test, the panels were prepared as follows:
Step 1: Cleaning and Pretreatment
[0119] The coating systems were cleaned using Cleaner 1, rinsed
with deionized water, and pretreated at 27 .degree. C. in with
either Pretreatment 1 or Pretreatment 2 for 2 minutes. The panels
were then rinsed with deionized water.
Step 2: Application of Post Rinse
[0120] Next, for Post Rinses 1-3 and 5, respectively, the panels
were immersed in the post rinse solution for 1 minute and rinsed
with deionized water. The panels were then dried by for 5 minutes
at 55.degree. C. using forced air.
[0121] For Post Rinse 4, the cleaned and pretreated panels were
misted (i.e. coated) with Post Rinse 4. The panels were then dried
by for 5 minutes at 55.degree. C. using forced air.
Step 3: Application of Electrodepositable Coating Composition
[0122] Next, two 4''.times.12'' pretreated and post-rinsed panels
as prepared in Steps 1 and 2 above are placed on either side of a 4
mm shim and clamped together. The shimmed panels are immersed 27 cm
into the electrocoat bath (either Paint 1 or Paint 2) and coated as
described below. Throwpower readings are recorded as a percentage
by measuring the distance (in cm) from the bottom of the back side
of the panels to the point where no coating was deposited and
dividing that number by 27 cm.
[0123] Paint 1 was electrophoretically applied to the panels at
0.0008-0.0010 inches and cured for 25 minutes at 175.degree. C. in
an electric oven.
[0124] Paint 2 was electrophoretically applied to the panels at
0.0008-0.0010 inches and cured for 30 minutes at 93.degree. C. in
an electric oven.
[0125] The results are shown in Table 1 below:
TABLE-US-00002 TABLE 1 Throwpower Performance Paint 1,
Pretreatment/Post Rinse % Throwpower Paint 2, % Throwpower
Pretreatment 1/Post Rinse 5 69 34 Pretreatment 2/Post Rinse 1 67 32
Pretreatment 2/Post Rinse 2 66 32 Pretreatment 2/Post Rinse 3 55 38
Pretreatment 2/Post Rinse 4 67 31 Pretreatment 2/Post Rinse 5 56
30
[0126] As Table 1 confirms, the anionic post rinse compositions of
the present invention (Post Rinses 1, 2 and 4) applied after
Pretreatment 2 provided increased throwpower for a subsequently
applied cationic electrodepositable coating composition (Paint 1)
as compared to a deionized water post rinse (Post Rinse 5) and had
comparable throwpower to a zinc phosphate pretreatment system
(Pretreatment 1 with Post Rinse 5). The table also confirms that
the application of an cationic post rinse composition (Post Rinse
3) followed by the deposition of the cationic electrodepositable
coating composition (Paint 2) had virtually no effect on throwpower
as compared to a deionized water post rinse (Post Rinse 5).
[0127] In addition, the catonic post rinse compositions of the
present invention (Post Rinse 3) provided increased throwpower for
a subsequently applied anionic electrodepositable coating
composition (Paint 2) as compared to a deionized water post rinse
(Post Rinse 5) and increased throwpower to a zinc phosphate
pretreatment system (Pretreatment 1 with Post Rinse 5). The table
also confirms that the application of an anionic post rinse
composition (Post Rinses 1, 2 and 4) followed by the deposition of
the anionic electrodepositable coating composition had virtually no
effect on throwpower as compared to a deionized water post rinse
(Post Rinse 5).
Example 2
Evaluation of Corrosion Performance of Anionic or Cationic
Electrodepositable Coating Composition for Various
Pretreatment/Post Rinse Systems
[0128] In this example, the electrodeposited panels of Example 1
were also evaluated for corrosion performance. The test procedure
was performed using 40 cycles of GM-9511P and measuring the. The
results are shown in Table 2.
TABLE-US-00003 TABLE 2 Corrosion Performance - GM9511P 40 cycles,
mm Pretreatment/Post Rinse Paint 1 Paint 2 Pretreatment 1/Post
Rinse 5 5.5 2.7 Pretreatment 2/Post Rinse 1 7.6 6.4 Pretreatment
2/Post Rinse 2 8.1 9.7 Pretreatment 2/Post Rinse 3 7.3 7.9
Pretreatment 2/Post Rinse 4 9.4 8.2 Pretreatment 2/Post Rinse 5 8.2
8.0
[0129] As Table 2 confirms, the anionic post rinse compositions of
the present invention (Post Rinses 1, 2 and 4) applied after
Pretreatment 2 provided comparable corrosion resistance for a
subsequently applied cationic electrodepositable coating
composition (Paint 1) as compared to a deionized water post rinse
(Post Rinse 5).
[0130] In addition, the catonic post rinse compositions of the
present invention (Post Rinse 3) provided comparable corrosion
resistance for a subsequently applied anionic electrodepositable
coating composition (Paint 2) as compared to a deionized water post
rinse (Post Rinse 5).
[0131] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications which are within the spirit and scope of the
invention, as defined by the appended claims.
* * * * *