U.S. patent application number 10/231621 was filed with the patent office on 2005-11-17 for autodeposition metal dip coating process.
This patent application is currently assigned to Lord Corporation. Invention is credited to Rearick, Brett A., Weih, Mark A., Williams, James B..
Application Number | 20050252782 10/231621 |
Document ID | / |
Family ID | 23228960 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050252782 |
Kind Code |
A9 |
Williams, James B. ; et
al. |
November 17, 2005 |
Autodeposition metal dip coating process
Abstract
What is disclosed is a no-rinse autodeposition process to
dip-apply a metal part in an aqueous resin coating bath with an
immersion time and, wherein the removal rate of the dipped part is
kept equal or below drainage rate of mobile liquid portion, such
that upon removal of the part, drip edge formation is minimized and
a DFT is maintained within acceptable tolerance levels.
Inventors: |
Williams, James B.; (Erie,
PA) ; Weih, Mark A.; (Holly Springs, NC) ;
Rearick, Brett A.; (North East, PA) |
Correspondence
Address: |
LORD CORPORATION
PATENT & LEGAL SERVICES
111 LORD DRIVE
CARY
NC
27512
US
|
Assignee: |
Lord Corporation
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 0040858 A1 |
March 4, 2004 |
|
|
Family ID: |
23228960 |
Appl. No.: |
10/231621 |
Filed: |
August 30, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60316417 |
Aug 31, 2001 |
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Current U.S.
Class: |
205/137 ;
205/235 |
Current CPC
Class: |
B05D 7/142 20130101;
C09D 5/088 20130101 |
Class at
Publication: |
205/137 ;
205/235 |
International
Class: |
C25D 009/02 |
Claims
What is claimed is:
1. In an autodeposition coating process for forming a coating on a
electrochemically active metal substrate which is dipped in an
acidic bath, said coating derived from deposition of a dispersed
resin in the bath on interaction of multivalent ions entering the
aqueous phase, and wherein said substrate is characterized by no
rinsing step, and a substrate withdrawal rate that is less than the
drainage rate.
2. The process according to claim 1 wherein the electrochemically
active metal is selected from zinc, iron, aluminum, cold-rolled
steel, polished steel, picked steel, hot-rolled steel and
galvanized steel.
3. The process according to claim 1 wherein said substrate is
immersed in said acidic bath for a time of from 20 to 80 seconds
before withdrawal.
4. The process according to claim 1 wherein said metal substrate is
treated with a primer prior to dipping said substrate.
5. The process of claim 1 wherein said dispersed resin is a
vinyl-based resin.
6. The process of claim 1 wherein said resin is a condensation
resin.
7. The process according to claim 1 wherein the coating has an
average nominal dry film thickness of from 0.5 to 3 mils (0.0127 mm
to 0.076 mm).
8. The process according to claim 1 wherein said acidic bath has a
solids content of from 3% to 10%.
9. The process according to claim 1 wherein the withdrawal rate is
from 1 to 10 ft./min. (30.48 cm. To 25.4 cm.).
10. The process according to claim 1 wherein the dry film thickness
of said coating has a standard deviation of within 0.05 to 0.16
mils (0.00127 to 004 mm).
11. The process according to claim 1 wherein said dispersed resin
is based on a polymerizate from monomer selected from the group
consisting of styrene and butadiene, acrylate, alkyl-substituted
acrylate, vinyl halide monomer, vinylidene halide monomer, alkylene
monomer; halide-substituted alkylene monomer and acrylonitrile
monomer.
12. The process according to claim 11 wherein said dispersed resin
is selected from emulsions or dispersions of (poly)butadiene,
neoprene, styrene-butadiene rubber, acrylonitrile-butadiene rubber,
halogenated polyolefin, acrylic polymer, urethane polymer, epoxy,
polyester, ethylene-propylene copolymer rubber,
ethylene-propylene-diene terpolymer rubber, styrene-acrylic
copolymer, polyamide, and poly(vinyl acetate).
13. The process according to claim 1 wherein said dispersed resin
is a butadiene latex polymerized in the presence of a compound
selected from the group consisting of styrene sulfonic acid,
styrene sulfonate, poly(styrene sulfonic acid), or poly(styrene
sulfonate).
14. The process according to claim 1 wherein said bath comprises a
modified phenolic resin and a flexibilizer.
15. The process according to claim 4 wherein said primer comprises
a phenolic resole, and the coating on said primer comprises a
novolak.
16. The process of claim 1 wherein the coating polymer is derived
from vinyl monomers selected from the group consisting of acrylic
acid, methacrylic acid, acrylic acid esters, methacrylic acid
esters, vinyl amides, nitriles, vinyl esters, vinyl ethers, vinyl
halides, vinylidene halides, vinyl aromatic compounds, other
ethylenically unsaturated compounds and combinations thereof.
17. The process of claim 14 wherein said flexibilizer is selected
from (poly)butadiene, neoprene, styrene-butadiene rubber, nitrile
rubber, halogenated polyolefin, acrylic polymer, urethane polymer,
ethylene-propylene copolymer rubber, ethylene-propylene-diene
terpolymer rubber, styrene-acrylic copolymer, polyamide and
poly(vinyl acetate).
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to dip-application of aqueous
autodepositable compositions.
BACKGROUND OF THE INVENTION
[0002] Autodeposition is an aqueous process for coating metal that
is driven by reactions between the coating and metal substrate when
small amounts of multivalent metal ions are released from the metal
surface. The aqueous composition must contain a stabilized polymer
dispersion. The essential feature of an autodepositable coating is
that the dispersed material is stabilized by functional groups on
the polymer and/or provided by surface active agents which are
sensitive to multivalent ions entering the aqueous phase.
Deposition occurs by interaction of the multivalent ions and these
stabilizing functional groups causing the dispersion to precipitate
when sufficient concentration of multivalent ions occurs at the
metal surface.
[0003] Examples of autodepositing compositions are disclosed, for
example, in European Patent Publication 0132828, Bashir M. Ahmed,
U.S. Pat. No. 4,647,480 and Wilbur S. Hall, U.S. Pat. No.
4,186,219, U.S. Pat. No. 4,657,788, U.S. Pat. Nos. 5,691,048, and
4,657,788, and patents cited therein each of which is incorporated
herein by reference. Such compositions designed to particularly
effective when the resin material is provided in the form of a
dispersed polymer such as a sulfonate-functionalized novolak, or
latex made from the emulsion polymerized product of at least two
polymerizable ethylenically unsaturated monomers.
[0004] In the practice of dip-applied autodeposition coatings,
often the coating can be rinsed after withdrawal from the bath. In
some instances, rinsing is not undertaken. There remains some
limits on the process of autodepositing coatings on metal parts
without a rinse step. A problem arises without a rinse step
relating to accumulation of drainage along edges, that when dried
leads to what is referred to as drip edges. These drip edges result
in poorer protective coatings. In attempts to alieviate drip edges
other problems can arise, such as variable dry film thickness (DFT)
in different areas of the part surface. The need for a non-rinsing
coating method that deposits a sufficient amount of coating, with
an acceptable DFT uniformity, while reducing the incidence of drip
edges would be highly desirable in a dip-applied autodeposited
coating.
SUMMARY OF THE INVENTION
[0005] According to a preferred aspect of present invention there
is provided a no-rinse autodeposition process to dip-apply a metal
part in an aqueous coating bath containing a specified solids
level, at a specified bath temperature, immersion time and, wherein
the removal rate of the dipped part is kept equal or below drainage
rate of mobile liquid portion, such that upon removal of the part,
drip edge formation is minimized and a DFT is maintained within
acceptable tolerance levels.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0006] Unless otherwise indicated, description of components in
chemical nomenclature refers to the components at the time of
addition to any combination specified in the description, but does
not necessarily preclude chemical interactions among the components
of a mixture once mixed.
[0007] As used herein the term "autodeposited resin" shall mean all
resins which can be autodeposited in the autodeposition
process.
[0008] DFT is dry film thickness, and is measured using a
Fisherscope MMS Permascope and an average of 10 readings are taken
as the statistical sample on each part or panel.
[0009] "Primer" means a liquid composition applied to a surface as
an undercoat beneath a subsequently-applied covercoat. The
covercoat can be an adhesive and the primer/adhesive covercoat
forms an adhesive system for bonding two substrates together.
[0010] "Coating" means a liquid composition applied to a surface to
form a protective and/or aesthetically pleasing coating on the
surface.
[0011] "Electrochemically active metals" means iron and all metals
and alloys more active than hydrogen in the electromotive series.
Examples of electrochemically active metal surfaces include zinc,
iron, aluminum and cold-rolled, polished, pickled, hot-rolled and
galvanized steel.
[0012] "Ferrous" means iron and alloys of iron.
[0013] The autodeposited coatings are resin-containing
acidic-aqueous compositions comprising an acid, an oxidizing agent
and the aqueous dispersed resin. Examples of autodeposited
compositions are known. Those which are suitable in the present
invention are made as set forth in European Patent Publication
0132828 and U.S. Pat. Nos. 4,647,480 and 4,186,219.
[0014] The addition polymerized resins which can be autodeposited
generally comprise at least one ethylenically unsaturated monomeric
compound (e.g. vinyl-based resins). The preferred ethylenically
unsaturated monomers include styrene-butadiene; acrylate;
alkyl-substituted acrylates such as methyl methacrylate and ethyl
methacrylate; vinyl halides such as vinyl chloride; vinylidene
halides such as vinylidene chloride and vinylidene dichloride;
alkylenes such as ethylene; halide-substituted alkylenes such as
tetrafluoroethylene; and acrylonitriles such as acrylonitrile,
combinations thereof and the like.
[0015] Of the condensation type resins suitable herein are aqueous
dispersions of modified phenolic novolak resins. These are the
reaction product of a phenolic resin precursor, a modifying agent
and a multi-hydroxy phenolic compound. The modifying agent includes
at least one functional moiety that enables the modifying agent to
react with the phenolic resin precursor and at least one ionic
moiety. According to a preferred embodiment the modifying agent is
an aromatic compound. According to another embodiment the ionic
moiety of the modifying agent is sulfate, sulfonate, sulfinate,
sulfenate or oxysulfonate and the dispersed phenolic resin reaction
product has a carbon/sulfur atom ratio of 20:1 to 200:1.
[0016] The acid can be any acid that is capable of reacting with a
metal to generate a sufficient concentration of multivalent ions.
The acids which may be used in the autodepositing composition
include inorganic and strong organic acids, such as, for example,
hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid,
phosphoric acid, acetic acid, halogen--substituted acetic acid such
as chloroacetic acid and trichloroacetic acid, and citric acid.
Hydrofluoric acid is a preferred acid used in conjunction with
emulsion polymerized autodeposited resins. Phosphoric acid is a
preferred acid used in conjunction with modified phenolic
dispersion embodiments In the case of steel the multivalent ions
liberated from the metal surface are ferric and/or ferrous ions.
When the acid is mixed into the composition presumably the
respective ions are formed and exist as independent species in
addition to the presence of the free acid. In other words, in the
case of phosphoric acid, phosphate ions and free phosphoric acid
co-exist in the coating bath. As for modified phenolic dispersion
embodiments, the acid preferably is present in an amount of 5 to
300 parts by weight, more preferably 10 to 160 parts by weight,
based on 100 parts by weight of the resin dispersion.
[0017] The oxidizing agents which can be employed in an
autodepositing composition for use in the present invention include
peroxides such as hydrogen peroxide, chromates and dichromates such
as chromic acid and potassium dichromate, nitrates such as nitric
acid and sodium nitrate, persulfates such as sodium persulfate and
ammonium persulfate, perborates such as sodium perborate, iron
(III) such as ferric fluoride. Hydrogen peroxide and ferric
fluoride are the preferred oxidizing agents.
[0018] Exemplary autodepositing compositions for use in the present
invention are those where the resin is in the form of a latex (i.e.
an emulsion polymerization product of at least one polymerizable
ethylenically unsaturated monomer). Examples of such compositions
include Autophoretic.RTM. 800 Series autodepositing compositions
based on polyvinylidene resins and Autophoretic.RTM. 700 Series
autodepositing compositions based on acrylic resins, each
composition being made by Henkel. Such compositions preferably
contain hydrofluoric acid and hydrogen peroxide or iron (III)
fluoride as the oxidizing agent. Other commercially available
autodepositable coatings are provided by Lord Corporation under the
Autoseal trademark, e.g., MJ 2110 is most preferred, and is
disclosed in copending application Ser. No. 09/235, 201, hereby
incorporated by reference. Prior to applying a dip-applied
autodeposition coating, the most preferred metal treatment is
provided by the use of an aqueous metal treatment primer
composition disclosed in copending application Ser. No. 09/235,778
which is hereby incorporated by reference.
[0019] The coatings produced by autodepositing compounds under
autodepositing conditions generally have an average nominal
thickness of from 0.5 to 3 mils, preferably from about 1.0 to 2.0
mils, applied over a metal treatment having a thickness of from 0.1
to 0.5 mils .+-.0.05 mils. Water, preferably deionized water, is
utilized to establish the predetermined solids content. Although
the solids content may be varied as desired, the solids content of
the coating bath is in a range of from 3 to 10%. The bath
composition is waterborne and substantially free of volatile
organic compounds. In the practice of the invention the range of
the average DFT of autodeposited coating over the part surface is
kept within .+-.0.3 mils, preferably +/- 0.2 mils, by processing a
total solids bath in a range of solids of from 5 wt. % to 10%,
preferably 6 wt. % solids, at a bath temperature of from 15.degree.
C. to 40.degree. C., an Immersion time of from 20 to 80 seconds,
preferably from 30 to 75 seconds, and a part withdrawal rate of
from 1 to 10 ft./minute, preferably from 3 to 6 ft./min.
[0020] In a preferred embodiment of dip-applied method to coat a
metal part an aqueous autodeposition bath comprises a phenolic
resin dispersion, particularly an aqueous novolak dispersion and a
deposition control agent and an optional a flexibilizer component
in admixture therewith..
[0021] This rate of autodeposition is independent of the withdrawal
rate of the part. Typically the instantaneous rate of deposition
slows with the elapsed immersion time. This reduction in deposition
rate is referred to as "a self-limiting" feature, however to
immersion time is limited to maintain an optimal DFT. Even with the
formation of a gelled deposit on the immersed part, there are
components of the autodeposition system that further drain from the
gel as the part is withdrawn. The withdrawal rate is kept at or
below the drainage rate in the practice of the invention, such that
upon complete withdrawal, drip edges are reduced and most
preferably eliminated. The standard deviation of DFT measured at 10
points on the surface of the part is kept to within 0.05 mils to
0.16 mils despite the slow withdrawal rates.
[0022] In the most preferred embodiment, the coating when dried is
a thin, tightly bound interpenetrating organic/inorganic matrix of
phenolic/metal phosphates at the metal substrate interface. This
matrix can be further flexibilized with polymers. The flexibilizer
is any material that contributes flexibility and/or toughness to
the film formed from the composition. The toughness provided by the
flexibilizer provides fracture resistance to the film. The
flexibilizer should be non-glassy at ambient temperature and be an
aqueous emulsion latex or aqueous dispersion that is compatible
with the phenolic novolak resin dispersion. The flexibilizer
preferably is formulated into the composition in the form of an
aqueous emulsion latex or aqueous dispersion.
[0023] Suitable resin dispersions include aqueous latices,
emulsions or dispersions of (poly)butadiene, neoprene,
styrene-butadiene rubber, acrylonitrile-butadiene rubber (also
known as nitrile rubber), halogenated polyolefin, acrylic polymer,
urethane polymer, ethylene-propylene copolymer rubber,
ethylene-propylene-diene terpolymer rubber, styrene-acrylic
copolymer, polyamide, poly(vinyl acetate) and the like. Halogenated
polyolefins, nitrile rubbers and styrene-acrylic copolymers are
preferred.
[0024] A suitable styrene-acrylic polymer latex is commercially
available from Goodyear Tire & Rubber under the trade
designation PLIOTEC and described, for example, in U.S. Pat. No.
4,968,741; 5,122,566 and 5,616,635. According to U.S. Pat. No.
5,616,635, such a copolymer latex is made from 45-85 weight percent
vinyl aromatic monomers, 15-50 weight percent of at least one alkyl
acrylate monomer and 1-6 weight percent unsaturated carbonyl
compound. Styrene is the preferred vinyl aromatic monomer, butyl
acrylate is the preferred acrylate monomer and acrylic acid and
methacrylic acid are the preferred unsaturated carbonyl compound.
The mixture for making the latex also includes at least one
phosphate ester surfactant, at least one water-insoluble nonionic
surface active agent and at least one free radical initiator.
[0025] Nitrile rubber emulsion latex is generally made from at
least one monomer of acrylonitrile or an alkyl derivative thereof
and at least one monomer of a conjugated diene, preferably
butadiene. According to U.S. Pat. No. 4,920,176 the acrylonitrile
or alkyl derivative monomer should be present in an amount of 0 or
1 to 50 percent by weight based on the total weight of the
monomers. The conjugated diene monomer should be present in an
amount of 50 percent to 99 percent by weight based on the total
weight of the monomers. The nitrile rubbers can also optionally
include various co-monomers such as acrylic acid or various esters
thereof, dicarboxylic acids or combinations thereof. The
polymerization of the monomers typically is initiated via free
radical catalysts. Anionic surfactants typically are also added. A
suitable nitrile rubber latex is available from B. F. Goodrich
under the HYCAR.RTM. mark. Representative halogenated polyolefins
include chlorinated natural rubber, chlorine- and
bromine-containing synthetic rubbers including polychloroprene,
chlorinated polychloroprene, chlorinated polybutadiene,
hexachloropentadiene, butadiene/halogenated cyclic conjugated diene
adducts, chlorinated butadiene styrene copolymers, chlorinated
ethylene propylene copolymers and ethylene/propylene/non-conjugated
diene terpolymers, chlorinated polyethylene, chlorosulfonated
polyethylene, poly(2,3-dichloro-1,3-butadiene), brominated
poly(2,3-dichloro-1,3-butadi- ene), copolymers of
(c-haloacrylonitriles and 2,3-dichloro-1,3-butadiene, chlorinated
poly(vinyl chloride) and the like including mixtures of such
halogen-containing elastomers.
[0026] Latices of the halogenated polyolefin can be prepared
according to methods known in the art such as by dissolving the
halogenated polyolefin in a solvent and adding a surfactant to the
resulting solution. Water can then be added to the solution under
high shear to emulsify the polymer. The solvent is then stripped to
obtain a latex. The latex can also be prepared by emulsion
polymerization of the halogenated ethylenically unsaturated
monomers.
[0027] Butadiene latices are particularly preferred as the
flexibilizer. Methods for making butadiene latices are widely
available commercially, and are described, for example, in U.S.
Pat. Nos. 4,054,547 and 3,920,600, both incorporated herein by
reference. In addition, U.S. Pat. Nos. 5,200,459; 5,300,555; and
5,496,884 disclose emulsion polymerization of butadiene monomers in
the presence of polyvinyl alcohol and a co-solvent such as an
organic alcohol or a glycol.
[0028] The butadiene monomers useful for preparing a butadiene
polymer latex as a flexibilizer, can essentially be any monomer
containing conjugated unsaturation. Typical monomers include
2,3-dichloro-1,3-butadi- ene; 1,3-butadiene;
2,3-dibromo-1,3-butadiene isoprene; isoprene;
2,3-dimethylbutadiene; chloroprene; bromoprene;
2,3-dibromo-1,3-butadiene- ; 1,1,2-trichlorobutadiene; cyanoprene;
hexachlorobutadiene; and combinations thereof.
[0029] It is particularly preferred to use
2,3-dichloro-1,3-butadiene since a polymer that contains as its
major portion 2,3-dichloro-1,3-butadiene monomer units has been
found to be particularly useful in adhesive applications due to the
excellent bonding ability and barrier properties of the
2,3-dichloro-1,3-butadiene-based polymers. As described above, an
especially preferred embodiment of the present invention is one
wherein the butadiene polymer includes at least 60 weight percent,
preferably at least 70 weight percent, 2,3-dichloro-1,3-butadiene
monomer units.
[0030] The butadiene monomer can be copolymerized with other
monomers. Such copolymerizable monomers include
.alpha.-haloacrylonitriles such as .alpha.-bromoacrylonitrile and
.alpha.-chloroacrylonitrile; .alpha.,.beta.-unsaturated carboxylic
acids such as acrylic, methacrylic, 2-ethylacrylic,
2-propylacrylic, 2-butylacrylic and itaconic acids;
alkyl-2-haloacrylates such as ethyl-2-chloroacrylate and
ethyl-2-bromoacrylate; .alpha.-bromovinylketone; vinylidene
chloride; vinyl toluenes; vinylnaphthalenes; vinyl ethers, esters
and ketones such as methyl vinyl ether, vinyl acetate and methyl
vinyl ketone; esters amides, and nitriles of acrylic and
methacrylic acids such as ethyl acrylate, methyl methacrylate,
glycidyl acrylate, methacrylamide and acrylonitrile; and
combinations of such monomers. The copolymerizable monomers, if
utilized, are preferably .alpha.-haloacrylonitrile and/or
.alpha.,.beta.-unsaturated carboxylic acids. The copolymerizable
monomers may be utilized in an amount of 0.1 to 30 weight percent,
based on the weight of the total monomers utilized to form the
butadiene polymer.
[0031] In carrying out the emulsion polymerization to produce the
latex, conventional anionic and/or nonionic surfactants may be
utilized in order to aid in the formation of the latex. Typical
anionic surfactants include carboxylates such as fatty acid soaps
from lauric, stearic, and oleic acid; acyl derivatives of sarcosine
such as methyl glycine; sulfates such as sodium lauryl sulfate;
sulfated natural oils and esters such as Turkey Red Oil; alkyl aryl
polyether sulfates; alkali alkyl sulfates; ethoxylated aryl
sulfonic acid salts; alkyl aryl polyether sulfonates; isopropyl
naphthalene sulfonates; sulfosuccinates; phosphate esters such as
short chain fatty alcohol partial esters of complex phosphates; and
orthophosphate esters of polyethoxylated fatty alcohols. Typical
nonionic surfactants include ethoxylated (ethylene oxide)
derivatives such as ethoxylated alkyl aryl derivatives; mono- and
polyhydric alcohols; ethylene oxide/propylene oxide block
copolymers; esters such as glyceryl monostearate; products of the
dehydration of sorbitol such as sorbitan monostearate and
polyethylene oxide sorbitan monolaurate; amines; lauric acid; and
isopropenyl halide. A conventional surfactant, if utilized, is
employed in an amount of 0.01 to 5 parts, preferably 0.1 to 2
parts, per 100 parts by weight of total monomers utilized to form
the butadiene polymer.
[0032] The preferred dichlorobutadiene homopolymers have a
colloidal stabilizing system characterized by anionic surfactants.
Such anionic surfactants include alkyl sulfonates and alkyl aryl
sulfonates (commercially available from Stepan under the trade
designation POLYSTEP) and sulfonic acids or salts of alkylated
diphenyl oxide (for example, didodecyl diphenyleneoxide disulfonate
or dihexyl diphenyloxide disulfonate commercially available from
Dow Chemical Co. under the trade designation DOWFAX).
[0033] Especially preferred butadiene latexes as flexibilizers are
polymerized in the presence of a styrene sulfonic acid, styrene
sulfonate, poly(styrene sulfonic acid), or poly(styrene sulfonate)
stabilizer to form the latex. Poly(styrene sulfonate) is the
preferred stabilizer. This stabilization system is particularly
effective for a butadiene polymer that is derived from at least 60
weight percent dichlorobutadiene monomer, based on the amount of
total monomers used to form the butadiene polymer. The butadiene
polymer latex can be made by known emulsion polymerization
techniques that involve polymerizing the butadiene monomer (and
copolymerizable monomer, if present) in the presence of water and
the styrene sulfonic acid, styrene sulfonate, poly(styrene sulfonic
acid), or poly(styrene sulfonate) stabilizer. The sulfonates can be
salts of any cationic groups such as sodium, potassium or
quaternary ammonium. Sodium styrene sulfonate is a preferred
styrene sulfonate compound. Poly(styrene sulfonate) polymers
include poly(styrene sulfonate) homopolymer and poly(styrene
sulfonate) copolymers such as those with maleic anhydride. Sodium
salts of poly(styrene sulfonate) are particularly preferred and are
commercially available from National Starch under the trade
designation VERSA TL. The poly(styrene sulfonate) can have a weight
average molecular weight from 5.times.10.sup.4 to
1.5.times.10.sup.6, with 1.5.times.10.sup.5 to 2.5.times.10.sup.5
being preferred. In the case of a poly(styrene sulfonate) or
poly(styrene sulfonic acid) it is important to recognize that the
emulsion polymerization takes place in the presence of the
pre-formed polymer. In other words, the butadiene monomer is
contacted with the pre-formed poly(styrene sulfonate) or
poly(styrene sulfonic acid). The stabilizer preferably is present
in an amount of 0.1 to 10 parts, preferably 1 to 5 parts, per 100
parts by weight of total monomers utilized to form the butadiene
polymer.
[0034] The flexibilizer, if present, preferably is included in the
composition in an amount of 5 parts by weight to 300 parts by
weight, based on 100 parts by weight of the preferred phenolic
novolak resin dispersion. More preferably, the flexibilizer is
present in an amount of 25 parts by weight to 100 parts by weight,
based on 100 parts by weight of the phenolic novolak resin
dispersion.
[0035] The modified phenolic resin dispersion can be cured to form
a highly crosslinked thermoset via known curing methods for
phenolic resins. The curing mechanism can vary depending upon the
use and form of the phenolic resin dispersion. For example, curing
of the dispersed resole embodiment typically can be accomplished by
subjecting the phenolic resin dispersion to heat. Curing of the
dispersed novolak embodiment typically can be accomplished by
addition of an aldehyde donor compound.
[0036] Since the dispersed phenolic resin is a novolak, a curative
should be introduced in order to cure the film formed by the metal
treatment composition. It should be noted that the metal treatment
composition cannot itself include a phenolic resin curative as
these curatives are not storage stable under acidic conditions.
Curing of the film can be accomplished by the application of a
curative-containing topcoat over the metal treatment film.
Typically, the metal treatment composition is applied to a metal
surface (either conventionally or via autodeposition) and then
dried. The curative-containing autodeposited topcoat then is
applied to the thus treated metal surface. The curative contained
in the topcoat can be an aldehyde donor compound or an aromatic
nitroso compound. Topcoat compositions that include either one or
both of these curatives are well-known and commercially
available.
[0037] The aldehyde donor can be essentially be any type of
aldehyde known to react with hydroxy aromatic compounds to form
cured or crosslinked novolak phenolic resins. Typical compounds
useful as an aldehyde (e.g., formaldehyde) source in the present
invention include formaldehyde and aqueous solutions of
formaldehyde, such as formalin; acetaldehyde; propionaldehyde;
isobutyraldehyde; 2-ethylhexaldehyde; 2-methylpentaldehyde;
2-ethylhexaldehyde; benzaldehyde; as well as compounds which
decompose to formaldehyde, such as paraformaldehyde, trioxane,
furfural, hexamethylenetetramine, anhydromaldehydeaniline, ethylene
diamine formaldehyde; acetals which liberate formaldehyde on
heating; methylol derivatives of urea and formaldehyde; methylol
phenolic compounds; and the like.
[0038] It has been found that metal parts pre-primer coated with a
primer described in U.S. Ser. No. 09/235,778, formaldehyde species
generated from the resole present in the primer appear to co-cure
the novolak in the metal treatment coating via diffusion. In
addition, curing or crosslinking of the novolak may occur through
ionic crosslinking and chelation with the metal ions generated by
the acid-metal substrate reaction.
[0039] Additionally, high molecular weight aldehyde homopolymers
and copolymers can be employed as a latent formaldehyde source in
the practice of the present invention. A latent formaldehyde source
herein refers to a formaldehyde source which will release
formaldehyde only in the presence of heat such as the heat applied
during the curing of an adhesive system. Typical high molecular
weight aldehyde homopolymers and copolymers include (1) acetal
homopolymers, (2) acetal copolymers, (3) gamma-polyoxy-methylene
ethers having the characteristic structure:
R.sub.10O--(CH.sub.2O).sub.n--R.sub.11
[0040] and (4) polyoxymethylene glycols having the characteristic
structure:
HO--(R.sub.12O).sub.x--(CH.sub.2O).sub.n--(R.sub.13O).sub.x--H
[0041] wherein R.sub.10 and R.sub.11 can be the same or different
and each is an alkyl group having from about 1 to 8, preferably 1
to 4, carbon atoms, R.sub.12 and R.sub.13 can be the same or
different and each is an alkylene group having from 2 to 12,
preferably 2 to 8, carbon atoms; n is greater than 100, and is
preferably in the range from about 200 to about 2000; and x is in
the range from about 0 to 8, preferably 1 to 4, with at least one x
being equal to at least 1. The high molecular weight aldehyde
homopolymers and copolymers are further characterized by a melting
point of at least 75.degree. C., i.e. they are substantially inert
with respect to the phenolic system until heat activated; and by
being substantially completely insoluble in water at a temperature
below the melting point. The acetal homopolymers and acetal
copolymers are well-known articles of commerce. The
polyoxymethylene materials are also well known and can be readily
synthesized by the reaction of monoalcohols having from 1 to 8
carbon atoms or dihydroxy glycols and ether glycols with
polyoxymethylene glycols in the presence of an acidic catalyst. A
representative method of preparing these crosslinking agents is
described in U.S. Pat. No. 2,512,950, which is incorporated herein
by reference. Gamma-polyoxymethylene ethers are generally preferred
sources of latent formaldehyde and a particularly preferred latent
formaldehyde source for use in the practice of the invention is
2-polyoxymethylene dimethyl ether.
[0042] The aromatic nitroso compound can be any aromatic
hydrocarbon, such as benzenes, naphthalenes, anthracenes,
biphenyls, and the like, containing at least two nitroso groups
attached directly to non-adjacent ring carbon atoms. Such aromatic
nitroso compounds are described, for example, in U.S. Pat. No.
3,258,388; U.S. Pat. No. 4,119,587 and U.S. Pat. No. 5,496,884.
[0043] The control agent mentioned above is especially useful in
the metal treatment composition of the invention described above
but it could also be useful in any multi-component composition that
includes an autodepositable component. The autodepositable
component is any material that enables (either by itself or in
combination with the other components of the composition) the
multi-component composition to autodeposit on a metal surface.
Preferably, the autodepositable component is any water-dispersed or
water soluble resin that is capable of providing autodeposition
ability to the composition. It is believed that the present
invention will be used most widely in connection with coatings
formed from organic polymers in particular, those polymers derived
from ethylenically unsaturated compounds. Other organic polymers
useful in the instant invention are those that can be obtained in a
form suitable for compounding into an aqueous coating bath. Organic
resins include those derived from ethylenically unsaturated
monomers such as polyvinylidene chloride, polyvinyl chloride,
polyethylene, acrylic, acrylonitrile, polyvinyl acetate and
styrene-butadiene (see U.S. Pat. Nos. 4,414,350; 4,994,521; and
5,427,863; and PCT Published Patent Application No. WO 93/15154).
Urethane and polyester resins are also mentioned as being useful.
Certain epoxy and epoxy-acrylate resins are also said to be useful
autodeposition resins (see U.S. Pat. No. 5,500,460 and PCT
Published Patent Application No. WO 97/07163). Blends of these
resins may also be used.
[0044] The preferred autodepositable resins are aqueous phenolic
resin dispersions described in co-pending, commonly assigned U.S.
patent application Ser. No. 09/235,201, incorporated herein by
reference. The novolak version of this dispersed resin is described
above in connection with the metal treatment composition. There is
also a resole version with which the control agent of the invention
may be formulated into a multi-component composition.
[0045] The phenolic resin precursor and modifying agent used to
make the dispersed resole are the same as those described for the
dispersed novolak. However, the dispersed resole is produced by the
reaction of 1 mol of modifying agent(s) with 1 to 20 mol of
phenolic resin precursor(s). A dispersed resole typically can be
obtained by reacting a resole precursor or a mixture of resole
precursors with the modifying agent or a mixture of agents without
any other reactants, additives or catalysts. However, other
reactants, additives or catalysts can be used as desired.
Multi-hydroxy phenolic compound(s) can optionally be included in
relatively small amounts in the reactant mixture for the resole.
Synthesis of the resole does not require an acid catalyst.
[0046] Hydrophilic resoles typically have a F/P ratio of at least
1.0. According to the invention, hydrophilic resoles having a F/P
ratio much greater than 1.0 can be successfully dispersed. For
example, it is possible to make an aqueous dispersion of
hydrophilic resoles having a F/P ratio of at least 2 and
approaching 3, which is the theoretical F/P ratio limit.
[0047] According to a particularly preferred embodiment disclosed
in U.S. Ser. No. 09/235,201, wherein the dispersed phenolic resin
is a resole and the modifying agent is a naphthalene having a ionic
pendant group X and two reaction-enabling substituents Y, the
dispersed phenolic resin reaction product contains a mixture of
oligomers having structures believed to be represented by the
following formula III: 1
[0048] wherein X and Y are the same as in formulae Ia and Ib, a is
0 or 1; n is 0 to 5; R.sup.2 is independently --C(R.sup.5).sub.2--
or --C(R.sup.5).sub.2--O--C(R.sup.5).sub.2--, wherein R.sup.5 is
independently hydrogen, alkylol, hydroxyl, alkyl, aryl or aryl
ether; and R.sup.3 is independently alkylol, alkyl, aryl or aryl
ether. Preferably, R.sup.2 is methylene or oxydimethylene and
R.sup.3 is methylol. If 6,7-dihydroxy-2-naphthalenesulfonate,
sodium salt is the modifying agent, X will be
SO.sub.3.sup.-Na.sup.+ and each Y will be OH. It should be
recognized that in this case the hydroxy groups for Y will also act
as chelating groups with a metal ion.
[0049] The autodepositable component can be present in the
composition in any amount that provides for effective
autodeposition. In general, the amount can range from 1 to 50,
preferably 5 to 20, and more preferably 7 to 14, weight percent,
based on the total amount of non-volatile ingredients in the
composition.
[0050] The control agent is any material that is able to improve
the formation of an autodeposited coating on a metallic surface
and, optionally, improve the formation of another autodeposited
coating applied after the control agent-containing autodeposited
coating. Addition of the control agent also increases the
uniformity of the thickness of the autodeposited coating. The
control agent-containing composition does not require an ambient
staging period in order to develop fully the coating. In other
words, the metallic coating conversion is complete upon drying of
the coated substrate and any subsequent coating, primer or adhesive
compositions can be applied immediately after coating and drying of
the control agent-containing composition. The control agent also
must be compatible with the other components of the composition
under acidic conditions without prematurely coagulating or
destabilizing the composition.
[0051] The control agent may be a nitro compound, a nitroso
compound, an oxime compound, a nitrate compound, hydroxyl amine, or
a similar material. A mixture of control agents may be used.
Organic nitro compounds are the preferred control agents.
[0052] The organic nitro compound is any material that includes a
nitro group (--NO.sub.2) bonded to an organic moiety. Preferably,
the organic nitro compound is water soluble or, if water insoluble,
capable of being dispersed in water. Illustrative organic nitro
compounds include nitroguanidine; aromatic nitrosulfonates such as
nitro or dinitrobenzenesulfonate and the salts thereof such as
sodium, potassium, amine or any monovalent metal ion (particularly
the sodium salt of 3,5-dinitrobenzenesulfonate); Naphthol Yellow S;
and picric acid (also known as trinitrophenol). Especially
preferred for commercial availability and regulatory reasons is a
mixture of nitroguanidine and sodium nitrobenzenesulfonate.
[0053] The amount of control agent(s) in a multi-component
composition may vary, particularly depending upon the amount of any
acid in the composition. Preferably, the amount is up to 20 weight
%, more preferably up to 10 weight %, and most preferably 2 to 5
weight %, based on the total amount of non-volatile ingredients in
the composition. According to a preferred embodiment, the weight
ratio of nitroguanidine to sodium nitrobenzenesulfonate should
range from 1:10 to 5:1.
[0054] The organic nitro compound typically is mixed into the
composition in the form of an aqueous solution or dispersion. For
example, nitroguanidine is a solid at room temperature and is
dissolved in water prior to formulating into the composition.
[0055] The compositions of the invention may be prepared by any
method known in the art, but are preferably prepared by combining
and milling or shaking the ingredients and water in ball-mill,
sand-mill, ceramic bead-mill, steel-bead mill, high speed
media-mill or the like. It is preferred to add each component to
the mixture in a liquid form such as an aqueous dispersion.
[0056] For the salt chamber test the parts are scored to the metal
surface in a cross hatch pattern using a new razor blade and placed
in a standard salt spray chamber for 500 hours. Evaluation of
corrosion creep is made.
[0057] Experimental:
[0058] Autodepositable Coating:
1 Component Solids wet wt. % Dry wt. (Lb) Raven .RTM. 14 100 0.43
1.448 owder Marasperse .RTM. 100 0.14 0.472 BBOSO-4 Phenolic resin
51 1.42 19.616 Ga. Pacific 4000 ABS latex 50.250 10.4 17.696
Nitroguanidine 75 0.090 0.227 Deionized 0 77.52 00 water
[0059] Withdrawal Rate for Coating: The small adhesive dip line was
used to vary the withdrawal rate. The following withdrawal rates
were used.
[0060] Run 1--7.5 ft/min
[0061] Run 2--5.7 ft/min
[0062] Run 3--3.4 ft/min
[0063] Run 4--1.0 ft/min
[0064] Run 5--Control--Removed manually at 40 ft/min simulating
commercial withdrawal rates.
[0065] Processing of the HRS Panels is as follows:
2 Immersion Process Step Chemistry Time Temperature Comments
Alkaline Clean Challenge 4 minutes 175.degree. F. 8 oz/gal; 1245 w/
ultrasonics Rinse Tap Water 3 minutes RT Air bubbler on Acid Pickle
Challenge 5 minutes 130.degree. F. 7% by vol 2527 w/ultrasonics
Rinse Tap Water 15 80.degree. F. seconds Rinse Tap Water 30
120.degree. F. seconds MJ Metal MJ 1100 30 RT Lot 03221006
Treatment seconds DFT Range 0.19-0.25 mils Dry 7 minutes
220.degree. F. Cool part 4 minutes 120-130.degree. F. MJ Coating MJ
2110 15 RT Lot 03271006 seconds Dry 8 minutes 200.degree. F.
B-Stage 20 350.degree. F. Blue-M Oven minutes
[0066] Results:
3 Time elapsed to last Drip Run Number (sec) DFT AVG (STDEV) 1 (7.5
ft/min) 17 sec (One 1.03 (0.156) mils drip) 2 (5.7 ft/min) No Drips
1.14 (0.045) mils 3 (3.4 ft/min) No Drips 1.15 (0.054) mils 4 (1.0
ft/min) No Drips 1.20 (0.053) mils 5 (Control) 30 sec of Drips 1.03
(0.152) mils
* * * * *