Note: Descriptions are shown in the official language in which they were submitted.
. .
1042580 , ~
. ~ .
Background of the Invention - -
Electrodeposition as a coating application method involves the
deposition of a film-forming material under the influence of an applied
electrical potential and has become of increasing commercial importance.
Along with the increased use of such methods has been the development of
various compositions which provide more or less satisfactory coatings when
applied in this manner. However, most conventional coating techniques do
not produce commercially usable coatings, and electrodeposition of many
" ~ .
coating materials, even when otherwise successful, is often attended by
various disadvantages such as non-uniform coatings and by poor throw power,
,~ ~ , . . : .
i.e., the ability to coat~areas of the electrode which are remote or
shielded from the other electrode. In addition, the coatings obtained are
in many instances deficient in certain properties essential for the utili-
zation in certain applicatlons for which electrodeposition is o~herwise
suited. In particular, properties such as corrosion resistance and alkali
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resistance are difficult to ac~ ~eve w~th the resins conventionally
employed in electrodeposition processes, and many electrodeposited coat-
ings are subject to discoloration or staining because of chemical changes
associated with electrolytic phenomena at the electrodes and with the
types of resinous materials ordinarily utilized. This is especially true
with the conventional resin vehicles used in electrodeposition processes
which contain polycarboxylic acid resins neutraliæed with a base; these
deposit on the anode and because of their acidic nature tend to be sensi-
tive to common types of corrosive attack, e.g., by salt, alkali, etc.
Further anodic deposition tends to place the uncured coating in proximity
to metal ions evolved at the anode, thereby causing staining with many
coating systems.
The preparation of white or pastel films with high gloss, gloss
retention, and resistance to yellowing is a particular problem in electro-
depositable films.
Description of the Invention
It has now been found that aqueous compositions comprising a
capped or blocked organic polyisocyanate and a quaternary sulfonium group-
conta~ning resin may be electrodeposited on a cathode to produce coatings
with highly desirable properties, including alkali resistance, resistance
to staining, and resistance to yellowing.
The capped or blocked isocyanate which may be employed in the
compositions of the invention may be any isocyanate where the isocyanato
groups have been reacted with a compound so that the resultant capped iso-
cyanate is stable to hydroxyl groups at room temperature but reactive with
hydroxy and/or epoxy groups at elevated temperatures, usually between
about 200F. and about 600F.
- - , , . ., :. :,
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104Z580
In the preparation of the blocked organic polyisocyanate, any
suitable organic polyisocyanate may be used. Representative examples are
the aliphatic compounds such as trimethylene, tetramethylene, penta-
methylene, hexamethylene, 1,2-propylene, 1,2-butylene, 2,3-butylene,
1,3-butylene, ethylidine, and butylidene diisocyanates; the cycloalkylene
compounds such as 1,3-cyclopentane, 1,4-cyclohexane, and 1,2-cyclohexane
diisocyanates; the aromatic compounds such as m-phenylene, p-phenylene,
4,4'-diphenyl, 1,5-naphthalene, and 1,4-naphthalene diisocyanates; the
aliphatic-aromatic compounds such as 4,4'-diphenylene methane, 2,4- or
2,6-tolylene, or mixtures thereof, 4,4'-toluidine, and 1,4-xylylene diiso-
cyanates; the nuclear substituted aromatic compounds such as dianisidine
diisocyanate, 4,4'-diphenylether diisocyanate, and chloro-diphenylene
diisocyanate; the triisocyanates such as triphenyl methane-4,4',4"-
triisocyanate, 1,3,5-triisocyanate benzene, and 2,4,6-triisocyanate tolu-
ene; and the tetra-isocyanates such as 4,4'-diphenyl-dimethyl methane-
2,2'-5,5'-tetraisocyanate; the polymerized polyisocyanates such as tolylene
diisocyanate dimers and trimers, and the like.
In addition, the organic polyisocyanate may be a prepolymer de-
rived from a polyol including polyether polyol or polyester polyol, includ-
ing polyethers which are reacted with excess polyisocyanates to form iso-
cyanate terminated prepolymers may be simple polyols such as glycols, e.g.,
ethylene glycol and propylene glycol, as well as other polyols such as
glycerol, trimethylolpropane, hexanetriol, pentaerythritol, and the like,
as well as mono-ethers such as diethylene glycol, tripropylene glycol and
the like and polyethers, i.e., alkylene oxide condensates of the above.
Among the alkylene oxides that may be condensed with these polyols to form
polyethers are ethylene oxide, propylene oxide, butylene oxide, styrene
oxide, and the like. These are generally called hydroxy-terminated
-- 3 --
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.
. . . : . , : .
: . .: ~ ,
lO~ZS80
polyethers and can be linear or branched. Examples of polyethers include
polyoxyethylene glycol having a molecular weight of 1540, polyoxypropy-
lene glycol having a molecular weight of 1025, polyoxytetramethylene
glycol, polyoxyhexamethylene glycol, polyoxynonamethylene glycol, poly-
oxydecamethylene glycol, polyoxydodecamethylene glycol, and mixtures
thereof~ Other types of polyoxyalkylene glycol ethers can be used. Es-
pecially useful polyether polyols are those derived from reacting polyols
such as ethylene glycol, diethylene glycol, triethylene glycol, 1,4-
butylene glycol, 1,3-butylene glycol, 1,6-hexanediol, and their mixtures;
glycerol, trimethylolethane, trimethylolpropane, 1,2,6-hexanetriol,
pentaerythritol, dipentaerythritol, tripentaerythritol, polypentaerythri-
tol, sorbitol, methyl glucosides, sucrose, and the like with alkylene
oxides such as ethylene oxide, propylene oxide, their mixtures, and the
like.
Any suitable aliphatic aliphatic, cycloaliphatic, or aromatic
alkyl monoalcohol may be used as a blocking agent in accordance with the
present invention, such as, for example, aliphatic alcohols, such as
methyl, ethyl, chloroethyl, propyI, butyl, amyl, hexyl, heptyl, octyl,
nonyl, 3,3,5-trimethylhexanol, decyl, and lauryl alcohols, and the like;
the cycloaliphatic alcohols such as, for example, cyclopentanol, cyclo-
hexanol, and the like, the aromatlc-alkyl alcohols, such as, phenylcar-
binol, methylphenylcarbinol, and the like. Minor amounts of even higher
molecular weight relatively non-volati].e monoalcohols may be used, if de-
sired, to serve as plastici~ers in the coatings provided by thls invention.
¦~ Additional blocking agents include hydroxyl amines such as
ethanolamine and oximes such as methylethyl ketone oxime, acetone oxime,
and cyclohexanone oxlme.
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... . . . . . .
,
~042580
The organic polyisocyanate-blocking agent adduct is formed by
reacting a sufficient quantity of alcohol with the organic polyisocyanate
to insure that no free isocyanate groups are present. The reactlon be-
tween the organic polyisocyanate and the blocking agent is exothermic;
therefore, the polyisocyanate and the blocking agent are preferably ad-
mixed at temperatures no higher than 80C. and, preferably, below 50C.
to minimize the exotherm effect.
As previously stated, the composition employed in the method of
this invention is a coating composition comprising an aqueous dispersion
prepared from a fully capped or blocked organic polyisocyanate with a - -
resin solubilized through a quaternary sulfonium salt group.
Electrodepositable compositions, while referred to as "solu-
bilized", in fact are considered a complex solution, dispersion or sus-
pension, or combination of one or ~.ore of these classes in water which
acts as an electrolyte under the influence of an electric current. While,
no doubt in some circumstances the vehicle resin is in solution, it is
clear that in some instances, and perhaps in most, the vehicle resin is a
dispersion which may be called a molecular dispersion of molecular size
between a colloidal suspension and a true solution.
The sulfonium group-containing resins employed in the composi-
tions of this invention are ungelled, water-dispersible, epoxy resins
having in their molecule at least one 1,2-epoxy group per average mole-
cule and containing chemically-bound quaternary sulfonium base salts, the
quaternary sulfonium base salts preferably being salts of boric acid
and/or an acid having a dissociation constant greater than boric acid,
including organic and inorganic acids. Upon solubilization, at least a
portion of the salt is preferably a salt of an acid having a dissociation
constant greater than about 1 x 10 5 and especially where the resin is
:, ' ' ', ,' . "'. ~ . ,' ': ' .,'
,. . . . . . . .
1042580
oxyalkylene group free. Preferably, the acid i8 an organic, carboxylic
acid. The presently preferred acid is lactic acid. Preferably the resln
contains from about 0.1 to about 35 per cent by weight sulfur and at
least about 1 per cent of said sulfur and preferably about 20 per cent,
more preferably about 50 per cent, and most preferably, substantially all
of the sulfur being in the form of chemically-bound quaternary sulfonium
base salt groups.
The resins within the purview of this invention thus include
(a) epoxy group-containing resins containing, in addition, quaternary sul-
fonium groups which resins may or may not contain chemically-bound boron
or which may be dispersed for electrocoating with or without the addition
of a boron compound and especially boric acid or a precursor thereof; or
(b) epoxy group-containing resins containing, in addition, quaternary
sulfonium base salts of an acld having a dissociation constant greater
than 1 x 10 , which resin may or may not contain chemically-bound boron
or which resin may be disperæed for electrocoating with or without the
addition of a boron compound, and especially boric acid or a precursor
thereof.
The epoxy compound can be any monomeric or polymeric compound
or mixture of compounds having a 1,2-epoxy equivalency greater than 1.0,
that is, in which the average number of 1,2-epoxy groups per molecule is
greater than 1. It is preferred that the epoxy compound be resinous,
that is, a polyepoxide, i.e~, containing more than one epoxy group per
molecule and, preferably, containing free hydroxyl groups. The poly-
epoxide can be any of the well-known epoxides. Examples of these poly-
epoxldes have, for example, been described in U. S. Patents Nos.
2,467,171; 2,615,007; 2,716,123; 3,030,336; 3,053,855; and 3,075,999. A
useful class of polyepoxides are the polyglycidyl ethers of polyphenols,
: , ,
104ZS80
such as Bisphenol A. These may be produced, for example, by etherifi-
cation of a polyphenol with epichlorohydrin or dichlorohydrin in the
presence of an alkali. The phenolic compound may be bis(4-hydroxy-
phenyl)-2,2-propane, 3,4'-dihydroxybenzophenone, bis(4-hydroxyphenol)-
l,l-ethane, bis(4-hydroxyphenyl)l,l-isobutane; bis(4-hydroxytertiary-
butylphenyl)2,2-propane, bis(2-hydroxynaphthyl)methane, 1,5-dihydroxy-
naphthaline, or the like. Another quite useful class of polyepoxides
are produced similarly from novolak resins or similar polyphenol resins.
Also suitable are the similar polyglycidyl ethers of poly-
hydric alcohols which may be derived from such polyhydric alcohols as
ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene
glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerol,
bis(4-hydroxycyclohexyl)2,2-propane, and the like.
There can also be used polyglycidyl esters of polycarboxylic
acids which are produced by the reaction of epichlorohydrin or a similar
epoxy compound with an aliphatic or aromatic polycarboxylic acid, such
as oxalic acid, succinic acid, glutaric acid, terephthalic acid, 2,6-
naphthylene dicarboxylic acid, dimerized linolenic acid, and the like.
Examples are diglycidyl adipate and diglycidyl phthalate.
Also useful are polyepoxides derived from the epoxidation of
an olefinically unsaturated alicyclic compound. Included are diepoxides
comprising in part one or more monoepoxides. These polyepoxides are non-
phenolic and are obtained by epoxidation of alicyclic olefins, for exam-
ple, by oxygen and selected metal catalysts, by perbenzoic acid, by
acetal~ehyde monoperacetate, or by peracetic acid. Among such polyepox-
ides are the epoxyalicyclic ethers and esters, which are well known in
the art.
104Z580
Another clas8 of polyepoxides are tho9e contalning oxyalkylene
groups in the epoxy molecule. Such oxyalkylene groups are typically
groups of the general formula:
r -
t (CH2 c~ m n
where R is hydrogen or alkyl~ preferably lower alkyl (e.g., having 1 to
6 carbon atoms)~ and where~ in most instances~ m is 1 to 4 and n is 2 to
50. Such groups can be pendent to the main molecular chain of the poly-
epoxide or part of the main chain itself. The proportion of oxyalkylene
groups in the polyepoxide depends upon many factors, including the chain
length of the oxyalkylene group, the nature of the epoxy, and the degree
of water solubility desired. Usually the epoxy contains at least about
1 per cent by weight or more~ and preferably 5 per cent or more~ of oxy-
alkylene groups.
Some polyepoxides contain$ng oxyalkylene groups are produced
by reacting some of the epoxy group8 of a polyepoxide, such as the epoxy
resins mentioned above, with a monohydric alcohol containing oxyalkylene
groups. Such monohydric alcohols are conveniently produced by oxyalky-
lating an alcohol, such as methanol, ethanol, or other alkanol, with an
alkylene oxide. Ethylene oxide, 1,2-propylene oxide, and 1,2-butylene
oxide are especially useful alkylene oxides. Other monohydric alcohols
can be, for example, the commercially-available materials known as
Cellosolves and Carbitols, which are monoalkyl ethers of polyalkylene
glycols. The reaction of the monohydric alcohol and the polyepoxide is
generally carried out in the presence of a catalyst. Formic acld, di-
methylethanolamine, diethylethanolamine, N~N-dimethylbenzylamine, and,
in some cases, stannous chloride, are useful for this purpose.
~: :
104ZS80
Similar polyepoxides containing oxyalkylene groups can be
produced by oxyalkylating the epoxy resin by other means, such as by
direct reaction with an alkylene oxide.
The polyepoxide employed to produce the foregoing epoxies~con-
taining oxyalkylene groups should contain a sufficient number of epoxy
groups so that the average number of residual epoxy groups per molecule
remaining in the product after the oxyalkylation is greater than 1Ø
Where oxyalkylene groups are present, the epoxy resin preferably con-
tains from about 1.0 to about 90 per cent or more by weight of oxyalky-
lene groups.
These epoxides which tend to contain unreacted alcohols or
hydroxyl-containing by-products are presently less preferred unless puri-
fied to remove interfering hydroxyl-containing materials.
Other epoxy-containing compounds and resins include nitrogene-
ous diepoxides such as disclosed in U. S. 3,365,471; epoxy resins from
l,l-methylene bis(5-substituted hydantoin), U. S. 3,391,097; bis-imide
containing diepoxides, U. S. 3,450,711; epoxylated aminomethyldiphenyl
oxides, U. S. 3,312,664; heterocyclic N,N'-diglycidyl compounds, U. S.
3,503,979; amino epoxy phosphonates, British Patent 1,172,916; 1,3,5-
triglycidyl isocyanurates, as well as other epoxy-containing materials
known in the art.
The presently preferred class of resins which may be employed
are acrylic polymers containing epoxy groups and hydroxyl groups. Pref-
erably these acrylic polymers are polymers formed by copolymerizing an
unsaturated epoxy-containing monomer, such as, for example, glycidyl
acrylate or methacrylate, a hydroxyl containing unsaturated monomer, and
at least one other unsaturated monomer.
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1042580
Any polymerizable monomeric compound containlng at least one
CH2=C~ group, preferably in terminal position, may be polymerized with
the unsaturated glycidyl compounds. Rxamples of such monomers include:
(1) Monoolefinic and diolefinic hydrocarbons, that i8, mono-
mers containing only atoms of hydrogen and carbon, such as styrene,
alpha-methyl styrene, alpha-ethyl styrene, isobutylene (2-methyl
propene-l), 2-methyl-butene-1, 2-methyl-pentene-1, 2,3-dimethyl-butene-1
2,3-dimethyl-pentene-1, 2,4-dimethyl-pentene-1, 2,3,3,-trimethyl-
butene-l, 2-methyl-heptene-1, 2,3-dimethyl hexene-l, 2,4-dimethyl-
hexene-l, 2,5-dimethyl-hexene-1, 2-methyl-3-ethyl-pentene-1, 2,3,3-
trimethyl-pentene-l, 2,3,4-trimethyl-pentene-1, 2-methyl-octene-1, 2,6-
dimethyl-heptene-l, 2,6-dimethyl-octene-1, 2,3-dimethyl-decene-1,
2-methyl-nonadecene-1, ethylene, propylene, butylene, amylene, hexylene,
butadiene-1,3, isopropene, and the like;
(2) Halogenated monoolefinic and diolefinic hydrocarbons,
that is, monomers containing carbon, hydrogen, and one or more halogen
atoms, such as alpha-chlorostyrene, alpha-bromostyrene, 2,5-dichloro-
styrene, 2,5-dibromostyrene, 3,4-dichlorostyrene, ortho-, meta-, and
para-fluorostyrenes, 2,6-dichlorostyrene, 2,6-difluorostyrene, 3-fluoro-
4-chlorostyrene, 3-chloro-4-fluorostyrene, 2,4,5-trichlorostyrene, di-
chloromonofluorostyrenes, 2-chloropropene, 2-chlorobutene, 2-chloropen-
tene, 2-chlorohexene, 2-chloroheptene, 2-bromobutene, 2-bromoheptene,
2-fluorohexene, 2-flurobutene, 2-iodopropene, 2-iodopentene, 4-bromo-
heptene, 4-chloroheptene, 4-fluoroheptene, cis- and trans-1,2-dichloro-
ethylenes, 1,2-dibromoethylene, 1,2-difluoroethylene, 1,2-diiodoethylene,
chloroethylene (vinyl chloride), l,l-dichloroethylene (vinylidene chlo-
ride)9 bromoethylene, fluoroethylene, iodoethylene, l,l-dibromoethylene,
l,l-fluoroethylene, l,l-diiodoethylene, 1,1,2,2-tetrafluoroethylene, : -
-- 10 --
.. . . .. .. .. . . . . .
. . .
.. , . .~ , . .
" .' ', ' ' ' '' ~ ' ' . :
104Z580
l-chloro-2,2,2-trifluoroethylene, chlorobutadiene, snd other halogenated
diolefinic compounds;
(3) Esters of organic and inorganic acids, such as vinyl
acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl
valarate, vinyl caproate, vinyl enanthate, vinyl benzoate, vinyl tolu- -
ate, vinyl p-chlorobenzoate, vinyl-o-chlorobenzoate, and similar vinyl
halobenzoates, vinyl-p-methoxybenzoate, vinyl-o-methoxybenzoate, vinyl- --
p-ethoxybenzoate, methyl methacrylate, ethyl methacrylate, propyl
methacrylate, butyl methacrylate, amyl methacrylate, hexyl methacrylate,
heptyl methacrylate, octyl methacrylate, decyl methacrylate, methyl -
crotonate, and ethyl tiglate;
Methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl
acrylate, butyl acrylate, isobutyl acrylate, amyl acrylate, hexyl
acrylate, 2-ethylhexyl acrylate, heptyl acrylate, octyl acrylate, 3,5,5-
trimethylhexyl acrylate, decyl acrylate, and dodecyl acrylate;
Isopropenyl acetate, isopropenyl propionate, isopropenyl buty-
rate, isopropenyl isobutyrate, isopropenyl valerate, isopropenyl capro-
ate, isopropenyl enanthate, isopropenyl benzoate, isopropenyl p-chloro-
benzoate, isopropenyl o-chlorobenzoate, isopropenyl o-bromobenzoate,
isopropenyl m-chlorobenzoate, isopropenyl toluate, isopropenyl alpha-
chloroacetate, and isopropenyl alpha-bromopropionate;
Vinyl alpha-chloroacetate, vinyl alpha-bromoacetate, vinyl
alpha-chloropropionate, vinyl alpha-bromopropionate, vinyl alpha-
iodopropionate, vinyl alpha-chlorobutyrate, vinyl alpha-chlorovalerate,
and vinyl alpha-bromovalerate;
Allyl chloride, allyl cyanide, allyl bromide, allyl fluoride,
allyl iodide, allyl chlorocarbonate, allyl nitrate, allyl thiocyanate,
allyl formate, allyl acetate, allyl propionate, allyl butyrate, allyl
-- 11 --
.. .. . . . .
,
1042S80
valerate, allyl caproate, allyl-3,5,5-trimethyl hexoate, allyl benzoate,
allyl acrylate, allyl crotonate, allyl oleate, allyl chloroacetate,
allyl trichloroacetate, allyl chloropropionate, allyl chlorovalerate,
allyl lactate, allyl pyruvate, allyl aminoacetate, allyl acetoacetate,
allyl thioacetate, as well as methallyl esters corresponding to the
above allyl esters, as well as esters from such alkenyl alcohols as
beta-ethyl allyl alcohol, beta-propyl allyl alcohols, l-butene-4-ol,
2-methyl-butene-4-ol, 2(2,2-dimethylpropyl)-1-butene-4-ol, and 1-
pentene-4-ol;
Methyl alpha-chloroacrylate, methyl alpha-bromoacrylate,
methyl alpha-fluoroacrylate, methyl alpha-iodoacrylate ethyl alpha,
chloroacrylate, propyl alpha-chloroacrylate, isopropyl alpha-bromoacry-
late, amyl alpha-chloroacrylatè, octyl alpha-chloroacrylate, 3,5,5-
trimethylhexyl alpha-chloroacrylate, decyl alpha-chloroacrylate, methyl
alpha-cyanoacrylate, ethyl alpha-cyanoacrylate, amyl alpha-cyanoacrylate,
and decyl alpha-cyanoacrylate.
Dimethyl maleate, diethyl maleate, diallyl maleate, dimethyl
fumarate, diethyl fumarate, dimethallyl fumarate, and diethyl glutaconate;
Organic nitriles such as acrylonitrile, methacrylonitrile,
ethacrylonitrile, 3-octenenitrile, crotonitrile, oleonitrile, and the
like.
In carrying out the polymerization reaction, techniques well
known in the art may be employed. A peroxygen type catalyst is ordinar-
ily utilized. Diazo compounds or redox catalyst systems can also be em-
ployed as catalysts.
The preferred hydroxy-containing unsaturated monomers are hy-
droxyalkyl acrylates, for example, hydroxyethyl acrylate or methacrylate,
hydroxypropyl acrylate or methacrylate.
,'. , : . .
.. . . .. .. . . . .
..... . .. . .
104;~580
Another method of producing acrylic polymers which may be
utilized in this invention is to react an acrylic polymer containing
reactive sites, including hydroxy groups, with a epoxy-containing com-
pound such as the diglycidyl ether of Bisphenol A or other polyepoxldes
as enumerated elsewhere herein, to provide an epoxy group-containing
hydroxyl group containing acrylic polymer.
The resins of the invention are formed by reacting the epoxy
compound with a sulfide in the presence of an acid to form quaternary
sulfonium base group-containing resins.
The sulfide employed may be virtually any sulfide which reacts
with epoxy groups and which does not contain interfering groups. For
example, the sulfide may be aliphatic, mixed aliphatic-aromatic,
aralkyl, or cyclic. Examples of ~uch sulfides include diethyl sulfide,
dipropyl sulfide, dibutyl sulfide, diphenyl sulfide, dihexyl sulfide,
ethyl phenyl sulfide, tetramethylene sulfide, pentamethylene sulfide,
thiodiethanol, thiodipropanol, thiodibutanol, and the like.
The acid employed may be virtually any acid which forms a
quaternary sulfonium salt. Preferably the acid is an organic carboxylic
acid. Examples of acids which may be employed are boric acid, formic
acid, lactic acid, acetic acid, propionic acid, butyric acid, hydro- -
chloric acid, phosphoric acid, and sulfuric acid. Preferably, the acid
is an acid having a dissociat~on constant greater than about 1 x 10
The ratio of sulfide to acid is not unduly critical. Since one
mole of acid is utilized to form one mole of sulfonium group, it is pre-
ferred that at least about one mole of acid be present for each mole of
desired sulfide to sulfonium conversion.
The sulfide/acid mixture and the epoxy compound are reacted by
mlxing the components, usually at moderately elevated temperatures such
'' , ' ` ' .
,
104;2580
as 70C. - 110C. A solvent is not necessary, although one is often
used in order to afford better control of the reaction. Aromatic hydro-
carbons, monoalkyl ethers of ethylene glycol, aliphatic alcohols are
suitable solvents. The proportions of the sulfide and the epoxy com-
pound can be varied, and the optimum proportions depend upon the partic- -
ular reactants. Sufficient sulfide should be utilized to provide suffi-
cient quarternary sulfonium groups to solubilize the resin. Ordinarily,
however, from about 1 part to about 50 parts by weight of the sulfide
per 100 parts of epoxy compound is employed. The proportions are usually
chosen with reference to the amount of sulfur, which is typically from
about 0.1 to about 35 per cent, based on the total weight of the sulfide
and the epoxy compound. Since the sulfide salt reacts with the epoxide
groups of the epoxy resin employed, in order to provide an epoxy group-
containing resin, less of the sulfide than the stoichiometric equivalent
of the epoxide groups present is utilized so that the final resin is pro-
vided with one epoxy group per average molecule. When epoxy-free resins ~
are desired, the stoichiometry is adjusted to react all the epoxy groups, -
or the remaining epoxy groups are hydrolyzed or otherwise reacted.
Where it is~desired to incorporate boron into the resin mole-
cule, one method is to incorporate boron by means of an amine borate or
nitrogen-containing boron ester as described in Canadian Patent No.
81,848. The boron compound reacts with available epoxy groups to provide
quaternary ammonium borate groups in the resin molecule.
:
The reaction of the boron compound may be conducted simultane-
ously with sulfonium group formation since the reaction condit:lons for
this reaction are similar.
.
". ' " ' ,: ,
104Z580
The particular reactants, proportions, and reaction conditions
should be chosen in accordance with considerstions well known in the art
so as to avoid gellation of the product during the reaction. For exam-
ple, excessively severe reaction conditions should not be employed.
Similarly, compounds having reactive substituents should not be utilized
along with epoxy compounds with which those substituents might react ad-
versely at the desired conditions.
The product forming the resin of the invention may be cross-
linked to some extent; however, it remains soluble in certain organic
solvents and can be further cured to a hard, thermoset state. It is sig-
nificantly characterized by its epoxy content and chemically-bound
quaternary sulfonium content.
Aqueous compositions containing the above reaction products are
highly useful as coating compositions and can be applied by any conven-
tional method, such as by dipping, brushing, etc. They are, however,
eminently suited to application by electrodeposition.
The resins of the invention are water-dispersible per se; how-
ever, additional acid solubilizing agents may be added if desired.
When epoxy groups are present in the final resin, the presence
of a boron compound in the electrodeposited film is of substantial benefit
in that boron compounds apparently catalyze the cure of the deposited
film, allowing lower cure temperatures and/or harder films. Where the
resin is first prepared without the presence of boron and/or additional
boron is desired when the resin i8 dispersed, a compound of boron may be
added, preferably boric acid or a precursor thereof.
The acid or acidic solubilizing agent is preferably any acid
having a dissociation constant greater than 1 x 10 5. Preferably, the
acid or acidic solubilizing agent should be an organic acid having a
- 15 -
: .
104Z580
dissociation constant greater than about 1 x 10 , the presently pre-
ferred acid being lactic acid. The addition of acid aids in stabilizing
the resin since the epoxy may tend to further polymerize on storage
under highly alkaline conditions. In some cases the acid also helps to
obtain more complete dissolution of the resin. It is also desirable to
electrodeposit these coatings from an acidic or only slightly basic so-
lution (e.g., having a pH between about 3 and about 8.5), and the addi-
tion of acid thus is often useful to achieve the desired pH.
The resin of the invention, when placed in a water-containing
medium such as an electrodeposition, high solids feed concentrate or the -
electrodeposition bath, changes character. Since frequently the boron, ~ ~
if present and chemically bonded, is apparently weakly chemically-bound ~-
in the resin, it is subject to cleavage from the resin molecule and,
while the boron electrodeposits with the resin and is found in the elec-
trodeposited film, the boron may be removed from the water-containing - `
medium in whole or in part by separation means such as electrodialysis
or ultrafiltration in the form of boric acid.
Thus, the resin in aqueous medium can be characterized as a
solubilized resin having chemically-bound quaternary sulfonium base salts
and containing active crosslinking sites such as active hydrogens, pref-
erably hydroxyl and/or epoxy groups.
The resin contains from about 0.1 to about 35 per cent by
weight sulfur, at least about 1 per cent of said sulfur and preferably
about 20 per cent, more preferably 50 per cent, and most preferably sub-
stantially all~ of the sulfur being in the form of chemically-bound qua-
ternary sulfonium base salt groups.
These sulfonium group-containing resins are disclosed in
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104Z580
Canadian Patent No. 981,392. These electrodepositable resins,
while referred to as "solubilized", in fact are considered a complex so-
lution, dispersion, or suspension, or combination of one or more of these
classes in water, which acts as an electrolyte under the influence o an
electric current, while, no doubt, in some instances, or perhaps in most,
the resin is a dispersion which may be called a molecular dispersion of
molecular size between a colloidal suspension and a true solution.
The polyisocyanate-blocking agent adduct is preferably admixed
with the compound containing sulfonium base salt groups in ratios of from
about 0.5 to about 2.0 urethane groups for each reactivetcrosslinking
site, preferably hydroxyl groups.
The capped isocyanate-quaternary sulfonic resin mixture is
electrodeposited on a suitable substrate and cured at elevated tempera-
tures such as from about 250F. to about 600F. At these higher tempera-
tures the reactivity of the hydroxyl group, epoxy group, or other cross-
linking site is such to enable it to break the urethane link of the adduct
and react with the freed NC0 groups to form a substituted urea. The alco-
, .
hol released may either volatilize or remain in the mixture as a plasti-
cizer, depending essentially on its boiling point.
Aqueous compositions containing the above components are highly
useful as coating compositlons particularly suited to application by elec-
trodeposition. It is not always necessary to add a neutralizing agent to
the product in order to obtain a suitable aqueous composition, although
an acid or acidic neutralizing a~ent is more preferably added. It i9 de-
sirable to electrodeposit these coatings from a solution having a pH be-
tween 3 and about 9. The addltion of acid thus is often useful to achieve
the desired pH.
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iO4ZS80
The concentration of the product in water depends upon the
process parameters to be used and is in general not criticai, but ordin-
arily the ma~or proportion of the aqueous composition is water, e.g.,
the composition may contain 1 to 25 per cent by weight of the resin. In
most instances a pigment composition and, if desired, various additives
such as anti-oxidants, surface-active agents, and the like are included.
The pigment composition may be of any conventional type comprising, for
example, one or more pigments such as iron oxides, lead oxides, strontium
chromate, carbon black, titanium dioxide, talc, barium sulfate, cadmium
yellow, cadmium red, chromic yellow, and the like.
In electrodeposition processes employing the aqueous coating
compositions described above, the aqueous composition is placed in contact
with an electrically conductive anode and an electrically conductive
cathode, with the surface to be coated being the cathode. Upon passage
of electric current between the anode and the cathode, while in contact
with the bath containing the coating composition, an adherent film of the
coating composition is deposited on the cathode. This is in contrast to
processes utilizing polycarboxylic acid resins which deposit on the anode,
and many of the advantages described above are in large part attributed
to this cathodic deposition.
-.
The conditions under which the electrodeposition is carried out
are in general similar to those used ln electrodeposition of other types
of coatings. The applied voltage may be varied greatly and can be, for
example, as low as one volt or as high as several thousand volts, although
typically between 50 volts and 500 volts. The current density is usually
between about 1.0 ampere and 15 amperes per square foot and tends to de-
~ crease du-ing electrodeposition.
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1~4Z580
The method of the invention is applicable to the coating of any
electrically conductive substrate, and especially metals such as steel,
aluminum, copper, or the like.
After deposition, the coating is cured at elevated tempera-
tures by any convenient method such as in baking ovens or with banks of
infrared heat lamps. Curing temperatures are preferably from about
350F. to about 425F., although curing temperatures from about 250F.
to about 500F., or even 600F., may be employed if desired.
Illustrating the invention are the following examples which,
however, are not construed as limiting the invention to their details.
All parts and percentages in the examples, as well as throughout this
specification, are by weight unless otherwise specified.
EXAMPLE_I
The following sample illustrates the preparation of a quaternary
sulfonium salt-solubilized acrylic resin in an electrodepositable composi- - ~ -
tion containing a blocked organic polyisocyanate resin in combination therewith.
The acrylic resin was prepared as follows: The monomer feed composition was
as follows:
.
Uonomer Parts by Wei~ht
Methyl methacrylate 1300
Ethyl acrylate 1060
Hydroxyethyl acrylate 600
Styrene 600
Glycidyl methacrylate 440
The above monomer mixture also contained 60 parts of Vaz~ [azo-bis~isobutyro- -
nitrile)] and 120 parts of tertiary dodecyl mercaptan.
*Trade Mark
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104Z580
The polylner was prepared in the reaction flask equipped with a
thermometer, stirrer, reflux condenser, monomer addition means and a continu-
ous nitrogen gas blanket.
Into the reactor were charged 1000 parts of n-butyl Cellosolve.*
The contents of the reactor were heated to 90C. with agitation und&r a -
nitrogen blanket. One-quarter of the total of the monomers containing
inltiator and mercaptan were added over a period of 25 minutes. During this
time an exotherm was noted and the temperature increased.to 120C. After an
additional 25 minutes, the temperature dropped to 114C. and there was added,
over a 4-1/2 hour period, the remaining monomer composition. At the end of - -~
the addition, the temperature had risen to 143C. and the reaction mixture
was held between 130-140C. for an additional 4 hours. The reaction mixture
was th~n cooled and there was added 4 parts of 2,6-ditertiarybutyl paracresol.
The above reaction mixture was then cooled to 93C. and there was ~-
then added a mixture comprising 378 parts of thiodiethanol, 328 parts of
B5 percent lactic acid solution in water and 300 parts of deionized water.
This addition was made over a 2-minute period. The temperature of the reaction
mixture dropped to 80C. The reaction mixture was heated to between 97C.
and 101C. for 45 minutes and there was then added 200 parts of deionized
water.
The analysis of the final resin showed 71.3 percent solids, a
hydroxyl value of 176 and an epoxy value of infinity. The product had a
viscoslty of 54,000 centipoises. This product is identified as Polymer A.
A pigment paste was formed by admixing 210 parts of Polymer A with
600 par~s of titanium dioxide, 6 parts of a cationic surfactant (Aerosol C-61)*
and 75 parts of butyl Cellosolve. This mixture was ground in a laboratory
sand mill for 25 minutes. There was then added an additional 55 parts of
butyl Cellosolve.
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An electrodepositable composition was then formulated as follows:
There were admixed 35.3 parts of the above pigment paste, 51.6 parts of
Polymer A and 9.4 parts (7.5 parts of solids) of a 2-ethylhexanol capped
trifunctional aliphatic isocyanate (Desmodur N-100)*, the solvent present being
methyl-n-butyl ketone, 1.0 part dibutyl tin dilaurate and 625 parts of deionized
water. This provided an approximately 10 percent solids electrodepositable
composition.
The above composition was electrodeposited on zinc phosphate steel
panels at 300 volts for 120 seconds at a bath temperature of 77F. The
resultant electrodeposited film was baked at 350F. for 25 minutes. The film
build was 1.25 mils, the film had a 2H~ pencil hardness and withstood 80 inch
pounds direct impact and showed a slight failure at 80 inch pounds reverse
impact. The panel was highly resistant to acetone rubbing.
Calcium zinc phosphate treated steel panels were electrocoated under
similar conditions and showed a 60 gloss reading of 82-84.
Salt spray panels simllarly electrocoated passed an excess of 312
hours salt spray.
EXAMPLE II
In a manner similar to Example I, the following was prepared from a
.
monomer feed of the following composition:
Monomer Parts by Weight
Ethyl acrylate 2100
Methyl methacrylate 1800
Glycidyl methacrylate 900
2-hydroxyethyl acrylate 900
Styrene 300
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1~4;~580
The above monomer mixture also contained 180 parts of tertiary dodecyl
mercaptan and 90 parts of Vazo [azo-bis(isobutyronitrile)].
After the polymerization was complete, there was added to the
resultant polymer 6 parts of 2,6-ditertiarybutyl ~ cresol.
To the above polymer at 93C. there was added a mixture of 370
parts of thiodiethanol, 310 parts of 85 percent lactic acid and 300 parts of
deionized water. This mixture was added over a 2-minute period. The tempera-
ture of the mixture dropped to 84C. and the mixture was heated, with stirring,
to 98C. for 80 minutes, at which time an additional 360 parts of water were
added.
The analysis of the resultant polymer showed 72.5 percent solids, a
hydroxyl value of 159 and an epoxy value of 5087, with a viscosity of 46,800
centipoises. This polymer is hereinafter identified as Polymer B.
A pigment paste was prepared by admixing 212.2 parts of Polymer B,
196 parts of titanium dioxide, 4 parts of pigmentary silica and 192 parts
of butyl Cellosolve. The above mixture was ground in a Cowles mill to a 7+
grind.
An electrodepositable composition was prepared by admixing 181.5 parts
of Resin B, 130 parts of the above pigment paste and 32.4 parts of a ketoxime
blocked tri-functional aliphatic isocyanate (Desmodur N)(the 32.4 parts of
ketoxime comprising 25.9 parts solids dissolved in methyl-n-butyl ketone.
There was then added 2156 parts of deionized water to provide an approximately
10 percent solids electrodeposition bath having a pH of 7.7 and a conductivity
of 290 mmhos. Zinc phosphate treated steel panels were electrodeposited at
200 volts for 90 seconds at 77F. and baked at 350F. for 20 minutes. The
resultant film build was one mil. The film had a 2H pencil hardness and
withstood 160 inch pounds direct and reverse impact and had a 60 gloss of 72.
11~)4ZS80
In a manner similar to the above examples, various other monomers
as described hereinabove can be utilized or prepared and these interpolymers
can be reacted with other sulfide/acid combinations as disclosed heréinabove
to provide either epoxy containing or epoxy-free sulfonium salt group
solubilized resins, which can be combined with various capped isocyanates as
described above and electrodeposited or coated in a conventional manner to
provlde highly useful coating compositions.
According to the provi~ions of the Patent Statutes, there are
described above the invention and what are now considered to be its best
embodiments. However, within the scope of the appended claims, it is to be
understood that the invention can be practiced otherwise than as specifically
described.
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