PEINTURE A BASE D'EAU A INHIBITEUR DE CORROSION I

WATER-BASED PAINT WITH CORROSION INHIBITOR I

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
Water-based paints contain about 500 to about
2500 parts by weight barium nitrite per million parts by weight
paint formulation including water by excluding pigment. The
disclosure relates to their composition and method preparation.
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Revendications

The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows:
1. In a paint formulation which comprises a dispersion
of crosslinkable organic polymers in a solution of water
and organic amine the improvement wherein said paint
formulation contains about 500 to about 2500 parts by
weight barium nitrite per million parts by weight of
said paint formulation.
2. In a paint formulation which consists essentially
of a dispersion of thermosetting paint binder in an aqueous
solution of organic amine which consists essentially of:
A. 100 parts by weight paint binder resins con-
sisting essentially of
1. about 5 to about 95 parts by weight of a
solution polymer which is a carboxy-function-
al acrylic copolymer that
(a) is at least partially neutralized with
said aqueous solution of organic amine,
(b) is soluble in said aqueous solution,
(c) has average molecular weight (?n) in the
range of about 3,000 to about 20,000 and
(d) has Tg in the range of -15°C to 50°C, and
2. about 5 to about 95 parts by weight of an
emulsion polymer having functionality selected
from carboxy functionality and hydroxy func-
tionality and is an acrylic copolymer that
(a) is essentially insoluble in said aqueous
solution,
(b) has average molecular weight (?n) in the
range of about 3,000 to about 20,000 and
(c) has Tg in the range of -15°C to 50°C, and
38

B. about 15 to about 35 parts by weight of an amino
resin crosslinking agent for said solution polymer
and said emulsion polymer,
the improvement wherein said paint formulation contains
about 500 to about 2500 parts by weight barium nitrite per
million parts by weight of said paint formulation.
3. The paint formulation of claim 1 or 2, which contains
1000 to 2500 parts by weight barium nitrite per million parts
of said paint formulation.
4. The paint formulation of Claim 2, wherein 50 to 65
weight percent of said paint formulation is water and said
dispersion has a pH between 7 and 10.
5. The paint formulation of Claim 2, wherein an equal
volume of an essentially non-ionizable organic solvent for
said solution polymer is substituted for about 5 to about
20 volume percent of said water.
6. The paint formulation of Claim 5, wherein said
organic solvent is an alcohol.
7. In a method of preparing a paint formulation com-
prising a dispersion of crosslinkable organic polymers in a
solution of water and organic amine, the improvement which
comprises the addition of barium nitrite in an amount
providing in said paint formulation a barium nitrite con-
centration in the range of about 500 to about 2500 parts
by weight barium nitrite per million parts by weight of
said paint formulation including water.
39

Description

~ 3
Water-based paints of the prior art ha~e included
"solution paints" and "emulsion (or latex) paints" with
distinction being made with reference to the manner in which
the sole or principal binder is dispersed within the aqueous
medium. ~Iybrid, water-based paints are now available which
include both a solution polymer and a latex.
Many conventional water-based industrial paints,
especially those based on synthetic polymer latexes, are
corrosive to mild steel. Introduction of these paints into
automotive assembly plants currently requires that existing
mild steel paint handling facilities be replaced by stainless
steel, plastic or other corrosion resistant materials.
Obviously, the development of a non-corrosive, water-based
paint is a more attractive alternative than replacing such
equipment but formulation of a non-corrosive, water-based
paint, especially an emulsion or hybrid paint, presents pro-
blems without any obvious solution.
Ideally, a water-based paint should be formulated
to provide first the paint desired and this formulation
supplemented with an additive that (l) will render the form-
ulation non-corrosive, (2) will not coagulate the latex, and
(3) will not affect any property of the paint deleteriously
either before during or after its application to a substrate
~r require reformulation.
The corrosion of mild steel depends on the ratio
of aggressive ion concentration to inhibitor ion concentration.
Dependiny on this ratio, three conditions may exist: general
corrosion; localized corrosion in the form of pitting or
crevice corrosion, and complete immunity, i.e., no corrosion.
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Immunity can be achieved by decreasing the aggressive ion
concentration and by increasing inhibitor ion concentration.
In ~h~ water-based enamels based on synthetic polymer
latexes, the most significant aggressive ions are usually
free sulfate ions. The sulfate ion is present in the latex
as one of the decomposition products o~ the commonly used
persulfate initiator, or as a residue from addition oE FeS04
as one component of an activated initiator system.
There are a great many corrosion inhibiting additives
for aqueous systems. The details of the mechanisms of pro~
tection and the classification of corrosion inhibitors are
described in detail in "Corrosion Inhibitors", edited by C.C.
Nathan, National Association o~ Corrosion Engineers, Houston,
Texas (1973) and in "Electrodeposition and CorrOsiQn Processes",
by J. M. West, D. Van Nostrand Co., Ltd., London, England
(1965).
It has been found, however, that conventional add-
itive approaches to control of paint corrosivity are not sat-
isfactory in application to water-based enamels, and specific-
ally in application to hybrid, water-based enamels. Con-
ven$ional additives which have been tried and found wanting
for this purpose include ben20ate, silicate, chromate, phosphate r : : .
nitrite, bicarbonate, and sulfite salts, organic amines,
polyols, benzotriazole and related heterocyclic compounds, and
mixtures of these and various other known inh:ibitors.
Even when incorporated at the 0.5 weight percent
level~ adsorptive inhibitors such as hexamethylene diamine and
morpholine do not stop the corrosion of mild steel in a typical
hybrid enamel formulation. Cathodic inhibitors such as
bicarbonates have been found simîlarly ineffective.
Anodic inhibitors such as sodium nitrite and potassium
chromate inhibit corrosion but are not acceptable as paint
additives. Both of these inhibit the cure of a thermosetting
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~ 6283
paint. Potassium chromate cannot be used in paints because
of the resultant colorin~.
Ammonium nitrite does not inhibit paint cure and does
inhibit corrosion but it is unstable in solution and soon
decomposes to form water and nitrogen gas.
Amine nitrites are also unsuitable when used alone~
For example, dicyclohexylaminenitrite, at the 0.5 weight per-
cent level, inhibits corrosion but interferes with cure and
- causes white paints to turn yellow. The latter problems are
avoided at lower concentrations, but the corrosion protection
afforded is not adequate when the concentration drops to a
level where the others are obtained.
It now has been discovered that limited amounts of
barium nitrite, unlike other nitrites, effectively inhibit
corrosion from water-based paints of the type comprising a
dispersion of crosslinkable organic polymers in a solution
of water and organic amine, to which they are added without
significant effect on curing or other properties of the
paint. Barium nitrite may be used advantageously in com-
bination with amine nitrites. These additives may be usedwith any of the principal types of water-based industrial
paints, i.e., resin solutions, resin emulsions and resin
emulsion-resin solution hybrids although the corrosion
problem is most severe and the value of the additive is
greatest with the emulsions and emulsion-solutions that
they customarily contain corrosion inducing sulfate ions.
Barium nitrite is not fugitive from solution in the
manner of ammonium nitrite. The corrosion protection pro-
vided by barium nitrite is equivalent to that afforded by
3G alkali metal nitrites. ~nlike the alkali metal nitrites,
barium nitrite does not inhibit crosslinking of the paint
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;2133
film in the curing ovenO
sarium nitrite is employed in an amount that will provide
a concentration of NO2 in the paint formulation in the range
between 200 parts per million, hereinafter referred to as
ppm, and 1000 ppm (basis paint formulation weight excluding
any pigment but including water - this basis is used through-
out this specification wherever the term ppm appears). This
is equivalent to about 500 to about 2500 ppm of Ba(NO2)2.
In a pre~erred embodiment about 1000 to about 2500 ppm,
Ba(NO2)2 are used~
This invention is applicable to any water-based
paints but its advantages are most pronounced with emulsion
(synthetic latex) paints, i.e., solely emulsion paints and
emulsion-solution hybrid paints, which are prepared usin~
persulfate initiators or initiator systems which include
sulfate ion yielding components, e.g., FeSO4.
To avoid endless and useless repetition, this inven-
tion will be illustrated by its use in emulsion-solution
hybrid enamels. The preferred water-hased enamels are those
disclosed in U.K. Patent No. 1,496,198.
The hybrid, water-based paint compositions preferred
for use in this invention employ in combination a low mole-
cular weight emulsion polymer and a low molecular weight
solution polymer with the latter being present in an amount
sufficient to contribute significantly to the composition of
the polymeric binder, i.e., at least about 5 weight percent of
, .,~ :, .: ~:
this polymeric combination. They differ from the conventional
emul8ion type paints employing a water-soluble thickener poly-
mer in at least three compositional respects irrespective of
chemical functionality, namely (1) the emulsion polymers
have significantly lower molecular weights, (2) the solution
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1~7~2~33
polymers have significantly lower molecular weights, and
(3) the solution polymers are employed in significantly
higher concentrations than are the water-soluble thickener
polymers.
More specifically, the hybrid paint compositions us~d
in thîs invention, exclusive of optional components such as
pi~ments, particulate ~illers and catalysts, have a li~uid
continuous aqueous phase. About 30 to about 50% by weight
of this phase, exclusive of the a~orecited optional com-
ponents, is made up of a mixture of (a) an amino resin
crosslinking agent; (b) a mixture of at least two copolymers
of acxylic monome~s; and (cl an amine. The balance is water
or, in certain embodiments, water and an organic solvent.
The mixture of copolymers comprises (1) about 5 to about
95, preferably about 5 to about 50, and most preferably about
10 to about 30,lparts by weight of a "solution polymer", i.e.,
a carboxy-functioIlal copolymer of acrylic monomers that ~i)
is at least partially neutralized with an ~mine, (ii) is
soluble in said aqueous phase, (iii) has average molecular
weight (Mn) in the range of about 3,000 to about 20,000
and (iv) has Tg in the range of -15 to 50C., and (2) .
about 5 to about 95, pxeferably abo ut 50 to about 95 and
most preerably about 50 to about 70 parts by weight of an
"emu]sion polymer", i.e., a copolymer of acrylic monomers
have carboxy, hydroxy or carboxy and hydroxy ~unctionality
that (i) is essentially insoluble in ~aid continuolls phase,
(ii3 has average molecular weight (Mn) in the range of
about 2,000 to about 20,000 and (iii) has Tg of -15 to
50C. The amino resin cross~inking agent is present in an
amount in the range o~ about 15 to about 35 weigh~ percent .
of the sum of the weighk of solution polymer and the weight ~.

1~762~33
of emulsion polymer. The amine is a water~soluble amine
and is present in an amount sufficient to solubilize the
solution polymer in the aqueous phase at a pH range of
about 7.1 to about 8.5. In certain embodiments, herein
a~ter illustrated, these hybrid compositions include
organic cosolvents while in other embodiments such solvents
are not presentO
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83
When applied to the substrate to be coated by
spraying, these water-based paints including pigments,
particulate fillers, and catalysts, if any, contain between
about 50 and about 65% by weight water or in those embodiments
wherein such solvents are used, water and organic cosolvents.
_reparation of Water-Based Paint
A number of methods can be used to prepare the
water-based paints preferred for use in this invention.
In a first general method, at least one of -the
polymers, usually the solution polymer, is polymerized in
solution in a water miscible or dilutable organic solvent
while the other polymer, usually the emulsion polymer, is
prepared by an emulsion polymerization in water. The
resultant water-based paint will contain a conventional,
essentially non-reactive, water-miscible or dilutable organic
paint solvent. The concentration of organic solvent in such
paints will be at least about 5% by volume of the volatile
phase, i.e., organic solvent and water, and preferably in the
range of about 10 to about 20 volume percent of the ~olatile
phase.
In a second general method both the solution polymer
and the emulsion polymer are prepared by emulsion polymerization
in water. The paints thus prepared are prepared without
organic solvents~and thus employed free of same. Organic
solvents in the amounts used in the first general method may
be added to the dispersion, i desired.
A third general method is the same as the first
general method except for the difference that in carrying out
the emulsion polymerization the suractant, i.e., surface
active agent or emulsifier, is replaced by a solutlon polymer
hereinafter more fully described.
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3L~76i~83
A fourth general method is the same as the second
general method except for the difference that in carrying out
one or both, preferably both, of the emulsion polymeriza-tions
the surfactant is replaced by a solution polymer hereinafter
more fully described.
The advantage provided by the third and fourth
general methods is that elimination of the conventional
surfactant eliminates the problem o~ incompatibility and
water sensitivity associated with the use of surfactants.
Polymer Composition Water-Based Paints
(A) The solution polymer in these paints has
carboxy functionality and may also have hydroxy functionality
and/or amide functionality. These polymers contain about 5 -'
to about 30 mole percent of acrylic or methacrylic acid and
70 to 95 mole percent of olefinically unsaturated monomers
copolymerizable with such acid component. Preferably, these
other olefinically unsaturated monomers are monoacrylates or ~',''' '
monomethacrylates. In the embodiment wherein the,primary
solution polymer has only carboxy functionality, these are
preferably esters of acrylic acid or methacrylic acid and a
-Cl - C8 monohydric alcohol. ~C8 - C12 monovinyl hydrocarbons
such as styrene, alpha methyl styrene, t-butyl styrene, and
vinyl toluene may comprise up to about 30 mole percent of
such polymer. Vinyl monomers such as vinyl chloride,
acrylonitrile, methacrylonitrile and vinyl acetate may be,
included in the copolymer as modifying monomers. However,
when employed, these modifying monomers should constitute
only between about O and about 33, preferably 0 to about 15,
mole percent of such polymer. In the embodiment wherein the , ' ,
solution polymer has both carboxy functionality and hydroxy
functionality, the copolymer contalns about 5 to about 25
mole percent of acrylic or methacrylic acid, about 5 to about ,
25 mole percent of a hydroxyalkylacrylate or methacrylate,
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,

~ L~7~2~3
e.g., hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxy-
ethyl methacrylate or hydroxypropyl methacrylate, and a
remainder of the same monofunctional monomers as set forth
above for the solely carboxy-functional polymer. In still
another embodiment, the polymer has amide functionality in
addition to carboxy functionality. Such-a polymer contains
about 5 to about 25 mole percent acrylic acid or methacrylic
acid, about 5 to about 25 mole percent of acrylamide, meth- -
acrylamide~ N-methylolacrylamide, N-methylolmethacrylamide, or
the alkyl ether of a me~hylolacrylamide or a methylolmeth-
acrylamide, e.g.~ N~isobutoxymethylolacrylamide, with the remainder
of the same monofunctional monomers as set forth above for the
solely carboxy-~unctional polymer. A portion o~ the amide
functional monomers may be replaced with an equimolar amount
of one of the aforementioned hydroxyacrylates or hydroxy-
methacrylates.
Other monomers not heretofore mentioned may be used
in these polymers if used in limited concentrations. These
include 2-acrylamide-2-methylpropanesulfonic acid and
methacryloyloxyethylphosphate, which may comprise up to about
3% of such polymer.
(B) The emulsion polymer in these paints has
caxboxy functionality, hydroxy functionality or carboxy and
hydroxy functionality. These polym~rs contain 0 to 15 mole
percent acrylic acid or methacrylic acid, preferably 0 to 10
mole percent, and 85 to 100 mole percent of other olefinically
unsaturated monomers that are copolymerizable with each other
and with the acid component when the latter is used. Such
other olefinically unsaturated monomers are the same in type
and of the same percentage distribution range as those hereto-
fore disclosed for the solution polymer with the exception of
the acid monomers content above noted.
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~7~83
In -those embodiments, wherein both the solution
polymer and the emulsion polymer have hydroxy funtionality
and carboxy functionality, it is preferred to have a greater
concentration of carboxy functionality on the solution polymer
relative to the emulsion polymer and a greater concentration
of the hydroxy functionality on ~he emulsion polymer relative
to the solution polymer.
Thus, the combinations involved include ~a) a
carhoxy-functional solution polymer and a hydroxy-functional
emulsion polymer, (b) a carboxy-functional solution polymer
and a car~oxy-functional emulsion polymer, (c) a carboxy-
functional solution polymer and a carboxy-functional, hydroxy-
functional emulsion polymer r (d) a carboxy-functional and
hydroxy-functional solution polymer and a hydroxy-functional
emulsion polymer, (e) a carboxy-functional, hydroxy-functional
solution polymer and a carboxy-funct:ional and hydroxy-
functional emulsion polymer, (f) a carboxy-functional and
amide-functional solution polymer and a hydroxy-functional
emulsion polymer, (g) a carboxy-functional and amide- ```
functional solution polymer and a carboxy-functional emulsion
polymer, (h) a carboxy-functional and amide-functional solution
polymer and a carboxy-functional and hydroxy-functional
emulsion polymeir, (i) a carboxy-functional, hydroxy-functional,
and amide-functional solution polymer and a hydroxy-functional
emulsion polymer, (j) a carbox~-functional, hydroxy-functional,
amide-functional solution polymer and a carboxy-functional
emulsion polymer, and (k) a carboxy-functional, hydroxy-
functional, amide-functional solution polymer and a carboxy-
functional, hydroxy-functional emulsion polymer. Amide
functlonality may also be incorporated into the emulsion
polymer but this is more difficult to achieve efficiently
than in the solution polymer, particularly in the case of
modi~ied amide functionality, e.g., N-methylolacrylamide
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33
(C) The amino resin crosslinking agent, may be
and is hereafter illustra-ted as a conventional amino resin
crosslinking agent of the type long in use as a crosslinking
agent in acrylic enamels, e.g., melamine-formaldehyde resins
and urea-formaldehyde resins.
Detailed Description o~ First General Method ~or
Preparing Water-Based Paints Described Herein
A. Preparation of Solution Copolymer
In preparing the water-soluble copolymer, the
~unctional monomers and the remaining monoethylenically
unsaturated monomers are mixed and reacted ~y conven-tional
free radical initiated polymerization in such proportions
as to obtain the copolymer desired. A large number of
free radical initiators are known to the art and are
suitable for this purpose. These include benzoyl peroxide;
t-butyl peroctoate; t-butyl perbenzoate; lauryl peroxide;
t-butyl-hydroxy peroxide; acetylcyclohexane sulfonyl peroxide;
diisobutyryl peroxide; di-(2-ethylhexyl) peroxydicarbonate;
diisopropyl peroxydicarbonate; t-butylperoxypivalate; decanoyl
peroxide; azobis(2-methyl propionitrile); e~c. ~he polymer-
ization is carried out in solution using a solvent which is
miscible or dilutable with water. The solvent concentration
at this stage is ordinarily about 30 to 60 weight percent o~
the polymerization solution. The polymeri~ation is carried
~out at a temperature between about 45C. and the reflux
temperature of the reaction mixture. Included among the
suitable solvents are n-propyl alcohol, isopropyl alcohol,
dioxane, ethylene glycol monomethyl ether, ethylene glycol
monoethyl ether, ethylene glycol monobutyl ether, diethylene
3~ glycol monobutyl ether, diethylene glycol monomethyl ether
acetate, diethylene glycol monoethyl ether, diethylene glycol
monobutyl ether, ethylene glycol monomethyl ether acetate,
diethylene glycol monoethyl ether acetate, etc. The copolymer
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1Q17~ii;Z 83
thus obtained is neutralized with amine to a pH of about 6
to 10 and diluted to desired ~iscosity with water or organic
solvent.
B. Preparation of Emulsion Copolymer
In preparing the emulsion copolymer, the functional
monomers are mixed and reacted by conventional free-radical
initiated polymerization in aqueous emulsion to obtain the
copolymer desired.
Conventional surfactants, chain transfer agents, and
initiators are employed in the emulsion polymerization. The
monomer charge is usually emulsified by one or more micello-
forming compounds composed of a hydrophobic part, such as a
hydrocarbon group containing six or more carbon atoms, and a
hydrophilic part, such as hydroxyl groups, alkali metal,
ammonium c~rboxylate groups, sulfonate groups, phosphate or
sulfate partial ester groups, or a polyether chain. Exemplary
emulsifying agents include alkali metal sulfonates of styrene,
naphthalene, decyl benzene, and dodecyl benæene; sodium
dodecyl sulfate; sodium stearate; sodium oleate; the sodium
alkyl aryl polyether sulfates and phosphates; the ethylene
oxide condensates of long chain fatty acids, alcohols, and
mercapta~s, and the alkali metal salts of resin acids. These
materials a~d the techni~les of their employment in emulsion
polymerization are well known.
As will be disclosed later herein, the solution
polymer may also be prepared by emulsion polymerization. In
such preparation, the resultant acid~~unctional copolymer
latex is converted to a polymer solution by the addition of
an appropriate b~ase, usually ammonia or an organic amine.
There are, however, different needs involved in the after-
preparation employment of the emulsion polymer that is used
as such in formulation of paint and the solution polymer which :
although prepared by emulsion polymerization is subsequently
converted to a solution polymer and used as such. These needs --
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should be taken into consideration in the preparation procedure.
In the use ~f emulsion polymerization to produce
a solution polymer, there is no need for the resulting latex
to be stable under conditions different from those ensuing
at the end of the polymerization process since the latex no
longer exists, as such, a~ter the polymer goes into solution
- upon neutralization. To facilitate such conversion to solution
polymers, polymers prepared by emulsion polymerization for use
as solution polymers ordinarily contain a higher concentration
of carboxyl groups and a lower concentration of deci~ed1y
hydrophobic monomers, e.g., 2-ethylhexyl acrylate, relative
to the corresponding concentrations in the polymers prepared
by emulsion polymerization for use as such.
In contrast, latices which are used as such in
the formulation of paint are required to remain essentially
as stable latices throughout the processes of polymerization,
paint formulation, and product distribution and use. This
implies a requirement of stability, i.e., freedom from
coagulum formation through time and under a variety of pM
conditions, solvent environment, etc. These requirements
are best met, and hence it is preferred to use, an alkali
metal or ammonium persulfate either as the sole polymerization
initiator, or as one constituent of a mixed initiator system.
In those embodiments in ~hich con~entional surfactants,
are used, a combination of anionic and nonionic surfactants
provide a more stable latex. Such surfactant mixtures are
well known in the art.
C; Formulation of Paint
The polymer solution and th0 polymer late~ pre-
pared according to the aforedescribed procedures are subse~-
uently conyerted into a paint using conventional paint form-
ulation techniques. Typically, a mill base is prepared which
.
comprise~ the bulk of the pigment and/or particulate filler
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o~ the paint formulation. The mill ~ase is "let down" i.e.,
blended with the remaining polymeric and liquid constituents
of the final formulation. ~ mill base, prepared by con-
ventional sand grinding, ball milling, or pebble milling
generally comprises all or a part of the water soluble resin,
pigments, organic cosolvents/ and ~ay also comprise a quantity
of amine in excess of that required to solubilize the solution
polymer. To complete the paint, the polymer late~ which has
been neutralized to a pH range of 5.0 to 10, preferably 5
to 9, is added with mild agitation to the balance of the water
required in the total formulation. The balance of the water-
soluble resin, crosslinking agent, and millbase are added
slowly with agitation. Additional quantities of pigment may
be added subsequently as slurries in organic solvents or as
separate mill bases to adjust the color as desired. The
viscosity of the finished paint is determined and adjusted
as required to obtain desired application properties. I -
Alternately, all or a portion of the (preferably
neutralize~ polymer latex, water, organic cosolvent, and -
amine may be added to the solution polymer and pigments prior
to ball milling r sand grinding, or pebble milling. This pro~
ceaure is advantayeo~sly employed to reduce the viscosity of
mill bases prepared using the solution polymers o~ relatively
high moIecular weight.
The water-based paints used as transparent overcoats
in the process of this invention are formulated in the same
way as the pigmented basecoats, save only for the omission
of pigments or substantial reduction in the quantity thereof~ -
D. Use of Organic Amines
Organic amines are used to neutralize carboxyl
groups on the solution polymer and hence to render it soluble
in the aqueous dispersion. They are also used to maintain
the p~ of the finished paint formulation above about 7, e.g.,
in the range o~ 7-10, preferably between 7 and 9.5, and with -~
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~762~33
certain pigments such as aluminum flakes preferably bet~leen
7 and 9, to pr:event premature reaction of the functional groups
on the acrylic copolymer with the amino resin crosslinking
agent. Those skilled in the art will be aware that in certain
embodiments the paint dispersion can be made up at a pH
outside the p~ range for application and later adjusted to
the desired pH shortly before it is applied. A portion oE the
amine, e.gO, preferably between about 60 and 100% of the
amount chemically equivalent to the carboxyl functionality of
the polymer is added to the solution polymer directly. Ad-
vantageously, a small additional portion of amine is used to
raise the pH of the emulsion polymer to about 5 to about 10,
preferably 5 to 9, prior to finishing the paint formulation
so that the mill base is not subjected to the low pH environ-
ment of the polymer latex ~pH about 2.5). Suitable amine~
are amines (1) which are soluble in the aqueous medium of
the paint, (2) that ionize suficiently in such aqueous medium
to solubilize the solution polymer, (3) that ionize sufficiently
in such a~ueous medium when employed in suitable amounts -to
provide the paint dispersion with a pH of at least about 7,
preferably 7.2 or higher, and thereby keep the rate of reaction
between reactive groups of the amino resin (crosslinking agent)
negligihle prior to curing and (4) that allow Eor rapid curing
of the enamel upon heating~ Suitable amines include alkyl,
alkanol and aryl primary, secondary and tertiary amines.
Preferred are secondary and tertiaryalkyl and alkanol amines
having a boiling point within the range of 80 - 200C. By
way of example, these include N,N-dimethyl ethanolamine, ~ -
N,N-diethylethanolamine, isopropanolamine, morpholine, N-meth-
ylmorpholine, N-ethylmorpholine, N-methylethanolamine, 2,6-
dimethylmorpholine, methoxypropylamine, and 2-amino-2-methyl-
l-propanol.
E. Catalysts
Catalysts for the curing of resins described herein
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~62~33
are not norinally required to obtain satisfactory film prop-
erties. If desired, however, for purposes of lowering the
film baking temperature or of further improving cured film
propertles, strong acid catalysts can be employed in an
amount not in excess o~ 3~ by weight of the total ~inished
paint formulation. Said strong acid catalysts may be intro-
duced either as copolymerizable species incorporated in one
or both acrylic copolymers, e.g., 2-acrylamide-2-methyl-
propanesulfonic acid, or as a non-polymerizable additive,
- e.g~, p-toluenesulfonic acid. It is generally preferred not
to add such catalysts, however, as th~y may tend to increase
the water sensitivity of the cured film and may deleteriously
affect storage stability of the liquid paint.
F. Cosolvents
In those embodiments wherein a volatile organic
solvent is employed as a cosolvent, i.e., solution of the
solution polymer also being affected by the use of a water-
soluble amine, the following solvents are suitable for this
use include: n-propyl alcohol, isopropyl alcohol, butanol,
2-butoxyethanol, 2(2-butoxy)ethoxyethanol, n-octyl alcohol,
dioxane, ethylene glycol monomethyl ether, ethylene ~lycol
monoethyl ether, ethylene glycol monobutyl ether, diethylene
glycol monomethyl ether, diethylene glycol monoethyl ether,
diethylene glycol monoethyl ether, diethylene glycol mono-
butyl ether, ethylene ~lycol monomethyl ether acetate,
diethylene glycol monoethyl ether acetate, etc.
'~.
Detailed Description of Second General Method
For Preparing Water-Based Paints Described ~Ierein
A. Preparation of Solution Polymer
In this method, the water-soluble copolymer is
produced by emulsion polymerization. The functional monomers
are mixed and reacted by conventional free-radical initiated
polymerization in aqueous emulsion to obtain the copolymer
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;Zg33
desired. The resulting acid-functional copolymer latex is
converted to a polymer solution by the addition of an app-
ropriate base, usually ammonia or an organic amine.
Conventional surfactants, chain transfer agents,
and initiators are employed in the emulsion polymerization.
The monomer charge is usually emulsified by one or more micel-
leforming compounds composed of a hydrophobic part, such as a
hydrocarbon group containing six or more carbon atoms, and a
~ydrophilic part, such as hydroxyl group, alkali metal or
ammonium carboxylate groups, phosphate or sulfate partial
ester groups, sulfonate groups, or a polyether chain. Ex-
emplary emulsifying agents include alkali metal sulfonates
of styrene, naphthalene, decyl benzene and dodecyl benzene;
sodium dodecyl sulfate; sodium stearate; sodium oleate, the
t sodium alkyl aryl polyether or sul~ates and phosphates; the
ethylene oxide condensates of long chain fatty acids, alco-
hols, and mercaptans, and the alkali metal salts of rosin
acids. These materials and the techniques of their employment
in emulsion formation and maintenance are well known. As
previously pointed out, however, when emulsion polymerization
is used to produce a solution polymer, there is no need for
the resulting latex to be stable under conditions different
from those ensuing at the end of the polymerization process
since the latex no longer exists as such after the polymer goes
into solution upon neutralization. To facilitate such con-
version to solution polymers, polymers prepared by emulsion
polymerization for use as a solution polymer ordinarily contain
a higher concentration of carboxyl groups and a lower con-
centration of decidedly hydrophilic monomers, e.g.,
2~ethylhexyl acrylate, relative to the corresponding con-
centrations in the polymexs prepared for use as emulsion poly-
mers. Further, the teaching hereinbefore set forth with
respect to the choice of initiators when preparing the latter,
i.e., using an alkali metal or ammonium persulfate either as
the sole polymerization initiator or as one constituent of a
19

~1~76Z~33
mixed initiator s~s-tem -to avoid coaglum formation through time
and under a variety of pH conditions, solven-t environment, etc.,
is applicable where -the polymer is to be converted to a
solution polymer. Such initiators may be used when preparing
the solution polymer by emulsion polymerization but conventional
peroxide initiators are quite suitable for this. Hence, this
method offers an advantage, in this respect, in that the
concentration of ionic inorganic contaminants, e.g., sulfate
ions, in the paint formulation is reduced. A chain transfer
agent or mixture of chain transfer agents may be added to the
~eaction medium to limit the molecular weight of the polymer,
such chain trans~er agents are generally mercaptans such as
dodecanothiol, benzene-thiol, l-octanethiol, pentanethiol and
butanethiol. These are conventional materials employed in a
conventional manner. The polymerization initiator is composed
of one or more water-soluble, free-radical-generating species
such as hydrogen pero~ide or the sodium, potassium or ammonium ~ -
persulfates, perbo~rates, peracetates, percarbonates and the like.
As is well known in the art, these initiators may be associated
with activating systems such as re~ox system which may in-
corporate mild reducing agents, such as sulfites and thio-
sul~ites and redox reaction promoters such as transition metal
ions. ~s hereinbefore mentioned, however, it is desira~le to
maintain a low concentration of non-polymeric ionic species
in the finished paint formulation in order that the cured
paint film may have optimium resistance to water. Hence it
is preferred to use a minimum concentration of such optional
inor~anic salts as ferrous sulfate, sodium bisulfate, and the
like. Those skilled in the art will be aware that other
emulsifying agents, polymerization initiators and chain
transfer agents may be used which are compatible with the
polymerization system herein required and with the attainment
- 20

~6;Z~3
of acceptable curecl paint film properties.
B. Preparation o~ Emulsion Copolymer
The emulsion copolymer may be prepared using the
same procedures hereinbefore recited for preparation of the
emulsion copolymer in part ~. of the first general method.
C. Formulation of Paint
The polymer solution and the polymer latex prepared
according to the aforedescribed procedures may be subsequently
converted into a paint using the same procedures hereinbefore
recited for formulation of paint in part C. of the first
general method. ~
D. Use of Organic ~mines .
The use of organic amines and amines which are
suitable for such use are the same for this general method
as hereinbefore described in detail in part D. of the first
general method.
E. Catalysts ~.
The use of catalysts and catalysts which are suitable
for curing the reslns hereinbefore described and hereinafter
illustrated are the same for this general method as hereinbefore
described in detail in part D. of the first general method.
F. Cosolvents ..
The use and choice of cosolvents for use with this
general method ma~ be the same as hereinbefore described in
part F. of the first yeneral method.
Detailed Description o~ Third General M~thod
For Preparing Water-Based Paints Described Herein
.
The third general method for preparing the paints
disclosed herein is identical with the first general method
hereinbefore described in detail except for the difference
that al~ or a part of the surfactant, i.e., surface active
, ' :
- 21
..

1~7~283
a~ent or emulsifier, employed in preparing the emulsion
polymer, is replaced with a stabilizer polymer, that is id-
entical with or similar to, the solution polymer heretofore
described in the first and second general methods and employed
as a primary constituent of the paints described herein.
The stabilizer polymer of the third and fourth
general methods is carboxy functional and soluble in the
aqueous phase of these paint dispersions and is either the
same as the primary solution polymer, heretofore discussed,
or similar to such solution polymer and compati~le with the
system. The average molecular weight (Mn) of the stabilizer
polymer may be the same as that of the primary solution
polymer, i.e., between 3,000 and 20,000 but advisedly is of
lower molecular weight than the primary solution polymer.
Preerably, the average molecular weight o this third co-
polymer is in the range of about 3,000 to about 8,000. Its
Tg is in the range of -15 - 50C. When the stabilizer polymer
is used in lieu of the surfactant to prepare either the
solution polymer or the emulsion polymer, it is present in a
concentration in the range of about 0~2 to about 10, preerably
about 0.5 to about ~, weight percent based on the wei~ht of
polymer to be prepared.
The stabilizer polymer may be prepared by any o
several methods, including (1) the method used to prepare the
solution polymer of the first general method of paint pre-
paration, i.e., polymerization in solution in a water miscible
or dilutable or~anic solvent; (2) the method used to prepare
the solution polymer or the second general method of paint
preparation, i.e., emulsion polymerization using an emulsifier
or auractant; (3) emulsion polymerization using in lieu of a
surfactant a small amount o the intended polymer rom a
previous preparation; and (4) a method of emulsion polymeri-
zation described hereinafter which employs neither surfactant
22
:.
. . -

~(~7~ 33
nor a water soluble polymer in lieu thereof. In the latter,
conventional chain transfer agents and polymerization in-
iators are used as described hereinbefore for the preparation
of a solution'polymer by emulsion polymerization. A mixture
of monomers includin~ carboxyfunctional monomers and a chain
transfer agent is added slowly to a stir-red mixture of in-
itiator and water maintained at a suitable reaction temp-
erature, e.g., between 45 and 95C. It is preferred to add
simultaneously with the monomer mixture an additional quantity
of polymerization initiator to sustain a sufficient initiator
concentration throughout the polymerization. The polymer latex
so obtained is filtered and neutrali~ed with ammonia or water-
soluble amine to render it water soluble.
Detailed Description of Fourth General Method
For Preparing Paints Described Herein
The fourth general method for preparin~ the paints
disclosed herein is identical wi.th the second general method
hereinbefore described in detail except for the difference
that all or a part of the surfactant used to prepare the
.
solution polymer, the emulsion polymer or, preferab~y, both
the solution polymer and the emulsion polymer is replaced by
a stabilizer polymer, such as heretofore described in detail
' in the description of the third ~eneral method.
This invention will be more fully understoocl from
the following illustrative examples:
Example 1
A, Preparation of hybrid water-based enamel.
A heat curable coating composition suitable for
automotive topcoat application is prepared from an aqueous
acrylic copolymer latex, an aqueous solution of a second
acrylic copolymer, and an amino resin crosslinking agent,
here a melamine resin, in the manner hereinafter set forth:
~ 23
-
- .. . ., . ........ , . . ,, : . : ~ . - -
- . . . : ,

1~7~ 3
Step I - Preparation of Acry]ic Copolymer Latex
Monomers and AdditivesParts by Weight
methylmethacrylate 5
styrene 25
2-ethylhexylacrylate 20
butylmethacrylate 30
hydroxypropylmethacrylate 18
acrylic acid 2
l-octane thiol 0.5
Triton(trademark)X-200~
Triton X-305 3
water 70
potassium persulfate 0.5
Reactor Charge
water 50
Triton X-200 1
potassium persulfate U.l
(1) a product of Rohm and EIaas Company, character-
ized as an anioni~ surfactant containing 28~ active component
described as the sodium salt of an alkyl aryl polyether
sulfonate.
(2) a product of Rohm and Haas Company, character-
ized as a nonionic surfactant containing 70% active component
described as an alkyl aryl-polyether alcohol averaging 30
ethylene oxide units per molecule.
The reactor charge is heated to 95 C. in a reaction
vessel equippea with a stirrer, reflux conde~ser, addition
funnel and thermometer. The monomer mixture and listed
additives are mixed and an emulsion is formed by stirring.
The monomer mixture is added to the reactor over a one-hour
period; temperature is maintained at g5C. for two hours
following completion of monomer mixture addition. The latex
- - 24
.
, . :
..
: .... : :

~L~37~Z~3
so obt.ained is :Eormulated into paint as hereinafter described~
Step II. Preparation of water soluble polymer.
_ nomers and Il~itiator Parts by Weiyht
styrene 25
2-ethylhexylacrylate 20
butyl methacrylate 37
acryli.c acid 8
hydroxy propylmethacrylate 10
t-butyl perbenzoate 3
lOReactor Charge
2(2 butoxyethoxy) ethanol 35
A mixture of monomers and initiator as listed is
added to the reactor (which is maintained at 130C.) over a
90-minute period. The temperature is maintained at 130 C.
for an additional 2.5 hours. (The entire polym~rization
is carried out under a nitrogen atmosphere.) The polymer
solution is cooled to room temperature, neutraliæed with
90~ of the calculated equivalent weight ~based on acid
functional comonomer) of N,N-dimethylethanolamine, and re-
duced to 60% solids with water.
Step III. Formulation of Paint
An enamel is prepared from the descri~ed latex and
solution polymer according to the ormula:
Parts by Wei~ht
Component
water 7.6
latex from Step I 57.5
colorant mill bases (l) and -~
aluminum flake pigment paste 6.9
2(2-butoxyethoxy)ethanol l.9 ~ ~
polymer soluti.on from S'tep II 13.2 ~-
"~esimene" (Trademark) 740( ) 12.9
(l) colorant mill bases are prepared from con~
ventional p.igments using the polymer solution from Step II.
- 2S

~6~Z~3
~2) a product o~ Monsan~o Company and a w~ter
reducible methylated melamine resin.
The enamel so obtained is adjusted to pH 7.8 using,
N,N-dimethylethanol amine; viscosity is adjusted ko 25 sec.
Fo~d cup No. 4 by addition of wa-ter.
B. Evaluation of Paint Corrosivity.
I. Static immersion test
Mild steel coupons are cut to size 1.3 x 8 cm.
decreased with trichloroethylene, and immersed halfway in a
20g. sample of the enamel prepared in part A of this example.
After 30 days immersion, the test coupons are removed, rinsed
with distilled water, and inspected for evidence of corrosion
below, above and ak the liquid level of the paint. There is
substantial deposit of paint solids coagulated by corrosion
products at the paint liquid level and along the edges of
the test coupons. There is scattered rusting oE the test
coupon above the paint liquid level.
II. Circulating System Test.
A pilot scale circulating s~stem comprising about
200 ft. of 1.5 in. mild steel pipe joined with standard
fittings (malleable cast iron, steel seated unions) is used
in further evaluation of corrosivity. Other components oE
the system are constructed of corrosion resistant materials
(stainless steel, nylon, Mylar, Teflon, and the like). A
flow of 5 gpm with approximately 6 psi back pressure is
mainta:ined in the system. Circulation is continued for 8
weeks. Pipe and union sections are removed, sectioned
lengthwise, and examined for evidence of corrosion. Corrosion
deposits are removed using a commercial stripper ~Stauffer
Chemical Company Surfclean) to allow inspection of the under-
lying pipe for evidence of localized pitting corrosion. The
enamel prepared in part A of this example is found to corrode
- -
- 26

~6~762~33
the mild steel pipe badly, leaving a heavy deposit of coag-
ulated paint solids mixed with corrosion products. Severe
pitting of the pipe is observed.
C. Evaluation of Corrosion Inhibitors
I. Barium nitrite
Paint samples are prepared (using enamel from part
A of this example) containing 250,500, 1000, and 2000 and
3000 ppm Ba(NO2)2, corresponding approximately to 100,200,
400, 800 and 1200 ppm NO2. These samples are evaluated for
corrosivity using the static immersion test method pre-
scribed under part B(I) of this example. Addition of 500
ppm BatNO2)2 or more reduces corrosivity of the paint;
addition of 1000 ppm Ba(NO2)2 or more effectively eliminate
attack on mild steel in these tests. Addition of 2000 ppm
or more Ba(NO2)2 tends to impair solvent resistance (the
film softens when exposed to xylene); the paint tends to
coagulate upon addition of 3000 ppm Ba(NO2)2.
II. Other nltrites
By comparison with the results in part G(I) of
this example, sodium and potassium nitrite are equally as ~;
effective in terms of corrosion inhibition when added in
amounts calculated to yield the same concentration of NO2
in the paint. Both sodium and potassium nitrite interere
with cure (solvent resistance) at all levels effective for
corrosion inhihition.
~mmonium nitrite is similarly effective as a
corrosion inhibitor and does not inhibit cure. The pro-
tec-tion is shortlived, however. ~t 450 ppm NO2, for example,
NH4NO2 provides effective inhibition for two to three weeks; ;
Ba(NO2) 2' tested under identical conditions, provides pro-
tection for at least 4 to 6 weeks.
N,N-dimethylethanolamine nitrite is not as
effective as Ba(NO2)2 (evaluated at equal levels ~f NO2
'
- 27

~Q7~'~83
.
under identical conditions~) At 400 ppm NO2, the organic
amine nitrite allows the mild steel test coupon to corrode
freely while sa(NO2)2, as noted above, eEfectively stops the
corrosion.
III. Combination of Ba(NO2)2 with organic amine
nitrite.
A paint sample is prepared (using -the enamel from
part A of this example) containing 250 ppm Ba(NO2)2 and 900
ppm N,N-dimethylethanolamine nitrite. This sample is
evaluated for corrosivity, solvent resistance and settling
and coagulation as hereinbefore discussed. It is essentially
non-corrosive to mild steel in the static immersion test,
is equivalent in solvent resistance to unmodified paint,
and does not exhibit coagulation or undue settling. A pilot
scale circulating test on this paint system indicates sub-
stantial reduction in corrosivity. A liyht deposit of
corrosion products and coagulated paint is formed. Some
pitting of the pipe is observed, but its severity is greatly
reduced in comparison with unmodified paint.
...
Example 2
.
A. Preparation of Hybrid Water Based Enamel
The procedures set forth in part A of Example 1
are followed with the differences that: in Step I, pre-
paration of acrylic copolymer latex, the monoMer composition
is altered by the replacement of methylmethacrylate and
2-ethylhexylacrylate hy a mixture of 5 parts by weight
styrene and 20 parts by weight butylmethacrylate; in Step 2,
the preparation of water-soluble polymer, the polymer
solution in neutralized with 60% of the calculated equivalent
weight (based on acid functional comonomer) of N,N-dimethyle-
thanolamine; and in Step 3, formulation of paint, the form-
: ' . ' .
- 28

~7~ii;283
ulation comprises 11.9 parts by w~ight water, 47.1 parts
latex, 20.9 parts polymer solution, 12.9 parts Resimene
740, 0.3 parts 2(2-butoxyethoxy)ethanol, the balance being
colorant mill bases and aluminum flake plgment paste.
B. Evaluation of Corrosivity
The paint prepared in Part A of this example is
tested according to the static immersion test set forth in
Example 1. The paint actively corrodes mild steel as
evidenced by formation of a heavy deposit of coagulated
paint and corrosion products at the paint liquid level.
C. Evaluation of Corrosion Inhibitors
To the paint prepared in Part A of this example
is added 250 ppm Ba(N02)2 and 900 ppm, N,N-dimethylethanolamine
nitrite. The modified paint does not corrode mild steel in
the static immersion test.
Example 3
The procedures of Example 2 are repeated with
equivalent results using, in the formulation of paint, a
latex prepared from 30 parts by weight styrene, 20 parts by
weight ethyl acrylate, 30 parts by weight butyl methacrylate,
18 parts by weight hydroxypropyl methacrylate, and 2 parts
by weight acrylic acid; ammonium persulfate is substituted
for potassium persulfate. The remainder of the paint com-
position is prepared as previously set forth.
Example 4
The procedures of Rxample 2 are repeated with
equivalent results usin~, in the formulation of paint,Cymel
(Trademark) 301, a product of American Cyanamid and a water
dispersible methylated melamlne resin, in place of Resimene
740.
- 29

_amp]e 5
The procedures of Examp]e 4 are repeated with
equivalent results using, in the formulation of paint, a
polymer solution neutralized with 75% (based on khe acid
functional monomer) of the calculated equivalent weight
of N,N-dimethylethanolamine.
Example 6
The procedures of Example S are repeated with the
difference that the corrosion inhibitor added is Ba(NO2)2
and i~s concentration is 1000 ppm. No corrosive attack is
observed on mild steel in the static immersion test.
Example 7
A. Preparation of Hybrid Water-Based Enamel
A heat-curable coating composition suitable for
automotive topcoat application is prepared from an aqueous
acrylic copolymer latex, an aqueous solution of a second `
acrylic copolymer, and an amino resin crosslinking agent,
here a melamine resin, in the manner hereinafter set forth:
Step I. Preparation of Acrylic Copolymer Latex
Monomers and Additives Parts by Weight
methyl methacrylate 41
methacrylic acid 4
ethyl acrylate 35
butyl acrylate 20 `
l-octanethiol
Triton X-200(1) 1
r~riton X-305(2) ` 4 5
Water 70
potassium persulfate 0.4
Reactor Charge
Water 30
.
- 30

Momomers and Additives 1~7~Z83 Parts by Weight
-
Triton X-200 2
potassium persulfate 0.1
(1) a product of ~ohm and Haas Company,
characterized as an anionic surfactant containing 28~
active componen~ described as the sodium salt of an alkyl
aryl polyether sulfonate.
(2~ a product of Rohm and Haas Company, character-
ized as a noniOnic suractant containing 70% active component
described as an alkylarylpolyether alcohol averaging 30
ethylene oxide units per molecule.
The reactor charge is heated to 50C. in a reaction :.
vessel equipped with a stirrer, reflux condenser, nitrogen
inlet type, addition funnel and thermometer. The monomer
mixture is mixed with the listed additives and an emul.sion .
is ormed by stirring. The monomer emulsion is added over
a four and one-hal~ hour period. The temperature is main-
tained at 50 5C. throughout the monomer addition and or ::
2 hours ~hereafter. A nitrogen sparge is maintainecl through-
out. The latex so formed is cooled to room temperature,
filtered, and formulated into paint as hereinafter described.
1'he molecul.ar weight of th.e polymer so prepared (Mn) is
about 6000. Its glass transition temperature, Tg, is akout
14C~ ~calculated from the monomeric composition without
regard to moleculax weight as are all Tg values herein given).
Step II. Preparation of Water Soluble Acrylic
Polymer
Monomer Mixture and Initicltor Parts ~ ..
methacrylic acid 15.0
methyl~.nethacrylate 15.0 . -
. 30 styrene 20.0
,
, . ' ' , ~ .
~ 31

~L~7~Z~33
Monomer Mixture and_IhitiatorParts by Wei~ht
butyl acrylate 40.0
butyl methacrylate 10.0
t-butylperoctoate 3.5
Reactor Cha _
isopropyl alcohol 45
A mixture of the monomers and initiator listed is
added to refluxing isopropyl alcohol over a 90-minute period.
An additional initiator chanye - 0.2 parts t-bu-tylperoctoate
in 5 parts isopropyl alcohol - is added 30 minukes aftex
completion of the monomer addition. The reaction mix-ture
is main-tained at reflux an additional 2 hours, cooled to
room temperature, neutralized with 90% o~ the calculated
equivalent weight (based on acid functional comonomer) of
dimethylethanolamine, and reduced to 60% by weight solids
~ith water. The polymer thus prepared has molecular weight
~Mn) of abou-t 9200. The glass transition temperature of
this polymer is about 18C.
'
Step XII. Formulation of Paint
A mill base is prepared by pebble milling together
the following materials.
onents Parts b~ Weigh
polymer solution from Step 2 5.5
titanium dioxide pigment 13.8
water 3,3
An enamel i9 then prepared by blending this mill
base with the following materials:
Components Parts by Weight
latex from Step I 42~5
water 19.0
isopropanol 1.0
propylene glycol 5.1
,
., . , ~ . -. . .

~L~7~;Z133
Components Parts by We ght
melamine c~slinking agent,
Cymel 30~ 4.6
10~ aqueous N,N-dimethylethanolamine 1.4
10% aqueous p-toluenesulfonic acid(2) 3.8
(1) a product of American Cyanamid Company, and
a commercial ~rade of hexamethoxymethylmelamine.
(2) the solution is adjusted to pH 8 by addition
of dimethylaminoethanol.
B. Evaluation of Corrosivity
The enamel prepared in Part-A of this example is
evaluated for corrosivity following the static immersion
test procedure described in Example 1. The enamel actively
corrodes mild steel as evidenced by a heavy deposit of rust
and coagulated paint at the paint liquid level.
C. Evaluation of Corrosion Inhibitor
To the enamel is added lr)O ppm Ba(NO2)2 and 1500 ppm
N,N-dimethylethanolamine nitrite. Corrosive attack on mild
steel in the static immersion test is greatly reduced. The
additives have no effect on solvent resistance of the cured
paint films.
' ' .
. Preparati.on of Enamel
Step I. Preparation of Stabilizer Polymer -
There is charged to a reactor 200 parts of water.
The reactor charye is heated to boiling and then cooled to
95C. To the reactor charge is added Solution A, a solution
of 0.1 parts of ammonium persulfate in 0.8 parts of water.
A solution hereinafter termed Solution B, is prepared from
O.4 parts of ammonium persulfate in 2.5 parts water. A
reactant monomer and chain transfer agent mix-ture is formed
from the following materials:
,
_ 33

7~'~83
Ma-terials Parts by Wei~ht
methyl methacry]ate 35
methacrylic acid 15
butyl acrylate 50
l-octanethiol 2
The monomer mixture and Solution B are sirnul-
taneously charged to the reactor by incremental addition
over a two-hour period. The temperature of the reaction
mixture is maintained for 3 hours after addition of the
last of th~ reactants. The latex so obtained is cooled
to room temperature and filtered. The polymer thus obtained,
hereinafter termed stabilizer polymer I, is then neutralized
with N,N-dimethylethanolamine in an amount equivalent to the
acid monomer content of the polymer.
A clear solution is obtained.
Step II Preparation of Emulsion'Polym~r
An emulsion polymer is produced by first preparing
the following: (1) there is charged to the reactor 200
parts of water and 4.25 parts of the stabilizer polymer from
Z0 Step I; (2) the following materials are thoroughly mixed:
Matexials Parts b~ Weight
st~rene 20.0
methacrylic acid 15.0
butyl acrylate 55.0
butyl methacrylate 10.0
l-octanethiol
(3~ there are dissolved in 0.5 parts of ammonium persulfate
and one part of 2-acrylamide-2methylpropanesulfonic acid in
2.5 parts of water; and (4) there is dissolved 0.2 parts of
ammonium persulfate in 5 parts of water. After these are
prepared the emulsion polymer is prepared using the procedure
and conditions used to prepare the stabili2er polymer of
Step I. In such, the order of addition of the four above
- 3~ -

83
listed components is as follows: (4) îs added to (1) in the
reactor and (2) and (3) are added simultaneously to the
mixture of (1) and (4).
Step III. Preparation of the Solution Polymer
The procedures and steps of Step II of this example
are repeated with the following employment of reactant
monomers:
Materials Parts by Weight . .
methyl methacrylate 35
methacrylic acid 15 ~:.
butyl acrylate 50
l-octanethiol
After this latex is cooled and filtered, it is
neutralized with N,N-dimethylethanolamine to the amount ..
equ.ivalent to the methacrylic acid constituent of the polymer.
...
Step IV. Formulation of Water-Based Enamel
.. ... .
Materials Parts by Weight
solution polymer from Step III14.1
Cymel 300 6.5
titanium dioxide . 16.1
water " . 6.4
The above materials are ball milled for 16 hours
and mixed (let down~ with the following materials:
Materials Parts by Weight
-
latex from Step II (includes
both emulsion polymer and
stabilizer polymer I) 47.3
10% aqueous N,N-dimethylethanolamine 9.6
.:, .
- . .

~'7~
B. Evaluation of Corrosivity
The enamel so prepared is tested in accordance
with the procedures set forth in Example 1 - static immersion
test. The enamel actively corrodes onto steel as evidenced
by a heavy deposit of rust a~d coagulated paint at the paint
liquid level.
C. Evaluation o~ Corrosion Inhibitor
To the enamel is added 800 ppm Ba(NO2)2 and 900 ppm
N,N-dimethylethanolamine nitrite. Corrosive attack on mild
steel in the static immersion test is greatly reduced. The
additives have no effect on solvent resistance of cured paint
films.
Exam~
The procedures of Example 2 are repeated wi-th
equivalent results using triethylamine nitrite in place of
N,N-dimethylaminoethanol nitrite.
,
~e ~
The procedures of Example 2 are repeated using
morpholine nitrite in place of dimethylethanolamine nitrite.
Results are equivalent.
The term "acrylic monomer" as used herein means a
compound selected from the group consisting of glycidyl
acrylate, glycidyl methacrylate, acrylic acid, hydroxyethyl
acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate,
hydroxypropyl methacrylate, esters of acrylic acid and a
Cl - C~ monohydric alcohol, and esters of methacrylic acid
and a Cl - C8 monohydric alcohol.
The term "acrylic copolymer" means a copolymer of
monoethylenically unsaturated compounds at least a major
portion of which are acrylic monomers. -~
:
'
- 36

~76~1 33
The term "major portion" means in excess of sn
weight percent of the entity referred to.
The term "minor portion" means less than 50 wei~ht
percent of the entity referred to.
Many modific~tions of -the foregoing examples will
be apparent to those skilled in the art i.n view of this
specification. It is intended that al.l such modifications
which fall within the scope of this invention as defined in
the claims shall be considered to be a part of this invent.ion.
- 37 - -