PIGMENTED AIR DRYING LATEX PAINTS HAVING SUPERIOR GLOSS

PEINTURES DE LATEX PIGMENTEES SECHANT A L'AIR AVEC UN BRILLANT SUPERIEUR

English Abstract

ABSTRACT OF THE DISCLOSURE
A high gloss, water base, pigmented latex is
provided by grinding a pigment into a water-free solution
of a carboxyl-functional addition solution copolymerized
copolymer of monoethylenically unsaturated monomers inclu-
ding at least about 10%, by weight of monoethylenically
unsaturated carboxylic acid in water miscible alcoholic
organic solvent, the copolymer being at least partially
neutralized at the time of grinding with an hydroxy amine,
to render the said copolymer dispersible in water, and
thereby form a nonaqueous pigment paste, and then mixing
the nonaqueous pigment paste with an air drying aqueous
latex of aqueous emulsion copolymerized copolymer particles.
The invention includes the latex paint so-produced.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of producing a high gloss, air
drying water base, pigmented latex paint comprising,
grinding 3-12 parts of pigment into a water-free solution
containing 1 part of an at least partially neutralized
carboxyl-functional addition solution copolymerized
copolymer of 10% to 40% of monoethylenically unsaturated
carboxylic acid, the major proportion of said pigment being
titanium dioxide and said solution containing 40% to 70%
of alcoholic organic solvent based on the weight of the
solution copolymer, said copolymer being at least partially
neutralized with an hydroxy amine having the formula:
<IMG>
in which R is hydrogen or an alkyl group, R' is an alkylene
group, and X is either R or R'OH, to render the said copoly-
mer disperisble in water, and thereby form a nonaqueous
pigment paste, and then mixing the nonaqueous pigment paste
with an air drying aqueous latex consisting essentially of
emulsified aqueous emulsion copolymer particles having a
Tg below 20°C., the copolymer of said latex containing less
than about 4% of reactive monomers.
2. A method as recited in claim 1 in which said
hydroxy amine is a tertiary amine and said R and R' groups
contain from 1-4 carbon atoms.
3. A method as recited in claim 2 in which said
hydroxy amine is dimethyl ethanol amine.
11

4. A method as recited in claim 1 in which said solution
copolymer contains from 15% to 30% of monoethylenically unsat-
urated carboxylic acid.
5. A method as recited in claim 1 in which said solution
copolymer and said aqueous emulsion copolymer each include more
than 50% by weight of a blend of methyl methacrylate and C1-C8
alkyl acrylate.
6. A method as recited in claim 1 in which from 5-10
parts of pigment are ground into said water free solution con-
taining 1 part of said at least partially neutralized solution
copolymer.
7. A method as recited in claim 6 in which said alcoholic
organic solvent consists essentially of 2-ethoxy ethanol and 2-
butoxy ethanol.
8. A method as recited in claim 1 in which said aqueous
emulsion copolymer consists of a blend of methyl methacrylate and
C2-C4 alkyl acrylate, up to about 1% of monoethylenic carboxylic
acid and up to about 2% of a monoethylenic amine-functional
monomer.
9. The high gloss, water base, pigmented air drying latex
paint produced by grinding 3-12 parts of pigment into a water-
free solution containing 1 part of an at least partially neutral-
ized carboxyl-functional addition solution copolymerized copoly-
mer of 10% to 40% of monoethylenically unsaturated carboxylic
acid, the major proportion of said pigment being titanium diox-
ide and said solution containing 40% to 70% of alcoholic organic
solvent based on the weight of the solution copolymer, said
copolymer being at least partially neutralized with a hydroxy
amine having the formula:
12

<IMG>
in which R is hydrogen or an alkyl group, R' is an alkylene
group, and X is either R or R'OH, to render the said copolymer
dispersible in water, and thereby form a nonaqueous pigment
paste, and then mixing the nonaqueous pigment paste with an air
drying aqueous latex consisting essentially of emulsified
aqueous emulsion copolymer particles having a Tg below 20°C,
the copolymer of said latex containing less than about 4% of
reactive monomers.
13

Description

~2~6;2S
This invention relates to high gloss, water base, pigmented air
drying latex house paints.
Conventional air drying latex paints develop little gloss, as is
well known. These conventional latex paints include pigment which is dis-
persed in the water phase by means of surfactants or wetting agents, and this
leads to low gloss. The pigment is quite differently dispersed in this in-
vention, leading to a very significant increase in gloss, as will be illus-
trated.
According to one aspect of the present invention there is pro-
vided a method of producing a high gloss, air drying water base, pigmentedlatex paint comprising, grinding 3 - 12 parts of pigment into a water-free
solution containing 1 part of an at least partially neutralized carboxyl-
functional addition solution copolym0rized copolymer of 10% to 40% of mono-
ethylenically unsaturated carboxylic acid, the major proportion of said pig-
ment being titanium dioxide and said solution containing 40% to 70% of alco-
holic organic solvent based on the weight of the solution copolymer, said
copolymer being at least partially neutralized with a hydroxy amine having
the formula:
X
R - N - R'OH
in which R is hydrogen or an alkyl group, R' is an alkylene group, and X is
either R or R'OH, to render the said copolymer dispersible in water, and
thereby form a nonaqueous pigment paste, and then mixing the nonaqueous pig-
ment paste with an air drying aqueous latex consisting essentially of emul-
sified aqueous emulsion copolymer particles having a Tg below 20C., the co-
polymer of said latex containing less than about 4% of reactive monomers.
The organic solvent is preferably an alcoholic solvent. The invention fur-
ther provides the latex paint so-produced.
Referring more particularly to the solution copolymerized copoly-
mer of monoethylenically unsaturated monomers containing a high level of car-
boxyl functionality, any
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addition copoly~er of monoethylenically unsaturated
monomers may be used, the usual monomers being acrylic
or vinyl acetate, including at least about 10% by weight
of monoethylenically unsaturated carboxylic acid. However,
in this invention, it is preferred that both the solution
copolymer and also the emulsion copolymerized latex copoly-
mer contain a major proportion (more than 50% by weight)
of acrylic esters, more particularly constituted by a blend
of methyl methacrylate with alkyl acrylate in which the
alkyl group contains from 1-8 carbon atoms. Styrene, vinyl
toluene, or vinyl acetate may be used in place of the methyl
methacrylate, but these are less preferred. Acrylonitrile
may also be present. These are nonreactive monoethylenic
monomers. Hydroxy functional monomers may also be present,
such as 2-hydroxyethyl acrylate, and amide groups are also
permissible, such as are provided by acrylamide, meth-
acrylamide, or other monoethylenic carboxylic acid amide.
The copolymers of high acidity are solution
copolymers which denotes copolymerization in organic solvent
solution. Water miscible organic solvents, and especially
alcohols, such as butanol, 2-ethoxy ethanol and 2-butoxy
ethanol, are preferably selected in this invention since
the copolymer is ultimately dispersed in the aqueous medium
provided by the latex.
At least 10%, up to about 40%, of the copolymer
is to be constituted by monoethylenically unsaturated
carboxylic acid. Many acids are appropriate, particularly
acrylic acid. Other appropriate acids are methacrylic
acid, crotonic acid, itaconic acid, monobutyl maleate, and
the like. Preferred proportions are from 15-30% of the
copolymer.

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The solution copolymerization which is used is
a conventional one which is carried out in solvent solution
in the presence of a free radical polymerization catalyst.
Preferred water miscible organic solvents are 2-ethoxy
ethanol and 2-butoxy ethanol, though numerous others are
well known and useful herein, such as isopropanol, acetone,
and the like.
The copolymer solution is then at least partially
neutralized with an amine, hydroxy amines giving the best
lQ results. Neutralization is carried out to the extend needed
for subsequent dispersion in water, neutralization to at
least about 50% of the acidity of the copolymer being
generally contemplated.
While amines, such as triethyl amine or ammonium
hydroxide (usually considered an amine in the art of solu-
bilizing carboxyl copolymers) are generally useful, hydroxy
amines yield significantly better gloss. Hydroxy amines
have the formula:
X
R-N-R'OH,
in which R is hydrogen, or an alkyl group, preferably an
alkyl group containing 1-4 carbon atoms, R' is an alkylene
group, preferably containing 1-4 carbon atoms, and X is
either R or R'OH.
Appropriate hydroxy amines are illustrated by pro-
panol amine, diethanol amine, dipropanol amine, dimethyl
ethanol amine, dimethyl propanol amine, diethyl ethanol
amine, methyl diethanol amine, ethyl diethanol amine, and
the like. Tertiary amines containing at least one hydroxy
group are particularly contemplated, and the invention will
be illustrated using dimethyl ethanol amine.

~12~fi'~S
While any pigment may be included in the paints of
this invention, titanium dioxide pigment, both rutile and
anatase, are particularly contemplated. The hydroxy amines
are especially significant in achieving the effect of dis-
persion and high gloss containing results contemplated
herein when titanium dioxide pigment is relied upon to pro-
vide the major proportion of the pigmentation. The propor-
tion of pigment should be sufficient to provide a paste in
known fashion. A pigment volume concentration of at least
10% is usual.
After neutralization of at least a portion of
the carboxyl functionality contained in the copolymer
solution, the pigment is added and conventional grinding
is carried out to produce a pigment paste. In preferred
practice, from 3-12 parts by weight of pigment are dis-
persed in the copolymer-solvent solution per part of
copolymer, more preferab].y from 5-lO parts of pigment per
part of copolymer. The aqueous latex providing the bulk
of the resin solids of the paint is then added either
directly or after preliminary admixture of a small amount
of water, into the neutralized solvent solution.
The neutralized solution of carboxyl-functional
solution copolymer preferably contains from 40% to 70% of
solvent, based on the weight of the solution copolymer, to
provide a viscosity appropriate for grinding in the pigment.
While any conventional air drying emulsion
copolymer latex used in the paint industry may be employed
herein, vinyl acetate-butyl acrylate copolymers, vinyl
acetate-ethylene copolymers, and methyl methacrylate-ethyl
acrylate (or butyl acrylate) copolymers illustrate the more
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62S
usual paint latices, and the methyl methacrylate-acrylic
ester copolymers are preferred. In general, aqueous
emulsion copolymers having a Tg below 20C. are useful
herein since these provide air dry paints. Tg denotes
the glass transition temperature and is well recognized
to define the nature of an emulsion copolymer which is not
significantly cross-linked in the emulsion. A small amount
of coalescing solvent, as is well known, may be present to
facilitate air drying. Reactive monomers cannot be present
in the large amounts needed for a baking system, for these
would have to be reacted in order to provide good film
properties, and baking is not available in a house paint.
Thus, up to about 1% of a carboxylic monomer may be included
for emulsion stability and up to about 2% of amine-functional
monomers may be present to maximize adhesion and other
properties, but larger amounts of reactive materials should
be avoided since these are inconsistent with an air dry
latex. The total proportion of reactive monomers should be
less than about 4%. The amine functional monomers are
illustrated in United States patents 3,356,653; 3,356,654;
3,356,655; and 3,509,0~5.
It is desired to call particular attention to some
of the superior attributes which are obtained in pigmented
paints formulated in accordance with this invention in com-
parison with other commercially available semigloss paints,
aside from the significant improvement in gloss which is
obtained. Thus, better visual hiding is obtained at the
same level of pigmentation, and the pigment dispersing
properties are superior. This enables dispersion in the
absence of the surfactants normally introduced to aid in

1~2~)~25
dispersing the pigment. This characteristic is particu-
larly beneficial from the standpoint of processing because
in the previous technique of grinding the pigment into
water containing a surfactant, foaming was troublesome.
Also, and from the product standpoint, higher solids con-
tent paints are enabled by this invention. The superior
dispersion also enables darker colors using smaller amounts
of prime pigment (the titanium dioxide), and the tendency
of the pigment to flocculate is avoided.
From the standpoint of application, it has been
found that wetting of the substrate is superior and the
rheology of the coating is better, causing brush marks to
flow out and become less discernible. The better wetting
which is obtained enables the formulation of paints in
which the polyester component normally introduced to provide
the desired chalk penetration can be eliminated. As a
result, one can wet chalky surfaces without introducing
any tendency to yellow.
It is also possible in this invention to reduce
the proportion of titanium dioxide pigment which is needed
for hiding, and this can be done by increasing the amount
of extender pigment, such as aluminum silicate. This is
not possible in the corresponding conventional system where
aluminum silicate introduction reduces gloss.
Throughout this specification, and particularly
in the examples and claims which follow, all proportions
are by weight unless otherwise specified.
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Example 1 (For Comparison)
Charge Composition (Pounds)
83 Water
4.5 Anionic Surfactant - sodium salt of polyacrylic acid
(Rohm and Haas Tamol 731*may be used)
125 Titanium dioxide rutile
Disperse the pigment using a high speed mixer
Add the following in order
425 Water
)dissolve0 10 Hydroxy ethyl cellulose)
thickener
8 Diethylene glycol monobutyl ether (coalescing agent)
319 Acrylic Emulsion Polymer (47% solids) - see note 1
4 Defoamer (Drew L-475*may be used)
1 Anionic surfactant (dioctyl sodium sulfosuccinate
[60% solids in isopropanol])
Solids: 28% by weight
Weight per gallon: 9.4 pounds
The formulation contains:
125 pounds of titanium dioxide pigment
150 pounds of emulsion polymer solids
Note 1 - The acrylic emulsion polymer utilized is made in
accordance with the teachings of Example 2 of United States
Patent 3,356,653 and had the following monomer composition:
53% methyl methacrylate
44% butyl acrylate
1% methacrylic acid
2% amino adduct (see Example 1 of Patent 3,356,653)
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*Trademarks

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Example 2
Example 1 was repeated, only the 4.5 pounds of the
anionic surfactant dispersant and the 83 pounds of water
were replaced with 27.2 pounds of water soluble acrylic
copolymer solution of Example 3 at 55% solids. The propor-
tion of acrylic emulsion was reduced to maintain the solids
content at 150 pounds:
135 pounds - 90% - Emulsion polymer solids
15 pounds - 10% - Water soluble acrylic polymer
]0 solids
Example 3
Charge Composition (grams)
1080 2-Ethoxy ethanol solvent - heat to 120C.
360 Methyl methacrylate
1700 Ethyl acrylate
520 Acrylic acid
Benzoyl peroxide
Add the above over a three hour period while
maintaining temperature at 120C. Hold one hour
and add:
12 Tertiary-butyl perbenzote
Hold 1 1/2 hours. Start cooling and add:
370 2-Ethoxy ethanol solvent
Cool to 70C. and add the following over
a 20 minute period:
650 Dimethyl ethanol amine.
Strain to provide an acrylic copolymer solution:
~onvolatile solids: 55%
Viscosity (Gardner) Z3
Acid value (nonvolatiles) 148
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~ queous latex paints prepared in accordance with
Examples 1 and 2 were compared as follows:
Gloss Example 1 Example 2
60 ~loss meter readlng
Dry 1 week at room temperature 36 78
Film Properties
Scrub resistance Good Good
Blocking resistance Good Good
Burnishing resistance Good Good
10 Stain removal Very good Very good
Hiding Good Very good
As will be seen, the invention has been illust-
rated by a comparison between two similar latex paints, one
produced in conventional fashion (Example 1), and the other
produced in accordance with the teachings of this invention
(Example 2).
The generally superior properties which are
produced have been described previously, and the marked
increase in gloss (from 36 to 78 measured on a 60 gloss-
meter) represents a large increase which stands out underthe most casual inspection.
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