Thixotropic thickening agent for aqueous systems

This invention relates to a thixotropic thickening agent and to a process for preparing the same. Such thixotropic thickening agents are particularly useful for thickening water reducible coatings. The thixotropic thickening agents of this invention are copolymers which are comprised of repeat units which are derived from methacrylic acid monomer, ethylacrylate monomer, and a water soluble crosslinking agent. The water soluble crosslinking agents which can be used include ethylene glycol dimethacrylate and alkylene bisacrylamides, such as N,N'-methylene bisacrylamide. A neutralized two weight percent aqueous solution of the thixotropic thickening agents of this invention will have a Brookfield RVT viscosity as measured at 50 rpm using a number 3 spindle within the range of 50 to 2000 centipoise (cps).

TECHNICAL FIELD 
This invention relates to thixotropic thickening agents for use in aqueous 
coating systems. For purposes of this patent application, an aqueous 
coating system is considered to be a colloidal dispersion of a resin in 
water which can be reduced by the addition of water and which forms a 
durable coating when applied to a substrate surface. The term aqueous 
coating system is used herein interchangeably with the term water 
reducible coating. Other names which are sometimes applied to water 
reducible coatings are water born, water solubilized, and water dilutable. 
BACKGROUND OF THE INVENTION 
Most conventional coating resins are insoluble in water. Therefore, in 
general practice they have been dissolved in a suitable organic solvent or 
dispersed in water with the aid of an emulsifying agent or surfactant in 
order to provide a coating composition suitable for application to a 
substrate surface. A serious disadvantage of organic solvent solutions is 
that they are potentially toxic, flammable, and environmental pollutants. 
Water reducible coatings do not present these problems and are, therefore, 
highly desirable. For this reason various water reducible coating resins, 
such as the one described in U.S. Pat. No. 4,474,926, have been developed. 
Water reducible coatings which utilize such resins have been developed for 
a variety of purposes, such as highway striping paint. 
Conventional thickening agents which are used in organic solvent based 
coatings do not normally act as thickening agents in aqueous coating 
systems. Nevertheless, there is a need for thickening agents which can be 
used in aqueous coating systems. The present invention relates to the 
development of a thickening agent for use in aqueous coating systems which 
has thixotropic properties. 
SUMMARY OF THE INVENTION 
This invention reveals a copolymer which can be utilized as a thixotropic 
thickening agent for use in aqueous coating systems which is comprised of 
repeat units which are derived from methacrylic acid monomer, 
ethylacrylate monomer, and a water soluble crosslinking agent; wherein 
from 25 to 55 weight percent of the repeat units in said copolymer are 
derived from ethylacrylate, wherein from 45 to 75 weight percent of the 
repeat units in said copolymer are derived from methacrylic acid wherein 
from 0.05 to 0.75 weight percent of the repeat units in said copolymer are 
derived from said water soluble crosslinking agent, and wherein the 
Brookfield RVT viscosity of a 2 weight percent solution of said copolymer 
at a pH within the range of 7 to 8 in water as measured at 50 rpm using a 
number 3 spindle is within the range of 50 to 2000 mPa.multidot.s. 
This invention also discloses a process for preparing a copolymer which can 
be utilized as a thixotropic thickening agent for use in aqueous coating 
systems which comprises copolymerizing from 25 to 55 phm of ethylacrylate 
monomer, from 45 to 75 phm of methacrylic acid monomer and from 0.05 to 
0.75 phm of a water soluble crosslinking agent so as to produce the 
copolymer, wherein the Brookfield viscosity of a 2 weight percent solution 
of said copolymer at a pH within the range of 7 to 8 in water as measured 
at 50 rpm using a number 3 spindle is within the range of 50 to 2000 
mPa.multidot.s. 
This invention further reveals an aqueous coating composition which is 
comprised of (a) a water reducible resin which is comprised of, based on 
100 weight percent of monomeric units within the water reducible resin: 
(1) from about 50 to about 90 percent of at least one monomer selected 
from the group consisting of styrene, .alpha.-methyl styrene and vinyl 
toluene, (2) from about 10 to about 40 of at least one alkyl acrylate 
monomer wherein the alkyl moiety contains from 3 to 5 carbon atoms, and 
(3) from about 1 to about 10 percent of at least one unsaturated carbonyl 
compound selected from the group consisting of acrylic acid, methacrylic 
acid, fumaric acid, itaconic acid, maleic acid and maleic anhydride; (b) a 
thixotropic thickening agent which is comprised of repeat units which are 
derived from methacrylic acid monomer, ethylacrylate monomer, and a water 
soluble crosslinking agent, wherein from 25 to 55 weight percent of the 
repeat units in said copolymer are derived from ethylacrylate monomer, 
wherein from 45 to 75 weight percent of the repeat units in said copolymer 
are derived from methacrylic acid monomer, and wherein from 0.05 to 0.75 
weight percent of the repeat units in said copolymer are derived from said 
water soluble crosslinking agent; (c) a pigment; (d) a plasticizer; and 
(e) water. 
DETAILED DESCRIPTION OF THE INVENTION 
The thixotropic thickening agents of this invention are prepared by 
copolymerizing methacrylic acid monomer, ethylacrylate monomer, and a 
water soluble crosslinking agent. The copolymers formed have molecular 
weights which are sufficient to result in aqueous solutions which contain 
2 weight percent of the copolymer to have Brookfield viscosities within 
the range of 50 to 2000 milliPascal.multidot.seconds (mPa.multidot.s) as 
measured at 50 rpm using a number 3 spindle. Brookfield viscosities are 
measured after the aqueous solutions are neutralized to a pH within the 
range of 7 to 8. A Brookfield viscosity of at least 50 mPa.multidot.s is 
required in order for the thixotropic thickening agent to have adequate 
viscosity increasing characteristics. Thickening agents which have 
Brookfield viscosities of over 2000 mPa.multidot.s have poor rheological 
properties. It is normally preferable for such copolymers to have 
Brookfield viscosities within the range of 500 to 1500 mPa.multidot.s. It 
is generally more preferable for such copolymers to have Brookfield 
viscosities within the range of 700 to 1000 mPa.multidot.s in order for 
them to have optimal rheological properties as well as good thickening 
characteristics. 
The copolymers which are utilized as the thixotropic thickening agents of 
this invention are comprised of repeat units which are derived from 
methacrylic acid and ethylacrylate. Such copolymers also contain repeat 
units which are derived from a water soluble crosslinking agent. Such 
copolymers can be represented by the structural formula: 
##STR1## 
wherein indicates that the repeat units derived from methacrylic acid 
and ethylacrylate can be distributed in a random manner and wherein x and 
y represent integers. Normally, from about 25 to 55 weight percent of the 
repeat units in such copolymers will be derived from ethylacrylate. 
Accordingly, from about 45 to 75 weight percent of the repeat units in 
such copolymers will be derived from methacrylic acid. It is generally 
preferred for such copolymers to have from 30 to 50 weight percent of the 
repeat units therein being derived from ethylacrylate with 50 to 70 weight 
percent of the repeat units therein being derived from methacrylic acid. 
It is normally more preferred for such methacrylic acid/ethylacrylate 
copolymers to be derived from 35 to 45 weight percent ethylacrylate and 
from 55 to 65 weight percent methacrylic acid. Normally, from about 0.05 
to 0.75 weight percent of the repeat units in such copolymers are derived 
from a water soluble crosslinking agent. It is normally preferred for 0.1 
to 0.3 weight percent of the repeat units in such copolymers to be derived 
from water soluble crosslinking agents. 
The copolymers used as the thixotropic thickening agents of this invention 
can be prepared utilizing conventional emulsion polymerization techniques. 
Such emulsion polymerizations are carried out in an aqueous medium which 
is comprised of water, an emulsifier, methacrylic acid monomer, 
ethylacrylate monomer, a water soluble crosslinking agent, and a free 
radical initiator. The emulsifier utilized in such polymerization is 
typically an ionic emulsifier and the free radical generator utilized is 
typically a redox system. The polymerization mediums utilized in preparing 
such copolymers are normally comprised of 200 to 500 parts by weight of 
water, 25 to 55 parts by weight of ethylacrylate monomer, 45 to 75 parts 
by weight of methacrylic acid monomer, 0.05 to 0.75 parts by weight of a 
water soluble crosslinking agent, 1-10 parts by weight of an emulsifier, 
and from 0.1 to 0.4 parts by weight of an initiator. The polymerization 
medium utilized will preferably contain 300 to 400 phm (parts per hundred 
parts by weight of monomer) of water, 2 to 8 phm of emulsifier, and 0.2 to 
0.3 phm of the initiator. It is normally preferable for such 
polymerization mediums to contain from 0.1 to 0.3 phm of a water soluble 
crosslinking agent. Such polymerization mediums will most preferably 
contain from 4 to 6 phm of emulsifier. 
Any water soluble crosslinking agent containing 2 or more vinyl groups can 
be utilized for crosslinking. For instance, N,N'-methylene bisacrylamide 
and polyethylene glycol dimethacrylate can be utilized as crosslinking 
agents. N,N'-alkylene bisacrylamides are highly preferred crosslinking 
agents. Such N,N'-alkylene bisacrylamides have the general structural 
formula: 
##STR2## 
wherein A is an alkylene group. The alkylene group in such N,N'-alkylene 
bisacrylamides normally contain from 1 to 8 carbon atoms. More typically 
the alkylene group in such alkylene bisacrylamides contains from 1 to 4 
carbon atoms. Some representative examples of such alkylene groups include 
methylene, ethylene, propylene, and butylene. N,N'-methylene bisacrylamide 
is a commercially available alkylene bisacrylamide which is an excellent 
choice as a crosslinking agent for utilization in practicing the process 
of this invention. N,N'-methylene bisacrylamide has the structural 
formula; 
##STR3## 
The preferred emulsifiers for use in preparing such copolymers are selected 
from the group consisting of disodium nonylphenoxy polyethyoxy 
sulfosuccinate, diammonium nonylphenoxy polyethyoxy sulfosuccinate, sodium 
lauryl polyethoxy sulfate, and ammonium lauryl polyethoxy sulfate. The 
sodium lauryl polyethoxy sulfates and ammonium lauryl polyethoxy sulfates 
which are most preferred for use as emulsifiers have the general 
structural formula: 
EQU CH.sub.3 (CH.sub.2).sub.11 O(CH.sub.2 CH.sub.2 O).sub.n SO.sub.3 M 
wherein M represents sodium or ammonium and wherein n is an integer from 8 
to 16 inclusive. The preferred disodium nonylphenoxy polyethoxy 
sulfosuccinates and diammonium nonylphenoxy polyethoxy sulfosuccinates 
have the general structural formula: 
##STR4## 
wherein M represents sodium or ammonium and wherein n represents an 
integer from 8 to 16 inclusive. 
The polymerizations utilized in preparing the copolymers of this invention 
are normally conducted at a polymerization temperature within the range of 
about 60.degree. F. (15.degree. C.) to about 100.degree. F. (38.degree. 
C.). It is generally preferable for such polymerizations to be conducted 
at a temperature within the range of 70.degree. F. (21.degree. C.) to 
95.degree. F. (35.degree. C.). In most cases it is more preferable for the 
polymerization to be carried out at a temperature between 80.degree. F. 
(27.degree. C.) and 90.degree. F. (32.degree. C.). Such polymerizations 
are normally conducted without utilizing a modifier, such as t-butyl 
mercaptan. This is because it has been determined that the utilization 
properties of the thixotropic thickening agent. The amount of 
polymerization time required normally ranges between about 0.5 and 10 
hours. More commonly, the polymerization time required will be within the 
range of about 1 to about 4 hours. In most cases a polymerization time of 
about 2 hours will be appropriate. Such polymerizations are normally 
carried out to a solids content within the range of 15 to 30 percent. More 
commonly, a solids content of 20 to 25 percent will be attained. The pH of 
the polymerization medium utilized is normally in the range of 1.5 to 4.5. 
In most cases the final pH of the polymerization medium will range from 
about 3.0 to about 3.5. 
The latex containing the crosslinked methacrylic acid-ethylacrylate 
copolymer can be diluted with water after the crosslinking reaction has 
been completed. In most industrial applications, the latex will not be 
diluted. However, the latex can be diluted to a solids content within the 
range of about 1% to about 10%. In most cases, it will be preferable to 
dilute the latex to a solids content within the range of 2% to 5%. After 
the latex is diluted, it is normally desirable to adjust the pH of the 
latex to within the range of 7 to 10. It is normally preferred for the 
latex to be adjusted to within the range of 8 to 9. The pH of the latex of 
the thixotropic thickening agent can be adjusted with any basic 
neutralizing agent. Sodium hydroxide and potassium hydroxide are preferred 
bases for utilization in adjusting the pH of the latex, although various 
amines and other basic materials can be utilized. 
Latices containing the thixotropic thickening agent of this invention can 
be utilized for suspending solid materials in aqueous coating systems. 
Coating systems containing the thixotropic thickening agents of this 
invention have a thixotropic character. Aqueous coating systems containing 
the thixotropic thickening agents of this invention have high build 
properties and can be applied as thick coatings without sagging. Due to 
the thixotropic character of such aqueous coating systems, under the high 
sheer rates encountered in applications by brush, roller, spray, or 
airless spray, the coatings thin and, therefore, flow and level properly. 
However, because of its thixotropic character such coatings reform without 
sagging. 
Aqueous coating compositions which contain the thixotropic thickeners of 
this invention are typically comprised of water, pigments, a water 
reducible coating resin, a plasticizer, and the thixotropic thickener. 
Such coating compositions normally contain from about 20 to 60 weight 
percent water, from about 5 to about 60 weight percent pigments, from 
about 15 to about 60 weight percent water reducible coating resin, from 
about 1 to about 6 weight percent plasticizer, and from about 0.5 to 4 
weight percent thixotropic thickening agent. The specific amount of water, 
pigments, coating, resin and plasticizer used in a coating composition 
will vary greatly and depends upon the application for which it is made 
(stain, anticorrosion paint, texture coating, high gloss enamel, highway 
paint, swimming pool paint, etc.) For example, it is generally preferred 
for stains to be comprised of 35 to 45 weight percent water, from 8 to 15 
percent water pigments, from about 40 to 50 weight percent water reducible 
coating resin, from about 2 to 4 weight percent plasticizer, and from 
about 1 to 3 weight percent of the thixotropic thickening agent. Other 
types of coating compositions, such as anticorrosion paints and highway 
paints, can contain much higher levels of pigments. For example, highway 
striping paints and anti-corrosion paints can contain 15 to 35 weight 
percent water, 40 to 60 weight percent pigments, 10 to 30 weight percent 
coating resins, 1 to 3 weight percent plasticizer, and 1 to 4 weight 
percent of the thixotropic thickening agent of this invention. Such 
aqueous coating compositions also commonly contain cosolvents, defoamers, 
and an antifreeze. For instance, such aqueous coating systems commonly 
contain from 4 to 8 percent of a cosolvent, from 0.5 to 2 weight percent 
of an antifreeze, and from 0.5 to 2 weight percent of a defoamer. 
The water reducible resin which is utilized in such aqueous coating 
compositions can be any water reducible resin known to persons skilled in 
the art for utilization in making water reducible coating compositions. A 
particularly preferred water reducible resin for utilization in such 
applications is comprised of repeat units which are derived from (1) at 
least one monomer selected from the group consisting of styrene. 
alpha-methylstyrene, and vinyl toluene; (2) at least one alkylacrylate 
monomer wherein the alkyl moiety contains from 3 to 5 carbon atoms; and 
(3) at least one unsaturated carbonyl compound selected from the group 
consisting of acrylic acid, methacrylic acid, fumaric acid, itaconic acid, 
maleic acid and maleic anhydride. Such water reducible resins typically 
contain from about 50 to about 90 percent of said members selected from 
the group consisting of styrene, alpha-methylstyrene, and vinyl toluene; 
from about 10 to about 40 percent of said alkylacrylate monomers; and from 
about 1 to about 10 percent of said unsaturated carbonyl compounds, based 
upon 100 weight percent of monomeric units within the resin. The water 
reducible resin will most preferably contain from about 65 to about 75 
weight percent styrene, from about 20 to 30 weight percent butylacrylate, 
from about 1 to about 3 weight percent acrylic acid, and from about 0.5 to 
about 2 weight percent methacrylic acid. 
The charge composition utilized in the synthesis of such water reducible 
coating resins is typically comprised of the appropriate monomers, water, 
a phosphate-ester surfactant and a free radical initiator. In order to 
increase the particle size of the resin, the monomers are optimally 
polymerized in the presence of at least one polyol. The monomer charged 
composition utilized in such polymerizations normally contains from about 
50 to about 90 percent by weight, based on total monomers, of at least one 
vinyl aromatic monomer selected from the group consisting of styrene, 
alpha-methylstyrene, and vinyl toluene; from about 10 to about 40 percent 
by weight, based on total monomers, of an alkylacrylate monomer; and from 
about 1 to about 10 percent by weight, based on total monomers, of an 
unsaturated carbonyl compound selected from the group consisting of 
acrylic acid, methacrylic acid, fumaric acid, itaconic acid, maleic acid 
and maleic anhydride. The ratio between the total amount of monomers 
present in the charge composition and water can range between about 0.2:1 
and about 1.2:1. It is generally preferred for the ratio of monomers to 
water in the charge composition to be within the range of 0.8:1 to 1.1:1. 
The charge composition also contains from about 1 phm to about 5 phm of a 
phosphate-ester surfactant. It is generally preferred to utilize 2.5 to 3 
phm of the phosphate-ester surfactant. Such phosphate-ester surfactants 
are commercially available from a wide variety of sources. For instance, 
some phosphate-ester surfactants which are commercially available include 
Cafacre-410 (GAF Corporation), Indoil (BASF-Wyandotte Corporation), Emphof 
(Whitco Chemical Corporation), Cyclophof (Cyclo Chemicals Corporation), 
Tryfac (Emery Industries), and Alcamet (Lonza Inc). 
In order to increase the particle size of the resin, it is highly desirable 
to include at least one polyol in the charge composition. Normally, from 
about 0.1 to about 2 phm of a polyol is included in the charge 
composition. It is preferred for the charge composition to contain 0.03 to 
0.4 phm of at least one polyol. It is more preferred for the charge 
composition to contain about 0.05 phm of a polyol. The polyols that are 
useful for increasing the particle size of the resin have the structural 
formula: 
##STR5## 
wherein n and m are integers and wherein indicates that the 
distribution of repeat units can be random. 
The free radical generator is normally employed at a concentration within 
the range of about 0.01 phm to about 1 phm. The free radical initiators 
which are commonly used include the various peroxygen compounds such as 
potassium persulfate, ammonium persulfate, benzoyl peroxide, hydrogen 
peroxide, di-t-butyl peroxide, dicumyl peroxide, 2,4-dichlorobenzoyl 
peroxide, decanoyl peroxide, lauryl peroxide, cumene hydroperoxide, 
p-menthane hydroperoxide, t-butyl hydroperoxide, acetyl acetone peroxide, 
methyl ethyl ketone peroxide, succinic acid peroxide, dicetyl 
peroxydicarbonate, t-butyl peroxyacetate, t-butyl peroxymaleic acid, 
t-butyl peroxybenzoate, acetyl cyclohexyl sulfonyl peroxide, and the like; 
the various azo compounds such as 2-t-butylazo-2-cyanopropane, dimethyl 
azodiisobutyrate, azodiisobutylronitrile, 
2-t-butylazo-1-cyanocyclohexance, 1-t-amylazo-1-cyanocyclohexane, and the 
like, the various alkyl perketals, such as 2,2-bis-(t-butylperoxy)butane, 
and the like. Water soluble peroxygen free radical initiators are 
especially useful in such aqueous polymerizations. 
After the charge composition is prepared, this emulsion polymerization is 
carried out at a temperature ranging between about 100.degree. F. 
(38.degree. C.) and 170.degree. F. (77.degree. C.). It is preferred to 
conduct the polymerization at a temperature ranging from about 120.degree. 
F. (50.degree. C.) up to about 150.degree. F. (65.degree. C.). Such 
polymerizations are generally carried out for a period of time ranging 
between about 2 hours up to about 24 hours. A polymerization time of 8 to 
10 hours is normally preferred. 
After the polymerization is completed, the latex formed can be diluted with 
additional water to the concentration (solids content) that is desired. 
This latex can be used in the preparation of water reducible coatings 
which contain the thixotropic thickening agents of this invention using 
techniques well known to those skilled in the art. 
This invention is illustrated by the following examples which are merely 
for the purpose of illustration and are not to be regarded as limiting the 
scope of the invention or manner in which it may be practiced. Unless 
specifically indicated otherwise, parts and percentages are given by 
weight.

EXAMPLES 1-5 
In this series of experiments five different thixotropic thickening agents 
were prepared. The thixotropic thickening agents synthesized in this 
series of experiments differed because varying amounts of crosslinking 
agent were utilized in their synthesis. The thixotropic thickening agents 
made in this series of experiments were synthesized in laboratory 
polymerization bottles. 
The polymerization bottles used were changed with 646 g of water, 9.5 g of 
an ethoxylated lauryl sulfate (surfactant), 68 g of ethylacrylate monomer, 
102 g of methacrylic acid monomer, 0.51 g of a 70% aqueous dispersion of 
t-butylhydroperoxide, 1.7 g of ferrous sulfate solution (an activator), 
and 0.51 g of sodium formaldehyde sulfoxylate (a reducing agent). 
N,N'-methylene bisacrylamide was utilized as the crosslinking agent in 
this series of experiments. The amount of N,N'-methylene bisacrylamide 
utilized was varied between 0.085 g and 0.425 g (between 0.05 phm and 0.25 
phm). The amount of N,N'-methylene bisacrylamide utilized in each of the 
polymerizations conducted in this series of experiments is shown in Table 
I. 
The polymerization bottles were placed in a constant temperature bath which 
was maintained at 85.degree. F. (29.degree. C.) immediately after being 
charged. The polymerizations were allowed to run for a period of about 2 
hours which typically resulted in a solids content of about 22%. No 
coagulum formed in any of the polymerization bottles. Table I shows the 
final solids content, pH, viscosity, and surface tension of each of the 
latices prepared in this series of experiments. 
TABLE I 
______________________________________ 
Amount of 
Crosslinking 
Final Surface 
Example Agent Solids pH Tension 
______________________________________ 
1 0.085 g 21.6 3.1 58.4 
2 0.17 g 21.6 3.3 58.0 
3 0.255 g 21.7 3.2 64.3 
4 0.34 g 21.5 3.2 63.3 
5 0.425 g 21.6 3.2 58.6 
______________________________________ 
The latices made which contained the thixotropic thickening agents of this 
invention had outstanding properties as thickening agents for water 
reducible coatings. 
EXAMPLE 6 
A water reducible coating was prepared utilizing the latex containing the 
thixotropic thickening agent prepared in Example 3. The coating prepared 
was a stain which was made by admixing 57.9 g of ethylene glycol 
monopropylether (as a cosolvent), 8.8 g of diethylene glycol 
monomethylether (as an antifreeze), 2.1 g of triethylamine, 10.2 g of a 
defoamer which was comprised of a mineral oil, emulsifier, and silica 
derivative (Drew Y-250), 25.9 g of butylbenzyl phosphate (as a 
plasticizer), 51.7 g of aluminum silicate (pigment), 51.7 g of red iron 
oxide (pigment), 370 g of Pliolite.RTM. WR-D (a water reducible coating 
resin), 325 g of water, and 15 g of the thixotropic thickening agent 
prepared in Example 3. The coating thus prepared had excellent 
characteristics as a stain for woods. It was painted onto shake shingles. 
There were no problems encountered in the application. In fact, it was 
very easy to apply the stain prepared in this experiment to the wood 
shingles. The shingles which were stained have a very good appearance. 
The thixotropic thickener utilized in making the stain made in this 
experiment provided the stain with a thixotropic character. Accordingly, 
the stain was easy to apply and provided the shingles stained with a 
highly satisfactory coating. This example clearly illustrates that the 
thixotropic thickeners of this invention can be utilized to thicken water 
reducible coating systems. 
EXAMPLE 7 
A water reducible anti-corrosion paint was made by admixing 95 g of 
ethylene glycol monopropylether, 10 g of diethylene glycol monoethylether, 
10 g of triethylamine, 10 g of defoamer, 20 g of a chlorinated paraffin 
(as a plasticizer), 5 g of a dispersing aid, 450 g of Pliolite.RTM. WR-D 
(a water reducible coating resin), 100 g of titanium dioxide, 25 g of zinc 
oxide, 250 g of zinc phosphate, 25 g of an organozinc compound (an 
anti-corrosion pigment), 75 g of a potassium aluminosilicate (an extender 
pigment), 100 g of water, and 19.7 g of the thixotropic thickening agent 
prepared in Example 3. The anti-corrosion paint made had a thixotropic 
character. 
The anti-corrosion paint made was painted onto steel panels. There were not 
problems encountered in the application and the painted panels have a good 
appearance. This example clearly shows that the thixotropic thickeners of 
this invention can be used to make water reducible anti-corrosion paints 
which have a thixotropic character. 
EXAMPLE 8 
A swimming pool paint was made by admixing 83 g of ethylene glycol 
monopropyl ether, 11.7 g of triethylamine, 31.4 g of butyl benzyl 
phosphate, 10 g of diethylene glycol monomethyl ether, 0.3 g of surface 
active agents, 1.5 g of defoamer, 4.1 g of an alkanolamine titanate, 170.6 
g of water, 416.5 g of Pliolite.RTM. WR-D, 228.8 g of titanium dioxide, 
70.7 g of silicon dioxide, 16.9 of potassium aluminosilicate, 4 g of a 
green pigment dispersion, and 13.2 g of a thixotropic thickening agent 
made by the process specified in Example 3. The swimming pool paint made 
was determined to be thixotropic in nature. 
EXAMPLE 9 
A thixotropic thickening agent was made utilizing the procedure specified 
in Example 2 except that ethylene glycol dimethacrylate was used as the 
water soluble crosslinking agent in place of the methylene bisacrylamide 
used in Example 3. A swimming pool paint was then made using the procedure 
specified in Example 8 except hat 13.8 g of the thixotropic thickening 
agent which was crosslinked with ethylene glycol dimethacrylate was used 
in place of the thixotropic thickening agent which was crosslinked with 
methylene bisacrylamide. The swimming pool paint made had a thixotropic 
character. This example shows that the thixotropic thickening agents of 
this invention which are crosslinked with ethylene glycol dimethacrylate 
can be used to provide water reducible coatings with a thixotropic 
character. 
EXAMPLE 10 
A semi-gloss white enamel was made by admixing 56 g of ethylene glycol 
monopropyl ether, 9 g of diethylene glycol monomethyl ether, 9 g of 
triethylamine, 10 g of a defoamer, 25 g of a butyl benzyl phosphate 
plasticizer, 4 g of an alkanolamine titanate, 479 g of Pliolite.RTM. WR-D, 
225 g of titanium dioxide, 160 g of water, and 13.2 g of a thixotropic 
thickening agent made by the process specified in Example 3. The white 
enamel made was determined to have a thixotropic character. 
While certain representative embodiments and details have been shown for 
the purpose of illustrating the invention, it will be apparent to those 
skilled in this art that various charges and modifications may be made 
therein without departing from the scope of the invention.