Electrocoating process using shear stable cationic latex

Cationic electrocoat latices, containing blocked isocyanate crosslinker and which are usually unstable toward pumping and shear forces, can be stabilized by conducting the emulsion polymerization in a solvent-water mixture containing from about 20 to 30 percent solvent. Ethanol is a preferred solvent. Preferably the crosslinker is first emulsified and then added to the emulsion polymerization system prior to or during polymerization to produce mechanically stable latex that is virtually free of grit.

The invention relates to improved cationic latices useful in coatings and 
to a process for imparting both cleanliness and shear stability to such 
latexes especially amino stabilized cationic latices. 
BACKGROUND OF THE INVENTION 
Although water-borne cationic resin systems are well know, the use of latex 
binders in cathodic electrocoating is quite new and has not yet achieved 
full commercial acceptance. Coassigned U.S. Ser. No. 513,621 filed July 
14, 1983, now U.S. Pat. No. 4,512,860, which gives background information 
on electrocoating and especially latex for cathodic deposition, is 
incorporated herein by reference. Also incorporated by reference are 
coassigned U.S. Ser. No. 716,665 filed Mar. 27, 1985; and U.S. Ser. No. 
716,664 filed Mar. 27, 1985, now U.S. Pat. No. 4,579,889, which relate to 
the stabilization of cationic latices and paints suitable for 
electrocoating. The term "latex" is defined as a polymer or copolymer 
prepared from one or more monomers in an aqueous environment by emulsion 
polymerization techniques. Such latex, usually having an average particle 
size from about 400 .ANG. to about 10,000 .ANG. and an average molecular 
weight ranging from about 10,000 up to and above 250,000, is quite 
different from the water-reducible or ionizable polymers prepared, not in 
aqueous medium, but in solvent systems or neat. The latter 
water-reducible, cation-active polymers have been in commercial use for 
electrodeposition coatings for some time. The latex polymers and 
cation-active latices of the present invention are preferred over the 
commercial water-borne or water-reducible coatings. Such cationic latices 
are known to be inherently less stable than their anionic counterpart 
systems. For electrodeposition coatings, it is necessary to develop a 
latex that can be pumped and will be relatively insensitive to shear 
forces. 
Stability to shear is a necessary property for an electrocoating bath. In a 
commercial operation, the coating is continuously sheared by centrifugal 
pumping which passes the material through ultrafiltration membranes at a 
rate of 35-40 gallons/min. Instability of the coating, leading to 
agglomeration of particles after shear, would cause fouling of the 
ultrafiltration membrane, application problems, and loss of coating 
properties. The term "stable cationic latex" or "stable cationic latex 
paint composition" in the context of the present invention means a latex 
that when subjected to shear forces and/or pumping will be substantially 
non-agglomerated as determined by the HB/DCP shear test using a disc 
centrifuge described hereinafter. 
U.S. Pat. No. 3,640,935 (Abriss) teaches a method of improving latex 
stability by adding to the latex a nonionic surface-active agent (0.5-3%) 
as a solution in a water-soluble glycol. Heretofore a prepared latex was 
judged to be stable if it did not set to a gel after thirty minutes in the 
Hamilton Beach shear test. It now appears this test is not critical enough 
to determine particle agglomeration and gelling tendency. A HB/DCB shear 
test using a disc centrifuge (cf U.S. Pat. No. 4,311,039) was developed to 
critically examine latex products and to more critically access the degree 
of latex agglomeration. It was found that cationic latices often readily 
agglomerate when subjected to shear. Attempts to improve mechanical 
stability by increasing the cationic precursor amine monomer content or by 
the addition of conventional surfactants or additives, were insufficient 
to upgrade the latex to prevent severe agglomeration as determined by the 
new HB/DCB shear test method. Higher amine monomer level in the latex 
synthesis quite often diminishes latex conversion and increases dirt 
(coagulum) levels. In the instant invention improved latex stabilization 
and cleanliness have been achieved by an improved process for 
incorporating the crosslinker in an emulsion polymerization using a mixed 
aqueous/organic medium. 
BRIEF SUMMARY OF THE INVENTION 
One object of the invention is to provide a substantially grit-free and 
shear stable amine functional cationic latex prepared by emulsion 
polymerizing ethylenically unsaturated monomers and unsaturated amino 
group containing monomers in an aqueous medium wherein the emulsion 
polymerization is conducted (1) in an organic solvent/water system 
containing from about 10 to 40 weight percent water-miscible or 
water-soluble solvent selected from the group consisting of C.sub.1-12 
alkanols, ketones, esters, ethers, glycols, and alkoxyalkanols; and (2) in 
the presence of one or more latent crosslinking agents adapted to cure 
with functional groups in said polymer latex. 
Another object relates to the latex prepared by emulsion polymerization in 
the presence of crosslinking agent which is incorporated into the 
polymerization system prior to or during the monomer polymerization either 
as an aqueous emulsion or as a solution in monomers. 
A further object is an electrocoating paint and process for coating metal 
substrate incorporating said improved latex.

DETAILED DESCRIPTION OF THE INVENTION 
This invention relates to structured cationic latices stabilized against 
mechanical shear which are prepared by emulsion polymerization of various 
ethylenically unsaturated monomers in a water/solvent mixture. 
The term "structured cation-active latices" includes those where the 
cation-activity is derived from amino-containing monomers and/or from 
charge carrying species derived from bound initiator fragments such as 
amidino fragments resulting from the polymerization initiator. The former 
monomers can participate in the polymerization by virtue of ethylenic 
unsaturation; the latter impart cation activity by attachment to the 
polymer chains. "Stability" is defined as the absence of agglomerated 
latex particles as shown by disc centrifuge photosedimentometer traces 
after subjecting the latex to 30 minutes of mechanical shear using a 
Hamilton Beach high speed mixer. Such latices are preferably stabilized by 
the process of the instant invention which utilizes a solvent/water system 
for the emulsion polymerization and preferably the prior emulsification of 
the crosslinking agent. When the emulsion polymerization is conducted in 
20% ethanol-water or isopropanol-water, the product latex shows no 
significant particle agglomeration as noted by disc centrifuge particle 
size analysis, even after 30 minutes of high shear stirring. The presence 
of the solvent also provides a convenient method of incorporating highly 
water-insoluble crosslinkers, such as blocked isocyanates, into latices 
and particularly introducing them prior to or during the polymerization. 
Crosslinkers, such as for example chain-extended adducts of polyols with 
isophorone diisocyanate blocked with caprolactam, are water insoluble, 
large molecules which are difficult to incorporate into latices. If 
dissolved in monomer and added during polymerization, the crosslinker 
precipitates as a crystalline grit and consequently deposited films remain 
uncured after baking. With the addition of approximately 20% ethanol or 
isopropanol to the aqueous polymerization medium, grit is dramatically 
reduced and films cured properly. These solvents do not interfere with 
either the emulsion polymerization process, the electrodeposition or cure 
of the instant systems. 
The cationic latices which comprise a major portion of the improved coating 
composition useful in electrodeposition coating of conductive substrate, 
particularly metal substrate, are prepared in an aqueous medium by 
emulsion polymerization of monomers having ethylenically unsaturated 
monomer. Preferred latices are described in coassigned U.S. Pat. No. 
4,512,860 noted above. These can include all-acrylic or methacrylic 
monomers and mixtures of acrylics or methacrylics with other monomer types 
such as for example unsaturated hydrocarbon monomers, i.e. styrene, vinyl 
toluene and the like. 
The term "latex" is understood to comprise a polymer or copolymer prepared 
from ethylenically unsaturated monomers in an aqueous environment by 
emulsion polymerization. The resin binder particles in a latex 
advantageously have a particle size from about 400 to 10,000 .ANG. and 
were preferably in the 1500-6000 .ANG. range. A cationic latex is a latex 
having a salt-forming precursor component, capable of being ionized with 
an acid type reaction whereby the ionized salt portion helps to effect 
water dispersibility of the latex binder. When the salt-forming precursor, 
preferably a primary, secondary or tertiary amine portion, is part of the 
polymeric chain, then such latices are said to be structurally cation 
active. When the cation portion is merely added as a non-polymeric unit, 
the latex is said to be cation active by the fact that the positively 
charged ions reside on the surface of the polymer particle. These 
non-structural types are not deemed to be structurally cation active. 
The vinyl monomers most useful in forming the structured cation latex 
include acrylic and methacrylic esters, for example, methylmethacrylate, 
ethylmethacrylate, 2-ethylhexylmethacrylate, butylacrylate, isobornyl 
acrylate, isobutyl methacrylate and the corresponding hydroxy acrylates, 
e.g. hydroxyethyl acrylate, hydroxypropyl acrylate; also the glycol 
acrylates, allyl acrylates; and epoxy acrylates. Other suitable vinyl 
monomers include vinyl acetate, vinyl and vinylidene halides, e.g. vinyl 
chloride, vinylidene chloride amides such as methacrylamide and 
acrylamide; hydrocarbons such as butadiene, styrene, vinyl toluene and the 
like. 
For structured cationic latex, additional vinyl monomers having base 
functionality are required. Amino groups are preferably incorporated in 
the vinyl monomers by using tertiary, secondary or primary amino 
functional acrylates, methacrylates, and acrylamides such as for example, 
dimethylaminoethyl methacrylate or acrylate, or dimethylaminopropyl 
acrylamide or methacrylamide. Such amine functional monomers are 
copolymerized in an aqueous system to build an amino functionality into 
the acrylate polymer which, when partially or fully neutralized with an 
ionizer, impart the cationic properties to the acrylic latex. Hydroxy 
functional monomers, such as hydroxypropyl methacrylate can be used at 
concentrations of 0.5 parts per hundred monomer (pphm) to over 20 pphm and 
preferably 5-15 pphm. Amine monomers, such as dimethylaminoethyl 
methacrylate preferably can be used at levels of about 0.01 and 5 pphm. 
The structured cation-active latices prepared by emulsion polymerization in 
an aqueous medium and paints comprising the combination of said latex with 
various pigment grinds are preferably stabilized by the prepolymerization 
addition of specific organic solvents, preferably water-soluble organic 
alcohols, added in an amount sufficient to prevent latex particle 
agglomeration which would normally result when the latex is pumped or 
subjected to shear forces. By "water-soluble" solvent is meant an organic 
solvent, either water-miscible or having a solubility in water of at least 
20 weight percent. Said solvents include for example, alcohols, glycols, 
ketones, esters particularly hydrophillic functional esters, ethers and 
cyclic ethers, hydroxylated ethers and the like, preferably those having 
up to 12 carbon atoms. The solvent can be used in amounts of about 1 to 50 
percent and preferably 15-35 percent basis water plus organic solvent 
content in the emulsion polymerization. Suitable solvents are organic 
alcohols such as for example, methanol, ethanol, isopropanol; 2-(2-ethoxy 
ethoxy)ethanol; 2-(2-butoxy ethoxy)ethanol; 2-(2-methoxy ethoxy)-ethanol; 
2-methoxy ethanol; 2-butoxy ethanol; 2-ethoxy ethanol; 2 -butoxy propanol; 
2-butoxy ethoxy propanol and the propoxy propanols; also useful are known 
glycols including ethylene and propylene glycols. Ethanol and isopropanol 
are most preferred due to their availability, cost and ease of removal 
prior to electrodeposition, if desired. In addition to the surprising 
mechanical stability afforded to the latex systems, it was observed that 
the presence of solvent was not detrimental to the electrocoating 
compositions and process and the characteristics of the resulting film. 
The amount of stabilizer solvent used during the polymerization process is 
critical in that it must be sufficient to prevent polymer agglomeration 
when the product latex is pumped or otherwise subjected to shear forces 
and yet comply with environmental (VOC) regulations. Of course, the 
composition of the latex will influence the choice of solvent and amount 
needed for stabilization. 
As noted earlier, the selection of initiator is important in that it can 
contribute to the cation activity of the latex by attachment of charged 
initiator fragment species to the polymer. The initiators produce free 
radicals for the latex polymerization and can be, for example, certain 
redox systems such as: hydroxylamine hydrochloride in combination with 
t-butylhydroperoxide, azo types such as 2,2'-azobis(amidinopropane 
hydrochloride) ("AAP"), 2,2'-azobis isobutyronitrile ("AIBN"), 
2,2'-azobis(2-isopropylimidazolium)dichloride, 
2,2'-azobis(2-aminopropane)sulfate, or even an electron beam or gamma 
radiation. 
Useful crosslinking agents which may be incorporated into emulsion polymer 
latex systems of the instant invention include known crosslinkers as for 
example, phenol formaldehyde, methylated melamine, urea formaldehyde, 
glycolurils, blocked isocyanates including polymerizable blocked 
isocyanates. Preferred agents are the blocked isocyanates including 
dimerized or trimerized isocyanates as represented in part by Huls B1370, 
a triisocyanurate of isophorone diisocyanate blocked with acetone oxime 
(60% in xylene/butyl acetate) commercially available from Chemische Werke 
Huls. Equally useful are chain-extended isophorone diisocyanates capped 
with E-caprolactam such as Goodyear VITEL C10045A or Carbill CR 2400. 
Preferred blocked isocyanates derived from polymerizable vinyl 
unsaturation include for example vinyl benzyl isocyanates, vinyl aryl 
isocyanates, vinyl phenyl, isopropenylphenyl and isopropenylbenzyl 
isocyanates and the like as exemplified in U.S. Pat. No. 3,654,336; 
4,379,767; 4,399,074; 4,399,073; and 4,439,616. In this category the most 
preferred crosslinker is meta-isopropenyl-alpha,alpha-dimethylbenzyl 
isocyanate fully blocked with common blocking agents. Suitable blocking 
agents are those known in the art including alcohols, phenols, ketoximes 
and the like. Especially preferred blocking agents are caprolactam and 
2-ethylhexyl alcohol or mixtures thereof. The general method of 
preparation is to add the isocyanate to the blocking agent with or without 
a catalyst, such as an organo-tin compound, over a period of time 
sufficient to control the exotherm, at a temperature high enough to 
achieve a reasonable blocking rate but low enough to prevent 
polymerization through the double bond or the reverse deblocking reaction. 
This temperature is normally 50.degree.-120.degree. C., depending on the 
particular isocyanate/blocking agent combination and the catalyst in use. 
Normally, a 0 to 10% excess of blocking agent is used; reaction is 
complete when free NCO content is essentially zero, as determined by 
either infra-red absorption spectroscopy or titration with standard 
n-butylamine solution. 
Aqueous coatings of the above type may be applied either by conventional 
coating techniques or by electrodeposition. For cathodic electrodeposition 
it is necessary to neutralize or partially neutralize the amine portion of 
the polymer. Thus by neutralizing the amino resins desirable, aqueous 
compositions can be obtained for electrodeposition from solutions or 
dispersions of pH between 1 and 6 and preferably between about 2 and 5. 
This can be accomplished by acidification of all or part of the amino 
group functionality by an inorganic acid or an organic acid such as for 
example formic, acetic, or lactic acid and the like. In determining the 
degree of neutralization for a particular system, an amount of 
neutralizing acid is selected to solubilize or disperse the resin. 
Phosphoric acid is the preferred inorganic acid and lactic acid is a 
preferred organic acid for the acidification or partial acidification to 
form the amino cation active polymer compositions. In the preferred method 
the neutralizing acid is added before or during the polymerization. 
Usually the cathodic resin composition will be present in water at 
concentrations from about 1 percent to about 30 percent by weight of resin 
for coating purposes although more concentrated aqueous compositions are 
generally desired for synthesis, storage, and shipping. Preferred useful 
bath concentrations are from 5 to 20 weight percent. The unpigmented 
compositions may be electrocoated to deposit clear coatings on the cathode 
electrode. More commonly these compositions will be used in combination 
with various pigment compositions and other additives known to the 
electrocoating art. Conventional pigment-containing compositions include 
organic and inorganic pigments and additives such as titanium dioxide, 
oxides, carbon black, talc, barium, sulfate as well as pigments or pseudo 
pigments known as plastic pigments such as polystyrene particles and the 
like. 
Contrary to prior concepts that addition of organic solvent components to a 
latex paint often has caused gross destabilization and gellation, it is 
now found that the stability of the instant latex and paint toward shear 
is remarkably improved over the non-stabilized latex paint without 
detriment to corrosion, film integrity, and other desirable coating 
characteristics. 
As noted above, coassigned U.S. Pat. No. 4,512,860 teaches an improvement 
using ion exchange techniques to treat the new latex systems prepared by 
emulsion polymerization of monomers in an aqueous environment and having 
cation active groups supplied by nitrogen-containing monomers or by 
initiators. By such treatment "amino" fragments, and low molecular weight 
monomers, are rendered non-conflicting with good elecrtrocoat systems. In 
the present invention using specific solvent stabilizers, and crosslinker 
incorporation, some latex systems can be used in electrocoating processes 
without prior ion exchange purification or other type of cleaning to 
remove ionic contamination. This represents an additional processing and 
cost advantage. 
Hamilton Beach Test. The latex was strained through a 200-mesh sieve and an 
amount sufficient to contain 100 grams solids was weighted into a 24-ounce 
milkshake cup. Two grams defoamer was added and the sample was mixed for 
30 minutes using the medium speed setting of Hamilton Beach Milkshake 
Mixer Model No. 30. The sample was removed and its consistency noted i.e., 
fluid. paste, dilatent, solid, etc. The weight of the residue (grit) 
retained on the sieve was expressed as percentage of the original latex 
solids. 
Shear Stability Test. The disc centrifuge photosedimentometer (DCP) is 
known to be useful for determining particle size and particle size 
distribution for latex emulsions and other polymer systems (cf U.S. Pat. 
No. 3,475,968 and U.S. Pat. No. 4,311,039). The same concept, namely 
forcing particles (usually less than 2.mu. in size) under high centrifugal 
force radically outwardly through a spin fluid or medium, is readily 
adaptable for the evaluation of particle agglomeration of the instant 
latex composition. Larger and denser particles traverse the medium faster 
than do those of smaller particle size. This technique is adaptable for 
both pigmented and non-pigmented latex systems. Optical analysis of the 
exiting particles provide a trace similar to those shown in FIG. 1. FIG. 
1-A represents a shear-unstable latex which before shear is applied as a 
single broad peak at 2-6 minutes. FIG. 1-B shows the same latex after 
subjecting to Hamilton Beach mixing for 30 minutes. It is noted that as 
the latex agglomerates, the 4-minute unagglomerated peak decreases and an 
agglomerated latex peak appears at about 0.8 minute. All tests were run at 
disc centrifuge speeds of 3,586 rpm using dilute nonionic surfactant 
solution as spin medium. 
In the electrocoating process the aqueous cathodic bath containing the 
neutralized cationic resin, pigments, additives, etc., is placed in 
contact with an electrically conductive anode, an electrically conductive 
cathode serving as the article to be coated. Current is applied (usually 
D.C.) at voltages between 50 and 500 volts whereby the organic resin 
migrates and is deposited on the conductive substrate to be coated such as 
for example steel, aluminum, iron and the like. Other bath components such 
as pigments, filler and additives are conveyed with the cathodically 
charged resin and deposited on the substrate. After deposition the coating 
substrate is removed from the bath and rinsed with deionized water prior 
to effecting a cure. The deposited coatings cure at elevated temperatures 
by the usual techniques of heating in ovens or with infra-red heaters. 
Curing temperatures usually range from about 300.degree. F. to about 
425.degree. F. 
The following illustrative Examples should not be narrowly construed. 
Unless otherwise indicated, parts and percentages are by weight and 
temperature is given in degrees Centigrade. 
EXAMPLE 1 
An emulsion polymer latex was prepared using the following ingredients and 
procedure: 
______________________________________ 
A 379 g ethanol 
1515 g H.sub.2 O 
3 g Triton X 405* 
1.8 g H.sub.3 PO.sub.4 (85%) 
B 21 g butylacrylate 
35 g methylmethacrylate 
C 1.5 g 2,2'azobis(2-amidinopropane)HCl 
59 g H.sub.2 O 
D 705 g butylacrylate 
519 g methylmethacrylate 
120 g hydroxypropylmethacrylate 
3 g dimethylaminoethylmethacrylate 
2.8 g n-dodecylmercaptan 
179 g B1370 Crosslinker 
E 2.8 g 2,2'-azobis(2-amidinopropane)HCL 
120 g H.sub.2 O 
18 g Triton X 405 
______________________________________ 
*Triton X 405 surfactant from Rohm & Haas. 
"A" was charged to a reactor and heated to 75.degree. C. under a nitrogen 
blanket. Components "B" were added followed by "C" five minutes later. The 
crosslinker (Huls B1370) was dissolved in the monomer mix "D". After about 
20 minutes, "D" and "E" were pumped in parallel streams over a period of 4 
and 41/2 hours, respectively. The temperature was held for one hour and 
the reaction product cooled. 
EXAMPLES 2-7 
The procedure of Example 1 was repeated using no solvent (Control, Example 
2) and with various solvents used in place of the ethanol (See Table I). 
Cold-rolled steel panels (Bonderite 1000 treatment) were cathodically 
electrocoated at 5% solids for 1 minute at 200 volts. Cure was effected by 
heating in a forced air oven at 350.degree. F. for 20 minutes. Panels 
typically exhibited 70% gloss (60.degree.) and resisted 70 MEK rubs. Shear 
stability was evaluated using the Hamilton Beach and the Disc Centrifuge 
Agglomeration Tests. Results are shown in Table I. Stable latices 
exhibited little or no agglomeration as evidenced by the identify of the 
disc centrifuge traces compared with unsheared latex samples. Grit 
evaluation of the latex by filtration through a 200-mesh stainless steel 
sieve gave a value of weight (grams) retained on filter compared with 
original charge (grams). Results are shown in Table I. 
TABLE I 
______________________________________ 
Exam- MEK 
ple No. 
Solvent Grit* Cure Stability 
Rubs** 
______________________________________ 
1 20% ethanol 2 Yes Yes 90 
2 None 87 No No 10 
3 20% isopropanol 
17 Yes Yes 70 
4 20% acetone 28 Yes Partial 60 
5 20% propylene 
26 Yes Partial 60 
glycol 
6 30% ethanol 17 Yes Not 95 
Evaluated 
______________________________________ 
*Grams grit per gallon latex sample; (all latices contained 107 g 
crosslinker (per gallon)). 
**Number of double rubs to break through coating using moderate pressure 
and methylethyl ketone soaked rag. 
EXAMPLE 8 
A stable cationic electrocoat latex was prepared as follows: Blocked 
isocyanate crosslinker, 350 g (Huls B1370) was dispersed in 3.5 g Triton X 
405 and 350 g H.sub.2 O and emulsified in a Gaulin two-stage homogenizer 
at 300 kg/cm.sup.2 in stage one and 50 kg/cm.sup.2 in stage two. 
______________________________________ 
A 379 g ethanol 
1515 g H.sub.2 O 
6 g Triton X 405 
2 g H.sub.3 PO.sub.4 (85%) 
B 21 g butylacrylate 
35 g methylmethacrylate 
C 1.4 g 2,2'-azobis(2-amidinopropane)HCl 
59 g H.sub.2 O 
D 702 g butylacrylate 
519 g methylmethacrylate 
120 g hydroxypropylmethacrylate 
2.8 g dimethylaminoethylmethacrylate 
2.8 g n-dodecylmercaptan 
E 2.8 g 2,2-azobis(2-amidinopropane)HCl 
15 g Triton X 405 
117 g H.sub.2 O 
______________________________________ 
"A" components were heated to 75.degree. C. under nitrogen and "B" 
components added thereto followed by "C" five minutes later. 
Components "D", "E" and the emulsified crosslinker (Huls B1370) were pumped 
simultaneously over 4, 41/2, and 3 hours, respectively. After holding 
temperature at 75.degree. C. for one hour, the product latex was evaluated 
for grit and for shear stability. After shearing on a Hamilton Beach 
Scovill mixer (Model 30, medium speed setting), the latex showed 
negligible agglomeration as evidenced by the disc centrifuge trace (cf 
FIG. 2). 
EXAMPLES 9-11 
Example 8 was repeated using emulsified crosslinker (Huls B1370) and 10% 
ethanol/water polymerization medium (Example 9) and with no solvent 
additive (Example 11). Example 10 used 20% ethanol as polymerization 
medium, but differs from Example 8 in that the crosslinker was added as a 
solution in the monomer mix. The various latices were evaluated for grit 
content, shear stability and ability to cure as shown in Table II. 
Example 8 (emulsified crosslinker and 20% ethanol) represented the best 
overall performance and gave negligible grit, good cure and was shear 
stable whereas the same procedure using 10% ethanol (Example 9) was 
grit-free, cured properly, but was not stable toward shear forces. 
Similarly when no solvent is used, the resulting latices are not shear 
stable as shown in Examples 11 and 2. Obviously, the system (Example 8) 
using a solvent/water medium for emulsion polymerization and 
preemulsification of crosslinker is the preferred method. 
FIG. 1 shows the results of shear forces on a shear unstable latex. The 
latex of Example 11 was evaluated using the disc centrifuge 
photosedimentometer (DSC) tracing both before (FIG. 1-A) and after (FIG. 
1-B) subjecting to Hamilton Beach Shear Test (30 minutes at medium speed). 
The unagglomerated peak at 4.0 minutes decreases and a new peak 
(agglomerated particle) appears at about 0.8 minutes. In contrast, the 
stabilized bi-modal latex of Example 8 remains substantially 
unagglomerated (cf FIG. 2-A and FIG. 2-B) after Hamilton Beach mixing. 
TABLE II 
______________________________________ 
Experi- Grit.sup.+ 
ment (gram/ Shear 
No. Solvent gallon) Cure Stability 
Crosslinker 
______________________________________ 
8 20% ETOH 0.05 Yes Yes emulsified* 
9 10% ETOH 0.1 Yes No emulsified* 
10 20% ETOH 2.0 Yes Yes in monomer** 
11 none 0.1 Yes No emulsified* 
2 none 87 No No in monomer** 
______________________________________ 
.sup.+ Grams grit per gallon latex sample; (all latices contained 107 g 
crosslinker per gallon). 
*Crosslinker incorporated as per Example 8 
**Crosslinker dissolved in monomer mix.