Styrene-acrylic latex containing a hetero-unsaturated monomer and paper-coating compositions produced therefrom

An emulsion polymerized latex copolymer used as a binder in paper-coating compositions with improved dry and wet binding strength comprising an ester of an ethylenically unsaturated carboxylic acid and a saturated alcohol and a hetero-unsaturated monomer selected from the group consisting of allyl acrylate, allyl methacrylate, crotyl acrylate or crotyl methacrylate. A paper-coating composition in the form of an aqueous dispersion comprising a pigment and said emulsion polymerized latex copolymer is further characterized in that said pigment is present in an amount from about 99 to about 77 weight percent based on total dry solids. A coated paper article in the form of a fibrous sheet coated on at least one surface with the paper-coating composition is also provided.

BACKGROUND OF THE INVENTION 
This invention generally relates to an emulsion polymerized latex copolymer 
used as a binder in paper-coating compositions. More particularly, the 
invention relates to paper-coating compositions containing such latex and 
to papers coated with such paper-coating compositions. 
Colloidally stable aqueous dispersions of polymers, which dispersions are 
typically referred to in the art as latexes, are generally known to be 
useful alone and in various formulations as coatings and impregnants for 
various substrates. A wide variety of such latexes of differing 
homopolymeric and copolymeric compositions have been developed with 
specific chemical and/or mechanical properties for particular end-use 
applications. Specifically, many latexes have been developed for use in 
paper-coating compositions. Paper coating compositions are generally 
combinations of a binder (latex and/or "natural" binder) and a pigment. 
Paper-coating compositions are applied to the surface of paper in order to 
give the paper greater stiffness, opacity, whiteness, brightness, gloss, 
smoothness and/or ink receptivity. 
Latexes employing a monovinylidene aromatic monomer such as styrene and an 
aliphatic conjugated diene such as butadiene have been very popular for 
the production of latexes, especially those designed for paper-coating 
compositions. In these compositions, butadiene acts somewhat as a 
cross-linking agent, giving the latexes excellent properties. Recently, 
attempts have been made to produce paper-coating latexes which do not 
include significant amounts of butadiene. Specifically, attempts have been 
made to produce latexes from acrylic esters. Since the monomers in these 
formulations do not naturally cross-link the resulting polymer latexes, it 
is necessary to introduce a separate cross-linking agent such as divinyl 
benzene. While the performance of these latexes (with cross-linking agent) 
might be expected to be equivalent with styrene/butadiene latexes, they 
are in fact considerably inferior in performance. Specifically, these 
latexes suffer from poor dry and wet binding strength. 
Since price projections for these acrylic monomers are favorable, and since 
their polymers have better light stability and age stability than 
styrene/butadiene polymers, it would be desirable to have an acrylic latex 
which does not contain an aliphatic conjugated diene, but which has 
performance in paper-coating compositions equal to formulations containing 
an aliphatic conjugated diene. 
SUMMARY OF THE INVENTION 
The present invention provides for an emulsion polymerized latex copolymer 
used as a binder in paper coating compositions with improved dry and wet 
binding strengths. The latex copolymer comprises (a) an ester of an 
ethylenically unsaturated carboxylic acid and a saturated alcohol and (b) 
a hetero-unsaturated monomer selected from the group consisting of an 
allyl acrylate or allyl methacrylate in an amount from about 0.05 to about 
3.0 percent based on total monomer weight or a crotyl acrylate or crotyl 
methacrylate in an amount from about 0.20 to about 5.0 percent based on 
total monomer weight. In a preferred embodiment the (a) monomer is an 
ester of acrylic acid or methacrylic acid with a C.sub.1 to C.sub.9 
saturated alcohol. Also the latex copolymer can additionally comprise 
monovinylidene aromatic monomers and ethylenically unsaturated carboxylic 
acid monomers. 
The present invention further provides for a paper-coating composition in 
the form of an aqueous dispersion comprising a pigment, and an emulsion 
polymerized latex copolymer comprising (a) an ester of an ethylenically 
unsaturated carboxylic acid and a saturated alcohol, and (b) a 
hetero-unsaturated monomer selected from the group consisting of an allyl 
acrylate or allyl methacrylate in an amount from about 0.05 to about 3.0 
percent based on total monomer weight or a crotyl acrylate or crotyl 
methacrylate in an amount of from about 0.20 to about 5.0 percent based on 
total monomer weight; the composition is further characterized in that the 
pigment is present in an amount from about 99 to about 77 weight percent 
based on total dry solids. The pigments employed can be a mineral filler, 
a plastic filler or a mixture thereof. 
Still further, the present invention provides for a coated paper article in 
the form of a fibrous sheet coated on at least one surface with a 
paper-coating composition comprising a pigment, and an emulsion 
polymerized latex copolymer comprising (a) an ester of an ethylenically 
unsaturated carboxylic acid and a saturated alcohol, and (b) a 
hetero-unsaturated monomer selected from the group consisting of an allyl 
acrylate or allyl methacrylate in an amount from about 0.05 to about 3.0 
percent based on total monomer weight or a crotyl acrylate or crotyl 
methacrylate in an amount from aout 0.20 to about 5.0 percent based on 
total monomer weight; the composition is further characterized in that the 
pigment is present in an amount from about 99 to about 77 weight percent 
based on total dry solids. 
DETAILED DESCRIPTION OF THE INVENTION 
Preparation of the latexes of the invention requires the use of an ester of 
an ethylenically unsaturated carboxylic acid and a saturated alcohol, and 
a heterofunctional monomer containing both vinyl and either allyl or 
crotyl unsaturation. Though not required, these latexes preferably also 
include a monovinylidene aromatic monomer, an ethylenically unsaturated 
carboxylic acid, and an ester of an ethylenically unsaturated carboxylic 
acid and a C.sub.10 to C.sub.25 saturated alcohol. These latexes are 
produced via conventional emulsion polymerization techniques and are 
utilized in conventional paper-coating formulations. 
Esters of ethylenically unsaturated carboxylic acids and saturated alcohols 
suitable for use in the invention include esters which are addition 
polymerizable in an emulsion system. Polymers composed primarily of soft 
esters, i.e., those esters which if homopolymerized would have a glass 
transition temperature (T.sub.g) of less than about 25.degree. C. 
(298.degree. K.), exhibit dramatic increase in both wet and dry pick 
resistance when prepared and used according to the invention. Polymers 
composed primarily of hard esters, i.e., those esters which if 
homopolymerized would have a T.sub.g of greater than about 25.degree. C., 
exhibit less improvement in pick resistance than the soft esters, but it 
is with the hard esters that improvement is most needed. Prior art 
paper-coating compositions made with soft polymers typically have 
reasonably good pick resistance, but improvements are commercially 
desirable. However, compositions made with hard polymers (chosen because 
of the stiffness they impart to the coated paper) generally have very poor 
pick resistance, and any improvement is very significant. Thus, although 
the hard polymers have less improvement in pick resistance, their smaller 
improvement is as important or more important than the greater improvement 
shown by the soft polymers. Examples of suitable esters include acrylates 
such as methyl acrylate, ethyl acrylate, n- and iso-propyl acrylate, n-, 
iso-, sec- and tert-butyl acrylate, hexyl acrylate, cyclohexyl acrylate, 
2-ethylhexyl acrylate and butyl chloracrylate, and methacrylates such as 
methyl methacrylate, ethyl methacrylate, n- and iso-propyl methacrylate, 
n-, iso-, sec- and tert-butyl methacrylate, hexyl methacrylate, cyclohexyl 
methacrylate, 2-ethylhexyl methacrylate and lauryl methacrylate. Mixtures 
of the esters may be used. Of these esters, butyl acrylate is especially 
preferred. 
For the most part, the esters used in the invention are desirably those 
formed from C.sub.1 to C.sub.9 saturated alcohols. However, it is 
optional, but desirable, to have as a minor proportion of the ester 
charge, an ester formed from a C.sub.10 to C.sub.25 saturated alcohol. 
The presence of a long chain ester, i.e., an ester of an ethylenically 
unsaturated carboxylic acid and a C.sub.10 to C.sub.25 saturated alcohol, 
increases the wet binding strength of paper-coating compositions made with 
the latex, without sacrificing dry binding strength. An especially 
preferred ester in this category is lauryl methacrylate. 
The latexes of the invention also require a hetero-unsaturated monomer. By 
"hetero-unsaturated" is meant a monomer having at least two addition 
polymerizable double bonds. The hetero-unsaturated monomer will have one 
vinyl bond and one crotyl or allyl bond. In a preferred embodiment, the 
hetero-unsaturated monomer is an ester of an unsaturated alcohol and an 
unsaturated carboxylic acid. In a more preferred embodiment, the 
hetero-unsaturated compound is allyl methacrylate, allyl acrylate, crotyl 
methacrylate, or crotyl acrylate. The allyl acrylate or allyl methacrylate 
is preferably present in an amount from about 0.05 to about 3.0 percent 
based on total monomer weight while the crotyl acrylate or crotyl 
methacrylate is preferably present in an amount from about 0.20 to about 
5.0 percent based on total monomer weight. 
Though not required, the use of a monovinylidene aromatic monomer, an 
ethylenically unsaturated carboxylic acid, and an ester of an 
ethylenically unsaturated acid and a C.sub.10 to C.sub.25 saturated 
alcohol, is preferred. 
The presence of a monovinylidene aromatic monomer is useful for increasing 
the T.sub.g of the latex. Its inclusion is desirable when a relatively 
stiff coated product is desired. 
Suitable monovinylidene aromatic monomers useful in the invention include 
those monomers wherein a radical of the formula: 
##STR1## 
(wherein R is hydrogen or a lower alkyl such as an alkyl having from 1 to 
4 carbon atoms) is attached directly to an aromatic nucleus containing 
from 6 to 10 carbon atoms, including those wherein the aromatic nucleus is 
substituted with alkyl or halogen substituents. Typical of these monomers 
are styrene; .alpha.-methylstyrene; ortho-, meta- and para-methylstyrene; 
ortho-, meta- and para-ethylstyrene; o,p-dimethylstyrene; 
o,p-diethylstyrene; ispropylstyrene, o-methyl-p-isopropylstyrene; 
p-chlorostyrene; p-bromostyrene; o,p-dichlorostyrene; o,p-dibromostyrene; 
vinylnaphthalene; diverse vinyl (alkylnaphthalenes) and vinyl 
(halonaphthalenes) and comonomeric mixtures thereof. Because of 
considerations such as cost, availability, ease of use, etc., styrene and 
vinyltoluene are preferred and styrene is especially preferred as the 
monovinylidene aromatic monomer. In a preferred embodiment, a 
monovinylidene aromatic monomer and a soft ester of an ethylenically 
unsaturated carboxylic acid and a saturated alcohol are copolymerized to 
form a polymer which is harder than the ester but softer than the aromatic 
monomer. 
The presence of an ethylenically unsaturated carboxylic acid enhances the 
processability and the colloidal stability of the resulting latex. In some 
instances the acid also provides increased adhesion to a substrate to 
which the latex is applied. Examples of suitable acids include acrylic 
acid, methacrylic acid, itaconic acid, crotonic acid, 2-chloroacrylic 
acid, 2-bromoacrylic acid, 3-chloroacrylic acid, 2,3-dichloroacrylic acid, 
3,3-dichloroacrylic acid, 2-phenolacrylic acid, 3-phenolacrylic acid, 
vinylbenzoic acid, isopropenolbenzoic acid and the like. Of these acids, 
itaconic acid is especially preferred. 
The ester of an ethylenically unsaturated carboxylic acid and a saturated 
alcohol, preferably in combination with a monovinylidene aromatic monomer, 
makes up the bulk of the polymer, with the remaining ingredients being 
present in minor proportion. The proportions of the monovinylidene 
aromatic monomer and the ester should be adjusted to give the coating 
compositions made with the latex optimum performance. Three properties 
particularly controllable by varying the monovinylidene aromatic monomer 
ester ratio are the glass transition temperature and the dry and wet pick 
resistance. Generally, the ester will be present at from about 30 to about 
100 percent, preferably about 40 to about 80 percent, and most preferably 
from about 45 to about 70 percent by weight, based on the total monomer 
weight excluding the weight of the heterofunctional monomer. Generally, 
the monovinylidene aromatic monomer will be present in an amount from 
about 0 to about 70 percent, preferably from about 20 to about 60 percent, 
and most preferably from about 30 to about 55 percent based on total 
monomer weight excluding the weight of the heterofunctional monomer. 
The hetero-unsaturated monomer should be present in an amount to obtain an 
optimum combination of dry and wet pick resistance. It has been found that 
when allyl acrylate or allyl methacrylate are employed the preferred range 
is from about 0.05 to about 3.0 percent by weight hetero-unsaturated 
monomer based on the total monomer weight. The more preferred range being 
from about 0.1 to about 2.0 percent gives an excellent balance in 
properties for coating paper such as dry and wet pick strengths, gloss and 
brightness. Alternatively, where crotyl acrylate or crotyl methacrylate 
are employed a higher and broader range has been found to give the best 
results. Although the mechanism is not completely understood, it has been 
observed that the crotyl acrylate and crotyl methacrylate do not cause the 
latex to swell when admixed. This lack of swelling signifies the absence 
of sufficient crosslinking. The crotyl compounds are believed to instead 
provide strength by their extensive branching. Thus a higher and broader 
range is employed to take advantage of the crotyl compound's physical 
effect on the latex system. Preferably from about 0.20 to about 5.0 
percent by weight hetero-unsaturated monomer based on the total monomer 
weight. The more perferred range for crotyl acrylate and crotyl 
methacrylate being from about 0.6 to about 4.0 percent. The optimum 
proportion of hetero-unsaturated monomer, however, may vary depending upon 
the specific latex formulation to which it is added and upon the specific 
hetero-unsaturated monomer used, as was previously indicated. The ranges 
as taught above for the specified monomers are demonstrated in Tables I-IV 
which follow. 
As previously indicated the presence of an ethylenically unsaturated 
carboxylic acid is optional, but preferred. When used, it should be 
present in a concentration such that the latex has increased colloidal 
stability. Generally, the latex will have the acid present in a 
concentration of about 0 to about 10 percent, preferably about 2 to about 
5 percent based on total monomer weight. 
As indicated above, the presence of an ester of an ethylenically 
unsaturated acid and a C.sub.10 -C.sub.25 saturated alcohol as part of the 
ester charge is optional but greatly preferred. This long chain ester 
should be added as part of the monomer charge in a concentration such that 
the wet pick resistance is substantially increased without substantially 
decreasing the dry pick resistance. Desirably, the long chain ester is 
present in a concentration to increase the wet pick resistance by at least 
20 percent. Generally, the long chain ester will be present at from about 
0.1 to about 20 percent, preferably about 0.5 to about 10 percent, and 
most preferably from about 1 to about 5 percent by weight, based on the 
total monomer weight. 
In addition to the hereinbefore described monomers, the monomer charge 
employed to form the above-described latex can also, optionally, contain 
one or more other monomers which have only one polymerizable double bond, 
and are addition polymerizable with those required monomers. Examples of 
such suitable optional monomers include nitriles of the above-described 
monoethylenically unsaturated carboxylic acids (e.g., acrylonitrile and 
methacrylonitrile) as well as vinyl halide and vinylidene halide monomers, 
and the like. The amount of such optional monomers employed in the latex 
is not particularly critical as long as the amount thereof is not so much 
as to cause the latex to become deficient in performance, specifically wet 
and dry pick resistance. Importantly, these optional monomers may not 
impart substantial cross-linking to the latex. Thus, almost all compounds 
having more than one addition polymerizable double bond are not generally 
suitable for use in significant concentrations as optional monomers. 
While the total amount of the aforementioned optional monomers employed in 
preparing the latex may range from 0 to about 50 weight percent, it is 
generally preferable to employ such monomers at a level of from 0 to about 
10, most preferable from 0 to about 5 weight percent, based upon the total 
weight of the monomer charge employed in preparing the latex. 
The preparation of the latexes of the invention is conveniently conducted 
pursuant to well-known conventional emulsion polymerization techniques. 
Thus, for example, the monomer charge desired to be employed is dispersed 
in an aqueous medium with agitation and with the aid of from about 0.1 to 
about 5 weight percent (based upon the monomer charge) of conventional 
anionic and/or nonionic emulsifiers (e.g., potassium, N-dodecyl sulfonate, 
sodium isooctobenzene sulfonate, sodium laurate, nonylphenol ethers of 
polyethylene glycols and the like) and thereafter polymerizing the 
resulting aqueous dispersion. 
Conventional emulsion polymerization catalysts can be employed in the 
foregoing polymerization. Specific examples thereof include peroxides such 
as hydrogen peroxide, t-butyl hydroperoxide, cumene hydoperoxide; 
persulfates such as sodium persulfate, potassium persulfate and ammonium 
persulfate; and azo compounds. Typically, such catalyst are employed in an 
amount ranging from about 0.01 to about 5 weight percent based upon the 
monomer weight. In general, the polymerization is conducted at a 
temperature of from about 30.degree. to about 100.degree. C., and at a pH 
of from about 2 to about 8. 
While potentially useful, the use of chain transfer agents such as 
N-dodecylmercaptan, bromoform and carbon tetrachloride, is not 
recommended. 
Following completion of the polymerization, the solids content of the 
resulting latex can be adjusted to the level desired by adding water 
thereto or by distilling water therefrom. Generally, the desired polymer 
solids content will be from about 20 to about 65 weight percent, and such 
solids content is typically obtainable directly from the instant 
polymerization process without the need for any such further adjustment. 
Following the preparation, the resulting latexes can be advantageously 
employed in a wide variety of end use applications, and in such instances 
latexes are employed pursuant to known techniques and procedures which are 
conventionally employed with other types of latexes. In particular, the 
latexes of the invention are suitable for use in paper-coating 
compositions. 
The term "coating color" is often applied in the art to aqueous 
paper-coating compositions comprising a binder and a pigment. In the 
coating colors of the invention, the binder and the pigment are mixed in 
such proportions that, for each 100 parts by weight of dry pigment, from 
about 1 to about 30, preferaly from about 4 to about 25 parts by weight on 
a dry basis of binder are present in the mixture. On a weight percent 
basis, these proportions would translate to an amount of pigment of from 
about 99 to about 77 weight percent and preferably from about 96 to about 
80 weight percent based on total dry solids, respectively. The latex 
disclosed herein can be the sole binder employed in the coating colors of 
the invention, or other binders known in the art (e.g., other latexes or 
natural binders such as casein, protein, starch, etc.) can be used in 
conjunction with the latexes of the invention. 
The total solids content of the coating colors of the invention does not 
differ substantially from that in conventional coating colors, and depends 
largely on the equipment being used to coat the composition onto the 
paper. Generally, it is desirable to have from about 30 to about 80 
percent, preferably about 40 to about 70 percent total solids in the paper 
coating composition. 
Pigments which can be employed in the coating compositions of the invention 
include known mineral pigments, plastic pigments and mixtures thereof. 
Any mineral pigment suitable for use in conventional mineral pigmented 
coating compositions can be employed in the paper-coating compositions of 
the invention. Examples of such suitable mineral pigments for use in the 
coating compositions of the invention include finely divided clays 
(especially of a kaolin type), calcium carbonate, titanium dioxide, satin 
white, etc. Other materials such as talc, blanc fixe, ochra, carbon black, 
aluminum powder and other pigment or filler material can be employed in 
minor amounts in conjuction with the aforementioned mineral pigments. 
Plastic pigments suitable for use in the aqueous paper-coating compositions 
of the invention include those known to be useful in plastic pigmented 
coatings, such as those described in U.S. Pat. No. 3,949,138. Such plastic 
pigments are generally characterized as plastic, polymeric particles which 
have a number average particle diameter of from about 0.3 to about 0.8 
micrometers and are not film-forming at temperatures and pressures 
selected to dry or finish the coated paper. By "nonfilm-forming" is meant 
that the plastic particles do not coalesce to form a film at ambient 
temperature or at temperatures and pressures selected to dry or finish the 
coated article. Other plastic pigments suitable for use in the aqueous 
paper coating compositions of the invention include those described in 
U.S. Pat. Nos. 3,968,319; 3,293,144 and 3,988,522. 
The coating colors of the invention can optionally contain other additives 
such as thickeners (e.g., alginic acid or carboxymethylcellulose) and 
curing agents (e.g., melamine formaldehyde resins, urea formaldehyde 
resins and glyoxal) to achieve specific coating properties. When 
thickeners and/or curing agents are employed, they generally constitute 
individually, from about 1 to about 5 percent of the total binder weight 
on a dry basis. 
The aforementioned components can be combined to form the coating colors of 
the invention in any convenient manner. As a general rule, however, it is 
convenient and preferable to disperse the pigment (or pigment mixture) and 
other powdery components in water and adjust the pH of the resulting 
dispersion into a value between about 6 and about 9 before mixing such 
dispersion with the latex. The dispersion temperature at the time of the 
latex addition is not critical; but, it is usually good practice not to 
add the latex to a mixture about 65.degree. C.-70.degree. C. This will 
help to prevent the formation of a film or skin on the surface of the 
pigment mixture. Tetrasodiumpyrophosphate is often used as a dispersing 
aid, particularly where mineral pigments constitute all or a portion of 
the pigment or pigment mixture. 
The coating colors of the invention are conveniently applied to the paper 
by conventional means such as letter-press print roll coater, off-set roll 
coater, size press, air knife or blade coater. It is good practice to not 
excessively heat the coating colors of the invention during application. 
The traditional methods recognized in the art of paper-coating are 
preferred with temperatures not in excess of 80.degree. C. during 
application. 
After application, the coating is dried by any convenient method. 
Generally, however, drying is accomplished by causing a current of air to 
impinge upon the surface of the coated material. The temperature of the 
air may vary up to about 320.degree. C., but the duration of contact is 
such that the coating is not heated to above about 100.degree. C. 
After drying, the coated paper product can be finished pursuant to 
processes conventionally employed in the art such as gloss calendering, 
super calendering and the like, and can be subsequently printed in any 
desirable conventional fashion. However, in this regard, it should be 
noted that a particular advantage of the present invention is that the 
paper-coatings thereof exhibit improved adhesion of the paper-coating 
pigment to paper substrate relative to comparable coatings employing 
conventional acrylic latexes. Thus, papers coated with the coating 
compositions of the invention can be printed with relatively viscous inks 
at relatively high speeds.

Other aspects of the invention will be apparent from the following 
examples. In the examples all parts and percentages are by weight unless 
otherwise specified. 
METHODS USED IN THE EXAMPLES 
Coating Compositions 
Unless otherwise specified, the latexes are blended with a No. 1 clay 
(Hydrafine, available from J. M. Huber Corp., Borger, TX, USA) dispersion 
prepared by mixing 100 parts clay, 0.1 part tetrasodium phosphate and 
sufficient water to yield a 70 percent dispersion. For wet and dry pick 
resistance, 10 parts (solids) latex are blended with 100 parts (solids) 
clay dispersion to give a 47 percent total solids coating composition. For 
stiffness and optical properties, 18 parts (solids) latex are blended with 
100 parts (solids) of clay dispersion to produce a 47 percent total solids 
coating composition. Unless otherwise noted the coating compositions are 
coated onto paper samples at 15 lbs/ream with a Meyer Rod, dried at 
105.degree. C. and calendered at 1200 pli, 4 nips. 
Dry and Wet Pick Resistance 
Dry and wet pick resistance are measured with an IGT printability tester 
according to ASTM T-499 su-64. Results are reported in feet/minute for a 
specified ink number. For a given ink number, larger speed values indicate 
better results. For a given coating sample, as ink numbers go down, speed 
values will increase. 
Gloss 
Gloss is measured on a Gardner Multipurpose reflectometer. Results are 
reported as percent reflectance for a specified angle of incidence. Larger 
values mean greater gloss. 
Brightness 
Brightness is measured on a Gardner Brightness Meter. Larger values mean 
greater brightness. 
K & N Ink Receptivity 
The ink receptivity of the coatings was determined by placing a smear of K 
& N testing ink on the sheet for 2 minutes, after which the ink is removed 
and the brightness of the inked area recorded. Ink receptivity values are 
reported as a percent drop in sheet brightness. 
Stiffness 
For stiffness measurements, papers were coated on both sides. Stiffness is 
measured on a Clark Softness-Stiffness Tester. Results are reported in 
centimeters. Larger values mean greater stiffness. 
Heliotest Printability 
Heliotest printability is a measure of smoothness of the coated paper which 
was developed by the Paper Institute of France. It consists of a printing 
disc that can be mounted on an IGT Pick tester. The disc has been etched 
with cells varying from 80 to 40 microns in a strip of 100 mm long and 7 
mm wide. The cells are filled with ink via a doctor blade and then 
transferred or printed on the coated paper test strip. The IGT sector, to 
which the test strip is mounted, is equipped with the standard hard paper 
backing. Printing pressure is maintained at 40 Kg/cm.sup.2. Printing speed 
accelerates, and starts at the small cell size (40 microns) at about 160 
ft/min and increases to approximately 430 ft/min at the 80 micron cell 
size. The numerical value given as the test result is the length of print 
in mm required to accumulate 20 missing dots. Counting starts at the 
larger cell size. Larger values mean better results. An average value of 7 
test strips per coating formulation is used. 
EXAMPLE 1 
Using conventional emulsion polymerization techniques, 49 parts vinyl 
acetate, 49 parts butyl acrylate, and 2 parts acrylic acid are polymerized 
to yield a 48 percent solids latex and is filtered through a 325 mesh 
screen. In a similar manner, several more latexes are prepared, each 
having varying amounts of allyl methacrylate (AMA) or crotyl methacrylate 
(CMA). A clay dispersion is prepared from 100 parts English clay (Dinkey 
"A," available from English China Clays Ltd., Cornwall, UK), 0.1 part 
sodium polyacrylate (Dispec N-40, available from Allied Colloid Inc., 
Fairfield, NJ, USA), 0.2 part inorganic dispersant (Calgon T, available 
from Calgon Corp., Pittsburg, PA, USA), 0.3 part caustic soda, and 
sufficient water to yield a 70 percent solids dispersion. A coating 
composition is prepared by mixing 100 parts of clay dispersion, 0.5 part 
carboxymethyl cellulose and 5 parts latex to yield a 47 percent solids 
composition. The compositions are coated onto paper with a laboratory 
scale blade coater, and the coated samples are calendered at 400 pli and 4 
nips. The finished samples are then evaluated for smoothness (Heliotest) 
and dry pick resistance (IGT). The results are shown in Table I. 
TABLE I 
__________________________________________________________________________ 
Dry Pick 
Hetero-functional 
Thickener.sup.(1) 
Coat Wt. 
Heliotest 
#1 Ink 
Sample 
Type 
(Wt %) 
(Wt %) lbs/ream 
mm/20 dots 
(Ft/Min.) 
75.degree. Gloss 
Brightness 
__________________________________________________________________________ 
1* AMA 0 0.5 4.9 48.7 127 34.5 72.8 
2 AMA 0.1 0.5 4.8 49.8 184 36.1 72.6 
3 AMA 0.3 0.5 5.3 41.4 167 34.5 72.4 
4 AMA 0.5 0.5 5.4 45.8 161 34.7 73.0 
5 AMA 1.0 0.5 5.3 42.4 107 35.4 72.4 
6 AMA 0.5 0.25 5.6 66.2 133 37.4 72.3 
7 AMA 0.5 0 6.0 86.2 109 39.3 73.7 
8 CMA 2.0 0.5 5.5 60.1 158 35.4 72.3 
__________________________________________________________________________ 
*Not an example of the invention. 
.sup.(1) Carboxymethyl cellulose. 
EXAMPLE 2 
Using conventional emulsion polymerization conditions and techniques, 
varying ratios of styrene (S), butyl acrylate (BA), itaconic acid (IA) and 
allyl methacrylate (AMA) are polymerized in a continuous addition batch 
reactor equipped with a heat source, stirrer and nitrogen purge, to yield 
a 48 percent solids latex. The latexes are formulated with clay, coated 
onto paper, and evaluated, as described in Methods Used in the Examples, 
supra. The results are shown in Table II. 
TABLE II 
__________________________________________________________________________ 
Dry IGT Pick K & N Ink 
Sample 
S/BA/IA/AMA 
Ink No. 
Ft/min. 
Wet Pick 
75.degree. Gloss 
Brightness 
(% drop) 
__________________________________________________________________________ 
2-1* 
41/56/3/0 
5 233 40 80 77.0 13.4 
2-2 41/56/3/0.55 
5 314 30 79 77.0 17.7 
2-3* 
35/62/3/0 
5 214 35 79 77.1 17.7 
2-4 35/62/3/0.55 
5 339 25 79 77.0 16.9 
2-5* 
29/68/3/0 
5 215 30 80 77.5 18.2 
2-6 29/68/3/0.55 
5 355 25 80 77.4 16.5 
2-7* 
40/56/4/0 
5 260 30 80 76.6 15.4 
2-8 40/56/4/0.55 
5 326 
2-9* 
51/46/3/0 
3 343 
2-10 
51/46/3/0.55 
3 381 
__________________________________________________________________________ 
*Not an example of the invention. 
EXAMPLE 3 
In a manner similar to Example 2, a series of latexes is prepared with 35 
parts styrene, 62 parts butyl acrylate and varying amounts of allyl 
methacrylate and crotyl methacrylate. The results are shown in Table III. 
TABLE III 
__________________________________________________________________________ 
Hetero-unsaturated K & N Ink 
Sample 
Type Parts 
#5 Ink, Ft/min. 
Wet Pick 
75.degree. Gloss 
Brightness 
(% drop) 
__________________________________________________________________________ 
3-1* 
AMA 0 230 30 80 76.7 12.9 
3-2 AMA 0.11 270 30 79 76.7 13.0 
3-3 AMA 0.33 300 25 80 76.4 12.6 
3-4 AMA 0.55 300 40 79 76.4 12.3 
3-5 AMA 0.77 300 30 80 76.2 11.7 
3-6 AMA 1.1 310 30 81 75.8 11.5 
3-7 AMA 2.2 260 15 81 75.4 14.0 
3-8* 
CMA 0 260 45 51.0 77.1 21.6 
3-9 CMA 0.6 290 50 51.8 77.0 21.2 
3-10 
CMA 0.84 300 55 51.6 77.0 20.9 
3-11 
CMA 1.2 370 45 51.9 76.9 19.5 
3-12 
CMA 1.8 410 55 51.9 77.0 20.3 
3-13 
CMA 2.4 370 50 51.4 76.9 20.8 
3-14 
CMA 3.0 390 30 53.1 77.0 20.3 
__________________________________________________________________________ 
*Not an example of the invention. 
EXAMPLE 4 
In a manner similar to Example 2, several latexes are made with varying 
amounts of styrene (S), butyl acrylate (BA), itaconic acid (IA), lauryl 
methacrylate (LMA), and allyl methacrylate (AMA). The latexes are 
formulated, coated and evaluated. The results are shown in Table IV. 
These results show that lauryl methacrylate enhances the wet pick 
resistance of the paper-coatings of the invention. 
TABLE IV 
__________________________________________________________________________ 
Dry Pick K & N Ink 
Sample 
S/BA/IA/LMA/AMA 
#6 Ink, Ft/min. 
Wet Pick 
75.degree. Gloss 
Brightness 
(% drop) 
__________________________________________________________________________ 
1* 35/62/3/0/0 250 30 79.1 73.2 16.9 
2 32/62/3/3/0 270 60 79.8 73.2 18.7 
3 32/62/3/3/0.55 
370 60 79.5 73.2 16.0 
4 35/62/3/0/0.55 
390 30 80.0 72.8 16.2 
__________________________________________________________________________ 
*Not an example of the invention. 
COMATIVE EXAMPLE 1 
In a manner similar to Example 2, a series of latexes having 35 parts 
styrene (S), 62 parts butyl acrylate (BA), 3 parts itaconic acid (IA) and 
varying amounts of divinyl benzene (DVB) and iso-octyl thioglycollate 
(IOTG). The results are shown in Table V. 
The results show that the practice of the invention and the use of divinyl 
benzene are not equivalent. 
TABLE V 
__________________________________________________________________________ 
Dry Pick 
DVB/IOTG 
#5 Ink, Ft/Min. 
Wet Pick 
75.degree. Gloss 
Brightness 
K & N Ink (% drop) 
__________________________________________________________________________ 
0/0* 300 30 -- -- -- 
0.1/0* 320 30 82.0 72.5 16.4 
0.3/0* 335 20 81.5 72.2 18.8 
0.5/0* 300 20 82.2 72.3 20.4 
0.1/0.1* 
170 30 82.3 72.7 16.4 
0.3/0.3* 
230 30 82.5 72.6 15.9 
0.5/0.5* 
290 20 84.3 72.4 16.1 
Control 
433 25 82.7 72.2 16.4 
Acrylic.sup.(1) 
__________________________________________________________________________ 
*Not an example of the invention. 
.sup.(1) 0.55 parts AMA, no DVB or IOTG.