Latex composition employing specifically defined alcohol ethoxylate surfactant and hydrophobic defoaming agent

An improved latex composition is provided that has been found to exhibit a superior ability to form a substantially uniform polymeric film when applied to a substrate. The composition is capable of being handled and applied to a substrate in the absence of excessive foaming. The aqueous composition includes as essential components specified concentrations of a specifically-defined normally liquid predominantly hydrophobic nonionic alcohol ethoxylate surfactant, and a solely hydrophobic defoaming agent (e.g., a hydrocarbon-based mineral oil). It is possible for the composition to be applied even to a hydrophobic substrate (e.g., a polyester film substrate). Compositions of the present invention, following application to a substrate and the volatilization of the water component, form a substantially uniform polymeric film that can serve as a coating or adhesive.

BACKGROUND OF THE INVENTION 
The spontaneous generation of deleterious unwanted foam during the handling 
and application of polymeric latices to form a film upon a substrate has 
been recognized to lead to imperfections and concomitant nonuniformity in 
the resulting coating. Accordingly, it has been a common practice to also 
include a defoaming agent in such latices often in a substantial 
concentration. However, such defoaming agents have often been found to 
interfere with the wetting and coverage of the surface of the substrate by 
the latex composition and thereby to interfere with the formation of the 
desired continuous and uniform polymeric film upon the substrate once the 
water component is volatilized. It further has been a common practice to 
seek to remedy this deficiency in surface wetting and coverage through the 
further inclusion in the latex composition of an anionic surfactant. 
However, such anionic surfactants have been found commonly to increase the 
overall foaming propensity of the latex composition and to nevertheless 
contribute to the nonuniformity of the resulting film in spite of the best 
intentions of those seeking to apply a highly uniform polymeric film. It 
has been observed that such nonuniformity of the resulting polymeric film 
is particularly troublesome when the substrate that receives the latex 
composition tends to repel water and possesses a hydrophobic surface. 
Commonly, polymeric latices are exposed to agitation or other high shear 
conditions at some point during handling and/or during application to a 
substrate (e.g., by spraying or the use of high speed transfer rolls) 
prior to the volatilization of the water component. Such conditions can 
lead to the production of copious quantities of foam that can adversely 
influence the character of the resulting polymeric film that is applied to 
a substrate. Where foam bubbles are present, the coverage of the substrate 
by the polymeric particles present in the latex composition tends to be 
hindered. 
It is an object of the present invention to provide an improved latex 
composition for use in coating or adhesive end uses that exhibits a 
superior ability to form a uniform film upon a substrate. 
It is an object of the present invention to provide an improved latex 
composition wherein the polymeric particles are present at a relatively 
high concentration and there is a good resistance to excessive foaming 
even if agitation or other high shear conditions are encountered. 
It is an object of the present invention to provide an improved latex 
composition that can be applied to a substrate by spraying in the absence 
of excessive foaming. 
It is an object of the present invention to provide an improved latex 
composition that has the ability to well wet and cover the surface of a 
substrate that is to receive a polymeric film to thereby facilitate 
uniform spreading in the absence of excessive foaming. 
It is an object of the present invention to provide an improved latex 
composition that has the ability to well wet and cover the surface of a 
hydrophobic substrate that is to receive a polymeric film. 
It is an object of the present invention to provide an improved latex 
composition wherein a defoaming agent is present in a relatively low 
concentration in conjunction with a relatively low concentration of a 
specifically defined nonionic surfactant that has been found through 
empirical research to yield a highly compatible overall composition that 
makes possible the formation of a substantially uniform film upon a 
substrate. 
It is an object in a preferred embodiment of the present invention to 
provide an improved latex composition wherein the total surfactant 
concentration is relatively low and an anionic surfactant is absent. 
It is a further object of the present invention to provide a latex 
composition that is particularly suited for forming a clear polymeric 
coating on a paper substrate. 
It is a further object of the present invention to provide a latex 
composition that well forms a pressure-sensitive adhesive layer when 
applied to the surface of a hydrophobic polyester film substrate and the 
water component is volatilized. 
It is another object of the present invention to provide a process for 
forming a substantially uniform polymeric film on a substrate while 
utilizing a latex composition in the absence of excessive foaming. 
These and other objects and advantages of the presently claimed invention 
will be apparent to those of ordinary skill in the art from a reading of 
the following detailed description and appended claims. 
Our companion patent application Ser. No. 321,112 (now U.S. Pat. No. 
5,525,657) entitled "Improved Latex Composition Employing Specifically 
Defined Ethylene Oxide/Propylene Oxide Block Copolymer Surfactant and 
Hydrophobic Defoaming Agent" is being filed concurrently herewith. 
SUMMARY OF THE INVENTION 
It has been found that an improved latex composition suitable for coating 
or adhesive end uses which exhibits a superior ability to form a 
substantially uniform film upon a substrate in the absence of excessive 
foaming during handling and during application to a substrate consists 
essentially of: 
(a) an aqueous dispersion medium, 
(b) approximately 40 to 60 percent by weight of discrete solid polymeric 
particles present in the aqueous dispersion medium formed by the 
polymerization of at least one ethylenically-unsaturated monomer, 
(c) approximately 0.25 to 1.5 (preferably approximately 0.75 to 1) percent 
by weight dissolved in the aqueous medium of a normally liquid 
predominantly hydrophobic nonionic alcohol ethoxylate surfactant of the 
formula: 
EQU R--O--(CH.sub.2 CH.sub.2 O).sub.x --H, 
having a molecular weight of approximately 260 to 600 (preferably 
approximately 290 to 470) wherein R is an alkyl group containing 
approximately 8 to 14 (preferably 10 to 13) carbon atoms, and x is 
approximately 3 to 9 (preferably 3 to 6), and 
(d) approximately 0.05 to 1 (preferably approximately 0.25 to 0.5) percent 
by weight dispersed in the aqueous medium of a solely hydrophobic 
defoaming agent. 
It has been found that a process for the application in the absence of 
excessive foaming of a substantially uniform polymeric film to a substrate 
comprises: 
(a) applying to a substrate a layer of a latex composition consisting 
essentially of (i) an aqueous dispersion medium, (ii) approximately 40 to 
60 percent by weight of discrete polymeric particles present in the 
aqueous dispersion medium formed by the polymerization of at least one 
ethylenically-unsaturated monomer, (iii) approximately 0.25 to 1.5 
(preferably approximately 0.75 to 1) percent by weight dissolved in the 
aqueous medium of a predominantly hydrophobic nonionic alcohol ethoxylate 
surfactant of the formula: 
EQU R--O--(CH.sub.2 CH.sub.2 O).sub.x --H, 
having a molecular weight of approximately 260 to 600 (preferably 
approximately 290 to 470) where R is an alkyl group containing 
approximately 8 to 14 (preferably 10 to 13) carbon atoms, and x is 
approximately 3 to 9 (preferably approximately 3 to 6), and (iv) 
approximately 0.05 to 1 (preferably approximately 0.25 to 0.5) percent by 
weight dispersed in the aqueous medium of a solely hydrophobic defoaming 
agent, and 
(b) removing water by volatilization from the layer of latex composition 
present on the substrate to form a substantially uniform polymeric film on 
the substrate that is suitable for use as a coating or adhesive. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
The improved latex composition of the present composition incorporates 
approximately 40 to 60 (preferably 45 to 55) percent by weight of discrete 
solid polymeric particles formed by the polymerization of at least one 
ethylenically-unsaturated monomer in an aqueous dispersion medium. Such 
polymeric particles commonly are formed by emulsion polymerization in 
accordance with known technology. Representative polymeric particles 
include styrene-butadiene polymers, acrylic polymers, vinyl acetate 
polymers, vinyl chloride polymers, and mixtures of these. Particularly 
good results have been achieved when utilizing styrene-butadiene polymeric 
particles that are composed of approximately 25 to 45 percent styrene by 
weight. Polymeric particles of carboxylated styrene-butadiene polymers can 
be utilized. Preferred acrylic polymers include the copolymers of 
acrylonitrile, acrylic acid, methacrylic acid, butylacrylic acid, styrene, 
and mixtures of these. The solid polymeric particles that are dispersed in 
the aqueous medium commonly possess a number average particle size of 
approximately 0.05 to 3 microns, and preferably a number average particle 
size of approximately 0.1 to 0.5 micron. 
When the latex composition is intended to form a protective or decorative 
coating upon a substrate, the polymeric particles commonly are selected 
which possess the ability to form a firm relatively nontacky layer upon 
solidification in accordance with known technology. When the latex 
composition is intended to form an adhesive layer (e.g., a 
pressure-sensitive adhesive) upon a substrate, the polymer particles 
commonly are selected which are inherently tacky following solidification 
or can be so rendered in accordance with known technology. Representative 
resins that optionally may be added to influence tackiness include 
alkylaryl hydrocarbon resins, glycerol esters of rosin, tall oil resins, 
etc. 
A normally liquid predominantly hydrophobic nonionic alcohol ethyoxylate 
surfactant of the formula indicated hereafter is dissolved in the aqueous 
medium of the improved latex composition of the present invention in a 
relatively low concentration of approximately 0.25 to 1.5 percent by 
weight, and preferably in a concentration of approximately 0.75 to 1 
percent by weight. Such specifically-defined nonionic surfactant possesses 
a molecular weight of approximately 260 to 600, and preferably 
approximately 290 to 470, and the formula: 
EQU R--O--(CH.sub.2 CH.sub.2 O).sub.x --H, 
where R is an alkyl group containing approximately 8 to 14 (preferably 10 
to 13) carbon atoms, and x is approximately 3 to 9 (preferably 3 to 6). 
The nonionic surfactant is predominantly hydrophobic in the sense that the 
molecular structure is more hydrophobic than hydrophilic. Such surfactants 
are known in the art and can be formed in accordance with known 
techniques. Such formation reaction commonly involves the addition of 
ethylene oxide to an aliphatic monohydric alcohol of the specified chain 
length. Representative aliphatic monohydric alcohols include octyl 
alcohol, nonyl alcohol, decyl alcohol, dodecyl alcohol (i.e., lauryl 
alcohol), tridecyl alcohol, and tetradecyl alcohol, etc. Such alcohols 
preferably are provided as mixtures of primarily branched-chain molecules. 
In particularly preferred embodiments, the nonionic surfactant as defined 
above (a) is formed by the reaction of branched-chain decyl alcohol 
molecules having 10 carbon atoms per molecule with 4 moles of ethylene 
oxide and possesses a molecular weight of approximately 330, or (b) is 
formed by the reaction of branched-chain tridecyl alcohol molecules having 
13 carbon atoms per molecule with 9 moles of ethylene oxide and possesses 
a molecular weight of approximately 590. 
A solely hydrophobic defoaming agent is dispersed in the aqueous medium of 
the improved latex composition of the present invention in the relatively 
low concentration of approximately 0.05 to 1 percent by weight and 
preferably in a concentration of approximately 0.25 to 0.5 percent by 
weight. Such defoaming agent has been found to be highly compatible with 
the previously defined nonionic surfactant and when present in such 
relatively low concentration has been found to facilitate good wetting and 
coverage of a substrate with the latex composition of the present 
invention even if such substrate is hydrophobic in nature. The defoaming 
agent is considered to be solely hydrophobic in its molecular structure in 
the sense that it is basically hydrophobic throughout and for all 
practical purposes lacks a hydrophilic character at any portion of the 
molecule. Representative solely hydrophobic defoaming agents include 
hydrocarbon-based mineral oils, organosiloxanes (including emulsions of 
organo-modified polyfunctional polysiloxanes), metal soaps, etc. Fatty 
acids may be present with the hydrocarbon-based mineral oils. Also, silica 
particles having relatively sharp surfaces optionally may be present in 
conjunction with the solely hydrophobic defoaming agent. When silica 
particles are present with such defoaming agents, they serve primarily to 
puncture foam bubbles rather than to impart a hydrophilic character to the 
defoamer. In a particularly preferred embodiment, the solely hydrophobic 
defoaming agent is a hydrocarbon-based mineral oil having a boiling point 
of approximately 600.degree. to 900.degree. F. 
In a preferred embodiment no anionic surfactant is present in the improved 
latex composition of the present invention. The absence of such anionic 
surfactant has been found to contribute to the ability of the composition 
to form a substantially uniform film upon a substrate in the absence of 
excessive foaming during handling and during application to a substrate. 
Alternatively, other components optionally can be present in the latex 
composition of the present invention such as particulate inert fillers, 
colorants, glycols, thickeners, plasticizers, solvents, auxiliary resins, 
etc., so long as they do not modify the basic character of the 
composition. When forming a clear coating, particulate fillers should be 
omitted as will be apparent to those skilled in the art. 
The improved latex composition of the present invention can be applied to a 
wide variety of substrates. As previously indicated, good results are 
achievable even if the substrate is hydrophobic in nature. A decorative or 
protective coating can be readily applied to a substrate. Alternatively, 
the resulting uniform film that is applied to a substrate that can serve 
the role of an adhesive (e.g., a pressure-sensitive adhesive). 
The improved latex composition can be applied to a substrate by 
conventional coating techniques without the necessity to minimize 
agitation in an effort to impede excessive foam formation. In a preferred 
embodiment, the latex composition is simply applied by spraying to form a 
uniform layer of the composition on a substrate, and the water component 
is removed by volatilization to form a substantially uniform polymeric 
film. Other representative techniques that can be utilized to form the 
layer on the substrate include the usage of a high speed transfer roller, 
the usage of a Byrd applicator, a Meyer bar, an air knife, a reverse roll, 
a reverse gravure, a die slot, etc. For instance, the layer of improved 
latex composition can be applied in a thickness of approximately 20 to 50 
microns and dried to form a substantially uniform film having a thickness 
of approximately 10 to 25 microns. The volatilization can be expedited 
through the application of heat in accordance with techniques known in the 
art for the specific polymeric particles of the latex that are selected. 
For instance, heating for 1 to 10 minutes at approximately 80.degree. to 
105.degree. C. can be utilized. 
The following Examples are presented as specific illustrations of the 
present invention. It should be understood, however, that the invention is 
not limited to the specific details set forth in the Examples. 
In the Examples that are presented hereafter various latex compositions 
were evaluated for their propensity to form foam, for their spreading 
ability when applied to a hydrophobic substrate, and for their propensity 
(or lack thereof) to form a film on a hydrophobic substrate that includes 
imperfections termed "fish eyes". 
More specifically, the tendency of the latex composition to foam was 
evaluated through the use of a standard test procedure wherein a 300 ml 
beaker was completely filled with the latex composition, the net weight of 
the filled beaker was recorded as "A", the contents of the beaker were 
transferred to a Hobart mixer, the latex composition was agitated for 10 
minutes in the Hobart mixer at a speed selected to produce substantial 
agitation in the absence of splattering, the 300 ml. beaker was again 
filled with a portion of the composition obtained from the Hobart mixer, 
and the net weight of the contents of the beaker including foam was 
recorded as "B". The percent foam was calculated while using the following 
formula: 
EQU Percent Foam=1-"B "/"A".times.100. 
The spreading ability of the latex composition was determined on the 
surface of a hydrophobic substrate that was represented by a polyester 
film. The latex was introduced by the use of a pipette to the space below 
a Byrd applicator in a quantity sufficient to cover the entire surface of 
the substrate, and next was applied to the substrate. The latex 
composition was drawn down to a thickness of approximately 25 microns 
through the use of the Byrd applicator that was pulled downward to 
distance of 8 inches. This spreading test was carried out in triplicate in 
each instance. Following drying the films that were provided on the 
hydrophobic substrate had a thickness of approximately 12 microns and were 
evaluated according to their spreading ability and the presence or absence 
of imperfections known as "fish eyes" as previously stated. 
The spreading ability was determined by visual observation with respect to 
general appearance of the resulting dried film. Each film was evaluated 
(a) for the possible presence of "edge creep" wherein the edges of the 
drawdown contract toward the middle of the test pattern, (b) for "orange 
peel" wherein the surface of the film is mottled in a random pattern, and 
(c) for the presence or absence of complete coverage. The following rating 
system for this spreading ability was utilized: 
1=Poor, 
2=Fair, 
3=Good, 
4=Very Good, and 
5=Excellent. 
The "fish eye" evaluation of the coating was also carried out by visual 
observation wherein the film was examined for the possible presence of 
areas with no observable coverage by the polymeric particles of the latex. 
Such voids can range from tiny specks to large circular voids where there 
is little or no polymeric coverage. The observation of such "fish eye" 
voids was rated on the following scale: 
1=Many, 
2=Few, and 
3=None.

EXAMPLE NO. I 
Latex compositions were formed while employing 50 percent by weight of 
styrene-butadiene polymeric particles consisting of approximately 26 
percent by weight of recurring units derived from styrene in an aqueous 
dispersion medium. The styrene-butadiene particles were formed by emulsion 
polymerization and possessed a number average particle size of 
approximately 0.3 micron. 
A normally liquid predominantly hydrophobic nonionic alcohol ethoxylate 
surfactant having a molecular weight of approximately 330 formed by the 
reaction of primarily branched-chain decyl alcohol molecules having 10 
carbon atoms per molecule with 4 moles of ethylene oxide was utilized in a 
concentration of approximately 1.0 percent by weight, and a 
hydrocarbon-based mineral oil defoaming agent having a boiling point of 
approximately 695.degree. to 840.degree. F. was present in a concentration 
of 0.5 percent by weight. 
Following volatilization of the aqueous component a substantially uniform 
inherently tacky film was provided on the hydrophobic substrate that was 
suitable for service as a pressure-sensitive adhesive. 
When evaluated in accordance with the prescribed procedures the latex 
composition yielded the following test results: 
Percent Foam: 1.6 (Very Low) 
Spreading Ability: 4 (Very Good) 
Fish Eyes: 2 to 3 (Few to None). 
COMATIVE EXAMPLES 
For comparative purposes it was found that when a like quantity of a 
commonly utilized anionic sodium dioctyl sulfosuccinate surfactant was 
substituted for the predominantly hydrophobic nonionic alcohol ethoxylate 
surfactant and the mineral oil defoaming agent was omitted from the latex 
composition, that an excessive foaming value of 62.0 percent was observed. 
Such value would indicate the exhibition of excessive foaming during 
handling and during application to a substrate where high shear conditions 
are encountered. Also, even when the mineral oil defoamer was added to 
this comparative composition in a concentration of 1.0 percent by weight 
instead of 0.5 percent by weight, an excessive foaming value of 41.5 
percent still was observed that well exceeded the value obtained in 
Example I. 
EXAMPLE NO. II 
Example I was repeated with the exception of 0.25 percent by weight of the 
hydrocarbon-based mineral oil defoaming agent was utilized in the latex 
composition there described instead of 0.5 percent by weight. 
When evaluated in accordance with the previously described procedures, the 
latex composition yielded the following results: 
Percent Foam: 4.3 (Low) 
Spreading Ability: 4 to 5 (Very Good to Excellent) 
Fish Eyes: 2 to 3 (Few to None). 
EXAMPLE NO. III 
Example I was repeated with the exception that the predominantly 
hydrophobic nonionic alcohol ethoxylate surfactant in a concentration of 
0.5 percent by weight was utilized in the latex there described instead of 
1.0 percent by weight. 
When evaluated in accordance with the previously-described procedures, the 
latex composition yielded the following results: 
Percent Foam: 2.5 (Very Low) 
Spreading Ability: 4 to 5 (Very Good to Excellent) 
Fish Eyes: 2 to 3 (Few to None). 
EXAMPLE NO. IV 
Example I was repeated with the exception that the predominantly 
hydrophobic nonionic alcohol ethoxylate surfactant had a molecular weight 
of approximately 590 and was formed by the reaction of primarily 
branched-chain tridecyl alcohol molecules having 13 carbon atoms per 
molecule with 9 moles of ethylene oxide. 
When evaluated in accordance with the previously-described procedures, the 
latex composition yielded the following results: 
Percent Foam: 1.1 (Very Low) 
Spreading Ability: 3 to 4 (Good to Very Good) 
Fish Eyes: 2 (Few). 
EXAMPLE NO. V 
Example I was repeated with the exception that the predominantly 
hydrophobic nonionic alcohol ethoxylate surfactant had a molecular weight 
of approximately 590 and was formed by the reaction of primarily 
branched-chain tridecyl alcohol molecules having 13 carbon atoms per 
molecule with 9 moles of ethylene oxide and the hydrocarbon-based mineral 
oil defoaming agent was provided in a lesser concentration of only 0.25 
percent by weight in the latex composition. 
When evaluated in accordance with the previously-described procedures, the 
latex composition yielded the following results: 
Percent Foam: 6.1 (Low) 
Spreading Ability: 3 to 4 (Good to Very Good) 
Fish Eyes: 2 (Few). 
EXAMPLE NO. VI 
Example I can be repeated with the exception that the latex composition 
includes 50 percent by weight of styrene-acrylic polymeric particles 
instead of styrene-butadiene polymeric particles and is applied to a 
moving paper substrate by spraying. The polymeric particles were formed by 
emulsion polymerization and possess a number average particle size of 
approximately 0.30 micron. The latex is handled and is applied to the 
paper substrate in the absence of excessive foaming. 
Following volatilization of the aqueous component a quality substantially 
uniform clear film coating is provided on the paper substrate. 
Although the invention has been described with preferred embodiments, it is 
to be understood that variations and modification may be resorted to as 
will be apparent to those skilled in the art. Such variations and 
modifications are to be considered within the purview and scope of the 
claims appended hereto.