CA1297124C - Copolymers as thickeners and modifiers for latex systems - Google Patents

Abstract

Abstract A thickened aqueous copolymer solution useful for thickening and improving the properties of latex systems comprising a copolymer having as monomeric units: about 79-99 percent of a (meth)acrylic acid salt of sodium, potassium, or ammonium; about 0-20 percent of (meth)acrylic acid; about 0-20 percent of a lower alkyl ester of (meth)acrylic acid; about 1-21 percent of surfactant units selected from the reaction product of a monoethylenically unsaturated monoisocyanate with a nonionic surfactant having hydroxyl or amine functionality; or an ester of a monoethylenically unsaturated dicarboxylic acid, with a polyoxalkylene alkyl ether or a polyoxyalkylene sorbitan ester, and about 0-1 percent of a copolymerizable polyethylenically unsaturated monomer, said percentages being by weight based on the total weight of monomeric units in said copolymer.

Description

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Copolymers as Thickeners and Modifiers for Latex Systems Background of the Invention This invention relates to aqueous copolymer solutions which thicken, modify rheology, stabilize, and otherwise improve the physical properties of latex systems and dried film resulting from application of latex systems to substrates. Of particular importance is the increase in tensile strength of dry latex films provided by the addition of the novel copolymer solutions to latex coating compositions.
Variou~ polymeric materials have been used to thicken latex formulations, improve their mechanical stability, suspend added fillers, and to impart to the formulations the required flow properties and viscosity for application, as well as impart desirable properties to dried films and coatings after application. Sodium polyacrylate solutions resulting from hydrolysis of polymethyl acrylate are used as thickeners, especially in styrene-butadiene latex compositions containing calcium carbonate and/or kaolin fillers.
Such polyacrylate solutions are generally supplied at a viscosity low enough for pumping from tank trucks an~
for rapid mixing into the latex compositions, yet they are cost effective in thickening latex compositions.
They fill a need in highly-automated upholstery fabric backing and carpet backing latex adhesive applications.
The alkali reactive type of thickeners, a typical example of which is disclosed in U.S. Patent No.

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~2--3,070,561, are copolymer emulsions in which the copolymer chain contains both ester and carboxyl groups. Neutralization of the carboxyl groups by addition of alkali at ambient temperature leaves the ester group unaffected, but converts the emulsion to a relatively clear alkali metal or ammonium salt solutlon of greatly increased viscosity.
Recent improvements of alkali reactive thickeners are disclosed in U.S. Patents Nos. 4,351,754, 4,384,096, 4,514,552, 4,~00,761 and 4,616,074. Such improvements result from inclusion of certain sur~actant monomers in these associative copolymer thickeners. Such thickeners and their thickening mechanism are discussed in "Water-Soluble Polymers" by J.E. Glass, Editor, American Chemical Society, Washington D.C. (1986). These products have been found to be useful in only a limited number of applications~
and have been found to be unsatisfactory in the thickening of highly-loaded styrene-butadiene latex compositions used as carpet and fabric backing adhesives which generally are applied by automated methods in carpet and upholstery mills.
Other types of associative thickeners are described in the patent literature. Thus, U.S. Patent No. 3,708,445 discloses aqueous solution co~olymers of certain surfactant monomers with carboxylic acid monomers, to be useful in thickening latex compositionsJ
U.S. Patent No. 4,138,381 discloses glycol solution terpolymers of certain surfactant monomers with alkyl (~eth)acrylate and carboxylic acid monomers ` `:
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to be useful for thickening aqueous polymeric latices.
U.S. Patent No. 4,268,641 describes copolymers of certain types of surfactant acrylates with carboxyl-containing, ethylenically unsaturated hydrocarbons. Such copolymers generally are polymerized in an organic liquid from which the copolymer precipitates. When base-neutralized the copolymers are useful as thickeners.
In spite of the considerable research activity in this field, the sodium polyacrylate so~ution thickeners resulting from hydrolysis of polyacrylic acid esters remain the thickeners of first choice for many textile back coating and adhesive applications.
These polymers, sometimes crosslinked, have continued in use for almost thirty years without substantial change. However, changes in equipment, compound formulations, and other conditions of use dictate a constant demand for changes and improvements in these polymer thickeners.
It is an object of this invention to provide thickeners for latex and latex-based formulations which significantly improve the overall rheological properties thereof while retaining the pro~en benefits of the hydrolyzed polyacrylate products.
An unexpected additional benefit of the ~ ~
present invention is an increase in tensile strength~of dried latex coatings by the inclusion in the latices o the c~polymer solution~ of thls inventlon.

' . . , ~Z~7~2 Summary of the Invention According to this invention new aqueous solutions of anionic copolymers are prepared either by emulsion polymerization or solvent polymerization. The former procedure preferably is employed where the copolymers are obtained by copolymerization of an alkyl ester (meth)acrylate, surfactant monomer and optionally a small amount of a copolymerizable polyethylenically unsaturated crosslinking monomer.
Following polymerization the major portion of the ester groups are hydrolyzed by addition of base to provide acrylate salt groups, whereby the copolymer goes into solution with resultant thickening of the aqueous system in which the copolymer is present.
However, because of the greater solubility of (meth)acrylic acid, as compared to the lower alkyl esters thereof, the copolymerization can be carried out in a solvent for the monomers, such as water, where (meth)acrylic acid per se is used as a monomer rather than a lower alkyl ester thereof. The major portion of the carboxyl groups are neutralized before, during or after polymerization with resulting thickening of the aqueous system.
As will be seen from the following detailed description and specific examples, the copolymer solutions of this invention not only are highly efficient thickeners for latex formulations, but provide such formulations with improved properties and increase the tensile strength of coatings of the dried latices.

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~;:97:~24 Detailed Description of khe Invention As noted previously the copolymers of this invention are prepared either by emulsion polymerization or by polymerization in a solvent for the monomers. The route selected will depend on the solubility of the monomers in the reaction med~um which preferably is ~ater. In either instance there results an aqueous copolymer solution comprlsing a copolymer of:
~A) about 79-99 percent of a(meth)acrylic acid salt o~ sodium, potassium or ammonium;
(B) about 0-20 percent of (meth)acrylic acid;
tC) about 0-20 percent Or a lower alkyl ester of (meth)acryl~c acid;
(D) about 1-21 percent o~ surfactant monomer units selected from:
(1) the reaction product of a monoethylenically unsaturated monoisocyanate with a nonionic sur~actant having hydroxyl or amine functionality; or (2) an ester of a monoethylenically unsaturated dicarboxylic acid containing from 4 to 8 carbon atoms with a polyoxalkylene alkyl ether ~ontaining from 4 to 100 oxyalkylene groups and from 6 to 22 carbon atoms in the alkyl group, or a polyoxyalkylene sorbitan ester of the formula ,,, j, ~

. ~ , 1~'7124 H(OCH2CH2)p 0 O(CH2cH20)qRl ~ ~ H0(CH2CH20)rR1 o ¦ R
CH2O(c~2cH2o)s~R2 where each of p, q, r and s is an integer and the sum of the integers is from 0 to 100, R1 is H or CR2, and R2 is an alkyl or alkenyl group containing from 11 to 17 carbon atoms, and (E) about 0-1 percent of a copolymerizable polyethylenically unsaturated monomer, said percentages being by weight based on the total weight of monomer units.
Preferably, the copolymer is composed of (A) about 92-99 percent (meth)acrylate salt, (B) about 0-8 percent (meth)acrylic acid, ~C) about 0-8 percent (meth)acrylic lower alkyl ester, (D) about 1-8 percent surfactant monomer units, and (E) about 0.1-0.5 percent crosslinking monomer units.
(A) The (meth)acrylic acid salts The terms "(meth)acrylic acid" and "(meth)acrylate'i as used in this specification and appended claims refer to acrylic and methacrylic acid and acrylates and methacrylates, i.e. lower alkyl esters of the acids, respectively. As noted previously, in the polymerization reaction by which the copolymers are synthesized, either the acids per se and/or the lower alkyl esters may be used as monomers. In either instanoe, however, the resulting copolymers are treated "
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with base. Where acid monomer units per se are present, the major portion of the free carboxyl groups 2re neutralized to form salts. Preferred neutralizing alkaline reactants are sodium, potassium and ammonium hydroxide.
The conversion of the carboxyl groups into salt groups renders the copolymers water soluble so that there is formed a substantially clear aqueous solution of substantially increased viscosity.
(B? (Meth)acrylic acid (Meth)acrylic acid per se may be used as one of the monomers in the polymerization reaction, and in the copolymer (meth)acrylic acid units may be present up to about 20 percent by failure to neutralize (meth)acrylic acid monomer or hydrolyze lower alkyl (meth)acrylate ester monomer. Preferably, the copolymer does not contain more than about 8 percent of tmeth)acrylic acid units.
(C) The lower alkyl (meth)acrylates The lower alkyl (meth)acrylates which may be used in the copolymerization reaction have the general formula CH2=CYZ

where Y is hydrogen or CH3 and Z is COR, where R is alkyl containing from 1 to ~ carbon atoms. Examples of such nonionic acrylates are methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methyacrylate and butyl methacrylate. Preferred .

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monomers are methyl and ethyl tmeth)acrylate and mixtures thereof.
The nonionic acrylate units in the copolymer generally comprise up to about 20 percent of the total monomer units, and preferably about 0-8 percent. It can be seen, however, that where a (meth)acrylate is employed as a monomer in the polymerization reaction a considerably larger proportion thereof may be present.
The percentages given ~or the nonionic uniks are those remaining subsequent to alkaline hydrolysis.
Where nonionic (meth)acrylate units are present, the ma~or por~ion thereof are hydrolyzed by alkali, particularly sodium and potassium hydroxide whereby the ester groups are converted to alkali metal salt groups.
(D) The surfactant monomers ~ 1) The surfactant monomer produced by reacting a monoethylenically unsaturated monoisocyanate with a nonionic surfactant having amine and hydroxyl functionality.
The mono~ers employed in preparing the copolymers according to this invention are reaction products of a monoethylenically unsaturated monoisocyanate with a nonionic surfactant having amine or hydroxyl functionality. Preferred monoisocyanates useful in preparing the urethane monomers have the ~ormula Z - C--O -A- N=C-0 where A is an alkylene group of the formula (CH2)n, where n is an integer rrom 1 to 20, and Z is CH2=CH-, CH2=C(CH3)-, or CH2=CH-CH2. A particularly preferred type of monoisocyanate of the above formula is ~Lz~

isocyanatoethyl methacrylate (Dow Chemical Company).
A preferred $socyanate of another class is alpha, alpha-dimethyl-m-isopropenyl benzyl isocyanate (American Cyanamid Corp.).
Preferred nonionic surfactants for reaction with the monoisocyanates to provide monomers are those of the formula R30~~~CnH2nO ~ H
where R3 is an alkyl or alkenyl group containing from 6 to 22 carbon atoms, typically octadecyl, or an alkaryl group containing rrom 8 ko 22 carbon atoms, typically octylphenyl or nonylphenyl, n is an integer o~ from 2 to 4, and w is an integer of from 6 to 100, or a sorbitan fatty ester of the formula H(OCH2CH2)p~ 0(CH2CH;~O)qR1 ~ ~ H~tCH2cH~O)r~1 O I

CH20(cH2cH20)scR2 where each of p, q, r and s is an integer and the sum of said integers is from 0-100, Rl is H or COR2, and R2 is an alkyl or alkenyl group containing from 11 to 17 carbon atoms.
~ ather than ~aving hydroxyl functionality, the nonionic surfactant which is reacted with the monoisocyanate may haYe amine functionality, and preferably is a primary amine having the formula ~ 4 (0CnH2n ~ H2 where R4 is octylphenyl or nonylphenyl, n is an inteBer from 2 to 4 and z is an integer from 3-20.

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~Z97~ 4 Examples of the nonionic surfactants which can be reacted with the monoisocyanates are polyoxyethyléne alcohols such as poly(oxyethylene)20 stearyl ether and poly(oxyethylene)4 lauryl ether; ethyoxylated alkyl phenols such as poly(oxyethylene)4 nonylphenol; sorbitan fatty acid esters, such as sorbitan monooleate and sorbitan monostearate; polyoxyethylene sorbitan fatty esters9 such poly(oxyethylene)20 sorbitan monolaurate and poly(oxyethylene)20 monostearate. Suitable amine surfactants include such primary amines as nonylphenoxy poly[(oxypropylene)2 (oxyethylene)g 5] amine.
These surfactant reactants for the most part are commercially available. By employing a suitable stannous catalyst, the condensation may be carried out at a relatively low temperature, e.s. 40C to 60C and essentially quantitative yields obtained. No by-products are formed, and thus purification of the product is unnecessary. This feature of the reaction is important in determining and controlling the amount of bound surfactant monomer present in the copolymer, whereby copolymer reproducibility is readily accomplished.
(2) The nonionic surfactant monomers produced by esterification of ethylenically unsaturated dicarboxylic acids.
Another group of nonionic surfactant monomers useful in synthesizing copolymers of the present invention are those produced by esterification of an ethylenically unsaturated dicarboxylic acid with either , . .

1297~24 a polyoxyalkylene ether or a polyoxyalkylene sorbitan ester.
Dibasic acids useful in preparing such monomers include maleic, fumaric, itaconic, mesaconic, citraconic and methylene malonic acid~ Maleic and itaconic acid are particularly preferred. In some cases anhydrides of the dicarboxylic acid can be substituted for the acid to produce the ester.
Preferred nonionic surfactants produced by esterification of ethylenically unsaturated dicarboxylic acids are obtained by reacting the acid with nonionic surfactant of the formula R50---~CnH2nO~H
where R5 in an alkyl or alkenyl group containing from 6 to 22 carbon atoms, n is an integer of from 2 to 4~ and v is an integer from 6 to 100. Typical of this class of nonionic surfactants is poly(oxyethylene)20 stearyl ether.
A partlcularly preferred group of nonionic surfactants for reaction with a dicarboxylic acid are the polyoxyethylene sorbitan fatty esters discussed hereinabove, as exemplified by poly(oxyethylene)20 sorbitan~monooleate.
Preferably the nonionic surfactant monomer comprises about 1 to about 21 percent of the copolymer, the percentage being by weight based on total weight of monomer units. The particularly preferred amount of such nonionic surfactant monomer is from about 1 to about 8 percent.
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~Z97~;~4 Preparation of the sur~actant monomers i~ described in detail in Example I, and in Example II there is a detailed description of the method of nonionic surfactant monomers produced by esterificationO General conditions for the reaction are also described in the references cited above in the prior art discussionD Such procedures are well known, and the details thereof are not to be construed as limiting this invention.
(E) The optional polyethylenically unsaturated erosslinking monomer.
A small amount, such as O to 1 percent, preferably 0.1 to 0.5 percent, of a polyethylenically unsaturated monomer may be added as a crosslinking agent for the copolymers. Such monomers include diallyl phthalate, vinyl crotonate, allyl methacrylate, divinyl be~nzene, and the like.

The Copolymerization Reactions ~ hen (meth)acrylic acid ester monomers are used as the major source of carboxylic monomer units in the copolymers, the copolymerization preferably is carried out by ordinary emulsion polymerization techniques, at a ccncentration of monomer in ~ater of about 16~. Typical practice is described in Example III.
There is oonsiderable latitude in choice of reaction temperature, initiator system, and emulsifier(s).
Choice of emulsifier, in particular, can be used to vary product properties. Pre-emulsion of monomers is useful in minimizing coagulum rormation. Conditions for basic 9 ~ 2 hydrolysis of the ¢opolymer emulsion are not critical, provided that the hydrolysis is continued until the b~e is consumed and a solution is formed. The amount of base should be sufficient so that in the copolymer there are at least 79~ by weight of (meth)acrylic acid salt units. It is good practice to add the base slowly to the copolymer emulsion which preferably has been cooled to ambient temperature with good stirring. Preferred conditions for carrying out the hydrolysis are a reaction temperature of 90 to 95C, with a 4 to 16 hour cook time. If a volatile base is chosen, the hydrolysis may be conducted under pressure. It is convenient to keep the alcohol liberated on hydrolysis in the resulting thickened aqueous solution of copolymer product, for the alcohol has little effect on product properties. However, the alcohol can optionally be removed by distillation if the end use application of the composition requires absence of alcohol.
Solution polymerization is preferred when monomer salt units (A) of the copolymer result from neutralization of the acid per se. A convenient technique is the concurrent feeding of initiator solution and of a mixture of the monomers to a reactor containing water held at 40 to 100C. Such common expedients as nitrogen spargin~, and the use of redox initiating systems, metal activators, and chain lenKth regulators may be employed.
The degree of hydrolysis or neutralization in preparation of the copolymers may be chosen within wide limits, subject to end use requirements of compatibility ,: '- ' .", ., .. . ~ .

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7 ~ % 4 and ef~ectiveness $n the formulation to be thlckened and provided that the copolymers contain at least 79%, ~y weight, Or carboxylic acid salt un~ts. The products resulting from ester hydrolysis are necessarily at a pH
above 7. Neutralized copolymer solutions may have a pH
as low as 6. Generally, opt~mum thickening performance is achieved when the copolymer solution has a pH range of 8 to 12.
The avera~e molecular weights of copolymers are estimated to be bet~een about 1009000 and 5,000,000.
Preferred copolymers ha.ve an average molecular weight of from about 200,000 to 1,000,000.
Generally the copolymer ~olutions of this invention will have a solids content of from about 8~ to about 20~. As can be seen by reference to Tables C-E3, supra., the amount of copolymer solution added to a latex to thicken it and improve its rheological properties will be such as to provide from about 0.2 to about 3 parts by weight of copolymer, dry basis, based on 100 dry parts o~ latex.
The copolymer products may be dried, to reduce ~hipping costs, or to remove solvent, aqueous or organi c.

Example I
Preparation of a sur~actant monomer.
400g ~0.347 mole~ of a dried polyoxyethylene stearyl ether (SA 20A, Mazer Chemicals, Inc.) were slowly melted in a 1-liter reactor fitted with a thermometer, stlrrer, reflux condenser, and heatinB

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mantle. When the temperature of the ether reached 40C, 0.69g of the monomethyl ether of hydroquinone and 0.67g of stannous octoate were added. The melt was then heated to 50C and 53.8g (0.348 mole) of isocyanatoethyl methacrylate (Dow Chemical Co., USA) were added dropwise from an addition funnel over a two-hour period while the reaction mixture was maintained at 45 to 50C. The reaction mixture was then cooked 1 hour at 50~C. The final product after cooling was a white wax.
Table A lists various surfactants reacted with isocyanatoethyl methacrylate, using the procedure of Example I.
TABLE A
*CPS
Number Surfactant .
1 Poly(oxyethylene)20 stearyl ether 2 Poly(oxyethylene)20 sorbitan monostearate 3 Nonyl phenoxy poly [(oxypropylene)2(oxyethylene)9 5] amine *CPS = Copolymerizable surfactant monomer Example II
Preparation of the surfactant monomer octadecyl poly(oxyethylene)19 ethyl itaconate.
A mixture of 198.8g (0.175 mole) of octadecyl poly(oxyethylene)19 ethanol, 150g toluene, and 0.5g of the monomethyl ether of hydroquinone were charged to a 500 ml. reaction flask equipped with a thermometer, mechanical stirrer, heating mantle and Dean-Stark receiver. The mixture was heated to reflux to remove -..
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-any residual water ln the surfactant. The mlxture was cooled to 70C and 22.8g of itaoonic acid (0.175 mole) and 1.0g Or paratoluene sulfonic acid were added. The mixture was again heated to reflux. After 4 hours, approximately 95~ of the theoretical amount of water had been removed. Tbe toluene was then removed ùnder vacuum.
The product; after cooling, was a white wax which was used without purification. This procedure is applicable to ethoxylated fatty alcohols generally.
The above surfactant ls designated as CPS 4 in Table B.

EXAMPLE III
) Preparation o~ a copolymer of the----inYention by emulsion polymerization and hydrolysis./
A mixture of 345g water, 2.8g o~ ethoxylated nonyl phenol (Igepal C0-990, GAF Corpor\tion), and 0. 37g soda ash were charged to a 1-liter reacto~r fitted with a thermometer, stirrer, condenser, and h'e'a'ting mantle.
A pre-emulsion of monomers was~ prepared in a beaker by mlxing 182 g water, 2.8g of the monomer prepared according to Example I, 8.0g ethoxylated nonyl phenol, 46.4g tO.539 eq.) methyl acrylate, 46~4g (0.463 eq.) ethyl aorylate, and 0.20g divinyl benzene.
The reactor charge was heated to B0C and 0.57g potasslum persulfate was added. The monomer pre-emulsion and 12g of a 5 percent solution of potassium persulfate were added from addition funnels at constant rate's over 90 minutes while maintaining the reaction mixture at 80C. The latex formed was cooked *Trademark . . .

~Z~7~2 at 880C for 1 h~ur, 1ooB water were added, and the mixture was cooled to 30C.
145g of a 25 percent solution of sodium hydroxide tO.906 eq.) were added to the latex with mixing over 10 minutes. The mixture was beated to 90 to 95C and cooked at that temperature for 16 hours.
The product was a clear solution having a solids content of 13.0 percent9 a viscosity of 12,000 cps, and a pH of 8.9.
The procedure of this Example III was used to prepare the copolymers designated Copolymer Solu~ion (CS) numbers 1 through 8 in Table B.

Example IV
Preparation of a copolymer solution by aqueous solution polymerization and neutralization To a 1.5 liter reaction flask equipped with a thermometer~ mechanical stirrer, heating mantle, nitrogen inlet and condenser, were charged 920g of city water, 178.2g of acrylic acid and 2~7g of the monomer of Example I.
The reactor charge was heated to 40C and purged with nitrogen. At 40C, 1.08g of an 8i26 percent aqueous ~olut~on of ammonium persulfate were added followed after 1 minute by addition of 0.54g of a 4 3~
solution of sodium metabisulfite. An exotherm was noted after a few minutes. The temperature then rose to 70C
to 800C within 10 minutes. The resulting polymer was then held at 70C to 800C for 1 hour. The product was . ' . , . ' ~ ~ . . . , ' ' ~
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cooled and a 50 percent sodium hydroxide solution was added to increase the pH to 8 to 9.
The copolymers thus prepared are designated CS
Nos. 9 and 10 in Table B.

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~Z9~24 Description of Application of the Copolymer Solutions The rheological properties that the ~opolymer solutions of this invention contribute to a latex coating system were evaluated using a typical carpet coating formulation, Such carpet coatings consist of a latex binder with 100 to 800 parts by weight of filler, usually calcium carbonate. Also, such type coatings usually contain a frothing aid to facilitate the aeration of the coatings. The viscositieis of the coatings are modified wlth a thickener, such as a copolymer solution of this invention, to achieve the desired rheological properties.
The properties which the copolymer solut~ons of this invention contribute to a carpet coating system are given in Table C. The coating system used in this e~aluation consisted of 100 dry parts of styrene butadiene latex ~Reichold Chemical, Inc. Latex 69700), 600 dry parts of calcium carbonate filler, and 1.2 parts of foaming agent (Stanfax 234). The total solids of the composition was adjusted to 83 percent with water. The several tests employed in determining the properties Or the coating system are described hereinbelow.
The copolymer solutions of this invention were used to increase the viscosity of the above-described coating formulation to an initial viscosity of 14000 cps + 400, as measured with RVT Brookfield viscometer at 20 rpm.
The coatings were left undisturbed for 24 hour~ before the statlc viscosity was measured. The coatings were then agitated for 5 minutes before the restir vlscos1ty was measured. If there is a * rade-mark ~;.`

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substantial increase in these viscosities, the coating will be difficult to transfer and penetration of the coating into a substrate will be adversely affected. A
decrease in these viscosities does not interfere with transfer, but the penetration into the substrate may be excessive resulting in excessive usage of coating material and/or defective carpet.
The shear rate viscosities, also measured with a RVT Brookfield viscometer, give a good indication of the pseudoplastic properties of the novel copolymer solutions to the coating system. Viscosity readings are taken at 1, 20, and 50 rpm which give three shear rates.
The greater the difference between the low and high shear viscosities, the more pseudoplastic the coating will be. A certain amount of this type of flow is necessary to achieve the proper flow on the substrats.
The pseudoplastic flow of coating formulations containing the copolymer solutions of this invention is well within the operating range of coating equipment (see Table C).
The yield testing as used in the carpet industry and discussed here is not really a measure of yield point in rheological terms. It is a stress relaxation determination which gives an indication of coating flow at very low shear rates. In the test a Brookfield viscometer is used (in Table C, below, a model RVT with #3 spindle was used), and the spindle is turned by hand to its limit of a 100 dial reading while in the coating.
The spindle is held in this position for 10 seconds. This is importaht because of the ~Z9~

viscoelasticity of many coatings~ After the 10 second hold, the spindle is released and readings are taken at various time periods. A one minute reading has become somewhat standard in the carpet in~ustry. This stress relaxation test gives a good indication of the coating's ability to penetrate into a substrate, and if the yield is high, the coating's high ride property. The copolymer solutions of this invention demonstrate a useful range of coating placement properties.
Since most coatings regardless of type are heated to speed the curing process, the coating viscosities at elevated temperatures are important to the quality of the final product. This type of testing is referred to as heat stability. The coating is heated under agitation in a bath to various temperatures which depend on the coating application equipment, and viscosities are recorded. The temperatures evaluated here are 100F, 140F, and 160F (37.8, 60 and 71 C) which are useful for carpet type coatings.
If the viscosities increase as the temperature increases, the coatings will ride high once the substrate is in the oven. If the viscosities decrease as the temperature increases, the coatings will penetrate into the substrate during initial cure. The data in Table C show that the copolymer solutions of this invention maintain a useful range of heat stability (see Table C).
Many coatings are aerated or frothed before application to a substrate. The frothed viscosity gives another important rheologioal property of a coating.
The coatings are frothed ln a Hobart to a density o~

, 9 7 ~ ~ 4 800 grams per liter. A BrookPield viscosity is recorded using the RVT with a #6 spindle. This viscosity controls the placement oP the coating prior to curing.
The copolymer solution of this invention demonstrates useful ranges of frothed viscosities as shown by the data in Table C.

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Latex films were used for tensile testing.
The films consisted of 100 dry parts of a styrene butadiene latex, and 0.5 parts of a thickener. This material was drawn down on teflon sheet using a bird bar (.030"). The resulting film was air-dried at room temperature for 12 hours, removed from the teflon plate and oven-cured for 10 minutes at 140C. The tensile pulls were made with a 1/2" dumbbell. Table D sets forth data which show that the thickener solutions of this invention all contribute to higher tensile strength as compared to the commercial thickeners in Table D.

TABLE_ Thickener*_ Percent Elongation PSI

CS No. 1 667 2411 *Thickeners A to E are all commercial thickeners The data in Tables E-1, E-2, and E-3 demonstrate the universal properties provided latices by the copolymer solutions of this invention. Different styrene butadiene latexes and formulations were used in each table. The data in the tables indicate improved flow and dispersing properties provided each latex used by inclusion of a copolymer solution of this invention.

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Claims (22)

1. A thickened aqueous copolymer solution useful for thickening and improving the rheology and dry tensile strength of latex systems comprising a copolymer having as monomeric units:
(A) about 79-99 percent of a (meth)acrylic acid salt of sodium, potassium or ammonium;
(B) about 0-20 percent of (meth)acrylic acid;
(C) about 0-20 percent of a lower alkyl ester of (meth)acrylic acid;
(D) about 1-21 percent of surfactant units selected from:
(1) the reaction product of a monoethylenically unsaturated monoisocyanate with a nonionic surfactant having hydroxyl or amine functionality; or (2) an ester of a monoethylenically unsaturated dicarboxylic acid containing from 4 to 8 carbon atoms with a polyoxalkylene alkyl or alkenyl ether containing from 4 to 100 oxyalkylene groups and from 6 to 22 carbon atoms in the alkyl or alkenyl group; and (E) about 0-1 percent of a copolymerizable polyethylenically unsaturated monomer, said percentages being by weight based on the total weight of monomeric units in said copolymer.

2. The copolymer solution according to claim 1 in which said copolymer is composed of (A) about 92-99 percent (meth)acrylate salt units, (B) about 0-8 percent (meth) acrylic acid units, (C) about 0-8 percent (meth)acrylic lower alkyl ester units, (D) about 1-8 percent surfactant monomer units, and (E) about 0.1-0.5 percent crosslinking monomer units.

3. The copolymer solution according to claim 1 in which said (meth)acrylic acid salt units (A) comprise sodium acrylate units.

4. The copolymer solution according to claim 1 in which said alkyl (meth)acrylate units (C) have the general formula CH2=CYZ
where Y is hydrogen or CH3 and Z is COR, where R is alkyl containing from 1 to 4 carbon atoms.

5. The copolymer solution according to claim 4 in which said alkyl (meth)acrylate units (C) are selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methyacrylate, propyl methacrylate and butyl methacrylate.

6. The copolymer solution according to claim 1 in which said surfactant monomer units are the reaction product of an isocyanate having the formula Z-?-O-A-N=C=O
where A is an alkylene group of the formula (CH2)n, n is an integer from 1 to 20, and Z is CH2=CH-, CH2=C(CH3)-, or CH2=CH-CH2-, or of alpha-, alpha-, alpha-, dimethyl-m-isopropenyl benzyl isocyanate, with a nonionic surfactant of the formula R30-(CnH2nO)w-H
where R3 is an alkyl or alkenyl group containing from 6 to 22 carbon atoms, or an alkaryl group containing from B to 22 carbon atoms, n is an integer of from 2 to 4, and w is an integer of from 6 to 100.

7. The copolymer solution according to claim 6 in which said monomer is the reaction product of isocyanatoethyl methacrylate and an alkoxylated fatty alcohol or an alkoxylated alkyl phenol.

8. The copolymer solution according to claim 7 in which said monomer is the reaction product of isocyanatoethyl methacrylate and poly(oxyethylene)20 stearyl ether.

9. The copolymer solution according to claim 6 in which said surfactant monomer units are the reaction product of an isocyanate of the formula Z-C-0-A-N=C=0 where A is an alkylene group of the formula (CH2)n, n is an integer of from 1 to 20, Z is CH2=CH-, CH2=C(CH3)-, CH2=CH-CH2-, or of alpha-, alpha-, dimethyl-m-isopropenyl benzyl isocyanate, and a nonionic surfactant of the formula R4(OCnH2n)y(OCH2?)z-NH2 where R4 is octylphenyl or nonylphenyl, n is an integer from 2 to 4, y is an integer from 3-20, R5 is CH3 or = CH2CH3, and z is an integer from 0-10.

10. The copolymer solution according to claim 9 in which said surfactant monomer is the urea reaction product of isocyanatoethyl methacrylate and nonylphenoxy.
poly[(oxypropylene)2(oxyethylene9.5] amine.

11. The copolymer solution according to claim 1 in which said nonionic surfactant ester monomer is the reaction product of a monoethylenically unsaturated dibasic acid selected from the group consisting of maleic, fumaric, itaconic, mesaconic, citraconic and methylene malonic acid with a nonionic surfactant of the formula R5O-(CnH2nO)v-H
where R5 is an alkyl or alkenyl group containing from 6 to 22 carbon atoms, n is an integer of from 2 to 4, and v is an integer from 6 to 100.

12. The copolymer solution according to claim 1 in which said polyethylenically unsaturated crosslinking monomer is selected from the group consisting of diallyl phthalate, vinyl crotonate, ally methacrylate, and divinyl benzene.

13. The copolymer solution according to claim 1 in which the major portion of said (meth)acrylate salt monomeric units (A) are obtained by hydrolysis of lower alkyl (meth)acrylate monomeric units.

14. The copolymer solution according to claim 13 in which said solution has a pH greater than about 7.

15. The copolymer solution according to claim 1 in which the major portion of said (meth)acrylate salt units (A) are obtained by neutralization of the carboxyl groups of (meth)acrylic acid monomers.

16. The copolymer solution according to claim 15 in which said solution has a pH of at least about 6.

17. A dry copolymer product comprising a copolymer having as monomeric units:
(A) about 79-99 percent of a (meth)acrylic acid salt of sodium, potassium or ammonium;
(B) about 0-20 percent of (meth)acrylic acid;

(C) about 0-20 percent of a lower alkyl ester of (meth)acrylic acid;
(D) about 1-21 percent of surfactant units selected from:
(1) the reaction product of a monoethylenically unsaturated monoisocyanate with a nonionic surfactant having hydroxyl or amine functionality; or (2) an ester of a monoethylenically unsaturated dicarboxylic acid containing from 4 to 8 carbon atoms with a polyoxalkylene alkyl or alkenyl ether containing from 4 to 100 oxyalkylene groups and from 6 to 22 carbon atoms in the alkyl or alkenyl group; and (E) about 0-1 percent of a copolymerizable polyethylenically unsaturated monomer, said percentages being by weight based on the total weight of monomeric units in said copolymer.

18. The dry copolymer product according to claim 17 in which said copolymer is composed of (A) about 92-99 percent (meth)acrylate salt units, (B) about 0-8 percent (meth) acrylic acid units, (C) about 0-8 percent (meth)acrylic lower alkyl ester units, (D) about 1-8 percent surfactant monomer units, and (E) about 0.1-0.5 percent crosslinking monomer units.

19. A method of improving the rheological properites of a latex composition which comprises adding thereto from about 0.2 to about 3 parts by weight, dry basis of a copolymer of claim 1, in aqueous solution, based on 100 dry parts of latex, said solution having a solids content of from about 8 to about 20.

20. A method of improving the rheological properties of a latex composition which comprises adding thereto from about 0.5 to about 2.5 parts by weight, dry basis of a copolymer of claim 2, in aqueous solution, based on 100 dry parts of latex, said solution having a solids content of from about 10 to about 15.

21. A copolymerizable monomer comprising the reaction product of a nonionic surfactant of the formula where R4 is octylphenyl or nonylphenyl, n is an integer from 2 to 4, y is an integer from 3 to 20, R5 is -CH3 or -CH2CH3, and z is an integer from 0-10 reacted with isocyanatoethyl methacrylate or alpha-, alpha-, dimethyl-m-isopropenylbenzyl isocyanate.

22. A copolymerizable surfactant comprising a reaction product of isocyanatoethyl methacrylate or alpha-, alpha-, dimethyl-m-isopropenyl benzyl isocyanate and nonylphenoxy poly[(oxypropylene)2(oxyethylene)9.5] amine.