GB2071122A - Preparation of copolymer latices - Google Patents

Abstract

High solids, low viscosity copolymer latices, especially useful when formulated as surface coatings, are prepared from (a) at least one vinyl ester monomer in an amount representing from about 50 weight percent to about 95 weight percent of total monomer charge and (b) at least one acrylate ester and/or methacrylate ester monomer representing the balance of the total monomer charge. The latices are prepared in a multi-stage polymerization sequence in which a significant portion of the total vinyl ester monomer charge is polymerized together with from 0 to about 50 weight percent of the total acrylate ester and/or methacrylate ester monomer in the initial stage in an aqueous emulsion reaction medium containing a suitable catalyst and thereafter, the remaining portion of the total vinyl ester monomer charge together with the remaining portion of the acrylate ester and/or methacrylate ester monomer charge is polymerized in the reaction medium containing additional catalyst if needed and polymerization is continued substantially to completion. The examples are directed towards copolymers of butyl acrylate with vinyl acetate.

Description

SPECIFICATION Preparation of copolymer latices This invention relates to the field of copolymer lattices and, more particularly, to such latices having high solids content and low viscosity and being prepared from a mixture of copolymerization monomers including a vinyl ester and an acrylate or methacrylate ester.

Numerous procedures for the emulsion polymerization and copolymerization of various ethylenically unsaturated monomers, vinyl esters, acrylate esters and methacrylate esters among them, have been known for some time. In general, a latex derived from a vinyl ester and one or more other monomers copolymerizable therewith is prepared by first charging an aqueous phase containing water, surface active agent, buffer, catalyst or catalyst system of the free radical type and usually a protective colloid such as polyvinyl alcohol (PVA), to a reactor.The monomers are thereafter charged to the reactor either as separate streams with mixing occurring in the reactor or in admixture, and either all at once or incrementally, and following heating to polymerization temperature, polymerization is thereafter permitted to proceed, accompanied by constant agitation, sub stantially to completion. The resulting latex is cooled and filtered and can be used in many applications, e.g. in paints and other surface coating compositions, adhesives and textile treating agents.

Emulsion polymerization procedures featuring one or more aspects of the aforedescribed method of preparing copolymer latices are described in U.S.

Patent Nos. 2,496,384; 2,520,959; 3,248,356; 3,404,114; 3,423,353; 3,483,171; 3,804,881; and, 4,039,500. U.S. Patent No.3,423,353 to Levine et al.

in particular describes latices obtained from vinyl acetate and one or more other comonomers including alkyl acrylates and methacrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate and n-propyl methacrylate, the latices being said to possess higher solids contents than obtainable using conventional emulsion polymerization techniques, while at the same time having reduced viscosities and improved freeze-thaw stability. The latices are prepared in the conventional manner and once polymerization is substantially complete, a relatively large amount of water-soluble polymerization catalyst or initiator is added to the emulsion to reduce viscosity and increase particle size.It is speculated by patentees that this post-addition of catalyst results in some degradation of the surface active agent and the ether linkage-containing protective colloid when used, reducing their molecular weights by an oxidative mechanism which involves rupture of the ether linkages. This oxidative degradation is thought to reduce the effectiveness of the surface active agent and protective colloid resulting in some agglomeration of particles. The larger average particle size of the emulsion is believed to be also responsible for the reduction in visc,osity.

It has now been discovered that latices derived from vinyl esters and acrylate and/or methacrylate esters having high solids contents and low viscosity can be prepared by the polymerization itself without further manipulative steps such as the post-addition of relatively large quantities of catalyst of U.S. Patent No. 3,423,353 to Levine et al.

The post-addition of catalyst to latices prepared by the process of this invention may have no significant effect on the viscosities of the products, demonstrat ing that the viscosities of the latices are for the most part fixed during polymerization.

In accordance with the present invention copolymer latices are prepared from (a) at least one vinyl ester monomer in an amount representing from about 50 weight percent to about 95 weight percent of total monomer charge, and (b) at least one monomer selected from acrylate ester and methacrylate ester monomers representing the balance of the total monomer charge by polymerizing in a first stage a significant portion of the total vinyl ester monomer (e.g. at least about 10 weight percent and preferably at least about 50 weight percent of the total vinyl ester monomer) together with from 0 to about 50 weight percent of the total acrylate and/or methacrylate ester monomer in an aqueous emulsion reaction medium containing a polymerization catalyst, and thereafter polymerizing in a second stage the remaining portion of the total vinyl ester monomer charge together with the remaining amount of the acrylate and/or methacrylate ester monomer in the reaction medium containing additional catalyst if needed, polymerization being continued substantially to completion.Preferably, during the first stage, the ratio of vinyl ester to acrylate and/or methacrylate monomer is greater than about 4.5 until about 40-60% of the total monomer charge is added, and during the second addition the ratio of vinyl ester monomer to acrylate and/or methacrylate monomer is less than about 4.5 until the total remaining amount of monomer has been added to the polymerization reactor. One or more other ethylenically unsaturated monomers co-polymerizable with monomers (a) and (b) present in an amount of up to 5 weight percent of the total monomer charge can be added at the commencement of or during the polymerization sequence. It may be advantageous to initially polymerize a small amount, i.e. about 5%, of the total vinyl ester monomer in the reactor prior to commencement of the first stage polymerization.

The process herein contemplates the use of known and conventional surface active agents, buffers, protective colloids, catalysts, and the like, in the usual amounts, and can be carried out in equipment heretofore employed for emulsion polymerization.

Typically, the latices produced in accordance with this invention will possess a solids content from about 60 to about 70 weight percent and even higher. The viscosities of the high solids latices herein are generally but a fraction of the viscosities of latices prepared in the usual manner, i.e. by simultaneous addition of monomers, and will usually not exceed 15,000 cp. Brookfield viscosity (RVF, Spindle No. 1) at 2 rpm. Viscosities of latices of equivalent high solids which are prepared in the conventional way have attained 50,000 cp. Brookfield viscosity (RVF, Spindle No. 5) at 2 rpm. The combination of high solids content and low viscosity makes the latices of this invention useful for formulation as paints and other surface coatings.

The latices prepared in accordance with the process of this invention contain copolymers of at least one vinyl ester and at least one acrylate and/or methacrylate ester. Generally, when preparing these copolymers, from about 50 weight percent to about 95 weight percent, and preferably from about 65 weight percent to about 85 weight percent, of vinyl ester will be copolymerized with from about 5 weight percent to about 50 weight percent, and preferably from about 15 weight percent to about 35 weight percent, of acrylate and/or methacrylate ester based on the total weight of the monomers present.

Among the vinyl esters which can be advantageously used in this invention are included vinyl formate, vinyl propionate, vinyl butyrate and vinyl chloroacetate. Vinyl acetate is especially preferred for use herein. Illustrative of acrylate esters and methacrylate esters which can be used in this invention to good effect are methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate, sec-butyl acrylate, amyl acrylate, isoamyl acrylate, hexyl acrylate, 2-ethylhexylacrylate, octyl acrylate, 3, 5, 5-trimethylhexyl acrylate, decyl acrylate, dodecyl acrylate, cetyl acrylate, octadecyl acrylate, cyclohexyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, hexyl methacrylate, 2-ethylbutyl methacrylate, octyl methacrylate, 3,5, 5-trimethylhexyl methacrylate, decyl methacrylate, cyclohexyl methacrylate, nor bornenyl methacrylate, benzyl methacrylate, phenyl methacrylate, and neopentyl methacrylate. Butyl acrylate has been found to be especially advantage ous for use herein.

As previously stated, up to 5 weight percent of the total weight of the monomers present can be one or more additional ethylenically unsaturated monomers illustrative of which are the following: ethylene, propylene, 1-butene, 2-butene, isobutylene,1-pentene,2 2- methyl - 2- butene, 1-hexene, 4 - methyl - 1 - pentene, 3,3 - dimethyl - 1 butene, 2,4,4 - trimethyl - 1 - pentene, 6 - ethyl - 1 - hexene,1-heptene,1-octene,1-decene,1-dodeceneF allene, butadiene, isoprene, chloroprene, 1,5 - hex- adiene, 1, 2,5- hexatriene, divinylacetylene, cyclopentadiene, dicyclopentadiene, norbornene, norbornadiene, methylnorbornene, cyclohexene, styrene, alpha - chlorostyrene, alphamethyl styrene, allylbenzene, phenylacetylene, 1 - phenyl - 1, 3-butadiene, vinylnaphthalene, 4-methylstyrene, 2,4 - di - methylstyrene, 3-ethylstyrene, 2, 5- diethyl- styrene, 2-methoxystyrene, 4 - methoxy - 3- methyl styrene, 4-chlorostyrene, 3,4 4 - dimethyl - alpha - methylstyrene, 3- bromo - 4 - methyl - alpha methylstyrene, - dichlorostyrene, 4- fluorostyrene, 3-iodostyrene, 4-cyanostyrene, 4-vinylbenzoic acid, 4-acetoxystyrene, 4-vinyl benzyl alcohol, 3-hydroxystyrene, 1,4 - dihydroxystyrene, 3-nitrostyrene, 2-aminostyrene, 4 - N, N dimethylaminostyrene, 4-phenylstyrene, 4 - chloro 1 - vinyl - naphthalene, acrylic acid, methacrylic acid, acrolein, methacrolein, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-methyl methacrylamide, chloroacrylic acid, methyl chloroacrylic acid, chioroacrylonitrile, ethacrylonitrile, N-phenyl acrylate, N, N - diethylacrylamide, N-cyclohexyl acrylamide, vinyl chloride, vinylidene chloride, vinylidene cyanide, vinyl fluoride, vinylidene fluoride, trichloroethene, methyl vinyl ketone, methyl isopropenyl ketone, phenyl ketone, methyl alpha chlorovinyl ketone, ethyl vinyl ketone, divinyl ketone, hydroxymethyl vinyl ketone, ohloromethyl vinyl ketone, allilydene diacetate, methyl vinyl ether, isopropyl vinyl ether, butyl vinyl ether, 2-ethylhexyl vinyl ether, 2-methoxyethyl vinyl ether, 2-ch lo roethyl vinyl ether, methoxyethoxyethyl vinyl ether, hydroxyethyl vinyl ether, aminoethyl vinyl ether, alpha - methylvinyl methyl ether, divinyl ether, divinyl ether of ethylene glycol or diethylene glycol or triethanolamine, cyclohexyl vinyl ether, benzyl vinyl ether, phenethyl vinyl ether, cresyl vinyl ether, hydroxyphenyl vinyl ether, chlorophenyl vinyl ether, naphthyl vinyl ether, dimethyl maleate, diethyl maleate, di - (2 - ethylhexyl) maleate, maleic anhydride, dimethyl fumarate, dipropyl fumarate, vinyl ethyl sulfide, divinyl sulfide, vinyl p-tolyl sulfide, divinyl sulfone, vinyl ethyl sulfone, vinyl ethyl sulfoxide, vinyl sulfonic acid, sodium vinyl sulfonate, vinyl sulfonamide, vinyl benzamide, vinyl pyridine, N-vinyl pyrollidone, N-vinyl carbazole, N - (vinyl benzyl) - pyrrolidine, N - (vinyl benzyl) - pyrrolidine, N - (vinyl benzyl) piperidine, 1-vinyl pyrene, 2-isopropenyl furan, 2-vinyl dibenzofuran, 2- methyl 5-vinyl pyridine, 3-isopropenyl pyridine, 2-vinyl piperidine, 2-vinyl quinoline, 2-vinyl benzoxazole, 4 - methyl-5-vinyl thiazole, vinyl thiophene, 2-isopropenyl thiophene, indene, coumarone, 1-chloroethyl vinyl sulfide, vinyl 2-ethoxyethyl sulfide, vinyl phenyl sulfide, vinyl 2-naphthyl sulfide, allyl mercaptans, divinyl sulfoxide, vinyl phenyl sulfoxide, vinyl chlorophenyl sulfoxide, methyl vinyl sulfonate, vinyl sulfoanilide, and the like.Part or all of these optional monomers can be charged to the reactor at the commencement of or during the polymerization sequence. In some instances, these monomers may be used at a concentration below about two weight percent to avoid undue coagulation.

The surface active agents contemplated by this invention include any of the known and conventional surface active and emulsifying agents, principally the nonionic and anionic materials, and mixtures thereof heretofore employed in the emulsion copolymerization of vinyl acetataand ethylene, the nonionic surfactants being especially preferred.

Among the nonionic surface active agents which have been found to provide good results are included the "lgepals" (G.A.F.), the "Tweens" (Atlas Chemical) and the "Pluronics" (BASF Wyandotte).

The "lgepals" are members of a homologous series of alkylphenoxypoly (ethyleneoxy) ethanols which can be represented by the general formula

wherein R represents an alkyl radical and n represents the number of mols of ethylene oxide employed, among which are alkylphenoxypoly (ethyleneoxy) ethanols having alkyl groups containing from about 7 to about 18 carbon atoms, inclusive and having from about 4 to about 100 ethyleneoxy units, such as the heptylphenoxypoly (ethylenoxy) ethanols, nonylphenoxypoly (ethyleneoxy) ethanols and dodecylphenoxypoly (ethyleneoxy) ethanols; the sodium or ammonium salts of the sulfate esters of these alkylphenoxypoly (ethyleneoxy) ethanols, alkylpoly (ethyleneoxy) ethanols; alkylpoly (propyleneoxy) ethanols; octylphenoxyethoxyethyldimethylbenzylammonium chloride; polyethylene glycol t dodecylthioether. The "Tweens" are polyoxyalkylene derivatives of fatty acid partial esters of sorbitol anhydride such as the polyoxyalkylene derivatives of sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate and sorbitan trioleate. The "Pluronics" are condensates of ethylene oxide with a hydrophobic base formed by condensing propylene oxide with propylene glycol, and the like. Other suitable nonionic surfactants which can be employed herein are ethylene oxide derivatives of long chain fatty alcohols such as octyl, dodecyl, lauryl or cetyl alcohol.Anionic surface active agents which can be used herein include the alkali metal sulfates of C12 to C14 alcohols such as sodium lauryl sulfate and alkali metal salts of alkyl benzene sulfonic acids and alkyl toluene sulfonic acids having aliphatic side chains of about 10 to about 15 carbon atoms, and the like. The surface active agent is generally employed at from about 3% to about 5% and preferably, at from about 3.5% to about 4.5%, by weight of the total monomers present.

A protective colloid is generally incorporated in the aqueous emulsions of this invention. Such known and conventional protective colloids as the partially and fully hydrolyzed polyvinyl alcohols, cellulose ethers, (e.g. hydroxymethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose and ethoxylated starch derivatives), the natural and synthetic gums (e.g. gum tragacanth and gum arabic), polyacrylic acid, poly (methyl vinyl ether/maleic anhydride) and polyvinyepyrrolidone, are well suited for use herein, preferably at a level of from about 0.1 % to about 2% by weight of the emulsion. Polyvinyl pyrrolidone and the partially hydrolyzed polyvinyl alcohols are especially advantageous for use in this invention.

The catalysts used in the copolymerization reac -tion can be the known and conventional free radical polymerization catalysts heretofore used for the preparation of copolymer latices and include inorganic peroxides such as hydrogen peroxide, sodium perchlorate and sodium perborate, inorganic persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate and reducing agents such as sodium hydrogen sulfite. Catalyst (including co-catalyst reducing agent, if employed) is generally utilized at a level of from about 0.1% to about 1% by weight of total comonomers. The catalyst can be added to the reaction medium all at once or it can be divided into two or more parts and added to the reactor medium with each addition of monomer or during either or both polymerization sequences.

An alkaline buffering agent such as sodium bicarbonate, ammonium bicarbonate, sodium acetate, and the like, may be added to the aqueous system to maintain the pH at the desired level. The amount of buffer is generally about 0.01 to 0.5% by weight based on the monomers.

The method by which the monomers are charged to the reactor is not critical. The monomers can be added to the reaction medium as a steady stream, drop-wise or in periodic increments; the vinyl ester and acrylate/methacrylate ester can be admixed prior to being charged to the reactor or these monomers can be introduced to the reactor as separate streams. Advantageously, the monomers are added as a steady stream over periods ranging from about 1 hour to about 5 hours and preferably over a period of from about 2 hours to about 3 hours.

The reaction temperature herein can be selected at levels which have heretofore been employed in emulsion polymerization. For both polymerization sequences the temperature can range from about 0 C. to about 1 OO"C, preferably from about ambient temperature to about 80"C, with the reaction medium being constantly stirred or otherwise agitated. The substantial completion of polymerization is usually indicated when free monomer content of the latex emulsion is below about 1% and preferably below about 0.5%.

In the Examples which follow, in which conventional equipment was used and weight parts are given, Examples 1 to 11 are illustrative of the copolymer latices and emulsion polymerization process of this invention while comparative examples 1A and 1 B are given by way of illustrating the prior art latices and polymerization procedures. Components of the emulsion media employed in the Exampies are identified as follows: Component Source Composition Triton X-405 Rohm and Haas Octylphenoxy Company polyethoxy ethanol Triton QS-9 Rohm and Haas Phosphate ester, Company acid form Tamol 850 Rohm and Haas Sodium salt of Company polymeric carboxylic acid Sipon ESY Alcolac, Inc.Sodium lauryl ether sulfate MonomerX-980 Rohm and Haas Trimethylol Company propane trimethyacrylate Sodium lauryl sulfate Butyl Carbitol Union Carbide Diethylene Corporation glycol monobutyl ether Plasticizer Cincinnati Milacron Surfactant Chemicals, Inc.

Natrosol 250MR Hercules, Inc. Hydroxyethyl cellulose Trycol PO-407 Emery Industries Octyl phenol condensed with 40 units of ethylene oxide CMP Acetate Troy Chemical Preservative Corporation preparation containing 10% by weight of chloromethoxy propyl mercuric acetate Example 1 To a 2000 ml resin flask equipped with stirrer, reflux condenser, addition funnel and thermometer were added the following solutions: (a) Deionized water 200 parts Polyvinylpyrrolidone 2.5 parts (b) Deionized water 220 parts TRITON X-405 40 parts TRITON QS-9 12.5 parts Sodium hydroxide to pH 10 followed by 40 parts of vinyl acetate. The reactor was heated with a water bath and at 60"C., 1.65 parts of ammonium persulfate in 10 parts of water were added all at once.At 72"C., the addition of 320 parts of vinyl acetate was started and then continued at 78-80"C, over about 65 minutes. Thereafter, a mixture of 360 parts of vinyl acetate and 150 parts of butyl acrylate was added over about 120 minutes.

When all the monomer mixture had been added, 0.2 part of ammonium persulfate was introduced and the batch was given an additional 30 minutes at 80"C. to completely consume the monomers. Cooled to room temperature, the copolymer latex had a 65.2 percent solids content and a Brookfield Viscosity (RVF, Spindle No.2) of 2700 cp at 2 rpm and 800 cp at 20 rpm.

Comparative Example IA In this example. which is illustrative of the prior art, a single stage addition of monomers was used.

The protective colloid was omitted in order to avoid unmanageable viscosity for the completed latex.

To a 2000 ml resin flask equipped as in Example 1 were added: Deionized water 450 parts TRITON X405 37 parts TRITON QS-9 25 parts Sodium hydroxide to pH 10 The solution was brought to 70"C with a controlled temperature water bath and 1.65 parts of ammonium persulfate in 10 parts of water were added all at once, followed by a mixture of 720 parts of vinyl acetate and 150 parts of butyl acrylate monomers added over about 140 minutes. The reaction temperature rapidly rose to, and was controlled at, 80"C during addition of the monomers. Following the monomeraddition,0.3 part of ammonium per- sulfate in 10 parts of water additionally was added.

The reaction temperature was held at 80"C for another hour and then the batch was cooled to room temperature. The copolymer latex had 64.6 percent solids content and Brookfield viscosity (RVF, Spindle No.5) of 50,000 cp at 2 rpm and 12,100 cp at 20 rpm.

This viscosity was altogether too high for a good latex paint formulation.

Comparative Example 7B This example is also illustrative of the prior art procedure of copolymerizing all of the monomers simultaneously. The following recipe was prepared and added to a resin flask equipped as in Example 1: gm Vinyl acetate 718 Butyl acrylate 147 Deionized water 470 Triton X-405 37 Triton OS-9 25 NaOH 2.5 (NH4)2S208 1.65+0.3 The surface active agents were dissolved in the water and the solution's pH was adjusted to 11.6 with the NaOH (dissolved in H20). The solution was charged to the reactor, heated to 70"C. At this point the first part of the (N H4)2S208 was added and the addition of the monomer blend commenced.The addition rate was fast during the first 2 hours of polymerization (approximately 80% of the monomer was added during this period). During the last half hour the monomer addition rate was lowered (with the latex becoming fairly viscous). Upon completion of the monomer addition, the second part of the catalyst was added (dissolved in 500 ml H2O). Afterwards, the batch was kept at about 80"C for about 1 hour. The polymerization temperature was 80"C 1"C. The resulting latex had a good appearance but was very viscous; it did not contain any gel but it contained numerous air bubbles.The following properties of the latex were observed: Solids: 64.6% Brookfield Viscosity (Spindle No. 5) r.p.m. 2 4 10 20 reading 25 32.5 46 60.5 factor 2000 1000 400 200 cp 50000 32500 13400 12100 The drawdown on a glass plate was clear but contained many bubbles.

While the latex of Example 1 is an excellent candidate for use in paints, it is readily apparent that the latices produced in accordance with the prior art procedure of simultaneous copolymerization are not suitable materials for surface coating formulations.

Example 2 To the resin flask reactor of Example 1 were added: Deionized water 420 parts TRITON X-405 40 parts SIPON ESY 20 parts Polyvinylpyrrolidone 5 parts Sodium acetate 3.2 parts Vinyl acetate 40 parts Ammonium persulfate 1.65 parts in Water 10 parts At 72"C., the addition of 320 parts of vinyl acetate was started, then continued at 78-80"C. over about 65 minutes. Thereafter, a mixture of 360 parts of vinyl acetate and 150 parts of butyl acrylate was added over about 120 minutes. When all the monomer mixture had been added, 0.2 part of ammonium persulfate was introduced and the batch was held an additional 30 minutes at 80 C to consume remaining monomers.When cooled to room temperature, the copolymer latex was found to have 64.8 percent solids and a Brookfield viscosity (RVF, Spindle No. 1) of 550 cp at 2 rpm and 280 cp at 20 rpm.

Example 3 To the resin flask reactor of Example 1 were added: Deionized water 335 parts TRITON X-405 50 parts SIPON ESY 22 parts Polyvinylpyrrolidone 5 parts Sodium acetate 3.2 parts Vinyl acetate 40 parts After the addition at 600C. of 1.65 parts of ammonium persulfate in 10 parts of water, 320 parts of vinyl acetate were added over 75 minutes at 78 80"C. followed by a solution of 0.1 part of ammonium persulfate in 5 parts of water, then a mixture of 360 parts of vinyl acetate and 150 parts of butyl acrylate over 135 minutes.

To complete polymerization, 0.5 part of ammonium persulfate was intermittently added over the next hour. The latex batch, cooled to room temperature, contained 69.5 percent solids and had a Brookfield viscosity (RVF, Spindle No. 2) of 1200 cp at 2 rpm and 570 cp at 20 rpm.

Example 4 Example 2 was repeated except that 8.7 parts of acrylic acid were included inthe second monomer addition; i.e., of vinyl acetate-butyl acrylate mixture.

The latex contained 65.8 percent solids and had a Brookfield viscosity (RVF, Spindle No.2) of 2600 cp at 2 rpm and 900 cp at 20 rpm.

Example 5 To test the performance of the high solids latices of th is invention, standard latex paints were prepared from the copolymer latices of Example 1 (Part A) and Example 2 (Part B). Using normal paint making procedures, a pigment grind was prepared and then let down with latex, water and thickener solution to arrive at suitable brushing viscosities. The viscosity of the Part A paint was 77 Krebs Units (K.U.) and that of the Part B paint was 84 Krebs Units (K.U.).

Both paints were drawn down on a Leneta contrast chart, using a 6 mil drawdown bar. The dry drawdowns were examined and found to be quite satisfactory with no latex coagulation or pigment agglomeration present. Hiding power was considered to be entirely acceptable. Brushouts were made on compressed paperboard, both one and two coats, with an overnight dry between coats. Application of the two paints was accomplished without noting difficulties of any sort. Viscosities were checked after one month for shelf stability and found to be excellent. The Part A paint increased by only 2 K.U.

and the Part B paint remained the same.

Example 6 The following were added to a resin flask as in Example 1: gm Vinyl acetate 720 Butyl acrylate 150 Deionized water 455 Triton X-405 40 Sipon ESY 20 Polyvinylpyrrolidone 5 NaO2CCH3 3.2 (NH4)2S208 165+0.1 + 0.2 The surface active agents, polyvinylpyrrolidone and buffer were dissolved in cold water. The solution plus 40 gm of vinyl acetate were charged to the reactor and heated. At 60"C., the first part of the catalyst was added and when the reaction temperature reached 72"C., the addition of the first stage of monomer (320 gm vinyl acetate) was started. During this addition (65 minutes) the polymerization temperature was kept between 76-78"C. with cooling.

Immediately after completing the addition of the first stage, the addition of the second stage (360gm vinyl acetate admixed with 150 gm butyl acrylate) was started. The reaction temperature dropped, and light heating was necessary to keep the reaction temperature from falling. The rate of addition was somewhat low in order to prevent the build-up of free monomer in the reactor which might otherwise produce foam.

Catalyst was added both when the addition had started and upon its completion. After completion of the monomer addition (160 minutes) the temperature rose to 84"C. The latex obtained had a good appearance. Very little grit remained on the filter after the latex had been screened.

The following properties of the latex were observed: Solids: 64.8% Brookfield Viscosity (Spindle No. 1) r.p.m. 2 4 10 20 reading 11 185 35 56 factor 50 25 10 5 cp 550 462 360 280 Glass drawdown of the latex appeared very good; the latex was somewhat hazy but gel/bubble-free.

Example 7 The following were added to a resin flask as in Example 1: gm Vinyl acetate 740 Butylacrylate 157 Deionized water 455 Triton X-405 40 Triton QS-9 12.5 Polyvinylpyrrolidone 3.5 NaOH 1.2 (NH4)2S208 1.65 The polyvinylpyrrolidone/su rface active agent solution was prepared and pH adjusted as in the previous examples. First stage addition of monomer (55 minutes) consisted of increments of 40 and 320 gm vinyl acetate. Second stage addition (140 minutes) consisted of a mixture of 380 gm vinyl acetate and 157gm butyl acrylate. While the second stage of monomer was slightly increased to compensate for possible losses, the solids content indicated that this was not necessary. When the addition of the second stage was started, as usual the reaction temperature dropped.At this point 0.1 gm of extra catalyst was added, but without much result. The reaction temp erature was then regulated by controlling the monomer flow and bath temperature. At the begin ning of the second stage, the temperature dropped to 75"C., but during the major part, it was between 78-80"C. At the end of the monomer addition, 0.2gm of (NH4)2S208 was added. The temperature rose to 83"C. No foam was observed. The latex contained the usual amount of grit, but once this grit was removed by filtration the product had an acceptable appearance.The following properties of the latex were observed: Solids: 65.7% Brookfield Viscosity (Spindle No.2) r.p.m. 2 4 10 20 reading 8 12 20 29 factor 200 100 40 20 cp 1600 1200 800 580 Glass drawdown of the latex gave a slight haze but the latex was nevertheless of good overall appearance.

Example 8 The following interior paint formulations were prepared with the copolymer latices of Examples 6 and7: Pigment Grind (in a Cowles Dissolver) gm Water 516 CMP Acetate 1 EthyleneGlycol 96 Butyl Carbitol 68 K2CO3 4 Tamol 850 8 Plasticizer Surfactant 12 3% Natrosol 250 MR 600 T1O2 600 Calcined Clay 240 Whitening (atomite) 1000 Total 3145 Paint A B Pigment Grind 394 394 Latex of Example 6 80.5 Latex of Example - 80.5 Water 93 95 3% Natrosol 250 MR 15 13 Klebs Units (K.U.) 84 77 Drawdowns of Paints A and B were made on Leneta contrast charts using a 6 mil drawdown bar.

The paints were brushed on compressed paperboard, both one and two coats, with an overnight dry between coats. The paperboard panel was sealed with the diluted latex of Example 6 before application of the paint. Both drawdowns and brushings were satisfactory. No coagulation of latex or pigment agglomeration occurred with either paint.

Viscosities: Paint A 84 K.U.

Paint B 79 K.U.

Example 9 The following were added to a resin flask as in Example 1: gm Vinyl acetate 735 Butyl acrylate 150 Deionized water 360 Triton X-405 50 Sipon ESY 22 Polyvinylpyrrolidone 5 NaO2CCH3 32 (NH4)2S2Oa 1.65 + 0.1 + 10.5 First stage addition of monomer (360gm of vinyl acetate over 75 minutes) was completed and after about 130cc of monomer mixture from the second stage addition (360gm of vinyl acetate mixed with 1 50gm butyl acrylate) remained to be added, the final addition of catalyst was started (0.5gm ammonium sulfate in 20ccH2O). The resulting latex had a good appearance while containing the usual amount of grit which was readily removable by filtration or similar means.The following properties of the latex were observed: Solids: 69.3-.5% Brookfield Viscosity (Spindle No.2) r.p.m. 2 4 10 20 reading 6 9.5 17.5 28.5 factor 200 100 40 20 cp 1200 950 700 570 Glass drawdown of the latex made several days after the product was made gave a very good gel and bubble free coating.

Example 10 The following were added to a resin flask as in Example 2: gm Vinyl acetate 720 Butyl acrylate 150 Acrylic acid 8.7 Deionized water 435 Triton X-405 40 Sipon ESY 20 Polyvinylpyrrolidone 5 NaO2CCH3 3.2 (NH4)2S2Oss 1.65 + 0.2 The polymerization was started as in Example 6 but with 360gm of vinyl acetate being added in the first stage (over 65 minutes) and 360gm of vinyl acetate admixed with 150gm butyl acrylate and 8.7gm acrylic acid being added in the second stage (over 160 minutes). During the second stage, the addition rate and bath temperature were regulated so that reaction temperature was always close to the bath temperature (78-80"C). No catalyst addition was made at the start of the addition of the second stage.

The final catalyst addition was started about 5 minutes after completion of the addition and extended over a period of about 15 minutes. After completion of the monomer addition, the reaction temperature for about 40 minutes was slightly above or equal to the bath temperature. Approximately 15 minutes after the reaction temperature had begun to decline, the contents of the reactor were cooled to room temperature. The resulting latex had no free monomer odor and had a good, nearly grit-free appearance. Screening of the monomer was very easily accomplished.

The following properties of the latex were observed: Solids: 65.8% Brookfield Viscosity (Spindle No. 2) rpm 2 4 10 20 reading 13 19 31 45 factor 200 100 40 20 cp 2600 1900 1240 900 Glass drawdown of the latex gave a gel and bubble free coating of very good overall appearance.

Example 11 This example results in a latex of high viscosity, polymerization being conducted in a sequence of two stages but with a mixture of vinyl acetate and butyl acrylate being polymerized at each stage of monomer addition. The following were added to a resin flask as in Example 1: gm Vinyl acetate 700 Butyl acrylate 150 MonomerX-980 26 Acrylic acid 8.7 Deionized water 450 Emersaí 6400 20 Trycol PO-407 40 Polyvinylpyrrolidone 2 NaO2CCH3 4 (NH4)2S2O8 16 To facilitate the dissolution of the Emersal 6400, some water was added to the surface active agent followed by heating.

The monomer mixtures were prepared as follows: Initial Stage First Second Stage Stage (gm) (gum) Vinyl acetate 40 310 350 Butyl acrylate 0 65 85 Monomer X-980 0 13 13 Acrylic acid 0 4.35 4.35 First stage addition of monomer took place over 80 minutes and second stage addition of monomer was carried out over 85 minutes. No extra catalyst was added upon completion of the monomer additions.

The resulting latex which contained the usual small amount of grit had a good appearance with just a trace of dilatancy.

The following properties of the latex were observed: Solids: 65.2% Brookfield Viscosity (Spindle No.3) r.p.m. 2 4 10 20 reading 16.5 21 30 39 factor 500 250 100 50 cp 8250 5250 3000 1950 Glass drawdown of this latex had good appear ance with only a slight haze.

Claims (16)

1. A process for preparing a copolymer latex from (a) vinyl ester monomer(s) amounting to from about 50 weight percent to about 95 weight percent of total monomer charge and (b) monomer(s) selected from acrylate ester and methacrylate ester monomers constituting the balance of the total monomer charge, the process comprising polymerizing in a first stage a significant portion of the total (a) and from 0 to about 50 weight percent of the total (b) in an aqueous emulsion reaction medium containing a polymerization catalyst, and thereafter polymerizing in a second stage the remaining portion of the total monomer charge in the reaction medium containing additional catalyst if needed, polymerization being continued substantially to completion.

2. A process according to claim 1 wherein at least 10 weight percent of the total vinyl ester monomer charge is polymerized in the first stage.

3. A process according to claim 2 wherein at least 25 weight percent of the total vinyl ester monomer charge is polymerized in the first stage.

4. A process according to any of claims 1 to 3 in which the vinyl ester monomer is vinyl acetate.

5. A process according to any of claims 1 to 4 in which the acrylate ester monomer is butyl acrylate.

6. A process according to any of claims 1 to 5 in which a total of from about 65 weight percent to about 85 weight percent of vinyl ester is copolymerized with a total of from about 35 weight percent to about 15 weight percent of acrylate and/or methacrylate ester.

7. A process according to any of claims 1 to 6 in which less than about 60 weight percent of the total vinyl ester monomer present is initially added to the reaction medium with the balance thereof being sequentially added to the reaction medium with the acrylate and/or methacrylate ester.

8. A process according to any of claims 1 to 7 wherein the reaction medium includes non-ionic and/or anionic surface active agent.

9. A process according to any of claims 1 to 8 in which the reaction medium contains a protective colloid.

10. A process according to any of claims 1 to 9 in which the reaction medium contains an alkaline buffering agent.

11. A process according to any of claims 1 to 10 in which the balance of the total vinyl ester monomer charge together with the balance of the acrylate ester andlor methacrylate ester monomer charge is added incrementally in the second step, and wherein the ratio of vinyl ester monomer to acrylate and/or methacrylate monomer in the first incremental addition is greater than about 4.5 until about 40-60% of the total monomer charge is added, and thereafter, in a second incremental addition, the ratio of vinyl ester monomer to acrylate and/or methacrylate monomer is less than about 4.5 until the remaining amount of monomers is added to the reactor.

12. A process according to any of claims 1 to 10 In which during the first stage, the ratio of vinyl ester to acrylate and/or methacrylate monomer is greater than about 4.5 until about40-60% ofthetotal monomer charge is added, and during the second addition the ratio of vinyl ester monomer to acrylate and/or methacrylate monomer is less than about 4.5 until the total remaining amount of monomer has been added to the polymerization reactor.

13. A process for preparing high solids, low vis- comity copolymer latices from.: (a) at least one vinyl ester monomer in an amount representing from about 50 weight percent to about 95 weight percent of total monomer charge, and (b) at least one monomer selected from acrylate ester monomer or methacrylate ester monomer representing the balance of the total monomer charge; which comprises polymerizing in a first stage a sig nificant portion of the total vinyl ester monomer charge and from 0 to about 50 weight percent of the total acrylate ester and/or methacrylate ester monomer in an aqueous emulsion reaction medium containing a polymerization catalyst, and thereafter polymerizing in a second stage the remaining portion of the total vinyl ester monomer charge together with the remaining portion of the acrylate ester and/or methacrylate ester monomer in the reaction medium containing additional catalyst if needed, polymerization being continued substantially to completion.

14. A modification of a process according to any of claims 1 to 13 in which a total of up to 5 weight percent of the total monomer charge of one or more other ethylenically unsaturated monomers copolymerizable with monomers (a) and (b) is added at the commencement of and/or during polymerization.

15. A process for preparing a copolymer latex, the process being substantially as hereinbefore described in any one of Examples 1 to 11.

16. A latex prepared by a process according to any of claims 1 to 15.