NO149663B - AROUND, COLLODIAL DISPERSON OF CATIONIC STRUCTURED PARTICLE LATEKE, AND PROCEDURE FOR THE PREPARATION OF SUCH - Google Patents

Description

The invention relates to latex dispersions and methods

for the production of such dispersions. The latexes are particulate and cationically structured, and the polymer particles in the latex

sen has stabilizing, pH-independent ions chemically bound at or near the surface of the particles.

Latexes require aids to provide colloidal stabilization in aqueous media. The usual colloidal stabilization is provided by surfactants which are usually anionic or cationic but may be nonionic, especially in mixtures with anionic or cationic surfactants. Although they contribute to the required colloidal stability, the surfactants can interfere with the coating performance of the latex even if the amount is limited and less than the desired stability is achieved. Another method is to copolymerize with non-ionic monomers a small proportion of an ionic monomer to produce a stable latex with little or no conventional surfactant, as described in US patent 3,637,432. However, such processes require special combinations of monomers and special polymerization techniques. Although such processes produce latexes with little or no surfactant, varying amounts of water-soluble products are created by carrying out the process and remain in the product: US Patent 3,236,820 describes the reaction of anionic latexes of polymers of vinyl benzyl chloride with sulfides to produce water-soluble cationic polymers. By starting with an anionic emulsion, the conversion of the polymerized vinyl benzyl chloride units on the particle to cationic groups causes destabilization of the latex. If the proportion of vinyl benzyl chloride units in the polymer is not high enough to make the polymer water soluble in the converted form, the latex will coagulate.

The invention relates to an aqueous, colloidal dispersion of cationically structured particle latex, and the dispersion is characterized by a non-ionic, organic polymer core in the form of a

•copolymer of styrene or butadiene or a polymer of an acrylic or methacrylic ester, and which is encapsulated by a thin layer of a water-insoluble organic copolymer of an ethylenically unsaturated, activated halogen monomer in the form of vinyl benzyl chloride and which has pH-independent cationic groups chemically bound to the copolymer by or

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near the particle surface in an amount of 0.01 - 0.5 meq. per gram of latex copolymer and 0.4 - 2.5 meq. per grams of copolymer in the thin layer.

The latexes can be obtained during copolymerization under emulsion polymerization conditions of an ethylenically unsaturated, activated-halogen monomer on the particle surface of a latex of a nonionic, organic polymer which is slightly cationic in the presence of absorbed cationic surfactant. Alternatively, the precursor may contain, as the polymeric component, particles of a copolymer of an ethylenically unsaturated, activated halogen monomer and an ethylenically unsaturated, nonionic monomer devoid of an activated halogen, where the activated halogens are uniform or arbitrarily distributed in the particles. The latexes of each type are reacted with a nonionic nucleophile to form latexes having structured particles consisting of a water-insoluble, nonionic, organic polymer core encapsulated with a layer of a copolymer with pH-independent, cationic groups chemically bonded at or near the outer surface of the structural particle, the amount of said groups being sufficient to provide a major part of the colloidal stability, but insufficient to make the polymer water-soluble.

The invention also relates to a method for producing an aqueous, colloidal dispersion as indicated above, by reacting, at a temperature of 0 - 80°C, (A) a latex of copolymer particles which have activated halogens chemically bound in them, and

(B) a water-stable non-ionic nucleophile which has the ability to diffuse through aqueous media, and the method is characterized in that as latex (A) a latex is used which consists of (1) a non-ionic polymer core in the form of a copolymer of styrene or butadiene or a polymer of an acrylic or methacrylic ester, and which is encapsulated by a thin layer of a water-insoluble copolymer of an ethylenically unsaturated, activated halogen monomer in the form of vinyl benzyl chloride or (2) a copolymer latex of ( a) an ethylenically unsaturated, nonionic monomer devoid of activated halogen, and (b) an ethylenically unsaturated, activated-halogen monomer, the total amount of the activated halogen in latex (A) being 0.01 - 1 .4 meq. per grams of polymer and 0.4 - 2.5 meq. per grams of polymer in a thin layer at or near the latex particle surface; in that latex (A) is produced by emulsion polymerization at 0 -

80°C in the presence of a free radical catalyst and contains a small, stabilizing amount of a cationic surfactant or a mixture thereof, and nonionic surfactant in an amount less than that required to initiate new particles in presence of additional monomers; whereby pH-independent cationic groups are chemically bound to the particles at or near the particle surface in an amount sufficient to provide a major part of the colloidal stability of the latex.

A latex for use in the dispersions according to the invention can comprise solid polymer particles colloidally dispersed in water, whose composition and production method are known per se, but which are subsequently modified so that the particles in the starting latex are encapsulated with a copolymer of an ethylenically unsaturated activated -halogen monomer with a hydrophobic, ethylenically unsaturated monomer devoid of activated halogen. The resulting latex comprises colloidally dispersed particles having reactive halogen groups on or near the surface of the particles. Such a latex can then be reacted with a nonionic, low molecular weight nucleophilic compound to form a latex with particles of polymer with pH-independent cationic groups chemically bonded to the particle surface. The colloidal stability of the latex is thereby improved, and other beneficial properties are achieved.

There are many known latexes that can serve as starting latexes for the production of activated halogen-containing latexes, and the composition is not strictly critical. Such latexes are produced by methods that are well known in the field. Preformed latexes that have essentially no residual monomers are used, but advantageously these starting latexes can be produced by emulsion polymerization as the first step in the production of latex products where some monomer and some free radicals remain at the time of adding the activated halogen monomer. The starting latex, or components and process methods for producing such a latex, are selected from among the known latex mixtures which are essentially free of anionic groups and/or anionic surfactants adsorbed or otherwise attached to the polymer particles that make up the latex. Preferably, the latex is slightly cationic, usually from the presence of a small amount of a cationic surfactant. To obtain the best results, the starting latex should not contain an amount of surfactant sufficient to initiate new particles when additional monomer is introduced. The composition of the polymeric component in the starting latex also affects certain properties of the final product, as it constitutes a major part of the product's total mass. Therefore, a selection will be made in so far as according to the desired polymeric properties that these previously known materials are known to possess, in order to supplement the properties that are advantageous in the encapsulating component according to the invention. Therefore, by way of illustration but not limitation, for the vast majority of products a starting latex which is film forming at room temperature would be selected, but there are applications for which a non-film forming starting latex would be selected, e.g. for plastic pigments. Ordinarily, the starting latexes have a particle size of from approx. 500 Angstroms to approx. 10,000 Ångstrøm, preferably from approx. 800 to approx. 3,000 Å. If the products are to be used in such a way that certain generally recognized characteristics are required, e.g. low electrolyte concentration, such characteristics will be considered when weighing up the starting latex and the ingredients to be used when carrying out subsequent parts of the process. Such selections are professional and are not considered inventive aspects of the new products and the method described here.

Typically, the starting latexes are obtained by emulsion polymerization of one or more monomers. Such monomers are represented by the same monomers indicated below for copolymerization with the activated halogen-containing monomers.

The starting latices for encapsulation may also consist essentially of polymers which are not readily prepared from monomers by emulsion polymerization, either because no substantial polymerization is achieved at a commercially acceptable rate under normal emulsion polymerization conditions, such as with isobutene, or because a particular form of the polymerized monomer is desired, e.g. stereospecific polyisoprene, stereospecific polybutadiene and the like. Representative preformed polymers are polymers and copolymers of the monoolefins having from 2 to 20 carbon atoms, e.g. ethylene, propylene, 1-butene, 2-butene, isobutene, pentene, hexene, octene, dodecene, hexadecene, octadecene, and especially such monoolefins having up to 8 carbon atoms. Particularly common types are the various ethylene/propylene copolymers.

Illustrative of further polymers which may be constituents of the Starting Latex for encapsulation are alkyd resins, > block and graft copolymers; e.g. styrene/butadiene graft and block copolymers; epoxy resins, e.g. the reaction products of epichlorohydrin and bisphenol-A; and thermosetting vinyl ester resins; e.g. the reaction products of approximately equimolar amounts of a polyepoxide and an unsaturated mbnocarboxylic acid, e.g. acrylic acid and methacrylic acid or unsaturated fatty acids, e.g. oleic acid.

Processes for producing the above-described polymers and methods for converting the polymers into latexes are well known and do not form part of this invention.

In one method of obtaining a latex suitable for subsequent reaction according to the method according to the present invention, the particles of a starting latex are encapsulated with a thin layer of a copolymer of an ethylenically unsaturated activated-halogen monomer either by the addition of activated-halogen -monomer or a mixture of such monomers to the reaction mixture of the starting latex before all monomers are converted to polymer or by adding the activated-halogen monomer together with one or more hydrophobic monomers to the starting latex containing practically no residual monomers, and initiating and continuing the polymerization of the monomers thus added for substantially completing the conversion. Other latexes suitable for the reaction according to the method according to the invention can be obtained by direct emulsion pdlymerization of an ethylenically unsaturated, activated-halogen monomer and an ethylenically unsaturated, non-ionic monomer devoid of an activated halogen. Latexes containing particles of copolymer having activated halogens uniformly or arbitrarily distributed in the particles are thereby obtained.

The activated halogen monomers for each latex type should be sufficiently activated to react at a reasonable rate after polymerization with subsequently added nucleophilic agents, but should be so reactive that they are readily hydrolyzed in an aqueous medium. Such suitable monomers are represented by ethylenically unsaturated benzyl chloride or bromide monomers, ethylenically unsaturated aliphatic bromide monomers and ethylenically unsaturated aliphatic iodide monomers. Specific preferred activated halogen monomers ef represented by vinylbenzyl chloride, vinylbenzyl bromide, 2-chloromethylbutadiene, vinyl bromide and bromoalkyl acrylate or bromoalkyl methacrylate, especially 2 bromomethyl acrylate or 2-bromomethyl methacrylate.

The activated halogen monomers are oil soluble, easy to polymerize in emulsion, do not inhibit free radical polymerization, and diffuse at a satisfactory rate through the aqueous medium of a latex to the latex particle.

The hydrophobic ethylenically unsaturated monomer that can be copolymerized with the activated halogen monomer can be selected from the known wide variety of nonionic ethylenically unsaturated monomers that are polymerizable in aqueous emulsion to form a water-insoluble polymer. These monomers are well known in the art and are therefore illustrated below only by way of representative examples. The non-ionic ethylenically unsaturated monomers are represented by, but not limited to, hydrocarbon monomers, e.g. styrenic compounds, e.g. styrene, a-methylstyrene, ar-methylstyrene, ar-ethylstyrene, a,ar-dimethylstyrene, ar-methylstyrene, ar-ethylstyrene, a,ar-dimethylstyrene, ar,ar-dimethylstyrene and t-butylstyrene; the conjugated dienes, e.g. butadiene and isoprene; the hydrocarbon monomers which have been modified to have non-ionic substituents, e.g. hydroxystyrene, methoxystyrene and cyanostyrene; the unsaturated alcohol esters, e.g. vinyl acetate and vinyl propionate; the unsaturated ketones, e.g. vinyl methyl ketone and methyl isopropyl ketone; the unsaturated ethers, e.g. vinyl ethyl ether and vinyl raethyl ether; and the non-ionic derivatives of ethylenically unsaturated carboxylic acids, e.g. acrylic acid esters, e.g. methyl acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate and lauryl acrylate; methacrylic acid esters, e.g. methyl acrylate, ethyl methacrylate; the maleic acid esters, e.g. dimethyl maleate, diethyl maleate and dibutyl maleate; the fumaric acid esters, e.g. dimethyl fumarate, diethyl fumarate and dibutyl fumarate, and the itaconic acid esters, e.g. dimethyl itaconate, diethyl itaconate and dibutyl itaconate; and the nitriles, e.g. acrylonitrile and methacrylonitrile. Even if they are not in the preferred class, they can. non-ionic monomers containing halogens which are not activated are used, e.g. monochlorostyrene, dichlorostyrene, vinyl fluoride and chloroprene. Also non-ionic monomers that form water-soluble homopolymers, e.g. acrylamide, methacrylamide, hydroxyacrylate and hydroxyethyl methacrylate, can be mixed with a hydrophobic monomer in small amounts up to approx. 10%, based on the amount of hydrophobic monomer.

With the expression "pH-independent groups", applied to ionic groups, it is meant that the groups are predominantly in ionized form over a certain pH range, e.g. 2-12.

With the term "non-ionic", applied to the monomers

in this description, it is meant that the monomers are not ionic in and of themselves or do not become ionic by a simple change of the pH value. To illustrate: While a monomer containing an amine group is non-ionic at high pH, the addition of a water-soluble acid lowers the pH and forms a water-soluble salt; therefore, such a monomer is not included.

When carrying out the polymerization of the activated halogen-containing monomer with the embodiments where it is desired not to have activated halogens in the interior of the particle, the ratio between monomer and total polymer in the latex must be kept low at any given time during the process, so that particularly avoids swelling of the existing latex particles. With too much swelling, i.e. too much monomer dissolved in the polymer, some polymerization can occur in the interior of the particle.

If this occurs, the reactive halogens are buried in the particle. The activated halogen monomer is added to the starting latex over a short period of time or added as a "shot" in one or more portions. Optionally, but preferably, a hydrophobic monomer which is devoid of an activated halogen or a mixture of such monomers is also added, usually in admixture with the activated halogen monomer. The polymerization is advantageously carried out at as low a temperature as possible to provide a practical rate of polymerization, so as to avoid hydrolysis of the activated halogen monomer. Such temperatures

o o o varies from approx. 0 C to approx. 80 c, preferably from approx. 50 C to: approx. 70°C. Unless the starting latex is produced in situ, an initiator system (catalyst) is added to activate the latex particle surface, i.e. set up a steady state concentration of free radicals. Continued addition of the initiator system after addition of monomers can be carried out, if desired - especially when a redox system is used. The polymerization reaction is continued until the monomers are practically completely copolymerized.

The product obtained by the method described above is a latex in which the colloidally dispersed polymer particles, which have a particle size of from approx. 500 to approx. 10,000 Å, consists of the starting latex particles encapsulated with a bound layer having a thickness of from a monomolecular layer of the copolymer to approx. 100 Å, as the layer consists of a functional polymer with activated halogen groups on the outer surface.

The amount of activated-halogen monomer copolymerized

in the encapsulation layer in the structural particle latex varies from approx. 0.01 to approx. 1.4 m-equivalent, preferably from approx. 0.04 to approx.

0.5 m-equivalent, per grams of total polymer in the latex. However, must

there be a sufficient amount of the hydrophobic monomer that is copolymerized with the activated halogen monomer so that for each gram of polymer in the encapsulation layer, i.e. the shell, there is no more than 3.0 m-eq. of the copolymerized activated-halogen monomer. The proportion of activated halogen monomer is inversely dependent on the particle size of the latex being encapsulated and also inversely dependent on the molecular cross-sectional area of the activated halogen monomer. Therefore, one would not use the minimum amount of activated halogen monomer with a starting latex of the smallest particle size.

The initiators used in the polymerization of the activated halogen monomers are of the type that produce free radicals and are suitable peroxygen compounds, e.g.: the inorganic peroxides, e.g. hydrogen peroxide; the organic hydroperoxides, e.g. cumene hydroperoxide and t-butyl hydroperoxide; the organic peroxides, e.g. benzoyl peroxide, acetyl peroxide, lauroyl peroxide, peracetic acid and perbenzoic acid - occasionally activated by water-soluble reducing agents, e.g. a ferrio compound, sodium bisulphite or hydroxylamine hydrochloride -

and other free radical-producing materials, e.g. 2,2'-azobisisobutyronitrile.

The organic hydroperoxides and 2,2'-azobis-isobutyronitrile are preferred.

The surface-active agents which are used either in the starting latex or as additives for further stabilization of the latex products are cationic surface-active agents or non-ionic surface-active agents or mixtures thereof.

The cationic surfactants include the classes of salts of aliphatic amines, particularly the fatty amines, quaternary ammonium salts and hydrates, fatty amides derived from disubstituted diamines, fatty chain derivatives of pyrridinium compounds, ethylene oxide condensation products of fatty amines, sulfonium compounds, isothiouronium compounds and phosphonium compounds. Specific examples of the cationic surfactants are dodecylamine acetate, dodecylamine hydrochloride, tetradecylamine hydrochloride, hexadecylamine acetate, aluryldimethylamine citrate, octadecylamine sulfate, dodecylamine lactate, cetyltrimethylammonium bromide, cetylpyridinium chloride, an ethanolated alkylguanidinamine complex, stearyldimethylbenzylammonium chloride, cetyldimethylamine oxide, cetyldimethylbenzylammoniumpyridinonium chloride, tetradecylphenoxybenzylethylbromide, diisobutyl diisobutylamine ammonium chloride, l-(2-hydroxyethyl)-2-mixed pentadecyl and heptadecyl)-2-imidazoline, resin amine ethoxylate, oleylimidazoline, octadecylethylmethylsulfonium methylsulfate, dodecyl bis-if-hydroxyethylsulfonium acetate, dodecylbenzyldimethylsulfonium chloride, dodecylbenzyltrimethylphosphonium chloride, S-p- dodecylbenzyl-N,N,N',N'-tetramethylisothiouronium chloride and the like.

Typical non-ionic emulsifiers (surfactants) are compounds formed by reaction of an alkylene oxide, e.g. ethylene oxide, propylene oxide or butylene oxide with long-chain fatty alcohols, long-chain fatty acids, alkylated phenols, long-chain alkyl mercaptans, long-chain alkyl primary amines, e.g. cetylamine, the alkylene oxides being reacted in a ratio of e.g. 5 more moles. 20 mol or higher, e.g. up to 50 mol per moles of co-reactant. Similar effective compounds are mono-esters, e.g. the reaction products of a polyethylene glycol with a long-chain fatty acid, e.g. glycerol monostearate, sorbitan trioleate, and partial and complete esters of long-chain carboxylic acids with polyglycol esters of polyhydric alcohols. By "long chain" in the above description is usually meant an aliphatic group with from 6 carbon atoms to 20 or more.

The preferred surfactants are surfactants which have pH-independent cationic groups, and particularly preferred are the fugitive surfactants, e.g. cationic surfactants where the cationic group is sulfonium, sulfoxonium, isothiouronium or a reducible quaternary nitrogen group, e.g. pyridinium, isoquinolinium and kino-linium.

The latex according to the above description, which contains particles of the starting latex encapsulated with a relatively thin coating of a copolymer of the active "halogen" monomer with a hydrophobic ethylenically unsaturated monomer, can then be reacted with a nonionic, water-stable low molecular weight nucleophilic compound , which can diffuse through an aqueous phase, to form particles of polymer with pH-independent cationic groups, i.e. onium ions, chemically linked to the particle surface. Ordinarily, the particles are approximately spherical.

Alternatively, a latex of a copolymer having activated halogens uniformly or randomly placed in the polymer particles constituting the latex may be reacted with a nonionic nucleophile to produce a cationic structural particle latex, provided that compositions and conditions are chosen so that only the activated halogens at or near the surface of the particle reacts with the nucleophile. The amount of activated halogen in such copolymers should. do not exceed approx. 3.0 m-equiv./g.. Since the reaction rate for the activated halogens at or near the surface of the particle in such copolymers is significantly greater than for halogens in the interior of the particle, kinetic data will show when the thin layer near the surface has reacted. With copolymers having larger amounts of activated halogen monomer polymerized in the particle, swelling of the particle occurs as the nucleophile reacts, further reaction within the particle may occur easily, control of the reaction to obtain a structured particle is difficult, and- the same beneficial results are not achieved.

For each active halogen that reacts with a nonionic nucleophile, one charge is produced that is bound to the polymer and one halide ion is released. In the reaction between a nucleophile and an activated halogen, structural particle latex or with a latex having activated halogens distributed throughout the latex particle, the amount of halogen reacted so that it is provided from approx. 0.01 to approx. 0.5 m-equiv. of charge per grams of polymer. Preferably, the area is from approx. 0.04 to approx. 0.35 m-equiv. charge per grams of polymer. However, the amount of bound charge in the thin, reacted layer near the surface of the particle,

from approx. 0.4 to approx. 2.5 m-equiv. for each gram of polymer in the layer.

The nucleophilic compounds which are applicable in the execution of the invention are non-ionic, carbon-containing nucleophiles which are stable in and can diffuse through aqueous media which have a heteroatom as the center of the nucleophilicity, where all covalent bonds in the heteroatom are to a carbon atom.

The nucleophilic compounds which are advantageously used in the practice of the invention are represented by the following classes of compounds, sometimes called . Lewis bases:

(a) monobasic aromatic nitrogen compounds (b) tetra(lower alkyl)thiourea compounds (c) R1~S-R2 where R 1 and R 2 are individually lower alkyl, hydroxy-lower alkyl or where R 1 and R 2 are combined as one alkylene radical with 3-5 carbon atoms (d) where R2 and R^ are individually lower alkyl or hydroxy-lower alkyl, or are combined as one alkylene radical with 3-5 carbon atoms, and R^ is lower alkyl, aralkyl or aryl except when R2 and R^ together are an alkylene radical, as R ^ is lower alkyl or hydroxy-lower alkyl, and (e)

wherein R 1 , R 2 and R 3 are individually lower alkyl, hydroxy-lower alkyl or aryl.

In this description, the term lower alkyl means an alkyl with 1-4 carbon atoms, e.g. methyl, ethyl, propyl, iso-propyl, n-butyl and isobutyl.

Representative specific nucleophilic compounds are pyridine, quinoline, isoquinoline, tetramethylthiourea, tetraethylthiourea, hdyroxyethylmethylsulfide, hydroxyethylethylsulfide, dimethylsulfide, diethylsulfide, methyl-n-propylsulfide, methylbutylsulfide, dibutylsulfide, dihydroxyethylsulfide, bis-hydroxybutylsulfide, trimethylenesulfide, thiacyclohexane, tetrahydrothiophene , N-methylpiperidine, N-ethylpyrrolidine, N-hydroxyethylpyrrolidine, trimethylphosphine, triethylphosphine, tri-n-butylphosphine, triphenyl-phosphine, trimethylamine, triethylamine, tri-n-propylamine, tri-isobutylamine, hydroxyethyldimethylamine, butyldimethylamine, tri-hydroxyethylamine, triphenylphosphorus and N,N,N-dimethylphenethylamide.

In carrying out the reaction between the nucleophilic compound and the particles of latex having activated halogens chemically bound to its surface, the latex is gently stirred while the nucleophilic compound is added, as the compound as such or in the form of a solution. Gentle stirring may be continued throughout the following reaction, or stirring may optionally be stopped after dispersion of the compound in the latex. The reaction is usually carried out at ambient temperature, although temperatures from approx. 0 to approx. 80°C can be used. The reaction occurs spontaneously at a rate that depends on the reactivity of the activated halogen and of the nucleophile. It is preferred to carry out the reaction until a predominant proportion of the colloidal stability of the product is provided by the resulting chemically bonded cationic groups. Usually no catalyst is required, although a small amount of iodide ion with the less reactive materials may be used to facilitate the reaction. When a desired degree. of reaction is reached, any excess nucleophile is usually removed by standard methods, e.g. dialysis, vacuum stripping and steam distillation.

Other pH-independent cationic groups can be substituted for cationic groups which are chemically bound to the latex particles according to the above description by carrying out a further reaction with such cationic groups. For example, a cationic structured particle latex that has sulfonium groups chemically bound to the structured particles at or near the particle surface can be reacted with hydrogen peroxide at a temperature of from approx. 20' to approx. 80°c, preferably at ambient temperature, for a sufficient period of time to oxidize part or all of the sulfonium groups to sulfoxonium groups. Such treatment also reduces the smell of the latex. For the best results with such an oxidation reaction, the hydrogen peroxide is used in excess, e.g. from 2 to 10 moles of hydrogen peroxide for each mole of sulfonium groups.

When the products are to be used for metal coating, it is preferred to react with an activated halogen latex that contains only as much activated halogen as desired converted into bound charge. The activated halogens are then completely converted into cationic groups, and there is no bound activated halogen in the product.

The cationic latexes according to the invention have significantly improved chemical and mechanical stability. However, too many applications have, e.g. when coating hydrophobic substrates, latexes stabilized by charges chemically bound to the particle surface, too high a surface tension to provide good wetting of the hydrophobic surface. In such cases, addition to the latex of small amounts, e.g. from approx. 0.01 to approx. 0.1 m-eq./g polymer, of conventional cationic or non-ionic surfactant advantageously.

For other purposes, the presence of even small amounts of water-soluble surfactants is harmful. The latexes according to the invention are very advantageous for such purposes. ■ Since a sufficient amount of charge is chemically bound to the particle surface to provide colloidal,; stability, exhaustive dialysis or ion exchange can be used to remove water-soluble material from the latex and replace counterions, if desired, while preserving cationic functionality and colloidal stability of the latex.

A simple test is suitable for distinguishing the latexes with regard to shear stability: A drop of latex is placed in the palm of the hand and rubbed back and forth with a finger. When the latex is cut, it gradually dries out and forms a film. Unstable latexes coagulate before drying, usually after 1 to 3 rubs. Stable latexes can be rubbed more than 5 cycles before they fail. Latexes that tolerate 20 rubs are very stable and can

rub to dryness before they harden.

The rub test corresponds to a more advanced one

test where a drop of latex is cut in a cone and plate viscometer ("Rotovisco" rotational viscometer). A very stable la-

tex according to the rubbing test can be cut for more than 15 minutes at 194 rpm without coagulation of the latex.

The particles in the latexes according to the invention,

i.e. the starting latexes and products, are generally approximately spherical in shape and have a particle size (diameter) of from approx. 500 to approx. 10,000 Å.

The following examples illustrate ways in which the present invention can be practiced, but should not be taken as limiting the invention. All parts and percentages are by weight unless otherwise expressly stated. The particle sizes shown in the examples are average particle diameters obtained by light scattering measurements, except when otherwise indicated.

Example i

A thermoplastic acrylic latex is prepared in the following way: A monomer mixture is prepared from 1,072 grams of ethyl acrylate and 528 grams of methyl methacrylate, and to this mixture are added 24 grams of dodecanethiol and 5 grams of an 82.7% solution of t-butyl hydroperoxide to form a monomer feed solution.

A germ latex is prepared from 750 grams of a solution of surfactant, prepared in advance by stirring 710 grams of water and 40.0 grams of a 25% active solution of dodecylbenzyldimethylsulfonium chloride for 2 hours under a stream of nitrogen to which is added 25 grams of the monomer feed solution, followed by a continuously added reducing stream pumped for approx. 2 hours at a rate of 7.6 7 grams per hour, the stream being a portion of a solution

-which is prepared in advance from 9 grams of hydroxylamine hydrochloride diluted to 500 grams with deionized water. Monomer feed solution is added to the germ latex at a rate of 55 grams per hour during the continuation of a reducing flow of the same rate of addition and composition as in the germ latex and during, simultaneous pumping into the reaction mixture, a rate of 20 grams per hour, of a solution of surfactant previously prepared from 400 grams of deionized water and 100 grams of a 25% active solution of dodecylbenzyldimethylsulfonium chloride. After 20 hours, the conversion is approx. 85%, the continuous additions are stopped, 15 grams of vinyl benzyl chloride are added and the reaction is allowed to continue for another 2 hours. The temperature is maintained at 50°C during the reaction. A latex (C-1) is thereby obtained with a solids content of 47.6%, a pH value of 2.8, a particle size of 1,250 Å, and which contains a polymer with a molecular weight of 74,000 with a chloride ion content of 0.113 m- equiv. per grams of polymer.

A portion of latex (C-1) is diluted with water to a solids content of 23.8%, 2.12 parts of trimethylamine per 100 parts of the diluted latex is added with gentle stirring, and the resulting mixture is allowed to stand at room temperature for 5 days. A latex (I-A) is obtained containing 0.242 m-eq. of total charge per grams of polymer of which 0.129 m-eq. is present from quaternary ammonium groups bound to each gram of polymer in the latex.

Another portion of latex C-1 is treated as described for Example 2, except that 2.24 parts of dimethyl sulfide is used instead of the trimethylamine. A latex (I-B) is obtained containing 0.23 7 m-eq. total charge per grams of polymer of which 0.124 m-eq. is present from sulfonium groups bound to each gram of polymer in the latex.

Example II

Latexes are produced by a semi-continuous method according to the following description. Different mixtures are prepared for addition in separate streams.

S start water solution

8.75 grams of 85.5% aqueous solution of phosphoric acid 1,000 grams of water

sufficient ammonium hydroxide to adjust the pH

value for the above solution to 5.0

20 grams (on an active basis) of dodecylbenzyldimethylsulfonium chloride

sufficient water to 2,000 grams of solution

sufficient ammonium hydroxide to adjust the pH

value to 5.0

Continuous emulsifier flow

125 grams (on an active basis) of dodecylbenzyldimethylsulfonium chloride

sufficient water to give 1,000 grams of an aqueous solution containing 125 grams (on an active basis) of dodecylbenzyldimethylsulfonium chloride.

Continuous initiator current

500 grams of an aqueous solution containing 27.5

grams (on an active basis) of t-butyl hydroperoxide..

Continuous reductant flow

500 grams of an aqueous solution containing 14 grams of hydroxylamine hydrochloride.

First monomer solution

1,500 grams of butadiene

1,200 grams of styrene

300 grams of butyl acrylate

3 grams of dodecanethiol (chain transfer agent)

Other monomer solution

250 grams of butyl acrylate

50 grams of vinyl benzyl chloride

3 grams of dodecanethiol

Process

The starting water solution is placed in a 7.57 1 Pfaudler reactor equipped with a crow's-foot stirrer, and the partially filled reactor

tor is flushed with nitrogen 4 times, after which 100 grams of the first

monomer solution is added, the pressure in the reactor is raised to 2.45 kg/cm 2 with nitrogen, and the temperature is raised to 50 oC. The continuous initiator stream and the continuous reductant stream are started, each at a rate of 10 g/min. hour. After 3 hours of such addition under agitation (at 235 rpm for the stirrer), the monomer solution and the continuous emulsifier stream are pumped in

in the reactor at rates of respectively' 40 and 110 grams per hour, in a period of 19 hours. The continuous initiator stream, the continuous reducing agent stream and the continuous emulsifier stream are maintained while the second monomer solution is fed at a rate of 50 grams per hour for a period of 3 hours. The continuous initiator flow, the continuous reducing agent flow, stirring and maintaining the polymerization temperature at 50°C are continued for a further 45 minutes. A latex (C-2) with 40.4% solids and a particle size of approx. 1,120

To be achieved.

Another latex is prepared as described for latex C-2 with the exception that the first monomer solution was fed in

20 hours rather than in 19, the second monomer solution is not added and the feeding of the continuous initiator stream, the continuous reducing agent stream and the maintenance of stirring and reaction temperature at 50°C are continued for 4 hours after stopping the first monomer solution feeding. Latex C-3 (not according to the invention) is obtained with a solids content of 39.2% and a particle size of 1,115 Å. With a portion of the latex, sufficient dodecylbenzyldimethylsulfonium chloride is mixed to provide a further 0.09 m-equiv. of sulfonium ion per grams of polymer in the latex, and the pH value is adjusted to 7.6. (Latex C-3A)

With a portion of latex C-2 is mixed, with gentle stirring, dimethyl sulfide in an amount calculated to provide an excess based on the amount of active halogen in the latex. The resulting mixture is allowed to stand at room temperature for approx. 16 hours. The latex (Il-A) is then steam distilled and found to contain 0.05 m-eq. bound sulfonium cation per grams of polymer. A portion of II-A is diluted with water to 10% solids content, and the pH value is adjusted to a value of 7.0. In a pump stability test it is found that only a small amount of coagulation is observed and that very little change in viscosity has occurred when the test is stopped after 21 days. Comparative latex C-3A, when subjected to the same test, exhibits severe coagulation after 9 days. For the pump test, 3,000 ml of the 10% solids latex is placed in a 3.785 L container and pumped with a Model 9M143 Teel centrifugal immersion pump operating at 3,000 rpm. Water is added periodically to replace what is lost through evaporation, i.e. to maintain the same volume and concentration. The latex is periodically observed for destabilization. The test is stopped after the coagulation has become severe enough to block the pump or after 21 days, whichever occurs first.

Example III

Two latexes are prepared according to the recipe in Table I containing copolymers of vinyl benzyl chloride with the same average composition, but with different placement of the polymerized vinyl benzyl chloride in the latex polymer particles.

The latexes are prepared in a 7.57 L glass-lined Pfaudler kettle equipped with a crow's-foot agitator. The water, soap, chain transfer agent and initiator are placed in the reactor at room temperature, the stirrer is started, the reactor is closed and the system is flushed 4 times with nitrogen. The monomers (with the exception of the vinyl benzyl chloride in latex C-5) are forced into the reactor, and the reactor contents are heated to 50°C and held at this temperature for 20 hours. The temperature is then raised to 70°C, and the reaction is allowed to continue at this temperature until the reactor pressure reaches a constant value. The resulting latex C-4 is cooled and removed from the reactor. For latex C-5, the vinyl benzyl chloride monomer is added to the reactor at this point and stirring at a temperature of 70°C is continued for 2 hours. The product (latex C-5) is then cooled and removed from the reactor.

Analyzes of the products show the following results:

To each latex is added 2% (based on polymer solids) of dodecylbenzyldimethylsulfonium chloride, and then each latex is diluted with water to a solids content of 20%.

To half of the diluted latex C-5 is added.

4 moles of a nucleophile, dimethyl sulfide, for each mole polymerized

vinyl benzyl chloride in the latex. The resulting reaction is allowed to proceed at 30°C for the time shown in Table III below, to produce latex III-A. The other half of latex C-5 is treated in the same manner except that the same molar ratio of another nucleophile, trimethylamine, is used instead of the dimethyl sulfide to make latex III-B.

One half of latex C-4 is processed as described for latex III-A to prepare comparison latex C-4A. The other half of latex C-4 is treated in the same manner as for latex III-B to prepare comparison latex C-4B. The conversion of the benzyl chloride group to the benzyl onium ion is observed by titrating the chloride ion with silver nitrate solution.

The data is shown in table in.

These data show that comparison latex C-4 which

has relatively uniform distribution of the copolymerized vinyl benzyl chloride, converted more slowly and to a lesser extent than the structural particle latex, i.e. latex C-5.

Examples IV-XI

A series of latexes is produced in the same way as for latex C-5 with the following composition:

The resulting products, where X is 2.5 or 5.0, are compounded with sufficient additional dodecylbenzyldimethylsulfonium chloride to provide a total of 2% by weight, based on the polymer in the latex. Each latex is diluted with water to an éfc solids content of 20%. Portions of each diluted latex are then reacted with a nucleophile by the method described in Example III, for the time period shown in Table IV, to obtain the products IV-XI. Conversion to the onium ion is monitored by titration of the chloride ion released in the reaction, and the products are vacuum driven off before evaluation. The stability of the latex products is evaluated with the rubbing test described above. The data are shown in Table IV.

The samples shown as <1 coagulate immediately when a

drop of the latex is touched with a finger. The samples shown as >20 can be rubbed to dryness without coagulation.

The latexes are applied in side-by-side test patches on the same piece of standard redwood table cover. The test table is then sequentially air-dried for 65 hours, immersed in a bath of deionized water and observed for coating behavior. For comparison with the cationic latexes according to the invention, a very stable anionic latex containing a copolymer of styrene, butadiene, hydroxyethyl acrylate and itaconic acid is coated and tested in the same way (comparative example c-8).

The anionic latex (C-8) begins to be absorbed

of the wood immediately after application (poor persistence). The cationic latexes, IV-XI, remain on the surface and show no tendency to be absorbed (excellent persistence). After drying, the anionic latex provides a coating with a matte appearance. The cationic latexes IV-XI provide clear, shiny coatings that adhere strongly to the surface of the wood. The test results are summarized in table V.

It can be seen that, with the exception of latex IX, has

all the cationic latexes tested superior water resistance after air drying in comparison with a stable anionic latex of the styrene/butadiene copolymer group-

Examples XII-XIX

A precursor latex is prepared in a batch emulsion polymerization reactor using 2% azobisisobutyronitrile as initiator, 1% dodecylbenzyldimethylsulfonium chloride as surfactant and 0.1 part dodecanethiol and 0.1 part 2,6-di-t-butyl-p -cresol as chain transfer agents for every 100 parts of monomers. The initiator, surfactant, chain transfer agents and 233 parts water are placed in the reactor. Two parts of 2-hydroxyethyl acrylate and 1.33 parts of styrene are added, and the reactor is flushed with nitrogen. Sufficient additional styrene to provide a total of 30 parts and 63 parts of butadiene is added, the temperature is raised to 50°C and held there for 4 hours, after which it is raised to 70°C and held there until the rate of pressure drop levels off, i.e. approx. . 7 hours. 5 parts of vinyl benzyl chloride are then added, and the temperature is maintained at 70°C for a further 2 hours. The reactor contents are stirred during the entire reaction period. After the reactor is vented and the reaction mixture is cooled, the product turns out to be a fluid latex (C-9) having a solids content of 27.7%, a particle size of 1,250 Å and a pH value of 3.7. The latex is unstable to cut (less than 1 rub).

Different nucleophiles, as shown in Table VI, are mixed with separate portions of latex C-9 and allowed to react at the temperature and for the time indicated in the table. The reaction time is chosen according to the approximate amount of time required to obtain products that are very rubbing stable, i.e. stable for more than 20 rubbings. For example XII and example XVII, the reaction is carried out at a temperature varying from 25 to 50 oC. After the reaction, the resulting latexes are driven off under vacuum and filtered. The pH value of the filtered products is adjusted to the desired range so that mixtures are obtained which are used for coating aluminum test panels (Parker 3003-H14, 10.16 cm x 15.24 cm x 0.6 cm). These mixtures are shown in Table VII.

Coated duplicate panels for each example are fired in an oven at 175°C, one panel for 5 minutes and the other panel for 30 minutes. The burnt panels are then immersed in water at 70°C for 2 hours, and their appearance is recorded before and after the water treatment. The data are shown in Table VIII.

Furthermore, it is found that the adhesion of the coatings is good for all the burned-in panels from Examples XII-XIX before the hot water treatment, as determined by the application of a piece of pressure-sensitive tape (Scotch tape), after which the tape was quickly torn off. After the water treatment, the adhesion is fixed in the same way after excess water is blown off the panels, and they are air-dried in air at ambient temperature for 30 minutes. In this test, none of the coating is removed from any of the panels.

Examples XX-XXII

A latex is prepared in a batch recipe by emulsion polymerization reaction of 40 parts styrene and 55 parts butyl acrylate in 300 parts water using 0.2 part dodecanethiol, 2 parts azobisisobutyronitrile and 5 parts dodecylbenzyldimethylsulfonium chloride with stirring for 17 hours at 50°C and 1

hour at 70°C to provide a monomer conversion of

about. 90%, after which 5 parts of 2-bromomethyl methacrylate are added and the same reaction conditions are maintained for a further 2 hours. After the reactor is vented and cooled, the product is found to be a fluid latex (C-10) with a solids content of 25.7% and a particle size of 1.0 70 Å. The latex has poor shear stability (less than 1 rub).

The nucleophiles as shown in Table IX are mixed with separate portions of latex C-10, and the resulting mixtures are allowed to stand at 25°c until the reactions have progressed at least until the latex products are rub-stable.

Example XXIII

A 126 gram portion of latex XX which contained 31.1% solids and had a total of 0.16 m-eq. sulfonium group per grams of polymer, of which 0.06 m-eq. is chemically bound at or near the surface of the particles, is mixed with a 7:1 excess of hydrogen peroxide (4.97 grams of a 30% solution, and the resulting mixture is stirred in a closed reactor at 35°c for 22 hours. A substantial proportion of the sulfonium groups are oxidized to sulfoxonium groups There is no loss in colloidal stability and the product has significantly less odor than latex XX.

Examples XXIV-XXVI

A latex is prepared by emulsion polymerization reaction of 40 parts styrene, 55 parts butyl acrylate in 300 parts water using 0.2 part dodecanethiol, 2 parts azobisisobutyronitrile and 4 parts dodecylbenzyldimethylsulfonium chloride with stirring for 18 hours at 50°C and 2 hours at 70°C for providing a monomer conversion of approx. 90%, after which 5 parts of 2-chloromethylbutadiene are added and the same reaction conditions are maintained for a further 2 hours. After the reactor is ventilated and cooled, the product is found to be a fluid latex (C-ll) with a solids content of 24.3% and a particle size of 1,450 Å. The latex has poor shear stability, i.e. less than 1 rub.

The nucleophiles shown in Table X are mixed with separate portions of latex C-II, and the resulting mixtures are allowed to stand at 35°C at least until the reactions have progressed sufficiently for the products to be very rub stable (more than 20 rubs).

Example XXVII

A latex is prepared by an emulsion polymerization reaction of 50 parts methyl methacrylate and 45 parts butyl acrylate in 300 parts water using 0.2 part dodecanethiol, 2 parts azobisisobutyronitrile and 4 parts dodecylbenzyldimethylsulfonium chloride with stirring for 16 hours at 50°C and 3 hours at 70° C to provide a monomer conversion of approx. 90%, after which 5 parts of vinyl bromide are added and the same reaction conditions are maintained for a further 2 hours. After the reactor is vented and cooled, the product turns out to be a fluid latex (C-12) with a solids content of 23.8% and a particle size of 1,490 Å. The latex has poor shear stability (less than 1 rub).

With a portion of latex C-12, mix 0.52 m-equiv. tetramethylthiourea for each gram of polymer in the latex portion,

and the resulting mixture is allowed to stand at 25°C for 7 days. The latex product is shear stable (more than 20 rubs) and has a total charge of 0.28 m-eq. and a bound charge of 0.20 m-eq. for each gram of polymer in the latex.

Examples XXVIII-XXIX

A latex is prepared by batch emulsion polymerization of 54 parts styrene, 44 parts butadiene and 2 parts 2-hydroxyethyl acrylate using 0.1 part dodecanethiol as chain transfer agent, 2,2'-azobisisobutyronitrile as catalyst,

1 part (active base) of dodecylbenzyldimethylsulfonium chloride as emulsifier and a polymerization time of 3 hours at 50°C and 7 hours at 70°C. After being cooled and filtered through cheesecloth, the resulting initial latex (C-13) which has a solids content of 37.9% is allowed to stand for 18 months. As determined by microscopic examination, the latex particles are relatively uniform in size and have an average particle diameter of 1,265 Å. Sufficient deionized water is mixed with 1,980 parts (wet basis) of the starting latex to provide 4,000 parts by weight of diluted latex. Diluted latex C-13 and 10 parts of 2,2'-azobisisobutyronitrile are placed in a reactor which is then flushed with nitrogen. After the reactor contents are heated to 50°C, a monomer mixture containing 200 parts styrene and 50 parts vinyl benzyl chloride is forced into the reactor by pressure. The temperature of the reactor contents is raised to 70° and maintained for 4 hours while the contents are stirred. After the resulting product is cooled and filtered, it turns out that a latex (C-14) has been obtained

which contains 21.0% solids. As determined by microscopic examination, the latex particles are relatively uniform in size and have an average diameter of 1,444 Å. Comparing the microgram of latex C-13 with the microgram of latex C-14, there is no evidence that any new particles have been initiated. Latex C-14 contains 0.042 m-eq. chloride ion per grams of solids (from the emulsifier).

With a portion of latex C-14, 2 moles of trimethylamine are mixed for each mole of polymerized vinylbenzyl chloride in the latex, and the mixture is stirred for 20 hours at ambient temperature. The resulting latex (XXVIII) is friction stable and contains 0.085 m-eq. chloride ion for each gram of solid - indicating a reaction of 0.043 m-eq. trimethylamine per grams of solids (0.085 - 0.042). Excess trimethylamine is removed by vacuum distillation (Rinco Evaporator).

Another portion of latex C-14 is treated in the same way as described for latex 28, with the exception that the reaction time is 4 days instead of 20 hours. The latex (XXIX) is friction-stable and is found to contain 0.24 m-eq. chloride ion per grams of solid - which indicates a reaction of 0.2 m-eq. trimethylamine per gram of solid (0.24 - 0.042).

Example XXX

A latex is prepared essentially as described in Example II, with the exception that (a) the second monomer solution is not added; (b) the first monomer solution consists of 26% styrene, 24% vinylbenzyl chloride and 40% butadiene as monomers and 0.1 part dodecanethiol per 100 parts monomer; and (c) the continuous initiator stream, the continuous reducing agent stream, the stirring and the reaction temperature of 50°C are continued for 4 hours after stopping the feeding of the first monomer solution. The product is a fluid latex with 39.8% polymer solids. The latex is filtered and dialyzed against deionized water for 72 hours. <*>The emulsifier level is adjusted to 0.1 m-eq. dodecylbenzyldimethylsulfonium chloride per grams of solids. The latex is diluted to 20% solids (latex C-15). To latex C-15, add 0.25 m-equiv. dimethyl sulphide per grams of polymer solid, and the resulting mixture is stirred at 30°c. Samples are taken periodically, and the unreacted vinyl benzyl chloride is removed from the samples to stop the reaction. The samples are titrated against chloride ion to determine the sulfonium concentration. The results are shown in Table XI.

These results show that the particles swell significantly by 0.64 m-eq. of bound charge per grams of polymer or more. The high charge latexes cannot be concentrated above 35% solids without becoming very thick and, in many cases, without gelation. The latexes with 0.1 - 0.32 m-eq. bound charge per grams are very stable and have a low viscosity. They contain significant amounts (1.25 - 1.47 m-eq.) of unconverted benzyl chloride groups. When cast and dried, the latexes form hydrophobic films that can be cross-linked by oxidative curing via the butadiene double bonds. The chloromethyl groups in the resulting cross-linked films are then available for quaternization to give an ionic membrane.

Claims (8)

1. Aqueous, colloidal dispersion of cationic structured particle latex, characterized by a nonionic, organic polymer core in the form of a copolymer of styrene or butadiene or a polymer of an acrylic or methacrylic ester, and which is encapsulated by a thin layer of a water-insoluble organic copolymer of an ethylenically unsaturated, activated halogen monomer in the form of vinyl benzyl chloride and having pH-independent cationic groups chemically bound to the copolymer at or near the particle surface in an amount of 0.01-0.5 meq. per grams of latex copolymer and 0.4-2.5 meq. per grams of copolymer in the thin layer. 2. Aqueous, colloidal dispersion as stated in claim 1, characterized in that the amount of cationic groups is 0.04-0.35 meq. per grams of structured particles and where the amount of cationic groups is less than 1.6 meq. per grams of copolymer in the thin layer. 3. Aqueous, colloidal dispersion as stated in claim 1 or 2, characterized in that the cationic groups are predominantly sulfonium groups, isothiouronium groups, or quaternary ammonium groups, and where the quaternary ammonium groups are preferably pyridinium groups. 4. Aqueous, colloidal dispersion as stated in claim 1, characterized in that the water-insoluble copolymer layer has a thickness of no more than approx. 100 Å. 5. Process for producing an aqueous colloidal dispersion of cationically structured, particulate latex as set forth in claim 1, by reacting, at a temperature of 0-80°C, (A) a latex of copolymer particles having activated halogens chemically bound per se, and (B) a water-stable non-ionic nucleophile which has the ability to diffuse through aqueous media, characterized in that as latex (A) a latex is used which consists of (1) a non-ionic polymer core in the form of a copolymer of styrene or butadiene or a polymer of an acrylic or methacrylic ester, and which is encapsulated by a thin layer of a water-insoluble copolymer of an ethylenically unsaturated, activated halogen monomer in the form of vinyl benzyl chloride, or (2) a copolymer latex of (a), an ethylenically unsaturated, nonionic monomer devoid of activated halogen, and (b) an ethylenically unsaturated activated halogen monomer, the total amount of the activated halogen in latex (A) being 0.01-1.4 meq. per grams of polymer and 0.4-2.5 meq. per grams of polymer in a thin layer at or near the latex particle surface; in that latex (A) is produced by emulsion polymerization at 0-80°C in the presence of a free radical catalyst and contains a small, stabilizing amount of a cationic surfactant or a mixture thereof, and non-ionic surfactant in an amount which is less than that required to initiate new particles in the presence of additional monomers; whereby pH-independent cationic groups are chemically bound to the particles at or near the particle surface in an amount sufficient to provide a major part of the colloidal stability of the latex. 6. Method as stated in claim 5, characterized in that the reaction is carried out until the pH-independent cationic groups are present in an amount of 0.01-0.5 meq. per grams of copolymer and in an amount of 0.4-1.6 meq. per grams of polymer in the thin surface layer. 7. Method as stated in claim 5, characterized in that it includes the step of adding stabilizing amounts of a cationic surfactant or a non-ionic surfactant, or a mixture thereof after the copolymerization step. 8. Method as stated in claim 5, characterized in that the temperature is kept at 50-70°C during the reaction between the latex copolymer (A) and the nucleophile (B), and that the water-stable nucleophile (B) is used (1) a tetra (C1-C4-alkyl)thiourea, or a compound of formula (2) RjSRj, (3) RjRjRjN, (4) RjR^P, (5) R'N (5) or (6) P( (o) ) 3 where <R>1<#> R2, <R>3 is individually C₁-C₂-alkyl and R' is H or C₁-C₂-alkyl.