FIELD OF THE INVENTION The invention relates to a method for preparing carboxylated latexes used in the manufacture of various articles by a dip-molding method followed by the curing of a polymer film. Latex produced in such a manner exhibits, in particular, ideal properties for the manufacture of all-purpose gloves. In addition, the present invention relates to a composition for producing film articles by a dip-molding method. BACKGROUND

A method for preparing polymer latex is known, which is especially suitable for the manufacture of dip molded articles (patent RU2399635, POLYMERLATEX GMBH (DE), Ltd. (JP), 20.09.2010). The method relates to making latex by radical emulsion polymerization, wherein the latex includes polymer particles containing structural units derived from at least one conjugated diene component whereby said polymer particles comprise at least one hard phase segment having a glass transition temperature (Tg) of at least 50°C and at least one soft phase segment having a glass transition temperature (Tg) of 10°C at most, with the total amount of hard phase segments being 2 to 40 wt.% and the total amount of the soft phase segments being 60 to 98 wt.% based on the total weight of the polymer particles. The technical result is a polymer latex that can be used for obtaining a latex composition, which has a long-term stability and can be used for conventional dip-molding processes for making latex articles whereby no crosslinking either by radiation or by crosslinking agents is necessary.

However, this method involves a multi-step procedure and sequential supplying of monomers under continuous control of the size of particles and their number. That aspect significantly complicates the process.

In US7273906 patent (ZEON CORPORATION (JP), 25.09.2007), latex for use in the manufacture of articles is prepared by a dip-forming method using 50 to 89.5 wt. parts of a conjugated diene monomer, 10 to 40 wt. parts of a nitrile-containing monomer, 0.5 to 10 wt. parts of an unsaturated acid monomer and 0 to 20 wt. parts of other copolymerizable vinyl monomer. The latex is proposed to be synthesized so that in the first step, a reactor is fed with at least 80% of the conjugated diene based on the total weight of the monomer used in the reaction, 50% of the total weight of the nitrile- containing monomer, and 10 to 90% of the total amount of the unsaturated acid. The rest of the monomers are added to the reaction mixture when the conversion rate of the monomers of the first portion reaches 60%. The latex prepared by this method allows the production of gloves having good softness of touch, high tensile strength, and comfortable fittingness.

However, in this patent nothing is mentioned about chemical-and-colloidal properties of the prepared latex, its stability during synthesis, processing, and storage. In addition, the claimed composition suggests the use of a fourth monomer in the synthesis formulation, but without any data about its glass transition temperature, which can result in a latex having a low co-polymer glass transition temperature, and, as a consequence, in a sticky film.

RU2 193571 patent (Federal'noe gosudarstvennoe unitamoe predprijatie "Nauchno-issledovatel'skij institut sinteticheskogo kauchuka im. akad. S.V. Lebedeva" (RU), 27.11.2002) discloses a method for preparing butadiene-nitrile rubbers by water- emulsion copolymerization of butadiene with acrylic acid nitrile in the presence of an initiating system, a chain transfer agent, and carboxylic acid soaps as an emulsifier, followed by coagulation of latex with calcium chloride, the method being characterized by using an additional emulsifier, which is sodium C12-C14 alkylsulfoethoxylate with an oxyethylation degree of 1-5, in an amount of 0.05 to 0.50 wt. part based on 100 wt. parts of monomers, wherein the total amount of the emulsifiers is from 0.55 to 2.50 wt. parts based on 100 wt. parts of monomers. The method allows for the achievement of a highly stable polymerization system at low amounts of the emulsifier, while maintaining a good coagulation ability of the prepared latex, obtainment of "pure" butadiene-nitrile rubbers having a reduced amount of residual emulsifier and characterized by a higher complex of physical-mechanical parameters of vulcanizates on their basis and a better frost resistance.

However, in this method, the emulsifying system includes an NF dispersing agent which has a low biodegradability and leads to contamination of effluents.

According to the method for preparing a carboxylated nitrile latex according to CN 103694410 patent (SHANGHAI QIANGSHENG CHEMICAL CO LTD, 26.04.2017), the latex is prepared by polymerization of a mixture of monomers in an aqueous medium at a temperature of 50-75°C, wherein the mixture consists of from 10 to 85% of a conjugated diene, from 10 to 50% of acrylonitrile and an ethylenically unsaturated acid in an amount of 1 to 10%, and a mixture of anionic and non-anionic emulsifying agents used as an emulsifier in an amount of 0.2 to 8% by weight of monomers, wherein the anionic emulsifying agent is sodium alkyl sulfate comprising a C8-C20 alkyl radical, and wherein the non-ionic emulsifying agent is oxyethylated alkylphenol with an oxyethylation degree of 8-15.

However, oxyethylated alkylphenols are non-biodegradable products, which can lead to contamination of water effluents resulting from the synthesis and processing of latex. In addition, it is known that an increase in the oxyethylation degree of alkylphenol from 8 and higher at a temperature above 60°C leads to dehydration of oxyethyl groups, which can decrease the stabilizing ability of the emulsifying mixture during high- temperature synthesis.

According to the method disclosed in RU2527855 patent (Federal'noe gosudarstvennoe byudzhetnoe obrazovatel'noe uchrezhdenie vysshego obrazovaniya "Yaroslavl state technical University" (RU), 10.06.2014), the synthesis of a polymer base of an impregnating composition for tyre cord is performed in three steps. In the first step, latex is prepared from a butadiene-styrene-butyl acrylate seed copolymer, the main chain of which comprises a copolymer of butadiene, styrene and butyl acrylate at a ratio of (13- 45):(50-80):(5-12), respectively. The copolymer is prepared by using a combination of anionic surfactants, in particular, sodium alkylbenzene sulfonate and sodium salt of oxyethylated alkylphenol sulfate or oxyethylated fatty alcohol with an oxyethylation degree of 10 to 40. In the second step of polymerization, butadiene, methacrylic acid, and methacrylamide at a ratio of (93.0-97.5):(2-5):(0.5-2.0), respectively, are grafted to the main polymer chain, wherein the ratio of the main polymer to the total number of monomers is (20-35):(65-80). In the third step, unpolymerized 1,3-butadieneis distilled off, followed by adjusting the pH of the polymer base to 9.0-9.5.

However, this method is a multi-step process; in addition, the sodium salt of oxyethylated alkylphenol according to the proposed technical solution is a product that is not completely biodegradable. European manufacturers of latexes seek to exclude oxyethylated alkylphenols from synthesis formulations. In particular, “APE-free” is a known term that characterizes environmentally friendly latexes, i.e. comprising no ethoxylated alkylphenols. In addition, emulsifiers having such a high oxyethylation degree are prone to dehydration of oxyethyl groups under heating, which can lead to loss of dispersion stability even at temperatures above 40°C. Among other things, this technical solution does not disclose chemical-and-colloidal- properties of the prepared latexes, their resistance to various types of stress.

The closest to the present invention in technical essence and achieved result is a method for preparing latex compositions described in EP3412717 application (LG CHEMICAL LTD (KR), 08.05.2019). According to this method, a latex composition is prepared by an ion deposition method, wherein the composition is characterized by that it comprises a carboxylic acid-modified nitrile based copolymer latex copolymerized with conjugated diene-based monomers, ethylenically unsaturated nitrile monomers and ethylenically unsaturated acid monomers; and monoglyceride. The addition of fatty acid monoglyceride as a co-emulsifier allows a reduction in the stickiness of the resulting latex articles, wherein monoglyceride can be added both in the step of synthesis of a polymer dispersion and to the resulting latex.

However, the use of fatty acid monoglycerides as additives during synthesis can lead to a significant increase in the cost of latex because fatty acid monoglycerides are food emulsifiers and are more expensive than anionic surfactants conventionally used in emulsion polymerization with anionic surfactants. This technical solution also does not provide data on the assessment of chemical-and-colloidal parameters of the resulting nitrile-containing dispersions.

DESCRIPTION OF THE INVENTION

An objective of the present invention is to develop a method for preparing a latex, which would be ideally suited for use in the manufacture of protective rubber articles by a dip-molding method.

This objective is attained by the present invention that relates to a method for preparing a latex by aqueous emulsion polymerization of a) from 55 to 88 wt. parts of conjugated diene monomers, b) from 10 to 40 wt. parts of ethylenically unsaturated monomers comprising a nitrile group, and c) from 2.0 to 10 wt. parts of unsaturated carboxylic acid-based monomers in the presence of a redox initiating system, a chain transfer agent, and an emulsifier mixture including (1) salts of alkyl(aryl)sulfonic acids and (2) oxyethylated salts of fatty alcohol ester sulphates with an oxyethylation degree of 2 to 10, wherein the ratio of (1 ):(2) is (2.0-3.0):(0.1-1.0) wt. parts based on 100 wt. parts of monomers, and wherein emulsifier (2) is fed during the process when the conversion rate of monomers reaches 20 to 30% and, optionally, when the conversion rate reaches 50 to 60%. In addition, the present invention relates to a carboxylated latex characterized by a glass transition temperature in the range of from -50 to -10°C, a particle size in the range from 60 to 150 nm, a stiffness measured by Defoe method of 2500-6000 gf (gram-force) as measured in accordance with GOST 10201-75.

The present invention also relates to a composition for producing film articles by a dip-molding method, the composition comprising 96-97% of a latex based on the dry matter, 2.5 to 3.5% of curing agents, 0.2 to 0.3% of salts of fatty alcohol ester sulphates, and 0.1 to 0.2% of an antioxidant, based on 100% dry matter of the composition, in particular, relates to a composition consisting of said components.

In another aspect, the present invention relates to an article made from a latex composition by a dip-molding method, characterized by a weight of not more than 3.5 g, the absence of defects (slumps, perforations), high physical-mechanical properties, and by the absence of color and residual stickiness.

The technical result (technical effect) of the present invention resides in the production of a latex characterized by a stable particle size in the range from 60 to 150 nm, a high resistance to mechanical stress (determined by Maron's method) and resistance to sub-zero temperatures (frost resistance) to -40°C. The method for preparing a latex is characterized by an increased environmental friendliness due to the exclusion of a non- biodegradable NF dispersing agent (leucanol) from the reaction mix formulation. Films made of the prepared latex are transparent, colorless, and characterized by the absence of defects, as well as by high physical-mechanical properties (a conventional stress at 300% elongation of 4.6-7.5 MPa, a relative tensile strength of at least 28 MPa with an elongation of at least 550%) and by the absence of residual stickiness. Gloves produced from the latex according to the invention are thin and colorless and have a weight of not more than 3.5 g. Latex according to the invention is intended for the production of rubber gloves and other protective articles produced by submersible dipping a mold coated with an electrolyte layer into a latex composition (ion deposition method). It is known that rubber gloves are widely used in various industrial fields to protect the skin from the aggressive media action: in the household, petrochemical industry, electronic industry, medicine, etc. However, as a rule, the gloves used in medicine are made of natural or carboxylated butadiene-nitrile copolymer. Recently, natural latex gloves have been used ever less since it has been established that non-rubber impurities of natural origin contained in the natural latex can cause allergies. In addition, the supply of natural latex is unstable and depends on the crop productivity of hevea plantations. Gloves made of carboxylated nitrile butadiene latex are free of the above disadvantages, have physical-mechanical characteristics close to natural latex, which ensures the predominant use of nitrile- containing latexes in the manufacture of articles by a dip-molding method. However, attempts to increase production volumes of nitrile-containing articles are faced with stricter requirements for their quality. On the one hand, the latexes used to produce articles by a dip-molding method should have high aggregative stability, while ensuring a thin strong film during an ion deposition process. In addition, a cured film should have high strength characteristics and concurrently satisfy the requirement to a light color and low stickiness. It is also important that a glove has a weight of not more than 4 grams, in addition to high strength characteristics of the film. Thus, the glove made of a nitrile- containing latex should be colorless, thin, durable, providing tactile sensitivity, free of residual stickiness and free of external defects, such as slumps, bubbles and cracks. The latex according to the present invention ideally meets the above requirements.

For synthesis of latexes used for the manufacture of film articles by a dip-molding method, it is preferred to use carboxylating agents such as unsaturated carboxylic acids since the presence of a carboxyl group in the polymer phase provides a more efficient combined curing of a latex film: on the one hand, during ion deposition the crosslinking of the polymer is provided by interactions between the carboxyl groups of a copolymer with the cation of an electrolyte coagulant deposited on a mold corresponding to the article, and on the other hand, chemical bonds in the polymer matrix are formed in the presence of curing agents. In addition, during ion deposition, carboxyl-containing polymers behave as polymer electrolytes, the reactivity of which depends on the dissociation degree of carboxyl groups and increases with increasing the pH value. All these factors make it possible to enhance the polymer crosslinking process, wherein sulfuric vulcanization provides crosslinking through unreacted double bonds of a conjugated diene, and salts and oxides of multivalent metals crosslink polymer chains through carboxyl groups. The introduction of carboxyl-containing monomers into the polymer chain also provides an increase in the aggregative stability of a colloidal system due to the formation of inherent, negatively charged carboxylate (COO ) groups formed during neutralization of latex in the conditioning step. This allows an increased resistance of latex to various destabilizing actions: mixing, pumping through pipes, introduction of various fillers, including curing agents.

A mixture comprising a) conjugated dienes, b) ethylenically unsaturated monomers comprising a nitrile group, and c) unsaturated carboxylic acid-based monomers is used as monomers suitable for preparing a latex according to the present invention.

The conjugated diene is selected, in particular, but not as a limitation thereof, from a C4-C12 conjugated diene, for example, from 1,3 -butadiene, isoprene, 2,3-dimethyl-l,3- butadiene, piperylene, 2-methyl-3-ethyl-l, 3-butadiene, 3 -methyl- 1,3-pentadiene, 2- methyl-3-ethyl-l,3-pentadiene, 1,3-hexadiene, 2-methyl- 1,3-hexadiene, 1,3-heptadiene, 3-methyl- 1,3-heptadiene, 1,3-octadiene, 3-butyl- 1, 3 -octadiene, 3, 4-dimethyl- 1,3- hexadiene, 4,5-diethyl-l,3-octadiene, phenyl- 1,3-butadiene, 2, 3-diethyl- 1,3-butadiene, 2, 3-di-n-propyl- 1,3-butadiene, and 2 -methyl-3 -isopropyl- 1,3-butadiene.

Preferred conjugated dienes are 1,3 -butadiene, isoprene, and piperylene.

1,3-Butadiene is most preferred.

The amount of the conjugated diene used according to the present method is in the range of 55 wt. parts to 88 wt. parts, preferably from 60 to 75 wt. parts, most preferably from 63 to 70 wt. parts based on 100 wt. parts of the monomer mixture.

In the manufacture of film articles, mainly gloves, by a dip-molding method, ethylenically unsaturated monomers comprising a nitrile group are used as a comonomer, thus ensuring a low polymer solubility in non-polar solvents such as liquid hydrocarbons and petroleum oils. In addition, a nitrile-containing monomer provides a latex film with a required set of strength characteristics.

In particular, but not as a limitation thereof, the useful ethylenically unsaturated monomers comprising a nitrile group include acrylonitrile, methacrylonitrile, a-cyano- ethyl-acrylonitrile and fumaronitrile. In the most preferred embodiment, acrylic acid nitrile is used. The content of the ethylenically unsaturated monomer comprising a nitrile group in the latex according to the present invention is from 10 to 40 wt. parts, preferably from 15 to 40 wt. parts, more preferably from 25 to 35 wt. parts based on 100 wt. parts of the monomer mixture.

The carboxylating agent in the monomer mixture is selected from the group of ethylenically unsaturated carboxylic acids. In one embodiment, the carboxylating agent is selected from the group of ethylenically unsaturated carboxylic acids having from 3 to 5 carbon atoms and one or two carboxyl groups. The used carboxylating agents include, in particular, but not as a limitation thereof, alpha(methylene)carboxyl-containing acids or mixtures thereof, for example, such as acrylic, methacrylic, itaconic, fumaric acids, or mixtures thereof. Preferred carboxylating agents are acrylic and methacrylic acids; and methacrylic acid is most preferred.

The content of unsaturated carboxylic acid-based monomers in the latex according to the invention is from 2 to 10 wt. parts, preferably from 2 to 7 wt. parts, most preferably from 3 to 7 wt. parts based on 100 wt. parts of the monomer mixture.

According to the present method, latex is prepared by using a mixture of emulsifiers, consisting of (1) salts of alkyl(aryl)sulfonic acids and (2) oxyethylated salts of fatty alcohol ester sulphates, wherein (1):(2) = (2.0-3.0):(0.1-1.0) wt. parts, and wherein component (2) is fed during the process when the conversion rate of monomers reaches 20-30% and, optionally, when the conversion rate reaches 50-60%. Preferably, the ratio of emulsifiers (1):(2) is (2.1-2.8):(0.2-0.8) wt. parts, most preferably (1):(2) = (2.2-2.5):(0.2-0.5) wt. parts based on 100 wt. parts of monomers. Surprisingly, it has been found that such a ratio of emulsifiers in the reaction mix formulation provides a colloidal system characterized by aggregative stability during the synthesis of latex and stripping of residual monomers, as well as during storage, mechanical stress and exposure to subzero temperatures. In addition, the proposed mixture of emulsifiers ensures a uniform defect-free film formation, while maintaining high strength characteristics, the absence of color and stickiness of the article produced by ion deposition.

Emulsifiers that can be used in the synthesis of latexes include surfactants of various nature: anionic, nonionic, cationic and amphoteric.

As emulsifier (1), anionic emulsifiers are used, in particular, salts of alkyl(aryl)sulfonic acids that form the surface-active RS0 ₃ anion in a wide pH range upon dissociation in aqueous solutions, which is especially important when the emulsion polymerization reaction runs in an acidic medium. The salts of alkyl(aryl)sulfonic acids are selected from the group of alkylbenzene sulfonates C _n Fb _n+i CeFLSCbNa, wherein an alkyl substituent C _n tfe _n+i is a linear or branched saturated hydrocarbon radical generated as a result of the removal of one hydrogen atom from the linear or branched saturated hydrocarbon of the general formula C _n H2 _n+ 2. Linear alkyls in the molecule are preferred due to their more complete biodegradability. To ensure the surface activity of the molecule, the length of an alkyl radical, determined by the number of carbon atoms in the chain, n is usually from 10 to 18 (n=10-18), which ensures an effective emulsifying ability. The emulsifier typically contains a mixture of alkylbenzene sulfonates comprising alkyl radicals of different lengths, which are mainly represented by decylbenzene sulfonate, undecylbenzene sulfonate, dodecylbenzene sulfonate, etc. The alkylaryl sulfonate molecule also contains a 0 ₆ ¾ aryl group, which is an aromatic hydrocarbon moiety, where one or more hydrogen atoms in the aromatic hydrocarbon molecule, for example in benzene (CeFL), are substituted with other hydrocarbon groups; especially common aryls are C6H5, C6H4, etc. Wherein, aryl is always bound to the secondary carbon atom of the alkyl chain of the alkylaryl sulfonate. Alkylaryl sulfonates also include derivatives of aromatic compounds having fused benzene rings. Examples of alkylaryl sulfonates with a fused benzyl ring are sodium salts of mono-, di- and tri- butylnaphthalene sulfonic acids, as well as a NF dispersing agent (leucanol). Linear or branched alkyl sulfonates include compounds of the formula C _n H2n+i(CH2-CH2)m- SCbNa, wherein the number of carbon atoms, n+m, is preferably from 12 to 18. Emulsifiers also may include salts of a-olefin sulfonates or alkene sulfonates of the formula C _n Fh _n SCbNa, which are products of sulfonation, with sulfuric anhydride, of unsaturated linear hydrocarbons, alkenes, having one double bond in the molecule (preferably at the primary carbon atom), referred to as a-olefin sulfonates. Examples of such surfactants are salts of linear sulfonated olefins comprising a double bond at a- position, wherein the total number of carbon atoms in the molecule is C8-C20, as well as salts of fatty alcohol ester sulphates - alkyl sulfates, wherein the alkyl is preferably linear C12-C18 alkyl. Sodium dodecyl sulfate (sodium lauryl sulfate) C fbsOSCLNa is especially preferred. The emulsifiers (1) are preferably selected from the group of alkylbenzene sulfonates and alkyl sulfates.

Sodium alkylbenzene sulfonate is most preferred.

Emulsifiers in the synthesis of latexes are used as a rule in dosages of 1.0 to 10 wt. parts, the preferred dosage range of the emulsifier is from 0.8 to 8.0 wt. parts, the most preferred range is from 1.5 to 6.0 wt. parts based on 100 wt. parts of monomers. If the concentration of the emulsifier is below or above the specified range, it may result in a reduction of the stability of the colloidal system and, as a consequence, in the formation of coagulum. However, the use of the mixture of emulsifiers according to the invention is effective so that it allows for a reduced consumption of an emulsifier to a total value of 4 wt. parts as the maximum possible consumption. Therefore, according to the present invention, the preferred dosage range of the emulsifier is from 2.1 to 4.0 wt. parts based on 100 wt. parts of monomers.

Oxyethylated salts of fatty alcohol ester sulphates with a various oxyethylation degree are used as emulsifier (2). Oxyethylated salts with an oxyethylation degree of 2 to 10 are preferred, and the most preferred oxyethylation degree is from 2 to 6. If the oxyethylation degree is less than 2, the stabilizing effect will be minimal, and in case of a higher oxyethylation degree, latex will lose stability upon heating due to dehydration of hydroxyethyl groups.

The use of emulsifier (2) instead of the traditional NF dispersing agent (sodium salt of the naphthalene-formaldehyde polycondensation product) allows avoiding the appearance of beige tint in the latex and film and unexpectedly increases the aggregative stability of the colloidal system both during synthesis and in the stripping step, as well as during storage, maturation of a latex composition containing a curing agent dispersion.

According to the present invention, emulsifier (2) is supplied not at the beginning of the process together with emulsifier (1), but together with the initiator during the polymerization process, namely, when the conversion rate of monomers reaches 20-30% and, optionally, when it reaches 50-60%. When emulsifier (2) is supplied twice, the supplied portions are preferably equal.

In accordance with the present invention, a redox initiating system is used. When redox systems are used, additional salts of transition metals, such as iron, cobalt or nickel, are used in combination with a suitable complexing agent such as sodium ethylenediamine tetraacetate, sodium nitrilotriacetate, trisodium phosphate, or tetrapotassium diphosphate.

Emulsion polymerization is initiated using polymerization initiators which are decomposed into radicals in an aqueous medium, such as peroxo and azo compounds.

Peroxo compounds include hydrogen peroxide, peroxodisulfates, peroxodiphosphates, hydroperoxides, peracids, peracid esters, peracid anhydrides and peroxides having two organic moieties. Salts of persulfuric acid and perphosphoric acid include sodium, potassium, and ammonium salts. Suitable organic hydroperoxides are, for example, tert- butyl hydroperoxide, cumene hydroperoxide, and -menthane hydroperoxide. Suitable peroxides having two organic moieties are dibenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, di-t-butyl peroxide, dicumyl peroxide, t-butyl perbenzoate, t-butyl peracetate, etc. Suitable azo compounds are azobisisobutyronitrile, azobisvaleronitrile and azobis(cyclohexan nitrile).

Hydrogen peroxide, hydroperoxides, peracids, peracid esters, persulfate, and peroxodiphosphate can also be used in combination with a reducing agent, thereby ensuring the decomposition of the initiator into radicals at a lower temperature, and a lower temperature promotes the production of a polymer with a minimum degree of branching.

The amount of an initiator introduced into the reaction system is from 0.01 to 0.5 wt. part based on 100 wt. parts of monomers, preferably from 0.02 to 0.5 wt. part based on 100 wt. parts of monomers, even more preferably from 0.02 to 0.1 wt. part, and most preferably from 0.02 to 0.03 wt. part. If the content of the initiator in the system is below the specified range, the polymerization rate of monomers is too low, and the product recovery time increases. If the content of the initiator is above the specified range, the process is difficult to control because of a high speed. In addition, increased dosages of the initiator often lead to the formation of too many polymer particles with a total surface area such that the amount of the emulsifier introduced is insufficient to stabilize the system.

Suitable reducing agents for use in combination with an oxidizing agent are sulfenates, sulfmates, sulfoxylates, dithionite, sulfite, metabisulfite, disulfite, sugar, urea, thiourea, xanthogenates, thioxanthogenates, hydrazinium salts, amines and amine derivatives such as aniline, dimethylaniline, monoethanolamine or triethanolamine. Preferred redox initiating systems are, for example: 1) potassium peroxodisulfate in combination with triethanolamine, 2) ammonium peroxodiphosphate in combination with sodium metabisulfite (Na ₂ S ₂ 0s), 3) p-menthane hydroperoxide/sodium formaldehyde sulfoxylate (rongalite C) in combination with ferrous sulphate (FeS04), sodium ethylenediamine acetate and trisodium phosphate; 4) cumene hydroperoxide/sodium formaldehyde sulfoxylate in combination with ferrous sulfate (FeSC ) and sodium ethylene diamine acetate (complexing agent) and trisodium phosphate buffer.

The molar amount of the reducing agent is in the range of 50 to 500% based on the molar amount of the initiator used and is from 0.015 to 0.02 wt. parts. The amount of the complexing agent depends on the amount of the used transition metal and is usually equimolar to it.

Latex is prepared in the presence of a chain transfer agent selected from standard agents used in the emulsion polymerization process.

These molecular weight regulators/chain transfer agents are organic thiocompounds. The chain transfer agent is selected, in particular, from thiocompounds such as n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, /er/-dodecyl mercaptan, n-hexadecyl mercaptan, n-tetradecyl mercaptan, and tert- tetradecyl mercaptan. The regulators also include xanthogen disulphides, in particular, such as dimethyl xanthogen disulfide, diethyl xanthogen disulfide, and diisopropyl xanthogen disulfide; thiuram disulphides, such as tetramethylthiuram disulphide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide; halogenated hydrocarbons, such as chloroform, carbon tetrachloride; hydrocarbons, such as pentaphenylethane, alpha-methylstyrene dimer, acrolein, allyl alcohol, 2-ethylhexyl thioglycolate, terpinolene, a-terpinene, g- terpinene, and dipentene.

Preferred chain transfer agents are mercaptans and xanthogen disulfides, thiuram disulfides, 1,1-diphenylethylene, a-methylstyrene dimer. In particular, the most common and widely available chain transfer agent is tertiary dodecyl mercaptan.

All the recited chain transfer agents can be used individually or in various combinations (two or more) in a total amount of up to 1.0 wt. part, in particular from 0.1 to 1.0 wt. part based on 100 wt. parts of monomers, preferably from 0.15 to 0.8, most preferably from 0.18 to 0.4 wt. part. If the content of the chain transfer agent is less than the specified range based on 100 wt. parts of monomers, the physical-mechanical properties of the articles prepared by a submersible dipping method will be significantly lower, and if the dosage of the chain transfer agent is more than the specified range, the stability of the colloidal system will decrease during synthesis, resulting in the formation of coagulum.

In addition, when latex is prepared by emulsion polymerization, buffers are used to ensure a stable pH value of the media during the synthesis process. Such substances include alkali metal phosphates and pyrophosphates, such as trisodium phosphate and sodium pyrophosphate. The amount of buffer is from 0.01 to 1 wt. part based on the total number of monomers.

In addition, during the synthesis and conditioning of latex, it is possible to add small amounts of pH-regulating substances, antiaging agents, antiseptic agents preventing the growth of fungi and bacteria in an aqueous media, antifoaming agents, etc.

Due to the presence of emulsifiers in latexes, they (latexes) have an increased foaming ability, which slows down the process of their processing and leads to the appearance of defects in articles. To prevent latex from foaming, various antifoaming agents are used, mainly emulsions of silicone oligomers, as well as mineral oils, alcohols, esters, and alkylaminosulfonates, at dosages starting from 0.02% by volume.

The synthesis of latex is carried out in reactors equipped with a mixing device and a jacket for thermal regulation of the process. Latex can be prepared in a continuous, semi-continuous or batch mode, and seed particles can be used in all of these modes of synthesis. The most preferred seed latexes are latexes based on polystyrene and polybutadiene copolymers, carboxylated copolymer latexes based on acrylonitrile, styrene or methyl methacrylate, in which vinyl carboxylic acid is present in an amount of up to 10 wt. parts based on the total weight of monomers.

The temperature of the polymerization reaction is in the range of from 10 to 40°C, preferably 13 to 35°C, and most preferably 15 to 30°C.

In particular, a batch polymerization process is carried out as follows. First, a reactor is charged with water, emulsifier (1), trisodium phosphate buffer, iron sulfate, a complexing agent, which is a disodium salt of ethylenediaminetetraacetate, and then monomers are added. Monomers are fed together with a chain transfer agent and at least 50% of the total calculated amount of peroxo or azo compounds as an initiator, in the form of a mixture or in separate streams in an arbitrary order that has no effect on the final properties of the prepared latex. However, if the conjugated diene is 1,3 -butadiene, it is fed last into the reaction mixture after purging the reactor with nitrogen. A separate supply of 1,3-butadiene is due to the peculiarities of its aggregation state, namely its gaseous state at room temperature (the boiling point of 1,3-butadiene is -4.5°C). The resulting mixture is heated with constant stirring to a temperature of 10 to 40°C, after that the calculated amount of a reducing agent, rongalite, is loaded in 5 wt. parts of water. The polymerization process is carried out to a conversion rate of monomers of 20-30%, and then emulsifier (2) and the remaining amount of the initiator are loaded, and the reaction is performed to a desired conversion. Emulsifier (2) can be added twice, namely, after reaching the conversion rate of 20-30% and 50-60%. In this case, the calculated amount of the initiator is divided into three portions: at least 0.01 wt. part is fed at the beginning of the process, and the remaining amount is introduced in equal portions at each supply of the emulsifier (2). The resulting dispersion is cooled to room temperature. The reached conversion rate of monomers is in the range of 70-99.9%, preferably 75-99.9%, and the most preferred range is from 75 to 90%. The end of the polymerization reaction is controlled by supplying a stopper, for example, sodium dimethyldithiocarbamate in an amount of 0.2 wt. part based on 100 wt. parts of monomers, and thereafter unreacted monomers are removed, the pH of the latex is adjusted to 8.2-9.0 by adding a 2-3% sodium or potassium alkali solution or a 10% ammonia solution; wherein the use of a mixture of these neutralizing agents is also possible.

The resulting latex is characterized by a glass transition temperature in the range of from -50 to -10°C. If the glass transition temperature of the latex polymer is below - 50°C, the strength properties of the latex film are reduced. If the glass transition temperature of the polymer is above -10°C, the films based on such latex are prone to cracking and tearing, which is extremely undesirable.

The particle size of the latex according to the invention is in the range of from 50 to 200 nm, preferably in the range from 60 to 180 nm, most preferably from 80 to 150 nm. The stiffness of the latex polymer measured by Defoe method is in the range of 2500- 6000 gf, preferably in the range of 3000-5000 gf, most preferably 3500-5000 gf. The stiffness index measured by Defoe method correlates with the physical-mechanical characteristics of cured latex films: if the stiffness lower than 2500 gf, the strength characteristics of the cured latex films are lower; if stiffness measured by Defoe method is higher than 6000 gf, the relative elongation will be below the requirements of ASTM D 6319 standards (standard for medical gloves).

A composition for producing film articles by a submersible dipping method is prepared on the basis of the latex according to the invention, wherein the composition comprises 96 to 97% of the latex, 2.5 to 3.5% of curing agents, 0.2 to 0.3% of salts of fatty alcohol ester sulphates, and 0,1 to 0.2% of an antioxidant, based on the total dry weight (100%) of the composition.

Sulfur, zinc oxide, zinc diethyldithiocarbamate, and titanium dioxide can be used in the composition as curing agents. Curing agents are introduced into the latex composition in the form of dispersions in an emulsifier. The emulsifier is selected from the group of salts of fatty alcohols ester sulphates or oxyethylated salts of fatty alcohol ester sulphates with an oxyethylation degree of 2-10. Oxyethylated salts of fatty alcohol ester sulphates with an oxyethylation degree of 2-10 are preferred. Methods for preparing dispersions of curing agents are well known in the art.

However, the time required to prepare a dispersion of each of the ingredients can vary significantly. A dispersion of zinc oxide, zinc diethyldithiocarbamate, or titanium dioxide can be prepared using a ball or colloid mill, and the optimal processing time of these components is 24 hours. The preparation of a sulfur dispersion requires a much more time because sulfur is poorly dispersed, so the time for preparing this dispersion is at least 72 hours.

The emulsifiers introduced into the formulations for preparing dispersions act as stabilizers for the size of dispersed particles and prevent their agglomeration and precipitation from the dispersion. Typically, a NF dispersing agent is used as a dispersion stabilizer, which is a naphthalenesulfonic acid-formaldehyde condensation product and ensures effective stabilization of particles, but causes coloration of curing agent dispersions, which gives dark tints to articles made by a dipping method. Alkali metal salts of higher fatty alcohol ester sulphates and oxyethylated salts of ester sulphates are proposed to use as a dispersing and wetting agent according to the present invention; it is most preferred to use oxyethylated sulphates of higher fatty alcohol esters with an oxyethylation degree of 2-10, the solutions of which are colorless and environmentally friendly. Typically, 50% dispersions of each of the curing agents are prepared, wherein the dosage of the dispersing agent is 1.0-5.0 wt. parts based on 100 wt. parts of a dispersible ingredient, higher dosages of an emulsifier lead to non-productive expenditures, and lower dosages do not provide a desired level of aggregative stability of the dispersion. It is also possible to prepare a complex (combination) dispersion of curing agents, comprising also an antioxidant additive.

In addition to accelerators and curing agents, dispersions usually contain antiaging additives (antioxidants) on the basis of phenols, sterically hindered phenols, derivatives of diphenylamines, organophosphorus compounds, thioesters, etc., which are mainly intended for inhibition of interactions between the generated peroxide radicals and unsaturated polymer bonds. The most common antioxidants used to suppress thermal oxidative degradation are 2,2-methyIene-bis(4-methyl-6-butylphenol) (Agidol 2), 4- methyl-2,6-ditretbutylphenol (Agidol 1), 4,6-bis(octylthiomethylphenol)-o-cresol (Irganoxl520), etc. As a rule, antioxidants are introduced into latexes in the form of dispersions in dosages of 0.1-0.5 wt. part per latex polymer.

The latex composition is prepared as follows: curing agent dispersions in an aqueous solution of an emulsifier (the combination of 0.6 wt. part of sulfur, 1.5 wt. parts of zinc oxide, 1.0 wt. part of titanium dioxide, 1.0 wt. part of zinc diethyldithiocarbamate is most preferred), 0.2 wt. part of an antioxidant, and 0.3 wt. part of an emulsifier on the basis of oxyethylated ester sulphates of higher fatty alcohols with an oxyethylation degree of 2-10 are carefully introduced in a random order to the latex distilled and neutralized to a pH of 8.0-12.0, with stirring and avoiding the foam formation.

The latex composition according to the invention has a mass fraction of dry matter of 5 to 45%, preferably of 8 to 35%, most preferably of 10 to 33%. If the concentration of latex is lower than the specified range, the efficiency of the gel deposition on a mold decreases; if the concentration is higher than the specified range, the formation of coagulum during storage is possible, and the viscosity of the latex can increase, preventing an effective deposition of gel on the mold. pH of the latex composition is maintained at a level of 8-12, preferably 8.0 to 10.0, most preferably 9.5 to 10.0. The necessary pH level of the composition is achieved by the introduction of neutralizing agents selected from hydroxides of sodium, potassium, ammonia or mixtures thereof, at a concentration of 1-10%. The resulting latex composition undergoes maturation for 24 hours at a temperature of 20-25°C with periodic gentle stirring at an interval of 3 to 5 hours.

Articles produced by a submersible dipping method can be prepared by a well- known method of direct submersion of a mold in a latex composition or by a coagulation dipping method. The coagulation dipping method is preferred, where the mold corresponding to the article is submersed into a coagulation solution of electrolyte (a), and the electrolyte is deposited on the surface of the mold, wherein, for doing this, the mold is submersed into the electrolyte solution for 2-5 seconds and then dried at a temperature of 25°C for 3-5 minutes. Then this mold with the layer of electrolyte (a) is submersed into a latex composition where polymer gel is deposited on the surface of the mold for 5 seconds (b), thereby ensuring an optimal thickness of the deposited polymer gel (0.05-0.06 mm) and the weight of a final article of not more than 3.5 grams. After that, the mold with the layer of polymer gel is subjected to heat treatment (c).

The coagulation solution is an aqueous or alcoholic electrolyte solution; it is also possible to use a mixture of an aqueous-alcoholic solution as a solvent. The concentration of the electrolyte in the solution is from 5% to 50%, preferably from 10% to 40%. Halides of 2- and 3-valence metals can be used as coagulants, such as barium chloride, calcium chloride, magnesium chloride, zinc chloride, aluminum chloride, as well as nitrates of barium, calcium, and zinc; acetates of barium, calcium, and zinc; sulfates of calcium, magnesium, and aluminum. Calcium nitrate and calcium chloride, and mixtures thereof are preferred.

In step (c) during heat treatment, evaporation of moisture and crosslinking of polymer chains in the latex film (curing) occur. Heat treatment is generally carried out in 2 steps: the first step of moisture evaporation is conducted at a temperature of from 70 to 150°C for 1-20 minutes, and the second step, the curing as such, is conducted at a temperature of 100-180°C for 5-30 minutes.

During heat treatment, water is evaporated from the latex film, due to which the film acquires density, and strength is achieved due to the interaction of copolymer double bonds of a conjugated diene with curing agents and due to the interaction of carboxyl groups with cations of the electrolytes deposited on the dipping mold (curing). The simultaneous action of the last two factors provides the finished article with a desired level of strength characteristics. The resulting article is characterized by a weight of not more than 3.5 g, the absence of color and residual stickiness.

EMBODIMENTS OF THE INVENTION

Test methods:

1) The mass fraction of dry matter of latex was determined by drying a sample of a certain mass to a constant weight according to GOST 25709;

2) Determination of the hydrogen ion exponent, pH-value, was carried out according to GOST 11604;

3) Determination of the surface tension of latex at the interface with air was carried out according to GOST 20216-74.

4) Determination of the latex resistance to mechanical stress was carried out on a Maron device. To this purpose, 75 ml of latex with a known dry residue was stirred at a speed of 1500 rpm in a narrow gap between the rotor and stator for 5 minutes. After the dynamic action, the latex was filtered through a nylon mesh, the coagulum separated from the latex was washed and dried to constant weight at a temperature of 105°C. The amount of coagulum, expressed as a percentage of the total polymer mass in the analyzed sample, was considered as a measure of the latex resistance to mechanical stress. Resistance to mechanical stress was defined as the amount of coagulum after treatment in a Maron device (Kolloidnaya chimia sinteticheskikh lateksov: Uchebnoe posobie [Colloid chemistry of synthetic latexes: Textbook] /R.E. Neumann, O.G. Kiseleva, A.K. Egorov, T.M. Vasilieva. - Voronezh: Voronezh State University, 1984. - 196 p.);

5) The appearance of the film was determined visually by the presence of defects in the form of cracks, etc.

6) The content of residual acrylic acid nitrile (AAN) was determined chromatographically according to TU 38.103578-85, para 4.7.

7) The average particle diameter was determined using a Zetatrac instrument according to ISO 13320:2009.

8) Frost resistance of latex was evaluated according to the method described in the USSR author's certificate No. SU 1328353.

9) Physical-mechanical properties of cured latex films were determined according to ASTM D 412. 10) Storage stability was determined by the amount of coagulum in 1 liter of latex after keeping it in a tightly closed container for six months at a temperature of 25 and 50°C. For this purpose, after the test period the latex was filtered through a nylon mesh, the coagulum separated from the latex was washed, dried to constant weight at a temperature of 105°C. The amount of coagulum, expressed as a percentage of the total polymer mass in the analyzed sample, was considered as a measure of the storage stability of the latex.

11) The latex viscosity was determined using a Brookfield viscometer according to ISO 2555:1989.

12) The foaming ability of latex was determined by a method consisting in manually shaking a cylinder with latex and then measuring the volume of foam formed in the cylinder. For this purpose, 10 ml of latex was placed in a 25 ml volumetric cylinder having a diameter of 20 mm, the cylinder was closed and shaken sharply 10 times with constant force, after which the volume of the resulting foam was determined.

13) The resistance of latex to the introduction of a dispersion of curing agents during the maturation of the latex mixture was determined by the amount of coagulum in the composition after mixing periodically for 24 hours. For this purpose, the dispersion of curing agents in an amount of 5 wt. parts per polymer was added with stirring to 1L of latex which was pre-diluted to a dry residue content of 28-32%. The composition was allowed to maturate for 24 hours at a temperature of 18 to 22°C, wherein the composition was stirred for 5 minutes at a speed of 60 rpm every two hours. After the maturation time, the composition was filtered through a nylon mesh, the separated coagulum was washed, dried to constant weight at a temperature of 105°C. The amount of coagulum, expressed as a percentage based on the total polymer weight in the analyzed sample, was considered as a measure of the resistance of latex to the introduction of a dispersion of curing agents.

14) The film stickiness was determined organoleptically by touching the cured film with a finger. The result was scored from 0 to 5, wherein 0 meant the absence of stickiness, 5 meant a high stickiness.

15) The glass transition temperature of polymer was determined by differential scanning calorimetry (DSC) according to ISOl 1357-2:1999. 16) The stability of latex during the synthesis was determined by the amount of coagulum formed during the synthesis based on the total amount of latex polymer produced in the polymerization process.

17) The stability of latex during distillation of residual monomers was determined by vacuum degassing of 1 liter of latex on a rotary-film evaporator at a temperature of 60°C to the content of a residual nitrile-containing monomer of not more than 0.01%. The result was evaluated as a percentage of the formed coagulum relative to the amount of latex polymer fed for degassing.

18) The method for producing articles by a submersible dipping method:

18.1. A coagulant mixture for an ion deposition process was prepared by mixing 40 wt. parts of calcium nitrate and 60 wt. parts of water.

18.250% curing agent dispersions were prepared in a ball mill, as follows: a sulfur dispersion was prepared for 72 hours by mixing 100 wt. parts of sulfur, 100 wt. parts of water, and 5 wt. parts of sodium salt of fatty alcohol ester sulphate with an oxyethylation degree of 2 to 10. Similarly, dispersions of titanium dioxide, zinc oxide, ethylcimate were prepared with the difference that the dispersion time was 24 hours.

18.3. A latex mixture was prepared by mixing the curing agent dispersions so that the mixture comprised 0.6 wt. part of sulfur, 1.0 wt. part of titanium dioxide, 1.5 wt. parts of zinc oxide, and 1.0 wt. part of zinc diethyldithiocarbamate, based on 100 wt. parts of dry matter previously diluted to a 35% concentration of latex at a temperature of 18-25°C. The mixture was allowed to stand with periodic stirring for 24 hours.

18.4. A porcelain mold for dipping was preheated to 55°C and submersed into a coagulant solution for 3 seconds. Then the mold was kept in air at room temperature for 5 minutes and submersed into the latex mixture (18.3) for 5 seconds. After that, the resulting polymer layer was held in air for 5 minutes, followed by drying at a temperature of 80°C for 20 minutes and curing for 20 minutes at 110°C.

19. The Defoe stiffness of latex polymer was determined according to GOST 10201-75, wherein the latex polymer was prepared in accordance with GOST 11604-79.

20. The quality of latex articles (gloves) was checked for compliance with ASTM

D6319.

The essence of the proposed technical solution is illustrated by the following examples of specific embodiment, which illustrate, but not limit the scope of the present invention. A person skilled in the art will appreciate that the invention is not limited to them, and the same effect can be achieved by applying equivalent features/solutions.

Comparative example (according to EP3412717)

To a 10 L high-pressure reactor equipped with a stirrer and a thermoregulation jacket and purged with nitrogen, 3 wt. parts of sodium alkylbenzene sulfonate, 0.1 wt. part of glycerol monostearate, 0.5 wt. part of /e/7-dodecyl mercaptan and 140 wt. parts of demineralized water were added, followed by the addition, with stirring, of 100 wt. parts of a monomer mixture comprising 28 wt.% of acrylonitrile, 67 wt.% of butadiene, and 5 wt.% of methacrylic acid, and the temperature was raised to 38°C. After raising the temperature, 0.3 wt. part of potassium persulfate as an initiator was added. When the conversion rate reached 95%, the polymerization was stopped by adding 0.1 wt. part of sodium dimethyl dithiocarbamate. Unreacted monomers were removed, and ammonia water, an antioxidant, and an antifoaming agent were added to the resulting latex for neutralization. The characteristics of the carboxylated butadiene-nitrile latex thus prepared were the following: the mass fraction of dry matter was 45% and pH was 8.5.

Example 1

In a 20-liter apparatus, equipped with a stirrer and a thermoregulation jacket, an aqueous phase comprising 110 wt. parts of deoxygenated and demineralized water, 3.0 wt. parts of sodium alkylbenzene sulfonate (ABS) as emulsifier (1), 0.8 wt. part of trisodium phosphate (TSP), 0.007 wt. part of Trilon B as a complexing agent, and 0.0018 wt part of iron sulfate were added. The apparatus was purged with nitrogen, followed by the addition of the total mixture of monomers comprising 88 wt. parts of butadiene, 10 wt. parts of acrylic acid nitrile, and 2 wt. parts of methacrylic acid, as well as 0.1 wt. part of tertiary dodecyl mercaptan (TDM) as chain transfer agent and 0.02 wt. part of pinan hydroperoxide (PHP) as initiator, which were pre-dissolved in nitrile acrylic acid. In addition, an initiator emulsion to be supplied during the process was separately prepared, the emulsion consisting of 0.01 wt. part of PHP, 1.0 wt. part of emulsifier (2) with an oxyethylation degree of 2 to 6 (OD2-6) and 5 wt. parts of water; an activator solution comprising 0.018 wt. part of rongalite in 5 wt. parts of water was also prepared. After stirring the aqueous phase with the monomer mixture, the initiating system and tertiary dodecyl mercaptan in the reactor for 50 minutes at 15°C, the rongalite solution was fed into the reactor, which was considered the beginning of the polymerization reaction. When the conversion rate of monomers reached 25% and 50%, a half of the prepared volume of the initiator emulsion was fed into the apparatus. The polymerization process took place at 22°C. 12 hours after the start of the reaction, the conversion rate of monomers was 70%, the mass fraction of dry matter in latex was 32.5%. Then, sodium dimethyldithiocarbamate as a stopper was added to the apparatus in an amount of 0.2 wt. part per polymer in the form of a 5% solution, and a 10% solution of ammonia as a neutralizing agent was added until the pH value reached 7.5. Unreacted monomers were then removed from latex, with use of a rotary film evaporator at 60°C and supplying an antifoaming agent. After this, the latex was conditioned by adding a 10% ammonia solution to a pH value of 8.5.

Example 2.

The synthesis of latex was performed similarly to example 1 with the difference that the content of ABS in the aqueous phase was 2.4 wt. parts, the ratio of components in the monomer phase was the following: 78 wt. parts of butadiene, 15 wt. parts of acrylic acid nitrile, 7 wt. parts of methacrylic acid, and 0.8 wt. part of TDM. Emulsifier (2) was OD2-6 in an amount of 0.3 wt. part.

The initiator emulsion and emulsifier (2) were fed when the conversion rate reached 30%. The polymerization process was performed at a temperature of 30°C for 10 hours to a conversion rate of 82%. The mass fraction of dry matter in latex before the removal of residual monomers was 39.1%.

Example 3.

The synthesis of latex was performed similarly to example 1 with the difference that the content of sodium olefin sulfonate in the aqueous phase was 2.5 wt. parts, the ratio of components in the monomer phase was the following: 80 wt. parts of butadiene, 10 wt. parts of acrylic acid nitrile, 10 wt. parts of methacrylic acid, and 0.22 wt. part of

TDM. Emulsifier (2) was OD2-6 in an amount of 0.8 wt. part.

The initiator emulsion was fed when the conversion rate reached 25% and 60%. The polymerization process was performed at a temperature of 28°C for 14 hours to a conversion rate of 99.9%. The mass fraction of dry matter in latex before the removal of residual monomers was 46.0%.

Example 4 The synthesis of latex was performed similarly to example 1 with the difference that the content of sodium alkylbenzene sulfonate was 2.8 wt. parts, the ratio of components in the monomer phase was the following: 73 wt. parts of butadiene, 25 wt. parts of acrylic acid nitrile, 2 wt. parts of methacrylic acid, 0.3 wt. part of TDM, and 0.015 wt. part of PHP. Emulsifier (2) was OD2-6 in an amount of 0.1 wt. part. The initiator emulsion in emulsifier (2) were fed when the conversion rate reached 25%.

The polymerization process was performed at a temperature of 20°C for 10 hours to a conversion rate of 75%. The mass fraction of dry matter in latex before the removal of residual monomers was 36.5%.

Example 5

The synthesis of latex was performed similarly to example 1 with the difference that emulsifier (1) was sodium alkyl sulfonate in an amount of 2.6 wt. parts, the ratio of components in the monomer phase was the following: 65 wt. parts of butadiene, 32 wt. parts of acrylic acid nitrile, 3 wt. parts of methacrylic acid, and 0.015 wt. parts of PHP. To prepare the initiator emulsion, OD10 was used as emulsifier (2) in an amount of 0.2 wt. part.

Emulsifier (2) was fed when the conversion rate reached 30% and 60%. The polymerization process was performed at a temperature of 24°C for 11 hours to a conversion rate of 80%. The mass fraction of dry matter in latex before the removal of residual monomers was 38.0%.

Example 6

The synthesis of latex was performed similarly to example 1 with the difference that emulsifier (1) was sodium lauryl sulfate in an amount of 2.2 wt. parts, the ratio of components in the monomer phase was the following: 67 wt. parts of butadiene, 30 wt. parts of acrylic acid nitrile, 3 wt. parts of methacrylic acid, 0.4 wt. part of TDM, and 0.015 wt. part of GPP. Emulsifier (2) was OD2-6 in an amount of 1.0 wt. part.

The initiator emulsion in emulsifier (2) were fed when the conversion rate reached 20% and 50%. The polymerization process was performed at a temperature of 28°C for 9 hours to a conversion rate of 79%. The mass fraction of dry matter in latex before the removal of residual monomers was 37.7%.

Example 7 The synthesis of latex was performed similarly to example 1 with the difference that the content of ABS in the aqueous phase was 2.3 wt. parts, the ratio of components in the monomer phase was the following: 66 wt. parts of butadiene, 30 wt. parts of acrylic acid nitrile, 4 wt. parts of methacrylic acid, 0.20 wt. part of TDM, and 0.015 wt. part of PHP. To prepare an initiator emulsion, emulsifier (2) with an oxyethylation degree of 2- 6 was used in an amount of 0.4 wt. part. The initiator emulsion was fed when the conversion rate reached 25% and 60%. The polymerization process was performed at a temperature of 22°C for 11 hours to a conversion rate of 78%. The mass fraction of dry matter in latex before the removal of residual monomers was 37.2%.

Example 8

The synthesis of latex was performed similarly to example 1 with the difference that the content of ABS in the aqueous phase was 2.0 wt. parts, the ratio of components in the monomer phase was the following: 66 wt. parts of butadiene, 29 wt. parts of acrylic acid nitrile, 5 wt. parts of methacrylic acid, 0.18 wt. part of TDM, and 0.015 wt. part of PHP. To prepare an initiator emulsion, OD10 was used as emulsifier (2) in an amount of 0.2 wt. part. The initiator emulsion was fed when the conversion rate reached 30% and 55%. The polymerization process was performed at a temperature of 29°C for 12 hours to a conversion rate of 90%. The mass fraction of dry matter in latex before the removal of residual monomers was 41.2%.

Example 9

The synthesis of latex was performed similarly to example 1 with the difference that emulsifier (1) was sodium alkyl sulfonate in an amount of 2.4 wt. parts, the ratio of components in the monomer phase was the following: 63 wt. parts of butadiene, 30 wt. parts of acrylic acid nitrile, 7 wt. parts of methacrylic acid, 0.3 wt. part of TDM, and 0.015 wt. part of PHP. To prepare an initiator emulsion, emulsifier (2) with an oxyethylation degree of 2-6 was used in an amount of 0.3 wt. part. The initiator emulsion was fed when the conversion rate reached 30%. The polymerization process was performed at a temperature of 28°C for 10 hours to a conversion rate of 78%. The mass fraction of dry matter in latex before the removal of residual monomers was 37.2%.

Example 10

The synthesis of latex was performed similarly to example 1 with the difference that the content of ABS in the aqueous phase was 2.5 wt. parts, the ratio of components in the monomer phase was the following: 55 wt. parts of butadiene, 40 wt. parts of acrylic acid nitrile, 5 wt. parts of methacrylic acid, 1.0 wt. part of TDM, and 0.01 wt. part of PHP. To prepare an initiator emulsion, emulsifier (2) with an oxyethylation degree of 10 (OD10) was used in an amount of 0.3 wt. part. The initiator emulsion was fed when the conversion rate reached 30%. The polymerization process was performed at a temperature of 20°C for 10 hours to a conversion rate of 86%. The mass fraction of dry matter in latex before the removal of residual monomers was 40.3%.

Example 11

The synthesis of latex was performed similarly to example 1 with the difference that the content of ABS in the aqueous phase was 1.9 wt. parts, the ratio of components in the monomer phase was the following: 53 wt. parts of butadiene, 46 wt. parts of acrylic acid nitrile, 1 wt. part of methacrylic acid, 1.5 wt. parts of TDM, and 0.015 wt. part of PHP as an initiator. To prepare an initiator emulsion, OD10 was used as emulsifier (2) in an amount of 1.2 wt. part. The initiator emulsion was fed when the conversion rate reached 35%. The polymerization process was performed at a temperature of 20°C for 8 hours to a conversion rate of 85%. The mass fraction of dry matter in latex before the removal of residual monomers was 39.7%.

Example 12

The synthesis of latex was performed similarly to example 1 with the difference that the emulsifier was sodium lauryl sulfate in an amount of 3.1 wt. parts, the ratio of components in the monomer phase was the following: 79 wt. parts of butadiene, 10 wt. parts of acrylic acid nitrile, 11 wt. parts of methacrylic acid, 0.1 wt. part of TDM, and 0.01 wt. part of PHP as an initiator. To prepare an initiator emulsion, OD2-6 was used as emulsifier (2) in an amount of 0.1 wt. part. The initiator emulsion was fed when the conversion rate reached 15% and 50%. The polymerization process was performed at a temperature of 22°C for 14 hours to a conversion rate of 95%. The mass fraction of dry matter in latex before the removal of residual monomers was 43.8%.

Example 13

The synthesis of latex was performed similarly to example 1 with the difference that the emulsifier was ABS in an amount of 2.5 wt. parts, the monomer phase comprised 79 wt. parts of butadiene, 25 wt. parts of methacrylic acid nitrile, 5 wt. parts of acrylic acid as a carboxylating agent, 0.3 wt. part of TDM, and 0.012 wt. part of PHP as an initiator. To prepare a initiator emulsion, OD2-6 was used as emulsifier (2) in an amount of 0.2 wt. part. The initiator emulsion was fed when the conversion rate reached 25% and 50%. The polymerization process was performed at a temperature of 23°C for 16 hours to a conversion rate of 98%. The mass fraction of dry matter in latex before the removal of residual monomers was 45.2%.

Example 14

The synthesis of latex was performed similarly to example 1 with the difference that the emulsifier was ABS in an amount of 2.4 wt. parts, the monomer phase comprised 65 wt. parts of isoprene, 32 wt. parts of AAN, a mixture of 2 wt. parts of acrylic acid and 1.0 wt. part of methacrylic acid as a carboxyling agent, 0.5 wt. part of TDM, and 0.015 wt. part of PHP as initiator. To prepare an initiator emulsion, OD10 was used as emulsifier (2) in an amount of 0.3 wt. part. The initiator emulsion was fed when the conversion rate reached 30% and 50%. The polymerization process was performed at a temperature of 25°C for 14 hours to a conversion rate of 99%. The mass fraction of dry matter in latex before the removal of residual monomers was 46.0%.

Example 15

The synthesis of latex was performed similarly to example 1 with the difference that the emulsifier was sodium alkyl sulfonate in an amount of 2.2 wt. parts, the monomer phase comprised 70 wt. parts of piperylene, 23 wt. parts of methacrylic acid nitrile, a mixture of 5 wt. parts of methacrylic acid and 2 wt. parts of acrylic acid as a carboxyling agent, 0.5 wt. part of TDM, and 0.020 wt. part of PHP as an initiator. To prepare an initiator emulsion, OD2-6 was used as emulsifier (2) in an amount of 0.1 wt. part. The initiator emulsion was fed when the conversion rate reached 30% and 60%. The polymerization process was performed at a temperature of 25°C for 15 hours to a conversion rate of 95%. The mass fraction of dry matter in latex before the removal of residual monomers was 43.4%. Table 1

The latex synthesis formulation Table 1. Continuation

*Dosage, wt. part based on 100 wt. parts of monomers according to the examples

As it can be seen from the data in Table 1, the obtained samples are characterized by a conversion rate of monomers in the range of 75-90%, and the stability during synthesis and stripping of latexes is high since the total amount of coagulum did not exceed 2.5%. The NF dispersing agent (leucanol) has been excluded from the synthesis formulation, thereby increasing the environmental friendliness of the process.

Table 2

Colloidal-and-chemical properties of latexes

Data in table 2 clearly demonstrate that the latexes prepared according to the present invention are characterized by stability in particle size of from 60 to 150 nm. These latexes are also characterized by a high stability at mechanical stress and during storage, and the latexes are resistant to the introduction of a dispersion of curing agents and to the exposure of sub-zero temperatures (frost resistance) up to -40°C.

Table 3

Properties of films prepared by ion deposition

As it can be seen from the data in table 3, cured films based on the latexes according to the invention have higher physical-mechanical properties compared to the film of the comparative example. The films prepared have no color and residual stickiness and are characterized by the absence of defects.