RU2677260C1 - Method of producing latex and application of obtained latex produced therewith - Google Patents

Abstract

FIELD: manufacturing technology.SUBSTANCE: invention relates to a method for producing latexes used for the production of various products by submersible dipping. Latex is obtained in semi-periodic mode, by obtaining a seed latex, adding to the seed latex water, at least one protective colloid, an initiating system, and part of the main mixture of monomers. Main part of the monomers contains 80–85 wt. % of conjugated diene and carboxylate agent of the total amount in the composition of the main mixture and 100 wt.% vinyl monomer selected from vinyl ethers, nitriles and arylolefins, based on the total amount of this monomer in the main mixture. Simultaneously with the monomers, a molecular weight regulator, an emulsifier and a polymerization activator are introduced. 45–75 minutes before the end of dosing the main part of the mixture of monomers in the reaction zone injected the remaining 15–20 wt. % monomers of the main mixture.EFFECT: latex and its use as a material for the production of various products by submersible dipping is described.28 cl, 4 tbl, 7 ex

Description

FIELD OF THE INVENTION

The invention relates to a method for producing latexes used for the production of various products by immersion dipping followed by vulcanization of a polymer film. In particular, the latex obtained in accordance with the method of the present invention is suitable for the production of gloves for various purposes.

BACKGROUND

The conditions for the synthesis of latexes containing a conjugated diene as a monomer largely determine the properties of the target latex, especially if the consumer is interested in the strength and elastic properties of the polymer film - indicators that are extremely important for products such as surgical, household and other types of gloves, balls, probes, latex threads and similar products, combined with the oil and gas resistance of latex protective coatings.

To obtain an aqueous dispersion of a polymer based on an unsaturated diene with the least number of branching and crosslinking of the polymer at high degrees of conversion, it is only necessary to use a periodic emulsion polymerization method in which all monomers are loaded into the reactor in one go. The achieved result is explained by the high mobility of polymer radicals in polymer monomer drops due to the high concentration of monomer in polymer monomer particles (PMP). However, during polymerization in a batch process with loading monomers in one go, it is extremely difficult to control the colloidal chemical parameters of the system, and the slightest deviations in the process (for example, in the number of loaded components, temperature, mixing speed) can significantly change the course of the reaction and, as a result, colloidal characteristics of the target product.

Methods of continuous and semi-periodic synthesis of latex are devoid of these disadvantages, which is caused by a specific, calculated feed rate of monomers and emulsifier in the reaction zone. At the same time, the monomers entering the reaction medium are usually concentrated in growing PMPs, thus ensuring the growth of polymer particles formed in the first stage of the reaction (after the first loading of monomers). The methods of continuous and semi-periodic synthesis of latex make it possible to control the particle size, make it possible to pre-calculate the desired final size of the globules, and ensure the constancy of the colloidal chemical characteristics of the system. However, when these synthesis methods are implemented, the monomer concentration in the PMP is lower than in the batch process, which leads to an increase in the viscosity of the dispersed phase and reduces the mobility of the polymer chain. Less mobile polymer chains are prone to branching and crosslinking reactions. For this reason, to ensure the operational properties of the polymer, such as elasticity and strength, a continuous process is carried out up to 75-80% of the conversion of monomers.

The use of polymer seeds in a semi-periodic method of latex synthesis allows to reduce the effect of polymer structuring at high degrees of conversion, provides both the controllability of the colloidal chemical properties of the system, the regularity and linearity of the polymer phase, and the absence of gel fractions in it characteristic of crosslinked branched polymers when conversion is achieved monomers close to 100%.

In the application KR 20110019176, 02.25.2011, [1], a method for producing acrylonitrile butadiene latex is disclosed. The known method includes the step of polymerizing acrylonitrile, butadiene and ethylenically unsaturated acid to obtain seed latex, the step of preparing a pre-emulsion of monomers of acrylonitrile, monomers of butadiene and monomers of ethylenically unsaturated acid, and the step of supplying ethylene unsaturated acid monomers to the pre-emulsion to feed and emulsion. The disadvantage of this method is the supply of ethylenically unsaturated acid at the end of the polymerization reaction, which is accompanied by the risk of the formation of a homopolymer acid (ethylenically unsaturated acid, which was fed into the process) in the aqueous phase of the dispersion, and can lead to an uncontrolled increase in the viscosity of the system, and this adversely affects the technological properties of latex .

US patent 6870019, 08/15/2002, [2], discloses a method for producing latex used to obtain molded products. Latex is obtained by emulsion polymerization of a monomer mixture in the presence of sodium alkylbenzenesulfonate. Synthesized latex is used to obtain medical and other latex gloves. According to the patent [2], for the implementation of the known method, the fractional composition of the sodium alkylbenzenesulfonate used is critical — it must contain at least 10% of the C ₁₃ -C ₂₀ fraction. This circumstance necessitates additional control of the fractional composition of the emulsifier, which under industrial conditions will lead to an increase in time during the incoming control of the emulsifier.

US Pat. No. 5,750,618, 05/12/1998, [3] describes a method for producing latexes based on conjugated dienes selected from butadiene, isoprene, chloroprene and mixtures thereof, and optionally vinyl compounds that copolymerize with conjugated dienes. According to US Pat. No. 5,750,618, the monomers are introduced into the seed latex with a particle size of 10 to 80 nm, wherein the seed latex mainly consists of monomers used in the main process, or is an inorganic pigment. The polymerization process is carried out in the presence of an activator and an emulsifier, the introduction of the emulsifier is controlled so that the latex has a certain size of polymer particles. In this case, the feed rate of the monomer is also controlled depending on the polymerization rate so that the ratio of the speeds is 1: (0.05-0.7), respectively.

However, in the known method, a separate control is necessary for the speed of the polymerization process and the feed rate of the monomers, and requires separate monitoring of these parameters and constant additional adjustments to the feed rate of the monomers.

In the application US 4130523, 12.19.1978, [4], a method for producing high solids polymer latex is disclosed, which comprises the steps of:

(A) initiating latex formation by feeding the emulsion polymerizable monomer to an aqueous polymerization medium containing a sufficient amount of polymerization catalyst to initiate polymerization of the monomer;

(B) obtaining a stable seed latex while supplying the specified monomer, a polymerization catalyst, stabilizing the emulsion of the amount of surfactant and buffer in the reaction zone;

(C) obtaining an intermediate latex while supplying the specified monomer, a polymerization catalyst, stabilizing the emulsion of the amount of surfactant and buffer in the reaction zone;

(D) continuously withdrawing a portion of the latex obtained in steps (B) and (C) from the reaction zone to the storage zone, said steps being carried out until the intermediate latex in the reaction zone has a solids content of 55 to 65 vol. %;

(E) obtaining the final latex by continuously feeding the latex allotted to the reaction zone until the desired solids content is obtained.

The specified method of producing latex is multi-stage, and in addition, it will lead to latex with a wide distribution of particle sizes, which negatively affects the process of film formation and leads to the formation of defects in the films. Also, a reduction in particle monodispersity produces opaque, cloudy films.

The closest in technical essence and the achieved result is a method of producing latex, known from the application WO 2016093689 A1, 06.16.2016, [5], disclosing a polymer latex composition for use by the method of immersion molding, containing the reaction product obtained by the method of free radical emulsion polymerization in aqueous medium ethylenically unsaturated monomers, namely: (a) from 19.9 to 90 wt. % of at least one aliphatic conjugated diene, (b) from 9.9 to 80 wt. % of at least one unsaturated nitrile, (C) from 0.1 to 10 wt. % of at least one ethylenically unsaturated acid, (d) from 0 to 19 wt. % of at least one aromatic vinyl compound and (e) from 0 to 20 wt. % of at least one additional ethylenically unsaturated compound other than any of compounds (a) to (d). Mass percentages are based on the total number of monomers; emulsion polymerization is carried out in the presence of a degraded polysaccharide.

However, a degraded polysaccharide taken in the indicated amounts can adversely affect the color of the polymer film.

The disadvantages of the known technical solutions for the prototype should also include a long dosing time in the reactor ingredients at the second stage of synthesis. There is a high probability of increasing the viscosity of the obtained latex due to high dosages of degraded starch, which negatively affects the thickness of the deposited gel when molding products by immersion dipping.

SUMMARY OF THE INVENTION

The present invention is to develop a method for producing latex, applicable in the manufacture of protective rubber products by dipping; in particular, latex, which is highly resistant to negative temperatures, the introduction of vulcanizing agents and mechanical stresses associated with the processes of mixing and pumping latex through pipes.

The technical result of the present invention is to obtain latex, the particles of which have a shell with a lower glass transition temperature in comparison with the inner part of the particle, which facilitates their coalescence upon receipt of the film and increases the frost resistance of the latex. In addition, the latex obtained according to the present invention has improved frost resistance compared to latexes synthesized without the use of protective colloids, is characterized by increased resistance to the introduction of vulcanizing agents and improved film-forming properties.

The specified technical result is achieved through the implementation of the proposed method for producing latex, according to which the process is carried out in stages, with the redistribution of the feed flows of the conjugated diene and unsaturated acid. This technique leads to the enrichment of the surface of polymer particles with a low glass transition temperature (a soft shell forms on the particles), which allows to improve the coalescence of globules during gel deposition. In addition, the combination of a soft shell of polymer particles and the use of a mixture of protective colloids in a selected concentration range makes it possible to increase the frost resistance of latex to -16 ° C, while the latex freezes at a temperature of -3 ÷ -4 ° C, but restores its working properties when defrosting. This provides advantages for the year-round transportation and storage of the latex of the present invention, compared with the storage of traditional latex, carried out at a temperature not lower than + 5 ° C.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for producing latex in semi-periodic mode, comprising the following stages:

1) obtaining seed latex;

2) adding to the seed latex of water, at least one protective colloid, the initiating system and part of the main mixture of monomers containing 80-85 wt. % conjugated diene and carboxylating agent of their total amount in the composition of the main mixture, and 100 wt. % vinyl monomer of the total amount of this monomer in the composition of the main mixture, as well as the introduction of a molecular weight regulator, emulsifier and polymerization activator simultaneously with the monomers;

3) the introduction into the reaction zone of the remaining 15-20 wt. % of the monomers of the main mixture 45-75 minutes before the end of dosing of the main part of the mixture of monomers.

In addition, the invention relates to latex obtained by this method, and the use of such latex for the manufacture of products by dipping.

According to the proposed method, a mixture of monomers containing a conjugated diene, a vinyl monomer and a carboxylating agent are divided into two parts: the first, main part of the mixture is 80-85 wt. % of the total mixture of monomers, the second part is 15-20 wt. % of the total mixture of monomers.

The polymerization is carried out in a semi-batch mode, with the introduction of the seed latex and a mixture of monomers, and the mixture of monomers is introduced gradually, at a certain speed so that the feed time of the first part of the mixture of monomers was from 5 to 7 hours, the feed time of the second part is approximately 5 hours. Simultaneously with the introduction of a mixture of monomers, a molecular weight regulator, an emulsifier and a polymerization activator are fed into the reaction medium.

The feed rate of the mixture of monomers and emulsifier according to the present method is controlled so that the polymerization proceeds only on the seeds of the seed latex, and the formation of new particles did not occur. In the claimed method, this is achieved while maintaining in the reaction zone a mass ratio between the polymer and monomer phases at the level of (0.5-0.8) :( 1.0-1.2), respectively. To achieve the indicated ratio, a second portion of monomers is introduced into the reaction zone 45-75 minutes before the end of dosing of the main (first) mixture of monomers.

The seed latex is synthesized in situ at stage 1), directly in the polymerization reactor before the start of stage 2) of the inventive method, or it is preliminarily obtained in a separate reactor, and then fed to the reaction zone at stage 2). The dosage of the seed latex according to the present method is from 0.01 to 15 wt. parts per 100 wt. parts of the main mixture of monomers. Preferably, from 0.1 to 10 wt. parts per 100 wt. parts of the main mixture of seed latex monomers, most preferably from 1 to 5 wt. parts per 100 wt. parts of the main mixture of monomers.

The particle size of the seed latex is 10-90 nm, preferably the latex particles have a size of from 20 to 80 nm, in the most optimal embodiment, the seed latex with a particle size of 30-80 nm is used.

The monomers for preparing the seed latex in step 1) may be selected from or different from the monomers forming the basic mixture.

As monomers suitable for the preparation of seed latex, vinyl monomers are used as the only monomer, or mixtures thereof with other vinyl monomers or conjugated dienes.

In particular, vinyl monomers are selected from nitriles, aromatic vinyl compounds, acrylic carboxylates, ethylenically unsaturated amides, vinyl carboxylates, ethylenically unsaturated amines. Suitable nitriles are selected, for example, from acrylonitrile, methacrylonitrile, α-cyano-ethyl-acrylonitrile and fumaronitrile. Suitable aromatic vinyl compounds include, for example, compounds such as styrene and α-methyl styrene. Suitable acryl carboxylates are selected, for example, from methyl acrylate, ethyl acrylate, butyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate and glycidyl methacrylate. Ethylenically unsaturated amides are selected, in particular, from such as acrylamide, methacrylamide, N, N-dimethylacrylamide and N-methylolacrylamide. As the vinyl carboxylate, for example, vinyl acetate is used. Ethylenically unsaturated amines are selected from, for example, methylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, 2-vinylpyridine.

In particular, 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene and 2-methyl-1,3-butadiene are used as conjugated dienes of the monomer mixture of the present method.

In one embodiment of the invention, ethylenically unsaturated acids are carboxylating agents used to prepare the seed latex. Examples of such ethylenically unsaturated acids include, but are not limited to, monobasic acids such as (meth) acrylic acid and crotonic acid; examples of dibasic acids include maleic acid, fumaric acid, itaconic acid, and their anhydrides and esters, for example, monoesters of dibasic acids ( half esters) such as methyl maleate, methyl nitaconoate.

Monomers such as styrene, acrylonitrile, methyl methacrylate, butyl acrylate, 1,3-butadiene, vinyl carboxylic acid, or mixtures thereof, are preferred for seed latex.

Most preferred as seed are latexes based on polystyrene, polybutadiene copolymers, carboxylated copolymer latexes based on acrylonitrile, styrene or methyl methacrylate, where vinyl carboxylic acid is present in an amount of up to 10 wt. parts of the total mass of monomers.

In addition, inorganic pigments having a particle size of 50 to 100 nm, for example, such as silicon dioxide (silica), can be used as a seed, instead of a seed latex. see, for example, US Pat. No. 5,750,618. To stabilize the resulting latex, and also to control the particle size of the target latex, emulsifiers are used in the process of preparing seed latex, for example, such as anionic emulsifiers selected from the group consisting of salts of higher fatty sulfated alcohols, higher alkyl sulfonates, alkylaryl sulfonates, aryl sulfonates, as well as products of their condensation with formaldehyde, salts of sulfosuccinates, adducts of sulfated esters with ethylene oxide. Preferably, sodium lauryl sulfate and / or sodium alkylbenzenesulfonate are used as emulsifier.

The total amount of emulsifier involved in the polymerization of latex according to the claimed method, is chosen so as to avoid destabilization of the system (that is, to prevent coagulation), and, at the same time, to ensure the growth of particles only seed latex.

In particular, the amount of emulsifier used in the preparation of seed latex is from 1 to 20 wt. % based on the total number of monomers, in the preferred embodiment, from 2 wt. % up to 10 wt. %

Additionally, buffers and chelating agents are used in the preparation of seed latex by emulsion polymerization. As such substances, alkali metal phosphates and pyrophosphates are used, as well as alkali metal salts of ethylenediaminetetraacetic acid, in particular, such as sodium ethylene diamine tetraacetate (Trilon B), or inorganic salts, such as trisodium phosphate, sodium pyrophosphate. The amount of buffer and chelating agent is from 0.01 to 1 wt. parts based on the total number of monomers.

Obtaining seed latex is carried out in the presence of a polymerization initiator and molecular weight regulator, typical of the emulsion polymerization process. Typically, the initiator is selected from water-soluble persulfates, preferably ammonium or potassium persulfate is used. The amount of initiator used is from 0.1 to 10 wt. %, preferably from 0.5 to 2 wt. % based on the total number of monomers.

Typical molecular weight regulators / chain transfer agents are organic thio compounds. The molecular weight regulator is selected from a number of compounds such as n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-hexadecyl mercaptan, n-tetradecyl mercaptan, t-tetradecyl mercaptan. Xanthogen disulphides, in particular such as dimethyl xanthohendisulphide, diethyl xanthohendisulphide and diisopropyl xanthogen disulphide may also be used as a regulator; thiuram disulfides such as tetramethylthiuram disulfide, tetraethyl thiuram disulfide, tetrabutylthiuram disulfide; halogenated hydrocarbons such as chloroform, carbon tetrachloride, hydrocarbons such as pentaphenylethane, dimer of alphamethylstyrene, acrolein, allyl alcohol, 2-ethylhexyl thioglycolate, terpinolene, α-terpinene, γ-terpinene, dipentene.

Preferably, mercaptans and xanthogendisulfides, thiuram disulfides, 1,1-diphenylethylene, α-methylstyrene dimer are used as molecular weight regulator. All of these regulators can be used individually or in various combinations (two or more) in a total amount of up to 5 wt. %, in particular from 0.2 wt. parts to 2.0 wt. parts per 100 wt. parts of monomers. In particular, the most common and generally available molecular weight regulator is mercaptan.

As monomers used in stages 2) -3) of the method according to the present invention, conjugated dienes and monomers of the vinyl and / or vinyl aryl series are used. The conjugated diene is selected, in particular, from 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, piperylene, 2-methyl-3-ethyl-1,3-butadiene, 3-methyl-1, 3-pentadiene, 2-methyl-3-ethyl-1,3-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-1,3-octadiene, phenyl-1,3-butadiene, 2, 3-diethyl-1,3-butadiene, 2,3-di-n-propyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene.

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

Most preferred is the use of 1,3-butadiene.

The amount of conjugated diene used according to the present method is in the range of 35 wt. % to 80 wt. %, preferably from 35 to 70 wt. % of the total number of monomers in the composition of the main mixture.

The specified vinyl series monomer is selected from vinyl esters, nitriles and aryl olefins. In particular, the vinyl monomer is selected from nitriles (meth) acrylic acid, butyl acrylate, styrene, alpha-methyl styrene. In the most preferred embodiment, nitrile of acrylic acid is used.

The amount of vinyl monomer used in the present invention is from 15 to 45 wt. %, preferably from 18 to 40 wt. % of the total number of monomers in the composition of the main mixture.

The carboxylating agent included in the monomer mixture used in stages 2) -3) of the present process is selected from the group of ethylenically unsaturated carboxylic acids. In particular, alpha (methylene) carboxylated acids or mixtures thereof, for example, such as acrylic, are used as carboxylating agents. , methacrylic, itaconic, fumaric acids, or mixtures thereof.

The content of the specified carboxylating agent is 1-10 wt. %, preferably from 2 to 5 wt. % of the total number of monomers in the composition of the main mixture.

Upon receipt and modification of finished latexes, a number of additives are optionally used, in particular, natural and synthetic protective colloids,

which play the role of viscosity modifiers, surface-active additives that improve the resistance of compositions to mechanical stress, the distribution of inert fillers in the dispersion.

Water-soluble polymers of both natural and artificial origin are used as protective colloids. Of the natural polymers, polysaccharides are most widely used, and of artificial polymers, cellulose modification products.

A preferred artificial protective colloid is a water-soluble cellulose ether and glycolic acid, which is prepared using ethylene oxide, methyl chloride, propylene oxide, monochloracetic acid, or mixtures thereof. Particularly preferred are carboxymethyl cellulose (CMC) and its derivatives, the degree of carboxyl substitution (C3) of which is from about 0.7 to about 2.9, more preferably from about 0.7 to about 1.5, and most preferably from about 1.0 to about 1.4.

Used according to the claimed method carboxymethylcellulose derivatives include, without limitation, metilkarboksimetiltsellyulozu, etilkarboksimetiltsellyulozu, hydroxyethylcarboxymethyl cellulose, gidroksipropilkarboksimetiltsellyulozu, metoksietilkarboksimetiltsellyulozu, ethoxyethyl carboxymethylcellulose, and diethyl or mixtures thereof.

In one embodiment of the invention, hydroxyethyl cellulose (HEC) is used, the preferred degree of hydroxyethyl molar substitution (MOH) being from about 1.6 to about 4.0, more preferably from about 1.8 to about 3.5, and most preferably from about 1.8 to about 2.9.

In addition, hydrophobically-modified cellulose ethers can be used as protective colloids. Suitable hydrophobically-modified cellulose ethers are, in particular, cellulose ethers which are substituted with a hydrocarbon containing 4-25 carbon atoms, the mass amount of this hydrocarbon being from about 0.1 to about 3.0 wt. %, more preferably from about 0.1 to about 2.0 wt. % of the total amount of hydrophobically-modified cellulose ether.

A preferred hydrophobically-modified cellulose ether is hydrophobically-modified hydroxyethyl cellulose (HMHEC). A preferred hydrophobically-modified hydroxyethyl cellulose is hydroxyethyl cellulose, which is further substituted with a hydrocarbon containing 4-25 carbon atoms, the mass amount of this hydrocarbon being from about 0.1 to about 3.0%, more preferably from about 0.1 to about 2.0 % of the total amount of hydrophobically-modified hydroxyethyl cellulose. In a preferred embodiment, the degree of hydroxyethyl molar substitution of said HMHEC is from about 2.9 to about 4.0, more preferably from about 2.9 to about 3.5.

Other cellulose ethers that can be used as protective colloids of the present invention include ethyl hydroxyethyl cellulose (EHEC), methyl cellulose (MC), methyl hydroxypropyl cellulose (MGPC) and hydroxypropyl cellulose (GPC).

Other compounds that can be used as protective colloids are hydroxyethylated starch derivatives, partially and fully hydrolyzed polyvinyl alcohol, polyacrylic acid, alkali metal polyacrylates (e.g. potassium, sodium), polyacrylates, polyacrylamide, methyl vinyl ether copolymer, maleic anhydride, maleic anhydride. , water-soluble starch glue, gelatin, water-soluble alginates, casein, agar, natural and artificial gums. Low molecular weight polysaccharides also include dextrin - a polysaccharide formed from starch in the process of its destruction in an acidic environment at elevated temperatures, the degree of dextrinization can vary from 60% to 100%.

The protective colloid is used in an amount effective to stabilize the latex system. In particular, the concentration of the protective colloid during the emulsion polymerization process can be varied over a wide range, the upper limit being determined only by economic and practical considerations based on what properties the final product should have.

In a preferred embodiment, the upper limit of the concentration of the protective colloid is approximately 5.0 wt. %, more preferably 3.5 wt. % and most preferably about 2.5 wt. % of the total amount of monomers in the reaction mixture. A preferred lower limit is about 0.005 wt. % A more preferred lower limit is about 0.05 wt. % and most preferred lower limit is about 0.1 wt. % of the total number of monomers.

The protective colloid of the invention can be used either individually or in combination with other protective colloids or surfactants. For example, a CMC derivative can be used as the sole stabilizer or in combination with one or more surfactants.

According to the present invention, an initiating system consisting of a free radical initiator, a buffer and activators is used. The initiators used are inorganic peroxy compounds, such as hydrogen peroxide, potassium or ammonium persulfates, peroxycarbonates and peroxyborates, organic hydroperoxides, such as alkyl hydroperoxides, dialkyl peroxides, mixtures of alkyl hydroperoxides and dialkyl peroxides, ethers such as non-organobutyric butyl butyl peroxides. The amount of initiator is usually from 0.01 to 5 wt. parts to the total number of monomers, the preferred amount of initiator is from 0.05 to 2.0 wt. parts.

Organic and inorganic initiators may be used in combination with one or more activators. Examples of suitable activators are sulfur dioxide, alkali metal disulfites, alkali metal and ammonium hydrosulfites, thiosulfates, dithionites and formaldehyde sulfoxylates, hydroxylamine hydrochloride, hydrazine sulfate, glucose and ascorbic acid. The choice of preferred initiator and activator depends on the nature of the monomers used in the process and the temperature of the polymerization reaction.

Also, when preparing the latex of the present invention, a buffer and a pH adjuster may be used, if necessary.

Seed latex is produced in a batch process in a suitable polymerization reactor, for example, in an autoclave equipped with a stirrer and a thermoregulation system. Water, an emulsifier, a buffer, a dispersant are charged to the reactor, and then monomers are fed. The resulting mixture with constant stirring is heated to 45-75 ° C, after which half of the calculated amount of initiator is loaded in the form of an aqueous solution. The polymerization is carried out to 55-65% of the conversion of monomers, and then the remaining amount of initiator is introduced and the reaction is brought to 100% conversion. The resulting dispersion is cooled to room temperature and used for the synthesis of basic, target latex. The seed latex is prepared either in a separate reactor or in situ in the same polymerization reactor in which the target latex is synthesized.

In order to obtain a basic latex, at least one protective colloid, initiator, activator and buffer are added to the seed latex in the polymerization reactor. A mixture of monomers is prepared in a separate reactor. The reactor is cooled to a temperature of 5 ° C. The content of diene and unsaturated acid in this mixture is 20% lower than the calculated value. In addition, in a separate container, a mixture of water, activator and emulsifier is prepared. At the first stage of the reaction, the autoclave containing water-soluble ingredients is heated to 30 ° C, after which a continuous supply of the monomer mixture is started, and an aqueous solution of emulsifier and activator is also fed in parallel for 5 hours. The reaction temperature is 40 ° C. 1 hour before the end of the filing of the first portion of the monomer mixture, the remaining monomers are fed in for 5 hours while dosing the activator and emulsifier solution in parallel. The reaction temperature in the reactor is maintained at 38-40 ° C, the process is carried out to a dry residue of 45% (99% conversion). The obtained latex after the introduction of ammonia to a pH value of 7.5 is freed from residual monomers by distillation on a rotary-film evaporator at a temperature of 55 ° C.

The present invention also relates to latex obtained by the method described above. Such latex is characterized, in particular, by a frost resistance temperature of -16 ° C.

In addition, another object of the present invention is the use of the said latex for the manufacture of products, for example, such as gloves, by dipping.

MODES FOR CARRYING OUT 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 pH pH was carried out on an ionomer EV-74.

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

4) The latex resistance to mechanical stress was determined using a Maron instrument. To this end, 75 ml of latex with a known dry residue was mixed at a speed of 1500 rpm in a narrow gap between the rotor and stator for 5 minutes. After the dynamic action ended, 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 in relation to the total polymer mass in the analyzed sample, was considered as a measure of the latex resistance to mechanical stress. Resistance to mechanical stress is defined as the amount of coagulum after treatment in a Maron device (Colloid chemistry of synthetic latexes: Textbook. / R.E. Neumann, OG Kiseleva, AK Egorov, TM Vasilieva. - Voronezh: VSU Publishing House, 1984.- 196 p.).

5) The appearance of the film was determined visually.

6) The determination of the mass fraction of volatile substances was determined according to GOST R 54546 (ASTM D 57745668 method C).

7) The content of residual nitrile of acrylic acid (NAC) is determined chromatographically according to TU 38.103578-85 p. 4.7.

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

9) Evaluation of frost resistance of latex was carried out according to the method described in the USSR copyright certificate No. 1328353.

10) Physico-mechanical properties of vulcanized latex films were determined according to DIN 53504.

The essence of the proposed technical solution is illustrated below by the examples of specific performance, which illustrate, but do not limit the scope of the claims of this invention. Specialists in this field will be clear that it is not limited only to them and the same effect can be achieved by applying equivalent formulas.

Example 1 (according to the invention)

Getting seed latex (stage 1)).

In a reactor equipped with a stirrer and a temperature-controlled jacket, serves 120 wt. parts of water, 3.5 wt. parts of an emulsifier - sodium lauryl sulfate, 0.03 wt. parts of the buffer - trilon B., 0.5 wt. parts of a dispersant based on naphthalenesulfonic acid (NF), then monomers and a molecular weight regulator, 42.5 wt. parts of styrene, 0.3 wt. parts of tertiary dodecyl mercaptan (TDM), and 2.5 wt. parts of methacrylic acid. After purging the reactor with nitrogen, 55.0 wt. parts of butadiene. The resulting mixture is heated to 64 ° C with stirring, after which half the calculated amount of the initiator is ammonium persulfate (0.03 wt. Parts) in the form of a 4.5% aqueous solution. The polymerization is carried out up to 65% of the conversion of monomers, then enter the remaining amount of initiator. The process is carried out up to 100% conversion of monomers. The resulting dispersion is cooled to room temperature and used to obtain the target latex.

Obtaining the target latex (stage 2).

The target latex is obtained in a 2 liter steel autoclave equipped with a stirrer and a temperature-controlled jacket. Seed latex, water, a protective colloid, which is a mixture of carboxymethyl cellulose (CMC) and dextrin, the initiator is tertiary butyl hydroperoxide, the activator is ferrous sulfate, and the buffer is disodium salt of ethylenediaminetetraacetic acid. In a separate reactor equipped with a stirrer and a temperature-controlled jacket, a mixture of monomers is prepared, consisting of nitrile of acrylic acid, methacrylic acid, into which, after the reactor is purged with nitrogen, butadiene is introduced. The reactor with monomers after loading all the ingredients is cooled to a temperature of 5 ° C. The content of butadiene and unsaturated acid in the resulting mixture is 20% lower than the calculated value. In addition, in a separate container, a mixture of water, an activator — sodium sulfoxylate (rongalite) and sodium alkylbenzenesulfonate emulsifier is prepared. In the first stage of the reaction, the autoclave containing water-soluble ingredients and the seed is heated to 30 ° C, after which the first monomer mixture is continuously fed into it, and an aqueous solution of emulsifier and activator is simultaneously fed for 5 hours. The polymerization temperature is 40 ° C. 1 hour before the end of the supply of the first part of the monomer mixture, start the flow of the second part of the monomer mixture. The second part of the mixture of monomers is served for 5 hours with parallel dosing of a mixture of solutions of activator and emulsifier. The temperature in the polymerizer is maintained at 38-40 ° C, the polymerization is carried out to a dry residue of 45% (99% conversion). The obtained latex after the introduction of ammonia until pH = 7.5 is freed from the residual monomers by distillation on a rotary-film evaporator at a temperature of 55 ° C.

Example 2

The polymerization is carried out analogously to example 1. As an additive, 0.5 wt. parts of low molecular weight CMC and 1.5 wt. parts of dextrin. The second part of the monomer mixture begins to be administered after 5 hours from the moment the first part of the monomer mixture is introduced. The results are presented in tables.

Example 3

The polymerization is carried out analogously to example 1. To obtain the seed latex, butadiene, methyl methacrylate (MMA), methacrylic and acrylic acids are used. As an additive, 0.5 wt. parts of low molecular weight CMC and 2.0 wt. parts of dextrin. The results are presented in tables.

Example 4

The polymerization is carried out analogously to example 1. To obtain the seed latex, nitrile of acrylic acid, butadiene and methacrylic acid are used. As an additive, 0.5 wt. parts of low molecular weight CMC and 2.5 wt. parts of dextrin. The results are presented in tables.

Example 5

The polymerization is carried out analogously to example 1. The second part of the mixture of monomers begin to be introduced into the reactor after 6 hours from the moment the introduction of the first part of the mixture. The results are presented in tables.

Example 6

The polymerization is carried out analogously to example 1. As the seed used latex obtained in example 4. The second part of the mixture of monomers begin to enter after 5 hours from the start of introduction of the first part of the mixture. The results are presented in tables.

Comparative example (prototype)

In a reactor equipped with a stirrer and a temperature-controlled jacket, load 1.5 wt. parts of seed latex with a particle size of 36 nm and 90.5 wt. parts of water, based on 100 wt. parts of monomers, including the seed, enter 5 wt. parts of degraded starch with a degree of destruction of 60%. After that, the reactor is purged with nitrogen and heated to 30 ° C. Then, 0.05 wt. parts of sodium dodecylbenzenesulfonate, 0.05 wt. parts of sodium salt of ethylenediaminetetraacetic acid (trilon B) 0.05 parts of rongalite, 0.005 wt. parts of ferrous sulfate and 0.08 parts of cumene hydroperoxide. A mixture of monomers is introduced into the resulting solution for 5 hours together with a molecular weight regulator, tertiary dodecyl mercaptan. 2.0 wt.% Are added over 10 hours. parts of sodium dodecylbenzenesulfonate, 0.2 wt. parts of sodium tetrapyrophosphate and 22 wt. parts of water. Over 14 hours add 0.13 may parts of the coactivator - sodium sulfoxylate formaldehyde in 8 wt. parts of water, and after 10 hours from the start of the supply of the coactivator, 0.04 wt. parts of tert-butyl hydroperoxide in 2 wt. parts of water. The polymerization is continued until 98% conversion is achieved, resulting in a total solids content of 45%. The polymerization is quickly stopped by the addition of 0.2 wt. parts of a 5% aqueous diethyl hydroxylamine solution. The pH value is adjusted with ammonia to pH 7.5 and the residual monomers are removed by vacuum distillation at 60 ° C.

List of abbreviations shown in table 1:

NAC - Acrylic Nitrile

MMA - Methyl Methacrylate

List of abbreviations shown in table 3:

CMC - carboxymethyl cellulose

NAC - Acrylic Nitrile

MAK - methacrylic acid

TDM - Tertiary Dodecyl Mercaptan

GTB - tertiary butyl hydroperoxide

DEGA - diethylhydroxylamine

As can be seen from the presented experimental data, the inventive method allows to obtain polymer particles with a shell having a lower glass transition temperature compared to the glass transition temperature of the inner part of the particle, which, on the one hand, facilitates their coalescence upon receipt of the film by plasticizing the surface of the particles, and another unexpectedly improves the frost resistance of latex. In addition, the latex obtained according to the present method has improved frost resistance compared to latexes synthesized without the use of protective colloids; it is characterized by increased resistance to the introduction of vulcanizing agents (when the mixture ripens and mixes, coagulum does not form) and improved film-forming properties. In particular, films made by casting on cellophane have no visual defects, and, in addition, there are no defects in the preparation of a film by coagulant dipping. In addition, the latex samples obtained in accordance with the claimed method have high resistance to mechanical stresses, as well as high stability to freeze / thaw, which ensures the maintenance of operational properties even after complete freezing of the latex at the indicated temperature. This is a very important positive aspect of the invention, since, as a rule, latexes that do not contain special additives are prone to complete or partial coagulation after exposure to temperatures below -3.5 ° C, which complicates the delivery of latexes to the final consumer in the winter season. In addition, unlike the prototype, the proposed method eliminates the stage of monopolymerisation of monomers when, to bind residual monomers (NAC) and volatile components, an additional supply of hydroperoxide is used at the end of the polymerization reaction, causing additional polymer crosslinking and loss of latex film elasticity.

Thus, it is shown that the developed method for producing latex allows to obtain a product with high resistance to mechanical stresses even after the introduction of vulcanizing agents, to reduce the risk of film defects during ion deposition, to achieve high physicomechanical properties of the vulcanized film, and also to obtain latex resistant to exposure to freezing temperatures.

Claims (31)

1. The method of producing latex in semi-periodic mode, comprising the following stages: 1) obtaining seed latex; 2) adding to the seed water latex, at least one protective colloid, the initiating system, part of the main mixture of monomers containing 80-85 wt. % conjugated diene and carboxylating agent of their total amount in the composition of the main mixture, and 100 wt. % vinyl monomer, selected from vinyl esters, nitriles and aryl olefins, of the total amount of this monomer in the composition of the main mixture, and, simultaneously with the monomers, the introduction of a molecular weight regulator, emulsifier and polymerization activator; 3) the introduction into the reaction zone of the remaining 15-20 wt. % of the monomers of the main mixture 45-75 minutes before the end of dosing of the main part of the mixture of monomers. 2. The method according to p. 1, characterized in that the seed latex is characterized by a particle size of 10-90 nm. 3. The method according to p. 2, characterized in that the particles of the seed latex have a size of from 20 to 80 nm. 4. The method according to p. 2, characterized in that the particles of the seed latex have a size of 30-80 nm. 5. The method according to p. 1, characterized in that the seed latex is synthesized in the reaction zone in situ or pre-synthesized, and then fed to the reaction zone. 6. The method according to p. 1, characterized in that the seed latex is used in an amount of from 0.01 to 15 wt. parts per 100 wt. parts of the main mixture of monomers. 7. The method according to p. 6, characterized in that from 0.1 to 10 wt. parts of seed latex per 100 wt. parts of the main mixture of monomers. 8. The method according to p. 6, characterized in that the seed latex is used in an amount of from 1 to 5 wt. parts per 100 wt. parts of the main mixture of monomers. 9. The method according to p. 1, characterized in that to obtain the seed latex used the same monomers as for the main synthesis, or different from them. 10. The method according to p. 1, characterized in that as the monomers that can be used to obtain the seed latex, use the vinyl monomer as the only monomer or in a mixture with other vinyl monomers or conjugated dienes. 11. The method according to p. 10, characterized in that the vinyl monomers are selected from nitriles, aromatic vinyl compounds, acrylic carboxylates, ethylenically unsaturated amides, vinyl carboxylates, ethylenically unsaturated amines. 12. The method according to p. 10, characterized in that 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene and 2-methyl-1,3-butadiene are used as conjugated dienes. 13. The method according to p. 10, characterized in that upon receipt of the seed latex, ethylenically unsaturated acids are used as vinyl row monomers. 14. The method according to p. 10, characterized in that the seed latex is a latex based on polystyrene copolymers, polybutadiene copolymers, a carboxylated copolymer latex based on acrylonitrile, styrene or methyl methacrylate. 15. The method according to p. 1, characterized in that the mixture of monomers contains conjugated dienes and monomers of the vinyl aryl series. 16. The method according to p. 15, characterized in that the conjugated dienes are selected from the group of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, piperylene, 2-methyl-3-ethyl-1,3 -butadiene, 3-methyl-1,3-pentadiene, 2-methyl-3-ethyl-1,3-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-1,3-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. 17. The method according to p. 15, characterized in that the conjugated diene is selected from 1,3-butadiene, isoprene and piperylene. 18. The method according to p. 15, characterized in that the most preferred conjugated diene is 1,3-butadiene. 19. The method according to p. 1, characterized in that the content of the conjugated diene in the composition of the main mixture of monomers is from 35 wt. % to 80 wt. % 20. The method according to p. 1, characterized in that the content of the vinyl monomer in the composition of the main mixture of monomers is from 15 wt. % up to 45 wt. % 21. The method according to p. 1, characterized in that the carboxylating agent is selected from the group of ethylenically unsaturated carboxylic acids. 22. The method according to p. 21, characterized in that the carboxylating agent is selected from acrylic, methacrylic, fumaric and itaconic acids. 23. The method according to p. 1, characterized in that the content of carboxylating agent in the composition of the main mixture of monomers is from 1 to 10 wt. % 24. The method according to p. 1, characterized in that these protective colloids are optionally used in combination with surfactants. 25. The method according to p. 1, characterized in that the amount of protective colloid is approximately from 0.005 to 5.0 wt. % of the total amount of monomers in the reaction mixture. 26. Latex for the manufacture of products by immersion dipping, obtained by the method according to paragraphs. 1-25. 27. Latex according to claim 26, characterized by a temperature of frost resistance up to -16 ° C. 28. The use of latex in paragraphs. 26, 27, as a material for the manufacture of products by immersion dipping.