JP6477012B2 - Method for producing polymer latex - Google Patents

Description

  The present invention relates to a method for producing a polymer latex capable of suppressing foaming when recovering unreacted monomers in the production process of the polymer latex.

  In the method for producing a polymer latex, an antifoaming agent is added to the polymer latex in order to suppress foaming of the polymer latex when the unreacted monomer in the polymer latex is recovered by heating. For example, in patent document 1 (Unexamined-Japanese-Patent No. 2003-48917), defoamers, such as fatty acid ester, phosphate ester, metal soap, and silicone, are used.

  Generally, the defoaming effect by an antifoamer fully expresses in a high temperature region of 50 ° C. or higher. On the other hand, in the low temperature region below 20 ° C., the antifoaming effect by the antifoaming agent may not be sufficiently exhibited. As a result, even when the antifoaming agent is used, the temperature at which the unreacted monomer is recovered is low. There was a possibility that the polymer latex foamed and the droplets blocked the monomer recovery line. In addition, the productivity of the polymer latex may be reduced due to the necessity of interrupting the monomer recovery operation until the foaming stops. When unreacted monomer remains in the polymer latex, a viewpoint of eliminating waste of raw materials (for example, reusing the unreacted monomer) and an environmental hygiene viewpoint (for example, removing an odor caused by the unreacted monomer) Etc.).

  Further, in order to sufficiently exhibit the antifoaming effect in the low temperature region, the defoaming effect can be obtained by increasing the addition amount of the antifoaming agent, but the polymers in the polymer latex aggregate to each other, and the polymer aggregate is It sometimes occurred. When the polymer aggregates adhere to the wall surface in the production container, there is a possibility that the aggregates become foreign matters and enter the product. Therefore, it is necessary to frequently clean the container, which has been a cause of reducing the productivity of the polymer latex.

Japanese Patent Laid-Open No. 2003-48917

  The present invention has been made in view of the above-described prior art, and is a polymer latex capable of suppressing foaming in an unreacted monomer recovery step even in a low temperature region and suppressing the generation of polymer aggregates. The object is to provide a manufacturing method.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by using a specific amount of a specific antifoaming agent, and based on this finding, the present invention has been completed. .

The gist of the present invention for solving the above problems is as follows.
[1] A method for producing a polymer latex comprising a step of obtaining a mixture containing a polymer latex and an unreacted monomer by emulsion polymerization, and a step of recovering the unreacted monomer from the mixture,
The mixture in the step of recovering the unreacted monomer contains 0.01 parts by mass or more and 0.1 parts by mass or less of a self-emulsifying antifoaming agent having a cloud point of 10 ° C. or less with respect to 100 parts by mass of the polymer in the mixture. A method for producing a polymer latex.

[2] The method for producing a polymer latex according to [1], wherein in the step of recovering the unreacted monomer, the temperature of the mixture is raised from a temperature range of less than 20 ° C.

[3] The method for producing a polymer latex according to [1] or [2], wherein the self-emulsifying antifoaming agent includes a polyoxyether ester structure.

  According to the method for producing a polymer latex according to the present invention, by using a predetermined amount of a specific antifoaming agent, foaming in the unreacted monomer recovery step can be suppressed even in a low temperature region, and the productivity of the polymer latex can be reduced. Excellent. Moreover, since generation | occurrence | production of the polymer aggregate can be suppressed, the frequency of washing | cleaning for removing the aggregate adhering to the wall surface in a manufacturing container can be decreased.

  The method for producing a polymer latex according to the present invention includes a step of obtaining a mixture containing a polymer latex and an unreacted monomer by emulsion polymerization, and a step of recovering the unreacted monomer from the mixture. The mixture in the step of recovering contains 0.01 part by mass or more and 0.1 part by mass or less of a self-emulsifying antifoaming agent having a cloud point of 10 ° C. or less with respect to 100 parts by mass of the polymer in the mixture.

Step of obtaining a mixture containing polymer latex and unreacted monomer by emulsion polymerization (Step 1)
In the present invention, the mixture containing the polymer latex obtained by emulsion polymerization and the unreacted monomer is not particularly limited. Examples of the polymer latex include diene polymer aqueous dispersions, acrylic polymer aqueous dispersions, fluorine polymer aqueous dispersions, and silicone polymer aqueous dispersions. Moreover, the unreacted monomer in this invention means the monomer which remained in the system, without reacting among the raw material monomers used in order to obtain polymer latex.

The diene polymer aqueous dispersion is an aqueous dispersion of a polymer (diene polymer) containing a monomer unit obtained by polymerizing a conjugated diene such as butadiene or isoprene. The ratio of the monomer unit obtained by polymerizing the conjugated diene in the diene polymer is preferably 40% by mass or more, more preferably 50% by mass or more, and further preferably 60% by mass or more.
In the present invention, the monomer unit means a structural unit in a polymer formed by polymerizing the monomer.

  Diene polymers include conjugated diene homopolymers; copolymers of different types of conjugated dienes; copolymers with other monomers copolymerizable with conjugated dienes; and their hydrogenated products. Can be mentioned.

  Examples of the conjugated diene include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, and 2-chloro-1. 1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 2,4-hexadiene, and the like.

  Examples of the other copolymerizable monomers include α, β-unsaturated nitrile compounds such as (meth) acrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile; (meth) acrylic acid, itaconic acid, fumaric acid, etc. Unsaturated carboxylic acids: aromatics such as styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, divinylbenzene Vinyl monomers; olefins such as ethylene and propylene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; methyl vinyl ether, ethyl Vinyl ether, butyl vinyl Vinyl ethers such as ruether; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocycle-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole; (Meth) acrylic acid ester compounds such as methyl acrylate; hydroxyalkyl group-containing compounds such as β-hydroxyethyl (meth) acrylate; (meth) acrylamide, N-methylol (meth) acrylamide, acrylamide-2-methylpropane Examples include amide monomers such as sulfonic acid. In addition, the conjugated diene and the other copolymerizable monomer may each be used alone or in combination of two or more at any ratio. Moreover, in this specification, (meth) acryl includes both acryl and methacryl.

  Specific examples of the diene polymer include styrene / butadiene copolymer (SBR), styrene / isoprene copolymer (SIR), isobutylene / isoprene copolymer (butyl rubber), ethylene / propylene / diene copolymer, acrylonitrile. -Butadiene copolymer (NBR), hydrogenated SBR, hydrogenated NBR and the like. These polymers can be used alone or in combination of two or more.

The acrylic polymer aqueous dispersion is a general formula (1): CH ₂ = CR ¹ -COOR ² (wherein R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkyl group or a cycloalkyl group). Is an aqueous dispersion of a polymer (acrylic polymer) containing a monomer unit derived from a compound represented by (hereinafter sometimes referred to as “(meth) acrylic ester compound”). The ratio of the monomer unit derived from the (meth) acrylic acid ester compound in the acrylic polymer is preferably 40% by mass or more, more preferably 50% by mass or more, and further preferably 60% by mass or more.

  Specific examples of the (meth) acrylic acid ester compound include ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, T-butyl (meth) acrylate, n-amyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, Examples include stearyl (meth) acrylate.

  Acrylic polymers include homopolymers of (meth) acrylic acid ester compounds; copolymers of different types of (meth) acrylic acid ester compounds; other monomers copolymerizable with (meth) acrylic acid ester compounds. And a copolymer with a monomer. These polymers can be used alone or in combination of two or more.

  Examples of the other copolymerizable monomers include α, β-unsaturated nitrile compounds such as (meth) acrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile; (meth) acrylic acid, itaconic acid, fumaric acid, etc. Unsaturated carboxylic acids; carboxylic acid esters having two or more carbon-carbon double bonds such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate; Unsaturated esters containing fluorine in the side chain such as octylethyl (meth) acrylate; styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxy Methyl Stille , Α-methylstyrene, aromatic vinyl monomers such as divinylbenzene; amide monomers such as (meth) acrylamide, N-methylol (meth) acrylamide, acrylamide-2-methylpropanesulfonic acid; ethylene, propylene, etc. Olefins; diene monomers such as butadiene and isoprene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; Vinyl ethers such as ethyl vinyl ether and butyl vinyl ether; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl vinyl ketone; N-vinyl pyrrolidone, vinyl pyridine and vinyl imi Heterocycle-containing vinyl compounds such as tetrazole; glycidyl ethers such as allyl glycidyl ether; and glycidyl esters such as glycidyl (meth) acrylate. In addition, the compound represented by General formula (1) and the other monomer which can be copolymerized may be used individually by 1 type, respectively, and may combine 2 or more types by arbitrary ratios, respectively.

  The fluorine-based polymer aqueous dispersion is an aqueous dispersion of a polymer (a fluorine-based polymer) containing a monomer unit obtained by polymerizing a fluorine-containing monomer. The ratio of the monomer unit obtained by polymerizing the fluorine-containing monomer in the fluoropolymer is preferably 70% by mass or more, more preferably 80% by mass or more.

  Fluoropolymers include homopolymers of fluorine-containing monomers; copolymers of different types of fluorine-containing monomers; copolymerization with other monomers copolymerizable with fluorine-containing monomers Examples include coalescence.

  Examples of the fluorine-containing monomer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, vinyl trifluoride chloride, vinyl fluoride, and perfluoroalkyl vinyl ether.

  Examples of the other copolymerizable monomers include olefins such as ethylene, propylene, and 1-butene; aromatic vinyl monomers such as styrene, α-methylstyrene, t-butylstyrene, vinyltoluene, and chlorostyrene. Α, β-unsaturated nitrile compounds such as (meth) acrylonitrile; (meth) acrylic acid ester compounds such as methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate; ) Amide monomers such as acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide; Unsaturated carboxylic acids such as (meth) acrylic acid, itaconic acid, fumaric acid, crotonic acid and maleic acid ; Contains epoxy groups such as allyl glycidyl ether and glycidyl (meth) acrylate Unsaturated compound; amino group-containing unsaturated compound such as (meth) acryldimethylaminoethyl, diethylaminoethyl (meth) acrylate; sulfonic acid group-containing unsaturation such as styrene sulfonic acid, vinyl sulfonic acid, (meth) allyl sulfonic acid Saturated compound; sulfate group-containing unsaturated compound such as 3-allyloxy-2-hydroxypropanesulfuric acid; phosphate group such as (meth) acrylic acid-3-chloro-2-phosphate, 3-allyloxy-2-hydroxypropanephosphate And unsaturated compounds.

  Specific examples of the fluoropolymer include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Examples thereof include polyvinyl fluoride and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. These polymers can be used alone or in combination of two or more.

  The silicone polymer aqueous dispersion is an aqueous dispersion of a silicone polymer such as silicone rubber, fluorosilicone rubber, and polyimide silicone.

  The mixture containing the polymer latex and the unreacted monomer in the present invention can be obtained, for example, by mixing the above monomers and emulsion polymerization in water. The method for mixing the monomers is not particularly limited, and examples thereof include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type. In addition, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used. The method for emulsion polymerization is not particularly limited, and a conventionally known emulsion polymerization method may be employed.

  Examples of the polymerization initiator used for emulsion polymerization include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; t-butyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide Organic peroxides such as oxide and t-butylperoxyisobutyrate; azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, methyl azobisisobutyrate, etc. Is . These polymerization initiators can be used alone or in combination of two or more. The peroxide initiator can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium bisulfite.

  Moreover, you may use a molecular weight modifier at the time of emulsion polymerization. Examples of molecular weight modifiers include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan; dimethylxanthogen disulfide, diisopropylxanthogendi Xanthogen compounds such as sulfides; thiuram compounds such as terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide; phenols such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol Compounds; allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane and carbon tetrabromide; thioglycolic acid Thiomalate, 2-ethylhexyl thioglycolate, diphenylethylene, etc. α- methylstyrene dimer. These molecular weight modifiers can be used alone or in combination of two or more.

  The surfactant used for the emulsion polymerization is not particularly limited, and may be any of an anionic surfactant, a nonionic surfactant, and a cationic surfactant. These surfactants may be used individually by 1 type, and may be used in combination of 2 or more type.

  Specific examples of anionic surfactants include fatty acid salts such as sodium myristate, potassium palmitate, sodium oleate, and potassium linolenate; alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate; higher alcohol sulfates; alkyls Examples thereof include sulfosuccinate; rosinate and the like.

  Specific examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ether, polyoxyethylene alkyl ester, polyoxyethylene sorbitan alkyl ester, and the like.

  Specific examples of the cationic surfactant include alkyltrimethylammonium chloride, dialkylammonium chloride, and benzylammonium chloride.

  Further, in the emulsion polymerization, pH adjusters such as sodium hydroxide and ammonia; various additives such as a dispersant, a chelating agent, an oxygen scavenger, a builder, and a stabilizer can be appropriately used.

  The polymerization temperature for carrying out the polymerization reaction is not particularly limited, but is usually 0 ° C. or higher, preferably 1 ° C. or higher, more preferably 3 ° C. or higher, and usually 100 ° C. or lower, preferably 50 ° C. or lower, more preferably Less than 20 ° C, more preferably 10 ° C or less, particularly preferably 7 ° C or less. Emulsion polymerization is performed in such a temperature range, and the polymerization reaction is stopped at a predetermined polymerization conversion rate by adding a polymerization terminator or cooling the polymerization system. The polymerization conversion rate when stopping the polymerization reaction is preferably 90% by mass or more, more preferably 95% by mass or more, based on the total monomers used for the polymerization.

  The content of the unreacted monomer in the mixture containing the polymer latex and the unreacted monomer is preferably 40% by mass or less, more preferably 35% by mass or less, and particularly preferably 25% by mass or less with respect to the polymer in the mixture. Usually, it is 1% by mass or more. According to the method for producing a polymer latex according to the present invention, even if the content of the unreacted monomer after the polymerization reaction is within the above range, the unreacted monomer can be sufficiently recovered by the following step 2. Recovering unreacted monomers is a way to eliminate waste of raw materials (for example, reusing unreacted monomers) and from an environmental hygiene viewpoint (for example, odor of polymer latex caused by unreacted monomers) Etc.).

Step of recovering unreacted monomer from the mixture containing polymer latex and unreacted monomer (Step 2)
In the step of recovering unreacted monomers from the mixture obtained in Step 1 (Step 2), a predetermined amount of a self-emulsifying antifoaming agent having a cloud point of 10 ° C. or lower is added to the mixture. Thus, the mixture obtained by the process 1 is 0.01 mass part or more and 0.1 mass part or less of self-emulsification type | mold antifoamers with a cloud point of 10 degrees C or less with respect to 100 mass parts of polymers in a mixture. Will be included.
When the content of the self-emulsifying antifoaming agent is small, the mixture foams when the unreacted monomer is recovered, and the unreacted monomer cannot be sufficiently recovered, so that the productivity of the polymer latex is lowered. On the other hand, when there is much content of a self-emulsification type antifoamer, the polymers in polymer latex will aggregate. As a result, polymer agglomerates may adhere to the wall surface in the production container, and the agglomerates may become foreign matter and be mixed into the product. Therefore, it is necessary to frequently clean the container, which decreases the productivity of the polymer latex. Further, when forming a polymer latex, it is difficult to obtain a uniform film and the film forming property is poor. By setting the content of the self-emulsifying antifoaming agent in the mixture obtained in step 1 within a predetermined range, foaming of the mixture in the step of recovering unreacted monomers is suppressed, and the polymer at the time of producing the polymer latex The generation of aggregates can be suppressed. Moreover, when film-forming polymer latex, it is easy to obtain a uniform film and is excellent in film forming property.
From such a point of view, the content of the self-emulsifying antifoaming agent is preferably 0.02 parts by mass or more, more preferably 0.03 parts by mass or more, preferably 0.003 parts by mass with respect to 100 parts by mass of the polymer. 07 parts by mass or less, more preferably 0.05 parts by mass or less.

  The self-emulsifying antifoaming agent in the present invention is a solution in which 0.1 g of antifoaming agent is dropped into 99.9 g of distilled water and allowed to stand at 25 ° C. for 24 hours. And what is cloudy. In addition, in the antifoamer which does not correspond to a self-emulsification type antifoamer, for example, an oil type antifoamer, an antifoamer does not disperse | distribute to the whole distilled water, but stays on the liquid level or bottom face of distilled water.

  Among the self-emulsifying antifoaming agents defined as described above, those having a cloud point of 10 ° C. or lower are used in the present invention. When the cloud point of the self-emulsifying antifoaming agent exceeds 10 ° C., sufficient antifoaming effect when the step of recovering unreacted monomer from the mixture obtained in Step 1 is performed in a low temperature region (for example, less than 20 ° C.). Can't get. In the present invention, by setting the cloud point of the self-emulsifying antifoaming agent to 10 ° C. or less, the defoaming effect in the unreacted monomer recovery step can be achieved in a wide range from a low temperature region to a high temperature region (for example, 50 ° C. or more). Can be obtained. From such a viewpoint, the cloud point of the self-emulsifying antifoaming agent is preferably 8 ° C. or lower, more preferably 0 ° C. or lower, further preferably −4 ° C. or lower, and particularly preferably −5 ° C. or lower. From the viewpoint of obtaining the defoaming effect in a wide temperature range, the lower limit of the cloud point of the self-emulsifying antifoaming agent is not limited. In addition, the measuring method of a cloud point is mentioned later. In Table 1, the case where the cloud point cannot be measured by the cloud point measurement method described later is represented as “−5 ° C. or lower”. In this case, it can confirm that it has a cloud point by making the density | concentration of a self-emulsification type antifoamer high.

  Moreover, the chemical structure of the self-emulsifying antifoaming agent in the present invention is not particularly limited. Examples of the chemical structure of the self-emulsifying antifoaming agent include a polyoxyether structure and a polyoxyether / ester structure. Among these, it is preferable that the self-emulsifying antifoaming agent includes a polyoxyether ester structure. The defoaming effect can be enhanced by the self-emulsifying antifoaming agent containing a polyoxyether / ester structure.

  Examples of such a self-emulsifying type antifoaming agent include polyoxyethylene alkyl ester, polyoxyethylene sorbitan alkyl ester, and the like, for example, commercially available Drewplus 49000GP, Drewplus 4005 (manufactured by Ashland) can be used. . These self-emulsifying antifoaming agents can be used singly or in combination of two or more in any ratio. The cloud point can be controlled by combining these self-emulsifying antifoaming agents.

  The unreacted monomer recovery step includes, for example, a step of sucking the unreacted monomer recovery line connected to a container in which a mixture containing the polymer latex and the unreacted monomer is stored under reduced pressure, and from the liquid level of the mixture. A step of detecting the height of the foamed layer to be generated, and a self-emulsifying antifoaming agent in an amount changed according to the ratio of the detected height of the foamed layer to the allowable height of the foamed layer (foamed layer ratio) It is preferable to have the process of supplying.

  The change in the supply amount of the self-emulsifying antifoaming agent according to the foam layer ratio is preferably a continuous or multi-stage change. It is preferable to make the change to increase the amount.

  In Step 2 of the present invention, the method of changing the supply amount of the self-emulsifying antifoaming agent is not particularly limited, and examples thereof include a method of changing the supply rate of the self-emulsifying antifoaming agent.

  As a method for changing the supply speed of the self-emulsifying antifoaming agent, for example, (1) the antifoaming agent is sucked into the container side at a predetermined pressure inside the antifoaming agent supply line connected to the upper part of the container. A method of changing the degree of opening of the control valve, which is adjustable on the supply line, or (2) provided on the defoamer supply line and sucking the defoamer supply line toward the container Examples include a method of changing the suction capacity of the defoamer supply metering pump for supplying the antifoaming agent, that is, changing the defoamer supply capacity into the container by changing the stroke of the defoamer metering pump. It is done. Of these, the latter method is preferred.

  In the case of changing the opening degree of the control valve provided on the antifoaming agent supply line in (1), the opening degree of the control valve is increased as the foam layer ratio increases, and the foam layer ratio decreases. Preferably, the control valve is controlled so as to reduce the opening degree. When the opening of the control valve is increased while the inside of the defoamer supply line is sucked into the container at a predetermined pressure, the defoamer supply speed increases and the defoamer supply rate increases. If the opening degree of the control valve is decreased, the supply speed of the antifoaming agent into the container is decreased and the supply amount of the antifoaming agent is reduced.

  In the case of changing the stroke of the defoamer supply metering pump provided on the defoamer supply line of (2), as the foam layer ratio increases, the stroke increases, and as the foam layer ratio decreases, It is preferable to control to reduce the stroke. If the stroke of the defoamer supply metering pump is increased while the opening of the control valve provided on the defoamer supply line is fully open, the defoamer supply rate into the container will increase and disappear. When the supply amount of the foaming agent increases and the stroke is decreased, the supply rate of the antifoaming agent into the container becomes slow and the supply amount of the antifoaming agent decreases.

  Further, as a method of changing the supply amount of the self-emulsifying antifoaming agent without changing the supply rate of the self-emulsifying antifoaming agent, a relatively excessive supply rate (for example, 100 mass of the polymer in the polymer latex). For example, a method of intermittently changing the supply time of the defoamer supply metering pump set to 0.5 to 5 parts by mass / hour). For example, with respect to a supply command for 5 seconds, a supply command for 20 seconds is a supply amount per unit time longer than the supply command time, which is four times the supply amount. It is also possible to control the supply speed and supply time of the self-emulsifying antifoaming agent in parallel.

  The allowable height of the foam layer is at the nozzle position of the unreacted monomer recovery line connected to the container or above the liquid level of the stored mixture (polymer latex containing unreacted monomer). Arbitrary positions can be set. Specifically, the allowable height of the foamed layer is preferably 50 to 100, more preferably 80 to 100, when the height from the liquid level of the stored mixture to the nozzle position of the recovery line is 100. Particularly preferred is a height corresponding to 90-100.

  The outlet shape of the defoamer supply line into the container is not particularly limited, and may be a shape in which the nozzle protrudes into the container, or the self-emulsifying antifoaming agent is sprayed into the container. You may have a shape.

  The attachment position of the defoaming agent supply line is not particularly limited, but it is preferable to attach it at a position above the position set as the allowable height of the foamed layer.

  The supply method of the self-emulsifying antifoaming agent may be continuous or intermittent. The self-emulsifying antifoaming agent does not need to be continuously supplied, and once the self-emulsifying antifoaming agent is supplied, the height of the foam layer is lowered. Then, the self-emulsifying antifoaming agent may be supplied when the height of the foam layer rises again thereafter. Of course, it may be a method in which a small amount is continuously supplied to maintain equilibrium.

  The container only needs to have a strength enough to withstand vacuum suction, and may be a pressure resistant container. If there is a sufficient empty volume, the polymerization can in which the mixture containing the polymer latex and the unreacted monomer is produced may be used as a container for recovering the unreacted monomer as it is after the polymerization reaction. The capacity of the container is preferably about 1.3 to 3 times the capacity of the mixture stored in the container, and more preferably about 1.5 to 2.5 times.

  The recovery of the unreacted monomer is preferably performed while stirring the stored mixture by stirring means such as a stirring blade provided in the container. As a stirring condition, a condition that does not promote the growth of the foamed layer by stirring may be appropriately selected.

  It is preferable that the unreacted monomer recovery line is connected to a position as high as possible on the upper surface of the container.

  The means (foaming level detecting means) for detecting the height of the foamed layer generated from the liquid level of the mixture is preferably provided above the position of the permissible height of the foamed layer, and the nozzle of the unreacted monomer recovery line More preferably above the position.

  In step 2 of the present invention, it is preferable to raise the temperature of the mixture stored in the container from a temperature range of less than 20 ° C. The temperature region (low temperature region) of less than 20 ° C. is preferably 1 ° C. or more, more preferably 3 ° C. or more, preferably less than 20 ° C., more preferably 15 ° C. or less, still more preferably 10 ° C. or less, particularly preferably. It is 7 degrees C or less. In Step 2, it is preferable to heat the mixture to a temperature region (high temperature region) of 50 ° C. or higher after the low temperature region. The high temperature region is preferably 60 ° C. or higher, more preferably 65 ° C. or higher, preferably 90 ° C. or lower, more preferably 80 ° C. or lower. In the method for producing a polymer latex of the present invention, a self-emulsification type antifoaming agent having a cloud point of 10 ° C. or lower is used, and therefore, a process for recovering unreacted monomers in a wide temperature range from a low temperature range to a high temperature range. It is possible to obtain a sufficient defoaming effect. The degree of vacuum in the unreacted monomer recovery step is set so that the pressure in the container (pressure reduction) is preferably −67 kPa or less, more preferably −80 kPa or less. By setting the degree of vacuum to a predetermined value or less, the unreacted monomer can be efficiently recovered.

  As the temperature adjusting means for raising the temperature of the mixture in step 2, for example, a steam blowing line connected to the lower part of the container, a jacket capable of supplying a heat medium, or the like is used.

  By the above steps, unreacted monomers are removed from the mixture, and a polymer latex with reduced unreacted monomers can be obtained. In addition, as for polymer latex, you may adjust pH and solid content concentration as needed. Moreover, you may add a well-known dispersing agent, a thickener, anti-aging agent, antiseptic | preservative, an antibacterial agent, an anti-blister agent etc. to polymer latex as needed. Furthermore, you may add well-known antifoaming agents (henceforth "other antifoaming agents") other than a self-emulsification type antifoaming agent in the range which does not prevent the effect of this invention. Examples of other antifoaming agents include oil type antifoaming agents.

  The solid content concentration of the polymer latex thus produced is preferably 10 to 60% by mass, more preferably 30 to 55% by mass. The polymer latex may contain residual monomers that cannot be recovered by the production method of the present invention, but its concentration is, for example, about 10 to 5000 ppm, from the viewpoint of eliminating waste of raw materials and from the viewpoint of environmental hygiene. Is considered to be no problem.

  Polymer latex is, for example, organic pigments, light scattering agents, light scattering aids in coatings such as paper, fiber and leather, paints, etc .; thermal insulation layers for thermal printer paper, thermal transfer printer paper and thermal paper undercoat Glove, sealing material, belt, etc.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, unless otherwise indicated, the part and% in a present Example are a mass reference | standard.

Example 1
A polymerization reactor was charged with 5 parts of a surfactant (sodium dodecylbenzenesulfonate aqueous solution having a solid content of 10%), 0.1 part of a stabilizer (sodium sulfate) and 150 parts of water, and this was mixed with 39 parts of raw material monomer (acrylonitrile). , 1,3-butadiene 61 parts) and a molecular weight modifier (t-dodecyl mercaptan) 0.5 part, and in the presence of 0.1 part of a polymerization initiator (cumene hydroperoxide) at 5 ° C. Emulsion polymerization was started.
After the polymerization reaction for 16 hours, 0.1 part of a polymerization terminator (2,2,6,6-tetramethylpiperidine-1-oxyl) is added to terminate the polymerization, and contains a polymer latex and an unreacted monomer. A mixture (solid content concentration 30%) was obtained. At this time, the content of the unreacted monomer was 17.6% with respect to the polymer in the polymer latex.

<Defoaming evaluation>
200 g of a mixture containing a polymer latex and an unreacted monomer kept at 60 ° C. (solid content concentration: 30%) was poured from a height of 60 cm on the floor to a graduated cylinder placed on the floor, and whipped constantly. The time at which the mixture was put into the graduated cylinder was set to 0 seconds, and by 15 seconds, 3.6 g of a 0.5% aqueous solution of self-emulsifying antifoaming agent 1 (Drewplus 49000GP, manufactured by ASHLAND) was A self-emulsifying type antifoaming agent equivalent to 0.03 part per 100 parts of the coalesced) was put in along the circumference of the inner wall of the graduated cylinder. Then, the bubble height was read and recorded over time until after 300 seconds. The same operation was performed when the temperature of the mixture was 10 ° C. In addition, the measuring cylinder used what was made into the same temperature as measurement temperature previously.
The bubble height for each elapsed time was plotted on a graph, and the defoaming rate was calculated from the slope when approximated by a linear function. The larger the defoaming speed, the better the defoaming effect.

<Repel evaluation>
Self-emulsifying antifoaming agent 1 (Drewplus 49000GP, manufactured by Ashland) was added to a mixture containing the obtained polymer latex and unreacted monomer (solid concentration 30%) with respect to 100 parts of the polymer in the polymer latex. 0.03 part equivalent was added, and the temperature of the mixture was raised from 5 ° C. (temperature at the end of polymerization) to 30 ° C., and the pressure was reduced to −67 kPa to recover unreacted monomers that were easy to recover. The residual monomer concentration after recovering the unreacted monomer was 3000 ppm with respect to the polymer in the polymer latex.
2 g of the polymer latex after recovery of the unreacted monomer was placed on an OHP film (VF-10, manufactured by KOKUYO Co., Ltd.) and stretched into a film shape with a wire bar to prepare a polymer latex wet film. The wet film had a thickness of 83 μm.
The number of repellants that were created immediately after the wire bar was pulled and after 10 seconds was counted. The same operation was performed 3 times, the total number of repels was determined, and repelling was evaluated according to the following criteria. The smaller the repellency, the less likely the agglomerates are produced during the production of the polymer latex, and the better the film formability of the polymer latex.
In addition, repellency is a region where the polymer in the polymer latex appears to aggregate when the film is formed, and the ratio of the polymer is reduced. Usually, the color of the formed film (for example, white) becomes light. This can be confirmed.
A: No repelling occurs.
B: 1 to 3 repels are generated.
C: Four or more repellencies are generated.

<Measurement of cloud point>
A 0.1% by mass aqueous solution of a self-emulsifying antifoaming agent was prepared, and the cloud point of the self-emulsifying antifoaming agent was measured according to JIS K2269 (1987).

(Example 2)
Each evaluation was performed in the same manner as in Example 1 except that the amount of the self-emulsifying antifoaming agent 1 added was equivalent to 0.01 part with respect to 100 parts of the polymer in the polymer latex.

(Example 3)
Each evaluation was performed in the same manner as in Example 1 except that the amount of the self-emulsifying antifoaming agent 1 was changed to 0.04 part with respect to 100 parts of the polymer in the polymer latex.

Example 4
Each evaluation was performed in the same manner as in Example 1 except that the amount of the self-emulsifying antifoaming agent 1 was set to 0.08 parts with respect to 100 parts of the polymer in the polymer latex.

(Example 5)
Each evaluation was performed in the same manner as in Example 1 except that instead of the self-emulsifying antifoaming agent 1, the self-emulsifying antifoaming agent 2 (mixture of Drewplus 49000GP and Drewplus 4005) was used. In addition, the mass ratio (Drewplus 49000GP: Drewplus4005) of Drewplus49000GP and Drewplus4005 in the self-emulsification type antifoaming agent 2 was 1: 1.

(Example 6)
Each evaluation was performed in the same manner as in Example 5 except that the addition amount of the self-emulsifying antifoaming agent 2 was equivalent to 0.01 part with respect to 100 parts of the polymer in the polymer latex.

(Example 7)
Each evaluation was performed in the same manner as in Example 1 except that instead of the self-emulsifying antifoaming agent 1, the self-emulsifying antifoaming agent 3 (mixture of Drewplus 49000GP and Drewplus 4005) was used. In addition, the mass ratio (Drewplus 49000GP: Drewplus4005) of Drewplus49000GP and Drewplus4005 in the self-emulsification type antifoaming agent 3 was 3: 7.

(Example 8)
Each evaluation was performed in the same manner as in Example 5 except that the addition amount of the self-emulsifying antifoaming agent 3 was set to 0.01 parts with respect to 100 parts of the polymer in the polymer latex.

Example 9
Each evaluation was performed in the same manner as in Example 2 except that self-emulsifying antifoaming agent 4 (Drewplus 4005) was used instead of self-emulsifying antifoaming agent 1.

(Comparative Example 1)
Each evaluation was performed in the same manner as in Example 2 except that another antifoaming agent (DEFOMAX520, manufactured by Toho Chemical Industry Co., Ltd.) was used instead of the self-emulsifying antifoaming agent 1.

(Comparative Example 2)
Instead of the self-emulsifying antifoaming agent 1, another antifoaming agent (DEFOMAX520, manufactured by Toho Chemical Industry Co., Ltd.) was used, and the amount added was equivalent to 0.1 part with respect to 100 parts of the polymer in the polymer latex. Each evaluation was performed in the same manner as in Example 1.

From Table 1 and Table 2 above, it can be seen that by using a specific amount of a specific antifoaming agent, the defoaming effect is excellent even in a low temperature region, and the film forming property of the polymer latex is excellent.

Claims (1)

A method for producing a polymer latex comprising a step of obtaining a mixture containing a polymer latex and an unreacted monomer by emulsion polymerization, and a step of recovering the unreacted monomer from the mixture,
The mixture in the step of recovering the unreacted monomer contains at least one selected from polyoxyethylene alkyl ester and polyoxyethylene sorbitan alkyl ester with respect to 100 parts by mass of the polymer in the mixture. the emulsion type antifoam seen containing 0.1 part by weight 0.01 part by weight, in the step of recovering the unreacted monomer, the mixture is heated from a temperature region of less than 20 ° C., a method of manufacturing polymer latex .