JP7342871B2 - Method for manufacturing polymer latex - Google Patents

Description

The present invention relates to a method for producing a polymer latex, and more particularly, to a method for producing a polymer latex that can be produced in a short time while achieving a high yield.

BACKGROUND ART Conventionally, membrane molded products such as dip molded products obtained by dip molding a latex composition containing latex of natural rubber or synthetic rubber have been suitably used as nipples, balloons, gloves, balloons, sacks, and the like.

For example, in Patent Document 1, as a method for producing synthetic rubber latex, an emulsion is obtained by mixing a solution of synthetic rubber obtained by dissolving synthetic rubber in an organic solvent and an aqueous solution of an emulsifier. , discloses a method in which the organic solvent is removed by heating the obtained emulsion under reduced pressure at a temperature higher than the boiling point of the organic solvent. However, the technique disclosed in Patent Document 1 has a problem in that it takes time to remove the organic solvent, resulting in poor productivity.

Patent No. 5260738

An object of the present invention is to provide a method for producing a polymer latex that can be produced in a short time while achieving a high yield.

As a result of intensive research to solve the above problems, the present inventors have found that a solution or dispersion of a polymer obtained by dissolving or dispersing the polymer in an organic solvent is mixed with an aqueous solution of an emulsifier. The above objective can be achieved by distilling off the organic solvent from the emulsion in a container adjusted to a pressure condition of 0.02 MPa or higher in terms of gauge pressure. They discovered this and completed the present invention.

That is, according to the present invention, the organic solvent is distilled off from an emulsion obtained by mixing a solution or dispersion of a polymer obtained by dissolving or dispersing the polymer in an organic solvent and an aqueous solution of an emulsifier. A method for producing a polymer latex, comprising the step of:
A method for producing a polymer latex is provided, in which the organic solvent is distilled off from the emulsion in a container adjusted to a pressure condition of 0.02 MPa or higher in terms of gauge pressure.

In the method for producing a polymer latex of the present invention, the content of the organic solvent in the emulsion before distilling off the organic solvent is preferably 30 to 60% by weight.
In the method for producing a polymer latex of the present invention, it is preferable that the organic solvent is distilled off from the emulsion in a container adjusted to a pressure condition of 0.02 to 0.18 MPa in terms of gauge pressure.
In the method for producing a polymer latex of the present invention, the organic solvent is preferably distilled off from the emulsion at a temperature equal to or higher than the boiling point of the organic solvent.
In the method for producing a polymer latex of the present invention, it is preferable that the organic solvent is an organic solvent selected from cyclohexane, normal hexane, cyclopentane, and normal pentane.
In the method for producing a polymer latex of the present invention, it is preferable that the organic solvent is distilled off by heating by introducing pressure-controlled steam into a jacket provided in the container.
In the method for producing a polymer latex of the present invention, the polymer is preferably a synthetic polyisoprene and/or a styrene-isoprene-styrene copolymer.
In the method for producing a polymer latex of the present invention, the content of the emulsifier in the emulsion before distilling off the organic solvent is 0.1 to 30 parts by weight based on 100 parts by weight of the polymer. It is preferable that there be.

According to the method for producing a polymer latex of the present invention, production can be performed in a short time while achieving a high yield, thereby making it possible to improve productivity.

FIG. 1 is a diagram showing an example of an emulsification apparatus used in the method for producing polymer latex of the present invention.

The method for producing polymer latex of the present invention includes:
A step of distilling off the organic solvent from an emulsion obtained by mixing a solution or dispersion of a polymer obtained by dissolving or dispersing the polymer in an organic solvent and an aqueous solution of an emulsifier,
The organic solvent is distilled off from the emulsion in a container adjusted to a pressure condition of 0.02 MPa or higher in terms of gauge pressure.

<Emulsion>
The emulsion used in the production method of the present invention is obtained by mixing a solution or dispersion of a polymer obtained by dissolving or dispersing the polymer in an organic solvent and an aqueous solution of an emulsifier.

The polymer solution or dispersion is not particularly limited as long as it is a solution or dispersion in which the polymer is dissolved or dispersed in an organic solvent.

The polymer is not particularly limited and various polymers can be used without limitation, such as natural rubber; homopolymers of conjugated diene monomers such as synthetic polybutadiene, synthetic polyisoprene, and synthetic polychloroprene; Copolymer; styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-isoprene-styrene block copolymer, acrylonitrile-butadiene copolymer, acrylonitrile-isoprene copolymer, acrylonitrile-butadiene-isoprene copolymer , a copolymer of a conjugated diene monomer such as butyl acrylate-butadiene copolymer and another monomer copolymerizable therewith; acrylate-based (co)polymers, and the like. Among these, natural rubber, synthetic polyisoprene, and styrene-isoprene-styrene block copolymer are preferable from the viewpoint of higher effects when the production method of the present invention is applied, and synthetic polyisoprene and styrene-isoprene- Styrene block copolymers are more preferred.

Examples of cases in which the polymer constituting the polymer solution or dispersion used in the production method of the present invention are synthetic polyisoprene and/or styrene-isoprene-styrene block copolymers are illustrated below. The polymer solution or dispersion used in the method is not limited to the solution or dispersion of synthetic polyisoprene and/or styrene-isoprene-styrene block copolymer.

The synthetic polyisoprene may be a homopolymer of isoprene, or may be a copolymer of isoprene and another copolymerizable ethylenically unsaturated monomer. The content of isoprene units in the synthetic polyisoprene is preferably 70% by weight or more based on the total monomer units, since it is easy to obtain membrane molded products such as dip molded products that are flexible and have excellent tensile strength. More preferably 90% by weight or more, still more preferably 95% by weight or more, particularly preferably 100% by weight (isoprene homopolymer).

Examples of other ethylenically unsaturated monomers copolymerizable with isoprene include conjugated diene monomers other than isoprene such as butadiene, chloroprene, and 1,3-pentadiene; acrylonitrile, methacrylonitrile, fumaronitrile, α- Ethylenically unsaturated nitrile monomers such as chloroacrylonitrile; vinyl aromatic monomers such as styrene and alkylstyrene; methyl (meth)acrylate (meaning "methyl acrylate and/or methyl methacrylate", below) , ethyl (meth)acrylate, etc.), ethylenically unsaturated carboxylic acid ester monomers such as ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; etc. can be mentioned. These other ethylenically unsaturated monomers copolymerizable with isoprene may be used alone or in combination.

Synthetic polyisoprene can be produced by isoprene in an organic solvent using a conventionally known method, for example, using a Ziegler polymerization catalyst consisting of trialkylaluminium-titanium tetrachloride or an alkyllithium polymerization catalyst such as n-butyllithium or sec-butyllithium. A synthetic polyisoprene solution obtained by dissolving synthetic polyisoprene in an organic solvent can be obtained by solution polymerizing the synthetic polyisoprene and other copolymerizable ethylenically unsaturated monomers used as necessary. . Note that the solution of synthetic polyisoprene obtained by solution polymerization may be used as it is in the emulsification process, but after removing solid synthetic polyisoprene from the solution obtained by solution polymerization, it may be dissolved in an organic solvent. , may be used.

Examples of organic solvents used in polymerization include aromatic hydrocarbon solvents such as benzene, toluene, and xylene; alicyclic hydrocarbon solvents such as cyclopentane, cyclopentene, cyclohexane, and cyclohexene; butane, normal pentane, normal hexane, Suitable examples include aliphatic hydrocarbon solvents such as heptane; halogenated hydrocarbon solvents such as methylene chloride, chloroform, and ethylene dichloride; and the like. Note that these organic solvents can also be suitably used when solid synthetic polyisoprene is taken out from a solution obtained by solution polymerization and then dissolved in an organic solvent again.

There are four types of isoprene units in synthetic polyisoprene, depending on the bonding state of isoprene: cis bond units, trans bond units, 1,2-vinyl bond units, and 3,4-vinyl bond units. From the viewpoint of improving the tensile strength of the resulting membrane molded product such as a dip molded product, the content of cis bond units in the isoprene units contained in the synthetic polyisoprene is preferably 70% by weight or more, based on the total isoprene units. It is more preferably 90% by weight or more, and still more preferably 95% by weight or more.

The weight average molecular weight of the synthetic polyisoprene is preferably 10,000 to 5,000,000, more preferably 500,000 to 5,000,000, even more preferably in terms of standard polystyrene by gel permeation chromatography analysis. is 800,000 to 3,000,000. By setting the weight average molecular weight of the synthetic polyisoprene within the above range, the tensile strength of the obtained membrane molded body when formed into a membrane molded body such as a dip molded body is improved, and the synthetic polyisoprene latex becomes easier to manufacture. Tend.

The polymer Mooney viscosity (ML1+4, 100° C.) of the synthetic polyisoprene is preferably 50-80, more preferably 60-80, even more preferably 70-80.

Styrene-isoprene-styrene block copolymer is a block copolymer of styrene and isoprene. The content ratio of styrene units and isoprene units in the styrene-isoprene-styrene block copolymer is not particularly limited, but the weight ratio of "styrene units: isoprene units" is usually 1:99 to 90:10, preferably 3 :97 to 70:30, more preferably 5:95 to 50:50, still more preferably 10:90 to 30:70.

The styrene-isoprene-styrene block copolymer can be produced by a conventionally known method, for example, using a Ziegler polymerization catalyst consisting of trialkylaluminium-titanium tetrachloride or an alkyllithium polymerization catalyst such as n-butyllithium or sec-butyllithium. By block copolymerizing isoprene and styrene in an organic solvent, it is possible to obtain a solution of styrene-isoprene-styrene block copolymer in which the styrene-isoprene-styrene block copolymer is dissolved in the organic solvent. can. Note that the solution of the styrene-isoprene-styrene block copolymer obtained by block copolymerization may be used as it is in the emulsification step, but the solid styrene-isoprene-styrene block copolymer solution obtained by block copolymerization may be used as is. After taking out the copolymer, it may be dissolved in an organic solvent and used. Moreover, as the organic solvent used for polymerization, the same ones as the above-mentioned synthetic isoprene can be mentioned.

The content ratio of cis bond units in the isoprene units contained in the styrene-isoprene-styrene block copolymer is determined based on the total isoprene units, from the viewpoint of improving the tensile strength of the resulting membrane molded product such as a dip molded product. The content is preferably 90% by weight or more, more preferably 95% by weight or more, and still more preferably 98% by weight or more.

The weight average molecular weight of the styrene-isoprene-styrene block copolymer is preferably 10,000 to 1,000,000, more preferably 50,000 to 500, as determined by gel permeation chromatography analysis in terms of standard polystyrene. 000, more preferably 100,000 to 300,000. By setting the weight average molecular weight of the styrene-isoprene-styrene block copolymer within the above range, the tensile strength of the obtained film-formed body when made into a membrane-formed body such as a dip-molded body is improved, and the styrene-isoprene block copolymer - Styrene block copolymer latex tends to be easier to produce.

The polymer Mooney viscosity (ML1+4, 100° C.) of the styrene-isoprene-styrene block copolymer is preferably 50-80, more preferably 60-80, even more preferably 70-80.

The content of the polymer in the polymer solution or dispersion used in the production method of the present invention is not particularly limited, but is preferably 3 to 30% by weight, more preferably 5 to 20% by weight, and even more preferably It is 7 to 15% by weight.

The emulsifier constituting the aqueous emulsifier solution used in the production method of the present invention is not particularly limited, but anionic emulsifiers can be preferably used. Examples of anionic emulsifiers include fatty acid salts such as sodium laurate, potassium myristate, sodium palmitate, potassium oleate, sodium linolenate, sodium rosinate, and potassium rosinate; sodium dodecylbenzenesulfonate, and dodecylbenzenesulfonic acid. Alkylbenzenesulfonates such as potassium, sodium decylbenzenesulfonate, potassium decylbenzenesulfonate, sodium cetylbenzenesulfonate, potassium cetylbenzenesulfonate; sodium di(2-ethylhexyl)sulfosuccinate, di(2-ethylhexyl)sulfosuccinic acid Potassium, alkyl sulfosuccinates such as sodium dioctyl sulfosuccinate; alkyl sulfate ester salts such as sodium lauryl sulfate and potassium lauryl sulfate; polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene lauryl ether sulfate and potassium polyoxyethylene lauryl ether sulfate Ester salts; monoalkyl phosphates such as sodium lauryl phosphate and potassium lauryl phosphate; and the like.

Among these anionic emulsifiers, fatty acid salts, alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfate ester salts, and polyoxyethylene alkyl ether sulfate ester salts are preferred, as they more appropriately suppress the generation of aggregates in the resulting polymer latex. Fatty acid salts and alkylbenzene sulfonates are more preferable, fatty acid salts are even more preferable, and sodium rosinate and potassium rosinate are more preferable from the viewpoint of being able to prevent oxidation and further increase the stability of the obtained polymer latex. Particularly preferred. It is also preferable to use a combination of a fatty acid salt and an alkylbenzene sulfonate.

The content ratio of the emulsifier in the aqueous solution of the emulsifier used in the production method of the present invention is not particularly limited, but is preferably 0.1 to 5% by weight, more preferably 0.3 to 3% by weight, and even more preferably 0. .5 to 2% by weight.

In the production method of the present invention, a solution or dispersion of a polymer obtained by dissolving or dispersing such a polymer in an organic solvent and an aqueous solution of an emulsifier are supplied to a mixing device and mixed. , an emulsion can be obtained. When obtaining an emulsion, it is preferable to continuously supply a polymer solution or dispersion and an aqueous emulsifier solution to a mixing device to continuously obtain an emulsion.

Here, FIG. 1 is a diagram showing an example of an emulsification apparatus used in the method for producing polymer latex of the present invention. As shown in FIG. 1, the emulsification apparatus shown in FIG. A solvent recovery tank 80 is provided.

In the following, a method for producing an emulsion used in the present invention will be explained with reference to FIG. 1, but the method is not particularly limited to the embodiment using the emulsification apparatus shown in FIG.

That is, to explain with reference to FIG. 1, a polymer solution or dispersion liquid from a polymer tank 10 and an emulsifier aqueous solution from an emulsifier tank 20 are continuously sent to a mixing device 30, whereby the mixing device By continuously mixing the polymer solution or dispersion and the emulsifier aqueous solution in the container 30, an emulsion can be continuously obtained. In the emulsifying apparatus shown in FIG. 1, the emulsified liquid thus continuously obtained is continuously supplied to the storage tank 40.

At this time, when the polymer solution or dispersion liquid and the emulsifier aqueous solution are continuously fed to the mixing device 30, the supply ratio thereof is not particularly limited, but it is possible to more appropriately advance the emulsification of the polymer. From the viewpoint of being able to produce the following, the volume ratio of "polymer solution or dispersion: emulsifier aqueous solution" is preferably 1:2 to 1:0.3, more preferably 1:1.5 to 1:0.5. , more preferably 1:1 to 1:0.7.

The method of continuously feeding the polymer solution or dispersion and the emulsifier aqueous solution from the polymer tank 10 and the emulsifier tank 20 to the mixing device 30 is not particularly limited. The emulsifier aqueous solution may be directly sent to the mixing device 30 by a pump, or a premixing device such as a line mixer may be provided upstream of the mixing device 30. It is also possible to perform premixing by using the above method, and send the premixed state to the mixing device 30.

The mixing device 30 is not particularly limited, but it is preferable to use a mixing device that can perform continuous mixing. "Colloid Mill" (manufactured by Shinko Pantech Co., Ltd.), product name "Thrasher" (manufactured by Nippon Coke Industries Co., Ltd.), product name "Trigonal Wet Pulverizer" (manufactured by Mitsui Miike Kakoki Co., Ltd.), product name "Cavitron" (product name Eurotech (manufactured by Taiheiyo Kiko Co., Ltd.), the trade name "Milder" (manufactured by Taiheiyo Kiko Co., Ltd.), the trade name "Fine Flow Mill" (manufactured by Taiheiyo Kiko Co., Ltd.), etc. can be used. Note that the conditions for the mixing operation by the mixing device 30 are not particularly limited, and the processing temperature, processing time, etc. may be appropriately selected so as to obtain a desired dispersion state.

When the polymer solution or dispersion and the emulsifier aqueous solution are continuously sent to the mixing device 30 and mixed, the temperature of the polymer solution or dispersion and the emulsifier aqueous solution is not particularly limited. The temperature is preferably 20 to 100°C, more preferably 40 to 90°C, and even more preferably 60 to 80°C, from the viewpoint of being able to perform the process well. The temperature at which these are mixed is the temperature at which the polymer solution or dispersion is stored in the polymer tank 10, and the temperature at which the aqueous emulsifier solution is stored in the emulsifier tank 10, so that the mixing temperature is a desired temperature. What is necessary is just to control by adjusting the temperature at the time of storing in 20, respectively. For example, when a 60° C. polymer solution or dispersion and a 60° C. emulsifier aqueous solution are mixed in the mixing device 30, when the polymer solution or dispersion is stored in the polymer tank 10, The temperature at which the aqueous solution of the emulsifier is stored in the emulsifier tank 20 may be set at 60°C.

The content of the organic solvent in the emulsion used in the production method of the present invention is usually 30 to 60% by weight, preferably 35 to 60% by weight, based on 100% by weight of all components constituting the emulsion. %, more preferably 37 to 50% by weight.

Further, the content of the emulsifier in the emulsion used in the production method of the present invention is usually 0.1 to 30 parts by weight, preferably 1 to 20 parts by weight, more preferably 3 parts by weight, based on 100 parts by weight of the polymer. ~15 parts by weight.

<Organic solvent distillation step>
In the production method of the present invention, from an emulsion obtained by mixing a solution or dispersion of a polymer obtained by dissolving or dispersing the polymer in an organic solvent and an aqueous solution of an emulsifier as described above, An organic solvent distillation step is provided to distill off (remove) the organic solvent.
In the production method of the present invention, the organic solvent is distilled off (removed) from the emulsion in the organic solvent distillation step in a container adjusted to a pressure condition of 0.02 MPa or higher in terms of gauge pressure. This will be carried out at

In the following, a specific embodiment of the organic solvent distillation step of the production method of the present invention will be explained with reference to FIG. 1, but the present invention is particularly limited to the embodiment using the emulsification apparatus shown in FIG. It's not something you can do.

That is, referring to FIG. 1, a specific embodiment of the organic solvent distillation step of the production method of the present invention will be described. In the organic solvent distillation step, the organic solvent is sent from the mixing device 30 and stored in the storage tank 40. The organic solvent contained in the emulsion is distilled off while the pressure in the storage tank 40 is controlled to a pressure of 0.02 MPa or more in terms of gauge pressure.

Here, the storage tank 40 includes a stirring blade 50, and further includes a jacket (not shown) on the outside thereof for circulating steam. Further, above the storage tank 40, a distillation piping 60 and a condenser 70 connected to the distillation piping 60 are provided.

In the organic solvent distillation step of the production method of the present invention, the pressure within the storage tank 40 is adjusted and the organic solvent is distilled off as follows. That is, in the organic solvent distillation step of the production method of the present invention, the system consisting of the storage tank 40, the distillation piping 60, and the condenser 70 is kept in a closed system sealed from the outside air, and the stirring blade 50 The emulsion stored in the storage tank 40 is heated by continuously injecting pressure-regulated steam into a jacket provided on the outside of the storage tank 40 while stirring the emulsion. Then, as the organic solvent evaporates (evaporates or boils) from the heated emulsion, the pressure inside the storage tank 40 increases, and as a result, the inside of the storage tank 40 becomes pressurized. On the other hand, a part of the organic solvent vaporized from the heated emulsion passes through the distillation piping 60, is cooled by the condenser 70, and is recovered into the organic solvent recovery tank 80.

In the organic solvent distillation step of the production method of the present invention, the organic solvent is distilled off while maintaining the pressurized state by utilizing the pressure increase inside the storage tank 40 due to the vaporization of the organic solvent. It is something to do. Specifically, the organic solvent is distilled off while the pressure inside the storage tank 40 is maintained at a pressurized condition of 0.02 MPa (gauge pressure) or higher. The upper limit of the pressure inside the storage tank 40 in the organic solvent distillation step is not particularly limited, but is preferably 0.18 MPa (gauge pressure) or less from the equipment standpoint. In the organic solvent distillation step, it is preferable to distill off the organic solvent while maintaining the pressure inside the storage tank 40 at a pressurized condition of 0.05 to 0.09 MPa (gauge pressure). It is more preferable to distill off the organic solvent under a pressurized condition of .07 to 0.09 MPa (gauge pressure). Note that the pressure inside the storage tank 40 in the organic solvent distillation step can be adjusted by, for example, the heating temperature at which the emulsion stored in the storage tank 40 is heated. For example, the higher the heating temperature is, the higher the pressing force can be.

According to the organic solvent distillation step of the production method of the present invention, the organic solvent is distilled off under such pressurized conditions of 0.02 MPa (gauge pressure) or higher. By removing the organic solvent, the organic solvent contained in the emulsion can be distilled off in a short time while achieving a high yield. In particular, as a result of the studies conducted by the present inventors, it has been found that organic solvents are generally distilled off under reduced pressure conditions; found that the time required for distilling off the organic solvent is shortened, and based on this knowledge, the organic solvent is distilled off under pressurized conditions of 0.02 MPa (gauge pressure) or higher.

In addition, according to the organic solvent distillation step of the production method of the present invention, foaming on the liquid surface can be suppressed by applying a pressure of 0.02 MPa (gauge pressure) or more. , the emulsion is stored in a relatively large amount, preferably 50 to 85% by volume, more preferably 55 to 85%, even more preferably 70 to 85% by volume, based on the volume of the storage tank 40, and processed in one operation. Even when the amount is relatively large, it is possible to effectively suppress the problem that a part of the emulsion liquid flows into the capacitor 70 due to foaming, which reduces the yield. And, thereby, productivity can be improved.

Furthermore, according to the organic solvent distillation step of the production method of the present invention, since the pressurization condition is 0.02 MPa (gauge pressure) or more, the inside of the storage tank 40 is filled with vaporized organic solvent, Thereby, the wall surface of the storage tank 40 can be kept in a wet state while the organic solvent is being distilled off. Therefore, even if the emulsion adheres to the wall surface of the storage tank 40, it is possible to effectively prevent the emulsion from solidifying and the polymer component remaining attached to the wall surface of the storage tank 40. It is possible to suppress a decrease in yield due to the polymer component remaining attached to the wall surface, and as a result, it is possible to realize a high yield.

The heating temperature for heating the emulsion stored in the storage tank 40 when distilling off the organic solvent under pressurized conditions of 0.02 MPa (gauge pressure) or higher is not particularly limited. The temperature may be set according to the desired pressure, but the boiling point Tb of the organic solvent contained in the emulsion (i.e., the organic solvent derived from the polymer solution or dispersion) at atmospheric pressure The temperature is preferably Tb or higher, preferably in the range of Tb+1 to Tb+35°C, more preferably in the range of Tb+5 to Tb+35°C, and even more preferably in the range of Tb+10 to Tb+30°C. Note that when the emulsion contains two or more types of organic solvents, the heating temperature may be set based on the boiling point of the organic solvent with a larger content. By setting the heating temperature within the above range, the pressure inside the storage tank 40 in the organic solvent distillation step can be appropriately controlled. Note that the heating temperature can be adjusted as appropriate by adjusting the flow rate and flow rate of the steam introduced into the jacket provided on the outside of the storage tank 40.

The pressurizing pressure inside the storage tank 40 in the organic solvent distillation step may be within the above range in terms of gauge pressure, but is preferably in the range of 0.1213 to 0.2813 MPa, more preferably 0.1513 to 0.1513 MPa in terms of absolute pressure. 0.1913 MPa, more preferably 0.1713 to 0.1913 MPa.

In addition, in the organic solvent distillation step, in order to maintain the above pressure, the system consisting of the storage tank 40, distillation piping 60, and condenser 70 is kept in a closed system sealed from the outside air. Although it is preferable to carry out distillation, on the other hand, immediately after the start of heating the storage tank 40, for the purpose of removing the air contained in the storage tank 40, a The pressure valve may be opened to remove air. At this time, it is desirable to close the pressure valve to create a closed system after the removal of the air contained in the storage tank 40 is completed and the liquefaction of the organic solvent by the condenser 70 is confirmed.

Alternatively, the pressurizing pressure inside the storage tank 40 in the organic solvent distillation process may be adjusted by the heating temperature, but in addition to the adjustment by the heating temperature, it may be adjusted by a pressure valve connected to the upper part of the condenser 70. The methods may be used in combination.

In the production method of the present invention, the organic solvent is distilled off from the emulsion under a pressure condition of 0.02 MPa (gauge pressure) or higher in the organic solvent distillation step, based on 100% by weight of the polymer in the emulsion. It is preferable to carry out the process until the content of the organic solvent in the emulsion becomes preferably 500 ppm by weight or less, more preferably 100 ppm by weight or less. In addition, in the production method of the present invention, the organic solvent is distilled off from the emulsion under pressure conditions of 0.02 MPa (gauge pressure) or higher. After distilling off the organic solvent under pressure conditions of 0.02 MPa (gauge pressure) or higher until the content of the organic solvent in the emulsion is reduced to preferably 1% by weight or less. , distillation of the organic solvent under reduced pressure conditions may be carried out in combination. In this case, a vacuum pump may be connected to the downstream side of the condenser 70, and the pressure may be reduced by the vacuum pump.

As described above, according to the production method of the present invention, a polymer latex can be obtained. In addition, the polymer latex obtained in this way contains pH adjusters, antifoaming agents, preservatives, chelating agents, oxygen scavengers, dispersants, anti-aging agents, etc. that are commonly blended in the latex field. Additives may be added.

Examples of pH adjusting agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal hydrogen carbonates such as sodium hydrogen carbonate; ammonia ; organic amine compounds such as trimethylamine and triethanolamine; and the like, but alkali metal hydroxides or ammonia are preferred.

Further, if necessary, in order to increase the solid content concentration of the polymer latex, a concentration operation by centrifugation may be performed.

The volume average particle diameter of the polymer latex produced by the production method of the present invention is preferably 0.1 to 10 μm, more preferably 0.5 to 3 μm, and even more preferably 1 to 2 μm. By setting the volume average particle diameter within the above range, the viscosity of the latex becomes appropriate, making it easy to handle, and it is possible to suppress the formation of a film on the surface of the latex when the polymer latex is stored.

The solid content concentration of the polymer latex produced by the production method of the present invention is preferably 30 to 70% by weight, more preferably 40 to 70% by weight. By setting the solid content concentration within the above range, it is possible to suppress separation of polymer particles when the polymer latex is stored, and it is also possible to suppress the formation of coarse aggregates due to aggregation of polymer particles with each other. .

The polymer latex of the present invention thus obtained can be made into a latex composition by, for example, blending various additives such as a crosslinking agent, and the latex composition can be used as a dip-molded product or the like. In addition to being used to obtain film molded products, it can also be used for adhesive applications.

Hereinafter, the present invention will be explained based on more detailed examples, but the present invention is not limited to these examples. In addition, in the following, "parts" are based on weight unless otherwise specified. In addition, the tests and evaluations were as follows.

<Example 1>
(Preparation of n-hexane solution (a) of synthetic polyisoprene)
Synthetic polyisoprene (trade name "Nipol IR2200L(R)", manufactured by Nippon Zeon Co., Ltd.) is mixed with normal hexane (boiling point: 69°C), and the temperature is raised to 60°C while stirring to dissolve it, and the synthetic polyisoprene is dissolved. A n-hexane solution (a) of synthetic polyisoprene having a concentration of 15% by weight was prepared.

(Preparation of emulsifier aqueous solution (b1))
An emulsifier aqueous solution (b1) having a potassium rosinate concentration of 1.2% by weight was prepared by mixing potassium rosinate as a fatty acid emulsifier with water at a temperature of 60°C.

(Manufacture of synthetic polyisoprene latex)
Then, using the n-hexane solution (a) of the synthetic polyisoprene prepared above and the emulsifier aqueous solution (b1), a synthetic polyisoprene latex was produced using the emulsification apparatus shown in FIG. 1.

Specifically, the normal hexane solution (a) of the synthetic polyisoprene prepared above is stored in the polymer tank 10 while being heated to 60°C, and the above solution is stored in the emulsifier tank 20. The prepared emulsifier aqueous solution (b1) was stored at 60°C and was mixed into a line as a pre-mixing device so that the weight ratio of "synthetic polyisoprene" to "emulsifier" was 10:1. After premixing with a mixer, the mixture is continuously supplied to the mixing device 30 to continuously obtain an emulsion (the proportion of normal hexane in the emulsion is 37.7% by weight). The emulsified liquid was continuously discharged into a storage tank 40 which was kept in a sealed state by closing valves other than those connected to the mixing device 30. As the mixing device 30, a homogenizer (trade name "Milder", manufactured by Taiheiyo Kiko Co., Ltd.) was used. Further, the pressure in the closed storage tank 40 before the emulsion was discharged from the mixing device 30 was 0 MPa (gauge pressure).

Next, when the amount of the emulsified liquid in the storage tank 40 becomes 56% by volume with respect to the volume of the storage tank 40, the transfer of the emulsified liquid from the mixing device 30 to the storage tank 40 is stopped, and the mixing is continued. After closing the valve of the piping connected to the device 30 and starting stirring by the stirring blade 50, the emulsion is heated by flowing steam into a jacket (not shown) provided on the outside of the storage tank 40. It started. Furthermore, at the start of heating, the pressure valve connected to the top of the condenser 70 is opened to remove the air in the storage tank 40, and after the condensation of normal hexane vapor by the condenser 70 is confirmed, the pressure valve is closed. The system consisting of the storage tank 40, the distillation piping 60, and the condenser 70 was made into a closed system sealed from the outside air. In this example, the temperature of the emulsion is raised to 85°C by heating with steam, and the pressure inside the storage tank 40 is 0.08 MPa (gauge pressure) when the temperature of the emulsion reaches 85°C. Met.
In this example, the normal hexane in the emulsion was continued to be distilled off under the conditions that the temperature of the emulsion was 85° C. and the pressure inside the storage tank 40 was 0.08 MPa (gauge pressure).

When normal hexane is distilled off, the amount of normal hexane recovered by the condenser 70 is measured every hour, and the content of normal hexane in the emulsion is determined to be 100% by weight of the synthetic polyisoprene in the emulsion. On the other hand, when it was determined that the concentration was 100 ppm by weight or less, it was determined that the distillation of normal hexane was completed, and the distillation of normal hexane under pressurized conditions was completed. In Example 1, the organic solvent distillation time, which is the time from when the start of condensation of normal hexane vapor was confirmed in the condenser 70 until the completion of distillation of normal hexane, was 9 hours (described later). The organic solvent distillation time was measured in the same manner in Examples 1 to 4 and Comparative Examples 1 and 2.) In addition, during this period, when the foam surface height due to the foaming of the emulsion in the storage tank 40 was observed, it was found that the height of the foam surface was 72% of the storage tank volume (maximum foam surface height: 72%). there were. Furthermore, in Example 1, after the completion of distillation of n-hexane, the proportion of synthetic polyisoprene adhering to the wall surface of the storage tank 40 is 100% by weight of the total amount of synthetic polyisoprene contained in the emulsion. On the other hand, it was 1.3% by weight, and the volume average particle diameter of the obtained synthetic polyisoprene latex was 1.09 μm.

<Example 2>
The emulsion was prepared in the same manner as in Example 1, except that the heating temperature of the emulsion by steam heating when distilling off normal hexane in the storage tank 40 was changed from 85°C to 78°C. Normal hexane was distilled off. In Example 2, the pressure inside the storage tank 40 was 0.06 MPa (gauge pressure) when the temperature of the emulsion was 78°C. The results are shown in Table 1.

<Example 3>
In place of normal hexane, normal pentane (boiling point: 36°C) is used, and when normal pentane is distilled off in the storage tank 40, the emulsion is heated to a temperature of 85°C by heating with steam. Normal pentane was distilled off from the emulsion in the same manner as in Example 1, except that the temperature was changed from 1 to 67°C. In Example 3, the pressure inside the storage tank 40 was 0.04 MPa (gauge pressure) when the temperature of the emulsion was 67°C. The results are shown in Table 1.

<Example 4>
Styrene-isoprene-styrene copolymer (trade name "Quintac 3620", manufactured by Nippon Zeon Co., Ltd., described as "SIS" in Table 1) was used instead of synthetic polyisoprene, and cyclohexane was used instead of n-hexane. An emulsion was obtained in the same manner as in Example 1, except that cyclohexane (boiling point: 80°C) was used. Cyclohexane was distilled off from the emulsion in the same manner as in Example 1, except that the heating temperature was changed from 85°C to 82°C. In Example 4, when the temperature of the emulsion was 82° C., the pressure inside the storage tank 40 was 0.07 MPa (gauge pressure). The results are shown in Table 1.

<Comparative example 1>
When normal hexane is distilled off in the storage tank 40, the heating temperature of the emulsion by steam heating is changed from 85°C to 60°C, and the pressure inside the storage tank 40 is set to -0. Normal hexane was distilled off from the emulsion in the same manner as in Example 1, except that the pressure was reduced to 02 MPa (gauge pressure). In Comparative Example 1, a pressure reduction pump was connected to the downstream side of the condenser 70, and the pressure inside the storage tank 40 was adjusted to −0.02 MPa (gauge pressure) by reducing the pressure with the pressure reduction pump. The results are shown in Table 1.

<Comparative example 2>
An emulsion was obtained in the same manner as in Example 1, except that cyclohexane was used instead of normal hexane. The emulsion was prepared in the same manner as in Example 1, except that the heating temperature was changed from 85°C to 86°C and the pressure in the storage tank 40 was reduced to -0.02MPa (gauge pressure). of cyclohexane was distilled off. In Comparative Example 2, a pressure reduction pump was connected to the downstream side of the condenser 70, and the pressure inside the storage tank 40 was adjusted to −0.02 MPa (gauge pressure) by reducing the pressure with the pressure reduction pump. In Comparative Example 2, the emulsion foamed violently, and a portion of the emulsion entered the condenser 70 through the distillation piping 60, making it impossible to continuously distill off cyclohexane. Ta.

As shown in Table 1, when the pressure inside the storage tank 40 is increased to 0.02 MPa (gauge pressure) or higher and the organic solvent is distilled off from the emulsion, the wall surface of the polymer tank 40 is It was possible to shorten the distillation time of the organic solvent while minimizing adhesion to the organic solvent, and as a result, it was possible to produce in a short time while achieving a high yield (Examples 1 to 4).

On the other hand, when the organic solvent is distilled off from the emulsion by reducing the pressure inside the storage tank 40 at a temperature of 60°C, the maximum foam surface height becomes as high as 90% by volume, and the organic solvent The solvent distillation time became longer, and furthermore, the amount of polymer adhesion to the wall surface of the tank 40 increased (Comparative Example 1).
In addition, when the organic solvent is distilled off from the emulsion by increasing the temperature to 86° C. and reducing the pressure inside the storage tank 40, the emulsion foams violently and some of the emulsion The organic solvent entered the condenser 70 from the storage tank 40 (the maximum bubble surface height exceeded 100%), and the organic solvent could not be continuously distilled off (Comparative Example 2).

Claims (8)

A step of distilling off the organic solvent from an emulsion obtained by mixing a solution or dispersion of a polymer obtained by dissolving or dispersing the polymer in an organic solvent and an aqueous solution of an emulsifier in a container. A method for producing a polymer latex, the method comprising:
The distillation of the organic solvent from the emulsion was adjusted to a pressure condition of 0.02 MPa or more in terms of gauge pressure by maintaining a pressurized state using the pressure increase inside the container due to vaporization of the organic solvent. A method for producing polymer latex in a container. The method for producing a polymer latex according to claim 1, wherein the content of the organic solvent in the emulsion before distilling off the organic solvent is 30 to 60% by weight. The method for producing a polymer latex according to claim 1 or 2, wherein the organic solvent is distilled off from the emulsion in a container adjusted to a pressure condition of 0.02 to 0.18 MPa in terms of gauge pressure. The method for producing a polymer latex according to any one of claims 1 to 3, wherein the organic solvent is distilled off from the emulsion at a temperature equal to or higher than the boiling point of the organic solvent. The method for producing a polymer latex according to any one of claims 1 to 4, wherein the organic solvent is an organic solvent selected from cyclohexane, normal hexane, cyclopentane, and normal pentane. The method for producing a polymer latex according to any one of claims 1 to 5, wherein the organic solvent is distilled off by heating by introducing pressure-regulated steam into a jacket provided in the container. . The method for producing a polymer latex according to any one of claims 1 to 6, wherein the polymer is a synthetic polyisoprene and/or a styrene-isoprene-styrene copolymer. Any one of claims 1 to 7, wherein the content of the emulsifier in the emulsion before distilling off the organic solvent is 0.1 to 30 parts by weight based on 100 parts by weight of the polymer. A method for producing a polymer latex.

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