Method for manufacturing rubbery latex

Abstract

To provide a method for producing rubbery latex with excellent polymerization stability and acid agglomeration stability. [Solution] A method for producing rubbery latex, comprising step 1 of emulsion polymerization of a monomer mixture (I) containing at least one diene monomer or a monomer mixture (II) containing at least one alkyl acrylate monomer, in the presence of an emulsifier mixture containing a salt of compound A containing one or more selected from rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3), and a salt of a compound represented by the following formula (1). RO-(AO) n -CH2-COOH (1) (In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is between 1 and 50.)

Description

[Technical Field]

[0001] The present invention relates to a method for producing rubbery latex and an emulsifier for emulsion polymerization used in the method for producing said rubbery latex. [Background technology]

[0002] Acrylonitrile-butadiene-styrene (ABS) resin and acrylonitrile-styrene-acrylic acid ester (ASA) resin exhibit excellent properties such as mechanical strength, moldability, and surface gloss, and are used in a wide range of fields, including automotive parts and electrical equipment components. ABS resin and ASA resin are typically produced by emulsion polymerization of a monomer mixture containing at least some of the monomers that make up these resins to produce a rubbery latex, and then by grafting the rubbery latex through emulsion polymerization.

[0003] The properties of ABS and ASA resins are related to the size of the rubber particles (i.e., dispersed phase) in the rubber latex. When the average particle size of the rubber is large, the ABS resin prepared from that latex has excellent impact resistance, while when it is small, the resin has excellent gloss. Furthermore, gloss is preferable when the particle size is uniform. In other words, a narrow particle size distribution is preferable. ABS and ASA resins manufactured from rubber latex containing coarse particles have poor gloss. Thus, the particle size and particle size distribution of rubber particles in rubber latex are extremely important factors that affect the performance of ABS and ASA resins. In addition, the grafting rate of ABS and ASA resins greatly affects the impact resistance and gloss of ABS and ASA resins. Therefore, in order to prepare high-performance ABS and ASA resins, advanced particle size control during the preparation of rubber latex and control of the grafting rate during the preparation of ABS resin latex and ASA resin latex are required.

[0004] In the production of ABS resin latex and ASA resin latex, which are used to manufacture ABS resin and ASA resin, respectively, that have a well-balanced performance in terms of impact strength, flow properties, gloss, etc., rubbery latex with an average particle size of 150 to 500 nm of its dispersed phase is often used as a raw material. Rubbery latex is manufactured by emulsion polymerization, and the average particle size of its dispersed phase is usually less than 150 nm. Therefore, instead of using the rubbery latex as is in the production of ABS resin latex and ASA resin latex, rubbery latex manufactured by emulsion polymerization is usually subjected to a treatment to increase the particle size of its dispersed phase, and this prepared rubbery latex is then used in graft copolymerization. One method for increasing the particle size of the dispersed phase of rubbery latex involves adding an acidic substance such as sulfuric acid or acetic acid to the rubbery latex to lower its pH and cause the dispersed phase (rubber) particles to adhere to each other. However, this method has problems such as difficulty in adjusting the processing conditions for emulsion polymerization and the processing conditions for increasing the particle size of the dispersed phase, which reduces the stability of the rubbery latex and generates aggregates and coarse particles.

[0005] Furthermore, there are the following problems. Specifically, in the process of preparing graft copolymer latex (e.g., ABS resin latex and ASA resin latex) by graft copolymerizing aromatic vinyl monomers and vinyl monomers having cyano groups into rubbery latex using emulsion polymerization, if the amount of emulsifier is small, a large amount of aggregates and coarse particles are generated. On the other hand, if the amount of emulsifier is large, ABS resin latex and ASA resin latex with a small amount of aggregates and coarse particles are prepared. However, in this case, it is difficult to increase the grafting rate, and the ABS resin produced from the ABS resin latex prepared in this way, and the ASA resin produced from the ASA resin latex, have low physical properties such as impact resistance, gloss, and heat resistance.

[0006] On the other hand, emulsifiers conventionally used to produce rubbery latex and graft copolymer latex include alkali metal salts of higher fatty acids such as semi-hardened beef tallow fatty acids, alkali metal salts of resin acids, and sulfonates such as sodium dodecylbenzenesulfonate. Of these emulsifiers, alkali metal salts of higher fatty acids are commonly used as emulsifiers in both the preparation of rubbery latex by emulsion polymerization and the preparation of graft copolymer latex by emulsion polymerization, because the copolymer produced can be easily extracted from the latex produced using these emulsifiers.

[0007] Alkali metal salts of higher fatty acids are produced from natural oils and fats. For example, potassium salts of partially hydrogenated tallow fatty acids (semi-hardened tallow fatty acids) derived from beef tallow are widely used as emulsifiers for the preparation of rubbery latex and graft copolymer latex. However, the composition of higher fatty acids in conventional higher fatty acid salt-based emulsifiers is determined based on the fatty acid composition of the raw material oils and fats, and is not appropriately set. In fact, conventional higher fatty acid salt-based emulsifiers each have their own advantages and disadvantages, and therefore have not always been satisfactory in the production of rubbery latex and graft copolymer latex.

[0008] Therefore, Patent Document 1 aims to develop a method for producing latex with low content of aggregates and coarse particles, which is useful for producing graft copolymers such as ABS resin that have excellent physical properties such as impact resistance, gloss, and heat resistance. The method involves (I) polymerizing at least one diene monomer with a monomer other than a diene monomer that can be copolymerized with the diene monomer by emulsion polymerization to prepare a (co)polymer, and then processing the (co)polymer with an aromatic vinyl monomer and a vinyl monomer having a cyano group. A method for producing a graft copolymer latex is disclosed, comprising step (II) of copolymerizing a graft copolymer with a graft copolymer and / or a (meth)acrylate monomer by emulsion polymerization, wherein step (I) and / or step (II) are carried out in the presence of a fatty acid salt mixture consisting of palmitate, stearate, and octadecenoate, where the weight ratio of the acid is palmitate / stearate / octadecenoate = 45~70 / 5~20 / 15~30. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 9-110943 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, the preparation of fatty acid salt mixtures such as semi-hardened palm stearin oil and semi-hardened beef tallow used in the method described in Patent Document 1 requires special equipment for semi-hardening, and there is a need for an emulsifier for emulsion polymerization that can be prepared by a simple method. Furthermore, there is a need for an emulsifier for emulsion polymerization that can solve problems such as the formation of aggregates when increasing the particle size of the dispersed phase in rubbery latex by adding acid. [Means for solving the problem]

[0011] In light of the current situation, the present inventors diligently conducted research with the aim of developing a method for producing rubbery latex that is useful for manufacturing graft copolymers such as ABS resin and ASA resin with excellent physical properties, and that exhibits excellent polymerization stability and acid aggregation stability. As a result of their investigation, the inventors found that the above objective can be achieved by using a mixture of a specific fatty acid salt and a specific compound as an emulsifier in the manufacturing process of rubbery latex made of (co)polymers such as rubber, and in the manufacturing process of graft copolymer latex. In other words, the present invention relates to the following [1] to [3]. [1] A method for producing a rubbery latex, comprising step 1 of emulsion polymerization of a monomer mixture (I) containing at least one diene monomer or a monomer mixture (II) containing at least one alkyl acrylate monomer, in the presence of an emulsifier mixture containing a salt of compound A containing one or more selected from rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3), and a salt of a compound represented by the following formula (1). RO-(AO) n -CH2-COOH (1) (In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is between 1 and 50.) A method for producing a graft copolymer comprising step 3 of emulsion polymerization of a rubbery latex produced by the manufacturing method described in [1] with a monomer mixture (III) containing an aromatic vinyl monomer and one or more selected from vinyl monomers having a cyano group and (meth)acrylate monomers, A method for producing a graft copolymer, wherein the emulsion polymerization is carried out in the presence of an emulsifier mixture containing a salt of compound A, which contains one or more selected from rosin acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3), and a salt of a compound represented by the following formula (1). RO-(AO) n -CH2-COOH (1) (In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is between 1 and 50.) [3] An emulsifier for emulsion polymerization comprising a salt of compound A, which contains one or more selected from rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond having 12 to 18 carbon atoms (A3), and a salt of a compound represented by the following formula (1). RO-(AO) n -CH2-COOH (1) (In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is between 1 and 50.) [Effects of the Invention]

[0012] According to the present invention, a method for producing a rubbery latex with excellent polymerization stability and acid aggregation stability, and an emulsifier for emulsion polymerization used in the production method can be provided. [Modes for carrying out the invention]

[0013] [Method for manufacturing rubbery latex] The present invention provides a method for producing a rubbery latex, comprising step 1 of emulsion polymerization of a monomer mixture (I) containing at least one diene monomer or a monomer mixture (II) containing at least one alkyl acrylate monomer, in the presence of an emulsifier mixture containing a salt of compound A, which contains one or more selected from rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3), and a salt of a compound represented by formula (1).

[0014] RO-(AO) n -CH2-COOH (1) (In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is between 1 and 50.)

[0015] According to the method for producing a rubber latex of the present invention, a method for producing a rubber latex excellent in polymerization stability and acid coagulation stability can be provided. Although the detailed reason is not clear, it is considered as follows. When emulsion-polymerizing the monomer mixture (I) or the monomer mixture (II) in the presence of an emulsifier mixture containing a salt of compound A and a salt of the compound represented by the formula (1), the compound represented by the formula (1) is considered to improve the polymerization stability of the method for producing a rubber latex by suppressing the aggregation of resin particles by suppressing the collision of the resin particles generated by polymerization. Also, in Step 2 of increasing the particle size of the dispersed substance in the rubber latex, the compound represented by the formula (1) is considered to moderately relax the collision of the dispersed substance and suppress the excessive aggregation of the salt of compound A or the carboxylic acid derived from the salt of compound A, thereby improving the acid coagulation stability.

[0016] (Definition) In the present invention, the description "N1 to N2" indicates a range including N1 and N2, and is synonymous with "N1 or more and N2 or less" unless otherwise specified. In the present invention, the term "rubber latex" refers to a latex composed of a copolymer containing at least a structural unit derived from a diene monomer or at least a structural unit derived from a (meth)acrylic acid alkyl ester monomer. In the present invention, "acid coagulation stability" is the stability when an acid is added to the rubber latex to increase the particle size of the dispersed substance. In the present invention, the fatty acid is a monovalent fatty acid unless otherwise specified, and includes all isomers. In the present invention, "(meth)acrylic acid" means acrylic acid or methacrylic acid, and "(meth)acrylate" means acrylate or methacrylate.

[0017] ≪Step 1≫ In the method for producing rubbery latex of the present invention, step 1 is a step of emulsion polymerization of a monomer mixture (I) containing at least one diene monomer or a monomer mixture (II) containing at least one alkyl acrylate monomer, in the presence of an emulsifier mixture containing a salt of compound A, which contains one or more selected from rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3), and a salt of a compound represented by formula (1).

[0018] <Emulsifier mixture> In step 1, an emulsifier mixture is used that contains a salt of compound A, which includes one or more selected from rosinic acid (A1), saturated fatty acids having 12 to 18 carbon atoms (A2), and unsaturated fatty acids having one double bond with 12 to 18 carbon atoms (A3), as well as a salt of the compound represented by formula (1).

[0019] The content of each fatty acid and the compound represented by formula (1) in the emulsifier mixture of the present invention can be measured, for example, by subjecting the mixture of methylated fatty acids and the compound represented by formula (1) to gas chromatography, gas chromatography-mass spectrometry, or the like. Methylation of fatty acids and compounds represented by formula (1) can be carried out by adding acid to an emulsifier mixture to obtain a mixture of fatty acids and compounds represented by formula (1), extracting these with an organic solvent, and then treating with a methylating agent. Examples of methylating agents include diazomethane and (trimethylsilyl)diazomethane.

[0020] [Compound A] Compound A contains one or more selected from rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3). The rosinic acid (A1), saturated fatty acid (A2), and unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3) contained in Compound A may be one type or a combination of multiple types.

[0021] (Rosin acid (A1)) Rosin acid (A1) is a compound having a carboxyl group found in natural resin rosin, unrefined rosin, refined rosin, and modified rosin. Specifically, examples include abietic acid, neoabietic acid, palastic acid, pimaric acid, isopimaric acid, sandaracopimaric acid, dehydroabietic acid, and abietic acid, neoabietic acid, palastic acid, pimaric acid, isopimaric acid, sandaracopimaric acid, dehydroabietic acid, and lepopimaric acid. Rosin acid (A1) may also be a disproportionated rosin acid such as dehydroabietic acid.

[0022] The salt of rosinic acid (A1) is preferably a potassium salt, sodium salt, lithium salt, ammonium salt, or lower amine salt, and more preferably a potassium salt. Examples of lower amine salts of rosinic acid (A1) include salts of rosinic acid (A1) having a countercation derived from an amine, preferably with 9 or fewer carbon atoms, more preferably with 2 to 9 carbon atoms. Examples of such lower amines include monoethanolamine, triethylamine, and N,N-diisopropylethylamine.

[0023] (Saturated fatty acids (A2) with 12-18 carbon atoms) The saturated fatty acid (A2) having 12 to 18 carbon atoms may be linear or branched, but from the viewpoint of availability, it is preferably a linear saturated fatty acid (A2) having 12 to 18 carbon atoms. Furthermore, from the viewpoint of availability, the saturated fatty acid (A2) having 12 to 18 carbon atoms is one or more selected from saturated fatty acids with 12 carbon atoms, 14 carbon atoms, 16 carbon atoms, and 18 carbon atoms. From the viewpoint of improving the polymerization stability of the method for producing rubbery latex, the saturated fatty acid (A2) having 12 to 18 carbon atoms is preferably a saturated fatty acid (A2) having carboxyl groups at the ends of the carbon chain, and more preferably a straight-chain saturated fatty acid (A2) having carboxyl groups at the ends, and is one or more selected from lauric acid, myristic acid, palmitic acid, and stearic acid.

[0024] The salt of the saturated fatty acid (A2) having 12 to 18 carbon atoms is preferably a potassium salt, sodium salt, lithium salt, ammonium salt, or lower amine salt, and more preferably a potassium salt. Examples of lower amine salts of saturated fatty acids (A2) having 12 to 18 carbon atoms include salts of saturated fatty acids (A2) having 9 or fewer carbon atoms, more preferably 2 to 9 carbon atoms, that have a countercation derived from an amine. Examples of such lower amines include monoethanolamine, triethylamine, and N,N-diisopropylethylamine.

[0025] (Unsaturated fatty acid (A3) having one double bond between 12 and 18 carbon atoms) The unsaturated fatty acid (A3) having one double bond between 12 and 18 carbon atoms may be linear or branched, but from the viewpoint of availability, it is preferably a linear unsaturated fatty acid (A3) having one double bond between 12 and 18 carbon atoms. Furthermore, from the viewpoint of availability, the unsaturated fatty acid (A3) having one double bond between 12 and 18 carbon atoms is one or more selected from an unsaturated fatty acid having one double bond between 12 carbon atoms, an unsaturated fatty acid having one double bond between 14 carbon atoms, an unsaturated fatty acid having one double bond between 16 carbon atoms, and an unsaturated fatty acid having one double bond between 18 carbon atoms. From the viewpoint of improving the handling properties and polymerization stability of the rubbery latex manufacturing method, the unsaturated fatty acid (A3) having one double bond between 12 and 18 carbon atoms is preferably an unsaturated fatty acid (A3) having one double bond between 12 and 18 carbon atoms with a carboxyl group at the end of the carbon chain. From the viewpoint of availability, it is more preferably a straight-chain unsaturated fatty acid (A3) having one double bond between 12 and 18 carbon atoms with a carboxyl group at the end.

[0026] The salt of the unsaturated fatty acid (A3) having one double bond between 12 and 18 carbon atoms is preferably a potassium salt, sodium salt, lithium salt, ammonium salt, or lower amine salt, and more preferably a potassium salt. Lower amine salts of unsaturated fatty acids (A3) having one double bond between 12 and 18 carbon atoms include, for example, salts of unsaturated fatty acids (A3) having one double bond between 12 and 18 carbon atoms, preferably salts of unsaturated fatty acids (A3) having one double bond between 9 and 18 carbon atoms, and preferably salts of salts of an amine derived from an amine with 9 or fewer carbon atoms. Examples of such lower amines include monoethanolamine, triethylamine, and N,N-diisopropylethylamine.

[0027] Compound A may also contain carboxylic acids other than rosinic acid (A1), saturated fatty acids having 12 to 18 carbon atoms (A2), and unsaturated fatty acids having one double bond with 12 to 18 carbon atoms (A3). Examples of such carboxylic acids include unsaturated fatty acids having two or more double bonds with 12 to 18 carbon atoms, and fatty acids with 20 or more carbon atoms.

[0028] Furthermore, compound A may be a carboxylic acid consisting substantially of a saturated fatty acid (A2) having 12 to 18 carbon atoms and an unsaturated fatty acid (A3) having one double bond with 12 to 18 carbon atoms. In this case, compound A does not contain rosinic acid (A1). When compound A contains saturated fatty acids (A2) having 12 to 18 carbon atoms and unsaturated fatty acids (A3) having one double bond with 12 to 18 carbon atoms, the total content of saturated fatty acids (A2) and unsaturated fatty acids (A3) having one double bond with 12 to 18 carbon atoms in the fatty acids constituting compound A is preferably 90% by mass or more, more preferably 93% by mass or more, and even more preferably 96% by mass or more, from the viewpoint of improving the polymerization stability of the method for producing rubbery latex. The mass ratio (A2 / A3) of saturated fatty acid (A2) having 12 to 18 carbon atoms and unsaturated fatty acid (A3) having one double bond with 12 to 18 carbon atoms is preferably 40 / 60 or higher, more preferably 45 / 55 or higher, and even more preferably 50 / 50 or higher, from the viewpoint of improving the polymerization stability of the method for producing rubbery latex. In saturated fatty acids (A2) having 12 to 18 carbon atoms, the mass ratio of saturated fatty acids having 12 to 15 carbon atoms to saturated fatty acids having 16 to 18 carbon atoms (saturated fatty acids having 12 to 15 carbon atoms / saturated fatty acids having 16 to 18 carbon atoms) is preferably 55 / 45 or less, more preferably 50 / 50 or less, and even more preferably 45 / 55 or less, from the viewpoint of improving the polymerization stability of the method for producing rubbery latex. In an unsaturated fatty acid (A3) having one double bond between 12 to 18 carbon atoms, the mass ratio of an unsaturated fatty acid having one double bond between 12 to 15 carbon atoms to an unsaturated fatty acid having one double bond between 16 to 18 carbon atoms (unsaturated fatty acid having one double bond between 12 to 15 carbon atoms / unsaturated fatty acid having one double bond between 16 to 18 carbon atoms) is preferably 10 / 90 or less, more preferably 5 / 95 or less, and even more preferably 0 / 100, from the viewpoint of availability.

[0029] (Method for producing compound A and a salt of compound A) Compound A may be prepared by mixing rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), an unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3), and other carboxylic acids. Furthermore, the salt of compound A may be prepared by mixing rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), an unsaturated fatty acid having 12 to 18 carbon atoms and one double bond (A3), and other carboxylic acids, followed by mixing a potassium compound, a sodium compound, a lithium compound, ammonia, and a lower amine. Examples of potassium compounds, sodium compounds, and lithium compounds include potassium hydroxide, sodium hydroxide, and lithium hydroxide, respectively. The mixing is preferably carried out by adding the mixture of carboxylic acids to an aqueous solution of the potassium compound, sodium compound, lithium compound, ammonia, and lower amine.

[0030] [Salt of the compound represented by formula (1)] The emulsifier mixture contains a salt of compound A, in addition to a salt of the compound represented by formula (1). The emulsifier mixture may contain one or more salts of the compounds represented by formula (1).

[0031] RO-(AO) n -CH2-COOH (1)

[0032] In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is 1 to 50.

[0033] The salt of the compound represented by formula (1) is preferably a potassium salt, sodium salt, lithium salt, ammonium salt, or lower amine salt, and more preferably a potassium salt. Examples of lower amine salts of the compound represented by formula (1) include, for example, salts of rosinic acid (A1) having a countercation derived from an amine, preferably with 9 or fewer carbon atoms, more preferably with 2 to 9 carbon atoms. Examples of such lower amines include monoethanolamine, triethylamine, and N,N-diisopropylethylamine.

[0034] Salts of the compound represented by formula (1) may be prepared by mixing the compound represented by formula (1) with a potassium compound, a sodium compound, a lithium compound, ammonia, and a lower amine. Examples of potassium compounds, sodium compounds, and lithium compounds include potassium hydroxide, sodium hydroxide, and lithium hydroxide, respectively. The mixing is preferably carried out by adding the compound represented by formula (1) to an aqueous solution of the potassium compound, sodium compound, lithium compound, ammonia, and a lower amine. The salt of the compound represented by formula (1) may be produced simultaneously with the production of the salt of compound A by mixing a mixture of rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), an unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3), and other carboxylic acids with the compound represented by formula (1), along with a potassium compound, a sodium compound, a lithium compound, ammonia, and a lower amine.

[0035] Examples of hydrocarbon groups having 4 to 22 carbon atoms include straight-chain hydrocarbon groups and branched-chain hydrocarbon groups, with straight-chain hydrocarbon groups being preferred. The chain length of the hydrocarbon group having 4 to 22 carbon atoms is preferably 6 or more, more preferably 8 or more, and even more preferably 10 or more, from the viewpoint of improving the polymerization stability of the rubbery latex manufacturing method, and preferably 20 or less, and more preferably 18 or less, from the viewpoint of improving the handling and availability of the rubbery latex manufacturing method.

[0036] In formula (1), (AO) n This refers to a repeating unit of an ethyleneoxy group or a propyleneoxy group. AO represents an ethyleneoxy group or a propyleneoxy group, preferably an ethyleneoxy group. Furthermore, n represents the number of repetitions of the repeating unit represented by AO, i.e., the number of moles of ethyleneoxy group or propyleneoxy group added, and from the viewpoint of polymerization stability and acid agglomeration stability of the rubbery latex production method, it is 1 or more, preferably 2 or more, and 50 or less, preferably 40 or less, more preferably 30 or less, and even more preferably 20 or less.

[0037] When the compound represented by formula (1) is a commercially available product, or when the compound represented by formula (1) is a mixture, n represents the weighted average of the number of repeats of the repeating unit represented by AO, and from the viewpoint of polymerization stability and acid agglomeration stability of the method for producing rubbery latex, it is preferably 1 or more, more preferably 2 or more, and preferably 40 or less, more preferably 30 or less, and even more preferably 20 or less.

[0038] The mass ratio of the compound represented by formula (1) to compound A in the emulsified mixture (compound represented by formula (1) / compound A) is preferably 1 / 99 or more, more preferably 1.5 / 98.5 or more, and even more preferably 2 / 98 or more, from the viewpoint of improving the polymerization stability and acid agglomeration stability of the rubbery latex production method, and from the viewpoint of economic efficiency, it is preferably 60 / 40 or less, more preferably 50 / 50 or less, and preferably 40 / 60 or less.

[0039] <Monomer mixture> In step 1, a monomer mixture (I) containing at least one diene monomer or a monomer mixture (II) containing at least one alkyl (meth)acrylate monomer is used as the monomer mixture.

[0040] [Monomer mixture (I)] The monomer mixture (I) contains at least one diene monomer. Examples of diene monomers include butadiene, isoprene, chloroprene, etc., with butadiene being preferred. The monomer mixture (I) may contain monomers other than diene monomers. Examples of monomers other than diene monomers include aromatic vinyl monomers such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, and p-methylstyrene, and vinyl monomers having a cyano group such as methacrylonitrile and acrylonitrile. The monomer mixture (I) may also contain the alkyl (meth)acrylate monomers shown below.

[0041] From the viewpoint of obtaining a resin with excellent impact resistance, the content of diene monomers in monomer mixture (I) is preferably 60.0% by mass or more, more preferably 70.0% by mass or more, even more preferably 80.0% by mass or more, and preferably 100% by mass or less.

[0042] [Monomer mixture (II)] The monomer mixture (II) contains at least one alkyl (meth)acrylate monomer. Examples of alkyl (meth)acrylate monomers include methyl (meth)acrylate and butyl (meth)acrylate, and butyl acrylate is preferred from the viewpoint of availability and obtaining a resin with excellent impact resistance and weather resistance. From the viewpoint of efficiently obtaining graft polymers from the resulting rubbery latex, the monomer mixture (II) preferably contains alkenyl (meth)acrylate monomers such as allyl (meth)acrylate in addition to alkyl (meth)acrylate monomers. The monomer mixture (II) may contain monomers other than alkyl (meth)acrylate monomers and alkenyl (meth)acrylate monomers. Examples of monomers other than alkyl (meth)acrylate monomers and alkenyl (meth)acrylate monomers include aromatic vinyl monomers such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, and p-methylstyrene, and vinyl monomers having a cyano group such as methacrylonitrile and acrylonitrile. The monomer mixture (II) may also contain the above-mentioned diene monomers.

[0043] From the viewpoint of obtaining a resin with excellent impact resistance, the content of alkyl (meth)acrylate monomers in monomer mixture (II) is preferably 60.0% by mass or more, more preferably 70.0% by mass or more, even more preferably 80.0% by mass or more, and preferably 99.6% by mass or less, more preferably 99.0% by mass or less, and even more preferably 98.5% by mass or less.

[0044] In step 1, the total amount of compound A and the compound represented by formula (1) per 100 parts by mass of monomer mixture (I) or monomer mixture (II) is preferably 0.1 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more, from the viewpoint of polymerization stability of the method for producing rubbery latex, and preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.5 parts by mass or less, from the viewpoint of economic efficiency. Note that the total amount of compound A and the compound represented by formula (1) is the amount based on the acid.

[0045] (Radical polymerization initiator) As the radical polymerization initiator used in the emulsion polymerization of Step 1, any of those commonly used in emulsion polymerization can be used. Examples of radical polymerization initiators include water-soluble persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; organic peroxides such as hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, and cumene hydroperoxide; and azo-based initiators such as azobis-diisobutyronitrile and 2,2-azobis(2-amidinopropane) dihydrochloride. From the viewpoint of polymerization reactivity, workability, and economy, water-soluble persulfates and organic peroxides are preferred, and one or more selected from sodium persulfate, potassium persulfate, ammonium persulfate, and t-butyl hydroperoxide are more preferred. Furthermore, as polymerization initiators, redox-type initiators combining a peroxide compound with a water-soluble reducing agent such as sodium sulfite, rongalit, or ascorbic acid can also be used.

[0046] In step 1, the amount of radical polymerization initiator used is preferably 0.05 parts by mass or more, more preferably 0.10 parts by mass or more, and even more preferably 0.15 parts by mass or more, per 100 parts by mass of monomer mixture (I) or monomer mixture (II), from the viewpoint of manufacturing efficiency, and preferably 2.00 parts by mass or less, more preferably 1.00 part by mass or less, and even more preferably 0.50 parts by mass or less, from the viewpoint of economic efficiency.

[0047] In step 1, the amount of monomer mixture (I) or monomer mixture (II) added is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, relative to the total mass of monomer mixture (I) or monomer mixture (II) and dispersion medium, from the viewpoint of manufacturing efficiency and economics, and preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less, from the viewpoint of polymerization stability of the method for producing rubbery latex.

[0048] In step 1, the dispersion medium is an aqueous medium, preferably water. Here, "aqueous" means that water makes up the largest proportion in the medium. As the water in the aqueous medium, ion-exchanged water or distilled water is preferably used. The aqueous medium may further contain an organic solvent. Examples of such organic solvents include aliphatic alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, and 2-propanol; ketones having 3 to 8 carbon atoms, such as acetone and methyl ethyl ketone; and water-soluble organic solvents such as ethers, such as diethyl ether and tetrahydrofuran. From an environmental standpoint, the water content in the aqueous medium is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass.

[0049] In step 1, there are no particular restrictions on the emulsion polymerization conditions, but the polymerization temperature is adjusted by the decomposition temperature of the polymerization initiator. From the viewpoint of manufacturing efficiency, a temperature of 20°C to 80°C is preferred. Similarly, from the same viewpoint, the polymerization time is preferably 2 hours to 36 hours. In step 1, emulsion polymerization may be stopped by cooling the reaction system, or by adding a pH adjuster and a polymerization inhibitor.

[0050] In step 1, polymerization auxiliary materials such as chain transfer agents, dispersants, oxygen scavengers, chelating agents, particle size modifiers, surfactants, molecular weight modifiers, inorganic salts, and pH adjusters may be used as needed. The type and amount of these materials used are not particularly limited.

[0051] The average particle size of the resin particles used as the dispersed phase in the rubbery latex produced in step 1 is preferably 40 nm or more, more preferably 50 nm or more, and even more preferably 60 nm or more, from the viewpoint of obtaining a resin with excellent impact resistance, and from the viewpoint of polymerization stability of the rubbery latex production method, it is preferably 150 nm or less, more preferably 120 nm or less, and even more preferably 110 nm or less. Furthermore, the resin particles used as the dispersed phase in the rubbery latex are polymer particles of monomer mixture (I) or monomer mixture (II).

[0052] ≪Process 2≫ The present invention's method for producing rubbery latex may also include, in addition to step 1, step 2, which increases the particle size of the dispersed phase in the rubbery latex produced in step 1. From a productivity standpoint, step 2 may use the rubbery latex obtained in step 1 as is, or, from the viewpoint of facilitating particle size control of the dispersed phase, the dispersed phase may be filtered from the rubbery latex obtained in step 1 before proceeding.

[0053] In step 2, the resin particles as a dispersed phase are fused together by adding an acid component or salt, or by mechanical force, thereby increasing the particle size of the dispersed phase. In particular, step 2 is preferably carried out by adding an acid component. When an acid component is used in step 2, the acid component is preferably an inorganic acid such as hydrochloric acid or sulfuric acid, and an organic acid such as acetic acid, and more preferably acetic acid. The pH of the rubbery latex after the addition of the acid component is preferably 5.5 or less, more preferably 5.0 or less, and even more preferably 4.5 or less, from the viewpoint of increasing the particle size of the dispersed phase after agglomeration, and from the viewpoint of the stability of the dispersed phase after acid agglomeration, it is preferably 2.5 or higher, more preferably 3.0 or higher, and even more preferably 3.5 or higher. When salt is used in step 2, the salt is preferably a sodium salt, potassium salt, or calcium salt, and more preferably a sodium salt, from the viewpoint of increasing the particle size of the dispersed phase after agglomeration. The amount of salt added to the rubbery latex is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of polymer of monomer mixture (I) or monomer mixture (II), from the viewpoint of the stability of the dispersed phase after acid agglomeration, and from the viewpoint of economy, preferably 10 parts by mass or less, more preferably 9 parts by mass or less, and even more preferably 8 parts by mass or less. When mechanical force is applied in step 2, the mechanical force can be applied to the rubbery latex using, for example, an ultrasonic homogenizer or a high-pressure homogenizer, and from the viewpoint of productivity, a high-pressure homogenizer is preferred.

[0054] The temperature at which step 2 is performed is preferably 20°C to 50°C, from the viewpoint of keeping the average particle size of the dispersed particles in the rubbery latex within the desired range.

[0055] The average particle size of the dispersed phase in the rubbery latex obtained in step 2 is preferably greater than 130 nm, more preferably 140 nm or more, and even more preferably 150 nm or more, from the viewpoint of obtaining a resin with excellent impact resistance, and preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 350 nm or less, from the viewpoint of the stability of graft polymerization in step 3.

[0056] [Graft copolymer] ≪Step 3≫ The present invention provides a method for producing a graft copolymer, comprising step 3 of emulsion polymerization of a monomer mixture (III) containing a rubbery latex produced by the above production method and an aromatic vinyl monomer, and one or more selected from vinyl monomers having a cyano group and (meth)acrylate monomers, in the presence of an emulsifier mixture.

[0057] [Monomer mixture (III)] Monomer mixture (III) comprises an aromatic vinyl monomer and one or more selected from vinyl monomers having a cyano group and (meth)acrylate monomers. Examples of aromatic vinyl monomers and vinyl monomers having cyano groups include the aromatic vinyl monomers and vinyl monomers having cyano groups shown in monomer mixture (I) and monomer mixture (II) above. Examples of (meth)acrylate monomers include methyl (meth)acrylate.

[0058] In step 1, if monomer mixture (I) containing at least one diene monomer is used, monomer mixture (III) preferably contains an aromatic vinyl monomer and a vinyl monomer or (meth)acrylate monomer having a cyano group. Furthermore, if a monomer mixture (II) containing at least one alkyl acrylate monomer is used in step 1, it is preferable that monomer mixture (III) contains an aromatic vinyl monomer and a vinyl monomer having a cyano group.

[0059] <Emulsifier mixture> Examples of emulsifier mixtures used as emulsifiers for emulsion polymerization in step 3 include those used in step 1, and the preferred range is also the same. If step 3 is performed in a one-pot manner from step 1, it is not necessary to add the emulsifier mixture again in step 3, but it may be added if necessary. If the method for producing rubbery latex includes step 2 above, and an acidic component is added in step 2, the emulsifier mixture used in step 1 may be regenerated and used by adding a basic component.

[0060] (Radical polymerization initiator) The radical polymerization initiator used in the emulsion polymerization of step 3 is the same as the radical polymerization initiator used in step 1, and the amount of radical polymerization initiator used per monomer mixture (III) is the same as the amount of radical polymerization initiator used per 100 parts by mass of monomer mixture (I) or monomer mixture (II) shown in step 1.

[0061] In step 3, the amount of monomer mixture (III) blended with 100 parts by mass of dispersed phase in the rubbery latex obtained above is preferably 35% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, from the viewpoint of obtaining a resin with excellent impact resistance, and preferably 65% ​​by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less, from the viewpoint of economic efficiency.

[0062] In step 3, the amount of monomer mixture (III) added is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, relative to the total mass of the rubbery latex, monomer mixture (III), and dispersion medium, from the viewpoint of economic efficiency, and preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less, from the viewpoint of improving the polymerization stability of the rubbery latex production method. In step 3, the dispersion medium is an aqueous medium, preferably water, and the preferred aqueous medium and the water content in the aqueous medium are the same as in step 1.

[0063] In step 3, there are no particular restrictions on the emulsion polymerization conditions, but preferably they are the same as those in step 1. In step 3, emulsion polymerization may be stopped by cooling the reaction system, or by adding a pH adjuster and a polymerization inhibitor.

[0064] The graft copolymer can be recovered from the graft copolymer latex obtained by emulsion polymerization in step 3 using known methods. For example, the graft copolymer can be precipitated by adding an acid component such as hydrochloric acid or sulfuric acid, or a salt such as magnesium chloride, magnesium sulfate, or calcium chloride, and then recovered by filtration or other means.

[0065] (Compound) The graft copolymer obtained above may be mixed with other resins to form a compound having a sea-island structure in which the graft copolymer is contained as domains and the other resin as a matrix. As for other resins, copolymerization of monomers used as monomer mixture (III) is preferred from the viewpoint of compatibility with graft copolymers. That is, for example, when monomer mixture (III) containing an aromatic vinyl monomer and a (meth)acrylate monomer is used, the other resin may be a copolymer of the aromatic vinyl monomer and the (meth)acrylate monomer, and when monomer mixture (III) containing an aromatic vinyl monomer and a vinyl monomer having a cyano group is used, the other resin may be a copolymer of the aromatic vinyl monomer and the vinyl monomer having a cyano group.

[0066] The mixing of the graft copolymer with other resins is preferably carried out using, for example, a twin-screw extruder. There are no particular restrictions on the mixing temperature, but from the viewpoint of improving the miscibility with other resins, it is preferable that it be between 200°C and 300°C.

[0067] [Emulsifier for emulsion polymerization] The emulsifier for emulsion polymerization of the present invention includes a salt of compound A, which contains one or more selected from rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3), as well as a salt of a compound represented by the following formula (1).

[0068] RO-(AO) n -CH2-COOH (1)

[0069] In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is 1 to 50.

[0070] Examples of salts of compound A and salts of the compound represented by formula (1) include those similar to those of salts of compound A and salts of the compound represented by formula (1) contained in the emulsifier mixture used in step 1 above, and the preferred range is also the same.

[0071] The mass ratio of the compound represented by formula (1) to compound A in the emulsifier for emulsion polymerization (compound represented by formula (1) / compound A) is preferably 1 / 99 or more, more preferably 1.5 / 98.5 or more, and even more preferably 2 / 98 or more, from the viewpoint of improving the polymerization stability of emulsion polymerization and stability during acid aggregation, and from the viewpoint of economic efficiency, preferably 60 / 40 or less, more preferably 50 / 50 or less, and preferably 40 / 60 or less.

[0072] The emulsifier for emulsion polymerization of the present invention can be used for emulsion polymerization of polymerizable monomers, and preferably for emulsion polymerization of monomer mixtures containing at least one of monomer mixture (I), monomer mixture (II), and monomer mixture (III).

[0073] With respect to the embodiments described above, the present invention further discloses a method for producing a rubbery latex, a method for producing a graft copolymer using the rubbery latex, and an emulsifier for emulsion polymerization used in the method for producing the rubbery latex. <1> A method for producing a rubbery latex, comprising step 1 of emulsion polymerization of a monomer mixture (I) containing at least one diene monomer or a monomer mixture (II) containing at least one alkyl acrylate monomer, in the presence of an emulsifier mixture containing a salt of compound A containing one or more selected from rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3), and a salt of a compound represented by the following formula (1). RO-(AO) n -CH2-COOH (1) (In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is between 1 and 50.) <2> The mass ratio of the compound represented by formula (1) to compound A (compound represented by formula (1) / compound A) is 1 / 99 or more and 60 / 40 or less, preferably 1.5 / 98.5 or more and 50 / 50 or less, more preferably 2 / 98 or more and 40 / 60 or less. <1> A method for producing the rubbery latex described above. <3> The mass ratio (A2 / A3) of the saturated fatty acid (A2) having 12 to 18 carbon atoms and the unsaturated fatty acid (A3) having one double bond with 12 to 18 carbon atoms is 40 / 60 or more, preferably 45 / 55 or more, more preferably 50 / 50 or more, and preferably 100 / 0 or less. <1> or <2> A method for producing the rubbery latex described above. <4> In the saturated fatty acid (A2) having 12 to 18 carbon atoms, the mass ratio of saturated fatty acid having 12 to 15 carbon atoms to saturated fatty acid having 16 to 18 carbon atoms (saturated fatty acid having 12 to 15 carbon atoms / saturated fatty acid having 16 to 18 carbon atoms) is 55 / 45 or less, preferably 50 / 50 or less, and more preferably 45 / 55 or less. <1> ~ <3> A method for producing rubbery latex as described in any of the following. <5> In the unsaturated fatty acid (A3) having one double bond between 12 to 18 carbon atoms, the mass ratio of the unsaturated fatty acid having one double bond between 12 to 15 carbon atoms to the unsaturated fatty acid having one double bond between 16 to 18 carbon atoms (unsaturated fatty acid having one double bond between 12 to 15 carbon atoms / unsaturated fatty acid having one double bond between 16 to 18 carbon atoms) is 10 / 90 or less, preferably 5 / 95 or less, and more preferably 0 / 100. <1> ~ <4> A method for producing rubbery latex as described in any of the following. <6> The salt of compound A and the salt of the compound represented by formula (1) are at least one selected from the group consisting of potassium salts, sodium salts, lithium salts, ammonium salts, and lower amine salts. <1> ~ <5> A method for producing rubbery latex as described in any of the following. <7> In formula (1), the chain length of the hydrocarbon group of R is 6 or more, preferably 8 or more, more preferably 10 or more, and 20 or less, preferably 18 or less. <1> ~ <6> A method for producing rubbery latex as described in any of the following. <8> In formula (1), AO is preferably an ethylene oxy group. <1> ~ <7> A method for producing rubbery latex as described in any of the following. <9> In formula (1), n is 1 or more, preferably 2 or more, and 50 or less, preferably 40 or less, more preferably 30 or less, still more preferably 20 or less, and is a method for producing a rubbery latex according to any one of <1> to <8>. <10> The total amount of the compound A and the compound represented by formula (1) with respect to 100 parts by mass of the monomer mixture (I) or the monomer mixture (II) is 0.1 part by mass or more and 5.0 parts by mass or less, preferably 1.0 part by mass or more and 4.0 parts by mass or less, more preferably 2.0 parts by mass or more and 3.5 parts by mass or less, still more preferably 2.5 parts by mass or more and 3.5 parts by mass or less, and is a method for producing a rubbery latex according to any one of <1> to <9>. <11> A method for producing a rubbery latex according to any one of <1> to <10>, which includes step 2 of increasing the particle size of the dispersed substance in the rubbery latex produced in step 1. <12> The method for producing a rubbery latex according to <11>, wherein step ② is performed by adding an acid component. <13> The pH of the rubbery latex after the addition of the acid component is 5.5 or less, preferably 5.0 or less, more preferably 4.5 or less, and 2.5 or more, preferably 3.0 or more, more preferably 3.5 or more, and is a method for producing a rubbery latex according to <12>. <14> A method for producing a graft copolymer, which includes step ③ of emulsion polymerization of a rubbery latex produced by the production method according to any one of <1> to <13>, an aromatic vinyl monomer, and one or more selected from a vinyl monomer having a cyano group and a (meth)acrylate monomer, and The emulsion polymerization is carried out in the presence of an emulsifier mixture containing one or more selected from rosin acid (A1), a saturated fatty acid (A2) having 12 to 18 carbon atoms, and an unsaturated fatty acid (A3) having one double bond having 12 to 18 carbon atoms, and a salt of a compound represented by the following formula (1). A method for producing a graft copolymer. R-O-(AO) n -CH2-COOH (1) (In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is between 1 and 50.) <15> <1> ~ <13> The amount of monomer mixture (III) blended with 100 parts by mass of dispersed phase in rubbery latex produced by any of the manufacturing methods described herein is 35% by mass or more, preferably 40% by mass or more, more preferably 45% by mass or more, and 65% by mass or less, preferably 60% by mass or less, more preferably 55% by mass or less. <15> A method for producing the graft copolymer described above. <16> An emulsifier for emulsion polymerization comprising a salt of compound A, which contains one or more selected from rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond having 12 to 18 carbon atoms (A3), and a salt of a compound represented by the following formula (1). RO-(AO) n -CH2-COOH (1) (In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is between 1 and 50.) <17> The mass ratio of the compound represented by formula (1) to the compound A is 1 / 99 or more and 60 / 40 or less, preferably 1.5 / 98.5 or more and 50 / 50 or less, and more preferably 2 / 98 or more and 40 / 60 or less. <16> The emulsifier for emulsion polymerization described above. [Examples]

[0074] The present invention will be specifically described below with reference to examples, but the present invention is not limited in any way by these examples.

[0075] [Average particle size of particles in latex] Using a particle size and molecular weight measurement system (manufactured by Otsuka Electronics Co., Ltd., product name: ELSZ-1000ZS), the average particle size of particles in rubbery latex was measured after diluting the rubbery latex 30,000 times. The measurement and analysis method used was the cumulant average particle size obtained by accumulating 70 measurements.

[0076] [Manufacturing of emulsifier mixtures] Manufacturing Example 1 (Manufacturing of Emulsifier Mixture 1) In a 300 mL four-necked flask equipped with a stirrer and a raw material inlet, 98.01 g of deionized water and 7.59 g of 48% potassium hydroxide solution (manufactured by Kanto Chemical Co., Ltd.) were charged. Then, 15.33 g of purified stearic acid 450V (manufactured by Kao Corporation) and 4.07 g of Kao Akipo RLM-45 (manufactured by Kao Corporation) were added. The mixture was heated to 75°C and stirred for 2 hours to obtain emulsifier mixture 1 with a solid content of 17.5% by mass. The content of each compound in emulsifier mixture 1 is shown in Table 1.

[0077] Manufacturing Example 2 (Manufacturing of Emulsifier Mixture 2) In a 500 mL four-necked flask equipped with a stirrer and a raw material inlet, 240.51 g of deionized water and 19.86 g of 48% potassium hydroxide solution (manufactured by Kanto Chemical Co., Ltd.) were charged. Then, 46.07 g of DFA-T45 (manufactured by Miyoshi Oil & Fat Co., Ltd.) and 1.25 g of Kao Akipo RLM-45 (manufactured by Kao Corporation) were added. The mixture was heated to 75°C and stirred for 2 hours to obtain emulsifier mixture 2 with a solid content of 17.5% by mass. The content of each compound in emulsifier mixture 2 is shown in Table 1.

[0078] Manufacturing Example 3 (Manufacturing of Emulsifier Mixture 3) In a 300 mL four-necked flask equipped with a stirrer and a raw material inlet, 134.08 g of deionized water and 12.18 g of 48% potassium hydroxide solution (manufactured by Kanto Chemical Co., Ltd.) were charged. Then, 4.69 g of Lunac L-98 (manufactured by Kao Corporation), 4.99 g of Lunac MY-98 (manufactured by Kao Corporation), 7.48 g of Lunac P-95 (manufactured by Kao Corporation), 6.23 g of Lunac S-90V (manufactured by Kao Corporation), 1.42 g of oleic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), and 1.40 g of Kao Akipo RLM-45 (manufactured by Kao Corporation) were added. The mixture was heated to 75°C and stirred for 2 hours to obtain emulsifier mixture 3 with a solid content of 17.5% by mass. The content of each compound in emulsifier mixture 3 is shown in Table 1.

[0079] Comparative manufacturing example 1 (manufacturing of emulsified mixture C1) In a 300 mL four-necked flask equipped with a stirrer and a raw material inlet, 170.53 g of deionized water and 14.37 g of 48% potassium hydroxide solution (manufactured by Kanto Chemical Co., Ltd.) were charged. Then, 33.50 g of purified stearic acid 450V (manufactured by Kao Corporation) was added, the mixture was heated to 75°C, and stirred for 2 hours to obtain an emulsion mixture C1 with a solid content of 17.5% by mass. The content of each compound in emulsion mixture C1 is shown in Table 1.

[0080] Comparative manufacturing example 2 (manufacturing of emulsified mixture C2) In a 1L four-necked flask equipped with a stirrer and a raw material inlet, 330.60g of deionized water and 27.60g of 48% potassium hydroxide solution (manufactured by Kanto Chemical Co., Ltd.) were charged. Then, 65.00g of DFA-T45 (manufactured by Miyoshi Oil & Fat Co., Ltd.) was added, the mixture was heated to 75°C, and stirred for 2 hours to obtain an emulsion mixture C2 with a solid content of 17.5% by mass. The content of each compound in emulsion mixture C2 is shown in Table 1.

[0081] Comparative manufacturing example 3 (manufacturing of emulsified mixture C3) In a 1L four-necked flask equipped with a stirrer and a raw material inlet, 448.61g of deionized water and 41.81g of 48% potassium hydroxide solution (manufactured by Kanto Chemical Co., Ltd.) were charged. Then, 16.45g of Lunac L-98 (manufactured by Kao Corporation), 17.50g of Lunac MY-98 (manufactured by Kao Corporation), 26.25g of Lunac P-95 (manufactured by Kao Corporation), 21.88g of Lunac S-90V (manufactured by Kao Corporation), and 5.43g of Lunac OV (manufactured by Kao Corporation) were added. The mixture was heated to 75°C and stirred for 2 hours to obtain an emulsion mixture C3 with a solid content of 17.5% by mass. The content of each compound in emulsion mixture C3 is shown in Table 1.

[0082] Comparative manufacturing example 4 (manufacturing of emulsifier C4) In a 300 mL four-necked flask equipped with a stirrer and a raw material inlet, 341.76 g of deionized water and 16.11 g of 48% potassium hydroxide solution (manufactured by Kanto Chemical Co., Ltd.) were charged. Then, 70.00 g of Kao Akipo RLM-45 (manufactured by Kao Corporation) was added, the mixture was heated to 75°C, and stirred for 2 hours to obtain emulsifier C4 with a solid content of 17.6% by mass.

[0083] [Table 1]

[0084] [Manufacturing of rubbery latex] Example 1 (Manufacturing of rubbery latex 1) (Process 1) In a 1L four-necked flask equipped with a stirrer and a raw material inlet, 270.76g of deionized water, 0.21g of potassium persulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, and 5.14g of emulsifier mixture 1 (0.90g as active ingredient) were mixed to obtain an aqueous solution with a pH of 11.0. 7.5g of butyl acrylate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the obtained aqueous solution, nitrogen purging was performed, and the temperature was raised to 80°C for 30 minutes to carry out emulsion polymerization. Subsequently, 21.39g of emulsifier mixture 1 (3.75g as active ingredient), 0.09g of potassium persulfate, and a mixed aqueous solution of 57.21g of deionized water, along with 142.5g of butyl acrylate, were added dropwise over 2 hours. After the dropwise addition was complete, the mixture was aged for another hour at 80°C. This was cooled to 30°C and filtered through a 200-mesh wire mesh to remove coarse particles, yielding a rubbery latex in which resin particles with an average particle size of 91 nm were dispersed.

[0085] (Process 2) 25 g of the rubbery latex produced in step 1 above was placed in a screw vial and stirred with a magnetic stirrer at 600 rpm. A 5% by mass aqueous acetic acid solution was gradually added dropwise to lower the pH to 4.5, and then a 10% by mass aqueous acetic acid solution was added dropwise to obtain a polymer emulsion solution with a pH of 4.0. After standing for 5 hours, aggregates were removed by filtration through a 200-mesh wire mesh to obtain rubbery latex 1 with an average particle size 2 of the dispersed phase growing to 151 nm.

[0086] Examples 2 and 3, and Comparative Examples 1-4 (Production of rubber latex 2 and 3, and rubber latex C1-C4) In Example 1, the emulsifier mixture 1 was changed to the emulsifier mixture shown in Table 2, and the amount of each emulsifier mixture used relative to 100 parts by mass of butyl acrylate was changed as shown in Table 2. The same procedure was followed to obtain rubber latex 2 and 3, and rubber latex C1 to C4. Table 2 shows the average particle size 1 of the resin particles in the rubber latex produced in Step 1, and the average particle size 2 of the resin particles in rubber latex 2 and 3, and rubber latex C1 to C4, produced in Step 2.

[0087] 〔evaluation〕 The polymerization stability and acid aggregation stability of the examples and comparative examples were evaluated by the following method. The evaluation results are shown in Table 2.

[0088] (Polymerization stability) In step 1, the coarse particles removed by filtration through a 200-mesh wire mesh were washed with water and then dried under reduced pressure at 105°C for 2 hours. The dried aggregates were weighed, and the ratio of coarse particles to the mass of butyl acrylate used as a raw material was used as an indicator for evaluating polymerization stability. The ratio of coarse particles to the mass of butyl acrylate used as a raw material is shown in Table 2. A lower ratio of coarse particles indicates better emulsion polymerization stability.

[0089] (Acid aggregation stability) In step 2, the aggregates removed by filtration through a 200-mesh wire mesh were washed with water and then dried under reduced pressure at 105°C for 2 hours. The dried coarse particles were weighed, and the ratio of aggregates to the mass of dispersed phase in the rubbery latex produced in step 1 was used as an indicator for evaluating acid agglomeration stability. A lower ratio of aggregates indicates better acid agglomeration stability.

[0090] [Table 2]

[0091] Table 2 shows that the polymerization stability of the rubber latex production methods in Examples 1-3 was comparable to or superior to that of the rubber latex production methods of the corresponding comparative examples. Furthermore, the average particle size 1 of the rubber latex in the examples was comparable to that of the rubber latex production methods of the comparative examples. From the above, it can be seen that the production method of the present invention exhibits comparable stability in emulsion polymerization compared to conventional rubber latex production methods. Note that the blending ratios of the saturated fatty acid (A2) salts and unsaturated fatty acid (A3) salts in emulsion mixtures 1-3 used in Examples 1-3 were the same as the blending ratios of the saturated fatty acid (A2) salts and unsaturated fatty acid (A3) salts in emulsion mixtures C1-C3 used in the corresponding comparative examples 1-3. Furthermore, the acid agglomeration stability of the rubber latex production methods in Examples 1 to 3 was superior to that of the corresponding rubber latex production methods in Comparative Examples 1 to 3. In Comparative Example 4, acid agglomeration hardly progressed in step 2, and the particle size of the dispersed phase in the rubber latex obtained in step 1 hardly increased.

Claims

1. A method for producing a rubbery latex, comprising step 1 of emulsion polymerization of a monomer mixture (I) containing at least one diene monomer or a monomer mixture (II) containing at least one alkyl acrylate monomer, in the presence of an emulsifier mixture containing a salt of compound A containing one or more selected from rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond having 12 to 18 carbon atoms (A3), and a salt of a compound represented by the following formula (1). R-O-(AO) ｎ - CH ２ - COOH (1) (In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is 1 to 50.)

2. A method for producing a rubbery latex according to claim 1, wherein the mass ratio of the compound represented by formula (1) to the compound A (compound represented by formula (1) / compound A) is 1 / 99 or more and 60 / 40 or less.

3. The method for producing a rubbery latex according to claim 1, wherein the salt of compound A and the salt of the compound represented by formula (1) are at least one selected from the group consisting of potassium salts, sodium salts, lithium salts, ammonium salts, and lower amine salts.

4. A method for producing a rubbery latex according to claim 1, wherein the total amount of compound A and the compound represented by formula (1) per 100 parts by mass of the monomer mixture (I) or monomer mixture (II) is 0.1 parts by mass or more and 5.0 parts by mass or less.

5. A method for producing rubbery latex according to claim 1, comprising step 2 of increasing the particle size of the dispersed phase in the rubbery latex produced in step 1.

6. A method for producing a graft copolymer comprising step 3 of emulsion polymerization of a rubbery latex produced by the manufacturing method described in any one of claims 1 to 5, and a monomer mixture (III) containing an aromatic vinyl monomer and one or more selected from vinyl monomers having a cyano group and (meth)acrylate monomers, A method for producing a graft copolymer, wherein the emulsion polymerization is carried out in the presence of a compound A, which contains one or more compounds selected from rosin acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond with 12 to 18 carbon atoms (A3), and an emulsifier mixture containing a salt of a compound represented by the following formula (1). R-O-(AO) ｎ - CH ２ - COOH (1) (In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is 1 to 50.)

7. An emulsifier for emulsion polymerization comprising a salt of compound A, which contains one or more selected from rosinic acid (A1), a saturated fatty acid having 12 to 18 carbon atoms (A2), and an unsaturated fatty acid having one double bond having 12 to 18 carbon atoms (A3), and a salt of a compound represented by the following formula (1). R-O-(AO) ｎ - CH ２ - COOH (1) (In formula (1), R is a hydrocarbon group having 4 to 22 carbon atoms, AO represents an ethylene oxy group or a propylene oxy group, and n is 1 to 50.)

8. The emulsifier for emulsion polymerization according to claim 7, wherein the mass ratio of the compound represented by formula (1) to the compound A is 1 / 99 or more and 60 / 40 or less.

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