Method for producing carboxyl group-containing liquid nitrile rubber

Abstract

The present invention provides a method for producing a carboxyl group-containing liquid nitrile rubber in which a latex of the carboxyl group-containing liquid nitrile rubber is brought into contact with a monovalent or divalent metal salt under conditions having a pH of 5 or less, thereby salting out the carboxyl group-containing liquid nitrile rubber and separating the carboxyl group-containing liquid nitrile rubber from an aqueous phase.

Description

[0001] This application is a divisional application of the invention patent application with the application number 202080007836.8. The filing date of the original application is January 15, 2020, and the invention title is "Method for manufacturing carboxyl group-containing liquid nitrile rubber". Technical Field

[0002] The present invention relates to a method for manufacturing a carboxyl group-containing liquid nitrile rubber. More specifically, the present invention relates to a method for manufacturing a carboxyl group-containing liquid nitrile rubber capable of manufacturing a carboxyl group-containing liquid nitrile rubber, which has excellent stability during storage and can achieve excellent surface smoothness when mixed with an adhesive polymer to form an adhesive material for a flexible printed circuit board. Background Art

[0003] Liquid diene rubbers such as liquid nitrile rubber are used as main components of coatings, primers, adhesives, etc., and can be used as a plasticizer capable of co-crosslinking by blending with solid rubber.

[0004] For example, in Patent Document 1, an oil-resistant rubber composition containing a liquid nitrile rubber containing a methacrylic acid unit as a carboxyl group-containing monomer unit and a solid nitrile rubber is disclosed.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Publication No. 50-27486. Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] On the one hand, the storage stability of existing liquid nitrile rubbers such as the liquid nitrile rubber used in the above Patent Document 1 is insufficient. When stored for a certain period, the viscosity will increase. Therefore, when compounded with solid rubber, resin, etc., there is a problem that the properties of the obtained compound are unstable.

[0010] The present invention has been completed in view of such actual situations, and aims to provide a method for manufacturing a carboxyl group-containing liquid nitrile rubber capable of manufacturing a carboxyl group-containing liquid nitrile rubber, which has excellent stability during storage and can achieve excellent surface smoothness when mixed with an adhesive polymer to form an adhesive material for a flexible printed circuit board.

[0011] Solutions to the Problems

[0012] The inventors of the present invention conducted in-depth research to achieve the above object, and as a result, it was found that when separating the carboxyl group-containing liquid nitrile rubber from the latex of the carboxyl group-containing liquid nitrile rubber, the carboxyl group-containing liquid nitrile rubber is brought into contact with a monovalent or divalent metal salt under the condition that the pH is 5 or less, and the carboxyl group-containing liquid nitrile rubber is salting-out, whereby the above object can be achieved, and thus the present invention was completed.

[0013] That is, according to the present invention, a method for producing a carboxyl group-containing liquid nitrile rubber can be provided, which has a step of bringing the latex of the carboxyl group-containing liquid nitrile rubber into contact with a monovalent or divalent metal salt under the condition that the pH is 5 or less, thereby causing salting-out of the carboxyl group-containing liquid nitrile rubber and separating it from the aqueous phase.

[0014] In the production method of the present invention, it is preferable that the above carboxyl group-containing liquid nitrile rubber contains a carboxyl group-containing monomer unit in a proportion of 1 to 20% by weight.

[0015] In the production method of the present invention, it is preferable that the above carboxyl group-containing liquid nitrile rubber contains an α,β-ethylenically unsaturated nitrile monomer unit in a proportion of 10 to 59% by weight.

[0016] In the production method of the present invention, it is preferable that the above carboxyl group-containing liquid nitrile rubber contains a conjugated diene monomer unit in a proportion of 40 to 89% by weight.

[0017] In the production method of the present invention, it is preferable that the above monovalent or divalent metal salt is a monovalent or divalent metal salt of an inorganic acid.

[0018] In the production method of the present invention, it is preferable that the above monovalent or divalent metal salt is a divalent metal salt, and the usage amount of the above divalent metal salt is 1 to 10 parts by weight with respect to 100 parts by weight of the carboxyl group-containing liquid nitrile rubber contained in the latex of the carboxyl group-containing liquid nitrile rubber.

[0019] In the production method of the present invention, it is preferable that the latex of the above carboxyl group-containing liquid nitrile rubber is brought into contact with an aqueous solution containing the above monovalent or divalent metal salt under the condition that the pH is 5 or less, thereby causing salting-out of the carboxyl group-containing liquid nitrile rubber.

[0020] In the production method of the present invention, it is preferable that the concentration of the above monovalent or divalent metal salt in the aqueous solution containing the above monovalent or divalent metal salt is 1 to 10% by weight.

[0021] Advantages of the Invention

[0022] According to the production method of the present invention, a carboxyl group-containing liquid nitrile rubber having excellent stability during storage and excellent surface smoothness when mixed with an adhesive polymer to form an adhesive material for a flexible printed circuit board can be produced. Detailed Embodiments

[0023] The manufacturing method of the carboxyl group-containing liquid nitrile rubber of the present invention has a step of bringing the latex of the carboxyl group-containing liquid nitrile rubber into contact with a monovalent or divalent metal salt under the condition that the pH is 5 or less, thereby causing salting out of the carboxyl group-containing liquid nitrile rubber and separating it from the aqueous phase.

[0024] <Latex of carboxyl group-containing liquid nitrile rubber>

[0025] First, the latex of the carboxyl group-containing liquid nitrile rubber used in the present invention will be described.

[0026] The latex of the carboxyl group-containing liquid nitrile rubber used in the present invention is a dispersion in which the carboxyl group-containing liquid nitrile rubber is dispersed in water.

[0027] The carboxyl group-containing liquid nitrile rubber contained in the latex of the carboxyl group-containing liquid nitrile rubber is a carboxyl group-containing nitrile rubber having a liquid state at 25°C (flowable at 25°C). For the carboxyl group-containing liquid nitrile rubber, the Mooney viscosity measured according to, for example, JIS K6300 is usually 1 or less, or the viscosity is too low to measure the Mooney viscosity.

[0028] The carboxyl group-containing liquid nitrile rubber constituting the latex of the carboxyl group-containing liquid nitrile rubber is a liquid rubber that can be obtained by copolymerizing, for example, an α,β-ethylenically unsaturated nitrile monomer, a carboxyl group-containing monomer, and, if necessary, a monomer copolymerizable with them.

[0029] The α,β-ethylenically unsaturated nitrile monomer is not particularly limited, and preferably has 3 to 18 carbon atoms, and particularly preferably has 3 to 9 carbon atoms. Specific examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, etc., and acrylonitrile is preferred. These α,β-ethylenically unsaturated nitrile monomers can be used alone or in combination of two or more.

[0030] The content of the α,β-ethylenically unsaturated nitrile monomer unit in the carboxyl group-containing liquid nitrile rubber is preferably 10 to 59% by weight, more preferably 13 to 53% by weight, and further preferably 17 to 47% by weight. By making the content of the α,β-ethylenically unsaturated nitrile monomer unit within the above range, the solvent resistance and cold resistance can be balanced and excellent.

[0031] As the carboxyl group-containing monomer, as long as it can copolymerize with the α,β-ethylenically unsaturated nitrile monomer and has one or more unsubstituted (free) carboxyl groups that are not esterified or the like, it is not particularly limited. By using the carboxyl group-containing monomer, a carboxyl group can be introduced into the liquid nitrile rubber, thereby improving the solvent resistance and adhesiveness when a polymer blend with adhesiveness such as resin and solid rubber is made into an adhesive material.

[0032] Examples of the carboxyl group-containing monomers used in the present invention include α,β-ethylenically unsaturated monocarboxylic acid monomers, α,β-ethylenically unsaturated polycarboxylic acid monomers, and α,β-ethylenically unsaturated dicarboxylic acid monoester monomers. In addition, the carboxyl group-containing monomers also include monomers in which the carboxyl groups of these monomers form carboxylate salts. Furthermore, acid anhydrides of α,β-ethylenically unsaturated polycarboxylic acids can also be used as carboxyl group-containing monomers because the acid anhydride groups will cleave to form carboxyl groups after copolymerization.

[0033] Examples of the α,β-ethylenically unsaturated monocarboxylic acid monomers include acrylic acid, methacrylic acid, ethylacrylic acid, crotonic acid, cinnamic acid, and the like.

[0034] Examples of the α,β-ethylenically unsaturated polycarboxylic acid monomers include fumaric acid, maleic acid and other butenedioic acids; itaconic acid; citraconic acid; mesaconic acid; glutaconic acid; allylmalonic acid; yunconic acid, etc. In addition, examples of the acid anhydrides of α,β-ethylenically unsaturated polycarboxylic acids include maleic anhydride, itaconic anhydride, citraconic anhydride, etc.

[0035] Examples of the α,β-ethylenically unsaturated dicarboxylic acid monoester monomers include maleic acid monoalkyl esters such as maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid monopropyl ester, maleic acid monobutyl ester; maleic acid monocycloalkyl esters such as maleic acid monocyclopentyl ester, maleic acid monocyclohexyl ester, maleic acid monocycloheptyl ester; maleic acid monoalkylcycloalkyl esters such as maleic acid monomethylcyclopentyl ester, maleic acid monoethylcyclohexyl ester; fumaric acid monoalkyl esters such as fumaric acid monomethyl ester, fumaric acid monoethyl ester, fumaric acid monopropyl ester, fumaric acid monobutyl ester; fumaric acid monocycloalkyl esters such as fumaric acid monocyclopentyl ester, fumaric acid monocyclohexyl ester, fumaric acid monocycloheptyl ester; fumaric acid monoalkylcycloalkyl esters such as fumaric acid monomethylcyclopentyl ester, fumaric acid monoethylcyclohexyl ester; citraconic acid monoalkyl esters such as citraconic acid monomethyl ester, citraconic acid monoethyl ester, citraconic acid monopropyl ester, citraconic acid monobutyl ester; citraconic acid monocycloalkyl esters such as citraconic acid monocyclopentyl ester, citraconic acid monocyclohexyl ester, citraconic acid monocycloheptyl ester; citraconic acid monoalkylcycloalkyl esters such as citraconic acid monomethylcyclopentyl ester, citraconic acid monoethylcyclohexyl ester; itaconic acid monoalkyl esters such as itaconic acid monomethyl ester, itaconic acid monoethyl ester, itaconic acid monopropyl ester, itaconic acid monobutyl ester; itaconic acid monocycloalkyl esters such as itaconic acid monocyclopentyl ester, itaconic acid monocyclohexyl ester, itaconic acid monocycloheptyl ester; itaconic acid monoalkylcycloalkyl esters such as itaconic acid monomethylcyclopentyl ester, itaconic acid monoethylcyclohexyl ester, etc.

[0036] The carboxyl group-containing monomers can be used alone or in combination of two or more. Among these, from the aspect that the effect of introducing carboxyl groups into the liquid nitrile rubber becomes more significant, α,β-ethylenically unsaturated monocarboxylic acid monomers are preferred, acrylic acid or methacrylic acid is preferred, and methacrylic acid is more preferred.

[0037] The content of the carboxyl group-containing monomer unit in the carboxyl group-containing liquid nitrile rubber is preferably 1 to 20% by weight, more preferably 2 to 15% by weight, and still more preferably 3 to 10% by weight. By making the content of the carboxyl group-containing monomer unit within the above range, the solvent resistance and adhesiveness can be improved when a bonding material is prepared by polymer blending with a resin, a solid rubber, etc.

[0038] In addition, the carboxyl group-containing liquid nitrile rubber constituting the latex used in the present invention is preferably copolymerized from an α,β-ethylenically unsaturated nitrile monomer, a carboxyl group-containing monomer, and a conjugated diene monomer.

[0039] As the conjugated diene monomer, conjugated diene monomers having 4 to 6 carbon atoms such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene are preferred, 1,3-butadiene and isoprene are more preferred, and 1,3-butadiene is particularly preferred. The conjugated diene monomer can be used alone or in combination of two or more.

[0040] The content of the conjugated diene monomer unit in the carboxyl group-containing liquid nitrile rubber is preferably 40 to 89% by weight, more preferably 45 to 85% by weight, and still more preferably 50 to 80% by weight. By making the content of the conjugated diene monomer unit within the above range, good rubber elasticity can be ensured, and the oil resistance, heat aging resistance, and chemical stability are excellent.

[0041] In addition, the carboxyl group-containing liquid nitrile rubber can be copolymerized from an α,β-ethylenically unsaturated nitrile monomer, a carboxyl group-containing monomer, a conjugated diene monomer, and other monomers copolymerizable therewith. As such other monomers, α-olefin monomers, aromatic vinyl monomers, α,β-ethylenically unsaturated carboxylic acid ester monomers (except for monomers belonging to the above-mentioned "carboxyl group-containing monomers"), fluorine-containing vinyl monomers, copolymerizable anti-aging agents, etc. can be exemplified.

[0042] As the α-olefin monomer, α-olefin monomers having 3 to 12 carbon atoms are preferred, and examples thereof include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, etc.

[0043] As the aromatic vinyl monomer, examples thereof include styrene, α-methylstyrene, vinylpyridine, etc.

[0044] Examples of the α,β-ethylenically unsaturated carboxylic acid ester monomers include, for example: (meth)acrylic esters having an alkyl group with 1 to 18 carbon atoms such as methyl acrylate, ethyl acrylate, n-butyl acrylate, n-dodecyl acrylate, methyl methacrylate, and ethyl methacrylate (abbreviation for "methacrylate and acrylate", the same below); (meth)acrylic esters having an alkoxyalkyl group with 2 to 12 carbon atoms such as methoxymethyl acrylate, methoxyethyl acrylate, and methoxyethyl methacrylate; (meth)acrylic esters having a cyanoalkyl group with 2 to 12 carbon atoms such as α-cyanoethyl acrylate, α-cyanoethyl methacrylate, and α-cyanobutyl methacrylate; (meth)acrylic esters having a hydroxyalkyl group with 1 to 12 carbon atoms such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxyethyl methacrylate; (meth)acrylic esters having a fluoroalkyl group with 1 to 12 carbon atoms such as trifluoroethyl acrylate and tetrafluoropropyl methacrylate; α,β-ethylenically unsaturated dicarboxylic acid dialkyl esters such as dimethyl maleate, dimethyl fumarate, dimethyl itaconate, and diethyl itaconate; α,β-ethylenically unsaturated carboxylic acid esters containing a dialkylamino group such as dimethylaminoethyl acrylate and diethylaminoethyl acrylate, etc.

[0045] Examples of the fluorinated vinyl monomers include, for example: fluoroethyl vinyl ether, fluoropropyl vinyl ether, o-trifluoromethylstyrene, vinyl pentafluorobenzoate, difluoroethylene, tetrafluoroethylene, etc.

[0046] Examples of the copolymerizable anti-aging agents include, for example: N-(4-aminophenyl)phenylacrylamide, N-(4-aminophenyl)phenylmethacrylamide, N-(4-aminophenyl)phenylcinnamide, N-(4-aminophenyl)phenylcrotonamide, N-phenyl-4-(3-vinylbenzyloxy)aniline, N-phenyl-4-(4-vinylbenzyloxy)aniline, etc.

[0047] A plurality of these copolymerizable other monomers can be used in combination. With respect to all monomer units, the content of the other monomer units is preferably 50% by weight or less, more preferably 30% by weight or less, and still more preferably 10% by weight or less.

[0048] The latex of the carboxyl group-containing liquid nitrile rubber used in the present invention can be obtained by methods such as: a method of copolymerizing the above monomers by a known emulsion polymerization method; or a method of copolymerizing the above monomers by a known solution polymerization method or the like and then performing an emulsification operation on the obtained copolymer. From the viewpoint of industrial productivity, the emulsion polymerization method is preferred. In emulsion polymerization, in addition to using an emulsifier, a polymerization initiator, and a molecular weight regulator, commonly used polymerization auxiliary materials can also be used.

[0049] As the emulsifier, there is no particular limitation, and examples thereof include: nonionic emulsifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan alkyl esters; salts of fatty acids such as myristic acid, palmitic acid, stearic acid, oleic acid, and linolenic acid, alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, condensates of naphthalene sulfonates and formalin, higher alcohol sulfates, and anionic emulsifiers such as alkyl sulfosuccinates; copolymerizable emulsifiers such as sulfonic acid esters of α,β-unsaturated carboxylic acids, sulfuric acid esters of α,β-unsaturated carboxylic acids, and sulfonated alkyl aryl ethers. The addition amount of the emulsifier is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, relative to 100 parts by weight of the monomer for polymerization.

[0050] As the polymerization initiator, there is no particular limitation as long as it is a radical initiator, and examples thereof include: inorganic peroxides such as potassium persulfate, sodium persulfate, ammonium persulfate, potassium peroxophosphate, and hydrogen peroxide; organic peroxides such as tert-butyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, di-tert-butyl peroxide, tert-butyl cumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, dibenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, tert-butyl peroxyisobutyrate, and diisopropylbenzene hydroperoxide; and azo compounds such as azobisisobutyronitrile, azobis(2,4-dimethylvaleronitrile), azobis(cyclohexanecarbonitrile), and dimethyl azobisisobutyrate. These polymerization initiators can be used alone or in combination of two or more. As the polymerization initiator, inorganic or organic peroxides are preferred. When a peroxide is used as the polymerization initiator, it can also be used in combination with a reducing agent such as sodium bisulfite or ferrous sulfate as a redox polymerization initiator. The addition amount of the polymerization initiator is preferably 0.01 to 2 parts by weight relative to 100 parts by weight of the monomer for polymerization.

[0051] As the molecular weight regulator, there is no particular limitation, and examples thereof include: thiols such as tert-dodecyl mercaptan, n-dodecyl mercaptan, and octyl mercaptan; halogenated hydrocarbons such as carbon tetrachloride, dichloromethane, and dibromomethane; α-methylstyrene dimer; and sulfur-containing compounds such as tetraethylthiuram disulfide, tetramethylenethiuram disulfide, and diisopropylxanthogen disulfide. These can be used alone or in combination of two or more. Among them, thiols are preferred, and tert-dodecyl mercaptan is more preferred. The addition amount of the molecular weight regulator is preferably 8 to 15 parts by weight relative to 100 parts by weight of the monomer for polymerization.

[0052] Water is usually used as the medium for emulsion polymerization. The amount of water is preferably 80 to 500 parts by weight, more preferably 80 to 300 parts by weight, relative to 100 parts by weight of the monomer for polymerization.

[0053] In emulsion polymerization, polymerization auxiliary materials such as a stabilizer, a dispersant, a pH regulator, a deoxidizer, and a particle size regulator can be further used as needed. When using them, their types and amounts used are not particularly limited.

[0054] In addition, in emulsion polymerization, the polymerization temperature for emulsion polymerization is preferably 0 to 70°C, more preferably 3 to 40°C. By performing emulsion polymerization at such a low temperature, disproportionation reaction can be suppressed, whereby the viscosity of the obtained carboxyl group-containing liquid nitrile rubber before storage can be reduced, and the stability during storage can be further improved.

[0055] Furthermore, in emulsion polymerization, it is preferable to supplement and add a polymerization initiator and / or a molecular weight regulator at a stage where the polymerization conversion rate is preferably 40 to 80%, more preferably 50 to 70%. Thereby, the increase in the viscosity of the obtained carboxyl group-containing liquid nitrile rubber before storage can be appropriately suppressed, and the final polymerization conversion rate can be appropriately increased. In addition, when adding a polymerization initiator midway, when the addition amount at the polymerization initiation time is taken as 100 parts by weight, the addition amount is preferably 0 to 100 parts by weight, more preferably 20 to 50 parts by weight. When adding a molecular weight regulator midway, when the addition amount at the polymerization initiation time is taken as 100 parts by weight, the addition amount is preferably 0 to 50 parts by weight, more preferably 0 to 25 parts by weight. In addition, at this time, it is preferable to terminate the polymerization at a stage where the polymerization conversion rate is preferably 70 to 95%, more preferably 75 to 90%.

[0056] In addition, after emulsion polymerization is carried out according to the above method, a hydrogenation reaction can be carried out as needed to hydrogenate the carbon-carbon double bonds in the obtained copolymer. The hydrogenation reaction can use any of the conventionally known methods without limitation.

[0057] <Manufacturing method of carboxyl group-containing liquid nitrile rubber>

[0058] Next, the manufacturing method of the carboxyl group-containing liquid nitrile rubber of the present invention will be described.

[0059] The manufacturing method of the carboxyl group-containing liquid nitrile rubber of the present invention has a step of bringing the latex of the above carboxyl group-containing liquid nitrile rubber into contact with a monovalent or divalent metal salt under the condition that the pH is 5 or less (that is, the pH during salting-out operation is 5 or less), whereby the carboxyl group-containing liquid nitrile rubber undergoes salting-out and is separated from the aqueous phase.

[0060] In the production method of the present invention, the method of bringing the latex of the carboxyl group-containing liquid nitrile rubber into contact with a monovalent or divalent metal salt is not particularly limited, and examples thereof include a method of mixing an aqueous solution containing a monovalent or divalent metal salt with the latex of the carboxyl group-containing liquid nitrile rubber. At this time, any of the following methods can be adopted: (α) a method of adding the latex of the carboxyl group-containing liquid nitrile rubber to an aqueous solution containing a monovalent or divalent metal salt and mixing them; or (β) a method of adding an aqueous solution containing a monovalent or divalent metal salt to the latex of the carboxyl group-containing liquid nitrile rubber, and the method of (β) is preferred.

[0061] In addition, in the production method of the present invention, when bringing the latex of the carboxyl group-containing liquid nitrile rubber into contact with a monovalent or divalent metal salt, if they are brought into contact under the condition that the pH is 5 or less according to the production method of the present invention, by adopting such a process, the resulting carboxyl group-containing liquid nitrile rubber can have excellent stability during storage and excellent surface smoothness can be achieved when it is mixed with an adhesive polymer to form an adhesive material. Further, in the production method of the present invention, it is sufficient to bring them into contact under the condition that the pH of the mixed solution containing them formed by the contact of the latex of the carboxyl group-containing liquid nitrile rubber with a monovalent or divalent metal salt (that is, the pH during the salting-out operation) is 5 or less. For example, when mixing a monovalent or divalent metal salt in the form of an aqueous solution with the latex of the carboxyl group-containing liquid nitrile rubber, it is preferable to adopt a method of adjusting the pH of the aqueous solution of the monovalent or divalent metal salt to make the pH of the mixed solution formed when they are mixed (that is, the pH during the salting-out operation) 5 or less.

[0062] In the production method of the present invention, when bringing the latex of the carboxyl group-containing liquid nitrile rubber into contact with a monovalent or divalent metal salt, they are brought into contact under the condition that the pH is 5 or less. At this time, the pH (that is, the pH during the salting-out operation) is preferably 1 to 4.5, more preferably 1.5 to 4, and still more preferably 1.5 to 3. When the pH is too high, not only does the storage stability of the carboxyl group-containing liquid nitrile rubber during storage decrease, but also the effect of improving the surface smoothness when it is mixed with an adhesive polymer to form an adhesive material cannot be obtained.

[0063] As the monovalent or divalent metal salt, any metal salt containing metal ions that become monovalent or divalent when dissolved in water may be used, and there is no particular limitation. Examples thereof include salts of inorganic acids such as hydrochloric acid, nitric acid, and sulfuric acid, organic acids such as acetic acid, and metals selected from sodium, potassium, lithium, magnesium, calcium, zinc, nickel, tin, and the like.

[0064] As a monovalent or divalent metal salt, preferably a monovalent or divalent metal salt of an inorganic acid, specific examples of the monovalent or divalent metal of the inorganic acid include metal chlorides such as sodium chloride, potassium chloride, lithium chloride, magnesium chloride, calcium chloride, zinc chloride, nickel chloride, and tin chloride; nitrates such as sodium nitrate, potassium nitrate, lithium nitrate, magnesium nitrate, calcium nitrate, zinc nitrate, nickel nitrate, and tin nitrate; sulfates such as sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, zinc sulfate, nickel sulfate, and tin sulfate. Among these, a sodium salt of an inorganic acid, a calcium salt of an inorganic acid, and a magnesium salt of an inorganic acid are preferred, calcium chloride, sodium chloride, magnesium sulfate, and sodium sulfate are preferred, and calcium chloride is particularly preferred. The monovalent or divalent metal salt can be used alone or in combination of multiple kinds, and it is preferred to use at least a divalent metal salt.

[0065] With respect to 100 parts by weight of the carboxyl group-containing liquid nitrile rubber contained in the latex of the carboxyl group-containing liquid nitrile rubber, the usage amount of the monovalent metal salt is preferably 10 to 1000 parts by weight, more preferably 30 to 500 parts by weight, and further preferably 50 to 200 parts by weight. With respect to 100 parts by weight of the carboxyl group-containing liquid nitrile rubber contained in the latex of the carboxyl group-containing liquid nitrile rubber, the usage amount of the divalent metal salt is preferably 1 to 10 parts by weight, more preferably 2 to 8 parts by weight, and further preferably 2.5 to 5 parts by weight. By making the usage amount of the monovalent or divalent metal salt within the above range, the salting out of the carboxyl group-containing liquid nitrile rubber can be carried out more efficiently.

[0066] In addition, the temperature conditions when the latex of the carboxyl group-containing liquid nitrile rubber is brought into contact with the monovalent or divalent metal salt are not particularly limited, and it is preferably 10 to 100 °C, more preferably 20 to 90 °C. By adjusting the temperature of the latex of the carboxyl group-containing liquid nitrile rubber and adjusting the temperature of the monovalent or divalent metal salt when using the monovalent or divalent metal salt in the form of an aqueous solution, the temperature when they are brought into contact can be adjusted. The concentration of the monovalent or divalent metal salt when using the monovalent or divalent metal salt in the form of an aqueous solution is preferably 1 to 10% by weight, more preferably 2 to 5% by weight.

[0067] Moreover, in the manufacturing method of the present invention, as described above, under the condition that the pH is 5 or less, the latex of the carboxyl group-containing liquid nitrile rubber is brought into contact with the monovalent or divalent metal salt to cause salting out of the carboxyl group-containing liquid nitrile rubber. After separation from the aqueous phase, it is washed as needed, and then the aqueous phase is removed by evaporation, vacuum drying, etc., whereby the carboxyl group-containing liquid nitrile rubber can be obtained. In addition, at this time, after salting out and washing, since the oil layer containing the carboxyl group-containing liquid nitrile rubber and the water layer are separated, the following method can be adopted: after removing the water layer part by operations such as flowing out the water layer part from the container, the water is completely removed by evaporation, vacuum drying, etc.

[0068] The weight-average molecular weight (Mw) of the carboxyl group-containing liquid nitrile rubber obtained by the production method of the present invention is not particularly limited, and is preferably from 1,000 to 50,000, more preferably from 3,000 to 20,000. In addition, the viscosity of the carboxyl group-containing liquid nitrile rubber obtained by the production method of the present invention at 70°C is preferably from 2,000 to 12,000 mPa·s, more preferably from 3,000 to 10,000 mPa·s, and still more preferably from 3,500 to 6,800 mPa·s. Further, the viscosity of the carboxyl group-containing liquid nitrile rubber at 70°C can be measured, for example, in accordance with JIS Z8803 using a tuning fork type vibrating viscometer.

[0069] As described above, by the production method of the present invention, a carboxyl group-containing liquid nitrile rubber can be obtained. Moreover, the carboxyl group-containing liquid nitrile rubber obtained by such a production method of the present invention has excellent stability during storage. Therefore, the carboxyl group-containing liquid nitrile rubber obtained by the production method of the present invention can exhibit stable properties even when mixed with resins and solid rubbers and used in various applications such as adhesive materials, friction materials, and brake materials, and can be preferably used for these applications. In particular, since the carboxyl group-containing liquid nitrile rubber obtained by the production method of the present invention not only has excellent stability during storage, but also can achieve excellent surface smoothness when mixed with an adhesive polymer to form an adhesive material, among the above applications, it can be particularly preferably used for adhesive materials (especially adhesive materials for flexible printed circuit boards) by being combined with adhesive polymers such as adhesive resins and other rubbers.

[0070] In addition, the resins and solid rubbers combined with the carboxyl group-containing liquid nitrile rubber are not particularly limited, and examples thereof include solid rubbers such as acrylonitrile-butadiene rubber, styrene-butadiene rubber, butadiene rubber, isoprene rubber, acrylic rubber, ethylene-propylene rubber, polyurethane rubber, fluororubber, and silicone rubber; thermoplastic elastomer materials such as styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, and styrene-ethylene-butadiene-styrene block copolymer; resin materials such as PMMA, polyethylene, polypropylene, polystyrene, polycarbonate, ABS, vinyl chloride, and PET; and photo- or thermosetting resins such as epoxy resin, polyurethane resin, and thermo- or photocurable acrylate resin.

[0071] Examples

[0072] Examples and comparative examples are given below to more specifically illustrate the present invention. In addition, unless otherwise specified, "parts" in each example are based on weight.

[0073] Various physical properties were evaluated according to the following methods.

[0074] [Viscosity of carboxyl group-containing liquid nitrile rubber]

[0075] The viscosity of the carboxyl group-containing liquid nitrile rubber was measured at 70 °C in accordance with JIS Z8803 using a tuning fork type vibrating viscometer (product name "SV-10", manufactured by A&D Company, Limited). During the measurement, the sample amount was 20.2 g. As the glass cell for filling the sample, the product named "AX-SV-35" (manufactured by A&D Company, Limited) was used, and as the circulating water jacket for the glass cell, the product named "AX-SV-37" (manufactured by A&D Company, Limited) was used. In addition, as the software for analyzing the measurement results, the product named "RsVisco" (manufactured by A&D Company, Limited) was used.

[0076] [Viscosity of Carboxyl Group-Containing Liquid Nitrile Rubber after Storage at 40 °C for 1 Week]

[0077] The carboxyl group-containing liquid nitrile rubber was stored at 40 °C for 1 week. Then, the viscosity of the stored carboxyl group-containing liquid nitrile rubber was measured in the same manner as described above.

[0078] [Evaluation of Surface Smoothness]

[0079] 100 parts of bisphenol A type epoxy resin (product name "jER (registered trademark) 828EL", manufactured by Mitsubishi Chemical Corporation) and 30 parts of 4,4'-diaminodiphenylsulfonic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) as a curing agent were mixed with 50 parts of the carboxyl group-containing liquid nitrile rubber to prepare an adhesive composition, which was dissolved and dispersed in methyl ethyl ketone to prepare an adhesive solution with a solid content concentration of 30% by mass. Then, the obtained adhesive solution was applied to one side of a 25-μm-thick polyimide film so that the dried film thickness became 30 to 40 μm, and then dried at 150 °C for 20 minutes to form a cover film.

[0080] Then, the obtained cover film was laminated on the copper foil surface (wiring pattern surface) of a copper-clad laminate (copper-clad laminate formed by a wiring pattern of a 35-μm-thick copper foil and a 25-μm-thick polyimide base film) having a desired wiring pattern at a temperature of 200 °C and a pressure of 100 kg / cm 2 for 3 minutes to bond them, and the surface smoothness of the cover film at this time was evaluated. The surface smoothness was evaluated based on the following criteria. The determination of the surface smoothness was performed using a laser displacement meter and evaluated in the following two stages. This operation was performed on all 5 samples.

[0081] ○: In all 5 samples, the height of the unevenness was less than 8 μm.

[0082] ×: Among the 5 samples, it was found that the height of the unevenness in any one of them was 8 μm or more.

[0083] [Polymerization conversion rate]

[0084] An appropriate polymerization terminator is added to the polymerization reaction solution during the reaction. For the polymerized reaction solution that has been terminated, the total solid content is measured in accordance with JIS K 6387-2:2011, and the total solid content amount of the polymerization reaction solution is thereby obtained. Then, the solid content of auxiliary materials, which is the total of sodium dodecylbenzenesulfonate, sodium sulfate, molecular weight regulator, and polymerization initiator as emulsifiers, is subtracted from the total solid content amount. The polymerization conversion rate is calculated by dividing the corrected total solid content amount (total solid content amount - solid content amount of auxiliary materials), which is equivalent to the value obtained by subtracting the weight of the unreacted monomer mixture from the total weight of the monomer mixture used for polymerization, by the total weight of the monomer mixture used for polymerization. In addition, since the influence of polymerization auxiliary materials other than the above on the calculation is slight, they are not considered in this calculation.

[0085] <Production Example 1, Production of Latex (A-1) of Carboxyl-Containing Liquid Nitrile Rubber>

[0086] In a reaction vessel with an internal volume of 10 liters, 30 parts of an aqueous solution of sodium dodecylbenzenesulfonate (emulsifier) with a concentration of 10% by weight, 0.5 part of sodium hydroxide, 10 parts of an aqueous solution of sodium salt of naphthalene sulfonic acid formalin condensate with a concentration of 10% by weight, 0.2 part of sodium sulfate, 0.02 part of sulfuric acid, and 200 parts of ion-exchanged water were charged. 24 parts of acrylonitrile, 8 parts of methacrylic acid, and 10 parts of tert-dodecyl mercaptan (TDM) (molecular weight regulator, trade name "Sulfole 120", manufactured by Chevron Phillips Chemical Company) were added thereto. Then, after replacing the internal gas with nitrogen three times, the reaction vessel was maintained at 5°C, 68 parts of 1,3-butadiene, an appropriate amount of reducing agent and chelating agent were added, and then 0.12 part of dicumyl peroxide (polymerization initiator) was charged to initiate the polymerization reaction. Then, according to the above method, the polymerization reaction was continued while confirming the polymerization conversion rate. At the moment when the polymerization conversion rate reached 55%, 2 parts of tert-dodecyl mercaptan (TDM), 0.05 part of dicumyl peroxide (polymerization initiator), and an appropriate amount of reducing agent were added, and the polymerization reaction was further continued. At the moment when the polymerization conversion rate reached 85%, 1 part of an aqueous solution of sodium nitrite (polymerization terminator) with a concentration of 5% by weight was added to terminate the polymerization reaction. Next, relative to 100 parts of the polymer in the latex, an aqueous solution with a concentration of 10% in which 0.5 part of 2,5-di-tert-amylhydroquinone was dispersed with 0.1 part of sodium alkylbenzenesulfonate (product name "TAYCAPOWER LN2450", manufactured by TAYCA Corporation) was added, and then heated to 70°C. The residual monomers were recovered by steam distillation under reduced pressure at 70°C. Thereafter, 1.5 parts of dibutylhydroxytoluene was added as an anti-aging agent relative to 100 parts of the polymer in the latex to obtain a latex (A-1) of carboxyl group-containing liquid nitrile rubber. In addition, the pH of the obtained latex (A-1) of carboxyl group-containing liquid nitrile rubber was 2.5, and the composition of the carboxyl group-containing liquid nitrile rubber was as follows: acrylonitrile unit was 25% by weight, 1,3-butadiene unit was 67% by weight, and methacrylic acid unit was 8% by weight. Furthermore, the carboxyl group-containing liquid nitrile rubber contained in the obtained latex (A-1) of carboxyl group-containing liquid nitrile rubber was in a liquid state at 25°C, and the Mooney viscosity was measured according to JIS K6300, and as a result, the viscosity was too low to measure the Mooney viscosity.

[0087] <Production Example 2, Production of Latex (A-2) of Carboxyl Group-Containing Liquid Nitrile Rubber>

[0088] In a reaction vessel with an internal volume of 10 liters, an aqueous solution of 30 parts of sodium dodecylbenzenesulfonate (emulsifier) with a concentration of 10% by weight, 0.5 part of sodium hydroxide, an aqueous solution of 10 parts of sodium salt of naphthalene sulfonic acid formalin condensate with a concentration of 10% by weight, 0.2 part of sodium sulfate, 0.02 part of sulfuric acid, and 200 parts of ion-exchanged water were charged. Then, 33 parts of acrylonitrile, 4 parts of methacrylic acid, and 12 parts of tert-dodecyl mercaptan (TDM) (molecular weight regulator, trade name "Sulfole 120", manufactured by Chevron Phillips Chemical Company) were added thereto. Then, after replacing the internal gas with nitrogen three times, the reaction vessel was maintained at 10°C, 63 parts of 1,3-butadiene, an appropriate amount of reducing agent, and a chelating agent were added, and then 0.12 part of dicumyl peroxide (polymerization initiator) was charged to initiate the polymerization reaction. Then, according to the above method, while confirming the polymerization conversion rate, the polymerization reaction was continued. At the moment when the polymerization conversion rate reached 55%, 0.05 part of dicumyl peroxide (polymerization initiator) and an appropriate amount of reducing agent were added, and the polymerization reaction was further continued. At the moment when the polymerization conversion rate reached 80%, an aqueous solution of 1 part of sodium nitrite (polymerization terminator) with a concentration of 5% by weight was added to terminate the polymerization reaction. Next, relative to 100 parts of the polymer in the latex, an aqueous solution with a concentration of 10% in which 0.5 part of 2,5-di-tert-amylhydroquinone was dispersed with 0.1 part of sodium alkylbenzenesulfonate (product name "TAYCAPOWER LN2450", manufactured by TAYCA Corporation) was added, and then heated to 70°C. Residual monomers were recovered by steam distillation under reduced pressure at 70°C. After that, 1.5 parts of dibutylhydroxytoluene was added as an anti-aging agent relative to 100 parts of the polymer in the latex to obtain a latex (A-2) of carboxyl-containing liquid nitrile rubber. In addition, the pH of the obtained latex (A-2) of carboxyl-containing liquid nitrile rubber was 3, and the composition of the carboxyl-containing liquid nitrile rubber was as follows: acrylonitrile unit was 34% by weight, 1,3-butadiene unit was 61% by weight, and methacrylic acid unit was 5% by weight. Furthermore, the carboxyl-containing liquid nitrile rubber contained in the obtained latex (A-2) of carboxyl-containing liquid nitrile rubber was in a liquid state at 25°C, and the Mooney viscosity was measured according to JIS K6300. As a result, the viscosity was too low to measure the Mooney viscosity.

[0089] <Example 1>

[0090] Prepare an aqueous calcium chloride solution with a concentration of 2.5% by weight, add hydrochloric acid, and adjust the pH to 2. Then, while stirring the latex (A-1) of carboxyl-containing liquid nitrile rubber obtained in Production Example 1 at 80°C, add the aqueous calcium chloride solution adjusted to pH = 2 under stirring and mix them. Thus, salting out of the carboxyl-containing liquid nitrile rubber occurs, and the oil layer containing the carboxyl-containing liquid nitrile rubber is separated from the water layer. In addition, regarding the addition amount of the aqueous calcium chloride solution adjusted to pH = 2, the amount of calcium chloride is 3.5 parts relative to 100 parts of the carboxyl-containing liquid nitrile rubber in the latex (A-1) of carboxyl-containing liquid nitrile rubber. In addition, the pH of the mixed solution at this time (i.e., the pH during the salting-out operation) is 2.

[0091] Next, after removing the water layer, under stirring, relative to 100 parts of the carboxyl-containing liquid nitrile rubber, repeat the washing operation of adding 100 parts of ion-exchanged water, mixing at 60°C for 10 minutes, and then removing the water layer twice. After that, the evaporator volatilizes the water under the conditions of 110°C and -80 kPa (gauge pressure) to obtain the carboxyl-containing liquid nitrile rubber. Then, the viscosity (before storage; and after storing at 40°C for 1 week) of the obtained carboxyl-containing liquid nitrile rubber is measured and the surface smoothness is evaluated. The results are shown in Table 1.

[0092] <Example 2>

[0093] Instead of using the aqueous calcium chloride solution adjusted to pH = 2, use the aqueous calcium chloride solution adjusted to pH = 4.5, and otherwise perform the same operations as in Example 1 to perform salting out of the carboxyl-containing liquid nitrile rubber. Then, perform the water washing and water volatilization operations to obtain the carboxyl-containing liquid nitrile rubber, and perform the measurement and evaluation in the same manner. The results are shown in Table 1. In addition, the pH during the salting-out operation in Example 2 is 4.

[0094] <Example 3>

[0095] Instead of using the latex (A-1) of carboxyl-containing liquid nitrile rubber obtained in Production Example 1, use the latex (A-2) of carboxyl-containing liquid nitrile rubber obtained in Production Example 2, and otherwise perform the same operations as in Example 1 to perform salting out of the carboxyl-containing liquid nitrile rubber. Then, perform the water washing and water volatilization operations to obtain the carboxyl-containing liquid nitrile rubber, and perform the measurement and evaluation in the same manner. The results are shown in Table 1. In addition, the pH during the salting-out operation in Example 3 is 2.5.

[0096] <Example 4>

[0097] Instead of using an aqueous calcium chloride solution adjusted to pH = 2, an aqueous calcium chloride solution adjusted to pH = 4 was used. Otherwise, the procedure was the same as in Example 3. Salting out of the carboxyl group-containing liquid nitrile rubber was carried out, followed by washing with water and water evaporation operations to obtain the carboxyl group-containing liquid nitrile rubber. The measurement and evaluation were carried out in the same manner. The results are shown in Table 1. In addition, the pH during the salting-out operation in Example 4 was 4.

[0098] <Comparative Example 1>

[0099] Instead of using an aqueous calcium chloride solution adjusted to pH = 2, an aqueous calcium chloride solution adjusted to pH = 7 was used. Otherwise, the procedure was the same as in Example 1. Salting out of the carboxyl group-containing liquid nitrile rubber was carried out, followed by washing with water and water evaporation operations to obtain the carboxyl group-containing liquid nitrile rubber. The measurement and evaluation were carried out in the same manner. The results are shown in Table 1. In addition, the pH during the salting-out operation in Comparative Example 1 was 6.

[0100] <Comparative Example 2>

[0101] Instead of using an aqueous calcium chloride solution adjusted to pH = 2, an aqueous calcium chloride solution adjusted to pH = 10 with sodium hydroxide was used. Otherwise, the procedure was the same as in Example 1. Salting out of the carboxyl group-containing liquid nitrile rubber was carried out, followed by washing with water and water evaporation operations to obtain the carboxyl group-containing liquid nitrile rubber. The measurement and evaluation were carried out in the same manner. The results are shown in Table 1. In addition, the pH during the salting-out operation in Comparative Example 2 was 8.

[0102] <Comparative Example 3>

[0103] An aqueous aluminum sulfate solution with a concentration of 2.5% by weight was prepared, and hydrochloric acid was added to adjust it to pH = 2. Then, instead of using an aqueous calcium chloride solution adjusted to pH = 2, the obtained aqueous aluminum sulfate solution with pH = 2 was used, and its usage amount was 2 parts of aluminum sulfate relative to 100 parts of the carboxyl group-containing liquid nitrile rubber in the latex (A-1) of the carboxyl group-containing liquid nitrile rubber. Otherwise, the procedure was the same as in Example 1. Salting out of the carboxyl group-containing liquid nitrile rubber was carried out, followed by washing with water and water evaporation operations to obtain the carboxyl group-containing liquid nitrile rubber. The measurement and evaluation were carried out in the same manner. The results are shown in Table 1. In addition, the pH during the salting-out operation in Comparative Example 3 was 2.

[0104] [Table 1]

[0105]

[0106] For Comparative Examples 2 and 3, the viscosity became too high to be measured when stored at 40 °C for 1 week.

[0107] As shown in Table 1, in the case of adopting the process of salting out the carboxyl group-containing liquid nitrile rubber by contacting the latex of the carboxyl group-containing liquid nitrile rubber with a monovalent or divalent metal salt under the condition that the pH is below 5 and separating it from the aqueous phase, the increase in the viscosity of the obtained carboxyl group-containing liquid nitrile rubber when stored at 40°C for 1 week is suppressed, and the storage stability is excellent. Moreover, the surface smoothness is excellent when it is mixed with an adhesive polymer to form an adhesive material (Examples 1 to 4).

[0108] On the other hand, in the case of salting out the latex of the carboxyl group-containing liquid nitrile rubber under the condition that the pH is greater than 5, or in the case of using aluminum sulfate as a trivalent metal salt instead of the monovalent or divalent metal salt, the resulting carboxyl group-containing liquid nitrile rubber has a large increase in viscosity when stored at 40°C for 1 week, poor storage stability, and poor surface smoothness when mixed with an adhesive polymer to form an adhesive material (Comparative Examples 1 to 3).

Claims

1. A method for manufacturing a carboxyl group-containing liquid nitrile rubber, which comprises the following steps: Under the condition that the pH is 5 or less, bringing the latex of the carboxyl group-containing liquid nitrile rubber into contact with a monovalent or divalent metal salt, thereby causing salting out of the carboxyl group-containing liquid nitrile rubber and separating it from the aqueous phase. The pH of the mixed solution formed by bringing the latex of the carboxyl group-containing liquid nitrile rubber into contact with the monovalent or divalent metal salt is 5 or less. The pH of the mixed solution becomes 5 or less by adjusting the pH of the aqueous solution of the monovalent or divalent metal salt. The temperature condition when bringing the latex of the carboxyl group-containing liquid nitrile rubber into contact with the monovalent or divalent metal salt is 10 to 100 °C.

2. The method for manufacturing a carboxyl group-containing liquid nitrile rubber according to claim 1, wherein, The carboxyl group-containing liquid nitrile rubber contains carboxyl group-containing monomer units in a proportion of 1 to 20% by weight.

3. The method for manufacturing a carboxyl group-containing liquid nitrile rubber according to claim 2, wherein, The carboxyl group-containing liquid nitrile rubber contains α,β-ethylenically unsaturated nitrile monomer units in a proportion of 10 to 59% by weight.

4. The method for manufacturing a carboxyl group-containing liquid nitrile rubber according to claim 2 or 3, wherein, The carboxyl group-containing liquid nitrile rubber contains conjugated diene monomer units in a proportion of 40 to 89% by weight.

5. The method for manufacturing a carboxyl group-containing liquid nitrile rubber according to any one of claims 1 to 3, wherein, The monovalent or divalent metal salt is a monovalent or divalent metal salt of an inorganic acid.

6. The method for manufacturing a carboxyl group-containing liquid nitrile rubber according to any one of claims 1 to 3, wherein, The monovalent or divalent metal salt is a divalent metal salt, and the usage amount of the divalent metal salt is 1 to 10 parts by weight relative to 100 parts by weight of the carboxyl group-containing liquid nitrile rubber contained in the latex of the carboxyl group-containing liquid nitrile rubber.

7. The method for manufacturing a carboxyl group-containing liquid nitrile rubber according to any one of claims 1 to 3, wherein, Under the condition that the pH is 5 or less, bringing the latex of the carboxyl group-containing liquid nitrile rubber into contact with an aqueous solution containing the monovalent or divalent metal salt, thereby causing salting out of the carboxyl group-containing liquid nitrile rubber.

8. The method for manufacturing a carboxyl group-containing liquid nitrile rubber according to claim 7, wherein, The concentration of the monovalent or divalent metal salt in the aqueous solution containing the monovalent or divalent metal salt is 1 to 10% by weight.

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