Latex composition

Abstract

Provided is a latex composition obtained by blending, in a conjugated diene-based polymer latex, an aqueous dispersion of a sulfur-based vulcanizing agent and a xanthogen compound. The aqueous dispersion of the sulfur-based vulcanizing agent is obtained by dispersing the sulfur-based vulcanizing agent in water by using an anionic surfactant.

Description

[Technical Field]

[0001] The present invention relates to a latex composition that can provide a film-molded article, such as a dip-molded article, with high mechanical strength, such as tensile strength and tear strength, and excellent stability of the mechanical strength, as well as to a film-molded article, a dip-molded article, and an adhesive composition made from such a latex composition. [Background technology]

[0002] It has been known that latex compositions containing natural rubber latex can be dip-molded to obtain film-molded articles such as nipples, balloons, gloves, balloons, and sacks that are used in contact with the human body. However, natural rubber latex contains proteins that can cause immediate-type allergy (Type I) symptoms in the human body, which can be problematic when used in dip-molded articles that come into direct contact with biological mucous membranes or organs. Therefore, efforts have been made to remove proteins from natural rubber latex by purification or the like, or to use synthetic rubber latex instead of natural rubber.

[0003] For example, Patent Document 1 discloses a dip-molding composition comprising a latex composition prepared by blending zinc oxide, sulfur, and a vulcanization accelerator with synthetic polyisoprene latex, a synthetic rubber. While the technology of Patent Document 1 can prevent the occurrence of immediate-type allergies (Type I) caused by proteins derived from natural rubber, the vulcanization accelerator contained in the dip-molded article can sometimes cause delayed-type allergy (Type IV) symptoms upon contact with the human body. Furthermore, when a vulcanization accelerator that induces delayed-type allergy (Type IV) symptoms is not blended, the resulting dip-molded article lacks sufficient mechanical strength, such as tensile strength and tear strength, as well as the stability of the mechanical strength. Therefore, there has been a demand for improvements in the mechanical strength, such as tensile strength and tear strength, of dip-molded articles when a vulcanization accelerator that induces delayed-type allergy (Type IV) symptoms is not blended. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2014 / 129547 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a latex composition which can provide a film-molded product such as a dip-molded product having high mechanical strength such as tensile strength and tear strength and excellent stability of the mechanical strength, and to provide a film-molded product, a dip-molded product, and an adhesive composition each comprising such a latex composition. [Means for solving the problem]

[0006] As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by blending a sulfur-based vulcanizing agent and a xanthogen compound into a latex composition comprising a conjugated diene polymer latex, and blending the sulfur-based vulcanizing agent in the form of a dispersion in water using an anionic surfactant, thereby completing the present invention.

[0007] That is, according to the present invention, there is provided a latex composition obtained by blending a conjugated diene polymer latex with an aqueous dispersion of a sulfur-based vulcanizing agent and a xanthogen compound, wherein the aqueous dispersion of the sulfur-based vulcanizing agent is prepared by dispersing the sulfur-based vulcanizing agent in water using an anionic surfactant.

[0008] In the latex composition of the present invention, the amount of the sulfur-based vulcanizing agent is preferably 0.1 to 1.0 parts by weight, and more preferably 0.1 to 0.6 parts by weight, based on 100 parts by weight of the conjugated diene polymer contained in the conjugated diene polymer latex. In the latex composition of the present invention, the xanthogen compound is preferably blended with the conjugated diene polymer latex in the form of an aqueous dispersion obtained by dispersing the xanthogen compound in water using a nonionic surfactant and / or a nonionic anionic surfactant. In the latex composition of the present invention, the conjugated diene polymer latex is preferably a synthetic polyisoprene latex, a styrene-isoprene-styrene block copolymer latex, a deproteinized natural rubber latex, or a nitrile group-containing conjugated diene copolymer latex. In the latex composition of the present invention, the conjugated diene polymer latex is preferably a carboxy-modified conjugated diene polymer latex.

[0009] Furthermore, according to the present invention, there are provided a film-formed article, a dip-formed article, and an adhesive composition each comprising the above-mentioned latex composition. [Effects of the Invention]

[0010] According to the present invention, there can be provided a latex composition which can provide a film-molded product such as a dip-molded product having high mechanical strength such as tensile strength and tear strength and excellent stability of the mechanical strength, as well as a film-molded product, a dip-molded product, and an adhesive composition each comprising such a latex composition. DETAILED DESCRIPTION OF THE INVENTION

[0011] The latex composition of the present invention is a latex composition obtained by blending a conjugated diene polymer latex with an aqueous dispersion of a sulfur-based vulcanizing agent and a xanthogen compound, The aqueous dispersion of the sulfur-based vulcanizing agent is prepared by dispersing the sulfur-based vulcanizing agent in water using an anionic surfactant.

[0012] <Latex of conjugated diene polymer> The conjugated diene polymer latex used in the present invention is not particularly limited, but examples thereof include synthetic polyisoprene latex, styrene-isoprene-styrene block copolymer (SIS) latex, natural rubber latex from which proteins have been removed (deproteinized natural rubber), and nitrile group-containing conjugated diene copolymer latex. Among these, polymer latexes containing isoprene units such as synthetic polyisoprene latex, SIS latex, and deproteinized natural rubber latex are preferred, with synthetic polyisoprene latex being particularly preferred.

[0013] When synthetic polyisoprene latex is used as the latex of the conjugated diene polymer, the synthetic polyisoprene contained in the synthetic polyisoprene latex may be a homopolymer of isoprene or may be a copolymer of isoprene and another ethylenically unsaturated monomer copolymerizable with isoprene. The content of isoprene units in the synthetic polyisoprene is preferably 70% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and particularly preferably 100% by weight (homopolymer of isoprene) of all monomer units, since this facilitates the production of membrane-formed articles such as dip-formed articles that are flexible and have excellent tensile strength.

[0014] Examples of other ethylenically unsaturated monomers copolymerizable with isoprene include conjugated diene monomers other than isoprene, such as butadiene, chloroprene, and 1,3-pentadiene; ethylenically unsaturated nitrile monomers, such as acrylonitrile, methacrylonitrile, fumaronitrile, and α-chloroacrylonitrile; vinyl aromatic monomers, such as styrene and alkylstyrene; and ethylenically unsaturated carboxylic acid ester monomers, such as methyl (meth)acrylate (meaning "methyl acrylate and / or methyl methacrylate"; hereinafter, the same applies to ethyl (meth)acrylate, etc.), ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. These other ethylenically unsaturated monomers copolymerizable with isoprene may be used alone or in combination.

[0015] Synthetic polyisoprene can be obtained by a conventionally known method, for example, by solution polymerization of isoprene and other copolymerizable ethylenically unsaturated monomers, which are used as needed, in an inert polymerization solvent using a Ziegler polymerization catalyst comprising trialkylaluminum-titanium tetrachloride or an alkyllithium polymerization catalyst such as n-butyllithium or sec-butyllithium. The polymer solution of synthetic polyisoprene obtained by solution polymerization may be used as is for the production of synthetic polyisoprene latex, but solid synthetic polyisoprene can also be extracted from the polymer solution and then dissolved in an organic solvent for use in the production of synthetic polyisoprene latex. When a polymer solution of synthetic polyisoprene is obtained by the above-mentioned method, impurities such as residues of the polymerization catalyst remaining in the polymer solution may be removed. Furthermore, an antioxidant, which will be described later, may be added to the solution during or after polymerization. Commercially available solid synthetic polyisoprene may also be used.

[0016] There are four types of isoprene units in synthetic polyisoprene, depending on the bonding state of the isoprene: cis bonding units, trans bonding units, 1,2-vinyl bonding units, and 3,4-vinyl bonding units. From the viewpoint of improving the tensile strength of the resulting film-formed article, such as a dip-formed article, the content of cis bonding units among the isoprene units contained in the synthetic polyisoprene is preferably 70% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more, based on the total isoprene units.

[0017] The weight-average molecular weight of the synthetic polyisoprene, calculated as standard polystyrene by gel permeation chromatography analysis, is preferably 10,000 to 5,000,000, more preferably 500,000 to 5,000,000, and even more preferably 800,000 to 3,000,000. By setting the weight-average molecular weight of the synthetic polyisoprene within the above range, the tensile strength, tensile elongation, and tear strength of a film-formed product such as a dip-formed product are further improved, and the synthetic polyisoprene latex tends to be easier to produce.

[0018] In addition, the polymer Mooney viscosity (ML) of synthetic polyisoprene 1+4 , 100°C) is preferably 50 to 80, more preferably 60 to 80, and even more preferably 70 to 80.

[0019] Examples of methods for obtaining synthetic polyisoprene latex include: (1) a method in which a solution or fine suspension of synthetic polyisoprene dissolved or finely dispersed in an organic solvent is emulsified in water in the presence of an emulsifier, and the organic solvent is removed as necessary to produce a synthetic polyisoprene latex; and (2) a method in which isoprene alone or a mixture of isoprene and an ethylenically unsaturated monomer copolymerizable therewith is emulsion polymerized or suspension polymerized in the presence of an emulsifier to directly produce a synthetic polyisoprene latex. However, the above-mentioned production method (1) is preferred because it allows the use of synthetic polyisoprene having a high proportion of cis-bond units in the isoprene units and makes it easy to obtain a film-formed product such as a dip-formed product having excellent mechanical properties such as tensile strength.

[0020] Examples of organic solvents used in the production method (1) above include aromatic hydrocarbon solvents such as benzene, toluene, and xylene; alicyclic hydrocarbon solvents such as cyclopentane, cyclopentene, cyclohexane, and cyclohexene; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; and halogenated hydrocarbon solvents such as methylene chloride, chloroform, and ethylene dichloride. Of these, alicyclic hydrocarbon solvents and aliphatic hydrocarbon solvents are preferred, with pentane, cyclohexane, and n-hexane being more preferred, and n-hexane being particularly preferred.

[0021] The amount of the organic solvent used is preferably 2,000 parts by weight or less, more preferably 20 to 1,500 parts by weight, and even more preferably 500 to 1,500 parts by weight, based on 100 parts by weight of the synthetic polyisoprene.

[0022] As the emulsifier used in the above production method (1), it is preferable to use an ionic emulsifier, and among these, it is more preferable to use an anionic emulsifier. Examples of the anionic emulsifier include fatty acid salts such as sodium laurate, potassium myristate, sodium palmitate, potassium oleate, sodium linolenate, sodium rosinate, and potassium rosinate; alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate, potassium dodecylbenzenesulfonate, sodium decylbenzenesulfonate, potassium decylbenzenesulfonate, sodium cetylbenzenesulfonate, and potassium cetylbenzenesulfonate; alkyl sulfosuccinates such as sodium di(2-ethylhexyl)sulfosuccinate, potassium di(2-ethylhexyl)sulfosuccinate, and sodium dioctyl sulfosuccinate; alkyl sulfate ester salts such as sodium lauryl sulfate and potassium lauryl sulfate; polyoxyethylene alkyl ether sulfate ester salts such as polyoxyethylene lauryl ether sodium sulfate and polyoxyethylene lauryl ether potassium sulfate; and monoalkyl phosphates such as sodium lauryl phosphate and potassium lauryl phosphate.

[0023] Among these anionic emulsifiers, fatty acid salts, alkylbenzenesulfonates, alkylsulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates are preferred, with fatty acid salts and alkylbenzenesulfonates being particularly preferred.

[0024] Furthermore, because trace amounts of residual polymerization catalyst (particularly aluminum and titanium) derived from synthetic polyisoprene can be more efficiently removed and the formation of aggregates during production of the latex composition can be suppressed, it is preferable to use at least one selected from the group consisting of alkylbenzenesulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates in combination with a fatty acid salt, and it is particularly preferable to use an alkylbenzenesulfonate in combination with a fatty acid salt. Here, preferred fatty acid salts are sodium rosinate and potassium rosinate, and preferred alkylbenzenesulfonates are sodium dodecylbenzenesulfonate and potassium dodecylbenzenesulfonate. These emulsifiers may be used alone or in combination.

[0025] As described above, by using at least one selected from the group consisting of alkylbenzenesulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates in combination with a fatty acid salt, the obtained latex contains at least one selected from alkylbenzenesulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates, and a fatty acid salt.

[0026] Furthermore, examples of ionic emulsifiers other than anionic emulsifiers include copolymerizable emulsifiers such as sulfoesters of α,β-unsaturated carboxylic acids, sulfate esters of α,β-unsaturated carboxylic acids, and sulfoalkylaryl ethers.

[0027] Furthermore, nonionic emulsifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan alkyl esters may also be used in combination, as long as they do not inhibit coagulation by the coagulant used in dip molding.

[0028] The amount of emulsifier used in the above production method (1) is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 30 parts by weight, per 100 parts by weight of synthetic polyisoprene. When two or more types of emulsifiers are used, it is preferable that the total amount used be within the above range. For example, when at least one selected from alkylbenzenesulfonates, alkylsulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates is used in combination with a fatty acid salt, it is preferable that the total amount used be within the above range. By using the amount of emulsifier within the above range, the formation of aggregates during emulsification can be further suppressed.

[0029] When at least one anionic emulsifier selected from alkylbenzenesulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates is used in combination with a fatty acid salt, the weight ratio of "fatty acid salt" to "total of at least one emulsifier selected from alkylbenzenesulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates" is preferably in the range of 1:1 to 10:1, more preferably 1:1 to 7:1. By using at least one emulsifier selected from alkylbenzenesulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates in the above range, foaming that occurs during handling of the synthetic polyisoprene can be suppressed, eliminating the need for prolonged storage or the addition of an antifoaming agent, leading to improved workability and reduced costs.

[0030] The amount of water used in the above production method (1) is preferably 10 to 1,000 parts by weight, more preferably 30 to 500 parts by weight, and most preferably 50 to 100 parts by weight, relative to 100 parts by weight of the organic solvent solution of synthetic polyisoprene. The type of water used may include hard water, soft water, ion-exchanged water, distilled water, and zeolite water, with soft water, ion-exchanged water, and distilled water being preferred.

[0031] The apparatus for emulsifying a solution or fine suspension of synthetic polyisoprene dissolved or finely dispersed in an organic solvent in water in the presence of an emulsifier is not particularly limited, and any commercially available emulsifier or disperser can be used. The method for adding the emulsifier to the synthetic polyisoprene solution or fine suspension is not particularly limited, and the emulsifier may be added in advance to either water or the synthetic polyisoprene solution or fine suspension, or both, or may be added to the emulsion during the emulsification operation, and may be added all at once or in portions.

[0032] Examples of emulsifying devices include batch emulsifying machines such as "Homogenizer" (manufactured by IKA), "Polytron" (manufactured by Kinematica), and "TK Auto Homo Mixer" (manufactured by Tokushu Kika Kogyo Co., Ltd.); "TK Pipeline Homo Mixer" (manufactured by Tokushu Kika Kogyo Co., Ltd.), "Colloid Mill" (manufactured by Kobe Steel Pantech Co., Ltd.), "Slasher" (manufactured by Nippon Coke & Engineering Co., Ltd.), "Trigonal Wet Fine Grinding Mill" (manufactured by Mitsui Miike Chemical Engineering Co., Ltd.), and "Cavitron" (manufactured by Eurotech Co., Ltd.); Examples of suitable emulsifiers include continuous emulsifiers such as those under the trade name "Milder" (manufactured by Pacific Machinery & Engineering Co., Ltd.) and those under the trade name "Fine Flow Mill" (manufactured by Pacific Machinery & Engineering Co., Ltd.); high-pressure emulsifiers such as those under the trade name "Microfluidizer" (manufactured by Mizuho Kogyo Co., Ltd.), those under the trade name "Nanomizer" (manufactured by Nanomizer Co., Ltd.), and those under the trade name "APV Gaulin" (manufactured by Gaulin Co., Ltd.); membrane emulsifiers such as those under the trade name "Membrane Emulsifier" (manufactured by Reika Kogyo Co., Ltd.); vibration-type emulsifiers such as those under the trade name "Vibro Mixer" (manufactured by Reika Kogyo Co., Ltd.); and ultrasonic emulsifiers such as those under the trade name "Ultrasonic Homogenizer" (manufactured by Branson). The conditions for the emulsification operation using an emulsification apparatus are not particularly limited, and the processing temperature, processing time, and the like may be appropriately selected so as to achieve the desired dispersion state.

[0033] In the above production method (1), it is desirable to remove the organic solvent from the emulsion obtained through the emulsification operation. As a method for removing the organic solvent from the emulsion, a method capable of reducing the content of the organic solvent (preferably an alicyclic hydrocarbon solvent or an aliphatic hydrocarbon solvent) in the obtained synthetic polyisoprene latex to 500 ppm by weight or less is preferred, and for example, methods such as reduced pressure distillation, atmospheric pressure distillation, steam distillation, and centrifugation can be employed. The organic solvent can be removed while adding an antifoaming agent, which can suppress foaming of the synthetic polyisoprene.

[0034] Furthermore, after removing the organic solvent, if necessary, in order to increase the solid content concentration of the synthetic polyisoprene latex, a concentration operation may be carried out by a method such as reduced pressure distillation, atmospheric distillation, centrifugation, membrane concentration or the like. In particular, from the viewpoint of increasing the solid content concentration of the synthetic polyisoprene latex and reducing the amount of emulsifier remaining in the synthetic polyisoprene latex, centrifugation is preferred.

[0035] Centrifugation is preferably carried out using, for example, a continuous centrifuge under conditions of a centrifugal force of preferably 100 to 10,000 G, a solids concentration of the synthetic polyisoprene latex before centrifugation of preferably 2 to 15 wt%, a flow rate into the centrifuge of preferably 500 to 1700 kg / hr, and a back pressure (gauge pressure) of the centrifuge of preferably 0.03 to 1.6 MPa, and a synthetic polyisoprene latex can be obtained as a light liquid after centrifugation. This makes it possible to reduce the amount of emulsifier remaining in the synthetic polyisoprene latex.

[0036] The solids concentration of the synthetic polyisoprene latex is preferably 30 to 70% by weight, more preferably 40 to 70% by weight, and even more preferably 50 to 70% by weight. By setting the solids concentration to be equal to or higher than the lower limit of the above range, film-formed articles such as dip-formed articles described below become less likely to break. Furthermore, by setting the solids concentration to be equal to or lower than the upper limit of the above range, the viscosity of the synthetic polyisoprene latex is prevented from becoming too high, making it easier to transport through piping and to stir in a blending tank.

[0037] The volume average particle diameter of the synthetic polyisoprene latex is preferably 0.1 to 10 μm, more preferably 0.5 to 3 μm, and even more preferably 0.5 to 2.0 μm. By setting the volume average particle diameter within the above range, the viscosity of the latex becomes appropriate, making it easy to handle, and also preventing a film from being formed on the surface of the synthetic polyisoprene latex during storage.

[0038] The synthetic polyisoprene latex may also contain additives that are commonly used in the field of latex, such as a pH adjuster, an antifoaming agent, a preservative, a crosslinking agent, a chelating agent, an oxygen scavenger, a dispersant, and an antioxidant.

[0039] Examples of pH adjusters include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal bicarbonates such as sodium bicarbonate; ammonia; and organic amine compounds such as trimethylamine and triethanolamine; however, alkali metal hydroxides or ammonia are preferred.

[0040] As mentioned above, the latex of the conjugated diene polymer may be a latex of a styrene-isoprene-styrene block copolymer (SIS), where "S" represents a styrene block and "I" represents an isoprene block.

[0041] The SIS contained in the SIS latex can be obtained by a conventionally known method, for example, by block copolymerizing isoprene and styrene in an inert polymerization solvent using an active organic metal such as n-butyllithium as an initiator. The obtained SIS polymer solution can be used directly for producing the SIS latex, or solid SIS can be extracted from the polymer solution and then dissolved in an organic solvent to be used for producing the SIS latex. The method for producing the SIS latex is not particularly limited, but a preferred method is to emulsify a solution or fine suspension of SIS dissolved or finely dispersed in an organic solvent in water in the presence of an emulsifier, and then remove the organic solvent as necessary to produce the SIS latex. In this process, impurities such as polymerization catalyst residues remaining in the polymer solution after synthesis may be removed. An antioxidant, as described below, may be added to the solution during or after polymerization. Commercially available solid SIS may also be used.

[0042] As the organic solvent, the same solvents as those used in the case of the synthetic polyisoprene can be used, and aromatic hydrocarbon solvents and alicyclic hydrocarbon solvents are preferred, with cyclohexane and toluene being particularly preferred. The amount of the organic solvent used is usually 50 to 2,000 parts by weight, preferably 80 to 1,000 parts by weight, more preferably 100 to 500 parts by weight, and even more preferably 150 to 300 parts by weight, relative to 100 parts by weight of SIS.

[0043] Examples of emulsifiers include those similar to those mentioned above for synthetic polyisoprene, with anionic emulsifiers being preferred, and potassium rosinate and sodium dodecylbenzenesulfonate being particularly preferred.

[0044] The amount of the emulsifier used is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 30 parts by weight, relative to 100 parts by weight of SIS. By setting the amount of the emulsifier used within the above range, the stability of the obtained latex can be improved.

[0045] The amount of water used in the above-mentioned SIS latex production method is preferably 10 to 1,000 parts by weight, more preferably 30 to 500 parts by weight, and most preferably 50 to 100 parts by weight, relative to 100 parts by weight of the SIS organic solvent solution. Examples of the type of water used include hard water, soft water, ion-exchanged water, distilled water, and zeolite water. Furthermore, polar solvents, such as alcohols such as methanol, may be used in combination with water.

[0046] The apparatus for emulsifying the organic solvent solution or fine suspension of SIS in water in the presence of an emulsifier can be similar to that used for the synthetic polyisoprene. The method for adding the emulsifier is not particularly limited, and the emulsifier may be added in advance to either the water or the organic solvent solution or fine suspension of SIS, or both, or may be added to the emulsion during the emulsification operation, either all at once or in portions.

[0047] In the above-mentioned method for producing SIS latex, it is preferable to obtain SIS latex by removing the organic solvent from the emulsion obtained through the emulsification operation. The method for removing the organic solvent from the emulsion is not particularly limited, and methods such as reduced pressure distillation, atmospheric pressure distillation, steam distillation, and centrifugation can be used.

[0048] After removing the organic solvent, if necessary, the SIS latex may be concentrated by vacuum distillation, atmospheric distillation, centrifugation, membrane concentration or the like in order to increase the solid content of the SIS latex. The organic solvent can be removed while adding the antifoaming agent. Addition of the antifoaming agent can suppress foaming.

[0049] The solid content of the SIS latex is preferably 30 to 70% by weight, more preferably 40 to 70% by weight, and even more preferably 50 to 70% by weight. By setting the solid content at or above the lower limit of the above range, film-formed articles such as dip-formed articles described below become less likely to break. Furthermore, by setting the solid content at or below the upper limit of the above range, the viscosity of the SIS latex is prevented from becoming too high, making it easier to transport through piping and to stir in a blending tank.

[0050] The SIS latex may contain additives commonly used in the field of latexes, such as pH adjusters, antifoaming agents, preservatives, crosslinking agents, chelating agents, oxygen scavengers, dispersants, and antioxidants. Examples of pH adjusters include those similar to those used in the synthetic polyisoprene, and alkali metal hydroxides or ammonia are preferred. The pH of the SIS latex is not particularly limited, but as will be described later, when a latex composition is prepared using the SIS latex or the like and the latex composition is aged under specified conditions, it is preferred that the pH of the latex composition before aging is 10 or higher.

[0051] The content of styrene units in the styrene block in the SIS contained in the SIS latex obtained in this manner is preferably 70 to 100% by weight, more preferably 90 to 100% by weight, and even more preferably 100% by weight, based on the total monomer units. The content of isoprene units in the isoprene blocks in SIS is preferably 70 to 100% by weight, more preferably 90 to 100% by weight, and even more preferably 100% by weight, based on the total monomer units. The content ratio of styrene units to isoprene units in SIS, in terms of the weight ratio of "styrene units:isoprene units", is usually in the range of 1:99 to 90:10, preferably 3:97 to 70:30, more preferably 5:95 to 50:50, and even more preferably 10:90 to 30:70.

[0052] The weight-average molecular weight of the SIS, calculated as standard polystyrene by gel permeation chromatography analysis, is preferably 10,000 to 1,000,000, more preferably 50,000 to 500,000, and even more preferably 100,000 to 300,000. By setting the weight-average molecular weight of the SIS within the above range, the balance between tensile strength and flexibility of a film-formed product such as a dip-formed product tends to be improved, and the production of a SIS latex tends to be easier.

[0053] The volume average particle diameter of the latex particles (SIS particles) in the SIS latex is preferably 0.1 to 10 μm, more preferably 0.5 to 3 μm, and even more preferably 0.5 to 2.0 μm. By setting the volume average particle diameter of the latex particles within the above range, the viscosity of the latex becomes appropriate, making it easy to handle, and also preventing a film from forming on the surface of the SIS latex during storage.

[0054] As the latex of the conjugated diene polymer, as mentioned above, a latex of a nitrile group-containing conjugated diene copolymer can also be used.

[0055] The nitrile group-containing conjugated diene copolymer is a copolymer obtained by copolymerizing a conjugated diene monomer with an ethylenically unsaturated nitrile monomer, and may also be a copolymer obtained by copolymerizing, in addition to these, other ethylenically unsaturated monomers copolymerizable with these, which are used as needed.

[0056] Examples of conjugated diene monomers include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene. Among these, 1,3-butadiene and isoprene are preferred, with 1,3-butadiene being more preferred. These conjugated diene monomers can be used alone or in combination of two or more. The content of conjugated diene monomer units formed by conjugated diene monomers in the nitrile group-containing conjugated diene copolymer is preferably 56 to 78% by weight, more preferably 56 to 73% by weight, and even more preferably 56 to 68% by weight. By setting the content of conjugated diene monomer units within the above range, the resulting film-molded article, such as a dip-molded article, can be made to have sufficient tensile strength while also exhibiting excellent texture and elongation.

[0057] The ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an ethylenically unsaturated monomer containing a nitrile group, and examples thereof include acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile, and α-cyanoethylacrylonitrile. Among these, acrylonitrile and methacrylonitrile are preferred, with acrylonitrile being more preferred. These ethylenically unsaturated nitrile monomers can be used alone or in combination of two or more. The content of ethylenically unsaturated nitrile monomer units formed by the ethylenically unsaturated nitrile monomer in the nitrile group-containing conjugated diene copolymer is preferably 20 to 40% by weight, more preferably 25 to 40% by weight, and even more preferably 30 to 40% by weight. By setting the content of the ethylenically unsaturated nitrile monomer units within the above range, the resulting film-molded article, such as a dip-molded article, can be made to have sufficient tensile strength while also exhibiting excellent texture and elongation.

[0058] Examples of other ethylenically unsaturated monomers copolymerizable with the conjugated diene monomer and the ethylenically unsaturated nitrile monomer include ethylenically unsaturated carboxylic acid monomers, which are ethylenically unsaturated monomers containing a carboxyl group; vinyl aromatic monomers such as styrene, alkylstyrene, and vinylnaphthalene; fluoroalkyl vinyl ethers such as fluoroethyl vinyl ether; ethylenically unsaturated amide monomers such as (meth)acrylamide, N-methylol (meth)acrylamide, N,N-dimethylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, and N-propoxymethyl (meth)acrylamide; methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, dibutyl maleate, and butyl methacrylate. Examples of the ethylenically unsaturated carboxylic acid ester monomers include dibutyl acrylate, diethyl maleate, methoxymethyl (meth)acrylate, ethoxyethyl (meth)acrylate, methoxyethoxyethyl (meth)acrylate, cyanomethyl (meth)acrylate, 2-cyanoethyl (meth)acrylate, 1-cyanopropyl (meth)acrylate, 2-ethyl-6-cyanohexyl (meth)acrylate, 3-cyanopropyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, glycidyl (meth)acrylate, and dimethylaminoethyl (meth)acrylate; and crosslinkable monomers such as divinylbenzene, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol (meth)acrylate. These ethylenically unsaturated monomers can be used alone or in combination of two or more.

[0059] The ethylenically unsaturated carboxylic acid monomer is not particularly limited as long as it is an ethylenically unsaturated monomer containing a carboxyl group, but examples include ethylenically unsaturated monocarboxylic acid monomers such as acrylic acid and methacrylic acid; ethylenically unsaturated polycarboxylic acid monomers such as itaconic acid, maleic acid, and fumaric acid; ethylenically unsaturated polycarboxylic acid anhydrides such as maleic anhydride and citraconic anhydride; and ethylenically unsaturated polycarboxylic acid partial ester monomers such as monobutyl fumarate, monobutyl maleate, and mono-2-hydroxypropyl maleate. Among these, ethylenically unsaturated monocarboxylic acids are preferred, with methacrylic acid being particularly preferred. These ethylenically unsaturated carboxylic acid monomers can also be used as alkali metal salts or ammonium salts. Furthermore, the ethylenically unsaturated carboxylic acid monomers can be used alone or in combination of two or more. The content of ethylenically unsaturated carboxylic acid monomer units formed by ethylenically unsaturated carboxylic acid monomers in the nitrile group-containing conjugated diene copolymer is preferably 2 to 5 wt%, more preferably 2 to 4.5 wt%, and even more preferably 2.5 to 4.5 wt%. By setting the content of ethylenically unsaturated carboxylic acid monomer units within the above range, it is possible to obtain a film-formed article such as a dip-formed article having sufficient tear strength and excellent texture.

[0060] The content of other monomer units formed by other ethylenically unsaturated monomers in the nitrile group-containing conjugated diene copolymer is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 3% by weight or less.

[0061] The nitrile group-containing conjugated diene copolymer can be obtained by copolymerizing a monomer mixture containing the above-mentioned monomers, but a method of copolymerization by emulsion polymerization is preferred. As the emulsion polymerization method, a conventionally known method can be used.

[0062] When emulsion polymerizing a monomer mixture containing the above-mentioned monomers, commonly used polymerization secondary materials such as an emulsifier, a polymerization initiator, a molecular weight modifier, etc. The method of adding these polymerization secondary materials is not particularly limited, and any method such as initial lump addition, divided addition, or continuous addition may be used.

[0063] The emulsifier is not particularly limited, but examples include nonionic emulsifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan alkyl esters; anionic emulsifiers such as alkylbenzene sulfonates (e.g., potassium dodecylbenzene sulfonate and sodium dodecylbenzene sulfonate), higher alcohol sulfates, and alkyl sulfosuccinates; cationic emulsifiers such as alkyltrimethylammonium chloride, dialkylammonium chloride, and benzylammonium chloride; and copolymerizable emulsifiers such as sulfoesters of α,β-unsaturated carboxylic acids, sulfate esters of α,β-unsaturated carboxylic acids, and sulfoalkylaryl ethers. Among these, anionic emulsifiers are preferred, with alkylbenzene sulfonates being more preferred, and potassium dodecylbenzene sulfonate and sodium dodecylbenzene sulfonate being particularly preferred. These emulsifiers can be used alone or in combination. The amount of emulsifier used is preferably 0.1 to 10 parts by weight per 100 parts by weight of the monomer mixture.

[0064] The polymerization initiator is not particularly limited, but examples thereof include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; organic peroxides such as diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide, di-α-cumyl peroxide, acetyl peroxide, isobutyryl peroxide, and benzoyl peroxide; and azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, and methyl azobisisobutyrate. These polymerization initiators can be used alone or in combination of two or more. The amount of polymerization initiator used is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 2 parts by weight, per 100 parts by weight of the monomer mixture.

[0065] Furthermore, the peroxide initiator can be used as a redox polymerization initiator in combination with a reducing agent. Examples of the reducing agent include, but are not limited to, compounds containing reduced metal ions such as ferrous sulfate and cuprous naphthenate; sulfonic acid compounds such as sodium methanesulfonate; and amine compounds such as dimethylaniline. These reducing agents can be used alone or in combination of two or more. The amount of reducing agent used is preferably 3 to 1,000 parts by weight per 100 parts by weight of the peroxide.

[0066] The amount of water used in emulsion polymerization is preferably 80 to 600 parts by weight, particularly preferably 100 to 200 parts by weight, based on 100 parts by weight of all the monomers used.

[0067] Examples of methods for adding the monomers include adding the monomers to be used all at once to the reaction vessel, adding them continuously or intermittently as the polymerization progresses, and adding a portion of the monomers and reacting them to a specific conversion rate, followed by adding the remaining monomers continuously or intermittently to polymerize them. Any of these methods may be used. When the monomers are mixed and added continuously or intermittently, the composition of the mixture may be constant or may be varied. Furthermore, the various monomers to be used may be mixed in advance and then added to the reaction vessel, or each may be added separately to the reaction vessel.

[0068] Furthermore, if necessary, polymerization auxiliary materials such as chelating agents, dispersants, pH adjusters, oxygen scavengers, particle size adjusters, etc. may also be used, and the types and amounts of these are not particularly limited.

[0069] The polymerization temperature when carrying out emulsion polymerization is not particularly limited, but is usually 3 to 95° C., and preferably 5 to 60° C. The polymerization time is about 5 to 40 hours.

[0070] The monomer mixture is emulsion polymerized as described above, and when a predetermined polymerization conversion rate is reached, the polymerization reaction is terminated by cooling the polymerization system or adding a polymerization terminator. The polymerization conversion rate at the time of terminating the polymerization reaction is preferably 90% by weight or more, more preferably 93% by weight or more.

[0071] The polymerization terminator is not particularly limited, but examples thereof include hydroxylamine, hydroxyamine sulfate, diethylhydroxylamine, hydroxyamine sulfonic acid and its alkali metal salts, sodium dimethyldithiocarbamate, hydroquinone derivatives, catechol derivatives, and aromatic hydroxydithiocarboxylic acids such as hydroxydimethylbenzenethiocarboxylic acid, hydroxydiethylbenzenedithiocarboxylic acid, and hydroxydibutylbenzenedithiocarboxylic acid, and their alkali metal salts. The amount of the polymerization terminator used is preferably 0.05 to 2 parts by weight per 100 parts by weight of the monomer mixture.

[0072] After the polymerization reaction is terminated, if desired, unreacted monomers are removed and the solid content and pH are adjusted to obtain a latex of a nitrile group-containing conjugated diene copolymer.

[0073] Furthermore, to the latex of the nitrile group-containing conjugated diene copolymer, an antioxidant, a preservative, an antibacterial agent, a dispersant, etc. may be added as needed.

[0074] The number average particle size of the latex of the nitrile group-containing conjugated diene copolymer is preferably 60 to 300 nm, more preferably 80 to 150 nm. The particle size can be adjusted to a desired value by, for example, adjusting the amounts of the emulsifier and polymerization initiator used.

[0075] Furthermore, as the conjugated diene polymer latex, it is also possible to use latex of natural rubber from which proteins have been removed (deproteinized natural rubber), as described above. As the deproteinized natural rubber latex, what is known as "deproteinized natural rubber latex" can be used, which is obtained by a known protein removal method, such as a method in which proteins in natural rubber latex are decomposed with a protease or a surfactant, and then removed by washing or centrifugation.

[0076] As described above, the conjugated diene polymer used in the present invention may be synthetic polyisoprene, styrene-isoprene-styrene block copolymer (SIS), nitrile group-containing conjugated diene copolymer, deproteinized natural rubber, or the like, but is not limited to these, and may also be a butadiene polymer, a styrene-butadiene copolymer, or the like.

[0077] The butadiene polymer may be a homopolymer of 1,3-butadiene as a conjugated diene monomer, or may be a copolymer obtained by copolymerizing 1,3-butadiene as a conjugated diene monomer with another ethylenically unsaturated monomer that is copolymerizable with it.

[0078] The styrene-butadiene copolymer is a copolymer obtained by copolymerizing styrene with 1,3-butadiene as a conjugated diene monomer, and may also be a copolymer obtained by copolymerizing, in addition to these, other ethylenically unsaturated monomers copolymerizable with these, which are used as needed.

[0079] The conjugated diene polymer used in the present invention may be an acid-modified conjugated diene polymer obtained by modification with a monomer having an acidic group, and is preferably a carboxy-modified carboxy-modified conjugated diene polymer. The carboxy-modified conjugated diene polymer can be obtained by modifying the above-mentioned conjugated diene polymer with a monomer having a carboxyl group. Note that when an ethylenically unsaturated carboxylic acid monomer is used as the other possible ethylenically unsaturated monomer for the nitrile group-containing conjugated diene copolymer, the copolymer is already carboxy-modified, and therefore modification with a monomer having a carboxyl group, as described below, is not necessarily required.

[0080] The method for modifying a conjugated diene polymer with a monomer having a carboxyl group is not particularly limited, and examples thereof include a method of graft polymerizing a monomer having a carboxyl group onto a conjugated diene polymer in an aqueous phase. The method for graft polymerizing a monomer having a carboxyl group in an aqueous phase is not particularly limited, and any conventionally known method may be used, but a preferred method is, for example, adding a monomer having a carboxyl group and a graft polymerization catalyst to a latex of a conjugated diene polymer, and then reacting the monomer having a carboxyl group with the conjugated diene polymer in an aqueous phase.

[0081] The graft polymerization catalyst is not particularly limited, but examples thereof include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; organic peroxides such as diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di-t-butyl peroxide, isobutyryl peroxide, and benzoyl peroxide; and azo compounds such as 2,2'-azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, and methyl azobisisobutyrate. From the viewpoint of further improving the tensile strength of the resulting dip-molded film, organic peroxides are preferred, with 1,1,3,3-tetramethylbutyl hydroperoxide being particularly preferred. These graft polymerization catalysts may be used alone or in combination of two or more.

[0082] The above graft polymerization catalysts can be used alone or in combination of two or more. The amount of graft polymerization catalyst used varies depending on the type, but is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, per 100 parts by weight of the conjugated diene polymer. The method for adding the graft polymerization catalyst is not particularly limited, and known addition methods such as batch addition, divided addition, and continuous addition can be used.

[0083] Furthermore, organic peroxides can be used as redox polymerization initiators in combination with reducing agents. The reducing agent is not particularly limited, but examples thereof include compounds containing reduced metal ions such as ferrous sulfate and cuprous naphthenate; sulfinates such as sodium hydroxymethanesulfinate; and amine compounds such as dimethylaniline. These reducing agents may be used alone or in combination of two or more.

[0084] The amount of the reducing agent to be added is not particularly limited, but is preferably 0.01 to 1 part by weight per 1 part by weight of the organic peroxide.

[0085] The method of adding the organic peroxide and the reducing agent is not particularly limited, and known methods of addition such as batch addition, divided addition, and continuous addition can be used.

[0086] The reaction temperature when reacting the conjugated diene polymer with the monomer having a carboxyl group is not particularly limited, but is preferably 15 to 80° C., more preferably 30 to 50° C. The reaction time when reacting the conjugated diene polymer with the monomer having a carboxyl group may be appropriately set depending on the reaction temperature, but is preferably 30 to 300 minutes, more preferably 60 to 120 minutes.

[0087] When a conjugated diene polymer is reacted with a monomer having a carboxyl group, the solid content concentration of the latex of the conjugated diene polymer is not particularly limited, but is preferably 5 to 60% by weight, more preferably 10 to 40% by weight.

[0088] Examples of monomers having a carboxyl group include ethylenically unsaturated monocarboxylic acid monomers such as acrylic acid and methacrylic acid; ethylenically unsaturated polycarboxylic acid monomers such as itaconic acid, maleic acid, fumaric acid, and butenetricarboxylic acid; partial ester monomers of ethylenically unsaturated polycarboxylic acids such as monobutyl fumarate, monobutyl maleate, and mono-2-hydroxypropyl maleate; and polycarboxylic acid anhydrides such as maleic anhydride and citraconic anhydride. Ethylenically unsaturated monocarboxylic acid monomers are preferred because the effect of carboxy modification is more pronounced, with acrylic acid and methacrylic acid being more preferred, and methacrylic acid being particularly preferred. These monomers may be used alone or in combination of two or more. The carboxyl group may also be in the form of a salt with an alkali metal, ammonia, or the like.

[0089] The amount of the monomer having a carboxyl group used is preferably 0.01 to 100 parts by weight, more preferably 0.01 to 40 parts by weight, even more preferably 0.5 to 20 parts by weight, and even more preferably 2 to 5 parts by weight, based on 100 parts by weight of the conjugated diene polymer. By using the monomer having a carboxyl group in the above range, the viscosity of the obtained latex composition becomes more appropriate, making it easier to transfer, and further improving the tear strength of a film-formed article such as a dip-formed article formed using the obtained latex composition.

[0090] The method for adding the monomer having a carboxyl group to the latex of the conjugated diene polymer is not particularly limited, and known methods of addition such as batch addition, divided addition, and continuous addition can be employed.

[0091] The modification rate of the carboxy-modified conjugated diene polymer with a monomer having a carboxyl group may be appropriately controlled depending on the intended use of the resulting conjugated diene polymer latex composition, but is preferably 0.01 to 10% by weight, more preferably 0.2 to 5% by weight, even more preferably 0.3 to 3% by weight, and particularly preferably 0.4 to 2% by weight, for example, 0.4 to 1% by weight. The modification rate is expressed by the following formula: Modification rate (wt%) = (X / Y) x 100 In the above formula, X represents the weight of the unit of the monomer having a carboxyl group in the carboxy-modified conjugated diene polymer, and Y represents the weight of the carboxy-modified conjugated diene polymer. 1 H-NMR measurement was performed. 1 It can be determined by a method of calculation from the results of H-NMR measurement, or by a method of determining the acid amount by neutralization titration and then calculating from the determined acid amount.

[0092] The latex of the conjugated diene polymer (including an acid-modified conjugated diene polymer) used in the present invention may contain additives that are commonly used in the field of latexes, such as a pH adjuster, an antifoaming agent, a preservative, a chelating agent, an oxygen scavenger, a dispersant, and an antioxidant.

[0093] Examples of pH adjusters include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal bicarbonates such as sodium bicarbonate; ammonia; and organic amine compounds such as trimethylamine and triethanolamine; however, alkali metal hydroxides or ammonia are preferred.

[0094] The solids concentration of the latex of the conjugated diene polymer (including acid-modified conjugated diene polymer) used in the present invention is preferably 30 to 70% by weight, more preferably 40 to 70% by weight, and even more preferably 50 to 70% by weight. By setting the solids concentration within the above range, it is possible to more effectively prevent the generation of aggregates in the latex and more effectively prevent the separation of polymer particles during storage of the latex.

[0095] The latex composition of the present invention can be obtained by blending the above-mentioned latex of the conjugated diene polymer with an aqueous dispersion of a sulfur-based vulcanizing agent and a xanthogen compound.

[0096] The aqueous dispersion of the sulfur-based vulcanizing agent is prepared by dispersing the sulfur-based vulcanizing agent in water using an anionic surfactant.

[0097] Sulfur-based vulcanizing agents are solid at room temperature and insoluble in water, and therefore are usually used in a powder state. On the other hand, the present inventors have found that when a sulfur-based vulcanizing agent in a powder state is blended together with a xanthogen compound into a latex composition containing a conjugated diene polymer, the mechanical strengths, such as tensile strength and tear strength, and the stability of the mechanical strength of the resulting film-molded article, such as a dip-molded article, are insufficient. On the other hand, the present inventors have found that blending a sulfur-based vulcanizing agent in the form of an aqueous dispersion using an anionic surfactant into a latex composition containing a conjugated diene polymer improves the mechanical strengths, such as tensile strength and tear strength, and the stability of the mechanical strength of the resulting film-molded article, such as a dip-molded article. In particular, the present inventors have discovered that the problem of insufficient mechanical strength, such as tensile strength and tear strength, and stability of mechanical strength, when a sulfur-based vulcanizing agent is blended in a powder state into a latex composition containing a conjugated diene polymer is a problem specific to the use of a sulfur-based vulcanizing agent in combination with a xanthogen compound, and that the problem specific to the use of a sulfur-based vulcanizing agent in combination with such a xanthogen compound can be solved by blending the sulfur-based vulcanizing agent in the form of an aqueous dispersion using an anionic surfactant. In addition, the present inventors have also discovered that by blending the sulfur-based vulcanizing agent in the form of an aqueous dispersion using an anionic surfactant, sufficient mechanical strength and sufficient stability of mechanical strength can be achieved even when a relatively small amount of the sulfur-based vulcanizing agent is used. By reducing the amount of the sulfur-based vulcanizing agent used in this way, the resulting film-molded product, such as a dip-molded product, can have a more uniform vulcanization density while preventing over-vulcanization.

[0098] Sulfur-based vulcanizing agents include, but are not limited to, powdered sulfur, sulfur flowers, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, and other sulfur-containing compounds such as sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, caprolactam disulfide (N,N'-dithio-bis(hexahydro-2H-azepinone-2)), phosphorus-containing polysulfides, polymeric polysulfides, and 2-(4'-morpholinodithio)benzothiazole. Among these, sulfur is preferred. Sulfur-based vulcanizing agents can be used alone or in combination of two or more.

[0099] The volume average particle diameter of the sulfur-based vulcanizing agent in the aqueous dispersion of the sulfur-based vulcanizing agent is preferably 0.01 to 10 μm, more preferably 0.1 to 5 μm, and even more preferably 0.5 to 2 μm. By setting the volume average particle diameter of the sulfur-based vulcanizing agent in the above range, the dispersibility of the sulfur-based vulcanizing agent in the aqueous dispersion of the sulfur-based vulcanizing agent can be improved.

[0100] The content of the sulfur-based vulcanizing agent in the aqueous dispersion of the sulfur-based vulcanizing agent is preferably 30 to 70% by weight, more preferably 40 to 60% by weight, based on the total weight of the aqueous dispersion of the sulfur-based vulcanizing agent. By setting the content of the sulfur-based vulcanizing agent within the above range, the tensile strength of the resulting film-molded article, such as a dip-molded article, can be further increased while suppressing the occurrence of symptoms of delayed allergy (Type IV).

[0101] The anionic surfactant is not particularly limited, but for example, aromatic sulfonic acid derivatives, fatty acid salts, alkylbenzenesulfonates, alkylsulfosuccinates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, monoalkyl phosphates, etc. are preferred, and aromatic sulfonic acid derivatives are more preferred. The above anionic surfactants can be used alone or in combination of two or more.

[0102] The derivative of aromatic sulfonic acid is not particularly limited, but is preferably a compound represented by the following general formula (1). [ka] (In the above general formula (1), R 1 and R 2 are each independently a hydrogen atom or any organic group, and R 1 and R 2 may be bonded to each other to form a ring structure.

[0103] R 1 and R 2 When they do not bond with each other, R 1 and R 2 Examples of the organic group that can be the aryl group include, but are not limited to, alkyl groups having 1 to 30 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl; cycloalkyl groups having 3 to 30 carbon atoms, such as cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl; aryl groups having 6 to 30 carbon atoms, such as phenyl, biphenyl, naphthyl, and anthranyl; and alkoxy groups having 1 to 30 carbon atoms, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, t-butoxy, n-pentyloxy, n-hexyloxy, and phenoxy. These organic groups may have a substituent, and the position of the substituent may be any position.

[0104] Also, R 1 and R 2 When they bond to each other to form a ring structure, the ring structure is not particularly limited, but is preferably an aromatic compound, more preferably an aromatic compound having a benzene ring such as benzene or naphthalene, and particularly preferably naphthalene. Note that these ring structures may have a substituent, and the position of the substituent may be any position.

[0105] In the present invention, among the compounds represented by the above general formula (1), the derivatives of aromatic sulfonic acid are particularly preferably R 1 and R 2 are bonded to each other to form a ring structure, thereby forming a benzene ring structure in the above general formula (1). More specifically, it is preferable to use a compound having a structure represented by the following general formula (2). [ka] (In the above general formula (2), R 3 represents a divalent hydrocarbon group which may have a substituent.

[0106] In the above general formula (2), R 3 is not particularly limited as long as it is a divalent hydrocarbon group which may have a substituent, but is preferably an alkylene group having 1 to 10 carbon atoms, and particularly preferably a methylene group.

[0107] Furthermore, the aromatic sulfonic acid derivative preferably has a repeating structure represented by the above general formula (2), and the number of repeating units of the structure represented by the above general formula (2) is not particularly limited, but is preferably 10 to 100, more preferably 20 to 50.

[0108] The weight average molecular weight of the aromatic sulfonic acid derivative is preferably 500 to 100,000, more preferably 3,000 to 50,000, and even more preferably 5,000 to 30,000.

[0109] The content of the anionic surfactant in the aqueous dispersion of the sulfur-based vulcanizing agent is not particularly limited, but is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 8 parts by weight, and even more preferably 3 to 7 parts by weight, relative to 100 parts by weight of the sulfur-based vulcanizing agent. By setting the content of the anionic surfactant within the above range, the dispersibility of the sulfur-based vulcanizing agent in the aqueous dispersion of the sulfur-based vulcanizing agent can be further improved, and this can further increase the tensile strength and tear strength of the resulting film-molded article, such as a dip-molded article, and further increase the stability of the tensile strength and tear strength.

[0110] A preferred method for producing an aqueous dispersion of a sulfur-based vulcanizing agent is to mix the sulfur-based vulcanizing agent, an anionic surfactant, and water, and then subject the resulting mixture to a crushing treatment. The crushing treatment may be any treatment capable of crushing the sulfur-based vulcanizing agent contained in the aqueous dispersion or alleviating aggregation. Examples of the crushing treatment include, but are not limited to, a method using a crushing device that utilizes shearing or grinding action, a method using a stirring-type crushing device, or other known crushing devices. Specifically, crushing devices such as a roll mill, hammer mill, vibration mill, jet mill, ball mill, planetary ball mill, bead mill, sand mill, and three-roll mill can be used. Among these, a method using a ball mill, planetary ball mill, or bead mill for the crushing treatment is preferred.

[0111] For example, when the crushing treatment is performed using a ball mill, it is preferable to use media with a media size of preferably φ5 to φ50 mm, more preferably φ10 to φ35 mm, at a rotation speed of preferably 10 to 300 rpm, more preferably 10 to 100 rpm, for a treatment time of preferably 24 to 120 hours, more preferably 24 to 72 hours. Furthermore, when the crushing treatment is performed using a planetary ball mill, it is preferable to use media with a media size of preferably φ0.1 to φ5 mm, more preferably φ0.3 to φ3 mm, at a rotation speed of preferably 100 to 1000 rpm, more preferably 100 to 500 rpm, for a treatment time of preferably 0.25 to 5 hours, more preferably 0.25 to 3 hours. Furthermore, when the crushing treatment is carried out using a bead mill, it is preferable to use media having a media size of preferably φ0.1 to φ3 mm, more preferably φ0.1 to φ1 mm, and to carry out the crushing treatment under the conditions of a rotation speed of preferably 1000 to 10000 rpm, more preferably 1000 to 5000 rpm, and a treatment time of preferably 0.25 to 5 hours, more preferably 0.25 to 3 hours.

[0112] The amount of the aqueous dispersion of sulfur-based vulcanizing agent in the latex composition of the present invention is preferably 0.1 to 1.0 parts by weight, more preferably 0.1 to 0.8 parts by weight, even more preferably 0.1 to 0.6 parts by weight, and particularly preferably 0.2 to 0.6 parts by weight, per 100 parts by weight of the conjugated diene polymer contained in the latex composition. By adjusting the amount of the aqueous dispersion of sulfur-based vulcanizing agent to within the above range, the tear strength of the resulting film-formed article, such as a dip-molded article, can be further increased while suppressing the occurrence of delayed-type allergy (Type IV) symptoms. In the present invention, by incorporating the sulfur-based vulcanizing agent in the form of an aqueous dispersion using an anionic surfactant into the latex composition, sufficient mechanical strength and sufficient stability of the mechanical strength can be achieved even when the amount of sulfur-based vulcanizing agent is relatively small.

[0113] The xanthogen compound used in the present invention functions as a vulcanization accelerator when used in combination with a sulfur-based vulcanizing agent. That is, when a sulfur-based vulcanizing agent is blended into a latex composition as an aqueous dispersion of the sulfur-based vulcanizing agent, and a conjugated diene polymer in the latex composition is vulcanized with the sulfur-based vulcanizing agent to form a film-molded product such as a dip-molded product, the xanthogen compound functions as a vulcanization accelerator. Furthermore, the xanthogen compound functions as a vulcanization accelerator in the latex composition blended with the sulfur-based vulcanizing agent, and after vulcanization, it is decomposed into alcohol, carbon disulfide, and the like by heat applied during vulcanization. For example, the xanthogen compound is decomposed into alcohol, carbon disulfide, and the like by heat applied during the production of a film-molded product (heat of about 100 to 130°C when vulcanizing a conjugated diene polymer), and the components produced by the decomposition (alcohol, carbon disulfide, and the like) volatilize. As a result, the amount of residual xanthogen compound in the obtained film molding is reduced. That is, the latex composition of the present invention does not contain a vulcanization accelerator (for example, a dithiocarbamate vulcanization accelerator, a thiazole vulcanization accelerator, etc.) which has conventionally been a cause of the occurrence of delayed-type allergy (Type IV) symptoms, but contains a xanthogen compound as a vulcanization accelerator, thereby making it possible to reduce the amount of residual xanthogen compound in the obtained film molding such as a dip-molded product, and therefore making it possible to suppress the occurrence of delayed-type allergy (Type IV) symptoms in the obtained film molding.

[0114] Examples of xanthogen compounds include, but are not limited to, xanthogenic acid, xanthogen salts, xanthogen disulfide (a compound in which two xanthogenic acids are bonded via a sulfur atom or the like), and xanthogen polysulfide (a compound in which three or more xanthogenic acids are bonded via a sulfur atom or the like).

[0115] The xanthogenate is not particularly limited as long as it has a xanthogenic acid structure, and examples thereof include compounds represented by the general formula (ROC(=S)S)xZ (where R is a linear or branched hydrocarbon, Z is a metal atom, and x is a number matching the valence of Z, typically 1 to 4, preferably 2 to 4, and particularly preferably 2).

[0116] The xanthogenate represented by the general formula (ROC(=S)S)xZ is not particularly limited, but examples thereof include zinc dimethylxanthogenate, zinc diethylxanthogenate, zinc dipropylxanthogenate, zinc diisopropylxanthogenate, zinc dibutylxanthogenate, zinc dipentylxanthogenate, zinc dihexylxanthogenate, zinc diheptylxanthogenate, zinc dioctylxanthogenate, zinc di(2-ethylhexyl)xanthogenate, zinc didecylxanthogenate, zinc didodecylxanthogenate, potassium dimethylxanthogenate, potassium ethylxanthogenate, potassium propylxanthogenate, potassium isopropylxanthogenate, potassium butylxanthogenate, and pentylxanthogenate. Examples of suitable xanthogenates include potassium xanthogenate, potassium hexyl xanthogenate, potassium heptyl xanthogenate, potassium octyl xanthogenate, potassium 2-ethylhexyl xanthogenate, potassium decyl xanthogenate, potassium dodecyl xanthogenate, sodium methyl xanthogenate, sodium ethyl xanthogenate, sodium propyl xanthogenate, sodium isopropyl xanthogenate, sodium butyl xanthogenate, sodium pentyl xanthogenate, sodium hexyl xanthogenate, sodium heptyl xanthogenate, sodium octyl xanthogenate, sodium 2-ethylhexyl xanthogenate, sodium decyl xanthogenate, and sodium dodecyl xanthogenate. Among these, xanthogenates in which x is 2 or more in the general formula (ROC(=S)S)Z are preferred, isopropyl xanthogenates and butyl xanthogenates are more preferred, and zinc diisopropyl xanthogenate and zinc dibutyl xanthogenate are particularly preferred. These xanthogenates may be used alone or in combination.

[0117] Xanthogen disulfide is a compound in which two xanthogenic acids are bonded via a sulfur atom or the like, and is not particularly limited to, but examples thereof include dimethyl xanthogen disulfide, diethyl xanthogen disulfide, diisopropyl xanthogen disulfide, dibutyl xanthogen disulfide, dimethyl xanthogen polysulfide, diethyl xanthogen polysulfide, diisopropyl xanthogen polysulfide, and dibutyl xanthogen polysulfide. Of these, diisopropyl xanthogen disulfide and dibutyl xanthogen disulfide are preferred.

[0118] Xanthogen polysulfides are compounds in which three or more xanthogenic acids are bonded together via sulfur atoms, etc., and examples include xanthogen trisulfide, in which three xanthogenic acids are bonded together via sulfur, xanthogen tetrasulfide, in which four xanthogenic acids are bonded together via sulfur, and xanthogen pentasulfide, in which five xanthogenic acids are bonded together via sulfur.

[0119] Among the xanthogen compounds exemplified above, xanthogenates are preferred, and zinc diisopropylxanthogenate and zinc dibutylxanthogenate are particularly preferred, from the viewpoint of being able to further increase the tear strength of the resulting film-formed article, such as a dip-formed article.

[0120] The latex composition may contain one or more of these xanthogen compounds, but preferably two or more. For example, when xanthogenic acid is blended into the latex composition, a portion of the blended xanthogenic acid may exist in the form of a xanthogen salt, resulting in the latex composition containing two or more xanthogen compounds. Alternatively, a portion of the xanthogenic acid blended into the latex composition may exist in the form of a xanthogen disulfide or a xanthogen polysulfide due to the action of a sulfur-based vulcanizing agent in the latex composition. Similarly, when a xanthogen salt, xanthogen disulfide, or xanthogen polysulfide is blended into the latex composition, each of these may exist in the form of xanthogenic acid, xanthogen salt, xanthogen disulfide, or xanthogen polysulfide, respectively.

[0121] The amount of the xanthogen compound used (when multiple xanthogen compounds are contained, the total amount used) is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 7 parts by weight, even more preferably 0.5 to 5 parts by weight, and even more preferably 1 to 3 parts by weight, relative to 100 parts by weight of the conjugated diene polymer contained in the latex. By using the xanthogen compound in the above range, the tensile strength of the resulting film-formed article, such as a dip-formed article, can be further improved while suppressing the occurrence of delayed-type allergy (Type IV) symptoms.

[0122] The xanthogen compound may be blended into the conjugated diene polymer latex by any method, and is not particularly limited, but it is preferable that the xanthogen compound is blended into the conjugated diene polymer latex in the form of an aqueous dispersion obtained by dispersing the xanthogen compound in water using a surfactant. That is, it is preferable that the xanthogen compound is dispersed in water using a surfactant to obtain an aqueous dispersion of the xanthogen compound, and then the obtained aqueous dispersion of the xanthogen compound is blended into the conjugated diene polymer latex.

[0123] The surfactant used when dispersing the xanthogen compound in water is not particularly limited, but examples thereof include nonionic surfactants, nonionic anionic surfactants, anionic surfactants, etc. Among these, it is preferable to use nonionic surfactants and nonionic anionic surfactants, from the viewpoint of improving the tensile strength of a film molded product such as a dip molded product obtained after aging the obtained latex composition for a long period of time.

[0124] The anionic surfactant used when dispersing the xanthogen compound in water is not particularly limited, but examples thereof include the same anionic surfactants as those used when dispersing the sulfur-based vulcanizing agent in water to prepare the aqueous dispersion of the sulfur-based vulcanizing agent.

[0125] The nonionic surfactant used when dispersing the xanthogen compound in water is not particularly limited as long as it has a segment in its molecular main chain that acts as a nonionic surfactant. A preferred example of such a segment that acts as a nonionic surfactant is a polyoxyalkylene structure.

[0126] Specific examples of nonionic surfactants include polyoxyalkylene glycol, polyoxyalkylene alkyl ether, polyoxyalkylene alkylphenyl ether, polyoxyethylene styrenated phenyl ether, polyoxyethylene (hydrogenated) castor oil, polyoxyethylene alkylamine, and fatty acid alkanolamide.

[0127] Examples of polyoxyalkylene glycols include polyoxyethylene glycol, polyoxypropylene glycol, and polyoxypropylene glycol ethylene oxide adducts such as polyoxyethylene polyoxypropylene glycol.

[0128] Examples of polyoxyalkylene alkyl ethers include linear or branched ethers having 1 to 50 (preferably 1 to 10) propylene oxide and / or ethylene oxide units added. Among these, linear or branched ethers having 1 to 50 (preferably 1 to 10) propylene oxide units added, linear or branched ethers having 1 to 50 (preferably 1 to 10) ethylene oxide units added, and linear or branched ethers having a total of 2 to 50 (preferably 2 to 10) ethylene oxide units added in blocks or randomly are included. Examples of polyoxyalkylene alkyl ethers include polyoxyethylene oleyl ether, polyoxyethylene octyldodecyl ether, polyoxyethylene dodecyl ether, and polyoxyethylene lauryl ether. Among these, polyoxyethylene oleyl ether and polyoxyethylene octyldodecyl ether are preferred.

[0129] Examples of polyoxyalkylene alkylphenyl ethers include compounds in which 1 to 50 (preferably 1 to 10) propylene oxide and / or ethylene oxide units are added to an alkylphenol. Examples of polyoxyethylene styrenated phenyl ether include ethylene oxide adducts of (mono-, di-, tri-)styrenated phenol, and among these, polyoxyethylene distyrenated phenyl ether, which is an ethylene oxide adduct of distyrenated phenol, is preferred.

[0130] Polyoxyethylene (hydrogenated) castor oil includes ethylene oxide adducts of castor oil or hydrogenated castor oil.

[0131] Examples of fatty acid alkanolamides include lauric acid diethanolamide, palmitic acid diethanolamide, myristic acid diethanolamide, stearic acid diethanolamide, oleic acid diethanolamide, palm oil fatty acid diethanolamide, coconut oil fatty acid diethanolamide, and the like.

[0132] Among nonionic surfactants, nonionic surfactants having a polyoxyalkylene structure are preferred, nonionic surfactants having a polyoxyethylene structure are more preferred, hydrocarbyl ethers of polyoxyethylene are more preferred, polyoxyethylene alkyl ethers and polyoxyethylene distyrenated phenyl ether are further preferred, and polyoxyethylene distyrenated phenyl ether is particularly preferred. The nonionic surfactants may be used alone or in combination of two or more.

[0133] The nonionic-anionic surfactant used when dispersing a xanthogen compound in water is not particularly limited as long as it has a segment that acts as a nonionic surfactant and a segment that acts as an anionic surfactant in its molecular main chain.

[0134] Examples of nonionic anionic surfactants include compounds represented by the following general formula (3). R 4 -O-(CR 5 R 6 CR 7 R 8 O ) n -SO3M (3) (In the above general formula (3), R 4 represents an alkyl group having 6 to 16 carbon atoms or an aryl group having 6 to 14 carbon atoms which may be substituted with an alkyl group having 1 to 25 carbon atoms; R 5 ~R 8 are each independently selected from the group consisting of hydrogen and a methyl group, M is an alkali metal atom or an ammonium ion, and n is 3 to 40.

[0135] Specific examples of the compound represented by the general formula (3) above include polyoxyethylene alkyl ether sulfates such as polyoxyethylene lauryl ether sulfate, polyoxyethylene cetyl ether sulfate, polyoxyethylene stearyl ether sulfate, and polyoxyethylene oleyl ether sulfate; and polyoxyethylene aryl ether sulfates such as polyoxyethylene nonylphenyl ether sulfate, polyoxyethylene octylphenyl ether sulfate, and polyoxyethylene distyryl ether sulfate.

[0136] Among nonionic anionic surfactants, nonionic anionic surfactants having a polyoxyalkylene structure are preferred, and nonionic anionic surfactants having a polyoxyethylene structure are more preferred. The nonionic anionic surfactants may be used alone or in combination of two or more. The content of the nonionic surfactant and / or nonionic anionic surfactant in the aqueous dispersion of the xanthogen compound is not particularly limited, but is preferably 1 to 50 parts by weight, more preferably 3 to 30 parts by weight, and even more preferably 5 to 20 parts by weight, relative to 100 parts by weight of the xanthogen compound. When a nonionic surfactant and a nonionic anionic surfactant are used in combination, it is preferable that the total amount be within the above range.

[0137] A preferred method for producing an aqueous dispersion of a xanthogen compound is to mix a xanthogen compound, a surfactant, and water, and then subject the resulting mixture to a crushing treatment. The crushing treatment may be the same as the method described above for producing an aqueous dispersion of a sulfur-based vulcanizing agent.

[0138] The method for blending the aqueous dispersion of a sulfur-based vulcanizing agent and the xanthogen compound into the above-mentioned latex of a conjugated diene-based polymer is not particularly limited, but the aqueous dispersion of a sulfur-based vulcanizing agent and the xanthogen compound may be added in this order, or they may be added simultaneously.

[0139] In the latex composition of the present invention, an activator may be added to the above-mentioned latex of the conjugated diene polymer, in addition to the aqueous dispersion of the sulfur-based vulcanizing agent and the xanthogen compound, if necessary.

[0140] By adding an activator to the latex composition, when the conjugated diene polymer in the latex composition of the present invention is vulcanized with a sulfur-based vulcanizing agent to form a film-molded article such as a dip-molded article using the latex composition of the present invention, the activator acts as a vulcanization accelerator together with the xanthogen compound, thereby further improving the tear strength of the obtained film-molded article such as a dip-molded article.

[0141] The activator is not particularly limited, but a metal compound is preferred from the viewpoint of further improving the tear strength of the resulting film-formed article, such as a dip-formed article. Examples of the metal compound include, but are not limited to, metal oxides and metal compounds containing at least one carbon atom. The metal constituting the metal compound is not particularly limited, but is preferably a typical metal (at least one element selected from the group consisting of Group 1 elements, Group 2 elements, Group 12 elements, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, Group 17 elements, and Group 18 elements), more preferably a Group 2 element, Group 12 element, Group 13 element, or Group 14 element, even more preferably zinc, magnesium, calcium, aluminum, or lead, particularly preferably zinc, magnesium, or calcium, and most preferably zinc. These metal compounds may be used alone or in combination.

[0142] The metal oxide is not particularly limited, but from the viewpoint of further improving the tear strength of the resulting film-molded article such as a dip-molded article, zinc oxide, magnesium oxide, titanium oxide, calcium oxide, lead oxide, iron oxide, copper oxide, tin oxide, nickel oxide, chromium oxide, cobalt oxide, and aluminum oxide are preferred, and zinc oxide is more preferred.

[0143] As the metal compound containing at least one carbon atom, carbonates, bicarbonates, hydroxides, and organometallic compounds are preferred, with carbonates, bicarbonates, and organometallic compounds being more preferred, from the viewpoint of further improving the tear strength of the resulting film-formed article, such as a dip-formed article. Of these, inorganic salts such as carbonates and bicarbonates are particularly preferred, from the viewpoint of excellent stability of the compound itself and easy availability.

[0144] The amount of the activator used is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, and even more preferably 1 to 3 parts by weight, based on 100 parts by weight of the conjugated diene polymer contained in the latex composition. By using the activator in the above range, the tear strength of the obtained film-formed article such as a dip-formed article can be further improved.

[0145] The method for blending the activator is not particularly limited as long as it is a method that ultimately results in a mixture of the conjugated diene polymer latex and the activator.

[0146] Furthermore, a vulcanization accelerator may be further added to the latex composition within a range that can suppress the occurrence of delayed-type allergy (Type IV) symptoms in the resulting film-molded article such as a dip-molded article.

[0147] As the vulcanization accelerator, those usually used in dip molding can be used, for example, dithiocarbamic acids such as diethyldithiocarbamic acid, dibutyldithiocarbamic acid, di-2-ethylhexyldithiocarbamic acid, dicyclohexyldithiocarbamic acid, diphenyldithiocarbamic acid, dibenzyldithiocarbamic acid, and zinc salts thereof; 2-mercaptobenzothiazole, 2-mercaptobenzothiazole zinc ... Examples of suitable vulcanization accelerators include captothiazoline, dibenzothiazyl disulfide, 2-(2,4-dinitrophenylthio)benzothiazole, 2-(N,N-diethylthiocarbylthio)benzothiazole, 2-(2,6-dimethyl-4-morpholinothio)benzothiazole, 2-(4'-morpholinodithio)benzothiazole, 4-morpholinyl-2-benzothiazyl disulfide, and 1,3-bis(2-benzothiazyl mercaptomethyl)urea. The vulcanization accelerators may be used alone or in combination of two or more. From the viewpoint of further suppressing the occurrence of delayed-type allergy (Type IV) symptoms in the resulting film-molded article, such as a dip-molded article, the content of the xanthogen compound relative to the total content of the xanthogen compound and the vulcanization accelerator is preferably greater than 50% by weight, more preferably 80% by weight or more, and even more preferably 100% by weight.

[0148] Furthermore, the latex composition may further contain additives such as antioxidants; dispersants; reinforcing agents such as carbon black, silica, and talc; fillers such as calcium carbonate and clay; ultraviolet absorbers; and plasticizers, as required.

[0149] Antioxidants include 2,6-di-4-methylphenol, 2,6-di-t-butylphenol, butylhydroxyanisole, 2,6-di-t-butyl-α-dimethylamino-p-cresol, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, styrenated phenol, 2,2'-methylene-bis(6-α-methyl-benzyl-p-cresol), 4,4'-methylenebis(2,6-di-t-butylphenyl)propionate ... phenolic antioxidants that do not contain sulfur atoms, such as 2,2'-methylene-bis(4-methyl-6-t-butylphenol), alkylated bisphenols, and butylated products of p-cresol and dicyclopentadiene; 2,2'-thiobis-(4-methyl-6-t-butylphenol), 4,4'-thiobis-(6-t-butyl-o-cresol), 2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3,5-trimethyl-4-methyl-o-cresol), 2,2'-methylene-bis(4-methyl-6-t-butylphenol), alkylated bisphenols, and butylated products of p-cresol and dicyclopentadiene; Thiobisphenol-based antioxidants such as (triazin-2-ylamino)phenol; phosphite ester-based antioxidants such as tris(nonylphenyl)phosphite, diphenylisodecylphosphite, and tetraphenyldipropylene glycol diphosphite; sulfur ester-based antioxidants such as dilauryl thiodipropionate; phenyl-α-naphthylamine, phenyl-β-naphthylamine, and p-(p-toluenesulfonylamido)-diphenylamine Examples of antioxidants include amine-based antioxidants such as amine, 4,4'-(α,α-dimethylbenzyl)diphenylamine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, and butyraldehyde-aniline condensates; quinoline-based antioxidants such as 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline; and hydroquinone-based antioxidants such as 2,5-di-(t-amyl)hydroquinone. These antioxidants can be used alone or in combination of two or more.

[0150] The content of the antioxidant is preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, and even more preferably 1 to 3 parts by weight, based on 100 parts by weight of the conjugated diene polymer.

[0151] The method for mixing various compounding agents into the latex composition is not particularly limited, but examples thereof include a method in which, after obtaining a composition containing a conjugated diene polymer latex, a sulfur-based vulcanizing agent, and a xanthogen compound as described above, various compounding agents to be compounded as necessary are mixed into the obtained composition using a dispersing machine such as a ball mill, a kneader, a disperser, etc. At least a part of the various compounding agents may be compounded after aging, which will be described later.

[0152] The solid content of the latex composition of the present invention is preferably 10 to 60% by weight, more preferably 10 to 55% by weight.

[0153] In the present invention, in order to obtain a film-formed article such as a dip-molded article with sufficient mechanical properties, it is preferable to subject the latex composition of the present invention to aging (precrosslinking or prevulcanization) before subjecting it to film formation such as dip molding. The aging (prevulcanization) time is not particularly limited, but is preferably 8 to 120 hours, more preferably 24 to 72 hours. The aging (prevulcanization) temperature is not particularly limited, but is preferably 20 to 40°C. When using the latex composition of the present invention, after aging (prevulcanization) for a predetermined time, film formation such as dip molding may be continuously performed while maintaining the aging (prevulcanization) conditions (while continuing the aging (prevulcanization)). In this case, the aging (prevulcanization) time and aging (prevulcanization) temperature may be within the above-mentioned ranges. In particular, since the latex composition of the present invention contains a sulfur-based vulcanizing agent in the form of an aqueous dispersion and further contains a xanthogen compound, a film-formed article having high mechanical strength such as tensile strength and tear strength and excellent stability of the mechanical strength can be obtained.

[0154] <Film molding> The film-formed article of the present invention is not particularly limited, but is preferably a dip-formed article obtained by dip-forming the latex composition of the present invention. Dip-forming is a method in which a mold is immersed in the latex composition, the composition is deposited on the surface of the mold, the mold is then removed from the composition, and the composition deposited on the surface of the mold is then dried. The mold may be preheated before being immersed in the latex composition. Furthermore, a coagulant may be used as needed before the mold is immersed in the latex composition or after the mold is removed from the latex composition.

[0155] Specific examples of methods for using a coagulant include a method in which a mold before being immersed in the latex composition is immersed in a solution of the coagulant to adhere the coagulant to the mold (anodic coagulation immersion method), and a method in which a mold on which the latex composition has been deposited is immersed in a coagulant solution (Teague coagulation immersion method).Of these, the anodic coagulation immersion method is preferred in that it produces a dip-molded product with little thickness unevenness.

[0156] Specific examples of coagulants include water-soluble polyvalent metal salts such as metal halides such as barium chloride, calcium chloride, magnesium chloride, zinc chloride, and aluminum chloride; nitrates such as barium nitrate, calcium nitrate, and zinc nitrate; acetates such as barium acetate, calcium acetate, and zinc acetate; and sulfates such as calcium sulfate, magnesium sulfate, and aluminum sulfate. Among these, calcium salts are preferred, and calcium nitrate is more preferred. These water-soluble polyvalent metal salts can be used alone or in combination of two or more.

[0157] The coagulant can usually be used as a solution in water, alcohol, or a mixture thereof, and is preferably used in the form of an aqueous solution. This aqueous solution may further contain a water-soluble organic solvent such as methanol or ethanol, or a nonionic surfactant. The concentration of the coagulant varies depending on the type of water-soluble polyvalent metal salt, but is preferably 5 to 50% by weight, more preferably 10 to 30% by weight.

[0158] After the mold is removed from the latex composition, the deposit formed on the mold is usually dried by heating under suitable drying conditions.

[0159] The dip-molded layer formed on the mold is then heated to crosslink. Crosslinking of the dip-molded layer can typically be achieved by heat treatment at a temperature of 80 to 150°C, preferably for 10 to 130 minutes. Heating methods include external heating using infrared rays or heated air, or internal heating using high-frequency waves. External heating using heated air is preferred. Prior to heat treatment, the dip-molded layer may be immersed in water, preferably warm water at 30 to 70°C, for 1 to 60 minutes to remove water-soluble impurities (e.g., excess emulsifier, coagulant, etc.). The water-soluble impurities may be removed after the dip-molded layer has been heat-treated, but it is preferable to perform the process before heat treatment to more efficiently remove the water-soluble impurities.

[0160] The dip-molded layer is then removed from the dip-molding mold to obtain a dip-molded article. The removal method can be by peeling it off from the mold by hand, or by using water pressure or compressed air. After removal, the layer may be further heated at a temperature of 60 to 120°C for 10 to 120 minutes.

[0161] The film thickness of the dip-molded body is preferably 0.03 to 0.50 mm, more preferably 0.05 to 0.40 mm, and particularly preferably 0.08 to 0.30 mm.

[0162] Since the dip-molded article of the present invention is obtained using the above-mentioned latex composition, it has high mechanical strength such as tensile strength and tear strength, and excellent stability of the mechanical strength while suppressing the occurrence of symptoms of delayed-type allergy (Type IV), and is therefore particularly suitable for use as, for example, gloves. When the film-molded article is a glove, in order to prevent adhesion at the contact surfaces of the film-molded articles and to improve slippage when putting on and taking off, inorganic fine particles such as talc or calcium carbonate or organic fine particles such as starch particles may be sprinkled on the surface of the glove, an elastomer layer containing fine particles may be formed on the surface of the glove, or the surface layer of the glove may be chlorinated.

[0163] In addition to the above-mentioned gloves, the dip-molded article of the present invention can also be used for medical products such as baby bottle nipples, droppers, tubes, water pillows, balloon sacks, catheters, and condoms; toys such as balloons, dolls, and balls; industrial products such as pressure-molding bags and gas storage bags; and finger cots.

[0164] <Adhesive composition> In the present invention, the above-described latex composition of the present invention can be used as an adhesive composition.

[0165] The content (solid content) of the latex composition of the present invention in the adhesive composition is preferably 5 to 60% by weight, more preferably 10 to 30% by weight.

[0166] The adhesive composition preferably contains an adhesive resin in addition to the latex composition of the present invention. The adhesive resin is not particularly limited, but examples of suitable adhesive resins include resorcinol-formaldehyde resins, melamine resins, epoxy resins, and isocyanate resins. Among these, resorcinol-formaldehyde resins are preferred. Known resorcinol-formaldehyde resins (such as those disclosed in Japanese Patent Laid-Open Publication No. 55-142635) can be used. The reaction ratio of resorcinol to formaldehyde is typically 1:1 to 1:5, preferably 1:1 to 1:3, in terms of the molar ratio of "resorcinol:formaldehyde."

[0167] Furthermore, in order to further enhance the adhesive strength of the adhesive composition, the adhesive composition may contain conventionally used compounds such as 2,6-bis(2,4-dihydroxyphenylmethyl)-4-chlorophenol or similar compounds, isocyanates, blocked isocyanates, ethylene urea, polyepoxides, modified polyvinyl chloride resins, etc.

[0168] Furthermore, the adhesive composition may contain a crosslinking aid. The inclusion of a crosslinking aid can improve the mechanical strength of the composite obtained using the adhesive composition, which will be described later. Examples of crosslinking aids include quinone dioximes such as p-quinone dioxime; methacrylic acid esters such as lauryl methacrylate and methyl methacrylate; allyl compounds such as DAF (diallyl fumarate), DAP (diallyl phthalate), TAC (triallyl cyanurate), and TAIC (triallyl isocyanurate); maleimide compounds such as bismaleimide, phenylmaleimide, and N,Nm-phenylenedimaleimide; and sulfur.

[0169] An adhesive layer-forming substrate can be obtained using the adhesive composition of the present invention by forming an adhesive layer formed using the adhesive composition of the present invention on the surface of a substrate.

[0170] The substrate is not particularly limited, but a fibrous substrate can be used, for example. The type of fiber constituting the fibrous substrate is not particularly limited, and examples thereof include vinylon fiber, polyester fiber, nylon, polyamide fiber such as aramid (aromatic polyamide), glass fiber, cotton, rayon, etc. These can be appropriately selected depending on the intended use. The shape of the fibrous substrate is not particularly limited, and examples thereof include staple, filament, cord, rope, woven fabric (canvas, etc.), etc., and can be appropriately selected depending on the intended use. For example, an adhesive layer-forming substrate can be used as a substrate-rubber composite by adhering it to rubber via an adhesive layer. The substrate-rubber composite is not particularly limited, and examples thereof include a cored rubber toothed belt using a cord-shaped fibrous substrate and a rubber toothed belt using a fabric-like fibrous substrate such as canvas.

[0171] The method for obtaining a substrate-rubber composite is not particularly limited, but examples include a method in which an adhesive composition is applied to a substrate by immersion or the like to obtain an adhesive layer-formed substrate, and the adhesive layer-formed substrate is placed on rubber, followed by heating and pressurization. Pressurization can be performed using a compression (press) molding machine, metal roll, injection molding machine, or the like. The pressure is preferably 0.5 to 20 MPa, more preferably 2 to 10 MPa. The heating temperature is preferably 130 to 300°C, more preferably 150 to 250°C. The heating and pressurization treatment time is preferably 1 to 180 minutes, more preferably 5 to 120 minutes. The heating and pressurization method enables rubber molding and adhesion between the adhesive layer-formed substrate and the rubber to be performed simultaneously. It is preferable to form a mold on the inner surface of the mold of the compressor or the surface of the roll used for pressurization in order to impart a desired surface shape to the rubber of the target substrate-rubber composite.

[0172] Another embodiment of the substrate-rubber composite is a substrate-rubber-substrate composite. The substrate-rubber-substrate composite can be formed, for example, by combining a substrate (which may be a composite of two or more types of substrates) with a substrate-rubber composite. Specifically, a core wire, rubber, and a base fabric as the substrate are layered together (at this time, an adhesive composition is appropriately applied to the core wire and the base fabric to form an adhesive layer-forming substrate), and then heated and pressed to obtain a substrate-rubber-substrate composite.

[0173] The substrate-rubber composite obtained using the adhesive layer-forming substrate has excellent mechanical strength because it is made using the latex composition of the present invention, and therefore can be suitably used as belts such as flat belts, V-belts, V-ribbed belts, round belts, square belts, and toothed belts. Furthermore, the substrate-rubber composite obtained using such an adhesive layer-forming substrate has excellent oil resistance and can be suitably used as a belt in oil. Furthermore, the substrate-rubber composite obtained using the adhesive layer-forming substrate can also be suitably used for hoses, tubes, diaphragms, and the like. Examples of hoses include single-tube rubber hoses, multi-layer rubber hoses, braided-reinforced hoses, and cloth-wrapped-reinforced hoses. Examples of diaphragms include flat diaphragms and rolling-type diaphragms.

[0174] In addition to the above applications, substrate-rubber composites obtained using adhesive layer-forming substrates can be used as industrial products such as seals and rubber rolls. Examples of seals include moving part seals for rotation, oscillation, reciprocation, etc., and fixed part seals. Examples of moving part seals include oil seals, piston seals, mechanical seals, boots, dust covers, diaphragms, accumulators, etc. Examples of fixed part seals include O-rings and various gaskets. Examples of rubber rolls include rolls that are parts of office automation equipment such as printing machines and copying machines; rolls for textile processing such as spinning drawing rolls and spinning draft rolls; rolls for steelmaking such as bridle rolls, snubber rolls, and steering rolls; etc. [Example]

[0175] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In addition, the "parts" below are based on weight unless otherwise specified. Various physical properties were measured as follows.

[0176] <Solid content concentration> 2 g of sample was weighed out (weight: X2) onto an aluminum dish (weight: X1) and dried for 2 hours in a hot air dryer at 105°C. After cooling in a desiccator, the weight of the aluminum dish was measured (weight: X3), and the solid content was calculated according to the following formula. Solid content concentration (wt%)=(X3-X1)×100 / X2

[0177] <Modification rate of carboxy-modified synthetic polyisoprene> The number of carboxyl groups in the carboxyl-modified synthetic polyisoprene constituting the latex of carboxyl-modified synthetic polyisoprene was determined by neutralization titration using an aqueous sodium hydroxide solution. Then, based on the determined number of carboxyl groups, the modification rate by the monomer having a carboxyl group was calculated according to the following formula: Modification rate (wt%) = (X / Y) x 100 In the above formula, X represents the weight of the carboxyl group-containing monomer unit in the carboxy-modified synthetic polyisoprene, and Y represents the weight of the carboxy-modified synthetic polyisoprene.

[0178] <500% tensile stress, tensile strength, and tensile elongation of dip-molded body> Based on ASTM D412, the dip-molded article was punched out with a dumbbell (trade name "Super Dumbbell (model: SDMK-100C)" manufactured by Dumbbell Co., Ltd.) to prepare test specimens for measuring tensile strength. The test specimens were pulled at a pulling rate of 500 mm / min using a Tensilon universal testing machine (trade name "RTG-1210" manufactured by Orientec Co., Ltd.), and the tensile stress (unit: MPa) at an elongation of 500%, the tensile strength (unit: MPa) just before break, and the tensile elongation (unit: %) just before break were measured. The lower the 500% tensile stress value, the softer the dip-molded article is judged to be. Furthermore, the higher the tensile strength, the better the mechanical strength of the dip-molded article is judged to be. The 500% tensile stress and tensile elongation of the dip-molded articles were measured for dip-molded articles that had been aged (pre-vulcanized) for 48 hours. The tensile strength of the dip-molded articles was measured for dip-molded articles that had been aged (pre-vulcanized) for 48 hours and for dip-molded articles that had been aged (pre-vulcanized) for 96 hours.

[0179] <Rate of change in tensile strength of dip-molded body> The rate of change in tensile strength was calculated from the tensile strength of the dip-molded article whose aging (pre-vulcanization) time was 48 hours and the tensile strength of the dip-molded article whose aging (pre-vulcanization) time was 96 hours, measured as described above, according to the following formula. The lower the rate of change in tensile strength, the more excellent the stability of the tensile strength can be judged to be. Change in tensile strength (%) = {(tensile strength of dip-molded body with aging (pre-vulcanization) time of 96 hours) / (tensile strength of dip-molded body with aging (pre-vulcanization) time of 48 hours)} × 100

[0180] <Tear strength of dip-molded body> Based on ASTM D624-00, the dip-molded articles were left in a constant temperature and humidity chamber at 23°C and 50% relative humidity for at least 24 hours, and then punched out with a dumbbell (trade name "Die C", manufactured by Dumbbell Co., Ltd.) to prepare test specimens for measuring tear strength. The test specimens were pulled at a tensile speed of 500 mm / min using a Tensilon universal testing machine (trade name "RTG-1210", manufactured by A&D Co., Ltd.) to measure tear strength (unit: N / mm). The higher the tear strength, the better the mechanical strength of the dip-molded article. Furthermore, the tear strength of the dip-molded articles was measured for both dip-molded articles that had been aged (pre-vulcanized) for 48 hours and dip-molded articles that had been aged (pre-vulcanized) for 96 hours.

[0181] Example 1 (Production of carboxy-modified synthetic polyisoprene (A-1) latex) Synthetic polyisoprene (trade name "NIPOL IR2200L", manufactured by Nippon Zeon Co., Ltd.) was mixed with n-hexane (boiling point: 69°C), and the temperature was raised to 60°C with stirring to dissolve the mixture, thereby preparing an n-hexane solution of synthetic polyisoprene (a) with a synthetic polyisoprene concentration of 15 wt%.

[0182] On the other hand, potassium rosinate was added to water and dissolved by heating to 60° C. to prepare an emulsifier aqueous solution (b) with a concentration of 1.5% by weight.

[0183] Next, the synthetic polyisoprene n-hexane solution (a) obtained above and the emulsifier aqueous solution (b) were mixed using a mixer (product name "Multi-Line Mixer MS26-MMR-5.5L" manufactured by Satake Chemical Machinery Co., Ltd.) so that the potassium rosinate in the emulsifier aqueous solution (b) was 10 parts per 100 parts of synthetic polyisoprene in the synthetic polyisoprene n-hexane solution (a). Subsequently, the mixture was mixed and emulsified using an emulsifier (product name "Milder MDN310" manufactured by Pacific Machinery Co., Ltd.) at a rotation speed of 4100 rpm to obtain an emulsified dispersion (c). At this time, the combined feed flow rate of the synthetic polyisoprene n-hexane solution (a) and the emulsifier aqueous solution (b) was 2,000 kg / hr, the temperature was 60°C, and the back pressure (gauge pressure) was 0.5 MPa.

[0184] The resulting emulsion dispersion (c) was then heated to 80°C under a reduced pressure of -0.01 to -0.09 MPa (gauge pressure) to distill off the n-hexane, yielding an aqueous dispersion of synthetic polyisoprene (d). An antifoaming agent (product name "SM5515", manufactured by Dow Corning Toray Co., Ltd.) was continuously added by spraying to the emulsion dispersion (c) at a concentration of 300 ppm by weight relative to the synthetic polyisoprene in the emulsion dispersion (c). When distilling off the n-hexane, the emulsion dispersion (c) was adjusted to 70% or less by volume of the tank's volume, and the mixture was stirred slowly at 60 rpm using a three-stage inclined paddle impeller.

[0185] After the distillation of n-hexane was completed, the resulting aqueous dispersion of synthetic polyisoprene (d) was concentrated by centrifuging at 8,000 to 9,000 G using a continuous centrifuge (product name "SRG510", manufactured by Alfa Laval) to obtain a synthetic polyisoprene latex (e) with a solids concentration of 60 wt% as a light liquid. The centrifugation conditions were as follows: the solids concentration of the aqueous dispersion (d) before centrifugation was 8 wt%, the flow rate during continuous centrifugation was 1300 kg / hr, and the back pressure (gauge pressure) of the centrifuge was 0.1 MPa.

[0186] Next, the resulting synthetic polyisoprene latex (e) was diluted with 130 parts distilled water per 100 parts synthetic polyisoprene. Then, 0.8 parts of a sodium salt of β-naphthalenesulfonic acid formalin condensate (trade name "Demol T-45", manufactured by Kao Corporation) as a dispersant diluted with 4 parts distilled water per 100 parts synthetic polyisoprene was added to the synthetic polyisoprene latex (e) over 5 minutes. The synthetic polyisoprene latex (e) with the added dispersant was then placed in a nitrogen-substituted reactor equipped with a stirrer and heated to 30°C with stirring. In a separate vessel, 3 parts methacrylic acid as a carboxyl group-containing compound and 16 parts distilled water were mixed to prepare a diluted methacrylic acid solution. This diluted methacrylic acid solution was added over 30 minutes to a reactor maintained at 20°C.

[0187] In addition, a solution (f) consisting of 7 parts distilled water, 0.32 parts sodium formaldehyde sulfoxylate (trade name "SFS", manufactured by Mitsubishi Gas Chemical Company, Inc.), and 0.01 parts ferrous sulfate (trade name "Frost Fe", manufactured by Chubu Chelest Co., Ltd.) was prepared in a separate container. This solution (f) was transferred to a reaction vessel, and 0.5 parts 1,1,3,3-tetramethylbutyl hydroperoxide (trade name "Perocta H", manufactured by NOF Corporation) was added. The mixture was reacted at 20°C for 1 hour, and then concentrated using a centrifuge to obtain a latex of carboxy-modified synthetic polyisoprene (A-1). The modification rate of the resulting latex of carboxy-modified synthetic polyisoprene (A-1) was measured according to the method described above, and found to be 0.5 mol%.

[0188] (Preparation of aqueous sulfur dispersion) An aqueous sulfur dispersion was obtained by mixing 0.5 parts sulfur, 0.03 parts (6.0 parts per 100 parts sulfur) of sodium salt of β-naphthalenesulfonic acid formalin condensate (trade name "Demol T-45" manufactured by Kao Corporation) as an anionic surfactant, 0.004 parts of 5% aqueous potassium hydroxide solution, and 0.42 parts of water in a ball mill (trade name "Magnetic Ball Mill" manufactured by Nitto Kagaku Co., Ltd.). The mixing conditions for the ball mill were ceramic porcelain balls with diameters of 10 mm to 35 mm (a mixture of ceramic porcelain balls with diameters of 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, and 35 mm), and the mixing time was 50 rpm for 72 hours.

[0189] (Preparation of aqueous dispersion of xanthogen compound) An aqueous dispersion of a xanthogen compound was obtained by mixing and crushing 2.5 parts of zinc diisopropyl xanthogenate (trade name "Noccela ZIX" manufactured by Ouchi Shinko Chemical Industry Co., Ltd., volume average particle size: 14 μm, 95% volume cumulative diameter (D95): 55 μm) as a xanthogen compound, 0.45 parts of polyoxyethylene distyrenated phenyl ether (trade name "Emulgen A-60" manufactured by Kao Corporation) as a nonionic surfactant (18.0 parts per 100 parts of zinc diisopropyl xanthogenate), and 2.05 parts of water in a ball mill (trade name "Magnetic Ball Mill" manufactured by Nitto Kagaku Co., Ltd.). The mixing conditions for the ball mill were ceramic porcelain balls with diameters of 10 mm to 35 mm (a mixture of ceramic porcelain balls with diameters of 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, and 35 mm), at 50 rpm for 72 hours.

[0190] (Preparation of latex composition) While stirring the latex of the carboxy-modified synthetic polyisoprene (A-1) obtained above, the aqueous dispersion of sulfur prepared above was added in an amount equivalent to 0.5 parts in terms of sulfur, and the aqueous dispersion of a xanthogen compound was added in an amount equivalent to 2.5 parts in terms of zinc diisopropylxanthogenate, relative to 100 parts of the carboxy-modified synthetic polyisoprene (A-1) in the latex of the carboxy-modified synthetic polyisoprene (A-1).

[0191] Then, while stirring the obtained mixture, 1.5 parts of zinc oxide as an activator and 2 parts of an antioxidant (trade name "Wingstay L", manufactured by Goodyear) were added in aqueous dispersions of each compounding ingredient in an amount calculated on solid content per 100 parts of the carboxy-modified synthetic polyisoprene (A-1) in the mixture to obtain a latex composition. The obtained latex composition was divided into two portions, and one portion was aged (pre-vulcanized) for 48 hours in a thermostatic water bath adjusted to 25°C, and the other portion was aged (pre-vulcanized) for 96 hours in a thermostatic water bath adjusted to 25°C, thereby obtaining a 48-hour aged latex composition and a 96-hour aged latex composition.

[0192] (Production of dip-molded body) A commercially available ceramic hand mold (manufactured by Shinko Co., Ltd.) was washed and preheated in an oven at 70°C. It was then immersed for 5 seconds in an aqueous coagulant solution containing 18% by weight of calcium nitrate and 0.05% by weight of polyoxyethylene lauryl ether (trade name "Emulgen 109P", manufactured by Kao Corporation), and then removed from the aqueous coagulant solution. The hand mold was then dried in an oven at 70°C for 30 minutes or more to adhere the coagulant to the hand mold, thereby coating it with the coagulant.

[0193] The coagulant-coated hand mold was then removed from the oven and immersed in the 48-hour-aged latex composition obtained above for 10 seconds. The hand mold was then air-dried at room temperature for 10 minutes and then immersed in warm water at 60°C for 5 minutes to elute water-soluble impurities, forming a dip-molded layer on the mold. The dip-molded layer formed on the mold was then vulcanized by heating in an oven at 130°C for 30 minutes, cooled to room temperature, sprayed with talc, and peeled from the mold to obtain a glove-shaped dip-molded product (48-hour-aged product). Another glove-shaped dip-molded product (96-hour-aged product) was obtained in the same manner as above, except that the 96-hour-aged latex composition was used instead of the 48-hour-aged latex composition. The 500% tensile stress, tensile strength, tensile elongation, and tear strength of the resulting dip-molded products (48-hour-aged product and 96-hour-aged product) were measured according to the methods described above. The results are shown in Table 1.

[0194] <Example 2> A latex composition was prepared in the same manner as in Example 1, except that the amount of the aqueous sulfur dispersion added was changed to 1.0 part in terms of sulfur. Then, dip-molded articles (48-hour aged product and 96-hour aged product) were obtained and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0195] Example 3 An aqueous dispersion of a xanthogen compound was prepared in the same manner as in Example 2, except that 0.3 parts (12.0 parts per 100 parts of zinc diisopropylxanthogenate) of a polyoxyethylene alkyl ether sulfate (trade name "Alcoscope NS-230", manufactured by Toho Chemical Industry Co., Ltd.) was used as a nonionic anionic surfactant instead of polyoxyethylene distyrenated phenyl ether as a nonionic surfactant. A latex composition was prepared in the same manner as in Example 2. Then, dip-molded articles (48-hour aged product and 96-hour aged product) were obtained and evaluated in the same manner as in Example 2. The results are shown in Table 1.

[0196] Example 4 An aqueous dispersion of a xanthogen compound was prepared in the same manner as in Example 2, except that 0.15 parts (6 parts per 100 parts of zinc diisopropylxanthogenate) of a sodium salt of β-naphthalenesulfonic acid formalin condensate (trade name "Demol T-45", manufactured by Kao Corporation) was used as an anionic surfactant instead of polyoxyethylene distyrenated phenyl ether as a nonionic surfactant. A latex composition was then prepared in the same manner as in Example 2. Then, dip-molded articles (48-hour and 96-hour aged articles) were obtained and evaluated in the same manner as in Example 2. The results are shown in Table 1.

[0197] <Example 5> A latex composition was prepared in the same manner as in Example 4, except that the amount of the aqueous sulfur dispersion added was changed to 0.3 parts in terms of sulfur. Then, dip-molded articles (48-hour aged product and 96-hour aged product) were obtained and evaluated in the same manner as in Example 4. The results are shown in Table 1.

[0198] Example 6 A latex composition was prepared in the same manner as in Example 4, except that the amount of the aqueous sulfur dispersion added was changed to 0.1 parts in terms of sulfur. Then, dip-molded articles (48-hour aged product and 96-hour aged product) were obtained and evaluated in the same manner as in Example 4. The results are shown in Table 1.

[0199] <Comparative Example 1> A latex composition was prepared in the same manner as in Example 4, except that 0.5 parts of sulfur in powder form was added to the latex of carboxy-modified synthetic polyisoprene (A-1) instead of the aqueous sulfur dispersion. Then, dip-molded articles (48-hour aged product and 96-hour aged product) were obtained and evaluated in the same manner as in Example 4. The results are shown in Table 1.

[0200] <Comparative Example 2> An aqueous dispersion of a vulcanization accelerator was prepared in the same manner as in Comparative Example 1, except that 0.3 parts of zinc diethyldithiocarbamate (trade name "Noccela EZ", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), 0.5 parts of zinc dibutyldithiocarbamate (trade name "Noccela BZ-P", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), and 0.7 parts of zinc 2-mercaptobenzothiazole (trade name "Noccela MZ", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were used instead of zinc diisopropylxanthogenate as the xanthogen compound. A latex composition was prepared in the same manner as in Comparative Example 1. Then, dip-molded articles (48-hour and 96-hour aged articles) were obtained and evaluated in the same manner as in Comparative Example 1. The results are shown in Table 1.

[0201] <Comparative Example 3> A latex composition was prepared in the same manner as in Example 1, except that the aqueous dispersion of the vulcanization accelerator obtained in Comparative Example 2 was used instead of the aqueous dispersion of the xanthogen compound. Then, dip-molded articles (48-hour aged product and 96-hour aged product) were obtained in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

[0202] <Comparative Example 4> A latex composition was prepared in the same manner as in Comparative Example 3, except that the amount of the aqueous sulfur dispersion added was changed to 1.5 parts in terms of sulfur. Then, dip-molded articles (48-hour aged product and 96-hour aged product) were obtained in the same manner as in Comparative Example 3 and evaluated in the same manner. The results are shown in Table 1.

[0203] [Table 1]

[0204] As shown in Table 1, the latex compositions prepared by blending a conjugated diene polymer latex with an aqueous dispersion of a sulfur-based vulcanizing agent dispersed in water using an anionic surfactant and a xanthogen compound had good tensile stress and high mechanical strength, and also had a high rate of change in tensile strength, indicating excellent stability of the mechanical strength (Examples 1 to 6). Furthermore, since the obtained latex compositions did not contain a vulcanization accelerator that would cause symptoms of delayed-type allergy (Type IV), when they were dip-molded, it is believed that the resulting dip-molded articles can prevent the occurrence of delayed-type allergy (Type IV). On the other hand, when the latex composition contained sulfur in powder form, rather than in the form of an aqueous dispersion, the resulting dip-molded articles were inferior in mechanical strength (Comparative Examples 1 and 2). Furthermore, when the latex composition contained a compound other than a xanthogen compound as a vulcanization accelerator, the obtained dip-molded article was inferior in mechanical strength (Comparative Examples 3 and 4).

Claims

1. A latex composition comprising a conjugated diene polymer latex, an aqueous dispersion of a sulfur-based vulcanizing agent, and a xanthogen compound, the aqueous dispersion of the sulfur-based vulcanizing agent is prepared by dispersing the sulfur-based vulcanizing agent in water using an anionic surfactant; a content ratio of the sulfur-based vulcanizing agent in the aqueous dispersion of the sulfur-based vulcanizing agent is 30 to 70% by weight based on the total weight of the aqueous dispersion of the sulfur-based vulcanizing agent; the content of the anionic surfactant in the aqueous dispersion of the sulfur-based vulcanizing agent is 0.1 to 10 parts by weight relative to 100 parts by weight of the sulfur-based vulcanizing agent; the amount of the aqueous dispersion of the sulfur-based vulcanizing agent in the latex composition is such that the content of the sulfur-based vulcanizing agent is 0.1 to 1.0 parts by weight based on 100 parts by weight of the conjugated diene polymer contained in the latex composition, the xanthogen compound is a compound represented by the general formula (ROC(=S)S)x-Z (wherein R is a linear or branched hydrocarbon, Z is a metal atom, and x is a number equal to or greater than the valence of Z), The amount of the xanthogen compound used in the latex composition is 0.01 to 10 parts by weight based on 100 parts by weight of the conjugated diene polymer.

2. 2. The latex composition according to claim 1, wherein the amount of the sulfur-based vulcanizing agent is 0.1 to 0.6 parts by weight based on 100 parts by weight of the conjugated diene polymer contained in the conjugated diene polymer latex.

3. 3. The latex composition according to claim 1, wherein the xanthogen compound is dispersed in water using a nonionic surfactant and / or a nonionic anionic surfactant to form an aqueous dispersion, and the xanthogen compound is blended with the conjugated diene polymer latex.

4. The latex composition according to any one of claims 1 to 3, wherein the conjugated diene polymer latex is a synthetic polyisoprene latex, a styrene-isoprene-styrene block copolymer latex, a protein-removed natural rubber latex, or a nitrile group-containing conjugated diene copolymer latex.

5. 5. The latex composition according to claim 1, wherein the conjugated diene polymer latex is a latex of a carboxy-modified conjugated diene polymer.

6. A film-formed article comprising the latex composition according to any one of claims 1 to 5.

7. A dip-molded article obtained by dip-molding the latex composition according to any one of claims 1 to 5.

8. An adhesive composition comprising the latex composition according to any one of claims 1 to 5.

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