Latex composition and dip molded body

Abstract

The present invention provides a latex composition which contains a latex of a conjugated diene polymer and a silicone surfactant that has a silicon atom content of from 1.5% to 10% by weight. The present invention also provides a dip molded body which is obtained by dip molding this latex composition.

Description

[Technical Field]

[0001] The present invention relates to a latex composition that can provide a dip-molded article with excellent storage stability, thin film thickness, and excellent film thickness uniformity and tensile strength, and to a dip-molded article obtained by dip-molding with this composition. [Background technology]

[0002] Conventionally, it is known that various dip-molded products used in contact with the human body, such as nipples, balloons, gloves, sacks, etc., can be obtained by dip molding a latex composition containing rubber latex. Many of the latex compositions used in dip molding are developed for dip molding methods that use coagulants, such as the anode adhesion dipping method and the Teeg adhesion dipping method.

[0003] For example, Patent Document 1 discloses a glove dip composition comprising an elastomer and a silicon-containing organic coagulant for solidifying the glove dip composition. However, as in Patent Document 1, when using a coagulant, the resulting dip molded body tends to have a relatively thick film.

[0004] On the other hand, some latex compositions are used in the manufacture of thin-film dip-molded articles, such as medical gloves and condoms. Such thin-film dip-molded articles are generally manufactured by a direct immersion method without the use of a coagulant, in order to achieve a thin film thickness. Therefore, such latex compositions are required to provide dip-molded articles with thin film thickness, excellent film thickness uniformity, and superior tensile strength, making them suitable for applications such as medical gloves and condoms. However, conventional latex compositions have had the problem of insufficient film thickness uniformity when thin-film dip-molded articles are obtained by methods such as direct immersion. Furthermore, from the perspective of improving the productivity of dip-molded articles and suppressing molding defects, latex compositions are required to have suppressed aggregation during storage, i.e., excellent storage stability.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of such a situation, and an object thereof is to provide a latex composition that is excellent in storage stability, has a thin film thickness, and can provide a dip molded product excellent in film thickness uniformity and tensile strength.

Means for Solving the Problems

[0007] As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved by a latex of a conjugated diene polymer and a latex composition containing a silicone surfactant having a silicon atom content of 1.5 to 10% by weight, and has completed the present invention.

[0008] That is, according to the present invention, there is provided a latex composition containing a latex of a conjugated diene polymer and a silicone surfactant having a silicon atom content of 1.5 to 10% by weight.

[0009] The latex composition of the present invention preferably further contains a crosslinking agent. The latex composition of the present invention preferably further contains a crosslinking accelerator, and it is more preferable that the crosslinking accelerator is a xanthogen compound. In the latex composition of the present invention, it is preferable that the conjugated diene polymer is at least one selected from synthetic polyisoprene, natural rubber, and styrene-isoprene-styrene block copolymer. In the latex composition of the present invention, it is preferable that the silicone-based surfactant is a polyether-modified silicone. In the latex composition of the present invention, it is preferable that the HLB value of the silicone-based surfactant is 2 to 18. In the latex composition of the present invention, the content of the silicone-based surfactant is preferably 0.1 to 5 parts by weight per 100 parts by weight of the conjugated diene polymer. In the latex composition of the present invention, it is preferable that the silicone-based surfactant is a side-chain modified silicone.

[0010] Furthermore, according to the present invention, a dip-molded article is provided which is obtained by dip-molding the latex composition of the present invention described above. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a latex composition that can give a dip-molded article with excellent storage stability, thin film thickness, and excellent film thickness uniformity and tensile strength. [Modes for carrying out the invention]

[0012] The latex composition of the present invention contains a conjugated diene polymer latex and a silicone-based surfactant having a silicon atom content of 1.5 to 10% by weight.

[0013] The conjugated diene polymers that constitute the latex of the conjugated diene polymer used in the present invention are not particularly limited, but examples include synthetic polyisoprene, natural rubber, styrene-isoprene-styrene block copolymer (SIS), and nitrile group-containing conjugated diene copolymers. Among these, at least one selected from synthetic polyisoprene, natural rubber, and styrene-isoprene-styrene block copolymer (SIS) is preferred, at least one selected from synthetic polyisoprene, natural rubber from which protein has been removed (deproteinized natural rubber), and styrene-isoprene-styrene block copolymer (SIS) is more preferred, at least one selected from synthetic polyisoprene and styrene-isoprene-styrene block copolymer (SIS) is even more preferred, and synthetic polyisoprene is particularly preferred.

[0014] When synthetic polyisoprene is used as the conjugated diene polymer, the synthetic polyisoprene may be a homopolymer of isoprene, or it may be a copolymer of isoprene and other ethylenically unsaturated monomers copolymerizable with isoprene. The isoprene unit content 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 (isoprene homopolymer) relative to the total monomer units, as this makes it easier to obtain a dip molded article that is flexible and has superior tensile strength.

[0015] Other ethylenically unsaturated monomers copolymerizable with isoprene include, for example, 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," and similarly for 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 individually or in combination of multiple types.

[0016] Synthetic polyisoprene can be obtained by solution polymerization of isoprene and other copolymerizable ethylenically unsaturated monomers, as needed, in an inert polymerization solvent using conventionally known methods, such as a Ziegler polymerization catalyst consisting of 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 directly in the production of synthetic polyisoprene latex, or solid synthetic polyisoprene may be extracted from the polymer solution and dissolved in an organic solvent before being used in the production of synthetic polyisoprene latex.

[0017] When a polymer solution of synthetic polyisoprene is obtained by the method described above, impurities such as residue of the polymerization catalyst remaining in the polymer solution may be removed. Furthermore, an antioxidant, as described later, may be added to the solution during or after polymerization. Commercially available solid synthetic polyisoprene can also be used.

[0018] In synthetic polyisoprene, there are four types of isoprene units depending on the bonding state of the isoprene: cis-bonded units, trans-bonded units, 1,2-vinyl-bonded units, and 3,4-vinyl-bonded units. From the viewpoint of improving the tensile strength of the resulting dip molded article, the content of cis-bonded units in the isoprene units contained in 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, relative to the total isoprene units.

[0019] The weight-average molecular weight of synthetic polyisoprene 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, based on standard polystyrene equivalent as determined by gel permeation chromatography analysis. By setting the weight-average molecular weight of synthetic polyisoprene within the above range, the tensile strength of the dip molded article is further improved, as are the tensile elongation and tear strength, and the latex of the synthetic polyisoprene tends to be easier to produce.

[0020] Furthermore, the polymer Mooney viscosity (ML1+4, 100°C) of the synthetic polyisoprene is preferably 50-80, more preferably 60-80, and even more preferably 70-80.

[0021] Methods for obtaining synthetic polyisoprene latex include, for example, (1) a method of producing synthetic polyisoprene latex by 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, and removing the organic solvent if necessary; and (2) a method of directly producing synthetic polyisoprene latex by emulsion polymerization or suspension polymerization of isoprene alone or a mixture of isoprene and an ethylenically unsaturated monomer copolymerizable thereto in the presence of an emulsifier. However, the method of production (1) is preferred because it allows the use of synthetic polyisoprene with a high proportion of cis-bond units in the isoprene units, and makes it easier to obtain a dip molded article with superior tensile strength.

[0022] Examples of organic solvents used in the manufacturing method described in (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, pentane, cyclohexane, and n-hexane are more preferred, and n-hexane is particularly preferred.

[0023] The amount of 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, per 100 parts by weight of synthetic polyisoprene.

[0024] In the manufacturing method described in (1) above, it is preferable to use an ionic emulsifier, and more preferably an anionic emulsifier. Examples of anionic emulsifiers include fatty acid salts such as sodium laurate, potassium myristate, sodium palmitate, potassium oleate, sodium linolenate, sodium rosinate, and potassium rosinate; alkylbenzene sulfonates 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 dioctylsulfosuccinate; alkyl sulfate esters such as sodium lauryl sulfate and potassium lauryl sulfate; polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene lauryl ether sulfate and potassium polyoxyethylene lauryl ether sulfate; and monoalkyl phosphates such as sodium lauryl phosphate and potassium lauryl phosphate.

[0025] Among these anionic emulsifiers, fatty acid salts, alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfate esters, and polyoxyethylene alkyl ether sulfate esters are preferred, with fatty acid salts and alkylbenzene sulfonates being particularly preferred.

[0026] Furthermore, it is preferable to use at least one selected from the group consisting of alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates in combination with a fatty acid salt, as this allows for more efficient removal of trace amounts of residual polymerization catalyst (particularly aluminum and titanium) derived from synthetic polyisoprene, and suppresses the generation of aggregates during the production of latex compositions. It is particularly preferable to use alkylbenzene sulfonates in combination with a fatty acid salt. Here, sodium rosinate and potassium rosinate are preferred as fatty acid salts, and sodium dodecylbenzenesulfonate and potassium dodecylbenzenesulfonate are preferred as alkylbenzene sulfonates. These emulsifiers may be used individually or in combination of two or more.

[0027] As described above, by using at least one selected from the group consisting of alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates in combination with a fatty acid salt, the resulting latex will contain at least one selected from alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates, along with the fatty acid salt.

[0028] In addition to anionic emulsifiers, other ionic emulsifiers include copolymerizable emulsifiers such as sulfoesters of α,β-unsaturated carboxylic acids, sulfate esters of α,β-unsaturated carboxylic acids, and sulfoalkylaryl ethers.

[0029] 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.

[0030] The amount of emulsifier used in the manufacturing method described in (1) above 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. That is, for example, when at least one selected from alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfate esters, and polyoxyethylene alkyl ether sulfate esters 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 generation of aggregates during emulsification can be suppressed.

[0031] Furthermore, when using at least one anionic emulsifier selected from alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates in combination with a fatty acid salt, it is preferable that the weight ratio of "fatty acid salt" to "total amount of at least one emulsifier selected from alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates" be in the range of 1:1 to 10:1, and more preferably in the range of 1:1 to 7:1. By setting the weight ratio of at least one emulsifier selected from alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates within the above range, foaming that occurs when handling synthetic polyisoprene can be suppressed, thereby eliminating the need for prolonged standing or the addition of defoaming agents, leading to improved workability and cost reduction.

[0032] The amount of water used in the manufacturing method described in (1) above 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, per 100 parts by weight of the organic solvent solution of synthetic polyisoprene. Examples of the type of water used include hard water, soft water, deionized water, distilled water, and zeolite water, with soft water, deionized water, and distilled water being preferred.

[0033] 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 can be used as long as it is commercially available as an emulsifier or disperser. The method of adding the emulsifier to the solution or fine suspension of synthetic polyisoprene is not particularly limited and may be added in advance to either water or the solution or fine suspension of synthetic polyisoprene, or both, or it may be added to the emulsion during the emulsification process, and may be added all at once or in stages.

[0034] Examples of emulsification equipment include batch-type emulsifiers such as the "Homogenizer" (manufactured by IKA), "Polytron" (manufactured by Kinetica), and "TK Autohomomicker" (manufactured by Tokushu Kika Kogyo Co., Ltd.); "TK Pipeline Homomixer" (manufactured by Tokushu Kika Kogyo Co., Ltd.), "Colloid Mill" (manufactured by Shinko Pantech Co., Ltd.), "Slusher" (manufactured by Nippon Coke Industries Co., Ltd.), "Trigonal Wet Grinding Machine" (manufactured by Mitsui Miike Chemical Machinery Co., Ltd.), and "Cavitron" (manufactured by Eurotech Co., Ltd.), etc. Examples include continuous emulsifiers such as the "Milder" (manufactured by Taiheiyo Kiko Co., Ltd.) and the "Fine Flow Mill" (manufactured by Taiheiyo Kiko Co., Ltd.); high-pressure emulsifiers such as the "Microfluidizer" (manufactured by Mizuho Industries Co., Ltd.), the "Nanomizer" (manufactured by Nanomizer Co., Ltd.), and the "APV Gaurin" (manufactured by Gaurin Co., Ltd.); membrane emulsifiers such as the "Membrane Emulsifier" (manufactured by Reika Kogyo Co., Ltd.); vibratory emulsifiers such as the "Vibro Mixer" (manufactured by Reika Kogyo Co., Ltd.); and ultrasonic emulsifiers such as the "Ultrasonic Homogenizer" (manufactured by Branson Co., Ltd.). The conditions for emulsification using the emulsifier are not particularly limited, and the processing temperature, processing time, etc. should be appropriately selected to achieve the desired dispersion state.

[0035] In the manufacturing method described in (1) above, it is desirable to remove the organic solvent from the emulsion obtained after the emulsification operation. As a method for removing the organic solvent from the emulsion, a method that can reduce the content of the organic solvent (preferably an alicyclic hydrocarbon solvent) in the resulting synthetic polyisoprene latex to 500 ppm by weight or less is preferred, and methods such as vacuum distillation, atmospheric distillation, steam distillation, and centrifugation can be employed.

[0036] In the method described in (1) above, it is desirable to remove the organic solvent from the emulsion obtained after the emulsification operation to obtain synthetic polyisoprene latex. The method for removing the organic solvent from the emulsion is not particularly limited as long as it can reduce the total content of alicyclic hydrocarbon solvents and aromatic hydrocarbon solvents as organic solvents in the obtained synthetic polyisoprene latex to 500 ppm by weight or less, and methods such as vacuum distillation, atmospheric distillation, steam distillation, and centrifugation can be employed.

[0037] Furthermore, after removing the organic solvent, concentration operations such as vacuum distillation, atmospheric distillation, centrifugation, and membrane concentration may be performed as needed to increase the solid content concentration of the synthetic polyisoprene latex. In particular, centrifugation is preferred from the viewpoint of increasing the solid content concentration of the synthetic polyisoprene latex and reducing the amount of emulsifier residue in the synthetic polyisoprene latex.

[0038] Centrifugation is preferably carried out using a continuous centrifuge, with a centrifugal force of preferably 100 to 10,000 G, a solid content concentration of the synthetic polyisoprene latex before centrifugation of preferably 2 to 15% by weight, a flow rate of preferably 500 to 1700 kg / hr fed into the centrifuge, and a back pressure (gauge pressure) of preferably 0.03 to 1.6 MPa. Synthetic polyisoprene latex can be obtained as a light liquid after centrifugation. This reduces the amount of emulsifier residue in the synthetic polyisoprene latex.

[0039] The solid content concentration of the synthetic polyisoprene latex is preferably 10 to 70% by weight, more preferably 20 to 60% by weight, and even more preferably 30 to 50% by weight. Setting the solid content concentration above the lower limit of the above range makes the dip molded body, described later, less prone to tearing. Furthermore, setting the solid content concentration below the upper limit of the above range prevents the viscosity of the synthetic polyisoprene latex from becoming too high, making it easier to transfer in piping and stir in the mixing tank.

[0040] The volume-average particle size 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 size within this range, the latex viscosity becomes appropriate, making it easier to handle, and the formation of a film on the latex surface when the synthetic polyisoprene latex is stored can be suppressed.

[0041] Furthermore, synthetic polyisoprene latex may contain additives commonly used in the latex field, such as pH adjusters, defoamers, preservatives, crosslinking agents, chelating agents, oxygen scavengers, dispersants, and antioxidants.

[0042] Examples of pH adjusting agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal bicarbonates such as sodium bicarbonate; ammonia; and organic amine compounds such as trimethylamine and triethanolamine, but alkali metal hydroxides or ammonia are preferred.

[0043] Furthermore, as mentioned above, latex made from natural rubber from which proteins have been removed (deproteinized natural rubber) can also be used as the latex for the conjugated diene polymer. Deproteinized natural rubber latex can be obtained by known protein removal methods, such as decomposing the proteins in natural rubber latex with proteolytic enzymes or surfactants, and then removing them by washing or centrifugation. This is known as "deproteinized natural rubber latex."

[0044] Furthermore, as mentioned above, styrene-isoprene-styrene block copolymer (SIS) latex can also be used as the latex for conjugated diene polymers. In SIS, "S" represents the styrene block and "I" represents the isoprene block.

[0045] The SIS contained in SIS latex can be obtained by conventionally known methods, such as block copolymerizing isoprene and styrene in an inert polymerization solvent using an active organometallic initiator, such as n-butyllithium. The resulting polymer solution of SIS may be used directly in the production of SIS latex, or solid SIS may be extracted from the polymer solution and then dissolved in an organic solvent for use in the production of SIS latex. There are no particular limitations on the method for producing SIS latex, 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 remove the organic solvent as necessary to produce SIS latex. At this time, impurities such as residues of the polymerization catalyst remaining in the polymer solution after synthesis may be removed. Anti-aging agents, described later, may also be added to the solution during or after polymerization. Commercially available solid SIS can also be used.

[0046] As the organic solvent, the same one used in the case of the synthetic polyisoprene described above can be used, with aromatic hydrocarbon solvents and alicyclic hydrocarbon solvents being preferred, and cyclohexane and toluene being particularly preferred. The amount of organic solvent used is usually 50 to 2,000 parts by weight, preferably 80 to 1,000 parts by weight, more preferably 10 to 500 parts by weight, and even more preferably 150 to 300 parts by weight, per 100 parts by weight of SIS.

[0047] Examples of emulsifiers include those similar to those used for the synthetic polyisoprene described above, with anionic emulsifiers being preferred, and potassium rosinate and sodium dodecylbenzenesulfonate being particularly preferred.

[0048] The amount of emulsifier used is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 30 parts by weight, per 100 parts by weight of SIS. By using the above range for the amount of emulsifier, the storage stability of the resulting latex can be further improved.

[0049] The amount of water used in the above-described method for producing SIS latex 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, per 100 parts by weight of the SIS organic solvent solution. Examples of water types include hard water, soft water, deionized water, distilled water, and zeolite water. Polar solvents such as methanol and other alcohols may also be used in combination with water.

[0050] An apparatus for emulsifying an 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 described above. The method of adding the emulsifier is not particularly limited; it may be added beforehand to either water, the organic solvent solution or fine suspension of SIS, or both, or it may be added to the emulsion during the emulsification process, and it may be added all at once or in stages.

[0051] In the method for producing SIS latex described above, it is preferable to remove the organic solvent from the emulsion obtained after the emulsification process to obtain SIS latex. The method for removing the organic solvent from the emulsion is not particularly limited, and methods such as vacuum distillation, atmospheric distillation, steam distillation, and centrifugation can be employed.

[0052] Furthermore, after removing the organic solvent, if necessary, concentration operations such as vacuum distillation, atmospheric distillation, centrifugation, and membrane concentration may be performed to increase the solid content of the SIS latex.

[0053] The solid content concentration of the SIS latex is preferably 30 to 70% by weight, more preferably 50 to 70% by weight. By setting the solid content concentration above the lower limit of the above range, the resulting dip molded body becomes less prone to tearing. Furthermore, by setting the solid content concentration below the upper limit of the above range, it is possible to prevent the viscosity of the SIS latex from becoming too high, making it easier to transfer in piping and to stir in the mixing tank.

[0054] Furthermore, SIS latex may contain additives commonly used in the latex field, such as pH adjusters, defoamers, preservatives, crosslinking agents, chelating agents, oxygen scavengers, dispersants, and antioxidants. Examples of pH adjusters include those similar to those used for synthetic polyisoprene, with alkali metal hydroxides or ammonia being preferred. The pH of the SIS latex in this case is not particularly limited, but as will be described later, when a latex composition is made using SIS latex and the latex composition is aged under predetermined conditions, it is preferable that the pH of the latex composition before aging is 10 or higher.

[0055] The styrene unit content in the styrene block within the SIS in the SIS latex obtained in this way is preferably 70 to 100% by weight, more preferably 90 to 100% by weight, and even more preferably 100% by weight, relative to the total monomer units.

[0056] Furthermore, the isoprene unit content in the isoprene block within the SIS is preferably 70-100% by weight, more preferably 90-100% by weight, and even more preferably 100% by weight, relative to the total monomer units.

[0057] The content ratio of styrene units to isoprene units in SIS is typically in the range of 1:99 to 90:10 by weight ratio of "styrene units:isoprene units", preferably 3:97 to 70:30, more preferably 5:95 to 50:50, and even more preferably 10:90 to 30:70.

[0058] The weight-average molecular weight of SIS is preferably 10,000 to 1,000,000, more preferably 50,000 to 500,000, and even more preferably 100,000 to 300,000, based on standard polystyrene equivalent as determined by gel permeation chromatography analysis. By setting the weight-average molecular weight of SIS within the above range, the balance between tensile strength and flexibility of the dip-molded article is improved, and the latex of SIS tends to become easier to manufacture.

[0059] The volume-average particle size 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 size of the latex particles within the above range, the latex viscosity becomes appropriate, making it easier to handle, and the formation of a film on the latex surface when the SIS latex is stored can be suppressed.

[0060] As the conjugated diene polymer used in the present invention, as described above, synthetic polyisoprene, natural rubber, styrene-isoprene-styrene block copolymer (SIS), nitrile group-containing conjugated diene copolymer, etc. can be used, but the invention is not limited to these, and butadiene polymers, styrene-butadiene copolymers, etc. may also be used.

[0061] The butadiene polymer may be a homopolymer of 1,3-butadiene as a conjugated diene monomer, or it may be a copolymer obtained by copolymerizing 1,3-butadiene as a conjugated diene monomer with another ethylenically unsaturated monomer that is copolymerizable.

[0062] Furthermore, the styrene-butadiene copolymer is a copolymer obtained by copolymerizing styrene with 1,3-butadiene as a conjugated diene monomer, and in addition to these, copolymers may also be obtained by copolymerizing other ethylenically unsaturated monomers that can copolymerize with these, as needed.

[0063] Furthermore, 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 it is preferable that it be a carboxylated conjugated diene polymer. The carboxylated conjugated diene polymer can be obtained by modifying the above-mentioned conjugated diene polymer with a monomer having a carboxyl group. Note that if an ethylenically unsaturated carboxylic acid monomer is used as the other possible ethylenically unsaturated monomer for the nitrile group-containing conjugated diene copolymer, it is already carboxylated, so modification with a monomer having a carboxyl group, as described later, is not necessarily required.

[0064] There are no particular limitations on the method for modifying a conjugated diene polymer with a monomer having a carboxyl group, but one example is a method of graft polymerization of a conjugated diene polymer with a monomer having a carboxyl group in an aqueous phase. There are no particular limitations on the method of graft polymerization of a monomer having a carboxyl group in an aqueous phase, and conventionally known methods may be used, but for example, a preferred method is to add a monomer having a carboxyl group and a graft polymerization catalyst to the latex of a conjugated diene polymer, and then react the conjugated diene polymer with the monomer having a carboxyl group in an aqueous phase.

[0065] The graft polymerization catalyst is not particularly limited, but examples include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium superphosphate, 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 azobisisobutyrate methyl. From the viewpoint of improving the tensile strength of the resulting dip molded article, organic peroxides are preferred, and 1,1,3,3-tetramethylbutyl hydroperoxide is particularly preferred. These graft polymerization catalysts may be used individually or in combination of two or more.

[0066] The above-mentioned graft polymerization catalysts can be used individually or in combination of two or more types. 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. Furthermore, there are no particular limitations on the method of adding the graft polymerization catalyst, and known addition methods such as single addition, divided addition, and continuous addition can be employed.

[0067] Furthermore, organic peroxides can be used as redox polymerization initiators in combination with reducing agents. Reducing agents are not particularly limited, but examples include compounds containing metal ions in a reduced state, such as ferrous sulfate and cuprous naphthenate; sulfinates such as sodium hydroxymethanesulfinate; and amine compounds such as dimethylaniline. These reducing agents may be used individually or in combination of two or more.

[0068] The amount of reducing agent added is not particularly limited, but it is preferably 0.01 to 1 part by weight per 1 part by weight of organic peroxide.

[0069] The method of adding the organic peroxide and the reducing agent is not particularly limited, and known methods of addition such as single addition, divided addition, and continuous addition can be used for each.

[0070] The reaction temperature when reacting a conjugated diene polymer with a 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 a conjugated diene polymer with a monomer having a carboxyl group can be set appropriately according to the above reaction temperature, but is preferably 30 to 300 minutes, more preferably 60 to 120 minutes.

[0071] When reacting a conjugated diene polymer 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, and more preferably 10 to 40% by weight.

[0072] 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 butentricarboxylic 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. However, ethylenically unsaturated monocarboxylic acid monomers are preferred, acrylic acid and methacrylic acid are more preferred, and methacrylic acid is particularly preferred, as the effect of carboxyl modification becomes even more pronounced. These monomers may be used individually or in combination of two or more. Furthermore, the carboxyl group may also be a salt with alkali metals or ammonia.

[0073] The amount of monomer containing 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 particularly preferably 2 to 5 parts by weight, per 100 parts by weight of the conjugated diene polymer. By using the above range for the amount of monomer containing a carboxyl group, the tensile strength of the resulting dip molded article is further improved.

[0074] The method for adding monomers having carboxyl groups to the latex of a conjugated diene polymer is not particularly limited, and known addition methods such as batch addition, divided addition, and continuous addition can be employed.

[0075] The modification rate by monomers having carboxyl groups in carboxyl-modified conjugated diene polymers can 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. Degeneration rate (weight %) = (X / Y) × 100 In the above formula, X represents the weight of a monomer unit having a carboxyl group in the carboxy-modified conjugated diene polymer, and Y represents the weight of the carboxy-modified conjugated diene polymer. X is the weight of the carboxy-modified conjugated diene polymer. 1 H-NMR measurements were performed. 1 The acid content can be determined by methods such as calculating it from the results of H-NMR measurements, or by determining the amount of acid by neutralization titration and then calculating it from the determined amount of acid.

[0076] The latex composition of the present invention contains, in addition to the conjugated diene polymer latex described above, a silicone-based surfactant having a silicon atom content of 1.5 to 10% by weight.

[0077] The silicone-based surfactant used in the present invention is a surfactant consisting of a polymer having a polysiloxane skeleton. Examples of silicone-based surfactants include dimethyl silicone, in which the main chain consists of siloxane bonds and the polymer main chain ends and polymer side chains are composed of methyl groups, and methylhydrogen silicone, in which part of the side chains is hydrogen.

[0078] As silicone-based surfactants, modified silicones are preferred in which a modifying group such as a polyether group, fluoroalkyl group, phenyl group, alkyl group, or aralkyl group is introduced to a base silicone such as dimethyl silicone or methyl hydrogen silicone. More preferably, a main-chain end-modified modified silicone and / or a side-chain modified modified silicone are preferred in which a modifying group is introduced to at least a portion of the main chain ends of the base silicone, and a side-chain modified modified silicone is preferred in which a modifying group is introduced to at least a portion of the side chains of the base silicone. Hereinafter, modified silicones in which a polyether group, fluoroalkyl group, phenyl group, alkyl group, or aralkyl group is introduced to a base silicone may be referred to as "polyether-modified silicone," "fluoroalkyl-modified silicone," "phenyl-modified silicone," "alkyl-modified silicone," and "aralkyl-modified silicone," respectively. In modified silicones, only one type of modifying group may be introduced, or two or more types may be introduced.

[0079] As a modified silicone used as a silicone-based surfactant, modified dimethyl silicone, which is obtained by introducing a modifying group to dimethyl silicone as a base silicone, is preferred.

[0080] As the modifying group introduced into the modified silicone as a silicone-based surfactant, a polyether group, a fluoroalkyl group, a phenyl group, an alkyl group or an aralkyl group is preferable, and a polyether group is more preferable. That is, as the modified silicone as a silicone-based surfactant, polyether-modified silicone, fluoroalkyl-modified silicone, phenyl-modified silicone, alkyl-modified silicone or aralkyl-modified silicone is preferable, and polyether-modified silicone is more preferable.

[0081] Here, the polyether group is a substituent containing two or more repeating units containing an ether bond, and is not particularly limited. However, [-R 11 (C2H4O) a R 12 , [-R 13 (C3H6O) b R 14 , [-R 15 (C2H4O) c (C3H6O) d R 16 are preferably exemplified by organic groups mainly composed of ethylene oxide and propylene oxide units. Note that R 11 , R 12 , R 13 , R 14 , R 15 , R 16 are hydrocarbon groups, a, b are integers from 6 to 30, and c, d are integers from 1 to 20.

[0082] Specific examples of the modified silicone as a silicone-based surfactant include compounds represented by the following general formulas (1) to (3).

[0083]

Chemical formula

[0084] In the general formulas (1) to (3), R 1 , R 2 , R 3 are each a hydrogen atom or a methyl group, and X 1 , X2 These are each modifying groups, where m is a non-negative integer and n is a non-negative integer. Here, in general formulas (1) to (3), when m is 2 or greater, R is 2 or greater. 1 The elements may be identical or different, and there are two or more R elements. 2 These can be the same or different. Also, in general formula (3), if n is 2 or greater, then R is 2 or greater. 3 The two X's may be the same or different from each other, and there are two or more X's. 1 They may be identical or different from one another.

[0085] General formulas (1) and (2) represent main-chain end-modified silicones. General formula (3) represents side-chain modified silicones.

[0086] In general formulas (1) and (2), R 1 , R 2 Each of these is a hydrogen atom or a methyl group, and is not particularly limited, but all R 1 and R 2 It is preferable that the group is a methyl group. 1 and R 2 When is a methyl group, general formulas (1) and (2) represent main-chain terminal-modified dimethyl silicone.

[0087] In general formula (3), R 1 , R 2 , R 3 Each of these is a hydrogen atom or a methyl group, and is not particularly limited, but all R 1 , R 2 and R 3 It is preferable that the R is a methyl group. 1 , R 2 and R 3 When is a methyl group, general formula (3) represents side-chain modified dimethyl silicone.

[0088] In general formula (1), X 1 , X 2Each of these is a modifying group. Examples of modifying groups include polyether groups, fluoroalkyl groups, phenyl groups, alkyl groups, and aralkyl groups, with polyether groups being preferred. For example, when the modified silicone as a silicone-based surfactant is a polyether-modified silicone, in general formula (1), X 1 , X 2 At least one of them can be a polyether group, and is not particularly limited, but X 1 , X 2 It is preferable that both are polyether groups. 1 , X 2 When both are polyether groups, X 1 , X 2 These may be the same polyether group or different polyether groups.

[0089] In general formulas (1) to (3), m is an integer greater than or equal to 0 and is not particularly limited, but an integer greater than or equal to 1 is preferred.

[0090] As a modified silicone used as a silicone-based surfactant, compounds represented by general formula (1) or general formula (3) are preferred, where X is used in general formula (1). 1 , X 2 Polyether-modified silicone in which both are polyether groups, or in general formula (3) X 1 Polyether-modified silicones in which X is a polyether group are more preferred, and in general formula (3) X 1 Polyether-modified silicones in which the polyether group is a polyether group are even more preferred.

[0091] The silicon atom content of the silicone-based surfactant used in this invention is 1.5 to 10% by weight. The latex composition of this invention containing a silicone-based surfactant with a silicon atom content of 1.5 to 10% by weight provides a dip-molded article with excellent storage stability, thin film thickness, and excellent film thickness uniformity and tensile strength. In particular, when forming a multilayer dip-molded layer using the latex composition of this invention, when forming the second dip-molded layer after forming the first dip-molded layer, a layer made of the latex composition of this invention can be uniformly formed on the first dip-molded layer. As a result, defects such as pinholes can be effectively suppressed by the formation of the second dip-molded layer, and the entire formed dip-molded layer (the entire dip-molded layer consisting of the first and second dip-molded layers) can be made to have excellent uniformity.

[0092] If the silicone-based surfactant is a compound represented by general formulas (1) to (3), then the silicon atom content of the silicone-based surfactant is R 1 , R 2 , R 3 The properties can be adjusted by the type of modifying group, the type of modifying group, and the number of modifying groups introduced. In addition, if the compound is represented by general formula (3), it can also be adjusted by adjusting the ratio of m to n.

[0093] The silicon atom content of the silicone-based surfactant is not particularly limited, but may be 1.5 to 10% by weight, preferably 2 to 9% by weight, more preferably 2.5 to 7% by weight, and even more preferably 3 to 5% by weight. By having a silicon atom content within the above range, the uniformity of the film thickness of the resulting dip molded article can be further improved.

[0094] The HLB value (Hydrophile-Lipophile Balance) of the silicone-based surfactant used in this invention is not particularly limited, but is preferably 2 to 18, more preferably 8 to 17, and even more preferably 10 to 16. Having an HLB value within the above range can further improve the film thickness uniformity of the resulting dip-molded article.

[0095] In the latex composition of the present invention, the content of the silicone-based surfactant is not particularly limited, but is preferably 0.1 to 5 parts by weight, more preferably 0.3 to 3 parts by weight, and even more preferably 0.5 to 1.5 parts by weight, per 100 parts by weight of the conjugated diene polymer. By having the content of the silicone-based surfactant within the above range, the uniformity of the film thickness of the resulting dip molded article can be further improved.

[0096] The latex composition of the present invention preferably contains a crosslinking agent in addition to the latex of the conjugated diene polymer described above and a silicone-based surfactant having a silicon atom content of 1.5 to 10% by weight.

[0097] Sulfur-based vulcanizing agents are preferably used as crosslinking agents. Examples of sulfur-based vulcanizing agents include sulfur such as powdered sulfur, sulfurous salt, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur; and 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 polysulfide, high molecular weight polysulfides, and 2-(4'-morpholinodithio)benzothiazole. Among these, sulfur is preferably used. Crosslinking agents can be used alone or in combination of two or more.

[0098] The content of the crosslinking agent in the latex composition of the present invention is not particularly limited, but is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, and even more preferably 0.5 to 3 parts by weight, per 100 parts by weight of the conjugated diene polymer. By setting the crosslinking agent content within the above range, the tensile strength of the resulting dip molded article can be further increased while suppressing an increase in hardness.

[0099] Furthermore, the latex composition of the present invention preferably further contains a crosslinking accelerator. From the viewpoint of ensuring that the resulting dip-molded article exhibits favorable suppression of delayed-type allergy (Type IV) symptoms, xanthogenic compounds are preferably used as the crosslinking accelerator.

[0100] Xanthogene compounds are not particularly limited, but examples include xanthogenic acid, xanthogenic salt, xanthogene disulfide (a compound in which two xanthogenic acids are linked via a sulfur atom, etc.), and xanthogene polysulfide (a compound in which three or more xanthogenic acids are linked via a sulfur atom, etc.).

[0101] The xanthogenic acid salt can be any salt compound having a xanthogenic acid structure and is not particularly limited, but it is preferably a metal salt of xanthogenic acid, and among these, 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 that matches the valence of Z, usually 1 to 4, preferably 2 to 4, and particularly preferably 2) are preferred. Furthermore, among the metal salts of xanthogenic acid, zinc salt of xanthogenic acid is more preferred.

[0102] The xanthogenic salts represented by the general formula (ROC(=S)S)xZ above are not particularly limited, but include, for example, zinc dimethylxanthogenic acid, zinc diethylxanthogenic acid, zinc dipropylxanthogenic acid, zinc diisopropylxanthogenic acid, zinc dibutylxanthogenic acid, zinc dipentylxanthogenic acid, zinc dihexylxanthogenic acid, zinc diheptylxanthogenic acid, zinc dioctylxanthogenic acid, zinc di(2-ethylhexyl)xanthogenic acid, zinc didecylxanthogenic acid, zinc didodecylxanthogenic acid, potassium dimethylxanthogenic acid, potassium ethylxanthogenic acid, potassium propylxanthogenic acid, potassium isopropylxanthogenic acid, potassium butylxanthogenic acid, and pentylxanthogenic acid. Examples include potassium tonate, potassium hexylxanthogenicate, potassium heptylxanthogenicate, potassium octylxanthogenicate, potassium 2-ethylhexylxanthogenicate, potassium decylxanthogenicate, potassium dodecylxanthogenicate, sodium methylxanthogenicate, sodium ethylxanthogenicate, sodium propylxanthogenicate, sodium isopropylxanthogenicate, sodium butylxanthogenicate, sodium pentylxanthogenicate, sodium hexylxanthogenicate, sodium heptylxanthogenicate, sodium octylxanthogenicate, sodium 2-ethylhexylxanthogenicate, sodium decylxanthogenicate, sodium dodecylxanthogenicate, and the like. Among these, isopropyl xanthogenic salts and butyl xanthogenic salts are preferred, with x being 2 or more in the general formula (ROC(=S)S)xZ being preferred, diisopropyl xanthogenic salts and dibutyl xanthogenic salts being more preferred, zinc diisopropyl xanthogenic acid and zinc dibutyl xanthogenic acid being even more preferred, and zinc diisopropyl xanthogenic acid being particularly preferred. These xanthogenic salts may be used individually or in combination of multiple types.

[0103] Xanthogene disulfides are compounds in which two xanthogenic acids are bonded via a sulfur atom or the like, and are not particularly limited, but examples include dimethyl xanthogene disulfide, diethyl xanthogene disulfide, diisopropyl xanthogene disulfide, dibutyl xanthogene disulfide, dimethyl xanthogene polysulfide, diethyl xanthogene polysulfide, diisopropyl xanthogene polysulfide, and dibutyl xanthogene polysulfide. Among these, diisopropyl xanthogene disulfide and dibutyl xanthogene disulfide are preferred.

[0104] Xanthogene polysulfides are compounds in which three or more xanthogenic acids are linked via sulfur atoms or the like. Examples include xanthogene trisulfides, in which three xanthogenic acids are linked via sulfur; xanthogene tetrasulfides, in which four xanthogenic acids are linked via sulfur; and xanthogene pentasulfides, in which five xanthogenic acids are linked via sulfur.

[0105] These xanthogene compounds may be used individually or in combination of two or more.

[0106] Furthermore, in the present invention, a crosslinking accelerator other than a xanthogene compound may be used as a crosslinking accelerator instead of a xanthogene compound, or together with a xanthogene compound. From the viewpoint of ensuring that the resulting dip molded article exhibits suitably suppressed symptoms of delayed-type allergy (Type IV), it is preferable that the main component of the crosslinking accelerator (preferably 50% by weight or more, more preferably 80% by weight or more, and even more preferably 99% by weight or more) is a xanthogene compound.

[0107] Other crosslinking promoters besides xanthogene compounds can be those commonly used in dip molding, such as dithiocarbamates including diethyldithiocarbamic acid, dibutyldithiocarbamic acid, di-2-ethylhexyldithiocarbamic acid, dicyclohexyldithiocarbamic acid, diphenyldithiocarbamic acid, dibenzyldithiocarbamic acid, and their zinc salts; 2-mercaptobenzothiazole, 2-mercaptobenzothiazole zinc, 2-mercaptothiazoline, dibenzothiazyl disulfide, 2-(2,4-dinitrophenyl Examples include ruthio)benzothiazole, 2-(N,N-diethylthiocarbamoylthio)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. Among these, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, and zinc 2-mercaptobenzothiazole are preferred, and it is even more preferable to use these three in combination. The crosslinking accelerator can be used alone or in combination of two or more. On the other hand, from the viewpoint of ensuring that the resulting dip-molded article exhibits favorable suppression of delayed-type allergy (Type IV) symptoms, it is preferable that the product substantially contains no dithiocarbamates and their zinc salts, as well as 2-mercaptobenzothiazole zinc (preferably 0.1 parts by weight or less per 100 parts by weight of the conjugated diene polymer).

[0108] The content of the crosslinking accelerator in the latex composition of the present invention is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 7 parts by weight, and even more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the conjugated diene polymer. By setting the content of the crosslinking accelerator within the above range, the tensile strength of the resulting dip molded article can be further increased while suppressing an increase in hardness.

[0109] The latex composition of the present invention preferably further contains an activator. The activator can be any compound that has the effect of activating crosslinking, and is not particularly limited, but examples include metal oxides. Metal oxides are preferred because, when a carboxyl-modified conjugated diene polymer is used as the conjugated diene polymer, they also act as a crosslinking agent that crosslinks carboxyl groups, thereby further increasing the tensile strength of the resulting dip molded article.

[0110] Examples of metal oxides, though not particularly limited, include 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. Among these, zinc oxide is preferred from the viewpoint of improving the tensile strength of the resulting dip-molded article. These metal oxides may be used individually or in combination of multiple types.

[0111] The content of the activator in the latex composition of the present invention is not particularly limited, but is preferably 0.01 to 30 parts by weight, more preferably 0.1 to 10 parts by weight, and even more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the conjugated diene polymer. By setting the activator content within the above range, the tensile strength of the resulting dip molded article can be further improved.

[0112] The latex composition of the present invention may further contain, as needed, 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.

[0113] Anti-aging agents 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, styrene phenol, 2,2'-methylene-bis(6-α-methylbenzyl-p-cresol), and 4,4'-methylenebis(2,6-di-t-butylphenyl) Phenolic antioxidants that do not contain sulfur atoms, such as 2,2'-thiobis-(4-methyl-6-t-butylphenol), 2,2'-methylene-bis(4-methyl-6-t-butylphenol), alkylated bisphenols, and butylation reaction 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-thiobis-(4,6-bis(octylthio)-1,3,5-thiobis-(4,6-thiobis-(4,6-thiobis-o-cresol)-1,3,5-thiobis-(4,2'-thiobis-(4-methyl-6-t-butylphenol), 4,4'-thiobis-(6-t-butyl-o-cresol), 2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3,52'-thiobis-(4-methyl-6-t-butylphenol), 2,2'-thiobis-(4-methyl-6-t-butylphenol), 2,2'-thiobis-(4-methyl-6-t-butylphenol), 2,4'-thiobis-(6-t-butyl-o-cresol), 2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3 Thiobisphenol-based antioxidants such as lyazin-2-ylaminophenol; 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, p-(p-toluenesulfonylamide)-diphenyl Examples 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 condensate; 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 individually or in combination of two or more.

[0114] The content of the antioxidant in the latex composition of the present invention is preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, per 100 parts by weight of the conjugated diene polymer.

[0115] The method for preparing the latex composition of the present invention is not particularly limited, but examples include mixing the conjugated diene polymer latex described above with the silicone surfactant described above and various additives used as needed. In this case, it is also possible to prepare an aqueous dispersion of the additive components other than the conjugated diene polymer latex, and then mix the aqueous dispersion with the conjugated diene polymer latex. Furthermore, when using a crosslinking accelerator (especially when using a xanthogene compound as the crosslinking accelerator), it is preferable to prepare an aqueous dispersion containing the crosslinking accelerator and a polyoxyalkylene surfactant in advance and to incorporate them in the form of an aqueous dispersion.

[0116] The solid content concentration of the latex composition of the present invention is preferably 10 to 60% by weight, more preferably 10 to 55% by weight.

[0117] Furthermore, from the viewpoint of ensuring sufficient mechanical properties of the resulting dip-molded article, it is preferable to age (pre-crosslink) the latex composition of the present invention before subjecting it to dip molding. The aging temperature is not particularly limited, but is preferably 20 to 40°C.

[0118] A dip-molded article of the present invention can be obtained by dip molding the latex composition of the present invention. Since the dip-molded article of the present invention is obtained by dip molding the latex composition of the present invention, it can have a thin film thickness, and even when the film thickness is thin (for example, a film thickness of 100 μm or less), it has excellent film thickness uniformity and tensile strength.

[0119] Dip molding is a method in which a mold is immersed in a 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 dried. The drying conditions can be selected as appropriate. The mold may be preheated before being immersed in the latex composition.

[0120] Dip molding methods include immersing the mold in a coagulant solution before immersion in the latex composition to adhere the coagulant to the mold (anodic adhesion immersion method), immersing the mold with the latex composition deposited in it in a coagulant solution (Teeg adhesion immersion method), and depositing the latex composition onto the mold without using a coagulant (direct immersion method). However, from the viewpoint of obtaining a thin film thickness in the dip molded article, the dip molded article of the present invention is preferably obtained by the direct immersion method.

[0121] In the direct dipping method, the mold is immersed in the latex composition, then the mold is removed, and the latex composition adhering to the surface of the mold is deposited by drying or other means to form a dip-molded layer on the mold. The drying conditions can be selected as appropriate. In the direct dipping method, in order to suppress pinholes and unevenness of appearance, a two-step dipping method is usually employed, in which a first dip-molded layer is formed on the mold, and then the mold with the dip-molded layer is immersed again in the latex composition, removed, and dried to form a second dip-molded layer on the mold. When obtaining the dip-molded article of the present invention by the two-step dipping method, it is preferable to use the latex composition of the present invention for both the first and second dip-molding processes, from the viewpoint of further improving the uniformity of the film thickness and tensile strength of the dip-molded article. That is, it is preferable to form a first dip-molded layer by dip-molding the latex composition of the present invention, and then form a second dip-molded layer by dip-molding the latex composition of the present invention on the first dip-molded layer. By this method, a dip-molded article can be obtained comprising a first dip-molded layer formed by dip-molding the latex composition of the present invention, and a second dip-molded layer formed on the first dip-molded layer by dip-molding the latex composition of the present invention.

[0122] In the direct dipping method, since no coagulant is used, a dip-molded body with a thin film thickness and suppressed coagulant residue can be obtained. However, with only one dip molding (i.e., when only one layer is formed by dip molding), the thin film thickness may result in structural defects such as pinholes. From the viewpoint of suppressing such structural defects such as pinholes, a method of performing dip molding multiple times to create multiple dip-molded layers can be considered. However, the inventors' research revealed that when the dip layer is multilayered, sufficient affinity cannot be ensured between the newly formed layer and the lower layer, resulting in problems such as repulsion and unevenness, making it difficult to ensure uniformity of film thickness. In response to this, the inventors' diligent research revealed that the latex composition of the present invention described above can effectively solve these problems, and as a result, it is possible to achieve excellent film thickness uniformity and tensile strength even when a dip-molded body is obtained by the direct dipping method, particularly the double dipping method. Furthermore, by employing a direct immersion method, particularly a double immersion method, it is possible to reduce the film thickness of the resulting dip-molded body.

[0123] Next, the dip-molded layer formed on the mold is crosslinked by heating. Crosslinking of the dip-molded layer can usually be done by heat treatment at a temperature of 80 to 150°C, preferably for 10 to 130 minutes. As for the heating method, external heating by infrared rays or heated air or internal heating by high frequency can be used. Among these, external heating by heated air is preferred. Before heat treatment, the dip-molded layer may be immersed in water, preferably warm water at 30 to 70°C, for about 1 to 60 minutes to remove water-soluble impurities (for example, excess emulsifiers or coagulants). The removal of water-soluble impurities may be performed after heat treatment of the dip-molded layer, but it is preferable to perform it before heat treatment in order to remove water-soluble impurities more efficiently.

[0124] The dip-molded body is then obtained by detaching the dip-molded layer from the dip-molding mold. Detachment methods include peeling it off by hand or using water pressure or compressed air pressure. After detachment, a further heat treatment may be performed at a temperature of 60-120°C for 10-120 minutes.

[0125] The film thickness of the dip-molded article is preferably 10 to 500 μm, more preferably 10 to 100 μm, and particularly preferably 10 to 50 μm. The dip-molded article of the present invention exhibits excellent film thickness uniformity and tensile strength even when the film thickness is thin (for example, 100 μm or less).

[0126] The dip-molded articles of the present invention can be used for medical supplies such as gloves, bottle nipples, droppers, tubes, water pillows, balloon sacks, catheters, condoms, and probe covers; toys such as balloons, dolls, and balls; industrial supplies such as pressure-molding bags and gas storage bags; and finger cots, etc.

[0127] In particular, the dip-molded articles of the present invention exhibit excellent film thickness uniformity and tensile strength, even when the film thickness is thin, making them especially suitable for use as thin medical supplies such as medical gloves, condoms, and probe covers. [Examples]

[0128] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, the "parts" below refer to weight. Various physical properties were measured as follows.

[0129] <Solid content concentration> Two g of the sample was accurately weighed onto an aluminum dish (weight: X1) (weight: X2), and dried in a hot air dryer at 105°C for two hours. After cooling in a desiccator, the weight of the aluminum dish was measured (weight: X3), and the solid content concentration was calculated according to the following formula. Solid content concentration (wt%)=(X3-X1)×100 / X2

[0130] <Modification rate of carboxylated synthetic polyisoprene> The number of carboxyl groups in the carboxyl-modified synthetic polyisoprene constituting the latex was determined by neutralization titration using an aqueous sodium hydroxide solution. Then, based on the determined number of carboxyl groups, the modification rate by monomers containing carboxyl groups was calculated according to the following formula. Degeneration rate (weight %) = (X / Y) × 100 In the above formula, X represents the weight of the monomer unit having a carboxyl group in carboxy-modified synthetic polyisoprene, and Y represents the weight of carboxy-modified synthetic polyisoprene.

[0131] <Storage Stability> The latex composition was further aged (pre-vulcanized) for 48 hours in a constant temperature water bath adjusted to 25°C. The total aging time was 96 hours. After the weight of the aged latex composition was measured, it was filtered through a 200-mesh sieve, and the weight of the aggregates remaining on the sieve was measured. The aggregation ratio was calculated according to the following formula. Aggregation ratio (%) = Weight of aggregates ÷ Weight of latex composition after maturation × 100

[0132] Based on the aggregation ratio calculated above, the storage stability of the latex composition was evaluated according to the following criteria. ◎: The aggregation rate is 0%. (No aggregates remained on the sieve.) ○: The aggregation rate is greater than 0% and less than 1%. △: The aggregation rate is 1% or more but less than 5%. ×: The aggregation rate is 5% or higher.

[0133] <Appearance of the dip-molded layer> In the examples and comparative examples, after the formation of the first dip-molded layer, the first dip-molded layer was visually inspected for any areas where the dip-molded layer was not formed and for any unevenness in film thickness. Similarly, after the formation of the second dip-molded layer, the second dip-molded layer was visually inspected. If no areas where the dip-molded layer was not formed were observed and no unevenness in film thickness was observed, the appearance was judged to be good.

[0134] <Uniform film thickness> Ten measurement points were selected within 3 cm of the point on the dip-molded body corresponding to the point with the longest contact time with the latex composition (the tip of the glass mold) when the glass mold was immersed in the latex composition. The thickness of these ten points was measured, and the arithmetic mean of the measured thicknesses was calculated to determine the film thickness of the dip-molded body. The standard deviation σ of the thicknesses measured above was also calculated, and 3σ (three times the standard deviation σ) was determined. When the film thickness is similar, a smaller 3σ indicates better film thickness uniformity.

[0135] <Tensile strength> Based on ASTM D624-00, dip-molded bodies were left in a constant temperature and humidity chamber at 23°C and 50% relative humidity for more than 24 hours. Then, test specimens for tear strength measurement were prepared by punching them out with a dumbbell (product name "Die C," manufactured by Dumbbell Co., Ltd.). These test specimens were then pulled at a tensile speed of 500 mm / min using a Tensilon universal tester (product name "RTG-1210," manufactured by A&D Corporation), and the tear strength (unit: N / mm) was measured. A higher tear strength indicates a dip-molded body with superior tear strength.

[0136] <Example 1> (Manufacturing of latex from carboxylated synthetic polyisoprene (A-1)) 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 while stirring to dissolve it, and a synthetic polyisoprene n-hexane solution (a) with a synthetic polyisoprene concentration of 15% by weight was prepared.

[0137] On the other hand, potassium rosinate was added to water, and the temperature was raised to 60°C to dissolve it, preparing an aqueous emulsifier solution (b) with a concentration of 1.5% by weight.

[0138] Next, the n-hexane solution of synthetic polyisoprene (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 Industry Co., Ltd.) so that the amount of potassium rosinate in the emulsifier aqueous solution (b) was 10 parts for every 100 parts of synthetic polyisoprene in the n-hexane solution of synthetic polyisoprene (a). Subsequently, the mixture was mixed and emulsified using an emulsifier (product name "Milder MDN310", manufactured by Taiheiyo Kiko Co., Ltd.) at a rotation speed of 4100 rpm to obtain an emulsified dispersion (c). At this time, the total feed flow rate of the n-hexane solution of synthetic polyisoprene (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.

[0139] Next, the resulting emulsified dispersion (c) was heated to 80°C under reduced pressure of -0.01 to -0.09 MPa (gauge pressure) to remove n-hexane by distillation, yielding an aqueous dispersion of synthetic polyisoprene (d). During this process, an antifoaming agent (product name "SM5515", manufactured by Toray Dow Corning) was continuously added by spraying at an amount of 300 ppm by weight relative to the synthetic polyisoprene in the emulsified dispersion (c). When removing n-hexane by distillation, the volume of the emulsified dispersion (c) was adjusted to 70% or less of the tank volume, and a three-stage inclined paddle blade was used as the stirring impeller, with slow stirring performed at 60 rpm.

[0140] After the removal of n-hexane was complete, the resulting aqueous dispersion of synthetic polyisoprene (d) was concentrated by centrifugation at 8,000-9,000 G using a continuous centrifuge (product name "SRG510", manufactured by Alfa Laval) to obtain synthetic polyisoprene latex (e) with a solid content of 60% by weight as a light liquid. The centrifugation conditions were as follows: solid content of the aqueous dispersion (d) before centrifugation was 8% by weight, flow rate during continuous centrifugation was 1300 kg / hr, and back pressure (gauge pressure) of the centrifuge was 0.1 MPa.

[0141] Next, 130 parts of distilled water were added to 100 parts of synthetic polyisoprene in the obtained synthetic polyisoprene latex (e) to dilute it. Then, to the synthetic polyisoprene latex (e), 0.8 parts of the sodium salt of β-naphthalene sulfonic acid formalin condensate (trade name "Demol T-45", manufactured by Kao Corporation) as a dispersant was added over 5 minutes to 100 parts of synthetic polyisoprene, diluted with 4 parts of distilled water per 100 parts of synthetic polyisoprene. Next, the synthetic polyisoprene latex (e) with the added dispersant was charged into a reaction vessel with a stirrer that was purged with nitrogen, and the temperature was heated to 30°C while stirring. In addition, in a separate container, 3 parts of methacrylic acid as a carboxyl group-containing compound and 16 parts of distilled water were mixed to prepare a methacrylic acid dilution. This methacrylic acid dilution was added to the reaction vessel, which was kept at a temperature of 20°C, over 30 minutes.

[0142] Furthermore, using a separate container, solution (f) was prepared consisting of 7 parts distilled water, 0.32 parts sodium formaldehyde sulfoxylate (trade name "SFS", manufactured by Mitsubishi Gas Chemical Co., Ltd.), and 0.01 parts ferrous sulfate (trade name "Frost Fe", manufactured by Chubu Kirest Co., Ltd.). After transferring this solution (f) to a reaction vessel, 0.5 parts 1,1,3,3-tetramethylbutyl hydroperoxide (trade name "Perocta H", manufactured by Nippon Oil & Fats Co., Ltd.) was added and the mixture was reacted at 20°C for 1 hour. The mixture was then concentrated using a centrifuge to obtain the latex of carboxy-modified synthetic polyisoprene (A-1). The denaturation rate of the obtained carboxy-modified synthetic polyisoprene (A-1) latex was measured according to the method described above, and the denaturation rate was found to be 0.5 mol%.

[0143] (Preparation of an aqueous sulfur dispersion) A sulfur aqueous dispersion was obtained by crushing 0.5 parts sulfur as a crosslinking agent, 0.03 parts sodium salt of β-naphthalene sulfonic acid formalin condensate (product name "Demol T-45", manufactured by Kao Corporation) as an anionic surfactant (6.0 parts per 100 parts sulfur), 0.004 parts 5% potassium hydroxide aqueous solution, and 0.42 parts water using a ball mill (product name "Porcelain Ball Mill", manufactured by Nittokagaku Co., Ltd.). The mixing conditions using the ball mill were 50 rpm for 72 hours, using ceramic porcelain balls of φ10 mm to φ35 mm (a mixture of ceramic porcelain balls of φ10 mm, φ15 mm, φ20 mm, φ25 mm, φ30 mm, and φ35 mm).

[0144] (Preparation of aqueous dispersion of xanthogenic compounds) As a crosslinking accelerator, 2.5 parts of zinc diisopropylxanthogene (trade name "Noxellar ZIX", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., volume average particle size: 14 μm, 95% volume cumulative diameter (D95): 55 μm) as a xanthogene 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 diisopropylxanthogene), and 2.05 parts of water were mixed using a ball mill (trade name "Porcelain Ball Mill", manufactured by Nittokagaku Co., Ltd.) and subjected to crushing treatment to obtain an aqueous dispersion of the xanthogene compound. For the ball milling process, the mixing conditions were as follows: ceramic porcelain balls ranging from φ10mm to φ35mm (a mixture of ceramic porcelain balls of φ10mm, φ15mm, φ20mm, φ25mm, φ30mm, and φ35mm) were used, and the process was conducted at 50 rpm for 72 hours.

[0145] (Preparation of latex composition) While stirring the carboxy-modified synthetic polyisoprene (A-1) latex obtained above, add the aqueous dispersion of sulfur prepared above as a crosslinking agent in an amount equivalent to 1.0 part of sulfur, the aqueous dispersion of xanthogenic compound as a crosslinking accelerator in an amount equivalent to 2.5 parts of zinc diisopropylxanthogenic acid, and a polyether surfactant (product name "DOWSIL SH3746", general formula (3) X 1 is a polyether group and R 1 , R 2 , R 3 One part of a side-chain modified polyether-modified dimethyl silicone, manufactured by Dow-Toray Corporation, with a silicon atom content of 3.8% by weight and an HLB value of 16, in which all components are methyl groups, was added. Subsequently, the solid content concentration of the polymer latex was adjusted to 40% by weight.

[0146] Then, while stirring the resulting mixture, aqueous dispersions of each compounding agent were added in the following order on a solid content basis: 1.5 parts of zinc oxide as an activator and 2 parts of an antioxidant (product name "Wingstay L," Goodyear) per 100 parts of carboxy-modified synthetic polyisoprene (A-1) in the mixture. The mixture was then aged (pre-vulcanized) for 48 hours in a constant temperature water bath adjusted to 25°C to obtain the latex composition. The storage stability of the obtained latex composition dip molded articles was evaluated according to the method described above. The results are shown in Table 1.

[0147] (Manufacturing of dip-molded products) Using the latex composition and glass mold obtained above, a dip-molded body was manufactured by a direct immersion method. Specifically, the glass mold was immersed in the latex composition for 15 seconds and then removed. Subsequently, the latex composition adhering to the glass mold was dried at a temperature of 80°C for 5 minutes to form the first dip-molded layer. Furthermore, the glass mold with the first dip-molded layer formed on it was again immersed in the latex composition for 15 seconds and then removed. Subsequently, the latex composition adhering to the glass mold with the first dip-molded layer formed on it was dried at a temperature of 80°C for 5 minutes and then leached by immersion in 60°C hot water for 5 minutes to form the second dip-molded layer. The results of the appearance evaluation of the first and second dip-molded layers are shown in Table 1.

[0148] Next, the carboxy-modified synthetic polyisoprene (A-1) in the first and second dip-molded layers was subjected to vulcanization (post-vulcanization) by heat treatment at a temperature of 120°C for 20 minutes to form a dip-molded body. Then, the dip-molded body was peeled off the glass mold to obtain the dip-molded body. The obtained dip-molded body was evaluated and measured for film thickness uniformity and tensile strength according to the method described above. The results are shown in Table 1.

[0149] <Examples 2, 3 and Comparative Examples 1-4> A latex composition was obtained in the same manner as in Example 1, except that the type and amount of silicone-based surfactant used were changed as shown in Table 1, and then a dip-molded article was obtained. The results of evaluation, observation, and measurement in the same manner as in Example 1 are shown in Table 1. In Comparative Example 1, no silicone-based surfactant was used. Also, in Comparative Example 3, a dip-molded article could not be obtained.

[0150] [Table 1] The silicone-based surfactants used are as follows: DOWSIL SH3746: In general formula (3), X 1 is a polyether group and R 1 , R 2 , R 3 Side-chain modified polyether-modified dimethyl silicone, all of which are methyl groups, manufactured by Dow-Toray Corporation, silicon atom content 3.8% by weight, HLB value 16 KP-110: Polyether-modified silicone, manufactured by Shin-Etsu Chemical Co., Ltd., silicon atom content 4.0% by weight. DOWSIL SH8400: In general formula (3), X 1 is a polyether group and R 1 , R 2 , R 3 Side-chain modified polyether-modified dimethyl silicone, all of which are methyl groups, manufactured by Dow-Toray Corporation, silicon atom content 8.2% by weight, HLB value 8 TPA4380: Polyether-modified silicone, manufactured by Toshiba Silicone Co., Ltd., silicon atom content 0.6% by weight KF-6015: Polyether-modified silicone, manufactured by Shin-Etsu Chemical Co., Ltd., silicon atom content 15% by weight DOWSIL SM5512: Silicone defoaming emulsion, manufactured by Dow-Toray Corporation, silicon atom content exceeding 50% by weight.

[0151] As shown in Table 1, a latex composition containing a conjugated diene polymer latex and a silicone-based surfactant with a silicon atom content of 1.5 to 10% by weight can provide a dip molded article with excellent storage stability, thin film thickness, and excellent film thickness uniformity and tensile strength (Examples 1 to 3).

[0152] On the other hand, when the silicone-based surfactant was not included, or when the silicon atom content of the silicone-based surfactant was too low, the resulting dip-molded articles had poor film thickness uniformity (Comparative Examples 1 and 2). Furthermore, when the silicon atom content of the silicone-based surfactant was too high, storage stability was poor, and either a dip molded article could not be obtained (Comparative Example 3), or the obtained dip molded article had poor film thickness uniformity (Comparative Example 4).

Claims

1. A latex composition comprising a carboxylated synthetic polyisoprene latex having a modification rate of 0.01 to 10% by weight with monomers having carboxyl groups, and a silicone-based surfactant having a silicon atom content of 3 to 10% by weight.

2. The latex composition according to claim 1, further containing a crosslinking agent.

3. The latex composition according to claim 1 or 2, further containing a crosslinking accelerator.

4. The latex composition according to claim 3, wherein the crosslinking accelerator is a xanthogene compound.

5. The latex composition according to any one of claims 1 to 4, wherein the silicone-based surfactant is a polyether-modified silicone.

6. The latex composition according to any one of claims 1 to 5, wherein the HLB value of the silicone-based surfactant is 2 to 18.

7. The latex composition according to any one of claims 1 to 6, wherein the content of the silicone-based surfactant is 0.1 to 5 parts by weight per 100 parts by weight of the carboxy-modified synthetic polyisoprene.

8. The latex composition according to any one of claims 1 to 7, wherein the silicone-based surfactant is a side-chain modified silicone.

9. A dip-molded article obtained by dip-molding a latex composition according to any one of claims 1 to 8.

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