Film forming body

Abstract

The present invention provides a film molded body which is obtained using a latex composition that contains a latex of a conjugated diene polymer, a sulfur-based vulcanizing agent, a vulcanization accelerator and an anti-aging agent, and which has a thickness of from 20 μm to 300 μm, wherein: the anti-aging agent is composed of at least one agent that is selected from among phenolic anti-aging agents and quinoline-based anti-aging agents; and the molecular weight of the anti-aging agent is from 300 to 600.

Description

Technical Field

[0001] The present invention relates to a film molded body.

Background Art

[0002] Conventionally, it has been known that a dip molding composition containing rubber latex is dip molded to obtain a film molded body such as a dip molded body used in contact with the human body, such as a nipple, balloon, glove, balloon, sack, etc. Film molded bodies such as dip molded bodies are required to have excellent tensile strength from the viewpoint that they can be suitably used for these applications.

[0003] For example, Patent Document 1 discloses a dip molded body obtained by dip molding a dip molding composition containing synthetic polyisoprene latex, a sulfur-based vulcanizing agent, zinc oxide, a vulcanization accelerator, a specific dispersant, and a specific amount of a monovalent salt of dithiocarbamic acids. With the technique of Patent Document 1, a dip molded body excellent in tensile strength can be obtained.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] On the other hand, in recent years, the required characteristics for film molded bodies such as dip molded bodies have become stricter, and there is a demand for film molded bodies such as dip molded bodies in which a decrease in mechanical strength when stored at a high temperature (for example, about 70°C) is suppressed. The present invention has been made in view of such a situation, and an object thereof is to provide a film molded body in which a decrease in mechanical strength when stored at a high temperature is suppressed.

Means for Solving the Problems

[0006] As a result of intensive studies to achieve the above object, the present inventors have found that a film molded body obtained using a latex composition containing a latex of a conjugated diene polymer, a crosslinking agent, a crosslinking accelerator, and an antioxidant having a specific structure and molecular weight can suppress a decrease in mechanical strength when stored at high temperatures, and have thus completed the present invention.

[0007] That is, according to the present invention, there is provided a film molded body having a thickness of 20 to 300 μm, obtained using a latex composition containing a latex of a conjugated diene polymer, a sulfur-based vulcanizing agent, a vulcanization accelerator, and an antioxidant, wherein the antioxidant is at least one selected from a phenolic antioxidant and a quinoline-based antioxidant, and the molecular weight of the antioxidant is 300 to 600.

[0008] In the film molded body of the present invention, it is preferable that the antioxidant contains at least an aromatic compound (a) having two or more phenolic hydroxyl groups. In the film molded body of the present invention, it is preferable that the antioxidant contains at least an aromatic compound (a-1) having two or more hindered phenol structures. In the film molded body of the present invention, it is preferable that the antioxidant contains at least an aromatic compound (a-2) having two or more hindered phenol structures and having a diphenylmethane skeleton. In the film molded body of the present invention, it is preferable that the antioxidant contains an aromatic compound (a) having two or more phenolic hydroxyl groups and an aromatic compound (b-1) having one phenolic hydroxyl group and one or more -NH- bonds. In the film molded body of the present invention, it is preferable that the latex of the conjugated diene polymer is a latex of synthetic polyisoprene, a latex of a styrene-isoprene-styrene block copolymer, or a latex of natural rubber. In the film molded body of the present invention, it is preferable that the latex of the conjugated diene polymer is a latex of a carboxy-modified conjugated diene polymer. In the film molded body of the present invention, it is preferable that the swell index (SI) of the conjugated diene polymer is 105 to 300%. In the film molded body of the present invention, it is preferable that the content of the sulfur-based vulcanizing agent in the latex composition is 0.1 to 1.2 parts by weight with respect to 100 parts by weight of the conjugated diene polymer in the latex composition. In the film molded body of the present invention, it is preferable that the crosslinking accelerator is a xanthogen compound.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a film molded body in which a decrease in mechanical strength when stored at a high temperature is suppressed.

Modes for Carrying Out the Invention

[0010] The film molded body of the present invention is obtained by using a latex composition containing a latex of a conjugated diene polymer, a sulfur-based vulcanizing agent, a vulcanization accelerator, and an antioxidant having a specific structure and molecular weight.

[0011] As a result of investigations by the present inventors, even in a film molded body having excellent mechanical properties such as tensile strength and tear strength at normal temperature, when the film thickness is as thin as 20 to 300 μm, there is a problem that the mechanical strength significantly decreases when the film molded body is stored at a high temperature (for example, about 70°C). Then, in order to suppress the decrease in mechanical strength when a film molded body having a film thickness of 20 to 300 μm is stored at a high temperature (for example, about 70°C), as a result of intensive research by the present inventors, a film molded body obtained by using a latex composition containing a latex of a conjugated diene polymer, a crosslinking agent, a crosslinking accelerator, and an antioxidant having a specific structure and molecular weight can achieve the above object, and the present invention has been completed.

[0012] <Latex Composition> The latex composition used in the present invention contains a latex of a conjugated diene polymer.

[0013] The conjugated diene polymer constituting the latex of the conjugated diene polymer is not particularly limited, and examples thereof include synthetic polyisoprene, styrene-isoprene-styrene block copolymer (SIS), natural rubber (including natural rubber from which proteins have been removed), and the like. As the conjugated diene polymer, synthetic polyisoprene, styrene-isoprene-styrene block copolymer (SIS) or natural rubber (including natural rubber from which proteins have been removed) is preferable, synthetic polyisoprene, styrene-isoprene-styrene block copolymer (SIS) or natural rubber from which proteins have been removed is more preferable, synthetic polyisoprene or styrene-isoprene-styrene block copolymer (SIS) is even more preferable, and synthetic polyisoprene is particularly preferable.

[0014] When synthetic polyisoprene is used as the conjugated diene polymer, the synthetic polyisoprene may be a homopolymer of isoprene or a copolymer of isoprene and another ethylenically unsaturated monomer copolymerizable therewith. The content of isoprene units in the synthetic polyisoprene is preferably 70% by weight or more, more preferably 90% by weight or more, still more preferably 95% by weight or more, and particularly preferably 100% by weight (homopolymer of isoprene) based on all monomer units. When the content of isoprene units in the synthetic polyisoprene is within the above range, a decrease in mechanical strength when the film molded body of the present invention is stored at a high temperature can be more effectively suppressed.

[0015] Examples of other ethylenically unsaturated monomers copolymerizable with isoprene include conjugated diene monomers other than isoprene such as butadiene, chloroprene, 1,3 - pentadiene; ethylenically unsaturated nitrile monomers such as acrylonitrile, methacrylonitrile, fumaronitrile, α - chloroacrylonitrile; vinyl aromatic monomers such as styrene, alkylstyrene; ethylenically unsaturated carboxylic acid ester monomers such as methyl (meth)acrylate (meaning "methyl acrylate and / or methyl methacrylate", and the same applies to ethyl (meth)acrylate etc. below), ethyl (meth)acrylate, butyl (meth)acrylate, 2 - ethylhexyl (meth)acrylate; and the like. These other ethylenically unsaturated monomers copolymerizable with isoprene may be used alone or in combination of two or more.

[0016] Synthetic polyisoprene can be obtained by solution polymerization of isoprene and, if necessary, other copolymerizable ethylenically unsaturated monomers in an inert polymerization solvent using a conventionally known method, for example, a Ziegler - type polymerization catalyst composed of trialkylaluminum - titanium tetrachloride or an alkyllithium polymerization catalyst such as n - butyllithium, sec - butyllithium. The polymer solution of synthetic polyisoprene obtained by solution polymerization may be used as it is as a latex of synthetic polyisoprene, or after taking out the solid synthetic polyisoprene from the polymer solution and dissolving it in an organic solvent, it may be used as a latex of synthetic polyisoprene. Further, when a polymer solution of synthetic polyisoprene is obtained by the above - described method, impurities such as residues of the polymerization catalyst remaining in the polymer solution may be removed. Also, an antioxidant described later may be added to the solution during or after polymerization. Commercially available solid synthetic polyisoprene can also be used.

[0017] As isoprene units in synthetic polyisoprene, there are four types: cis-bond units, trans-bond units, 1,2-vinyl bond units, and 3,4-vinyl bond units, depending on the bonding state of isoprene. From the viewpoint of improving the tensile strength of film moldings such as the resulting dip moldings, the content ratio of cis-bond units in the isoprene units contained in synthetic polyisoprene is preferably 70% by weight or more, more preferably 90% by weight or more, and still more preferably 95% by weight or more, based on all isoprene units.

[0018] 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 still more preferably 800,000 to 3,000,000 in terms of standard polystyrene conversion by gel permeation chromatography analysis. When the weight-average molecular weight of synthetic polyisoprene is within the above range, the decrease in mechanical strength when the film molding of the present invention is stored at a high temperature can be more suppressed, and the synthetic polyisoprene latex tends to be easier to manufacture.

[0019] Also, the polymer Mooney viscosity (ML1+4, 100 °C) of synthetic polyisoprene is preferably 50 to 85, more preferably 60 to 85, and still more preferably 70 to 85.

[0020] Examples of methods for obtaining synthetic polyisoprene latex include: (1) emulsifying a solution or fine suspension of synthetic polyisoprene dissolved or finely dispersed in an organic solvent in water in the presence of an anionic surfactant, and removing the organic solvent as necessary to produce synthetic polyisoprene latex; (2) emulsion polymerization or suspension polymerization of isoprene alone or a mixture of isoprene and an ethylenically unsaturated monomer copolymerizable therewith in the presence of an anionic surfactant to directly produce synthetic polyisoprene latex. However, synthetic polyisoprene having a high ratio of cis-bond units in the isoprene units can be used, and since the decrease in mechanical strength when the film molding of the present invention is stored at a high temperature can be more suppressed, the production method (1) above is preferred.

[0021] Examples of the organic solvent used in the production method of (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; halogenated hydrocarbon solvents such as methylene chloride, chloroform, and ethylene dichloride; and the like. Among these, alicyclic hydrocarbon solvents are preferred, and cyclohexane is particularly preferred.

[0022] 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 still more preferably 500 to 1,500 parts by weight with respect to 100 parts by weight of the synthetic polyisoprene.

[0023] Examples of the anionic surfactant used in the production method of (1) above include fatty acid salts such as sodium laurate, potassium myristate, sodium palmitate, potassium oleate, sodium linolenate, and sodium 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 sulfate esters such as sodium polyoxyethylene lauryl ether sulfate and potassium polyoxyethylene lauryl ether sulfate; monoalkyl phosphates such as sodium lauryl phosphate and potassium lauryl phosphate; and the like.

[0024] Among these anionic surfactants, fatty acid salts, alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfate esters, and polyoxyethylene alkyl ether sulfate esters are preferred, and fatty acid salts and alkylbenzene sulfonates are particularly preferred.

[0025] In addition, it is possible to more efficiently remove trace amounts of polymerization catalysts (especially aluminum and titanium) derived from synthetic polyisoprene, and the generation of aggregates is suppressed when producing a conjugated diene polymer latex composition. Therefore, it is preferable to use in combination at least one selected from the group consisting of alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfate esters, and polyoxyethylene alkyl ether sulfate esters, and a fatty acid salt, and it is particularly preferable to use in combination an alkylbenzene sulfonate and a fatty acid salt. Here, as the fatty acid salt, sodium rosinate and potassium rosinate are preferred, and as the alkylbenzene sulfonate, sodium dodecylbenzenesulfonate and potassium dodecylbenzenesulfonate are preferred. These surfactants may be used alone or in combination of two or more.

[0026] As described above, by using in combination at least one selected from the group consisting of alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfate esters, and polyoxyethylene alkyl ether sulfate esters, and a fatty acid salt, the resulting latex contains at least one selected from alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfate esters, and polyoxyethylene alkyl ether sulfate esters, and a fatty acid salt.

[0027] In addition, in the production method described in (1) above, a surfactant other than an anionic surfactant may be used in combination. Examples of such surfactants other than anionic surfactants include copolymerizable surfactants such as sulfoesters of α,β-unsaturated carboxylic acids, sulfate esters of α,β-unsaturated carboxylic acids, and sulfoalkyl aryl ethers.

[0028] The amount of the anionic surfactant used in the production method described in (1) above is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 30 parts by weight, based on 100 parts by weight of synthetic polyisoprene. When using two or more types of surfactants, it is preferable that the total amount used is within the above range. That is, for example, when using at least one selected from alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfate esters, and polyoxyethylene alkyl ether sulfate esters in combination with a fatty acid salt, it is preferable that the total amount used is within the above range.

[0029] When using in combination at least one selected from alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfate esters, and polyoxyethylene alkyl ether sulfate esters as the anionic surfactant and a fatty acid salt, the weight ratio of these is preferably in the range of 1:1 to 10:1, more preferably in the range of 1:1 to 7:1, based on the total of the "fatty acid salt" and "at least one surfactant selected from alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl sulfate esters, and polyoxyethylene alkyl ether sulfate esters".

[0030] The amount of water used in the production 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, based on 100 parts by weight of the organic solvent solution of synthetic polyisoprene. Examples of the type of water used include hard water, soft water, ion-exchanged water, distilled water, zeolite water, etc., and soft water, ion-exchanged water, and distilled water are preferred.

[0031] An 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 anionic surfactant can be used without particular limitation as long as it is generally commercially available as an emulsifier or disperser. As a method for adding an anionic surfactant to the solution or fine suspension of synthetic polyisoprene, there is no particular limitation, and it 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 operation, and it may be added all at once or in portions.

[0032] Examples of the emulsifying apparatus include batch-type emulsifiers such as those with the trade name "Homogenizer" (manufactured by IKA), the trade name "Polytron" (manufactured by Kinematic), and the trade name "TK Auto Homomixer" (manufactured by Tokushu Kika Kogyo Co., Ltd.); continuous-type emulsifiers such as those with the trade name "TK Pipeline Homomixer" (manufactured by Tokushu Kika Kogyo Co., Ltd.), the trade name "Colloid Mill" (manufactured by Shinko Pantec Co., Ltd.), the trade name "Slasher" (manufactured by Nippon Coke & Engineering Co., Ltd.), the trade name "Trigonal Wet Pulverizer" (manufactured by Mitsui Miike Chemical Machinery Co., Ltd.), the trade name "Cavitron" (manufactured by Eurotech Co., Ltd.), the trade name "Milder" (manufactured by Taiheiyo Kiko Co., Ltd.), and the trade name "Fine Flow Mill" (manufactured by Taiheiyo Kiko Co., Ltd.); high-pressure emulsifiers such as those with the trade name "Microfluidizer" (manufactured by Mizuhopuro Co., Ltd.), the trade name "Nanomizer" (manufactured by Nanomizer Co., Ltd.), and the trade name "APV Gaulin" (manufactured by Gaulin Co., Ltd.); membrane emulsifiers such as those with the trade name "Membrane Emulsifier" (manufactured by Reika Kogyo Co., Ltd.); vibration-type emulsifiers such as those with the trade name "Vibro Mixer" (manufactured by Reika Kogyo Co., Ltd.); ultrasonic emulsifiers such as those with the trade name "Ultrasonic Homogenizer" (manufactured by Branson Co., Ltd.); and the like. The conditions for the emulsification operation by the emulsifying apparatus are not particularly limited, and the treatment temperature, treatment time, etc. may be appropriately selected so as to achieve a desired dispersion state.

[0033] In the production method described in (1) above, 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) in the resulting synthetic polyisoprene latex to 500 ppm by weight or less is preferred. For example, methods such as vacuum distillation, atmospheric distillation, steam distillation, and centrifugation can be employed.

[0034] Further, after removing the organic solvent, if necessary, a concentration operation may be performed by methods such as vacuum distillation, atmospheric distillation, centrifugation, and membrane concentration in order to increase the solid content concentration of the synthetic polyisoprene latex. In particular, from the viewpoint of increasing the solid content concentration of the synthetic polyisoprene latex and reducing the residual amount of the surfactant in the synthetic polyisoprene latex, it is preferable to perform centrifugation.

[0035] Centrifugation is preferably carried out, for example, using a continuous centrifuge under the conditions that the centrifugal force is preferably 100 to 10,000 G, the solid content concentration of the synthetic polyisoprene latex before centrifugation is preferably 2 to 15% by weight, the flow rate fed into the centrifuge is preferably 500 to 1700 Kg / hr, and the back pressure (gauge pressure) of the centrifuge is preferably 0.03 to 1.6 MPa. As the light liquid after centrifugation, a synthetic polyisoprene latex can be obtained. Thereby, the residual amount of the surfactant in the synthetic polyisoprene latex can be reduced.

[0036] The solid content concentration of the synthetic polyisoprene latex is preferably 30 to 70% by weight, more preferably 40 to 70% by weight. When the solid content concentration is within the above range, the latex viscosity becomes appropriate and it becomes easy to handle.

[0037] The volume average particle diameter of the synthetic polyisoprene latex is preferably from 0.1 to 10 μm, more preferably from 0.5 to 3 μm, and still more preferably from 0.5 to 2.0 μm. When the volume average particle diameter is within the above range, the latex viscosity becomes appropriate and easy to handle, and when the synthetic polyisoprene latex is stored, the formation of a film on the latex surface can be suppressed.

[0038] In addition, additives such as a pH adjuster, an antifoaming agent, a preservative, a crosslinking agent, a chelating agent, an oxygen scavenger, and a dispersant, which are usually blended in the field of latex, may be blended in the synthetic polyisoprene latex. Examples of the pH adjuster include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide; carbonates of alkali metals such as sodium carbonate and potassium carbonate; hydrogen carbonates of alkali metals such as sodium hydrogen carbonate; ammonia; organic amine compounds such as trimethylamine and triethanolamine; etc. Among them, hydroxides of alkali metals or ammonia are preferred.

[0039] In addition, as the conjugated diene polymer, as described above, a styrene-isoprene-styrene block copolymer (SIS) can also be used. In SIS, "S" represents a styrene block and "I" represents an isoprene block, respectively.

[0040] SIS can be obtained by block copolymerizing isoprene and styrene in an inert polymerization solvent using a known method, for example, an active organometal such as n-butyllithium as an initiator. The resulting polymer solution of SIS may be used as it is for the production of SIS latex, but after taking out solid SIS from the polymer solution, the solid SIS can be dissolved in an organic solvent and used for the production of SIS latex. The method for producing SIS latex is not particularly limited, but a method of emulsifying a solution or fine suspension of SIS dissolved or finely dispersed in an organic solvent in water in the presence of a surfactant and removing the organic solvent as necessary to produce SIS latex is preferred. At this time, impurities such as residues of the polymerization catalyst remaining in the polymer solution after synthesis may be removed. Further, an antioxidant described later may be added to the solution during or after polymerization. Also, commercially available solid SIS can be used.

[0041] As the organic solvent, the same solvents as those in the case of the above synthetic polyisoprene can be used, aromatic hydrocarbon solvents and alicyclic hydrocarbon solvents are preferred, and cyclohexane and toluene are 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 still more preferably 150 to 300 parts by weight with respect to 100 parts by weight of SIS.

[0042] As the surfactant, the same surfactants as those in the case of the above synthetic polyisoprene can be exemplified, anionic surfactants are preferred, and sodium rosinate and sodium dodecylbenzenesulfonate are particularly preferred.

[0043] The amount of the surfactant used is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 30 parts by weight with respect to 100 parts by weight of SIS.

[0044] 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 with respect to 100 parts by weight of the organic solvent solution of SIS. Examples of the type of water used include hard water, soft water, ion-exchanged water, distilled water, zeolite water, etc. Also, a polar solvent typified by alcohols such as methanol may be used in combination with water.

[0045] As the method for adding the monomer, the same methods as in the case of the above-described synthetic polyisoprene can be exemplified. Also, as the apparatus for emulsifying the organic solvent solution or fine suspension of SIS in water in the presence of a surfactant, the same apparatuses as in the case of the above-described synthetic polyisoprene can be exemplified. And the method for adding the surfactant is not particularly limited, and it may be added in advance to either water or the organic solvent solution or fine suspension of SIS, or both, or it may be added to the emulsion during the emulsification operation, and it may be added all at once or in portions.

[0046] In the above-described method for producing SIS latex, it is preferable to remove the organic solvent from the emulsion obtained through the emulsification operation 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, centrifugation, etc. can be adopted.

[0047] Also, after removing the organic solvent, if necessary, a concentration operation may be performed by methods such as vacuum distillation, atmospheric distillation, centrifugation, membrane concentration, etc. to increase the solid content concentration of the SIS latex.

[0048] The solid content concentration of the SIS latex is preferably 30 to 70% by weight, more preferably 50 to 70% by weight. When the solid content concentration is within the above range, the latex viscosity becomes appropriate and it becomes easy to handle.

[0049] In addition, additives such as pH adjusters, defoamers, preservatives, crosslinking agents, chelating agents, oxygen scavengers, dispersants, and antioxidants, which are commonly blended in the field of latex, may be blended into the SIS latex. Examples of the pH adjuster may be the same as those in the case of the above synthetic polyisoprene, and hydroxides of alkali metals or ammonia are preferable.

[0050] The content of styrene units in the styrene block in SIS contained in the thus obtained SIS latex is preferably 70 to 100% by weight, more preferably 90 to 100% by weight, and still more preferably 100% by weight with respect to all monomer units. Also, the content of isoprene units in the isoprene block in SIS is preferably 70 to 100% by weight, more preferably 90 to 100% by weight, and still more preferably 100% by weight with respect to all monomer units.

[0051] The content ratio of styrene units and isoprene units in SIS is in the weight ratio of "styrene units:isoprene units", usually in the range of 1:99 to 90:10, preferably 3:97 to 70:30, more preferably 5:95 to 50:50, and still more preferably 10:90 to 30:70.

[0052] The weight average molecular weight of SIS is preferably 10,000 to 1,000,000, more preferably 50,000 to 500,000, and still more preferably 100,000 to 300,000 in terms of standard polystyrene conversion by gel permeation chromatography analysis. When the weight average molecular weight of SIS is within the above range, the latex of SIS tends to be easily produced.

[0053] The volume average particle diameter of latex particles (SIS particles) in the SIS latex is preferably 0.1 to 10 μm, more preferably 0.5 to 3 μm, and still more preferably 0.5 to 2.0 μm. When the volume average particle diameter of the latex particles is within the above range, the latex viscosity becomes appropriate and easy to handle, and the formation of a film on the latex surface can be suppressed when the SIS latex is stored.

[0054] In addition, as the conjugated diene polymer, as described above, natural rubber can also be used. As the latex of natural rubber, the latex obtained from the natural rubber tree and the latex obtained by treating the latex can be used. For example, field latex collected from the natural rubber tree, commercially available natural rubber latex obtained by treating field latex with ammonia or the like can be used.

[0055] In addition, as the conjugated diene polymer, natural rubber from which proteins have been removed can also be used. Since the natural rubber from which proteins have been removed has had the proteins that cause immediate allergic (Type I) symptoms removed, the resulting film-formed body can be suitably used for applications in contact with the human body, such as nipples, balloons, gloves, balloons, sacks, etc. The method for obtaining the latex of natural rubber from which proteins have been removed is not particularly limited. However, for natural rubber latex, by reacting a urea compound in the presence of a surfactant to denature the proteins contained in the natural rubber, and then subjecting the natural rubber latex containing such denatured proteins to treatments such as centrifugation, coagulation of the rubber component, ultrafiltration, etc., the natural rubber and the denatured proteins can be separated, and by removing the denatured proteins, a latex of natural rubber from which proteins have been removed can be obtained.

[0056] In addition, as the conjugated diene polymer, as described above, synthetic polyisoprene, styrene-isoprene-styrene block copolymer (SIS), natural rubber (including natural rubber from which proteins have been removed), etc. can be used, but are not limited thereto, and nitrile group-containing conjugated diene copolymers, butadiene polymers, styrene-butadiene copolymers, etc. may also be used.

[0057] In addition, since the conjugated diene polymer can further suppress the decrease in mechanical strength when the film molded body of the present invention is stored at a high temperature, it is preferably a carboxy-modified conjugated diene polymer that has been carboxy-modified. The carboxy-modified conjugated diene polymer can be obtained by modifying the above-described conjugated diene polymer with a monomer having a carboxyl group.

[0058] The method for modifying the conjugated diene polymer with a monomer having a carboxyl group is not particularly limited. For example, a method of graft-polymerizing a monomer having a carboxyl group in an aqueous phase onto the conjugated diene polymer can be mentioned. The method for graft-polymerizing a monomer having a carboxyl group onto the conjugated diene polymer in an aqueous phase is not particularly limited, and a conventionally known method may be used. For example, after adding a monomer having a carboxyl group and an organic peroxide to the latex of the conjugated diene polymer, a method of reacting the monomer having a carboxyl group with the conjugated diene polymer in an aqueous phase is preferable.

[0059] The organic peroxide is not particularly limited. For example, diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di-t-butyl peroxide, isobutyryl peroxide, benzoyl peroxide, etc. can be mentioned. From the viewpoint of improving the mechanical strength of the resulting film molded body, 1,1,3,3-tetramethylbutyl hydroperoxide is particularly preferable. These organic peroxides may be used alone or in combination of two or more.

[0060] The addition amount of the organic peroxide is not particularly limited, but is preferably 0.01 to 3 parts by weight, more preferably 0.1 to 1 part by weight, based on 100 parts by weight of the conjugated diene polymer contained in the latex of the conjugated diene polymer.

[0061] In addition, organic peroxides can be used as redox polymerization initiators in combination with reducing agents. The reducing agent is not particularly limited, and examples thereof include compounds containing metal ions in a reduced state such as ferrous sulfate and cuprous naphthenate; sulfinates such as sodium hydroxymethanesulfinate; amine compounds such as dimethylaniline; and the like. These reducing agents may be used alone or in combination of two or more.

[0062] The addition amount of the reducing agent is not particularly limited, but is preferably 0.01 to 1 part by weight with respect to 1 part by weight of the organic peroxide.

[0063] The addition methods of the organic peroxide and the reducing agent are not particularly limited, and known addition methods such as batch addition, divided addition, and continuous addition can be used respectively.

[0064] The reaction temperature when reacting a monomer having a carboxyl group with a conjugated diene polymer is not particularly limited, but is preferably 15 to 80 °C, more preferably 30 to 50 °C. The reaction time when reacting a monomer having a carboxyl group with a conjugated diene polymer may be appropriately set according to the above reaction temperature, but is preferably 30 to 300 minutes, more preferably 60 to 120 minutes.

[0065] The solid content concentration of the latex of the conjugated diene polymer when reacting a monomer having a carboxyl group with the conjugated diene polymer is not particularly limited, but is preferably 5 to 60% by weight, more preferably 10 to 40% by weight.

[0066] Examples of the monomer 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 monoisopropyl maleate; polycarboxylic acid anhydrides such as maleic anhydride and citraconic anhydride; etc. However, since the effect of carboxyl modification becomes more prominent, ethylenically unsaturated monocarboxylic acid monomers are preferred, and acrylic acid and methacrylic acid are particularly preferred. These monomers may be used alone or in combination of two or more. In addition, the above carboxyl groups include those in the form of salts with alkali metals, ammonia, etc.

[0067] 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, and still more preferably 0.5 to 20 parts by weight with respect to 100 parts by weight of the conjugated diene polymer.

[0068] The method of adding the monomer having a carboxyl group to the latex of the conjugated diene polymer is not particularly limited, and known addition methods such as batch addition, divided addition, and continuous addition can be adopted.

[0069] The modification rate by the monomer having a carboxyl group in the carboxyl-modified conjugated diene polymer may be appropriately controlled according to the intended use of the obtained conjugated diene polymer latex composition, but is preferably 0.01 to 10% by weight, more preferably 0.2 to 5% by weight, still more preferably 0.3 to 3% by weight, and particularly preferably 0.4 to 2% by weight. When the modification rate by the monomer having a carboxyl group is within the above range, the viscosity of the latex of the obtained conjugated diene polymer becomes more appropriate, making it easier to transfer, and it is possible to further suppress the decrease in mechanical strength when the film molded body of the present invention is stored at a high temperature. The modification rate is represented by the following formula. Modification rate (% by weight) = (X / Y) × 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. X can be determined for the carboxy-modified conjugated diene polymer by 1 performing 1H-NMR measurement, 1 a method calculated from the results of the 1H-NMR measurement, or a method determined by neutralization titration to obtain the acid amount and then calculated from the obtained acid amount, etc.

[0070] The polymerization catalyst (graft polymerization catalyst) used for graft polymerization is not particularly limited. For example, 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; azo compounds such as 2,2'-azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, and methyl azobisisobutyrate; etc. can be mentioned. Among them, organic peroxides are preferred, and 1,1,3,3-tetramethylbutyl hydroperoxide is particularly preferred.

[0071] The above graft polymerization catalysts can be used alone or in combination of two or more. The amount of the graft polymerization catalyst used varies depending on its type, but is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, based on 100 parts by weight of the conjugated diene polymer. Also, the method of adding the graft polymerization catalyst is not particularly limited, and known addition methods such as batch addition, divided addition, and continuous addition can be adopted.

[0072] The swell index (SI) of the conjugated diene polymer (including the carboxy-modified conjugated diene polymer) used in the present invention is preferably 105 to 300%, more preferably 110 to 250, and even more preferably 120 to 200%. When the swell index (SI) is within the above range, a decrease in the mechanical strength when the film molded body of the present invention is stored at a high temperature can be more suppressed, and further, the tensile strength and tear strength of the film molded body of the present invention at room temperature can also be improved.

[0073] The swell index (SI) can be determined by forming a film of the latex of the conjugated diene polymer, immersing the obtained film of the conjugated diene polymer in toluene at 25°C for 1 hour, measuring the widths of the film before and after the toluene immersion, and measuring the linear swelling ratio. Specifically, the swell index (SI) can be determined according to the following formula. Swell index (SI) [%] = [((width of the film after toluene immersion) - (width of the film before toluene immersion)) / (width of the film before toluene immersion)] × 100

[0074] As a method for producing a measurement film for measuring the swell index (SI) of the latex of the conjugated diene polymer, for example, the following dip method can be employed. That is, in the dip method, first, an acid or an alkali is added to the latex of the conjugated diene polymer and adjusted to pH = 8.2. Then, a ceramic mold with a surface ground is prepared, washed, preheated in an oven at 70 °C for 30 minutes, and then immersed 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) for 5 seconds. Then, the ceramic mold is taken out of the aqueous coagulant solution, and the ceramic mold coated with the coagulant is dried in an oven at 70 °C for 20 minutes. Next, the ceramic mold coated with the coagulant is taken out of the oven, and the taken-out ceramic mold is immersed in the latex of the conjugated diene polymer adjusted to pH = 8.2 at 25 °C for 10 seconds and then taken out. The ceramic mold coated with the latex of the conjugated diene polymer is immersed in warm water at 60 °C for 2 minutes and then dried at room temperature for 6 hours to obtain a ceramic mold coated with a film for measurement. Then, after talc is sprayed thereon, the film for measurement can be obtained by peeling the film for measurement from the ceramic mold. The thickness of the film for measurement is not particularly limited, but it is preferably about 0.2 mm.

[0075] The method for adjusting the swell index (SI) of the latex of the conjugated diene polymer to the above range is not particularly limited. For example, a method of adjusting the type and composition of the conjugated diene polymer can be mentioned. Among them, when a carboxy-modified conjugated diene polymer is used as the conjugated diene polymer, the reaction temperature (modification reaction temperature) and reaction time (modification reaction time) when reacting a monomer having a carboxyl group with the conjugated diene polymer, a method of selecting the presence or absence of post-heating for the latex after the reaction, a method of adjusting the post-heating temperature and post-heating time when performing post-heating on the latex after the reaction, a method of adjusting the type and amount of use of the monomer having a carboxyl group used in the modification reaction, and further, in the modification reaction, a method of adjusting the type and amount of use of the reducing agent used in combination with the organic peroxide, etc. can be mentioned, and it is desirable to adjust these by appropriately combining them.

[0076] Additives such as a pH adjuster, an antifoaming agent, a preservative, a chelating agent, an oxygen scavenger, and a dispersant, which are usually blended in the field of latex, may be blended in the latex of the conjugated diene polymer (including the carboxy-modified conjugated diene polymer) used in the present invention.

[0077] Examples of the pH adjuster include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide; carbonates of alkali metals such as sodium carbonate and potassium carbonate; bicarbonates of alkali metals such as sodium bicarbonate; ammonia; organic amine compounds such as trimethylamine and triethanolamine; etc. Among them, hydroxides of alkali metals or ammonia are preferable.

[0078] The solid content concentration of the latex of the conjugated diene polymer (including the carboxy-modified conjugated diene polymer) used in the present invention is preferably 30 to 70% by weight, more preferably 40 to 70% by weight. By the solid content concentration being in the above range, the generation of aggregates in the latex can be more effectively suppressed, and the separation of polymer particles when the latex is stored can be more effectively suppressed.

[0079] The latex composition used in the present invention contains a sulfur-based vulcanizing agent.

[0080] The sulfur-based vulcanizing agent is not particularly limited. For example, sulfur such as powdered sulfur, sulfur flowers, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, etc.; 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, polymer polysulfide, 2-(4'-morpholinodithio)benzothiazole, etc. Among these, sulfur can be preferably used. The sulfur-based vulcanizing agent can be used alone or in combination of two or more.

[0081] The content of the sulfur-based vulcanizing agent in the latex composition is not particularly limited, but is preferably 0.01 to 3 parts by weight, more preferably 0.1 to 1.2 parts by weight, still 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 with respect to 100 parts by weight of the conjugated diene polymer contained in the latex composition. When the content of the sulfur-based vulcanizing agent is within the above range, in the obtained dip molded article, the tensile strength and tear strength at room temperature can be increased while suppressing the occurrence of symptoms of delayed-type allergy (Type IV).

[0082] The latex composition used in the present invention contains a vulcanization accelerator. From the viewpoint of making the obtained dip molded article preferably suppress the occurrence of symptoms of delayed-type allergy (Type IV), it is preferable to use a xanthogen compound as the vulcanization accelerator.

[0083] The xanthogen compound is not particularly limited. For example, xanthogenic acid, xanthogenate, xanthogen disulfide (a compound in which two xanthogenic acids are bonded via a sulfur atom or the like), xanthogen polysulfide (a compound in which three or more xanthogenic acids are bonded via a sulfur atom or the like), etc. can be mentioned.

[0084] The xanthate is not particularly limited as long as it has a xanthic acid structure. For example, compounds represented by the general formula (ROC(=S)S)x-Z (wherein R is a linear or branched hydrocarbon, Z is a metal atom, x is a number corresponding to the valence of Z, usually 1 to 4, preferably 2 to 4, particularly preferably 2) can be mentioned.

[0085] The xanthate salts represented by the general formula (ROC(=S)S)x-Z are not particularly limited. For example, zinc dimethyldithiocarbonate, zinc diethyldithiocarbonate, zinc dipropyldithiocarbonate, zinc diisopropyldithiocarbonate, zinc dibutyldithiocarbonate, zinc dipentyldithiocarbonate, zinc dihexyldithiocarbonate, zinc diheptyldithiocarbonate, zinc dioctyldithiocarbonate, zinc bis(2-ethylhexyl)dithiocarbonate, zinc didecyldithiocarbonate, zinc didodecyldithiocarbonate, potassium dimethyldithiocarbonate, potassium ethyldithiocarbonate, potassium propyldithiocarbonate, potassium isopropyldithiocarbonate, potassium butyldithiocarbonate, potassium pentyldithiocarbonate, potassium hexyldithiocarbonate, potassium heptyldithiocarbonate, potassium octyldithiocarbonate, potassium 2-ethylhexyldithiocarbonate, potassium decyldithiocarbonate, potassium dodecyldithiocarbonate, sodium methyl dithiocarbonate, sodium ethyl dithiocarbonate, sodium propyl dithiocarbonate, sodium isopropyl dithiocarbonate, sodium butyl dithiocarbonate, sodium pentyl dithiocarbonate, sodium hexyl dithiocarbonate, sodium heptyl dithiocarbonate, sodium octyl dithiocarbonate, sodium 2-ethylhexyl dithiocarbonate, sodium decyl dithiocarbonate, sodium dodecyl dithiocarbonate, etc. may be mentioned. Among these, xanthate salts in which x in the general formula (ROC(=S)S)x-Z is 2 or more are preferable, isopropyl xanthate salts and butyl xanthate salts are more preferable, and zinc diisopropyl dithiocarbonate and zinc dibutyl dithiocarbonate are particularly preferable. These xanthate salts may be used alone or in combination of two or more.

[0086] Xanthogen disulfide is a compound in which two xanthogenic acids are bonded via a sulfur atom or the like. Although not particularly limited, examples include dimethylxanthogen disulfide, diethylxanthogen disulfide, diisopropylxanthogen disulfide, dibutylxanthogen disulfide, dimethylxanthogen polysulfide, diethylxanthogen polysulfide, diisopropylxanthogen polysulfide, dibutylxanthogen polysulfide, etc. Among these, diisopropylxanthogen disulfide and dibutylxanthogen disulfide are preferred.

[0087] Xanthogen polysulfide is a compound in which three or more xanthogenic acids are bonded via a sulfur atom or the like. Examples include xanthogen trisulfide in which three xanthogenic acids are bonded via sulfur, xanthogen tetrasulfide in which four xanthogenic acids are bonded via sulfur, and xanthogen pentasulfide in which five xanthogenic acids are bonded via sulfur.

[0088] These xanthogen compounds may be contained singly in the latex composition, but it is preferable that two or more are contained. For example, when a xanthogenic acid is blended in the latex composition, a part of the blended xanthogenic acid may exist in the form of a xanthogenate, and as a result, the latex composition may contain two or more xanthogen compounds. Alternatively, a part of the xanthogenic acid blended in the latex composition may exist in the form of xanthogen disulfide or xanthogen polysulfide due to the action of a sulfur-based vulcanizing agent in the latex composition. Similarly, when a xanthogenate, xanthogen disulfide, or xanthogen polysulfide is blended in the latex composition, these may each exist in the form of any of xanthogenic acid, xanthogenate, xanthogen disulfide, and xanthogen polysulfide.

[0089] In the present invention, as a vulcanization accelerator, instead of or together with the xanthogen compound, a vulcanization accelerator other than the xanthogen compound may be used.

[0090] As vulcanization accelerators other than such xanthogen compounds, 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, zinc 2-mercaptobenzothiazole, 2-mercaptothiazoline, dibenzothiazyl disulfide, 2-(2,4-dinitrophenylthio)benzothiazole, 2-(N,N-diethylthiocarbamylthio)benzothiazole, 2-(2,6-dimethyl-4-morpholinothio)benzothiazole, 2-(4'-morpholino dithio)benzothiazole, 4-morpholinyl-2-benzothiazyl disulfide, 1,3-bis(2-benzothiazyl mercaptomethyl)urea and the like can be mentioned. The vulcanization accelerator can be used singly or in combination of two or more.

[0091] The content of the vulcanization accelerator in the latex composition (when a plurality of vulcanization accelerators are included, the total content thereof) is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 7 parts by weight, still more preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the conjugated diene polymer contained in the latex composition. By the content of the vulcanization accelerator being within the above range, the decrease in mechanical strength when the film molded body of the present invention is stored at a high temperature can be more suppressed, and the tensile strength and tear strength of the film molded body of the present invention at room temperature can also be improved.

[0092] Further, when the latex composition used in the present invention contains a xanthogen compound as a vulcanization accelerator, the latex composition used in the present invention may further contain an activator.

[0093] When crosslinking a film molded body obtained from a latex composition containing an activator, the activator acts as a vulcanization accelerator together with the above-described xanthogen compound, whereby it is possible to further suppress a decrease in tear strength when the film molded body after crosslinking is stored at a high temperature, and it is also possible to improve the tear strength of the film molded body after crosslinking at room temperature.

[0094] The activator is not particularly limited, but from the viewpoint of further improving the tear strength of the film molded body, it is preferable to use a metal compound. The metal compound is not particularly limited, and examples thereof include metal oxides and metal compounds containing at least one carbon atom. The metal constituting the metal compound is not particularly limited, but typical metals (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) are preferable, Group 2 elements, Group 12 elements, Group 13 elements, and Group 14 elements are more preferable, zinc, magnesium, calcium, aluminum, and lead are even more preferable, zinc, magnesium, and calcium are particularly preferable, and zinc is most preferable. These metal compounds may be used alone or in combination of a plurality of kinds.

[0095] The metal oxide is not particularly limited, but from the viewpoint of further improving the tear strength of the obtained dip molded body, 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 preferable, and zinc oxide is more preferable.

[0096] As the metal compound containing at least one carbon atom, carbonates, bicarbonates, hydroxides, and organometallic compounds are preferable from the viewpoint of further improving the tear strength of the obtained dip molded body, and carbonates, bicarbonates, and organometallic compounds are more preferable. Among these, inorganic salts such as carbonates and bicarbonates are particularly preferable from the viewpoint of excellent stability of the compound itself and excellent availability.

[0097] The content of the activator in the latex composition is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, and still more preferably 1 to 3 parts by weight with respect to 100 parts by weight of the conjugated diene polymer contained in the latex composition. By the content of the activator being within the above range, it is possible to further suppress the decrease in the tear strength when the film molded body of the present invention is stored at a high temperature, and it is also possible to improve the tear strength of the film molded body of the present invention at room temperature.

[0098] The method of blending the activator may be any method as long as the latex of the conjugated diene polymer and the activator are finally in a mixed state, and is not particularly limited.

[0099] The latex composition used in the present invention contains, as an antioxidant, at least one selected from phenolic antioxidants and quinoline antioxidants, and an antioxidant having a molecular weight of 300 to 600 (hereinafter sometimes referred to as "specific antioxidant").

[0100] In the present specification, the phenolic antioxidant is an aromatic compound having one or more phenolic hydroxyl groups (hydroxyl groups directly bonded to the benzene ring structure in the aromatic compound).

[0101] As the phenolic antioxidant as the specific antioxidant, an aromatic compound having a hindered phenol structure is preferable. In the present specification, the hindered phenol structure means a structure in which one of the two ortho positions of the phenolic hydroxyl group is substituted by a hydrocarbon group having 4 or more carbon atoms, and the other is substituted by a substituent other than a hydrogen atom. The hydrocarbon group having 4 or more carbon atoms located at one of the ortho positions of the phenolic hydroxyl group may have a substituent. As the aromatic compound having a hindered phenol structure, an aromatic compound having a structure in which one of the two ortho positions of the phenolic hydroxyl group is substituted by a tert-butyl group and the other is substituted by a substituent other than a hydrogen atom is preferable.

[0102] As the phenolic antioxidant as a specific anti-aging agent, it suffices that it has at least one phenolic hydroxyl group and its molecular weight is in the range of 300 to 600. For example, in the present invention, it can be classified into an aromatic compound (a) having two or more phenolic hydroxyl groups and an aromatic compound (b) having one phenolic hydroxyl group. In the present specification, the "compound having two or more phenolic hydroxyl groups" includes a compound having one or more benzene ring structures to which two or more phenolic hydroxyl groups are bonded, and a compound having two or more benzene ring structures to which one or more phenolic hydroxyl groups are bonded. That is, the phenolic hydroxyl groups present in two or more in the aromatic compound (a) having two or more phenolic hydroxyl groups may be bonded to the same benzene ring or to different benzene rings.

[0103] Examples of the aromatic compound (a) having two or more phenolic hydroxyl groups include 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-methylenebis(2,6-di-t-butylphenol), 2,2'-methylene-bis(6-α-methyl-benzyl-p-cresol), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 4,4'-thiobis(6-tert-butyl-o-cresol), 2,2'-thiobis-(4-methyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenol), bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylenebis(oxyethylene)], and the like. The molecular weight of the aromatic compound (a) having two or more phenolic hydroxyl groups is preferably 310 to 590, more preferably 320 to 540, and even more preferably 330 to 440.

[0104] As the aromatic compound (a) having two or more phenolic hydroxyl groups, since the obtained film-formed body can be made to more suppress the decrease in mechanical strength when stored at a high temperature, an aromatic compound (a-1) having two or more hindered phenol structures is preferable. Examples of the aromatic compound (a-1) having two or more hindered phenol structures include 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-methylenebis(2,6-di-t-butylphenol), 2,2'-methylene-bis(6-α-methyl-benzyl-p-cresol), 4,4'-thiobis(6-tert-butyl-o-cresol), 2,2'-thiobis-(4-methyl-6-t-butylphenol), bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylenebis(oxyethylene)], and the like.

[0105] As the aromatic compound (a-1) having two or more hindered phenol structures, an aromatic compound (a-2) having a diphenylmethane skeleton, with a molecular weight of 300 to 600 and having two or more hindered phenol structures, is more preferable. Examples of the aromatic compound (a-2) having a diphenylmethane skeleton and having two or more hindered phenol structures include 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-methylenebis(2,6-di-t-butylphenol), 2,2'-methylene-bis(6-α-methyl-benzyl-p-cresol), and the like. Among the aromatic compounds (a-2) having a diphenylmethane skeleton and having two or more hindered phenol structures, an aromatic compound (a-3) having a hindered phenol structure in each of the two benzene rings constituting the diphenylmethane skeleton is preferable, and among them, 4,4'-methylenebis(2,6-di-tert-butylphenol) or 2,2'-methylenebis(4-methyl-6-tert-butylphenol) is more preferable, and 2,2'-methylenebis(4-methyl-6-tert-butylphenol) is even more preferable.

[0106] Examples of the aromatic compound (b) having one phenolic hydroxyl group include 2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol, octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, octyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, 4,6-bis[(dodecylthio)methyl]-6-methylphenol, and the like. The molecular weight of the aromatic compound (b) having one phenolic hydroxyl group is preferably from 350 to 600, more preferably from 400 to 600, and still more preferably from 450 to 600.

[0107] As the aromatic compound (b) having one phenolic hydroxyl group, an aromatic compound (b-1) having one phenolic hydroxyl group and one or more -NH- bonds is preferable. The aromatic compound (b-1) having one phenolic hydroxyl group and one or more -NH- bonds can make the obtained film molded body excellent in ozone resistance deterioration. As the aromatic compound (b-1) having one phenolic hydroxyl group and one or more -NH- bonds, 2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol is preferable.

[0108] The quinoline-based antioxidant is a heterocyclic aromatic compound having one or more quinoline structures (quinoline which may have a substituent), and may be any one having a molecular weight in the range of 300 to 600. Examples of the quinoline-based antioxidant include 2,2,4-trimethyl-1,2-dihydroquinoline polymer.

[0109] As the specific antioxidant used in the present invention, those containing at least a phenolic antioxidant are preferred, those containing at least an aromatic compound (a) having two or more phenolic hydroxyl groups are more preferred, those containing an aromatic compound (a) having two or more phenolic hydroxyl groups and an aromatic compound (b) having one phenolic hydroxyl group are still more preferred, those containing an aromatic compound (a) having two or more phenolic hydroxyl groups and an aromatic compound (b-1) having one phenolic hydroxyl group and one or more -NH- bonds are even more preferred, those containing an aromatic compound (a-1) having two or more hindered phenol structures and an aromatic compound (b-1) having one phenolic hydroxyl group and one or more -NH- bonds are particularly preferred, and those containing an aromatic compound (a-2) having two or more hindered phenol structures and having a diphenylmethane skeleton and an aromatic compound (b-1) having one phenolic hydroxyl group and one or more -NH- bonds are most preferred.

[0110] When the specific antioxidant used in the present invention contains an aromatic compound (a) having two or more phenolic hydroxyl groups and an aromatic compound (b) having one phenolic hydroxyl group, the content ratio by weight of the aromatic compound (a) having two or more phenolic hydroxyl groups to the aromatic compound (b) having one phenolic hydroxyl group (aromatic compound (a) having two or more phenolic hydroxyl groups: aromatic compound (b) having one phenolic hydroxyl group) is preferably 1:99 to 99:1, more preferably 10:90 to 98:2, still more preferably 25:75 to 95:5, and particularly preferably 55:45 to 90:10.

[0111] The molecular weight of the specific anti-aging agent used in the present invention may be 300 to 600 and is not particularly limited. Further, two or more specific anti-aging agents may be used in combination as the specific anti-aging agent. When the latex composition contains two or more specific anti-aging agents, the molecular weight of the specific anti-aging agent is the weight average molecular weight of the two or more specific anti-aging agents. That is, in the present invention, the weight average molecular weight of the specific anti-aging agent contained in the latex composition is 300 to 600. The molecular weight of the specific anti-aging agent used in the present invention is preferably 310 to 590, more preferably 320 to 540, and even more preferably 330 to 440 because it can further suppress the decrease in mechanical strength when the film molded body of the present invention is stored at a high temperature.

[0112] The content of the specific anti-aging agent in the latex composition is preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, and even more preferably 0.5 part to 3 parts by weight with respect to 100 parts by weight of the conjugated diene polymer contained in the latex composition.

[0113] The latex composition used in the present invention may further contain an anti-aging agent other than the above-described specific anti-aging agent, but it is preferably not to contain an anti-aging agent other than the above-described specific anti-aging agent.

[0114] The latex composition may further contain various compounding agents such as a dispersant; a reinforcing agent such as carbon black, silica, talc, etc.; a filler such as calcium carbonate, clay, etc.; an ultraviolet absorber; a plasticizer; etc. as needed.

[0115] The method of mixing various compounding agents into the latex composition is not particularly limited. For example, after obtaining a composition containing a latex of a conjugated diene polymer, a sulfur-based vulcanizing agent, a vulcanization accelerator, and the above-described specific anti-aging agent, a ball mill, a kneader, a disperser, etc. are used to obtain the obtained composition. And a method of mixing various compounding agents to be blended as needed. Further, at least a part of the various compounding agents may be blended after aging described later.

[0116] The solid content concentration of the latex composition used in the present invention is preferably 1 to 40% by weight, more preferably 3 to 35% by weight, still more preferably 5 to 30% by weight, and particularly preferably 10 to 20% by weight. When the solid content concentration of the latex composition is within the above range, while maintaining a high level of aggregation stability of the latex, even when the obtained film-formed body is as thin as 20 to 300 μm in thickness, it is possible to further suppress the decrease in mechanical strength when the film-formed body is stored at a high temperature, and it is also possible to make the film-formed body excellent in tensile strength and tear strength at room temperature.

[0117] In addition, from the viewpoint of making the mechanical properties of the obtained film-formed body sufficient, the latex composition used in the present invention is preferably one that has been aged (pre-vulcanized) before being subjected to molding. The aging (pre-vulcanization) time is not particularly limited, but is preferably 8 to 120 hours, more preferably 24 to 72 hours. The temperature of aging (pre-vulcanization) is not particularly limited, but is preferably 20 to 40°C. Further, when using the above-described latex composition, after performing aging (pre-vulcanization) for a predetermined time, while maintaining the aging (pre-vulcanization) conditions (continuing the aging (pre-vulcanization)), molding such as dip molding may be continuously performed. In this case, the aging (pre-vulcanization) time and the aging (pre-vulcanization) temperature may be within the above ranges.

[0118] <Film-formed body> The film-formed body of the present invention is a film-formed body with a thickness of 20 to 300 μm obtained by using the above-described latex composition.

[0119] The thickness of the film-formed body of the present invention may be 20 to 300 μm, and is not particularly limited, but is preferably 50 to 280 μm, more preferably 100 to 260 μm, and particularly preferably 140 to 250 μm. The thickness of the film-formed body can be determined, for example, by selecting 5 measurement points from the film-formed body, measuring the thicknesses of the selected 5 points, and calculating the arithmetic mean.

[0120] The film-formed body of the present invention is not particularly limited, but a dip-molded body obtained by dip-molding the above-described latex composition is preferably used. Dip molding is a method in which a mold is immersed in a latex composition to deposit the composition on the surface of the mold, then the mold is pulled out of the composition, and thereafter, the composition deposited on the surface of the mold is dried. Note that the mold before being immersed in the latex composition may be preheated. Further, a coagulant can be used as necessary before the mold is immersed in the latex composition or after the mold is pulled out of the latex composition.

[0121] Specific examples of the method of using the coagulant include a method of immersing the mold before immersion in the latex composition in a coagulant solution to attach the coagulant to the mold (anode coagulation immersion method), a method of immersing the mold on which the latex composition has been deposited in a coagulant solution (tea coagulation immersion method), etc. Among them, the anode coagulation immersion method is preferable in that a dip-molded body with less thickness unevenness can be obtained.

[0122] Specific examples of the coagulant 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; sulfates such as calcium sulfate, magnesium sulfate, and aluminum sulfate; etc. Among them, calcium salts are preferable, and calcium nitrate is more preferable. These water-soluble polyvalent metal salts can be used alone or in combination of two or more.

[0123] The coagulant can usually be used as a solution of water, alcohol, or a mixture thereof, and is preferably used in an aqueous solution state. 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 the water-soluble polyvalent metal salt, but is preferably 5 to 50% by weight, more preferably 10 to 30% by weight.

[0124] After lifting the mold from the latex composition, it is usually heated to dry the deposit formed on the mold. The drying conditions can be appropriately selected.

[0125] It is preferable to subject the obtained dip-formed layer to a heat treatment for crosslinking.

[0126] Before performing the heat treatment, the obtained dip-formed 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 (such as excess emulsifiers and coagulants). The operation of removing water-soluble impurities may be performed after heat-treating the dip-formed layer, but it is preferably performed before the heat treatment in terms of more efficiently removing water-soluble impurities.

[0127] Crosslinking of the dip-formed layer is usually carried out by performing a heat treatment at a temperature of 80 to 150°C, preferably for 10 to 130 minutes. As the heating method, external heating by infrared rays or heated air or internal heating by high frequency can be adopted. Among them, external heating by heated air is preferable.

[0128] Then, by detaching the dip-formed layer from the dip-forming mold, the dip-formed body is obtained as a film-shaped film-formed body. As the detachment method, a method of peeling it by hand from the forming mold or peeling it by the pressure of water pressure or compressed air can be adopted. In addition, after detachment, a heat treatment may be further performed at a temperature of 60 to 120°C for 10 to 120 minutes. In addition, the film-formed body of the present invention may be obtained by any method as long as the above-described latex composition can be formed into a film (for example, a coating method, etc.) other than the method of dip-forming the above-described latex composition.

[0129] The film molded body of the present invention is one in which a decrease in mechanical strength when stored at high temperatures is suppressed. Therefore, the film molded body of the present invention can be suitably used as an article that requires mechanical properties such as tensile strength and tear strength and can be stored at a high temperature of about 70°C or lower, or an article that can be stored at room temperature for a long period of time. For example, the film molded body of the present invention can be particularly suitably used as gloves. When the film molded body is gloves, in order to prevent adhesion at the contact surface between the film molded bodies and improve slipperiness during attachment and detachment, inorganic fine particles such as talc and calcium carbonate or organic fine particles such as starch particles can be sprayed on the glove surface, or an elastomer layer containing fine particles can be formed on the glove surface, or the surface layer of the glove can be chlorinated.

[0130] In addition to the above-mentioned gloves, the film molded body of the present invention can also be used for medical supplies such as nipples for baby bottles, pipettes, tubes, water pillows, balloon sacs, catheters, condoms; toys such as balloons, dolls, balls; industrial supplies such as molds for pressure molding, bags for gas storage; finger bags, etc.

Examples

[0131] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited to these examples. In addition, "parts" below are based on weight unless otherwise specified. Various physical properties were measured as follows.

[0132] <Solid content concentration> 2 g of the sample was precisely weighed into an aluminum dish (weight: X1) (weight: X2), and this was dried in a hot air dryer at 105°C for 2 hours. Then, 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 calculation formula. Solid content concentration (weight%) = (X3 - X1) × 100 / X2

[0133] <Modification rate of carboxy-modified synthetic polyisoprene> Regarding the carboxy-modified synthetic polyisoprene that constitutes the latex of carboxy-modified synthetic polyisoprene, the number of carboxyl groups in the carboxy-modified synthetic polyisoprene was determined by neutralization titration using an aqueous sodium hydroxide solution. Subsequently, based on the obtained number of carboxyl groups, the modification rate by the monomer having a carboxyl group was determined according to the following formula. Modification rate (wt%) = (X / Y) × 100 In the above formula, X represents the weight of the unit of the monomer having a carboxyl group in the carboxy-modified synthetic polyisoprene, and Y represents the weight of the carboxy-modified synthetic polyisoprene.

[0134] <Swelling Index (SI)> Potassium hydroxide was added to the latex of carboxy group-modified synthetic polyisoprene and adjusted to pH = 8.2. Then, a ceramic mold with a ground surface was prepared, washed, preheated in an oven at 70 °C for 60 minutes, and then immersed 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) for 5 seconds. Then, the ceramic mold was taken out of the aqueous coagulant solution, and the ceramic mold coated with the coagulant was dried in an oven at 70 °C for 20 minutes. Next, the ceramic mold coated with the coagulant was taken out of the oven, and the taken-out ceramic mold was immersed in the latex of carboxy group-modified synthetic polyisoprene adjusted to pH = 8.2 at 25 °C for 10 seconds and then taken out. The ceramic mold coated with the latex of carboxy group-modified synthetic polyisoprene was immersed in warm water at 60 °C for 2 minutes and then dried at room temperature for 6 hours to obtain a ceramic mold coated with a film for measurement. Then, after talc was sprayed on this, the obtained film was peeled off from the ceramic mold to obtain a dip film with a thickness of 0.2 mm. Then, a test film with a diameter of 25 mm was cut out from the obtained dip film, and the obtained test film was immersed in toluene at 25 °C for 1 hour. The width of the test piece before and after the toluene immersion was measured, and the swelling index (SI) was calculated according to the following formula. Swelling index (SI) [%] = [((width of the film after toluene immersion) - (width of the film before toluene immersion)) / (width of the film before toluene immersion)] × 100

[0135] <Thickness of dip molded body> Five measurement points were selected within 3 cm from the location of the dip molded body corresponding to the location with the longest contact time with the coagulant solution (the tip of the glass mold) when the glass mold was immersed in the coagulant solution. Then, the thicknesses at the five selected points were measured, the arithmetic mean of the thicknesses at the five measured points was obtained, and the obtained value (unit: mm) was taken as the thickness of the dip molded body.

[0136] <Tensile Strength of Dip Molded Body> The dip molded body (dip molded body before aging) was heated at 70°C for 7 days to obtain a dip molded body after aging. Based on ASTM D412, the dip molded body before aging and the dip molded body after aging were punched out with a dumbbell (product name: "Super Dumbbell (Model: SDMK-100C)", manufactured by Dumbbell Co., Ltd.) to produce test pieces for measuring tensile strength. The test pieces were pulled at a tensile speed of 500 mm / min with a tensilon universal testing machine (product name: "RTG-1210", manufactured by Orientec Co., Ltd.), and the tensile strength (unit: MPa) immediately before fracture was measured.

[0137] <Tear Strength of Dip Molded Body> The dip molded body (dip molded body before aging) was heated at 70°C for 7 days to obtain a dip molded body after aging. Based on ASTM D624-00, the dip molded body before aging and the dip molded body after aging were left in a thermo-hygrostat chamber at 23°C and a relative humidity of 50% for 24 hours or more, and then punched out with a dumbbell (product name: "Die C", manufactured by Dumbbell Co., Ltd.) to produce test pieces for measuring tear strength. The test pieces were pulled at a tensile speed of 500 mm / min with a tensilon universal testing machine (product name: "RTG-1210", manufactured by A&D Co., Ltd.), and the tear strength (unit: N / mm) was measured.

[0138] <Production Example 1> (Production of Latex (A-1) of Carboxy-Modified Synthetic Polyisoprene) Synthetic polyisoprene (product 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 it, and an n-hexane solution (a) of synthetic polyisoprene with a synthetic polyisoprene concentration of 15% by weight was prepared.

[0139] On the other hand, potassium rosinate was added to water, and the temperature was raised to 60°C to dissolve it, and an aqueous emulsifier solution (b) with a concentration of 1.5% by weight was prepared.

[0140] Next, the n - hexane solution (a) of the synthetic polyisoprene obtained above and the aqueous emulsifier solution (b) were mixed using a mixer (product name: "Multi - line Mixer MS26 - MMR - 5.5L", manufactured by Satake Chemical Machinery Co., Ltd.) such that for 100 parts of the synthetic polyisoprene in the n - hexane solution (a) of the synthetic polyisoprene, the potassium rosinate in the aqueous emulsifier solution (b) was 10 parts. Subsequently, using an emulsifying device (product name: "Milder MDN310", manufactured by Taiheiyo Kiko Co., Ltd.), mixing and emulsification were carried out at a rotational speed of 4100 rpm to obtain an emulsified dispersion (c). At this time, the total feed flow rate of the n - hexane solution (a) of the synthetic polyisoprene and the aqueous emulsifier solution (b) was 2,000 kg / hr, the temperature was 60°C, and the back pressure (gauge pressure) was 0.5 MPa.

[0141] Next, the obtained emulsified dispersion (c) was heated to 80°C under a reduced pressure of - 0.01 to - 0.09 MPa (gauge pressure) to distill off n - hexane and obtain an aqueous dispersion (d) of synthetic polyisoprene. At this time, an antifoaming agent (trade name: "SM5515", manufactured by Toray Dow Corning Co., Ltd.) was continuously added while spraying so that the amount became 300 weight ppm with respect to the synthetic polyisoprene in the emulsified dispersion (c). When distilling off n - hexane, the emulsified dispersion (c) was adjusted so that it became 70% by volume or less of the tank volume, and a three - stage inclined paddle blade was used as the stirring blade, and slow stirring was carried out at 60 rpm.

[0142] After the distillation of n - hexane was completed, the obtained aqueous dispersion (d) of synthetic polyisoprene was concentrated by centrifugation at 8,000 - 9,000 G using a continuous centrifuge (product name: "SRG510", manufactured by Alfa Laval) to obtain a latex (e) of synthetic polyisoprene with a solid content concentration of 60% by weight as the light liquid. The conditions for centrifugation were: the solid content concentration of the aqueous dispersion (d) before centrifugation was 8% by weight, the flow rate during continuous centrifugation was 1300 kg / hr, and the back pressure (gauge pressure) of the centrifuge was 0.1 MPa.

[0143] Next, 130 parts of distilled water was added to and diluted with respect to 100 parts of the synthetic polyisoprene in the obtained latex (e) of synthetic polyisoprene. Then, to the latex (e) of synthetic polyisoprene, 0.8 part of the sodium salt of β-naphthalenesulfonic acid formalin condensate (trade name "Demol T-45", manufactured by Kao Corporation) as a dispersant, which was diluted with 4 parts of distilled water with respect to 100 parts of synthetic polyisoprene, was added over 5 minutes. Next, the latex (e) of synthetic polyisoprene to which the dispersant was added was charged into a reaction vessel equipped with a stirrer that had been purged with nitrogen, and the temperature was heated to 30°C while stirring. Also, using another 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 solution. This methacrylic acid dilution solution was added to the reaction vessel maintained at a temperature of 20°C over 30 minutes.

[0144] Furthermore, using another container, a solution (f) consisting of 7 parts of distilled water, 0.30 part of sodium formaldehyde sulfoxylate (trade name "SFS", manufactured by Mitsubishi Gas Chemical Company, Inc.), and 0.01 part of ferrous sulfate (trade name "Frost Fe", manufactured by Chubu Kirest Co., Ltd.) was prepared. After transferring this solution (f) into the reaction vessel, 0.5 part of 1,1,3,3-tetramethylbutyl hydroperoxide (trade name "Perocta H", manufactured by NOF Corporation) was added and reacted at 30°C for 1 hour to obtain a latex after the modification reaction. With respect to the obtained latex after the modification reaction, it was further reacted at 40°C for 1 hour and then concentrated with a centrifuge to obtain a latex (A-1) of carboxy-modified synthetic polyisoprene having a solid content concentration of 60% by weight. When the modification rate of the obtained latex (A-1) of carboxy-modified synthetic polyisoprene was measured according to the above method, the modification rate was 0.5 mol%. Using the obtained latex (A-1) of carboxy-modified synthetic polyisoprene, the swelling index (SI) was measured according to the above method. The swelling index (SI) of the carboxy-modified synthetic polyisoprene in the latex (A-1) of carboxy-modified synthetic polyisoprene was 125%. The results are shown in Table 1 as the results of Examples 1 to 3, 5 and Comparative Examples 1 to 4.

[0145] <Production Example 2> (Production of Latex (A-2) of Carboxy-Modified Synthetic Polyisoprene) In the same manner as in Production Example 1, after obtaining a latex (e) of synthetic polyisoprene, when performing the modification reaction with methacrylic acid, the usage amount of 1,1,3,3-tetramethylbutyl hydroperoxide (trade name "Peroct H", manufactured by NOF Corporation) was changed from 0.5 part to 0.3 part to obtain a latex after the modification reaction. The obtained latex after the modification reaction was further reacted at 40°C for 1 hour and then concentrated by a centrifuge to obtain a latex (A-2) of carboxy-modified synthetic polyisoprene having a solid content concentration of 60% by weight. Regarding the obtained latex (A-2) of carboxy-modified synthetic polyisoprene, when the modification rate was measured according to the above method, the modification rate was 0.5 mol%. Using the obtained latex (A-2) of carboxy-modified synthetic polyisoprene, the swelling index (SI) was measured according to the above method. The swelling index (SI) of the carboxy-modified synthetic polyisoprene in the latex (A-2) of carboxy-modified synthetic polyisoprene was 180%. The results are shown in Table 1 as the results of Example 4.

[0146] <Example 1> (Preparation of Aqueous Dispersion of Sulfur) 0.5 part of sulfur, 0.03 part of sodium salt of β-naphthalenesulfonic acid formalin condensate (trade name "Demol T-45", manufactured by Kao Corporation) as an anionic surfactant (6.0 parts with respect to 100 parts of sulfur), 0.004 part of 5% potassium hydroxide aqueous solution, and 0.42 part of water were subjected to a pulverization treatment by mixing with a ball mill (trade name "Ceramic Ball Mill", manufactured by Nittetsu Kagaku Co., Ltd.) to obtain an aqueous dispersion of sulfur. In addition, as the mixing conditions by the ball mill, ceramic magnetic balls of φ10 mm to φ35 mm (a mixture of ceramic magnetic balls of φ10 mm, φ15 mm, φ20 mm, φ25 mm, φ30 mm, and φ35 mm) were used, and the time was 72 hours at 50 rpm.

[0147] (Preparation of Aqueous Dispersion of Xanthogen Compound) 2.5 parts of zinc diisopropylxanthate (trade name: "Noxeller ZIX", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., volume average particle diameter: 14 μm, 95% volume cumulative diameter (D95): 55 μm) as a xanthogen compound, 0.45 parts of polyoxyethylene distyrylated phenyl ether (trade name: "Emulgen A-60", manufactured by Kao Corporation) as a nonionic surfactant (18.0 parts per 100 parts of zinc diisopropylxanthate), and 2.05 parts of water were mixed by a ball mill (trade name: "Ceramic Ball Mill", manufactured by Nittoh Kagaku Co., Ltd.) to perform a crushing process, thereby obtaining an aqueous dispersion of the xanthogen compound. The mixing conditions using the ball mill were as follows: Ceramic magnetic balls with a diameter of φ10 mm to φ35 mm (a mixture of ceramic magnetic balls with diameters of φ10 mm, φ15 mm, φ20 mm, φ25 mm, φ30 mm, and φ35 mm) were used, and the mixing was carried out at 50 rpm for 72 hours.

[0148] (Preparation of latex composition) While stirring the latex (A-1) of carboxy-modified synthetic polyisoprene obtained above, ion-exchanged water was injected to adjust the solid content concentration to 40% by weight. Next, based on 100 parts of the carboxy-modified synthetic polyisoprene in the latex (A-1) of carboxy-modified synthetic polyisoprene with the adjusted solid content concentration, an aqueous dispersion of sulfur prepared above was added in an amount equivalent to 0.5 part in terms of sulfur, and an aqueous dispersion of the xanthogen compound was added in an amount equivalent to 2.5 parts in terms of zinc diisopropylxanthate.

[0149] Then, while stirring the obtained mixture, based on 100 parts of carboxy-modified synthetic polyisoprene in the mixture, and in terms of solid content, 1.5 parts of zinc oxide as an activator, 1.5 parts of 2,2'-methylenebis(4-methyl-6-tert-butylphenol) (trade name "No Crack NS-6", manufactured by Ouchi Shinsei Chemical Industry Co., Ltd., molecular weight 340, an antioxidant which is an aromatic compound (a-3) having a hindered phenol structure in each of the two benzene rings constituting the diphenylmethane skeleton), 0.5 part of 6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(octylthio)-1,3,5-triazine (trade name "Irganox 565", manufactured by BASF, molecular weight 589, an antioxidant which is an aromatic compound (b-1) having one phenolic hydroxyl group and one or more -NH- bonds) were added as aqueous dispersions of each compounding agent. Then, aging (pre-vulcanization) was carried out in a constant temperature water bath adjusted to 25°C for 48 hours to obtain a latex composition.

[0150] (Manufacture of dip molded article) A commercially available ceramic hand mold (manufactured by Shinko Co., Ltd.) was washed and preheated in an oven at 70°C, and then immersed in a coagulant aqueous 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) for 5 seconds, and taken out from the coagulant aqueous solution. Then, the hand mold was dried in an oven at 70°C for 30 minutes or more to adhere the coagulant to the hand mold and coat the hand mold with the coagulant.

[0151] Thereafter, the mold coated with the coagulant was taken out of the oven and immersed in the 48-hour aged latex composition obtained above for 10 seconds. Then, the mold was 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, thereby forming a dip-molded layer on the mold. Thereafter, the dip-molded layer formed on the mold was vulcanized by heating in an oven at a temperature of 130°C for 30 minutes, then cooled to room temperature, talc was sprayed, and then peeled off from the mold to obtain a glove-shaped dip-molded body. And using the obtained dip-molded body, the thickness, tensile strength, and tear strength of the dip-molded body were measured according to the above method. The results are shown in Table 1.

[0152] <Example 2> A dip-molded body was obtained in the same manner as in Example 1, except that an aqueous dispersion of 6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(octylthio)-1,3,5-triazine was not added and the addition amount of the aqueous dispersion of 2,2'-methylenebis(4-methyl-6-tert-butylphenol) was changed from 1.5 parts to 2.0 parts in terms of solid content. Using the obtained dip-molded body, the thickness, tensile strength, and tear strength of the dip-molded body were measured according to the above method. The results are shown in Table 1.

[0153] <Example 3> A dip-molded article was obtained in the same manner as in Example 1, except that an aqueous dispersion of 4,4'-methylenebis(2,6-di-tert-butylphenol) (trade name "Ethanox 702", manufactured by Ethyl Corporation, molecular weight 425, an antioxidant which is an aromatic compound (a-3) having a hindered phenol structure in each of the two benzene rings constituting the diphenylmethane skeleton) was added in an amount of 2.0 parts on a solid content basis with respect to 100 parts of carboxy-modified synthetic polyisoprene in the mixture, instead of adding an aqueous dispersion of 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and an aqueous dispersion of 6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(octylthio)-1,3,5-triazine. Using the obtained dip-molded article, the thickness, tensile strength, and tear strength of the dip-molded article were measured according to the above method. The results are shown in Table 1.

[0154] <Example 4> A dip-molded article was obtained in the same manner as in Example 3, except that an aqueous dispersion of carboxy-modified synthetic polyisoprene latex (A-2) was used instead of the aqueous dispersion of carboxy-modified synthetic polyisoprene latex (A-1). Using the obtained dip-molded article, the thickness, tensile strength, and tear strength of the dip-molded article were measured according to the above method. The results are shown in Table 1.

[0155] <Example 5> A dip-molded article was obtained in the same manner as in Example 3, except that the solid content concentration of the aqueous dispersion of carboxy-modified synthetic polyisoprene latex (A-1) was changed from 40% by weight to 30% by weight. Using the obtained dip-molded article, the thickness, tensile strength, and tear strength of the dip-molded article were measured according to the above method. The results are shown in Table 1.

[0156] <Comparative Example 1> A dip molded article was obtained in the same manner as in Example 1, except that an aqueous dispersion of p-cresol and a butylated reaction product of dicyclopentadiene (trade name “Wingstay L”, manufactured by Goodyear, molecular weight 650, melting point 115 °C) was added in an amount of 2.0 parts on a solids basis per 100 parts of carboxy-modified synthetic polyisoprene in the mixture, without adding an aqueous dispersion of 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and an aqueous dispersion of 6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(octylthio)-1,3,5-triazine. Using the obtained dip molded article, the thickness, tensile strength, and tear strength of the dip molded article were measured according to the above method. The results are shown in Table 1.

[0157] <Comparative Example 2> A dip molded article was obtained in the same manner as in Comparative Example 1, except that the solid content concentration of the latex (A-1) of carboxy-modified synthetic polyisoprene was changed from 40% by weight to 50% by weight. Using the obtained dip molded article, the thickness, tensile strength, and tear strength of the dip molded article were measured according to the above method. The results are shown in Table 1.

[0158] <Comparative Example 3> A dip molded article was obtained in the same manner as in Example 1, except that an aqueous dispersion of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name “Irganox 1010”, manufactured by BASF, molecular weight 1120) was added in an amount of 2.0 parts on a solids basis per 100 parts of carboxy-modified synthetic polyisoprene in the mixture, without adding an aqueous dispersion of 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and an aqueous dispersion of 6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(octylthio)-1,3,5-triazine. Using the obtained dip molded article, the thickness, tensile strength, and tear strength of the dip molded article were measured according to the above method. The results are shown in Table 1.

[0159] <Comparative Example 4> A dip molded article was obtained in the same manner as in Example 1, except that an aqueous dispersion of dibutylhydroxytoluene (molecular weight 220) was added in an amount of 2.0 parts in terms of solid content based on 100 parts of carboxy-modified synthetic polyisoprene in the mixture, without adding an aqueous dispersion of 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and an aqueous dispersion of 6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(octylthio)-1,3,5-triazine. Using the obtained dip molded article, the thickness, tensile strength and tear strength of the dip molded article were measured according to the above method. The results are shown in Table 1.

[0160]

Table 1

[0161] As shown in Table 1, a film molded article having a thickness of 20 to 300 μm, obtained using a latex composition containing a latex of a conjugated diene polymer, a sulfur-based vulcanizing agent, a vulcanization accelerator, and an antioxidant, wherein the antioxidant is at least one selected from a phenolic antioxidant and a quinoline-based antioxidant and the molecular weight of the antioxidant is 300 to 600, had a suppressed decrease in mechanical strength when stored at 70°C (Examples 1 to 5).

[0162] On the other hand, a film molded article obtained using an antioxidant having a molecular weight of less than 300 or more than 600 had a large decrease in mechanical strength when stored at 70°C (Comparative Examples 1, 3, 4). In addition, a film molded article obtained using an antioxidant having a molecular weight of more than 600 had a large decrease in mechanical strength when stored at 70°C even when the thickness was more than 300 mm (Comparative Example 2).

Claims

1. A film molded body with a thickness of 20 to 300 μm, obtained by using a latex composition containing a latex of a conjugated diene polymer, a sulfur-based vulcanizing agent, a vulcanization accelerator, and an antioxidant, wherein the swell index (SI) of the conjugated diene polymer is 105 to 300%, the antioxidant is a phenolic antioxidant, and the molecular weight of the antioxidant is 300 to 600.

2. The film molded body according to claim 1, wherein the antioxidant contains at least an aromatic compound (a) having two or more phenolic hydroxyl groups.

3. The film molded body according to claim 1 or 2, wherein the antioxidant contains at least an aromatic compound (a-1) having two or more hindered phenol structures.

4. The film molded body according to any one of claims 1 to 3, wherein the antioxidant contains at least an aromatic compound (a-2) having two or more hindered phenol structures and having a diphenylmethane skeleton.

5. The film molded body according to any one of claims 1 to 4, wherein the antioxidant contains an aromatic compound (a) having two or more phenolic hydroxyl groups and an aromatic compound (b-1) having one phenolic hydroxyl group and one or more -NH- bonds.

6. The film molded body according to any one of claims 1 to 5, wherein the latex of the conjugated diene polymer is a latex of synthetic polyisoprene, a latex of a styrene-isoprene-styrene block copolymer, or a latex of natural rubber.

7. The film molded body according to any one of claims 1 to 6, wherein the latex of the conjugated diene polymer is a latex of a carboxy-modified conjugated diene polymer.

8. The film molded body according to any one of claims 1 to 7, wherein the content of the sulfur-based vulcanizing agent in the latex composition is 0.1 to 1.2 parts by weight based on 100 parts by weight of the conjugated diene polymer in the latex composition.

9. The film molded body according to any one of claims 1 to 8, wherein the vulcanization accelerator is a xanthogen compound.

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