Latex compositions and film-molded articles

Abstract

To provide a latex composition that offers excellent storage stability, suppresses the occurrence of delayed-type allergies (Type IV) in addition to immediate-type allergies (Type I), and can produce film-molded articles with high tensile strength and large elongation at break, with high production stability. [Solution] A latex composition is provided that contains a carboxyl group-containing conjugated diene rubber (A), a metal compound (B) containing a trivalent or higher metal, and a polyvalent carboxylic acid compound (C), and substantially does not contain a carbodiimide compound.

Description

Technical Field

[0001] The present invention relates to a latex composition and a film-formed body.

Background Art

[0002] Conventionally, a dip-formed body that is used in contact with the human body, such as a nipple, balloon, glove, balloon, sack, etc., is known by dip-forming a latex composition containing natural latex typified by natural rubber latex. However, since natural rubber latex contains proteins that cause immediate allergic (Type I) symptoms in the human body, there may be a problem as a dip-formed body that directly contacts living body mucous membranes or organs. Therefore, studies have been made on using latexes of synthetic rubbers such as nitrile rubber.

[0003] For example, Patent Document 1 discloses a latex composition obtained by blending zinc oxide, sulfur, and a vulcanization accelerator into an emulsion containing a carboxylated nitrile butadiene random terpolymer of acrylonitrile, carboxylic acid, and butadiene and having a total solid content of 15 to 25% by weight. However, with the technique of this Patent Document 1, while it is possible to prevent the occurrence of immediate allergy (Type I), when made into a film-formed body, due to sulfur and vulcanization accelerators contained in the film-formed body, allergic symptoms of delayed allergy (Type IV) may occur when touching the human body.

[0004] On the other hand, for example, Patent Document 2 discloses a technique in which, in a latex composition containing at least one base polymer, a crosslinking agent, and a pH adjuster, a mixture of a trivalent metal or a trivalent metal-based compound, a specific polyethylene glycol or a polyethylene glycol derivative, and a specific hydroxide salt is used as the crosslinking agent. According to the technique of this Patent Document 2, since it does not contain sulfur and sulfur compounds as vulcanization accelerators, it can suppress the occurrence of not only immediate allergy (Type I) but also delayed allergy (Type IV).

[0005] However, the latex composition described in Patent Document 2 could not adequately achieve both storage stability and the tensile strength and elongation at break of the resulting film-molded article. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 5697578 [Patent Document 2] International Publication No. 2016 / 72835 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a latex composition that offers excellent storage stability, suppresses the occurrence of delayed-type allergies (Type IV) in addition to immediate-type allergies (Type I), and can produce film-molded articles with high tensile strength and large elongation at break, with high production stability. [Means for solving the problem]

[0008] As a result of diligent research to solve the above problems, the inventors of the present invention have found that the above objectives can be achieved by blending a metal compound (B) containing a trivalent or higher metal and a polyvalent carboxylic acid compound (C) with a carboxyl group-containing conjugated diene rubber (A) latex, while substantially omitting the carbodiimide compound, and have completed the present invention.

[0009] In other words, the present invention provides the following latex compositions and film-molded articles. [1] A latex composition containing a carboxyl group-containing conjugated diene rubber (A), a metal compound (B) containing a metal of trivalent or higher valency, and a polycarboxylic acid compound (C), and substantially free of a carbodiimide compound. [2] The latex composition according to [1], wherein the content of the polycarboxylic acid compound (C) to the content of the metal compound (B) containing a metal with a valency of 3 or more is 1:0.3 to 1:10 in weight ratio of "metal compound (B) containing a metal with a valency of 3 or more: polycarboxylic acid compound (C)". [3] The latex composition according to [1] or [2], wherein the content of the metal compound (B) containing a trivalent or higher metal is 0.1 to 1.0 parts by weight per 100 parts by weight of the carboxyl group-containing conjugated diene rubber (A). [4] The latex composition according to any one of [1] to [3], wherein the content of ethylenically unsaturated carboxylic acid monomer units in the carboxyl group-containing conjugated diene rubber (A) is 5.5% by weight or more. [5] The latex composition according to any one of [1] to [4], wherein the total number of groups consisting of carboxyl groups and salts of carboxyl groups in the molecule of the polycarboxylic acid compound (C) is 2 to 6. [6] The latex composition according to any one of [1] to [5], wherein the molecular weight of the polycarboxylic acid compound (C) is 90 to 1000. [7] The latex composition according to any one of [1] to [6], wherein the polycarboxylic acid compound (C) is at least one selected from adipic acid, citric acid, phthalic acid and salts thereof. A film-molded article comprising a latex composition as described in any of [8] [1] to [7]. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a latex composition that offers excellent storage stability, suppresses the occurrence of delayed-type allergies (Type IV) in addition to immediate-type allergies (Type I), and provides a film-molded article with high tensile strength and large elongation at break, with high production stability. [Modes for carrying out the invention]

[0011] The latex composition of the present invention contains a carboxyl group-containing conjugated diene rubber (A) latex, a metal compound (B) containing a trivalent or higher metal, and a polycarboxylic acid compound (C), and substantially does not contain a carbodiimide compound.

[0012] Latex compositions may be used for molding after being stored for a long period of time. For example, a latex composition may be prepared and then transported for a long period of time by ship before being used for molding. In contrast, the latex composition of the present invention has excellent storage stability, and even when stored for a long period of time by ship or other means, aggregation is suppressed, and a good film molded article can be produced. Furthermore, the latex composition of the present invention can produce a film molded article with high tensile strength and large elongation at break with high production stability. In other words, by using the latex composition of the present invention, a film molded article with high tensile strength and large elongation at break can be produced whether the storage period of the latex composition is relatively short or long.

[0013] Latex of carboxyl group-containing conjugated diene rubber (A) The latex of the carboxyl group-containing conjugated diene rubber (A) used in the present invention is a copolymer latex obtained by copolymerizing a monomer mixture containing at least a conjugated diene monomer and an ethylenically unsaturated carboxylic acid monomer.

[0014] The latex of the carboxyl group-containing conjugated diene rubber (A) may be a copolymer latex obtained by copolymerizing a conjugated diene monomer and an ethylenically unsaturated carboxylic acid monomer, as well as other ethylenically unsaturated monomers copolymerizable with these, as may be used.

[0015] Examples of conjugated diene monomers include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene. Among these, 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred. These conjugated diene monomers can be used individually or in combination of two or more.

[0016] In the carboxyl group-containing conjugated diene rubber (A), the content of conjugated diene monomer units formed by conjugated diene monomers is preferably 38 to 96% by weight, more preferably 44 to 95.5% by weight, even more preferably 50 to 95% by weight, and particularly preferably 50.5 to 95% by weight. By setting the content of conjugated diene monomer units within the above range, storage stability can be further improved, and the resulting film molded article can have even higher tensile strength, even greater elongation at break, and excellent water resistance. Furthermore, when extremely high tensile strength or extremely large elongation at break is required, the content of conjugated diene monomer units is preferably 94.5% by weight or less, more preferably 94% by weight or less, even more preferably 93.5% by weight or less, and particularly preferably 93% by weight or less.

[0017] The ethylenically unsaturated carboxylic acid monomer is not particularly limited as long as it contains a carboxyl group, but examples include ethylenically unsaturated monocarboxylic acid monomers such as acrylic acid and methacrylic acid; ethylenically unsaturated polycarboxylic acid monomers such as itaconic acid, maleic acid, and fumaric acid; ethylenically unsaturated polycarboxylic acid anhydrides such as maleic anhydride and citraconic anhydride; and ethylenically unsaturated polycarboxylic acid partial ester monomers such as monobutyl fumarate, monobutyl maleate, and mono-2-hydroxypropyl maleate. Among these, ethylenically unsaturated monocarboxylic acids are preferred, and methacrylic acid is particularly preferred. These ethylenically unsaturated carboxylic acid monomers can also be used as alkali metal salts or ammonium salts. Furthermore, ethylenically unsaturated carboxylic acid monomers can be used alone or in combination of two or more types.

[0018] In the carboxyl group-containing conjugated diene rubber (A), the content of ethylenically unsaturated carboxylic acid monomer units formed by ethylenically unsaturated carboxylic acid monomers is preferably 4 to 12% by weight, more preferably 4.5 to 11% by weight, even more preferably 5 to 10% by weight, and particularly preferably 5 to 9.5% by weight. By setting the content of ethylenically unsaturated carboxylic acid monomer units within the above range, storage stability can be further improved, and the resulting film molded article can have even higher tensile strength, even greater elongation at break, and excellent water resistance. Furthermore, when extremely high tensile strength or extremely large elongation at break is required, the content of ethylenically unsaturated carboxylic acid monomer units is preferably 5.5% by weight or more, more preferably 6% by weight or more, even more preferably 6.5% by weight or more, and particularly preferably 7% by weight or more.

[0019] Examples of the conjugated diene monomer and other ethylenically unsaturated monomers copolymerizable with the ethylenically unsaturated carboxylic acid monomer include vinyl aromatic monomers such as styrene, alkylstyrene, vinylnaphthalene; fluoroalkyl vinyl ethers such as fluoroethyl vinyl ether; ethylenically unsaturated nitrile monomers such as acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile, α-cyanoethyl acrylonitrile; ethylenically unsaturated amide monomers such as (meth)acrylamide, N-methylol(meth)acrylamide, N,N-dimethylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-propoxymethyl(meth)acrylamide; ethylenically unsaturated carboxylic acid ester monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, dibutyl maleate, dibutyl fumarate, diethyl maleate, methoxymethyl (meth)acrylate, ethoxyethyl (meth)acrylate, methoxyethoxyethyl (meth)acrylate, cyanomethyl (meth)acrylate, 2-cyanoethyl (meth)acrylate, 1-cyanopropyl (meth)acrylate, 2-ethyl-6-cyanohexyl (meth)acrylate, 3-cyanopropyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, glycidyl (meth)acrylate, dimethylaminoethyl (meth)acrylate; crosslinkable monomers such as divinylbenzene, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol (meth)acrylate; and the like. These ethylenically unsaturated monomers can be used alone or in combination of two or more kinds.

[0020] The content ratio of other monomer units formed by other ethylenically unsaturated monomers in the carboxyl group-containing conjugated diene rubber (A) is preferably 0 to 50% by weight, more preferably 0 to 45% by weight, still more preferably 0 to 40% by weight.

[0021] As the carboxyl group-containing conjugated diene rubber (A), at least one selected from carboxyl group-containing nitrile rubber (a1), carboxyl group-containing styrene-butadiene rubber (a2), and carboxyl group-containing conjugated diene rubber (a3) is preferable.

[0022] The latex of the carboxyl group-containing nitrile rubber (a1) is a latex of a copolymer obtained by copolymerizing an ethylenically unsaturated nitrile monomer in addition to a conjugated diene monomer and an ethylenically unsaturated carboxylic acid monomer, and in addition to these, a latex of a copolymer obtained by copolymerizing other ethylenically unsaturated monomers copolymerizable with these as required may also be used.

[0023] Examples of the conjugated diene monomer include those described above. Among these, 1,3-butadiene and isoprene are preferable, and 1,3-butadiene is more preferable. These conjugated diene monomers can be used alone or in combination of two or more. The content ratio of the conjugated diene monomer units formed by the conjugated diene monomer in the carboxyl group-containing nitrile rubber (a1) is preferably 48 to 76% by weight, more preferably 49 to 70.5% by weight, still more preferably 50 to 70% by weight, and particularly preferably 50.5 to 70% by weight. By setting the content ratio of the conjugated diene monomer units within the above range, the storage stability can be further improved, and the obtained film molded body can have a higher tensile strength, a larger elongation at break, and excellent water resistance. Also, when an extremely high tensile strength or an extremely large elongation at break is required, the content ratio of the conjugated diene monomer units is preferably 69.5% by weight or less, more preferably 69% by weight or less, still more preferably 68.5% by weight or less, and particularly preferably 68% by weight or less.

[0024] Examples of ethylenically unsaturated carboxylic acid monomers include those mentioned above, among which ethylenically unsaturated monocarboxylic acids are preferred, and methacrylic acid is particularly preferred. These ethylenically unsaturated carboxylic acid monomers can also be used as alkali metal salts or ammonium salts. Furthermore, ethylenically unsaturated carboxylic acid monomers can be used alone or in combination of two or more types. The content of ethylenically unsaturated carboxylic acid monomer units formed by ethylenically unsaturated carboxylic acid monomers in the carboxyl group-containing nitrile rubber (a1) is preferably 4 to 12% by weight, more preferably 4.5 to 11% by weight, even more preferably 5 to 10% by weight, and particularly preferably 5 to 9.5% by weight. By setting the content of ethylenically unsaturated carboxylic acid monomer units within the above range, storage stability can be further improved, and the resulting film molded article can have even higher tensile strength, even greater elongation at break, and excellent water resistance. Furthermore, when extremely high tensile strength or extremely large elongation at break is required, the content of ethylenically unsaturated carboxylic acid monomer units is preferably 5.5% by weight or more, more preferably 6% by weight or more, even more preferably 6.5% by weight or more, and particularly preferably 7% by weight or more.

[0025] The ethylenically unsaturated nitrile monomer is not particularly limited as long as it contains a nitrile group, but examples include acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile, and α-cyanoethylacrylonitrile. Among these, acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is more preferred. These ethylenically unsaturated nitrile monomers can be used alone or in combination of two or more. The content of ethylenically unsaturated nitrile monomer units formed by ethylenically unsaturated nitrile monomers in the carboxyl group-containing nitrile rubber (a1) is preferably 20 to 40% by weight, and more preferably 25 to 40% by weight. By setting the content of ethylenically unsaturated nitrile monomer units within the above range, the resulting film molded article can have even higher tensile strength, even greater elongation at break, and superior water resistance.

[0026] Other ethylenically unsaturated monomers copolymerizable with conjugated diene monomers, ethylenically unsaturated carboxylic acid monomers, and ethylenically unsaturated nitrile monomers include, for example, those mentioned above (excluding ethylenically unsaturated nitrile monomers). These ethylenically unsaturated monomers can be used individually or in combination of two or more.

[0027] The content of other monomer units formed by other ethylenically unsaturated monomers in the carboxyl group-containing nitrile rubber (a1) is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 3% by weight or less.

[0028] The carboxyl group-containing styrene-butadiene rubber (a2) latex is a copolymer latex obtained by copolymerizing styrene with 1,3-butadiene as a conjugated diene monomer and an ethylenically unsaturated carboxylic acid monomer, and may also be a copolymer latex obtained by copolymerizing other ethylenically unsaturated monomers copolymerizable with these, as needed.

[0029] In the carboxyl group-containing styrene-butadiene rubber (a2), the content of butadiene units formed by 1,3-butadiene is preferably 48 to 76% by weight, more preferably 49 to 70.5% by weight, even more preferably 50 to 65% by weight, and particularly preferably 50.5 to 65% by weight. By setting the content of butadiene units within the above range, storage stability can be further improved, and the resulting film molded article can have even higher tensile strength, even greater elongation at break, and excellent water resistance. Furthermore, when extremely high tensile strength or extremely large elongation at break is required, the content of butadiene units is preferably 64.5% by weight or less, more preferably 64% by weight or less, even more preferably 63.5% by weight or less, and particularly preferably 63% by weight or less.

[0030] The ethylenically unsaturated carboxylic acid monomer is not particularly limited as long as it contains a carboxyl group, but for example, the same type as the latex of the carboxyl group-containing nitrile rubber (a1) described above can be used. The content of ethylenically unsaturated carboxylic acid monomer units formed by the ethylenically unsaturated carboxylic acid monomer in the carboxyl group-containing styrene-butadiene rubber (a2) is preferably 4 to 12% by weight, more preferably 4.5 to 11% by weight, even more preferably 5 to 10% by weight, and particularly preferably 5 to 9.5% by weight. By setting the content of ethylenically unsaturated carboxylic acid monomer units within the above range, storage stability can be further improved, and the resulting film molded article can have even higher tensile strength, even greater elongation at break, and superior water resistance. Furthermore, when extremely high tensile strength or extremely large elongation at break is required, the content of ethylenically unsaturated carboxylic acid monomer units is preferably 5.5% by weight or more, more preferably 6% by weight or more, even more preferably 6.5% by weight or more, and particularly preferably 7% by weight or more.

[0031] In the carboxyl group-containing styrene-butadiene rubber (a2), the content of styrene units formed by styrene is preferably 20 to 40% by weight, more preferably 25 to 40% by weight, and even more preferably 30 to 40% by weight. By setting the content of styrene units within the above range, the resulting film molded article can have even higher tensile strength, greater elongation at break, and superior water resistance.

[0032] Examples of ethylenically unsaturated monomers copolymerizable with 1,3-butadiene, ethylenically unsaturated carboxylic acid monomers, and styrene as conjugated diene monomers include, for example, those mentioned above (except styrene), as well as conjugated diene monomers other than 1,3-butadiene, such as isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene. The content of other monomer units formed by other ethylenically unsaturated monomers in the carboxyl group-containing styrene-butadiene rubber (a2) is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 3% by weight or less.

[0033] The latex of the carboxyl group-containing conjugated diene rubber (a3) ​​is a copolymer latex obtained by copolymerizing a conjugated diene monomer and an ethylenically unsaturated carboxylic acid monomer, and in addition to these, it may be a copolymer latex obtained by copolymerizing other ethylenically unsaturated monomers copolymerizable with these, as needed.

[0034] Examples of conjugated diene monomers include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene. These conjugated diene monomers may be used individually or in combination of two or more.

[0035] In the carboxyl group-containing conjugated diene rubber (a3), the content of conjugated diene monomer units formed by conjugated diene monomers is preferably 78 to 96% by weight, more preferably 84 to 95.5% by weight, even more preferably 87 to 95% by weight, and particularly preferably 87.5 to 95% by weight. By setting the content of conjugated diene monomer units within the above range, storage stability can be further improved, and the resulting film molded article can have even higher tensile strength, even greater elongation at break, and excellent water resistance. Furthermore, when extremely high tensile strength or extremely large elongation at break is required, the content of conjugated diene monomer units is preferably 94.5% by weight or less, more preferably 94% by weight or less, even more preferably 93.5% by weight or less, and particularly preferably 93% by weight or less.

[0036] The ethylenically unsaturated carboxylic acid monomer is not particularly limited as long as it contains a carboxyl group, but for example, the same type as the latex of the carboxyl group-containing nitrile rubber (a1) described above can be used. The content of ethylenically unsaturated carboxylic acid monomer units formed by the ethylenically unsaturated carboxylic acid monomer in the carboxyl group-containing conjugated diene rubber (a3) ​​is preferably 4 to 12% by weight, more preferably 4.5 to 11% by weight, even more preferably 5 to 10% by weight, and particularly preferably 5 to 9.5% by weight. By setting the content of ethylenically unsaturated carboxylic acid monomer units within the above range, storage stability can be further improved, and the resulting film molded article can have even higher tensile strength, even greater elongation at break, and superior water resistance. Furthermore, when extremely high tensile strength or extremely large elongation at break is required, the content of ethylenically unsaturated carboxylic acid monomer units is preferably 5.5% by weight or more, more preferably 6% by weight or more, even more preferably 6.5% by weight or more, and particularly preferably 7% by weight or more.

[0037] Other ethylenically unsaturated monomers copolymerizable with conjugated diene monomers and ethylenically unsaturated carboxylic acid monomers include, for example, those mentioned above. The content of other monomer units formed by other ethylenically unsaturated monomers in the carboxyl group-containing conjugated diene rubber (a3) ​​is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 3% by weight or less.

[0038] The carboxyl group-containing conjugated diene rubber (A) used in the present invention is obtained by copolymerizing a monomer mixture containing the above-mentioned monomers, but copolymerization by emulsion polymerization is preferred. Conventional known methods can be used as the emulsion polymerization method.

[0039] When emulsion polymerization is carried out on monomer mixtures containing the monomers described above, polymerization auxiliary materials such as emulsifiers, polymerization initiators, and molecular weight modifiers, which are commonly used, can be used. The method of adding these polymerization auxiliary materials is not particularly limited, and any method such as initial lump-sum addition, divided addition, or continuous addition may be used.

[0040] The emulsifier is not particularly limited, but examples include nonionic emulsifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan alkyl esters; anionic emulsifiers such as alkylbenzene sulfonates such as potassium dodecylbenzenesulfonate and sodium dodecylbenzenesulfonate, higher alcohol sulfate salts, and alkyl sulfosuccinates; cationic emulsifiers such as alkyltrimethylammonium chloride, dialkylammonium chloride, and benzylammonium chloride; and copolymerizable emulsifiers such as sulfoesters of α,β-unsaturated carboxylic acids, sulfate esters of α,β-unsaturated carboxylic acids, and sulfoalkylaryl ethers. Among these, anionic emulsifiers are preferred, alkylbenzenesulfonates are more preferred, and potassium dodecylbenzenesulfonate and sodium dodecylbenzenesulfonate are particularly preferred. These emulsifiers can be used alone or in combination of two or more. The amount of emulsifier used is preferably 0.1 to 10 parts by weight per 100 parts by weight of the monomer mixture.

[0041] Polymerization initiators are not particularly limited, but examples include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium superphosphate, and hydrogen peroxide; organic peroxides such as diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide, di-α-cumyl peroxide, acetyl peroxide, isobutyryl peroxide, and benzoyl peroxide; and azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, and azobisisobutyrate methyl. These polymerization initiators can be used individually or in combination of two or more. The amount of polymerization initiator used is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 2 parts by weight, per 100 parts by weight of the monomer mixture.

[0042] Furthermore, peroxide initiators can be used in combination with reducing agents as redox polymerization initiators. While not particularly limited, examples of reducing agents include compounds containing metal ions in a reduced state, such as ferrous sulfate and cuprous naphthenate; sulfonic acid compounds, such as sodium methanesulfonate; and amine compounds, such as dimethylaniline. These reducing agents can be used individually or in combination of two or more. The amount of reducing agent used is preferably 3 to 1000 parts by weight per 100 parts by weight of peroxide.

[0043] The amount of water used in emulsion polymerization is preferably 80 to 600 parts by weight, and particularly preferably 100 to 200 parts by weight, per 100 parts by weight of the total monomer used.

[0044] Methods for adding monomers include, for example, adding all monomers to be used in the reaction vessel at once, adding them continuously or intermittently as polymerization progresses, and adding a portion of the monomers and allowing the reaction to proceed to a specific conversion rate, after which the remaining monomers are added continuously or intermittently to polymerize. Any of these methods may be adopted. When monomers are mixed and added continuously or intermittently, the composition of the mixture may be kept constant or varied. In addition, each monomer may be added to the reaction vessel either after being mixed with the other monomers to be used beforehand, or added to the reaction vessel separately.

[0045] Furthermore, polymerization auxiliary materials such as chelating agents, dispersants, pH adjusters, oxygen absorbers, and particle size adjusters can be used as needed, and there are no particular limitations on the type or amount used.

[0046] The polymerization temperature during emulsion polymerization is not particularly limited, but is usually 3 to 95°C, preferably 5 to 60°C. The polymerization time is approximately 5 to 40 hours.

[0047] As described above, the monomer mixture is emulsion polymerized, and when a predetermined polymerization conversion rate is reached, the polymerization reaction is stopped by cooling the polymerization system or adding a polymerization inhibitor. The polymerization conversion rate at which the polymerization reaction is stopped is preferably 90% by weight or more, more preferably 93% by weight or more.

[0048] Polymerization inhibitors are not particularly limited, but examples include hydroxylamine, hydroxyamine sulfate, diethylhydroxylamine, hydroxyamine sulfonic acid and its alkali metal salts, sodium dimethyldithiocarbamate, hydroquinone derivatives, catechol derivatives, and aromatic hydroxydithiocarboxylic acids such as hydroxydimethylbenzenethiocarboxylic acid, hydroxydiethylbenzenedithiocarboxylic acid, and hydroxydibutylbenzenedithiocarboxylic acid, as well as their alkali metal salts. The amount of polymerization inhibitor used is preferably 0.05 to 2 parts by weight per 100 parts by weight of the monomer mixture.

[0049] After stopping the polymerization reaction, unreacted monomers can be removed as desired, and the solid content concentration and pH can be adjusted to obtain a latex of carboxyl group-containing conjugated diene rubber (A).

[0050] Furthermore, the carboxyl group-containing conjugated diene rubber (A) latex used in the present invention may optionally contain antioxidants, preservatives, antibacterial agents, dispersants, etc.

[0051] The number-average particle size of the latex of the carboxyl group-containing conjugated diene rubber (A) used in the present invention is preferably 60 to 300 nm, more preferably 80 to 150 nm. The particle size can be adjusted to a desired value by methods such as adjusting the amount of emulsifier and polymerization initiator used.

[0052] Metal compounds containing metals with a valency of 3 or higher (B) The latex composition of the present invention contains, in addition to the carboxyl group-containing conjugated diene rubber (A) described above, a metal compound (B) containing a trivalent or higher metal. In the latex composition of the present invention, the metal compound (B) containing a trivalent or higher metal acts as a crosslinking agent.

[0053] According to the present invention, instead of sulfur, which is normally used as a crosslinking agent, a metal compound (B) containing a metal with a valent or higher valency is used as the crosslinking agent. Furthermore, since a sulfur-containing vulcanization accelerator is not required for crosslinking, it is possible to effectively suppress not only immediate-type allergies (Type I) but also delayed-type allergies (Type IV) caused by sulfur or sulfur-containing vulcanization accelerators.

[0054] In the latex composition of the present invention, the sulfur content is preferably 0.1 parts by weight or less, and more preferably 0.01 parts by weight or less, per 100 parts by weight of the carboxyl group-containing conjugated diene rubber (A). Furthermore, in the latex composition of the present invention, the content of the sulfur-containing vulcanization accelerator is preferably 0.1 parts by weight or less, and more preferably 0.01 parts by weight or less, per 100 parts by weight of the carboxyl group-containing conjugated diene rubber (A).

[0055] The metal compound (B) containing a metal with a valency of 3 or higher can be any compound containing a metal with a valency of 3 or higher, and is not particularly limited. Examples include aluminum compounds, cobalt compounds, zirconium compounds, and titanium compounds. Among these, aluminum compounds are preferred because they can cure the carboxyl group-containing conjugated diene rubber (A) contained in the latex more effectively.

[0056] The aluminum compounds are not particularly limited, but examples include aluminum oxide, aluminum chloride, aluminum hydroxide, aluminum nitrate, aluminum sulfate, metal aluminum, ammonium aluminum sulfate, aluminum bromide, aluminum fluoride, potassium aluminum sulfate, aluminum isopropoxide, sodium aluminate, potassium aluminate, and sodium aluminum sulfite. These aluminum compounds can be used individually or in combination of two or more. Among these, aluminic acid and aluminates are preferred, aluminates are more preferred, and sodium aluminate is even more preferred, as they can make the effects of the present invention more pronounced.

[0057] The content of the metal compound (B) containing a trivalent or higher metal in the latex composition of the present invention is preferably 0.1 to 1.0 parts by weight, preferably 0.12 to 0.75 parts by weight, and more preferably 0.15 to 0.5 parts by weight, per 100 parts by weight of the carboxyl group-containing conjugated diene rubber (A) contained in the latex. By setting the content of the metal compound (B) containing a trivalent or higher metal within the above range, storage stability can be further improved, and the resulting film molded article can have even higher tensile strength, even greater elongation at break, and excellent water resistance.

[0058] Polycarboxylic acid compounds (C) The latex composition of the present invention contains a carboxyl group-containing conjugated diene rubber (A) latex and a metal compound (B) containing a trivalent or higher metal, in addition to a polyvalent carboxylic acid compound (C).

[0059] According to the present invention, by combining the carboxyl group-containing conjugated diene rubber (A) latex described above, a metal compound (B) containing a trivalent or higher metal, and a polyvalent carboxylic acid compound (C), the latex composition can provide a film molded article with excellent storage stability, high tensile strength, and large elongation at break, with high production stability.

[0060] In this disclosure, polycarboxylic acid compound (C) is a compound having at least one of a carboxyl group and a group consisting of a salt of a carboxyl group, and the total number of carboxyl groups and groups consisting of salts of carboxyl groups in the molecule is 2 or more. The total number of carboxyl groups and groups consisting of salts of carboxyl groups in the molecule of polycarboxylic acid compound (C) is preferably 2 to 6, more preferably 2 to 4, even more preferably 2 to 3, and particularly preferably 2.

[0061] Examples of carboxyl group salts include salts of alkali metals such as sodium and potassium with carboxyl groups; salts of alkaline earth metals such as calcium and magnesium with carboxyl groups; and salts of onium such as ammonium with carboxyl groups.

[0062] The molecular weight of the polycarboxylic acid compound (C) is preferably 90 to 1000, more preferably 100 to 500, even more preferably 110 to 300, particularly preferably 120 to 250, and most preferably 130 to 220.

[0063] The number of carbon atoms in the polycarboxylic acid compound (C) is preferably 2 to 15, more preferably 3 to 12, even more preferably 4 to 10, particularly preferably 5 to 9, and most preferably 6 to 8.

[0064] The total number of groups consisting of carboxyl groups and salts of carboxyl groups (total number of carboxyl groups and their salts / molecular weight) relative to the molecular weight of the polycarboxylic acid compound (C) is preferably 1 / 90 to 1 / 500, more preferably 1 / 50 to 1 / 250, even more preferably 1 / 55 to 1 / 150, particularly preferably 1 / 60 to 1 / 125, and most preferably 1 / 65 to 1 / 110.

[0065] The polycarboxylic acid compound (C) may have heteroatoms other than oxygen, but it is preferable that it does not have heteroatoms other than oxygen.

[0066] Specific examples of polycarboxylic acid compounds (C) include alkanes having two or more carboxyl groups, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid, and their salts; saturated aliphatic polycarboxylic acids containing alcoholic hydroxyl groups, such as malic acid, tartonic acid, 3-methylmalic acid, tartaric acid, citramalic acid, citric acid, and isocitric acid, and their salts; ethylenically unsaturated aliphatic polycarboxylic acids, such as maleic acid, fumaric acid, itaconic acid, and aconitic acid, and their salts; aromatic polycarboxylic acid compounds, such as phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid, trimellitic acid, trimesic acid, prenitic acid, melophanic acid, pyromellitic acid, benzenepentacarboxylic acid, melitic acid, and o-phenylenediacetic acid, and their salts. Polycarboxylic acid compounds (C) can be used alone or in combination of two or more.

[0067] Among these, alkanes having two or more carboxyl groups, saturated aliphatic polycarboxylic acids containing alcoholic hydroxyl groups, aromatic polycarboxylic acid compounds and salts thereof are preferred, and adipic acid, citric acid, phthalic acid, and salts thereof are more preferred.

[0068] The content of the polycarboxylic acid compound (C) in the latex composition of the present invention is not particularly limited, but is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 3 parts by weight, and even more preferably 0.3 to 2 parts by weight, per 100 parts by weight of the carboxyl group-containing conjugated diene rubber (A) contained in the latex. By setting the content of the polycarboxylic acid compound (C) within the above range, storage stability can be further improved, and the resulting film molded article can have even higher tensile strength, even greater elongation at break, and excellent water resistance.

[0069] In the latex composition of the present invention, the content of polycarboxylic acid compound (C) to the content of metal compound (B) containing a trivalent or higher metal is preferably 1:0.3 to 1:10, more preferably 1:0.6 to 1:8, and even more preferably 1:1 to 1:6, in terms of the weight ratio of "metal compound (B) containing a trivalent or higher metal: polycarboxylic acid compound (C)". By setting the content of polycarboxylic acid compound (C) to metal compound (B) containing a trivalent or higher metal within the above range, storage stability can be further improved, and the resulting film-molded article can have even higher tensile strength, even greater elongation at break, and superior water resistance.

[0070] Furthermore, in addition to the carboxyl group-containing conjugated diene rubber (A) latex, the metal compound (B) containing a trivalent or higher metal, and the polycarboxylic acid compound (C) described above, the latex composition of the present invention may further contain an alcoholic hydroxyl group-containing compound (D). Examples of the alcoholic hydroxyl group-containing compound (D) include sugars (d1), sugar alcohols (d2), and alcoholic hydroxyl group-containing monocarboxylic acid compounds (d3).

[0071] The sugars (d1) are not particularly limited and can be monosaccharides or polysaccharides in which two or more monosaccharides are linked by glycosidic bonds, but examples include monosaccharides such as erythrose, threose, ribose, lyxose, xylose, arabinose, allose, talose, gross, altrose, galactose, idose, erythrulose, xylulose, ribulose, psicose, fructose, sorbose, and tagatose; trehalose, maltose, isomaltose, cellobiose, genthiobiose, melibiose, lactose, sucrose, and palatinose. Examples include disaccharides such as s; trisaccharides such as maltotriose, isomalttriose, panose, cerototriose, manninotriose, solatriose, melegitose, planteose, gentianose, umbelliferose, lactosucrose, and raffinose; homooligosaccharides such as maltotetraose and isomaltotetraose; tetrasaccharides such as stachyose, cerototetraose, scorodose, liquinose, and panose; pentasaccharides such as maltopentaose and isomaltopentaose; and hexasaccharides such as maltohexaose and isomaltotehexaose. These may be used individually or in combination of two or more.

[0072] The sugar alcohol (d2) can be any sugar alcohol of a monosaccharide or polysaccharide, and is not particularly limited, but examples include trititol such as glycerin; tetrito such as erythritol, D-threitol, and L-threitol; pentitol such as D-arabinitol, L-arabinitol, xylitol, ribitol, and pentaerythritol; pentaerythritol; hexitol such as sorbitol, D-iditol, galactitol, D-glucitol, and mannitol; heptitol such as boremitol and perseitol; and octitol such as D-erythro-D-galacto-octitol. These may be used individually or in combination of two or more. Among these, hexitol, which is a sugar alcohol with 6 carbon atoms, is preferred, and sorbitol is more preferred.

[0073] The alcoholic hydroxyl group-containing monocarboxylic acid compound (d3) can be any monocarboxylic acid or a salt thereof having a hydroxyl group, and is not particularly limited, but examples include aliphatic hydroxy acids such as glycolic acid, lactic acid, glyceric acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, γ-hydroxybutyric acid, leucic acid, mevalonic acid, pantoic acid, ricinoleic acid, ricineradicic acid, cerebronic acid, quinic acid, shikimic acid, and serine; salicylic acid, creosote acids (homosalicylic acid, hydroxy(methyl)benzoic acid), vanillic acid, syringic acid, hydroxypropanoic acid, hydroxypentanoic acid, hydroxyhexanoic acid, hydroxyheptanoic acid, hydroxyoctanoic acid, hydroxynonanoic acid, hydroxydecanoic acid, and hydroxyu Examples include monohydroxybenzoic acid derivatives such as ndecanic acid, hydroxydodecanoic acid, hydroxytridecanoic acid, hydroxytetradecanoic acid, hydroxypentadecanoic acid, hydroxyheptadecanoic acid, hydroxyoctadecanoic acid, hydroxynonadecanoic acid, hydroxyicosanoic acid, and ricinoleic acid; dihydroxybenzoic acid derivatives such as pyrocatechuic acid, resorsilicic acid, protocatechuic acid, gentisic acid, and orceric acid; trihydroxybenzoic acid derivatives such as gallic acid; phenylacetic acid derivatives such as mandelic acid, benzyl acid, and atrolactinic acid; and aromatic hydroxy acids such as cinnamic acid and hydroxycinnamic acid derivatives such as melilotic acid, floretic acid, coumaric acid, umberic acid, caffeic acid, ferulic acid, and sinapic acid; and salts thereof. Examples of salts include alkali metal salts such as sodium and potassium; alkaline earth metal salts such as calcium and magnesium; and onium salts such as ammonium. These may be used individually or in combination of two or more. Among these, aliphatic hydroxy acids and their salts are preferred, aliphatic α-hydroxy acids and their salts are more preferred, glycolic acid, lactic acid, glyceric acid and their salts are even more preferred, and glycolic acid and glycolic acid salts are particularly preferred.

[0074] The content of the alcoholic hydroxyl group-containing compound (D) in the latex composition of the present invention is not particularly limited as long as it does not hinder the effects of the present invention, but may be 0 to 1.5 parts by weight or 0 to 0.5 parts by weight per 100 parts by weight of the carboxyl group-containing conjugated diene rubber (A).

[0075] The latex composition of the present invention substantially does not contain a carbodiimide compound. According to the present invention, by blending a metal compound (B) containing a trivalent or higher metal and a polyvalent carboxylic acid compound (C) with the carboxyl group-containing conjugated diene rubber (A) described above, while substantially omitting the carbodiimide compound, it is possible to provide a film molded article with excellent storage stability, high tensile strength, and large elongation at break, with high production stability.

[0076] Examples of carbodiimide compounds include compounds having a carbodiimide group and polycarbodiimides. Specifically, "substantially free of carbodiimide compounds" means that the concentration of carbodiimide compounds in the latex composition (total concentration of compounds having a carbodiimide group and polycarbodiimides) is 1000 ppm or less, preferably 100 ppm or less.

[0077] The latex composition of the present invention may further contain fillers, pH adjusters, thickeners, antioxidants, dispersants, pigments, softeners, and the like.

[0078] The latex composition of the present invention can be obtained, for example, by compounding a carboxyl group-containing conjugated diene rubber (A) with a metal compound (B) containing a metal of trivalent or higher, a polycarboxylic acid compound (C), and various compounding agents as needed. There are no particular limitations on the method of compounding the carboxyl group-containing conjugated diene rubber (A) with the metal compound (B) containing a metal of trivalent or higher and the polycarboxylic acid compound (C), but it is preferable to dissolve the metal compound (B) containing a metal of trivalent or higher and the polycarboxylic acid compound (C) in water or alcohol and add them in the form of an aqueous solution or alcohol solution, in order to ensure good dispersion of the metal compound (B) containing a metal of trivalent or higher and the polycarboxylic acid compound (C) in the resulting latex composition.

[0079] The solid content concentration of the latex composition of the present invention is preferably 10 to 40% by weight, more preferably 15 to 35% by weight. That is, the proportion of water in the latex composition of the present invention is preferably 60 to 90% by weight, more preferably 65 to 85% by weight. Furthermore, the pH of the latex composition of the present invention is preferably 8.0 to 12, more preferably 8.5 to 11.

[0080] film-molded body The film-molded article of the present invention is a film-like molded article made of the latex composition of the present invention. The film thickness of the film-molded article of the present invention is preferably 0.03 to 0.50 mm, more preferably 0.05 to 0.40 mm, and particularly preferably 0.08 to 0.30 mm.

[0081] The film-molded article of the present invention is not particularly limited, but it is preferably a dip-molded article obtained by dip molding the latex composition of the present invention. Dip molding is a method of immersing a dip mold in the latex composition, depositing the composition on the surface of the dip mold, then removing the dip mold from the composition, and then drying the composition deposited on the surface of the dip mold. The dip mold may be preheated before being immersed in the latex composition. Furthermore, a coagulant can be used as needed before immersing the dip mold in the latex composition or after removing the dip mold from the latex composition.

[0082] Specific examples of methods for using the coagulant include immersing the mold in a coagulant solution before immersion in the latex composition to allow the coagulant to adhere to the mold (anodic adhesion immersion method), and immersing the mold with the latex composition deposited in it in a coagulant solution (Teegue adhesion immersion method). However, the anodic adhesion immersion method is preferred because it yields a dip-molded body with less thickness variation.

[0083] Examples of coagulants include metal halides such as barium chloride, calcium chloride, magnesium chloride, zinc chloride, and aluminum chloride; nitrates such as barium nitrate, calcium nitrate, and zinc nitrate; acetates such as barium acetate, calcium acetate, and zinc acetate; and sulfates such as calcium sulfate, magnesium sulfate, and aluminum sulfate. Among these, calcium chloride and calcium nitrate are preferred. The coagulant is usually used as a solution of water, alcohol, or a mixture thereof. The concentration of the coagulant is usually 5 to 50% by weight, preferably 10 to 35% by weight.

[0084] If the dip-molded body is a glove or in other cases where beading (sleeve wrapping) is required for the sleeve portion, beading may be performed on the dip-molded layer to form the beaded portion (sleeve wrapping portion).

[0085] The resulting dip-molded layer is usually cured by heating. Before heating, the dip-molded layer may be immersed in water, preferably warm water at 30-70°C, for 1-60 minutes to remove water-soluble impurities (e.g., excess emulsifiers or coagulants). While the removal of water-soluble impurities may be performed after the heat treatment of the dip-molded layer, it is preferable to perform it before the heat treatment as it allows for more efficient removal of water-soluble impurities.

[0086] Generally, dip-molded layers are cured by heat treatment at a temperature of 100 to 150°C. However, the dip-molded layer made from the latex composition of the present invention can provide a film molded article with high tensile strength and large elongation at break, even when heated and cured at a relatively low temperature. When heating the dip-molded layer made from the latex composition of the present invention at a relatively low temperature, the heating temperature is, for example, less than 85°C, preferably 30 to 80°C, more preferably 40 to 75°C, and even more preferably 50 to 70°C. On the other hand, the dip-molded layer made from the latex composition of the present invention may be heated and cured at a temperature of 85°C or higher, specifically 100 to 150°C, as needed. The heating time is preferably 10 to 130 minutes, more preferably 20 to 100 minutes. As for the heating method, external heating by infrared rays or heated air, or internal heating by high frequency can be employed. Among these, external heating by heated air is preferred.

[0087] After curing the dip-molded layer, a halogenation treatment may be performed by contacting the surface of the cured dip-molded layer with a halogenating agent. In particular, if the dip-molded layer is heated and cured at a relatively low temperature, halogenation treatment is preferable. Among the halogens in the halogenating agent, chlorine, bromine, and iodine are preferred, with chlorine being more preferred due to its high reactivity and excellent handling properties. That is, it is particularly preferable to perform a chlorination treatment by contacting the surface of the cured dip-molded layer with a chlorinating agent. Since the film-molded article of the present invention is obtained using the latex composition of the present invention, even after halogenation treatment, it will have high tensile strength and large elongation at break.

[0088] Examples of halogenating agents include halogenated gases containing gaseous halogens and halogenated liquids in which halogens are dispersed or dissolved in a liquid. Among these, halogenated liquids are preferred from the viewpoint of easily bringing the dip-molded layer into contact with the halogenating agent.

[0089] The medium for dispersing or dissolving the halogen is not particularly limited, but water is preferred. Methods for dispersing or dissolving the halogen in the liquid medium include directly injecting the halogen into the medium, and reacting a halogen-generating compound in the medium to generate the halogen. The halogen concentration in the halogenated solution is not particularly limited, but is preferably 0.005 to 0.35 mol / L, more preferably 0.01 to 0.25 mol / L, and even more preferably 0.03 to 0.08 mol / L.

[0090] A preferred method for preparing the halogenated solution is to add sodium hypochlorite and hydrochloric acid to water to generate chlorine. The concentrations of sodium hypochlorite and hydrochloric acid are not particularly limited as long as they generate the preferred concentration of chlorine described above in the water. However, the concentration of sodium hypochlorite is preferably 0.03 to 0.8% by weight, more preferably 0.05 to 0.4% by weight, and the concentration of hydrochloric acid is preferably 0.03 to 0.8% by weight, more preferably 0.05 to 0.4% by weight.

[0091] Methods for contacting the surface of the cured dip-molded layer with a halogenating agent include, when using a halogenating gas, placing the dip-molded layer in a chamber filled with the halogenating gas for a predetermined time. When using a halogenating liquid, methods include immersing the dip-molded layer in the halogenating liquid, or spraying the halogenating liquid onto the dip-molded layer in a shower or mist manner. Among these, immersing the dip-molded layer in the halogenating liquid is preferred from the viewpoint of being able to contact the layer with the halogenating agent using simple equipment.

[0092] After halogenation treatment, it is preferable to perform a neutralization treatment using an alkaline aqueous solution such as an aqueous ammonia solution. It is also preferable to perform a cleaning treatment using a cleaning solution to remove unreacted halogen from the dip-molded layer after halogenation treatment. The order of these treatments is not particularly limited, and each treatment may be performed multiple times. Examples of neutralization and cleaning treatments include immersing the dip-molded layer in an alkaline aqueous solution or cleaning solution, or spraying the alkaline aqueous solution or cleaning solution onto the dip-molded layer in a shower or mist manner. Among these, immersing the dip-molded layer in an alkaline aqueous solution or cleaning solution is preferred from the viewpoint of being able to perform the treatment with simple equipment.

[0093] Then, by removing the dip-molded layer after curing, or the dip-molded layer after halogenation treatment, from the dip-molding mold, a dip-molded body as a film-molded body is obtained. Detachment methods include peeling it off by hand or using water pressure or compressed air pressure. After detachment, a further heat treatment may be performed at a temperature of 60-120°C for 10-120 minutes.

[0094] The film-shaped article of the present invention may be obtained by any method that can form the latex composition of the present invention into a film (for example, a coating method), in addition to the dip molding method of the latex composition of the present invention described above.

[0095] Since the film-molded articles of the present invention are obtained using the latex composition of the present invention described above, the occurrence of delayed-type allergies (Type IV) in addition to immediate-type allergies (Type I) is suppressed, and they have high tensile strength and large elongation at break. For this reason, the film-molded articles of the present invention are suitable for gloves used in medical, surgical, food, or industrial applications. Alternatively, the film-molded articles of the present invention can be used not only for gloves, but also for medical supplies such as baby bottle nipples, droppers, tubes, water pillows, balloon sacks, catheters, and condoms; toys such as balloons, dolls, and balls; industrial supplies such as pressure-molding bags and gas storage bags; and finger cots. [Examples]

[0096] The present invention will be described below based on more detailed examples, but the present invention is not limited to these examples. In the following, "parts" refers to weight unless otherwise specified. Furthermore, the tests and evaluations were conducted as follows.

[0097] <Tensile strength and elongation at break> From the dip-molded glove (glove) demolded from the glove mold, dumbbell-shaped test specimens were prepared using a dumbbell (Die-C: manufactured by Dumbbell Co.) in accordance with ASTM D-412. The resulting test specimens were then pulled at a tensile speed of 500 mm / min, and the tensile strength and elongation at break were measured. Higher values ​​for tensile strength and elongation at break are preferable.

[0098] <Water resistance (artificial sweat immersion test)> The tensile strength (TS1) of test specimens that were not immersed in artificial sweat solution was determined using the method described above. Additionally, a new dumbbell-shaped test specimen was prepared using the same method. The newly obtained test specimen was immersed in artificial sweat solution (an aqueous solution containing 2% sodium chloride, 1.75% ammonium chloride, 1.7% lactic acid, and 0.5% acetic acid, adjusted to pH 4.7 with sodium hydroxide) for 24 hours, then removed and dried at 23°C for 24 hours. The test specimens thus obtained, after being immersed in artificial sweat solution, were pulled at a tensile speed of 500 mm / min, and the tensile strength at fracture (TS2) was measured. The ratio (TS2 / TS1) of the tensile strength of the immersed test specimen to the tensile strength (TS1) of the unimmersed test specimen was calculated and evaluated according to the following criteria. A: The above ratio (TS2 / TS1) was 50% or more. B: The above ratio (TS2 / TS1) was less than 50%. A rating of A indicates excellent water resistance.

[0099] <Manufacturing Example 1 (Manufacturing of latex from carboxyl group-containing nitrile rubber (A-1))> In a pressure-resistant polymerization reaction vessel equipped with a stirrer, 64 parts of 1,3-butadiene, 29 parts of acrylonitrile, 7 parts of methacrylic acid, 0.25 parts of t-dodecyl mercaptan as a chain transfer agent, 132 parts of deionized water, 3 parts of sodium dodecylbenzenesulfonate, 1 part of sodium β-naphthalenesulfonic acid formalin condensate, 0.3 parts of potassium persulfate, and 0.005 parts of sodium ethylenediaminetetraacetate were charged, and polymerization was started while maintaining the polymerization temperature at 37°C. When the polymerization conversion rate reached 70%, the polymerization temperature was raised to 43°C and the reaction was continued until the polymerization conversion rate reached 95%. After that, 0.1 parts of sodium dimethyldithiocarbamate was added as a polymerization termination agent to stop the polymerization reaction. Then, unreacted monomers were removed from the obtained copolymer latex under reduced pressure, and the solid content concentration and pH were adjusted to obtain a carboxyl group-containing nitrile rubber (A-1) latex with a solid content of 40% by weight and a pH of 8.0. The composition of the obtained carboxyl group-containing nitrile rubber (A-1) was 64% by weight of 1,3-butadiene units, 29% by weight of acrylonitrile units, and 7% by weight of methacrylic acid units.

[0100] <Manufacturing Example 2 (Manufacturing of latex from carboxyl group-containing nitrile rubber (A-2))> Latex of carboxyl group-containing nitrile rubber (A-2) with a solid content of 40% by weight and pH 8.0 was obtained in the same manner as in Production Example 1, except that the amount of 1,3-butadiene used was changed from 64 parts to 60 parts, the amount of acrylonitrile used from 29 parts to 32 parts, and the amount of methacrylic acid used from 7 parts to 8 parts. The composition of the obtained carboxyl group-containing nitrile rubber (A-2) was 60% by weight of 1,3-butadiene units, 32% by weight of acrylonitrile units, and 8% by weight of methacrylic acid units.

[0101] <Manufacturing Example 3 (Manufacturing of latex from carboxyl group-containing nitrile rubber (A-3))> Latex of carboxyl group-containing nitrile rubber (A-3) with a solid content of 40% by weight and pH 8.0 was obtained in the same manner as in Production Example 1, except that the amount of 1,3-butadiene used was changed from 64 parts to 67.5 parts, the amount of acrylonitrile used from 29 parts to 26.5 parts, and the amount of methacrylic acid used from 7 parts to 6 parts. The composition of the obtained carboxyl group-containing nitrile rubber (A-3) was 67.5% by weight of 1,3-butadiene units, 26.5% by weight of acrylonitrile units, and 6% by weight of methacrylic acid units.

[0102] <Manufacturing Example 4 (Manufacturing of latex from carboxyl group-containing nitrile rubber (A-4))> Latex of carboxyl group-containing nitrile rubber (A-3) with a solid content of 40% by weight and pH 8.0 was obtained in the same manner as in Production Example 1, except that the amount of 1,3-butadiene used was changed from 64 parts to 67.5 parts, the amount of acrylonitrile used from 29 parts to 27 parts, and the amount of methacrylic acid used from 7 parts to 5.5 parts. The composition of the obtained carboxyl group-containing nitrile rubber (A-2) was 67.5% by weight of 1,3-butadiene units, 27% by weight of acrylonitrile units, and 5.5% by weight of methacrylic acid units.

[0103] <Example 1> <Preparation of latex composition> In the latex preparation for the latex, 250 parts (100 parts in terms of carboxyl group-containing nitrile rubber (A-1)) obtained in Production Example 1 were mixed with an aqueous solution containing 0.25 parts of sodium aluminate as a metal compound (B) containing a metal of trivalent or higher valency (C) and 0.75 parts of citric acid as a polyvalent carboxylic acid compound (C). Deionized water was then added to adjust the solid content concentration to 30% by weight to obtain a latex composition. The concentration of the carbodiimide compound in the obtained latex composition was 100 ppm or less. The obtained latex composition was stored at a temperature of 60°C for 24 hours.

[0104] <Dip molding> An aqueous coagulant solution was prepared by mixing 30 parts calcium nitrate, 0.05 parts polyethylene glycol octylphenyl ether (a nonionic emulsifier), and 70 parts water. Next, a ceramic glove mold (a ceramic glove mold with a roughened surface) that had been preheated to 70°C was immersed in this aqueous coagulant solution for 5 seconds. After removing it, it was dried at 70°C for 10 minutes to allow the coagulant to adhere to the glove mold. Then, the glove mold with the coagulant attached was immersed in the latex composition prepared above and stored for 24 hours for 10 seconds. After removing it, it was immersed in 50°C warm water for 90 seconds to dissolve water-soluble impurities and form a dip-molded layer on the glove mold. Next, the glove mold with the dip-molded layer was heat-treated at 60°C for 20 minutes to harden the dip-molded layer, obtaining a glove mold coated with a hardened dip-molded layer.

[0105] A chlorination treatment solution was prepared by adding 4.3 parts of a 5% sodium hypochlorite aqueous solution to 100 parts of water, then adding 0.6 parts of 36% hydrochloric acid dropwise and letting it stand for 30 minutes. The glove mold coated with the hardened dip molded layer prepared above was then immersed in the chlorination treatment solution for 120 seconds to perform the chlorination treatment. The glove mold coated with the chlorinated hardened dip molded layer was then immersed in 50°C hot water for 10 seconds and removed, then immersed in a 0.3% ammonia aqueous solution for 30 seconds and removed, and finally immersed in 50°C hot water for 60 seconds and removed. The chlorinated hardened dip molded layer, which had been washed in this manner, was dried at 50°C for 180 minutes and then peeled off the glove mold to obtain a dip molded body (glove). The above molding conditions are referred to as Condition 1 in Table 1. The film thickness of the obtained surface-treated dip molded product was 0.08 mm. The resulting dip-molded product (rubber glove) was evaluated for tensile strength and elongation at break according to the method described above. The results are shown in Table 1.

[0106] Furthermore, the resulting dip-molded products (rubber gloves) were obtained without the use of sulfur or sulfur-containing vulcanization accelerators, and in addition to immediate-type allergies (Type I), the occurrence of delayed-type allergies (Type IV) was also effectively suppressed (the same was true in other examples).

[0107] Furthermore, dip-molded products (rubber gloves) were obtained in the same manner as above, except that the storage time of the stored latex composition was changed from 24 hours to 14 days. Tensile strength, elongation at break, and water resistance (artificial sweat immersion test) were evaluated according to the method described above. Note that the storage condition of 60°C for 14 days is a test condition that assumes storage of the latex composition for a very long period of time. The results are shown in Table 1.

[0108] <Examples 2-5> A latex composition was prepared in the same manner as in Example 1, except that the types of carboxyl group-containing nitrile rubber (A-1) to (A-3) and the type of polycarboxylic acid compound (C) were changed to those listed in Table 1. Then, a dip-molded article (rubber glove) was obtained in the same manner as in Example 1, except that the obtained latex composition was used, and the tensile strength, elongation at break, and water resistance were evaluated according to the method described above. The results are shown in Table 1.

[0109] <Example 6> A latex composition was prepared in the same manner as in Example 1. Then, a glove mold coated with a cured dip-molded layer was obtained in the same manner as in Example 1, except that the curing conditions were changed from 60°C for 25 minutes to 120°C for 25 minutes. The obtained cured dip-molded layer was peeled off the glove mold to obtain a dip-molded body (rubber glove). The above molding conditions are referred to as Condition 2 in Table 1. The obtained dip-molded body (rubber glove) was then evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0110] <Comparative Example 1> To 250 parts of the carboxyl group-containing nitrile rubber (A-1) latex obtained in Production Example 1 (equivalent to 100 parts of carboxyl group-containing nitrile rubber (A-1)), an aqueous dispersion was added, which contained 1 part sulfur, 1.5 parts vulcanization accelerator (zinc dibutyldithiocarbamate), and 1.5 parts zinc oxide dispersed in water. Then, deionized water was added to adjust the solid content concentration to 30% by weight to obtain a latex composition.

[0111] Dip-molded articles (rubber gloves) were obtained in the same manner as in Example 1, except that the obtained latex composition was used, and their tensile strength, elongation at break, and water resistance were evaluated according to the method described above. The results are shown in Table 1.

[0112] <Comparative Example 2> A latex composition was prepared in the same manner as in Example 1, except that citric acid was not used. Then, a dip-molded product (rubber glove) was obtained in the same manner as in Example 1, except that the obtained latex composition was used, and the tensile strength, elongation at break, and water resistance were evaluated according to the method described above. The results are shown in Table 1.

[0113] <Comparative Example 3> A latex composition was prepared in the same manner as in Example 1, except that 0.75 parts of sorbitol were used instead of 0.75 parts of citric acid. Then, a dip-molded body (rubber glove) was obtained in the same manner as in Example 1, except that the obtained latex composition was used, and the tensile strength, elongation at break, and water resistance were evaluated according to the method described above. The results are shown in Table 1.

[0114] <Comparative Example 4> A latex composition was prepared in the same manner as in Example 1, except that 0.75 parts of a polyglycerin derivative (trade name "SY-Glyster CRS-75", manufactured by Sakamoto Pharmaceutical Co., Ltd.) and 3 parts of a carbodiimide compound (trade name "V-02-L2", manufactured by Nisshinbo Chemical Co., Ltd.) were used instead of 0.75 parts of citric acid. When the obtained latex composition was stored at 60°C for 14 days, excessive aggregation occurred, and the dip-molded layer could not be properly formed.

[0115] [Table 1]

[0116] As shown in Table 1, a latex composition containing a carboxyl group-containing conjugated diene rubber (A), a metal compound containing a trivalent or higher metal (B), and a polyvalent carboxylic acid compound (C), and substantially free of carbodiimide compounds, exhibited excellent storage stability, suppressed the occurrence of delayed-type allergies (Type IV) in addition to immediate-type allergies (Type I), and provided a film molded article with high tensile strength and large elongation at break with high production stability (Examples 1-6).

[0117] On the other hand, when sulfur, a vulcanization accelerator, and zinc oxide were incorporated without including a metal compound (B) containing a metal of trivalent or higher valency and a polycarboxylic acid compound (C), the resulting film-molded articles (especially those obtained after long-term storage of the latex composition) exhibited inferior elongation at break, and the occurrence of delayed-type allergies (Type IV) could not be suppressed (Comparative Example 1). Furthermore, when the polycarboxylic acid compound (C) was not included, the resulting film-molded articles (especially those obtained after long-term storage of the latex composition) exhibited inferior tensile strength (Comparative Examples 2-3). Furthermore, when a carbodiimide compound was included without the polycarboxylic acid compound (C), the storage stability was inferior (Comparative Example 4).

Claims

1. A latex of a carboxyl group-containing conjugated diene rubber (A), Metal compounds (B) containing metals with a valency of 3 or higher, It contains a polycarboxylic acid compound (C), A latex composition that is substantially free of carbodiimide compounds.

2. The latex composition according to claim 1, wherein the content of the polycarboxylic acid compound (C) to the content of the metal compound (B) containing a trivalent or higher metal is 1:0.3 to 1:10 in weight ratio of "metal compound (B) containing a trivalent or higher metal: polycarboxylic acid compound (C)".

3. The latex composition according to claim 1 or 2, wherein the content of the metal compound (B) containing a trivalent or higher metal, relative to 100 parts by weight of the carboxyl group-containing conjugated diene rubber (A), is 0.1 to 1.0 parts by weight.

4. The latex composition according to claim 1 or 2, wherein the content of ethylenically unsaturated carboxylic acid monomer units in the carboxyl group-containing conjugated diene rubber (A) is 5.5% by weight or more.

5. The latex composition according to claim 1 or 2, wherein the total number of groups consisting of carboxyl groups and salts of carboxyl groups within the molecule of the polycarboxylic acid compound (C) is 2 to 6.

6. The latex composition according to claim 1 or 2, wherein the molecular weight of the polycarboxylic acid compound (C) is 90 to 1000.

7. The latex composition according to claim 1 or 2, wherein the polycarboxylic acid compound (C) is at least one selected from adipic acid, citric acid, phthalic acid, and salts thereof.

8. A film-molded article comprising the latex composition according to claim 1 or 2.

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