WO2024181145A1 - Latex composition and film molded body - Google Patents

Abstract

Provided is a latex composition with which a film molded body that has high tensile strength and high elongation at break can be produced with high production stability, while ensuring excellent storage stability and a reduction in the occurrence of not only immediate allergy (Type I) but also delayed allergy (Type IV). Provided is a latex composition containing a latex of a carboxyl group-containing conjugated diene rubber (A), a metal compound (B) containing a trivalent or more metal, and a polyvalent carboxylic acid compound (C), but containing substantially no carbodiimide compound.

Description

Latex composition and film molded article

The present invention relates to a latex composition and a film molded body.

　Conventionally, latex compositions containing natural latex, such as natural rubber latex, have been dip molded into dip molded products such as nipples, balloons, gloves, balloons, and sacks that are used in contact with the human body. However, natural rubber latex contains proteins that cause symptoms of immediate allergy (Type I) in the human body, and so there have been some problems with dip molded products that come into direct contact with living mucous membranes or organs. Therefore, the use of synthetic rubber latex, such as nitrile rubber, has been considered.

For example, Patent Document 1 discloses a latex composition comprising an emulsion containing a carboxylated nitrile-butadiene random terpolymer of acrylonitrile, carboxylic acid, and butadiene, with a total solid content of 15 to 25% by weight, and containing zinc oxide, sulfur, and a vulcanization accelerator. However, while the technology of Patent Document 1 can prevent the occurrence of immediate-type allergies (Type I), when the film is formed, the sulfur and vulcanization accelerator contained in the film can cause delayed-type allergy (Type IV) symptoms when the film comes into contact with the human body.

In response to this, for example, Patent Document 2 discloses a technology in which a mixture of a trivalent metal or trivalent metal compound, a specific polyethylene glycol or polyethylene glycol derivative, and a specific hydroxide salt is used as the crosslinking agent in a latex composition containing at least one base polymer, a crosslinking agent, and a pH adjuster. This technology in Patent Document 2 does not contain sulfur or sulfur compounds that act as vulcanization accelerators, and therefore can suppress the occurrence of not only immediate-type allergies (Type I) but also delayed-type allergies (Type IV).

However, the latex composition of Patent Document 2 was unable to sufficiently achieve both storage stability and the tensile strength and elongation at break of the resulting film molded article.

Patent No. 5697578 WO 2016/72835

The present invention aims to provide a latex composition that has excellent storage stability, suppresses the occurrence of immediate-type allergies (Type I) as well as delayed-type allergies (Type IV), and can produce a film-shaped product with high tensile strength and large elongation at break with high production stability.

As a result of intensive research into solving the above problems, the inventors discovered that the above object could be achieved by blending a metal compound (B) containing a trivalent or higher metal and a polyvalent carboxylic acid compound (C) with a latex of a carboxyl group-containing conjugated diene rubber (A) while substantially not blending a carbodiimide compound, and thus completed the present invention.

That is, according to the present invention, there are provided the following latex composition and film molded article.
[1] A latex composition comprising a latex of 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 no carbodiimide compound.
[2] The latex composition according to [1], wherein the content of the polyvalent carboxylic acid compound (C) relative to the content of the metal compound (B) containing a trivalent or higher metal is in a weight ratio of 1:0.3 to 1:10 of "metal compound (B) containing a trivalent or higher metal:polyvalent carboxylic 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 part by weight based on 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 a content ratio of an ethylenically unsaturated carboxylic acid monomer unit 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 carboxyl groups and groups formed of a salt of a carboxyl group in the molecule of the polyvalent carboxylic acid compound (C) is 2 to 6.
[6] The latex composition according to any one of [1] to [5], wherein the polyvalent carboxylic acid compound (C) has a molecular weight of 90 to 1,000.
[7] The latex composition according to any one of [1] to [6], wherein the polyvalent carboxylic acid compound (C) is at least one selected from the group consisting of polyvalent carboxylic acids consisting of only hydrogen atoms, carbon atoms, and oxygen atoms, and salts thereof.
[8] The latex composition according to any one of [1] to [6], wherein the polyvalent carboxylic acid compound (C) is at least one selected from the group consisting of adipic acid, citric acid, phthalic acid, and salts thereof.
[9] The latex composition according to any one of [1] to [8], wherein the content of the polyvalent carboxylic acid compound (C) is 0.1 to 5 parts by weight based on 100 parts by weight of the carboxyl group-containing conjugated diene rubber (A).
[10] The latex composition according to any one of [1] to [9], wherein the carboxyl group-containing conjugated diene rubber (A) is at least one selected from the group consisting of a carboxyl group-containing nitrile rubber (a1), a carboxyl group-containing styrene-butadiene rubber (a2), and a carboxyl group-containing conjugated diene rubber (a3).
[11] A film formed from the latex composition according to any one of [1] to [10].

The present invention provides a latex composition that has excellent storage stability, suppresses the occurrence of immediate-type allergies (Type I) as well as delayed-type allergies (Type IV), and can produce film-shaped bodies with high tensile strength and large elongation at break with high production stability.

The latex composition of the present invention contains a latex of 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 is substantially free of a carbodiimide compound.

The latex composition may be subjected to molding after long-term storage. For example, the latex composition may be prepared, transported by ship or the like for a long period of time, and then subjected to 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 transport or the like, aggregation is suppressed and a good film molded product can be obtained. In addition, the latex composition of the present invention can provide a film molded product having 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 product having high tensile strength and large elongation at break can be obtained regardless of whether the storage period of the latex composition is relatively short or long.

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.

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 therewith, which are used as necessary.

Conjugated diene monomers include, for example, 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 alone or in combination of two or more kinds.

The content of the conjugated diene monomer units formed by the conjugated diene monomer in the carboxyl group-containing conjugated diene rubber (A) 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 the conjugated diene monomer units within the above range, storage stability can be further improved, and the obtained film molding can have higher tensile strength, higher elongation at break, and excellent water resistance. In addition, when extremely high tensile strength or extremely large elongation at break is required, the content of the 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.

The ethylenically unsaturated carboxylic acid monomer is not particularly limited as long as it is an ethylenically unsaturated monomer containing a carboxyl group, but examples thereof 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; ethylenically unsaturated polycarboxylic acid partial ester monomers such as monobutyl fumarate, monobutyl maleate, and mono-2-hydroxypropyl maleate; and the like. 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, the ethylenically unsaturated carboxylic acid monomers can be used alone or in combination of two or more.

The content of ethylenically unsaturated carboxylic acid monomer units formed by ethylenically unsaturated carboxylic acid monomers in the carboxyl group-containing conjugated diene rubber (A) 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 obtained film molding can have higher tensile strength, higher elongation at break, and excellent water resistance. In addition, 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.

Other ethylenically unsaturated monomers copolymerizable with the conjugated diene monomer and the ethylenically unsaturated carboxylic acid monomer include, for example, vinyl aromatic monomers such as styrene, alkylstyrene, and vinylnaphthalene; fluoroalkyl vinyl ethers such as fluoroethyl vinyl ether; ethylenically unsaturated nitrile monomers such as acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile, and α-cyanoethylacrylonitrile; ethylenically unsaturated amide monomers such as (meth)acrylamide, N-methylol (meth)acrylamide, N,N-dimethylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, and N-propoxymethyl (meth)acrylamide; methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, trifluoroethyl (meth)acrylate, and tetrafluoro (meth)acrylate. Ethylenically unsaturated carboxylic acid ester monomers such as propyl, 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, and dimethylaminoethyl (meth)acrylate; crosslinkable monomers such as divinylbenzene, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol (meth)acrylate; and the like. These ethylenically unsaturated monomers can be used alone or in combination of two or more.

The content 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, and even more preferably 0 to 40% by weight.

As the carboxyl group-containing conjugated diene rubber (A), at least one selected from the group consisting of a carboxyl group-containing nitrile rubber (a1), a carboxyl group-containing styrene-butadiene rubber (a2) and a carboxyl group-containing conjugated diene rubber (a3) is preferred.

The latex of the carboxyl group-containing nitrile rubber (a1) is a copolymer latex obtained by copolymerizing an ethylenically unsaturated nitrile monomer in addition to 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 monomers, which are used as necessary.

Conjugated diene monomers include, for example, those mentioned above, and among these, 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred. These conjugated diene monomers can be used alone or in combination of two or more. The content of conjugated diene monomer units formed by conjugated diene monomers in the carboxyl group-containing nitrile rubber (a1) is preferably 48 to 76% by weight, more preferably 49 to 70.5% by weight, even more preferably 50 to 70% by weight, and particularly preferably 50.5 to 70% by weight. By setting the content of the conjugated diene monomer units within the above range, storage stability can be further improved, and the obtained film molding can have higher tensile strength, 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 69.5% by weight or less, more preferably 69% by weight or less, even more preferably 68.5% by weight or less, and particularly preferably 68% by weight or less.

Examples of the ethylenically unsaturated carboxylic acid monomer include those mentioned above. 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. The ethylenically unsaturated carboxylic acid monomers can be used alone or in combination of two or more. The content of the ethylenically unsaturated carboxylic acid monomer unit formed by the ethylenically unsaturated carboxylic acid monomer 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 the ethylenically unsaturated carboxylic acid monomer unit within the above range, the storage stability can be further improved, and the obtained film molding can have higher tensile strength, 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.

The ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an ethylenically unsaturated monomer containing a nitrile group, and examples thereof include acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile, α-cyanoethylacrylonitrile, and the like. 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 the ethylenically unsaturated nitrile monomer unit formed by the ethylenically unsaturated nitrile monomer in the carboxyl group-containing nitrile rubber (a1) is preferably 20 to 40% by weight, more preferably 25 to 40% by weight. By setting the content of the ethylenically unsaturated nitrile monomer unit within the above range, the obtained film molding can have higher tensile strength, greater elongation at break, and excellent water resistance.

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

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.

The latex of the carboxyl group-containing styrene-butadiene rubber (a2) is a copolymer latex obtained by copolymerizing styrene in addition to 1,3-butadiene and an ethylenically unsaturated carboxylic acid monomer as a conjugated diene monomer, and may also be a copolymer latex obtained by copolymerizing other ethylenically unsaturated monomers copolymerizable with these monomers, which are used as necessary.

The content of butadiene units formed by 1,3-butadiene in the carboxyl group-containing styrene-butadiene rubber (a2) 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 molding can have higher tensile strength, higher elongation at break, and excellent water resistance. In addition, 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.

The ethylenically unsaturated carboxylic acid monomer is not particularly limited as long as it is an ethylenically unsaturated monomer containing a carboxyl group, but for example, the same as the latex of the carboxyl group-containing nitrile rubber (a1) described above can be used. The content ratio of the ethylenically unsaturated carboxylic acid monomer unit formed by the ethylenically unsaturated carboxylic acid monomer in the carboxyl group-containing styrene-butadiene rubber (a2) is preferably 4 to 12 wt%, more preferably 4.5 to 11 wt%, even more preferably 5 to 10 wt%, and particularly preferably 5 to 9.5 wt%. By setting the content ratio of the ethylenically unsaturated carboxylic acid monomer unit within the above range, it is possible to further improve storage stability, and the obtained film molding can have higher tensile strength, 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.

The content of styrene units formed by styrene in the carboxyl group-containing styrene-butadiene rubber (a2) 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 obtained film molding can have higher tensile strength, greater elongation at break, and excellent water resistance.

Conjugated diene monomers such as 1,3-butadiene, ethylenically unsaturated carboxylic acid monomers, and other ethylenically unsaturated monomers copolymerizable with styrene include, for example, those mentioned above (excluding 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.

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 may also be a copolymer latex obtained by copolymerizing other ethylenically unsaturated monomers copolymerizable with the above, which are used as necessary.

Conjugated diene monomers include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene. Any of these may be used alone as the conjugated diene monomer, or two or more of them may be used in combination.

The content of the conjugated diene monomer units formed by the conjugated diene monomer in the carboxyl group-containing conjugated diene rubber (a3) 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 the conjugated diene monomer units within the above range, storage stability can be further improved, and the obtained film molding can have higher tensile strength, higher elongation at break, and excellent water resistance. In addition, when extremely high tensile strength or extremely large elongation at break is required, the content of the 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.

The ethylenically unsaturated carboxylic acid monomer is not particularly limited as long as it is an ethylenically unsaturated monomer containing a carboxyl group, but for example, the same as the latex of the carboxyl group-containing nitrile rubber (a1) described above can be used. The content ratio of the ethylenically unsaturated carboxylic acid monomer unit formed by the ethylenically unsaturated carboxylic acid monomer in the carboxyl group-containing conjugated diene rubber (a3) is preferably 4 to 12 wt%, more preferably 4.5 to 11 wt%, even more preferably 5 to 10 wt%, and particularly preferably 5 to 9.5 wt%. By setting the content ratio of the ethylenically unsaturated carboxylic acid monomer unit within the above range, it is possible to further improve storage stability, and the obtained film molding can have higher tensile strength, 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.

Other ethylenically unsaturated monomers copolymerizable with the conjugated diene monomer and the ethylenically unsaturated carboxylic acid monomer 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.

The latex of 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 a method of copolymerization by emulsion polymerization is preferable. As the emulsion polymerization method, a conventionally known method can be used.

When emulsion polymerizing a monomer mixture containing the above-mentioned monomers, commonly used polymerization auxiliary materials such as emulsifiers, polymerization initiators, and molecular weight regulators can be used. There are no particular limitations on the method of adding these polymerization auxiliary materials, and any method such as initial lump-sum addition, divided addition, or continuous addition may be used.

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

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

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

The amount of water used during 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 monomers used.

Methods for adding monomers include, for example, adding the monomers to be used in a single batch to the reaction vessel, adding them continuously or intermittently as the polymerization progresses, or adding a portion of the monomers and reacting them to a specific conversion rate, and then polymerizing by adding the remaining monomers continuously or intermittently. Any of these methods may be used. When the monomers are mixed and added continuously or intermittently, the composition of the mixture may be constant or may be changed. Furthermore, the various monomers to be used may be mixed in advance and then added to the reaction vessel, or each monomer may be added to the reaction vessel separately.

Furthermore, if necessary, polymerization auxiliary materials such as chelating agents, dispersants, pH adjusters, oxygen scavengers, particle size adjusters, etc. can be used, and there are no particular limitations on the type or amount used.

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 about 5 to 40 hours.

The monomer mixture is emulsion polymerized as described above, and when a predetermined polymerization conversion rate is reached, the polymerization reaction is stopped by cooling the polymerization system or adding a polymerization terminator. The polymerization conversion rate when the polymerization reaction is stopped is preferably 90% by weight or more, and more preferably 93% by weight or more.

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

After the polymerization reaction is stopped, if desired, the unreacted monomers can be removed and the solids concentration and pH adjusted to obtain a latex of the carboxyl group-containing conjugated diene rubber (A).

In addition, antioxidants, preservatives, antibacterial agents, dispersants, etc. may be appropriately added to the latex of the carboxyl group-containing conjugated diene rubber (A) used in the present invention, as necessary.

The number average particle diameter 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 diameter can be adjusted to the desired value by, for example, adjusting the amounts of the emulsifier and polymerization initiator used.

Metal compound containing a trivalent or higher metal (B)
The latex composition of the present invention contains, in addition to the latex of 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.

In accordance with the present invention, instead of sulfur, which is normally used as a crosslinking agent, a metal compound (B) containing a trivalent or higher metal is used as the crosslinking agent, and furthermore, since no sulfur-containing vulcanization accelerator is required for crosslinking, the occurrence of delayed-type allergies (Type IV) caused by sulfur or sulfur-containing vulcanization accelerators can be effectively suppressed in addition to immediate-type allergies (Type I).

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

The metal compound (B) containing a trivalent or higher metal may be any compound containing a trivalent or higher metal, and may include, but is not limited to, aluminum compounds, cobalt compounds, zirconium compounds, titanium compounds, etc. Among these, aluminum compounds are preferred because they can more effectively cure the carboxyl group-containing conjugated diene rubber (A) contained in the latex.

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

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 obtained film molding can have higher tensile strength, greater elongation at break, and excellent water resistance.

Polycarboxylic acid compound (C)
The latex composition of the present invention contains the above-mentioned latex of the carboxyl group-containing conjugated diene rubber (A) and the metal compound (B) containing a trivalent or higher metal, as well as a polyvalent carboxylic acid compound (C).

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

In the present disclosure, the 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 groups consisting of carboxyl groups and salts of carboxyl groups in the molecule is 2 or more. The total number of groups consisting of carboxyl groups and salts of carboxyl groups in the molecule of the polycarboxylic acid compound (C) is preferably 2 to 6, more preferably 2 to 4, even more preferably 2 to 3, and particularly preferably 2.

Salts of carboxyl groups include salts of carboxyl groups with alkali metals such as sodium and potassium; salts of carboxyl groups with alkaline earth metals such as calcium and magnesium; salts of carboxyl groups with oniums such as ammonium; and so on.

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.

The number of carbon atoms in the polyvalent carboxylic 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.

The total number of groups consisting of carboxyl groups and salts of carboxyl groups relative to the molecular weight of the polyvalent carboxylic acid compound (C) (total number of carboxyl groups and their salts/molecular weight) 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.

The polycarboxylic acid compound (C) may have a heteroatom other than oxygen, but preferably has no heteroatoms other than oxygen. The polycarboxylic acid compound (C) is preferably at least one selected from the group consisting of polycarboxylic acids consisting only of hydrogen atoms, carbon atoms, and oxygen atoms, and salts thereof, and is more preferably a polycarboxylic acid consisting only of hydrogen atoms, carbon atoms, and oxygen atoms.

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 salts thereof; saturated aliphatic polycarboxylic acids containing alcoholic hydroxyl groups, such as malic acid, tartronic acid, 3-methylmalic acid, tartaric acid, citramalic acid, citric acid, and isocitric acid, and salts thereof; ethylenically unsaturated aliphatic polycarboxylic acids, such as maleic acid, fumaric acid, itaconic acid, and aconitic acid, and salts thereof; aromatic polycarboxylic acid compounds, such as phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid, trimellitic acid, trimesic acid, prenitic acid, meropenic acid, pyromellitic acid, benzenepentacarboxylic acid, mellitic acid, and o-phenylene diacetic acid, and salts thereof; and the like. The polycarboxylic acid compounds (C) can be used alone or in combination of two or more.

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, with adipic acid, citric acid, phthalic acid, and salts thereof being more preferred.

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 obtained film molding can have higher tensile strength, greater elongation at break, and excellent water resistance.

In the latex composition of the present invention, the content of the polycarboxylic acid compound (C) relative to the content of the 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 the polycarboxylic acid compound (C) relative to the metal compound (B) containing a trivalent or higher metal within the above range, storage stability can be further improved, and the obtained film molded body can have higher tensile strength, greater elongation at break, and excellent water resistance.

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

The sugar (d1) may be a monosaccharide or a polysaccharide in which two or more monosaccharides are linked by a glycosidic bond, and is not particularly limited thereto. Examples of the sugar include monosaccharides such as erythrose, threose, ribose, lyxose, xylose, arabinose, allose, talose, gulose, altrose, galactose, idose, erythrulose, xylulose, ribulose, psicose, fructose, sorbose, and tagatose; trehalose, maltose, isomaltose, cellobiose, gentiobiose, melibiose, lactose, sucrose, palatinose, and the like. disaccharides such as maltotriose, isomaltotriose, panose, cellotriose, manninotriose, solatriose, melezitose, planteose, gentianose, umbelliferose, lactosucrose, raffinose, and the like; homooligosaccharides such as maltotetraose and isomaltotetraose; tetrasaccharides such as stachyose, cellotetraose, scorodose, lyquinose, and panose; pentasaccharides such as maltopentaose and isomaltopentaose; and hexasaccharides such as maltohexaose and isomaltohexaose. These may be used alone or in combination of two or more.

The sugar alcohol (d2) may be a monosaccharide or polysaccharide sugar alcohol, and is not particularly limited. Examples of the sugar alcohol include tritols such as glycerin; tetritols such as erythritol, D-threitol, and L-threitol; pentitols such as D-arabinitol, L-arabinitol, xylitol, ribitol, and pentaerythritol; pentaerythritol; hexitols such as sorbitol, D-iditol, galactitol, D-glucitol, and mannitol; heptitols such as volemitol and perseitol; and octitols such as D-erythro-D-galacto-octitol. These may be used alone or in combination of two or more. Of these, hexitols, which are sugar alcohols having six carbon atoms, are preferred, and sorbitol is more preferred.

The alcoholic hydroxyl group-containing monocarboxylic acid compound (d3) may be a monocarboxylic acid having a hydroxyl group or a salt thereof, and is not particularly limited. Examples of the monocarboxylic acid compound (d3) include aliphatic hydroxy acids such as glycolic acid, lactic acid, glyceric acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, γ-hydroxybutyric acid, leucinic acid, mevalonic acid, pantoic acid, ricinoleic acid, ricinelaidic acid, cerebronic acid, quinic acid, shikimic acid, and serine; salicylic acid, creosote acid (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 hydroxypropyl ... Examples of the aromatic hydroxy acids include undecanoic acid, hydroxydodecanoic acid, hydroxytridecanoic acid, hydroxytetradecanoic acid, hydroxypentadecanoic acid, hydroxyheptadecanoic acid, hydroxyoctadecanoic acid, hydroxynonadecanoic acid, hydroxyicosanoic acid, and ricinoleic acid derivatives, dihydroxybenzoic acid derivatives such as pyrocatechuic acid, resorcylic acid, protocatechuic acid, gentisic acid, and orselliic acid, trihydroxybenzoic acid derivatives such as gallic acid, phenylacetic acid derivatives such as mandelic acid, benzilic acid, and atrolactic acid, and cinnamic acid and hydrocinnamic acid derivatives such as mellitic acid, phloretic acid, coumaric acid, umbellic acid, caffeic acid, ferulic acid, and sinapic acid; and salts thereof. Examples of the salts include salts of alkali metals such as sodium and potassium; salts of alkaline earth metals such as calcium and magnesium; salts of oniums such as ammonium; and the like. These may be used alone 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 its salts are particularly preferred.

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 is within a range that does not impede the effects of the present invention, but it 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).

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

Carbodiimide compounds include compounds having a carbodiimide group and polycarbodiimide. "Substantially free of carbodiimide compounds" specifically means that the concentration of carbodiimide compounds in the latex composition (the total concentration of compounds having a carbodiimide group and polycarbodiimide) is 1000 ppm or less, preferably 100 ppm or less.

The latex composition of the present invention may further contain fillers, pH adjusters, thickeners, antioxidants, dispersants, pigments, softeners, etc.

The latex composition of the present invention can be obtained, for example, by blending a metal compound (B) containing a trivalent or higher metal, a polyvalent carboxylic acid compound (C), and various compounding agents used as necessary with a latex of a carboxyl group-containing conjugated diene rubber (A). The method of blending the metal compound (B) containing a trivalent or higher metal and the polyvalent carboxylic acid compound (C) with the latex of a carboxyl group-containing conjugated diene rubber (A) is not particularly limited, but it is preferable to dissolve the metal compound (B) containing a trivalent or higher metal and the polyvalent carboxylic acid compound (C) in water or alcohol and add them in the form of an aqueous solution or alcohol solution, since this allows the metal compound (B) containing a trivalent or higher metal and the polyvalent carboxylic acid compound (C) to be well dispersed in the resulting latex composition.

The solids concentration of the latex composition of the present invention is preferably 10 to 50% by weight, more preferably 10 to 40% by weight. That is, the proportion of water in the latex composition of the present invention is preferably 50 to 90% by weight, more preferably 60 to 90% by weight. The pH of the latex composition of the present invention is preferably 8.0 to 12, more preferably 8.5 to 11.

The film molded article of the present invention is a film-shaped 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.

The film molded body of the present invention is not particularly limited, but is preferably a dip molded body obtained by dip molding the latex composition of the present invention. Dip molding is a method in which a dip molding mold is immersed in the latex composition, the composition is deposited on the surface of the dip molding mold, the dip molding mold is then lifted out of the composition, and the composition deposited on the surface of the dip molding mold is then dried. The dip molding mold may be preheated before being immersed in the latex composition. Furthermore, a coagulant may be used as necessary before the dip molding mold is immersed in the latex composition or after the dip molding mold is lifted out of the latex composition.

Specific examples of methods for using a coagulant include a method in which the mold before being immersed in the latex composition is immersed in a solution of the coagulant to adhere the coagulant to the mold (anodic adhesion immersion method), and a method in which the mold on which the latex composition has been deposited is immersed in a coagulant solution (Teague adhesion immersion method). The anodic adhesion immersion method is preferred because it produces a dip-molded body with minimal thickness unevenness.

The coagulant may, for example, be metal halides such as barium chloride, calcium chloride, magnesium chloride, zinc chloride, or aluminum chloride; nitrates such as barium nitrate, calcium nitrate, or zinc nitrate; acetates such as barium acetate, calcium acetate, or zinc acetate; or sulfates such as calcium sulfate, magnesium sulfate, or aluminum sulfate. Of these, calcium chloride and calcium nitrate are preferred. The coagulant is usually used as a solution in water, alcohol, or a mixture thereof. The coagulant concentration is usually 5 to 50% by weight, and preferably 10 to 35% by weight.

If the dip-molded product is a glove or other such product that requires beading (rolling of sleeves) on the sleeves, the dip-molded layer may be beaded to form the beading portion (rolling of sleeves).

The dip-molded layer obtained is usually cured by heating. Before heating, the dip-molded layer may be immersed in water, preferably in warm water at 30 to 70°C, for about 1 to 60 minutes to remove water-soluble impurities (such as excess emulsifier and coagulant). The operation of removing water-soluble impurities may be performed after the dip-molded layer has been heat-treated, but it is preferable to perform the operation before heat treatment in order to remove water-soluble impurities more efficiently.

The dip-molded layer is generally cured by a heat treatment at a temperature of 100 to 150°C. On the other hand, the dip-molded layer made of the latex composition of the present invention can provide a film molded body having high tensile strength and large elongation at break even when it is heated and cured at a relatively low temperature. The heating temperature when the dip-molded layer made of the latex composition of the present invention is heated at a relatively low 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 of 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 necessary. The heating time is preferably 10 to 130 minutes, more preferably 20 to 100 minutes. The heating method can be external heating using infrared rays or heated air, or internal heating using high frequency waves. Of these, external heating using heated air is preferred.

After the dip-molded layer is cured, a halogenation treatment may be performed by contacting a halogenating agent with the surface of the cured dip-molded layer. In particular, when the dip-molded layer is cured by heating at a relatively low temperature, it is preferable to perform a halogenation treatment. As the halogen in the halogenating agent, chlorine, bromine, and iodine are preferable, and chlorine is more preferable because of its high reactivity and ease of handling. In other words, it is particularly preferable to perform a chlorination treatment by contacting a chlorinating agent with the surface of the cured dip-molded layer. Since the film molded body of the present invention is obtained using the latex composition of the present invention, it has high tensile strength and large elongation at break even when it is subjected to a halogenation treatment.

Halogenating agents include halogenated gases containing gaseous halogens and halogenated liquids in which halogens are dispersed or dissolved in liquid. Among these, it is preferable to use halogenated liquids from the viewpoint of easily bringing the dip-molded layer into contact with the halogenating agent.

The medium in which the halogen is dispersed or dissolved is not particularly limited, but water is preferred. Methods for dispersing or dissolving the halogen in the liquid medium include a method in which the halogen is directly injected into the medium, and a method in which a compound that generates the halogen is reacted in the medium to generate the halogen. The halogen concentration in the halogenating liquid 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.

The preferred method for preparing the halogenated liquid is to add sodium hypochlorite and hydrochloric acid to water to generate chlorine. There are no particular limitations on the concentrations of sodium hypochlorite and hydrochloric acid as long as they generate the above-mentioned preferred concentrations of chlorine in water, but 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.

When a halogenated gas is used, the method of contacting the surface of the dip-molded layer after hardening with a halogenating agent can be, for example, a method of placing the dip-molded layer in a chamber filled with halogenated gas for a specified time. When a halogenated liquid is used, the method can be, for example, a method of immersing the dip-molded layer in the halogenated liquid, or a method of spraying the halogenated liquid onto the dip-molded layer in a shower or mist form. Of these, the method of immersing the dip-molded layer in the halogenated liquid is preferred from the viewpoint of being able to contact the dip-molded layer with the halogenating agent using simple equipment.

After the halogenation treatment, it is preferable to carry out a neutralization treatment using an alkaline aqueous solution such as an aqueous ammonia solution. It is also preferable to carry out a cleaning treatment using a cleaning liquid to remove unreacted halogen from the dip-molded layer after the halogenation treatment. The order of these treatments is not particularly limited, and each treatment may be carried out multiple times. Methods for the neutralization treatment and cleaning treatment include a method of immersing the dip-molded layer in an alkaline aqueous solution or cleaning liquid, and a method of spraying the alkaline aqueous solution or cleaning liquid onto the dip-molded layer in a shower or mist form. Among these, the method of immersing the dip-molded layer in an alkaline aqueous solution or cleaning liquid is preferable from the viewpoint of being able to carry out the treatment using simple equipment.

Then, the dip-molded layer after hardening or the dip-molded layer after halogenation treatment is detached from the dip-molding mold to obtain a dip-molded body as a film-molded body. The detachment method can be peeling from the mold by hand or by using water pressure or compressed air pressure. After detachment, a further heat treatment at a temperature of 60 to 120°C for 10 to 120 minutes can be performed.

The film molded article of the present invention may be obtained by any method other than the above-mentioned method of dip molding the latex composition of the present invention, as long as it is a method (e.g., a coating method) that can mold the above-mentioned latex composition of the present invention into a film.

The film molded product of the present invention is obtained using the latex composition of the present invention described above, and therefore the occurrence of delayed allergies (Type IV) as well as immediate allergies (Type I) is suppressed, and the film molded product has high tensile strength and large elongation at break. Therefore, the film molded product of the present invention is suitable for gloves for medical, surgical, food, or industrial applications. Alternatively, the film molded product of the present invention can be used for medical products such as baby bottle nipples, droppers, tubes, water pillows, balloon sacks, catheters, and condoms; toys such as balloons, dolls, and balls; industrial products such as pressure molding bags and gas storage bags; finger cots, etc., in addition to gloves.

The present invention will be explained below in more detail with reference to examples, but the present invention is not limited to these examples. In the following, "parts" are by weight unless otherwise specified. Tests and evaluations were performed according to the following.

<Tensile strength and elongation at break>
A dumbbell-shaped test piece was prepared from the dip-molded product (glove) released from the glove mold using a dumbbell (Die-C: manufactured by Dumbbell Co., Ltd.) according to ASTM D-412. The obtained test piece was then pulled at a pulling speed of 500 mm/min to measure the tensile strength and elongation at break. The larger the values of tensile strength and elongation at break, the more preferable.

<Water resistance (artificial sweat immersion test)>
The tensile strength (TS ₁ ) of the test piece that was not immersed in the artificial sweat was determined by the above method. In addition, a new dumbbell-shaped test piece was prepared by the above method. The test piece was immersed in artificial sweat (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. The test piece thus obtained, which had been immersed in artificial sweat, was pulled at a pulling speed of 500 mm/min, and the tensile strength at break ( _TS2 ) was The ratio of the tensile strength (TS ₂ ) of the test piece immersed in the artificial sweat to the tensile strength (TS ₁ ) of the test piece not immersed in the artificial sweat was calculated as TS ₂ /TS ₁ ) was calculated and evaluated according to the following criteria.
A: The ratio (TS ₂ /TS ₁ ) was 50% or more.
B: The ratio (TS ₂ /TS ₁ ) was less than 50%.
When the above evaluation is A, it can be determined that the water resistance is excellent.

<Production Example 1 (Production of Latex of Carboxyl Group-Containing Nitrile Rubber (A-1))>
Into 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-naphthalenesulfonate formalin condensate, 0.3 parts of potassium persulfate, and 0.005 parts of sodium ethylenediaminetetraacetate were charged, and polymerization was started by maintaining the polymerization temperature at 37° C. Then, 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%, and then 0.1 parts of sodium dimethyldithiocarbamate was added as a polymerization terminator to terminate the polymerization reaction. Then, unreacted monomers were distilled off from the obtained copolymer latex under reduced pressure, and the solid content and pH were adjusted to obtain a latex of a carboxyl group-containing nitrile rubber (A-1) having 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.

<Production Example 2 (Production of Latex of Carboxyl Group-Containing Nitrile Rubber (A-2))>
A latex of a carboxyl group-containing nitrile rubber (A-2) having a solid content concentration of 40% by weight and a pH of 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 was changed from 29 parts to 32 parts, and the amount of methacrylic acid used was changed 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.

<Production Example 3 (Production of latex of carboxyl group-containing nitrile rubber (A-3))>
A latex of a carboxyl group-containing nitrile rubber (A-3) having a solid content concentration of 40% by weight and a pH of 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 was changed from 29 parts to 26.5 parts, and the amount of methacrylic acid used was changed 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.

<Production Example 4 (Production of Latex of Carboxyl Group-Containing Nitrile Rubber (A-4))>
A latex of a carboxyl group-containing nitrile rubber (A-3) having a solid content concentration of 40% by weight and a pH of 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 was changed from 29 parts to 27 parts, and the amount of methacrylic acid used was changed 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.

Example 1
<Preparation of latex composition>
A mixed aqueous solution of 0.25 parts of sodium aluminate as a metal compound (B) containing a trivalent or higher metal and 0.75 parts of citric acid as a polyvalent carboxylic acid compound (C) was added to 250 parts of the latex of the carboxyl group-containing nitrile rubber (A-1) obtained in Production Example 1 (100 parts in terms of carboxyl group-containing nitrile rubber (A-1)). 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 same was true in Examples 2 to 5 and Comparative Examples 1 to 3 described below.) The obtained latex composition was stored at a temperature of 60° C. for 24 hours.

<Dip molding>
A coagulant aqueous solution was prepared by mixing 30 parts of calcium nitrate, 0.05 parts of polyethylene glycol octylphenyl ether, which is a nonionic emulsifier, and 70 parts of water. Next, a ceramic glove mold (a ceramic glove mold with a roughened surface) preheated to 70°C was immersed in this coagulant aqueous solution for 5 seconds, pulled out, and then dried at a temperature of 70°C for 10 minutes to attach the coagulant 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, pulled out, and then immersed in hot water at 50°C for 90 seconds to elute water-soluble impurities, thereby forming a dip-molded layer on the glove mold. Next, the glove mold with the dip-molded layer formed was heat-treated at a temperature of 60°C for 20 minutes to harden the dip-molded layer, and a glove mold covered with a hardened dip-molded layer was obtained.

A chlorination treatment liquid was prepared by adding 4.3 parts of a 5% aqueous solution of sodium hypochlorite to 100 parts of water, dropping 0.6 parts of 36% hydrochloric acid, and leaving it for 30 minutes. The glove mold covered with the cured dip molding layer obtained above was immersed in the chlorination treatment liquid for 120 seconds to perform chlorination treatment. The glove mold covered with the chlorinated cured dip molding layer was immersed in hot water at 50°C for 10 seconds, then pulled out, immersed in a 0.3% aqueous ammonia solution for 30 seconds, then pulled out, and further immersed in hot water at 50°C for 60 seconds, then pulled out. The chlorinated cured dip molding layer washed in this way was dried at a temperature of 50°C for 180 minutes, and then peeled off from 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 molding was 0.08 mm. The tensile strength and elongation at break of the obtained dip-molded product (rubber glove) were evaluated according to the above-mentioned method. The results are shown in Table 1.

The dip-molded product (rubber glove) obtained was obtained without using sulfur or a sulfur-containing vulcanization accelerator, and in addition to immediate-type allergy (Type I), the occurrence of delayed-type allergy (Type IV) was also effectively suppressed (the same was true for other examples).

In addition, 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, and the tensile strength, elongation at break, and water resistance (artificial sweat immersion test) were evaluated according to the above method. The storage conditions of 60°C for 14 days are test conditions assuming the storage of the latex composition for a very long period of time. The results are shown in Table 1.

<Examples 2 to 5>
A latex composition was prepared in the same manner as in Example 1, except that the types of carboxyl group-containing nitrile rubbers (A-1) to (A-3) and the type of polyvalent carboxylic acid compound (C) were changed to those shown in Table 1. 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 above-mentioned methods. The results are shown in Table 1.

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

<Comparative Example 1>
An aqueous dispersion in which 1 part of sulfur, 1.5 parts of a vulcanization accelerator (zinc dibutyldithiocarbamate), and 1.5 parts of zinc oxide were dispersed in water was added to 250 parts of the latex of the carboxyl group-containing nitrile rubber (A-1) obtained in Production Example 1 (100 parts calculated as the carboxyl group-containing nitrile rubber (A-1)). Deionized water was then added to the mixture to adjust the solid content concentration to 30% by weight, thereby obtaining a latex composition.

　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 above-mentioned methods. The results are shown in Table 1.

<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 above-mentioned methods. The results are shown in Table 1.

<Comparative Example 3>
A latex composition was prepared in the same manner as in Example 1, except that 0.75 parts of sorbitol was used instead of 0.75 parts of citric acid. 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 above-mentioned methods. The results are shown in Table 1.

<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 (product name "SY-Glyster CRS-75", manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.) and 3 parts of a carbodiimide compound (product 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 a dip-molded layer could not be properly formed.

As shown in Table 1, the latex composition, which contains a latex of 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 does not substantially contain a carbodiimide compound, has excellent storage stability, suppresses the occurrence of immediate-type allergies (Type I) as well as delayed-type allergies (Type IV), and can produce a film molded product with high tensile strength and large elongation at break with high production stability (Examples 1 to 6).

On the other hand, in the case where sulfur, a vulcanization accelerator and zinc oxide were blended without blending the metal compound (B) containing a trivalent or higher metal and the polyvalent carboxylic acid compound (C), the elongation at break of the obtained film molded product (particularly, the film molded product obtained after storing the latex composition for a long period of time) was inferior, and the occurrence of delayed-type allergy (Type IV) could not be suppressed (Comparative Example 1).
In addition, when the polyvalent carboxylic acid compound (C) was not blended, the tensile strength of the obtained film molded article (particularly, the film molded article obtained after storing the latex composition for a long period of time) was inferior (Comparative Examples 2 to 3).
Furthermore, when the polyvalent carboxylic acid compound (C) was not blended but the carbodiimide compound was blended, the storage stability was poor (Comparative Example 4).

Claims (11)

1. A latex of a carboxyl group-containing conjugated diene rubber (A),
   A metal compound (B) containing a trivalent or higher metal;
   A polyvalent carboxylic acid compound (C),
   A latex composition that is substantially free of a carbodiimide compound.
2. The latex composition according to claim 1, wherein the content of the polyvalent carboxylic acid compound (C) relative to the content of the metal compound (B) containing a trivalent or higher metal is 1:0.3 to 1:10 in terms of the weight ratio of "metal compound (B) containing a trivalent or higher metal:polyvalent carboxylic 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 is 0.1 to 1.0 part 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 claims 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 claims 1 to 4, wherein the total number of groups consisting of carboxyl groups and salts of carboxyl groups in the molecule of the polyvalent carboxylic acid compound (C) is 2 to 6.
6. The latex composition according to any one of claims 1 to 5, wherein the molecular weight of the polyvalent carboxylic acid compound (C) is 90 to 1000.
7. The latex composition according to any one of claims 1 to 6, wherein the polycarboxylic acid compound (C) is at least one selected from the group consisting of polycarboxylic acids consisting of only hydrogen atoms, carbon atoms, and oxygen atoms, and salts thereof.
8. The latex composition according to any one of claims 1 to 7, wherein the polyvalent carboxylic acid compound (C) is at least one selected from the group consisting of adipic acid, citric acid, phthalic acid, and salts thereof.
9. The latex composition according to any one of claims 1 to 8, wherein the content of the polyvalent carboxylic acid compound (C) is 0.1 to 5 parts by weight per 100 parts by weight of the carboxyl group-containing conjugated diene rubber (A).
10. The latex composition according to any one of claims 1 to 9, wherein the carboxyl group-containing conjugated diene rubber (A) is at least one selected from the group consisting of carboxyl group-containing nitrile rubber (a1), carboxyl group-containing styrene-butadiene rubber (a2), and carboxyl group-containing conjugated diene rubber (a3).
11. A film-formed body made of the latex composition according to any one of claims 1 to 10.