JP7476542B2 - Latex composition for dip molding and dip molded article - Google Patents

Description

The present invention relates to a latex composition for dip molding, and more specifically, to a latex composition for dip molding that can suppress dripping during molding and give a dip molded product with excellent oil grip properties.

Traditionally, protective gloves that have improved solvent resistance, grip, abrasion resistance, etc., by covering textile gloves with rubber or resin have been used for a variety of purposes, including manufacturing work in factories, light work, construction work, and agricultural work.

Since such protective gloves are usually used in contact with the human body, they are required to have excellent mechanical strength, such as abrasion resistance, durability, as well as excellent flexibility.

For example, Patent Document 1 discloses a method for manufacturing a laminate, which includes a coagulant solution application step of applying a coagulant solution to a fiber substrate, and a coagulation step of contacting a polymer latex with the fiber substrate to which the coagulant solution has been applied to coagulate the polymer and thereby forming a polymer layer on the fiber substrate, and uses as the coagulant solution a solution obtained by dissolving or dispersing 0.2 to 7.0% by weight of a metal salt as a coagulant and 0.1 to 7.0% by weight of an organic acid in a solvent.

International Publication No. 2018/061868

The technology of Patent Document 1 above provides a laminate that is excellent in flexibility and abrasion resistance and is suitable for use in protective gloves. However, there is room for improvement in grip performance when wet with oil (i.e., oil grip performance), and further improvement is required from the viewpoint of suitable use in applications where the product is wet with oil. In addition, from the viewpoint of preventing molding defects and contamination of manufacturing equipment, it is also required to suppress dripping during molding.

The present invention has been made in consideration of these circumstances, and aims to provide a latex composition for dip molding that can suppress dripping during molding and give a dip molded article with excellent oil grip properties. Another aim of the present invention is to provide a dip molded article obtained using such a latex composition for dip molding.

As a result of intensive research by the inventors to solve the above problems, they discovered that a dip molding latex composition containing a latex of a conjugated diene polymer (A) having a glass transition temperature of 10°C or less, a latex of a polymer (B) having a glass transition temperature of more than 10°C, and a thickener and having a solids concentration of 42% by weight or more and 55% by weight or less can suppress dripping during molding and can give a dip molded product with excellent oil grip properties, thus completing the present invention.

That is, according to the present invention, a latex composition for dip molding is provided that contains a latex of a conjugated diene polymer (A) having a glass transition temperature of 10°C or less, a latex of a polymer (B) having a glass transition temperature of more than 10°C, and a thickener, and has a solids concentration of 42% by weight or more and 55% by weight or less.

In the dip molding latex composition of the present invention, the thickener preferably has an acid amount of 2.5 mmol/g or less.
In the dip molding latex composition of the present invention, the solid content is preferably 43.5% by weight or more and 55% by weight or less.
In the dip molding latex composition of the present invention, the conjugated diene polymer (A) is preferably a nitrile group-containing conjugated diene polymer.
In the dip molding latex composition of the present invention, the content of the conjugated diene polymer (A) is preferably 40 parts by weight or more in 100 parts by weight of the polymer component.
In the dip molding latex composition of the present invention, the glass transition temperature of the polymer (B) is preferably 30° C. or higher, and more preferably 50° C. or higher.
In the dip molding latex composition of the present invention, the polymer (B) preferably contains a monomer unit having a halogen atom.
In the dip molding latex composition of the present invention, the polymer (B) is preferably a vinyl chloride resin.
In the dip molding latex composition of the present invention, the vinyl chloride resin preferably does not contain a plasticizer.
The dip molding latex composition of the present invention preferably further contains a sulfur-based crosslinking agent.

According to the present invention, there is also provided a dip-molded article obtained by using the above-mentioned latex composition for dip molding.
Furthermore, according to the present invention, there is provided a dip-molded article obtained by immersing a substrate in the above-mentioned latex composition for dip molding.
In the dip-molded article of the present invention, the polymer layer made of the latex composition for dip molding preferably has a thickness of 0.05 to 1.0 mm.

The present invention provides a latex composition for dip molding that can suppress dripping during molding and give a dip molded article with excellent oil grip properties, as well as a dip molded article obtained using such a latex composition for dip molding.

FIG. 1 is a graph showing an example of a hydrochloric acid amount-electrical conductivity curve obtained when measuring the acid amount of a water-soluble polymer.

<Latex composition for dip molding>
The dip molding latex composition of the present invention contains a latex of a conjugated diene polymer (A) having a glass transition temperature of 10° C. or lower, a latex of a polymer (B) having a glass transition temperature of more than 10° C., and a thickener, and has a solid content concentration of 42% by weight or more and 55% by weight or less.

The conjugated diene polymer (A) having a glass transition temperature of 10°C or less (hereinafter referred to as "conjugated diene polymer (A)") constituting the latex of the conjugated diene polymer (A) having a glass transition temperature of 10°C or less (hereinafter referred to as "latex of conjugated diene polymer (A)") is not particularly limited as long as it is a polymer having units derived from a conjugated diene monomer, and examples thereof include nitrile rubber (NBR), natural rubber (NR), styrene-butadiene rubber (SBR), synthetic polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-isoprene copolymer rubber, and styrene-isoprene-styrene copolymer rubber. Among these, synthetic rubber is preferred from the viewpoint of making the effects of the present invention more pronounced, and conjugated diene polymers containing nitrile groups such as NBR (hereinafter referred to as "nitrile group-containing conjugated diene polymers") are more preferred.

The nitrile group-containing conjugated diene polymer is not particularly limited, but may be, for example, a copolymer of an α,β-ethylenically unsaturated nitrile monomer, a conjugated diene monomer, and other copolymerizable ethylenically unsaturated acid monomers that are used as necessary.

The α,β-ethylenically unsaturated nitrile monomer is not particularly limited, but an ethylenically unsaturated compound having a nitrile group and preferably having 3 to 18 carbon atoms can be used. Examples of such α,β-ethylenically unsaturated nitrile monomers include acrylonitrile, methacrylonitrile, and halogen-substituted acrylonitrile, and among these, acrylonitrile is particularly preferred. These α,β-ethylenically unsaturated nitrile monomers may be used alone or in combination of two or more.

The content of the α,β-ethylenically unsaturated nitrile monomer units in the nitrile group-containing conjugated diene polymer is preferably 10 to 45% by weight, more preferably 20 to 40% by weight, and even more preferably 25 to 40% by weight, based on the total monomer units. By setting the content of the α,β-ethylenically unsaturated nitrile monomer units within the above range, the dip-molded product obtained can have excellent solvent resistance.

As the conjugated diene monomer, conjugated diene monomers having 4 to 6 carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene, are preferred, with 1,3-butadiene and isoprene being more preferred, and 1,3-butadiene being particularly preferred. These conjugated diene monomers may be used alone or in combination of two or more.

The content of the conjugated diene monomer units in the nitrile group-containing conjugated diene polymer is preferably 40 to 80% by weight, more preferably 52 to 78% by weight, and even more preferably 55 to 75% by weight, based on the total monomer units. By setting the content of the conjugated diene monomer units within the above range, the obtained dip-molded article can be made to have excellent flexibility.

The nitrile group-containing conjugated diene polymer may also be a copolymer of a monomer forming an α,β-ethylenically unsaturated nitrile monomer unit and a monomer forming a conjugated diene monomer unit with another copolymerizable ethylenically unsaturated acid monomer.

Such other copolymerizable ethylenically unsaturated acid monomers are not particularly limited, but examples thereof include carboxyl group-containing ethylenically unsaturated monomers, monocarboxylate group-containing ethylenically unsaturated monomers, dicarboxylate diester group-containing ethylenically unsaturated monomers, sulfonic acid group-containing ethylenically unsaturated monomers, and phosphoric acid group-containing ethylenically unsaturated monomers.

Examples of carboxyl group-containing ethylenically unsaturated monomers include, but are not limited to, ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; ethylenically unsaturated polycarboxylic acids and their anhydrides such as fumaric acid, maleic acid, itaconic acid, maleic anhydride, and itaconic anhydride; and partial esters of ethylenically unsaturated polycarboxylic acids such as methyl maleate and methyl itaconate.

Examples of the monocarboxylate group-containing ethylenically unsaturated monomer include, but are not limited to, acrylic acid esters such as methyl acrylate; methacrylic acid esters such as methyl methacrylate; and crotonate esters such as methyl crotonate.

The dicarboxylate diester group-containing ethylenically unsaturated monomer is not particularly limited, but examples include maleic acid diesters such as dimethyl maleate; itaconic acid diesters such as methyl itaconate; and the like.

Examples of sulfonic acid group-containing ethylenically unsaturated monomers include, but are not limited to, vinyl sulfonic acid, methyl vinyl sulfonic acid, styrene sulfonic acid, (meth)allyl sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, and 2-acrylamido-2-hydroxypropane sulfonic acid.

Phosphate group-containing ethylenically unsaturated monomers include, but are not limited to, (meth)acrylic acid-3-chloro-2-propyl phosphate, (meth)acrylic acid-2-ethyl phosphate, and 3-allyloxy-2-hydroxypropane phosphate.

These other copolymerizable ethylenically unsaturated acid monomers can be used as alkali metal salts or ammonium salts, and may be used alone or in combination of two or more. Among the above other copolymerizable ethylenically unsaturated acid monomers, carboxyl group-containing ethylenically unsaturated monomers are preferred, ethylenically unsaturated monocarboxylic acids are more preferred, acrylic acid and methacrylic acid are even more preferred, and methacrylic acid is particularly preferred.

When the nitrile group-containing conjugated diene polymer contains units of other copolymerizable ethylenically unsaturated acid monomers, the content of the units of other copolymerizable ethylenically unsaturated acid monomers is preferably 0.1 to 15% by weight, more preferably 1 to 10% by weight, and even more preferably 2 to 8% by weight, based on the total monomer units.

The latex of the nitrile group-containing conjugated diene polymer can be obtained, for example, by emulsion polymerization of a monomer mixture containing the above-mentioned monomers. In the emulsion polymerization, commonly used polymerization auxiliary materials such as emulsifiers, polymerization initiators, and molecular weight regulators can be used.

The emulsifier used in the emulsion polymerization is not particularly limited, but examples thereof include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants, with anionic surfactants being preferred. Specific examples of the anionic surfactant include fatty acid salts such as sodium laurate, potassium myristate, sodium palmitate, potassium oleate, sodium linolenate, and sodium rosinate; alkyl benzene sulfonates such as sodium dodecyl benzene sulfonate, potassium dodecyl benzene sulfonate, sodium decyl benzene sulfonate, potassium decyl benzene sulfonate, sodium cetyl benzene sulfonate, and potassium cetyl benzene sulfonate; alkyl sulfosuccinates such as sodium di(2-ethylhexyl)sulfosuccinate, potassium di(2-ethylhexyl)sulfosuccinate, and sodium dioctyl sulfosuccinate; alkyl sulfates such as sodium lauryl sulfate and potassium lauryl sulfate; polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene lauryl ether sulfate and potassium polyoxyethylene lauryl ether sulfate; and monoalkyl phosphates such as sodium lauryl phosphate and potassium lauryl phosphate.
The amount of the emulsifier used in the emulsion polymerization is preferably 0.5 to 10 parts by weight, more preferably 1 to 8 parts by weight, based on 100 parts by weight of the total monomers used.

The polymerization initiator is not particularly limited, but a radical initiator is preferable. The radical 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 t-butyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, dibenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, and t-butylperoxyisobutyrate; azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate; and the like. Among these, inorganic peroxides or organic peroxides are preferable, inorganic peroxides are more preferable, and persulfates are particularly preferable. These polymerization initiators may be used alone or in combination of two or more.
The amount of the polymerization initiator used is preferably 0.01 to 2 parts by weight, more preferably 0.05 to 1.5 parts by weight, based on 100 parts by weight of the total monomers used.

The molecular weight regulator is not particularly limited, but examples thereof include α-methylstyrene dimer, mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, octyl mercaptan, etc., halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, methylene bromide, etc., sulfur-containing compounds such as tetraethylthiuram disulfide, dipentamethylenethiuram disulfide, diisopropylxanthogen disulfide, etc., and among these, mercaptans are preferred, with t-dodecyl mercaptan being more preferred. These molecular weight regulators may be used alone or in combination of two or more.
The amount of the molecular weight regulator used varies depending on the type, but is preferably 0.1 to 1.5 parts by weight, more preferably 0.2 to 1.0 part by weight, based on 100 parts by weight of the total monomers used.

Emulsion polymerization is usually carried out in water. The amount of water used is preferably 80 to 500 parts by weight, more preferably 100 to 200 parts by weight, per 100 parts by weight of the total monomers used.

During emulsion polymerization, if necessary, polymerization secondary materials other than those mentioned above may be used. Examples of polymerization secondary materials include chelating agents, dispersants, pH adjusters, oxygen scavengers, particle size adjusters, etc., and there are no particular limitations on the types or amounts used.

Examples of the method of adding the monomers include a method of adding the monomers to be used in a reaction vessel all at once, a method of adding them continuously or intermittently as the polymerization proceeds, a method of adding a part of the monomers and reacting them to a specific conversion rate, and then adding the remaining monomers continuously or intermittently to polymerize them, and any of these methods may be adopted. When the monomers are mixed and added continuously or intermittently, the composition of the mixture may be constant or may be changed.
In addition, the various monomers to be used may be mixed in advance and then added to the reaction vessel, or may be added separately to the reaction vessel.

The polymerization temperature during emulsion polymerization is not particularly limited, but is usually 0 to 95°C, and preferably 5 to 70°C. The polymerization time is not particularly limited, but is usually about 5 to 40 hours.

After the polymerization reaction is stopped, unreacted monomers may be removed and the solids concentration and pH may be adjusted, if desired.

The glass transition temperature of the conjugated diene polymer (A) constituting the latex of the conjugated diene polymer (A) is 10°C or lower, preferably -45 to -10°C, and more preferably -40 to -10°C. If the glass transition temperature of the conjugated diene polymer (A) is too high, the resulting dip molded article will have poor oil grip properties. There are no particular limitations on the method for setting the glass transition temperature of the conjugated diene polymer (A) in the above range, but examples include a method for setting the content ratio of each monomer unit constituting the conjugated diene polymer (A) in the above range.

The volume average particle diameter of the particles of the conjugated diene polymer (A) constituting the latex of the conjugated diene polymer (A) is preferably 30 to 1000 nm, more preferably 50 to 500 nm, and even more preferably 70 to 200 nm. By setting the volume average particle diameter of the particles of the conjugated diene polymer (A) within the above range, the polymer (B) having a glass transition temperature of more than 10°C can be more satisfactorily finely dispersed in the conjugated diene polymer (A) in the obtained dip-molded product, thereby improving the abrasion resistance.

From the viewpoint of setting the surface tension of the dip molding latex composition in the preferred range described below, the surface tension of the latex of the conjugated diene polymer (A) at 25°C is preferably 28 to 72 mN/m, more preferably 29 to 65 mN/m, and even more preferably 30 to 60 mN/m. The surface tension of the latex of the conjugated diene polymer (A) can be adjusted by, for example, adjusting the amount of emulsifier used in emulsion polymerization or adjusting the volume average particle size of the particles of the conjugated diene polymer (A) constituting the latex of the conjugated diene polymer (A).

The polymer (B) having a glass transition temperature of more than 10°C (hereinafter referred to as "polymer (B)" as appropriate) constituting the latex of polymer (B) having a glass transition temperature of more than 10°C (hereinafter referred to as "latex of polymer (B)" as appropriate) is not particularly limited and may be any polymer having a glass transition temperature of more than 10°C. However, from the viewpoints of the oil grip property, chemical permeation resistance, and oil resistance during continuous use of the resulting dip-molded product, a polymer containing a monomer unit having a halogen atom is preferred.

The halogen atom is not particularly limited, but for example, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom are preferred. Among these, a chlorine atom is preferred from the viewpoint of the oil grip property, chemical permeation resistance, and oil resistance during continuous use of the resulting dip-molded body. In other words, as the polymer (B), a polymer containing a monomer unit having a chlorine atom is more preferred.

The monomer having a halogen atom that forms the monomer unit having a halogen atom is not particularly limited, but examples thereof include unsaturated alkyl halides, unsaturated alcohol esters of halogen-containing saturated carboxylic acids, (meth)acrylic acid haloalkyl esters, (meth)acrylic acid haloacyloxyalkyl esters, (meth)acrylic acid (haloacetylcarbamoyloxy)alkyl esters, halogen-containing unsaturated ethers, halogen-containing unsaturated ketones, halomethyl group-containing aromatic vinyl compounds, halogen-containing unsaturated amides, and haloacetyl group-containing unsaturated monomers. Among these, from the viewpoint of the oil grip properties, chemical permeability resistance, and oil resistance during continuous use of the resulting dip-molded product, it is preferable to use unsaturated alkyl halides, and vinyl chloride is more preferable, and it is more preferable that the polymer (B) is a vinyl chloride resin having vinyl chloride units as the main component.

The vinyl chloride resin as polymer (B) may be either a vinyl chloride homopolymer or a copolymer of vinyl chloride and a monomer copolymerizable with vinyl chloride. The vinyl chloride resin as polymer (B) is preferably a vinyl chloride homopolymer. When the vinyl chloride resin is a copolymer, the content of vinyl chloride monomer units in the vinyl chloride resin is preferably 50% by weight or more, more preferably 75% by weight or more, and even more preferably 90% by weight or more.

Monomers that can be copolymerized with vinyl chloride include α-olefin monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene; aromatic monomers such as styrene, α-methylstyrene, and vinylpyridine; α,β-ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, and cinnamic acid; α,β-ethylenically unsaturated monocarboxylic acid esters such as ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; α,β-ethylenically unsaturated polyvalent carboxylic acids such as maleic acid, fumaric acid, and itaconic acid; α,β-ethylenically unsaturated polyvalent carboxylic acids such as monomethyl maleate, monoethyl maleate, and monoethyl itaconate. Examples of the vinyl chloride resin include α,β-ethylenically unsaturated polycarboxylic acid polyesters such as dimethyl maleate, di-n-butyl fumarate, dimethyl itaconate, and di-2-ethylhexyl itaconate; vinyl ester monomers such as vinyl acetate and vinyl propionate; α,β-ethylenically unsaturated monocarboxylic acid amides such as acrylamide and methacrylamide; N-substituted maleimides; vinyl ether monomers such as vinyl methyl ether, vinyl ethyl ether, and vinyl cetyl ether; and vinylidene compounds such as vinylidene chloride. Among these, vinyl ester monomers and α,β-ethylenically unsaturated monocarboxylic acid esters are preferred, and vinyl acetate and (meth)acrylic acid esters are more preferred. That is, the vinyl chloride resin as the polymer (B) is preferably a copolymer of vinyl chloride and vinyl acetate, or a copolymer of vinyl chloride and (meth)acrylic acid ester.

The method for producing the vinyl chloride resin latex as polymer (B) is not particularly limited as long as it is a method capable of polymerizing the above-mentioned monomers, but examples include known methods such as emulsion polymerization by radical polymerization, seeded emulsion polymerization, and fine suspension polymerization.

The K value of the vinyl chloride resin as polymer (B), measured according to JIS K 7367-2, is preferably 50 to 95, and more preferably 60 to 80.

The vinyl chloride resin as polymer (B) preferably contains 20 parts by weight or less of a plasticizer per 100 parts by weight of polymer (B), and more preferably contains no plasticizer, which can improve the oil grip properties of the dip-molded article obtained. In this case, "containing no plasticizer" means that the vinyl chloride resin particles constituting the vinyl chloride resin latex do not substantially contain any plasticizer, and for example, the plasticizer content is suppressed to 10 ppm by weight or less.

As the polymer (B), in addition to vinyl chloride resin, for example, polystyrene resin, polymethyl methacrylate resin, PTFE resin, acrylic resin, etc. may be used. As the polymer (B), vinyl chloride resin or polystyrene resin is preferable, and vinyl chloride resin is more preferable from the viewpoint of the oil grip property, chemical permeation resistance, and oil resistance during continuous use of the obtained dip molded body. These polymers may be used alone or in combination of two or more kinds.

The glass transition temperature of the polymer (B) constituting the latex of the polymer (B) is more than 10°C, preferably 30°C or higher, more preferably 50°C or higher, and even more preferably 70°C or higher. The upper limit of the glass transition temperature of the polymer (B) is not particularly limited, but is preferably 200°C or lower, more preferably 150°C or lower.

The dip molding latex composition of the present invention is preferably a latex composition for dip molding obtained by mixing, in a latex state, a latex of a conjugated diene polymer (A) having a glass transition temperature of 10°C or less and a latex of a polymer (B) having a glass transition temperature of more than 10°C. By mixing the latex of the conjugated diene polymer (A) and the latex of the polymer (B) in a latex state, when a dip molded article is obtained using such a latex composition, dripping during molding can be further suppressed, and the obtained dip molded article can have even better oil grip properties.

In particular, by mixing the latex of the conjugated diene polymer (A) and the latex of the polymer (B) in the latex state, the particles of the conjugated diene polymer (A) and the particles of the polymer (B) can be uniformly finely dispersed in the latex composition. Then, when a dip molded product is obtained by dip molding, the polymer (B) can be co-precipitated in a state in which the polymer (B) is finely dispersed in the matrix of the conjugated diene polymer (A) in the obtained dip molded product. Therefore, the action of the finely dispersed polymer (B) can make the obtained dip molded product have even better oil gripping properties. Furthermore, since it is easy to make the matrix of the conjugated diene polymer (A) continuous and uniform in the obtained dip molded product, the obtained dip molded product can also have excellent chemical permeability resistance. In the present invention, it is preferable to prepare a latex composition by mixing the latex of the conjugated diene polymer (A) and the latex of the polymer (B) in a latex state, but the latex composition for dip molding of the present invention is not particularly limited to one obtained by mixing these latexes, as long as it is a dispersion of particles of the conjugated diene polymer (A) and particles of the polymer (B) in an aqueous medium.

If the glass transition temperature of the polymer (B) constituting the latex of polymer (B) is too low, the resulting dip-molded product will have poor oil grip properties. There are no particular limitations on the method for setting the glass transition temperature of polymer (B) within the above range. For example, when using a vinyl chloride resin latex as the latex of polymer (B), the content of vinyl chloride monomer units in the vinyl chloride resin is preferably 50% by weight or more, more preferably 75% by weight or more.

The volume average particle diameter of the particles of polymer (B) constituting the latex of polymer (B) is preferably 0.05 to 500 μm, more preferably 0.05 to 60 μm, even more preferably 0.05 to 50 μm, even more preferably 0.05 μm or more and less than 3 μm, and particularly preferably 0.05 μm or more and less than 0.5 μm. By setting the volume average particle diameter of the particles of polymer (B) within the above range, polymer (B) can be more satisfactorily finely dispersed in the conjugated diene polymer (A) in the obtained dip-molded product, thereby improving the abrasion resistance.

From the viewpoint of setting the surface tension of the dip molding latex composition in the preferred range described below, the surface tension of the latex of polymer (B) at 25°C is preferably 34 to 72 mN/m, more preferably 35 to 65 mN/m, and even more preferably 36 to 60 mN/m. The surface tension of the latex of polymer (B) can be adjusted by, for example, adjusting the amount of emulsifier used in emulsion polymerization or adjusting the volume average particle size of the particles of polymer (B) that constitute the latex of polymer (B).

The content of the conjugated diene polymer (A) and the content of the polymer (B) in the dip molding latex composition of the present invention are not particularly limited, but the content of the conjugated diene polymer (A) in 100 parts by weight of the polymer component contained in the dip molding latex composition (in the case where only the conjugated diene polymer (A) and the polymer (B) are contained as the polymer component, the total of 100 parts by weight of the conjugated diene polymer (A) and the polymer (B)) is preferably 40 parts by weight or more, more preferably 40 to 95 parts by weight, and even more preferably 40 to 80 parts by weight. In addition, the content of the polymer (B) relative to 100 parts by weight of the polymer component contained in the dip molding latex composition is preferably 5 to 80 parts by weight, more preferably 10 to 70 parts by weight, and even more preferably 20 to 60 parts by weight. Furthermore, the content ratio of the conjugated diene polymer (A) and the polymer (B) in the dip molding latex composition of the present invention is preferably 99:1 to 10:90, more preferably 95:5 to 20:80, even more preferably 90:10 to 30:70, and particularly preferably 75:25 to 45:55, in terms of the weight ratio of "conjugated diene polymer (A):polymer (B)". By setting the content of the conjugated diene polymer (A) and the polymer (B) within the above ranges, the oil grip property of the obtained dip molded article can be further improved.

The dip molding latex composition of the present invention contains a thickener in addition to the latex of the conjugated diene polymer (A) and the latex of the polymer (B).

Examples of the thickener used in the present invention include vinyl compounds such as polyvinyl alcohol and polyvinylpyrrolidone; cellulose derivatives and salts thereof such as hydroxyethyl cellulose, hydroxypropyl cellulose, and carboxymethyl cellulose; polycarboxylic acid compounds and sodium salts thereof such as polyacrylic acid; and polyoxyethylene derivatives such as polyethylene glycol ether. Among these, vinyl compounds and their carboxylic acid modified compounds or polyoxyethylene derivatives are preferred from the viewpoint of chemical permeation resistance, and vinyl compounds and their carboxylic acid modified compounds are more preferred. In addition, as the thickener, it is preferred to use a nonionic thickener from the viewpoint of chemical permeation resistance, and it is particularly preferred to use polyvinyl alcohol. These thickeners may be used alone or in combination of two or more.

When polyvinyl alcohol is used as the thickener, the degree of saponification of the polyvinyl alcohol is preferably 75 mol% or more, more preferably 80 mol% or more. The upper limit of the degree of saponification of the thickener is not particularly limited, but is usually 99.9 mol% or less. When the degree of saponification of the polyvinyl alcohol is in the above range, the obtained dip molded product has excellent oil grip properties and excellent chemical permeation resistance.

The acid amount of the thickener is not particularly limited, but is preferably 10 mmol/g or less, more preferably 5 mmol/g or less, even more preferably 2.5 mmol/g or less, and particularly preferably 1 mmol/g or less. The lower limit of the acid amount of the thickener is not particularly limited, but is usually 0.001 mmol/g or more. When the acid amount of the thickener is within the above range, the obtained dip molded product has excellent oil grip properties and excellent chemical permeation resistance.

The acid amount of the thickener used in the present invention can be measured, for example, by the following method.
First, 50 g of a thickener aqueous solution (the solid content of the thickener in 50 g of the thickener aqueous solution is W (g)) adjusted to a solid content concentration of 0.2 to 1% by adding distilled water is placed in a 200 ml glass container washed with distilled water, and a solution conductivity meter (Kyoto Electronics Manufacturing Co., Ltd.: CM-117, cell type used: K-121) is set and stirring is started. Next, while continuing stirring, 0.1 N sodium hydroxide is added so that the pH of the aqueous solution becomes 12 or more, and the electrical conductivity after 6 minutes is measured, and the measured value is the electrical conductivity at the start of measurement. Then, 0.5 ml of 0.1 N hydrochloric acid is added to this thickener aqueous solution, and the electrical conductivity is measured after 30 seconds, and 0.5 ml of 0.1 N hydrochloric acid is added again and the electrical conductivity is measured after 30 seconds. This operation is repeated at 30 second intervals until the electrical conductivity becomes at least twice that at the start of measurement. The obtained electrical conductivity data is plotted on a graph with the vertical axis: electrical conductivity (mS) and the horizontal axis: cumulative amount of hydrochloric acid added (mmol), and a hydrochloric acid amount-electrical conductivity curve having two inflection points as shown in FIG. 1 is obtained. The X coordinates of the obtained two inflection points and the X coordinate at the end of hydrochloric acid addition are respectively designated P ₁ , P ₂ and P ₃ in ascending order of value, and the data in the three sections of X coordinates from zero to P ₁ , P ₁ to P ₂ and P ₂ to P ₃ are respectively approximated by the least squares method to obtain straight lines L ₁ , L ₂ and L _3. In addition, the X coordinate of the intersection of L ₁ and L ₂ is designated A ₁ (mmol), and the X coordinate of the intersection of L ₂ and L ₃ is designated A ₂ (mmol). The amount of acid per 1 g of thickener is then calculated from the following formula.
Amount of acid per 1 g of thickener=(A ₂ −A ₁ )/W (mmol/g)

When two or more types of thickeners are used in combination, the thickeners are mixed in the same ratio as the thickeners in the dip molding latex composition to obtain a thickener mixture, and the acid amount of the thickener mixture obtained by measuring the acid amount in the same manner as above can be used as the acid amount of the thickener.

The viscosity of the thickener used in the present invention in a 4 wt% aqueous solution is not particularly limited, but is preferably 1 mPa·s or more, more preferably 10 mPa·s or more, and preferably 20,000 mPa·s or less, and more preferably 10,000 mPa·s or less. The viscosity of the thickener used in the present invention in a 1 wt% aqueous solution is not particularly limited, but is preferably 1 mPa·s or more, more preferably 10 mPa·s or more, and preferably 20,000 mPa·s or less, and more preferably 10,000 mPa·s or less. The viscosity of the thickener aqueous solution can be measured, for example, using a B-type viscometer at 25°C and a rotation speed of 6 rpm.

The amount of the thickener used in the present invention is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, and even more preferably 0.15 to 4.5 parts by weight, per 100 parts by weight of the polymer component contained in the dip molding latex composition. When the amount of the thickener is within the above range, the obtained dip molded article has excellent resistance to chemical permeation.

In addition, the dip molding latex composition of the present invention preferably further contains a sulfur-based crosslinking agent in addition to the latex of the conjugated diene polymer (A), the latex of the polymer (B), and the thickener.

Examples of sulfur-based crosslinking agents include, but are not limited to, powdered sulfur, sulfur flowers, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, and other sulfur; sulfur-containing compounds such as sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, dibenzothiazyl disulfide, caprolactam disulfide, phosphorus-containing polysulfide, and polymeric polysulfides; sulfur-donating compounds such as tetramethylthiuram disulfide, dimethyldithiocarbamate selenium, and 2-(4'-morpholinodithio)benzothiazole; and the like. These sulfur-based crosslinking agents may be used alone or in combination of two or more.

The content of the sulfur-based crosslinking agent is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, and even more preferably 0.1 to 2 parts by weight, per 100 parts by weight of the polymer component contained in the dip molding latex composition.

In addition, the dip molding latex composition of the present invention preferably further contains a crosslinking accelerator (vulcanization accelerator) and zinc oxide in addition to the sulfur-based crosslinking agent.
The crosslinking accelerator (vulcanization accelerator) is not particularly limited, but examples thereof include dithiocarbamic acids such as diethyldithiocarbamic acid, dibutyldithiocarbamic acid, di-2-ethylhexyldithiocarbamic acid, dicyclohexyldithiocarbamic acid, diphenyldithiocarbamic acid, and dibenzyldithiocarbamic acid, and zinc salts thereof; 2-mercaptobenzothiazole, 2-mercaptobenzothiazole zinc, 2-mercaptothiazoline, dibenzothiazyl disulfide, 2-(2,4-dinitrophenylthio)benzo Examples of the crosslinking accelerator include thiazole, 2-(N,N-diethylthiocarbamoylthio)benzothiazole, 2-(2,6-dimethyl-4-morpholinothio)benzothiazole, 2-(4'-morpholino dithio)benzothiazole, 4-morpholinyl-2-benzothiazyl disulfide, and 1,3-bis(2-benzothiazyl mercaptomethyl)urea. Among these, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, 2-mercaptobenzothiazole, and zinc 2-mercaptobenzothiazole are preferred. These crosslinking accelerators may be used alone or in combination of two or more.

The content of the crosslinking accelerator is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the polymer component contained in the dip molding latex composition. The content of zinc oxide is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the polymer component contained in the dip molding latex composition.

The solid content concentration of the dip molding latex composition of the present invention is 42% by weight or more and 55% by weight or less, and is not particularly limited, but the lower limit of the solid content concentration is preferably 43.5% by weight or more, more preferably 43.8% by weight or more, and even more preferably 44.1% by weight or more. The upper limit of the solid content concentration is not particularly limited, but is preferably 53.0% by weight or less. If the solid content concentration of the dip molding latex composition is too low, it is not possible to suppress dripping during molding and to develop the oil grip property of the resulting molded product. On the other hand, if the solid content concentration of the dip molding latex composition is too high, it becomes difficult to disperse the polymer (B) well in the dip molding latex composition, and it becomes difficult to finely disperse the polymer (B) well in the matrix of the conjugated diene polymer (A) in the resulting dip molded product, so that the resulting molded product has poor oil grip property.

Methods for adjusting the solids concentration of the dip molding latex composition to the above-mentioned range include, for example, a method for adjusting the solids concentration of each component, such as the latex of the conjugated diene polymer (A) and the latex of the polymer (B), and a method for adjusting the solids concentration by a concentration treatment or dilution treatment, which will be described later. Among these, the method for adjusting the solids concentration by a concentration treatment is preferred from the viewpoint of productivity.

The pH of the dip molding latex composition of the present invention is preferably 5 to 13, more preferably 7 to 10, and even more preferably 7.5 to 9. By adjusting the pH of the dip molding latex composition to fall within the above range, the mechanical stability is improved, making it possible to suppress the generation of coarse aggregates during the transfer of the dip molding latex composition, and the viscosity of the dip molding latex composition becomes appropriate, improving the handleability of the dip molding latex composition.

The viscosity of the dip molding latex composition of the present invention at 25°C is preferably 1,000 to 100,000 mPa·s, more preferably 1,500 to 50,000 mPa·s, and even more preferably 2,500 to 20,000 mPa·s. The viscosity of the dip molding latex composition at 25°C can be measured, for example, using a B-type viscometer at 25°C and a rotation speed of 6 rpm. The viscosity of the dip molding latex composition at 25°C can be adjusted, for example, by adjusting the concentration of the polymer component in the dip molding latex composition or by adding a compound having a thickening effect to the dip molding latex composition.

The surface tension of the dip molding latex composition of the present invention at 25°C is preferably 34 to 72 mN/m, more preferably 35 to 65 mN/m, and even more preferably 36 to 60 mN/m. By setting the surface tension of the dip molding latex composition in the above range, the oil grip property of the obtained dip molded article can be further improved. In addition, the surface tension of the dip molding latex composition can be adjusted, for example, by a method of adjusting the surface tension of the latex of the conjugated diene polymer (A) or the latex of the polymer (B) to the above range, or by a method of adjusting the surface tension of the latex of the polymer (B) constituting the latex of the polymer (B) to the above range.

The dip molding latex composition of the present invention may contain fillers such as carbon black, silica, calcium carbonate, aluminum silicate, magnesium silicate, calcium silicate, magnesium oxide, zinc (meth)acrylate, magnesium (meth)acrylate, and titanium oxide. The dip molding latex composition of the present invention may contain additives other than the water-soluble salts and fillers, such as antioxidants, antioxidants, preservatives, antibacterial agents, wetting agents, dispersants, pigments, dyes, reinforcing agents, and pH adjusters, in predetermined amounts, if necessary.

The dip molding latex composition of the present invention can be prepared, for example, by mixing the above-mentioned components and, if necessary, concentrating or diluting them. The order of mixing the components is not particularly limited, but from the viewpoint of further increasing the dispersibility of each component, it is preferable to mix the latex of the conjugated diene polymer (A) and the latex of the polymer (B) in advance, and then add the thickener and each component to be blended as necessary and mix them. The method of mixing the latex of the conjugated diene polymer (A) and the latex of the polymer (B) is not particularly limited, but from the viewpoint of further increasing the dispersibility, it is preferable to mix the latex of the conjugated diene polymer (A) and the latex of the polymer (B) in the latex state (latex blend).

The dip molding latex composition of the present invention is preferably obtained through a concentration process. The concentration process method is not particularly limited, but examples include reduced pressure distillation, atmospheric distillation, centrifugation, membrane concentration, and the like. Among these, a concentration method involving heating is preferred, and reduced pressure distillation involving heating is more preferred. By employing a concentration method involving heating, it is possible to reduce bacteria that cause odor or inhibit the growth of bacteria that cause odor, and the dip molding latex composition can have excellent low odor properties.

In concentration methods involving heating, the heating temperature is preferably 50°C to 100°C. In addition, in reduced pressure distillation, the pressure is preferably 20 kPa to 90 kPa.

The concentration treatment may be performed on a mixture containing some of the components to be blended in the dip molding latex composition, or on a mixture containing all of the components to be blended in the dip molding latex composition. From the viewpoint of dispersibility and production efficiency of the dip molding latex composition, it is preferable to perform the concentration treatment on a mixture of the latex of the conjugated diene polymer (A) and the latex of the polymer (B).

That is, the method for producing the dip molding latex composition of the present invention is preferably a method in which the latex of the conjugated diene polymer (A) and the latex of the polymer (B) are mixed in advance, the resulting mixture is then subjected to a concentration treatment to increase the solids concentration, and then a thickener and each component that is blended as necessary are added and mixed to bring the solids concentration into the above range.

<Dip-molded body>
The dip-molded article of the present invention is a molded article obtained by using the above-mentioned latex composition for dip molding of the present invention, and is usually obtained by dip molding using the above-mentioned latex composition for dip molding of the present invention.

The dip molded article of the present invention is a molded article obtained using the dip molding latex composition of the present invention described above, and therefore has at least a polymer layer containing the conjugated diene polymer (A) (hereinafter, appropriately referred to as "conjugated diene polymer (A)") having a glass transition temperature of 10°C or less and the polymer (B) (hereinafter, appropriately referred to as "polymer (B)") having a glass transition temperature of more than 10°C. The preferred range of the content ratio of the conjugated diene polymer (A) to the polymer (B) in the dip molded article of the present invention is the same as the preferred range of the content ratio of the conjugated diene polymer (A) to the polymer (B) in the dip molding latex composition of the present invention described above.

The dip-molded article of the present invention may be a film-molded article made of a latex composition for dip molding, obtained by immersing a dip-molding mold in a latex composition for dip molding, such as the latex composition for dip molding of the present invention described above, or may be a laminate of a substrate and a polymer layer made of a latex composition for dip molding, obtained by immersing the substrate in a latex composition for dip molding. In the following, the dip-molded article of the present invention will be described by taking as an example a case where the substrate is a laminate of a polymer layer made of a latex composition for dip molding, but the present invention is not limited to such an embodiment.

The substrate is not particularly limited, but when the dip-molded article of the present invention is used as a protective glove, a fiber substrate can be suitably used. The fiber substrate is not particularly limited, but for example, a fiber made of twisted monofilament yarn woven into a glove shape can be used. The average thickness of the fiber substrate is preferably 50 to 3,000 μm, more preferably 100 to 2,000 μm.

The dip-molded article of the present invention can be produced, for example, by immersing a substrate in the latex composition for dip molding to form a polymer layer made of the latex composition for dip molding on the substrate. In this case, it is preferable to immerse the substrate in the latex composition for dip molding while the substrate is already placed over a mold having a desired shape.

The mold for covering the substrate is not particularly limited, and various materials such as porcelain, glass, metal, and plastic can be used. The shape of the mold can be the desired shape according to the shape of the final product. For example, when the dip-molded product of the present invention is used as a protective glove, it is preferable to use various types of molds for gloves, such as a mold having a shape from the wrist to the fingertips, as the mold for covering the substrate.

In addition, before immersing the substrate in the dip molding latex composition, it is preferable to immerse the substrate in a coagulant solution and adhere the coagulant solution to the substrate. In this case, it is preferable to immerse the substrate in the coagulant solution while the substrate is covered with a molding die having a desired shape. Examples of molding dies having a desired shape include those mentioned above. In addition, it is preferable to remove the solvent contained in the coagulant solution by drying after adhering the coagulant solution to the substrate. The drying temperature at this time is not particularly limited and may be selected according to the solvent used, but is preferably 10 to 80°C, more preferably 15 to 70°C. In addition, the drying time is not particularly limited, but is preferably 600 to 1 second, more preferably 300 to 5 seconds.

Next, the substrate with the coagulant solution applied thereto is placed over a mold of the desired shape and immersed in the dip molding latex composition, causing the dip molding latex composition to coagulate and forming a polymer layer made of the dip molding latex composition onto the substrate.

After the substrate is immersed in the dip molding latex composition, it is preferable to dry it. The drying temperature is not particularly limited, but is preferably 10 to 80°C, more preferably 15 to 80°C. The drying time is not particularly limited, but is preferably 120 minutes to 5 seconds, more preferably 60 minutes to 10 seconds.

When using a dip molding latex composition containing a sulfur-based crosslinking agent, the dip molding latex composition may be one that has been aged (also called pre-vulcanized).

The temperature conditions for aging are not particularly limited, but are preferably 20 to 50°C. The aging time is preferably 4 hours or more and 120 hours or less, more preferably 24 hours or more and 72 hours or less, from the viewpoint of preventing peeling between the substrate and the polymer layer made of the dip molding latex composition, and from the viewpoint of improving the abrasion resistance when the obtained dip molded article is used as a protective glove.

Next, it is preferable to heat the dip molding latex composition attached to the substrate to crosslink the polymer components contained in the dip molding latex composition.

The heating temperature for crosslinking is preferably 60 to 160°C, more preferably 80 to 150°C. By setting the heating temperature within the above range, the time required for the crosslinking reaction can be shortened, improving the productivity of the dip-molded body, and the oxidative deterioration of the polymer components caused by excessive heating can be suppressed, improving the physical properties of the obtained dip-molded body. The heating time for crosslinking can be appropriately selected depending on the heating temperature, but is usually 5 to 120 minutes.

For the dip-formed article thus obtained, it is preferable to remove water-soluble impurities (emulsifiers, water-soluble polymers, coagulants, etc.) from the polymer layer by immersing the polymer layer formed on the substrate in warm water at 20 to 80°C for about 0.5 to 60 minutes, if necessary. Although the process of immersing the polymer layer in warm water may be carried out after crosslinking the polymer components in the polymer layer, it is preferable to carry out the process before crosslinking the polymer components in the polymer layer, since this allows for more efficient removal of water-soluble impurities.

After immersion in warm water, further drying may be performed. The drying temperature and drying time are not particularly limited, but can be the same as the drying temperature and drying time in the drying process after immersion in the dip molding latex composition described above.

Then, after forming a polymer layer on the substrate while the substrate is covered with the mold as described above, the dip-molded product can be obtained by removing it from the mold (or demolding it). Methods for removing the product include peeling it off from the mold by hand, or peeling it off with water pressure or compressed air pressure.

Before or after the dip-molded body is removed from the molding die, it may be further subjected to a heat treatment (post-crosslinking step) at a temperature of 60 to 120°C for 10 to 120 minutes. In addition, after the dip-molded body is removed from the molding die, a surface treatment layer may be formed on the inner and/or outer surface of the dip-molded body by a chlorination treatment, coating treatment, or the like.

The dip-molded article of the present invention thus obtained is a polymer layer formed on a substrate by coagulation using a coagulant, the layer being made of the dip-molding latex composition of the present invention. The thickness of the layer can be made relatively thick, preferably 0.05 to 1.0 mm, more preferably 0.06 to 0.8 mm, even more preferably 0.07 to 0.7 mm, and particularly preferably more than 0.3 mm and 0.7 mm or less, thereby improving the abrasion resistance of the dip-molded article obtained. In addition, while a relatively thick layer usually tends to have a reduced oil grip, the dip-molded article of the present invention can achieve excellent oil grip even when the layer is relatively thick (for example, more than 0.3 mm).

The dip-molded article of the present invention has excellent oil grip properties and can be suitably used, for example, for glove applications, particularly for protective gloves. In the above, the dip-molded article of the present invention is described as a laminate of a substrate and a polymer layer made of a dip-molding latex composition. However, as described above, the present invention is not limited to such an embodiment, and it is of course possible to obtain a film-molded article made of the dip-molding latex composition by immersing a dip-molding mold in the dip-molding latex composition.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Note that the "parts" below are by weight unless otherwise specified. Note that various physical properties were measured as follows.

<Acid content of thickener>
The acid content of the thickener was measured by the following method.
First, 50 g of a thickener aqueous solution (the solid content of the thickener in 50 g of the thickener aqueous solution is W (g)) was added to a 200 ml glass container washed with distilled water to adjust the solid content concentration to 0.2 to 1% by adding distilled water, and the solution was set in a solution conductivity meter (Kyoto Electronics Manufacturing Co., Ltd.: CM-117, cell type used: K-121) and stirring was started. Next, while continuing stirring, 0.1 N sodium hydroxide was added so that the pH of the aqueous solution became 12 or more, and the electrical conductivity after 6 minutes was measured, and the measured value was taken as the electrical conductivity at the start of the measurement. Then, 0.5 ml of 0.1 N hydrochloric acid was added to this thickener aqueous solution, and the electrical conductivity was measured 30 seconds later, and 0.5 ml of 0.1 N hydrochloric acid was added again, and the electrical conductivity was measured 30 seconds later. This operation was repeated at 30 second intervals until the electrical conductivity became twice as high as that at the start of the measurement.

The obtained electrical conductivity data was plotted on a graph with the vertical axis: electrical conductivity (mS) and the horizontal axis: cumulative amount of hydrochloric acid added (mmol), and a hydrochloric acid amount-electrical conductivity curve having two inflection points as shown in FIG. 1 was obtained. The X coordinates of the obtained two inflection points and the X coordinate at the end of hydrochloric acid addition were designated P ₁ , P ₂ and P ₃ in ascending order of value, respectively, and the data in the three sections with X coordinates from zero to P ₁ , P ₁ to P ₂ and P ₂ to P ₃ were approximated by the least squares method to obtain straight lines L ₁ , L ₂ and L ₃ , respectively. In addition, the X coordinate of the intersection of L ₁ and L ₂ was designated A ₁ (mmol), and the X coordinate of the intersection of L ₂ and L ₃ was designated A ₂ (mmol). The amount of acid per 1 g of thickener was calculated from the following formula.
Amount of acid per 1 g of thickener=(A ₂ −A ₁ )/W (mmol/g)

<Viscosity of thickener>
The thickener was weighed out precisely, placed in a beaker, and dissolved uniformly by adding water and stirring with a stirrer to obtain a 1% by weight or 4% by weight aqueous solution of the thickener. The viscosity of the aqueous solution of the thickener was measured at 25° C. and 6 rpm using a B-type viscometer and rotor No. M3.

<Solids Concentration of Latex Composition for Dip Molding>
2 g of the sample was weighed out (weight: X2) onto an aluminum dish (weight: X1), and this was dried for 2 hours in a hot air dryer at 105° C. Then, after cooling in a desiccator, the weight including the aluminum dish was measured (weight: X3), and the solid content concentration was calculated according to the following formula.
Solid content concentration (wt%)=(X3-X1)×100/X2

<Viscosity of latex composition for dip molding>
The viscosity of the dip molding latex composition was measured using a Brookfield viscometer and a rotor No. M3 at 25° C. and a rotation speed of 6 rpm.

<Volume average particle size>
The volume average particle diameter of the particles of the nitrile group-containing conjugated diene polymer (A-1) constituting the latex of the nitrile group-containing conjugated diene polymer (A-1) and the volume average particle diameter of the particles of the vinyl chloride resin (B-1) constituting the latex of the vinyl chloride resin (B-1) were measured using a light scattering diffraction particle measuring device (manufactured by Coulter, product name "LS-230").

<Oil grip>
Cylindrical metal molds weighing 1.0 kg, 2.0 kg, 3.0 kg, 4.0 kg, 5.0 kg, 7.0 kg, and 10 kg were prepared, and test oil IRM903 was applied to these metal molds. Then, workers were asked to wear protective gloves (dip-molded bodies) and lift the metal molds with test oil IRM903 applied in order of weight from lightest to lightest, and the maximum weight they could lift was determined. The above measurement was carried out by 10 workers, and the average value of the maximum weight they could lift was calculated and evaluated into levels from LEVEL 0 to LEVEL 3. It can be determined that the higher the maximum weight they could lift, the better the oil grip property.
LEVEL 3: 2.9 kg or more LEVEL 2: 1.7 kg or more, less than 2.9 kg LEVEL 1: Less than 1.7 kg

<Chemical permeability resistance>
The amount of oil permeated was measured according to the following procedure.
(1) A protective glove (dip-molded product) was cut into a suitable circular shape to prepare a sample.
(2) 2 mL of test oil IRM903 was placed in a reagent bottle.
(3) The sample (dip-molded product) was placed on top of a reagent bottle containing test oil IRM903 so that the rubber layer of the sample was in contact with the liquid.
(4) The reagent bottle and the sample were firmly attached to each other using a fixture.
(5) In order to allow the test oil IRM903 to come into contact with the sample, the reagent bottle was turned upside down, placed on a piece of filter paper whose weight (W1) had been measured in advance, and left at room temperature.
(6) After leaving it for 24 hours, the weight (W2) of the filter paper was measured.
(7) The amount of test oil IRM903 that permeated the sample (oil permeation amount) was calculated using the following formula.
Oil permeation amount (g) = W2 - W1
It can be determined that the smaller the value of the oil permeation amount, the better the resistance to chemical permeation against chemicals such as oil.

<Drips during molding>
The polymer layer of the protective glove (dip-molded product) was visually observed to evaluate the presence or absence of defects due to dripping during molding, such as abnormal shapes at the edge of the protective glove and uneven thickness of the protective glove.

Example 1
(Preparation of aqueous dispersion of colloidal sulfur)
An aqueous dispersion of colloidal sulfur having a solid content of 50% by weight was prepared by grinding and stirring 1.0 part of colloidal sulfur (manufactured by Hosoi Chemical Industry Co., Ltd.), 0.5 part of a dispersant (manufactured by Kao Corporation, product name "Demol N"), 0.0015 part of a 5 wt % aqueous potassium hydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.) in a ball mill for 48 hours.

(Preparation of aqueous dispersions of zinc dibutyldithiocarbamate, zinc oxide, and titanium oxide)
An aqueous dispersion of zinc dibutyldithiocarbamate, an aqueous dispersion of zinc oxide, and an aqueous dispersion of titanium oxide were prepared in the same manner as above, except that zinc dibutyldithiocarbamate (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), zinc oxide (manufactured by Seido Chemical Industry Co., Ltd.), and titanium oxide were used instead of colloidal sulfur, respectively.

(Preparation of Latex of Nitrile Group-Containing Conjugated Diene Polymer (A-1))
A polymerization reactor was charged with 65 parts of 1,3-butadiene as a conjugated diene monomer, 30 parts of acrylonitrile as an α,β-ethylenically unsaturated nitrile monomer, 5 parts of methacrylic acid as an ethylenically unsaturated monocarboxylic acid monomer, 0.4 parts of t-dodecyl mercaptan, 132 parts of ion-exchanged water, 3 parts of sodium dodecylbenzenesulfonate, 0.5 parts of a β-naphthalenesulfonic acid formalin condensate sodium salt, 0.3 parts of potassium persulfate, and 0.05 parts of ethylenediaminetetraacetic acid sodium salt, and polymerization was carried out while maintaining the polymerization temperature at 30 to 40° C., and the reaction was continued until the polymerization conversion reached 94%, thereby obtaining a copolymer latex.

Then, after removing unreacted monomers from the obtained copolymer latex, the pH and solid content of the copolymer latex were adjusted to obtain a latex of nitrile group-containing conjugated diene polymer (A-1) having a solid content of 40% by weight, pH=8, and a surface tension of 31 mN/m at 25°C. The glass transition temperature (Tg) of the nitrile group-containing conjugated diene polymer (A-1) contained in the obtained latex of nitrile group-containing conjugated diene polymer (A-1) was measured and found to be -27°C. In addition, the volume average particle diameter of the particles of the nitrile group-containing conjugated diene polymer (A-1) constituting the latex of the nitrile group-containing conjugated diene polymer (A-1) was 110 nm, and the monomer composition of the nitrile group-containing conjugated diene polymer (A-1) was almost the same as the charge ratio.

(Preparation of dip molding latex composition)
The latex of the nitrile group-containing conjugated diene polymer (A-1) obtained above and the latex of the vinyl chloride resin (B-1) (manufactured by Nissin Chemical Industry Co., Ltd., product name "Vinyblan 985") were mixed so that the weight ratio of "nitrile group-containing conjugated diene polymer (A-1):vinyl chloride resin (B-1)" was 70:30, and 5% by weight of potassium hydroxide was added to prepare a latex composition having a solid content concentration of 42.5% by weight and a pH of 9.0. Note that, as for the latex of the vinyl chloride resin (B-1), the glass transition temperature (Tg) of the vinyl chloride resin (B-1) was 80°C, the volume average particle diameter of the particles of the vinyl chloride resin (B-1) was 0.08 μm, and the vinyl chloride resin (B-1) was substantially free of a plasticizer.

Next, the latex composition obtained above was concentrated by vacuum distillation at 80°C for 5 hours under reduced pressure conditions of 70 kPa to obtain a concentrated latex composition with a solids concentration of 46.4% by weight.

Then, 5% by weight of potassium hydroxide was added again to adjust the pH to 9.0, and the aqueous dispersions of the compounding agents prepared above were added so that, in terms of solid content, 1.0 part of colloidal sulfur, 1.0 part of zinc dibutyldithiocarbamate, 1.5 parts of zinc oxide, and 3.0 parts of titanium oxide were added to 100 parts of the polymer component of the concentrated latex composition obtained above, and the mixture was stirred for 24 hours. When the aqueous dispersions of the compounding agents were added, a predetermined amount was added slowly while the latex composition was being stirred. After the compounding agents were uniformly mixed, 0.5 parts of PVA22-88 (polyvinyl alcohol, manufactured by Kuraray Co., Ltd., product name "Kuraray Poval 22-88", acid amount 0.1 mmol/g, viscosity of 4% by weight aqueous solution 15 mPa·s, average degree of polymerization 1750, degree of saponification 88 mol%) was added as a thickener to obtain a latex composition for dip molding. The solids concentration and viscosity of the obtained dip molding latex composition were measured according to the above-mentioned methods. The results are shown in Table 1.

(Preparation of coagulant solution)
A coagulant solution was prepared by dissolving calcium nitrate as a coagulant in methanol at a ratio of 3.0% by weight.

(Production of protective gloves (dip-molded bodies))
First, the dip molding latex composition obtained above was aged (also called pre-vulcanization) at a temperature of 30° C. for 48 hours. Next, a ceramic glove mold covered with a glove-shaped fiber substrate (material: nylon, linear density: 300 denier, gauge number: 13 gauge, thickness: 0.8 mm) was immersed in the coagulant solution prepared above for 5 seconds, and after being pulled out of the coagulant solution, was dried at a temperature of 30° C. for 1 minute. Thereafter, the ceramic glove mold was immersed in the dip molding latex composition for 5 seconds, and after being pulled out of the dip molding latex composition, was dried at a temperature of 30° C. for 30 minutes, and then heated at a temperature of 70° C. for 10 minutes to crosslink the latex composition, thereby forming a polymer layer having a thickness of 0.6 mm on the fiber substrate. Then, the ceramic glove mold on which the polymer layer was formed was immersed in hot water at 60°C for 90 seconds to dissolve water-soluble impurities from the polymer layer, and then dried at 30°C for 10 minutes, and further heat-treated at 125°C for 30 minutes to crosslink the polymer in the polymer layer. Next, the fiber substrate on which the polymer layer was formed was peeled off from the ceramic glove mold to obtain a protective glove (dip-molded product). Then, using the obtained protective glove (dip-molded product), the chemical permeation resistance and oil grip property were measured according to the above-mentioned method, and dripping during molding was evaluated. The results are shown in Table 1.

Example 2
The latex composition obtained in the same manner as in Example 1 was concentrated by vacuum distillation at 80°C for 6 hours under a reduced pressure of 70 kPa to obtain a concentrated latex composition having a solid content of 49.2% by weight. Using the concentrated latex composition obtained, a latex composition for dip molding was obtained in the same manner as in Example 1, except that the amount of PVA22-88 used was changed to 0.4 parts, and evaluation was performed in the same manner. The results are shown in Table 1.

Then, using the obtained dip molding latex composition, a protective glove (dip molded product) having a polymer layer with a thickness of 0.6 mm was obtained in the same manner as in Example 1, and was evaluated in the same manner. The results are shown in Table 1.

Example 3
The latex composition obtained in the same manner as in Example 1 was concentrated by vacuum distillation at 80°C under reduced pressure of 70 kPa for 6.2 hours to obtain a concentrated latex composition having a solid content of 49.8% by weight. Using the obtained concentrated latex composition, a latex composition for dip molding was obtained in the same manner as in Example 1, except that the amount of PVA22-88 used was changed to 0.3 parts, and evaluation was performed in the same manner. The results are shown in Table 1.

Then, using the obtained dip molding latex composition, a protective glove (dip molded product) having a polymer layer with a thickness of 0.6 mm was obtained in the same manner as in Example 1, and was evaluated in the same manner. The results are shown in Table 1.

Example 4
A dip molding latex composition was obtained in the same manner as in Example 3, except that 0.4 parts of PVA95-88 (polyvinyl alcohol, manufactured by Kuraray Co., Ltd., product name "Kuraray Poval 95-88", acid amount 0.6 mmol/g, viscosity of 4 wt% aqueous solution 90 mPa·s, average polymerization degree: 3500, saponification degree 88 mol%) was used instead of 0.3 parts of PVA22-88, and evaluation was performed in the same manner. The results are shown in Table 1.

Then, using the obtained dip molding latex composition, a protective glove (dip molded product) having a polymer layer with a thickness of 0.6 mm was obtained in the same manner as in Example 1, and was evaluated in the same manner. The results are shown in Table 1.

Example 5
A latex composition having a solid content concentration of 40.9% by weight was obtained in the same manner as in Example 1, except that the blending ratio of the latex of the nitrile group-containing conjugated diene polymer (A-1) and the latex of the vinyl chloride resin (B-1) was changed to 60:40 in terms of the weight ratio of "nitrile group-containing conjugated diene polymer (A-1):vinyl chloride resin (B-1)".

The obtained latex composition was concentrated by vacuum distillation at 80°C for 6 hours under reduced pressure conditions of 70 kPa to obtain a concentrated latex composition with a solids concentration of 47.0% by weight. Using the obtained concentrated latex composition, a latex composition for dip molding was obtained in the same manner as in Example 1, except that the amount of PVA22-88 used was changed to 0.3 parts, and evaluation was performed in the same manner. The results are shown in Table 1.

Then, using the obtained dip molding latex composition, a protective glove (dip molded product) having a polymer layer with a thickness of 0.6 mm was obtained in the same manner as in Example 1, and was evaluated in the same manner. The results are shown in Table 1.

<Comparative Example 1>
A latex composition was obtained in the same manner as in Example 1. The aqueous dispersions of each compounding agent prepared above were added to 100 parts of the polymer component of the obtained latex composition so that the amounts were 1.0 part of colloidal sulfur, 1.0 part of zinc dibutyldithiocarbamate, 1.5 parts of zinc oxide, and 3.0 parts of titanium oxide, calculated as solid content, and the mixture was stirred for 24 hours. When the aqueous dispersions of each compounding agent were added, a predetermined amount was slowly added while the latex composition was being stirred. After the compounding agents were uniformly mixed, 1.1 parts of PVA22-88 was added as a thickener to obtain a latex composition for dip molding. The obtained latex composition for dip molding was evaluated in the same manner. The results are shown in Table 1.

Then, using the obtained dip molding latex composition, a protective glove (dip molded product) having a polymer layer with a thickness of 0.6 mm was obtained in the same manner as in Example 1, and was evaluated in the same manner. The results are shown in Table 1.

<Comparative Example 2>
Except for changing the amount of PVA22-88 to 0.7 parts, a dip molding latex composition was obtained and evaluated in the same manner as in Comparative Example 1. The results are shown in Table 1.

Then, using the obtained dip molding latex composition, a protective glove (dip molded product) having a polymer layer with a thickness of 0.6 mm was obtained in the same manner as in Example 1, and was evaluated in the same manner. The results are shown in Table 1.

<Comparative Example 3>
A latex composition having a solid content concentration of 45% by weight was obtained in the same manner as in Example 1, except that the vinyl chloride resin (B-1) latex was not blended, and the nitrile group-containing conjugated diene polymer (A-1) latex was blended in terms of solid content relative to 100 parts of the polymer component. Next, a dip molding latex composition was obtained and evaluated in the same manner as in Comparative Example 1, except that 0.3 parts of carboxymethylcellulose (manufactured by Daicel Corporation, trade name "Daicel 2200", acid amount: 3.7 mmol/g, viscosity of 1% by weight aqueous solution: 850 mPa·s, weight average molecular weight: 550,000) was used instead of 1.1 parts of PVA22-88. The results are shown in Table 1.

Then, using the obtained dip molding latex composition, a protective glove (dip molded product) having a polymer layer with a thickness of 0.6 mm was obtained in the same manner as in Example 1, and was evaluated in the same manner. The results are shown in Table 1.

As shown in Table 1, the dip molding latex composition contains a latex of a conjugated diene polymer (A) having a glass transition temperature of 10°C or less, a latex of a polymer (B) having a glass transition temperature of more than 10°C, and a thickener, and has a solids concentration of 42% by weight or more and 55% by weight or less. This results in suppressing dripping during molding and producing a dip molded product with excellent oil grip properties (Examples 1 to 5).

On the other hand, when the solid content of the dip molding latex composition was less than 42% by weight, dripping during molding could not be suppressed (Comparative Examples 1 and 2).
Furthermore, when a vinyl chloride resin latex was not blended as the latex of polymer (B) having a glass transition temperature of more than 10° C., the obtained dip-molded article had poor oil grip properties (Comparative Example 3).

Claims (11)

The present invention comprises a latex of a conjugated diene polymer (A) having a glass transition temperature of 10° C. or lower, a latex of a polymer (B) having a glass transition temperature of more than 10° C., and a thickener,
A dip molding latex composition having a solid content concentration of 42% by weight or more and 55% by weight or less,
The conjugated diene polymer (A) is a nitrile group-containing conjugated diene polymer,
The polymer (B) is a vinyl chloride resin ,
The thickener is polyvinyl alcohol,
The thickener has an acid amount of 2.5 mmol/g or less. 2. The dip-molding latex composition according to claim 1 , wherein the solid content is from 43.5% by weight to 55% by weight. The dip molding latex composition according to claim 1 or 2, wherein the conjugated diene polymer (A) is a copolymer of an α,β-ethylenically unsaturated nitrile monomer, a conjugated diene monomer, and a carboxyl group-containing ethylenically unsaturated monomer. 4. The latex composition for dip molding according to claim 1 , wherein the content of the conjugated diene polymer (A) is 40 parts by weight or more in 100 parts by weight of the polymer component. 5. The latex composition for dip molding according to claim 1 , wherein the glass transition temperature of the polymer (B) is 30° C. or higher. 6. The latex composition for dip molding according to claim 5 , wherein the glass transition temperature of the polymer (B) is 50° C. or higher. 7. The dip-molding latex composition according to claim 1 , wherein the vinyl chloride resin does not contain a plasticizer. The dip molding latex composition according to any one of claims 1 to 7 , further comprising a sulfur-based crosslinking agent. A dip-molded article obtained by using the dip-molding latex composition according to any one of claims 1 to 8 . A dip-molded article obtained by immersing a substrate in the latex composition for dip molding according to any one of claims 1 to 9 . 11. The dip-molded article according to claim 9 , wherein the polymer layer made of the latex composition for dip molding has a thickness of 0.05 to 1.0 mm.

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