Latex composition and dip-molded article

Abstract

The present invention provides a latex composition which contains 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, wherein if CS(A) (% by weight) is the chemical stability of the latex of a conjugated diene polymer (A) to CaCl2, said latex having a solid content concentration of 20% by weight, and CS(B) (% by weight) is the chemical stability of the latex of a polymer (B) to CaCl2, said latex having a solid content concentration of 20% by weight, the value of (CS(B) – CS(A)) is more than 0% by weight.

Description

[Technical Field]

[0001] The present invention relates to a latex composition, and more particularly to a latex composition that can give a dip-molded article having excellent oil grip properties. [Background technology]

[0002] Conventionally, protective gloves that have improved solvent resistance, gripping properties, abrasion resistance, etc. by covering fiber gloves with rubber, resin, etc. have been used for various purposes such as manufacturing work in factories, light work, construction work, agricultural work, etc.

[0003] Such protective gloves are usually used in contact with the human body, and therefore are required to have excellent oil grip properties in addition to excellent mechanical strength such as abrasion resistance and durability.

[0004] 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 fibrous substrate, and a coagulation step of contacting a polymer latex with the fibrous substrate to which the coagulant solution has been applied to coagulate the polymer, thereby forming a polymer layer on the fibrous substrate, and the coagulant solution is prepared by dissolving or dispersing 0.2 to 7.0 wt % of a metal salt as a coagulant and 0.1 to 7.0 wt % of an organic acid in a solvent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 061868 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the technology of Patent Document 1, a laminate having excellent flexibility and abrasion resistance can be obtained, which 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). Further improvement is required from the viewpoint of being suitable for use in applications where the gloves come into contact with oil.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a latex composition which can give a dip-molded article having excellent oil grip property. Another object of the present invention is to provide a dip-molded article obtained using such a latex composition. [Means for solving the problem]

[0008] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that, in a latex composition containing a latex of a conjugated diene polymer (A) having a glass transition temperature of 10°C or lower and a latex of a polymer (B) having a glass transition temperature of more than 10°C, the above-mentioned problems can be solved by making the chemical stability CS(A) of the latex of the conjugated diene polymer (A) to CaCl2 and the chemical stability CS(B) of the latex of the polymer (B) to CaCl2 have a specific relationship, and have thus completed the present invention.

[0009] That is, according to the present invention, there is provided a latex composition comprising a latex of a conjugated diene polymer (A) having a glass transition temperature of 10°C or lower and a latex of a polymer (B) having a glass transition temperature of more than 10°C, wherein, when the chemical stability of the latex of the conjugated diene polymer (A) to CaCl2 when the solid content concentration is 20% by weight is CS(A) (wt%), and the chemical stability of the latex of the polymer (B) to CaCl2 when the solid content concentration is 20% by weight is CS(B) (wt%), the value of (CS(B) - CS(A)) is more than 0% by weight.

[0010] The volume average particle size of the polymer particles contained in the latex composition of the present invention is preferably 250 nm or less. The volume average particle size of the polymer particles contained in the latex composition of the present invention is preferably 200 nm or less. In the latex composition of the present invention, it is preferred that the volume average particle diameter of particles of the polymer (B) contained in the latex of the polymer (B) is smaller than the volume average particle diameter of particles of the conjugated diene polymer (A) contained in the latex of the conjugated diene polymer (A). In the latex composition of the present invention, it is preferable that the volume average particle diameter of the particles of the polymer (B) contained in the latex of the polymer (B) is 200 nm or less. In the latex composition of the present invention, it is preferable that the volume average particle diameter of the particles of the polymer (B) contained in the latex of the polymer (B) is 100 nm or less. In the latex composition of the present invention, the solid content concentration is preferably 30% by weight or more. In the latex composition of the present invention, the polymer (B) preferably has a sulfate group at the polymer chain end as a residue of a polymerization initiator. In the latex composition of the present invention, the polymer (B) is preferably a polymer containing a styrene monomer unit or a (meth)acrylic acid ester monomer unit, and more preferably a polymer containing a (meth)acrylic acid ester monomer unit. In the latex composition of the present invention, the conjugated diene polymer (A) preferably contains at least one selected from styrene-butadiene rubber, nitrile rubber, and polyisoprene rubber. In the latex composition of the present invention, the conjugated diene polymer (A) is preferably a carboxyl group-containing conjugated diene polymer. In the latex composition of the present invention, the content ratio of the conjugated diene polymer (A) to the polymer (B) is preferably 1:9 to 9:1 in terms of the weight ratio of "conjugated diene polymer (A):polymer (B)".

[0011] According to the present invention, there is also provided a dip-molded article made using the above latex composition. The dip-formed article of the present invention is preferably a glove. [Effects of the Invention]

[0012] According to the present invention, there are provided a latex composition capable of giving a dip-molded article having excellent oil gripping properties, and a dip-molded article obtained using such a latex composition. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing an example of a hydrochloric acid amount-electrical conductivity curve obtained when measuring the acid amount of a water-soluble polymer. DETAILED DESCRIPTION OF THE INVENTION

[0014] <Latex composition> The latex composition of the present invention is a latex composition containing a latex of a conjugated diene polymer (A) having a glass transition temperature of 10°C or lower and a latex of a polymer (B) having a glass transition temperature of more than 10°C, The chemical stability of the latex of the conjugated diene polymer (A) against CaCl when the solid content concentration is 20% by weight is defined as CS(A) (% by weight), When the solid content concentration of the latex of the polymer (B) is 20% by weight, the chemical stability against CaCl is expressed as CS(B) (% by weight), The value of (CS(B)-CS(A)) is greater than 0% by weight.

[0015] 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)") may be any polymer having units derived from a conjugated diene monomer, and is not particularly limited. 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, from the viewpoint of making the effects of the present invention more pronounced, synthetic rubber is preferred, nitrile rubber (NBR), styrene-butadiene rubber (SBR), and synthetic polyisoprene rubber (IR) are more preferred, and conjugated diene polymers containing nitrile groups such as NBR (hereinafter referred to as "nitrile group-containing conjugated diene polymers") are even more preferred. These conjugated diene polymers may also be conjugated diene polymers containing carboxyl groups (hereinafter referred to as "carboxyl group-containing conjugated diene polymers")

[0016] The nitrile group-containing conjugated diene polymer is not particularly limited, but for example, a polymer obtained by copolymerizing an α,β-ethylenically unsaturated nitrile monomer, a conjugated diene monomer, and, if necessary, other copolymerizable ethylenically unsaturated acid monomers can be used.

[0017] 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.

[0018] 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 weight of all monomer units. By setting the content of the α,β-ethylenically unsaturated nitrile monomer units within the above range, the obtained dip-molded article can be made to have excellent solvent resistance.

[0019] 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, 1,3-butadiene and isoprene are more preferred, and 1,3-butadiene is particularly preferred. These conjugated diene monomers may be used alone or in combination of two or more.

[0020] 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 weight of the 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.

[0021] The nitrile group-containing conjugated diene polymer may also be a copolymer of a monomer that forms an α,β-ethylenically unsaturated nitrile monomer unit and a monomer that forms a conjugated diene monomer unit with another copolymerizable ethylenically unsaturated acid monomer.

[0022] Such other copolymerizable ethylenically unsaturated acid monomers are not particularly limited, and examples thereof include carboxyl group-containing ethylenically unsaturated monomers, monocarboxylic acid ester group-containing ethylenically unsaturated monomers, dicarboxylic acid diester group-containing ethylenically unsaturated monomers, sulfonic acid group-containing ethylenically unsaturated monomers, and phosphoric acid group-containing ethylenically unsaturated monomers. Among these, carboxyl group-containing ethylenically unsaturated monomers and dicarboxylic acid diester group-containing ethylenically unsaturated monomers are preferred, since they can make the nitrile group-containing conjugated diene polymer contain a carboxyl group, thereby making it possible to obtain a dip-molded article having superior tensile strength and abrasion resistance.

[0023] The carboxyl group-containing ethylenically unsaturated monomer is not particularly limited, but examples thereof include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; ethylenically unsaturated polycarboxylic acids and anhydrides thereof 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.

[0024] The monocarboxylic acid ester group-containing ethylenically unsaturated monomer is not particularly limited, but examples thereof include acrylic acid esters such as methyl acrylate; methacrylic acid esters such as methyl methacrylate; and crotonate esters such as methyl crotonate.

[0025] The dicarboxylic acid diester group-containing ethylenically unsaturated monomer is not particularly limited, but examples thereof include maleic acid diesters such as dimethyl maleate; itaconic acid diesters such as methyl itaconate; and the like.

[0026] The sulfonic acid group-containing ethylenically unsaturated monomer is not particularly limited, but examples thereof include 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.

[0027] The phosphoric acid group-containing ethylenically unsaturated monomer is not particularly limited, but examples thereof include (meth)acrylic acid-3-chloro-2-propyl phosphate, (meth)acrylic acid-2-ethyl phosphate, and 3-allyloxy-2-hydroxypropane phosphate.

[0028] 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 further preferred, and methacrylic acid is particularly preferred.

[0029] 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.

[0030] 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. During emulsion polymerization, commonly used polymerization auxiliary materials such as an emulsifier, a polymerization initiator, and a molecular weight modifier can be used.

[0031] The emulsifier used in 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 anionic surfactants 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 sulfate ester salts such as sodium lauryl sulfate and potassium lauryl sulfate; polyoxyethylene alkyl ether sulfate ester salts such as sodium polyoxyethylene lauryl ether sulfate and potassium polyoxyethylene lauryl ether sulfate; monoalkyl phosphates such as sodium lauryl phosphate and potassium lauryl phosphate; and sodium salt of β-naphthalenesulfonic acid formalin condensate. The amount of the emulsifier used in 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 all the monomers used.

[0032] The polymerization initiator is not particularly limited, but a radical initiator is preferred.The radical initiator is not particularly limited, but for example, 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 azobismethylisobutyrate; and the like. Among these, inorganic peroxides or organic peroxides are preferred, inorganic peroxides are more preferred, and persulfates are particularly preferred. 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 all the monomers used.

[0033] When a peroxide is used as a polymerization initiator, it can also be used in combination with a reducing agent as a redox polymerization initiator. Examples of the reducing agent include, but are not limited to, compounds containing reduced metal ions such as ferrous sulfate and cuprous naphthenate; sulfonic acid compounds such as sodium methanesulfonate; amine compounds such as dimethylaniline; and carboxylic acid compounds such as sodium ethylenediaminetetraacetate. 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 the peroxide.

[0034] The molecular weight modifier is not particularly limited, but examples thereof include α-methylstyrene dimer; mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, and octyl mercaptan; halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, and methylene bromide; sulfur-containing compounds such as tetraethylthiuram disulfide, dipentamethylenethiuram disulfide, and diisopropylxanthogen disulfide; and the like. Among these, mercaptans are preferred, and t-dodecyl mercaptan is more preferred. These molecular weight modifiers may be used alone or in combination of two or more. The amount of molecular weight modifier 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 all the monomers used.

[0035] Emulsion polymerization is usually carried out in water, and 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 all the monomers used.

[0036] In emulsion polymerization, if necessary, other polymerization secondary materials may be used, such as a chelating agent, a dispersant, a pH adjuster, an oxygen scavenger, a particle size adjuster, etc., and the type and amount of these materials are not particularly limited.

[0037] Examples of the method for adding the monomers include a method in which the monomers to be used are added all at once to a reaction vessel, a method in which the monomers are added continuously or intermittently as the polymerization proceeds, a method in which a portion of the monomers is added and reacted to a specific conversion rate, and then the remaining monomers are added continuously or intermittently to polymerize, and any of these methods may be employed. When the monomers are mixed and added continuously or intermittently, the composition of the mixture may be constant or may be changed. 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.

[0038] 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.

[0039] After the polymerization reaction is terminated, if desired, the unreacted monomer may be removed and the solid content concentration and pH may be adjusted.

[0040] 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., more preferably −40 to −10° C., and particularly preferably −35 to −15° 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 adjusting the glass transition temperature of the conjugated diene polymer (A) to fall within the above range, and examples thereof include a method in which the content ratio of each monomer constituting the conjugated diene polymer (A) falls within the above range.

[0041] The chemical stability (CS(A)) of the latex of the conjugated diene polymer (A) to CaCl2, as described below, in relation to the chemical stability (CS(B)) of the latex of the polymer (B) to CaCl2, (CS(B) - CS(A)) may be such that the value of (CS(B) - CS(A)) exceeds 0% by weight. The chemical stability (CS(A)) of the latex of the conjugated diene polymer (A) to CaCl2 is preferably greater than 0% by weight and not more than 0.5% by weight, more preferably 0.001 to 0.25% by weight, and even more preferably 0.005 to 0.1% by weight. By setting the chemical stability (CS(A)) of the latex of the conjugated diene polymer (A) to CaCl2 within the above range, the oil grip property of the resulting dip-molded article can be further improved.

[0042] In the present invention, the chemical stability (CS(A)) of the latex of the conjugated diene polymer (A) to CaCl2 can be measured as the chemical stability to CaCl2 when the solids concentration of the latex of the conjugated diene polymer (A) is 20% by weight, as follows. First, the latex of the conjugated diene polymer (A) is diluted with distilled water to prepare a latex of the conjugated diene polymer (A) diluted to a solids concentration of 20% by weight. In addition, approximately 5 to 10 types of aqueous CaCl2 solutions are prepared at different concentrations (wt%) between 0.01 and 5% by weight. Here, the change in chemical stability when the CaCl2 concentration is changed tends to be greater as the CaCl2 concentration is lower and smaller as the CaCl2 concentration is higher. That is, at relatively low concentrations of 0.3 wt% or less, a change in concentration of about 0.1 wt% changes the chemical stability, while at relatively high concentrations of over 0.3 wt%, varying the concentration in increments of 0.2 to 0.25 wt% tends to be sufficient to confirm changes in chemical stability. Keeping this in mind when preparing the CaCl2 aqueous solutions, approximately 5 to 10 different CaCl2 aqueous solutions are prepared, with smaller increments for lower CaCl2 concentrations and larger increments for higher CaCl2 concentrations. Next, 6 to 7 g of each of the prepared CaCl2 aqueous solutions with different concentrations is weighed into a dish, and 0.03 to 0.04 g of the diluted conjugated diene polymer (A) latex is dropped into it. After dropping, the mixture is left to stand for 1 minute, and then the dish is gently shaken to mix. After mixing, the occurrence of aggregates is checked visually or otherwise. Among the aqueous CaCl2 solutions to which no aggregates were generated when the diluted latex of the conjugated diene polymer (A) was added dropwise, the CaCl2 concentration of the aqueous CaCl2 solution having the maximum CaCl2 concentration is defined as the chemical stability (CS(A)) of the latex of the conjugated diene polymer (A).

[0043] 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 1,000 nm, more preferably 50 to 500 nm, even more preferably 70 to 200 nm, and particularly preferably 90 to 150 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 above 10°C can be more effectively finely dispersed in the conjugated diene polymer (A) in the obtained dip-molded article, thereby improving abrasion resistance. The volume average particle diameter of the particles of the conjugated diene polymer (A) constituting the latex of the conjugated diene polymer (A) can be measured, for example, using a light scattering / diffraction particle analyzer.

[0044] The tetrahydrofuran insoluble content of the polymer (A) is not particularly limited, but is preferably 20 to 80% by weight, more preferably 30 to 70% by weight, and even more preferably 40 to 60% by weight. The tetrahydrofuran insoluble content of the polymer (A) is an index showing the gel content of the polymer (A).

[0045] The tetrahydrofuran insoluble content of polymer (A) can be measured, for example, by the following method. First, a latex of polymer (A) is applied to a substrate by a casting method or the like, and then dried to obtain a dry film, and the weight of the dry film is measured. The dry film obtained is then immersed in tetrahydrofuran at 25°C for 24 hours. The immersed film is then dried at 105°C for 3 hours to remove the tetrahydrofuran, and the weight of the film after the tetrahydrofuran removal is measured. The tetrahydrofuran insoluble content can be determined from these weight measurement results.

[0046] The polymer (B) having a glass transition temperature of more than 10°C (hereinafter referred to as "polymer (B)") constituting the latex of polymer (B) having a glass transition temperature of more than 10°C (hereinafter referred to as "latex of polymer (B)") is not particularly limited as long as it has a glass transition temperature of more than 10°C and, when made into a latex, has higher chemical stability to CaCl than the latex of the conjugated diene polymer (A). That is, it is sufficient that the glass transition temperature is more than 10°C and, when the solid content concentration of the latex of polymer (B) is 20 wt%, the chemical stability to CaCl of the latex of the conjugated diene polymer (A) is CS(B) (wt%), so that the value of (CS(B) - CS(A)) exceeds 0 wt%.

[0047] The chemical stability CS(B) (wt %) of the latex of polymer (B) against CaCl when the solid content concentration is 20 wt % can be measured as the chemical stability of the latex of polymer (B) against CaCl when the solid content concentration is 20 wt % in the same manner as the method for measuring the chemical stability (CS(A)) of the latex of conjugated diene polymer (A) against CaCl described above.

[0048] The polymer (B) is not particularly limited, but examples thereof include acrylic resin, PTFE resin, acrylonitrile-styrene (AS) resin, polyurethane, etc., among which acrylic resin is preferred from the viewpoint of its high oil grip improving effect. These polymers may be used alone or in combination of two or more. When two or more polymers are used in combination as the polymer (B), the chemical stability (CS(B)) of the latex containing the two or more polymers used in combination against CaCl may be such that (CS(B)) exceeds 0% by weight in relation to the chemical stability (CS(A)) of the latex of the conjugated diene polymer (A) against CaCl. For example, when polymer (B) is a combination of a first polymer and a second polymer, a latex containing only the first polymer may satisfy (CS(B)-CS(A))=0% by weight or more, while a latex containing only the second polymer may have CS(B)-CS(A)=0% by weight or less. However, the latex containing both the first polymer and the second polymer may satisfy (CS(B)-CS(A))=0% by weight or more. For example, when polymer (B) is a combination of an acrylic resin and a polymer other than acrylic resin, examples of the polymer used in combination with the acrylic resin include polystyrene resin, PTFE resin, acrylonitrile-styrene (AS) resin, and polyurethane. In this case, the weight ratio of the acrylic resin to the polymer other than acrylic resin is preferably 1:9 to 9:1, more preferably 3:7 to 7:3.

[0049] Examples of acrylic resins include homopolymers of acrylic acid esters, methacrylic acid esters, acrylic acid, or methacrylic acid, copolymers of acrylic acid esters and acrylic acid, copolymers of acrylic acid esters and methacrylic acid, copolymers of methacrylic acid esters and acrylic acid, copolymers of methacrylic acid esters and methacrylic acid, copolymers of acrylic acid esters, methacrylic acid esters, and acrylic acid, copolymers of acrylic acid esters, methacrylic acid esters, and methacrylic acid, and copolymers of acrylic acid esters, methacrylic acid esters, acrylic acid, and methacrylic acid. Among these, it is preferable to use homopolymers of acrylic acid esters, methacrylic acid esters, acrylic acid, or methacrylic acid, and it is more preferable to use homopolymers of methacrylic acid esters.

[0050] Examples of acrylic acid esters used to form the acrylic resin include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-pentyl acrylate, sec-pentyl acrylate, isopentyl acrylate, neopentyl acrylate, n-hexyl acrylate, isohexyl acrylate, neohexyl acrylate, sec-hexyl acrylate, and tert-hexyl acrylate. Of these, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, and n-butyl acrylate are preferred, and methyl acrylate is more preferred.

[0051] Examples of methacrylic acid esters used to form the acrylic resin include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, sec-pentyl methacrylate, isopentyl methacrylate, neopentyl methacrylate, n-hexyl methacrylate, isohexyl methacrylate, neohexyl methacrylate, sec-hexyl methacrylate, and tert-hexyl methacrylate. Of these, methyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, and n-butyl methacrylate are preferred, methyl methacrylate is more preferred, and a homopolymer of methyl methacrylate (polymethyl methacrylate) is particularly preferred.

[0052] The acrylic resin as polymer (B) may be a copolymer of an acrylic acid ester monomer, a methacrylic acid ester monomer, an acrylic acid monomer, or a methacrylic acid monomer with other monomers copolymerizable therewith.

[0053] Other copolymerizable monomers 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 polycarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; α,β-ethylenically unsaturated polycarboxylic acid monoesters such as monomethyl maleate, monoethyl maleate, and monoethyl itaconate; dimethyl maleate, fumaric acid, and the like. Examples of suitable copolymerizable monomers include α,β-ethylenically unsaturated polycarboxylic acid polyesters such as di-n-butyl itaconate, 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, aromatic monomers are preferred, and styrene is more preferred. The content of units of other copolymerizable monomers is preferably 1 to 99% by weight, more preferably 5 to 95% by weight.

[0054] The method for producing the acrylic resin latex as polymer (B) is not particularly limited as long as it is a method capable of polymerizing the above-mentioned monomers, and examples thereof include known methods such as emulsion polymerization by radical polymerization, seed emulsion polymerization, and fine suspension polymerization.

[0055] The polymer (B) is preferably one obtained by using a persulfate such as sodium persulfate, potassium persulfate, or ammonium persulfate as a polymerization initiator. By using a persulfate as a polymerization initiator, the polymer (B) can have a sulfate group at the polymer chain end as a residue of the polymerization initiator, and thus the latex of the polymer (B) can be made to have better chemical stability.

[0056] The weight average molecular weight (Mw) of the acrylic resin as the polymer (B) is not particularly limited, but is preferably 10,000 to 10,000,000, and more preferably 10,000 to 5,000,000.

[0057] 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 70° C. or higher, even more preferably 95° C. or higher, and particularly preferably 105° 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.

[0058] In the latex composition of the present invention, the difference (CS(B)-CS(A)) between the chemical stability of the latex of polymer (B) against CaCl2 (CS(B)) and the chemical stability of the latex of conjugated diene polymer (A) against CaCl2 is greater than 0% by weight, preferably 0.1 to 40.0% by weight, more preferably 0.3 to 40.0% by weight, even more preferably 0.5 to 5% by weight, and particularly preferably 0.7 to 2% by weight. If the difference in chemical stability (CS(B)-CS(A)) is too low, the resulting dip-molded article will have poor oil grip properties.

[0059] The chemical stability (CS(B)) of the latex of polymer (B) to CaCl2 in relation to the chemical stability (CS(A)) of the latex of conjugated diene polymer (A) to CaCl2, (CS(B)-CS(A)) may be within the above range. The chemical stability (CS(B)) of the latex of polymer (B) to CaCl2 is not particularly limited, but is preferably 0.1 to 40.0 wt%, more preferably 0.2 to 40.0 wt%, even more preferably 0.3 to 40.0 wt%, still more preferably 0.5 to 5 wt%, and particularly preferably 0.7 to 2 wt%. By ensuring that the chemical stability (CS(B)) of the latex of polymer (B) to CaCl2 within the above range, the oil grip property of the resulting dip-molded article can be further improved.

[0060] The latex composition of the present invention is preferably a latex composition obtained by mixing, in a latex state, a latex of a conjugated diene polymer (A) having a glass transition temperature of 10° C. or lower 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 gripping properties.

[0061] In particular, by mixing a latex of a conjugated diene polymer (A) and a latex of a polymer (B) in a latex state, particles of the conjugated diene polymer (A) and particles of the polymer (B) can be uniformly and finely dispersed in the latex composition. When a dip-molded article is obtained by dip-molding, the polymer (B) can be co-precipitated in a finely dispersed state in the matrix of the conjugated diene polymer (A) in the obtained dip-molded article. Therefore, the finely dispersed polymer (B) can provide the obtained dip-molded article with even better oil gripping properties. While the latex composition of the present invention is preferably prepared by mixing a latex of a conjugated diene polymer (A) and a latex of a polymer (B) in a latex state, the latex composition of the present invention is not particularly limited to a composition obtained by mixing these latexes, as long as particles of the conjugated diene polymer (A) and particles of the polymer (B) are dispersed in an aqueous medium.

[0062] If the glass transition temperature of the polymer (B) constituting the latex of the polymer (B) is too low, the dip-molded article obtained will have poor oil grip properties. The method for adjusting the glass transition temperature of the polymer (B) to the above range is not particularly limited, but for example, when a vinyl chloride resin latex is used as the latex of the polymer (B), a method in which 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, can be mentioned.

[0063] From the viewpoint of further enhancing the oil grip property of the obtained dip-molded article, it is preferable that the volume average particle diameter of the particles of polymer (B) constituting the latex of polymer (B) is smaller than the volume average particle diameter of the particles of conjugated diene-based polymer (A) constituting the latex of conjugated diene-based polymer (A).

[0064] The volume average particle diameter of the polymer (B) particles constituting the latex of polymer (B) is preferably 1 to 200 nm, more preferably 5 to 160 nm, even more preferably 5 to 120 nm, still more preferably 10 to 100 nm, and particularly preferably 20 to 80 nm. By setting the volume average particle diameter of the polymer (B) particles within the above range, the polymer (B) can be more effectively finely dispersed in the conjugated diene polymer (A) in the obtained dip-molded article, thereby improving abrasion resistance. The volume average particle diameter of the polymer (B) particles constituting the latex of polymer (B) can be measured, for example, using a light scattering diffraction particle analyzer (manufactured by Coulter, product name "LS-230").

[0065] The tetrahydrofuran insoluble content of polymer (B) is not particularly limited, but is preferably 5 to 60% by weight, more preferably 10 to 50% by weight, and even more preferably 20 to 40% by weight. The tetrahydrofuran insoluble content of polymer (B) is an index showing the gel content of polymer (B). When the tetrahydrofuran insoluble content of polymer (B) is within the above range, the chemical stability of the obtained latex composition can be further improved, and in turn, the oil grip property of the obtained dip-molded article can be further improved. The tetrahydrofuran insoluble content of polymer (B) can be measured in the same manner as the tetrahydrofuran insoluble content of polymer (A).

[0066] The contents of the conjugated diene polymer (A) and the polymer (B) in the 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 components contained in the latex composition (when the latex composition contains only the conjugated diene polymer (A) and the polymer (B) as the polymer components, the total of the conjugated diene polymer (A) and the polymer (B) is 100 parts by weight) 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. Furthermore, the content of the polymer (B) in 100 parts by weight of the polymer components contained in the 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) to the polymer (B) in the latex composition of the present invention, expressed as a weight ratio of "conjugated diene polymer (A):polymer (B)", is preferably 99:1 to 1:99, more preferably 90:10 to 10:90, even more preferably 80:20 to 20:80, and particularly preferably 75:25 to 25:75. By setting the contents 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.

[0067] The latex composition of the present invention may further contain a water-soluble polymer.

[0068] Examples of water-soluble polymers 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 such as polyacrylic acid and sodium salts thereof; and polyoxyethylene derivatives such as polyethylene glycol ether. Preferred water-soluble polymers are cellulose derivatives and salts thereof, and more preferred are carboxymethyl cellulose and sodium salts thereof. The content of the water-soluble polymer is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, per 100 parts by weight of the polymer component contained in the first latex composition.

[0069] The acid amount of the water-soluble polymer is not particularly limited, but is preferably 10 mmol / g or less. That is, the first latex composition used in the present invention preferably contains a water-soluble polymer having an acid amount of 10 mmol / g or less.

[0070] When the latex composition of the present invention contains a water-soluble polymer having an acid amount of 10 mmol / g or less in addition to the latex of the conjugated diene polymer (A) and the latex of the polymer (B), the obtained dip-molded article can have more excellent oil grip properties.

[0071] The acid content of the water-soluble polymer is preferably 10 mmol / g or less, more preferably 5 mmol / g or less, and even more preferably 2.5 mmol / g or less. The lower limit of the acid content of the water-soluble polymer is not particularly limited, but is usually 0.001 mmol / g or more. When the acid content of the water-soluble polymer is within the above range, the obtained dip-molded article has excellent oil grip properties.

[0072] The water-soluble polymer having an acid amount of 10 mmol / g or less is not particularly limited, and examples thereof include vinyl compounds such as polyvinyl alcohol and polyvinylpyrrolidone; carboxylic acid-modified vinyl compounds such as carboxylic acid-modified polyvinyl alcohol and carboxylic acid-modified polyvinylpyrrolidone; cellulose derivatives and salts thereof such as hydroxyethyl cellulose, hydroxypropyl cellulose, and carboxymethyl cellulose; polyoxyethylene derivatives such as polyethylene glycol ether; etc. These water-soluble polymers may be used alone or in combination of two or more.

[0073] The acid content of the water-soluble polymer can be measured, for example, by the following method. First, 50 g of a water-soluble polymer solution (W (g) represents the amount of water-soluble polymer solids in 50 g of water-soluble polymer solution) was placed in a 200 ml glass container washed with distilled water and adjusted to a solids concentration of 0.2-1% with distilled water. The container was then placed in a solution conductivity meter (Kyoto Electronics Manufacturing Co., Ltd.: CM-117, cell type: K-121) and stirring was initiated. Next, while continuing stirring, 0.1 N sodium hydroxide was added to the solution so that the pH of the solution was 12 or higher. The electrical conductivity was measured after 6 minutes, and this measurement was taken as the initial electrical conductivity. Then, 0.5 ml of 0.1 N hydrochloric acid was added to the water-soluble polymer solution, and the electrical conductivity was measured 30 seconds later. Another 0.5 ml of 0.1 N hydrochloric acid was added, and the electrical conductivity was measured 30 seconds later. This procedure was repeated at 30-second intervals until the electrical conductivity reached at least twice the initial value. The obtained electrical conductivity data was then plotted on a graph with the vertical axis representing electrical conductivity (mS) and the horizontal axis representing the cumulative amount of hydrochloric acid added (mmol), yielding a hydrochloric acid amount-electrical conductivity curve with two inflection points, as shown in Figure 1. The X-coordinates of the two obtained inflection points and the X-coordinate at the end of hydrochloric acid addition were designated P1, P2, and P3, respectively, in ascending order. The data within the three X-coordinate ranges from zero to P1, P1 to P2, and P2 to P3 were fitted with straight lines L1, L2, and L3, respectively, using the least squares method. The X-coordinate of the intersection of L1 and L2 was designated A1 (mmol), and the X-coordinate of the intersection of L2 and L3 was designated A2 (mmol). The amount of acid per gram of water-soluble polymer was then calculated using the following formula: Amount of acid per 1g of water-soluble polymer = (A2-A1) / W (mmol / g)

[0074] When two or more kinds of water-soluble polymers are used in combination, the water-soluble polymers are mixed in the same ratio as the ratio of the water-soluble polymers present in the latex composition of the present invention to obtain a water-soluble polymer mixture, and the acid amount of the water-soluble polymer mixture obtained by measuring the acid amount in the same manner as above can be used as the acid amount of the water-soluble polymer.

[0075] The viscosity of a 4 wt % aqueous solution of the water-soluble polymer 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 a 1 wt % aqueous solution of the water-soluble polymer 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 aqueous solution of the water-soluble polymer can be measured, for example, using a Brookfield viscometer at 25°C and a rotation speed of 6 rpm.

[0076] The water-soluble polymer may be any polymer as long as it is soluble in water, and the solubility of the water-soluble polymer in water is not particularly limited, but is preferably 1 g or more, more preferably 7 g or more, and particularly preferably 10 g or more per 100 g of water at a temperature of 25° C. The upper limit of the solubility of the water-soluble polymer in water is not particularly limited, but is usually 1,000,000 g or less.

[0077] The weight average molecular weight (Mw) of the water-soluble polymer is not particularly limited, but is preferably 100 or more, more preferably 1,000 or more, and is preferably 5,000,000 or less, more preferably 3,000,000 or less.

[0078] The amount of the water-soluble polymer to be blended 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, based on 100 parts by weight of the polymer component contained in the latex composition of the present invention. When the amount of the water-soluble polymer to be blended is within the above range, the obtained dip-molded article has better oil grip properties.

[0079] In the latex composition of the present invention, the volume average particle diameter of the polymer particles is preferably 30 to 250 nm, more preferably 30 to 200 nm, even more preferably 50 to 180 nm, and particularly preferably 80 to 150 nm. By setting the volume average particle diameter of the polymer particles in the latex composition within the above range, the resulting latex composition can be made to have excellent storage stability, and the resulting dip-molded article can be made to have excellent oil grip properties. The volume average particle diameter of the polymer particles in the latex composition of the present invention can be measured, for example, using a light scattering / diffraction particle analyzer.

[0080] The solids concentration of the latex composition of the present invention is preferably 20 to 65% by weight, more preferably 30 to 60% by weight, and even more preferably 35 to 55% by weight. By controlling the solids concentration of the latex composition within the above range, the transport efficiency of the latex composition can be improved, and the viscosity of the latex composition becomes appropriate, improving the handleability of the latex composition.

[0081] The solid content of the latex composition of the present invention can be adjusted to the above range by, for example, adjusting the solid content of each component such as the latex of the conjugated diene polymer (A), or by a concentration treatment or dilution treatment, which will be described later. Among these, the concentration treatment is preferred from the viewpoint of productivity.

[0082] The pH of the 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 latex composition within the above range, the mechanical stability is improved, making it possible to suppress the generation of coarse aggregates during transportation of the latex composition, and the viscosity of the latex composition becomes appropriate, improving the handleability of the latex composition.

[0083] The latex composition of the present invention may further contain fillers such as carbon black, silica, calcium carbonate, aluminum silicate, magnesium silicate, calcium silicate, magnesium oxide, zinc (meth)acrylate, magnesium (meth)acrylate, titanium oxide, etc. If necessary, the first latex composition used in the present invention may further contain predetermined amounts of 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.

[0084] The 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 improving the dispersibility of each component, a method is preferred in which the latex of the conjugated diene polymer (A) and the latex of the polymer (B) are premixed, and then a thickener and each component to be blended as necessary are added and mixed. 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 improving the dispersibility, a method of mixing the latex of the conjugated diene polymer (A) and the latex of the polymer (B) in the latex state (latex blending) is preferred.

[0085] The latex composition of the present invention is preferably obtained through a concentration treatment. The concentration treatment method is not particularly limited, but examples thereof include vacuum distillation, atmospheric distillation, centrifugation, membrane concentration, etc. Among these, a concentration method involving heating is preferred, and vacuum distillation involving heating is more preferred. By employing a concentration method involving heating, it is possible to reduce bacteria that cause odor or to inhibit the growth of bacteria that cause odor, thereby making the latex composition excellent in low odor properties.

[0086] In a concentration method involving heating, the heating temperature is preferably 50° C. to 100° C. In addition, in a reduced pressure distillation, the pressure is preferably 20 kPa to 90 kPa.

[0087] The concentration treatment may be performed on a mixture containing some of the components to be blended in the latex composition, or on a mixture containing all of the components to be blended in the latex composition. From the viewpoints of dispersibility of the latex composition and production efficiency, 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).

[0088] That is, as a method for producing the latex composition of the present invention, a method is preferred in which a latex of the conjugated diene polymer (A) and a latex of the polymer (B) are mixed in advance, and then the obtained mixture is subjected to a concentration treatment to increase the solid content concentration, and then each component to be blended as necessary is added and mixed to adjust the solid content concentration to the above-mentioned range.

[0089] <Dip-molded body> The dip-molded article of the present invention is a molded article obtained using the above-mentioned latex composition of the present invention, and is usually obtained by dip-molding the above-mentioned latex composition of the present invention.

[0090] The dip-molded article of the present invention is a molded article obtained using the latex composition of the present invention described above, and therefore has at least a polymer layer containing the conjugated diene polymer (A) having a glass transition temperature of 10° C. or lower and the 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 latex composition of the present invention described above.

[0091] The dip-molded article of the present invention may be a film-molded article made of the latex composition for dip molding, which is obtained by immersing a dip-molding mold in a latex composition for dip molding such as the latex composition of the present invention described above, or may be a laminate of a substrate and a polymer layer made of the latex composition for dip molding, which is obtained by immersing the substrate in the latex composition for dip molding. Hereinafter, a case where the dip-molded article of the present invention is a laminate of a substrate and a polymer layer made of the latex composition for dip molding will be described as an example, but the present invention is not limited to such an embodiment.

[0092] The substrate is not particularly limited, but when the dip-molded article of the present invention is used as a protective glove, a fibrous substrate can be suitably used. The fibrous substrate is not particularly limited, but for example, a glove can be formed by weaving a twisted monofilament yarn. The average thickness of the fibrous substrate is preferably 50 to 3,000 μm, more preferably 100 to 2,000 μm.

[0093] 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 in a state in which the substrate is previously placed on a molding die having a desired shape.

[0094] 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 may be a desired shape according to the shape of the final product. For example, when the dip-molded article of the present invention is used as a protective glove, it is preferable to use various types of molds for gloves, such as molds having a shape from the wrist to the fingertips, as the mold for covering the substrate.

[0095] Furthermore, before immersing the substrate in the dip-molding latex composition, it is preferable to first immerse the substrate in a coagulant solution to 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 first placed over a mold of the desired shape. Examples of molds of the desired shape include those described above. Furthermore, after adhering the coagulant solution to the substrate, it is preferable to remove the solvent contained in the coagulant solution by drying. The drying temperature is not particularly limited and may be selected depending on the solvent used, but is preferably 10 to 80°C, more preferably 15 to 70°C. The drying time is not particularly limited, but is preferably 600 to 1 second, more preferably 300 to 5 seconds.

[0096] Next, the substrate with the coagulant solution attached thereto is placed over a molding die of a desired shape, and is immersed in the latex composition for dip molding while it is still in this state, thereby coagulating the latex composition for dip molding and adhering a polymer layer made of the latex composition for dip molding onto the substrate.

[0097] After immersing the substrate in the latex composition for dip molding, it is preferable to dry the substrate. 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.

[0098] When a latex composition for dip molding containing a sulfur-based crosslinking agent is used, the latex composition for dip molding may be aged in advance (also referred to as pre-vulcanized).

[0099] The temperature condition for aging is not particularly limited, but is 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.

[0100] 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.

[0101] The heating temperature for crosslinking is preferably 60 to 160°C, more preferably 80 to 150°C. By setting the heating temperature within this range, the time required for the crosslinking reaction can be shortened, thereby improving the productivity of dip-molded articles, and oxidation degradation of the polymer component due to excessive heating can be suppressed, thereby improving the physical properties of the obtained dip-molded articles. The heating time for crosslinking can be appropriately selected depending on the heating temperature, but is usually 5 to 120 minutes.

[0102] It is preferable to remove water-soluble impurities (such as emulsifiers, water-soluble polymers, and coagulants) from the polymer layer of the dip-formed article thus obtained 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 treatment 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 treatment before crosslinking the polymer components in the polymer layer, since this allows for more efficient removal of water-soluble impurities.

[0103] After immersion in warm water, drying may be further performed. The drying temperature and drying time at this time are not particularly limited, but can be the same as the drying temperature and drying time in the drying step after immersion in the latex composition for dip molding described above.

[0104] Then, after forming a polymer layer on the substrate while the substrate is placed over the mold as described above, the dip-molded article can be obtained by removing it from the mold (or demolding it). Methods for removing it from the mold include peeling it off by hand, or by using water pressure or compressed air.

[0105] Before or after the dip-molded article is removed from the mold, it may be further subjected to a heat treatment (post-crosslinking step) at a temperature of 60 to 130°C for 10 to 120 minutes. After the dip-molded article is removed from the mold, a surface treatment layer may be formed on the inner and / or outer surfaces of the dip-molded article by a chlorination treatment, a coating treatment, or the like.

[0106] The dip-molded article of the present invention thus obtained is a polymer layer formed on a substrate by coagulation using a coagulant, which is made of the latex composition of the present invention. The thickness of the polymer layer is preferably 0.05 to 1.0 mm, more preferably 0.06 to 0.8 mm, and even more preferably 0.07 to 0.7 mm, thereby improving the abrasion resistance of the dip-molded article obtained. While a relatively thick film usually tends to reduce oil grip properties, the dip-molded article of the present invention can achieve excellent oil grip properties even when the film is relatively thick.

[0107] The dip-molded article of the present invention may further include other polymer layers in addition to the substrate and the polymer layer composed of the latex composition of the present invention. That is, the dip-molded article may include two or more polymer layers on a substrate. The other polymer layers are not particularly limited, but are preferably polymer layers formed using a latex composition other than the latex composition of the present invention. Examples of such latex compositions include latex compositions containing a nitrile group-containing conjugated diene polymer, a styrene-butadiene rubber (SBR) latex, a synthetic polyisoprene rubber (IR) latex, etc. Among these, a latex composition containing a nitrile group-containing conjugated diene polymer is preferred from the viewpoint of providing the resulting dip-molded article with excellent oil permeation resistance. Furthermore, the latex of the nitrile group-containing conjugated diene polymer may be, for example, the latex of the nitrile group-containing conjugated diene polymer described above as an example of the latex of the conjugated diene polymer (A). From the viewpoint of improving the oil gripping property of the resulting dip-molded article, it is preferred that the polymer layer made of the latex composition of the present invention be the outermost layer.

[0108] In the case where two or more polymer layers are provided, the film thickness of each polymer layer is not particularly limited. For example, it is preferable that the total film thickness of all polymer layers is within the above-mentioned preferred film thickness range of the polymer layer made of the latex composition of the present invention.

[0109] In the case of an embodiment having two or more polymer layers, the manufacturing method is not particularly limited, but examples thereof include a method in which a coagulant solution is applied to a substrate, and then the substrate is immersed in a latex composition for forming another polymer layer at any timing, and then dried and washed appropriately to form another polymer layer, and then a polymer layer made of the latex composition of the present invention is formed thereon according to the above-mentioned method.

[0110] The dip-molded article of the present invention has excellent oil grip properties and can be suitably used, for example, for gloves, particularly for protective gloves. Although the above description has been given by exemplifying the case where the dip-molded article of the present invention is a laminate of a substrate and a polymer layer made of the latex composition for dip molding, as mentioned above, the present invention is not limited to such an embodiment, and it is of course also possible to form a film-molded article made of the latex composition for dip molding by immersing a dip-molding mold in the latex composition for dip molding. [Example]

[0111] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following, "parts" are by weight unless otherwise specified. Various physical properties were measured as follows.

[0112] <Volume average particle size> The volume average particle size of the polymer particles constituting each polymer latex was measured using a light scattering diffraction particle analyzer (manufactured by Coulter, trade name "LS-230").

[0113] <Solids content of the dip molding latex composition> 2 g of sample was weighed out (weight: X2) onto an aluminum dish (weight: X1) and dried for 2 hours in a hot air dryer at 105°C. After cooling in a desiccator, the weight of the aluminum dish was measured (weight: X3), and the solid content was calculated according to the following formula. Solid content concentration (wt%)=(X3-X1)×100 / X2

[0114] <Tetrahydrofuran insoluble content> The latex of each polymer (polymers (A-1), (B-1) to (B-5)) was applied to a substrate by a casting method, and then dried at 25°C for 120 hours to obtain a dry film. The weight (W1 (kg)) of the dry film was measured. The dry film was then immersed in tetrahydrofuran at 25°C for 24 hours, and the immersed film was then dried at 105°C for 3 hours to remove the tetrahydrofuran. The weight (W2 (kg)) of the film after tetrahydrofuran removal was then measured, and the tetrahydrofuran insoluble content was calculated according to the following formula. Tetrahydrofuran insoluble content (unit: weight %) = 100 × W2 (kg) / W1 (kg)

[0115] <Chemical stability measurement> The latex of the conjugated diene polymer (A) and the latex of the polymer (B) were each diluted with distilled water to a solid content of 20% by weight. Additionally, distilled water was used to prepare aqueous CaCl2 solutions of the following concentrations: 0.01% by weight, 0.1% by weight, 0.2% by weight, 0.3% by weight, 0.5% by weight, 0.75% by weight, 1.0% by weight, 1.2% by weight

[0116] 6 to 7 g of each of the above-mentioned CaCl2 aqueous solutions was weighed onto a dish, and 0.03 to 0.04 g of 20 wt% diluted latex was dropped into it. After dropping, the solution was left to stand for 1 minute and then gently shaken to mix. After mixing, the occurrence of agglomerates was visually determined. The maximum concentration of CaCl2 aqueous solution at which the occurrence of agglomerates was not confirmed was taken as the chemical stability of the polymer latex, and the chemical stability of the latex of conjugated diene polymer (A) (CS(A)) and the chemical stability of the latex of polymer (B) (CS(B)) were calculated. The difference in chemical stability (CS(B) - CS(A)) was calculated by subtracting the chemical stability of the latex of conjugated diene polymer (A) (CS(A)) from the chemical stability of the latex of polymer (B) (CS(B)).

[0117] <Oil grip> Metal molds were prepared with different weights ranging from 0.5 kg to 15.0 kg in 0.5 kg increments. Three workers were asked to wear protective gloves (dip-molded products) and lift the dry metal molds in order of weight, starting with the lightest. The maximum weight (W3 (kg)) that could be lifted was determined for each of the three workers. Next, test oil IRM903 was applied to the metal molds. Three workers were asked to wear protective gloves (dip-molded products) and lift the metal molds with test oil IRM903 applied in order of weight, starting with the lightest. The maximum weight (W4 (kg)) that could be lifted was determined for each of the three workers. The scores calculated for each of the three workers using the following formula were then arithmetically averaged to calculate an average score for evaluation. The higher the score, the greater the maximum weight that could be lifted, and the better the oil grip performance. (Score) = 100 x W3 (kg) / W4 (kg)

[0118] Example 1 (Preparation of aqueous dispersion of colloidal sulfur) An aqueous dispersion of colloidal sulfur with a solids concentration 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, trade name "Demol N"), 0.0015 parts of a 5 wt % aqueous potassium hydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.) and 1.0 part of water in a ball mill for 48 hours.

[0119] (Preparation of aqueous dispersions of zinc dibutyldithiocarbamate, zinc oxide, and titanium oxide) An aqueous dispersion of zinc dibutyldithiocarbamate with a solids concentration of 50% by weight, an aqueous dispersion of zinc oxide with a solids concentration of 50% by weight, and an aqueous dispersion of titanium oxide with a solids concentration of 50% by weight 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.

[0120] (Preparation of Latex of Nitrile Group-Containing Conjugated Diene Polymer (A-1)) A polymerization reactor was charged with 66 parts of 1,3-butadiene as a conjugated diene monomer, 30 parts of acrylonitrile as an α,β-ethylenically unsaturated nitrile monomer, 4 parts of methacrylic acid as an ethylenically unsaturated monocarboxylic acid monomer, 1 part of t-dodecyl mercaptan, 200 parts of ion-exchanged water, 3 parts of sodium dodecylbenzenesulfonate, 1 part of β-naphthalenesulfonic acid formalin condensate sodium salt, 0.1 parts of potassium persulfate, and 0.1 parts of ethylenediaminetetraacetic acid sodium salt, and the polymerization temperature was maintained at 30 to 40°C to carry out polymerization until the polymerization conversion reached 95%, thereby obtaining a copolymer latex. Then, unreacted monomers were removed from the obtained copolymer latex, and the pH and solids concentration of the copolymer latex were adjusted to obtain a latex of a nitrile group-containing conjugated diene polymer (A-1) with a solids concentration of 45 wt%, pH = 8.5, and CS (A) = 0.1 wt%. The glass transition temperature (Tg) of the nitrile group-containing conjugated diene polymer (A-1) contained in the obtained latex of the nitrile group-containing conjugated diene polymer (A-1) was measured and found to be -24°C. 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 126 nm, and the monomer composition of the nitrile group-containing conjugated diene polymer (A-1) was approximately the same as the charging ratio.

[0121] (Preparation of polymethyl methacrylate resin (B-1) latex) A polymerization reactor was charged with 100 parts of methyl methacrylate, 6 parts of benzenesulfonic acid ester of 1,1'-oxybistetrapropylene derivative, 0.1 parts of t-dodecyl mercaptan, 200 parts of ion-exchanged water, 1.5 parts of potassium persulfate, and 0.1 parts of sodium ethylenediaminetetraacetate, and polymerization was carried out while maintaining the polymerization temperature at 30 to 70°C until the polymerization conversion reached 95%, thereby obtaining a polymer latex. Then, by adjusting the pH and solid content of the polymer latex, a polymethyl methacrylate resin (B-1) latex with a solid content of 30 wt%, pH = 8.5, and CS (B) = 1.0 wt% was obtained. The glass transition temperature (Tg) of the polymethyl methacrylate resin (B-1) contained in the obtained polymethyl methacrylate resin (B-1) latex was measured and found to be 123°C. The volume average particle diameter of the polymethyl methacrylate resin (B-1) particles constituting the polymethyl methacrylate resin (B-1) latex was 77 nm.

[0122] (Preparation of latex composition for dip molding) The latex of the nitrile group-containing conjugated diene polymer (A-1) obtained above and the latex of the polymethyl methacrylate resin (B-1) were mixed so that the weight ratio of "nitrile group-containing conjugated diene polymer (A-1):polymethyl methacrylate resin (B-1)" was 7:3, and 5 wt % of potassium hydroxide was added to prepare a latex composition with a solids concentration of 46 wt % and a pH of 8.9.

[0123] The aqueous dispersions of the ingredients prepared above were added to 100 parts of the polymer component of the latex composition obtained above, so that the solid content was 1.0 part colloidal sulfur, 1.0 part zinc dibutyldithiocarbamate, 1.5 parts zinc oxide, and 3.0 parts titanium oxide. The aqueous dispersions of the ingredients were added slowly in the prescribed amounts while the latex composition was being stirred. After the ingredients were uniformly mixed, 1.2 parts of carboxymethyl cellulose (manufactured by Daicel Corporation, trade name "Daicel 2200", weight average molecular weight: 550,000, acidity: 3.7 mmol / g) was added as a water-soluble polymer to adjust the solid content to obtain a dip-molding latex composition (I) with a solid content of 44% by weight, a viscosity at 25°C of 3,000 mPa·s, and a (CS(B)-CS(A)) ratio of 0.9.

[0124] (Preparation of dip molding latex composition (II)) The aqueous dispersions of the ingredients prepared above were added to the latex of the nitrile group-containing conjugated diene polymer (A-1) so that the solids content was 1.0 part colloidal sulfur, 1.0 part zinc dibutyldithiocarbamate, 1.5 parts zinc oxide, and 3.0 parts titanium oxide per 100 parts of the polymer component. The aqueous dispersions of the ingredients were added slowly in the prescribed amounts while the latex composition was being stirred. After the ingredients were uniformly mixed, 0.3 parts of carboxymethyl cellulose (manufactured by Daicel Corporation, trade name "Daicel 2200", weight average molecular weight: 550,000, acidity: 3.7 mmol / g) was added as a water-soluble polymer to adjust the solids concentration, resulting in a dip-molding latex composition (II) with a solids concentration of 43% by weight and a viscosity of 3,000 mPa·s at 25°C.

[0125] (Preparation of coagulant solution) A coagulant solution was prepared by dissolving calcium nitrate as a coagulant in methanol at a ratio of 3.0 wt %.

[0126] (Production of protective gloves (dip-molded products) having a single polymer layer) First, the dip-molding latex composition (I) obtained above was aged (also referred to as pre-vulcanization) at 30°C for 48 hours. Next, a ceramic glove mold covered with a glove-shaped fiber substrate (material: nylon, linear density: 300 denier, gauge: 13 gauge, thickness: 0.8 mm) was immersed in the coagulant solution prepared above for 5 seconds, removed from the coagulant solution, and dried at 30°C for 1 minute. Thereafter, the ceramic glove mold was immersed in the dip-molding latex composition (I) for 5 seconds, removed from the dip-molding latex composition (I), dried at 30°C for 30 minutes, and then heated at 70°C for 10 minutes to crosslink the latex composition, forming a polymer layer with a thickness of 0.6 mm on the fiber substrate. The ceramic glove mold on which the polymer layer was formed was then dried at 30°C for 10 minutes and then heat-treated at 125°C for 30 minutes to crosslink the polymer in the polymer layer. The fiber substrate on which the polymer layer was formed was then peeled off from the ceramic glove mold to obtain a protective glove (dip-molded product) with a single polymer layer. The oil grip property of the resulting protective glove (dip-molded product) was measured according to the method described above. The results are shown in Table 1.

[0127] (Production of protective gloves (dip-molded products) having two polymer layers) First, the dip-molding latex composition (II) obtained above was aged (also referred to as pre-vulcanization) at 30°C for 48 hours. Next, a ceramic glove mold covered with a glove-shaped fiber substrate (material: nylon, linear density: 300 denier, gauge: 13 gauge, thickness: 0.8 mm) was immersed in the coagulant solution prepared above for 5 seconds, removed from the coagulant solution, and dried at 30°C for 1 minute. The ceramic glove mold was then immersed in the dip-molding latex composition (II) for 5 seconds, removed from the dip-molding latex composition (II), and dried at 30°C for 30 minutes to form a dip layer (first dip layer) containing a nitrile group-containing conjugated diene polymer on the fiber substrate. The ceramic glove mold with the first dip layer formed thereon was dried at 70°C for 20 minutes.

[0128] The dip-molding latex composition (I) obtained above was aged (also referred to as pre-vulcanization) at a temperature of 30° C. for 48 hours. Next, the ceramic glove mold on which the first dip layer had been formed was immersed in the dip-molding latex composition (I) for 5 seconds, and after being pulled out from the dip-molding latex composition (I), it was dried at a temperature of 30° C. for 30 minutes, thereby forming a dip layer (second dip layer) containing the nitrile group-containing conjugated diene polymer (A-1) and the polymethyl methacrylate resin (B-1) on the first dip layer.

[0129] The ceramic glove mold on which the first and second dip layers were formed was then dried at 30°C for 10 minutes, and then heat-treated at 125°C for 30 minutes to crosslink the polymers in the first and second dip layers, forming the first and second polymer layers, respectively. The fiber substrate on which the first and second polymer layers were formed was then peeled off from the ceramic glove mold to obtain a protective glove (dip-molded product) having two polymer layers: a first polymer layer thickness of 0.13 mm, a second polymer layer thickness of 0.03 mm, and a total thickness of the first and second polymer layers of 0.16 mm. The obtained protective glove (dip-molded product) having two polymer layers was then evaluated for oil gripping ability. The results are shown in Table 1.

[0130] <Example 2> Except for changing the solid content concentration of the dip-molding latex composition to 38% by weight, a dip-molding latex composition (III) was obtained in the same manner as in Example 1, and a protective glove having a single polymer layer (dip-molded product) and a protective glove having two polymer layers (dip-molded product) were obtained in the same manner as in Example 1, and evaluated in the same manner. The results are shown in Table 1.

[0131] Example 3 A dip-molding latex composition (IV) was obtained in the same manner as in Example 1, except that the mixing ratio of the latex of the nitrile group-containing conjugated diene polymer (A-1) and the latex of the polymethyl methacrylate resin (B-1) was 5:5 by weight (nitrile group-containing conjugated diene polymer (A-1):polymethyl methacrylate resin (B-1)), and the solid content was 35% by weight. A protective glove having a single polymer layer (dip-molded product) and a protective glove having two polymer layers (dip-molded product) were obtained in the same manner as in Example 1, and evaluated in the same manner. The results are shown in Table 1.

[0132] Example 4 (Preparation of polymethyl methacrylate resin (B-2) latex) A polymerization reactor was charged with 100 parts of methyl methacrylate, 6 parts of benzenesulfonic acid ester of a 1,1'-oxybistetrapropylene derivative, 0.1 parts of t-dodecyl mercaptan, 200 parts of ion-exchanged water, 0.3 parts of potassium persulfate, and 0.1 parts of sodium ethylenediaminetetraacetate, and polymerization was carried out while maintaining the polymerization temperature at 30 to 70°C until the polymerization conversion reached 95%, thereby obtaining a polymer latex. Then, by adjusting the pH and solid content of the polymer latex, a polymethyl methacrylate resin (B-2) latex with a solid content of 30% by weight, pH = 8.5, and CS (B) = 0.5 was obtained. The glass transition temperature (Tg) of the polymethyl methacrylate resin (B-2) contained in the obtained polymethyl methacrylate resin (B-2) latex was measured and found to be 123°C. The volume average particle diameter of the polymethyl methacrylate resin (B-2) particles constituting the polymethyl methacrylate resin (B-2) latex was 106 nm.

[0133] Then, in place of the latex of polymethyl methacrylate resin (B-1), a latex of polymethyl methacrylate resin (B-2) was used, and the solid content concentration of the dip-molding latex composition was changed to 38% by weight, except that a dip-molding latex composition (V) having (CS(B)-CS(A))=0.4 was prepared in the same manner as in Example 1, and a protective glove having a single polymer layer (dip-molded product) and a protective glove having two polymer layers (dip-molded product) were obtained and evaluated in the same manner. The results are shown in Table 1.

[0134] <Example 5> (Preparation of latex of methyl methacrylate-styrene copolymer resin (B-3)) A polymerization reactor was charged with 40 parts of methyl methacrylate, 60 parts of styrene, 6 parts of benzenesulfonic acid ester of a 1,1'-oxybistetrapropylene derivative, 0.1 parts of t-dodecyl mercaptan, 200 parts of ion-exchanged water, 1.5 parts of potassium persulfate, and 0.1 parts of sodium ethylenediaminetetraacetate, and polymerization was carried out while maintaining the polymerization temperature at 30 to 70°C until the polymerization conversion reached 90%, thereby obtaining a polymer latex. After removing unreacted monomers from the resulting polymer latex, the pH and solids concentration of the polymer latex were adjusted to obtain a latex of methyl methacrylate-styrene copolymer resin (B-3) with a solids concentration of 30% by weight and a pH of 8.5. The glass transition temperature (Tg) of the methyl methacrylate-styrene copolymer resin (B-3) contained in the resulting latex of methyl methacrylate-styrene copolymer resin (B-3) was measured and found to be 104°C. The volume average particle diameter of the methyl methacrylate-styrene copolymer resin (B-3) particles constituting the latex of methyl methacrylate-styrene copolymer resin (B-3) was 75 nm.

[0135] Then, a latex composition for dip molding (VI) having (CS(B)-CS(A))=0.1 was prepared in the same manner as in Example 1, except that the latex of polymethyl methacrylate resin (B-1) was replaced with the latex of methyl methacrylate-styrene copolymer resin (B-3) and the solid content concentration of the latex composition for dip molding was set to 39% by weight. A protective glove having a single polymer layer (dip-molded product) and a protective glove having two polymer layers (dip-molded product) were obtained in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

[0136] <Comparative Example 1> A dip-molding latex composition (VII) having (CS(B)-CS(A))=0 was prepared in the same manner as in Example 1, except that the polymethyl methacrylate resin (B-1) latex was replaced with polyvinyl chloride (B-4) latex (trade name "Viniblan 985" manufactured by Nissin Chemical Industry Co., Ltd.; the glass transition temperature (Tg) of the polyvinyl chloride (B-4) was 80°C, the volume average particle diameter of the polyvinyl chloride (B-4) particles was 84 nm, CS(B)=0.1, and the polyvinyl chloride (B-4) was substantially free of plasticizers) and the solids concentration of the dip-molding latex composition was 42% by weight. A dip-molding latex composition (VII) having (CS(B)-CS(A))=0 was prepared in the same manner as in Example 1, and protective gloves having a single polymer layer (dip-molded product) and protective gloves having two polymer layers (dip-molded product) were obtained and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0137] <Comparative Example 2> (Preparation of polystyrene resin (B-5) latex) A polymerization reactor was charged with 100 parts of styrene, 6 parts of benzenesulfonic acid ester of a 1,1'-oxybistetrapropylene derivative, 0.1 parts of t-dodecyl mercaptan, 200 parts of ion-exchanged water, 1.5 parts of potassium persulfate, and 0.1 parts of sodium ethylenediaminetetraacetate, and polymerization was carried out while maintaining the polymerization temperature at 30 to 70°C until the polymerization conversion reached 90%, thereby obtaining a polymer latex. Then, by adjusting the pH and solid content of the polymer latex, a latex of polystyrene resin (B-45) having a solid content of 30% by weight, pH=8.5, and CS(B)=0.01% by weight was obtained. The glass transition temperature (Tg) of the polystyrene resin (B-5) contained in the obtained latex of polystyrene resin (B-5) was measured and found to be 92°C. The volume average particle diameter of the polystyrene resin (B-5) particles constituting the latex of polystyrene resin (B-5) was 74 nm.

[0138] Then, a dip-molding latex composition (VIII) having (CS(B)-CS(A))=-0.09 was prepared in the same manner as in Example 1, except that the polymethyl methacrylate resin (B-1) latex was replaced with a polystyrene resin (B-5) latex and the solids concentration of the dip-molding latex composition was 39% by weight. A protective glove having a single polymer layer (dip-molded product) and a protective glove having two polymer layers (dip-molded product) were obtained in the same manner as in Example 1, and evaluated in the same manner. The results are shown in Table 1.

[0139] [Table 1]

[0140] As shown in Table 1, when a latex composition contains a latex of a conjugated diene polymer (A) having a glass transition temperature of 10°C or lower and a latex of a polymer (B) having a glass transition temperature of more than 10°C, and the difference (CS(B) - CS(A)) between the chemical stability of the latex of the conjugated diene polymer (A) to CaCl2 (CS(A)) and the chemical stability of the latex of the polymer (B) to CaCl2 (CS(B)) is more than 0% by weight, the obtained dip-molded article had excellent oil gripping properties regardless of whether it had only a single layer or two layers (Examples 1 to 5). On the other hand, when the difference in chemical stability (CS(B)-CS(A)) was 0 or less, the obtained dip-molded articles had poor oil grip properties (Comparative Examples 1 and 2).

Claims

1. A latex composition comprising a latex of a conjugated diene polymer (A) having a glass transition temperature of 10°C or lower and a latex of a polymer (B) having a glass transition temperature of more than 10°C, the conjugated diene polymer (A) is a nitrile group-containing conjugated diene polymer, the polymer (B) is a homopolymer of an acrylic acid ester, a methacrylic acid ester, acrylic acid, or methacrylic acid; When the solid content of the latex of the conjugated diene polymer (A) is 20% by weight, the amount of CaCl ２ The chemical stability against CS (A) (wt%) is When the solid content of the latex of the polymer (B) is 20% by weight, the CaCl ２ When the chemical stability against CS(B) (wt%) is A latex composition having a value of (CS(B)-CS(A)) greater than 0% by weight.

2. 2. The latex composition according to claim 1, wherein the volume average particle diameter of the polymer particles contained in the latex composition is 250 nm or less.

3. 3. The latex composition according to claim 2, wherein the polymer particles have a volume average particle size of 200 nm or less.

4. 4. The latex composition according to claim 1, wherein a volume average particle diameter of particles of the polymer (B) contained in the latex of the polymer (B) is smaller than a volume average particle diameter of particles of the conjugated diene polymer (A) contained in the latex of the conjugated diene polymer (A).

5. 5. The latex composition according to claim 1, wherein the volume average particle diameter of the particles of the polymer (B) contained in the latex of the polymer (B) is 200 nm or less.

6. 6. The latex composition according to claim 5, wherein the volume average particle diameter of the particles of the polymer (B) contained in the latex of the polymer (B) is 100 nm or less.

7. 7. The latex composition according to claim 1, wherein the solid content is 30% by weight or more.

8. 8. The latex composition according to claim 1, wherein the polymer (B) has a sulfate group at a polymer chain terminal as a residue of a polymerization initiator.

9. 9. The latex composition according to claim 1, wherein the conjugated diene polymer (A) is a conjugated diene polymer containing a nitrile group and a carboxyl group.

10. 10. The latex composition according to claim 1, wherein a content ratio of the conjugated diene polymer (A) to the polymer (B) is 1:9 to 9:1 in terms of a weight ratio of "conjugated diene polymer (A):polymer (B)".

11. A dip-molded article obtained by dip-molding the latex composition according to any one of claims 1 to 10.

12. The dip-formed article according to claim 11, which is a glove.

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