Latex composition for dip molding and dip molded article

Abstract

Provided is a latex composition that is for dip molding and that contains a latex of a conjugated diene-based polymer (A) having a methyl ethyl ketone undissolvable content of 50 wt% or less, and a latex of a polymer (B) having a methyl ethyl ketone undissolvable content or 55 wt% or more.

Description

Technical Field

[0001] The present invention relates to a latex composition for dip molding, and more particularly to a latex composition for dip molding that can provide a dip molded article excellent in oil grip property, flexibility, and chemical permeation resistance.

Background Art

[0002] Conventionally, in various applications such as factory manufacturing work, light work, construction work, and agricultural work, protective gloves with improved grip properties, abrasion resistance, etc. have been used by coating fiber gloves with rubber, resin, or the like.

[0003] From the viewpoint of workability, such protective gloves are required to be excellent in flexibility while having sufficient wet grip property when oil adheres, that is, oil grip property and chemical permeation resistance.

[0004] For example, Patent Document 1 discloses a glove having a fiber substrate, a first polymer composition that adheres to at least a part of the fiber substrate and forms a polymer coating, and a plurality of protrusion structures that exist on the polymer coating and contain a second polymer composition, wherein the polymer coating and the plurality of protrusion structures contain different polymer compositions.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] According to the technology of Patent Document 1, although gloves with excellent oil grip properties can be obtained, the flexibility is not sufficient. Further, in Patent Document 1, chemical permeation resistance has not been studied, and from the viewpoint of preventing chemicals from permeating when handling chemicals, further improvement in chemical permeation resistance is also required. In addition, in the technology of Patent Document 1, since it is necessary to form two coating layers, there is also a problem that the process is complicated.

[0007] The present invention has been made in view of such a situation, and an object thereof is to provide a dip molding latex composition capable of providing a dip molded article excellent in oil grip properties, flexibility, and chemical permeation resistance.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have found that a latex composition containing a latex of a conjugated diene polymer (A) having a methyl ethyl ketone insoluble content of 50% by weight or less and a latex of a polymer (B) having a methyl ethyl ketone insoluble content of 55% by weight or more can provide a dip molded article obtained by dip molding with excellent oil grip properties, flexibility, and chemical permeation resistance, and thus have completed the present invention.

[0009] That is, according to the present invention, there is provided a dip molding latex composition containing a latex of a conjugated diene polymer (A) having a methyl ethyl ketone insoluble content of 50% by weight or less and a latex of a polymer (B) having a methyl ethyl ketone insoluble content of 55% by weight or more.

[0010] In the dip molding latex composition of the present invention, it is preferable that the Young's modulus of the conjugated diene polymer (A) is 0.8 MPa or less and the Young's modulus of the polymer (B) is 1 MPa or more. In the latex composition for dip molding of the present invention, it is preferable that the methyl ethyl ketone swelling degree of the conjugated diene polymer (A) is 55 times or more and the methyl ethyl ketone swelling degree of the polymer (B) is 45 times or less. In the latex composition for dip molding of the present invention, it is preferable that the conjugated diene polymer (A) is a nitrile group-containing conjugated diene polymer having a methyl ethyl ketone-insoluble component of 50% by weight or less. In the latex composition for dip molding of the present invention, it is preferable that the content of the conjugated diene polymer (A) in 100 parts by weight of the polymer component is 40 parts by weight or more. In the latex composition for dip molding of the present invention, it is preferable that the polymer (B) is a nitrile group-containing conjugated diene polymer having a methyl ethyl ketone-insoluble component of 55% by weight or more, or a polyurethane resin. The latex composition for dip molding of the present invention preferably further contains a sulfur-based crosslinking agent.

[0011] Further, according to the present invention, there is provided a dip-molded article obtained by using the above-described latex composition for dip molding. Furthermore, according to the present invention, there is provided a dip-molded article obtained by immersing the above-described latex composition for dip molding in a substrate.

Effects of the Invention

[0012] According to the present invention, it is possible to provide a latex composition for dip molding capable of providing a dip-molded article excellent in oil grip properties, flexibility, and chemical permeation resistance, and a dip-molded article excellent in oil grip properties, flexibility, and chemical permeation resistance.

Brief Description of the Drawings

[0013]

Figure 1

Modes for Carrying Out the Invention

[0014] <Latex composition for dip molding> The latex composition for dip molding of the present invention is a latex composition containing a latex of a conjugated diene polymer (A) having a methyl ethyl ketone-insoluble component of 50% by weight or less and a latex of a polymer (B) having a methyl ethyl ketone-insoluble component of 55% by weight or more. In the latex composition for dip molding of the present invention, as long as particles of a conjugated diene polymer (A) having a methyl ethyl ketone-insoluble component of 50% by weight or less and particles of a polymer (B) having a methyl ethyl ketone-insoluble component of 55% by weight or more are contained in a dispersed state (i.e., in a latex state) in an aqueous medium such as water, it is not particularly limited. However, it is preferably a mixture of a latex of a conjugated diene polymer (A) having a methyl ethyl ketone-insoluble component of 50% by weight or less and a latex of a polymer (B) having a methyl ethyl ketone-insoluble component of 55% by weight or more, and more preferably a mixture formed by mixing these in a latex state.

[0015] The conjugated diene polymer (A) having a methyl ethyl ketone-insoluble component of 50% by weight or less that constitutes the latex of the conjugated diene polymer (A) (hereinafter, appropriately referred to as "the latex of the conjugated diene polymer (A)") (hereinafter, appropriately referred to as "the conjugated diene polymer (A)") may be any polymer having units derived from conjugated diene monomers and is not particularly limited. For example, nitrile rubber (NBR), natural rubber (NR), styrene-butadiene rubber (SBR), synthetic polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-isoprene copolymer rubber, styrene-isoprene-styrene copolymer rubber, etc. may be mentioned. Among these, from the viewpoint that the effects of the present invention become more remarkable, synthetic rubber is preferable, and a conjugated diene polymer containing a nitrile group such as NBR (hereinafter, appropriately referred to as "nitrile group-containing conjugated diene polymer") is more preferable.

[0016] Although not particularly limited, as the nitrile group-containing conjugated diene polymer, those 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] Although not particularly limited, as the α,β-ethylenically unsaturated nitrile monomer, 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, halogen-substituted acrylonitrile, etc. 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 ratio of the α,β-ethylenically unsaturated nitrile monomer unit in the nitrile group-containing conjugated diene polymer is preferably 10 to 45% by weight, more preferably 20 to 40% by weight, and still more preferably 25 to 40% by weight based on all monomer units. By setting the content ratio of the α,β-ethylenically unsaturated nitrile monomer unit within the above range, the resulting dip molded article can 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, 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] In the nitrile group-containing conjugated diene polymer, the content ratio of the conjugated diene monomer unit is preferably 40 to 80% by weight, more preferably 52 to 78% by weight, and still more preferably 55 to 75% by weight with respect to all monomer units. By setting the content ratio of the conjugated diene monomer unit within the above range, the obtained dip molded article can be made more excellent in flexibility.

[0021] Further, the nitrile group-containing conjugated diene polymer may be a copolymer of a monomer forming an α,β-ethylenically unsaturated nitrile monomer unit, a monomer forming a conjugated diene monomer unit, and another ethylenically unsaturated acid monomer copolymerizable therewith.

[0022] Such other ethylenically unsaturated acid monomers copolymerizable therewith are not particularly limited, and examples thereof include carboxyl group-containing ethylenically unsaturated monomers, sulfonic acid group-containing ethylenically unsaturated monomers, and phosphoric acid group-containing ethylenically unsaturated monomers.

[0023] The carboxyl group-containing ethylenically unsaturated monomer is not particularly limited, and examples thereof include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; ethylenically unsaturated polyvalent carboxylic acids such as fumaric acid, maleic acid, itaconic acid, maleic anhydride, and itaconic anhydride and their anhydrides; partial esterified products of ethylenically unsaturated polyvalent carboxylic acids such as methyl maleate and methyl itaconate; and the like.

[0024] The sulfonic acid group-containing ethylenically unsaturated monomer is not particularly limited, and examples thereof include vinyl sulfonic acid, methyl vinyl sulfonic acid, styrene sulfonic acid, (meth)allyl sulfonic acid, 2-sulfonic acid ethyl (meth)acrylate, 2-acrylamido-2-hydroxypropanesulfonic acid, and the like.

[0025] The phosphoric acid group-containing ethylenically unsaturated monomer is not particularly limited, and examples thereof include 3-chloro-2-phosphoric acid propyl (meth)acrylate, 2-phosphoric acid ethyl (meth)acrylate, 3-allyloxy-2-hydroxypropane phosphoric acid, and the like.

[0026] These other copolymerizable ethylenically unsaturated acid monomers can also be used as alkali metal salts or ammonium salts, and may be used alone or in combination of two or more. Among the above-mentioned 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.

[0027] When a unit of another copolymerizable ethylenically unsaturated acid monomer is contained in the nitrile group-containing conjugated diene polymer, the content ratio of the unit of the other copolymerizable ethylenically unsaturated acid monomer 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 all monomer units.

[0028] 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 monomers. In emulsion polymerization, polymerization auxiliary materials such as emulsifiers, polymerization initiators, and molecular weight regulators, which are usually used, can be used.

[0029] The emulsifier used in emulsion polymerization is not particularly limited, and examples thereof include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Among them, anionic surfactants are 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; alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, potassium dodecylbenzene sulfonate, sodium decylbenzene sulfonate, potassium decylbenzene sulfonate, sodium cetylbenzene sulfonate, and potassium cetylbenzene sulfonate; alkyl sulfosuccinates such as sodium di(2-ethylhexyl) sulfosuccinate, potassium di(2-ethylhexyl) sulfosuccinate, and sodium dioctyl sulfosuccinate; alkyl sulfate esters such as sodium lauryl sulfate and potassium lauryl sulfate; polyoxyethylene alkyl ether sulfate esters such as sodium polyoxyethylene lauryl ether sulfate and potassium polyoxyethylene lauryl ether sulfate; monoalkyl phosphates such as sodium lauryl phosphate and potassium lauryl phosphate; and the like. 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 the total monomers used.

[0030] The polymerization initiator is not particularly limited, but a radical initiator is preferred. The radical initiator is not particularly limited, and 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-butyl cumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, dibenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, and t-butyl peroxyisobutyrate; azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate. 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.

[0031] The molecular weight regulator is not particularly limited, and 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. Among these, mercaptans are preferred, and t-dodecyl mercaptan is 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 its type, but is preferably 0.1 to 1.5 parts by weight, more preferably 0.2 to 1.0 parts by weight, based on 100 parts by weight of all the monomers used.

[0032] 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, based on 100 parts by weight of all monomers used.

[0033] In emulsion polymerization, if necessary, polymerization auxiliary materials other than those described above may be further used. Examples of polymerization auxiliary materials include chelating agents, dispersants, pH adjusters, deoxidizing agents, particle size adjusters, etc., and neither the types nor the amounts used thereof are particularly limited.

[0034] Examples of the monomer addition method include, for example, a method of adding all the monomers to be used in a reaction vessel at once, a method of continuously or intermittently adding them as the polymerization proceeds, a method of adding a part of the monomers and reacting them to a specific conversion rate, and then continuously or intermittently adding the remaining monomers for polymerization, etc. Any method may be adopted. When the monomers are mixed and added continuously or intermittently, the composition of the mixture may be constant or changed. Also, each monomer may be added to the reaction vessel after previously mixing the various monomers to be used, or may be added to the reaction vessel separately.

[0035] The polymerization temperature during emulsion polymerization is not particularly limited, but is usually 0 to 95 °C, preferably 5 to 70 °C. The polymerization time is not particularly limited, but is usually about 5 to 40 hours.

[0036] After stopping the polymerization reaction, if desired, unreacted monomers may be removed, and the solid content concentration and pH may be adjusted.

[0037] The methyl ethyl ketone-insoluble content of the conjugated diene polymer (A) that constitutes the latex of the conjugated diene polymer (A) used in the present invention is 50% by weight or less, preferably 0.01 to 40% by weight, more preferably 0.1 to 30% by weight, still more preferably 1 to 5% by weight, and particularly preferably 1.2 to 3.5% by weight. The methyl ethyl ketone-insoluble content is an index indicating the gel content of the conjugated diene polymer (A) contained in the latex of the conjugated diene polymer (A). If the methyl ethyl ketone-insoluble content is too high, the oil grip property and flexibility of the resulting dip-molded article will deteriorate.

[0038] Also, the degree of swelling of the conjugated diene polymer (A) that constitutes the latex of the conjugated diene polymer (A) used in the present invention in methyl ethyl ketone is preferably 55 times or more, more preferably 60 to 200 times, still more preferably 70 to 150 times, and particularly preferably 90 to 140 times. The degree of swelling in methyl ethyl ketone is an index indicating the swelling property of the conjugated diene polymer (A) contained in the latex of the conjugated diene polymer (A). By setting the degree of swelling in methyl ethyl ketone within the above range, the oil grip property and flexibility of the resulting dip-molded article can be further enhanced.

[0039] In the present invention, as a method for measuring the methyl ethyl ketone-insoluble content and the methyl ethyl ketone swelling degree of the conjugated diene polymer (A) that constitutes the latex of the conjugated diene polymer (A), for example, the following method can be mentioned. That is, first, the latex of the conjugated diene polymer (A) is applied onto a substrate by a casting method or the like and dried to obtain a dry film, and the weight of the dry film (this weight is referred to as "W1".) is measured. Next, the obtained dry film is immersed in methyl ethyl ketone under the conditions of 25°C for 24 hours. Then, after measuring the weight of the film after immersion (this weight is referred to as "W2".), it is dried at 105°C for 3 hours to remove methyl ethyl ketone. And for the film after removing methyl ethyl ketone, the weight (this weight is referred to as "W3".) is measured, and from the measurement results of these weights, the methyl ethyl ketone-insoluble content and the methyl ethyl ketone swelling degree can be determined according to the following formulas (1) and (2). Methyl ethyl ketone-insoluble content (unit: wt%) = (W3 / W1) × 100 ···(1) Methyl ethyl ketone swelling degree (unit: times) = W2 / W3 ···(2)

[0040] Note that the method for making the methyl ethyl ketone-insoluble content and the methyl ethyl ketone swelling degree of the conjugated diene polymer (A) that constitutes the latex of the conjugated diene polymer (A) fall within the above ranges is not particularly limited. For example, when manufacturing the latex of the conjugated diene polymer (A), methods such as adjusting the type of chain transfer agent and the amount of chain transfer agent used, and adjusting the polymerization temperature can be mentioned. For example, the more the amount of chain transfer agent used, the lower the methyl ethyl ketone-insoluble content tends to be, and the higher the methyl ethyl ketone swelling degree tends to be. Also, the lower the polymerization temperature, the lower the methyl ethyl ketone-insoluble content tends to be, and the higher the methyl ethyl ketone swelling degree tends to be.

[0041] In addition, the Young's modulus of the conjugated diene polymer (A) that constitutes the latex of the conjugated diene polymer (A) used in the present invention is not particularly limited, but is preferably 0.8 MPa or less, more preferably 0.01 to 0.8 MPa, still more preferably 0.1 to 0.8 MPa, and particularly preferably 0.1 to 0.3 MPa. The Young's modulus is an index indicating the hardness of the conjugated diene polymer (A) contained in the latex of the conjugated diene polymer (A). By setting the Young's modulus within the above range, the oil grip property and flexibility of the resulting dip-molded article can be further enhanced.

[0042] In the present invention, examples of the method for measuring the Young's modulus of the conjugated diene polymer (A) that constitutes the latex of the conjugated diene polymer (A) include, for example, the following method. That is, first, the latex of the conjugated diene polymer (A) is applied onto a substrate by a casting method or the like and dried to obtain a dried film. The obtained dried film is used to produce a dumbbell-shaped test piece using a dumbbell (Die-C: manufactured by Dumbbell Co., Ltd.) in accordance with ASTM D-412. Then, the obtained dumbbell-shaped test piece is pulled at a pulling speed of 500 mm / min, and the Young's modulus (E) can be measured from the stress (σ) and strain (ε) at 10% elongation according to E = σ / ε.

[0043] The method for setting the Young's modulus of the conjugated diene polymer (A) that constitutes the latex of the conjugated diene polymer (A) within the above range is not particularly limited. For example, methods such as adjusting the type and amount of the chain transfer agent used when producing the latex of the conjugated diene polymer (A) and adjusting the polymerization temperature can be mentioned. For example, the higher the amount of the chain transfer agent used, the lower the Young's modulus tends to be, and the lower the polymerization temperature, the lower the Young's modulus tends to be.

[0044] Also, the weight-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 weight-average particle diameter of the particles of the conjugated diene polymer (A) within the above range, in the dip-molded article obtained, a polymer (B) having a methyl ethyl ketone-insoluble component of 55% by weight or more in the conjugated diene polymer (A) can be more favorably finely dispersed, and thereby, the flexibility of the obtained dip-molded article can be further enhanced. The weight-average particle diameter of the particles of the conjugated diene polymer (A) can be measured, for example, by the laser diffraction scattering method.

[0045] Also, the glass transition temperature of the conjugated diene polymer (A) constituting the latex of the conjugated diene polymer (A) is not particularly limited, but is preferably 10°C or lower, more preferably -45 to -10°C, even more preferably -40 to -10°C, and even more preferably -33 to -20°C.

[0046] Also, as the polymer (B) having a methyl ethyl ketone-insoluble component of 55% by weight or more (hereinafter, appropriately referred to as "the latex of the polymer (B)") constituting the latex of the polymer (B) having a methyl ethyl ketone-insoluble component of 55% by weight or more (hereinafter, appropriately referred to as "the polymer (B)"), there is no particular limitation, and any polymer having a methyl ethyl ketone-insoluble component of 55% by weight or more may be used. Examples thereof include nitrile group-containing conjugated diene polymers, acrylic resins, PTFE resins, acrylonitrile-styrene (AS) resins, polyurethane resins, and vinyl chloride resins. From the viewpoint of making the obtained dip-molded article excellent in oil grip properties, flexibility, and chemical permeation resistance, it is preferably a nitrile group-containing conjugated diene polymer, a polyurethane resin, or a vinyl chloride resin, and more preferably a nitrile group-containing conjugated diene polymer or a polyurethane resin.

[0047] Examples of the nitrile group-containing conjugated diene polymer as the polymer (B) include those obtained in the same manner as the above-described conjugated diene polymer (A) (however, those obtained by controlling the polymerization conditions and the like so that the methyl ethyl ketone-insoluble content is 55% by weight or more). Further, from the viewpoint of making the methyl ethyl ketone-insoluble content 55% by weight or more, those obtained in the same manner as the above-described conjugated diene polymer (A) (for example, those having a methyl ethyl ketone-insoluble content of less than 55% by weight (particularly, 50% by weight or less)) that have been further subjected to a crosslinking reaction can be preferably used.

[0048] The polyurethane resin as the polymer (B) is not particularly limited as long as it is a resin having a urethane bond obtained by reacting a polyol and a polyisocyanate and has a methyl ethyl ketone-insoluble content of 55% by weight or more, and is not particularly limited.

[0049] The vinyl chloride resin as the polymer (B) may be either a vinyl chloride homopolymer or a copolymer of vinyl chloride and a monomer copolymerizable with vinyl chloride. 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 still more preferably 90% by weight or more.

[0050] Examples of monomers copolymerizable 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; esters of α,β-ethylenically unsaturated monocarboxylic acids such as ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; α,β-ethylenically unsaturated polycarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; mono-esters of α,β-ethylenically unsaturated polycarboxylic acids such as monomethyl maleate, monoethyl maleate, and monoethyl itaconate; poly-esters of α,β-ethylenically unsaturated polycarboxylic acids 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; vinylidene compounds such as vinylidene chloride; etc. Among these, vinyl ester monomers and esters of α,β-ethylenically unsaturated monocarboxylic acids are preferred, and vinyl acetate and (meth)acrylate 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)acrylate ester.

[0051] As a method for producing a latex of the vinyl chloride resin as the polymer (B), any method capable of polymerizing the above monomers may be used and is not particularly limited. Examples include known emulsion polymerization, seed emulsion polymerization, and miniemulsion polymerization by radical polymerization.

[0052] The K value of the vinyl chloride resin as the polymer (B) measured according to JIS K 7367-2 is preferably 50 to 95, more preferably 60 to 80.

[0053] The methyl ethyl ketone-insoluble content of the polymer (B) that constitutes the latex of the polymer (B) used in the present invention is 55% by weight or more, preferably 60 to 99% by weight, more preferably 70 to 97% by weight, and even more preferably 78 to 94% by weight. The methyl ethyl ketone-insoluble content is an index indicating the gel content of the polymer (B) contained in the latex of the polymer (B). If the methyl ethyl ketone-insoluble content is too small, the flexibility of the resulting dip-molded article will decrease.

[0054] Also, the methyl ethyl ketone swelling degree of the polymer (B) that constitutes the latex of the polymer (B) used in the present invention is preferably 45 times or less, more preferably 20 to 0.1 times, and even more preferably 15 to 1 times. The methyl ethyl ketone swelling degree is an index indicating the swelling property of the polymer (B) contained in the latex of the polymer (B). By setting the methyl ethyl ketone swelling degree within the above range, the oil grip property of the resulting dip-molded article can be further enhanced.

[0055] In the present invention, as a method for measuring the methyl ethyl ketone-insoluble content and the methyl ethyl ketone swelling degree of the polymer (B) that constitutes the latex of the polymer (B), for example, the same method as that for the latex of the conjugated diene polymer (A) described above can be adopted.

[0056] Incidentally, the method for making the methyl ethyl ketone-insoluble content and the methyl ethyl ketone swelling degree of the polymer (B) that constitutes the latex of the polymer (B) fall within the above ranges is not particularly limited. For example, when the polymer (B) is a nitrile group-containing conjugated diene polymer, methods such as performing a crosslinking reaction on the latex of the nitrile group-containing conjugated diene polymer obtained by emulsion polymerization or the like can be mentioned. For example, by performing a crosslinking reaction, crosslinking sites can be introduced into the nitrile group-containing conjugated diene polymer that constitutes the latex of the nitrile group-containing conjugated diene polymer. As a result, the methyl ethyl ketone-insoluble content can be increased, and the methyl ethyl ketone swelling degree can be suppressed to a low level. When the polymer (B) is a polyurethane resin, methods such as using a latex containing polyurethane resin beads obtained using a polyol having three or more functional groups and / or a polyisocyanate having three or more functional groups as the polyurethane resin can be mentioned. Further, when the polymer (B) is a vinyl chloride resin, methods such as using a latex or using a dispersion of powder can be mentioned.

[0057] Also, the Young's modulus of the polymer (B) that constitutes the latex of the polymer (B) used in the present invention is not particularly limited, but is preferably 1 MPa or more, more preferably 1 to 10,000 MPa, still more preferably 1 to 1,000 MPa, and particularly preferably 1 to 20 MPa. The Young's modulus is an index indicating the hardness of the polymer (B) contained in the latex of the polymer (B). By setting the Young's modulus within the above range, the oil grip property of the obtained dip molded article can be further enhanced.

[0058] In the present invention, as a method for measuring the Young's modulus of the polymer (B) that constitutes the latex of the polymer (B), for example, the same method as that for the latex of the conjugated diene polymer (A) described above can be employed.

[0059] The method for setting the Young's modulus of the polymer (B) within the above range, which constitutes the latex of the polymer (B), is not particularly limited. For example, when the polymer (B) is a nitrile group-containing conjugated diene polymer, methods such as performing a crosslinking reaction on the latex of the nitrile group-containing conjugated diene polymer obtained by emulsion polymerization or the like can be mentioned. Further, when the polymer (B) is a polyurethane resin, methods such as using a latex containing polyurethane resin beads obtained using a polyol having three or more functional groups and / or a polyisocyanate having three or more functional groups as the polyurethane resin can be mentioned.

[0060] According to the present invention, there is provided a latex composition for dip molding containing a latex of a conjugated diene polymer (A) having a methyl ethyl ketone-insoluble content of 50% by weight or less and a latex of a polymer (B) having a methyl ethyl ketone-insoluble content of 55% by weight or more. According to the present invention, by including the latex of the conjugated diene polymer (A) and the latex of the polymer (B), when a dip molded article is obtained using such a latex composition, the resulting dip molded article can be made excellent in oil grip property, flexibility, and chemical permeation resistance.

[0061] In the latex composition for dip molding of the present invention, as long as the particles of the conjugated diene polymer (A) and the particles of the polymer (B) are contained in a state of being dispersed in an aqueous medium such as water (that is, in a latex state), it may be prepared by a method capable of obtaining a composition in such a state. However, in the present invention, it is preferably obtained by mixing the latex of the conjugated diene polymer (A) and the latex of the polymer (B). In particular, according to the present invention, a configuration including the latex of the conjugated diene polymer (A) and the latex of the polymer (B), that is, the particles of the conjugated diene polymer (A) and the particles of the polymer (B) are dispersed in water, enables the particles of the conjugated diene polymer (A) and the particles of the polymer (B) to be uniformly and finely dispersed in the latex composition. As a result, when a dip-molded article is obtained by dip molding, in the resulting dip-molded article, the polymer (B) can be finely dispersed in the matrix of the conjugated diene polymer (A) and co-precipitated. By this, due to the action of the conjugated diene polymer (A) and the polymer (B) finely dispersed in the conjugated diene polymer (A), the resulting dip-molded article can be made excellent in oil grip property, flexibility, and chemical permeation resistance. In the present invention, it is preferable to form a latex composition by mixing the latex of the conjugated diene polymer (A) and the latex of the polymer (B), preferably in a latex state. This can enhance the above-mentioned action more effectively and make the resulting dip-molded article more excellent in oil grip property, flexibility, and chemical permeation resistance. Of course, the latex composition for dip molding of the present invention only needs to have the particles of the conjugated diene polymer (A) and the particles of the polymer (B) dispersed in an aqueous medium, and is not particularly limited to those obtained by mixing these latexes.

[0062] Also, the weight-average particle diameter of the polymer (B) particles constituting the latex of the polymer (B) is preferably 0.05 to 500 μm, more preferably 0.1 to 500 μm, still more preferably 0.1 to 60 μm, even more preferably 0.1 to 50 μm, and particularly preferably 0.1 μm or more and less than 3 μm. By setting the weight-average particle diameter of the polymer (B) particles within the above range, the polymer (B) can be more favorably finely dispersed in the conjugated diene polymer (A) in the obtained dip-molded article, and thereby the flexibility of the obtained dip-molded article can be further enhanced. The weight-average particle diameter of the polymer (B) particles can be measured, for example, by the laser diffraction scattering method.

[0063] Further, the glass transition temperature of the polymer (B) constituting the latex of the polymer (B) is not particularly limited, but is preferably -80 to 150 °C, more preferably -60 to 120 °C, and still more preferably -40 to 100 °C.

[0064] In the latex composition for dip molding of the present invention, the content of the conjugated diene polymer (A) and the content of the polymer (B) are not particularly limited. However, in 100 parts by weight of the polymer component contained in the latex composition for dip molding (when only the conjugated diene polymer (A) and the polymer (B) are contained as the polymer component, the total of the conjugated diene polymer (A) and the polymer (B) is 100 parts by weight), the content of the conjugated diene polymer (A) is preferably 40 parts by weight or more, more preferably 40 to 95 parts by weight, even more preferably 40 to 80 parts by weight, and even more preferably 60 to 75 parts by weight. Further, the content of the polymer (B) with respect to 100 parts by weight of the polymer component contained in the latex composition for dip molding is preferably 5 to 60 parts by weight, more preferably 10 to 60 parts by weight, even more preferably 20 to 60 parts by weight, and even more preferably 25 to 40 parts by weight. Furthermore, the content ratio of the conjugated diene polymer (A) and the polymer (B) in the latex composition for dip molding of the present invention is in the weight ratio of "conjugated diene polymer (A): polymer (B)", preferably 99:1 to 10:90, more preferably 95:5 to 20:80, even more preferably 90:10 to 30:70, even more preferably 80:20 to 40:60, particularly preferably 75:25 to 45:55, and most preferably 75:25 to 60:40. By setting the contents of the conjugated diene polymer (A) and the polymer (B) within the above ranges, the oil grip property, flexibility, and chemical permeation resistance of the obtained dip molded article can be further enhanced.

[0065] In addition, the latex composition for dip molding of the present invention preferably further contains a sulfur-based crosslinking agent in addition to the latex of the conjugated diene polymer (A) and the latex of the polymer (B).

[0066] The sulfur-based crosslinking agent is not particularly limited, and examples thereof include sulfur such as powdered sulfur, sulfur flowers, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur; sulfur-containing compounds such as sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, dibenzothiazyl disulfide, caprolactam disulfide, phosphorus-containing polysulfide, and polymer polysulfide; sulfur-donating compounds such as tetramethylthiuram disulfide, selenium dimethyldithiocarbamate, and 2-(4'-morpholinodithio)benzothiazole. These sulfur-based crosslinking agents may be used alone or in combination of two or more.

[0067] 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 still more preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of the polymer component contained in the dip molding latex composition.

[0068] 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. For example, dithiocarbamic acids such as diethyldithiocarbamic acid, dibutyldithiocarbamic acid, di-2-ethylhexyldithiocarbamic acid, dicyclohexyldithiocarbamic acid, diphenyldithiocarbamic acid, dibenzyldithiocarbamic acid, and their zinc salts; 2-mercaptobenzothiazole, zinc 2-mercaptobenzothiazole, 2-mercaptothiazoline, dibenzothiazyl disulfide, 2-(2,4-dinitrophenylthio)benzothiazole, 2-(N,N-diethylthiocarbamoylthio)benzothiazole, 2-(2,6-dimethyl-4-morpholinothio)benzothiazole, 2-(4'-morpholino-dithio)benzothiazole, 4-morpholinyl-2-benzothiazyl disulfide, 1,3-bis(2-benzothiazyl-mercaptomethyl)urea, etc. 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.

[0069] 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 latex composition for dip molding. Also, 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 latex composition for dip molding.

[0070] In addition, the latex composition for dip molding of the present invention may further contain a water-soluble polymer.

[0071] Examples of the water-soluble polymer include vinyl compounds such as polyvinyl alcohol and polyvinyl pyrrolidone; cellulose derivatives such as hydroxyethyl cellulose, hydroxypropyl cellulose, and carboxymethyl cellulose and salts thereof; polycarboxylic acid compounds such as polyacrylic acid and sodium salts thereof; polyoxyethylene derivatives such as polyethylene glycol ether; and the like. As the water-soluble polymer, cellulose derivatives and salts thereof are preferable, and carboxymethyl cellulose and sodium salts thereof are more preferable.

[0072] The water-soluble polymer only needs to be soluble in water, and the solubility of the water-soluble polymer in water is not particularly limited. However, it is preferably 1 g or more, more preferably 7 g or more, and particularly preferably 10 g or more with respect to 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.

[0073] 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, preferably 5,000,000 or less, and more preferably 3,000,000 or less.

[0074] 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, with respect to 100 parts by weight of the polymer component contained in the latex composition for dip molding.

[0075] The solid content concentration of the latex composition for dip molding 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 setting the solid content concentration of the latex composition for dip molding within the above range, the transportation efficiency of the latex composition for dip molding can be improved, and the viscosity of the latex composition for dip molding becomes appropriate, improving the handleability of the latex composition for dip molding.

[0076] The pH of the latex composition for dip molding of the present invention is preferably from 5 to 13, more preferably from 7 to 10, and still more preferably from 7.5 to 9. By setting the pH of the latex composition for dip molding within the above range, the mechanical stability can be improved, the generation of coarse aggregates during the transfer of the latex composition for dip molding can be suppressed, and the viscosity of the latex composition for dip molding becomes appropriate, improving the handleability of the latex composition for dip molding.

[0077] The viscosity of the latex composition for dip molding of the present invention at 25°C is preferably from 2,000 to 100,000 mPa·s, more preferably from 2,500 to 50,000 mPa·s, and still more preferably from 3,000 to 20,000 mPa·s. The viscosity of the latex composition for dip molding at 25°C can be measured, for example, using a B-type viscometer under the conditions of 25°C and a rotation speed of 6 rpm. Further, the viscosity of the latex composition for dip molding at 25°C can be adjusted, for example, by a method of adjusting the concentration of the polymer component in the latex composition for dip molding or by adding a compound having a thickening effect to the latex composition for dip molding.

[0078] In addition, 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 may be added to the latex composition for dip molding of the present invention. Further, various additives other than the above water-soluble salts and fillers, for example, antioxidants, anti-oxidants, preservatives, antibacterial agents, wetting agents, dispersants, pigments, dyes, reinforcing agents, pH adjusters, etc. can be added in a predetermined amount to the latex composition for dip molding of the present invention as needed.

[0079] The latex composition for dip molding of the present invention can be prepared, for example, by mixing the above-described components. The mixing order of each component is not particularly limited, but from the viewpoint of further enhancing the dispersibility of each component, after preliminarily mixing the latex of the conjugated diene polymer (A) and the latex of the polymer (B), each component to be blended as necessary is added and mixed. A method of mixing is preferred. 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 enhancing the dispersibility, a method of mixing the latex of the conjugated diene polymer (A) and the latex of the polymer (B) in a latex state (latex blend) is preferred.

[0080] <Dip molded article> The dip molded article of the present invention is a molded article obtained by using the above-described latex composition for dip molding of the present invention, and is usually obtained by dip molding using the above-described latex composition for dip molding of the present invention.

[0081] Since the dip molded article of the present invention is a molded article obtained by using the above-described latex composition for dip molding of the present invention, it has at least a polymer layer containing the conjugated diene polymer (A) having a methyl ethyl ketone-insoluble component of 50% by weight or less and the polymer (B) having a methyl ethyl ketone-insoluble component of 55% by weight or more as described above. The preferred range of the content ratio of the conjugated diene polymer (A) and the polymer (B) in the dip molded article of the present invention is the same as the above-described range as the preferred range of the content ratio of the conjugated diene polymer (A) and the polymer (B) in the latex composition for dip molding of the present invention.

[0082] As the dip-molded article of the present invention, a film molded article made of a latex composition for dip molding, which is obtained by immersing a dip molding die in a latex composition for dip molding such as the latex composition for dip molding of the present invention described above, may be used. Alternatively, a laminate of a base material and a polymer layer made of a latex composition for dip molding, which is obtained by immersing the base material in the latex composition for dip molding, may be used. In the following, the case where the dip-molded article of the present invention is a laminate of a base material and a polymer layer made of a latex composition for dip molding will be exemplified and described, but the present invention is not limited to such an embodiment.

[0083] The base material is not particularly limited. However, when the dip-molded article of the present invention is used as a protective glove, a fiber base material can be preferably used. The fiber base material is not particularly limited. For example, a material in which single fiber twisted yarns are used as the fibers and these twisted yarns are woven into a glove shape can be used. The average thickness of the fiber base material is preferably 50 to 3,000 μm, more preferably 100 to 2,000 μm.

[0084] The dip-molded article of the present invention can be produced, for example, by immersing a base material in a latex composition for dip molding to form a polymer layer made of the latex composition for dip molding on the base material. In this case, it is preferable to immerse the base material in the latex composition for dip molding in a state where the base material is previously covered with a molding die having a desired shape.

[0085] The molding die for covering the base material is not particularly limited, and various materials such as porcelain, glass, metal, and plastic can be used. The shape of the molding die 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 molding dies for gloves, such as a molding die having a shape from the wrist to the fingertips, as the molding die for covering the base material.

[0086] Before immersing the substrate in the dip - molding latex composition, it is preferable to previously immerse the substrate in a coagulant solution to attach the coagulant solution to the substrate. At this time, it is preferable to immerse the substrate in the coagulant solution in a state where the substrate is previously covered with a molding die of a desired shape. Examples of the molding die of a desired shape include those described above. Also, after attaching the coagulant solution to the substrate, it is preferable to remove the solvent contained in the coagulant solution by drying. The drying temperature at this time is not particularly limited and may be selected according to the solvent used, but is preferably 10 - 80°C, more preferably 15 - 70°C. Also, the drying time is not particularly limited, but is preferably 600 - 1 second, more preferably 300 - 5 seconds.

[0087] Next, the substrate with the coagulant solution attached is immersed in the dip - molding latex composition while still covered with a molding die of a desired shape, thereby coagulating the dip - molding latex composition and attaching a polymer layer composed of the dip - molding latex composition onto the substrate.

[0088] And after immersing the substrate in the dip - molding latex composition, it is preferable to perform drying. The drying temperature at this time is not particularly limited, but is preferably 10 - 80°C, more preferably 15 - 80°C. Also, the drying time is not particularly limited, but is preferably 120 minutes - 5 seconds, more preferably 60 minutes - 10 seconds.

[0089] In addition, when using a dip - molding latex composition containing a sulfur - based cross - linking agent, as the dip - molding latex composition, one that has been previously aged (also referred to as pre - vulcanized) may be used.

[0090] The temperature conditions during aging are not particularly limited, but are preferably 20 to 50°C. Also, from the viewpoint of preventing peeling between the base material and the polymer layer composed of the dip-forming latex composition, and from the viewpoint of improving the abrasion resistance when the obtained dip-formed article is used as a protective glove, 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.

[0091] Next, it is preferable to crosslink the polymer component contained in the dip-forming latex composition by heating the dip-forming latex composition adhered to the base material.

[0092] 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 to improve the productivity of the dip-formed article, and oxidative degradation of the polymer component due to excessive heating can be suppressed, thereby improving the physical properties of the obtained dip-formed article. The heating time for crosslinking may be appropriately selected according to the heating temperature, but is usually 5 to 120 minutes.

[0093] In addition, for the dip-formed article thus obtained, if necessary, the polymer layer formed on the base material is immersed in warm water at 20 to 80°C for about 0.5 to 60 minutes to remove water-soluble impurities (such as emulsifiers, water-soluble polymers, coagulants, etc.) from the polymer layer. This is preferable. Such a treatment of immersing the polymer layer in warm water may be performed after crosslinking the polymer component in the polymer layer, but from the viewpoint of more efficiently removing water-soluble impurities, it is preferably performed before crosslinking the polymer component in the polymer layer.

[0094] After immersion in warm water, further drying may be 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 dip-forming latex composition described above.

[0095] Then, after forming a polymer layer on the substrate with the substrate covered by the molding die as described above, the dip-molded article can be obtained by desorbing (or demolding) from the molding die. As the desorbing method, a method of peeling by hand from the molding die or peeling by the pressure of water pressure or compressed air can be adopted.

[0096] Before or after desorbing the dip-molded article from the molding die, a heat treatment (post-crosslinking step) may be further performed at a temperature of 60 to 120°C for 10 to 120 minutes. Further, after desorbing the dip-molded article from the molding die, a surface treatment layer such as a chlorination treatment or a coating treatment may be formed on the inner and / or outer surfaces of the dip-molded article.

[0097] The dip-molded article of the present invention thus obtained forms a polymer layer composed of the above-described dip-molding latex composition of the present invention on the substrate by coagulation using a coagulant. Therefore, the film thickness is preferably 0.05 to 1.0 mm, more preferably 0.06 to 0.8 mm, still more preferably 0.07 to 0.7 mm, and particularly preferably more than 0.3 mm and 0.7 mm or less, that is, relatively thick. Thereby, the abrasion resistance of the obtained dip-molded article can be enhanced.

[0098] Since the dip-molded article of the present invention uses the above-described dip-molding latex composition of the present invention, it is excellent in oil grip property, flexibility, and chemical permeation resistance, and can be suitably used, for example, for glove applications, particularly for protective glove applications. In the above, the case where the dip-molded article of the present invention is a laminate of a substrate and a polymer layer composed of a dip-molding latex composition has been exemplified and described. However, as described above, the present invention is not limited to such a mode at all, and it is of course possible to form a film molded article composed of a dip-molding latex composition obtained by immersing a dip-molding die in the dip-molding latex composition.

Examples

[0099] Hereinafter, the present invention will be described based on more detailed examples, but the present invention is not limited to these examples. In the following, "parts" are based on weight unless otherwise specified. Also, the tests and evaluations were conducted as follows.

[0100] <Glass transition temperature of polymer particles contained in latex> For each latex, the glass transition temperature of the polymer particles contained in the latex was measured using a differential thermal analysis measuring device ("EXSTAR DSC6220" manufactured by SII NanoTechnology Inc.) in accordance with JIS K7121.

[0101] <Weight average particle diameter of polymer particles contained in latex> For each latex, the weight average particle diameter of the polymer particles contained in the latex was measured by the laser diffraction scattering method using a particle size measuring device ("LS13320" manufactured by Beckman Coulter).

[0102] <Methyl ethyl ketone insoluble component and methyl ethyl ketone swelling degree of polymer particles contained in latex> Each latex was applied onto a substrate by the casting method and dried at 25°C for 120 hours to obtain a dried film, and the weight of the obtained dried film (this weight is referred to as "W1") was measured. Next, the obtained dried film was immersed in methyl ethyl ketone under the conditions of 25°C for 24 hours, and after measuring the weight of the film after immersion (this weight is referred to as "W2"), it was dried at 105°C for 3 hours to remove methyl ethyl ketone. Then, the weight of the film after removing methyl ethyl ketone (this weight is referred to as "W3") was measured, and using the measurement results of these weights, the methyl ethyl ketone insoluble component and the methyl ethyl ketone swelling degree were determined according to the following formulas (1) and (2). Methyl ethyl ketone insoluble component (unit: weight%) = (W3 / W1) × 100 ···(1) Methyl ethyl ketone swelling degree (unit: times) = W2 / W3 ···(2)

[0103] <Young's modulus of polymer particles contained in latex> Each latex was applied onto a substrate by the casting method and dried at 25°C for 120 hours to obtain a dried film. The obtained dried film was used to prepare a dumbbell-shaped test piece using a dumbbell (Die-C, manufactured by Dumbbell Co., Ltd.) according to ASTM D-412. Then, the obtained dumbbell-shaped test piece was pulled at a tensile speed of 500 mm / min, and the Young's modulus (E) was measured according to E = σ / ε from the stress (σ) and strain (ε) at 10% elongation. For those with a high methyl ethyl ketone-insoluble component, a good cast film could not be obtained. Therefore, by mixing with the latex of the nitrile group-containing conjugated diene polymer (A-1) obtained in Production Example 1 described below, a mixture with a solid content of 30% by weight was obtained. A dried film was obtained using the obtained mixture and measured in the same manner. The Young's modulus was measured by excluding the contribution of the nitrile group-containing conjugated diene polymer (A-1) from the obtained measurement results. More specifically, assuming that the contribution of the nitrile group-containing conjugated diene polymer (A-1) was 70% and the contribution of the measurement sample was 30%, the Young's modulus was determined.

[0104] <Oil grip property> Conical metal molds with weights of 1.0 kg, 2.0 kg, 3.0 kg, 4.0 kg, and 5.0 kg were prepared, and test oil IRM903 was attached to these metal molds. Then, an operator was asked to wear protective gloves (dip molded articles), and the metal molds with test oil IRM903 attached were lifted in order from the lighter weight, and the maximum weight that could be lifted was determined. The measurement was performed by the same operator. It can be judged that the greater the maximum weight that can be lifted, the better the oil grip property.

[0105] <Flexibility> The palm portion of the protective glove (dip-molded body) was cut into a shape of 60 mm × 60 mm to obtain a measurement sample. Then, for the measurement sample, using the push-in test device 20 shown in FIG. 1 disclosed in International Publication No. 2018 / 174068 (as the measurement part, the product name "HG1003-SL", manufactured by Horinouchi Electric Co., Ltd.), the Young's modulus was measured according to the method disclosed in International Publication No. 2018 / 174068. The specific conditions were as follows. In the measurement, among the surfaces on the side opposite to the surface (measurement surface) on which the polymer layer of the measurement sample was formed, a resin tape was attached to the portion corresponding to the plurality of suction holes of the suction table 30, and while performing suction by the suction table 30, the measurement was performed by pushing a spherical indenter from the rubber layer side. The measurement was also performed at three locations of the 60 mm × 60 mm measurement sample, and the average value of the measurement results of the Young's modulus at the three locations was obtained and taken as the Young's modulus of each example. If the Young's modulus is 580 kPa or less, it can be judged that the flexibility is sufficiently excellent. Spherical indenter: A spherical indenter made of SUS with a diameter of 10 mm Pushing speed: 0.5 mm / s Maximum load: 0.5 N Initial position of the spherical indenter: -6 mm (height position 6 mm from the suction table 30)

[0106] <Chemical permeability of the protective glove (dip-molded body)> With reference to the cup method described in JIS Z 0208, the solvent gas permeability of the protective glove (dip-molded body) was measured according to the following procedure. (1) The protective glove (dip-molded body) was cut into an appropriate circular size to obtain a sample. (2) The weight (W4) of the aluminum cup and the sample was measured. (3) 50 mL of n-hexane was put into the aluminum cup. (4) On the aluminum cup containing n-hexane, the sample (dip-molded body) was placed so that the rubber layer was in contact with the liquid. (5) The aluminum cup and the sample were firmly adhered using a fixture. (6) The weight (W5) of the entire aluminum cup was measured. (7) To allow n - hexane to contact the sample, the aluminum cup was turned over and left in a draft at room temperature. (8) After leaving it for 72 hours, the weight (W6) of the entire aluminum cup was measured. (9) The ratio at which n - hexane permeated through the sample and evaporated (solvent gas permeability) was calculated by the following formula. Solvent gas permeability (%) = 100 - ((W6 - W4) ÷ (W5 - W4) × 100) It can be judged that the smaller the value of the solvent gas permeability, the better the chemical resistance permeability.

[0107] <Production Example 1> (Preparation of latex of nitrile group - containing conjugated diene - based polymer (A - 1)) Into a polymerization reactor, 68 parts of 1,3 - butadiene as a conjugated diene monomer, 27 parts of acrylonitrile as an α,β - ethylenically unsaturated nitrile monomer, 5 parts of methacrylic acid as an ethylenically unsaturated monocarboxylic acid monomer, 0.5 part of t - dodecyl mercaptan, 132 parts of ion - exchanged water, 3 parts of sodium dodecylbenzenesulfonate, 0.5 part of sodium salt of β - naphthalenesulfonic acid formalin condensate, 0.3 part of potassium persulfate, and 0.05 part of sodium salt of ethylenediaminetetraacetic acid were charged. The polymerization was carried out while maintaining the polymerization temperature at 30 - 40 °C, and the reaction was continued until the polymerization conversion rate reached 94% to obtain a latex of the copolymer. Then, after removing the unreacted monomers from the latex of the obtained copolymer, by adjusting the pH and solid content concentration of the latex of the copolymer, a latex of a nitrile group-containing conjugated diene polymer (A-1) with a solid content concentration of 40% by weight and a pH of 8 was obtained. For the nitrile group-containing conjugated diene polymer (A-1) contained in the obtained latex of the nitrile group-containing conjugated diene polymer (A-1), when the monomer composition was measured, the monomer composition was almost the same as the charged ratio. Also, for the nitrile group-containing conjugated diene polymer (A-1) contained in the obtained latex of the nitrile group-containing conjugated diene polymer (A-1), the glass transition temperature (Tg), weight average particle diameter, methyl ethyl ketone-insoluble component, methyl ethyl ketone swelling degree, and Young's modulus were measured according to the above method. The results are shown in Table 1.

[0108] <Production Example 2> (Preparation of Latex of Nitrile Group-Containing Conjugated Diene Polymer (A-2)) Into a polymerization reactor, 68 parts of 1,3-butadiene as a conjugated diene monomer, 27 parts of acrylonitrile as an α,β-ethylenically unsaturated nitrile monomer, 5 parts of methacrylic acid as an ethylenically unsaturated monocarboxylic acid monomer, 0.6 part of t-dodecyl mercaptan, 132 parts of deionized water, 3 parts of sodium dodecylbenzenesulfonate, 1 part of sodium β-naphthalenesulfonate formaldehyde condensate, and 0.01 part of sodium sulfite were charged, and the temperature of the polymerization reaction vessel was maintained at 5°C. Then, a mixture of 6 parts of ion-exchanged water, 0.020 part of sodium ethylenediaminetetraacetate, 0.002 part of ferrous sulfate, and 0.02 part of sodium formaldehyde sulfoxylate was added to the polymerization reaction vessel, 0.04 part of 1,1,3,3-tetramethylbutyl hydroperoxide was added, and the temperature was maintained at 5°C for polymerization. The reaction was carried out until the polymerization conversion rate reached 94% to obtain a latex of a copolymer. Then, after removing the unreacted monomers from the latex of the obtained copolymer, by adjusting the pH and solid content concentration of the latex of the copolymer, a latex of a nitrile group-containing conjugated diene polymer (A-2) with a solid content concentration of 40% by weight and a pH of 8 was obtained. Regarding the nitrile group-containing conjugated diene polymer (A-2) contained in the latex of the obtained nitrile group-containing conjugated diene polymer (A-2), when the monomer composition was measured, the monomer composition was almost the same as the charged ratio. Also, regarding the nitrile group-containing conjugated diene polymer (A-2) contained in the latex of the obtained nitrile group-containing conjugated diene polymer (A-2), the glass transition temperature (Tg), weight average particle diameter, methyl ethyl ketone-insoluble content, methyl ethyl ketone swelling degree, and Young's modulus were measured according to the above method. The results are shown in Table 1.

[0109] <Production Example 3> (Preparation of latex of nitrile group-containing conjugated diene polymer (B-1)) To 100 parts of the nitrile group-containing conjugated diene polymer (A-1) in the latex of the nitrile group-containing conjugated diene polymer (A-1) obtained in Production Example 1, 5 parts of colloidal sulfur (manufactured by Hosoi Chemical Industry Co., Ltd.) and 5 parts of zinc dibutyldithiocarbamate (manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) were blended and mixed, and then left standing at 25°C for 12 hours, and then heated with stirring under the conditions of 80°C for 5 hours. Next, colloidal sulfur and zinc dibutyldithiocarbamate were removed by centrifugation, and the solid content concentration was adjusted to 40% by weight to obtain a latex of the nitrile group-containing conjugated diene polymer (B-1). Regarding the nitrile group-containing conjugated diene polymer (B-1) contained in the latex of the obtained nitrile group-containing conjugated diene polymer (B-1), when the monomer composition was measured, the monomer composition was almost the same as that of the nitrile group-containing conjugated diene polymer (A-1). Also, regarding the nitrile group-containing conjugated diene polymer (B-1) contained in the latex of the obtained nitrile group-containing conjugated diene polymer (B-1), the glass transition temperature (Tg), weight average particle diameter, methyl ethyl ketone-insoluble content, methyl ethyl ketone swelling degree, and Young's modulus were measured according to the above method. The results are shown in Table 1.

[0110] <Production Example 4> (Preparation of latex of nitrile group-containing conjugated diene polymer (B-2)) Instead of the latex of the nitrile group-containing conjugated diene polymer (A-1) obtained in Production Example 1, a latex of the nitrile group-containing conjugated diene polymer (A-2) obtained in Production Example 2 was used, and in the same manner as in Production Example 3, a latex of the nitrile group-containing conjugated diene polymer (B-2) was obtained. Regarding the nitrile group-containing conjugated diene polymer (B-2) contained in the obtained latex of the nitrile group-containing conjugated diene polymer (B-2), when the monomer composition was measured, the monomer composition was almost the same ratio as that of the nitrile group-containing conjugated diene polymer (A-2). Also, regarding the nitrile group-containing conjugated diene polymer (B-2) contained in the obtained latex of the nitrile group-containing conjugated diene polymer (B-2), the glass transition temperature (Tg), weight average particle diameter, methyl ethyl ketone-insoluble content, methyl ethyl ketone swelling degree, and Young's modulus were measured according to the above method. The results are shown in Table 1.

[0111] <Example 1> (Preparation of Aqueous Dispersion of Colloidal Sulfur) 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 part of a 5 wt% potassium hydroxide aqueous solution (manufactured by Wako Pure Chemical Industries, Ltd.), and 1.0 part of water were pulverized and stirred in a ball mill for 48 hours to prepare an aqueous dispersion of colloidal sulfur with a solid content concentration of 50 wt%.

[0112] (Preparation of Aqueous Dispersions of Zinc Dibutyldithiocarbamate, Zinc Oxide, and Titanium Oxide) Instead of colloidal sulfur, aqueous dispersions of zinc dibutyldithiocarbamate (manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.), zinc oxide (manufactured by Shodo Chemical Industry Co., Ltd.), and titanium oxide were each prepared in the same manner as above, except that zinc dibutyldithiocarbamate, zinc oxide, and titanium oxide were used, respectively.

[0113] (Preparation of Dip Molding Latex Composition) The latex of the nitrile group-containing conjugated diene polymer (A-1) obtained in Production Example 1 and the latex of the nitrile group-containing conjugated diene polymer (B-1) obtained in Production Example 3 were mixed so that the weight ratio of "nitrile group-containing conjugated diene polymer (A-1): nitrile group-containing conjugated diene polymer (B-1)" was 70:30, and 5 wt% potassium hydroxide was added to prepare a latex composition having a solid content concentration of 45 wt% and a pH of 8.

[0114] Then, based on 100 parts of the polymer component of the latex composition obtained above, the aqueous dispersions of the respective compounding agents prepared above were added so as to be 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 in terms of solid content. When adding the aqueous dispersions of the respective compounding agents, a predetermined amount was slowly added while stirring the latex composition. After the respective compounding agents were uniformly mixed, 0.3 part of carboxymethyl cellulose (manufactured by Daicel Corporation, trade name "Daicel2200", weight average molecular weight: 550,000, acid amount: 3.7 mmol / g) as a water-soluble polymer was added, and the solid content concentration was adjusted to obtain a dip molding latex composition having a solid content concentration of 40 wt% and a viscosity of 3,000 mPa·s at 25°C.

[0115] (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%.

[0116] (Production of protective gloves (dip molded articles)) First, the dip - molding latex composition obtained above was aged (also referred to as pre - vulcanization) under the conditions of a temperature of 30°C for 48 hours. Next, a ceramic glove - type 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. After being pulled out from the coagulant solution, it was dried under the conditions of a temperature of 30°C for 1 minute. Then, the ceramic glove - type mold was immersed in the above dip - molding latex composition for 5 seconds. After being pulled out from the dip - molding latex composition, it was dried under the conditions of a temperature of 30°C for 30 minutes, and then heated and cross - linked under the conditions of a temperature of 70°C for 10 minutes to form a polymer layer with a film thickness of 0.6 mm on the fiber substrate. Then, the ceramic glove - type mold with the polymer layer formed was immersed in warm water at 60°C for 90 seconds to elute water - soluble impurities from the polymer layer. After that, it was dried under the conditions of a temperature of 30°C for 10 minutes, and further heat - treated under the conditions of a temperature of 125°C for 30 minutes to perform a cross - linking treatment on the polymer in the polymer layer. Next, the fiber substrate with the polymer layer formed was peeled off from the ceramic glove - type mold to obtain a protective glove (dip - molded product). Then, using the obtained protective glove (dip - molded product), measurements of oil grip property, flexibility, and chemical - resistance permeability were carried out. The results are shown in Table 2.

[0117] <Example 2> A dip - molding latex composition with a solid - content concentration of 40% by weight and a viscosity of 3,000 mPa·s at 25°C was obtained in the same manner as in Example 1, except that the latex of the nitrile - group - containing conjugated diene - based polymer (B - 2) obtained in Production Example 4 was used instead of the latex of the nitrile - group - containing conjugated diene - based polymer (B - 1) obtained in Production Example 3. Then, using the obtained dip - molding latex composition, a protective glove (dip - molded product) having a polymer layer with a film thickness of 0.6 mm was obtained in the same manner as in Example 1 and evaluated in the same way. The results are shown in Table 2.

[0118] <Example 3> Instead of the latex of the nitrile group-containing conjugated diene polymer (B-1) obtained in Production Example 3, a latex of urethane resin beads (B-3) (C-200T manufactured by Negami Kogyo Co., Ltd.) was used, and a dip molding latex composition having a solid content concentration of 40% by weight and a viscosity of 3,000 mPa·s at 25°C was obtained in the same manner as in Example 1, except that the amount of carboxymethyl cellulose used as the water-soluble polymer was changed to 0.5 part. Then, using the obtained dip molding latex composition, a protective glove (dip molded body) having a polymer layer with a film thickness of 0.6 mm was obtained in the same manner as in Example 1, and evaluation was carried out in the same manner. The results are shown in Table 2. The results of measuring the glass transition temperature (Tg), weight average particle diameter, methyl ethyl ketone insoluble component, methyl ethyl ketone swelling degree, and Young's modulus of the urethane resin beads (B-3) contained in the latex of the urethane resin beads (B-3) are shown in Table 1 according to the above method.

[0119] <Example 4> Instead of the latex of the nitrile group-containing conjugated diene polymer (B-1) obtained in Production Example 3, a latex of urethane resin beads (B-4) (C-800T manufactured by Negami Kogyo Co., Ltd.) was used, and a dip molding latex composition having a solid content concentration of 40% by weight and a viscosity of 3,000 mPa·s at 25°C was obtained in the same manner as in Example 1, except that the amount of carboxymethyl cellulose used as the water-soluble polymer was changed to 0.5 part. Then, using the obtained dip molding latex composition, a protective glove (dip molded body) having a polymer layer with a film thickness of 0.6 mm was obtained in the same manner as in Example 1, and evaluation was carried out in the same manner. The results are shown in Table 2. The results of measuring the glass transition temperature (Tg), weight average particle diameter, methyl ethyl ketone insoluble component, methyl ethyl ketone swelling degree, and Young's modulus of the urethane resin beads (B-4) contained in the latex of the urethane resin beads (B-4) are shown in Table 1 according to the above method.

[0120] <Example 5> Instead of using the latex of the nitrile group-containing conjugated diene polymer (B-1) obtained in Production Example 3, a latex of a vinyl chloride resin (B-5) was used, and a dip molding latex composition having a solid content concentration of 40% by weight and a viscosity of 3,000 mPa·s at 25°C was obtained in the same manner as in Example 1, except that the amount of carboxymethyl cellulose used as the water-soluble polymer was changed to 1.0 part. Then, using the obtained dip molding latex composition, a protective glove (dip molded article) having a polymer layer with a film thickness of 0.6 mm was obtained in the same manner as in Example 1, and the evaluation was carried out in the same manner. The results are shown in Table 2. The results of measuring the glass transition temperature (Tg), weight average particle diameter, methyl ethyl ketone-insoluble component, methyl ethyl ketone swelling degree, and Young's modulus of the vinyl chloride resin (B-5) contained in the latex of the vinyl chloride resin (B-5) according to the above method are shown in Table 1.

[0121] <Example 6> Instead of using the latex of the nitrile group-containing conjugated diene polymer (A-1) obtained in Production Example 1, a latex of the nitrile group-containing conjugated diene polymer (A-2) obtained in Production Example 2 was used, and a dip molding latex composition having a solid content concentration of 40% by weight and a viscosity of 3,000 mPa·s at 25°C was obtained in the same manner as in Example 1. Then, using the obtained dip molding latex composition, a protective glove (dip molded article) having a polymer layer with a film thickness of 0.6 mm was obtained in the same manner as in Example 1, and the evaluation was carried out in the same manner. The results are shown in Table 2.

[0122] <Comparative Example 1> A dip molding latex composition having a solid content concentration of 40% by weight and a viscosity of 3,000 mPa·s at 25°C was obtained in the same manner as in Example 1, except that the latex of the nitrile group-containing conjugated diene polymer (B-1) obtained in Production Example 3 was not blended, and the blending was carried out in terms of solid content based on 100 parts of the polymer component of the latex of the nitrile group-containing conjugated diene polymer (A-1). Then, using the obtained dip molding latex composition, a protective glove (dip molded article) having a polymer layer with a film thickness of 0.6 mm was obtained in the same manner as in Example 1, and the evaluation was carried out in the same manner. The results are shown in Table 2.

[0123] <Comparative Example 2> A dip molding latex composition having a solid content concentration of 40% by weight and a viscosity of 3,000 mPa·s at 25°C was obtained in the same manner as in Example 1, except that the latex of the nitrile group-containing conjugated diene polymer (A-2) obtained in Production Example 2 was used instead of the latex of the nitrile group-containing conjugated diene polymer (B-1) obtained in Production Example 3. Then, using the obtained dip molding latex composition, a protective glove (dip molded article) having a polymer layer with a film thickness of 0.6 mm was obtained in the same manner as in Example 1, and the evaluation was carried out in the same manner. The results are shown in Table 2.

[0124]

Table 1

[0125]

Table 2

[0126] As shown in Table 1 and Table 2, according to the dip molding latex composition obtained by mixing the latex of the conjugated diene polymer (A) having a methyl ethyl ketone-insoluble component of 50% by weight or less and the latex of the polymer (B) having a methyl ethyl ketone-insoluble component of 55% by weight or more, the dip molded article obtained using this can be made excellent in oil grip property, flexibility, and chemical permeation resistance (Examples 1 to 6).

[0127] On the other hand, when the latex of the polymer (B) having a methyl ethyl ketone-insoluble content of 55% by weight or more was not blended, the resulting dip-molded article was inferior in oil grip properties (Comparative Examples 1 and 2).

Explanation of Signs

[0128] 10… Measurement sample 20… Pushing-in test device 21… Measuring table 22… Support arm 23… Horizontal arm 24… Coarse movement vertical movement mechanism 25… Fine movement vertical movement mechanism 26… Stage 27… Load cell 28… Load axis 29… Spherical indenter 30… Suction table

Claims

1. A latex composition for dip molding, comprising a latex of a conjugated diene polymer (A) having a methyl ethyl ketone-insoluble content of 50% by weight or less and a latex of a polymer (B) having a methyl ethyl ketone-insoluble content of 55% by weight or more, wherein the conjugated diene polymer (A) is a nitrile group-containing conjugated diene polymer containing a carboxyl group-containing ethylenically unsaturated monomer unit.

2. The latex composition for dip molding according to claim 1, wherein the conjugated diene polymer (A) has a Young's modulus of 0.8 MPa or less and the polymer (B) has a Young's modulus of 1 MPa or more.

3. The latex composition for dip molding according to claim 1 or 2, wherein the conjugated diene polymer (A) has a methyl ethyl ketone swelling degree of 55 times or more and the polymer (B) has a methyl ethyl ketone swelling degree of 45 times or less.

4. The latex composition for dip molding according to any one of claims 1 to 3, wherein the conjugated diene polymer (A) is a nitrile group-containing conjugated diene polymer having a methyl ethyl ketone-insoluble content of 50% by weight or less.

5. The latex composition for dip molding according to any one of claims 1 to 4, wherein the content of the conjugated diene polymer (A) in 100 parts by weight of the polymer component is 40 parts by weight or more.

6. The latex composition for dip molding according to any one of claims 1 to 5, wherein the polymer (B) is a nitrile group-containing conjugated diene polymer having a methyl ethyl ketone-insoluble content of 55% by weight or more or a polyurethane resin.

7. The latex composition for dip molding according to any one of claims 1 to 6, further containing a sulfur-based crosslinking agent.

8. A dip-molded article obtained by using the latex composition for dip molding according to any one of claims 1 to 7.

9. A dip-molded article obtained by immersing a substrate in the latex composition for dip molding according to any one of claims 1 to 7.

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