Composition for dip forming and glove, and methods for manufacturing composition for dip forming and glove

Abstract

Provided is a sulfur-free crosslinked composition for dip forming, including: a carboxylated diene rubber elastomer; a crosslinking agent that contains at least one of an organic crosslinking agent or a metal crosslinking agent with a valence of two or more; an antioxidant that contains at least one compound having a phenol structure and a sulfur atom; and water, wherein an amount of the at least one compound is 0.05 to 4 parts by weight relative to 100 parts by weight of the elastomer.

Description

Dip-forming composition and glove, and method for producing dip-forming composition and glove

[0001] The present disclosure relates to a dip-molding composition and a glove, and a method for producing the dip-molding composition and the glove.

[0002] Rubber gloves are widely used in various industrial and medical fields. Natural latex and synthetic latex are used as elastomers for rubber gloves. These include diene rubbers such as natural rubber (NR), polyisoprene rubber (IR), chloroprene rubber (CR), styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), and carboxylated acrylonitrile butadiene rubber (XNBR). Gloves made by dip molding, in which these elastomers are crosslinked with sulfur and a vulcanization accelerator, are generally used. Among these, gloves made by crosslinking the double bonds of butadiene in XNBR with sulfur and crosslinking the carboxyl groups with zinc oxide are most commonly used.

[0003] However, these sulfur crosslinked gloves have the problem that they cause type I allergy due to the protein contained in natural rubber, and type IV allergy due to the vulcanization accelerator accompanying sulfur vulcanization in synthetic rubber.

[0004] For this reason, accelerator-free gloves, which do not contain vulcanization accelerators and are made by using non-sulfur crosslinking of carboxylated diene rubber, have been developed. These include crosslinking the carboxyl groups of carboxylated diene rubber with an organic or metallic crosslinking agent, or incorporating a crosslinkable organic compound during polymerization to self-crosslink the latex. Gloves that have actually been put to practical use include polycarbodiimide crosslinked gloves, epoxy crosslinked gloves, aluminum crosslinked gloves, and several types of self-crosslinked gloves. These are manufactured by the anodic adhesion immersion method, or the so-called dip molding method. Conventionally, there have been various non-sulfur crosslinking methods, such as peroxide crosslinking, but none of them are suitable for glove manufacturing by dip molding.

[0005] To prevent aging of these rubber gloves, antioxidants have been used taking into consideration the type of rubber gloves, safety to the human body, deterioration environment, and manufacturing method. For rubber gloves, phenolic primary antioxidants, especially hindered phenolic primary antioxidants such as Wingstay (registered trademark), which are less likely to stain, have generally been used. Amine-based antioxidants have not been used due to their potential for staining.

[0006] US Patent No. 5,949,999 discloses an example of the use of Wingstay® hindered phenolic antioxidants in sulfur crosslinking.

[0007] Patent Document 2 discloses a method for manufacturing gloves that are prepared for a radiation irradiation step by dip-molding an accelerator-free latex composition containing a carboxyl group-containing conjugated diene rubber latex, an aluminum crosslinking agent, and a hindered phenol-based antioxidant. Patent Document 2 also discloses that the content of the hindered phenol-based antioxidant should be 0.5 wt% or more and 7.0 wt% or less.

[0008] Patent Document 3 discloses accelerator-free gloves in which carboxylated acrylonitrile butadiene is crosslinked with polycarbodiimide. In Patent Document 3, phenolic antioxidants such as butylated reaction product of p-cresol and cyclopentadiene (BPC) and 2,2'-methylene-bis-(4-methyl-6-butylphenol) (MBPC) are used.

[0009] Patent Document 4 discloses accelerator-free gloves in which carboxylated acrylonitrile butadiene is crosslinked with an epoxy crosslinking agent. Patent Document 4 also discloses that a hindered phenol type antioxidant, for example, Wingstay (registered trademark) L, can be used as the antioxidant.

[0010] Non-Patent Document 1 describes a conventional method for manufacturing carboxylated diene rubber gloves by sulfur vulcanization, and describes that non-staining phenolic compounds are often used as antioxidants (see page 2, 3.2.4).

[0011] Non-Patent Document 2 describes the development status of nitrile gloves that do not use vulcanization accelerators.

[0012] JP-T-11-509873 A International Publication No. 2020 / 066835 JP-A-2017-213914 A International Publication No. 2019 / 102985

[0013] Tetsuya Akabane, "Manufacturing Methods and Market Trends of Rubber Gloves," 2015, Journal of the Society of Rubber Industry, Japan, Vol. 88, No. 9. Norihide Enomoto, "Development of Nitrile Gloves without Vulcanization Accelerators," 2016, Production and Technology, Vol. 68, No. 4.

[0014] Rubber gloves undergo aging tests in accordance with ASTM D6319 (Standard Specification for Medical Nitrile Test Gloves) to ensure quality against rubber deterioration. Specific standards are that the gloves must be aged at 70°C for 168 hours, with a tensile strength of 14 MPa or more and an elongation of 400% or more. (See ASTM D6319, p. 2, 7.5.2 Accelerated Aging.)

[0015] By meeting this standard, it was thought that the quality of rubber gloves could be maintained for about three years. Accelerator-free gloves currently in use have also been sold after meeting this standard.

[0016] Conventionally, powdered gloves have been the norm for rubber gloves, with powder applied to the inside of the glove to make it easier to put on. However, powder is harmful, especially for medical gloves, so the surface of the glove is treated with chlorine in an online process after the glove is molded onto a hand mold to remove the slimy feeling. When the glove is then removed from the hand mold and turned inside out, the chlorine-treated surface is on the inside of the glove.

[0017] Furthermore, gloves for clean rooms are treated offline with chlorine to further smooth the surface of the gloves, reduce dust generation, and prevent metals from leaching from the surface of the gloves and transferring to the products they handle.

[0018] The development of this disclosure began with the aim of solving the problem of accelerator-free cleanroom aluminum cross-linked gloves turning brown within a few months of manufacture. It was also discovered that the same problem occurs with both epoxy cross-linked gloves and polycarbodiimide cross-linked gloves.

[0019] The present disclosure has been made in consideration of the problems that non-sulfur crosslinked gloves have. An object of the present disclosure is to provide a glove which can suppress at least one of deterioration in mechanical properties such as tensile strength and elongation and occurrence of yellowing over time, a dip-forming composition used for producing the glove, and a method for producing the dip-forming composition and the glove.

[0020] A non-sulfur-crosslinked dip-molding composition according to an embodiment of the present disclosure includes a carboxylated diene rubber elastomer, a crosslinking agent including at least one of an organic crosslinking agent and a divalent or higher metal crosslinking agent, an antioxidant including at least one compound having a phenol structure and a sulfur atom, and water, wherein the content of the at least one compound is 0.05 to 4 parts by weight per 100 parts by weight of the elastomer.

[0021] The carboxylated diene rubber elastomer may be an elastomer containing, in the polymer main chain, structural units derived from (meth)acrylonitrile, structural units derived from unsaturated carboxylic acid, and structural units derived from butadiene.

[0022] The at least one compound may include at least one compound having a phenol structure and at least one selected from the group consisting of a thioether structure, a polysulfide structure, and a thiol structure.

[0023] The at least one compound may include at least one compound having a phenol structure and a thioether structure or a polysulfide structure.

[0024] The at least one compound may include a compound having both a phenol structure and a sulfur atom in the same molecule.

[0025] The at least one compound may include two or more compounds, a compound having a phenol structure and a compound having a sulfur atom.

[0026] The organic crosslinking agent may contain at least one of a polycarbodiimide and an epoxy compound.

[0027] The divalent or higher metal crosslinking agent may contain at least one of a zinc compound and an aluminum compound.

[0028] A method for producing a non-sulfur-crosslinked dip-molding composition according to another embodiment of the present disclosure includes a step of mixing a carboxylated diene rubber elastomer, a crosslinking agent including at least one of an organic crosslinking agent and a divalent or higher metal crosslinking agent, and an antioxidant including at least one compound having a phenol structure and a sulfur atom, wherein the content of the at least one compound is 0.05 to 4 parts by weight per 100 parts by weight of the elastomer, and the at least one compound is added to the elastomer in the form of a dispersion dispersed in an aqueous solvent.

[0029] The carboxylated diene rubber elastomer may be an elastomer containing, in the polymer main chain, structural units derived from (meth)acrylonitrile, structural units derived from unsaturated carboxylic acid, and structural units derived from butadiene.

[0030] A glove according to another aspect of the present disclosure comprises a non-sulfur crosslinked elastomer which is a carboxylated diene rubber elastomer, a crosslinking agent containing at least one of an organic crosslinking agent and a divalent or higher metal crosslinking agent, and an antioxidant containing at least one compound having a phenol structure and a sulfur atom dispersed in the non-sulfur crosslinked elastomer, wherein the content of the at least one compound is 0.05 to 4 parts by weight based on 100 parts by weight of the non-sulfur crosslinked elastomer.

[0031] The carboxylated diene rubber elastomer may be a non-sulfur crosslinked elastomer containing structural units derived from (meth)acrylonitrile, structural units derived from unsaturated carboxylic acid, and structural units derived from butadiene in the polymer main chain.

[0032] A method for producing a glove according to another aspect of the present disclosure includes a step of dip-molding a glove with a dip-molding composition.

[0033] Figure 1 is a diagram showing an example of a typical yellowing mechanism caused by dibutylhydroxytoluene (BHT), an antioxidant. Figure 2 is a graph showing the relationship between heating time and color difference of test specimens in Examples 1 to 4 and Comparative Examples 1 to 5. Figure 3 is a graph showing the relationship between heating time and color difference of test specimens in Examples 5 to 10 and Comparative Example 6. Figure 4 is a graph showing the relationship between heating time and elongation at break of test specimens in Examples 5 to 10 and Comparative Example 6. Figure 5 is a graph showing the relationship between chlorine treatment time and tensile strength at break of gloves in Example 11 and Comparative Example 7.

[0034] As mentioned above, the development of this disclosure began with the aim of solving the problem of accelerator-free aluminum cross-linked gloves for cleanroom use turning brown within a few months of manufacture. Furthermore, when polycarbodiimide cross-linked gloves were subjected to offline chlorination for cleanroom use, cracks occurred in the glove film during the treatment. To solve this problem, we tried various treatment conditions after online and offline chlorination of the gloves, particularly conditions for water washing, neutralization, and reducing agents. We also found that such problems rarely occur with sulfur-vulcanized gloves. As a result, we found that these phenomena are mainly common to non-sulfur cross-linked gloves (accelerator-free gloves).

[0035] When we investigated why non-sulfur crosslinked gloves yellow more than sulfur crosslinked gloves over time, we found that non-sulfur crosslinked gloves are more susceptible to oxidation and deterioration than sulfur crosslinked gloves. One reason for this is thought to be that in sulfur crosslinked gloves, the polysulfide moiety used for crosslinking is oxidized instead of the main chain, which prevents the rubber glove from oxidizing and deteriorating. Another reason is thought to be that in sulfur crosslinked gloves, the vulcanization accelerator itself has the effect of an antioxidant. On the other hand, non-sulfur crosslinked gloves do not contain polysulfide moieties for crosslinking and do not contain a vulcanization accelerator, so they do not have the above-mentioned antioxidant function.

[0036] Generally, oxidative degradation of rubber progresses through the generation of radicals by oxygen in the air, which then trigger chain reactions and generate peroxides. To prevent this oxidative degradation of rubber, it is necessary to suppress the radical chain reaction and decompose the peroxides. Compounds containing phenolic structures can form stable radicals and suppress chain reactions. Furthermore, compounds containing sulfur atoms can decompose peroxides. When sulfur crosslinking, which uses sulfur-containing compounds, or vulcanization accelerators containing sulfur atoms is used in the crosslinking process, the addition of an antioxidant with a phenolic structure can suppress these two types of oxidative degradation. However, when sulfur-containing compounds are not used in the crosslinking process, even if the radical chain reaction can be suppressed, peroxides cannot be decomposed. Figure 1 shows an example of a typical yellowing mechanism that occurs with dibutylhydroxytoluene (BHT), a typical antioxidant. Using only compounds with phenolic structures that suppress radical chain reactions does not effectively prevent oxidative degradation and discoloration of rubber because there is no compound that decomposes peroxides.

[0037] Therefore, it was found that the yellowing of gloves over time can be suppressed by using an antioxidant having the functions of inhibiting radical chain reaction and decomposing peroxides in a predetermined ratio. Inhibiting radical chain reaction and decomposing peroxides is effective in stopping the successive reactions shown in Figure 1, for example, and is particularly effective in preventing oxidative degradation and discoloration of rubber. It is believed that by using the antioxidant, the deterioration of mechanical properties over time can also be suppressed by the same mechanism as above.

[0038] By the way, rubber gloves are treated with chlorine online or offline as needed. Chlorine treatment is especially important when using rubber gloves in an environment where dust and dirt components are undesirable, such as a clean room. Chlorine dissolves in water and is converted into Cl ２ +H ２As shown in the reaction formula O → HClO + HCl, hypochlorous acid (HClO) and hydrochloric acid (HCl) are produced. Hypochlorous acid partially oxidizes nitrile rubber, reducing its tackiness. Meanwhile, hydrochloric acid converts poorly soluble metal salts and metal oxides on the glove surface into metal chlorides. Generally, metal chlorides are soluble in water, and residual metals can be removed from the glove surface by washing with water, such as ion-exchanged water. Furthermore, online chlorination of rubber gloves reduces the tackiness of the inner surface of the glove and hardens it, thereby increasing slipperiness and improving the donning comfort of the glove.

[0039] In offline chlorination, the glove is turned inside out when it is removed from the former, so the adhesiveness of the outer surface of the glove is reduced to adjust the grip, and the HCl converts the metal compounds into water-soluble metal chlorides, facilitating the subsequent washing of the glove surface with deionized water. After this treatment, the chlorine is reduced and neutralized with a reducing agent, sodium thiosulfate, and an alkaline agent, such as KOH or sodium carbonate.

[0040] The chlorine component used in the chlorination treatment described above remains in the rubber glove even after the final reduction and neutralization treatments, causing aging of the rubber glove. Chlorine radicals generated from chlorine or derivatives such as hypochlorous acid abstract allyl hydrogen atoms from nitrile rubber, generating allyl radical species in the main chain of the latex. This radical reacts with oxygen to generate peroxide radicals (R-OO·), similar to oxidative aging caused by oxygen. These peroxide radicals then cause radical chain reactions, accelerating aging of the rubber glove. Thus, the radicals generated by the chlorine species remaining in the glove after chlorination have the same effect on aging of the rubber glove as oxygen in the air. Therefore, to prevent aging and deterioration of rubber gloves due to residual chlorine, it is important to prevent both the radical chain reaction and the accompanying oxidation reaction by peroxide, as in the case of aging caused by oxygen. The dip-forming composition and its manufacturing method, as well as the glove and its manufacturing method according to this embodiment, are described in detail below.

[0041] [Dip-forming composition] The dip-forming composition according to this embodiment is used as a dipping liquid, which is a raw material for gloves. The dip-forming composition contains an elastomer, a crosslinking agent, an antioxidant, and water. Each component will be described in detail below.

[0042] <Elastomer> The elastomer according to the present disclosure is a carboxylated diene rubber elastomer. The carboxylated diene rubber is a carboxylated modified version of at least one synthetic latex selected from the group consisting of polyisoprene rubber (IR), chloroprene rubber (CR), styrene butadiene rubber (SBR), and nitrile butadiene rubber (NBR). These rubbers have traditionally been used to manufacture gloves by dip molding using sulfur and a vulcanization accelerator. The carboxylated diene rubber elastomer can be produced by polymerizing a conjugated diene monomer and carboxylating it. The conjugated diene monomer is preferably a conjugated diene monomer having 4 to 6 carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, or chloroprene. 1,3-butadiene and isoprene are more preferred, and 1,3-butadiene is particularly preferred. The conjugated diene monomers may be used alone or in combination of two or more.

[0043] In this embodiment, the carboxylated diene rubber elastomer will be specifically described by taking carboxylated acrylonitrile butadiene rubber (XNBR), which is most commonly used in gloves, as an example. The carboxylated diene rubber elastomer may contain, for example, a structural unit derived from (meth)acrylonitrile, a structural unit derived from unsaturated carboxylic acid, and a structural unit derived from butadiene in the polymer main chain. Note that (meth)acrylonitrile is a concept that includes both acrylonitrile and methacrylonitrile.

[0044] In the elastomer, the structural unit derived from (meth)acrylonitrile may be 20% by weight to 40% by weight. That is, in the elastomer, the (meth)acrylonitrile residue may be 20% by weight to 40% by weight. By making the structural unit derived from (meth)acrylonitrile 20% by weight or more, the strength and chemical resistance of the glove can be improved. Also, by making the structural unit derived from (meth)acrylonitrile 40% by weight or less, the glove can be made flexible. The structural unit derived from (meth)acrylonitrile may be 25% by weight or more, or may be 30% by weight or more.

[0045] In the elastomer, the structural unit derived from unsaturated carboxylic acid may be 1% by weight to 10% by weight. That is, in the elastomer, the unsaturated carboxylic acid residue may be 1% by weight to 10% by weight. By making the structural unit derived from unsaturated carboxylic acid 1% by weight to 10% by weight, an appropriate crosslinked structure is formed, and good physical properties of the gloves can be maintained. The structural unit derived from unsaturated carboxylic acid may be 4% by weight or more. Furthermore, the structural unit derived from unsaturated carboxylic acid may be 6% by weight or less. The unsaturated carboxylic acid is not particularly limited, and may be a monocarboxylic acid or a polycarboxylic acid. The unsaturated carboxylic acid may be acrylic acid, methacrylic acid, crotonic acid, maleic acid, or fumaric acid. Among these, acrylic acid or methacrylic acid is preferred.

[0046] In the elastomer, the butadiene derived structural unit may be 50% by weight to 75% by weight. That is, in the elastomer, the butadiene residue may be 50% by weight to 75% by weight. By making the butadiene derived structural unit 50% by weight or more, the flexibility of the glove can be improved. The butadiene derived structural unit may be 60% by weight or more. The butadiene derived structural unit may be a 1,3-butadiene derived structural unit.

[0047] The polymer main chain may contain structural units derived from other polymerizable monomers in addition to structural units derived from (meth)acrylonitrile, unsaturated carboxylic acid, and butadiene. In the elastomer, the structural units derived from other polymerizable monomers may account for 30% by weight or less, 20% by weight or less, or 15% by weight or less.

[0048] The ratio of the structural units can be easily determined from the weight ratio (solid content ratio) of the raw materials used to produce the elastomer.

[0049] The other polymerizable monomer may include at least one of a self-crosslinking compound and a non-self-crosslinking compound. A self-crosslinking compound is a polymerizable compound contained in the polymer chain of an elastomer, and refers to a monomer having a functional group capable of forming intramolecular crosslinks or intermolecular crosslinks (hereinafter collectively referred to as "crosslinks"). That is, a self-crosslinking compound is a compound (polymerizable monomer) having a polymerizable unsaturated bond (a polymerizable unsaturated bond) and one or more functional groups capable of forming crosslinks. This polymerizable monomer may be a monofunctional monomer containing one of these specific functional groups, or a polyfunctional monomer containing two or more functional groups. In the case of a polyfunctional monomer, the multiple functional groups may be the same or different from each other. The crosslinks formed include bonds formed by elimination or substitution reactions between the carboxyl group of an unsaturated carboxylic acid and the functional group of a polymerizable monomer, or between the functional groups of a polymerizable monomer, such as ester bonds, amide bonds, imide bonds, and vinyl bonds.

[0050] Examples of the self-crosslinking compound include 2-hydroxyalkyl (meth)acrylate, n-methylolacrylamide, 4-hydroxybutyl acrylate glycidyl ether, 2-isocyanatoethyl methacrylate, 3-glycidoxypropyl methoxysilane, 2-(3,4-epoxycyclohexyl)ethyl methoxysilane, vinyl methoxysilane, vinyl ethoxysilane, vinyl tris(2-methoxyethoxy)silane, N-allylacrylamide, glycerin triacrylate, trimethylpropane triacrylate, N-(1,1-dimethyl-3-oxobutyl)acrylamide (diacetone acrylamide), N-(isobutoxymethyl)acrylamide, N-hydroxymethyl diacetone acrylamide, N-formyl-N'-acryloylmethylenediamine, 2-carboxylethyl (meth)acrylate, and succinic acid mono(2-(meth)acryloyloxyethyl). Examples of 2-hydroxyalkyl (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate.

[0051] A non-self-crosslinking compound is a compound that is polymerizable but not crosslinkable. Examples of non-self-crosslinking compounds include aromatic vinyl monomers, ethylenically unsaturated carboxylic acid amides, ethylenically unsaturated carboxylic acid alkyl ester monomers, and vinyl acetate. Examples of aromatic vinyl monomers include styrene, α-methylstyrene, and dimethylstyrene. Examples of ethylenically unsaturated carboxylic acid amides include (meth)acrylamide and N,N-dimethylacrylamide. Examples of ethylenically unsaturated carboxylic acid alkyl ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. These may be used alone or in combination. In this specification, (meth)acrylic is a term that encompasses both acrylic and methacrylic.

[0052] Alternatively, the elastomer may contain a polyfunctional organic compound that does not contain a polymerizable functional group but contains two or more functional groups in the molecule, thereby crosslinking the polymer chains. In this case, an organic crosslinking agent is incorporated into the elastomer in advance during polymerization, and the organic crosslinking agent is not particularly limited as long as it is a non-polymerizable (i.e., does not have a polymerizable unsaturated bond) polyfunctional organic compound.

[0053] The elastomer can be obtained by emulsion polymerization using polymerizable monomers containing (meth)acrylonitrile, unsaturated carboxylic acid, and butadiene, according to a standard method, using a polymerization liquid containing an emulsifier, a polymerization initiator, a molecular weight modifier, water, etc. The solids content of the polymerization liquid is preferably 30% to 60% by weight, more preferably 35% to 55% by weight. The emulsion polymerization liquid after synthesis of the elastomer can be used directly as the elastomer component of a dipping composition.

[0054] The emulsifier has a hydrophobic group and a hydrophilic group as a surfactant. Examples of the emulsifier include anionic surfactants such as dodecylbenzenesulfonate and aliphatic sulfonate; and nonionic surfactants such as polyethylene glycol alkyl ether and polyethylene glycol alkyl ester. Among these, the emulsifier preferably contains an anionic surfactant.

[0055] The polymerization initiator is not particularly limited as long as it is a radical initiator, and examples thereof include inorganic peroxides such as ammonium persulfate and potassium perphosphate; organic peroxides such as t-butyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, t-butylcumyl peroxide, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide and t-butylperoxyisobutyrate; and azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile and methyl azobisisobutyrate.

[0056] Examples of the molecular weight regulator include mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan, and halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, and methylene bromide. The molecular weight regulator preferably contains mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan.

[0057] Latex contains water and elastomer as a solid component. Latex is an emulsion in which elastomer particles are dispersed, surrounded by a membrane of emulsifier. The outside of the membrane is hydrophilic, and the inside of the membrane is hydrophobic. Within the particle, the carboxyl groups are oriented toward the inside of the membrane.

[0058] In the dip-molding composition, the elastomer may be in the form of particles. The average particle diameter of the elastomer may be approximately 50 nm to 250 nm. By setting the average particle diameter to 50 nm or more, the specific surface area increases and interparticle cross-linking becomes stronger. Furthermore, by setting the average particle diameter to 250 nm or less, syneresis can be reduced. In this specification, the value of "average particle diameter" is used, unless otherwise specified, as the value calculated as the average particle diameter of particles observed in several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0059] The content of the elastomer in the dip-molding composition may be 15% by weight or more, or 18% by weight or more, and may be 35% by weight or less, or 30% by weight or less.

[0060] <Crosslinking Agent> The crosslinking agent is substantially a non-sulfur-based crosslinking agent. That is, the dip-molding composition is substantially free of sulfur compounds, such as sulfur crosslinkers and vulcanization accelerators. The respective contents of the sulfur crosslinker and vulcanization accelerator contained in the dip-molding composition are, for example, less than 1% by weight, and may even be less than 0.1% by weight. Examples of the sulfur crosslinking agent include polysulfides. Examples of the crosslinking accelerator include sulfur-containing compounds such as dithiocarbamate-based vulcanization accelerators, such as dithiocarbamate, thiuram-based vulcanization accelerators, such as tetramethylthiuram disulfide (TMTD), thiazole-based crosslinking accelerators, such as mercaptobenzothiazole (MBT), sulfenamide-based crosslinking accelerators, guanidine-based crosslinking accelerators, and thiourea-based crosslinking accelerators.

[0061] Examples of non-sulfur crosslinked structures include crosslinks between carboxy groups crosslinked by a non-sulfur crosslinking agent. The non-sulfur crosslinking agent may contain at least one of an organic crosslinking agent and a metal crosslinking agent. Such crosslinking agents can crosslink carboxy groups by reacting with the carboxy groups. The organic crosslinking agent may contain at least one of a polycarbodiimide and a polyepoxy compound. Metal crosslinking agents will be described later.

[0062] (Polycarbodiimide) Polycarbodiimide is a compound having multiple carbodiimide groups (-N=C=N-). The carbodiimide groups react with the carboxy groups of an elastomer, thereby crosslinking the carboxy groups together. Polycarbodiimide can be obtained by decarboxylation condensation of diisocyanate. The number of carbodiimide functional groups per molecule of polycarbodiimide (degree of polymerization) may be 4 to 20. By setting the degree of polymerization to 4 or more, multi-point crosslinking between the carboxy groups of the elastomer can be achieved, and improved fatigue durability can be expected compared to two-point crosslinking. The degree of polymerization may be 5 or more, or 9 or more.

[0063] The diisocyanate used in the synthesis of polycarbodiimide may contain at least one selected from the group consisting of aromatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates. From the viewpoint of weather resistance, the diisocyanate is preferably an aliphatic diisocyanate or an alicyclic diisocyanate. The diisocyanate may include at least one selected from the group consisting of 1,5-naphthylene diisocyanate, 4,4-diphenylmethane diisocyanate, 4,4-diphenyldimethylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, methylcyclohexane diisocyanate, and tetramethylxylylene diisocyanate.

[0064] The polycarbodiimide may be a compound obtained by decarboxylation condensation of diisocyanate and having isocyanate residues at both ends. In addition, in order to prevent the carbodiimide group from reacting with water, at least a part of the terminal isocyanate residues may have R １ -O-(CH ２ -CHR ２ -O-) ｎ A hydrophilic segment represented by —H may be added (wherein R １ is an alkyl group having 1 to 4 carbon atoms, R ２ (wherein n is a hydrogen atom or a methyl group, and n is an integer of 5 to 30.) The hydrophilic segments may be attached to both ends of the polycarbodiimide, or to only one end. The polycarbodiimide may be a mixture of polycarbodiimide having a hydrophilic segment and polycarbodiimide not having a hydrophilic segment. Polycarbodiimide having an effective hydrophilic segment forms micelles in water, and the highly reactive polycarbodiimide portion is located within the micelles, thereby suppressing reaction with water.

[0065] The end of the polycarbodiimide to which the hydrophilic segment is not added is (R ３ ) ２ N-R ４ It may be sealed with a sealing agent represented by —OH (wherein R ３ is an alkyl group having 6 or less carbon atoms, and R ４ is alkylene or polyoxyalkylene having 1 to 10 carbon atoms). From the viewpoint of availability, R ３ is preferably an alkyl group having 4 or less carbon atoms.

[0066] In the dip-forming composition, the polycarbodiimide content may be more than 0.2 wt % and not more than 4.0 wt % based on the solid content of the dip-forming composition. When the polycarbodiimide content exceeds 0.2 wt %, high fatigue durability exceeding that of sulfur-crosslinked gloves can be achieved. When the polycarbodiimide content is 4.0 wt % or less, profitability is good. The polycarbodiimide content may be 0.3 wt % or more. Furthermore, the polycarbodiimide content may be 2.5 wt % or less, or may be 2.0 wt % or less.

[0067] The average particle size of the polycarbodiimide micelles is preferably 5 to 30 nm. The average particle size of the polycarbodiimide micelles refers to the average particle size of the individual micelles formed by the polycarbodiimide, measured by dynamic light scattering under the following conditions: Measuring device: Zetasizer Nano ZS (manufactured by Malvern) Light source: He-Ne (40 mW) 633 nm Measurement temperature: 25°C Dispersion medium viscosity: 0.887 cP (value for water used) Dispersion medium refractive index: 1.33 (value for water used) Sample preparation: 100-fold dilution with ion-exchanged water

[0068] The degree of polymerization of the polycarbodiimide may be 5 or more, and the average particle size of the micelles may be 30 nm or less. In this case, it is expected that a cured film having high fatigue resistance can be produced even after a certain period of time has passed since the preparation of the dip-forming composition.

[0069] (Polyepoxy Crosslinking Agent) The polyepoxy crosslinking agent contains an epoxy compound having an epoxy group. The polyepoxy compound has two or more epoxy groups per molecule. The polyepoxy compound may also have three or more epoxy groups per molecule. When the epoxy compound has three or more epoxy groups, crosslinking between elastomer molecules increases, thereby improving fatigue durability. Even if one epoxy group is deactivated, crosslinking can be performed using the remaining epoxy group, allowing for efficient crosslinking of the elastomer. This allows for a reduced amount of polyepoxy compound added. There is no particular upper limit on the number of epoxy groups the polyepoxy compound may have, but the number of epoxy groups may be eight or less. The epoxy compound may or may not have an aromatic ring.

[0070] From the viewpoint of fatigue durability, the average number of epoxy groups in the polyepoxy crosslinking agent is preferably more than 2.0, more preferably 2.3 or more, and even more preferably 2.5 or more. The average number of epoxy groups is determined by identifying each epoxy compound contained in the epoxy crosslinking agent by GPC (gel permeation chromatography). The number of epoxy groups in each polyepoxy compound is then multiplied by the number of moles of the epoxy compound to obtain the number of epoxy groups for each polyepoxy compound, and the sum of these values ​​is divided by the total number of moles of all polyepoxy compounds contained in the polyepoxy crosslinking agent.

[0071] The polyepoxy compound may include at least one selected from the group consisting of polyglycidyl ether, polyglycidyl amine, polyglycidyl ester, epoxidized polybutadiene, and epoxidized soybean oil.

[0072] The polyglycidyl ether may be at least one selected from the group consisting of diglycidyl ether, triglycidyl ether, tetraglycidyl ether, pentaglycidyl ether, hexaglycidyl ether, heptaglycidyl ether, and octaglycidyl ether. The triglycidyl ether may include at least one selected from the group consisting of glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol triglycidyl ether, pentaerythritol triglycidyl ether, and diglycerol triglycidyl ether. The tetraglycidyl ether may include at least one selected from the group consisting of sorbitol tetraglycidyl ether and pentaerythritol tetraglycidyl ether. Among these, it is preferable that the polyepoxy compound include at least one selected from the group consisting of glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol triglycidyl ether, diglycerol triglycidyl ether, and pentaerythritol tetraglycidyl ether.

[0073] The amount of polyepoxy crosslinking agent added may be 0.1 parts by weight or more, 0.4 parts by weight or more, or 0.5 parts by weight or more, per 100 parts by weight of elastomer, depending on the number of epoxy groups in one molecule and the purity of the epoxy compound, from the viewpoint of introducing a sufficient crosslinking structure between elastomers to ensure fatigue durability. Also, from the viewpoint of improving the properties of the elastomer, the amount of polyepoxy crosslinking agent added to the dip-molding composition may be 5 parts by weight or less, 1.0 part by weight or less, or 0.7 part by weight or less, per 100 parts by weight of elastomer.

[0074] The amount of polyepoxy compound added may be 0.05 parts by weight or more, 0.2 parts by weight or more, or 0.25 parts by weight or more, per 100 parts by weight of elastomer, depending on the number of epoxy groups in one molecule and the purity of the polyepoxy compound, from the viewpoint of introducing a sufficient crosslinking structure between elastomers to ensure fatigue durability. Furthermore, from the viewpoint of improving the properties of the elastomer, the upper limit of the amount of polyepoxy crosslinking agent added to the dip-molding composition may be 2.5 parts by weight or less, 0.5 parts by weight or less, or 0.35 parts by weight or less, per 100 parts by weight of elastomer.

[0075] The water solubility of the polyepoxy crosslinking agent may be 10 to 70%. When the water solubility is 10% or more, the solubility in water and XNBR is high, resulting in good productivity. A dip-molding composition having an excellent pot life suitable for mass production can be obtained. When the water solubility is 70% or less, a dip-molding composition having an excellent pot life suitable for mass production can be obtained.

[0076] Water solubility measurement method 1. Accurately weigh out 25.0 g of polyepoxy crosslinking agent into a beaker and add 225 g of water (25°C). 2. Stir and mix vigorously for 15 minutes at room temperature (23°C ± 2°C), then leave to stand for 1 hour. 3. Measure the volume (mL) of the oily substance that has settled at the bottom of the beaker. 4. Calculate the water solubility using the following formula: Water solubility (%) = (25.0 (g) - (volume of oily substance (mL) × density of polyepoxy crosslinking agent (g / mL)) / 25.0 × 100

[0077] The polyepoxy crosslinking agent may have a MIBK (methyl isobutyl ketone) / water partition ratio of 27% or more. By using a polyepoxy crosslinking agent with a MIBK / water partition ratio of 27% or more, the polyepoxy crosslinking agent can easily penetrate into the lipophilic regions of the XNBR particles, preventing deactivation of the polyepoxy crosslinking agent. This allows for a dip-molding composition with a pot life of 3 days or more. The MIBK / water partition ratio is preferably 30% or more, more preferably 50% or more, and even more preferably 70% or more. On the other hand, in the case of a polyepoxy crosslinking agent with a MIBK / water partition ratio of 27% or more but less than 30%, it is also preferable that the polyepoxy crosslinking agent be 1.0 part by weight or more per 100 parts by weight of elastomer.

[0078] The MIBK / water partition ratio can be measured as follows. First, approximately 5.0 g of water, approximately 5.0 g of MIBK, and approximately 0.5 g of polyepoxy crosslinking agent are precisely weighed and added to a test tube. The weight of MIBK is M (g), and the weight of polyepoxy crosslinking agent is E (g). This mixture is stirred and mixed for 3 minutes at a temperature of 23°C ± 2°C, and then 1.0 x 10 ３ The mixture was centrifuged under conditions G for 10 minutes to separate the water layer and the MIBK layer. The weight of the MIBK layer was then measured and designated ML (g). MIBK / water partition coefficient (%) = (ML (g) - M (g)) / E (g) x 100. Note that the method for measuring the MIBK / water partition coefficient in this specification was based on the weights of water and MIBK. However, because MIBK dissolves a small amount of water, a negative percentage was obtained as an experimental value. However, since measurements were performed using the same standard, it was considered possible to use this as a standard.

[0079] The dip-molding composition may contain a polyepoxy crosslinking agent and a dispersing agent. The weight ratio of the polyepoxy crosslinking agent to the dispersing agent in the dip-molding composition is preferably polyepoxy crosslinking agent:dispersing agent=1:4 to 1:1.

[0080] The dispersant is preferably one or more selected from the group consisting of monohydric lower alcohols, glycols, ethers, and esters. Examples of monohydric lower alcohols include methanol and ethanol. Examples of glycols include HO—(CH２ CHR １ -O) ｎ１ -H(R １ represents hydrogen or a methyl group, and n1 represents an integer of 1 to 3. Specific examples of glycols include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and tripropylene glycol. Specific examples of ethers include R ２ O-(CH ２ CHR １ -O) ｎ２ -R ３ (R １ represents hydrogen or a methyl group, R ２ represents an aliphatic hydrocarbon group having 1 to 5 carbon atoms, and R ３ represents hydrogen or an aliphatic hydrocarbon group having 1 to 3 carbon atoms, and n2 represents an integer of 0 to 3. Specific examples of ethers include glycol ethers such as diethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and triethylene glycol dimethyl ether. Examples of esters include those in which R ２ O-(CH ２ CHR １ -O) ｎ３ —(C═O)—CH ３ (R １ represents hydrogen or a methyl group, R ２represents an aliphatic hydrocarbon group having 1 to 5 carbon atoms, and n3 represents an integer of 0 to 3.) Examples of esters include diethylene glycol monoethyl ether acetate and diethylene glycol monobutyl ether acetate. These may be used alone or in combination of two or more. The dispersant may be used without premixing with water. A monohydric lower alcohol is preferred as the dispersant. Methanol, ethanol, and diethylene glycol are also preferred as the dispersant. From the standpoints of volatility and flammability, diethylene glycol is preferred as the dispersant. Diethylene glycol is also presumed to be suitable because it has a highly hydrophilic glycol group and an ether structure, contains a lipophilic hydrocarbon structure, and is easily soluble in both water and elastomers.

[0081] (Metal Crosslinking Agent) The metal crosslinking agent forms a crosslink with the carboxyl group of XNBR by an ionic bond. The metal crosslinking agent may contain a polyvalent metal compound having a divalent or higher metal. Examples of the divalent or higher metal include magnesium, aluminum, calcium, titanium, chromium, iron, cobalt, zinc, zirconium, tin, and lead. The metal crosslinking agent may contain at least one of a zinc compound and an aluminum compound. Use of such a metal crosslinking agent can be expected to improve the tensile strength of the glove, suppress swelling in artificial sweat, and improve organic solvent impermeability.

[0082] Examples of zinc compounds include zinc oxide and zinc hydroxide. Of these, zinc oxide is commonly used. The amount of zinc oxide added may be 0.2 to 4.0 parts by weight based on the total solid content of the dip-forming composition. This can improve the tensile strength of the glove. The amount of zinc oxide added may be 0.8 parts by weight or more. Alternatively, the amount of zinc oxide added may be 1.5 parts by weight or less.

[0083] The aluminum compound may include aluminum hydroxylate or aluminate. Examples of aluminum hydroxylate include aluminum citrate and aluminum lactate. Examples of aluminate include sodium aluminate and potassium aluminate. When an aluminate is used, the dip-forming composition may include a stabilizer. Examples of the stabilizer include alcohol compounds, hydroxycarboxylic acids, and hydroxycarboxylic acid salts. Examples of alcohol compounds include sugar alcohols such as sorbitol, sugars such as glucose, and polyhydric alcohols such as glycerin and ethylene glycol. Examples of hydroxycarboxylic acids include glycolic acid, citric acid, malic acid, and lactic acid. Examples of hydroxycarboxylic acid salts include metal salts of the above hydroxycarboxylic acids.

[0084] In the dip-forming composition, the aluminum compound is a tetrahydroxyaluminate ion ([Al(OH) ４ ] － The aluminum complex ions may be present in the form of aluminum complex ions such as Al(OH) in the leaching step S5 described below. ３ In the curing step S8, ３＋ The amount of the aluminum compound to be added is 1 / 2 of aluminum oxide (Al ２ O ３ ) is preferably 0.2 to 1.5 parts by weight.

[0085] The metal crosslinking agent may contain a zinc compound and an aluminum compound. This can reduce hardening of the glove and provide a glove with excellent elongation. The total amount of the zinc compound and the aluminum compound added is preferably 0.7 to 2.3 parts by weight based on the total amount of solid content of the dip-forming composition. ２ O ３ The ratio of ZnO:Al ２ O ３ It is preferable that the ratio is 1:0.6 to 1:1.2.

[0086] <Antioxidant> The dip-forming composition contains an antioxidant containing at least one compound having a phenol structure and a sulfur atom. The at least one compound may include at least one compound having a phenol structure and at least one selected from the group consisting of a thioether structure, a polysulfide structure, and a thiol structure. The at least one compound may include at least one compound having a phenol structure and a thioether structure or a polysulfide structure. The at least one compound may include a compound having both a phenol structure and a sulfur atom in the same molecule, or may include two or more compounds, namely, a compound having a phenol structure and a compound having a sulfur atom. The at least one compound may include a compound having both a phenol structure and a sulfur atom in the same molecule, and may also include at least one of a compound having a phenol structure and a compound having a sulfur atom. The at least one compound may have a single phenol structure or multiple phenol structures. The at least one compound may have a single sulfur atom or multiple sulfur atoms. The content of the at least one compound is 0.05 to 4 parts by weight per 100 parts by weight of the elastomer. By setting the content of the above compound to 0.05 parts by weight or more, it is possible to suppress at least one of deterioration of mechanical properties and yellowing over time. Also, by setting the content of the above compound to 4 parts by weight or less, it is possible to obtain gloves with a soft feel. The content of at least one compound may be 0.1 to 2 parts by weight based on 100 parts by weight of elastomer.

[0087] A compound having both a phenol structure and a sulfur atom in the same molecule, or a compound having a phenol structure, is a compound containing a phenol compound. The compound having a phenol structure may include at least one phenol compound selected from the group consisting of hindered phenol compounds, semi-hindered phenol compounds, and less-hindered phenol compounds. A hindered phenol compound is a phenol compound having bulky substituents at two ortho positions relative to the hydroxy group of the phenol structure. A semi-hindered phenol compound is a phenol compound having a bulky substituent at one ortho position relative to the hydroxy group of the phenol structure and a non-bulky substituent at the other ortho position. A less-hindered phenol compound is a less-hindered phenol compound having a bulky substituent at one ortho position relative to the hydroxy group of the phenol structure and a hydrogen atom at the other ortho position. Examples of bulky substituents include substituents having a tertiary carbon, such as a t-butyl group. Examples of non-bulky substituents include substituents having a primary carbon, such as a methyl group.

[0088] The compound having both a phenol structure and a sulfur atom in the same molecule may be a compound having a phenol structure and at least one structure selected from the group consisting of a thioether structure, a polysulfide structure, and a thiol structure in the same molecule. The compound may have only one phenol structure in the same molecule, or may have multiple phenol structures. The compound having both a phenol structure and a sulfur atom in the same molecule may include, for example, at least one selected from the group consisting of 2-methyl-4,6-bis[(octylthio)methyl]phenol (CAS No.: 110553-27-0), 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine (CAS No.: 991-84-4), 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (CAS No.: 41484-35-9), and 4,4'-thiobis(3-methyl-6-t-butyl-phenol) (CAS No.: 96-69-5).

[0089] The content of the compound having both a phenol structure and a sulfur atom in the same molecule may be 0.05 to 4 parts by weight based on 100 parts by weight of the elastomer. By setting the content of the compound to 0.05 parts by weight or more, it is possible to suppress at least one of deterioration of mechanical properties and yellowing over time. Furthermore, by setting the content of the compound to 4 parts by weight or less, it is possible to obtain gloves with a soft feel. The content of the compound having both a phenol structure and a sulfur atom in the same molecule may be 0.1 to 2 parts by weight based on 100 parts by weight of the elastomer.

[0090] The compounds having a phenol structure include butylated reaction products of p-cresol with dicyclopentadiene and isobutylene (CAS No.: 68610-51-5), tris-(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate (CAS No.: 27676-62-6), 4,4'-butylidenebis(6-t-butyl-3-methylphenol) (CAS No.: 85-60-9), n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (CAS No.: 2082-79-3), pentaerythritol, and the like. Lithritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (CAS number: 6683-19-8), 2,6-di-t-butyl-4-methylphenol (CAS number: 128-37-0), 2,6-di-t-butylphenol (CAS number: 128-39-2), 2,6-di-t-butyl-4-hydroxymethylphenol (CAS number: 88-26-6), 2,4-dimethyl-6-t-butylphenol (CAS number: 1879-09-0), butylhydroxyanisole (CAS number: 250 13-16-5), 2,2'-methylenebis-(4-methyl-6-t-butylphenol) (CAS number: 119-47-1), 2,2'-methylenebis(4-ethyl-6-t-butylphenol) (CAS number: 88-24-4), 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (CAS number: 35074-77-2), 1,3,5-trimethyl-2,4,6-tris-(3,5-di-t-butyl-4-hydroxybenzyl)benzene (CAS number: 1709-70-2 ), triethylene glycol-bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate] (CAS number: 36443-68-2), 3-t-butyl-4-hydroxyanisole (CAS number: 121-00-6), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane (CAS number: 1843-03-4), 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane (CAS number: 90498-90-1). The compound having a phenol structure does not necessarily include a compound having both a phenol structure and a sulfur atom in the same molecule. The compound having a phenol structure may have only one phenol structure in the same molecule, or may have multiple phenol structures.

[0091] The content of the compound having a phenol structure may be 0.01 to 2 parts by weight based on 100 parts by weight of the elastomer. By setting the content of the compound having a phenol structure to 0.01 part by weight or more, it is possible to suppress at least one of deterioration of mechanical properties and yellowing over time. Furthermore, by setting the content of the compound having a phenol structure to 2 parts by weight or less, it is possible to obtain gloves with a soft feel.

[0092] The compound having a sulfur atom may be a compound having at least one selected from the group consisting of a thioether structure, a polysulfide structure, and a thiol structure. The compound having a sulfur atom may be a compound having a thioether structure or a polysulfide structure. Examples of the compound having a sulfur atom include dilauryl 3,3'-thiodipropionate (CAS number: 123-28-4), dimyristyl 3,3'-thiodipropionate (CAS number: 16545-54-3), 3-laurylthiopropionic acid (CAS number: 1462-52-8), distearyl 3,3'-thiodipropionate (CAS number: 693-36-7), 3,3'-thiodipropionic acid (CAS number: 111-17-1), The compound may contain at least one selected from the group consisting of ditridecyl-3,3'-thiodipropionate (CAS No.: 10595-72-9), tetrakis[methylene-3-(dodecylthio)propionate]methane (CAS No.: 29598-76-3), and thiobis(2-tert-butyl-5-methyl-4,1-phenylene)bis(3-(dodecylthio)propionate) (CAS No.: 66534-05-2). The compound having a sulfur atom does not necessarily contain a compound having both a phenol structure and a sulfur atom in the same molecule. The compound having a sulfur atom may have only one sulfur atom in the same molecule, or may have multiple sulfur atoms.

[0093] The content of the compound having a sulfur atom may be 0.01 to 2 parts by weight based on 100 parts by weight of the elastomer. By setting the content of the compound having a sulfur atom to 0.01 part by weight or more, it is possible to suppress at least one of deterioration of mechanical properties and yellowing over time. Furthermore, by setting the content of the compound having a sulfur atom to 2 parts by weight or less, it is possible to obtain gloves with a soft feel.

[0094] The content of the compound having a sulfur atom may be greater than the content of the compound having a phenol structure in terms of weight ratio. Alternatively, the content of the compound having a sulfur atom may be less than the content of the compound having a phenol structure in terms of weight ratio. Alternatively, the content of the compound having a sulfur atom may be the same as the content of the compound having a phenol structure in terms of weight ratio. The content of the compound having a sulfur atom is preferably 2 to 4 times the content of the compound having a phenol structure in terms of weight ratio.

[0095] Preferably, at least one compound contains a compound having both a phenolic structure and a sulfur atom in the same molecule. Compounds having a phenolic structure generally react with radicals to generate phenoxy radicals. These phenoxy radicals are stabilized by the presence of bulky substituents, such as t-butyl groups, at the adjacent ortho-position, suppressing the radical chain reaction that causes rubber degradation. However, further reaction of these phenoxy radicals generates quinone compounds. The generation of quinone compounds can cause the composition to turn yellow to brown, even if the compound having a phenolic structure itself is normally colorless. In blends containing two compounds, one having a phenolic structure and one having a sulfur atom, the compound having a phenolic structure itself discolors as oxidative degradation progresses. On the other hand, in the case of compounds having both a phenolic structure and a sulfur atom, the sulfur atom decomposes the peroxide compound, thereby inhibiting further reaction of the phenoxy radical. This inhibition of oxidative degradation can prevent the compound itself from denaturing, which is believed to further suppress yellowing.

[0096] <Other Optional Components> The dip-forming composition may contain, in addition to the elastomer, crosslinking agent, antioxidant, and water, other optional components such as a pH adjuster, a moisturizer, a dispersant, a pigment, and a chelating agent.

[0097] Potassium hydroxide is typically used as the pH adjuster. The amount of potassium hydroxide used is typically 0.1 to 2.0 parts by weight per 100 parts by weight of the dip-molding composition. Examples of humectants include polyols, with divalent or trivalent compounds being preferred. The amount of humectant used may be approximately 1.0 to 5.0 parts by weight per 100 parts by weight of the elastomer. Anionic surfactants are preferred as dispersants, including carboxylates, sulfonates, phosphates, polyphosphate esters, polymerized alkylarylsulfonates, polymerized sulfonated naphthalenes, and polymerized naphthalene / formaldehyde condensation polymers, with sulfonates being preferred. The amount of dispersant used is preferably approximately 0.5 to 2.0 parts by weight per 100 parts by weight of the elastomer in the dip-molding composition. Examples of pigments include titanium dioxide. Examples of chelating agents include sodium ethylenediaminetetraacetate.

[0098] As described above, the non-sulfur-crosslinked dip-molding composition according to the present embodiment contains a carboxylated diene rubber elastomer, a cross-linking agent containing at least one of an organic cross-linking agent and a divalent or higher metal cross-linking agent, an antioxidant, and water. The carboxylated diene rubber elastomer may contain structural units derived from (meth)acrylonitrile, structural units derived from unsaturated carboxylic acid, and structural units derived from butadiene in its polymer main chain. The antioxidant contains at least one compound having a phenol structure and a sulfur atom. The content of the at least one compound is 0.05 to 4 parts by weight per 100 parts by weight of the elastomer. The dip-molding composition according to the present embodiment can form a glove that can suppress at least one of deterioration in mechanical properties and yellowing over time.

[0099] [Method for Producing Dip-Forming Composition] Next, a method for producing a non-sulfur-crosslinked dip-forming composition according to this embodiment will be described. The method for producing a dip-forming composition includes mixing the above-described carboxylated diene rubber elastomer with a crosslinking agent and an antioxidant. The carboxylated diene rubber elastomer may contain structural units derived from (meth)acrylonitrile, structural units derived from an unsaturated carboxylic acid, and structural units derived from butadiene in the polymer main chain. The crosslinking agent includes at least one of an organic crosslinking agent and a divalent or higher metal crosslinking agent. The antioxidant includes at least one compound having a phenol structure and a sulfur atom. The content of the at least one compound is 0.05 to 4 parts by weight per 100 parts by weight of the elastomer. The method for producing a dip-forming composition according to this embodiment can produce the above-described dip-forming composition. Details of the materials used and the amounts added are the same as those described above, and therefore will not be described here.

[0100] In the method for producing a dip-forming composition according to this embodiment, the at least one compound having a phenol structure and a sulfur atom may be added to the elastomer in the form of a dispersion in an aqueous solvent. That is, the antioxidant may be in the form of a dispersion. This improves the dispersibility of the at least one compound having a phenol structure and a sulfur atom in the dip-forming composition. The content of the at least one compound having a phenol structure and a sulfur atom in the dispersion may be 25% by weight to 75% by weight, or 40% by weight to 60% by weight.

[0101] [Gloves] Next, a glove according to this embodiment will be described. The glove according to this embodiment comprises a non-sulfur crosslinked elastomer which is a carboxylated diene rubber, a crosslinking agent, and an antioxidant. The carboxylated diene rubber elastomer may contain a structural unit derived from (meth)acrylonitrile, a structural unit derived from an unsaturated carboxylic acid, and a structural unit derived from butadiene in its polymer main chain. The crosslinking agent contains at least one of an organic crosslinking agent and a divalent or higher metal crosslinking agent. The antioxidant is dispersed in the non-sulfur crosslinked elastomer. The antioxidant contains at least one compound having a phenol structure and a sulfur atom. The content of the at least one compound is 0.05 to 4 parts by weight per 100 parts by weight of the non-sulfur crosslinked elastomer. The glove according to this embodiment can suppress at least one of deterioration in mechanical properties and yellowing over time.

[0102] The glove is made of a cured film formed by curing the above dip-forming composition. The composition of the carboxylated diene rubber elastomer (e.g., XNBR) contained in the cured film may be the same as that added to the above dip-forming composition.

[0103] Furthermore, the elastomer in the dip-molding composition is crosslinked by a crosslinking agent consisting essentially of a non-sulfur-based crosslinking agent to form a non-sulfur-crosslinked elastomer. Specifically, the carboxyl groups of the carboxylated diene rubber elastomer are crosslinked to form a non-sulfur-crosslinked elastomer. When polycarbodiimide is used as the crosslinking agent, the non-sulfur-crosslinked elastomer has a polycarbodiimide crosslinked structure. When a zinc compound is used as the crosslinking agent, the non-sulfur-crosslinked elastomer has a zinc crosslinked structure. When an aluminum compound is used as the crosslinking agent, the non-sulfur-crosslinked elastomer has an aluminum crosslinked structure.

[0104] The thickness of the gloves can be adjusted depending on the purpose, for example, within the range of 50 to 100 μm, and they can be used as accelerator-free disposable gloves for medical, food, and clean room use.

[0105] [Glove manufacturing method] Next, a method for manufacturing a glove according to this embodiment will be described. The glove manufacturing method includes a step of dip-molding a glove with a dip-molding composition. According to the glove manufacturing method according to this embodiment, the above-mentioned glove can be manufactured.

[0106] The dip molding process may include a coagulation liquid application step S1, a stirring step S2, a dipping step S3, a gelling step S4, a leaching step S5, a beading step S6, a pre-curing step S7, a curing step S8, and an online chlorination step S9. When producing gloves for clean rooms, the process may further include an offline chlorination step S10 after the gloves are removed from the former.

[0107] (Solution Liquid Application Step S1) In the solidification liquid application step S1, the mold or former (glove mold) is typically immersed in the solidification liquid. The mold or former to which the solidification liquid has been applied may be dried at 50°C to 70°C to dry the entire or a portion of its surface. The time for applying the solidification liquid to the surface of the mold or former is determined appropriately and may be approximately 10 to 20 seconds. The solidification liquid is an aqueous solution containing, for example, a coagulant such as calcium nitrate or calcium chloride, or a flocculating agent such as an inorganic salt effective in precipitating the elastomer, preferably 5 to 40 wt%, more preferably 8 to 35 wt%. The solidification liquid also preferably contains, as a release agent, approximately 0.5 to 2 wt%, for example, approximately 1 wt%, of potassium stearate, calcium stearate, mineral oil, or ester-based oil. The solidification liquid serves to coagulate the elastomer in the dipping step S3 described below, and calcium ions contained in the solidification liquid form calcium crosslinks in the cured film.

[0108] (Stirring step S2) Stirring step S2 is a step of stirring the dip-forming composition. Stirring step S2 is also called maturing following the maturing step in sulfur vulcanization, but in the case of non-sulfur crosslinkable gloves, it is a step of stirring the dip-forming composition to disperse and mix as uniformly as possible and defoaming. In actual mass production, it is carried out for about 1 to 2 days. In the dipping tank of this stirring step S2 and dipping step S3, the usable time (pot life) of the crosslinking agent is about 3 to 5 days in practice.

[0109] (Dipping Step S3) The dipping step S3 is a step of applying a dip-forming composition to the mold or former to which the coagulating liquid has been applied. In the dipping step S3, the mold or former after drying in the coagulating liquid application step S1 may be immersed in the dip-forming composition for, for example, 10 to 30 seconds under the temperature condition of the dipping liquid of 25 to 40°C. In the dipping step S3, calcium ions contained in the coagulating liquid may cause the elastomer in the dip-forming composition to aggregate on the surface of the mold or former to form a film.

[0110] (Gelling Step S4) In the gelling step S4, the film pulled out from the dip-forming composition is gelled to a certain extent to prevent the elastomer from leaching in the leaching step S5. The film at this stage is called a cured film precursor. For sulfur-vulcanized XNBR gloves, gelling is typically performed by heating and drying at 100°C to 120°C for 30 seconds to 4 minutes. However, for non-sulfur crosslinked gloves, optimal conditions are set for each crosslinking agent. For example, for polycarbodiimide crosslinked gloves, room temperature is preferable when the pH adjuster is a volatile base; even if a humectant is added, raising the temperature to the above range will deactivate the crosslinking agent. When the pH adjuster is an alkali metal hydroxide, heating to the above range is possible, but in either case, gelation will occur without drying the cured film precursor.

[0111] (Leaching step S5) In the leaching step S5, the cured film precursor attached to the glove mold is washed with water after the gelling step S4 to remove excess water-soluble substances. When the pH adjuster is a volatile base in the case of non-sulfur crosslinked gloves, particularly polycarbodiimide crosslinked gloves, the temperature and time of leaching are adjusted in this step to reduce the amount of calcium, potassium, and other substances that hinder crosslinking of polycarbodiimide in the curing step S8 to a certain level or less.

[0112] (Beading Step S6) The beading step S6 is a step of rolling up the cuff of the glove after the leaching step S5 is completed.

[0113] (Pre-curing step S7) The pre-curing step S7 is a step that is performed after the beading step S6 and before the curing step S8, in which the mold or former is dried in an oven at 60 to 90°C, more preferably 65 to 80°C, for example, for 30 seconds to 10 minutes. The presence of the pre-curing step S7 makes it possible to prevent partial expansion of the glove that may occur due to a sudden decrease in moisture in the curing step S8. This step and the next step may be collectively referred to as the curing step.

[0114] (Curing step S8) In the curing step S8, the cured film precursor is heated and dried, and the elastomer is crosslinked with a crosslinking agent to obtain a glove formed of a cured film. Generally, the cured film precursor is heated and dried at a temperature of 100°C to 140°C for 15 to 30 minutes.

[0115] (Online Chlorination Step S9) In the online chlorination step S9, the cured film on the hand mold produced in the curing step S8 is chlorinated as is, neutralized, washed, and then dried. This step is carried out as follows: - The surface of the cured film is washed with water to remove chemicals and the like, and then dried. The washing conditions are typically 30 to 80°C and 60 to 80 seconds. - The cured film is immersed in a treatment bath containing an aqueous solution with a chlorine concentration of 600 ppm to 1200 ppm for 5 to 10 seconds to remove stickiness (tackiness) from the surface of the cured film. At this time, the surface thickness of the cured film is slightly reduced. - After chlorination, the cured film is reduced and neutralized using a reducing agent such as sodium thiosulfate or an alkaline agent such as KOH or sodium carbonate. Note that chlorine remains in the rubber gloves even after the above treatment. - The cured film is washed with water and dried.

[0116] After the online chlorination step S9, the cured film is removed from the hand mold while being turned inside out to obtain a glove. At this time, the chlorinated side becomes the inside of the glove when worn, and the inside of the glove can be made non-sticky, and the part of the glove that comes into contact with the hand can be made smooth, thereby obtaining a glove in which the hand can easily slip inside the glove.

[0117] Normal gloves are manufactured through the online processes S2 to S9.

[0118] (Offline chlorination step S10) The offline chlorination step S10 is an offline step for converting normal gloves into clean room gloves. In the clean room, the glove surface is smoothed and impurity metals are removed in order to reduce dust generation from the gloves and prevent metal elution or transfer from the glove surface to the product. The offline chlorination step S10 is carried out according to the following procedure.

[0119] - The process of removing the gloves from the former by turning them inside out and chlorinating the outside of the gloves. The gloves are placed in a chlorination treatment device, and chlorine water is added to immerse the gloves. The chlorination treatment device is equipped with a horizontal cylindrical basket, and the gloves can be placed in the basket and rotated to perform treatment while stirring. Examples of chlorination conditions are as follows: The gloves are pre-washed and immersed in chlorine water with a chlorine concentration of 200 to 400 ppm for 5 to 25 minutes, and then neutralized. The gloves are further rinsed several times with water, dried, and cooled. - The process of washing the chlorinated gloves with pure water. Examples of pure water washing conditions are as follows: The gloves are washed twice for 10 to 20 minutes in ion-exchanged water with a resistivity of 18 MΩ cm or higher. The washing procedure involves washing, draining, centrifugal dehydration, and drying. As a result, impurity metals contained on the glove surface become chlorides, increasing their solubility, and are removed by washing with pure water. The chlorine concentration is appropriately set depending on the purpose of the clean room. Even after the above treatment, chlorine remains in the rubber gloves.

[0120] In the above-described manufacturing method, the glove mold is immersed in the dip-molding composition only once. However, it is also possible to manufacture gloves by immersing the mold multiple times (two or three times). This method is effective in preventing pinholes, which are a concern when attempting to thin the glove to about 50 μm. It is also an effective means for manufacturing thick gloves. When immersing multiple times, the dipping step S3 and the gelling step S4 may be repeated.

[0121] Hereinafter, the present embodiment will be described in more detail with reference to examples and comparative examples, but the present embodiment is not limited to these examples.

[0122] Test pieces for Examples 1 to 4 and Comparative Examples 1 to 5 were prepared as follows.

[0123] (Preparation of Dip-Forming Composition) 300 g of latex containing XNBR (BST8503S from Bangkok Synthetics Co., Ltd.: solids content 45.1%) was placed in a 1 L beaker (manufactured by AS ONE Corporation, barrel diameter 105 mm x height 150 mm). 100 g of water was added to dilute the latex, and stirring was initiated. The pH of this liquid was preliminarily adjusted to 9.5 using a 5 wt % aqueous potassium hydroxide solution. Thereafter, a polyepoxy crosslinking agent (trade name "Denacol EX-321" manufactured by Nagase ChemteX Corporation: solid content (epoxy compound content) 50 wt%, epoxy equivalent 141 (g / eq.), average number of epoxy groups 2.7, MIBK / water distribution ratio 87%), zinc oxide as a metal crosslinking agent (trade name "CZnO-50" manufactured by Farben Technique (M): solid content (zinc oxide content) 50 wt%), titanium oxide as a white pigment (trade name "PW-601" manufactured by Farben Technique (M): solid content (titanium oxide content) 71.4 wt%), and an antioxidant were added as shown in Table 1, and water was added to adjust the solid content concentration to 25%, followed by stirring and mixing overnight to produce a dip-molding composition. The dip-molding composition was continued to stir in a beaker until use. Table 1 shows the blend amounts converted into solid content.

[0124] The following antioxidant was used. Antioxidant (Phe1) Dispersion of Phe1 in an aqueous solvent Solid content (Phe1 content): 50.3% by weight Phe1: Wingstay (registered trademark) L (butylated reaction product of p-cresol with dicyclopentadiene and isobutylene: CAS number 68610-51-5) (compound having a phenol structure) (see chemical formula (1) below)

[0125]

[0126] Antioxidant (Phe1 + Pho) Dispersion in which Phe1 and Pho are dispersed in an aqueous solvent Solid content (total content of Phe1 and Pho): 48.4 wt% Phe1: See above Pho: Tris(2,4-di-t-butylphenyl)phosphite: CAS number 31570-04-4 Trade name "Irgafos168" manufactured by BASF Japan Ltd. (see chemical formula (2) below) The content of Pho relative to the total of Phe1 and Pho is 75 wt%.

[0127]

[0128] Antioxidant (Phe1 + Sul) 1 Dispersion in which Phe1 and Sul are dispersed in an aqueous solvent Solid content (total content of Phe1 and Sul): 52.8 wt% Phe1: See above Sul: Ditridecyl-3,3'-thiodipropionate: CAS number 10595-72-9 (compound having a sulfur atom) Trade name "ADK STAB AO-503" manufactured by ADEKA Corporation (see chemical formula (3) below) The content of Sul relative to the total of Phe1 and Sul is 75 wt%.

[0129]

[0130] Antioxidant (Phe / Sul) Dispersion of Phe / Sul dispersed in an aqueous solvent Solid content: (Phe / Sul content) 53.2 wt% Phe / Sul: 2-methyl-4,6-bis[(octylthio)methyl]phenol: CAS number 110553-27-0 (compound having both a phenol structure and a sulfur atom in the same molecule) Product name "Irganox 1520L" manufactured by BASF Japan Ltd. (see chemical formula (4) below)

[0131]

[0132] (Preparation of coagulation liquid) 19.6 g of release agent was diluted approximately two-fold using a portion of 30 g of water that had been weighed out in advance. Then, the diluted release agent solution was slowly added to a solution in which 0.56 g of surfactant was dissolved in 42.0 g of water. The surfactant used was "Teric 320" manufactured by Huntsman Corporation. The release agent used was "S-9" manufactured by CRESTAGE INDUSTRY (solid content concentration 25.46 wt%). The remaining S-9 in the container was washed away with the remaining water while the entire amount was added, and the mixture was stirred for 3 to 4 hours to prepare an S-9 dispersion.

[0133] Next, a calcium nitrate aqueous solution was prepared by dissolving 143.9 g of calcium nitrate tetrahydrate in 153.0 g of water in a 1 L beaker (manufactured by AS ONE Corporation, barrel diameter 105 mm x height 150 mm), and the previously prepared S-9 dispersion was added to the calcium nitrate aqueous solution while stirring. This solution was adjusted to a pH of 8.5 to 9.5 with 5% aqueous ammonia, and water was added so that the final solids concentration was 20% calcium nitrate anhydrate and 1.2% S-9, yielding 500 g of coagulated solution. The obtained coagulated solution was continuously stirred in the 1 L beaker until use.

[0134] (Production of cured film) The solidifying solution obtained as described above was heated to approximately 50°C while stirring, filtered through a 200-mesh nylon filter, and then placed in an immersion container. A ceramic plate (200 x 80 x 3 mm, hereinafter referred to as "ceramic plate") that had been washed and then heated to 70°C was immersed in the solidifying solution (solidifying solution application step). Specifically, after the tip of the ceramic plate contacted the surface of the solidifying solution, the ceramic plate was immersed for 6 seconds up to a position 18 cm from the tip, held immersed for 6 seconds, and then removed for 6 seconds. The solidifying solution adhering to the ceramic plate surface was quickly shaken off, and the ceramic plate surface was dried. After drying, the ceramic plate was again heated to 70°C in preparation for immersion in the dip-forming composition.

[0135] The dip-forming composition was filtered through a 200-mesh nylon filter while still at room temperature, and then placed in an immersion container. A 70°C ceramic plate with the coagulation liquid attached thereto was immersed in the dip-forming composition. Specifically, the ceramic plate was immersed for 6 seconds, held for 6 seconds, and then removed for 6 seconds. The ceramic plate was held in the air until the dip-forming composition stopped dripping, and droplets of the dip-forming composition adhering to the tip were gently shaken off.

[0136] The ceramic plate immersed in the dip-forming composition was dried at 23°C ± 2°C for 30 seconds (gelling step), and then washed with warm water at 50°C for 5 minutes (leaching step). It was then dried at 70°C for 5 minutes (pre-curing step), and thermally cured at 130°C for 30 minutes (curing step). The resulting cured film (average thickness: 0.08 mm) was cleanly peeled off from the ceramic plate and stored in an environment of 23°C ± 2°C and 50% ± 10% humidity until subjected to physical property testing.

[0137] [Evaluation] (Color Difference Measurement) The test pieces of Examples 1 to 4 and Comparative Examples 1 to 5 were placed in an oven set at 100°C and removed after 1 day, 4 days, 7 days, and 11 days. Then, the color difference (ΔE) was measured for the surface of each test piece using a color difference meter (product name "CR-400" manufactured by Konica Minolta) in accordance with JIS-Z 8730:2009. The color difference was calculated based on the color difference of the test piece on day 0, which had not been subjected to aging treatment.

[0138]

[0139] As shown in Table 1 and Figure 2, the test pieces of Examples 1 to 4 show smaller color differences before and after aging than the test pieces of Comparative Examples 1 to 5. These results show that the test pieces using an antioxidant containing at least one compound having a phenolic structure and a sulfur atom show less discoloration due to aging than test pieces using a compound having a phenolic structure alone or a phosphite compound in combination. Furthermore, the test pieces of Examples 3 and 4 show less discoloration due to aging than the test pieces of Examples 1 and 2, respectively. These results show that an antioxidant containing a compound having both a phenolic structure and a sulfur atom in the same molecule is superior to an antioxidant containing two types of compounds: a compound having a phenolic structure and a compound having a sulfur atom.

[0140] Next, similarly to the above examples, test pieces for Examples 5 to 10 and Comparative Example 6 were prepared with the formulations shown in Table 2. However, instead of BST8503S, the latex used was NL105 (manufactured by LG Chemical Co., Ltd.; solids content (elastomer content) 45% by weight). Furthermore, instead of the polyepoxy crosslinking agent (EX-321; solids content 50%), a polycarbodiimide crosslinking agent (manufactured by Nisshinbo Chemical Inc.; product name "V-02-L2"; solids content (polycarbodiimide content) 40.0%; number of carbodiimide functional groups per molecule: 9.4) was used. Furthermore, the antioxidants used were antioxidant (Phe2), the above antioxidant (Phe1+Sul)1, antioxidant (Phe1+Sul)2, and the above antioxidant (Phe / Sul). Table 2 shows the blending amounts converted into solids.

[0141] Antioxidant (Phe2) Dispersion of Phe2 dispersed in an aqueous solvent Solid content (Phe2 content): 50% by weight Phe2: Wingstay (registered trademark) L (butylated reaction product of p-cresol with dicyclopentadiene and isobutylene: CAS No. 68610-51-5) (compound having a phenol structure)

[0142] Antioxidant (Phe1 + Sul)2 Dispersion in which Phe1 and Sul are dispersed in an aqueous solvent Solid content (total content of Phe1 and Sul): 52.8% by weight Phe1: See above Sul: See above The content of Sul relative to the total of Phe1 and Sul is 50% by weight.

[0143] [Evaluation] (Color Difference Measurement) The color difference was measured in the same manner as above.

[0144] (Elongation at break) For the test specimens of Examples 5 to 10 and Comparative Example 6, JIS K6251 No. 5 dumbbell test specimens were cut out, and the elongation at break was measured using a TENSILON universal tensile testing machine RTC-1310A manufactured by A&D Co., Ltd. at a test speed of 500 mm / min, a chuck distance of 75 mm, and a gauge length of 25 mm. The elongation at break was calculated based on the following formula: Elongation at break (%) = 100 × (gauge length at break in tensile test - gauge length before tensile test) / gauge length before tensile test

[0145]

[0146] As shown in Table 2 and Figures 3 and 4, the test pieces of Examples 5 to 10 showed smaller color differences before and after aging and superior elongation at break after aging compared to the test piece of Comparative Example 6. These results indicate that test pieces using an antioxidant containing at least one compound having a phenolic structure and a sulfur atom exhibit less discoloration and deterioration in physical properties due to aging than test pieces using a compound having a phenolic structure alone. Furthermore, the test pieces of Examples 9 and 10 exhibited less discoloration due to aging than the test pieces of Examples 5 and 6 and Examples 7 and 8, respectively, and superior elongation at break after aging. These results indicate that an antioxidant containing a compound having both a phenolic structure and a sulfur atom in the same molecule is superior to test pieces using an antioxidant containing two compounds, a compound having a phenolic structure and a compound having a sulfur atom. Furthermore, the test pieces of Examples 5 and 6 exhibited less discoloration due to aging than the test pieces of Examples 7 and 8, respectively. These results indicate that the content of the compound having a sulfur atom is preferably greater than the content of the compound having a phenolic structure.

[0147] Next, test pieces of Example 11 and Comparative Example 7 were prepared as follows and subjected to chlorine treatment.

[0148] (Preparation of Dip-Forming Composition) 300 g of latex containing XNBR (NL151 manufactured by LG Chemicals: solid content (elastomer content) 45 wt%) was placed in a 1 L beaker (manufactured by AS ONE Corporation, barrel diameter 105 mm x height 150 mm). 100 g of water was added to dilute the latex, and stirring was initiated. The pH of this liquid was preliminarily adjusted to 9.9 using a 5 wt% aqueous potassium hydroxide solution. Thereafter, a polyepoxy crosslinking agent (Denacol EX-321: solid content (epoxy compound content) 50% by weight), an aluminum crosslinking agent (polyhedral aluminum lactate compound: solid content (aluminum compound content) 3.6% by weight), titanium oxide as a white pigment (trade name "PW-601" manufactured by Farben Technique (M): solid content (titanium oxide content) 71.4% by weight), an antioxidant (Phe3), and the above-mentioned antioxidant (Phe1+Sul)1 were added as shown in Table 3, and water was added to adjust the solid content concentration to 30%. The mixture was stirred overnight to produce a dip-molding composition. The dip-molding composition was kept stirring in a beaker until use. Table 3 shows the blend amounts converted into solid content.

[0149] Antioxidant (Phe3): Trade name "CVOX-50" manufactured by Farben Technique (M). Dispersion of Phe3 dispersed in an aqueous solvent. Solid content (Phe3 content): 52.88% by weight. Phe3: Butylated reaction product of p-cresol with dicyclopentadiene and isobutylene: CAS No. 68610-51-5 (compound having a phenol structure).

[0150]

[0151] (Preparation of coagulation liquid) 19.6 g of release agent was diluted approximately two-fold using a portion of 30 g of water that had been weighed out in advance. Then, the diluted release agent solution was slowly added to a solution in which 0.56 g of surfactant was dissolved in 42.0 g of water. The surfactant used was "Teric 320" manufactured by Huntsman Corporation. The release agent used was "S-9" manufactured by CRESTAGE INDUSTRY (solid content concentration 25.46%). The remaining S-9 in the container was washed away with the remaining water while the entire amount was added, and the mixture was stirred for 3 to 4 hours to prepare an S-9 dispersion.

[0152] Next, a calcium nitrate aqueous solution was prepared by dissolving 143.9 g of calcium nitrate tetrahydrate in 153.0 g of water in a 1 L beaker (manufactured by AS ONE Corporation, barrel diameter 105 mm x height 150 mm), and the previously prepared S-9 dispersion was added to the calcium nitrate aqueous solution while stirring. This solution was adjusted to a pH of 8.5 to 9.5 with 5% aqueous ammonia, and water was added so that the final solids concentration was 30% calcium nitrate anhydrate and 1.2% S-9, yielding 500 g of coagulation solution. The obtained coagulation solution was continuously stirred in the 1 L beaker until use.

[0153] (Production of cured film) The solidifying solution obtained as described above was heated to approximately 50°C while stirring, filtered through a 200-mesh nylon filter, and then placed in an immersion container. A ceramic plate (200 x 80 x 3 mm, hereinafter referred to as "ceramic plate") that had been washed and then heated to 60°C was immersed in the solidifying solution (solidifying solution application step). Specifically, after the tip of the ceramic plate contacted the surface of the solidifying solution, the ceramic plate was immersed for 10 seconds up to a position 18 cm from the tip, held immersed for 5 seconds, and then removed for 5 seconds. The solidifying solution adhering to the ceramic plate surface was quickly shaken off, and the ceramic plate surface was dried. After drying, the ceramic plate was again heated to 60°C in preparation for immersion in the dip-forming composition.

[0154] The dip-forming composition was filtered through a 200-mesh nylon filter while still at room temperature, and then placed in an immersion container. A ceramic plate at 60°C with the coagulation liquid attached thereto was immersed in the dip-forming composition. Specifically, the ceramic plate was immersed for 10 seconds, held for 5 seconds, and then removed for 5 seconds. The ceramic plate was held in the air until the dip-forming composition stopped dripping, and droplets of the dip-forming composition adhering to the tip were gently shaken off.

[0155] The ceramic plate immersed in the dip-forming composition was dried at 50°C for 2 minutes (gelling step), washed with warm water at 50°C for 2 minutes (leaching step), dried at 70°C for 5 minutes (pre-curing step), and thermally cured at 130°C for 30 minutes (curing step). After the curing step, the ceramic plate was washed with warm water at 50°C for 2 minutes (post-leaching step).

[0156] (Chlorination) After the post-leaching process, the gloves were immersed for 20 seconds in chlorine water adjusted to 800 ppm as online chlorination. Subsequently, they were neutralized with an aqueous solution prepared from sodium carbonate, sodium thiosulfate, and hypochlorous acid, washed three times with water, and dried in an oven at 70°C for 15 minutes. The gloves were then removed from the hand mold and stored at a temperature of approximately 20 to 35°C for one week. Subsequently, offline chlorination was performed by immersing the gloves in chlorine water adjusted to the concentrations shown in Table 4 for a predetermined time. After removing the gloves from the chlorine water, they were neutralized with an aqueous solution prepared from sodium carbonate, sodium thiosulfate, and hypochlorous acid, as in the online chlorination, washed three times with water, and dried in an oven at 70°C for 15 minutes.

[0157] [Evaluation] The thickness of the chlorine-treated gloves was measured according to the standard of ASTM-6319-00. The tensile strength at break (TSB) of the chlorine-treated gloves was also measured according to the standard of ASTM D412. The results are shown in Table 4.

[0158]

[0159] As shown in Table 4 and Fig. 5, the tensile strength of the glove of Example 11 was not significantly affected even when chlorine treatment was performed. On the other hand, it was found that the tensile strength at break of the glove of Comparative Example 7 tends to decrease due to chlorine treatment. From these results, it can be seen that the resistance to chlorine treatment is also improved by using an antioxidant containing at least one compound having a phenol structure and a sulfur atom.

[0160] Chlorine treatment of elastomers generates radicals, which may cause deterioration of physical properties. On the other hand, since the physical properties of the glove of Example 11 were not deteriorated even after chlorine treatment, it is presumed that the radicals generated by chlorine treatment are decomposed. It is considered that such gloves can suppress at least one of deterioration of mechanical properties and yellowing over time. That is, compared with sulfur crosslinked gloves, non-sulfur crosslinked gloves are more rapidly deteriorated by heat or chlorine treatment, and as a result, it is considered that deterioration of tensile strength, elongation, softness and yellowing over time of gloves can be suppressed during storage until use.

[0161] The entire contents of Japanese Patent Application No. 2022-076972 (filing date: May 9, 2022) and Japanese Patent Application No. 2023-003683 (filing date: January 13, 2023) are incorporated herein by reference.

[0162] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment.

[0163] According to the present disclosure, it is possible to provide a glove that can suppress the deterioration of mechanical properties such as tensile strength, elongation, and softness over time and yellowing due to aging of accelerator-free gloves associated with heat or chlorine treatment, a dip-forming composition used for producing the glove, and a method for producing the dip-forming composition and the glove.

Claims

1. A non-sulfur-crosslinked dip-molding composition comprising: a carboxylated diene rubber elastomer; a crosslinking agent containing at least one of an organic crosslinking agent and a divalent or higher metal crosslinking agent; an antioxidant containing at least one compound having a phenol structure and a sulfur atom; and water, wherein the content of the at least one compound is 0.05 to 4 parts by weight per 100 parts by weight of the elastomer.

2. The dip-molding composition according to claim 1, wherein the carboxylated diene rubber elastomer is an elastomer containing structural units derived from (meth)acrylonitrile, structural units derived from an unsaturated carboxylic acid, and structural units derived from butadiene in the polymer main chain.

3. The dip-forming composition according to claim 1 or 2, wherein the at least one compound includes at least one compound having the phenol structure and at least one selected from the group consisting of a thioether structure, a polysulfide structure, and a thiol structure.

4. The dip-forming composition according to any one of claims 1 to 3, wherein the at least one compound includes at least one compound having the phenol structure and a thioether structure or a polysulfide structure.

5. The dip-forming composition according to any one of claims 1 to 4, wherein the at least one compound includes a compound having both the phenol structure and the sulfur atom in the same molecule.

6. The dip-forming composition according to any one of claims 1 to 5, wherein the at least one compound comprises two or more compounds of the compound having a phenol structure and the compound having a sulfur atom.

7. The dip-forming composition according to any one of claims 1 to 6, wherein the organic crosslinking agent includes at least one of a polycarbodiimide and an epoxy compound.

8. A dip-forming composition according to any one of claims 1 to 7, wherein the divalent or higher metal crosslinking agent includes at least one of a zinc compound and an aluminum compound.

9. A method for producing a non-sulfur crosslinkable dip-molding composition, comprising: a step of mixing a carboxylated diene rubber elastomer; a crosslinking agent containing at least one of an organic crosslinking agent and a divalent or higher metal crosslinking agent; and an antioxidant containing at least one compound having a phenol structure and a sulfur atom, wherein the content of the at least one compound is 0.05 to 4 parts by weight per 100 parts by weight of the elastomer, and the at least one compound is added to the elastomer in the form of a dispersion dispersed in an aqueous solvent.

10. The method for producing a dip-molding composition according to claim 9, wherein the carboxylated diene rubber elastomer is an elastomer containing structural units derived from (meth)acrylonitrile, structural units derived from an unsaturated carboxylic acid, and structural units derived from butadiene in the polymer main chain.

11. A glove comprising: a non-sulfur crosslinked elastomer which is a carboxylated diene rubber elastomer; a crosslinking agent containing at least one of an organic crosslinking agent and a divalent or higher metal crosslinking agent; and an antioxidant containing at least one compound having a phenol structure and a sulfur atom dispersed in the non-sulfur crosslinked elastomer, wherein the content of the at least one compound is 0.05 to 4 parts by weight per 100 parts by weight of the non-sulfur crosslinked elastomer.

12. The glove according to claim 11, wherein the carboxylated diene rubber elastomer is a non-sulfur crosslinked elastomer containing structural units derived from (meth)acrylonitrile, structural units derived from unsaturated carboxylic acid, and structural units derived from butadiene in a polymer main chain.

13. A method for producing gloves, comprising the step of dip-molding a glove with the dip-molding composition according to claim 1 or 2.