Method for producing glove, dip-molding composition, and glove

Abstract

Provided is a method for producing a glove using a dip-molding composition that contains: an elastomer including 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; an epoxy crosslinking agent; water; and a catalyst, the pH of the dip-molding composition being 9.0 or higher, and the catalyst being used for reacting the elastomer and the epoxy crosslinking agent.

Description

Glove manufacturing method, dip-molding composition and glove

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

[0002] Nitrile gloves made by dip molding have been widely used in various industrial and medical fields. The manufacturing process involves crosslinking zinc oxide with sulfur and sulfur-based vulcanization accelerators, such as thiazoles, thiurams, and carbamates. However, because sulfur crosslinkers and sulfur-based vulcanization accelerators can cause type IV allergies, accelerator-free gloves have been proposed. Representative accelerator-free gloves include those that use self-crosslinking latexes containing organic crosslinking compounds instead of sulfur crosslinking, those that use organic crosslinkers such as polycarbodiimides and epoxy crosslinkers (Patent Documents 1 and 2), and those that use stabilized aluminum crosslinkers (Patent Document 3). These accelerator-free gloves utilize improved crosslinkers and optimized manufacturing conditions to meet dip molding requirements. For example, Patent Documents 1 and 2 address the issue of ensuring the pot life (usable time) of epoxy crosslinked gloves to make them suitable for dip molding. In this way, accelerator-free gloves can be made with various characteristic physical properties.

[0003] International Publication No. WO 2019 / 102985 International Publication No. WO 2019 / 194056 International Publication No. WO 2022 / 124833

[0004] Epoxy crosslinked gloves have the characteristics of softness, good elongation, high stress retention, and good fatigue resistance even when used alone. In addition, gloves with various properties can be produced by using crosslinking agents other than epoxy crosslinking agents or characteristic latexes in the manufacture of epoxy crosslinked gloves. For this reason, the present inventors aim to popularize these gloves. However, when the present inventors studied epoxy crosslinked gloves, they recognized that epoxy crosslinked gloves have a problem of high energy cost due to their high crosslinking temperature. For example, when the crosslinking temperature is high, CO ２This can lead to the problem of high emissions of hydroxybenzoates. Furthermore, in recent years, from the viewpoint of Sustainable Development Goals (SDGs), there has been an increasing demand for product development with low environmental impact. Therefore, the present inventors have investigated low temperature crosslinking with an epoxy crosslinking agent. Regarding this, low temperature crosslinking of an epoxy crosslinking agent was attempted in Patent Document 1, but at that time, gloves could not be stably obtained.

[0005] The present disclosure provides a method for producing gloves with low environmental impact, which allows gloves to be stably obtained even with low-temperature crosslinking. The present disclosure also provides a dip-molding composition with which gloves can be stably obtained with low environmental impact. Furthermore, the present disclosure provides gloves produced by the above-mentioned production method.

[0006] At least one aspect of the present disclosure is as follows: [1] A dip-molding composition comprising: an elastomer having a structural unit derived from (meth)acrylonitrile, a structural unit derived from an unsaturated carboxylic acid, and a structural unit derived from butadiene in a polymer main chain; an epoxy crosslinking agent; water; and a catalyst, wherein the pH is 9.0 or higher, and the catalyst is a catalyst for a reaction between the elastomer and the epoxy crosslinking agent. [2] A method for manufacturing a glove, comprising: (1) a step of attaching a coagulant containing calcium ions to a glove mold; (2) a dispersing step of stirring a dip-forming composition; (3) a dipping step of immersing the glove mold to which the coagulant of (1) has been attached in the dip-forming composition to aggregate and attach the dip-forming composition to the glove mold; (4) a gelling step of forming a cured film precursor on the glove mold to which the dip-forming composition has been attached; (5) a leaching step of washing the cured film precursor formed on the glove mold; (6) a beading step of wrapping the cuff of a glove; and (7) a curing step of heating and drying the cured film precursor that has been subjected to the beading step at a temperature of 40 to 80°C for 1 to 20 minutes to obtain a cured film, wherein the steps (3) to (7) are performed in the above order, and the dip-forming composition is A method for manufacturing a glove, comprising: an elastomer comprising a structural unit derived from (meth)acrylonitrile, a structural unit derived from an unsaturated carboxylic acid, and a structural unit derived from butadiene in a polymer main chain; an epoxy crosslinking agent; water; and a catalyst, wherein the pH of the dip-forming composition is 9.0 or higher, and the catalyst is a catalyst for a reaction between the elastomer and the epoxy crosslinking agent. [3] A method for manufacturing a glove as described in [2], wherein the steps (3) and (4) are repeated twice in this order. [4] A method for manufacturing a glove as described in [2] or [3], wherein the catalyst is one or more compounds selected from the group consisting of primary amines, secondary amines, tertiary amines, quaternary ammonium compounds, and nitrogen-containing heterocyclic compounds. [5] A method for manufacturing a glove as described in [4], wherein the catalyst is one or more compounds selected from the group consisting of tertiary amines, quaternary ammonium compounds, and nitrogen-containing heterocyclic compounds.[6] The method for manufacturing a glove according to [4] or [5], wherein the number of carbon atoms of the compound is 6 to 40. [7] The method for manufacturing a glove according to any one of [4] to [6], wherein the compound is one or more compounds selected from the group consisting of hexadecylamine, di-n-octylamine, N,N-dimethylcyclohexylamine, 1,8-diazabicyclo[5.4.0]-7-undecene, 1,4-diazabicyclo[2.2.2]octane, benzalkonium halide, benzyltriethylammonium halide, benzyltriethylammonium hydroxide, long-chain alkylpyridinium halide, and long-chain alkylpyridinium hydroxide. [8] The method for manufacturing a glove according to [2] to [7], wherein the total content of the catalysts in the dip-forming composition is 0.01 to 0.20 parts by mass based on 100 parts by mass of the elastomer. [9] A method for manufacturing a glove according to any one of [2] to [8], wherein a total content of said catalysts in said dip-forming composition is 0.1 to 30 parts by mass with respect to 100 parts by mass of said epoxy crosslinking agent.

[10] A method for manufacturing a glove according to any one of [2] to [9], wherein said epoxy crosslinking agent contains an epoxy compound having three or more epoxy groups in one molecule.

[11] A method for manufacturing a glove according to any one of [2] to

[10] , wherein said elastomer contains 15 to 40% by mass of structural units derived from (meth)acrylonitrile, 1 to 10% by mass of structural units derived from unsaturated carboxylic acid, and 50 to 75% by mass of structural units derived from butadiene.

[12] A glove manufactured by the manufacturing method according to any one of [2] to

[11] .

[0007] According to the present disclosure, there is provided a method for producing gloves with low environmental impact, which enables gloves to be stably obtained. Also, according to the present disclosure, there is provided a dip-molding composition with low environmental impact, which enables gloves to be stably obtained. Furthermore, according to the present disclosure, there is provided a glove produced by the above production method.

[0008] 1 is an explanatory diagram illustrating a reaction between an elastomer and an epoxy crosslinking agent. FIG. 2 is a cross-sectional view schematically illustrating an example of a fatigue durability testing device.

[0009] Preferred embodiments of the present disclosure will be described below, but the present disclosure is not limited to these embodiments and may be modified or changed in various ways. The expressions "XX or more and YY or less" and "XX to YY" that represent a numerical range mean a numerical range including the lower and upper limits, which are the endpoints, unless otherwise specified. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined in any way.

[0010] In the present disclosure, "fatigue durability" refers to the resistance of a glove to deterioration and breakage due to sweat of a user (worker). A specific evaluation method will be described later.

[0011] The configuration of the present disclosure will be specifically described below.

[0012] 1. Dip-forming Composition The dip-forming composition of the present disclosure comprises an elastomer having 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, an epoxy crosslinking agent, a catalyst for the reaction of the elastomer and the epoxy crosslinking agent, and water. The dip-forming composition may further comprise one or more crosslinkers selected from the group consisting of zinc oxide and aluminum crosslinking agents. This dip-forming composition, as a dipping liquid for gloves, can satisfy the physical properties required for gloves and the like produced by dip-forming even at low temperature crosslinking due to the action of the catalyst.

[0013] <Elastomer> Elastomer contains structural units derived from (meth)acrylonitrile, structural units derived from unsaturated carboxylic acid, and structural units derived from butadiene in polymer main chain. This elastomer is also referred to as carboxylated (meth)acrylonitrile butadiene elastomer or simply "XNBR". Also, gloves obtained by using XNBR as elastomer are also simply called "XNBR gloves".

[0014] The ratio of each structural unit in the elastomer is not particularly limited. The structural units derived from (meth)acrylonitrile, i.e., (meth)acrylonitrile residues, in the elastomer are preferably 15 to 40 mass%, more preferably 20 to 40 mass%. The structural units derived from unsaturated carboxylic acid, i.e., unsaturated carboxylic acid residues in the elastomer are preferably 1 to 10 mass%. The structural units derived from butadiene, i.e., butadiene residues in the elastomer are preferably 50 to 75 mass%. The ratio of these structural units can be conveniently determined from the mass ratio of the raw materials used to produce the elastomer.

[0015] The structural units derived from (meth)acrylonitrile are the main factor imparting strength to gloves. If the amount is too small, the strength tends to be insufficient, whereas if the amount is too large, the gloves may become too hard although the chemical resistance increases. From this viewpoint, the ratio of the structural units derived from (meth)acrylonitrile in the elastomer is more preferably 25 to 40 mass%. The amount of the structural units derived from (meth)acrylonitrile can be determined by converting the amount of nitrogen atoms determined by elemental analysis into the amount of nitrile groups.

[0016] The butadiene derived structural unit is an element that gives flexibility to gloves, and if the content is less than 50 mass %, the gloves tend to lose flexibility. The ratio of butadiene derived structural unit in the elastomer is more preferably 55 to 70 mass %, particularly preferably about 60 mass %. The butadiene derived structural unit is preferably a 1,3-butadiene derived structural unit.

[0017] The amount of structural units derived from unsaturated carboxylic acids is preferably 1 to 10% by mass, more preferably 2 to 6% by mass, and even more preferably 2 to 4% by mass. The structural units derived from unsaturated carboxylic acids react with the epoxy groups of the epoxy crosslinking agent to form a crosslinked structure. Furthermore, when the dip-molding composition contains a metal crosslinking agent, they form an ionic bond with the metal crosslinking agent. The residue that does not react with the epoxy crosslinking agent or metal crosslinking agent bonds with calcium derived from the coagulant. If the amount of structural units derived from unsaturated carboxylic acids is large, molded articles obtained using the dip-molding composition tend to be hard. The amount of structural units derived from unsaturated carboxylic acids can be determined by quantifying the carboxyl groups and carbonyl groups derived from the carboxyl groups using infrared spectroscopy (IR) or the like.

[0018] The unsaturated carboxylic acid forming the structural unit derived from the unsaturated carboxylic acid is not particularly limited and may be a monocarboxylic acid or a polycarboxylic acid. More specifically, acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, etc. are mentioned. Among them, acrylic acid and / or methacrylic acid (hereinafter referred to as "(meth)acrylic acid") is preferably used, and more preferably methacrylic acid is used.

[0019] The polymer main chain may contain structural units derived from other polymerizable monomers. The structural units derived from other polymerizable monomers are preferably contained in the elastomer in an amount of 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. There is no particular lower limit, and for example, the structural units derived from other polymerizable monomers may be contained in the elastomer in an amount of 1 to 20% by mass, 1 to 15% by mass, or 1 to 10% by mass.

[0020] It is preferable that the polymer main chain consists essentially of structural units derived from (meth)acrylonitrile, structural units derived from unsaturated carboxylic acid, and structural units derived from butadiene. "Consisting essentially of only" means that the polymer main chain is allowed to contain trace amounts of other structural units. That is, it means that the polymer main chain is allowed to contain trace amounts of structural units other than the above-mentioned structural units (for example, the amount of each of the other structural units in the elastomer is 0.5 mass% or less).

[0021] Preferred polymerizable monomers include aromatic vinyl monomers such as styrene, α-methylstyrene, and dimethylstyrene; ethylenically unsaturated carboxylic acid amides such as (meth)acrylamide and N,N-dimethylacrylamide; ethylenically unsaturated carboxylic acid alkyl ester monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and vinyl acetate. These may be used alone or in combination.

[0022] Elastomers can be produced by emulsion polymerization using unsaturated carboxylic acids such as (meth)acrylonitrile and (meth)acrylic acid, butadienes such as 1,3-butadiene, and optionally other polymerizable monomers, along with commonly used emulsifiers, polymerization initiators, molecular weight modifiers, etc., according to standard procedures. Emulsion polymerization can be broadly divided into cold rubber (e.g., polymerization temperatures of 5-25°C) and hot rubber (e.g., polymerization temperatures of 25-50°C). Cold rubber produces linear elastomers, while hot rubber produces branched elastomers. Various manufacturers develop unique elastomers by adjusting the amounts and timing of addition of the polymerization initiators, molecular weight modifiers, and other agents, as well as the polymerization conversion rate. During emulsion polymerization, water is preferably added in an amount that results in a solids content of 30-60% by mass, more preferably 35-55% by mass. The emulsion polymerization liquid after elastomer synthesis can be used directly as the elastomer component of a dip-molding composition.

[0023] Examples of the emulsifier include anionic surfactants such as linear alkylbenzene sulfonates and aliphatic sulfonates; and nonionic surfactants such as polyethylene glycol alkyl ethers and polyethylene glycol alkyl esters, with anionic surfactants being preferred.

[0024] 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.

[0025] Examples of the molecular weight modifier include mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan, and halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, and methylene bromide, with mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan being preferred.

[0026] Even if the type and amount of polymerizable monomers used in the dip-molding composition are the same, the physical properties (intrinsic properties of the elastomer) can vary significantly depending on the emulsion polymerization conditions and the amount of added chemicals, significantly affecting the physical properties of the resulting molded product, such as a glove. The inventors have broadly classified elastomers into four categories: those with low MEK insolubles and low Mooney viscosity, those with low MEK insolubles and high Mooney viscosity, those with high MEK insolubles and low Mooney viscosity, and those with high MEK insolubles and high Mooney viscosity. Mooney viscosity indicates molecular weight. Conventional elastomers have progressed from low MEK insolubles and low Mooney viscosity to those with high MEK insolubles. Furthermore, elastomers with low MEK insolubles are linear, while those with high MEK insolubles are highly entangled and branched latexes. Any of the above elastomers can be used in low-temperature crosslinking using the elastomer and epoxy crosslinker reaction catalyst of the present disclosure. That is, the elastomer may be linear or branched. However, if one wishes to take advantage of the characteristics of the epoxy crosslinking agent, such as increased stress retention due to intraparticle crosslinking, and good softness and elongation, it is believed that an elastomer with a high MEK insoluble content and a low Mooney viscosity is preferable. Furthermore, while the elastomer is not believed to have any fundamental effect on the present disclosure, a certain curing time is required during curing, as moisture is evaporated at low temperatures and then water seeps out from between the elastomer particles. For this reason, it is believed that an elastomer with good water-repelling properties is preferable.

[0027] The dip-forming composition may contain a combination of multiple elastomers. The content of the elastomer in the dip-forming composition is not particularly limited, but is preferably 10 to 35% by mass, and more preferably 12 to 30% by mass, based on the total amount of the dip-forming composition.

[0028] <Epoxy Crosslinking Agent> The dip-molding composition of the present disclosure contains an epoxy crosslinking agent as an essential crosslinking agent. The dip-molding composition of the present disclosure further contains a catalyst for the reaction of the epoxy crosslinking agent, which allows crosslinking of the elastomer to proceed even at low temperatures.

[0029] 1. Epoxy Crosslinking Agents The epoxy crosslinking agent is not particularly limited, and known agents can be used. For example, an epoxy crosslinking agent containing an epoxy compound having two or more epoxy groups per molecule (hereinafter also referred to as a divalent or higher epoxy compound) can be used. The epoxy compound is preferably an epoxy compound having three or more epoxy groups per molecule (hereinafter also referred to as a trivalent or higher epoxy compound). The number of epoxy groups present in one molecule of the epoxy compound is not particularly limited, but is preferably 2 to 7, 3 to 7, 2 to 5, or 3 to 5, for example.

[0030] Preferred examples of divalent or higher epoxy compounds include epoxy compounds having two or more glycidyl ether groups per molecule. Examples of divalent or higher epoxy compounds include reaction products of epihalohydrin with alcohols having two or more hydroxyl groups per molecule. The number of hydroxyl groups present in one alcohol molecule is preferably 2 to 7, 3 to 7, 2 to 5, or 3 to 5. As the epihalohydrin, one or more selected from the group consisting of epichlorohydrin, epibromohydrin, and epiioditehydrin can be used. Among these, epichlorohydrin is particularly preferred. Furthermore, the divalent or higher epoxy compound may have a parent skeleton containing an alicyclic, aliphatic, or aromatic hydrocarbon.

[0031] An example of a trivalent epoxy compound is shown in the following formula (I), and an example of a divalent epoxy compound is shown in the following formula (II). In the following formulas (I) and (II), R is not particularly limited as long as it is a parent skeleton having an alicyclic, aliphatic, or aromatic hydrocarbon, and may contain any functional group. R: a main skeleton having an alicyclic, aliphatic, or aromatic hydrocarbon R: a main skeleton having an alicyclic, aliphatic, or aromatic hydrocarbon

[0032] An example of a trivalent or higher epoxy compound is polyglycidyl ether. Specific examples of polyglycidyl ethers include polyglycerol polyglycidyl ether, glycerol polyglycidyl ether, sorbitol polyglycidyl ether, and trimethylolpropane polyglycidyl ether. Specific examples of polyglycerol polyglycidyl ethers include diglycerol tetraglycidyl ether and diglycerol triglycidyl ether. Specific examples of glycerol polyglycidyl ethers include glycerol triglycidyl ether. Specific examples of sorbitol polyglycidyl ethers include sorbitol triglycidyl ether, sorbitol tetraglycidyl ether, sorbitol pentaglycidyl ether, and sorbitol hexaglycidyl ether. Specific examples of trimethylolpropane polyglycidyl ethers include trimethylolpropane triglycidyl ether.

[0033] Further, an example of using an epoxy crosslinking agent containing one or more selected from the group consisting of glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, diglycerol triglycidyl ether, sorbitol triglycidyl ether, and sorbitol tetraglycidyl ether can be mentioned, and an example of using an epoxy crosslinking agent containing one or more selected from the group consisting of glycerol triglycidyl ether and trimethylolpropane triglycidyl ether can be mentioned.

[0034] Examples of epoxy crosslinking agents containing divalent or higher epoxy compounds include polyalkylene glycol diglycidyl ether, diglycidyl amine, diglycidyl ester, epoxidized polybutadiene, epoxidized soybean oil, etc. Examples of divalent epoxy compounds include compounds represented by the following formula (III): In formula (III), R Ｗ and R Ｘ are independently hydrogen or an alkyl group having 1 to 10 carbon atoms, and in this alkyl group, a hydrogen atom bonded to a carbon atom may be substituted;１ and A ２ is 1,4-phenylene or 1,4-cyclohexylene, R Ｙ and R Ｚ are independently alkylene having 1 to 6 carbon atoms, m and n are independently 0 to 6, and ring A １ and A ２ is 1,4-phenylene, 1≦m+n≦6, and ring A １ and A ２ When m is 1,4-cyclohexylene, 0≦m+n≦6.

[0035] The epoxy crosslinking agent actually used is a mixture of different valences, but examples of suitable crosslinking agents for dip molding include the following products manufactured by Nagase ChemteX Corporation.

[0036] (Average Number of Epoxy Groups) For example, even in a trivalent or higher epoxy crosslinking agent, divalent epoxy compounds may be included as a side reaction. Therefore, the epoxy crosslinking agent is evaluated using the average number of epoxy groups. The average number of epoxy groups is determined by identifying each epoxy compound contained in the epoxy crosslinking agent by GPC, multiplying the number of epoxy groups in one molecule of each epoxy compound by the number of moles of the epoxy compound, and then dividing the total number by the total number of moles of all epoxy compounds contained in the epoxy crosslinking agent. From the viewpoint of dip molding, the average number of epoxy groups in the epoxy crosslinking agent is preferably greater than 2.0, and more preferably 2.25 or more. However, even if the average number of epoxy groups is 2.0 or less, a divalent epoxy crosslinking agent having a hydrophobic skeleton can also be used.

[0037] (Molecular Weight) From the viewpoint of dispersibility in water, the molecular weight of the epoxy compound contained in the epoxy crosslinking agent is preferably 150 to 1,500, more preferably 175 to 1,400, and even more preferably 200 to 1,300.

[0038] The total content of epoxy crosslinking agents in the dip-molding composition depends on the number of epoxy groups in one molecule of the epoxy compound and its purity, but can be 0.2 parts by mass or more per 100 parts by mass of elastomer. On the other hand, an excessive content may actually degrade the properties of the elastomer, so it is considered preferable that the upper limit of the total content of epoxy crosslinking agents is 5 parts by mass per 100 parts by mass of elastomer. The total content of epoxy crosslinking agents in the dip-molding composition may be 0.2 to 5 parts by mass, or 0.4 to 3 parts by mass, per 100 parts by mass of elastomer.

[0039] 2. Crosslinking reaction of epoxy crosslinking agents in dip molding and crosslinking promotion by catalysts

[0040] (1) The present disclosure will now be described as to how gloves can be stably obtained by crosslinking an epoxy crosslinking agent at low temperature in dip molding.

[0041] Crosslinking of elastomers with epoxy crosslinking agents occurs through the following reaction: Note that, for the sake of simplicity, monovalent epoxy compounds are used in the following formula (X), and R' is a group that constitutes the elastomer.

[0042] The epoxy compound forms crosslinks through the carboxyl group in XNBR. In the manufacturing method of gloves, the crosslinking reaction is carried out by the ring-opening reaction of the epoxy group. That is, the ring-opening reaction of the epoxy group is necessary for the crosslinking reaction. However, in the dip molding composition, the ring-opening reaction of the epoxy group generally does not proceed easily at low temperature unless there is an accelerating effect such as a catalyst. As a result, it is not possible to stably obtain gloves by crosslinking the epoxy crosslinking agent at low temperature.

[0043] (2) On the other hand, in the manufacturing method of a glove of the present disclosure, a dip-molding composition containing an elastomer, an epoxy crosslinking agent and a catalyst for the reaction of the epoxy crosslinking agent is used. FIG. 1 is an explanatory diagram for explaining the reaction between the elastomer and the epoxy crosslinking agent. The catalyst for the reaction abstracts hydrogen from the carboxy group in XNBR and converts the carboxy group into a carboxylate (COO －) . This carboxylate is likely to react nucleophilically with epoxy group even at low temperature. Therefore, by the nucleophilic reaction of carboxylate with epoxy group, the elastomer and the epoxy crosslinking agent react sufficiently even at low temperature to form crosslinks. That is, by the dip molding composition containing the elastomer, the epoxy crosslinking agent and the reaction catalyst, gloves can be obtained stably with low environmental load.

[0044] 3. Deactivation of epoxy crosslinking agent in dip molding Since the dip molding composition is highly basic, the epoxy crosslinking agent in the dip molding composition may be deactivated by hydrolysis. When producing gloves, for example, by dip molding, if the maturation time is long or if the epoxy crosslinking agent is used while adding the dipping solution to the dipping bath, it is preferable to prevent the epoxy crosslinking agent from being deactivated for at least about 3 days. Therefore, it is preferable to select an epoxy crosslinking agent with a long pot life (usable time).

[0045] In the present disclosure, the dip-forming composition, or so-called dipping liquid, is an alkaline aqueous dispersion of XNBR particles. In the dipping liquid, the XNBR particles have a hydrophobic environment within them, while the spaces between them are hydrophilic. The environment of this dipping liquid is nearly identical to that of a mixture of MIBK and water. A high MIBK / water distribution ratio means that a larger proportion of the epoxy crosslinker enters the hydrophobic regions (lipophilic regions) within the XNBR particles and is stable. Meanwhile, the epoxy crosslinker in the hydrophilic regions of the dipping liquid undergoes rapid hydrolysis under alkaline conditions, e.g., at a pH of approximately 10, and is deactivated within a relatively short period of time.

[0046] In the water-based paints and solvent-based paints in which epoxy crosslinking agents have traditionally been used, the crosslinking reaction occurs in a relatively short time due to evaporation, so the above-mentioned problems do not occur.

[0047] The MIBK / water partition coefficient is the proportion of MIBK distributed in a mixture of methyl isobutyl ketone (MIBK), which has a similar hydrophobicity to a carboxylic acid-modified nitrile copolymer (hereinafter referred to as XNBR), and an epoxy crosslinking agent when mixed with water. Specifically, it is measured as follows. First, approximately 5.0 g of water, approximately 5.0 g of MIBK, and approximately 0.5 g of epoxy crosslinking agent are precisely weighed and added to a test tube. The weight of MIBK is defined as M (g), and the weight of epoxy crosslinking agent as E (g). This mixture is thoroughly stirred and mixed at 23°C ± 2°C for 3 minutes, and then centrifuged at 1.0 x 103 G for 10 minutes to separate the water layer and the MIBK layer. The weight of the MIBK layer is then measured and designated as ML (g). The MIBK / water partition coefficient (%) is then calculated using the following formula: MIBK / water partition ratio (%) = (ML (g) - M (g)) / E (g) × 100

[0048] Based on the experimental results of the present inventors, it is believed that epoxy crosslinking agents suitable for dip molding are preferably trivalent or higher epoxy crosslinking agents with an MIBK / water distribution ratio of 27% or higher. In addition, it is believed that divalent epoxy crosslinking agents are preferably suitable for dip molding because they have adequate stability in the dipping solution.

[0049] 4. Characteristics of epoxy cross-linked dip-molded products

[0050] Epoxy crosslinking is characterized by its high fatigue resistance. However, in applications requiring strength, its contribution to tensile strength is small, so it has been necessary to provide strength through ionic crosslinking with zinc oxide or other materials.

[0051] In this disclosure, we focus on the fact that many multifunctional epoxy crosslinkers with high MIBK / water partition ratios are contained within the hydrophobic region of latex particles. This means that the epoxy crosslinker can react with carboxylic acids (hereinafter also referred to as buried carboxylic acids) within the latex particles to increase the crosslink density within the particles and potentially improve the stress retention of molded products such as gloves. To achieve this, it is preferable that the elastomer has a structure that is moderately entangled and difficult to unravel. Furthermore, the dip-molding composition is premised on the presence of buried carboxylic acids within the latex particles that bond with the epoxy crosslinker.

[0052] The carboxyl groups of the latex particles are mostly present at the particle interface, and as the pH of the dip-molding composition increases, they are oriented outward and take the form of carboxylate groups. When the dip-molding composition contains a metal crosslinking agent, the carboxylate groups react with the metal crosslinking agent during curing to form interparticle crosslinks.

[0053] Furthermore, intra-particle crosslinking occurs when the carboxylic acid in the latex particle reacts with the epoxy crosslinker. If the elastomer is a branched elastomer, the structure of the latex particle makes it easier to secure buried carboxylic acid that crosslinks intra-particlely with the epoxy crosslinker. Therefore, the elastomer may be a branched elastomer. In this way, epoxy crosslinking of the latex can provide stress retention.

[0054] Furthermore, it was found that when XNBR was crosslinked using an epoxy crosslinking agent, the degree of loss in softness and elongation was less than when other metal crosslinking agents were used.

[0055] <Catalyst for Reaction of Elastomer and Epoxy Crosslinking Agent> The dip-molding composition contains a catalyst. The catalyst is a catalyst for the reaction of the elastomer and the epoxy crosslinking agent. As described above, the dip-molding composition is a so-called O / W emulsion in which an oil phase containing an elastomer is dispersed in an aqueous solution. Because the pH of the dip-molding composition is 9.0 or higher, carboxylates are oriented on the outside of the elastomer particles. On the other hand, carboxy groups remain inside the elastomer particles due to the oil phase. According to the inventors' studies, the reactivity of carboxy groups with epoxy groups is lower than the reactivity of carboxylates with epoxy groups. However, by including the catalyst in the dip-molding composition, a crosslinked structure formed by the elastomer and the epoxy crosslinking agent can be formed inside the elastomer particles. This is believed to be due to the following mechanism. By including the catalyst in the dip-molding composition, the catalyst can reach the interior of the elastomer particles in the dip-molding composition. It is believed that the catalyst ionizes the carboxyl groups inside the elastomer particles to carboxylates, which facilitates the reaction between the elastomer and the epoxy crosslinking agent.

[0056] The catalyst is not particularly limited as long as it can react the elastomer and the epoxy crosslinking agent, but it is preferably a catalyst that abstracts hydrogen from the carboxyl group in the elastomer to ionize it into a carboxylate. The catalyst is a deprotonation catalyst. As described above, carboxylate is more reactive with epoxy groups than carboxyl groups, and therefore, the catalyst easily reacts the elastomer and the epoxy crosslinking agent.

[0057] Examples of the catalyst include base catalysts. The base catalyst functions as a deprotonation catalyst. The base catalyst is not particularly limited, but is preferably an organic base catalyst. The organic base catalyst is more likely to be incorporated into the oil phase (elastomer particles) of the dip-forming composition. As a result, the elastomer and the epoxy crosslinking agent are more likely to react favorably. For example, from the viewpoint of abstracting hydrogen from the carboxyl group, the catalyst is preferably one or more compounds selected from the group consisting of primary amines, secondary amines, tertiary amines, quaternary ammonium compounds, and nitrogen-containing heterocyclic compounds, and more preferably one or more compounds selected from the group consisting of tertiary amines, quaternary ammonium compounds, and nitrogen-containing heterocyclic compounds. Of these, the catalyst is preferably a nitrogen-containing heterocyclic compound. Examples of nitrogen-containing heterocyclic compounds include nitrogen-containing aromatic heterocyclic compounds. In the case of nitrogen-containing aromatic heterocyclic compounds, the nitrogen atoms in the aromatic rings share the π electrons of the aromatic rings, thereby enhancing the basicity of the nitrogen atoms and improving the nucleophilicity of the nitrogen atoms themselves and the counter anions. As a result, various physical properties of the gloves are more likely to be improved.

[0058] The carbon number of one or more compounds selected from the group consisting of primary amines, secondary amines, tertiary amines, quaternary ammonium compounds, and nitrogen-containing heterocyclic compounds is preferably 6 to 40, and more preferably 12 to 40. Here, the carbon number of the compound refers to the total number of carbon atoms contained in the compound. When the carbon number is within the above range, the catalyst is more likely to be contained in the oil phase of the dip-forming composition. As a result, the elastomer and the epoxy crosslinker are more likely to react favorably.

[0059] The primary amine is a compound represented by the following formula (1-1), the secondary amine is a compound represented by the following formula (1-2), and the tertiary amine is a compound represented by the following formula (1-3): NH ２ R ａ (1-1) NHR ａ R ｂ (1-2) NR ａ R ｂ R ｃ (1-3) In formulas (1-1) to (1-3), R ａ , R ｂ and R ｃ each independently represents an arbitrary organic group.

[0060] The organic group is not particularly limited, but examples thereof include hydrocarbon groups such as aliphatic hydrocarbon groups and aromatic hydrocarbon groups, and among these, alkyl groups are preferred. The number of carbon atoms in the hydrocarbon group is not particularly limited, but may be 1 to 19. Among these, R ａ , R ｂ and R ｃ Preferably, one or two groups selected from the group consisting of have 6 or more carbon atoms, more preferably 12 or more. The more carbon atoms in the alkyl group, the higher the hydrophobicity becomes, and the easier it is to exist inside the elastomer particle, which is preferable. Furthermore, it is preferable that the remaining groups have 1 to 5 carbon atoms. Specifically, for example, R ａ has 6 or more carbon atoms, and R ｂ and R ｃ may each independently have 1 to 5 carbon atoms. ａ has 12 or more carbon atoms, and R ｂ and R ｃ may each independently have 1 to 5 carbon atoms. ａ and R ｂ each independently has 6 or more carbon atoms, and R ｃ The carbon number of the dip-molding composition may be 1 to 5. When the carbon number is within the above range, the catalyst is more easily contained in the oil phase of the dip-molding composition, and as a result, the elastomer and the epoxy crosslinking agent are more easily reacted with each other.

[0061] Also, R ａ , R ｂ and Rｃ The range of carbon atoms of one or two groups selected from the group consisting of is not particularly limited, but is preferably 6 to 19, and more preferably 12 to 19, for example.

[0062] Also, R ａ , R ｂ and R ｃ The organic groups may form a ring together. For example, R ａ and R ｂ may form a ring, and R ａ and R ｃ may form a ring, and R ｂ and R ｃ may form a ring.

[0063] Examples of primary amines include hexadecylamine, octadecylamine, 4-hexylaniline, 4-hexadecylaniline, 9,9-bis(4-aminophenyl)fluorene, and 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene. Of these, hexadecylamine is preferred.

[0064] Examples of secondary amines include di-n-octylamine, di-n-decylamine, diphenylamine, and N,N-diphenylbenzidine, with di-n-octylamine being preferred.

[0065] Examples of tertiary amines include N,N-dimethylcyclohexylamine, N,N-dimethylhexadecylamine, 1,8-bis(dimethylamino)naphthalene, 1,8-diazabicyclo[5.4.0]-7-undecene, and 1,4-diazabicyclo[2.2.2]octane. Of these, one or more selected from the group consisting of 1,8-diazabicyclo[5.4.0]-7-undecene and 1,4-diazabicyclo[2.2.2]octane are preferred.

[0066] Furthermore, the organic group may further have an amino group. For example, the catalyst may have multiple primary amines in one molecule, or may have a primary amine and a secondary amine. That is, the catalyst may contain two or more amines selected from the group consisting of primary amines, secondary amines, and tertiary amines in one molecule. Examples include histidine and N-methyl-1,3-propanediamine. There is no particular upper limit, and the catalyst may contain two to four amines selected from the group consisting of primary amines, secondary amines, and tertiary amines in one molecule.

[0067] The quaternary ammonium compound is a compound consisting of a quaternary ammonium cation and an anion, and is a compound represented by the following formula (2): [NR ｄ R ｅ R ｆ R ｇ ] ＋ ・X － In formula (2), R ｄ , R ｅ , R ｆ , and R ｇ represents any organic group, and X represents any anion.

[0068] The organic group is not particularly limited, but examples thereof include hydrocarbon groups such as aliphatic hydrocarbon groups and aromatic hydrocarbon groups, and among these, benzyl groups and alkyl groups are preferred. The number of carbon atoms in the hydrocarbon group is not particularly limited, but may be 1 to 19. Among these, R ｄ , R ｅ , R ｆ , and R ｇ Preferably, one or two groups selected from the group consisting of have 6 or more carbon atoms, more preferably 12 or more carbon atoms. The remaining groups preferably have 1 to 5 carbon atoms. Specifically, for example, R ｄ has 6 or more carbon atoms, and R ｅ , R ｆ , and R ｇ may each independently have 1 to 5 carbon atoms. ｄ has 12 or more carbon atoms, and R ｅ , R ｆ , and R ｇ may each independently have 1 to 5 carbon atoms.ｄ and R ｅ each independently has 6 or more carbon atoms, and R ｆ and R ｇ may each independently have 1 to 5 carbon atoms. When the number of carbon atoms is within the above range, the catalyst is more easily contained in the oil phase of the dip-molding composition. As a result, the elastomer and the epoxy crosslinking agent are more easily reacted with each other.

[0069] Also, R ｄ , R ｅ , R ｆ , and R ｇ The range of carbon atoms of one or two groups selected from the group consisting of is not particularly limited, but is preferably 6 to 19, and more preferably 12 to 19, for example.

[0070] Also, R ｄ , R ｅ , R ｆ , and R ｇ The organic groups may form a ring together. For example, R ｄ and R ｅ may form a ring, and R ｄ and R ｆ may form a ring, and R ｄ and R ｇ may form a ring, and R ｅ and R ｆ may form a ring, and R ｅ and R ｇ may form a ring, and R ｆ and R ｇ may form a ring.

[0071] The anion of the quaternary ammonium compound is not particularly limited, and examples thereof include halide ions such as chloride ions, bromide ions, and iodide ions; hydroxide ions; alkoxy ions; etc. That is, the anion is preferably one or more selected from the group consisting of halide ions and hydroxide ions.

[0072] Examples of the quaternary ammonium compound include benzalkonium halides such as benzalkonium chloride, benzyltriethylammonium chloride, benzyltriethylammonium bromide, and benzyltriethylammonium iodide, and benzyltriethylammonium hydroxide. Among these, one or more compounds selected from the group consisting of benzyltriethylammonium bromide, benzyltriethylammonium iodide, and benzyltriethylammonium hydroxide are preferred.

[0073] Nitrogen-containing heterocyclic compounds are compounds having a heterocyclic structure containing nitrogen in the molecule. Nitrogen-containing aromatic heterocyclic compounds are compounds having an aromatic heterocyclic structure containing nitrogen in the molecule. Examples of aromatic heterocyclic structures include pyridine structures, imidazoline structures, pyrazine structures, pyrimidine structures, azepine structures, quinoline structures, and indole structures. Among these, pyridine structures are preferred. Compounds having a pyridine structure are preferred because they have a planar molecular structure and can easily penetrate into the interior of elastomer particles. Nitrogen-containing aromatic heterocyclic compounds may have any substituent other than the aromatic heterocyclic structure. Specific examples of compounds having a pyridine structure include N-alkylpyridinium hydroxide and N-alkylpyridinium halide. The number of carbon atoms in the alkyl group in these compounds is not particularly limited, but is preferably 6 or more, and more preferably 12 or more. The range of carbon atoms in the alkyl group is not particularly limited, but is preferably 6 to 19, and more preferably 12 to 19. A larger number of carbon atoms in the alkyl group is particularly preferred because it increases hydrophobicity and makes it more likely to exist inside the elastomer particles. That is, the alkyl group is preferably a long-chain alkyl group. For example, the alkyl pyridinium halide may be a long-chain alkyl pyridinium halide, and the N-alkyl pyridinium hydroxide may be a long-chain alkyl pyridinium hydroxide.

[0074] More specific examples of compounds having a pyridine structure include hexadecylpyridinium halides such as hexadecylpyridinium chloride; and hexadecylpyridinium hydroxide.

[0075] The total content of the catalyst in the dip-forming composition is preferably 0.01 to 0.20 parts by mass, more preferably 0.025 to 0.1 parts by mass, based on 100 parts by mass of the elastomer. The total content of the catalyst in the dip-forming composition is preferably 0.1 to 30 parts by mass, more preferably 1 to 30 parts by mass, and even more preferably 2.5 to 20 parts by mass, based on 100 parts by mass of the epoxy crosslinking agent. Within the above ranges, the amount of catalyst remaining in the final rubber glove product is significantly reduced.

[0076] <Dispersant for Epoxy Crosslinking Agent> The dip-molding composition may contain a dispersant. The mass ratio of the polyepoxy crosslinking agent to the dispersant in the dip-molding composition (polyepoxy crosslinking agent:dispersant) is preferably 1:4 to 1:1.

[0077] 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—(CH ２ 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 ３represents 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 ２ represents an aliphatic hydrocarbon group having 1 to 5 carbon atoms, and n3 represents an integer of 0 to 3.) Examples of the ester include diethylene glycol monoethyl ether acetate and diethylene glycol monobutyl ether acetate. These may be used alone or in combination of two or more.

[0078] The dispersant may be used without being mixed with water in advance. The dispersant is preferably a monohydric lower alcohol. It is also preferable to use methanol, ethanol, or diethylene glycol as the dispersant. From the viewpoint of volatility and flammability, it is preferable to use diethylene glycol as the dispersant. Diethylene glycol is presumably 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.

[0079] <Metal Crosslinking Agent> The dip-molding composition of the present disclosure may contain a metal crosslinking agent. As a metal crosslinking agent, zinc oxide has traditionally been used as a reaction accelerator in dip molding since the days of sulfur vulcanization with NR (natural rubber) and NBR (nitrile rubber). It has also been used as a crosslinking agent for XNBR through ionic bonding with carboxyl groups. Zinc oxide has been used as an essential crosslinking agent from the viewpoints of maintaining strength and film-forming properties. However, zinc oxide has drawbacks, such as lowering the stress retention rate of molded products, reducing elongation, and impairing softness.

[0080] In contrast, aluminum crosslinkers have not been put to practical use in dip molding due to their instability and difficulty in handling. However, in recent years, aluminum crosslinkers that solve the aluminum stabilization problem have been put to practical use. There are two methods for using aluminum crosslinkers in dip molding. One method involves dispersing a hydroxy acid aluminum compound with a pH of 2 to 4 in water to prepare a dispersion, adjusting the pH of the resulting dispersion to 7 or higher, and adding it to latex with a pH of, for example, approximately 8.5, in order to prevent coagulation of the rubber component due to acid shock in the latex. Examples of aluminum hydroxy acids include aluminum glycolate, aluminum lactate, aluminum citrate, aluminum tartrate, aluminum malate, and aluminum gluconate. Among these, aluminum lactate is preferred because it has a small molecular weight, dissolves in water during the leaching process, and is less likely to remain in the glove. Furthermore, polynuclear aluminum lactate is most preferred. When purchasing an aluminum crosslinker, commercially available aluminum crosslinkers include products such as Taxeram M-160L and AS800 manufactured by Taki Chemical Co., Ltd. The other method is to add sugar or sugar alcohol and hydroxy acid or hydroxy acid salt to sodium aluminate at a pH of about 13, and then add the resulting mixture to latex. Glyoxal and sorbitol can be used as stabilizers for sodium aluminate. Furthermore, the inventors believe that zinc oxide and aluminum crosslinkers are preferably used separately, since they interfere with each other. In other words, the metal crosslinker is preferably zinc oxide or aluminum crosslinker.

[0081] Zinc oxide and aluminum crosslinkers crosslink smoothly even in the low-temperature crosslinking process of the present disclosure. It is believed that zinc oxide reacts with the carboxyl groups of the latex through ionic bonding or the aggregation of the latex due to zinc oxide particles. Furthermore, among aluminum crosslinkers, it is believed that aluminum hydroxylate undergoes two types of crosslinking reactions with the latex during the dip-molding composition and curing. The first reaction occurs in the dip-molding latex composition immediately after blending the aluminum crosslinker with the XNBR latex. Carboxylate groups on the surface of the latex particles react with hydroxy ions released from the aluminum hydroxylate, forming aluminum crosslinks bonded to the rubber molecular chains. The second reaction occurs during the curing process, when the carboxyl groups of the XNBR undergo a dehydration reaction with the oxide ions of the aluminum crosslinker, bonding the carboxyl groups of the XNBR to aluminum, forming a crosslinked structure.

[0082] The advantages of using aluminum hydroxylate are described below. First, the use of aluminum hydroxylate prevents gelation of the aluminum crosslinker in the present disclosure in the weakly alkaline range, thereby providing stability. Generally, aluminum in water is prone to gelation (polymerization) in the weakly alkaline range (pH 7.0 to 11.0), and aluminum crosslinkers present stability issues during long-term storage and the manufacturing process of dip-molded products. However, aluminum hydroxylate has a strong bond between aluminum ions and carboxyl ions (carboxylates) of the hydroxy acid, and the hydroxy acid sterically protects the aluminum, preventing gelation. Furthermore, hydroxy acid has an alcoholic hydroxyl group. This improves the affinity of aluminum hydroxylate with water, thereby improving its solubility and dispersion in water. Second, because aluminum hydroxylate efficiently reacts with the carboxyl groups contained in the carboxylic acid-modified nitrile copolymer, a small amount can be added, preventing leaching into the leaching solution during manufacturing.

[0083] In addition, aluminum hydroxylate can reduce the incorporation of calcium into the molded product, which reduces the rubber elasticity of the molded product, thereby improving the rubber elasticity of the molded product. When the dip molding latex composition contains an aluminum crosslinking agent, the latex crosslinks with aluminum from the time of immersion. Therefore, the reaction between calcium derived from the coagulant and XNBR is suppressed.

[0084] Both aluminum and zinc cross-linking can reduce the softness and elongation of molded products. However, zinc cross-linking and aluminum cross-linking have the following different characteristics:

[0085] Both zinc crosslinking and aluminum crosslinking create ionic bonds between latex particles, maintaining the strength of the molded product. However, zinc crosslinking has weaker bond strength than aluminum, and therefore easily cleaves under external force and re-crosslinks with other carboxyl groups, resulting in the loss of the three-dimensional structure of the carboxylic acid-modified nitrile copolymer and a decrease in rubber elasticity. In contrast, aluminum crosslinking creates stronger bonds between particles, dramatically increasing stress retention. Furthermore, aluminum hydroxylates have the effect of reducing calcium content, further increasing stress retention. Aluminum crosslinkers such as aluminum hydroxylates are preferred because they contain organic groups, which tend to reside inside elastomer particles, and aluminum compounds can also act as co-catalysts for the reaction between epoxy groups and carboxyl groups.

[0086] Furthermore, unlike zinc oxide, aluminum crosslinkers can improve fatigue durability because the bonding strength of the ionic bond between aluminum ions and carboxyl groups is stronger than that between zinc oxide and carboxyl groups.

[0087] Compared to zinc, aluminum has a larger valence and a shorter ionic radius, so according to Coulomb's law, the ionic bond strength that forms the cross-linked structure is thought to be stronger than that of zinc. Therefore, gloves cross-linked with aluminum have the least elution in artificial sweat compared to those cross-linked with calcium or zinc oxide. This means that aluminum cross-linked gloves are the most resistant to sweat when worn.

[0088] Epoxy crosslinking agents also react with the carboxylic acids embedded in the latex particles to increase the crosslink density within the particles, while aluminum crosslinking agents firmly bond the particles together to prevent them from slipping apart, while epoxy crosslinking also increases the stress retention rate, but its function differs from that of aluminum crosslinking in that it increases the crosslink density within the particles through intra-particle crosslinking, thereby increasing the stress retention rate.

[0089] The bonding method of these crosslinkers affects the elasticity and viscosity of molded articles produced using them to different degrees, resulting in different properties of the molded articles. Epoxy crosslinking is necessary to maintain the softness and elongation of the latex itself. Furthermore, aluminum crosslinking is preferable to maintain tensile strength and elasticity. This is because epoxy crosslinking alone may not provide sufficient tensile strength and elasticity, and aluminum crosslinking alone results in hardness and reduced elongation. The inventors believe that the simultaneous use of epoxy and aluminum crosslinkers is an optimal crosslinking agent combination. The total amount of epoxy and aluminum crosslinkers added is preferably 0.2 to 1.6 parts by mass, and more preferably 0.4 to 1.4 parts by mass.

[0090] When epoxy crosslinking agent is used alone, interparticle crosslinking is weak, and when aluminum crosslinking agent is used alone, intraparticle crosslinking is weak. When moldings are made from the above latex by combining these, in the best embodiment, gloves that meet the standards for surgical gloves and have good rubber elasticity can be made.

[0091] Furthermore, compared to metal crosslinkers such as aluminum crosslinkers, epoxy crosslinking mainly enhances intra-particle crosslinking, so it has been found that even when irradiated with gamma rays, there is little change in basic physical properties such as tensile strength, elongation, and stress retention in products that require sterilization, such as surgical gloves. This is thought to be due to the fact that the intra-particle crosslinking is enhanced by epoxy crosslinking, so there is little change in physical properties due to crosslinking formation in the butadiene part of the particle caused by gamma ray irradiation.

[0092] The zinc oxide content is preferably 0.1 to 1.5 parts by mass, more preferably 0.8 to 1.0 part by mass, per 100 parts by mass of the elastomer. If the zinc oxide content is less than 0.1 part by mass, it is difficult to obtain sufficient interparticle crosslinking, and the tensile strength of the molded product is likely to decrease.

[0093] The content of the aluminum crosslinking agent is preferably 0.1 to 0.7 parts by mass, more preferably 0.2 to 0.7 parts by mass, calculated as aluminum oxide, per 100 parts by mass of the elastomer. If the content of the aluminum crosslinking agent is less than 0.1 part by mass, sufficient interparticle crosslinking is unlikely to be achieved, and the tensile strength of the molded product is likely to decrease. If the content is more than 0.7 parts by mass, the thickening effect on the dip-molding composition may be too great. Furthermore, molded products obtained using the dip-molding composition may be hard and difficult to stretch.

[0094] <pH Adjuster> The dip-forming composition may contain a pH adjuster. The dip-forming composition must be adjusted to an alkaline state during the maturation process (dispersion process) described below. One reason for making the composition alkaline is as follows. That is, if the dip-forming composition is made alkaline, at least a portion of the carboxyl groups of the elastomer particles become carboxylates and are oriented toward the outside of the elastomer particles. As a result, when using a metal crosslinking agent such as zinc oxide or a coagulant containing calcium ions, this ensures sufficient interparticle crosslinking of the elastomer by zinc and calcium. From the above perspective, the pH of the dip-forming composition is 9.0 or higher. The preferred pH is 9.5 to 10.5. A lower pH reduces the orientation of the carboxyl groups of the elastomer toward the outside of the particles, making interparticle crosslinking more insufficient, but enhances intraparticle crosslinking. Therefore, the lower the pH, the higher the stress retention rate tends to be. The pH values ​​are measured at 25°C. The pH adjuster may be one or more selected from the group consisting of ammonium compounds, amine compounds, and alkali metal hydroxides. Among these, alkali metal hydroxides are preferred because they facilitate pH adjustment, gelling conditions, and other manufacturing conditions. Potassium hydroxide (hereinafter also referred to as KOH) is the most convenient. The amount of pH adjuster added is not particularly limited, but may be, for example, 0.1 to 4.0 parts by mass, 0.5 to 3.0 parts by mass, or 1.0 to 2.5 parts by mass per 100 parts by mass of the elastomer in the dip-forming composition. Typically, 1.8 to 2.0 parts by mass is used industrially.

[0095] <Antioxidant> In accelerator-free gloves such as epoxy crosslinked gloves of the present disclosure, it has been found that hindered phenol type antioxidants, such as Wingstay L, which have been conventionally used as antioxidants in dip molding, are vulnerable to chlorine treatment and aging. Therefore, in the present disclosure, the antioxidant may include at least one compound having a phenol structure and a sulfur atom. The total content of the at least one compound may be 0.05 to 4 parts by mass per 100 parts by mass of elastomer.

[0096] <Other Components> The dip-forming composition contains the above-mentioned components and water, and may contain other optional components. The water content in the dip-forming composition may be, for example, 78 to 92 mass %.

[0097] The dip-forming composition may further contain various other additives, such as pigments and chelating agents. Examples of the pigment include titanium dioxide. Examples of the chelating agent include sodium ethylenediaminetetraacetate.

[0098] The dip-molding composition can be prepared by mixing an elastomer, an epoxy crosslinking agent, a catalyst, water, and, if necessary, various additives such as a humectant, a dispersant, and a pH adjuster, using a conventional mixing means, for example, a mixer.

[0099] 2. Glove Manufacturing Method The glove manufacturing method of the present disclosure comprises the following steps: (1) a step of attaching a coagulant containing calcium ions to a glove mold; (2) a dispersing step of stirring a dip-forming composition; (3) a dipping step of immersing the glove mold to which the coagulant (1) has been attached in the dip-forming composition to aggregate and attach the dip-forming composition to the glove mold; (4) a gelling step of forming a cured film precursor on the glove mold to which the dip-forming composition has been attached; (5) a leaching step of cleaning the cured film precursor formed on the glove mold; (6) a beading step of forming a bead around the cuff of the glove; and (7) a curing step of heating and drying the cured film precursor that has been subjected to the beading step at 40 to 80°C for 1 to 20 minutes to obtain a cured film. The steps (3) to (7) are then performed in the above order. Furthermore, the above manufacturing method may also be a double-dipping method in which the steps (3) and (4) are repeated twice in the above order.

[0100] In this specification, the term "cured film precursor" refers to a film composed of elastomer coagulated on a glove mold by a coagulant in the dipping process, which is gelled to some extent by dispersing calcium in the film in the subsequent gelling process, and which has not yet been subjected to final curing.

[0101] Each step will be explained in detail below. (1) Step of applying a coagulant containing calcium ions to a glove mold. The step of applying a coagulant containing calcium ions to a glove mold is called the coagulant applying step. (a) The mold or former (glove mold) is applied with Ca as a coagulant and gelling agent. ２＋The mold or former is immersed in a coagulant solution containing 5 to 40% by mass, preferably 8 to 35% by mass, of ions. The time for adhering the coagulant to the surface of the mold or former is determined appropriately, typically about 10 to 20 seconds. Calcium nitrate or chloride is used as the coagulant. Other inorganic salts effective in precipitating elastomers may also be used. Of these, calcium nitrate is preferred. This coagulant is typically used as an aqueous solution containing 5 to 40% by mass. Furthermore, the solution containing the coagulant preferably contains about 0.5 to 2% by mass, e.g., about 1% by mass, of potassium stearate, calcium stearate, mineral oil, or ester oil as a release agent. (b) The mold or former with the coagulant solution attached is placed in an oven with an internal temperature of about 110°C to 140°C for 1 to 3 minutes, and dried to adhere the coagulant to the entire or partial surface of the glove mold. It should be noted that the surface temperature of the mold after drying is about 60°C, which affects subsequent reactions. (c) Calcium not only functions as a coagulant to form a film on the surface of the glove mold, but also contributes to a significant part of the cross-linking function of the final glove. The metal cross-linking agent added later can be said to reinforce the weak point of this cross-linking function of calcium.

[0102] (2) Dispersion step of stirring the dip-forming composition. The dispersion step of stirring the dip-forming composition is the maturation step. As explained in the section on (a) pH adjusters for dip-forming compositions, the maturation step involves adjusting the pH of the dip-forming composition to 9.0 or higher and dispersing it uniformly while stirring. (b) In actual glove manufacturing processes, this step is usually performed in a large-scale tank, so maturation can take about 24 hours. The dip-forming composition is poured into a dip bath and dipped, with the water being added as the water level in the dip bath drops. Therefore, it is preferable to prevent the epoxy crosslinker from being deactivated for about 4 days, and at least 2 days. In the dip bath, the pH tends to decrease with use time, so the pH may be adjusted.

[0103] (3) Dipping step This is a step in which the dip-forming composition (dipping liquid) stirred in the maturation step is poured into a dipping tank, and the mold or former to which the coagulant has been applied and dried in the coagulant application step is immersed in this dipping tank usually for 1 to 60 seconds under a temperature condition of 25 to 35° C. In this step, the calcium ions contained in the coagulant cause the elastomer contained in the dip-forming composition to aggregate on the surface of the mold or former, forming a film.

[0104] (4) Gelling Step In the gelling step, a cured film precursor is formed on the glove mold to which the dip-forming composition is attached. The gelling temperature is usually within a range of 50°C to 120°C. The gelling step time is usually 30 seconds to 5 minutes, and in another embodiment, about 1 to 3 minutes.

[0105] (5) Leaching process (a) The leaching process is a process for washing away excess chemicals and impurities, such as calcium, that may interfere with subsequent curing and that have precipitated on the surface of the cured film precursor. The former is immersed in warm water at 30 to 80°C for 1 to 5 minutes.

[0106] (6) Beading process: This is a process for reinforcing the cuff end of the glove made of the cured film precursor after the leaching process by rolling up the cuff end to form a ring of appropriate thickness. If this is done in a wet state after the leaching process, the adhesion of the rolled part will be good.

[0107] (7) Curing Step (a) The curing step is a step in which the material is heated and dried to complete crosslinking and form a cured film as a glove. In the glove manufacturing method of the present disclosure, a cured film precursor is heated and dried at 40 to 80°C for 1 to 20 minutes to obtain a cured film. The temperature in the curing step is preferably 50 to 70°C, more preferably 55 to 65°C. (b) In the present disclosure, which uses a catalyst for the reaction of an elastomer and an epoxy crosslinking agent, a curing temperature of 120°C or higher is sometimes required in the conventional production of epoxy crosslinked gloves. However, even with low-temperature crosslinking at 50°C, a molded product having the necessary physical properties for a glove can be produced. The curing step time requires a certain amount of time for moisture to ooze out from between the latex particles due to osmotic pressure after evaporation of moisture by heating. The time is 1 to 20 minutes, preferably 10 to 20 minutes. The low-temperature crosslinking using the epoxy crosslinking agent of the present disclosure is generally not dependent on the latex, but latex with good water-repelling properties is considered preferable. Other factors that affect low-temperature crosslinking include the method of making gel, the concentration relationship between coagulant and latex, and the state of the coagulated film during dipping. By using low-temperature crosslinking as described above, compared with the manufacturing method of epoxy crosslinked gloves that requires high curing temperature, CO ２ (c) When a metal crosslinking agent is used in combination, crosslinking occurs without any problems under the above curing conditions. In particular, aluminum crosslinking agents have the same problems as those in (b) above.

[0108] (8) Double-dipping: The above description of the so-called single-dipping method has been given for the manufacturing method of gloves. In contrast, the dipping process and gelling process may be performed two or more times, which is usually called double-dipping. Double-dipping is performed when manufacturing thick gloves (film thickness of about 200 to 300 μm) and also when manufacturing thin gloves, for the purpose of preventing pinholes. One thing to note about double-dipping is that the gelling process must be performed for a sufficient period of time in order to allow calcium to precipitate sufficiently to the film surface in the first gelling process, in order to aggregate XNBR in the second dipping process.

[0109] 3. Gloves The glove of the present disclosure is a glove produced by the glove manufacturing method of the present disclosure. The glove is made of a cured film formed by curing a dip-forming composition, and the composition of the elastomer (XNBR) contained in the cured film can be the same as that added to the dip-forming composition. As described above, the glove of the present disclosure is obtained using a dip-forming composition containing a catalyst, and compared to gloves obtained using a dip-forming composition not containing a catalyst, it is possible to produce gloves having epoxy crosslinking properties such as excellent fatigue resistance, softness, and elongation, and high stress retention, even at low temperature crosslinking.

[0110] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass." In the following description, "parts by mass" generally indicates the number of parts by mass relative to 100 parts by mass of elastomer.

[0111] 1. Materials used in this example

[0112] In this example, the elastomers listed in Table 1 were used. In the table, in the column of residue amount, AN represents acrylonitrile, and MAA represents methacrylic acid.

[0113] In this example, the epoxy crosslinking agents listed in Table 3 were used.

[0114] In this example, the catalysts listed in Tables 4 and 6 were used as catalysts for the reaction of the elastomer and the epoxy crosslinker.

[0115] In this example, the metal crosslinking agents shown in Table 5 were used as the metal crosslinking agents.

[0116] In this example, diethylene glycol (manufactured by Kanto Chemical Co., Ltd.) was used as a dispersant for the epoxy crosslinking agent, a product name "CVOX-50" (manufactured by Farben Technique (M) Co., Ltd.) was used as an antioxidant, and a KOH aqueous solution and ion-exchanged water were used as a pH adjuster.

[0117] 2. Production of Cured Film in this Example: The cured film was produced by the dip-molding method described below. (1) Preparation of Dip-molding Composition: 100 parts by mass of the elastomer listed in Table 6 (solids content: 45% by mass) was placed in a container. 0.5 parts by mass of an epoxy crosslinker, 0.8 parts by mass of zinc oxide, 0.2 parts by mass of an antioxidant, and 0.5 parts by mass of diethylene glycol were added to the container. After 2 hours, 0.05 parts by mass of the catalyst listed in Table 6 was added to the container. Water and an aqueous KOH solution were then added so that the total solids content of the composition was 24% by mass and the pH was 10, and the mixture was stirred and mixed for 18 hours. The resulting dip-molding composition was continuously stirred in the container until use.

[0118] (2) Production of cured film

[0119] (i) Preparation of coagulation liquid and adhesion to ceramic plate: 22.5 parts by mass of CTF-3BG2 (BIO COSMIC SDN BHD) (trade name, solids concentration 42.3%) as a release agent was diluted approximately twice with a portion of 30 parts by mass of water previously measured, and then stirred for 3 to 4 hours. Subsequently, calcium nitrate was added to a 1 L beaker (manufactured by AS ONE Corporation, body diameter 105 mm x height 150 mm) so that the anhydrous calcium nitrate was 20%, and the release agent and water were added to obtain 500 parts by mass of coagulation liquid. The resulting coagulation liquid was continuously stirred in the 1 L beaker until use. The resulting coagulation liquid was heated to approximately 50 °C while stirring, filtered through a 200 mesh nylon filter, and then placed in an immersion container. A washed ceramic plate (200 x 80 x 3 mm, hereinafter referred to as "ceramic plate") heated to 70 °C was immersed in the beaker. Specifically, after the tip of the ceramic plate contacted the surface of the solidifying liquid, the ceramic plate was immersed for 4 seconds up to 18 cm from the tip, held there for 4 seconds, and then removed for 3 seconds. The solidifying liquid adhering to the surface of the ceramic plate was quickly shaken off, and the surface of the ceramic plate was dried. After drying, the ceramic plate was again heated to 70 ° C in preparation for immersion in the dip-forming composition.

[0120] (ii) Preparation of Cured Film: The dip-forming composition was filtered through a 200-mesh nylon filter while still at room temperature, then placed in a dipping container. A ceramic plate at 70°C with the coagulation solution attached was immersed in the dipping container. Specifically, the ceramic plate was immersed for 6 seconds, held for 4 seconds, and then removed for 3 seconds. The ceramic plate was held in the air until the latex stopped dripping, and any latex droplets adhering to the tip were gently shaken off (dipping process). The latex-immersed ceramic plate was dried at 50°C for 2 minutes (gelling process) and leached in 70°C hot water for 2 minutes (leaching process). The film was then thermally cured at 60°C for 17 minutes (curing process). The resulting cured film was cleanly peeled off from the ceramic plate and stored at 23°C ± 2°C and 50% ± 10% humidity for 1 week until subjected to physical property testing.

[0121] 3. Evaluation of Physical Properties of Cured Films in This Example In this example, the physical properties of the resulting cured films were evaluated using the following evaluation items, which are typically used to evaluate glove performance. (1) Mechanical Properties (Breaking Strength, Elongation, 500% Modulus, Toughness, SR) JIS K6251 No. 5 dumbbell test specimens were cut out from the cured films after storage. Marked lines were then drawn on the dumbbell test specimens so that the distance between the marks was 25 mm. The film thickness was measured at three points between the marks, and the average film thickness of the cured film was determined. The measurement points were determined so that the three measurement points were evenly spaced. The breaking strength (TS) of the test specimens was measured using a SHIMADZU small tabletop tester (product name: EZ-LX). Ｂ ), elongation to break (E Ｂ The modulus at 500% elongation (500%M), and toughness were measured. The test speed was set to 500 mm / min, and the distance between chucks was set to 75 mm. A stress relaxation test (SR) was also conducted. Test specimens (JIS K6263 No. 2 strips) were cut out from the cured films after storage. The test specimens were then measured using a SHIMADZU small benchtop testing machine (product name: EZ-LX). The test speed was 500 mm / min, the maximum stroke was 40 mm, and the holding time was 600 seconds.

[0122] (2) Fatigue Durability: JIS K6251 No. 1 dumbbell test specimens were cut from the cured films and immersed in artificial sweat (containing 20 g of sodium chloride, 17.5 g of ammonium chloride, 17.05 g of lactic acid, and 5.01 g of acetic acid per liter, adjusted to pH 4.7 with sodium hydroxide solution). The fatigue durability was evaluated using the durability testing apparatus shown in Figure 2. Specifically, a 120 mm long dumbbell test specimen was clamped between a fixed chuck and a movable chuck at locations 15 mm from each of its two ends, and the portion of the specimen from the fixed chuck side down to 60 mm below the fixed chuck was immersed in the artificial sweat. The movable chuck was moved to a minimum position (relaxed state) at 147 mm (123%) and held there for 11 seconds. The specimen was then moved to a maximum position (elongated state) at 195 mm (163%) and then back to the minimum position (relaxed state) over 1.8 seconds, completing one cycle. The time for one cycle was 12.8 seconds, and was multiplied by the number of cycles until the test specimen broke to obtain the fatigue endurance time (minutes).

[0123] (3) Toluene Swelling Ratio A 5 cm square test piece was cut from the cured film, and the mass of the test piece before swelling with toluene was measured. The test piece was placed in a 30 mL beaker and immersed in toluene for 72 hours. After 72 hours, the sample was removed, a 5 kg weight was placed on top, and the sample was allowed to stand for 20 seconds. After standing, the mass of the test piece was measured and used as the mass of the test piece after swelling with toluene. The toluene swelling ratio was calculated using the following formula: {(Mass of test piece after swelling with toluene) / (Mass of test piece before swelling with toluene)}×100

[0124] Experiment 1 The purpose of this experiment is to confirm that the required performance of epoxy crosslinked gloves can be achieved even at low temperature crosslinking of 60°C by using a catalyst for the reaction of elastomer and epoxy crosslinking agent. This experiment was carried out using the materials, manufacturing method, and physical property evaluation already described. Furthermore, the gloves containing the catalyst were designated as examples, and the gloves without the catalyst were designated as comparative examples. The results of the experiment are shown in Table 1 below.

[0125]

[0126] Cured films according to Examples 21 and 22 were produced and their physical properties evaluated in the same manner as in Example 10, except that the type of catalyst used was changed to that shown in Table 7. The results are shown in Table 7.

[0127]

[0128] Cured films according to Examples 23 to 25 were produced and their physical properties evaluated in the same manner as in Example 10, except that the amounts of the catalysts used were changed to those shown in Table 8. The results are shown in Table 8.

[0129]

[0130] Cured films according to Examples 26 to 28 were produced and their physical properties were evaluated in the same manner as in Example 10, except that the curing time was changed to that shown in Table 9. The results are shown in Table 9.

[0131]

[0132] Cured films according to Examples 29 and 30 were produced and their physical properties evaluated in the same manner as in Example 10, except that the curing temperature was changed to that shown in Table 10. The results are shown in Table 10.

[0133]

[0134] From the results of this experiment, comparing the ones with catalyst (Examples 1 to 30) with those without catalyst (Comparative Examples 1 to 4), it can be seen that the ones with catalyst have better fatigue durability. Among the catalysts, HDPCM in particular showed the greatest improvement in fatigue durability. Also, for latex, the tendency of improved fatigue durability due to catalyst is clearly seen in BST8503S and NL129D. As a result, it can be seen that at a low curing temperature of 60°C, epoxy crosslinking is promoted by using a catalyst that promotes crosslinking of the epoxy crosslinking agent, which improves fatigue durability and other physical properties meet the performance required for gloves.

Claims

1. A dip-molding composition comprising an elastomer having 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, an epoxy crosslinking agent, water, and a catalyst, wherein the pH is 9.0 or higher, and the catalyst is a catalyst for the reaction between the elastomer and the epoxy crosslinking agent.

2. A method for manufacturing a glove, comprising: (1) a step of attaching a coagulant containing calcium ions to a glove mold; (2) a dispersing step of stirring a dip-forming composition; (3) a dipping step of immersing the glove mold to which the coagulant of (1) has been attached in the dip-forming composition to aggregate and attach the dip-forming composition to the glove mold; (4) a gelling step of forming a cured film precursor on the glove mold to which the dip-forming composition has been attached; (5) a leaching step of washing the cured film precursor formed on the glove mold; (6) a beading step of wrapping the cuff of a glove; and (7) a curing step of heating and drying the cured film precursor that has been subjected to the beading step at a temperature of 40 to 80°C for 1 to 20 minutes to obtain a cured film, wherein steps (3) to (7) are performed in the above order, and the dip-forming composition is A method for manufacturing a glove, comprising: an elastomer, the elastomer comprising a structural unit derived from (meth)acrylonitrile, a structural unit derived from unsaturated carboxylic acid, and a structural unit derived from butadiene in a polymer main chain; an epoxy crosslinking agent; water; and a catalyst, wherein the dip-molding composition has a pH of 9.0 or more, and the catalyst is a catalyst for a reaction between the elastomer and the epoxy crosslinking agent.

3. The method for manufacturing gloves according to claim 2, wherein the steps (3) and (4) are repeated twice in that order.

4. The method for manufacturing a glove as claimed in claim 2 or 3, wherein the catalyst is one or more compounds selected from the group consisting of primary amines, secondary amines, tertiary amines, quaternary ammonium compounds and nitrogen-containing heterocyclic compounds.

5. The method for producing gloves according to claim 4, wherein the catalyst is one or more compounds selected from the group consisting of tertiary amines, quaternary ammonium compounds and nitrogen-containing heterocyclic compounds.

6. The method for manufacturing gloves according to claim 4 or 5, wherein the compound has 6 to 40 carbon atoms.

7. The method for manufacturing a glove according to any one of claims 4 to 6, wherein the compound is one or more compounds selected from the group consisting of hexadecylamine, di-n-octylamine, N,N-dimethylcyclohexylamine, 1,8-diazabicyclo[5.4.0]-7-undecene, 1,4-diazabicyclo[2.2.2]octane, benzalkonium halide, benzyltriethylammonium halide, benzyltriethylammonium hydroxide, long-chain alkylpyridinium halide, and long-chain alkylpyridinium hydroxide.

8. The method for manufacturing a glove according to any one of claims 2 to 7, wherein the total content of said catalyst in said dip-forming composition is 0.01 to 0.20 parts by mass per 100 parts by mass of said elastomer.

9. The method for manufacturing a glove according to any one of claims 2 to 8, wherein the total content of said catalyst in said dip-forming composition is 0.1 to 30 parts by mass per 100 parts by mass of said epoxy crosslinking agent.

10. The method for manufacturing a glove according to any one of claims 2 to 9, wherein the epoxy crosslinking agent contains an epoxy compound having three or more epoxy groups in one molecule.

11. The method for manufacturing a glove according to any one of claims 2 to 10, wherein said elastomer contains 15 to 40% by mass of structural units derived from (meth)acrylonitrile, 1 to 10% by mass of structural units derived from unsaturated carboxylic acid, and 50 to 75% by mass of structural units derived from butadiene.

12. A glove produced by the manufacturing method according to any one of claims 2 to 11.

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