Dip-forming composition and molded body thereof

Abstract

A composition for dip molding containing at least a carboxyl-group-containing nitrile rubber elastomer, an epoxy crosslinking agent that contains an epoxy compound having a parent skeleton that has three or more glycidyl ether groups per molecule and also has an alicyclic, aliphatic, or aromatic hydrocarbon, and a pH regulator, wherein: the elastomer contains 50-78 wt% (inclusive) of structural units derived from a conjugated diene monomer, 20-30 wt% (inclusive) of structural units derived from an ethylenically unsaturated nitrile monomer, and 3.5-6 wt% (inclusive) of structural units derived from an ethylenically unsaturated carboxylic acid monomer; the MEK insoluble content of the elastomer is 60-80 wt% (inclusive); and the MIBK / water distribution coefficient of the epoxy crosslinking agent is 50% or higher.

Description

[Technical Field]

[0001] The present invention relates to a dip-forming composition and a molded article thereof. [Background technology]

[0002] BACKGROUND ART Molded articles such as gloves, condoms, catheters, tubes, balloons, nipples, and sacks are known which are obtained by dip molding latex compositions of natural rubber or synthetic rubber.

[0003] Molded products made from natural rubber have the inherent high stress retention rate of rubber, are flexible, and have excellent rubber elasticity. However, natural rubber latex contains proteins that can cause Type I allergy symptoms in the human body, and many problems have been reported when using products that come into direct contact with the human body.

[0004] In contrast, molded articles obtained from synthetic rubber do not contain proteins, which has the advantage of reducing the risk of type I allergies. Known synthetic rubbers include isoprene rubber, chloroprene rubber, and carboxyl-containing acrylonitrile butadiene rubber (XNBR). Of these, isoprene rubber is structurally similar to natural rubber, and has high stress retention and flexible rubber elasticity similar to natural rubber. Structurally, chloroprene is a partially chlorinated butadiene, and like isoprene rubber, has a relatively high stress retention and flexible rubber elasticity. However, all of these have the drawback of being very expensive. Isoprene monomer, the raw material for isoprene rubber, is produced by methods such as propylene dimerization, isoamylene dehydrogenation, and solvent extraction of C5 fractions. Compared to butadiene, which can be obtained in large quantities from the fractionation of C4 fractions during petroleum production, isoprene monomer requires chemical reactions and complex manufacturing processes. Furthermore, isoprene monomer is polymerized by solution polymerization, and after isoprene rubber is produced, the solvent is separated and the resulting product is emulsified with water to produce isoprene rubber latex for dipping. Thus, a manufacturing process involving various chemical reactions is required to obtain a molded product from isoprene rubber. On the other hand, chloroprene is mainly produced industrially by subjecting monovinylacetylene, obtained by dimerization of acetylene, to an addition reaction with hydrochloric acid, and therefore cannot be produced inexpensively.

[0005] On the other hand, XNBR is a copolymer of butadiene, acrylonitrile, and unsaturated carboxylic acid. It is widely used in the manufacture of dip-molded products because it can be mass-produced inexpensively. Conventionally, molded products were produced by covalently bonding butadiene residues with sulfur and a vulcanization accelerator and ionic crosslinking between carboxyl groups (X) with zinc. However, due to the problem of type IV allergies caused by vulcanization accelerators, accelerator-free molded products that do not use sulfur or vulcanization accelerators have been proposed in recent years. For example, dip-molded products have been proposed using self-crosslinking with crosslinkable organic compounds (Patent Document 1), crosslinking with organic crosslinking agents such as polycarbodiimide compounds and epoxy compounds (Patent Documents 2 and 3), and crosslinking with metal crosslinking agents such as aluminum, which form a covalent bond (Patent Document 4).

[0006] As mentioned above, XNBR is a copolymer of butadiene, acrylonitrile, and unsaturated carboxylic acid. The double bonds in butadiene give it the characteristic of being rubber. In that sense, butadiene is the base component. Acrylonitrile and unsaturated carboxylic acid are components that change the properties of XNBR when copolymerized with butadiene, and depending on the content, various properties such as chemical resistance, tensile strength, elongation, and modulus can be achieved. In addition, in the case of XNBR, the film-forming properties, ease of production, and physical properties of the resulting latex are affected by adjusting the polymerization temperature, chain transfer agent, polymerization method, and polymerization conversion rate. Taking gloves as an example, in recent years, XNBR produced by low-temperature polymerization has become the primary material used to improve the tensile strength of thinner gloves, resulting in molded products with satisfactory tensile strength and elongation. Low-temperature polymerization transforms XNBR into a linear polymer, improving the tensile strength of the XNBR itself. Furthermore, when the pH of linear XNBR latex is adjusted to the alkaline side, the carboxylic acid in XNBR easily ionizes, becoming a carboxylate ion. This ionization easily orients the XNBR particle surface, facilitating the formation of metal ion crosslinks, improving interparticle strength. However, linear XNBR exhibits lower rubber elasticity than branched XNBR, making it increasingly inferior to natural rubber in terms of basic physical properties such as stress retention and flexibility. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2012 / 043894 [Patent Document 2] International Publication No. 2017 / 217542 [Patent Document 3] International Publication No. 2019 / 194056 [Patent Document 4] Japanese Patent Application Publication No. 2018-9272 Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, various crosslinking methods have been proposed for XNBR, but satisfactory results have not been achieved in terms of stress retention and flexibility, and improvements have been desired. Therefore, the present invention aims to provide gloves which have improved wearability, fit, tightness of the cuff and ease of delicate work using fingertips by improving stress retention and flexibility while maintaining tensile strength and fatigue durability required for gloves by using a carboxyl group-containing nitrile rubber elastomer such as XNBR. [Means for solving the problem]

[0009] As a result of intensive investigations into solving the above-mentioned problems, the present inventors have found that by using an elastomer having an appropriate crosslinked structure, in particular an elastomer having an MEK-insoluble content within a specific range, and further by carrying out crosslinking using a specific organic crosslinking agent in the process of producing a dip-molded article using a dip-molding composition containing the elastomer, it is possible to produce a molded article having a high stress retention while maintaining a low modulus (flexibility), and have thus completed the present invention.

[0010] [1] A dip-molding composition comprising at least a carboxyl group-containing nitrile rubber elastomer, an epoxy crosslinking agent containing an epoxy compound having three or more glycidyl ether groups in one molecule and having a mother skeleton containing an alicyclic, aliphatic or aromatic hydrocarbon, and a pH adjuster, The elastomer contains structural units derived from conjugated diene monomers. 50 % by weight or more and 78% by weight or less of structural units derived from ethylenically unsaturated nitrile monomers, 20% by weight or more and 30% by weight or less of structural units derived from ethylenically unsaturated carboxylic acid monomers, and The MEK insoluble content of the elastomer is 60% by weight or more and 80% by weight or less, and The dip-molding composition has an MIBK / water distribution ratio of the epoxy crosslinking agent of 50% or more, as measured by the following method. MIBK / water partition ratio measurement method: 5.0 g of water, 5.0 g of methyl isobutyl ketone (MIBK), and 0.5 g of epoxy crosslinker were weighed out in a test tube, and the mixture was stirred at 23°C ± 2°C for 3 minutes. After mixing, the resulting mixture was 1.0 x 10 3 Centrifuge at 1000 G for 10 minutes to separate the aqueous and MIBK layers. The MIBK layer is separated and weighed, and the MIBK / water distribution coefficient is calculated using the following formula. MIBK / water distribution rate (%) = (weight of MIBK layer after distribution (g) - weight of MIBK before distribution (g)) / added weight of cross-linking agent (g) × 100 The above measurement was carried out three times, and the average value was taken as the MIBK / water partition coefficient. [2] The dip-forming composition according to [1], wherein the elastomer contains structural units derived from an ethylenically unsaturated carboxylic acid monomer in an amount of 3.5% by weight or more and 5.0% by weight or less. [3] The dip-molding composition according to either [1] or [2], wherein the amount of the epoxy crosslinking agent added per 100 parts by weight of the elastomer is 0.3 parts by weight or more and 2.5 parts by weight or less. [4] The dip-forming composition according to any one of [1] to [3], wherein the pH is adjusted to 9.5 or more and 10.5 or less with the pH adjuster. [5] The dip-forming composition according to any one of [1] to [4], further comprising zinc oxide as a crosslinking agent. [6] The dip-forming composition according to [5], wherein the amount of zinc oxide added is 0.2 parts by weight or more and 0.6 parts by weight or less per 100 parts by weight of the elastomer. [7] The dip-forming composition according to any one of [1] to [6], which has an MEK swelling rate of 5 to 10 times. [8] A molded article which is a cured product of the dip-molding composition according to any one of [1] to [7]. [9] The molded article according to [8], which has a stress retention rate of 50% or more according to the following measurement method. Stress retention measurement method: A test piece is prepared in accordance with ASTM D412, a gauge line is marked with a distance of 25 mm, and the test piece is pulled under conditions of a chuck distance of 90 mm and a pulling speed of 500 mm / min. When the test piece has stretched twice, the pulling is stopped and the stress M0 is measured. The test piece is further held in place for 6 minutes, and the stress M6 is measured, and the stress retention is calculated using the following formula. Stress retention rate (%) = (M6 / M0) x 100

[10] The molded article according to [8] or [9], which is a glove.

[11] (1) a coagulant application step of applying a coagulant to a glove mold; (2) a maturation step of preparing the dip-forming composition according to any one of [1] to [7] and stirring the mixture; (3) a dipping step of immersing a glove mold in a dip-forming composition; (4) a gelling step in which the film formed on the glove mold is gelled to produce a cured film precursor; (5) a leaching step to remove impurities from the cured film precursor formed on the glove mold; (6) Beading process to make a bead at the cuff of the glove. (7) a curing step of heating and drying at a temperature required for the crosslinking reaction; The method for producing a dip-formed article includes carrying out the steps (3) to (7) in the above order. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a dip-molding composition which is used to prepare molded articles such as gloves, which not only satisfy the basic physical properties required for molded articles such as tensile strength, elongation, and fatigue durability, but also have significantly improved stress retention and modulus compared to conventional molded articles. Furthermore, by using this dip-molding composition, molded articles having the above properties can be obtained even without containing latex protein which causes type I allergy or vulcanization accelerator which causes type IV allergy. The present invention can be applied not only to gloves but also to molded articles such as condoms, catheters, tubes, balloons, nipples, and sacks. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of a fatigue durability testing device. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes in detail the embodiments of the present invention, but these descriptions are examples (typical examples) of the embodiments of the present invention, and the present invention is not limited to these contents as long as it does not deviate from the gist of the invention. In this specification, "weight" and "mass" are used interchangeably, and therefore hereinafter, "weight" will be used consistently. In this specification, unless otherwise specified, "%" means "% by weight" and "parts" means "parts by weight". Unless otherwise specified, "parts by weight" generally indicates the number of parts by weight per 100 parts by weight of elastomer. Furthermore, in this specification, when "~" is used to express a numerical value or a physical property value, the values ​​before and after the "~" are included.

[0014] Each embodiment of the present invention relates to a dip-molding composition (also simply referred to as a "dip-molding composition") for producing a dip-molded article of a soft carboxyl-containing nitrile rubber elastomer (also simply referred to as a "carboxyl-containing nitrile rubber elastomer") having high stress retention, a method for producing a molded article using the composition, and a molded article produced using the composition. For this reason, in this embodiment, a crosslinked structure is first introduced into the carboxyl-containing nitrile rubber elastomer to enhance rubber elasticity, and then crosslinked with an epoxy crosslinking agent that penetrates into latex particles made of the elastomer and can perform intra-particle crosslinking, thereby achieving a high stress retention rate for the molded article. The stress retention rate is used herein as one of the indicators for defining a dip-molded article with good stretchability. The stress retention rate indicates the ratio of the stress of a dip-molded article under tension to its initial value after a certain period of time has passed, and represents the degree to which the stress that tends to return to its original state is retained. The inventors also confirmed that by minimizing the amount of carboxylic acid, a soft molded body can be obtained despite a high stress retention rate, and that the molded body according to this embodiment is softer than the conventional molded body in terms of softness, as measured by the 100%, 300%, and 500% modulus. The modulus represents the stress at 100%, 300%, and 500% elongation, and the lower the stress, the softer the molded body. Hereinafter, the dip-molding composition for producing a dip-molded article according to each embodiment of the present invention, the method for producing a molded article using the composition, and the molded article produced using the composition will be described. In this section, the characteristics of the carboxyl group-containing nitrile rubber elastomer and the epoxy crosslinking agent will be described. In this specification, the term "carboxyl group-containing nitrile rubber elastomer" refers to a polymer obtainable by polymerizing monomers such as a conjugated diene, an ethylenically unsaturated nitrile monomer, and an ethylenically unsaturated carboxylic acid monomer (also simply referred to as an "elastomer"). A composition containing an elastomer obtainable by emulsion polymerization is also referred to as a synthetic latex composition, or simply as a latex composition, and elastomer particles dispersed in a synthetic latex composition are also referred to as latex particles, or simply as particles.

[0015] 1. Dip-molding composition The dip-molding composition according to this embodiment (also simply referred to as "dip-molding composition") contains, as essential components, a carboxyl group-containing nitrile rubber elastomer and an epoxy crosslinking agent, which will be explained below in order, and is usually a mixed solution with water, the pH of which is adjusted with a pH adjuster. In addition, the composition may contain zinc oxide, and usually contains further necessary components.

[0016] (1) Carboxyl group-containing nitrile rubber elastomer <Crosslinked structure of carboxyl group-containing nitrile rubber elastomer> The carboxyl group-containing nitrile rubber elastomer is characterized by having an MEK-insoluble content of 60% by weight or more and 80% by weight or less, which is achieved by introducing a crosslinked structure beforehand during emulsion polymerization. The crosslinked structure introduced during the polymerization process of the elastomer contained in the latex composition increases the crosslink density of the dip-molded article, contributing to the development of stress retention. By using this latex composition, it is possible to provide a dip-molded article that is flexible like a natural rubber molded article and has a high stress retention, even though it is molded from a dip-molding composition containing a synthetic latex composition. The technique of pre-vulcanizing natural rubber latex compositions by introducing crosslinks into the elastomer contained in the latex composition to impart a minimal level of crosslinking during dipping, thereby achieving the desired performance, is commonly used as a pre-vulcanization technique. However, synthetic latex compositions have significantly inferior film-forming properties compared to natural rubber latex compositions, making this a difficult technique to use to obtain the appropriate physical properties. When using synthetic latex compositions, such as latex compositions containing carboxyl group-containing nitrile rubber elastomers, to produce molded articles by dipping, it is necessary to introduce crosslinks in parallel with the film-forming process. While there have been occasional examples of dip-processed articles being produced using partially crosslinked synthetic latex compositions, dipping synthetic latex compositions that have 60% or more crosslinks by weight prior to the film-forming process have resulted in poor physical strength and significantly reduced durability.

[0017] In the composition according to the present embodiment, since the synthetic latex composition already contains a crosslinked structure, it is possible to obtain a dip-molded article that satisfies sufficient physical properties by only introducing a minimum amount of crosslinked structure in the dip-molded article preparation process. Furthermore, the dip-molded article thus obtained is characterized by an extremely soft feel and excellent stress retention. In the present invention, the degree of crosslinking provided in the polymerization process of the elastomer in the synthetic latex composition is preferably 60% by weight or more and 80% by weight or less of all crosslinked structures finally introduced. The crosslinked structures introduced in the polymerization process of the elastomer in the synthetic latex composition have a different chemical bonding method from the crosslinked structures introduced during the molding of general latex or rubber. When the polymerization reaction proceeds by radical polymerization, the crosslinked structures can be controlled by addition of radicals to the polymer side chain, chain transfer, etc. The crosslinked structures formed in the polymerization process of the synthetic latex composition include carbon-carbon bonds, ester bonds, hydrogen bonds, coordination structures, etc., but carbon-carbon bonds are stronger, resulting in a good balance between softness and stress retention in the final molded product.

[0018] The degree of crosslinking can be measured with good reproducibility by measuring the degree of solubility of the polymer in a solvent with a similar polarity to the polymer. If the polymer is carboxyl group-containing acrylonitrile butadiene rubber (XNBR), the degree of crosslinking can be estimated by measuring the insoluble content using methyl ethyl ketone (MEK) as the solvent. MEK for dip-molded products No When the soluble content is 1% by weight or less and the MEK insoluble content of the elastomer contained in the synthetic latex composition is 60% by weight, it is approximately 60%. weight It can be assumed that % of the crosslinked structure was introduced during the dip-molded product manufacturing process. The MEK insoluble content is an index for measuring the degree to which the crosslinked structure has been formed in the polymer structure. In order to improve the stress retention of a dip-molded article using a carboxyl group-containing nitrile rubber elastomer, it is effective to increase the number of crosslinked structures in the dip-molded article, because the molecular chains of the dip-molded article with an increased number of crosslinked structures are more strongly entangled with each other, making it difficult for the entanglement to be unwound when stretched, and the molecular chains return to their original molecular structure, thereby increasing the so-called rubber elasticity and the stress retention.

[0019] Synthetic latex compositions are typically a mixture of latex particles and water. The latex particles are usually coated with a surfactant, and when finally dehydrated to form a film, the particles form a laminated structure. In this specification, the space between these laminated latex particles is referred to as interparticle, while the space inside each particle is referred to as intraparticle, to distinguish between the two. Compared to natural rubber latex compositions, synthetic latex compositions suffer from weak interparticle bonds. The inventors have discovered that elastomers with a high degree of crosslinking can incorporate many carboxyl groups into their particles, allowing them to be further crosslinked with a crosslinking agent suitable for intraparticle crosslinking, thereby increasing the crosslink density of molded articles and further improving stress retention. Meanwhile, the weak interparticle bonds common to synthetic latex compositions have traditionally been addressed by using metal crosslinking agents such as zinc. The elastomers of this embodiment can be partially crosslinked between particles, particularly by crosslinking with an epoxy crosslinking agent, to solve this problem. Furthermore, the addition of a metal crosslinking agent such as zinc can further increase interparticle crosslinking. This elastomer has a high pH dependency due to the presence of many carboxyl groups within the particles. In other words, the properties of the molded product change depending on whether the carboxyl groups, which serve as crosslinking points for the crosslinking agent, are present at the particle interface or within the particles. Typically, latex compositions are adjusted to a pH of approximately 8.3, resulting in many carboxyl groups within the elastomer particles. Therefore, if the final pH of the dip-molding composition is adjusted below 9.5, the carboxyl groups remain within the particles, resulting in a high stress retention rate and fewer carboxyl groups at the particle interface, resulting in a low tensile strength. On the other hand, if the pH of the dip-molding composition is increased above 10.5, the carboxyl groups within the particles will be exposed to the particle interface, resulting in the opposite effect. Therefore, in the present invention, it is desirable to adjust the pH of the dip-molding composition to between 9.5 and 10.5 using a pH adjuster.

[0020] <Composition of carboxyl group-containing nitrile rubber elastomer> The composition of the carboxyl group-containing nitrile rubber elastomer contains, as essential structural units, structural units derived from a conjugated diene monomer, structural units derived from an ethylenically unsaturated carboxylic acid monomer, and structural units derived from an ethylenically unsaturated nitrile monomer, and may optionally contain structural units derived from other copolymerizable monomers. The elastomer composition is characterized by a lower content of structural units derived from ethylenically unsaturated carboxylic acid monomers in the carboxyl group-containing nitrile rubber elastomer than usual in order to improve the flexibility of the dip-molded article. Furthermore, when many carboxyl groups bond with calcium ions derived from the coagulant, the molecular chains become more susceptible to breakage due to physical external forces, and structural misalignment occurs more easily when calcium recombines with different carboxyl groups. This causes the entanglement structure of the rubber molecular chains to change, making it impossible to return to its original state, and the stress retention rate of the dip-molded article also decreases. Each monomer will be explained below.

[0021] <Conjugated diene monomer> The conjugated diene monomer used in this embodiment is not particularly limited as long as it has radical polymerization reactivity. Specific examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene. These conjugated diene monomers can be used alone or in combination of two or more. The structural unit derived from the conjugated diene monomer is a factor that mainly imparts flexibility to the molded article. The content of the conjugated diene monomer relative to the total monomers is usually 50% by weight or more and 78% by weight or less, and preferably 60% by weight or more and 75% by weight or less.

[0022] <Ethylenically unsaturated nitrile monomer> The ethylenically unsaturated nitrile monomer used in this embodiment may be any monomer having both a polymerizable unsaturated bond and a nitrile group in one molecule, such as acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile, and α-cyanoethylacrylonitrile. Among these, acrylonitrile and methacrylonitrile are preferred, with acrylonitrile being more preferred. The structural unit derived from the ethylenically unsaturated nitrile monomer is the component that primarily imparts strength to the molded article; if the amount is too small, the strength will be insufficient, while if the amount is too large, the molded article will have increased chemical resistance but will be too hard. The content of the ethylenically unsaturated nitrile monomer is 20% by weight or more and 30% by weight or less, preferably 21% by weight or more and 28% by weight or less, of the total monomers. Even if the amount of the ethylenically unsaturated nitrile monomer is increased, it is relatively difficult to increase the modulus and there is almost no effect on the stress retention rate. Therefore, the amount can be appropriately set within the above range depending on the application, such as chemical resistance and film thickness.

[0023] <Ethylenically unsaturated carboxylic acid monomer> The structural units derived from the ethylenically unsaturated carboxylic acid monomer serve as crosslinking points with the crosslinking agent. The type of ethylenically unsaturated carboxylic acid monomer is not particularly limited and may be a monocarboxylic acid or a polycarboxylic acid. Specific examples include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, maleic anhydride, and citraconic anhydride, with acrylic acid and methacrylic acid being preferred. These ethylenically unsaturated carboxylic acid monomers may be used alone or in any combination and ratio of two or more. The content of the structural units derived from the ethylenically unsaturated carboxylic acid monomer in the elastomer is preferably 3.5% by weight or more and 6% by weight or less, more preferably 3.5% by weight or more and 5.0% by weight or less, and even more preferably 3.5% by weight or more and 4.5% by weight or less. Since increasing the amount of the ethylenically unsaturated carboxylic acid monomer significantly increases the modulus, it is preferable to keep the amount as small as possible within the above range.

[0024] <Other copolymerizable monomers> In this embodiment, other monomers copolymerizable with the conjugated diene monomer, ethylenically unsaturated nitrile monomer, and ethylenically unsaturated carboxylic acid monomer can be used as needed. The other copolymerizable monomers may be any monomers having a polymerizable unsaturated bond in the molecule, and include ethylenically unsaturated sulfonic acid monomers such as acrylamidopropanesulfonic acid and styrenesulfonic acid; methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, monoethyl itaconate, monobutyl fumarate, monobutyl maleate, dibutyl maleate, dibutyl fumarate, ethyl maleate, mono-2-hydroxypropyl maleate, methoxymethyl (meth)acrylate, ethoxyethyl (meth)acrylate, methoxyethoxyethyl (meth)acrylate, cyanomethyl (meth)acrylate, Examples of suitable copolymerizable monomers include ethylenically unsaturated carboxylic acid ester monomers such as 2-cyanoethyl (meth)acrylate, 1-cyanopropyl (meth)acrylate, 2-ethyl-6-cyanohexyl (meth)acrylate, 3-cyanopropyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, glycidyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, 2-sulfoethyl acrylate, and 2-sulfopropyl methacrylate; vinyl aromatic monomers such as styrene, alkylstyrene, and vinylnaphthalene; fluoroalkyl vinyl ethers such as fluoroethyl vinyl ether; vinylpyridine; and non-conjugated diene monomers such as vinylnorbornene, dicyclopentadiene, and 1,4-hexadiene. Typically, the content of other copolymerizable monomers relative to the total monomers is 0% by weight or more and 5% by weight or less, preferably 0% by weight or more and 3% by weight or less. Here, "0% by weight" means that the above-mentioned monomers are not included (below the detection limit), and this embodiment may be implemented in this manner.

[0025] <Method for producing synthetic latex composition> Hereinafter, the method for producing a synthetic latex composition will be described mainly using a synthetic latex composition of carboxyl group-containing acrylonitrile butadiene rubber (XNBR) as an example, but the aspect of the carboxyl group-containing nitrile rubber elastomer of the present embodiment is not limited to this elastomer. The method for producing the synthetic latex composition according to this embodiment can be carried out by a conventional polymerization method, and the polymerization reactor may be a batch, semi-batch, or continuous polymerization reactor. The monomers may be added to the polymerization reactor all at once, continuously or intermittently as the polymerization reaction progresses, or a portion of the monomers are added and reacted to a specific conversion rate, followed by continuous or continuous addition of the remaining monomers. Any of these addition methods may be employed. The monomers to be added may be premixed or individually added. When various monomers are mixed, the mixing ratio may be constant or variable. The features of a method for preparing a synthetic latex composition containing an elastomer having a MEK insoluble content of 60% by weight or more and having soft basic properties are described below. A molded article produced using the synthetic latex composition according to the present embodiment obtained by the production method described below can have basic physical properties such as high stress retention and rubber elasticity, including flexibility, compared to a molded article produced using conventional linear XNBR polymerized at low temperature.

[0026] To prepare a synthetic latex composition containing an elastomer with an MEK insoluble content of 60% by weight or more, the composition can be prepared by a method such as using a relatively high polymerization temperature, a relatively small amount of chain transfer agent, or increasing the polymerization conversion rate to a specific conversion rate and then further increasing the polymerization temperature. The polymerization temperature during the polymerization reaction is set to a relatively high temperature of 20°C or higher and 60°C or lower, preferably 25°C or higher and 50°C or lower, to decrease the molecular weight of the elastomer in the synthetic latex composition, increase the number of branched chains, and increase the MEK insoluble content. By using a relatively large amount of the polymerization initiator, the molecular weight of the elastomer in the synthetic latex composition is reduced, the number of branched chains is increased, and the amount of MEK insolubles is increased. The amount of chain transfer agent is set to as small as possible, between 0.2% and 0.8% by weight, to increase the branched chains and the MEK insoluble content. In this embodiment, the MEK insoluble content is 60% by weight or more and 80% by weight or less, preferably 65% ​​by weight or more and 75% by weight or less, and more preferably 68% by weight or more and 72% by weight or less. Furthermore, if the MEK insoluble content exceeds 80% by weight, film-forming properties deteriorate, making it difficult to form a uniform film and dip-molding.

[0027] Next, in order to produce a molded product with a soft feel, it is necessary to make the MEK-insoluble content of the elastomer in the synthetic latex composition 60% by weight or more, and at the same time, to keep the MEK swelling ratio of the cast film low. When the MEK insoluble content is 0% by weight or more and 10% by weight or less, the MEK swelling ratio is 100 times or more, when the MEK insoluble content is 30% by weight or more, the swelling ratio is 30 times or more and 70 times or less, and when the MEK insoluble content is 60% by weight or more, the swelling ratio is 5 times or more and 25 times or less, and the swelling ratio for a particularly soft texture is set to be in the range of 5 times or more and 10 times or less. The MEK swelling ratio and the MEK insoluble content can be measured by the method described in the Examples below. When the elastomer contained in the synthetic latex composition reaches a predetermined polymerization conversion rate, the polymerization reaction is terminated by cooling the polymerization system or adding a polymerization terminator. The polymerization conversion rate at which the polymerization reaction is terminated is usually 80% or higher, preferably 90% or higher, and more preferably 93% or higher. The additives used in the polymerization reaction will be described below.

[0028] <Emulsifier> The emulsifier is not particularly limited, but is preferably one that is commonly used in emulsion polymerization, for example, nonionic emulsifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan alkyl esters; fatty acids such as myristic acid, palmitic acid, oleic acid, and linolenic acid and salts thereof; phosphate esters such as isopropyl phosphate and polyoxyethylene alkyl ether phosphate; alkyl diphenyl ether disulfonates; lauryl diphenyloxysulfonic acid disodium salt; alkyl naphthalene sulfonates; Examples of emulsifiers include anionic emulsifiers such as sodium salts of benzenesulfonic acid-formalin condensates, sodium dialkyl sulfosuccinates, alkylbenzenesulfonates, alkylarylsulfonates, higher alcohol sulfates, and alkylsulfosuccinates; cationic emulsifiers such as ammonium chlorides such as trimethylammonium chloride and dialkylammonium chloride, benzylammonium salts, and quaternary ammonium salts; and copolymerizable emulsifiers containing double bonds such as sulfoesters of α,β-unsaturated carboxylic acids, sulfate esters of α,β-unsaturated carboxylic acids, and sulfoalkylaryl ethers. The amount of emulsifier used is not particularly limited, but is generally 0.1 to 10 parts by weight, preferably 0.5 to 6.0 parts by weight, per 100 parts by weight of the monomer mixture. The emulsifiers may be used alone or in combination. Furthermore, they may be used all at once or in portions during the preparation of the synthetic latex composition.

[0029] <Chain transfer agent> Examples of chain transfer agents include mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, and mercaptoethanol; halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, and methylene bromide; and α-methylstyrene dimer. Mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan are preferred. The chain transfer agent may be used all at once at the start of the polymerization reaction or added as needed as the polymerization reaction progresses. Alternatively, the chain transfer agent may be used both at the start of the polymerization reaction and during the polymerization reaction. In this embodiment, a synthetic latex composition containing an elastomer with many branched rubber molecular chains and a large amount of MEK-insoluble components is typically obtained by minimizing the amount of chain transfer agent.

[0030] <Aqueous solvent> Water is typically used as the aqueous solvent, and the amount thereof is typically 70 to 250 parts by weight, preferably 80 to 170 parts by weight, per 100 parts by weight of the monomer mixture. If the amount of aqueous solvent is less than 70 parts by weight, stability during the polymerization process may decrease. If the amount of aqueous solvent is more than 250 parts by weight, post-processing of the resulting synthetic latex composition requires more time and energy, resulting in an inefficient production process for the synthetic latex composition.

[0031] <Polymerization initiator> The polymerization initiator is not particularly limited, but examples thereof include potassium persulfate, ammonium persulfate, sodium persulfate, perphosphate, hydrogen peroxide, t-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, p-menthane hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, di-t-butyl peroxide, di-α-cumyl peroxide, acetyl peroxide, isobutyryl peroxide, benzoyl peroxide, and azobisisobutyronitrile. These polymerization initiators can be used alone or in combination of two or more. The amount of polymerization initiator used is typically 0.001 to 10 parts by weight, preferably 0.01 to 5 parts by weight, and more preferably 0.01 to 2 parts by weight, per 100 parts by weight of the monomer mixture.

[0032] Peroxide initiators can also be used in combination with reducing agents as redox polymerization initiators. The reducing agent is not particularly limited, but examples include compounds containing reduced metal ions such as ferrous sulfate and cuprous naphthenate, sulfonates such as sodium methanesulfonate, formaldehyde sulfoxylate salts such as sodium formaldehyde sulfoxylate, 2-hydroxy-2-sulfonatoacetate salts such as disodium salt of 2-hydroxy-2-sulfonatoacetate, 2-hydroxy-2-sulfinatoacetate salts such as disodium salt of 2-hydroxy-2-sulfinatoacetate, amines such as formdimethylaniline, and ascorbic acid. These reducing agents can be used alone or in combination of two or more. The amount of reducing agent used is not particularly limited, but the weight ratio to the peroxide (peroxide / reducing agent) is preferably 0.01 to 100, and more preferably 0.1 to 50.

[0033] <Polymerization terminator> The polymerization terminator is not particularly limited, and examples thereof include nitrites such as sodium nitrite, potassium nitrite, and ammonium nitrite, ascorbic acid, citric acid, hydroxylamine, hydroxyamine sulfate, diethylhydroxylamine, hydroxyamine sulfonic acid and alkali metal salts thereof, 2,2,6,6-tetramethylpiperidinooxyl compounds such as 4-benzoyloxy-2,2,6,6-tetramethylpiperidinooxyl, sodium dimethyldithiocarbamate, dimethyldithiocarbamate, hydroquinone derivatives, catechol derivatives, resorcinol derivatives, aromatic hydroxydithiocarboxylic acids such as hydroxydimethylbenzenedithiocarboxylic acid, hydroxydiethylbenzenedithiocarboxylic acid, and hydroxydibutylbenzenedithiocarboxylic acid, and alkali metal salts thereof. The polymerization terminator may be added after or simultaneously with the addition of an inorganic base aqueous solution such as a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, or aqueous ammonia. The amount of the polymerization terminator used is usually 0.01 to 5 parts by weight, preferably 0.03 to 2 parts by weight, based on 100 parts by weight of the monomer mixture. After the polymerization reaction is terminated, the desired latex is prepared by removing unreacted monomers, adjusting the solid content and pH, and adding surfactants, antioxidants, preservatives, antibacterial agents, etc., as needed. In the latex preparation method of the present invention, polymerization secondary materials such as oxygen scavengers, dispersants, surfactants, chelating agents, molecular weight regulators, particle size regulators, antioxidants, preservatives, etc. can be added as needed. The polymerization secondary material components may be organic or inorganic compounds.

[0034] <Evaluation of the crosslinked structure of carboxyl group-containing nitrile rubber elastomer> There are various methods for evaluating the degree of crosslinking of carboxyl group-containing nitrile rubber elastomers, but an easy and reproducible evaluation method is to measure the amount of insoluble matter in the polymer's parent solvent. The degree of cross-linking structureThere is a way to estimate this. When the polymer is XNBR, the degree of crosslinking can be evaluated by measuring the amount of insoluble matter in methyl ethyl ketone (MEK). Normally, the MEK insoluble matter is affected by the crosslinking structure between primary polymer chains generated in emulsion polymerization and the increase in side chain polymers growing from the primary polymer chains. The detailed method for measuring the MEK insoluble content will be described in the Examples.

[0035] (2) Epoxy crosslinking agent The objective of this invention is to produce a molded article with high stress retention and softness. To this end, the above-mentioned elastomer has an MEK-insoluble content of 60% by weight or more, and a crosslinked structure is introduced into the particles, ensuring the presence of many carboxyl groups within the particles. To address this issue, it was necessary to select a crosslinking agent suitable for increasing the crosslink density and stress retention by penetrating the particles in large quantities to crosslink with the carboxyl groups within the latex particles and enriching the intra-particle crosslinks. Meanwhile, the inventors noted that when an epoxy crosslinking agent is used as a crosslinking agent, a portion of it penetrates into the latex particles in large quantities and can form intra-particle crosslinks with the carboxyl groups within the particles. The dip-molding composition is composed of water and latex particles, each of which has a hydrophilic region and a lipophilic region (hydrophobic region). Since the contents of the latex particles are similar to methyl isobutyl ketone (MIBK), the inventors measured the MIBK / water partition coefficient of the epoxy crosslinker. This was done by looking at the ratio of the epoxy crosslinker dissolving in a water / MIBK mixture, and we thought that the higher the solubility in MIBK, the more the epoxy crosslinker would enter the latex particles and contribute to intra-particle crosslinking.

[0036] On the other hand, the inventors have used the MIBK / water partition ratio of an epoxy crosslinking agent as a criterion for selecting an epoxy crosslinking agent with a longer pot life, since the epoxy crosslinking agent is deactivated by hydrolysis in the hydrophilic region under alkaline conditions. According to this, it has been found that an epoxy crosslinking agent having an MIBK / water partition ratio of 27% or more, having three or more glycidyl ether groups in one molecule, and having a mother skeleton with alicyclic, aliphatic or aromatic hydrocarbon, i.e., containing an epoxy compound which is trivalent or more and poorly soluble in water, can obtain a pot life of about 3 days, which is the minimum required for glove production, and a pot life of about 5 days at 50% or more, and 70% or more at 7 days or more. In this embodiment, taking into consideration that a large amount of epoxy crosslinking agent is to be penetrated into the particles, an MIBK / water distribution ratio of 50% or more is used. Also, the crosslinked structure of covalent bond by epoxy crosslinking agent is hard to break, unlike the ionic bond by zinc, so there is an advantage that the inherent softness of the latex is not impaired. The following explains the process step by step.

[0037] a. Epoxy crosslinking agents containing an epoxy compound having three or more glycidyl ether groups in one molecule and a parent skeleton containing alicyclic, aliphatic, or aromatic hydrocarbons. <Epoxy compound having three or more glycidyl ether groups in one molecule and a mother skeleton containing alicyclic, aliphatic, or aromatic hydrocarbon> Epoxy compounds usually have three or more glycidyl ether groups and a parent skeleton containing alicyclic, aliphatic, or aromatic hydrocarbons (hereinafter also referred to as "trivalent or higher epoxy compounds"). Epoxy compounds having three or more glycidyl ether groups can usually be produced by reacting epichlorohydrin with an alcohol having three or more hydroxyl groups per molecule.

[0038] Examples of alcohols having three or more hydroxyl groups that form the parent skeleton of trivalent or higher epoxy compounds include aliphatic glycerol, diglycerol, triglycerol, polyglycerol, sorbitol, sorbitan, xylitol, erythritol, trimethylolpropane, trimethylolethane, and pentaerythritol; and aromatic cresol novolac and trishydroxyphenylmethane. Among the trivalent or higher epoxy compounds, it is preferable to use polyglycidyl ether. Specifically, it is preferable to use an epoxy crosslinking agent containing at least one selected from glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol triglycidyl ether, sorbitol tetraglycidyl ether, pentaerythritol triglycidyl ether, and pentaerythritol tetraglycidyl ether, and among these, it is more preferable to use an epoxy crosslinking agent containing at least one selected from trimethylolpropane triglycidyl ether, triethylolpropane triglycidyl ether, pentaerythritol triglycidyl ether, and pentaerythritol tetraglycidyl ether.

[0039] <Epoxy crosslinking agents containing trivalent or higher epoxy compounds> Among epoxy crosslinking agents, those containing an epoxy compound having a glycidyl ether group can generally be produced by reacting a hydroxyl group of an alcohol with epihalohydrin as follows: In the following (I), a monohydric alcohol is used for the sake of simplicity.

[0040] [ka] The epoxy compounds contained in epoxy crosslinkers range from divalent to roughly heptavalent, depending on the number of hydroxyl groups in the raw alcohol. However, due to side reactions during the reaction process, even when synthesizing a trivalent epoxy compound as the target, several types of compounds are produced, and these usually include divalent epoxy compounds. Therefore, for example, trivalent epoxy crosslinkers are generally mixtures of divalent and trivalent epoxy compounds. Usually, even those that are called trivalent epoxy crosslinkers contain about 50% of the trivalent epoxy compound, which is the main component. Furthermore, some epoxy crosslinking agents are poorly soluble in water, which is largely due to the influence of chlorine and other substances contained in the structure of the epoxy compound.

[0041] The epoxy crosslinking agent is preferably an epoxy crosslinking agent containing a trivalent or higher epoxy compound obtained by reacting epihalohydrin with an alcohol having three or more hydroxyl groups. The epihalohydrin may be one or more selected from epichlorohydrin, epibromohydrin, and epiioditehydrin. Among these, epichlorohydrin is preferred. A trivalent or higher epoxy crosslinking agent and a divalent epoxy crosslinking agent can be mixed and used. Alternatively, when producing a trivalent or higher epoxy crosslinking agent, an alcohol having three or more hydroxyl groups and an alcohol having two hydroxyl groups can be mixed and reacted.

[0042] <Crosslinking reaction between epoxy compounds and carboxyl groups of XNBR> The crosslinking reaction between the epoxy compound and the carboxyl group of XNBR occurs as shown in the following formula (II): Note that, for the sake of simplicity, a monovalent epoxy compound is used as the epoxy compound shown in (II) below.

[0043] [ka] The object for the epoxy compound to form crosslinks is the carboxyl group in XNBR. To form crosslinks with an epoxy compound, as optimal conditions, it can be heated at 120°C or higher in the curing process to cause the ring-opening reaction of the epoxy group.

[0044] <Epoxy crosslinking agent with a MIBK / water partition ratio of 50% or more> The epoxy crosslinking agent is required to have a MIBK / water partition ratio of 50% or more. More preferably, the MIBK / water partition ratio is 70% or more. The MIBK / water partition ratio is related to the pot life of the epoxy crosslinking agent with a valence of three or more. When the MIBK / water partition ratio is 50% or more, the pot life is 5 days, and when the MIBK / water partition ratio is 70% or more, it is 7 days or more. Therefore, it was judged that 50% or more was good and adopted. Note that the upper limit of the MIBK / water partition ratio does not require a special setting and may be 100% or less. The dip molding composition is divided into the hydrophobic region of the latex particles and the hydrophilic region of the solvent. Among the epoxy crosslinking agents, those that are poorly soluble in water and are likely to enter the inside of the latex particles, which are the hydrophobic region of the elastomer, are preferably used. Furthermore, many of the epoxy crosslinking agents are present inside the latex particles in the dip molding composition, and by reacting with the carboxyl groups inside the latex particles to crosslink the elastomer, it is considered that the crosslink density of the molded body can be increased and the stress retention rate can be raised.

[0045] 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 the epoxy crosslinking agent are accurately weighed and added to a test tube. Let the weight of MIBK be M(g) and the weight of the epoxy crosslinking agent be E(g). After thoroughly stirring and mixing this mixture at a temperature of 23°C ± 2°C for 3 minutes, it is centrifuged at 1.0×10 3 G for 10 minutes and separated into an aqueous layer and a MIBK layer. Then, the weight of the MIBK layer is measured and designated as ML(g). MIBK / water partition ratio (%) = (ML(g) - M(g)) / E(g) × 100 The above measurement was carried out three times, and the average value was taken as the MIBK / water partition coefficient.

[0046] b. Properties of suitable epoxy crosslinkers <Average number of epoxy groups> As mentioned above, even in the case of trivalent or higher epoxy crosslinkers, divalent epoxy compounds may be included as a side reaction. Therefore, when evaluating each product, it is important to understand the average number of epoxy groups and the proportion of compounds with trivalent epoxy groups. The average number of epoxy groups is obtained by identifying each epoxy compound contained in the epoxy crosslinking agent by gel permeation chromatography (GPC), multiplying the number of epoxy groups in one molecule of each epoxy compound by the number of moles of the epoxy compound to obtain the number of epoxy groups for each epoxy compound, and then dividing the total value by the total number of moles of all epoxy compounds contained in all epoxy compounds contained in the epoxy crosslinking agent. The average number of epoxy groups in the epoxy crosslinking agent used in this embodiment is preferably more than 2.0, and from the viewpoint of obtaining good physical properties of the molded product, the average number of epoxy groups is more preferably 2.3 or more, and even more preferably 2.5 or more. On the other hand, the upper limit can be, for example, 7 or less, or even 4 or less.

[0047] <Epoxy equivalent> From the viewpoint of obtaining good stress retention and fatigue durability of the molded body, the epoxy equivalent of the epoxy compound is preferably 100 g / eq. or more, and is preferably 230 g / eq. or less, and more preferably 200 g / eq. or less. The epoxy equivalent of an epoxy compound is the average molecular weight of the epoxy compound divided by the average number of epoxy groups, and indicates the average weight per epoxy group. This value can be measured by the perchloric acid method.

[0048] <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 or more and 1,500 or less, more preferably 175 or more and 1,400 or less, and even more preferably 200 or more and 1,300 or less.

[0049] c. Amount of epoxy crosslinker added The amount of epoxy crosslinking agent added is usually 0.2 parts by weight or more, preferably 0.3 parts by weight or more, and more preferably 0.5 parts by weight or more, per 100 parts by weight of elastomer, and usually 2.5 parts by weight or less, preferably 2.0 parts by weight or less, and more preferably 1.5 parts by weight or less. If the amount of epoxy crosslinking agent added is too small, the stress retention rate will decrease, but if the amount added is more than 2.5 parts by weight, for example 3 parts by weight, the tensile strength and elongation will decrease.

[0050] (3) Dispersant for epoxy crosslinking agents The epoxy compound needs to be uniformly dispersed in the dip-molding composition. On the other hand, when an epoxy crosslinker has an MIBK / water distribution ratio of 50% or more, the higher the MIBK / water distribution ratio, the more difficult it is to add the crosslinker to the latex and the more difficult it is to disperse the crosslinker. If the epoxy compound is highly hydrophilic, there will be no problem with water dispersibility. However, for epoxy compounds that have been used in solvent-based paints, the inventors considered dissolving the epoxy crosslinking agent using a dispersant and then blending it into the elastomer. In particular, when the MIBK / water partition ratio is 50% or higher, cloudiness tends to appear when dissolved in water, so we thought that dispersion with a dispersant was necessary.Furthermore, dispersion with a dispersant is also necessary for actual mass production.

[0051] The dispersant for the epoxy crosslinking agent (compound) is preferably at least one selected from the group consisting of monohydric lower alcohols, glycols represented by the following formula (E1), ethers represented by the following formula (E2), and esters represented by the following formula (E3). HO-(CH2CHR 1 '-O)n1 -H (E1) (In the above formula (E1), R 1 ' represents hydrogen or a methyl group, and n1 represents an integer of 1 to 3. R 2 'O-(CH2CHR 1 '-O) n2 -R 3 ' (E2) (In formula (E2), R 1 ' represents hydrogen or a methyl group, and 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. R 2 'O-(CH2CHR 1 '-O) n3 -(C=O)-CH3(E3) (In formula (E3), R 1 ' represents hydrogen or a methyl group, and R 2 ' represents an aliphatic hydrocarbon group having 1 to 5 carbon atoms, and n3 represents an integer of 0 to 3.

[0052] Examples of the monohydric lower alcohol include methanol and ethanol. Examples of the glycol represented by formula (E1) include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and tripropylene glycol. Among the ethers represented by formula (E2), glycol ethers include 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, triethylene glycol dimethyl ether, etc. Furthermore, as the ether represented by formula (2), an ether in which n2=0 can also be used. Examples of the ester represented by formula (E3) include diethylene glycol monoethyl ether acetate and diethylene glycol monobutyl ether acetate. When the above-mentioned epoxy compound dispersants are used, they may be used alone or in combination of two or more. It is preferable that the above-mentioned dispersants are used without being mixed with water in advance.

[0053] Among the above dispersants, alcohols are preferred, and it is particularly preferred to use methanol, ethanol, or diethylene glycol, with diethylene glycol being particularly preferred from the viewpoint of volatility and flammability. Diethylene glycol is presumably suitable because it has a highly hydrophilic glycol group and an ether structure, and at the same time contains a hydrophobic hydrocarbon structure, and is easily soluble in both water and elastomers.

[0054] In the dip-molding composition, the weight ratio of the epoxy crosslinking agent containing an epoxy compound to the dispersant is preferably 1:4 or more and 1:1 or less. When an epoxy compound having a high MIBK / water distribution ratio is used in preparing a dip-molding composition, it is preferable to dissolve the epoxy compound in a dispersant for the epoxy compound beforehand and then mix it with other components of the dip-molding composition.

[0055] (4) Metallic cross-linking agents In this embodiment, a metal crosslinking agent may be further included as a crosslinking agent. From the viewpoint of improving the film-forming properties of the film, a metal crosslinking agent can be added in addition to the epoxy crosslinking agent. For example, adding a small amount of a zinc compound is effective. The zinc compound acts as an interparticle crosslink through ionic crosslinking, maintaining the tensile strength of the molded body, preventing swelling and a decrease in tensile strength in artificial sweat, and is expected to improve organic solvent impermeability. However, this is a negative factor in improving the stress retention rate and softness, which are the objectives of the present invention. However, in order to improve the film-forming properties of the above-mentioned molded body, it is beneficial to add an amount that does not affect the above negative factors. Examples of zinc compounds include zinc oxide and zinc hydroxide, with zinc oxide being the most commonly used. The zinc oxide used in the present invention is not particularly limited, and commonly used zinc oxides can be used. When zinc oxide is contained in the dip-forming composition according to this embodiment, the amount of zinc oxide added is 0.1 part by weight or more and 1.0 part by weight or less, preferably 0.2 part by weight or more and 0.7 part by weight or less, and more preferably 0.2 part by weight or more and 0.6 part by weight or less, relative to 100 parts by weight of the elastomer in the dip-forming composition.

[0056] (5) pH adjuster The conventional approach to pH adjustment of XNBR dip molding compositions is to orient the carboxyl groups oriented on the inside of the particles to the outside at the interface of the latex particles, thereby creating carboxylate ions (COO - To achieve this, the pH of the latex was typically raised from approximately 8.3 to between 10 and 11. This allowed the zinc and calcium ions in the metal crosslinking agent to crosslink with the organic crosslinking agent, which crosslinks between particles. This improved the tensile strength and fatigue durability of the resulting molded body and eliminated the interparticle crosslinking that was a drawback of synthetic rubber latex. Furthermore, the latex particles themselves had a minimum crosslinking structure, with an MEK insoluble content between 0 and 30% by weight. Linear chains were often used, and many carboxyl groups were present at the particle interface. In this sense, a higher pH, such as 10.5, was considered preferable, but a pH above 11 resulted in a hard film, and this was considered the limit.

[0057] However, in this embodiment, the goal is to retain as many carboxyl groups as possible inside the latex particles, enhance intra-particle crosslinking using an epoxy crosslinker that penetrates into the particle interior, and improve stress retention. Therefore, if the pH is increased above 10.5, for example, the carboxyl groups will be oriented toward the outside of the particle interface, resulting in a decrease in stress retention. Furthermore, because the epoxy crosslinker also contributes to inter-particle crosslinking, a pH lower than 9.5 increases stress retention but decreases strength. In this sense, pH adjustment is important in this embodiment, and a pH adjuster is preferably used. For example, the pH is adjusted to preferably 9.5 or more and 10.5 or less, more preferably 10.0 or more and 10.5 or less. Regarding pH adjustment, the lower the pH, the higher the stress retention, the easier it is to elongate, and the softer the material becomes. On the other hand, the higher the pH, the higher the tensile strength. As the pH adjuster, ammonia compounds, amine compounds, and alkali metal hydroxides can be used. Among these, it is preferable to use alkali metal hydroxides because the manufacturing conditions such as pH adjustment and gelling conditions are easy, and among them, potassium hydroxide (KOH) is the easiest to use. In the following examples, the pH adjuster will be mainly explained using KOH. The amount of pH adjuster added is about 0.1 to 3.0 parts by weight per 100 parts by weight of the elastomer in the dip-molding composition, but typically about 1.8 to 2.0 parts by weight is used industrially.

[0058] (6) Other ingredients The dip-forming composition contains the above-mentioned components and water, and may generally contain other optional components.

[0059] The dip-forming composition may further contain a dispersant. The dispersant is preferably an anionic surfactant, such as a carboxylate, a sulfonate, a phosphate, a polyphosphate ester, a polymerized alkylarylsulfonate, a polymerized sulfonated naphthalene, or a polymerized naphthalene / formaldehyde condensation polymer, and is preferably a sulfonate.

[0060] Commercially available dispersants can be used, such as BASF's Tamol NN9104. The amount of dispersant used is preferably 0.5 to 2.0 parts by weight per 100 parts by weight of the elastomer in the dip-molding composition.

[0061] The dip-forming composition may further contain various other additives. Examples of such additives include antioxidants, pigments, and chelating agents. Examples of the antioxidant include hindered phenol-type antioxidants such as Wingstay L. Examples of the pigment include titanium dioxide. Examples of the chelating agent include sodium ethylenediaminetetraacetate.

[0062] The dip-molding composition of the present embodiment can be prepared by mixing an elastomer, an epoxy crosslinking agent, usually a pH adjuster, water, and, if necessary, various additives such as a humectant, a dispersant, and an antioxidant, using a conventional mixing means, for example, a mixer.

[0063] 2. Manufacturing method of molded body Another embodiment of the present invention is a molded article (dip-molded article) that is a cured product of the dip-molding composition, which can be used as, for example, surgical, laboratory, industrial, or household gloves, condoms, medical devices such as catheters, balloons, nipples, sacks, etc., and is particularly suitable for use as gloves. A method for producing gloves when the molded article is a glove will be described below.

[0064] The method for producing a molded article, which is a cured product of the dip-forming composition, is not particularly limited and includes a step of solidifying the dip-forming composition onto a mold or former (glove mold) for dip-forming to form a film, and a step of forming a crosslinked structure in the elastomer. Examples of methods for solidifying the dip-forming composition include direct immersion, coagulation immersion, electric immersion, and thermal immersion. Any of these methods may be used, but the direct immersion and coagulation immersion methods are preferred. Hereinafter, a method for producing a glove as a molded article in the case where the coagulation dipping method is adopted as a method for coagulating and forming a film from the dip-forming composition will be described in detail.

[0065] The glove can be produced, for example, by the following production method. (1) Coagulant application process (a process of applying a coagulant to a glove mold), (2) Maturation step (a step of preparing and stirring a dip-molding composition), (3) a dipping step (a step of immersing a glove mold in a dip-forming composition); (4) gelling process (a process of gelling the film formed on the glove mold to produce a cured film precursor); (5) a leaching step (a step of removing impurities from the cured film precursor formed on the glove mold); (6) Beading process (the process of wrapping the cuffs of the gloves), (7) Curing process (a process of heating and drying at the temperature required for the crosslinking reaction) The method for producing gloves comprises carrying out the steps (3) to (7) in the above order.

[0066] The following step (6') may be optionally included between the above steps (6) and (7). (6') Pre-curing step (a step of heating and drying the cured film precursor at a lower temperature than in the curing step)

[0067] Furthermore, after the above step (7), the following step (7') may be optionally included. (7') Anti-blocking treatment step The method of anti-blocking treatment is not particularly limited, and any method may be used, for example, immersion in an aqueous solution of sodium hypochlorite and hydrochloric acid or chlorination treatment in a chlorine gas chamber, polymer coating method in which a polymer having anti-blocking properties is applied to the molded body, slurry method in which the molded body is immersed in an aqueous solution containing a lubricant component, etc. Also, the anti-blocking treatment may be performed after the dip-molded body is released from the glove mold.

[0068] The above manufacturing method also includes a method of manufacturing gloves by repeating the steps (3) and (4) twice, that is, by double dipping.

[0069] 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.

[0070] Each step will be described in detail below. (1) Coagulant application process (a) A glove mold is prepared by adding Ca as a coagulant and gelling agent. 2+ The glove mold is immersed in a coagulant solution containing ions typically at least 5% by weight but not more than 40% by weight, preferably at least 8% by weight but not more than 35% by weight. The time for adhering the coagulant to the surface of the glove mold is determined appropriately, typically at least 10 seconds but not more than 20 seconds. Other inorganic salts that have the effect of precipitating elastomer may also be used. Among these, calcium nitrate is preferred. This coagulant is typically used as an aqueous solution containing at least 5% by weight but not more than 40% by weight. The coagulant solution preferably contains a release agent such as potassium stearate, calcium stearate, mineral oil, or ester oil in an amount of about 0.5% by weight or more and about 2% by weight or less, for example, about 1% by weight.

[0071] The coagulant solution is not particularly limited and is generally provided as a mixture of coagulant components, solvents, surfactants, wetting agents, inorganic fillers, demolding agents, etc. Examples of coagulant components include metal halides such as barium chloride, calcium chloride, magnesium chloride, aluminum chloride, and zinc chloride; nitrates such as barium nitrate, calcium nitrate, and zinc nitrate; acetates such as barium acetate, calcium acetate, and zinc acetate; sulfates such as calcium sulfate, magnesium sulfate, and aluminum sulfate; and acids such as acetic acid, sulfuric acid, hydrochloric acid, and nitric acid. These compounds can be used alone or in combination, with calcium nitrate and calcium chloride being more preferred. The solvent is selected from water, alcohols, acids, etc. as required. The surfactant is used for the purpose of uniformly adhering the coagulating liquid to the surface of the glove mold and facilitating demolding, and nonionic surfactants, metal soaps and other compounds are used. As the metal soap, calcium stearate, ammonium stearate, zinc stearate, and, if necessary, metal oxides, calcium carbonate, talc, inorganic fillers, etc. may be used.

[0072] (b) The glove mold with the coagulant solution attached is placed in an oven with an internal temperature of 110℃ or higher and 140℃ or lower for 1 minute or longer and 3 minutes or shorter to dry and allow the coagulant to adhere to the entire or part of the surface of the glove mold. At this time, it should be noted that the surface temperature of the glove mold after drying will be around 60℃, which will affect the 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 that may be added later can be said to reinforce the weak point of this cross-linking function of calcium.

[0073] (2) Maturation process As explained in the section on the pH adjuster for the dip-forming composition, this step involves adjusting the pH of the dip-forming composition, which is one embodiment of the dip-forming composition, to typically 9.5 to 10.5, and preferably 10.0 to 10.5, and then stirring the composition. This step is believed to disperse and homogenize the components in the dip-forming composition.

[0074] (3) Dipping process In the maturation step, the stirred dip-forming composition (dipping liquid) is poured into a dipping tank, and the glove mold to which the coagulant has been applied in the coagulant application step and dried is immersed in the dipping tank usually for 1 second or more and 60 seconds or less at a temperature of 25°C or more and 35°C or less. In this step, calcium ions contained in the coagulant cause the elastomer contained in the dip-molding composition to aggregate on the surface of the glove mold, forming a film.

[0075] (4) Gelling process The gelling process is intended to promote cross-linking of the elastomer to a certain extent to prevent deformation of the membrane during the subsequent leaching, and at the same time to disperse calcium in the membrane and ensure sufficient calcium cross-linking later. Gelling conditions are generally within the temperature range of 30°C to 140°C, and for 1 minute to 4 minutes.

[0076] (5) Leaching process (a) The leaching process is a process in which excess chemicals and impurities such as calcium precipitated on the surface of the cured film precursor are washed away with water, which may interfere with subsequent curing. Typically, the glove mold is immersed in hot water at 30°C or higher and 80°C or lower for 1.5 minutes to 4 minutes. (b) Leaching is an important process that removes the emulsifier, which is the membrane of the latex particles, to facilitate smooth crosslinking in the curing process, converts the metal crosslinker from complex ions to water-insoluble hydroxides and retains them in the film, and removes calcium from excess coagulant and potassium from pH adjusters.

[0077] (6) Beading process This is the process of rolling up the cuff end of the glove made of the cured film precursor after the leaching process to make a ring of appropriate thickness and reinforce it. If this is done in a wet state after the leaching process, the adhesion of the rolled part will be good.

[0078] (6') Pre-curing process (a) After the beading step, the cured film precursor is heated and dried at a temperature lower than that of the subsequent curing step. Typically, this step involves heating and drying at a temperature between 60°C and 90°C for 30 seconds to 5 minutes. If the high-temperature curing step is performed without the pre-curing step, moisture may evaporate rapidly, causing blisters-like protrusions on the gloves and impairing their quality. However, the curing step may be skipped. (b) Sometimes the temperature is raised to the final temperature of the curing process without going through this process, but if curing is done in multiple drying ovens and the temperature of the first drying oven is slightly lower, this first drying stage corresponds to the pre-curing process.

[0079] (7) Curing process The curing process is a process of heating and drying at high temperature to finally complete crosslinking and make a cured film for gloves. Usually, heating and drying are carried out at 90°C or higher and 140°C or lower for 10 minutes or longer and 30 minutes or shorter, preferably 15 minutes or longer and 30 minutes or shorter.

[0080] (8) Double dipping The glove manufacturing method described above is the so-called single dipping method. However, the dipping and gelling steps can be performed more than once, which is usually called double dipping. Double dipping is performed when manufacturing thick gloves (thickness over 200 μm and less than 300 μm) and also when manufacturing thin gloves to prevent pinholes from forming. One thing to note about double dipping is that the second dipping step requires a sufficient amount of time for the gelling step to aggregate the XNBR, and the first gelling step requires sufficient time for calcium to precipitate all the way to the membrane surface.

[0081] When evaluating the physical properties of a molded product produced using a dip-forming composition, the molded product is released from the glove mold, and then the temperature and humidity are regulated for at least one day before evaluation.

[0082] 3. Molded body Molded articles (also referred to as "dip-molded articles") produced using the dip-molding composition and the manufacturing method described above have superior stress retention compared to conventional XNBR molded articles, while also being soft. Conventional XNBR molded articles lose their inherent rubber elasticity due to the reduced crosslinking structure of the latex during polymerization, the extensive use of carboxylic acids, and the use of metal crosslinkers such as zinc to bridge the gap between particles. In contrast, the molded articles of this embodiment regain their inherent rubber elasticity, i.e., excellent stress retention and softness, while maintaining other physical properties. Furthermore, the present molded articles increase stress retention through the crosslinking structure of the XNBR itself, intra-particle crosslinking between carboxyl groups in the latex particles and epoxy crosslinkers. Furthermore, by minimizing carboxylic acid residues in the latex particles, minimizing crosslinking with calcium and zinc, and partially complementing inter-particle crosslinking with the epoxy crosslinker, softer molded articles can be produced. Stress retention can also be increased by sulfur vulcanization, which creates a large amount of intra-particle crosslinking in XNBR latex, but this increases the risk of Type IV allergies. Furthermore, the complementation of interparticle crosslinking by carboxylic acid residues in the latex particles and zinc crosslinking reduces the stress retention rate, resulting in a hard molded product. In this sense, the inventors believe that molded products using epoxy crosslinking are the best alternative to sulfur crosslinking among those currently available. The properties of the molded article will be explained below using a glove as an example.

[0083] The physical properties of the glove include tensile strength, modulus, elongation, stress retention, fatigue durability, etc. These physical properties can be measured by the test methods described below.

[0084] <Tensile strength, modulus and elongation> The tensile strength, modulus, and elongation of the dip-molded body were measured according to the method described in ASTM D412. Test specimens were prepared by punching out the dip-molded body using a DieC manufactured by Dumbbell. The test specimens were measured using a ZwickRoell AllroundLine universal testing machine Z-100 at a test speed of 500 mm / min, a chuck distance of 75 mm, and a gauge length of 25 mm. The standard glove properties are considered to be a tensile strength of 14 MPa or more and an elongation rate of 500% or more. Regarding modulus, we focused on the modulus at 100% elongation (100% modulus), the modulus at 300% elongation (300% modulus), and the modulus at 500% elongation (500% modulus), in particular from the perspective of achieving flexibility that does not hinder finger movement when wearing the glove. The moduli of XNBR gloves currently on the market are approximately 3-4 MPa for 100%, approximately 9-12 MPa for 300%, and approximately 20-35 MPa for 500%, which are considerably harder than those of natural rubber, which are approximately 1-1.5 MPa, 3-5 MPa, and 8-12 MPa, respectively. Therefore, the inventors have set the standard of 2 MPa or less for 100% modulus, 4 MPa or less for 300% modulus, and 15 MPa or less for 500% modulus, and believe that achieving these standards will provide sufficient benefits in terms of ease of delicate work involving fingertips.

[0085] FAB (Force at Break) may also be used as an index of tensile strength. In a tensile test of the film forming the molded article, the FAB (EN standard) is preferably 5.5 N or more, more preferably 6.0 N or more, with no particular upper limit. The FAB can be measured, for example, using a testing machine STA-1225 (manufactured by A&D) at a test speed of 500 mm / min and a chuck distance of 75 mm in accordance with the method of the EN455-2:2009 standard.

[0086] <Stress retention rate> The stress retention rate is measured as follows. A test piece is prepared from the dip-molded body (cured film) using DieC manufactured by Dumbbell Co., Ltd. in accordance with ASTM D412, and a gauge line is marked with a distance between the gauge lines of 25 mm. The test specimen was attached to a tensile testing machine with a 90 mm chuck distance and stretched at a rate of 500 mm / min. When the glove was stretched to twice its normal length, the stretching was stopped and the stress at 100% stretch, M0, was measured. The stress change was measured while the specimen was still held in place from the time stretching stopped, and the stress, M6, was measured after 6 minutes. The stress retention was calculated as (M6 / M0) x 100 (%). A higher stress retention indicates that the stress is maintained better after stretching and indicates a higher elastic deformation force that returns to the original shape when the external force is removed. This results in a better glove fit, a tighter cuff, and less wrinkling. The stress retention measured by the above method for conventional sulfur crosslinked XNBR gloves is in the range of 30%. Therefore, if the stress retention of the molding of the present embodiment is 50% or more, it is good as an XNBR glove, and more preferably 60% or more.

[0087] <Fatigue durability> Fatigue durability was measured by preparing a 120mm long JIS K6251 No. 1 dumbbell test piece from a dip-molded product (cured film), fixing the bottom, and immersing it in artificial sweat to a length of 60mm. The top of the test piece was then pulled, and the time until the test piece broke was measured. The test piece was repeatedly stretched and relaxed in the longitudinal direction between a maximum of 195mm and a minimum of 147mm. The stretching (195mm) and relaxation (147mm) were measured by holding the relaxed state for 11 seconds, then stretching to 195mm (163%) in 1.8 seconds, and then returning to 147mm (123%), repeating this cycle (1 cycle: 12.8 seconds). From the viewpoint of practical use as gloves, the fatigue durability is preferably 60 minutes or more.

[0088] More specifically, fatigue durability tests can be performed using a dumbbell-shaped test piece, similar to tensile tests on rubber products, using an apparatus like the one shown in Figure 1. As shown in Figure 1(a), the lower end of the test piece is clamped and immersed in artificial sweat up to 60 mm. The upper end of the test piece is clamped, and a pneumatic piston is used to stretch and contract the test piece vertically from the relaxed state shown in Figure 1(b) to the extended state shown in Figure 1(c) and back to the relaxed state shown in Figure 1(b). This stretching and contraction cycle (Figure 1(b) → Figure 1(c) → Figure 1(b)) is considered one cycle, and the number of cycles and time until failure are measured to evaluate the test piece. If the test piece fails, a photoelectric sensor responds and the device shuts down. [Example]

[0089] 1. Implementation method The present invention will be described in more detail below with reference to examples. The parts by weight of each additive are based on solids content, and for epoxy crosslinker the parts by weight are based on the total weight of the crosslinker. In the present examples, examples will be described in which a cured film or a glove was produced as a molded article that was a cured product of the dip-forming composition.

[0090] (1) Preparation of a synthetic latex composition containing a carboxyl group-containing nitrile rubber elastomer <Synthetic latex composition 1> After the inside of a pressure-resistant autoclave equipped with a stirrer was purged with nitrogen, 69 parts of 1,3-butadiene, 27 parts of acrylonitrile, 4 parts of methacrylic acid (total of 100 parts of the above monomers), 0.4 parts of a chain transfer agent (TDM: t-dodecyl mercaptan), 150 parts of water, 2.5 parts of an anionic emulsifier (SDBS: sodium dodecylbenzenesulfonate), an oxygen scavenger (sodium dithionite), 0.1 parts of a chelating agent EDTA (Chilest 400G: product of Chelest Chemical Co., Ltd.), a particle size modifier (potassium pyrophosphate), 0.005 parts of p-menthane hydroperoxide (PMHP) (NOF Corporation: Permenta H) and 0.02 parts of sodium formaldehyde sulfoxylate (SFS) as redox polymerization initiators, and 0.005 parts of ferrous sulfate were added, and the polymerization temperature was maintained at 25°C while stirring, and the reaction was carried out for 20 hours. After confirming that the polymerization conversion rate was 99%, a pH adjuster and a polymerization terminator were added to terminate the polymerization reaction. Unreacted monomers were removed from the obtained latex composition under reduced pressure, and the pH and concentration of the latex composition were adjusted with an aqueous ammonia solution to a solids concentration of 45% and a pH of 8.3. 0.5 parts by weight (solids equivalent) of an aqueous dispersion of a butylated reaction product of p-cresol and dicyclopentadiene (e.g., Bostex 362 manufactured by AKRON DISPERSIONS) was added as an antioxidant to 100 parts by weight of the latex to obtain a synthetic latex composition.

[0091] <Synthetic latex composition 2> A synthetic latex composition was obtained by producing it under almost the same conditions as synthetic latex composition 1, except that the ingredients were 73.5 parts of 1,3-butadiene, 22 parts of acrylonitrile, and 4.5 parts of methacrylic acid (total of 100 parts of the monomers) and the polymerization temperature was 45°C.

[0092] <Synthetic latex composition 3> After the inside of a pressure-resistant autoclave equipped with a stirrer was purged with nitrogen, 69.5 parts of 1,3-butadiene, 25 parts of acrylonitrile, 5.5 parts of methacrylic acid (a total of 100 parts of the monomers), 0.8 parts of a chain transfer agent (TDM: t-dodecyl mercaptan), 150 parts of water, 2.5 parts of an anionic emulsifier (SDBS: sodium dodecylbenzenesulfonate), an oxygen scavenger (sodium dithionite), 0.1 parts of a chelating agent EDTA (Chilest 400G: a product of Chelest Chemical Co., Ltd.), a particle size modifier (potassium pyrophosphate), 0.005 parts of p-menthane hydroperoxide (PMHP) (manufactured by NOF Corporation; Permenta H) and 0.02 parts of sodium formaldehyde sulfoxylate (SFS) as redox polymerization initiators, and 0.005 parts of ferrous sulfate were added, and the polymerization temperature was maintained at 15°C while stirring, and the reaction was carried out for 20 hours. After confirming that the polymerization conversion rate was 87%, a pH adjuster and a polymerization terminator were added to terminate the polymerization reaction. Unreacted monomers were removed from the obtained latex composition under reduced pressure, and the pH and concentration of the latex composition were adjusted with an aqueous ammonia solution to a solids concentration of 45% and a pH of 8.3. 0.5 parts by weight (solids equivalent) of an aqueous dispersion of a butylated reaction product of p-cresol and dicyclopentadiene (e.g., Bostex 362 manufactured by AKRON DISPERSIONS) was added as an antioxidant to 100 parts by weight of the latex to obtain a synthetic latex composition.

[0093] <Synthetic latex composition 4> A latex composition was obtained by producing under the same conditions as Synthetic Latex Composition 1, except that the composition had the same composition as Synthetic Latex Composition 1, the chain transfer agent was 0.7 parts, and the polymerization conversion rate was 96%.

[0094] <Synthetic latex composition 5> A latex composition was obtained by producing under almost the same conditions as Synthetic Latex Composition 1, except that the composition was the same as Synthetic Latex Composition 1, the chain transfer agent was 0.5 parts, and the polymerization conversion rate was 98%.

[0095] <Synthetic latex composition 6> The latex composition was obtained by manufacturing it under almost the same conditions as synthetic latex composition 1, except that methacrylic acid was 3 parts and 1,3-butadiene was 70 parts.

[0096] <Synthetic latex composition 7> The latex composition was obtained by manufacturing it under almost the same conditions as synthetic latex composition 1, except that methacrylic acid was 6.5 parts and 1,3-butadiene was 66.5 parts.

[0097] <Synthetic latex composition 8> The latex composition was obtained by manufacturing it under almost the same conditions as synthetic latex composition 1, except that the amount of acrylonitrile was 22 parts and 1,3-butadiene was 74 parts.

[0098] <Synthetic latex composition 9> The latex composition was obtained by manufacturing it under almost the same conditions as synthetic latex composition 1, except that the amount of acrylonitrile was 25 parts and 1,3-butadiene was 71 parts.

[0099] The properties of the elastomers used in this experiment are shown in Table 1 below.

[0100]

Table 1

[0101] The properties of the elastomers used in this experiment were measured as follows. <MEK swelling ratio and MEK insoluble content> The MEK swelling ratio and MEK insoluble content were measured as follows. Approximately 0.2 g of a dried synthetic latex composition sample was weighed accurately, and the weight of the dried synthetic latex composition before immersion (W1) was measured. The dried sample was placed in an 80-mesh metal basket, and the basket was immersed in 80 mL of MEK in a 100 mL beaker. The beaker was covered with Parafilm and allowed to stand at room temperature for 24 hours. The mesh basket was then removed from the beaker and weighed. The weight of the basket was subtracted to obtain the swollen weight of the synthetic latex composition (W2). The sample was then hung in a draft chamber and dried for 1 hour. After drying under reduced pressure at 105°C for 1 hour, the weight was measured, and the weight of the basket was subtracted to obtain the weight of the dried synthetic latex composition after immersion (W3). The MEK swelling ratio is calculated using the following formula. MEK swelling ratio (unit: times) = (W2(g) / W3(g)) The MEK insoluble content is calculated using the following formula: MEK insoluble amount (unit: weight %) = (W3(g) / W1(g))×100 The dried synthetic latex composition sample was prepared as follows: After stirring the latex in a 500 mL bottle at 500 rpm for 30 minutes, 14 g of the latex was weighed into a 180 × 115 mm stainless steel tray and dried at 23°C ± 2°C and 50 ± 10% RH for 5 days to form a cast film, which was then cut into 5 mm squares to prepare dried synthetic latex composition samples.

[0102] (2) Crosslinking agent <Epoxy crosslinking agent> The epoxy crosslinking agent used in the examples was "Denacol EX-321" (trade name) manufactured by Nagase ChemteX Corporation, and its physical properties are as follows: Epoxy equivalent: 140g / eq. Average number of epoxy groups: 2.7 MIBK / water distribution ratio: 87% Active ingredient content: 27% The epoxy equivalent weight is a catalog value, and the average number of epoxy groups is an analytical value. The method for measuring the MIBK / water partition coefficient is the method described in the detailed description of the invention. In the examples in which an epoxy crosslinking agent was used, the agent was mixed with an equal amount of diethylene glycol before being added.

[0103] <Metal crosslinking agent> Zinc oxide was used as the metal cross-linking agent. The zinc oxide used in the examples was "CZnO-50" (trade name) manufactured by Farben Technique (M).

[0104] (3) Manufacturing and evaluation of molded products <Production of molded products (gloves) for Experiments 1 to 3 and 5> A cleaned and heated ceramic glove mold was dipped in 14% by weight calcium nitrate, 1.5 weight % calcium stearate mixed aqueous solution, and then dried for 3 minutes under conditions where the surface temperature of the mold was 70°C to allow the coagulant to adhere to the mold. Next, based on Table 2, an epoxy crosslinking agent and zinc oxide were added as crosslinking agents to each of the above synthetic latex compositions in Experiments 1 to 3, and a sulfur crosslinking agent and zinc oxide were added in Experiment 5. In addition, in all of Experiments 1 to 3 and 5, titanium oxide was added as a pigment, and the mixture was stirred uniformly, and the pH was adjusted to 10.0 with KOH. Next, a glove mold was immersed in the obtained dip-forming composition for 30 seconds or more and 60 seconds or less, then removed and heated at 80°C for 1 minute to gel the film on the glove mold. The glove mold with the film laminated thereon was immersed in warm water at 60°C or more and 70°C or less for 3 minutes for leaching treatment, then left in a test oven and heated at 70°C for 5 minutes, and then, without removing it from the oven, was subjected to heat treatment at 130°C for 20 minutes. After cooling the glove mold surface to 40°C, the glove mold was immersed for 40 seconds in a chlorinated bath containing sodium hypochlorite and hydrochloric acid adjusted to an active chlorine concentration of 900 ppm to 1000 ppm. The glove mold was then rinsed with water, washed with a 0.4% aqueous sodium sulfate solution, and then rinsed again with water. The mold was then dried at 100°C for 5 minutes. After the mold was thoroughly cooled to room temperature, the film was removed from the mold. The film thus prepared was conditioned at 25°C and 55% RH for 24 hours and then evaluated for various properties, as described below. The results are shown in Table 2. In this specification, PMHP in Table 2 stands for p-menthane hydroperoxide, and SFS stands for sodium formaldehyde sulfoxylate.

[0105] <Production of molded body (film) in Experiment 4> The washed and heated ceramic plate was immersed in 20% by weight of calcium nitrate, 1.0 weight % sodium stearate mixed solution, and then heated and dried until the surface temperature of the immersed plate reached 60°C to allow the coagulant to adhere to it. Next, varying amounts of epoxy crosslinker and / or zinc oxide were added as crosslinkers to the latexes in Table 1, and the mixture was stirred to homogenize. In all experiments, the pH was adjusted to 10.0 with KOH. Next, an immersion plate was immersed in the obtained dip-molding composition for 10 to 15 seconds, then removed and heated for 2 minutes at 50°C to gel the film on the immersion plate. The immersion plate with the film laminated thereon was immersed in warm water at 50°C for 2 minutes for leaching treatment, and then heated in a test oven at 70°C for 5 minutes and then heat-treated at 130°C for 30 minutes. After cooling sufficiently at room temperature, the film was removed from the immersion plate. The film thus prepared was left at room temperature for one week, and then conditioned at a humidity of 50 to 60% RH for 12 hours or more, and the properties were evaluated.

[0106] <Evaluation of molded products> <Stress retention rate> The stress retention rate was measured according to the method described above.

[0107] <Tensile strength, modulus and elongation> The tensile strength, modulus and elongation were measured according to the methods described above.

[0108] <Fatigue durability> The test piece was 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, and adjusted to pH 4.7 with an aqueous sodium hydroxide solution), and the fatigue durability was evaluated according to the method described above.

[0109] <Experiment A> The gloves used in Experiments 1 to 3 and 5 were all made by the method described above in <Manufacturing of molded bodies (gloves) for Experiments 1 to 3 and 5>. In experiments 1 to 3, the MEK insoluble content was 68 weight% , 71 weight% The synthetic latex compositions 1 and 2 are used, and an epoxy crosslinking agent is added to the latex composition. Weight part , 2 Weight part and zinc oxide 0.3 Weight part , 0.5 Weight part In contrast, in Experiment 4, the MEK insoluble content was 30 weight % of synthetic latex composition 3, to which 1% of epoxy crosslinking agent was added. Weight part , zinc oxide 0.5 Weight part In Experiment 5, the MEK insoluble content was 68%. weight % synthetic latex composition 1, which is sulfur vulcanized and zinc crosslinked. The measurement results for the gloves are shown in Table 2.

[0110] [Table 2]

[0111] The results in Table 2 reveal the following: The gloves of Experiments 1 to 3 have a stress retention rate of over 60% and a 500% modulus of 6 to 7 MPa, which is soft and shows high rubber elasticity. They also have good elongation, tensile strength and fatigue durability. The high stress retention rate is due to the high MEK insoluble content of the synthetic latex composition and the crosslinking of the epoxy crosslinking agent. Next, the reason why the gloves are soft and stretchy is because the epoxy crosslinker does not make the gloves hard or lose their stretchability. Also, the tensile strength is maintained by the zinc crosslinking, and the fatigue durability is provided by the epoxy crosslinker. The glove in Experiment 4 has a significantly lower stress retention rate compared to Experiments 1 to 3, and the 500% modulus is also hard at 12.49 MPa, which is close to the physical properties of conventional XNBR gloves. This is because the MEK insoluble content of the synthetic latex composition is 30 weight %. The gloves in Experiment 5 are made of synthetic latex composition with high MEK insoluble content, crosslinked with conventional sulfur vulcanization and zinc oxide, but the stress retention rate in particular is about 10% or more lower than Experiments 1 to 3, and fatigue durability is also worse. This is the result of changing epoxy crosslinking to sulfur crosslinking.

[0112] <Experiment B> The most important technical feature of the present invention is that the MEK insoluble content is 60 to 80 weight %. In this experiment, the composition of the latex and the addition of the crosslinking agent were the same as in Experiment 1, but the amount of the chain transfer agent and the polymerization method were changed, and the synthesized latex composition had an MEK insoluble content of 68%. weight %, whereas in Experiment 6 the MEK insoluble content was 38.5%. weight %, 59.1 in Experiment 7 weight % synthetic latex composition was used to examine how the film properties change depending on the MEK insoluble content. In addition, the MEK insoluble content is 80 weight It was difficult to create a film for anything over %.

[0113] [Table 3]

[0114] As shown in Table 3, the MEK insoluble content in Experiment 6 was 38.5 weight The stress retention rate of the molded body at 47. 8% In contrast, when the MEK insoluble content was 59.1 wt% in Experiment 7, the stress retention rate was 58.5%, and when the MEK insoluble content was 68.0 wt% in Experiment 1, the stress retention rate was 61.6%, which is approximately 60%. weight %, the stress retention rate improved significantly.

[0115] <Experiment C> The second important technical feature of the present invention is that the amount of carboxylic acid is 3.5% by weight to 6% by weight. In Experiment 1, synthetic latex composition 1 containing 4.0% by weight of methacrylic acid was used, and by subjecting it to epoxy cross-linking and zinc cross-linking, a soft glove with high stress retention was produced. In this experiment, under almost the same conditions as in Experiment 1, synthetic latex composition 6 containing 3.0% by weight of methacrylic acid and synthetic latex composition 7 containing 6.5% by weight of methacrylic acid were used to verify how the film properties change depending on the amount of methacrylic acid.

[0116] [Table 4]

[0117] Table 4 shows that in Experiment 8 (3 wt.% methacrylic acid), the 500% modulus, elongation, and stress retention were good, but the tensile strength and fatigue durability were poor. In contrast, in Experiment 9 (6.5 wt.% methacrylic acid), the 500% modulus, elongation, and stress retention were poor, but the tensile strength was high. This suggests that a methacrylic acid content of 3.5 wt.% to 6 wt.%, and more preferably 3.5 wt.% to 5 wt.%, is preferable. Furthermore, increasing the amount of methacrylic acid leads to a deterioration in the 500% modulus and elongation, and a lower amount is better for maintaining softness and elongation. Carboxylic acid is an important element in XNBR, and consideration must be given to the amount of buried carboxylic acid for epoxy crosslinking within particles, sufficient zinc crosslinking between particles, and avoiding excessive crosslinking with calcium.

[0118] <Experiment D> In this embodiment, the range of acrylonitrile content of XNBR is set to 20-30% by weight. Usually, 25-30% by weight is called medium nitrile, and the blending amount of acrylonitrile in XNBR gloves is 27 weight % is the most common. In experiment 1, acrylonitrile was 27 weight The figure is %. Acrylonitrile is an important element in XNBR gloves because it maintains tensile strength and increases oil resistance due to the polarity of the nitrile group (-C=N). Therefore, medium nitrile has been used in XNBR gloves. On the other hand, 20-24 weight Low nitrile content below 27%, 25% and 22% by weight weakens tensile strength and oil resistance, so there are almost no XNBR gloves that are currently manufactured with this. However, since the glove becomes softer as the amount of acrylonitrile is reduced, in this experiment we tried to make the latex softer by using acrylonitrile amounts of 27%, 25%, and 22% by weight. Furthermore, in this experiment, the amount of epoxy crosslinking agent and the amount of zinc oxide were changed, and the performance of the resulting molded products was also evaluated.

[0119] [Table 5-1]

[0120] [Table 5-2]

[0121] [Table 5-3]

[0122] First, synthetic latex compositions 1, 8, and 9 containing 27%, 25%, and 22% by weight of acrylonitrile were prepared. 9 Looking at the overall picture, all of the gloves are sufficiently soft compared to conventional XNBR gloves. In particular, the gloves with 22% acrylonitrile by weight are the softest. The stress retention rate is also good, at around 60%. Next, 0.3 wt.% epoxy crosslinker alone was used. Department , 0.5 wt. Department , 1.0 weight Department Looking at the examples where the amount of epoxy crosslinker is increased, the stress retention rate increases. On the other hand, the flexibility and elongation decrease. Furthermore, the combination of epoxy crosslinker and zinc oxide maintains good stress retention. Although flexibility is also significantly better than conventional products, increasing the amount of zinc tends to decrease flexibility elongation. Considering this, adding 0.2 to 0.7 parts by weight of zinc oxide is considered appropriate. While adding more than 1.0 part by weight of epoxy crosslinker is considered appropriate, stress retention is expected to exceed 70%, but flexibility elongation will decrease. In this experiment, the pH of the dip-forming composition was set to 10.0. If the pH exceeds 10.5, the number of carboxyl groups oriented outward at the particle interface increases, weakening the epoxy crosslinking, which is primarily intraparticle crosslinking. On the other hand, if the pH is set below 9.5, the amount of buried carboxylic acid crosslinking with the epoxy increases, making the film softer, but also making it sticky and difficult to form. In addition, the epoxy crosslinker EX-321 used in all experiments had an equivalent weight of 140 g / eq. The epoxy crosslinking agent equivalent weight is preferably 100 to 200 g / eq, but those with a larger equivalent weight may be By increasing the amount of , it is possible to obtain results similar to those of this experiment.

[0123] <Experiment E> The intrinsic properties (physical properties of films crosslinked only with calcium derived from the coagulant without a crosslinking agent) of synthetic latex compositions 1, 8, and 9 are shown in Table 6.

[0124] [Table 6]

[0125] As described above, according to the present invention, it is possible to provide a dip-molded article using a carboxyl group-containing nitrile rubber elastomer, which has excellent stress retention and flexibility similar to those of natural rubber, a dip-molding composition for producing the same, and a production method thereof.

Claims

1. A dip-molding composition comprising at least a carboxyl group-containing nitrile rubber elastomer, an epoxy crosslinking agent containing an epoxy compound having three or more glycidyl ether groups in one molecule and having a mother skeleton containing an alicyclic, aliphatic or aromatic hydrocarbon, and a pH adjuster, the elastomer contains 50% by weight or more and 75% by weight or less of structural units derived from conjugated diene monomers, 20% by weight or more and 30% by weight or less of structural units derived from ethylenically unsaturated nitrile monomers, and 3.5% by weight or more and 6% by weight or less of structural units derived from ethylenically unsaturated carboxylic acid monomers, The MEK insoluble content of the elastomer is 60% by weight or more and 80% by weight or less, and The dip-molding composition has an MIBK / water distribution ratio of the epoxy crosslinking agent of 50% or more, as measured by the following method. MIBK / water partition ratio measurement method: 5.0 g of water, 5.0 g of methyl isobutyl ketone (MIBK), and 0.5 g of epoxy crosslinker were weighed out in a test tube, and the mixture was stirred at 23°C ± 2°C for 3 minutes. After mixing, the resulting mixture was 1.0 x 10 ３ The mixture is centrifuged at 1000 G for 10 minutes to separate the aqueous layer and the MIBK layer. The MIBK layer is separated and weighed, and the MIBK / water distribution coefficient is calculated using the following formula. MIBK / water distribution rate (%)=(weight of MIBK layer after distribution (g)−weight of MIBK before distribution (g)) / addition weight of crosslinker (g)×100 The above measurement was carried out three times, and the average value was taken as the MIBK / water partition coefficient.

2. The dip-forming composition according to claim 1, wherein the elastomer contains structural units derived from ethylenically unsaturated carboxylic acid monomers in an amount of 3.5% by weight or more and 5.0% by weight or less.

3. 3. The dip-molding composition according to claim 1, wherein the amount of the epoxy crosslinking agent added is 0.3 parts by weight or more and 2.5 parts by weight or less based on 100 parts by weight of the elastomer.

4. The dip-forming composition according to any one of claims 1 to 3, wherein the pH is adjusted to 9.5 or more and 10.5 or less with the pH adjuster.

5. The dip-forming composition according to any one of claims 1 to 4, further comprising zinc oxide as a crosslinking agent.

6. The dip-forming composition according to claim 5 , wherein the amount of the zinc oxide added is 0.2 parts by weight or more and 0.6 parts by weight or less based on 100 parts by weight of the elastomer.

7. The dip-forming composition according to any one of claims 1 to 6, wherein the MEK swelling ratio is 5 to 10 times.

8. A molded article which is a cured product of the dip-molding composition according to any one of claims 1 to 7.

9. The molded article according to claim 8, which has a stress retention rate of 50% or more as measured by the following method. Stress retention measurement method: A test specimen is prepared in accordance with ASTM D412, marked with a gauge line distance of 25 mm, and pulled under conditions of a chuck distance of 90 mm and a pulling speed of 500 mm / min. When the test specimen is elongated to twice its original length, the pulling is stopped and the stress M0 is measured. The test specimen is further held and, after 6 minutes, the stress M6 is measured and the stress retention is calculated using the following formula. Stress retention rate (%) = (M6 / M0) x 100

10. The molded article according to claim 8 or 9, which is a glove.

11. (1) a coagulant application step of applying a coagulant to a glove mold; (2) a maturation step of preparing the dip-forming composition according to any one of claims 1 to 7 and stirring the mixture; (3) a dipping step of immersing a glove mold in a dip-forming composition; (4) a gelling step in which the film formed on the glove mold is gelled to form a cured film precursor; (5) a leaching step for removing impurities from the cured film precursor formed on the glove mold; (6) Beading process to make a roll at the cuff of the glove. (7) a curing step of heating and drying at a temperature required for the crosslinking reaction; The method for producing a dip-formed article includes carrying out the steps (3) to (7) in the above order.

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