Nitrile rubber composition and rubber crosslinked matter

Abstract

To provide a nitrile rubber composition and a rubber crosslinked matter which have excellent ozone resistance and whose compression set is inhibited so as to be applicable to a wide range of uses.SOLUTION: A nitrile rubber composition according to the present invention includes 3-40 pts.wt. of unsaturated acid metal salt and 0.5-2.5 pts.wt. of a silane coupling agent with respect to 100 pts.wt. of nitrile rubber containing vinyl chloride resin. A rubber crosslinked matter according to the present invention is made by crosslinking with the nitrile rubber composition according to the present invention.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a nitrile rubber composition and a rubber crosslinked product.

Background Art

[0002] Since nitrile rubber is excellent in oil resistance and has relatively good abrasion resistance and the like, a rubber crosslinked product obtained by crosslinking nitrile rubber (composition) is used as a seal member, a vibration-proof member, etc. used in pneumatic equipment, instruments and containers related to food hygiene, automobiles, water supply, and various other industries.

[0003] In such nitrile rubber, various improvements have been made for the purpose of improving its performance and enhancing its usefulness. As an example, Patent Document 1 (International Publication No. 2012 / 105645) describes blending vinyl chloride resin with nitrile rubber.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Nitrile rubber containing a vinyl chloride resin as exemplified in Patent Document 1 has improved ozone resistance, which is resistance to the progress of deterioration due to ozone and the occurrence of cracks. On the other hand, when the content of the vinyl chloride resin increases, the compression set, which does not completely return to the state before deformation even after being released after the deformed state is maintained, tends to increase (that is, the compression set rate increases). As a result, for example, the sealing performance and the like deteriorate. Therefore, a rubber crosslinked product obtained by crosslinking a nitrile rubber (composition) containing a certain amount of vinyl chloride resin is limited to applications such as the exterior parts of a camera, where ozone resistance is required while compression set is less likely to be a problem. For these reasons, there has been a demand for a nitrile rubber, that is, its composition or crosslinked product, which has both satisfactory ozone resistance and improved compression set and has a wider range of applications including food hygiene applications and the like.

Means for Solving the Problems

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a nitrile rubber composition and a rubber crosslinked product that have excellent ozone resistance, suppressed compression set, and are applicable to a wide range of uses.

[0007] The present invention solves the above problems by means as described below as one embodiment.

[0008] The nitrile rubber composition according to the present invention is characterized by containing 3 to 40 parts by weight of an unsaturated acid metal salt and 0.5 to 2.5 parts by weight of a silane coupling agent with respect to 100 parts by weight of a nitrile rubber containing a vinyl chloride resin.

[0009] In the nitrile rubber composition according to the present invention, the content ratio of the vinyl chloride resin is preferably 21 to 35 parts by weight with respect to 100 parts by weight of the nitrile rubber. In the nitrile rubber composition according to the present invention, the nitrile rubber is preferably acrylonitrile-butadiene rubber.

[0010] Further, the rubber crosslinked product according to the present invention is characterized in that the nitrile rubber composition according to the present invention is crosslinked. Note that the "rubber crosslinked product" as used in this specification and the like includes rubber products obtained by crosslinking and molding a rubber composition.

[0011] The nitrile rubber composition according to the present invention or the rubber crosslinked product according to the present invention has improved ozone resistance and compression set, and can be applied to a wide range of uses. In particular, the nitrile rubber composition according to the present invention can have a certain degree of moldability and handleability even without containing a plasticizer such as phthalic acid ester which is a substance subject to regulations related to food hygiene, and the rubber crosslinked product according to the present invention can also be applied to food hygiene uses such as food container packaging, toys, and other utensils related to food hygiene.

Effects of the Invention

[0012] The nitrile rubber composition according to the present invention or the rubber crosslinked product obtained by crosslinking it has excellent ozone resistance, and the compression set is suppressed, and it can be applied to a wide range of uses.

Modes for Carrying Out the Invention

[0013] The nitrile rubber composition according to the present invention contains a nitrile rubber containing a vinyl chloride resin, other unsaturated acid metal salts and a silane coupling agent, and further optional components such as a vulcanizing agent. "Nitrile rubber containing a vinyl chloride resin" can be paraphrased as "nitrile rubber blended with a vinyl chloride resin" from the viewpoint of the production method of the nitrile rubber composition. This is a notation assuming that in the present invention, commercially available products as nitrile rubbers containing (blended with) a vinyl chloride resin may be used in practice. On the other hand, it is naturally allowed that the nitrile rubber and the vinyl chloride resin are used separately. Therefore, the nitrile rubber composition according to the present invention may also be paraphrased as one containing a nitrile rubber, a vinyl chloride resin, an unsaturated acid metal salt and a silane coupling agent, and further optional components such as a vulcanizing agent.

[0014] The nitrile rubber composition is a composition for producing a rubber crosslinked product. Usually, a crosslinking agent such as a vulcanizing agent for sulfur crosslinking (vulcanization) or a peroxide for peroxide crosslinking (PO crosslinking) is compounded until the final stage of use, but it is an optional component as a constituent requirement for achieving the object of the present invention. Therefore, when the present invention is applied to the rubber industry, which is the technical field to which it belongs, the nitrile rubber composition according to the present invention can apply to both the masterbatch (A kneading) before the crosslinking agent is kneaded and the final batch (B kneading) after the crosslinking agent is kneaded. Hereinafter, the embodiments for carrying out the present invention will be specifically described.

[0015] [Nitrile Rubber Composition and Rubber Crosslinked Product] The nitrile rubber composition according to the present embodiment contains 3 to 40 parts by weight of an unsaturated acid metal salt and 0.5 to 2.5 parts by weight of a silane coupling agent with respect to 100 parts by weight of the nitrile rubber containing a vinyl chloride resin. According to the combination and content ratio of these components, both ozone resistance and improvement of compression set are satisfied, and it can be applied to a wide range of uses.

[0016] Nitrile rubber is, firstly, a copolymer having at least 1,3-butadiene and acrylonitrile as monomer components. This includes, for example, rubbers called acrylonitrile-butadiene rubber and the like, abbreviated as NBR. Secondly, in addition, it may optionally contain one or more monomer components. This includes, for example, rubbers called carboxylated nitrile rubber and the like, abbreviated as XNBR, in which carboxylic acids such as methacrylic acid and acrylic acid are introduced as the third monomer, and rubbers called acrylonitrile-butadiene-isoprene rubber and the like, abbreviated as NBIR, in which isoprene is introduced as the third monomer (a part of 1,3-butadiene is replaced by isoprene). That is, the "nitrile rubber" referred to in this specification and the like includes NBR, XNBR, and NBIR. Among these, a single type may be applied, or a combination of multiple types may be applied, but NBR is most preferably applied. The content ratios of 1,3-butadiene and acrylonitrile, as well as the content ratio between the two, are not limited. For example, the so-called medium nitrile with the content of acrylonitrile units (i.e., bound acrylonitrile) being 25% by weight or more and less than 31% by weight of the total weight of the nitrile rubber, and the so-called medium-high nitrile with 31% by weight or more and less than 36% by weight are preferred, and 30 - 35% by weight spanning these medium to medium-high nitriles is more preferred.

[0017] Vinyl chloride resin is, firstly, a polymer or copolymer in which the main constituent monomer constituting the resin is vinyl chloride (monomer). By main constituent, it means that the content of vinyl chloride units (i.e., bound vinyl chloride) is 50 - 100% by weight of the total weight of the vinyl chloride resin, more preferably 60 - 100% by weight, and even more preferably 70 - 100% by weight. This naturally includes polyvinyl chloride abbreviated as PVC. Secondly, the vinyl chloride resin may be subjected to chemical or physical treatment, which includes, for example, crosslinked PVC and partially crosslinked PVC. Note that the degree of polymerization and molecular weight of vinyl chloride and other monomer components are not limited. The vinyl chloride resin may be applied alone or in combination of multiple types.

[0018] Here, there are commercially available products as nitrile rubbers containing vinyl chloride resins. As described above, the "nitrile rubber containing vinyl chloride resin" according to this embodiment means allowing the use of these commercially available products. Among these commercially available products, there are those obtained by adding additives such as stabilizers to vinyl chloride resins subjected to suspension polymerization or emulsion polymerization, etc., and then mixing them with nitrile rubbers, or polymer alloys in which some chemical or physical changes have occurred between vinyl chloride resins and nitrile rubbers, etc., and the use of these is also allowed. On the other hand, the "nitrile rubber containing vinyl chloride resin" according to this embodiment essentially means containing vinyl chloride resin and nitrile rubber in the nitrile rubber composition according to this embodiment. Therefore, it is of course allowed that nitrile rubber and vinyl chloride resin are used separately, for example, simply blending a commercially available product of nitrile rubber and a commercially available product of vinyl chloride resin, and being applied as the "nitrile rubber containing vinyl chloride resin". Also, for example, a commercially available product of nitrile rubber containing vinyl chloride resin may be used in combination with a commercially available product of a single nitrile rubber and / or a commercially available product of a single vinyl chloride resin.

[0019] The content of such vinyl chloride resin is preferably 21 to 35 parts by weight, more preferably 21 to 30 parts by weight, more preferably 21 to 27 parts by weight, more preferably 21 to 25 parts by weight, more preferably 22 to 25 parts by weight, more preferably 22 to 24 parts by weight, and even more preferably 22 to 23 parts by weight with respect to 100 parts by weight of nitrile rubber. The vinyl chloride resin particularly contributes to the improvement of ozone resistance together with a silane coupling agent. However, if its content is too small, the effect cannot be obtained sufficiently and the ozone resistance tends to decrease. Also, if the content of the vinyl chloride resin is too large, the compression set rate tends to increase.

[0020] Examples of nitrile rubbers applicable to this embodiment include, for example, Nipol DN201 (Nipol is a registered trademark, the same applies hereinafter), Nipol 1042, Nipol 1052J, Nipol DN202, Nipol DN212, Nipol DN219, Nipol DN3335, Nipol DN3350, Nipol DN3380, Nipol DN206, Nipol DN207, Nipol DN211, Nipol DN221, Nipol DN223, Nipol DN1032L, Nipol DN1042AL, Nipol DN1201, Nipol DN1201L (all manufactured by Zeon Corporation, Japan), and the like. In addition, examples of nitrile rubbers applicable to this embodiment also include, for example, NBR N238H, NBR N232SH, NBR N237H, NBR N236H, NBR N230S, NBR N232S, NBR N237, NBR N233, NBR N230SL, NBR N231L, NBR N230SV, NBR N239SV, NBR N530, NBR T496, NBR N210S, NBR N280 (all manufactured by ENEOS MATERIALS, Inc.), and the like.

[0021] Furthermore, examples of nitrile rubbers containing vinyl chloride resin applicable to this embodiment include, for example, Nipol 1203W, Nipol DN502W, Nipol DN508SCR (all manufactured by Zeon Corporation, Japan), and the like. In addition, examples of nitrile rubbers containing vinyl chloride resin applicable to this embodiment also include, for example, JSR NV60 (JSR is a registered trademark, the same applies hereinafter), JSR NV60, JSR NV72, JSR NV73, JSR NV74, JSR NV75, JSR NV76 (all manufactured by JSR Corporation), and the like.

[0022] In addition, the nitrile rubber composition may additionally contain one or more rubbers other than nitrile rubber as long as the content of nitrile rubber is not exceeded. Examples of such rubbers include natural rubber (NR), fluororubber (FKM), hydrogenated nitrile rubber (HNBR), isoprene rubber (IR), styrene rubber (SBR), butadiene rubber (BR), butyl rubber (IIR), chloroprene rubber (CR), ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), and other silicone rubbers (SI) such as vinylmethyl silicone rubber (VMQ) and fluorosilicone rubber (FVMQ). Hydrogenated nitrile rubber (HNBR) is obtained by hydrogenating (adding hydrogen to) all or part of the C=C bonds of 1,3-butadiene polymerized with nitrile rubber, and generally has a higher tensile strength than ordinary nitrile rubber. On the other hand, the nitrile rubber composition according to this embodiment or the rubber crosslinked product thereof having a tensile strength equivalent to that of HNBR is also one of the features, and a rubber having a certain durability can be provided at a lower cost.

[0023] Next, the unsaturated acid metal salt is a monomer of the metal salt of an unsaturated acid, and particularly contributes to improving the crosslink density of the rubber together with the silane coupling agent and improving the compression set. Further, according to the comparative examples in the examples described later, those not containing the unsaturated acid metal salt had insufficient ozone resistance, so it is considered that it also has an effect on ozone resistance together with the silane coupling agent. As the unsaturated acid metal salt, metal salts of unsaturated carboxylic acids such as acrylic acid and methacrylic acid are suitable, and one kind alone may be applied, or a plurality of kinds may be combined and applied. Also, among commercially available products, there are aqueous solutions, powders, etc., and any of them can be used.

[0024] Examples of the metal unsaturated acid salts applicable to this embodiment include ZA30 (zinc acrylate), MA35 (magnesium acrylate), CA25 (calcium acrylate), PA (potassium acrylate), ZDA-100 (zinc acrylate), ZDA-90 (zinc acrylate), S-MA (sodium methacrylate), P-MA (potassium methacrylate), M-CP (zinc methacrylate), R-20S (zinc methacrylate), R-MMA2 (magnesium methacrylate) (all manufactured by Asada Chemical Industry Co., Ltd. The names in parentheses are the substance names), and the like. In addition, other examples of the metal unsaturated acid salts applicable to this embodiment include, for example, Sun Ester SK-30 (zinc methacrylate), Sun Ester SK-13 (magnesium methacrylate) (both manufactured by Sanshin Chemical Industry Co., Ltd. The names in parentheses are the substance names), and the like.

[0025] The content of such a metal unsaturated acid salt is preferably 3 to 40 parts by weight, more preferably 3 to 35 parts by weight, more preferably 3 to 30 parts by weight, more preferably 3 to 25 parts by weight, more preferably 3 to 20 parts by weight, more preferably 3 to 15 parts by weight, more preferably 3 to 10 parts by weight, and still more preferably 3 to 5 parts by weight, based on 100 parts by weight of the nitrile rubber containing vinyl chloride resin. The parts by weight of the nitrile rubber containing vinyl chloride resin referred to here is the combined parts by weight of all the vinyl chloride resins and all the nitrile rubbers contained in the nitrile rubber composition, and this is taken as 100 parts by weight.

[0026] Next, the silane coupling agent is an organosilicon compound having two types of functional groups with different reactivities in one molecule. As an example, the silane coupling agent includes those having a structure with an organic functional group capable of reacting with and interacting with an organic substance (for example, chemical bonding with an organic substance) and a hydrolyzable silyl group. Examples of the organic functional group include a vinyl group, a vinyl group-containing alkyl group, an epoxy group, an epoxy group-containing alkyl group, a methacryl group, a methacryl group-containing alkyl group, an acrylic group, an acrylic group-containing alkyl group, an amino group, an amino group-containing alkyl group, a mercapto group, a mercapto group-containing alkyl group, and the like. The hydrolyzable silyl group is a silyl group having at least one of a monovalent hydrolyzable atom directly bonded to a silicon atom (an atom that generates a silanol group by reacting with water) and a monovalent hydrolyzable group directly bonded to the silicon atom (a group that generates a silanol group by reacting with water). Examples of the silane coupling agent according to this example include vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, and the like.

[0027] In addition, as another example, a silane coupling agent having a structure with two hydrolyzable silyl groups via a polysulfide-containing hydrocarbon group (for example, a polysulfide-containing alkylene group) can be mentioned. The two hydrolyzable silyl groups may have the same structure or different structures. Examples of the silane coupling agent according to this example include bis(3-triethoxysilylpropyl) disulfide (abbreviation: TESPD), bis(3-triethoxysilylpropyl) tetrasulfide (abbreviation: TESPT), and the like.

[0028] The silane coupling agent strengthens crosslinking together with the vinyl chloride resin and contributes to the improvement of ozone resistance. Furthermore, together with the metal salt of an unsaturated acid, it improves the crosslinking density and improves the compression set. The silane coupling agent may be applied alone or in combination of two or more kinds.

[0029] The content of such a silane coupling agent is preferably 0.5 to 2.5 parts by weight, more preferably 0.5 to 2.0 parts by weight, more preferably 0.5 to 1.5 parts by weight, more preferably 0.5 to 1.0 parts by weight, more preferably 0.5 to 0.9 parts by weight, and still more preferably 0.5 to 0.8 parts by weight, based on 100 parts by weight of the nitrile rubber containing the vinyl chloride resin. Here, the parts by weight of the nitrile rubber containing the vinyl chloride resin is the total parts by weight of all the vinyl chloride resins and all the nitrile rubbers contained in the nitrile rubber composition, and this is taken as 100 parts by weight.

[0030] In addition, the nitrile rubber composition according to the present embodiment may contain optional components usually contained in rubber compositions other than the nitrile rubber, vinyl chloride resin, metal salt of unsaturated acid, and silane coupling agent, which are constituent elements. Examples of such optional components include vulcanizing agents, vulcanization accelerators or vulcanization aids, vulcanization retarders, peroxides, reinforcing agents or fillers, processing aids, softening agents, anti-aging agents or antioxidants, and the like. The classification names and classification methods of each component (substance) vary in distribution and the like, and what is shown here is just an example.

[0031] Examples of vulcanizing agents for sulfur crosslinking include, for example, powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, etc., and also sulfur compounds such as sulfur chloride (e.g., sulfur monochloride, sulfur dichloride, etc.), morpholine disulfide, alkylphenol disulfide, etc.

[0032] Examples of peroxides for PO crosslinking include dialkyl peroxides such as dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane, 1,4(1,3)-bis[(t-butylperoxy)isopropyl]benzene, 2,5-dimethyl-2,5-bis(t-butylperoxy)-hexane, and other hydroperoxides, peroxy esters, diacyl peroxides, etc.

[0033] Examples of vulcanization accelerators or vulcanization aids that can be used together with the vulcanizing agent include sulfenamide-based ones such as N-cyclohexyl-2-benzothiazylsulfenamide (CBS), thiuram-based ones such as tetramethylthiuram disulfide (TMTD), and other organic agents such as thiazole-based, dithiocarbamate-based, guanidine-based ones, as well as inorganic agents such as zinc oxide (zinc white). Also, a vulcanization retarder for scorch prevention may be blended together with these. Note that some of these substances are also those to be blended during PO crosslinking. For example, zinc oxide (zinc white) is one of them, and an effect of improving heat resistance can be expected.

[0034] Examples of reinforcing agents or fillers include carbon black, calcium oxide, magnesium oxide, calcium silicate, calcium carbonate, magnesium carbonate, silica, clay, etc. By blending these, the strength of the rubber can be improved. Among these, carbon black is particularly suitable for the nitrile rubber composition according to this embodiment and can more stably suppress the compression set. Also, carbon black may be blended as a black coloring agent.

[0035] Examples of processing aids include stearic acid, metal stearates such as zinc stearate, waxes, paraffins, etc. By incorporating these, appropriate flexibility can be imparted to rubber and resin. Further, examples of softening agents include oils such as paraffinic oil and naphthenic oil. By incorporating these, the viscosity of the nitrile rubber composition can be reduced. These processing aids or softening agents facilitate molding and improve the release property from molding members such as rolls, thereby improving the moldability and handleability of the nitrile rubber composition.

[0036] Furthermore, similar to processing aids, etc., it is not prohibited to contain a plasticizer that appropriately imparts flexibility to rubber and resin. However, as plasticizers for rubber, phthalic acid esters such as bis(2-ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), and adipic acid esters such as bis(2-ethylhexyl) adipate (DEHA), diisononyl adipate (DINA), diisodecyl adipate (DIDA) are included, and they also include substances subject to regulations related to food hygiene. In this regard, the nitrile rubber composition according to the present embodiment has predetermined viscosity stability, etc. depending on the combination and content ratio of the components related to its constituent requirements, and thereby a certain degree of moldability and handleability can be ensured. According to the examples described later, by not incorporating a plasticizer containing these substances, the sink mark or swelling phenomenon called sink mark, which is one of the indicators of processability, caused by molding defects is prevented, and satisfactory processability is obtained. Therefore, the composition according to the present embodiment and the rubber crosslinked product crosslinked therefrom can also be applied for food hygiene purposes such as food container packaging, toys, and other utensils related to food hygiene that comply with food hygiene standards.

[0037] In addition, examples of anti-aging agents or antioxidants include compounds such as aliphatic or aromatic hindered amine-based compounds.

[0038] Crosslinking the nitrile rubber composition according to the above embodiment yields a rubber crosslinked product. The rubber crosslinked product according to this embodiment satisfies both ozone resistance and improvement in compression set, and is applicable to a wide range of uses including food hygiene applications. In addition, the rubber crosslinked product according to this embodiment has excellent sealing properties because of its good compression set. Therefore, the rubber crosslinked product according to this embodiment can be suitably applied as a rubber crosslinked product for compression or sealing (crimping or adhesion).

[0039] [Method for producing nitrile rubber composition and rubber crosslinked product] Subsequently, in the method for producing a nitrile rubber composition according to this embodiment, 3 to 40 parts by weight of an unsaturated acid metal salt and 0.5 to 2.5 parts by weight of a silane coupling agent are blended with 100 parts by weight of a nitrile rubber blended with a vinyl chloride resin.

[0040] In addition, the method for producing a rubber crosslinked product according to this embodiment crosslinks the rubber composition produced by the method for producing a rubber composition according to this embodiment.

[0041] Details of the combination and blending ratio of the components in the method for producing a nitrile rubber composition according to this embodiment are as described for the nitrile rubber composition according to this embodiment. Among these, "nitrile rubber blended with vinyl chloride resin" means allowing the use of a commercially available product as a nitrile rubber already blended with vinyl chloride resin, that is, a nitrile rubber containing vinyl chloride resin, in the blending of vinyl chloride resin and nitrile rubber. On the other hand, "nitrile rubber blended with vinyl chloride resin" according to this embodiment essentially means blending vinyl chloride resin and nitrile rubber in the nitrile rubber composition to be produced. Therefore, for example, simply blending a commercially available product of nitrile rubber and a commercially available product of vinyl chloride resin and applying it as "nitrile rubber blended with vinyl chloride resin" is of course allowed.

[0042] Also, regarding the blending amounts of the unsaturated acid metal salt and the silane coupling agent, the parts by weight of the nitrile rubber blended with the vinyl chloride resin are the total parts by weight of all the vinyl chloride resins and all the nitrile rubbers blended in the nitrile rubber composition, and this is taken as 100 parts by weight.

[0043] And, if the specified blending ratios of each blending component are adhered to, the nitrile rubber composition can be produced by applying the usual production method for rubber compositions. Also, the rubber crosslinked product can be produced by applying the usual crosslinking method to the produced nitrile rubber composition. As an example, while kneading each component including nitrile rubber, vinyl chloride resin, unsaturated acid metal salt, and silane coupling agent in the order according to a conventional method, a so-called masterbatch (A kneading) before adding a crosslinking agent and the like is obtained. This masterbatch can be stored. For kneading, kneading machines such as a Banbury mixer, internal mixer, kneader, etc., which are usually used in the rubber industry, the technical field to which the present invention belongs, can be used. Next, while kneading the masterbatch by adding agents (components) related to crosslinking, such as a vulcanizing agent, vulcanization accelerator or vulcanization aid, vulcanization retarder, peroxide, etc., in the order according to a conventional method, a so-called final batch (B kneading) after adding the crosslinking agent and the like is obtained and separated using a roll machine. Then, this is pressurized and heated to promote crosslinking and molded into a desired shape to obtain a rubber product. In this example, the nitrile rubber composition corresponds to the masterbatch (A kneading) to the final batch (B kneading), and the rubber crosslinked product corresponds to the rubber product.

Examples

[0044] According to the blending of each example shown in Table 1, the blending components were kneaded according to a conventional method using a Banbury mixer: 6D (Kobe Steel, Ltd.) and a kneader: DX75 - 215 (Japan Spindle Manufacturing Co., Ltd.) to produce a nitrile rubber composition. The materials used are shown below.

[0045] [Materials Used] [Type of ingredient (substance) / Name of ingredient (substance)] Display name in Table 1: Product name (; Notes) (Manufacturer), however, if the ingredient (substance) name and product name are the same, the product name is omitted. [Acrylonitrile butadiene rubber] NBR: NBR N210S (; acrylonitrile content 30%) (ENEOS) [PVC-containing acrylonitrile butadiene rubber] PVC-containing NBR: JSR NV73 (PVC content 30%) (JSR Corporation) [Vulcanization aid / zinc oxide] Zinc oxide (1): Zinc oxide type 1 (Sakai Chemical Industry Co., Ltd.) [Vulcanization aid / zinc oxide] Zinc oxide (2): Activated zinc oxide AZO (Seido Chemical Industry Co., Ltd.) [Processing aid / stearic acid] Stearic acid: Lunac S-10 (Lunac is a registered trademark) (Kao Corporation) [Processing aid / zinc stearate] Zinc stearate (Daikyo Chemical Industry Co., Ltd.) [Reinforcing agent / Carbon black] Carbon black (1): Asahi #70 (Asahi Carbon Co., Ltd.) [Reinforcing agent / Carbon black] Carbon black (2): Asahi #50 (Asahi Carbon Co., Ltd.) [Plasticizer / Diisodecyl phthalate] Diisodecyl phthalate: Sanso Cizer DIDP (Sanso Cizer is a registered trademark) (Shin Nippon Rika Co., Ltd.) [Silane coupling agent / Bis(3-triethoxysilylpropyl)tetrasulfide] Silane coupling agent (TESPT) (Sanyo Trading Co., Ltd.) [Unsaturated acid metal salts / zinc methacrylate] Zinc methacrylate: R-20S (Asada Chemical Industry Co., Ltd.) [Vulcanizing agent / 4,4'-dithiodimorpholine (N,N'-dimorpholine disulfide)] Sulfur compound: ACTOR R (ACTOR is a registered trademark) (Kawaguchi Chemical Industry Co., Ltd.) [Vulcanization accelerator / Tetramethylthiuram disulfide] Vulcanization accelerator (1): Noccela TT-P (TT) (Noccela is a registered trademark, the same applies below) (Ouchi Shinko Chemical Industry Co., Ltd.) [Vulcanization accelerator / N-cyclohexyl-2-benzothiazylsulfenamide] Vulcanization accelerator (2): Noccela CZ-G (CZ) (Ouchi Shinko Chemical Industry Co., Ltd.) [Peroxide / 2,5-dimethyl-2,5-bis(t-butylperoxy)-hexane] Peroxide: Perhexyne 25B-40(; Perhexyne is a registered trademark)(Nippon Yushi Co., Ltd.)

[0046] [Preparation of test samples] (Ozone resistance test) The nitrile rubber composition according to each example was put into a mold of 150 mm × 150 mm × 2 mm and crosslinked at 160 °C and 15 MPa for an appropriate time by a 70 t molding machine (Ninmei Kikai Co., Ltd.). Then, it was naturally cooled, further kept at a constant temperature of 150 °C for 2 hours in a constant temperature bath, and then naturally cooled to obtain a crosslinked product for ozone resistance evaluation.

[0047] Next, from the manufactured crosslinked product, using a test piece punching blade conforming to JIS K 6251 specified by JIS K 6259 regarding ozone resistance, a dumbbell-shaped No. 1 test piece with a parallel part length of 40 mm, a parallel part width of 10 mm, and a parallel part thickness of 2 mm was prepared in accordance with the standard.

[0048] (Compression set test) The nitrile rubber composition according to each example was put into a mold with a diameter of 29.0 ± 0.05 mm and a height of 12.50 ± 0.13 mm, and crosslinked by pressurization and heating in the same manner as for the above ozone resistance evaluation, and further kept at a constant temperature to allow the reaction to proceed, to prepare a test piece for compression set evaluation in a straight cylindrical shape.

[0049] (Food hygiene test) The nitrile rubber composition according to each example was crosslinked by pressurization and heating in the same manner as for the above ozone resistance evaluation, and further kept at a constant temperature to allow the reaction to proceed, and processed into a predetermined shape to obtain a crosslinked product sample for food hygiene standard conformity evaluation.

[0050] [Test method] (Ozone resistance test) With reference to ISO 1431 and JIS K 6259:2004 regarding ozone resistance, static ozone degradation tests and dynamic ozone degradation tests were conducted using an ozone degradation tester: ozone weather meter OMS-LVCP (Suga Test Instruments Co., Ltd.). In the static ozone degradation test, for each test piece marked with a gauge line with a gauge line distance of 20 mm, a static elongation of 20% of tensile strain was continuously applied for 2000 hours or more in an atmosphere with an ozone concentration of 100 ± 10 pphm, a temperature of 40 ± 2 °C, and a humidity of 65% or less.

[0051] In the dynamic ozone degradation test, for each test piece marked with a gauge line with a gauge line distance of 20 mm, a dynamic elongation of 20% of tensile strain every 30 seconds was continuously applied for 1000 hours in an atmosphere with an ozone concentration of 100 ± 10 pphm, a temperature of 40 ± 2 °C, and a humidity of 65% or less. Subsequently, for the test pieces in which no cracks were confirmed in the observation after 1000 hours, a gauge line with a gauge line distance of 40 mm was marked, and a dynamic elongation of 80% of tensile strain every 30 seconds was continuously applied for another 1000 hours in an atmosphere with an ozone concentration of 200 ± 20 pphm, a temperature of 40 ± 2 °C, and a humidity of 65% or less.

[0052] (Compression set test) With reference to JIS K 6262:2013 regarding compression set, a compression device that can be fixed with bolts and nuts was used with a test piece sandwiched between two compression plates together with a spacer. Spacers with a thickness of 9.52 (+0.01 / -0.02) mm were inserted on both sides of the test piece, and the test piece and the spacers were sandwiched between the upper and lower compression plates and crimped until the upper and lower compression plates were in close contact with the spacers, and the test piece was fixed in a state of being compressed by 25%. Then, the entire compression device was placed in a thermostat as it was and kept at a constant temperature of 100 ± 1 °C for 70 hours. After that, the compression device was taken out of the thermostat, and the test piece was removed from the compression device and allowed to cool naturally for 30 minutes. Then, the thickness of the center part of the test piece was measured before and after the compression. For the measurement, a constant-pressure thickness gauge: Six Gauge PG-12A (; applied load 0.4905 N (about 50 g) or less, measuring head applied surface diameter 5 mm) (TecLock Co., Ltd.) was used.

[0053] (Food hygiene test) For each crosslinked product sample, it was entrusted to an external institution (Chemical Substances Evaluation and Research Institute, Incorporated Administrative Agency) to test its compliance with "Notification No. 370 of the Ministry of Health and Welfare in 1959, Standards for Foods, Additives, etc., Part 3, Utensils and Containers and Packaging, D, Specifications for Utensils or Containers and Packaging or Their Raw Materials by Material, 3, Rubber Utensils or Containers and Packaging (1) Rubber Utensils (excluding nursing bottles) or Containers and Packaging (Revised: Notification No. 595 of the Ministry of Health, Labour and Welfare in 2012)" based on the Food Sanitation Law.

[0054] [Evaluation] (Ozone Resistance Test) The presence or absence of cutting of dumbbell-shaped test pieces was confirmed. Furthermore, regarding cracks, referring to Appendix 1 of JIS K 6259:2004, the test pieces were observed with the naked eye and a 10-fold magnifying glass. Those in which the dumbbell shape maintained its initial state, the number of cracks was A or less according to the evaluation criteria of this standard, and the size could not be confirmed were regarded as "no cracks were confirmed", while those in which the dumbbell shape maintained its initial state, the number of cracks was B or more according to the same evaluation criteria, and the size could clearly be confirmed were regarded as "cracks were confirmed", and they could be classified into either category. Then, the static ozone degradation test and the dynamic ozone degradation test were evaluated as follows respectively.

[0055] Static Ozone Degradation Test ○: After observing the test piece after 2000 hours, no cracks or cutting were confirmed. ×: After observing the test piece after 2000 hours, cracks or cutting were confirmed. Dynamic Ozone Degradation Test ◎: After observing the test piece after 2000 hours, no cracks or cutting were confirmed. ○: After observing the test piece after 1000 hours, no cracks or cutting were confirmed. ×: After observing the test piece after 1000 hours, cracks or cutting were confirmed.

[0056] Also, referring to the descriptions in JIS D 0205:1987 regarding the weather resistance test method for automotive parts and its old standard: 1976, the test time was approximately converted as follows. Ozone exposure at an ozone concentration of 100 pphm and a temperature of 40°C for 10 to 15 hours in this test: Equivalent to one year in the outdoor exposure test Ozone exposure at an ozone concentration of 100 pphm and a temperature of 40°C for 1000 to 1500 hours in this test: Equivalent to 100 years in the outdoor exposure test Ozone exposure at an ozone concentration of 200 pphm and a temperature of 40°C for 5 to 7.5 hours in this test: Equivalent to one year in the outdoor exposure test Ozone exposure at an ozone concentration of 200 pphm and a temperature of 40°C for 500 to 750 hours in this test: Equivalent to 100 years in the outdoor exposure test

[0057] According to the above conversion, the evaluation "○" in this static ozone degradation test corresponds to at least 100 years or more in the outdoor exposure test, and it can be said that the evaluation "○" or above in the dynamic ozone degradation test also corresponds to at least 100 years or more in the outdoor exposure test.

[0058] (Compression set test) As described above, using a constant-pressure thickness measuring instrument, the thicknesses of the center parts of the test piece before compression and the test piece after compression (the test piece that was removed from the compression device together with the thermostatic bath and removed from the compression device and allowed to cool naturally for 30 minutes) were measured respectively, and referring to JIS K 6262:2013, the compression set rate was calculated by the following formula. Compression set rate (%) = [Unrecovered thickness (mm) / Thickness of the test piece compressed (mm)] × 100 Unrecovered thickness (mm) = Thickness of the test piece before compression (mm) - Thickness of the test piece after compression (mm) Thickness of the test piece compressed (mm) = Thickness of the test piece before compression (mm) - Thickness of the spacer (mm)

[0059] The calculated compression set rate was evaluated as follows. ○: Compression set rate is less than 30% ×: Compression set rate is 30% or more

[0060] (Food hygiene test) The test results and the formulation of phthalic acid esters were evaluated as follows. Regulations on phthalic acid esters vary by country and region and are not uniformly regulated. However, since diisodecyl phthalate (DIDP), which was used as a plasticizer in this test, is a substance whose use in toys is regulated in Japan, here, the formulation of phthalic acid ester (DIDP) was evaluated as not meeting the food hygiene standards. ○: Conforms to the standards in all test items and does not contain phthalic acid esters. ×: Does not conform to the standards in one or more test items or contains phthalic acid esters.

[0061] (Evaluation of the presence or absence of sink marks) When each test sample was prepared, the appearance of each sample (crosslinked product) after preparation was observed with the naked eye to confirm the presence or absence of surface defects such as dents, bulges, and other molding defects, that is, sink marks, and evaluated as follows. ○: No surface defects (sink marks) were found in all samples related to the case. ×: Surface defects (sink marks) were found in one or more samples related to the case.

[0062] [Test results] The formulation of each case and the test results of each case are shown in Table 1.

[0063]

Table 1

[0064] Examples 1 and 2 were excellent in ozone resistance, also good in compression set, showed no sink marks, and further conformed to food hygiene standards. Specifically, in the static ozone degradation test, in Examples 1 and 2, since no cracks were confirmed in the test pieces even after 2000 hours, it was presumed that they had resistance to ozone cracking against outdoor exposure for 130 to 200 years or more under the static load. Also, in the dynamic ozone degradation test, in Example 1, no cracks were confirmed after 1000 hours. Then, even after another 1000 hours with the ozone concentration doubled and the tensile strain set at 80%, no cracks were confirmed. Therefore, it was presumed that they had resistance to outdoor exposure for 200 to 300 years or more under the dynamic load. Also, in Example 2, no cracks were confirmed after 1000 hours. After that, when the test conditions were made stricter as described above, the test piece was cut after 400 hours, but no cracks were confirmed. And even in this case, it was presumed that they had resistance to outdoor exposure for at least 100 years or more (120 to 180 years or more) under the dynamic load.

[0065] Also, in Examples 1 and 2, the compression set rate was suppressed to less than 30%, 26% in Example 1 and 28% in Example 2 (rounding off the first decimal place). Also, Examples 1 and 2 were not compounded with zinc oxide and phthalic acid ester (DIDP), and conformed to the standards regarding each item of the material test related to food hygiene standards, that is, the standards related to the detection of cadmium, lead, and 2-mercaptoimidazoline, and also conformed to the standards regarding each item of the elution test, that is, phenol, formaldehyde, zinc, heavy metal (lead), and the evaporation residue related to 20% ethanol, distilled water, and 4% acetic acid. Furthermore, for any of the cross-linked products related to Examples 1 and 2, no appearance defects due to dents, bulges, and other molding defects, that is, sink marks, were found.

[0066] Since PVC contains 30% in NBR, Examples 1 and 2 have a formulation in which 22.5 parts by weight of vinyl chloride resin (PVC) is contained per 100 parts by weight of nitrile rubber. Also, Comparative Examples 1 and 2 have a formulation in which 22.5 parts by weight of PVC is contained per 100 parts by weight of nitrile rubber, Comparative Example 3 has a formulation containing 15.0 parts by weight, and Comparative Example 4 has a formulation containing 20.1 parts by weight.

[0067] Looking at the comparative examples, in Comparative Example 1 where neither the unsaturated acid metal salt (zinc methacrylate) nor the silane coupling agent (TESPT) was compounded, both ozone resistance and compression set were poor (evaluation: ×), and even when a reinforcing agent (carbon black) and a plasticizer (diisodecyl phthalate) were compounded, it did not reach the level of the examples. Also, for Comparative Examples 2 - 4 where the silane coupling agent (TESPT) was compounded but the unsaturated acid metal salt (zinc methacrylate) was not compounded, in Comparative Example 2 where the content of the silane coupling agent (TESPT) was relatively low (0.5 part by weight), the compression set was poor (evaluation: ×). Furthermore, in Comparative Example 2, the ozone resistance was also poor (evaluation: ×). On the other hand, in Comparative Examples 3 and 4 where the content of the silane coupling agent (TESPT) was relatively high (2.3 parts by weight), the compression set was good (evaluation: ○), but the ozone resistance was poor (evaluation: ×). It was also considered that one of the factors for the good compression set was that the improvement function of the compression set was compensated by the compounding of carbon black. Also, one of the factors for the poor ozone resistance was considered to be the relatively low content of PVC (Comparative Example 3: 15.0 parts by weight, Comparative Example 4: 20.1 parts by weight). Also, for Comparative Examples 1 and 2 where the plasticizer (diisodecyl phthalate) was compounded, it did not meet the food hygiene standards (evaluation: ×), and for Comparative Examples 3 and 4 where the plasticizer (diisodecyl phthalate) was not compounded, sink marks were confirmed (evaluation: ×).

[0068] From the above results and the ordinary knowledge of those skilled in the art, it can be said that it is preferable to compound 3 parts by weight or more and about 40 parts by weight or less, more preferably 3 to 30 parts by weight, of an unsaturated acid metal salt with respect to 100 parts by weight of nitrile rubber containing vinyl chloride resin. Also, it is preferable to compound 0.5 or more and about 2.5 parts by weight or less, more preferably 0.5 to 0.8 parts by weight, of a silane coupling agent. In particular, the unsaturated acid metal salt can sufficiently achieve the object of the present invention in a small amount of 3 to 5 parts by weight with respect to 100 parts by weight of nitrile rubber containing vinyl chloride resin. Further, it can be said that it is preferable to contain 21 parts by weight or more and about 35 parts by weight or less of vinyl chloride resin with respect to 100 parts by weight of nitrile rubber.

[0069] The present invention encompasses the following technical ideas. [Invention 1]: A method for producing a nitrile rubber composition, characterized in that 3 to 40 parts by weight of an unsaturated acid metal salt and 0.5 to 2.5 parts by weight of a silane coupling agent are compounded with respect to 100 parts by weight of nitrile rubber containing vinyl chloride resin.

[0070] [Invention 2]: A method for producing a nitrile rubber composition according to [Invention 1], characterized in that the compounding ratio of the vinyl chloride resin is 21 to 35 parts by weight with respect to 100 parts by weight of the nitrile rubber.

[0071] [Invention 3]: A method for producing a nitrile rubber composition according to [Invention 1] or [Invention 2], characterized in that the nitrile rubber is acrylonitrile-butadiene rubber.

[0072] [Invention 4]: A method for producing a rubber crosslinked product, characterized by crosslinking a nitrile rubber composition produced by the production method of [Invention 1] or [Invention 2].

[0073] [Invention 5]: A method for producing a rubber crosslinked product for food hygiene, characterized by crosslinking a nitrile rubber composition produced by the production method of [Invention 1] or [Invention 2].

Claims

1. With respect to 100 parts by weight of nitrile rubber containing vinyl chloride resin, 3 to 40 parts by weight of an unsaturated acid metal salt, and 0.5 to 2.5 parts by weight of a silane coupling agent, characterized by containing A nitrile rubber composition.

2. The content ratio of the vinyl chloride resin is 21 to 35 parts by weight with respect to 100 parts by weight of the nitrile rubber, The nitrile rubber composition according to claim 1, characterized by this.

3. A rubber crosslinked product obtained by crosslinking the nitrile rubber composition according to claim 1 or claim 2.

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