Vulcanizing agent, rubber composition, and vulcanized rubber

Abstract

To provide a vulcanizer that has excellent dispersibility in a rubber composition and allows the production of a rubber product having excellent elongation at break, thermal aging resistance and wear resistance and also provide a rubber composition containing the vulcanizer, and a vulcanized rubber prepared by using the same.SOLUTION: A vulcanizer is a product from the reaction that occurs, in the presence of a vulcanization accelerator, between a resin containing at least one of an unsaturated double bond and an aromatic ring and having a softening point of 50-140°C and sulfur.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a vulcanizing agent, a rubber composition, and a vulcanized rubber. [Background technology]

[0002] Compositions containing diene rubber and sulfur are known, and these compositions can be rapidly crosslinked (vulcanized) by heating to form desired rubber products (vulcanized rubbers). For example, Patent Document 1 discloses a rubber composition containing a rubber component containing a diene rubber, silica and / or carbon black, and a masterbatch of sulfur and a resin having an acid value of 5 or more. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-182983 Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors evaluated rubber compositions containing a masterbatch as a vulcanizing agent as described in Patent Document 1 and found that the dispersibility of the vulcanizing agent in the rubber composition may be insufficient, and that the rubber product (vulcanized rubber) obtained using the same may have insufficient performance in at least one of the following properties: elongation at break, heat aging resistance, and abrasion resistance.

[0005] Therefore, an object of the present invention is to provide a vulcanizing agent that has excellent dispersibility in a rubber composition and that can produce a rubber product that is excellent in elongation at break, heat aging resistance, and abrasion resistance. Another object of the present invention is to provide a rubber composition containing the vulcanizing agent and a vulcanized rubber obtained using the same. [Means for solving the problem]

[0006] As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by the following configuration.

[0007] [1] A vulcanizing agent obtained by reacting a resin having at least one of an unsaturated double bond and an aromatic ring and a softening point of 50 to 140°C with sulfur in the presence of a vulcanization accelerator. [2] The vulcanizing agent according to [1], wherein the amount of sulfur used in the reaction is 30 to 90 mass % based on the total amount of sulfur used and the amount of resin used. [3] The vulcanizing agent according to [1] or [2], wherein the reaction is carried out at a temperature of 100 to 180°C. [4] A composition comprising a diene rubber and the vulcanizing agent according to any one of [1] to [3], A rubber composition comprising 0.5 to 10 parts by mass of the vulcanizing agent per 100 parts by mass of the diene rubber, A rubber composition that satisfies the following requirement A or B. Requirement A: The rubber composition does not contain sulfur. Requirement B: The rubber composition further contains more than 0 part by mass and not more than 10 parts by mass of sulfur per 100 parts by mass of the diene rubber. [5] A vulcanized rubber obtained using the rubber composition described in [4]. [Effects of the Invention]

[0008] According to the present invention, there is provided a vulcanizing agent that has excellent dispersibility in a rubber composition and that can produce a rubber product that is excellent in elongation at break, heat aging resistance, and abrasion resistance. The present invention also provides a rubber composition containing the vulcanizing agent and a vulcanized rubber obtained using the same. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an endothermic curve obtained by measuring vulcanizing agent 1 produced in an example using a differential scanning calorimeter. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, unless otherwise specified, each component may be used alone or in combination of two or more substances. When a component contains two or more substances, the content of the component means the total content of the two or more substances.

[0011] [Vulcanizing agent] The vulcanizing agent of the present invention is obtained by reacting a resin having at least one of an unsaturated double bond and an aromatic ring and a softening point of 50 to 140°C (hereinafter also referred to as "specific resin") with sulfur in the presence of a vulcanization accelerator.

[0012] The mechanism by which the problem of the present invention is solved by adopting such a configuration is not entirely clear, but the present inventors speculate as follows. First, the vulcanizing agent of the present invention is a mixture of organosulfur compounds having complex and diverse structures, and it is impossible or impractical to directly identify it by structure or properties. Even under such circumstances, the present inventors assume that the vulcanizing agent synthesized in the presence of a vulcanization accelerator has a structure derived from a sulfur atom and the specific resin, specifically, a structure resulting from a reaction between a sulfur atom and the specific resin. Furthermore, since the vulcanizing agent of the present invention is obtained using a resin (specific resin) with a low softening point, it is believed that the compatibility between the vulcanizing agent and other components in the rubber composition is improved, resulting in good dispersion of the vulcanizing agent in the rubber composition. Furthermore, when a rubber product is produced using the vulcanizing agent of the present invention, the structure derived from the specific resin is also incorporated into the polymer of the rubber product, which is believed to result in improved elongation at break, heat aging resistance, and abrasion resistance of the rubber product. Hereinafter, the superiority of at least one of the dispersibility of the vulcanizing agent in the rubber composition produced, and the elongation at break, heat aging resistance, and abrasion resistance of the rubber product produced, is also referred to as the superior effect of the present invention.

[0013] <Sulfur> Examples of sulfur used in preparing the vulcanizing agent of the present invention include powdered sulfur, precipitated sulfur, highly dispersible sulfur, insoluble sulfur, etc. The sulfur may be surface-treated. In order to obtain better effects of the present invention, the content of sulfur (sulfur atoms) relative to the total mass of the vulcanizing agent of the present invention is preferably 10 to 95 mass%, more preferably 30 to 90 mass%, even more preferably 30 to 80 mass%, and particularly preferably 35 to 70 mass%. The content of sulfur (sulfur atoms) relative to the total mass of the vulcanizing agent may include sulfur atoms derived from a vulcanization accelerator, which will be described later. Furthermore, in order to obtain better effects of the present invention, the content of sulfur is preferably 10 to 95 mass%, more preferably 30 to 90 mass%, even more preferably 30 to 80 mass%, and particularly preferably 35 to 70 mass%, relative to the total mass of a mixture containing sulfur, a specific resin, and a vulcanization accelerator (hereinafter, the mixture may be referred to as a "vulcanizing agent-forming composition") prepared to produce the vulcanizing agent of the present invention.

[0014] <Specific resin> The specific resin used to prepare the vulcanizing agent of the present invention has at least one of an unsaturated double bond and an aromatic ring, and has a softening point of 50 to 140°C.

[0015] The specific resin may have at least one of an unsaturated double bond and an aromatic ring, and from the viewpoint of achieving better effects of the present invention, it is preferable that the specific resin has an unsaturated double bond, and it is more preferable that the specific resin has both an unsaturated double bond and an aromatic ring. Unless otherwise specified, the unsaturated double bond in the present invention does not include a carbon-carbon double bond constituting an aromatic ring. Specific examples of the unsaturated double bond include a vinyl structure, an allyl structure, a propenyl structure, an isoprene structure, and a cycloalkene structure. Specific examples of the aromatic ring include a benzene ring and a naphthalene ring, with a benzene ring being preferred in terms of achieving better effects of the present invention.

[0016] The softening point of the specific resin is 50 to 140°C. The lower limit of the softening point is preferably 55°C or higher, more preferably 60°C or higher, even more preferably 70°C or higher, and particularly preferably 75°C or higher, in terms of achieving better effects of the present invention. The upper limit of the softening point is preferably 130°C or lower, more preferably 120°C or lower, even more preferably 110°C or lower, and particularly preferably 100°C or lower, in terms of achieving better effects of the present invention. Here, the softening point is a softening point measured in accordance with JIS K2207:1996.

[0017] The specific resin is preferably a thermoplastic resin. Examples of the thermoplastic resin include natural resins such as terpene resins and rosin resins, petroleum resins, coal resins, phenol resins, styrene resins, indene resins (homopolymers of indene, copolymers of styrene compounds and indene, copolymers of coumarone and indene), and synthetic resins such as xylene resins. Among these, terpene resins and rosin resins are preferred, and terpene resins are more preferred, because they provide better effects of the present invention. Examples of terpene resins include α-pinene resin, β-pinene resin, limonene resin, hydrogenated limonene resin, dipentene resin, terpene phenol resin, terpene styrene resin, aromatic modified terpene resin, hydrogenated terpene resin, etc. Among these, aromatic modified terpene resin is preferred because it provides better effects of the present invention.

[0018] In order to obtain better effects of the present invention, the content of the partial structure derived from the specific resin is preferably 5 to 90 mass%, more preferably 10 to 70 mass%, still more preferably 20 to 70 mass%, and particularly preferably 30 to 65 mass%, relative to the total mass of the vulcanizing agent of the present invention. Furthermore, in order to obtain better effects of the present invention, the content of the specific resin is preferably 5 to 90 mass%, more preferably 10 to 70 mass%, even more preferably 20 to 70 mass%, and particularly preferably 30 to 65 mass%, relative to the total mass of the vulcanizing agent-forming composition.

[0019] In the vulcanizing agent of the present invention, the content of sulfur (sulfur atom) relative to the total content of sulfur (sulfur atom) and the partial structure derived from the specific resin is preferably 10 to 95 mass%, more preferably 30 to 90 mass%, still more preferably 30 to 80 mass%, and particularly preferably 35 to 70 mass%. In the reaction for producing the vulcanizing agent of the present invention, the amount of sulfur used relative to the total amount (total mass) of sulfur and the specific resin used is preferably 10 to 95 mass%, more preferably 30 to 90 mass%, still more preferably 30 to 80 mass%, and particularly preferably 35 to 70 mass%. Note that the amount used corresponds to the content of sulfur or the specific resin relative to the total amount of sulfur and the specific resin used in the vulcanizing agent-forming composition.

[0020] <Vulcanization accelerator> In producing the vulcanizing agent of the present invention, the sulfur and the specific resin are reacted in the presence of a vulcanization accelerator. In order to obtain better effects of the present invention, the vulcanization accelerator is preferably a sulfur-containing vulcanization accelerator containing one or more (preferably 1 to 10) sulfur atoms in one molecule. In order to obtain better effects of the present invention, it is also preferable that the vulcanization accelerator contains one or more (preferably 1 to 3) metal atoms (zinc, tellurium, copper, and / or sodium, etc.) in one molecule. Examples of the vulcanization accelerator include dithiocarbamate vulcanization accelerators, sulfenamide vulcanization accelerators, thiazole vulcanization accelerators, guanidine vulcanization accelerators, and thiuram vulcanization accelerators. Among them, the vulcanization accelerator is preferably a dithiocarbamate vulcanization accelerator, since it provides better effects of the present invention.

[0021] Examples of dithiocarbamate vulcanization accelerators include zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc dibenzyldithiocarbamate, tellurium diethyldithiocarbamate, copper dimethyldithiocarbamate, and sodium diethyldithiocarbamate.

[0022] Examples of sulfenamide vulcanization accelerators include N-cyclohexylbenzothiazole sulfenamide, Nt-butylbenzothiazole sulfenamide, N-oxydiethylenebenzothiazole sulfenamide, N,N-dicyclohexylbenzothiazole sulfenamide, and (morpholinodithio)benzothiazole.

[0023] Examples of thiazole vulcanization accelerators include di-2-benzothiazolyl disulfide, mercaptobenzothiazole, benzothiazyl disulfide, zinc salt of mercaptobenzothiazole, (dinitrophenyl)mercaptobenzothiazole, and (N,N-diethylthiocarbamoylthio)benzothiazole.

[0024] Examples of the guanidine vulcanization accelerator include diphenylguanidine, di(o-tolyl)guanidine, and o-tolylbiguanide.

[0025] Examples of thiuram vulcanization accelerators include tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide, tetrakis(2-ethylhexyl)thiuram disulfide, and tetrabenzylthiuram disulfide.

[0026] A part or all of the vulcanization accelerator may be incorporated into the vulcanizing agent of the present invention. In order to obtain better effects of the present invention, the total content of the partial structures derived from the vulcanization accelerator is preferably 0.1 to 10 mass%, more preferably 1 to 8 mass%, and even more preferably 2 to 5 mass%, based on the total mass of the vulcanizing agent of the present invention. In addition, in order to obtain better effects of the present invention, the content of the vulcanization accelerator is preferably 0.1 to 10 mass%, more preferably 1 to 8 mass%, and even more preferably 2 to 5 mass%, relative to the total mass of the vulcanizing agent forming composition.

[0027] When synthesizing the vulcanizing agent of the present invention, components other than those described above may be added to the system (to the vulcanizing agent-forming composition) within a range that does not impair the performance of the vulcanizing agent to be synthesized.

[0028] <Production of vulcanizing agent> The vulcanizing agent of the present invention is obtained by reacting the above sulfur with the above specific resin in the presence of the above vulcanization accelerator. The reaction is preferably carried out under heating in order to obtain better effects of the present invention. The temperature in the reaction (i.e., the temperature of the vulcanizing agent-forming composition) is preferably 100 to 180° C., more preferably 110 to 170° C., and even more preferably 120 to 160° C. The heating is maintained for preferably 0.5 to 20 hours, more preferably 1 to 10 hours, and even more preferably 2 to 5 hours. The heating may be carried out continuously or intermittently.

[0029] The reaction may be carried out, for example, by mixing the sulfur, the specific resin, and the vulcanization accelerator components used in the production of the vulcanizing agent together to obtain a vulcanizing agent-forming composition, and then reacting the resulting vulcanizing agent-forming composition. Alternatively, the vulcanizing agent-forming composition may be obtained by sequentially mixing some or all of the components, or by heating some or all of the components before the vulcanizing agent-forming composition is completed. For example, a heated (or unheated) portion of each of the components may be added to another heated (or unheated) portion of each of the components to complete the vulcanizing agent-forming composition, and then the sulfur and the specific resin in the completed vulcanizing agent-forming composition may be reacted. Before the vulcanizing agent-forming composition is completed, some of the components may have already started to react.

[0030] Alternatively, for example, the vulcanizing agent-forming composition may be obtained by adding the specific resin and the vulcanization accelerator to sulfur that has been heated to 116 to 200°C (preferably 120 to 180°C) and turned into a liquid, and the obtained vulcanizing agent-forming composition may be continued to be heated to react the sulfur with the specific resin, thereby obtaining the vulcanizing agent of the present invention.

[0031] The obtained vulcanizing agent may be subjected to a washing treatment or the like to remove unreacted components (unreacted sulfur, unreacted specific resin, and / or unreacted vulcanization accelerator) from the vulcanizing agent.

[0032] [Rubber composition] The present invention also relates to a rubber composition. The rubber composition of the present invention contains the vulcanizing agent of the present invention. In order to obtain better effects of the present invention, the rubber composition preferably contains a diene rubber and the vulcanizing agent. In addition, in order to obtain better effects of the present invention, the rubber composition preferably contains 0.5 to 10 parts by mass, more preferably 0.6 to 8 parts by mass, and even more preferably 0.8 to 5 parts by mass of the vulcanizing agent per 100 parts by mass of the diene rubber. Furthermore, the rubber composition preferably satisfies the following requirement A or B. Requirement A: The rubber composition does not contain sulfur. Requirement B: The rubber composition further contains more than 0 parts by mass and not more than 10 parts by mass (preferably more than 0 parts by mass and less than 5 parts by mass, more preferably more than 0 parts by mass and less than 3 parts by mass) of sulfur per 100 parts by mass of the diene rubber. The sulfur in the requirements A and B is sulfur that is added to the rubber composition separately from the sulfur atoms contained in the vulcanizing agent.

[0033] <Diene rubber> As described above, the rubber composition preferably contains a diene rubber. The diene rubber is not particularly limited as long as it has a double bond in the main chain, and known diene rubbers can be used. Examples of diene rubbers include natural rubber (NR), butadiene rubber (BR), isoprene rubber (IR), acrylonitrile-butadiene rubber (NBR), aromatic vinyl-conjugated diene copolymer rubber (e.g., styrene-butadiene rubber (SBR), styrene-isoprene rubber, styrene-butadiene-isoprene rubber (SBIR)), styrene-isoprene rubber (SIR), and styrene-isoprene-butadiene rubber (SIBR). The diene rubber may also be a derivative in which a side chain, one end, or both ends are modified with at least one functional group selected from the group consisting of an alkyl group, an allyl group, an amino group, an isocyanate group, a hydroxyl group, a thiol group, a vinyl group, an epoxy group, a carboxy group, a carbonyl group-containing group, an amide group, an ester group, an imide group, a nitrile group, a thiocyanate group, an alkoxy group, a silyl group, an alkoxysilyl group, and a nitro group. Of these, the diene rubber is preferably NR or SBR. In order to obtain better effects of the present invention, the content of the diene rubber is preferably 20 to 90 mass %, more preferably 30 to 80 mass %, and even more preferably 40 to 70 mass %, based on the total mass of the rubber composition.

[0034] <Vulcanizing agent> The rubber composition contains the vulcanizing agent of the present invention, as described above. The vulcanizing agent of the present invention and the preferred content thereof are as described above.

[0035] <Sulfur> The rubber composition may contain sulfur. Examples of the sulfur contained in the rubber composition include the sulfur described above as the sulfur that can be used to prepare the vulcanizing agent of the present invention. The preferred content of sulfur in the rubber composition is as described above.

[0036] <Vulcanization accelerator> The rubber composition may contain a vulcanization accelerator. Examples of the vulcanization accelerator contained in the rubber composition include the vulcanization accelerators described as vulcanization accelerators that can be used to produce the vulcanizing agent of the present invention. In order to obtain better effects of the present invention, the content of the vulcanization accelerator in the rubber composition is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the diene rubber.

[0037] <Filler> The rubber composition may include a filler. The filler is not particularly limited and can be used without any particular limitation. Examples of fillers include carbon black and white fillers (excluding zinc oxide). White fillers include, for example, silica, calcium carbonate, talc, and mica. In order to obtain better effects of the present invention, the content of the filler in the rubber composition is preferably 0.1 to 350 parts by mass, more preferably 10 to 200 parts by mass, and even more preferably 20 to 90 parts by mass, per 100 parts by mass of the diene rubber.

[0038] <Other ingredients> The rubber composition may contain other components in addition to the above-mentioned components. The other components may further include additives such as zinc oxide, stearic acid, and / or antioxidants. The content of these additives can be determined appropriately within a range that does not impair the object of the present invention. For example, when the rubber composition contains zinc white (zinc oxide), the content thereof is preferably 0.5 to 20 parts by mass per 100 parts by mass of the diene rubber. When the rubber composition contains stearic acid, the content thereof is preferably 0.1 to 15 parts by mass per 100 parts by mass of the diene rubber.

[0039] <Method of manufacturing rubber composition> The method for producing the rubber composition is not particularly limited, and the rubber composition can be produced by a known method for producing a rubber composition. Examples of the method for producing the rubber composition include a method in which the above-mentioned components are kneaded using an apparatus (for example, a Banbury mixer, a kneader, or a roll). In this case, the components may be mixed simultaneously or stepwise.

[0040] [Vulcanized rubber] The present invention also relates to a vulcanized rubber. The vulcanized rubber of the present invention is a vulcanized rubber obtained using the above-mentioned rubber composition. The method for producing the vulcanized rubber is not particularly limited, and examples thereof include a method in which the rubber composition is heated. The heating temperature is not particularly limited, but is preferably 130 to 200° C. The vulcanization time is preferably 10 to 240 minutes. The vulcanized rubber can be used, for example, in tires (particularly pneumatic tires), conveyor belts, hoses, golf balls, civil engineering materials such as seismic isolation rubber, industrial sealing materials, fenders, medical equipment, and the like. [Example]

[0041] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0042] [Manufacturing of vulcanizing agents] <Production of vulcanizing agent 1> 75 g of sulfur (Tsurumi Chemical Industry Co., Ltd., finely divided sulfur with Kinkaji oil) was added to the flask, and the contents of the flask were heated to a temperature of 130°C. It was confirmed that all of the sulfur in the flask had become liquid. Next, 75 g of YS Resin TO125 (manufactured by Yasuhara Chemical Co., Ltd., aromatic modified terpene resin, softening point 125°C, specific resin, containing unsaturated double bonds and aromatic rings) and 3 g of zinc diethyldithiocarbamate (a vulcanization accelerator) were added to the flask. The temperature of the contents of the flask was adjusted to 130°C, and the adjusted temperature was maintained for 3 hours, allowing the sulfur in the flask to react with the specific resin, yielding vulcanizing agent 1. The obtained vulcanizing agent 1 was measured by a differential scanning calorimeter (DSC), and the resulting endothermic curve is shown in Figure 1. The DSC measurement was carried out at a temperature rise rate of 10°C / min. In the endothermic curve of FIG. 1, the endothermic peaks corresponding to sulfur and the specific resin have disappeared, which indicates that a vulcanizing agent, which is a reaction product of sulfur and the specific resin, has been produced.

[0043] <Other vulcanizing agents> Vulcanizing agents 2 to 5 were produced in the same manner as in "Production of vulcanizing agent 1," except that the type and amount of resin, and whether or not a vulcanization accelerator was used, were changed as shown in the table below. Vulcanizing agents 2 and 3 are vulcanizing agents of the present invention because sulfur, a specific resin, and a vulcanization accelerator were used in the production of the vulcanizing agents. Vulcanizing agent 4 is produced using sulfur, a resin with a softening point of 145°C ("FMR0150" described below), and a vulcanization accelerator, but does not use a specific resin, so it corresponds to a comparative vulcanizing agent. Vulcanizing agent 5 is produced using sulfur and a specific resin, but does not use a vulcanization accelerator, and therefore corresponds to a comparative vulcanizing agent. In addition, in the production of any vulcanizing agent, the total mass of the added amount of sulfur and the added amount of resin was fixed to a constant amount (150 g). YS Resin TO85: Manufactured by Yasuhara Chemical Co., Ltd., an aromatic modified terpene resin with a softening point of 85°C and classified as a specific resin. It contains unsaturated double bonds and aromatic rings. Gum rosin: Arakawa Chemical Co., Ltd., China Gum Rosin WW, softening point 65°C, specific resin. It contains unsaturated double bonds but no aromatic rings. FMR0150: Mitsui Chemicals, 4-methyl-α-methylstyrene-indene copolymer, softening point 145°C, not a specified resin.

[0044] [Production of rubber composition] The components shown in the tables below were mixed in a 1 L Banbury mixer to prepare rubber compositions for each Example or Comparative Example. In the tables, the content of each component is shown in parts by mass relative to 100 parts by mass of diene rubber.

[0045] [Manufacture of Vulcanized Rubber] The obtained rubber composition was pressed in a predetermined mold at 160 °C for 20 minutes to obtain rubber test pieces (vulcanized rubber) for each example or comparative example.

[0046] [Test] [Dispersion] The rubber composition was visually observed, and the dispersion of the vulcanizing agent was evaluated according to the following evaluation criteria. 〇: Particles of the vulcanizing agent cannot be confirmed in the rubber composition. ×: Particles of the vulcanizing agent can be confirmed in the rubber composition.

[0047] [Elongation at Break Index] For the rubber test pieces, the elongation at break (EB) at room temperature (23 °C) was measured based on JIS K6251:2017 (Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Tensile Properties). . And the elongation at break index was calculated from the following formula. Elongation at break index: (EB of each rubber test piece / reference EB) × 100 In the evaluations of Comparative Examples 1-1 to 1-7 and Examples 1-1 to 1-3, the EB of the rubber test piece of Comparative Example 1-1 was used as the reference EB. In the evaluations of Comparative Examples 2-1 to 2-7 and Examples 2-1 to 2-3, the EB of the rubber test piece of Comparative Example 2-1 was used as the reference EB. The larger the elongation at break index, the more difficult it is to break, which means excellent elongation at break.

[0048] [M300 Change Rate Index] For the rubber test pieces before heat aging without performing the heat aging treatment described later, the 300% modulus was measured at room temperature (23 °C) based on JIS K6251 (Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Heat Aging Properties). Also, for the rubber test pieces after heat aging, which were subjected to a heat aging treatment of leaving them in an oven heated to 70 °C for 96 hours, the 300% modulus was measured at room temperature (23 °C) in the same manner as above, and the change rate of the 300% modulus (M300 change rate) was determined based on the formula shown below. M300 change rate (%): 100 × {(300% modulus of rubber test piece before heat aging) - (300% modulus of rubber test piece after heat aging)} / (300% modulus of rubber test piece after heat aging) The evaluations of Comparative Examples 1-1 to 1-7 and Examples 1-1 to 1-3 were expressed as an index (M300 change index) with the M300 change rate of the rubber test piece of Comparative Example 1-1 set to 100. The evaluations of Comparative Examples 2-1 to 2-7 and Examples 2-1 to 2-3 were expressed as an index (M300 change index) with the M300 change rate of the rubber test piece of Comparative Example 2-1 set to 100. The smaller the M300 change index, the less heat aging occurs and the better the heat aging resistance.

[0049] <Wear resistance index> The abrasion loss of the rubber test pieces (rubber test pieces before heat aging) was measured at a temperature of 20°C and a slip ratio of 50% using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho) in accordance with JIS K6264-1, 2:2005. The abrasion resistance index was then calculated using the following formula. Abrasion resistance index: (standard abrasion amount / abrasion amount of each rubber test piece) x 100 In the evaluation of Comparative Examples 1-1 to 1-7 and Examples 1-1 to 1-3, the amount of wear of the rubber test piece of Comparative Example 1-1 was used as the reference amount of wear. In the evaluation of Comparative Examples 2-1 to 2-7 and Examples 2-1 to 2-3, the wear amount of the rubber test piece of Comparative Example 2-1 was used as the reference wear amount. The larger the wear resistance index, the smaller the amount of wear and the better the wear resistance.

[0050] [result] The formulations of each rubber composition and the evaluation results are shown in Tables 1 and 2 below. In the table, the descriptions in parentheses in the columns for vulcanizing agents 1 to 5 indicate the characteristics of each vulcanizing agent at the time of production. For example, the description "(TO125 / sulfur = 5 / 5)" for vulcanizing agent 1 indicates that when vulcanizing agent 1 was synthesized, TO125 and sulfur were added so that the mass ratio of TO125 / sulfur was 5 / 5. For example, the description "(no vulcanization accelerator used)" for vulcanizing agent 5 indicates that no vulcanization accelerator was used when synthesizing vulcanizing agent 5. Note that all of the other vulcanizing agents use a vulcanization accelerator when synthesizing them.

[0051] [Table 1]

[0052] [Table 2]

[0053] Details of the components in each composition are as follows: NR:TSR20 SBR: Nipol1502 manufactured by Nippon Zeon CB: Cabot Japan Show Black N220 Zinc oxide: Zinc oxide type 3 manufactured by Seido Chemical Industry Co., Ltd. Stearic acid: Stearic acid manufactured by NOF CORPORATION Vulcanization accelerator: Noccela NS-P manufactured by Ouchi Shinko Chemical Co., Ltd. Sulfur: Tsurumi Chemical Industry Co., Ltd. Kinka-in oil-filled fine powder sulfur Resin 1: Yasuhara Chemical YS Resin TO125, aromatic modified terpene resin, softening point 125°C Resin 2: Yasuhara Chemical YS Resin TO85, aromatic modified terpene resin, softening point 85°C Resin 3: Arakawa Chemical Co., Ltd. China Gum Rosin WW, softening point 65°C Resin 4: Mitsui Chemicals FMR0150 (4-methyl-α-methyl-styrene / indene copolymer) softening point 145°C

[0054] From the results shown in Tables 1 and 2, it was confirmed that the use of the vulcanizing agent of the present invention enables the production of rubber products that have excellent dispersibility in rubber compositions, as well as excellent elongation at break, heat aging resistance, and abrasion resistance. In particular, comparison of Examples 1-1 to 1-3 and Examples 2-1 to 2-3 confirmed that when a specific resin having both an unsaturated double bond and an aromatic ring was used (Examples 1-1 to 1-2 and Examples 2-1 to 2-2), the heat aging resistance and abrasion resistance of the rubber product were superior. Furthermore, a comparison of Examples 1-1 to 1-3 and Examples 2-1 to 2-3 confirmed that when a specific resin with a softening point of 120°C or less was used (Examples 1-2 to 1-3 and Examples 2-2 to 2-3), the breaking elongation of the rubber product was superior.

Claims

1. It is obtained by reacting a resin having an unsaturated double bond and a softening point of 50 to 140°C with sulfur in the presence of a vulcanization accelerator, the resin is a terpene-based resin or a rosin-based resin, In the reaction, the amount of sulfur used is 30 to 90 mass% with respect to the total amount of sulfur used and the amount of resin used.

2. The vulcanizing agent according to claim 1 , wherein the resin further comprises an aromatic ring.

3. The vulcanizing agent according to claim 1 or 2, wherein the reaction temperature is 100 to 180°C.

4. A rubber composition comprising a diene rubber and the vulcanizing agent according to any one of claims 1 to 3, A rubber composition comprising 0.5 to 10 parts by mass of the vulcanizing agent per 100 parts by mass of the diene rubber, A rubber composition that satisfies the following requirement A or requirement B. Requirement A: The rubber composition does not contain sulfur. Requirement B: The rubber composition further contains more than 0 part by mass and not more than 10 parts by mass of sulfur per 100 parts by mass of the diene rubber.

5. A vulcanized rubber obtained using the rubber composition according to claim 4.

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