Rubber composition

Abstract

To provide a rubber composition excellent in initial adhesiveness and hygrothermally resistant adhesiveness to metals, especially brass and galvanized metals represented by steel cords, and a rubber-metal composite which can be resorcin-free and formaldehyde-free due to inclusion of the rubber composition.　Provided are: a rubber composition comprising 0.1-30 parts by weight of, relative to 100 parts by weight of a diene rubber, a C5 / C9 petroleum resin having a weight average molecular weight of less than 5,000 in terms of standard polystyrene by gel permeation chromatography and an acid value of 1-75 (mg-KOH / g); and use of the rubber composition for bonding a vulcanized rubber and a metal component.

Description

rubber composition

[0001] The present invention relates to a rubber composition that has excellent initial adhesion and wet heat resistance to metals, particularly to brass such as steel cords, and to zinc-plated metals, and further to a rubber-metal composite that can be made resorcinol- and formaldehyde-free by using a vulcanizate of the rubber composition.

[0002] Rubber products such as tires, conveyor belts, and hoses used in fields such as automobiles, industrial parts, and construction materials are used as composites with metal plates, metal fibers, and wires, particularly steel cords, as reinforcing materials. The surfaces of steel cords are typically plated with brass, zinc, or other materials to inhibit corrosion. Resorcinol resins are also widely used to improve adhesion between rubber and steel cords. However, it has been reported that amine components, which are by-produced from sulfenamide vulcanization accelerators used in vulcanizing rubber compositions, corrode the plating on the steel cord surface in the presence of humid heat in the usage environment, thereby reducing adhesion between rubber and steel cords. Therefore, there is a need to improve not only the initial adhesion between rubber and steel cords but also their long-term adhesion with humidity and heat.

[0003] As a method for improving the adhesion between rubber and steel cord, for example, a method of capturing amine components in rubber by using an excess amount of hexamethoxymethylmelamine in a resorcinol resin has been reported (see, for example, Non-Patent Document 1). Other methods include a method of applying a composition consisting of rubber, a primary fatty acid having 6 to 10 carbon atoms, and its metal salt as a filler rubber for steel cord reinforcement (see, for example, Patent Document 1), a method of improving the initial adhesion and water-resistant adhesion of a sulfur-vulcanizable rubber component to a zinc-plated steel cord by using a rubber composition containing a polymer terminally modified with maleic anhydride or a carboxyl group, and zinc dimethacrylate and / or zinc diacrylate (see, for example, Patent Document 2), and a method of improving the initial adhesion and water-resistant adhesion of a zinc-plated steel cord by using a rubber composition containing a diene rubber, cobalt benzoate, rosin, and / or a derivative thereof. Proposals have been made for a method of improving the initial adhesion and moist heat resistant adhesion of metal cords and / or galvanized steel cords (see, for example, Patent Document 3), a method of achieving both initial adhesion and crack resistance of the coated rubber by coating a metal cord with a rubber composition containing a tackifier such as an alkylphenol resin (see, for example, Patent Document 4), and a method of improving moist heat resistant adhesion by using a rubber composition containing a diene rubber, an unsaturated fatty acid of 11 or more, and a fatty acid cobalt salt to capture amine components presumably derived from a vulcanization accelerator that cause corrosion at the adhesive interface (see, for example, Patent Document 5).

[0004] Journal of the Society of Rubber Science and Technology of Japan, Vol. 75, No. 11, p. 488 (2002)

[0005] Japanese Patent Publication No. 58-161604 Japanese Patent Publication No. 2006-176580 Japanese Patent Publication No. 2007-99868 Japanese Patent Publication No. 2019-112746 Japanese Patent Publication No. 2021-138930

[0006] However, the method proposed in Non-Patent Document 1 involves the reaction of formaldehyde liberated from hexamethoxymethylmelamine with resorcinol to harden the rubber, but it also generates harmful resorcinol and formaldehyde. Furthermore, while the proposals in Patent Documents 1 to 5 all show some degree of effect on initial adhesion or wet heat resistance, they are not satisfactory, and further improvements in adhesion between rubber and steel cord are desired. Therefore, the present invention aims to provide a rubber composition that is applicable to steel cords and has excellent initial adhesion and wet heat resistance, as well as a rubber-metal composite that can be made resorcinol- and formaldehyde-free by using this rubber composition. The term "resorcinol- and formaldehyde-free" as used herein means that resorcinol, formaldehyde, or resorcinol-formaldehyde condensates are not used as raw materials.

[0007] As a result of intensive research into solving the above problems, the present inventors have found that by incorporating a specific C5 / C9 petroleum resin into a diene rubber, a rubber composition can be obtained that makes it possible to provide a rubber-metal composite that is excellent in initial adhesion and wet heat resistance adhesion without generating resorcinol and formaldehyde, and have thereby completed the present invention.

[0008] That is, the present invention resides in the following [1] to

[11] . [1] A rubber composition comprising, per 100 parts by weight of a diene-based rubber, 0.1 to 30 parts by weight of a C5 / C9 petroleum resin having a weight-average molecular weight of less than 5,000 as measured by gel permeation chromatography relative to standard polystyrene standards and an acid value of 1 to 75 (mg-KOH / g). [2] The rubber composition according to [1], wherein the diene-based rubber is at least one rubber selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, and ethylene propylene diene rubber. [3] The rubber composition according to [1] or [2], wherein the C5 / C9 petroleum resin is at least one modified C5 / C9 petroleum resin selected from the group consisting of unsaturated carboxylic acid-modified C5 / C9 petroleum resin, acid anhydride-modified C5 / C9 petroleum resin, and phenol-modified C5 / C9 petroleum resin. [4] The rubber composition according to any one of [1] to [3], wherein the softening point of the C5 / C9 petroleum resin is 70 to 150°C. [5] The rubber composition according to any one of [1] to [4], wherein the weight average molecular weight of the C5 / C9 petroleum resin is 500 to 4,000. [6] The rubber composition according to any one of [1] to [5], wherein the rubber composition is a rubber composition for bonding plated metal members. [7] The rubber composition according to [6], wherein the rubber composition for bonding plated metal members is a rubber composition for bonding brass-plated metal members or a rubber composition for bonding zinc-plated metal members. [8] The rubber composition according to [6] or [7], wherein the rubber composition for bonding plated metal members is a rubber composition for bonding steel cords. [9] A rubber-metal composite formed by bonding a plated metal member and rubber, wherein the rubber is a vulcanized rubber of the rubber composition according to any one of [1] to [8].

[10] The rubber-metal composite according to [9], wherein the plated metal member is a steel cord and the composite is a tire belt, a conveyor belt, or a hose.

[11] The rubber-metal composite according to [9] or

[10] , wherein the rubber-metal composite is free of resorcinol and formaldehyde.

[0009] According to the present invention, by blending a specific amount of a specific C5 / C9 petroleum resin with a diene rubber component, it is possible to provide a rubber composition and vulcanized rubber that exhibit excellent initial adhesion and wet heat resistance adhesion to metal components, particularly steel cords, and a rubber-metal composite with excellent durability can be provided.

[0010] The rubber composition of the present invention contains, per 100 parts by weight of diene rubber, 0.1 to 30 parts by weight of a C5 / C9 petroleum resin having a weight average molecular weight of less than 5,000 as determined by gel permeation chromatography in terms of standard polystyrene and an acid value of 1 to 75 (mg-KOH / g).

[0011] The diene rubber constituting the rubber composition of the present invention may be any rubber that falls within the category known as diene rubber, such as natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, ethylene propylene diene rubber, etc., and these may be used alone or in mixtures. The method for producing the diene rubber is not particularly limited, and the diene rubber may be an anionic polymerized product, a coordinated anionic polymerized product, a radical polymerized product, or an emulsion polymerized product, or may be a commercially available product. Furthermore, the molecular terminals of the rubber may be modified with functional groups such as amine, amide, silyl, alkoxysilyl, carboxyl, or hydroxyl, or may be epoxidized. Natural rubber is preferred, as it results in a rubber composition with particularly excellent adhesive strength.

[0012] The C5 / C9 petroleum resin constituting the rubber composition of the present invention is a C5 / C9 petroleum resin obtained by copolymerizing a C5 fraction, which is an aliphatic fraction obtained by separating and refining petroleum products, and a C9 fraction, which is an aromatic fraction, and the C5 / C9 petroleum resin has a weight average molecular weight (hereinafter sometimes referred to as Mw) of less than 5,000 in terms of standard polystyrene as determined by gel permeation chromatography (hereinafter sometimes referred to as GPC) and an acid value of 1 to 75 (mg-KOH / g). As components constituting the C5 fraction, which is an aliphatic fraction, any components known as fractions having a boiling point range of 20 to 110°C that are generally obtained by thermal cracking and refining of petroleum products can be used. Examples include conjugated diolefinically unsaturated hydrocarbons having 4 to 6 carbon atoms, such as isoprene, trans-1,3-pentadiene, cis-1,3-pentadiene, cyclopentadiene, and methylcyclopentadiene; monoolefinically unsaturated hydrocarbons having 4 to 6 carbon atoms, such as butene, 2-methyl-1-butene, 2-methyl-2-butene, 1-pentene, 2-pentene, and cyclopentene; aliphatic saturated hydrocarbons such as cyclopentane, 2-methylpentane, 3-methylpentane, and n-hexane; and mixtures thereof. As components constituting the C9 fraction, which is an aromatic fraction, any fraction known to have a boiling point range of 140 to 280°C that is generally obtained by thermal cracking and refining of petroleum products can be used, and examples thereof include vinyl aromatic hydrocarbons having 8 to 10 carbon atoms, such as styrene, α-methylstyrene, β-methylstyrene, vinyltoluene, indene, and alkyl derivatives of indene; olefins having 10 or more carbon atoms; saturated aromatic compounds having 9 or more carbon atoms; dicyclopentadienes such as dicyclopentadiene, methyldicyclopentadiene, and dimethyldicyclopentadiene; and mixtures thereof.

[0013] The composition ratio of the C5 component to the C9 component in the C5 / C9 petroleum resin is not particularly limited as long as it falls within the category known as a C5 / C9 petroleum resin, and examples thereof include those containing 10 to 70% by weight of the C5 component and 90 to 30% by weight of the C9 component. Of these, those containing 20 to 40% by weight of the C5 component and 80 to 60% by weight of the C9 component are preferred because they provide particularly excellent adhesion to metals such as steel cords when made into rubber compositions or vulcanized rubbers. The C5 / C9 petroleum resin efficiently captures the amine component and partially migrates to the surface of metals such as steel cords, thereby suppressing contact between the metal and corrosion-causing substances such as the amine component, water, and oxygen, thereby improving adhesion. The C5 / C9 petroleum resin has a Mw of less than 5,000 as determined by GPC in terms of standard polystyrene, and a Mw of less than 5,000 provides excellent compatibility with rubber, and is preferably 500 to 4,000, more preferably 500 to 3,500. However, if the Mw is 5,000 or more, the compatibility with diene rubber is poor, making it difficult to prepare a rubber composition.

[0014] The C5 / C9 petroleum resin, when used in a rubber composition, captures amine components as an acid component, making it possible to provide a rubber composition that exhibits excellent adhesion to metal surfaces when used in a vulcanized rubber-metal composite. The acid value is 1 to 75 (mg-KOH / g), with an acid value of 1 to 50 (mg-KOH / g) being preferred. Since this resin exhibits particularly excellent amine component capture, an acid value of 5 to 30 (mg-KOH / g) is preferred. If the acid value is less than 1 (mg-KOH / g), the amine component cannot be sufficiently captured, and the resulting rubber composition and vulcanized rubber will have poor adhesion to metal components. On the other hand, if the acid value exceeds 75 (mg-KOH / g), the compatibility with diene rubber will be poor, and the resulting rubber composition will have poor processability and mechanical properties. The acid value can be measured, for example, by a method conforming to JIS K-0070 (1992). The C5 / C9 petroleum resin preferably has a softening point of 70 to 150° C., as this will result in particularly excellent compatibility and ease of handling when made into a rubber composition, and the softening point is preferably 70 to 130° C., more preferably 90 to 120° C., as this will result in a rubber composition or vulcanized rubber that is particularly excellent in adhesion to metal members and steel cords. The softening point can be measured, for example, by a method in accordance with JIS K-2531 (1960) (ring and ball method).

[0015] The method for producing the C5 / C9 petroleum resin is not particularly limited. For example, a method can be used in which a catalyst is added to a feedstock oil containing the above-mentioned C5 fraction and C9 fraction, and optionally other components, followed by heating and polymerization. The catalyst used in this process can be a typical Friedel-Crafts catalyst, such as aluminum trichloride, aluminum tribromide, boron trifluoride, or its phenol complex or butanol complex. Of these, aluminum trichloride, a boron trifluoride phenol complex, and a boron trifluoride butanol complex are preferred. The polymerization temperature is preferably 0 to 100°C, and particularly preferably 0 to 80°C. The catalyst amount and polymerization time can be arbitrarily selected. For example, a range of 0.1 to 2.0 parts by weight of catalyst per 100 parts by weight of feedstock oil and 0.1 to 10 hours is preferred. The reaction pressure is preferably atmospheric pressure to 1 MPa.

[0016] The C5 / C9 petroleum resin is preferably a modified C5 / C9 petroleum resin such as an unsaturated carboxylic acid-modified C5 / C9 petroleum resin, an acid anhydride-modified C5 / C9 petroleum resin, or a phenol-modified C5 / C9 petroleum resin, because these resins enable more efficient capture of amine components as an acid component, thereby enabling the provision of rubber compositions and vulcanized rubbers that have excellent adhesion to metal components, particularly steel cords. These resins may be used alone or in mixtures. In this case, examples of unsaturated carboxylic acids include unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid; unsaturated polycarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid; and partial esters of unsaturated polycarboxylic acids such as monomethyl maleate and monoethyl fumarate. Examples of acid anhydrides include unsaturated polycarboxylic acid anhydrides such as maleic anhydride and itaconic anhydride. Examples of phenols include phenol and alkyl-substituted phenols. Maleic anhydride is particularly preferred because it allows for the easy introduction of modifying groups into the olefin residues of the C5 / C9 petroleum resin using heat, peroxides, or the like.

[0017] The rubber composition of the present invention contains 0.1 to 30 parts by weight of the C5 / C9 petroleum resin per 100 parts by weight of diene rubber, preferably 1 to 15 parts by weight, and more preferably 2 to 10 parts by weight. If the amount of C5 / C9 petroleum resin is less than 0.1 parts by weight, the amine component capture effect is poor, and the resulting composition exhibits poor adhesion to metal members, particularly steel cords. On the other hand, if the amount is more than 30 parts by weight, the rubber hardness is reduced, and products using the composition exhibit poor reinforcing effects. Furthermore, when preparing the rubber composition, commonly used compounding agents, such as silica, carbon black, calcium carbonate, talc, clay, mica, alumina, aluminum hydroxide, glass fiber, glass beads, glass balloons, and carbon fiber, may be blended within the scope of the present invention. Furthermore, silane coupling agents, softeners, plasticizers, flame retardants, antioxidants, zinc oxide, magnesium oxide, stearic acid, and organic acid cobalt salts may be appropriately selected and blended within the usual blending amounts. When preparing a rubber composition, a method may be used in which appropriately selected compounding ingredients are blended and mixed using a mixer such as a Banbury mixer, pressure kneader, or open roll mill. The rubber composition of the present invention can be used for various purposes as a general rubber or vulcanized rubber (sometimes referred to as a crosslinked rubber), and can produce a (vulcanized) rubber that is particularly excellent in initial adhesion and wet heat resistance. To produce a vulcanized rubber, a vulcanization (crosslinking) agent, a vulcanization (crosslinking) accelerator, a vulcanization (crosslinking) accelerator auxiliary, etc., which are typically blended in a vulcanized rubber, can be blended and vulcanized (crosslinked) by heating, for example, with steam. The vulcanization (crosslinking) agent used in this process is not particularly limited, and examples thereof include sulfur, organic peroxides, and thiuram crosslinking agents. The vulcanization (crosslinking) accelerator is not particularly limited, and examples thereof include thiazoles, thiurams, thioureas, sulfenamides, dithiocarbamic acids, guanidines, and mixtures thereof.Examples include hexamethylenetetramine, diphenylguanidine, ethylenethiourea, 2-mercaptobenzothiazole, N-(tert-butyl)-2-benzothiazole sulfenamide, N-cyclohexylbenzothiazole-2-sulfenamide, tetramethylthiuram disulfide, and zinc dimethyldithiocarbamate.

[0018] The rubber obtained by vulcanizing the rubber composition of the present invention can be used as a rubber material in various applications. Furthermore, the vulcanized rubber exhibits excellent initial adhesion and wet heat resistance to metal members, particularly plated metal members, such as metal plates, metal cords, metal fibers, and wires, and is also resorcinol- and formaldehyde-free. Therefore, the rubber composition is suitable for rubber-metal composites, which are adhesives between plated metal members and rubber, such as vulcanized rubber-coated metal plates, vulcanized rubber-metal plate laminates, vulcanized rubber-coated metal cords, vulcanized rubber-coated wires, metal fiber-reinforced vulcanized rubbers, and wire-reinforced vulcanized rubbers. In particular, the rubber composition has performance suitable for use as a rubber composition for adhering steel cords, making it suitable for rubber-metal composites in which the metal member is a steel cord, particularly a brass-plated or zinc-plated steel cord. Specific examples include steel cord-reinforced rubbers containing at least plated steel cords as a constituent material, and more specifically, tire belts, conveyor belts, hoses, and the like, making it possible to provide tires, conveyor belts, and hoses with excellent durability.

[0019] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The raw materials, analytical methods, test methods and evaluation methods used in the examples and comparative examples are as follows.

[0020] 1. Raw Materials 1) Diene Rubber Natural rubber (hereinafter sometimes referred to as NR): manufactured by Shinko Boeki Co., Ltd. (product name) SVR3L. Isoprene rubber (hereinafter sometimes referred to as IR): manufactured by Nippon Zeon Co., Ltd. (product name) Nipol IR2200. Butadiene rubber (hereinafter sometimes referred to as BR): manufactured by Nippon Zeon Co., Ltd. (product name) Nipol BR1220. Styrene-butadiene rubber (hereinafter sometimes referred to as SBR): manufactured by Nippon Zeon Co., Ltd. (product name) Nipol 1502.

[0021] 2) Petroleum Resin <Feedstock Oil> The feedstock oils were a C5 fraction with a boiling range of 20 to 110°C obtained by cracking and refining naphtha, and a C9 fraction with a boiling range of 140 to 280°C. Table 1 shows the composition of the C5 fraction, and Table 2 shows the composition of the C9 fraction.

[0022]

[0023]

[0024] <Catalysts for producing C5 / C9 petroleum resins and C9 petroleum resins> Boron trifluoride phenol: 30% by weight boron trifluoride (manufactured by Stella Chemifa Co., Ltd.). <Catalysts for producing C5 petroleum resins> Aluminum chloride (manufactured by Sigma-Aldrich). 3) Fillers, compounding agents, etc. Carbon black ("CB" in the table): Asahi Carbon (trade name: Asahi #60). Zinc oxide: Sakai Chemical Industry (trade name: Zinc Oxide Type 1). Oil: Idemitsu Kosan (trade name: Diana Process Oil PW-90). Stearic acid: NOF (trade name: NAA-180). Cobalt stearate: DIC (trade name: Co-STEARATE). Anti-aging agent: Ouchi Shinko Chemical Industry (trade name: Nocrac 810-NA). Vulcanizing agent ("sulfur" in the table): Insoluble sulfur, Sanfel (trade name) manufactured by Sanshin Chemical Industry Co., Ltd. Vulcanization accelerator: N-(tert-butyl)-2-benzothiazole sulfenamide (hereinafter sometimes referred to as TBBS), Sancerer NS-G (trade name) manufactured by Sanshin Chemical Industry Co., Ltd.

[0025] 4) Metallic parts Brass plate: Made from standard test pieces.

[0026] 2. Analysis and Evaluation Methods 1) Measurement of Mw: Mw was measured by gel permeation chromatography (GPC) using standard polystyrene as the standard substance. 2) Measurement of Acid Value: Acid value was measured according to a method in accordance with JIS K-0070 (1992). 3) Measurement of Softening Point: Softening point was measured according to a method in accordance with JIS K-2531 (1960) (ring and ball method). 4) Measurement of Peel Strength and Rubber Residual Rate of Rubber-Metal Composite: Using a tensile tester (manufactured by A&D, (trade name) Tensilon RTG), the obtained rubber-metal composite was cut into a test piece of 100 mm in length and 25 mm in width, and the initial adhesive peel strength was measured according to the peel test method described in JIS K6256-2. For the measurement of wet heat adhesive peel strength, a rubber-metal composite was used that had undergone an accelerated wet heat aging test at a temperature of 80°C and a relative humidity of 96% for 4 weeks. In addition, the peeled surface on the metal side after the peel test was observed using a digital microscope (Hirox, product name HRX-01), and the image obtained was binarized to measure the residual rubber rate on the metal side.

[0027] Synthesis Example 1 (Production of C5 / C9 Petroleum Resins G and A) 500 g of feedstock oil consisting of 30 wt% C5 fraction and 70 wt% C9 fraction obtained by cracking naphtha was prepared and charged into a 2-liter glass autoclave. Next, after adjusting to 40 ° C under a nitrogen atmosphere, 1.0 g of boron trifluoride phenol complex was added as a Friedel-Crafts catalyst relative to the feedstock oil and polymerized for 2 hours. Thereafter, the catalyst was deactivated with aqueous caustic soda solution, the oil phase was recovered, and the unreacted feedstock oil was distilled off to obtain C5 / C9 petroleum resin G. The physical properties (molecular weight, acid value, softening point) of the obtained C5 / C9 petroleum resin G are shown in Table 3. Furthermore, 200 g of the obtained C5 / C9 petroleum resin G and 0.6 g of maleic anhydride were charged into a 1-liter glass autoclave, and the mixture was reacted for 10 minutes with stirring at 200°C in a nitrogen stream with an oxygen concentration of 2 ppm to obtain a maleic anhydride group-modified C5 / C9 petroleum resin, C5 / C9 petroleum resin A. The physical properties of the obtained C5 / C9 petroleum resin A are shown in Table 3.

[0028] Synthesis Examples 2 and 3 (Production of C5 / C9 Petroleum Resins B and C) C5 / C9 petroleum resins modified with maleic anhydride groups were obtained in the same manner as in Synthesis Example 1, except that the amount of maleic anhydride added per 200 g of C5 / C9 petroleum resin G was changed to the amount shown in Table 3. The physical properties of the obtained C5 / C9 petroleum resins B and C are shown in Table 3.

[0029] Synthesis Examples 4 and 5 (Production of C5 / C9 Petroleum Resins D and E) C5 / C9 petroleum resins modified with maleic anhydride groups, namely, C5 / C9 petroleum resins D and E, were obtained in the same manner as in Synthesis Example 2, except that the ratios of the C5 fraction and C9 fraction as feedstock oils were set to the amounts shown in Table 3. The physical properties of the obtained C5 / C9 petroleum resins D and E are shown in Table 3.

[0030] Synthesis Example 6 <Production of C5 / C9 Petroleum Resin F> 500 g of feedstock oil consisting of 20 wt% C5 fraction and 80 wt% C9 fraction obtained by cracking naphtha was prepared and charged into a 2-liter glass autoclave. Next, after adjusting to 40 ° C under a nitrogen atmosphere, 1.0 g of boron trifluoride phenol complex as a Friedel-Crafts catalyst and 1.5 g of phenol were added to the feedstock oil and polymerized for 2 hours. Thereafter, the catalyst was deactivated and removed with an aqueous caustic soda solution, the oil phase was recovered, and unreacted feedstock oil was removed from the oil phase by distillation to obtain C5 / C9 Petroleum Resin F, a phenol-modified C5 / C9 petroleum resin. The physical properties of the obtained C5 / C9 Petroleum Resin F are shown in Table 3.

[0031] Synthesis Example 7 <Production of C5 / C9 Petroleum Resin H> 500 g of feedstock oil consisting of 30 wt% C5 fraction and 70 wt% C9 fraction obtained by cracking naphtha was prepared and charged into a 2-liter glass autoclave. Next, after adjusting the temperature to 40°C under a nitrogen atmosphere, 1.0 g of boron trifluoride phenol complex was added as a Friedel-Crafts catalyst to the feedstock oil and polymerized for 2 hours. Thereafter, the catalyst was deactivated with an aqueous caustic soda solution, the oil phase was recovered, and the unreacted feedstock oil was removed by distillation to obtain a C5 / C9 petroleum resin. Furthermore, 100 g of C5 / C9 petroleum resin and 300 g of xylene were charged into a 1-liter glass autoclave, and 0.2 g of di-t-butyl peroxide and 8 g of maleic anhydride were added. The mixture was reacted at 130°C with stirring for 10 minutes, and then the xylene was distilled off to obtain C5 / C9 petroleum resin H, which is a maleic anhydride group-modified C5 / C9 petroleum resin. The physical properties of the obtained C5 / C9 petroleum resin H are shown in Table 3.

[0032] Synthesis Examples 8 and 9 (Production of C5 Petroleum Resins A and B) A 2-liter glass autoclave was charged with 500 g of a feedstock oil consisting of a C5 fraction obtained by cracking naphtha. Next, after adjusting the temperature to 40 ° C under a nitrogen atmosphere, 1 g of aluminum chloride and 2 g of xylene were added as a Friedel-Crafts catalyst to the feedstock oil and polymerized for 3 hours. Thereafter, the catalyst was deactivated with an aqueous caustic soda solution, the oil phase was recovered, and the unreacted feedstock oil was removed by distillation to obtain a C5 petroleum resin. Furthermore, a 1-liter glass autoclave was charged with 100 g of C5 petroleum resin and 300 g of xylene, and 0.2 g of di-t-butyl peroxide and 0.8 g or 2 g of maleic anhydride were added. The reaction was carried out at 130 ° C for 10 minutes with stirring, and then the xylene was removed by distillation to obtain C5 petroleum resins A and B, which are maleic anhydride group-modified C5 petroleum resins. The physical properties of the obtained C5 petroleum resins A and B are shown in Table 3.

[0033] Synthesis Examples 10 and 11 (Production of C9 Petroleum Resins A and B) 500 g of feedstock oil consisting of 100 wt. % C9 fraction obtained by cracking naphtha was prepared and charged into a 2-liter glass autoclave. Next, after adjusting the temperature to 40°C under a nitrogen atmosphere, 1.2 g of boron trifluoride phenol complex was added as a Friedel-Crafts catalyst to the feedstock oil and polymerized for 2 hours. The catalyst was then deactivated with aqueous caustic soda, the oil phase was recovered, and the unreacted feedstock oil was distilled off to obtain a C9 petroleum resin. Furthermore, 200 g of C9 petroleum resin was charged into a 1-liter glass autoclave, and 0.8 g or 2.8 g of maleic anhydride was added. The reaction was carried out for 10 minutes at 200°C under a nitrogen stream with an oxygen concentration of 2 ppm while stirring, to obtain maleic anhydride group-modified C9 petroleum resins A and B. The physical properties of the obtained C9 petroleum resins A and B are shown in Table 3.

[0034]

[0035] Example 1 300 g of natural rubber (SVR3L, product name, manufactured by Shinko Boeki Co., Ltd.) was charged into a lab mixer (780 cc, manufactured by Daihan Co., Ltd.), and the following were added relative to 100 parts by weight of the diene rubber (natural rubber): 8 parts by weight of C5 / C9 petroleum resin A, 40 parts by weight of carbon black (Asahi Carbon, product name Asahi #60), 2 parts by weight of oil (Idemitsu Kosan, product name Diana Process Oil PW-90), 0.5 parts by weight of stearic acid (Fujifilm Wako Pure Chemical Industries Co., Ltd.), 1 part by weight of cobalt stearate (Co-STEARATE, product name, manufactured by DIC), 8 parts by weight of zinc oxide (Inoue Lime Industry Co., Ltd.), and 0.8 parts by weight of an antioxidant (Nocrac 6C, product name, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), and the rubber composition was taken out after a total mixing time of 5 minutes. The ram pressure and rotation speed were adjusted so that the temperature of the rubber composition at the time of removal would be 140 to 150° C. The rubber composition was obtained by cooling to room temperature.

[0036] Subsequently, 5 parts by weight of sulfur (manufactured by Sanshin Chemical Industry, trade name: Sunfel) as a vulcanizing agent and 0.5 parts by weight of a vulcanization accelerator (manufactured by Ouchi Shinko Chemical Industry, trade name: Noccela NS-G) were added and kneaded for 1 minute, followed by sheeting using an 8-inch roll to obtain an unvulcanized rubber composition. The resulting unvulcanized rubber composition sheet was laminated on a brass plate (manufactured by Standard Test Piece), and the vulcanized rubber and brass plate were vulcanized and bonded using a heated press at a vulcanization temperature of 150°C for 30 minutes to obtain a rubber-brass plate composite. Test specimens were prepared from the resulting rubber-brass plate composite, and evaluations of initial adhesion, wet heat adhesion, and rubber residual rate were performed. The evaluation results are shown in Table 4. The resulting rubber-brass plate composite exhibited excellent initial adhesion, wet heat adhesion, and rubber residual rate, confirming that the resulting rubber composition is suitable as a rubber composition for bonding steel cord.

[0037] Example 2 A rubber composition and a rubber-brass plate composite were prepared and evaluated in the same manner as in Example 1, except that 25 parts by weight of C5 / C9 petroleum resin A was used instead of 8 parts by weight of C5 / C9 petroleum resin A. The results are shown in Table 4. The obtained rubber-brass plate composite had excellent initial adhesion, wet heat adhesion, and rubber residual rate, and it was confirmed that the obtained rubber composition is suitable as a rubber composition for bonding steel cord.

[0038] Examples 3 to 5: Rubber compositions and rubber-brass plate composites were prepared and evaluated in the same manner as in Example 1, except that IR, NR / BR in a weight ratio of 70 / 30, and NR / SBR in a weight ratio of 70 / 30 were used instead of NR. The results are shown in Table 4. The obtained rubber-brass plate composites were excellent in initial adhesion, wet heat adhesion, and rubber residual rate, and it was confirmed that the rubber compositions are suitable as rubber compositions for bonding steel cord.

[0039] Examples 6 to 10: Rubber compositions and rubber-brass plate composites were prepared and evaluated in the same manner as in Example 1, except that C5 / C9 petroleum resins B to F were used instead of C5 / C9 petroleum resin A. The results are shown in Table 4. The obtained rubber-brass plate composites were excellent in initial adhesion, wet heat adhesion, and rubber residual rate, and it was confirmed that the rubber compositions are suitable as rubber compositions for bonding steel cords.

[0040]

[0041] Comparative Example 1 A rubber composition and a rubber-brass plate composite were prepared and evaluated in the same manner as in Example 1, except that C5 / C9 petroleum resin A was not used. The results are shown in Table 5. The obtained rubber-brass plate composite was inferior in initial adhesive peel strength, wet heat adhesive peel strength, and rubber residual rate. Comparative Examples 2 to 14 A rubber composition and a rubber-brass plate composite were prepared and evaluated in the same manner as in Example 1, except that the compounding ingredients and compounding amounts of the rubber composition were as shown in Tables 5 and 6. The results are shown in Tables 5 and 6. The obtained rubber-brass plate composite was inferior in initial adhesive peel strength, wet heat adhesive peel strength, and rubber residual rate.

[0042]

[0043]

[0044] The entire contents of the claims, specification and abstract of Japanese Patent Application No. 2024-147225 filed on August 29, 2024 are hereby incorporated by reference as the disclosure of the specification of the present invention.

[0045] The rubber composition of the present invention is resorcinol- and formaldehyde-free and has excellent initial adhesion and wet heat resistance. It is particularly possible to provide a rubber composition for bonding steel cords, and the rubber composition can be suitably used for metal-reinforced rubber structures such as tires, conveyor belts, and hoses that contain at least plated steel cords as components.

Claims

1. A rubber composition comprising, per 100 parts by weight of diene rubber, 0.1 to 30 parts by weight of a C5 / C9 petroleum resin having a weight average molecular weight of less than 5,000 as determined by gel permeation chromatography in terms of standard polystyrene and an acid value of 1 to 75 (mg-KOH / g).

2. The rubber composition according to claim 1, wherein the diene rubber is at least one rubber selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, and ethylene propylene diene rubber.

3. A rubber composition according to claim 1 or 2, characterized in that the C5 / C9 petroleum resin is at least one modified C5 / C9 petroleum resin selected from the group consisting of unsaturated carboxylic acid-modified C5 / C9 petroleum resin, acid anhydride-modified C5 / C9 petroleum resin, and phenol-modified C5 / C9 petroleum resin.

4. A rubber composition according to any one of claims 1 to 3, characterized in that the softening point of the C5 / C9 petroleum resin is 70 to 150°C.

5. A rubber composition according to any one of claims 1 to 4, characterized in that the weight average molecular weight of the C5 / C9 petroleum resin is 500 or more and 4,000 or less.

6. The rubber composition according to any one of claims 1 to 5, which is a rubber composition for bonding plated metal members.

7. The rubber composition according to claim 6, wherein the rubber composition for bonding plated metal members is a rubber composition for bonding brass-plated metal members or a rubber composition for bonding zinc-plated metal members.

8. The rubber composition according to claim 6 or 7, wherein the rubber composition for bonding plated metal members is a rubber composition for bonding steel cords.

9. A rubber-metal composite comprising a plated metal member and rubber bonded together, wherein the rubber is a vulcanized rubber of the rubber composition according to any one of claims 1 to 8.

10. The rubber-metal composite according to claim 9, wherein the plated metal member is a steel cord and the composite is a tire belt, a conveyor belt, or a hose.

11. The rubber-metal composite according to claim 9 or 10, which is free of resorcinol and formaldehyde.

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