rubber composition

Abstract

The present invention provides a rubber composition that has excellent initial adhesion and wet heat resistance to metals, particularly brass (typically steel cord) and zinc-plated metals, and a rubber-metal composite that can be made resorcinol- and formaldehyde-free by using the rubber composition. [Solution] A rubber composition containing 100 parts by weight of diene rubber and 0.1 to 30 parts by weight of a C5 / C9 petroleum resin having a weight average molecular weight of less than 5,000 in terms of standard polystyrene measured by gel permeation chromatography and an acid value of 1 to 75 (mg-KOH / g), and an application in which vulcanized rubber of the rubber composition is bonded to a metal member.

Description

[Technical Field]

[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. [Background technology]

[0002] Rubber products such as tires, conveyor belts, and hoses used in the fields of automobiles, industrial parts, and construction materials are often constructed as composites using metal plates, metal fibers, and wires, particularly steel cords, as reinforcements. Steel cords are typically plated with brass or zinc to prevent corrosion. Resorcinol resins are also widely used to improve adhesion between the rubber and steel cords.

[0003] On the other hand, it has been reported that the amine components produced as by-products of sulfenamide vulcanization accelerators used in vulcanizing rubber compositions corrode the plating on the surface of steel cords in the humid and heat-exposed environment in which they are used, reducing the adhesion between the rubber and steel cord. Therefore, there is a need to improve not only the initial adhesion between rubber and steel cord, but also the long-term adhesion resistance to humidity and heat.

[0004] Therefore, as a method for improving the adhesion between rubber and steel cord, a method has been reported in which an excess amount of hexamethoxymethylmelamine is used in a resorcinol resin to capture amine components in the rubber (see, for example, Non-Patent Document 1).

[0005] Further, there is 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 reinforcing material (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 its derivatives. 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, unsaturated fatty acid of C11 or more, and fatty acid cobalt salt to capture amine components presumably derived from vulcanization accelerators that cause corrosion at the adhesive interface (see, for example, Patent Document 5). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Journal of the Society of Rubber Science and Technology of Japan, Vol. 75, No. 11, p. 488 (2002) [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 58-161604 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-176580 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-99868 [Patent Document 4] Japanese Patent Application Publication No. 2019-112746 [Patent Document 5] Patent Publication No. 2021-138930 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the method proposed in Non-Patent Document 1, although formaldehyde liberated from hexamethoxymethylmelamine reacts with resorcinol to harden, there is a problem in that harmful substances, resorcinol and formaldehyde, are generated. Also, in the proposals of Patent Documents 1 to 5, although some degree of effect on initial adhesion or adhesion resistant to wet heat was observed, the results were not satisfactory, and further improvement in adhesion between rubber and steel cord was expected.

[0009] Therefore, an object of the present invention is to provide a rubber composition that is applicable to steel cords and has excellent initial adhesion and wet heat resistance, and further to provide a rubber-metal composite that can be made resorcinol- and formaldehyde-free by using the rubber composition. Note that "resorcinol- and formaldehyde-free" means that resorcinol, formaldehyde, or resorcinol-formaldehyde condensates are not used as raw materials, etc. [Means for solving the problem]

[0010] As a result of intensive research conducted by the present inventors to solve the above-mentioned problems, they discovered that by adding a specific C5 / C9 petroleum resin to a diene-based rubber, a rubber composition can be obtained that makes it possible to provide a rubber-metal composite that has excellent initial adhesion and wet heat-resistant adhesion without generating resorcinol or formaldehyde, and thus completed the present invention.

[0011] That is, the present invention comprises the following [1] to [9]. [1] A rubber composition comprising 100 parts by weight of diene rubber and 0.1 to 30 parts by weight of a C5 / C9 petroleum resin having a weight average molecular weight of less than 5000 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 [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] The rubber composition according to [1], wherein the C5 / C9 petroleum resin is at least one modified C5 / C9 petroleum resin selected from the group consisting of 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 [1], wherein the C5 / C9 petroleum resin is a C5 / C9 petroleum resin having a softening point of 70 to 150°C. [5] The rubber composition according to [1], which is a rubber composition for bonding plated metal members. [6] The rubber composition according to [5], 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. [7] The rubber composition according to [5], wherein the rubber composition for bonding plated metal members is a rubber composition for bonding steel cords. [8] A rubber-metal composite in the form of an adhesive bond between a plated metal member and rubber, characterized in that the rubber is a vulcanized rubber of the rubber composition described in [1]. [9] The rubber-metal composite according to [8], wherein the plated metal member is a steel cord, and the composite is a tire belt, a conveyor belt, or a hose.

[0012] The present invention will be described in detail below.

[0013] The rubber composition of the present invention contains 100 parts by weight of diene rubber and 0.1 to 30 parts by weight of a C5 / C9 petroleum resin having a weight average molecular weight of less than 5000 as determined by gel permeation chromatography in terms of standard polystyrene and an acid value of 1 to 75 (mg-KOH / g).

[0014] 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, polyisoprene rubber, polybutadiene rubber, styrene-butadiene rubber, and ethylene propylene diene rubber, which 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.

[0015] 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 is a C5 / C9 petroleum resin having a weight average molecular weight (hereinafter sometimes referred to as Mw) of less than 5000 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).

[0016] The components constituting the C5 fraction, which is an aliphatic fraction, can be any fraction known to have a boiling point range of 20 to 110°C that is generally obtained by thermal cracking and refining of petroleum, and examples thereof 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.

[0017] The components constituting the C9 fraction, which is an aromatic fraction, can be 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, 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.

[0018] 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 called a C5 / C9 petroleum resin, and examples include those with 10-70 wt% C5 component and 90-30 wt% C9 component. Of these, those with 20-40 wt% C5 component and 80-60 wt% C9 component are preferred because they provide particularly excellent adhesion to metals such as steel cords when made into rubber compositions and vulcanized rubbers. The C5 / C9 petroleum resin efficiently captures amine components and partially migrates to the surface of metals such as steel cords, thereby suppressing contact between the metal and corrosion-causing substances such as amine components, water, and oxygen, thereby improving adhesion.

[0019] The C5 / C9 petroleum resin has a Mw of less than 5000 as determined by GPC in terms of standard polystyrene, and having an Mw of less than 5000 results in excellent compatibility with rubber, and it is particularly preferable that the Mw is 500 to 4000, and more preferably 500 to 3500. However, if the Mw is 5000 or more, the compatibility with diene rubber is poor, making it difficult to prepare a rubber composition.

[0020] The C5 / C9 petroleum resin, when incorporated into a rubber composition, traps amine components as an acid component, enabling the formation of a vulcanized rubber-metal composite, thereby providing a rubber composition with excellent adhesion to metal surfaces. The acid value is 1 to 75 (mg-KOH / g), with 1 to 50 (mg-KOH / g) being preferred, and 5 to 30 (mg-KOH / g) being particularly preferred due to its excellent amine component trapping effect. If the acid value is less than 1 (mg-KOH / g), the amine components cannot be sufficiently trapped, resulting in a rubber composition and vulcanized rubber with poor adhesion to metal components. On the other hand, if the acid value is greater than 75 (mg-KOH / g), the compatibility with diene rubbers is poor, resulting in poor processability and mechanical properties. The acid value can be measured, for example, by a method conforming to JIS K-0070 (1992).

[0021] 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 and vulcanized rubber that are 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).

[0022] 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. Among these, aluminum trichloride, boron trifluoride phenol complex, and 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 catalyst of 0.1 to 2.0 parts by weight per 100 parts by weight of the feedstock oil is used, and polymerization is carried out for 0.1 to 10 hours. The reaction pressure is preferably atmospheric pressure to 1 MPa.

[0023] 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 providing rubber compositions and vulcanized rubbers with excellent adhesion to metal components, particularly steel cords. 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.

[0024] The rubber composition of the present invention comprises 0.1 to 30 parts by weight of the C5 / C9 petroleum resin per 100 parts by weight of diene rubber. If the amount of C5 / C9 petroleum resin is less than 0.1 part by weight, the amine component capture effect is poor, resulting in 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, resulting in poor reinforcing effects in products using the composition. 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 compounded 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 compounded within the usual compounding 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. 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 moisture-heat resistance. When preparing a vulcanized rubber, the composition may be blended with, for example, a vulcanization (crosslinking) agent, a vulcanization (crosslinking) accelerator, or a vulcanization (crosslinking) accelerator auxiliary, which are typically blended in a vulcanized rubber, and then 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.

[0025] 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 has 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 can be made resorcinol- and formaldehyde-free. Therefore, the rubber composition is suitable for rubber-metal composites, 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 containing steel cords, particularly brass- or zinc-plated steel cords, as the metal member. Specific examples include steel-cord-reinforced rubbers containing at least plated steel cords as their constituent materials, such as tire belts, conveyor belts, and hoses. These rubber composites can provide tires, conveyor belts, and hoses with excellent durability. [Effects of the Invention]

[0026] 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 to provide a rubber-metal composite with excellent durability. [Example]

[0027] Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. The raw materials, analysis, test methods, and evaluation methods used in the examples and comparative examples are as follows.

[0028] 1. Raw materials 1) Dienic rubber Natural rubber (hereinafter sometimes referred to as NR): SVR3L manufactured by Shenggong Trading Co., Ltd. Isoprene rubber (hereinafter sometimes referred to as IR): Nipol IR2200 manufactured by Nippon Zeon Co., Ltd. Butadiene rubber (hereinafter sometimes referred to as BR): Nipol BR1220 manufactured by Nippon Zeon Co., Ltd. Styrene-butadiene rubber (hereinafter sometimes referred to as SBR): Nipol1502 manufactured by Nippon Zeon Co., Ltd.

[0029] 2) Petroleum resin <Raw material oil> The C5 fraction, which is a fraction with a boiling range of 20 to 110 °C obtained by the decomposition and purification of naphtha, and the C9 fraction with a boiling range of 140 to 280 °C were used as the raw material oil. Table 1 shows the composition of the C5 fraction, and Table 2 shows the composition of the C9 fraction respectively.

[0030]

Table 1

[0031]

Table 2

[0032] <C5 / C9 petroleum resin, catalyst for manufacturing C9 petroleum resin> Boron trifluoride phenol: 30 wt% boron trifluoride product (manufactured by Stella Chemifa Corporation).

[0033] <Catalyst for manufacturing C5 petroleum resin> Aluminum chloride (manufactured by Sigma-Aldrich).

[0034] 3) Fillers, compounding agents, etc. Carbon black: Asahi Carbon (product name) Asahi #60. Zinc oxide: Zinc oxide type 1 manufactured by Sakai Chemical Industry Co., Ltd. (product name). Oil: Idemitsu Kosan (product name) Diana Process Oil PW-90. Stearic acid: NOF Corporation (trade name) NAA-180. Cobalt stearate: DIC (trade name) Co-STEARATE. Anti-aging agent: Nocrac 810-NA (product name) manufactured by Ouchi Shinko Chemical Industry. Vulcanizing agent: Insoluble sulfur, Sanfer (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.

[0035] 4) Metallic materials Brass plate: Made from standard test piece.

[0036] 2.Analysis and evaluation methods 1) Measurement of Mw The Mw was measured by gel permeation chromatography (GPC) using standard polystyrene as the standard substance.

[0037] 2) Acid value measurement The acid value was measured by a method in accordance with JIS K-0070 (1992).

[0038] 3) Measurement of softening point The softening point was measured by a method in accordance with JIS K-2531 (1960) (ring and ball method).

[0039] 4) Measurement of peel strength and rubber remaining rate of rubber-metal composite Using a tensile tester (manufactured by A&D, product name: Tensilon RTG), the resulting rubber-metal composites were cut into test pieces measuring 100 mm in length and 25 mm in width, and the peel strength was measured according to the peel test method specified in JIS K6256-2. For measuring the heat-and-humidity adhesion, rubber-metal composites were subjected to an accelerated heat-and-humidity aging test at a temperature of 80°C and a relative humidity of 96% for four weeks. After the peel test, the peeled surface on the metal side was observed with a digital microscope (manufactured by Hirox, product name: HRX-01), and the resulting image was binarized to measure the percentage of rubber remaining on the metal side.

[0040] Synthesis Example 1 (Production of C5 / C9 Petroleum Resins G and A) A 2-liter glass autoclave was charged with 500 g of feedstock oil, consisting of 30 wt% C5 fraction and 70 wt% C9 fraction obtained by cracking naphtha. The temperature was then adjusted to 40°C under a nitrogen atmosphere. 1.0 g of boron trifluoride phenol complex was added as a Friedel-Crafts catalyst and polymerized for 2 hours. The catalyst was then deactivated with aqueous caustic soda, the oil phase was recovered, and the unreacted feedstock was removed by distillation to obtain C5 / C9 petroleum resin G. The physical properties (molecular weight, acid value, softening point) of the resulting C5 / C9 petroleum resin G are shown in Table 3.

[0041] 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 at 200°C with stirring 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.

[0042] Synthesis Examples 2 and 3 (Production of C5 / C9 Petroleum Resins B and C) C5 / C9 petroleum resins B and C, which are maleic anhydride group-modified C5 / C9 petroleum resins, 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 shown in Table 3. The physical properties of the obtained C5 / C9 petroleum resins B and C are shown in Table 3.

[0043] Synthesis Examples 4 and 5 (Production of C5 / C9 Petroleum Resins D and E) C5 / C9 petroleum resins D and E, which are maleic anhydride group-modified C5 / C9 petroleum resins, were obtained in the same manner as in Synthesis Example 2, except that the proportions of the C5 fraction and the C9 fraction as the raw material 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.

[0044] Synthesis Example 6 <Production of C5 / C9 Petroleum Resin F>[[]]END]] In a 2-liter glass autoclave, 500 g of a raw material oil composed of 20% by weight of a C5 fraction and 80% by weight of a C9 fraction obtained by the decomposition of naphtha as the raw material oil was prepared and charged. Next, after adjusting the temperature to 40°C under a nitrogen atmosphere, 1.0 g of boron trifluoride phenol complex as a Friedel-Crafts type catalyst and 1.5 g of phenol were added to the raw material oil, and polymerization was carried out for 2 hours. Then, the catalyst was deactivated and removed with an aqueous sodium hydroxide solution, the oil phase was recovered, and the unreacted raw material oil was removed by distillation from the oil phase to obtain a phenol-modified C5 / C9 petroleum resin, C5 / C9 petroleum resin F. The physical properties of the obtained C5 / C9 petroleum resin F are shown in Table 3.

[0045] Synthesis Example 7 <Production of C5 / C9 Petroleum Resin H>[[]]END]] In a 2-liter glass autoclave, 500 g of a raw material oil composed of 30% by weight of a C5 fraction and 70% by weight of a C9 fraction obtained by the decomposition of naphtha as the raw material oil was prepared and charged. Next, after adjusting the temperature to 40°C under a nitrogen atmosphere, 1.0 g of boron trifluoride phenol complex as a Friedel-Crafts type catalyst was added to the raw material oil, and polymerization was carried out for 2 hours. Then, the catalyst was deactivated with an aqueous sodium hydroxide solution, the oil phase was recovered, and the C5 / C9 petroleum resin was obtained by distilling off the unreacted raw material oil.

[0046] Furthermore, 100 g of the C5 / C9 petroleum resin and 300 g of xylene were charged into a 1-liter glass autoclave, 0.2 g of di-t-butyl peroxide and 8 g of maleic anhydride were added, and after reacting at 130°C with stirring for 10 minutes, the xylene was distilled off to obtain a maleic anhydride group-modified C5 / C9 petroleum resin, C5 / C9 petroleum resin H. The physical properties of the obtained C5 / C9 petroleum resin H are shown in Table 3.

[0047] Synthesis Examples 8 and 9 (Production of C5 Petroleum Resins A and B) A 2-liter glass autoclave was charged with 500 g of C5 fraction obtained by cracking naphtha. The temperature was then adjusted to 40°C under a nitrogen atmosphere. Friedel-Crafts catalysts, 1 g of aluminum chloride and 2 g of xylene, were added to the feedstock and polymerized for 3 hours. The catalyst was then deactivated with an aqueous caustic soda solution, the oil phase was recovered, and the unreacted feedstock was removed by distillation to obtain a C5 petroleum resin.

[0048] Furthermore, 100 g of C5 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 0.8 g or 2 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 maleic anhydride-modified C5 petroleum resins, C5 petroleum resins A and B. The physical properties of the obtained C5 petroleum resins A and B are shown in Table 3.

[0049] 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. 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 an aqueous caustic soda solution, the oil phase was recovered, and the unreacted feedstock oil was removed by distillation to obtain a C9 petroleum resin.

[0050] Furthermore, 200 g of C9 petroleum resin was placed in a 1-liter glass autoclave, and 0.8 g or 2.8 g of maleic anhydride was added. The mixture was reacted for 10 minutes at 200°C with stirring in a nitrogen stream with an oxygen concentration of 2 ppm to obtain maleic anhydride-modified C9 petroleum resins, C9 petroleum resins A and B. The physical properties of the obtained C9 petroleum resins A and B are shown in Table 3.

[0051] [Table 3]

[0052] Example 1 A lab mixer (manufactured by Daihan Co., Ltd., capacity 780 cc) was charged with 300 g of natural rubber (manufactured by Shinko Boeki, product name SVR3L). The following was added to 100 parts by weight of diene rubber (natural rubber): 8 parts by weight of C5 / C9 petroleum resin A, 40 parts by weight of carbon black (manufactured by Asahi Carbon, product name Asahi #60), 2 parts by weight of oil (manufactured by Idemitsu Kosan, product name Diana Process Oil PW-90), 0.5 parts by weight of stearic acid (manufactured by Fujifilm Wako Pure Chemical Industries), 8 parts by weight of zinc oxide (manufactured by Inoue Lime Industry), and 0.8 parts by weight of antioxidant (manufactured by Ouchi Shinko Chemical Industry, product name Nocrac 6C). After a total mixing time of 5 minutes, the rubber composition was removed. The ram pressure and rotation speed were adjusted so that the temperature of the rubber composition at the time of removal was 140 to 150°C. The mixture was cooled to room temperature to obtain a rubber composition.

[0053] Next, 5 parts by weight of sulfur (manufactured by Sanshin Chemical Industry, product name Sunfel) as a vulcanizing agent and 0.5 parts by weight of a vulcanization accelerator (manufactured by Ouchi Shinko Chemical Industry, product 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 obtained 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 hot press at a vulcanization temperature of 150°C for 30 minutes to obtain a rubber-brass plate composite.

[0054] Test pieces were prepared from the resulting rubber-brass plate composite and evaluated for initial adhesion, adhesion under wet heat, and rubber residual rate. The evaluation results are shown in Table 4. The resulting rubber-brass plate composite had excellent initial adhesion, adhesion under wet heat, and rubber residual rate, and it was confirmed that the resulting rubber composition is suitable as a rubber composition for bonding steel cord.

[0055] 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.

[0056] 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 at a weight ratio of 70 / 30, and NR / SBR at 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 composition is suitable as a rubber composition for bonding steel cord.

[0057] 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 composition is suitable as a rubber composition for bonding steel cord.

[0058] [Table 4]

[0059] 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 poor in initial adhesive peel strength, wet heat adhesive peel strength, and rubber residual rate.

[0060] 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 poor in initial adhesive peel strength, wet heat adhesive peel strength, and rubber residual rate.

[0061] [Table 5]

[0062] [Table 6] [Industrial Applicability]

[0063] 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 as a metal-reinforced rubber structure such as a tire, conveyor belt, or hose, which has at least a plated steel cord as a component.

Claims

1. A rubber composition comprising 100 parts by weight of diene rubber and 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. 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. 2. The rubber composition according to claim 1, wherein the C5 / C9 petroleum resin is at least one modified C5 / C9 petroleum resin selected from the group consisting of carboxylic acid-modified C5 / C9 petroleum resins, acid anhydride-modified C5 / C9 petroleum resins, and phenol-modified C5 / C9 petroleum resins.

4. 2. The rubber composition according to claim 1, wherein the C5 / C9 petroleum resin has a softening point of 70 to 150°C.

5. 2. The rubber composition according to claim 1, which is a rubber composition for bonding plated metal members.

6. 6. The rubber composition according to claim 5, 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.

7. 6. The rubber composition according to claim 5, wherein the rubber composition for bonding plated metal members is a rubber composition for bonding steel cords.

8. A rubber-metal composite which is an adhesion product of a plated metal member and rubber, wherein the rubber is a vulcanized rubber of the rubber composition according to claim 1.

9. 9. The rubber-metal composite according to claim 8, wherein the plated metal member is a steel cord, and the composite is a tire belt, a conveyor belt, or a hose.

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