Rubber composition for tire and tire

Abstract

To provide a tire inner liner having high durability (for example, high breaking strength), which has been conventionally required.SOLUTION: A rubber composition for tire comprises, based on 100 pts.mass of a rubber component including butyl rubber, 20-70 pts.mass of carbon black, and 0.5-10 pts.mass of random polypropylene having a melting point of 110-155°C and a melt mass flow rate (MFR) of 6-50 g / 10 min measured at 230°C under a load of 2.16 kg.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition for tires and a tire, and more particularly to a rubber composition for tires that has low heat buildup and can impart practically sufficient breaking strength even when blended with recycled butyl rubber, and a tire using the same. [Background technology]

[0002] An inner liner is disposed in the innermost layer of a tubeless pneumatic tire, and provides the tire with properties such as air permeation prevention performance and oxidation degradation prevention performance. Techniques for improving the physical properties of inner liners are disclosed in, for example, Patent Documents 1 to 3.

[0003] For example, an inner liner needs to have low air permeability and high durability (e.g., high breaking strength) as a casing component. The casing component refers to the tire framework excluding the tread rubber, belt layer, belt cover layer, and sidewall rubber, and includes the bead core, bead filler, carcass layer, reinforcing layer around the bead, and inner liner. Furthermore, growing environmental awareness has led to a demand for tires to use a high proportion of recycled materials. Examples of recycled materials include used tires and tubes, which have been desulfurized to produce recycled butyl rubber for use in tire inner liners. However, recycled butyl rubber contains impurities such as inorganic fillers and residual vulcanizing agents, and increasing the amount of recycled butyl rubber used reduces breaking strength, which is an issue. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2010-505968 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-100135 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-177278 Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, an object of the present invention is to provide a rubber composition for tires which has high breaking strength and is capable of imparting excellent durability, and a tire using the same. [Means for solving the problem]

[0006] As a result of extensive research, the present inventors have discovered that the above-mentioned problems can be solved by blending specific amounts of carbon black and random polypropylene having specific physical properties with a rubber component containing butyl rubber, and have thus been able to complete the present invention.

[0007] Specifically, the present invention provides a rubber composition for tires, characterized by containing, per 100 parts by mass of a rubber component containing a butyl-based rubber, 20 to 70 parts by mass of carbon black and 0.5 to 10 parts by mass of a random polypropylene having a melting point of 110 to 155°C and a melt mass-flow rate (MFR) of 6 to 50 g / 10 min measured at a temperature of 230°C under a load of 2.16 kg. The present invention also provides a tire using the rubber composition for a tire. [Effects of the Invention]

[0008] The random polypropylene used in the present invention has high fluidity and low crystallinity, which promotes wettability with rubber components and molecular entanglement, resulting in good dispersion in the rubber component matrix. Furthermore, the random polypropylene has a melt mass-flow rate (MFR) measured at 230°C within a specific range, which promotes wettability and molecular entanglement, suppresses the formation of foreign matter in the random polypropylene, and provides a rubber composition for tires with excellent breaking strength. This also allows for the compounding of more recycled butyl rubber than conventional methods, thereby reducing environmental impact. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will now be described in further detail.

[0010] (rubber component) The rubber component used in the present invention contains a butyl rubber, and the butyl rubber preferably accounts for 80 parts by mass or more per 100 parts by mass of the rubber component. Examples of butyl rubber include any butyl rubber used for inner liners, such as butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), isobutylene-paramethylstyrene copolymers and their halides. Commercially available butyl rubbers include brominated butyl rubber, such as BROMOBUTYL 2255 manufactured by Japan Butyl Co., Ltd. Recycled butyl rubber can also be used. Recycled butyl rubber is recycled rubber whose main component is butyl rubber obtained by devulcanizing rubber recovered from used tires and tubes. Here, "mainly composed of butyl rubber" means that the butyl rubber component accounts for 50% by mass or more of 100% by mass of recycled butyl rubber. Recycled butyl rubber may contain inorganic fillers, residual vulcanizing agents, and the like in addition to butyl rubber. When referring to the amount of recycled butyl rubber in this specification, the amount of butyl rubber contained in the recycled butyl rubber is used as the basis. The blending amount of the recycled butyl rubber based on this standard is preferably 10 to 60 parts by mass per 100 parts by mass of the rubber component.

[0011] In addition to the butyl rubber, any diene rubber can be blended into the rubber component. As the diene rubber, any diene rubber used in rubber compositions for tires can be used, such as natural rubber (NR) and synthetic isoprene rubber (IR). When a diene rubber is used, the blending amount is preferably 20 parts by mass or less, more preferably 5 to 15 parts by mass, per 100 parts by mass of the rubber component.

[0012] (carbon black) The carbon black used in the present invention preferably has a nitrogen adsorption specific surface area N2SA of 20 to 60 m from the viewpoint of improving the effects of the present invention. 2 / g, and more preferably 20 to 50m 2 In the present invention, N2SA is measured in accordance with JIS K6217-2.

[0013] (random polypropylene) The random polypropylene used in the present invention is characterized by having a melt mass flow rate (MFR) measured at a temperature of 230° C. under a load of 2.16 kg of 6 to 50 g / 10 min. From the viewpoint of improving the effects of the present invention, the melt mass flow rate (MFR) of the random polypropylene measured at a temperature of 230°C under a load of 2.16 kg is preferably more than 6 g / 10 min, more preferably 8 g / 10 min or more. The upper limit of the MFR is, for example, preferably 50 g / 10 min or less, more preferably 40 g / 10 min or less. From the viewpoint of improving the effects of the present invention, the melting point of the random polypropylene is, for example, 110 to 155°C, preferably 130°C or higher and 160°C or lower, and more preferably 130°C or higher and 150°C or lower. In this specification, the melt mass flow rate (MFR) is measured at a temperature of 230°C and a load of 2.16 kg in accordance with "Test method for melt mass flow rate (MFR) of plastics - thermoplastics" specified in JIS K7210:1999. The melting point is measured by differential scanning calorimetry (DSC) in accordance with ASTM D3418 at a heating rate of 10°C / min.

[0014] Examples of random polypropylenes include propylene-ethylene random copolymers, propylene-1-butene random copolymers, and propylene-ethylene-1-butene random copolymers, which are preferred from the viewpoint of the effects of the present invention. Note that the random polypropylene used in the present invention can optionally use comonomers other than those mentioned above, as long as the MFR requirement of the present invention is satisfied.

[0015] The random polypropylene used in the present invention may have a hydrolytically condensable silyl group in the molecule (hereinafter, it may be referred to as a silyl group-containing random polypropylene).

[0016] The silyl group-containing random polypropylene can be obtained, for example, by grafting a hydrolytically condensable silane compound onto random polypropylene, which is a base resin. Specifically, a reaction process can be adopted in which random polypropylene and a free radical generator are brought into the coexistence and heated to decompose the free radical generator, and the generated free radicals abstract hydrogen from the random polypropylene to generate polymer radicals to which a hydrolytically condensable silane compound is added.

[0017] Examples of the hydrolytic condensable silane compound include vinyl silane compounds such as vinyl trimethoxysilane, vinyl triethoxysilane, and vinyl tris(β-methoxyethoxy)silane; amino silane compounds such as γ-aminopropyl trimethoxysilane, γ-aminopropyl triethoxysilane, N-β-(aminoethyl)γ-aminopropyl trimethoxysilane, β-(aminoethyl)γ-aminopropylmethyl dimethoxysilane, and N-phenyl-γ-aminopropyl trimethoxysilane; and β-(3,4-epoxycyclohexyl)ethyl trimethylsilane. Examples of usable silane compounds include epoxysilane compounds such as trimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane; acrylic silane compounds such as γ-methacryloxypropyltrimethoxysilane; polysulfide silane compounds such as bis(3-(triethoxysilyl)propyl)disulfide and bis(3-(triethoxysilyl)propyl)tetrasulfide; and mercaptosilane compounds such as 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane.

[0018] Examples of the free radical generator include known organic peroxides, such as dicumyl peroxide, benzoyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, t-butylperoxyisopropyl carbonate, t-butylperoxybenzoate, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, methyl ethyl ketone peroxide, 2,2-bis(t-butylperoxy)butane, and cumene hydroperoxide.

[0019] The conditions for the reaction process for graft copolymerizing the random polypropylene base resin with the hydrolytically condensable silane compound include, for example, blending 0.1 to 10 parts by mass of the hydrolytically condensable silane compound with 100 parts by mass of the random polypropylene base resin, and mixing the resulting blend at a temperature above the melting point of the random polypropylene. The amount of free radical generator added is, for example, approximately 0.01 to 0.5 parts by mass per 100 parts by mass of the random polypropylene. The reaction conditions for the graft copolymerization are known and are disclosed, for example, in Japanese Patent No. 5768696. During the reaction process, known additives, such as antioxidants, can also be added to the reaction system.

[0020] From the viewpoint of improving the effects of the present invention, the density of the random polypropylene is, for example, 0.860 g / cm 3 More than 1.000g / cm 3 Preferably, it is 0.880 g / cm or less. 3 More than 0.980g / cm 3 More preferably, it is 0.890 g / cm or less. 3 More than 0.970g / cm 3 It is particularly preferred that: The density in the present invention can be measured by the method described in JIS K 7112. When the random polypropylene is a silyl group-containing random polypropylene, the density of the random polypropylene refers to the density of the unmodified random polypropylene that is the base resin before it has hydrolytically condensable silyl groups. The random polypropylene in the rubber composition for tires may have any morphology and / or dispersion state.

[0021] (Compounding ratio of rubber composition for tires) The rubber composition for tires of the present invention is characterized by containing, per 100 parts by mass of the rubber component, 20 to 70 parts by mass of carbon black and 0.5 to 10 parts by mass of a random polypropylene having a melting point of 110 to 155°C and a melt mass flow rate (MFR) of 6 to 50 g / 10 min measured at a temperature of 230°C under a load of 2.16 kg. If the amount of carbon black is less than 20 parts by mass or exceeds 70 parts by mass per 100 parts by mass of the rubber component, the breaking properties will decrease. If the amount of random polypropylene mixed is less than 0.5 parts by mass per 100 parts by mass of the rubber component, the amount is too small to achieve the effects of the present invention, and conversely, if it exceeds 10 parts by mass, the breaking properties will decrease.

[0022] In addition, from the viewpoint of improving the effects of the present invention, the blending amount of carbon black is preferably 20 to 50 parts by mass per 100 parts by mass of the rubber component. In addition, from the viewpoint of improving the effects of the present invention, the blending amount of the random polypropylene is preferably 0.5 to 7 parts by mass per 100 parts by mass of the rubber component.

[0023] (Other ingredients) In addition to the above-mentioned components, the rubber composition for tires of the present invention may contain various additives that are generally compounded in rubber compositions, such as vulcanizing or crosslinking agents, vulcanization or crosslinking accelerators, fillers, antioxidants, plasticizers, resins, and curing agents, and these additives can be kneaded by a general method to form a composition, which can then be used for vulcanization or crosslinking. The amounts of these additives that can be compounded may be conventional amounts, as long as they do not deviate from the object of the present invention.

[0024] (inorganic filler) The rubber composition of the present invention preferably contains an inorganic filler in order to improve its effects. Examples of the inorganic filler include platy inorganic fillers such as clay, talc, bentonite, and montmorillonite, and among these, clay and / or talc are preferred. The blending amount of the inorganic filler is preferably 5 to 40 parts by mass, and more preferably 5 to 30 parts by mass, based on 100 parts by mass of the rubber component.

[0025] The rubber composition for a tire of the present invention can be suitably used as an inner liner of a tire. The thickness (gauge thickness) of the inner liner is preferably 0.2 mm to 20 mm. The tire of the present invention is preferably a pneumatic tire, which can be filled with air, an inert gas such as nitrogen, or other gases. [Example]

[0026] The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0027] (Preparation of various random polypropylenes) The following materials were used as random polypropylene: Random polypropylene A: Novatec PP MG05ES manufactured by Japan Polypropylene Corporation Random polypropylene B: SunAllomer PM731V manufactured by SunAllomer Co., Ltd. Random polypropylene C: SunAllomer PM931M manufactured by SunAllomer Co., Ltd. Random polypropylene D: SunAllomer PM940M manufactured by SunAllomer Co., Ltd. Random polypropylene E: SunAllomer PMA20V manufactured by SunAllomer Co., Ltd. Random polypropylene F: Prime Polypro E-333GV manufactured by Prime Polymer Co., Ltd. The melting points and melt mass flow rates (MFR) of the various random polypropylenes measured at a temperature of 230° C. and a load of 2.16 kg are shown in Table 1 below.

[0028] [Table 1]

[0029] Standard Example 1, Examples 1 to 8, and Comparative Examples 1 to 5 Sample preparation In the formulation (parts by mass) shown in Table 2, the components excluding the vulcanization system (vulcanization accelerator, sulfur) were mixed for 5 minutes in a Banbury mixer at 80°C. The temperature reached at this time was 150°C. Next, the vulcanization system was added and mixed using a roll to obtain a rubber composition. Each obtained rubber composition (unvulcanized) was press-vulcanized in a mold (15 cm x 15 cm x 0.2 cm) at 148°C for 30 minutes to prepare vulcanized rubber test pieces, which were then evaluated as follows.

[0030] Breaking strength: From the vulcanized rubber test pieces prepared as described above, JIS No. 3 dumbbell-shaped test pieces (thickness: 2 mm) were punched out in accordance with JIS K6251, and tests were conducted at a pulling rate of 500 mm / min in an atmosphere of 20°C to measure the tensile breaking strength. The results obtained were expressed as an index, with the value of Reference Example 1 being 100. The larger the index, the better the breaking strength. An index of less than 95 or 105 or greater can be considered to indicate a significant decrease or improvement in breaking strength.

[0031] The results are shown in Table 2. Table 1 also shows the proportion (mass%) of recycled butyl rubber in the rubber component.

[0032] [Table 2]

[0033] *1:NR(SIR20) *2: Butyl rubber (BROMOBUTYL 2255 manufactured by Japan Butyl Co., Ltd.) *3: Recycled butyl rubber (butyl tubular manufactured by Muraoka Rubber Industry Co., Ltd., butyl rubber content = 55% by mass, carbon black content = 32% by mass, other components = 13% by mass) *4: Carbon black GPF (Niteron #GN manufactured by Nippon Steel Carbon Co., Ltd., nitrogen adsorption specific surface area (N2SA) = 27m 2 / g) *5: Zinc oxide (Zinc oxide type 3 manufactured by Seido Chemical Industry Co., Ltd.) *6: Stearic acid (NOF Corporation Beads Stearic Acid YR) *7: Sulfur (Mucron OT-20 manufactured by Shikoku Chemicals Corporation) *8: Vulcanization accelerator DM (Sansera DM manufactured by Sanshin Chemical Industry Co., Ltd.) *9: Talc (Imerys HARtalc)

[0034] The results in Table 2 show that the rubber compositions of each Example contain 20 to 70 parts by mass of carbon black and 0.5 to 10 parts by mass of random polypropylene having a melting point of 110 to 155°C and a melt mass-flow rate (MFR) of 6 to 50 g / 10 min measured at a temperature of 230°C and a load of 2.16 kg per 100 parts by mass of rubber component containing butyl rubber. Therefore, compared to the tire rubber composition of Standard Example 1, the rubber compositions have superior breaking strength, and can maintain breaking strength sufficient for practical use even when the amount of recycled butyl rubber is increased.

[0035] In Comparative Example 1, the amount of carbon black blended was less than the lower limit specified in the present invention, and therefore the breaking strength was reduced. In Comparative Example 2, the amount of carbon black blended exceeded the upper limit specified in the present invention, and therefore the breaking strength was reduced. In Comparative Example 3, the blending amount of random polypropylene was less than the lower limit specified in the present invention, so no improvement in breaking strength was observed. In Comparative Example 4, the blending amount of random polypropylene exceeded the upper limit specified in the present invention, and therefore the breaking strength was reduced. In Comparative Example 5, the melt mass flow rate (MFR) of the random polypropylene measured at a temperature of 230° C. and a load of 2.16 kg was below the lower limit specified in the present invention, and therefore the breaking strength was reduced.

[0036] The present invention includes the following embodiments. Embodiment 1: A rubber composition for tires, characterized by containing, relative to 100 parts by mass of a rubber component containing butyl rubber, 20 to 70 parts by mass of carbon black, and 0.5 to 10 parts by mass of a random polypropylene having a melting point of 110 to 155°C and a melt mass flow rate (MFR) of 6 to 50 g / 10 min measured at a temperature of 230°C under a load of 2.16 kg. Embodiment 2: The carbon black has a nitrogen adsorption specific surface area N2SA of 20 to 60 m 2 The rubber composition for a tire according to embodiment 1, wherein the rubber content is in the range of / g. Embodiment 3: 3. The rubber composition for tires according to claim 1 or 2, wherein the butyl rubber comprises recycled butyl rubber, and the recycled butyl rubber accounts for 10 to 60 parts by mass per 100 parts by mass of the rubber component. Embodiment 4: 4. The rubber composition for a tire according to any one of embodiments 1 to 3, wherein the butyl rubber accounts for 80 parts by mass or more in 100 parts by mass of the rubber component. Embodiment 5: 5. The rubber composition for a tire according to any one of embodiments 1 to 4, wherein the rubber component contains a diene rubber in addition to the butyl rubber, and the proportion of the diene rubber in 100 parts by mass of the rubber component is 20 parts by mass or less. Embodiment 6: A tire using the rubber composition for tires according to any one of embodiments 1 to 5, wherein the random polypropylene is selected from a propylene-ethylene random copolymer, a propylene-1-butene random copolymer, and a propylene-ethylene-1-butene random copolymer. Embodiment 7: 7. The rubber composition for a tire according to any one of embodiments 1 to 6, further comprising clay and / or talc. Embodiment 8: A tire using the rubber composition for a tire according to any one of embodiments 1 to 7. Embodiment 9: A tire using the rubber composition for a tire according to any one of embodiments 1 to 7 as an inner liner.

Claims

1. A rubber composition for tires, characterized by containing, per 100 parts by mass of a rubber component containing a butyl-based rubber, 20 to 70 parts by mass of carbon black, and 0.5 to 10 parts by mass of a random polypropylene having a melting point of 110 to 155°C and a melt mass-flow rate (MFR) of 6 to 50 g / 10 min measured at a temperature of 230°C under a load of 2.16 kg.

2. The nitrogen adsorption specific surface area N of the carbon black ２ SA is 20 to 60m ２ 2. The rubber composition for a tire according to claim 1, wherein the viscosity of the rubber composition for a tire is in the range of 1 / g.

3. The rubber composition for a tire according to claim 1, characterized in that the butyl-based rubber contains recycled butyl rubber, and the proportion of the recycled butyl rubber in 100 parts by mass of the rubber component is 10 to 60 parts by mass.

4. 2. The rubber composition for a tire according to claim 1, wherein the butyl rubber accounts for 80 parts by mass or more of 100 parts by mass of the rubber component.

5. 2. The rubber composition for a tire according to claim 1, wherein the rubber component contains a diene rubber in addition to the butyl rubber, and the proportion of the diene rubber in 100 parts by mass of the rubber component is 20 parts by mass or less.

6. 2. The rubber composition for tires according to claim 1, wherein the random polypropylene is selected from the group consisting of a propylene-ethylene random copolymer, a propylene-1-butene random copolymer, and a propylene-ethylene-1-butene random copolymer.

7. 2. The rubber composition for a tire according to claim 1, further comprising clay and / or talc.

8. A tire using the rubber composition for tires according to claim 1.

9. A tire using the rubber composition for a tire according to claim 1 as an inner liner.

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