Rubber composition for tire

Abstract

To provide a rubber composition for a tire which maintains and improves elongation at break and hardness, improves wear resistance and improves low-heat generation and further has excellent processability.SOLUTION: There is provided a rubber composition for a tire which comprises a diene-based rubber containing 10 mass% or more of an isoprene-based rubber, carbon black having a CTAB adsorption specific surface area of 30 to 130 m2 / g, silica having a CTAB adsorption specific surface area of 60 to 180 m2 / g and a glyoxal-cellulose ether reaction product, which is a cellulose ether surface-treated by the reaction with glyoxal and contains 5 pts.mass or more of the carbon black, 5 pts.mass or more of the silica and 1 to 30 pts.mass of the glyoxal-cellulose ether reaction product, based on 100 pts.mass of the diene-based rubber.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition for a tire, and a tire using the rubber composition for a tire in an undertread, a sidewall, or a rim cushion. [Background technology]

[0002] In pneumatic tires and the like, there is a demand for improving fuel economy performance during driving in order to reduce the environmental impact. Technologies for suppressing heat generation are also being developed for rubber compositions that constitute parts (mainly tire casing components), such as tire sidewalls, which are subject to repeated large deformations during driving and therefore are prone to heat generation and have a certain impact on the fuel economy performance of tires.

[0003] For example, Patent Document 1 discloses a rubber composition having a nitrogen adsorption specific surface area (N2SA) of 20 to 50 m for 100 parts by mass of diene rubber containing 30 to 70 parts by mass of butadiene rubber. 2 / g and DBP oil absorption is 50 to 150 cm 3 The paper discloses a rubber composition suitable for tire sidewalls, which has excellent heat buildup, processability, and tackiness over time, and is obtained by blending 30 to 60 parts by mass of carbon black (weight / 100g), 0.5 to 10 parts by mass of paraffin wax, 0.5 to 10 parts by mass of an amine-based antioxidant, and 0.5 to 20 parts by mass of a polyglycerol fatty acid ester derived from a fatty acid having 6 to 24 carbon atoms. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-122108 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the increasing performance levels required of vehicles in recent years, there is a demand for tire sidewalls and the like to not only improve fuel economy (low heat buildup) but also maintain or improve abrasion resistance, hardness, elongation at break, etc. There is also a demand for improved processability and compatibility between low heat buildup and processability. In other words, there is room for further improvement in the abrasion resistance, elongation at break, hardness, low heat buildup, processability, etc. of rubber compositions used in tire sidewalls and the like.

[0006] Therefore, an object of the present invention is to provide a rubber composition for tires which maintains or improves breaking elongation and hardness, improves abrasion resistance, improves low heat buildup, and further has excellent processability. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors have conducted extensive research and have discovered a method for producing a diene rubber containing 10% by mass or more of an isoprene rubber and a rubber composition having a CTAB adsorption specific surface area of ​​30 to 130 m 2 / g and carbon black with a CTAB adsorption specific surface area of ​​60 to 180 m 2 The present inventors have found that a rubber composition for tires containing silica having a surface treatment ratio of 1 / g and a glyoxal-cellulose ether reactant, which is a cellulose ether surface-treated by a reaction with glyoxal, and containing 5 parts by mass or more of the carbon black, 5 parts by mass or more of the silica, and 1 to 30 parts by mass of the glyoxal-cellulose ether reactant per 100 parts by mass of the diene rubber, maintains or improves elongation at break and hardness, improves abrasion resistance, improves low heat buildup, and further has excellent processability, thereby completing the present invention.

[0008] That is, the present invention provides the following: <1> ~ <4> This includes embodiments of the present invention. <1> A diene rubber containing 10% by mass or more of isoprene rubber and a CTAB adsorption specific surface area of ​​30 to 130 m 2 / g and carbon black with a CTAB adsorption specific surface area of ​​60 to 180 m 2 / g of silica and a glyoxal-cellulose ether reactant, which is a cellulose ether surface-treated by reaction with glyoxal; A rubber composition for tires containing 5 parts by mass or more of the carbon black, 5 parts by mass or more of the silica, and 1 to 30 parts by mass of the glyoxal-cellulose ether reactant relative to 100 parts by mass of the diene rubber. <2> The CTAB adsorption specific surface area of ​​the silica is 60 to 120 m 2 / g, <1> The rubber composition for a tire according to claim 1. <3> The cellulose ether of the glyoxal-cellulose ether reactant is methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, or hydroxyethyl methyl cellulose. <1> or <2> The rubber composition for a tire according to claim 1. <4> <1> ~ <3> A tire using the rubber composition for a tire according to any one of the above items in an undertread, a sidewall, or a rim cushion. [Effects of the Invention]

[0009] According to the present invention, it is possible to obtain a rubber composition for a tire that maintains or improves breaking elongation and hardness, improves abrasion resistance, improves low heat buildup, and has excellent processability, as well as a tire that uses this rubber composition for a tire in the undertread, sidewall, or rim cushion. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will now be described. The present invention relates to a diene rubber containing 10% by mass or more of an isoprene rubber and a rubber composition having a CTAB adsorption specific surface area of ​​30 to 130 m 2 / g and carbon black with a CTAB adsorption specific surface area of ​​60 to 180 m 2 / g of silica and a glyoxal-cellulose ether reactant, which is a cellulose ether surface-treated by a reaction with glyoxal, and the rubber composition for tires contains 5 parts by mass or more of the carbon black, 5 parts by mass or more of the silica, and 1 to 30 parts by mass of the glyoxal-cellulose ether reactant per 100 parts by mass of the diene rubber. Hereinafter, this will also be referred to as the "rubber composition for tires of the present invention."

[0011] In the present invention, unless otherwise specified, a numerical range expressed using "to" means a numerical range in which the numerical value before "to" is the lower limit and the numerical value after "to" is the upper limit.

[0012] The components contained in the rubber composition for tires of the present invention, their contents, etc. will be described in detail below.

[0013] [Diene rubber] The diene rubber contained in the rubber composition for tires of the present invention is a rubber component having a double bond in the polymer main chain. Specific examples include natural rubber (NR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), synthetic isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, and isoprene-butadiene copolymer rubber. The diene rubber contains 10% by mass or more of isoprene rubber. In other words, the diene rubber contained in the rubber composition for tires of the present invention is a diene rubber containing 10% by mass or more of isoprene rubber. This allows the effects of the present invention (particularly the effects of low heat buildup, elongation at break, and hardness) to be achieved in combination with the components described below. Here, "isoprene rubber" refers to natural rubber and / or synthetic isoprene rubber. When both natural rubber and synthetic isoprene rubber are included, the above-mentioned mass ratio refers to the combined mass ratio of these rubbers. In particular, in the present invention, it is preferable that the diene rubber contained in the rubber composition for tires of the present invention is a diene rubber containing 10% by mass or more of natural rubber, since the effects of the present invention are more easily exhibited.

[0014] The mass proportion (content) of isoprene-based rubber (more preferably natural rubber) in this diene-based rubber is 10% by mass or more as described above, but from the viewpoint of the effects of the present invention, the lower limit is more preferably 20% by mass or more, even more preferably 30% by mass or more, even more preferably 40% by mass or more, and even more preferably 45% by mass or more. The upper limit may be, for example, 80% by mass or less, 70% by mass or less, or 60% by mass or less. Furthermore, in the rubber composition for tires of the present invention, it is preferable that the diene rubber contains 10% by mass or more of isoprene-based rubber (more preferably natural rubber) and also contains butadiene rubber, as this makes it easier to achieve the effects of the present invention. In particular, while satisfying the above, the diene rubber preferably contains a total of 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more of isoprene-based rubber (more preferably natural rubber) and butadiene rubber. The diene rubber may consist of isoprene-based rubber (more preferably natural rubber) and butadiene rubber, i.e., contain a total of 100% by mass of isoprene-based rubber and butadiene rubber.

[0015] The weight average molecular weight of the diene rubber contained in the rubber composition for tires of the present invention is preferably 50,000 to 3,000,000, and more preferably 100,000 to 2,000,000. In the present invention, the "weight average molecular weight" refers to a value measured in terms of standard polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent. The GPC measurement is carried out at 40°C using a column (MIXED-B, manufactured by Polymer Laboratories) as a measuring instrument.

[0016] The rubber composition for tires of the present invention may contain rubber components other than diene-based rubber, but it is preferable that 90% by mass or more of the rubber components contained are diene-based rubber, more preferably 95% by mass or more are diene-based rubber, and even more preferably that the rubber components contained consist of diene-based rubber (100% by mass of diene-based rubber).

[0017] [Carbon black] The carbon black contained in the rubber composition for tires of the present invention is not particularly limited as long as it has a CTAB adsorption specific surface area within a predetermined range, and any known carbon black blended into rubber compositions for applications such as tires can be used. Specific examples of carbon black that can be used include ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, FEF, and GPF. These carbon blacks may be used alone or in combination of two or more. Here, "carbon black" refers to fine carbon particles made of primary particles with a diameter of about 3 to 500 nm that are manufactured under industrial quality control.

[0018] This carbon black has a CTAB adsorption specific surface area of ​​30 to 130 m 2 / g. By blending a specified amount of carbon black with such a CTAB adsorption specific surface area, a synergistic effect with the specified silica and glyoxal-cellulose ether reactant, which will be described later, can be achieved, improving abrasion resistance without affecting the effect of improving low heat buildup. The lower limit is 50m 2 / g or more is more preferable, and 70m 2 / g or more is more preferable, and 85m 2 / g or more is more preferable, and 95m 2 / g or more is more preferable. 2 It is more preferable that the CTAB adsorption specific surface area of ​​the carbon black to be blended is 130 m / g or less. 2If the CTAB adsorption specific surface area of ​​the carbon black to be compounded is more than 30 m / g, the heat buildup of the resulting rubber composition tends to be increased. 2 If the tensile strength is less than 1 / g, the mechanical properties of the resulting rubber composition tend to be insufficient. Here, the CTAB adsorption specific surface area of ​​this carbon black is a value measured in accordance with JIS K 6217-3:2001 "Part 3: Determination of specific surface area - CTAB adsorption method." When a single type of carbon black is used, this value is the value of the CTAB adsorption specific surface area of ​​that carbon black. When two or more types are used in combination, this value is the value obtained by multiplying the CTAB adsorption specific surface area of ​​each carbon black used in combination by its respective proportion (mass proportion) and adding the results together. In this calculation, the sum of the proportions of each carbon black used is set to 1.0.

[0019] The rubber composition for tires of the present invention contains 5 parts by mass or more of the above-mentioned carbon black per 100 parts by mass of the diene rubber. Furthermore, from the viewpoint of the effects of the present invention, the lower limit of the carbon black content is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more. The upper limit is preferably 90 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less, and even more preferably 35 parts by mass or less. Note that if the carbon black content is less than 5 parts by mass per 100 parts by mass of the diene rubber, the mechanical properties of the resulting rubber composition tend to be insufficient. Here, when a plurality of types of carbon black are contained, the carbon black content refers to the total content thereof.

[0020] [silica] The silica contained in the rubber composition for tires of the present invention is not particularly limited as long as the CTAB adsorption specific surface area is within a predetermined range, and any known silica used in applications such as tires can be used. Specific examples of silica that can be used include wet silica, dry silica, fumed silica, and diatomaceous earth. Silica produced using biomass materials such as rice husks as raw materials may also be used. One type of silica may be used alone, or two or more types may be used in combination. Here, "silica" refers to a particulate material made of silicon dioxide (SiO2) or containing silicon dioxide as the main component (for example, containing 80% by mass or more, or even 90% by mass or more).

[0021] This silica has a CTAB adsorption specific surface area of ​​60 to 180 m 2 / g. By blending a specified amount of silica with such a CTAB adsorption specific surface area, a synergistic effect with the aforementioned specified carbon black and the glyoxal-cellulose ether reaction product described below can be achieved, improving abrasion resistance without affecting the effect of improving low heat buildup. The lower limit is 70 m 2 / g or more is more preferable, and 80m 2 / g or more is more preferable. 2 / g or less is more preferable, and 150m 2 / g or less is more preferable, and 135m 2 / g or less is more preferable, and 120m 2 More preferably, it is less than 110m 2 / g or less is more preferable, and 100m 2 / g or less is more preferable, and 90m 2 It is more preferable that the CTAB adsorption specific surface area of ​​the silica to be blended is 180 m / g or less. 2 If the CTAB adsorption specific surface area of ​​the silica to be compounded is more than 60 m / g, the heat buildup of the resulting rubber composition tends to be increased. 2If the tensile strength is less than 1 / g, the mechanical properties of the resulting rubber composition tend to be insufficient. Here, the CTAB adsorption specific surface area of ​​silica is a value measured in accordance with JIS K 6430:2008, Appendix G. When one type of silica is used alone, this value is the value of the CTAB adsorption specific surface area of ​​that silica. When two or more types are used in combination, this value is the value obtained by multiplying the CTAB adsorption specific surface area of ​​each silica used in combination by its use ratio (mass ratio) and adding the results together. In this calculation, the total use ratio of each silica is set to 1.0.

[0022] The rubber composition for tires of the present invention contains 5 parts by mass or more of the above-mentioned silica per 100 parts by mass of the diene rubber. Furthermore, from the viewpoint of the effects of the present invention, the lower limit of the silica content is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, even more preferably 30 parts by mass or more, and even more preferably 35 parts by mass or more. The upper limit is preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, even more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less. If the silica content is less than 5 parts by mass per 100 parts by mass of the diene rubber, the mechanical properties of the resulting rubber composition tend to be insufficient. Here, when a plurality of types of silica are contained, the content of silica means the total content thereof.

[0023] Furthermore, the rubber composition for tires of the present invention is more preferably configured so that the silica content is greater than the carbon black content while satisfying the above, because this facilitates increased interaction between the glyoxal-cellulose ether reactant described below and the silica (the glyoxal-cellulose ether reactant described below and the silica are more likely to be located in close proximity in the rubber composition for tires of the present invention), further enhancing the dispersibility of the silica and making it easier to achieve the effects of the present invention (particularly reinforcing performance).In other words, the rubber composition for tires of the present invention is more preferably configured so that the silica content is greater than the carbon black content.

[0024] [Glyoxal-cellulose ether reaction products] The glyoxal-cellulose ether reaction product contained in the rubber composition for tires of the present invention is a reaction product obtained by surface-treating a cellulose ether in which some of the hydroxyl groups in cellulose have been etherified (ether-substituted) with glyoxal. In other words, it is a cellulose ether that has been surface-treated by reaction with glyoxal. The phrase "surface-treated by reaction with glyoxal" refers to the modification (surface modification) of one or more functional groups (primarily hydroxyl groups) of the cellulose ether through reaction with glyoxal. In particular, a crosslinked reaction product (glyoxal-cellulose ether crosslinked reaction product) in which at least some of the hydroxyl groups in the cellulose ether have reacted with glyoxal through glyoxal treatment to crosslink the cellulose ether molecules is preferred, but is not limited to this. Glyoxal (C2H2O2, CAS No. 107-22-2) is a compound represented by the following formula (1) and is also known as oxalic aldehyde or ethanedial.

[0025] [ka]

[0026] It is presumed that this glyoxal-cellulose ether reaction product has higher elastic properties due to the reaction with glyoxal (e.g., by becoming a cross-linked reaction product), which gives it excellent low heat buildup in addition to reinforcing properties. In particular, since the above-mentioned effects are more easily exhibited, the glyoxal-cellulose ether reaction product is more preferably one whose viscosity when made into a 2% by mass aqueous solution at room temperature (20°C) (viscosity of a 2% by mass aqueous solution at 20°C) is 2000 mPa·s or more, even more preferably 2400 mPa·s or more, even more preferably 3000 mPa·s or more, even more preferably 3500 mPa·s or more, even more preferably 4500 mPa·s or more, even more preferably 6000 mPa·s or more, even more preferably 9000 mPa·s or more, even more preferably 12000 mPa·s or more, even more preferably 14000 mPa·s or more, even more preferably 17000 mPa·s or more, and even more preferably 20000 mPa·s or more. There is no particular upper limit to this viscosity, but it may be, for example, 150,000 mPa·s or less, or 100,000 mPa·s or less. The viscosity mentioned above is the viscosity value measured using a B-type viscometer according to JIS Z 8803:2011 for an aqueous solution containing 2% by mass of the glyoxal-cellulose ether reactant (dissolved to a concentration of 2% by mass) at 20°C.

[0027] The cellulose used as the raw material for the cellulose ether may be derived from either wood or non-wood sources (e.g., bacteria, algae, cotton), and is not particularly limited. The cellulose ether is also not limited, but, because it more easily exhibits the effects of the present invention, it is preferably methylcellulose, in which methyl groups have been introduced into the hydroxyl groups of cellulose; hydroxypropylmethylcellulose, in which methyl and hydroxypropyl groups have been introduced into the hydroxyl groups of cellulose; hydroxyethylcellulose, in which hydroxyethyl groups have been introduced into the hydroxyl groups of cellulose; or hydroxyethylmethylcellulose, in which methyl and hydroxyethyl groups have been introduced into the hydroxyl groups of cellulose. It is particularly preferred that the cellulose ether is hydroxypropylmethylcellulose. In other words, the rubber composition for tires of the present invention preferably contains one or more selected from the group consisting of glyoxal-methylcellulose reactant, glyoxal-hydroxypropylmethylcellulose reactant, glyoxal-hydroxyethylcellulose reactant, and glyoxal-hydroxyethylmethylcellulose reactant. Of these, glyoxal-hydroxypropylmethylcellulose reactant is particularly preferred.

[0028] In addition, from the viewpoint of ease of compounding into rubber compositions for tires and the effect thereof, it is preferable that the glyoxal-cellulose ether reaction product is in a powder form (powder), and its average particle diameter (D 50 It is more preferable that the average particle diameter (D) is 1 to 1000 μm. 50 The lower limit of the thickness is more preferably 5 μm or more, even more preferably 10 μm or more, even more preferably 30 μm or more, and even more preferably 50 μm or more. The upper limit is more preferably 300 μm or less, even more preferably 200 μm or less, and even more preferably 150 μm or less. Here, this "average particle diameter (D 50 ) is the volume-based average particle diameter (50% volume cumulative distribution diameter (D 50 )).

[0029] The rubber composition for tires of the present invention contains 1 to 30 parts by mass of the glyoxal-cellulose ether reactant (in total, if two or more types are used) per 100 parts by mass of the diene rubber. The lower limit is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more. The upper limit is preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less. If the content of the glyoxal-cellulose ether reactant is less than 1 part by mass or more than 30 parts by mass per 100 parts by mass of the diene rubber, the effects of the present invention tend not to be fully achieved.

[0030] Furthermore, although not limited thereto, the rubber composition for a tire of the present invention more preferably contains 5 to 80 parts by mass of the glyoxal-cellulose ether reactant (in total, if two or more types are used) per 100 parts by mass of the silica, while still satisfying the above requirements, because this facilitates a stronger interaction between the silica and the glyoxal-cellulose ether reactant. The lower limit is more preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, even more preferably 30 parts by mass or more, and even more preferably 35 parts by mass or more, and the upper limit is more preferably 65 parts by mass or less, even more preferably 50 parts by mass or less.

[0031] [Other ingredients] The rubber composition for a tire of the present invention may further contain appropriate amounts of various additives that are generally used in rubber compositions for a tire, such as inorganic fillers (clay, mica, talc, alumina, calcium carbonate, magnesium carbonate, aluminum hydroxide, titanium oxide, calcium sulfate, barium sulfate, etc.), organic fillers (organic fillers, for example, lecithin, etc.), resin components, process oils (aroma oils, paraffin oils, etc.), zinc oxide (zinc white), stearic acid, antioxidants, plasticizers, curing agents, vulcanizing agents (for example, sulfur, etc.), vulcanization accelerators, and vulcanization accelerator aids, within the range that does not significantly affect the effects of the present invention, and these additives can be kneaded by a known method to form a rubber composition for a tire.

[0032] For example, the content of the process oil in the rubber composition for a tire of the present invention is preferably 1 to 30 parts by mass, more preferably 3 to 15 parts by mass, per 100 parts by mass of the diene rubber. Also, the contents of stearic acid, zinc oxide, and antioxidant in the rubber composition for a tire of the present invention are each preferably 1 to 5 parts by mass per 100 parts by mass of the diene rubber. The content of the vulcanizing agent in the rubber composition for tires of the present invention is preferably 0.5 to 3.5 parts by mass, more preferably 1.0 to 3.0 parts by mass, per 100 parts by mass of the diene rubber. The content of the vulcanization accelerator in the rubber composition for tires of the present invention, either as a primary accelerator alone or as a blend with a secondary accelerator, is also preferably 0.5 to 3.5 parts by mass, more preferably 1.0 to 3.0 parts by mass, per 100 parts by mass of the diene rubber.

[0033] The rubber composition for a tire of the present invention may further contain a silane coupling agent to further enhance the dispersibility of the silica described above. The silane coupling agent is not particularly limited as long as it is a silane compound having a hydrolyzable group and an organic functional group. The hydrolyzable group is also not limited, but examples include an alkoxy group, a phenoxy group, a carboxy group, and an alkenyloxy group. An alkoxysilyl group in which the alkoxy group is bonded to a silicon atom is preferred. When the hydrolyzable group is an alkoxysilyl group, the alkoxy group preferably has 1 to 16 carbon atoms, and more preferably has 1 to 4 carbon atoms. Examples of alkoxy groups having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, and a propoxy group.

[0034] The organic functional group is not limited, but may be any group capable of forming a chemical bond with an organic compound, such as an epoxy group, a vinyl group, an acryloyl group, a methacryl group, an amino group, a sulfide group (particularly, a polysulfide group (-S n - (n is an integer of 2 or more), a mercapto group, a blocked mercapto group (protected mercapto group) (for example, an octanoylthio group), and the like. Among these, a sulfide group (particularly a disulfide group or a tetrasulfide group), a mercapto group, and a blocked mercapto group are preferred. Such silane coupling agents may be used alone or in combination of two or more thereof. The silane coupling agent is preferably a sulfur-containing silane coupling agent.

[0035] The rubber composition for tires of the present invention preferably contains 1 to 20 parts by mass, and more preferably 2 to 10 parts by mass, of the silane coupling agent per 100 parts by mass of the silica.

[0036] [Manufacturing method etc.] The method for producing the rubber composition for tires of the present invention may be conventional and is not particularly limited. As an example of the production method, the rubber composition for tires of the present invention can be produced by kneading and mixing the diene rubber, carbon black, silica, glyoxal-cellulose ether reactant, and other components, as necessary, at room temperature or at an elevated temperature using a mixer such as a Banbury mixer, kneader, or roll mill, to a predetermined blend. When vulcanization-related components (e.g., sulfur, vulcanization accelerator, vulcanization accelerator aid) are used, it is preferable to first mix the other components at an elevated temperature, cool the mixture, and then mix the vulcanization-related components. Alternatively, components other than the vulcanization-related components may be mixed to form a masterbatch, and then the vulcanization-related components may be mixed. Furthermore, the glyoxal-cellulose ether reactant may be compounded in powder form.

[0037] The rubber composition for tires of the present invention obtained in the above manner maintains or improves (at least does not decrease) the breaking elongation and hardness, improves the abrasion resistance, and enhances the low heat buildup, resulting in an excellent balance between the low heat buildup and hardness, and furthermore, the viscosity of the rubber composition before vulcanization is low, resulting in excellent processability (a combination of low heat buildup and processability).

[0038] Furthermore, by using this rubber composition for a tire of the present invention for the undertread, sidewall, or rim cushion (at least one selected from the group consisting of these), which are tire casing components (components that form the tire around the cap tread), a tire can be obtained in which the component has an excellent balance of abrasion resistance, elongation at break, low heat buildup, and hardness. In other words, the rubber composition for a tire of the present invention is suitable as a rubber composition for the undertread, sidewall, or rim cushion of a tire. However, the rubber composition for a tire of the present invention may also be used for other tire components. The tire is preferably a pneumatic tire, and the gas to be filled in the pneumatic tire can be, for example, air, inert gases such as nitrogen, argon, and helium, or other gases.

[0039] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples, and various modifications are possible within the technical concept of the present invention. [Example]

[0040] (Preparation and Evaluation of Rubber Compositions for Tires) Rubber compositions for tires having the formulations shown in Table 1 below were prepared.

[0041] Specifically, the components (excluding sulfur and vulcanization accelerator) in the amounts shown in the upper part of Table 1 below were mixed for 5 minutes at a temperature of approximately 150°C in a 1.7-liter internal Banbury mixer. The mixture was then discharged from the mixer and cooled to obtain a masterbatch. The cellulose ether and glyoxal-cellulose ether reactant were both blended in powder form. Furthermore, the masterbatch was mixed with predetermined amounts of sulfur and vulcanization accelerator in the Banbury mixer, and the resulting mixture was press-vulcanized at 170°C for 10 minutes in a mold to produce the tire rubber compositions (vulcanized rubber test pieces) of Comparative Examples 1 and 2 and Examples 1 to 6.

[0042] The obtained rubber compositions for tires (vulcanized rubber test pieces) of Comparative Examples 1 and 2 and Examples 1 to 6 were evaluated for hardness, heat buildup, elongation at break, and wear as follows: Furthermore, the Mooney viscosity of each mixture before press vulcanization was measured as follows.

[0043] <Mooney viscosity> The Mooney viscosity of each mixture obtained before press vulcanization was measured in accordance with JIS K 6300-1:2013 using a Mooney viscometer with an L-shaped rotor (38.1 mm diameter, 5.5 mm thickness) under the conditions of a preheating time of 1 minute, a rotor rotation time of 4 minutes, 100°C, and 2 rpm. The results are shown in the lower part of the following Table 1. The results are expressed as an index with the value of Comparative Example 1 being 100, and the smaller the index, the lower the viscosity and the better the processability.

[0044] <Hardness> The rubber hardness (HS) of each of the obtained test pieces of the vulcanized rubber composition was measured at a temperature of 20°C using a durometer type A (manufactured by Toyo Seiki Seisakusho, Ltd.) in accordance with JIS K 6253-3:2012. The results are also shown in the lower part of Table 1. The results are expressed as an index, with the value of Comparative Example 1 being 100.

[0045] <Fever> For each of the obtained vulcanized rubber composition test pieces, tan δ60°C was measured using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisaku-sho, under conditions of initial strain of 10%, amplitude of ±2%, frequency of 20 Hz and temperature of 60°C. The results are also shown in the lower part of Table 1. The results are expressed as an index with the value of Comparative Example 1 being 100, and the smaller the index, the more difficult it is to generate heat (low heat buildup).

[0046] <Elongation at break> A tensile test was carried out on each of the obtained vulcanized rubber composition test pieces at a tensile speed of 500 mm / min in accordance with JIS K 6251:2010, and the elongation at break (= elongation at break: Eb) was measured at room temperature (20°C). The results are also shown in the lower part of Table 1. The results are expressed as an index, with the value of Comparative Example 1 being 100.

[0047] <Wear (Pico)> The amount of wear of each of the obtained vulcanized rubber test pieces was measured using a Pico abrasion tester in accordance with JIS K 6264-2:2005 (Pico abrasion test). The results are also shown in the upper bottom row of Table 1 below. The results are expressed as an index with the value of Comparative Example 1 being 100, and the smaller the amount of wear, the larger the index. In other words, the larger the index, the more excellent the wear resistance.

[0048] [Table 1]

[0049] The details of each component in Table 1 above are as follows: NR: Natural rubber (STR20, glass transition temperature (Tg): -65°C, manufactured by Bonbandit) BR: Butadiene rubber (Nipol BR1220, glass transition temperature (Tg): -110°C, manufactured by Zeon Corporation) Carbon black: Show Black N234 (CTAB adsorption specific surface area: 115m 2 / g, manufactured by Gabot Japan) ·Silica 1: Zeosil 1165MP (CTAB adsorption specific surface area: 165m 2 / g, manufactured by Solvay) ·Silica 2: Zeosil 115GR (CTAB adsorption specific surface area: 115m 2 / g, manufactured by Solvay) ·Silica 3: Zeosil 1085GR (CTAB adsorption specific surface area: 84m 2 / g, manufactured by Solvay) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide, manufactured by Evonik Degussa) Cellulose ether: Hydroxypropyl methylcellulose (Metolose 60SH-4000, Shin-Etsu Chemical Co., Ltd.) *Cellulose ether not treated with glyoxal Glyoxal-cellulose ether reaction product 1: Hydroxypropylmethylcellulose surface-treated with glyoxal (Hi-Metolose hi90SH-4000, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity of 2% by weight aqueous solution at 20°C: 3980 mPa·s) *Glyoxal-treated cellulose ether Glyoxal-cellulose ether reaction product 2: Hydroxypropylmethylcellulose surface-treated with glyoxal (Hi-Metolose hi90SH-30000, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity of 2% by weight aqueous solution at 20°C: 24,400 mPa·s) *Glyoxal-treated cellulose ether Zinc oxide: Zinc oxide (3 types of zinc oxide, manufactured by Seido Chemical Industry Co., Ltd.) Stearic acid: Stearic acid beads (manufactured by NOF CORPORATION) Anti-aging agent 1: VULKANOX 4020 / LG (manufactured by LANXESS) Anti-aging agent 2: VULKANOX HS / LG (manufactured by LANXESS) Wax: Ozoace 0015A (manufactured by Nippon Seiro Co., Ltd.) Aroma oil: Extract No. 4S (Shell Lubricants Japan) Sulfur: Insoluble sulfur (Mucron OT-20S, manufactured by Shikoku Chemicals Corporation) Vulcanization accelerator: Sulfenamide vulcanization accelerator (Suncerer CM-G, manufactured by Sanshin Chemical Industry Co., Ltd.)

[0050] From these results, it was found that the CTAB adsorption specific surface area was 115 m for 100 parts by mass of diene rubber containing 50% by mass of natural rubber. 2 25 parts by mass of carbon black having a specific surface area of ​​84 to 165 m 2Examples 1 to 6, which contained 40 parts by mass of silica with a density of 1 / g and 5 to 25 parts by mass of a glyoxal-cellulose ether reactant, maintained (index difference from the reference by 3% or less) or improved (index increased by 5% or more from the reference), improved abrasion resistance (index increased by 5% or more from the reference), maintained (index difference from the reference by 3% or less) or improved (index increased by 5% or more from the reference), improved low heat buildup (index decreased by 5% or more from the reference), and showed an excellent balance between hardness and low heat buildup. Furthermore, the viscosity before press vulcanization was low (index decreased by 5% or more from the reference), and the processability was excellent. In particular, the CTAB adsorption specific surface area of ​​the silica contained was 84 to 115 m. 2 Examples 5 and 6, which contained glyoxal-cellulose ether reactants with a viscosity of 1000 kJ / g and a higher viscosity in a 2% by mass aqueous solution at 20°C, had low viscosities before press vulcanization and also showed significantly improved low heat buildup and elongation at break, making them extremely excellent. Of these, Example 6, which contained silica with a lower CTAB adsorption specific surface area, was particularly excellent in terms of processability, low heat buildup, and elongation at break. On the other hand, in Comparative Example 2, which contained a cellulose ether that had not been surface-treated, the viscosity before press vulcanization was almost the same as the standard, the abrasion resistance was lower than the standard, and the elongation at break was also significantly lower than the standard.Furthermore, although the hardness improved, the low heat buildup property did not improve.

Claims

1. A diene rubber containing 10% by mass or more of isoprene rubber and a CTAB adsorption specific surface area of ​​30 to 130 m 2 / g and carbon black with a CTAB adsorption specific surface area of ​​60 to 180 m 2 / g of silica and a glyoxal-cellulose ether reactant, which is a cellulose ether surface-treated by reaction with glyoxal; A rubber composition for tires containing 5 parts by mass or more of the carbon black, 5 parts by mass or more of the silica, and 1 to 30 parts by mass of the glyoxal-cellulose ether reactant relative to 100 parts by mass of the diene rubber.

2. The CTAB adsorption specific surface area of ​​the silica is 60 to 120 m 2 The rubber composition for a tire according to claim 1, wherein the viscosity of the rubber composition for a tire is 1 / g.

3. 3. The rubber composition for a tire according to claim 1, wherein the cellulose ether of the glyoxal-cellulose ether reactant is methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, or hydroxyethyl methyl cellulose.

4. A tire using the rubber composition for a tire according to claim 1 or 2 in an undertread, a sidewall, or a rim cushion.

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