Rubber composition for side tread and method for producing the same

Abstract

To provide a rubber composition for a side tread which has excellent cut resistance and low heat generation properties, maintains or improves hardness and breaking elongation and further maintains a balance between these properties.SOLUTION: There is provided a rubber composition for a side tread which comprises 20 to 38 pts.mass of carbon black having a CTAB adsorption specific surface area of 20 to 60 m2 / g based on 100 pts.mass of a diene-based rubber containing 35 to 65 mass% of an isoprene-based rubber and 35 to 65 mass% of a butadiene-based rubber, wherein the ratio of the mass of carbon black contained in the present part of the isoprene-based rubber of the rubber composition to the total mass of the carbon black contained in the rubber composition is 60 mass% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition for a side tread and a method for producing the same. [Background technology]

[0002] In pneumatic tires and the like, there is a demand for improving fuel economy during driving in order to reduce environmental impact. To this end, efforts have been made to suppress heat generation in the rubber composition that constitutes the tread rubber layer of the tire. In recent years, in order to further improve fuel economy, studies have been made to suppress heat generation in the rubber composition that constitutes the side tread rubber layer (rubber composition for side tread).

[0003] For example, Patent Document 1 discloses a method for producing a rubber composition having a nitrogen adsorption specific surface area (N2SA) of 50 m for 100 parts by mass of a diene rubber consisting of 30 parts by mass or more of natural rubber and 5 to 70 parts by mass of a specified modified butadiene rubber. 2 The present invention discloses a rubber composition for tire side treads, which has high elasticity and low heat buildup without impairing processability, and is characterized by blending 5 to 60 parts by mass of carbon black having a viscosity of 1000 psi or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-053269 Summary of the Invention [Problem to be solved by the invention]

[0005] The affinity of carbon black blended as a filler in a rubber composition varies depending on the type of rubber component, and it may be difficult to fully absorb the carbon black into the isoprene-based rubber during the mixing process with a diene-based rubber component containing an isoprene-based rubber and a butadiene rubber. For example, when approximately equal amounts of natural rubber and butadiene rubber are used as the diene-based rubber component, it is difficult to fully incorporate carbon black into the natural rubber portion of the resulting rubber composition. The side tread rubber layer of a tire is required to have excellent cut resistance against contact with curbs, etc., as well as a certain level of elongation at break and hardness. Therefore, in order to achieve these physical properties, it is conceivable to blend a larger amount of carbon black into the rubber composition used in the side tread rubber layer along with the specified diene-based rubber component containing an isoprene-based rubber and a butadiene rubber, taking the above into consideration. However, this makes it difficult to improve low heat buildup (the property of being less likely to generate heat) and to maintain a balance between these properties. That is, there is room for improvement in the rubber composition used in the side tread rubber layer in terms of achieving both cut resistance and low heat buildup, and maintaining a balance between cut resistance, low heat buildup, hardness, and elongation at break.

[0006] Therefore, an object of the present invention is to provide a rubber composition for a side tread which is excellent in cut resistance and low heat buildup, and which maintains or improves hardness and elongation at break, while also maintaining a balance between these properties. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors have conducted extensive research and have found that a CTAB adsorption specific surface area of ​​20 to 60 m is obtained for 100 parts by mass of a diene rubber containing 35 to 65% by mass of an isoprene rubber and 35 to 65% by mass of a butadiene rubber. 2The present inventors have found that a rubber composition for a side tread containing 20 to 38 parts by mass of carbon black having a molecular weight of 1 / g, wherein the ratio of the mass of the carbon black contained in the isoprene-based rubber-existing portion of the rubber composition to the total mass of the carbon black contained in the rubber composition is 60% by mass or more, has a relatively small amount of carbon black mixed in but contains a predetermined amount or more of carbon black in the isoprene-based rubber-existing portion, has excellent cut resistance and low heat buildup, maintains or improves hardness and elongation at break, and also maintains a balance between these properties, and have completed the present invention.

[0008] That is, the present invention provides the following: <1> ~ <7> This includes embodiments of the present invention. <1> A CTAB adsorption specific surface area of ​​20 to 60 m is used for 100 parts by mass of diene rubber containing 35 to 65% by mass of isoprene rubber and 35 to 65% by mass of butadiene rubber. 2 A rubber composition for a side tread containing 20 to 38 parts by mass of carbon black having a viscosity of 1000 ppm or less, the proportion of the mass of the carbon black contained in the isoprene-based rubber-existing portion of the rubber composition to the total mass of the carbon black contained in the rubber composition is 60 mass% or more; A rubber composition for side treads. <2> The butadiene rubber is a butadiene rubber containing more than 50% by mass of neodymium-catalyzed butadiene rubber. <1> The rubber composition for a side tread according to claim 1. <3> The rubber composition contains 2.5 parts by mass or more of sulfur and a vulcanization accelerator in total relative to 100 parts by mass of the diene rubber. <1> or <2> The rubber composition for a side tread according to claim 1. <4> <1> ~ <3> A tire comprising a side tread rubber layer formed from the rubber composition for a side tread according to any one of the above items. <5> A CTAB adsorption specific surface area of ​​20 to 60 m is used for 100 parts by mass of diene rubber containing 35 to 65% by mass of isoprene rubber and 35 to 65% by mass of butadiene rubber. 2 A method for producing a rubber composition for a side tread containing 20 to 38 parts by mass of carbon black having a molecular weight of 1 / g, a first mixing step of mixing raw materials including the diene rubber containing all of the isoprene rubber and all or part of the butadiene rubber removed, and the carbon black; A second mixing step of mixing a part or all of the butadiene rubber into the mixture obtained in the first mixing step. A method for producing a rubber composition for a side tread. <6> The butadiene rubber is a butadiene rubber containing more than 50% by mass of neodymium-catalyzed butadiene rubber. <5> A method for producing the rubber composition for a side tread according to claim 1. <7> The rubber composition contains 2.5 parts by mass or more of sulfur and a vulcanization accelerator in total per 100 parts by mass of the diene rubber. <5> or <6> A method for producing the rubber composition for a side tread according to claim 1. [Effects of the Invention]

[0009] According to the present invention, it is possible to obtain a rubber composition for a side tread that has excellent cut resistance and low heat buildup, and maintains or improves hardness and elongation at break, while also maintaining a balance between these properties, and a tire that includes a side tread rubber layer formed from this rubber composition for a side tread. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will now be described. The present invention provides a rubber composition having a CTAB adsorption specific surface area of ​​20 to 60 m per 100 parts by mass of a diene rubber containing 35 to 65% by mass of an isoprene rubber and 35 to 65% by mass of a butadiene rubber. 2 The present invention also provides a rubber composition for a side tread containing 20 to 38 parts by mass of carbon black having a CTAB adsorption specific surface area of ​​20 to 60 m / g, wherein the ratio of the mass of the carbon black contained in the isoprene-based rubber present portion of the rubber composition to the total mass of the carbon black contained in the rubber composition is 60% by mass or more.2 The present invention is also a method for producing a rubber composition for a side tread containing 20 to 38 parts by mass of carbon black having a molecular weight of 1 / g, the method comprising: a first mixing step of mixing raw materials containing a diene rubber containing all of the isoprene rubber and some or all of the butadiene rubber removed, and the carbon black; and a second mixing step of mixing some or all of the butadiene rubber with the mixture obtained in the first mixing step. Hereinafter, these methods are also referred to as "the rubber composition of the present invention" and "the method for producing the rubber composition 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 of the present invention, their contents, etc. will be described in detail below.

[0013] [Diene rubber] The diene rubber contained in the rubber composition of the present invention is a rubber component having a double bond in the polymer main chain. This diene rubber contains 35 to 65 mass% of isoprene rubber and 35 to 65 mass% of butadiene rubber (BR). That is, the diene rubber contained in the rubber composition of the present invention is a diene rubber containing 35 to 65 mass% of isoprene rubber and 35 to 65 mass% of butadiene rubber. Here, "isoprene rubber" refers to natural rubber (NR) and / or synthetic isoprene rubber (IR), and the above mass ratio refers to the total mass ratio of both natural rubber and synthetic isoprene rubber when both are contained. In particular, in the present invention, it is preferable that the isoprene rubber is natural rubber, i.e., that the diene rubber contained in the rubber composition of the present invention contains 35 to 65 mass% of natural rubber and 35 to 65 mass% of butadiene rubber, because the effects of the present invention are more easily exhibited.

[0014] The mass proportion (content) of butadiene rubber in this diene rubber is 35 to 65 mass%, but from the viewpoint of the effects of the present invention, the lower limit is preferably 40 mass% or more, more preferably 45 mass% or more, and the upper limit is preferably 60 mass% or less, more preferably 55 mass% or less. The mass proportion (content) of isoprene-based rubber (more preferably natural rubber) in this diene-based rubber is also 35 to 65 mass%, but from the viewpoint of the effects of the present invention, the lower limit is more preferably 40 mass% or more, and even more preferably 45 mass% or more, and the upper limit is preferably 60 mass% or less, and more preferably 55 mass% or less.

[0015] The diene rubber may be composed of an isoprene rubber and a butadiene rubber, or may further contain a diene rubber component other than the isoprene rubber and the butadiene rubber. Specifically, the diene rubber may contain styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, isoprene-butadiene copolymer rubber, etc. However, the total amount of these components is preferably 10% by mass or less, more preferably 5% by mass or less, and may be substantially absent (e.g., less than 1% by mass). Among these components, the styrene-butadiene copolymer rubber, which, like the butadiene rubber, is likely to affect the absorption of carbon black into the isoprene rubber, is preferably present in the diene rubber in an amount of 10% by mass or less, more preferably 5% by mass or less, or even 3% by mass or less, and even more preferably substantially absent.

[0016] In the rubber composition of the present invention, it is more preferable that the butadiene rubber in the diene rubber contains more than 50% by mass of neodymium-catalyzed butadiene rubber. This configuration provides even better low heat buildup and maintains a high level of balance among cut resistance, low heat buildup, hardness, and elongation at break. It is particularly preferable that the butadiene rubber in the diene rubber contains 70% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more of neodymium-catalyzed butadiene rubber. The butadiene rubber in the diene rubber may be entirely neodymium-catalyzed butadiene rubber (composed of neodymium-catalyzed butadiene rubber). Furthermore, from the viewpoint of further reducing the likelihood of carbon black absorption into the butadiene rubber, the glass transition temperature (Tg) of the neodymium-catalyzed butadiene rubber is preferably −110°C or higher, and even more preferably −108°C or higher. The upper limit of this temperature is not particularly limited, but it may be, for example, −85°C or lower, or −95°C or lower. Here, "neodymium-catalyzed butadiene rubber" refers to butadiene rubber synthesized (polymerized) using a neodymium catalyst (synthesized in the presence of a neodymium catalyst). The "glass transition temperature (Tg)" is the temperature at the intersection of the low-temperature baseline and the slope of the transition region (inclined straight line) in a thermogram measured by differential scanning calorimetry (DSC) at a heating rate of 20°C / min. For oil-extended products, the glass transition temperature is the temperature in a state that does not contain any oil-extending component (oil).

[0017] The weight average molecular weight of the diene rubber contained in the rubber composition of the present invention is preferably 50,000 to 3,000,000, and more preferably 100,000 to 2,000,000. In particular, when the above-mentioned neodymium-catalyzed butadiene rubber is used, the weight average molecular weight is more preferably 500,000 or more, and even more preferably 600,000 or more, because this makes it easier to exhibit the effects of the present invention. 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.

[0018] The rubber composition 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).

[0019] [Carbon black] The carbon black contained in the rubber composition 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 carbon black used in applications such as tires can be used. Specific examples of carbon black that can be used include various grades such as FF, FEF, GPF, SRF, FT, and MT. These carbon blacks may be used alone or in combination of two or more. The term "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.

[0020] This carbon black has a CTAB adsorption specific surface area of ​​20 to 60 m 2 / g. By blending a predetermined amount of carbon black with such a CTAB adsorption specific surface area, it is possible to effectively improve cut resistance while maintaining low heat buildup. The lower limit is 25 m 2 / g or more is more preferable. 2 / g or less is more preferable, and 50m 2 More preferably, it is less than 45m 2 / g or less is more preferable, and 40m2 / g or less is more preferable, and 35m 2 It is more preferable that the CTAB adsorption specific surface area of ​​the carbon black to be blended is less than 60 m / g. 2 If the CTAB adsorption specific surface area of ​​the carbon black to be compounded is more than 20 m / g, the heat buildup of the resulting rubber composition may increase. 2 If it is less than 1 / g, the mechanical properties of the resulting rubber composition may be insufficient. Here, the CTAB adsorption specific surface area of ​​this carbon black is a value measured in accordance with JIS K6217-3:2001 "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 use ratio and adding the results together. In this calculation, the sum of the use ratios of each carbon black is set to 1.0.

[0021] The rubber composition of the present invention contains 20 to 38 parts by mass of the above-described carbon black per 100 parts by mass of diene rubber. The lower limit is more preferably 25 parts by mass or more, and even more preferably 30 parts by mass or more. The upper limit is more preferably 35 parts by mass or less. The rubber composition of the present invention is characterized in that, even with such a relatively low carbon black content, it exhibits excellent cut resistance, maintains or improves hardness and elongation at break, and maintains a good balance between these properties. If the carbon black content is less than 20 parts by mass per 100 parts by mass of diene rubber, the resulting rubber composition may have insufficient mechanical properties. If the carbon black content is more than 38 parts by mass per 100 parts by mass of diene rubber, the resulting rubber composition may have increased heat buildup and may lose balance with other physical properties such as hardness.

[0022] In the rubber composition of the present invention, the carbon black is sufficiently present in the isoprene-based rubber-existing portion. Specifically, the ratio of the mass of carbon black contained in the isoprene-based rubber-existing portion of the rubber composition of the present invention to the total mass of carbon black contained in the rubber composition of the present invention (mass of carbon black in the isoprene-based rubber-existing portion × 100 / mass of all carbon black in the rubber composition) is 60 mass% or more. This allows the above-mentioned effects to be fully exhibited. Here, the "carbon black contained in the isoprene-based rubber-existing portion" refers to carbon black that is absorbed into the isoprene-based rubber in the rubber composition of the present invention and that substantially coexists in the region where the isoprene-based rubber molecules are present (where it may interact with the isoprene-based rubber molecules). This mass proportion is measured and calculated by mapping and analyzing STEM images of at least 10 locations obtained by observing the surface and cross section of the rubber composition with a STEM (scanning transmission electron microscope, such as JEOL Ltd.'s JEM-2800) using analysis software or the like.

[0023] Such a configuration can be obtained by producing the rubber composition of the present invention using the above components by the production method described below. The lower limit of the mass ratio of carbon black contained in the isoprene-based rubber-containing portion of the rubber composition of the present invention to the total mass of carbon black contained in the rubber composition of the present invention is preferably 61% by mass or more, more preferably 63% by mass or more, even more preferably 65% ​​by mass or more, and even more preferably 67% by mass or more. While the upper limit is not particularly limited, examples include a range of less than 75% by mass, or even 70% by mass or less.

[0024] [Other ingredients] The rubber composition of the present invention may further contain various additives that are generally used in rubber compositions, such as inorganic fillers other than those mentioned above (silica, clay, mica, talc, alumina, calcium carbonate, magnesium carbonate, aluminum hydroxide, titanium oxide, calcium sulfate, barium sulfate), organic fillers (organic fillers, for example, lecithin), zinc oxide (zinc white), stearic acid, process oil, resin components, antioxidants, plasticizers, curing agents, vulcanizing agents (for example, sulfur), vulcanization accelerators, and vulcanization accelerator aids, within the range that does not significantly affect the effects of the present invention. 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).

[0025] For example, the contents of stearic acid and zinc oxide in the rubber composition of the present invention are each preferably 1 to 5 parts by mass per 100 parts by mass of the diene rubber.

[0026] The rubber composition of the present invention preferably contains sulfur and a vulcanization accelerator as vulcanizing agents. The total content of sulfur and the vulcanization accelerator in the rubber composition of the present invention may be, for example, more than 2.0 parts by mass per 100 parts by mass of the diene rubber, but is preferably 2.5 parts by mass or more. The lower limit is more preferably 2.6 parts by mass or more, and even more preferably 2.7 parts by mass or more. The upper limit may be 5.0 parts by mass or less, 4.5 parts by mass or less, 4.0 parts by mass or less, or 3.5 parts by mass or less. Although not limited thereto, preferred examples of vulcanization accelerators include sulfenamide vulcanization accelerators containing benzothiazole rings (vulcanization accelerators having a benzothiazole ring structure and a substituent containing an S-N bond in the molecule) from the viewpoint of facilitating the vulcanization of isoprene-based rubber containing a certain amount of carbon black. While sulfur is preferred as the vulcanizing agent, other compounds with crosslinking function between polymers, such as peroxides, may also be used as vulcanizing agents other than sulfur. These may also be used in combination.

[0027] As described above, the rubber composition of the present invention is characterized by the fact that, due to the above-mentioned configuration, even with a relatively small amount of carbon black, it exhibits excellent cut resistance and low heat buildup (i.e., both cut resistance and low heat buildup are achieved), while maintaining or improving hardness and elongation at break, and further maintaining a balance between these. Therefore, when an inorganic filler other than carbon black is added, it is preferably incorporated as a replacement for the carbon black. That is, the rubber composition of the present invention preferably contains 20 to 38 parts by mass of the carbon black per 100 parts by mass of the diene rubber, and the total content of the carbon black and the inorganic filler other than carbon black is also preferably 20 to 38 parts by mass per 100 parts by mass of the diene rubber (in other words, this total content is also 38 parts by mass or less per 100 parts by mass of the diene rubber). Alternatively, the rubber composition may be substantially free of inorganic fillers other than carbon black (less than 1 part by mass per 100 parts by mass of the diene rubber).

[0028] [Manufacturing method etc.] The method for producing the rubber composition of the present invention is to prepare a rubber composition having a CTAB adsorption specific surface area of ​​20 to 60 m per 100 parts by mass of diene rubber containing 35 to 65% by mass of isoprene rubber and 35 to 65% by mass of butadiene rubber. 2 The method for producing a rubber composition for a side tread containing 20 to 38 parts by mass of carbon black having a carbon black content of 1 / g includes a first mixing step of mixing raw materials containing the diene rubber containing all of the isoprene rubber and some or all of the butadiene rubber removed, and the carbon black, and a second mixing step of mixing some or all of the butadiene rubber with the mixture obtained in the first mixing step. The first mixing step and the second mixing step will be described in detail below.

[0029] <First mixing process> The first mixing step in the method for producing a rubber composition of the present invention is a step of mixing raw materials containing a diene rubber containing all of the isoprene rubber and some or all of the butadiene rubber, and the entire amount of carbon black (total blending amount). That is, this first mixing step is a step of mixing a diene rubber containing all of the isoprene rubber (total blending amount) and some or all of the butadiene rubber (for example, a diene rubber containing more than 50 mass%, or even 70 mass% or more, or even 80 mass% or more of the total butadiene rubber, or a diene rubber mainly composed of isoprene rubber, such as one containing 90 mass% or more of isoprene rubber) with the entire blending amount of a predetermined carbon black, and further mixing other components if necessary. Therefore, all of the isoprene rubber to be blended is mixed in this first mixing step. The diene rubber mixed in this first mixing step is not limited as long as it contains all or part of the butadiene rubber and all of the isoprene rubber. For example, it may contain all of the diene rubber components except for the removed butadiene rubber. In cases where rubber components other than the isoprene rubber and butadiene rubber are not substantially mixed, it is more preferable to mix all of the components except for all or part of the butadiene rubber, the vulcanizing agent, and the vulcanization accelerator in this first mixing step. It is also more preferable to remove all (the entire amount of) the butadiene rubber in this first mixing step. In other words, it is more preferable to mix all of the butadiene rubber in the second mixing step. On the other hand, when a styrene-butadiene copolymer rubber is mixed as part of the diene rubber, it is more preferable to mix all or part of this styrene-butadiene copolymer rubber in the second mixing step, similar to the butadiene rubber. This mixing method may be a conventional method and is not particularly limited. For example, a method of kneading and mixing using a kneading machine such as a Banbury mixer, kneader, or roll at room temperature or at a high temperature (preferably at a high temperature of 100°C or higher, more preferably 100 to 200°C) is shown. From the viewpoint of the effects of the present invention, the mixing time is more preferably 1.5 minutes or more, and even more preferably 2 minutes or more. The upper limit may be 5 minutes or less, or may be 4 minutes or less.

[0030] <Second mixing process> The second mixing step in the method for producing a rubber composition of the present invention is a step of mixing a part or all of the butadiene rubber removed in the first mixing step with the mixture obtained in the first mixing step. If necessary, other components (other components not mixed in the first mixing step, such as styrene-butadiene copolymer rubber) may also be mixed in this second mixing step. This mixing method may also be a conventional method and is not particularly limited. For example, a method of kneading and mixing at room temperature or at a high temperature (e.g., 100 to 200°C) using a kneading machine such as a Banbury mixer, kneader, or roll is shown. The mixing time may be the same as in the first mixing step described above. Furthermore, it is preferable to cool the mixture obtained in this second mixing step and then separately mix (e.g., vulcanization press) the vulcanizing agent and vulcanization accelerator.

[0031] In this way, by first mixing the diene rubber mainly containing isoprene rubber with the entire amount of carbon black in the first mixing step as described above, and then mixing some or all of the butadiene rubber with the resulting mixture in the second mixing step as described above, the resulting rubber composition will have a predetermined amount of carbon black contained in the isoprene rubber-existing portion of the rubber composition. In other words, the ratio of the mass of carbon black contained in the isoprene rubber-existing portion of the rubber composition to the total mass of carbon black contained in the resulting rubber composition will be 60 mass% or more, and the effects of the present invention will be fully exhibited.

[0023] Note that, when the entire amount of diene rubber containing predetermined amounts of both isoprene rubber and butadiene rubber is mixed with the entire amount of carbon black in one step, the amount of carbon black in the isoprene rubber-containing portion does not exceed the predetermined amount, as described above. For example, when the entire amount of diene rubber containing 60% by mass of natural rubber and 40% by mass of butadiene rubber is mixed with the entire amount of carbon black in one step, the mass proportion of carbon black in the isoprene rubber-containing portion (mass proportion relative to the total amount) is less than 60% by mass. However, when mixing is performed using the method for producing a rubber composition of the present invention, the mass proportion of carbon black in the isoprene rubber-containing portion can be made 60% by mass or more.

[0032] In the method for producing a rubber composition of the present invention, it is more preferable that the butadiene rubber used contains more than 50 mass% of neodymium-catalyzed butadiene rubber, as described above. Furthermore, the mass proportion, glass transition temperature, weight average molecular weight, etc. of the neodymium-catalyzed butadiene rubber in the butadiene rubber used may be the same as described above. It is more preferable to use sulfur as a vulcanizing agent, and the total content of sulfur and vulcanization accelerator is preferably 2.5 parts by mass per 100 parts by mass of the diene rubber.

[0033] The rubber composition of the present invention can be produced by the above-described method for producing a rubber composition of the present invention. The resulting rubber composition of the present invention contains a predetermined amount of carbon black in the isoprene-based rubber-containing portion, and is a rubber composition that, with a relatively small amount of carbon black added, is excellent in cut resistance and low heat buildup (these properties can be achieved simultaneously), maintains or improves hardness and elongation at break, and maintains a good balance between these properties.

[0034] By using the rubber composition of the present invention in the side tread portion (sidewall portion), a tire having excellent cut resistance and low heat buildup in the side tread portion can be obtained. In other words, it can be said that the rubber composition of the present invention is suitable for constituting a side tread rubber layer (sidewall rubber layer) (preferred for side treads). The rubber composition of the present invention may also be used in other tire components. The tire is preferably a pneumatic tire, and the gas to be filled in the pneumatic tire may be, for example, air, inert gas such as nitrogen, argon, or helium, or other gases.

[0035] 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]

[0036] (Preparation and Evaluation of Rubber Compositions) Rubber compositions having the formulations shown in Table 1 below were prepared.

[0037] Specifically, for the Reference Example and Comparative Examples 1, 3 to 8, the components (all components except sulfur and vulcanization accelerator) in the parts by mass shown in the upper part of Table 1 below were mixed for 5 minutes (mixing step) using a 1.7-liter internal Banbury mixer, heated to around 150°C, and then discharged from the mixer and cooled to room temperature. Furthermore, predetermined amounts of sulfur and vulcanization accelerator were mixed and kneaded using the Banbury mixer, and the mixture was press-vulcanized at 170°C for 10 minutes in a predetermined mold to produce a rubber composition (vulcanized rubber composition test piece).

[0038] In Comparative Example 2 and Examples 1 to 8, the components (excluding neodymium-catalyzed butadiene rubber (NdBR), sulfur, and vulcanization accelerator) in the parts by mass shown in the upper part of Table 1 below were mixed for 2.5 minutes (first mixing step) using a 1.7-liter internal Banbury mixer after heating to approximately 150°C. NdBR was then added and mixed for an additional 2.5 minutes (second mixing step), and the mixture was then discharged from the mixer and cooled to room temperature. That is, in Comparative Example 2 and Examples 1 to 8, the entire amount of NdBR was added and mixed in the second mixing step. Furthermore, predetermined amounts of sulfur and vulcanization accelerator were mixed and kneaded using the Banbury mixer, and the mixture was press-vulcanized at 170°C for 10 minutes in a predetermined mold to produce a rubber composition (vulcanized rubber composition test piece).

[0039] Furthermore, in Example 9, the components (80% by mass of NdBR, sulfur, and vulcanization accelerators excluded) in the mass parts shown in the upper row of Table 1 below were mixed for 2.5 minutes (first mixing step) using a 1.7-liter internal Banbury mixer after heating to approximately 150°C. The remaining 80% by mass of NdBR was then added and mixed for another 2.5 minutes (second mixing step), and the mixture was then discharged from the mixer and cooled to room temperature. That is, in Example 9, 20% by mass of the total NdBR was added and mixed in the first mixing step, and the remaining 80% by mass was added and mixed in the second mixing step. Furthermore, predetermined amounts of sulfur and vulcanization accelerators were mixed and kneaded using the Banbury mixer. The resulting mixture was press-vulcanized at 170°C for 10 minutes in a predetermined mold to produce a rubber composition (vulcanized rubber composition test piece).

[0040] The rubber compositions (vulcanized rubber composition test pieces) obtained in the reference example, comparative examples 1 to 8, and examples 1 to 9 were evaluated for hardness, elongation at break, heat buildup, and cut resistance as follows.

[0041] <Hardness> The rubber hardness (HS) of each of the obtained vulcanized rubber composition test pieces was measured at a temperature of 20°C using a durometer type A (manufactured by Toyo Seiki Seisakusho, Ltd.) in accordance with JIS K6253-3:2012. The results are shown in the lower part of Table 1 below. The results are expressed as an index, with the value of the reference example being 100.

[0042] <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 K6251:2010, 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 the reference example being 100.

[0043] <Fever> For each vulcanized rubber composition test piece obtained, tan δ(60°C) was measured using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho, under conditions of initial strain 10%, amplitude ±2%, frequency 20 Hz and temperature 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 the reference example being 100, and the smaller the numerical value, the more difficult it is to generate heat (low heat generation).

[0044] <Cut resistance> The test pieces of each vulcanized rubber composition were measured for flex crack growth resistance in accordance with JIS K6260. 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 the reference example being 100, and the smaller the crack growth, the higher the index. In other words, the higher the index, the better the cut resistance.

[0045] [Table 1]

[0046] The details of each component in Table 1 above are as follows: NR: Natural rubber (SIR20, manufactured by NUSIRA) BR1: Cobalt-catalyzed butadiene rubber (CоBR, Nipol BR1220 (cis-1,4-bond content: 98 mol%, glass transition temperature Tg = -106°C, weight average molecular weight Mw = 450,000), manufactured by Zeon Corporation) BR2: Neodymium-catalyzed butadiene rubber (NdBR, Buna CB22 (cis-1,4-bond content: 98 mol%, glass transition temperature Tg = -106°C, weight average molecular weight Mw = 750,000), manufactured by ARLANXEO) BR3: Neodymium-catalyzed butadiene rubber (NdBR, Buna CB24 (cis-1,4-bond content: 97 mol%, glass transition temperature Tg = -106°C, weight average molecular weight Mw = 620,000), manufactured by ARLANXEO) CB1: Carbon black (Nitelon #55S (CTAB adsorption specific surface area: 30 m 2 / g, nitrogen adsorption specific surface area N2SA: 30m 2 / g), manufactured by Shin-Nichika Carbon Co., Ltd. CB2: Carbon black (Asahi #70K (CTAB adsorption specific surface area: 75 m 2 / g, nitrogen adsorption specific surface area N2SA:71m 2 / g), manufactured by Asahi Carbon Co., Ltd. Zinc oxide: Zinc oxide (ZM Silesia) Stearic acid: Lunac S-25 (Kao Corporation) Sulfur: MIDAS-105 (Bigensha) Vulcanization accelerator: Vulkacit NZ / EG (manufactured by Bayer, N-(tert-butyl)-2-benzothiazole sulfenamide: CAS No. 95-31-8)

[0047] These results indicate that the rubber compositions of Examples 1 to 8, obtained by the process in which the entire amount of the predetermined amount of neodymium-catalyzed butadiene rubber was added and mixed in the second mixing step, were superior in cut resistance and low heat buildup compared to the reference example (cut resistance was improved by 5% or more compared to the reference example, and tan δ (60°C) was significantly reduced, i.e., both were achieved). They also had excellent hardness or elongation at break, and a high level of balance between these properties was maintained. The rubber composition of Example 9, obtained by the process in which a portion (80% by mass) of the predetermined amount of neodymium-catalyzed butadiene rubber was added and mixed in the second mixing step, also had similar properties. STEM image analysis revealed that the ratio of the mass of carbon black contained in the natural rubber portion of the rubber composition to the total mass of carbon black contained in the rubber composition was 63% by mass or more (lower row of Table 1 above). These rubber compositions were therefore recognized as suitable for use in forming side tread rubber layers.

[0048] On the other hand, the rubber compositions of Comparative Examples 1 and 3 to 8, obtained by a manufacturing method in which neodymium-catalyzed butadiene rubber was added and mixed with other raw materials containing carbon black in a single mixing step, did not exhibit superior cut resistance or low heat buildup compared to the reference example, and some also exhibited reduced hardness and elongation at break. Specifically, when the amount of natural rubber in the diene rubber was low (when the amount of neodymium-catalyzed butadiene rubber was high), cut resistance and elongation at break were reduced (Comparative Example 1). When the amount of neodymium-catalyzed butadiene rubber in the diene rubber was low, heat buildup increased but cut resistance did not improve (Comparative Example 3). When the CTAB adsorption specific surface area of ​​the carbon black was outside the range, heat buildup significantly increased (Comparative Example 4). When the amount of carbon black was low, cut resistance and hardness decreased (Comparative Example 5). When the amount of carbon black was high, low heat buildup did not occur and cut resistance did not improve (Comparative Examples 6 to 8). In some cases, elongation at break and hardness were reduced (Comparative Examples 6 and 8). Furthermore, because these rubbers were obtained by adding and mixing the natural rubber and neodymium-catalyzed butadiene rubber together with carbon black in a single mixing step, the ratio of the mass of carbon black contained in the natural rubber-present portion of the rubber composition to the total mass of carbon black contained in the rubber composition was insufficient (see the lower part of Table 1 above). Furthermore, in Comparative Example 2, which was obtained by a manufacturing method in which the neodymium-catalyzed butadiene rubber was added and mixed in a second mixing step like Examples 1 to 8, the ratio of the mass of carbon black contained in the natural rubber-present portion of the rubber composition to the total mass of carbon black contained in the rubber composition was 60 mass%, but the proportion of natural rubber in the diene rubber was low, so the elongation at break was lower than that of the reference example.

Claims

1. A CTAB adsorption specific surface area of ​​20 to 60 m is used for 100 parts by mass of a diene rubber containing 35 to 65% by mass of an isoprene rubber and 35 to 65% by mass of a butadiene rubber. 2 A rubber composition for a side tread containing 20 to 38 parts by mass of carbon black having a viscosity of 1000 psi / g, a ratio of the mass of the carbon black contained in the isoprene-based rubber-existing portion of the rubber composition to the total mass of the carbon black contained in the rubber composition is 60 mass% or more; A rubber composition for side treads.

2. The rubber composition for a side tread according to claim 1, wherein the butadiene rubber is a butadiene rubber containing more than 50% by mass of neodymium-catalyzed butadiene rubber.

3. The rubber composition for a side tread according to claim 1 or 2, comprising 2.5 parts by mass or more in total of sulfur and a vulcanization accelerator per 100 parts by mass of the diene rubber.

4. A tire comprising a side tread rubber layer formed from the rubber composition for a side tread according to claim 1 or 2.

5. A CTAB adsorption specific surface area of ​​20 to 60 m is used for 100 parts by mass of a diene rubber containing 35 to 65% by mass of an isoprene rubber and 35 to 65% by mass of a butadiene rubber. 2 A method for producing a rubber composition for a side tread, comprising: a first mixing step of mixing raw materials including the diene rubber containing all of the isoprene rubber and all or a part of the butadiene rubber removed, and the carbon black; A second mixing step of mixing a part or all of the butadiene rubber into the mixture obtained in the first mixing step. A method for producing a rubber composition for a side tread.

6. The method for producing a rubber composition for a side tread according to claim 5, wherein the butadiene rubber is a butadiene rubber containing more than 50% by mass of neodymium-catalyzed butadiene rubber.

7. 7. The method for producing a rubber composition for a side tread according to claim 5, wherein the rubber composition contains 2.5 parts by mass or more of sulfur and a vulcanization accelerator in total per 100 parts by mass of the diene rubber.

Images