Reclaimed rubber-containing rubber composition and pneumatic tire

Abstract

To provide a reclaimed rubber-containing rubber composition which is excellent in fracture characteristics and fatigue resistance when made into a vulcanized rubber, and to provide a pneumatic tire including a rubber part formed by vulcanizing and molding the reclaimed rubber-containing rubber composition.SOLUTION: The reclaimed rubber-containing rubber composition contains a reclaimed rubber. A vulcanized rubber of the following specific rubber composition for evaluation prepared using the reclaimed rubber exhibits a rubber elastic modulus of 2.0 MPa or more as measured by an atomic force microscope. The rubber composition for evaluation is a rubber composition containing 20 pts.mass of the reclaimed rubber based on 100 pts.mass of an isoprene rubber and containing no carbon black.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber composition containing recycled rubber, and a pneumatic tire having a rubber portion formed by vulcanization molding of the rubber composition containing recycled rubber. [Background technology]

[0002] In recent years, due to increasing environmental awareness, there has been a strong demand for recycling waste vulcanized rubber generated from used tires and other rubber products.

[0003] The following Patent Document 1 describes a reclaimed rubber-containing rubber composition that contains reclaimed rubber obtained by subjecting powdered rubber that has been subjected to a particle size reduction process and adjusted so that the powder contains 25% or more of rubber that has passed through a 145 mesh sieve, and then further processing the powdered rubber using the oil pan method. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-35663 A Summary of the Invention [Problem to be solved by the invention]

[0005] As a result of intensive research, the present inventors have found that there is room for further improvement in the fracture properties and fatigue resistance of the reclaimed rubber-containing rubber composition obtained by the above-mentioned conventional technology when it is made into vulcanized rubber.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a rubber composition containing recycled rubber that has excellent fracture properties and fatigue resistance when made into a vulcanized rubber, and a pneumatic tire having a rubber portion formed by vulcanizing the rubber composition containing recycled rubber.

[0007] The above problems can be solved by the following configuration: That is, the present invention relates to a reclaimed rubber-containing rubber composition (1) that contains reclaimed rubber, characterized in that the reclaimed rubber is a reclaimed rubber having a rubber elastic modulus of 2.0 MPa or more as measured by an atomic force microscope for a vulcanized rubber of a specific rubber composition for evaluation described below. Rubber composition for evaluation: a rubber composition containing 20 parts by mass of the reclaimed rubber per 100 parts by mass of isoprene rubber and containing no carbon black

[0008] In the above-mentioned reclaimed rubber-containing rubber composition (1), the rubber composition for evaluation is preferably a reclaimed rubber-containing rubber composition (2) containing 1.5 parts by mass of sulfur per 100 parts by mass of isoprene rubber.

[0009] In the above reclaimed rubber-containing rubber composition (1) or (2), a reclaimed rubber-containing rubber composition (3) containing 1 to 10 parts by mass of the reclaimed rubber is preferred, where the total amount of the rubber components is taken as 100 parts by mass.

[0010] In any one of the reclaimed rubber-containing rubber compositions (1) to (3) above, a reclaimed rubber-containing rubber composition (4) is preferred in which the reclaimed rubber is reclaimed rubber derived from tire treads.

[0011] In any of the above reclaimed rubber-containing rubber compositions (1) to (4), the reclaimed rubber is preferably a reclaimed rubber composition (5) containing 50 parts by mass or more of at least one rubber selected from the group consisting of natural rubber and isoprene rubber, when the total amount of the rubber components is 100 parts by mass.

[0012] The present invention also relates to a pneumatic tire (6) having a rubber portion formed by vulcanizing any one of the reclaimed rubber-containing rubber compositions (1) to (5). Effect of the Invention

[0013] The reclaimed rubber-containing rubber composition according to the present invention contains a specific reclaimed rubber, specifically, reclaimed rubber that exhibits a rubber elasticity modulus of 2.0 MPa or more when measured with an atomic force microscope for the vulcanized rubber of the specific rubber composition for evaluation described below. Rubber composition for evaluation: a rubber composition containing 20 parts by mass of the reclaimed rubber per 100 parts by mass of isoprene rubber and containing no carbon black

[0014] An atomic force microscope (hereafter simply referred to as AFM) is a type of microscope that detects the atomic force acting on a probe and a sample, and is broadly synonymous with an SPM. The AFM probe is attached to the tip of a cantilever, and various physical properties can be measured by changing the type of cantilever and the method of signal detection. The distance dependence of the force acting on the probe and sample with an AFM is the most basic measurement quantity, and is called a force curve. A force curve is plotted by taking the amount of movement of the piezoelectric element that controls the distance between the probe and the sample on the horizontal axis and the amount of displacement of the cantilever on the vertical axis. If the spring constant k of the cantilever is known, the displacement can be converted to force (N). When the probe and the sample are brought close to each other and finally come into contact, a repulsive force is applied, and the repulsive force increases as the force is pressed. If the sample is softer than the spring constant of the cantilever, such as vulcanized rubber, the surface of the sample deforms when the probe is pressed, and the displacement of the cantilever and the amount of movement of the piezoelectric element do not match, resulting in nonlinearity. From this relationship, the local elastic modulus of the sample can be evaluated. Note that in order to calculate the quantitative value of the elastic modulus, it is necessary to know the contact area between the probe and the sample surface, but in reality, it is impossible to actually measure this. For this reason, a theoretical calculation formula for a contact model that assumes the shape of the probe tip to be a sphere is usually fitted to the force curve, and the elastic modulus is obtained from the fitting parameters.

[0015] The inventors measured the vulcanized rubber of the rubber composition for evaluation, which contains 20 parts by mass of recycled rubber per 100 parts by mass of isoprene rubber and does not contain carbon black, by AFM. It was found that the recycled rubber, which increases the rubber modulus of the matrix region excluding the recycled rubber in the vulcanized rubber to 2.0 MPa or more, can maintain and improve the fracture properties and fatigue resistance of the vulcanized rubber when blended with unvulcanized rubber (new rubber). The reason for this effect is unclear, but it is believed that the reason is that the reclaimed rubber has an excellent reinforcing effect due to the enhanced compatibility effect and improved dispersibility of the reclaimed rubber when blended with new rubber, and therefore the adverse effect of the reclaimed rubber on the fracture properties and fatigue resistance can be significantly reduced compared to the case of blending general reclaimed rubber. Furthermore, when the reclaimed rubber is reclaimed rubber derived from tire treads, particularly when the reclaimed rubber is reclaimed rubber containing 50 parts by mass or more of at least one type selected from the group consisting of natural rubber and isoprene rubber when the total amount of the rubber components is taken as 100 parts by mass, this is preferred because it leads to improved breaking strength of the vulcanized rubber of the reclaimed rubber-containing rubber composition.

[0016] The reclaimed rubber-containing rubber composition according to the present invention has excellent fracture properties and fatigue resistance when vulcanized, and is therefore useful as a rubber composition for pneumatic tires, particularly as a rubber composition for the tread of pneumatic tires. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The reclaimed rubber-containing rubber composition according to the present invention contains reclaimed rubber. The reclaimed rubber will be described below.

[0018] Reclaimed rubber is generally produced by crushing waste rubber such as waste tires and subjecting it to a devulcanization treatment. Waste tires contain a wide variety of components such as treads and sidewalls that constitute tires, but in the present invention, from the viewpoint of improving the breaking strength of the vulcanized rubber of the reclaimed rubber-containing rubber composition, it is preferable that the reclaimed rubber is reclaimed rubber derived from tire treads. Examples of reclaimed rubber derived from tire treads include reclaimed rubber produced from waste rubber obtained by scraping the tread portion during the production of retread tires.

[0019] In the present invention, from the viewpoint of improving the breaking strength of the vulcanized rubber of the reclaimed rubber-containing rubber composition, when the total amount of the rubber components is taken as 100 parts by mass, the reclaimed rubber is preferably a reclaimed rubber containing 50 parts by mass or more, and more preferably 70 parts by mass or more, of at least one type selected from the group consisting of natural rubber and isoprene rubber.

[0020] The reclaimed rubber contained in the reclaimed rubber-containing rubber composition according to the present invention can be produced from, for example, tire tread components of truck and bus tires, which are rich in natural rubber. Specifically, the tire tread components are pulverized to a maximum diameter of 500 μm with a cracker roll, and then an air flow splitter is used to recover rubber powder with a maximum diameter of 150 μm, which can be used as the raw material for production.

[0021] It is preferable to further treat the rubber powder obtained above by the oil pan method. For example, the rubber powder subjected to the above-mentioned micronization treatment is placed in an autoclave, a regenerant is added, and a desulfurization reaction is carried out in a steam atmosphere at a temperature of about 200°C for 3 to 6 hours. The regenerant used is a regenerant known to those skilled in the art, such as thiophenol, n-butylamine, etc.

[0022] The reclaimed rubber contained in the reclaimed rubber-containing rubber composition according to the present invention is produced, for example, by the method described above and has the following properties. Reclaimed rubber is blended into the specific rubber composition for evaluation described below, and the resulting vulcanized rubber exhibits a rubber elastic modulus of 2.0 MPa or more as measured with an atomic force microscope. Rubber composition for evaluation: a rubber composition containing 20 parts by mass of the reclaimed rubber per 100 parts by mass of isoprene rubber and containing no carbon black In addition, if the rubber composition for evaluation contains carbon black, it becomes difficult to distinguish the AFM elastic modulus image due to the addition of recycled rubber, so in the present invention, the rubber composition for evaluation used does not contain carbon black.

[0023] The rubber composition for evaluation is preferably rubber composition for evaluation (1) containing 1.5 parts by mass of sulfur per 100 parts by mass of isoprene rubber, and in particular, rubber composition for evaluation (2) having the following formulation is preferable. (Rubber composition for evaluation (2)) - 100 parts by weight of "Isoprene rubber (Mooney viscosity (ML(1+4) 75.0-90.0): product name "Nipol@IR2200", manufactured by Zeon Corporation" 20 parts by weight of "recycled rubber" Stearic acid: product name "Lunac S-20", manufactured by Kao Corporation, 2 parts by weight - 2 parts by weight of "Zinc Oxide: Product name "Zinc Oxide Type 1", manufactured by Mitsui Mining & Smelting Co., Ltd." - "Vulcanization accelerator: Product name "Noccela NS", manufactured by Ouchi Shinko Chemical Industry Co., Ltd." 1.5 parts by weight Sulfur: 1.5 parts by weight of "Powdered sulfur for rubber 150 mesh" manufactured by Hosoi Chemical Industry Co., Ltd.

[0024] In the present invention, the rubber elastic modulus of the vulcanized rubber measured by an atomic force microscope is the average elastic modulus of a matrix area observed in a 128 pixel x 128 pixel and 5 μm x 5 μm square. The rubber elastic modulus of the vulcanized rubber measured by an atomic force microscope is 2.0 MPa or more, and more preferably 2.5 MPa or more. There is no particular upper limit, but an example of the upper limit is about 5.0 MPa.

[0025] The reclaimed rubber used in the present invention has a specific surface area of ​​100 to 120 m based on the BET method. 2 It is preferable that the rubber composition contains carbon black having a specific surface area of ​​100 / g. Since such carbon black has a large specific surface area, it is preferable because it has an effect of increasing the reinforcing properties when the reclaimed rubber is blended with new rubber that has not yet been vulcanized.

[0026] The reclaimed rubber used in the present invention is preferably designed to have a gel fraction of 75% or less, which is preferable because it enhances the compatibility effect when the reclaimed rubber is blended with new rubber that has not yet been vulcanized, thereby improving the dispersibility of the reclaimed rubber.

[0027] The reclaimed rubber used in the present invention preferably has an average particle size d70 of 100 μm or less and an average particle size d90 of 150 μm or less. This is preferable because the gel fraction of the reclaimed rubber is lowered due to the large amount of polymeric substances eluted during the devulcanization treatment. The method for measuring the particle size distribution of the reclaimed rubber will be described later.

[0028] From the viewpoint of recycling, it is preferable that the recycled rubber-containing rubber composition according to the present invention contains as much recycled rubber as possible. However, from the viewpoint of improving the breaking strength of the vulcanized rubber of the recycled rubber-containing rubber composition, it is preferable that the recycled rubber is contained in an amount of 1 to 10 parts by mass when the total amount of the rubber components is taken as 100 parts by mass.

[0029] The reclaimed rubber-containing rubber composition of the present invention can be compounded with an appropriate amount of compounding agents normally used in the rubber industry, such as unvulcanized rubber (new rubber), fillers, sulfur, vulcanization accelerators, silane coupling agents, zinc oxide, stearic acid, vulcanization retarders, organic peroxides, antioxidants, softeners such as wax and oil, and processing aids, in addition to the reclaimed rubber.

[0030] As the rubber component (unvulcanized rubber (new rubber)), diene rubber is preferred, and examples thereof include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, and styrene-isoprene-butadiene copolymer rubber. These may be used alone or in combination of two or more. As the diene rubber, natural rubber, butadiene rubber, and styrene butadiene rubber, or a blend of two or more of these, are preferred.

[0031] The reclaimed rubber-containing rubber composition according to the present invention preferably contains carbon black as a filler. As the carbon black, for example, SAF, ISAF, HAF, FEF, GPF, and other carbon blacks normally used in the rubber industry, as well as conductive carbon blacks such as acetylene black and ketjen black, can be used. The reclaimed rubber-containing rubber composition according to the present invention preferably contains 0 to 70 parts by mass of carbon black, more preferably 30 to 70 parts by mass, when the total amount of rubber components other than the reclaimed rubber is taken as 100 parts by mass.

[0032] The reclaimed rubber-containing rubber composition according to the present invention may contain silica as a filler. As the silica, wet silica, dry silica, sol-gel silica, surface-treated silica, and the like, which are generally used for rubber reinforcement, are used. Among these, wet silica is preferred.

[0033] When silica is contained as a filler, it is also preferable to contain a silane coupling agent together. The silane coupling agent is not particularly limited as long as it contains sulfur in the molecule, and various silane coupling agents that are compounded together with silica in rubber compositions can be used. Examples of the silanes include sulfide silanes such as bis(3-triethoxysilylpropyl)tetrasulfide (e.g., "Si69" manufactured by Degussa), bis(3-triethoxysilylpropyl)disulfide (e.g., "Si75" manufactured by Degussa), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, and bis(2-trimethoxysilylethyl)disulfide; mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane.

[0034] The sulfur may be any ordinary rubber sulfur, such as powdered sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur, etc. The reclaimed rubber-containing rubber composition according to the present invention preferably contains 0.5 to 5 parts by mass of sulfur when the total amount of rubber components other than the reclaimed rubber is taken as 100 parts by mass.

[0035] As the vulcanization accelerator, those vulcanization accelerators usually used for rubber vulcanization, such as sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators, may be used alone or in appropriate mixtures.

[0036] As the age resistor, age resistors generally used for rubber, such as aromatic amine-based age resistors, amine-ketone-based age resistors, monophenol-based age resistors, bisphenol-based age resistors, polyphenol-based age resistors, dithiocarbamate-based age resistors, and thiourea-based age resistors, may be used alone or in appropriate mixtures.

[0037] There are no particular limitations on the method for compounding the reclaimed rubber and each of the above-mentioned components in the reclaimed rubber-containing rubber composition according to the present invention, and any of the following may be used: a method in which the compounding components other than the vulcanization components, such as sulfur and vulcanization accelerator, are pre-mixed to form a master batch, and the remaining components are then added and further kneaded; a method in which the components are added in any order and kneaded; or a method in which all of the components are added simultaneously and kneaded.

[0038] The reclaimed rubber-containing rubber composition according to the present invention has excellent fracture properties and fatigue resistance when vulcanized, and is therefore useful as a rubber composition for pneumatic tires, particularly as a rubber composition for the tread of pneumatic tires. EXAMPLES

[0039] The present invention will be explained more specifically below by describing examples thereof.

[0040] (Example of reclaimed rubber manufacturing) The tire tread material was scraped off from truck and bus tires and pulverized to a maximum diameter of 500 μm using a cracker roll. Furthermore, an airflow diverter was used to produce rubber powder pulverized to a maximum diameter of 150 μm. By pulverizing the obtained rubber powder, the specific surface area of ​​the rubber powder increases, and the desulfurization effect increases. The finely pulverized rubber powder was placed in an autoclave, a regenerating agent was added, and the desulfurization reaction was carried out in a steam atmosphere at a temperature of about 200 ° C for 3 to 6 hours (oil pan method treatment) to produce regenerated rubbers A to B. In addition, commercially available regenerated rubber C (manufactured by Asahi Regenerated Rubber Co., Ltd., product name "High Strength Regenerated Rubber"), regenerated rubber D (manufactured by Muraoka Rubber Co., Ltd., product name "Tire Recycle White Line Mark"), and regenerated rubber E (rubber powder obtained by crushing the TB tread material with a cracker roll and classifying the crushed rubber powder by airflow classification) were prepared. The polymer ratios constituting each regenerated rubber are shown in Table 1. In Table 1, "NR" means natural rubber and "BR" means butadiene rubber. The average particle size (d50, d70 and d90) of each reclaimed rubber is also shown in Table 1. The measurement method is as follows.

[0041] <Rubber elastic modulus measured by atomic force microscope for vulcanized rubber of rubber composition for evaluation> In the compounding of the rubber composition for evaluation (2) described above, a rubber composition for evaluation (2) (composition containing recycled rubber) containing 20 parts by mass of recycled rubbers A to E per 100 parts by mass of isoprene rubber was prepared as the recycled rubber, and the AFM elastic modulus image was observed. When carbon black was mixed, it was difficult to see the increase or decrease in the elastic modulus image due to the addition of recycled rubber, so a non-filler compounding was adopted. The average elastic modulus of the matrix area was calculated. The average elastic modulus of the matrix area of ​​the composition containing recycled rubber is shown in Table 1.

[0042] <Average particle size of each recycled rubber (d50, d70 and d90)> The particle size distribution of rubber powder was measured using Shimadzu SALD2300. The laser diffraction and scattering method is a method in which a group of particles is irradiated with laser light, and the particle size distribution is calculated from the intensity distribution pattern of the diffracted and scattered light emitted from the particles. When a particle is irradiated with a laser beam, the particle emits light in various directions, such as forward and backward, up and down, left and right. This light is called "diffracted and scattered light." The intensity of the diffracted and scattered light draws a certain spatial pattern in the direction in which the light is emitted. This is the "light intensity distribution pattern." It is known that the "light intensity distribution pattern" changes into various shapes depending on the size of the particles. By detecting the light intensity distribution pattern, the average particle size (d50, d70, and d90) of each recycled rubber was measured.

[0043] [Table 1]

[0044] As can be seen from the results in Table 1, when no recycled rubber was blended into the rubber composition for evaluation (2) (shown as "No recycled rubber" in Table 1), the rubber elasticity modulus of the vulcanized rubber was only 0.9, but the rubber elasticity moduli of recycled rubbers A to C were 2.0 MPa or more, and in particular, the rubber elasticity moduli of recycled rubbers A and B were 2.5 MPa or more.

[0045] (Preparation of Reclaimed Rubber-Containing Rubber Composition) Each component was blended according to the blending recipes in Tables 2 to 4 with respect to 100 parts by mass of the rubber component (natural rubber) excluding the reclaimed rubber, and kneaded using a lab mixer manufactured by Daihan Co., Ltd. to produce reclaimed rubber-containing rubber compositions according to Examples 1 to 3 and Comparative Examples 1 and 2. For example, Example 1-(1) is a reclaimed rubber-containing rubber composition containing reclaimed rubber A, meaning that 1 part by mass of reclaimed rubber A is contained with respect to 100 parts by mass of the rubber component (natural rubber), and Comparative Example 1-(5) is a reclaimed rubber-containing rubber composition containing reclaimed rubber D, meaning that 5 parts by mass of reclaimed rubber D is contained with respect to 100 parts by mass of the rubber component (natural rubber).

[0046] Details of each component in Tables 2 to 4 are as follows. Natural rubber: STR20 Carbon black (HAF): "Seast 3" manufactured by Tokai Carbon Co., Ltd. Stearic acid: Kao Corporation's "Lunac S-20" Zinc oxide: "Zinc oxide type 1" manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: "Powdered sulfur for rubber 150 mesh" manufactured by Hosoi Chemical Industry Co., Ltd. - Vulcanization accelerator: "Noccela NS" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0047] Next, the obtained rubber composition containing reclaimed rubber was vulcanized under conditions of 150° C. for 25 minutes to prepare test pieces of a predetermined shape, and the following tests were carried out using the obtained test pieces.

[0048] <Breaking strength> The breaking strength (MPa) of the samples prepared using JIS No. 3 dumbbells was measured in accordance with JIS K6251. In Tables 2 to 4, the breaking strength of Comparative Example 1-(1), Comparative Example 1-(3), and Comparative Example 1-(5), which contain 1, 3, and 5 parts by mass of reclaimed rubber D per 100 parts by mass of the rubber component (natural rubber), is set to 100, and the results are shown as index evaluations. The larger the value, the higher the breaking strength, indicating that the rubber will have excellent fracture properties when vulcanized.

[0049] <Elongation at break> The elongation at break (%) of the samples prepared using JIS No. 3 dumbbells was measured in accordance with JIS K6251. In Tables 2 to 4, the elongation at break of Comparative Example 1-(1), Comparative Example 1-(3), and Comparative Example 1-(5), which contain 1, 3, and 5 parts by mass of reclaimed rubber D per 100 parts by mass of the rubber component (natural rubber), is set to 100, and index evaluation is shown. A larger value indicates a higher elongation at break and excellent fracture properties when made into a vulcanized rubber.

[0050] <Fatigue resistance> In accordance with JIS K6260, vulcanized rubber was repeatedly elongated (at a constant strain) using a De Mattia testing machine, and the number of elongations until breakage (cracking) was measured to determine fatigue resistance (flex cracking resistance). In Tables 2 to 4, the tear strength of Comparative Example 1-(1), Comparative Example 1-(3), and Comparative Example 1-(5), which contain 1, 3, and 5 parts by mass of reclaimed rubber D per 100 parts by mass of rubber component (natural rubber), is set to 100, and index evaluation is shown. A larger value indicates a higher breaking elongation and excellent fatigue resistance when made into vulcanized rubber.

[0051] [Table 2]

[0052] From the results in Table 2, it can be seen that the vulcanized rubber of the reclaimed rubber-containing rubber composition according to Example 1-(1) to Example 3-(1) has high breaking strength and breaking elongation, excellent fracture properties, and also excellent fatigue resistance. In particular, it can be seen that the vulcanized rubber of the reclaimed rubber-containing rubber composition according to Example 1-(1) to Example 2-(1), which contains reclaimed rubber having a rubber modulus of 2.5 MPa or more as measured by atomic force microscope in the matrix region excluding the reclaimed rubber in the vulcanized rubber of the rubber composition for evaluation, has higher breaking strength and breaking elongation, excellent fracture properties, and further excellent fatigue resistance.

[0053] [Table 3]

[0054] From the results in Table 3, it can be seen that the vulcanized rubber of the reclaimed rubber-containing rubber composition according to Example 1-(3) to Example 3-(3) has high breaking strength and breaking elongation, excellent fracture properties, and also excellent fatigue resistance. In particular, it can be seen that the vulcanized rubber of the reclaimed rubber-containing rubber composition according to Example 1-(3) to Example 2-(3), which contains reclaimed rubber having a rubber modulus of 2.5 MPa or more as measured by atomic force microscope in the matrix region excluding the reclaimed rubber in the vulcanized rubber of the rubber composition for evaluation, has higher breaking strength and breaking elongation, excellent fracture properties, and further excellent fatigue resistance.

[0055] [Table 4]

[0056] From the results in Table 4, it can be seen that the vulcanized rubber of the reclaimed rubber-containing rubber composition according to Example 1-(5) to Example 3-(5) has high breaking strength and breaking elongation, excellent fracture properties, and also excellent fatigue resistance. In particular, it can be seen that the vulcanized rubber of the reclaimed rubber-containing rubber composition according to Example 1-(5) to Example 2-(5), which contains reclaimed rubber having a rubber modulus of 2.5 MPa or more as measured by atomic force microscope in the matrix region excluding the reclaimed rubber in the vulcanized rubber of the rubber composition for evaluation, has higher breaking strength and breaking elongation, excellent fracture properties, and further excellent fatigue resistance.

Claims

1. A reclaimed rubber-containing rubber composition comprising reclaimed rubber, A reclaimed rubber-containing rubber composition, characterized in that the reclaimed rubber is a reclaimed rubber having a rubber elasticity modulus of 2.0 MPa or more as measured by an atomic force microscope for a vulcanized rubber of a specific rubber composition for evaluation described below. Rubber composition for evaluation: a rubber composition containing 20 parts by mass of the reclaimed rubber per 100 parts by mass of isoprene rubber and containing no carbon black

2. 2. The reclaimed rubber-containing rubber composition according to claim 1, wherein the rubber composition for evaluation contains 1.5 parts by mass of sulfur per 100 parts by mass of isoprene rubber.

3. The reclaimed rubber-containing rubber composition according to claim 1, wherein the reclaimed rubber is contained in an amount of 1 to 10 parts by mass when the total amount of the rubber components is 100 parts by mass.

4. 2. The reclaimed rubber-containing rubber composition according to claim 1, wherein the reclaimed rubber is reclaimed rubber derived from tire treads.

5. 2. The reclaimed rubber-containing rubber composition according to claim 1, wherein the reclaimed rubber is a reclaimed rubber containing 50 parts by mass or more of at least one rubber selected from the group consisting of natural rubber and isoprene rubber, when the total amount of the rubber components is 100 parts by mass.

6. A pneumatic tire comprising a rubber portion formed by vulcanization molding the reclaimed rubber-containing rubber composition according to claim 1.

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