Rubber material, method for producing same, and tire

Abstract

Provided is a rubber material which uses a rubber powder and which is capable of obtaining a rubber member having excellent mechanical properties and low loss properties. Provided is a rubber material obtained by dispersing a rubber powder (A) in a rubber base material (B), the rubber material being characterized in that the rubber powder (A) is obtained by disposing an unvulcanized rubber layer (a2) on the surface of a vulcanized rubber powder (a1), and the unvulcanized rubber layer (a2) contains a crosslinking agent.

Description

Technical Field

[0001] The present invention relates to a rubber material, a method for producing the same, and a tire. Background Art

[0002] Currently, research is being conducted on the utilization of rubber powder (vulcanized rubber powder) obtained from waste rubber and used tires.

[0003] For example, PTL 1 discloses a material comprising rubber powder also obtained from waste of used vulcanized rubber products, as well as specific aggregates and binders, exhibiting excellent wear resistance and anti-slip properties after wear due to use, and can be used as an elastic paving material for sidewalks, etc.

[0004] Prior art literature

[0005] Patent Literature

[0006] PTL 1: JP 2010-242430 A Summary of the invention

[0007] Problem that the invention aims to solve

[0008] Here, it is also expected to utilize the above-mentioned rubber powder, for example, in the manufacture of tires. However, studies conducted by the present inventors have found that the rubber material obtained by simply compounding and kneading the above-mentioned rubber powder into a rubber component is insufficient in achieving the performance required for tire components, particularly in balancing at least mechanical properties and low loss, and there is still room for improvement.

[0009] Therefore, the present invention aims to solve the problems of the above-mentioned prior art and provide a rubber material allowing a rubber member excellent in mechanical characteristics and low loss to be obtained by utilizing rubber powder, a method for producing the same, and a tire using the rubber material.

[0010] Solutions for solving problems

[0011] Main features of the present invention for solving the above-mentioned problems are as follows.

[0012] [1] A rubber material comprising a rubber powder (A) dispersed in a rubber base material (B),

[0013] The rubber powder (A) is obtained by disposing an unvulcanized rubber layer (a2) on the surface of a vulcanized rubber powder (a1), and the unvulcanized rubber layer (a2) contains a crosslinking agent.

[0014] [2] The rubber material according to [1], wherein M1 / M2 of the rubber powder (A) is 0.5 or more and 2.5 or less, wherein M1 represents the mass of the vulcanized rubber powder (a1) and M2 represents the mass of the unvulcanized rubber layer (a2).

[0015] [3] The rubber material according to [1] or [2], wherein the unvulcanized rubber layer (a2) contains sulfur as a cross-linking agent.

[0016] [4] The rubber material according to any one of [1] to [3], wherein the unvulcanized rubber layer (a2) contains a diene rubber.

[0017] [5] The rubber material according to [4], wherein the unvulcanized rubber layer (a2) contains natural rubber as the diene rubber, and the proportion of the natural rubber in the rubber component is 50% by mass or more.

[0018] [6] A tire comprising the vulcanized product of the rubber material according to any one of [1] to [5].

[0019] [7] A method for producing a rubber material according to any one of [1] to [5], the method comprising:

[0020] a pre-mixing step of mixing the vulcanized rubber powder (a1) and the unvulcanized rubber layer (a2) with a rubber component to obtain a masterbatch as a precursor of the rubber powder (A); and

[0021] The main kneading step is to knead the masterbatch and the rubber base (B) with the rubber component to disperse the rubber powder (A) formed by pulverizing the masterbatch in the rubber base (B).

[0022] Effects of the Invention

[0023] According to the present invention, a rubber material that allows a rubber member excellent in mechanical characteristics and low loss properties to be obtained by utilizing rubber powder, a method for producing the same, and a tire using the rubber material can be obtained. DETAILED DESCRIPTION

[0024] Hereinafter, the present invention will be shown and explained in detail based on embodiments.

[0025] Note that the compounds described in this specification may be partially or entirely derived from fossil resources, biological resources such as plant resources, or renewable resources such as used tires. Alternatively, they may be derived from a mixture of two or more of fossil resources, biological resources, and renewable resources.

[0026] (Rubber material)

[0027] The rubber material of one embodiment of the present invention (hereinafter sometimes referred to as "the rubber material of the present embodiment") is a rubber material comprising a rubber powder (A) dispersed in a rubber base material (B). In the rubber material of the present embodiment, the rubber powder (A) is characterized in that an unvulcanized rubber layer (a2) is arranged on the surface of the vulcanized rubber powder (a1) and the unvulcanized rubber layer (a2) contains a crosslinking agent.

[0028] According to the rubber material of the present embodiment, a rubber member excellent in mechanical characteristics and low loss property can be obtained by utilizing rubber powder.

[0029] It should be noted that, in this specification, the term "rubber material" refers to a material containing at least a rubber component.

[0030] It is inferred that the rubber material of the present embodiment shows excellent mechanical properties and the reason of low loss property as follows. Specifically, it is believed that in the conventional rubber material obtained by only mixing and kneading vulcanized rubber powder (corresponding to the vulcanized rubber powder (a1) in the rubber material of the present embodiment) into the rubber substrate, the crosslinking agent such as sulfur present in the rubber substrate migrates and mainly stays at the interface between the vulcanized rubber powder and the rubber substrate. As a result, when the rubber material is vulcanized, the crosslinking degree in the rubber substrate tends to weaken (the network structure becomes looser). On the contrary, in the rubber material of the present embodiment, by covering the surface of the vulcanized rubber powder (a1) with the unvulcanized rubber layer (a2) of specific composition, the unvulcanized rubber layer (a2) is used as a barrier layer during vulcanization, thereby reducing the adverse effect of crosslinking (network structure) in the rubber substrate (B). As a result, it is believed that the sufficient crosslinking property of the rubber substrate and the fact that the rubber powder (A) is dispersed contribute to the high mechanical properties.

[0031] In addition, it is believed that in the rubber material of the present embodiment, by covering the surface of the vulcanized rubber powder (a1) with the unvulcanized rubber layer (a2), the sulfur density gradient at the interface between the vulcanized rubber powder and the rubber substrate is reduced. In addition, if there are only vulcanized rubber powder (a1) with high hardness and rubber substrate (B) with low hardness, there is a possibility of high loss. However, it is speculated that the low-loss unvulcanized rubber layer (a2) between them improves the low-loss property of the rubber material.

[0032] The rubber material of the present embodiment can be generally produced by the method for producing the rubber material of the present invention which will be described later.

[0033] <Rubber powder (A)>

[0034] The rubber powder (A) in the rubber material of this embodiment is constituted by disposing the unvulcanized rubber layer (a2) on the surface of the vulcanized rubber powder (a1). The rubber powder (A) can be regarded as a part constituting the island phase in the rubber material of this embodiment.

[0035] In the rubber material of the present embodiment, the content of the rubber powder (A) is preferably 5 parts by mass or more relative to 100 parts by mass of the rubber component of the rubber base material (B). In this case, the effect of improving mechanical properties and low loss can be more fully obtained. From a similar point of view, the content of the rubber powder (A) is more preferably 10 parts by mass or more, even more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more. On the other hand, in order to reduce the influence on various properties ensured by the rubber base material (B), the content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, and even more preferably 60 parts by mass or less.

[0036] It should be noted that the content of the rubber powder (A) mentioned above refers substantially to the total content of the vulcanized rubber powder (a1) and the unvulcanized rubber layer (a2).

[0037] Next, the vulcanized rubber powder (a1) and the unvulcanized rubber layer (a2) constituting the rubber powder (A) will be described.

[0038] The vulcanized rubber powder (a1) is not particularly limited, but it may be generally a vulcanized product of a rubber composition containing a diene rubber. In addition, the vulcanized rubber powder (a1) may be obtained from waste rubber (e.g., waste of vulcanized rubber products such as hoses and belts) or used tires. In addition, commercially available products may also be used as the vulcanized rubber powder (a1).

[0039] The particle size of the vulcanized rubber powder (a1) is not particularly limited, but it is preferably 300 μm or less. If the particle size of the vulcanized rubber powder (a1) is 300 μm or less, the influence on various properties ensured by the rubber base material (B) can be further reduced.

[0040] It should be noted that the particle size of the vulcanized rubber powder (a1) can be confirmed, for example, by observation under a scanning electron microscope (SEM) or other microscopes.

[0041] The unvulcanized rubber layer (a2) is a layer formed on the surface of the vulcanized rubber powder (a1) and can be formed by a rubber composition containing a rubber component for the unvulcanized rubber layer (a2) (hereinafter sometimes referred to as "rubber composition for the unvulcanized rubber layer"). As the rubber component for the unvulcanized rubber layer (a2), a diene rubber is preferably used. In other words, it is preferred that the unvulcanized rubber layer (a2) contains a diene rubber. In this case, the function of the unvulcanized rubber layer (a2) as a barrier layer can be further enhanced. The diene rubber in the unvulcanized rubber layer (a2) can be a single type or a combination of two or more types.

[0042] Examples of the diene rubber include, for example, natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), and isoprene rubber (IR).

[0043] In addition, preferably unvulcanized rubber layer (a2) comprises natural rubber as diene rubber, and the ratio of natural rubber in rubber component is more than 50 mass %.In this case, the rubber of better vulcanization state can be obtained by vulcanization.From similar viewpoint, the ratio of natural rubber in the rubber component of unvulcanized rubber layer (a2) is more preferably more than 70 mass %, even more preferably more than 85 mass %.In addition, in unvulcanized rubber layer (a2), the ratio of natural rubber in rubber component can be 100 mass %, but is preferably less than 95 mass %.

[0044] It is required that the unvulcanized rubber layer (a2) (unvulcanized rubber layer rubber composition) includes a crosslinking agent. By including a crosslinking agent, the unvulcanized rubber layer (a2) can effectively suppress the migration and uneven distribution of the crosslinking agents such as sulfur in the rubber substrate (B) to the interface between rubber powder (A) and the rubber substrate (B), thereby improving various characteristics, including mechanical properties. The example of a crosslinking agent, for example, includes a sulfur-based crosslinking agent such as sulfur, an organic peroxide-based crosslinking agent, a polyamine crosslinking agent (polyamine crosslinking agent), a resin crosslinking agent and an oxime-nitrosamine-based crosslinking agent (oxime-nitrosoamine-based crosslinking agent). The crosslinking agent compounded into the unvulcanized rubber layer (a2) can be a single one or a combination of two or more.

[0045] In particular, it is preferred that the unvulcanized rubber layer (a2) contains sulfur (elemental sulfur) as a crosslinking agent. Since the rubber base material (B) also generally contains sulfur, the use of sulfur in the unvulcanized rubber layer (a2) can further suppress the migration and uneven distribution of sulfur in the rubber base material (B) to the interface, thereby further improving various properties, including mechanical properties.

[0046] Preferably, the content of crosslinking agent in every 100 parts by mass of rubber component in the unvulcanized rubber layer (a2) is greater than the content of sulfur in every 100 parts by mass of rubber component in the rubber substrate (B). Specifically, the content of crosslinking agent in every 100 parts by mass of rubber component in the unvulcanized rubber layer (a2) is preferably 2.0 parts by mass or more, more preferably 3.0 parts by mass or more. In this case, the function of the unvulcanized rubber layer (a2) as a barrier layer during vulcanization is further enhanced, so that the rubber substrate (B) forms a good crosslinking (network structure). On the other hand, the content of crosslinking agent in every 100 parts by mass of rubber component in the unvulcanized rubber layer (a2) can be, for example, 10.0 parts by mass or less, preferably 8.0 parts by mass or less.

[0047] In addition to the above-mentioned components, the unvulcanized rubber layer (a2) (rubber composition for unvulcanized rubber layer) may also appropriately contain other compounding agents, for example, fillers such as carbon black, vulcanization accelerators, vulcanization aids, vulcanization accelerating aids, retarders, antioxidants, antioxidants, softeners, foaming agents, plasticizers and processability improvers, each in an appropriate amount within the scope not impairing the purpose of the present invention.

[0048] In the rubber material of the present embodiment, M1 / M2 is preferably 0.5 or more and 2.5 or less, wherein, in the rubber powder (A), M1 represents the mass (content) of the vulcanized rubber powder (a1) and M2 represents the mass (content) of the unvulcanized rubber layer (a2).

[0049] If M1 / M2 is 0.5 or more, the effect of improving mechanical properties brought about by the vulcanized rubber powder (a1) itself can be more reliably obtained. In addition, from the viewpoint of more effectively using the vulcanized rubber powder and facilitating recycling, M1 / M2 is more preferably 0.5 or more, even more preferably 0.6 or more, and still even more preferably 0.7 or more.

[0050] In addition, if M1 / M2 is 2.5 or less, the formation of the unvulcanized rubber layer (a2) on the surface of the vulcanized rubber powder (a1) can be more reliably achieved. In addition, from the viewpoint that the unvulcanized rubber layer (a2) can be more effectively used as a barrier layer, M1 / M2 is more preferably 2.3 or less, and even more preferably 2.2 or less.

[0051] In the rubber material of this embodiment, the maximum thickness of the unvulcanized rubber layer (a2) in the rubber powder (A) is preferably 300 μm or less. If the maximum thickness is 300 μm or less, the influence on various properties ensured by the rubber base material (B) can be sufficiently reduced.

[0052] The maximum thickness of the unvulcanized rubber layer (a2) in the rubber powder (A) can be confirmed, for example, by observing a cross section of the rubber material under a microscope such as a scanning electron microscope (SEM). In addition, the thickness of the unvulcanized rubber layer (a2) in the rubber powder (A) can be adjusted, for example, by adjusting the compounding ratio of the rubber component for the vulcanized rubber powder (a1) and the unvulcanized rubber layer (a2) in the pre-mixing step of the rubber material manufacturing method of the present invention to be described later. In other words, if the amount of the rubber component for the unvulcanized rubber layer (a2) in the pre-mixing step is reduced relative to the vulcanized rubber powder (a1), the thickness of the unvulcanized rubber layer (a2) tends to decrease.

[0053] The unvulcanized rubber layer (a2) may be arranged on only a part of the surface of the vulcanized rubber powder (a1) or may be arranged on the entire surface of the vulcanized rubber powder (a1).

[0054] <Rubber base material (B)>

[0055] The rubber substrate (B) can be regarded as the part constituting the sea phase in the rubber material of the present embodiment. In addition, the rubber substrate (B) can be formed by a rubber composition (hereinafter, sometimes referred to as "rubber composition for substrate") containing a rubber component for the rubber substrate (B). As the rubber component for the rubber substrate (B), a diene rubber is preferably mentioned. In other words, it is preferred that the rubber substrate (B) contains a diene rubber. The diene rubber in the rubber substrate (B) can be a single one or a combination of two or more.

[0056] The rubber type (or combination of rubber types) of the rubber component for the rubber base material (B) and the rubber type (or combination of rubber types) of the rubber component for the unvulcanized rubber layer (a2) may be the same or different. In addition, when the combination of rubber types of the rubber component for the rubber base material (B) and the rubber component for the unvulcanized rubber layer (a2) is the same, their compositions may be the same or different. However, in order to clearly distinguish the unvulcanized rubber layer (a2) and the rubber base material (B) in the rubber material, it is preferred that the combination or composition of rubber types of the rubber component for the rubber base material (B) and the rubber component for the unvulcanized rubber layer (a2) is different.

[0057] The rubber substrate (B) preferably comprises at least one selected from natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR) and isoprene rubber (IR), more preferably comprises at least one of natural rubber and butadiene rubber, and even more preferably comprises both natural rubber and butadiene rubber.

[0058] The rubber substrate (B) (rubber composition for substrate) generally contains sulfur (elemental sulfur). In addition, in addition to the above components, the rubber substrate (B) may contain other compounding agents, such as fillers such as carbon black, vulcanization accelerators, vulcanization aids, vulcanization accelerating aids, retarders, antioxidants, antioxidants, softeners, foaming agents, plasticizers and processability improvers, each in an appropriate amount within the scope not impairing the purpose of the present invention.

[0059] It should be noted that the rubber base material (B) in the rubber material of the present embodiment is usually in an unvulcanized state, similar to the unvulcanized rubber layer (a2). Therefore, when the rubber material of the present embodiment is applied to a rubber member such as a tire, the above-mentioned rubber material (particularly the rubber base material (B) and the unvulcanized rubber layer (a2)) can be appropriately vulcanized before application.

[0060] (Method for producing rubber material)

[0061] A method for producing a rubber material according to an embodiment of the present invention (hereinafter, sometimes referred to as "the production method of the present embodiment") is a method for producing the rubber material of the present embodiment described above. The production method of the present embodiment includes a pre-mixing step of mixing vulcanized rubber powder (a1) and an unvulcanized rubber layer (a2) rubber component to obtain a masterbatch as a precursor of the rubber powder (A) and a main mixing step of mixing the masterbatch with the rubber component for the rubber base material (B).

[0062] According to such a production method of the present embodiment, a rubber material that allows a rubber member excellent in mechanical characteristics and low loss properties to be obtained, more specifically, the rubber material of the present embodiment described above, can be produced.

[0063] It should be noted that, unless otherwise specifically described below, the rubber powder (A), vulcanized rubber powder (a1), unvulcanized rubber layer (a2) and rubber base material (B) according to the manufacturing method of this embodiment are the same as those described for the rubber material, and therefore, the description will be appropriately omitted.

[0064] <Pre-mixing step>

[0065] As described above, in the pre-kneading step, at least the vulcanized rubber powder (a1) and the unvulcanized rubber layer (a2) are kneaded with the rubber component. As a result, a masterbatch (rubber block) as a precursor of the rubber powder (A) is obtained.

[0066] It should be noted that in the pre-mixing step, a mixing machine such as a roll, an internal mixer or a Banbury rotor may be used. Furthermore, the mixing temperature in the pre-mixing step is preferably a temperature at which the unvulcanized rubber layer (a2) does not undergo crosslinking (vulcanization).

[0067] In the pre-mixing step, it is preferred to adjust the compounding ratio of the vulcanized rubber powder (a1) and the rubber component for the unvulcanized rubber layer (a2). Specifically, in the pre-mixing step, it is preferred that M1 / M2 is 0.5 or more and 2.5 or less, wherein M1 represents the compounding amount (mass) of the vulcanized rubber powder (a1) and M2 represents the compounding amount (mass) of the unvulcanized rubber layer (a2).

[0068] If M1 / M2 is 0.5 or more, the effect of improving mechanical properties due to the vulcanized rubber powder (a1) itself can be more reliably obtained. In addition, from the viewpoint of more effectively using the vulcanized rubber powder and facilitating recycling, M1 / M2 is more preferably 0.5 or more, even more preferably 0.6 or more, and still even more preferably 0.7 or more.

[0069] In addition, if M1 / M2 is 2.5 or less, the formation of the unvulcanized rubber layer (a2) on the surface of the vulcanized rubber powder (a1) can be more reliably achieved, and the unvulcanized rubber layer (a2) can be more effectively used as a barrier layer. From a similar viewpoint, M1 / M2 is more preferably 2.3 or less, and even more preferably 2.2 or less.

[0070] It should be noted that the above-mentioned M1 / M2 corresponds to M1 / M2 described previously with respect to the rubber material of the present embodiment.

[0071] In the pre-mixing step, a cross-linking agent is preferably compounded in addition to the vulcanized rubber powder (a1) and the rubber component for the unvulcanized rubber layer (a2). It should be noted that the type and compounding amount (content) of such a cross-linking agent correspond to those described previously for the unvulcanized rubber layer (a2) (rubber composition for unvulcanized rubber layer) in the rubber material of the present embodiment.

[0072] Furthermore, in the premixing step, other compounding agents may be compounded in addition to the above components. It should be noted that the description of such other compounding agents corresponds to those described previously for the unvulcanized rubber layer (a2) (rubber composition for unvulcanized rubber layer) in the rubber material of the present embodiment.

[0073] When a crosslinking agent is used in the pre-mixing step, it is preferred to carry out primary mixing (non-pre-mixing) in which components other than the vulcanization system (e.g., vulcanization accelerator, vulcanization aid, and vulcanization accelerating aid) (including the crosslinking agent) are first mixed, followed by secondary mixing (pre-mixing) in which the above-mentioned vulcanization system is compounded and mixed.

[0074] When such multi-stage kneading as described above is performed, from the viewpoint of reliably obtaining a desired masterbatch and ultimately obtaining a desired rubber material, it is preferred that the primary kneading temperature is 150° C. or lower and the secondary kneading temperature is 20° C. or higher and 80° C. or lower.

[0075] <Main mixing step>

[0076] Next, in the main mixing step, the masterbatch obtained in the pre-mixing step is mixed with the rubber component for the rubber base material (B). As a result, the masterbatch is micronized to form a rubber powder (A), and the rubber powder (A) is dispersed in the rubber base material (B). As a result, the rubber material of the present embodiment is obtained.

[0077] It should be noted that in the main mixing step, similar to the pre-mixing step, a mixing machine such as a roller, an internal mixer and a Banbury rotor can be used. In addition, in the main mixing step, preferably the mixing temperature is a temperature at which the unvulcanized rubber layer (a2) and the rubber substrate (B) do not undergo crosslinking (vulcanization). In addition, in the main mixing step, it is important to mix under appropriate conditions (such as temperature, time and rotor speed) to micronize the masterbatch and to disperse the rubber powder (A) in the rubber substrate (B).

[0078] In the main kneading step, the compounding ratio between the masterbatch and the rubber component for the rubber base material (B) is preferably adjusted. Specifically, in the main kneading step, the compounding amount of the masterbatch is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 20 parts by mass or more, and still even more preferably 30 parts by mass or more, and is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, and still even more preferably 60 parts by mass or less, relative to 100 parts by mass of the rubber component for the rubber base material (B).

[0079] It should be noted that, as previously described for the rubber material of the present embodiment, the above-mentioned compounding amount corresponds to the content of the rubber powder (A) per 100 parts by mass of the rubber component of the rubber base material (B).

[0080] In the main kneading step, sulfur (elemental sulfur) is usually compounded in addition to the masterbatch and the rubber component for the rubber base material (B).

[0081] Furthermore, in the main kneading step, other compounding agents may be compounded in addition to the above components. It should be noted that the description of such other compounding agents corresponds to those previously described for the rubber base material (B) (base rubber composition) in the rubber material of the present embodiment.

[0082] In the main kneading step, it is preferred to carry out primary kneading (non-pre-kneading) in which the vulcanization system (e.g., vulcanization accelerator, vulcanization aid, and vulcanization accelerating aid) and components other than the masterbatch are first kneaded, followed by secondary kneading (pre-kneading) in which the above-mentioned vulcanization system and the masterbatch are compounded and kneaded. Alternatively, in the main kneading step, it is also preferred to carry out primary kneading in which the vulcanization system (e.g., sulfur) and components other than the masterbatch are first kneaded, followed by intermediate kneading in which the above-mentioned masterbatch is compounded and kneaded, and then secondary kneading in which the above-mentioned vulcanization system is compounded and kneaded.

[0083] When multi-stage kneading as described above is carried out, from the viewpoint of reliably obtaining the desired rubber material, the temperature of the primary kneading is preferably 150°C or less, the temperature of the intermediate kneading is preferably 150°C or less, more preferably 80°C or less, and the temperature of the secondary kneading is preferably 20°C or more and 80°C or less.

[0084] (tire)

[0085] A tire according to one embodiment of the present invention includes a vulcanized product of the rubber material of the present embodiment described above.

[0086] Since such a tire uses the rubber material of the present embodiment described above, it is excellent in mechanical characteristics and low loss properties.

[0087] The above tire can be obtained by vulcanizing the rubber material of the present embodiment described above according to a conventional method and applying it to a specific member, or by vulcanization molding according to a conventional method, and specific manufacturing conditions and vulcanization conditions are not particularly limited.

[0088] Example

[0089] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

[0090] The components were mixed and kneaded according to the recipe summarized in Table 1 according to a conventional method (pre-mixing) to prepare a master batch M (precursor of rubber powder (A)). During the mixing, the components other than sulfur and the vulcanization accelerator were mixed at 150° C. or less for 3 minutes for the first mixing, and then, for the second mixing, sulfur and the vulcanization accelerator were compounded and mixed at 80° C. or less for 70 seconds.

[0091] Table 1

[0092]

[0093] *1NR: Natural rubber, TSR#20

[0094] *2SBR: Oil-extended styrene-butadiene rubber, "ESBR 1723", manufactured by ENEOS Corporation

[0095] *3 Carbon black: "SEAST KHA", HS-HAF grade, manufactured by Tokai Carbon Co., Ltd.

[0096] *4Other chemicals: including oil-extended components of SBR

[0097] *5 Vulcanized rubber powder: "crushed product", manufactured by RUBBER TECH Co., Ltd., particle size 300 μm or less

[0098] Next, the rubber material was prepared by appropriately using the above master batch M, and the respective components were compounded and kneaded according to a conventional method (primary kneading) in accordance with the formulation summarized in Table 2. In the kneading process, for the primary kneading, the components other than the sulfur and the vulcanization accelerator were kneaded, and subsequently, for the secondary kneading, the sulfur and the vulcanization accelerator were compounded and kneaded.

[0099] Observation of the rubber materials of Examples 1 and 2 under a scanning electron microscope (SEM) confirmed that the rubber powder (A) in which the rubber layer (a2) was arranged on the surface of the vulcanized rubber powder (a1) was dispersed in the rubber base material (B). In addition, further observation under SEM confirmed that the particle size of the vulcanized rubber powder (a1) was 300 μm or less. In addition, further observation under SEM also confirmed that the maximum thickness of the rubber layer (a2) arranged on the surface of the vulcanized rubber powder (a1) was significantly less than 300 μm.

[0100] On the other hand, when the cross section of the rubber material of Comparative Example 2 was observed under SEM, it was confirmed that the vulcanized rubber powder was dispersed in the rubber base material.

[0101] Next, for the rubber material obtained in each example, after vulcanization at 160° C. for 15 minutes, the following evaluation was performed.

[0102] (Evaluation of Mechanical Properties)

[0103] According to JIS K 6251:2010, the vulcanized rubber material is subjected to a tensile test. Specifically, a sheet of each rubber material having a thickness of 2 mm is punched into a ring (JIS No. 5 type) to prepare a sample. Then, stress measurement is performed by stretching the sample at a speed of 100 ± 5 mm / min at room temperature (24 ° C) until the sample breaks, to measure the tensile strength (Tb) of the rubber material. The tensile strength of each embodiment is represented by an index, wherein the tensile strength value of Comparative Example 1 is 100. The results are summarized in Table 2. The larger the index value, the more excellent the mechanical properties.

[0104] (Evaluation of low loss)

[0105] The values ​​of tan δ of the vulcanized rubber material at dynamic strains of 0.1%, 1%, 3% and 10% were measured using a dynamic shear viscoelasticity measuring device (manufactured by Rheometric Inc.) at a temperature of 50° C. and a frequency of 15 Hz. The values ​​of tan δ of each embodiment and comparative example are expressed as an index, wherein the value of comparative example 1 is 100. The results are summarized in Table 2. The smaller the index value, the better the low loss property.

[0106] Table 2

[0107]

[0108] *6BR: Butadiene rubber, "BR 01", manufactured by ENEOS Corporation

[0109] As can be understood from Table 2, a rubber member (vulcanized product) excellent in mechanical characteristics and low loss property is obtained by using the rubber material according to the example of the present invention.

[0110] Industrial Applicability

[0111] According to the present invention, a rubber material that allows a rubber member excellent in mechanical characteristics and low loss properties to be obtained by utilizing rubber powder, a method for producing the same, and a tire using the rubber material can be obtained.

Claims

1. A rubber material, characterized in that: It is made of rubber powder (A) dispersed in a rubber base material (B). The rubber powder (A) is obtained by disposing an unvulcanized rubber layer (a2) on the surface of a vulcanized rubber powder (a1), and the unvulcanized rubber layer (a2) contains a crosslinking agent.

2. The rubber material according to claim 1, wherein M1 / M2 of the rubber powder (A) is 0.5 or more and 2.5 or less, wherein: M1 represents the mass of the vulcanized rubber powder (a1) and M2 represents the mass of the unvulcanized rubber layer (a2). 3 . The rubber material according to claim 1 , wherein the unvulcanized rubber layer ( a2 ) contains sulfur as the cross-linking agent. 4 . The rubber material according to claim 1 , wherein the unvulcanized rubber layer ( a2 ) comprises a diene rubber. 5 . The rubber material according to claim 4 , wherein the unvulcanized rubber layer ( a2 ) contains natural rubber as the diene rubber, and the proportion of the natural rubber in the rubber component is 50% by mass or more.

6. A tire, characterized in that: A vulcanizate comprising the rubber material according to any one of claims 1 to 5.

7. A method for manufacturing a rubber material according to any one of claims 1 to 5, characterized in that the method comprises: A pre-mixing step of mixing the vulcanized rubber powder (a1) and the unvulcanized rubber layer (a2) with a rubber component to obtain a masterbatch as a precursor of the rubber powder (A); and The main kneading step is to knead the masterbatch and the rubber component for the rubber base (B) to disperse the rubber powder (A) formed by pulverizing the masterbatch in the rubber base (B).

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