Method for producing modified rubber particle

Abstract

To provide a method for producing a modified rubber particle with improved strength and elasticity, and further provide a method for producing a modified rubber particle that, when blended into a rubber composition, can suppress the deterioration of loss tangent, strength and elasticity in the resulting rubber composition.SOLUTION: The present invention provides [1] a method for producing a modified rubber particle including the step for applying compressive shear stress to particles of cross-linked rubber, [2] a method for producing a rubber composition including the step for blending a modified rubber particle that has been obtained by the modified rubber particle production method set forth in [1], and [3] a method for producing a rubber molding including the step for vulcanizing a rubber composition that has been obtained by the rubber composition production method set forth in [2].SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing modified rubber particles, a method for producing a rubber composition, and a method for producing a rubber molded article. [Background technology]

[0002] In recent years, there has been a demand for greater sustainability in order to realize a recycling-oriented society. For example, used rubber such as scrap tires is often used in parts that require periodic replacement, and is therefore generated in large quantities. Used rubber is recycled, for example, by using it as fuel for thermal recycling or by processing it into powdered rubber and using it as a material for elastic materials, etc.

[0003] Patent Document 1 discloses a method for producing finely pulverized rubber that aims to provide an easy-to-operate method for producing finely pulverized rubber without reducing work efficiency, and is characterized by comprising a finely pulverizing process in which rubber raw material processed into chips from unnecessary rubber is subjected to coarse pulverization, medium pulverization and finish pulverization while adding an anti-adhesion agent using a fine pulverizing means, successively transforming the coarsely pulverized rubber into finely pulverized rubber, via medium pulverization, and then to finely pulverized rubber, and a classification and recovery process in which the finely pulverized rubber is classified and at least a portion of it is recovered as a fine powder rubber product. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-176560 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the finely ground rubber obtained by Patent Document 1 is compounded with a rubber molded product, there is a problem that the rubber molded product is not sufficiently mixed, and various physical properties such as fuel efficiency, strength, and elasticity are deteriorated. In particular, the finely ground rubber contained in the rubber molded product may cause the strength and elasticity of the rubber molded product to be insufficient. The present invention relates to a method for producing modified rubber particles which, even when compounded with a rubber composition, can suppress deterioration in the loss tangent, strength and elasticity of the resulting rubber molded article. [Means for solving the problem]

[0006] The present inventors have discovered that by applying compressive shear stress to crosslinked rubber particles obtained from used rubber or the like, modified rubber particles with improved strength and elasticity can be obtained, and that when the modified rubber particles are compounded into a rubber molded product, deterioration of various physical properties can be suppressed. The present invention relates to the following [1] to [3]. [1] A method for producing modified rubber particles, comprising a step of applying compressive shear stress to crosslinked rubber particles. [2] A method for producing a rubber composition, comprising a step of compounding the modified rubber particles obtained by the method for producing modified rubber particles described in [1] above. [3] A method for producing a rubber molded article, comprising a step of vulcanizing the rubber composition obtained by the method for producing a rubber composition according to [2] above. Effect of the Invention

[0007] According to the present invention, there can be provided a method for producing modified rubber particles which, even when compounded with a rubber composition, can suppress deterioration in the loss tangent, strength and elasticity of the resulting rubber molded article. [Brief description of the drawings]

[0008] [Figure 1] 1 is a microscopic image of the surface of the unvulcanized rubber composition obtained in Example B2 before it was molded into a sheet-shaped molded article. [Diagram 2]1 is a microscopic image of the surface of the unvulcanized rubber composition obtained in Comparative Example C1 before it was molded into a sheet-shaped molded article. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Method of manufacturing modified rubber particles] The method for producing modified rubber particles of the present invention includes a step of applying compressive shear stress to particles of crosslinked rubber.

[0010] According to the present invention, it is possible to obtain modified rubber particles that can suppress the deterioration of the loss tangent, strength, and elasticity of the obtained rubber molded article even when compounded with a rubber composition. Furthermore, according to the present invention, it is possible to obtain modified rubber particles with improved strength and elasticity. Conventionally, when recycling crosslinked rubber such as used rubber, it has been processed into particles by applying impact shear stress using a cutter mill, hammer mill, etc., and used as a part of the raw material for a new rubber molded product. In such a method of applying impact shear stress, the crosslinked rubber is simply granulated, that is, its shape is simply changed. On the other hand, in the present invention, by applying a compressive shear stress to the crosslinked rubber particles, a so-called mechanochemical treatment can be performed, and the crosslinking points and the main chain bonds of the crosslinked rubber can be partially cut by the action of the compressive shear stress and the radicals generated by the stress, and the crosslinked rubber is modified. As a result, the obtained modified rubber particles are considered to have improved strength and elasticity compared to conventional crosslinked rubber particles. Furthermore, since the modified rubber particles obtained by the present invention are in a decrosslinked state compared to the crosslinked rubber particles before modification, they are more compatible with other materials such as the rubber components before crosslinking when blended into a rubber composition. Therefore, it is considered that the modified rubber particles obtained by the present invention can suppress the decrease in loss tangent, strength and elasticity of the resulting rubber molded article, even when blended into a rubber composition, compared to the case where conventional crosslinked rubber particles are blended. In addition, as described above, the modified rubber particles obtained by the present invention can suppress the deterioration of the physical properties of the rubber molded product containing the modified rubber particles, and therefore, compared with the conventional crosslinked rubber particles, it is possible to compound a larger amount of the modified rubber particles into the rubber composition. In other words, the rubber particles obtained by the present invention are more excellent in recyclability than the conventional crosslinked rubber particles.

[0011] In the present invention, the step of applying a compressive shear stress is preferably a step of applying a compressive shear stress using a vibration mill. By using a vibration mill, the compressive shear stress can be efficiently applied to the crosslinked rubber particles, and the decrease in the loss tangent, strength, and elasticity of the rubber molded article containing the modified rubber particles can be easily suppressed. As the vibrating mill, from the viewpoint of efficiently applying compressive shear stress to the particles of the crosslinked rubber, any one of a vibrating rod mill, a vibrating ball mill and a vibrating tube mill is preferable, and a vibrating rod mill is more preferable. The step of applying compressive shear stress may be either a batch process or a continuous process. The material of the device and the material of the medium used in the step of applying compressive shear stress are not particularly limited, and examples thereof include iron, stainless steel, alumina, zirconia, silicon carbide, silicon nitride, glass, etc., but from the viewpoint of the crushing efficiency of the crosslinked rubber particles, iron, stainless steel, zirconia, silicon carbide, and silicon nitride are preferred, and further from the viewpoint of industrial use, iron or stainless steel is more preferred.

[0012] From the viewpoint of efficiently applying compressive shear stress to the crosslinked rubber particles, when a vibrating mill is used in the step of applying compressive shear stress and the medium is a rod (i.e., when the step of applying compressive shear stress is a step of applying compressive shear stress using a vibrating rod mill), the outer diameter of the rod is preferably 10 mm or more, more preferably 20 mm or more, even more preferably 25 mm or more, and is preferably 60 mm or less, more preferably 50 mm or less, even more preferably 45 mm or less. The preferred range of the rod filling rate varies depending on the type of vibration mill. From the viewpoint of efficiently applying compressive shear stress to the crosslinked rubber particles, the filling rate is preferably 10% by volume or more, more preferably 30% by volume or more, even more preferably 50% by volume or more, still more preferably 60% by volume or more, relative to the volume of the vibration mill, and is preferably 97% by volume or less, more preferably 90% by volume or less, and even more preferably 80% by volume or less. If the filling rate is within this range, the frequency of contact between the crosslinked rubber particles and the rod is increased, and the crosslinked rubber particles can be efficiently subjected to compressive shear stress without impeding the movement of the medium. Here, the filling rate refers to the volume of the rod relative to the volume of the stirring part of the vibration mill.

[0013] The processing time in the step of applying compressive shear stress cannot be determined in general depending on the type of vibration mill, the material, shape, size and filling rate of the rod, the filling rate of the crosslinked rubber particles, etc., but in the case of batch processing, from the viewpoint of efficiently applying compressive shear stress to the crosslinked rubber particles and from the viewpoint of productivity, the lower limit is preferably 1 minute or more, more preferably 2 minutes or more, and the upper limit is preferably 120 minutes or less, more preferably 60 minutes or less, even more preferably 45 minutes or less, even more preferably 30 minutes or less, and even more preferably 10 minutes or less. Even when continuous processing is performed, the processing speed in the step of applying compressive shear stress will vary depending on the type and size of the vibration mill, the rod filling rate, etc., but from the viewpoint of productivity, the supply rate of the crosslinked rubber particles is preferably 5 kg / h or more, more preferably 10 kg / h or more, and from the viewpoint of efficiently applying compressive shear stress to the crosslinked rubber particles, it is preferably 100 kg / h or less, more preferably 80 kg / h or less.

[0014] The treatment temperature in the step of applying compressive shear stress is, from the viewpoint of suppressing deterioration of the crosslinked rubber particles due to heat and from the viewpoint of suppressing energy load, preferably 5°C or higher, more preferably 10°C or higher, even more preferably 15°C or higher, and is preferably 250°C or lower, more preferably 200°C or lower, even more preferably 150°C or lower, even more preferably 100°C or lower.

[0015] (Crosslinked rubber particles) In the present invention, the particles of crosslinked rubber are preferably particles of used rubber, that is, in the present invention, the crosslinked rubber is preferably used rubber. Examples of used rubber include waste tires, tubes, rubber crawlers, conveyor belts, and anti-vibration rubber. Of these, waste tires are preferred from the viewpoint of recyclability. The type of rubber in the used rubber preferably includes at least one of natural rubber and synthetic rubber. As the synthetic rubber, diene rubber is preferable, and examples thereof include polyisoprene rubber, styrene-butadiene copolymer rubber, 1,4-polybutadiene rubber, ethylene-propylene-diene terpolymer, chloroprene rubber, butyl rubber, halogenated butyl rubber, and acrylonitrile-butadiene rubber.

[0016] The crosslinked rubber particles can be obtained by pulverizing the used rubber described above. The method for producing modified rubber particles of the present invention preferably includes a step of pulverizing the used rubber to obtain crosslinked rubber particles before the step of applying compressive shear stress to the crosslinked rubber particles. As a method for fine pulverization, for example, used rubber is crushed into chips (about 35 mm) and then further granulated (about 8 mm or less). From the viewpoint of productivity, examples of devices for crushing used rubber into chips include shredders, slitter cutters, rotary cutters, and the like. From the viewpoint of productivity, examples of the pulverizer for granulating used rubber include a knife mill, a cutter mill, and a hammer mill.

[0017] The average particle size of the crosslinked rubber particles is preferably 10 mm or less, more preferably 1 mm or less, and even more preferably 0.2 mm or less, from the viewpoint of efficiently applying compressive shear stress to the crosslinked rubber particles and efficiently obtaining modified rubber particles, and is preferably 0.01 mm or more, more preferably 0.05 mm or more, and even more preferably 0.1 mm or more, from the viewpoint of making it easier to bring the average particle size and particle size distribution of the obtained modified rubber particles into the ranges described below and to make it easier to compound them into a rubber composition. From the viewpoint of efficiently obtaining modified rubber particles and facilitating incorporation into a rubber composition, the proportion of crosslinked rubber particles having a particle diameter of 90 μm or less is preferably 0.1 mass% or more, more preferably 1 mass% or more, even more preferably 2 mass% or more, and is preferably 20 mass% or less, more preferably 15 mass% or less, even more preferably 10 mass% or less. From the viewpoint of efficiently obtaining modified rubber particles and facilitating incorporation into a rubber composition, the proportion of crosslinked rubber particles having a particle diameter of 150 μm or less is preferably 1 mass % or more, more preferably 5 mass % or more, even more preferably 10 mass % or more, and is preferably 40 mass % or less, more preferably 30 mass % or less, even more preferably 20 mass % or less. From the viewpoint of efficiently applying compressive shear stress to the crosslinked rubber particles and efficiently obtaining modified rubber particles, the proportion of crosslinked rubber particles having a particle diameter of 1000 μm or less is preferably 90 mass% or more, more preferably 95 mass% or more, and even more preferably 99 mass% or more. In the present invention, the particle size distribution and average particle size of the crosslinked rubber particles can be measured by a sieving test, specifically by the method described in the Examples.

[0018] <Physical properties of modified rubber particles> In the present invention, from the viewpoint of ease of incorporation into a rubber composition, the average particle size of the modified rubber particles obtained is preferably larger than the average particle size of the crosslinked rubber, more preferably 20 mm or less, even more preferably 5 mm or less, even more preferably 1 mm or less, and is preferably 0.3 mm or more, more preferably 0.5 mm or more, even more preferably 0.7 mm or more. In the present invention, the particle size distribution and average particle size of the modified rubber particles can be measured in the same manner as in the case of the particle size distribution and average particle size of the crosslinked rubber particles described above, specifically by the method described in the Examples. In the present invention, the proportion of the modified rubber particles obtained having a particle size of 90 μm or less is, from the viewpoint of suppressing a decrease in the loss tangent, strength, and elasticity of the rubber molded article obtained by blending the modified rubber particles into a rubber composition, and from the viewpoint of ease of blending the modified rubber particles into a rubber composition, preferably less than the proportion of the crosslinked rubber particles having a particle size of 90 μm or less, more preferably 5 mass% or less, even more preferably 0.3 mass% or less, and even more preferably 0.1 mass% or less. In the present invention, the proportion of the modified rubber particles obtained having a particle size of 150 μm or less is preferably less than the proportion of the crosslinked rubber particles having a particle size of 150 μm or less, from the viewpoint of suppressing decreases in the loss tangent, strength, and elasticity of the rubber molded article obtained by blending the modified rubber particles into a rubber composition, and from the viewpoint of ease of blending the modified rubber particles into a rubber composition, and is preferably 10 mass % or less, more preferably 1 mass % or less, and even more preferably 0.1 mass % or less. In the present invention, the proportion of the modified rubber particles obtained having a particle size of 500 μm or less is, from the viewpoint of suppressing a decrease in the loss tangent, strength, and elasticity of the rubber molded article obtained by blending the modified rubber particles into a rubber composition, and from the viewpoint of ease of blending the modified rubber particles into a rubber composition, preferably less than the proportion of the crosslinked rubber particles having a particle size of 500 μm or less, and is preferably 20 mass% or less, more preferably 5 mass% or less, even more preferably 1 mass% or less, and even more preferably 0.1 mass% or less.

[0019] [Method of manufacturing rubber composition] The method for producing a rubber composition in the present invention preferably includes a step of blending the modified rubber particles obtained by the above-mentioned method for producing modified rubber particles. That is, the rubber composition obtained in the present invention preferably includes modified rubber particles. By having a step of blending the modified rubber particles obtained by the above-mentioned method for producing modified rubber particles, it is easy to suppress the decrease in loss tangent, strength and elasticity of the obtained rubber molded body. As the step of blending the modified rubber particles, for example, it is preferable to blend it together with other materials such as the rubber component described later.

[0020] (Rubber component) In the present invention, the rubber composition preferably contains a rubber component in addition to the modified rubber particles. As the rubber component, natural rubber and synthetic rubber can be used. Among these, one or more types selected from natural rubber and diene-based synthetic rubber are preferred from the viewpoints of preventing a decrease in the loss tangent, strength, and elasticity of the resulting rubber molded product, and from the viewpoints of availability, etc. Examples of natural rubber include SMR, SIR, STR, and RSS, with SMR20, STR20, RSS#3, RSS#4, and the like being preferred. Natural rubber can be used after being modified. Examples of modified natural rubber include epoxidized natural rubber and hydrogenated natural rubber. Examples of diene-based synthetic rubbers include polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber, and butyl rubber.

[0021] Among these, from the viewpoint of suppressing deterioration in the loss tangent, strength, and stretchability of the resulting rubber molded article, at least one selected from natural rubber, modified natural rubber, IR, BR, SBR, and NBR is preferred, and at least one selected from BR, SBR, and natural rubber is more preferred. BR or SBR can also be used in combination with natural rubber. The copolymer rubber may be a block copolymer or a random copolymer, but is preferably a random copolymer from the viewpoint of suppressing deterioration in the loss tangent, strength and elasticity of the resulting rubber molded article. The rubber components may be used alone or in combination of two or more kinds.

[0022] (Inorganic filler) In the present invention, the rubber composition preferably contains an inorganic filler from the viewpoint of suppressing deterioration in the loss tangent, strength and elasticity of the obtained rubber molded article. As the inorganic filler, silica and carbon black are preferred, and carbon black is more preferred.

[0023] The silica is not particularly limited, and wet silica, dry silica, and colloidal silica can be used. Among these, wet silica, which is mainly composed of hydrated silicic acid, is preferred. The wet silica includes precipitated silica, gel silica, and sol-gel silica, and precipitated silica is more preferred. The BET specific surface area of ​​the silica (measured in accordance with ISO 5794 / 1) is preferably 50 m from the viewpoint of suppressing the deterioration of the loss tangent, strength and elasticity of the obtained rubber molded product. 2 / g or more, more preferably 100m 2 / g or more, more preferably 150m 2 / g or more, and preferably 350m 2 / g or less, more preferably 300m 2 / g or less, more preferably 250m 2 / g or less. From the viewpoint of suppressing deterioration in the loss tangent, strength and elasticity of the obtained rubber molded article, the average secondary particle size of the silica is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 18 μm or more, and is preferably 100 μm or less, more preferably 80 μm or less, even more preferably 50 μm or less.

[0024] An example of a commercially available silica product is Nipsil AQ (BET specific surface area: 205 m) manufactured by Tosoh Silica Corporation. 2 / g), Nipsil KQ (BET specific surface area: 240 m 2 / g) and Ultrasil VN3 (BET specific surface area: 175 m 2 / g) etc.

[0025] The carbon black is not particularly limited, and may be high, medium or low structure carbon black of grades such as SAF, ISAF, IISAF, N339, HAF, FEF, GPF, SRF, etc., or a carbon and silica dual phase filler in which silica is supported on the surface of carbon black, etc. Among these, SAF, ISAF, IISAF, N339, HAF and FEF grade carbon black are preferred. The DBP absorption of carbon black (measured according to ASTM D2414-65T) is preferably 70 cm 3 / 100g or more, more preferably 80cm 3 / 100g or more, more preferably 90cm 3 / 100g or more. The nitrogen adsorption specific surface area (N2AS, measured in accordance with JIS K 6217-2:2017) of the carbon black is preferably 50 m 2 / g or more, more preferably 60m 2 / g or more, more preferably 70m 2 / g or more.

[0026] In the present invention, alumina, calcium carbonate, clay, talc, zeolite, diatomaceous earth, etc. may further be used as an inorganic filler, if necessary.

[0027] (sulfur) In the present invention, the rubber composition preferably contains sulfur in order to be vulcanized into a rubber molded article. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, and the like, which are commonly used in the rubber industry. Sulfur can be used alone or in combination of two or more kinds.

[0028] (Other Ingredients) In the present invention, the rubber composition may contain, in addition to the above-mentioned components, various additives usually used in the rubber industry, such as antioxidants, scorch inhibitors, softeners, stearic acid, process oil, zinc oxide, vulcanizing agents, vulcanization accelerators, etc., as desired, within the scope of the object of the present invention.

[0029] In the present invention, since the rubber composition obtained has the above-mentioned constitution, it is possible to suppress the decrease in the loss tangent, strength and elasticity of the obtained rubber molded article. Therefore, it can be suitably used as a material for obtaining rubber molded articles such as tires, tire inner liners, treads, tread bases, carcasses, sidewalls, bead parts, etc. of tires, various rubber belts, various sealing materials, vibration isolating and anti-vibration materials, shoe soles, etc., preferably as a material for obtaining tire components and tires, more preferably as a material for obtaining tires.

[0030] In the present invention, the rubber composition contains or is blended with modified rubber particles, a rubber component, an inorganic filler, sulfur, and, if necessary, other components. In order to suppress deterioration in the loss tangent, strength, and elasticity of the resulting rubber molded body, the amount of modified rubber particles is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 0.8 parts by mass or more, even more preferably 2 parts by mass or more, even more preferably 4 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, per 100 parts by mass of the rubber component.

[0031] From the viewpoint of suppressing deterioration in the loss tangent, strength and elasticity of the obtained rubber molded article, the amount of the rubber component in the rubber composition is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, and is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less.

[0032] From the viewpoint of suppressing deterioration in the loss tangent, strength and elasticity of the obtained rubber molded body, the content of the inorganic filler is preferably 30 parts by mass or more, more preferably 35 parts by mass or more, even more preferably 40 parts by mass or more, and preferably 70 parts by mass or less, more preferably 65 parts by mass or less, even more preferably 60 parts by mass or less, per 100 parts by mass of the rubber component.

[0033] The sulfur content is, from the viewpoint of sufficiently vulcanizing the unvulcanized rubber composition and suppressing deterioration in the loss tangent, strength and elasticity of the obtained rubber molded body, preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 0.8 parts by mass or more, and preferably 3 parts by mass or less, more preferably 2.5 parts by mass or less, and even more preferably 2 parts by mass or less, per 100 parts by mass of the rubber component.

[0034] [Production of rubber composition] In the present invention, the rubber composition can be produced by kneading a composition containing modified rubber particles, an inorganic filler, and other components as necessary with a rubber component to obtain a rubber kneaded product, and then adding and mixing sulfur into the obtained rubber kneaded product.

[0035] More specifically, for example, the rubber component is kneaded with modified rubber particles, an inorganic filler, and, if necessary, components such as an antioxidant and stearic acid using a kneading machine such as a Banbury mixer, a roll, or an intensive mixer at, for example, 140°C or higher. The above kneading temperature is preferably 143°C or higher, more preferably 146°C or higher, even more preferably 148°C or higher, from the viewpoint of better dispersing and dissolving the modified rubber particles in the rubber component and suppressing deterioration in the loss tangent, strength and elasticity of the obtained rubber molded body, and is preferably 165°C or lower, more preferably 160°C or lower, even more preferably 158°C or lower, even more preferably 155°C or lower. After obtaining the rubber mixture, sulfur is further added and mixed. From the viewpoint of preventing a vulcanization reaction, the temperature at which sulfur is added and mixed is preferably less than 140° C., more preferably 130° C. or less, even more preferably 125° C. or less, and still more preferably 120° C. or less. In addition to sulfur, zinc oxide, a vulcanization accelerator, etc. can be added as necessary and mixed with the rubber kneaded product to obtain an unvulcanized rubber composition.

[0036] [Method of manufacturing rubber molded body] The method for producing a rubber molded article in the present invention preferably includes a step of vulcanizing the above-mentioned rubber composition. The above-mentioned rubber composition is molded by a known method, and heated or heated and pressurized at preferably 130° C. or higher, more preferably 135° C. or higher, and even more preferably 140° C. or higher, and preferably 200° C. or lower, more preferably 170° C. or lower, and even more preferably 150° C. or lower, to form a vulcanized rubber molded article. In the present invention, the contents of the rubber component, modified rubber particles and inorganic filler contained in the rubber molded product are the same as those in the above-mentioned rubber composition. The obtained rubber molded product suppresses deterioration in loss tangent, strength and elasticity compared to rubber molded products that contain conventional crosslinked rubber particles, and therefore can be suitably used as rubber molded products such as tires, tire inner liners, treads, tread bases, carcasses, sidewalls, bead portions and other tire components, as well as various rubber belts, various sealing materials, vibration isolating and anti-vibration materials, shoe soles and the like, preferably as tire components and tires, more preferably as tires.

[0037] [Tire manufacturing method] The method for producing a tire in the present invention preferably includes a step of vulcanizing the above-mentioned rubber composition. Specifically, the method for producing a tire in the present invention can be the same as the method for producing the rubber molded article in the present invention. In the present invention, the contents of the rubber component, modified rubber particles and inorganic filler contained in the tire are the same as those in the above-mentioned rubber composition. The tire obtained by the tire manufacturing method of the present invention contains modified rubber particles as described above. Therefore, the tire obtained by the present invention is less susceptible to deterioration in loss tangent, strength, and elasticity compared to a rubber molded body containing conventional crosslinked rubber particles, and therefore can be suitably used not only for tires for general vehicles but also for tires for construction vehicles, etc. EXAMPLES

[0038] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Each property value was measured and evaluated by the following methods.

[0039] [Preparation of modified rubber particles] <Process of applying compressive shear stress> (Example A1) 500 g of crosslinked rubber particles (rubber chips (particles), Shinsei Rubber Co., Ltd., "#50", derived from waste tires) were placed into a batch-type vibration mill (Chuo Kakoki Co., Ltd., "FV10 type" (vibration rod mill), mill inner diameter 284 mm, depth 520 mm, total container capacity 32.9 L), and 63 stainless steel rods with a diameter of 30 mm, length 510 mm, and circular cross-section were loaded into the vibration mill and treated for 3 minutes under conditions of an amplitude of 8 mm and a vibration frequency of 20 Hz to obtain modified rubber particles 1. The temperature after treatment was 50°C.

[0040] (Example A2) Modified rubber particles 2 were obtained under the same conditions as in Example A1, except that the treatment time was changed to 15 minutes.

[0041] [Preparation of sheet-shaped molded bodies of crosslinked rubber particles and modified rubber particles] Crosslinked rubber particles (rubber chips (particles), Shinsei Rubber Co., Ltd., "#50", derived from waste tires) and modified rubber particles 1 and 2 were filled into a frame surrounded by a 2 mm thick, 11 cm x 17 cm SUS plate, and each was heated at 10 MPa and 145°C for 10 minutes to obtain a sheet-like molded body.

[0042] [Preparation of sheet-shaped molded product of vulcanized rubber composition] <Examples B1 to B3, Comparative Examples C1 and C2, and Reference Example D1> The raw material components shown in Table 3 were prepared, and the components other than zinc oxide, sulfur, and vulcanization accelerator were mixed in the formulation shown in Table 3 using a Banbury mixer at a maximum temperature of 150°C for 4 minutes to obtain a rubber mixture. The obtained rubber mixture was mixed again at a maximum temperature of 150°C for 2 minutes and 30 seconds. Next, zinc oxide, sulfur, and a vulcanization accelerator were added to the obtained rubber mixture, and the mixture was mixed at a maximum temperature of 110°C for 2 minutes to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was filled into a frame surrounded by a 2 mm thick, 11 cm x 17 cm SUS plate, and heated at 10 MPa and 145°C for 20 minutes to obtain a sheet-shaped molded product of a vulcanized rubber molded product. Reference Example D1 is an example that does not contain any of crosslinked rubber particles and modified rubber particles.

[0043] Details of each component shown in Tables 1 to 3 are as follows. (Rubber component) SBR*1: Emulsion polymerization SBR (manufactured by Zeon Corporation, "IPOL 1502", styrene content 23.5% by mass) (rubber particles) Cross-linked rubber particles*2: Rubber chips (particles) (Shinsei Rubber Co., Ltd., "#50", derived from waste tires) (Inorganic filler) Carbon black*3: Carbon black (manufactured by Tokai Carbon Co., Ltd., "Seast 3", DBP absorption: 101 cm 3 / 100g, N2AS:79m 2 / g) (Additives) Anti-aging agent*4: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., "Nocrac 6C") Stearic acid*5: Stearic acid (Kao Corporation, "Lunac S-70V") Zinc oxide*6: Zinc oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., "Zinc oxide (first grade)") Sulfur*7: Sulfur (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., "Sulfur (powder, chemical grade)") (Vulcanization accelerator) CBS*8: N-cyclohexyl-2-benzothiazolylsulfenamide (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., "Noccela CZ-G")

[0044] [Evaluation method] <Measurement of particle size distribution of rubber particles> Test sieves with mesh sizes of 90, 150, 250, 500, 1000 and 2800 μm, as specified in JIS Z 8801, were stacked on a tray in order from the bottom up. A sample was placed on the top sieve, and the sample was classified by shaking for 3 minutes using an electromagnetic sieve shaker (Retze, AS200 Basic). The test sieves used were utility model models manufactured by Iida Seisakusho Co., Ltd. The results are shown in Tables 1 and 2.

[0045] <Measurement of the average particle size of rubber particles> The weight of the rubber particles remaining on each sieve was measured, and then the mesh size of each sieve and the mass ratio (remaining percentage) R of the particles that could not pass through the sieve (the particles remaining on the sieve and the particles remaining on the sieve with larger mesh sizes) to the total mass ratio were plotted on a semi-logarithmic graph (horizontal axis: particle size (logarithmic scale), vertical axis: remaining percentage), and the particle size corresponding to R=50% was determined and used as the average particle size.

[0046] <Measurement of loss tangent (tan δ)> The loss tangent (tan δ) of the obtained sheet-like molded product was measured at a temperature of 50°C, a dynamic strain of 5%, and a frequency of 10 Hz using a viscoelasticity measuring device (TA Instruments, ARES-G2). The results for the rubber particles are shown in Table 2, and the results for the vulcanized rubber molded product are shown in Table 3. Table 2 shows the relative values ​​when the storage modulus and loss tangent of a sheet-shaped molded product of crosslinked rubber particles (rubber chips (particles), manufactured by Shinsei Rubber, "#50", derived from waste tires) were set at 100. Table 3 shows the relative values ​​when the storage modulus and loss tangent of the sheet-like molded article of Reference Example D1 were set at 100, respectively. The smaller the relative value of tan δ, the smaller the rolling resistance and heat generation of the tire when used in the tire, and the more excellent the fuel efficiency performance.

[0047] <Measurement of breaking elongation and breaking stress> According to JIS K 6251:2010, the obtained sheet-like molding was punched out into a predetermined dumbbell shape to prepare a measurement sample, and a tensile test was performed using the measurement sample to measure the breaking elongation, which is the elongation at break, and the breaking stress, which is the stress at break. The results for the rubber particles are shown in Table 2, and the results for the vulcanized rubber molding are shown in Table 3. Table 2 shows the relative values ​​when the storage modulus and loss tangent of a sheet-shaped molded product of crosslinked rubber particles (rubber chips (particles), manufactured by Shinsei Rubber, "#50", derived from waste tires) were set at 100. Table 3 shows the relative values ​​when the storage modulus and loss tangent of the sheet-like molded article of Reference Example D1 were set at 100, respectively. In the examples, the higher the breaking elongation and breaking stress, the more suppressed the decrease in strength and stretchability, as compared with the corresponding comparative examples.

[0048] [Table 1]

[0049] [Table 2]

[0050] [Table 3]

[0051] From the results of Tables 1 and 2, it can be confirmed that when unmodified crosslinked rubber particles are compared with modified rubber particles 1 (Example A) and 2 (Example A2), the decrease in breaking elongation and breaking stress is suppressed in modified rubber particles 1 and 2. Therefore, it can be confirmed that the manufacturing method of the modified rubber particles of the present invention can obtain modified rubber particles by including a step of applying a compressive shear stress. In addition, from Table 3, when comparing Example B1 and Example B2, both of which contain 5 parts of rubber particles, with Comparative Example C1, it can be confirmed that Examples B1 and B2, which contain 5 parts of modified rubber particles obtained by the process of applying compressive shear stress, have a lower performance than Reference Example D1 in terms of loss tangent (tan δ), elongation at break, and stress at break. Similarly, when comparing Example B3 and Comparative Example C2, both of which contain 1 part of rubber particles, it can be confirmed that Example B3, which contains 1 part of modified rubber particles obtained by the process of applying compressive shear stress, has a lower performance than Reference Example D1 in terms of loss tangent (tan δ), elongation at break, and stress at break.

[0052] FIG. 1 is an SEM image of the surface of the unvulcanized rubber composition obtained in Example B2, which contains 5 parts of modified rubber particles 2, before being molded into a sheet-like molded body, and FIG. 2 is an SEM image of the surface of the unvulcanized rubber composition obtained in Comparative Example C1, which contains 5 parts of unmodified crosslinked rubber particles, before being molded into a sheet-like molded body. 1 and 2, it can be seen that, although the modified rubber particles 2 have a larger average particle diameter than the unmodified crosslinked rubber particles, the rubber particles are more dispersed and compatible in Example B2, which contains the modified rubber particles 2. As a result, as described above, it is considered that the decrease in performance from Reference Example D1 in terms of loss tangent (tan δ), elongation at break, and stress at break is suppressed in Example B2 compared to Comparative Example C1. Therefore, it can be confirmed that by blending the modified rubber particles obtained by the method for producing modified rubber particles of the present invention into a rubber composition, the decrease in loss tangent (tan δ), strength, and elasticity of the resulting rubber molded article can be suppressed.

Claims

**Claim 1** A method for producing modified rubber particles, comprising a step of applying a compression-shear stress to particles of crosslinked rubber. **Claim 2** The method for producing modified rubber particles according to claim 1, wherein the step of applying the compression-shear stress is a step of applying the compression-shear stress using a vibration mill. **Claim 3** The method for producing modified rubber particles according to claim 1, wherein the crosslinked rubber is used rubber. **Claim 4** The method for producing modified rubber particles according to claim 3, wherein the used rubber is waste tire. **Claim 5** A method for producing a rubber composition, comprising a step of blending modified rubber particles obtained by the method for producing modified rubber particles according to any one of claims 1 to 4. **Claim 6** A method for producing a rubber molded article, comprising a step of vulcanizing the rubber composition obtained by the method for producing a rubber composition according to claim 5.

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