Rubber composition

Abstract

To provide a rubber composition having reduced Mooney viscosity and excellent workability by using a processability improving agent even when modified cross-linked rubber particles are contained, and a rubber molded product containing the rubber composition, as well as methods for producing the rubber composition and the rubber molded product.SOLUTION: The present invention provides [1] a rubber composition containing modified cross-linked rubber particles, a workability improver and an uncross-linked rubber component, where the modified cross-linked rubber particles have been processed by a step of applying shear stress to the cross-linked rubber particles using a vibration mill, [2] a rubber molded body obtained by vulcanizing [1] the rubber composition, [3] a method for producing a rubber composition comprising a step for blending modified cross-linked rubber particles, a workability improver and an uncross-linked rubber component, where the modified cross-linked rubber particles have been processed by the step of applying shear stress to the cross-linked rubber particles using a vibration mill, and [4] a method for producing a rubber molded body comprising a step for vulcanizing a rubber composition obtained by [3] the producing method of the rubber composition.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber composition, a rubber molded article using the rubber composition, and a method for producing the rubber composition and the 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] Furthermore, Patent Document 1 discloses recycled devulcanized rubber that is characterized in that the sulfur crosslinks have been broken and that contains carbon black with a particle size of 100 nm or less, with the aim of providing recycled devulcanized rubber that can be used alone as a recycled rubber raw material for recycled rubber molded products that have practical rubber properties. Furthermore, Patent Document 2 discloses a method for producing reclaimed rubber, the method being aimed at providing a method for producing reclaimed rubber having rubber properties sufficient for practical use on its own as a raw material for reclaimed rubber extrusion products, in which a shear force is applied to vulcanized rubber placed in an internal mixer to give it fluidity and plasticity, thereby carrying out a reclaiming process, while a kneading finish time is preset based on the apparent activation energy value of the vulcanized rubber in its original, unvulcanized state, and the reclaimed rubber is removed from the internal mixer after the load torque of the internal mixer during the reclaiming process has passed its peak and before the kneading finish time has elapsed, starting from the peak. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-227724 [Patent Document 2] JP 2005-231091 A Summary of the Invention [Problem to be solved by the invention]

[0005] In order to obtain a sufficient decrosslinking effect, the rubber material obtained by modifying the vulcanized (crosslinked) rubber obtained according to Patent Documents 1 and 2 needs to be heated at a high temperature during processing. Therefore, the rubber material obtained according to Patent Documents 1 and 2 suffers from a decrease in molecular weight and softening, and when used in a rubber composition, a decrease in physical properties is unavoidable. On the other hand, the present inventors have already discovered that by subjecting crosslinked rubber particles to compressive shear stress treatment using a vibrating mill or the like, the particles become more de-crosslinked than the crosslinked rubber particles before modification, and when these modified rubber particles are blended into a rubber composition, the modified crosslinked rubber particles have loss tangent, strength and elasticity equal to or greater than those of a vulcanized rubber composition using only uncrosslinked rubber as the rubber component (Patent Application No. 2022-156500). Although the modified crosslinked rubber particles were found to have the effect of improving the loss tangent, strength and elasticity, when added to a rubber composition, the Mooney viscosity increased, and the processability was not sufficient. The present invention provides a rubber composition having excellent processability and reduced Mooney viscosity by using a processability improver even when the rubber composition contains modified crosslinked rubber particles, a rubber molded article containing the rubber composition, and methods for producing the rubber composition and the rubber molded article. [Means for solving the problem]

[0006] The present inventors have found that the above problems can be solved by using modified crosslinked rubber particles obtained by applying shear force to crosslinked rubber particles such as used rubber using a vibration mill. The present invention relates to the following [1] to [4]. [1] A rubber composition comprising modified crosslinked rubber particles, a processability improver, and an uncrosslinked rubber component, the modified crosslinked rubber particles being treated by a process of applying shear stress to the crosslinked rubber particles using a vibrating mill. [2] A rubber molded article obtained by vulcanizing the rubber composition of [1] above. [3] A method for producing a rubber composition, comprising a step of blending modified crosslinked rubber particles, a processability improver, and an uncrosslinked rubber component, wherein the modified crosslinked rubber particles are modified crosslinked rubber particles that have been treated by a step of applying shear stress to the crosslinked rubber particles using a vibrating mill. [4] 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 [3] above. Effect of the Invention

[0007] According to the present invention, even when modified crosslinked rubber particles are contained, by using a processability improver, it is possible to provide a rubber composition having excellent processability by reducing the Mooney viscosity, a rubber molded article containing the rubber composition, and a method for producing the rubber composition and the rubber molded article. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Rubber composition] The rubber composition of the present invention contains modified crosslinked rubber particles, a processability improver, and an uncrosslinked rubber component, and the modified crosslinked rubber particles are modified crosslinked rubber particles that have been treated by a process of applying shear stress to the crosslinked rubber particles using a vibrating mill.

[0009] According to the present invention, it is possible to obtain a rubber composition having a reduced Mooney viscosity and improved processability. Although the detailed reason for this is not clear, it is believed to be as follows. When recycling crosslinked rubber such as used rubber, it has been processed into particles by applying shear stress using a cutter mill, hammer mill, etc., and used as part of the raw material for new rubber molded products. However, in the method of applying shear stress using a cutter mill, hammer mill, etc., the crosslinked rubber is merely granulated. On the other hand, the modified crosslinked rubber particles used in the present invention are obtained by applying shear stress to crosslinked rubber particles by a vibration mill, that is, by carrying out a so-called mechanochemical treatment.Therefore, the modified crosslinked rubber particles used in the present invention are in a state where the bonds at the crosslinking points of the crosslinked rubber are partially cut by the action of the applied shear stress and the generated radicals, and are in a decrosslinked state.As a result, the modified crosslinked rubber particles used in the present invention are easily compatible with the processability improver and the uncrosslinked rubber component, so that the Mooney viscosity is reduced and the processability is improved. In addition, the modified crosslinked rubber particles used in the present invention suppress the decrease in molecular weight, etc., compared to rubber materials treated by conventional methods such as those described in Patent Documents 1 and 2, and therefore, even when used in a rubber composition, the decrease in physical properties can be suppressed. In addition, since the modified crosslinked rubber particles used in the present invention can suppress deterioration of physical properties, it is possible to compound a larger amount of the modified crosslinked rubber particles in the rubber composition. In other words, the rubber composition of the present invention has better recyclability than a rubber composition using a conventional crosslinked rubber.

[0010] <Modified crosslinked rubber particles> The modified crosslinked rubber particles in the present invention are modified crosslinked rubber particles that have been treated by a step of applying a shear stress to the crosslinked rubber particles using a vibrating mill. The modified crosslinked rubber particles of the present invention are treated by the above steps to be in a decrosslinked state, which makes them more compatible with processability improvers and other materials, thereby reducing the Mooney viscosity of the rubber composition of the present invention and improving processability. In addition, since the modified crosslinked rubber particles of the present invention are treated by the above-mentioned process, the sulfur component that formed the crosslinking point during decrosslinking is difficult to be removed by volatilization, etc., and is likely to remain in the modified crosslinked rubber particles. Furthermore, it is considered that the sulfur component that formed the crosslinking point remaining in the modified crosslinked rubber particles retains the ability to recrosslink the rubber component. Therefore, it is considered that the modified crosslinked rubber particles of the present invention can be recrosslinked without adding a crosslinking agent such as sulfur.

[0011] (Step of applying shear stress to crosslinked rubber particles using a vibration mill) The modified crosslinked rubber particles of the present invention are obtained by subjecting the crosslinked rubber particles to a process of applying shear stress using a vibration mill. By using a vibration mill, it is possible to efficiently apply shear stress to the crosslinked rubber particles, and to modify the crosslinked rubber particles, such as by removing crosslinks. As a result, the rubber composition of the present invention containing the modified crosslinked rubber particles has a reduced Mooney viscosity and is excellent in processability. As the vibrating mill, from the viewpoint of efficiently applying a compressive shear stress to the crosslinked rubber particles, one selected from 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 shear stress using a vibration mill may be either a batch type or a continuous type. There are no particular limitations on the material of the vibration mill or the material of the medium, and examples thereof include iron, stainless steel, alumina, zirconia, silicon carbide, silicon nitride, glass, etc. From the viewpoint of the efficiency of pulverizing the crosslinked rubber particles, iron, stainless steel, zirconia, silicon carbide, and silicon nitride are preferred, and from the viewpoint of industrial use, iron or stainless steel is more preferred.

[0012] When a vibrating rod mill is used as the vibrating mill, from the viewpoint of efficiently applying shear stress to the crosslinked rubber particles, 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, but from the viewpoint of efficiently applying shear stress to the crosslinked rubber particles, it is preferably 10% by volume or more, more preferably 30% by volume or more, even more preferably 50% by volume or more, even more preferably 60% by volume or more, and preferably 97% by volume or less, more preferably 90% by volume or less, and even more preferably 80% by volume or less, relative to the volume of the vibration rod mill. If the filling rate is within this range, the frequency of contact between the crosslinked rubber particles and the rod is improved, and the crosslinked rubber particles can be efficiently subjected to compressive shear stress without interfering with the movement of the medium. Here, the filling rate refers to the volume of the rod relative to the volume of the stirring section of the vibration mill.

[0013] In the case of batch processing, the processing time varies 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 from the viewpoint of efficiently applying shear stress to the crosslinked rubber particles and from the viewpoint of productivity, it is preferably 1 minute or more, more preferably 2 minutes or more, and 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 20 minutes or less. When continuous processing is performed, the supply rate of the crosslinked rubber particles and the processing rate in the step of applying 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, it 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] From the viewpoint of suppressing deterioration of the modified crosslinked rubber particles due to heat and from the viewpoint of suppressing energy load, the treatment temperature is preferably 10°C or higher, more preferably 15°C or higher, even more preferably 20°C or higher, and is preferably 150°C or lower, more preferably 130°C or lower, even more preferably 120°C or lower, even more preferably 100°C or lower. In addition, by keeping the treatment temperature within the above range, the sulfur components that formed crosslinking points in the modified crosslinked rubber particles can be easily retained, and the modified crosslinked rubber particles can be made to be in a state where they can be easily re-crosslinked without adding a crosslinking agent such as sulfur. In addition, since the treatment temperature of the present invention is within the above range, it is possible to suppress a decrease in the molecular weight of the modified crosslinked rubber particles, and even when used in a rubber composition, it is possible to suppress a decrease in physical properties.

[0015] Conventional methods for treating rubber materials may involve the use of rejuvenating agents to facilitate decrosslinking of the rubber material. On the other hand, in the present invention, it is preferable that the regenerating agent such as phenylhydrazine / iron chloride-based regenerating agent, organic amine / copper chloride-based regenerating agent, thiol / amine-based regenerating agent, and dimethyl sulfoxide / methyl iodide-based regenerating agent is not substantially blended in the process of applying shear stress to the crosslinked rubber particles by a vibration mill. By substantially not blending the regenerating agent, it is possible to suppress the decrease in the molecular weight of the modified crosslinked rubber particles, and even when used in a rubber composition, it is possible to suppress the decrease in physical properties. By substantially not blending, it is meant that the blending amount of the regenerating agent is preferably 2 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.1 parts by mass or less, and even more preferably 0 parts by mass, relative to 100 parts by mass of the crosslinked rubber particles.

[0016] (Crosslinked rubber particles) In the present invention, the crosslinked rubber particles are preferably those obtained by granulating 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.

[0017] The crosslinked rubber particles can be obtained by pulverizing the above-mentioned used rubber. In the present invention, when obtaining the modified crosslinked rubber particles, it is preferable to have a step of pulverizing the used rubber to obtain crosslinked rubber particles before the step of applying shear stress to the crosslinked rubber particles by a vibration mill. 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.

[0018] 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 shear stress to the crosslinked rubber particles and efficiently obtaining modified crosslinked 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 crosslinked rubber particles into the ranges described below and to make it easier to incorporate them into a rubber composition. From the viewpoint of efficiently obtaining modified crosslinked 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 crosslinked 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 shear stress to the crosslinked rubber particles and efficiently obtaining modified crosslinked 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 are measured by a sieving test, specifically by the method described in the Examples.

[0019] (Physical properties of modified crosslinked rubber particles) In the present invention, the average particle size of the modified crosslinked rubber particles is, from the viewpoint of reducing the Mooney viscosity of the rubber composition and improving processability, preferably 0.3 mm or more, more preferably 0.5 mm or more, even more preferably 0.7 mm or more, and is preferably 20 mm or less, more preferably 5 mm or less, even more preferably 1 mm or less. In the present invention, the particle size distribution and average particle size of the modified crosslinked rubber particles are measured in the same manner as in 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 modified crosslinked rubber particles having a particle size of 90 μm or less is preferably 5 mass % or less, more preferably 0.3 mass % or less, and even more preferably 0.1 mass % or less, from the viewpoint of reducing the Mooney viscosity of the rubber composition and improving processability. In the present invention, the proportion of modified crosslinked rubber particles having a particle size of 150 μm or less is preferably 10 mass % or less, more preferably 1 mass % or less, and even more preferably 0.1 mass % or less, from the viewpoint of reducing the Mooney viscosity of the rubber composition and improving processability. In the present invention, the proportion of modified crosslinked rubber particles having a particle size of 500 μm or less 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, from the viewpoint of reducing the Mooney viscosity of the rubber composition and improving processability.

[0020] The ratio of the swelling ratio of modified crosslinked rubber particles measured by the swelling ratio measurement method described below to the swelling ratio of crosslinked rubber particles measured by the swelling ratio measurement method described below (swelling ratio of modified crosslinked rubber particles / swelling ratio of crosslinked rubber particles) is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, even more preferably 0.91 or more, even more preferably 0.92 or more, and is preferably 0.98 or less, more preferably 0.97 or less, even more preferably 0.96 or less. (Method of measuring swelling ratio) The modified crosslinked rubber particles or crosslinked rubber particles are heated at 10 MPa and 145°C for 10 minutes to form a sheet-like molded product with a thickness of 2 mm. The obtained sheet-like molded product is used as a test piece in the shape of a dumbbell No. 5 as specified in JIS K 6251:2017. The obtained test piece is immersed in 100 mL of xylene at room temperature (23°C) for 3 days. The weight of the test piece before and after immersion is measured, and the swelling ratio is calculated based on the following formula. Swelling ratio (%) = (weight of test piece after immersion / weight of test piece before immersion) x 100

[0021] The swelling ratio being within the above range means that the swelling ratio of the modified crosslinked rubber particles is smaller than the swelling ratio of the crosslinked rubber particles before modification. It is considered that the above swelling ratio measurement method is due to the fact that the sulfur components that formed the remaining crosslinking points are re-crosslinked when the modified crosslinked rubber particles are formed into a sheet-shaped molding. At this time, the modified crosslinked rubber particles are re-crosslinked and crosslinked between the modified crosslinked rubber particles, so that the sheet-shaped molding of the modified crosslinked rubber particles is in a crosslinked state as a whole, and therefore the swelling ratio ratio is within the above range. Furthermore, the fact that the swelling ratio of the modified crosslinked rubber particles is within the above range indicates that the particles are in a state where they can be re-crosslinked, as described above. In other words, the modified crosslinked rubber particles themselves are considered to be in a de-crosslinked state, as described above. Therefore, in the rubber composition of the present invention, since the swelling ratio ratio of the modified crosslinked rubber particles is within the above range, the modified crosslinked rubber particles become more compatible with the processability improver and the uncrosslinked rubber component, making it easier to reduce the Mooney viscosity and improve processability.

[0022] <Processability improver> The rubber composition of the present invention contains a processability improver. By containing the processability improver in the rubber composition, adhesion to metal parts of a kneading facility can be suppressed, so that the Mooney viscosity can be reduced and processability can be improved. In the present invention, from the viewpoint of reducing the Mooney viscosity of the rubber composition and improving the processability, the processability improver is preferably at least one selected from glycerin fatty acid esters, stearylamine derivatives, and process oils, and more preferably at least one selected from glycerin fatty acid esters and stearylamine derivatives. The processability improvers may be used alone or in combination of two or more.

[0023] (Glycerol fatty acid ester) A glycerin fatty acid ester is a compound in which at least one of the three OH groups contained in glycerin is bonded to a COOH group of a fatty acid via an ester bond. The glycerin fatty acid ester is preferably at least one selected from a glycerin fatty acid monoester obtained by esterifying one glycerin molecule with one fatty acid molecule, a glycerin fatty acid diester obtained by esterifying one glycerin molecule with two fatty acid molecules, and a glycerin fatty acid triester obtained by esterifying one glycerin molecule with three fatty acid molecules, and a glycerin fatty acid monoester is more preferred.

[0024] From the viewpoint of reducing the Mooney viscosity of the rubber composition and improving processability, the fatty acid constituting the glycerin fatty acid ester preferably has a carbon number of 8 or more, more preferably has a carbon number of 10 or more, even more preferably has a carbon number of 12 or more, still more preferably has a carbon number of 14 or more, and still more preferably has a carbon number of 16 or more, and is preferably has a carbon number of 28 or less, more preferably has a carbon number of 22 or less, and still more preferably has a carbon number of 18 or less. In particular, when the carbon number of the fatty acid constituting the glycerin fatty acid ester is 8 or more, the affinity with the above-mentioned modified crosslinked rubber particles and the uncrosslinked rubber component can be increased, and therefore blooming of the glycerin fatty acid ester can be easily suppressed. The fatty acid may be linear or branched, but is preferably linear, and may be saturated or unsaturated, but is preferably saturated. The fatty acid is particularly preferably a linear saturated fatty acid. Specific examples of the fatty acid include caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, linoleic acid, linolenic acid, araginic acid, arachidonic acid, behenic acid, etc. Among these, one or more selected from lauric acid, myristic acid, palmitic acid, and stearic acid are preferred, one or more selected from palmitic acid and stearic acid are more preferred, and stearic acid is even more preferred.

[0025] As the glycerin fatty acid ester, from the viewpoint of reducing the Mooney viscosity of the rubber composition and improving the processability, one or more selected from lauric acid monoglyceride, myristic acid monoglyceride, palmitic acid monoglyceride, and stearic acid monoglyceride are preferable, one or more selected from palmitic acid monoglyceride and stearic acid monoglyceride are more preferable, and stearate monoglyceride is even more preferable.

[0026] (Stearylamine derivatives) The stearylamine derivative is preferably a compound in which hydrogen atoms on the amino group of stearylamine are substituted with an alkyl group, such as a methyl group, an ethyl group, a propyl group, or a butyl group. As the stearylamine derivative, from the viewpoint of reducing the Mooney viscosity of the rubber composition and improving the processability, one or more selected from dimethylstearylamine, diethylstearylamine, dipropylstearylamine, ethylmethylstearylamine, ethylpropylstearylamine and methylpropylstearylamine are preferred, and dimethylstearylamine is more preferred.

[0027] (Process oil) The process oil preferably has a pour point of 40° C. or less. As the process oil, from the viewpoint of reducing the Mooney viscosity of the rubber composition and improving processability, one or more types selected from aromatic process oil, naphthenic process oil, and paraffinic process oil are preferable, and naphthenic process oil is more preferable.

[0028] <Uncrosslinked rubber component> The rubber composition of the present invention contains an uncrosslinked rubber component. The uncrosslinked rubber component is preferably at least one selected from natural rubber and diene synthetic rubber from the viewpoints of reducing the Mooney viscosity of the rubber composition and improving processability, as well as from the viewpoints of availability. Examples of natural rubber include SMR, SIR, STR, and RSS, with SMR20, STR20, RSS#3, RSS#4, and the like being preferred. Modified natural rubber obtained by modifying natural rubber can also be used. 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. Among these, from the viewpoint of reducing the Mooney viscosity of the rubber composition and improving processability, one or more selected from natural rubber, modified natural rubber, IR, BR, SBR, and NBR are preferred, one or more selected from BR, SBR, and natural rubber are more preferred, and natural rubber is even more preferred. BR or SBR may be used in combination with natural rubber. The copolymer rubber may be a block copolymer or a random copolymer, but from the viewpoints of reducing the Mooney viscosity of the rubber composition and improving the processability, a random copolymer is preferred. The uncrosslinked rubber components may be used alone or in combination of two or more kinds.

[0029] (Inorganic filler) The rubber composition of the present invention is characterized in that it is possible to improve physical properties such as strength of a rubber molded article to be obtained, It is preferable that the composition contains an inorganic filler. As the inorganic filler, silica and carbon black are preferable, and carbon black is more preferable.

[0030] 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 improving the processability of the rubber composition. 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 improving the processability of the rubber composition, the average secondary particle diameter 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.

[0031] 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, one or more types selected from SAF, ISAF, IISAF, N339, HAF and FEF grade carbon black are preferred, and HAF grade carbon black is more 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.

[0032] In the present invention, alumina, calcium carbonate, clay, talc, zeolite, diatomaceous earth, etc. may further be used as an inorganic filler, if necessary.

[0033] (sulfur) The rubber composition of the present invention preferably contains sulfur in order to vulcanize it 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.

[0034] (Other Ingredients) In addition to the above-mentioned components, the rubber composition of the present invention may contain, if desired, various additives usually used in the rubber industry, such as antioxidants, scorch inhibitors, softeners, stearic acid, zinc oxide, vulcanizing agents, vulcanization accelerators, etc., within the scope of the object of the present invention.

[0035] (Content of each ingredient) In the rubber composition of the present invention, the content of the modified crosslinked rubber particles, from the viewpoint of reducing the Mooney viscosity and improving processability, 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, even more preferably 6 parts by mass or less, per 100 parts by mass of the uncrosslinked rubber component.

[0036] In the rubber composition of the present invention, the content of the uncrosslinked rubber component in the rubber composition is, from the viewpoint of reducing the Mooney viscosity and improving processability, preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less.

[0037] In the rubber composition of the present invention, the content of the inorganic filler is, from the viewpoint of improving physical properties such as strength of the obtained rubber molded product, 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 uncrosslinked rubber component.

[0038] The sulfur content, from the viewpoint of sufficiently vulcanizing the unvulcanized rubber composition and from the viewpoint of reducing the Mooney viscosity and improving processability, 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, and is 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 uncrosslinked rubber component.

[0039] [Rubber molding] The rubber molded article of the present invention is obtained by vulcanizing the above-mentioned rubber composition of the present invention. The vulcanization method can be a known method, and specifically, the vulcanization can be performed by the manufacturing method of the rubber molded article described later. In the present invention, the content of the modified crosslinked rubber particles and the inorganic filler contained in the rubber molded product is the same as that of the rubber composition described above. The content of the components derived from the uncrosslinked rubber component is the same as that of the uncrosslinked rubber component of the rubber composition described above. The rubber molded product of the present invention can be suitably used as tire components such as tires, tire inner liners, treads, tread bases, carcasses, sidewalls, and bead portions, 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, and more preferably as tires.

[0040] [Method of manufacturing rubber composition] The method for producing a rubber composition of the present invention includes a step of blending modified crosslinked rubber particles, a processability improver, and an uncrosslinked rubber component, and the modified crosslinked rubber particles are modified crosslinked rubber particles that have been treated by a step of applying shear stress to the crosslinked rubber particles using a vibrating mill. More specifically, the method for producing the rubber composition of the present invention includes the following steps 1 and 2. Step 1: A step of kneading a mixture containing modified crosslinked rubber particles and a processability improver with an uncrosslinked rubber component to obtain a rubber kneaded product. Step 2: A step of adding and mixing sulfur to the rubber mixture obtained in step 1 to obtain a rubber composition.

[0041] (Process 1) More specifically, in step 1, a mixture containing modified crosslinked rubber particles, a processability improver, and optionally an inorganic filler, an antioxidant, stearic acid, etc., is kneaded with an uncrosslinked rubber component using a kneader to obtain a rubber mixture. Examples of the kneading machine include a Banbury mixer, a roll, and an intensive mixer. The kneading temperature is, from the viewpoint of further dispersing and incorporating the modified crosslinked rubber particles and the processability improver in the uncrosslinked rubber component, reducing the Mooney viscosity of the obtained rubber composition, and improving the processability, preferably 140°C or higher, more preferably 143°C or higher, even more preferably 146°C or higher, still more preferably 148°C or higher, and is preferably 165°C or lower, more preferably 160°C or lower, even more preferably 158°C or lower, and even more preferably 155°C or lower.

[0042] (Process 2) In step 2, sulfur is added to and mixed with the rubber kneaded product obtained in step 1, thereby obtaining the rubber composition of the present invention. 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, and the like can be added and mixed as necessary to obtain an unvulcanized rubber composition.

[0043] [Method of manufacturing rubber molded body] The method for producing a rubber molded article in the present invention includes a step of vulcanizing the above-mentioned rubber composition. More specifically, the above-mentioned rubber composition can be molded by a known method, heated or heated and pressurized to form a vulcanized rubber molded article. The temperature conditions for the heating or heating and pressurization are 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.

[0044] [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 content of the modified crosslinked rubber particles and the inorganic filler contained in the tire is the same as that of the rubber composition described above. Also, the content of the components derived from the uncrosslinked rubber component is the same as that of the uncrosslinked rubber component of the rubber composition described above. The tire obtained by the tire manufacturing method of the present invention can be suitably used not only for tires for general vehicles, but also for tires for trucks, buses, construction vehicles, etc. In particular, it is preferable to provide the tire in the tread portion from the viewpoint of ease of recycling. EXAMPLES

[0045] 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.

[0046] [Preparation of modified crosslinked rubber particles] (Production Example 1) 500g 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 284mm, depth 520mm, total container capacity 32.9L), and 63 stainless steel rods with a diameter of 30mm, length 510mm, and circular cross section were loaded as rods, and treated for 3 minutes under conditions of an amplitude of 8mm and a vibration frequency of 20Hz to obtain modified crosslinked rubber particles. The temperature after treatment was 50°C.

[0047] (Production Example 2) Modified crosslinked rubber particles were obtained under the same conditions as in Production Example 1, except that the treatment time was changed to 15 minutes.

[0048] [Preparation of rubber composition] <Examples 1 to 5, Reference Example 1, and Comparative Examples 1 to 5> The raw material components shown in Table 2 were prepared, and the components excluding zinc oxide, sulfur, and vulcanization accelerator were kneaded in a Banbury mixer at a maximum temperature of 150°C for 4 minutes according to the compounding recipe shown in Table 2 to obtain a rubber kneaded product. The obtained rubber kneaded product was kneaded again at a maximum temperature of 150°C for 2 minutes and 30 seconds. Next, zinc oxide, sulfur, and vulcanization accelerator were added to the obtained rubber kneaded product, and kneaded for 2 minutes at a maximum temperature of 110°C to obtain a rubber composition (unvulcanized). Reference Example 1 is an example that does not contain either crosslinked rubber particles or modified crosslinked rubber particles.

[0049] Details of each component shown in Tables 1 and 2 are as follows. [Uncrosslinked rubber component] ·NR: Natural rubber: RSS #3 [Rubber particles] Cross-linked rubber particles: Shinsei Rubber Co., Ltd., product name: #50 (rubber chip powder (particles), derived from waste tires) [Processability improver] Processability improver 1: Kao Corporation, product name: Excel VS-95 (monoglyceride stearate) Processability improver 2: Kao Corporation, product name: Farmin DM8098 (dimethylstearylamine) Processability improver 3: Made by Nippon San Oil Co., Ltd., product name: Sansen 410 (naphthenic process oil) [Inorganic filler] Carbon black: Tokai Carbon Co., Ltd., product name: Seast 3, (HAF, DBP absorption: 101 cm 3 / 100g, N2AS:79m 2 / g) [Additives] Anti-aging agent: Manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product name: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) Stearic acid: Kao Corporation, product name: Lunac S-70V Zinc oxide: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Product name: Zinc oxide (first grade) Sulfur: Fujifilm Wako Pure Chemical Industries, Ltd. Product name: Sulfur (powder, chemical grade) Vulcanization accelerator: Manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product name: Noccela CZ-G (sulfenamide vulcanization accelerator, N-cyclohexyl-2-benzothiazolyl sulfenamide)

[0050] [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 8801-1:2019 were stacked on a tray in order from the bottom up. A sample was placed on the top sieve and shaken for 3 minutes using an electromagnetic sieve shaker (Retze, AS200 Basic) to classify the sample. Each of the test sieves used was a utility model type manufactured by Iida Seisakusho Co., Ltd. The results are shown in Table 1.

[0051] <Measurement of the average particle size of rubber particles> In the particle size distribution measurement, the weight of the rubber particles remaining on each sieve was measured, and then the size of the openings of each sieve and the mass ratio (residual percentage) R of the particles that could not pass through the sieve (particles remaining on the sieve and particles remaining on the sieve with larger openings) to the total particles were plotted on a semi-logarithmic graph (horizontal axis: particle size (logarithmic scale), vertical axis: residual percentage), and the particle size corresponding to R=50% was calculated and used as the average particle size. The results are shown in Table 1.

[0052] <Measurement of swelling ratio in modified crosslinked rubber particles> (Creating test pieces) The crosslinked rubber particles (manufactured by Shinsei Rubber Co., Ltd., product name: #50) and the modified crosslinked rubber particles of Production Examples 1 and 2 were filled into a frame surrounded by SUS plates measuring 2 mm in thickness and 11 cm x 17 cm, and heated at 10 MPa and 145°C for 10 minutes to obtain sheet-like molded products. The obtained sheet-like molded products were punched into a dumbbell-shaped No. 5 shape specified in JIS K 6251:2017 to prepare test pieces for measuring the swelling ratio. (Measurement of swelling ratio and swelling ratio ratio) The test piece was immersed in 100 mL of xylene for 3 days at room temperature (about 23° C.). The weight of the test piece before and after immersion was measured, and the swelling ratio was calculated based on the following formula. Swelling ratio (%) = (weight of test piece after immersion / weight of test piece before immersion) x 100 From the swelling ratio thus obtained, the ratio of the swelling ratio of the modified crosslinked rubber particles of Production Example 1 or 2 to the swelling ratio of the crosslinked rubber particles (i.e., rubber particles before modification) (swelling ratio of modified crosslinked rubber particles / swelling ratio of crosslinked rubber particles) was obtained. The swelling ratios thus obtained are shown in Table 1.

[0053] <Measurement of Mooney Viscosity of Rubber Composition> The rubber compositions (unvulcanized) of the Examples, Reference Examples, and Comparative Examples were measured for Mooney viscosity [ML1+4] at 100°C using "MVR VR-1130" manufactured by Ueshima Seisakusho Co., Ltd. based on JIS K 6300-1:2013. The Mooney viscosity was shown as a relative value when the Mooney viscosity of the rubber composition of Reference Example 1 was taken as 100. The smaller the Mooney viscosity value, the better the processability. The results are shown in Table 2.

[0054] [Table 1]

[0055] From the results in Table 1, it was confirmed that the modified crosslinked rubber particles of Production Examples 1 and 2 had a larger average particle size than the unmodified crosslinked rubber particles. It is presumed that the particle size of the modified crosslinked rubber particles of Production Examples 1 and 2 became larger because the crosslinking points in the crosslinked rubber particles were cut and some of the sulfur components that were the crosslinking points were re-crosslinked by the process of applying shear stress using a vibration mill. In addition, the ratio of the swelling ratio of the modified crosslinked rubber particles to that of the crosslinked rubber particles before modification was decreased in the test pieces of the modified crosslinked rubber particles of Production Examples 1 and 2, so it was confirmed that the modified crosslinked rubber particles were decrosslinked by the process of applying shear stress using a vibration mill. On the other hand, since a sheet-shaped molded product was obtained by heating the modified crosslinked rubber particles at 145°C for 10 minutes without vulcanization, it is believed that the sulfur atoms present in the sulfur crosslinks also contain sulfur functional groups having a certain degree of reactivity. Therefore, from Table 1, it can be seen that the modified crosslinked rubber particles used in the present invention are de-crosslinked by being treated in a process of applying shear stress using a vibrating mill, and are modified to a state where they can be re-crosslinked without the addition of a crosslinking agent such as sulfur. In addition, from the above, it is expected that by using the modified crosslinked rubber particles of the present invention in combination with uncrosslinked rubber to produce a rubber molded body, the amount of sulfur added can be reduced compared to when only uncrosslinked rubber is used as the rubber component.

[0056] [Table 2]

[0057] Furthermore, from Table 2, it can be seen that Examples 1 to 5, which contain modified crosslinked rubber particles and a processability improver, have reduced Mooney viscosity compared to Comparative Example 1, which contains unmodified crosslinked rubber particles and no processability improver, and Comparative Examples 2 and 3, which contain unmodified crosslinked rubber particles and a processability improver. Furthermore, it can be seen that Examples 1 to 5, which contain modified crosslinked rubber particles and a processability improver, have reduced Mooney viscosity compared to Comparative Examples 4 and 5, which contain modified crosslinked rubber particles but do not contain a crosslinkability improver. Therefore, it can be confirmed that the rubber composition of the present invention has a reduced Mooney viscosity and excellent processability.

Claims

1. It contains modified crosslinked rubber particles, a processability improver, and an uncrosslinked rubber component. A rubber composition in which the modified crosslinked rubber particles are modified crosslinked rubber particles that have been treated by a process of applying shear stress to crosslinked rubber particles using a vibratory mill.

2. The rubber composition according to claim 1, wherein the processing temperature in the step of applying the shear stress is 10°C or more and 150°C or less.

3. The rubber composition according to claim 1, wherein the average particle diameter of the modified crosslinked rubber particles is 0.3 mm or more and 20 mm or less.

4. The rubber composition according to claim 1, wherein the crosslinked rubber is used rubber.

5. The rubber composition according to claim 4, wherein the used rubber is a waste tire.

6. The rubber composition according to claim 1, wherein the processability improver is one or more selected from glycerin fatty acid esters, stearylamine derivatives, and process oils.

7. The rubber composition according to claim 1, wherein the uncrosslinked rubber component is one or more selected from natural rubber and diene-based synthetic rubber.

8. The rubber composition according to claim 1, wherein the ratio of the swelling rate of the modified crosslinked rubber particles measured by the method for measuring the swelling rate of the crosslinked rubber particles to the swelling rate of the modified crosslinked rubber particles measured by the method for measuring the swelling rate of the modified crosslinked rubber particles (swelling rate of modified crosslinked rubber particles / swelling rate of crosslinked rubber particles) is 0.90 or more and 0.98 or less. (Method for measuring swelling rate) The modified crosslinked rubber particles or the crosslinked rubber particles are heated at 10 MPa and 145°C for 10 minutes to form a sheet-like molded body with a thickness of 2 mm. The obtained sheet-like molded body is used to form a dumbbell-shaped test piece in the shape of type 5 as specified in JIS K 6251:2017. The obtained test piece is immersed in 100 mL of xylene at room temperature (approximately 23°C) for 3 days. The weight of the test piece before immersion and the weight of the test piece after immersion are measured, and the swelling rate is calculated based on the following formula. Swelling rate (%) = (Weight of test specimen after immersion / Weight of test specimen before immersion) × 100

9. A rubber molded article obtained by vulcanizing a rubber composition according to any one of claims 1 to 8.

10. The process includes a step of blending modified crosslinked rubber particles, a processability improver, and an uncrosslinked rubber component. A method for producing a rubber composition, wherein the modified crosslinked rubber particles are modified crosslinked rubber particles obtained by a process of applying shear stress to crosslinked rubber particles using a vibratory mill.

11. A method for producing a rubber molded article, comprising the step of vulcanizing a rubber composition obtained by the method for producing a rubber composition described in claim 10.