Method for producing rubber composition

Abstract

To provide a method for producing a rubber composition capable of efficiently producing a rubber composition comprising a high molecular weight polymer component from a crosslinked rubber in a short time.SOLUTION: There is provided a method for producing a rubber composition comprising a polymer component having a high molecular weight of 150000 or more from a crosslinked rubber, which comprises a step of obtaining the rubber composition by applying a shear force to the crosslinked rubber while heating the crosslinked rubber at a temperature of 160°C or more and 190°C or less in a solvent having an SP value of 7.0 (cal / cm3)1 / 2 or more and 9.7 (cal / cm3)1 / 2 or less and a spontaneous ignition temperature of 220°C or more and 300°C or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a rubber composition.

Background Art

[0002] From the viewpoints of the environment and resource conservation, recycling crosslinked rubber and reusing it as new crosslinked rubber have been studied.

[0003] For example, Patent Document 1 aims to provide a method for producing a rubber composition capable of producing a liquid hydrocarbon in a high yield even under milder conditions. A crosslinked rubber is heated at 0.1 to 2.0 MPa and 300 °C or lower in a reaction solvent containing a primary alcohol having 2 or more carbon atoms to obtain a rubber composition containing a liquid hydrocarbon. A method for producing a rubber composition is disclosed.

[0004] Patent Document 2 discloses a method for efficiently and simply producing reusable liquid hydrocarbon and carbon black from vulcanized rubber waste. Vulcanized rubber such as vulcanized rubber waste is pyrolyzed in the presence of a hydrogen-donating solvent to produce liquid hydrocarbon and carbon black. A method is disclosed.

[0005] In addition, a method of crosslinking a crosslinked rubber using 2-butanol under conditions of a pressure of 3.4 MPa or more in a temperature range of 150 to 300 °C (see, for example, Patent Document 3), a method of crosslinking a crosslinked rubber using an alcohol and a ketone-based solvent in a temperature range of 200 to 350 °C under conditions of a pressure of 3.4 to 34 MPa or more (see, for example, Patent Document 4), and a method of decomposing vulcanized rubber using water and an organic solvent (alcohol) at a temperature above the vapor pressure of each solvent in an atmosphere of 300 psi or more including an inert gas and at a temperature zone of 285 °C or lower and above the saturated vapor pressure (see, for example, Patent Document 5) are disclosed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] However, in the conventional method for producing a rubber composition from crosslinked rubber, there was room for improvement in terms of efficiency, such as the need for pre-micronization of the crosslinked rubber or the decomposition of the crosslinked rubber under a high-temperature environment.

[0008] Therefore, an object of the present invention is to solve the above problems of the prior art and provide a method for producing a rubber composition in which a polymer component having a high molecular weight can be efficiently produced from crosslinked rubber in a short time. [Means for Solving the Problems]

[0009] As a result of intensive studies, the present inventors have found that by applying a shearing force to crosslinked rubber while heating the crosslinked rubber in a specific solvent, a rubber composition having a high molecular weight polymer component can be efficiently obtained from the crosslinked rubber in a short time without the need for micronization of the crosslinked rubber or the like.

[0010] The gist of the method for producing a rubber composition of the present invention for solving the above problems is as follows.

[0011] [1] A method for producing a rubber composition having a weight average molecular weight of 150,000 or more of a polymer component from crosslinked rubber, wherein the SP value is 7.0 (cal / cm 3 ) 1 / 2 or more and 9.7 (cal / cm 3 ) 1 / 2A method for producing a rubber composition, comprising a step of obtaining the rubber composition by applying a shearing force to the crosslinked rubber while heating the crosslinked rubber at a temperature of 160°C or higher and 190°C or lower in a solvent having a spontaneous ignition temperature of 220°C or higher and 300°C or lower. According to the method for producing a rubber composition described in [1] above, a rubber composition having a polymer component with a high molecular weight can be efficiently produced from the crosslinked rubber.

[0012] [2] The method for producing a rubber composition according to [1], wherein the solvent is at least one solvent selected from anethole, limonene, and cyclohexane. According to the method for producing a rubber composition described in [2] above, a rubber composition can be more efficiently produced from the crosslinked rubber, and a rubber composition having a higher molecular weight of the polymer component can be produced.

[0013] [3] The method for producing a rubber composition according to [1] or [2], wherein the solvent is used in a range where the mass ratio of the solvent to the crosslinked rubber (mass of solvent: mass of crosslinked rubber) is 0.1:1 to 5:1. According to the method for producing a rubber composition described in [3] above, a rubber composition can be more efficiently produced from the crosslinked rubber, and a rubber composition having a higher molecular weight of the polymer component can be produced.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide a method for producing a rubber composition that can efficiently produce a rubber composition having a polymer component with a high molecular weight from a crosslinked rubber in a short time.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, the method for producing a rubber composition of the present invention will be exemplified and described in detail based on its embodiments.

[0016] The compounds described in this specification may be partially or entirely derived from fossil resources, may be derived from biological resources such as plant resources, or may be derived from recycled resources such as used tires. They may also be derived from a mixture of any two or more of fossil resources, biological resources, and recycled resources. In addition, in this specification, the notation "a~b" in the description of a numerical range represents a to b, unless otherwise specified.

[0017] <Method for producing a rubber composition>

[0018] The method for producing a rubber composition according to this embodiment is a method for producing a rubber composition having a weight average molecular weight of the polymer component of 150,000 or more from a crosslinked rubber, The SP value (solubility parameter) is 7.0 (cal / cm 3 ) 1 / 2 or more and 9.7 (cal / cm 3 ) 1 / 2 or less, and in a solvent having a spontaneous ignition temperature of 220°C or more and 300°C or less, while heating the crosslinked rubber at a temperature of 160°C or more and 190°C or less, applying a shearing force to the crosslinked rubber to obtain the rubber composition (hereinafter, sometimes simply referred to as "the step of obtaining the rubber composition"). According to the method for producing a rubber composition of this embodiment, a rubber composition having a high molecular weight polymer component can be efficiently produced from a crosslinked rubber. As a result, it is also possible to suppress emissions of carbon dioxide and the like, and to produce a rubber composition with a reduced environmental load. In this specification, the "polymer component" refers to a component generated by the de-crosslinking of the rubber component of the crosslinked rubber.

[0019] In the step of obtaining the rubber composition, in addition to cutting the bonds of the crosslinked rubber by the effects of heat and solvent, the bonds of the crosslinked rubber are also cut by applying a shearing force to the crosslinked rubber. Therefore, since the bonds of the crosslinked rubber are cut by both the cutting of the bonds of the crosslinked rubber by the effects of heat and solvent and the cutting of the bonds of the crosslinked rubber by the shearing force, the de-crosslinking of the crosslinked rubber can be performed more efficiently. In the method for producing the rubber composition of the present embodiment, in the bonds between carbon atoms derived from rubber molecules constituting the crosslinked rubber (carbon-carbon bonds), the bonds between the carbon atoms and heteroatoms (oxygen atoms, sulfur atoms, etc.) derived from the crosslinking agent (for example, carbon-sulfur bonds), etc., it is considered that the bonds are cleaved by heat, solvent effects, and shear, and radicals and / or new bonds are generated. The highly reactive radical species generated by undergoing these cleavages react with a solvent having an SP value of 7.0 (cal / cm 3 ) 1 / 2 or more and 9.7 (cal / cm 3 ) 1 / 2 or less, and a spontaneous ignition temperature of 220°C or more and 300°C or less, and it is considered that the reaction of the radicals is terminated. Therefore, it is presumed that the bonds between the radicals are less likely to occur, and the recombination of the cleaved carbon-carbon bonds, carbon-sulfur bonds, etc. is also less likely to occur. In the present invention, the "shearing force" refers to a mechanical force that cuts bonds such as carbon-carbon bonds and carbon-sulfur bonds of the crosslinked rubber with a mechanical force using the device described below, and can be controlled through adjustment of the shear rate.

[0020] In the method for producing the rubber composition of the present embodiment, examples of the device for applying a shearing force include a roll machine, a Banbury mixer, an extruder such as a single-screw extruder or a twin-screw extruder, a gear pump, an intermeshing mixer, a kneader, and a conical kneader. These may be used alone or in combination of two or more. As a method for applying a shearing force to the crosslinked rubber, uniaxial shearing or biaxial shearing is preferable. For example, by using a single-screw extruder, uniaxial shearing can be applied to the crosslinked rubber, and by using a twin-screw extruder, biaxial shearing can be applied to the crosslinked rubber.

[0021] Also, the shear rate when applying a shearing force to the crosslinked rubber may be the shear rate applied to the object to be sheared when using an extruder or the like. The shear rate is preferably, for example, 2000 s -1 or less, and more preferably the maximum shear rate is 1000 s -1 or less.

[0022] (Step of obtaining a rubber composition) - Temperature - In the step of obtaining a rubber composition, the crosslinked rubber, solvent, etc. are heated at 160°C or higher and 190°C or lower. By setting the heating temperature to 190°C or lower, oxidation and heat-induced degradation of the polymer component can be suppressed. Also, by setting the heating temperature to 160°C or higher, the sulfur bonds of the crosslinked rubber are easily broken, and the bonds can be cleaved in a short time to decompose the crosslinked rubber.

[0023] - Pressure - In the step of obtaining a rubber composition, the pressure applied to the crosslinked rubber, solvent, etc. is preferably 0.1 MPa or higher and 15 Pa or lower within the above temperature range. This is because when the pressure exceeds 15 MPa, the decomposition reaction of the crosslinked rubber tends to proceed. Also, being 15 MPa or lower is excellent in resource and energy savings. Further, the pressure in the step of obtaining a rubber composition is more preferably 7 MPa or higher and 15 MPa or lower.

[0024] - Atmosphere - The reaction atmosphere in the step of obtaining a rubber composition is not particularly limited, and the reaction may proceed under an atmosphere of a gas composed of an inert gas such as argon gas or nitrogen gas (hereinafter simply referred to as an inert gas atmosphere), or under an atmosphere of a gas composed of air (hereinafter simply referred to as an air atmosphere), or under a mixed gas atmosphere of air and an inert gas. When using an inert gas, two or more kinds of inert gases may be mixed and used. Also, the reaction atmosphere in the step of obtaining a rubber composition may be an atmosphere of supercritical carbon dioxide. From the viewpoint of performing the decomposition of the crosslinked rubber with more delicate equipment and further reducing energy consumption, it is preferable to heat the crosslinked rubber in an aerobic environment, that is, in an oxygen-containing atmosphere, more preferably in an atmosphere of a gas containing air, and even more preferably in an air atmosphere.

[0025] (Other steps) In addition to the step of obtaining the above rubber composition, the method for producing the rubber composition of the present embodiment may further include a step of removing residual crosslinked rubber and / or a step of pulverizing the residual crosslinked rubber component. By removing the residual crosslinked rubber from the rubber composition in the step of removing the residual crosslinked rubber, the degree of de-crosslinking of the rubber composition can be increased. Further, even when the rubber composition contains crosslinked rubber, by pulverizing the residual crosslinked rubber component in the step of pulverizing the residual crosslinked rubber component, the crosslinked rubber contained in the rubber composition becomes finer, and even if a certain amount of crosslinked rubber was contained in the rubber composition, there will be no significant impact when used as the rubber composition. Further, the method for producing the rubber composition of the present embodiment may include any other steps as long as the effects of the present invention are not impaired, in addition to the step of obtaining the above rubber composition, the step of removing residual crosslinked rubber, and the step of pulverizing the residual crosslinked rubber component.

[0026] (Crosslinked rubber) The crosslinked rubber, which is a raw material in the method for producing the rubber composition of the present embodiment, is a crosslinked product of a rubber component. The crosslinked rubber may contain a crosslinking agent, a filler, etc. in addition to the rubber component. As the crosslinked rubber used in the method for producing the rubber composition of the present embodiment, for example, rubber products such as waste tires, rubber hoses, conveyor belts, rubber bladders, rubber articles constituting these rubber products, and rubber scraps such as waste rubber generated when manufacturing these rubber products and rubber articles can be used.

[0027] - Rubber component - The rubber component, which is a raw material of the crosslinked rubber, may be either a diene rubber or a non-diene rubber. Examples of the diene rubber include at least one selected from the group consisting of natural rubber (NR) and synthetic diene rubbers. Examples of the synthetic diene rubber include polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), halogenated butyl rubber, acrylonitrile-butadiene rubber (NBR), and the like. Examples of non-diene rubbers include butyl rubber, ethylene-propylene rubber, urethane rubber, silicone rubber, acrylic rubber, and the like. These rubber components may be used alone or in combination of two or more.

[0028] Among these, since diene rubbers are generally used in rubber products such as tires, the rubber component preferably contains 50% by mass or more of diene rubber, more preferably 70% by mass or more of diene rubber, and even more preferably 90% by mass or more of diene rubber. Further, the diene rubber is preferably one or more selected from the group consisting of natural rubber, polyisoprene rubber, and styrene-butadiene copolymer rubber.

[0029] - Crosslinking agent - In general, a crosslinking agent for the rubber component is used in rubber products. The crosslinking agent for the rubber component is not particularly limited, and examples thereof include sulfur-based crosslinking agents, organic peroxide-based crosslinking agents, inorganic crosslinking agents, polyamine crosslinking agents, resin crosslinking agents, sulfur compound-based crosslinking agents, and oxime-nitrosoamine-based crosslinking agents. Since sulfur-based crosslinking agents (vulcanizing agents) are usually used for the rubber component in tires and the like, the crosslinked rubber preferably contains a vulcanized product vulcanized with a vulcanizing agent, that is, vulcanized rubber. The content of vulcanized rubber in the crosslinked rubber is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass, that is, the crosslinked rubber is vulcanized rubber.

[0030] - Filler - The crosslinked rubber may contain a filler. Tires generally contain reinforcing fillers such as carbon black and silica in order to improve various functions such as durability and abrasion resistance of the tires. The filler may be used alone either silica or carbon black, or both silica and carbon black may be used. The content of the filler in the crosslinked rubber is not particularly limited, and may be, for example, 10 to 300 parts by mass with respect to 100 parts by mass of the rubber component.

[0031] When carbon black is used as the filler, the carbon black is not particularly limited and can be appropriately selected according to the purpose. As the carbon black, for example, those of FEF, SRF, HAF, ISAF, and SAF grades can be used.

[0032] When silica is used as the filler, the silica is not particularly limited and can be used according to the application, such as general grade silica, special silica surface-treated with a silane coupling agent, etc. As the silica, for example, wet silica can be used.

[0033] -Other Components- The crosslinked rubber may be a crosslinked product obtained by crosslinking a rubber composition containing, in addition to the rubber component, compounding agents usually used in the rubber industry, such as softeners, stearic acid, anti-aging agents, zinc oxide, vulcanization accelerators, etc. Tires generally contain vulcanized rubber obtained by vulcanizing a rubber composition containing these compounding agents.

[0034] (Solvent) The method for producing the rubber composition of this embodiment is carried out in a solvent having an SP value (solubility parameter) of 7.0 (cal / cm 3 ) 1 / 2 or more and 9.7 (cal / cm 3 ) 1 / 2 or less, and a natural ignition temperature of 220°C or more and 300°C or less (hereinafter, sometimes simply referred to as "solvent"). With such a solvent, while swelling the rubber, the highly reactive radical species generated by the cleavage of the crosslinked rubber bonds react with the solvent, and it is considered that the reaction of the radicals can be stopped and the bonding of the radicals to each other can be prevented.

[0035] The SP value is 7.0 (cal / cm 3 ) 1 / 2 or more and 9.7 (cal / cm 3 ) 1 / 2Hereinafter, examples of solvents having a spontaneous ignition temperature of 220°C or higher and 300°C or lower include anethole, limonene, terpene compounds, cyclohexane, drying oils, and the like. These may be used alone or in combination of two or more.

[0036] The SP value is 7.0 (cal / cm 3 ) 1 / 2 or higher and 9.7 (cal / cm 3 ) 1 / 2 or lower, and the solvent having a spontaneous ignition temperature of 220°C or higher and 300°C or lower is preferably at least one solvent selected from anethole, limonene, and cyclohexane. Since these solvents have the property of being easily oxidized, it is considered that this property can prevent the cleavage of the main chain of the polymer component and improve the molecular weight of the polymer component. Anethole has an SP value of 8.4 (cal / cm 3 ) 1 / 2 , and the spontaneous ignition temperature is estimated from the spontaneous ignition temperature of another compound having an approximate chemical structure and is 235 to 245°C. Limonene has an SP value of 8.3 (cal / cm 3 ) 1 / 2 , and the spontaneous ignition temperature is 235°C. Cyclohexane has an SP value of 8.2 (cal / cm 3 ) 1 / 2 , and the spontaneous ignition temperature is 245°C.

[0037] In the method for producing the rubber composition of the present embodiment, the solvent has an SP value of 7.0 (cal / cm 3 ) 1 / 2 or higher, preferably 7.3 (cal / cm 3 ) 1 / 2 or higher, and the SP value is 9.7 (cal / cm 3 ) 1 / 2 or lower, preferably 9.0 (cal / cm 3 ) 1 / 2 or lower, and more preferably 8.8 (cal / cm 3 ) 1 / 2 or lower. In addition, the solvent has a spontaneous ignition temperature of 220°C or higher and 300°C or lower, more preferably 250°C or lower, and even more preferably 240°C or lower.

[0038] In the method for producing the rubber composition of the present embodiment, the solvent is preferably a compound that can be separated from the rubber composition by heating, or a liquid medium that has an affinity for a liquid medium in which the rubber composition does not swell. With a solvent having such characteristics, the solvent and the rubber composition can be easily separated after depolymerization, and a rubber composition with higher purity can be obtained. In addition, the heating temperature for separating from the rubber composition is, for example, 100°C or higher. Examples of the liquid medium in which the rubber composition does not swell include acetone and supercritical carbon dioxide fluid. Note that the SP value of the solvent can be calculated by the Fedors method. The spontaneous ignition temperature of the solvent can be measured by the ASTM ignition point test.

[0039] In the method for producing the rubber composition of the present embodiment, it is preferable to use the solvent in a range where the mass ratio of the solvent to the crosslinked rubber (mass of the solvent: mass of the crosslinked rubber) is 0.1:1 to 5:1. By using the solvent within the above range, solvolysis is further promoted, the recombination of radicals generated by thermal decomposition is suppressed, and the crosslinked rubber can be efficiently decomposed. The amount of the solvent used is more preferably such that the mass ratio of the solvent to the crosslinked rubber (mass of the solvent: mass of the crosslinked rubber) is 0.5:1 to 3:1, and even more preferably 0.5:1 to 1:1. When the amount of the solvent used is within such a range, not only can the crosslinked rubber be efficiently decomposed, but also the environmental load can be reduced because the amount of the solvent used is small.

[0040] (Additive) The method for producing the rubber composition of the present embodiment may further be carried out in the presence of an additive. Examples of the additive include a basic reducing agent, an amine-based reducing agent, and a compound having an aromatic ring and a sulfur atom. Among them, a compound having an aromatic ring and a sulfur atom is preferable. When the rubber composition is produced in the presence of such an additive, the molecular weight of the polymer component can be further improved. Examples of the compound having an aromatic ring and a sulfur atom include diphenyl disulfide, mercaptobenzothiazole, dibenzothiazole disulfide, and the like. These may be used alone or in combination of two or more. Among these, one or more compounds selected from diphenyl disulfide, mercaptobenzothiazole, and dibenzothiazole disulfide are preferable.

[0041] In another preferred embodiment, the compound having an aromatic ring and a sulfur atom may be a disulfide compound. As the disulfide compound, diaryl disulfide is preferable. Examples of the disulfide compound include diphenyl disulfide, dimethyl disulfide, allyl disulfide, dibutyl disulfide, and the like. These may be used alone or in combination of two or more.

[0042] The addition amount of the additive is preferably such that the mass ratio of the mass of the additive to the mass of the crosslinked rubber (mass of the additive: mass of the crosslinked rubber) is 0.1:100 to 10:100, and more preferably 1:100 to 10:100.

[0043] In the method for producing the rubber composition of the present embodiment, in addition to the solvent and the additive, other substances can also be used as long as the effects of the present invention are not impaired.

[0044] <Rubber composition obtained by the method for producing a rubber composition> The rubber composition obtained by the method for producing a rubber composition of the present embodiment contains a polymer component, and the weight average molecular weight (Mw) of the polymer component is 150,000 or more. The polymer component refers to a component generated by the de-crosslinking of the rubber component of the crosslinked rubber.

[0045] It is preferable that the weight average molecular weight (Mw) of the polymer component of the rubber composition is 150,000 or more, more preferably 200,000 or more, and even more preferably 250,000 or more. Natural rubber (raw rubber) before vulcanization generally has a weight average molecular weight (Mw) of about 500,000 to 1,000,000, and it is more preferable that the Mw of the polymer component of the rubber composition is closer to these values. The weight average molecular weight (Mw) can be measured by gel permeation chromatography (GPC).

[0046] The rubber composition may have a degree of de-crosslinking of 30% or more, preferably 50% or more, more preferably 70% or more, and particularly preferably 100%. The degree of de-crosslinking is defined as the ratio of the mass of the polymer component obtained by de-crosslinking to the mass of the polymer component extracted using a solvent from the uncrosslinked rubber having the same compounding components as the crosslinked rubber.

[0047] In addition to the polymer component, the rubber composition may contain other components. Examples of other components contained in the rubber composition may include fillers such as carbon black and silica used in crosslinked rubber, and compounding agents commonly used in the rubber industry such as crosslinking agents.

[0048] The obtained rubber composition can provide good physical properties after vulcanization when used alone or when mixed with an unvulcanized (unused) rubber component or the like.

Examples

[0049] Examples are given below to explain the present invention in more detail, but the present invention is not limited to the following examples at all.

[0050] <Measurement method> In the examples and comparative examples, various physical property measurements of the raw materials and rubber compositions used were carried out as follows.

[0051] (1) Weight-average molecular weight (Mw) of the polymer component in the rubber composition The weight-average molecular weight (Mw) of the polymer component in the rubber composition was determined by gel permeation chromatography (GPC) measurement under the following conditions. The weight-average molecular weight (Mw) is in terms of polystyrene conversion. · Column: Manufactured by Tosoh Corporation: TSKgel GMHXL · Eluent: Tetrahydrofuran · Flow rate: 1 mL / min · Temperature: 40 °C · Detector: RI

[0052] (2) Degree of de-crosslinking of the rubber composition The ratio of the mass of the polymer component obtained by performing de-crosslinking to the mass of the polymer component extracted using a solvent from the uncrosslinked rubber having the same compounding ingredients as the crosslinked rubber was calculated.

[0053] (3) SP value (solubility parameter) of the solvent The SP value of the solvent was calculated by the Fedors method.

[0054] (4) Autoignition temperature of the solvent For solvents other than anethole, the autoignition temperature of the solvent was measured based on ASTM·E659 using Yoshida Seisakusho, model AM-659. For anethole, the autoignition temperature of a compound having an approximate chemical structure was measured, and the autoignition temperature was estimated based on the differences in chemical structure.

[0055] <Substances used in the production of the rubber composition> Anethole (solvent): SP value = 8.4 (cal / cm 3 ) 1 / 2 , autoignition temperature 235 - 245 °C) Limonene (solvent): SP value = 8.3 (cal / cm 3 ) 1 / 2 , autoignition temperature 235 °C) Cyclohexane (solvent): SP value = 8.2 (cal / cm 3 ) 1 / 2 , autoignition temperature 245 °C) Diphenyldisulfide (DPDS) (additive))

[0056] <Manufacture of rubber composition> (Example 1) Into a high-pressure kneading mixer (self-made device) with an internal volume of 51.7 cc, 10 g of vulcanized rubber in the form of small flakes about 1 mm in size and 10 g of anethole (solvent) were charged. The charged materials were subjected to a treatment of applying mechanical shear force with a tangential type kneading disk under a heating state of 180 °C to cut the sulfur bonds in the crosslinked rubber. The rotation speed was set at 60 rpm and the treatment was continued for 60 minutes. Based on the clearance between the kneading disks and the rotation speed at the end, the crosslinked rubber was subjected to shear at a maximum speed of 163.4 s -1 .

[0057] (Example 2) A rubber composition was produced in the same manner as in Example 1, except that diphenyldisulfide (DPDS) was added as an additive in addition to the vulcanized rubber and the solvent.

[0058] (Example 3) A rubber composition was produced in the same manner as in Example 1, except that the solvent was changed to limonene.

[0059] (Example 4) A rubber composition was produced in the same manner as in Example 3, except that diphenyldisulfide (DPDS) was added as an additive in addition to the vulcanized rubber and the solvent.

[0060] (Example 5) A rubber composition was produced in the same manner as in Example 2, except that the solvent was changed to cyclohexane.

[0061] (Comparative Example 1) A rubber composition was produced in the same manner as in Example 1, except that no solvent was charged.

[0062] (Comparative Example 2) A rubber composition was produced in the same manner as in Comparative Example 1, except that diphenyldisulfide (DPDS) was added as an additive in addition to the vulcanized rubber.

[0063] (Comparative Example 3) A rubber composition was produced in the same manner as in Example 5, except that the temperature in the production of the rubber composition was set at 150°C.

[0064] (Comparative Example 4) A rubber composition was produced in the same manner as in Example 1, except that the solvent was changed to toluene.

[0065] ><Evaluation of Rubber Composition> The weight average molecular weight (Mw) and degree of de-crosslinking of the polymer component in the rubber compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were measured by the above method. The results are shown in Table 1.

[0066]

Table 1

[0067] From Table 1, it can be seen that in a solvent having an SP value of 7.0 (cal / cm 3 ) 1 / 2 or more and 9.7 (cal / cm 3 ) 1 / 2 or less, and a spontaneous ignition temperature of 220°C or more and 300°C or less, by applying a shearing force to the crosslinked rubber while heating the crosslinked rubber at a temperature of 160°C or more and 190°C or less, a rubber composition having a high molecular weight polymer component can be efficiently obtained in a short time.

Industrial Applicability

[0068] According to the present invention, it is possible to provide a method for producing a rubber composition capable of efficiently producing a rubber composition having a high molecular weight polymer component from a crosslinked rubber in a short time.

Claims

1. A method for producing a rubber composition having a weight-average molecular weight of 150,000 or more of a polymer component from crosslinked rubber, with an SP value of 7.0 (cal / cm ３ ) １／２ or more and 9.7 (cal / cm ３ ) １／２ or less, and in a solvent having a spontaneous ignition temperature of 220°C or more and 300°C or less, while heating the crosslinked rubber at a temperature of 160°C or more and 190°C or less, applying a shearing force to the crosslinked rubber to obtain the rubber composition. The method for producing a rubber composition includes this step.

2. The method for producing a rubber composition according to claim 1, wherein the solvent is at least one solvent selected from anethole, limonene, and cyclohexane.

3. The method for producing a rubber composition according to claim 1, wherein the solvent is used in a range where the mass ratio of the solvent to the crosslinked rubber (mass of solvent: mass of crosslinked rubber) is 0.1:1 to 5:1.

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