Method for producing rubber composition, re-crosslinked rubber, tire and rubber industrial goods

Abstract

To provide a liquid hydrocarbon production method that makes it possible to produce liquid hydrocarbons of increased molecular weight at a high decomposition rate even under mild conditions, and a re-crosslinked rubber, a tire, and a rubber industrial product obtainable from a rubber composition produced by the production method.SOLUTION: A liquid hydrocarbon production method includes heating a crosslinked rubber at 300°C or less in a reaction solvent that has a boiling point of 230°C or less and contains an aldehyde having a hydrocarbon group with a carbon number of 2 or greater, thereby producing a rubber composition that contains a liquid hydrocarbon.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a rubber composition, a re-crosslinked rubber, a tire, and rubber industrial products.

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. For example, Patent Document 1 discloses a method for obtaining a rubber composition containing a liquid hydrocarbon by heating crosslinked rubber at 300°C or lower in a reaction solvent containing a primary alcohol having 2 or more carbon atoms.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the method described in Patent Document 1, even under mild conditions, although liquid hydrocarbons can be recovered in a high yield, further study is required to obtain high-molecular-weight liquid hydrocarbons.

[0005] An object of the present invention is to provide a method for producing a rubber composition capable of producing a liquid hydrocarbon having a higher molecular weight at a high decomposition rate even under mild conditions, a re-crosslinked rubber, a tire, and rubber industrial products obtained from the rubber composition produced by the production method, and solving this object is an issue.

Means for Solving the Problems

[0006] <1> A method for producing a rubber composition, which comprises heating a crosslinked rubber in a reaction solvent containing an aldehyde having a hydrocarbon group with 2 or more carbon atoms and a boiling point of 230 ° C or lower at 300 ° C or lower to obtain a rubber composition containing a liquid hydrocarbon.

[0007] <2> The method for producing a rubber composition according to <1>, wherein the hydrocarbon group has 3 to 16 carbon atoms. <3> The method for producing a rubber composition according to <1> or <2>, wherein the hydrocarbon group has 6 to 10 carbon atoms. <4> The method for producing a rubber composition according to any one of <1> to <3>, wherein the hydrocarbon group is a linear saturated aliphatic group. <5> The method for producing a rubber composition according to any one of <1> to <4>, wherein the aldehyde contains nonanal.

[0008] <6> The method for producing a rubber composition according to any one of <1> to <5>, wherein the crosslinked rubber is heated at 150 to 250 ° C. <7> The method for producing a rubber composition according to any one of <1> to <6>, wherein the crosslinked rubber is a crosslinked product of a rubber component containing 50 to 100% by mass of a diene rubber. <8> The method for producing a rubber composition according to any one of <1> to <7>, wherein the crosslinked rubber contains a vulcanized rubber.

[0009] <9> A re-crosslinked rubber obtained by re-crosslinking a rubber composition produced by the method for producing a rubber composition according to any one of <1> to <8>, wherein the rubber composition contains a liquid hydrocarbon produced by the method for producing a rubber composition according to any one of <1> to <7> as a rubber component, and the content of the liquid hydrocarbon in the rubber component is 1 to 100% by mass.

[0010] <10> A tire made of the re-crosslinked rubber according to <9>. <11> Rubber industrial products made of the re-crosslinked rubber according to <9>.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a method for producing a rubber composition capable of producing a liquid hydrocarbon having a higher molecular weight at a high decomposition rate even under mild conditions, a re-crosslinked rubber, a tire, and rubber industrial products obtained from the rubber composition produced by the production method.

Embodiments for Carrying Out the Invention

[0012] <Method for Producing Rubber Composition> The method for producing a rubber composition of the present invention includes a step of heating a crosslinked rubber in a reaction solvent containing an aldehyde having a hydrocarbon group with 2 or more carbon atoms and a boiling point of 230°C or lower at 300°C or lower to obtain a rubber composition containing a liquid hydrocarbon (hereinafter, may be referred to as a "decomposition step"). The method for producing a rubber composition of the present invention may have a drying step of drying the reaction product obtained in the decomposition step in addition to the decomposition step. In addition, the liquid hydrocarbon contained in the rubber composition produced by the production method of the present invention is a rubber molecule constituting the crosslinked rubber, and although it varies depending on the composition of the crosslinked rubber, when a crosslinked rubber derived from waste tires is used, it usually includes natural rubber, styrene-butadiene copolymer rubber, etc. Note that "liquid" means being in a liquid state at room temperature (25°C) and atmospheric pressure (0.1 MPa) or being easily solubilized in petroleum components (such as alcohol, diethyl ether, tetrahydrofuran) to become a liquid state.

[0013] According to the method for producing the rubber composition of the present invention, 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 thermal and solvent effects, and radicals and / or new bonds are generated. It is considered that hydrogen atoms released from aldehydes having a hydrocarbon group with 2 or more carbon atoms are attracted to the highly reactive radical species generated by these cleavages, and the radical reaction is stopped. Aldehydes having a hydrocarbon group with 2 or more carbon atoms are considered to be more likely to undergo hydrogen donation than alcohols, more likely to cause the termination of the radical reaction, and more likely to cause the termination of the radical reaction. In addition, with respect to oxygen required for the cleavage of the main chain of the rubber molecule, the primary aldehyde is oxidized to change to a primary carboxylic acid, thereby consuming the oxygen in the autoclave. As a result, since the cleavage of the main chain is suppressed, it is considered that a liquid hydrocarbon having a higher molecular weight than before can be obtained at a higher decomposition rate. Hereinafter, the details of the method for producing the rubber composition of the present invention will be described.

[0014] 〔Crosslinked rubber〕 The crosslinked rubber is a crosslinked product of a rubber component. As the rubber component that is a raw material of the crosslinked rubber, either a diene rubber or a non-diene rubber may be used. 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 the non-diene rubber 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.

[0015] Among these, since diene rubbers are generally used in rubber products such as tires, the rubber component preferably contains 50 mass% or more of a diene rubber. That is, the crosslinked rubber is preferably a crosslinked product of a rubber component containing 50 to 100 mass% of a diene rubber. More preferably, the rubber component contains 70 mass% or more of a diene rubber, and still more preferably, it contains 90 mass% or more of a diene rubber. Further, the diene rubber is preferably at least one selected from the group consisting of natural rubber, polyisoprene rubber, and styrene-butadiene copolymer rubber.

[0016] The crosslinking agent for the rubber component is not particularly limited, and examples thereof include sulfur-based crosslinking agents, organic peroxide-based crosslinking agents, acid crosslinking agents, polyamine crosslinking agents, resin crosslinking agents, sulfur compound-based crosslinking agents, and oxime-nitrosoamine-based crosslinking agents. Since a sulfur-based crosslinking agent (vulcanizing agent) is usually used for the rubber component of tires and the like, the crosslinked rubber preferably contains a vulcanized product vulcanized with a vulcanizing agent, that is, vulcanized rubber. By heating the vulcanized rubber at 300 °C or lower in a reaction solvent containing an aldehyde having a hydrocarbon group with 2 or more carbon atoms, the carbon-sulfur bonds mainly constituting the molecular structure of the vulcanized rubber undergo bond cleavage by heat and an exchange reaction due to a solvent effect or the like, and hydrogen atoms released from the aldehyde having a hydrocarbon group with 2 or more carbon atoms are attracted to the highly reactive radical species generated by the cleavage, and it is considered that the reaction of the radicals stops. The content of the vulcanized rubber in the crosslinked rubber is preferably 50 mass% or more, more preferably 70 mass% or more, still more preferably 90 mass% or more, and particularly preferably that the crosslinked rubber is vulcanized rubber (content is 100 mass%).

[0017] (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 tire durability and abrasion resistance. The filler may be either silica or carbon black used alone, or both silica and carbon black may be used.

[0018] 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. For example, it is preferable to use wet silica. The carbon black is not particularly limited and can be appropriately selected according to the purpose. For example, carbon blacks of FEF, SRF, HAF, ISAF, and SAF grades are preferable. The content of the filler in the crosslinked rubber is preferably 20 to 100 parts by mass, more preferably 30 to 90 parts by mass, based on 100 parts by mass of the rubber component.

[0019] The crosslinked rubber may be a crosslinked product of a rubber composition containing, in addition to the rubber component and the above filler, compounding agents usually used in the rubber industry, such as softeners, stearic acid, anti-aging agents, zinc oxide, vulcanization accelerators, etc., as required. Tires generally contain vulcanized rubber obtained by vulcanizing a rubber composition containing these compounding agents.

[0020] 〔Reaction solvent〕 The reaction solvent has a boiling point of 230°C or lower and contains an aldehyde having a hydrocarbon group with 2 or more carbon atoms. By selecting an aldehyde having a boiling point of 230°C or lower and having a hydrocarbon group with 2 or more carbon atoms as the reaction solvent, the crosslinking points of the crosslinked rubber are decomposed, but the cleavage of the main chain of the rubber molecules is suppressed, and the molecular weight of the recovered liquid hydrocarbon can be maintained high. This is presumably because oxidation deterioration occurs when alcohol is used as the reaction solvent, but oxidation deterioration is less likely to occur with aldehydes. If the number of carbon atoms of the hydrocarbon group of the aldehyde is less than 2, the molecular weight of the recovered liquid hydrocarbon cannot be maintained high. From the perspective of maintaining a higher molecular weight of the recovered liquid hydrocarbon, the hydrocarbon group preferably has 3 to 16 carbon atoms, more preferably 4 to 14 carbon atoms, still more preferably 4 to 12 carbon atoms, and even more preferably 6 to 10 carbon atoms.

[0021] The boiling point of the reaction solvent is 230 °C or lower under room temperature (25 °C) and atmospheric pressure (0.1 MPa). When the boiling point of the reaction solvent exceeds 230 °C, purification becomes difficult. The lower limit of the boiling point is not particularly limited, and it is usually higher than 80 °C and preferably liquid at 25 °C. The boiling point of the reaction solvent is preferably 85 °C or higher, more preferably 90 °C or higher, still more preferably 95 °C or higher, even more preferably 100 °C or higher, and even more preferably 105 °C or higher. Also, the boiling point of the reaction solvent is preferably 225 °C or lower, more preferably 220 °C or lower.

[0022] The hydrocarbon group of the aldehyde has a boiling point of 230 °C or lower and is not particularly limited as long as it has 2 or more carbon atoms. Examples include aliphatic groups and aromatic groups. The aliphatic group may be linear or branched, and may be a saturated aliphatic group or an unsaturated aliphatic group. Examples of the aliphatic group include ethyl group, 1-propyl group, 1-butyl group, 2-butyl group, tert-butyl group, 1-pentyl group, 2-methyl-1-pentyl group, 1-hexyl group, 1-heptyl group, 1-octyl group, 1-nonyl group, 1-decyl group, 1-dodecyl group; vinyl group, propenyl group, etc. Examples of the aromatic group include phenyl group and naphthyl group. The aldehyde having a hydrocarbon group with 2 or more carbon atoms may be used alone or in combination of two or more. In addition, it is not particularly limited except for having the above hydrocarbon group. For example, it may further have substituents such as a halogen atom, alkoxy, amino group, nitro group, sulfonyl group, and hydroxy group. The number of carbon atoms of the alkyl group (R) in the alkoxy (RO-) is preferably 1 to 8.

[0023] Aldehydes with a boiling point of 230 °C or lower and having a hydrocarbon group with 2 or more carbon atoms specifically include, for example, aldehydes having a propyl group (propanal), aldehydes having a butyl group (butanal), aldehydes having a pentyl group (pentanal), aldehydes having a hexyl group (hexanal), aldehydes having a heptyl group (heptanal), aldehydes having an octyl group (octanal), aldehydes having a nonyl group (nonanal), aldehydes having a decyl group (decanal), aldehydes having a phenyl group (benzaldehyde, cinnamaldehyde, etc.). It may have an alkyl group in the side chain. In the case of aldehydes having a phenyl group, for example, alkyl cinnamaldehydes can be mentioned, and amyl cinnamaldehyde is particularly preferred. When there are isomers, isomers are included. For aldehydes with a boiling point of 230 °C or lower and having a hydrocarbon group with 2 or more carbon atoms, solvents from various reagent manufacturers such as Tokyo Chemical Industry Co., Ltd. and FUJIFILM Wako Pure Chemical Corporation may be used.

[0024] The boiling point of the reaction solvent can be confirmed by the catalogs of various reagent manufacturers, and can also be confirmed by various books, for example, "Chemical Dictionary" by Tokyo Kagaku Dojin Co., Ltd., "Chemical Handbook" by Maruzen Co., Ltd., etc. For example, according to the catalog of Tokyo Chemical Industry Co., Ltd., the boiling point of 1 - hexanal is 131 °C, the boiling point of 1 - heptanal is 155 °C, the boiling point of 1 - octanal is 170 °C, the boiling point of 1 - nonanal is 192 °C, the boiling point of 1 - decanal is 208 °C, and the boiling point of benzaldehyde is 179 °C.

[0025] Among the above, from the viewpoint of maintaining a higher molecular weight of the recovered liquid hydrocarbon, the hydrocarbon group is preferably an aliphatic group, more preferably a saturated aliphatic group, and even more preferably a linear saturated aliphatic group. Specifically, the aldehyde having a boiling point of 230°C or lower and a hydrocarbon group having 2 or more carbon atoms is preferably at least one selected from the group consisting of aldehydes having a hexyl group (hexanal), aldehydes having a heptyl group (heptanal), aldehydes having an octyl group (octanal), and aldehydes having a nonyl group (nonanal), and aldehydes having a nonyl group (nonanal) are more preferred.

[0026] The reaction solvent may consist of an aldehyde having a boiling point of 230°C or lower and a hydrocarbon group having 2 or more carbon atoms, or may contain other solvents in addition to the aldehyde. However, from the viewpoint of increasing the decomposition rate of the liquid hydrocarbon, it is preferable that the aldehyde having a boiling point of 230°C or lower and a hydrocarbon group having 2 or more carbon atoms is the main component of the reaction solvent. Here, the main component means that the content of the aldehyde having a boiling point of 230°C or lower and a hydrocarbon group having 2 or more carbon atoms in the reaction solvent exceeds 50% by volume. The content of the aldehyde having a boiling point of 230°C or lower and a hydrocarbon group having 2 or more carbon atoms in the reaction solvent is preferably 70% by volume or more, more preferably 90% by volume or more, and may even be 100% by volume or more.

[0027] In the decomposition step, it is preferable to use the reaction solvent in a range where the ratio (Vs / Wg) of the volume [mL] (Vs) of the reaction solvent to the mass [mg] (Wg) of the crosslinked rubber is preferably 0.001 / 1 to 1 / 1, more preferably 0.005 / 1 to 0.1 / 1. By using the reaction solvent in the above range, the solvolysis reaction is more promoted, sufficient hydrogen atoms are supplied to the crosslinked rubber, the recombination of radicals generated by thermal decomposition is suppressed, and the crosslinked rubber can be efficiently decomposed.

[0028] 〔Reaction conditions of the decomposition step〕 (Temperature) In the decomposition step, the crosslinked rubber and the reaction solvent are heated at 300°C or lower. By setting the heating temperature to 300°C or lower, excellent energy savings can be achieved, and a decrease in the decomposition rate due to side reactions or the like can be suppressed. Incidentally, the heating temperature in the decomposition step may also be referred to as the decomposition temperature. By heating the crosslinked rubber at a lower temperature, the reaction involving the solvent can be prioritized to decompose the crosslinked rubber. The heating temperature is preferably 150°C or higher, more preferably 155°C or higher, still more preferably 160°C or higher, even more preferably exceeding 180°C, and preferably 250°C or lower, more preferably 240°C or lower, still more preferably 230°C or lower, even more preferably 220°C or lower, and even more preferably 210°C or lower.

[0029] (Decomposition time) In the decomposition step, the time for heating the crosslinked rubber (decomposition time) is preferably 30 minutes to 20 hours, more preferably 60 minutes to 18 hours, from the viewpoint of sufficiently advancing the decomposition reaction of the crosslinked rubber. When the crosslinked rubber does not contain a filler, the decomposition time can be 240 minutes or less, preferably 180 minutes or less.

[0030] (Pressure) In the decomposition step, the pressure applied to the crosslinked rubber and the reaction solvent is not particularly limited. From the viewpoints of the reaction rate of the decomposition reaction of the crosslinked rubber and resource and energy savings, it is preferably 0.1 to 2.0 MPa(G), more preferably 0.1 to 1.5 MPa(G). The unit "MPa(G)" means that the pressure is gauge pressure. When the pressure is 2.0 MPa(G) or lower, it is difficult to lower the molecular weight of the liquid hydrocarbon, and when the pressure is 0.1 MPa(G) or higher, the reaction solvent easily penetrates into the crosslinked rubber, and the reaction rate is easily increased.

[0031] (Atmosphere) In the decomposition step at 300°C or lower, the reaction atmosphere is not particularly limited, and the reaction may proceed in 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 in an atmosphere of a gas composed of air (hereinafter simply referred to as an air atmosphere), or in 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. From the viewpoint of performing the decomposition of the crosslinked rubber with more delicate equipment and further reducing the 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 still more preferably in an air atmosphere.

[0032] 〔Drying step〕 The method for producing the rubber composition of the present invention preferably has a drying step of drying the reaction product (rubber composition containing a liquid hydrocarbon) obtained in the decomposition step. For the reaction product, for example, warm air at 100 to 150°C may be blown. The warm air may be air or an inert gas such as nitrogen gas.

[0033] As described above, by heating the crosslinked rubber at 300°C or lower in a reaction solvent containing an aldehyde having a hydrocarbon group with a boiling point of 230°C or lower and having 2 or more carbon atoms, a rubber composition containing a liquid hydrocarbon can be obtained. The rubber composition thus obtained may be referred to as "decomposition-generated organic matter". The rubber composition (decomposition-generated organic matter) generally contains, in addition to the liquid product containing the liquid hydrocarbon obtained by the thermal decomposition of the crosslinked rubber, a solid content remaining without decomposition. Further, when waste tires are used as the crosslinked rubber, since tires usually contain a filler, the solid content also contains a filler. Before vulcanization, the raw rubber, in the case of isoprene rubber (IR), generally has a weight average molecular weight (Mw) of about 1.2 million and a number average molecular weight (Mn) of about 400,000. In the case of styrene-butadiene copolymer rubber (SBR), generally, the weight average molecular weight (Mw) is about 400,000 and the number average molecular weight (Mn) is about 100,000. The closer the Mw and Mn of the obtained liquid hydrocarbon are to these values, the more it means that rubber with a molecular chain close to the raw rubber is obtained. The Mw and Mn of the liquid hydrocarbon can be measured, for example, by gel permeation chromatography (GPC).

[0034] The liquid hydrocarbon produced by the above method can be used for the regeneration of crosslinked rubber. In addition, for the regeneration of crosslinked rubber, not only the liquid hydrocarbon alone is used as a raw material, but also in a state where the liquid hydrocarbon and the solid content obtained in the decomposition step are mixed, that is, without separating the liquid hydrocarbon from the rubber composition obtained in the decomposition step, the rubber composition may be used as a raw material for recycled rubber as it is. Thus, the rubber composition obtained by the method for producing a rubber composition of the present invention is a recycled rubber capable of regenerating crosslinked rubber (re-crosslinked rubber), and the method for producing a rubber composition of the present invention is a method for producing recycled rubber. However, the rubber composition (recycled rubber) in the present invention does not include powdered rubber obtained by pulverizing vulcanized rubber into powder.

[0035] <Re-crosslinked rubber> The re-crosslinked rubber of the present invention is a re-crosslinked rubber obtained by re-crosslinking a rubber composition produced by the method for producing a rubber composition of the present invention, contains the liquid hydrocarbon contained in the rubber composition as a rubber component, and the content of the liquid hydrocarbon in the rubber component is 1 to 100% by mass. That is, the re-crosslinked rubber of the present invention is a re-crosslinked product of a rubber composition containing a liquid hydrocarbon obtained by thermal decomposition of crosslinked rubber as a rubber component, and the rubber component contains at least 1% by mass of the liquid hydrocarbon, and may be 100% by mass. The content of the liquid hydrocarbon in the rubber component may be 5% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more. Further, the content of the liquid hydrocarbon in the rubber component may be 70% by mass or less, 60% by mass or less, or 50% by mass or less.

[0036] When the content of the liquid hydrocarbon in the rubber component is less than 100% by mass, the other rubber components used together with the liquid hydrocarbon are not particularly limited. Incidentally, the other rubber components used together with the liquid hydrocarbon may be referred to as pure rubber components. Examples of the pure rubber component include the above-mentioned rubber components cited as the rubber components that are the raw materials of the crosslinked rubber. Among them, at least one selected from the group consisting of natural rubber (NR) and synthetic diene rubbers is preferable, and at least one selected from the group consisting of natural rubber, polyisoprene rubber, polybutadiene rubber, and styrene-butadiene copolymer rubber is more preferable.

[0037] The rubber composition used as the raw material of the re-crosslinked rubber of the present invention may contain, in addition to the rubber component containing the liquid hydrocarbon, a filler, a vulcanizing agent, a vulcanization accelerator, a softening agent, stearic acid, an antioxidant, zinc white, and the like. As described above, the rubber composition produced by the production method of the rubber composition of the present invention contains, in addition to the liquid product containing the liquid hydrocarbon obtained by thermal decomposition of the crosslinked rubber, the solid content remaining without decomposition, and the solid content may also contain a filler. The rubber composition used as the raw material of the re-crosslinked rubber may contain the solid content remaining without decomposition. By producing the re-crosslinked rubber using the solid content remaining without decomposition together with the liquid hydrocarbon obtained by thermal decomposition of the crosslinked rubber, the environmental burden can be further reduced. The re-crosslinking conditions of the rubber composition produced by the production method of the rubber composition of the present invention are not particularly limited. The re-crosslinked rubber of the present invention may be a re-crosslinked rubber obtained by vulcanizing a rubber component containing a liquid hydrocarbon with a vulcanizing agent.

[0038] <Tire> The tire of the present invention is made of the re-crosslinked rubber of the present invention. By configuring the tire using a re-crosslinked rubber obtained by re-crosslinking a rubber composition containing a liquid hydrocarbon obtained by thermal decomposition of crosslinked rubber, a tire with a small environmental load can be obtained. The tire may be obtained by crosslinking after molding using an uncrosslinked rubber composition according to the type and members of the tire to be applied, or after obtaining a semi-crosslinked rubber from an uncrosslinked rubber composition once through a pre-crosslinking process or the like, and then further performing full crosslinking after molding using this. As the gas filled in the tire, in addition to normal air or air with adjusted oxygen partial pressure, inert gases such as nitrogen, argon, and helium can be used.

[0039] <Rubber industrial products> The rubber industrial products of the present invention are made of the re-crosslinked rubber of the present invention. Examples of rubber industrial products include automotive parts excluding the above tires, hose tubes, vibration-proof rubbers, conveyor belts, crawlers, cables, sealing materials, etc., ship parts, building materials, etc. By configuring the rubber industrial products using the re-crosslinked rubber of the present invention, industrial products with a small environmental load can be obtained.

Examples

[0040] Hereinafter, the present invention will be described in more detail with reference to examples, but these examples are for the purpose of exemplifying the present invention and do not limit the present invention in any way.

[0041] <Preparation of vulcanized rubber> The following vulcanized rubbers were prepared as vulcanized rubbers. Vulcanized rubber (IR): A vulcanized rubber obtained by vulcanizing polyisoprene rubber Vulcanized rubber (SBR): A vulcanized rubber obtained by vulcanizing styrene-butadiene copolymer rubber Vulcanized rubber (NR): Vulcanized rubber obtained by vulcanizing a rubber composition containing at least natural rubber and carbon black

[0042] <Production A of Liquid Hydrocarbons> 〔Example 1a〕 (Decomposition step) 0.4 g of vulcanized rubber (IR) in the form of small pieces about 1 mm in size and 5 mL of 1-nonanal were charged into an autoclave (manufactured by EYELA, pressure-resistant container, trade name "HIP-30L"). The inside of the autoclave was sealed, and the autoclave was placed in a heating container (manufactured by EYELA, personal organic synthesis apparatus Chemistation, trade name "PPV-CTRL1"), and the charged materials were heated at 200 °C for 2 hours in an air atmosphere. After the heating was completed, the heating container was returned to room temperature (25 °C) with cooling water, and the reaction product was brought to room temperature.

[0043] (Drying step) The reaction product obtained in the decomposition step was dried under the condition of nitrogen flow at 130 °C using a spray-type test tube concentrator (manufactured by EYELA, trade name "MGS-3100") to obtain the decomposition-produced organic matter of Example 1a.

[0044] 〔Examples 2a to 6a, Comparative Examples 1a to 5a〕 The decomposition step and the drying step were carried out in the same manner as in Example 1a, except that the reaction solvent was changed to the solvents shown in Table 1, to obtain the decomposition-produced organic matter of Examples 2a to 6a and Comparative Examples 1a to 5a.

[0045] <Production B of Liquid Hydrocarbons> 〔Examples 1b to 3b〕 The decomposition step and the drying step were carried out in the same manner, except that the heating temperature and heating time of the charged materials in the decomposition step of Example 1a were changed from 200 °C and 2 hours to the reaction conditions shown in Table 2, to obtain the decomposition-produced organic matter of Examples 1b to 2b. In addition, for comparison, in Table 2, the results under the same conditions as in Example 1a were shown as Example 3b.

[0046] <Production C of Liquid Hydrocarbons> 〔Examples 1c to 5c〕 As the vulcanized rubber, instead of vulcanized rubber (IR), vulcanized rubber (SBR) was used, and as the reaction solvent, the reaction solvents shown in Table 3 were used. Otherwise, the decomposition step and the drying step were carried out in the same manner as in Example 1a to obtain the decomposition-produced organic substances of Examples 1c to 5c.

[0047] [Comparative Example 1c] As the vulcanized rubber, instead of vulcanized rubber (IR), vulcanized rubber (SBR) was used. Otherwise, the decomposition step and the separation step were carried out in the same manner as in Comparative Example 1a to obtain the decomposition-produced organic substance of Comparative Example 1c.

[0048] [Comparative Example 2c] As the vulcanized rubber, instead of vulcanized rubber (IR), vulcanized rubber (SBR) was used. Otherwise, the decomposition-produced organic substance of Comparative Example 2c was obtained in the same manner as in Comparative Example 2a.

[0049] [Comparative Example 3c] As the vulcanized rubber, instead of vulcanized rubber (IR), vulcanized rubber (SBR) was used. Otherwise, the decomposition-produced organic substance of Comparative Example 3c was obtained in the same manner as in Comparative Example 3a.

[0050] <Analysis of Decomposition-Produced Organic Substances> The decomposition-produced organic substances obtained in the examples and comparative examples were dissolved in tetrahydrofuran and analyzed by gel permeation chromatography (GPC). From the analysis results, the solubilization rate and the weight average molecular weight (Mw) of the decomposition-produced organic substances were measured. In addition, a calibration curve was created using tetrahydrofuran solutions of pure rubber components with different concentrations. The liquid hydrocarbons in tetrahydrofuran were quantified using the calibration curve, and the decomposition rate was calculated.

[0051] The conditions for GPC measurement are as follows. ·Column: Manufactured by Tosoh Corporation: TSKgel GMHXL ·Eluent: Tetrahydrofuran ·Flow rate: 1 mL / min ·Temperature: 40 °C ·Detector: RI

[0052] In Table 1, with the weight-average molecular weight (Mw) obtained in Comparative Example 1a set as 100.0, the weight-average molecular weights (Mw) of Examples 1a to 6a and Comparative Examples 2a to 5a were indexed. Also, with the decomposition rate obtained in Comparative Example 1a set as 100.0, the decomposition rates of Examples 1a to 6a and Comparative Examples 2a to 5a were indexed.

[0053] In Table 2, with the weight-average molecular weight (Mw) obtained in Comparative Example 1a set as 100.0, the weight-average molecular weights (Mw) of Examples 1b to 3b were indexed. Also, with the decomposition rate obtained in Comparative Example 1a set as 100.0, the decomposition rates of Examples 1b to 3b were indexed.

[0054] In Table 3, with the weight-average molecular weight (Mw) obtained in Comparative Example 1c set as 100.0, the weight-average molecular weights (Mw) of Examples 1c to 5c and Comparative Examples 2c to 3c were indexed. Also, with the decomposition rate obtained in Comparative Example 1c set as 100.0, the decomposition rates of Examples 1c to 5c and Comparative Examples 2c to 3c were indexed. The results are shown in Tables 1 to 3.

[0055]

Table 1

[0056]

Table 2

[0057]

Table 3

[0058] <Production of Liquid Hydrocarbons D> 〔Example 1d〕 In Example 1a, the vulcanized rubber (IR) was changed to vulcanized rubber (NR); and the heating time (decomposition time) of the input was changed from 2 hours to the time shown in Table 4, and the decomposition process was carried out in the same manner. Thereafter, purification for solvent removal was carried out, and the drying process was advanced to obtain the decomposition-produced organic matter of Example 1d.

[0059] [Comparative Example 1d] In Comparative Example 1a, the vulcanized rubber (IR) was changed to vulcanized rubber (NR); the reaction solvent was changed from 1-heptanol to 1-octanol; and the heating time (decomposition time) of the input was changed from 6 hours to the time shown in Table 4. The decomposition process and the separation process were carried out in the same manner, and the decomposition-generated organic matter of Comparative Example 1d was obtained.

[0060] [Comparative Example 2d] In Comparative Example 1a, the vulcanized rubber (IR) was changed to vulcanized rubber (NR); the reaction solvent was changed from 1-heptanol to 1-octanol; and the heating time (decomposition time) of the input was changed from 6 hours to the time shown in Table 4. The decomposition process and the separation process were carried out in the same manner, and the decomposition-generated organic matter of Comparative Example 2d was obtained.

[0061] [Manufacture of Re-vulcanized Rubber] A rubber composition was prepared according to the content shown in Table 5 and vulcanized to obtain a vulcanized rubber.

[0062] The details of the components shown in Table 5 are as follows. NR: Natural rubber Carbon black: SAF grade 6C: Antioxidant, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, manufactured by Ouchi Shinsei Chemical Industry Co., Ltd., trade name "No Crack 6C" DM: Vulcanization accelerator, di-2-benzothiazolyldisulfide, manufactured by Sanshin Chemical Industry Co., Ltd., trade name "Sanseler DM" NS: Vulcanization accelerator, N-t-butyl-2-benzothiazylsulfenamide, manufactured by Ouchi Shinsei Chemical Industry Co., Ltd., trade name "Noxseler NS" DPG: Vulcanization accelerator, 1,3-diphenylguanidine, manufactured by Sanshin Chemical Industry Co., Ltd., trade name "Sanseler D"

[0063] [Analysis of Decomposition-Generated Organic Matter] The manufactured decomposition-generated organic matter was analyzed in the same manner as the decomposition-generated organic matter of Example 1a, and the weight average molecular weight (Mw) and the decomposition rate were measured and shown in Table 4 with three significant figures. The molecular weights shown in Table 4 are, for example, in the case of Example 1d, 271×10 3 , that is, it means 271,000.

[0064] <Characteristics Evaluation of Vulcanized Rubber> For Comparative Examples 1e to 5e, Example 1e, and Example 2e, the tensile strength and loss tangent (tanδ) of each vulcanized rubber were evaluated and shown in Table 5.

[0065] 1. Tensile Strength The tensile strength of each vulcanized rubber was evaluated from the viewpoint of the breaking strength (TB; Tensile strength at Break). The breaking strength was measured as the maximum tensile force required to stretch the vulcanized rubber to 100% elongation at room temperature (23°C) and break it based on JIS K 6251 (2017). The obtained value of the breaking strength was expressed as an index with the value of the breaking strength of Comparative Example 1e being 100. The larger the index value, the greater the breaking strength of the vulcanized rubber.

[0066] 2. Loss Tangent (tanδ) The loss tangent (tanδ) of each vulcanized rubber was measured using a viscoelasticity measuring device (manufactured by Rheometric Scientific) under the conditions of a temperature of 50°C, a strain of 10%, and a frequency of 15 Hz. The obtained value of tanδ was expressed as an index with the reciprocal value of the tanδ of Comparative Example 1e being 100. The larger the index value, the better the low heat generation property of the vulcanized rubber.

[0067]

Table 4

[0068]

Table 5

[0069] As can be seen from Tables 1 to 3, in the examples, a rubber composition containing a higher molecular weight liquid hydrocarbon can be produced at a higher decomposition rate compared to the comparative examples. Also, as can be seen from Table 4, the vulcanized rubber produced from the rubber composition containing the liquid hydrocarbon of the example maintains a high tensile strength even when 70 parts by mass is added (Example 2e), compared to the vulcanized rubber produced from the rubber composition containing the liquid hydrocarbon of the comparative example, and it can be seen that tanδ can also be maintained.

Claims

1. A method for producing a rubber composition, comprising heating a crosslinked rubber in a reaction solvent containing an aldehyde having a hydrocarbon group with 2 or more carbon atoms and a boiling point of 230 °C or lower at 300 °C or lower to obtain a rubber composition containing a liquid hydrocarbon, wherein the hydrocarbon group has 6 to 10 carbon atoms.

2. The method for producing a rubber composition according to claim 1, wherein the hydrocarbon group is a linear saturated aliphatic group.

3. The method for producing a rubber composition according to claim 1 or 2, wherein the aldehyde contains nonanal.

4. The method for producing a rubber composition according to any one of claims 1 to 3, wherein the crosslinked rubber is heated at 150 to 250 °C.

5. The method for producing a rubber composition according to any one of claims 1 to 4, wherein the crosslinked rubber is a crosslinked product of a rubber component containing 50 to 100% by mass of a diene rubber.

6. The method for producing a rubber composition according to any one of claims 1 to 5, wherein the crosslinked rubber contains a vulcanized rubber.

7. A method for producing a re-crosslinked rubber, comprising: obtaining a rubber composition by the method for producing a rubber composition according to any one of claims 1 to 6; and re-crosslinking the obtained rubber composition to obtain a re-crosslinked rubber, wherein the liquid hydrocarbon contained in the rubber composition is included as a rubber component, and the content of the liquid hydrocarbon in the rubber component is 1 to 100% by mass.

8. A method for producing a tire, comprising producing a tire with the re-crosslinked rubber obtained by the method for producing a re-crosslinked rubber according to claim 7.

9. A method for producing a rubber industrial product, comprising producing a rubber industrial product with the re-crosslinked rubber obtained by the method for producing a re-crosslinked rubber according to claim 7. ​

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