Devulcanized rubber, rubber composition containing the devulcanized rubber, and pneumatic tire having a rubber portion formed by vulcanization molding of the rubber composition

Abstract

To provide a desulfurized rubber that shows excellent physical properties after vulcanization, a rubber composition containing a desulfurized rubber and having excellent processability, and a pneumatic tire including a rubber portion composed of a vulcanized and molded rubber composition.SOLUTION: A desulfurized rubber includes the mixture of a desulfurizing agent containing a compound represented by the formula (1), (2), (3) or (4) (R1-R8 independently represent a hydrogen atom, an oxygen atom, or an alkyl group) and a vulcanized rubber.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a devulcanized rubber exhibiting good physical properties and processability after vulcanization, a rubber composition containing the devulcanized rubber, and a pneumatic tire having a rubber portion formed by vulcanization molding of the rubber composition. [Background technology]

[0002] In recent years, due to increasing environmental awareness, there has been a strong demand for recycling waste vulcanized rubber generated from used tires and other rubber products.

[0003] The following Patent Document 1 describes a devulcanizing agent for vulcanized rubber that contains a halogenated diphenyl disulfide compound.

[0004] The following Patent Document 2 describes a desulfurizing agent containing a disulfide compound and a trivalent phosphorus compound. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-323004 [Patent Document 2] Japanese Patent Application Publication No. 8-337603 Summary of the Invention [Problem to be solved by the invention]

[0006] As a result of intensive research, the present inventors have found that the above-mentioned conventional techniques are primarily intended to improve the odor of devulcanized rubber, and that there is room for further improvement in the post-vulcanization physical properties of rubber compositions containing devulcanized rubber.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a devulcanized rubber that exhibits good physical properties after vulcanization, a rubber composition that contains the devulcanized rubber and has excellent processability, and a pneumatic tire that has a rubber portion formed by vulcanization molding of the rubber composition. [Means for solving the problem]

[0008] The above problems can be solved by the following configuration. That is, the present invention provides a compound represented by any one of the following formulas (1) to (4): [ka] The present invention relates to a devulcanized rubber obtained by mixing a devulcanizing agent containing (R1 to R8 each independently represent a hydrogen atom, an oxygen atom, or an alkyl group) with vulcanized rubber.

[0009] In the above devulcanized rubber, the devulcanizing agent preferably contains at least one selected from the group consisting of 2,2'-dithiodianiline and 2,2'-dithiodianiline.

[0010] The present invention also relates to a rubber composition containing the devulcanized rubber, which preferably contains 1 to 30 parts by mass of the devulcanized rubber when the total amount of unvulcanized rubber components in the rubber composition is taken as 100 parts by mass.

[0011] Furthermore, the present invention relates to a pneumatic tire having a rubber portion formed by vulcanization molding of the above-mentioned rubber composition. Effect of the Invention

[0012] Conventional devulcanizing agents tend to cut not only the sulfur crosslinks in vulcanized rubber but also the main chains of rubber molecules, so when the devulcanized vulcanized rubber is re-vulcanized, the post-vulcanization physical properties such as tensile strength tend to deteriorate.

[0013] The devulcanized rubber according to the present invention uses a sulfide compound having an amino group as a devulcanizing agent, and is prepared by mixing the mixture of the compound and vulcanized rubber, and therefore exhibits good physical properties after vulcanization. The reason for the good vulcanization properties is believed to be that the amino group of the devulcanizing agent nucleophilically promotes the cleavage reaction of the sulfur crosslinks in the vulcanized rubber, so that the cleavage of the sulfur crosslinks proceeds selectively while the cleavage of the main chain of the rubber molecules is suppressed. In addition, as the cleavage of the sulfur crosslinks of the vulcanized rubber proceeds selectively, the Mooney viscosity of the devulcanized rubber and the rubber composition containing the devulcanized rubber decreases, improving processability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The devulcanized rubber according to the present invention comprises a compound represented by any one of the following formulas (1) to (4): [ka] (R1 to R8 each independently represent a hydrogen atom, an oxygen atom, or an alkyl group) is mixed with vulcanized rubber. The desulfurizing agent may contain each of the compounds represented by formulas (1) to (4) alone, or may contain a plurality of compounds among the compounds represented by formulas (1) to (4).

[0015] As the compound represented by the above formulae (1) to (4), dithioaniline in which x is 2 is preferable, and particularly preferable examples include 2,2'-dithiodianiline having amino groups in the ortho positions relative to the sulfide bond in both phenyl groups, and 4,4'-dithiodianiline having amino groups in the para positions relative to the sulfide bond in both phenyl groups.

[0016] The devulcanizing agent used in the present invention may contain compounds other than the compounds represented by the above formulas (1) to (4). However, in order to obtain a devulcanized rubber that exhibits good post-vulcanization physical properties and processability, and in order to suppress the odor of the obtained devulcanized rubber, the content of the compound represented by the above formula (1) in the devulcanizing agent is preferably 80 mass% or more, more preferably 90 mass% or more, and particularly preferably 100 mass%.

[0017] The vulcanized rubber that is the raw material for devulcanized rubber is made by vulcanizing rubber components, and vulcanized rubber waste materials generated from used tires and other rubber products can be suitably used. Examples of rubber components that are the raw material for vulcanized rubber include natural rubber, polyisoprene rubber, olefin-based rubber such as ethylene propylene rubber (EPM), halogenated butyl rubber such as brominated butyl rubber (Br-IIR), and other synthetic rubbers including polyurethane rubber, acrylic rubber, fluororubber, silicone rubber, and chlorosulfonated polyethylene.

[0018] The sulfur used as the raw material for vulcanized rubber may be any ordinary rubber sulfur, such as powdered sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur, etc.

[0019] The vulcanized rubber that is the raw material for devulcanized rubber can be a rubber composition that has been vulcanized by appropriately blending, together with a rubber component and sulfur, compounding agents that are normally used in the rubber industry, such as vulcanization accelerators, carbon black, silica, silane coupling agents, zinc oxide, stearic acid, vulcanization retarders, organic peroxides, antioxidants, softeners such as wax and oil, and processing aids, as necessary.

[0020] As the carbon black, any carbon black known to those skilled in the art can be used, such as SAF, ISAF, HAF, FEF, GPF, etc. When the total amount of the rubber components in the vulcanized rubber that is the raw material for the devulcanized rubber is taken as 100 parts by mass, the content of the carbon black is preferably 30 to 100 parts by mass, and more preferably 30 to 60 parts by mass.

[0021] As the vulcanization accelerator, those vulcanization accelerators usually used for rubber vulcanization, such as sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators, may be used alone or in appropriate mixtures.

[0022] As the age resistor, age resistors generally used for rubber, such as aromatic amine-based age resistors, amine-ketone-based age resistors, monophenol-based age resistors, bisphenol-based age resistors, polyphenol-based age resistors, dithiocarbamate-based age resistors, and thiourea-based age resistors, may be used alone or in appropriate mixtures.

[0023] The compounding ratio of the devulcanizing agent, which is the raw material for the devulcanized rubber, to the vulcanized rubber is preferably 0.5 to 20 parts by mass, and more preferably 1 to 10 parts by mass, when the total amount of the rubber components in the vulcanized rubber is 100 parts by mass.

[0024] The devulcanized rubber according to the present invention is obtained by mixing the devulcanizing agent and the vulcanized rubber. There is no particular limitation on the method of mixing the devulcanizing agent and the vulcanized rubber, but an example of the method is passing the devulcanizing agent and the vulcanized rubber through a roll known to those skilled in the art while mixing the devulcanizing agent and the vulcanized rubber so that the devulcanizing agent can cut the sulfur crosslinks of the vulcanized rubber. In this case, the roll temperature may be appropriately cooled or heated.

[0025] Since the obtained devulcanized rubber has selectively cut sulfur crosslinks of the vulcanized rubber to be reused, good post-vulcanization physical properties can be obtained even when mixed with unvulcanized (unused) rubber components. When the total amount of unvulcanized rubber components in the rubber composition is taken as 100 parts by mass, it is preferable that the devulcanized rubber is contained in an amount of 1 to 30 parts by mass. The rubber components, sulfur, vulcanization accelerators, carbon black, silica, silane coupling agents, zinc oxide, stearic acid, vulcanization retarders, organic peroxides, antioxidants, softeners such as wax and oil, processing aids, etc. that can be used to constitute the rubber composition containing the devulcanized rubber can be the same as those described above.

[0026] In addition, the method for compounding the devulcanized rubber and each of the above-mentioned components is not particularly limited, and any of the following may be used: a method in which the compounding components other than the vulcanization components such as sulfur and a vulcanization accelerator are previously mixed to prepare a master batch, and the remaining components are then added and further kneaded; a method in which the components are added in any order and kneaded; and a method in which all of the components are added simultaneously and kneaded.

[0027] The rubber composition containing the devulcanized rubber has excellent processability and excellent physical properties after vulcanization. Therefore, the devulcanized rubber and the rubber composition containing the devulcanized rubber according to the present invention are particularly suitable for use in pneumatic tires having a large amount of rubber. EXAMPLES

[0028] The present invention will be explained more specifically below by describing examples thereof.

[0029] (Preparation of vulcanized rubber as raw material for devulcanized rubber) For 100 parts by mass of the rubber component, a Daihan Lab Mixer was used according to the compounding recipe in Table 1. In the first mixing stage, the compounding ingredients other than sulfur and the vulcanization accelerator were added to the rubber component and kneaded, and then in the second mixing stage, sulfur and the vulcanization accelerator were added to the obtained kneaded product and kneaded to prepare a rubber composition.

[0030] [Table 1]

[0031] Details of each component in Table 1 are as follows. Natural rubber: STR20 Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd. Zinc oxide: "Zinc oxide type 1" manufactured by Mitsui Mining & Smelting Co., Ltd. Anti-aging agent: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Kao Corporation's "Lunac S-20" Sulfur: "Powdered sulfur for rubber 150 mesh" manufactured by Hosoi Chemical Industry Co., Ltd. - Vulcanization accelerator: "Noccela NS" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0032] The rubber composition was vulcanized at 150°C for 25 minutes to produce a sheet-like vulcanized rubber, and the vulcanized rubber was pulverized using a roll (6-inch roll manufactured by Kansai Roll Co., Ltd.) to prepare powdered vulcanized rubber (vulcanized rubber powder).

[0033] (Manufacture of devulcanized rubber) The vulcanized rubber powder and devulcanizing agent were mixed in the ratio shown in Table 2, and then the mixture of vulcanized rubber powder and devulcanizing agent was cooled using a roll (6-inch roll manufactured by Kansai Roll Co., Ltd.) with a surface cooled to 25°C, and was repeatedly passed through the roll for 40 minutes at minimum intervals while being cooled, thereby producing devulcanized rubber according to Examples 1 to 4 and Comparative Example 2. For the purpose of comparison, in Comparative Example 1, rubber that was not devulcanized was produced.

[0034] [Table 2]

[0035] Details of each desulfurizing agent in Table 2 are as follows. Desulfurizing agent 1 (compound represented by formula (1)): "2,2'-dithiodianiline" manufactured by Tokyo Chemical Industry Co., Ltd. Desulfurizing agent 2 (compound represented by formula (1)): "4,4'-dithiodianiline" manufactured by Tokyo Chemical Industry Co., Ltd. Desulfurization agent 3: "Diphenyl disulfide" manufactured by Tokyo Chemical Industry Co., Ltd.

[0036] (Preparation of Rubber Composition) Each component was compounded with respect to 100 parts by mass of the rubber component according to the compounding recipe in Table 3, and kneaded using a lab mixer manufactured by Daihan Co., Ltd. to prepare the rubber compositions of Examples 5-8 and Comparative Examples 3-5.

[0037] Details of each component in Table 3 are as follows: Natural rubber: STR20 Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd. Zinc oxide: "Zinc oxide type 1" manufactured by Mitsui Mining & Smelting Co., Ltd. Anti-aging agent: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Kao Corporation's "Lunac S-20" Sulfur: "Powdered sulfur for rubber 150 mesh" manufactured by Hosoi Chemical Industry Co., Ltd. - Vulcanization accelerator: "Noccela NS" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0038] (Evaluation of rubber composition processability (Mooney viscosity measurement)) Measurements were performed in accordance with JIS K6300 (with an L-shaped rotor), with 1 minute preheating and 4 minutes measurement at a temperature of 100° C. The values ​​are expressed as an index with the value of Comparative Example 3 being 100. A smaller value indicates a lower Mooney viscosity of the rubber composition and better processability.

[0039] (Evaluation of physical properties after vulcanization of vulcanized rubber containing devulcanized rubber (measurement of tensile product and tensile strength)) The rubber compositions of Examples 5 to 8 and Comparative Examples 3 to 5 were vulcanized at 150° C. for 25 minutes to prepare test specimens of predetermined shapes, and the following tests were carried out using the test specimens obtained. Tensile product: The tensile strength and elongation at break were measured in a tensile test (dumbbell type No. 3) in accordance with JIS K6251, and the product was taken as the tensile product. It was expressed as an index with the value of Comparative Example 3 being 100. The larger the value, the better the physical properties after vulcanization. Note that vulcanized rubber of a rubber composition containing devulcanized rubber tends to have significantly worse elongation at break than vulcanized rubber of a rubber composition containing non-devulcanized rubber. For this reason, even if the value is less than 100, if it is 95 or more, it is acceptable compared to the value (100) of Comparative Example 3, which is a vulcanized rubber of a rubber composition containing non-devulcanized rubber. Tear strength: Tear strength was measured using a tear test (crescent type) in accordance with JIS K6252, and expressed as an index with the value of Comparative Example 3 set at 100. A higher value indicates better physical properties after vulcanization.

[0040] [Table 3]

[0041] It is evident from the results in Table 3 that the rubber compositions according to Examples 5 to 8 have excellent processability, and the vulcanized rubbers thereof have excellent physical properties after vulcanization.

Claims

1. A devulcanized rubber obtained by mixing a devulcanizing agent containing 4,4'-dithiodianiline with vulcanized rubber.

2. A rubber composition comprising the devulcanized rubber according to claim 1.

3. 3. The rubber composition according to claim 2, wherein the devulcanized rubber is contained in an amount of 1 to 30 parts by mass when the total amount of unvulcanized rubber components in the rubber composition is taken as 100 parts by mass.

4. A pneumatic tire comprising a rubber portion formed by vulcanization molding the rubber composition according to claim 2 or 3.

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