Devulcanized rubber manufacturing method

Abstract

To provide a production method of desulfurized rubber that exhibits excellent physical properties after vulcanization.SOLUTION: In a production method of desulfurized rubber, desulfurized rubber is produced by mixing and heating vulcanized rubber and a desulfurizing agent while imposing shearing strength. A heating temperature in mixing is 100°C or lower. The vulcanized rubber is diene rubber. The desulfurizing agent is an amine compound which is solid at 25°C. Preferably, the vulcanized rubber and the desulfurizing agent are mixed and heated while imposing shearing strength using any one or more among a roller, a banbury mixer, an extruder, a gear pump, a mesh type mixer, a kneader, and Co-Kneader. Preferably, the diene rubber is at least one kind selected from the group consisting of natural rubber, butadiene rubber, and styrene-butadiene rubber.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing devulcanized rubber that exhibits good physical properties after vulcanization. [Background technology]

[0002] In recent years, with the rise in environmental awareness, there has been a strong demand for the reuse of waste vulcanized rubber generated from used tires and other rubber products.

[0003] Patent Document 1 listed below describes a method for obtaining a re-vulcanizable devulcanized product, in which the devulcanizing agent is an amine compound, the rubber contains an EPDM polymer, the sulfur-crosslinked rubber is heated to a temperature of 250 to 350°C during devulcanization, and the devulcanization of the sulfur-crosslinked rubber is carried out at a pressure of 5 to 10 MPa. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4633988 Summary of the Invention [Problem to be solved by the invention]

[0005] As a result of extensive research, the present inventors have found that the above-mentioned conventional techniques are limited in the types of rubber that can be used to make vulcanized rubber, which is the raw material for devulcanized rubber.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing devulcanized rubber that exhibits good physical properties after vulcanization.

[0007] The above problems can be solved by the following configuration: The present invention relates to a method for producing devulcanized rubber, which produces devulcanized rubber by heating and mixing vulcanized rubber and a devulcanizing agent while applying shearing force, characterized in that the heating temperature during mixing is 100°C or less, the vulcanized rubber is a diene rubber vulcanized rubber, and the devulcanizing agent is an amine compound that is solid at 25°C.

[0008] In the above-mentioned method for producing devulcanized rubber, it is preferable to heat and mix the vulcanized rubber and the devulcanizing agent while applying shear force using one or more of a roller mill, a Banbury mixer, an extruder, a gear pump, an intermeshing mixer, a kneader, and a co-kneader.

[0009] In the above-mentioned method for producing devulcanized rubber, the diene rubber is preferably at least one selected from the group consisting of natural rubber, butadiene rubber, and styrene-butadiene rubber. [Effects of the Invention]

[0010] In the method for producing devulcanized rubber according to the present invention, a vulcanized rubber is produced by heating and mixing a vulcanized rubber and a devulcanizing agent while applying shear force. However, by controlling the heating temperature during mixing to 100°C or below, even vulcanized rubbers made from diene rubbers, which do not have high heat resistance, are prevented from scission of the main chains of the rubber molecules due to heating, thereby improving the physical properties of the resulting devulcanized rubber and of rubber compositions containing the devulcanized rubber after vulcanization. To efficiently achieve devulcanization of vulcanized rubber even when the heating temperature during mixing is 100°C or below, the present invention uses an amine compound that is solid at 25°C as the devulcanizing agent while applying shear force when heating and mixing the vulcanized rubber and the devulcanizing agent. As a result, the physical properties of the resulting devulcanized rubber and of rubber compositions containing the devulcanized rubber after vulcanization are improved. The reason why such an effect is obtained is not clear, but it is thought that when vulcanized rubber and a solid amine compound at 25°C are mixed at a heating temperature of 100°C or less during mixing, the melting of the amine compound is moderately suppressed, shear force is efficiently applied to the vulcanized rubber and amine compound, and the nucleophilic attack of the amine compound on the sulfur cross-linking sites of the vulcanized rubber proceeds efficiently, which may result in the selective cleavage reaction of the sulfur cross-linking sites of the vulcanized rubber.

[0011] If devulcanized rubber obtained using a short-chain alkylamine compound such as normal butylamine as a devulcanizing agent is used as a tire raw material, there is concern that rubber containing the devulcanized rubber will be released to the outside as the tire wears, posing an environmental problem. However, amine compounds that are solid at 25°C have a low environmental impact. In addition, amine compounds that are solid at 25°C are easier to work with than amine compounds that are liquid. Therefore, the method for producing devulcanized rubber according to the present invention not only produces devulcanized rubber that exhibits good post-vulcanization physical properties, but is also excellent in terms of the environment and workability. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the method for producing devulcanized rubber according to the present invention, the vulcanized rubber used as the raw material is a vulcanized rubber of a diene rubber. The diene rubber is not particularly limited, and examples thereof include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, and styrene-isoprene-butadiene copolymer rubber. These may be used alone or in combination of two or more. Preferred diene rubbers are natural rubber, butadiene rubber, and styrene-butadiene rubber, or a blend of two or more of these.

[0013] The method for producing devulcanized rubber according to the present invention uses an amine compound that is solid at 25°C as a devulcanizing agent. Amine compounds that are solid at 25°C generally fall under the category of long-chain alkylamine compounds, and long-chain alkylamine compounds having 12 to 18 carbon atoms are preferred. Examples of such alkylamine compounds include hexadecylamine (16 carbon atoms, melting point 26°C), dodecylamine (12 carbon atoms, melting point 44°C), and stearylamine (18 carbon atoms, melting point 53°C).

[0014] In the method for producing devulcanized rubber according to the present invention, from the viewpoint of producing devulcanized rubber that exhibits good post-vulcanization physical properties, it is preferable that the amount of devulcanizing agent used relative to the vulcanized rubber is 1 to 30 parts by mass when the total amount of the vulcanized rubber is 100 parts by mass.

[0015] The sulfur used as a raw material for vulcanized rubber may be any ordinary rubber sulfur, such as powdered sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur, etc.

[0016] The vulcanized rubber that is the raw material for devulcanized rubber can be a rubber composition that has been vulcanized and contains, in addition to 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 needed.

[0017] 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 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 carbon black is preferably 30 to 100 parts by mass, and more preferably 30 to 60 parts by mass.

[0018] As the vulcanization accelerator, vulcanization accelerators commonly 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.

[0019] As the antiaging agent, antiaging agents commonly used for rubber, such as aromatic amine antiaging agents, amine-ketone antiaging agents, monophenol antiaging agents, bisphenol antiaging agents, polyphenol antiaging agents, dithiocarbamate antiaging agents, and thiourea antiaging agents, may be used alone or in appropriate mixtures.

[0020] In the method for producing devulcanized rubber according to the present invention, a vulcanized rubber and a devulcanizing agent are heated and mixed while applying shear force. Examples of methods for applying shear force to the vulcanized rubber and the devulcanizing agent include a rolling mill, Banbury mixer, extruder, gear pump, intermeshing mixer, kneader, or co-kneader commonly used by those skilled in the art, in which the vulcanized rubber and the devulcanizing agent are heated and mixed while applying shear force. In the present invention, when applying shear force to the vulcanized rubber and the devulcanizing agent, a rolling mill, Banbury mixer, extruder, gear pump, intermeshing mixer, kneader, or co-kneader may be used alone or in combination. When a rolling mill is used, examples include a method in which the devulcanizing agent and the vulcanized rubber are passed through a rolling mill known to those skilled in the art so that the devulcanizing agent can cleave the sulfur crosslinks in the vulcanized rubber while mixing them. When a Banbury mixer is used, for example, the devulcanizing agent and vulcanized rubber are placed in the Banbury mixer and stirred in the Banbury mixer so that the devulcanizing agent can sever the sulfur crosslinks in the vulcanized rubber. The shear pressure when applying shear force may be the same as the shear pressure applied to the material to be kneaded when using a roller or Banbury mixer, and may be, for example, about 0.1 to 10 MPa.

[0021] The heating temperature when the vulcanized rubber and devulcanizing agent are mixed under heat must be controlled to 100° C. or less. From the viewpoint of producing devulcanized rubber that exhibits good post-vulcanization physical properties by effectively applying shear force to the vulcanized rubber and the amine compound that is solid at 25° C., the heating temperature is preferably 50° C. or less, and particularly preferably below the melting point of the devulcanizing agent used.

[0022] The resulting devulcanized rubber has selectively cleaved the sulfur crosslinks of the vulcanized rubber to be reused, and therefore, even when mixed with unvulcanized (virgin) rubber components, good post-vulcanization physical properties can be obtained. The rubber composition preferably contains 1 to 30 parts by mass of devulcanized rubber, assuming the total amount of unvulcanized rubber components in the rubber composition is 100 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, and the like that can be used to constitute the rubber composition blended with the devulcanized rubber are the same as those described above.

[0023] The method for compounding the devulcanized rubber and the above-mentioned components is not particularly limited, and any of the following may be used: a method in which the components other than the vulcanization-related components such as sulfur and vulcanization accelerator are pre-mixed to form 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 the components are added simultaneously and kneaded.

[0024] The rubber composition containing the devulcanized rubber has excellent processability and excellent physical properties after vulcanization. Therefore, the devulcanized rubber according to the present invention and the rubber composition containing the devulcanized rubber are particularly suitable for use in pneumatic tires having a large amount of rubber. [Example]

[0025] The present invention will be explained in more detail below by way of examples.

[0026] (Preparation of vulcanized rubber as raw material for devulcanized rubber) A Daihan Lab Mixer was used to mix 100 parts by mass of rubber components according to the compounding recipe in Table 1. In the first mixing stage, all compounding ingredients except for sulfur and vulcanization accelerator were added to the rubber components and kneaded, and then in the second mixing stage, sulfur and vulcanization accelerator were added to the resulting mixture and kneaded to prepare a rubber composition.

[0027] [Table 1]

[0028] Details of each component in Table 1 are as follows: Natural rubber: STR20 Styrene butadiene rubber: Asahi Kasei "Tufden 2000" Butadiene rubber: Asahi Kasei "NF35" Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd. Silica: Oriental Silica "Nipsil AQ" 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: Hosoi Chemical Industry Co., Ltd. "Powdered sulfur for rubber, 150 mesh" Vulcanization accelerator 1: "Noccela NS" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: "Noccela D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0029] The rubber composition was vulcanized at 150°C for 25 minutes to produce a sheet of 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 (NR type) and powdered vulcanized rubber (mixed type).

[0030] (Devulcanized rubber manufacturing) The powdered vulcanized rubber (NR type) or vulcanized rubber (mixed type) was mixed with a devulcanizing agent in the proportions 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. The mixture was repeatedly passed through the roll at minimum intervals for 40 minutes to produce devulcanized rubbers according to Examples 1 to 7 (heating temperature during mixing: 25°C). For comparison, in Comparative Examples 1 and 2, non-devulcanized powdered vulcanized rubber (NR type) and vulcanized rubber (mixed type) were used as they were.

[0031] [Table 2]

[0032] Details of each desulfurizing agent in Table 2 are as follows: Desulfurizing agent 1: "Hexadecylamine" manufactured by Tokyo Chemical Industry Co., Ltd. (carbon number 16, melting point 26°C) Desulfurizing agent 2: Tokyo Chemical Industry Co., Ltd. "Dodecylamine" (carbon number 12, melting point 44°C) Desulfurizing agent 3: "Stearylamine" manufactured by Tokyo Chemical Industry Co., Ltd. (carbon number 18, melting point 53°C)

[0033] (Preparation of Rubber Composition) Each component was blended with 100 parts by mass of the rubber component according to the formulation in Table 3, and kneaded using a Daihan Lab Mixer to prepare a rubber composition containing the devulcanized rubber produced in Examples 1 to 7, or the non-devulcanized vulcanized rubber (NR type) and vulcanized rubber (mixed type) of Comparative Examples 1 and 2.

[0034] 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: Hosoi Chemical Industry Co., Ltd. "Powdered sulfur for rubber, 150 mesh" Vulcanization accelerator: "Noccela NS" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0035] (Evaluation of physical properties after vulcanization of vulcanized rubber containing devulcanized rubber (tensile strength measurement)) The rubber compositions containing the devulcanized rubbers produced in Examples 1 to 7, or the non-devulcanized vulcanized rubbers (NR type) and vulcanized rubbers (mixed type) of Comparative Examples 1 and 2 were vulcanized at 150°C for 25 minutes to prepare test specimens of a predetermined shape, and the following tests were carried out using the obtained test specimens. 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 1 set to 100. A larger value indicates better physical properties after vulcanization.

[0036] [Table 3]

[0037] The results in Table 3 show that the vulcanized rubbers (vulcanized rubbers 3 to 9) of the rubber compositions containing the devulcanized rubbers produced in Examples 1 to 7 have superior post-vulcanization physical properties compared to the vulcanized rubbers (vulcanized rubbers 1 to 2) of the rubber compositions containing the non-devulcanized vulcanized rubber vulcanized rubbers (NR type) and vulcanized rubbers (mixed type) of Comparative Examples 1 and 2.

Claims

1. A method for producing devulcanized rubber, comprising heating and mixing vulcanized rubber and a devulcanizing agent while applying a shear force, the method comprising: the desulfurizing agent is hexadecylamine, dodecylamine, or stearylamine; The heating temperature during mixing is equal to or lower than the melting point of the desulfurizing agent used, the vulcanized rubber is a diene rubber vulcanized rubber, The method for producing devulcanized rubber, wherein the devulcanizing agent is an amine compound that is solid at 25°C.

2. 2. The method for producing devulcanized rubber according to claim 1, wherein the vulcanized rubber and the devulcanizing agent are heated and mixed while applying shear force using one or more of a roll mill, a Banbury mixer, an extruder, a gear pump, an intermeshing mixer, a kneader, and a co-kneader.

3. 3. The method for producing devulcanized rubber according to claim 1, wherein the diene rubber is at least one selected from the group consisting of natural rubber, butadiene rubber, and styrene-butadiene rubber.

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