JP2007099950A - Method for production of natural rubber and rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a natural rubber that can reduce the rubber viscosity by mastication, thus improves the miscibility, dispersibility of raw material rubber and compounding of the ingredients and increases the fabrication property, additionally saves the manufacturing cost. <P>SOLUTION: In this method for production of natural rubber, at least one selected from the group consisting of compounds having a molecular weight of more than 200 typified by following compounds (1) and (2) is added and carried out the mastication to prepare natural rubber, wherein the compounds (1) are tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide and dipentamethylenethiuram tetrasulfide and the compound (2) is dibenzothiazyl disulfide. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing natural rubber and a rubber composition. More specifically, the present invention relates to a natural rubber that can reduce the viscosity of raw natural rubber and improve the dispersibility, mixing property, processability, etc. of the compounding agent of the rubber composition. The present invention relates to a rubber production method and a rubber composition using natural rubber produced by this method.

  Natural rubber is widely used in large quantities in industrial and household rubber products such as tires, anti-vibration rubbers, belts, hoses and the like because of its excellent physical properties. Such rubber products are mixed with various compounding agents such as vulcanizing agents and reinforcing agents. In order to facilitate the mixing work and the molding workability of the rubber products, the natural rubber used as a raw material is first kneaded. Process is essential.

  Natural rubber has a higher molecular weight and higher viscosity than other synthetic rubbers, and therefore, kneading that cuts the main chain of rubber molecules to lower the molecular weight and imparts plasticity to raw rubber is generally performed. Kneading is to impart sufficient plasticity by applying mechanical shearing force to the raw rubber, which makes it easy to disperse various compounding agents such as vulcanizing agents and fillers. Furthermore, in the subsequent processes such as rolling and extrusion, the operability is improved by improving the dimensional stability and the surface condition and making it difficult to scorch.

  In such a mastication process, large-scale facilities are required to secure the plasticity of natural rubber, and the power, labor, and time are required and the cost is affected.

Conventionally, various peptizers have been used as peptizers to improve the peptization effect, but amine compounds and maleimide compounds should be added to further reduce the viscosity of unvulcanized rubber and improve processability. Is proposed (Patent Documents 1 and 2), and it is disclosed that a drying process after washing natural rubber in two or more stages is performed (Patent Document 3).
JP 2001-192506 A JP 2002-69242 A JP-A-11-292902

  By the way, as the above-mentioned chelating agent, an aromatic disulfide compound and an aromatic mercaptan compound having an action of chemically cutting rubber molecules to impart plasticity are used, but usually 0.01 parts by weight per 100 parts by weight of raw rubber. Generally, it is added in a small amount of about 5 parts by weight. That is, it is necessary to use a chelating agent, which is costly. In addition, in the use of amine compounds and maleimide compounds described in Patent Documents 1 and 2, it is rather a special compound, and in Patent Document 3, it is a multi-step process, which is cost and processability. It cannot be said that it is advantageous compared to the use of a peptizer.

  In view of the above problems, an object of the present invention is to reduce the viscosity of natural rubber, improve the mixing and dispersibility of raw rubber and compounding agent, and further improve the molding processability, and further reduce the manufacturing cost of natural rubber. It is an object of the present invention to provide a production method and a rubber composition using natural rubber produced by the method.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors chemically cut rubber molecules from compounding agents already used in large quantities as rubber compounding agents in the same manner as chelating agents. The inventors have found a specific component having an effect of imparting plasticity and have arrived at the present invention.

That is, the present invention provides a natural rubber characterized by adding one or more selected from the group of compounds having a molecular weight of 200 or more represented by the following general formula (1) and general formula (2). It is a manufacturing method.

In formula, n is an integer of 2-4. R _{1 to} R ₄ are hydrocarbon groups, which may all be the same or different.

  In the present invention, the compound represented by the general formula (1) is tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis (2-ethylhexyl) thiuram disulfide, dipentamethylenethiuram tetrasulfide, The compound represented by the general formula (2) is preferably dibenzothiazyl disulfide.

  The compounding amount of the compound is preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the natural rubber component.

  Furthermore, this invention is a rubber composition using the natural rubber manufactured by the manufacturing method of the said natural rubber.

  According to the present invention, the viscosity of the raw rubber can be effectively reduced by adding the above-mentioned compound during mastication of unvulcanized rubber, particularly natural rubber, and the raw rubber and compounding agent can be kneaded and dispersed. And moldability can be improved. In addition, since the compound according to claim 2 is a vulcanization accelerator that is already used as a normal rubber compounding agent, the compounding agent can be obtained at low cost and has little influence on the production cost of the rubber composition. It can be said.

That is, the rubber composition production method of the present invention is one or more selected from the group of compounds having a molecular weight of 200 or more represented by the following general formula (1) and general formula (2) when kneading natural rubber. It is to add and knead.

In formula, n is an integer of 2-4. R _{1 to} R ₄ are hydrocarbon groups, which may all be the same or different.

The hydrocarbon group of R _{1 to} R _{4 in} the general formula (1) is aliphatic or aromatic, and examples thereof include an alkyl group, an alkenyl group, an aryl group, a cycloalkyl group, a cycloalkenyl group, and a phenyl group. Can be mentioned.

  Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secondary butyl, t-butyl, pentyl, isopentyl, secondary pentyl, neopentyl, t-pentyl, hexyl, secondary hexyl, heptyl, 2 Secondary heptyl, octyl, 2-ethylhexyl, secondary octyl, nonyl, secondary nonyl, decyl, secondary decyl, undecyl, secondary undecyl, dodecyl, secondary dodecyl, tridecyl, isotridecyl, secondary tridecyl, tetradecyl, secondary tetradecyl , Hexadecyl, secondary hexadecyl, stearyl, icosyl, docosyl, tetracosyl, triacontyl, 2-butyloctyl, 2-butyldecyl, 2-hexyloctyl, 2-hexyldecyl, 2-octyldecyl, 2-hexyldecyl, 2-octyl Decyl, 2-decyl tetradecyl, 2-dodecyl-hexadecyl, 2-hexadecyl octadecyl, 2-tetradecyl-octadecyl, monomethyl branched - and the like isostearyl group.

  Examples of the alkenyl group include vinyl, allyl, propenyl, butenyl, isobutenyl, pentenyl, isopentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tetradecenyl, oleyl group and the like.

  As an aryl group, for example, phenyl, toluyl, xylyl, cumenyl, mesityl, benzyl, phenethyl, styryl, cinnamyl, benzhydryl, trityl, ethylphenyl, propylphenyl, butylphenyl, pentylphenyl, hexylphenyl, heptylphenyl, octylphenyl, Nonylphenyl, decylphenyl, undecylphenyl, dodecylphenyl, phenylphenyl, benzylphenyl, styrenated phenyl, p-cumylphenyl, α-naphthyl, β-naphthyl group and the like can be mentioned.

  Examples of the cycloalkyl group and cycloalkenyl group include a cyclopentyl, cyclohexyl, cycloheptyl, methylcyclopentyl, methylcyclohexyl, methylcycloheptyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, methylcyclopentenyl, methylcyclohexenyl, methylcycloheptenyl group. Etc.

  Among the above hydrocarbon groups, a methyl group, an ethyl group, a propyl group, a butyl group and the like are preferable.

  The compounds represented by the general formulas (1) and (2) have a molecular weight of 200 or more, and if the molecular weight is less than 200, the radical scavenging action is insufficient and the main chain scission of the rubber molecules is reduced. It becomes difficult to obtain the effect of reducing the viscosity of natural rubber by kneading.

  These compounds may be used alone or in combination of two or more.

  Among the compounds represented by the general formula (1), tetramethylthiuram disulfide (TT), tetraethylthiuram disulfide (TET), tetrabutylthiuram disulfide (TBT), tetrakis (2-ethylhexyl) thiuram disulfide (TOT), dith Pentamethylene thiuram tetrasulfide (TRA) is used in a large amount in a normal rubber compounding agent as a thiuram vulcanization accelerator, and is easily available, and the compounding cost is advantageous.

  Of the compounds represented by the general formula (2), dibenzothiazyl disulfide (DM) is used as a thiazole vulcanization accelerator in ordinary rubber compounding, and is also advantageous in terms of cost.

  The compounding amount of the compound is preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the natural rubber component. If the blending amount is less than 0.5 parts by weight, the effect of the invention cannot be obtained sufficiently, and if it exceeds 10 parts by weight, the effect of decreasing the viscosity is saturated, which is uneconomical.

  The type of natural rubber used in the present invention is not particularly limited. For example, natural rubbers of various grades (grades) classified by RSS (ribbed smoked sheet) # 1-6, TMR (technically rated rubber) SMR, STR, SIR, etc. are used. Moreover, these natural rubbers can be mixed and used at an arbitrary ratio.

  In the present invention, the mixing device used for the mastication work is not particularly limited. For example, various types and capacities of mixers such as an open roll, a Banbury mixer, a closed mixer such as a kneader can be used, and these may be used in combination.

  The method for producing natural rubber according to the present invention comprises adding the above compound to natural rubber and kneading at a kneading temperature of 100 to 160 ° C., preferably 150 ° C. or less, for 2 to 20 minutes, preferably within 15 minutes. To produce a kneaded rubber having a desired viscosity, for example, Mooney viscosity adjusted to 30 to 65. This mastication process may be performed in multiple stages.

  In addition to the compound according to the present invention, a conventional chelating agent may be added and used in combination.

  The rubber composition of the present invention can be obtained by blending various blending agents with natural rubber alone or blended with synthetic rubber produced by the above production method, and by mold vulcanization, open vulcanization, injection molding, etc. Used for various rubber products.

  Synthetic rubbers used in blends include isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), diene synthetic rubber such as nitrile rubber (NBR), butyl rubber (IIR), ethylene propylene rubber (EPM) , EPDM) and other non-diene synthetic rubbers may be used, and a plurality of them may be used, and the blend ratio with natural rubber is also arbitrary.

  In addition, the rubber composition includes fillers such as carbon black and silica, vulcanizing agents such as sulfur, vulcanization accelerators commonly used in the rubber industry, process oils, anti-aging agents, zinc white, stearic acid. Various compounding agents such as vulcanization aids can be appropriately compounded and used according to the purpose of use of the rubber product.

  Next, the present invention will be described in further detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

  The kneaded rubbers of Examples 1 and 2 and Comparative Examples 1 to 6 shown in Table 1 were prepared by adding additives to the raw rubber and using a Banbury mixer and a 20-inch open roll having a capacity of 20 liters (A) to ( C) was prepared by mastication in three stages. The Mooney viscosity (ML1 + 4, 100 ° C.) at each stage was measured according to JIS K6300. The results are shown in Table 1.

  Raw rubber used is natural rubber (SIR3L), SBR (manufactured by JSR, SBR1502), additives are DM (dibenzothiazyl disulfide), CZ (N-cyclohexyl-2-benzothiazylsulfenamide), amount added (Parts by weight) are as shown in Table 1.

(A) The mastication conditions of the Banbury mixer were masticated at a start temperature of 80 ° C. for 4 minutes and discharged from the mixer (discharge temperature 120 ° C.) to obtain a masticated rubber (A).
(B) Once cooled, the kneaded rubber (A) is reintroduced into the Banbury mixer, masticated at a start temperature of 80 ° C. for 4 minutes, discharged from the mixer (discharge temperature 130 ° C.) to obtain a kneaded rubber (B), a sample B.
(C) The masticated rubber (B) once cooled was masticated while turning back for 2 minutes with a roll having a roll surface temperature of 80 ° C. to obtain a sheet having a thickness of 1 cm.

  Next, 100 parts by weight of each kneaded rubber (B), 50 parts by weight of carbon black (N330), 3 parts by weight of zinc white, 1 part by weight of stearic acid, 25 parts by weight of aroma oil, 2 parts by weight of sulfur, vulcanization acceleration 1 part by weight of an agent (CZ) was blended and mixed for 3 minutes with a Banbury mixer to prepare a rubber composition. As a result of observing the carbon black dispersibility with an optical microscope for the vulcanized rubber of the obtained rubber composition, the dispersibility of Examples 1 and 2 to which DM according to the present invention was added was a comparative example in which CZ was added. It was better than 2 and 3.

  As is apparent from the results in Table 1, the kneaded rubber (natural rubber) of Examples 1 and 2 according to the present invention effectively reduces the viscosity by reducing the molecular weight due to main chain scission of the rubber molecules by the compound according to the present invention. It can reduce, and it can also contribute to the improvement of mixability and workability. On the other hand, when CZ outside the scope of the present invention is added, the effect of lowering the viscosity of the rubber is clearly low, and the effect of lowering the viscosity is not expressed against the synthetic rubber such as SBR. It can be seen that there are specific effects only on natural rubber.

  The natural rubber obtained by the present invention can be suitably used as a rubber material for various rubber products such as tires, vibration-proof rubbers, conveyor belts, belts and hoses.

Claims (4)

A method for producing natural rubber, comprising adding one or more selected from the group of compounds having a molecular weight of 200 or more represented by the following general formula (1) and general formula (2) and masticating.

In formula, n is an integer of 2-4. R _{1 to} R ₄ are hydrocarbon groups, which may all be the same or different. The compound represented by the general formula (1) is tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis (2-ethylhexyl) thiuram disulfide, dipentamethylenethiuram tetrasulfide,
The method for producing natural rubber according to claim 1, wherein the compound represented by the general formula (2) is dibenzothiazyl disulfide. 3. The method for producing natural rubber according to claim 1, wherein the compounding amount of the compound is 0.5 to 10 parts by weight with respect to 100 parts by weight of the natural rubber component. A rubber composition produced by using the natural rubber produced by the method for producing natural rubber according to claim 1.