JP2008143972A - Manufacturing method for natural rubber composition, natural rubber composition and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a natural rubber composition appropriately adjusting a viscosity of the natural rubber composition by a simple kneading method without increasing the number of kneading step and enhancing carbon black dispersibility. <P>SOLUTION: In the manufacturing method for the natural rubber composition, the rubber composition containing 20-120 pts.wt. of carbon black and/or silica at its total amount based on 100 pts.wt. of natural rubber is manufactured. At the first kneading step, a formulated compound in which 15-30 pts.wt. of carbon black and/or silica and 2-20 pts.wt. of zinc oxide are added to 100 pts.wt. of natural rubber is kneaded, and at the second kneading step, the residual amount of carbon black and/or silica and the formulation agent other than a vulcanization system are added/kneaded to the rubber mixture obtained at the first step. At the third kneading step, the rubber mixture obtained at the second step is re-kneaded, and at the fourth kneading step, a vulcanization system formulation agent is added/kneaded to the rubber mixture obtained in the third step. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a natural rubber composition used for rubber products such as pneumatic tires, and more specifically, imparts a desired Mooney viscosity to the rubber composition without increasing the number of kneading steps, thereby improving processability. Furthermore, the present invention relates to a method for producing a natural rubber composition capable of further improving the dispersibility of carbon black and silica, a natural rubber composition obtained by the production method, and a pneumatic tire using the natural rubber composition.

  Natural rubber is widely used as a rubber material for pneumatic tires, anti-vibration rubber, seismic isolation rubber, various industrial and household rubber products. Such natural rubber has a rubber composition obtained by kneading a rubber compound to which a reinforcing agent such as carbon black and silica and various compounding agents are kneaded by a kneading machine through a processing process such as rolling and a molding process. It is used for the sulfur process.

  Conventionally, natural rubber has a rubber molecular weight larger than that of synthetic rubber, and various compounding agents are difficult to knead uniformly than synthetic rubber. Therefore, rubber is kneaded with a kneading accelerator as the first step of the kneading process. It is practiced to adjust the molecular weight appropriately to lower the rubber viscosity. In this mastication, carbon mastication may be performed in which a reinforcing agent such as carbon black is partially added and kneaded. In the second kneading step, the remaining reinforcing agent such as carbon black and a compounding agent other than the vulcanization system are added and kneaded, and in the final step, a vulcanization system compounding agent such as sulfur and a vulcanization accelerator is added and kneaded. To obtain a rubber composition.

  By the way, in natural rubber compounding such that the compounding amount of carbon black or silica of the rubber composition is 20 parts by weight or more, even if a peptizer is used in the first step, the viscosity reduction after mastication is not sufficient, The rubber composition desired after the final kneading step cannot be obtained, and there is a problem that the dispersion of carbon black, silica and various compounding agents becomes insufficient. In order to adjust the rubber viscosity, the rubber mixture after the completion of the second kneading process may be re-kneaded one to several times, and the kneading process takes a long time and affects productivity. Further, the peptizers are expensive, and there are problems that the use of a large amount thereof involves an increase in the cost of the rubber composition and a decrease in rubber physical properties.

  In Patent Document 1 below, an ester of an aromatic polycarboxylic acid and a polyoxyalkylene derivative is added to natural rubber instead of a peptizer to reduce the gel amount of natural rubber and improve processability. A method of kneading is described. Patent Document 2 proposes a natural rubber masterbatch having an amide bond decomposition process of natural rubber latex, and describes that the processability and reinforcement of the natural rubber composition are improved.

In addition, in order to solve the problem of bad odor such as ammonia and butyraldehyde generated during mastication of natural rubber and the deterioration of the environment, a method of masticating by adding zinc oxide to natural rubber during mastication is disclosed (patent document) 3, 4).
JP 2002-69235 A JP 2004-99625 A JP-A-11-222502 JP 2006-257237 A

  However, the mastication method described in Patent Document 1 requires a specific compounding agent such as an ester of an aromatic polyvalent carboxylic acid and a polyoxyalkylene derivative. In addition, in the technique described in Patent Document 2, natural rubber latex is used. It is necessary to use a protease or an aromatic polycarboxylic acid derivative in this step, and there is a problem that the process is complicated and costs increase.

  Further, Patent Documents 3 and 4 are effective in reducing bad odor when kneaded with natural rubber, but do not mention at all about the viscosity adjustment and dispersibility improvement of the rubber composition by adding zinc oxide.

  Accordingly, an object of the present invention is to provide a natural rubber composition that tends to have the above problems in kneadability including 20 parts by weight or more of carbon black and / or silica in the total amount in view of the above situation. Natural rubber composition that can adjust the viscosity of natural rubber composition moderately by a simple kneading method and improve the dispersibility of carbon black, silica, and various compounding agents that affect processability and reinforcement It is providing the manufacturing method of a rubber composition.

  As a result of intensive studies to solve the above problems, the present inventor has found that zinc oxide, which is generally added to a rubber composition, has an appropriate amount of carbon black or silica in the first step (kneading step) during natural rubber kneading. Together with the kneading, it has been found that zinc oxide can moderately reduce the rubber viscosity of the natural rubber composition by the action of breaking the intermolecular bond of the natural rubber.

  That is, the present invention is a method for producing a natural rubber composition for producing a rubber composition containing 20 to 120 parts by weight of carbon black and / or silica in a total amount with respect to 100 parts by weight of natural rubber. In the first kneading step, a blend obtained by adding 15 to 30 parts by weight of carbon black and / or silica and 2 to 20 parts by weight of zinc oxide to 100 parts by weight of natural rubber is kneaded, and then the second kneading. In the step, the remaining carbon black and / or silica and a compounding agent other than the vulcanization system are added and kneaded to the rubber mixture obtained in the first step, and the rubber obtained in the second step in the third kneading step. In the fourth kneading step, the mixture is kneaded again, and a vulcanizing compounding agent is added to the rubber mixture obtained in the third step, followed by kneading.

  In the method for producing the natural rubber composition of the present invention, the third kneading step can be omitted.

  The present invention also provides a natural rubber composition obtained by the above-described method for producing a natural rubber composition.

  Furthermore, the present invention is a pneumatic tire characterized in that the natural rubber composition is used in at least a part of a pneumatic tire.

  According to the method for producing a natural rubber composition of the present invention, even in a natural rubber composition containing a relatively large amount of carbon black or silica, zinc oxide is combined with carbon black and silica in the first kneading step (kneading step). By a simple method of kneading, the rubber viscosity can be lowered moderately, imparting a desired rubber viscosity to the rubber composition without increasing the number of kneading steps, improving processability, and further, carbon black and silica, The dispersibility of various compounding agents can be improved and the rubber properties can be improved.

  Hereinafter, embodiments of the present invention will be described.

  The natural rubber composition according to the present invention contains carbon black and / or silica in a total amount of 20 to 120 parts by weight with respect to 100 parts by weight of natural rubber. Examples of natural rubber include ribbed smoked sheets (RSS # 1 to # 4), technical rating rubber (TSR), and the like.

  In the present invention, examples of the kneader used include rubber kneading equipment usually used in the rubber industry, such as a closed Banbury mixer, a pressure kneader, and an open roll, for mass production in the tire industry and the like. A Banbury mixer is suitable.

  In the present invention, the carbon black used is not particularly limited, and carbon black having various colloidal characteristics, particle diameters, and the like can be used. Specific examples include various grades of carbon black such as SAF, ISAF, HAF, FEF, GPF, SRF, and MT, and these can be used alone or in combination as a function of the rubber composition.

  Further, the natural rubber composition of the present invention can be used by blending silica, and may be blended with silica alone or in combination with the above carbon black. Examples of the silica include precipitated silica and dry silica by a wet method, and the grade thereof is not particularly limited, and commercially available products such as Nipsil AQ and VN3 of Tosoh Silica Co., Ltd. and Ultrazil VN3 of Degussa Corporation can be used.

  The blending amount of carbon black and / or silica of the natural rubber composition in the present invention is blended by 20 to 120 parts by weight in total with respect to 100 parts by weight of the natural rubber component. When the compounding amount of carbon black or silica is less than 20 parts by weight, sufficient reinforcing effect cannot be obtained, and characteristics such as strength, elastic modulus, and abrasion resistance of the rubber composition are not sufficiently expressed. The rubber viscosity is increased and the kneadability and processability are inferior, and the dispersibility of the carbon black is also deteriorated so that the expected rubber properties cannot be exhibited.

  The natural rubber composition according to the present invention may contain a synthetic rubber in addition to natural rubber as a rubber component. In this case, the natural rubber is contained in the rubber composition at 50% by weight or more, preferably 60% by weight or more. If the natural rubber component is less than 50% by weight, characteristics specific to natural rubber such as rubber strength and wear resistance cannot be obtained.

  Rubber components other than natural rubber 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 ( Examples thereof include olefin-based synthetic rubbers such as EPM and EPDM, and one or more selected from these groups can be selected and blended with natural rubber. These synthetic rubbers are added and kneaded to the natural rubber mixture obtained in the first kneading step in the kneading step after the second kneading step.

  The production method of the natural rubber composition of the present invention is the first kneading step (kneading) with respect to 100 parts by weight of the natural rubber of the total amount of all carbon black and silica blended in the rubber composition. The compound which added 15-30 weight part of the inside and 2-20 weight part of zinc oxide was thrown into kneading machines, such as a Banbury mixer, and knead | mixed.

  If the amount of carbon black or silica in the first step is less than 15 parts by weight, the rubber viscosity of the mixture is too low, and the workability such as over-adhesion to the roll is reduced in the roll operation after kneading and exceeds 30 parts by weight. And carbon black tend to be poorly dispersed, which adversely affects the dispersibility of the final mixed rubber.

  Moreover, if the addition amount of zinc oxide in the first step is in the range of 2 to 20 parts by weight, the total amount blended in the rubber composition may be added, or a part of zinc oxide is divided. And may be added. If the amount of zinc oxide is less than 2 parts by weight, the number of cuts in the intermolecular bonds of natural rubber will be insufficient and the effect of reducing the viscosity of the rubber will not be manifested. The workability such as over-adhesion on the roll is reduced by the roll work.

  In the first step, the peptizer (peptizer) used in the conventional mastication step can be used in combination, but the amount added can be reduced to a smaller amount than in the past, This can contribute to cost reduction of the rubber composition. The amount of the peptizer is usually less than 0.2 parts by weight with respect to 100 parts by weight of the natural rubber component, and in the present invention, it should be reduced to 0.1 parts by weight or less, and further to 0.05 parts by weight or less. Can do.

  Peptide accelerators include pentamethylene dithiocarbamic acid piperidine salt, dibenzamide diphenyl disulfide, a mixture of dibenzamide diphenyl disulfide and stearic acid, or a zinc salt of benzamide thiophenol, a cyclohexylamine salt of 2-mercaptobenzothiazole, 2- Examples include mercaptobenzothiazole, N-cyclohexyl-2-benzothiazolylsulfenamide, and N-phenyl-N′-isopropyl-p-phenylenediamine. One or more selected from these are used. be able to.

  In the next second kneading step, the remaining carbon black and silica in the rubber mixture obtained in the first step, the remaining zinc oxide when not added in the first step, various blends other than the vulcanization system Addition agent and other synthetic rubber when blended with rubber are added and kneaded with a kneader such as a Banbury mixer until the rubber temperature reaches a predetermined temperature.

  In the next third kneading step, the rubber mixture obtained in the second step is kneaded again with a kneader such as a Banbury mixer until a predetermined temperature is reached, and then discharged from the kneader. This step is performed when the rubber viscosity is adjusted in the first and second steps, and when the dispersibility of the compounding agent such as carbon black is insufficient. This can shorten the kneading cycle and improve productivity.

  The fourth kneading step is the final kneading step in the present invention. In the fourth step, the rubber mixture obtained in the third step (or the rubber mixture obtained in the second step when the third step is omitted) is added to a vulcanizing agent such as sulfur, a vulcanization accelerator, and a vulcanization acceleration aid. A natural rubber composition can be obtained by adding a vulcanizing compounding agent such as an agent and kneading with a kneading machine such as a Banbury mixer at a predetermined kneading temperature.

  In addition to the above components, the natural rubber composition according to the present invention can be appropriately mixed with a rubber compounding agent used in a normal rubber composition. Examples of compounding agents include calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, alumina, clay, talc, magnesium oxide and other reinforcing agents, anti-aging agents, plasticizers such as oil and wax, stearic acid, petroleum Examples thereof include resins, vulcanizing agents such as sulfur, vulcanization accelerators, vulcanization acceleration aids, and the like.

  The natural rubber composition according to the present invention is used for various industrial and household rubber products such as anti-vibration rubber, seismic isolation rubber, and conveyor belt as well as various parts such as treads, sidewalls and bead parts of pneumatic tires. Can be used.

  EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to only these examples.

  In the first step shown in Table 1, 100 parts by weight of natural rubber was mixed with a predetermined amount of carbon black, zinc oxide, and peptizer, and charged into a 200 liter Banbury mixer. After kneading to a predetermined temperature, the mixture was discharged from the kneader to obtain a rubber mixture. The sheet processability of this rubber mixture was evaluated using a biaxial 20 inch roll. “○” when there is no problem in sheet workability, “△” when there is some problem such as easy sticking to the roll during sheet processing or difficulty in winding around the roll, but “△” when the sheet can be processed. Those that could not be processed due to adhesion or inability to wind were shown in the table as “x”. When the sheet workability was evaluated as “x”, the evaluation was stopped without performing the subsequent process evaluation.

  Next, in the second kneading step, after the rubber mixture obtained in the first step is once cooled to room temperature, the remaining carbon black and zinc oxide listed in Table 1 are added, and a compounding agent other than the vulcanization system is added, The rubber was kneaded with the Banbury mixer until the rubber temperature reached a predetermined temperature, discharged, and cooled to room temperature.

  In the next third kneading step, the rubber mixture obtained in the second step was kneaded again with the Banbury mixer until a predetermined temperature was reached, then discharged, and cooled to room temperature. However, Examples 2 and 3 omitted this step.

  In the fourth kneading step (final kneading step), sulfur and a vulcanization accelerator are added to the rubber mixture obtained in the second or third step and kneaded until the predetermined temperature is reached by the Banbury mixer. A natural rubber composition was obtained by discharging. The natural rubber composition was evaluated for Mooney viscosity and carbon black dispersibility according to the following methods. The results are shown in Table 1.

[Mooney viscosity]
The Mooney viscosity (ML1 + 4) at 100 ° C. was measured according to JIS K6300.

[Carbon black dispersibility]
Using a viscoelasticity measuring device RPA2000 manufactured by Alpha Technologies Co., Ltd., using a vulcanized rubber vulcanized at 150 ° C. for 30 minutes as a sample, under conditions of a temperature of 60 ° C. and a frequency of 1.667 Hz, the strain is increased to 0.5 to 45% The value (Pain effect) obtained by subtracting the minimum shear force from the maximum shear force when changed was shown as an index with the conventional example being 100. The larger the value, the better the carbon black dispersibility.

  The rubber components and compounding agents used in Examples and Comparative Examples are the following materials.

・ Natural rubber: Made in Thailand, RSS # 3
Carbon black (N326): Tokai Carbon Co., Ltd., Seast 300
・ Kneading accelerator: Ouchi Shinsei Chemical Co., Ltd., Nocizer SD
・ Zinc oxide: Mitsui Mining & Mining Co., Ltd., Zinc Hua No. 3 ・ Aroma oil: Japan Energy Co., Ltd., Aroma oil ・ Anti-aging agent: Kawaguchi Chemical Co., Ltd., Antage 6C
・ Stearic acid: Kao Corporation, LUNAC S-25
・ Sulfur: Shikoku Kasei Co., Ltd., insoluble sulfur / vulcanization accelerator DZ: Kawaguchi Chemical Co., Ltd., Accel DZ-G

  From Table 1, Example 1 according to the present invention has improved sheet processability, improved rubber viscosity and carbon black dispersibility over the conventional example, and in Examples 2 and 3 in which the kneading process is reduced to three times, sheet processability The rubber viscosity and carbon black dispersibility can be maintained at the same level as in the conventional example. In Example 4, it was confirmed that the sheet processability after the first step was good, and the subsequent evaluation was stopped. On the other hand, Comparative Example 1 with too much zinc oxide and Comparative Example 2 in which carbon black was not added in the first step, the rubber viscosity was too low and the sheet processability after the first step became excessively sticky to the roll. In Comparative Example 3 having a large amount of carbon black, the rubber viscosity could not be lowered, and it was difficult to wrap around the roll, and the carbon black dispersibility was inferior.

  The rubber composition obtained by the production method of the natural rubber composition of the present invention includes a vibration isolating rubber, a seismic isolation rubber, a conveyor belt, a hose, etc., including each part such as a tread, a sidewall, and a bead part of a pneumatic tire. It can be used for various industrial and household rubber products.

Claims (4)

A method for producing a natural rubber composition for producing a rubber composition comprising 20 to 120 parts by weight of carbon black and / or silica in a total amount of 100 parts by weight of natural rubber,
In the first kneading step, a blend of 15 to 30 parts by weight of carbon black and / or silica and 2 to 20 parts by weight of zinc oxide is added to 100 parts by weight of natural rubber,
In the second kneading step, the remaining carbon black and / or silica and a compounding agent other than the vulcanization system are added and kneaded to the rubber mixture obtained in the first step,
In the third kneading step, the rubber mixture obtained in the second step is kneaded again,
In the fourth kneading step, a vulcanizing compounding agent is added to the rubber mixture obtained in the third step and kneaded. A method for producing a natural rubber composition. The method for producing a natural rubber composition according to claim 1, wherein the third kneading step is omitted. A natural rubber composition obtained by the method for producing a natural rubber composition according to claim 1 or 2. A pneumatic tire using the natural rubber composition as at least a part of a pneumatic tire.