JP2005263999A - Manufacturing process of rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing process of a rubber composition which improves the rolling resistance of a tire while maintaining the processability on a practical level. <P>SOLUTION: The manufacturing process of the rubber composition containing 20-100 pts.wt. of an inorganic filler such as silica to 100 pts.wt. of a diene rubber comprises a first step in which the diene rubber, part of the inorganic filler and a silane coupling agent expressed by general formula (1) are mixed, a second step in which the rest of the inorganic filler is added to and mixed with the mixture obtained above and a third step in which a vulcanizing additive is added to and mixed with the mixture. Zinc white is added at the second step or the third step. (C<SB>n</SB>H<SB>2n+1</SB>O)<SB>3</SB>Si-C<SB>m</SB>H<SB>2m</SB>-S-CO-C<SB>k</SB>H<SB>2k+1</SB>(1) (wherein. n is an integer of 1-3; m is an integer of 1-5; and k is an integer of 5-9). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a rubber composition containing an inorganic filler such as silica, and more particularly to a method for producing a rubber composition suitable for a tread rubber of a pneumatic tire.

  Recently, with increasing interest in the environment, tires are also strongly required to have low fuel consumption. In response to such demands, if an inorganic filler such as silica and a silane coupling agent are added to the tread rubber of the tire, the rolling resistance is reduced, resulting in a fuel-efficient tire. Therefore, an inorganic filler and a silane coupling agent are used. Various blended rubber compositions have been proposed (see Patent Documents 1 and 2 below).

  Patent Document 3 listed below proposes a novel protected mercaptosilane as a silane coupling agent to be added together with an inorganic filler such as silica.

By the way, zinc oxide is added to this type of rubber composition as an additive. And when manufacturing a rubber composition, generally various additives are added and mixed in a plurality of stages with respect to the diene rubber. At that time, zinc white is usually together with an inorganic filler and a silane coupling agent. It is added to the diene rubber in the first stage (first step).
JP2003-155383A. JP2003-155384A. JP-T-2001-505225. JP 2000-212329A.

  In order to further reduce the rolling resistance, the present inventors have studied from the aspect of the preparation method of the rubber composition. In the first step of adding the silane coupling agent, the addition time of the zinc white is determined. However, it was found that the rolling resistance of the tire using the rubber composition is reduced and the reinforcing property is increased by adopting a later process. This is because when zinc white is added in the first step, zinc white adsorbs the inorganic filler and the inorganic filler is contaminated by zinc white, thereby reacting with the silane coupling agent and the polymer chain of the rubber component (mutually). It is presumed that this is due to inhibition of the action.

  However, in the compounding using a conventional general silane coupling agent, the unvulcanized viscosity of the rubber increases as the zinc white charging time is delayed from the first step to the second step, and further to the third step. It has been found that the workability deteriorates and the degree of change in viscosity with time (viscosity increases with time) increases, and there is a practical problem.

  In addition, as a suppressor for the increase in the unvulcanized viscosity of rubber, Patent Document 4 proposes 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (4-Hydroxy-TEMPO). However, this drug is very expensive and impractical.

  The present invention has been made in view of the above points, and an object thereof is to provide a method for producing a rubber composition that can improve rolling resistance of a tire while maintaining workability at a practical level. To do.

  The present inventor uses the specific protected mercaptosilane as a silane coupling agent, and performs the addition of the inorganic filler, the silane coupling agent, and zinc white to the diene rubber in a predetermined order. As a result, the present invention has been completed.

That is, the method for producing a rubber composition according to the present invention is a method for producing a rubber composition containing 20 to 100 parts by weight of an inorganic filler with respect to 100 parts by weight of a diene rubber. A first step of mixing a part of the filler and a silane coupling agent represented by the following general formula (1), and adding the remainder of the inorganic filler to the mixture obtained in the first step A second step of mixing, and a third step of adding and mixing the vulcanizing compound to the mixture obtained in the second step, and adding zinc white in the second step or the third step. It is characterized by that.
_{(C n H 2n + 1 O} ) 3 Si-C m H 2m -S-CO-C k H 2k + 1 (1)
In the formula, n is an integer of 1 to 3, m is an integer of 1 to 5, and k is an integer of 5 to 9.

  In this invention, it is preferable that the addition amount of the inorganic filler in the said 2nd process is 20 to 60 weight% of the whole compounding quantity of an inorganic filler.

  In the present invention, the diene rubber is a styrene-butadiene rubber alone or a blend of 50% by weight or more of styrene-butadiene rubber and 50% by weight or less of another diene rubber, and the silane coupling agent is You may mix | blend 2-25 weight part with respect to 100 weight part of said inorganic fillers.

  According to the present invention, since the diene rubber, the inorganic filler, and the silane coupling agent are mixed without adding zinc white in the first step, the inorganic filler is contaminated with zinc white and the silane coupling agent. The problem that the reaction is hindered can be solved, and the rolling resistance of the tire can be improved. In addition, by using the specific silane coupling agent described above, the viscosity increase of unvulcanized rubber due to the introduction of zinc white in the subsequent process is suppressed, and the change with time of the viscosity is suppressed, so that the workability is deteriorated. Can be prevented. Furthermore, the dispersibility of the inorganic filler can be improved by adding the inorganic filler in two stages of the first step and the second step. Moreover, even if zinc oxide is added together with the remainder of the inorganic filler in the second step, the silane coupling agent is added and mixed with the inorganic filler in the first step, so a good reaction of the silane coupling agent is ensured. Therefore, the dispersibility of the inorganic filler can be improved and the rolling resistance of the tire can be improved without impairing the workability.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  The diene rubber used in the present invention is not particularly limited. In addition to natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene- Examples include diene-based synthetic rubbers such as isoprene-butadiene copolymer rubber and nitrile rubber, and these may be used alone or in combination of two or more.

  In the present invention, it is particularly preferable to use a styrene-butadiene rubber alone or a blend rubber of 50% by weight or more of styrene-butadiene rubber and 50% by weight or less of another diene rubber as the diene rubber.

  Examples of the inorganic filler used in the present invention include silica, clay, aluminum hydroxide, magnesium hydroxide and the like. These may be used alone or in combination of two or more. Of these, silica is particularly suitable for improving the rolling resistance of the tire. The compounding quantity of an inorganic filler shall be 20-100 weight part with respect to 100 weight part of diene rubbers, More preferably, it is 40-100 weight part. When the blending amount of the inorganic filler is less than 20 parts by weight, the effect of improving rolling resistance cannot be obtained.

  The silane coupling agent used in the present invention is a protected mercaptosilane represented by the general formula (1). Such protected mercaptosilane can be produced according to the method described in JP-T-2001-505225. The silane coupling agent is preferably used in an amount of 2 to 25 parts by weight, and more preferably 5 to 15 parts by weight with respect to 100 parts by weight of the inorganic filler.

  Although the compounding quantity of the zinc white used by this invention is not specifically limited, Usually, it is 0.1-10 weight part with respect to 100 weight part of diene rubbers, More preferably, it is 0.5-5 weight part.

  Examples of the vulcanizing compound used in the present invention include various known vulcanization accelerators in addition to a vulcanizing agent such as sulfur.

  In addition to the above-described components, the rubber composition of the present invention may contain various additives such as other reinforcing fillers such as carbon black, anti-aging agents, stearic acid, and softening agents. The carbon black is preferably blended in an amount of 0 to 100 parts by weight with respect to 100 parts by weight of the diene rubber. Moreover, it is preferable that the compounding ratio of an inorganic filler and carbon black is an inorganic filler / carbon black = 1/2-1/0 by weight ratio.

  Next, a method for preparing this rubber composition will be described.

  In preparing the rubber composition, first, in the first step, the inorganic filler and the specific silane coupling agent are added to and mixed with the diene rubber, and then in the second step, The remainder of the inorganic filler is added to and mixed with the obtained mixture, and then, in the third step as the final step, the vulcanized compounding agent is added to and mixed with the mixture obtained in the second step. These mixing can be performed using a known mixer, and the temperature at the time of mixing is not particularly limited. In the first step and the second step, stirring and mixing are performed until the temperature reaches about 150 to 180 ° C. It is preferable.

  Here, particularly in the present invention, zinc white is added in either the second step or the third step, and is not added in the first step. Thus, by adding zinc white in the second step or the third step, contamination of the inorganic filler by zinc white can be prevented, and the inorganic filler and the silane coupling agent can be suitably reacted. When this rubber composition is used as a tread rubber for a tire, the rolling resistance of the tire can be reduced and the reinforcement can be improved.

  In the first step, all of the diene rubber and the silane coupling agent are added, and part of the inorganic filler is added and mixed. The amount of the inorganic filler added in the first step is preferably 40 to 80% by weight of the total amount of the inorganic filler. On the other hand, the inorganic filler added in the second step is the remainder excluding the amount added in the first step, and is preferably 20 to 60% by weight of the total amount. If the ratio of the inorganic filler added in the second step exceeds 60% by weight, it will be contaminated by the zinc white added in the second step, making it difficult to obtain the effect of reducing the rolling resistance described above, and processability. Tend to get worse.

  In the first step, in addition to the three components of diene rubber, inorganic filler, and silane coupling agent, various reinforcing fillers such as carbon black, anti-aging agents, stearic acid, softeners, and the like. You may mix | blend an additive. However, zinc white and vulcanizing compound are not added in the first step.

  In addition, the mixture may be once taken out of the mixer and cooled after each of the above steps, or may proceed to the next step while remaining in the mixer. In addition, a step of adding and mixing the above-mentioned other additives between the first step and the second step, or between the second step and the third step, or mixing without adding anything is added. You can also. That is, in the present invention, the number of steps is not limited to the above three steps, and the number of steps may be four or more. However, in any case, the third step in which the vulcanizing agent is added is the final step.

  Various rubber products such as tires can be obtained by vulcanizing and molding the unvulcanized rubber thus obtained by a known vulcanization molding method.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Preparation of rubber composition)
Based on the formulation shown in Table 1, a tire tread rubber composition was prepared. Specifically, first, in the first step, each component shown in the first step in Table 1 is kneaded for 3 to 5 minutes with a 1.5 liter closed mixer, and the internal temperature reaches 165 ± 5 ° C. The mixture was then removed. Next, in the second step, using the same closed mixer as described above, the components shown in the second step in Table 1 are added to the mixture, and the mixture is kneaded for 3 to 5 minutes. After reaching 5 ° C., the mixture was removed. Finally, in the third step, using the same closed mixer as above, each component shown in the third step in Table 1 was added and kneaded for 1 to 2 minutes to obtain each rubber composition. The details of each component in Table 1 are as follows.

・ Diene rubber: Styrene-butadiene rubber “SBR1502” manufactured by JSR
・ Silica: Degussa “Ultrasil VN3”
Protected mercaptosilane: coupling agent represented by the above formula (1) (n = 2, m = 3, k = 7), “NXT” manufactured by GE Silicones
General-purpose coupling agent: bis- (3-triethoxysilylpropyl) tetrasulfide, “Si-69” manufactured by Degussa
Carbon black: ISAF, “Seast 6” manufactured by Tokai Carbon
・ Aroma-based process oil: “Process X140” manufactured by JOMO
・ Wax: “Sunnock N” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Anti-aging agent: “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.
・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
・ Zinc flower: “Zinc flower 1” manufactured by Mitsui Kinzoku Co., Ltd.
・ Sulfur: “5% oil-treated powder sulfur” manufactured by Hosoi Chemical Industry Co., Ltd., 150 mesh powder sulfur ・ Vulcanization accelerator: “Soxinol CZ” manufactured by Sumitomo Chemical Co., Ltd.

(Evaluation)
Each rubber composition obtained was evaluated for processability, change in viscosity over time, and tire rolling resistance. Each evaluation method is as follows.

Processability: Based on JIS K6300, the unvulcanized viscosity of each rubber composition was measured, and displayed as an index with the value of Comparative Example 1 being 100. A smaller index indicates a lower viscosity, that is, better workability.

・ Change in viscosity over time: Unvulcanized viscosity one month after mixing is measured according to JIS K6300, and the unvulcanized viscosity of each rubber composition immediately after mixing is defined as 100, and the increase relative to that is displayed as an index. did.

Rolling resistance: Using each rubber composition as a tread rubber, a 185 / 70R14 radial tire for passenger cars was produced in accordance with a standard method, and the conditions were a speed of 80 km / h, an air pressure of 2 kg / cm ² , and a load of 400 kg using a uniaxial drum tester. The rolling resistance was measured by using an index with the value of Comparative Example 1 as 100. It shows that rolling resistance is so small that an index | exponent is small.

  As shown in Table 1, a specific protected mercaptosilane is used as a silane coupling agent, silica is added in a predetermined amount in two steps, a first step and a second step, and zinc white is added. By putting it in the second step or the third step, the rolling resistance of the tire could be improved without impairing the workability and suppressing the increase in viscosity over time.

  The method for producing a rubber composition of the present invention is particularly suitable for the preparation of a tread rubber composition for tires. However, various methods for blending an inorganic filler as a rubber composition for other parts of the tire and other than the tire are also possible. It can be used for a rubber composition.

Claims (4)

A method for producing a rubber composition containing 20 to 100 parts by weight of an inorganic filler with respect to 100 parts by weight of a diene rubber,
A first step of mixing a diene rubber, a part of the inorganic filler, and a silane coupling agent represented by the following general formula (1);
A second step of adding and mixing the remainder of the inorganic filler to the mixture obtained in the first step;
A third step of adding and mixing the vulcanizing compound to the mixture obtained in the second step,
A method for producing a rubber composition, wherein zinc white is added in the second step or the third step.
_{(C n H 2n + 1 O} ) 3 Si-C m H 2m -S-CO-C k H 2k + 1 (1)
(In the formula, n is an integer of 1 to 3, m is an integer of 1 to 5, and k is an integer of 5 to 9)   The method for producing a rubber composition according to claim 1, wherein the amount of the inorganic filler added in the second step is 20 to 60% by weight of the total amount of the inorganic filler.   The diene rubber is composed of styrene-butadiene rubber alone or a blend of 50% by weight or more of styrene-butadiene rubber and 50% by weight or less of another diene rubber, and 100 parts by weight of the inorganic filler is used as the silane coupling agent. The method for producing a rubber composition according to claim 1 or 2, wherein 2 to 25 parts by weight of the rubber composition is blended.   The manufacturing method according to claim 1, wherein the rubber composition is a tire tread rubber composition.