JP4813818B2 - Tread rubber composition for studless tire and method for producing the same - Google Patents

Description

  The present invention relates to a tread rubber composition for studless tires used as a tread rubber for studless tires used for running on snowy and snowy roads, and a method for producing the same.

  Generally, a tread rubber used in a tread portion of a studless tire, particularly a studless tire for a passenger car, has a low rubber hardness at a low temperature (for example, 50 to JIS hardness) in order to improve the ground contact property with the road surface on ice. Furthermore, in order to increase the frictional force on ice, methods such as blending of a foaming agent and hollow particles, blending of hard granular materials such as vegetable granules, and the like are taken. However, when these methods are used, there is a demerit that wear resistance generally tends to deteriorate.

  Conventionally, carbon black is generally blended as a reinforcing filler in tread rubber, but by using silica instead of carbon black, changes in rubber hardness from room temperature to low temperature can be reduced. Therefore, silica may be blended to increase the frictional force on ice.

  However, since silica has a lower dispersibility with respect to diene rubber than carbon black, it is necessary to increase the discharge temperature when mixing the rubber composition to 140 to 160 ° C. In particular, in a tread rubber compound for a studless tire, since the Mooney viscosity is generally low, the temperature rise rate is slow at the time of mixing, and therefore the mixing time becomes long. In addition, since silica has poor dispersibility compared to carbon black, there is a problem that disadvantages such as a decrease in wear resistance occur.

  In Patent Document 1 below, in order to improve the dispersibility of silica in a rubber composition, hydrophobized silica is kneaded in advance with a solution-polymerized styrene butadiene rubber alone or a blend rubber of this and butadiene rubber. A technique for making a master batch is disclosed. In addition, in Patent Document 2 below, in order to improve the dispersibility of silica, silica is pre-blended and reacted with an alkoxysilyl group-containing styrene butadiene rubber obtained by reacting a silane coupling agent with a vinyl group of a styrene butadiene rubber. A technique for making a master batch is disclosed.

In any of the techniques disclosed in these patent documents, silica is masterbatched in advance in order to achieve uniform dispersion of silica in the rubber composition. Since it is a butadiene rubber, it takes a great amount of mixing time to produce a masterbatch, and it is difficult to improve dispersibility. Further, in these techniques, since the entire amount of silica to be filled is blended in a master batch, it takes time to knead the final rubber composition.
Special table 2002-515515 gazette JP 2004-59999 A

  The present invention has been made in view of the above points, and can reduce the mixing time without impairing the performance on ice, and can improve the wear resistance. The tread rubber composition for studless tires And it aims at providing the manufacturing method.

  The tread rubber composition for studless tires according to the present invention is a rubber composition containing 20 to 60 parts by weight of silica with respect to 100 parts by weight of the rubber component, and the rubber component is 20 to 20% of the total weight of the silica. It is characterized by comprising 40-80 parts by weight of natural rubber kneaded by 70% by weight and masterbatch, and 20-60 parts by weight of butadiene rubber having a cis content of 90% by weight or more.

Moreover, the manufacturing method which concerns on this invention is a manufacturing method of the tread rubber composition for studless tires containing 20-60 weight part of silica with respect to 100 weight part of rubber components,
(1) A step of blending a part of the silica with natural rubber and kneading to obtain a master batch;
(2) a step of blending the obtained master batch with a butadiene rubber having a cis content of 90% by weight or more and the remainder of the silica and kneading,
The masterbatch contains 40 to 80 parts by weight of natural rubber as the rubber component and 20 to 70% by weight of the total weight of the silica. In the step (2), 20 to 70% of the butadiene rubber is used as the rubber component. It is characterized by blending 60 parts by weight.

  According to the present invention, natural rubber that is poorly kneadable (dispersible) into a rubber component is kneaded with natural rubber in advance, thereby increasing the dispersibility of silica and having relatively good compatibility with silica. By enhancing the reinforcing property, the reinforcing property of the entire tread rubber composition can be enhanced, and deterioration of wear resistance can be prevented. Moreover, the performance on ice can be maintained or improved by increasing the dispersibility of silica.

  Silica is generally poorly dispersible in rubber and has a low bulk specific gravity, so that it takes a long time to disperse. Particularly, a tread rubber composition for studless tires generally has a relatively low Mooney viscosity, so that it is kneaded. Sometimes it takes time to increase to a predetermined discharge temperature, but according to the present invention, a masterbatch of natural rubber compounded with silica is prepared in advance, so that a tread rubber having a stable quality in a relatively short time. A composition can be produced.

  Also, the mixing time in the subsequent process can be shortened by mixing a predetermined amount of the remaining amount of silica at the time of kneading with butadiene rubber instead of compounding the silica only in the master batch. And the overall mixing time can be further shortened.

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

  In the tread rubber composition of the present invention, the rubber component comprises 40-80 parts by weight of a masterbatch natural rubber, 20-60 parts by weight of a butadiene rubber having a cis content of 90% by weight or more, and other diene rubbers 0-20. The other diene rubber is an optional component. If the butadiene rubber having a cis content of 90% or more is less than 20 parts by weight, it is difficult to ensure performance on ice. Moreover, if the natural rubber made into a masterbatch is less than 40 weight part, the effect of this invention mentioned above cannot be exhibited.

  As the other diene rubber, various diene rubbers usually used as a tread rubber composition for tires can be used. For example, natural rubber, isoprene rubber, styrene butadiene which are not masterbatched as described above. Examples thereof include rubber and butadiene rubber other than the above. Preferably, 0 to 20 parts by weight of natural rubber and / or isoprene rubber is blended.

In the tread rubber composition of the present invention, the silica is not particularly limited, and examples thereof include wet silica, dry silica, colloidal silica, and precipitated silica. It is particularly preferable to use wet silica containing hydrous silicic acid as a main component. Silica preferably has a CTAB specific surface area (cetyltrimethylammonium bromide adsorption specific surface area) of 90 to 180 m ² / g. In the present invention, the CTAB specific surface area is a value measured according to ASTM D3765.

  The blending amount of silica is 20 to 60 parts by weight with respect to 100 parts by weight of the rubber component, and if it is less than 20 parts by weight, sufficient performance on ice cannot be ensured. And, 20 to 70% by weight of the blended amount is pre-kneaded with natural rubber to form a masterbatch, which is blended into the tread rubber composition in the state of this masterbatch, and the remaining 80 to 30% by weight is the masterbatch. It is added as a powder in the subsequent kneading step of the tread rubber composition, not as a batch.

  In the tread rubber composition of the present invention, a coupling agent may be blended in order to promote the binding of silica to the rubber component. Examples of coupling agents include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3 Examples include various silane coupling agents such as mercaptopropyltriethoxysilane, 3-nitropropyltrimethoxysilane, and γ-aminopropyltriethoxysilane. The blending amount of the coupling agent is preferably 8 to 12 parts by weight with respect to 100 parts by weight of silica.

Carbon black can also be mix | blended with the tread rubber composition of this invention with a silica. Carbon black having a CTAB specific surface area of 80 to 120 m ² / g is preferably used. Carbon black is preferably blended in an amount of 30 parts by weight or less, that is, 0 to 30 parts by weight based on 100 parts by weight of the rubber component.

  In the tread rubber composition of the present invention, in addition to the above-described components, hard granules such as plant granules, oil, anti-aging agent, zinc white, stearic acid, softener, vulcanizing agent, vulcanization accelerator Various additives generally used in a tire tread rubber composition can be blended. As the above-mentioned plant granular material, seed husks such as walnuts and straws that are harder than ice, in other words, have a Mohs hardness of 2 or more, or the cores of fruits such as peaches and plums by known methods. The pulverized granule formed by pulverization is mentioned, and the vegetable granule is preferably blended in an amount of 1 to 20 parts by weight with respect to 100 parts by weight of the rubber component.

  Next, the manufacturing method of the tread rubber composition of this invention is demonstrated. The manufacturing method includes the following steps.

(1) Masterbatch production process First, a part of the silica to be filled is blended with natural rubber and kneaded using a mixer to produce a masterbatch. Since natural rubber generally has a high molecular weight, it is easy to apply a shearing force of stirring by a mixer at the time of kneading. Therefore, the temperature rise rate can be increased to a predetermined discharge temperature at an early stage, and the mixing time can be shortened. . Moreover, since natural rubber contains impurities such as fatty acid and protein, it has a relatively good compatibility with silica, is excellent in dispersibility, and can enhance reinforcement. From such a viewpoint, it is preferable to form a master batch of silica using natural rubber alone. In addition, rubbers other than natural rubber can be blended as a rubber component of the masterbatch within a range not impairing the effects of the present invention (for example, 10% by weight or less).

  The amount of silica compounded in the masterbatch is 40-80 parts by weight of natural rubber blended as a masterbatch with respect to 100 parts by weight of the rubber component in the tread rubber composition, and blended in the tread rubber composition. It is appropriately set so that 20 to 70% by weight of the total silica weight is blended as a master batch.

  Here, if the ratio of the silica compounded as the master batch is less than 20% by weight, the dispersibility of the silica is inferior, and the effect of improving the wear resistance cannot be obtained. On the contrary, if this ratio exceeds 70% by weight, the amount of silica added in the next step (2) decreases, so that the rate of temperature rise in this step (2) becomes slow and mixing occurs. The time will be longer.

  In addition, although the discharge temperature from the mixer at the time of making a masterbatch is not specifically limited, It is preferable to set so that it may become 130-150 degreeC.

(2) Tread rubber composition kneading step Next, the master batch obtained above is blended with butadiene rubber having a cis content of 90% by weight or more and the remainder of the silica and kneaded. At that time, the rubber component is added to the mixer so that 40-80 parts by weight of the masterbatch natural rubber and 20-60 parts by weight of the butadiene rubber are blended, and the remaining weight of silica is the total weight. 80-30% by weight of silica is added in powder form.

  More specifically, the tread rubber composition can be kneaded as follows. First, the masterbatch and all polymers (that is, rubber components) including the butadiene rubber are put into a mixer and stirred. After a predetermined time has elapsed (for example, after 10 to 15 seconds have elapsed), the remainder of the silica is charged. At that time, other solid additives such as carbon black and zinc white are also added. However, vulcanizing additives such as vulcanizing agents and vulcanization accelerators are not added at this stage.

  After a predetermined time (for example, after 20 to 40 seconds), a liquid additive such as oil is added and kneaded until the temperature is increased to a predetermined discharge temperature (for example, 140 to 160 ° C.). In this way, by adding a filler such as silica or carbon black, and then adding a liquid additive such as oil, slipping of the mixer rotor caused by oil adhering around the rubber polymer is prevented. And the malfunction that the shearing force at the time of kneading cannot be obtained can be avoided. That is, the above-mentioned slip prevention can be achieved by adsorbing oil with the filler. The filler and the liquid additive may be added at the same time. After the temperature rises, the kneaded material is discharged from the mixer and cooled.

(3) Compounding of vulcanizing additive The kneaded product of the rubber composition not containing the vulcanizing system obtained as described above is put into a mixer, and a vulcanizing agent and a vulcanization accelerator are added and vulcanized. The tread rubber composition can be prepared by stirring and taking out until the temperature rises to a predetermined temperature (for example, 100 to 120 ° C.) below the temperature.

  The tread rubber composition thus obtained can form a tread portion of a studless tire by vulcanization molding according to a conventional method.

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

(Step 1: Preparation of master batch)
Using a 270 L closed mixer, 7 types of master batches MB1 to 7 were kneaded according to the formulation shown in Table 1 below (1 part by weight in the table is 1.2 kg). At that time, the discharge temperature from the mixer was set to 140 ° C. Each component in Table 1 is as follows.

・ Natural rubber: STR20
-Butadiene rubber: JSR "BR01" (cis content 97%)
Silica 1: “Ultrasil VN3” manufactured by Degussa (CTAB = 170 m ² / g)
・ Silica 2: “ZEOPOL8715” manufactured by HUBER (CTAB = 115 m ² / g)

  Table 1 shows the mixing time of each master batch. As a result, the higher the silica content, the faster the rate of temperature rise and the shorter the mixing time.

(Step 2: kneading of the tread rubber composition)
Using the master batch obtained above, Examples 1 to 4 and Comparative Example 1 were conducted in a 270 L closed mixer according to the formulation shown in Table 2 below (1 part by weight in the table is 1.0 kg). ~ 4 tread rubber compositions were prepared by kneading. Specifically, first, all of the rubber components including the master batch are put into a mixer, stirred for 10 seconds, and then the remainder of silica and other solid additives (excluding vulcanizing additives) are added. Stir for 30 seconds. Thereafter, oil was added and stirred until the temperature was raised to 150 ° C. After the temperature was raised, the oil was discharged from the mixer. Each component in Table 2 is as follows.

・ Natural rubber, butadiene rubber, silica 1 and silica 2: same as the above step 1 ・ Carbon black: “Seast 6” manufactured by Tokai Carbon (CTAB = 109 m ² / g)
-Coupling agent: Degussa “Si69”
Paraffin oil: “Process P200” manufactured by Japan Energy.

  In this step 2, each rubber composition is mixed with 2 parts by weight of zinc white (Mitsui Kinzoku “Zinc Hana 1”) and 2 parts by weight of stearic acid (Kao “Lunac S-20”). 2 parts by weight of anti-aging agent (“Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.), 2 parts by weight of wax (“OZOACE0355” manufactured by Nippon Seiki Co., Ltd.) Walnut shell powder))) 5 parts by weight.

(Process 3: Compounding of vulcanizing additive)
Each kneaded product discharged from the mixer is cooled and then charged into a 270 L closed mixer, 1 part by weight of sulfur (“Turumi Chemical” powder sulfur), a vulcanization accelerator (Sumitomo Chemical “Sokushinol CZ”) Each tread rubber composition was prepared by adding 1.5 parts by weight and stirring and mixing until the temperature was raised to 110 ° C.

  Studless tires were produced using each of the obtained tread rubber compositions, and the wear resistance and braking performance on ice surfaces (ice braking performance) were evaluated. The tire size was 185 / 70R14, and each rubber composition was applied to the tread and vulcanized and molded according to a conventional method. Each rim used was 14 × 6JJ. Each measurement / evaluation method is as follows.

Abrasion resistance: The above tire is mounted on a 2000 cc FF vehicle, rotated back and forth every 2500 km, and the remaining grooves after running 10,000 km (average value of remaining grooves of four tires) were measured. The value was expressed as an index with a value of 100. A larger index indicates better wear resistance.

・ Ice braking performance: The tire is mounted on a 2000cc FF vehicle, and the braking distance is measured by running an ABS from 40km / h on an icy road (-5 ± 3 ° C) (average value of n = 10). The index was expressed as an index with Comparative Example 1 as 100. The larger the index, the shorter the braking distance and the better the braking performance.

In addition, 5 batches of each tread rubber composition were prepared, and the Mooney viscosity (ASTM D1646) at 100 ° C. of each batch after mixing in Step 2 was measured, and the difference between the maximum value and the minimum value was obtained. Viscosity variation was evaluated.

  The results are as shown in Table 2. In Examples 1 to 4 according to the present invention, the mixing average time in Step 2 is short, the mixing average time in the sum of Step 1 and Step 2 is also short, and the workability is excellent. It was a thing. Further, in the tread rubber compositions of Examples 1 to 4, the variation in Mooney viscosity at the end of Step 2 is small, and thus the quality is stable, and the wear resistance and the performance on ice are improved. It was.

  On the other hand, in Comparative Examples 1-4, the variation in Mooney viscosity was large, and the wear resistance and performance on ice were inferior. For example, in Comparative Example 4, the masterbatch was not used, so the mixing time in step 1 was not required, but the mixing time in step 2 was long, the variation in Mooney viscosity was large, and the wear resistance and on-ice performance were also large. It was inferior to. Further, in Comparative Example 2, since 75% by weight of silica was blended as a master batch, the mixing time in Step 1 was short, but the mixing time in Step 2 was long, and the total mixing time was long. This was because the amount of silica added in No. 2 was small, and the variation in Mooney viscosity at the end of Step 2 was large, the dispersibility of silica was poor, and the effect of improving the performance on ice was not observed. Furthermore, in Comparative Example 3 in which silica was masterbatched with not only natural rubber but also a blend rubber of natural rubber and butadiene rubber, the mixing time in Step 1 was long and the dispersibility of silica was poor. The improvement effect like was not recognized.

  The rubber composition and the manufacturing method according to the present invention can be used for manufacturing a studless tire.

Claims (2)

A tread rubber composition for studless tires containing 20 to 60 parts by weight of silica with respect to 100 parts by weight of a rubber component,
40 to 80 parts by weight of natural rubber obtained by kneading 20 to 70% by weight of the total weight of the silica into a master batch and 20 to 60 parts by weight of butadiene rubber having a cis content of 90% by weight or more. A tread rubber composition for studless tires, comprising: A method for producing a tread rubber composition for studless tires containing 20 to 60 parts by weight of silica with respect to 100 parts by weight of a rubber component,
(1) A step of blending a part of the silica with natural rubber and kneading to obtain a master batch;
(2) a step of blending the obtained master batch with a butadiene rubber having a cis content of 90% by weight or more and the remainder of the silica and kneading,
The masterbatch contains 40 to 80 parts by weight of natural rubber as the rubber component and 20 to 70% by weight of the total weight of the silica. In the step (2), 20 to 70% of the butadiene rubber is used as the rubber component. A method for producing a tread rubber composition for studless tires, comprising blending 60 parts by weight.