JP6957981B2 - Manufacturing method of rubber composition for tires - Google Patents

Description

The present invention relates to a method for producing a rubber composition for a tire, and more specifically, a rubber composition for a tire that improves the yield when producing a rubber composition containing recycled butyl rubber and improves the tire durability to a level higher than the conventional level. Regarding the manufacturing method of things.

In recent years, recycled butyl rubber may be added to the inner liner from the viewpoint of environmental measures and cost reduction. Regenerated butyl rubber is produced by subjecting vulcanized butyl rubber to a treatment such as desulfurization. However, the vulcanization accelerator may remain in the regenerated butyl rubber even after the desulfurization treatment. Therefore, when the rubber composition containing the regenerated butyl rubber is processed and molded, the residual vulcanization accelerator reacts with the rubber composition, and the members are liable to be burnt or shrink. Therefore, there is a concern that the yield at the time of manufacturing the pneumatic tire may be deteriorated, or the adhesiveness of the splice portion of the inner liner may be deteriorated, and the tire durability may be lowered.

Patent Document 1 proposes to prevent the burning of rubber organisms by blending hydrotalcite together with regenerated butyl rubber. However, in order to improve productivity and reduce costs, the rubber composition is made more stable in processing, and the demand from consumers for improving tire durability is higher, so that recycled butyl rubber is included. Further improvement of the rubber composition was required.

Japanese Unexamined Patent Publication No. 2015-203103

An object of the present invention is to provide a method for producing a rubber composition for a tire, which improves a yield when producing a rubber composition containing regenerated butyl rubber and improves tire durability to a level higher than the conventional level.

The method for producing a rubber composition for a tire of the present invention that achieves the above object is a rubber component containing 10 to 40% by mass of butyl rubber derived from recycled butyl rubber and 60 to 90% by mass of butyl rubber and / or butyl halogenated rubber. A rubber composition containing an inorganic filler and a vulcanization accelerator having a benzothiazole structure is mixed in two or more steps, and the butyl rubber derived from the regenerated butyl rubber is mixed in one step of the two or more steps. It is characterized in that the total amount of the above and at least one part of the vulcanization accelerator are mixed.

In the method for producing a rubber composition for a tire of the present invention, the entire amount of butyl rubber derived from recycled butyl rubber and part or all of the vulcanization accelerator are mixed in a one-step step, so that they remain in the recycled butyl rubber. It is possible to suppress discoloration and shrinkage caused by the vulcanization accelerator, improve the yield, improve the adhesiveness of the splice portion of the inner liner, and improve the tire durability more than the conventional level.

The inorganic filler is preferably carbon black and plate-shaped mineral, and the carbon black and plate-shaped mineral can be blended in a total of 30 to 120 parts by mass with respect to 100 parts by mass of the rubber component.

Even if the butyl rubber derived from the regenerated butyl rubber contains a thiuram-based vulcanization accelerator, it is possible to suppress discoloration and shrinkage during processing.

Further, zinc oxide is preferably blended only in the last step of the two or more steps, whereby discoloration and shrinkage can be further suppressed.

Further, the tire rubber composition obtained by the method for producing a tire rubber composition of the present invention can be used for an inner liner to manufacture a pneumatic tire. The obtained pneumatic tire can be stably produced with excellent quality and has excellent tire durability.

The rubber composition for tires produced in the present invention contains butyl rubber derived from recycled butyl rubber, butyl rubber and / or halogenated butyl rubber as rubber components, and the total of these is 100% by mass of the rubber component. Butyl rubber and halogenated butyl rubber are unused raw materials (virgin materials). Recycled butyl rubber is recycled rubber whose main component is butyl rubber, which is obtained by desulfurizing rubber recovered from used tires and tubes. Here, the fact that butyl rubber is the main component means that the butyl rubber component is 50% by mass or more in 100% by mass of the regenerated butyl rubber. In addition to butyl rubber, the regenerated butyl rubber may contain an inorganic filler, a residual vulcanizing agent, and the like. In particular, even in a recycled rubber in which a thiuram-based vulcanization accelerator remains, burning and shrinkage can be suppressed by applying the present invention.

The regenerated butyl rubber is contained in an amount of 10 to 40% by mass, preferably 20 to 30% by mass, as a butyl rubber derived from the regenerated butyl rubber in 100% by mass of the rubber component. If the amount of butyl rubber derived from recycled butyl rubber is less than 10% by mass, recyclability cannot be improved. Further, if it exceeds 40% by mass, there is a concern that the performance required for the inner liner may deteriorate.

The rubber component other than the regenerated butyl rubber is butyl rubber and / or halogenated butyl rubber, and the content thereof is 60 to 90% by mass, preferably 60 to 70% by mass, based on 100% by mass of the rubber component.

The rubber composition for a tire contains an inorganic filler. Examples of the inorganic filler include carbon black, plate-like minerals, silica, talc, calcium carbonate, aluminum oxide, titanium oxide and the like. Of these, carbon black and plate-like minerals are preferable. Examples of plate-like minerals include flat talc, mica, clay, and bituminous coal. Of these, flat talc is preferable.

The average particle size of the plate-shaped mineral is preferably 4.9 to 7.5 μm, more preferably 5.5 to 7.1 μm. The aspect ratio Ar of the plate-shaped mineral is preferably 3.0 to 7.0, more preferably 3.4 to 5.4. By blending such a plate-shaped mineral into the rubber composition, the air permeation prevention performance can be further improved.

Specifically, by setting the average particle size of the plate-shaped mineral to 4.9 μm or more, it is possible to make the rubber composition excellent in air permeability resistance. Further, by setting the average particle size of the plate-shaped mineral to 7.5 μm or less, it is possible to prevent deterioration of bending fatigue resistance due to repeated strain in the rubber composition. In the present specification, the average particle size of the plate-shaped mineral is the median size (D50: particle size of 50% of the cumulative particle size distribution) measured by the laser diffraction method.

Further, by setting the aspect ratio Ar of the plate-shaped mineral to 3.0 or more, the air permeability can be sufficiently suppressed. Further, by setting the aspect ratio Ar of the plate-shaped mineral to 7.0 or less, it is possible to prevent the bending fatigue resistance of the rubber composition from being deteriorated due to repeated strain. The aspect ratio Ar of the plate-shaped mineral is measured by the following formula (1).
Ar = (Ds-Dl) / Ds (1)
(In the formula, Ar is the aspect ratio, Ds is the 50% particle size determined by the cumulative distribution measured by the centrifugal sedimentation method, and Dl is the 50% particle size determined by the cumulative distribution measured by the laser diffraction method of coherent light. Represents the diameter.)

The 50% particle size Ds measured by the centrifugal sedimentation method can be measured using, for example, a Cedigrag 5100 particle size measuring device manufactured by Micromeritex Instruments. Further, the 50% particle size Dl measured by the laser diffraction method of coherent light can be measured by using a laser Malvern Mastersizer 2000 diffraction type particle distribution measuring device manufactured by Malvern.

The nitrogen adsorption specific surface area of carbon black is not particularly limited, but is preferably 30 to 90 m ² / g, and more preferably 30 to 60 m ² / g. If the nitrogen adsorption specific surface area of carbon black ^{is less than 30 m 2} / g, the strength of the compound may deteriorate. Further, if the nitrogen adsorption specific surface area of carbon black ^{exceeds 90 m 2} / g, the mixing and rolling processability may be deteriorated. In the present specification, the nitrogen adsorption specific surface area of carbon black shall be measured based on JIS K6217-2.

In the present invention, carbon black and plate-like minerals may be blended in a total amount of preferably 30 to 120 parts by mass, more preferably 40 to 90 parts by mass with respect to 100 parts by mass of the rubber component. If the total of carbon black and plate-like minerals is less than 30 parts by mass, the strength and air permeability of the compound deteriorate. If the total amount of carbon black and plate-like minerals exceeds 120 parts by mass, the mixing and rolling processability deteriorates.

Of these, the plate-shaped mineral is preferably blended in an amount of 5 to 80 parts by mass, more preferably 15 to 40 parts by mass with respect to 100 parts by mass of the rubber component. If the blending amount of the plate-shaped mineral is less than 5 parts by mass, the air permeation prevention performance cannot be sufficiently enhanced, which makes it unsuitable for use as an inner liner. If the blending amount of the plate-shaped mineral is more than 80 parts by mass, the weight of the tire is increased, which is not preferable.

In the present invention, the rubber composition always contains a vulcanization accelerator having a benzothiazole structure. Examples of the vulcanization accelerator having a benzothiazole structure include a thiazole-based vulcanization accelerator and a sulfenamide-based vulcanization accelerator, for example, 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, 2- ( 4'-morpholinodithio) benzothiazole, zinc salt of 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, N-cyclohexyl-2-benzothiazolesulfenamide, N-oxydiethylene-2-benzothiazolesulfenamide Fenamide, N- (tert-butyl) -2-benzothiazolesulfenamide, and the like can be exemplified.

It is considered that by mixing the regenerated butyl rubber in the presence of a vulcanization accelerator having a benzothiazole structure, the action of the vulcanization accelerator remaining in a high temperature state is suppressed. That is, even if the so-called super-accelerator thiuram-based vulcanization accelerator remains in the regenerated butyl rubber, the action of the thiuram-based vulcanization accelerator is suppressed by coexisting with the vulcanization accelerator having a benzothiazole structure. However, it is possible to prevent discoloration and shrinkage.

The blending amount of the vulcanization accelerator having a benzothiazole structure is preferably 0.1 to 2.0 parts by mass, more preferably 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the regenerated butyl rubber content. It is good to do. By setting the blending amount of the vulcanization accelerator having a benzothiazole structure within such a range, it is possible to suppress the occurrence of discoloration and shrinkage in the rubber composition containing the regenerated butyl rubber.

In the production method of the present invention, the rubber composition for a tire is sequentially mixed and kneaded. That is, the above-mentioned rubber composition is mixed in two or more steps, and the total amount of butyl rubber derived from regenerated butyl rubber and at least one part of the vulcanization accelerator are mixed in one step of the two or more steps. It is characterized by mixing.

Usually, a rubber composition for a tire is prepared by mixing and kneading raw materials other than a vulcanization compound such as sulfur and a vulcanization accelerator, and after cooling the obtained kneaded product, the vulcanization compound is added. It is mixed in a two-step process of mixing. The production method of the present invention includes the above-mentioned two-step process, and a mixing step may be further added.

In the present invention, it is necessary to mix the entire amount of butyl rubber derived from regenerated butyl rubber and a part or all of the vulcanization accelerator in a one-step step. That is, by coexisting the thiuram-based vulcanization accelerator remaining in the regenerated butyl rubber and the vulcanization accelerator having a benzothiazole structure and allowing them to act competitively, the discoloration and shrinkage caused by the thiuram-based vulcanization accelerator can be removed. It can be suppressed.

The step of mixing the regenerated butyl rubber and the vulcanization accelerator having a benzothiazole structure together is a step of adding the vulcanization compounding agent and mixing at a relatively low temperature even in the mixing and kneading steps before adding the vulcanization type compounding agent. But it may be. The steps before adding the vulcanization-based compounding agent can be mixed and kneaded using a Banbury mixer, a kneader or the like. The step after adding the vulcanization-based compounding agent can be mixed and kneaded using a Banbury mixer, kneader, roll, etc., but it is preferable to use a roll while checking the mixed state. ..

In the present invention, various compounding agents generally used for tire rubber compositions such as vulcanization or cross-linking agents, anti-aging agents, plasticizers, processing aids, liquid polymers, and thermosetting resins can be blended. can. Such a compounding agent can be added and kneaded by a general method to obtain a rubber composition. These blending amounts can be conventional general blending amounts as long as they do not contradict the object of the present invention.

A pneumatic tire can be manufactured by using the rubber composition for a tire obtained by the manufacturing method of the present invention in an inner liner. Since the rubber composition for tires produced by the present invention suppresses discoloration, the yield at the time of production can be improved. Further, since the shrinkage of the rubber composition is suppressed, when the sheet-shaped rolled sheet is wound around the tire drum and the inner liner is formed by the wrap splice, the shrinkage of the rolled sheet is small and the adhesive force of the splice portion is maintained at a high level. Tire durability can be made excellent. As a result, it is possible to reduce the occurrence of defective tire products.

Hereinafter, the present invention will be further described with reference to Examples, but the scope of the present invention is not limited to these Examples.

Eight kinds of rubber compositions (Examples 1 to 5 and Comparative Examples 1 to 3) having the formulations shown in Table 1 were mixed with 1.8 L of the components described in the "first stage of kneading" column in the table. It was kneaded with a mixer for 5 minutes, released and cooled. A rubber composition for a tire was prepared by mixing the components described in the "second stage of kneading" column including this with an open roll.

The obtained eight kinds of rubber compositions were rolled into a sheet shape having a thickness of 2.0 mm and a width of 510 mm, and cut into a length of 1600 mm. The sheet length immediately after rolling and the sheet length 1 hour after rolling were measured, and the sheet shape retention rate was calculated by the following general formula.
Sheet shape retention rate = (sheet length 1 hour after rolling) / (sheet length immediately after rolling) x 100
The obtained results are shown in the "Sheet shape retention rate" column of Table 1 as an index for setting the value of Comparative Example 1 to 100. The larger this index is, the smaller the shrinkage of the sheet is and the better the shape stability is.

Further, 10 pneumatic tires having a tire size of 11R22.5 using the obtained eight kinds of rubber compositions for tires as an inner liner were vulcanized and molded. Using the obtained pneumatic tire, the tire durability and the adhesiveness of the splice portion were evaluated by the following methods.

Tire durability (drum running test)
The obtained pneumatic tire is mounted on a standard rim, filled with gas having an oxygen concentration of 67.5% and air of 22.5%, and the air pressure is set to the JATMA specified air pressure, and an indoor drum tester (drum) conforming to JIS D4230. 170% of the JATMA specified load was applied over a diameter of 1707 mm), and the mileage until a tire failure occurred was measured under the conditions of a speed of 40 km / h and 30 ° C. The tires of one example or comparative example were subjected to a drum running test 10 times each, and the average mileage until failure was measured. The obtained results are shown in the column of "tire durability" in Table 1 as an index for setting the value of Comparative Example 1 to 100. The larger this index is, the longer the average mileage until failure is long, and the better the tire durability is.

Adhesion of splice portion The inner surface of the failed pneumatic tire subjected to the above drum running test (N = 10) was visually observed, and the presence or absence of peeling of the splice portion of the inner liner was evaluated according to the following criteria.
◯; There is no peeling on the splice part of the inner liner.
Δ: 1-2 defective tires with peeled inner liner splices ×; 3 or more defective tires with peeled inner liner splices

The types of raw materials used in Table 1 are shown below.
-Halogenated butyl rubber: LANXESS RUBBER X_BUTYL BB X2
-Recycled butyl rubber: WUXI WANFENG RUBBER BUTYL RECLAIMED RUBBER, butyl rubber content of about 55%, lot-natural rubber confirmed to contain thiuram-based vulcanization accelerator by GC-MAS analysis-Natural rubber: RSS # 3
-Flat talc: Made by Imerys Talk Luzenac France, with an average particle size of 5.7 μm and an aspect ratio of 4.7.
-Carbon black: Niteron #GN manufactured by Shin Nikka Carbon Co., Ltd., nitrogen adsorption specific surface area is 35 m ² / g
-Process oil: Idemitsu Kosan Diana Process NH-70S
-Stearic acid: Stearic acid 50S manufactured by Nissin Rika Co., Ltd.
・ Vulcanization accelerator: Noxeller DM-PO manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
・ Zinc oxide: Zinc oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. ・ Sulfur: Oil-treated sulfur manufactured by Hosoi Chemical Industry Co., Ltd.

As is clear from Table 1, it was confirmed that the rubber compositions for tires of Examples 1 to 5 were excellent in the sheet shape retention rate, the tire durability and the adhesiveness of the splice portion.

Since the rubber composition for a tire of Comparative Example 2 contains natural rubber as a rubber component, the air permeation prevention property as an inner liner is deteriorated, and the tire durability is inferior.
In the rubber composition for tires of Comparative Example 3, regenerated butyl rubber and a vulcanization accelerator having a benzothiazole structure were not mixed and kneaded in the same step, so that the sheet shape retention rate was small and shrinkage was likely to occur. As a result, the splice portion was peeled off and the tire durability was reduced.

Claims (5)

A rubber composition containing a rubber component containing 10 to 40% by mass of butyl rubber derived from regenerated butyl rubber and 60 to 90% by mass of butyl rubber and / or butyl halogenated rubber, an inorganic filler, and a vulcanization accelerator having a benzothiazole structure. The product is mixed in two or more steps, and at least one part of the vulcanization accelerator is mixed with the total amount of butyl rubber derived from the regenerated butyl rubber in one step of the two or more steps. A method for producing a characteristic rubber composition for tires. The first aspect of claim 1, wherein the inorganic filler is carbon black and a plate-shaped mineral, and the carbon black and the plate-shaped mineral are blended in a total of 30 to 120 parts by mass with respect to 100 parts by mass of the rubber component. A method for producing a rubber composition for tires. The method for producing a rubber composition for a tire according to claim 1 or 2, wherein the butyl rubber derived from the regenerated butyl rubber contains a thiuram-based vulcanization accelerator. The method for producing a rubber composition for a tire according to any one of claims 1 to 3, wherein zinc oxide is blended only in the last step of the two or more steps. A method for producing a pneumatic tire, which comprises forming an inner liner using the rubber composition for a tire obtained by the production method according to any one of claims 1 to 4.