JP2021187861A - Rubber composition for tires - Google Patents

Abstract

To provide a tire rubber composition that can improve on-ice performance while maintaining satisfactory wear resistance.SOLUTION: A tire rubber composition contains a tubular inorganic mineral having a hollow cyclic structure of 0.5 pt.mass to 20 pts.mass, relative to 100 pts.mass of a rubber component composed of natural rubber and a diene rubber containing a butadiene rubber, where the proportion of polybutadiene rubber is 30 mass% or more in the diene rubber.SELECTED DRAWING: None

Description

The present invention relates to a rubber composition for a tire intended to be used mainly for a tread portion of a studless tire.

In the rubber composition used for the tread part of winter tires (for example, studless tires) that are expected to run on ice and snow road surfaces, various materials are blended in order to obtain excellent on-ice performance and on-snow performance. Is being considered. For example, Patent Document 1 proposes to add a heat-expandable microcapsule to a rubber composition constituting a tread portion in order to obtain good performance on ice. In such tires, the heat-expandable microcapsules form a large number of bubbles in the rubber, and these bubbles absorb and remove the water film on the ice surface when the tread steps on the ice surface, resulting in excellent on-ice performance. Can be obtained. However, if various materials are blended for the purpose of improving the performance on ice in this way, there is a concern that the performance of other tires may be affected. Therefore, as for the materials to be additionally blended for the purpose of improving the performance on ice, an appropriate material (a material having little influence on the required performance other than the performance on ice) can be selected in consideration of the required performance other than the performance on ice. It is desirable to have more choices of materials that can be used. Therefore, it is also being considered to improve the performance on ice by using various materials that have not been used conventionally.

Japanese Unexamined Patent Publication No. 2019-156951

An object of the present invention is to provide a rubber composition for a tire capable of improving the performance on ice while maintaining good wear resistance.

The rubber composition for a tire of the present invention that achieves the above object contains 0.5% by mass of a tubular inorganic mineral having a hollow annular structure with respect to 100 parts by mass of a diene-based rubber containing 30% by mass or more of butadiene rubber and natural rubber. It is characterized in that it is blended by mass to 20 parts by mass.

As a result of diligent research on a compounding agent for imparting excellent on-ice performance to a rubber composition for a tire, the inventor of the present invention has found that a tubular inorganic mineral having a hollow annular structure absorbs water like a capillary phenomenon due to its structure. Focusing on the possibility of exhibiting this, it was found that excellent on-ice performance can be obtained by blending this tubular inorganic mineral with a rubber composition for tires. In the present invention, based on this finding, the rubber composition for a tire is composed of the above-mentioned formulation, and in particular, a tubular inorganic mineral is blended, so that the tread absorbs the water film on the ice surface when stepping on the ice surface. It can be removed and excellent on-ice performance can be obtained. In addition, when blending this tubular inorganic mineral, the blending amount of the tubular inorganic mineral is within the above-mentioned appropriate range, so that it is possible to suppress the influence on other tire performance (wear resistance performance). It is possible to achieve both excellent on-ice performance and wear resistance.

In the present invention, it is preferable that the white filler is blended in an amount of 30 parts by mass or more with respect to 100 parts by mass of the rubber component, and the JIS hardness at room temperature is less than 60. By blending the white filler and setting the rubber hardness appropriately in this way, the rubber composition is appropriately softened, which is advantageous for improving the performance on ice.

In the present invention, the tubular inorganic mineral is preferably made of aluminum silicate. Aluminum silicate is produced as a mineral having various structures depending on the production conditions in nature, and may be produced as a mineral having a hollow cyclic structure (halloysite). Therefore, the tubular inorganic mineral of the present invention is naturally used. It will be possible to secure it as a mineral. In addition, the tubular inorganic mineral (halloysite) made of aluminum silicate has the inner surface (center) of the hollow annular structure _{having characteristics similar to Al 2} O ₃ , while the outer surface has characteristics similar to _{SiO 2.} Due to the property of having, the characteristics of the outer surface improve the dispersion of the white filler (silica) in the rubber composition, which is advantageous for appropriately softening the rubber composition and improving the performance on ice. ..

In the present invention, the surface of the tubular inorganic mineral is preferably pH 5-9. This makes it possible to improve tubular inorganic minerals in rubber.

The rubber composition for a tire of the present invention preferably has a glass transition temperature of −60 ° C. or lower. As a result, the physical characteristics of the rubber composition for tires are further improved, which is advantageous for improving the performance on ice.

In the present invention, it is preferable that the butadiene rubber contains a terminal-modified butadiene rubber. As a result, the physical characteristics of the rubber composition for tires are further improved, which is advantageous for improving the performance on ice.

In the present invention, it is preferable that the aromatic-modified terpene resin is blended with the rubber component. As a result, the physical characteristics of the rubber composition for tires are further improved, which is advantageous for improving the performance on ice.

The above-mentioned rubber composition for a tire of the present invention can be suitably used for a tread portion of a studless tire. The studless tire using the rubber composition for a tire of the present invention in the tread portion can achieve both low heat generation and wet performance to a high degree due to the above-mentioned excellent physical properties. The studless tire to which the rubber composition for a tire of the present invention is applied is preferably a pneumatic tire, but may be a non-pneumatic tire. In the case of a pneumatic tire, the inside thereof can be filled with an inert gas such as air or nitrogen or other gas.

In the rubber composition for a tire of the present invention, the rubber component is a diene-based rubber and always contains natural rubber and butadiene rubber. By including these two types of rubber, flexibility and wear resistance at low temperatures can be improved. The blending amount of the butadiene rubber is 30% by mass or more, preferably 40% by mass to 80% by mass in 100% by mass of the diene rubber. The blending amount of the natural rubber is 20% by mass to 70% by mass, preferably 25% by mass to 70% by mass in 100% by mass of the diene rubber. If the blending amount of the butadiene rubber is less than 30% by mass, the flexibility at low temperature may be adversely affected.

The butadiene rubber used in the present invention may be a terminal-modified butadiene rubber. The terminal-modified butadiene rubber is a butadiene rubber in which both or one of its molecular ends is modified with a functional group having reactivity with a silanol group on the silica surface. By using the terminal-modified butadiene rubber as the butadiene rubber, it is possible to further improve the wear resistance while maintaining the performance on ice at a high level. The functional group that reacts with the silanol group is preferably a polyorganosiloxane group, a hydroxyl group-containing polyorganosiloxane structure, an alkoxysilyl group, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, an imino group, an epoxy group, an amide group, and the like. At least one selected from a thiol group and an ether group can be mentioned. When the terminal-modified butadiene rubber is used, the vinyl unit content thereof is preferably 3% by mass to 70% by mass, more preferably 5% by mass to 50% by mass. If the vinyl unit content of the modified butadiene rubber is less than 3% by mass, the workability is lowered. If the vinyl unit content of the modified butadiene rubber exceeds 70% by mass, the performance on ice deteriorates. The vinyl unit content of the modified butadiene rubber shall be measured by infrared spectroscopic analysis (Hampton method). The increase / decrease in the vinyl unit content in the modified butadiene rubber can be appropriately adjusted by a usual method such as a catalyst. The method for preparing the modified butadiene rubber is not particularly limited, and a usual production method can be applied.

The rubber composition for a tire of the present invention may also contain a diene-based rubber other than natural rubber and butadiene rubber (terminally modified butadiene rubber). As the other diene-based rubber, for example, rubber generally used for tire rubber compositions (particularly, winter tire rubber compositions) such as isoprene rubber and styrene-butadiene rubber can be used. These other diene rubbers can be used alone or as any blend.

The rubber composition for a tire of the present invention is always blended with a tubular inorganic mineral having a hollow annular structure. According to the findings of the inventor of the present invention, it is assumed that the tubular inorganic mineral having a hollow annular structure exhibits water absorption like a capillary phenomenon due to its structure. Therefore, the rubber composition for a tire of the present invention is excellent because it can absorb and remove the water film on the ice surface when the tread steps on the ice surface by blending a tubular inorganic mineral having a hollow annular structure. It is possible to obtain performance on ice. The blending amount of the tubular inorganic mineral with respect to 100 parts by mass of the above-mentioned diene rubber is 0.5 parts by mass to 20 parts by mass, preferably 1 part by mass to 15 parts by mass. If the blending amount of the tubular inorganic mineral is less than 1 part by mass, the desired effect cannot be obtained because it is equivalent to substantially not blending the tubular inorganic mineral. If the blending amount of the tubular inorganic mineral exceeds 20 parts by mass, the proportion of the inorganic mineral in the rubber composition becomes too large, and the inorganic mineral becomes substantially a foreign substance in the rubber composition and deteriorates the rubber physical properties. , There is a risk that the breaking strength (wear resistance) will decrease. In addition, the effect of improving the performance on ice may be limited.

As the tubular inorganic mineral, any one having a hollow annular structure as described above can be used. In particular, a tubular inorganic mineral made of aluminum silicate can be preferably used. Aluminum silicate is produced as a mineral having various structures (kaolinite or kaolin having a plate-like structure, halloysite having a hollow annular structure, etc.) depending on the production conditions in nature. , It becomes possible to secure the tubular inorganic mineral of the present invention as a natural mineral. That is, since the tubular inorganic mineral (halloysite) made of aluminum silicate has a naturally hollow cyclic structure, no special processing is required when blending it into the rubber composition in order to improve the performance on ice, and the cost is high. It is useful in terms of surface. Furthermore, halloysite has the property that the inner surface (central part) of the hollow annular structure _{has properties similar to Al 2} O ₃ , while the outer surface has _{properties similar to SiO 2} , so that the outer surface of the halloysite has a property similar to that of SiO 2. Depending on the properties, it tends to have a high affinity with silica. Therefore, when the white filler (silica) is blended with the rubber composition as described later, if a tubular inorganic mineral (halosite) made of aluminum silicate is used in combination, the white filler (silica) in the rubber composition can be used. The dispersion becomes good, which is advantageous for achieving both on-ice performance and wear resistance. A mineral made of aluminum silicate and having a plate-like structure (originally called kaolinite or kaolin as described above) may be referred to as "haloysite", but the halloysite in the present invention is described above. It refers to a substance having a hollow annular structure.

As the tubular inorganic mineral, those having a surface pH preferably in the range of 5 to 9, more preferably in the range of 6 to 8 may be used. Examples of the tubular inorganic mineral having such physical characteristics (surface pH 5-9) include the above-mentioned halloysite. By using a tubular inorganic mineral (haloysite) having such physical characteristics, the white filler (silica) is well dispersed when the white filler (silica) is blended into the rubber composition as described later, so that the white filler (silica) is dispersed well on ice. It is advantageous to improve the performance.

The tubular inorganic mineral has a hollow annular structure (substantially cylindrical shape), and its aspect ratio is preferably 7 to 50, more preferably 10 to 20. By using a tubular inorganic mineral having such an appropriate shape, it is advantageous to obtain excellent on-ice performance due to its structure. If the aspect ratio is less than 7, the tube shape (substantially cylindrical shape) is not substantially formed, so that the desired effect cannot be sufficiently obtained. If the aspect ratio exceeds 50, the wear resistance may deteriorate. The tubular inorganic mineral may have the above-mentioned aspect ratio, but its tube shape (substantially cylindrical shape) has an average outer diameter of, for example, 0.1 nm to 100 nm, an average inner diameter of, for example, 0.05 nm to 100 nm, and an average length. For example, it is preferably 0.5 nm to 1 μm. The aspect ratio, the average outer diameter, the average inner diameter, and the average length can be measured by analyzing the observation images of the electron microscope.

A white filler can be added to the rubber composition for a tire of the present invention. By blending the white filler, the suppleness of the rubber composition can be ensured and the performance on ice can be improved. The blending amount of the white filler is preferably 30 parts by mass or more, and more preferably 32 parts by mass to 150 parts by mass with respect to 100 parts by mass of the diene rubber. If the blending amount of the white filler is less than 30 parts by mass, the above-mentioned suppleness cannot be sufficiently ensured, and the effect of improving the performance on ice cannot be sufficiently expected. In addition, the mechanical properties of the rubber composition cannot be sufficiently ensured, and the basic tire performance (for example, hardness and wear resistance) may deteriorate.

Examples of the white filler include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, and calcium sulfate. These may be used alone or in combination of two or more. Among them, silica is preferable, and the heat generation can be made more excellent.

Examples of silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like, and these may be used alone or in combination of two or more. CTAB adsorption specific surface area of silica is not particularly limited, preferably 100m ² / g~300m ² / g, may more preferably at 120m ² / g~230m ² / g. By setting the CTAB adsorption specific surface area of silica to 100 m ² / g or more, the wear resistance of the rubber composition can be ensured. Further, by setting the CTAB adsorption specific surface area of silica to 300 m ² / g or less, low heat generation can be improved. In the present specification, the CTAB specific surface area of silica is a value measured by ISO 5794.

In the present invention, it is preferable to add a silane coupling agent together with silica. By blending a silane coupling agent, the dispersibility of silica with respect to diene-based rubber can be improved, and the balance between wear resistance and on-ice performance can be further improved. The type of silane coupling agent is not particularly limited as long as it can be used in a rubber composition containing silica, and for example, bis- (3-triethoxysilylpropyl) tetrasulfide and bis (3-). Sulfur-containing silane coupling agents such as triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthiopropyltriethoxysilane can be exemplified. .. The blending amount of the silane coupling agent is preferably 3% by mass to 20% by mass, more preferably 5% by mass to 15% by mass, based on the weight of silica. If the blending amount of the silane coupling agent is less than 3% by mass of the silica blending amount, the silica dispersion may not be sufficiently improved. If the blending amount of the silane coupling agent exceeds 20% by mass of the silica blending amount, the silane coupling agents are condensed with each other, and the desired hardness and strength in the rubber composition cannot be obtained.

The rubber composition for a tire of the present invention may contain carbon black as a filler in addition to the white filler described above. When carbon black is blended, the blending amount thereof is preferably 10 parts by mass to 170 parts by mass, and more preferably 15 parts by mass to 150 parts by mass with respect to 100 parts by mass of the diene rubber. Even when carbon black is contained, by containing a small amount of carbon black in this way, the mechanical properties (hardness and wear resistance) of the rubber composition are not impaired without interfering with the above-mentioned effect of improving the low heat generation property. Basic tire performance such as sex) can be improved. The carbon black may be used as the nitrogen adsorption specific surface area N ₂ SA is, for example, 60m ² / g~200m ² / g. In the present specification, the nitrogen adsorption specific surface area N ₂ SA of carbon black shall be measured according to JIS K6217-2.

An aromatic-modified terpene resin can be blended in the rubber composition for a tire of the present invention. By blending the aromatic-modified terpene resin in this way, the performance on ice and the abrasion resistance can be improved. The aromatic-modified terpene resin is obtained by polymerizing a terpene and an aromatic compound. Examples of terpenes include α-pinene, β-pinene, dipentene, limonene and the like. Examples of the aromatic compound include phenol, styrene, α-methylstyrene, vinyltoluene, indene and the like. These aromatic-modified terpene resins are particularly effective because they have good compatibility with diene-based rubbers. The blending amount of the aromatic-modified terpene resin is preferably 2 parts by mass to 30 parts by mass, and more preferably 5 parts by mass to 20 parts by mass with respect to 100 parts by mass of the diene rubber. When the blending amount of the aromatic-modified terpene resin is less than 2 parts by mass, it is substantially the same as when the aromatic-modified terpene resin is not blended, so that further improvement in on-ice performance cannot be expected. If the blending amount of the aromatic-modified terpene resin exceeds 20 parts by mass, sufficient flexibility in a low temperature state cannot be sufficiently ensured, and the performance on ice may deteriorate.

The rubber composition for tires of the present invention is generally used for rubber compositions for tires such as vulcanization or cross-linking agents, vulcanization accelerators, antiaging agents, plasticizers, processing aids, liquid polymers and thermosetting resins. The various additives used can be blended within a range that does not impair the object of the present invention. In addition, these additives can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or cross-linking. The blending amount of these additives can be a conventional general blending amount as long as it does not contradict the object of the present invention. The rubber composition for a tire can be produced by mixing each of the above components using a normal rubber kneading machine, for example, a Banbury mixer, a kneader, a roll, or the like.

The above-mentioned rubber composition for a tire of the present invention can be suitably used for a tread portion of a pneumatic tire, particularly a winter tire (for example, a studless tire) which is expected to travel on an ice-snow road surface. The pneumatic tire using the rubber composition for a tire of the present invention in the tread portion can highly achieve both excellent on-ice performance and wear resistance due to its excellent physical properties.

The above-mentioned rubber composition for a tire of the present invention has a JIS hardness of less than 60, preferably 45 to 59 at room temperature. By setting the rubber hardness in an appropriate range in this way, it is possible to secure mechanical properties suitable as a tread portion of a pneumatic tire (particularly, a winter tire such as a studless tire). The rubber hardness can be set, for example, by the amount of oil blended in the rubber composition and the amount of filler. For example, when the hardness is set in the above range depending on the blending amount of the oil, the oil is preferably 2 parts by mass to 60 parts by mass, more preferably 5 parts by mass to 40 parts by mass with respect to 100 parts by mass of the above-mentioned diene rubber. It is recommended to mix by mass. In the present invention, the rubber hardness is measured at room temperature (temperature 20 ° C.) by type A of a durometer according to JIS K6253.

In the above-mentioned rubber composition for tires of the present invention, the glass transition temperature is set to −60 ° C. or lower, preferably −64 ° C. or lower. Setting the glass transition temperature in an appropriate range in this way is advantageous for improving the performance on ice. The glass transition temperature can be set by, for example, the rubber type, the blending amount of the resin, and the like. For example, the blending amount of the butadiene rubber may be 30% by mass or more in 100% by mass of the diene-based rubber, and the blending amount of the natural rubber may be 20% by mass to 70% by mass in 100% by mass of the diene-based rubber. In the present invention, the glass transition temperature can be measured by differential scanning calorimetry (DSC).

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.

In preparing 12 kinds of rubber compositions for tires (Standard Example 1, Comparative Examples 1 to 4, Examples 1 to 7) having the compositions shown in Table 1, the components excluding sulfur and the vulcanization accelerator were 1. The mixture was kneaded in a 7 L rubbery mixer for 5 minutes and released when the temperature reached 145 ° C. to form a masterbatch. Sulfur and a vulcanization accelerator were added to the obtained masterbatch and kneaded with an open roll at 70 ° C. to obtain 12 kinds of rubber compositions for tires.

Using the obtained rubber composition for tires, vulcanize at 170 ° C. for 10 minutes using a mold having a predetermined shape (inner dimensions: length 150 mm, width 150 mm, thickness 2 mm) to obtain a vulcanized rubber test piece. Created. The hardness of this vulcanized rubber test piece was measured under the condition of a temperature of 20 ° C. by a durometer type A in accordance with JIS K6253, and is shown together with the "hardness" in Table 1. The average glass transition temperature of this vulcanized rubber test piece was measured by differential scanning calorimetry (DSC) and is also shown in the “Glass transition temperature” column of Table 1.

The obtained rubber composition for tires was evaluated for breaking strength and on-ice performance by the method shown below using the above-mentioned vulcanized rubber test piece.

Breaking strength Using the above-mentioned vulcanized rubber test piece, a dumbbell type JIS No. 3 test piece was produced in accordance with JIS K6251. Using this test piece, a tensile test was performed at room temperature (23 ° C.) at a tensile speed of 500 mm / min, and the tensile breaking strength was measured. The evaluation results are shown in the column of "break strength" in Table 1 as an index with the value of Standard Example 1 as 100 using the obtained values. The larger this index is, the higher the breaking strength is, and it means that the mechanical properties (for example, wear resistance) are excellent.

Performance on ice A studless tire (tire size: 195 65R15) using the obtained rubber composition for tires in the tread portion was vulcanized and molded. The obtained studless tire was assembled to a standard rim, filled with an air pressure of 250 kPa, mounted on a test vehicle, and subjected to a sensory test by a test driver on a test course consisting of an ice road. The obtained results are shown in the "Performance on ice" column of Table 1 as an index with the value of Standard Example 1 as 100. The larger this index value is, the better the performance on ice is.

The types of raw materials used in Table 1 are shown below.
・ NR: Natural rubber, TSR20
-BR: Butadiene rubber, NIPOL BR1220 manufactured by Zeon Corporation
-Modified BR: Terminally modified butadiene rubber, NIPOL BR1261 manufactured by Zeon Corporation (modifying group: polyorganosiloxane group)
-CB: Carbon Black, Cabot Japan Show Black N339 (Nitrogen Adsorption Specific Surface Area N ₂ SA: 94 m ² / g)
-White filler: Silica, Rodia's Zeosil 1165MP (CTAB specific surface area: 159m ² / g)
-Inorganic mineral 1: Tubular inorganic mineral (halloysite), Dragonite HP-A manufactured by APPLIED MINERALS (aspect ratio: 10 to 20, pH = 7)
-Inorganic mineral 2: A crushed product of the above inorganic mineral 1 assuming a spherical inorganic mineral (aspect ratio: 1 to 5)
-Inorganic mineral 3: Plate-like inorganic mineral (kaolin), Kaolin Clay RC-1 manufactured by Takehara Chemical Industry Co., Ltd.
-Silane coupling agent: Si69 manufactured by Evonik Degussa
・ Oil: Showa Shell Sekiyu Extract No. 4 S
-Liquid BR: Liquid butadiene rubber, LBR302 manufactured by Kuraray Co., Ltd.
-Resin: Aromatic modified terpene resin (orange oil), TO-125 manufactured by Yasuhara Chemical Co., Ltd.
-Anti-aging agent: SANTOFLEX 6PPD manufactured by Solutia Europe
・ Wax: Paraffin wax manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. ・ Sulfur: Kinka Ink Oil-containing fine powder sulfur manufactured by Tsurumi Kagaku Kogyo Co., Ltd. ・ Vulcanization accelerator: Noxeller CZ-G manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

As is clear from Table 1, the rubber compositions for tires of Examples 1 to 7 improved the breaking strength (wear resistance) and the performance on ice, and both of these performances were highly compatible. On the other hand, in Comparative Example 1, since the blending amount of the tubular inorganic mineral was too small, the effect of improving the breaking strength and the performance on ice could not be obtained. In Comparative Example 2, since the amount of the tubular inorganic mineral compounded was too large, the breaking strength was rather lowered. In Comparative Example 3, since a spherical inorganic mineral was blended instead of a tubular inorganic mineral, the effect of improving the performance on ice could not be obtained, and the breaking strength was lowered. In Comparative Example 4, since the plate-shaped inorganic mineral was blended instead of the tubular inorganic mineral, the performance on ice deteriorated.

Claims (8)

A tire characterized in that 0.5 parts by mass to 20 parts by mass of a tubular inorganic mineral having a hollow annular structure is blended with 100 parts by mass of a diene-based rubber containing 30% by mass or more of butadiene rubber and natural rubber. Rubber composition for. The rubber composition for a tire according to claim 1, wherein a white filler is blended in an amount of 30 parts by mass or more with respect to 100 parts by mass of the rubber component, and the JIS hardness at room temperature is less than 60. The rubber composition for a tire according to claim 1 or 2, wherein the tubular inorganic mineral is aluminum silicate. The rubber composition for a tire according to any one of claims 1 to 3, wherein the surface of the tubular inorganic mineral has a pH of 5 to 9. The rubber composition for a tire according to any one of claims 1 to 4, wherein the glass transition temperature is −60 ° C. or lower. The rubber composition for a tire according to any one of claims 1 to 5, wherein the butadiene rubber contains a terminal-modified butadiene rubber. The rubber composition for a tire according to any one of claims 1 to 6, wherein an aromatic-modified terpene resin is further blended with the diene-based rubber. A studless tire using the rubber composition for a tire according to any one of claims 1 to 7 for a tread portion.