Rubber composition for tires and studless tires using the same

Abstract

On icy and snowy roads, the coefficient of friction decreases compared to ordinary roads, making them more slippery. Therefore, numerous methods have been proposed to improve the ice performance (braking performance on ice) of studless tires. The objective of the present invention is to provide a rubber composition that has excellent ice performance while suppressing environmental impact. [Solution] The above problem was solved by a tire rubber composition containing 100 parts by mass of diene rubber containing 30 parts by mass or more of butadiene rubber, 30 to 100 parts by mass of carbon black and / or white filler, and 1 to 30 parts by mass of polyhydroxyalkanoic acid powder having two types of monomer units.

Description

Technical Field

[0001] The present invention relates to a rubber composition for tires and a studless tire using the same, and more particularly, to a rubber composition that suppresses environmental impact and has excellent ice performance, and a studless tire using the same.

Background Art

[0002] On icy and snowy road surfaces, the friction coefficient is lower than that on ordinary road surfaces, making it easier to slip. Therefore, conventionally, many methods have been proposed to improve the ice performance (braking performance on ice) of studless tires. For example, there is a method of blending polymer fine particles into the tread rubber of a tire to impart surface roughness to the tread rubber. However, there are concerns about environmental problems caused by the material that has fallen off from the tread. Therefore, at present, there is a need for a method that is environmentally friendly and further improves ice performance. In addition, although techniques for blending biodegradable polymers into tread rubber are disclosed in, for example, Patent Documents 1 to 4 below, the technical idea of using polyhydroxyalkanoic acid powder having two or more kinds of monomer units of the present invention described below to improve ice performance is not disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] The object of the present invention is to provide a rubber composition for tires that suppresses environmental impact and has excellent ice performance, and a studless tire using the same. [Means for solving the problem]

[0005] As a result of diligent research, the inventors discovered that the above problems can be solved by blending a specific amount of polyhydroxyalkanoic acid powder into diene rubber, and thus completed the present invention.

[0006] In other words, the present invention provides a tire rubber composition characterized by containing 100 parts by mass of a diene rubber containing 30 parts by mass or more of butadiene rubber, 30 to 100 parts by mass of carbon black and / or white filler, and 1 to 30 parts by mass of polyhydroxyalkanoic acid powder having monomer units represented by the following general formulas (1) and (2).

[0007] [ka]

[0008] (In the formula, R1 and R2 each independently represent a saturated hydrocarbon group having 1 to 22 carbon atoms. However, R1 and R2 cannot simultaneously represent a saturated hydrocarbon group having 1 carbon atom.) Furthermore, the present invention provides a studless tire using the aforementioned tire rubber composition. [Effects of the Invention]

[0009] The present invention provides a tire rubber composition and a studless tire using the same, which contains 30 to 100 parts by mass of carbon black and / or a white filler, and 1 to 30 parts by mass of polyhydroxyalkanoic acid powder having monomer units represented by the general formulas (1) and (2), respectively, with respect to 100 parts by mass of diene rubber containing 30 parts by mass or more of butadiene rubber. The polyhydroxyalkanoic acid powder used in the present invention has monomer units represented by general formulas (1) and (2), respectively. The presence of the monomer unit represented by general formula (2) imparts flexibility and toughness to the polyhydroxyalkanoic acid powder, making it possible to further improve the ice performance of the tread rubber, which is based on sufficient surface roughness, compared to the conventional technology. [Modes for carrying out the invention]

[0010] The present invention will be described in more detail below.

[0011] (Diene-based rubber) The diene rubber used in this invention can be any diene rubber that can be incorporated into tire rubber compositions, such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), and ethylene-propylene-diene polymer (EPDM). These may be used individually or in combination of two or more. Furthermore, their molecular weight and microstructure are not particularly limited, and they may be end-modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl groups, etc., or epoxidized. The weight-average molecular weight of the diene rubber is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000. In this specification, the weight-average molecular weight is the weight-average molecular weight (Mw) obtained by gel permeation chromatography (GPC) measurement on a standard polystyrene basis. Furthermore, from the viewpoint of improving ice performance, it is preferable that butadiene rubber accounts for 30 parts by mass or more, preferably 40 parts by mass or more, of 100 parts by mass of diene rubber, and a form that uses natural rubber in combination is even more preferable. Also, the diene rubber preferably has a glass transition temperature (Tg) of -50°C or lower. By defining the Tg in this way, the performance on ice is improved. When a plurality of types of diene rubber are included, the Tg referred to in this specification is a value calculated based on the sum of the products of the glass transition temperature of each rubber multiplied by the weight fraction of each rubber, that is, the weighted average. At the time of calculation, the sum of the weight fractions of each component is set to 1.0. The glass transition temperature (Tg) referred to in the present invention is measured by differential scanning calorimetry (DSC) under the condition of a heating rate of 20°C / min to measure the thermogram, and refers to the temperature at the midpoint of the transition region. More preferably, the average Tg is -60°C or lower.

[0012] (Carbon black) Examples of the carbon black used in the present invention include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPE, and SRF. These may be used alone or in combination of two or more. Also, from the viewpoint of improving the performance on ice, the carbon black preferably has a nitrogen adsorption specific surface area (N2SA) of 10 to 300 m 2 / g, and more preferably 50 to 150 m 2 / g. The nitrogen adsorption specific surface area (N2SA) is a value measured in accordance with JIS K 6217-2:2001 "Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single point method".

[0013] [[ID=--]] (White filler) Specific examples of the white filler used in the present invention include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, calcium sulfate, etc. These may be used alone or in combination of two or more. Among these, silica is preferable because the performance on ice is better.

[0014] Examples of silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. These may be used alone or in combination of two or more. Silica derived from biomass materials such as rice husks may also be used.

[0015] From the perspective of improving ice performance, silica preferably has a CTAB adsorption specific surface area of 50 to 300 m 2 / g, more preferably 90 to 200 m 2 / g. The CTAB adsorption specific surface area is a value measured according to JIS K6217-3:2001 "Part 3: Method for determining specific surface area - CTAB adsorption method" for the amount of n-hexadecyltrimethylammonium bromide adsorbed on the silica surface.

[0016] (Polyhydroxyalkanoic acid powder) The polyhydroxyalkanoic acid powder used in the present invention has monomer units represented by the following general formulas (1) and (2) respectively and has biodegradability.

[0017]

Chemical formula

[0018] (In the formula, R1 and R2 each independently represent a saturated hydrocarbon group having 1 to 22 carbon atoms. However, R1 and R2 do not simultaneously represent a saturated hydrocarbon group having 1 carbon atom.)

[0019] The polyhydroxyalkanoic acid powder used in the present invention preferably has a form in which R1 and R2 each independently represent a saturated hydrocarbon group having 1 to 12 carbon atoms, more preferably a form in which they represent a saturated hydrocarbon group having 1 to 8 carbon atoms, still more preferably a form in which they represent a saturated hydrocarbon group having 1 to 5 carbon atoms, and particularly preferably has the following structure. In the following, m and n represent the number of repeating units.

[0020]

Chemical formula

[0021] [ka]

[0022] [ka]

[0023] The polyhydroxyalkanoic acid powder used in this invention can be given more flexibility and toughness than the 3HB homopolymer due to the presence of monomer units represented by general formula (2), which has a larger number of carbon atoms than general formula (1). This allows for the formation of sufficient surface roughness in the tread rubber, further improving ice performance compared to the conventional technology. From this viewpoint, PHBV is particularly preferred among the above.

[0024] Furthermore, the polyhydroxyalkanoic acid powder used in this invention is preferably configured in the following ways, from the viewpoint of improving ice performance. (A) The average particle size of the polyhydroxyalkanoic acid powder is preferably 1000 μm or less, more preferably 300 μm, and particularly preferably 100 μm or less. The lower limit of the average particle size is, for example, 1 μm or more. Within this particle size range, excellent ice performance can be provided without impairing the fracture properties required for the tire. The average particle size of (A) the polyhydroxyalkanoic acid powder can be adjusted by conventional methods, such as sieving. (B) Preferably, the decomposition rate of the polyhydroxyalkanoic acid powder in soil is 90% or more within two years, or the decomposition rate of the polyhydroxyalkanoic acid powder in seawater is 90% or more within six months. Specifically, the decomposition rate in soil can be measured according to ISO 17556, and it is preferable that the degree of biodegradation in soil under a composting environment at an ambient temperature (25°C) is 90% or more within two years (absolute or relative). Furthermore, the decomposition rate in seawater can be measured according to ASTM D6691, and it is preferable that the degree of biodegradation in seawater at 30°C is 90% or more within six months (absolute or relative). (C) The weight-average molecular weight of the polyhydroxyalkanoic acid powder is preferably 200,000 to 800,000, more preferably 300,000 to 600,000, and particularly preferably 350,000 to 550,000. (D) It is preferable that the polyhydroxyalkanoic acid powder satisfies the following formula (1).

[0025]

number

[0026] (In formula (1), x represents the total amount (mol%) of monomer units represented by general formulas (1) and (2) of the polyhydroxyalkanoic acid powder, and m represents the proportion (mol%) of monomer units represented by general formula (1) to the total amount of monomer units.)

[0027] In other words, it is preferable that the monomer unit represented by general formula (2) is 0.8 mol% or more and 30 mol% or less, relative to the total amount of monomer units represented by general formulas (1) and (2), and more preferably 1 mol% or more and 10 mol% or less.

[0028] The more combinations of conditions (A) to (D) described above are met, the more the effects of the present invention are improved.

[0029] (Compounding ratio of rubber composition for tires) The tire rubber composition of the present invention is characterized by containing 30 to 100 parts by mass of carbon black and / or white filler and 1 to 30 parts by mass of the polyhydroxyalkanoic acid powder, with respect to 100 parts by mass of diene rubber containing 30 parts by mass or more of butadiene rubber. If the amount of carbon black and / or white filler added to 100 parts by mass of the diene rubber is less than 30 parts by mass, the mechanical properties and abrasion resistance of the rubber composition deteriorate. Conversely, if it exceeds 100 parts by mass, the low-temperature flexibility of the rubber composition decreases, resulting in poor performance on ice. If the amount of polyhydroxyalkanoic acid powder added to 100 parts by mass of the diene rubber is less than 1 part by mass, the amount added is too small to achieve the effects of the present invention. Conversely, if it exceeds 30 parts by mass, the rolling performance (low rolling resistance) of tires, etc., or the mechanical properties of the rubber composition will decrease.

[0030] The amount of carbon black and / or white filler added is preferably 45 to 90 parts by mass per 100 parts by mass of diene rubber. When carbon black is added, the amount is preferably 1 to 30 parts by mass per 100 parts by mass of diene rubber. When silica is added, the amount is preferably 30 to 90 parts by mass per 100 parts by mass of diene rubber. The amount of polyhydroxyalkane powder blended is preferably 2 to 20 parts by mass, and more preferably 5 to 15 parts by mass, per 100 parts by mass of diene rubber.

[0031] (Other ingredients) In addition to the components mentioned above, the rubber composition for tires in the present invention may contain various additives commonly used in rubber compositions, such as vulcanizing or crosslinking agents; vulcanizing or crosslinking accelerators; zinc oxide; antioxidants; plasticizers; silane coupling agents; and thermally expandable microcapsules. These additives can be mixed in a conventional manner to form a composition which can then be used for vulcanization or crosslinking. The amounts of these additives can also be conventional amounts, as long as they do not contradict the purpose of the present invention.

[0032] Furthermore, the tire of the present invention can be prepared using the tire rubber composition of the present invention, and is preferably a pneumatic tire, which can be filled with air, nitrogen or other inert gases and other gases. The tire of the present invention is also preferably applied to a tread, especially a capped tread, to make a studless tire. [Examples]

[0033] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0034] Standard example, Examples 1-6, and Comparative Examples 1-3 Sample preparation In the formulations (parts by mass) shown in Table 1, the components excluding the vulcanization system (vulcanization accelerator, sulfur) were kneaded in a 1.7-liter sealed Banbury mixer for 5 minutes, then released from the mixer and cooled to room temperature. Subsequently, the composition was put back into the same Banbury mixer, the vulcanization system was added and kneaded to obtain a rubber composition. The obtained rubber composition was press-vulcanized at a temperature of less than 150°C for 10 minutes, and its physical properties were measured using the test methods described below.

[0035] Ice Performance: Samples were prepared by attaching the obtained vulcanized rubber test pieces to a flattened cylindrical rubber base. The samples were immersed in room temperature water for 24 hours. After immersion, the ice friction coefficient of the samples was measured using an ice friction tester under the conditions of a measurement temperature of -1.5°C, a load of 98N, and a road surface speed of 20 km / h. The obtained ice friction coefficient is expressed as an index, with the standard example value set to 100. A larger index indicates greater ice friction force and superior ice performance.

[0036] The results are shown in Table 1.

[0037] [Table 1]

[0038] *1: NR (STR20, manufactured by Bombandit, glass transition temperature = -65°C) *2: BR (Nipol BR1220 manufactured by Nippon Zeon Co., Ltd., glass transition temperature = -110℃) *3: Carbon black (Show Black N339 manufactured by Cabot Japan) *4: Silica (ULTRASIL VN3 manufactured by Evonik DeGussa) *5: Silane coupling agent (Si69 manufactured by Evonik DeGussa, bis(3-triethoxysilylpropyl)tetrasulfide) *6: Oil (Extract No. 4S manufactured by Showa Shell Sekiyu K.K.) *7: Polyhydroxyalkanoate 1 (see Table 2 below) *8: Polyhydroxyalkanoate 2 (see Table 2 below) *9: Polyhydroxyalkanoate 3 (see Table 2 below) *10: Polyhydroxyalkanoate 4 (see Table 2 below) *11: Polylactic acid (see Table 2 below) *12: Sulfur (Sulfur processed by Hosoi Chemical Industry Co., Ltd.) *13: Vulcanization accelerator (Sancellar CM-G manufactured by Sanshin Chemical Industry Co., Ltd., sulfenamide-based vulcanization accelerator)

[0039] [Table 2]

[0040] As shown in Table 1, the rubber compositions of each example contained 30 to 100 parts by mass of carbon black and / or white filler, and 1 to 30 parts by mass of polyhydroxyalkanoic acid powder having monomer units represented by general formulas (1) and (2), respectively, with respect to 100 parts by mass of diene rubber containing 30 parts by mass or more of butadiene rubber. As a result, the ice performance was improved compared to the standard example. In contrast, Comparative Examples 1 and 2 used a 3HB homopolymer, and therefore the ice performance was not improved as much as in the respective examples, or in fact, the ice performance was reduced. Comparative Example 3, which uses polylactic acid, did not show the same level of improvement in ice performance as the other examples.

[0041] The present invention encompasses the following embodiments. Embodiment 1: A tire rubber composition characterized by containing, per 100 parts by mass of diene rubber containing 30 parts by mass or more of butadiene rubber, 30 to 100 parts by mass of carbon black and / or white filler, and 1 to 30 parts by mass of polyhydroxyalkanoic acid powder having monomer units represented by the following general formulas (1) and (2).

[0042] [ka]

[0043] (In the formula, R1 and R2 each independently represent a saturated hydrocarbon group having 1 to 22 carbon atoms. However, R1 and R2 cannot simultaneously represent a saturated hydrocarbon group having 1 carbon atom.) Embodiment 2: The tire rubber composition according to Embodiment 1, characterized in that the average particle size of the polyhydroxyalkanoic acid powder is 1000 μm or less. Embodiment 3: The tire rubber composition according to Embodiment 1 or 2, characterized in that the decomposition rate of the polyhydroxyalkanoic acid powder in soil is 90% or more within two years, or the decomposition rate of the polyhydroxyalkanoic acid powder in seawater is 90% or more within six months. Embodiment 4: The tire rubber composition according to any one of Embodiments 1 to 3, characterized in that the weight-average molecular weight of the polyhydroxyalkanoic acid powder is 200,000 to 800,000. Embodiment 5: The tire rubber composition according to any one of Embodiments 1 to 4, characterized in that the polyhydroxyalkanoic acid powder satisfies the following formula (1).

[0044]

number

[0045] (In formula (1), x represents the total amount (mol%) of monomer units represented by general formulas (1) and (2) of the polyhydroxyalkanoic acid powder, and m represents the proportion (mol%) of monomer units represented by general formula (1) to the total amount of monomer units.) Embodiment 6: A studless tire using the rubber composition described in any of Embodiments 1 to 5.

Claims

1. A tire rubber composition characterized by containing, per 100 parts by mass of diene rubber containing 30 parts by mass or more of butadiene rubber, 30 to 100 parts by mass of carbon black and / or white filler, and 1 to 30 parts by mass of polyhydroxyalkanoic acid powder having monomer units represented by the following general formulas (1) and (2). 【Chemistry 1】 (In the formula, R1 and R2 each independently represent a saturated hydrocarbon group having 1 to 22 carbon atoms. However, R1 and R2 cannot simultaneously represent a saturated hydrocarbon group having 1 carbon atom.)

2. The tire rubber composition according to claim 1, characterized in that the average particle size of the polyhydroxyalkanoic acid powder is 1000 μm or less.

3. The tire rubber composition according to claim 1, characterized in that the decomposition rate of the polyhydroxyalkanoic acid powder in soil is 90% or more within two years, or the decomposition rate of the polyhydroxyalkanoic acid powder in seawater is 90% or more within six months.

4. The tire rubber composition according to claim 1, characterized in that the weight-average molecular weight of the polyhydroxyalkanoic acid powder is 200,000 to 800,000.

5. The tire rubber composition according to claim 1, characterized in that the polyhydroxyalkanoic acid powder satisfies the following formula (1). [Math 1] (In formula (1), x represents the total amount (mol%) of monomer units represented by general formulas (1) and (2) in the polyhydroxyalkanoic acid powder, and m represents the ratio (mol%) of monomer units represented by general formula (1) to the total amount of monomer units.)

6. A studless tire using the tire rubber composition described in claim 1.

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