Rubber composition for tires and tires using the same

Abstract

Rubber compositions for tires, and especially tires using these compositions, require improved strength. It is known that reducing the 100% modulus is effective in improving fracture characteristics such as tensile strength and elongation at break. However, since 100% modulus affects the tire's driving performance, the industry seeks to improve fracture characteristics without reducing the 100% modulus. [Solution] The above problem was solved by a tire rubber composition containing 0.5 to 10 parts by mass of polyhydroxyalkanoic acid powder having two types of monomer units, per 100 parts by mass of diene rubber.

Description

Technical Field

[0001] The present invention relates to a rubber composition for tires and a tire using the same, and more particularly, to a rubber composition for tires capable of improving fracture properties such as fracture strength and fracture elongation without reducing the 100% modulus, and a tire using the same.

Background Art

[0002] For rubber compositions for tires, especially for tires using the same, an improvement in strength is required. It is known that reducing the 100% modulus is effective for improving fracture properties such as fracture strength and fracture elongation. However, since the 100% modulus affects the running performance of tires, in the industry, it is required to improve the fracture physical properties without reducing the 100% modulus. Although technologies for blending biodegradable polymers into tread rubber are disclosed in, for example, Patent Documents 1 to 4 below, a technical idea of using polyhydroxyalkanoic acid powder having two or more kinds of monomer units of the present invention described below to improve fracture properties such as fracture physical properties and fracture elongation without reducing the 100% modulus 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

[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 0.5 to 10 parts by mass of polyhydroxyalkanoic acid powder having monomer units represented by the following general formulas (1) and (2), respectively, and having a weight-average molecular weight of 100,000 to 550,000, per 100 parts by mass of diene rubber.

[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.) The present invention also provides a tire using the aforementioned tire rubber composition. [Effects of the Invention]

[0009] The present invention provides a tire rubber composition and a tire using the same, which contains 0.5 to 10 parts by mass of polyhydroxyalkanoic acid powder having monomer units represented by general formulas (1) and (2) respectively, per 100 parts by mass of diene 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 an effect of improving the 100% modulus and fracture properties to the polyhydroxyalkanoic acid powder, making it possible to improve fracture properties without reducing the 100% modulus. [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. Also, the rubber composition for tires of the present invention preferably contains 50 parts by mass or more of NR in 100 parts by mass of the diene rubber. NR has the property that when stretched, its orientation aligns and it crystallizes. In the present invention, the polyhydroxyalkanoic acid powder is presumed to have the effect of promoting the crystallization of NR, and even with a small amount of blending, the crystallization can be achieved, leading to an improvement in the fracture properties of the rubber. From this perspective, in 100 parts by mass of the diene rubber, NR preferably occupies 50 parts by mass or more.

[0012] (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 a weight average molecular weight of 100,000 to 550,000. The polyhydroxyalkanoic acid powder used in the present invention has biodegradability.

[0013] [Chemical formula]

[0014] (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.)

[0015] 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 representing a saturated hydrocarbon group having 1 to 8 carbon atoms, still more preferably a form representing 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.

[0016] [Chemical formula]

[0017] [Chemical formula]

[0018] [ka]

[0019] The polyhydroxyalkanoic acid powder used in this invention, due to the presence of monomer units represented by general formula (2) which have a larger number of carbon atoms than general formula (1), can be given improved 100% modulus and fracture properties compared to the 3HB homopolymer. This makes it possible to provide a tire rubber composition with improved fracture properties such as fracture physical properties and fracture elongation without reducing the 100% modulus. From this viewpoint, PHBV is particularly preferred among the above.

[0020] The polyhydroxyalkanoic acid powder used in this invention has a weight-average molecular weight of 100,000 to 550,000. If the weight-average molecular weight is less than 100,000, the fracture properties decrease, while if it exceeds 550,000, the processability or rolling performance (low rolling resistance) of tires, etc., decreases.

[0021] Furthermore, from the viewpoint of further improving fracture properties without reducing the modulus by 100%, the polyhydroxyalkanoic acid powder used in the present invention preferably has the following form. (A) The weight-average molecular weight of the polyhydroxyalkanoic acid powder is preferably 200,000 to 550,000, and more preferably 350,000 to 550,000. (B) It is preferable that the polyhydroxyalkanoic acid powder satisfies the following formula (1).

[0022]

number

[0023] (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.)

[0024] In other words, it is preferable that the monomer unit represented by general formula (2) is 0.8 mol% or more and 10 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 8 mol% or less. (C) 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. The average particle size can be adjusted by conventional methods, such as sieving.

[0025] The more combinations of conditions (A) to (C) described above are met, the more the effects of the present invention are improved.

[0026] Furthermore, from the viewpoint of superior environmental performance, the polyhydroxyalkanoic acid powder used in the present invention preferably satisfies the following condition (D). (D) 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).

[0027] (Carbon Black) The tire rubber composition of the present invention preferably contains carbon black. Examples of carbon black used in the tire rubber composition of the present invention include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPE, and SRF, which may be used individually or in combination of two or more. Furthermore, from the viewpoint of improving the effects of the present invention, carbon black should have a nitrogen adsorption specific surface area (N2SA) of 50 to 200 m². 2 It is preferable that the amount is / g, and 70-150m 2 It is even more preferable that it be / g. The nitrogen adsorption specific surface area (N2SA) was measured according to JIS K 6217-2:2001 "Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single point method".

[0028] (Compounding ratio of rubber composition for tires) The rubber composition for tires of the present invention is characterized by containing 0.5 to 10 parts by mass of the polyhydroxyalkanoic acid powder per 100 parts by mass of diene rubber. If the amount of polyhydroxyalkanoic acid powder added to 100 parts by mass of the diene rubber is less than 0.5 parts by mass, the amount added is too small to achieve the effects of the present invention, while if it exceeds 10 parts by mass, the elongation at break and tensile strength decrease.

[0029] The amount of polyhydroxyalkane powder blended is preferably 0.5 to 8 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of diene rubber. Furthermore, when PHBV is used as the polyhydroxyalkanoic acid, it can achieve the same effect even with a smaller amount compared to other polyhydroxyalkanoic acids. Therefore, the amount of PHBV is preferably 2 to 5 parts by mass per 100 parts by mass of diene rubber. Furthermore, when carbon black is added, the amount added is preferably 25 to 70 parts by mass, and more preferably 30 to 60 parts by mass, per 100 parts by mass of diene rubber.

[0030] (Other ingredients) In addition to the components mentioned above, the rubber tire composition of the present invention may contain various additives commonly used in rubber tire compositions, such as vulcanizing or crosslinking agents; vulcanizing or crosslinking accelerators; zinc oxide; antioxidants; plasticizers; white fillers such as silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium dioxide, and calcium sulfate; and silane coupling agents. 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 the conventional amounts, as long as they do not contradict the purpose of the present invention.

[0031] Furthermore, the tire of the present invention can be prepared using the tire rubber composition of the present invention. In this case, the maximum kneading temperature of the tire rubber composition before the addition of the vulcanization system (vulcanizing or crosslinking agent, vulcanization or crosslinking accelerator) is preferably 120 to 170°C, more preferably 125 to 165°C, and particularly preferably 130 to 160°C. Setting the maximum kneading temperature in this way has the advantage of improving the mixing and dispersion state of compounding agents such as carbon black and silica. The tire of the present invention is preferably a pneumatic tire and can be filled with air, an inert gas such as nitrogen, and other gases. Furthermore, the tire of the present invention is suitable for use with treads, especially cap treads. [Examples]

[0032] 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.

[0033] Standard Example 1, Examples 1-6, and Comparative Examples 1-5 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. The maximum kneading temperature during this process was 130°C. Next, the kneaded mixture was released from the mixer and allowed to cool to room temperature. Subsequently, the composition was returned to the same Banbury mixer, the vulcanization system was added and kneaded to obtain a tire rubber composition. The obtained tire 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.

[0034] 100% Tensile Stress, Tensile Strength, Elongation at Break, and Fracture Energy: 100% tensile stress (100% modulus), tensile strength, elongation at break, and fracture energy were measured according to JIS K6251 "Vulcanized rubber and thermoplastic rubber - Method for determining tensile properties". The results are shown as an index with the value of Standard Example 1 set to 100 (see formula below). A larger index indicates that the vulcanized tire rubber composition is well reinforced, has greater mechanical strength, and exhibits superior fracture characteristics. • 100% tensile stress index = (100% tensile stress of each formulation) / (100% tensile stress of standard example 1) × 100 • Tensile strength index = (Fracture stress of each compound) / (Fracture stress of standard example 1) × 100 • Breaking elongation index = (Breaking elongation of each formulation) / (Breaking elongation of standard example 1) × 100 • Destruction energy index = (Destruction energy of each formulation) / (Destruction energy of standard example 1) × 100

[0035] The results are shown in Table 1.

[0036] [Table 1]

[0037] *1: NR (STR20, manufactured by Techbihan, glass transition temperature = -70 to -80°C) *2: BR (Nipol BR1220 manufactured by Nippon Zeon Co., Ltd., glass transition temperature = -110℃) *3: Carbon Black A (SAF, manufactured by Tokai Carbon Co., Ltd., Seast 9) *4: Carbon Black B (HAF, manufactured by Nippon Steel Carbon Co., Ltd., Nitelon #200) *5: Sulfur (Sulfur processed by Hosoi Chemical Industry Co., Ltd.) *6: Vulcanization accelerator (Sancellar CM-G manufactured by Sanshin Chemical Industry Co., Ltd., sulfenamide-based vulcanization accelerator) *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: Maximum mixing temperature of the tire rubber composition when the components excluding the vulcanizing agent are mixed for 5 minutes in a sealed Banbury mixer.

[0038] [Table 2]

[0039] As shown in Table 1, the tire rubber compositions of each example contain 0.5 to 10 parts by mass of polyhydroxyalkanoic acid powder having monomer units represented by general formulas (1) and (2) respectively and having a weight-average molecular weight of 100,000 to 550,000, per 100 parts by mass of diene rubber. Compared to Standard Example 1, fracture properties such as fracture physical properties and fracture elongation were improved without reducing the 100% modulus. In contrast, Comparative Examples 1 and 2 showed reduced tensile strength and elongation at break because the amount of polyhydroxyalkanoic acid used exceeded the upper limit specified in the present invention. Comparative Examples 3 and 4 are examples using 3HB homopolymers, resulting in decreased tensile strength, elongation at break, and fracture energy. Comparative Example 5, which uses polylactic acid, exhibited reduced tensile strength, elongation at break, and fracture energy.

[0040] Examples 7-8 The above-mentioned "Standard Example 1, Examples 1-6, and Comparative Examples 1-5" were repeated, except that each component was changed as shown in Table 3 below. The results are shown in Table 3.

[0041] [Table 3]

[0042] As shown in Table 3, the tire rubber compositions of each example contain 0.5 to 10 parts by mass of polyhydroxyalkanoic acid powder having monomer units represented by general formulas (1) and (2) respectively and having a weight-average molecular weight of 100,000 to 550,000, per 100 parts by mass of diene rubber. Compared to Standard Example 1, fracture properties such as fracture physical properties and fracture elongation were improved without reducing the 100% modulus.

[0043] Examples 9-12 The above-mentioned "Standard Example 1, Examples 1-6, and Comparative Examples 1-5" were repeated, except that each component was changed as shown in Table 4 below. The results are shown in Table 4.

[0044] [Table 4]

[0045] Based on the results in Table 4 and the inventors' studies, it was found that the amount of carbon black added is preferably 25 to 70 parts by mass, and more preferably 30 to 60 parts by mass, per 100 parts by mass of diene rubber. Furthermore, it was found that the desired effect can be achieved even when the mixture contains butadiene rubber in addition to natural rubber.

[0046] Standard Example 2, Examples 13-15 The above-mentioned "Standard Example 1, Examples 1-6, and Comparative Examples 1-5" were repeated, except that each component was changed as shown in Table 5 below. The results are shown in Table 5. Note that "Standard Example 1" in "Standard Example 1, Examples 1-6, and Comparative Examples 1-5" should be read as "Standard Example 2," and Examples 13-15 are compared with Standard Example 2.

[0047] [Table 5]

[0048] Based on the results in Table 5 and the inventors' investigations, it was found that even when the type of carbon black is changed, the amount of carbon black blended is preferably 25 to 70 parts by mass, and more preferably 30 to 60 parts by mass, per 100 parts by mass of diene rubber.

[0049] Examples 16-19 The above-mentioned "Standard Example 1, Examples 1-6, and Comparative Examples 1-5" were repeated, except that the components and maximum mixing temperature were changed as shown in Table 6 below. The results are shown in Table 6.

[0050] [Table 6]

[0051] Based on the results in Table 6 and the inventors' investigations, it was found that the maximum mixing temperature of the tire rubber composition before the addition of the vulcanization system (vulcanizing or crosslinking agent, vulcanization or crosslinking accelerator) is preferably 120 to 170°C, and more preferably 125 to 165°C.

[0052] The present invention encompasses the following embodiments. Embodiment 1: A tire rubber composition characterized by containing 0.5 to 10 parts by mass of polyhydroxyalkanoic acid powder having monomer units represented by the following general formulas (1) and (2), respectively, and having a weight-average molecular weight of 100,000 to 550,000, per 100 parts by mass of diene rubber.

[0053] [ka]

[0054] Furthermore, R1 and R2 cannot simultaneously represent a saturated hydrocarbon group with one carbon atom. Embodiment 2: The tire rubber composition according to Embodiment 1, characterized in that the polyhydroxyalkanoic acid powder satisfies the following formula (1).

[0055]

number

[0056] (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 3: The tire rubber composition according to Embodiment 1 or 2, characterized in that the tire rubber composition contains carbon black, and the carbon black content is 20 to 80 parts by mass per 100 parts by mass of the diene rubber. Embodiment 4: A tire rubber composition according to any one of Embodiments 1 to 3, characterized in that natural rubber accounts for 50 parts by mass or more of 100 parts by mass of the diene rubber. Embodiment 5: A tire using the tire rubber composition described in any of Embodiments 1 to 4.

Claims

1. A tire rubber composition characterized by containing 0.5 to 10 parts by mass of polyhydroxyalkanoic acid powder having monomer units represented by the following general formulas (1) and (2), respectively, and having a weight-average molecular weight of 100,000 to 550,000, per 100 parts by mass of diene rubber. 【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 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.)

3. The tire rubber composition according to claim 1, characterized in that the tire rubber composition contains carbon black, and the carbon black content is 20 to 80 parts by mass per 100 parts by mass of the diene rubber.

4. The tire rubber composition according to claim 1, characterized in that natural rubber accounts for 50 parts by mass or more of 100 parts by mass of the diene rubber.

5. A tire using the rubber composition for tires described in claim 1.

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