Rubber composition for tires and pneumatic tire using the same

Abstract

Rubber composition for tires containing per 100 parts by mass of a rubber component: 1 to 30 parts by mass of a phosphate having a coagulation point of -50 °C or lower, and 1 to 20 parts by mass of a thermoplastic elastomer having a peak tanδ of 1.5 to 2.0 and an initial peak temperature in a range of -20 °C to 20 °C, as determined by a dynamic viscoelasticity test specified in JIS K6394 and measured under the conditions of a frequency of 10 Hz, a static strain of 10% and a dynamic strain of 0.15%, wherein the rubber component has been selected from a group comprising a natural rubber, an isoprene rubber, a butadiene rubber, a styrene-butadiene rubber, a styrene-isoprene copolymer rubber, a butadiene-isoprene copolymer rubber and a styrene-isoprene-butadiene copolymer rubber, and wherein the thermoplastic elastomer is a styrene thermoplastic elastomer having a polystyrene as a hard segment, and wherein the thermoplastic elastomer is a block copolymer having a hydrogenated polydiene as a soft segment.

Description

[Technical field]

[0001] The present invention relates to a rubber composition for tires and also to a pneumatic tire using the same. [State of the art]

[0002] Pneumatic tires must not only deliver excellent fuel efficiency but also provide excellent grip on wet roads, i.e., wet grip. However, these properties contradict each other, making it difficult to simultaneously improve them. In addition, at low temperatures, the elastic modulus of a rubber compound increases, leading to a decrease in grip properties. Therefore, even winter tires have problems with low-temperature performance.

[0003] As a tire capable of reducing the rolling resistance of a tire tread, that is, improving fuel efficiency without impairing other properties, particularly wet grip, PTL 1 discloses a tire characterized in that the tread contains a rubber composition including at least one kind of a diene elastomer, at least one kind of a reinforcing filler, and more than 10 phr of a hydrogenated thermoplastic styrene (“TPS”) elastomer.

[0004] However, PTL 1 is silent on low-temperature performance, and there is still room for further improvements in fuel efficiency, wet grip, and low-temperature performance.

[0005] US 2017 / 121490 A1 discloses a rubber composition and a pneumatic tire. The rubber composition contains a rubber component including a diene rubber; an inorganic filler having a BET of 10 to 120 m 2 / g, which is formed from a compound of the following formula, magnesium sulfate or silicon carbide; and a finely divided carbon black with a BET of 151 m 2 / g or more and / or a low-temperature plasticizer having a freezing point of -10 °C or lower, wherein the rubber composition comprises, per 100 parts by mass of the rubber component, 1 to 70 parts by mass of the inorganic filler, 5 to 140 parts by mass of the fine-particle carbon black, and 1 to 30 parts by mass of the low-temperature plasticizer, the combined amount of the filler and the carbon black being 50 to 190 parts by mass, and mM-xSiO y-zH2O, wherein M represents at least one metal selected from the group consisting of Al, Mg, Ti, Ca, and Zr, or an oxide or hydroxide of the metal; m represents an integer from 1 to 5; x represents an integer from 0 to 10; y represents an integer from 2 to 5; and z represents an integer from 0 to 10.

[0006] US 2008 / 0188621 A1 discloses a rubber composition comprising 60 to 0.1 parts by weight of a non-conjugated polyene copolymer, which is a random copolymer containing 96 to 70 mol percent of structural units derived from an alpha-olefin and 4 to 30 mol percent of structural units derived from a non-conjugated polyene, and having a glass transition temperature of -25 to 20°C, 40 to 99.9 parts by weight of a diene rubber, and at least one member selected from the group of specific polymers. [List of citations][Patent literature] [PTL 1] JP 2013-510939 T (the term “JP ... T” here means a published Japanese translation of a PCT patent application) [PTL 2] JP 2014-189698 A [PTL 3] JP 2015-110703 A [PTL 4] JP 2015-110704 A [Summary of the invention][Problem to be solved by the invention]

[0007] In view of the above points, an object of the invention is to provide a rubber composition for tires capable of improving fuel efficiency, wet grip and low temperature performance, and also to provide a pneumatic tire using the same.

[0008] Incidentally, PTLs 2 to 4 disclose a rubber composition blended with a hydrogenated thermoplastic elastomer to improve grip. However, they are silent regarding fuel efficiency and low-temperature performance. [Means of solving the problem]

[0009] In order to achieve the above-mentioned objects, the rubber composition for tires according to the invention contains, per 100 parts by mass of a rubber component, 1 to 30 parts by mass of a phosphate having a coagulation point of -50°C or lower, and 1 to 20 parts by mass of a thermoplastic elastomer having a peak value of tanδ of 1.5 to 2.0 and an initial temperature of the peak value in a range of -20°C to 20°C, which were measured by the dynamic viscoelasticity test specified in JIS K6394 under the conditions of a frequency of 10 Hz, a static strain of 10%, and a dynamic strain of 0.15%, wherein the rubber component is selected from a group consisting of a natural rubber, an isoprene rubber, a butadiene rubber, a styrene-butadiene rubber, a Styrene-isoprene copolymer rubber,a butadiene-isoprene copolymer rubber and a styrene-isoprene-butadiene copolymer rubber, and wherein the thermoplastic elastomer is a styrene thermoplastic elastomer having a polystyrene as a hard segment, and wherein the thermoplastic elastomer is a block copolymer having a hydrogenated polydiene as a soft segment.

[0010] The pneumatic tire according to the invention is manufactured with the above-mentioned rubber composition for tires. [Advantages of the invention of the task]

[0011] The rubber composition for tires according to the invention makes it possible to obtain a pneumatic tire having improved fuel efficiency, improved wet grip and improved low temperature performance. [Mode for carrying out the invention]

[0012] The aspects relevant to the implementation of the invention are described in detail below.

[0013] A rubber composition for tires according to this embodiment contains, per 100 parts by mass of a rubber component, 1 to 30 parts by mass of a phosphate having a coagulation point of -50 °C or lower, and 1 to 20 parts by mass of a thermoplastic elastomer having a peak value of tan δ of 1.5 to 2.0 and an initial temperature of the peak value in a range of -20 °C to 20 °C, which were measured by the dynamic viscoelasticity test specified in JIS K6394 under the conditions of a frequency of 10 Hz, a static strain of 10%, and a dynamic strain of 0.15%. Incidentally, for use in the dynamic viscoelasticity test, a thermoplastic elastomer is formed into a 2 mm thick sheet with a roller, then vulcanized at 160 °C for 30 minutes, punched out into a strip-shaped dumbbell with a width of 5 mm and a length of 20 mm, and used.

[0014] The rubber component is selected from a group consisting of natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. These diene rubbers can be used alone, and it is also possible to use a mixture of two or more types.

[0015] The phosphate according to this embodiment is not particularly limited as long as it has a coagulation point of -50°C or lower. For example, tris(2-ethylhexyl) phosphate (TOP), triethyl phosphate (TEP), and the like can be used. When a phosphate having a coagulation point of -50°C or lower is used, excellent fuel efficiency and low-temperature performance are likely to be obtained. Here, the coagulation point of a phosphate is a value measured using a differential scanning calorimeter (DSC-60A manufactured by Shimadzu Corporation).Specifically, a phosphate was hermetically sealed in an aluminum cell and placed in a sample holder, and then, while the sample holder was heated from -100 °C to 25 °C at 20 K / min in a nitrogen atmosphere, the difference in the amount of heat from the standard substance was measured, and the temperature at which the endothermic peak was observed was determined as the coagulation point.

[0016] The proportion of phosphate is 1 to 30 parts by mass, preferably 1 to 20 parts by mass, and more preferably 5 to 20 parts by mass per 100 parts by mass of the rubber component. When the proportion is 1 to 30 parts by mass, excellent fuel efficiency and low-temperature performance are likely to be achieved.

[0017] The thermoplastic elastomer of this embodiment has a peak tan δ of 1.5 to 2.0 and a peak initial temperature in a range of -20°C to 20°C, which were measured by the dynamic viscoelasticity test specified in JIS K6394 under the conditions of a frequency of 10 Hz, a static strain of 10%, and a dynamic strain of 0.15%. As such a thermoplastic elastomer, one having a peak tan δ and a peak initial temperature satisfying the above-mentioned ranges can be selected from among commercially available thermoplastic elastomers. Specific examples thereof include "SOES 1605" manufactured by Asahi Kasei Corporation and "HYBRAR 7125" manufactured by Kuraray Co. Ltd.

[0018] The thermoplastic elastomer is a styrene thermoplastic elastomer having polystyrene as a hard segment, and a hydrogenated styrene thermoplastic elastomer having a hydrogenated polydiene as a soft segment. Examples of the hydrogenated polydiene include a hydrogenated polyisoprene, a hydrogenated polybutadiene, and a hydrogenated styrene / butadiene copolymer. That is, it is particularly preferable that the thermoplastic elastomer is a thermoplastic elastomer having polystyrene as a hard segment and at least one member selected from the group consisting of a hydrogenated polyisoprene, a hydrogenated polybutadiene, and a hydrogenated styrene / butadiene copolymer as a soft segment.

[0019] In the case where the thermoplastic elastomer is a styrene thermoplastic elastomer, the peak value of tan δ increases with a decrease in molecular weight. In addition, the peak initial temperature increases with an increase in the styrene content and decreases with a decrease in the styrene content. Therefore, it is also possible to use a thermoplastic elastomer produced by adjusting the molecular weight and styrene content to adjust the peak value of tan δ and the peak initial temperature within the above ranges.

[0020] In the case where the thermoplastic elastomer is a styrene thermoplastic elastomer, the content of styrene is not particularly limited, but it is preferably 15 to 40 mass%, and more preferably 20 to 35 mass%.

[0021] The proportion of the thermoplastic elastomer is not particularly limited, but it is preferably 1 to 20 parts by mass, more preferably 5 to 20 parts by mass, and even more preferably 5 to 15 parts by mass per 100 parts by mass of the rubber component.

[0022] In the rubber composition according to this embodiment, carbon black and / or silica can be used as a reinforcing filler. That is, the reinforcing filler can be carbon black alone, silica alone, or a combination of carbon black and silica. A combination of carbon black and silica is preferred. The proportion of the reinforcing filler is not particularly limited, and preferably, for example, it is 20 to 120 parts by mass, more preferably, it is 20 to 100 parts by mass, and even more preferably, it is 30 to 80 parts by mass per 100 parts by mass of the rubber component.

[0023] Carbon black is not particularly limited, and various known types can be used. The proportion of carbon black is preferably 1 to 70 parts by mass, and more preferably 1 to 30 parts by mass per 100 parts by mass of the rubber component.

[0024] The silica is also not particularly limited, but it is preferable to use a wet silica, such as a wet-precipitated silica or a wet-gelled silica. When silica is included, in consideration of the balance of the tan δ of the rubber, reinforcing properties, and the like, its content is preferably 10 to 100 parts by mass, and more preferably 15 to 70 parts by mass per 100 parts by mass of the rubber component.

[0025] In the case where silicon dioxide is included, a silane coupling agent such as a sulfide silane and a mercaptosilane may be further included. In the case where a silane coupling agent is included, its proportion is preferably 2 to 20 parts by mass per 100 parts by mass of silicon dioxide.

[0026] In the rubber composition according to this embodiment, in addition to the components described above, the formulated chemicals used in the usual rubber industry, such as process oils, a zinc oxide, a stearic acid, softeners, plasticizers, waxes, antioxidants, vulcanizing agents and vulcanization accelerators, can be appropriately blended within the usual range.

[0027] Examples of vulcanizing agents include sulfur components such as sulfur powder, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersed sulfur. The proportion of the vulcanizing agent is preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component. In addition, the proportion of the vulcanization accelerator is preferably 0.1 to 7 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0028] The rubber composition according to this embodiment can be prepared by kneading in the usual manner using a commonly used mixer such as a Banbury mixer, a kneader, or a roll. That is, in the first mixing step, a phosphate, a thermoplastic elastomer, and other additives other than a vulcanizing agent and a vulcanization accelerator are added and mixed to a rubber component, and in the final mixing step, a vulcanizing agent and a vulcanization accelerator are added and mixed to the resulting mixture, whereby the rubber composition can be prepared.

[0029] The rubber composition obtained in this way can be used for tires. The rubber composition can be used for various parts of a tire, such as the tread portion and sidewall portion of pneumatic tires of various sizes for various applications, including automobile tires, large tires for trucks and buses, and so on. A pneumatic tire, for example, can be manufactured by extrusion and then combining with other parts, followed by vulcanization molding at 140 to 180°C.

[0030] The type of pneumatic tire according to this embodiment is not particularly limited. Examples include various tires, such as automobile tires and heavy-duty tires for trucks and buses, as described above. [Examples]

[0031] Examples of the invention are shown below, but the invention is not limited to these examples. <Beispiele und Vergleichsbeispiele>

[0032] Using a Banbury mixer, according to the recipe (parts by mass) shown in Table 1 below, first in the first mixing stage (non-processing kneading step), the components except the vulcanization accelerator and the sulfur were added and mixed (outlet temperature = 160 °C), and in the last mixing stage (processing kneading step), the vulcanization accelerator and the sulfur were added to the obtained mixture and mixed (outlet temperature = 90 °C), thereby preparing the rubber composition.

[0033] The details of the components in Table 1 are as follows. - SBR: “VSL5025-0HM”, manufactured by LANXESS - BR: “BR150B”, manufactured by Ube Industries, Ltd. - Thermoplastic elastomer 1: “SOES 1605” manufactured by Asahi Kasei Corporation, a styrene / butadiene-styrene block copolymer hydrogenated with styrene, which has a peak tan δ of 1.58, a peak onset temperature of 18 °C, a number average molecular weight of 1.12 × 10 5 and a weight average molecular weight of 2.18 × 10 5 has - Thermoplastic elastomer 2: “HYBRAR 7125”, manufactured by Kuraray Co. Ltd., a styrene-hydrogenated isoprene-styrene block copolymer, which has a peak tan δ of 1.84 and an initial peak temperature of -6 °C - Thermoplastic elastomer 3: “SOES 1611” manufactured by Asahi Kasei Corporation, a styrene / butadiene-styrene block copolymer hydrogenated with styrene, which has a peak tan δ of 0.83, a peak onset temperature of 9 °C, a number-average molecular weight of 1.34 × 10 5 and a weight average molecular weight of 1.70 × 10 5 has - Thermoplastic elastomer 4: “Tuftec H1062”, manufactured by Asahi Kasei Corporation, a styrene-hydrogenated ethylene / butadiene-styrene block copolymer, which has a peak tan δ of 0.86 and an initial peak temperature of -47 °C - Phosphate 1: Tris(2-ethylhexyl)phosphate (TOP) manufactured by Daihachi Chemical Industry Co. Ltd. and having a coagulation point of -70 °C or less - Phosphate 2: Triethyl phosphate (TEP), manufactured by Daihachi Chemical Industry Co. Ltd. and having a coagulation point of -56 °C - Phosphate 3: Trixylenyl phosphate (TXP), manufactured by Daihachi Chemical Industry Co., Ltd., with a coagulation point of -15 °C - Silicon dioxide: “Nipsil AQ”, manufactured by Tosoh Silica Corporation - Carbon black: “DIABLACK N341”, manufactured by Mitsubishi Chemical Corporation - Silane coupling agent: “Si69”, manufactured by Evonik - Oil: “Process NC 140”, produced by JX Energy - Zinc oxide: “Zinc Oxide No. 1”, manufactured by Mitsui Mining & Smelting Co. Ltd. - Antioxidant: “Antigen 6C”, manufactured by Sumitomo Chemical Co. Ltd. - Stearic acid: “LUNAC S-20”, manufactured by Kao Corporation - Wax: “OZOACE0355”, manufactured by Nippon Seiro Co. Ltd. - Sulphur: “5% oil-treated sulfur powder” manufactured by Tsurumi Chemical Industry Co. Ltd. - Vulcanization accelerator 1: “SOXINOL CZ”, manufactured by Sumitomo Chemical Co., Ltd. - Vulcanization accelerator 2: “Nocceler D”, manufactured by Ouchi Shinko Chemical Industrial Co. Ltd.

[0034] The peak value of tan δ and the peak-onset temperature of each thermoplastic elastomer described above are the values ​​obtained by measuring the loss factor tan δ with a viscoelasticity tester manufactured by Toyo Seiki Co. Ltd. at a temperature within a range of -60°C to 100°C according to JIS K6394. The measurement conditions were as follows: frequency: 10 Hz, static strain: 10%, dynamic strain: 0.15%. Incidentally, as a sample, a thermoplastic elastomer was molded into a 2 mm thick sheet with a roller, then vulcanized at 160°C for 30 minutes, punched into a strip-shaped dumbbell with a width of 5 mm and a length of 20 mm, and used.

[0035] The coagulation point of each phosphate described above was measured as follows. Using a differential scanning calorimeter (DSC-60A, manufactured by Shimadzu Corporation), a phosphate was hermetically sealed in an aluminum cell and placed in a sample holder. Then, while the sample holder was heated from -100°C to 25°C at 20 K / min in a nitrogen atmosphere, the difference in heat quantity from the standard substance was measured. The coagulation point is the temperature at which the maximum endothermic value was observed.

[0036] The wet grip, fuel efficiency, and low-temperature performance of each obtained rubber composition were evaluated. The evaluation methods are as follows. - Wet adhesion: Using a sample of a predetermined shape prepared by vulcanizing the resulting rubber composition at 160°C for 30 minutes, the loss tangent tanδ was measured using a viscoelasticity tester manufactured by Toyo Seiki Co. Ltd. in accordance with JIS K6394. The measurement conditions were as follows: frequency: 10 Hz, static elongation: 10%, dynamic elongation: 1%, temperature: 0°C. The result was expressed as an index, which takes the value 100 for Comparative Example 1. A larger index indicates better wet adhesion. - Fuel Efficiency: Using a sample of a predetermined shape prepared by vulcanizing the obtained rubber composition at 160°C for 30 minutes, the loss factor tanδ was measured using a viscoelasticity tester manufactured by Toyo Seiki Co. Ltd. in accordance with JIS K6394. The measurement conditions were as follows: frequency: 10 Hz, static strain: 10%, dynamic strain: 1%, temperature: 60°C. The result was expressed as an index, which takes the value 100 for Comparative Example 1. A smaller index indicates better fuel efficiency. - Low-temperature performance: Using a sample of a predetermined shape prepared by vulcanizing the obtained rubber composition at 160°C for 30 minutes, the loss tangent tanδ was measured using a viscoelasticity tester manufactured by Toyo Seiki Co. Ltd. in accordance with JIS K6394. The measurement conditions were as follows: frequency: 10 Hz, static strain: 10%, dynamic strain: 1%, temperature: -15°C. The result was expressed as an index, which takes the value 100 for Comparative Example 1. A smaller index indicates better low-temperature performance. [Table 1] Comparison example 1 Comparison example 2 Comparison example 3 Comparison example 4 Comparison example 5 Comparison example 6 Comparison example 7 Comparison example 8 SBR 70 70 70 70 70 70 70 70 BR 30 30 30 30 30 30 30 30 Thermoplastic elastomer 1 - - 10 - - - - 10 Thermoplastic elastomer 2 - - - - - - - - Thermoplastic elastomer 3 - - - 10 - 10 - - Thermoplastic elastomer 4 - - - - 10 - 10 - Phosphate 1 - 10 - - - 10 10 - Phosphate 2 - - - - - - - - Phosphate 3 - - - - - - - 10 Silicon dioxide 70 70 70 70 70 70 70 70 soot 10 10 10 10 10 10 10 10 Silane coupling agents 7 7 7 7 7 7 7 7 Öl 20 10 20 20 20 10 10 10 zinc oxide 3,0 3,0 3,0 3,0 3,0 3,0 3,0 3,0 Antioxidants 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 Stearic acid 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 wax 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 sulfur 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 Vulcanization accelerator 1 1,8 1,8 1,8 1,8 1,8 1,8 1,8 1,8 Vulcanization accelerator 2 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 Adhesion in wet conditions 100 96 106 104 98 98 100 117 Fuel efficiency 100 84 110 108 102 96 94 106 Performance at low temperatures 100 88 110 112 105 95 95 102 [Table 1] (continued) Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 SBR 70 70 70 70 70 70 BR 30 30 30 30 30 30 Thermoplastic elastomer 1 5 10 - - - - Thermoplastic elastomer 2 - - 10 10 10 10 Thermoplastic elastomer 3 - - - - - - Thermoplastic elastomer 4 - - - - - - Phosphate 1 10 10 10 - - - Phosphate 2 - - - 5 10 20 Phosphate 3 - - - - - - Silicon dioxide 70 70 70 70 70 70 soot 10 10 10 10 10 10 Silane coupling agents 7 7 7 7 7 7 Öl 10 10 10 15 10 - zinc oxide 3,0 3,0 3,0 3,0 3,0 3,0 Antioxidants 2,0 2,0 2,0 2,0 2,0 2,0 Stearic acid 2,0 2,0 2,0 2,0 2,0 2,0 wax 2,0 2,0 2,0 2,0 2,0 2,0 sulfur 1,5 1,5 1,5 1,5 1,5 1,5 Vulcanization accelerator 1 1,8 1,8 1,8 1,8 1,8 1,8 Vulcanization accelerator 2 2,0 2,0 2,0 2,0 2,0 2,0 Adhesion in wet conditions 108 118 115 114 116 114 Fuel efficiency 88 94 92 96 93 88 Performance at low temperatures 92 95 94 97 94 90

[0037] The results are shown in Table 1. A comparison between Examples 1 to 6 and Comparative Examples 1 to 8 shows that when a predetermined thermoplastic elastomer and a predetermined phosphate are used together, wet adhesion, fuel efficiency, and low-temperature performance are improved. [Industrial applicability]

[0038] The rubber composition for tires of the invention can be used for various tires for automobiles, light trucks, buses and the like.

Claims

[1] Rubber composition for tires containing per 100 parts by mass of a rubber component: 1 to 30 parts by mass of a phosphate having a coagulation point of -50 °C or lower, and 1 to 20 parts by mass of a thermoplastic elastomer having a peak tanδ of 1.5 to 2.0 and an initial peak temperature in a range of -20 °C to 20 °C, as determined by a dynamic viscoelasticity test specified in JIS K6394 and measured under the conditions of a frequency of 10 Hz, a static strain of 10% and a dynamic strain of 0.15%, wherein the rubber component has been selected from a group comprising a natural rubber, an isoprene rubber, a butadiene rubber, a styrene-butadiene rubber, a styrene-isoprene copolymer rubber, a butadiene-isoprene copolymer rubber and a styrene-isoprene-butadiene copolymer rubber, and wherein the thermoplastic elastomer is a styrene thermoplastic elastomer having a polystyrene as a hard segment, and wherein the thermoplastic elastomer is a block copolymer having a hydrogenated polydiene as a soft segment. [2] Use of the rubber composition according to claim 1 for producing a tire. [3] A pneumatic tire made with the rubber composition for tires according to claim 1.