Rubber composition and tire using the same

Abstract

To improve weight saving and low rolling properties of a tire in order to reduce an environmental load, improve a balance of physical properties such as hardness, fracture physical property and storage modulus to highly strengthen a tire in order to save the weight of the tire, and solve a problem of an increase of tanδ (60°C) being an index of rolling resistance as a conflicting property to an effective increase of an amount of filler such as silica for higher strength.SOLUTION: A rubber composition in which silica is compounded by 5 pts.mass or more for 100 pts.mass of diene-based rubber, and furthermore thermoplastic polyurethane elastomer having a softening point of 120 to 160°C is compounded.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a rubber composition and a tire using the same, and more particularly to a rubber composition capable of improving the balance of physical properties such as hardness, fracture physical properties, and storage elastic modulus while maintaining or improving low rolling resistance, and a tire using the same.

Background Art

[0002] In recent years, there has been a demand for weight reduction and improvement of low rolling resistance of tires in order to reduce the environmental impact. To achieve weight reduction of tires, it is required to improve the balance of physical properties such as hardness, fracture physical properties, and storage elastic modulus and increase the strength. Increasing the amount of fillers such as silica is effective for increasing the strength, but there is a problem that tanδ(60°C), which is an index of rolling resistance, increases as an antagonistic performance.

[0003] Although the technique of blending polyurethane into a rubber composition can be found in Patent Documents 1 to 5 below, the technique of blending a thermoplastic polyurethane elastomer having a specific softening point in a rubber composition containing silica has not been disclosed in the prior art.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a rubber composition capable of improving the balance of physical properties such as hardness, fracture physical properties, and storage elastic modulus while maintaining or improving low rolling resistance, and a tire using the same.

Means for Solving the Problems

[0006] As a result of intensive studies, the present inventors have found that the above problems can be solved by blending a thermoplastic polyurethane elastomer having a specific softening point in a rubber composition containing silica, and have completed the present invention.

[0007] That is, the present invention provides a rubber composition characterized in that 5 parts by mass or more of silica is blended with 100 parts by mass of a diene rubber, and further a thermoplastic polyurethane elastomer having a softening point of 120 to 160 ° C is blended.

Effects of the Invention

[0008] In the rubber composition of the present invention, 5 parts by mass or more of silica is blended with 100 parts by mass of a diene rubber, and further a thermoplastic polyurethane elastomer having a softening point of 120 to 160 ° C is blended. Therefore, the polar groups (urethane bonds) contained in the thermoplastic polyurethane elastomer interact with silica, improving the balance of physical properties such as hardness, fracture physical properties at normal temperature to high temperature, and storage elastic modulus, and it is also possible to maintain or improve tanδ(60 °C).

Modes for Carrying Out the Invention

[0009] Hereinafter, the present invention will be described in more detail.

[0010] (Diene Rubber) The diene rubber used in the present invention can be any diene rubber that can be compounded into a rubber composition. For example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), ethylene-propylene-diene terpolymer (EPDM), etc. can be mentioned. These may be used alone or in combination of two or more. Also, its molecular weight and microstructure are not particularly limited, and it may be end-modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group, etc., or may be epoxidized. The weight average molecular weight (Mw) of the diene rubber is not particularly limited, but for reasons such as more excellent effects of the present invention, 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 (Mw) is a standard polystyrene conversion value obtained by gel permeation chromatography (GPC) measurement. Also, from the viewpoint of improving the effects of the present invention, the diene rubber used in the present invention consists of NR and BR. When the total amount of the diene rubber is 100 parts by mass, NR preferably occupies 30 to 65 parts by mass and BR preferably occupies 35 to 70 parts by mass. In this preferred form, NR includes IR.

[0011] (Silica) Specific examples of the silica used in the present invention include, for example, wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. These may be used alone or in combination of two or more. From the viewpoint of improving the effects of the present invention, the silica preferably has a CTAB adsorption specific surface area of 60 to 150 m 2 / g, and more preferably 60 to 120 m 2 / g. The CTAB adsorption specific surface area is a value obtained by measuring the adsorption amount of n-hexadecyltrimethylammonium bromide on the silica surface in accordance with JIS K6430:2008.

[0012] (Thermoplastic polyurethane elastomer) The thermoplastic polyurethane elastomer used in the present invention is known and not particularly limited. For example, it can be obtained by copolymerizing a polyisocyanate, a polyol, and a chain extender. Examples of the polyisocyanate include aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate; alicyclic diisocyanates such as 1,4-cyclohexane diisocyanate, isophorone diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate; aromatic diisocyanates such as p-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, and 4,4'-diphenylmethane diisocyanate, and the like. Examples of the polyol include polyether polyol, polyester polyol, and the like. Examples of the polyether polyol include polyoxyethylene glycol, polyoxypropylene glycol, polyoxyethylene oxypropylene glycol, polyoxytetramethylene glycol, polyoxyhexamethylene glycol, and the like. Examples of the polyester polyol include polyethylene adipate, polytetramethylene adipate, polyhexamethylene adipate, polytetramethylene sebacate, poly(diethylene glycol adipate), poly(hexamethylene glycol-1,6-carbonate), polycaprolactone, and the like. Examples of the chain extender include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, bisphenol A, p-xylylene glycol, and the like.

[0013] The softening point of the thermoplastic polyurethane elastomer used in the present invention is 120 to 160 °C. If the softening point is less than 120 °C, the strength will decrease. Conversely, if it exceeds 160 °C, it will not melt during mixing and will not be uniformly dispersed in the compound. More preferably, the softening point of the thermoplastic polyurethane elastomer is 125 to 145 °C. The softening point is measured in accordance with JIS K6220-1.

[0014] From the viewpoint of high strength, the 100% modulus of the thermoplastic polyurethane elastomer used in the present invention at 23 °C is preferably 5.0 MPa or more, and more preferably 5 MPa to 10 MPa. The 100% modulus is measured in accordance with JIS K6251, and is the value (MPa) obtained by performing a tensile test at 23 °C and 500 mm / min and measuring the stress at 100% elongation.

[0015] Commercially available thermoplastic polyurethane elastomers can be used in the present invention. Examples include Rezamin P2288 (ether type, softening point = 134 °C, glass transition temperature = -35 °C, 100% modulus = 6 MPa), Rezamin P1078F (ester type, softening point = 141 °C, glass transition temperature = -10 °C, 100% modulus = 8 MPa) manufactured by Dainichi Seika Kogyo Co., Ltd.

[0016] (Mixing ratio of rubber composition) In the rubber composition of the present invention, 5 parts by mass or more of silica is blended based on 100 parts by mass of the diene rubber. The blending amount of silica is preferably 5 to 100 parts by mass, and more preferably 10 to 70 parts by mass based on 100 parts by mass of the diene rubber. The blending amount of the thermoplastic polyurethane elastomer is preferably 1 to 30 parts by mass, and more preferably 5 to 20 parts by mass based on 100 parts by mass of the diene rubber.

[0017] (Other components) In addition to the above-described components, the rubber composition of the present invention can be blended with various additives generally blended in rubber compositions, such as vulcanizing or crosslinking agents, vulcanization or crosslinking accelerators, zinc oxide, silane coupling agents, carbon black, various fillers, antioxidants, plasticizers, etc. The blending amounts of these additives can be set to conventional general blending amounts as long as they do not conflict with the object of the present invention.

[0018] The rubber composition of the present invention can be kneaded by a general method to obtain a composition and used for vulcanization or crosslinking. Here, it is preferable to adopt a temperature equal to or higher than the softening point of the thermoplastic polyurethane elastomer during the kneading and / or during the vulcanization or crosslinking.

[0019] Since the rubber composition of the present invention can maintain or improve low rolling resistance and also improve the balance of physical properties such as hardness, breaking physical properties, and storage elastic modulus, it is preferably used for tire applications. Further, the tire of the present invention is preferably a pneumatic tire, and is particularly preferably used for the sidewall or rim cushion of a pneumatic tire. The pneumatic tire can be filled with an inert gas such as air or nitrogen and other gases.

[0020] In the case of the sidewall application and the rim cushion application, from the viewpoint of improving the effects of the present invention, the ratio of silica to the thermoplastic polyurethane elastomer is preferably 1:1 to 14:1, more preferably 1.5:1 to 10:1 in terms of the former: the latter (mass ratio).

Examples

[0021] Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited to the following examples.

[0022] Standard Example 1, Examples 1 to 6, and Comparative Examples 1 to 3 Preparation of Samples In the formulation (parts by mass) shown in Table 1, the components excluding the inorganic filler, vulcanization accelerator, and sulfur were kneaded in a 1.7-liter sealed Banbury mixer for 5 minutes, then the inorganic filler was added thereto and kneaded, and the rubber was discharged out of the mixer and cooled at room temperature. Next, the rubber was put back into the same mixer, the vulcanization accelerator and sulfur were added, and kneading was further carried out to obtain a rubber composition. Next, the obtained rubber composition was press-vulcanized at 160 °C for 20 minutes in a predetermined mold to obtain a vulcanized rubber test piece, and the physical properties of the vulcanized rubber test piece were measured by the test methods shown below.

[0023] Hardness (20 °C): Measured at a temperature of 20 °C using a Type A durometer in accordance with JIS K6253. The results were shown as an index with Standard Example 1 being 100. A larger index means higher hardness. Tensile strength at break (TB): Measured at room temperature or 100 °C by a tensile test in accordance with JIS K6251. The unit is MPa. The results were shown as an index with Standard Example 1 being 100. A larger index means higher tensile strength at break (TB). Elongation at break (EB): Measured at room temperature or 100 °C by a tensile test in accordance with JIS K6251. The unit is %. The results were shown as an index with Standard Example 1 being 100. A larger index means higher elongation at break (EB). E’(20 °C): In accordance with JIS K6394, using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho, the storage elastic modulus E’(20 °C) at 20 °C was determined under the conditions of an initial strain of 10%, an amplitude of ±2%, and a frequency of 20 Hz. The results were shown as an index with Standard Example 1 being 100. A larger index means higher storage elastic modulus. tanδ(60 °C): Tested at 60 °C in accordance with JIS K6394. The results were shown as an index with Standard Example 1 being 100. A smaller index means lower rolling resistance.

[0024] In addition, the value obtained by multiplying TB and EB at 100 °C was determined. This is designated as 100 °C TB×EB. The 100 °C TB×EB of each example was indexed with the 100 °C TB×EB of Standard Example 1 being 1.00. A larger index means higher strength, and the index is preferably 1.05 or more.

[0025] The results are shown together in Table 1.

[0026]

Table 1

[0027] *1: NR(STR20) *2: BR1 (Product name Nipol BR1220 manufactured by Zeon Corporation, Japan) *3: BR2 (Product name BR511 manufactured by ENEOS MATERIALS Co., Ltd.) *4: Carbon black ISAF (Product name SHOW BLACK N234 manufactured by Cabot Japan Ltd., CTAB adsorption specific surface area: 115 m 2 / g) *5: Carbon black FEF (Product name SHOW BLACK N550 manufactured by Cabot Japan Ltd., CTAB adsorption specific surface area: 40 m 2 / g) *6: Silica (Zeosil115GR manufactured by Solvay, CTAB specific surface area = 115 m 2 / g)) *7: Thermoplastic polyurethane elastomer 1 (Resamin P2275 (ether type, softening point = 96 °C, glass transition temperature = -42 °C, 100% modulus = 3 MPa) manufactured by Dainichi Seika Kogyo Co., Ltd. *8: Thermoplastic polyurethane elastomer 2 (Resamin P2288 (ether type, softening point = 134 °C, glass transition temperature = -35 °C, 100% modulus = 6 MPa) manufactured by Dainichi Seika Kogyo Co., Ltd. *9: Thermoplastic polyurethane elastomer 3 (P1078F (ester type, softening point = 141 °C, glass transition temperature = -20 °C, 100% modulus = 8 MPa) manufactured by Dainichi Seika Kogyo Co., Ltd. *10: Silane coupling agent (Si69 manufactured by Evonik, bis(3-triethoxysilylpropyl)tetrasulfide) *11: Aromatic oil (Extract No. 4S manufactured by Showa Shell Sekiyu KK) *12: Antioxidant 1 (6PPD manufactured by Flexsys) *13: Anti-aging agent 2 (Nocrack 224 manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) *14: Wax (OZOACE-0015A manufactured by Nippon Seiro Co., Ltd.) *15: Stearic acid (Stearic acid 50S manufactured by Nisshin Rika Co., Ltd.) *16: Zinc oxide (Zinc oxide type 3 manufactured by Shoindo Chemical Industry Co., Ltd.) *17: Insoluble sulfur (Crystex HS OT 20 (80 mass% of pure sulfur content) manufactured by FLEXSYS) *18: Vulcanization accelerator 1 (Nocceler NS-P manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) *19: Vulcanization accelerator 2 (Soxinol D-G manufactured by Sumitomo Chemical Co., Ltd.)

[0028] From the results in Table 1, the rubber compositions of the respective examples are characterized in that, based on 100 parts by mass of the diene rubber, 5 parts by mass or more of silica is compounded, and further a thermoplastic polyurethane elastomer having a softening point of 120 to 160°C is compounded. Therefore, it can be seen that, compared with Standard Example 1, while maintaining or improving low rolling resistance, the balance of physical properties such as hardness, breaking physical properties, and storage elastic modulus is improved. On the other hand, in Comparative Example 1, since silica was not compounded, the elongation at break at room temperature and tanδ (60°C) deteriorated. In Comparative Example 2, since the softening point of the thermoplastic polyurethane elastomer is less than the lower limit defined in the present invention, the breaking stress at room temperature, the elongation at break at high temperature, and tanδ (60°C) deteriorated. In Comparative Example 3, since neither silica nor the thermoplastic polyurethane elastomer was compounded, the elongation at break at room temperature and tanδ (60°C) deteriorated.

[0029] The present invention includes the following embodiments. Embodiment 1: A rubber composition characterized in that, based on 100 parts by mass of the diene rubber, 5 parts by mass or more of silica is compounded, and further a thermoplastic polyurethane elastomer having a softening point of 120 to 160°C is compounded. Embodiment 2: The CTAB specific surface area of the silica is 60 to 150 m 2The sealant composition according to Embodiment 1, characterized by being / g. Embodiment 3: The sealant composition according to Embodiment 1 or 2, characterized in that the 100% modulus at 23 °C of the thermoplastic polyurethane elastomer is 5.0 MPa or more. Embodiment 4: The sealant composition according to any one of Embodiments 1 to 3, characterized in that the diene rubber consists of natural rubber and butadiene rubber, and when the total amount of the diene rubber is 100 parts by mass, the natural rubber is 30 to 65 parts by mass and the butadiene rubber is 35 to 70 parts by mass. Embodiment 5: A pneumatic tire using the rubber composition according to any one of Embodiments 1 to 4 for a sidewall or a rim cushion.

Claims

1. A rubber composition characterized in that 5 parts by mass or more of silica is compounded with 100 parts by mass of a diene rubber, and a thermoplastic polyurethane elastomer having a softening point of 120 to 160°C is further compounded.

2. The CTAB specific surface area of the silica is 60 to 150 m ２ / g, and the rubber composition according to claim 1 is characterized in that.

3. The rubber composition according to claim 1, wherein the 100% modulus at 23°C of the thermoplastic polyurethane elastomer is 5.0 MPa or more.

4. The rubber composition according to claim 1, wherein the diene rubber consists of natural rubber and butadiene rubber, and when the total amount of the diene rubber is 100 parts by mass, the natural rubber is 30 to 65 parts by mass and the butadiene rubber is 35 to 70 parts by mass.

5. A pneumatic tire using the rubber composition according to claim 1 for a sidewall or a rim cushion.

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