JP2011038058A - Rubber composition for base tread and studless tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition enhancing heat resistance, suppressing a change in performances such as a change in hardness of particularly rubber by use thereof for a long period of time(deterioration due to curing of the rubber), prolonging the life without lowering on-ice performances, further shortening the vulcanization time and enhancing the cross-linking efficiency though having good scorch resistance without increasing the amount of an antioxidant, and to provide a studless tire using the rubber composition in a base tread of the tire. <P>SOLUTION: The rubber composition for the base tread incudes a rubber component containing an isoprene-based rubber, silica, a specific mercaptobenzothiazole and/or a specified bisbenzothiazolyl disulfide, and a thiuram-based vulcanization accelerator. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a rubber composition for a base tread and a studless tire using the same.

Conventionally, spiked tires have been used for running on snowy and snowy roads, and chains have been attached to tires. However, environmental problems such as dust problems have occurred, and studless tires have been developed as alternatives to snowy and snowy road running tires. . Since studless tires are used on snowy road surfaces, where the road surface unevenness is larger than that of general road surfaces, the material and design are devised. For example, rubber compositions containing a diene rubber excellent in low temperature characteristics and a large amount of a softening agent have been developed to enhance the softening effect.

Further, in recent years, the characteristics required for studless tires include not only the performance on ice and snow but also various aspects such as handling stability, wear resistance, and riding comfort, and various measures have been made to improve these performances. For example, it is known that a tread of a tire has a two-layer structure of a cap tread (surface layer) and a base tread (inner surface layer). In the base tread, diene rubbers such as natural rubber and butadiene rubber are widely used as a rubber component, but there is a problem that the rubber deteriorates with age (curing deterioration).

Conventionally, anti-aging agents have been widely used in rubber compositions used for tires and the like in order to increase the heat resistance of the rubber composition. Anti-aging agents include amines such as N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine (6PPD) and N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD). Anti-aging agents are widely used.

When the hardness of a studless tire increases due to deterioration over time (curing deterioration), the performance on ice (braking performance on ice) may be significantly reduced. Therefore, conventionally, it has been dealt with by a method of increasing the anti-aging agent or a method of selecting a softening agent. However, the method of increasing the amount of the anti-aging agent has a problem that the surface of the anti-aging agent is browned due to the precipitation of the anti-aging agent on the tire surface, thereby causing an appearance defect of the tire. Further, in the method of selecting a softening agent, depending on the type of softening agent, the performance on ice itself is lowered, so that both the performance on ice and the anti-curing property are not sufficient.

Therefore, it is desired to provide a rubber composition that can improve heat resistance and extend the life without increasing the amount of anti-aging agent.

Patent Document 1 discloses a rubber composition in which N- (1-methylheptyl) -N′-phenyl-p-phenylenediamine as an antiaging agent and a wax are blended with a diene rubber. However, there is still room for improvement in terms of improving heat resistance.

Japanese Patent Laid-Open No. 10-324779

The present invention solves the above-mentioned problems, improves heat resistance without increasing the amount of anti-aging agent, and suppresses performance changes such as changes in hardness (rubber deterioration due to rubber use) due to long-term use of rubber. Rubber composition that can extend the life without lowering, further reduce the vulcanization time while improving the scorch resistance, and increase the crosslinking efficiency, and studless using the rubber composition for the base tread of the tire The object is to provide a tire.

The present inventors can improve heat resistance by blending a rubber component containing isoprene-based rubber, silica, and a compound represented by the following formulas (I) and / or (II), and in particular, curing of rubber. It was found that deterioration can be suppressed. However, this method has created new problems such as an increase in vulcanization time and a decrease in crosslinking efficiency. Therefore, as a result of intensive studies, the present inventors have further improved the heat resistance and further solved the new problem by adding a thiuram vulcanization accelerator to the above three components. I found out that I can.
That is, the present invention relates to a rubber for base tread containing a rubber component containing an isoprene-based rubber, silica, a compound represented by the following formula (I) and / or (II), and a thiuram vulcanization accelerator. Relates to the composition.

（式（Ｉ）、（ＩＩ）において、Ｒ^１及びＲ^２は、同一若しくは異なって、水素原子、アルキル基、アリール基又はアラルキル基を表す。但し、Ｒ^１及びＲ^２が同時に水素原子である場合を除く。）

(In the formulas (I) and (II), R ¹ and R ² are the same or different and each represents a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group, provided that R ¹ and R ² are hydrogen atoms at the same time. Except in cases.)

The isoprene-based rubber is preferably at least one selected from the group consisting of isoprene rubber, natural rubber and modified natural rubber.

The compound is preferably a compound represented by the following formula (III).

The rubber composition preferably has a hardness at 25 ° C. of 42 to 70.

The present invention also relates to a studless tire having a base tread produced using the rubber composition.

According to the present invention, silica, a compound represented by the above formula (I) and / or (II), and a thiuram vulcanization accelerator are blended with a rubber component containing an isoprene-based rubber. Heat resistance can be improved without degrading performance, especially performance changes such as hardness changes due to long-term use of rubber (especially rubber curing deterioration) can be suppressed, and deterioration of performance on ice with age can be suppressed. It becomes. Furthermore, while having good scorch resistance, the vulcanization time can be shortened, and the crosslinking efficiency can be improved. Such an effect of suppressing curing deterioration is very large as compared with SBR systems such as SBR and carbon black blended systems. Moreover, since the crosslinking efficiency is improved, the wear resistance and cut resistance can be improved. Therefore, without increasing the amount of anti-aging agent such as 6PPD, the life of the rubber composition can be extended without deteriorating the performance on ice, and further, the vulcanization time can be shortened while having good scorch resistance. This is possible, and the crosslinking efficiency can be improved, so that it can be suitably applied to the base tread of a studless tire.

The rubber composition of the present invention contains a rubber component containing isoprene-based rubber, silica, a compound represented by the above formula (I) and / or (II), and a thiuram vulcanization accelerator. By using isoprene-based rubber as a rubber component, and by further compounding silica and the compounds represented by the above formulas (I) and (II), heat resistance can be improved, and performance such as hardness change due to long-term use of rubber It is possible to suppress changes, in particular, rubber curing deterioration. Furthermore, by adding a thiuram vulcanization accelerator to the above three components, the heat resistance is improved, and further, a new vulcanization time and a reduction in crosslinking efficiency caused by adding the above three components. The problem can be solved (scorching resistance can be secured, crosslinking efficiency can be improved and vulcanization time can be shortened). Furthermore, since the crosslinking efficiency is increased by the thiuram vulcanization accelerator, the amount of sulfur not involved in effective cross-linking between rubber molecules in the rubber composition is reduced. Can be prevented.

Here, the curing deterioration of rubber is a deterioration phenomenon in which the rubber becomes harder than the initial state when heat is applied under the condition where oxygen is present as a deterioration factor. Can be effectively suppressed. Such curing deterioration suppressing effect is a so-called heat fatigue resistance (preventing blow and chunk generation) and heat sag resistance, and is an effect different from that of isoprene-based rubber, silica, and formulas (I) and (II). It is specifically produced when three components with a compound are used.

Further, when these three components are used, the effect of improving heat resistance (particularly, the effect of suppressing curing deterioration) is generated synergistically. For example, silica and compounds of formulas (I) and (II) are added to styrene butadiene rubber. Compared with the case where is blended, a very large curing deterioration suppressing effect is produced.

In the present invention, isoprene-based rubber is used as the rubber component. In the present invention, the heat resistance (particularly, the effect of suppressing the curing deterioration) can be improved despite using a rubber having an isoprene skeleton. Examples of the isoprene-based rubber include isoprene rubber (IR), natural rubber (NR), and modified natural rubber. NR includes deproteinized natural rubber (DPNR) and high-purity natural rubber (HPNR). Modified natural rubber includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Etc. Moreover, as NR, what is common in tire industry, such as SIR20, RSS # 3, TSR20, can be used, for example. Among these, NR is preferable for the reason of improving efficiency during supply.

In the present invention, 100% by mass of the rubber component contains 20% by mass or more, preferably 30% by mass or more, more preferably 40% by mass or more of isoprene-based rubber. If it is less than 20% by mass, the effect of suppressing curing deterioration may not be sufficiently obtained. Further, the content of the isoprene-based rubber is preferably 80% by mass or less, more preferably 70% by mass or less, and still more preferably 60% by mass or less. When it exceeds 80 mass%, workability may be reduced.

In addition to isoprene-based rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR) can be used as rubber components. And acrylonitrile butadiene rubber (NBR). A rubber component may be used independently and may use 2 or more types together. Among these, BR is preferable because the performance on ice can be secured.

The BR is not particularly limited. For example, BR1220 and BR1250H manufactured by Nippon Zeon Co., Ltd., BR130B and BR150B manufactured by Ube Industries, Ltd., BR with high cis content, VCR412 and VCR617 manufactured by Ube Industries, Ltd. BR containing a syndiotactic polybutadiene crystal such as can be used.

In the present invention, BR is preferably contained in 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, and most preferably 50% by mass or more in 100% by mass of the rubber component. If it is less than 10% by mass, sufficient performance on ice required for a studless tire may not be obtained.
The BR content is preferably 80% by mass or less, more preferably 70% by mass or less, and still more preferably 60% by mass or less. When it exceeds 80 mass%, workability may be reduced.

In the present invention, silica is used. Thereby, while being able to improve heat resistance (especially hardening deterioration inhibitory effect), wear resistance performance, cut resistance performance, and performance on ice required as a studless tire can be exhibited. Examples of the silica include, but are not limited to, dry method silica (anhydrous silicic acid), wet method silica (anhydrous silicic acid), and the like, and wet method silica is preferable because it has many silanol groups. Silica may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of the silica is preferably 50 m ² / g or more, more preferably 80 m ² / g or more, and still more preferably 100 m ² / g or more. If it is less than 50 m < ² > / g, there exists a tendency for the reinforcement of rubber | gum to fall. Further, N ₂ SA of silica is preferably 250 m ² / g or less, more preferably 230 m ² / g or less, and still more preferably 200 m ² / g or less. If it exceeds 250 m ² / g, the rubber viscosity tends to increase and the processability tends to deteriorate.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

The content of silica is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and still more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the effect of suppressing curing deterioration and the performance on ice may not be sufficiently obtained, and the vulcanization rate and the crosslinking efficiency are hardly lowered by adding silica, and the vulcanization rate and the crosslinking efficiency are lowered. There is a possibility that the suppression effect becomes small. The silica content is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 20 parts by mass or less, most preferably 15 parts by mass or less, and most preferably 10 parts by mass or less. When it exceeds 40 parts by mass, workability and workability may be deteriorated.

The rubber composition of the present invention preferably contains a silane coupling agent together with silica.
As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-tri Ethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilyl) Butyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) Trisulfi Bis (2-trimethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4 -Triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropylbenzothiazoli And sulfide systems such as tetratetrasulfide and 3-triethoxysilylpropylbenzothiazole tetrasulfide. Moreover, mercapto type, vinyl type, glycidoxy type, nitro type, chloro type and the like can also be mentioned. Of these, bis (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) disulfide are preferably used from the viewpoint of the reinforcing effect and processability of the silane coupling agent. These silane coupling agents may be used alone or in combination of two or more.

The content of the silane coupling agent is preferably 1 part by mass or more and more preferably 2 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 1 mass part, there exists a tendency for fracture strength to fall large. Moreover, 15 mass parts or less are preferable, and, as for content of this silane coupling agent, 10 mass parts or less are more preferable. When the amount exceeds 15 parts by mass, effects such as an increase in fracture strength and a reduction in rolling resistance due to the addition of the silane coupling agent tend not to be obtained.

In the present invention, a compound represented by the following formula (I) and / or (II) and a thiuram vulcanization accelerator are used in combination as a vulcanization accelerator. In the case of a rubber composition containing isoprene-based rubber or isoprene-based rubber and BR as a rubber component, it is often inferior in heat resistance and aging resistance, and performance changes such as hardness change (especially deterioration due to curing) due to long-term use. Although it tends to increase, the use of the compounds of formulas (I) and (II) can suppress changes in performance. However, on the other hand, the vulcanization time increases and the crosslinking efficiency decreases. On the other hand, when a guanidine accelerator is used in combination, the reduction in crosslinking efficiency is somewhat improved, but it is still insufficient. In addition, the scorch time is shortened and there is a concern of rubber burns. In the present invention, since a specific vulcanization accelerator called a thiuram vulcanization accelerator is used in combination, the crosslinking efficiency can be sufficiently improved while obtaining appropriate scorch resistance. Therefore, it is possible to shorten the vulcanization time while maintaining good scorch resistance in the unvulcanized rubber composition, improve the rolling resistance characteristics and wear resistance of the vulcanized rubber composition, and further increase the crosslinking efficiency. Can also be improved.

（式（Ｉ）、（ＩＩ）において、Ｒ^１及びＲ^２は、同一若しくは異なって、水素原子、アルキル基、アリール基又はアラルキル基を表す。但し、Ｒ^１及びＲ^２が同時に水素原子である場合を除く（即ち、同一の環に結合しているＲ^１及びＲ^２がともに水素原子である化合物を除く）。）

(In the formulas (I) and (II), R ¹ and R ² are the same or different and each represents a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group, provided that R ¹ and R ² are hydrogen atoms at the same time. Except for the case (that is, excluding compounds in which R ¹ and R ² bonded to the same ring are both hydrogen atoms).

As R ¹ and R ² , the alkyl group preferably has 1 to 10 carbon atoms, the aryl group has 6 to 10 carbon atoms, and the aralkyl group has 7 to 10 carbon atoms. Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, iso-butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, Examples include 2-ethylhexyl group, octyl group, nonyl group, decyl group and the like. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a biphenyl group, a naphthyl group, an anthryl group, and a phenanthryl group. Examples of the aralkyl group include a benzyl group and a phenethyl group. The hydrocarbon group of R ^{1 to} R ² may be linear, branched or cyclic. Of the alkyl group, aryl group, and aralkyl group, an alkyl group is preferable, and the alkyl group preferably has 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms. Further, ^{R 1} is an alkyl group, ^{R 2} is preferably a hydrogen atom. In this case, the effect of suppressing curing deterioration can be obtained favorably.

Specific examples of the compound represented by the formula (I) include bis (4-methylbenzothiazolyl-2) -disulfide, bis (4-ethylbenzothiazolyl-2) -disulfide, bis (5- Methylbenzothiazolyl-2) -disulfide, bis (5-ethylbenzothiazolyl-2) -disulfide, bis (6-methylbenzothiazolyl-2) -disulfide, bis (6-ethylbenzothiazolyl) -2) -disulfide, bis (4,5-dimethylbenzothiazolyl-2) -disulfide, bis (4,5-diethylbenzothiazolyl-2) -disulfide, bis (4-phenylbenzothiazolyl-) 2) -disulfide, bis (5-phenylbenzothiazolyl-2) -disulfide, bis (6-phenylbenzothiazolyl-2) -disulfide, etc. That. Specific examples of the compound represented by the above formula (II) include 2-mercapto-4-methylbenzothiazole, 2-mercapto-4-ethylbenzothiazole, 2-mercapto-5-methylbenzothiazole, 2-mercapto- 5-ethylbenzothiazole, 2-mercapto-6-methylbenzothiazole, 2-mercapto-6-ethylbenzothiazole, 2-mercapto-4,5-dimethylbenzothiazole, 2-mercapto-4,5-diethylbenzothiazole, Examples include 2-mercapto-4-phenylbenzothiazole, 2-mercapto-5-phenylbenzothiazole, 2-mercapto-6-phenylbenzothiazole and the like. Of these, bis (4-methylbenzothiazolyl-2) -disulfide, bis (5-methylbenzothiazolyl-2) -disulfide, mercapto-4-methylbenzothiazole, and mercapto-5-methylbenzothiazole are preferable. . In the formulas (I) and (II), the compound represented by the formula (I) is preferably used. Furthermore, among the compounds described above, the compound (4m-MBTS) represented by the formula (III) is particularly preferably used. When using the above compounds, the effect of suppressing curing deterioration can be obtained satisfactorily.

式（Ｉ）、（ＩＩ）で表される化合物は、単独で用いてもよく、２種以上を併用してもよい。該化合物の市販品として、例えば、ＮＯＣＩＬ社の製品を使用することができる。

The compounds represented by the formulas (I) and (II) may be used alone or in combination of two or more. As a commercial product of the compound, for example, a product of NOCIL can be used.

The total content of the compounds represented by the above formulas (I) and (II) is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, further preferably 100 parts by mass of the rubber component. Is 0.4 parts by mass or more. If the amount is less than 0.1 parts by mass, the effect of suppressing curing deterioration may not be sufficiently obtained. The total content is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, and still more preferably 2.0 parts by mass or less. If it exceeds 5.0 parts by mass, it may be difficult to maintain an appropriate crosslinking density and crosslinking form.

Examples of thiuram vulcanization accelerators include tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide, tetramethylthiuram monosulfide (TMTM), dipentamethylene thiuram disulfide, dipentamethylene thiuram monosulfide, dipentamethylene thiuram tetrasulfide. Examples thereof include sulfide, dipentamethylene thiuram hexasulfide, tetrabutyl thiuram disulfide, pentamethylene thiuram tetrasulfide, tetrakis (2-ethylhexyl) thiuram disulfide and the like. Of these, TMTM, tetraethylthiuram disulfide, and tetrabutylthiuram disulfide are preferable from the viewpoint of improving the crosslinking efficiency, maintaining appropriate scorch resistance, shortening the vulcanization time, and lowering the toxicity compared to TMTD.

The content of the thiuram vulcanization accelerator is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and further preferably 0.3 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 0.1 part by mass, the effect of improving the scorch resistance and crosslinking efficiency may not be obtained. The content of the thiuram vulcanization accelerator is preferably 1 part by mass or less, more preferably 0.8 part by mass or less, and still more preferably 0.6 part by mass or less. If it exceeds 1 part by mass, the thiuram vulcanization accelerator may bloom, the scorch time may be shortened, or the cost may be increased unnecessarily.

In the present invention, other vulcanization accelerators may be blended together with the compounds represented by the above formulas (I) and (II) and thiuram vulcanization accelerators. Can get to.
Other vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N′-dicyclohexyl- Examples include 2-benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), and diphenylguanidine (DPG). 0.1 to 2.0 parts by mass may be blended.

In addition to the above components, the rubber composition of the present invention includes compounding agents conventionally used in the rubber industry, for example, fillers such as carbon black, stearic acid, zinc oxide, various anti-aging agents, wax, oil, sulfur. Alternatively, a vulcanizing agent such as a sulfur compound can be appropriately blended as necessary.

Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. By blending carbon black, it is possible to enhance the reinforcement.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 80 m ² / g or more, and more preferably 100 m ² / g or more. If it is less than 80 m < ² > / g, there exists a possibility that it may become disadvantageous to the reinforcement of rubber | gum. Also, _N 2 SA of carbon black is preferably 200 meters ² / g or less, more preferably 150m ² / g. If it exceeds 200 m ² / g, the dispersibility of the carbon black may be disadvantageous.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

When carbon black and silica are blended, the total content of carbon black and silica is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and further preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. Particularly preferred is 35 parts by mass or more. If it is less than 10 parts by mass, the effect of suppressing curing deterioration may not be obtained satisfactorily. The total content is preferably 80 parts by mass or less, more preferably 60 parts by mass or less. When it exceeds 80 mass parts, there exists a possibility that the dispersibility of a filler may deteriorate.

In the present invention, an amine-based anti-aging agent is preferably used as an anti-aging agent because of its excellent destructive properties, and heat resistance (especially an effect of inhibiting curing deterioration) can be improved without increasing the amount used. is there. Examples of amine-based antioxidants include diphenylamine-based and p-phenylenediamine-based amine derivatives. Examples of the diphenylamine derivative include p- (p-toluenesulfonylamide) -diphenylamine, octylated diphenylamine, and the like. Examples of p-phenylenediamine derivatives include N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine (6PPD), N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD). ), N, N′-di-2-naphthyl-p-phenylenediamine, and the like.

The content of the amine anti-aging agent is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the fracture characteristics may not be improved. Moreover, this content becomes like this. Preferably it is 6 mass parts or less, More preferably, it is 4 mass parts or less. If it exceeds 6 parts by mass, bloom may be generated on the surface.

The rubber composition of the present invention may contain oil. By blending oil, processability can be improved and the strength of the rubber can be increased. As the oil, for example, process oil, vegetable oil, or a mixture thereof can be used.
As the process oil, for example, a paraffin process oil, an aroma process oil, a naphthenic process oil, or the like can be used. Specific examples of the paraffinic process oil include PW-32, PW-90, PW-150, and PS-32 manufactured by Idemitsu Kosan Co., Ltd. Specific examples of the aroma-based process oil include AC-12, AC-460, AH-16, AH-24, and AH-58 manufactured by Idemitsu Kosan Co., Ltd. As vegetable oils and fats, castor oil, cottonseed oil, sesame oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut water, rosin, pine oil, pineapple, tall oil, corn oil, rice bran oil, beet flower oil, sesame oil, Examples include olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. Among these, paraffinic process oils and aroma based process oils are preferably used because they are advantageous in processability.

When the rubber composition contains oil, the oil content is preferably 15 parts by mass or more, and more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 15 parts by mass, the workability improving effect may not be sufficiently obtained. The oil content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and still more preferably 40 parts by mass or less. If it exceeds 60 parts by mass, the load on the process may increase.

In the present invention, sulfur can be suitably used as a vulcanizing agent. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.
The sulfur content is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the effect may be small. Moreover, this content becomes like this. Preferably it is 6 mass parts or less, More preferably, it is 4 mass parts or less. If it exceeds 6 parts by mass, the effect of suppressing the curing deterioration may not be sufficiently obtained.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing.

The hardness at 25 ° C. of the rubber composition of the present invention (after vulcanization) is preferably 70 or less, more preferably 60 or less, and still more preferably 55 or less. If it exceeds 70, the performance on ice may be significantly reduced. Further, the hardness at 25 ° C. is preferably 42 or more, more preferably 46 or more. If it is less than 42, the tread portion of the studless pattern is greatly collapsed and the expected performance on ice may be deteriorated. The hardness at 25 ° C. can be adjusted to the above range by adjusting the combination of the above components and the mixing ratio.
The hardness at 25 ° C. is a value obtained by the measurement method described in Examples described later.

The rubber composition of the present invention is used as a base tread of a studless tire. The base tread is an inner layer portion of a tread having a multilayer structure. In the case of a tread having a two-layer structure, the tread includes a surface layer (cap tread) and an inner surface layer (base tread).

A tread having a multilayer structure is produced by pasting a sheet into a predetermined shape, or by inserting it into two or more extruders and forming it into two or more layers at the head outlet of the extruder. Can do.

The studless tire of the present invention can be produced by a normal method using the rubber composition. That is, the rubber composition is extruded in accordance with the shape of the base tread at an unvulcanized stage, molded by a normal method on a tire molding machine, and bonded together with other tire members to form an unvulcanized tire. Form. This unvulcanized tire can be heated and pressed in a vulcanizer to produce a studless tire.

The studless tire of the present invention is suitably used as a studless tire for passenger cars and trucks / buses.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: RSS # 3
BR: BR150B manufactured by Ube Industries, Ltd. (cis content 97 mass%, ML _{1 + 4} (100 ° C.) 40, 5% toluene solution viscosity at 25 ° C. = 48 cps, Mw / Mn 3.3)
Carbon black: N220 (N ₂ SA: 111 m ² / g) manufactured by Cabot Japan
Silica: Ultrasil VN3 (N ₂ SA: 175 m ² / g) manufactured by Tegusa
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Tegusa
Oil: PS-32 made by Idemitsu Kosan Co., Ltd.
Stearic acid: Tungsten zinc oxide manufactured by NOF Corporation: Zinc oxide type 2 anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N- (1,3- Dimethylbutyl) -N′-phenyl-p-phenylenediamine)
Wax: Ozoace wax manufactured by Nippon Seiwa Co., Ltd. Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. TBBS: Noxeller NS (N-tert-butyl- manufactured by Ouchi Shinsei Chemical Co., Ltd.) 2-benzothiazolylsulfenamide)
Vulcanization accelerator 4m-MBTS: Bis (4-methylbenzothiazolyl-2) -disulfide (formula (III)) manufactured by NOCIL
Vulcanization accelerator TMTM: Noxeller TS (tetramethylthiuram monosulfide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator DPG: Noxeller D (diphenylguanidine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1-5 and Comparative Examples 1-3
According to the contents shown in Table 1, materials other than sulfur and a vulcanization accelerator were kneaded for 5 minutes at 150 ° C. using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 3 minutes at 80 ° C. using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized with a 0.5 mm thick mold at 170 ° C. for 15 minutes to obtain a vulcanized rubber composition.

Each of the obtained unvulcanized rubber compositions was molded into a base tread shape, bonded together with other tire members, and vulcanized at 170 ° C. for 15 minutes to obtain a test studless tire (tire size: 195 / 65R15 ) Was manufactured.

(Deterioration conditions)
The vulcanized rubber composition prepared above and the test studless tire were thermally deteriorated in an oven at 80 ° C. for 168 hours. What was obtained was used as a deteriorated sample (vulcanized rubber composition after heat deterioration, test studless tire after heat deterioration).

The following evaluation was performed using the obtained unvulcanized rubber composition, vulcanized rubber composition, test studless tire, vulcanized rubber composition after heat deterioration, and test studless tire after heat deterioration. . Each test result is shown in Table 1.

<Vulcanization test>
The obtained unvulcanized rubber composition was subjected to a vulcanization test at a measurement temperature of 170 ° C. according to JIS K 6300, using a vibration type vulcanization tester (Jurassic Curast Meter). A vulcanization rate curve was obtained.
The minimum value of the torque of the vulcanization speed curve was ML, the maximum value was MH, and the difference (MH−ML) was the torque increase value (ME). The torque increase value of Example 1 was set to 100, and the result of each example was displayed as an index. The larger the torque increase value, the higher the crosslinking efficiency and the better.
Also, the time to reach ML + 0.95ME (95% torque rise point) T ₉₅ (min), which is an index of the optimum vulcanization time, is read, and the result of each example is displayed as an index with the time T _{95 of} Example 1 being 100. did. As vulcanization time T ₉₅ is large, the vulcanization time becomes longer, poor productivity.

<Hardness (25 ° C)>
For vulcanized rubber composition and vulcanized rubber composition after heat deterioration, the hardness at 25 ° C. is measured with a type A durometer in accordance with JIS K6253 “vulcanized rubber and thermoplastic rubber—How to obtain hardness”. did.

<Performance on ice>
About the obtained test studless tire (new article) (tire size 195 / 65R15) and the test studless tire after heat deterioration (tire size 195 / 65R15), using a domestically produced FR car (2000 cc) as a test vehicle, At an air temperature of −1 to −6 ° C., stepping on the lock brake at 30 km / h on an ice plate, measuring the braking stop distance, and setting the braking stop distance of the new test studless tire of Example 1 to 100, the following formula The braking index on ice was displayed as an index. The larger the braking index on ice, the better the braking performance on ice. In addition, in order to level the surface of the test tire before the test, the leveling running was performed for 100 km each.
(Brake index on ice) = (Brake stop distance of Example 1) / (Stop distance) × 100

<Abrasion resistance>
The obtained studless tire for test (tire size 195 / 65R15) was mounted on a domestic FR vehicle (2000 cc), and the amount of wear after running 30000 km was measured. The value of the amount of wear in Example 1 was taken as 100 and displayed as an index. It shows that it is excellent in abrasion resistance performance, so that an index | exponent is large.

<Cut resistance>
The test studless tire (tire size 195 / 65R15) obtained was mounted on a domestic FR vehicle (2000cc), and after traveling for 1000km on a rough road where rocks, quarrying, etc. were scattered, the cut scratches that occurred in the tread were visually observed. Thus, Comparative Example 1 was evaluated as 100 by sensory evaluation by an inspector. The larger the value, the better the cut resistance.

表１により、イソプレン系ゴムと、シリカと、４ｍ−ＭＢＴＳと、チウラム系加硫促進剤であるＴＭＴＭとを配合した実施例では、熱劣化による硬度の上昇および熱劣化による氷上性能の低下を抑制することができた。また、トルク上昇値が低下したり、加硫時間Ｔ_９５が大幅に増大することもなかった。一方、４ｍ−ＭＢＴＳを配合していない比較例１では、熱劣化による硬度の上昇および熱劣化による氷上性能の低下を抑制することができず、さらに、実施例と比べて、耐摩耗性能、耐カット性能が低く、トルク上昇値が小さく（架橋効率が低く）、加硫時間Ｔ_９５が大きかった。また、イソプレン系ゴムと、シリカと、４ｍ−ＭＢＴＳとを配合しているものの、ＴＭＴＭを配合していない比較例２は、実施例と比べて、トルク上昇値が小さく（架橋効率が低く）、加硫時間Ｔ_９５が大きく、さらに、耐カット性能が低かった。また、４ｍ−ＭＢＴＳと、チウラム系加硫促進剤であるＴＭＴＭとを配合しているものの、シリカを配合していない比較例３では、熱劣化による硬度の上昇および熱劣化による氷上性能の低下を抑制することができず、さらに、実施例と比べて、耐カット性能が低かった。

According to Table 1, in an example in which isoprene-based rubber, silica, 4m-MBTS, and TMTM which is a thiuram-based vulcanization accelerator are blended, an increase in hardness due to thermal degradation and a decrease in performance on ice due to thermal degradation are suppressed. We were able to. Further, it lowered torque rise value, vulcanization time T ₉₅ was not be greatly increased. On the other hand, in Comparative Example 1 in which 4m-MBTS was not blended, it was not possible to suppress an increase in hardness due to thermal deterioration and a decrease in performance on ice due to thermal deterioration. cutting performance is low, less torque rise value (low cross-linking efficiency), vulcanization time T ₉₅ is large. Moreover, although the isoprene-based rubber, silica, and 4m-MBTS are blended, the comparative example 2 in which TMTM is not blended has a small torque increase value (low crosslinking efficiency) compared to the examples. vulcanization time T ₉₅ is large, further, cut resistance was low. Moreover, although 4m-MBTS and TMTM which is a thiuram vulcanization accelerator are blended, in Comparative Example 3 in which no silica is blended, the hardness increases due to thermal degradation and the performance on ice due to thermal degradation decreases. In addition, the anti-cut performance was lower than in the examples.

Claims (5)

A rubber composition for a base tread containing a rubber component containing an isoprene-based rubber, silica, a compound represented by the following formula (I) and / or (II), and a thiuram vulcanization accelerator.

(In the formulas (I) and (II), R ¹ and R ² are the same or different and each represents a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group, provided that R ¹ and R ² are hydrogen atoms at the same time. Except in cases.) The base tread rubber composition according to claim 1, wherein the isoprene-based rubber is at least one selected from the group consisting of isoprene rubber, natural rubber, and modified natural rubber. The rubber composition for base treads according to claim 1 or 2, wherein the compound is a compound represented by the following formula (III).

The rubber composition for a base tread according to any one of claims 1 to 3, wherein the hardness at 25 ° C is 42 to 70. The studless tire which has a base tread produced using the rubber composition in any one of Claims 1-4.