JPH11227409A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire which improves the lower heating performance and which is excellent in productivity with out damaging gripping performance. SOLUTION: With the pneumatic tire consisting of a tread layer, the rubber comosition of a tread layer contains 15 or more wt. parts of white fillers in relation to 100 wt. parts of dien base rubber components which do not contain 50 or more wt. parts of rubber selected form among a group of consisting of stylene-butadien rubber(SBR), bytyl rubber (IIR), and ethylene propylene rubber(EPDM), and contains 0.2 to 5.0 wt. parts of vulcanizing accelerators expressed by a formula in relation to 100 wt. parts of rubber component. In the formula, R<1> and R<2> represents independently alkyl group with the number of carbon 1 or 10 or aryl group with the number of carbon 6 to 10. The aryl group may be in straight chain, in branch chain, or annular.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire using a white filler for a tread portion, and more particularly to a technique for improving productivity of a pneumatic tire.

[0002]

2. Description of the Related Art In recent years, studies have been made to reduce the rolling resistance of tires in order to save fuel consumption of automobiles in accordance with social demands for energy saving and resource saving. The rolling resistance of a tire can be reduced by reducing the heat build-up of the tire, but this also reduces the temperature of the tire during running, especially for large tires, to improve the durability of the tire. Also leads to.

It is generally known that a rubber composition having a small hysteresis loss may be used as a tread rubber in order to reduce the heat build-up of a tire. However, when a rubber composition having a small hysteresis loss is used for the tread rubber, grip performance with a road, particularly grip performance on a wet road surface tends to decrease, which is not preferable in terms of safety. Therefore, both low heat generation performance and grip performance are required.

[0004] In response to the above demand, it is known that a tire having both low heat generation performance and high grip performance can be obtained by using a rubber composition containing a white filler, particularly silica or aluminum hydroxide, in a tread. ing.

[0005] However, rubber compositions containing a white filler are often slow in vulcanization rate, which poses a problem in vulcanization productivity.
Particularly when this is to be used for a tread of a pneumatic tire, the tread portion often has the thickest gauge among the unvulcanized tire portions, and the vulcanization productivity is determined by the vulcanization speed of this portion. In many cases, vulcanization productivity may be sacrificed. Further, if the inside of the tread is sufficiently vulcanized, there is a problem that the surface of the tread is over-vulcanized (overcured) due to poor thermal conductivity and the physical properties are deteriorated.

[0006] In particular, in tires where low heat build-up is important or large tires where durability is important, natural rubber or butadiene rubber is mainly used. There has been a demand for a tire tread rubber that is exothermic, has a high vulcanization rate, and has little deterioration in physical properties during overvulcanization.

Various investigations have been made on these problems, but regarding rubber compounding agents, rubber chemistry and technology 67 has been used to improve the physical properties of rubber compositions by using silica and a thiophosphoryl compound in combination.
No. 672-686, but there is no description about the specific metal salt used in the present invention, no description regarding application to tires, low heat build-up as described above,
There are no studies or suggestions for the required characteristics of tires such as high grip performance and high productivity.

Further, US Pat. No. 3,426,003 discloses a combination of zinc dithiophosphate and a thiuram compound as a combination of vulcanizing agents for butyl rubber, which is mainly composed of natural rubber and butadiene rubber. Further, there is no description of a white filler which is essential in the present invention.

Further, British Patent No. 1,288,616 describes that the discoloration is improved by using zinc dithiophosphate in combination with a white filler. Absent.

JP-A-47-9488 discloses a method of vulcanizing a rubber mixture comprising a diene rubber component, a specific diradical dithiophosphate, a known vulcanization accelerator and sulfur. It is described that the obtained vulcanized product has excellent heat aging prevention properties. However, this rubber mixture does not substantially contain a white filler such as silica, nor has a tire using this rubber composition been studied, and there is no description regarding the required characteristics of the tire as described above. Nor is there any suggestion about these things.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and it is an object of the present invention to achieve a high balance between low heat generation performance, durability and grip performance, and high productivity. It is to provide a pneumatic tire.

[0012]

Means for Solving the Problems The present inventors have focused on polymers and various compounding agents to be compounded in tread rubber, and as a result of diligent studies, have found that the following means can solve the problems. It was completed.

That is, (1) The pneumatic tire of the present invention is a pneumatic tire having a tread layer, wherein the rubber composition of the tread layer comprises styrene-butadiene rubber (SBR), butyl rubber (IIR) and ethylene. 15 parts by weight or more of a white filler is contained with respect to 100 parts by weight of a diene rubber component not containing 50 parts by weight or more of a rubber selected from the group consisting of propylene rubber (EPDM), and the following general formula (I) A vulcanization accelerator represented by a rubber component 100
It is characterized by comprising 0.2 to 5.0 parts by weight with respect to parts by weight.

[0014]

Embedded image (Wherein, R ¹ and R ² are each independently a carbon number of 1 to 1)
0 represents an alkyl group or an aryl group having 6 to 10 carbon atoms. This alkyl group may be linear, branched or cyclic. (2) In the above item (1), the diene rubber component 1
00 parts by weight of natural rubber (NR) and isoprene rubber (I
The total amount of R) and butadiene rubber (BR) is preferably at least 50 parts by weight. (3) In the above item (1), the vulcanization accelerator represented by the general formula (I) is preferably a vulcanization accelerator represented by the following formula (II).

[0015]

Embedded image (4) In the above item (1), the white filler in the rubber composition is preferably silica or aluminum hydroxide. (5) In the above item (1), the content of the white filler is preferably 15 to 85 parts by weight based on 100 parts by weight of the rubber component. (6) In the above item (4), the silane coupling agent is preferably contained in an amount of 1 to 15% by weight based on the amount of silica. (7) In the above item (1), the rubber composition may contain the vulcanization accelerator represented by the general formula (I) in an amount of 0.2 to 2.0 parts by weight based on 100 parts by weight of the rubber component. It is preferred to include. (8) In the above item (1), the rubber composition contains a vulcanization accelerator represented by the general formula (I) and a vulcanization accelerator containing a benzothiazole unit, and is included in the rubber composition. It is preferable that the molar amount of the benzothiazole unit is 1/2 or more of the molar amount of the vulcanization accelerator represented by the general formula (I). (9) In the above item (8), the vulcanization accelerator containing the benzothiazole unit is selected from the group consisting of mercaptobenzothiazole, dibenzothiazolyl disulfide, benzothiazolylsulfenamide and benzothiazolylsulfenimide. Preferably, at least one compound is used. (10) In the above item (8), the vulcanization accelerator containing the benzothiazole unit may be an alkylated mercaptobenzothiazole, a bis (alkylated benzothiazolyl) disulfide, an alkylated benzothiazolylsulfenamide and an alkylated benzothiazolyl. Preferably, the compound is at least one compound selected from the group consisting of rusulfenimide.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION As the diene rubber component used in the rubber composition of the tread layer of the pneumatic tire of the present invention, natural rubber (NR), synthetic rubber such as styrene-butaene rubber (SBR), isoprene rubber (IR) ), Butadiene rubber (BR), butyl rubber (including halogenated butyl rubber) (IIR), ethylene-propylene rubber (EP
DM) and the like, but SBR, IIR and / or EPDM are added in an amount of 5 parts by weight per 100 parts by weight of the diene rubber component.
It is necessary in the present invention that the content is not more than 0 parts by weight. The rubber component may be used alone or as a blend of two or more. It is not preferable to include SBR, IIR and / or EPDM in an amount of 50 parts by weight or more, since the low heat generation performance is greatly impaired. From the viewpoint of low heat build-up and durability, the total amount of NR, IR and BR in 100 parts by weight of the rubber component is preferably 50 parts by weight or more.

Further, the rubber composition of the tread layer of the pneumatic tire of the present invention comprises the vulcanization accelerator represented by the above general formula (I) in an amount of 0.2 to 5.0 with respect to 100 parts by weight of the rubber component. Parts by weight, preferably 0.2 to 2.0 parts by weight. If the amount is less than 0.2 part by weight, the effect of improving the vulcanization rate is low, and if the amount exceeds 5.0 parts by weight, no further improvement in the effect is observed, and further increase in the amount from the economical viewpoint is effective. is not.

R ¹ and R ^{2 of the} zinc dithiophosphate represented by the general formula (I) of the vulcanization accelerator used in the present invention.
Is independently an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms, and the alkyl group may be any of linear, branched or cyclic. Among them, R ¹
And R ² have 3 to 4 carbon atoms as shown in the above formula (II).
Are preferred. Zinc dithiophosphates having an alkyl group having 2 or less carbon atoms tend to have low solubility in rubber, and if the number of carbon atoms is 5 or more, the effect cannot be further improved. Is not always effective.

These vulcanization accelerators include, for example, O,
Zinc O'-dipropyldithiophosphate, zinc O, O'-diisopropyldithiophosphate, zinc O, O'-di-n-butyldithiophosphate, zinc O, O'-di-sec-butyldithiophosphate, O, O Zinc '-di-t-butyldithiophosphate, O, O'-Zinc diphenyldithiophosphate, O,
O'-dicyclohexyldithiophosphate zinc and the like. Among them, zinc O, O'-diisopropyldithiophosphate and zinc O, O'-di-n-butyldithiophosphate are preferred. These vulcanization accelerators can be used alone or in a mixture of two or more.

The rubber composition used for the tread of the pneumatic tire of the present invention requires a white filler.

Examples of the white filler include silica, aluminum hydroxide, clay, talc, calcium carbonate, magnesium carbonate and the like, and silica and aluminum hydroxide are highly compatible with low heat generation performance and grip performance. Is mentioned.

This white filler must be added in an amount of 15 parts by weight or more based on 100 parts by weight of the rubber component.
A range of -85 parts by weight is preferred. If the amount is less than 15 parts by weight, the effect of improving the low heat generation performance and the grip performance is not sufficient.
It is not preferable to add more than parts by weight because the viscosity of the rubber becomes too high and the workability deteriorates. The white filler can be used alone or as a mixture of two or more.

Carbon black can also be used in combination with the white filler. However, in order to achieve a high balance between low heat generation performance and grip performance, the content of the white filler must be 4% of the total filler.
It is preferably at least 0% by weight.

As the rubber composition used for the tread of the pneumatic tire of the present invention, zinc oxide, stearic acid, an antioxidant, and WA commonly used together with the above essential components are used.
Components such as X, a silane coupling agent, and a vulcanizing agent can be appropriately blended within a range that does not impair the effects of the present invention.

In the present invention, when silica is used as the white filler, it is preferable to use a silane coupling agent.

Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2- Trimethoxysilylethyl)
Tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane , 3-chloropropyltrimethoxysilane, 3
-Chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2-chloroethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N, N -Dimethylthiocarbamoyltetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyltetrasulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, 3-triethoxysilylpropylbenzothiazoletetrasulfide, 3-triethoxy Silylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyl Rutrimethoxysilane, N-β
-(Aminoethyl) -γ-aminopropyltrimethoxysilane and the like, among which bis (3-triethoxysilylpropyl) tetrasulfide, 3-mercaptopropyltriethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl -Γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane and the like are preferable.

Also, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, 3-nitropropyldimethoxymethylsilane, 3-chloropropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N -Dimethiocarbamoyltetrasulfide, dimethoxymethylsilylpropylbenzothiazole tetrasulfide and the like can also be mentioned.

The amount of the silane coupling agent is preferably 1 to 15% by weight, more preferably 5 to 12% by weight, based on silica. If the amount of the silane coupling agent is less than 1% by weight, the coupling effect is small,
If it exceeds 15% by weight, gelation is caused, which is not preferable.

Examples of the vulcanizing agent include sulfur and a donor of sulfur. The amount of the vulcanizing agent is 0.5 to 5.0 parts by weight, preferably 0.5 to 5.0 parts by weight, based on 100 parts by weight of the rubber component. ~ 2 parts by weight. If the amount is less than 0.5 part by weight, the breaking strength and abrasion resistance of the vulcanized rubber decrease, and if it exceeds 5.0 parts by weight, the rubber elasticity is impaired.

The rubber composition for the tread layer of the pneumatic tire of the present invention contains, as a vulcanization accelerator, a vulcanization accelerator containing a benzothiazole unit in addition to the vulcanization accelerator represented by the general formula (I). It is preferable that the molar amount of the benzothiazole unit contained in the rubber composition is at least １ ／ of the molar amount of the vulcanization accelerator represented by the general formula (I).

The benzothiazole-containing vulcanization accelerator used in combination is preferably mercaptobenzothiazole, alkylated mercaptobenzothiazoles, dibenzothiazolyl disulfide, bisalkylated benzothiazolyl disulfide, benzothiazolyl sulphene. Amides, alkylated benzothiazolylsulfenamides, benzothiazolylsulfenimides, alkylated benzothiazolylsulfenimides, preferably alkylated benzothiazolylsulfenamides and / or alkylated benzothiazolyls Rusulfenimides can be mentioned.

Specifically, for example, mercaptobenzothiazole, 4-methylmercaptobenzothiazole,
4-ethylmercaptobenzothiazole, 2,2′-dithiobismercaptobenzothiazole, 2,2′-dithiobis (4-methylmercaptobenzothiazole),
2,2'-dithiobis (4-ethylmercaptobenzothiazole), N-tert-butyl-2-benzothiazolylsulfenamide, N-tert-butyl-2-
(4-methylbenzothiazolylsulfenamide), N
-Tert-butyl-2- (4-ethylbenzothiazolylsulfenamide), N-cyclohexyl-2-benzothiazolylsulfenamide, N-cyclohexyl-
2- (4-methylbenzothiazolylsulfenamide), N-cyclohexyl-2- (4-ethylbenzothiazolylsulfenamide), N-tert-butyl-
2-benzothiazolylsulfenimide, N-tert
-Butyl-2- (4-methylbenzothiazolylsulfenimide), N-tert-butyl-2- (4-ethylbenzothiazolylsulfenimide), N-cyclohexyl-2-benzothiazolylsulfenimide, Examples thereof include N-cyclohexyl-2- (4-methylbenzothiazolylsulfenimide) and N-cyclohexyl-2- (4-ethylbenzothiazolylsulfenimide). Among them, N-tert-butyl-2-benzothiazolylsulfenamide, N-cyclohexyl-2-
Benzothiazolylsulfenamide, N-tert-butyl-2-benzothiazolylsulfenimide, N-cyclohexyl-2-benzothiazolylsulfenimide and the like are preferred.

If the molar amount of the benzothiazole unit is less than 1/2 of the molar amount of the vulcanization accelerator represented by the general formula (I), the effect of improving the vulcanization rate is small, and vulcanization cannot be carried out for a long time. , The effect of improving productivity is reduced. .

The use of a dithiophosphoric acid-based accelerator which is not a zinc salt and a benzothiazole-based accelerator is described in Rubber Chemistry and Technology, Vol. 62.
Although it is described on pages 569-584, according to the description of this document, the optimum vulcanization time (Optimum cure time) is determined.
e) is a direction of elongation when used together, which is opposite to the present invention as can be seen from the examples described later.
In the case of this document, the fact that dithiophosphoric acid is not a zinc salt used in the present invention is considered to prolong vulcanization contrary to the present invention.

The rubber composition used in the present invention is obtained by kneading using a kneading machine such as a roll, an internal mixer, a Banbury mixer and the like. You.

[0036]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the present invention.

Various measurements were made by the following methods.

(1) Evaluation of vulcanization rate and pervulcanization resistance The vulcanization rate and pervulcanization resistance were measured by FLEXSYS MDR200.
It measured using 0.

The vulcanization rate was measured at t'90 at 160 ° C. in accordance with ASTM D5289-95. The value was expressed as an index with the value of Comparative Example 1 being 100. The smaller the value, the faster the vulcanization rate and the better the productivity.

The super vulcanization resistance was measured by measuring the torque value after 2 minutes and 20 minutes at 190 ° C., and the ratio was expressed as a percentage according to the following equation. The closer the number is to 100, the smaller the change in physical properties with respect to overvulcanization is, and the better.

[0041] (2) Evaluation of low heat generation performance The low heat generation performance was evaluated for the rebound resilience using a Dunlop-type trixometer. The value was expressed as an index with the value of Comparative Example 1 being 100. The larger the value, the better it is because it is difficult to convert the energy applied to the rubber into heat.

(Examples 1 to 4, Comparative Examples 1 and 2) According to the compounding recipe shown in Table 1, kneading and compounding were performed to obtain a rubber composition. The vulcanization rate, pervulcanization resistance and low heat generation performance of each rubber composition were measured. Table 1 shows the results.

[0043]

[Table 1] As shown in Table 1, by using the rubber component, the white filler and the vulcanization accelerator of the present invention, the vulcanization rate is high,
Since a rubber composition having high pervulcanization resistance and low heat generation performance can be obtained, a tire having good performance can be manufactured with high productivity.

Examples 1 to 4 of Table 1 and Comparative Examples 1 and 2
A prototype pneumatic radial tire for passenger cars (size 195 / 60R15) and a heavy duty pneumatic radial tire for trucks and buses (size 1000R20) in which the six types of rubber compositions are arranged on a tread were obtained. As compared with the comparative tires, the vulcanization time was shortened and the rolling resistance was small. In the tires of Examples 1 and 3, both the vulcanization time and the rolling resistance were dramatically improved.

[0045]

According to the present invention, the productivity of a pneumatic tire with improved low heat generation performance can be improved without impairing the grip performance.

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Claims (10)

[Claims] 1. A pneumatic tire having a tread layer, wherein the rubber composition of the tread layer is selected from the group consisting of styrene-butadiene rubber (SBR), butyl rubber (IIR) and ethylene propylene rubber (EPDM). 100 parts by weight of a diene rubber component not containing 50 parts by weight or more of a rubber containing at least 15 parts by weight of a white filler and a vulcanization accelerator represented by the following general formula (I) A pneumatic tire comprising 0.2 to 5.0 parts by weight based on parts by weight. Embedded image (Wherein, R ¹ and R ² are each independently a carbon number of 1 to 1)
0 represents an alkyl group or an aryl group having 6 to 10 carbon atoms. This alkyl group may be linear, branched or cyclic. ) 2. The total amount of natural rubber (NR), isoprene rubber (IR) and butadiene rubber (BR) in 100 parts by weight of the diene rubber component is 50 parts by weight or more. The pneumatic tire as described. 3. The pneumatic tire according to claim 1, wherein the vulcanization accelerator represented by the general formula (I) is a vulcanization accelerator represented by the following formula (II). Embedded image 4. The pneumatic tire according to claim 1, wherein the white filler in the rubber composition is silica or aluminum hydroxide. 5. The rubber composition according to claim 1, wherein the content of said white filler is 10%.
The pneumatic tire according to claim 1, wherein the amount is 15 to 85 parts by weight with respect to 0 parts by weight. 6. The pneumatic tire according to claim 4, wherein the silane coupling agent is contained in an amount of 1 to 15% by weight based on the amount of silica. 7. The rubber composition is obtained by adding the vulcanization accelerator represented by the general formula (I) to 100 parts by weight of a rubber component.
2. The composition of claim 1, comprising 0.2 to 2.0 parts by weight.
The pneumatic tire as described. 8. The rubber composition contains a vulcanization accelerator represented by the general formula (I) and a vulcanization accelerator containing a benzothiazole unit, and the mole of the benzothiazole unit contained in the rubber composition The amount is at least 1/2 of the molar amount of the vulcanization accelerator represented by the general formula (I).
The pneumatic tire as described. 9. The vulcanization accelerator containing a benzothiazole unit, wherein at least one selected from the group consisting of mercaptobenzothiazole, dibenzothiazolyl disulfide, benzothiazolylsulfenamide and benzothiazolylsulfenimide. The pneumatic tire according to claim 8, which is a compound. 10. The vulcanization accelerator containing a benzothiazole unit is an alkylated mercaptobenzothiazole,
9. The pneumatic device according to claim 8, wherein the compound is at least one compound selected from the group consisting of bis (alkylated benzothiazolyl) disulfide, alkylated benzothiazolylsulfenamide, and alkylated benzothiazolylsulfenimide. tire.