JPH10251449A - Rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber compsn. which has a higher heat resistance than conventionally achieved and is suitable for tire treads by compounding a raw rubber with a specified amt. of an antimony dithiophosphate having a specific structure as a vulcanization accelerator. SOLUTION: This compsn. contains 0.1-10 pts.wt. at least one antimony dithiophosphate represented by the formula (R<1> and R<2> are each independently 19C or lower alkyl, alkenyl, or cycloalkyl) based on 100 pts.wt. at least one raw rubber selected from among natural and synthetic diene rubbers. The antimony dithiophosphate may be used alone or together with other vulcanization accelerators, 2-benzothiazoylsulfenamide and 2-benzothiazoylsulfenimide being pref. Pref., 100 pts.wt. raw rubber contains at least 50 pts.wt. styrene-butadiene copolymer. Silica is suitable as a filler for this compsn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a rubber composition,
More specifically, the present invention relates to a rubber composition having excellent heat resistance and used for a tire tread or the like.

[0002]

2. Description of the Related Art In recent years, as the performance and speed of automobiles have increased, tires, especially tread members, have been required to have higher heat resistance than ever.

[0003] Tetramethylthiuram disulfide (T), which has hitherto been used as a heat-resistant crosslinking agent and a vulcanization accelerator,
MTD) and tetramethylthiuram monosulfide (TM
TM) becomes difficult to use for various reasons, and zinc dithiophosphate and dithiophosphate disulfide have attracted attention as vulcanization accelerators to replace them, and some of them have been put to practical use.

Focusing on zinc dithiophosphate, rubber compositions using the same are known from US Pat. Nos. 1,288,616 and 3,426,003 (Flexis, USA). JP-A-54-85243 uses zinc dithiophosphate as a sulfur-free crosslinking component.
Further, zinc dithiophosphate salts have been described in many documents. J. , J
ohansson A. H. Rubber World
d, 212 (5), 30 (1995) used zinc dithiophosphate as a nitrosamine-free promoter and also disclosed Kempermann, Theo, Rubber C.
hem. Technol. , 55 (2) 391-406.
(1982) describes that zinc dithiophosphate has an effect of improving heat resistance.

[0005] Rubber compositions using the above-mentioned zinc dithiophosphate and dithiophosphate disulfide have excellent heat resistance, but they have limitations, and it has become clear that they will not be able to sufficiently meet the need for higher heat resistance in the future. .

[0006] Similarly to zinc dithiophosphate, TMTD
Even when tetraoctylthiuram disulfide or tetrabenzylthiuram disulfide used as an alternative compound is used, the obtained heat resistance is at a level equivalent to zinc dithiophosphate and is not sufficient.

On the other hand, antimony dithiophosphate is known as an additive for a lubricant, but there is no example of using it in a rubber composition.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and an object of the present invention is to provide a rubber composition having higher heat resistance than the prior art.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies focusing on metal dithiophosphate salts of vulcanization accelerators.
The present inventors have found that the problems can be solved by the following means using antimony dithiophosphate, which has not received attention as a vulcanization accelerator, and have completed the present invention.

That is, (1) The rubber composition of the present invention comprises:
0.1 to 10 parts by weight of at least one kind of antimony dithiophosphate represented by the following general formula (I) is contained in 100 parts by weight of at least one kind of rubber raw material selected from the group consisting of natural rubber and diene-based synthetic rubber. It is characterized by the following.

General formula (I)

[0012]

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(In the formula, R ¹ and R ² each independently represent an alkyl group, alkenyl group or cycloalkyl group having 19 or less carbon atoms.) (2) The rubber composition of the present invention has the above-mentioned (1). Wherein R ¹ and R ^{2 of the} antimony dithiophosphate represented by the general formula (I) described in the above item (1) are each independently an alkyl group or a cycloalkyl group having 8 or less carbon atoms. .

(3) In the rubber composition of the present invention, in the above item (2), the antimony dithiophosphate described in the above item (2), a benzothiazole derivative represented by the following general formula (II) and a benzothiazole derivative represented by the following general formula (II): (III) at least one compound selected from the group consisting of thiuram compounds.

Formula (II)

[0016]

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[Wherein R ³ is a hydrogen atom, a thiobenzothiazolyl group represented by the following formula 1 or an amino group represented by the formula 2 (R ⁴ and R ⁵ are each independently a hydrogen atom, carbon number 2
To 4 alkyl groups or cyclohexyl groups). Here, the case where R ⁴ and R ⁵ are simultaneously a hydrogen atom is excluded. Equation 1

[0018]

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Equation 2

[0020]

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Formula (III)

[0022]

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(Wherein R ⁶ , R ⁷ , R ⁸ and R ⁹ are each independently an alkyl group having 1 to 8 carbon atoms, a cyclohexyl group, a phenol group, a benzyl group, or R ⁶ and R ⁷ , and R ⁸ Represents a pentamethylene group or a methylpentamethylene group having a cyclic structure in which R ⁹ and R ⁹ are linked.) (4) In the rubber composition of the present invention, in the above-mentioned item (3), the general formula (3) characterized in that R ^6, R ^7, R ⁸ and R ⁹ of the thiuram compound represented by III) are each independently a 2-ethylhexyl group or a benzyl group.

(5) The rubber composition of the present invention is characterized in that, in the above item (1), at least one kind of vulcanization accelerator selected from the group consisting of 2-benzothiazoylsulfenamide and 2-benzothiazoylsulfenimide An agent is included.

(6) In the rubber composition of the present invention, the styrene-butadiene copolymer according to the item (1) is
It is characterized in that 50 parts by weight or more is contained in 00 parts by weight.

(7) The rubber composition of the present invention is characterized in that in the above item (1), silica or aluminum hydroxide as a reinforcing filler is contained in an amount of 15 to 85 parts by weight based on 100 parts by weight of the rubber raw material. Features.

(8) The rubber composition of the present invention is characterized in that, in the above item (7), the reinforcing filler is silica.

(9) The rubber composition of the present invention is characterized in that, in the item (7), the tertiary amine compound is contained in an amount of 1 to 15% by weight based on the amount of the reinforcing filler.

(10) The rubber composition of the present invention comprises the above (8)
In the above item, the silane coupling agent is contained in an amount of 1 to 15% by weight based on the amount of silica.

(11) The rubber composition of the present invention comprises the above (7)
In the paragraph, carbon black as a reinforcing filler is contained in an amount of 20 to 150 parts by weight based on 100 parts by weight of the rubber raw material.

(12) The rubber composition according to the present invention is characterized in that
In the section, the styrene-butadiene copolymer is 50 parts by weight or more in 100 parts by weight of the rubber raw material, and the silica as the reinforcing filler is 15 to 85 parts by weight based on 100 parts by weight of the rubber raw material.
At least one vulcanization accelerator selected from the group consisting of 2-benzothiazoylsulfenamide and 2-benzothiazoylsulfenimide is included, and the tertiary amine compound is added to the reinforcing filler in an amount relative to the amount of the reinforcing filler. , 1-1
It is characterized by containing 5% by weight.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION The rubber raw material used in the present invention is at least one selected from the group consisting of natural rubber and diene-based synthetic rubber. That is, from natural rubber (NR) and many diene-based synthetic rubbers, they may be used alone or in a blend of two or more of them. Examples of the diene-based synthetic rubber include synthetic polyisoprene rubber (IR), polybutadiene rubber (BR), styrene butadiene rubber (SBR), and butyl rubber (IIR).
And the like.

In the present invention, among these rubber raw materials, for example, SBR alone, SBR / NR blend, SBR / NR
NR / BR blends and the like are preferably used from the viewpoint of effects. When using two or more blends as rubber raw materials,
SBR is preferably contained in an amount of 50 parts by weight or more, more preferably 70 parts by weight or more, in 100 parts by weight of the rubber raw material.

The antimony dithiophosphate used in the present invention is represented by the above general formula (I), and is used alone or in a mixture of two or more. In the formula, R ¹ and R ² each independently represent an alkyl group, alkenyl group or cycloalkyl group having 19 or less carbon atoms, and an alkyl group or cycloalkyl group having 8 or less carbon atoms is preferable.

As the antimony dithiophosphate, for example, antimony O, O-dibutyldithiophosphate, O, O
Antimony-diisopropyldithiophosphate, antimony O, O-dipropyldithiophosphate, antimony O, O-diethyldithiophosphate, antimony O, O-dimethyldithiophosphate, antimony O, O-bis (2-ethylhexyl) dithiophosphate, O, O-bis (4-methylpentyl) antimony dithiophosphate and the like can be mentioned. Among them,
From the viewpoint of the effect, antimony O, O-dibutyldithiophosphate, antimony O, O-diisopropyldithiophosphate,
O, O-bis (2-ethylhexyl) antimony dithiophosphate is preferred.

It is also preferable to use antimony dithiophosphate in combination with zinc dithiophosphate. The amount of antimony dithiophosphate is 0.1 to 100 parts by weight of the rubber raw material.
10 parts by weight, preferably 0.2 to 3 parts by weight. If the compounding amount is less than 0.1, sufficient performance cannot be obtained, and if the compounding amount exceeds 10, not only the effect will not be improved but also the workability will decrease.

The method for producing antimony dithiophosphate used in the present invention is not particularly limited. Usually, sodium hydroxide is gradually added to an aqueous dithiophosphoric acid solution, and
After preparing sodium dithiophosphate, an acetone solution of antimony trichloride is added dropwise, and the antimony dithiophosphate obtained as a precipitate is purified and dried to be produced.

In the present invention, antimony dithiophosphate represented by the general formula (I) may be used alone, but it may be used together with the benzothiazole derivative represented by the general formula (II) and the benzothiazole derivative represented by the general formula (III). It is preferable to use together with at least one vulcanization accelerator selected from the group consisting of thiuram compounds, which lengthens Mooney scorch time, and an effect equivalent to that obtained when a smaller amount of antimony dithiophosphate is used alone is obtained. .

Examples of the benzothiazole derivative include 2-mercaptobenzothiazole, dibenzothiazyl disulfide, N-cyclohexyl-2-benzothiazylsulfenamide, N, N-dicyclohexyl-2
-Benzothiazylsulfenamide, N, N-diisopropyl-2-benzothiazylsulfenamide, Nt
-Butyl-2-benzothiazylsulfenamide, t-
Butyl-2-benzothiazylsulfenimide, cyclohexyl-2-benzothiazylsulfenimide and the like. Among them, Nt-butyl-2-
Benzothiazylsulfenamide, t-butyl-2-benzothiazylsulfenimide and the like are preferred.

Examples of the thiuram compound include tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetra (2-ethylhexyl) thiuram disulfide, tetrabenzylthiuram disulfide,
Tetraisobutylthiuram disulfide and the like can be mentioned, and among these, tetra (2-ethylhexyl) thiuram disulfide, tetrabenzylthiuram disulfide, tetraisobutylthiuram disulfide and the like are preferable from the viewpoint of the effect.

The reinforcing filler that can be used in the present invention is not particularly limited, but usually at least one selected from carbon black and reinforcing inorganic fillers such as silica and aluminum hydroxide is used. Among the reinforcing inorganic fillers, silica is preferred.

The compounding amount of silica or aluminum hydroxide is preferably 15 to 85 parts by weight with respect to 100 parts by weight of the rubber raw material. If carbon black is not present, the compounding amount is less than 15 parts by weight. When the amount exceeds 85 parts by weight, workability such as heating and extrusion is deteriorated, which is not preferable.

As carbon black, for example, SA
F, ISAF, HAF, FEF, GPF and the like are preferable.
The compounding amount of carbon black is preferably 20 to 150 parts by weight based on 100 parts by weight of the rubber raw material. If the amount is less than 20 parts by weight, the reinforcing effect of the carbon black is insufficient, and if it exceeds 150 parts by weight, workability is remarkably reduced, which is not preferable.

In the present invention, when silica is used as the reinforcing 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, and bis (2-triethoxysilylpropyl) tetrasulfide. 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.

Further, 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 based on silica. If the amount of the silane coupling agent is less than 1% by weight, the coupling effect is small, and if it exceeds 15% by weight, gelation is caused, which is not preferable.

In the present invention, when silica or aluminum hydroxide is used as the reinforcing filler, a tertiary amine compound is preferably used. Examples of the tertiary amine compound include trioctylamine, trilaurylamine, dimethylstearylamine, dimethyldecylamine, dimethylmyristylamine, dilaurylmonomethylamine, dimethyloctadecenylamine, and dimethylhexadecenylamine. Above all, flash point and low heat generation,
Dimethylstearylamine is preferred from the viewpoint of improving dispersion.

The amount of the tertiary amine compound is preferably 1 to 15% by weight, more preferably 3 to 10% by weight, based on silica or aluminum hydroxide.

The rubber composition of the present invention contains, in addition to the above components,
If necessary, it is possible to appropriately add compounding agents usually used in the rubber industry, such as a softener, an antioxidant, a vulcanizing agent, and a vulcanization accelerating aid.

The rubber composition of the present invention is obtained by kneading using a kneading machine such as a roll, an internal mixer, a Banbury mixer, etc., and is preferably used for a tire tread or the like after vulcanization after molding. However, it can be applied to all rubber products requiring heat resistance such as engine mounts.

[0052]

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.・ Network structure analysis of various vulcanizates The vulcanizate using no metal dithiophosphate as a control, the vulcanizate using zinc O, O-diisopropyldithiophosphate as a conventional example, and antimony O, O-diisopropyldithiophosphate (Equimolar to the above zinc dithiophosphate)
Using the vulcanized product using the above as an example of the present invention, the network structure of each vulcanized product of the control, the conventional example and the present invention was measured, and a comparative analysis was performed. Table 1 shows the results.

[0053]

[Table 1]

The formulations of the control, the conventional example and the present invention are based on Comparative Example 1, Comparative Example 4 and Example 2, respectively.
Kneading and vulcanization of these compounds were carried out in the same manner as in the examples. The measuring method of the network structure is described in Rubber Chem. T
echnol. , 62, 571 (1989).

As can be seen from Table 1, the vulcanizates of the conventional example (using zinc dithiophosphate) with respect to the control are considered to have improved heat resistance because the monosulfide network content is increased. The vulcanizate of the present invention example (using antimony dithiophosphate) has a further increased monosulfide network content and an increased disulfide network content as compared with the conventional example, so it is presumed that higher heat resistance can be obtained. You. -The measurement of the heat resistance of the vulcanizates in Examples and Comparative Examples was performed as follows.

The blowout temperature was used as an index of heat resistance. Blow-out temperature is measured by Rubber World,
214, No. 6, 24 (1996), the starting temperature was 80 ° C.
At a constant stress of 25 kgf and 25 Hz, this is the temperature at which bubbles first appeared inside the rubber. Therefore, it is evaluated that the higher the blowout temperature, the better the heat resistance.

Since the blowout temperature cannot be evaluated when the modulus changes extremely, a 200% modulus (M2
00) was measured in the range of 4 to 7 MPa. Note that M2
00 was measured according to JIS K6301 (1975). (Examples 1 to 16) (Comparative Examples 1 to 15) According to the basic compounding recipes shown in Table 2 and the individual compounding recipes shown in Tables 3 to 6, kneading was carried out using a usual Banbury mixer to prepare a rubber composition. did. This rubber composition was used in a MDR2000 manufactured by Flexis (formerly Monsanto) in the U.S.A., and had a T90 value of 1.5 to 1.5 obtained by measuring at 145 [deg.] C.
Vulcanization was performed at 145 ° C. for a time equivalent to 2.0 times.
The heat resistance of this vulcanized product was measured. Table 3 ~
6 is shown.

[0058]

[Table 2]

[0059]

[Table 3]

[0060]

[Table 4]

[0061]

[Table 5]

[0062]

[Table 6]

The following can be seen from Tables 3 to 6. The blowout temperature can be improved by increasing the modulus by increasing Nt-benzothiazolylsulfenamide, which is a conventional accelerator (Comparative Examples 1 to 3), but there is a limit. Those using zinc dithiophosphate (Comparative Examples 4 to 8) and tetra (2-ethylhexyl) thiuram disulfide together (Comparative Examples 9 to 10) have an effect of improving the blowout temperature (heat resistance) of about 5 ° C. . On the other hand, those using antimony dithiophosphate together with zinc dithiophosphate and tetra (2-ethylhexyl) thiuram cis sulfide have a further improved 5 ° C. blowout temperature (Examples 1 to 8). It turns out that it shows heat resistance. By combining antimony dithiophosphate and zinc dithiophosphate (Example 11) or tetra (2-ethylhexyl) thiuram disulfide (Examples 9 to 10), higher heat resistance can be obtained. Antimony dithiophosphate shows a certain high heat resistance with respect to the conventional accelerator even when the raw material rubber composition and the amount of carbon are changed (Examples 12 to 16, Comparative Example 1)
1 to 15).

[0064]

Since the rubber composition of the present invention has the above-described structure, it has an excellent effect of improving heat resistance.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08K 5/40 C08K 5/40 5/44 5/44 5/47 5/47 5/54 5/54 C08L 9/00 C08L 9 / 00 9/06 9/06 // (C08L 9/06 7:00 9:00)

Claims (12)

[Claims] 1. An antimony dithiophosphate represented by the following general formula (I) is added in an amount of 0.1 to 0.1 parts by weight of at least one rubber raw material selected from the group consisting of natural rubber and diene-based synthetic rubber. A rubber composition comprising from 10 to 10 parts by weight. General formula (I) (In the formula, R ¹ and R ² each independently represent an alkyl group, alkenyl group or cycloalkyl group having 19 or less carbon atoms.) 2. The antimony dithiophosphate represented by the general formula (I) according to claim 1, wherein R ¹ and R ² are each independently an alkyl group or a cycloalkyl group having 8 or less carbon atoms. The rubber composition according to claim 1, wherein 3. The antimony dithiophosphate according to claim 2, at least one selected from the group consisting of a benzothiazole derivative represented by the following general formula (II) and a thiuram compound represented by the following general formula (III): The rubber composition according to claim 2, comprising a compound of the formula (1). General formula (II) [Wherein, R ³ is a hydrogen atom, a thiobenzothiazolyl group represented by the following formula 1 or an amino group represented by the formula 2 (R ⁴ and R ⁵ each independently represent a hydrogen atom, An alkyl group or a cyclohexyl group). Here, the case where R ⁴ and R ⁵ are simultaneously a hydrogen atom is excluded. Formula 1 Formula 2 General formula (III) (Wherein, R ⁶ , R ⁷ , R ⁸ and R ⁹ each independently represent an alkyl group having 1 to 8 carbon atoms, a cyclohexyl group, a phenol group, a benzyl group, or R ⁶ and R ⁷ , and R ⁸ and R ⁹ Represents a pentamethylene group or a methylpentamethylene group of a cyclic structure linked to each other.) 4. The thiuram compound represented by the general formula (III) according to claim 3, wherein R ⁶ , R ⁷ , R ⁸ and R ⁹ are each independently a 2-ethylhexyl group or a benzyl group. The rubber composition according to claim 3, characterized in that: 5. The rubber composition according to claim 1, wherein the rubber composition contains at least one vulcanization accelerator selected from the group consisting of 2-benzothiazoylsulfenamide and 2-benzothiazoylsulfenimide. Stuff. 6. The rubber composition according to claim 1, wherein the styrene-butadiene copolymer is contained in an amount of 50 parts by weight or more based on 100 parts by weight of the rubber raw material. 7. The rubber composition according to claim 1, wherein the reinforcing filler silica or aluminum hydroxide is contained in an amount of 15 to 85 parts by weight based on 100 parts by weight of the rubber raw material. 8. The rubber composition according to claim 7, wherein the reinforcing filler is silica. 9. The rubber composition according to claim 7, wherein the tertiary amine compound is contained in an amount of 1 to 15% by weight based on the amount of the reinforcing filler. 10. The rubber composition according to claim 8, wherein the silane coupling agent is contained in an amount of 1 to 15% by weight based on the amount of silica. 11. The rubber composition according to claim 7, wherein the reinforcing filler carbon black is contained in an amount of 20 to 150 parts by weight based on 100 parts by weight of the rubber raw material. 12. The styrene-butadiene copolymer is 50 parts by weight or more per 100 parts by weight of the rubber raw material, and the reinforcing filler silica is 15 to 85 parts by weight based on 100 parts by weight of the rubber raw material, and 2-benzothiazoyl is used. Each of at least one vulcanization accelerator selected from the group consisting of sulfenamide and 2-benzothiazoylsulfenimide is contained, and a tertiary amine compound is added to the reinforcing filler in an amount of 1 to
The rubber composition according to claim 1, which is contained in an amount of from 15 to 15% by weight.