JPH07157597A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE:To obtain a rubber composition for tire tread having strong road surface gripping power, not substantially damaging wear resistance. CONSTITUTION:This rubber composition for tire tread is obtained by mixing 100 pts.wt. of a diene-based rubber with 60-200 pts.wt. of carbon black having >=100m<2>/g CTAB and >=50ml/100g 24M4DBP oil absorption and at least 5-50 pts.wt. of a low-molecular weight block polymer of A-B-A structure (A is a vinyl aromatic compound polymer block and B is a diene-based polymer block) having 2,000-50,000 weight-average molecular weight(Mw) among those of 5-50 pts.wt. of this low-molecular weight block polymer and 5-200 pts.wt. of a softener.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention provides a ta in a high temperature range (60 ° C to 100 ° C) without substantially impairing wear resistance.
Rubber composition for tire treads having improved nδ, loss compliance and SS characteristics (stress-strain characteristics) to improve road surface grip force (dry road, wet road) during high speed running, especially tread for high speed running tires The present invention relates to a rubber composition used in.

[0002]

2. Description of the Related Art Heretofore, a rubber composition containing a large amount of a softening agent such as aromatic oil has been used in order to improve the road grip. However, it is not preferable to add a large amount of the softening agent in this way, since the loss compliance is increased while the wear resistance is significantly impaired. Therefore, it has been extremely difficult to achieve both road grip and abrasion resistance.

Therefore, in recent years, many inventions have been made in order to solve such a trade-off problem by making full use of various polymerization techniques. For example, in JP-A-61-203145, a low molecular weight diene copolymer is disclosed, and in JP-A-64-14258, a low molecular weight high-styrene emulsion-polymerized styrene-butadiene copolymer rubber (E
-SBR) is blended with another polymer to solve the above antinomy problem. In addition, JP-A-63
No. 101440, JP-A-63-33436, JP-A-64-16845, JP-A-1-197541, JP-A-3-28244 and the like, the use of low molecular weight polymers as a softening agent Trying to solve the antinomy problem. However, the present situation is that neither the road surface gripping force nor the wear resistance is satisfactorily improved.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to overcome the above-mentioned drawbacks of the prior art, has a large road surface gripping force, and does not substantially impair wear resistance. An object of the present invention is to provide a rubber composition for a tire tread, particularly a tread rubber composition for a high performance tire used for high speed running.

[0005]

According to the present invention, CTAB is 100 m ² / g or more and 24 parts by weight per 100 parts by weight of diene rubber.
Carbon black with M4DBP oil absorption of 50ml / 100g or more
60 to 200 parts by weight are compounded, and the weight average molecular weight (M
w) 5 to 50 parts by weight of a low molecular weight block polymer having an ABA structure of 2,000 to 50,000 (wherein A represents a vinyl aromatic polymer block and B represents a diene polymer block). Further, there is provided a rubber composition for a tire tread containing at least 5 to 50 parts by weight of the low molecular weight block polymer among 5 to 200 parts by weight of a softening agent.

As described above, in the present invention, by blending at least the low molecular weight block polymer among the low molecular weight block polymer and the softening agent, the high temperature region (60 ° C. to 60 ° C.) can be obtained without substantially impairing wear resistance. (100 ℃)
It is possible to improve tan δ, loss compliance, and S-S characteristics at, and thereby improve the road surface gripping force during high-speed running.

The structure of the present invention will be described in detail below. (1) Diene rubber. Various diene rubbers are used. Examples thereof include natural rubber, butadiene rubber, emulsion-polymerized styrene-butadiene copolymer rubber having a high styrene content, solution-polymerized styrene-butadiene copolymer rubber having a high styrene content, acrylonitrile-butadiene copolymer rubber, and chloroprene rubber.

(2) Carbon black. CTAB is 100 m ² / g or more, preferably 130 to 300 m ² / g, 24
M4DBP oil absorption is 50ml / 100g or more, preferably 90 ~
It is 130 ml / 100 g. If CTAB is less than 100 m ² / g, improvement in wear resistance and grip strength cannot be expected as compared with the use of ordinary carbon black. The 24M4DBP oil absorption is a particularly important characteristic for carbon black. By increasing the 24M4DBP oil absorption, it is possible to improve the dispersibility of carbon black with a very small particle size, and at the same time, increase tensile strength and wear resistance. You can improve your sex. When the 24M4DBP oil absorption is less than 50 ml / 100 g, not only the dispersibility deteriorates, but also the wear resistance decreases.

(3) Softener. What is usually used for compounding the rubber may be used, for example, aromatic oil (aromatic oil), secondary transition point (T
g) is -40 ° C or less paraffinic oil, naphthenic oil, or various plasticizers. (4) AB with a weight average molecular weight (Mw) of 2,000 to 50,000
-A low molecular weight block polymer having an A structure. The weight average molecular weight is a standard polystyrene conversion value measured by GPC.

Here, the block polymer (block copolymer) is obtained by using a vinyl aromatic compound which is a monomer and a diene compound which is a monomer, for example, by using an anionic polymerization catalyst.
-BA A polymer having a block structure. A is a polymer block of a vinyl aromatic compound.
Further, B is a diene polymer block, which is a block of a homopolymer of a conjugated diene or a copolymer of a conjugated diene and a vinyl aromatic compound. For example, B is SB
R (styrene-butadiene copolymer rubber), BR (butadiene rubber), IR (isoprene rubber), SIR (styrene-isoprene copolymer rubber), BIR (butadiene-isoprene copolymer rubber), binary block SBR ( It is composed of two kinds of SBR having different amounts of bound styrene and vinyl)). These exemplary (co)
Polymer vinyl (1,2) bond content or 1,2 bond and 3,4
The total amount of bonds is usually 10-70%, the amount of bound styrene is 5-
50%.

The vinyl aromatic compound is, for example, styrene, p-methylstyrene, m-methylstyrene, p-te.
These are rt-butyl styrene, α-methyl styrene, chloromethyl styrene and vinyltoluene. Styrene, p-methylstyrene and α-methylstyrene are preferred. The diene compound is, for example, butadiene, isoprene, pentadiene or 2,3-dimethylbutadiene. butadiene,
Isoprene is preferred.

In order to produce the block polymer of the vinyl aromatic compound and the diene compound, for example, a method of sequentially adding the monomers, that is, the A (styrene) component is polymerized, and then the B component monomer is added to complete the polymerization. Further, the block polymer may be obtained by adding the component A and polymerizing again, or by the coupling method, that is, the initial A
After the components have been polymerized, half of the predetermined amount of the component B may be added and polymerized, and then coupled with a commonly used coupling agent to obtain an ABA type block polymer. The coupling agent used here is
Specifically, for example, phenyl acetate, ethyl benzoate,
Dichlorosilane, dimethyldichlorosilane, dibutyldibromotin, methyltrichlorosilane, methyltribromosilane, phenyltrichlorosilane, tetrachlorosilane, tetramethoxysilane, tin tetrachloride, (dichloromethyl) trichlorosilane, (dichlorophenyl) trichlorosilane, Hexachlorodisilane, etc. can be mentioned.

This block polymer has a ratio of 2A: B.
(Polymerization ratio) is 10 to 70:90 to 30, and 2A + B = 100. If the ratio of A is less than 10, there are few components that melt at 100 ° C or more, and the required road surface gripping force cannot be obtained. Also, if it exceeds 70, it becomes too hard, which is not preferable. This block polymer has a weight average molecular weight (Mw) of 2,000 to 50,000. When it is less than 2,000, the road surface gripping effect is greatly improved, but the breaking strength is greatly reduced, and it is not suitable for use in tires. If it exceeds 50,000, the molecular weight becomes too large and tan δ at 60 to 100 ℃
And loss compliance becomes difficult to increase.

When this block polymer is a block polymer produced by the sequential addition method, so-called chemical modification may be carried out at the molecular chain end by reacting with a specific compound. As this specific compound, a reaction substance having an atomic group represented by the following formula, N-substituted-
Amino ketones, N-substituted-amino thioketones, N-
Substituted-amino aldehydes and N-substituted-amino thioaldehydes are preferred.

[0015] In the above formula, M is oxygen or sulfur.

As the compound having the atomic group of the above formula,
For example, N-methyl-β-propiolactam, Nt-
Butyl-β-propiolactam, N-methoxyphenyl-β-propiolactam, N-phenyl-β-propiolactam, N-naphthyl-β-propiolactam, N-
Methyl-2-pyrrolidone, Nt-butyl-2-pyrrolidone, N-phenyl-2-pyrrolidone, N-methoxyphenyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-benzyl-2-pyrrolidone, N -Naphthyl-2
-Pyrrolidone, N-methyl-5-methyl-2-pyrrolidone, Nt-butyl-5-methyl-2-pyrrolidone, N
-Phenyl-5-methyl-2-pyrrolidone, N-methyl-3,3-dimethyl-2-pyrrolidone, Nt-butyl-3,3-dimethyl-2-pyrrolidone, N-phenyl-
3,3-dimethyl-2-pyrrolidone, N-methyl-2-
Piperidone, Nt-butyl-2-piperidone, N-phenyl-2-piperidone, N-methoxyphenyl-2-
Piperidone, N-vinyl-2-piperidone, N-benzyl-2-piperidone, N-naphthyl-2-piperidone,
N-methyl-3,3-dimethyl-2-piperidone, N-
t-butyl-3,3-dimethyl-2-piperidone, N-
Methyl-ε-caprolactam, N-phenyl-ε-caprolactam, N-methoxyphenyl-ε-caprolactam, N-vinyl-ε-caprolactam, N-benzyl-
ε-caprolactam, N-naphthyl-ε-caprolactam, N-methyl-ω-laurylolactam, N-phenyl-ω-laurylolactam, Nt-butyl-ω-laurylolactam, N-vinyl-ω- Laurilolactam, N-
N-Substituted-lactams such as benzyl-ω-laurylolactam and their corresponding thiolactams; 1,3-dimethylethyleneurea, 1,3-diphenylethyleneurea, 1,3-di-t-butylethyleneurea , N-substituted-ethylene ureas such as 1,3-divinylethylene urea and the corresponding N-substituted-thioethylene ureas.
Examples of N-substituted-amino (thio) ketones include 4-dimethylaminobenzophenone, 4-diethylaminobenzophenone, 4-di-t-butylaminobenzophenone,
4-diphenylaminobenzophenone, 4,4'-bis
(Dimethylamino) benzophenone, 4,4'-bis (diethylamino) benzophenone, 4,4'-bis (di-t
-Butylamino) benzophenone, 4,4'-bis (diphenylamino) benzophenone, 4,4'-bis (divinylamino) benzophenone, 4-dimethylaminoacetophenone, 1,3-bis (diphenylamino) -2-propanone, 1,7-bis (methylethylamino) -4-
Heptanone and the like and their corresponding thioketones. Examples of N-substituted amino (thio) aldehydes include 3-dimethylaminopropionaldehyde, 3-diethylaminopropionaldehyde, 4-dimethylaminobenzaldehyde, 3-dicyclohexylaminopropionaldehyde, 3,5-bis (dicyclohexylamino) benzaldehyde, and -Diphenylaminobenzaldehyde, 4-divinylaminobenzaldehyde and the like can be mentioned.

(5) In the present invention, the diene rubber 100
60 to 200 parts by weight of the carbon black is blended with respect to parts by weight, and 5 to 50 parts of the low molecular weight block polymer is added.
At least 5 to 50 parts by weight of the low molecular weight block polymer is blended out of 5 parts by weight and 5 to 200 parts by weight of a softening agent. If the blending amount of this low molecular weight block polymer is less than 5 parts by weight, the abrasion resistance will be impaired. On the other hand, if it exceeds 50 parts by weight, the tan δ of the rubber composition will be small and the viscosity will decrease, and the loss compliance will also decrease. Becomes smaller and becomes difficult to be deformed, so the road grip force will decrease. It is preferably 10 to 40 parts by weight. Further, the rubber composition for a tire tread of the present invention can be appropriately compounded with a compounding agent such as sulfur and an antioxidant, if necessary.

[0018]

[Examples] Rubber compositions having the compounding contents (parts by weight) shown in Table 1
(No.1 to No.7) were produced. In this case, CTAB is 137m
95 parts by weight of carbon black each having an oil absorption of 98 ml / 100 g of ² / g and 24M4DBP was used. Then, after vulcanizing these rubber compositions, their tensile properties (100% modulus, 300% modulus, tensile strength (kgf / cm ² ), elongation
(%)), Viscoelasticity (hysteresis loss (tan δ), loss compliance (E "/ (E ^* ) ² )), Lupke impact resilience, and pico-wear were evaluated by the following (E": loss elastic modulus, E ^*). : Complex elastic modulus). The results are shown in Table 1. The relationship between loss compliance (100 ° C.) and pico-wear for these rubber compositions is shown in FIG. 1, and the relationship between loss compliance (100 ° C.) and 300% modulus is shown in FIG. 2, respectively. Evaluation method for 100% modulus and 300% modulus : JIS K
Tensile strength when the test piece is stretched 100% according to 6301
(kgf / cm ² ) was defined as 100% modulus, and tensile strength (kgf / cm ² ) when stretched 300% was defined as 300% modulus. Evaluation method of tensile strength (kgf / cm ² ) : Based on JIS K 6301. Elongation (%) evaluation method : Based on JIS K 6301. tan δ, loss compliance (E "/ (E ^* ) ² ) Evaluation method
Method : Measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho under the conditions of strain 10 ± 2%, frequency 20Hz, and ambient temperature 100 ° C. The measurement results are displayed as an index. Evaluation method for Lupke impact resilience : JIS K 63 at a temperature of 100 ° C
Measured according to 01. The measurement result is an index
display. Pico wear evaluation method : ASTM D22 using Pico wear tester
Measured according to 28. Index display.

The larger the value of tan δ and the loss compliance, and the smaller the value of impact resilience, the better the road surface gripping force. Also, the larger the pico-wear (wear resistance), the better.

[0020] Note) * 1 Solution-polymerized SBR, total styrene content 45% by weight, total vinyl content 55% by weight. * 2 Total styrene content 45% by weight, total vinyl content 59% by weight, weight average molecular weight 26,000.

* 3 Weight average molecular weight (Mw) of 25,000
A low molecular weight block polymer having a (styrene block)-(SBR)-(styrene block) structure. 67% by weight of total styrene, 59% by weight of total vinyl, 20% of each styrene block. In Table 1, No. 1 and No. 2 are rubber compositions in which 50 parts by weight and 60 parts by weight of a softening agent are mixed with 100 parts by weight of diene rubber (conventional example). No. 3 is a rubber composition in which 10 parts by weight of the 60 parts by weight of the softening agent in No. 2 are replaced with liquid SBR (comparative example). No.4 is No.2
A rubber composition obtained by replacing 10 parts by weight of the 60 parts by weight of the softening agent in 1. with a liquid block polymer (Example of the present invention).

No. 5 is a rubber composition prepared by mixing 70 parts by weight of a softening agent with 100 parts by weight of a diene rubber.
(Conventional example). No. 6 is a rubber composition obtained by replacing 20 parts by weight of 70 parts by weight of the softening agent in No. 5 with liquid SBR (comparative example). No. 7 is a rubber composition obtained by replacing 20 parts by weight of 70 parts by weight of the softening agent in No. 5 with a liquid block polymer (Example of the present invention).

No. 8 is a rubber composition prepared by mixing 90 parts by weight of a softening agent with 100 parts by weight of diene rubber.
(Conventional example). No. 9 is a rubber composition obtained by replacing 40 parts by weight of 90 parts by weight of the softening agent in No. 8 with a liquid block polymer (Example of the present invention). As is clear from Table 1, No. 4 (example of the present invention) is No. 1 and No. 2 (conventional example),
Compared to No. 3 (Comparative Example), tan δ is larger and the Lupke impact resilience is smaller. No. 7 (Example of the present invention) is also No. 9 (Comparative example) and No. 9 (Comparative example).
Compared with No. 8 (Comparative Example), (Invention Example) has a larger tan δ and a smaller Ryukke impact resilience. From this, it is understood that the rubber compositions of the present invention (No. 4, No. 7, No. 9) have excellent road surface gripping power.

Further, as can be seen from FIGS. 1 and 2, N
o.4, No.7, and No.9 are No.1, No.2, No.5, No.8,
Compared to No.3 and No.6, pico wear and 300 due to increased loss compliance (improved road grip)
The% modulus decreases slowly (the decrease rate is small). Therefore, the rubber composition of the present invention (No. 4, No. 7, N
o.9) has excellent wear resistance.

[0025]

As described above, according to the present invention, the predetermined amount of the softening agent is replaced with the specific low molecular weight block polymer, so that the road surface gripping power is improved without substantially impairing the wear resistance. It becomes possible.

[Brief description of drawings]

[Fig.1] Loss compliance of rubber composition (100 ℃)
FIG. 3 is a relational diagram between Pico wear and.

[Fig.2] Loss compliance of rubber composition (100 ℃)
It is a relationship diagram between and 300% modulus.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuyoshi Kayama 2-1, Oiwake, Hiratsuka-shi, Kanagawa Yokohama Rubber Co., Ltd. Hiratsuka Factory (72) Inventor, Kazuyuki Umeda 2-1, Oiwake, Hiratsuka-shi, Kanagawa Yokohama Rubber Co., Ltd. Ceremony company Hiratsuka Plant (72) Inventor Fumitoshi Suzuki 2-15-33 Isogo Isogo-ku, Yokohama-shi, Kanagawa Nihon Zeon Isogo Dormitory (72) Inventor Shuichi Akita 553-1 Shinanomachi, Totsuka-ku, Yokohama-shi Kanagawa Prefecture Park Hills N −204

Claims (1)

[Claims] 1. CTA for 100 parts by weight of diene rubber
B is 100 m ² / g or more and 24M4DBP oil absorption is 50 ml / 100 g or more 60 to 200 parts by weight of carbon black is blended, and the weight average molecular weight (Mw) is 2,000 to 50,000 AB-
5 to 50 parts by weight of a low molecular weight block polymer having an A structure (wherein A represents a polymer block of a vinyl aromatic compound and B represents a diene polymer block) and a softening agent 5 to 5 parts by weight.
A rubber composition for a tire tread, in which at least 5 to 50 parts by weight of the low molecular weight block polymer is blended in 200 parts by weight.