JPH11209517A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber composition for tire tread having excellent rolling resistance and wear resistance. SOLUTION: This tire rubber composition for incompatible tire tread is obtained by compounding 100 pts.wt. of a rubber comprising 50-90 pts.wt. of an SBR modified with a modifying agent such as a compound containing a group of the formula -CX-N= (X is oxygen or sulfur), benzophenone, thiobenzophenone, an isocyanate compound and/or a halogenated tin compound and 40-10 pts.wt. of a cis-BR 40 having >=90% cis-content with 30-80 pts.wt. of carbon having 70-350 m<2> /g nitrogen specific surface area and >=105-200 ml/100 g DBP oil absorption and 5-60 pts.wt. of wet silica so as to make 40-100 pts.wt. of the total of the carbon and the silica. The SBR and the cis-BR satisfy the relation 0.0002<=χeff -χs <=0.012.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rubber composition for a tire tread, and more particularly to a rubber composition for a tire tread having very low rolling resistance and excellent abrasion resistance.

[0002]

2. Description of the Related Art In recent years, development of tires for automobiles has been promoted in which the rolling resistance of the tires is reduced from the viewpoint of fuel economy of the automobile and the wear resistance is excellent from the viewpoint of tire life. From such a point of view, various formulations have been proposed, but the fact is that a material which can sufficiently withstand practical use has not yet been developed. In addition, a rubber composition for a tire tread having a rubber polymer modified with an appropriate functional group and having the above properties has also been proposed, but in recent years, a tire having a lower rolling resistance has been required, and such a tire has been required. Not enough for the needs.

[0003]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a rubber composition for a tire tread excellent in rolling resistance and abrasion resistance by solving the above-mentioned problems of the prior art.

[0004]

According to the present invention, a group represented by the formula -C
X-N = (wherein X represents an oxygen or sulfur atom), modified with at least one modifier selected from the group consisting of benzophenone, thiobenzophenone, isocyanate compounds and tin halide compounds. Modified solution polymerized styrene butadiene copolymer rubber (SBR),
With respect to 100 parts by weight of rubber containing 50 to 90 parts by weight and 40 to 10 parts by weight of cis-polybutadiene (cis-BR) having a cis content of 90% or more, the nitrogen specific surface area (N ₂ S)
A) 70 to 350 m ² / g and DBP oil absorption of 105 to 2
SBR and cis-BR are prepared by blending 30 to 80 parts by weight of carbon black of at least 00 ml / 100 g and 5 to 60 parts by weight of wet silica so that the total amount of carbon black and silica is 40 to 100 parts by weight. Is 0.0002
Provided is an incompatible rubber composition for a tire tread that satisfies a relationship of ≦ χ _eff −χ _s ≦ 0.012.

[0005]

DETAILED DESCRIPTION OF THE INVENTION We have the group -CX-N = (X
ＯO or S), a benzophenone, a thiobenzophenone, an isocyanate compound or a modified solution-polymerized SBR modified with a tin halide,
It has been found that the above object can be achieved by blending with is-BR and blending carbon / silica with it. That is, a styrene-butadiene copolymer rubber (SB
R) is obtained by modifying the above R) with a suitable modifying agent described above.
It is known that BR is firmly bonded to carbon to form a firm gel, and the rolling resistance is reduced. However, there is a drawback that the elongation at break is reduced and abrasion resistance is deteriorated. It was not enough to satisfy the high demands of wear. The wear resistance was improved by blending BR. Due to the incompatibility, the grip performance required for the tire could be secured. The rolling resistance was also at a satisfactory level due to the silica compounding. However, when the emulsion-polymerized SBR is used, the expected effect is not exhibited in consideration of the affinity for silica as compared with the solution-polymerized SBR. Also, SBR
The higher the vinyl content, the higher the affinity for silica and the greater the effect. The properties such as breaking strength and modulus can be improved by further blending natural rubber with modified SBR and cis-BR. As described above, according to the present invention, a rubber composition for a tire tread containing a modified SBR, cis-BR and, if necessary, a natural rubber, and carbon and silica modified with an amino group, an isocyanate group, and the like as described above. Provided. Here, the modified SBR
And cis-BR are incompatible.

The solution-polymerized SBR compounded as the first rubber component in the rubber composition for a tire tread of the present invention is a styrene-butadiene copolymer rubber solution-polymerized by a general method, and may be used alone or in any mixture. Can be used.

The modification of SBR is known per se, and examples of the modifying agent include compounds having a -CX-N = group (where X = O or S), benzophenone, thiobenzophenone, isocyanate compounds and tin halide compounds. It can be appropriately selected and used from among others. Such modification methods are described in, for example, JP-A-60-137913 and JP-A-61-42552 (-CX-N = group modification), JP-A-59-117514 (benzophenone), and JP-A-61-117514. -103903 and 61-103904
Publication (Tin-modified, benzophenone-modified, -CX-N =
Group modification) and JP-A-63-245405 (isocyanate modification) and the like, which can be appropriately performed by those skilled in the art. In terms of the ease of reaction (bonding) with rubber molecules, (thio) aminobenzophenones,-
The use of CX-N = containing compounds is preferred.

[0008] The position of the SBR modified by the modifying agent may be at any of the molecular terminal, the main chain and the side chain, and the amount of modification is not particularly limited, but a compound containing a Sn atom or an amino group may be used. It is preferable that the SBR is 0.1 to 100 moles bonded per mole of the molecular chain.

The amount of the modified SBR to be compounded in the rubber composition for a tire tread of the present invention is 50 to 90 parts by weight (phr) per 100 parts by weight of the total rubber, preferably 50 to 80 phr.
It is. If the amount is too large, the abrasion resistance deteriorates, which is not preferable. On the other hand, if the amount is too small, the grip force on wet and dry road surfaces decreases, which is not preferable.

The cis-BR compounded as the second component in the rubber composition for a tire tread of the present invention is a general cis-BR,
Any BR polymerized by a solution polymerization method can be used, but only has a cis content of 90% or more, preferably 95 to
Must be 100%. It has a cis content of 90%
If the amount is less than the above, the effect of improving the abrasion resistance is insufficient, which is not preferable.

The amount of cis-BR compounded in the rubber composition for a tire tread of the present invention is 40 to 10 parts by weight (phr), preferably 40 to 20 phr, per 100 parts by weight of the total rubber.
It is. If the amount is too large, it is not preferable because the reduction in grip force is large, and if it is too small, the effect of improving the abrasion resistance is insufficient.

The rubber composition for a tire tread of the present invention contains 40 parts per 100 parts by weight of the total rubber as an optional rubber component.
Natural rubber is added in an amount of not more than 10 parts by weight (phr), preferably 10 to 30 phr. If the amount is too large, the gripping force is undesirably reduced. In addition, by blending natural rubber with the rubber composition for a tire tread of the present invention, strength such as breaking strength and modulus can be improved.

The rubber composition for a tire tread of the present invention contains carbon black and silica as reinforcing agents.
The carbon black used in the present invention has a nitrogen specific surface area (N ₂ SA) of 70 to 350 m ² / g, preferably 85 to ²⁰⁰ m ² / g, and a DBP oil absorption of 105 to 2.
The amount of carbon black is 30 to 80 parts by weight (phr) per 100 parts by weight of rubber, preferably 30 to 70 phr. As long as the above requirements are satisfied, the carbon black may be any carbon black that has been generally compounded in a rubber composition for a tire.

If the amount of carbon black is too small, the abrasion resistance deteriorates, which is not preferable. On the contrary, if the amount is too large, the rolling resistance increases, which is not preferable. On the other hand, if the N ₂ SA of the carbon black is too small, the abrasion resistance deteriorates, which is not preferable. On the contrary, if the N ₂ SA is too large, the mixing processability deteriorates, which is not preferable. Further, if the DBP oil absorption of the carbon black is too small, the abrasion resistance becomes insufficient, which is not preferable. Conversely, if the DBP oil absorption is too large, the mixing processability deteriorates, which is not preferable.

The carbon black N ₂ SA and D
The method for measuring the BP oil absorption is as follows. 1) Nitrogen adsorption specific surface area (N ₂ SA) (m ² / g): AS
Measured according to TM D 3037 (30733) Method C. 2) DBP (dibutyl phthalate) oil absorption (ml / 100
g): Measured in accordance with JIS K6221 "Test method for carbon black for rubber", 6.1.2 (1) Method A.

The rubber composition for a tire tread of the present invention further contains 5 to 60 parts by weight, preferably 10 to 50 parts by weight of wet silica. As such silica, any wet silica that has conventionally been generally compounded in rubber compositions for tires can be used. If the amount of the wet silica is too small, the rolling resistance deteriorates, which is not preferable. On the other hand, if the amount is too large, the mixing processability deteriorates, which is not preferable.

The amount of carbon black and silica compounded in the rubber composition for a tire tread of the present invention is such that the total amount of silica and carbon black is 40 to 100 parts by weight per 100 parts by weight of rubber ( phr), preferably 50-90 phr. If the total amount of the carbon black and silica compounding reinforcing agents is too small, the abrasion resistance becomes insufficient, which is not preferable. On the contrary, if the total amount is too large, the mixing processability deteriorates, which is not preferable.

The modified SBR and ci used in the present invention
As described above, the s-BR is the difference (χ _eff −) between the interaction parameter (χ _eff ) between the compounded rubbers and the interaction parameter (χ _s ) of the spinodal point of the rubber blend system.
χ _s ) needs to be in the range of 0.0002 to 0.012. Thus interaction parameter (χ _{ef f),} i.e. the interaction parameter chi parameter and spinodal point (chi _s) the difference between (χ _eff -χ _s)
By setting the value in a specific range, the compounded rubbers can be made incompatible with each other, and the wet grip, abrasion resistance and low-temperature embrittlement can be highly balanced. Where _{eff eff} is Macromolecules, 24, 4844 (199
It is calculated by the following equation shown in 1).

The χ _eff = χ ₁ -χ ₂ ············ Further, chi _s is calculated by the formula of thermodynamics below. _{2χ s = 1 / N 1 φ} 1 + 1 / N 2 φ 2 ····· N 1: 1 component of the polymerization degree, N _2: 2 component of the polymerization degree, phi _1:
1 component mole fraction phi _2: 2 component molar fraction chi _eff of <chi _s: compatible, χ _eff> χ _s: incompatible _{χ 1 = aeχ SV + afχ SB} + bdχ SV + bfχ VB + cd χ SB + ceχ VB χ _{2 = abχ SV + acχ SB +} bcχ VB + deχ SV + df χ SB + efχ VB χ SV = 56.5 × 10 -3 + 5.62 / T χ SB = 8.43 × 10 -3 + 10.2 / T χ VB = 2. 69 × 10 ⁻³ + 1.87 / T

Styrene content Vinyl content Butadiene content SBR abc cis-BR d = 0 ef

Χ _SV : interaction parameter between styrene unit and 1,2-bonded butadiene unit パ_ラメ_ータ_SB : interaction parameter between styrene unit and 1,4-bonded butadiene unit χ _VB : 1,2-bonded butadiene unit and 1, Interaction parameter of 4-bonded butadiene unit χ _eff : Interaction parameter between polymers χ ₁ : Interaction parameter between polymer molecules χ ₂ : Interaction parameter within polymer molecule χ _s : Interaction of spinodal point of polymer blend system Parameters

The rubber composition for a tire tread according to the present invention further comprises sulfur, a vulcanization accelerator, an antioxidant, a filler,
Various additives generally compounded in a rubber composition for a tire tread, such as a softener and a plasticizer, can be compounded. The rubber composition of the present invention can be vulcanized by a general method to obtain a tire tread.

[0023]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but it goes without saying that the technical scope of the present invention is not limited to these Examples.

Standard Examples, Examples 1 to 3 and Comparative Examples 1 to 5 The components (in parts by weight) shown in Table I were compounded as follows to produce rubber compositions.

[0025]

[Table 1]

The physical properties of the polymer of Table I are as shown in Table II.

[0027]

[Table 2]

Other components except for sulfur and the vulcanization accelerator were:
Knead with an 8 liter closed mixer for 3-5 minutes.
The masterbatch released when the temperature reached 5 ± 5 ° C. was kneaded with a vulcanization accelerator and sulfur with an 8-inch open roll to obtain a rubber composition. This composition was press-vulcanized at 160 ° C. for 20 minutes in a 15 × 15 × 0.2 cm mold to prepare a target test piece (rubber sheet), tan δ (60 ° C.), Lambourn abrasion, 300% The modulus and breaking strength were measured. The results are shown in Table III.

[0029]

[Table 3]

The test methods for evaluating physical properties are as follows. 1) Measurement of tan δ: Initial strain 10%, dynamic strain ± using a viscoelastic spectrometer (manufactured by Toyo Seiki Co., Ltd.)
Measured at a temperature of 60 ° C with 2% frequency and 20Hz. The value of the standard example was set to 100, and the value was indicated by an index. The higher the number, the more t
It shows that the value of anδ is large. Tan δ at 0 ° C. correlates with the wet grip of the tire, and a larger value indicates a higher wet grip force. 60 ° C. correlates with the rolling resistance of the tire, and a smaller value indicates a smaller rolling resistance. 2) Lambourn abrasion: measured according to JIS K6301. The index was indicated by an index with the value of the standard example being 100. The larger the value, the better the wear resistance. 3) 300% modulus: 50% in a constant temperature room at 23 ° C. with a JIS No. 3 dumbbell according to JIS K6300.
Tested at a pull rate of 0 mm / min. The index was indicated by an index with the value of the standard example being 100. The higher the value, the higher the modulus. 4) Breaking strength: JIS3 according to JIS K6300
No. dumbbell was used for testing at a constant temperature of 23 ° C. at a tensile speed of 500 mm / min. An index with the standard example as 100. The larger the value, the higher the breaking strength.

[0031]

As described above, according to the present invention, specific carbon black and silica are blended in a rubber component of a specific modified solution-polymerized SBR, a specific cis-BR, and an optional natural rubber. As a result, a rubber composition for a tire tread having extremely low rolling resistance and excellent abrasion resistance can be obtained.

Claims (2)

[Claims] At least one selected from the group consisting of compounds having a group -CX-N = (wherein X represents an oxygen or sulfur atom), benzophenone, thiobenzophenone, isocyanate compounds and tin halide compounds. Solution-modified styrene-butadiene copolymer rubber (SBR) modified with various kinds of modifiers in an amount of 50 to 90 parts by weight and a cis content of 9
0% or more of cis-polybutadiene (cis-BR) 40 to
For 100 parts by weight of rubber containing 10 parts by weight, nitrogen specific surface area (N ₂ SA) 70 to 350 m ² / g and DBP
An oil-absorbing amount of 30 to 80 parts by weight of carbon black having an oil absorption of 105 to 200 ml / 100 g or more and 5 to 60 parts by weight of wet silica are blended so that the total amount of carbon black and silica is 40 to 100 parts by weight. cis-BR
Are incompatible with each other, satisfying the following relationship: 0.0002 ≦ χ _eff −χ _s ≦ 0.012. 2. The rubber further contains 4 parts by weight of rubber per 100 parts by weight.
The rubber composition for a tire tread according to claim 1, which contains 0 parts by weight or less of a natural rubber.