JPH11209519A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber composition for tire tread having excellent wet skid performances, rolling resistance and wear resistance. SOLUTION: This tire rubber composition for incompatible tire tread is obtained by compounding a rubber composed of 80-20 pts.wt. based on 100 pts.wt. of a rubber of an SBA (A) having -45 to -10 deg.C Tg and 20-70 pts.wt. based on 100 pts.wt. of the rubber of a modified solution polymerization SBR (B) having a Tg lower than that of the SBR (A) modified with a compound containing a group of the formula -CX-N= (X is an oxygen or a sulfur atom), benzophenone, an isocyanate compound and/or a halogenated tin compound with 80-80 pts.wt. based on 100 pts.wt. of the rubber 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 (A) and the modified SBR (B) satisfy the relation 0.0002<=χeff -χs <=0.012.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for a tire tread, and more particularly to a wet grip performance,
The present invention relates to a rubber composition for a tire tread excellent in rolling resistance and abrasion resistance.

[0002]

2. Description of the Related Art In recent years, as tires for automobiles, excellent braking performance on wet road surfaces, that is, excellent wet grip performance and wear resistance, from the viewpoint of reduction of tire rolling resistance from the viewpoint of automobile fuel efficiency and from the viewpoint of tire life, have been achieved. Excellent tires are being developed. From such a viewpoint, various proposals have been made for blending with rubbers having different glass transition temperatures (Tg) to utilize the wear resistance and low temperature embrittlement of low Tg rubber and wet skid resistance of high Tg rubber. The fact is that a device that can 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 wet grip performance, rolling resistance and abrasion resistance by solving the above-mentioned problems in the prior art. is there.

[0004]

According to the present invention, an unmodified solution-polymerized styrene-butadiene copolymer rubber (SBR) (A) having a glass transition temperature Tg of -45 ° C to -10 ° C is added to 100 parts by weight of rubber. 80-20 parts by weight and SBR
A compound having a lower Tg than (A) and having a group -CX-N = (wherein X represents an oxygen or sulfur atom), a benzophenone, an isocyanate compound and a tin halide compound; The rubber containing 20 to 70 parts by weight of the modified solution-polymerized SBR (B) modified with one type of modifier per 100 parts by weight of the rubber has a nitrogen specific surface area (N ₂ SA) of 70 to 350 m per 100 parts by weight of the rubber. ² /
g and DBP oil absorption of 105 to 200 ml / 100 g or more 30 to 80 parts by weight of carbon black and wet silica 5 to 6
0 parts by weight and the total amount of carbon black and silica is 4
0-100 parts by weight, SBR
(A) and modified SBR (B) are 0.0002 ≦ χ _eff −
The rubber composition for a tire tread relationship incompatible satisfying the chi _s ≦ 0.012 is provided.

[0005]

DETAILED DESCRIPTION OF THE INVENTION We have the group -CX-N = (X
ＯO or S), a modified solution-polymerized SBR (B) modified with a benzophenone, an isocyanate compound or a tin halide is insoluble in solution-polymerized SBR
It has been found that the above object can be achieved by blending with (A) and blending carbon / silica with it.
That is, it is known that a modified SBR obtained by modifying a styrene-butadiene copolymer rubber (SBR) with the above-mentioned suitable modifier is firmly bonded to carbon to form a firm gel. Is the glass transition temperature (Tg)
It has been found that they can be taken up more by SBR having a higher SBR, improve wet grip and abrasion resistance, and reduce rolling resistance. However, emulsion polymerization SBR
In the case where is used, the affinity for silica is lower than that of solution-polymerized SBR, and the expected effect is not exhibited. Also, SBR
The higher the vinyl content, the higher the affinity for silica and the greater the effect. Further, by blending a natural rubber with the solution-polymerized SBR, characteristics such as breaking strength and modulus can be improved. As described above, according to the present invention, as described above, the modified SBR (B) modified with an amino group, an isocyanate group, etc., and the non-modified solution-polymerized SBR having a high Tg
(A) and, if necessary, a rubber composition for a tire tread comprising natural rubber and carbon and silica, and a high Tg non-modified solution polymerized SBR (A) having a vinyl content of 2
It is preferably from 5 to 75% by weight. SBR (A) and (B) are incompatible.

Unmodified solution-polymerized SBR compounded as the first rubber component in the rubber composition for a tire tread of the present invention
(A) has a Tg of -45 ° C to -10 ° C, preferably -40 ° C.
It is a solution-polymerized styrene-butadiene copolymer rubber at a temperature of -15 ° C, and can be used alone or in any mixture. If the Tg of the SBR (A) is lower than -45 ° C, the wet grip performance becomes insufficient, which is not preferable.
If it exceeds 10 ° C., not only does the low-temperature embrittlement performance deteriorate,
It is not preferable because the hardness in the low temperature range is increased, and the wet grip performance is rather lowered.

The amount of SBR (A) compounded in the rubber composition for a tire tread of the present invention is 80 to 20 parts by weight (phr) per 100 parts by weight of the total rubber, preferably 70 to 30 ph.
r. If the amount is too large, low-temperature performance and abrasion resistance deteriorate, which is not preferable. On the contrary, if the amount is too small, the effect of improving wet grip is small, which is not preferable.

A modified solution-polymerized SBR compounded as a second rubber component in the rubber composition for a tire tread of the present invention.
(B) requires a lower Tg than SBR (A),
If the Tg is higher than the Tg of the SBR (A), the desired wet grip, abrasion resistance and rolling resistance cannot be improved, which is not preferable. The preferred Tg difference is 1
5-65 ° C.

The modification of SBR itself is known, and examples of the modifying agent include compounds having a —CX—N ＝ group (X = O or S), benzophenone, isocyanate compounds and tin halide compounds. Can be selected and used. Such a modification method is described in, for example,
JP-A-137913 and JP-A-61-42552 (-CX-N = group-modified), JP-A-59-117514
No. (benzophenone), JP-A-61-103903
And JP-A-61-103904 (tin-modified, benzophenone-modified, -CX-N = group-modified),
No. 245405 (isocyanate modification) and the like, which can be appropriately performed by those skilled in the art. Speaking of the ease of reaction (bonding) with rubber molecules,
The use of (thio) aminobenzophenones, -CX-N = containing compounds is preferred.

[0010] 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 (B) compounded in the rubber composition for a tire tread of the present invention is 20 to 70 parts by weight (phr) per 100 parts by weight of the total rubber, preferably 30 to 6 parts by weight.
0 phr. If the amount is too large, the wet grip deteriorates, which is not preferable. On the other hand, if the amount is too small, the rolling resistance and the wear resistance deteriorate.

The rubber composition for a tire tread of the present invention contains 50 as an optional rubber component per 100 parts by weight of the total rubber.
Natural rubber is added in an amount of not more than 40 parts by weight (phr), preferably 40 to 10 phr. If the amount is too large, the wet grip 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.
It is. 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 50-95 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.

[0018] As used in the present invention SBR (A) and modified SBR (B) is, as described above, the interaction parameters of the interaction parameter (chi _eff) and spinodal point of the rubber blend system of rubber between blended (chi _s ) And the difference (χ
_eff -χ _s ) needs to be in the range of 0.0002 to 0.012. Thus interaction parameter (chi _eff), i.e. Kai parameters and spinodal point interaction parameter of (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 χ _eff is described in Macromolecules, 24, 4844 (19
91) is calculated by the following equation.

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 (A) abc SBR (B) def

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 4 and Comparative Examples 1 to 4 The components (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 mold of 15 × 15 × 0.2 cm to prepare a target test piece (rubber sheet).
° C), Lambourn abrasion, 300% modulus and breaking strength. 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 0 ° C and 60 ° C at 2% and a frequency of 20Hz.
The value of the standard example was set to 100, and the value was indicated by an index. The higher the number, the higher the value of tan δ. Tan at 0 ° C
δ 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, T
Non-denatured solution polymerization SBR (g) at -45 ° C to -10 ° C
By blending a specific carbon black and wet silica with a rubber component of the modified solution-polymerized SBR (B) described above and an optional natural rubber, the wet grip and the rolling resistance are highly balanced, and the wear resistance is further improved. A rubber composition for a tire tread having excellent properties can be obtained.

Claims (3)

[Claims] 1. A glass transition temperature Tg of -45 ° C. to -10
Styrene-butadiene copolymer rubber (SBR) (A) at 80 ° C.
0 parts by weight and Tg lower than SBR (A),
A denaturing solution modified with at least one denaturing agent selected from the group consisting of a compound having XN = (wherein X represents an oxygen or sulfur atom), benzophenone, an isocyanate compound and a tin halide compound; Polymerized SBR (B)
Is 20 to 70 parts by weight per 100 parts by weight of rubber, and nitrogen specific surface area (N ₂ S
A) 70 to 350 m ² / g and DBP oil absorption of 105 to 2
30 to 80 parts by weight of carbon black of not less than 00 ml / 100 g 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, and modified with SBR (A). An incompatible rubber composition for a tire tread that satisfies the relationship of 0.0002 ≦ χ _eff −χ _s ≦ 0.012 with SBR (B). 2. The rubber further contains 5 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. 3. The rubber composition for a tire tread according to claim 1, wherein the SBR (A) has a vinyl content of 25 to 75% by weight and a styrene content of 5 to 40% by weight.