JPH107844A - Pneumatic tire - Google Patents

Abstract

(57) [Problem] To provide a pneumatic tire with improved wear resistance and chipping resistance. The pneumatic tire comprises: (a) 50 to 90 parts by weight of natural rubber and / or polyisoprene rubber;
8-40 parts by weight of a styrene-butadiene copolymer rubber or polybutadiene rubber having a glass transition temperature of -75 ° C. or less, and (c) a block (A) of polyisoprene having a cis content of 70% by weight or more and a styrene content of less than 20% by weight. 1,2-
An AB (or B ') type block copolymer comprising a block (B) of poly (styrene-butadiene) or a block (B') of polybutadiene having a vinyl bond content of less than 50% comprises 0.5 to 20 parts by weight. Carbon black having a CTAB surface area of more than 125 ml / g and a C-DBP oil absorption of 100 to 150 ml / 100 g per 100 parts by weight of rubber
The tread is constituted by a rubber composition mixed with 55 parts by weight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having improved wear resistance and chipping resistance.

[0002]

2. Description of the Related Art Conventionally, treads of pneumatic tires include:
A plurality of polymers are blended and used to improve various performances. In particular, when it is intended to enhance abrasion resistance and low heat generation, natural rubber (NR) or polyisoprene rubber (I
R) is often blended with a low glass transition temperature (low Tg) styrene-butadiene copolymer rubber (SBR) or polybutadiene rubber (BR). But,
In such a blend system, although the abrasion resistance and the low heat generation property are improved, there is a disadvantage that the breaking strength and the breaking energy are low, so that the chipping resistance is inferior.

[0003] The reason why the breaking strength and the breaking energy are low in the polymer blend system is that the polymers do not mix well with each other (incompatible). Because of the incompatibility, a phase separation interface exists in the blend system, and the interface serves as a starting point of fracture, resulting in a decrease in fracture energy. Further, since sea islands are present in the blend system due to incompatibility, carbon black added in the blend system for reinforcement occurs, so that the breaking strength is reduced.

To solve this problem, it has been proposed to incorporate carbon black having a small particle size and a low structure into a blend system. However, even in this case, it is not sufficient to secure abrasion resistance.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a tread rubber having a fine phase structure by adding a specific block polymer to a blend system of incompatible polymers to thereby provide abrasion resistance and chipping resistance. And to provide a pneumatic tire with improved performance.

[0006]

The pneumatic tire of the present invention comprises (a) natural rubber and / or polyisoprene rubber 50;
(B) 8 to 40 parts by weight of a styrene-butadiene copolymer rubber or polybutadiene rubber having a glass transition temperature of -75 ° C. or less, and (c) a block of polyisoprene having a cis content of 70% by weight or more (A) AB (or B ') type block comprising a poly (styrene-butadiene) block (B) or a polybutadiene block (B') having a styrene content of less than 20% by weight and a 1,2-vinyl bond content of less than 50% The CTAB surface area is 125 m ^{2 with} respect to 100 parts by weight of a rubber consisting of 0.5 to 20 parts by weight of a copolymer.
The tread is characterized by comprising a rubber composition containing 35 to 55 parts by weight of carbon black having a C-DBP oil absorption of more than 100 / g and a C-DBP oil absorption of 100 to 150 ml / 100 g.

[0007] A specific AB (or B ') type block copolymer compatible with (a) NR and / or IR and (b) SBR or BR which are incompatible with each other is blended. In addition, a specific fine carbon black is blended to form a rubber composition. In this rubber composition, the phase structure of these rubber components is refined (ideally compatibilized in an ideal case) to obtain a uniform rubber. A phase is formed, and carbon black is uniformly dispersed in the phase, so that the rubber composition constitutes a tread of a tire,
The breaking strength and the breaking energy can be increased, and the wear resistance and chipping resistance can be improved.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The NR, IR, SBR having a glass transition temperature (Tg) of -75 ° C. or less, and BR having a glass transition temperature (Tg) of -75 ° C. or less may be general commercial products. . Here, the reason why the Tg is set to −75 ° C. or less is that if it exceeds −75 ° C., the abrasion resistance and the heat build-up are undesirably reduced.

The AB (or B ') type block copolymer is a block copolymer comprising the following block (A) and block (B) or block (B'). Block (A ): IR block having a cis content of 70% by weight or more. If the cis content is less than 70% by weight, the compatibility with NR or IR becomes poor, and the desired refinement of the phase structure cannot be obtained.

Blocks (B) and (B ' ): Blocks of poly (styrene-butadiene) or polybutadiene having a styrene content of less than 20% by weight and a 1,2-vinyl bond content of less than 50%. When the styrene content is 20% by weight or more, Tg is -7.
The desired effect cannot be obtained because it becomes incompatible with SBR or BR at 5 ° C. or lower. In addition, 1,2-vinyl bond content 50%
Even above, the Tg becomes incompatible with SBR or BR having a temperature of -75 ° C. or lower, so that the expected effect cannot be obtained, which is not preferable.

The ratio (weight ratio) of A / B (or B ') in the AB (or B') type block copolymer is 2
It is good to be 0-80 / 80-20. Outside this range, entanglement with the matrix rubber (NR, IR, SBR at Tg-75 ° C. or less, BR at Tg-75 ° C. or less) decreases, and the contribution to the compatibilization of the matrix rubber becomes insufficient. The AB (or B ') type block copolymer preferably has a molecular weight of 30,000 or more.
It is preferably from 000 to 800,000. 30,000
If it is less than 10, it is not preferable because entanglement with the matrix is small and co-crosslinking property is reduced.

The AB (or B ') type block copolymer is generally prepared by polymerizing isoprene, for example, in an organic solvent such as hexane using an organic alkali metal compound catalyst such as butyllithium. The block (A) is produced, and styrene and butadiene or butadiene alone are further added to this block in a living terminal state to produce a block (B) or a block (B ′). In this production, the desired block copolymer can be obtained by appropriately selecting the monomer compounding ratio, the vinylating agent, the polymerization conditions, and the like as desired. Furthermore, this A
-B (or B ') type block copolymers, for example,
It may be coupled with tin tetrachloride, silicon tetrachloride, or the like. Alternatively, a block (A) and a block (B) or a block (B ') are respectively produced in accordance with a conventional method, and this is coupled with a coupling agent such as tin tetrachloride or silicon tetrachloride. It can also be produced by ringing. Such AB (or B ') type block copolymer is, for example, represented by the following formula:

[0013]

Embedded image May be terminal-modified with a modifying agent such as an amide compound, an imide compound, a lactam compound, or a urea compound. Such terminal modification can be performed by adding an appropriate modifier in a living state after the copolymerization of the AB (or B ') type block copolymer is completed.

The carbon black used in the present invention has a CTAB surface area of more than 125 m ² / g and a C-DBP oil absorption of 100 to 150 ml / 100 g. When the CTAB surface area is 125 m ² / g or less, the heat generation becomes low, but both abrasion resistance and chipping resistance cannot be improved. When the C-DBP oil absorption is less than 100 ml / 100 g, the improvement of the abrasion resistance is insufficient.
If it exceeds g, the elongation decreases, and the decrease in chipping resistance is extremely undesirable. CTAB surface area is ASTM D 3765-80
It is measured according to the method described above. C-DBP oil absorption is 2
Also referred to as 4M4DBP oil absorption, ASTM D 3493
It is measured according to.

In the present invention, (a) 50 to 90 parts by weight of NR and / or IR, (b) 8 to 40 parts by weight of SBR or BR having a Tg of −75 ° C. or lower, and (c) AB ( Or a rubber composition comprising 35 to 55 parts by weight of the carbon black with respect to 100 parts by weight of a rubber consisting of 0.5 to 20 parts by weight of the block copolymer B ') to form a tread, Forming tires. If the compounding ratio is out of these ranges, the refinement or compatibilization of the phase structure of the matrix rubber becomes insufficient. A sufficient effect can be obtained even with a small amount of the block copolymer used in the present invention.

The rubber composition may contain, if necessary, sulfur, a vulcanization accelerator, an antioxidant, a filler, a softener, a plasticizer, etc., which are generally compounded in other rubber compositions for tires. An agent can be compounded. Examples will be described below.

[0017]

Examples Each component was blended according to the blending contents (parts by weight) shown in Tables 1 and 2 to obtain a rubber composition (Examples 1 to 3, Comparative Example 1)
To 8). At the time of compounding, after mixing the vulcanization accelerator, the compounding agent excluding sulfur, and the raw rubber with a 1.7 liter Banbury mixer for 5 minutes, the mixture was mixed with the vulcanization accelerator and sulfur, and an 8-inch test was conducted. The mixture was kneaded with a kneading roll machine for 4 minutes to obtain a rubber composition. These rubber compositions are mixed with 150
A test specimen was prepared by press vulcanization at 30 ° C. for 30 minutes, and was used to evaluate its wear resistance and chipping resistance as described below. Table 2 shows the results. Abrasion resistance : JIS K6 using Lambourn abrasion tester
According to H.264, the measurement was performed under the conditions of a load of 4.0 kg and a slip ratio of 30%. (Wear amount of Comparative Example 3) × 100 / (abrasion amount of sample) was taken as 100 and indexed. The larger the index value, the better the wear resistance. Chipping resistance : By measuring the breaking energy. For the breaking energy, a tensile test was performed based on JIS K 6301, and the area from the stress-strain curve up to breaking was used as the breaking energy. The index was indicated as an index with Comparative Example 3 as 100. The larger the index value, the higher the breaking energy and the better the chipping resistance.

[0018]

[Table 1] Table 1 100 parts by weight of rubber (described in Table 2) Carbon black Variable amount (described in Table 2) 5 parts by weight of zinc oxide 3 parts by weight of stearic acid 2 parts by weight of antioxidant 3 parts by weight of aromatic oil Sulfur yellow 1.5 parts by weight Vulcanization accelerator 1.0 part by weight

[0019]

[Table 2]

Note) * 1 Block (A): cis content 8
0% IR, Block (B): SBR with styrene content 12% by weight, 1.2-vinyl bond content 20%, A / B (weight ratio) = 50/50. * 2 CTAB surface area 110 m ² / g, C-DBP oil absorption 95 ml / 100 g.

* 3 CTAB surface area 140 m ² / g, C
-DBP oil absorption: 105 ml / 100 g. * 4 CTAB surface area 140 m ² / g, C-DBP oil absorption 93 ml / 100 g.

In Table 2, Comparative Example 3 is a case where the AB type block copolymer is not blended. Compared with Comparative Example 3, the rubber compositions (Examples 1 to 4) of the present invention are superior in both abrasion resistance and chipping resistance (breaking energy). Comparative Example 1 is BR, SBR, AB
Comparative Example 2 is a case where no AB block copolymer is blended (Comparative Example 3 is different from Comparative Example 3 in that SBR is used. In contrast, Comparative Example 2 uses BR).

Comparative Example 4 is a case where carbon black outside the range of the present invention is used, Comparative Example 5 is a case where NR and SBR are respectively used in amounts outside the range of the present invention, and Comparative Example 6 is a case where carbon black of the present invention is used. Comparative Example 7 is a case where carbon black is used in an amount outside the range of the present invention, and Comparative Example 8 is a case where carbon black outside the present invention is used. Some rubber compositions of Table 2 were used as tread rubbers for 10
00R20 14PR A large truck tire was manufactured, and an actual running test was performed on a course of 90/10 on a good road / bad road, and the abrasion resistance was evaluated from the remaining groove after running 5 × 10 ⁴ km as follows. At the same time, the chipping resistance was evaluated by visually observing the appearance. Table 3 shows the results.

Abrasion resistance : after running the actual vehicle (running distance 5 × 10
⁴ km) by measuring the remaining groove of the tire, wear amount 1mm
The running distance per hit was calculated, and the wear resistance was evaluated based on the running distance. The evaluation results were indicated by an index with a tire using the rubber composition of Comparative Example 3 as a tread rubber being 100. The larger the index value, the better the wear resistance. Chipping resistance : The appearance was visually evaluated by a five-point method. The larger the value, the better the chipping resistance.

[0025]

[Table 3] From Table 3, it is understood that the tire using the tread rubber as the rubber composition in the present invention is excellent in both abrasion resistance and chipping resistance.

[0026]

As described above, according to the present invention,
(a) Natural rubber and / or polyisoprene rubber 50-9
0 parts by weight, (b) styrene-butadiene copolymer rubber or polybutadiene rubber having a glass transition temperature of −75 ° C. or less
40 parts by weight, and (c) a block (A) of polyisoprene having a cis content of 70% by weight or more and a styrene content of 20% by weight.
AB (or B ') type block copolymer 0.5 comprising a block (B) of poly (styrene-butadiene) or a block (B') of polybutadiene having a 1,2-vinyl bond content of less than 50% Rubber content of 10 to 20 parts by weight
0 parts by weight, CTAB surface area exceeds 125 m ² / g and C-
Since the tread is composed of a rubber composition containing 35 to 55 parts by weight of carbon black having a DBP oil absorption of 100 to 150 ml / 100 g, it is possible to improve abrasion resistance and chipping resistance.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location C08L 53:02) (72) Inventor Tetsuji Kawamen 2-1 Oiwake, Hiratsuka-shi, Kanagawa Prefecture Yokohama Rubber Co., Ltd. (72) Inventor Masao Nakamura 1-2-1 Yoko, Kawasaki-ku, Kawasaki-city, Kanagawa Prefecture Inside the Zeon Corporation General Development Center (72) Inventor Takeshi Torutari 1-2, Night-light, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture -1 Inside Zeon Corporation Development Center

Claims (3)

[Claims] (1) 50 to 90 parts by weight of natural rubber and / or polyisoprene rubber, (b) glass transition temperature -75 ° C
8 to 40 parts by weight of the following styrene-butadiene copolymer rubber or polybutadiene rubber, and (c) a block (A) of polyisoprene having a cis content of 70% by weight or more and a 1,2-vinyl bond at a styrene content of less than 20% by weight. AB comprising a block (B) of poly (styrene-butadiene) or a block (B ') of polybutadiene having a content of less than 50%
(Or B ′) type block copolymer 0.5 to 20 parts by weight of rubber and 100 parts by weight of CTAB surface area of 1 part by weight.
Above 25 m ² / g, C-DBP oil absorption is 100-150 ml / 100
A pneumatic tire having a tread composed of a rubber composition containing 35 to 55 parts by weight of carbon black. 2. A ratio (weight ratio) of A / B (or B ') in the AB (or B') type block copolymer is 2
The pneumatic tire according to claim 1, wherein the ratio is from 0 to 80/80 to 20. 3. The AB (or B ′) type block copolymer has a molecular weight of 30,000 or more.
The pneumatic tire according to any one of the above items.