JPH1159143A - Pneumatic tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire for heavy load improving durability of a bead part by improving rim wear resistance and bead toe damage resistance. SOLUTION: This pneumatic tire for heavy load is constituted by constituting a chafer rubber layer 4 of a bead part 1 by a rubber composition of a full rubber part 100 weight part constituted of a (a) NR and/or IR 40 to 20 pts.wt. a (b) SBR or BR 40 to 80 pts.wt. of a glass transition temperature -85 deg.C or below and an A-B (or B') type block copolymer 20 to 5 pts.wt. constituted of a block (A) of IR of cis content 70 wt.% or more and a block (B) of SBR of less than styrene content 20 wt.% and not more than 1, 2-vinyl coupled content 50% or a block (B') of BR.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty pneumatic tire having improved rim abrasion resistance and bead toe damage resistance and improved bead portion durability.

[0002]

2. Description of the Related Art Heavy-load pneumatic tires, such as trucks and buses, which are filled with a high internal pressure and are subjected to heavy loads, cause a failure in a bead portion, which is one of places where stress strain is significantly concentrated during running. Sometimes. As a result of this failure, the bead surface wears out due to rubbing and becomes fatigued, causing settling and delamination, and also missing the bead toe when removing the tire from the rim or mounting it on the rim. Would.

As a countermeasure against this failure, a chafer rubber layer extending from the bead toe portion to the height near the upper edge of the rim flange via the bead heel portion is arranged on the surface of the bead portion. Conventionally, a rubber composition comprising natural rubber (NR) and polybutadiene rubber (BR) has been used for the chafer rubber layer (Japanese Patent Application Laid-Open Nos. 7-81335 and 7-266813).

However, in such an NR / BR system, since the polymers do not mix well (incompatibility), the breaking strength of the rubber composition is low, and the set resistance (prevention of settling), which is one of the disadvantages of BR, is as follows. Gender) is remarkably easy to appear,
As a result, there has been a problem that rim rubbing occurs, delamination occurs, and chipping of the bead toe portion easily occurs.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a chafer rubber layer comprising a rubber composition having a fine phase structure by adding a specific block polymer to a blend system of incompatible polymers. Another object of the present invention is to provide a heavy-duty pneumatic tire having improved rim rub resistance and bead toe damage resistance and improved bead portion durability.

[0006]

According to the pneumatic tire for heavy load of the present invention, the end of the carcass layer is folded around the bead core from the inside to the outside of the tire and wound up. A fur rubber layer is disposed, and the chafer rubber layer is placed on the natural rubber (N)
R) rubber and / or polyisoprene rubber (IR) 40-
20 parts by weight, (b) 40-80 parts by weight of styrene-butadiene copolymer rubber (SBR) or polybutadiene rubber (BR) having a glass transition temperature of -85 ° C. or less, and (c) polyisoprene having a cis content of 70% by weight or more AB comprising a block (A) and a block (B) of poly (styrene-butadiene) or a block of polybutadiene (B ') having a styrene content of less than 20% by weight and a 1,2-vinyl bond content of less than 50% (or B ') The composition is characterized by comprising a rubber composition comprising 20 to 5 parts by weight of the block copolymer and having a total rubber content of 100 parts by weight.

[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. Therefore, in this rubber composition, the phase structure of these rubber components is refined (in an ideal case, they are compatibilized) to form a uniform rubber phase. By configuring the chafer rubber layer, it is possible to improve the rim rub resistance and the bead toe damage resistance, thereby improving the bead portion durability.

[0008]

In FIG. 1, in a bead portion 1, an end of a carcass layer 2 is wound around a bead core 3 from the inside of the tire to the outside (from the inside to the outside in the tire axial direction). On the surface of the bead portion 1, a chafer rubber layer 4 is arranged from the inside to the outside of the tire. A reinforcing layer 5 made of a steel cord is arranged between the winding portion 2 a of the carcass layer 2 outside the tire and the chafer rubber layer 4 to reinforce the bead portion 1. As shown in FIG. 1, the chafer rubber layer 4 outside the tire extends to a height near the upper edge of the rim flange 7 of the rim 6.

In the present invention, NR, IR, SBR having a glass transition temperature (Tg) of -85 ° C. or less, and BR having a glass transition temperature (Tg) of -85 ° C. or less in a rubber composition used to constitute the chafer rubber layer 4 May be general commercial products. Here, the reason why the Tg is set to −85 ° C. or less is that if the temperature exceeds −85 ° C., the abrasion resistance and the heat generation are reduced, which is not preferable.

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 -8.
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-85 ° C. or less, BR at Tg-85 ° C. or less) is reduced, and the contribution to the compatibilization of the matrix rubber becomes insufficient. The molecular weight of each block component of the AB (or B ') type block copolymer is 30,000.
The above is preferable, and 50,000 to 800,000 is preferable. If it is less than 30,000, entanglement with the matrix is small, and co-crosslinking property is undesirably 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:

[0014]

Embedded image

A compound having a bond represented by the formula:
The terminal may be modified with a modifying agent such as an amide compound, an imide compound, a lactam compound, and 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. In the present invention, (a) 40 to 20 parts by weight of NR and / or IR, (b) Tg-85 ° C
40 to 80 parts by weight of the following SBR or BR; and (c)
20 to 5 of the AB (or B ') type block copolymer
The chafer rubber layer 4 is composed of a rubber composition of 100 parts by weight of the total rubber consisting of parts by weight to form a pneumatic tire for heavy load. 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. This rubber composition preferably has a JIS hardness after vulcanization of more than 67. If the hardness is less than 67, the chafer rubber layer 4 becomes soft, and the rim abrasion resistance and the bead toe damage resistance are deteriorated.

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 The respective components were blended according to the blending contents (parts by weight) shown in Table 1 to obtain rubber compositions (Examples 1 and 2, Conventional Examples 1 and 2, and Comparative Example 1). At the time of compounding, the vulcanization accelerator, the compounding agent excluding sulfur, and the raw rubber were mixed with a 1.7 liter Banbury mixer for 5 minutes, and then the mixture was mixed with the vulcanization accelerator and sulfur, followed by an 8-inch test. The mixture was kneaded with a kneading roll machine for 4 minutes to obtain a rubber composition. 160 ° C. of these rubber compositions
For 20 minutes to prepare a test piece, and various tests were performed using the test piece as described below to evaluate the rubber properties. Table 1 shows the results.

Tensile strength (Mpa ): Measured according to JIS K6301. The index is represented by setting the conventional example 1 to 100. The larger the index value, the higher the tensile strength. Hardness (JIS ): Measured according to JIS K6301. The higher the value, the harder.

Abrasion resistance : JIS using a pico abrasion tester
It measured according to K6264. (Wear amount of Conventional Example 1) × 100 / (wear amount of sample) was indicated by an index. The larger the index value, the better the wear resistance. Set resistance : Measured according to JIS K6262.
The sample was set in a compression set tester and left in a gear oven at 100 ° C. for 24 hours to measure the settling. The index is represented by setting the conventional example 1 to 100. The larger the index value is, the more excellent the set resistance is, and it indicates that the set is prevented.

Heat resistance : Using a flexometer manufactured by Goodrich Co., Ltd., load 25 kg, stroke 4.4 mm,
1800r. p. m, the temperature difference after 25 minutes at an ambient temperature of 100 ° C. The index is represented by setting the conventional example 1 to 100. The larger the index value, the smaller the heat generation and the better the durability. The chafer rubber layer 4 in FIG. 1 was constructed from various rubber compositions (Examples 1 and 2, Conventional Examples 1 and 2, and Comparative Example 1) shown in Table 1 to produce pneumatic tires for heavy loads. The rim abrasion resistance, bead toe damage resistance, and indoor bead portion durability were evaluated as follows. Table 1 shows the results.

Rim abrasion resistance : The tire of each example has a load capacity of 10
Mounted on a ton truck, on-the-spot running, 100,000 km
After running, it was collected, the rim was unraveled, and rim rubbing of the rim flange (abrasion of chafer rubber) was confirmed. 5 visually
It was evaluated by the point method. The higher the value, the better the rim abrasion resistance.

Bead toe damage resistance : The vehicle was run on the same conditions under the same conditions as above, the rubber deficiency of the bead toe portion was confirmed, the rim was repeatedly removed, and the performance against bead toe deficiency was visually evaluated by a five-point method. did. The higher the value, the better the bead toe damage resistance. Indoor bead durability : A tire with the tread of the tire buffed to the remaining groove of 0.5 mm is subjected to an internal pressure load on the circumference of a steel drum.
The tire using the rubber composition of Conventional Example 1 was expressed as an index by evaluating the running distance until the bead failure occurred by pressing the tire under running under the normal conditions of the IS standard. The larger the index value, the higher the bead portion durability.

[0023]

[Table 1]

As is evident from Table 1, the rubber compositions of Examples 1 and 2 are more excellent in rubber properties than other rubber compositions (Conventional Examples 1 and 2 and Comparative Example 1). Further, Examples 1 to
The tire using the rubber composition of No. 2 was compared with the tire using the other rubber composition (conventional examples 1 and 2 and comparative example 1), and thus the rim abrasion resistance, the bead toe damage resistance, and the indoor bead portion durability were compared. It turns out that it is excellent in all of them.

[0025]

As described above, according to the present invention,
(a) Natural rubber and / or polyisoprene rubber 40-2
0 parts by weight, (b) styrene-butadiene copolymer rubber or polybutadiene rubber 40 having a glass transition temperature of -85 ° C. or lower
And (c) a block of polyisoprene (A) having a cis content of 70% by weight or more and a block of poly (styrene-butadiene) having a styrene content of less than 20% by weight and a 1,2-vinyl bond content of less than 50%. AB (or B ') type block copolymer comprising (B) or polybutadiene block (B') 20 to 5 parts by weight of total rubber content 10
0 parts by weight of the rubber composition, the chafer rubber layer in the bead portion of the pneumatic tire for heavy load,
The rim abrasion resistance and the bead toe damage resistance can be enhanced to improve the bead portion durability.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view in the tire meridian direction showing an example of a bead structure of a heavy-duty pneumatic tire of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Bead part 2 Carcass layer 3 Bead core 4 Chafer rubber layer 5 Reinforcement layer 6 Rim
7 Rim flange

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI C08L 53/02 C08L 53/02

Claims (4)

[Claims] 1. A chafer rubber layer is arranged from the inside to the outside of the tire on the surface of a bead portion obtained by folding the end of the carcass layer around the bead core from the inside to the outside of the tire and winding up the carcass layer. (a) 40 to 20 parts by weight of natural rubber and / or polyisoprene rubber, (b)
Styrene-butadiene copolymer rubber or polybutadiene rubber having a glass transition temperature of −85 ° C. or less, 40 to 80 parts by weight,
And (c) a block of polyisoprene (A) having a cis content of 70% by weight or more and 1,2 having a styrene content of less than 20% by weight.
A total of 20 to 5 parts by weight of 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%. A heavy duty pneumatic tire comprising a rubber composition having a rubber content of 100 parts by weight. 2. A ratio (weight ratio) of A / B (or B ') in the AB (or B') type block copolymer is 2
The pneumatic tire for heavy load according to claim 1, wherein the weight is 0 to 80/80 to 20. 3. The molecular weight of each block component of the AB (or B ′) type block copolymer is 30,000.
The heavy-duty pneumatic tire according to any one of claims 1 to 2, which is as described above. 4. A rubber composition having a JIS hardness of 6 after vulcanization.
The heavy-duty pneumatic tire according to any one of claims 1 to 3, wherein the number is more than 7.