JP2000026657A - Bead section-reinforcing rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain bead section-reinforcing rubber compositions with a small permanent set and a small change in hardness after traveling. SOLUTION: Bead section-reinforcing rubber composition comprises 100 pts.wt. rubber component composed of a natural rubber and a butadiene rubber with a content of the butadiene rubber of not less than 40 wt.% and 1-20 pts.wt. silica, at the same time, without containing any silane coupling agent or 100 pts.wt. rubber component composed of a butadiene rubber containing 1,2- syndiotactic polybutadiene fibers and a natural rubber with a content of the butadiene rubber containing 1,2-syndiotactic polybutadiene fibers of not less than 40 wt.% and 1-25 pts.wt. silica, at the same time, without containing any silane coupling agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rubber composition used for reinforcing a bead portion of a tire.

[0002]

2. Description of the Related Art Conventionally, for example, tires for trucks and buses have been reused by cutting a worn tread surface and providing a new tread rubber (retread) after the end of the first life. rear,
It is required that there is no abnormality in parts other than the tread.

However, due to the recent increase in the size of vehicles, the increase in the load capacity, and the high-speed running, the chafer portion (the portion where the tire and the rim rub) of the bead portion of the tire for trucks and buses is affected by heat and mechanical effects. Durability,
While fatigue resistance and appropriate hardness are required, there is a problem that the hardness increases after the end of the first life, and the chip is missing when the rim is assembled during the second life.

Further, if the hardness of the rubber composition constituting the chafer portion of the bead portion of the tire is too low, the bead is deformed, which is not preferable. The chafer part is missing.

In this respect, for example, controlling the type and amount of carbon black contained in the rubber composition for reinforcing a bead portion;
Although a crystalline polymer has been used as a rubber component, an increase in hardness due to running has not been sufficiently suppressed.

Further, for example, Japanese Patent Application Laid-Open No. 9-302146
JP-A-9-302149 and JP-A-3-197
No. 207 discloses a rubber composition for reinforcing a bead portion having high hardness and excellent in fracture resistance, tough chipping resistance, rim shift resistance and the like, but contains a silane coupling agent as an essential component. Therefore, the cost is high, the hardness is improved, but depending on the type of the silane coupling agent, the change with time is large, and there is a problem that bead deformation is large,
The suppression of the change in hardness after running was not sufficient.

[0007]

SUMMARY OF THE INVENTION In view of the above facts, an object of the present invention is to obtain a rubber composition for reinforcing a bead portion having a small change in hardness after running and a small permanent deformation.

[0008]

SUMMARY OF THE INVENTION The present invention comprises natural rubber and butadiene rubber, and comprises butadiene rubber in an amount of 40% by weight.
Silica 1 to 100 parts by weight of the rubber component
The present invention relates to a rubber composition for reinforcing a bead portion which contains no more than 25 parts by weight and does not contain a silane coupling agent.

Further, the present invention provides a rubber component comprising butadiene rubber containing 1,2-syndiotactic polybutadiene fiber and natural rubber and containing not less than 40% by weight of butadiene rubber containing 1,2-syndiotactic polybutadiene fiber. The present invention also relates to a bead portion reinforcing rubber composition containing 1 to 25 parts by weight of silica and 100 parts by weight and containing no silane coupling agent.

In these cases, it is preferable that the composition further contains 1 to 10 parts by weight of polyethylene glycol.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The rubber component constituting the rubber composition of the present invention comprises natural rubber (NR) and butadiene rubber (B
R). This is because there are great merits such as suppression of hardness change, low heat build-up, and suppression of bead deformation.

Further, from the viewpoint of low heat build-up and maintaining hardness,
More than 40% by weight of the rubber component is BR. All of the rubber components may be BR. Further, from the viewpoint of the extrusion performance of the rubber material in the process, preferably from 20 to 80% by weight of the rubber component, and from the viewpoint of stabilizing the extruded shape, particularly preferably from 30 to 80% by weight of the rubber component.
70% by weight is BR.

Further, the BR has the following characteristics: elongation occurs while maintaining hardness, permanent deformation is small, change over time due to running is small, and extrusion characteristics are good. , 2-syndiotactic polybutadiene fibers. in this case,
The content of 1,2-syndiotactic polybutadiene fiber may be 6 to 17% by weight of the total amount of BR and 1,2-syndiotactic polybutadiene fiber. This is because if it is less than 6%, the hardness decreases, and the expected performance cannot be obtained, and if it exceeds 17% by weight, the workability is poor. Further, the content is preferably 10 to 15% by weight.

Further, in the rubber composition of the present invention, 1,2
-The mixing ratio in the case of using the BR containing the syndiotactic polybutadiene fiber may be such that the total amount of the 1,2-syndiotactic polybutadiene fiber and the BR is in the range described above for the case of the BR alone.

1,2 which can be used in the present invention
Examples of BR containing syndiotactic polybutadiene fiber include VCR-303 manufactured by Ube Industries, Ltd.
412, 617 and the like.

The silica used in the present invention is not particularly limited as long as it has been conventionally used in the field of tires. For example, it is referred to as the dispersibility (easy dispersion) of silica in a rubber composition. From the viewpoint, the BET specific surface area is 60 to 250 m ² and the DBP oil absorption is 100 to
It is preferably 300 ml / 100 g, and further,
From the viewpoint of reducing the Mooney viscosity of the compounded rubber, the BET specific surface area is 60 to 200 m ² and the DBP oil absorption is 10
Particularly preferred is 0 to 250 ml / 100 g.

Commercially available silicas include, for example, Nipsil VN3, Nipsil AQ, Toksir UR manufactured by Nippon Silica Co., Ltd., Ultrasil VN3 and Ultrasil VN2 manufactured by Degussa.

The amount of silica in the present invention is as follows:
It may be 1 to 25 parts by weight based on 100 parts by weight of the diene rubber. This is because if it exceeds 25 parts by weight, the permanent deformation of the rubber composition becomes large, the portion in contact with the rim is deformed, and rim chafing may occur. In addition, the Mooney viscosity becomes high, and burning tends to occur due to heat generation due to high load, and the extrusion performance becomes difficult.

Further, the compounding amount of silica is preferably 1 to 20 parts by weight with respect to 100 parts by weight of the diene rubber from the viewpoint of reduction of permanent set, and further, from the viewpoint of reduction of Mooney viscosity. Particularly preferred is 1 to 15 parts by weight.

Here, when silica is used as a tread rubber in the field of tires, a silane coupling agent is usually used to chemically bond silica and a rubber component in order to maintain the reinforcing property (abrasion resistance) of the rubber. Is used in conjunction with
In the present invention, since the silane coupling agent is not used, there is no problem in that the rubber of the tow is missing in the rim assembly during the second life.

Next, in the rubber composition of the present invention, in order to prevent the problem that a vulcanization accelerator is adsorbed on silica to cause a delay effect of vulcanization when vulcanizing the rubber composition. And polyethylene glycol.

This polyethylene glycol physically or chemically coats the silica surface, so that silanol groups or siloxane groups present on the silica surface adsorb the vulcanization accelerator or stearic acid or zinc oxide. To prevent

The polyethylene glycol used in the present invention has the following formula (1): H (CH ₂ CH ₂ O) _n OH (where n = 5)
１００100).

The amount of polyethylene glycol in the present invention may be 1 to 10 parts by weight based on 100 parts by weight of the diene rubber. This is because the blending amount is 10
If the amount is more than 10 parts by weight, it plays a role as a plasticizer, and the Mooney viscosity and hardness are reduced, which is disadvantageous for permanent deformation. On the other hand, if the compounding amount is less than 1 part by weight, the Mooney viscosity becomes too high and the processability is poor, the permanent deformation of the rubber composition becomes large, and the portion in contact with the rim is deformed when the rim is assembled. This is because finging may occur, and burns are likely to occur due to heat generation due to a high load, and extrusion performance becomes difficult. More preferably, it is 1 to 8 parts by weight.

The rubber composition of the present invention may contain, in addition to the above-mentioned components, fillers such as talc, clay, carbon black, glass and reinforcing short fibers such as polyamide, paraffin-based, aroma-based, and naphthene-based. Softeners such as process oils, tackifiers such as coumarone indene resin, rosin resin, cyclopentadiene resin,
Vulcanizing agents such as sulfur and peroxide, vulcanization accelerators, vulcanization aids such as stearic acid and zinc oxide, vulcanization retarders, antiaging agents, etc. are required as long as the effects of the present invention are not impaired. Can be appropriately compounded according to the conditions.

Next, a method for producing the tread rubber composition of the present invention will be described.

The rubber composition for a tread of the present invention can be obtained by kneading the above components all at once by a conventional method. However, the rubber component is preferred because the adsorption of polyethylene glycol to silica is performed preferentially. First, carbon black, silica, and polyethylene glycol are kneaded, and then, a softener, a tackifier, a vulcanization accelerator, an antioxidant, and the like are mixed. Finally, it is preferable to knead the mixture by a method of appropriately compounding a vulcanizing agent, a vulcanization accelerator and a vulcanization retarder.

The rubber composition of the present invention obtained as described above can be suitably used for reinforcing a bead portion of a tire, particularly for a chafer portion of the bead portion. Here, FIG. 1 shows a schematic cross-sectional view of the vicinity of the bead portion for explaining the chafer portion of the bead portion. In FIG. 1, 1 is a chafer portion, 2 is a sidewall portion, 3 is an inner liner, 4 is a bead, 5 is a bead apex, and 6 is a ply. The rubber composition for reinforcing a bead portion of the present invention can be particularly suitably used for the chafer portion 1. Among them, it can be suitably used particularly in a truck / bus tire to which a large load is applied.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0030]

EXAMPLES Examples 1 to 4 Using a 1.7-liter Banbury mixer manufactured by Kobe Steel, Ltd., at a temperature of 150.degree. Reinforcing rubber compositions 1 to 4 were produced.

NR Compounding ratio shown in Table 1 BR Compounding ratio shown in Table 1 Silica Compounding ratio shown in Table 1 PEG Compounding ratio shown in Table 1 Carbon black 65 parts by weight Antioxidant 2 parts by weight Stearic acid 3 parts by weight Zinc oxide 4 Parts by weight sulfur 1 part by weight vulcanization accelerator 3 parts by weight vulcanization retarder 0.38 parts by weight

Here, as BR, VCR-412 manufactured by Ube Industries, Ltd. (polybutadiene contains 12% by weight of 1,2-syndiotactic polybutadiene fiber), and as silica, Ultrasil VN3 (manufactured by Degussa Co., Ltd.) BET
Specific surface area: 175 m ² , DBP oil absorption: 160 ml / 1
00g) and polyethylene glycol No. manufactured by NOF Corporation. 4000 (expression
(1), n is 90), carbon black is Showa Black N330 manufactured by Showa Cabot Co., Ltd., and OD (polyme manufactured by Ouchi Shinko Chemical Co., Ltd.) is used as an anti-aging agent.
r of 2,2,4-trimethyl-1,2-dihydroquinoline), as a vulcanization accelerator, TBBS manufactured by Ouchi Shinko Chemical Co., Ltd.
(N-tert-butyl-2-benzothiazolyl-sulfenamide), and a retarder PVI (N- (cyclohexylthio) phthalimide) manufactured by Flexis Corporation was used as a vulcanization retarder.

When the rubber composition for reinforcing a bead portion of the present invention obtained as described above is applied to a tire, it has the effect of reducing permanent deformation and change in hardness (increase) after running. The following test was conducted to evaluate such effects. Table 1 shows the results.

[Test] First, in order to evaluate the processability and scorch (burn) stability of the obtained rubber composition, Mooney viscosity (ML _{1 + 4} ) and scorch time (130 ° C.) according to JIS-K6300 were measured. t ₁₀ ) was measured. From the viewpoint of excellent workability, it is better that these values are large.

Next, in order to evaluate the change in hardness after running, the obtained rubber composition was vulcanized at 150 ° C. for 35 minutes, and the JIS-A hardness (H _s ) at 20 ° C. was measured. by heating at 300 hours in an oven at 100 ° C. aged, after the state after the running was measured JIS-a hardness (H _s') again. Then, the formula: was obtained hardness change ratio by _{((H s' -H s)} / H s) × 100. The smaller the hardness change rate is, the better the deterioration with the lapse of time and the absence of rubber chipping during rim assembly.

In order to obtain the condition after running, the aging conditions were adopted because the hardness change and the swell change when the conventional bead portion reinforcing rubber composition (Comparative Example 4) was aged under such conditions. However, it was similar to that when the vehicle was actually driven.

Further, in order to evaluate the presence or absence of rubber chipping when assembling the rim, the elongation at break (E) before and after the above-mentioned aging was evaluated.
_B (orig.) And E _B (Ag.)) Was measured. It is preferable that the difference (absolute value) between these values is smaller, so that the rim is less likely to break in the rim assembly during rotation.

Further, in order to evaluate the permanent deformation, the permanent strain at a constant stress was measured. That is, a 2 mm thick slab obtained by vulcanizing the obtained rubber composition at 150 ° C. for 35 minutes is punched out with a JIS No. 3 dumbbell, and a 20 mm mark is marked. It is stretched at a constant stress of 18 kg / cm ² and left in an oven at 100 ° C. for 24 hours. After being removed from the oven, the stress was removed, the sample was left at room temperature for 30 minutes, and then the distance R between the marked lines was measured. From this R, the constant stress strain (%) = ((R−20) / 20) × 100 was used to determine the constant stress strain (permanent deformation rate). The smaller the value, the smaller the permanent deformation and the better.

Comparative Examples 1 to 5 Comparative rubber compositions 1 to 5 were obtained in the same manner as in Example 1 except that the mixing ratios were changed as shown in Table 1, and the same tests as in Example 1 were conducted. Table 1 shows the results. SBR1502 manufactured by Sumitomo Chemical Co., Ltd. was used as SBR, and bis (3-triethoxysilylpropyl) tetrasulfide (Si69) was used as a silane coupling agent.

[0040]

[Table 1]

From the evaluation results of Example 1 and Comparative Example 1, when the amount of the natural rubber is increased, the elongation (E _B ) is increased, but the hardness is reduced, and the permanent deformation is increased, which is disadvantageous for rim chafing. It turns out that it is.

From the evaluation results of Example 1 and Comparative Example 2, the addition of SBR increases the elongation (E _B ).
It can be seen that the hardness increase after aging is large and the permanent deformation is large.

Further, from the evaluation results of Example 1 and Comparative Example 3, when the amount of silica was increased, the modulus was decreased and the elongation (E
_B ) increases, but the Mooney viscosity increases, which makes it difficult to extrude the dough, and that the permanent deformation increases.

From the evaluation results of Example 1 and Comparative Example 4, the addition of silica increased the elongation,
It can be seen that the increase in hardness is also small.

From the evaluation results of Example 1 and Comparative Example 5, when Si69 was added to the chip at the time of assembling the rim,
It can be seen that the scorch is easy to burn quickly and the expected growth cannot be obtained.

[0046]

According to the present invention, a rubber composition for reinforcing a bead portion having a small permanent deformation and a small change in hardness after running can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view around a bead portion for explaining a chafer portion of the bead portion.

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Claims (3)

[Claims] 1. A natural rubber and butadiene rubber,
Rubber component 10 containing at least 40% by weight of butadiene rubber
A rubber composition for reinforcing a bead portion containing 1 to 25 parts by weight of silica and 0 to 100 parts by weight and containing no silane coupling agent. 2. A natural rubber comprising butadiene rubber containing 1,2-syndiotactic polybutadiene fiber and natural rubber,
Rubber component 10 containing 40% by weight or more of butadiene rubber containing 1,2-syndiotactic polybutadiene fiber
A rubber composition for reinforcing a bead portion containing 1 to 25 parts by weight of silica and 0 to 100 parts by weight and containing no silane coupling agent. 3. Polyethylene glycol 1 to 10
The rubber composition for reinforcing a bead portion according to claim 1 or 2, comprising parts by weight.