JP2011157495A - Rubber composition for tire rim cushion and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tire rim cushion which has high hardness and low heat generation property and can suppress deterioration of breaking elongation due to aging, and to provide a pneumatic tire using the rubber composition for tire rim cushion. <P>SOLUTION: The rubber composition for tire rim cushion is obtained by mixing 70 to 110 pts.mass of carbon black having a nitrogen adsorption specific surface area (N<SB>2</SB>SA) of 60 to 110 m<SP>2</SP>/g and 3 to 15 pts.mass of ultrahigh molecular weight polyethylene having a molecular weight of 1,000,000 to 4,000,000 and further mixing a vulcanization accelerator and sulfur to 100 pts.mass of diene-based rubber, wherein the rate in pts.mass of the vulcanization accelerator to the sulfur as vulcanization accelerator/sulfur is 0.8 to 1.5. The pneumatic tire using the rubber composition for tire rim cushion for the rim cushion (11) is also disclosed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a rubber composition for a tire rim cushion and a pneumatic tire using the same, and more particularly, a rubber for a tire rim cushion that has high hardness and low heat generation and can suppress a decrease in elongation at break due to aging. The present invention relates to a composition and a pneumatic tire using the composition.

  In a vehicle, tires are mounted via rubber of a rim and a rim cushion. If the rubber in this portion is soft, the fitting is deteriorated and rim displacement occurs, so that high hardness is required. As a countermeasure, there is a method of increasing the hardness by increasing the amount of carbon black or increasing the amount of the vulcanizing agent and / or the vulcanization accelerator. However, heat generation becomes large and heat aging tends to proceed. In addition, the elongation at break decreases due to the aging of the rubber, and the occurrence of cracks becomes a problem.

  In addition, the technique which uses ultra high molecular weight polyethylene for a pneumatic tire is known (for example, refer patent document 1, 2). However, the prior art uses high molecular weight polyethylene itself at a predetermined location of a pneumatic tire, and the constitution and effect of the present invention described below, that is, the high molecular weight polyethylene is one component in the rubber composition. There is no disclosure or suggestion of using this as a tire rim cushion to obtain high hardness, low heat buildup and aging resistance.

Japanese Patent Laid-Open No. 4-71910 JP-A-9-164809

  Accordingly, an object of the present invention is to provide a rubber composition for a tire rim cushion, which has high hardness and low heat build-up, and can suppress a decrease in elongation at break due to aging, and a pneumatic tire using the same.

As a result of intensive research, the inventors compounded a specific amount of carbon black and a specific amount of ultra-high molecular weight polyethylene having specific characteristics into a diene rubber, and specified a blending ratio of a vulcanization accelerator and sulfur. As a result, it was found that the above problems could be solved, and the present invention could be completed.
That is, the present invention is as follows.
1. More than 70 to 110 parts by mass of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 60 to 110 m ² / g and a molecular weight of 1,000,000 to 4,000,000 per 100 parts by mass of the diene rubber. While blending 3 to 15 parts by mass of high molecular weight polyethylene, and further blending a vulcanization accelerator and sulfur, the ratio of the vulcanization accelerator to the mass part of sulfur is 0. A rubber composition for a tire rim cushion, which is 8 to 1.5.
2. A pneumatic tire using the rubber composition for a tire rim cushion according to 1 above as a rim cushion.

  According to the present invention, the specific amount of carbon black having specific characteristics and the specific amount of ultrahigh molecular weight polyethylene are blended with the diene rubber, and the blending ratio of the vulcanization accelerator and sulfur is identified. It is possible to provide a rubber composition for a tire rim cushion and a pneumatic tire using the same, which have low heat build-up and can suppress a decrease in breaking elongation due to aging.

It is a fragmentary sectional view of an example of a pneumatic tire.

  Hereinafter, the present invention will be described in more detail.

FIG. 1 is a partial cross-sectional view of an example of a pneumatic tire.
In FIG. 1, a pneumatic tire is composed of a pair of left and right bead portions 1 and sidewalls 2, and a tread 3 connected to both sidewalls 2, and a carcass layer 4 in which a steel cord is embedded between the bead portions 1 and 1 is mounted. Then, the end portion of the carcass layer 4 is turned up around the bead core 5 and the bead filler 6 from the tire inner side to the outer side. The bead filler 6 is composed of two members, the upper part being an upper bead filler 62 and the lower part being a lower bead filler 64. In the tread 3, a belt layer 7 is disposed over the circumference of the tire outside the carcass layer 4. Belt cushions 8 are disposed at both ends of the belt layer 7. An undertread 31 is disposed on the inner peripheral side of the tread 3. An inner liner 9 is provided on the inner surface of the pneumatic tire to prevent the air filled inside the tire from leaking to the outside of the tire, and a tie rubber 10 for bonding the inner liner 9 is attached to the carcass layer 4. It is laminated between the inner liner 9. In the bead portion 1, a rim cushion 11 is disposed at a portion in contact with the rim.

  The rubber composition of the present invention is particularly useful for the formation of the above-described rim 11. Next, each component of the rubber composition of the present invention will be described.

(Diene rubber)
As the diene rubber component used in the present invention, any diene rubber that can be blended in the rubber composition can be used. For example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR) ), Styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), and the like. These may be used alone or in combination of two or more. The molecular weight and microstructure are not particularly limited, and may be terminally modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group or the like, or may be epoxidized.
Among these diene rubbers, NR and BR are preferable as the diene rubber from the viewpoint of the effect of the present invention.

(Carbon black)
The carbon black used in the present invention needs to have a nitrogen adsorption specific surface area (N ₂ SA) of 60 to 110 m ² / g. Preferably, it is 65-100 m < ² > / g. When the nitrogen adsorption specific surface area (N ₂ SA) is less than 60 m ² / g, the rate of decrease in elongation at break is deteriorated when the hardness is high, and conversely when it exceeds 110 m ² / g, high hardness and low heat generation are caused. It is not preferable because they cannot be made compatible. The nitrogen adsorption specific surface area (N ₂ SA) is a value determined in accordance with JIS K6217-2.

(Ultra high molecular weight polyethylene)
The ultra high molecular weight polyethylene used in the present invention needs to have a molecular weight in the range of 1,000,000 to 4,000,000. Preferably, the molecular weight is in the range of 1,000,000 to 3,000,000. If the molecular weight is less than 1,000,000, the effect of improving the elastic modulus and the rate of decrease in elongation at break due to aging is reduced, which is not preferable. Conversely, if the molecular weight exceeds 4,000,000, dispersibility in rubber deteriorates. Therefore, it is not preferable. In addition, the molecular weight as used in the field of this invention means a viscosity average molecular weight, and is a value measured by the intrinsic viscosity method (ASTM D4020).
As the ultra-high molecular weight polyethylene used in the present invention, commercially available ones can be used, for example, Miteron XM-220 (Molecular weight = 2,000,000) manufactured by Mitsui Chemicals, Ltd., Mitsui Chemicals, Inc. Examples thereof include Hi-Zex Million 240S (molecular weight = 2,000,000), Hi-Zex Million 320MU (molecular weight = 3,000,000), Hi-Zex Million 341L (molecular weight = 4,000,000), and the like.

(filler)
The rubber composition for a tire rim cushion of the present invention can contain various fillers. The filler is not particularly limited and may be appropriately selected depending on the application. Examples thereof include inorganic fillers. Examples of the inorganic filler include silica, clay, talc, calcium carbonate and the like.

(Combination ratio of rubber composition for tire rim cushion)
The rubber composition for a tire rim cushion of the present invention is a carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 60 to 110 m ² / g of 70 to 110 parts by mass and a molecular weight of 1,000,000 to 4,000,000. 3 to 15 parts by mass of the ultrahigh molecular weight polyethylene is further blended, and further a vulcanization accelerator and sulfur are blended, and the ratio of the vulcanization accelerator to the mass part of sulfur is the vulcanization accelerator / the sulfur. The (A / S ratio) is 0.8 to 1.5.
When the blending amount of the carbon black is less than 70 parts by mass, the hardness and the elastic modulus are unfavorably lowered. On the contrary, when it exceeds 110 parts by mass, the exothermic property is deteriorated and the decrease in elongation at break due to aging cannot be suppressed.
If the blending amount of the ultra high molecular weight polyethylene is less than 3 parts by mass, the blending amount is too small to achieve the effects of the present invention. Conversely, if the blending amount exceeds 15 parts by mass, the elastic modulus becomes too high. It is not preferable.
When the ratio of the vulcanization accelerator / the sulfur is less than 0.8, the elongation at break due to aging is lowered and heat generation is increased, which is not preferable. On the other hand, when the ratio exceeds 1.5, the elastic modulus is lowered.
In addition, although the kind in particular of a vulcanization accelerator is not restrict | limited, a sulfenamide type | system | group vulcanization accelerator is preferable from the point of an effect in this invention.

A more preferable blending ratio of the carbon black is 70 to 90 parts by mass with respect to 100 parts by mass of the diene rubber.
A more preferable blending ratio of the ultra high molecular weight polyethylene is 5 to 10 parts by mass with respect to 100 parts by mass of the diene rubber.
A more preferable ratio of the vulcanization accelerator / the sulfur is 1 to 1.5.
In addition, it is preferable to mix | blend 1-2.5 mass parts of sulfur with respect to 100 mass parts of diene rubbers.

  The rubber composition for a tire rim cushion of the present invention is generally blended with a rubber composition such as a vulcanization or cross-linking agent, a cross-linking accelerator, various oils, an anti-aging agent, and a plasticizer in addition to the above-described components. Various additives can be blended, and such additives can be kneaded by a general method to form a composition, which can be used for vulcanization or crosslinking. The blending amounts of these additives can be set to conventional general blending amounts as long as the object of the present invention is not violated.

  The rubber composition for a tire rim cushion of the present invention can be used for producing a pneumatic tire according to a conventional method for producing a pneumatic tire.

  EXAMPLES Hereinafter, although an Example and a comparative example further demonstrate this invention, this invention is not restrict | limited to the following example.

Examples 1-2 and Comparative Examples 1-9
Preparation of sample In the composition (parts by mass) shown in Table 1, the components excluding the vulcanization system (vulcanization accelerator, sulfur) were kneaded for 5 minutes with a 1.7 liter closed Banbury mixer, and then released outside the mixer. And cooled to room temperature. Subsequently, the composition was put into the Banbury mixer again, and a vulcanization system was added and kneaded to obtain a rubber composition. Next, the obtained rubber composition was press vulcanized at 150 ° C. for 30 minutes in a predetermined mold to prepare a vulcanized rubber test piece. The physical properties of the obtained vulcanized rubber specimens were measured by the following test methods.

Hardness: measured at 23 ° C. according to JIS K6253. Assuming that the value obtained in Comparative Example 1 is 100, the larger the index, the higher the hardness.
Elastic modulus: Measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho under the conditions of a temperature of 20 ° C., an elongation deformation rate of 10 ± 2%, and a frequency of 20 Hz. The comparative example 1 was set to 100 and evaluated by an index. The larger the index, the better the elastic modulus.
Exothermic property: Tan δ at 60 ° C. was measured at an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz in accordance with JIS K6394. The reciprocal of the measured value was taken, and this value was shown as an index with the value of Comparative Example 1 being 100. A larger index indicates a lower exothermic property.
Rate of decrease in elongation at break after aging: according to JIS K6251, elongation at break of sample at 20 ° C. and rate of change in elongation at break at 20 ° C. of sample heat-aged at 70 ° C. for 96 hours ((thermal aging Pre-heat aging) / pre-heat aging) was calculated, the reciprocal of the rate of change was taken, and this value was expressed as an index with Comparative Example 1 taken as 100. It shows that the fall of the breaking elongation by aging is suppressed, so that an index | exponent is large.
The results are shown in Table 1.

* 1: NR (STR20)
* 2: BR (manufactured by ZEON Corporation, Nipol BR1220)
* 3: Ultra high molecular weight polyethylene (Mitsui Chemicals, Mipperon XM-220, molecular weight = 2,000,000)
* 4: Ultra high molecular weight polyethylene (manufactured by Mitsui Chemicals, Hi-Z Million 030S, molecular weight = 500,000)
* 5: Carbon black (manufactured by Tokai Carbon Co., Ltd., Seest 300, N ₂ SA = 81 m ² / g)
* 6: Vulcanization accelerator (Ouchi Shinsei Chemical Co., Ltd., Noxeller NS-P)
* 7: Stearic acid (Chiba Fatty Acid Co., Ltd., industrial stearic acid)
* 8: Zinc flower (Zodo oxide, manufactured by Shodo Chemical Industry Co., Ltd.)
* 9: Sulfur (manufactured by Tsurumi Chemical Co., Ltd., fine powdered sulfur with Jinhua seal oil)

As is clear from Table 1 above, the rubber composition for tire rim cushions prepared in Examples 1 and 2 has a specific amount of ultrahigh molecular weight polyethylene and a specific amount of carbon black having specific characteristics in a diene rubber. Since it is blended and the blending ratio of the vulcanization accelerator and sulfur is specified, it has high hardness and low exothermicity compared to the conventional representative comparative example 1, and the decrease in breaking elongation due to aging is suppressed. ing. This result shows that the rubber composition for tire rim cushions prepared in Examples 1 and 2 is particularly suitable for use in a tire rim cushion.
On the other hand, Comparative Example 2 is an example in which the amount of carbon black is reduced in the rubber composition of Comparative Example 1, and the hardness and elastic modulus are deteriorated.
Comparative Example 3 is an example in which the amount of carbon black is increased in the rubber composition of Comparative Example 1, and low exothermic properties cannot be obtained, and a decrease in elongation at break due to aging cannot be suppressed.
Comparative Example 4 is an example in which the A / S ratio was lowered in the rubber composition of Comparative Example 1, low exothermic property was not obtained, and the decrease in elongation at break due to aging could not be suppressed.
Comparative Example 5 is an example in which the A / S ratio was increased in the rubber composition of Comparative Example 1, the elastic modulus was deteriorated, and low exothermic properties were not obtained.
In Comparative Example 6, the amount of ultrahigh molecular weight polyethylene exceeds the upper limit defined in the present invention, so the elastic modulus becomes very high and cannot be put to practical use.
In Comparative Example 7, since the molecular weight of the ultrahigh molecular weight polyethylene was less than the lower limit specified in the present invention, none of the physical properties was sufficiently improved.
In Comparative Example 8, since the blending amount of carbon black was less than the lower limit specified in the present invention, the hardness and elastic modulus were lowered.
In Comparative Example 9, since the A / S ratio exceeds the upper limit defined in the present invention, the hardness is not improved.

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall 3 Tread 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Belt cushion 9 Inner liner 11 Rim cushion

Claims (2)

More than 70 to 110 parts by mass of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 60 to 110 m ² / g and a molecular weight of 1,000,000 to 4,000,000 per 100 parts by mass of the diene rubber. While blending 3 to 15 parts by mass of high molecular weight polyethylene, and further blending a vulcanization accelerator and sulfur, the ratio of the vulcanization accelerator to the mass part of sulfur is 0. A rubber composition for a tire rim cushion, which is 8 to 1.5.   A pneumatic tire using the rubber composition for a tire rim cushion according to claim 1 as a rim cushion.

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