JPH08311246A - Rubber composition for tire bead filler - Google Patents

Abstract

PURPOSE: To impart a high elastic modulus and an excellent fatigue resistance to a rubber compsn. for tire bead filler in order to enhance the stiffness of a bead of a pneumatic tire and thus improve the fuel consumption properties, maneuverability, durability, and wt. reduction of the tire. CONSTITUTION: The compsn. is prepd. by compounding 100 pts.wt. rubber component contg. 10-40wt.% syndiotactic 1,2-polybutadiene rubber formed by dispersing 10-25wt.% syndiotactic polybutadiene in a cis-1,4-polybutadiene matrix with 7-30 pts.wt. silica, does not contain a silane coupling agent, and has a dynamic elastic modulus of 45MPa or higher.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a rubber composition used as a bead filler for pneumatic tires for automobiles. More specifically, it relates to a rubber composition for bead fillers having a high dynamic elastic modulus and fatigue resistance which uses VCR and silica and does not use a silane coupling agent which is usually used in combination with silica.

[0002]

2. Description of the Related Art A carcass ply for reinforcing a carcass of a pneumatic tire for an automobile is folded back from the inside of a bead core toward the outside and locked by the bead core, and the folded portion extends along a side wall and terminates. And forms a winding portion. The bead core that occurs at this time,
A space surrounded by the carcass ply body and the winding portion is filled with a bead filler having a substantially triangular cross section. Increase the rigidity of the bead part of the tire to increase the tire's dynamic performance,
In order to improve durability and reduce rolling resistance, the bead filler was made to have a large amount of carbon black, short fibers, or novolac-type phenol formalin resin to increase hardness. A rubber composition is used. However, in the method of blending carbon black or short fibers, there is a limit to increase the hardness while maintaining other necessary properties, and when a higher hardness is required, for example, JP-A-53-4059. No. 53-119501 and No. 54-38003.
Novolak type alkylphenol formalin resin as described in Japanese Patent Publication No.
A rubber composition of 0 kg / cm ² or more was mainly used.

[0003]

In order to reduce the weight of the tire and reduce the weight of the bead filler in response to demands for environmental issues such as resource saving, reduction of carbon monoxide emission, and safety, the rigidity of the bead portion is reduced. Thin the bead part while maintaining
Alternatively, it is necessary to further increase the rigidity to improve the athletic performance and durability of the tire to make it a safer tire. Since the rigidity of the bead filler depends largely on the rigidity of the bead filler, it is necessary to further increase the dynamic elastic modulus of the rubber composition forming the bead filler to 45 MPa or more. When carbon black is added in an amount necessary to make the dynamic elastic modulus of 45 MPa or more, fatigue resistance is poor and heat generation is high, and separation is likely to occur at the tip of the winding portion. When the short fibers are excessively mixed to obtain a pressure of 50 MPa or more, the short fibers are entangled in the rubber to form a lump, and the short fibers are not directly bonded to the rubber. Becomes the starting point of the crack, and the crack easily occurs, and the durability decreases.
Novolac-type phenolic resins have poor curing efficiency in general-purpose rubbers such as natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber, and a considerable amount remains unreacted. Since it is large and is essentially incompatible with general-purpose rubber, it has the drawback that when mixed in a large amount, mechanical properties such as strength, fatigue resistance, creep resistance, etc. decrease and heat generation increases. There is.

An object of the present invention is excellent in fatigue resistance, and
It is intended to provide a rubber composition for a bead filler of a pneumatic tire having a dynamic elastic modulus of MPa or more.

[0005]

SUMMARY OF THE INVENTION The present invention provides cis 1, 4
10-40% by weight of syndiotactic 1,2-polybutadiene rubber in which syndiotactic 1,2-polybutadiene is dispersed in a polybutadiene matrix
7 to 30 relative to 100 parts by weight of a rubber component composed of natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber, and one or more general-purpose rubbers.
A rubber composition for a tire bead filler having a dynamic elastic modulus of 45 MPa or more, which contains at least parts by weight of silica and does not contain a silane coupling agent which is usually used when silica is used as a filler.

The syndiotactic 1,2 is incorporated in the matrix of cis 1,4-polybutadiene used in the present invention.
-Syndiotactic 1,2-polybutadiene rubber in which polybutadiene is dispersed (hereinafter abbreviated as VCR)
For example, 1,3 butadiene is polymerized using an organoaluminum-cobalt compound-based 1,4 cis polymerization catalyst described in JP-A-5-194658, and then organic cobalt-
It can be produced by a method of completing the polymerization by adding an aluminum compound-based syndiotactic 1,2 polymerization catalyst, and a syndiotactic 1,2 content of 10 to 25% by weight is commonly called VCR and is commercially available. Things can be used.

As the silica, one having a weak acidity of 5 to 7 and a nitrogen adsorption specific surface area of 150 to 300 m ² / g is used.

[0008]

When the VCR content in the rubber component is less than 10% by weight, a dynamic elastic modulus of 45 MPa or more cannot be obtained, and 40% by weight
When it is more than that, the breaking property is inferior, which is not preferable. If the amount of silica compounded is less than 7 parts with respect to 100 parts by weight of the rubber component (hereinafter abbreviated as "parts"), the effect of improving fatigue resistance cannot be obtained. If the amount of carbon black is reduced or the amount of oil blended is increased to maintain the above value, a dynamic elastic modulus of 45 MPa or more cannot be obtained. It should be noted that silica having a pH of more than 7 or silica having a nitrogen adsorption specific surface area of less than 150 m ² / g has a small reinforcing property and therefore cannot increase the dynamic elastic modulus of the rubber composition.

Usually, when silica is used as a filler, mercaptopropyltrimethoxysilane and bis- are used for the purpose of strengthening the bond between silica and rubber to reduce heat generation.
An organosilicon compound such as (3 triethoxysilyl-propyl) -tetrasulfide, a so-called silane coupling agent is used in combination, but it is important not to use the silane coupling agent because it reduces fatigue resistance. In addition, it is not preferable to use so-called activators such as diethylene glycol and hexylamine.

[0010]

[Example] Using a test Banbury mixer, in addition to the amounts (parts) of the rubber component, silica, carbon black, and an oil-modified phenolic resin (Sumitomo Modres Co., trade name Sumilite Resin PR-13349) shown in Table 1, zinc. Hana 3 parts,
1 part of stearic acid, 5 parts of oil and 1 part of anti-aging agent (trade name Nocrac 6C manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added and mixed, and after molding into a sheet and cooling, 2 parts of sulfur and acceleration of vulcanization 1 part of the agent CBS and 1 part of hexamethylenetetramine were added and mixed again to obtain an unvulcanized rubber composition. These are press-heated at a temperature of 150 ° C. for 30 minutes using a predetermined mold, vulcanized and molded into a predetermined shape, and a dynamic elastic modulus and fatigue resistance test are performed according to the following methods, and the results are shown in Table 1. Show.

The dynamic modulus of elasticity was determined by using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. at a temperature of 30 ° C. and an elongation of 15%.
The measurement was performed under the condition of a frequency of 50 Hz. Fatigue resistance test, J
The measurement was performed according to the bending test method described in IS K6301, and is shown as an index based on Comparative Example 1.

[0012]

[Table 1]

Compared to Comparative Example 1, which is a conventional method of blending an oil-modified phenolic resin to increase the elastic modulus, each of the Examples has a large elastic modulus and excellent fatigue resistance. Comparative Example 2 is an example in which silica is used but VCR is not used, and Comparative Example 3 is an example in which VCR is used but silica is not used, both of which have the effect of improving the dynamic elastic modulus and fatigue resistance. small. Comparative Example 4 is an example in which a silane coupling agent is used and the elastic modulus is large, but the fatigue resistance is poor, and Comparative Example 5 is an example in which VCR and silica are not used but an oil-modified phenol resin is used in a large amount. The elastic modulus is increased, but the fatigue resistance is inferior. Comparative Example 6 is an example using more than 30 parts of silica and the processability is inferior, and the dynamic elastic modulus is low. Comparative Example 7 has a VCR of 40%.
This is an example in which the number is increased, and the tensile strength is inferior and not practical.

[0014]

[Effect of the Invention] When silica is used, by using VCR and silica together without using the silane coupling agent used, it is possible to increase the dynamic elastic modulus while improving fatigue resistance.

Claims (2)

[Claims] 1. A rubber composition for forming a bead filler having a substantially triangular cross section, which is filled in a space formed by a carcass ply of a pneumatic tire, a winding portion of the carcass ply, and a bead core. -Syndiotactic 1,2-polybutadiene in which syndiotactic 1,2-polybutadiene is dispersed in a matrix of polybutadiene
A rubber composition for a tire bead filler, which contains 7 to 30 parts by weight of silica based on 100 parts by weight of a rubber component containing 10 to 40% by weight of polybutadiene rubber and does not contain a silane coupling agent. . 2. The rubber composition for a tire bead filler according to claim 1, which has a dynamic elastic modulus of 45 MPa or more.