JP2003118310A - Tire side wall and its rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire side wall excellent in thermal conductivity, in an extrusion characteristic and in electroconductivity. SOLUTION: This rubber composition for the tire side wall constitutes its characteristic feature of containing acetylene black Lc of which is 20-50 Åand DBP absorption of which is 150-400 cm<3> /100 g in diene rubber, butyl rubber and/or olefinic rubber. In this case, acetylene black and furnace black are doubly used, and it is favorable that acetylene black is replaced with furnace black of less than 4 mass multiplying quantity of acetylene black. Additionally, this tire side wall constitutes its characteristics feature of being made of a compact body of this rubber composite for the tire side wall.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a tire sidewall containing acetylene black and a rubber composition thereof.

[0002]

2. Description of the Related Art Pneumatic tires are required to have a strength capable of withstanding external forces due to weight and ground contact rotation, appropriate rigidity, air leakage, and heat dissipation, and the inside of the tire has a complicated structure. . Natural rubber, styrene-butadiene rubber, etc. generally used in rubber compositions for tires are
Carbon black is blended in order to impart these characteristics because the reinforcing property, the conductivity, etc. are insufficient by itself. Furnace black is used as the carbon black, and FEF (Fast Extruding) is taken into consideration, especially in consideration of maintaining flexibility of rubber and workability of extrusion.
Furnace), SRF (Semi Reinfor)
Cing Furnace), GPF (General
Soft carbon such as Purpose Furnace) is used.

[0003]

In recent years, various proposals have been made for tire improvement in consideration of the environment and pursuit of safety.

The sidewall portion has a function of supporting the vehicle weight on the side surface of the tire, is a portion to which the maximum external pressure is applied during traveling, and is formed of a thick rubber layer in order to provide reinforcement. A run-flat tire that improves the load-carrying capacity of the sidewall by increasing the thickness of the sidewall and can run a certain distance at a predetermined speed even if the tire is flat and the air pressure is lost (for example, Japanese Patent Publication No. 7-108610, Japanese Patent Application Laid-Open No. 5-31001.
3 and JP-A-2-283508).

However, in the tire manufacturing process, generally, when the rubber plate is heated from both sides, if the thickness doubles, the time required for the central portion of the thickness of the rubber plate to reach the same temperature as the outside is four times as long. It is said that the vulcanization time of thick sidewalls is large. Since the unvulcanized rubber has a poor thermal conductivity, the temperature rise is slow, and the time required for vulcanization molding is 15 to 20 minutes for a passenger car tire and 45 to 60 minutes for a large tire such as a truck. Long vulcanization times result in increased energy consumption as well as different vulcanization conditions in the intricately entangled layer regions of the tire. Therefore, for example, excessive vulcanization of the tire surface layer causes excessive heat generation during operation or deterioration of tire characteristics such as large rolling resistance.

In order to solve such a problem, a method of reducing the vulcanization load of the surface layer portion by gradually vulcanizing in the tire vulcanizing step can be considered, but it is manufactured according to a conventional tire assembling method. The total energy consumption will be longer than in the case of tire vulcanization. Further, Japanese Patent Application Laid-Open No. 10-329232 proposes a method of increasing the thermal conductivity and shortening the vulcanization time by vulcanizing a tire or a part thereof in a deaerated state. However, not only must a special kneading device having a degassing function be used, but special consideration must be taken to prevent gas absorption even in the degassed kneaded product.

Also in the extrusion characteristics when the furnace black is filled, the dispersibility is poor because the structure is undeveloped, and the stable operation is hindered due to variations in extrusion energy and temperature during extrusion, and during rubber vulcanization. It may cause uneven vulcanization. Soft carbon having relatively good extrusion characteristics is used for the sidewall, but there is still room for improvement.

On the other hand, it is known that when silica is used as a reinforcing agent in the tread portion, both low rolling resistance performance and wet skid resistance performance are improved at the same time. But,
From the idea that the tread portion alone is still insufficient, it has been proposed to incorporate silica into the sidewall portion (for example, Japanese Patent Laid-Open No. 10-36559).

However, when silica is blended, there is a problem that static electricity easily accumulates in the vehicle because silica is electrically insulating, and there is a risk that sparks will be generated when trying to open the lid of the fuel tank, for example. Therefore, it may cause radio wave interference such as radio noise while driving. In the case of general tires, such static electricity problem can be solved by compounding furnace black, but when silica is further compounded, since silica is an insulator, only compounding of furnace black is necessary. I couldn't solve it enough.

An object of the present invention is to easily provide a tire sidewall excellent in thermal conductivity, extrusion characteristics and conductivity and a rubber composition thereof in order to solve the above problems.

[0011]

That is, the present invention provides L
c is 20 ~ 50Å, DBP absorption is 150 ~ 400cm
³ / 100g of acetylene black was added to diene rubber,
A rubber composition for a tire sidewall, which is contained in butyl rubber and / or olefin rubber. In this case, it is preferable that acetylene black and furnace black are used in combination, and the acetylene black is replaced by furnace black in an amount of 4 mass times or less the amount of acetylene black. Also,
The present invention is a tire sidewall comprising a molded product of the rubber composition for a tire sidewall.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below.

The acetylene black used in the present invention has a Lc of 20 to 50Å and a DBP absorption of 150 to 400.
cm ³ / 100g belongs to.

Lc is an average thickness of a graphite crystal structure in which planes of carbon mesh are layered, and the larger Lc, the more developed the crystal structure. The thermal conductivity of the rubber composition containing carbon black is greatly influenced by the carbon black crystal structure, and in the acetylene black of the present invention, when Lc is less than 20Å, the crystallinity is the same as that of furnace black generally used. Therefore, even if a sidewall is formed using this, the thermal conductivity is not improved. Further, when Lc exceeds 50Å, the thermal conductivity of the rubber molded body tends to be improved due to the development of crystals, but the interaction between acetylene black and the rubber is reduced, so that the dispersibility is reduced and the thermal conductivity is reduced. Not only will there be variations, but the reinforcement will also be reduced.

The DBP absorption of acetylene black is an indicator of the degree of structure development, dispersibility,
Contributes to conductivity. DBP absorption 150cm ^3/10
If it is less than 0 g, a sufficient reinforcing effect of the rubber molded article cannot be obtained, the dispersibility is lowered and the extrusion processability is deteriorated. Also,
The conductivity is also poor because the formation of the conductive path is not sufficient. DB
If P absorption exceeds 400 cm ^3/100 g, when compounded to the rubber, very large shearing force is required, which causes only either heating value increases and the rubber deterioration deteriorated extrusion processability .

The acetylene black used in the present invention can be produced by controlling the temperature, atmosphere and residence time by a pyrolysis reaction method of hydrocarbons and / or an incomplete combustion method.

The rubber component filled with the acetylene black according to the present invention is one or more selected from diene rubber, butyl rubber and olefin rubber. Examples of the diene rubber include natural rubber, styrene / butadiene rubber, butadiene rubber, acrylonitrile / butadiene rubber, chloroprene rubber, isoprene rubber, ethylene / propylene / diene terpolymer, and the like, and butyl rubber. In addition to ordinary butyl rubber, there are halogenated butyl rubber such as chlorinated butyl rubber and brominated butyl rubber, and the olefin rubber includes ethylene / propylene rubber and the like.

To give an example of the composition, acetylene black 5 to 5 parts with respect to 100 parts of the rubber component (parts by mass, hereinafter the same).
60 parts, in many cases 5 parts zinc oxide, 2 to 5 parts vulcanizing agent and vulcanization accelerator, 10 parts process oil, a small amount of conventional additives such as processing aids and antioxidants. Be compounded. When silica powder is blended, 7 parts or less of a silane coupling agent is blended. The blending amount of silica powder is usually 60 parts or less. In addition to the above main components, other rubber / resin components and / or various fillers may be added for the purpose of imparting reinforcing properties, fluidity, processability, and the like.

In addition to the acetylene black used in the present invention, the above-mentioned acetylene black can be used by mixing a commonly used furnace black to the extent that the characteristics are not impaired. When an appropriate amount of furnace black is mixed, the effect of suppressing bending fatigue is increased while maintaining the characteristics of acetylene black, and the durability of the tire due to riding on a curb can be further enhanced. The proportion of the furnace black used in combination is preferably 4 mass times or less of the acetylene black, and the acetylene black is replaced with the furnace black.

As a method of manufacturing the sidewall, a known method incorporated in a series of tire manufacturing steps can be applied. In summary, various rubbers and carbon black, other fillers, process oils, processing aids, etc. are kneaded with a Banbury mixer in the "mixing step", and the sidewalls and other parts are separately separated in the "member processing step". To process. Subsequently, in the "molding process", each part including the sidewall is assembled into one tire by a molding machine, and in the "vulcanization process", it is sandwiched with a heated mold and bladder and vulcanized to complete the tire production. The physical properties of the sidewall can be grasped by kneading with the above composition, evaluating the extrusion characteristics thereof, and evaluating the characteristics of the vulcanized rubber sheet.

In order to reinforce a part of the side wall of the present invention, a rubber composition other than the rubber composition of the present invention, for example, a rubber composition such as a diene rubber containing carbon fibers is used. , That part can also be configured.

[0022]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

Examples 1 to 5 Comparative Examples 1 and 2 "FX-35" and "AB granules" manufactured by Denki Kagaku Kogyo Co., Ltd. were used as acetylene blacks of Examples, and "Seast" manufactured by Tokai Carbon Co., Ltd. was used as a furnace black of Comparative Examples. SO "
Using (FEF) (the physical properties thereof are shown in Table 1), a rubber molded body was manufactured with a composition of sidewall specifications. That is, each material was mixed with a Banbury mixer at 120 ° C. with the composition shown in Table 2, and precision kneading was performed using an 8-inch roll. After one day, rolling was performed to evaluate the extrusion characteristics. Subsequently, vulcanization was performed at 160 ° C. for 15 minutes to prepare a vulcanized rubber sheet, and the extrusion characteristics and vulcanized product characteristics were evaluated according to the following. The results are shown in Table 2.

(1) Extrusion Characteristics The extrusion test was carried out by a single screw extruder (L / D (59.
76 mm) = 16). The extrusion conditions are as follows: screw rotation speed 50 rpm; temperature: screw side (50
(° C) -head (80 ° C) -base (80 ° C), and extrudability (extrusion length, die swell) was evaluated using a Garvey die. In addition, the shape of the extrudate conforms to ASTM D-2230, and the evaluation points (maximum 16 points: die expansion and foaming,
The state of the edge, the surface smoothness, the state of the corner, and a maximum of 4 points each) are shown.

(2) Properties of vulcanizate (a) In order to evaluate the reinforcing effect of the rubber sheet with normal physical properties, T
B (breaking strength), EB (elongation), HS (hardness), TR
(Tear strength) was measured. <TB and EB> JIS K 6251 <HS> JIS K 6253 <TR> JIS K 6252 (b) Thermal conductivity The specific heat, density and thermal diffusivity were measured according to the following formulas,
The thermal conductivity was calculated by the formula: specific heat x density x thermal diffusivity. <Specific heat> DSC scanning method (Seiko Denshi DSC200). Sample weight: 30 mg, standard sample: α-Al ₂ O ₃ (30 m
g) Measurement temperature: 300K <Density> Archimedes method (weight method in water). Density = dry mass / (dry mass-mass in water) <Thermal diffusivity> Laser flash method (“LF manufactured by Rigaku Corporation”
/ TCM FA8510B ”). (C) Akron wear resistance The Akron wear resistance was measured according to JIS K 6264. (D) A 20 mm × 100 mm × 2 mm sample was cut out from the volume resistivity rubber sheet and measured according to SRIS2301.

The Lc and DBP absorption of carbon black were measured as follows. (3) From the diffraction line of the (002) plane in the X-ray diffraction method using the Lc Cu-Kα ray, the equation, Lc (Å) = (180 · K · λ) /
(Π · β · COSθ). However, K =
Form factor 0.9, λ = wavelength of X-ray (1.54Å), θ =
The angle showing the maximum value in the (002) diffraction line absorption band, and the half value width in β = (002) diffraction line absorption band are shown in angles.

(4) DBP Absorption The DBP absorption was measured according to JIS K6217.

[0028]

[Table 1]

[0029]

[Table 2]

From Tables 1 and 2, the rubber composition for tire sidewall manufactured in Example 1 is excellent in both extrusion characteristics and vulcanizate characteristics as compared with Comparative Example 1 although the filling amount is small. Was there. Therefore, the good extrudability can improve the workability at the time of forming the sidewall. It was also shown that the physical properties in normal state and the abrasion resistance of Akron are good, and the strength of the sidewall can be secured. Good thermal conductivity leads to shortening of vulcanization time and reduction of uneven vulcanization.

Also in Example 2, the extrudability was good, the conductivity was high, and the physical properties in the normal state and the abrasion resistance of Akron were comparable.

Even when a part of the acetylene black was replaced with a general furnace black for a sidewall (FEF: "SEAST SO") (Examples 3 to 4), good characteristics were obtained. This rubber composition for tire sidewalls is more effective in suppressing bending fatigue than using acetylene black alone, and is expected to further improve the durability of the tire due to riding on a curb.

Further, also in the rubber composition for tire sidewalls (Example 5) containing silica, Comparative Example 2
Compared with, it showed good characteristics. It can be seen that since it is also excellent in conductivity, it becomes a silica-containing sidewall that is excellent in eliminating static electricity.

[0034]

According to the present invention, thermal conductivity, extrusion characteristics,
A tire sidewall having excellent conductivity is provided. The rubber composition for a tire sidewall used in the present invention can be applied to the production of each part of the tire by utilizing the properties such as thermal conductivity, extrusion characteristics, and conductivity in addition to the sidewall of the present invention. .

Continued front page    (72) Inventor Hiroshi Kurosaka             2209 Aomi, Aomi-cho, Nishikubiki-gun, Niigata Prefecture             Chemical Industry Co., Ltd.

Claims (3)

[Claims] 1. Lc is 20 to 50 Å and DBP absorption is 1
50~400cm ³ / 100g acetylene black, diene rubber, butyl rubber and / or olefinic tire sidewall rubber composition characterized by formed by incorporating in the rubber. 2. The rubber composition for a tire sidewall according to claim 1, wherein the acetylene black is replaced with furnace black in an amount not more than 4 times its mass. 3. A tire sidewall comprising a molded product of the rubber composition for a tire sidewall according to claim 1 or 2.