Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-08-28
2002-03-12
Hoke, Veronica P. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S218000, C524S242000, C524S449000, C524S450000, C524S493000, C524S494000, C152S905000
Reexamination Certificate
active
06355710
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rubber composition and a pneumatic tire produced by using the rubber composition and, more particularly, to a rubber composition which comprises, as a reinforcing filler, an inorganic filler comprising silica and/or silicate as the main component and exhibits improved fuel consumption, workability and productivity in vulcanization, and a pneumatic tire produced by using the rubber composition.
2. Description of the Related Arts
Heretofore, carbon black has been generally used as a reinforcing filler for rubber composition because carbon black can provide higher reinforcement and more excellent abrasion resistance than other fillers.
In recent years, energy consumption of automobiles must be decreased to achieve energy saving as the social requirement. To decrease heat buildup of a rubber composition for tires for this purpose, carbon black may be used in a smaller amount, or carbon black having a greater particle diameter may be used. It is known, however, that the reinforcing property, abrasion resistance and wet skid resistance inevitably deteriorate when any of the above methods is used.
As a filler which can achieve both of a smaller heat buildup and an improved wet skid resistance, hydrous silica (precipitated silica) has been known. The use of precipitated silica is described in many patent applications such as Japanese Patent Applications Laid-Open Nos. Heisei 3(1991)-252431, Heisei 6(1994)-248116, Heisei 7(1995)-70369, Heisei 7(1995)-188466, Heisei 7(1995)-196850, Heisei 8(1996)-225684, Heisei 8(1996)-245838 and Heisei 8(1996)-33687.
Particles of silica, however, tend to aggregate together through hydrogen bonding of a silanol group which is a functional group present on the surface of a silica particle and this phenomenon causes drawbacks. For example, it is necessary that the time for mixing be increased to improve dispersion of silica into rubber, Mooney viscosity of a rubber composition containing silica increases due to insufficient dispersion of silica into rubber, and workability in processing such as extrusion becomes poor.
Moreover, since the surface of a silica particle is acidic, basic substance used as a vulcanization accelerator is adsorbed on its surface. This causes an insufficient vulcanization which leads to an undesirably low modulus value.
To overcome the above problems, a silane coupling agent has been developed. Dispersion of silica into rubber still, however, remains insufficient and, in particular, it is difficult to achieve an industrially excellent dispersion of silica.
Under the above circumstances, the present inventors proposed a rubber composition comprising a specific tertiary amine in combination with silica (International Patent Publication No. 97-35461). In this rubber composition, dispersion of silica is improved, viscosity of unvulcanized rubber is low, heat buildup decreases and abrasion resistance is improved. The rubber composition is, however, not sufficiently satisfactory with respect to the scorching property and the vulcanization time.
It is known that retardation in vulcanization can be prevented by adding an activator such as polyethylene glycol, diethylene glycol, triethanolamine and a hydroxyl fatty acid salt of triethanolamine to a rubber composition containing silica. Scorching of the rubber composition, however, tends to take place when an activator is added, undesirable phenomenon such as deterioration in the workability takes place and, further, no improvement in low heat buildup property is observed.
SUMMARY OF THE INVENTION
The present invention has an object to provide a rubber composition which exhibits excellent dispersion of an inorganic filler containing at least one filler selected from silica and silicates as the main component and, as the result of the excellent dispersion, can achieve decreased viscosity of unvulcanized rubber, excellent workability, improved fuel consumption, a decreased time of vulcanization and improved productivity in vulcanization, and a pneumatic tire produced by using the rubber composition.
As the result of intensive studies by the present inventors to achieve the above object, it was found that the above object can be achieved by using a rubber composition comprising a specific addition salt of an amine and, optionally, a coupling agent in combination with an inorganic filler containing silica and/or silicate as the main component. The present invention has been completed based on the above knowledge.
The present invention provides:
(1) A rubber composition which comprises (A) at least one rubber component selected from the group consisting of natural rubber and diene synthetic rubbers, (B) an inorganic filler comprising at least one filler selected from the group consisting of silica and silicate as a main component, (C) an addition salt of an amine represented by general formula (I):
wherein R
1
represents a saturated or unsaturated alkyl group having 8 to 24 carbon atoms, an aryl group having 6 to 24 carbon atoms or an aralkyl group having 7 to 24 carbon atoms, R
2
and R
3
each independently represent hydrogen atom, a saturated or unsaturated alkyl group having 1 is to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms or a group represented by any of general formulae:
—(CH
2
O)
p
H, —(CH
2
CH
2
O)
p
H, —CH(CH
3
)CH
2
O)
p
H
and
—(CH
2
CH
2
CH
2
O)
p
H
wherein a total of p representing an integer of 1 to 4 when at least one of R
2
and R
3
represents any of above groups, and R
4
represents a saturated or unsaturated alkyl group having 6 to 24 carbon atoms, an aryl group having 6 to 24 carbon atoms or an aralkyl group having 7 to 24 carbon atoms, and, optionally, (D) a coupling agent in an amount of 1 to 20% by weight of component (B); and
(2) A pneumatic tire produced by using the above rubber composition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the rubber composition of the present invention, one or more of rubber selected from the group consisting of natural rubber and diene synthetic rubber is used as component (A). Examples of the diene synthetic rubbers include polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR) and butyl rubber (IIR) and halogenated butyl rubber.
Any of the natural rubber and the diene synthetic rubber of component (A) can be used singly or in combination of two or more.
In the composition of the present invention, an inorganic filler comprising silica and/or silicate as the main component is used as component (B).
The type of the above inorganic filler is not particularly limited. Examples of the inorganic filler include precipitated silica, fumed silica, aluminum silicate such as kaolin and clay, magnesium silicate, calcium silicate and aluminum hydroxide. Among these inorganic fillers, precipitated silica is preferable. It is preferable that the inorganic filler comprising silica and/or silicate as the main component has a specific surface area in the range of 80 to 300 m
2
/g as measured in accordance with the mercury porosimetry method. Due to the specific surface area in the range of 80 to 300 m
2
/g, dispersion of the inorganic filler into the rubber is improved and the rubber composition can exhibit excellent workability and abrasion resistance. From the standpoint of the balance between the reinforcing property, workability and abrasion resistance, it is more preferable that the specific surface area is in the range of 100 to 250 m
2
/g. The specific surface area S
Hg
is calculated in accordance with the following equation: S
Hg
(m
2
/g)=2V/r, wherein pores are considered to be cylinders, V(m
3
/g) represents the total volume of the pores and r(m) represents the average diameter of the pores.
In the rubber composition of the present invention, it is preferable that the content of the inorganic filler comprising silica and/or silicate as the main component of component (B) is in the range of 10 to
Nishi Isao
Takano Tetsuo
Tsuchihashi Masaaki
Yanagisawa Kazuhiro
Bridgestone Corporation
Hoke Veronica P.
Sughrue & Mion, PLLC
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