Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-11-18
2002-11-12
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S785000, C524S789000, C524S847000, C524S862000, C524S925000
Reexamination Certificate
active
06479582
ABSTRACT:
TECHNICAL FIELD
The present invention relates to rubber compositions suitable for uses such as tires and belts.
BACKGROUND ART
Generally, a part of a rotational force applied to a tire mounted on an automobile and the like is converted to heat energy through a rolling resistance, leading to energy loss. Accordingly, the increased rolling resistance during running results in the substantial increase in fuel consumption of automobiles. Also, exhaust gases therefrom add to the environmental pollution. For such reasons, the society strongly demands reduction in rolling resistance of tires which have been used worldwide in large volumes.
Among a variety of fillers used in rubber compositions, the most important and widely-used filler is carbon black. The carbon black is particularly excellent in its ability to reinforce rubbers. This makes it an essential filler for tires, belts and the like which require sufficient strength, abrasion resistance and fatigue resistance. Furthermore, the carbon black itself is semiconductive—conductive and thus effective to impart conductivity to the otherwise insulative rubber.
However, the character of carbon black that adheres strongly to rubber increases rolling resistance of tires. This has led to the recent investigations which use silica in stead of carbon black.
Rubbers exhibit improved resistance to oil and acid when containing silica as a filler than when containing carbon black only. It has been also recognized that the silica-containing rubbers show the reduced resistance to repeated deformation as a result of lower hysteresis when deformed. Therefore, the silica-containing rubbers, when used in tires, are said to show reduced rolling resistance, relative to the rubber containing carbon black, to result in the increased fuel-efficiency and the reduced occurrence to pollute the environment.
Notwithstanding the above, the use of silica has been found to impose various problems that result from its non-conductive nature, as contrary to carbon black, which fails to impart antistatic properties to insulative materials such as rubber. For example, a danger of spark ignition during refueling may exist if static electricity produced in an automobile is accumulated therein without being discharged through a road surface. There is another problem of radio interference, such as a radio noise, which may be caused by the influence of the produced static electricity.
Various attempts have been made to solve such problems. For example, an attempt has been made to reduce rolling resistance by using rubber materials having low glass transition points, such as natural rubbers and cis-polybutadiene rubber, or alternatively, by controlling the type, amount or the like of the carbon black and softener used. However, the former shows a tendency to result in the marked reduction in wet skid resistance while the latter to result in the reduction in abrasion resistance. It has been thus difficult to satisfy all conditions simultaneously.
The combined use of carbon black and silica has also been contemplated. For antistatic purposes, the volume specific resistance must be maintained at a value of not exceeding 10
8
&OHgr;.cm. This requires carbon black to be added to the composition in the amount of not lower than about 50% by weight. Such high loading of carbon black, while used in combination with silica, leads to the difficulty for silica to develop its characteristic properties, which is a problem.
Also, silica exists in various forms, e.g., contains water of crystallization or has a hydrophilic nature due to the presence of silanol groups at its particle surface, to thereby show poor “wettability” to rubber. This leads to its poor adhesion to rubber that may cause phase separation and the like to result in the reduction in strength and durability of the rubber composition.
In order to solve such silica-associated problems, a method is proposed which hydrophobates a silica filler surface by treatment with cold plasma (Japanese Patent Laid Open No. Sho 61-255945).
Also, an attempt has been made to modify surface properties of a silica filler by treating its surface with a mercapto silane coupling agent and the like.
Another attempt utilizes a combination of carbon black, silica and carbon fiber to form a conduction path (Japanese Patent Laid Open No. Hei 8-127674).
However, the above-described conventional methods have all suffered from the difficulty to simultaneously develop the respective benefits of carbon black and silica filler loaded in the rubber composition, because carbon black and silica filler have discrete surface properties and bonding strengths to rubber.
It is an object of the present invention to provide a rubber composition which can develop the respective benefits of carbon black and silica filler, which is excellent in strength, abrasion resistance and antistatic properties, and which exhibits low rolling resistance.
DISCLOSURE OF THE INVENTION
A rubber composition of the present invention is characterized as being rendered conductive by incorporating, into rubber, a silica filler having a conductive surface layer.
Due to the incorporation of the silica filler having a conductive surface layer, the rubber composition of the present invention has imparted thereto excellent strength, abrasion resistance and antistatic properties, as well as low rolling resistance.
A constitution of the rubber composition in accordance with the present invention is below explained in detail.
Rubber in the Rubber Composition
Examples of rubbers for use in the rubber composition of the present invention include natural and synthetic rubbers. Those natural and synthetic rubbers can be used alone or in combination.
Applicable natural rubbers include those generally used in the art. Modified rubbers, such as epoxidized natural rubbers, can also be employed for the natural rubber in the present invention.
Examples of synthetic rubbers include styrene-butadiene rubber, ethylene-propylene rubber, isoprene rubber, butadiene rubber, halogenated rubbers (chlorobutyl rubber, bromobutyl rubber and the like), silicone rubber, urethane rubber and the like. These may be used alone or in any combination of two or more types.
The above listing of specific rubbers is for exemplary purposes only, and is not intended to limit the present invention.
Silica Filler Having a Conductive Surface Layer
The silica filler having a conductive surface layer for use in the present invention may be a silica filler having on its surface a conductive layer, for example, composed of carbon or conductive tin oxide. The amount of conductive surface layer is preferably in the range of 0.1-50 parts by weight, more preferably 3-30 parts by weight, based on 100 parts by weight of the silica filler. If the amount of conductive surface layer is excessively small, sufficient conductivity may not be imparted to the rubber composition. On the other hand, if it is excessively large, the effect of addition of the silica filler to the rubber composition, i.e., the reduced rolling resistance, may not be obtained.
A blending proportion of the silica filler having a conductive surface layer (hereinafter referred to as “conductive silica filler”) to rubber is preferably in the range of 5-80% by weight, more preferably in the range of 20-70% by weight. If the blended proportion of the conductive silica filler is excessively small, sufficient conductivity may not be obtained for the composition. On the other hand, if the blended proportion of the conductive silica filler is excessively large, its effectiveness shows little increase while the composition's physical properties remain satisfied. The blending proportion is accordingly maintained within the above-specified range.
Representative examples of silica fillers for use in the present invention are hydrated silica and unhydrated silica. However, any substance which is comprised principally of silica (SiO
2
) moieties can be employed. The silica moieties need not be 100%.
The silica filler can be provided in various forms, such as particulate, amorphous, pl
Hareyama Yukiya
Ogawa Hidetoshi
Harlan R.
Olson & Hierl Ltd.
Otsuka Chemical Co. Ltd.
Wu David W.
LandOfFree
Rubber composition does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rubber composition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rubber composition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2953086