Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1999-11-16
2001-07-24
Weisberger, Richard (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S375000, C428S391000, C524S014000, C524S015000, C524S016000, C524S492000, C524S430000, C523S149000, C523S209000, C523S216000
Reexamination Certificate
active
06265066
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a wet friction material to be mounted in an oil-immersed frictional engagement apparatus such as clutch and brake in the automatic transmission of vehicles such as automobile.
DESCRIPTION OF THE INVENTION
An automatic transmission for vehicles such as automobile normally comprises a multi-plate clutch having a plurality of friction plates each having a metallic substrate (core plate) provided with a wet friction material thereon and separator plates each formed by a single metallic plate or the like as opposite friction material alternately arranged. In operation, these plates are pressed against or released from each other in ATF (automatic transmission fluid) as a lubricant to transmit or cut driving power.
As the wet friction material to be incorporated in such an oil-immersed frictional engagement apparatus there may be normally used a paper-based wet friction material called “paper friction material”. This wet friction material is normally obtained by subjecting a fibrous base such as natural pulp fiber, organic synthetic fiber and inorganic fiber, a filler such as diatomaceous earth and cashew resin and a friction adjuster to wet paper making, impregnating the paper material thus obtained with a resin binder made of a thermosetting resin, and then heat-curing the material.
In the foregoing paper-based wet friction material, the thermosetting resin with which the paper material is impregnated as a resin binder not only plays a role of binding the fiber base and the filler but also exerts a great effect on the friction characteristics and abrasion resistance of the wet friction material. As such a resin binder there has heretofore been mainly used an unmodified phenolic resin, which exhibits an excellent heat resistance, a high mechanical strength and a relatively good abrasion resistance.
In recent years, the automobile industry is striving for the reduction of weight of various necessary parts and the enhancement of efficiency in quest of energy saving and weight reduction. On the other hand, the trend is for more automobile engines to be designed to operate at a higher speed and a higher output. Also in automobile transmission, it has been desired to improve the friction coefficient, heat resistance and durability of the wet friction material to keep up with the reduction of size and weight of frictional engagement apparatus and the enhancement of rotary speed and output of automobile engine. Further, the conventional wet friction material comprising an unmodified phenolic resin incorporated therein as a binder is disadvantageous in that it has a high crosslinking density. Thus, in the initial stage of operation, the conventional friction material exhibits a small friction coefficient due to local contact. Accordingly, as the operation proceeds, the friction surface is getting itself adapted to the opposite friction surface to show an increasing friction coefficient. As a result, the conventional wet friction material suffers; a drastic initial variation of friction coefficient. Moreover, under high temperature and humidity conditions, the conventional wet friction material suffers from seizing on the friction surface due to high temperature called heat spot on the opposite friction material (separator plate). Finally, the conventional wet friction material lacks prolonged stability of friction characteristics. Therefore, the conventional wet friction material leaves something to be desired.
In order to overcome these disadvantages, phenolic resins modified with various resins and resins other than phenolic resin such as silicone resins have been studied. Among these resins, silicone resins which have heretofore been studied are mainly composed of organochlorosilanes. These silicone resins exhibit an excellent heat resistance and durability due to siloxane bond in main skeleton. In addition, these silicone resins are available in a wide range of characteristics from flexible to rigid depending on the crosslinking density determined by the formulation and design of organosiloxanes as starting material. These silicone resins are excellent substitutes for phenolic resins as a binder for wet friction material. However, since these silicone resins normally undergo curing reaction at temperatures of as high as not lower than 200° C., they are not necessarily satisfactory from the standpoint of productivity and hence energy saving as compared with phenolic resins, which can be cured at a temperature of about 150° C. to 180° C. Thus, these silicone resins have never been put in practical use.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a wet friction material which exhibits an excellent heat resistance and durability, a high friction coefficient, a small initial variation of friction coefficient and an excellent heat spot resistance and can be cured at a relatively low temperature to make a great contribution to the enhancement of productivity and hence energy saving.
In order to solve the foregoing problems, the inventors made extensive studies of a hydrolytic solution of a silicon alkoxide. As a result, it was found that a hydrolytic solution of a silicon alkoxide not only exhibits the same excellent properties as the foregoing silicone resin but also can be cured at a relatively low temperature. In other words, it was found that a wet friction material comprising a fibrous base such as natural pulp fiber, organic synthetic fiber and inorganic fiber, a filler such as diatomaceous earth and cashew resin, a friction adjuster and a binder, the binder being a product of hardening of a hydrolytic solution of a silicon alkoxide, not only exhibits an excellent heat resistance and durability and a high friction coefficient but also can be cured at a relatively low temperature in the production process, thus attaining a far higher productivity than the conventional phenolic resin or the foregoing silicone resin. The present invention has thus been worked out.
Accordingly, the wet friction material according to the present invention comprises a fibrous base, a filler, a friction adjuster and a binder, wherein the binder is a product of hardening of a hydrolytic solution of a silicon alkoxide.
In the hydrolytic solution of a silicon alkoxide, the silicon alkoxide comprises tetrafunctional monomers or lower condensates thereof, singly or in admixture. In the hydrolytic solution of a silicon alkoxide, water is present in an amount of not less than the number of mols of silicon alkoxide and half the functional groups in silicon alkoxide is present in an amount of not more than hydrolyzable. Further, the hydrolytic solution of a silicon alkoxide is preferably adjusted acidic.
REFERENCES:
patent: 5563196 (1996-10-01), Kitahara et al.
patent: 5972090 (1999-10-01), Bremsblelage et al.
patent: 6060536 (2000-05-01), Matsumoto et al.
Mori Masahiro
Suzuki Makoto
Yagi Hirokazu
NSK-Warner Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
Weisberger Richard
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