Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2003-03-31
2004-12-14
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S137000, C524S033000, C524S034000, C523S156000
Reexamination Certificate
active
06831146
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a resin composition for use in manufacturing wet friction materials, and a wet friction material manufactured using the resin composition.
2. Description of the Prior Art
In automatic transmissions of vehicles and the like, wet friction materials are used. Generally, such an automatic transmission is provided with a multi-plate clutch in which a plurality of friction plates having wet friction materials are arranged in an alternate relation with separator plates which serve as friction mating members. Each of the friction plates is formed by adhering wet friction materials to both surfaces of a metallic core plate. Each of the separator plates is formed from a single plate such as a metallic plate. The multi-plate clutch is operative in ATF (automatic transmission fluid) which is used as a lubricant to transmit power or cut off power transmission by engaging these friction plates and separator plates or releasing the engagement therebetween.
A typical example of such a wet friction material which is used in oil (ATF) is a paper-based wet friction material which is also called as a paper friction material. In general, such a paper-based wet friction material is manufactured as follows. First, a paper body is made in a wet method using natural pulp fibers, organic synthetic fibers, inorganic fibers, and the like as a fibrous base material, and diatomite, cashew gum, and the like as a filler and a friction adjusting material. Then, a binder made of a thermosetting resin is impregnated into the thus formed paper body, and the thermosetting resin-impregnated paper body is then cured by heating, to thereby obtain a paper-based wet friction material.
In such a paper-based wet friction material, a thermosetting resin which is impregnated into a paper body as a binder has a function of keeping the binding among the fibrous base material and the filler and the like. Moreover, the thermosetting resin affects the frictional properties and the durability of a resultant wet friction material. As for such a binder, an unmodified phenolic resin is commonly used since the use of such a resin enables a resultant wet friction material to have good heat resistance and compressive fatigue properties and high physical strength.
However, a wet friction material manufactured using such an unmodified phenolic resin as a binder involves the following problem. Namely, since an unmodified phenolic resin has a high cross-linking density when cured, a wet friction material manufactured using such a resin becomes too rigid and therefore such a wet friction material causes uneven abutment with a separator plate when used. Consequently, the friction coefficient of such a wet friction material is small in the initial stage of use, but is gradually increased as the wet friction material is being used because a frictional surface of the wet friction material gradually becomes even. That is, the initial rate of change in friction coefficient of such a wet friction material becomes necessarily large. As a result, an additional process for making the surface of a wet friction material even is required in manufacturing process so that the wet friction material can exhibit a predetermined friction coefficient from the initial stage of use.
In recent years, researches on modified phenolic resins have been actively conducted in order to overcome such a problem, and as a result, an oil modified phenolic resin, an epoxy modified phenolic resin, and the like which exhibit excellent flexibility have been developed, and they are practically used in some wet friction materials. However, a problem exists with such modified phenolic resins in that wet friction materials manufactured using such modified phenolic resins are inferior to wet friction materials manufactured using an unmodified phenolic resin in heat resistance and compressive fatigue properties. As of now, a modified phenolic resin capable of manufacturing wet friction materials having satisfactory durability has not yet been realized. In addition, such a wet friction material manufactured using a modified phenolic resin is liable to exhibit &Dgr;&mgr;-V characteristic (friction coefficient−velocity) with negative gradient, thus resulting in the case that shift shock is caused when used in a clutch. Consequently, a high demand exists for a wet friction material which exhibits a small initial rate of change in friction coefficient, a large positive gradient of &Dgr;&mgr;-V characteristic, and high durability.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a resin composition for use in manufacturing wet friction materials (hereinafter, simply referred to as a “resin composition for wet friction materials”) which enables a resultant wet friction material to exhibit a small initial rate of change in friction coefficient, a large positive gradient of &Dgr;&mgr;-V characteristic, and high durability.
Also, it is another object of the present invention to provide a wet friction material which exhibits a small initial rate of change in friction coefficient, a large positive gradient of &Dgr;&mgr;-V characteristic, and high durability.
In order to achieve the stated objects, the present invention is directed to a resin composition for wet friction materials, which comprises a phenolic resin contained as a major component, the phenolic resin being formed as a result of the reaction between phenols and aldehydes in the presence of a basic catalyst, and a particulate filler contained as an additive, the filler having a specific surface area of 35 to 410 m
2
/g.
It is preferred that the resin composition for wet friction materials of the present invention further comprises a coupling agent. Further, the coupling agent is preferably a silane coupling agent.
Also, it is preferred that the resin composition for wet friction materials of the present invention further comprises a surfactant.
In the present invention described above, it is preferred that the phenolic resin is obtained by reacting the phenols and the aldehydes in a mole ratio (aldehydes/phenols) of 0.8 to 1.6.
Further, the weight average molecular weight of the phenolic resin is preferably equal to or less than 1,000, and the water percentage of the phenolic resin is preferably equal to or higher than 200%.
Furthermore, it is also preferred that the particulate filler is formed from at least one selected from the group including metallic oxide, metallic carbide, and metallic nitride. Further, the metallic oxide is preferably silicon dioxide having a silanol group concentration of equal to or less than 3 SiOH
m
2
.
Moreover, an average particle size of a primary particle of the particulate filler is preferably within the range of 5 to 50 nm.
Moreover, it is preferred that the particulate filler includes particles of which surfaces are treated with at least one selected from the group including halogenated silanes, alkoxysilanes, silazanes, and siloxanes.
Moreover, the amount of addition of the particulate filler is preferably 0.5 to 10 wt % relative to the solid content of the phenolic resin.
Moreover, the median diameter of particles of the particulate filler dispersed in the resin composition for wet friction materials is preferably equal to or less than 20 &mgr;m.
Another aspect of the present invention is directed to a wet friction material which comprises a paper body, and a binder impregnated into the paper body, the binder being formed of the resin composition for wet friction materials as described above.
REFERENCES:
patent: 5529666 (1996-06-01), Yesnik
Aiba Hiroshi
Mori Masahiro
Harness & Dickey & Pierce P.L.C.
Sumitomo Bakelite Company Limited
Truong Duc
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