Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1997-06-26
2001-09-04
Morris, Terrel (Department: 1771)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S153000, C523S155000, C524S035000, C524S445000, C106S036000
Reexamination Certificate
active
06284815
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to non-asbestos friction materials suitable for use in disc brake pads, drum brake linings, clutch facings, brake blocks and the like for industrial machinery, railway vehicles, commercial vehicles, and automobiles.
BACKGROUND OF THE INVENTION
Friction materials (disc brake pads, drum brake linings, clutch facings, etc.) for brakes and clutches generally contain a fibrous reinforcement such as organic fibers, inorganic fibers, metal fibers, etc., a thermosetting resin binder such as a phenolic resin, etc., and a filler such as a friction modifier (resin dust, rubber dust or the like), a solid lubricant (graphite, molybdenum disulfide and the like), etc., as the main components.
As the fibrous reinforcement, asbestos was conventionally used for such friction materials for a long time. However, asbestos, which is a carcinogenic substance presents safety and health problems during both manufacture and use. Under these circumstances, non-asbestos friction materials without asbestos have been widely used. In such non-asbestos friction materials, as the fibrous reinforcement, fibrillated aramid fibers (aramid pulp) or a combination of the aramid fibers and glass fibers have been widely used.
Fibrillated aramid fibers have the features that they have a light weight and a high strength as compared with metal fibers, etc., and have a high heat resistance in spite of organic fibers. However, because the aramid fibers are generally expensive, there is a problem that the friction materials using the aramid fibers have a large disadvantage in cost as compared with asbestos series friction materials. Accordingly, there is a need for non-asbestos friction materials having the same performance in heat resistance, mechanical strength, etc., as the friction material with the aramid fibers. But non-asbestos friction materials satisfying all of thermal and mechanical strength, effectiveness, fade characteristics, friction characteristics, etc., and cost have not yet been developed.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a friction material which is excellent in fade characteristics, stability of effectiveness, etc., and low in cost.
As the result of various investigations for achieving the above-described object, the inventors have discovered that the above-described object can be achieved by using at least sepiolite fibers, cellulose fibers, and an acryl pulp in combination as the fibrous reinforcement
That is, according to the first aspect of the present invention, there is provided a non-asbestos friction material comprising a non-asbestos fibrous reinforcement, a thermosetting resin binder, and a filler as the main components, wherein the fibrous reinforcement is a combination of plural kinds of non-asbestos fibers and contains at least sepiolite fibers, cellulose fibers, and an acryl pulp as the fibrous reinforcement.
Also, according to the second aspect of the present invention, there is provided the above-described non-asbestos friction material of this invention containing from 1 to 20% by weight of the sepiolite fibers, from 1 to 25% by weight of the cellulose fibers, and from 1 to 10% by weight of the acryl pulp to the total amount of the friction material.
Furthermore, according to the third aspect of the present invention, there is provided the above-described non-asbestos friction material, wherein the weight ratio of the sepiolite fibers/the cellulose fibers is from 1/1 to 1/3.
Moreover, according to the fourth aspect of the present invention, there is provided the above-described non-asbestos friction material, wherein the friction material contains aramid fibers in an amount of not more than 5% by weight to the total amount of the friction material and in particular, does not substantially contain aramid fibers.
Also, according to a fifth aspect of the present invention, there is provided the above-described non-asbestos friction material containing from 5 to 40% by weight of the non-asbestos fibrous reinforcement, from 5 to 20% by weight. of the thermosetting resin binder, and from 30 to 80% by weight of the filler.
The friction material of the present invention can maintain the same strength, heat resistance, effectiveness, fade characteristics, abrasion characteristics, etc., as the non-asbestos friction material containing a large amount of aramid fibers even by reducing the using ratio of the aramid fibers by using a combination of the sepiolite fibers, the cellulose fibers, and the acryl pulp as the fibrous reinforcement.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The friction material of the present invention is a non-asbestos friction material using non-asbestos fibers as the fibrous reinforcement, thermosetting resin binder, and filler as the main components.
In the present invention, the fibrous reinforcement is a combination of plural kinds of non-asbestos fibers and contains at least sepiolite fibers, cellulose fibers, and an acryl pulp as the fibrous reinforcement.
Sepiolite is a natural fibrous clay mineral, the main component is hydrous magnesium silicate, and also sepiolite further contains calcium oxide, magnesium oxide, aluminum oxide, silicon dioxide, iron oxide, etc., together with free water. The cross section of the single fiber of sepiolite has a crystal structure of alternatively accumulating talc and has a high adsorption effect owing to numberless fine pores existing in the fibers. Also, sepiolite has a thixotropy and when sepiolite is strongly stirred in water or a resin, it shows a thickening effect. Also, when the shearing force is large, it becomes a low viscosity, while when the shearing force is small, it becomes a high viscosity. Furthermore, when sepiolite is granulated with water and dried, solid particles are obtained and when the solid particles are heated, they become a ceramic-like material while gradually dehydrating and show a plasticity as kaolin. As the sepiolite fibers used in the present invention, it is preferred that the average fiber length thereof is from 30 to 50 &mgr;m and the average fiber diameter is from 0.1 to 0.4 &mgr;m.
There are no particular restrictions on the average fiber length and the average fiber diameter of the cellulose fibers used in the present invention but the average fiber length is preferably from 2 to 10 mm, and particularly preferably from 4.5 to 6.5 mm and the average fiber diameter is preferably from 10 to 100 &mgr;m, and particularly preferably from 30 to 40 &mgr;m. Such cellulose fibers are produced, for example, by a viscose method from a pulp.
The acryl pulp used in the present invention can be obtained from, as the raw material, acrylic fibers generally known as fibers for clothing, by fibrillating the acrylic fibers with a beater for paper manufacture, such as, for example, disc refiner, etc. Also, an acryl pulp having fibers which have almost parallel straw-form voids along the length direction of the fibers as trunks in the fibers, wherein many fine whisker-like filaments are branched from the trunks and said trunks are split in the length direction of the trunks to form plural fibers can be used.
Such acrylic fibers are made up of an acrylic copolymer composed of at least 60% by weight acrylonitrile and not more than 40% by weight an ethylenic monomer copolymerizable with acrylonitrile or a mixture of two or more kinds of such acrylic copolymers.
The ethylenic monomer copolymerizable with acrylonitrile includes, for example, acrylic acid or methacrylic acid and the esters thereof (such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, etc.), vinyl acetate, vinyl chloride, vinylidene chloride, acrylamide, methacrylamide, methacrylonitrile, allylsulfonic acid, methallylsulfonic acid, and styrenesulfonic acid.
There is no particular restriction on the freeness of the acryl pulp used in this invention, said freeness being the index of showing the extent of beating pulp in the paper manufacturing industry and the freeness can be properly se
Sasahara Shigemi
Watanabe Takayuki
Akebono Brake Industry Co. Ltd.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Guarriello John J.
Morris Terrel
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