Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-12-14
2003-12-30
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S152000, C260S998130
Reexamination Certificate
active
06670408
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a friction material, particularly relates to a friction material for an industrial machine, a railway vehicle, a baggage car, a passenger car, or the like, and more particularly relates to a friction material in a brake pad, a brake lining, a clutch facing, or the like, for the above-mentioned applications.
2. Description of the Related Art
In a friction material to be used mainly in a brake pad or the like, a fibrous reinforcement is used as one of materials for enhancing the strength of the friction material. Fibrous reinforcements used in place of asbestos fiber include glass fiber, steel fiber, Aramid fiber, potassium titanate fiber, etc. Since these fibrous reinforcements have their own properties respectively, a mixture of several kinds of them is used.
Of these fibrous reinforcements, potassium titanate fiber is rated highly, as abrasive hard inorganic fiber, in the point that not only can it improve the strength, the heat resistance and the wear resistance of the friction material as a whole, but also it can enhance the friction coefficient of the friction material through its abrasive property, and particularly it can ensure a high friction coefficient at the time of a high load such as high-speed braking or the like.
For example, as such background-art friction materials using potassium titanate fiber as a fibrous reinforcement, there are: a friction material in which one or more kinds of potassium titanate fibers with purity of 98% or higher are mixed (JP-B2-2767504, hereinafter referred to as “Background Art 1”); a friction material in which potassium titanate fiber having a sectional diameter in a range between 5 &mgr;m and 10 &mgr;m and having an aspect ratio in a range between 3 and 7 is mixed (JP-B2-2816906, equivalent to JP-A-5-139808, hereinafter referred to as “Background Art 2”); and a friction material in which two kinds of potassium titanate fibers different in fiber length and fiber diameter are mixed (JP-B2-2879364, hereinafter referred to as “Background Art 3”).
An object of the Background Art 1 is to make the purity of potassium titanate fiber high enough to give the fiber a high melting point and a high thermal conductivity so as to obtain an effect of conspicuously enhancing the friction coefficient and the wear resistance in a high temperature range. An object of the Background Art 2 is to use potassium titanate fiber having a specific fiber diameter and a specific aspect ratio so as to obtain a friction material having stable wear resistance, that is, so as to obtain a friction material having excellent wear resistance from a low temperature range to a high temperature range and a stable friction coefficient against a temperature change.
On the other hand, an object of the Background Art 3 is to obtain a friction material in which the friction noise performance and the high-temperature wear resistance are superior and the friction performance is also excellent. The Background Art 3 discloses that, by using two kinds of potassium titanate fibers, the face-to-face aggressiveness is reduced, the friction performance is stabilized from low temperature to high temperature, and the friction noise performance is enhanced.
In the Background Art 3, however, potassium titanate fibers which are very different in fiber length and fiber diameter are required to be used. That is, one kind of fiber has a fiber length of 0.1 to 3 mm and a fiber diameter of 10 to 60 &mgr;m while the other kind of fiber has a fiber length of 10 to 30 &mgr;m and a fiber diameter of 0.2 to 0.5 &mgr;m. Accordingly, there is a problem that it is difficult to uniformly mix and disperse fine needle-like fiber and comparatively bulky flake-like polycrystal fiber, and hence the manufacturing cost of the friction material is increased.
As described above, in the background-art friction material having potassium titanate fiber mixed, there is a problem that the friction noise property and the abnormal noise property are not taken into consideration at all, or even if attention is paid to the improvement of these properties, the manufacturing cost is expensive.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a friction material in which the friction noise property and the abnormal noise property can be improved only by using potassium titanate fibers which have hitherto existed on the market and which are different only in chemical composition, without necessity of using fibers which are so different in fiber diameter and fiber length that they are difficult to be mixed or dispersed uniformly.
In order to solve the foregoing problem, the present inventors carried out various researches about materials and forms of inorganic fibers using no potassium titanate fibers which were manufactured in different techniques so as to have different fiber diameters and lengths and which were high in manufacturing cost, but nevertheless giving a friction material a friction noise property, a wear resistance and an friction performance which were equal to those in the case of using the above-mentioned inorganic fibers.
Thus, taking it into consideration that, when potassium titanate fibers different in composition were used together, a friction material could be obtained to have a friction noise property, a wear resistance property and an friction performance which are similar to those in the case of using potassium titanate fibers which are different in fiber diameter and fiber length.
That is, the present invention solved the foregoing problem by the following friction materials.
(1) A friction material comprising a fibrous reinforcement, a friction modifier and a binder, wherein at least potassium hexatitanate fiber and potassium octatitanate fiber are used together as the fibrous reinforcement and mixed at a ratio in a range of from 2 wt % to 40 wt % of the whole of the friction material as total amount.
(2) A friction material according to (1), wherein a mixing ratio of the potassium hexatitanate fiber to the potassium octatitanate fiber is in a range between 1:4 and 4:1 by weight percentage.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A friction material is composed of a fibrous reinforcement, a friction modifier, a binder, etc. According to the present invention, as a fibrous reinforcement, asbestos is not used but two kinds of potassium titanate fibers different in composition are used.
The potassium titanate fibers to be used in the present invention may be manufactured without requiring any industrial purified titanium oxide having high purity as titanium oxide for starting material, but may be manufactured with titanium oxide having general industrial purity in the condition and process of a firing method, a KDC method, a fluxing method, a melting method, or the like. The chemical compositions of the potassium titanate fibers include potassium octatitanate (K
2
O.8TiO
2
), potassium hexatitanate (K
2
O.6TiO
2
), potassium tetratitanate (K
2
O.4TiO
2
), and so on. Particularly, it is preferable to use the former two with together.
The sizes of the potassium titanate fibers are not limited specifically. Polycrystal fibers of various sizes (the fiber sizes can be adjusted in a comparatively wide range through a treatment process and conditions after heating and melting) manufactured by the aforementioned melting method may be used together suitably. For example, comparatively large-size fibers having a sectional diameter of about 20 to 50 &mgr;m and a length of about 100 to 300 &mgr;m, or comparatively small-size fibers having a sectional diameter of about 5 to 10 &mgr;m and a length of about 15 to 100 &mgr;m may be used together.
The total amount of the above-mentioned two kinds of fibers in the friction material is set to be in a range between 2 wt % and 40 wt % of the whole of the friction material. If the total amount is smaller than 2 wt %, it is difficult to disperse the fibers uniformly when they are mixed and stirred. Accordingly, a desired friction noise preven
Haruta Mikiya
Hikichi Akihiro
Horiguchi Kazuya
Akebono Brake Industry Co. Ltd.
Cain Edward J.
Finnegan Henderson Farabow Garrett & Dunner LLP
Lee Katarzyna
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