Friction material

Abstract: A friction material containing dust having bismaleimidetriazine as a major ingredient. The dust is effective when contained in amount of 1 to 20 wt. % in the friction material. Compared with conventional friction material containing cashew dust, the generation rate of noise is reduced drastically, while the frictional performance is equivalent or higher.

Description: The present invention relates to a friction material for use, e.g. in brakes of cars and others, wherein, in particular, the noises generating on braking are prevented. The conventional mechanical brake rubs solid members one another by contacting them, thus noises generate inevitablly due to the vibrations of them. Today, it is difficult to completely prevent such noises, and we are coping to decrease the noises by such methods that a material absorbing the vibration is formulated in one of opposing brake pads, that an elastomer with good viscoelastic characteristics is allowed to intervene on the way of vibration transfer system, and the like. However, it cannot still be said to be sufficient. Here, the inventors have investigated the solution thereof and, paying an attention to the dust contained in the friction material of brake for following purposes, the investigations have been made further. Namely, the main functions of dust are 1 ○ improved brake feeling, 2 ○ increased efficacy, and 3 ○ prevention from noises. Types of dust include now rubber dust, cashew dust and modified articles thereof as shown in U.S. Patent 4,310,452 and 4,886,107 and these are incorporated into the pad for disk brake in a proportion of 2 to 10 wt.%. On the other hand, with respect to the environment surrounding the brake, the loading exerted on the brake pade is in a tendency to become increasingly severe, because the rigidity tends to decrease structurally from lightening in weight of the car body accompanying with large-sized cars and because the brake system is also progressing toward miniaturization and lightening as well. Hence, the requirement for the heat reistance of a brake pad is increasing, but, with said rubber dust, the purpose is attained by no means and, with cashew dust, it has been difficult to effect a stabilized function over a long period of time, though the heat resistance thereof is higher than that of rubber dust. Namely, the noises generating with a pad containing cashew dust have a strong tendency to generate more frequently as the braking is repeated. This is because of that, with increasing heat history due to the repetition of braking, the temperature of the brake pad increases gradually and ends up to become over the heat decomposition temperature (about 290°C) of cashew dust at last, thus exceeding the heat-resistant limit of cashew dust. JP-A-61 113 650 discloses a resin composition containing a fluorine type polymer and a bismaleimide triazine resin as a thermosetting resin compound, the fluorine polymer and the thermosetting resin penetrate to each other, and the mixture has an IPN (Interpenetrating Polymer Networks) structure. EP-A-0 324 908 on which the preamble of Claim 1 is based, discloses a friction material comprising a thermosetting resin binder which is a phenolic cyanate resin (derived from a phenolic cyanate-phenolic triazine precursor), a reinforcing material, an inorganic filler and a friction-resistant dust (powder). JP-A-62 270 635 discloses a friction material for a wet-type clutch or brake comprising a mixture of hydrogenated nitrile rubber and bismaleimide-triazine resin for improved durability. EP-A-0 222 394 discloses a friction material to be used in an ultrasonic motor, the friction material containing at least a rubber-like elastic body which may be a flexibility-given bismaleimide-triazine resin. The rubber-like elastic body is impregnated into fiber cloth and then formed into the friction material by heating and pressing. As a result of further investigations in view of the points aforementioned, a friction material with excellent heat resistance having prevented the generation of noises has been developed according to the invention. The present invention provides a friction material having heat-resisting properties comprising a thermosetting resin binder, a reinforcing material, an inorganic filler, and an organic dust for modifying the frictional properties, which is characterized in that a dust containing bismaleimidetriazine resin as the main component is contained as said organic dust. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a column diagram showing the result of brake noise test. The heat resistance and the residual carbon rate after the heat decomposition due to braking were compared between the bismaleimidetriazine (hereinafter referred to as BT resin) and conventional cashew dust as shown in Table 1. Dust Heat resistance (°C) Residual carbon rate (%) BT resin ca. 390 70 - 75 Cashew dust ca. 290 50 As shown, since the heat decomposition point (heat resistance) of BT resin is as higher as about 100°C over cashew dust, the available temperature range is broader, thus providing a characteristic of broader application range as a friction material. Moreover, since the residual amount of carbon after heat decomposition is also higher, that is, since the existing amount of thermally stable carbon is higher, the BT resin has an advantage that the change in the frictional characteristics including noise property decreases. Furthermore, the content of dust having said BT resin as a major ingredient in the friction material is effective in an amount of 1 to 20 wt. %, but, more preferably, 3 to 8 wt. % are better. As the binders, thermosetting resins such as phenol resin and polyimide resin can be used and they are preferable to be contained in a proportion of 5 to 20 wt. % in overall components of the friction material. As the reinforcing materials, one kind or not less than two kinds of metal fibers such as steel and copper, organic fibers such as Aramid and acrylic and inorganic fibers such as glass and carbon can be used in combination. The optimal proportion thereof is 10 to 40 wt. % in overall components of the friction material. Moreover, as the inorganic fillers, those having a grinding effect such as zircon sand, alumina, silica and magnesia, those having a lubricating effect such as graphite and molybdenum disulfide, those having a noise-reducing effect such as vermiculite and mica and those having an extending effect such as barium sulfate, calcium carbonate and calcium silicate can be used in combination. They may be contained in a proportion of 40 to 75 wt. % in overall components of the friction material. In the following, explanation will be made about the examples of the invention. Example The inventive friction materials and the comparative friction material comprising formulation compositions shown in Table 2 were produced. The physical properties of these friction materials are shown in Table 3. Formulating Material Friction material no. Inventive friction material 1 Inventive friction material 2 Inventive friction material 3 Inventive friction material 4 Comparative friction material 5 Binder Phenol resin 8 8 8 8 8 Dust Cashew dust - - - - 5 Rubber dust BT resin dust 2 5 10 15 - Inorganic filler Barium sulfate 15 15 15 15 15 Zircon sand 10 10 10 10 10 Graphite 12 12 12 12 12 Vermiculite 23 20 15 10 20 Reinforcing material Copper fibers 25 25 25 25 25 Aramid fibers 5 5 5 5 5 Physical property Inventive friction material 1 Inventive friction material 2 Inventive friction material 3 Inventive friction material 4 Comparative friction material 5 Hardness (HRS) 100 95 90 80 95 Specific gravity(g/cm³) 3.2 3.1 3.0 2.9 3.1 Porosity(%) 8 10 11 12 10 The friction materials as above were applied to a brake pad. Table 4 shows the results of a friction performance test carried out according to JASO 1201 and further Fig. 1 shows the results of a noise test. From Table 4, it can be seen that the brake pads using the inventive friction materials have equivalent or higher frictional performance over the pad using conventional comparative friction material. Moreover, according to Fig. 1, it is seen that the generation rate of noises of brakes using the inventive friction materials is obviously decreased compared with that of a conventional brake. As described, in accordance with the invention, conspicuous effects are exerted in that it is possible to drastically suppress the generation of noises on braking over the past without decreasing the frictional performance of the friction material.

Claims: A friction material having heat-resisting properties comprising a thermosetting resin binder, a reinforcing material, an inorganic filler, and an organic dust for modifying the frictional properties, characterized in that a dust containing bismaleimidetriazine resin as the main component is contained as said organic dust. The friction material of claim 1, wherein the dust containing bismaleimidetriazine resin as a main component is contained in an amount of 1 to 20 wt.%. The friction material of claim 1, wherein the dust containing bismaleimidetriazine resin as a main component is contained in an amount of 3 to 8 wt.%. A friction material having heat-resisting properties comprising 5 to 20 wt.% of a thermosetting resin binder, 10 to 40 wt.% of a reinforcing material, 40 to 75 wt.% of an inorganic filler and 1 to 20 wt.% of an organic dust for modifying the frictional properties being a dust containing bismaleimidetriazine resin as a main component.

Inventors: KAMIOKA NOBUO, TOKUMURA HIROSHI, YOSHINO TORU, KAMIOKA, NOBUO, TOKUMURA, HIROSHI, YOSHINO, TORU
Applicants: AKEBONO BRAKE IND, AKEBONO RES & DEV CENTRE, AKEBONO BRAKE INDUSTRY CO., LTD., AKEBONO RESEARCH AND DEVELOPMENT CENTRE LTD.
Application year: 1992
Main classification: F16D69
IPC codes: C09K3, F16D69