TECHNICAL FIELD

The present invention relates to a method of manufacturing a friction material used for a disc brake and a drum brake of automobiles such as a passenger car and a truck.

BACKGROUND OF TECHNOLOGY

Conventionally, a disc brake and a drum brake are used as a brake device of automobiles, and a disc brake pad and a brake shoe, each of which includes a metal base member and a friction material attached thereto, are used as a friction member.

The friction material is manufactured by the following steps: a mixing step for mixing a friction material composition including a binder, a fiber base, a lubricant, an organic friction modifier, an inorganic friction modifier, a pH adjuster, and a filler so as to obtain a raw friction material mixture; a heat-press-forming step for heat-press-forming the raw friction material mixture with a heatforming die; and a heat treatment step for completing curing of a thermosetting resin as binder.

When a temperature of the friction material reaches a high temperature due to frictional contact between the friction material and a metal disc rotor or a brake drum upon braking the automobile, decomposition gas is generated by heating the binder and the organic friction modifier in the friction material. It is known that the existence of decomposition gas between the friction material and the disc rotor or the brake drum causes so-called “brake fade” in which the friction coefficient decreases and the braking effectiveness decreases rapidly.

In order to prevent the brake fade in the initial stage of the use of the friction material, in the process of manufacturing the friction material, an entire frictional surface of the friction material after molding is heated at a high temperature called “scorching” so as to remove organic substances or the like that cause the brake fade by burning the same.

Conventionally, as a method of scorching, a method of pressing a heating plate against the surface of the friction material, and a method of heating the surface of the friction material by direct fire such as gas flame have been used; however, in recent years, methods of heat-treating the surface of the friction material with an infrared laser as disclosed in Patent Document 1 or heat-treating the surface of the friction material with a high-power diode laser as disclosed in Patent Document 2 has been adopted.

PRIOR ART DOCUMENTS

Patent Document

Patent document 1: US2002/046789APatent document 2: EP1262679A

SUMMARY OF THE INVENTION

Problems to be Solved

The methods of heat-treating the surface of the friction material with the laser disclosed in Patent document 1 and Patent document 2 are able to shorten the time period of the scorching step as compared to the conventional method of heating the surface of the friction material that heats the surface of the friction material by directly contacting the heat source to the surface thereof; however, there is a need for a method that can scorch uniformly from the surface of the friction material to a deep part of the surface thereof in a short period of time.

The present invention relates to a method of manufacturing a friction material for scorching a surface of a friction material used for a disc brake and a drum brake of an automobile such as a passenger car and a truck with a laser, and an object of the present invention is to provide a method of manufacturing a friction material that can be uniformly scorched into the deep part of a surface layer of the friction material in a short period of time.

Means to Solve Problems

In general, black raw materials such as carbonaceous materials such as a graphite and a coke, a triiron tetraoxide, a black cashew dust manufactured using furfural as a curing agent, and pulverized powders of tire tread rubber may be added as raw materials for a friction material.

As the result that the inventors of the present invention had intensively studied the raw friction materials forcing on the fact that the black raw material tends to absorb the energy of the laser easily among various raw materials contained therein, relating to the method of scorching the surface of the friction material with a laser, the inventors completed this invention by finding that uniform scorching can be performed into the deep part of the surface layer by adding the predetermined amount of one or more types of black raw materials to the friction material and setting the color tone of the surface of the friction material before scorching to the specific range.

The present invention relates to a method of scorching the surface of a friction material used for a disc brake and a drum brake of an automobile such as a passenger car and a truck with a laser and is based on the following technology.

(1) In a method of manufacturing a friction material, which includes a scorching step of scorching the surface of the friction material with a laser, the friction material contains 5 to 25% by weight of one or more types of black raw materials relative to the total amount of the friction material composition, and the L* of the CIE Lab of the surface of the friction material before scorching is 20 to 60.

(2) In the method of manufacturing the friction material according to (1), an energy density of the laser in the scorching is 150 to 2000 kW/m2, a distance between the laser irradiation surface and the surface of the friction material is 15 to 300 mm, and a scorching time is 0.5 to 60 seconds.

(3) In the method of manufacturing the friction material according to (1) or (2), a light source of the laser beam is a vertical cavity surface emitting laser module.

(4) In the method of manufacturing the friction material according to anyone of (1)-(3), a pre-heating step is performed immediately before the scorching step.

(5) In the method of manufacturing the friction material according to (4), the pre-heating step is a heat treatment step.

Effect of the Invention

According to the present invention, in the method of manufacturing the friction material in which the scorching is performed with a laser on the surface of the friction material used for the disc brake and the drum brake of the automobiles such as the passenger car and the truck, it is possible to provide the method of manufacturing the friction material that can provide the uniform scorching in the deep part of the surface layer in a short period of time.

