JPH03287629A - Friction material - Google Patents

Abstract

PURPOSE:To obtain a nonasbestine friction material excellent in heat resistance, abrasion resistance and mechanical strengths by using a mixture of specified sulfurized acrylic flame-resistant fibers as a reinforcement of friction material. CONSTITUTION:A friction material containing a sulfurized acrylic flame-resistant fiber as a reinforcement, wherein said fiber comprises a mixture of a sulfurized acrylic flame-resistant fiber having a sulfur content of below 3wt.% and a sulfurized acrylic flame-resistant fiber having a sulfur content of 3wt.% or above. The reinforcing fiber is preferred to be in the form of a fibrillated fiber which can give a friction material which is particularly excellent in an ability to catch a matrix resin and a powder such as a filler in the friction material and has high uniformity. It is desirable that the mixing ratio of the low-sulfur content fiber be 5-50wt.% based on the total weight of the high and low sulfur content fibers. The sulfurized acrylic flame-resistant fiber may contain base fibers such as aramid fiber, glass fiber, carbon fiber, phenol fiber or steel fiber. As the binders, phenolic resins, melamine resins or the like can be used. Graphite, silica powders, metallic powders or the like may be suitably added in order to improve the frictional properties.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a non-asbestos friction material that has excellent heat resistance, abrasion resistance and mechanical strength.

[Conventional technology]

Conventionally, asbestos has been widely used as a reinforcing material for friction materials such as automobile brakes. However, it has become clear that friction materials using asbestos as a reinforcing material turn into dust during the manufacturing process or during use, which may impair human health.

In view of environmental hygiene, there is an increasing demand for alternative fibers.

Glass fibers, carbon fibers, steel fibers, aromatic polyamide fibers, phenol fibers, flame-resistant fibers, and the like have been proposed as reinforcing fibers for friction materials in place of asbestos. Furthermore, for example, the present inventors also previously published JP-A No. 6:
No. 3-8424 discloses a sulfur-containing flame-resistant acrylic fiber with high strength, excellent abrasion resistance and heat resistance, which is obtained by heating and sulfurizing high-strength acrylic fiber in a sulfur-containing atmosphere such as sulfur dioxide gas. proposed a friction material based on

[Invention or problem to be solved]

However, as the performance of automobiles increases, the operating conditions have become more severe, and the required properties for friction materials have also become more severe. There is a growing demand for friction materials with excellent strength. Mechanical strength includes, for example, bending strength, impact strength, shear strength, and rotational fracture strength in clutch facings.

In view of these points, the present inventors conducted extensive studies on the sulfur content and form of the flame-resistant sulfur-containing acrylic fibers in order to improve the mechanical strength of friction materials using the flame-resistant acrylic fibers as reinforcement materials. However, the present invention was completed.

That is, an object of the present invention is to provide a novel friction material particularly excellent in mechanical strength and friction performance.

[Means to solve the problem]

In order to obtain a friction material having excellent mechanical strength and friction performance, the friction material is made of sulfur-containing acrylic flame-resistant fibers as a reinforcing material, and the sulfur content of the flame-resistant fibers is 3% by weight. This can be achieved by a friction material characterized by comprising a mixture of sulfur content of less than 3% by weight and sulfur content of 3% by weight or more.

[Function] The sulfur-containing acrylic flame-resistant fiber used in the present invention is
Its heat resistance and wear resistance are characterized by the introduction of sulfur bonds. The sulfur-containing flame-resistant acrylic fiber used in the present invention is a fiber obtained by heating and sulfurizing a high-strength, high-modulus acrylic fiber in a sulfur-containing atmosphere. The sulfur-containing atmosphere refers to gases such as sulfur dioxide, sulfur gas, carbon disulfide, hydrogen sulfide, and carbonyl sulfide, either alone or in combination.Sulfur dioxide in particular has excellent reactivity to acrylic fibers, and It is preferably used because it can be sulfurized uniformly. Further, the sulfurization reaction is preferably carried out in a temperature range of 230°C to 400°C.

Furthermore, flame-resistant fibers having a desired sulfur content can be obtained by controlling the reaction temperature and reaction time. In the present invention, two types of flame-resistant fibers are used: flame-resistant fibers with a sulfur content of less than 3% by weight (hereinafter simply referred to as low-sulfur fibers) and those with a sulfur content of 3% by weight or more (hereinafter simply referred to as high-sulfur fibers). Use fiber.

For example, the reinforcing fiber for friction material has a shape of 1 to 10 m.
Examples include cut fibers of m, fibers pulverized by various types of pulverizers, fibrillar fibers, and the like. Among these, fibrillar fibers are more preferable because they have excellent ability to trap powder such as the matrix resin and filler of the friction material and provide a friction material with high uniformity.

Since fibrillar fibers have excellent powder trapping properties, they are advantageous in that they improve the handling properties of friction material mixtures and preforms. In addition, fibrillar fibers have a large adhesion area with the matrix resin, contributing to improved mechanical strength. To fibrillate the fibers, conventional beating means such as beater refiners, various types of mills, jet air streams, etc. can be applied. High-strength acrylic fibers may be fibrillated using the above method and then heated and sulfurized, or fibrillated after heat sulfurized. However, when heating and sulfurizing fibrillated acrylic fibers, the fiber diameters of the fibrillar fibers are significantly different, making it difficult for the sulfurization reaction to proceed uniformly, and also making it more likely that heat will accumulate, so these points should be kept in mind. In the case of fibrillation after sulfurization, the higher the sulfur content, the more difficult the fibrillation becomes, so the sulfur content is preferably less than 3% by weight. Further, here, the degree of fibrillation of the fibrillar fibers is such that the furnace water level is 700 cc or less, preferably 600 cc or less.

The fibers thus obtained are mixed to form a reinforcing material for friction materials. In order to obtain the friction material of the present invention having excellent mechanical strength and friction performance, a mixture of low sulfur fibers and high sulfur fibers is used. Of course, the fibers may be in the form of fibrillar fibers, cut fibers, etc. alone, or fibers of various shapes may be mixed and used. At this time, the sulfur content of the low sulfur fiber is less than 3% by weight, preferably 0.5% by weight or more and less than 3% by weight. On the other hand, the sulfur content of the high sulfur fiber is 3% by weight or more, preferably 5% by weight or more, and more preferably 8% by weight or more.

In sulfur-containing acrylic flame-resistant fibers used for boat fishing, the higher the sulfur content, the higher the heat resistance of the fibers, but the fiber strength and toughness tend to decrease. In particular, when it exceeds 3% by weight, the strength decreases rapidly and it becomes difficult to form fibrils, but it has sufficient heat resistance as a reinforcing material for friction materials.
Provides wear resistance. Therefore, the friction material of the present invention can be obtained by mixing low sulfur fibers with high fiber strength and toughness and high sulfur fibers with excellent heat resistance.

The mixing ratio of the low sulfur fibers is preferably 5 to 50% by weight, more preferably 10 to 50% by weight based on the total weight of the high and low sulfur fibers.
It is 30% by weight. If the content of low sulfur fibers is less than 5% by weight, the produced friction material will not have sufficient mechanical strength. Moreover, if it is more than 50% by weight, properties such as abrasion resistance and heat resistance cannot be sufficiently imparted, and when used in a friction material, the friction performance at high temperatures decreases.

Other base fibers such as aramid fibers, glass fibers, carbon fibers, phenol fibers, steel fibers, and flame-resistant fibers can also be added to the sulfur-containing acrylic flame-resistant fibers blended above.

As the binder, commonly used phenolic resins, melamine resins, etc. can be used.

In addition to the above-mentioned binders, various fillers added for the purpose of improving friction properties such as graphite, silica powder, alumina powder, barium sulfate, metal powder, mica, clay, calcium carbonate, molybdenum disulfide, pallite, etc. , cashew dust, rubber dust, etc. may be mixed as appropriate.

The method for manufacturing the friction material is not particularly limited, and any conventional method may be used. For example, the aforementioned JP-A-63
The method described in JP-A-8424 and the like can be used. That is, the above-mentioned reinforcing fibers, binder, and other compounding agents are sufficiently mixed using a conventional blender mixer, preformed in a mold, heated and pressurized, and then polished to form a friction material. Friction materials can be made using this method.

〔Example〕

EXAMPLES Below, the effects of the present invention will be specifically explained with reference to Examples.

(1) Friction properties: JIS-D-4 plate-shaped friction materials based on flame-resistant fibers
It was measured according to the method specified in 411. The test conditions were a surface pressure of 10 kg/Cm2 and a friction speed of 7.8 m/sec. The wear rate measured at 250°C was investigated.

(2) Bending strength: Measured according to the measuring method specified in JIS-6911.

(3) Reactor water level: Canadian standard reactor water level, measured according to the method specified in JIS-P8121.

Examples 1 to 3, Comparative Examples 1 to 2 An AN copolymer with an intrinsic viscosity of 3.2 consisting of 99 mol% acrylonitrile (AN) and 1 mol% acrylamide was solution-polymerized in dimethyl sulfoxide (DMS○), The obtained spinning stock solution was subjected to dry-wet spinning. As a coagulation bath, 2
0'C, 55% DMSO aqueous solution was used. The obtained undrawn fiber yarn was stretched 5 times in hot water, and then washed with water for 18
Maximum stretching ratio of 9 in a dry heat tube at 0°C to 200°C
Secondary stretching at 0%, strength 13.2g/d, elongation 12.8
% of acrylic fibers were obtained.

Next, the acrylic fiber was heated with 20% sulfur dioxide gas and 80% nitrogen.
% mixed gas at 280'C for 30 and 120 minutes to produce a low sulfur fiber with a sulfur content of 2% by weight and a strength of 11.2 g/d, and a sulfur content of 10% by weight and a strength of 5.2
g/d high sulfur fibers were obtained. Furthermore, these two types of fibers were cut using a guillotine cutter to obtain two types of cut fibers each having a fiber length of 1 mm, a low sulfur fiber and a high sulfur fiber.

In addition, as fibrillated fibers of low sulfur fibers, the same low sulfur fibers as above were cut into fiber lengths of 5 mm using a guillotine cutter, 20 g of the fibers were dispersed in about 10 liters of water, and the clearance Q was then set to 1 mm. The fibrillar fibers were prepared by beating the fibers through a single disc refiner. The furnace water level of the fibrillated fibers was 550 cc.

As an example, the above two types of sulfur fibers having different sulfur contents were mixed in various ratios to form a reinforcing material for a friction material. In addition, as a comparative example, low sulfur fibers and high sulfur fibers were each used as reinforcing materials. Next, reinforcing material, powdered phenolic resin,
Calcium carbonate and copper powder volume ratio: 18:15:66:
They were mixed at a ratio of 1:1. Stir this mixture for about 1 minute using a household mixer, put the resulting mixture into a mold, and
A bottom mold was formed by hot pressing under the conditions of 000C and 200 kg/cm2. After the molded product was cured in an oven at 250° C. for 5 hours, the surface was polished with No. 600 sandpaper and cut into a desired size as a test piece, and its friction performance and bending strength were measured.

The results are shown in Table 1.

From Table 1, the friction material containing a mixture of low sulfur fiber and high sulfur fiber has higher bending strength and lower wear rate at high temperatures than the comparative example, which is a single material, and has good mechanical strength and friction performance. It can be seen that it is superior in both respects. That is, the friction material according to the present invention has a bending strength of 140 kg/cm.
2 or more and a wear rate of 20×10 −7 cm 3 /kg-m or less, a friction material that has both of these characteristics in a very well-balanced manner.

〔Effect of the invention〕

According to the present invention, in a friction material reinforced with sulfur-containing acrylic flame-resistant fibers having excellent heat resistance and abrasion resistance, by mixing fibers with different sulfur contents in a certain composition, the friction material can be improved. A friction material with improved bending strength and excellent mechanical strength and friction performance can be obtained.

As a result, it becomes possible to provide a friction material with higher safety and higher performance.

Claims (2)

[Claims] (1) A friction material made of sulfur-containing acrylic flame-resistant fibers as a reinforcing material, characterized in that the flame-resistant fibers are composed of a mixture of less than 3% by weight of sulfur and 3% by weight or more of sulfur. Friction material. (2) The friction material according to claim 1, wherein the sulfur-containing acrylic flame-resistant fiber is a fibrillar fiber.