JPH03166287A - Friction material - Google Patents

Abstract

PURPOSE:To obtain a friction material exhibiting little change of frictional coefficient even in water-absorbed state by hot-pressing an inorganic fiber base material, graphite, barium sulfate, a friction conditioner and a binder resin and surface-treating the molded product. CONSTITUTION:An inorganic fiber such as glass fiber is used at least as a part of a base material and compounded with graphite, barium sulfate, an organic or inorganic filler such as cashew dust as a friction conditioner and a binder resin such as phenolic resin. The mixture is hot-pressed and subjected to impregnation or vacuum impregnation of a surface-treating agent such as organic titanate compound to obtain the objective friction material composed of at least partially surface-treated inorganic fiber or inorganic filler.

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention is applicable to brakes for railways, trucks, passenger cars, etc., as well as brakes for stopping other rotating objects, or clutches for transmitting torque. The present invention relates to materials, and particularly aims to provide a friction material whose coefficient of friction does not change much even when the friction material absorbs water.

``Prior art'' As friction materials for brakes, clutches, etc., mineral fibers (slag wool), steel fibers, glass fibers, potash titanate whiskers, ceramic fibers, etc., or their composites, inorganic fibers alone or composites thereof are used. Three types of base materials: a base material combining inorganic fibers, graphite, barium sulfate (baryta), inorganic and organic fillers such as metal powder, rubber powder, and cashew dust (Jli! friction modifier), and phenol resin (organic binder). It is well known to use a mixture of the following and molded under heat and pressure.

``Problem to be solved by the invention'' With conventional friction materials, the friction material may become damaged after being exposed to a high humidity environment such as during the rainy season or after water is sprayed on the friction material during car washing. When water is absorbed, the friction coefficient exhibited by the friction material when dry changes significantly. Therefore, one of the characteristics required for a friction material is that the change in the coefficient of friction between the friction material when it is dry and when it absorbs water is small.

On the other hand, Japanese Patent Application No. 01-243237 states that the cause of the change in the coefficient of friction during water absorption is adhesion to the surface of the friction material or
Fluororesin-based Alternatively, a method has been proposed in which the surface of the friction material is treated with a silicone resin-based surface treatment agent to impart water repellency to the friction material.

However, fluorine-based resins have the problem of inhibiting the adhesion of the binder resin or lowering the coefficient of friction during friction, resulting in poor braking effectiveness.

Furthermore, silane-based surface treatment agents do not have sufficient water repellency.

"Means for Solving the Problems" An object of the present invention is to provide a friction material that eliminates the above-mentioned drawbacks.

This invention uses inorganic fibers such as glass fibers, potassium titanate fibers (or whiskers), mineral fibers, ceramic fibers, etc. as a base material or a part of the base material, and graphite, barium sulfate (baryta), cashew dust, etc. In a friction material manufactured by heat-pressing molding using a binder resin such as a phenolic resin together with an organic/inorganic filler, at least a portion of the inorganic fiber or inorganic filler is treated with an organic titanate-based surface treatment agent. It is a friction material with the following characteristics. In this case, both the inorganic fiber and the inorganic filler may be coated, and it is also effective to impregnate with an organic titanate surface treatment agent or vacuum impregnate.

The present inventors conducted numerous experiments on asbestos and non-asbestos-based friction materials using binder resin, and found that the change in friction coefficient (hereinafter referred to as μ) due to water wetting or moisture absorption of the friction material It was discovered that a larger cause was the residual presence of micron-sized pores inside. In other words, water attached to the surface of the friction material or liquefied and adsorbed from the air penetrates into the internal pores through narrow passages in the friction material, filling them, and water is released onto the surface during friction (used as a brake, etc.). The present invention was made based on the discovery that this is the main cause.

It was also found that the above-mentioned pores mainly exist where inorganic fibers such as glass fiber ceramic fibers are not completely dispersed one by one during the mixing process, and many fibers are crossed, clustered, or knotted. . As shown in Figure 1, where such fibers (1) overlap, the binder resin (2) containing the friction modifier (3) does not penetrate into the fiber mass, and the pores (4)
) is occurring. Among various inorganic fibers, the more difficult it is for the fibers to be dispersed one by one during the mixing process, the higher the rate of occurrence of pores and the more pronounced the change in μ. Therefore, if the fiber itself is made easier to disperse, the effect of reducing the change in μ can be expected. Additionally, it would be possible to fill these pores in advance, but since there is no suitable means for this, research has shown that it is effective to make the fiber or filler water-retaining in order to prevent water from entering the pores. Understood.

To impart water repellency, an organic titanate-based surface treatment agent is used to coat the inorganic fiber filler, a raw material of the friction material, or a portion thereof, or the friction material itself. In this case, effective surface treatment agents include water-reducing tetrastearoxytitanium, tri-n-butoxytitanium monostearate, and tetra-n-butoxytitanium. Also, tetra-i-propoxy titanium, di-n-butoxy,
Bistitanium is also effective. Furthermore, mixtures and derivatives of organic titanium can also be used.

The effect on μ during water absorption varies widely depending on the type of fiber used as the base material.

The change in μ is large in the case of a single fiber such as potassium titanate whisker with a size of 1 μm or less, or an aggregate of fibers with a crystal structure having internal voids. This is because this type of fiber has poor dispersibility during mixing and has a small diameter, so the binder resin cannot fill the gathering space or void. Next, it is also large in the case of glass fiber, but this is presumed to be because the wettability between the glass fiber and the binder resin is poor, leaving a space between the binder and the fiber. Therefore, when these fibers are used, it is particularly effective to pre-coat them with a water-repellent surface treatment agent in order to prevent changes in μ due to the influence of water.

Another embodiment of the present invention uses a material coated with the surface treatment agent for at least a portion of an organic or inorganic friction modifier (filler) other than inorganic fibers of the friction material. This is because the water repellent dispersed in the friction material together with the filler prevents moisture from passing through the narrow passages and from penetrating into the pores. However, this method is undeniably less effective because the water repellent is not concentrated in the pores. In yet another embodiment of the present invention, a molded friction material is impregnated or vacuum impregnated with a water-repellent surface treatment agent. This method can also prevent changes in μ due to moisture.

In the above two methods, the amount of surface treatment material added or impregnated is preferably within 1% of the weight of the friction material, although it depends on the amount and size of pores and narrow passages in the friction material. This is because if it exceeds 1%, the coefficient of friction during normal use will be affected. Moreover, if it is less than 0.001%, no effect will be produced.

"Example" Example 1 As sample A, the following volume ratio of the base material: 15% 15% 7% E glass 7 Eyeper aramid fiber #Steel fiber friction modifier Graphite barium sulfate (graphite) (Paraita) ・ ・ ・ ・ ・ 7% ・ ・ ・ ・ 18% Cashew dust ・・・15% Molybdenum disulfide ・・・1% Binder resin straight phenol ・ ・ ・ ・・2
In the next step, 2% of the raw material is mixed into (1) a ■ type blender with high speed rotating blades.
Mix for 5 minutes.

(2) The above-mentioned mixed powder is put into a mold at 165° C., and the press pressure is adjusted so that the porosity becomes 10%, and the powder is heated and pressed for 10 minutes.

(3) After molding, it is cured for 5 hours in a 230°C oven.

(4) Polish the outer shape.

A disc brake pad (sample) for a passenger car was manufactured using this method.

Next, E glass fiber was treated with 1% tetrastearoxytitanium surface treatment agent (sample A).
-1) Using E glass fiber coated with Tetler i-broboxytitanium (Sample A-2), disc brake pads for passenger cars were made using the same steps and steps as Sample 8. Sample A-1, Sample A -2.

The obtained sample pad was measured using a full-size dynamometer using JAS
After alignment was performed in accordance with O-C406-82, braking was performed once at an initial velocity of lOκ-/Hr and a disk temperature of 40°C as a baseline, and μ was measured. Thereafter, the pad was removed and left in a constant temperature and humidity atmosphere of 30° C. and 90% humidity for 24 hours, and approximately 2 cc of water was removed by spraying, and the pad was immediately set in a dynamometer and μ was measured under the above conditions.

The difference between μ before water absorption and μ after water absorption was as follows.

From the above results, it has been found that organic titanate-based surface treatment is a very effective means for reducing changes in the coefficient of friction due to water absorption.

Example 2 As sample B, potassium titanate fiber (Kubota Iron Works @
! A pad using 15% of TXAK-A) was performed in the same process as Sample A.

In sample B, titanate caulifiber was treated with a tri-n-butoxytitanium monostearate surface treatment agent (organotitanate surface treatment agent manufactured by Nippon Soda@) so that 0.5% of the organic titanate surface treatment agent remained attached. Sample B-1 was prepared in the same process using
I made a pad.

Next, in Sample B, barium sulfate (baryta), which is a friction modifier, was coated in the same manner as that applied to the titanate potassium fiber in Sample B-1.
I made a pad.

Further, Sample B was vacuum impregnated with the organic titanate-based surface treatment agent used in Sample B-1 and the solvent was evaporated, and then Sample B-3 was prepared using a pad impregnated with 0.1% of the treatment agent.

These samples were tested in the same manner as in Example 1 before water absorption;
The μ after water absorption was measured and the results were as follows.

From the above results, it is possible to prevent changes in μ due to water absorption by coating part of the inorganic fiber base material and filler with an organic titanate-based surface treatment agent, or by impregnating the pad with the same agent. I understand.

Example 3 As Sample C, a pad using 15% mineral fiber instead of the E glass fiber of Sample A of Example 1 was manufactured in the same process as Sample A.

In sample C, an organic titanate-based surface treatment agent diluted with a solvent was sprayed on Mineral Fnibar while stirring so that 0.5% of the tetran-butoxytitanium polymer surface treatment agent remained attached, and the solvent was removed by volatilization. Sample C-1 pad was made using the same material.

These samples were tested in the same manner as in Example 1, and the μ before and after water absorption was measured, and the results were as follows.

From the above results, it is clear that when the mineral fiber base material is treated with a derivative of an organic titanate surface treatment agent, the μ
It can be seen that changes in can be prevented.

"Effects of the Invention" As explained in detail above, compared to the friction material of the present invention, the friction coefficient does not change when water is absorbed. It is highly effective as a friction material because of its stable effectiveness and the ability to prevent driving hazards.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the state of pores in the friction material. 1: Fiber, base material 2: Binder resin 3: Friction adjustment material, filler 4: Pore

Claims (2)

[Claims] (1) Inorganic fibers such as glass fibers are used as a base material or part of the base material, and a binder resin such as phenolic resin is used to form the material under heat and pressure along with graphite, barium sulfate (baryta), and a friction modifier. A manufactured friction material characterized in that at least a portion of the inorganic fibers or inorganic filler is treated with an organic titanate-based surface treatment agent. (2) Inorganic fibers such as glass fibers are used as the base material or part of the base material, and binder resins such as phenolic resins are used along with organic and inorganic fillers such as graphite, barium sulfate (baryta), and cashew dust as a friction modifier. What is claimed is: 1. A friction material manufactured by heat-pressing molding using a friction material, which is impregnated with an organic titanate-based surface treatment agent or vacuum impregnated after the friction material is molded.