DETAIL DESCRIPTION OF THE INVENTION

Field of the Invention

This invention relates to a friction material, which is manufactured by forming a non-asbestos-organic (NAO) friction material composition used for a disc brake pad.

Background of the Invention

Conventionally, a disc brake is used as a braking device for a passenger car, and a disc brake pad, which has a metallic base member on which a friction material is affixed, is used as a friction material member.

The friction material used for the disc brake pad is mainly categorized into three types.

<Semi-Metallic Friction Material>

A semi-metallic friction material contains 30 weight % or more but less than 60 weight % of a steel fiber as a fiber base material relative to the total amount of the friction material composition.

<Low Steel Friction Material>

A low steel friction material contains a steel fiber in a part of the fiber base material and contains less than 30 weight % of the steel fiber relative to the total amount of the friction material composition.

<Non-Asbestos-Organic (NAO) Friction Material>

A NAO friction material does not contain a steel type fiber such as a steel fiber and a stainless steel fiber as the fiber base material.

Recently, quietness and stillness in braking operation is in demand, and a friction material using NAO friction material which generates less brake noise has been widely used.

However, such NAO friction material has a problem of causing seizure due to corrosion when it is used for a disc brake having an electronic parking brake function is employed in a fluid type service brake unit, as disclosed in Patent Document 1.

Seizure due to corrosion is phenomena in which a disc rotor and the friction material stick together due to the rust after leaving the automotive while the parking brake in operation for a long period of time.

Technique to add the pH adjuster such as an alkali metal salt and/or an alkaline earth metal salt into the friction material is known to inhibit the rusting that is a cause of the seizure due to corrosion.

Patent Document 2 discloses the friction material for a brake containing the fiber base material, the friction modifier, and the binder, which is characterized in containing, as the material that is effective in preventing iron rusting, a hydroxide that is the alkali metal or alkaline earth metal (such as a calcium hydroxide) and a carbonate that is the alkali metal or alkaline earth metal (such as a sodium carbonate).

Patent Document 3 discloses the friction material, which is manufactured by heat press forming the friction material composition, containing 0.2-5 weight % of the alkali metal salt (sodium carbonate or potassium carbonate) therein relative to the total amount of the friction material composition.

According to Patent Document 2 and Patent Document 3, the friction material disclosed therein can maintain pH of contacting surfaces between the friction material and the disc rotor alkaline and can inhibit the rusting of the disc rotor.

Also, method of inhibiting the rusting of the disc rotor by adding a water-repelling material in the friction material is considered therein.

Patent Document 4 discloses the non-asbestos disc brake pad for an automotive containing the fiber base material, the binder, and the friction modifier, where the binder at least contains a silicone modified resin, the friction modifier contains an abrasive with the average particle diameter of 0.5-5 μm and the Mohs hardness of 7 or more, and the organic filler containing the cashew dust with the average particle diameter of 250 μm or less.

According to the non-asbestos disc brake pad for an automotive disclosed in Patent Document 4, a water-repelling film that repels water which can be a cause of rusting can be formed on a friction surface of the disc rotor as a result of the friction by braking, thereby inhibiting the rusting of the disc rotor.

It can be understood that it is possible to obtain an extremely satisfactory effect of inhibition with respect to the rusting of the disc rotor by synergy to use both such as the pH adjuster and water-repelling material.

However, it was found that the inhibition effect was limited to an initial stage of the friction material usage, and if the automotive while the parking brake is in operation is left under a high humidity state for a long period of time, the rust inhibition effect dramatically drops and the sticking occurs at the end.

PRIOR ART

Patent Document

[Patent Document 1] JP Provisional Patent Publication No. 2008-45703[Patent Document 2] JP Provisional Patent Publication No. 2000-205318[Patent Document 3] JP Provisional Patent Publication No. 2001-107027[Patent Document 4] JP Provisional Patent Publication No. 2002-266915

SUMMARY OF THE INVENTION

Means to Resolve by the Invention

This invention provides a friction material, which is manufactured by forming an NAO friction material composition, used for a disc brake of such as a passenger car, where the friction material does not degrade an inhibition effect of rusting and prevents seizure due to corrosion even if the automotive while the parking brake in operation, is left under a high humidity state for a long period of time.

Means to Resolve the Problems

Inventors of this invention, after serious investigation, found that a water-repelling material is to be added in the friction material composition in order to eliminate water which normally can be a direct cause of rusting; however, for the friction material, which includes the alkali metal salt and/or the alkaline earth metal hydroxide as the pH adjuster, supplying appropriate absorbency in the friction material itself prevents from degrading the inhibition effect of the rusting even if the automotive while the parking brake is in operation is left under a high humidity state for a long period of time.

Furthermore, the inventors completed this invention as finding that the prevention of degrading the inhibition effect of the rusting is further improved by adding a specific metal sulfide as the lubricant, a specific porous particle as the friction modifier, and a specific titanate.

This invention relates to the friction material, which is manufactured by forming the NAO friction material composition, used for the disc brake assembled in such as the passenger car and is based on the following technologies.

(1) In the friction material, which is manufactured by forming the NAO friction material composition, including the binder, the fiber base material, the friction modifier, the lubricant, the pH adjuster, and the filler, the friction material composition contains 2-6 weight % of the alkali metal salt and/or the alkaline earth metal hydroxide as the pH adjuster relative to the total amount of the friction material composition, 1-7 weight % of fibrillated organic fiber as the fiber base material relative to the total amount of the friction material composition, 0.5-5 weight % of a normal activated carbon, which is a porous inorganic particle having a sulfite ion absorbing function, as the friction modifier relative to the total amount of the friction material composition, and 0-0.5 weight % of the water-repelling component relative to the total amount of the friction material composition.

(2) In the friction material based on the above (1), the pH adjuster is one kind or a combination of two or more kinds selected from the sodium carbonate, the potassium carbonate, the sodium bicarbonate, the potassium bicarbonate, and the calcium hydroxide.

(3) In the friction material based on either (1) or (2), the fibrillated organic fiber is one kind or a combination of two or more kinds selected from the aramid fiber, the cellulosic fiber, and the acrylic fiber.

(4) In the friction material based on any of (1)-(3), the friction material composition contains 0.5-6 weight % of the zinc sulfide as the lubricant relative to the total amount of the friction material composition.

(5) In the friction material based on any of (1)-(4), the friction material composition contains magnesium potassium titanate as the inorganic friction modifier.

Advantage of the Invention

In relation to the friction material, which is manufactured by forming the NAO friction material composition, used for the disc brake assembled in such as the passenger car, this invention can offer the on material that does not degrade the inhibitory effect of rusting and prevents the seizure due to corrosion even if the automotive while the parking brake in operation is left under a high humidity state for a long period of time.

