JP6042769B2 - Friction material - Google Patents

Description

  The present invention relates to a friction material obtained by molding a friction material composition of NAO (Non-Asbestos-Organic) material used for a disc brake pad of an automobile or the like.

  Conventionally, a disc brake is used as a braking device for an automobile, and a disc brake pad in which a friction material is attached to a metal base member is used as the friction member.

  The friction material includes a semi-metallic friction material containing 30% by weight or more and less than 60% by weight of steel fiber as a fiber base material, and steel fiber in a part of the fiber base material. Is classified into low steel friction material containing less than 30% by weight of the total friction material composition and NAO (Non-Asbestos-Organic) material that does not contain steel fibers such as steel fibers and stainless steel as the fiber base material. Yes.

  In recent years, friction materials that generate less brake noise have been demanded. Steel fibers and steel fibers are not included, and binders, fiber base materials, lubricants, metal titanates, inorganic friction modifiers, organic Disc brake pads using a friction material such as a friction adjusting material, a pH adjusting material, a filler, and the like and using a friction material made of NAO material have been widely used.

  In order to ensure fade resistance and wear resistance, the friction material of NAO material used for disc brake pads has copper components such as copper or copper alloy fibers or particles as essential components with respect to the total amount of the friction material composition. 5 to 20% by weight is added.

  However, in recent years, it has been suggested that such friction materials discharge copper as wear powder during braking, and the discharged copper may contaminate the water area by flowing into rivers, lakes, and oceans.

  Against this background, California and Washington in the United States have banned the sale of friction materials using friction materials containing 5% by weight or more of copper components and assembly into new cars since 2021. In addition, there is a bill that prohibits the sale of friction members using friction materials containing 0.5% by weight or more of copper components and the assembly into new cars.

  And since such regulations are expected to spread all over the world in the future, there is an urgent need to reduce the copper component contained in the friction material of NAO material, which is included in the friction material of NAO material Improvement of fade resistance and wear resistance, which is reduced by reducing the copper component, has become a problem.

  Patent Document 1 discloses a friction material containing 0.5 to 50% by weight of metal tin or tin alloy with respect to the total amount of the friction material composition and 0.001 to 4.999% by weight of copper with respect to the total amount of the friction material composition. A friction material formed by molding the composition is described.

  However, although the friction material described in Patent Document 1 satisfies the above-mentioned regulations regarding the content of the copper component, it cannot be said that the required performance of fade resistance and wear resistance is sufficiently ensured.

  In order to ensure fade resistance, it is effective to adjust the porosity of the friction material, and a porous material may be added to the friction material composition.

  Patent Document 2 discloses a porous sphere formed by bonding crystal grains of a titanate compound in a non-asbestos brake friction material containing a thermosetting resin as a binding component and containing a fiber base material, a filler, and an additive. A brake friction material having excellent fade resistance, characterized by containing particles, is described.

  The porous spherical particles described in Patent Document 2 are particles having a Mohs hardness of about 4. When a large amount of this porous spherical particle is added to the friction material composition in order to adjust the porosity of the friction material, the porous spherical particle dropped from the friction surface during braking grinds the friction material, and the friction material is likely to be worn. There is a problem.

US Published Patent No. 2010/0331447 Japanese Patent Laid-Open No. 10-139894

  The present invention secures the required performance of fade resistance and wear resistance while satisfying the laws and regulations concerning the content of copper component in the friction material molded from NAO friction material composition used for disc brake pads. It is an object to provide a friction material that can be used.

  As a result of intensive studies, the present inventors have found that a friction material obtained by molding a friction material composition of NAO material used for a disc brake pad contains a specific amount of digested dolomite particles as an inorganic friction modifier, and a friction material composition It was discovered that the above problem can be solved by using a friction material composition in which the total amount of copper components contained in the product is less than 5% by weight based on the total amount of the friction material composition, and the present invention has been completed.

  The present invention is a friction material obtained by molding a friction material composition of NAO material used for a disc brake pad, and is based on the following technique.

(1) A friction material used for a disc brake pad, wherein the friction material composition is formed by molding a friction material composition, and the friction material composition contains digested dolomite particles as an inorganic friction modifier in the total amount of the friction material composition. 5 to 25% by weight of the friction material, and the total amount of copper components contained in the friction material composition is less than 5% by weight with respect to the total amount of the friction material composition.

(2) The friction material according to (1), wherein the digested dolomite particles have an average particle diameter of 5 to 30 μm.

  According to the present invention, in a friction material obtained by molding a friction material composition of NAO material used for a disc brake pad, a friction material that can ensure fade resistance and wear resistance while satisfying the laws and regulations concerning the content of the copper component. Can provide.

  In the present invention, the friction material obtained by molding the friction material composition used for the disc brake pad contains 5 to 25% by weight of digested dolomite particles as an inorganic friction modifier in the total amount of the friction material composition. A friction material composition in which the total amount of copper components contained in the product is less than 5% by weight based on the total amount of the friction material composition is used.

Digested dolomite particles, also called dolomite plaster, are baked pulverized dolomite at a temperature of 900-1000 ° C to make light dolomite. After that, porous particles having a Mohs hardness of 2 to 3 and a specific surface area of 20 to 25 m ² / g obtained by pulverization with a pulverizer such as a ball mill.

  As described above, the porosity of the friction material can be improved by adding the digested dolomite particles to the friction material composition, and because the Mohs hardness is relatively low, the digested dolomite particles fall off from the friction surface during braking. Even in this case, the friction material is not ground.

  In addition, it is preferable to use digested dolomite particles having an average particle diameter of 5 to 30 μm because fade resistance and wear resistance are improved.

  In the present invention, the average particle size is a numerical value of 50% particle size measured by the laser diffraction particle size distribution method.

  By using the friction material composition described above, the friction material molded from the friction material composition of NAO material used for the disc brake pad, while satisfying the laws and regulations concerning the content of the copper component, the fade resistance and A friction material capable of ensuring the required performance of wear resistance can be provided.

  The friction material of the present invention includes, in addition to the digested dolomite particles, a binder, a fiber base material, a titanate, a lubricant, an inorganic friction modifier, an organic friction modifier, and a pH adjuster that are usually used for a friction material. And a friction material composition containing a filler and the like.

  As a binder, straight phenol resin, resin obtained by modifying phenol resin with various elastomers such as cashew oil, silicone oil, acrylic rubber, aralkyl-modified phenol resin obtained by reacting phenols, aralkyl ethers and aldehydes, Examples of the binder generally used for friction materials such as thermosetting resins in which various elastomers, fluoropolymers and the like are dispersed in a phenol resin can be used, and these can be used alone or in combination of two or more. . The content of the binder is preferably 4 to 12% by weight and more preferably 5 to 8% by weight with respect to the total amount of the friction material composition.

  As the fiber base material, organic fibers usually used for friction materials such as aramid fibers, cellulose fibers, poly-paraphenylenebenzobisoxazole fibers, acrylic fibers, copper fibers, bronze fibers, brass fibers, aluminum fibers, zinc fibers The metal fiber normally used for friction materials, such as these, is mentioned, These can be used individually by 1 type or in combination of 2 or more types.

  The organic fiber content is preferably 1 to 7% by weight, and more preferably 2 to 4% by weight, based on the total amount of the friction material composition.

  In the case of metal fibers, the content is preferably less than 7% by weight and more preferably less than 4% by weight with respect to the total amount of the friction material composition. When metal fibers containing a copper component are used, the total amount of the copper component is less than 5% by weight, preferably less than 0.5% by weight based on the total amount of the friction material composition. In addition, it is more preferable that a friction material composition does not contain a copper component from a viewpoint of environmental load reduction.

  The titanate preferably has a plate shape or an irregular shape, and is typically used for friction materials such as potassium titanate, lithium potassium titanate, and potassium magnesium titanate. These may be used alone or in combination of two or more. The content of titanate is preferably 7 to 35% by weight, more preferably 10 to 20% by weight, based on the total amount of the friction material composition.

  Lubricants such as molybdenum disulfide, zinc sulfide, tin sulfide, and composite metal sulfides, and carbonaceous lubricants such as artificial graphite, natural graphite, petroleum coke, activated carbon, and oxidized polyacrylonitrile fiber pulverized powder Lubricants usually used for friction materials such as materials can be mentioned, and these can be used alone or in combination of two or more. The content of the lubricant is preferably 2 to 13% by weight, more preferably 5 to 10% by weight, based on the total amount of the friction material composition.

  In addition to the above digested dolomite particles as inorganic friction modifiers, particles such as mica, vermiculite, iron trioxide, calcium silicate hydrate, glass beads, magnesium oxide, zirconium oxide, zirconium silicate, alumina, silicon carbide, etc. Inorganic friction modifiers such as wollastonite, sepiolite, basalt fiber, glass fiber, biosoluble artificial mineral fiber, rock wool and the like, and these may be used alone or in combination of two. A combination of the above can be used. The content of the inorganic friction modifier is preferably 15 to 50% by weight, more preferably 20 to 45% by weight, based on the total amount of the friction material composition together with the digested dolomite particles.

  Organic friction modifiers are usually used for friction materials such as cashew dust, crushed powder of tire tread rubber, vulcanized rubber powder such as nitrile rubber, acrylic rubber, silicone rubber, butyl rubber or unvulcanized rubber powder. An adjusting material is mentioned, These can be used individually by 1 type or in combination of 2 or more types. The content of the organic friction modifier is preferably 3 to 8% by weight, more preferably 4 to 7% by weight, based on the total amount of the friction material composition.

  As the pH adjusting material, a pH adjusting material usually used for friction materials such as calcium hydroxide can be used. The pH adjusting material is preferably 2 to 6% by weight, more preferably 2 to 3% by weight, based on the total amount of the friction material composition.

  As the balance of the friction material composition, a filler such as barium sulfate or calcium carbonate is used.

  The friction material used for the disc brake of the present invention is a mixing step in which a predetermined amount of the friction material composition is uniformly mixed using a mixer, and the obtained friction material raw material mixture is separately cleaned in advance. Processed and stacked with a back plate coated with adhesive, put into a thermoforming mold, heat-pressed to form by heating and pressurization, heating the resulting molded product to complete the curing reaction of the binder It is manufactured through a heat treatment process, a painting process, a paint baking process, and a polishing process for forming a friction surface by a rotating grindstone.

  If necessary, before the heat and pressure molding step, granulation step for granulating the friction material raw material mixture, kneading step for kneading the friction material raw material mixture, granulation obtained in the friction material raw material mixture or granulation step The preform and the kneaded product obtained in the kneading process are put into a preforming mold, and a preforming process for molding the preform is performed, and the scorch process is performed after the heat and pressure molding process.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Methods for producing friction materials of Examples 1 to 9 and Comparative Examples 1 to 3]
The friction material composition having the composition shown in Table 1 was mixed for 5 minutes with a Redige mixer, and pre-molded by pressurizing at 30 MPa in a molding die for 10 seconds. This preform is placed on a steel back plate that has been previously washed, surface-treated, and coated with an adhesive, and molded in a thermoforming mold at a molding temperature of 150 ° C. and a molding pressure of 40 MPa for 10 minutes, and then 200 Heat treatment (post-curing) was carried out at 5 ° C. for 5 hours, and polishing was performed to form a friction surface to produce a disc brake pad for a passenger car (Examples 1 to 9, Comparative Examples 1 to 3).

  The resulting friction material was evaluated for fade resistance and wear resistance. The evaluation results are shown in Table 2, and the evaluation criteria are shown in Table 3.

  ADVANTAGE OF THE INVENTION According to this invention, in the friction material which shape | molded the friction material composition of NAO material used for a disc brake pad, it can ensure fade resistance and abrasion resistance, satisfying the regulation regarding content of a copper component. A friction material can be obtained, which has extremely high practical value.

Claims (2)

  A friction material used for a disc brake pad, wherein the friction material composition is formed by molding a digested dolomite particle as an inorganic friction modifier with respect to the total amount of the friction material composition. A friction material containing -25% by weight, wherein the total amount of copper components contained in the friction material composition is less than 5% by weight based on the total amount of the friction material composition.   The friction material according to claim 1, wherein the digested dolomite particles have an average particle diameter of 5 to 30 μm.