JP7252886B2 - friction material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a friction material molded from a friction material composition of an NAO material that contains a binder, a fiber base material, an inorganic friction modifier, an organic friction modifier, and does not contain a copper component, for use in disc brake pads.

2. Description of the Related Art Conventionally, disc brakes have been used as braking devices for passenger cars, and disc brake pads, in which a friction material is attached to a metallic base member, are used as friction members.

In recent years, there has been a demand for quieter brakes, and disc brake pads that use NAO (Non-Asbestos-Organic) friction materials that do not contain steel fibers such as steel fibers and stainless steel fibers as the fiber base material are widely used. It is coming into use.

In order to ensure the required performance of conventional NAO friction materials, copper components such as copper or copper alloy fibers or particles are added as an essential component of about 5 to 20% by weight based on the total amount of the friction material composition. It is

However, in recent years, it has been suggested that such friction materials emit copper as abrasion powder during braking, and that this discharged copper may pollute water areas by flowing into rivers, lakes, and oceans. There is a demand for a NAO friction material with reduced copper content.

As a friction material of NAO material with a reduced copper component, Patent Document 1 discloses a friction material composition containing a binder, an organic filler, an inorganic filler, and a fiber base material. Does not contain copper, or has a copper content of 0.5% by mass or less relative to the entire friction material composition, and contains 25 to 30% by mass of a non-needle-shaped titanate as an inorganic filler relative to the entire friction material composition. zirconium silicate having an average particle size of 0.4 to 0.6 μm and a maximum particle size of 1.1 μm as an inorganic filler is contained in an amount of 3 to 6% by mass based on the total friction material composition, and an average particle size of 20 A friction material composition containing 0.5 to 2.0% by mass of γ-alumina of up to 200 μm with respect to the entire friction material composition and a friction material obtained by molding the friction material composition are disclosed.

In order to secure the required coefficient of friction in the friction material of the NAO material, hard inorganic particles are sometimes added as an inorganic filler, and aluminum oxide particles are used as the hard inorganic particles.

Patent Document 2 describes a disc pad material for a passenger car containing 3-7% by volume of spherical aluminum oxide particles having a particle size of 1-10 μm and a sphericity of 0.95-1.

According to the invention described in Patent Document 2, it is possible to provide a disc pad for a passenger car that has a high coefficient of friction, excellent wear resistance and wear resistance to mating material, and remarkably reduced brake squeal.

Spherical aluminum oxide particles having a particle size of 1 to 10 μm and a sphericity of 0.95 to 1, which are added to the disc pad for passenger cars in Patent Document 2, do not have sufficient grinding action in the high speed and high temperature range. There is a problem that sufficient braking effect cannot be obtained.

Patent Document 3 discloses a friction material containing spherical α-alumina (aluminum oxide) particles having crystal grains, the average crystal grain size of the crystal grains being 150 to 1000 nm, and the average particle diameter being 5 to 400 μm. is described.

According to the invention described in Patent Document 3, the structure of α-alumina particles collapses during braking and spreads over the friction surface, thereby forming a stable abrasion powder coating on the friction surface, especially in the low speed range. While maintaining the stability of the coefficient of friction in, the aggression against the mating material can be mitigated and excellent wear resistance can be imparted.

Spherical α-alumina (aluminum oxide) particles having an average crystal grain size of 150 to 1000 nm and an average particle diameter of 5 to 400 μm added to the friction material of Patent Document 3 change their structure by braking. collapses.
As a result, the grinding action of α-alumina is not exhibited in the high-speed, high-temperature region, and there is a problem that sufficient braking effect cannot be obtained in the high-speed, high-temperature region.

JP 2018-131479 A JP-A-10-259837 JP 2017-149866 A

The present invention relates to a friction material molded from a friction material composition of an NAO material that contains a binder, a fiber base material, an inorganic friction modifier, an organic friction modifier, and does not contain a copper component, which is used for a disc brake pad, An object of the present invention is to provide a friction material having excellent braking effectiveness in high-speed, high-temperature regions and excellent wear resistance.

As a result of intensive studies by the present inventors, the friction material composition of the NAO material containing a binder, a fiber base material, an inorganic friction modifier, an organic friction modifier, and not containing a copper component, which is used for disc brake pads By using a friction material composition containing a specific amount of spherical amorphous alumina particles with a significantly larger average particle size than conventional friction materials as inorganic friction modifiers in molded friction materials, it is possible to improve performance in high-speed and high-temperature regions. The present inventors have found that the effectiveness of the brake is improved, and furthermore, by adding a specific amount of fluoropolymer particles as an organic friction modifier, the wear resistance is further improved, and have completed the present invention.

The present invention is a friction material molded from a friction material composition of an NAO material that contains a binder, a fiber base material, an inorganic friction modifier, an organic friction modifier, and does not contain a copper component, which is used for a disc brake pad. It is based on the following technologies.

(1) A friction material containing a binding material, a fiber base material, an inorganic friction modifier, an organic friction modifier, and not containing a copper component, which is molded from a NAO material composition used for disc brake pads, The friction material composition contains spherical amorphous alumina particles having an average particle diameter of 100 to 300 μm as the inorganic friction modifier in an amount of 0.5 to 6% by weight based on the total amount of the friction material composition.
(2) The friction material according to (1), which contains 0.5 to 5% by weight of fluoropolymer particles as the organic friction modifier with respect to the total amount of the friction material composition.

According to the present invention, a friction material molded from a friction material composition of an NAO material that contains a binder, a fiber base material, an inorganic friction modifier, an organic friction modifier, and does not contain a copper component, which is used for a disc brake pad. , it is possible to provide a friction material having excellent braking effectiveness in high-speed, high-temperature regions and excellent wear resistance.

In the present invention, a friction material that contains a binder, a fiber base material, an inorganic friction modifier, an organic friction modifier, and does not contain a copper component is molded from a friction material composition of an NAO material that is used for a disc brake pad. A friction material composition containing spherical amorphous alumina particles having an average particle size of 100 to 300 μm in an amount of 0.5 to 6% by weight based on the total amount of the friction material composition is used as an inorganic friction modifier.

By adding 0.5 to 6% by weight of spherical amorphous alumina particles with an average particle diameter of 100 to 300 μm to the total amount of the friction material composition as an inorganic friction modifier, the braking effectiveness at high speeds and high temperatures is improved. do.
If the average particle size of the spherical amorphous alumina particles is less than 100 μm, the grinding action of the amorphous alumina particles cannot be obtained, and sufficient braking effect cannot be obtained in a high-speed high-temperature region. If the particle size exceeds 300 μm, the abrasive action of the amorphous alumina particles becomes excessive, which causes the problem of abnormal wear of the friction material. More preferably, the spherical amorphous alumina particles have an average particle size of 150 to 250 μm.
In the present invention, the average particle size is the numerical value of the 50% particle size measured by the laser diffraction particle size distribution method.

Further, if the content of the spherical amorphous alumina particles is less than 0.5% by weight with respect to the total amount of the friction material composition, the abrasive action of the amorphous alumina particles cannot be obtained, and sufficient friction is not obtained in the high-speed and high-temperature range. If the braking effect cannot be obtained and the content exceeds 6% by weight based on the total amount of the friction material composition, the abrasive action of the amorphous alumina particles becomes excessive, resulting in abnormal wear of the friction material.
The amount of spherical amorphous alumina particles to be added is more preferably 1 to 5% by weight with respect to the total amount of the friction material composition.

The friction material of the present invention further contains fluorine-based polymer particles as an organic friction modifier in an amount of 0.5 to 5% by weight based on the total amount of the friction material composition.
By containing 0.5 to 5% by weight of the fluoropolymer particles having a lubricating action with respect to the total amount of the friction material composition, the wear resistance is further improved.

Examples of fluorine-based polymer particles include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and the like. One type can be used alone or two or more types can be used in combination.
Among them, it is preferable to use polytetrafluoroethylene (PTFE) powder alone from the viewpoint of heat resistance.

The friction material of the present invention contains, in addition to the above spherical amorphous alumina particles and fluoropolymer particles, binders, fiber base materials, inorganic friction modifiers, and organic friction modifiers that are commonly used in friction materials. It consists of a friction material composition.

Binders include straight phenolic resin, cashew oil-modified phenolic resin, acrylic rubber-modified phenolic resin, nitrile rubber (NBR)-modified phenolic resin, silicone rubber-modified phenolic resin, phenol-aralkyl resin (aralkyl-modified phenolic resin), and fluoropolymer dispersion. Binders commonly used in friction materials such as phenolic resins can be used, and these can be used singly or in combination of two or more.
The content of the binder is preferably 5 to 15% by weight, more preferably 6 to 10% by weight, based on the total amount of the friction material composition.

Examples of the fiber base material include organic fibers commonly used for friction materials such as aramid fiber, cellulose fiber, poly-paraphenylenebenzobisoxazole fiber, and acrylic fiber. Can be used in combination.
The content of the fiber base material is preferably 1 to 8% by weight with respect to the total amount of the friction material composition, and more preferably 3 to 5% by weight with respect to the total amount of the friction material composition.

Inorganic friction modifiers include molybdenum disulfide, zinc sulfide, tungsten sulfide, bismuth sulfide, iron sulfide, tin sulfide, composite metal sulfides, artificial graphite, natural graphite, Flaky graphite, elastic graphitized carbon, petroleum coke, activated carbon, polyacrylonitrile oxide fiber pulverized powder, barium sulfate, calcium carbonate, calcium hydroxide, phlogopite, muscovite, talc, triiron tetraoxide, calcium silicate hydrate , glass beads, magnesium oxide, zirconium oxide, zirconium silicate, γ-alumina, silicon carbide, non-whisker-like (plate-like, scale-like, columnar, irregular shape with multiple protrusions) titanate (titanate , potassium hexatitanate, potassium octatitanate, lithium potassium titanate, magnesium potassium titanate, etc.), wollastonite, sepiolite, basalt fiber, glass fiber, biosoluble artificial mineral fiber, rock wool, etc. Commonly used inorganic friction modifiers can be mentioned, and these can be used singly or in combination of two or more.
The content of the inorganic friction modifier, together with the spherical amorphous alumina particles, is preferably 70 to 90% by weight based on the total amount of the friction material composition, and 75 to 90% by weight based on the total amount of the friction material composition. 85% by weight is more preferable.

As organic friction modifiers, in addition to the above fluorine-based polymer particles, cashew dust, pulverized tire tread rubber powder, vulcanized rubber powder or unvulcanized rubber powder such as nitrile rubber, acrylic rubber, silicone rubber, butyl rubber, etc. Organic friction modifiers commonly used in friction materials can be mentioned, and these can be used singly or in combination of two or more.
The content of the organic friction modifier is preferably 4 to 15% by weight, more preferably 6 to 12% by weight, based on the total amount of the friction material composition.

The friction material used in the disc brake of the present invention is prepared by a mixing step of uniformly mixing a predetermined amount of a friction material composition using a mixer, the obtained friction material raw material mixture, and separately pre-cleaning and surface treatment. A heat and pressure molding process in which the back plate that has been treated and coated with the adhesive is placed on top of the back plate and put into a thermoforming mold and molded by heating and pressing. The resulting molded product is heated to complete the curing reaction of the binder. It is manufactured through a heat treatment process, an electrostatic powder coating process for applying powder coating, a coating baking process for baking the coating, and a polishing process for forming a friction surface with a rotating grindstone. In some cases, after the heat and pressure molding process, the manufacturing process is performed in the order of a painting process, a heat treatment process that also serves as baking of the paint, and a polishing process.

If necessary, a granulation step of granulating the friction material raw material mixture, a kneading step of kneading the friction material raw material mixture, and granulation obtained in the friction material raw material mixture or the granulation step before the heat and pressure molding step. The kneaded product obtained in the kneading step is put into a preforming mold to form a preformed product.

EXAMPLES Hereinafter, the present invention will be specifically described by showing examples and comparative examples, but the present invention is not limited to the following examples.

[Methods for producing friction materials of Examples 1 to 13 and Comparative Examples 1 to 4]
The friction material compositions having the compositions shown in Tables 1 and 2 were mixed in a Loedige mixer for 5 minutes, and preformed by pressurizing at 30 MPa for 10 seconds in a mold. This preform is placed on a steel back plate that has been washed, surface-treated, and coated with an adhesive in advance, and molded in a thermoforming mold at a molding temperature of 150 ° C. and a molding pressure of 40 MPa for 10 minutes. C. for 5 hours (post-curing) and polished to form a friction surface to produce disc brake pads for passenger cars (Examples 1 to 13, Comparative Examples 1 to 4).

The resulting friction material was evaluated for braking effectiveness and wear resistance in a high-speed, high-temperature region.
Evaluation methods and evaluation criteria are shown in Table 3, and evaluation results are shown in Tables 4 and 5.

As can be seen from each table, the compositions satisfying the composition of the present invention have good evaluation results in terms of braking effectiveness and wear resistance in high-speed, high-temperature regions.

According to the present invention, a friction material used in a disc brake pad, which is obtained by molding a friction material composition of an NAO material containing a binder, a fiber base material, an inorganic friction modifier , and an organic friction modifier , contains a copper component. It is possible to provide a friction material that satisfies the regulations concerning quantity, has excellent braking performance in high-speed and high-temperature regions, and has excellent wear resistance, and is of extremely high practical value.

Claims (2)

A friction material containing a binding material, a fiber base material, an inorganic friction modifier, an organic friction modifier, and a friction material composition of NAO material that does not contain a copper component, and is used for disc brake pads. A friction material containing spherical amorphous alumina particles having an average particle diameter of 100 to 300 μm as the inorganic friction modifier in an amount of 0.5 to 6% by weight based on the total amount of the friction material composition. 2. The friction material according to claim 1, wherein the friction material composition contains 0.5 to 5% by weight of fluoropolymer particles as the organic friction modifier.