Friction material composition and friction material

Abstract

To provide a friction material effective at a time of high-speed brake in a high temperature region and high in wear resistance and free from defect of a friction material, furthermore, low in rotor polishing property during running in a non-brake state in a usual temperature region.SOLUTION: A friction material composition is a friction material composition in which a content of copper in the friction material composition is less than 0.5 mass% as a copper element, and contains an inorganic filler (A) made of boehmite and another inorganic filler different from the boehmite and has a decomposition temperature of 600°C or higher and a Mohs hardness of 5 or lower, wherein a content of the boehmite in the friction material composition is 1 mass% or more and 24 mass% or less and a content of the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition is 1 mass% or more and 25 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a friction material composition and a friction material. [Background technology]

[0002] Friction materials are used in the disc brake pads and brake shoes of braking devices such as disc brakes and drum brakes.

[0003] Patent Document 1 describes that a friction material containing alumina hydrate represented by Al2O3·nH2O can suppress the decomposition of organic materials even at high temperatures such as 500°C or higher.

[0004] Patent Document 2 describes that a friction material containing calcium oxide and / or calcium hydroxide as the friction modifier component in an amount of 2 to 7 volume % based on the total composition, and further containing one or more friction modifier components selected from the group consisting of zeolite, activated clay, activated alumina, silica gel, powdered, granular or fibrous activated carbon, and sintered porous bodies in an amount of 1 to 20 volume % based on the total composition, has excellent stability of friction coefficient and reduction of low-frequency noise.

[0005] Patent Document 3 describes that a friction material containing flaky boehmite as a friction modifier has excellent friction and wear properties even at high temperatures, and is also excellent in productivity and workability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-221400 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-234086 [Patent Document 3] JP 2000-240702 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the friction materials of the above-mentioned prior art cannot satisfy all of the following requirements: (i) excellent braking effectiveness and wear resistance during high-speed braking at high temperatures; (ii) reduced pad chipping during high-speed braking at high temperatures; and (iii) low rotor abrasion during non-braking operation in the normal operating temperature range. Specifically, the technologies described in Patent Documents 1 and 3 provide insufficient measures to prevent pad chipping during high-speed braking at temperatures above 600°C. The friction material described in Patent Document 2 contains activated alumina, which results in high moisture absorption, resulting in low rust resistance and pad strength. Furthermore, because it contains activated alumina with a Mohs hardness of 6, the friction material described in Patent Document 2 exhibits high rotor abrasion during non-braking operation in the normal operating temperature range.

[0008] An object of one aspect of the present invention is to provide a friction material that exhibits high braking effectiveness and wear resistance during high-speed braking in a high-temperature range, is less likely to chip, and is less likely to abrade a rotor during running in a non-braking state in a normal temperature range. [Means for solving the problem]

[0009] As a result of intensive research to solve the above-mentioned problems, the present inventors have found for the first time that a friction material containing boehmite and a predetermined amount of inorganic filler (A) different from the boehmite, which has a decomposition temperature of 600°C or higher and a Mohs hardness of 5 or lower and a particle size of 1 μm or less, in a composition having a copper content of less than 0.5 mass % in terms of elemental copper, has excellent performance in all of the above-mentioned properties (i) to (iii), and have completed the present invention. That is, a friction material composition according to one embodiment of the present invention is a friction material composition having a copper content of less than 0.5% by mass in terms of elemental copper, and comprising boehmite and an inorganic filler (A) that is different from the boehmite and has a decomposition temperature of 600°C or higher and a Mohs hardness of 5 or lower, wherein the content of the boehmite in the friction material composition is 1% by mass or more and 24% by mass or less, and the content of the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition is 1% by mass or more and 25% by mass or less. [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to provide a friction material that has a copper content of less than 0.5 mass % in terms of elemental copper, yet exhibits high braking effectiveness and wear resistance and little chipping during high-speed braking in a temperature range of 600°C or higher, and further exhibits low rotor abrasion during running in a non-braking state in a normal temperature range. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a front view of a disc brake, schematically illustrating the mechanism by which DTV occurs. [Figure 2] FIG. 1 is a front view of a disk rotor alone in which DTV has occurred. DETAILED DESCRIPTION OF THE INVENTION

[0012] <1.Friction material composition> A friction material composition according to one embodiment of the present invention is a friction material composition having a copper content of less than 0.5% by mass in terms of elemental copper, and includes boehmite and an inorganic filler (A) different from the boehmite, the inorganic filler (A) having a decomposition temperature of 600°C or higher and a Mohs hardness of 5 or lower, wherein the boehmite content in the friction material composition is 1% to 24% by mass, and the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition is 1% to 25% by mass. The friction material composition of this embodiment is intended to be a composition containing friction material raw materials containing the above-mentioned components. The friction material composition of this embodiment can be used to form a friction material, as described below.

[0013] 〔Features〕 The friction material composition of this embodiment is environmentally friendly because it contains less than 0.5% by mass of elemental copper. Furthermore, because it contains a predetermined amount of boehmite and an inorganic filler (A) different from the boehmite, the inorganic filler (A) has a decomposition temperature of 600°C or higher, a Mohs hardness of 5 or lower, and a particle size of 1 μm or less, even in a composition containing less than 0.5% by mass of elemental copper, it has the excellent effect of providing a friction material that exhibits high braking effectiveness and wear resistance during high-speed braking at temperatures of 600°C or higher, is less likely to chip, and exhibits low rotor abrasion during non-braking driving in the normal operating temperature range.

[0014] Friction materials using the friction material composition of this embodiment have excellent braking effectiveness and wear resistance during high-speed braking at high temperatures (e.g., 600°C or higher, preferably 650°C or higher), and therefore can exhibit excellent performance in vehicles equipped with large batteries, such as electric vehicles (EVs) and hybrid electric vehicles (HEVs). Furthermore, friction materials using the friction material composition of this embodiment have low rotor abrasion during non-braking driving at normal temperatures (e.g., 200°C or lower), thereby minimizing the amount of uneven disc rotor wear (Disk Thickness Variation: DTV). Excessive DTV is known to be one of the causes of brake vibration (see, for example, JP 2005-273770 A). Therefore, disc brakes using a friction material using the friction material composition of this embodiment on the friction surface of the disc brake pad can minimize DTV growth during non-braking driving at normal temperatures, thereby achieving the excellent effect of reducing brake vibration. The DTV growth is a value measured by the method described in the Examples section below.

[0015] [Application] The friction material composition of this embodiment having the above-mentioned characteristics is particularly useful as a friction material composition for use in the friction surfaces of disc brake pads and drum brake shoes for electric vehicles (EVs) and hybrid electric vehicles (HEVs). This is because EVs / HEVs are heavier than conventional gasoline-powered vehicles due to the large batteries they are equipped with, and regenerative braking tends to contribute less to high-speed braking. As a result, the temperature of the brake pads or brake shoes is more likely to rise during high-speed braking in high-temperature ranges than in conventional gasoline-powered vehicles, and the temperature of the brake pads or brake shoes increases, increasing the frequency with which they reach high temperatures.

[0016] The use of the friction material composition of this embodiment is not particularly limited to EV / HEV, and it can be suitably used as a friction material used on the friction surfaces of disc brake pads, drum brake shoes, and the like, which are employed in all types of vehicles including motorcycles.

[0017] [Raw materials] The raw materials (friction material raw materials) contained in the friction material composition of this embodiment will be described below.

[0018] (copper) A friction material composition according to one embodiment of the present invention has a copper content of less than 0.5 mass% in terms of elemental copper. The friction material composition according to one embodiment of the present invention has an extremely low content of copper and copper alloys, which are highly environmentally harmful, and therefore provides an environmentally friendly friction material. From the perspective of providing a more environmentally friendly friction material, the copper content in the friction material composition is more preferably 0 mass% (copper-free). The copper contained in the friction material composition according to one embodiment of the present invention may be derived from copper fibers added as a fibrous base material.

[0019] (Boehmite) A friction material composition according to one embodiment of the present invention contains boehmite as one of the inorganic fillers, in an amount of 1% by mass or more and 24% by mass or less, based on 100% by mass of the friction material composition. Boehmite is also known as alumina monohydrate. In this specification, the term "boehmite" includes both crystalline boehmite represented by the general formula Al2O3·H2O and low-crystalline gel-like boehmite represented by the general formula Al2O3·nH2O (n is greater than 1 and less than 3). The former has a boehmite crystalline structure and is generally referred to as boehmite. The latter has a pseudo-boehmite crystalline structure and is referred to as pseudo-boehmite or boehmite gel. Among these, crystalline boehmite represented by Al2O3·H2O having a boehmite crystalline structure is preferred. The Mohs hardness of boehmite is 3.5 to 4. Crystalline boehmite and pseudo-boehmite are generally obtained by known production methods, such as hydrolysis of aluminum alkoxides such as aluminum isopropoxide, but natural sources may also be used. Crystalline boehmite and pseudo-boehmite can be distinguished by checking the powder X-ray diffraction spectrum using a known method.

[0020] (Actions and Effects of Boehmite) Boehmite forms a coating on the friction surface during high-speed braking at temperatures above 600°C. This coating increases the contact area on the friction surface, improving the friction coefficient (μ), and also improves wear resistance by protecting the friction surface. As a result, the heat resistance (effectiveness and wear resistance) of the friction material improves and pad chipping is reduced.

[0021] When the boehmite content in the friction material composition of this embodiment is 1% by mass or more based on 100% by mass of the friction material composition, the friction surface is sufficiently protected by the boehmite coating, thereby improving the heat resistance (effectiveness and wear resistance) of the friction material and achieving a significant effect in reducing pad chipping. Furthermore, when the boehmite content in the friction material composition of this embodiment is 24% by mass or less based on 100% by mass of the friction material composition, good pad formability is achieved.

[0022] Furthermore, as mentioned above, boehmite has a Mohs hardness of 3.5 to 4, which is lower than the particle hardness of alumina (equivalent to Mohs hardness 9) and activated alumina (equivalent to Mohs hardness 6). Therefore, by including boehmite in the friction material composition of this embodiment, rotor abrasion during non-braking operation in the normal operating temperature range can be reduced, resulting in the effect of reducing brake vibration. Diaspore is known as an alumina monohydrate with a different crystalline form from boehmite. Diaspore has a stronger crystalline structure than boehmite and a Mohs hardness of 6.5 to 7. Therefore, boehmite is preferable among alumina monohydrates from the viewpoint of reducing rotor abrasion during non-braking operation in the normal operating temperature range. Boehmite and diaspore can be distinguished by checking the powder X-ray diffraction spectrum using a known method.

[0023] (Preferable boehmite content) From the viewpoint of further improving the performance (effectiveness and wear resistance) of the friction material during high-speed braking in a high-temperature range, the content of boehmite in the friction material composition is preferably 3% by mass or more and 15% by mass or less, based on 100% by mass of the friction material composition.

[0024] (Preferable particle size of boehmite) The particle size of the boehmite is not limited, but an average particle size of 50 μm or less is preferable because it allows for uniform mixing without bias during the production of the friction material composition and the boehmite particles are less likely to fall off the friction surface during braking, resulting in stable improvement in the performance (effectiveness and wear resistance) of the friction material during high-speed braking at high temperatures. Furthermore, from the perspective of further reducing rotor abrasion during non-braking running in the normal operating temperature range, it is more preferable for the average particle size of the boehmite to be 10 μm or less. Furthermore, from the perspective of ease of handling during the production of the friction material composition, it is preferable for the average particle size of the boehmite to be 1 μm or more. The average particle size of the boehmite is the volume-based median diameter obtained by JIS Z 8825 "Particle Size Analysis - Laser Analysis and Scattering Method." When checking the particle size of boehmite after forming the friction material, the average particle size of particles corresponding to boehmite can be determined from an electron microscope image of the cross section of the friction material, by measuring the volumetric particle size distribution according to JIS Z 8827-1 "Particle size analysis - Image analysis methods - Part 1: Static image analysis methods" and then determining the median diameter.

[0025] (Preferable particle shape of boehmite) Examples of the particle shape of boehmite include scale-like, plate-like, granular, cubic, needle-like, and burr-like shapes. The particle shape of boehmite is not particularly limited, but since scale-like or plate-like boehmite has lubricity, from the viewpoint of improving braking effectiveness in the normal temperature range, the particle shape of boehmite is preferably granular, cubic, or needle-like. Furthermore, from the viewpoint of increasing the density of the pad and reducing chipping of the pad, the particle shape of boehmite is more preferably granular or cubic. Note that a cubic shape is one embodiment of the granular particle shape.

[0026] Particle shapes with a low aspect ratio (long diameter / thickness), expressed as the ratio of the long diameter to the thickness of the boehmite particle (for example, an aspect ratio (long diameter / thickness) of less than 4), are called granular or cubic, while particle shapes with a high aspect ratio (long diameter / thickness) (for example, an aspect ratio (long diameter / thickness) of 4 or more) are called scale-like or plate-like. Particle shapes with a high aspect ratio (long diameter / thickness) and a high aspect ratio (long diameter / minor diameter) are called acicular. Particle shapes in which many needle-shaped pieces are bound together to form a burr-like shape are called burr-like.

[0027] (Inorganic filler (A) with a particle size of 1 μm or less) The inorganic filler (A) is an inorganic filler different from boehmite, and refers to any inorganic filler having a decomposition temperature of 600°C or higher and a Mohs hardness of 5 or lower. A friction material composition according to one embodiment of the present invention contains the aforementioned predetermined amount of boehmite as one of the inorganic fillers, and also contains 1% by mass or more and 25% by mass or less of the inorganic filler (A) having a particle size of 1 μm or less, relative to 100% by mass of the friction material composition.

[0028] (Actions and effects of inorganic filler (A) with particle size of 1 μm or less) In one embodiment of the present invention, inorganic filler (A) particles having a particle size of 1 μm or less penetrate into the gaps between particles having a particle size exceeding 1 μm in the friction material composition, thereby increasing the filling rate of the friction material and forming a dense structure. As a result, a friction material using the friction material composition of this embodiment maintains a dense structure with few voids even when the binder resin decomposes at 600°C or higher. Furthermore, since the decomposition temperature of the inorganic filler (A) is 600°C or higher and the inorganic filler (A) itself is not easily decomposed, the dense structure with few voids can be maintained even during high-speed braking at temperatures above 600°C. As a result, the friction surface of the friction material is less likely to break down, resulting in excellent braking performance and wear resistance.

[0029] By setting the content of the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition of this embodiment to 1% by mass or more relative to 100% by mass of the friction material composition, the filling rate of the friction material increases and a sufficiently dense structure is formed, which makes the friction surface of the friction material less likely to collapse and provides significant effects in terms of improved effectiveness and wear resistance. Furthermore, by setting the content of the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition of this embodiment to 25% by mass or less relative to 100% by mass of the friction material composition, improved pad formability is achieved.

[0030] Furthermore, as described above, the Mohs hardness of the inorganic filler (A) is 5 or less. Therefore, by including the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition of this embodiment, it is possible to reduce rotor abrasion during running in a non-braking state in the normal temperature range, thereby achieving the effect of reducing the occurrence of brake vibration.

[0031] (Example of inorganic filler (A)) The inorganic filler (A) may be any inorganic filler having a decomposition temperature of 600°C or higher and a Mohs hardness of 5 or lower. Examples of inorganic fillers having a decomposition temperature of 600°C or higher and a Mohs hardness of 5 or lower include barium sulfate, calcium carbonate, and mica. To further densify the friction material, the inorganic filler (A) is preferably barium sulfate or calcium carbonate, which has a low aspect ratio (long diameter / thickness). The inorganic filler (A) may be used singly or in combination with multiple types. When multiple types of inorganic fillers (A) are used in combination, the content of the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition of this embodiment is the total amount of the multiple types of inorganic fillers (A) having a particle size of 1 μm or less. Although boehmite has a Mohs hardness of 5 or lower, its decomposition temperature is approximately 500°C, so the inorganic filler (A) is a different inorganic filler from boehmite.

[0032] (Decomposition temperature of inorganic filler (A)) The "decomposition temperature" used herein refers to the temperature at which weight loss begins, as determined by thermogravimetry (TG) according to JIS K 0129 "General Rules for Thermal Analysis." The temperature at which weight loss begins is the lowest temperature within the temperature range at which the weight equivalent to the molecules desorbed by heating decreases.

[0033] From the viewpoint of enhancing the effect at high temperatures, the inorganic filler (A) preferably has a decomposition temperature of 650°C or higher, more preferably 700°C or higher.

[0034] (Mohs hardness of inorganic filler (A)) The "Mohs hardness" described in this specification means the modified Mohs hardness, which is expressed in 15 levels from 1 to 15. The modified Mohs hardness can be measured according to a known measurement method.

[0035] From the viewpoint of the DTV growth amount, the inorganic filler (A) preferably has a Mohs hardness of 4.5 or less, more preferably 4 or less.

[0036] (Particle size of inorganic filler (A)) The friction material composition of this embodiment only needs to contain the aforementioned predetermined amount of inorganic filler (A) having a particle size of 1 μm or less, and may contain inorganic filler (A) having a particle size greater than 1 μm together with inorganic filler (A) having a particle size of 1 μm or less, as long as the effects of the present invention are not impaired. The upper limit of the particle size of inorganic filler (A) having a particle size greater than 1 μm is not particularly limited, and the particle size of inorganic fillers commonly used in the technical field can be preferably applied.

[0037] The amount of the inorganic filler (A) having a particle size of 1 μm or less contained in the friction material composition of this embodiment may be determined by the following method. 1. Measure the volumetric particle size distribution of the inorganic filler (A) according to JIS Z 8825 "Particle size analysis - laser analysis and scattering method." 2. From the particle size distribution of the inorganic filler (A) obtained, the cumulative value of particles of 1 μm or less is determined (unit: %). 3. The particle integrated value obtained in the previous section "2" indicates the proportion of particles of 1 μm or less contained in the inorganic filler (A). Therefore, the content of inorganic filler (A) with a particle size of 1 μm or less in the friction material can be calculated using the following formula. Content of inorganic filler (A) in friction material (mass%) x cumulative value of particles of 1 μm or less (%) / 100 The amount of inorganic filler (A) having a particle size greater than 1 μm contained in the friction material composition of this embodiment can be measured by a similar method.

[0038] (Preferable content of inorganic filler (A) having a particle size of 1 μm or less) From the viewpoint of further improving the performance (effectiveness and wear resistance) of the friction material during high-speed braking in a high-temperature range, the content of the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition is preferably 1% by mass or more and 20% by mass or less relative to 100% by mass of the friction material composition.

[0039] (Surface treatment of boehmite and inorganic filler (A)) The boehmite and inorganic filler (A) may be surface-treated. The use of surface-treated boehmite and inorganic filler (A) improves compatibility with the binder resin and improves water resistance.

[0040] As the surface treatment method, known methods can be used, such as a method of subjecting particles of boehmite and inorganic filler (A) to a treatment with a coupling agent, a treatment with phosphoric acid, etc.; a method of forming an inorganic layer of silica, alumina, etc. on the surface of particles of boehmite and inorganic filler (A); etc.

[0041] (Other ingredients) In addition to the above-mentioned components, the friction material composition of this embodiment contains, as friction material raw materials, a fibrous base material, a binder, an organic filler, and an inorganic filler different from boehmite and the inorganic filler (A).

[0042] (fiber substrate) Examples of the fibrous base material include organic fibers, inorganic fibers, and metal fibers. These fibers may be natural fibers or artificially synthesized synthetic fibers. Examples of organic fibers include aromatic polyamide fibers (aramid fibers), acrylic fibers, cellulose fibers, and carbon fibers. Examples of inorganic fibers include rock wool and glass fibers. Examples of metal fibers include fibers made of single metals such as steel, stainless steel, aluminum, zinc, and tin, as well as fibers made of alloys of these metals. One type of fibrous base material can be used alone, or multiple types can be used in combination. The content of the fibrous base material in the friction material composition is not particularly limited and can be a content commonly used in the relevant technical field.

[0043] (Binding material) The binder functions to bind the friction material raw materials in the friction material composition. The binder is not particularly limited as long as it can exhibit the above-mentioned properties, and binders known in the art can be preferably used. Specific examples of binders include resins such as phenolic resins, epoxy resins, melamine resins, and imide resins. One type of binder can be used alone, or multiple types can be used in combination. The content of the binder in the friction material composition is not particularly limited, and can be any content commonly used in the art. The binder may also contain modified components such as silicone rubber, acrylic rubber, and cashew oil.

[0044] (organic filler) The organic filler functions as a friction modifier to improve wear resistance, etc. The organic filler is not particularly limited as long as it can exhibit the above-mentioned properties, and organic fillers known in the art can be preferably used. Specific examples of organic fillers include cashew dust, rubber powder, tire powder, fluororesin, melamine cyanurate, and polyethylene resin. One type of organic filler can be used alone, or multiple types can be used in combination. The surface of the organic filler may also be coated with phosphoric acid or fluororesin. The content of the organic filler in the friction material composition is not particularly limited, and can be a content commonly used in the art.

[0045] (Another inorganic filler different from boehmite and inorganic filler (A)) The friction material composition of this embodiment may contain an inorganic filler other than boehmite and inorganic filler (A) to the extent that the effects of the present invention are not impaired. Examples of inorganic fillers other than boehmite and inorganic filler (A) that are well known in the art include zirconium oxide, iron oxide (ferrous oxide, ferric oxide, etc.), titanates, silicate compounds such as calcium hydroxide, calcium silicate, and zirconium silicate, and carbonate compounds such as magnesium carbonate and potassium carbonate. Examples of titanates include alkali metal titanates and alkali metal group II titanates, such as potassium titanate, sodium titanate, lithium titanate, lithium potassium titanate, and magnesium potassium titanate. These inorganic fillers may be used alone or in combination. The content of the inorganic filler other than boehmite and inorganic filler (A) is not particularly limited, and may be appropriately adjusted so that the total content of the inorganic filler, including boehmite and inorganic filler (A), falls within the range of inorganic filler content commonly used in the art.

[0046] By including zirconium oxide or titanate as an inorganic filler other than boehmite and inorganic filler (A), the coating formed on the friction surface during high-speed braking at temperatures above 600°C becomes stronger, and the heat resistance (effectiveness and wear resistance) of the friction material is further improved, which is preferable. In this case, the upper limit of the content of zirconium oxide and titanate is not particularly limited, and it may be appropriately adjusted so that the total content of the inorganic filler combined with the boehmite and inorganic filler (A) is the content of the inorganic filler adopted in the relevant technical field. The higher the content of zirconium oxide and titanate, the more the heat resistance of the friction material described above is improved, which is preferable.

[0047] The particle size of the inorganic filler other than boehmite and inorganic filler (A) is not particularly limited, and inorganic materials having an average particle size commonly used in the art can be preferably used. As mentioned above, particles of inorganic filler (A) with a particle size of 1 μm or less fill into the gaps between particles with a particle size exceeding 1 μm, thereby increasing the filling rate of the friction material and forming a dense structure. Considering this, the inorganic filler other than boehmite and inorganic filler (A) preferably contains particles with a particle size of more than 1 μm, and more preferably contains mostly particles with a particle size of more than 1 μm and substantially does not contain particles with a particle size of 1 μm or less. "Substantially does not contain particles with a particle size of 1 μm or less" means that the content of particles with a particle size of 1 μm or less is 20% by mass or less, 10% by mass or less, preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less of the total. The content of the inorganic filler having a particle size greater than 1 μm in the friction material composition of this embodiment may be appropriately adjusted so that the total content of the inorganic fillers, including the boehmite and the inorganic filler (A), falls within the range of inorganic filler contents accepted in the art.

[0048] (lubricant) The friction material composition of this embodiment may further contain a lubricant to the extent that the effects of the present invention are not impaired. The lubricant is not particularly limited, and lubricants known in the art can be preferably used. Specific examples of lubricants include coke, graphite, carbon black, graphite, and metal sulfides. Examples of metal sulfides include tin sulfide, antimony trisulfide, molybdenum disulfide, bismuth sulfide, iron sulfide, zinc sulfide, and tungsten sulfide. These lubricants can be used alone or in combination. The content of the lubricant is not particularly limited, and can be the content commonly used in the art.

[0049] (Method of manufacturing friction material composition) The friction material composition of this embodiment can be produced by a production method including a mixing step of blending and mixing the above-described friction material raw materials. From the viewpoint of uniformly mixing the friction material raw materials, the mixing step is preferably a step of mixing powdery friction material raw materials. The mixing method and mixing conditions in the mixing step are not particularly limited as long as the friction material raw materials can be uniformly mixed, and methods known in the art can be used. For example, the friction material raw materials may be mixed for about 10 minutes at room temperature using a known mixer such as a Fenchel mixer or a Lödige mixer. In the mixing step, the friction material raw material mixture may be cooled while mixing using a known cooling method to prevent the friction material raw materials from rising in temperature during mixing.

[0050] <2.Friction material> The friction material according to one embodiment of the present invention is obtained by molding the friction material composition according to one embodiment of the present invention. The effects and uses of the friction material according to this embodiment are the same as those described for the friction material composition according to one embodiment of the present invention, and therefore will not be repeated here.

[0051] (Method of manufacturing friction material) The friction material of this embodiment can be produced by a manufacturing method including a molding step of molding the friction material composition of one embodiment of the present invention. The molding method and molding conditions in the molding step are not particularly limited as long as they can mold one embodiment of the friction material composition of the present invention into a predetermined shape, and methods known in the art can be used. For example, one embodiment of the friction material composition of the present invention can be molded by compacting it with a press or the like. As a molding method using a press, either a hot press method in which one embodiment of the friction material composition of the present invention is heated and compacted to form a mold, or a cold press method in which one embodiment of the friction material composition of the present invention is compacted at room temperature without heating can be suitably used. When molding by the hot press method, for example, one embodiment of the friction material composition of the present invention can be molded into a friction material by setting the molding temperature to 140°C or higher and 200°C or lower (preferably 160°C), the molding pressure to 10 MPa or higher and 40 MPa or lower (preferably 20 MPa), and the molding time to 3 minutes or higher and 15 minutes or lower (preferably 10 minutes). When molding by room temperature pressing, for example, the friction material composition of the present invention can be molded into a friction material by setting the molding pressure to 50 MPa or more and 200 MPa or less (preferably 100 MPa) and the molding time to 5 seconds or more and 60 seconds or less (preferably 15 seconds). Furthermore, if necessary, a polishing step may be performed to polish the surface of the friction material to form a friction surface.

[0052] 3. Friction materials The present invention also encompasses a friction member that uses the friction material according to one embodiment of the present invention as a friction surface. The friction member may be configured to include only one embodiment of the friction material according to the present invention, or may be configured to integrate one embodiment of the friction material according to the present invention with a plate-like member such as a metal plate as a backing plate. The effects and uses of the friction member according to this embodiment are the same as those described for one embodiment of the friction material composition according to the present invention, and will not be repeated here.

[0053] When the friction member of this embodiment is configured by integrating a plate-shaped member with an embodiment of the friction material of the present invention, the embodiment of the friction material of the present invention and the plate-shaped member can be bonded by clamping the embodiment of the friction material of the present invention and the plate-shaped member, followed by heat treatment. The conditions for the clamping treatment are not particularly limited, but for example, 180°C, 1 MPa, and 10 minutes. The conditions for the heat treatment after the clamping treatment are also not particularly limited, but for example, 150°C or higher and 250°C or lower, and 5 minutes or longer and 180 minutes or shorter, preferably 230°C and 3 hours.

[0054] 〔summary〕 A first aspect of the present invention provides a friction material composition having a copper content of less than 0.5% by mass in terms of elemental copper, which comprises boehmite and an inorganic filler (A) different from the boehmite, the inorganic filler (A) having a decomposition temperature of 600°C or higher and a Mohs hardness of 5 or lower, wherein the boehmite content in the friction material composition is 1% to 24% by mass, and the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition is 1% to 25% by mass. This configuration provides the following advantages: even with a copper content of less than 0.5% by mass in terms of elemental copper, the friction material exhibits high braking effectiveness and wear resistance during high-speed braking at temperatures of 600°C or higher and is less likely to chip, and further exhibits low rotor abrasion during running without braking in a normal operating temperature range.

[0055] In the friction material composition according to Aspect 2 of the present invention, in the above-described Aspect 1, the boehmite preferably has an average particle size of 10 μm or less. With this configuration, it is possible to provide a friction material with lower rotor abrasion during running in a non-braking state in a normal temperature range.

[0056] A friction material composition according to a third aspect of the present invention is preferably the same as that of the first or second aspect, except that the boehmite content in the friction material composition is 3% by mass or more and 15% by mass or less, and the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition is 1% by mass or more and 20% by mass or less. This configuration provides a friction material that exhibits improved wear resistance and effectiveness during high-speed braking in a temperature range of 600° C. or more.

[0057] In a friction material composition according to a fourth aspect of the present invention, the boehmite is preferably granular boehmite in any one of the first to third aspects. This configuration can increase the density of the pad and reduce chipping of the pad.

[0058] A friction material according to a fifth aspect of the present invention is formed by molding the friction material composition according to any one of the first to fourth aspects.

[0059] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Example]

[0060] <Friction material raw materials> The main friction material raw materials used in the examples and comparative examples are as follows:

[0061] Boehmite (Al2O3·H2O): average particle size 1 μm, 8 μm, and 50 μm; particle shape is granular (aspect ratio (long diameter / thickness) 1.5) Activated alumina: average particle size 8μm · Barium sulfate (inorganic filler (A)): Two types of barium sulfate were used: one that does not contain particles with a particle size larger than 1 μm, and one that does not contain particles with a particle size smaller than 1 μm.

[0062] Calcium carbonate (inorganic filler (A)): As with barium sulfate, two types of calcium carbonate were used: one that does not contain particles with a particle size larger than 1 μm, and one that does not contain particles with a particle size of 1 μm or less.

[0063] Aluminum hydroxide and alumina (Al2O3): Aluminum hydroxide and alumina containing no particles larger than 1 μm in diameter were used.

[0064] Zirconium oxide, mica (inorganic filler (A)), iron oxide (composition: Fe2O3), and calcium hydroxide: Raw materials that do not contain particles with a particle size of 1 μm or less were used.

[0065] Raw materials other than the friction materials mentioned above were those commonly used in the art.

[0066] Table 1 shows the physical properties of the following inorganic fillers used in the examples and comparative examples as inorganic fillers with particle sizes of 1 μm or less.

[0067] [Table 1] Particles of these inorganic fillers with a particle size larger than 1 μm have the same physical properties as particles with a particle size of 1 μm or less.

[0068] Example 1 <Brake pad manufacturing> The raw materials were blended according to the blending ratios shown in Table 2 and mixed for about 10 minutes at room temperature (20°C) using a Loedige mixer to obtain a friction material composition. The blending amount of each raw material in Table 2 is expressed in mass % of the friction material composition.

[0069] The friction material composition was heated and compressed by a hot press using a molding press to obtain a molded product. The molding conditions for the hot press were as follows: Molding temperature: 160℃ Molding pressure: 20 MPa Molding time: 10 minutes The surface of the obtained molded article was polished using a polishing machine to form a friction surface, and a friction material was obtained. A brake pad of Example 1 was produced using this friction material, and a high-temperature test and an evaluation of the DTV growth amount after the test were performed. The brake pad produced in Example 1 had a friction material thickness of 12.5 mm and a friction material projected area of ​​55 cm. 2 It was.

[0070] Examples 2 to 10 Brake pads of Examples 2 to 10 were produced in the same manner as in Example 1, except that the raw materials were mixed according to the mixing ratios shown in Table 2.

[0071] Comparative Examples 1 to 10 Brake pads of Comparative Examples 1 to 10 were produced in the same manner as in Example 1, except that the raw materials were blended according to the blending ratios shown in Table 3.

[0072] <High temperature test> An AMS fade test (evaluation conditions published in the German automobile magazine Auto Motor Und Sport: vehicle speed 130 km / h, maximum rotor temperature 600°C or higher) was conducted, and the following evaluations were made for the brake pads of Examples 1 to 10 and Comparative Examples 1 to 10. The maximum rotor temperature in each test was 650 to 670°C.

[0073] (lowest friction coefficient) The lowest coefficient of friction during the AMS fade test was measured by the following method.

[0074] (Method for measuring the minimum coefficient of friction) Using the minimum torque during one braking, the friction coefficient for each braking was calculated using the formula specified in JIS D 0106. The lowest friction coefficient during the test was taken as the minimum friction coefficient.

[0075] The measurement results of the minimum friction coefficient were evaluated using a five-level score of A to E according to the following criteria. A: Improved by over 20% compared to Comparative Example 1 B: Improved by 10% or more and 20% or less compared to Comparative Example 1 C: Same as or equivalent to Comparative Example 1 D: Deterioration of 10% or more and 20% or less compared to Comparative Example 1 E: Deterioration of more than 20% compared to Comparative Example 1 Here, if the minimum friction coefficient of the brake pad being evaluated increased by 10% or more compared to the minimum friction coefficient of the brake pad of Comparative Example 1, it was evaluated as "improved," and if the minimum friction coefficient of the brake pad being evaluated decreased by 10% or more compared to the minimum friction coefficient of the brake pad of Comparative Example 1, it was evaluated as "deteriorated." If the increase or decrease in the minimum friction coefficient of the brake pad being evaluated was less than 10% compared to the minimum friction coefficient of the brake pad of Comparative Example 1, it was evaluated as the same as or equivalent to Comparative Example 1.

[0076] (wear amount) The amount of wear of the brake pads after the AMS fade test was measured by the following method.

[0077] (Method for measuring wear amount) The amount of wear was measured in accordance with JASO C427 6. Measurement method.

[0078] After the test, the amount of pad wear was measured at eight points on each brake pad, and the average value was taken as the "amount of pad wear."

[0079] The measurement results of the amount of wear were evaluated using a five-level score of A to E according to the following criteria. A: Improved by over 20% compared to Comparative Example 1 B: Improved by 10% or more and 20% or less compared to Comparative Example 1 C: Same as or equivalent to Comparative Example 1 D: Deterioration of 10% or more and 20% or less compared to Comparative Example 1 E: Deterioration of more than 20% compared to Comparative Example 1 Here, if the wear amount of the brake pad being evaluated decreased by 10% or more compared to the wear amount of the brake pad in Comparative Example 1, it was evaluated as "improved," and if the wear amount of the brake pad being evaluated increased by 10% or more compared to the wear amount of the brake pad in Comparative Example 1, it was evaluated as "worsened." If the increase or decrease in the wear amount of the brake pad being evaluated was less than 10% compared to the wear amount of the brake pad in Comparative Example 1, it was evaluated as the same as or equivalent to Comparative Example 1.

[0080] (presence or absence of chips) After the AMS fade test, the appearance of the brake pad was visually observed to check for chipping in the brake pad.

[0081] <Measurement of DTV growth (μm) after testing> As shown schematically in Figure 1, uneven wear (hereinafter simply referred to as DTV) occurs and grows when the brake friction material 12a of the inner pad 12 and the brake friction material 13a of the outer pad 13 lightly contact the friction surfaces 11a, 11b of the disc rotor 11 with a surface pressure that is much lighter than that during braking, due to the rotational runout of the disc rotor 11 (the runout angle θ and runout amount S are exaggerated in Figure 1) during driving without braking, and the contact areas are scraped away by the brake friction materials 12a, 13a of the pads 12, 13. Furthermore, this DTV is generally expressed as the difference between the maximum thickness To of the disc rotor 11 shown in Figure 2 and the minimum thickness T1 or T2.

[0082] Using a bench tester, the initial disc rotor runout S (see Figure 1) was set to 100 μm, and the test was repeated 50 times (vehicle speed 65 km / h → vehicle speed 0 km / h, deceleration 3.5 m / s 2 The test was repeated 30 times in total, and the DTV was compared with the initial DTV. The difference was recorded as the DTV growth amount (μm) after the test.

[0083] After the test, the measurement results of the DTV growth amount were evaluated using a three-level score of A to C according to the following criteria. A: Equivalent to or better than Comparative Example 1 B: Deterioration of 10% or more and 20% or less compared to Comparative Example 1 C: Deterioration of more than 20% compared to Comparative Example 1 Here, if the post-test DTV growth amount of the disc rotor being evaluated decreased by 10% or more compared to the post-test DTV growth amount of the disc rotor of Comparative Example 1, it was evaluated as "improved," and if the post-test DTV growth amount of the disc rotor being evaluated increased by 10% or more compared to the post-test DTV growth amount of the disc rotor of Comparative Example 1, it was evaluated as "deteriorated." If the increase or decrease in the post-test DTV growth amount of the disc rotor being evaluated was less than 10% compared to the post-test DTV growth amount of the disc rotor of Comparative Example 1, it was evaluated as the same as or equivalent to Comparative Example 1. If the post-test DTV growth amount score was A, it means that the post-test DTV growth amount was able to be kept small, and it can be said that the friction material has low rotor grindability during running in a non-braking state in the normal temperature range.

[0084] As mentioned above, DTV can be one of the causes of brake vibration, so the score of the evaluation result of the post-test DTV growth measurement result can be said to represent the likelihood of brake vibration occurring. In other words, the three-level score (A to C) of the post-test DTV growth measurement result represents the likelihood of brake vibration occurring as follows: A: Equivalent to or less brake vibration than Comparative Example 1. B: Brake vibration occurs slightly more than in Comparative Example 1. C: Brake vibration occurs much more frequently than in Comparative Example 1.

[0085] <Result> The evaluation results of the high-speed test and the evaluation results of the measurement of the DTV growth amount after the test are shown in Tables 2 and 3.

[0086] [Table 2]

[0087] [Table 3] Examples enclosed by a thick line in Table 2 are those that, among the Examples, achieved particularly favorable evaluation results in the high-temperature test and the measurement of the DTV growth amount after the test. As shown in Table 2, the brake pads of Examples 1 to 10 contained, as inorganic fillers, (i) 1 mass % or more and 24 mass % or less of boehmite and (ii) 1 mass % or more and 25 mass % or less of inorganic filler (A) having a particle size of 1 μm or less in the friction material composition. As a result, it was confirmed that, compared with the brake pad of Comparative Example 1, the brake pads of Examples 1 to 10 had higher braking effectiveness and wear resistance during high-speed braking at temperatures above 600°C, less chipping of the friction material, and a reduced DTV growth amount after the test.

[0088] From the results shown in Comparative Examples 1 to 6, it was confirmed that in order to achieve the effects of high braking effectiveness and wear resistance and less chipping of the friction material during high-speed braking in a temperature range of 600°C or higher, it is necessary to contain both boehmite and inorganic filler (A) with a particle size of 1 μm or less in predetermined amounts.

[0089] Furthermore, as shown in Comparative Examples 2, 7, and 8, the desired effect could not be obtained even when a predetermined amount of inorganic filler (A) having a particle size larger than 1 μm or an inorganic filler other than inorganic filler (A) having a particle size of 1 μm or less was contained. Therefore, it was confirmed that in order to achieve the effects of high effectiveness and wear resistance and reduced chipping of the friction material during high-speed braking at temperatures above 600°C, it is necessary to contain inorganic filler (A) having a particle size of 1 μm or less.

[0090] Furthermore, as shown in Comparative Example 9, even when a predetermined amount of activated alumina (Al2O3) was included instead of boehmite (Al2O3·H2O), the expected effect could not be obtained. Therefore, it was confirmed that the inclusion of boehmite (Al2O3·H2O), which is an alumina hydrate, is necessary to achieve the effects of high effectiveness and wear resistance during high-speed braking in a temperature range of 600°C or higher, reduced chipping of the friction material, and reduced DTV growth after the test.

[0091] From the above results, it has become clear that by including (i) 1 mass % or more and 24 mass % or less of boehmite as inorganic fillers and (ii) 1 mass % or more and 25 mass % or less of inorganic filler (A) having a particle size of 1 μm or less in the friction material composition, it is possible to provide a friction material that has high braking effectiveness and wear resistance and is less likely to chip during high-speed braking at temperatures of 600°C or more, even though the copper content is less than 0.5 mass % in terms of copper element, and that also has low rotor abrasion during running in a non-braking state in the normal temperature range. [Industrial Applicability]

[0092] The friction material composition and friction material according to one aspect of the present invention can be suitably used as friction members in braking devices of vehicles such as automobiles. [Explanation of symbols]

[0093] 11 Disc rotor 12 outer pad 13 Inner pad 12a, 13a Brake friction material θ Rotational swing angle S Rotational runout

Claims

1. The friction material composition has a copper content of less than 0.5% by mass in terms of elemental copper, Boehmite and and an inorganic filler (A) that is different from the boehmite and has a decomposition temperature of 600°C or higher and a Mohs hardness of 5 or lower, The content of the boehmite in the friction material composition is 1% by mass or more and 24% by mass or less, and The friction material composition has a content of the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition of 1 mass % or more and 25 mass % or less.

2. 2. The friction material composition according to claim 1, wherein the boehmite has an average particle size of 10 [mu]m or less.

3. The content of the boehmite in the friction material composition is 3% by mass or more and 15% by mass or less, and 3. The friction material composition according to claim 1, wherein the content of the inorganic filler (A) having a particle size of 1 μm or less in the friction material composition is 1% by mass or more and 20% by mass or less.

4. The friction material composition according to claim 1 , wherein the boehmite is granular boehmite.

5. A friction material obtained by molding the friction material composition according to any one of claims 1 to 4.

Images