Friction material composition and friction material

Abstract

A friction material composition according to one embodiment of the present invention has a copper content of less than 0.5% by mass in terms of elemental copper, with respect to the total amount of the friction material composition, the present invention is characterized by comprising: 0.05-1 mass% of one or two inorganic materials (excluding monoclinic zirconium oxide) selected from the group consisting of (1) inorganic materials having an average particle diameter of 1 [mu] m or less and a Mohs hardness of 7.5-8 and (2) inorganic materials having an average particle diameter of 50 [mu] m or less and a Mohs hardness of 6-7.5; 5 to 35 mass% of monoclinic zirconium oxide; and 0.5-10% by mass of magnesium hydroxide.

Description

Technical Field

[0001] This 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 discloses a friction component having a friction material and a back plate, wherein the friction material does not contain copper, or even if it does contain copper, the copper content is less than 0.5% by mass based on copper element, and contains inorganic fibers with a fiber length of 400 μm or more.

[0004] Patent Document 2 discloses a friction material for disc brake pads, which is formed from a friction material composition that does not contain copper. The friction material composition contains specific amounts of a binding material, organic fibers, metal sulfide lubricating material, carbonaceous lubricating material, titanate, wollastonite, particulate inorganic friction modifier with a Mohs hardness of 4.5 or higher and less than 8.0, inorganic friction modifier with a Mohs hardness of less than 4.5, organic friction modifier, and pH modifier. It does not contain substances with a Mohs hardness of 8.0 or higher, elemental metals other than copper, or alloys other than copper alloys.

[0005] Patent document 3 discloses a non-asbestos friction material, which is formed and cured from a non-asbestos friction material composition comprising a fiber substrate other than asbestos, a binder, an organic filler, and an inorganic filler. The characteristic is that it contains one or more inorganic materials selected from inorganic materials with a Mohs hardness of 4.5 or higher and inorganic materials with a Mohs hardness of less than 4.5 and containing more than 50% by weight of a component with a Mohs hardness of 4.5 or higher as grinding materials, and the volume ratio of the total amount of organic matter to the total amount of grinding material in the above composition (total amount of organic matter: total amount of grinding material) is 1.5:1 to 3.5:1.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2020 / 089979

[0009] Patent Document 2: Japanese Patent Application Publication No. 2014-159871

[0010] Patent Document 3: Japanese Patent Application Publication No. 2002-241737 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, the friction component described in Patent Document 1 lacks sufficient performance and wear resistance during high-speed braking in a high-temperature range, as well as wear resistance in a normal temperature range such as during urban driving. Furthermore, the friction material described in Patent Document 2 lacks sufficient performance during high-speed braking in a high-temperature range. Additionally, the non-asbestos-based friction material described in Patent Document 3 lacks sufficient ability to remove rust generated on the contact surfaces with mating components such as disc rotors and brake drums during light-load braking, resulting in insufficient rust removal performance under light-load conditions. Therefore, there is room for improvement in the friction materials of the prior art.

[0013] One objective of this invention is to provide a friction material that exhibits excellent performance and wear resistance during high-speed braking in a high-temperature range, and also possesses sufficient wear resistance in a conventional temperature range, thereby demonstrating excellent rust removal performance during light-load braking.

[0014] Methods for solving problems

[0015] In order to solve the above-mentioned problems, the inventors conducted in-depth research and first discovered that: in a friction material composition with a copper content of less than 0.5% by mass (calculated as copper element), friction materials containing specific amounts of inorganic materials with specific particle size and specific Mohs hardness, monoclinic zirconia and magnesium hydroxide exhibit excellent performance and wear resistance during high-speed braking in the high-temperature range, and also have sufficient wear resistance in the normal temperature range. Furthermore, they exhibit excellent rust removal performance during light-load braking, thus completing the present invention. That is, the following structure: a friction material composition of one aspect of the present invention, wherein the copper content in the friction material composition is less than 0.5% by mass based on copper element, and is configured to include, relative to the total amount of the friction material composition: 0.05% by mass and 1% by mass of one or two inorganic materials selected from the group consisting of (1) and (2) below (except monoclinic zirconia), namely, (1) an inorganic material with an average particle size of 1 μm or less and a Mohs hardness of 7.5 or more and 8 or less, (2) an inorganic material with an average particle size of 50 μm or less and a Mohs hardness of 6 or more and less than 7.5; 5% by mass and 35% by mass of monoclinic zirconia; and 0.5% by mass and 10% by mass of magnesium hydroxide.

[0016] Invention Effects

[0017] According to one aspect of the present invention, a friction material can be provided that, although the copper content, which has a high environmental load, is less than 0.5% by mass based on copper element, exhibits excellent performance and wear resistance during high-speed braking in a high-temperature range, and also has sufficient wear resistance in a normal temperature range, thereby providing excellent rust removal performance during light-load braking. Detailed Implementation

[0018] <1. Friction Material Composition>

[0019] A friction material composition of one aspect of the present invention, wherein the copper content in the friction material composition is less than 0.5% by mass based on copper element, wherein, relative to the total amount of the friction material composition described above, it comprises: 0.05% by mass and 1% by mass of one or two inorganic materials selected from the group consisting of (1) and (2) below (excluding monoclinic zirconia), namely, (1) an inorganic material with an average particle size of 1 μm or less and a Mohs hardness of 7.5 or more and 8 or less, (2) an inorganic material with an average particle size of 50 μm or less and a Mohs hardness of 6 or more and less than 7.5; 5% by mass and 35% by mass of monoclinic zirconia; and 0.5% by mass and 10% by mass of magnesium hydroxide. A friction material composition of one aspect of the present invention refers to a composition formed by combining friction material raw materials containing the above-mentioned components. A friction material composition of one aspect of the present invention can be used to form the friction material described later.

[0020] One aspect of the friction material composition of the present invention is environmentally friendly because the copper content in the friction material composition is less than 0.5% by mass based on elemental copper. Furthermore, it exhibits excellent effects as a friction material containing specific amounts of inorganic materials with specific particle sizes and specific Mohs hardness, monoclinic zirconia, and magnesium hydroxide. Therefore, although the copper content is less than 0.5% by mass based on elemental copper, it exhibits excellent performance and wear resistance during high-speed braking in a high-temperature range, and also possesses sufficient wear resistance in a conventional temperature range, resulting in excellent rust removal performance during light-load braking.

[0021] Friction materials using a friction material composition according to one aspect of the present invention exhibit improved wear resistance during high-speed braking in a high-temperature range (e.g., above 650°C), thereby simultaneously improving performance during high-speed braking in the high-temperature range. Furthermore, the improved wear resistance during high-speed braking in the high-temperature range can also be considered as an improvement in the strength of the friction material on the friction surface, thereby also promising an improvement in the heat resistance of the friction material.

[0022] Furthermore, friction materials using the friction material composition of one aspect of the present invention can balance wear resistance during high-speed braking in a high-temperature range with wear resistance within a conventional temperature range (e.g., 100°C to 200°C), thus exhibiting a superior longer lifespan compared to existing friction materials. Moreover, friction materials using the friction material composition of one aspect of the present invention, due to their excellent wear resistance, release less dust due to wear. As a result, they exhibit the superior effect of less dust pollution of the wheels and lower emissions of PM2.5 and PM10, which have a high environmental impact.

[0023] Furthermore, the friction material using the friction material composition of one aspect of the present invention exhibits excellent rust removal performance under light-load braking, thus effectively removing rust generated on the surface of the mating parts even under light-load braking. Therefore, the friction material is less likely to adhere to the mating parts due to rust generated on the contact surface with them. As a result, it exhibits excellent performance in reducing problems such as abnormal noise during engine start and surface peeling of the friction material. In this specification, "light-load braking" refers to a braking state in which the ratio (braking load) of braking force obtained through friction is reduced compared to conventional hydraulic brakes. More specifically, it refers to a friction-only braking state at low speeds with an initial speed of 10 km / h or less.

[0024] 〔use〕

[0025] The friction material composition of one aspect of the present invention, having the above-described features, 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, due to their large batteries, are heavier than conventional gasoline vehicles, and tend to have lower contributions from regenerative braking and regenerative coordinated braking during high-speed braking. Compared to conventional gasoline vehicles, the temperature of the brake pads or brake shoes tends to rise more easily during high-speed braking in the high-temperature range, increasing the frequency of reaching high temperatures.

[0026] Furthermore, in vehicles equipped with regenerative brakes or regenerative coordinated brakes, compared to existing hydraulic brakes, the ratio of braking force obtained through friction (braking load) is reduced at low to medium speeds (20-60 km / h) where brakes are used more frequently in the market, resulting in a light load. Therefore, there is a tendency for insufficient rust removal capacity due to the braking load. The friction material composition of one aspect of the present invention is particularly useful in vehicles equipped with regenerative brakes or regenerative coordinated brakes because of its excellent rust removal performance under light-load braking.

[0027] The use of the friction material composition of one aspect of the present invention is not particularly limited to EV / HEV, but can be applied to friction materials used in the friction surfaces of disc brake pads, drum brake shoes, etc., used in all vehicles, including two-wheeled vehicles.

[0028] 〔raw material〕

[0029] The following describes the raw materials (friction material raw materials) contained in a friction material composition according to one aspect of the present invention.

[0030] (copper)

[0031] One aspect of the friction material composition of the present invention comprises a copper content of less than 0.5% by mass, calculated as elemental copper. This friction material composition of the present invention, due to its very low content of environmentally harmful copper and copper alloys, effectively provides an environmentally friendly friction material. From the viewpoint of providing an even more environmentally friendly friction material, the copper content in the friction material composition is more preferably 0% by mass (copper-free). The copper contained in the friction material composition of one aspect of the present invention may be derived from copper fibers added as a fiber matrix.

[0032] (Inorganic materials)

[0033] One aspect of the friction material composition of the present invention contains, relative to 100% by mass, 0.05% by mass and less than 1% by mass of one or two inorganic materials selected from the group consisting of (1) and (2) below (except monoclinic zirconia): (1) Inorganic materials with an average particle size of less than 1 μm and a Mohs hardness of 7.5 or higher and less than 8; (2) Inorganic materials with an average particle size of 50 μm or less and a Mohs hardness of 6 or more but less than 7.5. Hereinafter, for ease of explanation, “one or two inorganic materials selected from the group consisting of (1) and (2)” will be referred to as “inorganic material (A)”, “(1) inorganic materials with an average particle size of 1 μm or less and a Mohs hardness of 7.5 or more but less than 8” will be referred to as “inorganic material (1)”, and “(2) inorganic materials with an average particle size of 50 μm or less and a Mohs hardness of 6 or more but less than 7.5” will be referred to as “inorganic material (2)”. In addition, “Mohs hardness” as described in this specification refers to Mohs hardness expressed as a value of 1 to 10. Mohs hardness can be measured according to known measurement methods. The above-mentioned inorganic particles can be added as grinding materials.

[0034] The inorganic material (A) can be either inorganic material (1) or inorganic material (2). Alternatively, it can be a combination of inorganic material (1) and inorganic material (2). For reasons explained later, it is preferable to use inorganic material (1) or inorganic material (2) alone as inorganic material (A). The reason is that when inorganic material (1) and inorganic material (2) are used in combination, inorganic material (1) with a Mohs hardness of 7.5 or higher and 8 or lower will cut and remove inorganic material (2) with a Mohs hardness of 6 or higher and less than 7.5, thereby causing the latter to lose its effect and achieving the same effect as when inorganic material (1) is used alone. When inorganic material (1) and inorganic material (2) are used in combination, it is preferable to adjust the amount of inorganic material (1) and inorganic material (2) such that the total content of inorganic material (1) and inorganic material (2) is 0.05% by mass or more and 1% by mass or less, and the content of inorganic material (1) alone is 0.05% by mass or more and 1% by mass or less, so as to fully obtain the effect of adding inorganic material (A).

[0035] (Inorganic materials (1))

[0036] Inorganic material (1) is an inorganic material particle with an average particle size of less than 1 μm and a Mohs hardness of more than 7.5 and less than 8, and is not a monoclinic zirconia inorganic material particle.

[0037] There is no particular limitation on the types of inorganic materials with a Mohs hardness of 7.5 or higher and 8 or lower. Examples of inorganic materials with such a Mohs hardness include zirconium silicate, beryl, and chromium oxide. Inorganic material (1) can be used alone or in combination. From the viewpoint of availability and cost, inorganic material (1) is preferably selected from one or more of the group consisting of zirconium silicate and chromium oxide.

[0038] (Inorganic materials (2))

[0039] Inorganic material (2) is an inorganic material particle with an average particle size of less than 50 μm and a Mohs hardness of more than 6 and less than 7.5, and is not a monoclinic zirconia inorganic material particle.

[0040] There is no particular limitation on the types of inorganic materials with a Mohs hardness of 6 or higher but less than 7.5. Examples of inorganic materials with such a Mohs hardness include stabilized zirconium oxide, cerium oxide, silica (including silica), magnesium oxide, high-alumina cement, cassiterite, and orthoclase. Stabilized zirconium oxide refers to zirconium oxide stabilized in a cubic crystal form at room temperature. One type of inorganic material (2) may be used alone or in combination. From the viewpoint of availability and cost, inorganic material (2) is preferably selected from one or more of the group consisting of stabilized zirconium oxide, cerium oxide, silica, magnesium oxide, cassiterite, and orthoclase.

[0041] (The role and effect of inorganic materials (A))

[0042] (i) Improved rust removal performance under light-load braking

[0043] Monoclinic zirconia (details will be described later) is easily worn, so even under light braking loads, zirconia particles can diffuse onto the friction surface. Inorganic materials (1) and (2), having a hardness close to that of monoclinic zirconia, moderately cut the zirconia particles diffused onto the friction surface due to wear, thus creating sharp angles. The zirconia particles that have just worn away and diffused onto the friction surface have low sharpness and therefore no rust removal ability, but by being cut into sharp angles by inorganic material (A), they can also help remove rust. Inorganic material (A) also helps remove rust as an abrasive material, but its rust removal performance under light braking loads is insufficient. In addition to the rust removal effect of inorganic material (A), the large number of zirconia particles that have become sharp angles remove rust under light loads, thus improving the rust removal performance under light braking loads. As a result, the rust removal performance under light braking loads is fully utilized.

[0044] The reasons why the hardness of the inorganic material (A) is suitable within the aforementioned specific range are as follows: The inorganic material (A) has a Mohs hardness of 6 or higher, thus sufficiently achieving the effect of appropriately cutting the monoclinic zirconia particles diffused onto the friction surface to make them acute angles. Furthermore, the inorganic material (A) has a Mohs hardness of 8 or lower, thus preventing complete grinding and removal of the monoclinic zirconia diffused onto the friction surface. Therefore, by ensuring the hardness of the inorganic material (A) is within the aforementioned range, rust removal performance under light-load braking can be improved.

[0045] Next, the reasons why the appropriate particle size varies depending on the hardness of the inorganic material (A) will be explained. First, as a premise, given the same content (mass%) of inorganic material (A) in the friction material composition, the smaller the particle size of inorganic material (A), the more particles exist per unit area. Furthermore, the more inorganic material (A) particles exist per unit area, the more uniformly the monoclinic zirconia particles diffused onto the friction surface can be cut.

[0046] The inorganic material (1) in the inorganic material (A) has a Mohs hardness of 7.5 or higher and 8 or lower, which is harder than monoclinic zirconia. Therefore, the particles of inorganic material (1) are less likely to become finer due to friction with monoclinic zirconia and are less likely to diffuse onto the friction surface. By making the average particle size of the inorganic material (1) less than 1 μm, the number of inorganic material (1) particles on the friction surface can be increased, and the monoclinic zirconia that has diffused onto the friction surface due to wear can be cut more uniformly. As a result, the number of monoclinic zirconia particles with sharp angles that contribute to rust removal performance under light-load braking can be increased, and rust removal performance under light-load braking can be improved.

[0047] The inorganic material (2) in the inorganic material (A) has a Mohs hardness of 6 or higher and less than 7.5, which is comparable to or lower than that of monoclinic zirconia. Therefore, through friction with the monoclinic zirconia that diffuses onto the friction surface due to wear in the initial stage of braking, the particles of the inorganic material (2) become finer and can diffuse onto the friction surface together with the monoclinic zirconia. Therefore, from the viewpoint of easy diffusion onto the friction surface, compared with the inorganic material (1), a wider range of particle sizes can be obtained to achieve the effect of cutting the particles of monoclinic zirconia into acute angles. That is, even if the average particle size of the inorganic material (2) exceeds 1 μm, the particles of the inorganic material (2) become finer through friction with the monoclinic zirconia and can diffuse onto the friction surface together with the monoclinic zirconia, thus, the effect of cutting the particles of monoclinic zirconia into acute angles can be fully obtained.

[0048] Furthermore, as the particles of the inorganic material (2) become larger, the time required for the particles of the inorganic material (2), which become finer through friction with monoclinic zirconia, to diffuse onto the friction surface tends to increase. However, by making the average particle size of the inorganic material (2) particles less than 50 μm, even in regenerative brakes and regenerative coordinated brakes with lower braking frequencies than existing hydraulic brakes, the particles of the inorganic material (2), which become finer through friction with monoclinic zirconia, can diffuse sufficiently onto the friction surface. As a result, the number of particles of monoclinic zirconia with acute angles that contribute to rust removal performance during light-load braking can be increased, thereby improving rust removal performance during light-load braking.

[0049] The average particle size of the inorganic material (1) or (2) is the median diameter (median particle size) of the volume reference obtained by JIS Z 8825 "Particle size analysis - Laser analysis and scattering method". After the particle size of the inorganic material (1) or (2) is confirmed after the friction material is formed, the median diameter can be determined by measuring the particle size distribution of the volume reference and calculating the average particle size of the particles corresponding to the inorganic material (1) or (2) based on the electron microscope image of the cross section of the friction material.

[0050] (ii) Improved wear resistance over the normal temperature range

[0051] By adjusting the particle size and proportion of inorganic materials (1) and (2) with specified Mohs hardness to the aforementioned specific range, wear resistance can be maintained within the normal temperature range. The reasons are as follows.

[0052] Inorganic materials (1) and (2) have higher hardness compared to cast iron and stainless steel, which are used as materials for disc rotors and brake drums. If the proportion of inorganic materials (1) and (2) exceeds 1% by mass, the grinding amount of the disc rotor and brake drum increases sharply, and the friction material is ground by the friction surfaces of the disc rotor and brake drum, which are made into sharp angles through grinding, thus greatly increasing the wear of the friction material. If the proportion of inorganic materials (1) and (2) is less than 1% by mass, the grinding amount of the disc rotor and brake drum is less, thus maintaining wear resistance within the normal temperature range.

[0053] In one embodiment of the present invention, the content of inorganic material (A) in the friction material composition is 0.05% by mass or more relative to 100% by mass of the friction material composition, thereby enabling more uniform cutting of monoclinic zirconia that has diffused onto the friction surface due to wear, and thus fully exhibiting the effect described above (i). Furthermore, if the content of inorganic material (A) in the friction material composition of one embodiment of the present invention is 1% by mass or less relative to 100% by mass of the friction material composition, sufficient wear resistance can be maintained within a normal temperature range.

[0054] (Monoclinic Zirconia)

[0055] One aspect of the friction material composition of the present invention contains, relative to 100% by mass, 5% by mass and 35% by mass of monoclinic zirconia. Monoclinic zirconia can be added as an inorganic filler. "Monoclinic zirconia" refers to zirconia with a monoclinic crystal system. The crystal system of zirconia changes with temperature. At room temperature (20°C), the crystal structure is monoclinic; as the temperature increases, it transforms into tetragonal at 1170°C and cubic at 2370°C. The phase transition is accompanied by a volume change.

[0056] Pure zirconium oxide is most stable in its monoclinic crystal system at room temperature, but by fusing with yttrium oxide and magnesium oxide, cubic crystals can also exist stably at room temperature. Zirconia stabilized in cubic crystal form at room temperature is called "stabilized zirconium oxide".

[0057] Monoclinic zirconia has a Mohs hardness of 6 to 7, but it differs from the aforementioned inorganic materials (A).

[0058] (The role and effects of monoclinic zirconia)

[0059] (i) Improved rust removal performance under light-load braking

[0060] Monoclinic zirconia is easily worn; therefore, even under light braking loads, zirconia particles can diffuse onto the friction surface. These zirconia particles, diffused onto the friction surface due to wear, are cut into acute angles by the inorganic material (A), thus aiding in rust removal. Consequently, rust removal performance is improved under light braking loads.

[0061] (ii) Improved wear resistance over the normal temperature range

[0062] Monoclinic zirconia has lower toughness compared to stabilized zirconia. Therefore, monoclinic zirconia exhibits lower machinability not only under non-braking conditions but also under braking conditions, resulting in lower rotor machinability in both states, and the magnesium hydroxide diffused onto the friction surface is less likely to disappear. Consequently, the rust-preventive properties provided by the magnesium hydroxide diffused onto the friction surface can be fully utilized. Furthermore, monoclinic zirconia's lower toughness compared to stabilized zirconia leads to better wear resistance in the brake pads.

[0063] (iii) Improved efficiency and wear resistance during high-speed braking in the high-temperature range

[0064] Monoclinic zirconia fuses with magnesium oxide (a substance formed from the dehydration of magnesium hydroxide in friction materials) due to the high heat generated by high-speed braking (high-load braking) within a high-temperature range, thus becoming stabilized zirconia. A stabilized zirconia coating is formed on the friction surface to protect it. Furthermore, the cubic zirconia formed by reacting with magnesium oxide does not undergo the volume change associated with a phase transition, thus minimizing the reduction in the strength of the friction material on the friction surface. As a result, the wear resistance of the brake pads is improved, leading to an increase in the coefficient of friction (μ).

[0065] The content of monoclinic zirconia in the friction material composition according to one aspect of the present invention affects the thickness of the stabilized zirconia coating formed on the friction surface. In one aspect of the present invention, the content of monoclinic zirconia in the friction material composition is 5% by mass or more relative to 100% by mass of the friction material composition, thereby enabling the formation of a stabilized zirconia coating with a thickness sufficient to exhibit the effects described above (iii). Furthermore, if the content of monoclinic zirconia in the friction material composition according to one aspect of the present invention is 35% by mass or less relative to 100% by mass of the friction material composition, the stabilized zirconia coating will not be excessively thick. As a result, magnesium hydroxide will not be embedded in the stabilized zirconia coating, thus fully exhibiting the rust resistance effect provided by magnesium hydroxide. Additionally, the stabilized zirconia coating is less prone to peeling off from the friction surface, thus preventing a decrease in friction area and a reduction in performance at high temperatures due to variations in coating thickness. Therefore, the effects described above (iii) can be fully exhibited.

[0066] (Particle size of monoclinic zirconia)

[0067] From the viewpoint of exhibiting the effects described in (i) to (iii) above, the particle size of monoclinic zirconia is not particularly limited. Therefore, monoclinic zirconia with a particle size typically used as an inorganic filler added to friction materials can be appropriately selected. From the viewpoint of operability in manufacturing friction material compositions, the average particle size of monoclinic zirconia is preferably 1 μm or more, more preferably 3 μm or more, more preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 10 μm or more. Furthermore, based on the reasons that it can be uniformly mixed without deviation during the manufacture of friction material compositions and has less impact on the reduction of wear resistance, the average particle size of monoclinic zirconia is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 16 μm or less.

[0068] The average grain size of monoclinic zirconia is the median diameter (median grain size) of the volume reference obtained through JIS Z 8825 "Particle Size Analysis - Laser Analysis and Scattering Method". After confirming the grain size of monoclinic zirconia following the formation of the friction material, the median diameter is determined by measuring the particle size distribution of the volume reference and calculating the average grain size of the particles corresponding to the monoclinic zirconia using an electron microscope image of the cross-section of the friction material, according to JIS Z 8827-1 "Particle Size Analysis - Image Analysis Method - Part 1: Static Image Analysis Method".

[0069] (Magnesium hydroxide)

[0070] One aspect of the friction material composition of the present invention contains, relative to 100% by mass, 0.5% by mass and 10% by mass of magnesium hydroxide as an inorganic filler. Magnesium hydroxide can be added as an inorganic filler.

[0071] (The role and effects of magnesium hydroxide)

[0072] (i) Improved rust removal performance under light-load braking

[0073] Magnesium hydroxide is alkaline and has low solubility in water, making it difficult for rainwater or other water to remove it from friction surfaces. Therefore, it can prevent the growth of strong rust on friction surfaces. As a result, it contributes to improved rust removal performance under light loads.

[0074] (ii) Improved wear resistance over the normal temperature range

[0075] Magnesium hydroxide has a Mohs hardness of 2-3, making it prone to chipping due to friction with mating components such as disc rotors and brake drums. Therefore, alkaline magnesium hydroxide readily and evenly diffuses onto the friction surface. As a result, friction materials containing magnesium hydroxide exhibit higher rust-preventive properties.

[0076] Furthermore, magnesium hydroxide has low solubility in water, making it less likely for alkali to be lost from brake pads (friction surfaces, etc.) due to immersion in water. Therefore, its rust-preventive effect is more durable than other alkaline materials. As a result, friction materials containing magnesium hydroxide maintain their rust-preventive effect even when exposed to rain, such as during the rainy season, or under conditions of severe wear, such as old brake pads.

[0077] The pH of magnesium hydroxide is 10.5, which is not high enough to promote the decomposition of resins contained in friction materials as a binder. Therefore, friction materials containing magnesium hydroxide are less prone to strength reduction due to resin decomposition. As a result, the brake pads exhibit good wear resistance. Furthermore, rotor corrosion is suppressed by the rust-preventive effect of magnesium hydroxide, thus maintaining wear resistance even with long-term use.

[0078] (iii) Improved efficiency and wear resistance during high-speed braking in the high-temperature range

[0079] Magnesium hydroxide exhibits heat resistance based on dehydration endothermic effects at 300–400 °C. Magnesium hydroxide, uniformly diffused onto the friction surface, transforms into magnesium oxide through dehydration. The magnesium oxide, due to the high heat generated by high-speed braking (high-load braking) within the high-temperature range, fuses with the monoclinic zirconia (described later), thereby contributing to the formation of a stabilized zirconia coating. Stabilized zirconia readily forms a stable coating and exhibits excellent heat resistance. The stabilized zirconia coating protects the friction surface, thereby improving wear resistance and consequently increasing the coefficient of friction (μ).

[0080] In one embodiment of the present invention, the content of magnesium hydroxide in the friction material composition is 0.5% by mass or more relative to 100% by mass of the friction material composition. This allows a sufficient amount of magnesium hydroxide to diffuse onto the friction surface, thus fully exhibiting the effects described in (i) to (iii). Furthermore, if the content of magnesium hydroxide in the friction material composition of one embodiment of the present invention is 10% by mass or less relative to 100% by mass of the friction material composition, the effect of magnesium hydroxide dehydration on volume change is smaller, and it is less likely to cause a decrease in the strength of the base material of the friction material. As a result, the brake pad exhibits good wear resistance within the normal temperature range and also achieves sufficient heat resistance.

[0081] (Particle size of magnesium hydroxide)

[0082] From the viewpoint of exhibiting the effects described in (i) to (iii) above, the particle size of magnesium hydroxide is not particularly limited. Therefore, magnesium hydroxide with a particle size typically used as an inorganic filler added to friction materials can be appropriately selected. However, from the viewpoint of operability in manufacturing friction material compositions, the average particle size of magnesium hydroxide is preferably 2 μm or more, more preferably 4 μm or more. Furthermore, for reasons such as the following, the average particle size of magnesium hydroxide is preferably 20 μm or less, more preferably 15 μm or less: it allows for uniform mixing without deviation during the manufacturing of friction material compositions, and the magnesium hydroxide particles are less likely to detach from the friction surface during braking; therefore, the improved performance and wear resistance during high-speed braking in the high-temperature range can be stably obtained at any position on the friction surface.

[0083] The average particle size of magnesium hydroxide is the median diameter (median particle size) of the volume reference obtained through JIS Z 8825 "Particle size analysis - Laser analysis and scattering method". If the particle size of magnesium hydroxide is confirmed after the friction material is formed, the median diameter can be determined by measuring the particle size distribution of the volume reference and calculating the average particle size of the particles corresponding to magnesium hydroxide using JIS Z 8827-1 "Particle size analysis - Image analysis method - Part 1: Static image analysis method" based on the electron microscope image of the cross-section of the friction material.

[0084] (Optimal content of each component)

[0085] From the viewpoint of further improving the rust removal performance under light-load braking, the content of inorganic material (A) in the friction material composition is preferably 0.2% by mass or more and 1% by mass or less relative to 100% by mass of the friction material composition.

[0086] Furthermore, from the viewpoint of further improving the efficiency and wear resistance during high-speed braking in the high-temperature range, the wear resistance in the normal temperature range, and the rust removal performance during light-load braking, the content of monoclinic zirconium oxide in the friction material composition is preferably 20% by mass or more and 30% by mass or less relative to 100% by mass of the friction material composition.

[0087] Furthermore, from the viewpoint of further improving the efficiency and wear resistance during high-speed braking in the high-temperature range, the wear resistance in the normal temperature range, and the rust removal performance during light-load braking, the content of magnesium hydroxide in the friction material composition is preferably 1% by mass or more and 5% by mass or less relative to 100% by mass of the friction material composition.

[0088] In a friction material composition according to one aspect of the present invention, preferably at least one of (a) the content of inorganic material (A), (b) the content of monoclinic zirconia, and (c) the content of magnesium hydroxide is the aforementioned preferred content. For example, it may be that only (a), only (b), or only (c) are the aforementioned preferred contents. Alternatively, it may be that a combination of (a) and (b), a combination of (a) and (c), or a combination of (b) and (c) are the aforementioned preferred contents. Alternatively, it may be that all of (a) to (c) are the aforementioned preferred contents.

[0089] From the viewpoint of exhibiting a more favorable effect, it is even more preferable that, in a friction material composition according to one aspect of the present invention, the content of inorganic material (A) in the friction material composition is 0.2% by mass or more and 1% by mass or less, the content of monoclinic zirconium oxide in the friction material composition is 20% by mass or more and 30% by mass or less, and the content of magnesium hydroxide in the friction material composition is 1% by mass or more and 5% by mass or less.

[0090] (Other ingredients)

[0091] Without impairing the effects of the present invention, in addition to the above-mentioned components, the friction material composition of one aspect of the present invention may also contain a fiber substrate, a binding material, an organic filler, and other inorganic fillers different from monoclinic zirconia and magnesium hydroxide as friction material raw materials.

[0092] (Metallic materials)

[0093] Examples of metallic materials include metal fibers and metal powders. Among these, fibers and powders can be composed of single metals such as steel, stainless steel, aluminum, zinc, and tin, as well as fibers and powders composed of their respective alloy metals. Metallic materials can be used alone or in combination. Metallic materials readily adhere to disc rotors and drum brakes; therefore, from the viewpoint of maintaining wear resistance within a normal temperature range, the content of metallic materials in the friction material composition is preferably 1.2% by mass or less.

[0094] (Fiber substrate)

[0095] Examples of fiber-based materials include organic fibers and inorganic fibers. These fibers can be natural fibers or artificially synthesized fibers. Examples of organic fibers include aromatic polyamide fibers (aramid fibers), acrylic fibers, cellulose fibers, and carbon fibers. Examples of inorganic fibers include asbestos and glass fibers. Furthermore, the aforementioned metal fibers can also be defined as fiber-based materials. One type of fiber-based material can be used alone, or multiple types can be used in combination. The content of the fiber-based material in the friction material composition is not particularly limited and can be set to a content commonly used in this technical field.

[0096] (Based on the material)

[0097] The binder material functions to bind the friction material raw materials in the friction material composition. There are no particular limitations on the binder material; any material that can perform the aforementioned properties is acceptable, and binders known in the art are preferred. Specific examples of binders include phenolic resins, epoxy resins, melamine resins, and imide resins. One binder material can be used alone, or multiple binders can be used in combination. The content of the binder material in the friction material composition is not particularly limited and can be set to a content commonly used in the art. Furthermore, the binder material may contain modifying components such as silicone rubber, acrylic rubber, and cashew nut oil.

[0098] (Organic filler material)

[0099] Organic filler materials function as friction modifiers to improve wear resistance, etc. There are no particular limitations on the organic filler material; any material that can achieve the aforementioned properties is acceptable, and organic filler materials known in the art are preferred. Specific examples of organic filler materials include rubber powder, tire powder, cashew nut powder, fluoropolymers, melamine cyanurate, and polyethylene resin. One type of organic filler material can be used alone, or multiple types can be used in combination. Furthermore, the organic filler material can have its surface covered with phosphoric acid or fluoropolymers. The content of the organic filler material in the friction material composition is not particularly limited; it can be set to a content commonly used in the art.

[0100] (Other inorganic filler materials that differ from monoclinic zirconia and magnesium hydroxide)

[0101] Without impairing the effects of the invention, the friction material composition of one aspect of the invention may also contain other inorganic filler materials different from monoclinic zirconia and magnesium hydroxide. As other inorganic filler materials different from monoclinic zirconia and magnesium hydroxide, inorganic materials with a Mohs hardness of less than 6 are preferred. As such inorganic materials, inorganic materials known in the art can be preferred, for example, barium sulfate, mica, iron oxide (ferrous oxide, ferric oxide, etc.), titanates, calcium hydroxide, etc. As titanates, for example, alkali metal titanates, alkali metal group II titanates, etc., and as specific examples, potassium titanate, sodium titanate, lithium titanate, potassium lithium titanate, potassium magnesium titanate, etc. These inorganic filler materials can be used alone or in combination. The content of other inorganic filler materials different from monoclinic zirconia and magnesium hydroxide in the friction material composition is not particularly limited, as long as the total content of the inorganic filler materials combined with monoclinic zirconia and magnesium hydroxide is appropriately adjusted to be within the range of inorganic filler material content used in the art.

[0102] By incorporating titanate as an inorganic filler material different from monoclinic zirconia and magnesium hydroxide, the coating formed on the friction surface during high-speed braking in a temperature range above 650°C becomes more robust, further improving the heat resistance (efficiency and wear resistance) of the friction material, which is therefore preferred. In this case, there is no particular upper limit to the titanate content; it can be appropriately adjusted so that the total content of the inorganic filler material, together with monoclinic zirconia and magnesium hydroxide, is the content of the inorganic filler material used in this technical field. The higher the titanate content, the better the heat resistance of the aforementioned friction material, which is also preferred.

[0103] In addition, the particle size of other inorganic fillers, which are different from monoclinic zirconium oxide and magnesium hydroxide, is not particularly limited, and inorganic materials with an average particle size commonly used in this technical field can be preferred.

[0104] (Lubricant)

[0105] Without impairing the effects of the invention, the friction material composition of one aspect of the invention may further include a lubricant. There are no particular limitations on the lubricant, and lubricants known in the art are preferred. Specific examples of lubricants include coke, lead (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 set to a content commonly used in the art.

[0106] Without impairing the effects of the invention, a friction material composition of one aspect of the invention may further comprise an inorganic material with a Mohs hardness greater than 8, but from the viewpoint of exhibiting preferred effects, it is preferable not to comprise an inorganic material with a Mohs hardness greater than 8.

[0107] (Method for manufacturing friction material composition)

[0108] One aspect of the friction material composition of the present invention can be manufactured by a manufacturing method including a mixing step of combining the above-mentioned friction material raw materials. From the viewpoint of uniformly mixing the friction material raw materials, the mixing step is preferably the step of mixing powdered 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, using a known mixer such as a Henschel mixer or a Loedige mixer, the friction material raw materials can be mixed at room temperature for about 10 minutes. In the mixing step, the mixture of friction material raw materials can be cooled while being mixed using a known cooling method to prevent the friction material raw materials from heating up during the mixing process.

[0109] <2. Friction Materials>

[0110] One aspect of the friction material of the present invention is formed from a friction material composition of the present invention. Regarding the friction material composition of the present invention in one aspect of the present invention, as previously described, it will not be repeated here.

[0111] (Manufacturing methods for friction materials)

[0112] A friction material according to one aspect of the present invention can be manufactured by a manufacturing method including a molding step of molding a friction material composition according to one aspect of the present invention. The molding method and molding conditions in the molding step are not particularly limited, as long as the friction material composition according to one aspect of the present invention can be molded into a predetermined shape, and methods known in the art can be used. For example, the friction material composition according to one aspect of the present invention can be molded by compacting it using a press or the like. As a molding method using a press, either a hot pressing process in which the friction material composition according to one aspect of the present invention is heated and compacted, or a room temperature pressing process in which the friction material composition according to one aspect of the present invention is compacted at room temperature without heating, is preferred. In the case of hot pressing, for example, 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) allows the friction material composition according to one aspect of the present invention to be molded into a friction material. When using a room-temperature pressing process for molding, for example, 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), the friction material composition of one aspect of the present invention can be molded into a friction material. Furthermore, if necessary, a grinding step can be performed to grind the surface of the friction material to form a friction surface.

[0113] <3. Friction Components>

[0114] Friction components using a friction material according to one aspect of the present invention as a friction surface are also included within the scope of the present invention. As a friction component, it can be a structure possessing only the friction material according to one aspect of the present invention, or a structure integrating a plate-like component such as a metal plate serving as a backing plate with the friction material according to one aspect of the present invention. Regarding the friction material according to one aspect of the present invention in a friction component according to one aspect of the present invention, as described above, it will not be repeated here.

[0115] In the case where the friction component of one aspect of the present invention is an integral structure of a plate-shaped component and a friction material of one aspect of the present invention, the friction material and the plate-shaped component of one aspect of the present invention are subjected to a pressing process, followed by heat treatment, thereby enabling the friction material and the plate-shaped component of one aspect of the present invention to be bonded. The pressing process conditions are not particularly limited, for example, 180°C, 1 MPa, and 10 minutes. Furthermore, the heat treatment conditions after the pressing process are not particularly limited, for example, 150°C or higher and 250°C or lower, 5 minutes or higher and 180 minutes or lower, preferably 230°C and 3 hours.

[0116] 〔Summarize〕

[0117] [1] The friction material composition of Embodiment 1 of the present invention, wherein the copper content in the friction material composition is less than 0.5% by mass based on copper element, wherein, Relative to the total amount of the above friction material composition, it includes: 0.05% by mass and 1% by mass of one or two inorganic materials selected from the group consisting of (1) and (2) below (excluding monoclinic zirconia), that is, (1) Inorganic materials with an average particle size of less than 1 μm and a Mohs hardness of 7.5 or higher and less than 8. (2) Inorganic materials with an average particle size of less than 50 μm and a Mohs hardness of 6 or higher but less than 7.5; Monoclinic zirconium oxide comprising more than 5% by mass and less than 35% by mass; and Magnesium hydroxide, 0.5% by mass or more and 10% by mass or less.

[0118] Based on this structure, the friction material can provide the following effects: although the copper content is less than 0.5% by mass, it has superior performance and wear resistance during high-speed braking in the high-temperature range compared to existing friction materials, and also has sufficient wear resistance in the normal temperature range, thus exhibiting excellent rust removal performance during light-load braking.

[0119] [2] The friction material composition of the present invention in the second embodiment is, in the above embodiment 1, the content of one or two inorganic materials selected from the group consisting of (1) and (2) is preferably 0.2% by mass or more and 1% by mass or less.

[0120] Based on this structure, the rust removal performance under light-load braking is further optimized.

[0121] [3] The friction material composition of the present invention in embodiment 3 is such that, in embodiment 1 or 2 above, the content of the monoclinic zirconia in the friction material composition is preferably 20% by mass or more and 30% by mass or less.

[0122] Based on this structure, the performance and wear resistance during high-speed braking in the high-temperature range, the wear resistance in the normal temperature range, and the rust removal performance during light-load braking are further optimized.

[0123] [4] The friction material composition of the present invention in any one of the above-mentioned methods 1 to 3 is such that the content of the above-mentioned magnesium hydroxide in the friction material composition is preferably 1% by mass or more and 5% by mass or less.

[0124] Based on this structure, the performance and wear resistance during high-speed braking in the high-temperature range, the wear resistance in the normal temperature range, and the rust removal performance during light-load braking are further optimized.

[0125] [5] The friction material composition of the present invention in embodiment 5 is, in embodiment 1 above, preferably, the content of one or two inorganic materials selected from the group consisting of (1) and (2) above is 0.2% by mass or more and 1% by mass or less, the content of the monoclinic zirconia in the friction material composition is 20% by mass or more and 30% by mass or less, and the content of the magnesium hydroxide in the friction material composition is 1% by mass or more and 5% by mass or less.

[0126] Based on this structure, the efficiency and wear resistance during high-speed braking in the high-temperature range, the wear resistance in the normal temperature range, and the rust removal performance during light-load braking are significantly optimized.

[0127] [6] The friction material of embodiment 6 of the present invention has a structure formed by molding a friction material composition of any one of embodiments 1 to 5.

[0128] This invention is not limited to the above embodiments, and various modifications can be made within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in each embodiment are also included in the technical scope of this invention.

[0129] Example

[0130] <Friction Material Raw Materials>

[0131] The main friction material raw materials used in the examples and comparative examples are as follows.

[0132] • Alumina: Average particle size 0.7μm, Mohs hardness 9

[0133] Zirconium silicate: average particle size 0.8 μm or 19 μm, Mohs hardness 7.5.

[0134] Stabilized zirconia: average particle size 35μm, Mohs hardness 7

[0135] • Mineral (cassiterite): Average grain size 190 μm, Mohs hardness 6.5

[0136] Monoclinic zirconia: average grain size ≥10μm, Mohs hardness 7

[0137] Magnesium hydroxide: average particle size 4μm, Mohs hardness 2

[0138] Titanate: Mohs hardness 4

[0139] Barium sulfate: Mohs hardness 3

[0140] Mica: Mohs hardness 3

[0141] Iron oxide: Mohs hardness 5

[0142] Calcium hydroxide: Mohs hardness 2

[0143] Iron fiber: Mohs hardness 4

[0144] Among these raw materials, particles of inorganic materials with a Mohs hardness of 6 or higher, excluding monoclinic zirconia, namely alumina, zirconium silicate, stabilized zirconia, and mineral particles, are added as grinding materials. Alumina particles with an average particle size of 0.7 μm and a Mohs hardness of 9 and zirconium silicate particles with an average particle size of 0.8 μm and a Mohs hardness of 7.5 are equivalent to inorganic materials (1). In addition, stabilized zirconia particles with an average particle size of 35 μm and a Mohs hardness of 7 are equivalent to inorganic materials (2).

[0145] In addition, particles of inorganic materials with a Mohs hardness of less than 6, namely particles of titanate, barium sulfate, mica, iron oxide, calcium hydroxide, and magnesium hydroxide, are added as inorganic fillers.

[0146] Other than the aforementioned friction materials, the materials used are those commonly used in this technical field.

[0147] [Example 1]

[0148] <Brake Pad Manufacturing>

[0149] The raw materials were mixed according to the proportions shown in Table 1, and then mixed in a Rodig mixer at room temperature (20°C) for approximately 10 minutes to obtain the friction material composition. Furthermore, the proportions of each raw material in Table 1 are expressed as a percentage by mass in the friction material composition. Additionally, blank columns in the table indicate that the component was not added.

[0150] A molding press is used to heat and compact the friction material composition through a hot pressing process to obtain a molded product. The molding conditions for the hot pressing process are as follows: Molding temperature: 160℃ Molding pressure: 20MPa Molding time: 10 minutes.

[0151] The surface of the molded part was ground using a grinding machine to form a friction surface, thereby obtaining a friction material. This friction material was used to fabricate the brake pad of Example 1, and high-temperature and driving simulation tests were conducted. Furthermore, the friction material of the brake pad fabricated in Example 1 had a thickness of 12.5 mm and a projected area of ​​55 cm². 2 .

[0152] [Examples 2-16]

[0153] The raw materials were mixed according to the proportions shown in Table 1, and the brake pads of Examples 2-8 were prepared using the same method as in Example 1. Additionally, the raw materials were mixed according to the proportions shown in Table 2, and the brake pads of Examples 9-16 were prepared using the same method as in Example 1.

[0154] [Comparative Examples 1-16]

[0155] The raw materials were prepared according to the proportions shown in Table 3, and the brake pads of Comparative Examples 1 to 8 were prepared using the same method as in Example 1. Additionally, the raw materials were prepared according to the proportions shown in Table 4, and the brake pads of Comparative Examples 9 to 16 were prepared using the same method as in Example 1.

[0156] High Temperature Test

[0157] The AMS fade test (evaluation conditions published by the German automotive magazine auto motor und sport: vehicle speed 130 km / h, maximum rotor temperature above 650°C) was conducted to evaluate the brake pads of Examples 1-16 and Comparative Examples 1-16. The maximum rotor temperature for each test was 650-670°C.

[0158] (Minimum coefficient of friction)

[0159] The lowest coefficient of friction during the AMS attenuation test was measured using the following method.

[0160] (Method for measuring the lowest coefficient of friction)

[0161] Using the lowest torque during a single braking process, calculate the friction coefficient for each brake according to the formula described in JIS D 0106. Set the lowest friction coefficient during the test as the minimum friction coefficient.

[0162] The measurement results of the lowest coefficient of friction are evaluated on a scale of 1 to 5 according to the criteria shown below.

[0163] 5: Compared to Comparative Example 1, the optimization exceeds 20%.

[0164] 4: Compared to Comparative Example 1, the optimization is more than 10% but less than 20%.

[0165] 3: Same as or equivalent to Comparative Example 1

[0166] 2: Compared to Comparative Example 1, the degradation is more than 10% but less than 20%.

[0167] 1: Compared to Comparative Example 1, the degradation exceeds 20%.

[0168] Here, if the minimum coefficient of friction of the brake pads of the evaluated object increases by more than 10% compared to the minimum coefficient of friction of the brake pads of Comparative Example 1, it is evaluated as "optimization"; if the minimum coefficient of friction of the brake pads of the evaluated object decreases by more than 10% compared to the minimum coefficient of friction of the brake pads of Comparative Example 1, it is evaluated as "deterioration". If the increase or decrease in the minimum coefficient of friction of the brake pads of the evaluated object is less than 10% compared to the minimum coefficient of friction of the brake pads of Comparative Example 1, it is evaluated as the same as or equivalent to Comparative Example 1.

[0169] (Wear amount)

[0170] The wear of brake pads after the AMS attenuation test was measured using the following method.

[0171] (Methods for measuring wear)

[0172] The wear amount was measured according to JASO C427 6. Measurement method.

[0173] After the test, for each brake pad, the wear amount was measured at eight locations, and the average value was set as the "average wear amount of the brake pad".

[0174] The wear measurement results are evaluated using a five-level scale of 1 to 5, based on the criteria shown below.

[0175] 5: Compared to Comparative Example 1, the optimization exceeds 20%.

[0176] 4: Compared to Comparative Example 1, the optimization is more than 10% but less than 20%.

[0177] 3: Same as or equivalent to Comparative Example 1

[0178] 2: Compared to Comparative Example 1, the degradation is more than 10% but less than 20%.

[0179] 1: Compared to Comparative Example 1, the degradation exceeds 20%.

[0180] Here, if the average wear of the brake pads of the evaluated object is reduced by more than 10% compared to the average wear of the brake pads of Comparative Example 1, it is evaluated as "optimization"; if the average wear of the brake pads of the evaluated object is increased by more than 10% compared to the average wear of the brake pads of Comparative Example 1, it is evaluated as "deterioration". If the increase or decrease in the average wear of the brake pads of the evaluated object is less than 10% compared to the average wear of the brake pads of Comparative Example 1, it is evaluated as the same as or equivalent to Comparative Example 1.

[0181] <Driving Simulation Wear Test>

[0182] The estimated life (in miles) of the brake pads for Examples 1-16 and Comparative Examples 1-16 was calculated using the following formula (1): Brake pad estimated life (in miles) = Brake pad thickness (mm) ÷ Average brake pad wear (mm) × Test distance (in miles) ... (1)

[0183] Wherein, "brake pad thickness (mm)" refers to the thickness of the brake pads before the LACT simulation test, and "average brake pad wear (mm)" refers to the average wear of the brake pads before the LACT simulation test. The measurement method is based on JASO C 427 6. Measurement Method. The average rotor temperature in the driving simulation wear test is 100~200℃.

[0184] The calculated brake pad life is evaluated using a five-level scale of 1 to 5, based on the criteria shown below.

[0185] 5: Compared to Comparative Example 1, the optimization exceeds 20%.

[0186] 4: Compared to Comparative Example 1, the optimization is more than 10% but less than 20%.

[0187] 3: Same as or equivalent to Comparative Example 1

[0188] 2: Compared to Comparative Example 1, the degradation is more than 10% but less than 20%.

[0189] 1: Compared to Comparative Example 1, the degradation exceeds 20%.

[0190] Here, if the estimated lifespan of the brake pads of the evaluated object increases by more than 10% compared to the estimated lifespan of the brake pads of Comparative Example 1, it is evaluated as "optimized". If the estimated lifespan of the brake pads of the evaluated object decreases by more than 10% compared to the estimated lifespan of the brake pads of Comparative Example 1, it is evaluated as "deteriorated". If the increase or decrease in the estimated lifespan of the brake pads of the evaluated object is less than 10% compared to the estimated lifespan of the brake pads of Comparative Example 1, it is evaluated as the same as or equivalent to Comparative Example 1.

[0191] <Light Load Rust Removal Test>

[0192] The light-load rust removal performance of the brake pads of Examples 1-16 and Comparative Examples 1-16 was evaluated using a bench testing machine. Simulations of regenerative brakes and regenerative coordinated brakes were performed, starting from 10 km / h (h) with friction brake braking.

[0193] Initial braking speed: 10 km / h

[0194] Final braking speed: 0 km / h (h)

[0195] Deceleration: 0.8 m / s 2

[0196] The rust removal rate is calculated according to the following formula (2).

[0197] Rust removal rate (%) = (rust thickness of disc rotor before braking - rust thickness of disc rotor after 100 braking cycles) ÷ rust thickness of disc rotor before braking × 100……(2)

[0198] The "rust thickness of the disc rotor before braking" is calculated according to the following formula (3). Rust thickness of the disc rotor before braking = Thickness of the disc rotor after rust formation - Thickness of the disc rotor before rust formation ... (3)

[0199] The thickness of the disc rotor is measured at multiple points near the center of the sliding surface using a micrometer, and the average value is used.

[0200] In this experiment, a disc rotor with a 50μm rust layer was used, so the "rust thickness of the disc rotor before braking" is 50μm.

[0201] Based on the calculated rust removal rate, the light-load rust removal performance is evaluated using a five-level scale of 1 to 5 according to the following benchmarks.

[0202] 5: Compared to Comparative Example 1, the optimization exceeds 20%.

[0203] 4: Compared to Comparative Example 1, the optimization is more than 10% but less than 20%.

[0204] 3: Same as or equivalent to Comparative Example 1

[0205] 2: Compared to Comparative Example 1, the degradation is more than 10% but less than 20%.

[0206] 1: Compared to Comparative Example 1, the degradation exceeds 20%.

[0207] Here, if the rust removal rate of the brake pads in the evaluation object increases by more than 10% compared to the rust removal rate of the brake pads in Comparative Example 1, it is evaluated as "optimization"; if the rust removal rate of the brake pads in the evaluation object decreases by more than 10% compared to the rust removal rate of the brake pads in Comparative Example 1, it is evaluated as "deterioration". If the increase or decrease in the rust removal rate of the brake pads in the evaluation object is less than 10% compared to the rust removal rate of the brake pads in Comparative Example 1, it is evaluated as the same as or equivalent to Comparative Example 1.

[0208] <Results>

[0209] The evaluation results from the high-speed test, the driving simulation wear test, and the light load rust removal test are shown in Tables 1-4.

[0210] [Table 1]

[0211] [Table 2]

[0212] [Table 3]

[0213] [Table 4]

[0214] As shown in Tables 1 and 2, it is confirmed that the brake pads of Examples 1 to 16, which contain specific amounts of inorganic materials with specific particle size and specific Mohs hardness, monoclinic zirconia and magnesium hydroxide, have superior performance and wear resistance during high-speed braking in the high-temperature range compared with the brake pads of Comparative Example 1. They also have sufficient wear resistance in the normal temperature range and excellent rust removal performance during light-load braking.

[0215] In particular, based on the comparison between Examples 1 to 16 and Comparative Examples 4 (excluding inorganic material (A)), 7 (excluding magnesium hydroxide), and 13 (excluding magnesium hydroxide), it was confirmed that the brake pads of Examples 1 to 16 exhibited a synergistic effect produced by the combination of inorganic material (A) with a specific particle size and a specific Mohs hardness, monoclinic zirconia, and magnesium hydroxide.

[0216] Furthermore, based on the results of the examples and comparative examples, it was confirmed that if the content of inorganic material (A) is the same, there is a tendency to fail to obtain sufficient light-load rust removal performance when the particle size of inorganic material (A) increases. Additionally, it was confirmed that while increasing the content of inorganic material (A) tends to optimize light-load rust removal performance, it also tends to deteriorate wear resistance within the normal temperature range. The brake pads of Examples 1-16 selected inorganic material (A) with specific particle size and specific Mohs hardness, and combined it with monoclinic zirconium oxide and magnesium hydroxide, thereby enabling sufficient improvement in light-load rust removal performance with a relatively small amount of inorganic material (A) added. Therefore, it is considered that the brake pads of Examples 1-16 can maintain sufficient wear resistance within the normal temperature range while sufficiently improving light-load rust removal performance.

[0217] Industrial availability

[0218] The friction material composition and friction material of one aspect of the present invention are applicable to friction components in braking devices of vehicles such as automobiles.

Claims

1. A friction material composition, The copper content in this friction material composition is less than 0.5% by mass (based on elemental copper). The friction material composition comprises, relative to the total amount of the friction material composition: The inorganic materials selected from the group consisting of (1) and (2) below, with a mass percentage of 0.05% and a mass percentage of 1%, except for monoclinic zirconia, are: (1) Inorganic materials with an average particle size of less than 1 μm and a Mohs hardness of 7.5 or higher and less than 8. (2) Inorganic materials with an average particle size of less than 50 μm and a Mohs hardness of 6 or higher but less than 7.5; Monoclinic zirconium oxide comprising more than 5% by mass and less than 35% by mass; and Magnesium hydroxide, 0.5% by mass or more and 10% by mass or less.

2. The friction material composition according to claim 1, wherein, The content of one or two inorganic materials selected from the group consisting of (1) and (2) in the friction material composition is 0.2% by mass or more and 1% by mass or less.

3. The friction material composition according to claim 1, wherein, The content of monoclinic zirconium oxide in the friction material composition is more than 20% by mass and less than 30% by mass.

4. The friction material composition according to claim 1, wherein, The content of magnesium hydroxide in the friction material composition is more than 1% by mass and less than 5% by mass.

5. The friction material composition according to claim 1, wherein, The content of one or two inorganic materials selected from the group consisting of (1) and (2) in the friction material composition is 0.2% by mass or more and 1% by mass or less. The content of monoclinic zirconium oxide in the friction material composition is 20% by mass or more and 30% by mass or less, and The content of magnesium hydroxide in the friction material composition is more than 1% by mass and less than 5% by mass.

6. A friction material formed from the friction material composition of any one of claims 1 to 5.

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