Friction material composition and friction material

Abstract

Provided is a friction material composition according to one embodiment of the present invention, in which the content of copper in the friction material composition is less than 0.5 mass% in terms of copper element. The friction material composition contains, each relative to the total amount of the friction material composition, the following: 0.05-1 mass% of one or two inorganic materials (excluding monoclinic zirconium oxide) selected from the group consisting of (1) an inorganic material having an average particle diameter of 1 µm or less and a Mohs' hardness of 7.5-8 and (2) an inorganic material having an average particle diameter of 50 μm or less and a Mohs' hardness of not less than 6 and less than 7.5; 5-35 mass% of monoclinic zirconium oxide; and 0.5-10 mass% of magnesium hydroxide.

Description

Friction material composition and friction material

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

[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 member having a friction material and a backing metal, in which the friction material does not contain copper, or if it contains copper, the copper content is less than 0.5 mass % in terms of copper element, and the friction material contains inorganic fibers having a fiber length of 400 μm or more.

[0004] Patent Document 2 discloses a friction material used for disc brake pads, which is obtained by molding a friction material composition that does not contain a copper component, and the friction material composition contains specific amounts of binders, organic fibers, metal sulfide-based lubricants, carbonaceous lubricants, titanates, wollastonite, particulate inorganic friction modifiers having a Mohs hardness of 4.5 or more and less than 8.0, inorganic friction modifiers having a Mohs hardness of less than 4.5, organic friction modifiers, and pH adjusters, and does not contain any substances having a Mohs hardness of 8.0 or more, elemental metals other than copper, or alloys other than copper alloys.

[0005] Patent Document 3 discloses a non-asbestos-based frictional material obtained by molding and curing a non-asbestos-based frictional material composition containing a fibrous base material excluding asbestos, a binder, an organic filler, and an inorganic filler, wherein the non-asbestos-based frictional material contains, as an abrasive, one or more inorganic substances selected from inorganic substances having a Mohs hardness of 4.5 or more and inorganic substances having a Mohs hardness of less than 4.5 and containing 50% by weight or more of components having a Mohs hardness of 4.5 or more, and wherein the volume ratio of the total amount of organic substances to the total amount of abrasives in the composition (total amount of organic substances:total amount of abrasives) is 1.5:1 to 3.5:1.

[0006] International Publication No. 2020 / 089979 Japanese Patent Application Laid-Open No. 2014-159871 Japanese Patent Application Laid-Open No. 2002-241737

[0007] However, the friction member described in Patent Document 1 lacks sufficient effectiveness and wear resistance during high-speed braking at high temperatures, and also lacks sufficient wear resistance in temperatures typically used in urban driving. The friction material described in Patent Document 2 lacks sufficient effectiveness during high-speed braking at high temperatures. The non-asbestos friction material described in Patent Document 3 lacks sufficient rust removal capability during light-load braking because it lacks the ability to remove rust that has formed on the contact surface with the friction-facing material, such as a disc rotor or brake drum, during light-load braking. Thus, there is room for improvement in the friction materials of the prior art.

[0008] An object of one aspect of the present invention is to provide a friction material that has excellent braking effectiveness and wear resistance during high-speed braking in a high-temperature range, and also has sufficient wear resistance in a normal temperature range, and further has excellent rust removal properties during light-load braking.

[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 an inorganic material having a specific particle size and a specific Mohs hardness, monoclinic zirconium oxide, and specific amounts of magnesium hydroxide in a friction material composition in which the copper content is less than 0.5 mass % in terms of elemental copper is excellent in effectiveness and wear resistance during high-speed braking at high temperatures, and also has sufficient wear resistance in the normal temperature range, and further has excellent rust removal properties during light-load braking, which has led to the completion of 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 the friction material composition contains, relative to the total amount of the friction material composition, 0.05% by mass or more and 1% by mass or less of one or two inorganic materials (excluding monoclinic zirconium oxide) selected from the group consisting of the following (1) and (2): (1) an inorganic material having 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 having 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 or more and 35% by mass or less of monoclinic zirconium oxide, and 0.5% by mass or more and 10% by mass or less of magnesium hydroxide.

[0010] According to one aspect of the present invention, it is possible to provide a friction material that has excellent effectiveness and wear resistance during high-speed braking in high-temperature ranges, has sufficient wear resistance even in the temperature range in which it is normally used, and further has excellent rust removal properties during light-load braking, while containing less than 0.5 mass % of copper element, which is an environmentally hazardous material.

[0011] <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 mass % in terms of elemental copper, and the friction material composition contains one or two inorganic materials (excluding monoclinic zirconium oxide) selected from the group consisting of (1) and (2) below in an amount of 0.05 mass % or more and 1 mass % or less, based on the total amount of the friction material composition: (1) an inorganic material having 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 having an average particle size of 50 μm or less and a Mohs hardness of 6 or more and less than 7.5, 5 mass % or more and 35 mass % or less of monoclinic zirconium oxide, and 0.5 mass % or more and 10 mass % or less of magnesium hydroxide. The friction material composition according to one embodiment of the present invention is intended to be a composition containing friction material raw materials containing the above-mentioned components. The friction material composition according to one embodiment of the present invention can be used to mold the friction material described below.

[0012] The friction material composition according to one embodiment of the present invention is environmentally friendly because it contains less than 0.5% by mass of copper as elemental copper. Furthermore, because it contains specific amounts of an inorganic material having a specific particle size and a specific Mohs hardness, monoclinic zirconium oxide, and magnesium hydroxide, it has the excellent effect of providing a friction material that, despite having a copper content of less than 0.5% by mass as elemental copper, exhibits excellent braking effectiveness and wear resistance during high-speed braking at high temperatures, sufficient wear resistance even in the normal operating temperature range, and excellent rust removal properties during light-load braking.

[0013] A friction material using the friction material composition according to one embodiment of the present invention has improved wear resistance during high-speed braking at high temperatures (e.g., 650°C or higher), and therefore can simultaneously achieve improved effectiveness during high-speed braking at high temperatures. Furthermore, improved wear resistance during high-speed braking at high temperatures can be said to improve the strength of the friction material at the friction surface, which can be expected to improve the heat resistance of the friction material.

[0014] Furthermore, a friction material using the friction material composition according to one embodiment of the present invention can achieve both wear resistance during high-speed braking at high temperatures and wear resistance in a normal temperature range (e.g., 100 to 200°C), thereby providing the excellent effect of a longer life than conventional friction materials. Furthermore, a friction material using the friction material composition according to one embodiment of the present invention has excellent wear resistance, and therefore produces less dust due to wear. As a result, the wheel is less likely to be soiled by dust, and the emissions of PM2.5 and PM10, which have a high environmental impact, are reduced.

[0015] Furthermore, a friction material using a friction material composition according to one embodiment of the present invention has excellent rust removal properties during light-load braking, and can sufficiently remove rust that has formed on the surface of a friction counter-face material even during light-load braking. Therefore, the friction material is less likely to adhere to the friction counter-face material due to rust that has formed on the contact surface with the friction counter-face material. As a result, excellent effects are achieved in that problems such as abnormal noise generation when starting the vehicle and surface peeling of the friction material are less likely to occur. Herein, "light-load braking" refers to a braking state in which the ratio of braking force obtained by friction (braking load) is lower than that of conventional hydraulic brakes. More specifically, it refers to a state in which friction is the only factor at a low speed where the initial speed of frictional braking is 10 km / hour (h) or less.

[0016] [Applications] The friction material composition according to one embodiment of the present invention, which has the characteristics described above, is particularly useful as a friction material composition for use in the friction surfaces of disc brake pads and brake shoes for drum brakes in 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 they tend to have a lower contribution of regenerative braking and regenerative-cooperative braking during 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.

[0017] Furthermore, in vehicles equipped with regenerative brakes or regenerative cooperative brakes, the proportion of braking force obtained by friction (braking load) decreases at medium to low speeds (20 to 60 km / h) where braking is frequently used in the market, resulting in a light load, compared to conventional hydraulic brakes. As a result, the rust removal power due to the braking load tends to be insufficient. The friction material composition according to one embodiment of the present invention has excellent rust removal properties during light-load braking, and is therefore particularly useful in vehicles equipped with regenerative brakes or regenerative cooperative brakes.

[0018] The use of the friction material composition according to one embodiment of the present invention is not particularly limited to EVs / HEVs, and the composition can be suitably used as a friction material for friction surfaces such as disc brake pads and drum brake shoes employed in general vehicles including motorcycles.

[0019] [Raw Materials] The raw materials (friction material raw materials) contained in the friction material composition according to one embodiment of the present invention will be described below.

[0020] (Copper) In the friction material composition according to one embodiment of the present invention, the copper content in the friction material composition is 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 has the effect of providing an environmentally friendly friction material. From the viewpoint of providing a more environmentally friendly friction material, it is more preferable that the copper content in the friction material composition is 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.

[0021] (Inorganic Material) A friction material composition according to one embodiment of the present invention contains, relative to 100% by mass of the friction material composition, 0.05% by mass or more and 1% by mass or less of one or two inorganic materials (excluding monoclinic zirconium oxide) selected from the group consisting of (1) and (2) below: (1) an inorganic material having 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 having an average particle size of 50 μm or less and a Mohs hardness of 6 or more and less than 7.5. Hereinafter, for convenience 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) an inorganic material having an average particle size of 1 μm or less and a Mohs hardness of 7.5 or more and 8 or less" will be referred to as "inorganic material (1)," and "(2) an inorganic material having an average particle size of 50 μm or less and a Mohs hardness of 6 or more and less than 7.5" will be referred to as "inorganic material (2)." The term "Mohs hardness" used in this specification refers to the Mohs hardness expressed as a value on a scale of 1 to 10. The Mohs hardness can be measured according to a known measurement method. The inorganic particles may be added as an abrasive.

[0022] The inorganic material (A) may be the inorganic material (1) alone or the inorganic material (2) alone. Alternatively, a combination of the inorganic material (1) and the inorganic material (2) may be used. For reasons described below, it is preferable to use the inorganic material (1) alone or the inorganic material (2) alone as the inorganic material (A). This is because, when the inorganic material (1) and the inorganic material (2) are used in combination, the inorganic material (1) having a Mohs hardness of 7.5 or more and 8 or less scrapes and removes the inorganic material (2) having a Mohs hardness of 6 or more and less than 7.5, thereby losing the effect of the latter, and the same effect as when the inorganic material (1) is used alone is achieved. When inorganic material (1) and inorganic material (2) are used in combination, it is preferable to adjust the amounts of inorganic material (1) and inorganic material (2) so 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, in order to fully obtain the effect of adding inorganic material (A).

[0023] (Inorganic Material (1)) The inorganic material (1) is particles of an inorganic material having an average particle size of 1 μm or less and a Mohs hardness of 7.5 or more and 8 or less, and is not monoclinic zirconium oxide.

[0024] The type of inorganic material having a Mohs hardness of 7.5 or more and 8 or less is not particularly limited. Examples of inorganic materials having such a Mohs hardness include zirconium silicate, beryl, and chromium oxide. The inorganic material (1) may be used alone or in combination of two or more. From the viewpoints of availability and cost, the inorganic material (1) is preferably one or more selected from the group consisting of zirconium silicate and chromium oxide.

[0025] (Inorganic Material (2)) Inorganic material (2) is particles of an inorganic material having an average particle size of 50 μm or less and a Mohs hardness of 6 or more and less than 7.5, and is not monoclinic zirconium oxide.

[0026] The type of inorganic material having a Mohs hardness of 6 or more and less than 7.5 is not particularly limited. Examples of inorganic materials having such a Mohs hardness include stabilized zirconium oxide, cerium oxide, silicon dioxide (including silica), magnesium oxide, alumina cement, and minerals such as cassiterite and orthoclase. Stabilized zirconium oxide refers to zirconium oxide stabilized in a cubic crystal form at room temperature. The inorganic material (2) can be used alone or in combination with multiple types. From the standpoints of availability and cost, the inorganic material (2) is preferably one or more types selected from the group consisting of stabilized zirconium oxide, cerium oxide, silicon dioxide, magnesium oxide, cassiterite, orthoclase, and other minerals.

[0027] (Actions and Effects of Inorganic Material (A)) (i) Improved Rust Removal During Light-Load Braking Monoclinic zirconium oxide (details will be described later) is easily worn away, so monoclinic zirconium oxide particles can spread across the friction surface even during light-load braking. Inorganic materials (1) and (2) have a hardness similar to that of monoclinic zirconium oxide, so they can moderately grind away the monoclinic zirconium oxide particles that have worn away and spread across the friction surface, forming an acute angle. Immediately after being worn away and spreading across the friction surface, the monoclinic zirconium oxide particles have low sharpness and do not have the power to remove rust, but by being ground to an acute angle by inorganic material (A), the monoclinic zirconium oxide particles can also contribute to rust removal. Inorganic material (A) also contributes to rust removal as an abrasive, but its rust removal ability during light-load braking is insufficient. In addition to the rust-removing effect of the inorganic material (A), the large amount of monoclinic zirconium oxide with acute angles removes rust under light loads, improving rust-removal properties during light-load braking, and as a result, rust-removal properties during light-load braking are fully exhibited.

[0028] The reason why the hardness of the inorganic material (A) is suitable within the above-mentioned specific range is as follows. When the Mohs hardness of the inorganic material (A) is 6 or more, the effect of forming an acute angle by appropriately grinding the monoclinic zirconium oxide particles spread on the friction surface can be sufficiently obtained. Furthermore, when the Mohs hardness of the inorganic material (A) is 8 or less, it is possible to prevent the monoclinic zirconium oxide particles spread on the friction surface from being completely ground and removed. Therefore, when the hardness of the inorganic material (A) is within the above-mentioned range, rust removal properties during light-load braking can be improved.

[0029] Next, the reason why the suitable particle size varies depending on the hardness of the inorganic material (A) will be explained. First, assuming that the content (mass %) of the inorganic material (A) in the friction material composition is the same, the smaller the particle size of the inorganic material (A), the greater the number of particles present per unit area. Also, the greater the number of particles of the inorganic material (A) present per unit area, the more uniformly the monoclinic zirconium oxide particles spread across the friction surface can be scraped off.

[0030] The inorganic material (1) among the inorganic materials (A) has a Mohs hardness of 7.5 or more and 8 or less, making it harder than monoclinic zirconium oxide. Therefore, the particles of the inorganic material (1) are less likely to become finer due to friction with the monoclinic zirconium oxide and to spread across the friction surface. By setting the average particle size of the inorganic material (1) particles to 1 μm or less, the number of inorganic material (1) particles on the friction surface can be increased, enabling the monoclinic zirconium oxide worn away and spread across the friction surface to be more uniformly scraped away. As a result, the amount of acute-angled monoclinic zirconium oxide particles that contribute to rust removal during light-load braking can be increased, improving rust removal during light-load braking.

[0031] The inorganic material (2) among the inorganic materials (A) has a Mohs hardness of 6 or more but less than 7.5, which is the same level as or less than monoclinic zirconium oxide. Therefore, the particles of the inorganic material (2) become finer due to friction with the monoclinic zirconium oxide that spreads on the friction surface due to wear at the beginning of braking, and can spread on the friction surface together with the monoclinic zirconium oxide. Therefore, from the viewpoint of ease of spreading on the friction surface, the range of particle sizes that can achieve the effect of sharply cutting the monoclinic zirconium oxide particles is wider than that of the inorganic material (1). In other words, even if the average particle size of the inorganic material (2) exceeds 1 μm, the particles of the inorganic material (2) become finer due to friction with the monoclinic zirconium oxide and can spread on the friction surface together with the monoclinic zirconium oxide, thereby sufficiently achieving the effect of sharply cutting the monoclinic zirconium oxide particles.

[0032] Furthermore, as the particles of inorganic material (2) become larger, the time required for the particles of inorganic material (2), which have become finer due to friction with monoclinic zirconium oxide, to spread across the friction surface tends to increase. However, by setting the average particle size of the particles of inorganic material (2) to 50 μm or less, the particles of inorganic material (2), which have become finer due to friction with monoclinic zirconium oxide, can be sufficiently spread across the friction surface, even in regenerative braking or regenerative cooperative braking, which are used less frequently than conventional hydraulic brakes. As a result, the amount of acute-angled monoclinic zirconium oxide particles that can contribute to rust removal during light-load braking can be increased, thereby improving rust removal during light-load braking.

[0033] The average particle size of inorganic material (1) or (2) is the volume-based median diameter obtained by JIS Z 8825 "Particle size analysis - Laser analysis / scattering method." When the particle size of inorganic material (1) or (2) is confirmed after the friction material is formed, the average particle size of particles corresponding to inorganic material (1) or (2) can be determined from an electron microscope image of the cross section of the friction material by measuring the volume-based particle size distribution according to JIS Z 8827-1 "Particle size analysis - Image analysis method - Part 1: Static image analysis method," and then the median diameter can be determined.

[0034] (ii) Improved Wear Resistance in Normal Operating Temperature Ranges By adjusting the particle size and blending amount of inorganic materials (1) and (2) having a predetermined Mohs hardness within the above-mentioned specific ranges, wear resistance in normal operating temperature ranges can be maintained. The reason for this is as follows: Inorganic materials (1) and (2) are harder than cast iron and stainless steel, which are used as materials for disc rotors and brake drums. If the blending amount of inorganic materials (1) and (2) exceeds 1% by mass, the amount of grinding of the disc rotor or brake drum increases rapidly, and the friction material is ground by the friction surface of the disc rotor or brake drum, which has become sharp due to grinding, resulting in a significant increase in the amount of wear of the friction material. If the blending amount of inorganic materials (1) and (2) is 1% by mass or less, the amount of grinding of the disc rotor or brake drum is small, allowing wear resistance in normal operating temperature ranges to be maintained.

[0035] When the content of inorganic material (A) in the friction material composition according to one embodiment of the present invention is 0.05% by mass or more relative to 100% by mass of the friction material composition, the monoclinic zirconium oxide that has worn away and spread on the friction surface can be more uniformly removed, thereby fully achieving the effect of (i) above. Furthermore, when the content of inorganic material (A) in the friction material composition according to 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 in the normal temperature range.

[0036] (Monoclinic Zirconium Oxide) The friction material composition according to one embodiment of the present invention contains 5% by mass or more and 35% by mass or less of monoclinic zirconium oxide, based on 100% by mass of the friction material composition. Monoclinic zirconium oxide may be added as an inorganic filler. "Monoclinic zirconium oxide" refers to zirconium oxide whose crystal system is monoclinic. Zirconium oxide undergoes a crystal system transition depending on temperature. At room temperature (20°C), it is monoclinic, and as the temperature is increased, the crystal structure changes to tetragonal at 1170°C and to cubic at 2370°C. The phase transition is accompanied by a change in volume.

[0037] Pure zirconium oxide is most stable in the monoclinic system at room temperature, but when fused with yttrium oxide or magnesium oxide, the cubic system becomes stable even at room temperature. Zirconium oxide stabilized in the cubic system at room temperature is called "stabilized zirconium oxide."

[0038] Monoclinic zirconium oxide has a Mohs hardness of 6 to 7, but is distinguished from the inorganic material (A) described above.

[0039] (Actions and Effects of Monoclinic Zirconium Oxide) (i) Improved Rust Removal During Light-Load Braking Monoclinic zirconium oxide is easily worn away, so monoclinic zirconium oxide particles can spread across the friction surface even during light-load braking. The monoclinic zirconium oxide particles that have worn away and spread across the friction surface are cut at acute angles by the inorganic material (A), allowing the monoclinic zirconium oxide particles to also contribute to rust removal. As a result, rust removal during light-load braking is improved.

[0040] (ii) Improved wear resistance in normal operating temperature ranges Monoclinic zirconium oxide has lower toughness than stabilized zirconium oxide. Therefore, monoclinic zirconium oxide has low grinding properties not only in the non-braking state but also in the braking state, resulting in low rotor grinding properties in both states, and the magnesium hydroxide spread on the friction surface is less likely to be lost. As a result, the rust prevention properties provided by the magnesium hydroxide spread on the friction surface are fully exhibited. Furthermore, because monoclinic zirconium oxide has lower toughness than stabilized zirconium oxide, the wear resistance of the pad is improved.

[0041] (iii) Improved braking effectiveness and wear resistance during high-speed braking at high temperatures. Monoclinic zirconium oxide fuses with magnesium oxide (magnesium hydroxide in the friction material that has been dehydrated) due to the high heat generated by high-speed braking (high-load braking) at high temperatures, forming stabilized zirconium oxide. The stabilized zirconium oxide coating formed on the friction surface protects the friction surface. Furthermore, by reacting with magnesium oxide to form cubic stabilized zirconium oxide, volume changes associated with phase transition are prevented, making it less likely for the friction material strength to decrease. As a result, the wear resistance of the pad is improved, and ultimately the friction coefficient (μ) is improved.

[0042] The thickness of the stabilized zirconium oxide coating formed on the friction surface varies depending on the content of monoclinic zirconium oxide in the friction material composition according to one embodiment of the present invention. When the content of monoclinic zirconium oxide in the friction material composition according to one embodiment of the present invention is 5% by mass or more relative to 100% by mass of the friction material composition, a stabilized zirconium oxide coating of sufficient thickness is formed to achieve the effect (iii) described above. Furthermore, when the content of monoclinic zirconium oxide in the friction material composition according to one embodiment of the present invention is 35% by mass or less relative to 100% by mass of the friction material composition, the stabilized zirconium oxide coating does not become too thick. As a result, magnesium hydroxide is not embedded in the stabilized zirconium oxide coating, and the rust resistance effect of magnesium hydroxide is fully achieved. Furthermore, because the stabilized zirconium oxide coating is less likely to peel off from the friction surface, it is possible to prevent variations in coating thickness from reducing the friction area and reducing effectiveness at high temperatures. Therefore, the effect (iii) described above is fully achieved.

[0043] (Particle size of monoclinic zirconium oxide) From the viewpoint of realizing the effects (i) to (iii) described above, the particle size of monoclinic zirconium oxide is not particularly limited. Therefore, monoclinic zirconium oxide having a particle size typically used as an inorganic filler added to friction materials can be appropriately selected. From the viewpoint of ease of handling during the production of the friction material composition, the average particle size of monoclinic zirconium oxide 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, for reasons such as enabling uniform mixing without bias during the production of the friction material composition and having little effect on the deterioration of wear resistance, the average particle size of monoclinic zirconium oxide is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 16 μm or less.

[0044] The average particle size of monoclinic zirconium oxide is the volume-based median size obtained by JIS Z 8825 "Particle size analysis - Laser analysis and scattering method." When checking the particle size of monoclinic zirconium oxide after forming the friction material, the average particle size of particles corresponding to monoclinic zirconium oxide can be determined from an electron microscope image of the cross section of the friction material by measuring the volume-based particle size distribution by JIS Z 8827-1 "Particle size analysis - Image analysis method - Part 1: Static image analysis method," and then the median size can be determined.

[0045] (Magnesium hydroxide) The friction material composition according to one embodiment of the present invention contains, as an inorganic filler, 0.5% by mass or more and 10% by mass or less of magnesium hydroxide, relative to 100% by mass of the friction material composition. Magnesium hydroxide may be added as an inorganic filler.

[0046] (Actions and Effects of Magnesium Hydroxide) (i) Improved rust removal during light-load braking Magnesium hydroxide is alkaline and has low solubility in water, making it difficult to remove from friction surfaces with water such as rain. This prevents the growth of strong rust on the friction surfaces. As a result, it contributes to improved rust removal during light-load braking.

[0047] (ii) Improved wear resistance in the normal operating temperature range. Magnesium hydroxide has a Mohs hardness of 2 to 3, and is easily broken down by friction with friction-facing materials such as disc rotors and brake drums. This allows alkaline magnesium hydroxide to spread evenly over the friction surface. As a result, friction materials containing magnesium hydroxide have a high anti-rust effect.

[0048] In addition, magnesium hydroxide has low solubility in water, making it difficult for alkali to be lost from the pad (friction surface, etc.) when wet. This allows its rust-preventing effect to last longer than other alkaline materials. As a result, friction materials containing magnesium hydroxide maintain their rust-preventing effect even when exposed to rain, such as during the rainy season, or when worn down, such as with old pads.

[0049] Magnesium hydroxide has a pH of 10.5, which is not high enough to promote the decomposition of the resin contained in the friction material as a binder. Therefore, friction materials containing magnesium hydroxide are less likely to experience a decrease in strength due to resin decomposition. As a result, the pad's wear resistance is improved. In addition, the rust-preventing effect of magnesium hydroxide suppresses rotor corrosion, allowing wear resistance to be maintained even after long-term use.

[0050] (iii) Improved effectiveness and wear resistance during high-speed braking in high-temperature ranges Magnesium hydroxide has a heat-resistant effect due to its dehydration endothermic effect at 300 to 400°C. Magnesium hydroxide spread evenly on the friction surface changes to magnesium oxide through dehydration. Magnesium oxide fuses with monoclinic zirconium oxide (described below) due to the high heat generated by high-speed braking (high-load braking) in high-temperature ranges, contributing to the formation of a stabilized zirconium oxide coating. Stabilized zirconium oxide is easy to form a stable coating and has excellent heat resistance. The stabilized zirconium oxide coating protects the friction surface, thereby improving wear resistance and ultimately improving the friction coefficient (μ).

[0051] When the content of magnesium hydroxide in the friction material composition according to one embodiment of the present invention is 0.5% by mass or more, based on 100% by mass of the friction material composition, a sufficient amount of magnesium hydroxide is spread across the friction surface, thereby fully achieving the effects (i) to (iii) described above. Furthermore, when the content of magnesium hydroxide in the friction material composition according to one embodiment of the present invention is 10% by mass or less, based on 100% by mass of the friction material composition, the effect of volume change due to dehydration of magnesium hydroxide is small, and a decrease in the strength of the friction material base material is unlikely to occur. As a result, the wear resistance of the pad is good in the normal operating temperature range, and sufficient heat resistance is also achieved.

[0052] (Particle size of magnesium hydroxide) From the viewpoint of realizing the effects (i) to (iii) described above, the particle size of the magnesium hydroxide is not particularly limited. Therefore, a magnesium hydroxide having a particle size typically used as an inorganic filler added to a friction material can be appropriately selected. However, from the viewpoint of ease of handling during the production of the friction material composition, the average particle size of the magnesium hydroxide is preferably 2 μm or more, and more preferably 4 μm or more. Furthermore, for reasons such as enabling uniform mixing without bias during the production of the friction material composition and preventing magnesium hydroxide particles from falling off the friction surface during braking, the effects of improving braking effectiveness and wear resistance during high-speed braking at high temperatures can be stably obtained at any location on the friction surface, the average particle size of the magnesium hydroxide is preferably 20 μm or less, and more preferably 15 μm or less.

[0053] The average particle size of magnesium hydroxide 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 magnesium hydroxide after the friction material is formed, the average particle size of particles corresponding to magnesium hydroxide can be determined from an electron microscope image of the cross section of the friction material by measuring the volume-based particle size distribution by JIS Z 8827-1 "Particle size analysis - Image analysis method - Part 1: Static image analysis method," and then the median diameter can be determined.

[0054] (Preferable Content of Each Component) From the viewpoint of further improving rust removability during light load braking, the content of the inorganic material (A) in the friction material composition is preferably 0.2% by mass or more and 1% by mass or less, based on 100% by mass of the friction material composition.

[0055] From the viewpoint of further improving the effectiveness and wear resistance during high-speed braking in a high-temperature range, the wear resistance in a normal temperature range, and the rust removability 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.

[0056] From the viewpoint of further improving the effectiveness and wear resistance during high-speed braking in a high-temperature range, the wear resistance in a normal temperature range, and the rust removability 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.

[0057] In the friction material composition according to one embodiment of the present invention, it is preferable that at least one of (a) the content of the inorganic material (A), (b) the content of the monoclinic zirconium oxide, and (c) the content of the magnesium hydroxide is the preferred content described above. For example, only (a), only (b), or only (c) may be the preferred content described above. Alternatively, the combination of (a) and (b), the combination of (a) and (c), or the combination of (b) and (c) may be the preferred content described above. Alternatively, all of (a) to (c) may be the preferred contents described above.

[0058] From the viewpoint of exhibiting a more preferable effect, in the friction material composition according to one embodiment of the present invention, it is more preferable that the content of the inorganic material (A) in the friction material composition is 0.2% by mass or more and 1% by mass or less, the content of the monoclinic zirconium oxide 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.

[0059] (Other Components) In addition to the above-described components, the friction material composition according to one embodiment of the present invention may contain, as friction material raw materials, a fibrous base material, a binder, an organic filler, and an inorganic filler other than monoclinic zirconium oxide and magnesium hydroxide, as long as the effects of the present invention are not impaired.

[0060] (Metallic Material) Examples of metallic materials include metallic fibers and metallic powders. Examples of metallic fibers and powders include fibers and powders made of a single metal such as steel, stainless steel, aluminum, zinc, and tin, as well as fibers and powders made of alloy metals thereof. One type of metallic material can be used alone, or multiple types can be used in combination. Since metallic materials tend to adhere to disc rotors and drum brakes, the content of the metallic material in the friction material composition is preferably 1.2% by mass or less from the viewpoint of maintaining wear resistance in the normal temperature range.

[0061] (Fiber substrate) Examples of the fiber substrate include organic fibers and inorganic 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. The above-mentioned metal fibers can also be defined as the fiber substrate. One type of fiber substrate can be used alone, or multiple types can be used in combination. The content of the fiber substrate in the friction material composition is not particularly limited and can be the content commonly used in the relevant technical field.

[0062] (Binder) 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 the content commonly used in the art. The binder may also contain modified components such as silicone rubber, acrylic rubber, and cashew oil.

[0063] (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 rubber powder, tire powder, cashew dust, fluororesin, melamine cyanurate, and polyethylene resin. One type of organic filler can be used alone, or multiple types can be used in combination. The organic filler may also be surface-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.

[0064] (Another Inorganic Filler Different from Monoclinic Zirconium Oxide and Magnesium Hydroxide) The friction material composition according to one embodiment of the present invention may contain an inorganic filler different from monoclinic zirconium oxide and magnesium hydroxide, provided that the effects of the present invention are not impaired. The inorganic filler different from monoclinic zirconium oxide and magnesium hydroxide is preferably an inorganic material having a Mohs hardness of less than 6. Examples of such inorganic materials include inorganic materials known in the art, such as barium sulfate, mica, iron oxide (ferrous oxide, ferric oxide, etc.), titanates, and calcium hydroxide. Examples of titanates include alkali metal titanates and alkali metal group II titanates. Specific examples include 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 monoclinic zirconium oxide and magnesium hydroxide in the friction material composition is not particularly limited, and may be appropriately adjusted so that the total content of the inorganic filler combined with the monoclinic zirconium oxide and magnesium hydroxide falls within the range of the content of the inorganic filler adopted in the technical field.

[0065] By including titanate as an inorganic filler other than monoclinic zirconium oxide and magnesium hydroxide, the coating formed on the friction surface during high-speed braking at temperatures above 650°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 titanate content is not particularly limited, and it may be appropriately adjusted so that the total content of the inorganic filler combined with the monoclinic zirconium oxide and magnesium hydroxide is the content of the inorganic filler adopted in the technical field. The higher the titanate content, the more the heat resistance of the friction material described above is improved, which is preferable.

[0066] Furthermore, the particle size of the inorganic filler other than monoclinic zirconium oxide and magnesium hydroxide is not particularly limited, and inorganic materials having an average particle size that is commonly employed in the relevant technical field can be preferably used.

[0067] (Lubricant) The friction material composition according to one embodiment of the present invention 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 a content commonly used in the art.

[0068] The friction material composition according to one embodiment of the present invention may contain an inorganic material having a Mohs hardness of greater than 8, as long as the effect of the present invention is not impaired. However, from the viewpoint of achieving a preferable effect, it is preferable that the friction material composition does not contain an inorganic material having a Mohs hardness of greater than 8.

[0069] (Method for Manufacturing Friction Material Composition) The friction material composition according to one embodiment of the present invention can be manufactured by a manufacturing 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 adopted. 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 Loedige mixer. In the mixing step, the friction material raw material mixture may be mixed while being cooled by a known cooling method so as to prevent the temperature of the friction material raw materials from increasing during mixing.

[0070] 2. Friction Material The friction material according to one aspect of the present invention is obtained by molding the friction material composition according to one aspect of the present invention. The friction material composition according to one aspect of the present invention in the friction material according to one aspect of the present invention has already been described, and therefore will not be described again here.

[0071] (Method for Manufacturing Friction Material) The friction material according to one embodiment of the present invention can be manufactured by a manufacturing method including a molding step of molding the friction material composition according to one embodiment 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 embodiment 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 embodiment 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 the friction material composition according to one embodiment of the present invention is heated and compacted to form a mold, or a room temperature press method in which the friction material composition according to one embodiment of the present invention is compacted at room temperature without heating can be suitably used. When molding by the hot press method, for example, the friction material composition according to one embodiment 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, the friction material composition according to one embodiment of the present invention can be molded into a friction material by, for example, 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.

[0072] <3. Friction Member> A friction member using the friction material according to one aspect of the present invention as a friction surface is also included in the scope of the present invention. The friction member may be configured to include only the friction material according to one aspect of the present invention, or may be configured to integrate the friction material according to one aspect of the present invention with a plate-shaped member such as a metal plate as a backing plate. The friction material according to one aspect of the present invention in the friction member according to one aspect of the present invention has already been described, so description thereof will not be repeated here.

[0073] When the friction member according to one embodiment of the present invention is configured by integrating a plate-shaped member with the friction material according to one embodiment of the present invention, the friction material according to one embodiment of the present invention and the plate-shaped member can be bonded together by clamping the friction material according to one embodiment 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.

[0074] [Summary] [1] A friction material composition according to a first aspect 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 containing, relative to the total amount of the friction material composition, one or two inorganic materials (excluding monoclinic zirconium oxide) selected from the group consisting of the following (1) and (2) in an amount of 0.05% by mass or more and 1% by mass or less: (1) an inorganic material having 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 having 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 or more and 35% by mass or less of monoclinic zirconium oxide, and 0.5% by mass or more and 10% by mass or less of magnesium hydroxide.

[0075] According to this configuration, it is possible to provide a friction material that has a copper content of less than 0.5 mass % in terms of copper element, yet is superior to conventional friction materials in effectiveness and wear resistance during high-speed braking in high-temperature ranges, has sufficient wear resistance even in the temperature range in which it is normally used, and further has excellent rust removal properties during light-load braking.

[0076] [2] In the friction material composition according to Aspect 2 of the present invention, in Aspect 1, the content of one or two inorganic materials selected from the group consisting of (1) and (2) in the friction material composition is preferably 0.2% by mass or more and 1% by mass or less.

[0077] This configuration has the effect of further improving rust removal properties during light load braking.

[0078] [3] In a friction material composition according to a third aspect of the present invention, in the friction material composition according to the first or second aspect, the content of the monoclinic zirconium oxide in the friction material composition is preferably 20% by mass or more and 30% by mass or less.

[0079] This configuration has the effect of further improving the effectiveness and wear resistance during high-speed braking in high-temperature ranges, the wear resistance in the normal temperature range, and the rust removal properties during light-load braking.

[0080] [4] In a friction material composition according to Aspect 4 of the present invention, in any one of Aspects 1 to 3, the content of the magnesium hydroxide in the friction material composition is preferably 1% by mass or more and 5% by mass or less.

[0081] This configuration has the effect of further improving the effectiveness and wear resistance during high-speed braking in high-temperature ranges, the wear resistance in the normal temperature range, and the rust removal properties during light-load braking.

[0082] [5] A friction material composition according to Aspect 5 of the present invention is the friction material composition according to Aspect 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 preferably 0.2% by mass or more and 1% by mass or less, the content of the monoclinic zirconium oxide in the friction material composition is preferably 20% by mass or more and 30% by mass or less, and the content of the magnesium hydroxide in the friction material composition is preferably 1% by mass or more and 5% by mass or less.

[0083] This configuration has the effect of further improving braking effectiveness and wear resistance during high-speed braking in high-temperature ranges, wear resistance in the normal temperature range, and rust removal properties during light-load braking.

[0084] [6] A friction material according to a sixth aspect of the present invention is formed by molding the friction material composition according to any one of the first to fifth aspects.

[0085] 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 each embodiment are also included in the technical scope of the present invention.

[0086] <Friction Material Raw Materials> The main friction material raw materials used in the examples and comparative examples are as follows.

[0087] Alumina: average particle size 0.7 μm, Mohs hardness 9 Zirconium silicate: average particle size 0.8 μm or 19 μm, Mohs hardness 7.5 Stabilized zirconium oxide: average particle size 35 μm, Mohs hardness 7 Mineral (cassiterite): average particle size 190 μm, Mohs hardness 6.5 Monoclinic zirconium oxide: average particle size 10 μm or more, Mohs hardness 7 Magnesium hydroxide: average particle size 4 μm, Mohs hardness 2 Titanate: Mohs hardness 4 Barium sulfate: Mohs hardness 3 Mica: Mohs hardness 3 Iron oxide: Mohs hardness 5 Calcium hydroxide: Mohs hardness 2 Iron fiber: Mohs hardness 4

[0088] Among these raw materials, inorganic particles with a Mohs hardness of 6 or higher, excluding monoclinic zirconium oxide, i.e., alumina, zirconium silicate, stabilized zirconium oxide, and mineral particles, were added as abrasives. 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 correspond to inorganic material (1). Stabilized zirconium oxide particles with an average particle size of 35 μm and a Mohs hardness of 7 correspond to inorganic material (2).

[0089] Furthermore, particles of inorganic materials having a Mohs hardness of less than 6, namely particles of titanate, barium sulfate, mica, iron oxide, calcium hydroxide, and magnesium hydroxide, were added as inorganic fillers.

[0090] Raw materials other than the friction materials mentioned above were those commonly used in the art.

[0091] [Example 1] <Preparation of brake pads> Each raw material was blended according to the blending ratio shown in Table 1, and mixed using a Lödige mixer at room temperature (20°C) for about 10 minutes to obtain a friction material composition. The blending amount of each raw material in Table 1 is expressed in mass% of the friction material composition. Blank spaces in the table indicate that the component was not added.

[0092] 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°C, molding pressure: 20 MPa, molding time: 10 minutes.

[0093] The surface of the obtained molded article was polished using a polishing machine to form a friction surface, and a friction material was obtained. This friction material was used to prepare a brake pad of Example 1, which was then subjected to a high-temperature test and a running simulation test. The brake pad prepared in Example 1 had a friction material thickness of 12.5 mm and a friction material projected area of ​​55 cm. ２ It was.

[0094] Examples 2 to 16 Brake pads of Examples 2 to 8 were produced in the same manner as Example 1, except that the raw materials were blended according to the blending ratios shown in Table 1. In addition, brake pads of Examples 9 to 16 were produced in the same manner as Example 1, except that the raw materials were blended according to the blending ratios shown in Table 2.

[0095] [Comparative Examples 1 to 16] Brake pads of Comparative Examples 1 to 8 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. Furthermore, brake pads of Comparative Examples 9 to 16 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 4.

[0096] <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 650°C or higher) was carried out, and the following evaluations were made for the brake pads of Examples 1 to 16 and Comparative Examples 1 to 16. The maximum rotor temperature in each test was 650 to 670°C.

[0097] (Minimum Friction Coefficient) The minimum friction coefficient during the AMS fade test was measured by the following method.

[0098] (Method for measuring minimum friction coefficient) Using the minimum torque during one braking, the friction coefficient for each braking was calculated according to the formula described in JIS D 0106. The lowest friction coefficient during the test was taken as the minimum friction coefficient.

[0099] The measurement results of the minimum friction coefficient were evaluated using a score of 1 to 5 according to the following criteria: 5: Improved by more than 20% compared to Comparative Example 1 4: Improved by 10% or more but not more than 20% compared to Comparative Example 1 3: Same as or equivalent to Comparative Example 1 2: Worsened by 10% or more but not more than 20% compared to Comparative Example 1 1: Worsened by more than 20% compared to Comparative Example 1 Here, if the minimum friction coefficient of the brake pad to be 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 to be evaluated decreased by 10% or more compared to the minimum friction coefficient of the brake pad of Comparative Example 1, it was evaluated as "worsened." If the increase or decrease in the minimum friction coefficient of the brake pad to be 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.

[0100] (Wear Amount) The wear amount of the brake pad after the AMS fade test was measured by the following method.

[0101] (Method for measuring the amount of wear) The amount of wear was measured in accordance with JASO C427 6. Measurement method.

[0102] After the test, the pad wear was measured at eight locations per brake pad, and the average value was taken as the "average pad wear."

[0103] The wear measurement results were evaluated using a five-point score of 1 to 5 according to the following criteria: 5: Improved by more than 20% compared to Comparative Example 1 4: Improved by 10% or more but not more than 20% compared to Comparative Example 1 3: Same as or equivalent to Comparative Example 1 2: Worsened by 10% or more but not more than 20% compared to Comparative Example 1 1: Worsened by more than 20% compared to Comparative Example 1 Here, a decrease in the average wear amount of the brake pad to be evaluated by 10% or more compared to the average wear amount of the brake pad of Comparative Example 1 was evaluated as "improved," and an increase in the average wear amount of the brake pad to be evaluated by 10% or more compared to the average wear amount of the brake pad of Comparative Example 1 was evaluated as "worsened." When the increase or decrease in the average wear amount of the brake pad to be evaluated was less than 10% compared to the average wear amount of the brake pad of Comparative Example 1, it was evaluated as the same as or equivalent to Comparative Example 1.

[0104] <Driving Simulation Wear Test> A test (commonly known as the LACT simulation test) was conducted using a bench tester simulating urban driving in Los Angeles (L.A.), and the estimated lifespan (estimated pad lifespan) (miles) of the brake pads of Examples 1 to 16 and Comparative Examples 1 to 16 was calculated using the following formula (1): Estimated pad lifespan (miles) = Pad thickness (mm) / Average pad wear (mm) × Test driving distance (miles) (1) Here, "pad thickness (mm)" refers to the thickness of the brake pad before the LACT simulation test, and "Average pad wear (mm)" refers to the average wear of the brake pad before the LACT simulation test. The measurement method was in accordance with JASO C427 6. Measurement Method. The average rotor temperature in the driving simulation wear test was 100 to 200°C.

[0105] The calculation results of the estimated pad life were evaluated using a score of 1 to 5 according to the following criteria: 5: Improved by more than 20% compared to Comparative Example 1 4: Improved by 10% or more but not more than 20% compared to Comparative Example 1 3: Same as or equivalent to Comparative Example 1 2: Worsened by 10% or more but not more than 20% compared to Comparative Example 1 1: Worsened by more than 20% compared to Comparative Example 1 Here, if the estimated pad life of the brake pad to be evaluated increased by 10% or more compared to the estimated pad life of the brake pad of Comparative Example 1, it was evaluated as "improved," and if the estimated pad life of the brake pad to be evaluated decreased by 10% or more compared to the estimated pad life of the brake pad of Comparative Example 1, it was evaluated as "worsened." If the increase or decrease in the estimated pad life of the brake pad to be evaluated was less than 10% compared to the estimated pad life of the brake pad of Comparative Example 1, it was evaluated as the same as or equivalent to Comparative Example 1.

[0106] <Light Load Rust Removal Test> The light load rust removal properties of the brake pads of Examples 1 to 16 and Comparative Examples 1 to 16 were evaluated using a bench tester. Braking using regenerative braking or regenerative cooperative braking was simulated, and braking using friction braking was started at 10 km / hour (h). Initial braking speed: 10 km / hour (h), Final braking speed: 0 km / hour (h), Deceleration: 0.8 m / s ２

[0107] The rust removal rate was calculated using the following formula (2): 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 x 100 ... (2) Here, the "rust thickness of disc rotor before braking" was calculated using the following formula (3): Rust thickness of disc rotor before braking = thickness of disc rotor after rust formation - thickness of disc rotor before rust formation ... (3) The thickness of the disc rotor was measured using a micrometer at multiple points near the center of the sliding surface, and the average value of the measurements was used.

[0108] In this test, a disc rotor with 50 μm of rust was used, so the "thickness of rust on the disc rotor before braking" was 50 μm.

[0109] Based on the calculation results of the rust removal rate, the light-load rust removability was evaluated using a five-point score of 1 to 5 according to the following criteria: 5: Improved by more than 20% compared to Comparative Example 1 4: Improved by 10% or more but not more than 20% compared to Comparative Example 1 3: Same as or equivalent to Comparative Example 1 2: Worse by 10% or more but not more than 20% compared to Comparative Example 1 1: Worse by more than 20% compared to Comparative Example 1 Here, if the rust removal rate of the brake pad to be evaluated increased by 10% or more compared to the rust removal rate of the brake pad of Comparative Example 1, it was evaluated as "improved," and if the rust removal rate of the brake pad to be evaluated decreased by 10% or more compared to the rust removal rate of the brake pad of Comparative Example 1, it was evaluated as "worsened." If the increase or decrease in the rust removal rate of the brake pad to be evaluated was less than 10% compared to the rust removal rate of the brake pad of Comparative Example 1, it was evaluated as the same as or equivalent to Comparative Example 1.

[0110] <Results> Tables 1 to 4 show the evaluation results of the high-speed test, the evaluation results of the running simulation wear test, and the evaluation results of the light-load rust removal test.

[0111]

[0112]

[0113] As shown in Tables 1 and 2, the brake pads of Examples 1 to 16 contain specific amounts of an inorganic material having a specific particle size and a specific Mohs hardness, monoclinic zirconium oxide, and magnesium hydroxide, and as a result, compared to the brake pad of Comparative Example 1, it was confirmed that they have superior effectiveness and wear resistance during high-speed braking at high temperatures, sufficient wear resistance even in the normal temperature range, and also excellent rust removal properties during light-load braking.

[0114] ​​​In particular, a comparison of Examples 1 to 16 with Comparative Example 4 (not containing inorganic material (A)), Comparative Example 7 (not containing magnesium hydroxide), and Comparative Example 13 (not containing magnesium hydroxide) confirmed that the brake pads of Examples 1 to 16 exhibited a synergistic effect due to the combination of inorganic material (A) having a specific particle size and a specific Mohs hardness, monoclinic zirconium oxide, and magnesium hydroxide.

[0115] Furthermore, from the results of the Examples and Comparative Examples, it was confirmed that, when the content of inorganic material (A) is the same, as the particle size of inorganic material (A) increases, light-load rust removal tends to be insufficient. Furthermore, it was confirmed that as the content of inorganic material (A) increases, light-load rust removal tends to improve, but on the other hand, wear resistance in the normal operating temperature range tends to deteriorate. For the brake pads of Examples 1 to 16, by selecting an inorganic material (A) having a specific particle size and a specific Mohs hardness and combining it with monoclinic zirconium oxide and magnesium hydroxide, light-load rust removal can be sufficiently improved with a small amount of inorganic material (A) added. Therefore, it was believed that the brake pads of Examples 1 to 16 were able to sufficiently improve light-load rust removal while maintaining sufficient wear resistance in the normal operating temperature range.

[0116] The friction material composition and friction material according to one embodiment of the present invention can be suitably used as friction members in braking systems of vehicles such as automobiles.

Claims

1. A friction material composition having a copper content of less than 0.5% by mass in terms of elemental copper, the friction material composition comprising, relative to the total amount of the friction material composition, one or two inorganic materials (excluding monoclinic zirconium oxide) selected from the group consisting of the following (1) and (2) in an amount of 0.05% by mass or more and 1% by mass or less: (1) an inorganic material having a Mohs hardness of 7.5 or more and 8 or less, and having an average particle size of 1 μm or less; (2) an inorganic material having a Mohs hardness of 6 or more and less than 7.5, and having an average particle size of 50 μm or less, and having a Mohs hardness of 6 or more and less than 7.5; 5% by mass or more and 35% by mass or less of monoclinic zirconium oxide; and 0.5% by mass or more and 10% by mass or less of magnesium hydroxide.

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

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

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

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

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

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