Friction material composition and friction material

Abstract

To provide a friction material that exhibits superior braking efficacy and wear resistance during rapid deceleration within high-temperature ranges, maintains sufficient wear resistance even in the normal temperature range, and further offers sufficient rust protection at the contact surface with the mating friction material.SOLUTION: A friction material composition contains copper in an amount of less than 0.5 mass% in terms of elemental copper. The friction material composition contains, as inorganic fillers, each of specific amounts of magnesium hydroxide and monoclinic zirconia oxide.SELECTED DRAWING: None

Description

Technical Field

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

[0002] A friction material is used for disc brake pads and brake shoes of braking devices such as disc brakes and drum brakes.

[0003] Patent Document 1 describes a friction material composition which, in a composition that does not contain copper as an element or has a copper content of 0.5 mass% or less calculated as elemental copper, contains a metal sulfide as an inorganic filler and also contains a reducing agent as an inorganic filler.

[0004] Patent Document 2 describes a friction material made of a thermosetting resin containing 5 to 75 volume% of non-fibrous magnesium hydroxide powder subjected to surface treatment to enhance affinity with the thermosetting resin.

[0005] Patent Document 3 describes that a copper component-free NAO friction material composition contains, based on the total amount of the friction material composition, 10 to 40% by weight of monoclinic zirconium oxide having an average particle diameter of 1 to 8 µm as an inorganic friction modifier, 1.5% by weight or more of elastic graphitized carbon as a carbonaceous lubricant, and calcined coke in a total amount of 2 to 8% by weight based on the total amount of the friction material composition together with said elastic graphitized carbon, wherein the weight ratio of said elastic graphitized carbon to said calcined coke is 4:6 to 8:2. Prior Art Documents Patent Documents

[0006] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2017-141352 Patent Document 2 Japanese Unexamined Patent Application Publication No. 10-158631 Patent Document 3 Japanese Unexamined Patent Application Publication No. 2017-71711 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, conventional friction materials, as described above, do not offer sufficient braking performance or wear resistance during high-speed braking at high temperatures. Furthermore, they exhibit poor corrosion resistance at the contact surfaces with friction-facing materials such as disc rotors and brake drums. Thus, there is room for improvement in conventional friction materials.

[0008] One aspect of the present invention aims to provide a friction material that exhibits excellent braking performance and wear resistance during high-speed braking in high-temperature ranges, has sufficient wear resistance even in normal operating temperature ranges, and further has sufficient rust prevention properties at the contact surface with the friction facing material. [Means for solving the problem]

[0009] The present inventors, after diligent research to solve the above problems, have discovered for the first time that a friction material containing specific amounts of magnesium hydroxide and monoclinic zirconium oxide as inorganic fillers, in a composition in which the copper content in the friction material composition is less than 0.5% by mass as copper element, exhibits excellent braking performance and wear resistance during high-speed braking in high-temperature ranges, as well as sufficient wear resistance in normal operating temperature ranges such as city driving, and further possesses sufficient rust prevention properties at the contact surface with the friction surface, thus completing the present invention. That is, a friction material composition according to one aspect of the present invention is a friction material composition in which the copper content in the friction material composition is less than 0.5% by mass as copper element, and contains magnesium hydroxide and monoclinic zirconium oxide as inorganic fillers, wherein the content of magnesium hydroxide in the friction material composition is 0.5% by mass or more and 10% by mass or less, and the content of monoclinic zirconium oxide in the friction material composition is 5% by mass or more and 35% by mass or less. [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to provide a friction material that has an environmentally harmful copper content of less than 0.5% by mass as copper element, yet exhibits excellent braking performance and wear resistance during high-speed braking in high-temperature ranges, sufficient wear resistance even in normal operating temperature ranges, and sufficient rust prevention properties at the contact surface with the friction surface. [Modes for carrying out the invention]

[0011] <1.Friction material composition> A friction material composition according to one aspect of the present invention is a friction material composition in which the copper content in the friction material composition is less than 0.5% by mass as copper element, and comprises magnesium hydroxide and monoclinic zirconium oxide as inorganic fillers, wherein the magnesium hydroxide content in the friction material composition is 0.5% by mass or more and 10% by mass or less, and the monoclinic zirconium oxide content in the friction material composition is 5% by mass or more and 35% by mass or less. The friction material composition of this aspect is intended to be a mixture of friction material raw materials containing the above components. The friction material composition of this aspect can be used to mold the friction material described later.

[0012] 〔Features〕 The friction material composition of this embodiment has a copper content of 0.5% by mass as copper element. Because it is completely free of harmful substances, it is environmentally friendly. Furthermore, because it contains specific amounts of magnesium hydroxide and monoclinic zirconium oxide as inorganic fillers, it provides excellent performance in terms of effectiveness and wear resistance during high-speed braking at high temperatures, sufficient wear resistance even in normal operating temperature ranges, and sufficient rust prevention at the contact surface with the friction surface, even though the copper content is less than 0.5 mass% as elemental copper.

[0013] The friction material using the friction material composition of this embodiment improves wear resistance during high-speed braking at high temperatures (e.g., 650°C or higher), thereby simultaneously achieving improved braking performance at high temperatures. Furthermore, improved wear resistance during high-speed braking at high temperatures also indicates improved friction material strength on the friction surface, which can be expected to improve the heat resistance of the friction material.

[0014] Furthermore, friction materials using the friction material composition of this embodiment can achieve both wear resistance during high-speed braking in high-temperature ranges and wear resistance in the normal operating temperature range (e.g., 100-200°C), thus exhibiting the excellent effect of a longer lifespan compared to conventional friction materials. Moreover, because friction materials using the friction material composition of this embodiment have excellent wear resistance, less dust is released due to wear. As a result, wheels are less likely to be soiled by dust, and the emission of PM2.5 and PM10, which have a high environmental impact, is reduced, resulting in excellent effects.

[0015] Furthermore, the friction material using the friction material composition of this embodiment has sufficient rust prevention properties at the contact surface with the friction surface, so the friction material is less likely to adhere to the friction surface due to rust generated at the contact surface. As a result, it exhibits excellent effects such as being less prone to problems such as the generation of abnormal noises when starting the vehicle and surface peeling of the friction material.

[0016] [Application] The friction material composition of this embodiment, having the characteristics described above, is particularly useful as a friction material composition for use in the friction surfaces of disc brake pads and drum brake shoes for electric vehicles (EVs) and hybrid electric vehicles (HEVs). This is because EVs / HEVs are heavier than conventional gasoline vehicles due to the large batteries they are equipped with, and regenerative braking tends to contribute less 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 high-temperature ranges, and the frequency of reaching high temperatures increases.

[0017] The friction material composition of this embodiment is not particularly limited to use in EVs / HEVs, but can be suitably used as a friction material for friction surfaces such as disc brake pads and drum brake shoes used in vehicles in general, including motorcycles.

[0018] [Raw materials] The raw materials (friction material raw materials) included in the friction material composition of this embodiment will be described below.

[0019] (Copper) In the friction material composition according to one aspect of the present invention, the content of copper in the friction material composition, calculated as elemental copper, is less than 0.5% by mass. The friction material composition according to one aspect of the present invention has an extremely low content of copper and copper alloys, which are highly environmentally hazardous, and thus exhibits the effect of being able to provide an environmentally friendly friction material. From the perspective of providing a more environmentally friendly friction material, it is more preferable that the content of copper in the friction material composition is 0% by mass (copper-free). The copper contained in the friction material composition according to one aspect of the present invention may be derived from copper fibers added as a fiber base material.

[0020] (Magnesium Hydroxide) The friction material composition according to one aspect of the present invention contains, as one type of inorganic filler, magnesium hydroxide in an amount of 0.5% by mass or more and 10% by mass or less based on 100% by mass of the friction material composition.

[0021] (Actions and Effects of Magnesium Hydroxide) (i) Improvement of wear resistance and rust resistance in normal temperature ranges Magnesium hydroxide has a Mohs hardness of 2 to 3 and is easily broken by friction with a friction-facing material such as a disc rotor or a brake drum. For this reason, alkaline magnesium hydroxide tends to spread uniformly on the friction surface. As a result, a friction material containing magnesium hydroxide has a high rust-preventing effect.

[0022] Furthermore, magnesium hydroxide has low solubility in water, so alkali is less likely to elute from a pad (such as a friction surface) when exposed to water. For this reason, the rust-preventing effect lasts longer than that of other alkaline materials. As a result, the friction material containing magnesium hydroxide maintains its rust-preventing effect even when exposed to rain such as during the rainy season or when the pad is heavily worn like an old pad.

[0023] Magnesium hydroxide has a pH of 10.5, which is not high enough to promote the decomposition of the resin contained as a binder in the friction material. For this reason, strength reduction caused by resin decomposition is less likely to occur in a friction material containing magnesium hydroxide. As a result, the wear resistance of the pad is improved.

[0024] (ii) Improved braking effectiveness and wear resistance during high-speed braking in high-temperature environments Magnesium hydroxide exhibits heat resistance through dehydration and endothermic reactions at temperatures of 300-400°C. When magnesium hydroxide is uniformly spread on a friction surface, it transforms into magnesium oxide through dehydration. Magnesium oxide, due to the high heat generated by high-speed braking (high-load braking) in high-temperature ranges, fuses with monoclinic zirconium oxide (described later), contributing to the formation of a stabilized zirconium oxide film. Stabilized zirconium oxide is easy to form a stable film and has excellent heat resistance. The stabilized zirconium oxide film improves wear resistance by protecting the friction surface, and consequently improves the coefficient of friction (μ).

[0025] In this embodiment, the magnesium hydroxide content in the friction material composition is 0.5% by mass or more per 100% by mass of the friction material composition, so that a sufficient amount of magnesium hydroxide spreads across the friction surface, and the effects of (i) and (ii) described above are fully realized. Furthermore, if the magnesium hydroxide content in the friction material composition in this embodiment is 10% by mass or less per 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 base material strength of the friction material is less likely to occur. As a result, the wear resistance of the pad in the normal operating temperature range is good, and sufficient heat resistance is also obtained.

[0026] (Preferred magnesium hydroxide content) From the viewpoint of further improving braking effectiveness and wear resistance during high-speed braking in high-temperature ranges, the magnesium hydroxide content in the friction material composition is preferably 0.8% by mass or more and 5% by mass or less based on 100% by mass of the friction material composition.

[0027] (Particle size of magnesium hydroxide) From the viewpoint of achieving the effects described in (i) and (ii) above, the particle size of magnesium hydroxide is not particularly limited. For this reason, magnesium hydroxide with a particle size commonly used as an inorganic filler added to friction materials can be appropriately selected. However, from the viewpoint of ease of handling during the manufacture of the friction material composition, the average particle size of 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 manufacture of the friction material composition, and preventing magnesium hydroxide particles from easily falling off the friction surface during braking, thereby stably obtaining improved braking performance and wear resistance at high speeds in high-temperature ranges at any location on the friction surface, the average particle size of magnesium hydroxide is preferably 20 μm or less, and more preferably 15 μm or less.

[0028] The average particle size of magnesium hydroxide shall be the median diameter (volume-based median diameter) obtained by JIS Z 8825 "Particle size analysis - Laser analysis and scattering method". When confirming the particle size of magnesium hydroxide after friction material formation, the average particle size of the particles corresponding to magnesium hydroxide can be determined by measuring the volume-based particle size distribution from an electron microscope image of the cross-section of the friction material using JIS Z 8827-1 "Particle size analysis - Image analysis method - Part 1: Static image analysis method", and then determining the median diameter.

[0029] (Monoclinic zirconium oxide) A friction material composition according to one aspect of the present invention contains, as one type of inorganic filler, monoclinic zirconium oxide in an amount of 5% by mass or more and 35% by mass or less per 100% by mass of the friction material composition. "Monoclinic zirconium oxide" refers to zirconium oxide whose crystal system is monoclinic. Zirconium oxide undergoes a phase transition with temperature. At room temperature (20°C), it is monoclinic, and as the temperature increases, the crystal structure changes to tetragonal at 1170°C and to cubic at 2370°C. The phase transition is accompanied by a volume change.

[0030] Pure zirconium oxide is most stable in a monoclinic crystal structure at room temperature, but when combined with magnesium oxide, a cubic crystal structure becomes stable even at room temperature. Zirconium oxide stabilized in a cubic crystal structure at room temperature is called "stabilized zirconium oxide."

[0031] (Mechanism of action and effects of monoclinic zirconium oxide) (i) Improved wear resistance and corrosion resistance in the normal operating temperature range. Monoclinic zirconium oxide has lower toughness compared to stabilized zirconium oxide. Therefore, monoclinic zirconium oxide exhibits low abrasiveness not only in non-braking conditions but also in braking conditions, resulting in low rotor abrasiveness in both states and less loss of magnesium hydroxide spread across the friction surface. As a result, the corrosion prevention provided by the magnesium hydroxide spread across the friction surface is fully realized. Furthermore, the lower toughness of monoclinic zirconium oxide compared to stabilized zirconium oxide leads to better wear resistance of the pads.

[0032] (ii) Improved braking effectiveness and wear resistance during high-speed braking in high-temperature environments Monoclinic zirconium oxide fuses with magnesium oxide (magnesium hydroxide in the friction material that has been altered by dehydration) due to the high heat generated by high-speed braking (high-load braking) in high-temperature ranges, becoming stabilized zirconium oxide. The stabilized zirconium oxide film formed on the friction surface protects the surface. Furthermore, because it reacts with magnesium oxide to become cubic stabilized zirconium oxide, volume changes associated with phase transitions are eliminated, making it less likely for the friction material strength on the friction surface to decrease. As a result, the wear resistance of the pad improves, and consequently, the coefficient of friction (μ) improves.

[0033] The thickness of the stabilized zirconium oxide film formed on the friction surface changes depending on the content of monoclinic zirconium oxide in the friction material composition of this embodiment. When the content of monoclinic zirconium oxide in the friction material composition of this embodiment is 5% by mass or more per 100% by mass of the friction material composition, a stabilized zirconium oxide film of sufficient thickness is formed so that the effect of (ii) above is exhibited. Furthermore, when the content of monoclinic zirconium oxide in the friction material composition of this embodiment is 35% by mass or less per 100% by mass of the friction material composition, the stabilized zirconium oxide film does not become too thick. As a result, magnesium hydroxide is not buried in the stabilized zirconium oxide film, so the rust-resistant effect of magnesium hydroxide is fully exhibited. In addition, since the stabilized zirconium oxide film is less likely to peel off from the friction surface, it is possible to prevent the friction area from decreasing due to variations in film thickness and the effectiveness from decreasing in the high-temperature range. Therefore, the effect of (i) above is fully exhibited.

[0034] (Preferred content of monoclinic zirconium oxide) From the viewpoint of further improving braking effectiveness and wear resistance during high-speed braking in high-temperature ranges, the content of monoclinic zirconium oxide in the friction material composition is preferably 20% by mass or more and 30% by mass or less based on 100% by mass of the friction material composition.

[0035] (Particle size of monoclinic zirconium oxide) From the viewpoint of achieving the effects described in (i) and (ii) above, the particle size of monoclinic zirconium oxide is not particularly limited. For this reason, monoclinic zirconium oxide with a particle size commonly used as an inorganic filler added to friction materials can be appropriately selected. From the viewpoint of ease of handling during the manufacture 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 manufacture of the friction material composition and minimizing the impact on the reduction 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.

[0036] The average particle size of monoclinic zirconium oxide shall be the median diameter (volume-based) obtained by JIS Z 8825 "Particle size analysis - Laser analysis and scattering method". When confirming the particle size of monoclinic zirconium oxide after friction material formation, the average particle size of the particles corresponding to monoclinic zirconium oxide can be determined by measuring the volume-based particle size distribution from an electron microscope image of the cross-section of the friction material using JIS Z 8827-1 "Particle size analysis - Image analysis method - Part 1: Static image analysis method", and then determining the median diameter.

[0037] (Non-vulcanized elastomer) A friction material composition according to one aspect of the present invention preferably contains a non-vulcanized elastomer as an organic filler. In this specification, "non-vulcanized elastomer" refers to an elastomer that has not been vulcanized. The non-vulcanized elastomer is preferably one that softens (is plastic) in the normal operating temperature range (e.g., 100-200°C) such as when driving in urban areas.

[0038] (Mechanism of action and effects of non-vulcanized elastomers) Since non-vulcanized elastomers soften within the normal operating temperature range, friction materials containing non-vulcanized elastomers exhibit improved wear resistance within that range. Furthermore, during braking within the normal operating temperature range (low-temperature braking), monoclinic zirconium oxide and magnesium hydroxide adhere to the softened non-vulcanized elastomer. This retains the monoclinic zirconium oxide and magnesium hydroxide on the friction surface, making them less likely to be lost. As a result, wear resistance and corrosion resistance are improved compared to friction materials that do not contain non-vulcanized elastomers.

[0039] (Types of non-vulcanized elastomers) From the viewpoint of achieving the aforementioned effects, the type of non-vulcanized elastomer is not particularly limited, and any non-vulcanized elastomer can be preferably used. Examples of non-vulcanized elastomers include non-vulcanized diene rubbers such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR); non-vulcanized non-diene rubbers such as butyl rubber (IIR), ethylene propylene rubber (EPM), urethane rubber (U), silicone rubber (Q), chlorosulfonated polyethylene (CSM), chlorinated polyethylene (CM), acrylic rubber (ACM), epichlorohydrin rubber (CO), and fluororubber (FKM); and thermoplastic elastomers such as 1,2-polybutadiene, ethylene-octene copolymer, and ethylene-α-olefin copolymer. Non-vulcanized elastomers can be used individually or in combination of multiple types.

[0040] Furthermore, from the viewpoint of achieving the aforementioned effects, the shape of the non-vulcanized elastomer is not particularly limited, and any shape can be used as appropriate. However, from the viewpoint of ease of mixing during the manufacture of the friction material composition, it is preferable that it be granular.

[0041] (Content of non-vulcanized elastomers) The content of the non-vulcanized elastomer in the friction material composition is not particularly limited and can be appropriately determined within a range in which the desired effects of including the non-vulcanized elastomer are sufficiently expressed. From the viewpoint of further improving the wear resistance and rust prevention of the friction material in the normal operating temperature range, the content of the non-vulcanized elastomer in the friction material composition is preferably 0.5% by mass or more, and more preferably 1% by mass or more, based on 100% by mass of the friction material composition. Furthermore, from the viewpoint of the blending balance with other components contained in the friction material composition, the content of the non-vulcanized elastomer in the friction material composition is preferably 10% by mass or less, and more preferably 3% by mass or less, based on 100% by mass of the friction material composition.

[0042] (Other ingredients) In addition to the components described above, the friction material composition of this embodiment may also contain, as friction material raw materials, a fibrous base material, a binder, another organic filler different from the non-vulcanized elastomer, and another inorganic filler different from magnesium hydroxide and monoclinic zirconium oxide.

[0043] (Fiber base material) Examples of fiber base materials include organic fibers, inorganic fibers, and metallic fibers. These fibers may be natural fibers or artificially synthesized synthetic fibers. Examples of organic fibers include aromatic polyamide fibers (aramid fibers), acrylic fibers, cellulose fibers, and carbon fibers. Examples of inorganic fibers include rock wool and glass fibers. Examples of metallic fibers include fibers made from single metals such as steel, stainless steel, aluminum, zinc, and tin, as well as fibers made from alloys of these metals. Fiber base materials can be used individually or in combination of multiple types. The content of fiber base materials in the friction material composition is not particularly limited and can be the content commonly used in the art.

[0044] (Binding material) The binder has the function of binding the friction material raw materials in the friction material composition. The binder is not particularly limited as long as it can exhibit the above performance, 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. The binder can be used alone or in combination of multiple types. The content of the binder in the friction material composition is not particularly limited and can be the content that is normally used in the art. The binder may also contain modified components such as silicone rubber, acrylic rubber, and cashew oil.

[0045] (Another organic filler, different from non-vulcanized elastomers) The friction material composition of this embodiment may contain an organic filler other than the non-vulcanized elastomer, to the extent that it does not impair the effects of the present invention. The organic filler functions as a friction modifier to improve wear resistance and other properties. The organic filler other than the non-vulcanized elastomer is not particularly limited as long as it can exhibit the above performance, and organic fillers known in the art can be preferably used. Specific examples of organic fillers other than the non-vulcanized elastomer include rubber powder, tire powder, cashew dust, fluororesin, melamine cyanurate, polyethylene resin, etc. The organic filler can be used alone or in combination of multiple types. The organic filler may also be coated on the surface with phosphoric acid or fluororesin. The content of the organic filler other than the non-vulcanized elastomer is not particularly limited, and the total content of the organic filler, including the non-vulcanized elastomer, should be adjusted as appropriate so that it falls within the range of organic filler content used in the art. The friction material composition of this embodiment may contain a small amount of vulcanized elastomer (e.g., vulcanized rubber) as long as it does not impair the effect of the non-vulcanized elastomer.

[0046] (Another inorganic filler, distinct from monoclinic zirconium oxide and magnesium hydroxide) The friction material composition of this embodiment may contain inorganic fillers other than monoclinic zirconium oxide and magnesium hydroxide, to the extent that they do not impair the effects of the present invention. As alternative inorganic fillers other than monoclinic zirconium oxide and magnesium hydroxide, inorganic substances known in the art can be preferably used, such as barium sulfate, mica, iron oxides (ferrous oxide, ferric oxide, etc.), titanates, calcium hydroxide, etc. Examples of titanates include alkali metal titanates, alkali metal group II titanates, etc., and specific examples include potassium titanate, sodium titanate, lithium titanate, lithium potassium titanate, magnesium potassium titanate, etc. These inorganic fillers can be used individually or in combination. The content of alternative inorganic fillers other than monoclinic zirconium oxide and magnesium hydroxide in the friction material composition is not particularly limited, and the total content of inorganic fillers, including monoclinic zirconium oxide and magnesium hydroxide, should be appropriately adjusted so that it falls within the range of inorganic filler content used in the art.

[0047] Inclusion of a titanate as an inorganic filler different from monoclinic zirconium oxide and magnesium hydroxide is preferable because it strengthens the film formed on the friction surface during high-speed braking at temperatures above 650°C, thereby improving the heat resistance (effectiveness and wear resistance) of the friction material. In this case, there is no particular upper limit to the titanate content, and it is sufficient to adjust the total content of the inorganic fillers, including monoclinic zirconium oxide and magnesium hydroxide, so that it matches the content of inorganic fillers used in the relevant art. A higher titanate content is preferable because it further improves the heat resistance of the friction material as described above.

[0048] Furthermore, the particle size of the inorganic filler other than monoclinic zirconium oxide and magnesium hydroxide is not particularly limited, and inorganic materials having average particle sizes commonly used in the art can be preferably used.

[0049] (Lubricant) The friction material composition of this embodiment may further contain a lubricant, to the extent that it does not impair the effects of the present invention. 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 individually or in combination. The lubricant content is not particularly limited and can be the content commonly used in the art.

[0050] (Method for manufacturing friction material composition) The friction material composition of this embodiment can be manufactured by a manufacturing method that includes a mixing step of blending the above-mentioned friction material raw materials. From the viewpoint of uniformly mixing the friction material raw materials, the mixing step is preferably a 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, the friction material raw materials can be mixed at room temperature for about 10 minutes using a known mixer such as a Fenschel mixer or a Redigge mixer. In the mixing step, the mixture of friction material raw materials may be cooled by a known cooling method so that the friction material raw materials do not heat up during mixing.

[0051] <2.Friction material> A friction material according to one aspect of the present invention is formed by molding a friction material composition according to one aspect of the present invention. The effects, uses, etc., of the friction material according to this aspect have been described in relation to one aspect of the friction material composition of the present invention and will not be repeated here.

[0052] (Manufacturing method for friction materials) The friction material of this embodiment can be manufactured by a manufacturing method that includes a molding step for molding a 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 one embodiment of the friction material composition of the present invention can be molded into a predetermined shape, and methods known in the art can be used. For example, one embodiment of the friction material composition of the present invention can be molded by pressing it with a press or the like. As a molding method by pressing, either a hot press method, in which one embodiment of the friction material composition of the present invention is heated and pressed to form the material, or a room temperature press method, in which one embodiment of the friction material composition of the present invention is pressed at room temperature without heating to form the material. When molding with a hot press method, for example, one embodiment of the friction material composition of the present invention can be molded into a friction material by setting the molding temperature to 140°C or higher and 200°C or lower (preferably 160°C), the molding pressure to 10 MPa or higher and 40 MPa or lower (preferably 20 MPa), and the molding time to 3 minutes or higher and 15 minutes or lower (preferably 10 minutes). When forming using a room-temperature press method, for example, by setting the forming pressure to 50 MPa or more and 200 MPa or less (preferably 100 MPa) and the forming time to 5 seconds or more and 60 seconds or less (preferably 15 seconds), one aspect of the friction material composition of the present invention can be formed into a friction material. Furthermore, if necessary, a polishing step may be performed to polish the surface of the friction material to form a friction surface.

[0053] <3. Friction Members> A friction member using a 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 have a configuration comprising only one aspect of the friction material of the present invention, or a configuration in which a plate-like member such as a metal plate as a backing plate and one aspect of the friction material of the present invention are integrated. The effects and uses of the friction member of this aspect have been described for one aspect of the friction material composition of the present invention, so they will not be repeated here.

[0054] When the friction member of this embodiment is configured in which a plate-shaped member and one embodiment of the friction material of the present invention are integrated, the embodiment of the friction material of the present invention and the plate-shaped member can be bonded together by clamping them and then heat-treating them. The conditions for the clamping process are not particularly limited, but for example, they may be 180°C, 1 MPa, and 10 minutes. Similarly, the conditions for the heat treatment after the clamping process are not particularly limited, but for example, they may be 150°C or higher and 250°C or lower, for 5 minutes or higher and 180 minutes or lower, preferably 230°C and 3 hours.

[0055] 〔summary〕 A friction material composition according to embodiment 1 of the present invention is a friction material composition in which the copper content in the friction material composition is less than 0.5% by mass as copper element, and comprises magnesium hydroxide and monoclinic zirconium oxide as inorganic fillers, wherein the content of magnesium hydroxide in the friction material composition is 0.5% by mass or more and 10% by mass or less, and the content of monoclinic zirconium oxide in the friction material composition is 5% by mass or more and 35% by mass or less.

[0056] This configuration provides a friction material that, despite having a copper content of less than 0.5 mass% as elemental copper, exhibits superior braking performance and wear resistance during high-speed braking at high temperatures compared to conventional friction materials, while also possessing sufficient wear resistance in normal operating temperature ranges and providing sufficient corrosion resistance at the contact surface with the friction mating material.

[0057] The friction material composition according to embodiment 2 of the present invention may also have a configuration that includes a non-vulcanized elastomer as an organic filler in embodiment 1 described above.

[0058] This configuration offers the benefit of further improving wear resistance and corrosion resistance within the normal operating temperature range.

[0059] The friction material composition according to embodiment 3 of the present invention may be configured such that, in embodiment 1 or 2, the content of magnesium hydroxide in the friction material composition is 0.8% by mass or more and 5% by mass or less, and the content of monoclinic zirconium oxide in the friction material composition is 20% by mass or more and 30% by mass or less.

[0060] This configuration results in improved braking performance and wear resistance during high-speed braking at high temperatures.

[0061] The friction material according to embodiment 4 of the present invention is configured to be formed by molding any one of the friction material compositions described in embodiments 1 to 3 above.

[0062] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Examples]

[0063] <Friction material raw materials> The main friction material raw materials used in the examples and comparative examples are as follows: • Monoclinic zirconium oxide: Average particle size 10 μm or larger • Stabilized zirconium oxide: Average particle size 10 μm or larger Magnesium hydroxide: average particle size 4 μm or average particle size 15 μm Magnesium oxide: Average particle size 2 μm • Non-vulcanized rubber (non-vulcanized elastomer): Granular SBR Aside from the friction materials mentioned above, the other materials used were those commonly used in this field.

[0064] [Example 1] <Brake pad manufacturing> The friction material composition was obtained by blending each raw material according to the blending ratios shown in Table 1 and mixing them using a Redigem mixer at room temperature (20°C) for about 10 minutes. The units for the blending amounts of each raw material in Table 1 are in mass % of the friction material composition.

[0065] A molded product was obtained by heating and compressing the friction material composition using a forming press in a hot pressing process. The forming conditions for the hot pressing process were as follows: Molding temperature: 160℃ Molding pressure: 20 MPa Molding time: 10 minutes.

[0066] The surface of the obtained molded product was polished using a polishing machine to form a friction surface and obtain a friction material. Using this friction material, the brake pad of Example 1 was manufactured, and high-temperature tests and driving simulation tests were performed. The brake pad manufactured in Example 1 had a friction material thickness of 12.5 mm and a friction material projected area of ​​55 cm². 2 That was the case.

[0067] [Examples 2-9] Brake pads for Examples 2-9 were manufactured in the same manner as in Example 1, except that each raw material was blended according to the mixing ratios shown in Table 1.

[0068] [Comparative Examples 1-12] The brake pads of Comparative Examples 1 to 12 were manufactured in the same manner as in Example 1, except that each raw material was blended according to the mixing ratios shown in Table 2.

[0069] <High Temperature Test> An AMS fade test (evaluation conditions published in the German automotive magazine auto motor und sport: vehicle speed 130 km / hour, maximum rotor temperature 650°C or higher) was conducted, and the brake pads of Examples 1-9 and Comparative Examples 1-12 were evaluated as follows.

[0070] The AMS fade test was performed on (A) brand-new brake pads that had not been used since manufacture, and (B) brake pads with a history of market use. "(B) Brake pads with a history of market use" simulated a state of advanced wear and exposure to rain. Specifically, after testing with new brake pads, a total of 15 liters of water was poured over them for 1 minute, and then the same test as with new brake pads was performed. The maximum rotor temperature in each test was 650-670°C.

[0071] (Minimum coefficient of friction) The lowest coefficient of friction during the AMS fade test was measured using the following method. (Method for measuring the minimum coefficient of friction) The friction coefficient for each braking condition was calculated using the formula described in JIS D 0106, based on the lowest torque during braking. The lowest friction coefficient observed during the test was defined as the minimum friction coefficient.

[0072] The measurement results for the minimum friction coefficient were evaluated on a 5-point scale from 1 to 5 according to the following criteria. 5: Improvement of more than 20% compared to Comparative Example 1 4: Improvement of 10% or more and 20% or less compared to Comparative Example 1. 3: Same as or equivalent to Comparative Example 1 2: Deterioration of 10% or more, but not exceeding 20%, compared to Comparative Example 1. 1: Worsened by more than 20% compared to Comparative Example 1. Here, an improvement was defined as a 10% or greater increase in the minimum friction coefficient of the brake pad being evaluated compared to the minimum friction coefficient of the brake pad in Comparative Example 1, and a deterioration was defined as a 10% or greater decrease in the minimum friction coefficient of the brake pad being evaluated compared to the minimum friction coefficient of the brake pad in Comparative Example 1. If the increase or decrease in the minimum friction coefficient of the brake pad being evaluated was less than 10% compared to the minimum friction coefficient of the brake pad in Comparative Example 1, it was evaluated as the same as or equivalent to Comparative Example 1.

[0073] (Amount of wear) The amount of brake pad wear after the AMS fade test was measured using the following method. (Method for measuring wear) The amount of wear was measured in accordance with JASO C427 6. Measurement Method.

[0074] After the test, the amount of pad wear was measured at eight points for each brake pad, and the average value was defined as the "average pad wear."

[0075] The wear measurement results were evaluated on a 5-point scale from 1 to 5 according to the following criteria. 5: Improvement of more than 20% compared to Comparative Example 1 4: Improvement of 10% or more and 20% or less compared to Comparative Example 1. 3: Same as or equivalent to Comparative Example 1 2: Deterioration of 10% or more, but not exceeding 20%, compared to Comparative Example 1. 1: Worsened by more than 20% compared to Comparative Example 1. Here, an improvement was defined as a decrease of 10% or more in the average wear amount of the brake pad being evaluated compared to the average wear amount of the brake pad in Comparative Example 1, and a deterioration was defined as an increase of 10% or more in the average wear amount of the brake pad being evaluated compared to the average wear amount of the brake pad in Comparative Example 1. If the increase or decrease in the average wear amount of the brake pad being evaluated was less than 10% compared to the average wear amount of the brake pad in Comparative Example 1, it was evaluated as the same as or equivalent to Comparative Example 1.

[0076] <Driving simulation wear test> A test was conducted using a test bench that simulated urban driving in Los Angeles (LA) (commonly known as the LACT simulation test), and the estimated lifespan of the brake pads (estimated pad life) (miles) was calculated using the following formula (1). Estimated pad life (miles) = Pad thickness (mm) ÷ Average pad wear (mm) × Test mileage (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.

[0077] Similar to the AMS fade test, the driving simulation wear test was also conducted using brake pads from Examples 1-9 and Comparative Examples 1-12, for (A) unused (new) brake pads and (B) brake pads with a history of market use. For "(B) brake pads with a history of market use," a total of 15L of water was poured over the brake pads and rotors after testing with new pads for 1 minute, and then the same test as with new brake pads was performed. The average rotor temperature for each test was 100-200°C.

[0078] The estimated pad lifespan was calculated and evaluated on a 5-point scale from 1 to 5 according to the following criteria. 5: Improvement of more than 20% compared to Comparative Example 1 4: Improvement of 10% or more and 20% or less compared to Comparative Example 1. 3: Same as or equivalent to Comparative Example 1 2: Deterioration of 10% or more, but not exceeding 20%, compared to Comparative Example 1. 1: Worsened by more than 20% compared to Comparative Example 1. Here, an improvement was defined as a 10% or greater increase in the estimated pad life of the brake pad being evaluated compared to the estimated pad life of the brake pad in Comparative Example 1, and a deterioration was defined as a 10% or greater decrease in the estimated pad life of the brake pad being evaluated compared to the estimated pad life of the brake pad in Comparative Example 1. If the increase or decrease in the estimated pad life of the brake pad being evaluated was less than 10% compared to the estimated pad life of the brake pad in Comparative Example 1, it was evaluated as the same as or equivalent to Comparative Example 1.

[0079] <Rust Resistance Evaluation> Rust adhesion tests were conducted in accordance with JIS D4414-2:1998 "Rust adhesion test method (immersion method)" to measure the rust adhesion strength.

[0080] Similar to the AMS fade test and the driving simulation wear test, the rust adhesion test was also performed using the brake pads of Examples 1-9 and Comparative Examples 1-12, on (A) unused (new) brake pads and (B) brake pads with a history of market use. For "(B) brake pads with a history of market use," a total of 15L of water was poured over the brake pads and rotors after the driving simulation wear test on new brake pads for 1 minute, and then the same test as for new brake pads was performed.

[0081] Based on the measurement results of rust adhesion strength, the degree of pad adhesion due to rust was evaluated on a 5-point scale from 1 to 5 according to the following criteria. 5: Improvement of more than 30% compared to Comparative Example 1 4: Improvement of 15% or more and 30% or less compared to Comparative Example 1. 3: Same as or equivalent to Comparative Example 1 2: Worsened by 15% or more, but not exceeding 30%, compared to Comparative Example 1. 1: Worsened by more than 30% compared to Comparative Example 1. Here, a reduction of 15% or more in the rust adhesion force of the brake pad being evaluated compared to the brake pad of Comparative Example 1 was evaluated as "improvement," and an increase of 15% or more in the rust adhesion force of the brake pad being evaluated compared to the brake pad of Comparative Example 1 was evaluated as "deterioration." If the increase or decrease in the rust adhesion force of the brake pad being evaluated was less than 15% compared to the brake pad of Comparative Example 1, it was evaluated as the same as or equivalent to Comparative Example 1.

[0082] <Result> The evaluation results for each aspect of the high-speed test, the evaluation results for the driving simulation wear test, and the evaluation results for the rust resistance evaluation are shown in Tables 1 and 2. [Table 1] [Table 2]

[0083] As shown in Table 1, the brake pads of Examples 1 to 9, by containing specific amounts of magnesium hydroxide and monoclinic zirconium oxide as inorganic fillers, were found to have superior braking performance and wear resistance at high speeds in high-temperature ranges compared to the brake pad of Comparative Example 1, as well as sufficient wear resistance in the normal operating temperature range, and also possessed sufficient rust prevention properties on the contact surface with the friction surface. Furthermore, a comparison between Examples 1 to 8 and Example 9 confirmed that incorporating non-vulcanized rubber as a non-vulcanized elastomer further improved wear resistance and rust prevention in the normal operating temperature range.

[0084] The monoclinic zirconium oxide in the friction material fuses with magnesium oxide (which is formed when magnesium hydroxide in the friction material is dehydrated) due to the high heat generated by high-speed braking at high temperatures, thereby becoming stabilized zirconium oxide. The stabilized zirconium oxide film formed on the friction surface protects the friction surface, improving wear resistance at high temperatures and consequently improving the coefficient of friction (μ) at high temperatures.

[0085] In contrast, the brake pad of Comparative Example 12, which contained stabilized zirconium oxide instead of monoclinic zirconium oxide, showed poor wear resistance in the normal operating temperature range. This was thought to be because stabilized zirconium oxide has a high Mohs hardness, making it highly aggressive and causing wear. Similarly, the brake pad of Comparative Example 11, which contained magnesium oxide instead of magnesium hydroxide, also showed reduced wear resistance in the normal operating temperature range and a worsened estimated pad life due to the high Mohs hardness of magnesium oxide.

[0086] Based on these findings, it was considered important that the monoclinic zirconium oxide and magnesium hydroxide blended into the friction material composition react with the high heat generated by high-speed braking in high-temperature ranges, thereby appropriately forming a stabilized zirconium oxide film on the friction surface. This is crucial for achieving both improved wear resistance and corrosion resistance in the normal operating temperature range and improved braking performance and wear resistance during high-speed braking in high-temperature ranges. [Industrial applicability]

[0087] A friction material composition and friction material according to one aspect 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 in which the copper content as copper element is less than 0.5% by mass, The inorganic filler contains magnesium hydroxide and monoclinic zirconium oxide. The content of magnesium hydroxide in the friction material composition is 0.5% by mass or more and 10% by mass or less, and The content of monoclinic zirconium oxide in the friction material composition is 5% by mass or more and 35% by mass or less. In the high-temperature range, a stabilized zirconium oxide film is formed on the friction surface by the monoclinic zirconium oxide and magnesium oxide obtained by dehydration of the magnesium hydroxide. Friction material composition.

2. The friction material composition according to claim 1, comprising a non-vulcanized elastomer as an organic filler.

3. The content of magnesium hydroxide in the friction material composition is 0.8% by mass or more and 5% by mass or less, and The friction material composition according to claim 1, wherein the content of monoclinic zirconium oxide in the friction material composition is 20% by mass or more and 30% by mass or less.

4. A friction material obtained by molding a friction material composition according to any one of claims 1 to 3.

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