Friction material composition, friction material, and friction member

Abstract

To provide a friction material composition capable of forming a friction material that can suppress judders.SOLUTION: A friction material composition comprises first graphite with an average particle size of 100 μm-500 μm of 6 mass%-9 mass% and second graphite with an average particle size of 10 μm-50 μm of 1 mass%-4 mass%, with a total content of graphite of 8 mass%-12 mass%, and also comprises rubber powder of 3 mass%-6 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a friction material composition, a friction material, and a friction member. [Background technology]

[0002] Friction materials such as disc brake pads and brake linings are used for braking in automobiles, railway vehicles, various industrial machines, etc. Friction materials perform their braking function by rubbing against opposing materials such as disc rotors and brake drums.

[0003] For example, in order to provide a friction material that achieves both frictional properties and vibrational properties, a friction material has been disclosed that includes a fiber base material, a friction modifier, and a binder, and that the content of at least one copper component selected from copper, copper alloys, and copper compounds is 5 mass % or less in terms of copper element, and that includes 2 to 7 mass % of elastic graphite, 3 to 10 mass % of chromite, and 3 to 15 mass % of steel fibers (see, for example, Patent Document 1). Furthermore, in order to provide a friction material composition that reduces brake vibration during high-temperature braking and low-temperature wear, a friction material composition has been disclosed that contains a binder, an organic filler, an inorganic filler, and a fibrous base material, and is characterized by not containing copper as an element in the friction material composition or having a copper content of 0.5 mass % or less, containing 2 to 5 mass % of steel fibers having a fiber length of 2500 μm or less, and containing a titanate with a layered crystal structure (see, for example, Patent Document 2). Furthermore, in order to provide a friction material composition that can suppress brake vibration during high-temperature braking, a friction material composition has been disclosed that contains a binder, an organic filler, an inorganic filler, and a fibrous base material, and is characterized in that the friction material composition does not contain copper as an element or the copper content is 0.5 mass % or less, and contains 2 to 5 mass % of steel fibers with a fiber length of 2500 μm or less (see, for example, Patent Document 3). Furthermore, in order to provide a friction material that can suppress brake vibration during high-temperature braking, a friction material molded from a friction material composition characterized by containing 1 to 4 weight % of cashew dust as an organic friction modifier, 7 to 12 weight % of muscovite as an inorganic friction modifier, and 0.5 to 5 weight % of aluminum particles as an inorganic friction modifier has been disclosed (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-093935 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-121244 [Patent Document 3] Japanese Patent Application Publication No. 2019-214731 [Patent Document 4] Patent Publication No. 2021-017521 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in recent years, the performance requirements for brakes have tended to become increasingly more stringent. In particular, there is a demand for friction materials that can prevent or reduce brake vibration (hereinafter sometimes referred to as "judder") during braking at high speeds. The present disclosure has been made in consideration of the above-described conventional circumstances, and one aspect of the present disclosure aims to provide a friction material composition capable of forming a friction material in which the occurrence of judder is suppressed, and a friction material and a friction member using the friction material composition. [Means for solving the problem]

[0006] Specific means for achieving the above object are as follows. <1> A friction material composition comprising 6% by mass to 9% by mass of first graphite having an average particle size of 100 μm to 500 μm, 1% by mass to 4% by mass of second graphite having an average particle size of 10 μm to 50 μm, a total graphite content of 8% by mass to 12% by mass, and 3% by mass to 6% by mass of rubber powder. <2> The mass ratio of the first graphite to the second graphite is 1 to 5. <1> The friction material composition according to claim 1. <3> The composition further contains zirconia, and the content of the zirconia is 25 mass% or less. <1> or <2> The friction material composition according to claim 1. <4> The mass ratio of the zirconia to the first graphite is 1.5 to 5.0. <3> The friction material composition according to claim 1. <5> The rubber powder contains tire rubber. <1> ~ <4> The friction material composition according to any one of the above. <6> The composition further contains a binder, and the binder content is 4% by mass to 20% by mass. <1> ~ <5> The friction material composition according to any one of the above. <7> The composition further contains a fiber base material, and the content of the fiber base material is 10% by mass to 40% by mass. <1> ~ <6> The friction material composition according to any one of the above. <8> Further, the composition contains a metal sulfide, and the content of the metal sulfide is 1% by mass to 3% by mass. <1> ~ <7> The friction material composition according to any one of the above. <9> <1> ~ <8> 10. A friction material formed using the friction material composition according to claim 9. <10> <9> A friction member comprising the friction material according to claim 1. [Effects of the Invention]

[0007] According to one aspect of the present disclosure, there is provided a friction material composition capable of forming a friction material in which the occurrence of judder is suppressed, and a friction material and a friction member using the friction material composition. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments for carrying out the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0009] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple substances corresponding to the component. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, the particles corresponding to each component may contain multiple types of particles. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In the present disclosure, the term "layer" includes cases where the layer is formed over the entire area when the area in which the layer exists is observed, as well as cases where the layer is formed over only a portion of the area. The average particle size of particles refers to the 50% (median) diameter (D50) determined from the volume distribution of particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer. The average particle size can be measured, for example, using an LA-920 (manufactured by Horiba, Ltd.).

[0010] [Friction material composition] The friction material composition of the present disclosure contains 6% by mass to 9% by mass of first graphite having an average particle size of 100 μm to 500 μm, 1% by mass to 4% by mass of second graphite having an average particle size of 10 μm to 50 μm, a total graphite content of 8% by mass to 12% by mass, and 3% by mass to 6% by mass of rubber powder. The friction material composition of the present disclosure may contain other components in addition to the above components. The friction material composition of the present disclosure makes it possible to form a friction material in which the occurrence of judder is suppressed. As a result of intensive research, the present inventors have found that a friction material composition capable of forming a friction material in which the occurrence of judder is suppressed can be obtained by incorporating first graphite having an average particle size of 100 μm to 500 μm, second graphite having an average particle size of 10 μm to 50 μm, and rubber powder in a predetermined ratio, thereby completing the present invention. The components constituting the friction material composition of the present disclosure will be described in detail below.

[0011] (graphite) The friction material composition of the present disclosure contains 6% to 9% by mass of first graphite having an average particle size of 100 μm to 500 μm, and 1% to 4% by mass of second graphite having an average particle size of 10 μm to 50 μm, for a total graphite content of 8% to 12% by mass. It is believed that the graphite contributes to stabilizing the friction coefficient of the friction material formed from the friction material composition. The content of the first graphite is preferably 6.0% by mass to 8.5% by mass, and more preferably 6.0% by mass to 8.0% by mass, based on the total friction material composition. The average particle size of the first graphite is preferably 150 μm to 450 μm, more preferably 200 μm to 400 μm, and even more preferably 250 μm to 350 μm. The content of the second graphite is preferably 1.5 to 4.0 mass %, and more preferably 2.0 to 3.5 mass %, based on the total friction material composition. The average particle size of the second graphite is preferably 15 μm to 45 μm, more preferably 20 μm to 40 μm. The total content of graphite in the friction material composition of the present disclosure is preferably 8.5 to 11.5 mass %, and more preferably 9.0 to 11.0 mass %, based on the total friction material composition. The mass ratio of the first graphite to the second graphite (first graphite / second graphite) is preferably 1 to 5, more preferably 1.2 to 4.5, and even more preferably 1.4 to 4.0.

[0012] Examples of graphite used in the present disclosure include petroleum pitch-based and coal pitch-based artificial graphite, natural graphite, and the like, and these may be used alone or in combination of two or more.

[0013] (rubber powder) The friction material composition of the present disclosure contains 3% to 6% by mass of rubber powder based on the total friction material composition. The rubber powder and organic fillers such as cashew dust described below are thought to contribute to improving the vibration damping properties of the friction material formed from the friction material composition and to suppress deterioration in noise and vibration performance, such as squealing, of the friction material. They are also thought to contribute to suppressing deterioration in the heat resistance of the friction material and suppressing strength reduction due to thermal history. The content of the rubber powder is preferably 3.5 to 6.0% by mass, and more preferably 4.0 to 5.5% by mass, based on the total friction material composition. Examples of rubber components constituting the rubber powder include tire rubber, natural rubber, acrylonitrile-butadiene rubber (NBR), acrylic rubber, isoprene rubber, polybutadiene rubber (BR), styrene butadiene rubber (SBR), silicone rubber, etc., which can be used alone or in combination of two or more. The rubber powder may be tire powder composed of tire rubber.

[0014] (cashew dust) The friction material composition of the present disclosure may contain cashew dust. There are no particular limitations on the cashew dust, and it may be any dust typically used in friction materials. Examples of cashew dust include particles obtained by pulverizing hardened cashew nut shell oil. The content of cashew dust is preferably 0.1 to 5.0% by mass, more preferably 0.5 to 4.0% by mass, and even more preferably 1.0 to 3.5% by mass, based on the total friction material composition.

[0015] (zirconia) The friction material composition of the present disclosure may contain zirconia (zirconium dioxide) to further suppress the occurrence of judder. The content of zirconia is preferably 25% by mass or less based on the total friction material composition, more preferably 10 to 25% by mass, and even more preferably 15 to 24% by mass, based on the total friction material composition. The mass ratio of zirconia to the first graphite (zirconia / first graphite) is preferably 1.5 to 5.0, more preferably 2.0 to 4.5, and even more preferably 2.5 to 4.0. The average particle size of zirconia is preferably 1 μm to 10 μm, more preferably 1 μm to 5 μm.

[0016] (metal sulfide) The friction material composition of the present disclosure may contain a metal sulfide in order to suppress a decrease in the friction coefficient of the friction material and improve crack resistance. Examples of metal sulfides used in the present disclosure include antimony trisulfide, tin sulfide, tin disulfide, molybdenum disulfide, iron sulfide, iron disulfide, bismuth sulfide, zinc sulfide, and tungsten disulfide, and these can be used alone or in combination of two or more. Among these, at least one selected from the group consisting of tin sulfide, antimony trisulfide, bismuth sulfide, zinc sulfide, and molybdenum disulfide is preferred, and antimony trisulfide is more preferred. The content of the metal sulfide is preferably 1 to 3 mass %, more preferably 1.2 to 2.8 mass %, and even more preferably 1.4 to 2.6 mass %, based on the total friction material composition.

[0017] (Inorganic filler) The friction material composition of the present disclosure may contain inorganic fillers other than graphite, zirconia used as needed, and metal sulfide. Other inorganic fillers include mica, titanates such as potassium titanate, lithium potassium titanate, sodium titanate, and magnesium potassium titanate, coke, calcium hydroxide (slaked lime), calcium oxide, sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, dolomite, iron oxide, vermiculite, calcium sulfate, granular potassium titanate, plate-like potassium titanate, talc, clay, zeolite, zirconium silicate, mullite, chromite, titanium oxide, magnesium oxide, silica, iron oxide, garnet, α-alumina, γ-alumina, and silicon carbide, and these can be used alone or in combination of two or more.

[0018] (Binding material) The friction material composition of the present disclosure may include a binder. The binder binds and integrates the graphite, rubber powder, etc. contained in the friction material composition, thereby giving the composition a predetermined shape and strength. There are no particular restrictions on the binder contained in the friction material composition of the present disclosure, and any known thermosetting resin used as a binder for friction materials can be used.

[0019] Examples of thermosetting resins include phenolic resins (resole-type phenolic resins and novolac-type phenolic resins), epoxy resins, polyimide resins, etc. Further examples include various modified phenolic resins such as acrylic-modified phenolic resins, silicone-modified phenolic resins, cashew-modified phenolic resins, epoxy-modified phenolic resins, and alkylbenzene-modified phenolic resins, and these can be used alone or in combination of two or more. It is particularly preferable to use at least one resin selected from the group consisting of phenolic resins, acrylic-modified phenolic resins, silicone-modified phenolic resins, and alkylbenzene-modified phenolic resins, as this resin provides good heat resistance, moldability, and coefficient of friction.

[0020] The binder content is preferably 4 to 20% by mass, more preferably 5 to 15% by mass, and even more preferably 6 to 10% by mass, based on the total friction material composition. By setting the binder content within the range of 4 to 20% by mass based on the total friction material composition, a decrease in the strength of the friction material can be further suppressed.

[0021] (fiber substrate) The friction material composition of the present disclosure may include a fibrous base material. The fibrous base material is contained in the friction material to provide a reinforcing effect. In the friction material composition of the present disclosure, inorganic fibers, metal fibers, organic fibers, carbon-based fibers, and the like, which are typically used as fiber substrates in the field of friction material compositions, can be used, and these can be used alone or in combination of two or more.

[0022] Examples of inorganic fibers that can be used include ceramic fibers, biodegradable ceramic fibers, mineral fibers, glass fibers, potassium titanate fibers, silicate fibers, and wollastonite, and these can be used alone or in combination of two or more.

[0023] The carbon-based fibers referred to here may be flame-retardant fibers, pitch-based carbon fibers, PAN (polyacrylonitrile)-based carbon fibers, activated carbon fibers, etc., and these may be used alone or in combination of two or more.

[0024] The mineral fibers referred to here are man-made inorganic fibers melt-spun mainly from blast furnace slag such as slag wool, basalt such as basalt fiber, and other natural rocks. Mineral fibers are preferably derived from natural minerals containing Al. Specifically, fibers containing one or more of SiO2, Al2O3, CaO, MgO, FeO, Na2O, etc. can be used, and more preferably, fibers containing Al among these can be used as mineral fibers. Since the adhesive strength tends to improve as the average fiber length of the mineral fibers contained in the friction material composition decreases, the average fiber length of the mineral fibers is preferably 500 μm or less, more preferably 100 μm to 400 μm, and even more preferably 110 μm to 350 μm. Here, the average fiber length refers to the number-average fiber length, which indicates the average length of the mineral fibers. The average fiber length refers to the arithmetic average when 50 mineral fibers are randomly selected and the fiber lengths are measured under an optical microscope. For example, an average fiber length of 200 μm means that 50 mineral fibers used as raw materials for the friction material composition are randomly selected and the fiber lengths are measured under an optical microscope, and the average value is 200 μm.

[0025] The mineral fibers used in this embodiment are preferably biosoluble. Biosoluble mineral fibers are mineral fibers that, even when ingested, are partially decomposed and excreted within a predetermined time period. Specifically, they refer to fibers with a chemical composition containing at least 18% by weight of alkali metal oxides and alkaline earth metal oxides (total content of sodium, potassium, calcium, magnesium, and barium oxides), and that satisfy the following criteria: a mass half-life of fibers 20 μm or larger in short-term biopermanence tests via respiration is 40 days or less; there is no evidence of excessive carcinogenicity in intraperitoneal tests; and there is no associated pathogenicity or tumorigenicity in long-term respiration tests (Nota Q (carcinogenicity exemption) of EU Directive 97 / 69 / EC). Examples of such biosoluble mineral fibers include SiO2-Al2O3-CaO-MgO-FeO-Na2O fibers, including fibers containing any combination of SiO2, Al2O3, CaO, MgO, FeO, Na2O, etc. Commercially available products include the Roxul series manufactured by LAPINUS FIBERS BV. "Roxul" includes SiO2, Al2O3, CaO, MgO, FeO, Na2O, etc.

[0026] As the metal fibers, copper or copper alloy fibers can be used in order to improve crack resistance and abrasion resistance. As the copper or copper alloy fibers, copper fibers, brass fibers, bronze fibers, etc. can be used, and these can be used alone or in combination of two or more.

[0027] Furthermore, metal fibers other than copper and copper alloys may be used as the metal fibers. Metal fibers other than copper and copper alloys may be contained from the viewpoint of improving the coefficient of friction and crack resistance.

[0028] Examples of metal fibers other than copper and copper alloys include fibers of simple metals or alloys of aluminum, iron, zinc, tin, titanium, nickel, magnesium, silicon, etc., and fibers containing metals as the main component, such as cast iron fibers. These can be used alone or in combination of two or more.

[0029] As the organic fiber, aramid fiber, cellulose fiber, acrylic fiber, phenolic resin fiber which may have a crosslinked structure, etc. can be used, and these can be used alone or in combination of two or more. As the organic fiber, it is preferable to use aramid fiber from the viewpoint of heat resistance.

[0030] The content of the fibrous base material is preferably 10% by mass to 40% by mass, more preferably 15% by mass to 35% by mass, and even more preferably 20% by mass to 30% by mass, based on the total friction material composition.

[0031] (Other ingredients) The friction material composition of the present disclosure may contain other materials in addition to the above-mentioned components, as needed. Other materials include organic additives such as fluorine-based polymers such as PTFE (polytetrafluoroethylene) from the viewpoint of wear resistance.

[0032] [Friction material] The friction material of the present disclosure is formed using the friction material composition of the present disclosure. The friction material of the present disclosure can be used as a friction material for disc brake pads, brake linings, etc. used in automobiles, etc. The friction material of the present disclosure suppresses the occurrence of judder, and is therefore suitable as a friction material for disc brake pads, which are subjected to a large load during braking.

[0033] The friction material of the present disclosure can be produced by molding the friction material composition of the present disclosure using a commonly used method. Preferably, it is produced by hot-press molding. Specifically, the friction material composition of the present disclosure is mixed using a mixer such as a Lödige mixer, a pressure kneader, or an Eirich mixer, and the mixture is preformed in a molding die. The resulting preform is heated and molded at a molding temperature of 140°C to 160°C and a molding pressure of 20MPa to 50MPa for 4 to 10 minutes, and the resulting molded product is heat-treated at 180°C to 250°C for 2 to 10 hours. Furthermore, the friction material may be subjected to painting, scorching, polishing, or other treatments as needed.

[0034] [Friction material] The friction member of the present disclosure includes the friction material of the present disclosure. In the friction member of the present disclosure, the friction material of the present disclosure preferably constitutes a friction surface of the friction member. The friction member of the present disclosure may have, for example, the following configuration. (1) Composition of friction material only (2) A configuration including a backing metal and the friction material of the present disclosure that serves as a friction surface provided on the backing metal. (3) In the configuration of (2) above, a primer layer for surface modification to enhance the adhesive effect of the backing metal to the friction material and an adhesive layer for bonding the backing metal to the friction material are further interposed between the backing metal and the friction material.

[0035] The friction material composition of the present disclosure is useful as a material for the "covering material" of a friction member because it suppresses the occurrence of judder. The "upholstery material" refers to the friction material that forms the friction surface of the friction member. [Example]

[0036] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples in any way.

[0037] [Making disc brake pads] The materials were blended according to the blending ratios (mass %) shown in Table 1 to obtain friction material compositions of Examples and Comparative Examples. The blending amount of each component in Table 1 is expressed in mass % of the friction material composition. In Table 1, "-" indicates that the corresponding component is not contained. Particulate potassium titanate was used as the potassium titanate. This friction material composition was mixed in a Lödige mixer (manufactured by Matsubo Corporation, product name: Lödige mixer M20), and this mixture was preformed in a molding press (manufactured by Oji Machinery Co., Ltd.). The resulting preform was hot-pressed together with a steel backing plate using a molding press (manufactured by Sanki Seiko Co., Ltd.) at a molding temperature of 145°C and a molding pressure of 30 MPa for 5 minutes. The resulting molded product was heat-treated at 200°C for 5 hours, polished using a rotary polisher, and scorched at 520°C for 5 minutes to produce a disc brake pad (friction material thickness 11 mm, friction material projected area 52 cm). 2 ) was obtained.

[0038] [Judder rating] The disc brake pad obtained as described above was attached to a dynamo tester and subjected to a test at 65 km / h and 3.5 m / s 2 The brakes were then applied 200 times at 120km / h and 3.0m / s 2 The braking was carried out 60 times at 60-second intervals, the maximum torque fluctuation was determined, and the result was evaluated based on the following criteria. A: Torque fluctuation is 150Nm or less B: Torque fluctuation is greater than 150 Nm and less than 200 Nm C: Torque fluctuation is over 200Nm and 400Nm or less D: Torque fluctuation exceeds 400 Nm

[0039] [Table 1]

[0040] As is clear from the evaluation results in Table 1, the brake pads formed using the friction material compositions of the Examples have less judder than the brake pads formed using the friction material compositions of the Comparative Examples.

Claims

1. The friction material composition contains 6% by mass to 9% by mass of first graphite having an average particle size of 100 μm to 500 μm, 1% by mass to 4% by mass of second graphite having an average particle size of 10 μm to 50 μm, a total graphite content of 8% by mass to 12% by mass, and 3% by mass to 6% by mass of rubber powder.

2. 2. The friction material composition according to claim 1, wherein the mass ratio of the first graphite to the second graphite is 1 to 5.

3. 3. The friction material composition according to claim 1, further comprising zirconia, the content of which is 25 mass % or less.

4. 4. The friction material composition according to claim 3, wherein the mass ratio of the zirconia to the first graphite is 1.5 to 5.

0.

5. 5. The friction material composition according to claim 1, wherein the rubber powder contains tire rubber.

6. 6. The friction material composition according to claim 1, further comprising a binder, the binder content being 4% by mass to 20% by mass.

7. The friction material composition according to any one of claims 1 to 6, further comprising a fibrous base material, the content of the fibrous base material being 10% by mass to 40% by mass.

8. 8. The friction material composition according to claim 1, further comprising a metal sulfide, the content of which is 1% by mass to 3% by mass.

9. A friction material formed using the friction material composition according to any one of claims 1 to 8.

10. A friction member comprising the friction material according to claim 9.

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