Friction material

Abstract

The present invention relates to a friction material comprising a friction regulator, a fiber base material, and a binder, wherein the friction regulator contains a tungsten powder, the content of the tungsten powder is 0.5-10.0 mass%, the fiber base material contains steel fiber, the content of the steel fiber is 1.0-30.0 mass%, and a copper component is not contained.

Description

Friction material

[0001] The present invention relates to a friction material used in brake pads, brake linings, clutch facings, etc. for automobiles, railway vehicles, industrial machines, etc.

[0002] Friction materials are used in brakes such as disc brakes and drum brakes, or clutches, and perform braking by friction with the mating material of the disc brake, etc. Properties required of friction materials include, for example, a high coefficient of friction, resistance to a decrease in the coefficient of friction under high load (fade characteristics), and low attack on the mating material.

[0003] Friction materials are composed of raw materials such as a fibrous base material that provides reinforcing properties, friction modifiers that provide friction and adjust friction performance, and binders that bind these components together. Copper, which has been used as one of the raw materials, spreads on the friction surface to form a film, which can contribute to the stability of the friction coefficient during high-speed braking and fade before thermal history. However, in light of recent environmental concerns, friction materials that are substantially copper-free are in demand.

[0004] Friction materials with a steel fiber content of a certain amount or less (low-steel materials) have a good balance of friction characteristics and are therefore widely used in Europe, where a sufficient friction coefficient is required, particularly during high-speed braking. Patent Document 1 describes a friction material that contains a specific amount of steel fibers and is substantially free of copper.

[0005] Japanese Patent Application Publication No. 2016-121245

[0006] However, the friction material described in Patent Document 1 has room for improvement in terms of fade resistance. Also, from the viewpoint of suppressing a phenomenon in which metal from the mating material (rotor) adheres to the sliding surface of the friction material, known as metal catch, a friction material with low attacking properties against the mating material is desired.

[0007] An object of the present invention is to provide a friction material that has good friction performance, particularly good fade resistance, and low attack on mating materials.

[0008] The inventors have found that the above-mentioned problems can be solved by including a specific amount of steel fibers and a specific amount of tungsten powder. Specifically, the present invention is as follows: A friction material including a friction modifier, a fibrous base material, and a binder, wherein the friction modifier contains tungsten powder, and the tungsten powder content is 0.5 to 10.0 mass %, the fibrous base material contains steel fibers, and the steel fiber content is 1.0 to 30.0 mass %, and the friction material does not contain a copper component.

[0009] According to the present invention, it is possible to provide a friction material that has good fade resistance and low attacking properties on mating materials.

[0010] The friction material of the present invention will be described in detail below.

[0011] A friction material according to an embodiment of the present invention (hereinafter also referred to as "according to the present embodiment") is a friction material including a friction modifier, a binder, and a fibrous base material, and contains 0.5 to 10.0 mass % of tungsten powder as the friction modifier, and 1.0 to 30.0 mass % of steel fibers as the fibrous base material, and does not contain a copper component.

[0012] <Fiber base material> The fiber base material is used for reinforcement when used as a friction material. Examples of the fiber base material include organic fibers, inorganic fibers, and metal fibers. Each of the fiber base materials may be used alone or in combination of two or more.

[0013] The friction material according to this embodiment contains 1.0 to 30.0% by mass of steel fibers. By including the steel fibers in this range, it is possible to obtain a friction material that has a good balance of friction characteristics, and that maintains a friction coefficient particularly during high-speed braking. The steel fiber content is preferably 5.0 to 30.0% by mass, and more preferably 5.0 to 28.0% by mass.

[0014] The average fiber length of the steel fibers is preferably 0.5 to 30 mm, more preferably 0.5 to 20 mm, and even more preferably 0.5 to 10 mm. If the average fiber length of the steel fibers is 0.5 mm or more, the strength of the friction material can be ensured. If the average fiber length of the steel fibers is 30 mm or less, the deterioration of the aggressiveness to the mating material can be suppressed.

[0015] The average fiber diameter of the steel fibers is preferably 10 to 600 μm, more preferably 30 to 500 μm, and even more preferably 50 to 400 μm. If the average fiber diameter of the steel fibers is 10 μm or more, the strength of the friction material can be ensured. If the average fiber diameter of the steel fibers is 600 μm or less, the deterioration of the attacking property of the mating material can be suppressed.

[0016] The average fiber length and average fiber diameter of the steel fibers can be measured by observation using a microscope or the like.

[0017] The friction material according to the present embodiment may contain metal fibers other than steel fibers, but it is preferable not to use copper fibers containing copper or bronze fibers.

[0018] Examples of organic fibers include aromatic polyamide (aramid) fibers and flame-resistant acrylic fibers.

[0019] Examples of inorganic fibers include biosoluble inorganic fibers, ceramic fibers, glass fibers, carbon fibers, and rock wool. Examples of biosoluble inorganic fibers include SiO ２ -CaO-MgO fiber, SiO ２ -CaO-MgO-Al ２ O ３ Fibers, SiO ２ Examples of the biosoluble ceramic fibers include MgO-SrO fibers and biosoluble rock wool.

[0020] The friction material according to the present embodiment preferably contains biosoluble inorganic fibers from the viewpoints of preventing metal catch and ensuring the strength of the friction material. This makes it easier to obtain a friction material with low attack on mating materials. The content of the biosoluble inorganic fibers in the friction material is preferably 1 to 10 mass %, more preferably 3 to 7 mass %.

[0021] The content of the fibrous base material in the friction material is preferably 10 to 50 mass % of the total amount of the fibrous base material, and more preferably 20 to 40 mass %, from the viewpoint of ensuring the strength of the friction material.

[0022] <Friction Modifier> Friction modifiers are used to impart desired friction characteristics such as wear resistance, heat resistance, fade resistance, etc. Examples of friction modifiers include inorganic fillers, organic fillers, abrasives, solid lubricants, and metal powders.

[0023] The friction material according to this embodiment contains 0.5 to 10.0 mass% of tungsten powder. By including the tungsten powder in this range, it is easy to obtain a friction material that has excellent fade resistance and little attack on mating materials. The content of the tungsten powder is preferably 1.0 to 5.0 mass%.

[0024] The average particle size of the tungsten powder is preferably 1 to 50 μm, more preferably 1 to 40 μm. When the average particle size of the tungsten powder is within this range, a friction material with excellent fade resistance is easily obtained. The average particle size can be determined from the particle size (D50) equivalent to a volume-based cumulative percentage of 50% measured using a laser diffraction particle size distribution analyzer.

[0025] The friction material according to the present embodiment may contain metal powders other than tungsten powder. Examples of other metal powders include aluminum, tin, and zinc powders. However, it is preferable that the friction material does not contain copper powder. These may be used alone or in combination of two or more.

[0026] The content of the metal powder in the friction material is preferably 1 to 20 mass % of the total amount of the metal powder, and more preferably 3 to 15 mass %.

[0027] Examples of inorganic fillers include titanates such as potassium titanate, lithium titanate, lithium potassium titanate, sodium titanate, calcium titanate, magnesium titanate, and magnesium potassium titanate, as well as inorganic materials such as barium sulfate, calcium carbonate, calcium hydroxide, calcium silicate, vermiculite, and mica. These may be used alone or in combination of two or more.

[0028] The content of the inorganic filler in the friction material is preferably 1 to 30% by mass, and more preferably 3 to 20% by mass.

[0029] Examples of organic fillers include various rubber powders (raw rubber powder, tire powder, etc.), rubber dust, resin dust, cashew dust, tire tread, melamine dust, etc. These may be used alone or in combination of two or more.

[0030] The content of the organic filler in the friction material is preferably 1 to 15% by mass, and more preferably 1 to 10% by mass.

[0031] Examples of the abrasive include zirconium oxide, aluminum oxide, silica, magnesium oxide, zirconia, zirconium silicate, chromium oxide, and iron oxide (Fe ３ O ４ ), chromite, etc. These may be used alone or in combination of two or more.

[0032] The content of the abrasive in the friction material is preferably 1 to 35 mass %, more preferably 3 to 30 mass %.

[0033] Examples of solid lubricants include graphite, coke, antimony trisulfide, molybdenum disulfide, tin sulfide, polytetrafluoroethylene (PTFE), etc. These may be used alone or in combination of two or more.

[0034] The content of the solid lubricant in the friction material is preferably 1 to 25 mass %, more preferably 3 to 20 mass %.

[0035] <Binder> The binder is used to integrate the fibrous base material and friction modifier contained in the friction material. Various commonly used binders can be used as the binder. Specific examples include straight phenolic resin, various modified phenolic resins with elastomers, and thermosetting resins such as melamine resin, epoxy resin, and polyimide resin. Examples of elastomer-modified phenolic resins include acrylic rubber-modified phenolic resin, silicone rubber-modified phenolic resin, and nitrile rubber (NBR)-modified phenolic resin. These binders can be used alone or in combination of two or more. The binder content in the friction material is preferably 1 to 20% by mass, more preferably 3 to 15% by mass.

[0036] The friction material of the present invention does not contain a copper component. Here, "does not contain a copper component" means that the copper component is not contained as an active component for exhibiting functions such as wear resistance, but does not mean that the friction material does not contain copper components as impurities, etc., which are inevitably contained in small amounts in the friction material. From the viewpoint of environmental load, it is preferable that the copper component mixed in as an impurity, etc., is 0.5 mass % or less.

[0037] A specific embodiment of the method for producing the friction material according to this embodiment can be carried out by a known production process, for example, by blending the above components and subjecting the blend to preforming, thermoforming, heating, polishing, etc. according to a conventional production method to produce the friction material. The general process for producing brake pads equipped with the friction material is shown below. (a) a process of forming a pressure plate into a predetermined shape using a sheet metal press; (b) a process of degreasing, chemical conversion and primer treatment on the pressure plate, and applying an adhesive; (c) a process of blending raw materials such as a fiber base material, friction modifier and binder, thoroughly homogenizing them by mixing, and molding them at room temperature under a predetermined pressure to produce a preform; (d) a thermoforming process (molding temperature 130-180°C, molding pressure 30-80 MPa, molding time 2-10 minutes) in which the preform and the adhesive-coated pressure plate are bonded together by applying a predetermined temperature and pressure; and (e) a process of after-curing (150-300°C, 1-5 hours), and finally performing finishing processes such as polishing, scorching and painting.

[0038] Based on the above, this specification discloses the following friction materials. [1] A friction material including a friction modifier, a fibrous base material, and a binder, wherein the friction modifier contains tungsten powder, and the content of the tungsten powder is 0.5 to 10.0 mass %, and the fibrous base material contains steel fibers, and the content of the steel fibers is 1.0 to 30.0 mass %, and the friction material does not contain a copper component. [2] The friction material according to [1], wherein the average particle size of the tungsten powder is 1 to 50 μm. [3] The friction material according to [1] or [2], wherein the fibrous base material contains biosoluble inorganic fibers. [4] The friction material according to [3], wherein the content of the biosoluble inorganic fibers is 1 to 10 mass %.

[0039] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0040] <Production of Friction Material> (Examples 1 to 5, Comparative Examples 1 to 3) The ingredients (mass%) shown in Table 2 were added to a mixer and mixed at room temperature for 4 minutes to obtain a friction material composition. The resulting friction material composition was then subjected to the following steps: (i) preforming, (ii) thermoforming, and (iii) heat treatment and scorching to produce brake pads equipped with the friction material. (i) Preforming: The mixture was placed in a preforming press mold and molded at room temperature for 10 seconds at 10 MPa to produce a preform. (ii) Thermoforming: This preform was placed in a thermoforming mold, and a metal plate (pressure plate) previously coated with adhesive was placed on top of it, followed by hot-press molding at 160°C and 50 MPa for 5 minutes. (iii) Heat Treatment and Scorching: This hot-pressed molded body was heat-treated at 250°C for 3 hours, and then the surface was polished. Next, the surface of this hot-pressed molded body was scorched and finished with a coating to obtain a friction material.

[0041] Tungsten powder (average particle size 30 μm): manufactured by Nippon Shinkinzoku Co., Ltd. Tungsten powder (average particle size 5 μm): manufactured by Nippon Shinkinzoku Co., Ltd. Molybdenum powder (average particle size 3.5 μm): manufactured by Nippon Shinkinzoku Co., Ltd.

[0042] The obtained friction material was subjected to a fade test under the conditions shown in Table 1 to evaluate its friction performance. The evaluation criteria were as follows. A or B was judged to be good. Fade μ A: Average friction coefficient is 0.29 or more B: Average friction coefficient is 0.25 or more but less than 0.29 C: Average friction coefficient is less than 0.25 Aggression to mating material A: Rotor wear amount is less than 2.5 g B: Rotor wear amount is 2.5 g or more but less than 6.0 g C: Rotor wear amount is 6.0 g or more

[0043]

[0044] The test results are shown in Table 2.

[0045]

[0046] The above results showed that the friction materials of Examples 1 to 5, which contain a specific amount of steel fibers and a specific amount of tungsten powder, do not decrease in average friction coefficient even during high-speed braking and have excellent fade resistance. They also showed small rotor wear and low attack on mating materials. In contrast, the friction material of Comparative Example 1, which contains a specific amount of steel fibers but no tungsten powder, showed low fade resistance and high attack on mating materials. The friction material of Comparative Example 2, which contains a specific amount of steel fibers but no tungsten powder and contains molybdenum powder, showed high attack on mating materials. The friction material of Comparative Example 3, which contains a specific amount of tungsten powder but a high content of steel fibers, showed low fade resistance.

[0047] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2023-198268) filed on November 22, 2023, the contents of which are incorporated herein by reference.

Claims

1. A friction material comprising a friction modifier, a fiber base material, and a binder, wherein the friction modifier contains tungsten powder, and the tungsten powder content is 0.5 to 10.0 mass %, the fiber base material contains steel fibers, and the steel fiber content is 1.0 to 30.0 mass %, and the friction material does not contain a copper component.

2. The friction material according to claim 1, wherein the average particle size of the tungsten powder is 1 to 50 μm.

3. The friction material according to claim 1 or 2, wherein the fibrous base material contains biosoluble inorganic fibers.

4. The friction material according to claim 3, wherein the content of the biosoluble inorganic fibers is 1 to 10 mass %.

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