Friction material

Abstract

This invention relates to a friction material comprising a friction adjusting material, a fiber substrate, and a bonding material. The friction adjusting material contains tungsten powder, the content of which is 0.5% to 10.0% by mass of the friction material. The fiber substrate contains steel fibers, the content of which is 1.0% to 30.0% by mass of the friction material. The friction material does not contain copper.

Description

Technical Field

[0001] This invention relates to friction materials used in brake blocks, brake pads, clutch pads, etc., in automobiles, railway vehicles, industrial machinery, etc. Background Technology

[0002] Friction materials are used in brakes such as disc brakes and drum brakes, or clutches, to exert a braking effect through friction with the material of the object being braked. Required properties for friction materials include, for example, a high coefficient of friction, resistance to decrease in coefficient of friction under high loads (attenuation characteristics), and low aggression towards the object being braked.

[0003] Friction materials are composed of raw materials such as a fiber substrate that provides reinforcement, a friction modifier that provides friction and adjusts its properties, and a bonding material that integrates these components. Copper, one of the raw materials, extends onto the friction surface to form a film, thus contributing to the stability of the coefficient of friction during high-speed braking before thermal degradation and during fading. However, from the perspective of recent environmental countermeasures, there is a need for friction materials that are substantially copper-free.

[0004] Here, friction materials with a fixed proportion of steel fibers (low-carbon steel) are widely used, especially in Europe where a good balance of frictional properties is required to ensure a high coefficient of friction during high-speed braking.

[0005] Patent document 1 describes a friction material containing a specific amount of steel fibers and substantially free of copper.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2016-121245 Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] However, there is room for improvement in the resistance to attenuation of the friction material described in Patent Document 1.

[0011] Furthermore, from the perspective of suppressing the phenomenon of metal from the target material (rotor) adhering to the sliding surface of the friction material, also known as metal trapping, friction materials with low aggression towards the target material are required.

[0012] The purpose of this invention is to provide a friction material with good frictional properties, particularly good resistance to attenuation, and low aggression towards the target material.

[0013] Technical means for solving problems

[0014] The inventors have discovered that the above problems can be solved by using a specific amount of steel fiber and a specific amount of tungsten powder.

[0015] That is, the present invention is as follows.

[0016] A friction material comprising a friction modifier, a fiber substrate, and a bonding material.

[0017] The friction-adjusting material contains tungsten powder.

[0018] The tungsten powder content is 0.5% to 10.0% by mass of the friction material.

[0019] The fiber substrate contains steel fibers.

[0020] The steel fiber content is 1.0% to 30.0% by mass of the friction material.

[0021] The friction material does not contain copper.

[0022] Invention Effects

[0023] According to the present invention, a friction material with good resistance to attenuation and low aggression towards the target material can be provided. Detailed Implementation

[0024] The friction material of the present invention will now be described in detail.

[0025] The friction material of the embodiment of the present invention (hereinafter also referred to as this embodiment) is a friction material comprising a friction adjusting material, a bonding material and a fiber substrate. As the friction adjusting material, it contains 0.5% to 10.0% by mass of tungsten powder of the friction material. As the fiber substrate, it contains 1.0% to 30.0% by mass of steel fiber of the friction material. The friction material does not contain copper.

[0026] <Fiber substrate>

[0027] Fiber-based substrates are used as reinforcements when used as friction materials.

[0028] Examples of fiber substrates include organic fibers, inorganic fibers, and metal fibers. Fiber substrates can be used individually or in combination of two or more types.

[0029] The friction material of this embodiment contains 1.0% to 30.0% by mass of steel fibers. By containing steel fibers within the above range, a friction material with a good balance of frictional properties, especially maintaining the coefficient of friction during high-speed braking, is easily obtained. The steel fiber content is preferably 5.0% to 30.0% by mass, more preferably 5.0% to 28.0% by mass.

[0030] The average fiber length of the steel fiber is preferably 0.5mm to 30mm, more preferably 0.5mm to 20mm, and even more preferably 0.5mm to 10mm.

[0031] If the average fiber length of the steel fiber is 0.5 mm or more, the strength of the friction material can be ensured. If the average fiber length of the steel fiber is less than 30 mm, the degradation of its aggression against the target material can be suppressed.

[0032] The average fiber diameter of the steel fiber is preferably 10μm to 600μm, more preferably 30μm to 500μm, and even more preferably 50μm to 400μm.

[0033] If the average fiber diameter of the steel fibers is greater than 10 μm, the strength of the friction material can be ensured. If the average fiber diameter of the steel fibers is less than 600 μm, the degradation of the material's aggression can be suppressed.

[0034] It should be noted that the average fiber length and average fiber diameter of steel fibers can be determined by observation using a microscope or similar instruments.

[0035] The friction material in this embodiment may include metal fibers other than steel fibers, but copper fibers or bronze fibers containing copper components are preferably not used.

[0036] Examples of organic fibers include aromatic polyamide fibers and flame-retardant acrylic fibers.

[0037] Examples of inorganic fibers include: biosoluble inorganic fibers, ceramic fibers, glass fibers, carbon fibers, and asbestos. Examples of biosoluble inorganic fibers include: SiO2-CaO-MgO fibers, SiO2-CaO-MgO-Al2O3 fibers, SiO2-MgO-SrO fibers, and other biosoluble ceramic fibers, as well as biosoluble asbestos.

[0038] From the viewpoint of preventing metal trapping and ensuring the strength of the friction material, the friction material of this embodiment preferably contains biosoluble inorganic fibers. This readily yields a friction material with low aggression towards the target material. The content of biosoluble inorganic fibers in the friction material is preferably 1% to 10% by mass, more preferably 3% to 7% by mass.

[0039] From the viewpoint of ensuring the strength of the friction material, the content of the fiber matrix in the friction material is preferably 10% to 50% by mass, more preferably 20% to 40% by mass, based on the total amount of fiber matrix.

[0040] Friction Adjustment Materials

[0041] Friction modifiers are used to impart desired frictional properties to friction materials, such as wear resistance, heat resistance, and resistance to wear.

[0042] Examples of friction modulating materials include: inorganic filler materials, organic filler materials, grinding materials, solid lubricants, and metal powders.

[0043] The friction material of this embodiment contains 0.5% to 10.0% by mass of tungsten powder. By containing tungsten powder within the above range, a friction material with excellent resistance to attenuation and low aggression towards the target material can be easily obtained. The content of tungsten powder is preferably 1.0% to 5.0% by mass.

[0044] The average particle size of the tungsten powder is preferably 1 μm to 50 μm, more preferably 1 μm to 40 μm. When the average particle size of the tungsten powder is within this range, it is easy to obtain a friction material with excellent resistance to wear.

[0045] The average particle size can be determined by the particle size (D50) corresponding to the cumulative percentage of the volume reference measured by a laser diffraction particle size distribution measuring device.

[0046] The friction material in this embodiment may also contain metal powders other than tungsten powder. Examples of other metal powders include aluminum, tin, and zinc powders. However, it is preferable not to include copper powder. These can be used individually or in combination of two or more.

[0047] The content of metal powder in the friction material is preferably 1% to 20% by mass, more preferably 3% to 15% by mass, based on the total amount of metal powder.

[0048] Examples of inorganic filler materials include: potassium titanate, lithium titanate, lithium potassium titanate, sodium titanate, calcium titanate, magnesium titanate, potassium magnesium titanate, and other titanates, barium sulfate, calcium carbonate, calcium hydroxide, calcium silicate, vermiculite, mica, and other inorganic materials. They can be used individually or in combination of two or more.

[0049] The content of inorganic filler material in the friction material is preferably 1% to 30% by mass, more preferably 3% to 20% by mass.

[0050] Examples of organic filler materials include various rubber powders (raw rubber powder, tire powder, etc.), rubber dust, resin dust, cashew dust, tire tread, melamine dust, etc. They can be used individually or in combination of two or more.

[0051] The content of organic filler in the friction material is preferably 1% to 15% by mass, more preferably 1% to 10% by mass.

[0052] Examples of abrasive materials include: zirconium oxide, aluminum oxide, silicon dioxide, magnesium oxide, zirconium silicate, chromium oxide, iron oxide (Fe3O4), and chromite. They can be used individually or in combination of two or more.

[0053] The content of grinding material in the friction material is preferably 1% to 35% by mass, more preferably 3% to 30% by mass.

[0054] Examples of solid lubricants include graphite, coke, antimony trisulfide, molybdenum disulfide, tin sulfide, and polytetrafluoroethylene (PTFE). They can be used individually or in combination of two or more.

[0055] The content of solid lubricant in the friction material is preferably 1% to 25% by mass, more preferably 3% to 20% by mass.

[0056] <Combined materials>

[0057] The bonding material is used to integrate the fiber substrate and friction modifier contained in the friction material.

[0058] As binding materials, a variety of commonly used binding materials can be used. Specifically, examples include linear phenolic resins, various modified phenolic resins formed from elastomers, melamine resins, epoxy resins, polyimide resins, and other thermosetting resins. Examples of elastomer-modified phenolic resins include acrylic rubber-modified phenolic resins, silicone rubber-modified phenolic resins, and nitrile rubber (NBR)-modified phenolic resins. It should be noted that these binding materials can be used alone or in combination of two or more.

[0059] The content of the bonding material in the friction material is preferably 1% to 20% by mass, more preferably 3% to 15% by mass.

[0060] The friction material of the present invention is copper-free. Here, "copper-free" means that it does not contain copper, which is an effective component for exhibiting functions such as wear resistance; for example, it does not mean that it also does not contain copper, which is inevitably present in trace amounts as impurities in friction materials. It should be noted that, from the viewpoint of environmental impact, the amount of copper mixed in as impurities is preferably 0.5% by mass or less.

[0061] As a specific method for manufacturing the friction material according to this embodiment, it can be carried out through known manufacturing processes. For example, the above-mentioned components can be formulated, and the formulation can be processed into friction material through preforming, thermoforming, heating, grinding and other processes according to conventional manufacturing methods.

[0062] The following shows the general process in manufacturing brake blocks with friction materials.

[0063] (a) The process of forming a sheet metal press into a specified shape by sheet metal stamping;

[0064] (b) The process of applying a degreasing treatment, chemical conversion treatment and primer treatment to the above-mentioned pressure plate, and applying an adhesive.

[0065] (c) The process of preparing raw materials such as fiber substrate, friction adjustment material and bonding material, thoroughly homogenizing them by mixing, and molding them at room temperature under specified pressure to produce a preform;

[0066] (d) Applying a specified temperature and pressure to the above preform and the pressure plate coated with adhesive to fix the two parts into one body in a thermoforming process (forming temperature 130℃~180℃, forming pressure 30MPa~80MPa, forming time 2 minutes~10 minutes);

[0067] (e) Post-curing (150℃~300℃, 1 hour~5 hours), followed by finishing processes such as grinding, scorching and coating.

[0068] Therefore, this specification discloses the following friction materials.

[0069] [1] A friction material comprising a friction modifier, a fiber substrate, and a bonding material.

[0070] The friction-adjusting material contains tungsten powder.

[0071] The tungsten powder content is 0.5% to 10.0% by mass of the friction material.

[0072] The fiber substrate contains steel fibers.

[0073] The steel fiber content is 1.0% to 30.0% by mass of the friction material.

[0074] The friction material does not contain copper.

[0075] [2] According to the friction material described in [1], wherein,

[0076] The average particle size of the tungsten powder is 1 μm to 50 μm.

[0077] [3] According to the friction material described in [1] or [2], wherein,

[0078] The fiber substrate comprises biosoluble inorganic fibers.

[0079] [4] According to the friction material described in [3], wherein,

[0080] The content of the biosoluble inorganic fiber is 1% to 10% by mass of the friction material.

[0081] Example

[0082] The present invention will be further illustrated below by way of examples and comparative examples, but the present invention is not limited to the examples described below.

[0083] <Manufacturing of Friction Materials>

[0084] (Examples 1-5, Comparative Examples 1-3)

[0085] The materials (mass %) shown in Table 2 were added to a mixer and mixed at room temperature for 4 minutes to obtain a friction material composition. Then, the obtained friction material composition was subjected to the following processes: (i) preforming, (ii) thermoforming, (iii) heat treatment and scorching, to produce a brake block with friction material.

[0086] (i) Preforming

[0087] The mixture is put into a pre-forming mold and molded at 10 MPa for 10 seconds at room temperature to produce a pre-formed body.

[0088] (ii) Thermoforming

[0089] The preform is placed into a thermoforming mold, and metal plates (pressure plates) pre-coated with adhesive are stacked and heated and pressed at 160℃ and 50MPa for 5 minutes.

[0090] (iii) Heat treatment, charring

[0091] The heated and pressurized molded body was subjected to a heat treatment at 250°C for 3 hours, and then the surface was ground.

[0092] Next, the surface of the heated and pressurized molded body is subjected to scorching treatment, followed by fine finishing and coating to obtain friction material.

[0093] Tungsten powder (average particle size 30μm): manufactured by Nippon Shin-Metal Co., Ltd.

[0094] Tungsten powder (average particle size 5μm): manufactured by Nippon Shin-Metal Co., Ltd.

[0095] Molybdenum powder (average particle size 3.5 μm): Manufactured by Nippon Shin-Metal Co., Ltd.

[0096] The obtained friction materials were subjected to attenuation tests under the conditions shown in Table 1 to evaluate their friction performance.

[0097] The evaluation criteria are as follows. If the result is A or B, it is judged as good.

[0098] • Attenuation μ

[0099] A: The average coefficient of friction is above 0.29.

[0100] B: The average coefficient of friction is greater than 0.25 and less than 0.29.

[0101] C: Average coefficient of friction is less than 0.25

[0102] • Offensiveness towards target materials

[0103] A: Rotor wear is less than 2.5g.

[0104] B: Rotor wear is greater than 2.5g but less than 6.0g.

[0105] C: Rotor wear is above 6.0g.

[0106] [Table 1]

[0107]

[0108] The results of the experiment are shown in Table 2.

[0109] [Table 2]

[0110]

[0111] The above results demonstrate that the friction materials of Examples 1 to 5, containing specific amounts of steel fibers and tungsten powder, do not experience a decrease in average friction coefficient even during high-speed braking, exhibiting excellent resistance to wear. Furthermore, they exhibit characteristics of low rotor wear and low aggression towards the target material.

[0112] In contrast, the friction material of Comparative Example 1, which contains a specific amount of steel fiber but no tungsten powder, results in low resistance to attenuation and high aggression towards the target material.

[0113] The friction material of Comparative Example 2, which contains a specific amount of steel fiber but no tungsten powder but molybdenum powder, resulted in a high degree of aggression against the target material.

[0114] Although it contains a specific amount of tungsten powder, the friction material in Comparative Example 3, which has a high content of steel fibers, results in low resistance to wear.

[0115] Although the present invention has been described in detail 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 invention. This application is based on Japanese Patent Application No. 2023-198268, filed on November 22, 2023, the contents of which are incorporated herein by reference.

Claims

1. A friction material, characterized in that, The friction material comprises a friction-adjusting material, a fiber substrate, and a bonding material. The friction-adjusting material contains tungsten powder. The tungsten powder content is 0.5% to 10.0% by mass of the friction material. The fiber substrate contains steel fibers. The steel fiber content is 1.0% to 30.0% by mass of the friction material. The friction material does not contain copper.

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

3. The friction material according to claim 1 or 2, wherein, The fiber substrate comprises biosoluble inorganic fibers.

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

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