Friction material

Abstract

To provide a friction material that exhibits superior wear resistance and fade resistance under high load conditions, among other frictional performance characteristics. [Solution] A friction material comprising a fibrous base material, a friction modifier, and a binder, wherein the copper content is 0.5% by mass or less in terms of copper element, the fibrous base material contains steel fibers, the steel fiber content is more than 20% by mass and less than 50% by mass, and the friction modifier contains titanium carbide powder.

Description

Technical Field

[0001] The present invention relates to friction materials used for brake pads, brake linings, clutch facings, etc. of automobiles, railway vehicles, industrial machines, and the like.

Background Art

[0002] Friction materials are used in brakes such as disc brakes and drum brakes, or clutches, and play a braking role by friction with mating materials such as disc brakes. Characteristics required for friction materials include, for example, the difficulty of the friction coefficient decreasing under high loads (fade characteristics), excellent wear resistance, and the like.

[0003] Friction materials are composed of raw materials such as a fiber base material that provides a reinforcing effect, a friction modifier that gives a frictional effect and adjusts its frictional performance, and a binder that integrates these components. Copper, which has been used as one of the raw materials, can contribute to the stability of the friction coefficient under high loads because it extends on the friction surface to form a film. However, from the perspective of recent environmental measures, friction materials substantially free of copper are required.

[0004] Patent Document 1 describes a friction material that contains a specific amount of steel fiber and is substantially free of copper in order to maintain the friction coefficient under high-speed fade conditions accompanied by a temperature rise due to braking.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] With the recent increase in vehicle weight due to the shift to electric vehicles, the load on friction materials has increased, and therefore, there was room for improvement in the friction material described in Patent Document 1 in terms of maintaining the coefficient of friction under high-speed fade conditions.

[0007] The present invention aims to provide a friction material that exhibits excellent wear resistance and fade resistance characteristics, particularly under high load conditions, within the realm of frictional performance. [Means for solving the problem]

[0008] The inventors have found that the above problems can be solved by including a specific amount of steel fibers and titanium carbide powder. In other words, the present invention relates to the following friction materials. A friction material comprising a fiber base material, a friction modifier and a binder, The copper content is 0.5% by mass or less in terms of copper element, The fibrous base material contains steel fibers, and the steel fiber content is greater than 20% by mass and less than 50% by mass. The aforementioned friction modifier is a friction material containing titanium carbide powder. [Effects of the Invention]

[0009] According to the present invention, a friction material with excellent wear resistance and fade resistance under high load conditions can be provided. [Modes for carrying out the invention]

[0010] The friction material of the present invention will be described in detail below. A friction material according to an embodiment of the present invention (hereinafter also referred to as "the friction material according to this embodiment") is a friction material comprising a fibrous base material, a friction modifier, and a binder, wherein the copper content is 0.5% by mass or less in terms of copper element, the fibrous base material contains steel fibers, the steel fiber content is more than 20% by mass and less than 50% by mass, and the friction modifier contains titanium carbide powder. Such friction materials can improve wear resistance and fade resistance under high load conditions.

[0011] <Textile base material> Fiber base materials are used as reinforcing materials when used as friction materials. Examples of fiber base materials include organic fibers, inorganic fibers, and metal fibers. These fiber base materials can be used individually or in combination of two or more types.

[0012] In the friction material according to this embodiment, the fibrous base material contains more than 20% by mass and less than 50% by mass of steel fibers. By including steel fibers within this range, a good balance of friction characteristics is obtained, and in particular, a friction material with excellent wear resistance is obtained, which suppresses friction material wear even under high load, and excellent fade resistance is obtained, which maintains the coefficient of friction even under high load. The steel fiber content is preferably 23 to 42% by mass, more preferably 25 to 37% by mass.

[0013] 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 15 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 towards the mating material can be suppressed.

[0014] The average fiber diameter of the steel fibers is preferably 10 to 600 μm, more preferably 10 to 550 μm, and even more preferably 10 to 500 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 mating material's aggressiveness can be suppressed.

[0015] The average fiber length and average fiber diameter of steel fibers can be measured by observing them with an optical measuring instrument such as a microscope.

[0016] The friction material according to this embodiment may contain metal fibers other than steel fibers, but it is preferable not to use copper fibers or bronze fibers that contain copper components.

[0017] Examples of the organic fiber include aromatic polyamide (aramid) fiber, flame-resistant acrylic fiber, and the like.

[0018] Examples of the inorganic fiber include bio-dissolvable inorganic fiber, ceramic fiber, glass fiber, carbon fiber, rock wool, and the like. Examples of the bio-dissolvable inorganic fiber include bio-dissolvable ceramic fibers such as SiO2-CaO-MgO-based fiber, SiO2-CaO-MgO-Al2O3-based fiber, SiO2-MgO-SrO-based fiber, and bio-dissolvable rock wool.

[0019] From the viewpoint of wear resistance, the friction material according to the present embodiment preferably contains aramid fiber. The content of aramid fiber in the friction material is preferably 0.3 to 1.0% by mass, and more preferably 0.3 to 0.5% by mass. When the content of aramid fiber is 0.3% by mass or more, the matrix strength in the high-temperature range is improved, and it is easy to obtain a friction material excellent in wear resistance in the high-temperature range. Further, when the content of aramid fiber is 1.0% by mass or less, it is possible to avoid the combustion of aramid fiber, which is an organic substance, at high temperature and the generation of gas and the reduction of the strength of the friction material.

[0020] From the viewpoint of ensuring the strength of the friction material, the content of the fiber base material in the friction material is preferably 10 to 70% by mass, and more preferably 20 to 60% by mass, based on the total amount of the fiber base material.

[0021] <Friction modifier> The friction modifier is used to impart desired friction characteristics such as wear resistance, heat resistance, fade resistance, etc. to the friction material. Examples of the friction modifier include abrasive, metal powder, inorganic filler, organic filler, solid lubricant, and the like.

[0022] In the friction material according to this embodiment, the friction modifier contains titanium carbide powder. By including titanium carbide powder, it is easier to obtain a friction material with excellent fade resistance. Titanium carbide powder is hard, with a Mohs hardness of 8 or higher, and has a high melting point of 3000°C or higher, so it has the property of being able to withstand high temperatures under high load conditions. In a friction material composition containing a specific amount of steel fibers, wear resistance can be ensured by the steel fibers, while the titanium carbide powder can maintain the coefficient of friction during braking under high load conditions. The titanium carbide powder content in the friction material is preferably 0.5 to 7% by mass, more preferably 0.5 to 4% by mass, and even more preferably 1.5 to 4% by mass.

[0023] Titanium carbide powder is classified as an abrasive material among friction modifiers. The average particle size of titanium carbide powder is preferably 1 to 200 μm, and more preferably 3 to 110 μm. By keeping the average particle size of the titanium carbide powder within this range, it is easier to obtain a friction material with excellent fade resistance. The average particle size can be determined by the value of the volume-based cumulative percentage equivalent particle size (D50) measured with a laser diffraction particle size distribution analyzer.

[0024] The friction material according to this embodiment may contain abrasive materials other than titanium carbide powder. Examples of other abrasive materials include zirconium oxide, aluminum oxide, silica, magnesium oxide, zirconium silicate, chromium oxide, iron(II,III) oxide (Fe3O4), chromite, tin oxide, and the like. These can be used individually or in combination of two or more.

[0025] The abrasive content in the friction material is preferably 1 to 35% by mass, more preferably 3 to 30% by mass, based on the total amount of abrasive material.

[0026] Examples of metal powders include aluminum, tin, zinc, and tungsten. However, it is preferable that copper powder is not included. These can be used individually or in combination of two or more.

[0027] The metal powder content in the friction material is preferably 1 to 20% by mass, and more preferably 3 to 15% by mass, based on the total amount of metal powder.

[0028] 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 barium sulfate, calcium carbonate, calcium hydroxide, calcium silicate, vermiculite, and mica. These can be used individually or in combination of two or more.

[0029] The inorganic filler content in the friction material is preferably 1 to 40% by mass, more preferably 1 to 35% by mass.

[0030] Examples of organic fillers include various rubber powders (raw rubber powder, tire powder, etc.), rubber dust, resin dust, cashew dust, tire tread, melamine dust, and the like. These can be used individually or in combination of two or more.

[0031] The friction material according to this embodiment preferably contains resin dust from the viewpoint of fade resistance. The resin dust content in the friction material is preferably 0.6% by mass or less, and more preferably 0.3% by mass or less. In particular, if the resin dust content is 0.3% by mass or less, the gas and tar generated when the resin dust decomposes at high temperatures under high load conditions are suppressed, and an appropriate transfer film is formed, stabilizing the coefficient of friction under high load, making it easier to obtain a friction material with excellent fade resistance.

[0032] The organic filler content in the friction material is preferably 0 to 15% by mass, and more preferably 0 to 10% by mass, based on the total amount of organic filler.

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

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

[0035] <Binding material> 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. Specifically, these include straight phenolic resins, various modified phenolic resins such as elastomers, thermosetting resins such as melamine resins, epoxy resins, and polyimide 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. These binders can be used individually or in combination of two or more types. 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 according to this embodiment has a copper content of 0.5% by mass or less in terms of copper element. Although a small amount of copper may inevitably be present in the friction material, it is preferable that it be substantially free of copper from the viewpoint of environmental impact.

[0037] A specific embodiment of the method for manufacturing the friction material according to this embodiment can be carried out by a known manufacturing process. For example, the above components can be blended, and the blended material can be produced by pre-molding, thermoforming, heating, polishing, and other processes according to a conventional manufacturing method. The following is a general process for manufacturing brake pads with friction material. (a) A process of forming a pressure plate into a predetermined shape by sheet metal pressing, (b) The process of degreasing the above pressure plate, chemical treatment and primer treatment, and then applying adhesive, (c) A process of blending raw materials such as 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 pre-molded body. (d) A thermoforming process in which the above pre-molded body and the pressure plate to which adhesive has been applied are fixed together as a single unit by applying a predetermined temperature and pressure (molding temperature 130-180°C, molding pressure 30-80 MPa, molding time 2-10 minutes), (e) After-curing (150-300°C, 1-5 hours), the final finishing process involves polishing, scorching, and painting.

[0038] Based on the above, this specification discloses the following friction materials. [1] A friction material comprising a fiber base material, a friction modifier and a binder, The copper content is 0.5% by mass or less in terms of copper element, The aforementioned fibrous base material contains steel fibers, The steel fiber content is greater than 20% by mass and less than 50% by mass, The aforementioned friction modifier is a friction material containing titanium carbide powder. [2] The friction material according to [1], wherein the titanium carbide powder content is 0.5 to 7% by mass. [3] The friction material according to [1] or [2], wherein the fibrous base material contains aramid fibers, and the aramid fiber content is 0.3 to 0.5% by mass. [4] The friction material according to any one of [1] to [3], wherein the friction modifier contains resin dust, and the content of the resin dust is 0.3% by mass or less. [5] The friction material according to any one of [1] to [4], wherein the average particle size of the titanium carbide powder is 1 to 200 μm. [Examples]

[0039] The present invention will be described in more detail below using examples, but the present invention is not limited to these.

[0040] <Manufacturing of friction materials> (Examples 1-12, Comparative Examples 1-3) The compounding materials (mass%) shown in Table 2 were placed in a mixing and stirring machine and mixed at room temperature for 4 minutes to obtain a friction material composition. Subsequently, the obtained friction material composition was subjected to the following steps to produce a brake pad equipped with the friction material: (i) pre-molding, (ii) thermoforming, (iii) heat treatment, and scorching. (i) Preformation The mixture was placed into the mold of a pre-forming press, and a pre-molded body was produced by molding at room temperature under 10 MPa for 10 seconds. (ii) Thermoforming This pre-molded body was placed in a thermoforming mold, a metal plate (pressure plate) with adhesive applied beforehand was placed on top, and heat and pressure molding was performed at 160°C and 45 MPa for 5 minutes. (iii) Heat treatment, scorching This heated and pressurized molded body was subjected to a heat treatment at 260°C for 30 minutes, after which the surface was polished. Next, the surface of this heated and pressurized molded body was subjected to a scorching treatment, followed by a finish coating to obtain a friction material.

[0041] Steel fiber: Average fiber length 3 mm, average fiber diameter 170 μm Titanium carbide powder A: Average particle size 3 μm Titanium carbide powder B: Average particle size 100 μm

[0042] <Friction performance> The obtained friction material was subjected to a fade test under the conditions shown in Table 1 by contacting it with a disc rotor, and its friction performance (fade resistance and wear resistance) under high load was confirmed. Fade resistance was evaluated using the average friction coefficient at the point when the disc rotor temperature reached 350°C during braking. An average friction coefficient of 0.30 or higher was considered good. The average friction coefficient is the average value of the fluctuation in the friction coefficient from the start to the end of braking during one braking cycle at the point when the disc rotor temperature reached 350°C. Wear resistance was evaluated by the amount of friction material wear after the fade test described above. A friction material wear of 0.80 mm or less was considered good.

[0043] The test results are shown in Table 2. Furthermore, the copper content in the friction materials of all examples and comparative examples is 0% by mass in terms of copper element.

[0044] [Table 1]

[0045] [Table 2]

[0046] Titanium carbide powder A: Average particle size 3 μm Titanium carbide powder B: Average particle size 100 μm

[0047] From the results above, it can be seen that the friction materials of Examples 1 to 12, which contain titanium carbide powder and a specific amount of steel fibers, exhibit excellent fade resistance and wear resistance. From a comparison of Examples 2, 5, and 6, it can be seen that a friction material with excellent fade resistance and wear resistance can be obtained when the aramid fiber content is preferably 0.3 to 1.0 mass%, and more preferably 0.3 to 0.5 mass%. A comparison of Examples 2, 7, and 8 shows that the inclusion of resin dust can improve fade resistance. In Example 7, where the resin dust content was 0.6% by mass, the fade resistance and abrasion resistance were within acceptable limits, but they were lower than in Example 8, where the resin dust content was 0.3% by mass. Therefore, a content of 0.3% by mass or less is preferable. From a comparison of Examples 2, 10, 11, and 12, it can be seen that a friction material with excellent fade resistance and wear resistance can be obtained when the titanium carbide powder content is 0.5 to 7% by mass, and is particularly preferable when it is 1.5 to 4% by mass. Comparing Example 2 and Example 9, both Example 2, with an average particle size of 3 μm for titanium carbide powder, and Example 9, with an average particle size of 100 μm, exhibited similarly excellent fade resistance, while the friction material of Example 9 showed superior wear resistance.

[0048] The friction material of Comparative Example 1, which had a steel fiber content of 50% by mass, exhibited insufficient wear resistance, with the friction material wear exceeding 0.8 mm. The friction material of Comparative Example 2, which had a steel fiber content of 20% by mass, had an average coefficient of friction of less than 0.3, indicating insufficient fade resistance. Furthermore, the friction material wear exceeded 0.8 mm, indicating insufficient wear resistance. The friction material in Comparative Example 3, which did not contain titanium carbide powder, exhibited insufficient wear resistance, with the friction material wear exceeding 0.8 mm.

Claims

1. A friction material comprising a fiber base material, a friction modifier and a binder, The copper content is 0.5% by mass or less in terms of copper element, The aforementioned fibrous base material contains steel fibers, The steel fiber content is more than 20% by mass and less than 50% by mass. The aforementioned friction modifier is a friction material containing titanium carbide powder.

2. The friction material according to claim 1, wherein the content of the titanium carbide powder is 0.5 to 7% by mass.

3. The friction material according to claim 1 or claim 2, wherein the fibrous base material contains aramid fibers, and the content of the aramid fibers is 0.3 to 0.5% by mass.

4. The friction material according to claim 1 or claim 2, wherein the friction modifier contains resin dust, and the content of the resin dust is 0.3% by mass or less.

5. The friction material according to claim 1 or claim 2, wherein the average particle size of the titanium carbide powder is 1 to 200 μm.

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