Friction material

Abstract

The present invention relates to a friction material which comprises a friction regulating material, a binder and a fiber base material, the friction regulating material containing stearate particles.

Description

Friction material

[0001] The present invention relates to a friction material used in automobiles, railway vehicles, industrial machines, etc.

[0002] The friction material is used in brakes such as disc brakes and drum brakes, or clutches, etc., and plays a braking role by friction with a mating material such as a disc brake. The performance required for the friction material includes low mating material aggressiveness and fade resistance. Mating material aggressiveness is a characteristic of excessively shaving the mating material such as a disc rotor during running. Fade resistance is a characteristic in which the friction coefficient is difficult to decrease under high load.

[0003] As a friction material with low mating material aggressiveness, for example, in Patent Document 1, a friction material containing a fluororesin such as PTFE (polytetrafluoroethylene) is disclosed. Since PTFE has lubricating properties due to a special crystal structure called a band structure, it is considered to contribute to the effect of suppressing mating material aggressiveness.

[0004] Japanese Patent Application Laid-Open No. 2023-175418

[0005] However, in recent years, the use of organic fluorine compounds (PFAS) has been restricted, and it is expected that a friction material not containing a fluororesin such as PTFE will be required.

[0006] In view of the above circumstances, an object of the present invention is to provide a friction material having excellent fade resistance and low mating material aggressiveness.

[0007] As a result of diligent research, the present inventors have found that the above problems can be solved by incorporating stearate particles as a friction modifier into the friction material, and have completed the present invention. That is, the present invention relates to the following <1> to <7>. <1> A friction material comprising a friction modifier, a binder and a fiber base material, wherein the friction modifier contains stearate particles. <2> The friction material according to <1>, wherein the friction modifier contains rubber dust. <3> The friction material according to <1> or <2>, wherein the stearate particles contain at least one of lithium stearate particles and zinc stearate particles. <4> The friction material according to any one of <1> to <3>, wherein the content of the stearate particles is 0.1 to 2.0% by mass. <5> The friction material according to any one of <1> to <4>, wherein the average particle diameter of the stearate particles is 1 to 20 μm. <6> The friction material according to <2>, wherein the rubber dust content is 0.5 to 10% by mass. <7> The friction material according to any one of <1> to <6>, wherein the copper content is 0.5% by mass or less in terms of copper element.

[0008] According to the present invention, it is possible to provide a friction material that has excellent fade resistance and low aggressiveness towards the mating material.

[0009] The present invention will be described in detail below, but these are merely examples of embodiments and the present invention is not limited to these.

[0010] In this specification, the average particle diameter can be determined by the value of the particle diameter equivalent to 50% of the cumulative percentage of volume (D50) measured by a laser diffraction particle size distribution analyzer.

[0011] The friction material according to an embodiment of the present invention (hereinafter also referred to as "the friction material of this embodiment") includes a friction modifier, a binder, and a fibrous base material. Each component will be described in detail below.

[0012] <Friction Modifiers> Friction modifiers are used to impart desired friction properties such as wear resistance, heat resistance, and fade resistance to friction materials.

[0013] In the friction material of this embodiment, the friction modifier contains stearate particles. Since stearate is a metal soap, it has excellent lubricity, and the inclusion of stearate particles in the friction material of this embodiment can suppress wear on the mating material. However, suppressing wear on the mating material makes it difficult to maintain good fade resistance, but by including stearate particles, wear on the mating material can be suppressed while maintaining fade resistance.

[0014] Furthermore, because stearate is in particulate form, it can be directly incorporated into the friction material, and it is presumed that the retained stearate particles can continuously exert their effect. In contrast, it is also conceivable to incorporate stearate by coating a carrier with it, but it is presumed that the coating will peel off with repeated braking, making it difficult to maintain the effect.

[0015] The average particle size of the stearate particles is preferably 1 to 20 μm, and more preferably 1 to 10 μm, from the viewpoint of aggressiveness towards the mating material.

[0016] Examples of stearate particles include lithium stearate particles, zinc stearate particles, magnesium stearate particles, calcium stearate particles, barium stearate particles, sodium stearate particles, aluminum stearate particles, and potassium stearate particles. These can be used individually or in combination of two or more types.

[0017] The content of stearate particles in the friction material of this embodiment is preferably 0.1 to 2.0% by mass, more preferably 0.2 to 1.5% by mass, and even more preferably 0.3 to 0.8% by mass, from the viewpoint of mating material aggressiveness and fade resistance.

[0018] Other friction modifiers include, for example, organic fillers, inorganic fillers, abrasives, lubricants, and metal powders.

[0019] Examples of organic fillers include various rubber powders (such as raw rubber powder), rubber dust (such as tire tread), resin dust, cashew dust, and melamine dust. These can be used individually or in combination of two or more.

[0020] Among organic fillers, it is particularly preferable to include rubber dust. By including rubber dust in the friction material of this embodiment, the aggressiveness towards the mating material can be effectively suppressed. The rubber dust improves the flexibility of the friction material and is expected to have the effect of improving the aggressiveness towards the mating material, especially at low temperatures and low surface pressures.

[0021] The rubber dust content in the friction material of this embodiment is preferably 0.5 to 10% by mass, more preferably 1 to 6% by mass, even more preferably 2 to 5% by mass, and particularly preferably 2 to 4% by mass. If the rubber dust content is 0.5% by mass or more, the aggressiveness towards the mating material can be well suppressed. Furthermore, rubber dust decomposes due to the heat generated during high-load braking, which can be a factor in reducing fade resistance, but if it is 10% by mass or less, fade resistance can be well maintained. Therefore, by blending rubber dust with stearate particles in the friction material within the above range, it is possible to further suppress aggressiveness towards the mating material while maintaining fade resistance.

[0022] Furthermore, the content of the organic filler in the friction material of this embodiment is preferably 1 to 15% by mass, more preferably 1 to 10% by mass.

[0023] 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, vermiculite, and mica. These can be used individually or in combination of two or more.

[0024] The inorganic filler content in the friction material of this embodiment is preferably 30 to 80% by mass, more preferably 40 to 70% by mass.

[0025] Examples of abrasive materials include zirconium oxide, alumina, silica, magnesium oxide, zirconia, zirconium silicate, chromium oxide, and iron(Fe) oxide. ３ O ４ Examples include chromites, etc. These can be used individually or in combination of two or more.

[0026] The abrasive content in the friction material of this embodiment is preferably 1 to 20% by mass, more preferably 3 to 15% by mass.

[0027] Examples of lubricants include graphite, coke, antimony trisulfide, molybdenum disulfide, tin sulfide, manganese sulfide, iron sulfide, and zinc sulfide. These can be used individually or in combination of two or more. In this embodiment of friction material, it is preferable that fluororesins such as polytetrafluoroethylene (PTFE) are not included.

[0028] The lubricant content in the friction material of this embodiment is preferably 1 to 20% by mass, more preferably 3 to 15% by mass.

[0029] Examples of metal powders include aluminum, tin, and zinc powders. These can be used individually or in combination of two or more types.

[0030] The metal powder content in the friction material of this embodiment is preferably 1 to 10% by mass, more preferably 1 to 5% by mass.

[0031] From the viewpoint of sufficiently imparting the desired friction characteristics to the friction material, the friction modifier is preferably used in an amount of 60 to 90% by mass, more preferably 70 to 90% by mass, of the entire friction material.

[0032] <Bonding Agent> A bonding agent is used to integrate the fibrous base material and friction modifier contained in the friction material. Various commonly used bonding agents can be used as the bonding agent. Specifically, examples include phenolic resins, various modified phenolic resins such as elastomers, thermosetting resins such as melamine resins, epoxy resins, and polyimide resins.

[0033] 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 can be used individually or in combination of two or more types.

[0034] From the viewpoint of the formability of the friction material, the binder is preferably used in an amount of 1 to 20% by mass, more preferably 3 to 15% by mass, of the entire friction material.

[0035] <Fiber substrate> The fiber substrate is used to impart strength to the friction material. Examples of the fiber substrate include organic fibers, inorganic fibers, metal fibers, etc. The fiber substrates can be used individually or in combination of two or more kinds.

[0036] Examples of the organic fibers include aromatic polyamide (aramid) fibers, flame-resistant acrylic fibers, etc.

[0037] Examples of the inorganic fibers include bio-soluble inorganic fibers, ceramic fibers, glass fibers, carbon fibers, rock wool, etc. Examples of the bio-soluble inorganic fibers include bio-soluble ceramic fibers such as SiO ２ -CaO-MgO-based fibers, SiO ２ -CaO-MgO-Al ２ O ３ -based fibers, SiO ２ -MgO-SrO-based fibers, etc., and bio-soluble rock wool.

[0038] Examples of the metal fibers include steel fibers, etc.

[0039] From the viewpoint of ensuring the strength of the friction material, the fiber substrate is preferably used at 3 to 30% by mass, more preferably 5 to 20% by mass in the whole friction material.

[0040] In the friction material of this embodiment, it is preferable that the copper content is 0.5% by mass or less in terms of copper element. The copper component may be unavoidably contained slightly in the friction material, but it is preferably not substantially contained from the viewpoint of reducing environmental load.

[0041] <Manufacturing method of friction material> The friction material of the present invention can be manufactured by a known manufacturing process. For example, the above components are blended, and the blend is subjected to steps such as preforming, hot forming, heating, grinding, etc. according to a normal manufacturing method to manufacture the friction material.

[0042] A method for manufacturing a brake pad provided with a friction material generally includes the following steps. (a) A step of forming a pressure plate into a predetermined shape by sheet metal pressing. (b) A step of subjecting the pressure plate to degreasing treatment, chemical conversion treatment, and primer treatment, and applying an adhesive. (c) A step of blending raw materials such as a friction modifier, a binder, and a fiber base material, homogenizing them sufficiently by mixing, and forming them at a predetermined pressure at room temperature to produce a preform. (d) A hot forming step (forming temperature: 130 to 180 °C, forming pressure: 30 to 80 MPa, forming time: 2 to 10 minutes) of fixing the preform and the pressure plate coated with the adhesive integrally by applying a predetermined temperature and pressure. (e) A step of performing after-cure (150 to 300 °C, 1 to 5 hours) and finally performing finishing treatments such as grinding, scorching, and painting.

[0043] Hereinafter, the present invention will be described in more detail with reference to examples and the like, but the present invention is not limited thereto.

[0044] (Examples 1-1 to 1-10, Comparative Examples 1-1 to 1-2, Examples 2-1 to 2-10, Comparative Examples 2-1 to 2-2) The compounding materials shown in Tables 1 to 2 were collectively charged into a mixing stirrer and mixed at room temperature for 4 minutes to obtain a mixture. The average particle diameters of the stearate particles are as follows. Lithium stearate particles: average particle diameter 8 μm Zinc stearate particles: average particle diameter 8 μm The obtained mixture was subjected to the following steps of (i) preforming, (ii) hot forming, (iii) heat treatment, and scorching to produce a friction material.

[0045] (i) Preforming The mixture was put into a mold of a preforming press and formed at 20 MPa for 10 seconds at room temperature to produce a preform. (ii) Hot forming This preform was put into a hot forming mold, and a metal plate (pressure plate) coated with an adhesive in advance was overlaid, and heat and pressure forming was performed at 150 °C and 35 MPa for 6 minutes. (iii) Heat treatment, scorching After performing a heat treatment at 250 °C for 3 hours on this heat and pressure formed body, the surface was ground. Next, a scorching treatment was performed on the surface of this heat and pressure formed body, and painting was performed for finishing to obtain a friction material.

[0046] The obtained friction materials were evaluated for mating material aggressiveness and fade resistance using the following methods. The results are shown in Tables 1 and 2.

[0047] <Attack on the opposing material> Test pieces were prepared from the friction material obtained above, pressed against a disc rotor with a surface pressure of 0.04 MPa, and tested at a speed of 60 km / h. The amount of disc rotor wear was measured after 40 hours. The measured amount of disc rotor wear was evaluated based on the following criteria: A: Less than 10 μm B: 10 μm or more, less than 20 μm C: 20 μm or more, less than 25 μm D: 25 μm or more

[0048] <Fade Resistance> Using the friction material obtained above, the first fade test was conducted in accordance with JASO C406, and the minimum friction coefficient during 10 braking cycles was measured. The measured minimum friction coefficient was evaluated based on the following criteria: A: 0.35 or higher B: 0.30 or higher, less than 0.35 C: 0.25 or higher, less than 0.30 D: less than 0.25

[0049]

[0050]

[0051] The results in Tables 1 and 2 show that the friction material in the examples exhibits low mating force and excellent fade resistance.

[0052] 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 invention. This application is based on Japanese Patent Application No. 2025-027279 filed on 21 February 2025, the contents of which are incorporated herein by reference.

Claims

1. A friction material comprising a friction modifier, a binder, and a fibrous base material, wherein the friction modifier contains stearate particles.

2. The friction material according to claim 1, wherein the friction modifier contains rubber dust.

3. The friction material according to claim 1 or claim 2, wherein the stearate particles contain at least one of lithium stearate particles and zinc stearate particles.

4. The friction material according to claim 1 or claim 2, wherein the content of the stearate particles is 0.1 to 2.0% by mass.

5. The friction material according to claim 1 or claim 2, wherein the average particle diameter of the stearate particles is 1 to 20 μm.

6. The friction material according to claim 2, wherein the rubber dust content is 0.5 to 10% by mass.

7. The friction material according to claim 1 or claim 2, wherein the copper content is 0.5% by mass or less in terms of copper element.

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