Friction material

Abstract

The purpose of the present invention is to provide a friction material having excellent initial efficacy and stability of effectiveness. The present invention relates to a friction material comprising a friction-adjusting material, a fiber base material and a binding material, wherein a zirconate is contained as the friction-adjusting material.

Description

Friction material

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

[0002] In recent years, the use of regenerative braking has increased compared to friction braking due to the shift to electric vehicles, which has led to a tendency for frictional braking performance of friction materials to decrease. For this reason, friction materials are required to ensure not only general effectiveness but also effectiveness even when there is little braking history (hereinafter referred to as "initial effectiveness").

[0003] Patent Document 1 discloses a friction material that contains zirconium oxide and titanate and has excellent wear resistance at high temperatures and suppresses metal catch.

[0004] Japanese Patent Application Publication No. 2020-117726

[0005] However, Patent Document 1 does not consider or confirm whether the initial effectiveness is ensured.

[0006] The present invention has been made in view of the above-mentioned conventional circumstances, and has as its object to provide a friction material that is excellent in initial effectiveness and effectiveness stability.

[0007] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by incorporating zirconate as a friction modifier in the friction material, and have thus completed the present invention.

[0008] That is, the present invention relates to the following items <1> to <4>. <1> A friction material including a friction modifier, a fibrous base material, and a binder, wherein the friction modifier contains a zirconate. <2> The friction material according to <1>, which contains 0.5% by mass or more but less than 20% by mass of the zirconate. <3> The friction material according to <1> or <2>, wherein the zirconate is one or more selected from the group consisting of calcium zirconate, barium zirconate, calcium titanate zirconate, barium titanate zirconate, magnesium zirconate, strontium zirconate, and barium calcium titanate zirconate. <4> The friction material according to any one of <1> to <3>, wherein the copper content is 0.5% by mass or less in terms of elemental copper.

[0009] The friction material of the present invention is excellent in initial effectiveness and stability of effectiveness.

[0010] The present invention will be described in detail below, but these are examples of preferred embodiments, and the present invention is not limited to these details. In this specification, numerical ranges indicated by "to" mean "greater than or equal to" or "less than or equal to."

[0011] The friction material of the present invention includes a friction modifier, a fibrous base material, and a binder, and contains a zirconate as the friction modifier. Each component will be described in detail below.

[0012] <Friction Modifier> (Zirconate) The friction material of the present invention contains zirconate as a friction modifier. By containing zirconate as a friction modifier, it is possible to obtain a friction material with excellent initial effectiveness and effectiveness stability. In this specification, zirconate generally refers to a salt composed of zirconium oxide and a basic oxide. The zirconate may be, for example, metazirconate: M Ｉ ２ ZrO ３ (M Ｉ represents Na, K, Sr, 1 / 2Ca, 1 / 2Pb, etc.), titanate zirconate: MTi １－ｘ Zr ｘ O ３ (M represents an alkaline earth metal such as Ca or Mg, and x represents 0 or more and less than 1.)

[0013] The reason why the inclusion of zirconate as a friction modifier improves the initial effectiveness and stability of effectiveness of the friction material of the present invention is not clear, but while the Mohs hardness of cast iron, which is commonly used as the mating rotor material, is about 4, the Mohs hardness of zirconate is 4 or higher, which is close to the Mohs hardness of cast iron. Therefore, it is speculated that the initial effectiveness is obtained and the stability of effectiveness is improved by the zirconate grinding the mating rotor material.

[0014] Specifically, when zirconia is used as a friction modifier, the difference between the Mohs hardness of cast iron and that of zirconia (8 to 9) is large, which results in a decrease in stability of braking effectiveness, such as a sudden increase in braking effectiveness under certain conditions. In contrast, when zirconate is used as a friction modifier, the Mohs hardness of the metals (excluding Zr) contained in the zirconate is lower than that of Zr, so the difference between the Mohs hardness of cast iron and that of zirconate becomes smaller than the difference between the Mohs hardness of cast iron and that of zirconia, which is presumably why stability of braking effectiveness improves.

[0015] In terms of Mohs hardness, the zirconate is preferably at least one selected from the group consisting of calcium zirconate, barium zirconate, calcium titanate zirconate, barium titanate zirconate, magnesium zirconate, strontium zirconate, and barium calcium titanate zirconate, more preferably at least one selected from the group consisting of calcium zirconate, barium zirconate, magnesium zirconate, and strontium zirconate, and even more preferably calcium zirconate.

[0016] Although there are no particular restrictions on the content of zirconate in the friction material of the present invention, it is preferably 0.5% by mass or more but less than 20% by mass, more preferably 0.5 to 15% by mass, and even more preferably 0.5 to 10% by mass of the entire friction material. A zirconate content of 0.5% by mass or more in the friction material is preferred because sufficient braking effectiveness can be obtained, and a content of less than 20% by mass is preferred because aggressiveness to the rotor, which is the mating material, is suppressed and the amount of wear of the rotor is reduced.

[0017] (Other Friction Modifiers) Other friction modifiers are used to impart desired friction characteristics such as wear resistance, heat resistance, and fade resistance to the friction material.

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

[0019] 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 fluoride, vermiculite, and mica. These may be used alone or in combination of two or more.

[0020] The content of the inorganic filler in the entire friction material is preferably 30 to 80 mass %, more preferably 40 to 70 mass %.

[0021] Examples of organic fillers include various rubber powders (raw rubber powder, tire powder, etc.), cashew dust, tire tread, melamine dust, etc. These may be used alone or in combination of two or more.

[0022] The content of the organic filler in the entire friction material is preferably 0.1 to 15 mass %, more preferably 0.5 to 10 mass %.

[0023] Examples of the abrasive include alumina, 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. Furthermore, as the zirconia, stabilized zirconia to which a stabilizer such as calcia or yttria has been added may be used, or unstabilized zirconia that does not contain the stabilizer may be used.

[0024] The preferred range of the content of the abrasive is expressed as the sum of the content of the abrasive and the content of the zirconate, i.e., the total content of the abrasive and the zirconate is preferably 1 to 40 mass %, more preferably 10 to 35 mass %, of the entire friction material.

[0025] Examples of solid lubricants include graphite, coke, molybdenum disulfide, tin sulfide, polytetrafluoroethylene (PTFE), etc. These may be used alone or in combination of two or more.

[0026] The content of the solid lubricant is preferably 1 to 20% by mass, more preferably 3 to 15% by mass in the whole friction material.

[0027] Examples of the metal powder include powders such as aluminum, tin, and zinc. These can be used alone or in combination of two or more.

[0028] The content of the metal powder is preferably 0 to 10% by mass, more preferably 0 to 5% by mass in the whole friction material.

[0029] From the viewpoint of sufficiently imparting the above desired frictional characteristics to the friction material, the content of the friction modifier is preferably 60 to 95% by mass, more preferably 70 to 90% by mass in the whole friction material.

[0030] <Binder> As the binder, various commonly used binders can be used. Specifically, thermosetting resins such as phenolic resins, various modified phenolic resins such as elastomer-modified phenolic resins, melamine resins, epoxy resins, and polyimide resins can be mentioned.

[0031] Examples of the elastomer-modified phenolic resin include acrylic rubber-modified phenolic resin, silicone rubber-modified phenolic resin, nitrile rubber (NBR)-modified phenolic resin, etc. These can be used alone or in combination of two or more.

[0032] From the viewpoint of the moldability of the friction material, the content of the binder is preferably used at 1 to 20% by mass, more preferably 3 to 15% by mass in the whole friction material.

[0033] <Fiber substrate> As the fiber substrate, various commonly used fiber substrates can be used. Specifically, organic fibers, inorganic fibers, and metal fibers can be mentioned.

[0034] Examples of the organic fiber include aromatic polyamide (aramid) fiber, flame-resistant acrylic fiber, etc.

[0035] Examples of the inorganic fiber include bio-soluble inorganic fiber, ceramic fiber, glass fiber, carbon fiber, rock wool, etc. Examples of the bio-soluble inorganic fiber include SiO ２ -CaO-MgO-based fiber, SiO２ -CaO-MgO-Al ２ O ３ Fibers, SiO ２ Examples of the biosoluble ceramic fibers include MgO-SrO fibers and biosoluble rock wool.

[0036] Examples of metal fibers include steel fibers, etc. These may be used alone or in combination of two or more.

[0037] The content of the fibrous base material is preferably 3 to 30 mass %, more preferably 5 to 20 mass %, of the entire friction material in order to ensure sufficient strength of the friction material.

[0038] The friction material of the present invention can exhibit the above-mentioned effects whether it contains a copper component as in the past, or whether it contains no copper component or only a small amount of copper component. However, from the viewpoint of environmental pollution and harmfulness to the human body, the content of the copper component in the friction material of the present invention is preferably 0.5 mass % or less, more preferably 0.3 mass % or less, and even more preferably 0.1 mass % or less, calculated as elemental copper. Furthermore, it is most preferable that the friction material of the present invention does not contain a copper component. Thus, the friction material of the present invention is also useful as a substitute for conventional friction materials that use copper-containing materials such as copper fibers and copper powder.

[0039] <Method for manufacturing 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, thermoforming, heating, and polishing according to a conventional manufacturing method to manufacture the friction material.

[0040] The manufacturing method of brake pads equipped with friction material generally comprises the following steps: (a) a step of forming a pressure plate into a predetermined shape using a sheet metal press; (b) a step of degreasing, chemical conversion and primer treatment of the pressure plate, and applying an adhesive; (c) a step of blending raw materials such as friction modifiers, binders and fiber base materials, thoroughly homogenizing the mixture by mixing, and forming at room temperature under a predetermined pressure to produce a preform; (d) a step of thermoforming the preform and the adhesive-coated pressure plate by applying a predetermined temperature and pressure to bond the two components together (forming temperature 130-180°C, forming pressure 30-80 MPa, forming time 2-10 minutes); and (e) a step of after-curing (150-300°C, 1-5 hours), and finally performing finishing treatments such as polishing, scorching and painting.

[0041] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0042] [Examples 1 to 7, Comparative Examples 1 to 5] The ingredients shown in Table 1 were all charged into a mixer and mixed at room temperature for 5 minutes to obtain a mixture. The resulting mixture was subjected to the following steps to produce friction materials.

[0043] (i) Preforming: The mixture was placed in a mold of a preforming press and molded at room temperature for 10 seconds at 20 MPa to produce a preformed body. (ii) Thermoforming: This preformed body was placed in a thermoforming mold, and a metal plate (pressure plate) pre-coated with adhesive was placed on top of it, followed by hot-press molding at 150°C and 35 MPa for 6 minutes. (iii) Heating: This hot-pressed molded body was heat-treated at 250°C for 3 hours, and the surface was polished. Next, a finish coating was applied to the area excluding the surface of this hot-pressed molded body to obtain a friction material.

[0044] The friction materials of Examples 1 to 7 and Comparative Examples 1 to 5 were evaluated in accordance with JASO C406 using a full-size dynamometer. The results are shown in Table 1.

[0045] [Measurement of Effect] The average coefficient of friction μ1 at the first effect speed V = 50 km / h and V = 100 km / h, and the average coefficient of friction μ2 at the second effect speed V = 50 km / h and V = 100 km / h were measured. Note that the terms "first effect" and "second effect" refer to the effects measured in accordance with JASO C406. Of these, the first effect corresponds to the initial effect described above.

[0046] [Evaluation of first effectiveness] The evaluation of first effectiveness was carried out as follows. Note that μ1 used in the evaluation of effectiveness is the numerical value of the average friction coefficient at speeds V=50 km / h and V=100 km / h. ◯ (Good): The average friction coefficient μ1 was 0.36 or more. × (Poor): The average friction coefficient μ1 was less than 0.36.

[0047] [Evaluation of braking stability] Using the average friction coefficients μ1 and μ2 obtained above, braking stability was calculated according to the following formula. Note that μ1 and μ2 used in the evaluation of braking stability are the numerical values ​​of the average friction coefficients at speeds V=50 km / h and V=100 km / h, respectively. Brake stability [%]=[(μ2-μ1) / μ2]×100

[0048] The efficacy stability was evaluated as follows: ◯ (good): efficacy stability was less than 15.0% Δ (no problem): efficacy stability was 15.0% or more and less than 20.0% × (poor): efficacy stability was 20.0% or more

[0049]

[0050] From the results in Table 1, it is clear that the friction materials of the examples are excellent in initial effectiveness and effectiveness stability.

[0051] Although various embodiments have been described above, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any manner as long as they do not deviate from the spirit of the invention.

[0052] This application is based on a Japanese patent application (Patent Application No. 2024-018649) filed on February 9, 2024, the contents of which are incorporated herein by reference.

[0053] The friction material of the present invention can be used in automobiles, railway vehicles, industrial machinery, etc.

Claims

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

2. The friction material according to claim 1, containing 0.5 mass % or more but less than 20 mass % of the zirconate.

3. The friction material according to claim 1 or 2, wherein the zirconate is at least one selected from the group consisting of calcium zirconate, barium zirconate, calcium titanate zirconate, barium titanate zirconate, magnesium zirconate, strontium zirconate, and barium calcium titanate zirconate.

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

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