Friction material

Abstract

To provide a friction material having excellent initial efficacy and stability of effectiveness.SOLUTION: 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.SELECTED DRAWING: None

Description

[Technical Field]

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

[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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-117726 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 does not consider or confirm the securing of initial effectiveness.

[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. [Means for solving the problem]

[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 provides the following <1> ~ <4> It is related to. <1> A friction material comprising a friction modifier, a fiber base material, and a binder, A friction material containing a zirconate as the friction modifier. <2> The zirconate is contained in an amount of 0.5% by mass or more and less than 20% by mass. <1> The friction material according to claim 1. <3> 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. <1> or <2> The friction material according to claim 1. <4> The copper content is 0.5 mass% or less in terms of copper element. <1> ~ <3> 10. The friction material according to claim 9, wherein the friction material is a friction material having a thickness of 100 nm or less. [Effects of the Invention]

[0009] The friction material of the present invention is excellent in initial effectiveness and stability of effectiveness. DETAILED DESCRIPTION OF THE INVENTION

[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 adjustment material> (zirconate) The friction material of the present invention contains a zirconate as a friction modifier. By containing a zirconate as a friction modifier, the friction material can be made to have excellent initial effectiveness and stability of effectiveness. In this specification, zirconate generally refers to a salt of zirconium oxide and a basic oxide. Zirconate includes, for example, metazirconate: I 2ZrO3(M I represents Na, K, Sr, 1 / 2Ca, 1 / 2Pb, etc.), titanate zirconate: MTi 1-x Zr x O3 (M represents an alkaline earth metal such as Ca or Mg, and x represents 0 or more and less than 1).

[0013] It is not clear why the inclusion of zirconate as a friction modifier improves the initial effectiveness and stability of the friction material of the present invention, 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 the 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 can result in a sudden increase in braking effectiveness and reduced stability under certain conditions. In contrast, when zirconate is used as a friction modifier, the Mohs hardness of the metals contained in the zirconate (excluding Zr) is lower than that of Zr, so the difference between the Mohs hardness of cast iron and that of zirconate is smaller than the difference between the Mohs hardness of cast iron and that of zirconia, which is presumably why braking effectiveness is more stable.

[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] The content of zirconate in the friction material of the present invention is not particularly limited, but is preferably 0.5 mass % or more and less than 20 mass %, more preferably 0.5 to 15 mass %, and even more preferably 0.5 to 10 mass % of the entire friction material. It is preferable that the zirconate content in the friction material is 0.5% by mass or more, as this provides sufficient braking effectiveness, and it is also preferable that the zirconate content is less than 20% by mass, as this reduces aggressiveness to the rotor, which is the mating material, and reduces the amount of wear on the rotor.

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

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

[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 %, and 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 %, and more preferably 0.5 to 10 mass %.

[0023] Examples of abrasives include alumina, silica, magnesium oxide, zirconia, zirconium silicate, chromium oxide, iron oxide (FeO), and chromite. These may be used alone or in combination of two or more. As the zirconia, stabilized zirconia containing a stabilizer such as calcia or yttria may be used, or unstabilized zirconia containing no 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 in the entire friction material is preferably 1 to 20 mass %, more preferably 3 to 15 mass %.

[0027] Examples of metal powders include powders of aluminum, tin, zinc, etc. These may be used alone or in combination of two or more.

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

[0029] The content of the friction modifier is preferably 60 to 95 mass %, more preferably 70 to 90 mass %, of the entire friction material, from the viewpoint of sufficiently imparting the above-mentioned desired friction characteristics to the friction material.

[0030] <Binding material> As the binder, various commonly used binders can be used, specifically, phenolic resin, various modified phenolic resins such as elastomers, melamine resin, epoxy resin, polyimide resin, and other thermosetting resins.

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

[0032] From the viewpoint of formability of the friction material, the content of the binder is preferably 1 to 20 mass %, more preferably 3 to 15 mass %, of the entire friction material.

[0033] <Fiber base material> As the fibrous substrate, various commonly used fibrous substrates can be used, specifically, organic fibers, inorganic fibers, and metal fibers.

[0034] Examples of organic fibers include aromatic polyamide (aramid) fibers and flame-resistant acrylic fibers.

[0035] Examples of inorganic fibers include biosoluble inorganic fibers, ceramic fibers, glass fibers, carbon fibers, rock wool, etc. Examples of biosoluble inorganic fibers include biosoluble ceramic fibers such as SiO-CaO-MgO fibers, SiO-CaO-MgO-AlO fibers, and SiO-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, from the viewpoint of ensuring 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 viewpoints 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 useful as a substitute for conventional friction materials that use materials containing copper components, such as copper fibers and copper powder.

[0039] <Method of manufacturing friction material> The friction material of the present invention can be produced by a known production process. For example, the above components are blended, and the blend is subjected to preforming, thermoforming, heating, polishing, and other processes according to a conventional production method to produce the friction material.

[0040] A method for manufacturing a brake pad having a friction material generally includes the following steps. (a) A process of forming a pressure plate into a predetermined shape using a sheet metal press. (b) A process of degreasing, chemical conversion coating, and primer coating the pressure plate, and then applying an adhesive. (c) A process in which raw materials such as friction modifiers, binders, and fiber base materials are blended, thoroughly homogenized by mixing, and molded at room temperature under a predetermined pressure to produce a preform. (d) A thermoforming process in which the preform and the pressure plate coated with adhesive are bonded together by applying a predetermined temperature and pressure (forming temperature: 130 to 180°C, forming pressure: 30 to 80 MPa, forming time: 2 to 10 minutes). (e) After-curing (150-300°C, 1-5 hours) and final finishing such as polishing, scorching, and painting. [Example]

[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 obtained mixture was subjected to the following steps to produce a friction material.

[0043] (i) Preforming The mixture was placed in a mold of a preforming press and molded at room temperature under 20 MPa for 10 seconds to prepare a preform. (ii) Thermoforming This preform was placed in a thermoforming mold, and a metal plate (pressure plate) to which an adhesive had been applied was placed on top of it, followed by heat and pressure 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.Then, the hot-pressed molded body was given a finish coating except for the surface, 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 efficacy] The average friction coefficient μ1 at the first speed V=50 km / h and V=100 km / h, and the average friction coefficient μ2 at the second speed V=50 km / h and V=100 km / h were measured. 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 mentioned above.

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

[0047] [Evaluation of effectiveness and stability] Using the average friction coefficients μ1 and μ2 obtained above, braking stability was calculated using the following formula: μ1 and μ2 used to evaluate braking stability are the average friction coefficients at speeds V=50 km / h and V=100 km / h, respectively. Effectiveness stability [%] = [(μ2-μ1) / μ2] x 100

[0048] The efficacy and stability were evaluated as follows. 〇 (Good): Efficacy stability was less than 15.0% △ (No problem): Efficacy stability was 15.0% or more but less than 20.0% × (bad): Efficacy stability was 20.0% or more

[0049] [Table 1]

[0050] The results in Table 1 show that the friction materials of the examples are excellent in initial effectiveness and effectiveness stability. [Industrial Applicability]

[0051] 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 fiber base material, and a binder, A friction material containing a zirconate as the friction modifier.

2. The friction material according to claim 1, comprising the zirconate in an amount of 0.5 mass % or more and less than 20 mass %.

3. 3. The friction material according to claim 1, 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. 3. The friction material according to claim 1, wherein the copper content is 0.5 mass % or less in terms of elemental copper.

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