Compositions for forming friction materials, friction materials, friction members, and disc brake pads for automobiles

Abstract

To provide a friction material-forming composition that enables the formation of a friction material, harmonizing a low μ ratio post-idling with reduced rotor wear.SOLUTION: A friction material-forming composition includes titanate, polytetrafluoroethylene, and zirconium oxide; and includes no copper, or includes copper with its content being more than 0 mass% and 0.5 mass% or less, calculated as the element, wherein the titanate content is 20 mass% or more and less than 35 mass%, the polytetrafluoroethylene content is 0.5 mass% or more and less than 5 mass%, and the volume average particle size of the zirconium oxide is more than 8.0 μm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a composition for forming a friction material, a friction material, a friction member, and an automotive disc brake pad.

Background Art

[0002] Conventionally, a disc brake has been used as a braking device for a passenger car, and a disc brake pad in which a friction material is attached to a metal base member has been used as the friction member. The friction material is manufactured by a manufacturing process including steps such as preforming, hot forming, and finishing using a friction material composition containing a fiber base material, a friction modifier, a binder, and the like.

[0003] As a friction material composition used for an automotive disc brake pad, for example, a friction material composition containing a fiber base material, a binder, and a friction modifier, having a copper content of 0.5 mass% or less in the friction material composition, and containing fluoropolymer particles having an average particle diameter of 0.5 to 8 μm has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a friction material used for an automotive disc brake pad (hereinafter also referred to as a "brake pad"), it is desirable to be able to suppress wear of the brake pad, changes in friction characteristics due to the use environment, brake noise during use, wear of the rotor in contact with the brake pad, and the like.

[0006] For example, the change in friction characteristics of brake pads due to the operating environment can be evaluated by the rate of change in the coefficient of friction (μ) before and after being left in high humidity conditions (for example, the ratio of the coefficient of friction after being left in high humidity conditions to the coefficient of friction before being left in high humidity conditions, hereinafter also referred to as the "post-leaving μ ratio"). For example, if the post-leaving μ ratio is greater than 1, the coefficient of friction increases due to high humidity conditions, making brake squeal more likely to occur during use. Therefore, it is desirable to be able to suppress the increase in the post-leaving μ ratio.

[0007] One possible method to suppress the increase in the μ ratio after standing is to adjust the individual components of the friction material composition, such as the fibrous base material, friction modifier, and abrasive. However, if one attempts to suppress the increase in the μ ratio after standing by adjusting the composition of each component while maintaining the desired coefficient of friction required for brake pads, wear on the rotor in contact with the brake pads becomes more likely. Therefore, there is a trade-off between a low μ ratio after standing and the suppression of rotor wear, and it is difficult to achieve both simultaneously.

[0008] This disclosure is made in view of the above circumstances, and aims to provide a friction material forming composition capable of producing a friction material that can achieve both a low after-storage μ ratio and suppression of rotor wear, a friction material obtained by molding the same, and a friction member and an automobile disc brake pad equipped with the friction material. [Means for solving the problem]

[0009] The following embodiments are included as means for solving the above problems. <1> It contains titanate, polytetrafluoroethylene, and zirconium oxide. It does not contain copper, or the copper content is greater than 0% by mass and less than or equal to 0.5% by mass on an elemental basis. The titanate content is 20% by mass or more and less than 35% by mass, The polytetrafluoroethylene content is 0.5% by mass or more and less than 5% by mass, A friction material forming composition in which the volume-average particle size of the zirconium oxide is greater than 8.0 μm. <2> Free of metal sulfides <1> The friction material forming composition described above. <3> The metal powder further contains a sacrificial corrosion protection agent for iron. <1> or <2> The friction material forming composition described above. <4> The zirconium oxide includes desiliconized zirconia. <1> ~ <3> A friction material forming composition as described in any one of the following. <5> The volume-average particle size of the polytetrafluoroethylene is 0.5 μm to 8.0 μm. <1> ~ <4> A friction material forming composition as described in any one of the following. <6> <1> ~ <5> A friction material obtained by molding a friction material forming composition described in any one of the above. <7> <6> A friction member comprising the friction material described above and a backing plate. <8> <6> Automotive disc brake pads equipped with the friction material described above. [Effects of the Invention]

[0010] This disclosure provides a friction material forming composition capable of producing a friction material that can achieve both a low after-storage μ ratio and suppression of rotor wear, a friction material obtained by molding the same, and a friction member and an automobile disc brake pad equipped with the friction material.

[0011] The following describes in detail the forms for implementing this disclosure. However, this disclosure is not limited to the following embodiments. In the following embodiments, the components (including elemental steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit this disclosure.

[0012] In this disclosure, the numerical range indicated using "~" includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples. In this disclosure, each component may contain only one substance or multiple substances. If multiple substances corresponding to each component are present in the composition, the content of each component means the total content of those multiple substances present in the composition, unless otherwise specified.

[0013] <Composition for forming friction material> The friction material forming composition of this disclosure comprises a titanate, polytetrafluoroethylene, and zirconium oxide, and is free of copper, or has a copper content greater than 0% by mass and 0.5% by mass or less on an elemental basis, has a titanate content of 20% by mass or more and less than 35% by mass, has a polytetrafluoroethylene content of 0.5% by mass or more and less than 5% by mass, and has a volume average particle size of zirconium oxide greater than 8.0 μm. With the friction material forming composition of this disclosure, a friction material that can achieve both a low μ ratio after standing and suppression of rotor wear can be produced by adjusting the composition of each component.

[0014] The friction material forming composition of this disclosure comprises a titanate, polytetrafluoroethylene (PTFE), and zirconium oxide, and may optionally contain other components. The components that may be included in the friction material forming composition of this disclosure will be described in detail below.

[0015] (Titanate) Examples of titanates included in friction material forming compositions include titanium and potassium-containing salts such as potassium hexatinate, potassium octatinate, lithium potassium titanate, and magnesium potassium titanate. Among these, potassium hexatinate is preferred from the viewpoint of increasing the μ level of the friction material. The content rate of potassium hexatitanate may be 50% to 100% by mass, or may be 80% to 100% by mass, relative to the total amount of titanate, from the viewpoint of easily adjusting the μ level to a desired range.

[0016] The content rate of titanate (preferably potassium hexatitanate) is 20% to less than 35% by mass relative to the total amount of the composition for forming a friction material, and may be 23% to 30% by mass, or may be 25% to 30% by mass, from the viewpoints of further reducing the μ ratio after standing and suppressing pad wear.

[0017] (Polytetrafluoroethylene (PTFE)) The volume average particle size of polytetrafluoroethylene may be 0.5 μm to 8.0 μm, may be 1.0 μm to 7.0 μm, or may be 2.0 μm to 6.0 μm. The polytetrafluoroethylene contained in the composition for forming a friction material may be in a state of secondary particles in which primary particles are condensed. The above-mentioned volume average particle size of polytetrafluoroethylene may be the volume average particle size of secondary particles.

[0018] The volume average particle size of the primary particles of polytetrafluoroethylene may be 100 nm to 200 nm, or may be 100 nm to 150 nm. From the viewpoint of reducing the primary particle size of polytetrafluoroethylene, it is preferable to use polytetrafluoroethylene produced by the direct polymerization method.

[0019] In the present disclosure, the volume average particle size of particles means the value (median diameter (D50)) when the integration from the small diameter side becomes 50% in the volume-based particle size distribution measured by a laser diffraction particle size distribution measuring device.

[0020] The content rate of polytetrafluoroethylene is 0.5% to less than 5% by mass relative to the total amount of the composition for forming a friction material, and may be 0.7% to 3% by mass, or may be 0.8% to 2% by mass, from the viewpoints of achieving both a low μ ratio after standing and suppressing rotor wear.

[0021] (Zirconium oxide) The volume-average particle size of zirconium oxide is greater than 8.0 μm, and from the viewpoint of achieving both suppression of torque vibration during fading, a low μ ratio after standing, and suppression of rotor wear, it may be between 8.0 μm and 20 μm, between 8.5 μm and 15 μm, or between 9.0 μm and 13 μm.

[0022] The zirconium oxide contained in the friction material forming composition preferably includes desiliconized zirconia, from the viewpoint of easily adjusting the μ level to a desired range. The desiliconized zirconia should have a low silicon concentration and high purity of zirconium oxide; for example, the amount of SiO2 is preferably 5% by mass or less, and more preferably 0.5% by mass or less, relative to the total particle size.

[0023] From the viewpoint of easily adjusting the μ level to a desired range, the content of desiliconized zirconia may be 50% to 100% by mass or 80% to 100% by mass relative to the total amount of zirconium oxide.

[0024] In the friction material forming composition, the zirconium oxide content may be 10% by mass or more and 30% by mass or less, 13% by mass or more and 25% by mass or less, or 15% by mass or more and 23% by mass or less, based on the total amount of the friction material forming composition.

[0025] (copper) The friction material forming composition does not contain copper, or its copper content is greater than 0% by mass and less than or equal to 0.5% by mass on an elemental basis. This prevents or suppresses the outflow of copper from the friction material.

[0026] (metal sulfide) It is preferable that the friction material forming composition does not contain metal sulfides. This suppresses the generation of metal oxides due to temperature changes, fluctuations in the friction coefficient (μ) due to metal oxides, and further suppresses changes in characteristics during use, such as the generation of iron components on the brake pad surface called metal pickup and increased rotor wear.

[0027] (Specific metal powder) The friction material forming composition preferably further contains a metal powder (hereinafter also referred to as "specific metal powder") that has a sacrificial corrosion protection effect on iron. This makes it possible to suppress rust on the friction material. The specific metal powder is preferably a metal powder with a higher ionization tendency than iron. A specific example of the specific metal powder is zinc powder.

[0028] (Other ingredients) The friction material forming composition may contain other components to the extent that it achieves the effects of the present invention. Examples of other components include resins such as binders and adhesives, friction modifiers, abrasives, fiber substrates, pH adjusters, and fillers.

[0029] Examples of resins used as binders and adhesives include straight phenolic resins, cashew oil-modified phenolic resins, acrylic rubber-modified phenolic resins, silicone rubber-modified phenolic resins, nitrile rubber (NBR)-modified phenolic resins, phenol-aralkyl resins, fluoropolymer-dispersed phenolic resins, and silicone rubber-dispersed phenolic resins.

[0030] In the friction material forming composition, the resin content may be 5% to 20% by mass, 6% to 15% by mass, or 8% to 12% by mass, based on the total amount of the friction material forming composition.

[0031] Examples of friction modifiers and abrasives (excluding titanates, polytetrafluoroethylene (PTFE), and zirconium oxide) include rubbers such as tire tread rubber, nitrile rubber, acrylic rubber, silicone rubber, and butyl rubber, friction dust, graphite, vermiculite, fluorphlogopite, muscovite, iron(II,III) oxide, calcium silicate, magnesium oxide, zirconium silicate, zircon, γ-alumina, α-alumina, silicon carbide, wollastonite, and sepiolite.

[0032] In the friction material forming composition, the total content of friction modifiers and abrasives (excluding titanates, polytetrafluoroethylene (PTFE), and zirconium oxide) may be 10% to 50% by mass, 15% to 40% by mass, or 20% to 35% by mass, based on the total amount of the friction material forming composition.

[0033] Examples of fiber base materials include basalt fibers, glass fibers, aramid fibers, cellulose fibers, poly(p-phenylenebenzobisoxazole) fibers, acrylic fibers, and rock wool.

[0034] In the friction material forming composition, the content of the fiber base material may be 5% to 20% by mass, 6% to 15% by mass, or 8% to 12% by mass, based on the total amount of the friction material forming composition.

[0035] Examples of pH adjusting agents include calcium hydroxide and magnesium hydroxide.

[0036] In the friction material forming composition, the pH adjusting agent content may be 1% to 10% by mass, 2% to 8% by mass, or 3% to 6% by mass, based on the total amount of the friction material forming composition.

[0037] Examples of fillers include barium sulfate, calcium sulfate, and calcium carbonate.

[0038] In the friction material forming composition, the filler content may be 5% to 20% by mass, 6% to 15% by mass, or 8% to 12% by mass, based on the total amount of the friction material forming composition.

[0039] <Friction material> The friction material of this disclosure is obtained by molding the friction material forming composition of this disclosure as described above. The friction material is obtained by molding the friction material forming composition by a conventionally known method. For example, a friction material can be produced by mixing titanate, polytetrafluoroethylene, zirconium oxide, and optionally the other components described above to prepare a friction material forming composition, and then heat-molding the prepared friction material forming composition. When resins such as binders and binders are used in the preparation of the friction material forming composition, the resins such as binders and binders may be heat-cured.

[0040] When heat-molding the friction material forming composition, the friction material forming composition may be heat-molded together with other components (for example, a backing plate as described later). After producing the friction material by heat-molding the friction material forming composition, the surface of the friction material may be polished as needed.

[0041] <Applications of friction materials> Applications of the friction material disclosed herein include friction members and automobile disc brake pads. A friction member may be configured to include the friction material disclosed herein and a backing plate. Methods for manufacturing friction members, automobile disc brake pads, etc., using the friction material forming composition include conventionally known methods. [Examples]

[0042] The above embodiments will be described in detail below with reference to examples, but the above embodiments are not limited to these examples.

[0043] [Manufacturing of disc brake pads] <Examples 1-3 and Comparative Examples 1-7> Each material was blended according to the blending ratio (mass%) shown in Table 1 to obtain each friction material forming composition. Blank spaces in Table 1 indicate that no material was blended. The following components were used as the resin, zirconium oxide, titanate, and PTFE. -Each material- • Resin (silicone rubber modified phenolic resin) • Zirconium oxide 1 (desiliconized zirconia with a volume-average particle size of 3.4 μm) • Zirconium oxide II (desiliconized zirconia with a volume-average particle size of 6.1 μm) • Zirconium oxide 3 (desiliconized zirconia with a volume-average particle size of 8.2 μm) • Zirconium oxide 4 (desiliconized zirconia with a volume-average particle size of 10.2 μm) • Zirconium oxide 5 (desiliconized zirconia with a volume-average particle size of 12.2 μm) • Titanate (potassium hexatinate) • PTFE (Volume-average particle size (secondary particles) 4.0 μm ± 2.0 μm)

[0044] The friction material forming composition was stirred and mixed in a Redigge mixer (manufactured by Matsubo Co., Ltd., product name: Redigge® Mixer M20), and the resulting mixture was heated and pressed together with an iron backing plate (6 mm thick) using a molding press (manufactured by Techno Marushichi Co., Ltd.). The resulting molded product was heat-treated at 200°C for 3.5 hours and polished using a rotary polishing machine. Next, the molded product was scorched at 500°C for 3 minutes, resulting in a thickness of 10 mm and a projected area of ​​60 cm². 2 We manufactured a disc brake pad equipped with the following friction material.

[0045] (μ ratio after standing, torque vibration during fade, pad wear and rotor wear) Using the disc brake pads prepared in each example and comparative example, the μ ratio after standing, torque vibration during fade, pad wear, and rotor wear were determined by tests conducted in accordance with the test conditions in Table 2. The μ ratio after standing was calculated from the average μ ratio of the first braking run for No. 6 and No. 9 ([μ for No. 9 (μ after standing, 2nd time, 0.5 MPa, 5 km / h) / μ for No. 6 (μ after standing, 1st time, 0.5 MPa, 5 km / h)] × 100). The torque vibration during fade was defined as the maximum value of torque fluctuation during one braking run for No. 14 and No. 18. Pad wear was calculated from the difference in brake pad thickness before and after the test, and rotor wear was calculated from the difference in rotor thickness before and after the test. In Table 2, the unit for initial velocity is km / h, and the unit for deceleration is m / s. 2 The unit of hydraulic pressure is MPa.

[0046] Table 1 shows the results for μ ratio after standing, torque vibration during fade, pad wear, and rotor wear. The evaluation criteria for each of these items are as follows. A rating of B or higher for each item indicates good results. -Evaluation criteria for μ ratio after standing- A: Less than 120% B: 120% or more, less than 130% C: 130% or more -Evaluation criteria for torque vibration during fade- A: Less than 400 Nm B: 400Nm or more and less than 600Nm C:600Nm or more -Pad wear evaluation criteria- A: Less than 2.20 mm B: 2.20mm or more and less than 2.80mm C:2.80mm or more - Criteria for evaluating rotor wear - A: Less than 0.020 B: 0.020 or higher, less than 0.025 C:0.025 or more

[0047] [Table 1]

[0048] [Table 2]

[0049] As shown in Table 1, in each embodiment, the evaluation results for the μ ratio after standing, torque vibration during fade, pad wear, and rotor wear were all B or higher. On the other hand, in each comparative example, at least one of the evaluation results for the μ ratio after standing, torque vibration during fade, pad wear, and rotor wear was C. More specifically, in each comparative example, at least one of the evaluation results for the μ ratio after standing and rotor wear was C.

Claims

1. It contains titanate, polytetrafluoroethylene, and zirconium oxide. It does not contain copper, or the copper content is greater than 0% by mass and less than or equal to 0.5% by mass on an elemental basis. The titanate content is 20% by mass or more and less than 35% by mass, The polytetrafluoroethylene content is 0.5% by mass or more and less than 5% by mass, The volume-average particle size of the zirconium oxide is greater than 8.0 μm. Free of metal sulfides A composition for forming a friction material.

2. It contains titanate, polytetrafluoroethylene, and zirconium oxide. It does not contain copper, or the copper content is greater than 0% by mass and less than or equal to 0.5% by mass on an elemental basis. The titanate content is 20% by mass or more and less than 35% by mass, The polytetrafluoroethylene content is 0.5% by mass or more and less than 5% by mass, The volume-average particle size of the zirconium oxide is greater than 8.0 μm. The zirconium oxide includes desiliconized zirconia. A composition for forming a friction material.

3. The friction material forming composition according to claim 1 or 2, further comprising a metal powder having a sacrificial corrosion protection effect on iron.

4. The friction material forming composition according to claim 1 or 2, wherein the volume-average particle size of the polytetrafluoroethylene is 0.5 μm to 8.0 μm.

5. A friction material obtained by molding the friction material forming composition according to claim 1 or 2.

6. The friction material according to claim 5, further comprising a metal powder having a sacrificial corrosion protection effect on iron in the friction material forming composition.

7. The friction material according to claim 5, wherein the volume average particle size of the polytetrafluoroethylene in the friction material forming composition is 0.5 μm to 8.0 μm.

8. A friction member comprising a friction material obtained by molding the friction material forming composition according to claim 1 or 2, and a backing plate.

9. The friction member according to claim 8, further comprising a metal powder having a sacrificial corrosion protection effect on iron in the friction material forming composition.

10. The friction member according to claim 8, wherein the volume average particle size of the polytetrafluoroethylene in the friction material forming composition is 0.5 μm to 8.0 μm.

11. An automobile disc brake pad comprising a friction material obtained by molding the friction material forming composition according to claim 1 or 2.

12. The automobile disc brake pad according to claim 11, further comprising a metal powder having a sacrificial corrosion protection effect on iron in the friction material forming composition.

13. The automobile disc brake pad according to claim 11, wherein the volume average particle size of the polytetrafluoroethylene in the friction material forming composition is 0.5 μm to 8.0 μm.

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