Friction pair

Abstract

[Problem] The present invention provides a friction pair having excellent low-speed performance stability, comprising a disc brake pad having a friction material composed of a friction material composition and a stainless steel disc rotor. The friction material composition comprises a binder, a fiber base material, and a friction modifier, and is free of copper and iron-based metal fibers. [Solution] The present invention utilizes a friction material composition containing 20-30% by weight of a titanate as an inorganic friction modifier relative to the total weight of the friction material composition, and is free of mica and vermiculite. The titanate is preferably lithium potassium titanate having a layered crystal structure.

Description

Technical Field

[0001] The present invention relates to a friction pair, in particular to a friction pair used in vehicles such as passenger cars. Background Art

[0002] Conventionally, as a friction member of a disc brake for a passenger car, a disc brake pad is used, in which a friction material is bonded to a metal base member.

[0003] In recent years, due to the demand for quiet braking, disc brake pads using a friction material called NAO material that produces less braking noise have become increasingly common.

[0004] NAO friction materials are formed from a friction material composition containing a binder, a fiber base material other than steel fibers, such as steel fibers and / or stainless steel fibers, and a friction modifier. These materials are categorized alongside semi-metallic friction materials and / or low-steel friction materials, which contain steel fibers as their fiber base material. Furthermore, recent regulations in the United States regarding copper content have led to the development of friction materials containing less than 5% copper by weight, or even no copper at all.

[0005] Patent Document 1 describes a friction material composition and a friction material obtained by molding the friction material composition. The friction material composition comprises a fiber base material, a friction adjusting material, and a binder. The copper content of the friction material composition is 0.5% by mass or less, calculated as copper element. The friction adjusting material comprises granular titanate obtained by granulating titanate, and the average particle size of the granular titanate is 100 to 250 μm.

[0006] Patent Document 2 describes a friction material composition comprising a fiber base material, an inorganic filler, an organic filler, and a binder, and containing a copper content of 0.5% by mass or less. The inorganic filler comprises an abrasive having an average particle size of 3 to 5 μm and an abrasive having an average particle size of 9 to 13 μm, and the inorganic filler comprises a titanate having an average particle size of 1.5 to 4.5 μm and a titanate having an average particle size of 15 to 45 μm.

[0007] As a counter-friction material for disc brake pads equipped with this friction material containing virtually no copper, a cast iron disc rotor as described in Patent Document 3 is used. This cast iron disc rotor has low corrosion resistance and suffers from rusting during use, necessitating a solution in the friction material.

[0008] For example, Patent Document 4 discloses a friction material comprising a binder, a friction adjusting material, and a fiber substrate. The friction material does not contain a copper component, but contains 10 to 20 volume % of at least one titanate compound having a plurality of protrusions, and 1 to 20 volume % of biosoluble inorganic fibers, thereby improving the rust removal properties of the abrasive material.

[0009] However, as the popularization of electric vehicles and hybrid vehicles promotes the installation of regenerative brakes, the braking load of the friction material of conventional hydraulic brakes decreases. Therefore, even if the technology of Patent Document 4 is used, sufficient rust removal performance cannot be achieved.

[0010] Therefore, disc rotors made of stainless steel having excellent rust resistance are increasingly used.

[0011] Patent Document 5 discloses a four-wheel disc rotor made of a stainless steel plate having a martensitic structure or a mixed structure of a martensitic phase and a ferrite phase.

[0012] Patent Document 6 describes a disc rotor for an automobile having a structure containing martensite and carbonitride, and optionally containing ferrite.

[0013] Patent Document 7 describes a disc rotor for automobiles made of a stainless steel plate, wherein the stainless steel plate is characterized by containing, in mass%, C: 0.005-0.100%, Si: 0.01-1.00%, Mn: 0.010-3.00%, P: 0.040% or less, S: 0.0100% or less, Cr: 10.0-14.0%, N: 0.005-0.100%, V: 0.03-0.30%, Al: 0.001-0.050%, B: 0.0002-0.0050%, Ni: 0-2.00%, Cu: 0-2.00%, Mo: 0-1.00%, W: 0-1.00%, Ti: 0-0.40%, Nb: 0-0.40%, Zr: 0-0.40%, Co: 0-0.400%, Sn: 0-0.40%, REM: 0-0.050% or less, Mg: 0-0.0100%, Ca: 0-0.0100%, Sb: 0-0.50%, Ta: 0-0.3000%, Hf: 0-0.3000%, Ga: 0-0.1000%, the remainder is composed of Fe and impurities, the metal structure is composed of ferrite phase, and 10-50 pieces / 100μm are present in any cross section. 2 Carbonitrides having a circle-equivalent diameter of 0.3 μm or more are present.

[0014] Against this backdrop, there is a need for a friction material composed of a copper-free friction material composition suitable for use with stainless steel disc rotors having excellent rust resistance. However, it has been shown that when a copper-free friction material used in combination with a conventional cast iron disc rotor is applied to a disc brake equipped with a stainless steel disc rotor, the effectiveness stability under low-speed conditions is significantly reduced.

[0015] Prior art literature

[0016] Patent Literature

[0017] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-57312

[0018] Patent Document 2: Japanese Patent Application Laid-Open No. 2018-162385

[0019] Patent Document 3: Japanese Patent Application Laid-Open No. 2-134425

[0020] Patent Document 4: Japanese Patent Application Laid-Open No. 2017-149971

[0021] Patent Document 5: Japanese Patent Application Laid-Open No. 2016-117925

[0022] Patent Document 6: Japanese Patent Application Publication No. 2019-173086

[0023] Patent Document 7: Japanese Patent Application Laid-Open No. 2019-178419 Summary of the Invention

[0024] Problems to be solved by the invention

[0025] An object of the present invention is to provide a friction pair having excellent low-speed performance stability, the friction pair comprising a disc brake pad having a friction material composed of a friction material composition containing a binder, a fiber base material, and a friction modifier, and containing no copper component and no iron-based metal fiber, and a stainless steel disc rotor.

[0026] Means used to solve problems

[0027] As a result of intensive research by the inventors of the present invention, a friction pair was discovered, comprising a disc brake pad having a friction material composed of a friction material composition, and a disc rotor made of stainless steel. The friction material composition contains a binder, a fiber base material, a friction adjusting material, and is free of copper components and iron-based metal fibers. The friction material composition contains a specific amount of titanate as a friction adjusting material. At the same time, by using a friction material composition free of mica and vermiculite, a friction pair having excellent effectiveness stability under low-speed conditions can be obtained, thereby completing the present invention.

[0028] The present invention relates to a friction pair comprising a disc brake pad having a friction material composed of a friction material composition, and a stainless steel disc rotor. The friction material composition contains a binder, a fiber base material, and a friction adjusting material, and does not contain copper components or iron-based metal fibers. The present invention is based on the following technology.

[0029] (1) A friction pair comprising a disc brake pad having a friction material composed of a friction material composition, and a disc rotor made of stainless steel, wherein the friction material composition contains a binder, a fiber base material, and a friction adjusting material and does not contain a copper component or iron-based metal fiber, wherein the friction material composition contains 20 to 30% by weight of titanate as an inorganic friction adjusting material relative to the total weight of the friction material composition and does not contain mica or vermiculite.

[0030] (2) The friction pair according to (1), wherein the titanate has a layered crystal structure.

[0031] (3) The friction pair according to (1), wherein the titanate is lithium potassium titanate.

[0032] Effects of the Invention

[0033] According to the present invention, a friction pair having excellent effectiveness stability under low-speed conditions can be provided, comprising a disc brake pad having a friction material composed of a friction material composition, and a stainless steel disc rotor, wherein the friction material composition contains a binder, a fiber base material, and a friction adjusting material and does not contain a copper component and iron-based metal fibers. DETAILED DESCRIPTION

[0034] The cast iron disc rotors used in the past required a relatively large amount of titanate to form a titanate transfer coating on the disc rotor surface, and mica or vermiculite needed to be added to the friction material composition to uniformly control the coating thickness, thereby achieving effectiveness stability under low-speed conditions.

[0035] On the other hand, it has been revealed that when mica or vermiculite with a Mohs hardness of 4 or less and cleavage properties is added to a stainless steel disc rotor (they are essential components for controlling the thickness of the titanate transfer film in the friction material used in cast iron disc rotors), the formation of the titanate transfer film is inhibited, making it impossible to achieve good performance stability under low-speed conditions.

[0036] Therefore, the present invention relates to a friction pair comprising a disc brake pad having a friction material composed of a friction material composition and a stainless steel disc rotor, wherein the friction material composition contains a binder, a fiber base material, and a friction modifier, and does not contain a copper component or iron-based metal fibers. The friction material composition contains 20 to 30% by weight of titanate as an inorganic friction modifier, based on the total weight of the friction material composition, and does not contain mica or vermiculite.

[0037] By adding 20 to 30 wt % of titanate as a friction modifier relative to the total weight of the friction material composition, a coating having an appropriate thickness can be formed on the surface of a stainless steel disc rotor.

[0038] As titanates, one of titanates having a tunnel-like crystal structure such as potassium hexatitanate, potassium octatitanate, and sodium hexatitanate, and titanates having a layered crystal structure such as lithium potassium titanate and magnesium potassium titanate can be used, or a combination of two or more can be used.

[0039] Among these, when focusing on the structure, it is preferable to use titanates having a layered crystal structure, and when focusing on the composition, it is preferable to use potassium magnesium titanate alone.

[0040] In addition, as for the shape of the titanate, titanates in a columnar, plate-like, granular, flaky, and irregular shape having a plurality of protrusions can be used.

[0041] Furthermore, by omitting mica or vermiculite, which has a Mohs hardness of 4 or less and exhibits cleavage properties and is an essential component of a friction material composition free of copper and iron-based metals, as used in conventional cast iron disc rotors, the formation of a titanate transfer film is not hindered, enabling excellent performance stability under low-speed conditions.

[0042] Examples of mica not contained in the friction material composition include phlogopite, muscovite, and sericite.

[0043] In the present invention, the old Mohs hardness scale of "1. Talc, 2. Gypsum, 3. Calcite, 4. Fluorite, 5. Apatite, 6. Orthoclase, 7. Quartz, 8. Topaz, 9. Corundum, 10. Diamond" is applied to the Mohs hardness.

[0044] Friction Material Composition

[0045] The friction material used in the friction pair of the present invention is composed of a friction material composition. The friction material composition contains, in addition to titanate, a binder, a fiber base material, and a friction adjusting material commonly used in friction materials.

[0046] As the adhesive material, there can be listed linear phenolic resin, acrylic rubber modified phenolic resin, silicone rubber modified phenolic resin, nitrile rubber modified phenolic resin, cashew oil modified phenolic resin, aralkyl modified phenolic resin (phenol aralkyl resin) obtained by reacting phenols, aralkyl ethers and aldehydes, acrylic rubber dispersed phenolic resin, silicone rubber dispersed phenolic resin, fluoropolymer dispersed phenolic resin and other adhesive materials commonly used in friction materials. They can be used alone or in combination of two or more.

[0047] The content of the binder is preferably 4 to 9 wt %, more preferably 6 to 8 wt %, relative to the total weight of the friction material composition.

[0048] Examples of the fiber base include organic fibers commonly used in friction materials, such as aramid fibers, acrylic fibers, cellulose fibers, and polyparaphenylenebenzobisoxazole fibers. These fibers may be used alone or in combination of two or more.

[0049] The content of the fiber base material is preferably 1 to 5 wt %, more preferably 2 to 4 wt %, based on the total weight of the friction material composition.

[0050] As the friction adjusting material, lubricating materials, inorganic friction adjusting materials, and organic friction adjusting materials can be used.

[0051] As lubricating materials, there can be listed carbonaceous lubricating materials such as artificial graphite, natural graphite, graphite flake powder, petroleum coke, coal coke, elastic graphitized carbon, and oxidized polyacrylonitrile fiber powder, and metal sulfide lubricating materials such as tin sulfide, molybdenum disulfide, iron sulfide, bismuth sulfide, zinc sulfide, and composite metal sulfide. They can be used alone or in combination of two or more.

[0052] The content of the lubricating material is preferably 10 to 18 wt %, more preferably 11 to 16 wt %, relative to the total weight of the friction material composition.

[0053] In addition to the above-mentioned titanates, inorganic friction adjustment materials can also include calcium hydroxide, calcium carbonate, barium sulfate, talc, dolomite, zeolite, ferrosoferric oxide, manganese manganese oxide, calcium silicate hydrate, magnesium oxide, silicon dioxide, zirconium oxide, zirconium silicate, γ-alumina, α-alumina, silicon carbide, wollastonite, sepiolite, basalt fiber, glass fiber, biosoluble ceramic fiber, rock wool, etc. They can be used alone or in combination of two or more.

[0054] The total content of the inorganic friction modifier and the titanate is preferably 60 to 82 wt %, more preferably 65 to 76 wt %, relative to the total amount of the friction material composition.

[0055] Examples of organic friction adjusting materials include cashew nut shell oil friction powder, tire tread rubber powder, polytetrafluoroethylene powder, or vulcanized rubber powder or unvulcanized rubber powder of acrylic rubber, isoprene rubber, nitrile rubber, styrene-butadiene rubber, butyl rubber, silicone rubber, and other organic friction adjusting materials commonly used in friction materials. These materials can be used alone or in combination of two or more.

[0056] The content of the organic friction adjusting material is preferably 3 to 8 wt %, more preferably 5 to 7 wt %, based on the total amount of the friction material composition.

[0057] <Method for manufacturing disc brake pads>

[0058] The disc brake pad according to the present invention is generally manufactured by the following process:

[0059] A mixing process is to uniformly mix the friction material composition (friction material raw material) prepared in a predetermined amount using a mixer to obtain a friction material raw material mixture.

[0060] The obtained friction material raw material mixture is superimposed on a backing plate that has been cleaned, surface treated, and coated with an adhesive material in advance, and then placed in a thermoforming mold for heat and pressure molding.

[0061] The obtained molded product is heated to complete the heat treatment process of the curing reaction of the adhesive material.

[0062] A coating process that uses spraying or electrostatic powder coating to apply the paint.

[0063] The coating baking process of the baking paint, and

[0064] A grinding process that uses a rotating grindstone to form a friction surface.

[0065] After the heat and pressure molding step, the product can be manufactured by sequentially performing a coating step, a heat treatment step also serving as paint baking, and a polishing step.

[0066] If necessary, before the heating and pressing process, the following steps can be carried out:

[0067] The granulation process of granulating the friction material raw material mixture,

[0068] The kneading process is to knead the friction material raw material mixture.

[0069] A preforming step of placing the friction material raw material mixture or the granulated product obtained in the granulating step and the kneaded product obtained in the kneading step into a preforming die to form a preform.

[0070] The scorching step may be performed after the heating and pressurizing step.

[0071] <Stainless steel disc rotor>

[0072] As the stainless steel disk rotor, for example, a disk rotor made of martensitic stainless steel or ferritic stainless steel can be used.

[0073] Example

[0074] The present invention will be described in detail below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0075] [Methods for producing friction materials of Examples 1 to 7 and Comparative Examples 1 to 3]

[0076] The friction material composition having the composition shown in Table 1 was placed in The mixture was mixed in a mixer for 5 minutes to obtain a friction composition mixture. The friction material composition mixture was pressurized at 30 MPa for 10 seconds in a molding die to obtain a friction material preform. The friction material preform was placed on a steel backing plate that had been previously cleaned, surface-treated, and coated with an adhesive, and then molded in a hot molding die at a molding temperature of 150°C and a molding pressure of 40 MPa for 10 minutes to obtain a friction material molded product. The friction material molded product was heat-treated (post-cured) at 200°C for 5 hours and then polished to form a friction surface, thereby producing a disc brake pad for a passenger car.

[0077] Table 1

[0078]

[0079] Furthermore, the friction material of the disc brake pad was cut into a size of 25 mm×15 mm×15 mm to obtain test pieces of Examples 1 to 7 and Comparative Examples 1 to 3.

[0080] Table 2 shows the "test conditions," "material of the grinding material," "evaluation items," and "evaluation criteria" used when these test pieces were used to examine the effectiveness stability under low-speed conditions.

[0081] Table 2

[0082]

[0083] Table 3 shows the evaluation results of “efficacy stability under low-speed conditions” shown in Table 2, which were performed for each Example and each Comparative Example.

[0084] Table 3

[0085]

[0086] It can be seen from Table 3 that the friction material meeting the conditions of the present invention is good in terms of effectiveness stability under low-speed conditions.

[0087] Industrial Applicability

[0088] According to the present invention, a friction pair can be provided that has excellent effectiveness stability under low-speed conditions. The friction pair includes a disc brake pad having a friction material composed of a friction material composition, and a stainless steel disc rotor. The friction material composition contains a binder, a fiber base material, and a friction adjusting material, and does not contain copper components or iron-based metal fibers. The friction pair has extremely high practical value.

Claims

1. A friction pair comprising a disc brake pad having a friction material composed of a friction material composition and a stainless steel disc rotor, wherein the friction material composition comprises: 6 to 8 wt% of the binder relative to the total weight of the friction material composition, A fiber base material made of organic fibers in an amount of 2 to 4% by weight relative to the total amount of the friction material composition, 11 to 16 wt% of lubricating material relative to the total weight of the friction material composition, 65 to 76 wt% of an inorganic friction modifier as a friction modifier relative to the total weight of the friction material composition; and 5 to 7 wt% of the organic friction modifier relative to the total weight of the friction material composition, It does not contain copper components and iron-based metal fibers, and is characterized by: The friction material composition contains 20 to 30 wt % of lithium potassium titanate having a layered crystal structure as an inorganic friction modifier relative to the total weight of the friction material composition, and does not contain mica or vermiculite.

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