Friction pair

Abstract

[Problem] To provide a friction pair comprising disk brake pads including a friction material comprising a friction material composition which comprises a binder, a fibrous base material, and friction regulators and contains neither a copper component nor iron-based metallic fibers, and a disk rotor comprising a cast iron material and nitride layers formed on surfaces thereof, the friction pair having an excellent braking effect and being inhibited from increasing in coefficient of friction through cold standing. [Solution] The friction material composition contains, as friction regulators, a bead-shaped inorganic friction regulator having an average particle diameter of 10-80 μm and a Mohs hardness of 7.5 or higher in an amount of 0.1-1 wt% with respect to the whole friction material composition, and also contains monoclinic zirconium oxide in an amount of 5-30 wt% with respect to the whole friction material composition. The friction material composition preferably further contains a porous inorganic friction regulator in an amount of 1-5 wt% with respect to the whole friction material composition.

Description

Friction Pair

[0001] The present invention relates to a friction pair, and more particularly to a friction pair for use in vehicles such as automobiles.

[0002] 2. Description of the Related Art Conventionally, disc brake pads, in which a friction material is attached to a metal base member, have been used as friction members for disc brakes in passenger vehicles.

[0003] In recent years, quieter brakes have become a requirement, and disc brake pads with a friction material called NAO material, which produces less brake noise, have become widely used.

[0004] This type of friction material is formed from a friction material composition containing a binder, a fibrous base material other than steel-based fibers, such as steel fibers or stainless steel fibers, and a friction modifier, and is classified as a friction material along with semi-metallic friction materials and low-steel friction materials that contain steel-based fibers as a fibrous base material. In recent years, due to legal restrictions on the copper content in the United States, the development of friction materials that contain only 5 wt % or less of copper, or that contain no copper at all, has become common.

[0005] Patent Document 1 discloses a friction material composition containing a binder, an organic filler, an inorganic filler, and a fibrous base material, in which the friction material composition does not contain copper or the copper content relative to the entire friction material composition is 0.5 mass % or less, the friction material composition contains 25 mass % to 30 mass % of non-acicular titanate as the inorganic filler relative to the entire friction material composition, and the friction material composition contains 3 mass % to 6 mass % of zirconium silicate as the inorganic filler having an average particle size of 0.4 μm to 0.6 μm and a maximum particle size of 1.1 μm relative to the entire friction material composition.

[0006] Patent Document 2 discloses a friction material composition containing a binder, an organic filler, an inorganic filler, and a fibrous base material, in which the copper content as an element does not exceed 0.5 mass %, the composition contains 1 mass % to 3 mass % of iron-based fibers or iron-based powder, and the composition contains 10 mass % to 30 mass % of wollastonite as the fibrous base material.

[0007] As a mating material for a disc brake pad to which such a friction material containing almost no copper component is attached, a disc rotor made of cast iron is used, as shown in Patent Document 3. Such a disc rotor made of cast iron has a problem of low corrosion resistance and rusting during use.

[0008] For this reason, disc rotors with excellent rust resistance and in which a nitride layer is formed on the surface of cast iron material have come to be used.

[0009] Patent Document 4 discloses a disc brake rotor having improved corrosion resistance and wear resistance by forming a surface layer on the surface of a base material made of cast iron, the surface layer containing a Fe-C-N compound as a main component and a dispersed hard material that is harder than the cast iron.

[0010] Patent Document 5 discloses a method for manufacturing a disk rotor having high corrosion resistance, which includes the steps of: degraphitizing a disk rotor material using a chemical cleaning method involving immersion in molten salt to remove the graphite from the surface of the material; nitrocarburizing the material to form a compound layer and an oxynitride layer on the surface of the material in that order; and immersing the material, on which the compound layer and oxynitride layer have been formed, in an oxidizing bath treatment in which the material is immersed in an oxidizing bath containing nitrates heated to 300 to 500 degrees Celsius for 10 to 60 minutes.

[0011] In light of this background, there is a demand for a friction material having a friction material composition that does not contain a copper component and that is compatible with disc rotors in which a nitride layer is formed on the surface of cast iron, which has excellent rust resistance. However, disc rotors in which a nitride layer is formed on the surface of cast iron are harder than disc rotors made of cast iron. Therefore, friction materials developed for conventional disc rotors made of cast iron lack the grindability of inorganic friction modifiers, making it impossible to obtain sufficient braking effectiveness. Furthermore, it is not possible to form an appropriate level of roughness on the disc rotor surface, which increases the contact area between the friction material and the disc rotor, causing an increase in the friction coefficient after being left in the cold and making squealing more likely to occur.

[0012] JP 2018-131479 A JP 2019-59941 A JP 2-134425 A JP 2010-53926 A JP 2016-164439 A

[0013] The present invention aims to provide a friction pair having a disc brake pad equipped with a friction material having a friction material composition that contains a binder, a fiber base material, and a friction modifier, but does not contain a copper component or iron-based metal fibers, and a disc rotor that is made of cast iron and has a nitride layer formed on the surface thereof, the friction pair having excellent braking effectiveness and suppressing an increase in the friction coefficient after being left in the cold.

[0014] Conventional friction materials used in cast iron disc rotors are designed to prevent excessive grinding of the disc rotor surface by preventing inorganic friction modifiers with a relatively high Mohs hardness from falling off the surface of the friction material. The inventors have discovered that, in a disc rotor having a nitride layer formed on the surface of cast iron, a bead-shaped inorganic friction modifier with a relatively high Mohs hardness is used as the inorganic friction modifier, and the composition is designed so that the bead-shaped inorganic friction modifier easily falls off the surface of the friction material, thereby achieving excellent braking performance and wear resistance of the friction material.

[0015] As a result of extensive research, the inventors have discovered that in a friction pair comprising: a disc brake pad equipped with a friction material having a friction material composition that contains a binder, a fibrous base material, and a friction modifier, but does not contain a copper component or iron-based metal fibers; and a disc rotor having a nitride layer formed on the surface of a cast iron material, the friction material composition containing: a bead-like inorganic friction modifier having a specific particle size and a Mohs hardness of 7.5 or more; monoclinic zirconium oxide; and a specific amount of a porous inorganic friction modifier, the friction pair has excellent braking effectiveness and is inhibited from increasing in friction coefficient after being left in a cold state, and have completed the present invention.

[0016] The present invention relates to a friction pair comprising: a disc brake pad having a friction material having a friction material composition that contains a binder, a fiber base material, and a friction modifier, but does not contain a copper component or iron-based metal fibers; and a disc rotor made of cast iron with a nitride layer formed on the surface thereof, and is based on the following technology.

[0017] (1) A friction couple comprising: a disc brake pad having a friction material having a friction material composition containing a binder, a fibrous base material, and a friction modifier, but not containing a copper component or iron-based metal fibers; and a disc rotor having a nitride layer formed on the surface of a cast iron material, wherein the friction material composition contains, as the friction modifier, 0.1% by weight to 1% by weight of a bead-shaped inorganic friction modifier having an average particle size of 10 μm to 80 μm and a Mohs hardness of 7.5 or more, based on the total amount of the friction material composition; and 1% by weight to 5% by weight of a porous inorganic friction modifier, based on the total amount of the friction material composition.

[0018] (2) The friction pair of (1), wherein the bead-shaped friction material composition contains 5 to 30% by weight of monoclinic zirconium oxide as a friction modifier based on the total amount of the friction material composition.

[0019] (3) The friction couple according to (1) or (2), wherein the bead-shaped inorganic friction modifier having a Mohs hardness of 7.5 or more is bead-shaped zirconium silicate.

[0020] (4) The friction couple according to any one of (1) to (3), wherein the porous inorganic friction modifier is calcium silicate hydrate.

[0021] According to the present invention, there can be provided a friction pair having: a disc brake pad equipped with a friction material having a friction material composition that contains a binder, a fiber base material, and a friction modifier, but does not contain a copper component or iron-based metal fibers; and a disc rotor made of cast iron and having a nitride layer formed on the surface thereof, the friction pair having excellent braking effectiveness and suppressing an increase in the friction coefficient after being left in the cold.

[0022] In an embodiment of the present invention, a friction couple includes a disc brake pad having a friction material having a friction material composition that contains a binder, a fibrous base material, and a friction modifier, but does not contain a copper component or iron-based metal fibers, and a disc rotor having a nitride layer formed on the surface of a cast iron material, wherein the friction modifier contains 0.1 to 1% by weight of a bead-shaped inorganic friction modifier having an average particle size of 10 μm to 80 μm and a Mohs hardness of 7.5 or more, based on the total amount of the friction material composition, and the friction modifier contains 5 to 15% by weight of monoclinic zirconium oxide, based on the total amount of the friction material composition.

[0023] The bead-like inorganic friction modifier has the function of grinding the friction surface of the disc rotor, which has a nitride layer formed on the surface of cast iron material.

[0024] However, if the bead-shaped inorganic friction modifier is firmly attached to the surface of the friction material, only localized grinding is possible, making it impossible to uniformly roughen the entire friction surface of the disc rotor, and the effect cannot be said to be sufficient.

[0025] Therefore, in the friction couple of the embodiment of the present invention, a specific amount of porous inorganic friction modifier is added so that the bead-shaped inorganic friction modifier, which has an average particle size of 10 μm to 80 μm and a Mohs hardness of 7.5 or more, easily falls off from the surface of the friction material.

[0026] Porous inorganic friction modifiers have a large specific surface area, and therefore consume a relatively large amount of binder to bind the porous inorganic friction modifiers together, which weakens the binding strength around the porous inorganic friction modifiers and makes the surrounding bead-like inorganic friction modifiers more likely to fall off.

[0027] The detached bead-like inorganic friction modifier thoroughly grinds the friction surface of the disc rotor, which is made of cast iron and has a nitride layer formed on the surface, resulting in excellent braking performance and also making the disc rotor surface moderately rough, which prevents the coefficient of friction from increasing after being left in the cold.

[0028] The bead-shaped inorganic friction modifier preferably has an average particle size of 10 μm to 80 μm, a Mohs hardness of 7.5 or more, and is contained in an amount of 0.1 to 1% by weight, more preferably 0.2 to 0.5% by weight, based on the total amount of the friction material composition.

[0029] If the content of the bead-shaped inorganic friction modifier is less than 0.1% by weight based on the total amount of the friction material composition, excellent braking performance cannot be obtained, and the increase in the coefficient of friction after being left in the cold cannot be suppressed.

[0030] If the content of the bead-like inorganic friction modifier exceeds 1% by weight based on the total amount of the friction material composition, the wear resistance of the friction material deteriorates.

[0031] As the bead-shaped inorganic friction modifier, one or more selected from zirconium silicate (Mohs hardness 7.5), α-alumina (Mohs hardness 9), and silicon carbide (Mohs hardness 9) can be used, and from the viewpoint of suppressing attack on the mating material, it is preferable to use bead-shaped zirconium silicate alone.

[0032] The content of the porous inorganic friction modifier is preferably 1 to 5% by weight, and more preferably 2 to 4% by weight, based on the total amount of the friction material composition.

[0033] If the content of the porous inorganic friction modifier is less than 1% by weight based on the total amount of the friction material composition, the bead-like inorganic friction modifier will not easily fall off, making it impossible to obtain excellent braking performance, and it will not be possible to suppress an increase in the friction coefficient after being left in the cold.

[0034] If the content of the porous inorganic friction modifier exceeds 5% by weight based on the total amount of the friction material composition, the binding strength of the binder decreases, resulting in a decrease in wear resistance.

[0035] The porous inorganic friction modifier may be one or more selected from zeolite, activated carbon, activated alumina, and calcium silicate hydrate, and from the viewpoint of suppressing a decrease in wear resistance, it is preferable to use calcium silicate hydrate alone.

[0036] Furthermore, the friction pair of the embodiment of the present invention has a specific amount of monoclinic zirconium oxide added to the friction material composition.

[0037] Monoclinic zirconium oxide has the property of undergoing a crystal transformation at temperatures around 800°C, changing to a tetragonal system with a volumetric shrinkage of approximately 20%. When the friction material is subjected to a history of high temperatures and high loads, the zirconium oxide shrinks, and as a result, it is prone to falling off from the surface of the friction material along with the surrounding bead-like inorganic friction modifier.

[0038] The content of monoclinic zirconium oxide is preferably 5 to 30% by weight, more preferably 8 to 15% by weight, based on the total amount of the friction material composition.

[0039] By setting the content of monoclinic zirconium oxide within the above range, the bead-shaped inorganic friction modifier is more likely to fall off after being subjected to a history of high temperature and high load, and the braking effectiveness and the effect of suppressing an increase in the friction coefficient after being left in the cold are further improved.

[0040] The Mohs hardness of the friction couple according to the embodiment of the present invention is the old Mohs hardness scale, which is expressed as "1. talc, 2. gypsum, 3. calcite, 4. fluorite, 5. apatite, 6. orthoclase, 7. quartz, 8. topaz, 9. corundum, 10. diamond."

[0041] The average particle size in the friction couple according to the embodiment of the present invention is the value of the 50% particle size measured by a laser diffraction particle size distribution measurement method.

[0042] <Friction Material Composition> The friction material used in the friction couple according to the embodiment of the present invention includes a bead-shaped inorganic friction modifier, a porous inorganic friction modifier, and monoclinic zirconium oxide, each having an average particle size of 10 μm to 80 μm and a Mohs hardness of 7.5 or higher, as well as a binder, a fibrous base material, and a friction modifier that are typically used in friction materials, as a friction material composition.

[0043] Examples of the binder include binders that are commonly used in friction materials, such as straight 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 with aralkyl ethers and aldehydes, acrylic rubber-dispersed phenolic resin, silicone rubber-dispersed phenolic resin, and fluoropolymer-dispersed phenolic resin, and these may be used alone or in combination of two or more.

[0044] The content of the binder is preferably 5 to 10% by weight, more preferably 6 to 8% by weight, based on the total amount of the friction material composition.

[0045] Examples of the fiber base material include organic fibers that are commonly used in friction materials, such as aramid fibers, acrylic fibers, cellulose fibers, and poly-paraphenylene benzobisoxazole fibers, and these can be used alone or in combination of two or more.

[0046] The content of the fibrous base material is preferably 1 to 8% by weight, and more preferably 2 to 5% by weight, based on the total amount of the friction material composition.

[0047] As the friction modifier, a lubricant, an inorganic friction modifier, or an organic friction modifier can be used.

[0048] Examples of lubricants include metal sulfide-based lubricants such as tin sulfide, molybdenum disulfide, iron sulfide, bismuth sulfide, zinc sulfide, and composite metal sulfides, and carbonaceous lubricants such as artificial graphite, natural graphite, crushed graphite sheet powder, petroleum coke, coal coke, elastic graphitized carbon, and crushed polyacrylonitrile oxide fiber powder, and these can be used alone or in combination of two or more.

[0049] The content of the lubricant is preferably 3 to 10% by weight, more preferably 5 to 8% by weight, based on the total amount of the friction material composition.

[0050] Examples of inorganic friction modifiers include bead-shaped inorganic friction modifiers, porous inorganic friction modifiers, and monoclinic zirconium oxide, each having an average particle size of 10 μm to 80 μm and a Mohs hardness of 7.5 or higher, as well as calcium hydroxide, calcium carbonate, barium sulfate, talc, dolomite, columnar titanates, plate-shaped titanates, particulate titanates, scaly titanates, irregularly shaped titanates having a plurality of protrusions (titanates include potassium titanate, lithium potassium titanate, magnesium potassium titanate, and sodium titanate), wollastonite, and sepiolite, and these may be used alone or in combination of two or more.

[0051] The content of the inorganic friction modifier, including the bead-shaped inorganic friction modifier having an average particle size of 10 μm to 80 μm and a Mohs hardness of 7.5 or more, the monoclinic zirconium oxide, and the porous inorganic friction modifier, is preferably 20% by weight to 60% by weight, and more preferably 30% by weight to 50% by weight, based on the total amount of the friction material composition.

[0052] Examples of the organic friction modifier include cashew dust, ground tire tread rubber powder, polytetrafluoroethylene powder, and organic friction modifiers commonly used in friction materials, such as vulcanized or unvulcanized rubber powders of acrylic rubber, isoprene rubber, nitrile butadiene rubber, styrene butadiene rubber, butyl rubber, and silicone rubber, and these may be used alone or in combination of two or more.

[0053] The content of the organic friction modifier is preferably 3 to 10% by weight, more preferably 4 to 8% by weight, based on the total amount of the friction material composition.

[0054] <Method for manufacturing disc brake pads> Disc brake pads according to embodiments of the present invention are typically manufactured through the following steps: a mixing step in which predetermined amounts of friction material compositions (friction material raw materials) are uniformly mixed in a mixer to obtain a friction material raw material mixture; a heat-pressure molding step in which the obtained friction material raw material mixture is placed on a back plate that has been separately cleaned, surface-treated, and coated with an adhesive, and the resulting mixture is placed in a thermoforming mold and heated and pressurized to form a mold; a heat treatment step in which the obtained molded product is heated to complete the curing reaction of the binder; a painting step in which paint is applied by spray painting or electrostatic powder coating; a paint baking step in which the paint is baked; and a polishing step in which the friction surface is formed using a rotary grinding wheel. Note that the heat-pressure molding step may be followed in this order by the painting step, the heat treatment step that also serves as paint baking, and the polishing step.

[0055] If necessary, before the heat-pressure molding step, a granulation step of granulating the friction material raw material mixture, a kneading step of kneading the friction material raw material mixture, and a pre-molding step of pouring the friction material raw material mixture or the granulated product obtained in the granulation step and the kneaded product obtained in the kneading step into a pre-molding mold to mold a pre-molded product may be performed, and a scorching step may be performed after the heat-pressure molding step.

[0056] <Disc rotor with nitride layer formed on the surface of cast iron material> The disc rotor according to an embodiment of the present invention is a disc rotor made of cast iron that has been nitrided to form a nitrogen compound layer on the surface and a nitrogen diffusion layer underneath.

[0057] EXAMPLES The present invention will be explained in detail below by showing examples and comparative examples of the friction couple of the present invention, but the present invention is not limited to the following examples.

[0058] [Method for Manufacturing Disc Brake Pads According to Examples 1 to 15 and Comparative Examples 1 to 6] Friction material compositions having the compositions shown in Tables 1, 2, and 3 were charged into a Lödige mixer and mixed for 5 minutes to obtain a friction material composition mixture. This friction material composition mixture was pressurized in a molding die at 30 MPa for 10 seconds to obtain a friction material preform. This friction material preform was placed on a steel back plate that had been previously cleaned, surface-treated, and coated with an adhesive, and molded in a thermoforming 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. This 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 passenger vehicle disc brake pads according to Examples 1 to 15 and Comparative Examples 1 to 6.

[0059] <Friction coefficient after cold storage> Specifically, after 3,000 cycles of lapping, the sample was left for 2 hours in an environment at a temperature of 0°C and a humidity of 40% RH, and braking was repeated twice at 120-second intervals at a vehicle speed of 10 km / h with brake fluid pressures of 0.5 MPa, 1.0 MPa, and 1.5 MPa, with a 30-minute wait between each cycle, for a total of 5 cycles. The maximum friction coefficient of the 30 braking cycles was used for evaluation as the friction coefficient after cold storage. The evaluation criteria were as follows: Excellent (◎): Less than 0.52 Good (○): 0.52 or more and less than 0.56 Fair (△): 0.56 or more and less than 0.60 Poor (×): 0.60 or more

[0060] <Wear resistance> In accordance with JASO C427 "Automobiles - Brake linings and disc brake pads - Dynamometer wear test method," the wear amount (mm) of the friction material was measured under conditions of an initial braking speed of 50 km / h, a braking deceleration of 0.3 G, appropriate number of braking cycles, and a brake temperature before braking of 200°C, and was converted into the wear amount per 1000 braking cycles and evaluated. The evaluation criteria are as follows: Excellent (◎): Less than 0.20 mm Good (○): 0.20 mm or more and less than 0.25 mm Fair (△): 0.25 mm or more and less than 0.30 mm Poor (×): 0.30 mm or more

[0061] The evaluation results are shown in Tables 1, 2 and 3.

[0062] From Tables 1 and 2, it can be seen that none of the friction pairs in Examples 1 to 15 were evaluated as poor (×) in terms of friction coefficient and wear resistance. ・Excellent friction coefficient (◎) and excellent wear resistance (◎): Example 2 ・Excellent friction coefficient (◎) and good wear resistance (○): Examples 3, 7, and 14 ・Good friction coefficient (○) and excellent wear resistance (◎): Examples 1, 6, 10, and 13 ・Good friction coefficient (○) and good wear resistance (○): Example 9 ・Excellent friction coefficient (◎) and fair wear resistance (△): Examples 4, 5, and 8 ・Fair friction coefficient (△) and excellent wear resistance (◎): Example 12 ・Good friction coefficient (○) and fair wear resistance (△): Examples 11 and 15 ・Fair friction coefficient (△) and good wear resistance (○): None ・Fair friction coefficient (△) and fair wear resistance (△): None This grouping can be done.

[0063] In contrast to this, as can be seen from Table 3, for all of the friction pairs of Comparative Examples 1 to 6, at least one of the friction coefficient and the wear resistance was evaluated as unacceptable (x).

[0064] According to the present invention, a friction pair having a disc brake pad equipped with a friction material having a friction material composition that contains a binder, a fiber base material, and a friction modifier, but does not contain a copper component or iron-based metal fibers, and a disc rotor having a nitride layer formed on the surface of a cast iron material, can be provided, which has excellent braking effectiveness and suppresses an increase in the friction coefficient after being left in the cold, and is of extremely high practical value.

Claims

1. A friction couple comprising: a disc brake pad equipped with a friction material having a friction material composition containing a binder, a fibrous base material, and a friction modifier, but containing no copper component or iron-based metal fibers; and a disc rotor having a nitride layer formed on the surface of a cast iron material, wherein the friction material composition contains, as the friction modifier, 0.1 to 1% by weight, based on the total amount of the friction material composition, of a bead-shaped inorganic friction modifier having an average particle size of 10 μm to 80 μm and a Mohs hardness of 7.5 or higher; and 1 to 5% by weight, based on the total amount of the friction material composition, of a porous inorganic friction modifier.

2. The friction pair according to claim 1, wherein the bead-shaped friction material composition contains monoclinic zirconium oxide as a friction modifier in an amount of 5 to 30% by weight based on the total amount of the friction material composition.

3. A friction couple according to claim 1 or 2, characterized in that the bead-shaped inorganic friction modifier having a Mohs hardness of 7.5 or more is bead-shaped zirconium silicate.

4. A friction couple according to any one of claims 1 to 3, characterized in that the porous inorganic friction modifier is calcium silicate hydrate.

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