FRICTION MATERIAL

Abstract

In the friction material used for the disc brake pad, which is manufactured by forming a non-asbestos-organic (NAO) friction material composition, it is an object of this invention to provide the friction material that satisfies the laws and regulations with respect to the amount of the copper component contained therein and at the same time inhibits the generation of the just-before-stopping noise. In the friction material used for the disc brake pad, which is manufactured by forming a non-asbestos-organic (NAO) friction material composition that contains the binder, the fiber base, the inorganic friction modifier, the organic friction modifier, and the lubricant but does not contain the copper component, the friction material composition contains 0.5-5 weight %, relative to the entire amount of the friction material composition, of the fluoropolymer particle with the average particle diameter of 10-1000 μm as the lubricant and 15-35 weight %, relative to the entire amount of the friction material composition, of the zirconium oxide with the average particle diameter of 1-8 μm as the inorganic friction modifier.

Claims

1. A friction material used for a disc brake pad, which is manufactured by forming a non-asbestos-organic (NAO) friction material composition that contains a binder, a fiber base, an inorganic friction modifier, an organic friction modifier, and a lubricant but does not contain a copper component, wherein the friction material composition contains 0.5-5 weight %, relative to the entire amount of the friction material composition, of a fluoropolymer particle with an average particle diameter of 10-1000 μm as the lubricant and 15-35 weight %, relative to the entire amount of the friction material composition, of a zirconium oxide with an average particle diameter of 1-8 μm as the inorganic friction modifier.

2. The friction material according to claim 1, wherein the fluoropolymer particle is a polytetrafluoroethylene (PTFE).

Description

EMBODIMENTS OF THE INVENTION

[0020] In this invention, 0.5-5 weight %, relative to the entire amount of the friction material composition, of a relatively large fluoropolymer particle with an average particle diameter of 10-1000 μm and 15-35 weight %, relative to the entire amount of the friction material composition, of a relatively large zirconium oxide with an average particle diameter of 1-8 μm are arranged to be added to the friction material composition.

[0021] By adding 0.5-5 weight %, relative to the entire amount of the friction material composition, of the fluoropolymer particle with the average diameter of 10-1000 μm together with 15-35 weight %, relative to the entire amount of the friction material composition, of the zirconium oxide with the average particle diameter of 1-8 μm, which is smaller than the average particle diameter of the above-identified fluoropolymer particle, the fluoropolymer particle is refined or minimized by a grinding effect of the zirconium oxide, and fine powder of the fluoropolymer particle is uniformly dispersed in the abrasive powder of the friction material.

As the result, the abrasive powder tends not to be blended with the water, which inhibits the generation of the abrasive powder aggregate and prevents the causation of the just-before-stopping noise.

[0022] Preferable average particle diameter of the fluoropolymer particle is 20-100 μm, and preferable amount of the fluoropolymer contained in the friction material composition is 0.8-3 weight % relative to the entire amount of the friction material composition. Preferable average particle diameter of the zirconium oxide is 2-5 μm, and preferable amount of the zirconium oxide contained in the friction material composition is 20-30 weight % relative to the entire amount of the friction material composition.

[0023] As the fluoropolymer particle used in this invention, either one of the fluoropolymers such as a polytetrafluoroethylene (PTFE), a tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), or a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or any combination of two or more of the fluoropolymer particles may be used.

Among the above-fluoropolymer particles, a single use of the polytetrafluoroethylene (PTFE) powder is preferable.

[0024] In addition, in this invention, the average particle diameter means D50 measured by a laser diffraction particle size distribution method.

[0025] The friction material of this invention is manufactured from the friction material composition that contains, in addition to the above-identified fluoropolymer particle with the average particle diameter of 10-1000 μm and the zirconium oxide with the average particle diameter of 1-8 μm, a binder, fiber base, a lubricant, an inorganic friction modifier, an organic friction modifier, a pH modifier, and a filler that are normally used for the friction material.

[0026] As the binder, either one of the binders that are normally used for the friction material such as a straight phenol resin, a cashew oil modified phenol resin, an acrylic rubber modified phenol resin, a silicone rubber modified phenol resin, a nitrile rubber (NBR) phenol resin, a phenol aralkyl resin (aralkyl modified phenol resin), a fluoropolymer dispersed phenol resin, and a silicone rubber dispersed phenol resin, or any combination of two or more of the above-identified binders may be used.

The amount of the binder contained therein is preferably 5-10 weight % relative to the entire amount of the friction material composition, more preferably 6-8 weight % relative to the entire amount of the friction material composition.

[0027] As the fiber base, either one of the fiber bases that are normally used for the friction material such as an aramid fiber, a cellulose fiber, a poly-phenylene benzbisoxazole fiber, and an acrylic fiber, or any combination of two or more of the above-identified fiber base materials may be used.

The amount of the fiber base contained therein is preferably 1-10 weight % relative to the entire amount of the friction material composition, more preferably 2-4 weight % relative to the entire amount of the friction material composition.

[0028] As the lubricant, in addition to the above-identified fluoropolymer particle with the average diameter of 10-1000 μm, either one of lubricants that are normally used for the friction material such as carbon-based lubricants such as a petroleum coke, a resilient graphitic carbon, an artificial graphite particle, and a natural graphite particle, and metal sulfide group lubricants such as a molybdenum disulfide, a zinc sulfide, an iron sulfide, a tin sulfide, and a composite metal sulfide, or any combination of two or more of the above-identified carbon-based lubricants may be used.

The amount of the lubricant contained therein, together with the above-identified fluoropolymer particle with the average diameter of 10-1000 μm, preferably is 5-13 weight % relative to the entire amount of the friction material composition, more preferably 6-11 weight % relative to the entire amount of the friction material composition.

[0029] As the inorganic friction modifier, in addition to the above-identified zirconium oxide with the average particle diameter of 1-8 μm, either one of particle inorganic friction modifiers such as a vermiculite, a phlogopite, a muscovite, a triiron tetroxide, a calcium silicate, a magnesium oxide, a zirconium silicate, a γ-alumina, an α-alumina, a silicon carbide, and a non-whisker-like (plate-like, scale, columnar, indefinite shape having multiple projections) titanate (potassium hexatitanate, a potassium octatitnate, a lithium potassium titanate, or a magnesium potassium titanate) or fiber inorganic friction modifiers such as a wollastonite, a sepiolite, a basalt fiber, a glass fiber, or a biosoluble artificial mineral fibers, and a rock wool, or any combination of two or more of the above-identified inorganic friction modifiers may be used.

The amount of the inorganic friction modifier contained therein, together with the above-identified zirconium oxide with the average particle size of 1-8 μm, preferably is 40-75 weight % relative to the entire amount of the friction material composition, more preferably 45-70 weight % relative to the entire amount of the friction material composition.

[0030] As the organic friction modifier, either one of the organic friction modifiers that are normally used for the friction material such as a cashew dust, tire tread rubber pulverized powder, and vulcanized rubber powders or unvulcanized rubber powders such as a nitrile rubber, an acrylic rubber, a silicone rubber, and a butyl rubber, or any combination of two or more of the above-identified organic friction modifiers may be used.

The amount of the organic friction modifier contained therein preferably is 4-10 weight % relative to the entire amount of the friction material composition, more preferably 6-8 weight % relative to the entire amount of the friction material composition.

[0031] As the pH modifier, the pH modifiers that are normally used for the friction material such as a calcium hydroxide may be used. The amount of the pH modifier contained therein preferably is 1-4 weight % relative to the entire amount of the friction material composition, more preferably 2-3 weight % relative to the entire amount of the friction material composition.

[0032] As remaining materials in the friction material composition, fillers such as a barium sulfate and a calcium carbonate may be used.

[0033] The friction material of this invention, which is used for a disc brake, is manufactured through a mixing process to uniformly mix the predetermined amount of the friction material composition by a mixer, a heat-press-forming process to superpose the obtained raw friction material mixture on a separately prepared, prewashed, pre-surface-treated, and pre-adhesive-coated back plate to be positioned in a heat-forming die and to heat-press-form the raw friction material mixture and the back plate, a heat treatment process to heat the obtained item to complete a curing effect of the binder contained therein, a coating process to coat the cured item, a baking process to bake the coating thereon, and a grinding process to grind a surface of the resulted item to form a friction surface.

[0034] As necessary, prior to the heat-press-forming process, a granulating process to granulate the raw friction material mixture, or a kneading process to knead the raw friction material mixture, and a preforming process to position either the raw friction material mixture or the granulated item obtained through the granulating process and the kneaded item obtained through the kneading process in a pre-forming die and to form a preformed intermediate item, may be performed, and a scorching process may be performed after the heat-press-forming process.

[0035] This invention is explained concretely using the Embodiments and the Comparative Examples of this invention in the following sections; however, this invention is not limited to the following Embodiments.

Embodiments 1-17 and Comparative Examples 1-8 of the Manufacturing Method of the Friction Material

[0036] The friction material compositions shown in Tables 1-3 are positioned in the Loedige mixer to be mixed for about 5 minutes and is pressed in a pre-forming die under 30 MPa for about 10 seconds to obtain the preformed intermediate item. The preformed intermediate item is superposed on the steel back plate, which is pre-washed, pre-surface treated, and pre-adhesive coated, to be heat-press-formed in the heat forming die at 150 centigrade under the forming pressure of 40 MPa for about 10 minutes. Then, heat treatment at 200 centigrade is performed on the coated item for about 5 hours to perform the heat treatment (postcuring), and the friction surface of the friction material is grinded to finally form the disc brake pad for a passenger car. (Embodiments 1-17 and Comparative Examples 1-8).

TABLE-US-00001 TABLE 1 Embodiments 1 2 3 4 5 6 7 8 9 binder straight phenol resin 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 fiber base aramid fiber 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Lubricant zinc sulfide 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 graphite 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 polytetrafluoroethylene particle (average particle diameter of 8 μm) polytetrafluoroethylene 1.0 particle (average particle diameter of 10 μm) Polytetrafluoroethylene 1.0 particle (average particle diameter of 20 μm) polytetrafluoroethylene 1.0 0.5 0.8 3.0 5.0 particle (average particle diameter of 40 μm) polytetrafluoroethylene 1.0 particle (average particle diameter of 100 μm) polytetrafluoroethylene 1.0 particle (average particle diameter of 1000 μm) polytetrafluoroethylene particle (average particle diameter of 1200 μm) inorganic zirconium silicate 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 friction platy potassium hexatitanate 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 modifier magnesia mica 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 platy potassium hexatitanate 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 zirconium oxide (average particle diameter of 0.5 μm) zirconium oxide (average particle diameter of 1 μm) zirconium oxide (average particle diameter of 2 μm) zirconium oxide (average 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 particle diameter of 3 μm) zirconium oxide (average particle diameter of 5 μm) zirconium oxide (average particle diameter of 8 μm) zirconium oxide (average particle diameter of 10 μm) bio-soluble artificial mineral 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 fiber organic cashew dust 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 friction pulverized powder of tire 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 modifier tread rubber pH calcium hydroxide 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 modifier filler barium sulfate 19.0 19.0 19.0 19.0 19.0 19.5 19.2 17.0 15.0 Total (weight %) 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 evaluation product appearance G G G G G G G G G result just-before-stopping noise E E E G P P G E E braking effectiveness P G E E E E E G P brake noise E E E E E E E E E

TABLE-US-00002 TABLE 2 Embodiments 10 11 12 13 14 15 16 17 binder straight phenol resin 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 fiber base aramid fiber 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Lubricant zinc sulfide 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 graphite 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 polytetrafluoroethylene particle (average particle diameter of 8 μm) polytetrafluoroethylene particle (average particle diameter of 10 μm) polytetrafluoroethylene particle (average particle diameter of 20 μm) polytetrafluoroethylene particle 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 (average particle diameter of 40 μm) polytetrafluoroethylene particle (average particle diameter of 100 μm) polytetrafluoroethylene particle (average particle diameter of 1000 μm) polytetrafluoroethylene particle (average particle diameter of 1200 μm) inorganic zirconium silicate 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 friction platy potassium hexatitanate 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 modifier magnesia mica 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 triiron tetraoxide 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 zirconium oxide (average particle diameter of 0.5 μm) zirconium oxide (average particle 25.0 diameter of 1 μm) zirconium oxide (average particle 25.0 diameter of 2 μm) zirconium oxide (average particle 15.0 20.0 30.0 35.0 diameter of 3 μm) zirconium oxide (average particle 25.0 diameter of 5 μm) zirconium oxide (average particle 25.0 diameter of 8 μm) zirconium oxide (average particle diameter of 10 μm) bio-soluble artificial mineral fiber 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 organic cashew dust 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 friction pulverized powder of tire tread 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 modifier rubber pH modifier calcium hydroxide 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 filler barium sulfate 19.0 19.0 19.0 19.0 29.0 24.0 14.0 9.0 Total (weight %) 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 evaluation product appearance G G G G G G G G result just-before-stopping noise E E E G P P G E braking effectiveness P G E E E E E G brake noise E E E E E E E E

TABLE-US-00003 TABLE 3 Comparative Examples 1 2 3 4 5 6 7 8 binder straight phenol resin 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 fiber base aramid fiber 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Lubricant zinc sulfide 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 graphite 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 polytetrafluoroethylene particle 1.0 (average particle diameter of 8 μm) polytetrafluoroethylene particle (average particle diameter of 10 μm) polytetrafluoroethylene particle (average particle diameter of 20 μm) polytetrafluoroethylene particle 0.3 6.0 1.0 1.0 1.0 1.0 (average particle diameter of 40 μm) polytetrafluoroethylene particle (average particle diameter of 100 μm) polytetrafluoroethylene particle (average particle diameter of 1000 μm) polytetrafluoroethylene particle 1.0 (average particle diameter of 1200 μm) inorganic zirconium silicate 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 friction platy potassium hexatitanate 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 modifier magnesia mica 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 triiron tetraoxide 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 zirconium oxide (average particle 25.0 diameter of 0.5 μm) zirconium oxide (average particle diameter of 1 μm) zirconium oxide (average particle diameter of 2 μm) zirconium oxide (average particle 25.0 25.0 25.0 25.0 13.0 38.0 diameter of 3 μm) zirconium oxide (average particle diameter of 5 μm) zirconium oxide (average particle diameter of 8 μm) zirconium oxide (average particle 25.0 diameter of 10 μm) bio-soluble artificial mineral fiber 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 organic cashew dust 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 friction pulverized powder of tire tread 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 modifier rubber pH modifier calcium hydroxide 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 filler barium sulfate 19.0 19.0 19.7 14.0 19.0 19.0 31.0 6.0 Total (weight %) 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 evaluation product appearance G G G G G G G G result just-before-stopping noise E E E G P P G E braking effectiveness P G E E E E E G brake noise E E E E E E E E

[0037] The obtained friction material was evaluated as to the product appearance, the just-before-stopping noise, the braking effectiveness, and the brake noise.

Evaluation standard is shown in Table 4 and Table 5, and Evaluation Result is shown in Table 1, Table 2, and Table 3.

TABLE-US-00004 TABLE 4 product appearance evaluation method visual evaluation of product appearance evaluation items existence of wrinkles and cracks evaluation standard good wrinkles and crack no good no wrinkles and crack

TABLE-US-00005 TABLE 5 Just-before-stopping noise Braking Effectiveness Brake Noise Evaluation Method Actual Vehicle Test Based on JASO C406 Based on JASO C402 rubbing at the initial speed of (Passenger Car Brake Device (Passenger Car Brake Actual 30 km/h with the deceleration Dynamometer Test Method) Vehicle Test Method) speed of 0.1 G for 3000 braking 2nd Effect Test cycles vehicle speed of 130 km/h at the ↓ deceleration speed of 0.3 G leaving one night ↓ moving forward and backward twice at the initial speed of 10 km at 0.5-3.0 MPa (0.5 pitch) Evaluation Items Just-before-stopping noise Average Friction Coefficient Rage of Incidence of Brake (Sensory Evaluation) Noise Evaluation E No noise unless searching 0.40 or more 0% Standard (very slight rustling) G No noise unless searching 0.37 or more but less than 0.40 over 0% but less than 5% (bearable noise if existed) P Bearable noise 0.34 or more but less than 0.37 5% or more but less than 10% F Uncomfortable noise less than 0.34 10% or more — Unable to evaluate because of Unable to evaluate because of Unable to evaluate because of the product wrinkle or crack the product wrinkle or crack the product wrinkle or crack

[0038] As shown in the respective Table, the composition arrangements that satisfy the composition standard of this invention do not show an adverse effect on the noise prevention effect and shows satisfactory evaluation results for inhibiting the generation of the just-before-stopping noise.

INDUSTRIAL APPLICABILITY

[0039] According to this invention, in the friction material used for the disc brake pad, which is manufactured by forming the NAO friction material composition, this invention can offer the friction material that satisfies the laws and regulations with respect to the amount of the copper component contained therein and at the same time inhibits the generation of the just-before-stopping noise, thereby offering great practical value.