Friction material

Abstract

The present invention addresses the problem of providing a disc brake pad friction material, which is capable of securing fade resistance and wear resistance while satisfying laws relating to copper component content and for which coating by electrostatic powder coating is favorable. As a means for solving the problem, a friction agent composition, which contains 0.3-5 weight % of flake graphite particles of 1-100 m mean particle diameter with respect to the total amount of the friction material composition as a lubricant and in which the total amount of copper components contained in the friction material composition is less than 5 weight % of the total amount of the friction material composition, is used. Preferably, the flake graphite particles are aggregates. It is also preferable that the friction material composition contains mica with a mean particle diameter of 100-400 m.

Claims

1. A friction material utilized for a disc brake pad, which is manufactured by forming a friction material composition, wherein said friction material composition contains 4-12 weight % of a binder relative to the total amount of the friction material composition, 3-8 weight % of an organic friction modifier relative to the total amount of the friction material composition, 7-35 weight % of a sheet shape titanate relative to the total amount of the friction material composition, and 0.3-5 weight % of an exfoliated graphite particle with an average particle diameter of 1-100 m, relative to a total amount of the friction material composition as a lubricant and a total amount of a copper component contained in the friction material composition is less than 5 weight % relative to the total amount of friction material composition.

2. The friction material according to claim 1, wherein said exfoliated graphite particle is included in the friction material composition in a form of particle aggregates with an average particle diameter of 30-500 m.

3. The friction material according to claim 1, wherein the friction material composition further contains 2-10 weight % of mica with an average particle diameter of 100-400 m relative to a total amount of the friction material composition.

4. The friction material according to claim 2, wherein the friction material composition further contains 2-10 weight % of mica with an average particle diameter of 100-400 m relative to a total amount of the friction material composition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view of an example of the disc brake pad using the friction material of this invention for the disc brake pad.

DETAILED DESCRIPTION OF THE INVENTION

(2) In relation to the friction material utilized for the disc brake pad, which is manufactured by forming the friction material composition, the friction material composition contains 0.3-5.0 weight % of the exfoliated graphite particle with an average particle diameter of 1-100 m as the lubricant relative to the total amount of the friction material composition and the total amount of the copper component contained in the friction material composition is less than 5 weight % relative to the total amount of the friction material composition.

(3) The above-defined exfoliated graphite particle is a graphite particle having a graphene-like and high aspect ratio, which has higher thermal conductivity than the natural flake graphite, the kish graphite, and the pyrolytic graphite, that is conventionally used for the friction material, and the addition of the friction material composition as described above improves the heat radiation of the friction material.

(4) Also, since the above-defined exfoliated graphite particle has high conductivity, the exfoliated graphite particle provides the conductivity to the friction material and does not decrease the property of coating due to the electrostatic powder coating when eliminating the copper component.

(5) The above-defined exfoliated graphite particle is a graphite particle obtained by pulverizing the expanded graphite particle as the result of the heat-expanding the natural flake graphite, kish graphite, and/or pyrolytic graphite for several score times to several hundred times.

(6) The expanded graphite is manufactured by adding the highly concentrated sulfuric acid, nitric acid, and oxidizing agent to the graphite particle such as the natural flake graphite, the kish graphite, and pyrolytic graphite, reacting the mixture at an appropriate temperature for an appropriate period of time to compound the sulfuric acid-graphite intercalation compound, and after washing, heating the same at 1000 centigrade to expand the graphite 100-300 times in the thickness direction.

(7) The above-defined exfoliated graphite particle is manufactured through the method of pulverizing the expanded graphite particle obtained such as by the above-described process while the liquid being filled in the aperture of the expanded graphite particle or while the liquid being frozen, the method of spreading the expanded graphite particle within the liquid to apply ultra sound within the liquid, the method of spreading the expanded graphite particle and grinding the medium after forming the medium within the liquid, and the method of finely pulverizing the graphite slurry by a grinding mill after obtaining the graphite slurry as powdering the expanded graphite being immersed in the dispersive medium.

(8) The above-defined exfoliated graphite particle, for example, can be commercially obtainable Surface Enhanced Flake Graphite series (ASBURYCARBONS, INC.)

(9) Also, the exfoliated graphite particle is preferably contained in the friction material composition while being aggregated to form the particle aggregates without the binder.

(10) By adding the exfoliated graphite particle to the friction material composition in the form of particle aggregates, the exfoliated graphite particle may be dispersed evenly in the friction material. The average particle diameter of the particle aggregates is preferably 30-500 m.

(11) The exfoliated graphite particle aggregates may be produced through conventional methods such as the particle sizing method using the particle sizing machine as compressing the above-defined exfoliated graphite particle with the roller compactor and the granulation method of using the conventional granulator such as the rotary drum granulator, the fluidized bed granulator, and the tumbling fluidized bed granulator.

(12) The exfoliated graphite particle aggregates, for example, can be commercially obtainable C-THERM series (US trademark registration by TIMCALS. A.).

(13) The exfoliated graphite particle has significantly high conductivity relative to the surface direction of the exfoliating form. In the friction material for the disc brake pad, the heat dissipation on the frictional surface of the friction material needs to be improved, and therefore the exfoliated graphite particle is tilted to preferably arrange the exfoliated graphite particle surface to be parallel to the friction surface.

(14) Accordingly, to improve the orientation of the above-defined exfoliated graphite particle, 2-10 weight % of the mica with 100-400 m of average particle diameter is added as the inorganic friction modifier relative to the total amount of the friction material composition.

(15) The mica tends to orient parallel to the friction surface when the friction material composition is formed in the metallic forming die, and as described above, by adding the mica to the friction material composition, the material contained in the friction material composition is entirely oriented in the same direction.

(16) Also, in this invention, the average particle diameter is to be the particle diameter of 50% measured by the laser diffraction particle sizing method.

(17) By using the above-described friction material composition, in the friction material used for the disc brake pad, which is manufactured by forming the NAO friction material composition, while satisfying laws relating to the required amount of the copper component, the demanded performance of the fade resistance and the wear resistance are secured, and further the good application property of coating is provided by the electrostatic powder coating.

(18) The friction material of this invention is made of the friction material composition including such as the above-described exfoliated graphite particle or exfoliated graphite particle aggregates, other than the mica, a binder, a fiber base material, a titanate, a lubricant, an inorganic friction modifier, an organic friction modifier, a pH adjuster, and a filler conventionally used in the friction material.

(19) The binder may be one or any combination of two or more of the conventional binders such as a straight phenolic resin, a resin obtained by modifying a phenolic resin with cashew oil, silicone oil, or various elastomers such as acrylic rubber, an aralkyl modified phenolic resin obtained by reacting phenolic compounds, aralkyl ether compounds, and aldehyde compounds, a thermosetting resin dispersing such as various elastomers and fluorine polymer in the phenolic resin. The amount of the binder contained therein is preferably 4-12 weight % and more preferably 5-8 weight % relative to the total friction material composition.

(20) The fiber base material may be one or any combination of two or more of the conventionally used organic fiber for the friction material such as an aramid fiber, a cellulose fiber, a poly-P-phenylene benzbisoxazole fiber, and an acrylic fiber or a conventionally used metallic fiber for the friction material such as a copper fiber, a bronze fiber, a brass fiber, an aluminum fiber, and a zinc fiber.

(21) The amount of the organic fiber base contained therein is preferably 1-7 weight %, more preferably 2-4 weight % relative to the total amount of the friction material composition.

(22) The amount of metallic fiber contained therein is preferably less than 7 weight %, more preferably less than 4 weight % relative to the total friction material component. When the metallic fiber containing a copper component is to be used, the total amount of the copper component is preferably less than 5 weight %, more preferably less than 0.5 weight % relative to the total amount of the friction material composition. Furthermore, from the point of view of reducing the burden on the environmental impact, no copper component is preferably included in the friction material composition.

(23) The titanate is preferably in a sheet shape or plate-like and includes one or any combination of two or more of conventionally used titanate such as a potassium titanate, a lithium potassium titanate, and a magnesium potassium titanate. The amount of the titanate contained therein relative to the total amount of the friction material composition is preferably 7-35 weight %, more preferably 17-25 weight %.

(24) As the lubricant, other than the above-described exfoliated graphite particle or the exfoliated graphite particle aggregates, the lubricant may be one or any combination of two or more of the conventionally used metallic sulfide type lubricant such as a molybdenum disulfide, a tungsten sulfide, a stannic sulfide, and a composite metal sulfide and the conventionally used carbon type lubricant such as a graphite other than the exfoliated graphite particle, a petroleum coke, an activated carbon, and a pulverized polyacrylonitrile oxidized fiber powder. The amount of the lubricant contained therein, in addition to the above exfoliated graphite particle, is preferably 2-13 weight %, more preferably 5-10 weight % relative to the total amount of the friction material composition.

(25) For the inorganic friction modifier, other than the above-described mica, the inorganic friction modifier may be one or any combination of the two or more of the particle inorganic friction modifier such as a vermiculite, a magnetite, a calcium silicate hydrate, a glass beads, a magnesium oxide, a zirconium oxide, a zirconium silicate, an alumina, and a silicon carbide and the fiber inorganic friction modifier such as a wollastonite, a sepiolite, a basalt fiber, a glass fiber, a biodissolvable artificial mineral fiber, and a rock wool. The amount of the inorganic friction modifier contained therein, in addition to the above-described mica, is preferably 15-50 weight %, more preferably 20-45 weight % relative to the total amount of the friction material composition.

(26) The organic friction modifier may be one or any combination of two or more of the organic friction modifiers conventionally used for the friction material such as a cashew dust, a powder of tire tread rubber, a vulcanized rubber powder or an unvulcanized rubber powder such as a nitrile rubber, an acrylic rubber, a silicone rubber, and an isobutylene-isoprene rubber. The amount of the organic friction modifier contained therein is preferably 3-8 weight %, more preferably 4-7 weight % relative to the total amount of the friction material composition.

(27) The pH adjuster may be pH adjuster conventionally used for the friction material such as the calcium hydroxide. The amount of the pH adjuster is preferably 2-6 weight %, more preferably 2-3 weight % relative to the total amount of the friction material composition.

(28) As the remainders of the friction material composition, the filler such as barium sulfate and the calcium carbonate may be used.

(29) The friction material used in the disc brake of this invention is manufactured through the mixing step of uniformly mixing the predetermined amount of friction material composition oriented therein using a mixer, the heat press forming step of heat press forming the obtained raw friction material mixture positioned in the heat forming die superposed on the separately pre-cleaned, surface treated, and adhesive applied back plate, the heat treatment step of heating the obtained molded product to complete the cure reaction of the binder, the electrostatic powder coating step of coating the powder coating thereon, the baking step of baking the coating, and the grinding step of forming the friction surface by the rotary grinding wheel. Also, after the heat press forming step, the heat treatment step performing both the coating step and baking step may be replaced before the grinding step.

(30) As necessary, prior to the heat press forming step, the granulation step of granulating the raw friction material mixture, the kneading step of kneading the raw friction material, and the pre-forming step of forming an unfinished preformed article by positioning the raw friction material mixture or the granulation obtained through the granulation step and the kneaded article obtained through the kneading step into the pre-forming die, are performed, and after the heat press forming step, the scorching step is performed.

Embodiments

(31) In the following sections, the embodiments and the comparative examples are shown; however, this invention is not limited to the embodiments described below.

(32) [Manufacturing Method for Friction Material in Embodiments 1-11 and Comparative Examples 1-6]

(33) The friction material composition shown in TABLE 1 and TABLE 2 is mixed for 5 minutes by the Loedige mixer and is pressed in the forming die under 30 MPa for 10 seconds to perform the preforming. This preforming product is superposed on the pre-cleaned, surface treated, adhesive coated steel back plate to form for 10 minutes in the heat forming die at the forming temperature of 150 centigrade under the forming pressure of 40 MPa, to heat treatment (post-curing) for 5 hours at 200 centigrade, to coat the epoxy resin powder coating by the electrostatic powder coating device, to heat to bake the coating for 4 minutes at 220 centigrade by the mid infrared ray heater, and to grind to form the friction surface for the disc brake pad of the automotive (Embodiments 1-11 and Comparative Examples 1-6).

(34) The fade resistance, the wear resistance, and the property of coating of the obtained friction material is evaluated. The results of the evaluation are shown in the TABLE 3 and TABLE 4 and the evaluation standard is shown in the TABLE 5.

(35) TABLE-US-00001 TABLE 1 E1 E2 E3 E4 E5 E6 E7 E8 E9 E10 E11 Binder Straight 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 Phenollic Resin Organic Aramid 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Fiber fiber Metallic Copper 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.0 Fiber Fiber Titanate Sheet 19.0 19.0 19.0 19.0 19.0 19.0 19.0 19.0 19.0 19.0 19.0 shape Potassium Titanate Lubricant Molybdenum 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Disulfide Flake Graphite (Average Particle Diameter: 0.5 m) Flake 5.0 Graphite (Average Particle Diameter: 1 m) Flake 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Graphite (Average Particle Diameter: 70 m) Flake 0.3 Graphite (Average Particle Diameter: 100 m) Flake Graphite (Average Particle Diameter: 200 m) Flake 3.0 3.0 Graphite Particle Aggregates Natural Squamous Graphite (Average Particle Diameter 100 m) Cokes 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Inorganic Alumina 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Friction Zirconium 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Modifier Silicate Zirconium 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 Oxide Magnetite 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Mica 10.0 (Average Particle Diameter: 50 m) Mica 6.0 10.0 13.0 6.0 6.0 6.0 6.0 (Average Particle Diameter: 100 m) Mica 1.0 2.0 (Average Particle Diameter: 400 m) Mica 2.0 (Average Particle Diameter: 500 m) Organic Cashew 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 Friction Dust Modifier Powder of 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Tire Tread Rubber pH Calcium 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 adjuster Hydroxide Filler Barium 19.7 22.0 21.0 21.0 13.0 13.0 10.0 17.0 15.0 17.0 13.0 Sulfate Total (Weight %) 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 E = Embodiment

(36) TABLE-US-00002 TABLE 2 CE 1 CE 2 CE 3 CE 4 CE 5 CE 6 Binder Straight Phenollic Resin 6.0 6.0 6.0 6.0 6.0 6.0 Organic Fiber Aramid fiber 3.0 3.0 3.0 3.0 3.0 3.0 Metallic Fiber Copper Fiber 0.0 0.0 0.0 0.0 10.0 0.0 Titanate Sheet shape Potassium 19.0 19.0 19.0 19.0 19.0 19.0 Titanate Lubricant Molybdenum Disulfide 2.0 2.0 2.0 2.0 2.0 2.0 Flake Graphite (Average 5.0 Particle Diameter: 0.5 m) Flake Graphite (Average 6.0 Particle Diameter: 1 m) Flake Graphite (Average Particle Diameter: 70 m) Flake Graphite (Average 0.1 Particle Diameter: 100 m) Flake Graphite (Average 0.3 Particle Diameter: 200 m) Flake Graphite Particle Aggregates Natural Squamous Graphite 3.0 3.0 (Average Particle Diameter 100 m) Cokes 2.0 2.0 2.0 2.0 2.0 2.0 Inorganic Alumina 1.0 1.0 1.0 1.0 1.0 1.0 Friction Zirconium Silicate 5.0 5.0 5.0 5.0 5.0 5.0 Modifier Zirconium Oxide 25.0 25.0 25.0 25.0 25.0 25.0 Magnetite 3.0 3.0 3.0 3.0 3.0 3.0 Mica (Average Particle Diameter: 50 m) Mica (Average Particle 6.0 6.0 6.0 6.0 6.0 6.0 Diameter: 100 m) Mica (Average Particle Diameter: 400 m) Mica (Average Particle Diameter: 500 m) Organic Cashew Dust 4.0 4.0 4.0 4.0 4.0 4.0 Fliction Powder of Tire Tread Rubber 2.0 2.0 2.0 2.0 2.0 2.0 Modifier pH adjuster Calcium Hydroxide 2.0 2.0 2.0 2.0 2.0 2.0 Filler Barium Sulfate 19.9 19.7 14.0 15.0 7.0 17.0 Total (Weight %) 100.0 100.0 100.0 100.0 100.0 100.0 CE = Comparative Example

(37) TABLE-US-00003 TABLE 3 E1 E2 E3 E4 E5 E6 E7 E8 E9 E10 E11 Stability of Friction Coefficient Fade Resistance Wear Resistance Property of Coating E = Example

(38) TABLE-US-00004 TABLE 4 CE1 CE2 CE3 CE4 CE5 CE6 Stability of Friction X X Coefficient Fade Resistance X X X Wear Resistance Property of X X Coating CE = Comparative Example

(39) TABLE-US-00005 TABLE 5 Stability of Friction Fade Property of Item of Evaluation Coefficient Resistance Wear Resistance Coating Evaluation Test JASO C406 JASO C427 Visual Check on Method Condition Passenger Car - Braking Brake Lining and the Coating Device - Dynamometer Disc Brake Pad - Condition of the Test Procedures Wear Test Friction Side Surface Procedure on Interia Dynamometer Evaluation 2nd Average 1st Fade 200 Centigrade Content Effectiveness Minimum Wear Amount Determination 0.40 or more 0.25 or more less than 0.10 mm Entirely Uniformly Standard Coated 0.37 or more, 0.22 or more, 0.10 mm or more, Entirely Coated less than 0.40 less than 0.25 less than 0.15 mm but Surface Irregularity Exists 0.34 or more, 0.19 or more, 0.15 mm or more, Uncoated less than 0.37 less than 0.22 less than 0.20 mm Portion Exists X less than 0.34 less than 0.19 0.20 mm or more No Coating

(40) According to this invention, in the friction material which is manufactured by forming the NAO friction material composition, the friction material secures the demanded performance of the fade resistance and the wear resistance, while satisfying laws of the required amount of the copper component contained therein and further provides good application property of coating by the electrostatic powder coating, which provides an extreme practical valuable.

(41) TABLE-US-00006 Brief Explanation of the References 1. Disc Brake Pad 2. Back Plate 3. Friction Material