Friction Material

Abstract

[OBJECT]

The present invention provides a friction material used for a disc brake pad, which is manufactured by forming a non-asbestos-organic (NAO) friction material composition, which is able to suppress an occurrence of noise just before a vehicle stops, while satisfying laws and regulations relating to the required amount of the content of the copper component.

[MEANS TO SOLVE THE PROBLEM]

The friction material for the disc brake pad is manufactured by forming the NAO friction material composition that is free of the copper component, the friction material composition practically does not include an iron component but includes 15-22 weight % of a non-whisker-like titanate, relative to the total amount of the friction material composition, as a titanate, 15-25 weight % of zirconium oxide with the average particle diameter of 1.0-4.0 μm, relative to the total amount of the friction material composition, as the inorganic friction modifier, and 4-6 weight % of cleavable mineral particles, relative to the total amount of the friction material composition, 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 is free of a copper component, wherein the friction material composition practically does not include an iron component but includes 15-25 weight % of a non-whisker-like titanate, relative to the total amount of the friction material composition, as the titanate, 15-25 weight % of zirconium oxide with the average particle diameter of 1.0-4.0 μm, relative to the total amount of the friction material composition, as an inorganic friction modifier, and 4-6 weight % of cleavable mineral particles, relative to the total amount of the friction material composition, as an inorganic friction modifier.

2. The friction material according to claim 1, wherein the non-whisker-like titanate is potassium titanate in an infinite shape.

3. The friction material according to claim 1, wherein the friction material composition includes 2-4 weight % of flaky graphite particles relative to the total amount of the friction material composition as a carbonaceous lubricant.

4. The friction material according to claim 2, wherein the friction material composition includes 2-4 weight % of flaky graphite particles relative to the total amount of the friction material composition as a carbonaceous lubricant.

Description

EMBODIMENT OF THE INVENTION

[0029] In the present invention, in order to suppress the wear of the mating member, 15-25 weight % of the non-whisker-like titanate relative to the total amount of the friction material composition as the titanate and 15-25 weight % of zirconium oxide with the average particle diameter of 1.0-4.0 μm relative to the total amount of the friction material composition as the inorganic friction modifier, are added thereto.

[0030] In the present invention, non-whisker-like titanate means titanate that is not in an acicular or whisker shape with the aspect ratio of 3 or more, and more concretely it means a platy titanate shaped in such as polygon, circle, or oval, or a titanate having an amoebic shape or a shape such as a piece of jigsaw puzzle as shown in the international publication no. 2008/123046.

[0031] By adding relatively large amount of the non-whisker-like titanate and the small particle sized zirconium oxide to the friction material composition, a film made of titanate and zirconium oxide is formed on the friction surface of the mating member.

[0032] This film prevents direct-grinding of the friction surface of the mating member by the inorganic friction modifier contained in the friction material acting as a grinding factor, thereby suppressing the generation of the abrasion powder of the mating member.

[0033] If the amount of the non-whisker-like titanate and zirconium oxide is insufficient, the problem that the sufficient inhibitory effect on the abrasive wear for the mating member cannot be obtained, may occur, and if the amount of the non-whisker-like titanate and zirconium oxide is excessive, the problem that the braking effectiveness becomes unstable, may occur.

[0034] Also, if the average particle diameter of the zirconium oxide is too small, the problem that the cracks tend to occur in the friction material due to deterioration of moldability of the friction material, may occur, and if the average particle size of the zirconium oxide is excessively large, the problem that the braking effectiveness becomes unstable, may occur.

[0035] The present invention, as an average particle diameter, uses a particle diameter (D50) measured by a laser diffraction method.

[0036] Furthermore, in the present invention, in order to suppress the generation of the abrasion powder aggregate, 4-6 weight % of the cleavable mineral particles relative to the total amount of the friction material composition is added therein.

[0037] The abrasion powder of the cleavable mineral particle discharged from the friction material is in a platy shape, and it is expected that if the platy particle is blended in the abrasion powder aggregates, slipping among the abrasion powder near the platy particle occurs, which tends to deteriorates the abrasive powder aggregate.

[0038] If the amount of cleavable mineral particles contained therein is insufficient, the problem that the inhibitory effect to prevent the generation of the abrasion powder aggregate cannot be obtained sufficiently, may occur, and if the amount of cleavable mineral particles contained therein is excessive, the friction surface of the mating member becomes like a mirror-finished surface, the problem that the brake squeaking tend to occur due to a sudden increase of the friction coefficient at the moisture absorption period, may occur.

[0039] Materials for the cleavable mineral particles may be such as mica and vermiculite, and one or combination of two materials may be used.

[0040] The average particle diameter of the cleavable mineral particle is preferably 50-700 μm, but the average diameter of 300-600 μm is more preferable.

[0041] Then, the friction material composition of the present invention practically does not contain the iron component, thereby suppressing the generation of rust that could be a factor to increase the cohesive force of the abrasion powder aggregate. Here, the definition for the iron component not practically contained is that materials having iron as a main component such as iron, iron alloy, and iron compounds is not added to the friction material composition.

[0042] The non-whisker-like titanate may be such as potassium titanate, lithium potassium titanate, and magnesium potassium titanate, and one or any combination of two or more of the above-mentioned titanate may be used; however, it is preferable to use an infinite shape potassium titanate alone.

[0043] When the infinite shape potassium titanate is used, while multiple potassium titanate pieces are complexly superposing each other, the composite film with the zirconium oxide is formed on the friction surface of the mating member. This composite film shows more strength than the film formed when the platy titanate is in use, and more preferable inhibitory effect for wearing of the mating member may be obtained.

[0044] Further, in the present invention, when in the low load braking action, because the abrasion powder tends to be discharged from the friction surface between the friction material and the mating member, 2-4 weight % of the flaky graphite particles relative to the total amount of the friction material composition is added to the friction material composition as the carbonaceous lubricant.

[0045] The flaky graphite particles may be obtained by precisely crushing the expanded graphite particles that are obtained by thermally expanding the particles of such as a natural squamous graphite, a kish graphite, and a pyrolytic graphite dozens of times or hundreds of times.

[0046] If the abrasion powder itself does not have the lubricity, the abrasion powder, while not being discharged from the friction surfaces of the friction material and the mating member, is accumulated in fine unevenness on the friction surfaces of the friction material and/or the mating member, which tends to generate the abrasion powder aggregate that could be a cause of the noise; however, by adding an appropriate amount of the flaky graphite particles to the friction material composition, the flaky graphite particles are blended in the generated abrasion powder, which provides lubricity to the abrasion powder itself, thereby smoothly ejecting the abrasion powder without accumulating in the fine unevenness on the above-described friction surfaces.

[0047] The friction material in the present invention is made from the friction material composition that includes conventional materials used for the friction material such as the binder, the fiber base, the lubricant, the inorganic friction modifier, the organic friction modifier, the pH adjuster, the filler or the like, in addition to the above-described non-whisker-like titanate, the zirconium oxide with the average particle diameter of 1.0-4.0 μm, the cleavable mineral particles, and the flaky graphite particles

[0048] The binder may be one or any combination of two or more of conventionally used binders for the friction material, selected from such as a straight phenolic resin, a resin obtained by modifying the phenolic resin with cashew oil, silicone oil, or various elastomers such as an acrylic rubber, an aralkyl modified phenolic resin obtained by reacting the phenolic compound, aralkyl ether compound and aldehyde compound, the thermosetting resin dispersing such as various elastomers or fluorine-containing polymer in the phenolic resin or the like. The content of the binder is preferably 5-8 weight % relative to the total amount of the friction material composition but more preferably 6-7 weight % relative to the total amount of the friction material composition.

[0049] The fiber base may be one or any combination of two or more of the conventionally used organic fibers for the friction material such as an aramid fiber, a cellulosic fiber, a poly-p-phenylenebenzobisoxazole (PBO) fiber, and an acrylic fiber. The content of the fiber base is preferably 1-4 weight % relative to the total amount of the friction material composition but more preferably 2-3 weight % relative to the total amount of the friction material composition.

[0050] The lubricant, other than the above described flaky graphite particles, may be one or any combination of two or more materials selected from the carbonaceous lubricant such as a petroleum coke, an artificial graphite particles, and a natural graphite particles, and metal sulfide type lubricant such as a molybdenum disulfide, a zinc sulfide, a tin sulfide, and a composite metal sulfide. The content of the lubricant is preferably 4-8 weight % relative to the total amount of the friction material composition together with the above-described flaky graphite particles but more preferably 5-7 weight % relative to the total amount of the friction material composition.

[0051] The inorganic friction modifier, other than the above-described zirconium oxide with the average particle diameter of 1.0-4.0 μm and the cleavable mineral particles with the average particle diameter of 300-600 μm, the inorganic friction modifier may be one or any combination of two or more of the materials selected from a particulate inorganic friction modifier such as a calcium silicate, a magnesium oxide, a y alumina, and a zirconium silicate, and a fibrous inorganic friction modifier such as a wollastonite, a sepiolite, a basalt fiber, a grass fiber, a biosoluble artificial mineral fiber, and rock wool.

[0052] The content of the inorganic friction modifier, together with the above-described zirconium oxide with the average particle diameter of 1.0-4.0 μm and the cleavable mineral particle with the average particle diameter of 300-600 μm, is preferably 25-40 weight % relative to the total amount of the friction material composition but more preferably 30-35 weight % relative to the total amount of the friction material composition.

[0053] The organic friction modifier may be one or any combination of two or more of the materials selected from the organic friction modifiers conventionally used for the friction material such as a cashew dust, pulverized powders of the tire tread rubber, a vulcanized rubber powder or an unvulcanized rubber powder such as a nitrile rubber, an acrylic rubber, a silicone rubber, and a butyl rubber.

[0054] The content of the organic friction modifier is preferably 4-8 weight % relative to the total amount of the friction material composition but more preferably 5-7 weight % relative to the total amount of the friction material composition.

[0055] The pH adjuster may be a conventionally used pH adjuster for the friction material such as the calcium hydroxide.

[0056] The pH adjuster is preferably 1-5 weight % relative to the total amount of the friction material composition but more preferably 2-4 weight % relative to the total amount of the friction material composition.

[0057] The filler such as the barium sulfate and the calcium carbonate is used as the remaining portion of the friction material composition.

[0058] The friction material of this invention used for the disc brake is manufactured through a mixing step to obtain a raw friction material mixture by uniformly mixing the predetermined amount of the friction material composition using a mixer, a heat press forming step to obtain a molded product by heat press forming the raw friction material mixture positioned in the heat forming die superposed on the separately pre-cleaned, surface treated, and adhesive applied back plate, a heat treatment step of heating the molded product to complete the cure reaction of the binder thereon, a coating step of applying the coating thereon, a baking step of baking the coating thereon, and a grinding step of forming the friction surface.

[0059] 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 mixture, and the pre-forming step of forming an unfinished preformed article by positioning the raw friction material mixture, the granulated raw friction material mixture obtained through the granulation step or the kneaded raw friction material mixture obtained through the kneading step into the pre-forming die, are performed. In addition, after the heat press forming step, the scorching step may be performed.

Embodiments

[0060] In the following sections, the embodiments and the comparative examples are disclosed to concretely explain this invention; however, this invention is not limited to the following embodiments.

[The Manufacturing Method of the Friction Material of Embodiments 1-20/Comparative Examples 1-8]

[0061] The each 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 form an unfinished pre-forming article. This unfinished pre-forming article is superposed on the previously cleaned, surface-treated and adhesive-coated steel back plate to form for 10 minutes in the heat press 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, and to grind to form the friction surface for the disc brake pad of the passenger car (Embodiments 1-20 and Comparative Examples 1-8).

TABLE-US-00001 TABLE 1 Embodiments 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Binder Straight 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 Phenolic Resin Fiber Aramid 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Fiber Carbon Coke 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Type Flaky 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Lubricant Graphite Particle Metal Zinc Sulfide 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Sulfide Type Lubricant Titanate Potassium 20.0 15.0 25.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 Titanate (Infinite Shape) Potassium 20.0 Titanate (Platy Shape) Lithium 20.0 Potassium Titanate (Platy Shape) Inorganic Biosoluable 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Friction Rock Wool Modifier Zirconium Oxide (Average Particle Diameter = 0.5 μm) Zirconium 20.0 Oxide (Average Particle Diameter = 1.0 μm) Zirconium 20.0 20.0 20.0 20.0 20.0 15.0 25.0 20.0 20.0 20.0 20.0 20.0 Oxide (Average Particle Diameter = 2.0 μm) Zirconium 20.0 Oxide (Average Particle Diameter = 4.0 μm) Zirconium Oxide (Average Particle Diameter = 5.0 μm) Zirconium 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Silicate Mica 5.0 (Average Particle Diameter = 50 μm) Mica 5.0 (Average Particle Diameter = 100 μm) Mica 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 (Average Particle Diameter = 300 μm) Mica 5.0 (Average Particle Diameter = 600 μm) Mica 5.0 (Average Particle Diameter = 700 μm) Vermiculite 5.0 (Average Particle Diameter = 600 μm) γ-Alumina 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Organic Cashew 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Friction Dust Modifier Pulverized 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Powder Of Tire Tread Rubber pH Calcium 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Adjuster Hydroxide Filler Barium 24.0 24.0 24.0 29.0 19.0 24.0 24.0 29.0 19.0 24.0 24.0 24.0 24.0 24.0 Sulfate Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

TABLE-US-00002 TABLE 2 Embodiments Comparative Examples 15 16 17 18 19 20 1 2 3 4 5 6 7 8 Binder Straight 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 Phenolic Resin Fiber Aramid 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Fiber Carbon Coke 2.0 2.0 4.0 3.0 1.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Type Flaky 3.0 3.0 1.0 2.0 4.0 5.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Lubricant Graphite Particle Metal Zinc Sulfide 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Sulfide Type Lubricant Titanate Potassium 20.0 20.0 20.0 20.0 20.0 20.0 10.0 30.0 20.0 20.0 20.0 20.0 20.0 20.0 Titanate (Infinite Shape) Potassium Titanate (Platy Shape) Lithium Potassium Titanate (Platy Shape) Inorganic Biosoluable 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Friction Rock Wool Modifier Zirconium 20.0 Oxide (Average Particle Diameter = 0.5 μm) Zirconium Oxide (Average Particle Diameter = 1.0 μm) Zirconium 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 10.0 30.0 20.0 20.0 Oxide (Average Particle Diameter = 2.0 μm) Zirconium Oxide (Average Particle Diameter = 4.0 μm) Zirconium 20.0 Oxide (Average Particle Diameter = 5.0 μm) Zirconium 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Silicate Mica (Average Particle Diameter = 50 μm) Mica (Average Particle Diameter = 100 μm) Mica 4.0 6.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 3.0 7.0 (Average Particle Diameter = 300 μm) Mica (Average Particle Diameter = 600 μm) Mica (Average Particle Diameter = 700 μm) Vermiculite (Average Particle Diameter = 600 μm) γ-Alumina 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Organic Cashew 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Friction Dust Modifier Pulverized 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Powder Of Tire Tread Rubber pH Calcium 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Adjuster Hydroxide Filler Barium 25.0 23.0 24.0 24.0 24.0 24.0 34.0 14.0 24.0 24.0 34.0 14.0 26.0 22.0 Sulfate Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

[0062] The obtained friction materials were evaluated with respect to the noise, the stability of braking effectiveness, the brake squeaking, and the product appearance. The results of the evaluation are shown in TABLE 3 and TABLE 4 while the evaluation standards are shown in TABLE 5 and TABLE 6.

TABLE-US-00003 TABLE 3 Embodiments 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Evaluation Noise ⊚ ◯ ◯ Δ ⊚ Δ ◯ ◯ ⊚ ◯ ⊚ ⊚ ⊚ ⊚ Result Stability of ⊚ ◯ ◯ ⊚ Δ ◯ Δ ⊚ Δ ⊚ ⊚ ⊚ ⊚ ⊚ Braking Effectiveness Squeaking Noise ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ◯ ◯ Product ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Appearance

TABLE-US-00004 TABLE 4 Embodiments Comparative Examples 15 16 17 18 19 20 1 2 3 4 5 6 7 8 Evaluation Result Noise ◯ ⊚ ◯ ⊚ ⊚ ⊚ X ⊚ — ◯ X ⊚ X ⊚ Stability of Braking ⊚ ⊚ ⊚ ⊚ ⊚ ◯ ⊚ X — X ⊚ X ⊚ ⊚ Effectiveness Squeaking Noise ⊚ ◯ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ — ⊚ ⊚ ⊚ ⊚ X Product Appearance ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ X ◯ ◯ ◯ ◯ ◯

TABLE-US-00005 TABLE 5 Noise Stability of Braking Effectiveness Squeaking Noise Evaluation Method Actual Vehicle Test Based on JASO C406 Burnish Burnish Passenger Car - Braking Device - Based on JASO C406 Initial Velocity: 30 km/h, Dynamometer Test Procedures Passenger Car - Braking Device - Deceleration: 0.1G Dynamometer Test Procedures Braking Cycle: 3,000 ↓ ↓ Assembled in the Actual Vehicle Allowed to Stand Overnight and Allowed to Stand Overnight ↓ ↓ 0.5-3.0 MPa (0.5 pitch) Initial Velocity: 5 km/h, Initial Velocity: 10 km/h Deceleration: 0.1G Forwarding and Backwarding: Braking Cycle: 10 twice Evaluation Items Noise at Vehicle Stopping Difference Between Friction High Frequency Noise (Sensory Evaluation) Coefficience (Average Value) on (Secondary Evaluation) of 2 kHz Low Temperature Effectiveness or more Test and Friction Coefficience (Sensory Evaluation) (Average Value) on Second Effectiveness Test Evaluation ⊚ Noise Discoverable Only After 0% or More but Less Than 3% No noise Standard Serous Attempts to Create Noise (Light Sliding Sound Level) ◯ Noise Discoverable Only After 3% or More but Less Than 6% Minimum Level Noise Serous Attempts to Create Noise (Bearable Level if Discovered) Δ Noise but Bearable Level 6% or More but Less Than 10% Small Noise X Disturbing Noise 10% or More Medium Level Noise — No Evaluation Because of No Evaluation Because of No Evaluation Because of Wrinkle or Crack on the Product Wrinkle or Crack on the Product Wrinkle or Crack on the Product

TABLE-US-00006 TABLE 6 Product Appearance Evaluation Method Visual Check on Product Appearance Evaluation Item Existence of Wrinkle and Crack Evaluation ◯ No Wrinkle or Crack Standard X Wrinkle or Crack

INDUSTRIAL APPLICABILITY

[0063] The present invention provides the friction material used for a disc brake pad, which is manufactured by forming a non-asbestos-organic (NAO) friction material composition, which is able to suppress the occurrence of noise just before the vehicle stops, while satisfying laws and regulations relating to the required amount of the content of the copper component.