Frictional material composition, frictional material, and friction member

Abstract

The present invention is concerned with a frictional material composition not containing copper as an element or having the content of copper of 0.5 mass % or less, the composition containing (A) potassium titanate; and (B) one or more selected from the group consisting of lithium potassium titanate and magnesium potassium titanate, in a total content of the component (A) and the component (B) of 10 to 35 mass %, wherein on heating a molded product of the frictional material composition to 500 C. at a temperature rise rate of 10 C./min under an air atmosphere, the mass reduction rate is 5 to 20%.

Claims

1. A frictional material composition not containing copper as an element or having the content of copper of 0.5 mass % or less, the composition comprising: (A) potassium titanate in an amount of 5 mass % or more; (B) one or more selected from the group consisting of lithium potassium titanate and magnesium potassium titanate in an amount of 5 mass % or more; (C) one or more selected from the group consisting of zirconium silicate, zirconium oxide, and magnesium oxide in an amount of 12 to 30 mass %; one or more selected from the group consisting of iron, tin, zinc, and aluminum in an amount of 0 to 3 mass % as a metal powder or a metal fiber; barium sulfate in an amount of 7 to 49 mass %; wherein: a total content of the component (A) and the component (B) is 10 to 30 mass %, and on heating a molded product of the frictional material composition to 500 C. at a temperature rise rate of 10 C./min under an air atmosphere, the mass reduction rate is from 10-17%.

2. The frictional material composition according to claim 1, wherein the one or more selected from the group consisting of iron, tin, zinc, and aluminum is present in an amount of 0.5 to 3 mass %.

3. The frictional material composition according to claim 1, wherein a content ratio of the component (A) and the component (B) [(A)/(B)] is from 0.1 to 10 in terms of a mass ratio.

4. The frictional material composition according to claim 1, further comprising an organic filler in an amount of 2 to 20 mass %.

5. The frictional material composition according to claim 1, further comprising a binder in an amount of 5 to 20 mass %.

6. A frictional material including a portion not containing copper as an element or having the content of copper of 0.5 mass % or less, the portion comprising: (A) potassium titanate in an amount of 5 mass % or more; (B) one or more selected from the group consisting of lithium potassium titanate and magnesium potassium titanate in an amount of 5 mass % or more; (C) one or more selected from the group consisting of zirconium silicate, zirconium oxide, and magnesium oxide in an amount of 12 to 30 mass %; one or more selected from the group consisting of iron, tin, zinc, and aluminum in an amount of 0 to 3 mass % as a metal powder or a metal fiber; barium sulfate in an amount of 7 to 49 mass %; wherein: a total content of the component (A) and the component (B) is 10 to 30 mass %, and on heating to 500 C. at a temperature rise rate of 10 C./min under an air atmosphere, the mass reduction rate is from 5 to 20%.

7. The frictional material according to claim 6, wherein the one or more selected from the group consisting of iron, tin, zinc, and aluminum in present in an amount of 0.5 to 3 mass %.

8. The frictional material according to claim 6, wherein a content ratio of the component (A) and the component (B) [(A)/(B)] is from 0.1 to 10 in terms of a mass ratio.

9. The frictional material according to claim 6, further comprising an organic filler in an amount of 2 to 20 mass %.

10. The frictional material according to claim 6, further comprising a binder in an amount of 5 to 20 mass %.

11. A friction member comprising the frictional material according to claim 6 and a backing plate integrated therewith.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The frictional material composition, the frictional material, and the friction member according to the present embodiments are hereunder described in detail, but it should be construed that the present invention is not limited to the following embodiments.

(2) The frictional material composition and the frictional material according to the present embodiments do not contain asbestos and are so-called non-asbestos frictional material composition and non-asbestos frictional material, respectively.

(3) [Frictional Material Composition]

(4) The frictional material composition according to the present embodiment is a frictional material composition not containing copper as an element or having the content of copper of 0.5 mass % or less, the composition containing

(5) (A) potassium titanate; and

(6) (B) one or more selected from the group consisting of lithium potassium titanate and magnesium potassium titanate,

(7) in a total content of the component (A) and the component (B) of 10 to 35 mass %, wherein

(8) on heating a molded product of the frictional material composition to 500 C. at a temperature rise rate of 10 C./min under an air atmosphere, the mass reduction rate is 5 to 20%.

(9) The frictional material composition according to the present embodiment does not contain copper as an element or has the content of copper of 0.5 mass % or less. Therefore, copper is not contained in an abrasion powder produced during braking, or the content of copper in the abrasion powder is an infinitesimal amount, and hence, there is no concern about pollution of rivers, lakes, and so on. From the viewpoint of suppressing the environmental hazards and toxicity to the human body, the content of copper in the frictional material composition is preferably less than 0.5 mass %, more preferably 0.3 mass % or less, and still more preferably 0.1 mass % or less, and it is especially preferred that copper is not contained.

(10) The frictional material composition according to the present embodiment provides a frictional material capable of revealing a friction coefficient which is stable even during light-load braking while having a composition with low environmental hazards and toxicity to the human body. Although the reason why such is caused is not always elucidated yet, the following may be conjectured.

(11) The present inventors have studied a titanate that is essential for the formation of TF and found that though the titanate is transferred onto the brake rotor surface due to braking, to form the TF, a sufficient amount of the TF cannot be formed through single use under a low-speed low-load condition; and that a favorable TF is formed by regulating a mass reduction rate under a specified condition to an appropriate range. This may be considered to be caused due to the matter that the mass reduction rate on heating to 500 C. exhibits a thermal decomposition amount of an organic material, such as mainly an organic filler, at a temperature corresponding to frictional heat during light-load braking, and by regulating the thermal decomposition amount at a relatively low temperature as 500 C. to an appropriate range, a favorable TF could be formed due to a spread product of the decomposition product and the titanate even during light-load braking.

(12) <Mass Reduction Rate on Heating to 500 C.>

(13) The frictional material composition according to the present embodiment is one in which on heating a molded product of the frictional material composition to 500 C. at a temperature rise rate of 10 C./min under an air atmosphere, the mass reduction rate is 5 to 20%.

(14) In this specification, in the case of referring to simply as mass reduction rate, it means the mass reduction rate on heating a molded product of the frictional material composition to 500 C. at a temperature rise rate of 10 C./min under an air atmosphere.

(15) In the frictional material composition according to the present embodiment, by regulating the mass reduction rate at 500 C. corresponding to the frictional heat during light-load braking to the aforementioned range, the thermal decomposition amount of the organic material represented by the organic filler in the frictional heat during light-load braking is regulated to an appropriate range, whereby a favorable TF can be formed on the disc rotor surface by the decomposition product and the titanate even during light-load braking.

(16) On the other hand, when the mass reduction rate is less than 5%, the amount of the decomposed organic filler, etc. is poor, and a favorable TF is not formed on the disc rotor surface. In addition, when the mass reduction rate is more than 20%, the amount of the decomposed organic filler, etc. becomes excessive, and the abrasion of the frictional material is promoted.

(17) From the aforementioned viewpoints, the mass reduction rate is preferably 5 to 18%, more preferably 6 to 15%, and still more preferably 11 to 15%.

(18) The mass reduction rate can be measured by the method described in the section of Examples.

(19) The frictional material is, in general, produced by a method of hot-press molding a pre-molded product obtained by pre-molding the frictional material composition, or a method of directly hot-press molding the frictional material composition and if desired, further performing a heat treatment to thermally cure the binder.

(20) A representative condition of hot-press molding for the purpose of obtaining a molded product which is provided for measuring the mass reduction rate is the condition described in the section of Examples. That is, the method is one in which after heating at 145 C. for 5 minutes, the heat treatment is performed at 200 C. for 4.5 hours.

(21) The present invention also provides a frictional material composition in the case of changing the aforementioned molding condition. For example, the present invention also provides a frictional material composition in which the molding condition is any one condition under which the temperature is in a range of from 150 to 250 C., and the time is in a range of from 2 to 10 hours, and the mass reduction rate of a molded product obtained through molding under the foregoing molding condition satisfies 5 to 20%.

(22) Examples of the method of allowing the mass reduction rate to fall within the aforementioned range include a method of regulating the kind of an organic component which the frictional material composition contains and the content thereof. A cashew dust, a rubber component, and the like which are used as the organic filler are relatively low in terms of a decomposition temperature, and therefore, they are decomposed by the frictional heat generated during light-load braking, to form a TF on the disc rotor surface. In consequence, by regulating the kind of such an organic component and the content thereof, the mass reduction rate on heating to a temperature of 500 C. corresponding to the frictional heat generated during light-load braking under an air atmosphere, whereby an appropriate amount of the TF can be formed on the disc rotor surface.

(23) <Constituent Components of Frictional Material Composition>

(24) Preferably, the frictional material composition according to the present embodiment contains one or more selected from the group consisting of an organic filler, an inorganic filler, a fiber base material, and a binder.

(25) The respective components which the frictional material composition according to the present embodiment contains are hereunder described.

(26) <Organic Filler>

(27) The organic filler is contained as a friction modifier to improve the sound vibration performance, the abrasion resistance, the stability of the friction coefficient during light-load braking, and the like of the frictional material.

(28) Examples of the organic filler include a cashew dust and a rubber component.

(29) The organic filler may be used alone, or may be used in combination of two or more thereof.

(30) As the cashew dust, for example, any cashew dust which is obtained by grinding a cashew nut shell oil having been polymerized and cured and which is typically used for a frictional material may be used.

(31) In the case where the frictional material composition contains the cashew dust, the content thereof is preferably 1 to 10 mass %, more preferably 2 to 8 mass %, and still more preferably 3 to 7 mass %. When the content of the cashew dust falls within the aforementioned range, not only the deterioration of the sound vibration performance, such as squeal which is caused due to an increase of elastic modulus of the frictional material, can be suppressed, but also the deterioration of the heat resistance and a lowering of the strength to be caused due to heat hysteresis can be suppressed. Furthermore, the stability of the friction coefficient during light-load braking can be enhanced.

(32) Examples of the rubber component include tire rubber, acrylic rubber, isoprene rubber, NBR (nitrile-butadiene rubber), and SBR (styrene-butadiene rubber). Of those, NBR and tire rubber are preferred, and a combined use of NBR and tire rubber is more preferred.

(33) In the case where the frictional material composition contains the rubber component, the content thereof is preferably 0.2 to 10 mass %, more preferably 0.5 to 5 mass %, and still more preferably 1 to 3 mass %.

(34) In the frictional material composition according to the present embodiment, a combined use of the cashew dust and the rubber component is preferred from the viewpoint of obtaining a stable friction coefficient even by light-load braking.

(35) In the case where the frictional material composition contains the cashew dust and the rubber component, a total content thereof is preferably 2 to 20 mass %, more preferably 3 to 12 mass %, and still more preferably 4 to 10 mass % from the viewpoint of enhancing the stability of the friction coefficient during light-load braking.

(36) In the case where the cashew dust and the rubber component are used in combination, the cashew dust coated with the rubber component may be used, and from the viewpoint of sound vibration performance, the cashew dust and the rubber component may be separately blended.

(37) The median diameter (D50) of cashew dust is preferably 1 to 800 m, and more preferably 10 to 500 m, still more preferably 50 to 400 m.

(38) A total content of the organic filler in the frictional material composition is preferably 2 to 20 mass %, more preferably 3 to 12 mass %, and still more preferably 4 to 10 mass %. When the total content of the organic filler falls within the aforementioned range, the deterioration of the sound vibration performance, such as squeal which is caused due to an increase of elastic modulus of the frictional material, can be suppressed, and the deterioration of the heat resistance and a lowering of the strength to be caused due to heat hysteresis can be suppressed.

(39) <Inorganic Filler>

(40) The inorganic filler is contained as the friction modifier to be used for the purpose of revealing a stable friction coefficient even by light-load braking and the purpose of avoiding the deterioration of the heat resistance of the friction material.

(41) The inorganic filler may be used alone, or may be used in combination of two or more thereof.

(42) The friction material composition according to the present embodiment contains (A) potassium titanate (hereinafter also referred to as component (A)) and (B) one or more selected from the group consisting of lithium potassium titanate and magnesium potassium titanate (hereinafter also referred to as component (B)). Preferably, the friction material composition according to the present embodiment further contains (C) one or more selected from the group consisting of zirconium silicate, zirconium oxide, and magnesium oxide (hereinafter also referred to as component (C)).

(43) (Component (A) and component (B))

(44) The component (A) and the component (B) spread onto the friction interface due to braking, thereby contributing to formation of a favorable TF. On the other hand, in the case where the frictional material composition contains the component (A) only without containing the component (B), the deterioration of the abrasion resistance occasionally becomes problematic, whereas in the case where the frictional material composition contains the component (B) only without containing the component (A), an extreme lowering of the friction coefficient occasionally becomes problematic.

(45) A total content of the component (A) and the component (B) in the frictional material composition is 10 to 35 mass %, preferably 13 to 30 mass %, and more preferably 15 to 25 mass %. When the aforementioned total content is 10 mass % or more, the stability of the friction coefficient is improved, whereas when it is 35 mass % or less, an extreme increase of porosity is suppressed, and a lowering of the mechanical strength of the frictional strength, a lowering of the stability of the friction coefficient to be caused due to moisture absorption, and adherence between the frictional material and the opposite material to be caused due to a rust can be suppressed.

(46) A content ratio of the component (A) and the component (B) in the frictional material composition [(A)/(B)] is preferably 0.1 to 10, more preferably 0.5 to 2, and still more preferably 0.8 to 1.2 in terms of a mass ratio from the viewpoint of the stability of the friction coefficient during light-load braking.

(47) Examples of the component (A) include potassium octatitanate and potassium hexatitanate.

(48) A median diameter (D50) of the component (A) is preferably 1 to 30 m, more preferably 2 to 20 m, and still more preferably 3 to 15 m.

(49) The component (B) is one or more selected from the group consisting of lithium potassium titanate and magnesium potassium titanate. The component (B) may be an embodiment containing lithium potassium titanate only and not containing magnesium potassium titanate, or may be an embodiment containing magnesium potassium titanate only and not containing lithium potassium titanate according to a desired performance.

(50) A median diameter (D50) of the component (B) is preferably 1 to 50 m, more preferably 5 to 45 m, and still more preferably 8 to 40 m.

(51) The component (A) and the component (B) are not restricted with respect to the particle size, the shape, and the like so long as the characteristic are not extremely deteriorated, and for example, the shape may be acicular, platy, granular, amoebic, or the like.

(52) <Component (C)>

(53) The component (C) is one or more selected from the group consisting of zirconium silicate, zirconium oxide, and magnesium oxide and acts as an abrasive material.

(54) The content of the component (C) in the frictional material composition is preferably 11 to 30 mass %, more preferably 11 to 25 mass %, and still more preferably 11 to 22 mass %. When the aforementioned content is 11 mass % or more, the aggression to the disc rotor that is an opposite material is appropriately imparted, a polishing groove during manufacture remaining on the brake rotor surface when it is new is polished, whereby a surface on which the TF is more readily fixed can be formed. Meanwhile, when the content of the component (C) is 30 mass % or less, the abrasion of the disc rotor can be suppressed without making the aggression to the disc rotor excessive.

(55) The median diameter (D50) of magnesium oxide is preferably 1 to 50 m, and more preferably 3 to 20 m.

(56) In the case where one selected from the group consisting of zirconium silicate, zirconium oxide, and magnesium oxide is contained as the component (C), an embodiment in which the remaining two are not contained may be adopted, and in the case where two selected from the group consisting of zirconium silicate, zirconium oxide, and magnesium oxide are contained as the component (C), an embodiment in which the remaining one is not contained may also be adopted.

(57) A median diameter (D50) of the component (C) is preferably 0.5 to 30 m, more preferably 0.5 to 20 m, and still more preferably 0.5 to 15 m. When the median diameter (D50) of the component (C) is 0.5 m or more, favorable friction coefficient and aggression to the disc rotor are revealed, whereas when it is 30 m or less, not only the dispersibility on the friction interface can be enhanced, and the friction coefficient can be made stable, but also the matter that the aggression to the opposite material becomes extremely high can be avoided.

(58) The median diameter (D50) of zirconium silicate is preferably 0.5 to 5 m, and more preferably 0.6 to 2 m.

(59) The median diameter (D50) of zirconium oxide is preferably 2 to 15 m, and more preferably 5 to 10 m.

(60) The median diameter (D50) of the component (C) can be measured by adopting a method, such as laser diffraction particle size distribution measurement. For example, the measurement can be performed with a laser diffraction/scattering type particle size distribution analyzer (trade name: LA-920 (manufactured by Horiba, Ltd.)).

(61) (Other Inorganic Filler)

(62) The frictional material composition according to the present embodiment may contain an inorganic filler other than the aforementioned respective components within a range where the effects of the present embodiment are not impaired.

(63) Examples of the other inorganic filler include tin sulfide, molybdenum disulfide, iron sulfide, bismuth sulfide, zinc sulfide, calcium hydroxide, calcium oxide, sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, dolomite, coke, graphite, mica, iron oxide, vermiculite, calcium sulfate, talc, clay, zeolite, mullite, chromite, titanium oxide, activated alumina, such as -alumina, and silica. Of those, one or more selected from the group consisting of graphite, tin sulfide, mica, calcium hydroxide, and barium sulfate are preferred.

(64) In the case where the frictional material composition contains graphite, the content thereof is, for example, 0.5 to 10 parts by mass, and preferably 1 to 3 parts by mass.

(65) In the case where the frictional material composition contains tin sulfide, the content thereof is, for example, 0.5 to 10 parts by mass, and preferably 1 to 3 parts by mass.

(66) In the case where the frictional material composition contains calcium hydroxide, the content thereof is, for example, 0.5 to 10 parts by mass, and preferably 1 to 3 parts by mass.

(67) In the case where the frictional material composition contains barium sulfate, the content thereof is, for example, 1 to 60 parts by mass, and preferably 5 to 50 parts by mass.

(68) In the case where the frictional material composition contains other inorganic filler, the total content is preferably 5 to 70 mass %, more preferably 10 to 65 mass %, and still more preferably 15 to 60 mass %.

(69) A total content of the inorganic filler in the frictional material composition is preferably 20 to 80 mass %, more preferably 30 to 80 mass %, and still more preferably 40 to 80 mass % from the viewpoint of providing a frictional material which is excellent in heat resistance and reveals a stable friction coefficient even by light-load braking.

(70) <Fiber Base Material>

(71) Preferably, the frictional material composition according to the present embodiment further contains a fiber base material. The fiber base material exhibits a reinforcing action or the like in the frictional material.

(72) Examples of the fiber base material include an organic fiber, an inorganic fiber, and a metal fiber.

(73) The fiber base material may be used alone, or may be used in combination of two or more thereof.

(74) Examples of the organic fiber include an aramid fiber, an acrylic fiber, a cellulose fiber, and a phenol resin fiber. Of those, an aramid fiber is preferred from the viewpoints of heat resistance and reinforcing effect.

(75) In the case where the frictional material composition according to the present embodiment contains an organic fiber, the content thereof is 0.5 to 10 mass %, more preferably 1 to 5 mass %, and still more preferably 2 to 4 mass %.

(76) Examples of the inorganic fiber include wollastonite, a ceramic fiber, a biodegradable ceramic fiber, a mineral fiber, a carbon fiber, a glass fiber, a potassium titanate fiber, and an aluminosilicate fiber. However, it is preferred that an inhalant potassium titanate fiber or the like is not contained from the viewpoint of toxicity to the human body.

(77) In this specification, it should be construed that the metal fiber is not included in the definition of the inorganic fiber.

(78) The aforementioned mineral fiber is an artificial inorganic fiber in which blast furnace slag for slag wool, basalt for basalt fiber, and other natural stone are melt-spun as the main component. The mineral fiber is preferably a natural mineral containing an Al element. Specifically, there is exemplified one containing one or more of SiO.sub.2, Al.sub.2O.sub.3, CaO, MgO, FeO, Na.sub.2O, and the like. Of those, a mineral fiber containing an Al element is preferred.

(79) An average fiber length of the mineral fiber is preferably 500 m or less, and more preferably 100 to 400 m. When the average fiber length is the aforementioned upper limit value or less, the bond strength with each of the components in the frictional material composition tends to become favorable. The average fiber length as referred to herein refers to a number average fiber length indicating an average value of the lengths of the corresponding fibers. For example, the average fiber length of 200 m indicates that when 50 mineral fibers to be used as the raw material of the frictional material composition are randomly selected and then measured for the fiber length with an optical microscope, an average value thereof is 200 m.

(80) In the case where the frictional material composition according to the present embodiment contains an inorganic fiber, the content thereof is preferably 0.5 to 10 mass %, more preferably 1 to 5 mass %, and still more preferably 2 to 4 mass %.

(81) Examples of the metal fiber include an iron-based fiber, a titanium fiber, a zinc fiber, and an aluminum fiber.

(82) In the case where the frictional material composition according to the present embodiment contains a metal fiber, the content thereof is preferably 0.5 to 5 mass %, more preferably 0.6 to 2 mass %, and still more preferably 0.7 to 1 mass %.

(83) The frictional material composition according to the present embodiment may also be one not containing a metal fiber according to a desired performance.

(84) In the case where the frictional material composition according to the present embodiment contains a fiber base material, the total content is preferably 4 to 40 mass %, more preferably 5 to 20 mass %, and still more preferably 6 to 10 mass %. When the total content of the fiber base material falls within the aforementioned range, it is possible to impart an appropriate reinforcing effect to the frictional material without giving a harmful influence, such as a remarkable lowering of efficacy characteristics.

(85) <Binder>

(86) Preferably, the frictional material composition according to the present embodiment contains a binder. The binder has an action of integrating the organic filler, the fiber base material, and the like contained in the frictional material composition with each other, thereby imparting a strength.

(87) The binder may be used alone, or may be used in combination of two or more thereof.

(88) As the binder, a thermosetting resin which is typically used for a frictional material composition can be used.

(89) Examples of the thermosetting resin include a phenol resin; and a variety of modified phenol resins, such as an acrylic rubber-modified phenol resin, a silicone rubber-modified phenol resin, a cashew-modified phenol resin, an epoxy-modified phenol resin, and an alkylbenzene-modified phenol resin. Of those, a phenol resin, an acrylic rubber-modified phenol resin, a silicone rubber-modified phenol resin, and an alkylbenzene-modified phenol resin are preferred from the viewpoint of providing favorable heat resistance, moldability, and friction coefficient.

(90) The content of the binder in the frictional material composition is preferably 5 to 20 mass %, more preferably 7 to 15 mass %, and still more preferably 8 to 12 mass %. When the content of the binder falls within the aforementioned range, not only an excellent strength can be imparted to the frictional material, but also the porosity of the frictional material is reduced, whereby the deterioration of the sound vibration performance, such as squeal which is caused due to an increase of elastic modulus, can be suppressed.

(91) <Metal Powder>

(92) The frictional material composition according to the present embodiment may contain a metal powder.

(93) Examples of the metal powder include an iron powder, a tin powder, a zinc powder, an aluminum powder, and an alloy powder thereof. The metal powder may be used alone, or may be used in combination of two or more thereof.

(94) In the case where the frictional material composition according to the present embodiment contains a metal powder, the content thereof is preferably 0.5 to 5 mass %, more preferably 0.5 to 3 mass %, and still more preferably 1 to 2 mass %. When the content of the metal powder is 0.5 mass % or more, the metal powder not only forms a TF on the disc rotor surface but also polishes or buries a polishing groove of the disc rotor when it is new, whereby the disc rotor surface on which a TF made of the organic filler, the titanate, the metal powder, and the like is readily fixed is produced, and the friction coefficient during light-load braking becomes stable. In addition, when the content of the metal powder is 5 mass % or less, excessive intermetallic adhesion or the like is suppressed, whereby extreme abrasion and deterioration of the frictional material and the disc rotor can be avoided.

(95) The metal powder is not restricted with respect to the particle size, the shape, and the like so long as the characteristic are not extremely deteriorated. The shape may be a spherical shape produced by a general atomizing method or the like, or a columnar shape produced by a general cutting method or the like. In addition, though the purity as the metal is preferably 90% or more, the metal powder surface may be changed to a metal oxide or the like due to long-term storage of the metal powder and the frictional material, or the like.

(96) The frictional material composition according to the present embodiment may also be one not containing a metal powder according to a desired performance.

(97) Preferably, the frictional material composition according to the present embodiment contains, as the metal powder or the metal fiber, one or more selected from the group consisting of iron, tin, zinc, and aluminum.

(98) In the case where the frictional material composition according to the present embodiment contains one or more selected from the group consisting of iron, tin, zinc, and aluminum, the content thereof is preferably 0.5 to 5 mass %, more preferably 0.6 to 4 mass %, and still more preferably 0.7 to 3.5 mass %.

(99) <Other Component>

(100) The frictional material composition according to the present embodiment may contain other component than the aforementioned respective components, as the need arises.

(101) <Frictional Material Produced by Molding the Frictional Material Composition According to the Present Embodiment>

(102) The present invention also provides a frictional material produced by molding the frictional material composition according to the present embodiment.

(103) The frictional material produced by molding the frictional material composition according to the present embodiment can be, for example, produced by a method of hot-press molding a pre-molded product obtained by pre-molding the frictional material composition according to the present embodiment, or a method of directly hot-press molding the frictional material composition according to the present embodiment and if desired, further performing a heat treatment to thermally cure the binder. A specific production method is described in the production method of the frictional material according to the present embodiment as mentioned later and in the section of Examples.

(104) [Frictional Material and Friction Member]

(105) The frictional material according to the present embodiment is a frictional material including a portion not containing copper as an element or having the content of copper of 0.5 mass % or less, the portion containing

(106) (A) potassium titanate; and

(107) (B) one or more selected from the group consisting of lithium potassium titanate and magnesium potassium titanate,

(108) in a total content of the component (A) and the component (B) of 10 to 35 mass %, wherein

(109) on heating to 500 C. at a temperature rise rate of 10 C./min under an air atmosphere, the mass reduction rate is 5 to 20%.

(110) The kind and content of each of the components to be contained in the frictional material according to the present invention as well as the mass reduction rate are those the same as described for the aforementioned frictional material composition according to the present embodiment, and preferred embodiments thereof are all the same, too.

(111) <Production Method of Frictional Material>

(112) The frictional material according to the present embodiment can be produced by a generally adopted method by using the frictional material composition according to the present embodiment. Specifically, the frictional material according to the present embodiment can be, for example, produced by uniformly mixing the frictional material composition according to the present embodiment by using a mixer, such as a Loedige (registered trademark) mixer, a pressure kneader, and an Eirich (registered trademark) mixer; pre-molding this mixture using a molding mold; molding the obtained pre-molded product under a condition at a molding temperature of 130 to 160 C. and a molding pressure of 20 to 50 MPa for a molding time of 2 to 10 minutes; and subjecting the obtained molded product to a heat treatment at 150 to 250 C. for 2 to 10 hours. The resultant may be further subjected to coating, a scorching treatment, a polishing treatment, etc., as the need arises.

(113) In the thus produced new frictional material, the mass reduction rate of the entirety of the frictional material has only to be in a range of from 5 to 20%. In addition, in the used frictional material, since it is subjected to heat hysteresis by the frictional heat generated during braking, the mass reduction rate of a portion of the frictional material after eliminating a portion having been subjected to heat hysteresis has only to be in a range of from 5 to 20%.

(114) In the production process of the frictional material, there is occasionally performed a scorching treatment in such a manner that the heat hysteresis by the frictional heat generated during the braking is previously given onto the surface of a new frictional material, so as to not change the efficacy of braking from the initial stage of use to the repeated use. The frictional material which has been subjected to a scorching treatment in this way is automatically already subjected to heat hysteresis even in a new frictional material. Even in this case, the mass reduction rate of a portion of the frictional material after eliminating a portion having been subjected to heat hysteresis has only to be in a range of from 5 to 20%.

(115) In the case of a new frictional material which has not been subjected to a scorching treatment, the aforementioned mass reduction rate can be examined from a decrease of mass on the occasion of performing thermogravimetric analysis (TG) using a sample obtained by shaving-out from the surface of the frictional material surface. In addition, in the case of a frictional material having been subjected to a scorching treatment, or in the case of a repeatedly used frictional material, the mass reduction rate of the frictional material can be examined by using a sample obtained by shaving-out from the surface after eliminating a portion having been subjected to a heat hysteresis.

(116) <Application of Frictional Material>

(117) The frictional material according to the present embodiment is used for the following embodiments (1) to (3).

(118) (1) A configuration of a frictional material only.

(119) (2) A configuration including a backing plate and a frictional material formed on the backing plate, the frictional material being the frictional material according to the present embodiment serving as a frictional surface.

(120) (3) A configuration further including, in the configuration of the above (2), a primer layer for the purpose of surface modification for enhancing a bonding effect of the backing plate between the backing plate and the friction member; and a bonding layer for the purpose of bonding between the backing plate and the friction member.

(121) Of those, it is preferred to use the frictional material as a friction member including the frictional material according to the present embodiment having the backing plate integrated therewith, as in the above (2) or (3).

(122) The aforementioned backing plate is used for the purpose of improving the mechanical strength of the friction member, and examples of a material thereof include metals, such as iron and stainless steel; and fiber-reinforced plastics, such as an inorganic fiber-reinforced plastic and a carbon fiber-reinforced plastic.

(123) As the aforementioned primer layer and bonding layer, any materials may be used as long as typically used for a friction member, such as a brake shoe.

(124) The frictional material according to the present embodiment is suitable as a frictional material for a disc brake pad and a brake lining of an automobile, etc. In addition, the frictional material according to the present embodiment can be used as a frictional material for a clutch facing, an electromagnetic brake, a retaining brake, etc., by subjecting the friction material to processes, such as molding, processing, and bonding to obtain desired shapes.

(125) Furthermore, the frictional material according to the present embodiment is useful as an over layer of the friction member, such as a disc brake pad and a brake lining, because it is excellent in stability of the friction coefficient, abrasion resistance at high temperatures, etc. The frictional material can also be used upon being formed as an under layer of the friction member. The over layer is the frictional material serving as a frictional surface of the friction member. The under layer is a layer placed between the frictional material serving as a frictional surface of the friction member and the backing plate for the purpose of improving the shear strength and the anti-crack properties in the vicinity of the bonding part between the frictional material and the backing plate.

EXAMPLES

(126) The frictional material composition and the frictional material according to the present embodiments are hereunder described in more detail by reference to Examples, but it should be construed that the present invention is by no means limited thereto.

Examples 1 to 7 and Comparative Examples 1 to 6

(127) [Production of Disc Brake Pad]

(128) Respective materials were blended according to blending amounts shown in Table 1, to obtain frictional material compositions of Examples 1 to 7 and Comparative Examples 1 to 6.

(129) Next, each of the frictional material compositions was mixed using a Loedige mixer (manufactured by MATSUBO Corporation, a product name: Loedige mixer M20). This mixture was pre-molded with a molding press (manufactured by OJIKIKAI CO., LTD). Subsequently, the obtained pre-molded product was hot press-molded together with a backing plate (made of iron) (manufactured by Hitachi Automotive Systems, Ltd.) using a molding press (SANKI SEIKO CO., LTD.) under a condition at a molding temperature of 145 C. and a molding pressure of 35 MPa for a molding time of 5 minutes. Subsequently, the obtained molded article was heated at 200 C. for 4.5 hours, polished with a rotary polisher, and then subjected to a scorching treatment at 500 C., to obtain a disc brake pad (frictional material thickness: 9.5 mm, frictional material projected area: 52 cm.sup.2).

(130) Various materials used in the Examples and Comparative Examples are as follows.

(131) [Binder]

(132) Resin A (phenol resin): HP491UP, manufactured by Hitachi Chemical Co., Ltd. Resin B (phenol resin): PR1950W, manufactured by Hitachi Chemical Co., Ltd.
[Organic Filler] Cashew dust: FF-1051, manufactured by Tohoku Chemical Industries, Ltd. Rubber component A (tire rubber powder): Powder TPA, manufactured by CAR QUEST Co., Ltd. Rubber component B (nitrile butadiene rubber): Nipol 1411, manufactured by Zeon Corporation
[Inorganic Filler] Titanate A (potassium octatitanate): Terracess TF-S, manufactured by Otsuka Chemical Co., Ltd. (shape: flaky, median diameter (D50): 7 m) Titanate B (lithium potassium titanate): Terracess L, manufactured by Otsuka Chemical Co., Ltd. (shape: flaky, median diameter (D50): 25 m) Titanate C (magnesium potassium titanate): Terracess PCS, manufactured by Otsuka Chemical Co., Ltd. Barium sulfate Graphite Tin sulfide Mica Calcium hydroxide Abrasive material A (zirconium silicate): MZ1000B, manufactured by DAIICHI KIGENSO KAGAKU KOGYO CO., LTD. (median diameter (D50): 1.6 m) Abrasive material B (zirconium oxide): BR-QZ, manufactured by DAIICHI KIGENSO KAGAKU KOGYO CO., LTD. (median diameter (D50): 6.5 m) Abrasive material C (magnesium oxide): Magnesium Oxide 2000 for industrial use, manufactured by Kyowa Chemical Industry Co., Ltd.
[Fiber Base Material] Aramid fiber (organic fiber) Mineral fiber (inorganic fiber) Copper fiber Iron fiber: #0, manufactured by GMT
[Metal Powder] Zinc powder: Zn-At-200, manufactured by Fukuda Metal Foil & Powder Co., Ltd. (average particle diameter: 25 to 38 m) Tin powder: AT-Sn No. 200, manufactured by Yamaishi Metal Co., Ltd. (median diameter (D50): 23 m) Aluminum powder: VA-40, manufactured by Yamaishi Metal Co., Ltd.
[Mass Reduction Rate at 500 C.]

(133) With respect to the disc brake pad obtained in each of the Examples, the mass reduction rate when heated at 500 C. under an air atmosphere was evaluated by performing thermogravimetric analysis (TG), while defining the content of the organic filler which may serve as a TF-forming component as an index. The mass reduction rate was calculated on the basis of the following formula.
Mass reduction rate (%)=(Weight reduction amount)100/(Weight before thermogravimetric analysis)

(134) For the evaluation, a sample collected from a layer in a depth of 2 to 3 mm from the surface of a new frictional material was used. For shaving-out of the sample, a milling cutter, an endmill, or the like was used. In the case where the particle size of the shaven-out sample was large, the sample was regulated with a mortar to a particle size suited for the thermogravimetric analysis. A measurement condition of the thermogravimetric analysis was set as follows.

(135) (Measurement Condition)

(136) Measurement device: Thermo plus EVO TG8120, manufactured by Rigaku Corporation Measurement atmosphere: Air atmosphere Measurement temperature range: 25 to 800 C. Temperature rise rate: 10 C./min Sample amount: 10 mg Sample vessel: Alumina-made

(137) In the thermogravimetric analysis results obtained under the aforementioned measurement condition, the mass reduction rate at 500 C. was calculated, and the evaluation was performed according to the following evaluation criteria. The results are shown in Table 1.

(138) (Evaluation Criteria)

(139) A: 11% or more and 15% or less

(140) B: 5% or more and less than 11%, or more than 15% and 20% or less

(141) C: 0% or more and less than 5%, or more than 20%

(142) With respect to the disc brake pad obtained in each of the Examples, the evaluation of various performances was performed using a brake dynamo tester (manufactured by Shin Nippon Tokki Co., Ltd.). In the experiment, the evaluation was performed in terms of an inertia moment of a half of Skyline V35, manufactured by Nissan Motor Co., Ltd. by using a Colette type caliper of general pin-slide type and a ventilated disc rotor (FC250) (gray cast iron), manufactured by Kiriu Corp.

(143) [Evaluation of Friction Coefficient (Efficacy Characteristics) at the 100th Time of Light-Load Braking]

(144) The braking at a vehicle speed of 40 km/h and 0.1 G was repeated 100 times at a disc rotor temperature of 50 C. at the starting time of braking, thereby measuring a friction coefficient at the 100th time of braking. In general, since the surface of a new frictional material has not been subjected to a running-in operation yet, the contact area with the disc rotator is small, and furthermore, the TF is not formed, so that the friction coefficient is low. When the braking is repeated, the friction coefficient increases and becomes stable. However, in the light-load braking at the aforementioned vehicle speed and deceleration and low disc rotor temperature, the friction coefficient becomes hardly stable. The friction coefficient was evaluated according to the following evaluation criteria. The results are shown in Table 1.

(145) (Evaluation Criteria)

(146) A: 0.37 or more and less than 0.43

(147) B: 0.34 or more and less than 0.37, or 0.43 or more and less than 0.47

(148) C: Less than 0.34, or 0.47 or more

(149) [Evaluation of Abrasion Resistance at 400 C.]

(150) An abrasion loss of each of the disc pads at a brake temperature prior to braking of 400 C. and 1000th time of braking was measured in conformity with JASO C427 and evaluated according to the following evaluation criteria. The results are shown in Table 1.

(151) (Evaluation criteria)

(152) A: Less than 0.60 mm

(153) B: 0.60 mm or more and less than 1.00 mm

(154) C: 1.00 mm or more

(155) TABLE-US-00001 TABLE 1 Example Item 1 2 3 4 5 6 7 Blending Binder Resin A 10 10 10 10 0 0 0 amount Resin B 0 0 0 0 10 10 10 (mass %) Organic Cashew dust 4 5 5 6 5 5 7 filler Rubber component A 1 2 2 2 2 0 0 Rubber component B 0 0 0 0 0 2 3 Inorganic Component (A) Titanate A 5 10 10 15 5 10 15 filler Component (B) Titanate B 5 10 0 15 5 10 15 Titanate C 0 0 10 0 0 0 0 Component (C) Abrasive material A 0 0 0 0 3 3 0 Abrasive material B 12 12 0 30 15 25 15 Abrasive material C 0 0 12 0 0 0 0 Graphite 2 2 2 2 2 2 2 Tin sulfide 2 2 2 2 2 2 2 Mica 2 2 2 2 2 2 2 Calcium hydroxide 2 2 2 2 2 2 2 Barium sulfate 49 36 36 7 40 19 18 Fiber base Aramid fiber 3 3 3 3 3 3 3 material Mineral fiber 3 3 3 3 3 3 3 Copper fiber 0 0 0 0 0 0 0 Iron fiber 0 1 0 0 0 1 2 Metal Zinc powder 0 0 1 0 0 1 1 powder Tin powder 0 0 0 1 0 0 0 Aluminum powder 0 0 0 0 1 0 0 Evaluation Mass reduction rate at 500 C. B A A A A A B results (10%) (12%) (13%) (14%) (13%) (13%) (17%) Friction coefficient at the 100th time of A A A A A A A light-load braking (0.37) (0.38) (0.37) (0.39) (0.40) (0.41) (0.38) Abrasion resistance at 400 C. B A A B B A B (0.65) (0.51) (0.49) (0.85) (0.91) (0.57) (0.71) Comparative Example Item 1 2 3 4 5 6 Blending Binder Resin A 6 10 10 10 0 8 amount Resin B 0 0 0 0 12 0 (mass %) Organic Cashew dust 3 5 5 5 10 3 filler Rubber component A 0 2 2 2 5 1 Rubber component B 0 0 0 0 2 0 Inorganic Component (A) Titanate A 10 20 0 3 10 15 filler Component (B) Titanate B 10 0 20 3 10 0 Titanate C 0 0 0 0 0 0 Component (C) Abrasive material A 0 9 0 0 3 0 Abrasive material B 12 10 10 10 20 15 Abrasive material C 0 0 0 0 0 0 Graphite 2 2 2 2 2 2 Tin sulfide 2 2 2 2 2 2 Mica 2 2 2 2 2 2 Calcium hydroxide 2 2 2 2 2 2 Barium sulfate 45 39 39 53 12 34 Fiber base Aramid fiber 3 3 3 3 3 3 material Mineral fiber 3 3 3 3 3 3 Copper fiber 0 0 0 0 0 10 Iron fiber 0 0 0 0 1 0 Metal Zinc powder 0 0 0 0 1 0 powder Tin powder 0 0 0 0 0 0 Aluminum powder 0 0 0 0 0 0 Evaluation Mass reduction rate at 500 C. C A A A C B results (4%) (13%) (12%) (13%) (21%) (10%) Friction coefficient at the 100th time of C A C C B A light-load braking (0.32) (0.40) (0.30) (0.31) (0.36) (0.40) Abrasion resistance at 400 C. B C A A C A (0.68) (1.07) (0.47) (0.55) (1.10) (0.55)

(156) Examples 1 to 7 exhibited the friction coefficient and abrasion resistance on the same levels with Comparative Example 6 containing copper. That is, it is noted that the frictional material composition according to the present embodiment is a composition with low environmental hazards and toxicity to the human body, which does not contain copper as an element or has the content of copper of 0.5 mass % or less, and it is able to reveal a stable friction coefficient even during light-load braking.

(157) On the other hand, Comparative Example 1 with a small mass reduction rate at 500 C., Comparative Example 2 containing potassium titanate only as the titanate, Comparative Example 3 containing lithium potassium titanate only as the titanate, Comparative Example 4 which contains both potassium titanate and lithium potassium titanate, but a total content thereof is small, and Comparative Example 5 in which the mass reduction rate at 500 C. is extremely large were inferior with respect to any of at least the friction coefficient or the abrasion resistance.

INDUSTRIAL APPLICABILITY

(158) As compared with conventional products, in accordance with the frictional material composition of the present invention, even if not using copper with a high environmental load, an appropriate amount of TF is formed even during light-load braking, thereby revealing a stable friction coefficient. Thus, the frictional material composition of the present invention is suitable for a frictional material and a friction member, such as a braking pad, etc. for not only general passenger cars but also passenger cars mounted with a regenerative coordination brake.