Frictional material composition, frictional material, and frictional member

Abstract

Provided are: a frictional material composition from which it is possible to form a low-steel material that produces less amount of fine abrasion powder and dust such as PM10 and PM2.5 during braking, even when copper components are not contained or contained in a small amount of less than 0.5 mass%; and a frictional material and a frictional member which use said frictional material composition.　This frictional material composition contains, as copper elements, less than 0.5 mass% of copper components. The frictional material composition contains a binding material, steel-based fibers, and a titanate. The contained amount of the steel-based fibers is not less than 10 mass% but less than 30 mass% with respect to 100 mass% of the total amount of the frictional material composition.

Description

Friction material composition, friction material, and friction member

[0001] The present invention relates to a friction material composition, and a friction material and a friction member using the friction material composition.

[0002] Friction materials used in brakes such as disc brakes and drum brakes that constitute braking devices for various vehicles, industrial machinery, etc. are required to have a large and stable friction coefficient, excellent wear resistance, and low attack on mating materials. Such friction materials are classified into three types: semi-metallic materials containing steel fibers such as steel fibers or stainless steel fibers as a fiber base material in a proportion of 30% by mass or more but less than 60% by mass; low-steel materials containing steel fibers in a proportion of 10% by mass or more but less than 30% by mass; and NAO (Non-Asbestos-Organic) materials that do not contain steel fibers. However, friction materials containing trace amounts of steel fibers are also classified as NAO materials.

[0003] In Japan and the United States, where comfort is emphasized, NAO materials are mainstream, as they are less aggressive to mating materials and have an excellent balance of noise and wear resistance.In Europe, low-steel materials are mainstream, as friction materials that are effective under any conditions, such as high-speed braking on the Autobahn, are preferred.

[0004] Compositions used in friction materials (hereinafter referred to as "friction material compositions") generally contain copper fibers or copper powder. The primary role of copper is to provide thermal conductivity. Because of its high thermal conductivity, copper diffuses heat generated during braking away from the friction surface, thereby reducing friction material wear due to excessive temperature rise and suppressing vibration during braking. The secondary role of copper is to protect the friction surface during high-temperature braking. Due to the malleability of copper, it spreads to the surface of the friction material during braking to form a coating. It also migrates to the surface of the mating material to form an adhesive coating (hereinafter referred to as a "transfer film"). These protective films reduce friction material wear during high-temperature braking and enable the development of a stable friction coefficient. However, friction materials containing copper generate wear particles that contain copper during braking, which may cause pollution of rivers, lakes, and oceans. Therefore, state laws have come into effect in California and Washington, USA, that prohibit the sale and installation in new vehicles of friction materials containing 5% or more by mass of copper from 2021 onwards, and 0.5% or more by mass of copper from 2025 onwards.

[0005] Therefore, in NAO materials, titanates such as potassium titanate, lithium potassium titanate, and magnesium potassium titanate have attracted attention as components other than copper that serve as transfer films. For example, a friction material composition containing lithium potassium titanate and graphite (Patent Document 1), a friction material composition containing two or more types of titanates and ceramic fibers (Patent Document 2), and a friction material composition containing a titanate with a tunnel-shaped crystal structure and a titanate with a layered crystal structure (Patent Document 3) have been proposed.

[0006] International Publication No. 2012 / 066968 Pamphlet Japanese Patent Application Laid-Open No. 2015-059143 Japanese Patent Application Laid-Open No. 2015-147913

[0007] While low-steel materials have a high friction coefficient and stable braking performance, they are highly aggressive to mating materials, causing wheel contamination due to wear particles from the friction material and rotor (mating material). Therefore, it is necessary not only to reduce the copper content in friction materials, but also to reduce the amount of wear particles generated during braking. One method for reducing wear particles is to reduce the load on friction brakes. One such method is the widespread adoption of regenerative braking systems in electric vehicles (EVs) and hybrid vehicles. However, EVs are heavier than gasoline-powered vehicles, and the level of regeneration in regenerative braking systems varies depending on the vehicle model and driving conditions, so the effectiveness of these systems in reducing wear particles is insufficient.

[0008] Furthermore, Europe is scheduled to regulate brake emissions after 2025. For example, a report published in April 2021 by AGVES (Advisory Group on Vehicle Emission Standards), an advisory group on vehicle exhaust gas standards established under the European Commission, proposed a limit of 10 PM (particulate matter) for low-steel materials. Currently, limit values ​​for PM2.5 and PN (PM number) are also under discussion, with emphasis being placed on the particle size of wear dust.

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a friction material composition that can form a low-steel material that generates little fine wear dust such as PM10 (particulate matter with an aerodynamic diameter of 10 μm or less) and PM2.5 (particulate matter with an aerodynamic diameter of 2.5 μm or less) during braking, even if the friction material composition does not contain a copper component or contains a small amount of copper component, such as less than 0.5 mass %, as well as a friction material and a friction member that use the friction material composition.

[0010] The present invention provides the following friction material composition, and a friction material and a friction member using the friction material composition.

[0011] Item 1. A friction material composition having a copper content of less than 0.5% by mass in terms of elemental copper, the friction material composition comprising a binder, steel-based fibers, and a titanate, wherein the content of the steel-based fibers is 10% by mass or more and less than 30% by mass, relative to 100% by mass of the total amount of the friction material composition.

[0012] Item 2. The friction material composition according to item 1, wherein the content of the titanate is 5% by mass or more and 30% by mass or less, based on 100% by mass of the total amount of the friction material composition.

[0013] Item 3. The friction material composition according to item 1 or 2, wherein a mass ratio of the titanate to the steel-based fibers (titanate / steel-based fibers) is 0.1 or more and 3.0 or less.

[0014] Item 4. The friction material composition according to any one of Items 1 to 3, wherein a mass ratio of the titanate to the binder (titanate / binder) is 0.4 or more and 8.0 or less.

[0015] Item 5. The friction material composition according to any one of Items 1 to 4, wherein the titanate is at least one of a titanate having a tunnel crystal structure and a titanate having a layered crystal structure.

[0016] Item 6: The titanate is A ｘ M ｙ Ti （２－ｙ） O ４ [wherein A is one or more alkali metals excluding Li, M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, and Mn, x is a number from 0.5 to 1.0, and y is a number from 0.25 to 1.0], A ０．１～０．８ Li ０．２～０．４ Ti １．６～１．８ O ３．６５～３．９５ [wherein A is one or more alkali metals other than Li], A ０．２～０．８ Mg ０．３～０．５ Ti １．５～１．７ O ３．７～３．９５ [wherein A is one or more alkali metals other than Li], A ０．５～０．７ Li （０．２７－ｘ） M ｙ Ti （１．７３－ｚ） O ３．８５～３．９５[wherein A is one or more alkali metals excluding Li, M is one or more selected from Mg, Zn, Ga, Ni, Cu, Fe, Al, and Mn (however, in the case of two or more ions, combinations of ions with different valences are excluded), and x and z are such that when M is a divalent metal, x=2y / 3, z=y / 3, and when M is a trivalent metal, x=y / 3, z=2y / 3, and y is in the range of 0.004≦y≦0.4], A ２ Ti ｎ O （２ｎ＋１） [wherein A is one or more alkali metals other than Li, and n is a number from 2 to 11], and A （２＋ｙ） Ti （６－ｘ） M ｘ O （１３＋ｙ／２－（４－ｚ）ｘ／２） [In the formula, A is one or more alkali metals excluding Li, M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, and Mn, z is the valence of element M and is an integer of 1 to 3, x is 0.05≦x≦0.5, and y is 0≦y≦(4−z)x]. The friction material composition according to any one of items 1 to 5,

[0017] Item 7. The friction material composition according to any one of Items 1 to 6, wherein the titanate has an alkali metal ion elution rate of 0.01% by mass or more and 15% by mass or less.

[0018] Item 8. The friction material composition according to any one of Items 1 to 7, wherein the titanate is at least one type of non-fibrous particle selected from the group consisting of spherical particles, columnar particles, plate-like particles, block particles, particles having a plurality of convex shapes, and irregularly shaped particles.

[0019] Item 9. The friction material composition according to any one of Items 1 to 8, wherein the titanate has an average particle size of 0.1 μm or more and 200 μm or less.

[0020] Item 10. The friction material composition according to any one of Items 1 to 9, wherein the steel fibers have an average fiber length of 0.1 mm or more and 5 mm or less.

[0021] Item 11. The friction material composition according to any one of Items 1 to 10, wherein the steel fibers are curled fibers.

[0022] Item 12. The friction material composition according to any one of Items 1 to 11, wherein the content of the carbon-based solid lubricant is less than 10% by mass, based on 100% by mass of the total amount of the friction material composition.

[0023] Item 13. A friction material, which is a molded product of the friction material composition according to any one of items 1 to 12.

[0024] Item 14. A friction member comprising the friction material according to Item 13.

[0025] According to the present invention, it is possible to provide a friction material composition that can form a low-steel material that generates little fine wear dust such as PM10 and PM2.5 during braking, even if it does not contain a copper component or the copper component content is as small as less than 0.5 mass %, as well as a friction material and a friction member that use the friction material composition.

[0026] Fig. 1 is a photograph showing a cross section of the friction member obtained in Example 1 after a friction test. Fig. 2 is a photograph showing a cross section of the friction member made of NAO material after a friction test.

[0027] Hereinafter, an example of a preferred embodiment of the present invention will be described. However, the following embodiment is merely an example, and the present invention is not limited to the following embodiment.

[0028] <1. Friction Material Composition> The friction material composition of the present invention is characterized in that the copper content is less than 0.5 mass% as copper element relative to 100 mass% of the total amount of the friction material composition, and the friction material composition contains a binder, steel fibers, and a titanate, and the steel fiber content is 10 mass% or more and less than 30 mass% relative to 100 mass% of the total amount of the friction material composition. The friction material composition of the present invention can also contain other materials as needed. In this specification, the term "friction material composition" refers to a composition used in a friction material.

[0029] In the present invention, the copper content is less than 0.5 mass % as copper element, relative to 100 mass % of the total amount of the friction material composition, and preferably no copper component is contained, thereby reducing the environmental impact compared to conventional friction material compositions. In this specification, "no copper component" means that copper fiber, copper powder, and copper-containing alloys (brass, bronze, etc.) and compounds are not blended as raw materials of the friction material composition.

[0030] Furthermore, since the friction material composition of the present invention has the above-mentioned constitution, it is possible to form a low-steel material that generates less fine wear dust such as PM10 and PM2.5 during braking. This point will be explained below with reference to FIGS.

[0031] In NAO materials, titanate has traditionally been known as a component other than copper that plays a role in the transfer film. By blending titanate into NAO materials, a coating like the one shown in Figure 2 is formed, which then migrates to the mating material and forms a transfer film. Furthermore, low-steel materials traditionally have difficulty forming a coating, and friction causes the iron in the rotor to fuse with the iron in the steel-based fibers, making the steel-based fibers more likely to detach from the pad. This creates unevenness on the friction surface, accelerating wear and increasing dust.

[0032] In contrast, when titanate is blended into a friction material composition containing 10% by mass or more but less than 30% by mass of steel fibers, as in the present invention, contrary to expectations, as shown in Figure 1, a coating is unlikely to form on the friction material surface, and the steel fibers do not detach. This is thought to be because the frictional heat causes the titanate to react with a binder such as a phenolic resin, and the resulting carbides are present on the friction surface, preventing iron from fusing together. This is thought to suppress the detachment of steel fibers, reducing wear and dust. Therefore, the low-steel material formed using the friction material composition of the present invention can reduce the amount of fine wear dust, such as PM10 and PM2.5, generated during braking. Furthermore, the amount of copper in the wear dust generated during braking is less than that of conventional products, thereby reducing environmental impact.

[0033] 1 is a photograph showing a cross section of the friction member obtained in Example 1 described later after a friction test. Also, FIG. 2 is a photograph showing a cross section of the friction member made of NAO material after a friction test.

[0034] (1-1. Binder) The binder binds together the steel fibers, titanate, etc. contained in the friction material composition and provides strength. There are no particular restrictions on the binder used in the friction material composition of the present invention, and thermosetting resins that are typically used as binders for friction materials can be used.

[0035] Examples of thermosetting resins include phenolic resins; elastomer-dispersed phenolic resins such as acrylic elastomer-dispersed phenolic resins and silicone elastomer-dispersed phenolic resins; modified phenolic resins such as acrylic-modified phenolic resins, silicone-modified phenolic resins, cashew-modified phenolic resins, epoxy-modified phenolic resins, and alkylbenzene-modified phenolic resins; formaldehyde resins; melamine resins; epoxy resins; acrylic resins; aromatic polyester resins; and urea resins. These may be used alone or in combination of two or more. Among these, phenolic resins (straight phenolic resins) and modified phenolic resins are preferred because they can further improve heat resistance, moldability, and friction properties.

[0036] The content of the binder in the friction material composition is preferably 5% by mass or more, more preferably 6% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, based on 100% by mass of the total amount of the friction material composition. By setting the binder content within the above range, an appropriate amount of binder is filled into the gaps in the blended materials, thereby achieving even better friction characteristics.

[0037] (1-2. Steel Fibers) Examples of steel fibers include steel fibers and stainless steel fibers, with steel fibers being preferred.

[0038] Examples of steel fibers include straight fibers obtained by chatter vibration cutting and curled fibers obtained by cutting long fibers. Straight fibers have a linear fiber shape. Curled fibers, on the other hand, have a shape with curved portions, and include simple arc-shaped fibers, wavy fibers, spiral or vortex-shaped fibers, etc.

[0039] Among these, the steel fibers are preferably curled fibers, from the viewpoint of reducing the amount of shedding from the friction material on the friction surface and more reliably maintaining the friction characteristics during high-temperature braking. Furthermore, it is more preferable that the curled fibers include a portion with a radius of curvature of 100 μm or less. In this case, the fibers are more firmly fixed to the friction material, and the shedding of the friction material from the friction surface is further reduced.

[0040] The average fiber length of the steel-based fibers is preferably 5 mm or less, more preferably 2.5 mm or less, from the viewpoint of further improving abrasion resistance at high temperatures. Also, from the viewpoint of further improving reinforcing properties, it is preferably 0.1 mm or more, more preferably 0.5 mm or more, and even more preferably 1.1 mm or more. Taking these into consideration, the average fiber length of the steel-based fibers is preferably 0.1 mm to 5 mm, more preferably 0.5 mm to 2.5 mm, and even more preferably 1.1 mm to 2.5 mm.

[0041] The average fiber diameter of the steel-based fibers is preferably 300 μm or less, more preferably 100 μm or less, from the viewpoint of further suppressing brake vibration at high temperatures. Also, from the viewpoint of further preventing the steel-based fibers from falling off, it is preferably 10 μm or more, more preferably 30 μm or more. Taking these into consideration, the average fiber diameter of the steel-based fibers is preferably 10 μm to 300 μm, more preferably 30 μm to 100 μm.

[0042] The average fiber length and average fiber diameter of the steel-based fibers can be confirmed using a microscope, etc. For example, they can be the average values ​​of 30 steel-based fibers observed under a microscope.

[0043] The content of the steel fibers is 10% by mass or more, preferably 12% by mass or more, and more preferably 15% by mass or more, relative to 100% by mass of the total amount of the friction material composition, and is less than 30% by mass, preferably 28% by mass or less, and more preferably 25% by mass or less.

[0044] (1-3. Titanate) Titanates have crystal structures such as tunnel structures and layer structures, and at least one of a tunnel crystal structure titanate and a layer crystal structure titanate is preferred. From the viewpoint of further reducing abrasion dust, a layer crystal structure titanate is preferred. Also, from the viewpoint of further increasing the coefficient of friction, a tunnel crystal structure titanate is preferred. Therefore, a combination of a tunnel crystal structure titanate and a layer crystal structure titanate may be used. On the other hand, as the titanate, from the viewpoint of further reducing abrasion dust, magnesium potassium titanate or lithium potassium titanate is preferred, and from the viewpoint of further increasing the coefficient of friction and further reducing abrasion dust, magnesium potassium titanate of a layer crystal structure is more preferred.

[0045] Examples of titanates having a layered crystal structure include: ｘ M ｙ Ti （２－ｙ） O ４ [wherein A is one or more alkali metals excluding lithium (Li), M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, and Mn, x is a number of 0.5 to 1.0, and y is a number of 0.25 to 1.0], A ０．１～０．８ Li ０．２～０．４ Ti １．６～１．８ O ３．６５～３．９５ [wherein A is one or more alkali metals other than Li], A ０．２～０．８ Mg ０．３～０．５ Ti １．５～１．７ O ３．７～３．９５ [wherein A is one or more alkali metals other than Li], A ０．５～０．７ Li （０．２７－ｘ） M ｙ Ti （１．７３－ｚ） O ３．８５～３．９５[In the formula, A is one or more alkali metals excluding Li, M is one or more selected from Mg, Zn, Ga, Ni, Cu, Fe, Al, and Mn (however, in the case of two or more, combinations of ions with different valences are excluded), and x and z are such that when M is a divalent metal, x = 2y / 3, z = y / 3, and when M is a trivalent metal, x = y / 3, z = 2y / 3, and y is 0.004≦y≦0.4]. ｘ M ｙ Ti （２－ｙ） O ４ [wherein A is one or more alkali metals excluding Li, M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, and Mn, x is a number from 0.5 to 1.0, and y is a number from 0.25 to 1.0], A ０．５～０．７ Li ０．２７ Ti １．７３ O ３．８５～３．９５ [wherein A is one or more alkali metals other than Li], and A ０．２～０．７ Mg ０．４０ Ti １．６ O ３．７～３．９５ wherein A is at least one selected from the group consisting of one or more alkali metals excluding Li.

[0046] Examples of the alkali metals other than lithium (Li) include sodium, potassium, rubidium, cesium, francium, etc. Among these, sodium and potassium are preferred because of their economical advantages.

[0047] Specific examples of titanates having a layered crystal structure include K ０．８ Li ０．２７ Ti １．７３ O ４ (lithium potassium titanate), K ０．７ Li ０．２７ Ti １．７３ O ３．９５ (lithium potassium titanate), K ０．６ Li ０．２７ Ti １．７３ O ３．９ (lithium potassium titanate), K ０．４ Li ０．２７ Ti １．７３ O ３．８ (lithium potassium titanate), K０．３ Li ０．２７ Ti １．７３ O ３．７ (lithium potassium titanate), K ０．８ Mg ０．４ Ti １．６ O ４ (Magnesium potassium titanate), K ０．７ Mg ０．４ Ti １．６ O ３．９５ (Magnesium potassium titanate), K ０．５ Mg ０．４ Ti １．６ O ３．９ (Magnesium potassium titanate), K ０．４ Mg ０．４ Ti １．６ O ３．８ (Magnesium potassium titanate), K ０．３ Mg ０．４ Ti １．６ O ３．７ (Magnesium potassium titanate), K ０．７ Li ０．１３ Mg ０．２ Ti １．６７ O ３．９５ (lithium magnesium potassium titanate), K ０．７ Li ０．２４ Mg ０．０４ Ti １．７２ O ３．９５ (lithium magnesium potassium titanate), K ０．７ Li ０．１３ Fe ０．４ Ti １．４７ O ３．９５ (lithium iron potassium titanate), etc.

[0048] Examples of titanates with tunnel crystal structures include A ２ Ti ｎ O （２ｎ＋１） [wherein A is one or more alkali metals other than Li, and n is a number from 2 to 11], A （２＋ｙ） Ti （６－ｘ） M ｘ O （１３＋ｙ／２－（４－ｚ）ｘ／２）[wherein A is one or more alkali metals excluding Li, M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, and Mn, z is the valence of element M and is an integer of 1 to 3, x is 0.05≦x≦0.5, and y is 0≦y≦(4−z)x], and preferably A ２ Ti ｎ O （２ｎ＋１） [wherein A is one or more alkali metals other than Li, and n is a number from 2 to 11], and more preferably A ２ Ti ｎ O （２ｎ＋１） [wherein A is one or more alkali metals other than Li, and n is a number from 4 to 9], and more preferably K ２ Ti ｎ O （２ｎ＋１） [wherein n is a number from 4 to 9] and Na ２ Ti ｎ O （２ｎ＋１） wherein n is a number from 4 to 8.

[0049] Specific examples of titanates with tunnel-shaped crystal structures include K ２ Ti ４．８ O １０．６ (4.8 potassium titanate), K ２ Ti ６ O １３ (potassium hexatitanate), K ２ Ti ６．１ O １３．２ (6.1 potassium titanate), K ２ Ti ７．９ O １６．８ (7.9 potassium titanate), K ２ Ti ８ O １７ (potassium titanate octahydrate), K ２ Ti １０．９ O ２２．８ (10.9 Potassium titanate), Na ２ Ti ６ O １３ (Sodium hexatitanate), Na ２ Ti ８ O １７ (Sodium titanate octahydrate), K ２．１５ Ti ５．８５ Al ０．１５ O １３．０(potassium aluminum titanate), K ２．２０ Ti ５．６０ Al ０．４０ O １２．９ (potassium aluminum titanate), K ２．２０ Ti ５．９０ Li ０．１０ O １２．９ (lithium potassium titanate), etc.

[0050] From the viewpoint of the working environment, the titanate is preferably a non-fibrous particle. Examples of non-fibrous particles include spherical particles (including those with slight surface irregularities and those with a substantially spherical cross section, such as an elliptical cross section), columnar particles (including those with a substantially columnar overall shape, such as rod-shaped, cylindrical, prismatic, rectangular, rectangular, substantially cylindrical, or substantially rectangular), plate-shaped particles, block-shaped particles, particles with multiple protrusions (e.g., amoeba-shaped, boomerang-shaped, cross-shaped, or confetti-shaped), and irregular shapes, and these shapes can also be used in combination. Among these, plate-shaped particles are preferred. The titanate may also be a porous particle. These various particle shapes can be arbitrarily controlled by the production conditions, particularly the raw material composition and the firing conditions. The particle shapes can also be analyzed, for example, by scanning electron microscope (SEM) observation.

[0051] As used herein, "non-fibrous particles" refers to particles having an L / B ratio of 5 or less, where the longest side of the rectangular parallelepiped having the smallest volume among the rectangular parallelepipeds circumscribing the particle (circumscribing rectangular parallelepiped) is the major axis L, the second longest side is the minor axis B, and the shortest side is the thickness T (B > T). Furthermore, "having multiple convex portions" refers to particles whose projected shape on a plane is different from at least a normal polygon, circle, ellipse, etc., and can have convex portions in two or more directions. Specifically, these convex portions refer to the portions corresponding to the protruding parts when a polygon, circle, ellipse, etc. (basic shape) is fitted to a photograph (projection drawing) taken by a scanning electron microscope (SEM).

[0052] The average particle size of the titanate is preferably 0.1 μm or more, more preferably 1 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, and particularly preferably 35 μm or less. When the average particle size is within the above range, the amount of abrasion dust generated can be further reduced.

[0053] In this specification, the average particle size refers to the particle size at 50% cumulative volume in the particle size distribution measured by laser diffraction (D ５０ ) This D ５０ is the particle size at which the cumulative value reaches 50% when the particle size distribution is calculated on a volume basis and the number of particles is counted from the smallest particle size on a cumulative curve with the total volume set to 100%.

[0054] The specific surface area of ​​the titanate is preferably 0.1 m ２ / g or more, more preferably 0.2m ２ / g or more, more preferably 0.5m ２ / g or more, preferably 10m ２ / g or less, more preferably 8m ２ / g or less, more preferably 6m ２ / g or less, particularly preferably 5m ２ The specific surface area can be measured in accordance with JIS Z8830.

[0055] In the present invention, the alkali metal ion elution rate of the titanate is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, even more preferably 0.1 mass% or more, and is preferably 15 mass% or less, more preferably 10 mass% or less, even more preferably 6 mass% or less, and particularly preferably 4 mass% or less.

[0056] In the curing reaction of novolac phenolic resin, an example of a binder used in a friction material composition, the ring-opening of a curing accelerator, such as hexamethylenetetramine, bonds with hydroxyl groups in the novolac phenolic resin, and initiates the curing reaction. However, if alkali metal ions are present, they undergo an ion exchange reaction with the hydrogen ions in the hydroxyl groups in the novolac phenolic resin, which is thought to inhibit the bond between hexamethylenetetramine (the curing accelerator) and the novolac phenolic resin (the thermosetting resin) (curing inhibition). On the other hand, it is thought that the wear and tear of the friction material caused by braking causes alkali components derived from titanates to leach out onto the friction surface.

[0057] Therefore, by setting the alkali metal ion elution rate to the above upper limit or less, it is possible to prevent the curing of the thermosetting resin from being inhibited during hot and pressure molding, and as a result, it is possible to further improve the crack resistance under high temperature and high load. Furthermore, by setting the alkali metal ion elution rate to the above lower limit or more, it is possible to suppress rusting of the rotor even if the friction material of the present invention is left unused for a long period of time after braking. In other words, by setting the alkali metal ion elution rate within the above range, it is possible to achieve both crack resistance of the friction material and suppression of rusting of the rotor.

[0058] In this specification, the alkali metal ion elution rate refers to the mass ratio of alkali metal ions eluted into water at 80°C from a measurement sample such as a titanate.

[0059] Furthermore, in the case of titanates, a treatment layer made of a surface treatment agent may be formed on the surface of the titanate in order to further improve dispersibility and adhesion to the binder.

[0060] The surface treatment agent is not particularly limited, but examples thereof include silane coupling agents, titanium coupling agents, etc. Among these, silane coupling agents are preferred, and amino-based silane coupling agents, epoxy-based silane coupling agents, or alkyl-based silane coupling agents are more preferred. The above surface treatment agents may be used alone or in combination of two or more.

[0061] Examples of amino-based silane coupling agents include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-ethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane.

[0062] Examples of epoxy-based silane coupling agents include 3-glycidyloxypropyl(dimethoxy)methylsilane, 3-glycidyloxypropyltrimethoxysilane, diethoxy(3-glycidyloxypropyl)methylsilane, triethoxy(3-glycidyloxypropyl)silane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0063] Examples of alkyl silane coupling agents include methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexylriethoxysilane, cyclohexylmethyldimethoxysilane, n-octyltriethoxysilane, and n-decyltrimethoxysilane.

[0064] A known surface treatment method can be used to form a treatment layer made of a surface treatment agent on the surface of the titanate, such as a wet method in which the surface treatment agent is dissolved in a solvent that promotes hydrolysis (e.g., water, alcohol, or a mixed solvent thereof) to prepare a solution, and the solution is sprayed onto the titanate.

[0065] The amount of the surface treatment agent used to treat the surface of the titanate is not particularly limited. In the case of a wet method, for example, a solution of the surface treatment agent may be sprayed so that the amount of the surface treatment agent is 0.1 to 20 parts by mass per 100 parts by mass of the titanate.

[0066] The titanate used in the present invention may be the above-mentioned titanate treated with the above-mentioned surface treatment agent to form granules. The average particle size of the granular titanate is preferably 100 μm or more and preferably 200 μm or less.

[0067] The content of the titanate is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, relative to 100% by mass of the total amount of the friction material composition, and is preferably 30% by mass or less, more preferably 28% by mass or less, and even more preferably 25% by mass or less. By setting the content of the titanate within the above range, wear dust can be further reduced.

[0068] The mass ratio of titanate to steel-based fibers (titanate / steel-based fibers) is preferably 0.1 or more, more preferably 0.6 or more, even more preferably 0.7 or more, and particularly preferably 0.8 or more, and is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 1.5 or less. By setting the mass ratio of titanate to steel-based fibers within the above range, detachment of the steel-based fibers can be further suppressed.

[0069] The mass ratio of titanate to binder (titanate / binder) is preferably 0.4 or more, more preferably 0.6 or more, even more preferably 1.5 or more, and particularly preferably 1.7 or more, and is preferably 8.0 or less, more preferably 5.0 or less, and even more preferably 3.0 or less. By setting the mass ratio of titanate to binder within the above range, the amount of carbide present on the friction surface can be optimized, and detachment of steel-based fibers can be further suppressed.

[0070] (1-4. Other Materials) In addition to the binder, steel fibers, and titanate described above, other materials typically used in friction material compositions (such as fibrous base materials, organic friction modifiers, inorganic friction modifiers, lubricants, pH adjusters, and fillers) may be blended into the friction material composition of the present invention, if necessary.

[0071] The content of the other materials in the friction material composition is preferably 20% by mass or more and preferably 80% by mass or less, based on 100% by mass of the total amount of the friction material composition.

[0072] (1-4-1. Fibrous base material) The fibrous base material exhibits reinforcing properties in the friction material. Examples of the fibrous base material include inorganic fibers, metal fibers, organic fibers, and carbon-based fibers. One of these may be used alone, or two or more may be used in combination.

[0073] When the friction material composition contains a fibrous base material other than steel fibers, the content thereof is preferably 0.1 mass % or more, and is preferably 40 mass % or less, more preferably 20 mass % or less, and even more preferably 10 mass % or less, relative to 100 mass % of the total amount of the friction material composition.

[0074] Examples of inorganic fibers include glass fibers, rock wool, ceramic fibers, biodegradable ceramic fibers, biodegradable mineral fibers, and biosoluble fibers (SiO ２ -CaO-SrO type fibers, wollastonite fibers, silicate fibers, mineral fibers, etc., and among these, rock wool is preferred.

[0075] Examples of metal fibers include straight or curled metal fibers whose main component is a metal such as aluminum, iron, zinc, tin, titanium, nickel, magnesium, silicon, or other metals or alloy fibers (excluding steel-based fibers).

[0076] Examples of organic fibers include aromatic polyamide (aramid) fibers, fibrillated aramid fibers, acrylic fibers (fibers of homopolymers or copolymers whose main raw material is acrylonitrile), fibrillated acrylic fibers, cellulose fibers, fibrillated cellulose fibers, and phenolic resin fibers.

[0077] Examples of carbon-based fibers include flame-resistant fibers, PAN-based carbon fibers, pitch-based carbon fibers, activated carbon fibers, and the like.

[0078] The fiber base material is preferably an aramid fiber, since this gives the friction material appropriate water absorption, makes it easier for moisture in the air to be absorbed inside the friction material, makes it easier for the alkaline component of the titanate to elute, and can be expected to have a rust-preventing effect on steel-based fibers.

[0079] From the viewpoint of further improving heat resistance, the fiber substrate is preferably a para-aramid fiber such as poly-p-phenylene terephthalamide.

[0080] In order to further improve the moldability of the friction material and the retention of the filler, the fiber base material is preferably fibrillated aramid fiber (also called aramid pulp).

[0081] The specific surface area of ​​the fibrillated aramid fibers is preferably 5 m ２ / g or more, preferably 25m ２ / g or less, more preferably 15m ２ The fiber length of the fibrillated aramid fibers is preferably 0.5 mm or more and preferably 1.2 mm or less.

[0082] When the friction material composition contains fibrillated aramid fibers, the content thereof is preferably 1% by mass or more, preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less, relative to 100% by mass of the total amount of the friction material composition. When the content of the fibrillated aramid fibers is equal to or more than the above-mentioned lower limit, the crack resistance and wear resistance become better, and when the content of the fibrillated aramid fibers is equal to or less than the above-mentioned upper limit, deterioration of the crack resistance and wear resistance due to uneven distribution of the fibrillated aramid fibers and other materials can be prevented.

[0083] When the friction material composition contains rock wool, the content thereof is preferably 1% by mass or more, preferably 10% by mass or less, and more preferably 9% by mass or less, based on 100% by mass of the total amount of the friction material composition. If the rock wool content is within the above range, the friction coefficient during high-load braking can be increased.

[0084] (1-4-2. Organic Friction Modifiers) Organic friction modifiers are friction modifiers that are blended with the aim of further improving the noise and vibration performance and wear resistance of friction materials. Examples of organic friction modifiers include unvulcanized or vulcanized rubber powders such as tire rubber, acrylic rubber, isoprene rubber, NBR (nitrile butadiene rubber), SBR (styrene butadiene rubber), chlorinated butyl rubber, butyl rubber, and silicone rubber; cashew dust; rubber-coated cashew dust; melamine dust; and the like. One of these may be used alone, or two or more may be used in combination.

[0085] When the friction material composition contains an organic friction modifier, the content thereof is preferably 0.1% by mass or more, and is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and particularly preferably 6% by mass or less, relative to 100% by mass of the total amount of the friction material composition.

[0086] (1-4-3. Inorganic Friction Modifiers) Inorganic friction modifiers are friction modifiers that are blended in for the purposes of preventing deterioration in the heat resistance of the friction material, improving the wear resistance, and further improving the coefficient of friction. Examples of inorganic friction modifiers include abrasives, metal powders, and other inorganic fillers.

[0087] The abrasive material can be appropriately selected based on the material of the rotor, which is the mating material, so that it acts as an abrasive material and improves the coefficient of friction, and can be selected based on the Mohs hardness of the mating material.

[0088] Examples of abrasives include silicon carbide, titanium oxide, alpha alumina, gamma alumina, silica (silicon dioxide), magnesia (magnesium oxide), zirconia (zirconium oxide), zircon (zirconium silicate), chromium oxide, iron oxide (iron trioxide, etc.), chromite, quartz, and iron sulfide.

[0089] Note that if the particle size of the abrasive is large, the coefficient of friction can be increased during heavy-load braking, but the coefficient of friction will be unstable during light-load braking. On the other hand, if the particle size of the abrasive is small, the coefficient of friction will be stable during light-load braking, but the coefficient of friction may be low. For these reasons, abrasives with a large average particle size and abrasives with a small average particle size may be used in combination. Specifically, it is preferable to use abrasives with an average particle size of 0.5 μm to 15 μm in combination with abrasives with an average particle size of 20 μm to 200 μm. Furthermore, the mass ratio of the abrasives with a small average particle size to the abrasives with a large average particle size (abrasives with a small average particle size / abrasives with a large average particle size) is preferably 0.1 or more, more preferably 2 or more, and preferably 10 or less, more preferably 8 or less, from the viewpoint of further reducing wear dust.

[0090] When the friction material composition contains an abrasive, the content thereof is preferably 0.1 mass % or more, preferably 30 mass % or less, and more preferably 15 mass % or less, based on 100 mass % of the total amount of the friction material composition.

[0091] Examples of the metal powder include powders of simple metals or alloys of aluminum, zinc, iron, tin, etc. One of these may be used alone, or two or more may be used in combination.

[0092] Other inorganic fillers include vermiculite, clay, mica, talc, dolomite, chromite, mullite, calcium silicate, etc. One of these may be used alone, or two or more may be used in combination.

[0093] (1-4-4. Lubricant) The lubricant is preferably a solid lubricant, and examples thereof include carbon-based solid lubricants, metal sulfide-based solid lubricants, polytetrafluoroethylene (PTFE), etc. One of these may be used alone, or two or more may be used in combination. The lubricant is preferably one or more selected from the group consisting of carbon-based solid lubricants and metal sulfide-based solid lubricants.

[0094] When the friction material composition contains a lubricant, the content thereof is preferably 0.1 mass % or more, more preferably 1 mass % or more, and is preferably 30 mass % or less, more preferably 20 mass % or less, relative to 100 mass % of the total amount of the friction material composition.

[0095] Examples of the carbon-based solid lubricant include synthetic or natural graphite (graphite), flake graphite, phosphate-coated graphite, carbon black, coke, activated carbon, and elastic graphitized carbon. From the viewpoint of further improving thermal conductivity, synthetic graphite and natural graphite are preferred. When a carbon-based solid lubricant is contained, its content is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, relative to 100% by mass of the total amount of the friction material composition, and is preferably less than 15% by mass, more preferably less than 10% by mass, and even more preferably 8% by mass or less. If the content of the carbon-based solid lubricant is equal to or greater than the lower limit, friction material wear at high temperatures tends to be improved, and if the content of the carbon-based solid lubricant is equal to or less than the upper limit, a decrease in the friction coefficient tends to be easily suppressed.

[0096] Examples of sulfur-based solid lubricants include antimony trisulfide, molybdenum disulfide, tin sulfide, iron sulfide, zinc sulfide, bismuth sulfide, and tungsten disulfide. From the viewpoint of less harmfulness to the human body, tin sulfide and molybdenum disulfide are preferred. When a sulfur-based solid lubricant is contained, its content is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, relative to 100% by mass of the total amount of the friction material composition. It is preferably less than 15% by mass, more preferably less than 10% by mass, and even more preferably 8% by mass or less. If the content of the sulfur-based solid lubricant is equal to or greater than the lower limit, rotor wear tends to be more effectively suppressed. If the content of the sulfur-based solid lubricant is equal to or less than the upper limit, the decrease in the friction coefficient tends to be more easily suppressed.

[0097] (1-4-5. pH Adjuster) Examples of pH adjusters include inorganic bases such as calcium hydroxide (slaked lime), sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, trisodium phosphate, disodium hydrogen phosphate, tripotassium phosphate, and dipotassium hydrogen phosphate, and organic bases such as imidazole, histidine, and hexamethylenediamine. From the viewpoint of cost and hygroscopicity, inorganic bases are preferred. One of these may be used alone, or two or more may be used in combination. The pH adjuster may also be used to prevent rust adhesion between the friction material and the mating material (rotor).

[0098] When the friction material composition contains a pH adjuster, the content thereof is preferably 0.1% by mass or more and preferably 8% by mass or less, based on 100% by mass of the total amount of the friction material composition.

[0099] (1-4-6. Filler) Examples of the filler include barium sulfate and calcium carbonate, and preferably barium sulfate. One of these may be used alone, or two or more may be used in combination.

[0100] Barium sulfate comes in two forms: elutriated barium sulfate (baryte powder), which is obtained by crushing a mineral called barite, washing it to remove iron, and elutriating it, and artificially synthesized precipitated barium sulfate. The particle size of precipitated barium sulfate can be controlled by the synthesis conditions, allowing for the production of fine barium sulfate with a low content of the desired coarse particles. It is preferable to use precipitated barium sulfate as the barium sulfate, from the viewpoint of further reducing impurities and achieving a more uniform particle size distribution of the barium sulfate particles.

[0101] (1-5. Method for Producing Friction Material Composition) The friction material composition of the present invention can be produced by (1) a method of mixing the components using a mixer such as a Loedige mixer ("Loedige" is a registered trademark), a pressure kneader, or an Eirich mixer ("Eirich" is a registered trademark); or (2) a method of preparing granules of the desired components and, if necessary, mixing other components using a mixer such as a Loedige mixer, a pressure kneader, or an Eirich mixer.

[0102] The content of each component in the friction material composition of the present invention can be appropriately selected depending on the desired friction characteristics, and the composition can be produced by the above-mentioned production method.

[0103] The friction material composition of the present invention may also be prepared by preparing a masterbatch containing a specific component at a high concentration, and then adding and mixing a thermosetting resin or the like to this masterbatch.

[0104] <2. Friction Material and Friction Member> In the present invention, the friction material composition is pre-molded at room temperature (20°C), and the resulting pre-molded body is subjected to heat and pressure molding (molding pressure of 10 MPa to 40 MPa, molding temperature of 150°C to 200°C). If necessary, the resulting molded body is heat-treated in a heating furnace (150°C to 220°C, held for 1 hour to 12 hours), and then the molded body is machined and polished, thereby producing a friction material having a predetermined shape.

[0105] The friction material of the present invention is used as a friction member formed from the friction material to form a friction surface. Examples of friction members that can be formed using the friction material include (1) a structure consisting of only the friction material, and (2) a structure having a substrate such as a backing metal and the friction material of the present invention provided on the substrate to provide a friction surface.

[0106] The substrate is used to further improve the mechanical strength of the friction member, and may be made of a metal, a fiber-reinforced resin, etc. Examples of the metal or fiber-reinforced resin include iron, stainless steel, glass fiber-reinforced resin, and carbon fiber-reinforced resin.

[0107] Friction materials usually have many fine pores formed inside, which act as escape routes for decomposition products (gases and liquids) at high temperatures, preventing a decrease in friction characteristics, and also preventing squealing by reducing the rigidity of the friction material and improving damping. In ordinary friction materials, the material composition and molding conditions are controlled so that the porosity is preferably 5% to 30%, and more preferably 10% to 25%.

[0108] The friction member of the present invention is made of the friction material composition of the present invention, and therefore generates little fine wear dust such as PM10 and PM2.5 even when it does not contain a copper component or when the copper component content is reduced. Therefore, the friction member of the present invention can be suitably used in brake systems in general, such as disc pads, brake linings, and clutch facings that constitute braking devices for various vehicles and industrial machinery, and can be suitably used particularly as a friction member for regenerative cooperative brakes.

[0109] The present invention will now be described in further detail with reference to specific examples.

[0110] The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the present invention.

[0111] (Examples 1 to 13 and Comparative Examples 1 and 2) <Production of Friction Member> The materials were blended according to the blending ratios shown in Tables 1 and 2, and mixed for 3 minutes using an Eirich mixer. The resulting mixture was placed in the cavity of a hot molding die heated to 150°C, and with a back plate (made of steel) still placed on top, the mixture was pressurized at a pressure of 15 MPa to 40 MPa for 240 seconds so that the porosity of the molded body was 15%. The resulting molded body was placed in a constant temperature dryer heated to 210°C, held there for 2 hours, and completely cured to obtain a friction member.

[0112]

[0113]

[0114] The materials used in Tables 1 and 2 were as follows, and the powder properties were measured as follows.

[0115] (Binder) Phenolic resin: Hexamethylenetetramine-blended novolac phenolic resin (straight phenolic resin) powder

[0116] (Titanates 1 to 3) Powder properties and the like are shown in Table 3.

[0117] Titanate 4: 403.1 g of titanium oxide, 377.2 g of potassium carbonate, and 3.8 g of lithium carbonate were mixed for 1 hour while being pulverized using a vibration mill. 500 g of the resulting pulverized mixed powder was placed in a crucible and fired in an electric furnace at 850°C for 4 hours under atmospheric conditions. The fired product was then crushed using a hammer mill to obtain a powder.

[0118] 100 g of the resulting powder was dispersed in 400 g of deionized water and stirred for 5 minutes to prepare a slurry. 23.5 g of 98% sulfuric acid was added to the dispersion and stirred for 1 hour, adjusting the pH to 12.9. The solids in the pH-adjusted slurry were filtered, washed with 135 g of deionized water at 80°C, and dried. After drying, the mixture was loaded into a crucible and fired in an electric furnace at 800°C for 4 hours under air atmosphere. The fired product was passed through a 20-mesh sieve to obtain the desired titanate 4.

[0119] The obtained titanate 4 has a particle shape with a plurality of protrusions and a tunnel-shaped crystal structure. ２．１０ Ti ５．９０ Li０．１０ O １２．９ The powder properties are shown in Table 3.

[0120]

[0121] (Steel-based fibers) Steel fiber 1: Curled fiber, average fiber length (cut length) 1.5 mm, average fiber diameter 50 μm, trade name "Cut Wool BS-1V", manufactured by Bonstar Sales Co., Ltd. Steel fiber 2: Straight fiber, average fiber length (cut length) 3 mm, average fiber diameter 60 μm, trade name "KC Metal Fiber", manufactured by Nijishi Co., Ltd.

[0122] (Other materials) Aramid fiber: fibrillated para-aramid fiber (aramid pulp), fiber length 0.89 mm, specific surface area 9.8 m ２ / g Barium sulfate: elutriated barium sulfate powder, average particle size 24 μm Mica: natural mica powder, average particle size 180 μm Zircon: zirconium silicate powder, average particle size 1.5 μm Alumina: α-alumina powder, average particle size 57 μm Tin sulfide: tin (II) sulfide powder, average particle size 7 μm Graphite: synthetic graphite powder, average particle size 730 μm

[0123] [Particle Shape of Titanate] The particle shape was confirmed using a field emission scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, product number "S-4800").

[0124] [Shape, Average Fiber Length, and Average Fiber Diameter of Steel-Based Fibers] The shape was observed using a digital microscope (Keyence Corporation, "VHX-1000"), and the average fiber length and average fiber diameter were each calculated as the average value of 30 fibers.

[0125] [Average particle size] Measurement was performed using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, product number "SALD-2100"), and the particle size at 50% cumulative volume in the obtained particle size distribution was taken as the average particle size. The average particle size of graphite was observed using a digital microscope (Keyence Corporation, "VHX-1000") and taken as the average of 30 particles, and the average particle size of tin sulfide was observed using a field emission scanning electron microscope (Hitachi High-Technologies Corporation, product number "S-4800") and taken as the average of 200 particles.

[0126] [Specific Surface Area] Measurement was carried out using an automatic specific surface area measuring device (manufactured by Micromeritics, product number "TriStar II 3020").

[0127] [Alkali Metal Ion Elution Rate] The mass (X) g of the sample was measured, and then the sample was added to ultrapure water to prepare a 1% by mass slurry. After stirring at 80°C for 4 hours, the solid content was removed using a membrane filter with a pore size of 0.2 μm to obtain an extract. The mass (Y) g of the alkali metal ions in the obtained extract was measured using an ion chromatograph (manufactured by Dionex Corporation, product number "ICS-1100"). Next, using the values ​​of the masses (X) g and (Y) g, the alkali metal ion elution rate (mass %) was calculated based on the formula [(Y) / (X)]×100.

[0128] <Evaluation of Friction Member> The Rockwell hardness and the amount of wear dust of the friction members prepared above were evaluated as follows.

[0129] (Rockwell Hardness) The Rockwell hardness of the surface of the friction member was measured in accordance with the method of JIS D 4421. The S scale was used as the hardness scale.

[0130] (Method of measuring the amount of wear dust, wear amount, and friction coefficient) The surface of the friction member prepared above was polished by 1.0 mm to be processed into a friction member for a scale dynamo test. The friction member and a rotor (a cast iron rotor belonging to the A type in the ASTM standard) were used to perform a test at 65 km / h and 3.5 m / s. ２The friction members and rotors were fitted under the above conditions in advance, and an abrasion dust collector was connected to a scale dynamometer. The abrasion dust collector was equipped with an MCI sampler (equipped with a filter to capture PM10-2.5 and PM2.5) manufactured by Tokyo Dylec Co., Ltd. and a CPC3772 (PN measuring instrument) manufactured by TSI. Using the friction members and rotors that had been fitted under the above conditions, an abrasion dust measurement test was conducted under the friction conditions shown in Table 4, and the mass (mass and number) of particulate matter, friction material wear, rotor wear, and average friction coefficient were measured. The mass (PM10-2.5 and PM2.5) and PN (particle number) of particulate matter collected by the filter were measured. The friction material wear, rotor wear, and average friction coefficient were also measured. The test was conducted twice, and the average value was used as the measurement result.

[0131]

[0132] The results are shown in Tables 5 and 6 below.

[0133]

[0134]

[0135] Tables 5 and 6 show that Examples 1 to 13, which used friction material compositions containing a binder, steel fibers, and titanate, with the steel fiber content being 10% by mass or more but less than 30% by mass, exhibited excellent friction characteristics and reduced the amount of fine wear dust, such as PM10 and PM2.5. On the other hand, Comparative Example 1, which used a friction material composition that did not contain titanate, and Comparative Example 2, which used a friction material composition with a steel fiber content of 30% by mass or more (14% by volume or more), did not adequately reduce the amount of wear dust. Example 12, which used the same total amount of solid lubricant as Examples 1 to 11 but with an increased graphite content, reduced the amount of fine wear dust, but also reduced the coefficient of friction. The wear dust reduction rates in Tables 5 and 6 were calculated based on Comparative Example 1, which had the same amount of steel fibers.

[0136] (Method for measuring the amount of rust on the rotor) The surface of the friction member prepared above was polished by 1.0 mm to be processed into a friction member for a scale dynamo test. The friction member and a rotor (a cast iron rotor of type A in the ASTM standard) were used to measure the amount of rust on the rotor at 65 km / h and 3.5 m / s. ２ The rotors subjected to friction tests under conditions of 100 braking cycles were cut into 35 mm x 40 mm pieces to prepare measurement samples. The non-friction surfaces of the measurement samples were masked with aluminum tape and left for 14 days in a desiccator containing a saturated potassium sulfate solution at a temperature of 35°C and a relative humidity of 95%. Observation of the measurement samples after leaving them revealed that the unmasked portions had increased in thickness due to rust. The rotor thicknesses were also measured with a micrometer after 1 day, 2 days, and 14 days of leaving them, and the difference from the rotor thickness before the test was recorded as the increase in thickness. The results are shown in Table 7 below.

[0137]

[0138] A comparison of Example 4 and Comparative Example 1 in Table 7 shows that although transfer films are less likely to form on low-steel materials, the incorporation of titanate suppresses rusting of the rotor.

Claims

1. A friction material composition having a copper content of less than 0.5 mass % in terms of elemental copper, The present invention includes a binder, a steel-based fiber, and a titanate. The friction material composition has a steel fiber content of 10% by mass or more and less than 30% by mass, relative to 100% by mass of the total amount of the friction material composition.

2. 2. The friction material composition according to claim 1, wherein the content of the titanate is 5% by mass or more and 30% by mass or less, relative to 100% by mass of the total amount of the friction material composition.

3. 3. The friction material composition according to claim 1, wherein a mass ratio of the titanate to the steel-based fibers (titanate / steel-based fibers) is 0.1 or more and 3.0 or less.

4. 3. The friction material composition according to claim 1, wherein a mass ratio of the titanate to the binder (titanate / binder) is 0.4 or more and 8.0 or less.

5. 3. The friction material composition according to claim 1, wherein the titanate is at least one of a titanate having a tunnel-shaped crystal structure and a titanate having a layered crystal structure.

6. The titanate is A ｘ M ｙ Ti （２－ｙ） O ４ [In the formula, A is one or more alkali metals other than Li, M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, and Mn, x is a number of 0.5 to 1.0, and y is a number of 0.25 to 1.0], A ０．１～０．８ Li ０．２～０．４ Ti １．６～１．８ O ３．６５～３．９５ [In the formula, A is one or more alkali metals other than Li], A ０．２～０．８ Mg ０．３～０．５ Ti １．５～１．７ O ３．７～３．９５ [In the formula, A is one or more alkali metals other than Li], A ０．５～０．７ Li （０．２７－ｘ） M ｙ Ti （１．７３－ｚ） O ３．８５～３．９５ [In the formula, A is one or more alkali metals excluding Li, M is one or more selected from Mg, Zn, Ga, Ni, Cu, Fe, Al, and Mn (however, when two or more types are used, combinations of ions with different valences are excluded), and x and z are, when M is a divalent metal, x=2y / 3, z=y / 3, and when M is a trivalent metal, x=y / 3, z=2y / 3, and y is 0.004≦y≦0.4], A ２ Ti ｎ O （２ｎ＋１） [In the formula, A is one or more alkali metals other than Li, and n is a number from 2 to 11], and A （２＋ｙ） Ti （６－ｘ） M ｘ O （１３＋ｙ／２－（４－ｚ）ｘ／２） The friction material composition according to claim 1 or claim 2, wherein A is at least one selected from the group consisting of: (in the formula, A is one or more alkali metals excluding Li; M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, and Mn; z is the valence of element M and is an integer of 1 to 3; x is 0.05≦x≦0.5; and y is 0≦y≦(4-z)x).

7. 3. The friction material composition according to claim 1, wherein the titanate has an alkali metal ion elution rate of 0.01% by mass or more and 15% by mass or less.

8. 3. The friction material composition according to claim 1, wherein the titanate is at least one type of non-fibrous particle selected from the group consisting of spherical particles, columnar particles, plate-like particles, block particles, particles having a plurality of convex shapes, and particles with an irregular shape.

9. 3. The friction material composition according to claim 1, wherein the titanate has an average particle size of 0.1 μm or more and 200 μm or less.

10. 3. The friction material composition according to claim 1, wherein the steel fibers have an average fiber length of 0.1 mm or more and 5 mm or less.

11. 3. The friction material composition according to claim 1, wherein the steel fibers are curled fibers.

12. 3. The friction material composition according to claim 1, wherein the content of the carbon-based solid lubricant is less than 10 mass % relative to 100 mass % of the total amount of the friction material composition.

13. A friction material which is a molded product of the friction material composition according to claim 1 or 2.

14. A friction member comprising the friction material according to claim 13.