JP2024081464A - Friction material composition, friction material, and friction member - Google Patents

Abstract

[Problem] To provide a friction material composition which, even if it does not contain a copper component or contains a small amount of copper component (less than 0.5 mass%), generates little fine wear dust such as PM10 and PM2.5 during braking and can form a low-steel material with a large friction coefficient.
[Solution] A friction material composition having a copper content of less than 0.5 mass% in terms of elemental copper, comprising a binder, steel-based fibers, and a titanate, the content of the steel-based fibers being 10 mass% or more and less than 30 mass%, relative to 100 mass% of the total amount of the friction material composition, the titanate being a salt of one or more elements selected from the group consisting of alkali metals and alkaline earth metals, and the decomposition rate of the titanate being 30 mass% or more and 100 mass% or less when heated at 800°C for 1 hour in a nitrogen atmosphere.
[Selection diagram] None

Description

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

Friction materials used in brakes such as disc brakes and drum brakes that make up the braking devices of various vehicles and industrial machines are required to have a large and stable friction coefficient, excellent wear resistance, and low attack on the mating material. Such friction materials are classified into three types: semi-metallic materials that contain steel-based fibers such as steel fibers and stainless steel fibers as a fiber base material in a ratio of 30% to less than 60% by mass; low-steel materials that contain steel-based fibers in a ratio of 10% to less than 30% by mass; and NAO (Non-Asbestos-Organic) materials that do not contain steel-based fibers. However, friction materials that contain a small amount of steel-based fibers are also classified as NAO materials.

In Japan and the United States, where comfort is important, NAO materials are mainstream because they are less aggressive to mating materials and have an excellent balance between noise and wear resistance. In Europe, low-steel materials are mainstream because friction materials that work under any conditions, such as high-speed braking on the autobahn, are preferred.

Copper fibers and copper powder are generally blended into the composition used for the friction material (hereinafter referred to as the "friction material composition"). The first role of copper is to provide thermal conductivity. Since copper has high thermal conductivity, it can diffuse heat generated during braking from the friction surface, thereby reducing wear of the friction material due to excessive temperature rise and suppressing vibration during braking. The second 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 and forms a coating. It also migrates to the surface of the mating material to form an adhesive coating (hereinafter referred to as the "transfer film"). These act as protective films to reduce wear of the friction material during high-temperature braking and enable the expression of a stable friction coefficient. However, it has been suggested that friction materials containing copper contain copper in the wear powder generated during braking, which may cause river, lake, and marine pollution, etc., so in California and Washington, US, state laws have been put into effect to prohibit the sale and installation of friction materials containing 0.5 mass% or more of copper in new cars from 2025 onwards.

Therefore, in NAO materials, titanates have been attracting attention as a component that plays a role in the transfer film other than copper. Titanates include titanates with tunnel crystal structures (e.g., potassium hexatitanate) and titanates with layered crystal structures (e.g., lithium potassium titanate and magnesium potassium titanate), and are used alone or in combination depending on the application of the friction material. For example, a friction material composition containing a non-fibrous titanate compound powder and a barium sulfate powder having a volume-based cumulative 50% particle size (D ₅₀ ) of 0.1 μm to 20 μm has been proposed (Patent Document 1).

International Publication No. 2018/164028

Although low-steel materials have a large friction coefficient and good stability, they are highly aggressive to mating materials, and dirt on wheels caused by wear dust from the friction material and rotor (mating material) is a problem. Therefore, it is necessary not only to reduce the copper content in the friction material, but also to reduce the amount of wear dust during braking. One method of reducing wear dust is to reduce the load on the friction brakes, and one of these is the spread of regenerative braking by converting cars to electric vehicles (EVs) and hybrids. However, in this case, it is expected that the mechanism will not work when the battery is fully charged, and the load on the brakes will increase due to the increase in the weight of the car due to the battery. In addition, regenerative braking is not effective enough in reducing wear dust because the level of regeneration is not uniform depending on the car model and driving conditions.

Furthermore, brake emissions are scheduled to be regulated in Europe from 2025 onwards. The Euro 7 proposal published by the European Commission on November 10, 2022 states that brake dust will be officially regulated in addition to the existing exhaust gas emissions regulations. Specifically, it is proposed that the PM (particulate matter) 10 value be 7 mg/km/vehicle or less from 2025 to 2034, and 3 mg/km/vehicle or less from 2035 onwards. However, conventional low-steel materials produce a lot of brake dust, making it difficult to achieve this as is. Furthermore, PM2.5 is currently being discussed, and the particle size of wear dust is also being emphasized.

On the other hand, potassium hexatitanate, which has a thermally stable crystal structure, is a promising titanate that provides a friction coefficient in the high load range, but its use is being discouraged, especially in Europe, due to concerns that it may contain WHO fibers (fibrous particles with a long axis of 5 μm or more, a short axis of 3 μm or less, and an aspect ratio of 3 or more) that exceed environmental standards. Lithium potassium titanate and magnesium potassium titanate are known as titanates that are free of concerns about containing WHO fibers, but although they have excellent abrasion resistance, the friction coefficient in the high load range is an issue, and no titanate suitable for low-steel materials is known.

The present invention has been made in consideration of the above circumstances, and aims to provide a friction material composition that does not contain a copper component or contains a small amount of copper component, less than 0.5 mass %, but generates little fine abrasion dust such as PM10 (particulate matter suspended in the air with a particle diameter of 10 μm or less) and PM2.5 (particulate matter suspended in the air with a particle diameter of 2.5 μm or less) during braking and can form a low-steel material with a high friction coefficient, as well as a friction material and friction member using the friction material composition.

The present invention provides the following friction material composition, as well as a friction material and a friction member using the friction material composition.

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, the content of the steel-based fibers being 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, the titanate being a salt of one or more elements selected from the group consisting of alkali metals and alkaline earth metals, and the decomposition rate of the titanate being 30% by mass or more and 100% by mass or less when the titanate is heated at 800°C for 1 hour in a nitrogen atmosphere.

Item 2. The friction material composition according to item 1, in which the production rate of titanate having a hollandite crystal structure when the titanate is heated at 800°C for 1 hour in a nitrogen atmosphere is 10% by mass or more and 100% by mass or less.

Item 3: The friction material composition according to item 1 or 2, wherein the titanate is at least one of lithium potassium titanate and magnesium potassium titanate.

Item 4: The friction material composition according to any one of items 1 to 3, wherein the titanate is a plate-like particle.

Item 5. The friction material composition according to any one of items 1 to 4, wherein the titanate has an average particle size of 0.1 μm or more and 100 μm or less.

Item 6. The friction material composition according to any one of Items 1 to 5, wherein the titanate has a specific surface area of 0.1 m ² /g or more and 10 m ² /g or less.

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.

Item 8: The friction material composition according to any one of items 1 to 7, 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.

Item 9: The friction material composition according to any one of items 1 to 8, in which the mass ratio of the titanate to the steel-based fibers (titanate/steel-based fibers) is 0.1 or more and 3.0 or less.

Item 10. The friction material composition according to any one of items 1 to 9, wherein the mass ratio of the titanate to the binder (titanate/binder) is 0.4 or more and 8.0 or less.

Item 11: The friction material composition according to any one of items 1 to 10, wherein the average fiber length of the steel-based fibers is 0.1 mm or more and 5 mm or less.

Item 12. The friction material composition according to any one of items 1 to 11, wherein the steel-based fibers are curled fibers.

Item 13. The friction material composition according to any one of items 1 to 12, 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.

Item 14: A friction material that is a molded product of the friction material composition described in any one of items 1 to 13.

Item 15: A friction member comprising the friction material described in Item 14.

According to the present invention, it is possible to provide a friction material composition that does not contain a copper component or contains a small amount of copper component (less than 0.5 mass%), but can form a low-steel material that generates little fine wear dust such as PM10 and PM2.5 during braking and has a high friction coefficient, as well as a friction material and a friction member that use the friction material composition.

The following describes an example of a preferred embodiment of the present invention. However, the following embodiment is merely an example. The present invention is not limited to the following embodiment.

<1. Friction material composition>
The friction material composition of the present invention has a copper content of less than 0.5 mass % in terms of copper element relative to 100 mass % of the total amount of the friction material composition, and is made of a binder, steel-based fibers, and titanium. The friction material composition contains a titanium oxide, the content of the steel fiber is 10% by mass or more and less than 30% by mass based on 100% by mass of the total amount of the friction material composition, and the titanate is an alkali metal and an alkaline earth metal. a salt of one or more elements selected from the group consisting of metals, the decomposition rate of the titanate being 30% by mass or more when the titanate is heated at 800° C. for 1 hour in a nitrogen atmosphere; The friction material composition of the present invention is characterized in that the content of the friction material is 100 mass % or less. In addition, the friction material composition of the present invention may further contain other materials as necessary. refers to a composition used in a friction material.

In the present invention, the content of copper component 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, so that the environmental load can be reduced compared to conventional friction material compositions. In this specification, "no copper component is contained" means that none of copper fibers, copper powder, and copper-containing alloys (brass, bronze, etc.) and compounds are blended as raw materials of the friction material composition.

In addition, because the friction material composition of the present invention has the above-mentioned configuration, it is possible to form a low-steel material that generates less fine wear dust such as PM10 and PM2.5 during braking and has a high friction coefficient.

Traditionally, titanate has been known as a component other than copper that plays a role in the transfer film in NAO materials. By blending titanate with NAO materials, a coating is formed, which then migrates to the mating material to form a transfer film. Traditionally, low-steel materials have been difficult to form a coating, and friction causes the iron of the rotor to fuse with the iron of 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.

In contrast, when titanate is blended into a friction material composition containing 10% by mass or more and less than 30% by mass of steel-based fibers as in the present invention, contrary to expectations, a coating is unlikely to be formed on the surface of the friction material, and furthermore, the steel-based fibers are unlikely to detach. This is thought to be because the frictional heat causes a binder such as phenolic resin to react with the titanate, and the resulting carbides and other substances are present on the friction surface, preventing the fusion of iron to iron. Therefore, it is thought that the detachment of steel-based fibers is suppressed, wear is reduced, and dust is also reduced. Therefore, the low-steel material formed by 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. In addition, since there is less copper in the wear dust generated during braking compared to conventional products, the environmental load can also be reduced.

As described above, the titanate used in the friction material composition of the present invention has a decomposition rate of 30% by mass or more and 100% by mass or less when heated at 800°C for 1 hour in a nitrogen atmosphere. The decomposition rate of the titanate can be calculated by measuring the content (mass%) of undecomposed material (titanate before heating) in the powder after heating at 800°C for 1 hour in a nitrogen atmosphere and using the following formula (1).

Decomposition rate (mass%) = 100 - percentage of undecomposed matter...Equation (1)

More specifically, the percentage of undecomposed titanate can be determined by performing X-ray diffraction measurements on samples before and after heating at 800°C for 1 hour in a nitrogen atmosphere.

For example, the X-ray diffraction spectrum of the mixture obtained by mixing the sample before and after heating with standard silicon powder is measured using an X-ray diffraction measurement device. As the standard silicon powder, for example, silicon powder (purity 99.9%) manufactured by Rare Metallic Co., Ltd. can be used. In addition, the mass ratio of the sample (powder) after heating to the standard silicon powder can be, for example, sample:silicon = 1:0.1 to 1:1.

Next, the integrated intensities of the peaks observed in the obtained X-ray diffraction pattern at diffraction angles 2θ = 10.9° to 11.6° derived from the titanate before heating and the undecomposed titanate after heating, and the peaks observed in the diffraction angles 2θ = 28.0° to 28.7° derived from the standard silicon powder, are measured. The content of the undecomposed titanate after heating can be determined from the ratio of the integrated intensity of the peak of the titanate before heating after normalization with the standard silicon powder to the integrated intensity of the peak of the titanate after heating.

The X-ray diffraction measurement can be performed by wide-angle X-ray diffraction method, and CuKα radiation (wavelength 1.5418 Å) can be used. As an X-ray diffraction measurement device, for example, Rigaku Corporation's "Ultima IV" can be used.

The inventors have found that by setting the decomposition rate of the titanate used in the friction material composition within the above range, it is possible to increase the friction coefficient when used in a friction material. In particular, in the present invention, it is possible to increase the friction coefficient of the friction material in the high load range.

Specifically, when a titanate whose decomposition rate is within the above range when heated at 800°C for 1 hour in a nitrogen atmosphere is used, it is believed that a titanate with a hollandite crystal structure will be generated under high load friction (high load region). Since particles with a hollandite crystal structure are harder than titanates with other structures, they act as an abrasive under high load friction and have a large friction coefficient. The above nitrogen atmosphere is set assuming, for example, the interface state (state where oxygen is blocked) when the pad and rotor are rubbing against each other.

For example, when the titanate is lithium potassium titanate, the decomposition rate is preferably 40% by mass or more, more preferably 55% by mass or more, and even more preferably 70% by mass or more, and preferably 100% by mass or less, from the viewpoint of further increasing the friction coefficient of the friction material and further improving the stability of the friction coefficient.

For example, when the titanate is magnesium potassium titanate, the decomposition rate is preferably 50% by mass or more, more preferably 65% by mass or more, and even more preferably 75% by mass or more, from the viewpoint of further increasing the friction coefficient of the friction material and further improving the stability of the friction coefficient, and is preferably 95% by mass or less, and even more preferably 89% by mass or less.

The titanate used in the friction material composition of the present invention preferably has a production rate of titanate with a hollandite crystal structure of 10% by mass or more and 100% by mass or less when heated at 800°C for 1 hour in a nitrogen atmosphere. The production rate can be obtained by measuring the content (mass%) of titanate with a hollandite crystal structure in the powder after heating the titanate at 800°C for 1 hour in a nitrogen atmosphere.

More specifically, the titanate is heated at 800°C for 1 hour in a nitrogen atmosphere, and then the resulting powder is subjected to X-ray diffraction measurement to determine the content of titanate with a hollandite crystal structure.

For example, the X-ray diffraction spectrum of the mixture obtained by mixing the heated sample (powder) with standard silicon powder is measured using an X-ray diffraction measurement device. As the standard silicon powder, for example, silicon powder (purity 99.9%) manufactured by Rare Metallic Co., Ltd. can be used. In addition, the mass ratio of the heated sample (powder) to the standard silicon powder can be 1:0.1 to 1:1.

Next, the integrated intensities of the peaks from the undecomposed material (titanate before heating) observed at diffraction angles 2θ = 10.9° to 11.6° in the obtained X-ray diffraction pattern, the peaks from the titanate with a hollandite crystal structure observed at diffraction angles 2θ = 27.5° to 28.0°, and the peaks from the standard silicon powder observed at diffraction angles 2θ = 28.0° to 28.7° are measured, and the content (mass%) of the titanate with a hollandite crystal structure can be calculated from a calibration curve created in advance (integral intensity calibration curve of the peaks from the standard silicon powder and the peaks from the titanate with a hollandite crystal structure).

For example, when the titanate is lithium potassium titanate, the production rate of the titanate having a hollandite crystal structure is preferably 20% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and preferably 100% by mass or less, from the viewpoint of further increasing the friction coefficient of the friction material and further improving the stability of the friction coefficient.

For example, when the titanate is magnesium potassium titanate, the production rate of the titanate having a hollandite crystal structure is preferably 15% by mass or more, more preferably 30% by mass or more, and is preferably 90% by mass or less, more preferably 75% by mass or less, even more preferably 60% by mass or less, and particularly preferably 45% by mass or less, from the viewpoint of further increasing the friction coefficient of the friction material and further improving the stability of the friction coefficient.

The friction material composition of the present invention will be described in more detail below.

(1-1. Binder)
The binder used in the friction material composition of the present invention integrates the steel fibers, titanates, etc. contained in the friction material composition to provide strength. There are no particular limitations on the binder used in the friction material composition of the present invention, and a thermosetting resin that is usually used as a binder for friction materials can be used.

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; urea resins, etc. One of these may be used alone, or two or more may be used in combination. Among these, phenolic resins (straight phenolic resins) and modified phenolic resins are preferred from the viewpoint of further improving the heat resistance, moldability, and friction characteristics of the friction material. As the phenolic resin, either resol-type phenolic resins or novolac-type phenolic resins can be used, but novolac-type phenolic resins are preferred from the viewpoint of production stability and cost. In addition, the novolac-type phenolic resin may contain additives such as a curing agent and a curing accelerator (e.g., hexamethylenetetramine, etc.) as necessary.

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, and even more preferably 12% by mass or less, based on 100% by mass of the total amount of the friction material composition. By keeping the binder content within the above range, an appropriate amount of binder is filled into the gaps in the blended materials, and even better friction characteristics can be obtained.

(1-2. Steel-based fibers)
Examples of the steel-based fibers used in the friction material composition of the present invention include steel fibers and stainless steel fibers, with steel fibers being preferred.

Examples of steel fibers include straight fibers obtained by chatter vibration cutting and curled fibers obtained by cutting long fibers. Straight fibers are linear fibers. Curled fibers, on the other hand, have a shape with curved parts, and include simple arcs, wavy fibers, and fibers bent in a spiral or vortex shape.

Among these, it is preferable that the steel fibers are curled fibers, from the viewpoint of reducing the amount of fiber that falls off 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 attached to the friction material, and the friction material is less likely to fall off the friction surface.

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, the average fiber length of the steel-based fibers is preferably 0.1 mm or more, more preferably 0.5 mm or more, and even more preferably 1.1 mm or more, from the viewpoint of further improving reinforcing properties.

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, the average fiber diameter of the steel-based fibers is preferably 10 μm or more, more preferably 30 μm or more, from the viewpoint of further preventing the steel-based fibers from falling off.

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

The content of the steel fibers is 10% by mass or more, preferably 12% by mass or more, 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, more preferably 23% by mass or less, even more preferably less than 20% by mass, and particularly preferably 18% by mass or less.

(1-3. Titanates)
The titanate used in the friction material composition of the present invention is a salt of one or more elements selected from the group consisting of alkali metals and alkaline earth metals.

Examples of the alkali metal include lithium, sodium, potassium, rubidium, cesium, and francium. Among them, from the viewpoint of further improving the friction and wear characteristics of the friction material, it is preferable that the alkali metal is one or more selected from the group consisting of lithium, sodium, and potassium.

Examples of alkaline earth metals include beryllium, magnesium, calcium, strontium, barium, and radium. Of these, magnesium or calcium is preferred as the alkaline earth metal from the viewpoint of further improving the friction and wear characteristics of the friction material.

Specific examples of the titanate include potassium titanate, sodium titanate, lithium potassium titanate, and magnesium potassium titanate. Among these, from the viewpoint of further improving the wear resistance of the friction material and further reducing the risk of containing WHO fiber, it is preferable that the titanate is at least one of lithium potassium titanate and magnesium potassium titanate.

In the present invention, the titanate is preferably a non-fibrous particle from the viewpoint of the working environment. Examples of non-fibrous particles include spherical (including those with slight irregularities on the surface and those with an approximately spherical shape such as an elliptical cross section), columnar (including those with an approximately columnar overall shape such as a rod, cylinder, prism, strip, approximately cylindrical, approximately strip), plate, block, shape with multiple protrusions (amoeba, boomerang, cross, confetti, etc.), and irregular shapes. Among these, the titanate is preferably a plate-shaped particle. The titanate may also be a porous particle. These various particle shapes can be arbitrarily controlled by the manufacturing conditions, particularly the raw material composition, the firing conditions, etc. In addition, the various particle shapes can be analyzed, for example, by observation with a scanning electron microscope (SEM).

In this specification, "non-fibrous particles" refers to particles in which the longest side of the rectangular parallelepiped with the smallest volume (circumscribed rectangular parallelepiped) among the rectangular parallelepipeds circumscribing the particle is the major axis L, the second longest side is the minor axis B, and the shortest side is the thickness T (B>T), with L/B being 5 or less. In addition, "having multiple convex portions" refers to a shape that, when projected onto a flat surface, is different from ordinary polygons, circles, ellipses, etc. and has convex portions in two or more directions. Specifically, these convex portions refer to the parts that correspond to the parts that protrude from a polygon, circle, ellipse, etc. (basic figures) that are fitted to a photograph (projection drawing) taken with a scanning electron microscope (SEM).

The average particle size of the titanate is preferably 0.1 μm or more, more preferably 1 μm or more, even more preferably 3 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, and particularly preferably 20 μm or less. When the average particle size of the titanate is within the above range, the friction characteristics can be further improved when the friction material is produced.

In this specification, the average particle size refers to the particle size ( _D50 ) at a volume-based cumulative 50% in the particle size distribution measured by a laser diffraction method. This _D50 is the particle size at the point where the cumulative value reaches 50% when the number of particles is counted from the smallest particle size on a cumulative curve obtained by calculating the particle size distribution on a volume basis and assuming the total volume to be 100%.

The specific surface area of the titanate is preferably 0.1 m ² /g or more, more preferably 0.3 m ² /g or more, even more preferably 0.5 m ² /g or more, and preferably 10 m ² /g or less, more preferably 6 m ² /g or less, and even more preferably 5 m ² /g or less. When the titanate is lithium potassium titanate, the specific surface area is preferably 1 m ² /g or more, preferably 3 m ² /g or less. When the titanate is magnesium potassium titanate, the specific surface area is preferably 2 m ² /g or more, preferably 4 m ² /g or less. When the specific surface area of the titanate is within the above range, the friction characteristics can be further improved when the friction material is produced. The specific surface area can be measured in accordance with JIS Z8830.

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 8 mass% or less.

When the titanate is lithium potassium titanate, the alkali metal ion elution rate is preferably 1% by mass or more, and preferably 6% by mass or less. When the titanate is magnesium potassium titanate, the alkali metal ion elution rate is preferably 0.5% by mass or more, more preferably 2.6% by mass or more, and preferably 6% by mass or less, and more preferably 3.5% by mass or less.

In the curing reaction of novolac phenolic resin, which is an example of a thermosetting resin used in a friction material composition, the curing agent (or curing accelerator), for example, hexamethylenetetramine, opens its ring and bonds with the hydroxyl groups in the novolac phenolic resin, initiating the curing reaction. However, if alkali metal ions are present at this time, they are thought to cause an ion exchange reaction with the hydrogen ions in the hydroxyl groups in the novolac phenolic resin, inhibiting the bond between hexamethylenetetramine (curing agent (or curing accelerator)) and the novolac phenolic resin (thermosetting resin) (curing inhibition). On the other hand, it is thought that the wear and destruction of the friction material due to braking causes alkali components derived from titanates to elute onto the friction surface.

Therefore, by setting the alkali metal ion elution rate to the above upper limit or less, it is possible to prevent inhibition of curing of the thermosetting resin during hot and pressure molding, and as a result, it is possible to further improve the crack resistance at high temperatures and high loads. In addition, 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 using the friction material composition 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 the crack resistance of the friction material and the suppression of rusting of the rotor at an even higher level.

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

In order to further improve the adhesion between the titanate and the binder used in the friction material composition, a treatment layer made of a surface treatment agent may be formed on the surface of the titanate. Examples of the surface treatment agent include silane coupling agents and titanium coupling agents. Among these, silane coupling agents are preferably used, and amino-based silane coupling agents, epoxy-based silane coupling agents, and alkyl-based silane coupling agents are more preferably used. The above surface treatment agents may be used alone or in combination of two or more types.

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.

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.

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

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. For example, a wet method can be used in which the surface treatment agent is dissolved in a solvent that promotes hydrolysis (e.g., water, alcohol, or a mixture thereof) to form a solution, and the solution is sprayed onto the titanate.

The amount of the surface treatment agent used to treat the surface of the titanate is not particularly limited, but 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 parts by mass or more and 20 parts by mass or less per 100 parts by mass of titanate.

As the titanate, a granulated form of titanate treated with the above-mentioned surface treatment agent or the above-mentioned binder can also be used. The average particle size of the granular titanate is preferably 100 μm or more and preferably 200 μm or less.

The method for producing the titanate used in the friction material composition of the present invention is not particularly limited, and it can be produced, for example, by mixing the raw titanate having a layered crystal structure (hereinafter referred to as the "raw titanate") with an acid (acid treatment) and calcining the compound obtained by the acid treatment.

Examples of raw titanates include those described in WO 2002/010069 and WO 2003/037797.

The acid used in the acid treatment is not particularly limited, and any known acid can be used. Examples of acids used in the acid treatment include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and organic acids such as acetic acid. Two or more acids may be used in combination as necessary.

The acid treatment can be carried out by mixing an acid with an aqueous slurry of the raw titanate. The concentration of the aqueous slurry is not particularly limited and can be selected appropriately from a wide range. Considering workability, the concentration of the aqueous slurry may be about 1% by mass to 30% by mass. The amount of acid mixed with the aqueous slurry is, for example, preferably 0.01 to 0.5 equivalents relative to the interlayer elements of the raw titanate.

After the acid treatment, the solids are separated from the slurry by filtration, centrifugation, etc. The separated solids can be washed with water and dried as necessary.

The calcination can be carried out using an electric furnace or the like, for example, at a temperature range of 100°C to 600°C, preferably 400°C to 600°C, for 1 to 12 hours, and more preferably 1 to 10 hours. After calcination, the resulting powder may be crushed to a desired size or sieved to loosen it. In this manner, the titanate used in the present invention can be obtained.

The titanate prepared by the above method is believed to be able to increase the decomposition rate of the titanate described above in a high-temperature nitrogen atmosphere, to easily produce titanate with a hollandite-type crystal structure, and to produce an appropriate amount of titanate without excessive decomposition of the titanate and production of titanate with a hollandite-type crystal structure.

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, even more preferably 25% by mass or less, particularly preferably 20% by mass or less, and most preferably 18% by mass or less. By keeping the titanate content within the above range, it is possible to further reduce wear dust.

The mass ratio of the titanate to the 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, even more preferably 1.5 or less, and particularly preferably 1.2 or less. By setting the mass ratio of the titanate to the steel-based fibers within the above range, detachment of the steel-based fibers can be further suppressed.

The mass ratio of the titanate to the binder (titanate/binder) is preferably 0.4 or more, more preferably 0.6 or more, even more preferably 1.5 or more, and 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 the titanate to the binder within the above range, the amount of carbide present on the friction surface can be optimized, and the detachment of steel-based fibers can be further suppressed.

(1-4. Other materials)
In addition to the above-mentioned binder, steel-based fiber, and titanate, other materials usually used in friction material compositions (such as a fibrous base material, an organic friction modifier, an inorganic friction modifier, a lubricant, a pH adjuster, and a filler) may be blended into the friction material composition of the present invention, if necessary.

The content of 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.

(1-4-1. Fiber 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.

When the friction material composition contains a fiber base material other than steel-based fibers, the content is preferably 0.1 mass% or more, and 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.

Examples of inorganic fibers include glass fibers, rock wool, ceramic fibers, biodegradable ceramic fibers, biodegradable mineral fibers, biosoluble fibers (SiO ₂ —CaO—SrO fibers, etc.), wollastonite fibers, silicate fibers, and mineral fibers.

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).

Examples of organic fibers include aromatic polyamide (aramid) fibers, fibrillated aramid fibers, acrylic fibers (homopolymer or copolymer fibers whose main raw material is acrylonitrile), fibrillated acrylic fibers, cellulose fibers, fibrillated cellulose fibers, and phenolic resin fibers.

Examples of carbon-based fibers include flame-retardant fibers, PAN-based carbon fibers, pitch-based carbon fibers, activated carbon fibers, and other carbon-based fibers.

The above-mentioned fiber base material is preferably aramid fiber, since it provides the friction material with appropriate water absorption, makes it easier for moisture in the air to be absorbed inside the friction material, makes it easier for the alkaline components of the titanate to dissolve, and is expected to provide a rust-preventing effect for steel-based fibers.

In order to further improve heat resistance, it is preferable that the fiber base material is a para-aramid fiber, such as poly-p-phenylene terephthalamide.

In order to further improve the moldability of the friction material and the retention of the filler, it is preferable that the fiber base material is fibrillated aramid fiber (also called aramid pulp).

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

When the friction material composition contains fibrillated aramid fibers, the content is preferably 1 mass% or more, preferably 10 mass% or less, more preferably 8 mass% or less, and even more preferably 6 mass% or less, based on 100 mass% of the total amount of the friction material composition. If the content of fibrillated aramid fibers is equal to or more than the above lower limit, the crack resistance and wear resistance are improved. Also, if the content of fibrillated aramid fibers is equal to or less than the above upper limit, deterioration of crack resistance and wear resistance due to uneven distribution of fibrillated aramid fibers and other materials can be more reliably prevented.

(1-4-2. Organic friction modifiers)
The organic friction modifier is a friction modifier that is blended for the purpose of further improving the noise and vibration performance and wear resistance of the friction material. Examples of the organic friction modifier include unvulcanized or vulcanized rubber powder 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, etc. Among these, one type may be used alone, or two or more types may be used in combination.

When the friction material composition contains an organic friction modifier, the content is preferably 0.1% by mass or more, and 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, based on 100% by mass of the total amount of the friction material composition.

(1-4-3. Inorganic friction modifiers)
Inorganic friction modifiers are friction modifiers that are blended for the purpose of preventing deterioration of the heat resistance of friction materials, improving wear resistance, and further improving the friction coefficient, etc. Examples of inorganic friction modifiers include abrasives, metal powders, and other inorganic fillers.

The abrasive material can be selected appropriately based on the material of the rotor, which acts as an abrasive and improves the coefficient of friction, and can be selected based on the Mohs hardness of the mating material.

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 tetroxide, etc.), chromite, quartz, and iron sulfide.

In addition, if the particle size of the abrasive is large, the friction coefficient can be increased during high-load braking, but the friction coefficient during light-load braking is not stable. On the other hand, if the particle size of the abrasive is small, the friction coefficient during light-load braking is stable, but there is a risk of the friction coefficient being 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. In addition, 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 wear dust.

When the friction material composition contains an abrasive, the content is preferably 0.1 mass % or more, preferably 30 mass % or less, more preferably 15 mass % or less, and even more preferably less than 10 mass % relative to 100 mass % of the total amount of the friction material composition, from the viewpoint of achieving both low wear dust and a high coefficient of friction.

Examples of metal powders include powders of metals such as aluminum, zinc, iron, and tin, either alone or in alloy form. One of these may be used alone, or two or more may be used in combination.

Other inorganic fillers include vermiculite, clay, mica, talc, dolomite, chromite, mullite, calcium silicate, titanates other than the titanates mentioned above (hereinafter referred to as "other titanates"). One of these may be used alone, or two or more may be used in combination.

Other titanates include potassium hexatitanates such as TERRACESS JSL, TERRACESS JSL-R, TERRACESS DP-R, TERRACESS DP-A, and TERRACESS DP-AS manufactured by Otsuka Chemical Co., Ltd., TXAX-MA and TXAX-A manufactured by Kubota Corporation, and TOFIX-S and TOFIX-SNR manufactured by Toho Titanium Co., Ltd.; sodium hexatitanates such as TERRACESS DSR manufactured by Otsuka Chemical Co., Ltd.; potassium octatitanates such as TERRACESS TF-SS, TERRACESS TF-S, TERRACESS TF-L, and TERRACESS JP manufactured by Otsuka Chemical Co., Ltd.; and TERRACESS PM and TERRACESS Potassium magnesium titanate such as PS; potassium lithium titanate such as TERRACESS L, TERRACESS L-SS, and TERRACESS JSM-M manufactured by Otsuka Chemical Co., Ltd., can be used. Other titanates that are preferably used include sodium hexatitanate, potassium octatitanate, potassium magnesium titanate, and potassium lithium titanate.

When the friction material composition contains other titanates, the mass ratio of the other titanates to the friction modifier of the present invention (other titanates/friction modifier of the present invention) is preferably 0.1 or more and preferably 3 or less, from the viewpoint of the friction coefficient in the high load region.

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

When the friction material composition contains a lubricant, the content is preferably 0.1 mass % or more, more preferably 1 mass % or more, and preferably 30 mass % or less, more preferably 20 mass % or less, based on 100 mass % of the total amount of the friction material composition.

Examples of the carbon-based lubricant include synthetic or natural graphite, flake graphite, phosphate-coated graphite, carbon black, coke, activated carbon, elastic graphitized carbon, etc., and from the viewpoint of imparting thermal conductivity, synthetic graphite and natural graphite are preferred. When a carbon-based lubricant is contained, the content is preferably 0.1 mass% or more, more preferably 1 mass% or more, and even more preferably 2 mass% or more, based on 100 mass% of the total amount of the friction material composition, and is preferably less than 15 mass%, more preferably less than 10 mass%, and even more preferably 8 mass% or less. If the content of the carbon-based lubricant is equal to or more than the above lower limit, the friction material wear at high temperatures tends to be good. Also, if the content of the carbon-based lubricant is less than the above upper limit or equal to or less than the above upper limit, the decrease in the friction coefficient tends to be easily suppressed.

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 further reducing harmfulness to the human body, the sulfur-based solid lubricant is preferably tin sulfide or molybdenum disulfide. When a sulfur-based solid lubricant is contained, the content is preferably 0.1 mass% or more, more preferably 1 mass% or more, and even more preferably 2 mass% or more, based on 100 mass% of the total amount of the friction material composition, and is preferably less than 15 mass%, more preferably less than 10 mass%, and even more preferably 8 mass% or less. If the content of the sulfur-based solid lubricant is equal to or more than the above lower limit, rotor wear tends to be suppressed. Also, if the content of the sulfur-based solid lubricant is less than the above upper limit or equal to or less than the above upper limit, the decrease in the friction coefficient tends to be easily suppressed.

(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 hydrogen carbonate, potassium hydrogen carbonate, trisodium phosphate, disodium hydrogen phosphate, tripotassium phosphate, dipotassium hydrogen phosphate, and organic bases such as imidazole, histidine, and hexamethylenediamine, and inorganic bases are preferred from the viewpoint of cost and hygroscopicity. 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).

When the friction material composition contains a pH adjuster, the content is preferably 0.1% by mass or more and preferably 8% by mass or less relative to 100% by mass of the total amount of the friction material composition.

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

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 precipitated barium sulfate, which is artificially synthesized. The particle size of precipitated barium sulfate can be controlled by the conditions during synthesis, making it possible to produce fine barium sulfate with a low content of the desired coarse particles. It is preferable to use precipitated barium sulfate from the viewpoint of further reducing impurities and making the particle size distribution of barium sulfate particles even more uniform.

(1-5. Method for producing friction material composition)
The friction material composition of the present invention can be produced by, for example, (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 a granule 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.

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.

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

2. Friction materials and friction members
In the present invention, the friction material composition is preliminarily molded at room temperature (20° C.), and the obtained preliminarily molded body is heated and pressurized (molding pressure: 10 MPa to 40 MPa, molding temperature: 150° C. to 200° C.), and if necessary, the obtained 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 to produce a friction material having a predetermined shape.

The friction material of the present invention is used as a friction member formed so that the friction material forms a friction surface. Examples of friction members that can be formed using the friction material include (1) a configuration consisting of only the friction material, and (2) a configuration having a base material such as a backing metal and the friction material of the present invention that is provided on the base material to provide a friction surface.

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

Friction materials usually have many tiny pores formed inside, which act as escape routes for decomposition products (gases and liquids) at high temperatures, preventing a decrease in frictional properties, and also prevent squealing by reducing the friction material's rigidity and improving damping. In normal 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%.

The friction member of the present invention is composed of the friction material composition of the present invention, and therefore generates little fine wear dust such as PM10 and PM2.5 and has a large friction coefficient even when it does not contain a copper component or contains a reduced amount of copper component. Therefore, the friction member of the present invention can be suitably used in brake systems in general, such as disc pads, brake linings, clutch facings, etc., that constitute the braking devices of various vehicles and industrial machines, and can be suitably used as a friction member for regenerative cooperative brakes in particular.

The present invention will now be described in more detail with reference to specific examples.

The present invention is not limited to the following examples, and can be modified as appropriate without departing from the spirit and scope of the invention.

(Synthesis Example 1)
A 20% by mass aqueous slurry of magnesium potassium titanate (manufactured by Otsuka Chemical Co., Ltd., product name: "TERRACESS PM") was prepared, and 0.27 equivalents of sulfuric acid relative to the potassium of magnesium potassium titanate was mixed with the aqueous slurry and stirred for 2 hours at room temperature (20°C). This aqueous slurry was suction filtered, washed with deionized water, and the separated cake (solid content) was dried at 110°C for 12 hours, baked at 500°C for 1 hour in an electric furnace, and then slowly cooled. The baked product was passed through a 20-mesh sieve to obtain the target titanate 1.

(Synthesis Example 2)
A 20% by mass aqueous slurry of lithium potassium titanate (manufactured by Otsuka Chemical Co., Ltd., product name "TERRACESS L") was prepared, and 0.24 equivalents of sulfuric acid relative to the potassium of the lithium potassium titanate was mixed with the aqueous slurry and stirred for 2 hours at room temperature (20° C.). The aqueous slurry was suction filtered, washed with deionized water, and the separated cake (solid content) was dried at 110° C. for 12 hours, baked at 500° C. for 1 hour in an electric furnace, and then slowly cooled. The baked product was passed through a 20-mesh sieve to obtain the target titanate 2.

(Examples 1 to 3 and Comparative Examples 1 to 3)
<Manufacture of friction members>
The materials were mixed according to the mixing ratios shown in Table 1, and mixed for 3 minutes using an Eirich mixer. The mixture was placed in the cavity of a hot molding die heated to 150°C, and with a back plate (material: steel) placed on top, it 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 molded body obtained was placed in a thermostatic dryer heated to 210°C and held there for 2 hours to completely harden, thereby obtaining a friction member.

The materials used in Table 1 are as follows, and the powder properties were measured as follows:

(Phenol resin)
Phenolic resin: Hexamethylenetetramine-containing novolac-type phenolic resin (straight phenolic resin) powder

(Titanate 1)
Titanate 1: Titanate 1 obtained in Synthesis Example 1, decomposition rate 81% by mass (product: hollandite type 36% by mass, others 45% by mass), plate-like particles, average particle diameter 6.1 μm, specific surface area 3.62 m ² /g, alkali metal ion elution rate 0.65% by mass.

(Titanate 2)
Titanate 2: Titanate 2 obtained in Synthesis Example 2, decomposition rate 100% by mass (product: hollandite type 99% by mass, others 1% by mass), plate-like particles, average particle size 16.0 μm, specific surface area 2.08 m ² /g, alkali metal ion elution rate 1.44% by mass.

(Titanate 3)
Titanate 3: magnesium potassium titanate (manufactured by Otsuka Chemical Co., Ltd., product name "TERRACESS PM", decomposition rate 0 mass%, plate-like particles, average particle size 6.9 μm, specific surface area 1.26 m ² /g, alkali metal ion elution rate 3.60 mass%

(Titanate 4)
Titanate 4: Lithium potassium titanate (manufactured by Otsuka Chemical Co., Ltd., product name: "TERRACESS L", decomposition rate 0 mass%, plate-like particles, average particle size 16.4 μm, specific surface area 0.81 m ² /g, alkali metal ion elution rate 2.10 mass%

(Steel Fiber)
Steel fiber: manufactured by Bonstar Sales Co., Ltd., product name "Cut Wool BS-1V", curled fiber, average fiber length (cut length) 1.5 mm, average fiber diameter 50 μm

(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)
Alpha 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

(Decomposition rate of titanate)
3 g of the sample was placed in an alumina furnace tube under a nitrogen atmosphere and heated at 800 ° C. for 1 hour using an electric tubular furnace. The X-ray diffraction spectrum of the mixture obtained by mixing 1 g of the heated sample with 0.5 g of standard silicon powder (manufactured by Rare Metallic Co., Ltd., silicon powder (purity 99.9%)) was measured using an X-ray diffraction measurement device (manufactured by Rigaku Corporation, product number "Ultima IV"). The integrated intensities of the peaks derived from the undecomposed material (titanate before heating) observed at diffraction angles 2θ = 10.9 ° to 11.6 ° in the obtained X-ray diffraction pattern, the peaks derived from titanate with a hollandite crystal structure observed at diffraction angles 2θ = 27.5 ° to 28.0 °, and the peaks derived from the standard silicon powder observed at diffraction angles 2θ = 28.0 ° to 28.7 ° were measured, and the content ratios (mass%) of the undecomposed material (titanate before heating) and titanate with a hollandite crystal structure were calculated from a calibration curve created in advance. In addition, the decomposition rate of titanate and the production rate of titanate having a hollandite type crystal structure were determined.

(Particle shape of titanate)
The results were confirmed using a field emission scanning electron microscope (Hitachi High-Technologies Corporation, product number "S-4800").

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

(Specific surface area)
The measurement was performed using an automatic specific surface area measuring device (manufactured by Micromeritics, product number "TriStar II 3020").

(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, which was stirred at 80° C. for 4 hours, after which the solids were 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.

(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 an average value of 30 pieces.

<Evaluation of friction materials>
The Rockwell hardness, average friction coefficient, friction material wear amount, and wear dust amount of the friction members produced above were evaluated as follows.

(Rockwell hardness)
The Rockwell hardness of the surface of the friction member was measured according to the method of JIS D 4421. The S scale was used as the hardness scale.

(Average friction coefficient and friction material wear amount)
The surface of the friction member prepared above was polished by 1.0 mm to process it into a friction member for a scale dynamo test. Using the friction member and a rotor (a cast iron rotor belonging to type A in the ASTM standard), a friction test was performed under the conditions of 65 km/h, 3.5 m/ ^s2 , and 500 braking operations. Using the friction member and rotor that had been previously subjected to the friction test under the above conditions, a test was performed under the friction conditions in Table 2, and the average friction coefficient, friction material wear amount, and rotor wear amount were measured. The test was performed twice, and the average value was used as the measurement result.

The results are shown in Table 3 below.

(Amount of wear dust)
The surface of the friction member prepared above was ground by 1.0 mm, and processed into a friction member for a scale dynamo test. Using the friction member and a rotor (cast iron rotor belonging to type A in the ASTM standard), a friction test was performed under the conditions of 65 km/h, 3.5 m/s ² , and 500 braking cycles, and an abrasion dust collector was connected to the scale dynamo. An MCI sampler (equipped with a filter to collect PM10-2.5 and PM2.5) manufactured by Tokyo Dylec Co., Ltd. was attached to the abrasion dust collector. Using the friction member and rotor that had been previously subjected to the abrasion test under the above conditions, a test was performed under the friction conditions in Table 2, and the mass of particulate matter (PM10-2.5 and PM2.5) collected by the filter was measured. The test was performed twice, and the average value was used as the measurement result.

The results of Examples 1 to 3 and Comparative Example 3 are shown in Table 4 below.

From Tables 3 and 4, it was confirmed that the friction material compositions of Examples 1 to 3 can form low-steel materials with a large friction coefficient and low generation of fine wear dust such as PM10 and PM2.5 during braking, even if they do not contain a copper component or the copper content is as small as less than 0.5 mass%.

On the other hand, the friction material compositions of Comparative Examples 1 and 2, which used titanates with a decomposition rate of less than 30% by mass, did not have sufficient friction coefficients. Also, the friction material composition of Comparative Example 3, which did not contain titanates, generated a large amount of wear dust.

Claims (15)

A friction material composition having a copper content of less than 0.5 mass % in terms of elemental copper,
The composite material comprises a binder, steel-based fibers, and a titanate;
The content of the steel fiber is 10% by mass or more and less than 30% by mass, based on 100% by mass of the total amount of the friction material composition;
the titanate is a salt of one or more elements selected from the group consisting of alkali metals and alkaline earth metals,
The friction material composition, wherein a decomposition rate of the titanate when the titanate is heated at 800° C. for 1 hour in a nitrogen atmosphere is 30% by mass or more and 100% by mass or less. The friction material composition according to claim 1, wherein the production rate of titanate having a hollandite crystal structure when the titanate is heated at 800°C for 1 hour in a nitrogen atmosphere is 10% by mass or more and 100% by mass or less. The friction material composition according to claim 1 or 2, wherein the titanate is at least one of lithium potassium titanate and magnesium potassium titanate. The friction material composition according to claim 1 or 2, wherein the titanate is a plate-like particle. The friction material composition according to claim 1 or 2, wherein the average particle size of the titanate is 0.1 μm or more and 100 μm or less. The friction material composition according to claim 1 or 2, wherein the titanate has a specific surface area of 0.1 m ² /g or more and 10 m ² /g or less. The friction material composition according to claim 1 or 2, wherein the alkali metal ion elution rate of the titanate is 0.01 mass% or more and 15 mass% or less. The friction material composition according to claim 1 or 2, 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. The friction material composition according to claim 1 or 2, wherein the mass ratio of the titanate to the steel-based fibers (titanate/steel-based fibers) is 0.1 or more and 3.0 or less. The friction material composition according to claim 1 or 2, wherein the mass ratio of the titanate to the binder (titanate/binder) is 0.4 or more and 8.0 or less. The friction material composition according to claim 1 or 2, wherein the average fiber length of the steel-based fibers is 0.1 mm or more and 5 mm or less. The friction material composition according to claim 1 or 2, wherein the steel-based fibers are curled fibers. The friction material composition according to claim 1 or 2, 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. A friction material that is a molded product of the friction material composition according to claim 1 or 2. A friction member comprising the friction material according to claim 14.