Lithium potassium titanium oxide and method for producing same, friction modifier, friction material composition, friction material, and friction member

Abstract

Provided is lithium potassium titanium oxide which can increase a friction coefficient in a high-load region and can improve the stability of a friction coefficient when used in a friction material.　The lithium potassium titanium oxide is represented by the compositional formula: K0.10 to 0.44Li0.27Ti1.73O3.65-3.82, in which the half width of a peak observed in a range of diffractive angles 2θ of 10.9° to 11.6° in an X-ray diffraction measurement of the lithium potassium titanium oxide is 0.20° or more.

Description

Lithium potassium titanate and its manufacturing method, friction modifier, friction material composition, friction material, and friction member

[0001] The present invention relates to lithium potassium titanate, a method for producing the lithium potassium titanate, and a friction modifier, a friction material composition, a friction material, and a friction member each using the lithium potassium titanate.

[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 material is mainstream because it is less aggressive to mating materials and has an excellent balance between squeal and wear resistance. In Europe, low-steel material was used to maintain the friction coefficient during high-speed braking, but with a trend toward luxury, NAO material, which is less likely to cause brake squeal, is now being used more often.

[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 copper has high thermal conductivity, it diffuses heat generated during braking from the friction interface, thereby reducing friction material wear due to excessive temperature rise and suppressing vibration during braking. The second role of copper is to protect the friction interface 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 and forms an adhesive coating (hereinafter referred to as "transfer film"). These act as protective films, reducing friction material wear during high-temperature braking and enabling the development of a stable friction coefficient. However, friction materials containing copper contain copper in the wear powder generated during braking, which has been suggested to be a cause of river, lake, and ocean pollution. Therefore, state laws have been enacted in the US states of California and Washington 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 have attracted attention as a component other than copper that plays a role in the transfer film. 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 these are used alone or in combination depending on the application of the friction material. For example, a friction material composition containing titanate and barium sulfate with an average particle size of 0.1 μm to 20 μm (Patent Document 1) has been proposed.

[0006] International Publication No. 2018 / 164028

[0007] Hybrid and electric vehicles, which have become increasingly popular in recent years, are equipped with regenerative brakes to recover frictional energy during braking. However, this mechanism does not function when the battery is fully charged, and it is anticipated that the load on the brakes will increase due to the increased vehicle weight caused by the battery. Furthermore, with the spread of heavy, large vehicles such as SUVs, it is becoming increasingly important for friction materials to have a high coefficient of friction in high-load areas. Furthermore, in some mountainous regions, there is an issue of insufficient braking force when overloaded vehicles descend steep roads.

[0008] 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, particularly in Europe, due to concerns about the inclusion of WHO fibers (fibrous particles with a major axis of 5 μm or more, a minor axis of 3 μm or less, and an aspect ratio of 3 or more) that exceed environmental standards.On the other hand, lithium potassium titanate is known as a titanate that does not involve concerns about the inclusion of WHO fibers, but although it has excellent wear resistance, its friction coefficient in the high load range is an issue.

[0009] An object of the present invention is to provide lithium potassium titanate, which, when used in a friction material, can increase the coefficient of friction in a high load region and also improve the stability of the friction coefficient; a method for producing the lithium potassium titanate; and friction modifiers, friction material compositions, friction materials, and friction members each using the lithium potassium titanate.

[0010] The present invention provides the following lithium potassium titanate, a method for producing the lithium potassium titanate, and a friction modifier, a friction material composition, a friction material, and a friction member each using the lithium potassium titanate.

[0011] Item 1 Composition formula K ０．１０～０．４４ Li ０．２７ Ti １．７３ O ３．６５～３．８２ wherein the full width at half maximum of a peak observed in an X-ray diffraction measurement of the lithium potassium titanate in a diffraction angle range of 2θ=10.9° to 11.6° is 0.20° or more.

[0012] Item 2. The lithium potassium titanate according to Item 1, wherein the lithium potassium titanate is in the form of plate-like particles.

[0013] Item 3. The lithium potassium titanate according to Item 1 or 2, wherein the lithium potassium titanate has an average particle size of 0.1 μm or more and 100 μm or less.

[0014] Item 4: The specific surface area of ​​the lithium potassium titanate is 0.1 m ２ / g or more, 10m ２ Item 4. The lithium potassium titanate according to any one of Items 1 to 3, wherein the SiO2 content is 1 / g or less.

[0015] Item 5. The lithium potassium titanate according to any one of Items 1 to 4, wherein the lithium potassium titanate has an alkali metal ion elution rate of 0.01% by mass or more and 15% by mass or less.

[0016] Item 6: A method for producing lithium potassium titanate according to any one of Items 1 to 5, comprising the steps of preparing a raw material lithium potassium titanate, and eluting a portion of potassium from the raw material lithium potassium titanate to produce a titanium to potassium oxide molar ratio (TiO ２ / K ２ O) to 8 to 35, and then firing.

[0017] Item 7. A friction modifier comprising the lithium potassium titanate according to any one of items 1 to 5.

[0018] Item 8. A friction material composition comprising the lithium potassium titanate of any one of items 1 to 5 and a binder, wherein the copper content is less than 0.5 mass % in terms of elemental copper.

[0019] Item 9. The friction material composition according to Item 8, wherein the content of the lithium potassium titanate is 1% by mass or more and 40% by mass or less, based on 100% by mass of the total amount of the friction material composition.

[0020] Item 10. The friction material composition according to Item 8 or Item 9, wherein the mass ratio of the lithium potassium titanate to the binder (lithium potassium titanate / binder) is 0.1 or more and 8 or less.

[0021] Item 11. The friction material composition according to any one of Items 8 to 10, wherein the content of the steel fiber is less than 10% by mass, based on 100% by mass of the total amount of the friction material composition.

[0022] Item 12. A friction material, which is a molded product of the friction material composition according to any one of items 8 to 11.

[0023] Item 13. A friction member comprising the friction material according to Item 12.

[0024] According to the present invention, it is possible to provide lithium potassium titanate, which, when used in a friction material, can increase the coefficient of friction in a high load region and also improve the stability of the friction coefficient; a method for producing the lithium potassium titanate; and a friction modifier, friction material composition, friction material, and friction member each using the lithium potassium titanate.

[0025] FIG. 1 is a graph showing the relationship between the number of braking cycles and the coefficient of friction during fading in the fading test of the friction members obtained in Examples 1 and 2 and Comparative Example 1.

[0026] 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.

[0027] <1. Lithium potassium titanate> The lithium potassium titanate of the present invention is represented by the composition formula K ０．１０～０．４４ Li ０．２７ Ti １．７３ O ３．６５～３．８２ The lithium potassium titanate is also characterized in that the half width of a peak observed in the diffraction angle 2θ range of 10.9° to 11.6° in X-ray diffraction measurement is 0.20° or more.

[0028] The present inventors have found that the compound of formula K ０．１０～０．４４ Li ０．２７ Ti １．７３ O ３．６５～３．８２In the lithium potassium titanate represented by the formula (1), it has been found that by making the half width of the peak in X-ray diffraction measurement of the lithium potassium titanate 0.20° or more, when used in a friction material, it is possible to increase the friction coefficient in a high load region and also to improve the stability of the friction coefficient.

[0029] The lithium potassium titanate of the present invention is a low-crystalline compound, unlike conventional compounds. In the present invention, "low-crystalline" refers to a compound that exhibits an intermediate peak in X-ray diffraction measurement, unlike an amorphous compound that does not have a specific peak, and unlike a crystalline compound that exhibits a steep peak.

[0030] In lithium potassium titanate, a peak corresponding to the crystal plane (020 plane) corresponding to the interlayer distance in X-ray diffraction measurement is usually observed in the diffraction angle 2θ range of 10.9° to 11.6°. An intermediate peak refers to a peak observed in this diffraction angle 2θ range of 10.9° to 11.6° with a half-width of 0.20° or more. Furthermore, amorphous in X-ray diffraction measurement refers to, for example, a peak with a half-width of 5.0° or more, where almost no peak is observed and a broad halo is observed.

[0031] The half-width of the peak in lithium potassium titanate is preferably 0.25° or more, preferably 1.0° or less, and more preferably 0.8° or less. In the present invention, the half-width means the width of the diffraction angle at half the height of the peak obtained by X-ray diffraction measurement. By adjusting the half-width within this range, a friction material with a large and stable friction coefficient can be obtained when used as a friction modifier. The half-width of the peak in lithium potassium titanate can be calculated, for example, by adjusting the molar ratio of titanium to potassium in terms of oxide (TiO ２ / K ２ O) can be adjusted.

[0032] The X-ray diffraction measurement can be performed by wide-angle X-ray diffraction using CuKα radiation (wavelength 1.5418 Å). As the X-ray diffraction measurement device, for example, Rigaku Corporation's Ultima IV can be used.

[0033] In the present invention, the lithium potassium titanate is preferably non-fibrous particles from the viewpoint of the working environment. 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. Among these, the lithium potassium titanate is preferably plate-shaped particles. The lithium potassium titanate may also be porous particles. These particle shapes can be arbitrarily controlled by the production conditions, particularly the raw material composition and firing conditions. Furthermore, the particle shapes can be analyzed, for example, by scanning electron microscope (SEM) observation.

[0034] 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).

[0035] In the present invention, the average particle size of the lithium potassium titanate is preferably 0.1 μm or more, more preferably 1 μm or more, and even more preferably 3 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. When the average particle size of the lithium potassium titanate is within the above range, the friction characteristics can be further improved when a friction material is produced.

[0036] In this specification, the average particle size refers to the particle size at 50% cumulative volume in the particle size distribution measured by a laser diffraction method. 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%.

[0037] In the present invention, the specific surface area of ​​the lithium potassium titanate is preferably 0.1 m ２ / g or more, more preferably 0.3m ２ / g or more, more preferably 0.5m ２ / g or more, preferably 10m ２ / g or less, more preferably 6m ２ / g or less, more preferably 4m ２ When the specific surface area of ​​lithium potassium titanate is within the above range, the friction characteristics of the produced friction material can be further improved. The specific surface area can be measured in accordance with JIS Z8830.

[0038] In the present invention, the alkali metal ion elution rate of lithium potassium titanate is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 1% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less.

[0039] In the curing reaction of novolac phenolic resin, an example of a thermosetting resin used in a friction material composition, the curing agent (or curing accelerator), for example, hexamethylenetetramine, undergoes ring-opening and bonds with hydroxyl groups in the novolac phenolic resin, initiating the curing reaction. However, if alkali metal ions are present at this time, 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 agent (or curing accelerator)) and the novolac phenolic resin (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 lithium potassium titanate to leach out onto the friction surface.

[0040] 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 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 using the lithium potassium titanate 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 high levels of crack resistance of the friction material and high levels of suppression of rotor rusting.

[0041] 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 lithium potassium titanate.

[0042] In the present invention, in order to further improve adhesion with 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 lithium potassium 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] A known surface treatment method can be used as a method for forming a treatment layer made of a surface treatment agent on the surface of lithium potassium titanate, and 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 mixed solvent thereof) to form a solution, and the solution is sprayed onto lithium potassium titanate.

[0047] The amount of the surface treatment agent used to treat the surface of the lithium potassium 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 parts by mass or more and 20 parts by mass or less per 100 parts by mass of lithium potassium titanate.

[0048] The lithium potassium titanate used in the present invention may be granulated by treating the lithium potassium titanate with the surface treatment agent or a binder described below. The average particle size of the granular lithium potassium titanate is preferably 100 μm or more and 200 μm or less.

[0049] (Method for Producing Lithium Potassium Titanate) The method for producing lithium potassium titanate of the present invention is not particularly limited, but it can be produced, for example, by the following method. First, raw material lithium potassium titanate (hereinafter referred to as "raw material KTLO") is prepared. Next, a portion of potassium is eluted from the raw material KTLO to obtain a titanium to potassium oxide molar ratio (TiO ２ / K ２ O) to 8 or more and 35 or less (8 to 35), and then calcining. ２ / K ２ O) is preferably 20 or less, more preferably 16 or less, and even more preferably 10 or less.

[0050] The raw material KTLO is, for example, K ０．８ Li ０．２７ Ti １．７３ O ４ , K. ０．５～０．７ Li ０．２７ Ti １．７３ O ３．８５～３．９５Lithium potassium titanate having a layered crystal structure such as lepidocrocite can be used.

[0051] Furthermore, the raw material KTLO can be obtained by, for example, firing a mixture of titanium oxide or a compound that generates titanium oxide when heated (these are collectively abbreviated as "titanium compounds"), potassium oxide or a compound that generates potassium oxide when heated (these are collectively abbreviated as "potassium compounds"), lithium oxide or a compound that generates lithium oxide when heated (these are collectively abbreviated as "lithium compounds"), and, if necessary, a flux.

[0052] The titanium compound that can be used includes low-order titanium oxide, titanium oxide hydrate, titanium oxide hydrate, titanium hydroxide, etc. The titanium compounds may be used alone or in combination of two or more.

[0053] Examples of potassium compounds include potassium oxide, potassium carbonate, potassium hydroxide, and potassium nitrate. Of these, potassium carbonate or potassium hydroxide is preferably used as the potassium compound. One potassium compound may be used alone, or two or more potassium compounds may be used in combination.

[0054] Examples of the lithium compound include lithium oxide, lithium hydroxide, and lithium carbonate. As the lithium compound, lithium hydroxide or lithium carbonate can be preferably used. One type of lithium compound may be used alone, or two or more types may be used in combination.

[0055] The mixing ratio of the titanium compound, potassium compound, and lithium compound can be appropriately adjusted depending on the composition formula of the target raw material KTLO. ０．８ Li ０．２７ Ti １．７３ O ４ In the case of producing the above, the molar ratio of Ti:K:Li may be set to 1.73:0.8:0.27.

[0056] As the flux, potassium chloride, potassium fluoride, potassium molybdate, potassium tungstate, etc. can be suitably used, since they generate crystals at a temperature lower than the melting point and, as the crystals grow, have an idiomorph surrounded by flat crystal faces that reflect the crystal structure, making it easier to specify the crystal orientation.

[0057] Calcination in the production of the raw material KTLO can be carried out using an electric furnace or the like. The calcination reaction can be completed by maintaining the material at a temperature in the range of 800°C to 1100°C for 1 hour to 24 hours. After calcination, the resulting powder may be crushed to a desired size or sieved to loosen the particles.

[0058] Potassium can be eluted from the raw KTLO by mixing an acid with an aqueous slurry in which the raw KTLO is dispersed in water. The concentration of the aqueous slurry is not particularly limited and can be selected appropriately from a wide range. Taking into account workability and other factors, the concentration of the aqueous slurry may be approximately 1% by mass to 30% by mass. After preparing the aqueous slurry, the solid content is separated from the slurry by filtration, centrifugation, or the like. The separated solid content can be washed with water and dried as necessary.

[0059] The acid used here is not particularly limited, and known acids can be used. Examples of the acid 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 needed. The amount of acid added to the aqueous slurry is determined based on the molar ratio of titanium to potassium in terms of oxide (TiO ２ / K ２ The potassium elution can make the lithium potassium titanate low-crystalline.

[0060] Calcination after potassium elution can be carried out using an electric furnace or the like. The calcination is preferably held at a temperature of 100°C to 600°C, preferably 400°C to 600°C, for 1 to 12 hours, and more preferably 1 to 10 hours. The amount of alkali metal ions eluted from lithium potassium titanate can be adjusted by adjusting the calcination temperature and calcination time.

[0061] After firing, the resulting powder may be crushed to a desired size or passed through a sieve to loosen the particles. In this manner, the lithium potassium titanate of the present invention can be obtained.

[0062] <2. Friction Material Composition> The friction material composition of the present invention contains the lithium potassium titanate of the present invention and a binder, and is characterized in that the copper content is less than 0.5 mass% in terms of copper element, relative to 100 mass% of the total amount of the friction material composition. In the above friction material composition, the lithium potassium titanate of the present invention can be used as a friction modifier. Furthermore, the friction material composition of the present invention can further contain other materials as necessary. In this specification, the term "friction material composition" refers to a composition used in a friction material.

[0063] The friction material composition of the present invention contains the lithium potassium titanate of the present invention as a friction modifier, and therefore can increase the coefficient of friction in the high load region of the friction material and also improve the stability of the friction coefficient.

[0064] Furthermore, by containing less than 0.5 mass % of copper element relative to 100 mass % of the total amount of the friction material composition, or preferably by not containing any copper element, the environmental impact can be reduced compared to conventional friction material compositions. In this specification, "not containing any copper element" 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.

[0065] According to the friction material composition of the present invention, excellent friction characteristics can be obtained even when no copper component is contained or when the copper component content is reduced.

[0066] The friction material composition of the present invention is preferably an NAO material in which the content of steel fibers, such as steel fibers or stainless steel fibers, is less than 10% by mass relative to 100% by mass of the total amount of the friction material composition, which facilitates the formation of a transfer film on the surface of the mating material and provides excellent friction and wear characteristics.

[0067] (2-1. Binder) The binder integrates friction modifiers, such as lithium potassium titanate, 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.

[0068] 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. 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 as thermosetting resins from the viewpoint of further improving heat resistance, moldability, and friction properties. While both resol-type and novolac-type phenolic resins can be used as phenolic resins, novolac-type phenolic resins are preferred from the viewpoint of production stability and cost. Furthermore, novolac-type phenolic resins may contain additives such as curing agents and curing accelerators (e.g., hexamethylenetetramine) as needed.

[0069] The content of the binder in the friction material composition is preferably 5% by mass or more, more preferably 8% by mass or more, and preferably 30% by mass or less, more preferably 20% 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.

[0070] (2-2. Lithium potassium titanate) The lithium potassium titanate used in the friction material composition of the present invention is the lithium potassium titanate of the present invention described above. The content of lithium potassium titanate in the friction material composition is preferably 1% by mass or more, more preferably 5% 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 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. By setting the content of lithium potassium titanate within the above range, even more excellent friction characteristics can be obtained.

[0071] The mass ratio of lithium potassium titanate to the binder (lithium potassium titanate / binder) is preferably 0.1 or more, more preferably 0.5 or more, even more preferably 1.1 or more, and preferably 8 or less, more preferably 6 or less, and even more preferably 4 or less. By setting the mass ratio of lithium potassium titanate to the binder within the above range, the formability of the friction material can be further improved, and an appropriate transfer film can be formed.

[0072] (2-3. Other Materials) In addition to the binder and the lithium potassium titanate of the present invention, other materials typically 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, as needed.

[0073] The content of the other materials in the friction material composition is preferably 30% by mass or more and preferably 94% by mass or less, based on 100% by mass of the total amount of the friction material composition.

[0074] (2-3-1. 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.

[0075] 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.

[0076] 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 7% by mass or less, based on 100% by mass of the total amount of the friction material composition. When the rock wool content is within the above range, the friction coefficient during high-load braking can be increased.

[0077] Examples of metal fibers include fibers of simple metals or alloys such as aluminum, iron, zinc, tin, titanium, nickel, magnesium, and silicon (steel fibers, stainless steel fibers, etc.), and straight or curled metal fibers whose main component is metal, such as cast iron fibers.

[0078] Examples of organic fibers include aromatic polyamide (aramid) fibers, fibrillated aramid fibers (aramid pulp), 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.

[0079] The organic fiber is preferably an aramid fiber, since it provides the friction material with a suitable water absorption property, facilitates the absorption of atmospheric moisture into the friction material, facilitates the elution of the alkali component of the titanate, and is expected to provide a rust prevention effect for the rotor. Furthermore, from the viewpoint of further improving the formability of the friction material and further improving the retention of the filler, the organic fiber is preferably a fibrillated aramid fiber (also called aramid pulp). The specific surface area of ​​the fibrillated aramid fiber 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.

[0080] 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, based on 100% by mass of the total amount of the friction material composition. When the content of the fibrillated aramid fibers is equal to or greater than the above-mentioned lower limit, crack resistance and wear resistance are improved. On the other hand, when the content of the fibrillated aramid fibers is equal to or less than the above-mentioned upper limit, deterioration of crack resistance and wear resistance due to uneven distribution of the fibrillated aramid fibers and other materials can be more reliably prevented.

[0081] Examples of carbon-based fibers include flame-resistant fibers, PAN-based carbon fibers, pitch-based carbon fibers, activated carbon fibers, and the like.

[0082] (2-3-2. 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.

[0083] 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.

[0084] (2-3-3. Inorganic Friction Modifiers) Inorganic friction modifiers (excluding the lithium potassium titanate) are friction modifiers that are blended with the friction material to prevent deterioration in heat resistance, improve wear resistance, or further improve the coefficient of friction. Examples of inorganic friction modifiers include abrasives, metal powders, and other inorganic fillers.

[0085] The abrasive can be appropriately selected so that it acts as an abrasive and improves the coefficient of friction depending on the material of the rotor, which is the mating material, and can be selected based on the Mohs hardness of the mating material. From the viewpoint of more effectively exhibiting the coefficient of friction by the abrasive, the Mohs hardness of the abrasive is preferably 6 or more and preferably 8 or less.

[0086] Examples of abrasives include silicon carbide (silicon carbide), titanium oxide, α-alumina, γ-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. Among these, zirconia (zirconium oxide) and zircon (zirconium silicate) are preferred. The average particle size of zirconia (zirconium oxide) is preferably 1 μm to 14 μm. The average particle size of zirconium silicate is preferably 0.2 μm to 2 μm.

[0087] When the friction material composition contains an abrasive, the content thereof is preferably 0.1 mass % or more, more preferably 5 mass % or more, and is preferably 30 mass % or less, more preferably 25 mass % or less, and even more preferably 18 mass % or less, relative to 100 mass % of the total amount of the friction material composition.

[0088] 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.

[0089] Examples of other inorganic fillers include vermiculite, clay, mica, talc, dolomite, chromite, mullite, calcium silicate, titanates other than the above-mentioned lithium potassium titanate (hereinafter referred to as "other titanates"), etc. One of these may be used alone, or two or more may be used in combination.

[0090] 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 and lithium potassium titanate such as TERRACESS L, TERRACESS L-SS, and TERRACESS JSM-M manufactured by Otsuka Chemical Co., Ltd. Preferred examples of other titanates include sodium hexatitanate, potassium octatitanate, magnesium potassium titanate, and lithium potassium titanate.

[0091] When the friction material composition contains another titanate, the mass ratio of the other titanate to the lithium potassium titanate of the present invention (other titanate / lithium potassium titanate 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.

[0092] (2-3-4. Lubricant) The lubricant is preferably a solid lubricant, and examples thereof include carbon-based lubricants, metal sulfide-based 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 lubricants and metal sulfide-based lubricants.

[0093] 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 20 mass % or less, more preferably 10 mass % or less, and even more preferably 5 mass % or less, relative to 100 mass % of the total amount of the friction material composition.

[0094] Examples of the carbon-based lubricant include synthetic or natural graphite (graphite), flake graphite, phosphate-coated graphite, carbon black, coke, activated carbon, and elastic graphitized carbon, with synthetic graphite and natural graphite being preferred in terms of providing thermal conductivity more reliably. Examples of the metal sulfide-based solid lubricant include antimony trisulfide, molybdenum disulfide, tin sulfide, iron sulfide, zinc sulfide, bismuth sulfide, and tungsten disulfide, with tin sulfide and molybdenum disulfide being preferred in terms of being less harmful to the human body. These may be used alone or in combination of two or more.

[0095] (2-3-5. pH Adjuster) Examples of the pH adjuster 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 viewpoints of cost and hygroscopicity, the pH adjuster is preferably an inorganic base. 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).

[0096] 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.

[0097] (2-3-6. Filler) Examples of the filler include barium sulfate and calcium carbonate. Preferably, barium sulfate can be used as the filler. One of these may be used alone, or two or more may be used in combination.

[0098] Barium sulfate comes in two forms: elutriated barium sulfate (baryte powder), which is obtained by crushing a mineral called barite, de-ironizing it, washing it, and elutriating it, and artificially synthesized precipitated barium sulfate. The particle size of precipitated barium sulfate can be controlled by adjusting the synthesis conditions, allowing for the production of fine barium sulfate with a low content of the desired coarse particles. The use of precipitated barium sulfate is preferred from the perspective of further reducing impurities and achieving a more uniform particle size distribution of the barium sulfate particles.

[0099] (2-4. 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.

[0100] 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.

[0101] 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.

[0102] <3. 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 subjected to heat treatment in a heating furnace (150°C to 220°C, held for 1 hour to 12 hours), and then the molded body is subjected to machining and polishing, thereby producing a friction material having a predetermined shape.

[0103] 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.

[0104] The substrate is used to further improve the mechanical strength of the friction member. Examples of the material for the substrate include metal and fiber-reinforced resin. Examples of metal and fiber-reinforced resin include iron, stainless steel, glass fiber-reinforced resin, and carbon fiber-reinforced resin.

[0105] 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 blend and molding conditions are controlled so that the porosity is preferably 5% to 30%, and more preferably 10% to 25%.

[0106] The friction member of the present invention is made of the friction material composition of the present invention, and therefore can obtain excellent friction characteristics 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.

[0107] The present invention will now be described in further detail with reference to specific examples.

[0108] The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the present invention.

[0109] <Production of lithium potassium titanate> (Synthesis Example 1) Production of titanate 1 Lithium potassium titanate (K ０．８ Li ０．２７ Ti １．７３ O ４A 20% by mass aqueous slurry of lithium potassium titanate was prepared, and 0.25 equivalents of sulfuric acid relative to the potassium in the lithium potassium titanate was mixed with the slurry and stirred for 2 hours at room temperature (20° C.). The aqueous slurry was suction filtered and washed with deionized water to separate a cake (solid content). The cake was dried at 110° C. for 12 hours, calcined at 500° C. for 1 hour in an electric furnace, and then slowly cooled. The calcined product was passed through a 20-mesh sieve to obtain the target titanate 1.

[0110] Synthesis Example 2: Production of Titanate 2 Titanate 2 was obtained in the same manner as in Synthesis Example 1, except that the equivalent of sulfuric acid was changed to 0.20 equivalents.

[0111] Synthesis Example 3: Production of Titanate 3 Lithium potassium titanate (manufactured by Otsuka Chemical Co., Ltd., trade name: TERRACESS L) was used as titanate 3 as it was.

[0112] <Measurement of Physical Properties of Titanates> The physical properties of titanates 1 to 3 were measured as follows, and the results are shown in Table 1.

[0113] (Composition Formula) The crystal structure was confirmed using an X-ray diffraction measurement device (manufactured by Rigaku Corporation, product number "Ultima IV"), and the composition formula was confirmed using an ICP-AES analyzer (manufactured by SII Nanotechnologies, product number "SPS5100").

[0114] (Half Width) An X-ray diffraction pattern was measured using an X-ray diffraction measurement device (manufactured by Rigaku Corporation, product number "Ultima IV"), and the half width of the peak appearing at a diffraction angle 2θ of 10.9° to 11.6° was calculated using the attached integrated intensity calculation software.

[0115] (Average particle size) Measurement was performed using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, product number "SALD-2300"), and the particle size at 50% cumulative volume in the obtained particle size distribution was taken as the average particle size.

[0116] (Specific Surface Area) Measurement was carried out using an automatic specific surface area measuring device (manufactured by Micromeritics, product number "TriStar II 3020").

[0117] (Particle Shape) The particle shape was confirmed using a field emission scanning electron microscope (manufactured by Hitachi High-Tech Corporation, product number "S-4800").

[0118] (Alkali Metal Ion Elution Rate) The mass (X) 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) 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) and (Y) g, the alkali metal ion elution rate (mass %) was calculated based on the formula [(Y) / (X)] x 100.

[0119]

[0120] <Production of Friction Member> (Examples 1-2 and Comparative Example 1) The materials were blended according to the blending ratios listed in Table 2 and mixed for 3 minutes using an Eirich mixer. The resulting mixture was pressurized at 15 MPa for 5 seconds at room temperature (20°C) to produce a temporary compact. The temporary compact was fitted into the cavity of a hot-molding mold heated to 150°C, and with a back plate (made of steel) placed on top, the mixture was pressurized at 10 MPa to 40 MPa for 300 seconds so that the porosity of the compact was 15%. Five degassing treatments were performed between 5 and 70 seconds, measured from the start of pressurization. The resulting compact was placed in a constant-temperature dryer heated to 220°C and held there for 2 hours to fully harden, yielding a friction member. The materials used in Table 2 other than the titanates were as follows:

[0121] (Binder) Phenolic resin: Hexamethylenetetramine-blended novolac-type phenolic resin powder

[0122] (Other materials) Barium sulfate: average particle diameter 1.6 μm Natural mica: average particle diameter 180 μm Cashew dust: average particle diameter 200 μm Iron oxide: average particle diameter 0.3 μm, Mohs hardness 6 Zirconium silicate: average particle diameter 1.1 μm, Mohs hardness 7.5 Antimony trisulfide: average particle diameter 1.5 μm Synthetic graphite: average particle diameter 730 μm Aramid fiber: fibrillated para-aramid fiber (aramid pulp), fiber length 0.89 mm, specific surface area 9.8 m ２ / g Slaked lime: average particle size 0.2 μm Rock wool: average fiber length 125 μm, maximum shot content (125 μm or more) 5.0%

[0123] <Evaluation of Friction Member> The Rockwell hardness and fade test of the friction members prepared above were evaluated as follows.

[0124] (Rockwell Hardness) The Rockwell hardness of the surface of the friction member was measured according to the method of JIS D4421. The hardness scale used was the S scale. The results are shown in Table 2 below.

[0125] (Fade Test) The surface (friction surface) of the friction member was polished to 1.0 mm, and a braking effectiveness test was performed based on JASO C406. However, the first fade test conditions were changed to a speed of 160 km / h, which is assumed to be a high load, and the braking effectiveness test was performed. The rotor used was a cast iron rotor that conforms to ASTM standard number A48 / A48M.

[0126] FIG. 1 is a graph showing the relationship between the number of braking cycles and the coefficient of friction during fading in the fading test of the friction members obtained in Examples 1 and 2 and Comparative Example 1.

[0127] FIG. 1 shows that Examples 1 and 2, which used lithium potassium titanate having a half width of 0.20° or more, had a larger friction coefficient in the high load region and also had excellent stability of the friction coefficient, compared to Comparative Example 1, which used lithium potassium titanate having a half width of less than 0.20°.

[0128] Furthermore, from the test results, the average value (average μ) of the 10 braking tests in the first fade test results and Δμ (maximum - minimum) were calculated from the difference between the maximum μ and minimum μ during the first fade. The results are shown in Table 2 below.

[0129]

Claims

1. Composition formula K ０．１０～０．４４ Li ０．２７ Ti １．７３ O ３．６５～３．８２ wherein the full width at half maximum of a peak observed in an X-ray diffraction measurement of the lithium potassium titanate in a diffraction angle range of 2θ=10.9° to 11.6° is 0.20° or more.

2. 2. The lithium potassium titanate according to claim 1, wherein the lithium potassium titanate is in the form of plate-like particles.

3. 3. The lithium potassium titanate according to claim 1, wherein the lithium potassium titanate has an average particle size of 0.1 μm or more and 100 μm or less.

4. The specific surface area of ​​the lithium potassium titanate is 0.1 m ２ / g or more, 10m ２ The lithium potassium titanate according to claim 1 or 2, wherein the SiO 2 content is 1 / g or less.

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

6. The method for producing lithium potassium titanate according to claim 1 or 2, preparing a raw material lithium potassium titanate; A portion of the potassium was eluted from the raw material lithium potassium titanate to obtain a titanium to potassium oxide molar ratio (TiO ２ / K ２ O) to 8 to 35, and then firing.

7. A friction modifier comprising the lithium potassium titanate according to claim 1 or 2.

8. A composition comprising the lithium potassium titanate according to claim 1 or 2 and a binder, A friction material composition having a copper content of less than 0.5 mass % in terms of elemental copper.

9. 9. The friction material composition according to claim 8, wherein the content of the lithium potassium titanate is 1% by mass or more and 40% by mass or less, relative to 100% by mass of the total amount of the friction material composition.

10. 9. The friction material composition according to claim 8, wherein a mass ratio of the lithium potassium titanate to the binder (lithium potassium titanate / binder) is 0.1 or more and 8 or less.

11. 9. The friction material composition according to claim 8, wherein the content of the steel fibers is less than 10% by mass, based on 100% by mass of the total amount of the friction material composition.

12. A friction material which is a molded product of the friction material composition according to claim 8.

13. A friction member comprising the friction material according to claim 12.