JP2009114051A - Hollow powder, method for producing the same, and friction material comprising the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide hollow powder, a method for producing the same, and a friction material comprising the same. <P>SOLUTION: A titanium compound and an alkali metal compound are mixed and fired, the resulting alkali titanate and an inorganic oxide powder (e.g., zircon) having Mohs hardness of 6-8 are dispersed in a solvent to form slurry, and this slurry is spray-dried and heat-treated, whereby hollow powder can be produced in which alkali titanate particles having a shape such as the shape of a rod, a column or a cylinder and inorganic oxide particles are united. When this hollow powder is used as a friction material, its wear resistance can be improved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hollow powder composed of alkali titanate and an inorganic oxide, and in particular, alkali titanate particles having a rod-like, columnar, columnar, strip-like, granular and / or plate-like shape, and Mohs hardness of 6-9. The present invention relates to a hollow body powder formed by bonding inorganic oxide particles, a manufacturing method thereof, and a friction material including the same.

  Alkali titanate is known as a material useful as a friction material for friction sliding members such as brake linings, disk pads, and clutch fading that constitute braking devices in automobiles, railway vehicles, aircraft, industrial machinery, and the like. Conventionally, as such a friction material, a friction material in which asbestos (asbestos) is dispersed in an organic or inorganic binder and formed by binding has been used. However, asbestos (asbestos) has insufficient friction and wear characteristics such as heat resistance, and has environmental health problems such as carcinogenicity, so there has been a strong demand for the development of alternatives in recent years. This is an urgent issue.

In response to such a demand, a friction material using an alkali titanate such as fibrous potassium titanate as a base fiber or a friction modifier has been proposed. In particular, potassium titanate fibers do not have carcinogenic properties such as asbestos, have excellent heat resistance, and have excellent characteristics that are effective in preventing fade phenomenon and improving the thermal stability of friction characteristics. In particular, among the potassium titanates represented by the general formula K ₂ O · nTiO ₂ (n is an integer of 1 to 12), the potassium 6 titanate fiber or the 8 potassium titanate fiber in which n is 6 or 8 has a tunnel structure. The friction material containing the above crystal structure has particularly excellent heat resistance and the like.

  However, many conventional potassium titanate fibers have an average fiber diameter of 0.1 to 0.5 μm and an average fiber length of 10 to 20 μm, and are recommended by the World Health Organization (WHO) (inhalable fibers and WHO fibers to be used: other than fibrous compounds having an average minor axis of 3 μm or less, an average fiber length of 5 μm or more, and an aspect ratio of 3 or more.

  Further, there is a problem that the conventional method for producing alkali titanate fibers or alkali titanate whiskers is complicated. For example, in the case of potassium titanate, a titanium compound such as titanium oxide and a potassium compound such as potassium carbonate are mixed and fired, then immersed in water for defibration, and further neutralized with acid to adjust the potassium component and dry. Manufactured. In particular, potassium 6 titanate and potassium 8 titanate, which are excellent in heat resistance, have a tunnel structure, so that it is difficult to grow crystals in a whisker shape or a fiber shape. First, potassium dititanate or tetratitanate having a layered crystal structure. It is necessary to synthesize potassium fibers and then adjust the pH, and then calcination again to convert them into tunnel-structure crystals, and to pass through special steps such as defibrating the obtained fibrous material. For this reason, there is a problem that the manufacturing cost increases, and the manufactured potassium titanate becomes an expensive material. Furthermore, potassium titanate fibers that have been industrialized have low bulk specific gravity, poor fluidity, shortage of supply in the manufacturing process, and problems such as blocking and adhering to the walls of the supply path. . In addition, when the friction material is manufactured, it is difficult to uniformly mix with the raw materials, and it is difficult to obtain a uniform friction material, and there is still a problem in terms of quality control.

  In order to solve these problems, potassium titanate having a layered / plate-like shape instead of a fibrous shape and having a major axis of 10 to 500 μm and a minor axis (thickness) of 50 to 1000 nm is disclosed (for example, see Patent Document 1). ). This potassium titanate does not have a fiber shape. However, such potassium titanate cannot be said to have sufficient handleability and fluidity when it is contained in a friction material as a friction modifier. Moreover, the manufacturing method of these potassium titanates is still complicated, and the present condition is that the manufacturing cost is high and economical merit cannot be enjoyed.

JP 2000-265157 A

  The object of the present invention is mainly in the form of a rod, a column, a column, a strip, excellent as a base material fiber for friction material and / or a friction modifier, in view of the above-mentioned problems. Provided are a hollow body powder obtained by combining alkali titanate particles having a granular and / or plate-like shape and inorganic oxide particles having a Mohs hardness of 6 to 9, a production method thereof, and a friction material containing the hollow body powder. There is.

  In such a situation, as a result of intensive studies by the present inventors, a rod-like, columnar, columnar, strip-like, granular and / or plate-like shape having a shape different from that of a conventional alkali titanate is obtained. Hollow body powder consisting of hollow shell made by combining alkali titanate compound particles with inorganic oxide particles has excellent handling and fluidity, and has excellent heat resistance when used as a friction modifier. It has been shown that this hollow body powder can be produced easily and inexpensively, and the present invention has been completed.

  That is, the hollow body powder of the present invention comprises an alkali titanate particle having a rod-like, columnar, columnar, strip-like, granular and / or plate-like shape, and an inorganic oxidation having a Mohs hardness of 6 to 9 (6 to 9). It consists of a shell of a hollow body combined with physical particles. The alkali titanate particles have an average minor axis of 3 μm to 10 μm, an average aspect ratio of 1.5 to 10 or an alkali titanate average minor axis of 1 μm to 3 μm, and an average major axis of 3 μm to 5 μm. It is preferable. The average particle diameter (outer diameter) of the hollow body powder is preferably 20 to 200 μm. With such a shape, the handleability is improved, and the material has excellent fluidity when adjusted as a friction material. In particular, when the alkali titanate particles constituting the hollow body powder of the present invention are potassium titanate, a single phase of potassium hexatitanate useful as a friction material, or a mixed phase of potassium titanate and potassium titanate is useful. It is good to make it. In addition, the inorganic oxide constituting the hollow body powder of the present invention is preferably contained in an amount of 1 to 3% by weight (1 to 3% by weight) with respect to the alkali titanate particles. As a result, a friction material containing such a hollow body powder as a friction material can increase its porosity, and can realize friction performance excellent in fade resistance, squeal resistance, and the like.

  In addition, the hollow body powder of the present invention includes a step of mixing an aggregate or granulated titanium compound and an alkali metal compound having an average particle size of 0.1 mm or more and 10 mm or less, and a mixture obtained by this mixing. A slurry is formed by dispersing the alkali titanate (first step) obtained by firing the above and the alkali titanate thus obtained and inorganic oxide powder having a Mohs hardness of 6 to 9 in a solvent. And a step of spray drying the slurry, and a step of heat-treating the powder obtained by spray drying (second step).

  In the present invention, the step of mixing the titanium compound and the alkali metal compound is performed by a vibrating rod mill. By mixing with a vibrating rod mill, the titanium compound and the alkali metal compound can be mixed more uniformly than in the case of mixing by other methods. As a result, an alkali titanate having a desired composition that does not contain an unreacted titanium compound can be produced by the first step. In particular, a potassium hexatitanate single phase preferable as a friction material or a potassium titanate mixed with potassium tetratitanate and potassium hexatitanate can be produced.

  The firing temperature of the mixture in the first step is preferably 800 ° C. or higher and 1300 ° C. or lower when the alkali metal compound is a potassium compound. In general, by increasing the firing temperature, potassium titanate having a long (large) average minor axis and an average length (average major axis) can be produced. In addition to the firing temperature, the shape (minor axis and major axis) of the potassium titanate particles obtained can also be adjusted by adjusting the heating rate during the firing process. That is, when the temperature rising rate is 0.5 ° C. to 2 ° C./min and the firing temperature is 1000 ° C. to 1300 ° C., the average minor axis is 3 μm or more and 10 μm or less, and the average aspect ratio (major axis / minor axis) is 1.5 to 10. Of potassium titanate can be obtained. Moreover, when the temperature rising rate is 2 ° C. to 5 ° C./min and the firing temperature is 1000 to 1300 ° C., potassium titanate having an average minor axis of 1 μm to 3 μm and an average major axis of 3 μm to 5 μm can be obtained. .

Further, the heat treatment step after spray drying in the second step is preferably performed at 750 ° C. or higher and 1300 ° C. or lower. By performing the heat treatment at such a temperature, a hollow body powder of alkali titanate composed of a shell having a hollow body structure in which the alkali titanate particles obtained by the first step and the inorganic oxide particles are combined can be produced. This hollow body powder has relatively high fracture strength (2.0 kg / cm ² or more) because adjacent alkali titanate particles are bonded by sintering or fusion by heat treatment at 750 ° C. or higher and 1300 ° C. or lower. . Therefore, when this is mixed as a friction material with other components, the alkali titanate particles constituting the hollow body powder can be mixed without separation. As a result, the porosity of the molded body can be increased, and friction performance excellent in fade resistance, squeal resistance, and the like can be realized.

  Hereinafter, the manufacturing method of the hollow body powder concerning this invention is demonstrated in detail. The hollow body powder production method of the present invention comprises a first step of producing an alkali titanate particle by mixing an aggregate or granulated titanium compound and an alkali metal compound, and firing the obtained mixture. It includes at least a second step in which alkali titanate particles and inorganic oxide powder having a Mohs hardness of 6 to 9 are dispersed in a solvent to form a slurry, which is spray-dried and then heat-treated.

  Therefore, first, a method for producing an alkali titanate in the first step of the present invention will be described below. Examples of the titanium compound used in the first step of the present invention include titanium dioxide, titanium suboxide, orthotitanic acid or a salt thereof, metatitanic acid or a salt thereof, titanium hydroxide, peroxotitanic acid or a salt thereof, and the like. Or these can be used in combination of 2 or more types. Among these, titanium dioxide is preferable. This is because it is excellent in miscibility and reactivity with the alkali metal compound and is inexpensive. The crystal form is preferably a rutile type or anatase type. In particular, when rutile type titanium dioxide is used, the resulting alkali titanate crystals are preferable.

  In the present invention, aggregates or granules of these titanium compounds are used as raw materials. Among these, an aggregate (including granules) or a granulated body of titanium dioxide is particularly preferable, and the average particle size is preferably 0.1 mm or more, more preferably 0.5 to 10 mm, and further preferably 0.5 to 1 mm. It is. If the average particle size is too small, it cannot be uniformly mixed with the alkali metal compound, and in order to mix more uniformly, when mixed with a mill having a high pulverization energy such as a vibration mill, it is fixed and mixed. This is because it becomes difficult. On the other hand, if it is too large, uniform mixing becomes difficult and the efficiency becomes poor. However, even a large aggregate or granulated body exceeding 10 mm can be used as an aggregate or granulated body of the titanium compound of the present invention by making it 10 mm or less by crushing and pulverizing.

  Here, the aggregate in the present invention is a secondary particle in which primary particles are aggregated, a tertiary particle in which secondary particles are aggregated, and / or an n + 1 primary particle in which more n-order particles are aggregated (n is 3 or more). An integer) or the like formed with coarse particles (including granules), and an average particle diameter of 0.1 mm or more and 10 mm or less. On the other hand, since the primary particles are usually difficult to monodisperse, such as titanium dioxide powder having an average particle size of about several μm (at most about 20 μm) or aggregates of titanium dioxide powder, secondary particles are formed. It does not include such things. However, the agglomerate of the present invention may contain a small amount of such titanium dioxide powder (a small amount that does not hinder uniform mixing). FIG. 1 shows an SEM photograph of a titanium oxide aggregate preferably used in the present invention, and FIG. 2 shows an SEM photograph of a conventional commercially available titanium oxide powder (for pigment).

  In addition, the average particle diameter of the aggregate or granulated body of the titanium compound in the present invention refers to a value measured according to a JISK0069 chemical product screening test method. Further, in this specification, the average particle diameter of the aggregate or granule is measured by this method unless otherwise specified.

  This aggregate of titanium dioxide is produced from titanium sulfate or titanyl sulfate (sulfuric acid method titanium oxide), produced by oxidizing or hydrolyzing titanium tetrachloride in the gas phase (gas phase method titanium oxide), Alternatively, it can be produced by neutralizing or hydrolyzing a titanium tetrachloride aqueous solution or alkoxy titanium. In particular, in general, in the production process before making a final product such as titanium oxide for pigment, coarse particles are removed by adjusting the particle size by pulverizing, pulverizing or classifying the aggregated particles. It is preferable to use an intermediate product before treatment, so-called clinker. That is, these clinker is a preferred aggregate of the titanium compound of the present invention, and by using the aggregate as a raw material, it is possible to uniformly mix the mixture by suppressing sticking of the mixture during pulverization and mixing with the alkali metal compound. It becomes. As a result, it is possible to produce a desired alkali titanate without undergoing treatment such as component adjustment of the raw material.

  Further, instead of the aggregate of titanium compound, a granulated body of titanium compound may be used. Such a granulated body can be produced by granulating commercially available fine titanium oxide by spray drying, adding a binder, kneading and granulating, or the like. By using such a granulated body of a titanium compound as a raw material, even if a mechanical mixing means such as a vibration mill with a high pulverization energy is employed, adhesion or sticking to the inner wall of the vibration mill can be suppressed. As a result, the titanium compound and the alkali metal compound can be mixed relatively uniformly as in the above-described aggregate titanium compound.

In the first step of the present invention, the mixing ratio of the raw materials when producing the alkali titanate is 1 for the alkali titanate (M ₂ O · nTiO ₂ : M is an alkali metal) produced by the alkali metal compound after the firing reaction. In terms of mole, the aggregate or granulated titanium compound is 0.5 to 10 moles, preferably 1 to 8 moles as titanium atoms, and the alkali metal compound is 1 to 3 moles, preferably 1 as alkali metal atoms. .5 to 2.5 moles. In particular, when potassium tetratitanate is produced, when 1 mole of potassium tetratitanate (K ₂ O · 4TiO ₂ ) produced after the calcination reaction is 1 mole, the titanium dioxide aggregate or granule is used as a titanium atom. It is 3.5 to 4.5 mol, preferably 3.8 to 4.2 mol, particularly preferably 4.0 mol, and the potassium compound is 1.8 to 2.2 mol, preferably 1.9, as a potassium atom. -2.1 mol, particularly preferably 2 mol. In the case of producing potassium 6 titanate, the titanium dioxide aggregate or granulated product is used as a titanium atom when the amount of potassium 6 titanate (K ₂ O · 6TiO ₂ ) produced after the baking reaction is 1 mol. 5 to 6.6 mol, preferably 5.8 to 6.2 mol, particularly preferably 6.0 mol, and the potassium compound is 1.8 to 2.2 mol, preferably 1.9 to 2, as a potassium atom. .1 mol, particularly preferably 2 mol. At this time, as described later, when adding metal titanium powder or titanium hydride powder to a mixture of titanium compound and alkali metal compound in an aggregate or granulation, the metal titanium powder or titanium hydride powder is oxidized and titanium dioxide. Therefore, it is necessary to adjust the mixing ratio by including the metal titanium powder or titanium hydride powder as a titanium source of the titanium compound in the aggregate or granulated body.

  In the present invention, the composition of the alkali titanate obtained in the first step can be controlled simply by adjusting the raw material ratio. In the conventional method, when the titanium compound and the alkali metal compound are reacted, the alkali metal compound is used in excess of the theoretical amount because the reactivity is low and the alkali metal compound is lost. However, in the method of the present invention, a mixture of a titanium compound and an alkali metal compound having a theoretical amount substantially the same as the target alkali titanate is used as a raw material, and this is subjected to a baking reaction to obtain alkali titanate particles having the target composition. Obtainable.

  As a mixing method in the present invention, either a dry mixing method or a wet mixing method can be adopted, but the dry mixing method is preferable from the viewpoint of simplifying the process. However, as a mixing means used for mixing, a conventional V-type blender, ball mill, or the like cannot sufficiently uniformly mix the titanium compound and the alkali metal compound in the aggregate or granulated body. For this reason, it is desirable to employ mechanical grinding means such as a vibration mill, a vibration rod mill, a vibration ball mill, a bead mill, a turbo mill, and a planetary ball mill. Particularly preferred is a vibrating rod mill filled with rod-shaped rods as grinding media. In the vibrating rod mill, the titanium compound and the alkali metal compound in the aggregate or granulated material are mixed while being pulverized to pulverize a powder having a large particle size between the rods, while excessively pulverizing a finer powder like a ball mill. There are few things. In particular, titanium oxide has strong adhesion due to the hydroxyl groups originally present on the surface, and the specific surface area increases as the particle size decreases. For this reason, when it is excessively pulverized, the pulverized material is easily fixed inside the vibration mill. However, in the present invention, such pulverized material is prevented from being fixed, and uniform pulverization and mixing can be performed as compared with other mixing methods. In particular, when using titanium dioxide aggregate or granulated material as a raw material as an aggregate of titanium compound as described above, and pulverizing and mixing with a vibrating rod mill, the coarse particles of titanium dioxide are pulverized and crushed. Overpulverization of primary particles that are fine to some extent is suppressed. As a result, sticking of titanium dioxide inside the mill is suppressed, and uniform mixing can be achieved. On the other hand, when a powder such as a titanium dioxide pigment is used as a raw material, fine primary particles are easily over-pulverized, easily fixed, and uniform mixing is difficult. In addition, when titanium ore such as ilmenite is used as a raw material, it is difficult to control the composition of alkali titanate, and therefore it is preferable to use pure titanium dioxide.

  In the present invention, the expression “uniform” refers to the case where the aggregate or granulated titanium compound in the present invention is not used as a raw material, for example, a pigment such as titanium dioxide powder is used as a raw material, and this is mixed with an alkali metal compound. This shows that the raw material is evenly dispersed as compared with the case of the above. Alternatively, it indicates that the raw material is dispersed more uniformly when mixed by a vibration mill in the present invention, particularly by a vibration rod mill, as compared with the case of mixing by a conventional V-type blender or ball mill.

  Further, when a titanium compound and an alkali metal compound are pulverized and mixed in a vibration mill, particularly a vibration lot mill, it is desirable to add an appropriate amount of alcohol. The amount of alcohol added is 0.1 to 3.0% by weight with respect to the weight of all pulverized products, including titanium compounds and alkali metal compounds, and additives such as anti-agglomeration agents to be described later. It is preferable to set it as 3 to 1.0 weight%. Further, it is preferable that the pulverization and mixing be performed at a temperature equal to or higher than the boiling point of the alcohol to which the temperature inside the mill is added, and the pulverization and mixing be performed while the alcohol is vaporized. Thereby, adhesion and adhesion of the titanium compound inside the mill can be suppressed, and a mixture in which the aggregate of the titanium compound and the alkali metal compound are more uniformly dispersed can be obtained. Alcohols include methanol, ethanol, amyl alcohol, allyl alcohol, propargyl alcohol, ethylene glycol, propylene glycol, erythrol, 2-ptene-1,4-diol, glycerin, pentaerythritol, arabit, sorbit, peptide. , Polyethylene glycol, polypropylene glycol, polyglycerin and the like. Of these, methanol and ethanol having a relatively low boiling point are preferred.

  Furthermore, an additive such as an anti-agglomeration agent or a lubricant may be added to suppress aggregation and adhesion of the titanium compound in a mixing container such as a vibration mill. The additive is preferably an additive that does not remain in the generated alkali titanate by decomposition, combustion, or vaporization when the titanium compound and alkali metal compound mixture is fired. Examples of such additives include celluloses, fatty acids, saccharides, cereals, ureas, polymers, and the like. Specifically, sugars such as methylcellulose, lignin, wood powder, pulp powder, natural fiber powder, stearic acid, ammonium stearate, sorbitan distearate, xylose, glucose, galactose, sucrose, starch, dextrin, wheat flour, soybean Powder, rice flour, sugar, urea, biurea, semicarbazide, guanidine carbonate, aminoguanidine, azodicarbonamide, acrylic resin powder, polypropylene powder, polyethylene powder, polystyrene powder, etc. Some wood powder, pulp powder and natural fiber powder are preferred.

  As a mixing method in the present invention, when a wet mixing method is used, pure water, a normal organic solvent such as alcohol, acetone, MEK, or THF is used as the solvent, but the dispersibility of the mixed powder is improved. In order to mix uniformly, it is preferable to use a surfactant and a dispersant in combination.

  Further, if necessary, the mixture of the aggregate or granulated titanium compound and alkali metal compound may further contain metal titanium powder or titanium hydride powder. In this case, it is preferable to set it as 0.01-0.2 mol with respect to 1 mol of titanium atoms in a titanium compound, Furthermore, it is preferable to set it as 0.03-0.1 mol. When titanium titanium powder or titanium hydride powder is blended in this way, it can be burned at the same time in the reaction vessel to suppress the occurrence of temperature distribution inside the reaction vessel, and the reaction can be performed more uniformly. An alkali titanate having a desired composition can be obtained.

  The alkali metal compound of the present invention is preferably one or more metals selected from potassium, sodium and lithium compounds. In particular, a potassium compound which is a raw material of potassium titanate useful as a friction modifier is preferable. Moreover, a lithium compound which is a raw material of lithium titanate useful as an electrode material for a lithium ion secondary battery is also preferably used. These alkali metal compounds are carbonates, hydroxides, oxalates and the like, and those that melt in the firing reaction are preferred, and carbonates or hydroxides are particularly preferred. These are preferable because they are easily melted or decomposed in the calcination reaction with the titanium compound, and the reaction easily occurs, and carbon dioxide gas, water, etc. are generated after the decomposition, and no impurities remain in the product. When producing potassium titanate, potassium oxide, potassium carbonate, potassium hydroxide, potassium oxalate, or the like is used as the potassium compound, and potassium carbonate is preferably used. These potassium compounds can be used alone or in combination of two or more. When producing sodium titanate, sodium carbonate, sodium hydroxide, sodium oxalate, or the like is used as the sodium compound, preferably sodium carbonate. When manufacturing lithium titanate, they are lithium carbonate and lithium hydroxide, and lithium carbonate is preferable. In the present invention, when potassium titanate is produced, a titanium compound such as titanium oxide and a potassium compound such as potassium carbonate are mixed to perform a baking reaction. In this case, the shape of the obtained potassium titanate is preferably controlled by mixing a lithium compound such as lithium carbonate with the potassium compound. In addition, addition of an alkaline earth metal compound such as a magnesium compound or a barium compound is also preferable because the formation of fibrous crystals can be suppressed.

  The uniform mixture of the aggregate or granulated titanium compound and alkali metal compound obtained as described above is fired to react the titanium compound and the alkali metal compound. Thereby, a rod-like, columnar, columnar, strip-like, granular and / or plate-like alkali titanate is obtained. Firing is carried out in a reaction vessel, or a binder is added to the mixture to form a molded body, which is directly fired. In consideration of the reactivity and the shape of the alkali alkali titanate obtained, it is preferable to fill the reaction vessel with the entire mixture and to fire.

  The reaction vessel for firing is preferably made of ceramics and is made of a normal ceramic material such as alumina, and when the above mixture is placed or charged, it is difficult for air to enter between the mixture. Is used. Specific examples include a cylindrical object, a columnar object having a recess, a rectangular object having a recess, a dish-like object, and the like. Among these, a cylindrical or rectangular object having a certain depth of recesses formed in a part of these is preferable in order to prevent infiltration of oxygen in the air during firing.

  Further, when filling the ceramic reaction vessel with the mixture, it is preferable to interpose a sheet material made of carbonized material at least at the bottom of the ceramic reaction vessel between the ceramic reaction vessel and the mixture. In this way, by interposing the sheet material, the alkali metal compound in the mixture melts at the time of firing, and the alkali metal compound is lost or the molten alkali metal compound penetrates into the ceramic reaction vessel. Can be avoided. Moreover, when these sheet materials are interposed at least in the inner wall portion formed by the concave portion of the ceramic reaction vessel in contact with the mixture, the loss of potassium compounds and the penetration into the ceramic reaction vessel can be avoided more reliably. It is more preferable because it is possible. Furthermore, it is particularly preferable that these sheet materials are interposed in the entire inner wall portion formed by the concave portion of the ceramic reaction vessel because the loss of the alkali metal compound and the penetration into the ceramic reaction vessel can be avoided almost completely.

  The sheet material made of carbonized material is carbonized when fired and finally burned out, and is made of a material that does not generate softened or fluidized material when fired. Fiber, bark or thermosetting resin is used. For example, in the case of paper, ordinary paper that is hard to be carbonized and softened such as vinyl chloride that is softened is used, and so-called unbleached kraft paper, double-bleached kraft paper, packaging such as single gloss bleach Information paper such as paper, cardboard base paper, newspaper paper, high-quality paper, medium-quality paper, recycled paper, book paper, cast-coated paper, art paper, PPC paper, and the like are used. Moreover, as natural fiber, cotton, hemp, silk, etc. are used, for example. Moreover, as a thermosetting resin, a phenol resin, an epoxy resin, a melamine resin etc. are used, for example. The shape of the sheet material is a sheet, a woven fabric, a non-woven fabric, or a bag.

The firing temperature varies depending on the type and crystal form of the alkali titanate, but in the case of potassium titanate, it is usually 800 to 1300 ° C, preferably 1000 to 1300 ° C. The shape of the obtained potassium titanate can be controlled by adjusting the firing temperature, and larger potassium titanate can be obtained by performing the firing temperature at a higher temperature. However, when the temperature is lower than 800 ° C., the reaction does not proceed sufficiently. Further, firing at a high temperature exceeding 1300 ° C. requires a furnace capable of withstanding it, which is expensive and close to the melting point of potassium titanate, making it difficult to control the shape and 1300 ° C. The following firing is preferred. In the case of Li ₄ Ti ₅ O ₁₂ having a spinel crystal structure in lithium titanate, the temperature is usually 800 to 1000 ° C., preferably 850 to 950 ° C. In the case of _Li 2 TiO ₃ is also usually 950 to 1,450 ° C., preferably from 950 to 1200 ° C.. In the case of 6 sodium titanate, the temperature is usually 400 to 900 ° C, preferably 500 to 800 ° C. Moreover, baking time is 1 to 10 hours in the said temperature range, Preferably it is 2 to 5 hours. Although it cools to normal temperature after a baking reaction, a temperature increase rate is 0.5-20 degree-C / min from room temperature to the said baking temperature, Preferably it carries out at the rate of 1-10 degree-C / min. The cooling rate may be from 0.5 to 10 ° C./min, preferably from 1 to 5 ° C./min, from the firing temperature to 300 ° C., preferably at a relatively slow cooling rate. Thus, the alkali titanate of this invention can be obtained by adjusting a calcination temperature, a temperature increase rate, and a cooling rate. In particular, in the method for producing potassium titanate according to the present invention, by using such a firing temperature, a relatively slow temperature increase rate and a relatively slow cooling rate, the growth of potassium titanate particles is promoted and shortened. A rod-like, columnar or plate-like crystal having a large diameter can be obtained. Especially, the shape of the obtained potassium titanate, especially the length of an average minor axis can be controlled by adjusting a calcination temperature and a temperature increase rate. For example, when the firing temperature is 1000 ° C. to 1300 ° C. and the rate of temperature rise is 0.5 to 2 ° C./min, potassium titanate having an average minor axis of 3 μm or more and 10 μm or less can be obtained. Here, the average minor axis of the obtained potassium titanate increases as the temperature increases with respect to the firing temperature and as the rate of temperature increase decreases. It should be noted that when the temperature rising rate is higher than 2 ° C./min, in particular, when the temperature rising rate is 2 ° C. to 5 ° C./min, potassium titanate having an average minor axis of 1 μm or more and 3 μm or less can be obtained.

  The alkali titanate obtained as described above is mechanically crushed or pulverized as necessary. In particular, when fibrous potassium titanate having a major axis of 5 μm or more is contained, it is preferable that this be crushed to be less than 5 μm. Here, known means can be adopted as the means for mechanically crushing or crushing, and a vibration mill, a vibration ball mill, a bead mill, a turbo mill, a planetary ball mill, and the like are used.

  Moreover, you may classify or sieve the alkali titanate after crushing or grinding | pulverization as needed. In particular, when fibrous potassium titanate is included, classification or sieving is preferably performed in order to remove those having a minor axis of less than 3 μm (or less than 1 μm in some cases) or powders.

  As mentioned above, in the manufacturing process of the alkali titanate in the 1st process of this invention, since the titanium compound and alkali metal compound of an aggregate or a granulated body are grind | pulverized and mixed uniformly, after baking reaction, crystallinity, purity An alkali titanate compound having a high desired composition can be obtained. In particular, in the production of potassium titanate, the target potassium titanate, 6 potassium titanate, or a mixture thereof can be directly subjected to the firing reaction without adjusting the components such as pH adjustment and acid washing, which has been conventionally performed after the firing reaction. Can be manufactured by. The potassium titanate obtained by such a method of the present invention has an average minor axis (or average thickness) of 3.0 to 10 μm and an average aspect ratio (major axis / minor axis) of 1.5 to 10. It has a rod shape, columnar shape, columnar shape, strip shape, granular shape and / or plate shape. The average minor axis was measured by image analysis of a scanning electron micrograph, and the particle diameter was measured for about 200 particles, and the average was obtained (the average minor axis and average length in the examples described below). (Average major axis) was also measured in the same manner). Similarly, the average aspect ratio is obtained by measuring the average minor axis and the average length (average major axis) with a scanning electron microscope and calculating the ratio. In addition, it is also a preferred embodiment that the above potassium titanate is mechanically crushed or pulverized and the aspect ratio is adjusted to less than 3, preferably less than 2.5.

  As for the shape of the potassium titanate, it is possible to obtain an average minor axis of 1 to 3 μm by adjusting the heating rate in addition to the firing temperature. In this case, the average minor axis is as short as 3 μm or less, but if necessary, the average major axis can be made 3 μm to 5 μm by crushing or grinding, and potassium titanate within the WHO recommended range is obtained. be able to.

  Next, the 2nd process of manufacturing a hollow body powder using the alkali titanate powder obtained by this 1st process is demonstrated below.

  First, alkali titanate particles obtained by the first step as described above, that is, alkali titanate particles such as mainly rod-like, columnar, cylindrical, strip-like, granular and / or plate-like potassium titanate, and Mohs A slurry of alkali titanate particles and inorganic oxide particles is prepared by dispersing an inorganic oxide powder having a hardness of 6 to 9 in a solvent together with a binder and stirring the mixture.

Here, examples of the inorganic oxide powder having a Mohs hardness of 6 to 9 include MgO (Mohs hardness: about 6), SiO ₂ (Mohs hardness: about 7), Cr ₂ O ₃ (Mohs hardness: about 6.5), Fe ₃ O ₄ (Mohs hardness: about 6), ZrO ₂ (Mohs hardness: about 7.5), ZrSiO ₄ (Zircon) (Mohs hardness: about 7.5), fused alumina (Mohs hardness: about 9), etc. It is done. When the Mohs hardness of the inorganic oxide powder is lower than the range of 6 to 9, the combined effect with an alkali metal titanate crystal (for example, Mohs hardness of potassium hexatitanate: about 3 to 4) cannot be sufficiently exhibited, In addition, particles having a higher hardness increase the face-to-face damage when applied to a friction material or the like. The number of inorganic oxide particles constituting the composite particles is not necessarily limited to one, and two or more inorganic oxide particles may be mixed as desired.

  The content of the inorganic oxide powder having a Mohs hardness of 6 to 9 (the total amount when two or more inorganic oxide particles are mixed) is 0.5 to 20% by weight. If the content is less than this, the effect of combining the inorganic oxide particles is not sufficiently exhibited. On the other hand, if the content exceeds 20% by weight, the characteristics of the alkali metal titanate crystals are weakened and applied to friction materials and the like. In some cases, the face-to-face damage is deteriorated. In particular, when the content is 1 to 3% by weight, particularly 1 to 2% by weight, the face-to-face damage is good, which is preferable. The average particle size of the inorganic oxide particles is preferably 1 to 10 μm. This is because fine particles having a particle size of less than 1 μm have little effect of improving the coefficient of friction in applications such as friction materials, and coarse particles exceeding 10 μm, on the other hand, cause deterioration in face-to-face damage.

  Further, organic polymers such as gelatin, dextrin, starch, gum arabic, cellulosic polymers, polyvinyl alcohol, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), polyvinyl pyrrole (PVP), hexa Propyl cellulose (HPC), phenol resin, epoxy resin, or the like can be used. Moreover, although an organic solvent and water can be used as a solvent, the water which is easy to handle is preferable. Furthermore, you may add other additives, such as surfactant, as needed. The total concentration of alkali titanate and binder in the slurry is preferably about 10 to 75% by weight. When the total concentration is less than 10% by weight, the production efficiency of the alkali titanate hollow body powder is lowered, which is not preferable. On the other hand, when the total concentration exceeds 75% by weight, the viscosity of the slurry becomes high, and it becomes difficult to obtain a hollow body powder having a particle size (outer diameter) of 200 μm or less, and the particle size distribution becomes too wide. .

  Thereafter, the produced slurry of alkali titanate and inorganic oxide is spray-dried by a spray dryer. For example, when spray drying is performed using a disk rotary spray dryer, the slurry is supplied onto a disk that rotates at high speed, and the slurry is sprayed into droplets by centrifugal force. Dry at a high temperature of from 800C to 800C. At this time, moisture is vaporized inside the droplet. At that time, the particles inside the droplets are pushed to the outside of the droplets along with the vaporization of moisture, and a spherical hollow body powder composed of a shell composed of alkali titanate particles and inorganic oxide particles is obtained. In addition to the disk rotating type, various types of spray dryers such as a pressure nozzle type, a two-fluid nozzle type, and an ultrasonic nozzle type can be used. Among these, the pressure nozzle method is a method in which high pressure is applied to the slurry and sprayed from the nozzle. The two-fluid nozzle method is a method in which slurry is sprayed together with compressed air or steam.

  The diameter (outer diameter) of the hollow body powder obtained by spray drying can be adjusted by the number of rotations of the disk and the nozzle diameter. In general, the larger the number of revolutions of the disk, the smaller the diameter of the particles obtained as the nozzle diameter decreases. For this reason, the average diameter (outer diameter) of the obtained alkali titanate hollow body powder is adjusted to 20 to 200 μm, preferably 50 to 150 μm. By adjusting in this way, handling becomes easy. In particular, a hollow powder composed of potassium titanate particles and inorganic oxide particles in this range is suitable as a friction modifier.

  Next, the powder of the hollow body obtained by spray drying is heat-treated. In this case, when the alkali titanate is potassium titanate powder, the heat treatment temperature is preferably 750 ° C. or higher and 1300 ° C. or lower. In the case of sodium titanate, it is preferably performed at 450 ° C. or higher and 900 ° C. or lower. Moreover, in the case of lithium titanate, it is preferable to carry out at 850 degreeC or more and 1200 degrees C or less. By performing heat treatment at such a temperature, adjacent alkali titanate particles are bonded together by sintering or fusion at the contact portion. FIG. 4 is a scanning electron micrograph of a hollow body powder of potassium titanate thus prepared and inorganic oxide particles having a Mohs hardness of 6 to 9. As can be seen from this drawing, adjacent potassium titanate particles having a rod-like, columnar, columnar, strip-like, granular, and / or plate-like shape are bonded to each other by sintering or fusion to form a spherical shape having a cavity inside A hollow powder having a shape is obtained.

This hollow body powder is composed of a spherical shell structure formed by bonding between adjacent alkali titanate particles and between alkali titanate particles and inorganic oxide particles having a Mohs hardness of 6 to 9. In addition, the alkali titanate particles and the inorganic oxide having a Mohs hardness of 6 to 9 may be present independently, or may be diffused and sintered with each other at the contact interface. The breaking strength of the hollow body powder is preferably 2.0 kg / cm ² or more. By setting such strength, when mixed with other materials, the fluidity is good, and the alkali titanate particles and the inorganic oxide particles constituting the shell can be mixed without being separated (dispersed). it can. For this reason, as will be described later, when this hollow body powder is blended with other components as a friction material, for example, in the mixing process when molding into a brake pad or the like, alkali titanate particles constituting the hollow body powder and inorganic oxidation The hollow body powder can be dispersed (mixed) relatively uniformly without separating (dispersing) the product particles. As a result, the porosity of the molded body can be increased, and friction performance excellent in fade resistance, squeal resistance, and the like can be realized.

  In addition, the hollow body powder in the present invention refers to a shell structure in which particles cover an internal space. For example, a balloon shape, a ping-pong ball shape, etc. are mentioned. This hollow body powder does not need to have a shell structure completely covered with particles, and also includes hollow body powders that partially have tears, gaps, voids, and / or gaps. The average diameter (outer diameter) is preferably 20 μm to 200 μm. Handling with such a particle size makes it easy to handle and suitable for use as a friction modifier. In addition, an average diameter here means the value which measured the diameter about 200 pieces by the image analysis of a scanning electron micrograph, and averaged it.

  As described above, in the method for producing a hollow body powder in the second step of the present invention, the alkali titanate particles obtained in the first step and the inorganic oxide powder having a Mohs hardness of 6 to 9 are contained in a solvent. By dispersing and forming a slurry, spray drying this, and further heat-treating, a hollow body powder having a hollow shape inside a rod-like, columnar, columnar, strip-like, granular and / or plate-like shape can be easily obtained Can be manufactured. When this hollow body powder is blended with other components to form a molded body, it can be dispersed relatively uniformly because of its shape, and the porosity of the resulting molded body can be improved. As a result, when the hollow body powder is composed of potassium titanate particles and an inorganic oxide, using this as a friction material can improve the heat resistance and fade resistance of the friction material. it can.

  Here, the blending amount of the alkali titanate in the friction material is preferably 3.0 to 50% by weight. If the amount is less than 3.0% by weight, the effect of improving the friction and wear characteristics may not be exhibited. If the amount exceeds 50% by weight, no further improvement in the effect of the friction and wear characteristics can be expected, which is economically disadvantageous. Because it becomes.

  As a specific example of the friction material of the present invention, for example, a friction material comprising a base fiber, a friction modifier and a binder can be exemplified. As a mixing ratio of each component in the friction material, 1 to 60 parts by weight of a base fiber, 20 to 80 parts by weight of a friction modifier (including alkali titanate such as potassium titanate), and 10 to 40 parts by weight of a binder. And 0 to 60 parts by weight of other components.

  Examples of the base fiber include resin fibers such as aramid fibers, metal fibers such as steel fibers and brass fibers, carbon fibers, glass fibers, ceramic fibers, rock wool, wood pulp, and potassium titanate fibers. These base fibers may be used after being subjected to a surface treatment agent such as a silane coupling agent, a titanate coupling agent, or a phosphate ester in order to improve dispersibility and adhesion with a binder.

  As the friction modifier in the friction material of the present invention, in addition to the hollow powder of the present invention, other friction modifiers may be used in combination as long as the effects of the present invention are not impaired. For example, organic powder such as vulcanized or unvulcanized natural, synthetic rubber powder, cashew resin powder, resin dust, rubber dust, carbon black, graphite powder, molybdenum disulfide, barium sulfate, calcium carbonate, clay, mica, talc, Examples thereof include diatomaceous earth, antigolite, sepiolite, montmorillonite, zeolite, or metal powders such as copper, aluminum, zinc and iron.

  As binders, thermosetting resins such as phenol resin, melanin resin, epoxy resin, acrylic resin, DAP (diallyl phthalate) resin, urea resin, natural rubber, nitrile rubber, butadiene rubber, styrene butadiene rubber, chloroprene rubber, poly Examples thereof include rubbers such as isoprene rubber and polymer elastomers, elastomers, polyamide resins, polyphenylene sulfide resins, organic resins such as thermoplastic resins such as polyimide resins and thermoplastic liquid crystalline resins, and inorganic binders such as alumina sol and silica sol.

  In addition to the above components, the friction material of the present invention may contain components such as a rust inhibitor, a lubricant, and an abrasive as necessary. There is no restriction | limiting in particular in the case of manufacture of the friction material of this invention, According to the manufacturing method of a conventionally well-known friction material, it can manufacture suitably.

  As an example of the method for producing a friction material according to the present invention, a base material fiber is dispersed in a binder, and a friction material composition is blended by combining a friction modifier and other components blended as necessary. An example is a method in which the composition is adjusted, and then the composition is put into a mold and heated under pressure to perform binder molding.

  As another example, the binder is dissolved and kneaded in a twin-screw extruder, and the side fiber is combined with the base fiber, the friction modifier, and other components blended as necessary, and after extrusion molding. An example of the method for machine-fiber processing into a desired shape can be given.

  As yet another example, the friction material composition is dispersed in water, etc., and is made on a papermaking net, dehydrated and made into a short shape, and then heated and pressed with a press machine to form a binder. An example is a method of appropriately cutting and polishing the obtained friction material to obtain a desired shape.

  The method for producing a hollow body powder according to the present invention can simplify the production process and is advantageous in terms of cost. Further, the hollow body powder production method according to the present invention can easily produce a spherical hollow body powder. And the potassium titanate particle manufactured by these manufacturing methods has a specific shape, such as a rod shape, a column shape, a column shape, a strip shape, a granular shape, or a plate shape, with few fiber shapes. Further, the hollow body powder has a hollow shell structure inside, which is advantageous in terms of fluidity. Furthermore, in particular, when the hollow body powder is composed of potassium titanate particles and inorganic oxide particles, when used as a friction material, the friction is stable over a wide temperature range from low temperature to high temperature. Has modulus and wear resistance. For this reason, the hollow body powder is suitable as a brake member material used in automobiles, railway vehicles, aircraft, various industrial devices, etc., for example, a material for clutch fading, and a brake material such as a brake lining and a disk pad. is there.

  Next, the present invention will be described more specifically with reference to examples. However, this is merely an example, and the present invention is not limited thereto.

Example 1
Aggregate titanium oxide (FIG. 1) 8.7 kg, powdered potassium carbonate 2.7 kg, titanium powder 447 g and wood chips 897 g with an internal volume of 250 liters, a diameter of 19 mm, a length of 1430 mm, 3200 g / Rod, filled into a vibration mill (manufactured by Chuo Kako Co., Ltd., trade name FV250) filled with 3010 kg of cylindrical rod media made of SS, added with 65 g of methanol, amplitude 8 mm, frequency 1000 times / minute, internal temperature 80 A mixture was obtained by pulverizing at 15 ° C. for 15 minutes. 500 g of the obtained mixture was filled in a ceramic reaction vessel having an open top, placed in an electric furnace, heated from room temperature to 1050 ° C. over 12 hours, and then in the range of 1000 to 1100 ° C. Baked for 5 hours. Then, it cooled to room temperature over 13 hours, and after cooling to normal temperature, this baked product was taken out. FIG. 3 shows an SEM photograph of this fired product, that is, aggregated potassium titanate. Since this baked product is agglomerated, this baked product was pulverized with a crusher (manufactured by Hosokawa Micron Corporation, Turbulizer TX-8) to obtain a baked product S having a desired shape (first step).

  The fired product S thus obtained was rod-shaped, columnar and / or cylindrical. The average minor axis was 3.0 μm, the average length (average major axis) was 5.9 μm, and the average aspect ratio was 2.0 (see FIG. 3). Further, when the fired product was analyzed by X-ray diffraction, it was a single-phase crystal of potassium titanate and did not contain unreacted titanium oxide. Thus, in the production method of the present invention, potassium titanate having a desired composition can be produced by a simple method, and the shape is a range recommended by WHO (average minor axis is 3 μm or less, average fiber length is 5 μm or more. And other than the fibrous compound having an aspect ratio of 3 or more).

Next, 10 kg of the obtained fired product S, 0.3 kg of zircon (ZrSiO ₄ , Mohs hardness: about 7.5), 0.2 kg of ethyl cellulose binder (trade name: Celna WN405, manufactured by Chukyo Yushi Co., Ltd.), Then, 0.1 kg of special polycarboxylic acid ammonium salt (trade name: KE-511, manufactured by Kyoyo Chemical Industry Co., Ltd.) as an additive was stirred and dispersed in a solvent of 10 kg of water to prepare a slurry of fired product S. . This slurry was spray-dried with a disk-type dryer. At that time, spray drying was performed at an atomizer rotation speed of 10000 rpm and a hot air temperature of 250 ° C. Next, the powder obtained by spray drying was placed in an electric furnace and heat-treated at 900 ° C. for 2 hours (second step). A scanning electron micrograph of the hollow body powder thus obtained is shown in FIG. The size (outer diameter) of the obtained hollow body powder was 50 to 100 μm. Further, FIG. 5 shows a Zr image obtained by a scanning electron microscope attached with an electron probe microanalyzer (EPMA) of hollow body powder having different visual fields. In this figure, the black part represents the presence part of zircon. As can be seen from this figure, a hollow body powder in which zircon is relatively uniformly dispersed is obtained. It was 3.8 kg / cm < ² > when the fracture strength of this hollow body was measured with the hardness meter (Fujiwara Manufacturing Co., Ltd. digital hardness meter KHT-40N type). Moreover, from the SEM observation of the hollow body, the adjacent potassium titanate particles constituting the hollow body powder were completely bonded at the contact portion.

Further, 15 parts by weight of the obtained hollow body powder, 3 parts by weight of aramid fiber (trade name: “Kevlar pulp”, length: 3.0 mm, manufactured by Toray DuPont Co., Ltd.), 10 parts by weight of a binder (phenol resin), Die by thoroughly mixing 9 parts by weight of organic additive (cashew dust), 10 parts by weight of graphite lubricant, 8 parts by weight of copper powder, and 30 parts by weight of barium sulfate with a mixer (Eirich Intensive Mixer, manufactured by Eirich) Then, binding molding (pressing force: 300 kgf / cm ² , temperature 150 ° C., 5 minutes) was performed. After molding, the mold was released and subjected to heat treatment (held at 160 ° C. for 1 hour and then held at 210 ° C. for 5 hours). Then, the grinding | polishing process was performed and the friction material of this invention was obtained. In addition, the organic additive and the lubricant that were normally added to the friction material were used. The porosity of the obtained friction material was measured. In addition, the friction material was subjected to a friction performance test by JASO C 406 “Brake device dynamometer test method for riding” to measure the friction coefficient and the face damage. The face-to-face damage property is a comparison of the state of wear by visual observation of the friction surface of the mating material after the test (◎: very little friction damage, ○: light, Δ: somewhat high). These measurement results are shown in Table 1.

(Comparative Example 1)
A hollow body powder was prepared in the same manner as in Example 1 except that the amount of zircon (ZrSiO ₄ , Mohs hardness: about 7.5) in Example 1 was changed to 0 kg (no addition). The size (outer diameter) of the obtained hollow body powder was 50 to 100 μm. It was 3.8 kg / cm < ² > when the fracture strength of this hollow body was measured with the hardness meter (Fujiwara Manufacturing Co., Ltd. digital hardness meter KHT-40N type). Moreover, from the SEM observation of the hollow body, the adjacent potassium titanate particles constituting the hollow body powder were completely bonded at the contact portion. Using the obtained hollow body powder, a friction material was produced in the same manner as in Example 1, and its wear coefficient and the like were measured in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)
A hollow body powder was produced without adding the zircon of Example 1 (ZrSiO ₄ , Mohs hardness: about 7.5). Instead, when producing a friction material, zircon (ZrSiO ₄ , Mohs hardness: about 7. A friction material was produced in the same manner as in Example 1 except that 0.75 parts by weight of 5) was added, and its wear coefficient and the like were measured in the same manner as in Example 1. The results are shown in Table 1. In Example 1, the same friction coefficient as in Comparative Example 2 was obtained with a small amount of added zircon.

(Example 2)
A hollow body powder was produced in the same manner as in Example 1 except that the amount of zircon (ZrSiO ₄ , Mohs hardness: about 7.5) in Example 1 was changed to 0.1 kg. It was 3.8 kg / cm < ² > when the fracture strength of this hollow body was measured with the hardness meter (Fujiwara Manufacturing Co., Ltd. digital hardness meter KHT-40N type). Moreover, from the SEM observation of the hollow body, the adjacent potassium titanate particles constituting the hollow body powder were completely bonded at the contact portion. Using the obtained hollow body powder, a friction material was produced in the same manner as in Example 1, and its wear coefficient and the like were measured in the same manner as in Example 1. The results are shown in Table 1.

  As can be seen from Table 1, by adding zircon in the hollow body powder of the present invention, a higher friction coefficient is obtained when these are used as friction materials than hollow body powder not containing zircon (Comparative Example 1). It can be maintained and the amount of wear can be reduced. In particular, by adjusting the amount of zircon added, good face-to-face damage can be obtained while maintaining a high friction coefficient. In addition, the same effect is confirmed also when using fused alumina (Mohs hardness: about 9) instead of zircon.

(Example 3)
Further, the firing pattern of Example 1 (first step) was “heated from room temperature to 1050 ° C. over 7 hours, and then fired in the range of 1000 to 1100 ° C. for 5.5 hours. Thereafter, 8 hours. The product was cooled to room temperature and then cooled to room temperature. " Since the fired product was an agglomerate containing a large amount of fibrous potassium titanate having a minor axis of 3 μm or less and a major axis of 5 μm or more, the fired product was crushed to obtain a desired shape (a shape in the range recommended by WHO). ) (Bar shape, columnar shape and / or columnar shape, average minor axis: 1.9 μm, average length (average major axis) 4.1 μm, average aspect ratio 2.3). This fired product was tested for the coefficient of friction and the like in the same manner as in Example 1. As a result, the same effect as in Table 1 was confirmed.

It is a scanning electron micrograph of the titanium oxide of the aggregate concerning this invention. It is a scanning electron micrograph of a commercially available titanium oxide for pigment. It is a scanning electron micrograph of potassium titanate obtained by the first step of the present invention. It is a scanning electron micrograph of the hollow body powder of the alkali titanate particle concerning this invention, and the inorganic oxide particle of Mohs hardness 6-8. It is a Zr image by the scanning electron microscope attached to the electron beam microanalyzer (EPMA: Electron Probe Microanalyzer) of the hollow body powder of a different visual field.

Claims (16)

  A hollow body powder comprising a hollow body-shaped shell in which alkali titanate particles having a rod-like, columnar, columnar, strip-like, granular and / or plate-like shape and inorganic oxide particles having a Mohs hardness of 6 to 9 are combined.   The hollow body powder according to claim 1, wherein the alkali titanate particles have an average minor axis of 3 μm to 10 μm and an average aspect ratio of 1.5 to 10.   The hollow body powder according to claim 1, wherein the alkali titanate has an average minor axis of 1 µm to 3 µm and an average major axis of 3 µm to 5 µm.   The hollow body powder according to any one of claims 1 to 3, wherein an average particle diameter of the hollow body powder is 20 to 200 µm.   The hollow body powder according to any one of claims 1 to 4, wherein the alkali titanate particles are composed of a single phase of potassium hexatitanate or a mixed phase of potassium tetratitanate and potassium titanate.   The hollow body powder according to any one of claims 1 to 5, wherein a content of the inorganic oxide particles having a Mohs hardness of 6 to 9 is 1 to 3 wt% with respect to the alkali titanate particles.   A friction material comprising the hollow powder according to any one of claims 1 to 6 as a friction modifier.   A step of mixing an aggregate or granulated titanium compound and an alkali metal compound having an average particle size of 0.1 mm or more and 10 mm or less, a step of firing the mixture obtained by the mixing and producing an alkali titanate, Dispersing the obtained alkali titanate and inorganic oxide powder having a Mohs hardness of 6-9 in a solvent to form a slurry, spray-drying the slurry, and heat-treating the powder obtained by spray-drying A process for producing a hollow body powder comprising at least the step of:   The method for producing a hollow body powder according to claim 8, wherein the step of mixing the titanium compound and the alkali metal compound is performed by a vibration rod mill.   The hollow body powder according to claim 8 or 9, wherein the titanium compound is titanium oxide and the alkali metal compound is a potassium compound, and the step of producing the alkali titanate by baking the mixture is performed at 800 ° C or higher and 1300 ° C or lower. Manufacturing method.   The method for producing an alkali titanate according to claim 10, wherein the baking is performed at a temperature rising rate of 0.5 ° C to 2 ° C / min and a baking temperature of 1000 ° C to 1300 ° C.   The method for producing an alkali titanate according to claim 10, wherein the baking is performed at a temperature rising rate of 2 ° C to 5 ° C / min and a baking temperature of 1000 ° C to 1300 ° C.   The manufacturing method of the hollow body powder in any one of Claims 10 thru | or 12 which heat-processes the powder obtained by making it spray-dry at 750 degreeC or more and 1300 degrees C or less.   The method for producing a hollow body powder according to claim 8 or 9, wherein the titanium compound is titanium oxide, and the alkali metal compound is a compound composed of at least one selected from potassium, sodium and lithium.   The method for producing a hollow body powder according to any one of claims 8 to 13, wherein the alkali titanate comprises a single phase of potassium hexatitanate or a mixed phase of potassium tetratitanate and potassium hexatitanate.   The method for producing a hollow body powder according to any one of claims 8 to 15, wherein a content of the inorganic oxide powder having a Mohs hardness of 6 to 9 is 1 to 3 wt% with respect to the alkali titanate.