JP2021059724A - Wear-resistant agent, coating agent, laminate, method for producing laminate, and base material coating method - Google Patents

Abstract

To provide a wear-resistant agent having wear resistance, a coating agent, a laminate employing the same, a method for producing the laminate, and a base material coating method.SOLUTION: A wear-resistant agent contains alumina particles each having a card-house structure that is formed from three or more sheets of tabular alumina, with the sheets of tabular alumina fixed to each other, the alumina particles having an average particle diameter of 3 μm or more and 1000 μm or less.SELECTED DRAWING: None

Description

The present invention relates to an abrasion resistant agent, a coating agent, a laminate, a method for producing the laminate, and a method for coating a base material.
The present application claims priority based on US62 / 912,662 provisionally filed in the United States on October 9, 2019, the contents of which are incorporated herein by reference.

It is common to form a coating film such as a resin composition on materials such as flooring materials, building materials, and automobile parts in order to impart wear resistance.

It is known that such coating materials contain inorganic particles in order to improve wear resistance. For example, Patent Document 1 discloses a floor board in which a coating film made of a synthetic resin composition containing a ceramic fiber piece and a ceramic abrasion resistance improver in a resin is formed on the surface of a base material. Patent Document 2 discloses a fitting member coated with a coating film containing a synthetic resin and inorganic particles.

Japanese Unexamined Patent Publication No. 62-225278 Japanese Unexamined Patent Publication No. 2005-273821

However, there continues to be a demand for additional compositions to achieve the wear resistance effect.

The present invention has been made in view of the above circumstances, and provides an abrasion resistant agent having abrasion resistance, a coating agent, and a laminate to which they are applied, a method for producing the laminate, and a method for coating a base material. provide.

That is, the present invention includes the following aspects.
(1) An abrasion resistant agent formed of three or more flat-plate alumina, having a card house structure to which the flat-plate alumina is fixed, and containing alumina particles having an average particle diameter of 3 μm or more and 1000 μm or less.
(2) The wear resistant agent according to (1) above, wherein the alumina particles contain silicon and / or germanium.
(3) The abrasion resistant agent according to (1) or (2) above, wherein the alumina particles contain molybdenum.
(4) The abrasion resistant agent according to (3) above, wherein the content of molybdenum with respect to 100% by mass of the alumina particles is 10% by mass or less in terms of molybdenum trioxide.
(5) A coating agent containing the wear-resistant agent according to any one of (1) to (4) above.
(6) A laminate having a base material and a layer containing the coating agent according to (5) above.
(7) A method for producing a laminate, which comprises applying the coating agent according to (5) above to a base material.
(8) A method for coating a base material, which comprises applying the coating agent according to (5) above to the base material.

According to the wear-resistant agent, the coating agent, and the laminate according to the present invention, it is possible to provide the wear-resistant agent, the coating agent, and the laminate capable of exhibiting good wear resistance.
Further, according to the method for producing a laminate according to the present invention, it is possible to produce a laminate capable of exhibiting good wear resistance.
Further, according to the base material coating method according to the present invention, good wear resistance can be imparted to the base material.

FIG. 1 is a schematic view showing an example of the configuration of alumina particles having a card house structure according to the embodiment. FIG. 2 is a schematic view showing another example of the configuration of alumina particles having a card house structure according to the embodiment.

Hereinafter, the abrasion resistant agent, the coating agent, the laminate, the method for producing the laminate, and the method for coating the base material according to the embodiment of the present invention will be described in detail.

<Abrasion resistant agent>
The wear-resistant agent according to an embodiment of the present invention (hereinafter, may be referred to as "wear-resistant agent of the embodiment" or simply "wear-resistant agent") is formed of three or more flat plates of alumina, and the flat plate is formed. It has a card house structure to which a like alumina is fixed, and contains alumina particles having an average particle size of 3 μm or more and 1000 μm or less.

The alumina particles contained in the abrasion resistant agent of the present embodiment have the above-mentioned structure, have a large specific surface area as compared with spherical alumina particles having the same shape, and have a card house structure in which flat alumina is fixed. Therefore, the wear-resistant agent of the present embodiment has good wear resistance.

<Alumina particles with a card house structure>
Alumina particles having a card house structure are formed of three or more flat plate-shaped aluminas, and have a card house structure in which the flat plate-shaped alumina are fixed to each other. Hereinafter, alumina particles having a card house structure may be simply abbreviated as alumina particles. The flat plate shape is, for example, a three-dimensional hexahedral plate shape, and the shape of the two-dimensional projection surface is a typical quadrangle with four corners (square plate shape), or a two-dimensional projection. An example of a polygon whose surface shape has five or more corners (hereinafter, the latter may be referred to as a polygon plate shape) can be exemplified. The alumina particles of the embodiment may contain potassium. The alumina particles of the embodiment may contain mullite and / or germanium compounds. Since the alumina particles have a cardhouse structure, they have an internal structure derived from flat alumina that constitutes the cardhouse structure, and because the specific surface area is higher than that of spherical alumina particles of the same particle size, wear resistance is improved. Effectively demonstrated.

The morphology of the alumina particles can be confirmed by a scanning electron microscope (SEM). The card house structure is, for example, a structure in which plate-shaped particles are not oriented and are arranged in a complicated manner. The term "card house structure" as used herein refers to a structure formed of three or more flat plate-shaped aluminas in which the flat plate-shaped aluminas are fixed to each other (see, for example, FIG. 1), for example, three or more flat plates. Alumina intersects and aggregates at two or more locations, and the intersecting plate-shaped aluminas may be arranged in a disorderly manner in the plane direction (see FIG. 2). The intersecting position may be any position of the flat plate alumina. The disorderly arrangement means that the directions in which the surfaces intersect with each other are not limited in any of the X-axis, Y-axis, and Z-axis directions, and the angles at which the surfaces intersect with each other are any angle. It doesn't matter. Details of "flat alumina" will be described later.

Although it depends on the average particle size of the required alumina particles, when used as an abrasion resistant agent, the number of flat alumina contained in one alumina particle is, for example, 3 to 10000, especially 10 to 5000, particularly 15. The number of sheets is preferably about 3000 in terms of performance and easy production.

The intersection of flat alumina is expressed by the fact that three or more flat alumina are fixed and aggregated in some interaction, for example, in the process of crystal formation by a firing step. As a result, it may look intrusive. The strength of the card house structure is increased by firmly adhering the flat alumina to each other.

Further, the intersection means that two or more surfaces intersect at one place, and there is no limitation on the position, diameter, area, etc. where the two or more surfaces intersect. Further, the number of orientations of the surfaces starting from the intersecting points may be three or four or more.

Further, the major axis, the minor axis, and the thickness of the surface of the flat plate-shaped alumina itself included in the card house structure may be of any size. Further, it may contain a plurality of sizes of flat alumina.

As described above, the flat plate-shaped alumina may be a square plate-shaped alumina or a polygonal plate-shaped alumina. In a single alumina particle, only one of the square plate-shaped alumina and the polygonal plate-shaped alumina may be present, or both may be present, and the ratio thereof is not limited.

In addition to the card house structure, particles such as substantially X-shaped (sometimes called twin-crystal alumina particles; see FIG. 1), substantially T-shaped, and substantially L-shaped, in which two flat-plate-shaped alumina intersect. Or, flat alumina composed of one sheet may be contained in any state. In order to obtain excellent fluidity, it is preferable that the content ratio of these is small, and the content ratio of alumina particles having a card house structure formed of three or more flat alumina and having the flat alumina fixed to each other is high. , 80% or more is preferable on a weight basis or a number basis. It is more preferably 90% or more, still more preferably 95% or more. The content ratio of twins and one flat alumina can be easily adjusted by general classification operations such as sieving and wind power classification.

Alumina particles having a cardhouse structure have extremely high crushing strength due to their unique structure, and do not easily crush even when external stress is applied. As a result, when blended with the coating agent, poor fluidity due to the anisotropy of the alumina particles themselves is unlikely to occur. Therefore, in addition to being able to fully bring out the original function of the alumina particles, even if it is mixed with the plate-shaped alumina particles and used, the plate-shaped alumina particles that tend to be oriented in the longitudinal direction are present in random directions. It becomes possible to make it. As a result, excellent mechanical strength, wear resistance, etc. can be exhibited not only in the longitudinal direction but also in the thickness direction.

Based on its unique structure, alumina particles have excellent fluidity as powder, and it is possible to increase the discharge of feeders used for machine transportation such as hoppers and feeders for application as industrial products. .. Since the alumina particles have voids inside due to their unique structure, the bulk specific gravity is not much different from that of the plate-shaped alumina particles, but the sphericality is higher and the crushing strength is higher as described above as compared with the plate-shaped alumina particles. Since it is hard to break, it is presumed that it has a high effect on the ease of transportation due to the rolling of alumina particles.

Alumina particles have a cardhouse structure. The card house structure is as described above. The alumina particles are preferably in a state in which the flat plate-shaped alumina has a polygonal shape of a quadrangle or more, and at least a part of the adjacent alumina particles are in contact with each other, and more preferably, the flat plate-shaped alumina is a polygonal plate having a pentagonal shape or more. The shape is such that at least a part of adjacent alumina particles are in contact with each other.

[Crystal form / α crystallization rate]
The alumina particles are aluminum oxide, and the crystal form is not particularly limited. For example, transition alumina having various crystal forms such as γ, δ, θ, and κ, or containing alumina hydrate in the transition alumina. However, it is basically preferable to be in the α crystal form because it is more excellent in mechanical strength.

The α crystallization rate of the alumina particles can be determined by XRD measurement.
For example, using a wide-angle X-ray diffraction (XRD) device (Ultima IV manufactured by Rigaku Co., Ltd.) described later, the prepared sample is placed on a holder for a measurement sample and set, and Cu / Kα ray, 40 kV / 40 mA, scan speed 2 degrees / The degree of α crystallinity is determined from the intensity ratio of the peak of α-alumina to the baseline by measuring under the condition of 10 to 70 ° in scanning range. The α crystallization rate varies depending on the firing conditions and the raw materials used, and from the viewpoint of improving the crushing strength and fluidity of the alumina particles, the α crystallization rate is preferably 90% or more, more preferably 95%. That is all. The sample to be measured may be alumina particles or flat alumina obtained by unraveling the cardhouse structure by some mechanical treatment.

[Average particle size]
The average particle size of the alumina particles having a cardhouse structure may be any size as long as the structure can be formed, but the average particle size is 3 μm or more in terms of excellent fluidity and improved wear resistance. It is preferably 10 μm or more. Further, if the size is too large, the coating film of the coating agent may have an appearance defect due to the exposure of the card house structure. Therefore, the average particle size is 1000 μm or less, preferably 300 μm or less, and more preferably 100 μm or less. ..
As an example of the numerical range of the above numerical values, it may be 3 μm or more and 300 μm or less, and may be 10 μm or more and 100 μm or less.
In the present specification, the "average particle size of alumina particles" is a value calculated as _{a volume-based median diameter D 50} from a volume-based cumulative particle size distribution measured by a laser diffraction type dry particle size distribution meter.

[Maximum particle size]
Further, the maximum particle size based on the volume of the alumina particles (hereinafter, may be simply referred to as “maximum particle size” in the present specification) is not particularly limited, but is usually 3000 μm or less, which is preferable. Is 1000 μm or less, more preferably 500 μm or less.

If the maximum particle size of the alumina particles is larger than the above upper limit, the alumina particles may protrude on the surface of the coating film of the coating agent, which may cause poor appearance, which is not preferable.

The average particle size and the maximum particle size of the alumina particles referred to here are the laser diffraction type particle size distribution of the alumina particles themselves having a card house structure formed by three or more flat plates and having the flat alumina fixed to each other. It is a value obtained by a dry method measured using a meter.
Further, the average particle size and the maximum particle size are, for example, dispersed in an appropriate solvent, and specifically, alumina particles are dispersed in a pure water medium containing sodium hexametaphosphate or the like as a dispersion stabilizer. The sample can also be estimated by a wet method, which is measured by a laser diffraction / scattering particle size distribution measuring device.

[Aspect ratio of flat alumina]
The flat alumina is preferably polygonal and has an aspect ratio of 2 to 500, which is the ratio of the particle size to the thickness. When the aspect ratio is 2 or more, it is advantageous and preferable to form a card house structure while maintaining the performance peculiar to flat plate alumina, and when the aspect ratio is 500 or less, the average particle size of the alumina particles can be adjusted. In addition to being easy to perform, it is preferable that the coating agent can suppress the occurrence of appearance defects and the decrease in mechanical strength due to the exposure of the card house structure. More preferably, the aspect ratio is 5 to 300, still more preferably 7 to 100, and particularly preferably 10 to 50. When the aspect ratio is 10 to 100, alumina particles having a card house structure having excellent optical characteristics such as thermal characteristics and brightness of flat plate alumina and high fluidity and wear resistance can be obtained, which is practical. It is preferable in that.

In this specification, the thickness of the flat plate alumina shall be the average value obtained by measuring the thicknesses of 10 pieces using a scanning electron microscope (SEM).

The particle size of the flat plate alumina means the arithmetic average value of the maximum length of the distance between two points on the contour line of the plate, and the value is measured using a scanning electron microscope (SEM). The value shall be adopted.

The major axis value of flat alumina means a value calculated by measuring the major axis of any 100 flat alumina particles from an image obtained by a scanning electron microscope (SEM).
As a method for determining the major axis of the flat plate-shaped alumina, for example, a method of observing the alumina particles with SEM and measuring the maximum length of the flat plate-shaped alumina located at the center of the alumina particles is used. Alternatively, a method of measuring the maximum length of a single piece obtained by performing a wind power classification operation on alumina particles by SEM may be used. Alternatively, a method may be used in which the card house structure is solved by some mechanical treatment to obtain a single piece and the maximum length is measured by SEM under the condition that the flat alumina itself is not destroyed.

Further, since the alumina particles having a card house structure preferably have an average particle diameter of 3 μm or more and 1000 μm or less, for example, the flat alumina particles constituting the alumina particles have, for example, a thickness of 0.01 μm to 5 μm and a major axis of 0.1 μm. It is preferably ~ 500 μm and the aspect ratio, which is the ratio of the major axis to the thickness, is 2 to 500. Among them, when these alumina particles are used as an abrasion resistant agent, the thickness of the flat plate alumina is 0.03 μm to 3 μm, the major axis is 0.5 μm to 100 μm, and the aspect ratio is good because of its good usability. Is more preferably 5 to 300. More preferably, the thickness of the flat alumina is 0.1 μm to 3 μm, the major axis is 1 μm to 30 μm, and the aspect ratio is 10 to 100.

[Silicon / Germanium]
Further, the alumina particles having a cardhouse structure preferably contain silicon (silicon atom and / or inorganic silicon compound) and / or germanium (germanium atom and / or inorganic germanium compound), and among them, silicon and / or inorganic germanium compound. / Or germanium is preferably contained on the surface of the flat alumina. In particular, it is preferable to locally contain it on the surface in a smaller amount than to contain it internally, for example, in order to effectively improve the affinity with the binder.

The silicon and germanium may be derived from the silicon, the silicon compound, and the germanium compound used as the shape control agent in the method for producing alumina particles described later.

The silicon contained in the alumina particles may be silicon alone or silicon in a silicon compound. The flat alumina particles according to the embodiment may _{contain at least one selected from the group consisting of mullite, Si, SiO 2} , SiO, and aluminum silicate produced by reacting with alumina, as silicon or a silicon compound. , The above substance may be contained in the surface layer. Mullite will be described later.

The amount of silicon and / or germanium unevenly distributed on the surface of the flat alumina containing silicon and / or germanium can be determined by, for example, analysis using a fluorescent X-ray analyzer (XRF) and X. It can be measured by analysis using X-ray photoelectron spectroscopy (XPS).

In general, the fluorescent X-ray analysis method (XRF) is a method for quantitatively analyzing the bulk composition of a material by detecting fluorescent X-rays generated by irradiation with X-rays and measuring the wavelength and intensity. In general, X-ray photoelectron spectroscopy (XPS) irradiates the sample surface with X-rays and measures the kinetic energy of photoelectrons emitted from the sample surface to analyze the elemental composition constituting the sample surface. This is the method to be performed. The uneven presence of silicon and / or germanium in and near the surface of flat alumina is specifically determined by the XRF analysis result of the product [Si] / [Al]% (bulk, molar ratio). ) Or [Ge] / [Al]% (bulk, molar ratio), and [Si] / [Al]% (surface) or [Ge] / [Al]% (surface) obtained from the XPS analysis result is It can be estimated from whether or not it shows a large value. This is because the flat alumina surface obtained by blending silicon and / or germanium has a large amount of silicon and / or germanium as compared with the innermost part of the flat alumina. The XRF analysis as described above can be performed using Primus IV or the like manufactured by Rigaku Co., Ltd. Further, XPS analysis can be performed using Quantera SXM or the like manufactured by ULVAC-PHI.

As the alumina particles, it is preferable that silicon atoms and / or inorganic silicon compounds are locally contained on the surface of the flat alumina constituting the alumina particles. In the XPS analysis, the value of the molar ratio [Si] / [Al] of Si to Al is preferably 0.001 or more, more preferably 0.01 or more, and preferably 0.02 or more. It is more preferably 0.1 or more, and particularly preferably 0.1 or more.
The upper limit of the molar ratio [Si] / [Al] in the XPS analysis is not particularly limited, but may be 0.5 or less, 0.4 or less, or 0.3. It may be as follows.

For the alumina particles, the value of the molar ratio [Si] / [Al] of Si to Al obtained in the XPS analysis is preferably 0.001 or more and 0.5 or less, and 0.01 or more and 0.4 or less. It is more preferably 0.02 or more and 0.3 or less, and particularly preferably 0.1 or more and 0.3 or less. When the molar ratio of Si to Al obtained by XPS analysis is within the above range, alumina particles having a cardhouse structure formed of flat alumina can be easily obtained, and the obtained alumina particles can be obtained. It is preferable because it exhibits excellent fluidity and crushing strength and can improve wear resistance. Further, for example, the affinity with the binder can be improved.

Due to the large amount of silicon atoms and / or inorganic silicon compounds on the surface of the flat alumina, not only the surface texture of the alumina particles made of the flat alumina can be made more hydrophobic as compared with the case where it is not present, but also It is possible to improve the affinity with organic compounds and various binders and matrices when used as an abrasion resistant agent. Further, the silicon atom and / or the silicon compound existing on the surface of the alumina particles is used as a reaction point to contribute to the reaction with various coupling agents including the organic silane compound, and the surface state of the alumina surface can be easily adjusted. Is also possible.

When the amount of Si on the surface of alumina particles is analyzed using the above-mentioned X-ray photoelectron spectroscopy (XPS) apparatus, the sample can be press-fixed on double-sided tape and the composition can be analyzed under the following conditions.
-X-ray source: monochromatic AlKα, beam diameter 100 μmφ, output 25 W
-Measurement: Area measurement (1000 μm square), n = 3
-Charge correction: C1s = 284.8eV

If the alumina particles further contain silicon, Si is detected by XRF analysis. The alumina particles according to the embodiment preferably have a molar ratio of Si to Al [Si] / [Al] obtained by XRF analysis of 0.0003 or more and 0.1 or less, preferably 0.0005 or more and 0. It is more preferably 08 or less, more preferably 0.005 or more and 0.05 or less, and further preferably 0.005 or more and 0.01 or less.

When the value of the molar ratio [Si] / [Al] obtained by the XRF analysis is within the above range, alumina particles having a cardhouse structure formed of flat alumina can be easily obtained, and the alumina particles can be easily obtained. The obtained alumina particles are preferable because they can exhibit excellent fluidity and crushing strength and can improve wear resistance.

The alumina particles contain silicon, which corresponds to the silicon or silicon compound used in the production method. The content of silicon with respect to 100% by mass of alumina particles obtained in the XRF analysis is preferably 0.01% by mass or more and 8% by mass or less in terms of _{silicon dioxide (SiO 2), and is 0.1% by mass or more.} It is more preferably 5% by mass or less, further preferably 0.5% by mass or more and 4% by mass or less, and particularly preferably 0.5% by mass or more and 2% by mass or less.
When the silicon content is within the above range, alumina particles having a card house structure formed of flat alumina can be easily obtained, and the obtained alumina particles exhibit excellent fluidity and crushing strength. However, it is preferable because the abrasion resistance can be improved.

The XRF analysis shall be performed under the same conditions as the measurement conditions described in Examples described later, or under compatible conditions in which the same measurement results can be obtained.

(germanium)
The alumina particles may contain germanium. Further, the alumina particles may contain germanium in the surface layer.
Alumina particles can be used as germanium or germanium compounds, for example, Ge, GeO ₂ , GeO, GeCl ₂ , GeBr ₄ , GeI ₄ , GeS ₂ , AlGe, GeTe, GeTe _3, As ₂ , GeSe, depending on the raw material used. , GeS ₃ As, SiGe, Li ₂ Ge, FeGe, SrGe, GaGe and the like, and at least one selected from the group consisting of oxides thereof and the like may be contained, and the above-mentioned substance is contained in the surface layer. May be good.
The "germanium or germanium compound" contained in the alumina particles according to the embodiment and the "raw material germanium compound" used as the shape control agent of the raw material may be the same type of germanium compound.

The alumina particles according to the embodiment may contain germanium or a germanium compound in the surface layer of the flat alumina constituting the alumina particles. By containing germanium or a germanium compound in the surface layer, for example, when a coating agent is produced by mixing with a resin, the coating agent has good compatibility with the resin, the adhesion is improved by the anchor effect, and the wear resistance is further excellent. A coating agent can be provided. Further, by containing germanium or a germanium compound having a low Mohs hardness in the surface layer of the alumina particles, it is possible to make it difficult to wear the equipment for producing the coating agent.

When the germanium or the germanium compound is contained in the surface layer of the flat plate alumina, a remarkable wear resistance effect and a reduction in wear of the equipment are exhibited. Here, the "surface layer" means within 10 nm from the surface of the flat alumina particles according to the embodiment. This distance corresponds to the XPS detection depth. The surface layer containing germanium is a very thin layer within 10 nm. For example, in the case of germanium dioxide, if there are many defects in the germanium dioxide structure on the surface and the interface, the compatibility with the resin is further improved. Therefore, the abrasion resistance can be remarkably exhibited as compared with germanium dioxide having no or few structural defects.
As for the alumina particles, it is preferable that germanium or a germanium compound is unevenly distributed on the surface layer of the flat alumina. Here, "unevenly distributed on the surface layer" means a state in which the mass of germanium or germanium compound per unit volume in the surface layer is larger than the mass of germanium or germanium compound per unit volume other than the surface layer. The uneven distribution of germanium or germanium compound on the surface layer can be determined by comparing the results of surface analysis by XPS and overall analysis by XRF. By unevenly distributing the germanium or the germanium compound on the surface layer, the germanium or the germanium compound is superior to the case where the germanium or the germanium compound is present not only on the surface layer but also on the non-surface layer (inner layer) in a smaller amount and at the same level based on the germanium or the germanium compound. It is possible to exert the wear resistance effect and the wear reduction effect of the equipment.

The content of germanium with respect to 100% by mass of alumina particles obtained in the XRF analysis is preferably 0.01% by mass or more and 8% by mass or less in terms of _{germanium dioxide (GeO 2), and is preferably 0.1% by mass or more.} It is more preferably 5% by mass or less, and further preferably 0.5% by mass or more and 4% by mass or less.

(Mullite)
The alumina particles according to the embodiment may contain mullite in the surface layer of the flat plate-like alumina constituting the alumina particles. By containing mullite in the surface layer, for example, when a coating agent is manufactured by mixing with a resin, the coating agent has good compatibility with the resin, has high adhesion due to the anchor effect, and has even more excellent wear resistance. Can be provided. Further, by including mullite having a low Mohs hardness in the surface layer of the alumina particles, it is possible to make it difficult for the equipment for producing the coating agent to be worn.

By containing mullite in the surface layer of flat alumina, a remarkable wear resistance effect and a wear reduction effect of equipment are exhibited. The "mullite" that the alumina particles may contain in the surface layer is a composite oxide of Al and Si and is _{represented by Al X} Si _{YO z,} but the values of x, y, and z are not particularly limited. A more preferable range is Al ₂ Si ₁ O _{5 to Al 6} Si ₂ O ₁₃ , for example, Al _2.85 Si ₁ O _6.3 , Al ₃ Si ₁ O _6.5 , Al _3.67 Si ₁ O _{7 It} contains .5, Al ₄ Si ₁ O ₈ or Al ₆ Si ₂ O _13. The flat alumina particles are Al _2.85 Si ₁ O _6.3 , Al ₃ Si ₁ O _6.5 , Al _3.67 Si ₁ O _7.5 , Al ₄ Si ₁ O ₈ and Al ₆ Si ₂ O. _The surface layer may contain at least one compound selected from the group consisting of 13. Here, the "surface layer" means within 10 nm from the surface of the flat alumina. This distance corresponds to the XPS detection depth. The surface layer of mullite is a very thin layer within 10 nm, and if there are many defects of mullite crystals on the surface and interface, the compatibility with the resin becomes better, and compared with mullite having no or few crystal defects. Further, the wear resistance effect can be remarkably exhibited.
As for the alumina particles, it is preferable that mullite is unevenly distributed on the surface layer of the flat alumina. Here, "unevenly distributed on the surface layer" means a state in which the mass of mullite per unit volume in the surface layer is larger than the mass of mullite per unit volume in other than the surface layer. The uneven distribution of mullite on the surface layer can be determined by comparing the results of surface analysis by XPS and overall analysis by XRF. By unevenly distributing mullite on the surface layer, the amount of mullite is smaller than that when mullite is present not only on the surface layer but also on other than the surface layer (inner layer). Can be demonstrated.

Further, the mullite on the surface layer may form a mullite layer, or may be in a state in which mullite and alumina are mixed. The interface between mullite and alumina on the surface layer may be in a state where mullite and alumina are in physical contact with each other, or mullite and alumina may form a chemical bond such as Si—O—Al. Compared to the combination of alumina and SiO ₂ , the combination containing alumina and mullite as essential components has a high degree of similarity in constituent atomic composition, and when the flux method is adopted, the above Si—O—Al is based on it. From the viewpoint of easiness of forming chemical bonds such as, alumina and mullite can be more firmly bonded and hard to be peeled off. From this, if the amount of Si is the same level, the combination of alumina and mullite as essential components is more preferable because the device can exhibit the wear resistance effect and the wear reduction effect of the device for a longer period of time. The technical effect of the combination of alumina and mullite as essential components can be expected with either alumina and mullite alone or with alumina, mullite and silica, but if anything, the former two combination is the level of technical effect. Will be higher.

Further, the presence or absence of mullite on the surface of the alumina particles can be analyzed using a wide-angle X-ray diffraction (XRD) apparatus such as Ultima IV manufactured by Rigaku Corporation.
For example, the sample is placed on a holder for a measurement sample having a depth of 0.5 mm, filled flat with a constant load, set in the wide-angle X-ray diffraction (XRD) apparatus, and Cu / Kα ray, 40 kV /. The measurement is performed under the conditions of 40 mA, a scanning speed of 2 degrees / minute, and a scanning range of 10 to 70 degrees.
Let A be the peak height of mullite observed at 2θ = 26.2 ± 0.2 degrees, and B be the peak height of α-alumina on the (104) plane observed at 2θ = 35.1 ± 0.2 degrees. With the baseline value of 2θ = 30 ± 0.2 degrees as C, the presence or absence of mullite can be determined from the following equation. The value of R may be, for example, 0.02 or more, 0.02 or more and 0.3 or less, 0.05 or more and 0.2 or less, and 0.1 or more and 0.12. It may be less than.
R = (AC) / (BC)
(R: Ratio of peak height A of mullite to peak height B of the (104) plane of α-alumina)

[molybdenum]
The alumina particles having a card house structure may contain molybdenum.

The molybdenum may be derived from the molybdenum compound used as the flux agent in the method for producing alumina particles described later.

Molybdenum has a catalytic function and an optical function. Further, by utilizing molybdenum, alumina particles having excellent fluidity can be produced in the production method as described later.

The molybdenum is not particularly limited, and includes molybdenum metal, molybdenum oxide, a partially reduced molybdenum compound, molybdate, and the like. It may be contained in the flat alumina particles in any or a combination of possible polymorphs of the molybdenum compound, and is contained in the flat alumina particles as α-MoO ₃ , β-MoO ₃ , MoO ₂ , MoO, molybdenum cluster structure and the like. May be.

The molybdenum-containing form is not particularly limited, and even if it is contained in a form of adhering to the surface of flat alumina of alumina particles having a cardhouse structure, it is in a form of being replaced with a part of aluminum having an alumina crystal structure. It may be included or a combination thereof.

The content of molybdenum with respect to 100% by mass of the alumina particles obtained in the XRF analysis is _{preferably 10% by mass or less in terms of molybdenum trioxide (MoO 3} ), and the firing temperature, firing time, and flux conditions are adjusted. By doing so, it is preferably 0.001% by mass or more and 8% by mass or less, more preferably 0.01% by mass or more and 8% by mass or less, and further preferably 0.1% by mass or more and 5% by mass or less. It is as follows. When the molybdenum content is 10% by mass or less, it is preferable because it improves the α single crystal quality of alumina.

The XRF analysis shall be performed under the same conditions as the measurement conditions described in Examples described later, or under compatible conditions in which the same measurement results can be obtained.

The analysis of the amount of Mo on the surface of the alumina particles can be performed using the above-mentioned X-ray photoelectron spectroscopy (XPS) apparatus.
For example, using the above-mentioned X-ray photoelectron spectroscopy (XPS) apparatus, a sample can be press-fixed on double-sided tape, and composition analysis can be performed under the following conditions. When [Mo] / [Al] (molar ratio) obtained from the XPS analysis result is the amount of Mo on the surface of the cardhouse type alumina particles, the amount of Mo is preferably 0.0005 or more.
-X-ray source: monochromatic AlKα, beam diameter 100 μmφ, output 25 W
-Measurement: Area measurement (1000 μm square), n = 3
-Charge correction: C1s = 284.8eV

[potassium]
Alumina particles having a card house structure may contain potassium.

Potassium may be derived from potassium that can be used as a flux agent in the method for producing alumina particles described later.
By utilizing potassium, alumina particles having excellent fluidity can be produced with high efficiency in the method for producing alumina particles described later.

The potassium is not particularly limited, but includes potassium oxide, a partially reduced potassium compound, and the like, in addition to potassium metal.

The form of potassium is not particularly limited, and even if it is contained in a form of adhering to the surface of flat alumina of alumina particles having a cardhouse structure, it is in a form of being replaced with a part of aluminum having a crystal structure of alumina. It may be included or a combination thereof.

Acquired in XRF analysis, the content of potassium to the alumina particles 100 mass%, with potassium oxide _(K 2 O) in terms, preferably at least 0.05 mass%, 0.05 to 5 wt% It is more preferably 0.1 to 3% by mass, and particularly preferably 0.1 to 1% by mass. Alumina particles having a potassium content within the above range are preferable because they have a card house structure and a value such as an average particle size is suitable. Further, it is preferable because it has excellent fluidity and can improve wear resistance.

The XRF analysis shall be performed under the same conditions as the measurement conditions described in Examples described later, or under compatible conditions in which the same measurement results can be obtained.

(Inevitable impurities)
Alumina particles may contain unavoidable impurities.

Inevitable impurities are derived from metal compounds used in manufacturing, are present in raw materials, or are inevitably mixed with alumina particles in the manufacturing process. It means impurities that do not affect the characteristics of alumina particles.

The unavoidable impurities are not particularly limited, and examples thereof include magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, cerium, and sodium. These unavoidable impurities may be contained alone or in combination of two or more.

The content of unavoidable impurities in the alumina particles is preferably 10,000 ppm or less, more preferably 1000 ppm or less, and even more preferably 10 to 500 ppm, based on the mass of the alumina particles.

(Other atoms)
Other atoms are those intentionally added to alumina particles for the purpose of imparting abrasion resistance, mechanical strength, electrical and magnetic functions, as long as the effects of the present invention are not impaired.

Examples of other atoms include, but are not limited to, zinc, manganese, calcium, strontium, yttrium and the like. These other atoms may be used alone or in combination of two or more.

The content of other atoms in the alumina particles is preferably 5% by mass or less, more preferably 2% by mass or less, based on the mass of the alumina particles.

[Organic compounds]
In one embodiment, the alumina particles may contain an organic compound. The organic compound exists on the surface of the alumina particles and has a function of adjusting the surface physical characteristics of the alumina particles. For example, the alumina particles containing an organic compound on the surface improve the affinity with the resin, so that the function of the alumina particles can be maximized as an abrasion resistant agent.

The organic compound is not particularly limited, and examples thereof include organic silane, alkylphosphonic acid, and polymer.

Examples of the organic silane include methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, iso-propyltrimethoxysilane, and iso-propyltri. Alkyltrimethoxysilanes or alkyltrichlorosilanes with alkyl groups from 1 to 22 such as ethoxysilane, pentiltrimethoxysilane, hexyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, trideca Fluoro-1,1,2,2-tetrahydrooctyl) trichlorosilanes, phenyltrimethoxysilanes, phenyltriethoxysilanes, p-chloromethylphenyltrimethoxysilanes, p-chloromethylphenyltriethoxysilanes and the like can be mentioned.

Examples of the phosphonic acid include methylphosphonic acid, ethylphosphonic acid, propylphosphonic acid, butylphosphonic acid, pentylphosphonic acid, hexylphosphonic acid, heptylphosphonic acid, octylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, octadecylphosphonic acid, and the like. Examples thereof include 2_ethylhexylphosphonic acid, cyclohexylmethylphosphonic acid, cyclohexylethylphosphonic acid, benzylphosphonic acid, phenylphosphonic acid and dodecylbenzenephosphonic acid.

As the polymer, for example, poly (meth) acrylates can be preferably used. Specifically, polymethyl (meth) acrylate, polyethyl (meth) acrylate, polybutyl (meth) acrylate, polybenzyl (meth) acrylate, polycyclohexyl (meth) acrylate, polyt-butyl (meth) acrylate, polyglycidyl (meth). Examples thereof include acrylate, polypentafluoropropyl (meth) acrylate, and other general-purpose polymers such as polystyrene, polyvinyl chloride, polyvinyl acetate, epoxy resin, polyester, polyimide, and polycarbonate.

The organic compound may be contained alone or may contain two or more kinds.

The contained form of the organic compound is not particularly limited, and may be linked to alumina by a covalent bond or may be coated with alumina.

The content of the organic compound is preferably 20% by mass or less, more preferably 10 to 0.01% by mass, based on the mass of the alumina particles. When the content of the organic compound is 20% by mass or less, it is preferable because the physical properties derived from the alumina particles can be easily expressed.

[Crush strength]
Alumina particles preferably have a higher crushing strength because the original fluidity of the alumina particles is impaired if the card house structure is broken due to mechanical dispersion such as compression and shearing. The crushing strength differs depending on the position, number, area, thickness and aspect ratio of the flat alumina intersecting, and the crushing strength required for various applications differs, and the crushing strength is 1 MPa to 100 MPa in terms of practicality. It is preferably 20 MPa to 100 MPa, more preferably 50 MPa to 100 MPa.
The crushing strength of the alumina particles can be measured using, for example, the NS-A100 type microparticle crushing force measuring device manufactured by Nanoseeds Co., Ltd., or the MCT-510 manufactured by Shimadzu Corporation. The difference between the peak value at the time of crushing and the baseline (when no force is applied) is defined as the crushing force F [N], and the crushing strength S [Pa] is the average value of 10 values calculated from the following equation. To do.

S = 2.8F / (π ・ D ² )
However, in the above formula, F is a crushing force [N] and D is a particle size [m].

As described above, the alumina particles are formed of three or more flat alumina particles and have a fixed card house structure. The present inventors have found that, as the alumina particles, those appropriately containing a silicon atom and / or an inorganic silicon compound have higher crushing strength as described above, as compared with those not containing these. The crushing strength differs depending on the content of the silicon atom and / or the inorganic silicon compound, and the more appropriately the crushing strength is, the higher the fluidity and crushing strength of the particles can be. Further, for example, it is possible to increase the crushing strength by adopting specific manufacturing conditions as the manufacturing method. The crushing strength can be arbitrarily adjusted even under the manufacturing conditions. For example, by raising the firing temperature, the crushing strength of the alumina particles can be further increased.

[Powder fluidity]
The alumina particle powder according to the embodiment has a unique structure of the alumina itself constituting the alumina particle, and preferably has a specific average particle size, so that the plate-shaped alumina particles and the dicrystalline alumina particles have a specific average particle size. However, in order to further increase the fluidity, the alumina particles forming a unit of card house structure are surrounded so as to include all the flat alumina constituting the particles. It is preferable that the shape of the maximum surrounding surface based on the volume is spherical or substantially spherical. Further, if necessary, a lubricant, fine particle silica, or the like may be optionally attached to improve the fluidity.

The fluidity of the alumina particles of the card house structure as a powder can be determined, for example, by measuring the angle of repose according to JIS R9301-2-2. The value of the angle of repose is preferably 50 ° or less because problems such as a hopper bridge, a feed neck, uneven supply, and a decrease in the discharge amount are unlikely to occur in mechanical transportation by a feeder, a hopper, or the like. More preferably, it is 40 ° or less.

The alumina particles may be formed of three or more flat plates of alumina, have a card house structure in which the flat plates of alumina are fixed to each other, and have an average particle diameter of 1 to 1000 μm. More preferably, as a card house structure fixed to the internal structure of the alumina particles, the three or more plate-shaped aluminas are crossed and assembled at two or more locations, and the intersecting flat plates of each other. The plane direction is preferably alumina particles in a disorderly arranged state.

Conventionally known twin alumina particles have a structure in which corners are conspicuous in terms of their shape, and have a shape that is harder to roll than the alumina particles according to the embodiment. Therefore, they have sufficient fluidity as a filler (filler) in the first place. Cannot be obtained. Further, even if the alumina particles have the same cardhouse structure as the alumina particles according to the embodiment, the fluidity is excellent when the average particle size is appropriately large. The alumina particles according to the embodiment exhibit particularly excellent fluidity due to the synergistic effect of the card house structure and its preferable average particle size.

[Isoelectric point pH]
The pH of the isoelectric point of the alumina particles is, for example, in the range of 2 to 8, preferably in the range of 2.5 to 7, and more preferably in the range of 3 to 6. Alumina particles having an isoelectric point pH within the above range have a high electrostatic repulsive force, and by themselves can enhance dispersion stability when blended into the above-mentioned object to be dispersed, further improving performance. It becomes easier to modify by surface treatment such as a coupling treatment agent intended for.

For the pH value of the isoelectric point, measure the zeta potential with a zeta potential measuring device (Zetasizer Nano ZSP, manufactured by Malvern), and use 20 mg of a sample and 10 mL of a 10 mM KCl aqueous solution with Rentaro Awatori (Sinky, ARE-310). ) Stir in the stirring / defoaming mode for 3 minutes and let stand for 5 minutes as the sample for measurement, add 0.1N HCl to the sample with an automatic titrator, and measure the zeta potential in the range up to pH = 2. (Applied voltage 100V, Monomodl mode) and evaluate the pH of the isoelectric point where the potential becomes zero.

[Specific surface area]
The specific surface area of the powder of alumina particles is in the range of usually 50~0.001m ² / g, preferably from ^{10m 2 /g~0.01m} 2 / g, more preferably 5.0 m ² / g The range is ~ ^{1 m 2 / g.} Within the above range, the number of flat alumina forming the card house structure is appropriate, the wear resistance is excellent, and the workability is excellent without a significant increase in viscosity when slurried.

This specific surface area can be measured by JIS Z 8830: BET 1-point method (adsorbed gas: nitrogen) or the like.

[Porosity]
The alumina particles are formed of three or more flat plates of alumina, and have a card house structure in which the flat plates of alumina are fixed to each other. Therefore, the alumina particles have voids, and when the proportion of voids is large, the shape tends to be uniform. Since the fluidity tends to be improved, the porosity is preferably 10% by volume or more. More preferably, it is 30% by volume or more. Further, if the proportion of voids is large, the crushing strength of the powder is low, so the porosity is preferably 90% by volume or less. More preferably, it is 70% by volume or less. When the porosity is in this range, the bulk specific gravity is appropriate, the fluidity is not impaired, and the handleability is also good. This porosity can be determined by measurement such as a gas adsorption method or a mercury intrusion method such as JIS Z 8831.

Briefly, the porosity is determined by mixing the alumina particles with a liquid curable compound such as an epoxy compound or a (meth) acrylic monomer and then curing the alumina particles, then cutting and polishing the cross section, and then observing the voids by SEM. Can be guessed.

<Manufacturing method of alumina particles>
Next, the details of the method for producing alumina particles according to the embodiment will be illustrated. The method for producing alumina particles according to this embodiment is not limited to the method for producing alumina particles shown below.

The average particle size, fluidity, specific surface area, mechanical strength, porosity, thickness and aspect ratio of the flat alumina particles of the alumina particles can be adjusted by the production method described in detail later. When the flux method is adopted as the production method, for example, a molybdenum compound (preferably a potassium compound) as a flux agent, an aluminum compound species, an average particle size of the aluminum compound, the purity of the aluminum compound, silicon, and a silicon compound. And at least one shape control agent selected from germanium compounds, other types of shape control agents, usage ratios with other shape control agents, at least one shape control agent selected from silicon, silicon compounds and germanium compounds and aluminum. It can be adjusted according to the presence state of the compound, the presence state of the shape control agent and the aluminum compound, and the like.

The alumina particles may be obtained based on any production method as long as they can have a card house structure. However, it is not preferable to obtain alumina having a peculiar structure called a card house structure by post-treatment using alumina having an existing structure because the manufacturing process becomes multi-step and the productivity is inferior. For example, a cardhouse structure can be selectively formed as a structure from an existing raw material of alumina, molybdenum can be easily contained therein, and potassium, silicon, germanium, etc. can be easily contained therein. From the viewpoint of productivity, it is preferable to adopt a method for producing alumina particles that can be contained in the particles at once.

That is, in obtaining alumina particles, a molybdenum compound, at least one shape control agent selected from a silicon, a silicon compound and a germanium compound, and, if necessary, an excellent in fluidity, dispersibility, and productivity. It is preferably obtained by firing the aluminum compound in the presence of other shape control agents.
In addition, almost all of the produced alumina particles can have a cardhouse structure, and in that they are more productive, at least one shape selected from molybdenum compounds and potassium compounds and silicon, silicon compounds and germanium compounds. It is preferably obtained by firing the aluminum compound in the presence of a control agent and, if necessary, another shape control agent.

More specifically, a preferred method for producing alumina particles includes a step of firing an aluminum compound (calcination step) in the presence of a molybdenum compound and at least one shape control agent selected from silicon, a silicon compound and a germanium compound. .. The firing step may be a step of firing the mixture obtained in the step of obtaining the mixture to be fired (mixing step). The mixture preferably further contains a potassium compound. The mixture preferably further contains a metal compound described below. As the metal compound, a yttrium compound is preferable.

When an organic compound is used as a molybdenum compound or a silicon compound, the organic component is burned out by firing. That is, in the alumina particles, the molybdenum compound reacts with the aluminum compound at a high temperature to form aluminum molybdate, and then when the aluminum molybdate further decomposes into alumina and molybdenum oxide at a higher temperature, the molybdenum is decomposed into alumina particles. It can be obtained more easily by incorporating it inside. Molybdenum oxide sublimates, but it can also be recovered and reused. Hereinafter, this manufacturing method is referred to as a flux method. This flux method will be described in detail later.

The shape control agent plays an important role in plate crystal growth. In the commonly used flux method using a molybdenum compound, molybdenum oxide reacts with an aluminum compound to form aluminum molybdate, and then the change in chemical potential in the process of decomposition of this aluminum molybdate is crystallized. Since it is a driving force, hexagonal bipyramidal polyhedron particles with a developed automorphic surface (113) are formed. In the production method of the embodiment, the shape control agent is localized near the particle surface in the α-alumina growth process, so that the growth of the automorphic surface (113) is significantly inhibited, and as a result, the shape control agent is relatively in the plane direction. It is considered that the growth of the crystal orientation becomes faster, the (001) plane or the (006) plane grows, and a plate-like morphology can be formed. By using the molybdenum compound as a flux agent, alumina particles having a high α crystallization rate, particularly an α crystallization rate of 90% or more, made of flat alumina containing molybdenum can be more easily formed.

It should be noted that the above mechanism is only speculative, and even if the effect of the present invention is obtained by a mechanism different from the above mechanism, it is included in the technical scope of the present invention.

By utilizing a molybdenum compound in the alumina particles, alumina has a high α crystal ratio and has an automorphic shape, so that excellent dispersibility with respect to the matrix, mechanical strength, and high thermal conductivity can be realized.

Further, since the alumina particles obtained by the above production method contain molybdenum in the particles, the isoelectric point of the zeta potential is shifted to the acidic side as compared with ordinary alumina, so that the alumina particles are excellent in dispersibility. Further, by utilizing the characteristics of molybdenum contained in alumina particles, it may be possible to apply it to applications such as oxidation reaction catalysts and optical materials.

[Manufacturing method of alumina particles by flux method]
The method for producing alumina particles is not particularly limited, but from the viewpoint that alumina having a high α crystallization rate at a relatively low temperature can be preferably controlled, a method for producing alumina particles is preferably a flux method using a molybdenum compound. Can be applied.

More specifically, a preferred method for producing alumina particles is in the presence of a molybdenum compound, at least one shape control agent selected from the group consisting of silicon, silicon compounds and germanium compounds, and optionally other shape control agents. , Including the step of firing an aluminum compound.

In the flux method, when the present inventors adopt a production method in which a molybdenum compound is used as a flux agent, a shape control agent is used in combination, and these are mixed with an aluminum compound and fired, the size of the raw material aluminum compound is large. The amount of the molybdenum compound used, the amount of the potassium compound used when the potassium compound is used as the flux agent, and the amount of the shape control agent used are important factors capable of selectively producing alumina particles. I found a new one.

In the flux method, it is also preferable to use a molybdenum compound and a potassium compound as a flux agent.
The compound containing molybdenum and potassium as a flux agent can be produced, for example, from a molybdenum compound and a potassium compound, which are cheaper and more easily available, in the firing process. Here, the case where the molybdenum compound and the potassium compound are used as the flux agent, the case where the compound containing molybdenum and potassium is used as the flux agent, and the case where both are used together and the molybdenum compound and the potassium compound are used as the flux agent are taken as an example. explain.

Compared to the case where only a molybdenum compound such as molybdenum trioxide is used in the method for producing alumina particles in which a molybdenum compound is used as an essential flux agent, a shape control agent is used in combination, and these are mixed with an aluminum compound and fired. When a molybdenum compound and a potassium compound are used as a flux agent, or when a compound containing molybdenum and potassium is used as a flux agent, the firing step is performed in the presence of a compound containing molybdenum and potassium which is difficult to vaporize. By doing so, the deterioration of the firing work environment is reduced without releasing the flux agent to the outside of the system, and further, molybdenum and potassium contained in the mixture of the alumina particles and the flux agent particles generated in the cooling step are contained. Since the compounds containing and are often highly water-soluble, it is possible to remove more molybdenum from alumina more easily.
By using a molybdenum compound and a potassium compound as a flux agent, or by using a compound containing molybdenum and potassium as a flux agent, and by including the above-mentioned cooling step, a card house structure can be formed without requiring strong crushing. Alumina particles having a card house structure can be obtained, and the yield of alumina particles having a cardhouse structure can be made very high. This means that the flux agent occupies between the alumina particles having a card house structure, the flux agent acts like a spacer, and the fusion of the particles is prevented, and the flux agent is used in the post-treatment step. It is considered that this is because it can be easily removed.
From the viewpoint of preventing the fusion of particles, the amount of the flux agent used (the amount of the molybdenum compound and the potassium compound compounded when the total amount of the raw material converted to oxide is 100% by mass) is Mo ₂ K ₂ O _7. It is preferably 2% by mass or more in terms of conversion.

[Mixing process]
The mixing step is a step of mixing raw materials such as an aluminum compound, a molybdenum compound, and a shape control agent to form a mixture. The mixture may further contain a potassium compound. The contents of the mixture will be described below.

(Aluminum compound)
The raw material aluminum compound is not particularly limited as long as it is a raw material of the above alumina particles and becomes alumina by heat treatment. For example, aluminum chloride, aluminum sulfate, basic aluminum acetate, aluminum hydroxide, boehmite, pseudo-boehmite, transition. Alumina (γ-alumina, δ-alumina, θ-alumina, etc.), α-alumina, mixed alumina having two or more kinds of crystal phases can be used, and aluminum hydroxide and / or transition alumina is preferable.

Further, the aluminum compound may be composed of only the aluminum compound or may be a complex of the aluminum compound and the organic compound. For example, an organic / inorganic composite obtained by modifying an aluminum compound using an organic silane compound, an aluminum compound composite on which a polymer is adsorbed, or the like can be preferably used. Since the organic components of the organic compound are burned down by firing, the content of the organic compound is not particularly limited when these composites are used, but from the viewpoint of efficiently producing alumina particles having a cardhouse structure. The content is preferably 60% by mass or less, and more preferably 30% by mass or less.

The specific surface area of the aluminum compound is not particularly limited. Since the molybdenum compound of the flux agent acts effectively, it is preferable that the specific surface area is large, but by adjusting the firing conditions and the amount of the molybdenum compound used, any specific surface area can be used as a raw material. ..

The shape of the alumina particles reflects the shape of the raw material aluminum compound according to the flux method described in detail below. Spherical, amorphous, aspected structures (wires, fibers, ribbons, tubes, etc.), sheets, etc. can be used, but spherical aluminum in terms of improving the fluidity of the powder. It is preferable to use a compound because the obtained alumina particles become closer to a spherical shape.

Further, in the method for producing alumina particles from an aluminum compound, the average particle size of the alumina particles also basically reflects the particle size of the raw material aluminum compound.

According to the flux method described below, in the firing step, mainly, crystal formation of flat alumina in the raw material aluminum compound particles and crossing of three or more adjacent flat alumina proceed and stick to the card. It is presumed to have a house structure. From this, it is presumed that the average particle size of the obtained alumina particles having a cardhouse structure mainly reflects the average particle size of the raw material aluminum particles.

Therefore, when an aluminum compound having a smaller average particle size is used as a raw material, alumina particles having a smaller average particle size can be easily obtained, and when an aluminum compound having a larger average particle size is used, the average particle size becomes higher. Large alumina particles can be easily obtained.

Since the alumina particles preferably have an average particle size of 3 μm or more and 1000 μm or less, they have the same or substantially the same average particle size as the alumina particles having a specific average particle size to be produced within the above range. It is better to use an aluminum compound.

Alumina particles having a cardhouse structure are fired in the presence of, for example, a molybdenum compound, at least one shape control agent selected from silicon, silicon compounds and germanium compounds, and if necessary, other shape control agents. Obtained by forming flat plate-like alumina in a method for producing alumina particles including a step, and contacting, crossing, and fixing the three or more flat-plate-like alumina with each other's crystal planes at a plurality of points at the same time as the formation. Can do things. Due to the fixing, the card house structure is not easily broken (unraveled) by external stress such as pressure, and a fixed state is obtained. For example, the flux conditions and the like when the flat plate-shaped alumina is formed affect the crushing strength and the like of the obtained alumina particles having a cardhouse structure.

As the amount of the molybdenum compound is smaller, three or more flat alumina sheets are adhered to the aluminum compound particles faster and more frequently, so that a strong card house structure having high crushing strength can be obtained.

According to the findings of the present inventors who focused on the flux method, specifically, for example, 1) as a raw material aluminum compound, it corresponds to the particle size of the desired alumina particle having an average particle size of 2 μm or more, especially 4 μm or more. 2) The amount of the molybdenum compound as a flux agent was 0.005 to 0.236 mol as the molybdenum metal of the molybdenum compound with respect to 1 mol of the aluminum metal of the aluminum compound, and 3) When the amount of the silicon compound as the shape control agent is 0.003 to 0.09 mol as the silicon metal of the silicon compound with respect to 1 mol of the aluminum metal of the aluminum compound, the fluidity is higher and the crushing strength is higher. It is preferable because alumina particles having a high card house structure can be obtained.

In the flux method, in a method for producing alumina particles in which a molybdenum compound and a potassium compound are used as a flux agent, silicon or a silicon compound is used in combination as a shape control agent, and these are mixed with an aluminum compound and fired, 1) specific. By using the raw material aluminum compound having an average particle size, 2) the amount of molybdenum compound and potassium compound used is limited to a specific range, and 3) the amount of silicon or silicon compound used is limited to a specific range. It is preferable because alumina particles formed of three or more plate-shaped aluminas in the range of the average particle size and characterized by having a cardhouse structure in which the plate-shaped aluminas are fixed to each other can be selectively produced.

Further, the average particle size and shape of the alumina particles having a card house structure can be arbitrarily adjusted by a crushing step and a classification step described later.

(Molybdenum compound)
The molybdenum compound functions as a flux agent in the α crystal growth of alumina, as will be described later. The molybdenum compound is not particularly limited, and examples thereof include molybdenum oxide and compounds containing an _{acid root anion (MoO x} ^{n−) in which a molybdenum metal is bonded to oxygen.}

The compound containing the acid radical anion _(MoO ^{x n-),} is not particularly limited, molybdate, sodium molybdate, potassium molybdate, lithium _{molybdate, H 3 PMo 12 O 40,} H 3 SiMo 12 O 40, Examples _{include NH 4} Mo ₇ O ₁₂ , molybdenum disulfide and the like.

It is also possible that the molybdenum compound contains sodium or silicon, in which case the molybdenum compound containing sodium or silicon serves as both a flux agent and a shape control agent.

Among the above-mentioned molybdenum compounds, it is preferable to use molybdenum oxide from the viewpoint of cost. Further, the above-mentioned molybdenum compound may be used alone or in combination of two or more.

Further, potassium molybdate _{(K 2 Mo n O 3n +} 1, n = 1~3) is for containing potassium may also have a function as described below potassium compound. In the production method of the embodiment, using potassium molybdate as a flux agent is synonymous with using a molybdenum compound and a potassium compound as a flux agent.

The amount of the molybdenum compound used is not particularly limited, but is preferably 0.005 to 0.236 mol as the molybdenum metal of the molybdenum compound with respect to 1 mol of the aluminum metal of the aluminum compound, and 0.007 to 0.09. It is more preferably mol, and even more preferably 0.01 to 0.04 mol. When the amount of the molybdenum compound used is in the above range, it is preferable because alumina particles having a card house structure made of flat alumina having a high aspect ratio and excellent dispersibility can be easily obtained. In addition, when a molybdenum compound is used as a flux agent when the flux method is adopted, since molybdenum is contained in the alumina particles, the unknown alumina particles are produced by any manufacturing method. You can identify the particles.

When the molybdenum compound and the potassium compound are used as the flux agent, the amount of the molybdenum compound used is not particularly limited, but the molar ratio of the molybdenum element to the aluminum element of the aluminum compound (molybdenum element / aluminum element) is 0.01. It is preferably ~ 3.0, more preferably 0.1 to 1.0, more productive, and even more preferably 0.30 to 0.70 in order to favorably proceed with crystal growth. .. When the amount of the molybdenum compound used is in the above range, it is preferable because alumina particles having a card house structure made of flat alumina having a high aspect ratio and excellent dispersibility can be easily obtained.

(Potassium compound)
When a molybdenum compound and a potassium compound are used as a flux agent, the potassium compound is not particularly limited, but potassium chloride, potassium chlorite, potassium chlorate, potassium sulfate, potassium hydrogen sulfate, potassium sulfite, potassium hydrogen sulfite, potassium nitrate, etc. Potassium carbonate, potassium hydrogen carbonate, potassium acetate, potassium oxide, potassium bromide, potassium bromide, potassium hydroxide, potassium silicate, potassium phosphate, potassium hydrogen phosphate, potassium sulfide, potassium hydrogen sulfide, potassium molybdenate, potassium tungstate, etc. Can be mentioned. At this time, the potassium compound contains an isomer as in the case of the molybdenum compound. Of these, potassium carbonate, potassium hydrogencarbonate, potassium oxide, potassium hydroxide, potassium chloride, potassium sulfate, or potassium molybdate is preferably used, and potassium carbonate, potassium hydrogencarbonate, potassium chloride, potassium sulfate, or molybdenum acid. It is more preferable to use potassium.

The above-mentioned potassium compound may be used alone or in combination of two or more.

Further, similarly to the above, since potassium molybdate contains molybdenum, it may also have a function as the above-mentioned molybdenum compound. In the production method of the embodiment, using potassium molybdate as a flux agent is synonymous with using a molybdenum compound and a potassium compound as a flux agent.

As a potassium compound used during raw material preparation or generated in the reaction of the temperature rising process during firing, a water-soluble potassium compound, for example, potassium molybdenumate, does not vaporize even in the firing temperature range and can be easily recovered by washing after firing. The amount of the molybdenum compound released to the outside of the firing furnace is also reduced, and the production cost can be significantly reduced.

When a molybdenum compound and a potassium compound are used as a flux agent, the molar ratio of the molybdenum element to the potassium element of the potassium compound (molybdenum element / potassium element) is preferably 5 or less, preferably 0.01 to 3. It is more preferable, and 0.5 to 1.5 is more preferable because the production cost can be further reduced. When the molar ratio (molybdenum element / potassium element) is within the above range, alumina particles having a preferable particle size can be obtained.

(Silicon or silicon compound)
In the method for producing alumina particles, it is preferable to use silicon or a silicon compound as a shape control agent in that the fluidity of the resulting alumina particles becomes better. Silicon or a silicon compound plays an important role in the flat crystal growth of alumina by calcining the alumina compound in the presence of the molybdenum compound.

Silicon, which is a silicon compound, is selectively adsorbed on the [113] plane of the α crystal of alumina, and by suppressing the selective adsorption of molybdenum oxide, which is a flux agent, on the [113] plane, the (001) plane or (001) plane or ( 006) It is possible to form a flat plate having a thermodynamically stable dense hexagonal lattice crystal structure with a well-developed surface. It is presumed that the larger the amount of silicon is, the more the crystal formation of the (001) plane or the (006) plane is promoted, and a flat plate-like alumina having a thin thickness can be obtained.

In addition, silicon is present in a sufficient amount that can be selectively adsorbed on the [113] plane of the α crystal of alumina, thereby suppressing the selective adsorption of molybdenum oxide on the [113] plane (001). It is possible to form a flat plate-like morphology having the most thermodynamically stable dense hexagonal lattice crystal structure with developed planes or (006) planes. As the amount of silicon increases, the intersections of the flat alumina with each other also have the most thermodynamically stable dense hexagonal lattice crystal structure like the other parts, and can be firmly fixed. Guessed. That is, as the amount of silicon increases appropriately, the crushing strength of the obtained alumina particles having a cardhouse structure improves.

The type of silicon or silicon compound is not particularly limited, and not only silicon atoms but also known silicon compounds can be used. Specific examples of these include metallic silicon (silicon atom), organic silane compounds, silicone resins, silica (SiO ₂ ) fine particles, silica gel, mesoporous silica, SiC, artificial synthetic silicon compounds such as mulite, and natural silicon compounds such as biosilica. And so on. Of these, it is preferable to use an organic silane compound, a silicone resin, and silica fine particles from the viewpoint that a composite or mixture with an aluminum compound can be formed more uniformly. The above-mentioned substances may be used alone or in combination of two or more.

When this silicon compound is an organic silicon compound, the organic component is burned down by firing to become a silicon atom or an inorganic silicon compound, which is contained in the alumina particles. When the silicon compound is an inorganic silicon compound, the silicon atom or the inorganic silicon compound that does not decompose at a high temperature at the time of firing is locally contained on the surface of the flat alumina by firing. From the above viewpoint, it is preferable to use a silicon atom and / or an inorganic silicon compound which can increase the content of silicon atom with a smaller amount if the molecular weight is the same.

The shape of silicon or a silicon compound is not particularly limited, and for example, spherical, amorphous, aspect-oriented structures (wires, fibers, ribbons, tubes, etc.), sheets, and the like can be preferably used.

The amount of silicon or the silicon compound used is not particularly limited, but it is preferable to use a sufficient amount that can be selectively adsorbed on the [113] plane of the α crystal of alumina, and the aluminum metal 1 of the aluminum compound as a raw material is used. The silicon metal of the silicon compound is preferably 0.003 to 0.09 mol, more preferably 0.005 to 0.04 mol, and further preferably 0.007 to 0.03 mol, based on the molar amount. preferable.
When the molybdenum compound and the potassium compound are used as the flux agent, the addition ratio of the silicon compound to the aluminum compound is preferably 0.01 to 10% by mass, more preferably 0.03 to 7% by mass, and 0. It is more preferably .03 to 3% by mass.
When the amount of the silicon compound used is in the above range, the aspect ratio of the flat-plate alumina is high, and alumina particles having excellent dispersibility can be easily obtained, which is preferable. If the amount of the silicon compound is insufficient, the adsorption of molybdenum oxide, which is a flux agent, on the [113] surface is often not sufficiently suppressed, and the aspect ratio of the flat alumina is small and the flat alumina is non-uniform. Tends to be. Further, if the amount of the silicon compound is insufficient, the produced alumina particles tend to be polyhedral alumina having a non-cardhouse structure, which is not preferable. Also the amount of silicon compound is too large, in addition to excess silicon is solely oxide, so will contain a heterogeneous crystals other than such alumina 3Al _{2 O} 3 _· 2SiO 2, not desirable.

Further, the silicon or the silicon compound may be arbitrarily added to the aluminum compound as described above, but may be contained as an impurity in the aluminum compound.

In the above production method, the method of adding silicon or a silicon compound is not particularly limited, and a dry blend method of directly adding and mixing as a powder, a method of mixing using a mixer, or a method of pre-dispersing and adding to a solvent or a monomer or the like can be used. You may use it.

By undergoing the step of firing the aluminum compound in the presence of the molybdenum compound and the silicon compound, alumina particles having a cardhouse structure in which silicon atoms and / or the inorganic silicon compound are unevenly distributed on or near the surface of the flat alumina can be obtained. It can be easily obtained. According to the findings of the present inventors, the use of the silicon compound at the time of preparation is an important factor for easily obtaining the cardhouse structure, while the silicon atoms unevenly distributed on and near the surface of the alumina particles produced by firing and / Alternatively, the presence of the inorganic silicon compound causes a large change in the surface state of alumina, which originally lacks an active point, and not only maximizes the excellent characteristics of alumina by itself, but also uses the active point as a starting point. It is an important factor that makes it possible to impart a better surface condition by integrating with a surface treatment agent by reaction.

(Germanium compound)
A germanium compound may be used as a shape control agent in combination with silicon or a silicon compound, or in place of silicon or a silicon compound. The germanium compound plays an important role in the flat crystal growth of alumina by calcining the alumina compound in the presence of the molybdenum compound.

The raw material germanium compound used as the shape control agent is not particularly limited, and known ones can be used. Specific examples of the raw material germanium compound include germanium metal, germanium dioxide, germanium monoxide, germanium tetrachloride, and an organic germanium compound having a Ge—C bond. The raw material germanium compound may be used alone or in combination of two or more. In addition, it may be used in combination with other shape control agents as long as the effects in the present invention are not impaired.

The shape of the raw material germanium compound is not particularly limited, and for example, a spherical, amorphous, aspected structure (wire, fiber, ribbon, tube, etc.), a sheet, or the like can be preferably used.

The amount of the germanium compound used is not particularly limited, but is preferably 0.002 to 0.09 mol, preferably 0.004 to 0.09 mol, of the germanium metal of the germanium compound with respect to 1 mol of the aluminum metal of the aluminum compound as a raw material. It is more preferably 0.04 mol, further preferably 0.005 to 0.03 mol.

(Other shape control agents)
In the alumina particles, as long as the formation of flat alumina by at least one shape control agent selected from silicon, silicon compounds and germanium compounds is not hindered, the fluidity, dispersibility, mechanical strength, and average particle size and the average particle size are required. In order to adjust the aspect ratio of the flat alumina, other shape control agents other than the above may be used. Similar to these, other shape control agents contribute to the growth of plate-like crystals of alumina by firing the alumina compound in the presence of the molybdenum compound.

The presence state of the other shape control agent is not particularly limited as long as it can come into contact with the aluminum compound. For example, a shape control agent, an aluminum compound and a physical mixture, a complex in which the shape control agent is uniformly or localized on the surface or inside of the aluminum compound, and the like can be preferably used.

Further, other shape control agents may be optionally added to the aluminum compound, but may be contained as impurities in the aluminum compound.

The method of adding the other shape control agent is not particularly limited, and a dry blend method in which the powder is directly added and mixed, a mixing method using a mixer, or a method in which the powder is dispersed in a solvent or a monomer in advance and added may be used. ..

Regarding other types of shape control agents, as with at least one shape control agent selected from silicon, silicon compounds and germanium compounds, molybdenum oxide is α-alumina in the presence of molybdenum compounds during high-temperature firing [113]. It is not particularly limited as long as it can suppress selective adsorption on the surface and form a plate-like morphology. It is preferable to use a metal compound other than the molybdenum compound and the aluminum compound in that the aspect ratio of the flat alumina is higher, the fluidity and dispersibility of the alumina particles are more excellent, and the productivity is more excellent. Alternatively, it is more preferable to use a sodium atom and / or a sodium compound.

The sodium atom and / or the sodium compound is not particularly limited, and known ones can be used. Specific examples of these include sodium carbonate, sodium molybdenum, sodium oxide, sodium sulfate, sodium hydroxide, sodium nitrate, sodium chloride, metallic sodium and the like. Of these, sodium carbonate, sodium molybdate, sodium oxide, and sodium sulfate are preferably used from the viewpoint of industrially easy availability and handling. The compound containing sodium or a sodium atom may be used alone or in combination of two or more.

The shape of the sodium atom and / or the sodium compound is not particularly limited, and for example, a spherical, amorphous, aspected structure (wire, fiber, ribbon, tube, etc.), a sheet, or the like can be preferably used.

The amount of the sodium atom and / or the sodium compound used is not particularly limited, but is preferably 0.0001 to 2 mol, preferably 0.001 to 1 mol, as the sodium metal with respect to 1 mol of the aluminum metal of the aluminum compound. Is more preferable. When the amount of the sodium atom and / or the sodium compound used is in the above range, alumina particles having a high aspect ratio and excellent dispersibility can be easily obtained, which is preferable.

(Metal compound)
The metal compound may have a function of promoting crystal growth of alumina, as will be described later. The metal compound can be used at the time of firing, if desired. Since the metal compound has a function of promoting crystal growth of α-alumina, it is not essential for the production of alumina particles.

The metal compound is not particularly limited, but preferably contains at least one selected from the group consisting of Group II metal compounds and Group III metal compounds.

Examples of the Group II metal compound include magnesium compounds, calcium compounds, strontium compounds, barium compounds and the like.

Examples of the Group III metal compound include scandium compounds, yttrium compounds, lanthanum compounds, and cerium compounds.

The above-mentioned metal compound means an oxide, a hydroxide, a carbon oxide, or a chloride of a metal element. For example, in the case of a yttrium compound, yttrium oxide (Y ₂ O ₃ ), yttrium hydroxide, and yttrium carbonate can be mentioned. Of these, the metal compound is preferably an oxide of a metal element. In addition, these metal compounds contain isomers.

Of these, the metal compound of the 3rd period element, the metal compound of the 4th period element, the metal compound of the 5th period element, and the metal compound of the 6th period element are preferable, and the metal compound of the 4th period element and the metal compound of the 4th period element. It is more preferably a metal compound of a 5-period element, and even more preferably a metal compound of a 5-period element. Specifically, it is preferable to use a magnesium compound, a calcium compound, an yttrium compound, and a lanthanum compound, more preferably a magnesium compound, a calcium compound, and an yttrium compound, and particularly preferably to use an yttrium compound.

The addition rate of the metal compound is preferably 0.02 to 20% by mass, more preferably 0.1 to 20% by mass, based on the mass conversion value of the aluminum atom in the aluminum compound. When the addition rate of the metal compound is 0.02% by mass or more, the crystal growth of α-alumina containing molybdenum can proceed favorably, which is preferable. On the other hand, when the addition rate of the metal compound is 20% by mass or less, alumina particles having a low content of impurities derived from the metal compound can be obtained, which is preferable.

(yttrium)
When the aluminum compound is fired in the presence of the yttrium compound as the metal compound, crystal growth proceeds more preferably in this firing step, and α-alumina and a water-soluble yttrium compound are produced. At this time, since the water-soluble yttrium compound is likely to be localized on the surface of α-alumina, which is an alumina particle, if necessary, washing with water, alkaline water, a warm liquid or the like is performed. , The yttrium compound can be removed from the alumina particles.

When the molybdenum compound is used as the flux agent, the amounts of the above aluminum compound, molybdenum compound and shape control agent used are not particularly limited, but the compound containing the molybdenum element is oxidized as molybdenum trioxide (MoO ₃ ). When the total amount of the raw material converted into a compound and converted into an oxide is 100% by mass, the following mixture of 1) or 2) may be fired.
1-1) Aluminum compounds containing 80% by mass or more of aluminum elements in terms of _{Al 2} O _{3 and}
Molybdenum compound of 1.0% by mass or more in terms of MoO _{3 and}
A silicon compound containing 0.4% by mass or more of silicon or a silicon element in terms of SiO _{2 and}
A mixture of.
1-2) Aluminum compounds containing 80% by mass or more of aluminum elements in terms of _{Al 2} O _{3 and}
Molybdenum compound of 1.0% by mass or more in terms of MoO _{3 and}
With a germanium compound of 0.4% by mass or more in terms of _{GeO 2,}
A mixture of.

By using the mixture of 1-1) or 1-2) above, alumina particles having a cardhouse structure can be produced with higher efficiency.
A common phenomenon that occurs when the mixture of 1-1) or 1-2) is fired is that at least a part of the original form of the aluminum compound used as a raw material is retained at the initial stage of crystal growth. It is conceivable that crystal growth will proceed. As a result, flat-plate alumina is formed on each of the starting points of each of the raw material aluminum compounds, so that a card house structure is formed in which the flat-plate alumina is formed of three or more flat-plate alumina and the flat-plate alumina is fixed to each other. It is thought that it will be done.

In 1-1) above _{, a silicon compound containing 0.4% by mass or more of silicon or a silicon element in terms of SiO 2} is used, and by using a relatively large proportion thereof, the shape deformation of the raw material aluminum compound is suppressed. , It is considered that the shape of the aluminum compound used as a raw material can be retained.
In 2) above _{, by using a germanium compound of 0.4% by mass or less in terms of GeO 2} and using a relatively large proportion thereof, the shape deformation of the raw material aluminum compound is suppressed, and the aluminum compound used as the raw material is used. It is thought that the shape can be retained.

In 1-1) above, when the total amount of the raw material converted to oxide is 100% by mass, the alumina particles having a card house structure and exhibiting excellent fluidity can be more easily produced. The blending amount of each raw material in the mixture is preferably as follows.
In 1-1) above, when the total amount of the raw material converted to oxide is 100% by mass, the blending amount of the aluminum compound is preferably 80% by mass or more in terms of _{Al 2} O _{3, and 85% by mass or more 99.} It is more preferably mass% or less, and further preferably 85 mass% or more and 95 mass% or less.
In the above 1-1), the time of the raw material total amount in terms oxide is 100 mass%, the molybdenum compound is preferably calculated as MoO ₃ 1.0 mass% or more, 2.0 wt% to 15 wt It is more preferably 4.0% by mass or more and 10% by mass or less.
In 1-1) above, when the total amount of the raw material converted to oxide is 100% by mass, the blending amount of silicon or a silicon compound containing a silicon element is preferably 0.4% by mass or more in terms of _{SiO 2.} , 0.4% by mass or more and 5.0% by mass or less, and more preferably 0.5% by mass or more and 2.0% by mass or less.

In the above 1-2), when the total amount of the raw material converted into oxide is 100% by mass, the alumina particles having a card house structure and exhibiting excellent fluidity can be more easily produced. The blending amount of each raw material in the mixture is preferably as follows.
In the above 1-2), the time of the raw material total amount in terms oxide is 100 mass%, the amount of the aluminum compound, is preferably in terms _{of Al} 2 _{O 3} at 80 wt% or more, 85 wt% 99 It is more preferably mass% or less, and further preferably 85 mass% or more and 95 mass% or less.
When the total amount of the raw material converted into oxides in 1-2) above is 100% by mass, the blending amount of the molybdenum compound is preferably 1.0% by mass or more in terms of _{MoO 3, and 2.0% by mass or more.} It is more preferably 15% by mass or less, and further preferably 4.0% by mass or more and 10% by mass or less.
In 1-2) above, when the total amount of the raw material converted to oxide is 100% by mass, the blending amount of the germanium compound is preferably 0.4% by mass or more in terms of _{GeO 2, and is 0.4% by mass.} It is more preferably 5.0% by mass or less, and further preferably 0.5% by mass or more and 2.0% by mass or less.

When the molybdenum compound and the potassium compound are used as the flux agent, the amounts of the above aluminum compound, molybdenum compound, potassium compound, and shape control agent used are not particularly limited, but the compound containing the molybdenum element and the potassium element, Alternatively, when a molybdenum compound containing a molybdenum element and a potassium compound containing a potassium element _{are converted into oxides as potassium molybdate (Mo 2} K ₂ O ₇ ) and the total amount of the raw materials converted into oxides is 100% by mass, the following 1) or a mixture of 2) may be fired.
2-1) Aluminum compounds containing 10% by mass or more of aluminum elements in terms of _{Al 2} O _{3 and}
Molybdenum compound and potassium compound of 50% by mass or more in terms of Mo ₂ K ₂ O _{7 and}
A silicon compound containing 0.3% by mass or more of silicon or a silicon element in terms of SiO _{2 and}
A mixture of.
2-2) Aluminum compounds containing 50% by mass or more of aluminum elements in terms of _{Al 2} O _{3 and}
Molybdenum compound and potassium compound of 30% by mass or less in terms of Mo ₂ K ₂ O _{7 and}
A silicon compound containing 0.01% by mass or more of silicon or a silicon element in terms of SiO _{2 and}
A mixture of.

By using the mixture of 2-1) or 2-2) above, alumina particles having a cardhouse structure can be produced with higher efficiency.
A common phenomenon that occurs when the mixture of 2-1) or 2-2) is fired is that at least a part of the original form of the aluminum compound used as a raw material is retained at the initial stage of crystal growth. It is conceivable that crystal growth will proceed. As a result, flat-plate alumina is formed on each of the starting points of each of the raw material aluminum compounds, so that a card house structure is formed in which the flat-plate alumina is formed of three or more flat-plate alumina and the flat-plate alumina is fixed to each other. It is thought that it will be done.

In 2-1) above, by using a silicon compound containing silicon or a silicon element of 0.3% by mass or more in terms of _{SiO 2, and using a relatively large proportion thereof, the shape deformation of the raw material aluminum compound is suppressed.} , It is considered that the shape of the aluminum compound used as a raw material can be retained.
In 2) above, the _{molybdenum compound and the potassium compound of 30% by mass or less in terms of Mo 2} K ₂ O ₇ are used, and by using a relatively small proportion thereof, the shape deformation of the raw material aluminum compound is suppressed. It is considered that the shape of the aluminum compound used as a raw material can be retained.

In 2-1) above, when the total amount of the raw material converted into oxide is 100% by mass, the alumina particles having a card house structure and exhibiting excellent fluidity can be more easily produced. The blending amount of each raw material in the mixture is preferably as follows.
In 2-1) above, when the total amount of the raw material converted to oxide is 100% by mass, the blending amount of the aluminum compound is preferably 10% by mass or more in terms of _{Al 2} O _{3 and 10% by mass or more 70.} It is more preferably 20% by mass or more, more preferably 45% by mass or less, and particularly preferably 25% by mass or more and 40% by mass or less.
In 2-1) above, when the total amount of the raw material converted to oxide is 100% by mass, the blending amount of the molybdenum compound and the potassium compound is preferably 50% by mass or more in terms of _{Mo 2} K ₂ O _7. It is more preferably 50% by mass or more and 80% by mass or less, further preferably 55% by mass or more and 75% by mass or less, and further preferably 60% by mass or more and 70% by mass or less.
In 2-1) above, when the total amount of the raw material converted to oxide is 100% by mass, the blending amount of silicon or a silicon compound containing a silicon element is preferably 0.3% by mass or more in terms of _{SiO 2.} , 0.3% by mass or more and 5% by mass or less, and more preferably 0.4% by mass or more and 3% by mass or less.

In 2-2) above, when the total amount of the raw material converted to oxide is 100% by mass, the alumina particles having a card house structure and exhibiting excellent fluidity can be more easily produced. The blending amount of each raw material in the mixture is preferably as follows.
In 2-2) above, when the total amount of the raw material converted to oxide is 100% by mass, the blending amount of the aluminum compound is preferably 50% by mass or more, and 50% by mass or more 96 in terms of _{Al 2} O _3. It is more preferably 60% by mass or more, more preferably 95% by mass or less, and particularly preferably 70% by mass or more and 90% by mass or less.
When the total amount of the raw material converted to oxide in 2-2) above is 100% by mass, the blending amount of the molybdenum compound and the potassium compound is preferably 30% by mass or less in terms of _{Mo 2} K ₂ O _7. It is more preferably mass% or more and 30 mass% or less, further preferably 3 mass% or more and 25 mass% or less, and particularly preferably 4 mass% or more and 10 mass% or less.
In 2-2) above, when the total amount of the raw material converted to oxide is 100% by mass, the blending amount of silicon or a silicon compound containing a silicon element is preferably 0.01% by mass or more in terms of _{SiO 2.} , 0.01% by mass or more and 5% by mass or less, more preferably 0.05% by mass or more and 3% by mass or less, and particularly preferably 0.15% by mass or more and 3% by mass or less. preferable.

When the mixture further contains the above-mentioned yttrium compound, the amount of the yttrium compound used is not particularly limited, but preferably Y ₂ O when the total amount of the raw material in terms of oxide is 100% by mass. A yttrium compound of 5% by mass or less in terms of _{3 can be mixed.} More preferably, can be mixed at the time of the raw material total amount in terms oxide is 100 mass%, the Y ₂ O ₃ in terms of at least 0.01 wt% 3 wt% or less of yttrium compound. More preferably for the progress of the crystal growth more suitably, mixed when the raw material total amount in terms oxide is 100 mass%, the Y ₂ O ₃ in terms of at least 0.1 wt% 1 wt% or less of yttrium compound can do.

When a molybdenum compound and a potassium compound are used as a flux agent, the aluminum compound is fired in the presence of the molybdenum compound and the potassium compound and at least one shape control agent selected from silicon, silicon compound and germanium compound. Therefore, alumina particles having a card house structure in which silicon and / or germanium are unevenly distributed on or near the surface of the flat alumina can be easily obtained. According to the findings of the present inventors, the use of at least one shape control agent selected from silicon, silicon compounds and germanium compounds at the time of preparation is an important factor for easily obtaining a cardhouse structure, while being produced by firing. The presence of silicon and / or germanium unevenly distributed on and near the surface of the alumina particles causes a large change in the surface state of alumina, which originally lacks active points, and only maximizes the excellent characteristics of alumina by itself. Not only that, but it is also an important factor that makes it possible to impart a better surface state by integrating with the surface treatment agent by the reaction, starting from the active point.

[Baking process]
The firing step is preferably a step of firing an aluminum compound in the presence of a molybdenum compound, at least one shape control agent selected from silicon, silicon compounds and germanium compounds, and if necessary, other shape control agents. is there. The firing step may be a step of firing the mixture obtained in the mixing step.

Alumina particles can be obtained, for example, by firing the aluminum compound in the presence of a molybdenum compound and a shape control agent. As mentioned above, this manufacturing method is called the flux method. Based on the above-mentioned flux method, it is presumed that the formation of the flat plate-shaped alumina and the formation of the card house structure due to the fixation of the three or more flat plate-shaped aluminas on the left proceed in parallel.

The flux method is classified as a solution method. More specifically, the flux method is a method of crystal growth utilizing the fact that the crystal-flux two-component phase diagram shows a eutectic type. The mechanism of the flux method is presumed to be as follows. That is, as the mixture of solute and flux is heated, the solute and flux become a liquid phase. At this time, since the flux is a flux, in other words, since the solute-flux two-component phase diagram shows a eutectic type, the solute melts at a temperature lower than its melting point to form a liquid phase. It becomes. If the flux is evaporated in this state, the concentration of the flux decreases, in other words, the effect of the flux on lowering the melting point of the solute is reduced, and the evaporation of the flux acts as a driving force to cause crystal growth of the solute (flux). Evaporation method). Crystal growth in a liquid phase flux agent is also a preferred method, and the solute and flux can also cause solute crystal growth by cooling the liquid phase (slow cooling method).

The flux method has merits such as being able to grow a crystal at a temperature much lower than the melting point, being able to precisely control the crystal structure, and being able to form a crystal having an automorphic shape.

In the production of alumina particles by the flux method using a molybdenum compound as the flux, the mechanism is not always clear, but it is presumed that the mechanism is as follows, for example. That is, when the aluminum compound is fired in the presence of the molybdenum compound, aluminum molybdate is first formed. At this time, the aluminum molybdate grows alumina crystals at a temperature lower than the melting point of alumina, as can be understood from the above description. Then, for example, by evaporating the flux, aluminum molybdate is decomposed and crystal growth is performed, so that alumina particles can be obtained. That is, the molybdenum compound functions as a flux, and alumina particles are produced via an intermediate called aluminum molybdate.

Here, when the potassium compound and the shape control agent are used in combination in the above flux method, alumina particles having a card house structure formed of three or more flat alumina can be produced with high efficiency. More specifically, when the molybdenum compound and the potassium compound are used in combination, the molybdenum compound and the potassium compound first react to form potassium molybdate. At the same time, the molybdenum compound reacts with the aluminum compound to form aluminum molybdate. Then, for example, aluminum molybdate decomposes in the presence of potassium molybdate and crystal grows in the presence of a shape control agent to produce alumina particles having a cardhouse structure formed of three or more flat alumina. Obtainable. That is, when the alumina particles are produced via an intermediate called aluminum molybdate, if potassium molybdate is present, the alumina particles having a card house structure formed of three or more flat alumina can be obtained. ..

As described above, the potassium or potassium compound serves as a flux agent as potassium molybdate.

It should be noted that the above mechanism is only speculative, and even if the effect of the present invention is obtained by a mechanism different from the above mechanism, it is included in the technical scope of the present invention.

The composition of potassium molybdate described above is not particularly limited, but usually contains molybdenum atom, potassium atom and oxygen atom. The structural formula is preferably expressed as _{K 2 Mo n O 3n + 1} . In this case, n is not particularly limited, but is preferably in the range of 1 to 3 because the promotion of alumina particle growth functions effectively. In addition, potassium molybdate may contain other atoms, and examples of the other atoms include sodium, magnesium, silicon, and the like.

In one embodiment of the present invention, the above-mentioned firing may be performed in the presence of a metal compound. That is, in the firing, the above-mentioned metal compound can be used in combination with the molybdenum compound and the potassium compound. Thereby, alumina particles having more excellent fluidity can be produced. The mechanism is not always clear, but it is presumed to be due to the following mechanism, for example. That is, the presence of the metal compound during the crystal growth of the alumina particles prevents or suppresses the overformation of the alumina crystal nuclei and / or promotes the diffusion of the aluminum compound necessary for the crystal growth of the alumina, in other words, the crystal. The function of preventing excessive generation of nuclei and / or increasing the diffusion rate of aluminum compounds is exhibited, enabling more precise control of the crystal growth direction of alumina and facilitating shape control such as reflecting the shape of the precursor. , It is considered that alumina particles with higher fluidity can be obtained. It should be noted that the above mechanism is only speculative, and even if the effect of the present invention is obtained by a mechanism different from the above mechanism, it is included in the technical scope of the present invention.

The firing method is not particularly limited, and can be performed by a known and commonly used method. When the firing temperature exceeds 700 ° C., the aluminum compound reacts with the molybdenum compound to form aluminum molybdate. Further, when the firing temperature becomes 900 ° C. or higher, aluminum molybdate is decomposed and flat alumina is formed by the action of the shape control agent. Further, the flat alumina is obtained by incorporating molybdenum into the aluminum oxide particles when the aluminum molybdate decomposes to form alumina and molybdenum oxide.

Further, at the time of firing, the states of the aluminum compound, the shape control agent, the molybdenum compound, and the potassium compound are not particularly limited, and the molybdenum compound, the potassium compound, and the shape control agent are present close to each other to the extent that they can act on the aluminum compound. It suffices if it is in a state of doing. Specifically, it may be a simple mixing of the powder of the molybdenum compound, the shape control agent and the aluminum compound, a mechanical mixing using a crusher or the like, or a mixing using a mortar or the like, and is in a dry state. , May be mixed in a wet state.

The conditions of the calcination temperature are not particularly limited, and are appropriately determined depending on the average particle size, fluidity, dispersibility, aspect ratio of the flat-plate alumina, etc. of the target alumina particles. Generally, the firing temperature may be 900 ° C. or higher, which is the decomposition temperature of _{aluminum molybdate (Al 2} (MoO ₄ ) _3).

Generally, in order to control the shape of α-alumina obtained after firing, it is necessary to perform high-temperature firing at 2000 ° C. or higher, which is close to the melting point of α-alumina. There is a big problem for industrial use.

The preferred method for producing alumina particles as described above can be carried out even at a high temperature of more than 2000 ° C., but even at a temperature of 1600 ° C. or lower, which is considerably lower than the melting point of α-alumina, α crystals. Alumina particles made of flat alumina having a high crystallization rate and a high aspect ratio can be formed.

According to the preferred production method as described above, alumina particles having a high aspect ratio of flat alumina and an α crystallization rate of 90% or more even when the maximum firing temperature is 900 ° C. to 1600 ° C. Can be easily and efficiently formed at low cost, and firing at a maximum temperature of 920 to 1500 ° C. is more preferable, and firing in a maximum temperature range of 950 to 1400 ° C. is most preferable.

As the firing temperature becomes higher, the α crystallization at the intersection of the flat alumina is also improved as in the other portions, and alumina particles having a card house structure having excellent mechanical strength can be obtained.

Regarding the firing time, it is preferable that the heating time to the predetermined maximum temperature is performed in the range of 15 minutes to 10 hours, and the holding time at the maximum firing temperature is performed in the range of 5 minutes to 30 hours. In order to efficiently form the flat alumina, the firing holding time is more preferably about 10 minutes to 15 hours.

As the holding time at the maximum firing temperature becomes longer, the α crystallization at the intersections of the flat-plate alumina is also improved as in the other portions, and alumina particles having a cardhouse structure excellent in crushing strength can be obtained.

The firing atmosphere is not particularly limited as long as the effects of the present invention can be obtained, but for example, an oxygen-containing atmosphere such as air or oxygen or an inert atmosphere such as nitrogen or argon is preferable, and in consideration of cost. The air atmosphere is more preferable.

The device for firing is not necessarily limited, and a so-called firing furnace can be used. The firing furnace is preferably made of a material that does not react with sublimated molybdenum oxide, and it is preferable to use a highly airtight firing furnace so that molybdenum oxide can be used efficiently. Examples of the firing furnace that can be used at this time include a tunnel furnace, a roller hearth furnace, a rotary kiln, and a muffle furnace.

In the above-mentioned suitable production method, alumina particles having a card house structure can be selectively obtained, and a powder containing the alumina particles in a proportion of 60% or more of the total can be easily obtained. By selecting and manufacturing more suitable conditions in the manufacturing method, among the alumina particles, the three or more flat alumina particles are aggregated at two or more crossing points. Since it is possible to more easily obtain a powder containing alumina particles having a card house structure in which the plane directions of the intersecting flat plates are arranged in a disorderly manner at a ratio of 80% or more of the total number of alumina particles. preferable.

[Cooling process]
When the molybdenum compound and the potassium compound are used as the flux agent, the method for producing the alumina particles may include a cooling step. The cooling step is a step of cooling the alumina crystal-grown in the firing step. More specifically, it may be a step of cooling the composition containing the alumina and the liquid phase flux agent obtained in the firing step.

The cooling rate is not particularly limited, but is preferably 1 to 1000 ° C./hour, more preferably 5 to 500 ° C./hour, and even more preferably 50 to 100 ° C./hour. When the cooling rate is 1 ° C./hour or more, the production time can be shortened, which is preferable. On the other hand, when the cooling rate is 1000 ° C./hour or less, the firing container is less likely to be cracked by heat shock and can be used for a long time, which is preferable.

The cooling method is not particularly limited, and a cooling device may be used even if it is naturally allowed to cool.

[Post-treatment process]
The method for producing alumina particles according to the embodiment may include a post-treatment step. The post-treatment step is a post-treatment step of alumina particles having a card house structure, and is a step of removing a flux agent. The post-treatment step may be performed after the above-mentioned firing step, after the above-mentioned cooling step, or after the firing step and the cooling step. Moreover, you may repeat it twice or more if necessary.

Post-treatment methods include cleaning and high temperature treatment. These can be done in combination.

The cleaning method is not particularly limited, but it can be removed by cleaning with water, an aqueous ammonia solution, an aqueous sodium hydroxide solution, or an acidic aqueous solution.

At this time, the molybdenum content can be controlled by appropriately changing the concentrations of the water used, the aqueous ammonia solution, the aqueous sodium hydroxide solution, and the acidic aqueous solution, the amount used, the cleaning site, the cleaning time, and the like.

Further, as a method of high temperature treatment, a method of raising the temperature above the sublimation point or boiling point of the flux can be mentioned.

[Crushing process]
Alumina particles may aggregate in the fired product and may not meet the particle size range suitable for the embodiment. Therefore, the alumina particles may be pulverized so as to satisfy the particle size range suitable for the embodiment, if necessary.

The method for crushing the fired product is not particularly limited, and conventionally known crushing methods such as ball mills, jaw crushers, jet mills, disc mills, spectromills, grinders, and mixer mills can be applied.

[Classification process]
Alumina particles are preferably classified in order to adjust the average particle size, improve the fluidity of the powder, or suppress the increase in viscosity when blended in a binder for forming a matrix.

The classification may be either wet or dry, but from the viewpoint of productivity, the dry classification is preferable. Dry classification includes classification by sieving and wind classification by the difference between centrifugal force and fluid drag. From the viewpoint of classification accuracy, wind classification is preferable, and an air flow classer using the Coanda effect. This can be performed using a classifier such as a swirling air flow type classifier, a forced vortex centrifugal classifier, or a semi-free vortex centrifugal classifier.

The above-mentioned pulverization step and classification step can be performed at a necessary stage including before and after the organic compound layer forming step described later. For example, the average particle size of the obtained alumina particles can be adjusted by the presence or absence of crushing and classification and selection of their conditions. The average particle size of the alumina particles is closely related to the angle of repose, and even if the above-mentioned manufacturing method and manufacturing conditions of the alumina particles cannot be sufficiently adjusted, the conditions such as classification and the like are used. The fluidity of the alumina particles can be adjusted by changing the average particle size of the alumina particles (indirectly changing the angle of repose) by selection.

Specifically, for example, when there is no alumina particle having a card house structure having a target average particle size, the alumina particle having a larger average particle size is classified to have a smaller average particle size. In comparison with each other having the same average particle size, alumina particles having a card house structure having better fluidity than known alumina particles can be obtained.

[Organic compound layer forming step]
In one embodiment, the above-mentioned method for producing alumina particles may further include an organic compound layer forming step of forming an organic compound layer on the surface of flat alumina. If necessary, the organic compound layer forming step is performed at a temperature at which the organic compound does not decompose, usually after a firing step, or after a post-treatment step.

The method for forming the organic compound layer on the surface of the flat alumina of the alumina particles is not particularly limited, and a known method can be appropriately adopted. For example, a method of bringing a solution or dispersion containing an organic compound into contact with alumina particles containing molybdenum and drying the particles can be mentioned.

Examples of the organic compound that can be used for forming the organic compound layer include an organic silane compound.

(Organic silane compound)
When the alumina particle having a card house structure contains a silicon atom and / or an inorganic silicon compound, the surface modification effect as described above can be expected as compared with the case where it does not contain the silicon atom and / or an inorganic silicon compound. It can also be used as a reaction product of an alumina particle containing an inorganic silicon compound and an organic silane compound. Compared to alumina particles containing silicon atoms and / or inorganic silicon compounds and having a cardhouse structure, alumina particles having a cardhouse structure, which is a reaction product of an organic silane compound, are flat plates constituting the alumina particles. Based on the reaction between the silicon atom and / or the inorganic silicon compound localized on the surface of the alumina particles and the organic silane compound, the affinity with the matrix can be improved, which is preferable.

Examples of the organic silane compound include methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, iso-propyltrimethoxysilane, and iso. -Alkyltrimethoxysilanes or alkyltrichlorosilanes with an alkyl group having 1-222 carbon atoms such as -propyltriethoxysilane, pentiltrimethoxysilane, hexyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane , (Tridecafluoro-1,1,2,2-tetrahydrooctyl) trichlorosilanes, phenyltrimethoxysilane, phenyltriethoxysilane, p-chloromethylphenyltrimethoxysilane, p-chloromethylphenyltriethoxysilane, etc. , Γ-Glysidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane and other epoxysilanes, γ-aminopropyltriethoxysilane, N- Aminosilanes such as β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane, 3-mercapto Mercaptosilane such as propyltrimethoxysilane, p-styryltrimethoxysilane, vinyltricrolsilane, vinyltris (β-methoxyethoxy) silane, vinyltrimethoxysilane, vinyltriethoxysilane, vinylsilane such as γ-methacryloxypropyltrimethoxysilane Further, epoxy-based, amino-based, and vinyl-based polymer-type silanes can be mentioned. The organic silane compound may be contained alone or may contain two or more kinds.

The organic silane compound may be covalently linked to at least a part or all of the silicon atom and / or the inorganic silicon compound on the surface of the flat alumina of the alumina particles by the reaction, and not only a part of the alumina but the whole may be linked. It may be coated with the above-mentioned reactant. As a method of providing the alumina on the surface, adhesion by immersion or chemical vapor deposition (CVD) can be adopted.

The amount of the organic silane compound used is preferably 20% by mass or less based on the silicon atom with respect to the mass of the silicon atom or the inorganic silicon compound contained in the surface of the flat alumina of the alumina particles, and is 10 to 0. It is more preferably 0.01% by mass. When the amount of the organic silane compound used is 20% by mass or less, it is preferable because the physical properties derived from the alumina particles can be easily expressed.

The reaction between the alumina particles containing silicon atoms and / or the inorganic silicon compound and the organic silane compound can be carried out by a known and commonly used filler surface modification method, for example, a spray method using a fluid nozzle, a shearing force. A certain stirring, a dry method such as a ball mill or a mixer, or a wet method such as an aqueous or organic solvent system can be adopted. It is desirable that the treatment using the shearing force be performed to such an extent that the alumina particles used in the embodiment are not destroyed.

The in-system temperature in the dry method or the drying temperature after the treatment in the wet method is appropriately determined in a region where it does not thermally decompose, depending on the type of the organic silane compound. For example, when treating with the above-mentioned organic silane compound, a temperature of 80 to 150 ° C. is desirable.

[Post-processing process]
In the method for producing alumina particles, an arbitrary step may be added during the production of the alumina particles, or a post-treatment step may be added to arbitrarily adjust the particle size, shape, etc., as long as the effect is not impaired. Examples thereof include granulation steps such as rolling granulation and compression granulation, and granulation by a spray-drying method using a binder as a binder, which can be easily obtained by using a commercially available device.

<Coating agent>
The wear resistant agent of the present embodiment is suitably blended in the coating agent. As one embodiment of the present invention, a coating agent containing the wear resistant agent of the embodiment (hereinafter, may be referred to as "coating agent of the embodiment" or simply "coating agent") can be provided. The coating agent is preferably used for materials such as flooring materials, building materials, and automobile parts, and is particularly preferably used for flooring materials.

The coating agent of the present embodiment may contain various optional components in addition to the above alumina particles, if necessary. Examples of the optional component include a solvent, a resin, a drying accelerator, a curing agent, a curing accelerator, a thickener, an anti-settling agent, an anti-repellent agent, an anti-sagging agent, a spreading agent, an antifoaming agent, and an ultraviolet absorber. , Light stabilizers, other pigments that do not correspond to the above alumina particles, and the like.
Examples of other pigments that do not correspond to the above alumina particles include various pigments such as coloring pigments and extender pigments.
As the coloring pigment, conventionally known pigments can be appropriately used according to the desired hue and performance. For example, azo-based, benzimidazolone-based, isoindolinone / isoindoline-based, phthalocyanine-based, quinacridone-based, and dioxazine. Organic pigments such as diketopyrrolopyrrole, quinophthalone, perylene / perinone, thioindigo, anthraquinone, slene, etc., and inorganic pigments such as iron oxide, carbon black, titanium oxide, zinc sulfide, etc. Examples of the extender pigment include barium sulfate, calcium carbonate, talc, kaolin and the like.
Further, various metals such as zinc powder and aluminum powder or metal salts may be used in combination.

As one embodiment of the present invention, a coating agent containing the alumina particles of the embodiment, a solvent, and a resin can be provided.

From the viewpoint of reducing the viscosity of the coating agent and facilitating the application, it is preferable that the coating agent contains a solvent. The solvent can disperse the alumina particles. The solvent can disperse or dissolve the above optional components.
Examples of the solvent include alcohol solvents such as ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol and isobutyl alcohol; ester solvents such as ethyl acetate, propyl acetate and butyl acetate, methyl ethyl ketone and methyl butyl ketone. Ketone solvents such as cyclohexanone; ether ester solvents such as methyl cellosolve acetate and butyl cellosolve acetate; amide solvents such as dimethylformamide and dimethylacetamide; aromatic hydrocarbon solvents such as toluene and xylene; hexane, heptane, white spirits and the like The aliphatic hydrocarbon solvent of the above; a mixed solvent of aromatic hydrocarbons such as mineral spirit and an aliphatic hydrocarbon; water, a mixture thereof and the like, but are not limited thereto.

The content ratio of the solvent with respect to the total mass 100% by mass of the coating agent may be, for example, 3 to 90% by mass, or 5 to 85% by mass.

The content ratio of the solid content (component excluding volatile components such as solvent) to 100% by mass of the total mass of the coating agent may be, for example, 10 to 97% by mass, or 15 to 95% by mass.

It is preferable that the coating agent contains a resin from the viewpoint of binding the alumina particles contained in the coating agent to each other and enhancing the adhesion between the base material and the coating agent.
As the resin, any resin that can be blended in the paint can be used, and conventionally known resins may be used. Examples of the resin include acrylic resin, polyester resin, alkyd resin, urethane resin, epoxy resin, vinyl chloride vinegar copolymer resin, polyamide resin, melamine resin, cellulose resin and the like. As the resin, one type may be used alone, or two or more types may be used in combination.
The content ratio of the resin (solid content) in the coating agent may be 5% by mass or more with respect to 100% by mass of the total mass of the solid content (component excluding volatile components such as solvent) of the coating agent. It may be 10 to 97% by mass, or 30 to 80% by mass.

From the viewpoint of effectively improving the wear resistance, the content ratio of the alumina particles in the coating agent may be 1 to 15% by mass or more with respect to 100% by mass of the total mass of the coating agent, and 2 to 10%. It may be% by mass, 2.5 to 8% by mass, or 3 to 7% by mass.

The coating agent of the present embodiment can be produced, for example, by a method including mixing the above-mentioned alumina particles and, if necessary, the above-mentioned optional components. Examples of the mixer that can be used at that time include a sand mill, a homomixer, a homogenizer, a colloid mill, a microfluidizer, a sonolator, and a cavitron.

<Laminated body>
The base material coated with the coating agent of the embodiment can be provided as a laminate having the base material and the layer containing the coating agent of the embodiment. Such a laminate is a useful one in which the base material is endowed with abrasion resistance. Examples of the layer containing the coating agent include a cured product of the coating agent of the embodiment. The cured product of the coating agent can be formed, for example, by drying or heat-curing the coating film of the coating agent applied to the base material at room temperature.

As an example, the dry film thickness of the layer containing the above coating agent is preferably 50 to 700 μm, more preferably 60 to 300 μm. When the dry film thickness is within the above range, wear resistance is satisfactorily exhibited.

The base material is not particularly limited, and examples thereof include a resin base material and a metal base material, and more specifically, materials such as flooring materials, building materials, and automobile parts can be exemplified.

<Method>
The coating agent of the present embodiment can be used by applying it to a base material. That is, in one embodiment, the present invention provides a method for producing a laminate, which comprises applying the coating agent to a substrate. According to the method for producing a laminate of the present embodiment, the above-mentioned laminate having wear resistance can be produced.
The method of applying the coating agent is not particularly limited, and can be applied by roll coating, spray, brush, spatula, bar coater, or dip coating. As a post-treatment method after painting, normal temperature drying to heat curing can be performed. The heating temperature in the case of heat curing is preferably in the range of 50 to 250 ° C, particularly preferably in the range of 60 to 230 ° C. The heating time is preferably in the range of 2 to 30 minutes, particularly preferably in the range of 5 to 20 minutes.

As described above, the coating agent of the present embodiment contains alumina particles having the above-mentioned constitution. The alumina particles have a larger specific surface area than spherical alumina particles having the same shape. Therefore, the wear-resistant agent of the present embodiment has good wear resistance.

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to the following Examples.

<Synthesis of alumina particles>
[Synthesis Example 1] Synthesis of Alumina Particles Aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd., average particle diameter 40 μm) 144.8 g, silicon dioxide (manufactured by Kanto Chemical Co., Inc., special grade) 0.95 g, and molybdenum trioxide (solar) 5 g (manufactured by Mining Co., Ltd.) was mixed in a dairy pot to obtain a mixture. The obtained mixture was placed in a crucible and fired in a ceramic electric furnace at 1100 ° C. for 10 hours. After the temperature was lowered, the crucible was taken out to obtain 97.0 g of a light blue powder. The obtained powder was crushed in a mortar until it passed through a 106 μm sieve.
Subsequently, 100 g of the obtained light blue powder was dispersed in 150 mL of 0.5% ammonia water, the dispersion solution was stirred at room temperature (25 ° C. or higher and 30 ° C. or lower) for 0.5 hours, and then the aqueous ammonia was filtered. Was removed, and the particles were washed with water and dried to remove molybdenum remaining on the particle surface, and 94.0 g of powder was obtained. Then, the fine particle component was classified and removed by an air flow classifier (HPC-ZERO type, a high-prec classifier manufactured by Powder Systems Co., Ltd.) utilizing the Coanda effect to obtain 66 g of alumina particle powder. Moreover, when the zeta potential was measured, it was found that the isoelectric point of the obtained alumina particles was pH 5.3.
It was confirmed by SEM observation that the obtained powder was alumina particles formed of three or more flat alumina and having a fixed cardhouse structure. The average particle size of the obtained powder was measured and found to be 35 μm. Further, it was confirmed that the flat plate-shaped alumina itself constituting the card house structure had a polygonal plate shape, a thickness of 400 nm, an average particle diameter of 8 μm, and an aspect ratio of 20. Further, when XRD measurement was performed, a sharp scattering peak derived from α-alumina appeared, and no alumina crystal system peak other than the α crystal structure was observed. The pregelatinization rate was 99% or more (almost 100%). Further, from the result of fluorescent X-ray quantitative analysis (XRF), the obtained particles contained 0.71% by mass of silicon in terms of silicon dioxide, 0.76% by mass of molybdenum in terms of molybdenum trioxide, and Si with respect to Al. The molar ratio [Si] / [Al] of was 0.007.
Further, as a result of analyzing the obtained powder by X-ray photoelectron spectroscopy (XPS), the [Si] / [Al] of the surface composition of the flat alumina of the alumina particles was 0.25, which was used in the quantitative analysis of fluorescent X-rays. It was confirmed that the silicon atom and / or the inorganic silicon compound was unevenly distributed on the surface of the flat alumina, which was significantly higher than the [Si] / [Al]% value of the bulk composition.
In addition, the formation of a mullite layer on the surface of flat alumina was confirmed by XRD measurement.
Moreover, when the specific surface area of the obtained powder was measured, it was found that it was 1.4 (m ² / g) and the angle of repose was 33 °.
Further, as a result of calculating the crushing strength of the obtained powder using a fine particle crushing force measuring device NS-A100 manufactured by Nanoseeds Co., Ltd., it was 28 MPa.

<Evaluation of Alumina Particles Obtained in Synthesis Examples and Commercially Available Spherical Alumina Particles>
[Shape analysis of alumina particles by scanning electron microscope]
Alumina particles obtained in the above synthesis example and commercially available spherical alumina particles (DAS-30 manufactured by Denka Co., Ltd.) are used as samples, and these are fixed to a sample support with double-sided tape, and the surface observation device (Keyence) is used. The presence or absence of a card house structure of alumina particles was confirmed by observing with VE-9800) manufactured by the same company.

[Measurement of major axis L of flat alumina]
The major axis L of the flat plate-shaped alumina is the maximum length of the distance between two points on the contour line of the plate for any 100 flat-plate-shaped alumina located in the center of the alumina particles, by scanning electron microscope (SEM). Was measured and calculated as an arithmetic mean value.

[Measurement of thickness D of flat alumina]
The average value of 10 thicknesses measured using a scanning electron microscope (SEM) was adopted and used as a thickness D (μm).

[Aspect ratio L / D of flat alumina]
The aspect ratio was calculated using the following formula.
(Aspect ratio) = (major axis L of flat alumina / thickness D of flat alumina)

[Measurement of average particle size of alumina particles by particle size distribution measurement]
The prepared sample was measured using a laser diffraction type dry particle size distribution meter (HELOS (H3355) & RODOS manufactured by Nippon Laser Co., Ltd.) under the conditions of a dispersion pressure of 0.3 MPa and a pulling pressure of 90 hPa, and based on the volume-based cumulative particle size distribution. , D ₅₀ (μm) was determined and used as the average particle size of the alumina particles.

[Measurement of angle of repose]
300 g of a sample was prepared, and the angle of repose of the sample was measured by a method according to JIS R9301-2-2.

[Measurement of specific surface area]
The prepared sample was pretreated under the condition of 300 ° C. for 3 hours, and then the specific surface area of the pretreated sample was measured using TriStar3000 manufactured by Micromeritics.

[Analysis of XRD peak intensity ratio and presence / absence of mullite]
The prepared sample is placed on a holder for a measurement sample having a depth of 0.5 mm, filled flat with a constant load, and set in a wide-angle X-ray diffraction (XRD) device (Ultima IV manufactured by Rigaku Co., Ltd.). The measurement was performed under the conditions of Cu / Kα ray, 40 kV / 40 mA, a scan speed of 2 degrees / minute, and a scanning range of 10 to 70 degrees.
Let A be the peak height of mullite observed at 2θ = 26.2 ± 0.2 degrees, and B be the peak height of α-alumina on the (104) plane observed at 2θ = 35.1 ± 0.2 degrees. With the baseline value of 2θ = 30 ± 0.2 degrees as C, the presence or absence of mullite was determined from the following formula.
When the value was 0.02 or more, mullite was judged to be "yes", and when the value was less than 0.02, mullite was judged to be "absent".

[Si amount of flat alumina surface layer]
Using the X-ray photoelectron spectroscopy (XPS) device Quantera SXM (ULVAC-PHI), the prepared sample was press-fixed on double-sided tape, and the composition was analyzed under the following conditions.

(Measurement condition)
・ X-ray source: monochromatic AlKα, beam diameter 100 μmφ, output 25 W ・ Measurement: area measurement (1000 μm square), n = 3
-Charge correction: C1s = 284.8eV

[Si] / [Al] obtained from the XPS analysis results was defined as the amount of Si in the surface layer of the flat alumina particles.

[Analysis of pregelatinization rate]
Place the prepared sample on a holder for a measurement sample with a depth of 0.5 mm, fill it flat with a constant load, set it in a wide-angle X-ray diffractometer (Ultima IV manufactured by Rigaku Co., Ltd.), and use Cu / Kα rays. The measurement was performed under the conditions of 40 kV / 40 mA, a scan speed of 2 degrees / minute, and a scanning range of 10 to 70 degrees. The pregelatinization rate was calculated from the ratio of the strongest peak heights of α-alumina and transition alumina.

[Analysis of the amount of Si contained in alumina particles]
Using a fluorescent X-ray (XRF) analyzer Primus IV (manufactured by Rigaku Co., Ltd.), about 70 mg of the prepared sample was taken on a filter paper, covered with a PP film, and the composition was analyzed.
[Si] / [Al] obtained from the XRF analysis result was defined as the amount of Si in the alumina particles.
The amount of silicon determined from the XRF analysis result was determined by silicon dioxide conversion (mass%) with respect to 100% by mass of alumina particles.

[Analysis of the amount of Mo contained in alumina particles]
Using a fluorescent X-ray analyzer Primus IV (manufactured by Rigaku Co., Ltd.), about 70 mg of the prepared sample was taken on a filter paper, covered with a PP film, and the composition was analyzed.
The amount of molybdenum determined from the XRF analysis result was determined by molybdenum trioxide conversion (mass%) with respect to 100% by mass of alumina particles.

[Measurement of crush strength]
The crushing strength was measured using a fine particle crushing force measuring device NS-A100 manufactured by Nanoseeds Co., Ltd. The difference between the peak value at the time of crushing and the baseline (when no force is applied) is defined as the crushing force F [N], and the crushing strength S [Pa] is the average value of 10 values calculated from the following equation. did.
S = 2.8F / (π ・ D ² )
In the above formula, F is a crushing force [N] and D is a particle size [m].

[Measurement of isoelectric point]
Zeta potential measurement was performed with a zeta potential measuring device (Malburn, Zetasizer Nano ZSP). 20 mg of the sample and 10 mL of a 10 mM KCl aqueous solution were stirred with Rentarou Awatori (Sinky, ARE-310) in the stirring / defoaming mode for 3 minutes, and the supernatant was allowed to stand for 5 minutes as a measurement sample. 0.1N HCl was added to the sample by an automatic titrator, and the zeta potential was measured in the range up to pH = 2 (applied voltage 100 V, Monomodl mode), and the pH of the isoelectric point at which the potential became zero was evaluated.

Table 1 below shows the oxide-equivalent formulation of the raw material compound (the total is 100% by mass) and the evaluation results of each alumina particle obtained in the synthesis example. In Table 1, "ND" is an abbreviation for not detected and indicates that it is not detected.

<Preparation of coating agent>
[Example 1]
Centrifugal stirrer (Fractec Co., Ltd.) in an amount of the alumina particles obtained in Synthesis Example 1 and the cellulose acetate butyrate resin solution (solid content concentration: 32%) in a ratio of alumina particles: cellulose butyrate acetate resin solution = 1/19. It was put into (manufactured by) and stirred at 3000 rpm for 1 minute to obtain a coating agent (A1).

[Comparative Example 1]
A coating agent (A2) was obtained in the same manner as in Example 1 except that the alumina particles obtained in Synthesis Example 1 were changed to commercially available spherical alumina particles (DAS-30 manufactured by Denka Corporation).

[Comparative Example 2]
Alumina particles were not mixed with the cellulose acetate resin solution (solid content concentration: 32%) to prepare a coating agent (A3).

<Evaluation of wear resistance>
The coating agent obtained in each example was applied onto a paper substrate so as to have a film thickness of 76.2 μm to obtain a test piece. Attach the obtained test piece to the test stand of the Sutherland type wear tester, attach plain paper to a 2 kg weight, reciprocate the weight 50 times so as to rub the plain paper against the test piece, and then wear resistance according to the following criteria. Gender was evaluated. The results are shown in Table 2.
◯: The surface of the test piece was almost not damaged.
Δ: Scratches on the surface of the test piece were conspicuous.
X: The surface of the test piece was full of scratches.

From the results shown in Table 2, it was confirmed that the coating agent of Example 1 had better wear resistance than the coating agents of Comparative Examples 1 and 2.

Each configuration in each embodiment and a combination thereof are examples, and the configuration can be added, omitted, replaced, and other changes are possible without departing from the spirit of the present invention. Moreover, the present invention is not limited to each embodiment, but is limited only to the scope of claims.

According to the wear-resistant agent of the present embodiment, it is possible to provide a wear-resistant agent having good wear resistance.

Claims (8)

An abrasion resistant agent formed of three or more flat-plate alumina, having a card house structure to which the flat-plate alumina is fixed, and containing alumina particles having an average particle diameter of 3 μm or more and 1000 μm or less. The wear resistant agent according to claim 1, wherein the alumina particles contain silicon and / or germanium. The wear-resistant agent according to claim 1 or 2, wherein the alumina particles contain molybdenum. The wear-resistant agent according to claim 3, wherein the content of molybdenum with respect to 100% by mass of the alumina particles is 10% by mass or less in terms of molybdenum trioxide. A coating agent containing the wear resistant agent according to any one of claims 1 to 4. A laminate having a base material and a layer containing the coating agent according to claim 5. A method for producing a laminate, which comprises applying the coating agent according to claim 5 to a substrate. A method for coating a base material, which comprises applying the coating agent according to claim 5 to the base material.

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