JP6346421B2 - Crystalline alumina laminated particle and method for producing the crystalline alumina laminated particle - Google Patents

Description

  The present invention relates to a crystalline alumina laminated particle having a structure in which a plurality of square plate-like alumina fine particles are laminated without overlapping at least two sides, and a method for producing the crystalline alumina laminated particle.

  The present invention is a crystalline alumina laminated particle having a structure in which a plurality of square plate-like alumina fine particles are laminated without overlapping at least two sides. About the square plate-like alumina fine particles constituting the crystalline alumina laminated particles, Many reports have been made.

In Patent Document 1, an aqueous solution of a metal salt is treated at 200 ° C. or higher and 160 kg / cm ² or higher, which is a subcritical or supercritical condition of water, and a metal oxide containing an oxyhydroxide that is a hydrate of a metal oxide. A method for producing physical particles is disclosed. The characteristics of the particles are that the particle size distribution is narrow, the shapes are uniform, the crystallinity is high, there are no branches and twins, and there is little secondary aggregation.

  Patent Document 2 discloses that aluminum hydroxide and a (meth) acrylic acid ester-based polymer are used as a pH adjuster and at least one hydroxide or alumina selected from sodium, potassium, barium, calcium and strontium. The manufacturing method of plate-like boehmite alumina is disclosed by hydrothermally treating at a temperature of 130 to 250 ° C. with an acid salt added to a pH of 8 or higher.

  Furthermore, as nano-sized alumina composite oxide fine particles, Patent Document 3 discloses that a boehmite alumina fine particle is incorporated into a gel by reacting an aqueous aluminum metal salt solution with an alkaline aqueous solution to produce a reaction mixture containing a gel substance in advance. Nano-sized alumina fine particles are disclosed by preventing adhesion and aggregation of alumina fine particles by using the sol-gel method.

  Patent Document 4 discloses a sol-gel method in which an aqueous alkali solution is added to an aqueous aluminum metal salt solution, and a gel-like substance of aluminum hydroxide is preliminarily produced in the obtained reaction mixture, thereby incorporating boehmite alumina fine particles into the gel. Nano-sized alumina fine particles have been disclosed by preventing adhesion and aggregation between the alumina fine particles. Moreover, it is disclosed that the obtained alumina fine particle has a hollow part inside, and uses such as an inorganic filler and a lightweight inorganic molded body are disclosed.

  However, there is no disclosure of crystalline alumina laminated particles having a structure in which square plate-like alumina fine particles are laminated without overlapping at least two sides, and there is no suggestion about their existence. Furthermore, little is known about the use of the particles.

Japanese Patent Laid-Open No. 04-050105 JP 2003-002641 A JP 2006-056739 A JP 2006-143487 A

  An object of the present invention is to provide a crystalline alumina laminated particle having a structure in which a plurality of square plate-like alumina fine particles are laminated without overlapping at least two sides, and a method for producing the crystalline alumina laminated particle.

(1) Crystalline alumina laminated particles having a structure in which a plurality of square plate-like alumina fine particles are laminated without overlapping at least two sides.
(2) The square plate-like alumina fine particles have an average particle diameter of 2 to 100 nm, an average thickness of 1 to 20 nm, and an aspect ratio (average particle diameter / average thickness) of 2 to 50. The crystalline alumina laminated particle according to the above (1), which is characterized by the following.
(3) The crystalline alumina laminated particles according to (1) or (2) above, wherein the average number of laminated square plate-like alumina fine particles is 3 to 20.
(4) The crystalline alumina laminated particles according to any one of (1) to (3) above, wherein the square plate-like alumina fine particles are mainly composed of alumina in a boehmite crystal phase.
(5) The crystalline alumina laminated particles according to any one of (1) to (4) above, wherein the average major axis has a length of 10 to 300 nm and an average thickness of 2 to 50 nm. Crystalline alumina laminated particles.
(6) The ratio of the specific surface area (SA1) when fired at 200 ° C. to the specific surface area (SA2) when fired at 350 ° C. ((SA2) / (SA1)) is 0 The crystalline alumina laminated particle according to any one of the above (1) to (5), which is in a range of .70 to 0.95.
(7) (A) Crystalline alumina laminated particle dispersion having a structure in which a plurality of square plate-like alumina fine particles are laminated so that at least two sides do not overlap by hydrothermal treatment of a dispersion of square plate-like alumina fine particles (B) The step of removing the basic substance remaining from the crystalline alumina laminated particles obtained in the step (A) to obtain a crystalline alumina laminated particle dispersion (1) above )-(6) The manufacturing method of the crystalline alumina laminated particle in any one of.
(8) The square plate-like alumina fine particles used in the step (A) of (7) are (a) after adding an acid to the aluminate solution, and then treating at a temperature of 50 to 100 ° C. to a range of 10 to 12 A step of obtaining a square plate-like alumina fine particle dispersion having a certain pH (b) a step of removing the remaining soluble inorganic salts and unreacted substances from the square plate-like alumina fine particle dispersion obtained in the step (a) (c) And (b) adding a basic substance to the square plate-like alumina fine particle dispersion obtained in the step (b) to make the size of the square plate-like alumina fine particles uniform. ) For producing crystalline alumina laminated particles.
(9) In the step (c), at least one selected from water-soluble alkali metal, alkaline earth metal and ammonium salts is used as the basic substance. The manufacturing method of the crystalline alumina laminated particle as described in 2.
(10) A dispersion of square plate-like alumina fine particles used in the step (A) (d) After the square plate-like alumina fine particles obtained by the step not including the steps (a) and (b) are used as a dispersion The method for producing crystalline alumina laminated particles according to (7) above, which is obtained by a step of adding a basic substance to uniformize the size of the square plate-like alumina fine particles.
(11) The crystallinity described in (7 ) to ( 10) above, wherein, in the step (A), the hydrothermal treatment temperature is 110 to 180 ° C., and the hydrothermal treatment time is 15 to 50 hours. A method for producing alumina laminated particles.
(12) In any one of the above (7) to (11), the concentration of the residual basic substance remaining in the crystalline alumina laminated particle dispersion obtained in the step (B) is 100 ppm or less. The manufacturing method of crystalline alumina laminated particle of description.
(13)
A method for producing the crystalline alumina laminated particles according to any one of (1) to (6) above,
(Z) A step of obtaining a dispersion of square plate-like alumina fine particles by the step (z1) or the step (z2),
(A) A dispersion of square plate-like alumina fine particles is hydrothermally treated at 110 to 180 ° C. for 1 to 30 hours to form a structure in which a plurality of square plate-like alumina fine particles are laminated so that at least two sides do not overlap. Obtaining a crystalline alumina laminated particle dispersion; and
(B) A step of removing the basic substance remaining from the crystalline alumina laminated particles obtained in the step (A) to obtain a crystalline alumina laminated particle dispersion.
Including
In the step (z1), (a) after adding an acid to the aluminate solution, a square plate-like alumina fine particle dispersion having a pH in the range of 10 to 12 is obtained by treating at a temperature of 50 to 100 ° C. Obtaining step,
(B) removing the remaining soluble inorganic salts and unreacted substances from the square plate-like alumina fine particle dispersion obtained in the step (a), and
(C) adding a basic substance to the square plate-like alumina fine particle dispersion obtained in the step (b) to further uniform the size of the square plate-like alumina fine particles,
In the step (z2), (d) the square plate-like alumina fine particles obtained by the step not including the step (a) and the step (b) are used as a dispersion, and then a basic substance is added to the square plate. Including uniformizing the size of the alumina fine particles,
The basic substance is tetramethylammonium hydroxide, ammonium hydroxide or ammonium carbonate.
A method for producing crystalline alumina laminated particles.
(14)
The production of crystalline alumina laminated particles according to (13) above, wherein the concentration of the residual basic substance remaining in the crystalline alumina laminated particle dispersion obtained in the step (B) is 100 ppm or less. Method.

  The present invention can provide a crystalline alumina laminated particle having a structure in which a plurality of square plate-like alumina fine particles are laminated without overlapping at least two sides, and a method for producing the crystalline alumina laminated particle.

  The crystalline alumina laminated particle of the present invention is an aggregate of a plurality of square plate-like alumina fine particles, and can be used as an abrasive by utilizing the irregularities on the particle surface. From the form of plate, film strength (bending strength, bending strength) (Elastic modulus, load deflection strength, etc.) It can be used as a resin filler aiming at improvement.

  Further, since the particle surface has a structure in which a plurality of square plate-like alumina fine particles are laminated without overlapping at least two sides, nano-order fractal irregularities are formed. Therefore, it can be applied to cosmetics, resin fillers, and surface coating materials (optical scattering, refractive index adjustment, etc.) that utilize optical characteristics due to the unevenness.

  Furthermore, the degree of freedom of mixing into organic and inorganic solvent paints is wide due to the synergistic effect of surface charge and particle shape, and it can be used for coating / molding as a fire-resistant flame retardant material and heat-resistant material.

Schematic diagram showing crystal axes Surface area decay curve SEM photograph of crystalline alumina laminated particles

Hereinafter, the crystalline alumina laminated particles according to the present invention will be described first.
<Square plate-like alumina fine particles>
The size of the primary particles of the square plate-like alumina fine particles is obtained by taking a transmission electron micrograph (TEM) of the alumina hydrate fine particles, measuring the particle diameter and thickness of 50 particles, and calculating the average value of each. The average particle diameter is preferably in the range of 2 to 100 nm, more preferably 3 to 80 nm, and the average thickness is preferably 1 to 20 nm, more preferably 2 to 15 nm. At this time, the ratio of the average particle diameter to the average thickness (aspect ratio) needs to be a plate-like form in the range of 2-50. When the aspect ratio is 1 or less, it is difficult to take a laminated structure, and there is a tendency to form a lump.

The primary particles of the alumina fine particles are not particularly limited as long as they are alumina hydrate fine particles. In the present invention, boehmite alumina hydrate fine particles are particularly preferable.
Boehmite alumina hydrate fine particles having a square plate shape on the market, such as DISPERAL-P2, CATAPAL-A, PURAL-SB, aluminum hydroxide fine particles made by Sasol, for example, VERSAL-R3 made by UOP, made by Nippon Light Metal Co., Ltd. B703, B1403, Showa Denko H-42, H-43, etc. can be suitably used.
<Crystalline alumina laminated particles>
In the crystalline alumina laminated particle of the present invention, the nano-sized alumina fine particles are not stacked with the crystal planes aligned, but are laminated in a shifted state (offset state), so that the plurality of alumina fine particles have at least two sides. The particles become a laminated structure without overlapping.

The number of laminated layers of crystalline alumina laminated particles is 3-20. The size is in the range where the length of the average major axis is 10 to 300 nm and the average thickness is 2 to 50 nm.
The size of the crystalline alumina laminated particles was measured using the transmission electron micrograph (TEM), and the length and thickness of the major axis and minor axis were measured for 50 particles, and the average value of the major axis length and The average value of the thickness can be obtained.

Moreover, the lamination | stacking state of crystalline alumina laminated particle can be confirmed with a transmission electron micrograph (TEM).
In general, since aluminum is an amphoteric oxide, in the low pH region, it takes a six-coordinated aluminum cation [Al (OH ₂ ) ₆ ] ³⁺ in which six water molecules are coordinated. The resulting alumina hydrogel forms an octahedral structure in which Al (OH) ₃ having a hexacoordinate structure is a unit unit, and has a boehmite structure in which the side and apex of the unit unit are shared.

Further, the growth of the c-axis is faster than the growth of the crystal axes in the a- and b-axis directions due to the influence of the coexisting anions, and it takes a primary particle shape of a whisker (needle) to a rod (column).
At high pH, on the other hand, tetra-hydroxo aluminum anions tetracoordinate-type [Al (OH) _4] ^- is taken up, which alumina hydrogel can be neutralized in a range of pH10 above has a 4-coordinated structure [ A tetrahedron structure having Al (OH) ₄ ] as a unit unit is formed, and a quasi-boehmite structure in which the ridges and sides of the unit unit are cross-linked (μ-OH type) with an oxygen element.

Further, the growth of the b and c axes is faster than the a axis of the crystal axis due to the coexisting cations, and it takes a plate-like primary particle shape.
Utilizing the properties of alumina, an alumina hydrogel having a tetracoordinate structure as a unit unit is selectively prepared, and the primary particles of the present invention are used in the pH range where crystals can be grown while maintaining the structure. A certain alumina fine particle can be obtained.

  The reason why the crystalline alumina laminated particles having a structure in which the alumina fine particles are laminated without overlapping at least two sides as in the present invention is not clear, but the alumina in which the crystal growth axis is defined as described above. Since the fine particles are prepared and the surface charge of the fine particles is low, and the interaction between the particle surfaces is weak because there is little residual ionic substance such as a basic substance between the surfaces, the charge on the side or vertex of the particles When the crystal growth mechanism in which particles having a structure extending in the direction of the controlled growth axis and the primary particles are laminated are laminated, the alumina fine particles are laminated. The fine particles themselves have surface charges, and when the alumina fine particles approach each other, dielectric polarization occurs due to the surface charges of the fine particles, and the crystals are stacked at the position where the polarization is neutralized. Since the alumina layered particles obtained et al, are further crystal growth surface control, estimates the crystal growth mechanism that has grown in the growth axis direction.

  Furthermore, nano-order irregularities (fractal surface) are formed on the particle surface of the crystalline alumina laminated particles of the present invention obtained by laminating, and not only for abrasives using these irregularities but also for optical system materials, etc. Can also be used.

Specific examples of the structure in which at least two sides are stacked without overlapping each other include those that are inclined in one direction and stacked in a staircase pattern, and those that are stacked with all four sides inclined without overlapping, etc. Not limited. In addition, the form which laminates | stacks all four sides is not included in this invention.
・ Relationship between specific surface area and primary particle size In general, the growth rate of three crystal axes is I.V. When all crystal axes grow at almost the same speed, II. It is divided roughly when the growth rate of crystal axes is different. The fluctuation amount of the specific surface area accompanying the growth of the average particle diameter of the primary particles tends to be large in the case of I and small in the case of II.

  Furthermore, focusing on the relationship between the specific surface area and the number of crystal growth axes, when the number of crystal growth axes is three axes (all three axes grow), the specific surface area tends to decay most rapidly. As the number of axes becomes two or one, the attenuation tends to become slow. A schematic diagram of the crystal axis and a schematic diagram of the tendency of attenuation are shown in FIGS. 1 and 2, respectively. In FIG. 2, the horizontal axis is the time axis, and the vertical axis indicates the specific surface area.

The crystalline alumina laminated particle of the present invention is characterized by having a structure in which square plate-like alumina fine particles are laminated without overlapping at least two sides. When crystalline alumina laminated particles are produced by changing the average particle size of the square plate-like alumina fine particles, the amount of change in which the average particle size of the square plate-like alumina fine particles becomes large and the amount of change in the specific surface area change so much. The specific surface area tends to disappear (decay) apparently below a certain level of specific surface area value (m ² / g).

From the above, it is suggested that the crystalline alumina laminated particles of the present invention grow in the specific crystal axis direction, and that the square plate-like alumina fine particles grow only in the specific crystal axis direction. This is thought to suggest.
-Relationship between specific surface area and firing Further, in the surface area of the crystalline alumina laminated particles of the present invention, the ratio of the surface area (SA1) when fired at 200 ° C to the specific surface area (SA2) when fired at 350 ° C ((SA2 ) / (SA1)) is in the range of 0.70 to 0.95, more preferably in the range of 0.75 to 0.93.

  The surface area of the inorganic oxide particles tends to decrease as the firing temperature increases. This is due to the fact that the pores of the particles are reduced by firing, and a phenomenon occurs in which the specific surface area decreases.

  In the crystalline alumina laminated particles of the present invention, the change in specific surface area is small even when the firing temperature is increased, and a phenomenon of extremely decreasing from the order of the surface area of the primary particles is not observed. From this, it is considered that the square plate-like alumina fine particles do not overlap at least two sides, but form a laminated structure while maintaining a crystal plane to some extent.

By forming such a laminated structure, it is considered that nano-order unevenness (fractal surface) is formed on the particle surface. The SEM photograph by a scanning electron microscope (Hitachi High-Technologies Corporation make, H-5500) is shown in FIG.
<Method for producing crystalline alumina laminated particle>
The method for producing crystalline alumina laminated particles according to the present invention includes:
(A) A step of obtaining a crystalline alumina laminated particle dispersion having a structure in which a plurality of square plate-like alumina fine particles are laminated so that at least two sides do not overlap by hydrothermally treating a dispersion of square plate-like alumina fine particles. (B) A step of removing the remaining basic substance from the crystalline alumina laminated particles obtained in the step (A) to obtain a crystalline alumina laminated particle dispersion.

The dispersion of square plate-like alumina fine particles is preferably obtained by including the following steps (a) to (c).
However, square plate-like alumina fine particles obtained by a step not including steps (a) and (b) can also be used, and in that case, a dispersion of square plate-like alumina fine particles can be obtained by step (d). . Examples of the square plate-like alumina fine particles obtained by the process not including steps (a) and (b) include the boehmite alumina hydrate fine particles described above, for example, DISPERAL-P2, CATAPAL-A, PURAL- SB, aluminum hydroxide fine particles, for example, VERSAL-R3 manufactured by UOP, B703, B1403 manufactured by Nippon Light Metal Co., Ltd., H-42, H-43 manufactured by Showa Denko KK and the like can be mentioned.

(A) Step of obtaining a square plate-like alumina fine particle dispersion having a predetermined pH by adding an acid to the aluminate solution and then treating at a predetermined temperature (b) The square obtained in the step (a) Step of removing residual soluble inorganic salt and unreacted substance from plate-like alumina fine particle dispersion (c) A basic substance is added to the square plate-like alumina fine particle dispersion obtained in the above step (b) for treatment. Step of obtaining a square plate-like alumina fine particle dispersion whose size has been made uniform When using a commercial product as the square plate-like alumina fine particle, a square plate-like alumina fine particle dispersion whose size has been made uniform in step (d) Can be obtained.

(D) After making the square plate-like alumina fine particles obtained by the step (a) and the step not including the step (b) into a dispersion, a basic substance is added to uniformize the size of the square plate-like alumina fine particles. Next, the steps of the manufacturing method will be described as follows.
<Process (A)>
In this step, the basic substance-added alumina fine particle dispersion having the same size obtained in the steps (a) to (c) or the step (d) is treated at a treatment temperature of 110 to 180 ° C. and a treatment time of 1 to 30 hours. By carrying out the hydrothermal treatment in the above range, a crystalline alumina laminated particle dispersion having a structure in which a plurality of square plate-like alumina fine particles are laminated without overlapping at least two sides is obtained.

  If the treatment temperature is less than the lower limit of the range, there is a possibility that the progress to the laminated structure does not proceed without overlapping at least two sides, and if the treatment temperature exceeds the upper limit of the range, it tends to aggregate, which is not preferable.

The treatment time is preferably treated under conditions appropriately selected from the above range.
<Process (B)>
In this step, the crystalline alumina laminated particle dispersion obtained in the above step (A) and having a laminated structure without overlapping at least two sides is concentrated with an ultrafiltration device, and the dilution rate is 1000 to 2000 times. Washing with a quantity of warm pure water at 60 ° C. and washing until the concentration of the remaining tetramethylammonium becomes 100 ppm or less, a crystalline alumina laminated particle dispersion having a laminated structure without overlapping at least two sides is obtained. It is preferable that the amount of warm pure water used for washing is washed in an amount appropriately selected from the above range.

The concentration of the remaining tetramethylammonium is preferably 100 ppm or less, more preferably 50 ppm or less. If it exceeds 100 ppm, the square plate-like crystalline alumina fine particles may agglomerate with time in the obtained dispersion, which is not preferable.
<Process (a)>
The square plate-like alumina fine particles are prepared by using aluminate as a raw material, and preparing an aluminate solution in which aluminate and sodium hydroxide are completely dissolved in a reaction vessel, and adding an inorganic acid or an organic acid to the solution. Then, a square plate-like alumina fine particle dispersion is obtained by treating at a temperature of 50 to 100 ° C. for 0.5 to 2 hours. The amount of the inorganic acid or organic acid added is adjusted so that the pH of the resulting dispersion is in the range of 10-12.

  As alumina used as a raw material, it is preferable to use an aluminate as a raw material. When other types of sulfuric acid or nitric acid-based alumina are used as raw materials, an assembly having a structure in which at least two sides do not overlap even if square plate-like fine particles are not obtained or square plate-like fine particles are obtained There is a tendency that the body cannot be obtained and the agglomerated product cannot be obtained.

As the inorganic acid, hydrochloric acid, sulfuric acid, nitric acid and the like can be used, and as the organic acid, carboxylic acid, sulfonic acid and the like can be used.
The dispersion obtained here has a pH of 10 to 12, preferably 10.5 to 11.5. If it is less than the lower limit, alumina fine particles having a crystal phase other than boehmite tend to be obtained, and the square plate-like alumina fine particles of the present invention are hardly obtained. Exceeding the upper limit is not preferable because the solubility of alumina itself increases and alumina fine particles cannot be obtained.

Furthermore, the treatment temperature is 50 to 100 ° C, preferably 70 to 90 ° C. When the temperature is lower than 50 ° C., the particle growth of the alumina fine particles in the boehmite crystal phase may not proceed, and when the temperature exceeds 100 ° C., a crystal phase other than boehmite tends to grow due to the interface concentration effect. Here, the interfacial concentration effect means that the dissolved substance is deposited in a scale shape at the interface between the boiling solvent and the gas / solid phase (interface between the liquid surface and the container wall).
The treatment time is preferably 0.5 to 2 hours.

By adding an aluminate solution and an inorganic acid or an organic acid to the square plate-like alumina fine particle dispersion obtained by this step in the same manner as described above, the crystal growth of the boehmite crystal phase can be promoted. It is possible to control the size of the obtained square plate-like alumina fine particles.
<Step (b)>
In this step, after separating the alumina fine particles and the mother liquor into the square plate-like alumina fine particle dispersion obtained in the step (a) by suction filtration, the alumina fine particle cake is washed with warm pure water at 80 ° C. Then, sodium chloride and adsorbed sodium ions contained in the cake are washed and removed, and then sufficiently dehydrated to obtain a square plate-like alumina fine particle cake.
Here, the amount of warm pure water used for washing is preferably washed under conditions appropriately selected from the range of 50 to 100 L until the pH of the filtrate becomes about 10 or less.
<Step (c)>
In this step, the square plate-like alumina fine particle cake obtained in the step (b) is dispersed and further added with a basic substance to obtain a basic substance-added alumina fine particle dispersion having a uniform size.

As the basic substance, at least one basic substance selected from alkali metal, alkaline earth metal, and ammonium water-soluble compounds can be used.
As the basic substance, hydroxides and carbonates such as sodium, potassium and lithium, inorganic amines such as ammonium hydroxide and ammonium carbonate, and the like can be used.

  Further, the basic substance is preferably a strongly basic substance, and the counter cation is bulky, and the crystal growth of the square plate-like particles and the structure in which at least two sides are laminated without overlapping. It is preferable for the production of crystalline alumina laminated particles. In the present invention, it is preferable to use tetramethylammonium hydroxide.

  The basic substance is added in an amount of 3 to 25 mol%, more preferably 5 to 20 mol%, with respect to the contained alumina. If the amount is less than the lower limit of the range, the effect of particle growth is weakened and only fine particles may be obtained. If the upper limit of the range is exceeded, aggregation tends to occur, which is not preferable.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
[Measuring method]
<Measurement of particle surface area>
The surface area of the fine particles of the present application is determined by nitrogen adsorption using a surface area measuring device (manufactured by Yuasa Ionics Co., Ltd., Multisorb 12) on a sample dried at 200 ° C. or 350 ° C. for 3 hours after drying the fine particles of the present application with a freeze dryer. Measured by the method (BET method). The value obtained by drying at 200 ° C. is SA1, and the value obtained by drying at 350 ° C. is SA2. The unit is expressed in m ² / g.
<PH measurement>
Regarding the pH measurement, a glass electrode of a pH meter (H22 manufactured by Horiba, Ltd .: F22) whose correction was completed with standard solutions of pH 4, 7, and 9 at 25 ° C. was inserted into the solution, and the pH measurement was performed. .
<Measurement of residual amount of basic substance>
Measurement of the basic substance amount was performed in accordance with JIS K0102 Kjeldahl method / neutralization titration method, and copper sulfate, sulfuric acid and potassium sulfate were added to the sample to decompose the organic matter. Next, after adding sodium hydroxide to make it alkaline, the organic substance is decomposed by distilling and absorbing the distilled ammonia into sulfuric acid), and ammonium ions in the exposed solution are neutralized by titration (to sodium hydroxide). The remaining sulfuric acid was quantified and the amount of ammonium ions was calculated).
<X-ray measurement>
For the crystal phase of the tetragonal plate-like crystalline alumina, using an X-ray diffraction measurement apparatus (SmartLab, manufactured by Rigaku Corporation), X-ray source: CuKα, output: 9 kW, tube voltage: 45 kV, tube current: 200 mA, Slit interval: 0.5 °, measurement angle 2θ: 10 ° to 70 °, scanning speed: 10 ° / min.
[Example 1]

<Method for Producing Crystalline Alumina Laminated Particle (1) Dispersion>
<Step (a)> 38.743 kg of pure water was put into a 100 L steam jacketed tank, and 0.815 kg of a sodium hydroxide solution having a concentration of 48% by mass (manufactured by Kanto Chemical Co., Ltd., special grade) was added thereto with stirring. .

In this solution, 2.740 kg of sodium aluminate (manufactured by Kanto Chemical Co., Inc., deer grade 1, 39% by mass in terms of alumina) was dissolved with stirring.
Furthermore, this solution was heated to 80 ° C. with stirring and held for 1 hour to obtain 42.298 kg of a completely dissolved aqueous sodium aluminate solution.

  6.269 kg of pure water was put into a 10 L tank with a steam jacket, and 0.453 kg of 35% by weight hydrochloric acid aqueous solution (manufactured by Kanto Chemical Co., Ltd., special grade) was mixed with stirring, and further heated to 80 ° C. to dilute hydrochloric acid 6.722 kg was obtained.

While maintaining this dilute sodium aluminate aqueous solution at 80 ° C., the whole amount of the dilute hydrochloric acid aqueous solution was added and mixed while stirring, and further kept at 80 ° C. with stirring for 1 hour to obtain a square plate-like alumina fine particle having a pH of 11.5 ( 1a) 49.020 kg of dispersion was obtained.
<Step (b)> After the alumina fine particle (1a) dispersion was dehydrated with a degassing plate filter and the mother liquor was separated, the alumina fine particle cake obtained in the form of a plate filter was heated to 80 ° C. hot pure water 50 under reduced pressure. ˜100 L was passed through to wash away sodium chloride and adsorbed sodium contained in the alumina fine particle cake. Thereafter, it was sufficiently dehydrated under reduced pressure to obtain 6.667 kg of alumina fine particle (1b) cake.
<Step (c)> To 6.667 kg of the alumina fine particle (1b) cake, 12.983 kg of pure water was added and dispersed by sufficiently stirring to obtain a diluted alumina fine particle dispersion of 19.650 kg. To this, tetramethylammonium hydroxide was added. An aqueous solution (manufactured by Kanto Chemical Co., Inc., concentration 27% by mass) was added to obtain 20.000 kg of a basic substance-added alumina fine particle (1c) dispersion.
<Step (A)> This basic substance-added alumina fine particle (1c) dispersion is put into an autoclave reactor, heated to 150 ° C. with stirring, reacted for 24 hours under pressure, a 30 to 50 nm square, and a thickness of 3 Crystalline alumina laminated particles (1A) that form secondary particles with a size of 100 to 200 nm in which 5 to 10 primary crystal particles with a size of -5 nm are aggregated in a laminated structure without overlapping at least two sides A dispersion was obtained.
<Step (B)> This crystalline alumina laminated particle (1A) dispersion is put in an ultrafiltration device, washed with warm pure water at a dilution rate of 1000 to 2000 times 60 ° C., and the residual nitrogen concentration is changed to tetramethyl. Washing was performed until the concentration in terms of ammonium was (CH ₃ ) ₄ N ⁺ <10 ppm, to obtain 20.000 kg of a 5 mass% alumina crystalline alumina laminated particle (1) dispersion.

Table 1 shows the properties of the crystalline alumina laminated particles (1).
[Example 2]

<Method for producing crystalline alumina laminated particle (2) dispersion>
<Step (a)> 38.743 kg of pure water was put into a 100 L steam jacketed tank, and 0.815 kg of a sodium hydroxide solution having a concentration of 48% by mass (manufactured by Kanto Chemical Co., Ltd., special grade) was added thereto with stirring. .

In this solution, 2.740 kg of sodium aluminate (manufactured by Kanto Chemical Co., Inc., deer grade 1, 39% by mass in terms of alumina) was dissolved with stirring.
Furthermore, this solution was heated to 80 ° C. with stirring and held for 1 hour to obtain 42.298 kg of a completely dissolved aqueous sodium aluminate solution.

  6.316 kg of pure water was put into a 10 L tank with a steam jacket, and 0.406 kg of 70% by mass nitric acid aqueous solution (manufactured by Kanto Chemical Co., Ltd., special grade) was mixed with stirring, and further heated to 80 ° C. to dilute nitric acid 6.722 kg was obtained.

While maintaining this dilute sodium aluminate aqueous solution at 80 ° C., the whole amount of the dilute nitric acid aqueous solution was added and mixed while stirring, and further kept at 80 ° C. with stirring for 1 hour to obtain a square plate-like alumina fine particle having a pH of 11.5 ( 2a) 49.020 kg of dispersion was obtained.
<Step (b)> After the alumina fine particle (2a) dispersion was dehydrated with a degassing plate filter and the mother liquor was separated, the alumina fine particle cake obtained in the form of a plate filter was heated to 80 ° C. hot pure water 50 under reduced pressure. ˜100 L of water is passed through to wash and remove sodium nitrate and adsorbed sodium contained in the alumina fine particle cake, and then sufficiently dehydrated under reduced pressure to obtain 6.667 kg of alumina fine particle (2b) cake.
<Step (c)> To 6.667 kg of the alumina fine particle (2b) cake, 12.983 kg of pure water was added and dispersed by sufficiently stirring to obtain an alumina fine particle diluted dispersion liquid of 19.650 kg, to which tetramethylammonium hydroxide was added. An aqueous solution (manufactured by Kanto Chemical Co., Inc., concentration 27 mass%) was added to obtain 20.000 kg of a basic substance-added alumina fine particle (2c) dispersion.
<Step (A)> This basic substance-added alumina fine particle (2c) dispersion is put into an autoclave reactor, heated to 150 ° C. with stirring, and reacted for 24 hours under pressure, a 30 to 40 nm square having a thickness of 3 Crystalline alumina laminated particles (2A) that form secondary particles with a size of 100 to 200 nm in which 5 to 10 primary crystal particles with a size of ˜4 nm are aggregated in a laminated structure without overlapping at least two sides A dispersion was obtained.
<Step (B)> This crystalline alumina laminated particle (2A) dispersion is placed in an ultrafiltration device, washed with 60 ° C. hot pure water having a dilution rate of 1000 to 2000 times, and the residual nitrogen concentration is changed to tetramethyl. Washing was performed until the concentration in terms of ammonium reached (CH ₃ ) ₄ N ⁺ <10 ppm, to obtain 20.000 kg of 5 mass% alumina crystalline alumina laminated particle (2) dispersion.

Table 1 shows the properties of the crystalline alumina laminated particles (2).
[Example 3]

<Method for producing crystalline alumina laminated particle (3) dispersion>
<Step (a)> 38.743 kg of pure water was put into a 100 L steam jacketed tank, and 0.815 kg of a sodium hydroxide solution having a concentration of 48% by mass (manufactured by Kanto Chemical Co., Ltd., special grade) was added thereto with stirring. .

In this solution, 2.740 kg of sodium aluminate (manufactured by Kanto Chemical Co., Inc., deer grade 1, 39% by mass in terms of alumina) was dissolved with stirring.
Furthermore, this solution was heated to 80 ° C. with stirring and held for 1 hour to obtain 42.298 kg of a completely dissolved aqueous sodium aluminate solution.

  6.493 kg of pure water was put into a 10 L tank with a steam jacket, and 0.229 kg of 96% by weight sulfuric acid aqueous solution (manufactured by Kanto Chemical Co., Ltd., special grade) was mixed with stirring, and further heated to 80 ° C. to dilute sulfuric acid 6.722 kg was obtained.

While maintaining this dilute sodium aluminate aqueous solution at 80 ° C., all of the dilute sulfuric acid aqueous solution was added and mixed while stirring, and further kept at 80 ° C. for 1 hour with stirring to obtain a square plate-like alumina fine particle (pH 11.5) 3a) 49.020 kg of dispersion was obtained.
<Step (b)> This square plate-like alumina fine particle (3a) dispersion was dehydrated with a degassing plate filter, and the mother liquor was separated, and then the mixture hydrogel cake obtained in a plate filter shape was subjected to 80 under reduced pressure. 50-100 L of warm pure water is passed through to wash away sodium sulfate and adsorbed sodium contained in the prepared hydrogel cake, and then sufficiently dehydrated under reduced pressure to obtain 6.667 kg of alumina fine particle (3b) cake.
<Step (c)> To 6.667 kg of the alumina fine particle (3b) cake, 12.983 kg of pure water was added and dispersed by sufficiently stirring to obtain an alumina hydrogel diluted dispersion liquid of 19.650 kg. To this, tetramethylammonium hydroxide was added. An aqueous solution (manufactured by Kanto Chemical Co., Inc., concentration 27% by mass) was added to obtain 20.000 kg of a basic substance-added alumina fine particle (3c) dispersion.
<Step (A)> This basic substance-added alumina fine particle (3c) dispersion is placed in an autoclave reactor, heated to 150 ° C. with stirring, reacted for 24 hours under pressure, 20 to 60 nm square and 2 in thickness. Crystalline alumina laminated particles (3A) forming 5 to 10 nm primary crystal particles having a size of 50 to 300 nm aggregated in a structure in which 5 to 10 primary crystal particles are laminated without overlapping at least two sides A dispersion was obtained.
<Step (B)> This crystalline alumina laminated particle (3A) dispersion is put into an ultrafiltration device, washed with warm pure water at a dilution rate of 1000 to 2000 times 60 ° C., and the residual nitrogen concentration is changed to tetramethyl. Washing was performed until the concentration in terms of ammonium reached (CH ₃ ) ₄ N ⁺ <10 ppm, to obtain 20.000 kg of 5 mass% alumina crystalline alumina laminated particle (3) dispersion.

Table 1 shows the properties of the crystalline alumina laminated particles (3).
[Example 4]

<Method for Producing Crystalline Alumina Laminated Particle (4) Dispersion>
<Step (d)> Commercially available crystalline alumina fine particle powder (manufactured by Sasol, DISPERAL-P2, concentration 72% by mass) 0.556 kg of pure water 19.094 kg is added and sufficiently stirred and dispersed to dilute and disperse the alumina hydrogel. The liquid was made 19.650 kg, and a tetramethylammonium hydroxide aqueous solution (manufactured by Kanto Chemical Co., Inc., concentration 27 mass%) was added thereto to obtain 20.000 kg of a basic substance-added crystalline alumina fine particle (4c) dispersion.
<Step (A)> This basic substance-added alumina fine particle (4c) dispersion is placed in an autoclave reactor, heated to 150 ° C. with stirring, reacted for 24 hours under pressure, 20 to 50 nm square and 4 in thickness. Crystalline alumina laminated particles (4A) forming 5 to 10 nm primary crystal particles having a size of 50 to 300 nm aggregated in a structure in which 5 to 10 primary crystal particles having a size of 8 nm are laminated without overlapping at least two sides A dispersion was obtained.
<Step (B)> This crystalline alumina laminated particle (4A) dispersion is put in an ultrafiltration device, washed with warm pure water at a dilution rate of 1000 to 2000 times 60 ° C., and the residual nitrogen concentration is changed to tetramethyl. Washing was performed until the concentration in terms of ammonium reached (CH ₃ ) ₄ N ⁺ <10 ppm, to obtain 20.000 kg of a 5 mass% alumina crystalline alumina laminated particle (4) dispersion.

Table 1 shows the properties of the crystalline alumina laminated particles (4).
[Comparative Example 1]
<Method for Producing Bulk Crystalline Alumina Particle (R1) Dispersion>
<Step (a)> 26.345 kg of pure water was put into a 50 L tank with a steam jacket, and 0.554 kg of a sodium hydroxide solution having a concentration of 48% by mass (manufactured by Kanto Chemical Co., Ltd., special grade) was added thereto with stirring. .

In this solution, 1.863 kg of sodium aluminate (manufactured by Kanto Chemical Co., Inc., deer grade 1, 39% by mass in terms of alumina) was dissolved with stirring.
Furthermore, this solution was heated to 80 ° C. with stirring and held for 1 hour to obtain 28.762 kg of a completely dissolved sodium aluminate aqueous solution.

  4. 321 kg of pure water was put into a 10 L tank with a steam jacket, and 0.250 kg of 98% by mass aluminum chloride nonahydrate (manufactured by Kanto Chemical Co., Ltd., deer special grade) was mixed with stirring, and further 80 The mixture was heated to 0 ° C. to obtain 4.571 kg of a diluted aluminum chloride aqueous solution.

While maintaining this dilute sodium aluminate aqueous solution at 80 ° C., the entire amount of the dilute aluminum chloride aqueous solution was added and mixed while stirring, and further maintained at 80 ° C. with stirring for 1 hour to obtain alumina fine particles (R1a) having a pH of 11.5. 33.333 kg of dispersion was obtained.
<Step (b)> After the alumina fine particle (R1a) dispersion was dehydrated with a degassing plate filter and the mother liquor was separated, the alumina fine particle cake obtained in the shape of a plate filter was heated to 80 ° C. hot pure water 50 under reduced pressure. After passing through 100 L, sodium chloride and adsorbed sodium contained in the alumina fine particle cake were washed and removed, and then sufficiently dehydrated under reduced pressure to obtain 6.667 kg of alumina fine particle (R1b) cake.
<Step (c)> To 6.667 kg of the alumina fine particle (R1b) cake, 12.983 kg of pure water is added and dispersed by sufficiently stirring to obtain an alumina fine particle diluted dispersion liquid of 19.650 kg. To this, tetramethylammonium hydroxide is added. 0.350 kg of an aqueous solution (manufactured by Kanto Chemical Co., Inc., concentration 27% by mass) was added to obtain 20.000 kg of a basic substance-added alumina fine particle (R1c) dispersion.
<Step (A)> This basic substance-added alumina fine particle (R1c) dispersion is placed in an autoclave reactor, heated to 150 ° C. with stirring, and allowed to react for 24 hours under pressure, 40 to 80 nm square and 4 in thickness. A bulk crystalline alumina particle (R1A) dispersion was obtained which formed secondary particles having a size of 150 to 400 nm in which 5 to 10 primary crystal particles having a size of ˜8 nm were aggregated in a bulk shape.
<Step (B)> This bulk crystalline alumina particle (R1A) dispersion is put into an ultrafiltration apparatus, washed with warm pure water at a dilution rate of 1000 to 2000 times 60 ° C., and the residual nitrogen concentration is changed to tetramethyl. Washing was performed until the concentration in terms of ammonium was (CH ₃ ) ₄ N ⁺ <10 ppm, to obtain 20.000 kg of a 5 mass% alumina crystalline alumina particle (R1) dispersion. The obtained crystalline alumina fine particles themselves were in a state of few things arranged as a square plate.

Table 1 shows the properties of the bulk crystalline alumina particles (R1).
[Comparative Example 2]
<Method for Producing Bulk Crystalline Alumina Particle (R2) Dispersion>
<Step (a)> 26.345 kg of pure water was put into a 50 L tank with a steam jacket, and 0.554 kg of a sodium hydroxide solution having a concentration of 48% by mass (manufactured by Kanto Chemical Co., Ltd., special grade) was added thereto with stirring. .

In this solution, 1.863 kg of sodium aluminate (manufactured by Kanto Chemical Co., Inc., deer grade 1, 39% by mass in terms of alumina) was dissolved with stirring.
Furthermore, this solution was heated to 80 ° C. with stirring and held for 1 hour to obtain 28.762 kg of a completely dissolved sodium aluminate aqueous solution.

  4.182 kg of pure water was put into a 10 L tank with a steam jacket, and 0.389 kg of 98 mass% aluminum nitrate nonahydrate (manufactured by Kanto Chemical Co., Ltd., deer special grade) was mixed with stirring, and further 80 ° C. To obtain 4.571 kg of diluted aluminum nitrate aqueous solution.

While maintaining this diluted sodium aluminate aqueous solution at 80 ° C., the whole amount of the diluted aluminum nitrate aqueous solution was added and mixed while stirring, and further maintained at 80 ° C. with stirring for 1 hour to obtain alumina fine particles (R2a) having a pH of 11.5 33.333 kg of dispersion was obtained.
<Step (b)> This alumina fine particle (R2a) dispersion was dehydrated with a degassing plate filter, and the mother liquor was separated. 50 to 100 L are passed through, and sodium nitrate and adsorbed sodium contained in the alumina fine particle cake are washed and removed, and then sufficiently dehydrated under reduced pressure to obtain 6.667 kg of alumina fine particle (R2b) cake.
<Step (c)> To 6.667 kg of the alumina fine particle (R2b) cake, 12.983 kg of pure water was added and dispersed by sufficiently stirring to obtain a diluted alumina fine particle dispersion of 19.650 kg, and tetramethylammonium hydroxide was added thereto. 0.350 kg of an aqueous solution (manufactured by Kanto Chemical Co., Inc., concentration 27 mass%) was added to obtain 20.000 kg of a basic substance-added alumina fine particle (R2c) dispersion.
<Step (A)> This basic substance-added alumina fine particle (R2c) dispersion is placed in an autoclave reactor, heated to 150 ° C. with stirring, and allowed to react for 24 hours under pressure, 40 to 60 nm square and 4 in thickness. A bulk crystalline alumina particle (R2A) dispersion was obtained which formed secondary particles with a size of 150 to 300 nm in which 5 to 10 primary crystal particles with a size of ˜6 nm were aggregated in a bulk shape.
<Step (B)> This bulk crystalline alumina particle (R2A) dispersion is put into an ultrafiltration apparatus, washed with warm pure water at a dilution rate of 1000 to 2000 times 60 ° C., and the residual nitrogen concentration is changed to tetramethyl. Washing was performed until the concentration in terms of ammonium reached (CH ₃ ) ₄ N ⁺ <10 ppm, to obtain 20.000 kg of a mass crystalline alumina particle (R2) dispersion of 5% by mass alumina. The obtained alumina particles were not a square plate shape but a rectangular parallelepiped shape and a shape with rounded corners.

Table 1 shows the properties of the bulk crystalline alumina particles (R2).
[Comparative Example 3]
<Method for Producing Bulk Crystalline Alumina Particle (R3) Dispersion>
<Step (a)> 26.345 kg of pure water was put into a 50 L tank with a steam jacket, and 0.554 kg of a sodium hydroxide solution having a concentration of 48% by mass (manufactured by Kanto Chemical Co., Ltd., special grade) was added thereto with stirring. .

In this solution, 1.863 kg of sodium aluminate (manufactured by Kanto Chemical Co., Inc., deer grade 1, 39% by mass in terms of alumina) was dissolved with stirring.
Furthermore, this solution was heated to 80 ° C. with stirring and held for 1 hour to obtain 28.762 kg of a completely dissolved sodium aluminate aqueous solution.

  3.981 kg of pure water was put into a 10 L tank with a steam jacket, and 0.590 kg of 57% by mass of aluminum sulfate 14 to 18 hydrate (manufactured by Kanto Chemical Co., Ltd., deer special grade) was mixed with stirring. The mixture was further heated to 80 ° C. to obtain 4.571 kg of a diluted aluminum sulfate aqueous solution.

While maintaining this diluted sodium aluminate aqueous solution at 80 ° C., the entire amount of the diluted aluminum sulfate aqueous solution was added and mixed while stirring, and further maintained at 80 ° C. with stirring for 1 hour to obtain alumina fine particles (R3a) having a pH of 11.5. 33.333 kg of dispersion was obtained.
<Step (b)> After the alumina fine particle (R3a) dispersion was dehydrated with a degassing plate filter and the mother liquor was separated, the alumina fine particle cake obtained in the form of a plate filter was heated to 80 ° C. under reduced pressure at 80 ° C. 50 to 100 L is passed through, and sodium sulfate and adsorbed sodium contained in the alumina fine particle cake are washed and removed, and then sufficiently dehydrated under reduced pressure to obtain 6.667 kg of alumina fine particle (R3b) cake.
<Step (c)> To 6.667 kg of the alumina fine particle (R3b) cake, 12.983 kg of pure water was added and dispersed by sufficiently stirring to obtain an alumina hydrogel diluted dispersion liquid of 19.650 kg, and tetramethylammonium hydroxide was added thereto. 0.350 kg of an aqueous solution (manufactured by Kanto Chemical Co., Inc., concentration: 27% by mass) was added to obtain 20.000 kg of a basic substance-added alumina fine particle (R3c) dispersion.
<Step (A)> This basic substance-added alumina fine particle (R3c) dispersion is placed in an autoclave reactor, heated to 150 ° C. with stirring, and allowed to react for 24 hours under pressure, 30 to 70 nm square with a thickness of 3 A bulk crystalline alumina particle (R3A) dispersion was obtained which formed secondary particles with a size of 100 to 300 nm in which 5 to 10 primary crystal particles with a size of ˜7 nm were aggregated in a bulk shape.
<Step (B)> This bulk crystalline alumina particle (R3A) dispersion is put into an ultrafiltration device, washed with 60 ° C. hot pure water having a dilution rate of 1000 to 2000 times, and the residual nitrogen concentration is changed to tetramethyl. Washing was performed until the concentration in terms of ammonium was (CH ₃ ) ₄ N ⁺ <10 ppm, to obtain 20.000 kg of an alumina particle (R3) dispersion of 5% by mass alumina. The obtained bulk crystalline alumina particles (3) were not a rectangular plate shape, but a rectangular parallelepiped shape and a shape with rounded corners.

Table 1 shows the properties of the bulk crystalline alumina particles (R3).
[Comparative Example 4]
<Method for Producing Bulk Crystalline Alumina Particle (R4) Dispersion>
<Step (d)> To a commercially available aluminum hydroxide reagent (Wako Pure Chemical Industries, Ltd., special grade, concentration 95% by mass) 1.610 kg, add pure water 18.040 kg, and sufficiently stir and disperse the aluminum hydroxide. 19.650 kg of a suspension was added, 0.350 kg of a tetramethylammonium hydroxide aqueous solution (concentration 27 mass%, manufactured by Kanto Chemical Co., Ltd.) was added thereto, and a basic substance-added aluminum hydroxide (R4c) suspension 20. 000 kg was obtained.
<Step (A)> This basic substance-added aluminum hydroxide (R4c) suspension is placed in an autoclave reactor, heated to 150 ° C. with stirring, and allowed to react for 24 hours under pressure, with a thickness of 600 to 900 nm square. A bulk crystalline alumina particle (R4A) suspension was obtained in which secondary particles having a size of 4000 to 4600 nm in which 8 to 15 primary crystal particles having a size of 400 to 800 nm were aggregated in a bulk shape were obtained.
<Step (B)> This massive crystalline alumina particle (R4A) suspension is put in an ultrafiltration apparatus, washed with warm pure water at a dilution rate of 1000 to 2000 times 60 ° C., and the remaining nitrogen concentration is changed to tetra. Washing was performed until the concentration in terms of methylammonium was (CH ₃ ) ₄ N ⁺ <10 ppm, to obtain 20.000 kg of an alumina particle (R4) suspension of 5% by mass alumina. The obtained massive crystalline alumina particles (R4) were not a square plate shape, but were irregular shapes of a rectangular parallelepiped and a cube.

Table 1 shows the properties of the bulk crystalline alumina particles (R4).
[Comparative Example 5]
<Method for Producing Bulk Crystalline Alumina Particle (R5) Dispersion>
<Step (d)> A commercially available crystalline alumina fine particle powder which is not in the shape of a square plate (Sasol, Catapal-200, concentration 80% by mass) is added to 0.500 kg of pure water 19.150 kg and dispersed by sufficiently stirring. 19.650 kg of alumina suspension was added, and 0.350 kg of tetramethylammonium hydroxide aqueous solution (concentration 27 mass%, manufactured by Kanto Chemical Co., Ltd.) was added thereto, and a basic substance-added crystalline alumina (R5c) suspension was added. 20.000 kg was obtained.
<Step (A)> This basic substance-added crystalline alumina (R5c) suspension is placed in an autoclave reactor, heated to 150 ° C. with stirring, reacted under pressure for 24 hours, and has a thickness of 40 to 100 nm square. A bulk crystalline alumina particle (R5A) suspension was obtained that formed secondary particles with a size of 200 to 400 nm in which 5 to 8 primary crystal particles with a size of 30 to 70 nm were agglomerated.
<Step (B)> This massive crystalline alumina particle (R5A) suspension is put in an ultrafiltration apparatus, washed with warm pure water at a dilution rate of 1000 to 2000 times 60 ° C., and the remaining nitrogen concentration is changed to tetra. Washing was performed until the concentration in terms of methylammonium was (CH ₃ ) ₄ N ⁺ <10 ppm, to obtain 20.000 kg of an alumina particle (R5) suspension of 5% by mass alumina. The obtained massive crystalline alumina particles (R5) were not square plates, but were irregular shapes such as rectangular parallelepipeds and cubes.

  Table 1 shows the properties of the bulk crystalline alumina particles (R5).

  The crystalline alumina laminated particle of the present invention can be used as an abrasive by utilizing the irregularities on the particle surface, and an improvement in film strength (bending strength, bending elastic modulus, load deflection strength, etc.) can be obtained from a plate-like form. .

Since the fractal unevenness on the particle surface is formed, optical characteristics such as optical scattering and refractive index adjustment due to the unevenness can be exhibited.
Since the particle shape is still a specific laminated structure, there is a technical effect that the degree of freedom of mixing into organic and / or inorganic solvent-based paints is wide due to a synergistic effect with the surface charge.

  The crystalline alumina laminated particle of the present invention is an aggregate of plate-like fine particles and can be used as an abrasive by utilizing the irregularities on the surface of the particle. From the form of plate, film strength (bending strength, bending elastic modulus, load) It can be used as a resin filler aiming at improvement in deflection strength.

  Furthermore, since the particle surface has a structure in which a plurality of square plate-like alumina fine particles are laminated without overlapping at least two sides, nano-order fractal irregularities are formed, so that optical characteristics resulting therefrom can be expected. , It can be applied to cosmetics, resin fillers, surface coating materials (optical scattering, refractive index adjustment, etc.) utilizing this.

  Due to the synergistic effect of surface charge and particle shape, there is a wide range of mixing with organic and inorganic solvent paints, etc., and it can be used for coating / molding as a fire-resistant flame-retardant material and heat-resistant material.

Claims (5)

A plurality of square plate-like alumina fine particles mainly composed of boehmite crystal phase alumina are laminated without overlapping at least two sides, the average major axis length is 10 to 300 nm, and the average thickness is 2 to 50 nm. Crystalline alumina laminated particles characterized by being in a range.   The square plate-like alumina fine particles have an average particle diameter of 2 to 100 nm, an average thickness of 1 to 20 nm, and an aspect ratio (average particle diameter / average thickness) of 2 to 50. The crystalline alumina laminated particle according to claim 1. In the crystalline alumina laminated particle, the ratio ((SA2) / (SA1)) of the specific surface area (SA1) when fired at 200 ° C. to the specific surface area (SA2) when fired at 350 ° C. is 0.70. The crystalline alumina laminated particle according to claim 1 or 2 , which is in a range of 0.95. A method for producing the crystalline alumina laminated particle according to any one of claims 1 to 3 ,
(Z) A step of obtaining a dispersion of square plate-like alumina fine particles by the step (z1) or the step (z2),
(A) A dispersion of square plate-like alumina fine particles is hydrothermally treated at 110 to 180 ° C. for 1 to 30 hours to form a structure in which a plurality of square plate-like alumina fine particles are laminated so that at least two sides do not overlap. A step of obtaining a crystalline alumina laminated particle dispersion; and (B) a step of removing the basic substance remaining from the crystalline alumina laminated particle obtained in the step (A) to obtain a crystalline alumina laminated particle dispersion. Including
In the step (z1), (a) a square plate of boehmite crystal phase having a pH in the range of 10 to 12 by treatment at a temperature of 50 to 100 ° C. after adding an acid to the aluminate solution. Obtaining an alumina fine particle dispersion;
(B) a step of removing the remaining soluble inorganic salts and unreacted substances from the square plate-like alumina fine particle dispersion obtained in the step (a), and (c) a square plate obtained in the step (b). A step of further adding a basic substance to the alumina fine particle dispersion to uniformize the size of the square plate alumina fine particles,
In the step (z2), (d) the square plate-like alumina fine particles obtained by the step not including the step (a) and the step (b) are used as a dispersion, and then a basic substance is added to the square plate. Including uniformizing the size of the alumina fine particles,
The method for producing crystalline alumina laminated particles, wherein the basic substance is tetramethylammonium hydroxide, ammonium hydroxide, or ammonium carbonate. The method for producing crystalline alumina laminated particles according to claim 4 , wherein the concentration of the residual basic substance remaining in the crystalline alumina laminated particle dispersion obtained in the step (B) is 100 ppm or less. .