Method for producing hollow spherical alumina particles

Abstract

Provided are hollow spherical alumina particles having an average particle size (D50) of 1.0 to 3.5 μm and a D90 of 6 μm or less. 【Solution means】 The present invention comprises a first step of spray-drying and dry granulating a predetermined basic aluminum lactate aqueous solution to form a hollow dry granulated product having a D50 of the dry granulated product of 1.0 to 4.5 μm, a D90 of 8 μm or less, and a volatile content controlled to 0 to 10% by mass, a second step of filling a firing sheath obtained in the first step with 50 to 80% by volume of the volume inside the sheath, and a third step of firing the firing sheath obtained in the second step. The method for producing hollow spherical alumina particles comprises controlling impurities in the basic aluminum lactate aqueous solution within a predetermined range, wherein the hollow spherical alumina particles have a D50 of 1.0 to 3.5 μm and a D90 of 6 μm or less in laser diffraction particle size distribution measurement, and are hollow and spherical inside.

Description

Technical Field

[0001] The present invention relates to a method for producing hollow spherical alumina particles.

Background Art

[0002] Hollow alumina particles are produced by various methods. The present inventors proposed a method for producing hollow spherical alumina particles in Japanese Patent No. 7560195 (Patent Document 1). In this patent, spherical alumina particles having a hollow interior and through-holes to the outside are obtained by drying and granulating an aqueous solution of basic aluminum lactate at a gas pressure of 0.01 to 1 MPa in air or an inert gas at a temperature of 210 to 280 °C, controlling the volatile content of the granulated product to 0 to 10% by mass and the bulk specific gravity to 0.2 to 0.7 g / cm3 to form a hollow dried granulated product, and then firing the dried granulated product obtained in the first step at a firing temperature in the range of 1050 °C or higher and lower than 1200 °C for 2 to 8 hours to obtain hollow spherical alumina particles. The aqueous solution of basic aluminum lactate contains iron (Fe) in an amount of 0 to 0.01% by mass, calcium (Ca) in an amount of 0 to 0.01% by mass, magnesium (Mg) in an amount of 0 to 0.01% by mass, and silicon (Si) in an amount of 0 to 0.01% by mass, and contains alkali metal element ions in an amount of 0.005 to 1.2% by mass, has a basicity of 60 to 80%, contains aluminum in an amount of 8 to 13% by mass in terms of Al2O3, and the obtained hollow spherical alumina particles have a D50 of 5 to 50 μm and a D90 of 200 μm or less in particle size distribution measurement, have a hollow interior and through-holes to the outside, a specific surface area of 1 to 20 m 2 / g, and the crystal phase shows an α phase.

[0003] The hollow spherical alumina particles obtained in Patent Document 1 have heat resistance, thermal shock resistance, chemical resistance, and high-temperature strength characteristics derived from α-alumina, and their hollow and spherical characteristics are excellent in lightweight, heat insulation, fluidity, etc. Therefore, they can be applied to high-functional compounding materials for resins, rubbers, etc., heat dissipation fillers related to electronic materials, polishing fillers for electronic components, etc. However, as described above, the alumina particles obtained in Patent Document 1 have an average particle size (D50) of 5 to 50 μm and a D90 of 200 μm or less, but there is a demand for alumina particles with a smaller particle size.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide hollow spherical alumina particles having a smaller particle size than the hollow spherical alumina particles obtained in the above Patent Document 1.

Means for Solving the Problems

[0006] That is, the present invention includes the following aspects: [1] A basic aluminum lactate aqueous solution is supplied at a liquid supply rate of 100 to 500 ml / min at a temperature of 180 to 280 °C in air or an inert gas under a gas pressure of 0.4 to 1 MPa and an air flow rate of 200 to 4,000 L / min, and dried and granulated by spray drying. In the laser diffraction particle size distribution measurement of the dried granulated product, D50 is 1.0 to 4.5 μm, D90 is 8 μm or less, the volatile matter is 0 to 10% by mass, and the bulk specific gravity is 0.2 to 0.7 g / cm 3 to form a first step of forming a hollow dried granulated product controlled to; A second step of filling 50 to 80% by volume of the volume inside the sheath of the dried granulated product obtained in the first step into a firing sheath; The fired sheath obtained in the second step is heated at a rate of 0.3 to 3 °C / min and fired at a firing temperature within the range of 1,050 °C or higher and less than 1,200 °C for 2 to 8 hours, and then cooled in the atmosphere at a rate of 0.3 to 10 °C / min while introducing air at 50 to 200 ml / min in the third step, in the method for producing hollow spherical alumina particles comprising: The basic aluminum lactate aqueous solution contains iron (Fe) in an amount of 0 to 0.01% by mass, calcium (Ca) in an amount of 0 to 0.01% by mass, magnesium (Mg) in an amount of 0 to 0.01% by mass, and silicon (Si) in an amount of 0 to 0.01% by mass, and contains alkali metal element ions in an amount of 0.005 to 1.2% by mass, has a basicity of 60 to 80%, and contains aluminum in an amount of 8 to 13% by mass in terms of Al2O3, The hollow spherical alumina particles have a D50 of 1.0 to 3.5 μm and a D90 of 6 μm or less in laser diffraction particle size distribution measurement, are hollow and spherical inside, and have a specific surface area of 1 to 20 m 2 / g, and a method for producing hollow spherical alumina particles, characterized in that. [2] The hollow spherical alumina particles have a bulk specific gravity of 0.3 to 0.7 g / cm 3 and the crystal phase of the hollow spherical alumina particles is the α-phase, and the method for producing hollow spherical alumina particles according to [1], characterized in that. [3] The hollow spherical alumina particles have a relative permittivity of 1.7 to 2.4 at a frequency f = 1 MHz measured by the volumetric method, and the method for producing hollow spherical alumina particles according to [1] or [2], characterized in that. [4] The basic aluminum lactate aqueous solution is obtained by mixing an aluminum chloride solution, either or both of sodium aluminate and potassium aluminate, and water to form a gel of aluminum hydroxide, washing the obtained gel with water, adding water to obtain an aluminum hydroxide slurry, and then adding lactic acid and reacting, and the method for producing hollow spherical alumina particles according to [1] or [2], characterized in that.

Advantages of the Invention

[0007] The hollow spherical alumina particles according to the present invention are derived from α-alumina, similar to the alumina particles of Patent Document 1, but have an average particle size (D50) of 1.0 to 3.5 μm and a D90 of 6 μm or less. The obtained alumina particles have heat resistance, thermal shock resistance, chemical resistance, and high-temperature strength characteristics, similar to those of Patent Document 1. The hollow and spherical characteristics are excellent in lightweight, heat insulation, fluidity, etc., and are expected to be applied to high-functional compounding materials for resins, rubbers, etc., heat dissipation fillers related to electronic materials, and polishing fillers for electronic components. In particular, hollow alumina particles with a small particle size are considered to contribute to reducing the relative dielectric constant of a thin resin sheet.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0009] (Definition of Terms) As used herein, "hollow" means that there are voids inside the particles, and does not mean that there is a completely spherical space. Therefore, there are voids or spaces in a part of the inside of the alumina particles. Also, since the alumina particles are small, particle formation may be insufficient, and for example, something like a cage shape as seen in FIG. 5 may occur. As used herein, "spherical" does not mean a perfect sphere, and an imperfect sphere, for example, a cage-shaped one, is also expressed as "spherical".

[0010] (Content of the Invention) In the present invention, an aqueous solution of basic aluminum lactate is supplied at a liquid supply rate of 100 to 500 ml / min at a temperature of 180 to 280°C in air or an inert gas under a gas pressure of 0.4 to 1 MPa and an air flow rate of 200 to 4,000 L / min, and dried and granulated by spray drying. In the measurement of the laser diffraction particle size distribution of the dried granulated product, D50 is 1.0 to 4.5 μm, D90 is 8 μm or less, the volatile content is 0 to 10% by mass, and the bulk specific gravity is 0.2 to 0.7 g / cm 3 to form a first step of forming a hollow dried granulated product controlled to a second step of filling the dried granulated product obtained in the first step into a firing sheath so that the volume inside the sheath is 50 to 80% by volume; a third step of heating the firing sheath obtained in the second step at a rate of 0.3 to 3°C / min, firing at a firing temperature in the temperature range of 1,050°C or higher and less than 1,200°C for 2 to 8 hours, and then cooling while introducing air at 50 to 200 ml / min in air at a rate of 0.3 to 10°C / min; in a method for producing hollow spherical alumina particles comprising the aqueous solution of basic aluminum lactate contains iron (Fe) in an amount of 0 to 0.01% by mass, calcium (Ca) in an amount of 0 to 0.01% by mass, magnesium (Mg) in an amount of 0 to 0.01% by mass, and silicon (Si) in an amount of 0 to 0.01% by mass, and contains alkali metal element ions in an amount of 0.005 to 1.2% by mass, the basicity is 60 to 80%, and aluminum is contained in an amount of 8 to 13% by mass in terms of Al2O3, The hollow spherical alumina particles have a D50 of 1.0 to 3.5 μm and a D90 of 6 μm or less in laser diffraction particle size distribution measurement, are hollow and spherical inside, and have a specific surface area of 1 to 20 m 2 / g, and it is characterized in that a method for producing the hollow spherical alumina particles can be provided.

[0011] (Raw material) As the raw materials used for synthesizing the hollow spherical alumina particles of the present invention, it is necessary to select the following: (I) The basic aluminum lactate aqueous solution is controlled to contain 0 to 0.01% by mass of iron (Fe), 0 to 0.01% by mass of calcium (Ca), 0 to 0.01% by mass of magnesium (Mg), and 0 to 0.01% by mass of silicon (Si). (II) The basic aluminum lactate aqueous solution contains alkali metal element ions in an amount of 0.005 to 1.2% by mass, has a basicity of 60 to 80%, and has 8 to 13% by mass of Al in terms of the mass of Al2O3. (III) The above-mentioned basic aluminum lactate aqueous solution is obtained by mixing an aluminum chloride solution, a sodium aluminate or potassium aluminate solution or a combination of both, and water as needed to form a gel of aluminum hydroxide, washing the gel with water, adding water to obtain an aluminum hydroxide slurry, and then adding lactic acid and reacting.

[0012] In the present invention, the basic aluminum lactate aqueous solution as the main raw material contains 0 to 0.01% by mass of iron (Fe), 0 to 0.01% by mass of calcium (Ca), 0 to 0.01% by mass of magnesium (Mg), and 0 to 0.01% by mass of silicon (Si), controls the amount of alkali metal, controls the basicity and aluminum content within a predetermined range, spray-dries it, bakes it at a temperature of 1050 °C or higher and lower than 1200 °C for 2 to 8 hours, and can provide hollow spherical alumina particles that meet the specified particle size, specific surface area, loss on drying, and loss on ignition, and meet the specified bulk specific gravity.

[0013] The present invention is manufactured by the following manufacturing method using the materials described in (I), (II), and (III) above.

[0014] (Manufacturing method) (Step 1) An aqueous solution of basic aluminum lactate that satisfies the requirements of (I) and (II) above (and (III) as necessary) is spray-dried and granulated at a temperature of 180 to 280°C in air or an inert gas at a gas pressure of 0.4 to 1 MPa and an air flow rate of 200 to 4,000 L / min with a liquid supply rate of 100 to 500 ml / min. In the measurement of the laser diffraction particle size distribution of the dry granulated product, D50 is 1.0 to 4.5 μm, D90 is 8 μm or less, the volatile content is 0 to 10% by mass, and the bulk specific gravity is 0.2 to 0.7 g / cm 3 to form a dry granulated product controlled to (Step 2) Filling the dry granulated product obtained in Step 1 into a firing sheath so that the volume inside the sheath is 50 to 80% by volume. (Step 3) Heating the firing sheath obtained in Step 2 at a rate of 0.3 to 3°C / min, firing at a firing temperature within a temperature range of 1,050°C or higher and less than 1,200°C for 2 to 8 hours, and then cooling while introducing air at a rate of 50 to 200 ml / min in the air at a rate of 0.3 to 10°C / min.

[0015] Hereinafter, the raw materials and manufacturing method used for the production of hollow spherical alumina particles will be described in detail.

[0016] (Aqueous solution of basic aluminum lactate) The aqueous solution of basic aluminum lactate used in the present invention has the following characteristics (I) to (II): (I) The aqueous solution of basic aluminum lactate is controlled to contain 0 to 0.01% by mass of iron (Fe), 0 to 0.01% by mass of calcium (Ca), 0 to 0.01% by mass of magnesium (Mg), and 0 to 0.01% by mass of silicon (Si). (II) The aqueous solution of basic aluminum lactate contains alkali metal element ions in an amount of 0.005 to 1.2% by mass, has a basicity of 60 to 80%, and contains 8 to 13% by mass of Al in terms of the mass of Al2O3.

[0017] The basic aluminum lactate aqueous solution used in the present invention is controlled such that, as described in the above (I), iron (Fe) is 0 to 0.01% by mass, calcium (Ca) is 0 to 0.01% by mass, magnesium (Mg) is 0 to 0.01% by mass, and silicon (Si) is 0 to 0.01% by mass. When the Fe content, Ca content, Mg content, and Si content contained in the basic aluminum lactate aqueous solution exceed 0.01% by mass, it will cause the formation of different crystal phases other than alumina during firing and defects such as coloring. The contents of Fe, Ca, Mg, and Si are preferably 0.007% by mass or less, more preferably 0.006% by mass or less, respectively.

[0018] The basic aluminum lactate aqueous solution used in the present invention needs to contain alkali metal element ions in an amount of 0.005 to 1.2% by mass, as described in the above (II). More preferably, it contains 0.01 to 0.5% by mass of alkali metal element ions. When the amount of alkali metal element ions is less than 0.005% by mass, the amount of alkali metal element ions is too small, and the temperature for phase transition to α-alumina becomes high, and α-alumina is not generated below 1200°C. On the other hand, when the amount of alkali metal element ions exceeds 1.2% by mass, the amount of alkali metal element ions is too large, and β-alumina and the like other than α-alumina are generated, and the desired α-alumina cannot be obtained.

[0019] The alkali metal element ion species contained in the basic aluminum lactate aqueous solution used in the present invention needs to be one or more selected from sodium and potassium.

[0020] The basic aluminum lactate aqueous solution used in the present invention preferably has a basicity of 60 to 80% and contains 8 to 13% by mass of Al in terms of the mass of Al2O3. When the basicity is less than 60%, there is a problem that the lactic acid content is too high and the solubility in water deteriorates. On the other hand, when it exceeds 80%, insoluble aluminum hydroxide precipitates, the liquid becomes cloudy, and there is a problem that hollow dried granules cannot be obtained when spray-dried. Also, when the Al content is less than 8% by mass in terms of the mass of Al2O3, there is a problem that hollow dried granules cannot be obtained when dried by spray-drying. On the other hand, when it exceeds 13% by mass, the amount of Al is too large, the storage stability is poor, precipitates occur in the basic aluminum lactate aqueous solution, and it is not suitable for spray-drying. The basicity of the basic aluminum lactate aqueous solution is preferably 62 to 78%, more preferably 64 to 76%. "Basicity" is a value indicating what percentage of the valence that can be substituted by a base is filled. Since aluminum is trivalent, if 2 / 3 (2 out of 3 valences) is used, it means 66.66% (i.e., about 67%), and it is measured in accordance with the method for measuring the basicity of liquid polyaluminum chloride for water supply specified in JIS K1475. The mass of aluminum (Al) in the basic aluminum lactate aqueous solution in terms of Al2O3 is preferably 8.5 to 12.5% by mass, more preferably 9 to 12% by mass. The mass of Al in terms of Al2O3 is what is usually used when using aluminum salts, and the amount of aluminum is specified by converting it to the mass of Al2O3.

[0021] The basic aluminum lactate aqueous solution used in the present invention is preferably obtained by the method described in (III). Specifically, (III) The basic aluminum lactate aqueous solution is obtained by mixing an aluminum chloride solution, a sodium aluminate or potassium aluminate solution or a combination of both, and water to form a gelled aluminum hydroxide, washing the gelled product with water, adding water to obtain an aluminum hydroxide slurry, and then adding lactic acid and reacting. Of course, the basic aluminum lactate aqueous solution may be obtained by any method as long as it satisfies the above (I) and (II). However, the basic aluminum lactate aqueous solution obtained in the above (III) is more preferable.

[0022] (Method for producing hollow spherical alumina particles) The hollow spherical alumina particles of the present invention are produced from the following steps 1 to 3: (Step 1) A basic aluminum lactate aqueous solution satisfying the requirements of the above (I) and (II) (and (III) as necessary) is spray-dried and granulated at a gas pressure of 0.4 to 1 MPa, an air flow rate of 200 to 4,000 L / min, a temperature of 180 to 280 °C in air or an inert gas, and a liquid supply rate of 100 to 500 ml / min. In the laser diffraction particle size distribution measurement of the dry granulated product, D50 is 1.0 to 4.5 μm, D90 is 8 μm or less, the volatile content is 0 to 10% by mass, and the bulk specific gravity is 0.2 to 0.7 g / cm 3 to form a dry granulated product controlled thereto. (Step 2) Filling the dry granulated product obtained in Step 1 into a firing sheath to 50 to 80% by volume of the volume inside the sheath. (Step 3) Heating the firing sheath obtained in Step 2 at a rate of 0.3 to 3 °C / min, firing at a firing temperature in the temperature range of 1,050 °C or higher and less than 1,200 °C for 2 to 8 hours, and then cooling while introducing air at 50 to 200 ml / min in air at a rate of 0.3 to 10 °C / min.

[0023] (Step 1) In Step 1, a basic aluminum lactate aqueous solution is spray-dried and granulated at a gas pressure of 0.4 to 1 MPa, an air flow rate of 200 to 4,000 L / min, a temperature of 180 to 280 °C in air or an inert gas, and a liquid supply rate of 100 to 500 ml / min. In the laser diffraction particle size distribution measurement of the dry granulated product, D50 is 1.0 to 4.5 μm, D90 is 8 μm or less, the volatile content is 0 to 10% by mass, and the bulk specific gravity is 0.2 to 0.7 g / cm 3Control to form a dried granulated product. If the gas pressure is less than 0.4 MPa, the gas pressure is too low to obtain a dried granulated product with a D50 of 1.0 to 4.5 μm and a D90 of 8 μm or less in laser diffraction particle size distribution measurement. On the other hand, when it exceeds 1 MPa, large compressors, boosters, etc. are required, and there is a problem of poor productivity. The gas pressure is preferably 0.2 to 0.8 MPa, more preferably 0.3 to 0.7 MPa. If the air flow rate is less than 200 L / min, the air flow rate is too low to obtain fine granulated particles. On the other hand, when it exceeds 4,000 L / min, large compressors, etc. are required, and there is a problem of poor productivity. The air flow rate is preferably 300 to 3,500 L / min, more preferably 500 to 3,000 L / min.

[0024] Step 1 is dried and granulated in air or an inert gas. Examples of the inert gas include noble gases (e.g., helium, neon, or argon) or nitrogen gas. Usually, it is carried out in air. The drying temperature is 180 to 280 °C, preferably 190 to 260 °C. If drying and granulating at a temperature lower than 180 °C, since the moisture content of the dried product is high, aggregates are likely to occur in the dried state, and it has the drawback of not becoming independent hollow spherical alumina after firing. If drying and granulating at a temperature exceeding 280 °C, part of the organic matter of basic aluminum lactate undergoes oxidation, the dried product turns brown, the physical properties deteriorate, and it has the drawback that the spherical shape collapses during firing.

[0025] If the liquid supply rate is less than 100 ml / min, there is a problem that the liquid supply rate is too low and the productivity deteriorates. If it exceeds 500 ml / min, the granulated particles become too large, and there are problems that granulated particles with a desired particle size cannot be obtained and the volatile content exceeds 10% by mass.

[0026] Drying granulation is carried out by spray drying. For spray drying, in order to make the D50 and D90 of the dried granulated product within a predetermined range, a method using, for example, a two-fluid nozzle or a four-fluid nozzle is used. Of course, any drying granulation method may be used as long as the D50 and D90 representing the particle size of the dried granulated product are within a predetermined range.

[0027] The dried granulated product has a D50 of 1.0 to 4.5 μm and a D90 of 8 μm or less, a volatile content of 0 to 10% by mass, and a bulk specific gravity of 0.2 to 0.7 g / cm 3 and needs to be controlled. D50 and D90 will also be described in the description of D50 and D90 of the final hollow spherical alumina particles to be described later, and can be obtained by dry measurement using a laser diffraction particle size distribution analyzer (Master Sizer 3000 manufactured by Malvern Panalytical). D50 means the diameter at which half of the population is below this value, and D90 means that 90% of the population is below this value. If D50 is less than 1.0, the cohesiveness of the particles is strong and it is difficult to use them in a dispersed state. If D50 is greater than 4.5 μm, the range of uses becomes narrow as a filler for adjusting the dielectric constant of a thin-layer resin sheet or a filler for adjusting the heat dissipation of a thin-layer resin sheet. The D50 of the dried granulated product is preferably 1.2 to 4.0 μm, more preferably 1.5 to 3.0 μm. The D90 of the dried granulated product is preferably 5.0 to 7.5 μm, more preferably 5.5 to 6.5 μm.

[0028] The dried granulated product obtained in Step 1 is controlled to have a volatile content of 0 to 10% by mass and a bulk specific gravity of 0.2 to 0.7 g / cm 3 If the volatile content exceeds 10% by mass, the drying is insufficient and the moisture content of the dried product is high. Therefore, aggregates are likely to be generated in the dried state, and it has the drawback that it does not become independent hollow spherical alumina after firing. The volatile content is preferably 0% by mass. The volatile content is preferably 1.0 to 9.0% by mass, more preferably 2.0 to 8.0% by mass. The dried granulated product has a bulk specific gravity of 0.20 to 0.7 g / cm 3 , preferably 0.25 to 0.65 g / cm 3 , more preferably 0.3 to 0.6 g / cm 3 . If the bulk specific gravity is less than 0.2 g / cm 3 , the hollowness increases and the thickness of the outer shell part becomes thin, so it has the drawback that the strength of the hollow spherical alumina particles decreases. If it is 0.70 g / cm 3If it is larger, the hollowness during granulation becomes smaller and the thickness of the outer shell part becomes larger, resulting in the drawbacks of being more likely to deform and less likely to form a spherical shape. The volatile content is measured using an A&D heating dry moisture meter MX50 under the conditions of 105°C for 30 minutes. The bulk specific gravity is the value obtained by dividing the mass by the volume. In the examples of the present invention, about 40 g of a sample (M) of the powder passed through a sieve with a mesh size of 1 mm, weighed with an accuracy of 0.1% by mass, was placed in a 100 ml graduated cylinder (minimum memory unit 1 ml), the surface was gently leveled, and the loose bulk volume (V0) was read, and the bulk specific gravity: M / V0 (g / cm 3 ) is calculated. The volatile content can be adjusted by the temperature and liquid feeding rate during granulation, and the bulk specific gravity can be controlled by the gas pressure during spray granulation.

[0029] (Step 2) In step 2 of the method for producing hollow spherical alumina particles of the present invention, the dried granulated product obtained in step 1 is put into a firing sheath and filled to 50 to 80% by volume of the volume inside the sheath. If the filling amount into the firing sheath is less than 50% by volume, the input amount during firing is reduced, and there is a problem of deteriorated productivity. If it exceeds 80% by volume, an incompletely fired part remains on the bottom surface of the sheath during firing, and stable firing cannot be achieved. The filling amount into the firing sheath is preferably 55 to 75% by volume of the volume inside the sheath, more preferably 60 to 70% by volume. The firing sheath is not particularly limited as long as it can withstand the firing conditions, but alumina or mullite-cordierite is preferred. If it is made of alumina or mullite-cordierite, within the firing temperature range, it is excellent in that there is no deformation in the firing sheath and no different crystal phases are formed due to element transfer from the firing sheath to the hollow spherical alumina.

[0030] (Step 3) In step 3 of the method for producing hollow spherical alumina particles of the present invention, the firing sheath obtained in step 2 is heated at a rate of 0.3 to 3°C / min, fired at a firing temperature within the temperature range of 1,050°C or higher and less than 1,200°C for 2 to 8 hours, and then cooled while introducing air at 50 to 200 ml / min in the atmosphere at a rate of 0.3 to 10°C / min.

[0031] When the heating rate in Step 3 is less than 0.3 °C / min, the time required for heating is too long, resulting in poor productivity. When it exceeds 3 °C / min, there is a problem that firing unevenness occurs in the powder inside the sheath, and stable hollow spherical alumina particles cannot be obtained. The heating rate is preferably 0.5 to 2.8 °C / min, more preferably 1.0 to 2.5 °C / min. When the firing temperature is less than 1050 °C, the firing is insufficient, and crystal phases other than α-alumina remain. When the firing temperature exceeds 1200 °C, a firing furnace with heat-resistant measures is required, resulting in poor productivity. The firing temperature is preferably 1070 to 1190 °C, more preferably 1090 to 1180 °C. If the firing time is less than 2 hours, the firing is insufficient, and crystal phases other than α-alumina remain. When it exceeds 8 hours, there is a problem of poor productivity. The firing time is preferably 2.5 to 7.5 hours, more preferably 3.0 to 7.0 hours.

[0032] During cooling, it is necessary to cool at a cooling rate of 0.3 to 10 °C / min. When the cooling rate is less than 0.3 °C / min, the time required for cooling is too long, resulting in poor productivity. When it exceeds 10 °C / min, there is a problem that the sheath is damaged by thermal stress, and stable hollow spherical alumina particles after firing cannot be recovered. The cooling rate is preferably 0.5 to 2.8 °C / min, more preferably 1.0 to 2.5 °C / min.

[0033] In the firing furnace, it is necessary to perform firing while introducing air at 50 to 200 ml / min in the atmosphere at any stage during heating, firing, and cooling. When the air introduction amount is less than 50 ml / min, the air introduction amount is too small, resulting in insufficient firing at the bottom of the sheath and firing defects. On the other hand, when the air introduction amount exceeds 200 ml / min, when firing for 2 to 8 hours in the range of 1050 to 1200 °C, the amount of air introduced is too large, causing the furnace to cool down, and there is a problem that sintering defects occur without reaching the maximum temperature during firing. The air introduction amount is preferably 60 to 180 ml / min, more preferably 70 to 170 ml / min.

[0034] (Hollow spherical alumina particles) The hollow spherical alumina particles of the present invention are produced by the above steps 1 to 3. The hollow spherical alumina particles obtained by this method have a D50 of 1.0 to 3.5 μm and a D90 of 6 μm or less in particle size distribution measurement, are spherical alumina particles with a hollow interior, and have a specific surface area of 1 to 20 m 2 / g and exhibit an α-phase in the crystal system (also referred to as the crystal phase).

[0035] The particle size distribution is obtained by dry measurement using a laser diffraction particle size distribution analyzer (MasterSizer 3000 manufactured by Malvern Panalytical). Fig. 1 shows the particle size distribution results of the alumina particles of Example 1. In the particle size distribution, D50 means the diameter below which half of the population lies, and D90 means that 90% of the population lies below this value. As shown in Fig. 1, it can be confirmed that the particle size distribution of the alumina particles of Example 1 has a D50 of 2.5 μm and a D90 of less than 6 μm. When D50 is less than 1.0 μm, there is a problem that aggregation becomes strong and dispersion becomes difficult. When D50 exceeds 3.5 μm, it becomes difficult to use as a filler for adjusting the dielectric constant of a thin-layer resin sheet or a heat dissipation filler for a thin-layer resin sheet. Furthermore, when D90 exceeds 6 μm, there is a problem that the usage as a filler for adjusting the dielectric constant of a filler for adjusting the dielectric constant of a thin-layer resin sheet or a thin-layer resin sheet becomes narrow.

[0036] The alumina particles obtained by the production method of the present invention are spherical with a hollow interior. "Hollow" does not mean a completely spherical hollow as described in the definition of the term. For example, as shown in electron micrographs of the alumina particles of Example 1 in Figs. 4 and 5, those that appear to be spherical but have cavities (Fig. 4) and those that have an insufficient spherical formation and exist in a cage-like shape are also included.

[0037] The hollow spherical alumina particles obtained by the production method of the present invention have a specific surface area of 1 to 20 m 2 / g, and the crystal system shows the α-phase. The specific surface area refers to the surface area per unit mass or per unit volume of an object. In the present invention, the specific surface area is measured with N2 using an automatic specific surface area measuring device (Gemini7 2390 manufactured by Shimadzu Corporation), and the data analyzed by the BET method is used. When the specific surface area of the alumina particles of the present invention is less than 1 m 2 / g, the specific surface area is too small, and there are few adsorption sites when performing surface treatment using a dispersant or the like, so there is a drawback that surface treatment becomes difficult. When it is greater than 20 m 2 / g, the adsorption amount of nitrogen gas (N2) on the alumina surface is too large, and there is a drawback that crystal growth as α-alumina is insufficient. The specific surface area of the hollow spherical alumina particles of the present invention is preferably 3 to 15 m 2 / g, more preferably 5 to 13 m 2 / g. The crystal system is of the α-type for the hollow spherical alumina particles of the present invention. In the present invention, it is not assumed that other crystal systems such as the γ-type are mixed in the alumina particles. The crystal system mainly uses the one measured by the θ / 2θ method with a Cu target using an X-ray diffractometer (specifically, MiniFlex manufactured by Rigaku Corporation).

[0038] The bulk specific gravity of the hollow spherical alumina particles in the present application is preferably 0.3 to 0.7 g / cm 3 More preferably, it is 0.45 to 0.65 g / cm 3 . When the bulk specific gravity is less than 0.3, the outer skin becomes too thin and cannot maintain its shape as hollow spherical alumina particles. On the other hand, when the bulk specific gravity exceeds 0.7 g / cm 3 , the outer skin becomes too thick and cannot perform the function as hollow spherical alumina particles. The bulk specific gravity is the value obtained by dividing the mass by the volume. Specifically, about 40 g of a sample (M) weighed with an accuracy of 0.1 mass% of the powder passed through a sieve with a mesh opening of 1 mm is put into a 100 ml graduated cylinder (minimum memory unit 1 ml), the surface is gently leveled, and the loose bulk volume (V0) is read, and the bulk specific gravity: M / V0 (g / cm 3 ) is calculated.

[0039] The hollow spherical alumina particles in the present invention must have a crystal phase of α-phase. If the α-phase is not formed, the relative permittivity at a frequency f = 1 MHz measured by the volumetric method will not satisfy 1.7 to 2.4. The measurement of the relative permittivity at f = 1 MHz was carried out by the volumetric method using a permittivity measurement system WKR6510P (manufactured by Toyo Technica Co., Ltd.). When the relative permittivity is less than 1.7, the air content is too large to maintain the shape of the hollow spherical alumina particles. When it exceeds 2.4, the permittivity is too large to be used as a low relative permittivity material. When the relative permittivity is large, it may generate heat when a high frequency is applied when compounded in a resin thin film, so it is not suitable for use in a resin thin film. The relative permittivity at f = 1 MHz is preferably 1.75 to 2.3, more preferably 1.8 to 2.2.

[0040] (Example) The present invention will be described in more detail with reference to examples. The present invention should not be construed as being limited to these examples. In the examples, unless otherwise specified, % and parts are based on mass.

[0041] (Example 1) Using a 10 L glass-lined (GL) stirred kettle with a jacket, first, cool water at 5 °C is circulated through the jacket. Next, 1451.1 g of tap water is added to the kettle and stirred, and 1911.4 g of an aluminum chloride aqueous solution (Al amount in terms of Al2O3: 10.0 mass%, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al amount in terms of Al2O3: 23.0 mass%, Na amount in terms of Na2O: 18.0%) are simultaneously added to obtain 5000 g of a hydrated aluminum oxide gel solution.

[0042] Next, the obtained gel solution was dehydrated using a centrifugal dehydrator, and the operations of adding water and stirring were repeated 7 times. The obtained washed gel weighed 2190 g. Next, using a 1 L glass separable flask installed on a mantle heater, 103.2 g of the obtained washed gel and 162.1 g of tap water were added and stirred for 30 minutes to obtain 265.4 g of a slurry. 39.7 g of lactic acid (90% lactic acid) was added to the obtained slurry, and after heating and stirring at 100 °C for 3 hours, it was gradually cooled to prepare 300 g of an aqueous solution of basic aluminum lactate of the present invention (Al content in terms of Al2O3: 8.4% by mass, basicity: 70.3%, sodium ion: 0.01% by mass, Si: 0.0052% by mass, Ca: 0.0043% by mass, Mg: 0.0009% by mass, Fe: 0.0015% by mass).

[0043] The obtained aqueous solution of basic aluminum lactate was granulated and dried using a two-fluid nozzle in a spray dryer (TR-160: manufactured by Pulice Co., Ltd.) at an inlet temperature of 250 °C, an outlet temperature of 115 °C, a gas pressure of 0.5 MPa, a liquid supply rate of 200 ml / min, and an air flow rate of 300 L / min to obtain collected dried granules (volatile content: 6.8% by mass). The obtained dried granules were filled in an alumina firing sheath at 60% by volume. Next, the temperature was raised at a rate of 1 °C / min, held at the peak firing condition of 1100 °C for 5 hours for firing, and the temperature was lowered at a rate of 1 °C / min to obtain hollow spherical alumina particles. Incidentally, the air introduction amount during heating, holding, and cooling (corresponding to introducing air at "50 to 200 ml / min" in the third step) was kept constant at 100 ml / min.

[0044] The particle size distribution of the dried granules before firing was measured, D50 and D90 were determined, and are shown in Table 1. The particle size distribution is the same as that measured for the hollow spherical alumina particles D50 and D90 described later, but was measured by dry method using a laser scattering particle size distribution analyzer (Mastersizer 3000 manufactured by Malvern Panalytical). D50 means the diameter at which half of the population is below this value, and D90 means that 90% of the population is below this value.

[0045] Also, the particle size distribution of the obtained alumina particles was measured, D50 and D90 were determined, and they were described in Table 5. The particle size distribution was measured by dry method using a laser scattering particle size distribution analyzer (Master Sizer 3000 manufactured by Malvern Panalytical). The particle size distribution results of the alumina particles of Example 1 are shown in a graph in Fig. 1. As described above, D50 means the diameter below which half of the population lies, and D90 means that 90% of the population lies below this value. Therefore, as shown in Fig. 1, it was confirmed that the particle size distribution of the alumina particles of Example 1 had a D50 of 2.5 μm and a D90 of 5.0 μm or less.

[0046] Table 1 also shows the specific surface area (m 2 / g), bulk density (g / cm 3 ), crystal system, relative permittivity at f = 1 MHz, and the contents of impurities such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe) of the obtained alumina particles. The specific surface area was measured with N2 using an automatic specific surface area measuring device (Gemini7 2390 manufactured by Shimadzu Corporation), and the data analyzed by the BET method is shown. The bulk density is the value obtained by dividing the mass by the volume. Specifically, about 40 g of a sample (M) of the powder passed through a sieve with an opening of 1 mm was weighed with an accuracy of 0.1 mass% and placed in a 100 ml graduated cylinder (minimum memory unit 1 ml). The surface was gently leveled, and the loose bulk volume (V0) was read, and the bulk density: M / V0 (g / cm 3 ) was calculated. The crystal system (crystal phase) was described in Table 1 based on the results measured by the θ / 2θ method using a Cu target with an X-ray diffractometer (MiniFlex manufactured by Rigaku Corporation). The relative permittivity at f = 1 MHz was measured by the capacitance method using a permittivity measurement system WKR6510P (manufactured by Toyo Technica Co., Ltd.). The contents of Na, K, Ca, Si, Mg, and Fe were measured using a desktop scanning electron microscope (SEM: JCM-7000 manufactured by JEOL Ltd.) and energy dispersive X-ray fluorescence analysis (EDX). The measurement results of the crystal system of the alumina particles obtained in Example 1 are shown in Fig. 2.

[0047] From the X-ray diffraction results of the alumina particles of Example 1 shown in FIG. 2, it was confirmed that α-alumina had been formed in the alumina particles of Example 1. Also, when the relative permittivity of the alumina particles at f = 1 MHz was measured by the volumetric method, it was confirmed that the relative permittivity was 2.0.

[0048] FIGS. 4 and 5 are SEM images of the alumina particles of Example 1 measured using a field emission scanning electron microscope (FE-SEM: JSM-7001F manufactured by JEOL Ltd.). FIG. 4 is an SEM image at 50,000 times magnification, and it is confirmed that microcrystals of α-alumina are aggregated to form the outer skin of the hollow spherical alumina. From the SEM image at 50,000 times magnification of the cross-section of the alumina particles of Example 1 in FIG. 5, it is confirmed that the hollow spherical alumina particles have a spherical structure. Therefore, it was confirmed that the alumina particles obtained in Example 1 are hollow spherical alumina particles.

[0049] (Example 2) Using a GL stirred kettle with a jacket having a capacity of 10 L, first, cooling water at 5°C is circulated through the jacket. Next, 1451.1 g of tap water is added to the kettle and while stirring, 1911.4 g of an aluminum chloride aqueous solution (Al amount in terms of Al2O3: 10.0 mass%, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al amount in terms of Al2O3: 23.0 mass%, Na amount in terms of Na2O: 18.0%) are simultaneously added to obtain 5000 g of a hydrated aluminum oxide gel solution.

[0050] Next, the obtained gel solution was dehydrated using a centrifugal dehydrator, and the operations of adding water and stirring were repeated 7 times. The obtained washed gel weighed 2190 g. Next, using a 1-L glass separable flask installed on a mantle heater, 103.2 g of the obtained washed gel was added, followed by 162.1 g of tap water, and the mixture was stirred for 30 minutes to obtain 265.4 g of a slurry. Next, 39.7 g of lactic acid (90% lactic acid) was added to the obtained slurry, and the mixture was heated and stirred at 100 °C for 3 hours, and then gradually cooled to prepare 300 g of an aqueous basic aluminum lactate solution of the present invention (Al content 8.4 mass% in terms of Al2O3, basicity 70.3%, sodium ion 0.01 mass%, Si: 0.0052 mass%, Ca: 0.0043 mass%, Mg: 0.0009 mass%, Fe: 0.0015 mass%).

[0051] The obtained aqueous basic aluminum lactate solution was granulated and dried using a two-fluid nozzle in a spray dryer (manufactured by Pris Co., Ltd., TR-160) at an inlet temperature of 250 °C, an outlet temperature of 115 °C, a gas pressure of 0.5 MPa, a liquid supply rate of 200 ml / min, and an air flow rate of 300 L / min. The collected dried granules (volatile content: 7.1 mass%) were filled in an alumina firing sheath at 70% by volume. Next, the temperature of the firing sheath was raised at a rate of 1 °C / min, held at the peak firing conditions of 1170 °C for 5 hours, and then cooled at a rate of 1 °C / min. As a result, hollow spherical alumina particles showing an α-phase in the crystal phase were obtained. Incidentally, the air introduction amount during heating, holding, and cooling was kept constant at 100 ml / min.

[0052] The particle size distribution of the dried granules before firing was measured, D50 and D90 were determined, and are shown in Table 1. The particle size distribution (D50 and D90), specific surface area, bulk density, crystal system, and relative permittivity at f = 1 MHz of the obtained alumina particles were measured by the method described in Example 1, and the results are shown in Table 5. Table 5 also shows the contents of impurities such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe) in the obtained alumina particles in the same manner as in Example 1.

[0053] (Example 3) Using a GL stirring kettle with a jacket and a capacity of 10 L, first perform a 5°C cooling water circulation in the jacket. Next, add 1451.1 g of tap water to the kettle and, while stirring, simultaneously add 1911.4 g of an aluminum chloride aqueous solution (Al content in terms of Al2O3: 10.0 mass%, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al content in terms of Al2O3: 23.0 mass%, Na content in terms of Na2O: 18.0%) to obtain 5000 g of a hydrated aluminum oxide gel solution.

[0054] Next, regarding the obtained gel solution, perform dehydration using a centrifuge, and repeat the operation of adding water and stirring 7 times. The obtained washed gel was 2190 g. Next, using a 1-L glass separable flask installed on a mantle heater, add 103.2 g of the obtained washed gel and then 162.1 g of tap water, and stir for 30 minutes to obtain a 265.4-g slurry. Next, add 39.7 g of lactic acid (lactic acid 90%) to the obtained slurry, perform heating and stirring at 100°C for 3 hours, and then slowly cool to prepare 300 g of an aqueous basic aluminum lactate solution of the present invention (Al content in terms of Al2O3: 8.4 mass%, basicity: 70.3%, sodium ion: 0.01 mass%, Si: 0.0052 mass%, Ca: 0.0043 mass%, Mg: 0.0009 mass%, Fe: 0.0015 mass%).

[0055] Perform granulation drying on the obtained aqueous basic aluminum lactate solution using a spray dryer (manufactured by Puris Co., Ltd., model TR-160) with an inlet temperature of 250°C, an outlet temperature of 118°C, a gas pressure of 0.5 MPa, a liquid supply rate of 150 ml / min, and an air supply rate of 350 L / min using a two-fluid nozzle. Fill the collected dried granules (volatile content: 6.0 mass%) in an alumina firing sheath at 60% by volume, raise the temperature at a rate of 1°C / min, hold at the peak firing conditions of 1100°C for 6 hours, lower the temperature at a rate of 1°C / min, and perform firing to obtain hollow spherical alumina particles with a crystal phase showing the α phase. Note that the air introduction amount during heating, holding, and cooling was kept constant at 85 ml / min.

[0056] The particle size distribution of the dried granulated product before firing was measured, D50 and D90 were determined, and they were described in Table 1. The particle size distribution (D50 and D90), specific surface area, bulk density, crystal system, and relative permittivity at f = 1 MHz of the obtained alumina particles were measured by the method described in Example 1, and the results were described in Table 5. Table 5 also described the contents of sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe), which are impurities of the obtained alumina particles, in the same manner as in Example 1.

[0057] (Example 4) Using a 10 L GL stirred kettle with a jacket, first, cool water at 5 °C was circulated through the jacket. Next, 1531.6 g of tap water was added to the kettle and stirred, and 1909.4 g of an aluminum chloride aqueous solution (Al content in terms of Al2O3: 10.0 mass%, basicity: 2.4%) and 1559.0 g of a sodium aluminate aqueous solution (Al content in terms of Al2O3: 20.0 mass%, Na content in terms of Na2O: 18.9%) were simultaneously added to obtain 5000 g of a aluminum hydroxide gel solution.

[0058] Next, the obtained gel solution was dehydrated using a centrifuge, and the operation of adding water and stirring was repeated 7 times. The obtained washed gel was 1920 g. Next, using a 1 L glass separable flask installed on a mantle heater, 103.2 g of the obtained washed gel and then 159.1 g of tap water were added and stirred for 30 minutes to obtain 262.3 g of a slurry. Next, 39.7 g of lactic acid (90% lactic acid) was added to the obtained slurry, and after heating and stirring at 100 °C for 3 hours, slow cooling was performed to prepare 300 g of the basic aluminum lactate aqueous solution of the present invention (Al content in terms of Al2O3: 8.9 mass%, basicity: 71.5%, sodium ion: 0.04 mass%, Si: 0.0048 mass%, Ca: 0.0038 mass%, Mg: 0.001 mass%, Fe: 0.001 mass%).

[0059] The obtained basic aluminum lactate aqueous solution was granulated and dried using a spray dryer (manufactured by Pris Co., Ltd., TR-160) at an inlet temperature of 250°C, an outlet temperature of 115°C, a gas pressure of 0.5 MPa, a liquid supply rate of 200 ml / min, and an air supply rate of 300 L / min with a two-fluid nozzle. The collected dried granules (volatile content: 6.5% by mass) were filled into a fired sheath of alumina at 70% by volume, heated at a rate of 1°C / min, held at the peak firing conditions of 1170°C for 5 hours, cooled at a rate of 1°C / min, and fired to obtain hollow spherical alumina particles with a crystal phase showing the α-phase. Incidentally, the air introduction amount during heating, holding, and cooling was kept constant at 100 ml / min.

[0060] The particle size distribution of the dried granules before firing was measured, D50 and D90 were determined, and are shown in Table 1. The particle size distribution (D50 and D90), specific surface area, bulk density, crystal system, and relative permittivity at f = 1 MHz of the obtained alumina particles were measured by the method described in Example 1, and the results are shown in Table 5. Table 5 also shows the contents of impurities such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe) in the obtained alumina particles, in the same manner as in Example 1.

[0061] (Example 5) Using a 10 L GL stirred kettle with a jacket, first, cooling water at 5°C was circulated through the jacket. Next, 1451.1 g of tap water was added to the kettle and stirred, and 1911.4 g of an aluminum chloride aqueous solution (Al content in terms of Al2O3: 10.0% by mass, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al content in terms of Al2O3: 23.0% by mass, Na content in terms of Na2O: 18.0%) were simultaneously added to obtain 5000 g of a hydrated aluminum oxide gel solution.

[0062] Next, the obtained gel solution was dehydrated using a centrifugal dehydrator, and the operations of adding water and stirring were repeated 7 times. The obtained washed gel weighed 2190 g. Next, using a 1 L glass separable flask installed on a mantle heater, 103.2 g of the obtained washed gel and then 162.1 g of tap water were added and stirred for 30 minutes to obtain 265.4 g of a slurry. Next, 39.7 g of lactic acid (90% lactic acid) was added to the obtained slurry, and after heating and stirring at 100 °C for 3 hours, slow cooling was performed to prepare 300 g of an aqueous solution of basic aluminum lactate of the present invention (Al content 8.4 mass% in terms of Al2O3, basicity 70.3%, sodium ion 0.01 mass%, Si: 0.0052 mass%, Ca: 0.0043 mass%, Mg: 0.0009 mass%, Fe: 0.0015 mass%).

[0063] The obtained aqueous solution of basic aluminum lactate was granulated and dried using a two-fluid nozzle in a spray dryer (manufactured by Pris Co., Ltd., model TR-160) at an inlet temperature of 250 °C, an outlet temperature of 118 °C, a gas pressure of 0.5 MPa, a liquid supply rate of 150 ml / min, and an air supply rate of 350 L / min. The collected dried granules (volatile content: 6.9 mass%) were filled at 60% by volume in a firing sheath of mullite cordierite, heated at a rate of 2 °C / min, fired under peak firing conditions of 1100 °C for 6 hours, and cooled at a rate of 2 °C / min to obtain hollow spherical alumina particles in which the crystal phase exhibited an α phase. Incidentally, the air introduction amount during heating, holding, and cooling was kept constant at 100 ml / min.

[0064] The particle size distribution of the dried granules before firing was measured, D50 and D90 were determined, and they are shown in Table 2. The particle size distribution (D50 and D90), specific surface area, bulk density, crystal system, and relative permittivity at f = 1 MHz of the obtained alumina particles were measured by the method described in Example 1, and the results are shown in Table 6. Table 6 also shows the contents of impurities such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe) in the obtained alumina particles in the same manner as in Example 1.

[0065] (Example 6) Using a GL stirring kettle with a jacket and a capacity of 10 L, first perform a 5°C cooling water circulation in the jacket. Next, add 1451.1 g of tap water to the kettle and, while stirring, simultaneously add 1911.4 g of an aluminum chloride aqueous solution (Al content in terms of Al2O3: 10.0 mass%, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al content in terms of Al2O3: 23.0 mass%, Na content in terms of Na2O: 18.0%) to obtain 5000 g of a hydrated aluminum oxide gel solution.

[0066] Next, regarding the obtained gel solution, perform dehydration using a centrifuge, and repeat the operation of adding water and stirring 7 times. The obtained washed gel was 2190 g. Next, using a 1-L glass separable flask installed on a mantle heater, add 103.2 g of the obtained washed gel and then 162.1 g of tap water, and stir for 30 minutes to obtain 265.4 g of a slurry. Next, add 39.7 g of lactic acid (90% lactic acid) to the obtained slurry, perform heating and stirring at 100°C for 3 hours, and then gradually cool to prepare 300 g of an aqueous basic aluminum lactate solution of the present invention (Al content in terms of Al2O3: 8.4 mass%, basicity: 70.3%, sodium ion: 0.01 mass%, Si: 52 ppm, Ca: 0.0043 mass%, Mg: 0.0009 mass%, Fe: 0.0015 mass%).

[0067] Perform granulation drying on the obtained aqueous basic aluminum lactate solution using a spray dryer (manufactured by GF of MDP-050 Co., Ltd.) at an inlet temperature of 200°C, an outlet temperature of 100°C, a gas pressure of 0.5 MPa, a liquid supply rate of 650 ml / min, and an air supply rate of 1000 L / min using a four-fluid nozzle, and fill the collected dried granulated product (volatile content: 6.6 mass%) in an alumina firing sheath at 60% by volume. Raise the temperature at a rate of 1°C / min, perform firing under peak firing conditions of 1100°C × 5 hours, and lower the temperature at a rate of 1°C / min to obtain hollow spherical alumina particles with a crystal phase showing an α phase. Note that the air introduction amount during heating, holding, and cooling was kept constant at 100 ml / min.

[0068] The particle size distribution of the dried granulated product before firing was measured, D50 and D90 were determined, and they were described in Table 2. The particle size distribution (D50 and D90), specific surface area, bulk density, crystal system, and relative permittivity at f = 1 MHz of the obtained alumina particles were measured by the method described in Example 1, and the results were described in Table 6. Table 6 also described the contents of impurities such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe) in the obtained alumina particles in the same manner as in Example 1.

[0069] (Example 7) Using a 10 L GL stirred kettle with a jacket, first, cool water at 5 °C was circulated through the jacket. Next, 1451.1 g of tap water was added to the kettle and stirred, and 1911.4 g of an aluminum chloride aqueous solution (Al content in terms of Al2O3: 10.0 mass%, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al content in terms of Al2O3: 23.0 mass%, Na content in terms of Na2O: 18.0%) were simultaneously added to obtain 5000 g of a hydrated aluminum oxide gel solution.

[0070] Next, the obtained gel solution was dehydrated using a centrifuge, and the operation of adding water and stirring was repeated 7 times. The obtained washed gel was 2190 g. Next, using a 1 L glass separable flask installed on a mantle heater, 103.2 g of the obtained washed gel and then 162.1 g of tap water were added and stirred for 30 minutes to obtain 265.4 g of a slurry. Next, 39.7 g of lactic acid (90% lactic acid) was added to the obtained slurry, and after heating and stirring at 100 °C for 3 hours, slow cooling was performed to prepare 300 g of an aqueous solution of basic aluminum lactate of the present invention (Al content in terms of Al2O3: 8.4 mass%, basicity: 70.3%, sodium ion: 0.01 mass%, Si: 0.0052 mass%, Ca: 0.0043 mass%, Mg: 0.0009 mass%, Fe: 0.0015 mass%).

[0071] The obtained basic aluminum lactate aqueous solution was granulated and dried using a spray dryer (MDP-050, manufactured by GF Co., Ltd.) with an inlet temperature of 180°C, an outlet temperature of 101°C, a gas pressure of 0.5 MPa, a liquid supply rate of 500 ml / min, and an air supply rate of 1,000 L / min using a four-fluid nozzle. The collected dried granulated product (volatile content: 7.6% by mass) was filled into a fired sheath of alumina at 60% by volume, heated at a rate of 1°C / min, and fired under peak firing conditions of 1100°C for 5 hours and cooled at a rate of 1°C / min to obtain hollow spherical alumina particles with a crystal phase showing the α-phase. During heating, holding, and cooling, the air introduction amount was kept constant at 100 ml / min.

[0072] The particle size distribution of the dried granulated product before firing was measured, D50 and D90 were determined, and are listed in Table 2. The particle size distribution (D50 and D90), specific surface area, bulk density, crystal system, and relative permittivity at f = 1 MHz of the obtained alumina particles were measured by the method described in Example 1, and the results are listed in Table 6. Table 6 also lists the contents of sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe), which are impurities in the obtained alumina particles, in the same manner as in Example 1.

[0073] (Example 8) Using a 1 L GL stirred kettle with a jacket, first, cool water at 5°C was circulated through the jacket. Next, while adding 153.1 g of tap water to the kettle and stirring, 190.4 g of an aluminum chloride aqueous solution (Al content in terms of Al2O3: 10.0% by mass, basicity: 2.4%), 153.9 g of a sodium aluminate aqueous solution (Al content in terms of Al2O3: 20.0% by mass, Na content in terms of Na2O: 18.9%), and 2 g of potassium aluminate powder were simultaneously added to obtain 500 g of a hydrated aluminum oxide gel solution.

[0074] Next, the obtained gel solution was dehydrated using a centrifugal dehydrator, and the operations of adding water and stirring were repeated 5 times. The obtained washed gel weighed 195 g. Next, using a 1-L glass separable flask installed on a mantle heater, 103.7 g of the obtained washed gel and then 156.6 g of tap water were added and stirred for 30 minutes to obtain 260.3 g of a slurry. Next, 39.7 g of lactic acid (90% lactic acid) was added to the obtained slurry, and after heating and stirring at 100 °C for 1.5 hours, it was gradually cooled to prepare 300 g of an aqueous solution of basic aluminum lactate (Al content 8.8 mass% in terms of Al2O3, basicity 72.4%, sodium ion 0.02 mass%, potassium ion 0.01 mass%, Si: 0.0047 mass%, Ca: 0.0050 mass%, Mg: 0.0006 mass%, Fe: 0.0011 mass%).

[0075] The obtained aqueous solution of basic aluminum lactate was granulated and dried using a two-fluid nozzle in a spray dryer (manufactured by Puris Co., Ltd., model TR-160) at an inlet temperature of 250 °C, an outlet temperature of 115 °C, a gas pressure of 0.5 MPa, a liquid supply rate of 200 ml / min, and an air supply rate of 300 L / min. The collected dried granules (volatile content: 7.0 mass%) were filled into a fired sheath of alumina at 60% by volume, heated at a rate of 1 °C / min, fired under peak firing conditions of 1100 °C for 5 hours, and cooled at a rate of 1 °C / min to obtain hollow spherical alumina particles in which the crystal phase showed the α phase. Incidentally, the air introduction amount during heating, holding, and cooling was kept constant at 100 ml / min.

[0076] The particle size distribution of the dried granules before firing was measured, D50 and D90 were determined, and they were listed in Table 2. The particle size distribution (D50 and D90), specific surface area, bulk density, crystal system, and relative permittivity at f = 1 MHz of the obtained alumina particles were measured by the method described in Example 1, and the results were listed in Table 6. Table 6 also listed the contents of impurities such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe) in the obtained alumina particles in the same manner as in Example 1.

[0077] (Comparative Example 1) Using a GL stirring kettle with a jacket and a capacity of 10 L, first, circulate cooling water at 5°C through the jacket. Next, add 1451.1 g of tap water to the kettle and, while stirring, simultaneously add 1911.4 g of an aluminum chloride aqueous solution (Al content in terms of Al2O3: 10.0 mass%, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al content in terms of Al2O3: 23.0 mass%, Na content in terms of Na2O: 18.0%) to obtain 5000 g of a aluminum hydroxide gel solution.

[0078] Next, the obtained gel solution was dehydrated using a centrifuge, and the operations of adding water and stirring were repeated 7 times. The obtained washed gel was 2190 g. Next, using a 1-L glass separable flask installed on a mantle heater, 103.2 g of the obtained washed gel and then 162.1 g of tap water were added and stirred for 30 minutes to obtain 265.4 g of a slurry. Next, 39.7 g of lactic acid (lactic acid 90%) was added to the obtained slurry, and after heating and stirring at 100°C for 3 hours, slow cooling was performed to prepare 300 g of a basic aluminum lactate aqueous solution (Al content in terms of Al2O3: 8.4 mass%, basicity: 70.3%, sodium ion: 0.01 mass%, Si: 0.0052 mass%, Ca: 0.0043 mass%, Mg: 0.0009 mass%, Fe: 0.0015 mass%).

[0079] The obtained basic aluminum lactate aqueous solution was granulated and dried using a spray dryer (manufactured by Puris Co., Ltd., model TR-160) at an inlet temperature of 250°C, an outlet temperature of 105°C, a liquid supply rate of 400 ml / min, and an atomizer at 18,000 rpm. The collected dried granules (volatile content: 7.3 mass%) were filled into a fired sheath of alumina at 60% by volume, heated at a rate of 1°C / min, fired under peak firing conditions of 1100°C for 5 hours, and cooled at a rate of 1°C / min. During heating, holding, and cooling, the air introduction amount was kept constant at 100 ml / min.

[0080] The particle size distribution of the dried granulated product before firing was measured, D50 and D90 were determined, and they were described in Table 3. The particle size distribution (D50 and D90), specific surface area, bulk density, crystal system, and relative permittivity at f = 1 MHz of the obtained alumina particles were measured by the method described in Example 1, and the results were described in Table 7. Table 7 also described the contents of sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe), which are impurities of the obtained alumina particles, in the same manner as in Example 1.

[0081] In Comparative Example 1, as described in Table 3, the D50 of the dried granulated product of the basic aluminum lactate aqueous solution was 49 μm and the D90 was 110 μm, which did not satisfy the D50 (1 to 4.5 μm) and D90 (8 μm or less) of the dried granulated product that are requirements of the present invention. The finally obtained hollow spherical alumina particles also had a D50 of 43 μm and a D90 of 105 μm, which did not satisfy the D50 (1.0 to 3.5 μm) and D90 (6 μm or less) that are requirements of the present invention, and the particle size of the hollow spherical alumina particles could not be reduced. This is presumably due to the use of an atomizer that cannot produce small dried granulated products in the drying granulation of the basic aluminum lactate aqueous solution. In spray drying, when the part for forming droplets is changed from a nozzle to an atomizer method, the productivity increases, but large droplets, that is, fine droplets cannot be produced.

[0082] (Comparative Example 2) Using a 10 L GL stirred kettle with a jacket, first, cooling water at 5 °C was circulated through the jacket. Next, while adding 1451.1 g of tap water into the kettle and stirring, 1911.4 g of an aluminum chloride aqueous solution (Al amount in terms of Al2O3: 10.0 mass%, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al amount in terms of Al2O3: 23.0 mass%, Na amount in terms of Na2O: 18.0%) were simultaneously added to obtain 5000 g of a hydrated aluminum oxide gel solution.

[0083] Next, the obtained gel solution was dehydrated using a centrifugal dehydrator, and the operations of adding water and stirring were repeated 7 times. The obtained washed gel weighed 2190 g. Next, using a 1-L glass separable flask installed on a mantle heater, 103.2 g of the obtained washed gel and then 162.1 g of tap water were added and stirred for 30 minutes to obtain a 265.4-g slurry. Next, 39.7 g of lactic acid (90% lactic acid) was added to the obtained slurry, and after heating and stirring at 100 °C for 3 hours, it was gradually cooled to prepare 300 g of an aqueous basic aluminum lactate solution (Al content 8.4 mass% in terms of Al2O3, basicity 70.3%, sodium ion 0.01 mass%, Si: 0.0052 mass%, Ca: 0.0043 mass%, Mg: 0.0009 mass%, Fe: 0.0015 mass%).

[0084] The obtained aqueous basic aluminum lactate solution was granulated and dried using a two-fluid nozzle in a spray dryer (manufactured by Pris Co., Ltd., model TR-160) at an inlet temperature of 150 °C, an outlet temperature of 85 °C, a gas pressure of 0.5 MPa, a liquid supply rate of 200 ml / min, and an air supply rate of 300 L / min. The collected dried granules (volatile content: 13.4 mass%) were filled in an alumina firing sheath at 60% by volume, heated at a rate of 1 °C / min, fired under peak firing conditions of 1100 °C × 5 hours, and cooled at a rate of 1 °C / min. The air introduction amount during heating, holding, and cooling was kept constant at 100 ml / min.

[0085] The particle size distribution of the dried granules before firing was measured, D50 and D90 were determined, and they were listed in Table 3. The particle size distribution (D50 and D90), specific surface area, bulk density, crystal system, and relative permittivity at f = 1 MHz of the obtained alumina particles were measured by the method described in Example 1, and the results were listed in Table 7. Table 7 also listed the contents of impurities such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe) in the obtained alumina particles in the same manner as in Example 1.

[0086] Even in Comparative Example 2, as described in Table 3, the D50 of the dried granulated product of the basic aluminum lactate aqueous solution was 130 μm and the D90 was 8800 μm, not satisfying the D50 (1 to 4.5 μm) and D90 (8 μm or less) of the dried granulated product which are requirements of the present invention. The finally obtained hollow spherical alumina particles also had a D50 of 125 μm and a D90 of 865 μm, not satisfying the D50 (1.0 to 3.5 μm) and D90 (6 μm or less) which are requirements of the present invention, and the particle size of the hollow spherical alumina particles could not be reduced. This is because the inlet temperature of the spray dryer was 150 °C and the outlet temperature was 85 °C, not within the range of 180 °C to 280 °C which is the temperature range used during spray drying. As a result, the volatile content of the aluminum lactate dried granulated product became high, powder sticking (aggregation lumps) occurred before firing, and the product was fired as aggregation lumps during firing, so it is considered that larger particles were formed.

[0087] (Comparative Example 3) Using a 10 L GL stirred kettle with a jacket, first, circulate cooling water at 5 °C through the jacket. Next, add 1451.1 g of tap water to the kettle and stir. While stirring, simultaneously add 1911.4 g of an aluminum chloride aqueous solution (Al content in terms of Al2O3: 10.0 wt%, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al content in terms of Al2O3: 23.0 wt%, Na content in terms of Na2O: 18.0%) to obtain 5000 g of a hydrated aluminum oxide gel solution.

[0088] Next, the obtained gel solution was dehydrated using a centrifugal dehydrator, and the operations of adding water and stirring were repeated 7 times. The obtained washed gel weighed 2190 g. Next, using a 1-L glass separable flask installed on a mantle heater, 103.2 g of the obtained washed gel and then 162.1 g of tap water were added and stirred for 30 minutes to obtain 265.4 g of a slurry. Next, 39.7 g of lactic acid (90% lactic acid) was added to the obtained slurry, and after heating and stirring at 100 °C for 3 hours, it was gradually cooled to prepare 300 g of an aqueous basic aluminum lactate solution (Al content in terms of Al2O3: 8.4 mass%, basicity: 70.3%, sodium ion: 0.01 wt%, Si: 0.0052 mass%, Ca: 0.0043 mass%, Mg: 0.0009 mass%, Fe: 0.0015 mass%).

[0089] The obtained aqueous basic aluminum lactate solution was granulated and dried using a two-fluid nozzle in a spray dryer (manufactured by Pris Co., Ltd., model TR-160) at an inlet temperature of 250 °C, an outlet temperature of 115 °C, a gas pressure of 0.5 MPa, a liquid supply rate of 200 ml / min, and an air flow rate of 300 L / min. The collected dried granules (volatile content: 6.8 mass%) were filled into a firing sheath of alumina at 95% by volume, heated at a rate of 1 °C / min, and fired under peak firing conditions of 1100 °C for 5 hours and cooled at a rate of 1 °C / min. The air introduction amount during heating, holding, and cooling was kept constant at 100 ml / min.

[0090] The particle size distribution of the dried granules before firing was measured, and D50 and D90 were determined and listed in Table 3. Although firing was carried out, it was impossible to measure D50, D90, and others of the obtained alumina particles due to poor firing. It was confirmed that the filling amount of the dried granules into the firing sheath during firing was as high as 95% by volume, resulting in insufficient firing, a large number of residual carbons being generated, and the material not being alumina.

[0091] (Comparative Example 4) Using a GL stirring kettle with a jacket and a capacity of 10 L, first, circulate cooling water at 5°C through the jacket. Next, add 1451.1 g of tap water to the kettle and, while stirring, simultaneously add 1911.4 g of an aluminum chloride aqueous solution (Al content in terms of Al2O3: 10.0 wt%, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al content in terms of Al2O3: 23.0 wt%, Na content in terms of Na2O: 18.0%) to obtain 5000 g of an aluminum hydroxide gel solution.

[0092] Next, the obtained gel solution was dehydrated using a centrifuge, and the operations of adding water and stirring were repeated 7 times. The obtained washed gel was 2190 g. Next, using a 1-L glass separable flask installed on a mantle heater, 103.2 g of the obtained washed gel and then 162.1 g of tap water were added and stirred for 30 minutes to obtain 265.4 g of a slurry. Next, 39.7 g of lactic acid (90% lactic acid) was added to the obtained slurry, and after heating and stirring at 100°C for 3 hours, it was gradually cooled to prepare 300 g of a basic aluminum lactate aqueous solution (Al content in terms of Al2O3: 8.4 mass%, basicity: 70.3%, sodium ion: 0.01 wt%, Si: 0.0052 mass%, Ca: 0.0043 mass%, Mg: 0.0009 mass%, Fe: 0.0015 mass%).

[0093] The obtained basic aluminum lactate aqueous solution was granulated and dried using a two-fluid nozzle in a spray dryer (manufactured by TR-160 Co., Ltd.) at an inlet temperature of 250°C, an outlet temperature of 115°C, a gas pressure of 0.5 MPa, a liquid supply rate of 200 ml / min, and an air flow rate of 300 L / min. The collected dried granulated product (volatile content: 6.8 mass%) was filled in an alumina firing sheath at 60% by volume, heated at a rate of 1°C / min, fired under peak firing conditions of 800°C × 5 hours, and cooled at a rate of 1°C / min. During heating, holding, and cooling, the air introduction amount was kept constant at 100 ml / min.

[0094] The particle size distribution of the dried granulated product before firing was measured, D50 and D90 were determined, and they were described in Table 3. The particle size distribution (D50 and D90), specific surface area, bulk density, crystal system, and relative permittivity at f = 1 MHz of the obtained alumina particles were measured by the method described in Example 1, and the results were described in Table 7. Table 7 also described the contents of impurities such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe) in the obtained alumina particles in the same manner as in Example 1.

[0095] In this case, since the firing temperature during firing is 800 °C, which is lower than 1050 °C, the crystal system of the obtained alumina particles is γ instead of α, so the specific surface area is high.

[0096] (Comparative Example 5) Using a 10 L GL stirred kettle with a jacket, first, cool water at 5 °C was circulated through the jacket. Next, 1451.1 g of tap water was added to the kettle and stirred, and 1911.4 g of an aluminum chloride aqueous solution (Al content in terms of Al2O3: 10.0 wt%, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al content in terms of Al2O3: 23.0 wt%, Na content in terms of Na2O: 18.0%) were simultaneously added to obtain 5000 g of a hydrated aluminum oxide gel solution.

[0097] Next, the obtained gel solution was dehydrated using a centrifuge, and the operation of adding water and stirring was repeated 7 times. The obtained washed gel was 2190 g. Next, using a 1 L glass separable flask installed on a mantle heater, 103.2 g of the obtained washed gel and then 162.1 g of tap water were added and stirred for 30 minutes to obtain 265.4 g of a slurry. Next, 39.7 g of lactic acid (90% lactic acid) was added to the obtained slurry, and after heating and stirring at 100 °C for 3 hours, it was gradually cooled to prepare 300 g of a basic aluminum lactate aqueous solution (Al content in terms of Al2O3: 8.4 mass%, basicity: 70.3%, sodium ion: 0.01 wt%, Si: 0.0052 mass%, Ca: 0.0043 mass%, Mg: 0.0009 mass%, Fe: 0.0015 mass%).

[0098] The obtained aqueous basic aluminum lactate solution was granulated and dried using a two-fluid nozzle in a spray dryer (manufactured by Puris Co., Ltd., model TR-160) at an inlet temperature of 250°C, an outlet temperature of 108°C, a gas pressure of 0.2 MPa, a liquid supply rate of 200 ml / min, and an air flow rate of 150 L / min. The collected dried granules (volatile content: 7.3% by mass) were filled into a fired sheath of alumina at 70% by volume, heated at a rate of 1°C / min, subjected to peak firing conditions of 1100°C for 5 hours, cooled at a rate of 1°C / min, and fired to obtain hollow spherical alumina particles with a crystal phase showing the α-phase. During heating, holding, and cooling, the air introduction amount was kept constant at 100 ml / min.

[0099] The particle size distribution of the dried granules before firing was measured, and D50 and D90 were determined and listed in Table 4. The particle size distribution (D50 and D90), specific surface area, bulk density, crystal system, and relative permittivity at f = 1 MHz of the obtained alumina particles were measured by the method described in Example 1, and the results are listed in Table 8. Table 8 also lists the contents of sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), silicon (Si), and iron (Fe), which are impurities in the obtained alumina particles, in the same manner as in Example 1.

[0100] In Comparative Example 5, since the gas pressure during spray drying was as low as 0.2 MPa and the air flow rate was also as low as 150 L / min, fine particles could not be produced when producing dried granules of aluminum lactate using the two-fluid nozzle of spray drying. As is clear from Table 4, the D50 of the obtained hollow spherical alumina particles was 12 μm and the D90 was also 34 μm, resulting in a large particle size. Comparative Example 5 corresponds to the alumina particles corresponding to Patent Document 1.

[0101] (Comparative Example 6) Using a GL stirring kettle with a jacket and a capacity of 10 L, first, circulate cooling water at 5 °C through the jacket. Next, add 1429.8 g of tap water to the kettle and stir while simultaneously adding 1909.4 g of an aluminum chloride aqueous solution (Al content in terms of Al2O3: 10.0 wt%, basicity: 2.4%) and 1660.8 g of a sodium aluminate aqueous solution (Al content in terms of Al2O3: 23.0 wt%, Na content in terms of Na2O: 18.0%) to obtain 5000 g of an aluminum hydroxide gel solution.

[0102] Next, regarding the obtained gel solution, the operation of dehydrating using a centrifuge and adding water and stirring was repeated 7 times. The obtained washed gel was 2190 g. Next, using a 1-L glass separable flask installed on a mantle heater, add 103.2 g of the obtained washed gel and then 152.1 g of tap water and stir for 30 minutes to obtain 255.3 g of a slurry. Next, add 34.7 g of lactic acid (90% lactic acid) and 10.0 g of calcium chloride to the obtained slurry, heat and stir at 100 °C for 3 hours, and then gradually cool to prepare 300 g of a basic aluminum lactate aqueous solution (Al content in terms of Al2O3: 8.2 mass%, basicity: 70.5%, sodium ion: 0.01 wt%, Si: 0.0050 mass%, Ca: 1.26 mass%, Mg: 0.0007 mass%, Fe: 0.0015 mass%).

[0103] The obtained basic aluminum lactate aqueous solution was granulated and dried using a two-fluid nozzle in a spray dryer (manufactured by Puris Co., Ltd., model TR-160) at an inlet temperature of 250 °C, an outlet temperature of 115 °C, a gas pressure of 0.5 MPa, a liquid supply rate of 200 ml / min, and an air flow rate of 300 L / min. The collected dried granules (volatile content: 7.4 mass%) were filled in an alumina firing sheath at 60% by volume, heated at a rate of 1 °C / min, fired under peak firing conditions of 1100 °C for 5 hours, and cooled at a rate of 1 °C / min. During heating, holding, and cooling, the air introduction amount was kept constant at 100 ml / min.

[0104] In Comparative Example 6, the content of Ca as an impurity of Ca was high, and a crystal phase other than α-alumina was formed during firing, so the hollow spherical alumina particles aimed at in the present invention could not be obtained. This is described in Table 8. Fig. 3 is a diagram showing the results measured by the θ / 2θ method using a Cu target with an X-ray diffractometer (MiniFlex manufactured by Rigaku Corporation) for the alumina particles obtained in Comparative Example 6. Fig. 3 is significantly different from Fig. 2 in the peak pattern of X-ray diffraction, and it can be understood that it is not the α-alumina crystal system.

[0105]

Table 1

[0106]

Table 2

[0107]

Table 3

[0108]

Table 4

[0109]

Table 5

[0110]

Table 6

[0111]

Table 7

[0112]

Table 8

[0113] Still, in Tables 5 to 8, "n.d." means that it cannot be measured.

[0114] As shown in Tables 1 to 2, in the particle size distributions of the dry granulated products of the basic aluminum lactate aqueous solutions obtained during the production of the hollow spherical alumina particles of Examples 1 to 8, the values of D50 and D90 were confirmed to be such that D50 was in the range of 1.0 to 4.5 μm and D90 was 8 μm or less. Also, as shown in Tables 5 and 6, the hollow spherical alumina particles shown in Examples 1 to 8 all showed α-alumina, and it was confirmed that in the particle size distribution measurement, D50 was 1.0 to 3.5 μm and D90 was 6 μm or less. Also, the specific surface area was confirmed to be 1 to 20 m 2 / g. Also, when these hollow spherical alumina particles were subjected to elemental analysis by energy dispersive fluorescent X-ray, it was confirmed that they contained alkali metal element ions (Na and K) in the range of 0.005 to 1.2 mass%, and the concentrations of Ca, Mg, Si, and Fe were not detected. Furthermore, Tables 5 and 6 also show that the relative permittivity at a frequency f = 1 MHz measured by the volumetric method was also in the range of 1.7 to 2.4, and when mixed into the resin sheet of the thin film, the particle size could be made small and the relative permittivity could be made low.

[0115] As shown in Table 3 and Table 7, in Comparative Example 1, since an atomizer is used in the granulation part of spray drying, in the measurement of the laser diffraction particle size distribution of the dried granulated product, D50 is as large as 43 μm and D90 is 105 μm, and fine droplets cannot be produced, so a dried granulated product with a small particle size cannot be produced. Therefore, even after firing, hollow spherical alumina with a fine particle size cannot be obtained. In Comparative Example 2, since the inlet temperature and outlet temperature of spray drying are low, the volatile content of the dried granulated product of aluminum lactate is high, and a large number of aggregates due to sticking are confirmed. When it is put into the firing sheath and fired, hollow spherical alumina remains in the form of agglomerates, so hollow spherical alumina with a small particle size (D50 is 1.0 to 3.5 μm, D90 is 6 μm or less) as the object of the present invention cannot be obtained. In Comparative Example 3, since the dried granulated product of aluminum lactate is filled in the firing sheath in an excessive amount of 95% by volume and fired, there are parts where firing is insufficient and residual carbon remains, so there is a problem of poor firing. In Comparative Example 4, the firing temperature during firing of the dried granulated product is 800 °C, which is lower than 1050 °C, so the crystal system exhibits a γ phase with a large specific surface area and does not become an α phase. In Comparative Example 5, since the gas pressure and air flow rate during spray drying are low, a dried granulated product with a small particle size cannot be obtained. As a result, even after firing, hollow spherical alumina with a small particle size (D50 is 1.0 to 3.5 μm, D90 is 6 μm or less) as the object of the present invention cannot be obtained. In Comparative Example 6, since the Ca content is too high, a composite oxide of aluminum and calcium is formed and it is not a single α-alumina phase.

[0116] The present invention also proposes the following aspects. [1] A first step of forming a hollow dried granulated product by supplying an aqueous solution of basic aluminum lactate in air or an inert gas at a gas pressure of 0.4 to 1 MPa and an air flow rate of 200 to 4,000 L / min at a temperature of 180 to 280 °C at a liquid supply rate of 100 to 500 ml / min and performing dry granulation by spray drying, wherein in the measurement of the laser diffraction particle size distribution of the dried granulated product, D50 is 1.0 to 4.5 μm, D90 is 8 μm or less, the volatile content is 0 to 10% by mass, and the bulk specific gravity is 0.2 to 0.7 g / cm 3 to control; A second step of filling 50 to 80% by volume of the volume inside the sheath of the fired granulated product obtained in the first step into the firing sheath, In the manufacturing method of hollow spherical alumina particles comprising a third step of heating the firing sheath obtained in the second step at 0.3 to 3 ° C. / min and firing at a firing temperature within a temperature range of 1,050 ° C. or higher and less than 1,200 ° C. for 2 to 8 hours, and then cooling while introducing air at 50 to 200 ml / min in the atmosphere at 0.3 to 10 ° C. / min, The basic aluminum lactate aqueous solution contains iron (Fe) in an amount of 0 to 0.01% by mass, calcium (Ca) in an amount of 0 to 0.01% by mass, magnesium (Mg) in an amount of 0 to 0.01% by mass, and silicon (Si) in an amount of 0 to 0.01% by mass, and contains alkali metal element ions in an amount of 0.005 to 1.2% by mass, has a basicity of 60 to 80%, and contains aluminum in an amount of 8 to 13% by mass in terms of Al2O3, The hollow spherical alumina particles have a D50 of 1.0 to 3.5 μm and a D90 of 6 μm or less in laser diffraction particle size distribution measurement, are hollow and spherical inside, and have a specific surface area of 1 to 20 m 2 / g, and a method for producing hollow spherical alumina particles, characterized in that. [2] The hollow spherical alumina particles have a bulk specific gravity of 0.3 to 0.7 g / cm 3 The method for producing hollow spherical alumina particles according to [1], characterized in that the crystal phase of the hollow spherical alumina particles is the α phase. [3] The hollow spherical alumina particles have a relative permittivity of 1.7 to 2.4 at a frequency f = 1 MHz measured by the volumetric method, and the method for producing hollow spherical alumina particles according to [1] or [2], characterized in that. [4] The basic aluminum lactate aqueous solution is obtained by mixing an aluminum chloride solution, either or both of sodium aluminate and potassium aluminate, and water to form a gel of aluminum hydroxide, washing the obtained gel with water, adding water to obtain an aluminum hydroxide slurry, and then adding lactic acid and reacting, and the method for producing hollow spherical alumina particles according to any one of [1] to [3], characterized in that.

Claims

1. A basic aluminum lactate aqueous solution is dried and granulated by spray drying at a gas pressure of 0.4 to 1 MPa, an air flow rate of 200 to 4,000 L / min in the atmosphere or inert gas, a temperature of 180 to 280°C, and a liquid supply rate of 100 to 500 ml / min. The dried granules are measured by laser diffraction particle size distribution measurement and have a D50 of 1.0 to 4.5 μm, a D90 of 8 μm or less, a volatile content of 0 to 10 mass%, and a bulk density of 0.2 to 0.7 g / cm. ３ A first step of forming a hollow dry granule having a controlled diameter; A second step of filling a sintering sheath with the dried granules obtained in the first step in an amount of 50 to 80% by volume of the internal volume of the sintering sheath; a third step of increasing the temperature of the sintered sheath obtained in the second step at a rate of 0.3 to 3°C / min, sintering the sintered sheath at a temperature within a range of 1,050°C or higher and lower than 1,200°C for 2 to 8 hours, and then decreasing the temperature at a rate of 0.3 to 10°C / min while introducing air at a rate of 50 to 200 ml / min in the atmosphere, The basic aluminum lactate aqueous solution contains iron (Fe) in an amount of 0 to 0.01 mass %, calcium (Ca) in an amount of 0 to 0.01 mass %, magnesium (Mg) in an amount of 0 to 0.01 mass %, silicon (Si) in an amount of 0.005 to 1.2 mass %, an alkali metal element ion in an amount of 0.005 to 1.2 mass %, a basicity of 60 to 80%, and aluminum in an amount of Al ２ O ３ It contains 8 to 13 mass% in terms of The hollow spherical alumina particles have a D50 of 1.0 to 3.5 μm and a D90 of 6 μm or less in a laser diffraction particle size distribution measurement, are hollow and spherical, and have a specific surface area of ​​1 to 20 m ２ / g.

2. The hollow spherical alumina particles have a bulk density of 0.3 to 0.7 g / cm 3 2. The method for producing hollow spherical alumina particles according to claim 1, wherein the crystal phase of the hollow spherical alumina particles is an α phase.

3. 3. The method for producing hollow spherical alumina particles according to claim 1, wherein the hollow spherical alumina particles have a relative dielectric constant of 1.7 to 2.4 at a frequency f=1 MHz as measured by a capacitance method.

4. 3. The method for producing hollow spherical alumina particles according to claim 1, wherein the basic aqueous aluminum lactate solution is obtained by mixing an aluminum chloride solution with either or both of sodium aluminate and potassium aluminate and water to form an aluminum hydroxide gel, washing the resulting gel with water, adding water to obtain an aluminum hydroxide slurry, and then adding lactic acid to cause a reaction.

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