Method for preparing highly fluid spherical aluminum nitride powder

Abstract

This invention provides a method for preparing highly fluid spherical aluminum nitride powder. [Solution] Step (A) provides aluminum nitride powder, a sintering aid, a dispersant, and a solvent, and performs primary wet ball mill mixing based on a first weight percent; Step (B) provides an adhesive and an organic alcohol-based additive, adds them to the mixture obtained in step (A) based on a second weight percent, and performs secondary wet ball mill mixing to form a mixed slurry; Step (C) atomizes the mixed slurry into droplets; Step (D) dries the atomized mixed slurry to obtain dried spherical aluminum nitride particles; and collects the dried spherical aluminum nitride particles, wherein the average particle size distribution D50 is in the range of 60 to 90 μm and the bulk density is 0.8 to 1.1 g / cm³. 3 The process includes step (E) obtaining a fluid spherical aluminum nitride powder which is in the range between and has an angle of repose of less than 30°.

Description

[Technical Field]

[0001] The present invention relates to a method for preparing spherical aluminum nitride powder, and more particularly to a method for preparing highly fluid spherical aluminum nitride powder using a centrifugal spray dryer. [Background technology]

[0002] Aluminum nitride (AlN) is a novel electroceramic material that is currently attracting attention as an advanced material due to its excellent properties such as thermal conductivity and electrical insulation. Its unique physical properties include high thermal conductivity, high electrical resistivity, low dielectric constant, low coefficient of thermal expansion, high heat resistance, high mechanical strength, high chemical stability, and non-toxicity, making it suitable for a wide range of applications, including electroceramic substrates, electronic device packaging materials, corrosion-resistant elements, and highly thermally conductive additives.

[0003] Aluminum nitride belongs to the hexagonal wurtzite structure, and its atoms are arranged in a tetrahedral configuration with strong covalent bonds. As a result, it has a high melting point, excellent thermal conductivity, and is a rare nonmetallic solid with a theoretical density of 3.26 g / cm³. 3 It satisfies four common rules: (1) low atomic weight, (2) strong atomic bonding, (3) simple crystal structure, and (4) high vibrational harmony of the crystal lattice, and its theoretical thermal conductivity reaches 320 W / mK. The thermal conductivity of commercially available aluminum nitride products is in the range of 170 to 230 W / mK. High-purity aluminum nitride is colorless and has light transmission ability, but its properties are easily affected by chemical purity and density. However, because aluminum nitride has a high affinity for oxygen atoms, during the process, some oxygen dissolves into the aluminum nitride crystal lattice, forming impurity defects and reducing thermal conductivity. This is because the presence of defects like impurities in the crystal lattice causes phonon scattering, and the thermal conductivity is clearly reduced. Aluminum nitride with low density also has low thermal conductivity.

[0004] The sintering preparation of densified aluminum nitride ceramics has been a focus of research for many years. Because aluminum nitride is a covalent material, solid-phase sintering is difficult, and it has been necessary to promote the overall densification sintering effect by adding a sintering aid with a low melting point, using the molten liquid phase generated during high-temperature sintering as a medium. Conventional aluminum nitride ceramic substrates are mainly prepared by the tape casting method and are used for forming sheet materials, however, this cannot be applied to aluminum nitride ceramic structural products with a thickness of more than 5 mm, and it has been necessary to use a dry press molding method for preparation. Dry press molding processes have strict requirements regarding the characteristics of the powder, such as its shape, particle size distribution, fluidity, and bulk density, so it was necessary to develop aluminum nitride powder granulation technology to prepare spherical aluminum nitride powder with high fluidity and an appropriate particle size distribution.

[0005] Conventional aluminum nitride ceramic powder granulation manufacturing processes have flaws in the solid-liquid ratio of the slurry. As the solid content of the slurry increases, the viscosity of the slurry increases, the diameter of the droplets increases during rotational atomization, and the kinetic energy of the centrifugal force becomes insufficient. As a result, the released droplets do not form perfect spheres, but tend to become elongated or fragmented, resulting in irregular shapes, making them unsuitable for spray granulation. Furthermore, if the temperatures at the inlet and outlet of the drying tower are not set appropriately, if the temperatures at the inlet and outlet are too low, the drying of the atomized droplets becomes incomplete, and powder granulation aggregation occurs. If the temperatures at the inlet and outlet are too high, the drying of the atomized droplet surface becomes too rapid, and a hard shell is quickly formed on the surface, hindering the normal shrinkage of the atomized droplets and ultimately resulting in hollow or concave, irregular powder granules.

[0006] Furthermore, in conventional aluminum nitride ceramic powder granulation manufacturing processes, the solid content and viscosity of the slurry affect the shape and roundness of the dried particles. Therefore, it was necessary to appropriately adjust the ratios of the slurry's adhesive, dispersant, additives, and solvent to obtain a suitable aluminum nitride slurry composition. If the temperature at the inlet and outlet of the drying tower was too high or too low, the drying rate of the mist particles would become too fast or too slow, resulting in aggregation and hollow depressions in the powder granulation. [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, the inventors believed that the above-mentioned shortcomings could be improved, and after diligent research, arrived at the present invention, which effectively improves the above-mentioned problems through a rational design.

[0008] The present invention has been made in view of the above circumstances, and one of its objectives is to solve the problems described above. Specifically, the present invention provides a method for preparing highly fluid spherical aluminum nitride powder, that is, by having a suitable aluminum nitride slurry formulation design and spray drying process parameter setting, and by adding an organic alcohol having high surface tension, the roundness and fluidity of the final spherical powder granulation are optimized, thereby increasing the yield of the subsequent preparation of aluminum nitride ceramic block material by dry press molding and high-temperature sintering, and improving the overall properties.

[0009] The objective of the present invention is to provide a method for preparing aluminum nitride ceramic granules that overcomes the problems of the prior art described above by optimizing the slurry formulation design and the centrifugal spray drying process, thereby obtaining highly fluid spherical aluminum nitride powder. [Means for solving the problem]

[0010] To solve the above problems, one aspect of the present invention provides a method for preparing highly fluid spherical aluminum nitride powder, comprising the steps of: (A) providing aluminum nitride powder, a sintering aid, a dispersant, and a solvent, and performing primary wet ball mill mixing based on a first weight percent; (B) providing an adhesive and an organic alcohol-based additive, adding them to the mixture obtained in step (A) based on a second weight percent, and performing secondary wet ball mill mixing to form a mixed slurry; (C) atomizing droplets from the mixed slurry; (D) drying the atomized mixed slurry to obtain dried spherical aluminum nitride particles; and collecting the dried spherical aluminum nitride particles, wherein the average particle size distribution D50 is in the range of 60 to 90 μm and the bulk density is 0.8 to 1.1 g / cm³. 3 The process includes step (E) obtaining a fluid spherical aluminum nitride powder which is in the range between and has an angle of repose of less than 30°.

[0011] Another aspect of the present invention, a method for preparing highly fluid spherical aluminum nitride powder, includes the steps of: (A) providing aluminum nitride powder, a sintering aid, a dispersant, and a solvent, and introducing them into a ball mill tank based on a first weight percent, and performing primary wet ball mill mixing; (B) providing an adhesive and an additive, introducing the adhesive and the additive into the ball mill tank of step (A) based on a second weight percent, and performing secondary wet ball mill mixing to form a mixed slurry having a constant viscosity; (C) transporting the mixed slurry to the sprayer turntable of a spray dryer at a fixed feed rate, and atomizing the droplets; (D) rotating the mixed slurry at high speed on the sprayer turntable, dispersing it as fine mist particles by the action of centrifugal force, introducing it into a drying tower having an inlet / outlet temperature control function, contacting it with dry nitrogen, evaporating the organic solvent in the mist particles, and obtaining dried spherical aluminum nitride particles; and collecting the dried spherical aluminum nitride particles in a bucket at the bottom of the drying tower, and determining the average particle size distribution D 50 The particle size is in the range of 60-90 μm, and the bulk density is 0.8-1.1 g / cm³. 3The process includes step (E) obtaining a highly fluid spherical aluminum nitride powder which is in the range of and has an angle of repose of less than 30°.

[0012] In a preferred example of the present invention, the aluminum nitride powder in step (A) has a purity of over 99%, an oxygen content of <1.0 wt%, and an average particle size in the range of 1 to 5 μm. The sintering aid is selected from the group consisting of rare earth element compounds such as yttrium oxide, yttrium fluoride, magnesium oxide, calcium oxide, calcium fluoride, or alkaline earth metal compounds. The dispersant is selected from the group consisting of citric acid, fish oil, polyethyleneimine, triethyl phosphate, polyacrylic acid, or sodium stearate. The solvent is selected from the group consisting of organic solvents such as anhydrous alcohol, methanol, isopropanol, ethyl acetate, methyl ethyl ketone, and 1-butanol.

[0013] In a preferred example of the present invention, the first wt% in step (A) is 29-45 wt% aluminum nitride powder, 1-5 wt% sintering aid, and 50-70 wt% solvent, which is converted to 0.1-3 wt% dispersant based on the weight of the aluminum nitride powder.

[0014] In a preferred example of the present invention, the primary wet ball mill mixing time in step (A) is in the range of 1 to 20 hours (hr).

[0015] In a preferred example of the present invention, the adhesive in step (B) is selected from the group consisting of polyvinyl butyral resin, acrylic resin, or phenolic resin. The additive is selected from the group consisting of organic alcohols such as ethylene glycol, cyclopentanol, and cyclohexanol.

[0016] In a preferred example of the present invention, the second wt% in step (B) is calculated based on the weight of the aluminum nitride powder, and is converted to 1 to 10 wt% of adhesive and 3 to 20 wt% of additives.

[0017] In a preferred example of the present invention, the secondary wet ball mill mixing time in step (B) ranges from 20 to 72 hours (hr).

[0018] In a preferred example of the present invention, the viscosity of the mixed slurry having a constant viscosity in step (B) ranges from 100 to 3000 cp.

[0019] In a preferred example of the present invention, steps (C) to (E) are carried out using a centrifugal spray drying device. The centrifugal spray drying device has a feed unit, a sprayer turntable, a drying tower, and a bucket.

[0020] In a preferred example of the present invention, the fixed feed rate of the mixed slurry in step (C) ranges from 3 to 10 kilograms per hour (kg / hr).

[0021] In a preferred example of the present invention, the rotation speed of the sprayer turntable in step (D) ranges from 5000 to 10000 rpm, the inlet temperature of the drying tower ranges from 90°C to 120°C, and the outlet temperature of the drying tower ranges from 60°C to 90°C.

[0022] Other features of the present invention will be clarified by the description in this specification and the accompanying drawings.

Brief Description of the Drawings

[0023] [Figure 1] It is a flowchart showing a method for preparing highly fluid spherical aluminum nitride powder according to a first embodiment of the present invention. [Figure 2] It is an optical microscope (OM) photograph (200 times) of aluminum nitride granulation using ethylene glycol as an additive according to an embodiment of the present invention. [Figure 3] It is a scanning electron microscope (SEM) photograph (3000 times) of aluminum nitride granulation using ethylene glycol as an additive according to an embodiment of the present invention. [Figure 4]This is an optical microscope (OM) image (200x magnification) of aluminum nitride granulation using cyclohexanol as an additive according to an embodiment of the present invention. [Figure 5] This is a scanning electron microscope (SEM) image (2000x magnification) of aluminum nitride granulation using cyclohexanol as an additive according to an embodiment of the present invention. [Figure 6] This is an optical microscope (OM) image (200x magnification) of aluminum nitride granules obtained by spray-drying a slurry with excessively high viscosity according to an embodiment of the present invention. [Modes for carrying out the invention]

[0024] The present invention will be described below through embodiments of the invention, but embodiments below this point do not limit the invention as defined in the claims. Furthermore, not all combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0025] (First embodiment) Figure 1 is a flowchart showing a method for preparing highly fluid spherical aluminum nitride powder according to a first embodiment of the present invention. The method mainly comprises the following steps. <Step S101>: Provide aluminum nitride powder, sintering aid, dispersant, and solvent, and put them into a ball mill tank based on weight % and perform wet ball mill mixing. Step S102: Provide an adhesive and an additive, put the adhesive and the additive into the ball mill tank of Step S101 based on weight %, and perform wet ball mill mixing to form a mixed slurry having a certain viscosity. <Step S103>: The mixed slurry is transported to the sprayer turntable of the spray dryer at a fixed feed speed, and the droplets are atomized and dried. <Step S104>: The mixed slurry mist droplets are introduced into a drying tower with temperature control functions at the inlet and outlet, and the organic solvent in the mist droplets is evaporated to obtain dried spherical particles. <Step S105>: The dried spherical particles are collected in a bucket at the bottom of the drying tower to obtain highly fluid spherical aluminum nitride powder.

[0026] In step S101 of the first embodiment of the present invention, the aluminum nitride powder is preferably aluminum nitride powder having a purity of more than 99%, an oxygen content of <1.0 wt%, and an average particle size in the range of 1 to 5 μm. In step S101, the sintering aid is preferably one of yttrium oxide or calcium oxide.

[0027] In step S101 of the first embodiment of the present invention, the dispersant is preferably one of fish oil or triethyl phosphate. The solvent in step S101 is preferably one selected from the group consisting of anhydrous alcohol, ethyl acetate, and 1-butanol.

[0028] In step S101 of the first embodiment of the present invention, the weight percent is preferably 35-40 wt% of aluminum nitride powder, 3-5 wt% of sintering aid, and 55-62 wt% of solvent, and is converted to 0.1-1 wt% of dispersant based on the weight of the aluminum nitride powder.

[0029] In step S101 of the first embodiment of the present invention, the wet ball mill mixing time is preferably in the range of 1 to 10 hours (hr).

[0030] In step S102 of the first embodiment of the present invention, the adhesive is preferably selected from the group consisting of polyvinyl butyral resin and acrylic resin. In step S102, the additive is preferably one of ethylene glycol or cyclohexanol.

[0031] In step S102 of the first embodiment of the present invention, the weight percent is preferably converted to 1 to 5 wt% of adhesive and 3 to 10 wt% of additive based on the weight of aluminum nitride powder.

[0032] In step S102 of the first embodiment of the present invention, the wet ball mill mixing time is preferably in the range of 20 to 48 hours (hr).

[0033] In step S102 of the first embodiment of the present invention, the viscosity of the mixed slurry having a constant viscosity is preferably in the range of 100 to 600 cP.

[0034] In step S103 of the first embodiment of the present invention, the fixed feed rate of the mixed slurry is preferably in the range of 3 to 5 kg / hr.

[0035] In step S104 of the first embodiment of the present invention, the rotation speed of the sprayer turntable is preferably in the range of 6000 to 8000 rpm. The inlet temperature of the drying tower is preferably in the range of 90°C to 100°C. The outlet temperature of the drying tower is preferably in the range of 60°C to 75°C.

[0036] The average particle size distribution D of the highly fluid spherical aluminum nitride powder obtained in step S105 of the first embodiment of the present invention 50 The particle size is in the range of 60-90 μm, and the bulk density is 0.8-1.1 g / cm³. 3 It is within the range of [a certain value], and the angle of repose is less than 30°.

[0037] By following the steps of the first embodiment of the present invention, a suitable solid content ratio and formulation of the slurry is designed so that the mixed slurry has an appropriate viscosity, and by adding an organic alcohol with high surface tension and controlling the spray drying parameters related to the rotation speed of the atomizer, inlet temperature and outlet temperature, a highly fluid spherical aluminum nitride powder that meets the requirements for average particle size distribution is obtained.

[0038] Figure 2 is an optical microscope (OM) image (200x magnification) of aluminum nitride granulation using ethylene glycol as an additive according to an embodiment of the present invention. Figure 3 is a scanning electron microscope (SEM) image (3000x magnification) of aluminum nitride granulation using ethylene glycol as an additive according to an embodiment of the present invention. The solid content of the slurry at the start of spray drying was 42 wt%, and the weight percentage composition of each component in the slurry was 37 wt% aluminum nitride (AlN) powder, 5 wt% yttrium oxide (Y2O3) powder, and 58 wt% ethyl acetate. Based on the weight of aluminum nitride (AlN) powder, 1 wt% polyvinyl butyral resin (PVB), 1 wt% fish oil, and 4 wt% ethylene glycol were added to the slurry. The parameters of the spray drying process were a feed rate of 4.7 kg / hr, an atomizer rotation speed of 6500 rpm, an inlet temperature of 95°C, and an outlet temperature of 70°C. The 200x OM image in Figure 2 and the 3000x SEM image in Figure 3 show granulated aluminum nitride powder that was spray-dried with ethylene glycol as an additive. All of the particles are perfectly spherical, and the SEM image shows that the particle size of each particle is approximately 70 μm.

[0039] Figure 4 is an optical microscope (OM) photograph (200x) of aluminum nitride granulation using cyclohexanol as an additive according to an embodiment of the present invention. Figure 5 is a scanning electron microscope (SEM) photograph (2000x) of aluminum nitride granulation using cyclohexanol as an additive according to an embodiment of the present invention. The solid content of the slurry at the start of spray drying is 40 wt%, and the composition of the weight percentages of each component in the slurry is 35 wt% aluminum nitride (AlN) powder, 5 wt% yttrium oxide (Y2O3) powder, and 60 wt% ethyl acetate. Based on the weight of the aluminum nitride (AlN) powder, 1 wt% polyvinyl butyral resin (PVB), 1 wt% fish oil, and 10 wt% cyclohexanol (Cyclohexanol) are added to the slurry. The parameters of the spray drying process are a feed rate of 4.53 kg / hr, a rotating speed of the atomizer of 6000 rpm, an inlet temperature of 95 °C, and an outlet temperature of 65 °C. From the 200x OM photograph in Figure 4 and the 2000x SEM photograph in Figure 5, aluminum nitride powder granulation spray-dried with cyclohexanol as an additive can be observed, and the morphology of its particles all exhibits a perfect spherical shape. It can be observed from the SEM photograph that the particle diameter of one particle is about 90 μm.

[0040] In the embodiment of the present invention, the measured data of the particle size analysis and flow characteristics of aluminum nitride powder granulation using ethylene glycol and cyclohexanol as additives are shown in Table 1 below. The average particle diameter D of aluminum nitride powder granulation with ethylene glycol (Ethylene glycol) as an additive 50 is 65.6 μm, the bulk density is 0.96 g / cm 3 and the angle of repose is 29°. The average particle diameter D of aluminum nitride powder granulation with cyclohexanol (Cyclohexanol) as an additive 50 is 82.6 μm, the bulk density is 1.07 g / cm 3 and the angle of repose is 26°. The measured specifications of commercially available aluminum nitride powder granulation in the market are that the average particle diameter D 50 is 78 μm and the bulk density is 0.99 g / cm 3The angle of repose is 28°. The measured particle size distribution and flow characteristics data of spherical aluminum nitride powder granules produced by the method of the present invention approximate those of commercially produced aluminum nitride powder granules, clearly demonstrating that the aluminum nitride powder granules prepared by the method of the present invention have a good spherical shape and excellent flowability.

[0041] Analysis of particle size and measured flow characteristics of aluminum nitride powder granulation using ethylene glycol and cyclohexanol as additives. [Table 1]

[0042] To maximize the efficiency of the spray drying apparatus and improve its productivity, the solid content of the slurry is increased as much as possible, the spray drying time is shortened, and the yield of powder granulation is increased. However, as the solid content increases, the viscosity of the slurry increases, and excessively high viscosity is detrimental to spray granulation, resulting in the generation of many granulated particles that approximate an ellipse shape, as shown in Figure 6, and making it easier to generate particles with hollow or concave spherical shapes. If the solvent content is too high, the viscosity of the slurry becomes too low, making it difficult to dry and shape the atomized droplets, increasing the humidity of the powder granulation, making the powder more prone to agglomeration, and reducing the yield of powder granulation. Therefore, the present invention designs the ratio and formulation of the solid content of the slurry so that the mixed slurry has an appropriate viscosity, adds an organic alcohol with high surface tension, and controls the spray drying parameters related to the feed rate, atomizer rotation speed, inlet temperature, and outlet temperature to obtain highly fluid spherical aluminum nitride powder that meets the requirements for average particle size distribution.

[0043] In summary, the method for preparing highly fluid spherical aluminum nitride powder according to the present invention involves designing the solid content ratio and formulation of the slurry to match the solid-liquid ratio of the slurry, ensuring that the mixed slurry has an appropriate viscosity, appropriately controlling the rotation speed and feed speed of the sprayer turntable, forming droplets to the required size for atomized particles when atomizing the slurry in a spray dryer, and setting the temperature of the inlet and outlet of the drying tower to an appropriate temperature to uniformly dry the atomized particles from the outside inward, thereby forming regular spherical particles. In this way, highly fluid spherical aluminum nitride powder that meets the requirements for average particle size distribution is obtained. Furthermore, the present invention optimizes the roundness and fluidity of the final spherical powder granulation by adding an organic alcohol with high surface tension, increasing the yield when preparing aluminum nitride ceramic block material by subsequent dry press molding and high-temperature sintering methods, and improving the overall properties.

[0044] The embodiments described above are merely for the purpose of explaining the technical concept and features of the present invention, and are intended to enable those familiar with the aforementioned technical field to understand and implement the content of the present invention, and are not intended to limit the scope of the claims of the present invention. Accordingly, various improvements or modifications having similar effects without departing from the spirit of the present invention shall be included in the claims described below. [Explanation of symbols]

[0045] S101~S105 Step

Claims

1. Step (A) provides aluminum nitride powder, a sintering aid, a dispersant, and a solvent, and performs primary wet ball mill mixing based on a first weight percentage. Step (B) provides an adhesive and an organic alcohol-based additive, which are added to the mixture obtained in step (A) above based on 2% by weight, and a secondary wet ball mill mixing is performed to form a mixed slurry. Step (C) of atomizing the mixed slurry into droplets, Step (D) involves drying the atomized mixed slurry to obtain dried spherical aluminum nitride particles, The dried spherical aluminum nitride particles were collected, and the average particle size distribution D ５０ The particle size is in the range of 60 to 90 μm, and the bulk density is 0.8 to 1.1 g / cm³. ３ A method for preparing highly fluid spherical aluminum nitride powder, comprising the step (E) of obtaining fluid spherical aluminum nitride powder having an angle of repose of less than 30°, wherein the angle of repose is within the range of .

2. The method for preparing highly fluid spherical aluminum nitride powder according to claim 1, characterized in that the aluminum nitride powder in step (A) has a purity of more than 99%, an oxygen content of <1.0 wt%, and an average particle size in the range of 1 to 5 μm; the sintering aid is selected from the group consisting of rare earth element compounds such as yttrium oxide, yttrium fluoride, magnesium oxide, calcium oxide, calcium fluoride, or alkaline earth metal compounds; the dispersant is selected from the group consisting of citric acid, fish oil, polyethyleneimine, triethyl phosphate, polyacrylic acid, or sodium stearate; and the solvent is selected from the group consisting of organic solvents such as anhydrous alcohol, methanol, isopropanol, ethyl acetate, methyl ethyl ketone, and 1-butanol.

3. The method for preparing highly fluid spherical aluminum nitride powder according to claim 1, wherein the first weight percent in step (A) is 29 to 45 wt% of aluminum nitride powder, 1 to 5 wt% of a sintering aid, and 50 to 70 wt% of a solvent, and is converted to 0.1 to 3 wt% of a dispersant based on the weight of the aluminum nitride powder.

4. The method for preparing highly fluid spherical aluminum nitride powder according to claim 1, characterized in that the adhesive in step (B) is selected from the group consisting of polyvinyl butyral resin, acrylic resin, or phenolic resin, and the additive is selected from the group consisting of organic alcohols such as ethylene glycol, cyclopentanol, and cyclohexanol.

5. The method for preparing highly fluid spherical aluminum nitride powder according to claim 1, characterized in that the second weight percent in step (B) is converted to 1 to 10 wt% of adhesive and 3 to 20 wt% of additives based on the weight of the aluminum nitride powder.

6. The method for preparing highly fluid spherical aluminum nitride powder according to claim 1, characterized in that the mixing slurry in step (B) has a viscosity in the range of 100 to 3000 cp.

7. The method for preparing highly fluid spherical aluminum nitride powder according to claim 1, characterized in that steps (C) to (E) are performed using a centrifugal spray dryer, the centrifugal spray dryer having a feed unit, a sprayer turntable, a drying tower, and a bucket.

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