WO2020171471A1 - Method for manufacturing plate-shaped alumina having excellent aspect ratio - Google Patents

Abstract

Disclosed is a method for manufacturing plate-shaped alumina having an excellent aspect ratio. According to one aspect of the present example, provided is a method for manufacturing plate-shaped alumina having a uniform particle size distribution, whereby aluminum hydroxide particles of a desired particle size are easily manufactured and, based thereon, plate-shaped alumina having a uniform particle size distribution is manufactured.

Description

Plate-shaped alumina manufacturing method with excellent angle ratio

The present invention relates to a method for producing a plate-shaped alumina having excellent squareness ratio and less aggregation.

The content described in this section merely provides background information on an embodiment of the present invention and does not constitute the prior art.

Plate-shaped alumina is widely used as various ceramics, abrasives, functional cosmetics, pigments, paints, heat dissipation, separators, or additives for increasing strength.

In the manufacture of such a plate-shaped alumina, conventionally, an aluminum compound, a transition alumina, or a heat-treated aluminum hydroxide after mechanical grinding has been used as the main raw material of the plate-shaped alumina. The alumina compound is obtained by processing aluminum hydroxide in another form, and includes aluminum sulfate, aluminum nitrate, or aluminum chloride. In the conventional process of manufacturing plate-shaped alumina, the alumina content of the raw material itself is lower than 30%, so the yield is low, and air pollutants such as sulfur, nitric acid, or hydrochloric acid are generated during the process. In addition, the conventional plate-shaped alumina manufacturing process has a problem that a separate process of aging is required after the aluminum compound is completely dissolved in an aqueous solution and then gelled by hydrolysis in order to use the aluminum compound.

The process of manufacturing plate-shaped alumina using transitional alumina such as boehmite, delta, beta, or gamma alumina is inconvenient in that pretreatment such as heat treatment or pressurization of aluminum hydroxide is required.

Aluminum hydroxide particles have characteristics that are difficult to grow into thin plate-shaped particles with a good aspect ratio, and even if they are grown in a plate shape, aggregation becomes severe. For this reason, the thickness of the plate-shaped alumina becomes thick and does not have a uniform particle size, and there is a problem that it is insufficient to use the aluminum hydroxide particles as a pigment. In addition, in order for aluminum hydroxide to grow into plate-shaped alumina, the aluminum hydroxide must be subjected to heat treatment and mechanically pulverized for a long time to separate the particle size. Thereafter, aluminum hydroxide can be grown into plate-shaped alumina by heat treatment with a fluorine compound and a large amount of flux by a mineralizing method.

At this time, during the pulverization and heat treatment of aluminum hydroxide, as a large amount of flux is added, the volume of the flux increases in proportion to the amount of flux during heat treatment. For this reason, a crucible used during heat treatment is often damaged due to an increase in the volume of the flux. In addition, after the heat treatment reaction, the plate-shaped alumina, which has undergone natural cooling, forms hardly agglomerated crystals due to the melted flux, and is deposited on the crucible wall and is not separated.

An embodiment of the present invention is to provide a method for manufacturing a plate-shaped alumina having a uniform particle size distribution without separate particle size separation based on the simple manufacturing of aluminum hydroxide particles having a desired particle size by using aluminum hydroxide as a raw material. .

In one embodiment of the present invention, by depositing aluminum hydroxide particles having a uniform size in a caustic soda solution and growing them into plate-shaped alumina particles having a uniform size, a high refractive index, high saturation and high luminance pearl luster can be provided when TiO2 is coated. One purpose is to provide a method for manufacturing plate-shaped alumina.

In addition, one embodiment of the present invention, by reducing the amount of flux added compared to the prior art, prevents crucible breakage in the heat treatment process in which the aluminum hydroxide particles grow in the form of plate-shaped alumina, and the plate-shaped alumina can be easily separated from the crucible. There is one object to provide a method for manufacturing alumina plate.

According to one aspect of this embodiment, the process of obtaining a solution by dissolving aluminum hydroxide in a caustic soda solution so that caustic soda and aluminum hydroxide are in a predetermined ratio (Al ₂ O ₃ /Na ₂ CO ₃ ), and seeding the solution (Seed) is added and stirred to precipitate aluminum hydroxide until the ratio of the caustic soda and aluminum hydroxide reaches a preset reference value to obtain a mixed solution, and a molten salt and a dispersant used as a flux are added to the mixed solution to mix. After the mixing process and the flux mixing process, a neutralization process of generating a neutralization solution by adding a neutralizing agent to the mixed solution, a drying process of drying the neutralization solution to produce an aluminum hydroxide compound, heat treatment of the aluminum hydroxide compound, and cooling A heat treatment process for generating a powder including plate-shaped alumina particles, a filtration process for producing a cake by filtering particles and fluxes having a predetermined size included in the plate-shaped alumina particles, and a filtration process for forming a cake, and converting the cake into a slurry, A decomposition process of decomposing at least one plate-shaped alumina particle or plate-shaped alumina twin aggregated in a slurry), and a particle removal process of drying the slurry and removing the plate-shaped alumina particles having a predetermined particle size from the dried slurry. It provides a plate-shaped alumina manufacturing method characterized by.

According to an aspect of this embodiment, the process of obtaining the solution is characterized in that 200 to 300 g/L (Na ₂ CO ₃ ) of caustic soda and aluminum hydroxide having a purity of 95% or more are used.

According to an aspect of the present embodiment, a predetermined ratio (Al ₂ O ₃ /Na ₂ CO ₃ ) of the caustic soda and aluminum hydroxide is 0.6 to 0.8, and the aluminum hydroxide is supersaturated.

According to an aspect of the present embodiment, a predetermined reference value in the process of obtaining the mixed solution is less than 0.3.

According to an aspect of the present embodiment, the heat treatment process is characterized in that the aluminum hydroxide compound is maintained for 1 to 4 hours in the first temperature section, the second temperature section, and the third temperature section, respectively, without additional gas addition.

As described above, according to one aspect of the present invention, aluminum hydroxide particles having a desired particle size are easily manufactured using general aluminum hydroxide (Wet-Al(OH) ₃ ) as a raw material, and based on this, a plate having a uniform particle size distribution There is an advantage that alumina can be produced.

According to an aspect of the present invention, aluminum hydroxide particles having a uniform size are deposited to grow into plate-shaped alumina particles having a uniform size, so that when TiO2 is coated, a high refractive index, high saturation, and high luminance pearl luster are obtained.

In addition, according to an aspect of the present invention, by reducing the amount of flux added compared to the prior art, breakage of the crucible is prevented and the plate-shaped alumina is easily separated from the crucible in the heat treatment process in which the aluminum hydroxide particles are grown in the form of plate-shaped alumina. There is an advantage.

1 is a flow chart showing a method for manufacturing a plate-like alumina according to an embodiment of the present invention.

2 is a view showing a result of observation under a scanning electron microscope of a plate-shaped alumina powder according to an embodiment of the present invention.

3 is a graph showing a particle size analysis result of a plate-shaped alumina powder according to an embodiment of the present invention.

4 is a graph showing the results of XRD (X-Ray Diffraction) analysis of the plate-shaped alumina powder according to an embodiment of the present invention.

In the present invention, various changes may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to a specific embodiment, it is to be understood to include all changes, equivalents, or substitutes included in the spirit and scope of the present invention. In describing each drawing, similar reference numerals have been used for similar elements.

Terms such as first, second, A, and B may be used to describe various elements, but the elements should not be limited by the terms. These terms are used only for the purpose of distinguishing one component from another component. For example, without departing from the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. The term and/or includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being "connected" or "connected" to another component, it is understood that it may be directly connected or connected to the other component, but other components may exist in the middle. Should be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component in the middle.

The terms used in the present application are used only to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "include" or "have" should be understood as not precluding the possibility of existence or addition of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification. .

Unless otherwise defined, all terms, including technical or scientific terms, used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in this application. Does not.

In addition, each configuration, process, process, or method included in each embodiment of the present invention may be shared within a range not technically contradicting each other.

1 is a flow chart showing a method for manufacturing a plate-like alumina according to an embodiment of the present invention.

Aluminum hydroxide is dissolved in caustic soda (S105).

200~300g/L of caustic soda solution and general aluminum hydroxide (Wet-Al(OH) ₃ ) having a purity of 95% or more are mixed so that aluminum hydroxide becomes supersaturated. If seeds are added in the future in the state of aluminum hydroxide supersaturation, aluminum hydroxide particles easily precipitate, so the ratio of alumina and caustic soda (Al ₂ O ₃ /Na ₂ CO ₃ , hereinafter abbreviated as A/C) is 0.6 It is preferable that aluminum hydroxide and caustic soda are mixed so that it is ~0.8. When caustic soda and aluminum hydroxide are mixed at an A/C ratio of 0.8 or more, aluminum hydroxide particles are wasted because aluminum hydroxide is not easily dissolved in caustic soda. On the contrary, when caustic soda and aluminum hydroxide are mixed at an A/C ratio of 0.6 or less, aluminum hydroxide saturation is lowered, so that aluminum hydroxide does not precipitate easily.

A mixture of caustic soda and general aluminum hydroxide (Wet-Al(OH) ₃ ) is completely dissolved by airtight heating for 3 to 4 hours under a pressure of 4 to 6 atmospheres and the temperature of the solution is raised to 150°C. Sodium aluminate supersaturated solution. After that, the temperature of the sodium aluminate supersaturated solution is lowered to 60 to 70°C.

As a seed is added to the sodium aluminate supersaturated solution, aluminum hydroxide is precipitated from the solution (S110).

A seed is added to the sodium aluminate supersaturated solution (hereinafter referred to as'solution solution'). The seed includes aluminum sulfate, aluminum hydroxide of 0.1 to 1.0 μm, or alumina GEL (aluminum ammonium sulfate, sodium aluminum sulfate), but is not limited thereto. When the seed is added to the solution and mixed, the dissolved aluminum hydroxide adheres to the seed, grows into particles, and precipitates. At this time, the seed serves as a nucleus of aluminum hydroxide particle growth. If the seeds are evenly dispersed in the solution and not mixed, aluminum hydroxide may aggregate and precipitate, so it is important to evenly disperse the seeds in the solution. Accordingly, stirring is performed on the solution to which the seed is added so that the seeds are evenly dispersed in the solution to allow aluminum hydroxide having a size of 1 to 10 μm to precipitate. Aluminum hydroxide adheres to the seed, grows into particles, and takes an average of 2 to 3 days to precipitate. In the case of precipitation for 2 to 3 days or longer, most of the aluminum hydroxide is precipitated and almost no precipitation occurs. Therefore, the stirring time is preferably 2 to 3 days. And the amount of the seed to be added is preferably 5 to 10% of the amount of aluminum hydroxide added. When the amount of seeds added is too small compared to the amount of aluminum hydroxide, the precipitation of aluminum hydroxide does not occur easily. Conversely, when the amount of the seed exceeds 10% of the amount of aluminum hydroxide, the aluminum hydroxide particles to be precipitated become too fine, and there is a concern that plate-shaped alumina having a small particle size may be generated from the aluminum hydroxide particles later.

When aluminum hydroxide having a size of 1 to 10 μm is precipitated to form particles, the A/C ratio of the solution is gradually lowered in proportion to the generated particles. At this time, the precipitation of aluminum hydroxide proceeds until the A/C ratio of the solution becomes less than 0.3. If the A/C ratio of the solution is 0.3 or more, aluminum hydroxide that can be precipitated in the solution remains, so that the A/C of the solution can be precipitated as much as possible from 1 to 10 μm in size. The precipitation of aluminum hydroxide proceeds until the ratio is less than 0.3. A mixed solution in which aluminum hydroxide particles are formed in the solution is obtained by precipitation of aluminum hydroxide.

As a flux, a molten salt and a dispersion are sequentially added to the mixture in which aluminum hydroxide is deposited, and then mixed (S115).

Aluminum hydroxide precipitates and molten salt is added as a flux to the mixed liquid present as particles. The molten salt plays a role in growing the aluminum hydroxide particles in a plate shape during the subsequent heat treatment process. The molten salt includes at least one of sodium sulfate, sodium carbonate, sodium hydrogen carbonate, potassium sulfate, potassium carbonate, potassium chloride, magnesium sulfate, sodium chloride, calcium sulfate and calcium carbonate. The molten salt is added in an amount of 40 to 80% based on the amount of aluminum hydroxide dissolved in the solution. For example, when 100 g of aluminum hydroxide is dissolved in the solution, the molten salt may be added by 50 g of sodium sulfate, or 50 g and 25 g of sodium sulfate and sodium carbonate, respectively. After the dissolved salt is added to the solution as above, the dispersant is added by 0.5 to 2% based on the amount of aluminum hydroxide dissolved in the solution so that the aluminum hydroxide particles can be dispersed. After the dispersant is added to the solution, stirring is performed for 3 to 5 hours. As the dispersant, sodium hexametaphosphate, monosodium phosphate, dibasic sodium phosphate, and trisodium phosphate may be used. The mixed solution to which the molten salt and dispersant are added has a strong alkali of pH 12-14 by the caustic soda in the mixed solution.

In the conventional aluminum hydroxide manufacturing process using general aluminum hydroxide, after depositing aluminum hydroxide, caustic soda, which is a waste liquid, is separated and discarded, but the present invention utilizes caustic soda as a mother liquor (Prognant Liquor) for dissolving molten salt. When caustic soda is used as the mother liquor, there is no need to add additional water to dissolve the molten salt. In addition, since the added flux is well deposited on the surface of aluminum hydroxide in the solution, the flux may be added in an amount of 60 to 70% less than that of a conventional plate-shaped alumina manufacturing process that adds 3 to 7 times the flux compared to aluminum hydroxide.

In order to neutralize the pH of the mixture in which the flux is mixed (hereinafter abbreviated as a flux mixture), a neutralizing agent is added to the flux mixture (S120).

As described above, a neutralizing agent is added to the flux mixture having a strong alkali of pH 12 including caustic soda to neutralize the pH of the flux mixture to 6-8. In this way, the pH of the flux mixture is neutralized, thereby creating an environment in which particles can grow. At this time, sulfuric acid, hydrochloric acid, or nitric acid having a high concentration of 90% or more may be used as the neutralizing agent. If the concentration of the neutralizing agent is too low, the production volume may increase and the drying time may increase.

The neutralized liquid is dried (S125).

The neutralization solution obtained by neutralizing the pH of the flux mixture is dried. Thus, the flux mixture is produced from the aluminum hydroxide compound. For drying the neutralized liquid, a hot air dryer or a distillation dryer may be used to dry the neutralized liquid within a temperature range of 110 to 200°C. Drying may proceed until the moisture in the neutralized solution is within 1%. If the neutralization liquid is not dried, moisture particles may cause agglomeration of plate-like alumina and may lead to abnormal particle growth. Thus, complete drying of the neutralized liquid proceeds.

The aluminum hydroxide compound is heat-treated (S130).

The aluminum hydroxide compound is pulverized into a powder having a diameter of 1 cm or less. During pulverization, a roll mill or a ball mill may be used as a crusher. Even if the aluminum hydroxide compound is not made into a powder, there is no problem in heat treatment, but if the aluminum hydroxide compound is in a powder form, a large amount can be heat treated at once, so the operation becomes easy, and heat can be applied evenly to the aluminum hydroxide compound. The powdered aluminum hydroxide compound is placed in a ceramic crucible and heat-treated in a general atmospheric atmosphere. In the heat treatment process of the aluminum hydroxide compound, the volume of the flux contained in the aluminum hydroxide compound is increased by the heat treatment, and the ceramic crucible is often damaged. The increasing flux volume is proportional to the amount of flux added to the aluminum hydroxide compound. At this time, compared to the conventional plate-shaped alumina manufacturing process in which a flux of 300 g to 700 g is added and heat-treated per 100 g of aluminum hydroxide, the plate-shaped alumina manufacturing process of the present invention adds 60 to 70% of the flux, so the volume of the flux Does not increase significantly. Accordingly, an embodiment of the present invention can prevent damage to a heat treatment vessel such as a ceramic crucible in the heat treatment process of the aluminum hydroxide compound.

When the powdered aluminum hydroxide compound is heat-treated, the aluminum hydroxide compound is grown in the form of plate-shaped alumina. In this case, the heat treatment may be performed for 1 to 4 hours by dividing a temperature section into a first temperature section, a second temperature section, and a third temperature section. And each temperature section can be formed by increasing the temperature by 3 ~ 5 ℃. This is because the melting temperature of each of the fluxes contained in the aluminum hydroxide compound is different from each other, so that the heat treatment is divided into several temperature sections to melt each flux. Here, the first temperature section may be 200 to 300°C, the second temperature section may be 700 to 900°C, and the third temperature section may be 1100 to 1300°C. In more detail, in the first temperature section, crystal water and water molecules inside the aluminum hydroxide contained in the aluminum hydroxide compound are evaporated, and in the second temperature section, the flux adheres to the aluminum hydroxide particles as the flux melts. And in the third temperature section, aluminum hydroxide particles grow in the form of plate-shaped alumina by the flux. The flux is melted at each temperature section and adheres to the aluminum hydroxide particles, and the particle growth is controlled so that the aluminum hydroxide particles grow only in the horizontal axis direction so that the aluminum hydroxide can grow in the form of plate-shaped alumina.

When the grown plate-shaped alumina is cooled, agglomerated powder containing plate-shaped alumina particles is formed.

The flux and fine particles are removed by filtration (S135).

A liquid such as hot water is added to the agglomerated powder including plate-shaped alumina particles, and the agglomerated plate-shaped alumina powder and the heat treatment vessel are separated. The agglomerated powder is formed by heat-treating and cooling an aluminum hydroxide compound, and the agglomeration strength of the agglomerated powder including plate-shaped alumina particles is proportional to the amount of flux added to the aluminum hydroxide compound. At this time, since the sheet-shaped alumina manufacturing process of the present invention adds 60 to 70% less flux than the conventional sheet-shaped alumina manufacturing process, the cohesive strength of the agglomerated powder is weakened. Therefore, since the agglomerated powder according to an embodiment of the present invention is more easily dissolved in a liquid such as hot water, the agglomerated powder can be easily separated from a heat treatment container such as a ceramic crucible. In this case, when hot water is used as a liquid, the temperature of the hot water is preferably 60 to 100° C. that can dissolve the water-soluble flux. When the plate-shaped alumina powder to which the liquid is added is stirred for 2 to 3 hours, the plate-shaped alumina particles are dispersed in a mixed liquid state. The plate-shaped alumina particles contain a water-soluble flux that is easily soluble in water and fine particles having a particle size of 5 μm or less, which have poor gloss among the plate-shaped alumina particles. In order to remove such water-soluble flux and fine particles, the mixed solution is filtered using a filtering device. When the mixed solution is filtered with a filtration device, a cake from which water-soluble flux and fine particles are removed is produced. As one of the filtering devices, a filter press having a porosity of 1 to 5 μm can be used.

The cake becomes slurry, and the plate-shaped alumina particles and twins agglomerated in the slurry are decomposed (S140).

Some water is added to the cake and stirred, so that the cake is slurried. Thereafter, the slurry is put into a grinder, and the grinder decomposes the twin and agglomerated platy alumina particles in the slurry for a predetermined time. The preset disintegration time may be suitable for 1 hour to 1 hour 30 minutes. This is because if the plate-shaped alumina particles of the slurry are decomposed for a predetermined time or longer, the plate-shaped alumina particles are broken, and if the plate-shaped alumina particles of the slurry are decomposed within a predetermined time or less, there is no effect of improving the aggregated particles and twin crystals.

Here, twin crystals are grown by crossing plate-shaped alumina particles. Since twin crystal particles give a rough feeling when used as a pigment, it is preferable to separate the plate-shaped alumina particles grown by crossing the twin crystals. As the grinder, a wet bead mill using a zirconia bead having a diameter of 0.3 to 1.0 Φ may be used. Wet bead mills can break down twins and some agglomerated particles. In addition, the plate-shaped particles decomposed by a wet bead mill have significantly fewer twins, and the flowability and dispersibility of the particles are remarkably good.

The slurry is dried and plate-like particles of a predetermined particle size are removed (S145).

The slurry is dried and the water contained in the slurry may cause the plate-shaped alumina particles to reaggregate. To prevent this, a commercial wet-dry cake dryer may be used. Wet and dry cake dryers dry the slurry at an outlet temperature of 130~250℃. When the slurry is dried with a wet-dry cake dryer, plate-shaped alumina having a certain particle size is produced. When drying the slurry, since various dryers capable of preventing agglomeration of the slurry can be used, the dryer is not limited to a wet-dry cake dryer.

After drying the slurry, plate-shaped alumina fine particles having a particle size of 5 μm or less are removed from the produced plate-shaped alumina by a filtration device. A bag filter may be used as a filtering device, but is not limited thereto. After the fine particles are removed by the filtration device, fine particles of 5 μm or less and large particles of 50 μm or more, which adversely affect pearl gloss, are removed from the dried plate-shaped alumina product. An air classifier may be used to remove fine particles of 5 μm or less and large particles of 50 μm or more. The air classifier puts air of a certain pressure to subside heavy things and floats light ones to collect each. Therefore, the air classifier can collect and remove fine particles of 5 μm or less and large particles of 50 μm or more, respectively. In addition, the air classifier can be used by separately collecting only the products of the desired particle size from the plate-shaped alumina products having a particle size of 5-50㎛.

Through the manufacturing method of the above process, excellent quality plate-shaped alumina having a narrow particle size distribution of 5 to 50 μm, a thickness of 0.1 to 0.5 μm, and an angle ratio of 50 to 200 can be manufactured.

<Experimental Example 1>

(1) Preparation of sodium aluminate solution

66.2 g of general aluminum hydroxide (Wet-Al(OH) ₃ ), 84.5 g of 50% caustic soda aqueous solution, and 94.5 ml of ultrapure water are stirred in a 500 ml pressure vessel, the vessel is 2 to 3 hours under a temperature of 150°C and a pressure of 5 atmospheres While exposed. Accordingly, aluminum hydroxide is completely dissolved in caustic soda to prepare a 200 ml sodium aluminate solution having a caustic soda (Na ₂ CO ₃ ) concentration of 280 g/L and A/C of 0.75.

(2) SEED addition and aluminum hydroxide precipitation

The temperature of the prepared sodium aluminate solution is lowered to 60°C or less. 6.62 g of aluminum hydroxide having a particle size of 0.3 μm was added to the sodium aluminate solution, followed by stirring, and precipitation proceeds for 3 days. A/C after the completion of precipitation was measured to be 0.25, and as a result of particle size analysis, aluminum hydroxide of 1 μm was deposited on the sodium aluminate solution.

(3) Flux mixing and neutralization solution preparation

20 g of sodium sulfate and 15 g of sodium carbonate were added to the sodium aluminate solution in which aluminum hydroxide was deposited, and 0.5 g of sodium hexametaphosphate was added, followed by stirring for 1 hour. Since it has the pH of the solution 14, sulfuric acid having a high concentration of 95% is added and the pH is neutralized to 7.

(4) Drying of neutralization liquid

The liquid neutralizing solution prepared by mixing the flux and neutralizing the pH is put in a stainless tray and put into a box-type general dryer. And the dryer heats the liquid neutralized liquid at 110°C for 48 hours. Accordingly, an aluminum hydroxide compound in which the liquid neutralization liquid is completely dried is produced.

(5) grinding and heat treatment

The aluminum hydroxide compound is put into a roll mill and pulverized into small powders with a diameter of 1 cm or less. The pulverized and powdered aluminum hydroxide compound is put in a 1L alumina crucible, and the alumina crucible is put in a box-type general electric furnace. Box-type general electric furnace heated up to 250℃ for 3 hours and maintained for 3 hours, raised to 850℃ for 5℃/min for 2 hours, increased to 1250℃ for 5℃/min and maintained for 4 hours, and then aluminum hydroxide at room temperature Cool the compound naturally.

(6) Obtaining plate-shaped alumina

By heat treatment, the powdered aluminum hydroxide compound is grown into plate-shaped alumina. At this time, since the plate-shaped alumina is still attached to the alumina crucible, a liquid is added and the plate-shaped alumina is separated from the alumina crucible. Then, the separated plate-like alumina passes through a filter to remove the water-soluble flux mixed with the liquid. The plate-shaped alumina from which the flux has been removed is dispersed by a sulfuric acid solution having a concentration of 10% to remove agglomerated plate-shaped alumina particles and salts remaining on the particle surface. Thereafter, when the plate-shaped alumina from which the flux and salt have been removed is dried at 110° C., 47 g of plate-shaped alumina having an excellent angle ratio of 50 to 200 and good dispersibility in water is produced. The resulting plate-like alumina has a particle size of 5 to 50 μm and a thickness of 0.1 to 0.5 μm.

<Experimental Example 2>

(1) SEED addition

It was prepared in the same manner as in Experimental Example 1. However, unlike Experimental Example 1, in Experimental Example 2, the seed (SEED) was changed to 25.4 g of aluminum sulfate and added. The plate-shaped alumina prepared according to Experimental Example 2 has an angle ratio of 50 to 190, and has good dispersibility in water. The plate-shaped alumina of Example 2 has a particle size of 5 to 51 μm and a thickness of 0.1 to 0.5 μm.

<Experimental Example 3>

(1) SEED addition

It was prepared in the same manner as in Experimental Example 1. However, unlike Experimental Example 1, Experimental Example 3 was changed to 20g of aluminum ammonium sulfate GEL prepared directly from the seed (SEED). Aluminum ammonium sulfate GEL is prepared in a GEL state by completely dissolving aluminum hydroxide in sulfuric acid and neutralizing it with aqueous ammonia. The plate-shaped alumina prepared by Experimental Example 3 had an angle ratio of 50 to 210, which was superior to Experimental Examples 1 and 2, and showed good dispersibility in water.

<Experimental Example 4>

(1) Flux mixing and neutralization solution preparation

It was prepared in the same manner as in Experimental Example 1. However, unlike Experimental Example 1, in Experimental Example 4, 20 g of potassium carbonate and 15 g of sodium carbonate were added to the sodium aluminate solution in which aluminum hydroxide was deposited, and 0.5 g of sodium hexametaphosphate was added and stirred for 1 hour. The plate-shaped alumina prepared according to Experimental Example 4 had an excellent angle ratio of 45 to 180, and showed good dispersibility in water.

<Comparative Example 1>

(1) SEED addition

It was prepared in the same manner as in Experimental Example 1. However, unlike Experimental Example 1, in Comparative Example 1, the SEED was changed to 6.62g of 20㎛ aluminum hydroxide. The plate-shaped alumina prepared according to Comparative Example 1 had a thick particle thickness, which was not good at an angle ratio of 10 to 130, and showed poor dispersibility.

<Comparative Example 2>

(1) Flux mixing and neutralization solution preparation

It was prepared in the same manner as in Experimental Example 1. However, unlike Experimental Example 1, in Comparative Example 2, 200 g of sodium sulfate and 100 g of sodium carbonate were added to the sodium aluminate solution in which aluminum hydroxide was deposited, and 0.5 g of sodium hexametaphosphate was added and stirred for 1 hour. The plate-shaped alumina prepared by Comparative Example 2 had severe aggregation and was not well separated from the crucible, and a large amount of twin crystals and large particles of 100 μm or more were generated, resulting in poor dispersibility.

The table below shows the particle size and angle ratio of the plate-shaped alumina prepared by each of the experimental examples and comparative examples.

Referring to the table above, as in Comparative Example 1, when aluminum oxide having a particle size of 0.1 to 1.0 μm or more is used as a seed, plate-shaped alumina having an irregular particle size distribution and poor particles is produced. Therefore, when a seed is added to the sodium aluminate supersaturated solution, it is preferable to use aluminum hydroxide having a size of 0.1 to 1.0 μm as the seed.

Referring to the table above, as in Comparative Example 2, when the molten salt is excessively added to the mixed solution present as particles due to the precipitation of aluminum hydroxide, plate alumina having an irregular particle size distribution of 1 to 135 μm and poor particles is prepared. Therefore, when aluminum hydroxide is precipitated and molten salt is added to the mixed solution present as particles, the molten salt is preferably added to the sodium aluminate supersaturated solution by 40 to 80% based on the amount of dissolved aluminum hydroxide.

FIG. 2 is a view showing a result of observation with a scanning electron microscope of a plate-shaped alumina powder according to an embodiment of the present invention, and FIG. 3 is a graph showing a particle size analysis result of a plate-shaped alumina powder according to an embodiment of the present invention. 4 is a graph showing the results of XRD (X-Ray Diffraction) analysis of the plate-shaped alumina powder according to an embodiment of the present invention.

2 to 4, the plate-shaped alumina prepared according to an embodiment of the present invention has a particle size in the range of 5 to 50 μm, and is shown to have an average particle size of 20 μm.

In FIG. 1, each process is described as sequentially executing, but this is merely illustrative of the technical idea of an embodiment of the present invention. In other words, a person of ordinary skill in the art to which an embodiment of the present invention belongs can change the order of the processes described in each drawing without departing from the essential characteristics of the embodiment of the present invention, or perform one or more of the processes. Since the process is executed in parallel and can be applied by various modifications and modifications, FIG. 1 is not limited to a time series order.

Meanwhile, the processes shown in FIG. 1 can be implemented as computer-readable codes on a computer-readable recording medium. The computer-readable recording medium includes all types of recording devices that store data that can be read by a computer system. That is, the computer-readable recording media include storage media such as magnetic storage media (eg, ROM, floppy disk, hard disk, etc.) and optical reading media (eg, CD-ROM, DVD, etc.). In addition, the computer-readable recording medium can be distributed over a computer system connected through a network to store and execute computer-readable codes in a distributed manner.

The above description is merely illustrative of the technical idea of the present embodiment, and those of ordinary skill in the technical field to which the present embodiment belongs will be able to make various modifications and variations without departing from the essential characteristics of the present embodiment. Accordingly, the present exemplary embodiments are not intended to limit the technical idea of the present exemplary embodiment, but are illustrative, and the scope of the technical idea of the present exemplary embodiment is not limited by these exemplary embodiments. The scope of protection of this embodiment should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present embodiment.

CROSS-REFERENCE TO RELATED APPLICATION

*This patent application claims priority in accordance with Article 119(a) of the U.S. Patent Law (35 USC § 119(a)) for patent application No. 10-2019-0021024 filed in Korea on February 22, 2019, All of its contents are incorporated by reference into this patent application. In addition, if this patent application claims priority for countries other than the United States for the same reason as above, all the contents are incorporated into this patent application as references.

Claims (5)

1. A process of dissolving aluminum hydroxide in a caustic soda solution so that the caustic soda and aluminum hydroxide have a predetermined ratio (Al ₂ O ₃ /Na ₂ CO ₃ ) to obtain a solution;

   Adding a seed to the solution and stirring to obtain a mixture solution by depositing aluminum hydroxide until the caustic soda and aluminum hydroxide ratio (Al ₂ O ₃ /Na ₂ CO ₃ ) reaches a preset reference value;

   A flux mixing process of adding and mixing a molten salt used as a flux and a dispersant to the mixed solution;

   After the flux mixing process, a neutralization process of adding a neutralizing agent to the mixed solution to generate a neutralizing solution;

   A drying process of drying the neutralized liquid to produce an aluminum hydroxide compound;

   A heat treatment process of heat-treating the aluminum hydroxide compound and then cooling to generate a powder including plate-shaped alumina particles;

   A filtration process of forming a cake by filtering particles having a predetermined size and a flux contained in the plate-shaped alumina particles;

   A decomposition process of converting the cake into a slurry and decomposing at least one plate-shaped alumina particle or plate-shaped alumina twin aggregated in the slurry; And

   Particle removal process of drying the slurry and removing plate-shaped alumina particles having a predetermined particle size from the dried slurry

   Plate-shaped alumina manufacturing method, characterized in that.
2. The method of claim 1,

   The process of obtaining the solution,

   Plate-shaped alumina manufacturing method, characterized in that using 200-300 g/L of caustic soda and aluminum hydroxide having a purity of 95% or more.
3. The method of claim 1,

   Plate-shaped alumina manufacturing method, characterized in that a predetermined ratio of the caustic soda and aluminum hydroxide (Al ₂ O ₃ /Na ₂ CO ₃ ) is 0.6 to 0.8.
4. The method of claim 1,

   Plate-shaped alumina manufacturing method, characterized in that the preset reference value in the process of obtaining the mixed solution is less than 0.3
5. The method of claim 1,

   The heat treatment process,

   Plate-shaped alumina manufacturing method, characterized in that the aluminum hydroxide compound is maintained for 1 to 4 hours in the first temperature section, the second temperature section, and the third temperature section, respectively, without adding a separate gas.

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