Boehmite and method for producing the same

Abstract

To provide boehmite in which a polymer dispersant is adhered or bonded to a particle surface and which does not exhibit dilatancy and is excellent in dispersibility. To provide a method for producing boehmite by adding a dispersant to a slurry of aluminum hydroxide and water and subjecting the slurry to hydrothermal treatment, by which boehmite not exhibiting dilatancy and excellent in dispersibility can efficiently be produced.SOLUTION: The present invention relates to boehmite in which a polymer dispersing agent is attached or bonded to surfaces of particles of the boehmite, the boehmite having a carbon content of 0.01% by weight to 0.17% by weight, an isoelectric point of pH2. 9 to 6.7, and exhibiting no dilatancy. The present invention relates to a method for producing the boehmite, including subjecting a slurry containing aluminum hydroxide, a polymer dispersant in an amount of 0.03% by weight to less than 1% by weight based on the weight of the aluminum hydroxide, and water to a hydrothermal treatment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to boehmite having excellent dispersibility and no dilatancy, in which a polymer dispersant adheres to or bonds to the particle surface, and to a method for producing the boehmite, which comprises adding a dispersant to a slurry of aluminum hydroxide and water and subjecting the slurry to hydrothermal treatment. [Background technology]

[0002] Boehmite, alumina monohydrate (AlO(OH)), is a versatile inorganic material used as a filler, reinforcing material, flame retardant, luminescent material, fireproof material, thickener, etc. It is also used as a catalyst support, an electrically conductive filler base material, a refractory material, a raw material for high-purity alumina, a raw material for sinterable alumina, and a raw material for fluorescent materials. Boehmite is produced by various methods, but the most common method is to hydrothermally treat a slurry of aluminum hydroxide and water. In this production method, a dispersant is sometimes added to the slurry to obtain boehmite with high dispersibility and excellent fillability in resins, etc. As an example of such a technique, Patent Document 1 provides a method for forming a crystalline boehmite product, the method comprising the steps of: preparing an aqueous slurry by mixing together water, a large aluminum oxide precursor, a highly dispersible boehmite grade, and, optionally, a dispersant; adjusting the pH of the slurry to be between about 8.0 and about 12.0; heating the slurry to a temperature between 120°C and 250°C for a time period of about 1.0 hour to about 24 hours; recovering the slurry to form a wet cake; and drying the wet cake to obtain the crystalline boehmite product, wherein the crystalline boehmite product exhibits an average particle size (d50) of less than 7,000 nanometers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2018-503583 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-described method for producing boehmite, in which a dispersant is added to a slurry of aluminum hydroxide and water and then the slurry is subjected to hydrothermal treatment, boehmite may not be produced, or the produced boehmite may exhibit dilatancy, which may reduce the handleability of the boehmite during production or use.

[0005] The present invention has been made in view of the above circumstances, and aims to provide boehmite that has excellent dispersibility and does not exhibit dilatancy, in which a polymer dispersant adheres to or bonds to the particle surface. Another aim of the present invention is to provide a method for producing boehmite that is less restricted by the weight ratio of water to aluminum hydroxide (hereinafter referred to as "water ratio") and that involves adding a dispersant to a slurry of aluminum hydroxide and water and subjecting the resulting mixture to hydrothermal treatment, and that can efficiently produce the boehmite. [Means for solving the problem]

[0006] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention. Specifically, the present invention relates to boehmite having a polymer dispersant attached to or bonded to the particle surface, characterized in that the boehmite has a carbon content of 0.01% by weight to 0.17% by weight, an isoelectric point of pH 2.9 to 6.7, and does not exhibit dilatancy (claim 1).

[0007] In the invention described in claim 1 above, the aspect ratio of the boehmite is preferably 2.2 to 55.0 (claim 2). Also, in the invention described in claim 1 above, the average major axis of the boehmite is preferably 0.6 μm to 7.4 μm (claim 3).

[0008] In each of the inventions described in claims 1 to 3 above, the polymer dispersant is preferably at least one selected from the group consisting of polyacrylic acid, sodium polyacrylate, ammonium polyacrylate, polystyrene sulfonic acid, sodium polystyrene sulfonate, sodium naphthylene sulfonate, carboxymethyl cellulose, polyethyleneimine, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, and polyvinyl porlidone (claim 4).

[0009] The present invention relates to a method for producing boehmite according to each of the inventions described in claims 1 to 3, characterized in that a slurry of aluminum hydroxide, a polymer dispersant having a loading ratio of 0.03 to less than 1% by weight relative to the weight of the aluminum hydroxide, and water is hydrothermally treated (claim 5). In the invention described in claim 5, the average particle size (d50) of the aluminum hydroxide is preferably 0.2 μm to 12 μm (claim 6). In the invention described in claim 5, the polymer dispersant is preferably at least one selected from the group consisting of polyacrylic acid, sodium polyacrylate, ammonium polyacrylate, polystyrene sulfonic acid, sodium polystyrene sulfonate, sodium naphthylene sulfonate, carboxymethyl cellulose, polyethyleneimine, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, and polyvinyl porlidone (claim 7).

[0010] In the invention described in claim 5 above, a particle morphology control agent may be added to the slurry (claim 8). In the invention described in claim 8, the addition rate of the particle morphology control agent relative to the weight of aluminum hydroxide is preferably 0.1% by weight to 20% by weight (claim 9). Furthermore, in the invention described in claim 8, the polymer dispersant is preferably at least one selected from the group consisting of polyacrylic acid, sodium polyacrylate, ammonium polyacrylate, polystyrene sulfonic acid, sodium polystyrene sulfonate, sodium naphthylene sulfonate, carboxymethyl cellulose, polyethyleneimine, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, and polyvinyl porlidone (claim 10). [Effects of the Invention]

[0011] The boehmite of the present invention does not exhibit dilatancy, so handling properties are not impaired during production or use of the boehmite. Furthermore, the boehmite of the present invention has excellent dispersibility and is less likely to form agglomerates, so it has excellent packing properties for filling into a packed object.

[0012] The method for producing boehmite of the present invention can produce boehmite that does not exhibit dilatancy and has excellent dispersibility. Furthermore, the method for producing boehmite of the present invention can efficiently produce the boehmite even under conditions of a low water ratio, and is expected to contribute to decarbonization by increasing productivity. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a scanning electron microscope image (hereinafter referred to as "SEM image") of the plate-like boehmite of Example 1. [Figure 2] 1 is an SEM image of the plate-like boehmite of Example 2. [Figure 3] 1 is an SEM image of the plate-like boehmite of Example 3. [Figure 4] 1 is an SEM image of the plate-like boehmite of Example 4. [Figure 5]1 is an SEM image of the scaly boehmite of Example 5. [Figure 6] 1 is an SEM image of the plate-like boehmite of Example 6. [Figure 7] 1 is an SEM image of the plate-like boehmite of Example 7. [Figure 8] 1 is an SEM image of the plate-like boehmite of Example 8. [Figure 9] 1 is an SEM image of the scaly boehmite of Example 9. [Figure 10] 1A and 1B are diagrams illustrating the major and minor diameters of various forms of boehmite particles, (a) a diagram illustrating the major and minor diameters of plate-like boehmite, and (b) a diagram illustrating the major and minor diameters of scaly boehmite. DETAILED DESCRIPTION OF THE INVENTION

[0014] The boehmite of the present invention has excellent dispersibility and does not exhibit dilatancy, with a polymeric dispersant adhering or bonding to the particle surface. Examples of the polymeric dispersant include anionic polymeric dispersants such as polyacrylic acid, sodium polyacrylate, ammonium polyacrylate, polymaleic acid, polyfumaric acid, polymethacrylic acid, polycrotonic acid, polyitaconic acid, polystyrene sulfonic acid, sodium polystyrene sulfonate, sodium naphthylene sulfonate, polyvinylphosphonic acid, styrene-maleic anhydride copolymer, and carboxymethyl cellulose, as well as polymers, copolymers, and salts of carboxylic acids, sulfonic acids, and phosphonic acids. Examples of cationic polymeric dispersants include polyethyleneimine, aminoalkyl (meth)acrylate copolymers, and polyvinyl imidazoline. Examples of nonionic polymeric dispersants include methylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, and polyvinyl porlidone.

[0015] The average molecular weight of the polymer dispersant is preferably 4,000 to 200,000, more preferably 5,000 to 170,000. If the average molecular weight of the polymer dispersant is less than 4,000, it is difficult to obtain the steric repulsion (steric hindrance) effect, and the dispersibility of boehmite cannot be improved. If the average molecular weight of the polymer dispersant is more than 200,000, the polymer dispersant may cause interparticle cross-linking, and may act more like a flocculant than a dispersant.

[0016] The carbon content, which is an index of the amount of polymer dispersant attached to or bonded to the surface of boehmite particles, is preferably 0.01 to 0.17% by weight, more preferably 0.02 to 0.15% by weight. If the carbon content is less than 0.01% by weight, the dispersibility of boehmite becomes poor and aggregation occurs. If the carbon content exceeds 0.17% by weight, boehmite is not formed or boehmite exhibiting dilatancy is formed.

[0017] The isoelectric point of the boehmite of the present invention is preferably pH 2.9 to 6.7, more preferably pH 3.0 to 6.5. Since the isoelectric point of the boehmite of the present invention is shifted to the acidic side, it has superior dispersibility compared to boehmite in which a polymer dispersant is not attached or bonded to the particle surface. Furthermore, the dispersion and aggregation state of the boehmite can be easily controlled by adjusting the pH of the slurry, which makes the boehmite easier to handle during production and use.

[0018] The aspect ratio of the boehmite of the present invention is preferably 2.2 to 55.0, more preferably 2.5 to 50.0, and most preferably 2.8 to 45.0. When the aspect ratio of boehmite is less than 2.2, the particle shape becomes nearly spherical, making it easy to form a densely packed structure, which changes from a densely packed structure to a sparsely packed structure when a large shear force is applied, making it easy to exhibit dilatancy. On the other hand, when the aspect ratio of boehmite exceeds 55.0, the mechanical strength of the boehmite decreases.

[0019] The average major axis of the boehmite of the present invention is preferably 0.6 μm to 7.4 μm, more preferably 0.7 μm to 6.6 μm, and most preferably 0.8 μm to 5.8 μm. If the average major axis of the boehmite is less than 0.6 μm, a large amount of polymer dispersant must be added to ensure sufficient dispersibility of the boehmite. Furthermore, increasing the amount of polymer dispersant added tends to increase the amount of polymer dispersant (carbon content) adhering to or bonding to the boehmite particle surfaces, which can lead to problems such as increased dilatancy and reduced heat resistance due to the amount of polymer dispersant adhering to or bonding to the boehmite particle surfaces. Furthermore, if the average particle diameter of the boehmite exceeds 7.4 μm, the boehmite in the slurry tends to settle in a short period of time, which is undesirable.

[0020] The boehmite of the present invention does not exhibit dilatancy. Therefore, the handling properties of the boehmite during production and use are not impaired. Dilatancy refers to the property of increasing viscosity as the shear rate increases. During production and use, boehmite is often used as a boehmite slurry in which it is dispersed in a dispersion medium such as water. Hereinafter, the inconveniences that arise when using a boehmite slurry of boehmite exhibiting dilatancy will be specifically described. (1) In the production of boehmite, dehydration methods such as centrifugation and pressure filtration are often used in the dehydration process of boehmite slurry. If the boehmite slurry exhibits dilatancy during the dehydration process, the boehmite slurry subjected to shear force by dehydration operations such as centrifugation and pressure filtration behaves like a solid, resulting in the inconvenience of insufficient dehydration. Furthermore, boehmite slurry exhibiting dilatancy behaves like a liquid when no shear force is applied (or under low shear force), resulting in the inconvenience of not being able to recover the boehmite as a cake after the dehydration operation of the boehmite slurry. (2) When using boehmite slurry, the boehmite may settle and accumulate. For example, when producing boehmite, decantation is sometimes performed as a dehydration operation for boehmite slurry. If the boehmite in the boehmite slurry settles and the resulting deposit exhibits dilatancy, it becomes difficult to recover or remix the deposit (reslurry). (3) When using boehmite slurry, the boehmite slurry may be stirred or pumped. If the boehmite slurry exhibits dilatancy, the viscosity of the boehmite slurry increases rapidly due to the shear force applied during stirring or pumping. This not only makes stirring or pumping the boehmite slurry difficult, but also leads to problems such as breakdowns of equipment such as stirrers and pumps. (4) Boehmite is sometimes used as a paste. If the boehmite paste exhibits dilatancy, the shear force applied when applying the paste causes the paste to behave like a solid, making it difficult to apply the paste evenly.

[0021] Next, a method for producing the boehmite of the present invention will be described. The boehmite of the present invention can be produced by hydrothermal treatment of a slurry of aluminum hydroxide, a polymer dispersant, and water. The lower the water ratio, the higher the proportion of aluminum hydroxide, and therefore the larger the amount of boehmite that can be produced in one batch, allowing for efficient production of boehmite. However, the lower the water ratio, the higher the viscosity of the slurry, which may result in no boehmite being produced or in the production of boehmite that exhibits dilatancy. The method for producing boehmite of the present invention can produce boehmite with excellent dispersibility that does not exhibit dilatancy, even at a low water ratio, without compromising the handleability of the boehmite during production or use.

[0022] The average particle size of the aluminum hydroxide raw material (average particle size d50 (volume basis) measured by laser diffraction / scattering) is preferably 0.2 μm to 12 μm, and more preferably 0.5 μm to 10 μm. If the average particle size of the aluminum hydroxide is less than 0.2 μm, the viscosity of the aluminum hydroxide and water slurry during production increases, resulting in poor productivity. If the average particle size of the aluminum hydroxide is more than 12 μm, boehmite aggregates are likely to form, and the aluminum hydroxide particles are likely to settle in a short period of time, potentially causing pipe clogging and resulting in poor productivity and damage to the production equipment.

[0023] The hydrothermal treatment in the method for producing boehmite of the present invention is preferably carried out in a pressure device such as an autoclave at a constant temperature of 160°C to 230°C. If the constant temperature is below 160°C, the reaction time will be long and the boehmite of the present invention may not be obtained. If the constant temperature is above 230°C, expensive high-pressure equipment will be required and the polymer dispersant will be easily denatured, so the boehmite of the present invention may not be obtained and it will be uneconomical in terms of energy. The constant temperature time is preferably in the range of 2 to 14 hours. If it is less than 2 hours, the boehmite of the present invention may not be obtained. If it exceeds 14 hours, it will be uneconomical in terms of energy. Furthermore, the slurry may or may not be stirred during the hydrothermal treatment. The boehmite of the present invention can be obtained by dehydrating, washing with water, and drying the slurry obtained after the hydrothermal treatment.

[0024] The addition rate of the polymer dispersant, which is the weight percentage of the polymer dispersant relative to the weight of aluminum hydroxide ("weight of polymer dispersant / weight of aluminum hydroxide" × 100), is preferably 0.03 wt% to less than 1 wt%, and more preferably 0.04 wt% to less than 1 wt%. If the addition rate of the polymer dispersant is less than 0.03 wt%, the dispersibility of the boehmite deteriorates, causing aggregation. If the addition rate of the polymer dispersant is 1 wt% or more, boehmite may not be produced, or the produced boehmite may exhibit dilatancy, which may reduce the handleability during the production and use of boehmite.

[0025] In the method for producing boehmite of the present invention, a particle morphology control agent can be added to the slurry of aluminum hydroxide, a polymer dispersant, and water, if necessary. By selecting and using a particle morphology control agent during the production of boehmite, the morphology of the boehmite particles can be selected from a variety of shapes, such as plate-like boehmite, hexagonal plate-like boehmite, fine plate-like boehmite, cubic boehmite, scaly boehmite, and needle-like boehmite.

[0026] The particle morphology control agent may be a known particle morphology control agent for boehmite. Examples of known particle morphology control agents for boehmite include nucleating agents (nucleating agents) such as aluminum hydroxide gel, boehmite, alumina sol, and aluminum nitrate, alkali metal salts such as sodium hydroxide, sodium carbonate, sodium phosphate, sodium sulfide, sodium borate, potassium hydroxide, potassium carbonate, potassium phosphate, and lithium hydroxide, magnesium hydroxide, magnesium oxide, magnesium chloride, magnesium carbonate, magnesium sulfate, magnesium nitrate, magnesium acetate, magnesium phosphate, magnesium borate, magnesium formate, magnesium acetate, magnesium propionate, magnesium maleate, magnesium oxalate, magnesium glutarate, magnesium succinate, magnesium malonate, and magnesium adipate. Examples of suitable particle morphology control agents include magnesium salts such as magnesium citrate, calcium salts such as calcium hydroxide, calcium nitrate, calcium acetate, and calcium formate, strontium salts such as strontium hydroxide, strontium nitrate, strontium acetate, and strontium formate, barium salts such as barium hydroxide, barium nitrate, barium acetate, and barium formate, ammonium salts such as ammonium phosphate, ammonium borate, and ammonium hydroxide, acids such as formic acid, acetic acid, propionic acid, oxalic acid, glutaric acid, succinic acid, malonic acid, maleic acid, adipic acid, citric acid, boric acid, nitric acid, sulfuric acid, and phosphoric acid, and borates such as sodium borate, magnesium borate, calcium borate, ammonium borate, barium borate, and strontium borate. These particle morphology control agents can be used alone or in combination of two or more.

[0027] The addition rate of the particle morphology control agent, which is the weight percentage of the particle morphology control agent relative to the weight of aluminum hydroxide ("weight of particle morphology control agent / weight of aluminum hydroxide" x 100), is preferably 0.1 to 20% by weight. If the addition rate of the particle morphology control agent is less than 0.1% by weight, the effect of the particle morphology control agent is less likely to be obtained, while if the addition rate of the particle morphology control agent is more than 20% by weight, boehmite formation is inhibited, handling is deteriorated, and corrosion of manufacturing equipment such as autoclaves is likely to occur.

[0028] Examples of resins that can be filled with the boehmite of the present invention include polyethylene, polyolefins (such as polypropylene and cyclic polyolefins), polyvinyl chloride, polyamides (such as nylon and urea resins), ABS resins, polyesters (such as polyethylene terephthalate, polybutylene terephthalate, and wholly aromatic polyesters), polycarbonate, polyacetal, polyphenylene sulfide, polyphenylene ether, polysulfone, polyethersulfone, polyimides (such as polyimide and polyetherimide), polyetheretherketone, epoxy resins, silicone resins, phenolic resins, alkyd resins, unsaturated polyesters, diallyl phthalate, polystyrene, fluororesins, saturated polyesters, urea resins, melamine-containing resins, polyurethanes, liquid crystal polymers, polyamideimides, maleimide-modified resins, acrylic resins, acrylonitrile-acrylic rubber-styrene resins, acrylonitrile-ethylene-propylene-diene rubber-styrene resins, and modified polyphenylene ethers. Examples of rubbers that can be filled with the boehmite of the present invention include silicone rubber, acrylic rubber, butyl rubber, ethylene propylene rubber, and olefin-based elastomers. [Example]

[0029] Next, examples embodying the present invention will be described in comparison with comparative examples, but the present invention is not limited to the following examples.

[0030] Example 1 20 g of aluminum hydroxide (Nippon Light Metal Co., Ltd., "BF013," average particle size: 1 μm; hereinafter the same) was prepared as a raw material. A 100 ml PTFE container was charged with water at a water-to-water ratio of 2. A dispersant, sodium polyacrylate (Toagosei Co., Ltd., "Aron T-50," average molecular weight approximately 6,000; hereinafter the same) was added at 0.05 wt% relative to the weight of the aluminum hydroxide. The solution was stirred to form a solution, after which 20 g of aluminum hydroxide was added. Furthermore, aluminum hydroxide gel (Tomita Pharmaceutical Co., Ltd., "Tomita-AD200P") was added as a particle morphology control agent at 0.3 wt% relative to the weight of the aluminum hydroxide. The mixture was stirred to prepare a slurry. The PTFE container was then placed in a pressure vessel and subjected to hydrothermal treatment at 200°C for 5 hours with stirring. The hydrothermally treated slurry was dehydrated, washed with water, and dried to obtain a sample.

[0031] Example 2 A sample was obtained in the same manner as in Example 1, except that polyacrylic acid ("Polyacrylic acid solution (approximately 25%)" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., average molecular weight approximately 150,000) was used as a dispersant and the amount added was 0.05 wt % relative to the weight of aluminum hydroxide.

[0032] Example 3 A sample was obtained in the same manner as in Example 1, except that sodium polystyrene sulfonate ("Poly(sodium 4-styrenesulfonate) solution" manufactured by Sigma-Aldrich Co. LLC, average molecular weight approximately 70,000) was used as a dispersant in an amount of 0.1 wt % relative to the weight of aluminum hydroxide.

[0033] Example 4 A sample was obtained in the same manner as in Example 1, except that polyethyleneimine ("30% polyethyleneimine P-70 solution" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., average molecular weight approximately 70,000) was used as a dispersant and the amount added was 0.5 wt % relative to the weight of aluminum hydroxide.

[0034] Example 5 10 g of aluminum hydroxide was prepared as a raw material. Water was placed in a 100 ml PTFE container so that the water ratio was 5. Sodium polyacrylate was added as a dispersant in an amount of 0.1 wt % relative to the weight of the aluminum hydroxide, and sodium carbonate was added as a particle morphology control agent in an amount of 14 wt % relative to the weight of the aluminum hydroxide. The mixture was stirred to form a solution, and then 10 g of aluminum hydroxide was added and stirred to mix, preparing a slurry. Next, this PTFE container was placed in a pressure vessel and subjected to hydrothermal treatment with stirring for 4 hours at 200° C. The slurry after the hydrothermal treatment was dehydrated, washed with water, and dried to obtain a sample.

[0035] Example 6 A sample was obtained in the same manner as in Example 1, except that no particle morphology control agent was added.

[0036] Example 7 A sample was obtained in the same manner as in Example 1, except that polyacrylic acid ("AQUALIC HL415" manufactured by Nippon Shokubai Co., Ltd., average molecular weight approximately 10,000) was used as a dispersant and the amount added was 0.05 wt % relative to the weight of aluminum hydroxide.

[0037] Example 8 A sample was obtained in the same manner as in Example 1, except that polyethyleneimine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., average molecular weight approximately 10,000) was used as a dispersant and the amount added was 0.5 wt % relative to the weight of aluminum hydroxide.

[0038] Example 9 A sample was obtained in the same manner as in Example 5, except that the hydrothermal treatment was carried out at 160° C. for 12 hours.

[0039] Comparative Example 1 A sample was obtained in the same manner as in Example 1, except that the amount of sodium polyacrylate added was 1% by weight relative to the weight of aluminum hydroxide.

[0040] Comparative Example 2 A sample was obtained in the same manner as in Example 1, except that the amount of polyacrylic acid ("Polyacrylic Acid Solution" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., average molecular weight approximately 150,000) added was 1 wt % relative to the weight of aluminum hydroxide.

[0041] Comparative Example 3 A sample was obtained in the same manner as in Example 5, except that the amount of sodium polyacrylate added was 1% by weight relative to the weight of aluminum hydroxide.

[0042] The boehmite in the above examples and comparative examples was evaluated by the evaluation methods described below.

[0043] 1. Presence or absence of boehmite The crystalline phase was measured using an X-ray diffractometer (D2 Phaser manufactured by Bruker Corporation). When no unreacted crystalline phase of the raw material aluminum hydroxide remained and only the crystalline phase of boehmite was observed, the sample was evaluated as "○", and when unreacted crystalline phase of the raw material aluminum hydroxide remained, the sample was evaluated as "×".

[0044] 2.Isoelectric point (1) A predetermined amount of sample was added to ion-exchanged water to prepare a suspension with a concentration adjusted to a level at which the zeta potential could be measured. (2) A diluted solution of sulfuric acid was added to the suspension to lower the pH of the suspension to about pH 2. Then, a diluted solution of ammonia water was added to the suspension to gradually increase the pH. At a predetermined pH, the zeta potential was measured using a zeta potentiometer ("ELS-2000" manufactured by Otsuka Electronics Co., Ltd.) to determine the pH at the isoelectric point where the zeta potential was 0 (zero). The temperature of the suspension was maintained at 25°C.

[0045] 3. Presence or absence of dilatancy in boehmite <Preparation of boehmite deposits> (1) 30 mL of soft water and 3 g of sample were added to a 50 mL centrifuge tube, and then the lid of the centrifuge tube was closed. The centrifuge tube was then shaken using a test tube mixer (Taitec Corporation's "Delta Mixer Se-08"; the same applies below) to prepare a suspension. (2) The suspension was sonicated using an ultrasonic homogenizer for 10 minutes or more to disperse the boehmite in the suspension. (3) The suspension in the centrifuge tube was agitated by shaking the centrifuge tube using a test tube mixer. (4) The mixture was centrifuged at 8,000 rpm for 10 minutes using a centrifuge (Kubota Shoji Co., Ltd.'s "Hybrid High-Speed ​​Refrigerated Centrifuge Model 6200") to separate the sediment from the supernatant. If the boehmite exhibits dilatancy, the shear force applied during centrifugation causes dilatancy, and a slurry of boehmite and water is obtained as a solid sediment. On the other hand, if the boehmite does not exhibit dilatancy, the boehmite settles during centrifugation and is obtained as a semi-solid sediment. (5) After centrifugation, the lid of the centrifuge tube was immediately opened and the supernatant was removed. (6) The centrifuge tube was closed and the tube was shaken using a test tube mixer to shake the sediment inside the tube. The sediment that had become solid due to dilatancy was released from its packing state by shaking, and the sediment changed from a solid to a liquid state. On the other hand, if the boehmite does not exhibit dilatancy, the sediment would remain in a semi-solid state. Hereinafter, both the sediment that was shaken to a liquid state and the sediment that was shaken to a semi-solid state will be referred to as boehmite sediment. (7) The boehmite deposit obtained in (6) above was subjected to measurement of water content and evaluation of the presence or absence of dilatancy. <Measurement of moisture content of boehmite deposits> The weight loss rate of the boehmite deposit when ignited at 130°C was measured using a moisture meter (MX-50 manufactured by A&D Co., Ltd.), and this was taken as the moisture content of the boehmite deposit. <Evaluation of the presence or absence of dilatancy> The boehmite deposits were evaluated for dilatancy using the following method. If the boehmite deposits exhibited dilatancy, they were evaluated as "present," and if they did not exhibit dilatancy, they were evaluated as "absent." Methods for evaluating dilatancy include evaluation methods using sensory tests and viscosity measurements using devices that can measure viscosity by changing the shear rate (such as an E-type viscometer or a rheometer). Below, evaluations were made using the evaluation method using a sensory test and the evaluation method using an E-type viscometer. (1) Evaluation method by sensory test The properties of the boehmite deposit (semi-solid or liquid) were evaluated visually, and if the boehmite deposit was semi-solid, it was evaluated that the boehmite did not exhibit dilatancy, as described above, and if the boehmite deposit was liquid, it was evaluated that the boehmite exhibited dilatancy, as described above. (2) Evaluation method using an E-type viscometer The evaluation using the E-type viscometer was carried out to confirm the dilatancy of the boehmite deposit obtained in the liquid state in the sensory test described above, and to confirm the dilatancy when it was difficult to determine whether the boehmite deposit was in the liquid state or semi-solid state in the sensory test described above. Using an E-type viscometer (Toki Sangyo Co., Ltd. "TVE-35H", the same applies below) and a standard rotor (Toki Sangyo Co., Ltd. "1°34' x R24", the same applies below), the shear rate was set to 0.5 sec -1 The shear rate was gradually increased from 120 seconds, and after the shear rate reached the upper limit of the measurable range, the shear rate was gradually decreased, and the viscosity of the boehmite deposit was measured by measuring the viscosity for 120 seconds at each predetermined shear rate. The viscosity measured 120 seconds after the start of measurement at each predetermined shear rate was plotted against the shear rate during measurement. When the viscosity increased as the shear rate for the boehmite deposit increased, it was evaluated as having dilatancy (if dilatancy was not exhibited, the viscosity would not increase at all even if the shear rate was increased). The temperature of the boehmite deposit was maintained at 25°C. When using a standard rotor with an E-type viscometer, the upper limit of the measurable shear rate was 383 sec. -1 It was.

[0046] 4. Scanning electron microscope observation and aspect ratio The particle morphology of the samples was observed using a scanning electron microscope (JSM-7500FA, manufactured by JEOL Ltd.). The major and minor axes of the boehmite particles of each morphology shown in Fig. 10 were measured at 30 or more points to determine the average major and minor axes, and the aspect ratio (average major axis / average minor axis) was calculated. The major axis refers to the longest diagonal line on the plane of the boehmite particle, as shown in Fig. 10, and the minor axis refers to the thickness of the boehmite particle, as shown in Fig. 10.

[0047] 5. Carbon content The carbon content of the boehmite samples was measured using a carbon / sulfur analyzer ("EMIA-20P" manufactured by Horiba, Ltd.), and the amount of polymer dispersant attached to or bonded to the surface of the boehmite particles was quantified as carbon.

[0048] Table 1 shows the production conditions for each example and comparative example, and Table 2 shows the evaluation results of the boehmite according to the above evaluation methods.

[0049] [Table 1]

[0050] [Table 2]

[0051] As shown in FIGS. 1 to 9, no agglomerates of boehmite were observed in each example, and individual boehmite particles were well dispersed.

Claims

1. The boehmite has a polymer dispersant attached or bonded to the particle surface, the boehmite having a carbon content of 0.01% by weight to 0.17% by weight, an isoelectric point of pH 2.9 to 6.7, and exhibiting no dilatancy.

2. 2. The boehmite according to claim 1, wherein the aspect ratio of the boehmite is 2.2 to 55.

0.

3. 2. The boehmite according to claim 1, wherein the average major axis of the boehmite is 0.6 μm to 7.4 μm.

4. The boehmite according to any one of claims 1 to 3, wherein the polymer dispersant is at least one selected from the group consisting of polyacrylic acid, sodium polyacrylate, ammonium polyacrylate, polystyrene sulfonic acid, sodium polystyrene sulfonate, sodium naphthylene sulfonate, carboxymethyl cellulose, polyethyleneimine, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, and polyvinyl porlidone.

5. The method for producing boehmite according to any one of claims 1 to 3, characterized in that a slurry of aluminum hydroxide, a polymer dispersant having an addition rate of 0.03 wt % to less than 1 wt % relative to the weight of aluminum hydroxide, and water is subjected to hydrothermal treatment.

6. The method for producing boehmite according to claim 5, characterized in that the average particle size (d50) of the aluminum hydroxide is 0.2 μm to 12 μm.

7. 6. The method for producing boehmite according to claim 5, wherein the polymer dispersant is at least one selected from the group consisting of polyacrylic acid, sodium polyacrylate, ammonium polyacrylate, polystyrene sulfonic acid, sodium polystyrene sulfonate, sodium naphthylene sulfonate, carboxymethyl cellulose, polyethyleneimine, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, and polyvinyl porlidone.

8. 6. The method for producing boehmite according to claim 5, wherein the slurry contains a particle morphology control agent.

9. 9. The method for producing boehmite according to claim 8, wherein the particle morphology control agent is added in an amount of 0.1% by weight to 20% by weight based on the weight of aluminum hydroxide.

10. 9. The method for producing boehmite according to claim 8, wherein the polymer dispersant is at least one selected from the group consisting of polyacrylic acid, sodium polyacrylate, ammonium polyacrylate, polystyrene sulfonic acid, sodium polystyrene sulfonate, sodium naphthylene sulfonate, carboxymethyl cellulose, polyethyleneimine, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, and polyvinyl porlidone.

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