Dispersion composition containing alumina particles or alumina hydrate particles and method for producing the same

Abstract

To provide a new composition which is usable as a filler mixed in a resin.SOLUTION: A dispersion composition contains a dispersion medium, and alumina particles or alumina hydrate particles which are dispersed in the dispersion medium and have a fibrous or acicular shape, and satisfies all of the following (A) to (E). (A) A major axis of a primary particle diameter of the alumina particles or alumina hydrate particles is 100 nm or more and 1,000 nm or less, and a minor axis thereof is 1 nm or more and 10 nm or less, (B) 0.2 mol% or more and 1.8 mol% or less of one or two kinds of atoms selected from magnesium and calcium are contained with respect to an aluminum atom, (C) 0.1 equivalent or more and 2.0 equivalent or less of an organic acid or an inorganic acid is contained with respect to the aluminum atom, (D) a dispersion medium is water, and (E) properties do not change at normal temperature for one month.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a dispersion composition containing alumina particles or alumina hydrate particles that can be used as a filler to be mixed with a transparent resin, and a method for producing the same. [Background technology]

[0002] In recent years, the increasing flexibility of displays such as liquid crystal displays (LCDs) and organic electroluminescent (OLED) displays, as well as electronic wiring boards, has led to a demand for high-performance freestanding films, sheets, and molded articles that offer flexibility, transparency, high heat resistance, and flexibility. While organic films such as plastics are flexible and lightweight, they suffer from low heat resistance and a high linear thermal expansion coefficient. In contrast, inorganic materials such as ceramics offer excellent heat resistance and low thermal expansion, but suffer from heavy weight and low flexibility. To address these drawbacks, organic-inorganic hybrid materials, which combine organic materials such as resins with inorganic particles, have been explored and are widely used industrially. Inorganic fillers include metal particles and metal oxide particles, with metal oxides such as silica, alumina, titania, and clay being used. Furthermore, the shape of particles can be exploited to enhance specific physical properties. Specifically, the use of sheet- or plate-shaped particles with a high aspect ratio (diameter / thickness) can be expected to provide gas barrier properties, while the addition of high-aspect-ratio (longer diameter / shorter diameter) particles such as fibrous particles can be expected to be highly effective in suppressing the linear thermal expansion coefficient. Furthermore, nanosizing inorganic fillers not only significantly improves their functionality but also maintains transparency. However, as inorganic filler particles become smaller, their surface area increases, and at the same time, their surface energy increases, making them more susceptible to particle aggregation. Nanosized fibrous particles, in particular, are expected to have a high filler effect, but they are prone to aggregation due to physical entanglement, making them difficult to handle as fillers. High filler loading is necessary to improve heat resistance, low thermal expansion, and thermal conductivity, but for the reasons mentioned above, it is difficult to achieve high loadings of nanosized fibrous particles.

[0003] As a prior art for fibrous particles, there is disclosed an alumina sol obtained by hydrolysis of aluminum alcoholate, characterized in that alumina hydrate particles or alumina particles having a fibrous or needle-like shape with a minor axis of 1 to 10 nm, a major axis of 100 to 10,000 nm, and an aspect ratio (major axis / minor axis) of 30 to 5,000 are dispersed in a solution (see Patent Document 1).

[0004] Another prior art proposed is a method for producing a highly transparent alumina sol made of pseudo-boehmite crystals with a minor axis of 10 nm or less and a major axis of 200 nm or less (see Patent Document 2).

[0005] Another prior art technique discloses acicular boehmite particles produced by growing particles from aluminum hydroxide as a raw material in the presence of metal ions such as Mg2+, Mn2+, and Zn2+ and anions such as carboxylate ions, nitrate ions, and sulfate ions (see Patent Document 3).

[0006] Another prior art technique disclosed is a method for producing acicular boehmite particles by adding an alkaline aqueous solution to an aqueous solution of aluminum metal salt to produce gel-like aluminum hydroxide, followed by a four-stage hydrothermal treatment process (see Patent Document 4).

[0007] However, the alumina sol in which fibrous or needle-shaped alumina hydrate particles or alumina particles are dispersed in a solution as disclosed in Patent Document 1 has a wide range of major fiber lengths, from 100 to 10,000 nm. In particular, if a large amount of long fibers exceeding 1,000 nm are contained, the stability of the filler dispersion over time may decrease, and high loading into a resin may be difficult due to steric hindrance of the long fibers.

[0008] The needle-shaped pseudo-boehmite particles having a minor axis of 10 nm and a major axis of approximately 100 nm disclosed in Patent Document 2 lose the characteristics derived from the fibrous shape, and may not exhibit sufficient performance as a filler.

[0009] The particles obtained by the manufacturing method disclosed in Patent Document 3 have problems such as large amounts of metal ions and sulfate ions being mixed into the alumina sol, which significantly affect the filler properties. Furthermore, the minor axis is 30 nm to 300 nm, the major axis is 1,000 nm to 10,000 nm, and the aspect ratio is 5 to 50. When the minor axis is 10 nm or more, alumina particles precipitate after the hydrothermal reaction and are filtered, purified, and then pulverized. This can reduce the transparency of the resin by adding the filler, and there is still room for improvement.

[0010] The method for producing acicular boehmite disclosed in the above-mentioned document 4 produces acicular boehmite with a minor axis of 5.5±0.5 nm, a major axis of 350±37 nm, and an aspect ratio of 45 to 80. However, this method requires a large amount of power for stirring due to the generation of a gel-like substance, and also requires a rapid temperature change during the particle growth process, resulting in complicated and time-consuming temperature control, so there is still room for improvement before it can be commercialized. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-132519 [Patent Document 2] Japanese Patent Application Publication No. 59-78925 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-037741 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-56739 Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a novel composition that can be used as a filler to be mixed into a resin. [Means for solving the problem]

[0013] The present inventors have conducted extensive research with the goal of producing a composition containing alumina particles or alumina hydrate particles that exhibit excellent filler performance. As a result, they have discovered that by allowing a trace amount of different metal atoms to coexist during the formation of fibrous or acicular particles, thereby inhibiting crystal growth in the major axis direction and controlling the fiber length to a specific length, it is possible to obtain a composition that has excellent filler effect and can be highly loaded into a resin, and have completed the present invention. In this specification, the filler effect refers to the uniformity when mixed into resin, the filling amount when mixed into resin, the transparency when mixed into transparent resin, and the effect on thermal expansion when mixed into transparent resin.

[0014] The gist of the present invention is as follows. [1] A dispersion composition comprising a dispersion medium and alumina particles or alumina hydrate particles having a fibrous or acicular shape dispersed in the dispersion medium, and satisfying all of the following (A) to (E): (A) the major axis of the primary particle diameter of the alumina particles or alumina hydrate particles is 100 nm or more and 1000 nm or less, and the minor axis is 1 nm or more and 10 nm or less; (B) containing 0.2 mol% or more and 1.8 mol% or less of one or two atoms selected from magnesium and calcium relative to aluminum atoms; (C) Contains an organic acid or an inorganic acid in an amount of 0.1 equivalent or more and 2.0 equivalents or less relative to aluminum atoms; (D) The dispersion medium is water; (E) Properties remain unchanged for one month at room temperature. [2] The dispersion composition according to [1], comprising alumina hydrate particles, the crystal system of which is boehmite or pseudo-boehmite. [3] The dispersion composition according to [1] or [2], which is used as a filler to be mixed into a transparent resin. [4] A method for producing the dispersion composition according to any one of [1] to [3], a step of hydrolyzing the aluminum alcoholate with an aqueous organic acid solution or an aqueous inorganic acid solution; The method includes a step of peptizing the obtained hydrolyzate in the presence of one or two atoms selected from magnesium and calcium at 100°C or higher and 200°C or lower, In the hydrolysis step, an organic acid or an inorganic acid is present in an amount of 0.1 equivalents or more and 2.0 equivalents or less relative to aluminum atoms, The above-mentioned production method, wherein in the peptization step, one or two atoms selected from magnesium and calcium are present in an amount of 0.2 mol % or more and 1.8 mol % or less relative to aluminum atoms. [Effects of the Invention]

[0015] According to the present invention, a novel composition can be provided that can be used as a filler to be mixed with a resin. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a scanning electron microscope image of the alumina dispersion composition of Example 2. [Figure 2] 1 is a scanning electron microscope image of the alumina dispersion composition of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0017] Next, one embodiment of the present invention will be described. This embodiment relates to a dispersion composition (hereinafter also referred to as an alumina dispersion composition) containing a dispersion medium and fibrous or acicular alumina particles or alumina hydrate particles dispersed in the dispersion medium. In this embodiment, the alumina particles or alumina hydrate have a primary particle diameter of 100 nm or more but 1000 nm or less and a minor axis of 1 nm or more but 10 nm or less, contain one or two atoms selected from magnesium and calcium in an amount of 0.2 mol % or more but 1.8 mol % or less relative to the aluminum atoms, contain an organic acid or inorganic acid in an amount of 0.1 equivalents or more but 2.0 equivalents relative to the aluminum atoms, the dispersion medium is water, and the properties do not change for one month at room temperature. In this specification, room temperature refers to the range of 20±15°C as defined in Japanese Industrial Standards (JIS Z 8703).

[0018] The alumina dispersion composition of this embodiment will be described in more detail. The alumina dispersion composition of this embodiment contains fibrous or acicular alumina particles or alumina hydrate particles synthesized by a sol-gel method using aluminum alcoholate as a raw material.

[0019] The alumina particles or alumina hydrate particles according to this embodiment have an average major axis of 100 nm to 1000 nm and an average minor axis of 1 nm to 10 nm. From the viewpoint of storage stability of the dispersion and filler performance, the alumina particles or alumina hydrate particles according to this embodiment preferably have an average major axis of 200 nm to 800 nm and an average minor axis of 2 nm to 8 nm.

[0020] If the average major axis exceeds 1,000 nm, the physical entanglement of the fibrous particles may reduce the storage stability of the dispersion, and steric hindrance of the fibers may make it difficult to highly fill the resin. If the average major axis is less than 100 nm, the characteristics derived from the fibrous shape may be reduced, and the performance as a filler may be reduced. If the average minor axis of the particles exceeds 10 nm, the transparency of the resin composition to which the filler is added may be reduced. If the average minor axis of the particles is less than 1 nm, the particles are so small that they tend to aggregate, which may increase the viscosity and reduce the storage stability.

[0021] Next, a method for producing the alumina dispersion composition of this embodiment will be described. This embodiment includes a step of hydrolyzing aluminum alcoholate with an aqueous organic acid solution or an aqueous inorganic acid solution, and a step of peptizing the aluminum alcoholate at 100°C or higher and 200°C or lower in the presence of one or two atoms selected from magnesium and calcium.

[0022] Examples of aluminum alcoholates include aluminum alkoxides such as aluminum ethoxide, aluminum isopropoxide, aluminum n-butoxide, and aluminum sec-butoxide, cyclic aluminum oligomers, and aluminum chelates such as diisopropoxy(ethylacetoacetato)aluminum and tris(ethylacetoacetato)aluminum.

[0023] Among these compounds, those having an alkoxyl group having 2 to 5 carbon atoms are preferred because they have moderate hydrolysis properties and by-products can be easily removed. Furthermore, these aluminum alcoholates may be in the form of a liquid, powder, or granules. The purity is not particularly limited, but is preferably 95% or higher, and more preferably 98% or higher, because this can further enhance the transparency of the alumina dispersion composition.

[0024] The organic or inorganic acid used for the hydrolysis of aluminum alcoholate is preferably a monovalent acid such as hydrochloric acid, nitric acid, formic acid, acetic acid, propionic acid, or butyric acid, with acetic acid being more preferred from the standpoints of ease of operation and economy. The amount of acid used is 0.1 to 2.0 times by mole, preferably 0.2 to 1.1 times by mole, relative to the amount of aluminum alcoholate. If the amount is less than 0.1 times by mole, the average major axis of the resulting particles may be small, while if the amount is more than 2.0 times by mole, the stability of the dispersion composition over time may be reduced.

[0025] The hydrolysis conditions are not particularly limited and can be appropriately determined by a person skilled in the art, but from the viewpoint of operability, etc., a temperature of 100°C or less and a time of 0.1 to 3 hours are preferred. The alcohol produced by the hydrolysis can be distilled off after the hydrolysis to prevent side reactions.

[0026] The solids concentration of the aqueous acid solution of aluminum alcoholate to be hydrolyzed is preferably 2 wt % or more and 15 wt % or less, more preferably 3 wt % or more and 10 wt % or less, from the viewpoints of ease of control of the average major diameter of the particles and ease of operation in the subsequent peptization treatment.

[0027] In this embodiment, an aluminum alcoholate hydrolyzate is peptized in the presence of one or two atoms selected from magnesium and calcium. Furthermore, in this embodiment, the peptization treatment is performed in the presence of 0.2 mol% or more and 1.8 mol% or less of one or two atoms selected from magnesium and calcium relative to the aluminum atoms. This inhibits crystal growth in the major axis direction of the alumina particles or alumina hydrate particles obtained by peptization, enabling the fiber length to be controlled to a specific shape. The preferred amount of one or two atoms selected from magnesium and calcium relative to the aluminum atoms is 0.5 mol% or more and 1.5 mol% or less.

[0028] If the content of one or two atoms selected from magnesium and calcium is less than 0.2 mol%, the effect of inhibiting growth in the major axis direction is insufficient, and many fibrous particles with major axes exceeding 1,000 nm may be produced. If the content exceeds 1.8 mol%, the reaction solution may become thicker during peptization, reducing stirrability, the dispersion composition may gel within one month, significantly reducing handleability, or aggregates may precipitate within one month, reducing the storage stability of the alumina dispersion composition. Furthermore, if the amount of foreign metals in the alumina dispersion composition exceeds 1.8 mol%, the transparency may decrease when added to a resin.

[0029] The metal ions of magnesium and calcium can be added as metal salts. Examples of salts of the above metal ions include magnesium formate, magnesium acetate, magnesium propionate, magnesium butyrate, magnesium carboxylate, calcium carboxylates such as calcium formate, calcium acetate, calcium propionate, and calcium butyrate, magnesium chloride, magnesium sulfate, magnesium nitrate, calcium chloride, calcium sulfate, and calcium nitrate. Furthermore, the timing of adding one or two atoms selected from magnesium and calcium is not particularly limited and can be appropriately determined by a person skilled in the art, but can be performed, for example, before or after the hydrolysis treatment.

[0030] In this embodiment, the peptization treatment is performed at a temperature of 100°C or higher and 200°C or lower, preferably 110°C or higher and 180°C or lower. Heating temperatures below 100°C require a long reaction time, and the formed crystals may be broken down by stirring, resulting in a decrease in the stability of the alumina dispersion composition. Heating temperatures above 200°C require the use of a container that can withstand high temperatures and high pressures, which is economically disadvantageous. The heating time is not particularly limited and can be appropriately determined by those skilled in the art. However, heating times below 0.1 hours may result in insufficient crystal growth, resulting in small particle sizes and reduced storage stability, compared to heating times within the range. Heating times above 10 hours may result in the formed crystals being broken down by stirring, resulting in a decrease in the stability of the alumina dispersion composition, compared to heating times within the range. The deflocculation treatment produces fibrous or acicular alumina particles or alumina hydrate particles having a primary particle diameter of 100 nm or more and 1000 nm or less and a primary particle diameter of 1 nm or more and 10 nm or less, thereby obtaining the alumina dispersion composition of this embodiment. The dispersion medium contained in the alumina dispersion composition of this embodiment can be the water used in the production method.

[0031] The alumina dispersion composition of this embodiment obtained by the above-described production method has excellent stability over time, and its properties do not change when left standing at room temperature for one month. In this specification, a change in properties refers to the occurrence of any of the following: deposition of precipitates due to aggregation, gelation due to a significant increase in viscosity, or the formation of opaque areas due to a significant decrease in transparency associated with a change in the dispersion state. If these changes in properties occur, when the alumina dispersion composition is added to a transparent resin, the transparency of the resin may decrease, the effect of the filler addition may be reduced, or a uniform resin mixture may not be obtained. Furthermore, if short fibers and long fibers are mixed in the alumina dispersion composition, separation into two layers occurs over time: an upper layer mainly composed of particles with a major axis of 1000 nm or less, and a lower layer mainly composed of particles with a major axis of more than 1000 nm. This may require homogenization by stirring or the like, particularly when used industrially, which may complicate the process. The alumina dispersion composition of the present embodiment is mainly composed of particles with a major axis of 1000 nm or less, and therefore is easy to handle because the occurrence of two-layer separation is suppressed. The alumina dispersion composition of this embodiment obtained by the above-described production method contains alumina hydrate particles, and the crystalline system of the alumina hydrate is boehmite or pseudo-boehmite. The boehmite or pseudo-boehmite crystalline system facilitates particle shape control by selectively growing specific crystal planes, resulting in particles with a characteristic fibrous shape. This is preferable because it provides a superior filler effect and enables higher loading into resins. In this specification, boehmite refers to a material represented by Al2O3·nH2O (n = 1 to 2.5) that exhibits a unique peak pattern (JCPDS 21-1307) in an X-ray diffraction chart. Pseudo-boehmite refers to a material represented by Al2O3·nH2O (n is greater than 1 and less than 2.5), which has lower crystallinity than boehmite and contains excess water between layers of the (020) plane. The X-ray diffraction chart of this pseudo-boehmite exhibits broader diffraction peaks than boehmite, but boehmite and pseudo-boehmite are not clearly distinguishable in an X-ray diffraction chart, and therefore no particular distinction is made in the present invention.

[0032] The alumina dispersion composition of the present embodiment can be mixed with, for example, a water-soluble transparent resin. In addition, by modifying the surfaces of alumina particles or alumina hydrate particles with a phosphoric acid derivative, a sulfonic acid derivative, or a silane coupling agent according to a conventional method, and then performing solvent substitution from aqueous to organic solvent, an alumina dispersion in which the alumina particles are uniformly dispersed in the organic solvent can be obtained, and the alumina dispersion can be used as a highly fillable filler for water-insoluble transparent resins. Examples of the phosphoric acid derivatives include phosphoric acid esters such as ethyl acid phosphate, butyl acid phosphate, butyl pyrophosphate, butoxyethyl acid phosphate, 2-ethylhexyl acid phosphate, oleyl acid phosphate, tetracosyl acid phosphate, phenyl acid phosphate, diphenyl acid phosphate, benzyl acid phosphate, n-octyl acid phosphate, (2-hydroxyethyl) methacrylate acid phosphate, dibutyl phosphate, bis(2-ethylhexyl) phosphate, lauryl acid phosphate, stearyl acid phosphate, ethylene glycol monoethyl ether acid phosphate, triethylene glycol monoethyl ether acid phosphate, and triethylene glycol monobutyl ether acid phosphate; ethyl phosphonic acid; butyl phosphonic acid; 1,4-butylene diphosphonic acid; Examples of the sulfonic acid derivatives include alkylsulfonic acids such as methanesulfonic acid and ethanesulfonic acid, aromatic sulfonic acids such as benzenesulfonic acid, p-toluenesulfonic acid, styrenesulfonic acid and alkylbenzenesulfonic acid, and their esters with lower alcohols, alkali metal salts and ammonium salts. The organic solvent that can be replaced by using the surface modifier or the like is not particularly limited as long as it can produce an alumina organosol and has the solubility for the target resin, and any general-purpose organic solvent can be used. Specifically, aliphatic hydrocarbons such as pentane, hexane, and heptane; aromatic hydrocarbons such as benzene, toluene, xylene, and chlorobenzene; alcohols such as methanol, ethanol, isopropyl alcohol, and n-butanol; cyclic ethers such as tetrahydrofuran and 1,4-dioxane; aliphatic ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; alicyclic ketones such as cyclopentanone and cyclohexanone; esters such as ethyl acetate and butyl acetate; glycols such as ethylene glycol, diethylene glycol, and triethylene glycol; ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, and diethylene glycol monomethyl ether. Examples of the solvent include ethers such as diethylene glycol dimethyl ether, triethylene glycol monomethyl ether, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate; acrylic acids such as acrylic acid, methyl acrylate, butyl acrylate, methacrylic acid, methyl methacrylate, and butyl methacrylate; halogenated hydrocarbons such as dichloromethane and chloroform; N-alkylamides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; nitrated hydrocarbons such as nitromethane and nitrobenzene; nitriles such as acetonitrile and benzonitrile; and sulfoxides such as dimethyl sulfoxide.

[0033] The method for producing the resin composite is not particularly limited, and for example, a resin composite in which the alumina dispersion composition of this embodiment and a resin are dissolved in an organic solvent is mixed and stirred, and then the solvent is removed from the mixture, thereby producing a resin composite in which the alumina dispersion composition is uniformly dispersed in the resin. The alumina dispersion composition of this embodiment can be highly filled with alumina as a filler, for example, with a content of 30 wt% or more, and can improve the physical properties of the resin, such as the linear thermal expansion coefficient, while maintaining high transparency. The alumina dispersion composition of the present embodiment can be blended with a (meth)acrylic resin, a polycarbonate resin, a polyolefin resin, a polyester resin, a polystyrene resin, a polyamide resin, a polyimide resin, an epoxy resin, a polyurethane resin, or a polyacetal resin to obtain a resin composite. The organic solvent for dissolving the alumina dispersion composition and resin of this embodiment is not particularly limited, and any organic solvent can be used as long as it has the ability to dissolve the target resin. The amount of the alumina dispersion composition of the present embodiment added to the resin composite is not particularly limited. However, in consideration of the transparency, physical properties, filler effect, and the like of the resulting resin composite, the alumina content is preferably 20 wt % or more and 60 wt % or less, and more preferably 30 wt % or more and 50 wt % or less.

[0034] As described above, the method according to this embodiment includes a step of hydrolyzing aluminum alcoholate with an aqueous organic acid solution or an aqueous inorganic acid solution, and a step of peptizing the aluminum alcoholate at 100°C or higher and 200°C or lower in the presence of one or two atoms selected from magnesium and calcium. By allowing a trace amount of a different metal to coexist during the peptization step of particle formation, crystal growth in the major axis direction is inhibited, thereby controlling the fiber length, and thereby producing alumina particles or alumina hydrate particles having a specific fibrous or acicular shape in high yield.

[0035] That is, according to the method of this embodiment, it is possible to provide a dispersion composition containing alumina particles or alumina hydrate particles having a major axis of 100 nm or more and 1000 nm or less and a minor axis of 1 nm or more and 10 nm or less, and having a fibrous or acicular shape, wherein the alumina dispersion composition contains one or two atoms selected from magnesium and calcium in an amount of 0.2 mol % or more and 1.8 mol % or less relative to the aluminum atoms, and further contains an organic acid or an inorganic acid in an amount of 0.1 equivalent or more and 2.0 equivalents or less relative to the aluminum atoms, the dispersion medium is water, and the properties of the alumina dispersion composition of this embodiment do not change for one month at room temperature. The alumina dispersion composition of the present embodiment has excellent filler effects, such as a reduction in the linear thermal expansion coefficient, an increase in resin strength, and no reduction in transparency, when added to a transparent resin. It can also be highly loaded into the transparent resin. Furthermore, its properties do not change for one month at room temperature, making it easy to handle as a filler. Therefore, the alumina dispersion composition of this embodiment is preferably used as a filler composition for transparent resins. [Example]

[0036] Next, the present invention will be explained in more detail by showing examples, but the present invention is not limited to the following examples in any way.

[0037] In the following examples, the average major axis and the average minor axis of the fibrous particles are shown as the number average values ​​of 20 samples randomly selected from electron micrographs. The alumina dispersions were visually inspected for changes in their properties over a period of one month and for the presence or absence of separation into two layers. Changes in properties ◯: No change in properties after 1 month (no precipitation, loss of transparency, or gelation) and good stability ×: Precipitation, loss of transparency, or gelation occurs within one month 2 layer separation 〇: No separation into two layers even after one month, good stability ×: Separation into two layers occurs within one month

[0038] The resin composite was prepared by mixing alumina dispersion with a photocurable acrylic resin monomer, drying the solvent, and then irradiating with UV (365 nm) for 3 minutes to produce a cured film. The visible light transmittance (600 nm) and linear thermal expansion coefficient (120-160°C) of the obtained cured film were measured. The film uniformity of the obtained cured film was also visually confirmed. The linear thermal expansion coefficient was measured at a measurement temperature of 30°C to 200°C, at a temperature increase rate of 10°C / min, for a hold time of 1 min, under a load of 20 mN in an air atmosphere, and the data from the second measurement was used. Film uniformity 〇: The entire surface is uniform and has good uniformity. ×: Partial aggregation and turbidity

[0039] The following measuring equipment was used: Scanning electron microscope (Hitachi High-Technologies, S-4800) Centrifuge (As One, CN-2060) ·UV irradiation device (Asahi Bunko, CL-1501) UV-visible spectrophotometer (Shimadzu Corporation, UV-1800) Thermomechanical analyzer (Rigaku, TMA-8310)

[0040] [Example 1] A 1-liter four-neck flask was charged with 500 g of ion-exchanged water and 35.7 g (0.593 mol) of acetic acid, and while stirring, 110 g (0.539 mol) of aluminum isopropoxide was added, and the generated isopropyl alcohol was distilled off. The reaction solution was transferred to a magnetically stirred autoclave, and while stirring, 0.87 g of magnesium acetate tetrahydrate (0.75 mol% aluminum) was added. The mixture was then reacted at 150°C for 3 hours to obtain the alumina dispersion composition of Example 1. The fibrous particles contained in the obtained alumina dispersion composition of Example 1 had an average minor axis of 8 nm and an average major axis of 490 nm. Furthermore, the alumina dispersion composition of Example 1 showed no change in properties or separation into two layers even after one month, and had good storage stability.

[0041] [Example 2] An alumina dispersion composition of Example 2 was obtained in the same manner as in Example 1, except that the amount of magnesium acetate tetrahydrate was changed to 1.16 g (1.00 mol % aluminum). The fibrous particles contained in the obtained alumina dispersion composition of Example 2 had an average minor axis of 7 nm and an average major axis of 430 nm. Furthermore, the alumina dispersion composition of Example 2 showed no change in properties or separation into two layers even after one month, demonstrating good storage stability. Figure 1 shows a scanning electron microscope image of the alumina dispersion composition of Example 2.

[0042] [Example 3] An alumina dispersion composition of Example 3 was obtained in the same manner as in Example 1, except that the amount of magnesium acetate tetrahydrate was changed to 1.74 g (1.50 mol % aluminum). The fibrous particles contained in the obtained alumina dispersion composition of Example 3 had an average minor axis of 7 nm and an average major axis of 480 nm. Furthermore, the alumina dispersion composition of Example 3 showed no change in properties or separation into two layers even after 1 month, and had good storage stability.

[0043] [Example 4] An alumina dispersion composition of Example 4 was obtained in the same manner as in Example 1, except that 0.58 g (0.50 mol % aluminum) of magnesium acetate tetrahydrate was used and the reaction time in the autoclave was 6 hours. The fibrous particles contained in the obtained alumina dispersion composition of Example 4 had an average minor axis of 8 nm and an average major axis of 500 nm. Furthermore, the alumina dispersion composition of Example 4 showed no change in properties or separation into two layers even after 1 month, and had good storage stability.

[0044] [Comparative Example 1] A 1-liter four-neck flask was charged with 500 g of ion-exchanged water and 35.7 g (0.593 mol) of acetic acid, and 110 g (0.539 mol) of aluminum isopropoxide was added with stirring. The generated isopropyl alcohol was then distilled off. The reaction solution was transferred to an electromagnetic stirring autoclave and reacted at 150°C for 3 hours with stirring to obtain an alumina dispersion composition of Comparative Example 1. The fibrous particles contained in the obtained alumina dispersion composition of Comparative Example 1 had an average minor axis of 6 nm and an average major axis of 1590 nm. Fig. 2 shows a scanning electron microscope image of the alumina dispersion composition of Comparative Example 1. Furthermore, although the alumina dispersion composition of Comparative Example 1 showed no change in properties even after one month, separation into two layers occurred.

[0045] Comparative Example 2 An alumina dispersion composition of Comparative Example 2 was obtained in the same manner as in Example 1, except that the amount of magnesium acetate tetrahydrate was changed to 0.12 g (0.10 mol % aluminum). The fibrous particles contained in the obtained alumina dispersion composition of Comparative Example 2 had an average minor axis of 8 nm and an average major axis of 1220 nm. Furthermore, although the alumina dispersion composition of Comparative Example 2 showed no change in properties even after one month, separation into two layers occurred.

[0046] Comparative Example 3 An alumina dispersion composition of Comparative Example 3 was obtained in the same manner as in Example 1, except that the amount of magnesium acetate tetrahydrate was changed to 2.32 g (2.00 mol % aluminum). The fibrous particles contained in the obtained alumina dispersion composition of Comparative Example 3 had an average minor axis of 8 nm and an average major axis of 340 nm. The alumina dispersion composition of Comparative Example 3 gelled due to an increase in viscosity within one month.

[0047] [Example A] The resulting alumina dispersion was used to prepare an acrylic resin composite. 300 g of the alumina dispersion obtained in Example 2, 300 g of methyl isobutyl ketone, and 7.5 g of dodecylbenzenesulfonic acid were mixed and dehydrated using a Dean-Stark apparatus to obtain a methyl isobutyl ketone dispersion of alumina particles. The alumina concentration in the dispersion was 5.0% by mass. 6 g of this methyl isobutyl ketone dispersion was mixed with 0.7 g of the acrylic resin monomer A-BPE-4 (manufactured by Shin-Nakamura Chemical Co., Ltd.), and 0.014 g of 1-benzophenone as a photoinitiator. The mixture was cast onto a PET film and placed on a hot plate at 80°C to remove the solvent. The mixture was then cured by irradiating with UV light (365 nm) for 3 minutes to obtain an acrylic resin composite film with an alumina content of 30 wt%. The resulting acrylic resin composite film was homogeneous, had a linear thermal expansion coefficient of 70 ppm / °C, and a transmittance of 88%.

[0048] [Comparative example A] An acrylic resin composite film with an alumina content of 30 wt% was obtained by the same procedure as in Example A, except that the alumina dispersion was the same as that obtained in Comparative Example 1. The obtained acrylic resin composite film had opaque areas due to filler aggregation and was non-uniform. The linear thermal expansion coefficient could not be measured because the film was brittle. The transmittance was 62%.

[0049] [Reference example 1] 150 g of Alumisol-A2 (manufactured by Kawaken Fine Chemicals, major axis 50 nm, minor axis 10 nm, crystalline form: boehmite, alumina concentration 10 wt%), 300 g of methyl isobutyl ketone, and 7.5 g of dodecylbenzenesulfonic acid were mixed and dehydrated using a Dean-Stark apparatus to obtain a methyl isobutyl ketone dispersion of alumina particles. The alumina concentration in the dispersion was 5.0 mass%. Using this methyl isobutyl ketone dispersion, an acrylic resin composite film with an alumina content of 30 wt% was obtained using the same procedure as in Example A. The obtained acrylic resin composite film was uniform, and had a linear thermal expansion coefficient of 161 ppm / °C and a transmittance of 86%.

[0050] [Reference example 2] 1.0 g of the acrylic resin monomer A-BPE-4 (Shin-Nakamura Chemical Co., Ltd.) was mixed with 0.02 g of benzophenone as a photoinitiator, and the mixture was cast onto a PET film and cured by irradiating with UV light (365 nm) for 3 minutes to obtain an acrylic resin film without added alumina particles. The resulting acrylic resin film was homogeneous, had a linear thermal expansion coefficient of 204 ppm / °C, and a transmittance of 90%.

[0051] Table 1 shows the evaluation results of the alumina dispersion compositions of the Examples and Comparative Examples. The crystal form of the alumina hydrate particles was determined by X-ray diffraction measurement of the freeze-dried powder of the alumina hydrate particles contained in the alumina dispersion compositions of Examples 1 to 4. The X-ray diffraction measurement was performed under the following conditions: diffraction angle 2θ = 3 to 90°, tube: Cu, tube voltage: 40 kV, tube current: 30 mA, sampling width: 0.020°, scanning speed: 4.0° / min, entrance slit: 5.0°, receiving slit: 0.114°. The measurement device used was an X-ray diffractometer (Rigaku, SmartLab). The crystal system of the alumina hydrate particles contained in the alumina dispersion compositions of Examples 1 to 4 was boehmite or pseudo-boehmite, and peak patterns specific to the boehmite structure (JCPDS 21-1307), such as a (020) plane peak at around 14.5° and a (120) plane peak at around 28.5°, were confirmed.

[0052] [Table 1]

[0053] Table 2 shows the evaluation results of the resin composites mixed with the alumina dispersion compositions prepared in the examples and comparative examples.

[0054] [Table 2]

[0055] As is clear from Table 1, the method of the present invention provides an alumina dispersion composition having a major axis of 100 nm or more and 1,000 nm or less and a minor axis of 1 nm or more and 10 nm or less, containing one or two atoms selected from magnesium and calcium in an amount of 0.2 mol % or more and 1.8 mol % or less relative to aluminum atoms, containing an organic acid or an inorganic acid in an amount of 0.1 equivalents or more and 2.0 equivalents or less relative to aluminum atoms, using water as a dispersion medium, and exhibiting no change in properties for one month at room temperature. Furthermore, as is clear from Table 2, the alumina dispersion composition of the present invention can be highly filled into resin, and can impart a high suppression effect on the linear thermal expansion coefficient while maintaining the transparency of the resin composite. [Industrial Applicability]

[0056] The alumina dispersion composition of the present invention can impart significant efficacy and effects when used as an additive filler for improving the heat resistance, low thermal expansion, and thermal conductivity of resin substrates used in displays such as liquid crystal displays and organic EL displays, and wiring boards for electronic devices.

Claims

1. A dispersion composition comprising a dispersion medium and fibrous or acicular alumina hydrate particles dispersed in the dispersion medium, the dispersion composition satisfying all of the following requirements (A) to (F): (A) The primary particles of the alumina hydrate particles have a major axis of 100 nm or more and 1000 nm or less and a minor axis of 1 nm or more and 10 nm or less. (B) containing magnesium atoms in an amount of 0.2 mol% or more and 1.8 mol% or less relative to aluminum atoms; (C) containing an organic acid or an inorganic acid in an amount of 0.1 equivalent or more and 2.0 equivalents or less relative to aluminum atoms; (D) The dispersion medium is water; (E) The properties do not change for one month at room temperature. (F) The crystal system of the alumina hydrate particles is boehmite or pseudoboehmite.

2. The dispersion composition described in claim 1, wherein the dispersion composition is used as a filler to be mixed into a transparent resin.

3. A method for producing the dispersion composition according to claim 1 or 2, comprising: a step of hydrolyzing the aluminum alcoholate with an aqueous organic acid solution or an aqueous inorganic acid solution; the aqueous solution containing the alumina hydrate particles obtained by the hydrolysis is peptized in the presence of magnesium atoms at a temperature of 100° C. or higher and 200° C. or lower using an autoclave; In the hydrolysis step, an organic acid or an inorganic acid is present in an amount of 0.1 equivalents or more and 2.0 equivalents or less relative to aluminum atoms, The aforementioned production method, wherein in the peptization step, magnesium atoms are present in an amount of 0.2 mol % or more and 1.8 mol % or less relative to aluminum atoms.

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