Dispersant for metal oxide fine particles and metal oxide fine particle dispersion composition

Abstract

To provide a dispersant that enables the production of a dispersion composition of metal oxide microparticles with high dispersibility of metal oxide microparticles and high stable dispersion stability.SOLUTION: A dispersant for metal oxide microparticles includes Bronsted acid and an imidazoline-based nonionic surfactant.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a dispersant capable of suitably dispersing metal oxide fine particles, and to a metal oxide fine particle dispersion composition in an organic solvent. [Background technology]

[0002] Metal oxide microparticles are used in a variety of fields, including rubber, resin, ink, paint, adhesive, paper, abrasive, coating agent, and pharmaceuticals. In recent years, hybrid materials in which metal oxide microparticles are used as fillers and combined with organic materials such as resin and rubber are expected to exhibit performance such as improved thermal and mechanical properties and controlled electrical properties. However, there has been a problem in that sufficient performance cannot be exhibited unless the metal oxide microparticles are uniformly dispersed in the organic material. Therefore, to address this problem, dispersants for metal oxide microparticles are used.

[0003] Typically, metal oxide microparticle dispersions are produced by using anionic surfactants such as carboxylic acid surfactants, sulfonic acid surfactants, and phosphate ester surfactants, or alkylamine salt-type cationic surfactants as surfactants that function as dispersants.

[0004] For example, Patent Document 1 discloses a technology for metal oxide microparticle dispersants in which a cationic surfactant having an alkylamine salt skeleton in its terminal functional group is used as a dispersant to reduce the viscosity, dispersibility, dispersion stability, and wettability of a metal oxide microparticle dispersion having a negative surface potential.

[0005] Patent Document 2 discloses a technology for improving the compatibility and dispersion stability of metal oxide microparticles with a positive surface potential and organic dispersion media by using an anionic surfactant having a sulfonic acid or phosphoric acid skeleton as a terminal functional group as a dispersant for the metal oxide microparticles.

[0006] Patent Document 3 discloses a technology for imparting wettability, dispersion stability, and handleability to a metal oxide microparticle dispersion having a positive surface potential by using an anionic surfactant functional group having a carboxylic acid or phosphoric acid skeleton as a terminal functional group as a dispersant for the metal oxide microparticle dispersant.

[0007] Patent Document 4 discloses a technology for imparting dispersibility to a metal oxide microparticle dispersion having a positive surface potential by using an anionic surfactant having a carboxy metal salt and a hydroxyl skeleton as a terminal functional group as a dispersant for the metal oxide microparticle dispersion.

[0008] Patent Document 5 discloses a technology for improving the compatibility and dispersion stability of alumina fine particle dispersants, which use an anionic surfactant having a carboxylic acid or sulfonic acid skeleton in the terminal functional group, between alumina fine particles with a positive surface potential and an organic dispersion medium.

[0009] Patent Document 6 discloses a technology for improving the compatibility and dispersibility of metal oxide fine particle dispersants, which use an anionic surfactant having a sulfonic acid skeleton in the terminal functional group, to disperse metal oxide fine particles having a positive surface potential with an organic dispersion medium.

[0010] As such, the surface potential of metal oxide microparticles varies depending on the type of metal oxide microparticle, and in the case of metal oxide microparticles with a positively charged surface potential, the addition of an anionic surfactant improves compatibility with the organic dispersion medium and dispersion stability, while in the case of metal oxide microparticles with a negatively charged surface potential, the addition of a cationic surfactant improves compatibility with the organic dispersion medium and dispersion stability.

[0011] On the other hand, when a cationic surfactant is added to metal oxide fine particles with a positive surface potential, or when an anionic surfactant is added to metal oxide fine particles with a negative surface potential, the dispersant may not be sufficiently adsorbed to the particle surface, causing aggregation. Therefore, it is necessary to select a dispersant based on the target particle material. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-129302 [Patent Document 2] Patent No. 6227013 [Patent Document 3] Japanese Patent Publication No. 2020-75247 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-174029 [Patent Document 5] Japanese Patent Application Laid-Open No. 2012-193052 [Patent Document 8] Special Publication No. 2003-517418 Summary of the Invention [Problem to be solved by the invention]

[0013] The main object of the present invention is to provide a dispersant that can be used to produce a metal oxide microparticle dispersant composition that has high dispersibility in organic solvents even for metal oxide microparticles with different surface potentials and excellent dispersion stability. [Means for solving the problem]

[0014] As a result of extensive research to achieve the above-mentioned object, the inventors have surprisingly found that by using a mixture of an imidazoline-type nonionic surfactant and a Brønsted acid as a dispersant for metal oxide microparticles, metal oxide microparticles with different surface potentials can be dispersed in an organic solvent, thereby completing the present invention.

[0015] That is, the present invention is as follows. A dispersant for dispersing metal oxide microparticles in a solvent, characterized in that it is composed of an imidazoline-type nonionic surfactant represented by the following general formula (1) and a Bronsted acid represented by the following general formula (2) in a molar ratio of (1):(2) = 30:70 to 50:50. [ka] [ka]

[0016] However, in the general formula (1), R 1 represents a linear or branched alkyl or alkylene group having 7 to 21 carbon atoms, and in the general formula (2), R 2 A dispersant for metal oxide fine particles, wherein A represents a linear or branched alkyl group, alkylene group, or phenyl group having 1 to 22 carbon atoms, a hydroxyalkyl group having 1 to 3 carbon atoms and having a primary or secondary hydroxy group, a hydroxyphenyl group, or an alkyl group or alkylene group in which at least one hydrogen atom is substituted with a fluorine atom, and A represents a carboxylic acid group, a sulfonic acid group, a monovalent phosphoric acid group, or a phosphoric acid ester group.

[0017] A dispersant for metal oxide fine particles according to the present invention, wherein the metal oxide fine particles to be dispersed are at least one selected from titanium oxide, silicon dioxide, iron oxide, zirconium dioxide, zinc oxide, aluminum oxide, pseudoboehmite, and cerium oxide.

[0018] The dispersant for metal oxide fine particles, wherein the metal oxide fine particles have an average primary particle size of 5 to 100 nm.

[0019] A metal oxide fine particle dispersion composition comprising the metal oxide fine particles and the dispersant for metal oxide fine particles. [Effects of the Invention]

[0020] The dispersant of the present invention has the advantage of enabling the production of a metal oxide microparticle dispersion composition that is highly dispersible and has excellent dispersion stability without being subject to such restrictions on the surface potential of the metal oxide microparticles, thereby enabling a wide range of material options for the metal oxide microparticles. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be carried out by appropriately modifying it within the scope of its gist.

[0022] As a result of intensive research conducted by the inventors to solve the various problems described above, they discovered that by using an imidazoline-type nonionic surfactant and a Brønsted acid as a dispersant for metal oxide microparticles, it is possible to prepare a dispersion of metal oxide microparticles with high dispersibility without being restricted by the surface potential of the metal oxide microparticles.

[0023] Although the mechanism by which dispersibility is expressed has not been clarified, the following can be speculated. First, it is thought that by mixing an imidazoline-type nonionic surfactant with a Brønsted acid, the protons of the Brønsted acid are conjugated on the imidazoline ring of the imidazoline-type nonionic surfactant, stabilizing it and turning it into a cationic surfactant. In particular, by using an imidazoline-type surfactant, proton stability is improved compared to when other tertiary amine-type cationic surfactants are used, and the following effects are thought to be significant. Since the cationic surfactant is in a neutralized state, it is believed that it will adsorb to the surface of the metal oxide fine particles regardless of the surface potential of the metal oxide fine particles. It is then believed that the imidazoline-type cationic surfactants adsorbed to the surface of the metal oxide fine particles in this way will sterically repel each other due to their hydrophobic groups. It is presumed that this adsorption and steric repulsion will produce an excellent dispersion effect and improve the dispersibility of the metal oxide fine particles. However, the functions and effects of this embodiment are not limited to these.

[0024] (Imidazoline-type nonionic surfactant)

[0025] The type of imidazoline-type nonionic surfactant is not particularly limited, and can be appropriately selected in consideration of the desired physical properties of the metal oxide fine particles. For example, an imidazoline-type nonionic surfactant represented by the general formula (1), which is generally readily available, can be used. [ka]

[0026] R in the general formula (1) 1 is not particularly limited, but from the viewpoint of availability, it is preferable that the carbon number be 1 to 22. Among these, from the viewpoint of dispersibility, the lower limit is more preferably 7 or more, even more preferably 11 or more, even more preferably 13 or more, still more preferably 15 or more, and even more preferably 17 or more. The upper limit is more preferably 22 or less. It may contain a double bond or a branch.

[0027] Specific examples of the imidazoline-type nonionic surfactant represented by general formula (1) include, for example, 2-(2-heptyl-2-imidazolin-1-yl)ethanol, 2-(2-octyl-2-imidazolin-1-yl)ethanol, 2-(2-nonyl-2-imidazolin-1-yl)ethanol, 2-(2-decyl-2-imidazolin-1-yl)ethanol, 2-(2-undecyl-2-imidazolin-1-yl)ethanol, 2-(2-dodecyl-2-imidazolin-1-yl)ethanol, and 2-(2-tridecyl-2-imidazolin-1-yl)ethanol. Examples of such ethanol include ethanol, 2-(2-tetradecyl-2-imidazolin-1-yl)ethanol, 2-(2-pentadecyl-2-imidazolin-1-yl)ethanol, 2-(2-hexadecyl-2-imidazolin-1-yl)ethanol, 2-[2-(2-hexyldecyl)-2-imidazolin-1-yl]ethanol, 2-(2-heptadecyl-2-imidazolin-1-yl)ethanol, 2-[2-(8-heptadecenyl)-2-imidazolin-1-yl]ethanol, and 2-(2-henicosyl-2-imidazolin-1-yl)ethanol.

[0028] The imidazoline-type nonionic surfactants may be used alone or in combination of two or more.

[0029] (Brønsted acid)

[0030] The A and R of the Bronsted acid represented by the general formula (2) that can be used in the metal oxide fine particle dispersant of this patent 2 is not particularly limited and can be appropriately selected taking into consideration the types of other components used, the desired physical properties, and the like. [ka]

[0031] R in general formula (2) 2can represent, because they are generally easy to obtain, an alkyl group, alkylene group, or phenyl group having 1 to 22 carbon atoms and a linear or branched structure; a hydroxyalkyl group, hydroxyphenyl group, having 1 to 3 carbon atoms and a primary or secondary hydroxy group; or an alkyl group or alkylene group in which at least one hydrogen atom is substituted with a fluorine atom. A in general formula (2) can represent a carboxylic acid group, a sulfonic acid group, a monovalent phosphoric acid group, a phosphoric acid ester group, etc. 2 The combination of and A is not particularly limited.

[0032] Specific examples include aliphatic carboxylic acids, aliphatic sulfonic acids, aliphatic phosphate esters, aromatic carboxylic acids, aromatic sulfonic acids, aromatic phosphate esters, aliphatic hydroxy acids, aromatic hydroxy acids, sulfate esters, vinyl group-containing sulfonic acids, fluorine atom-containing carboxylic acids, and fluorine atom-containing sulfonic acids.

[0033] Specific examples of aliphatic carboxylic acids include methanoic acid, ethanoic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, (Z)-octadec-9-enoic acid, (9Z,12Z)-octadeca-9,12-dienoic acid, (9Z,12Z,15Z)-9,12,15-octadecatrienoic acid, (5Z,8Z11Z,14Z)-5,8,11,14-icosatetraenoic acid, and 2-propenylacrylic acid.

[0034] Specific examples of aliphatic sulfonic acids include methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, heptanesulfonic acid, octanesulfonic acid, nonanesulfonic acid, decanesulfonic acid, dodecanesulfonic acid, tetradecanesulfonic acid, hexadecanesulfonic acid, and octadecanesulfonic acid.

[0035] Specific examples of aliphatic phosphate esters include dimethyl phosphate, diethyl phosphate, dibutyl phosphate, dipentyl phosphate, dihexyl phosphate, bis(2-ethylhexyl) phosphate, dioctyl phosphate, dinonyl phosphate, didecyl phosphate, didodecyl phosphate, ditridecyl phosphate, ditetradecyl phosphate, dihexadecyl phosphate, and dioctadecyl phosphate.

[0036] Specific examples of aromatic carboxylic acids include benzenecarboxylic acid, benzene-1,2-dicarboxylic acid, benzene-1,3-dicarboxylic acid, benzene-1,4-dicarboxylic acid, 2-hydroxybenzenecarboxylic acid, 3,4,5-trihydroxybenzenecarboxylic acid, benzenehexacarboxylic acid, and 3-phenylprop-2-enoic acid.

[0037] Specific examples of aromatic sulfonic acids include dodecylbenzenesulfonic acid and paratoluenesulfonic acid.

[0038] Specific examples of aromatic phosphate esters include diphenyl phosphate.

[0039] Specific examples of aliphatic hydroxy acids include hydroxyacetic acid, 2-hydroxypropionic acid, glyceric acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, γ-hydroxybutyric acid, and ricinoleic acid.

[0040] Specific examples of aromatic hydroxy acids include 2-hydroxybenzoic acid, 4-hydroxy-3-methoxybenzoic acid, diphenylglycolic acid, 2-methoxycinnamic acid, (E)-3,4-dihydroxycinnamic acid, 3-hydroxy-4-methoxycinnamic acid, and 4-hydroxy-3,5-dimethoxycinnamic acid.

[0041] Specific examples of sulfate esters include dodecyl sulfate.

[0042] Specific examples of vinyl group-containing sulfonic acids include 2-acrylamido-2-methylpropanesulfonic acid and parastyrenesulfonic acid.

[0043] Specific examples of fluorine atom-containing carboxylic acids include perfluorooctanoic acid.

[0044] Specific examples of fluorine atom-containing sulfonic acids include trifluoromethanesulfonic acid and perfluorooctanesulfonic acid.

[0045] Among these, it is preferable to use at least one selected from the group consisting of aliphatic carboxylic acids, aliphatic sulfonic acids, aliphatic phosphate esters, aromatic carboxylic acids, aromatic sulfonic acids, aromatic phosphoric acids, and the like, and examples thereof include methanoic acid, ethanoic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, (Z)-octadec-9-enoic acid, (9Z,12Z)-octadeca-9,12-dienoic acid, (9Z,12Z,15Z)-9,12,15-octadecatrienoic acid, (5Z,8Z,11Z,14Z) -5,8,11,14-Eicosatetraenoic acid, 2-propenylacrylic acid, methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, heptanesulfonic acid, octane sulfonic acid, nonanesulfonic acid, decanesulfonic acid, dodecanesulfonic acid, tetradecanesulfonic acid, hexadecanesulfonic acid, octadecanesulfonic acid, dimethyl phosphate, diethyl phosphate, dibutyl phosphate, dipentyl phosphate, dihexyl phosphate, bis(2-ethylhexyl) phosphate, dioctyl phosphate, dinonyl phosphate, phosphorus More preferably, the alkyl ester is at least one selected from the group consisting of didecyl phosphate, didodecyl phosphate, ditridecyl phosphate, ditetradecyl phosphate, dihexadecyl phosphate, dioctadecyl phosphate, benzenecarboxylic acid, benzene-1,2-dicarboxylic acid, benzene-1,3-dicarboxylic acid, benzene-1,4-dicarboxylic acid, 2-hydroxybenzenecarboxylic acid, 3,4,5-trihydroxybenzenecarboxylic acid, benzenehexacarboxylic acid, 3-phenylprop-2-enoic acid, dodecylbenzenesulfonic acid, paratoluenesulfonic acid, and diphenyl phosphate.

[0046] The Bronsted acid may be used alone or in combination of two or more kinds.

[0047] It is expected that the reaction product of an imidazoline-type nonionic surfactant and a methylating agent will also exhibit dispersibility similar to that of the present invention. However, the use of a methylating agent is more expensive than that of a Brønsted acid and requires a complicated synthesis procedure, so the use of a Brønsted acid is more preferable.

[0048] (molar ratio)

[0049] In the metal oxide fine particle dispersant of the present invention, the molar ratio of the imidazoline-type nonionic surfactant to the Bronsted acid is preferably imidazoline-type nonionic surfactant:Bronsted acid=30:70 to 50:50, more preferably 30:70, even more preferably 35:65, even more preferably 40:60, still more preferably 45:55, and even more preferably 50:50.

[0050] (Metal Oxide Fine Particle Dispersant Manufacturing Method)

[0051] The method for producing a dispersant for metal oxide fine particles according to this embodiment includes a step of mixing the imidazoline-type nonionic surfactant with the Bronsted acid. At this time, the salt may be formed. The dispersant may also be produced by previously mixing the imidazoline-type nonionic surfactant with the Bronsted acid. The other solvents and other additives described below may also be added. A specific method for producing the metal oxide microparticle dispersant according to this embodiment is, for example, to mix an imidazoline-type nonionic surfactant and a Brønsted acid within the above-mentioned molar ratio range using a dispersing machine such as a stirrer or a planetary mixer.

[0052] (metal oxide fine particles)

[0053] The metal oxide fine particle dispersant of the present invention can impart high dispersibility to metal oxide fine particles without being subject to such limitations on the surface potential of the metal oxide fine particles, and therefore, the type of metal oxide fine particles is not particularly limited, allowing for a wide range of material options.

[0054] Specific examples of metal oxide fine particles include widely used titanium oxide, silicon dioxide, iron oxide, zirconium dioxide, zinc oxide, aluminum oxide, pseudoboehmite, cerium oxide, and the like.

[0055] The average primary particle diameter of the metal oxide fine particles is not particularly limited, but is preferably 5 nm to 100 nm. The upper limit of this average primary particle diameter is more preferably 80 nm or less, even more preferably 60 nm or less, even more preferably 50 nm or less, still more preferably 30 nm or less, and even more preferably 20 nm or less. The average primary particle diameter here is a value calculated from specific surface area data by the BET method.

[0056] The metal oxide fine particles may be used alone or in combination of two or more kinds.

[0057] (Other solvents, other additives, etc.)

[0058] The solvent used in the metal oxide fine particle dispersion composition according to this embodiment is not particularly limited and can be appropriately selected depending on the type of metal oxide fine particles to be dispersed, etc. Examples of the solvent include ether solvents such as dibutyl ether, tetrahydrofuran, and dioxane; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, and N-methyl-2-pyrrolidone; ester solvents such as ethyl acetate, isopropyl acetate, propylene glycol monomethyl ether acetate, methyl acrylate, methyl methacrylate, and isobornyl acrylate; aromatic solvents such as xylene, toluene, and styrene; and hydrocarbon solvents such as hexane, methylcyclohexane, and mineral spirits.

[0059] Among these, from the viewpoint of dispersibility, it is preferable to use one or more solvents selected from the group consisting of ester solvents, aromatic solvents, hydrocarbon solvents, etc., and it is more preferable to use at least one solvent selected from the group consisting of methyl acetate, isopropyl acetate, propylene glycol monomethyl ether acetate, methyl acrylate, methyl methacrylate, isobornyl acrylate, xylene, toluene, styrene, hexane, methylcyclohexane, and mineral spirits.

[0060] Other additives may include known additives that are added to metal oxide fine particles, etc. Examples include leveling agents, ultraviolet absorbers, antioxidants, viscosity modifiers, and antistatic agents.

[0061] The content of each component is not particularly limited, and can be determined as appropriate in consideration of the type of component used, the intended use, and the like.

[0062] The content of metal oxide fine particles in the metal oxide fine particle dispersion composition is preferably 5 to 30% by mass. The lower limit of this content is more preferably 10% by mass or more, even more preferably 15% by mass or more, even more preferably 17% by mass or more, and even more preferably 19% by mass or more. The upper limit of this content is more preferably 30% by mass or less, even more preferably 27% by mass or less, and even more preferably 25% by mass or less.

[0063] The content of the dispersant for metal oxide fine particles per 100 parts by mass of metal oxide fine particles is preferably 10 to 100 parts by mass. The lower limit of this content is more preferably 15 parts by mass or more, even more preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more. The upper limit of this content is more preferably 100 parts by mass or less.

[0064] In a preferred embodiment of the metal oxide microparticle dispersion composition according to this embodiment, the upper limit of the average particle size of the metal oxide microparticles in the dispersion composition is preferably 150 nm or less. It is more preferably 140 nm or less, even more preferably 130 nm or less, and even more preferably 116 nm or less. There is no particular restriction on the lower limit, as long as it is equal to or greater than the primary particle size of the metal oxide microparticles used. The metal oxide microparticle dispersion composition according to this embodiment can exhibit high dispersibility. This average particle size is a value determined by photon correlation spectroscopy using a dynamic light scattering particle size distribution analyzer, and can be measured in accordance with the method described in the Examples below.

[0065] (Method for producing metal oxide fine particle dispersion composition)

[0066] The method for producing a metal oxide microparticle dispersion composition according to this embodiment includes a step of mixing the metal oxide microparticle dispersant of the present invention, which comprises an imidazoline-type nonionic surfactant and a Brønsted acid, with metal oxide microparticles, or a step of mixing an imidazoline-type nonionic surfactant, a Brønsted acid, and metal oxide microparticles. The method for producing a metal oxide microparticle dispersion composition according to this embodiment preferably involves dispersing and stabilizing the metal oxide microparticles in a solvent using a stirrer, a disperser, or the like, in the presence of the metal oxide microparticle dispersant obtained by mixing the imidazoline-type nonionic surfactant and the Brønsted acid, and other additives.

[0067] The mixing can be carried out by a known method. For example, a general method such as a planetary mixer, a dispersing machine such as a homogenizer, an ultrasonic agitator, a rocking mill, a ball mill, a jet mill, or a spike mill can be used. Suitable mixing conditions can be selected as appropriate, taking into consideration the ratio and properties of the components used.

[0068] The metal oxide fine particle dispersion composition according to this embodiment can be suitably used as a filler for organic substances and the like. [Example]

[0069] The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. Unless otherwise specified, all reagents used were of special grade or first grade manufactured by Tokyo Chemical Industry Co., Ltd.

[0070] (Preparation of Dispersant for Metal Oxide Fine Particles)

[0071] The imidazoline-type nonionic surfactant represented by general formula (1) was synthesized by a known method (JP 10-17554 A). The resulting imidazoline-type nonionic surfactant and 1 mole of Brønsted acid per mole of the imidazoline-type nonionic surfactant were then placed in an ointment jar. Subsequently, a planetary centrifugal mixer (device name: Awatori Rentaro (registered trademark) ARE-310, manufactured by Thinky Corporation) was used for 10 minutes of mixing and 5 minutes of degassing at room temperature to obtain metal oxide microparticle dispersions composed of the imidazoline-type nonionic surfactant and the Brønsted acid (Examples 1 to 94). The respective combinations and amounts added are shown in Tables 1 to 8. For comparison, an alkylamine-type nonionic surfactant was used instead of the imidazoline-type nonionic surfactant, and other compositions were prepared without surfactant or Bronsted acid, yielding Comparative Examples 1 to 9. The respective combinations and amounts added are shown in Table 9.

[0072] Details of the surfactants and Bronsted acids used are as follows:

[0073] Imidazoline-type nonionic surfactants [ka] (In the formula, -CR 1 The group represents a caprylic acid residue, a lauric acid residue, a myristic acid residue, an isopalmitic acid residue, a stearic acid residue, an oleic acid residue, a behenic acid residue, or a coconut oil fatty acid residue.

[0074] Alkylamine-type nonionic surfactant (compound represented by formula (3)) [ka] (Tokyo Chemical Industry Co., Ltd., purity 96% or higher)

[0075] Bronsted acid (special grade or first grade, manufactured by Tokyo Chemical Industry Co., Ltd.) Ethanoic acid Propanoic acid 2-Oxopropanoic acid 2-Propenoic acid 2-hydroxypropanoic acid Octanoic acid 2-Ethylhexanoic acid 9-Octadecenoic acid Trifluoroacetate 2-Acrylamide-2-methylpropanesulfonic acid Paratoluenesulfonic acid Dodecylbenzenesulfonic acid Dibutyl phosphate

[0076] Solvent (Tokyo Chemical Industry Co., Ltd., special grade or first grade) ·toluene Methylcyclohexane Ethyl acetate Methyl isobutyl ketone N-methyl-2-pyrrolidone Methyl methacrylate Isobornyl acrylate

[0077] (Preparation of Metal Oxide Fine Particle Dispersion Composition)

[0078] An ointment jar was charged with 30 to 100 parts by weight of a dispersant consisting of an imidazoline-type nonionic surfactant and a Bronsted acid per 100 parts by weight of metal oxide microparticles, and the necessary amount of solvent was added so that the metal oxide microparticles constituted 5 to 30% by weight of the dispersion composition, under the conditions shown in Tables 1 to 8. Subsequently, a planetary centrifugal mixer (model name: Awatori Rentaro ARE-310, manufactured by Thinky Corporation) was used for 10 minutes of mixing and 5 minutes of degassing at room temperature to obtain a metal oxide microparticle dispersion composition. If dispersion was insufficient, a further dispersion treatment was performed in an ice-water bath for 30 minutes using a homogenizer equipped with a microtip tapered type Φ3 (ultrasonic homogenizer NR-300M, manufactured by Microtec Nichion Co., Ltd.) to obtain a metal oxide microparticle dispersion composition (Examples 1 to 94). Similarly, Comparative Examples 1 to 9 were obtained under the conditions shown in Table 9.

[0079] The metal oxide fine particles used are as follows:

[0080] (A) Pseudoboehmite "Aluminum Sol-10A" manufactured by Kawaken Fine Chemicals Co., Ltd. Particle size (minor diameter x major diameter): 10 x 50 nm (arithmetic mean diameter determined by observation under an electron microscope), zeta potential +59.5 (value measured by zeta potential of a dispersion of metal oxide fine particles and distilled water) (a) Aluminum oxide TECNAN "TECNAPOW-AL2O3-100G" Particle size: 20-25nm (BET method catalog value), Zeta potential +35.00 (value measured by zeta potential of a dispersion of metal oxide particles and distilled water) (c) Cerium oxide TECNAN "TECNAPOW-CEO2-100G" Particle size: 5 to 10 nm (BET method catalog value), Zeta potential +1.614 (value measured by zeta potential of a dispersion of metal oxide particles and distilled water) (D) Iron oxide (trivalent) TECNAN "TECNAPOW-FE2O3-100G" Particle size: 10-20nm (BET method catalog value), Zeta potential +5.233 (value measured by zeta potential of a dispersion of metal oxide particles and distilled water) (E) Titanium oxide TECNAN "TECNAPOW-TIO2-100G" Particle size: 10-15nm (BET method catalog value), Zeta potential: +38.94 (value measured by zeta potential of a dispersion of metal oxide particles and distilled water) (K) Zinc oxide TECNAN "TECNAPOW-ZNO-100G" Particle size: 20-25nm (BET method catalog value), Zeta potential: +28.56 (value measured by zeta potential of a dispersion of metal oxide particles and distilled water) (G) Zirconium dioxide TECNAN "TECNAPOW-ZNO-100G" Particle size: 10-15nm (BET method catalog value), Zeta potential: +49.87 (value measured by zeta potential of a dispersion of metal oxide particles and distilled water) (H) Silicon dioxide TECNAN "TECNAPOW-SIO2-100G" Particle size: 10-15nm (BET method catalog value), Zeta potential: 13.97 (value measured by zeta potential of a dispersion of metal oxide particles and distilled water)

[0081] (Surface potential measurement of metal oxide particles)

[0082] Metal oxide particles were placed in a polypropylene container, and the necessary amount of distilled water was added to make a 1% by mass dispersion, followed by shaking. The zeta potential of the supernatant dispersion was then measured by electrophoresis using a zeta potential measuring device (Zetasizer® Pro, manufactured by Malvern Panalytical).

[0083] (Measurement of particle size of metal oxide fine particle dispersion)

[0084] The particle size was measured after diluting the metal oxide particle dispersion 20 times with a solvent. That is, after diluting the metal oxide particle dispersion sample 20 times with a solvent, the average particle size was measured by photon correlation spectroscopy using a dynamic light scattering particle size distribution analyzer (Zetasizer Pro, manufactured by Malvern Panalytical).

[0085] (Evaluation of Metal Oxide Fine Particle Dispersion Composition)

[0086] The metal oxide fine particle dispersion composition was visually evaluated according to the following criteria. Evaluation criteria ★: Uniformly dispersed, no agglomerates observed, transparent. ☆: Uniformly dispersed, no aggregates observed, transparent, but slightly suspended. ⊚: Uniformly dispersed, no aggregates observed, but suspended. ●: Dispersed, but some aggregates are visible. ◯: Aggregates are observed, but redispersibility is observed. △: Many aggregates are observed and have settled. The product is suspended but redispersible. ×: A large amount of aggregates were observed and precipitated. The aggregates were suspended and not redispersible.

[0087] Metal oxide fine particle dispersant and dispersion composition Example 1 [Table 1]

[0088] Metal oxide fine particle dispersant and dispersion composition example 2 [Table 2]

[0089] Metal oxide fine particle dispersant and dispersion composition example 3 [Table 3]

[0090] Metal oxide fine particle dispersant and dispersion composition Example 4 [Table 4]

[0091] Metal oxide fine particle dispersant and dispersion composition example 5 [Table 5]

[0092] Metal oxide fine particle dispersant and dispersion composition Example 6 [Table 6]

[0093] Metal oxide fine particle dispersant and dispersion composition Example 7 [Table 7]

[0094] Metal oxide fine particle dispersant and dispersion composition Example 8 [Table 8]

[0095] Comparative Examples of Metal Oxide Fine Particle Dispersant and Dispersion Composition [Table 9]

[0096] From the above, all of the metal oxide microparticle dispersants of the examples prepared within the scope of the present invention were not affected by the zeta potential of the metal oxide microparticles, and the dispersibility evaluation was high, at 0 or above. On the other hand, the metal oxide microparticle dispersants of the comparative examples were poorly dispersed, at Δ or below, and sedimentation of the metal oxide microparticles was confirmed in all cases. From these facts, it is presumed that the metal oxide microparticle dispersant of the present invention is adsorbed onto the surface of the metal oxide microparticles, and the adsorbed metal oxide microparticle dispersants repel each other due to steric repulsion, thereby achieving excellent dispersibility. As a result, it is thought that the metal oxide microparticle dispersion composition of the present invention exhibits dispersibility without being affected by the zeta potential of the metal oxide microparticles.

Claims

1. A dispersant for dispersing metal oxide fine particles in a solvent, characterized in that it comprises an imidazoline-type nonionic surfactant represented by the following general formula (1) and a Bronsted acid represented by the following general formula (2) in a molar ratio of (1):(2) = 30:70 to 50:50: 【Chemistry 1】 【Chemistry 2】 However, in the general formula (1), R １ represents a linear or branched alkyl or alkylene group having 7 to 21 carbon atoms, and in the general formula (2), R ２ represents any one of a linear or branched alkyl group, alkylene group, or phenyl group having 1 to 22 carbon atoms, a hydroxyalkyl group having 1 to 3 carbon atoms and having a primary or secondary hydroxy group, a hydroxyphenyl group, or an alkyl group or alkylene group in which at least one hydrogen atom is substituted with a fluorine atom, and A represents any one of a carboxylic acid group, a sulfonic acid group, a monovalent phosphoric acid group, and a phosphoric acid ester group.

2. 2. The dispersant according to claim 1, wherein the metal oxide fine particles are at least one selected from the group consisting of titanium oxide, silicon dioxide, iron oxide, zirconium dioxide, zinc oxide, aluminum oxide, pseudoboehmite, and cerium oxide.

3. The dispersant according to claim 1 or 2, wherein the metal oxide fine particles have an average primary particle size of 5 to 100 nm.

4. A dispersion composition comprising the metal oxide fine particles according to any one of claims 1 to 3 and the dispersant according to any one of claims 1 to 3.

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