JP7779499B2 - Dispersant for metal oxide fine particles and dispersion containing same - Google Patents

Description

The present invention relates to a dispersant and a dispersion containing this dispersant.

Non-aqueous dispersion compositions containing organic or inorganic powders dispersed in non-aqueous solvents are used in a variety of industrial fields. Examples of organic powders include organic pigments, and non-aqueous dispersion compositions containing organic pigments are used in paints, printing inks, inkjet inks, color filter resists, and writing instrument inks. Examples of inorganic powders include metal oxide fine particles such as ceramic powders. Due to their unique chemical and physical properties, they are used in a wide variety of materials, including pigments, ultraviolet and infrared absorbers, catalysts, antistatic agents, and transparent conductive films. Non-aqueous dispersion compositions containing metal oxide fine particles are also used in coating materials and molding materials that require transparency and high refractive index, dielectric layers for ceramic capacitors, semiconductor substrates, transparent conductive films, conductive inks, various sensors, and electronic components such as liquid crystal display elements, as well as abrasives and fireproofing materials.

In recent years, there has been a demand for improved product characteristics, such as smaller components, higher capacity, and higher efficiency, in electronic component applications. To meet these demands, there is a need to reduce the particle size of raw materials such as metal oxides and increase their concentration in non-aqueous dispersion compositions. When preparing non-aqueous dispersion compositions, organic or inorganic powders often lack sufficient dispersibility on their own, so dispersants are generally used to improve the fluidity and storage stability of non-aqueous dispersion compositions. Many polymeric dispersants have been proposed as such dispersants, such as polyacrylic acid and its copolymers, and copolymers of polyoxyalkylene derivatives and maleic anhydride.

However, with conventional polymeric dispersants, microparticulation can lead to a tendency for bridging aggregation, where the dispersant is adsorbed across particles, resulting in a decrease in dispersibility. The decrease in dispersibility that accompanies microparticulation of the dispersion can lead to problems such as thickening of the non-aqueous dispersion composition and settling of the dispersion. Non-aqueous dispersion compositions that experience these problems not only suffer from reduced productivity, processing characteristics, and ease of handling, but also lead to a decrease in the quality of the final product.

To solve these problems, Patent Document 1 proposes the use of polyoxypropylene monomethacrylic ether and an ester of trimellitic anhydride, which have enhanced lipophilicity, but their effectiveness on metal oxide microparticles was not fully satisfactory.

Furthermore, in Patent Document 2, by providing a polyoxyalkylene structure to the hydrophobic chain of the dispersant structure, compatibility with the dispersion medium is improved and three-dimensional repulsion can be obtained, but on the other hand, wettability with fine particles is insufficient and more energy is required for dispersion. As a result, there are problems with receiving a lot of thermal energy during dispersion, which makes secondary aggregation more likely to occur and increases viscosity.

Japanese Patent Application Laid-Open No. 2007-144402 JP 2016-147261 A

The present invention aims to provide a dispersant that finely disperses metal oxide microparticles in a non-aqueous solvent, and a dispersion of metal oxide microparticles with excellent dispersibility.

In order to solve the above problems, the present inventors have conducted extensive research and have completed the present invention by incorporating a polyoxypropylene (poly)glyceryl ether dibasic acid ester represented by formula (1) as a dispersant for metal oxide fine particles.
(In the formula, PO represents propylene oxide; k, l, and m represent the number of moles of propylene oxide added and are integers of 0 or more, and k+l+m=1 to 150; n represents the average degree of polymerization of (poly)glycerin calculated from the hydroxyl value and is an integer of 1 to 20; Ra, Rb, and Rc each independently represent a hydrogen atom or a residue of a dicarboxylic acid having 4 carbon atoms, provided that they are not all hydrogen atoms.)

By incorporating the dispersant of the present invention, particle reagglomeration and sedimentation can be suppressed, providing a dispersion with excellent dispersibility of metal oxide microparticles.

The following describes in more detail the embodiments for carrying out this description, but the scope of the present invention is not limited to these embodiments, and modifications and other changes made within the spirit of the present invention also belong to the present invention. Note that the range "to" includes both the upper and lower limits.

The (poly)glycerin used in the present invention is glycerin or a polyglycerin having an average degree of polymerization of 2 to 20 calculated from the hydroxyl value, more preferably glycerin or a polyglycerin having an average degree of polymerization of 2 to 10, and even more preferably a polyglycerin having an average degree of polymerization of 2 to 6. Here, the average degree of polymerization is the average degree of polymerization (n) of polyglycerin calculated from the hydroxyl value by terminal group analysis. Specifically, the average degree of polymerization is calculated from the following formulas (Formula 2) and (Formula 3).
(Formula 2) Molecular weight = 74n + 18
(Equation 3) Hydroxyl value = 56110(n + 2) / molecular weight The hydroxyl value in the above (Equation 3) is a numerical value that indicates the number of hydroxyl groups contained in polyglycerol, and refers to the number of milligrams of potassium hydroxide required to neutralize the acetic acid required to acetylate the free hydroxyl groups contained in 1 g of polyglycerol. The number of milligrams of potassium hydroxide is calculated in accordance with "Standard Test Methods for the Analysis of Fats, Oils and Related Compounds, 2013 Edition, Established by the Japan Oil Chemists'Society," edited by the Japan Oil Chemists' Society.

For polyglycerols having an average degree of polymerization of 2 to 20 calculated from the hydroxyl value, compositions with a molecular weight distribution are generally used, but two or more polyglycerols having different molecular weight distributions may be mixed, and polyglycerols with an average degree of polymerization of more than 20 may also be used as long as the average degree of polymerization of the polyglycerol mixture calculated from the hydroxyl value is 2 to 20.

Polyglycerol can be obtained by the dehydration condensation reaction of glycerol, synthesis using glycerol analogues such as glycidol, epichlorohydrin, and glycerol halohydrin, or by recovery of synthetic glycerol from the glycerol distillation residue.

The number of moles of propylene oxide added to the polyoxypropylene (poly)glyceryl ether used in the present invention is 1 to 150 moles, preferably 20 to 150 moles. When the number of moles of propylene oxide added is 20 to 150 moles, the steric hindrance effect is improved, resulting in better dispersibility. Furthermore, it is preferable that the number of moles of propylene oxide added is more than 0 and not more than 30 per hydroxyl group of (poly)glycerin.

The dicarboxylic acids having four carbon atoms used in the present invention include succinic acid, maleic acid, fumaric acid, and anhydrides thereof. These may be used alone or in combination of two or more.

The polyoxypropylene (poly)glyceryl ether dibasic acid ester of the present invention desirably has an acid value of 20 mgKOH/g to 200 mgKOH/g, preferably 25 mgKOH/g to 180 mgKOH/g, and more preferably 30 mgKOH/g to 170 mgKOH/g. An acid value of 20 mgKOH/g to 200 mgKOH/g improves the effect of suppressing re-aggregation of metal oxide fine particles, resulting in better dispersibility. Here, the acid value refers to the number of milligrams of potassium hydroxide required to neutralize the carboxy groups contained in 1 g of polyoxypropylene (poly)glyceryl ether dibasic acid ester. The number of milligrams of potassium hydroxide is measured in accordance with "Standard Testing Methods for the Analysis of Fats, Oils, and Related Materials, 2013 Edition," edited by the Japan Oil Chemists' Society, and calculated using the following formula (Formula 4):
(Formula 4) Acid value = (5.611×A×F)/B
A: Amount (mL) of 0.1 mol/L potassium hydroxide standard solution used
F: Factor of 0.1 mol/L potassium hydroxide standard solution B: Sample amount (g)

The dispersion of metal oxide microparticles of the present invention contains a polyoxypropylene (poly)glyceryl ether dibasic acid ester, metal oxide microparticles, and a non-aqueous solvent. The dispersant content is preferably 0.01% to 20% by weight, and more preferably 0.1% to 10% by weight.

The metal oxide microparticles contained in the dispersion of the present invention are not particularly limited, but examples include zirconium oxide, titanium oxide, hafnium oxide, zinc oxide, tin oxide, tungsten oxide, iron oxide, aluminum oxide, silicon oxide, molybdenum oxide, vanadium oxide, cobalt oxide, copper oxide, silver oxide, indium tin oxide, indium oxide, and antimony oxide. These may be used alone or in combination of two or more. From the viewpoint of high refractive index, zirconium oxide, titanium oxide, and hafnium oxide are preferred as metal oxide microparticles.

The primary particle size of the metal oxide microparticles is generally preferably 100 nm or less. When the primary particle size of the metal oxide microparticles is 100 nm or less, it is easier to obtain features such as high transparency of the dispersion.

The metal oxide microparticles desirably have a Z-average particle size of 300 nm or less, preferably 250 nm or less, and more preferably 200 nm or less, as determined by analyzing scattered light using a particle size distribution analyzer using dynamic light scattering.

The content of metal oxide microparticles is typically 0.1% to 50% by weight, and preferably 1% to 30% by weight. When the content of metal oxide microparticles is 50% by weight or less, the wettability of the metal oxide microparticles with the non-aqueous solvent is improved, resulting in a dispersion with excellent dispersibility. Furthermore, when the content of metal oxide microparticles is 0.1% by weight or more, it is easier to achieve features such as high refractive index.

The non-aqueous solvent contained in the dispersion of the present invention is not particularly limited, but examples include esters such as ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, and gamma-butyrolactone; ethers such as diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and propylene glycol monomethyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; and amides such as dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. These solvents may be used alone or in combination of two or more.

The ratio of dispersant to non-aqueous solvent contained in the dispersion of the present invention is typically 1:3 to 1:10,000 by weight, and preferably 1:4 to 1:1,000, from the viewpoint of the solubility of the dispersant in the dispersion.

The dispersion of metal oxide microparticles of the present invention can be blended with various additives such as thermoplastic resins, plasticizers, polymerizable monomers such as (meth)acrylic acid esters and epoxies, other dispersants, other surfactants, viscosity modifiers, antifoaming agents, antioxidants, radical polymerization initiators, acid generators, and base generators, as well as water-soluble organic solvents such as alcohols and glycol ethers, to the extent that the purpose of the dispersion is not impaired.

The dispersion of metal oxide microparticles of the present invention can be prepared in accordance with conventional preparation methods. For example, one method involves adding metal oxide microparticles to a non-aqueous solvent containing the dispersant of the present invention, followed by stirring, mixing, and dispersing at room temperature. Examples of dispersing machines that can be used include rocking mills, paint shakers, ball mills, bead mills, roll mills, sand mills, jet mills, homogenizers, planetary mixers, and ultrasonic dispersers, but the dispersion method is not limited to these. Furthermore, beads such as zirconia beads and alumina beads may also be used as needed.

The dispersion of metal oxide microparticles of the present invention may be in liquid or solid form, and if it is solid, it is sufficient that its liquidity is restored by vigorous stirring or shaking.

The dispersion of metal oxide microparticles of the present invention has excellent dispersibility and can be used in coating materials, anti-reflective films, optical components, and other electronic materials that require transparency and high refractive index.

Next, the present invention will be described in detail using examples and comparative examples, but the present invention is not limited to these examples.

(Synthesis of Dispersants A to G)
301.5 g of polyoxypropylene (poly)glyceryl ether having 40 moles of PO added and 48.6 g of succinic anhydride were placed in a reaction vessel, and sodium acetate was added as a catalyst. The mixture was heated to 70°C to 100°C under a nitrogen stream to react, yielding polyoxypropylene (poly)glyceryl ether succinate ester (Dispersant A) having an acid value of 83.4 mgKOH/g. Similarly, Dispersants B to G were produced by varying the degree of polymerization of polyglycerin, the moles of PO added to the polyoxypropylene (poly)glyceryl ether, and the charged weight. The details of each dispersant are shown in Table 1.

Example 1
0.5 g of Dispersant A and 8.5 g of toluene were added to a 50 mL plastic container and dissolved, and then 1.0 g of zirconium oxide (UEP-100, manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.) and 30 g of zirconia beads (φ1 mm) were added. This was dispersed at 600 rpm for 15 hours using a rocking mill (RM-05, manufactured by Seiwa Giken Co., Ltd.), and the zirconia beads were then removed by filtration to obtain a dispersion of zirconium oxide.

(Examples 2 to 10)
In Examples 2 to 10, dispersions were prepared in the same manner as in Example 1, except that the types and amounts of the non-aqueous solvent and dispersant were changed.

(Comparative Examples 1 to 3)
In Comparative Examples 1 to 3, dispersions were prepared in the same manner as in Example 1, Example 4 or Example 6, except that no dispersant was added and the amount of non-aqueous solvent added was increased.

(Measurement of particle size)
The dispersion was placed in a disposable cell, and the measurement temperature was set to 25°C. The particle size distribution was measured using a particle size distribution measuring device (Nanosizer ZS-100, manufactured by Malvern Corporation) that employs dynamic light scattering. Each measurement was carried out three times, and the particle sizes were compared using the average value of the Z-average particle size. The results are shown in Tables 2 and 3.

*: Zirconium oxide (UEP-100, D50 diameter: 0.6 μm, manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.)

In Examples 1 and 2, toluene was used as the non-aqueous solvent, and zirconium oxide dispersions with a Z-average particle size of 200 nm or less were obtained, whereas in Comparative Example 1, in which no dispersant was added, thickening and separation occurred, and no dispersion was obtained. In addition, in Examples 3 to 5, methyl ethyl ketone was used as the non-aqueous solvent, and zirconium oxide dispersions with a Z-average particle size of 300 nm or less were obtained, whereas in Comparative Example 2, in which no dispersant was added, thickening and separation occurred, and no dispersion was obtained.

*: Zirconium oxide (UEP-100, D50 diameter: 0.6 μm, manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.)

In Examples 6 to 10, propylene glycol monomethyl ether was used as the non-aqueous solvent, and zirconium oxide dispersions with a Z-average particle size of 450 nm or less were obtained, whereas in Comparative Example 3, in which no dispersant was added, thickening and separation occurred, and no dispersion was obtained. This demonstrates that dispersions of metal oxide microparticles using a specific polyoxypropylene (poly)glyceryl ether dibasic acid ester as a dispersant have excellent dispersibility for metal oxide microparticles.

Claims (6)

A dispersion of metal oxide fine particles, comprising a dispersant which is a polyoxypropylene (poly)glyceryl ether dibasic acid ester represented by formula (1), metal oxide fine particles, and a non-aqueous solvent .
(In the formula, PO represents propylene oxide; k, l, and m represent the number of moles of propylene oxide added and are integers of 0 or more, and k+l+m=1 to 150; n represents the average degree of polymerization of (poly)glycerol calculated from the hydroxyl value and is an integer of 1 to 20; Ra, Rb, and Rc each independently represent a hydrogen atom or a residue of a dicarboxylic acid having 4 carbon atoms, provided that they cannot all be hydrogen atoms.) 2. The dispersion of metal oxide fine particles according to claim 1, wherein the acid value of the polyoxypropylene (poly)glyceryl ether dibasic acid ester is 20 mg KOH/g to 200 mg KOH/g. 3. The dispersion of metal oxide fine particles according to claim 1, wherein the blending amount of the dispersant is 0.01% by weight to 20% by weight. 4. The dispersion of metal oxide fine particles according to claim 1, wherein the amount of the metal oxide fine particles blended is 0.1% by weight to 50% by weight. 5. The dispersion of metal oxide fine particles according to claim 1, wherein the metal oxide fine particles are zirconium oxide. A paint or ink containing the dispersion according to any one of claims 1 to 5 .