JP7844873B2 - White pigment dispersion and composition for forming white partitions containing the same - Google Patents

Description

This invention relates to a white pigment dispersion and a white septum-forming composition containing the same.

For example, in display panels using display elements such as micro-light-emitting diodes (LEDs) or organic electroluminescent (OLED) elements, a fine pattern is formed, partitioned by barriers to suppress the mixing of light colors, with light-emitting sections provided between these barriers. Such barriers are formed, for example, from a resin composition. As a composition that can constitute such a resin composition, colored compositions having opacity, reflectivity, etc., have been proposed to suppress the mixing of light colors (Patent Document 1).

Patent Document 1 describes a negative-type photosensitive coloring composition containing (A) a white pigment, (B) a siloxane resin, (C) a photopolymerization initiator, (D) a photopolymerizable compound, and (E) an organic solvent, wherein the (B) siloxane resin contains structural units derived from a fluorine-containing alkoxysilane compound and structural units derived from a bifunctional alkoxysilane compound, and these units are present in predetermined amounts. It is claimed that this configuration allows for the formation of a thick, cured film with high reflectivity, high resolution, and excellent heat resistance.

International Publication No. 2019/176785

However, while the reflectivity can be improved to some extent by using the composition described in, for example, Patent Document 1, there is still room for improvement to meet the market's demand for higher image quality.

Furthermore, in order to mitigate global warming in recent years, there is a need to reduce the power consumption of display elements. However, it is generally known that in the display elements described above, if the reflectivity of the partitions is low, it is necessary to increase the voltage in order to increase the color density of each section. As a result, in order to reduce power consumption, it is necessary to improve the reflectivity, but even using the composition described in Patent Document 1, for example, there is room for improvement in order to meet the recent demands for energy conservation.

Therefore, the object of the present invention is to provide a white pigment dispersion and a white partition-forming composition capable of forming partitions for display elements having good reflectivity.

The inventors diligently conducted research to solve the aforementioned problems. As a result, they discovered that it is possible to improve the reflectivity of the partition wall of a display element by using a combination of a specific polymer-based dispersant and a specific dispersion aid, thus completing the present invention. The gist of the present invention is as follows:

[1] A white pigment dispersion comprising a white inorganic pigment, a polymeric dispersant, a dispersion aid, and a solvent, wherein the polymeric dispersant is an acid-value type polymeric dispersant having a carboxyl group or a phosphate group, and the dispersion aid contains a compound having a phthalimide skeleton as an active ingredient, the phthalimide skeleton may have substituents directly attached to its carbon atoms, and the nitrogen atom in the phthalimide skeleton is linked to a group having a carboxyl group or a group having a nitrogen-containing six-membered ring quaternary ammonium cation.
[2] The white pigment dispersion according to paragraph [1], wherein the substituent directly attached to the carbon atom is independently a hydrogen atom, a halogen atom, an alkyl group, or an aromatic hydrocarbon group.
[3] The white pigment dispersion according to paragraph [1] or [2] above, wherein the group having a carboxyl group is a saturated hydrocarbon group having a carboxyl group, or an oxygen-containing five-membered ring residue having a carboxyl group.
[4] The white pigment dispersion according to any one of the preceding paragraphs [1] to [3], wherein the compound having the phthalimide skeleton in which the carboxyl group is linked to a nitrogen atom is at least one selected from the compounds represented by the following formula (1).

(In formula (1), ^R1 to ^R4 independently represent a hydrogen atom, a halogen atom, an alkyl group, or an aromatic hydrocarbon group, and X represents a divalent saturated hydrocarbon group which may have substituents or a group represented by the following formula (2). In formula (2), "*" represents a bond.)

[5] The white pigment dispersion according to any one of the preceding paragraphs [1] to [3], wherein the compound having the phthalimide skeleton to which the group having the nitrogen-containing six-membered ring quaternary ammonium cation is linked is at least one selected from the compounds represented by the following formula (3).

(In formula (3), ^R1 to ^R4 independently represent a hydrogen atom, a halogen atom, an alkyl group, or an aromatic hydrocarbon group, and A represents a group having a nitrogen-containing six-membered ring quaternary ammonium cation.)
[6] A composition for forming a white septum, comprising a white pigment dispersion as described in any one of paragraphs [1] to [5] above, and a component for forming a white septum.

According to the present invention, it is possible to provide a white pigment dispersion and a white partition-forming composition capable of forming partitions for display elements having good reflectivity.

(a) This figure shows the image taken in Example 1. (b) This figure shows the image taken in Comparative Example 3.

The white pigment dispersion according to the embodiment of the present invention comprises a white inorganic pigment, a polymeric dispersant, a dispersion aid, and a solvent. The polymeric dispersant is an acid-value type polymeric dispersant having a carboxyl group or a phosphate group. The dispersion aid contains a compound having a phthalimide skeleton as an active ingredient. The phthalimide skeleton may have substituents directly attached to its carbon atoms, and the nitrogen atom in the phthalimide skeleton is linked to a group having a carboxyl group or a group having a nitrogen-containing six-membered ring quaternary ammonium cation.

Such white pigment dispersions, by containing the aforementioned specific acid-value polymer-based dispersant and specific dispersion aid, are expected to maintain a good dispersion state not only within the dispersion itself but also within the coating film or septum. The improved dispersion state in the coating film results in a smoother surface, allowing for greater light reflection. Furthermore, even light transmitted through the titanium dioxide on the surface is reflected by the uniformly distributed titanium dioxide within the coating film, thereby improving reflectivity. As a result, the reflectivity of the resulting septum is expected to improve.

The aforementioned white inorganic pigment is not particularly limited as long as it can conceal or reflect the light emitted from the light-emitting part. Examples include alumina, magnesium oxide, antimony oxide, titanium oxide, zirconium oxide, aluminum hydroxide, magnesium hydroxide, barium sulfate, magnesium carbonate, barium carbonate, calcium carbonate, lead sulfate, lead phosphate, zinc phosphate, silicon dioxide, zinc oxide, tin oxide, strontium sulfide, strontium titanate, barium titanate, barium tungstate, calcium silicate, aluminum silicate, lead metasilicate, talc, mica, kaolin, clay, bismuth chloride oxide, and hollow silica particles. Of these, alumina, magnesium oxide, antimony oxide, titanium oxide, zirconium oxide, aluminum hydroxide, magnesium hydroxide, barium sulfate, magnesium carbonate, and barium carbonate are preferred, with titanium oxide being particularly preferred. These white inorganic pigments may be included individually or in combination of two or more. Titanium oxide may be of the anatase or rutile type, but the rutile type is preferred.

White inorganic pigments may be surface-treated. Examples of such surface treatments include coatings using inorganic compounds such as (hydrated) alumina, silica (high-density silica, porous silica), and zirconia, or organic compounds such as fatty acids, silicones, polyols, and amines, or combinations thereof.

From the viewpoint of reflectivity and coloring power, the average primary particle size of the white inorganic pigment is preferably 100 to 400 nm. The average primary particle size can be measured, for example, using a transmission electron microscope JEM-1011 manufactured by JEOL Ltd.

The content of the white inorganic pigment is preferably 50 to 80% by weight in the white pigment dispersion.

The polymeric dispersant can be any acid-value polymeric dispersant having a carboxyl group or a phosphate group (hereinafter sometimes referred to as an "acidic group"). For example, a polymeric dispersant containing a polymer having a carboxyl group or a phosphate group in its side chain as an active ingredient can be used. The main chain structure of the polymer is not particularly limited, but it is preferable to have structural units derived from monomers having carbon-carbon double bonds. Furthermore, when using multiple types of monomers, it is preferable to use a combination of those having acidic groups and those not having them from the viewpoint of adjusting the acid value. Such polymers are preferably copolymers. The copolymer may be a random copolymer, an alternating copolymer, a block copolymer, or any other copolymer. The structure of the block copolymer is not particularly limited, and examples include an AB-type block copolymer in which an A block derived from monomer A and a B block derived from a different monomer B are bonded, a BAB-type block copolymer having a B block-A block-B block structure, and an ABC-type block copolymer having an A block-B block-C block structure in which monomer A and a C block derived from monomer C, which is different from monomer B, are bonded. Furthermore, from the viewpoint of dispersibility and developability, the block copolymer preferably contains blocks having acidic groups and blocks without acidic groups. Each block may also be composed of structural units derived from a single monomer or from multiple monomers. When a block is composed of structural units derived from multiple monomers, each structural unit may be present within the block in any manner, such as random copolymerization or block copolymerization.

Examples of monomers having a carbon-carbon double bond include vinyl monomers having a carboxyl group or a phosphate group, and vinyl monomers without an acidic group.

Examples of vinyl monomers having acidic groups include (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, monomers obtained by reacting hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate with acid anhydrides such as maleic anhydride, succinic anhydride, and phthalic anhydride, vinyl monomers having carboxyl groups such as vinylbenzoic acid; vinyl monomers having sulfonic acid groups such as styrene sulfonic acid, dimethylpropyl sulfonic acid (meth)acrylamide, ethyl sulfonate (meth)acrylate, ethyl sulfonate (meth)acrylamide, and vinyl sulfonic acid; and vinyl monomers having phosphate groups such as methacryloyloxyethyl phosphate ester.

Examples of vinyl monomers that do not have an acidic group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, and methyl (meth)acrylate. Alkyl methacrylates such as n-decyl acid, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-stearyl (meth)acrylate; cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, bornyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate; alicyclic alkyl methacrylates such as (meth) Examples include aryl esters of (meth)acrylates such as benzyl acrylic acid, phenyl (meth)acrylate, and phenoxyethyl (meth)acrylate; hydroxyl-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; (meth)acrylates having polyethylene glycol structural units such as diethylene glycol mono(meth)acrylate, triethylene glycol mono(meth)acrylate, tetraethylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, methoxytetraethylene glycol (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate; and aromatic vinyl monomers such as styrene, α-methylstyrene, 4-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methoxystyrene, 2-hydroxymethylstyrene, and 1-vinylnaphthalene.

The acid value of the polymeric dispersant, or in other words, the polymer included as the active ingredient, is preferably greater than 0 mg KOH/g and less than or equal to 200 mg KOH/g, from the viewpoint of dispersion stability. The amine value may be present as long as it does not exceed the acid value, but it is more preferable that there is no amine value. Furthermore, the weight-average molecular weight of the polymer is preferably between 3000 and 30000.

Polymeric dispersants containing polymers having carboxyl groups or phosphate groups in their side chains as active ingredients can be those described in, for example, Japanese Patent Publication No. 6437628. Commercially available dispersants can also be used. Examples of commercially available dispersants include: Otsuka Chemical Co., Ltd.: Tarplus MD1000, D2011, MD1100; BASF: JDX-C3000A; Bic Chemie: DISPERBY K-111; Lubrizol: S36000; Kyoeisha Chemical Co., Ltd.: Floren G-700.

The content of the polymeric dispersant is preferably 1 to 20 parts by weight, and more preferably 1 to 10 parts by weight, per 100 parts by weight of the white inorganic pigment.

As mentioned above, the polymeric dispersant can be any acid-value polymeric dispersant having a carboxyl group or a phosphate group. However, from the viewpoint of forming a partition wall for a display element with better reflectivity, one having a carboxyl group is preferred.

The dispersing agent may be any compound having the specific structure described above, but from the viewpoint of forming a partition wall for the display element with better reflectivity, it is preferable that the compound having the phthalimide skeleton is at least one selected from the compounds represented by the following formulas (1) or (3).

(In formula (1), ^R1 to ^R4 independently represent a hydrogen atom, a halogen atom, an alkyl group, or an aromatic hydrocarbon group, and X represents a divalent saturated hydrocarbon group which may have substituents or a group represented by the following formula (2). In formula (2), "*" represents a bond.)

(In formula (3), ^R1 to ^R4 independently represent a hydrogen atom, a halogen atom, an alkyl group, or an aromatic hydrocarbon group, and A represents a group having a nitrogen-containing six-membered ring quaternary ammonium cation.)

When ^R1 to ^R4 in formulas (1) and (3) are independently alkyl groups, there are no particular limitations, but from the viewpoint of dispersion stability, groups with 1 to 6 carbon atoms are preferred. Furthermore, alkyl groups may or may not have substituents. Examples of substituents include hydroxyl groups, carboxyl groups, alkoxy groups, carboxylic acid ester groups, amino groups, and amide groups. When ^R1 to ^R4 are independently aromatic hydrocarbon groups, there are no particular limitations, but from the viewpoint of dispersion stability, groups with 6 to 12 carbon atoms are preferred. Aromatic hydrocarbon groups may or may not have substituents. Examples of substituents include hydroxyl groups, carboxyl groups, alkoxy groups, carboxylic acid ester groups, amino groups, and amide groups.

In the compounds represented by formulas (1) and (3), ^R1 to ^R4 are preferably hydrogen atoms or halogen atoms, respectively. There are no particular limitations on the halogen atom, but chlorine atoms are particularly preferred.

When X in formula (1) is a divalent saturated hydrocarbon group which may have substituents, such saturated hydrocarbon groups preferably have 1 to 10 carbon atoms, more preferably 1 to 4 carbon atoms. Such saturated hydrocarbon groups may be linear or branched, but linear is preferred. Examples of substituents include alkoxy groups, carboxylic acid ester groups, amino groups, amide groups, and the like.

When X in formula (1) is a group represented by formula (2), which may have substituents, examples of substituents include alkoxy groups, carboxylic acid ester groups, amino groups, amide groups, etc. It is preferable that the group represented by formula (2) does not have substituents.

The nitrogen-containing six-membered quaternary ammonium cation contained in the group represented by A in formula (3) is, for example, any of the cations listed in the group shown in formula (4) below. In formula (4), "*" represents a bond.

Examples of the dispersing agents described above are shown in the following formulas (5) to (7). Formula (5) is N-propionylphthalimide, formula (6) is 3,4,5,6-tetrachlorophthalimidopropionic acid, and formula (7) is 1-(4-(4-phenylphthalimide)phenyl)pyridinium sulfonic acid.

The dispersing agent content is preferably 1 to 10 parts by weight per 100 parts by weight of white inorganic pigment.

Dispersing agents can be synthesized according to standard methods, or commercially available ones can be used.

Various organic solvents can be used as solvents. For example, ethanol, isopropyl alcohol, 1-propyl alcohol, 1-butanol, 2-butanol, isopentyl alcohol, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, methoxymethyl acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monomethyl ether acetate, propylene glycol monopropyl ether, ethylene glycol monomethyl ether acetate, 1-methoxypropyl-2-acetate, acetol, acetylacetone, methyl isobutyl ketone, methyl ethyl ketone, methyl propyl ketone, methyl lactate, toluene, cyclopentanone, cyclohexane, n-heptane, benzene, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, isopentyl acetate, pentyl acetate, 3-hydroxy-3-methyl-2-butanone, 4-hydroxy-3-methyl-2-butanone Examples include 5-hydroxy-2-pentanone, ethylene glycol diethyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-tert-butyl ether, propylene glycol mono-n-butyl ether, propylene glycol mono-t-butyl ether, 2-ethoxyethyl acetate, 3-methoxy-1-butanol, 3-methoxy-3-methylbutanol, 3-methoxy-3-methylbutyl acetate, 3-methoxybutyl acetate, 3-ethoxypropionate ethyl, propylene glycol monomethyl ether propionate, dipropylene glycol methyl ether, diisobutyl ketone, diacetone alcohol, ethyl lactate, butyl lactate, dimethylformamide, dimethylacetamide, γ-butyrolactone, γ-valerolactone, δ-valerolactone, propylene carbonate, N-methylpyrrolidone, cyclohexanone, cycloheptanone, diethylene glycol monobutyl ether, and ethylene glycol dibutyl ether. These organic solvents may be used individually or in combination of two or more.

The content of the organic solvent is not particularly limited; for example, it can be such that the solid content in the white pigment dispersion is 51 to 85% by weight.

The white pigment dispersion may contain, in addition to the components mentioned above, any additives as needed. Examples of such additives include dispersion resins, antioxidants, UV absorbers, sedimentation inhibitors, and adhesion promoters. Examples of adhesion promoters are described below.

White pigment dispersions can be prepared according to standard methods. For example, they can be obtained by adding the aforementioned components to a known dispersion machine such as a bead mill, sand mill, or disperser and dispersing them. There are no particular limitations on how the components are added; they may be mixed simultaneously and then dispersed, or they may be added sequentially as appropriate. When dispersion is performed using a dispersion medium such as zirconia beads, the dispersion may be carried out with beads of a predetermined diameter, or it may be carried out multiple times while gradually decreasing the bead diameter. The bead diameter, temperature, time, and other conditions can be determined as appropriate.

The white partition-forming composition according to this embodiment includes the aforementioned white pigment dispersion and white partition-forming component. Because it includes the aforementioned white pigment dispersion, it becomes possible to form partitions for display elements with good reflectivity.

Examples of white septum-forming components include polymerizable components, polymers, and mixtures thereof.

Examples of polymers include thermoplastic urethane resins, (meth)acrylic resins, polyamide resins, polyimide resins, styrene-maleic acid resins, polyester resins, silicone resins, cardo resins, and epoxy resins.

The content of the polymer in the white septum-forming composition is preferably 20 to 60% by weight of the total solid content of the white septum-forming composition.

As the polymerizable component, any component usable in the relevant art can be used. For example, at least one addition polymerizable compound having at least one ethylenically unsaturated double bond, preferably one compound having at least one, preferably two or more, terminal ethylenically unsaturated bonds, can be used. Examples of such addition polymerizable compounds include monofunctional or polyfunctional acrylates. The content of the polymerizable component in the white septum-forming composition is preferably 20 to 60% by weight of the total solid content of the white septum-forming composition. When a photopolymerization initiator is used together with such an addition polymerizable compound, the polymerizable component includes the photopolymerization initiator.

The white septum-forming composition may contain various additives as needed, such as antioxidants, UV absorbers, sensitizers (sensitizing dyes), chain transfer agents, fluorine-based organic compounds, photopolymerization initiators, photopolymerization inhibitors, fillers, surfactants, adhesion promoters, anti-aggregation agents, and surface modifiers (leveling agents).

Among these additives, adhesion promoters can be used to improve the adhesion between the white barrier-forming composition and the substrate (glass plate) during development. Adhesion promoters commonly used in this art can be applied. Examples include silane compound-based adhesion promoters such as silane coupling agents, and polymer-based adhesion promoters. Of these, polymer-based adhesion promoters tend to be more effective. Commercially available polymer-based adhesion promoters can be used. Examples include, but are not limited to, BYK-4509, BYK-4510, and BYK-4512 from BIC Chemie Japan Co., Ltd.; Disparon APA-100 from Kusumoto Chemical Co., Ltd.; and TEGO AddBond LTW, TEGO AddBond LTW-B, TEGO AddBond LTH, TEGO AddBond HS, TEGO AddBond 1270, TEGO AddBond 2440, and TEGO AddBond 2220 ND from Evonik Japan. There are no particular limitations on the timing of adding the adhesion promoter. The entire amount may be added to the aforementioned white pigment dispersion beforehand and used to prepare the white partition-forming composition; the entire amount may be added during the preparation of the white partition-forming composition; or the adhesion promoter may be added in appropriate amounts to both the white pigment dispersion and the white partition-forming composition during their preparation. Furthermore, the content of the adhesion promoter in the white partition-forming composition can be appropriately determined depending on the type of adhesion promoter, etc. Generally, a small amount is sufficient.

The white septum-forming composition can be obtained, for example, by adding and dispersing the aforementioned components in a known dispersion machine such as a bead mill, sand mill, or disperser.

The above-described white partition-forming composition can form a cured product with good reflectivity, making it suitable for application to partitions in display elements such as micro-light-emitting diodes (LEDs) and organic electroluminescent (OLED) elements.

The embodiments of the present invention will be described in detail below based on examples.

The white inorganic pigments, polymer-based dispersants, dispersion aids, solvents, white coating film-forming components, and white partition-forming components used in Examples 1-3 and Comparative Examples 1-3, described later, are shown below.

(1) White inorganic pigment (1-1) CR-60
Ishihara Sangyo Co., Ltd., Typepeke CR-60, Rutile-type titanium oxide ( _TiO2 ), Average primary particle size: 0.21 μm, Surface treatment: Alumina.
(2) Polymer-based dispersants (2-1) MD1100
Otsuka Chemical Co., Ltd., Tarplus MD1100, an acid-value type polymer dispersant containing a carboxyl-group-containing BAB triblock copolymer as an active ingredient, acid value: 85 mg KOH/g, amine value: 0 mg KOH/g, weight-average molecular weight: 25700, solids content: 40% by weight.
(2-2) C3000A
BASF JDX-C3000A, an acid-value type polymer dispersant containing an acrylic polymer compound having a carboxyl group as an active ingredient, acid value: 85 mg KOH/g, amine value: 0 mg KOH/g, weight-average molecular weight: 10000, solids content: 100% by weight.

(3) Dispersing agent (3-1) Dispersing agent I
The active ingredient is the compound represented by formula (5) (N-propionylphthalimide), obtained according to a standard method, with a solid content of 100% by weight.

(3-2) Dispersing agent II
It contains as an active ingredient the compound represented by formula (6) (3,4,5,6-tetrachlorophthalimidopropionic acid), obtained according to a standard method, with a solid content of 100% by weight.

(3-3) Dispersing agent III
The active ingredient is the compound represented by formula (7), (1-(4-(4-phenylphthalimide)phenyl)pyridinium sulfonic acid), obtained according to a standard method, with a solid content of 100% by weight.

(3-4) Dispersing agent IV
The product contains as an active ingredient the compound shown in the following formula (8) obtained according to a standard method (2-({4,6-bis[(5-carbamoyl-2-methoxyphenol)amino]-1,3,5-triazine-2-yl}amino)benzenesulfonic acid), with a solid content of 100% by weight.

(3-5) Dispersing agent V
The product contains as an active ingredient the compound shown in the following formula (9) (N-(1-aminoethyl)phthalimide), obtained according to a standard method, with a solid content of 100% by weight.

(3-6) Dispersing agent VI
The active ingredient is the compound represented by the following formula (10) (4-(3-(dimethylamino)propoxy)butanal), obtained according to a standard method, with a solid content of 100% by weight.

(4) Solvent (4-1) Propylene glycol monomethyl ether acetate (PMA), manufactured by Kyowa Hakko Chemical Co., Ltd.

(5) Ingredients for forming white paint film (5-1) RD-Y-206
Alkali-soluble resin, Acrycure® RD-Y-206, manufactured by Nippon Shokubai Co., Ltd. ((meth)acrylic polymer, solids content: 40% by weight)

(6) Component for forming white partition walls (6-1) DPHA
Dipentaerythritol hexaacrylate, manufactured by Nippon Kayaku Co., Ltd. (6-2) 184
BASF Corporation, photopolymerization initiator, Omnirad® 184

(Example 1)
<Preparation of white pigment dispersion>
To 63.05 parts by weight (solids) of white inorganic pigment (CR-60), 5.2 parts by weight (solids) of polymeric dispersant (MD1100), and 1.95 parts by weight (solids) of dispersion aid I, solvent (PMA) was added so that the total concentration of the white inorganic pigment and dispersion aid I reached 65% by weight. 400 parts by weight of zirconia beads with a particle size of 0.5 mm were added per 100 parts by weight of the white pigment dispersion, and the mixture was dispersed with paint conditioner for 30 minutes. The solids content of the resulting white pigment dispersion was 70.2% by weight.

<Preparation of a composition for forming a white coating film>
To the obtained white pigment dispersion, a white coating film-forming component (RD-Y-206) was added so that the total ratio (solid content) of the white inorganic pigment and dispersion aid I when cured was 60% by weight. PMA was then added so that the solid content of the white coating film-forming composition was 46% by weight, and the mixture was stirred using a vortex mixer to obtain a white coating film-forming composition.

(Example 2)
A white pigment dispersion and a white coating film-forming composition were obtained in the same manner as in Example 1, except that dispersion aid I was replaced with dispersion aid II. The solid content concentration of the white pigment dispersion was 70.2% by weight.

(Example 3)
A white pigment dispersion and a white coating film-forming composition were obtained in the same manner as in Example 1, except that dispersion aid I was replaced with dispersion aid III. The solid content concentration of the white pigment dispersion was 70.2% by weight.

(Example 4)
<Preparation of white pigment dispersion>
A white pigment dispersion was obtained in the same manner as in Example 1, except that a solvent (PMA) was added to 67.9 parts by weight (solids) of white inorganic pigment (CR-60), 5.6 parts by weight (solids) of polymeric dispersant (C3000A), and 2.1 parts by weight (solids) of dispersion aid I, so that the total concentration of the white inorganic pigment and dispersion aid I was 70% by weight. The solids content of the obtained white pigment dispersion was 75.6% by weight.

<Preparation of a composition for forming a white coating film>
Using the obtained white pigment dispersion, a white coating film-forming composition was obtained in the same manner as in Example 1.

(Example 5)
A white pigment dispersion and a white coating film-forming composition were obtained in the same manner as in Example 4, except that dispersion aid I was replaced with dispersion aid II. The solid content concentration of the white pigment dispersion was 75.6% by weight.

(Example 6)
A white pigment dispersion and a white coating film-forming composition were obtained in the same manner as in Example 4, except that dispersion aid I was replaced with dispersion aid III. The solid content concentration of the white pigment dispersion was 75.6% by weight.

(Comparative Example 1)
A white pigment dispersion and a white coating film-forming composition were obtained in the same manner as in Example 1, except that dispersion aid I was replaced with dispersion aid IV. The solid content concentration of the white pigment dispersion was 70.2% by weight.

(Comparative Example 2)
A white pigment dispersion and a white coating film-forming composition were obtained in the same manner as in Example 1, except that dispersion aid I was replaced with dispersion aid V. The solid content concentration of the white pigment dispersion was 70.2% by weight.

(Comparative Example 3)
A white pigment dispersion and a white coating film-forming composition were obtained in the same manner as in Example 1, except that dispersion aid I was replaced with dispersion aid VI. The solid content concentration of the white pigment dispersion was 70.2% by weight.

(Comparative Example 4)
A white pigment dispersion and a white coating film-forming composition were obtained in the same manner as in Example 4, except that dispersion aid I was replaced with dispersion aid IV. The solid content concentration of the white pigment dispersion was 75.6% by weight.

(Comparative Example 5)
A white pigment dispersion and a white coating film-forming composition were obtained in the same manner as in Example 4, except that dispersion aid I was replaced with dispersion aid V. The solid content concentration of the white pigment dispersion was 75.6% by weight.

(Comparative Example 6)
A white pigment dispersion and a white coating film-forming composition were obtained in the same manner as in Example 4, except that dispersion aid I was replaced with dispersion aid VI. The solid content concentration of the white pigment dispersion was 75.6% by weight.

(evaluation)
<Formation of hardened film>
Each of the white coating-forming compositions obtained in Examples 1-6 and Comparative Examples 1-6 was applied to a 1 mm thick, 100 mm square glass plate using a spin coater (MIKASA Opticoat MS-A150) to prepare a coated film. During this process, the rotation speed was adjusted for each white coating-forming composition to achieve a film thickness of approximately 10 μm. After drying at room temperature for 3 minutes, the films were heated at 90°C for 2.5 minutes (pre-bake), followed by heating at 230°C for 30 minutes (post-bake) to obtain three cured films with different film thicknesses.

<Measurement of reflectance>
First, the number of visible granular particles in the obtained cured film was measured. Reflectance measurements were performed on cured films with fewer than 20 granular particles in a 5 cm square area. For films with 20 or more granular particles, reflectance measurements were not performed as they were unsuitable for practical use, and they were labeled as foreign matter in the reflectance measurement section of Table 1.
Next, the reflectance of each cured film obtained was measured using a spectrophotometer (Konica Minolta, product name CM-3700A). A D65 light source was selected, and the Y value was measured using the SCI method, with the average value of n=3 being calculated. For the cured films obtained using each white coating composition, a calibration curve was obtained by plotting the reflectance against the film thickness, and the reflectance at a film thickness of 10 μm was calculated from this calibration curve.

<Cross-sectional observation of the hardened film>
For the cured films formed on the surface of glass plates using the white coating-forming compositions obtained in Example 1 and Comparative Example 3, oblique views including the cross-section in the stacking direction of the glass plate and the cured film were acquired using a scanning electron microscope (Hitachi High-Tech Corporation, S-4800), and the cross-sectional structure was observed visually. Figure 1(a) shows the image of Example 1, and (b) shows the image of Comparative Example 3. In the oblique views shown in Figures 1(a) and (b), reference numeral 1 denotes the surface of the cured film formed on the glass plate surface, reference numeral 2 denotes the cross-section of the cured film, and reference numeral 3 denotes the cross-section of the glass plate.

Table 1 shows the component composition and calculated reflectance of the cured films for Examples 1-6 and Comparative Examples 1-6.

As shown in Table 1, it can be seen that using a combination of a predetermined polymer-based dispersant and a predetermined dispersion aid results in better reflectivity compared to comparative examples that do not use such a combination. Furthermore, in the cured film of Example 1 (Figure 1(a)), the surface (reference numeral 1 in Figure 1(a)) is smooth and even, and the titanium dioxide in the cross-section of the cured film (reference numeral 2 in Figure 1(a)) is dispersed throughout the entire cured film. In contrast, in the cured film of Comparative Example 3 (Figure 1(b)), the surface (reference numeral 1 in Figure 1(b)) is uneven, and a large difference between dense and sparse areas due to titanium dioxide aggregation was observed in the cross-section of the cured film (reference numeral 2 in Figure 1(b)).

(Example 7)
<Preparation of a composition for forming white septa>
To the white pigment dispersion obtained in Example 1, 27.2% by weight of DPHA and 8.0% by weight of Omnirad® 184 were added as white septum-forming components so that the total ratio (solid content) of the white inorganic pigment and dispersion aid I when cured film is 60% by weight. PMA was then added so that the solid content of the white septum-forming composition was 70% by weight, and the mixture was stirred with a vortex mixer to obtain a white septum-forming composition.

(evaluation)
<Formation of hardened film>
The white partition-forming composition obtained in Example 7 was applied to a 1 mm thick, 100 mm square glass plate using a spin coater (MIKASA, Opticoat MS-A150) to prepare a coated film. During this process, the rotation speed was adjusted to achieve a film thickness of approximately 10 μm, with the film thickness being a baseline. After drying at room temperature for 2.5 minutes, the film was heated at 90°C for 3 minutes (pre-bake). Furthermore, using an exposure device (Ushio Inc., UVC-02516S1LP01), ultraviolet light was irradiated onto the coated film at an exposure intensity of 900 mJ/ ^cm² , and then heated at 230°C for 30 minutes (post-bake) to obtain three cured films with different film thicknesses.

<Measurement of reflectance>
The reflectance of the cured film of the white partition-forming composition obtained in Example 7 was calculated in the same manner as for the cured film of the white coating-forming composition. The component composition of the cured film of Example 7 and the results of the reflectance calculation are shown in Table 2.

As shown in Table 2, even when a cured film is formed using a white partition-forming component, it exhibits better reflectivity than the comparative example, similar to Examples 1-6.

1. Surface of the hardened film 2. Cross-section of the hardened film 3. Cross-section of the glass plate

Claims (6)

A white pigment dispersion comprising a white inorganic pigment, a polymer-based dispersant, a dispersion aid, and a solvent,
The polymeric dispersant is an acid-value type polymeric dispersant having a carboxyl group or a phosphate group.
The aforementioned dispersing aid contains a compound having a phthalimide skeleton as an active ingredient,
The phthalimide skeleton may have substituents directly attached to its carbon atoms.
A white pigment dispersion wherein the nitrogen atom in the phthalimide skeleton is linked to a group having a carboxyl group or a group having a nitrogen-containing six-membered ring quaternary ammonium cation. The white pigment dispersion according to claim 1, wherein the substituent directly attached to the carbon atom is independently a hydrogen atom, a halogen atom, an alkyl group, or an aromatic hydrocarbon group. The white pigment dispersion according to claim 1 or 2, wherein the group having a carboxyl group is a saturated hydrocarbon group having a carboxyl group, or an oxygen-containing five-membered ring residue having a carboxyl group. The white pigment dispersion according to any one of claims 1 to 3, wherein the compound having the phthalimide skeleton in which the carboxyl group is linked to a nitrogen atom is at least one selected from the compounds represented by the following formula (1).
(In formula (1), ^R1 to ^R4 independently represent a hydrogen atom, a halogen atom, an alkyl group, or an aromatic hydrocarbon group, and X represents a divalent saturated hydrocarbon group which may have substituents or a group represented by the following formula (2). In formula (2), "*" represents a bond.)
The white pigment dispersion according to any one of claims 1 to 3, wherein the compound having the phthalimide skeleton to which the group having the nitrogen-containing six-membered ring quaternary ammonium cation is linked is at least one selected from the compounds represented by the following formula (3).
(In formula (3), ^R1 to ^R4 independently represent a hydrogen atom, a halogen atom, an alkyl group, or an aromatic hydrocarbon group, and A represents a group having a nitrogen-containing six-membered ring quaternary ammonium cation.) A composition for forming a white septum, comprising a white pigment dispersion according to any one of claims 1 to 5, and a component for forming a white septum.