JP7809583B2 - Dispersion liquid for black partition wall material - Google Patents

Description

The present invention relates to a dispersion liquid for a black partition wall material. More specifically, the present invention relates to a dispersion liquid for a black partition wall material that can increase the taper angle of the black partition wall material and reduce the reflectance, thereby enabling the production of high-resolution displays.

Conventionally, black partition wall materials used in displays are required to have high electrical insulation to prevent malfunctions. Carbon black, used as a black colorant, is coated on its surface with an insulating material to achieve high electrical insulation. If the coating is incomplete, electrical insulation is not achieved, and sufficient reliability is not achieved. Furthermore, flexible displays eliminate circular polarizers used for anti-reflection and use color filters to prevent reflection. Black partition wall materials used in color filters are required to have lower reflectivity than conventional materials. Lactam black is a black colorant that has attracted attention for these applications (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2021-86157

However, when the resin composition containing dispersed lactam black described in Patent Document 1 was used as a black partition wall material, it was not possible to obtain a sufficient taper angle, making it unsuitable for achieving high-definition displays.

The present invention was made in consideration of these conventional problems, and aims to provide a dispersion liquid for black partition wall materials that can increase the taper angle of black partition wall materials and reduce reflectance, thereby enabling the production of high-definition displays.

As a result of extensive research into solving the above problems, the inventors discovered that the above problems could be solved simultaneously by using a dispersant that combines finely divided lactam black with an acrylic dispersant that is a block copolymer, and thus completed the present invention. The present invention, which solves the above problems, mainly comprises the following features:

(1) A dispersion for a black partition wall material, comprising lactam black, an acrylic dispersant, a resin, and a solvent, wherein the lactam black has a volume-based particle size D50 value of 20 to 60 nm and a volume-based particle size D90 value of 40 to 110 nm, and the acrylic dispersant contains a block copolymer.

This configuration makes it possible to increase the taper angle of the resulting black partition wall material and reduce the reflectance, thereby providing a dispersion for black partition wall material that can be used to produce high-definition displays.

The present invention provides a dispersion for black partition wall material that can increase the taper angle of the black partition wall material and reduce the reflectance, enabling the production of high-resolution displays.

<Dispersion liquid for black partition material>
A dispersion for a black partition wall material (hereinafter also referred to as dispersion) according to one embodiment of the present invention contains lactam black, an acrylic dispersant, a resin, and a solvent. The lactam black has a volume-based particle size D50 value of 20 to 60 nm and a volume-based particle size D90 value of 40 to 110 nm. The acrylic dispersant contains a block copolymer. Each of these will be described below.

(Lactam Black)
The lactam black is a known lactam black having the following structure: Specifically, the lactam black is Irgaphor Black S 0100 CF (manufactured by BASF) or the like.

The lactam black of this embodiment is a lactam black obtained by micronizing a known lactam black. The micronization method is not particularly limited. One example is a method in which known lactam black is pretreated with a water-soluble inorganic salt and a wetting agent. Specifically, the pretreatment can be carried out by kneading the lactam black with the water-soluble inorganic salt and the wetting agent, and then filtering and washing the resulting pigment. Kneading can be carried out at a temperature of 40 to 100°C. Filtration and washing can be carried out by washing the inorganic salt with water or the like, followed by filtration. The water-soluble inorganic salt is sodium chloride, potassium chloride, or the like.

The volume-based particle size D50 value of the micronized lactam black of this embodiment may be 20 nm or more, and preferably 30 nm or more. The D50 value may be 60 nm or less, and preferably 50 nm or less. If the D50 value is less than 20 nm, the dispersion will have poor dispersion stability. On the other hand, if the D50 value exceeds 60 nm, the resulting black partition wall material will have a small taper angle and high reflectance.

The volume-based particle size D90 value of the micronized lactam black of this embodiment may be 40 nm or more, and preferably 50 nm or more. The D90 value may be 110 nm or less, and preferably 100 nm or less. If the D90 value is less than 40 nm, the dispersion will have poor dispersion stability. On the other hand, if the D90 value exceeds 110 nm, the resulting black partition wall material will have a smaller taper angle and higher reflectance.

The volume-based particle size D10 value of the micronized lactam black of this embodiment is preferably 5 nm or more, and more preferably 15 nm or more. Furthermore, the D10 value is preferably 40 nm or less, and more preferably 30 nm or less.

In this embodiment, the volume-based particle size can be measured by laser diffraction particle size measurement using a Nanotrac (UPA-EX150, manufactured by Nikkiso Co., Ltd.).

The dispersion of this embodiment is characterized by the volume-based particle diameters, particularly D50 and D90, falling within a specified range. By ensuring that D50 and D90 fall within the above ranges, the resulting black partition wall material has a larger taper angle and lower reflectance. The smaller the pigment particle diameter, the easier it is for light to transmit, resulting in less reflected light. Furthermore, as the pigment particle diameter decreases, UV light is more likely to diffract to the back side of the pigment, promoting overall curing and reducing thermal flow. Furthermore, as the pigment particle diameter decreases, the surface area of the pigment that interacts with the resin and dispersant increases. As a result, the coating film has stronger bonding strength within the coating film and is less susceptible to thermal flow.

The content of lactam black is not particularly limited. For example, the content of lactam black in the dispersion is preferably 5% by mass or more, and more preferably 10% by mass or more. Furthermore, the content of lactam black in the dispersion is preferably 30% by mass or less, and more preferably 25% by mass or less. By keeping the lactam black content within the above range, the dispersion has good dispersion stability.

(acrylic dispersant)
The acrylic dispersant includes a block copolymer (acrylic block copolymer). The acrylic block copolymer is not particularly limited. For example, the acrylic block copolymer is an acrylic block copolymer containing an amine compound as a monomer.

The types of blocks constituting the acrylic block copolymer containing a monomer that is an amine compound may be two or three or more. At least one of the blocks is a block containing a monomer that is an amine compound and has a radically polymerizable unsaturated bond.

The monomers constituting this block are acyclic amine compounds, heterocyclic amine compounds, or quaternary ammonium cation compounds, preferably acyclic amine compounds such as dimethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and dimethylaminobutyl (meth)acrylate; heterocyclic amine compounds such as vinylpyridine and pentamethylpiperidinyl (meth)acrylate; and quaternary ammonium cation compounds such as compounds obtained by quaternizing and cationizing dimethylaminopropyl (meth)acrylate with benzyl chloride. The block may consist of one of these monomers, or may be a block formed by random polymerization of two or more monomers, or a block formed by block polymerization of two or more monomers. Furthermore, structures consisting of blocks of pentamethylpiperidinyl methacrylate and/or dimethylaminopropyl acrylate and blocks of other polymerizable ethylenically unsaturated monomers are particularly preferred.

The other polymerizable block copolymerized with the block derived from the amine compound monomer may be a block consisting of one type of monomer, or a block formed by random polymerization of two or more types of monomers. It preferably does not contain units derived from monomers containing amino groups or pyridine rings. It is even more preferable that it does not contain carboxylic acid groups, hydroxyl groups, thiol groups, or sulfur- or phosphorus-containing groups. The block consisting of the other polymerizable ethylenically unsaturated monomer may be one type or two types.

Other polymerizable ethylenically unsaturated monomers include copolymers with at least one ethylenically unsaturated monomer selected from the group consisting of alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate; styrene; 2-hydroxyethyl (meth)acrylate; allyl (meth)acrylate; benzyl (meth)acrylate; cyclohexyl (meth)acrylate; glycerol (meth)acrylates such as glycerol monoacrylate; N-phenylmaleimide; polystyrene macromonomer; polymethyl methacrylate macromonomer; and carboepoxy diacrylate. However, it is preferable not to use N-vinylpyrrolidone or sulfur-containing monomers.

Block copolymers can be block resins synthesized by living radical polymerization or anionic polymerization.

The content of the acrylic dispersant is not particularly limited. For example, the content of the acrylic dispersant in the dispersion is preferably 0.5% by mass or more, and more preferably 1.0% by mass or more. The content of the acrylic dispersant in the dispersion is preferably 30.0% by mass or less, and more preferably 25.0% by mass or less. By keeping the content of the acrylic dispersant within the above range, the particle size distribution of the dispersion can be easily adjusted to a particle size within the desired range, resulting in good dispersion stability.

(resin)
The resin is not particularly limited. For example, the resin is preferably an alkali-soluble resin, and more preferably an acrylic copolymer resin, a maleic acid copolymer resin, a polyester resin obtained by a condensation polymerization reaction, a polyurethane resin, or the like. Among these, the resin is preferably an acrylic copolymer resin in terms of developability, flexibility in molecular design, and cost. By including an alkali-soluble resin, the dispersion liquid can be developed with an alkali developer, and a pattern such as a partition wall can be formed.

The alkali-soluble resin is not particularly limited, and examples thereof include resins containing anionic groups such as carboxyl groups, sulfonic acid groups, and phosphonic acid groups (-P(=O)(OH ₂ )).

From the viewpoint of alkaline developability, the acid value of the alkali-soluble resin is preferably 10 mgKOH/g or more, and more preferably 20 mgKOH/g or more. Furthermore, the acid value is preferably 300 mgKOH/g or less, and more preferably 200 mgKOH/g or less.

From the viewpoint of resist film formation, the weight-average molecular weight of the alkali-soluble resin is preferably 5,000 or more, and more preferably 10,000 or more. Furthermore, from the viewpoint of enhancing solubility, the weight-average molecular weight of the alkali-soluble resin is preferably 100,000 or less, and more preferably 50,000 or less. The weight-average molecular weight can be measured by gel permeation chromatography (GPC). For example, chromatography can be performed using a Water 2690 (manufactured by Waters) GPC apparatus and a PLgel 5μ MIXED-D (manufactured by Polymer Laboratories) column under the following conditions: tetrahydrofuran as the developing solvent, a column temperature of 25°C, a flow rate of 1 milliliter/minute, an RI detector, a sample injection concentration of 10 milligrams/milliliter, and an injection volume of 100 microliters. The weight-average molecular weight can be determined as a polystyrene-equivalent.

Alkali-soluble resins include acrylic copolymer resins, maleic acid copolymer resins, polyester resins obtained by condensation polymerization reactions, polyurethane resins, etc. Among these, acrylic copolymer resins are preferred as the alkali-soluble resin from the standpoints of developability, flexibility in molecular design, and cost.

The amount of alkali-soluble resin contained is not particularly limited. For example, the amount of alkali-soluble resin contained is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, per 100 parts by mass of lactam black. Furthermore, the amount of alkali-soluble resin contained is preferably 90 parts by mass or less, and more preferably 80 parts by mass or less, per 100 parts by mass of lactam black.

(solvent)
The solvent is not particularly limited, but from the viewpoint of stably dispersing lactam black and sufficiently dissolving resins and the like, preferred examples of the solvent include ester-based solvents, ether-based solvents, ether ester-based solvents, ketone-based solvents, aromatic hydrocarbon-based solvents, and nitrogen-containing solvents.

Ester solvents include methyl 2-hydroxypropionate, ethyl 2-hydroxypropionate, ethyl 2-hydroxy-2-methylpropionate, 3-methyl-3-methoxybutylpropionate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, methyl 3-ethoxypropionate, ethyl 3-ethoxypropionate, ethyl ethoxyacetate, hydroxyacetic acid esters, and n-amyl formate.

Ether solvents include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, and diethylene glycol methyl ethyl ether.

Ether ester solvents include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate.

Ketone solvents include methyl isobutyl ketone, cyclohexanone, 2-heptanone, and delta-butyrolactone.

Aromatic hydrocarbon solvents include toluene, xylene, and alkylnaphthalenes.

Nitrogen-containing solvents include N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

The solvent content is not particularly limited. For example, the solvent content in the dispersion is preferably 40% by mass or more, and more preferably 50% by mass or more. The solvent content in the dispersion is preferably 90% by mass or less, and more preferably 80% by mass or less. When the solvent content is within the above range, the dispersion exhibits excellent dispersion stability of lactam black.

Returning to the explanation of the dispersion as a whole, the method for preparing the dispersion of this embodiment is not particularly limited. To give one example, the dispersion can be prepared by mixing various materials and kneading overnight in a bead mill or the like.

The dispersion of this embodiment can increase the taper angle of the black partition material and reduce the reflectance, allowing for the production of high-resolution displays.

<Black partition material>
The black partition wall material is obtained by curing the above-described dispersion liquid. Specifically, first, the dispersion liquid of this embodiment is applied to a substrate to form a resin layer (coating film). Then, the resin layer is exposed to light through a mask with a predetermined pattern, and the exposed portions are photocured. Then, the unexposed portions and the partially exposed portions are developed with an alkaline developer to form the black partition wall material. Thereafter, the black partition wall material is post-baked as necessary.

The substrate is not particularly limited. Examples of substrates include glass substrates, silicon substrates, polycarbonate substrates, polyester substrates, polyamide substrates, polyamideimide substrates, polyimide substrates, aluminum substrates, printed wiring boards, and array substrates.

The method for applying the dispersion is not particularly limited. Examples of methods for applying the dispersion include screen printing, roll coating, curtain coating, spray coating, and spin coating. After applying the dispersion, the solvent contained in the resin layer may be evaporated, if necessary, by heating using a heating means such as a circulation oven, infrared heater, or hot plate. Heating conditions may be appropriately set depending on the composition of the dispersion used. Generally, heating conditions are a temperature of 50°C to 120°C and a time of 30 seconds to 30 minutes.

The method of exposing the resin layer is not particularly limited. For example, the exposure method is irradiation with active energy rays such as ultraviolet light or excimer laser light. The energy dose may be appropriately set depending on the composition of the dispersion. For example, the energy dye has an energy dose of 30 to 2000 mJ/ ^cm2 . The light source used for exposure is not particularly limited. For example, the light source may be a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, a xenon lamp, a metal halide lamp, or the like.

The alkaline developer used for development is not particularly limited. Examples of the developer include aqueous solutions of sodium carbonate, potassium carbonate, calcium carbonate, sodium hydroxide, potassium hydroxide, etc.; aqueous solutions of amine compounds such as ethylamine, diethylamine, and dimethylethanolamine; and aqueous solutions of p-phenylenediamine compounds such as tetramethylammonium, 3-methyl-4-amino-N,N-diethylaniline, 3-methyl-4-amino-N-ethyl-N-β-hydroxyethylaniline, 3-methyl-4-amino-N-ethyl-N-β-methanesulfonamidoethylaniline, 3-methyl-4-amino-N-ethyl-N-β-methoxyethylaniline, and sulfates, hydrochlorides, or p-toluenesulfonates thereof. Antifoaming agents, surfactants, etc. may be added to the alkaline developer as needed.

The black partition wall material formed by alkaline development can be post-baked to accelerate the curing of the resin. The post-baking conditions are not particularly limited. For example, the post-baking conditions are a temperature of 80°C to 250°C for 10 minutes to 4 hours.

The resulting black partition wall material has a large taper angle and low reflectance, allowing for the creation of high-resolution displays.

<Image display device>
The image display device (display) of this embodiment includes the above-described black partition wall material. Specific examples of the image display device include a liquid crystal display device and an organic EL display device. The image display device can be manufactured according to a conventional method except for forming the above-described black partition wall material.

The present invention will be explained in more detail below using examples. The present invention is not limited to these examples. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass."

The raw materials used are shown below.
<Lactam Black>
Lactam black: Irgaphor S100CF (manufactured by BASF)
Preparation of Micronized Lactam Black 800 parts by mass of the above lactam black, 8,000 parts by mass of sodium chloride having a particle size of 20 μm, and 1,920 parts by mass of diethylene glycol were placed in a tank of a Trimix TX-15 (manufactured by Inoue Seisakusho). The mixture was kneaded for 3 hours at 45°C at a current that was 70% of the rated current of 9.3 A, followed by salt milling. 1,300 parts by mass of the resulting kneaded mixture was placed in 3 liters of warm water and stirred for 1 hour while heating to 70°C to form a slurry. After repeated filtration and water washing to remove the sodium chloride and diethylene glycol, the mixture was dried overnight at 40°C to obtain 95 parts by mass of micronized lactam black.
Preparation of Micronized Lactam Black (Salt Trimming Enhanced Product) The same preparation method as in the above-mentioned preparation method of micronized lactam black was used, except that 400 parts by mass of lactam black was kneaded for 6 hours, to obtain 40 parts by mass of micronized lactam black (salt trimming enhanced product).
<Dispersant>
Preparation of Acrylic Dispersant (ABA Triblock) 17 g of methyl methacrylate (MMA), 24 g of butyl methacrylate (BMA), and 1 L of tetrahydrofuran (THF) were added to a degassed glass apparatus, followed by the addition of 4.5 mmol of a hexane solution of n-butyllithium, to synthesize a random copolymer of MMA and BMA. The mixture was then cooled to -78°C and stirred for 2 hours. Next, 33 g of pentamethylpiperidinyl methacrylate (PMPMA) was added and stirred for 2 hours to synthesize a PMPMA block moiety bonded to the random copolymer of MMA and BMA. Furthermore, 17 g of MMA and 24 g of BMA were added to synthesize an ABA triblock copolymer. After stirring for 2 hours, the reaction was terminated. The synthesized solution was dropped into a large amount of methanol to precipitate. The dispersant was collected using filter paper, washed several times with methanol, and dried under reduced pressure at 60°C to obtain an acrylic dispersant. The resulting acrylic dispersant was an ABA triblock copolymer, with the structure being BMA/MMA//b-PMPMA//b-BMA/MMA = (24/17)//18//(24/17). The monomers separated by "/" were polymerized randomly, and the monomers separated by "//b-" formed a block structure.
Acrylic dispersant (graft): BYKJET-9151 (manufactured by BYK-Chemie)
Urethane dispersant (graft): DISPERBYK-167 (manufactured by BYK-Chemie)
<Photopolymerizable compound>
DPEHA: Dipentaerythritol hexaacrylate (photopolymerization initiator)
Irgacure OXE02 (manufactured by BASF)
<Solvent>
PGME: Propylene glycol monomethyl ether PGMEA: Propylene glycol monomethyl ether acetate <Resin>
Folet ZAH-110 (alkali-soluble photosensitive resin, solid content 35% by mass, manufactured by Soken Chemical & Engineering Co., Ltd.)
ZCR-1569H (alkali-soluble photosensitive resin, solid content 70% by mass, manufactured by Nippon Kayaku Co., Ltd.)
<Leveling agent>
Megafac F-554 (DIC)

<Examples 1 to 4, Comparative Examples 1 to 6>
(Preparation of pigment dispersion for black partition wall material)
Various materials were mixed to obtain the compositions (units: mass%) shown in Table 1, and the mixture was milled overnight in a bead mill to prepare pigment dispersions for black partition wall materials of Examples 1 to 4 and Comparative Examples 1 to 6. The particle sizes of the dispersion compositions in the obtained dispersions were measured by a laser diffraction particle size measurement method using a Nanotrac (UPA-EX150, manufactured by Nikkiso Co., Ltd.) to determine the D10 particle size, D50 particle size, and D90 particle size. The results are shown in Table 1.

(Preparation of Pigment Dispersion Resist Composition for Black Partition Wall Material)
A composition comprising 40.00 parts by mass of the above dispersion having a pigment concentration of 15% by mass, 10.60 parts by mass of alkali-soluble photosensitive resin ZCR-1569H, 3.00 parts by mass of DPEHA, 0.80 parts by mass of Irgacure OXE02, 0.05 parts by mass of Megafac F-554, and 45.55 parts by mass of PGMEA was uniformly mixed using a high-speed stirrer, and then filtered through a filter having a pore size of 3 μm to obtain pigment dispersion resist compositions for black partition wall materials.

The viscosity stability, taper angle, and reflectance of the resulting resist composition were measured using the following methods. The results are shown in Table 1.

(viscosity stability)
The pigment dispersion resist compositions for black partition wall materials of the above Examples and Comparative Examples were stored at 40° C. for one week, and the change in viscosity before and after storage was measured and evaluated according to the following evaluation criteria.
Good: The viscosity change was 10% or less.
Δ: The viscosity change was more than 10% and 20% or less.
×: The viscosity change exceeded 20%.

(Taper angle)
The pigment dispersion resist compositions for black partition wall materials of the above examples and comparative examples were applied to a glass substrate (Corning 1737) using a spin coater to a film thickness of 1 μm and prebaked at 100°C for 2 minutes. Subsequently, the substrate was exposed to UV light at a cumulative dose of 40 mJ/ ^cm2 using a high-pressure mercury lamp with a 20 μm gap between the substrate and a photomask having a line pattern. Development was performed at 23°C in a 2.4% by mass aqueous solution of TMAH (tetramethylammonium hydroxide) using a shower at 0.07 MPa, followed by shower rinsing at 0.07 MPa. The resulting substrate was then postbaked at 250°C for 30 minutes. The resulting substrate was divided in the pattern width direction using a glass cutter. The divided surfaces of the 6 μm pattern were observed using an electron microscope, and the taper angle was measured by image analysis. The results are shown in Table 1. A larger taper angle is preferable.

(reflectance)
The same procedure as for the taper angle was carried out, but without any development after exposure, post-baking was carried out at 100°C for 30 minutes to obtain a coating film formed only in the solid area. The average reflectance (unit: %) of the coating surface of the obtained solid area at wavelengths of 360 to 740 nm was measured using a reflectometer (photal MC-7300:SC, manufactured by Otsuka Electronics Co., Ltd.). The results are shown in Table 1. The smaller the average reflectance value, the better.

As shown in Table 1, the dispersion for black partition wall material of the present invention was prepared so that the viscosity change was small and the volume-based particle size (particularly the D50 and D90 values) was within a specified range. This demonstrates that when used as a black partition wall material, the dispersion for black partition wall material of the present invention can increase the taper angle and produce a coating film with low reflectance, making it suitable as a display material.

Claims (1)

The ink contains lactam black, an acrylic dispersant, a resin, and a solvent,
The lactam black is
The volume-based particle size D10 value is 5 to 40 nm,
The volume-based particle size D50 is 20 to 60 nm,
The volume-based particle size D90 is 40 to 110 nm,
The acrylic dispersant contains a block copolymer.