JP7625243B2 - Black pigment dispersion - Google Patents

Description

The present invention relates to a black pigment dispersion containing lactam black and having excellent dispersibility.

LED backlights are now widely used in mobile devices, televisions, and other devices for the backlights used in LCD displays, due to their high resolution, low cost, and thin form factor.

Recently, in order to keep up with the trend towards higher resolution and brightness in color LCD displays, the color filter-on-array method (COA method), in which the color filter is provided on the TFT element substrate, and the black matrix-on-array method (BOA method), in which only the black matrix is provided on the TFT element substrate, have been proposed for active matrix LCD displays. Compared to forming the black matrix on the color filter side, this method eliminates the need for a margin for alignment with the active element side, allowing for a higher aperture ratio and, as a result, higher brightness.

When using such a structure, the black matrix requires a black colorant with a volume resistivity above a certain level and a relative dielectric constant below a certain level so that it does not cause a short circuit in the electrical circuit even when it is directly mounted on the TFT element. One example of such a black matrix has been proposed, in which multiple types of organic coloring pigments and carbon black are used as pigments (Patent Document 1).

Photosensitive compositions for black matrices that use organic black pigments as pigments are also known. Specifically, photosensitive compositions that use aniline black (Patent Document 2) or perylene black (Patent Document 3) are known.

Patent Document 4 discloses a lactam black dispersion for electrophoretic display applications, which contains lactam black (a black pigment having a lactam structure) with a particle size of 314 to 551 nm and a specific dispersant (Table 1).

Patent Document 5 discloses a black pigment dispersion composition containing lactam black, a purple pigment, a blue pigment, and/or a green pigment, and carbon black, which is used in liquid crystal display elements, solid-state imaging elements, infrared sensors, etc., and a black resist composition containing the same.

Patent Document 6 discloses a colored photosensitive resin composition for forming partition walls of organic electroluminescent devices, which contains an organic black pigment such as Irgaphor (registered trademark) Black S0100CF, which is a lactam black, an acrylic dispersant, an epoxy (meth)acrylate resin, a photopolymerizable monomer, and a photopolymerization initiator.

JP 2009-75446 A Japanese Patent Application Publication No. 8-44049 JP 2006-235153 A Special Publication No. 2012-515240 JP 2019-81857 A International Publication No. 2018/101314

Lactam black is a black pigment that has the advantages of being highly transparent to infrared and ultraviolet rays, having high insulating properties, and a low dielectric constant, but when made into a pigment dispersion, it has the disadvantage of having poor dispersibility. In other words, when preparing a pigment dispersion containing lactam black, there are problems with the dispersion gelling and the viscosity of the dispersion changing during storage.

As a result of extensive research into solving the above problems, the inventors discovered that when lactam black is used as a black pigment in a pigment dispersion, the dispersibility of lactam black can be improved by using it in combination with a specific dispersant in a specific ratio, and thus completed the present invention.

Specifically, the present invention provides
A black pigment dispersion containing at least a black pigment, a dispersant, and a solvent,
the black pigment is lactam black,
The dispersant is
Monomer A having the structure of Chemical Formula 1;
A monomer B having a nitrogen-containing aromatic heterocyclic group as a basic functional group;
A monomer C capable of polymerizing with said A and said B;
A copolymer consisting of
Regarding black pigment dispersions:

(In the formula, R1 is hydrogen or a methyl group; R2 is an alkyl group having 1 to 8 carbon atoms; n=4 to 23.)

The black pigment dispersion of the present invention is preferably one in which the average particle size (cumulant average particle size) of lactam black is 200 nm or less, preferably 160 nm or less, since this provides excellent dispersibility of lactam black. The black pigment dispersion of the present invention does not gel during preparation, and the viscosity change during storage is small.

The content of the black pigment is preferably 5% by mass or more and 25% by mass or less. If it is less than 5% by mass, the pigment concentration is low and coloring may be insufficient, and if it is more than 25% by mass, the viscosity becomes high and the handling properties are likely to be poor.

The black pigment dispersion of the present invention may further contain a pigment derivative having an acidic group, for example a derivative in which an acidic group has been introduced into a quinophthalone skeleton. By containing such a pigment derivative, the particle size can be made smaller, and the amount of dispersant required can be reduced.

The black pigment dispersion of the present invention may further contain an acrylic resin having an acidic group, a polyester resin, or a resin having a cardo structure. By containing such a resin, the effect of improving developability and adhesion can be obtained.

The black pigment dispersion of the present invention may further contain auxiliary components such as a viscosity modifier.

The black pigment dispersion of the present invention has excellent dispersibility of lactam black, does not gel during preparation, and is resistant to viscosity changes during storage.

The following describes an embodiment of the present invention.

(Black pigment)
As the lactam black, for example, Black 582 manufactured by BASF, Irgaphor (registered trademark) Black S0100CF, etc. can be used.

(Dispersant)
As the monomer A, a monomer corresponding to the Light Acrylate series manufactured by Kyoeisha Chemical Co., Ltd. or the New Frontier series manufactured by Daiichi Kogyo Seiyaku Co., Ltd. can be used.

Specific examples of monomer B include 4-vinylpyridine, 2-vinylpyridine, etc.

Monomer C is preferably a nonionic monomer from the viewpoint of not affecting the dispersibility of the pigment. As a nonionic monomer, a (meth)acrylic acid alkyl ester such as methyl methacrylate or butyl methacrylate is preferable.

The content of monomers A to C in the dispersant can be changed as appropriate so that the total content is 100 parts by mass, with monomer A being 20 to 60 parts by mass, monomer B being 10 to 40 parts by mass, and monomer C being 20 to 60 parts by mass.

The acid value and amine value of the dispersant, which is a block copolymer of monomers A to C, are determined by the functional groups contained in the block copolymer and their contents. The acid value (acid value converted into solid content) can be determined, for example, by a method conforming to DIN EN ISO 2114, and the amine value (amine value converted into solid content) can be determined, for example, by a method conforming to DIN 16945. The acid value of the dispersant is preferably 1 mgKOH/g or less. The amine value of the dispersant is more preferably 50 mgKOH/g or more and 200 mgKOH/g or less.

(solvent)
As the solvent, various organic solvents such as aromatic, ketone, ester, glycol ether, alcohol, aliphatic, etc. may be used. The organic solvent may be used alone or in combination of two or more kinds.

Examples of aromatic organic solvents include aromatic hydrocarbons such as toluene, xylene, and ethylbenzene.

Examples of ketone-based organic solvents include methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, acetylacetone, isophorone, acetophenone, and cyclohexanone.

Examples of ester-based organic solvents include ethyl acetate, n-butyl acetate, isobutyl acetate, isopropyl acetate, methyl propionate, 3-methoxybutyl acetate, ethyl glycol acetate, propylene glycol monomethyl ether acetate (PMA), propylene glycol monoethyl ether acetate, 3-methyl-3-methoxybutyl acetate, methyl monochloroacetate, ethyl monochloroacetate, butyl monochloroacetate, methyl acetoacetate, ethyl acetoacetate, butyl carbitol acetate, butyl lactate, ethyl 3-ethoxypropionate, ethylene glycol monobutyl ether acetate, ethylene glycol monomethyl ether acetate, propyl acetate, and 1,3-butylene glycol diacetate.

Examples of glycol ether-based organic solvents include water-soluble glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether, propylene glycol mono-n-butyl ether, and dipropylene glycol mono-n-butyl ether;
Examples of water-insoluble glycol ethers include ethylene glycol monohexyl ether, ethylene glycol 2-ethylhexyl ether, ethylene glycol phenyl ether, diethylene glycol n-hexyl ether, diethylene glycol 2-ethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, dipropylene glycol propyl ether, and propylene glycol methyl ether propionate.

Examples of the alcohol-based organic solvent include alkyl alcohols having 1 to 4 carbon atoms, such as ethanol, methanol, butanol, propanol, and isopropanol;
Examples of the glycol include ethylene glycol, propylene glycol, diethylene glycol, pentamethylene glycol, trimethylene glycol, 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, tripropylene glycol, polyethylene glycols with a molecular weight of 2000 or less, 1,3-propylene glycol, isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, glycerin, mesoerythritol, and pentaerythritol.

Examples of aliphatic organic solvents include aliphatic hydrocarbons such as n-pentane, n-hexane, and n-heptane.

From the viewpoint of ease of handling, it is preferable to adjust the solvent content so that the solids concentration, including pigments, etc., is 6 to 40% by weight.

<Production Example of Black Pigment Composition>
A black pigment dispersion was produced using the following raw materials and production method.

(Black pigment)
As the lactam black, Irgaphor (registered trademark) Black S0100CF (BASF) was used.

(solvent)
Propylene glycol monomethyl ether acetate (PMA) was used as the solvent.

(Dispersant)
Dispersants I to VI, which will be described later, were used as the dispersants. The amine value, Mp (peak top molecular weight), Mw/Mn (ratio of weight average molecular weight to number average molecular weight), NV (solid content or non-volatile content), and monomer composition (numbers indicate mass ratios of monomers) constituting each dispersant are as shown in Table 1. In Table 1, the structures indicated by the abbreviations in the monomer composition column are as shown in Table 2.

(Method for producing dispersant I)
287.3 parts by mass of methyl methacrylate (MMA), 0.6 parts by mass of butyl methacrylate (BMA), 142.4 parts by mass of methoxypolyethylene glycol methacrylate (MPEG9MA), 15 parts by mass of N-(tert-butyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-O-(2-carboxylprop-2-yl)hydroxylamine (Arkema, product name BlocBuilder MA), 436 parts by mass of propylene glycol monomethyl ether acetate (PMA), and 218 parts by mass of propylene glycol monomethyl ether (PM) were collected in a 2L stainless steel separable flask. The mixture was stirred with nitrogen bubbling, and the flask was heated to 125°C in an oil bath and reacted for 4 hours.

Next, 199.7 parts by mass of 4-vinylpyridine (4VPy), 196 parts by mass of PMA, and 98 parts by mass of PM were added to the flask, and the mixture was stirred while continuing to be bubbled with nitrogen and reacted at 125°C for 4 hours.

The solid content of the reaction mixture was 40.5% by weight. The resulting block copolymer was measured by GPC (gel permeation chromatography) and found to have a peak top molecular weight of 11,500 and an Mw/Mn ratio of 1.24. The amine value (solid content) was 168.6 mgKOH/g.

The block copolymer (dispersant I) thus obtained has a block having a constituent unit derived from MMA (monomer C), a constituent unit derived from BMA (monomer C), and a constituent unit derived from MPEG9MA (monomer A), and a block having a constituent unit derived from 4VPy (monomer A) as a basic group-containing unit. In other words, dispersant I is a linear block polymer having a block consisting of a basic group-containing unit at one end. Due to the monomer structure, dispersant I does not have an acidic group. The mass ratio of each constituent unit of dispersant I (MMA/BMA/MPEG9MA/4VPy) is 45.6/0.1/22.6/31.7.

(Preparation of Dispersant II)
Dispersant II was produced in the same manner as Dispersant I, except that DM was used instead of 4VPy. The mass ratio of each constituent unit of Dispersant II (MMA/BMA/MPEG9MA/DM) was 35.1/0.1/17.4/47.4.

(Preparation of Dispersant III)
Dispersant III was produced in the same manner as Dispersant I, except that DE was used instead of 4VPy. The mass ratio of each constituent unit of Dispersant III (MMA/BMA/MPEG9MA/DE) was 29.4/0.1/14.6/55.9.

(Preparation of Dispersant IV)
Dispersant IV was prepared in the same manner as Dispersant I, except that DMAPAA was used instead of 4VPy. The mass ratio of each constituent unit of Dispersant IV (MMA/BMA/MPEG9MA/DMAPAA) was 35.3/0.1/17.5/47.1.

(Preparation of Dispersant V)
Dispersant V was produced in the same manner as Dispersant I, except that DMAPMA was used instead of 4VPy. The mass ratio of each constituent unit of Dispersant V (MMA/BMA/MPEG9MA/DMAPMA) was 32.5/0.1/16.1/51.3.

(Preparation of Dispersant VI)
Dispersant VI was prepared in the same manner as Dispersant I, except that PMPMA was used instead of 4VPy. The mass ratio of each constituent unit of Dispersant VI (MMA/BMA/MPEG9MA/PMPMA) was 38.2/0.1/18.9/42.8.

[Example]
12 parts by mass of lactam black, 7.2 parts by mass of dispersant I (solid content equivalent) as a dispersant, and PMA as a solvent were collected in a polyethylene container. The amount of PMA was adjusted so that "lactam black + dispersant + solvent" was 100 parts by mass. 300 parts by mass of zirconia beads (φ0.3 mm) were placed in the container, and a dispersion treatment was carried out for 90 minutes using a paint shaker manufactured by Asada Iron Works Co., Ltd., to obtain a black pigment dispersion of the example (lactam black concentration 12% by mass, dispersant concentration 7.2% by mass).

[Comparative Example 1]
A black pigment dispersion of Comparative Example 1 was obtained in the same manner as in Examples, except that Dispersant II was used as the dispersant in an amount of 7.2 parts by mass calculated as solid content. In the black pigment dispersions of Comparative Examples 1 to 5, the lactam black concentration was 12% by mass, and the dispersant concentration was 7.2% by mass.

[Comparative Example 2]
A black pigment dispersion of Comparative Example 2 was obtained in the same manner as in Example, except that Dispersant III was used in an amount of 7.2 parts by mass calculated as solid content as the dispersant.

[Comparative Example 3]
A black pigment dispersion of Comparative Example 3 was obtained in the same manner as in Example, except that Dispersant IV was used in an amount of 7.2 parts by mass calculated as solid content as the dispersant.

[Comparative Example 4]
A black pigment dispersion of Comparative Example 4 was obtained in the same manner as in Example, except that Dispersant V was used in an amount of 7.2 parts by mass calculated as solid content as the dispersant.

[Comparative Example 5]
A black pigment dispersion of Comparative Example 5 was obtained in the same manner as in Example, except that Dispersant VI was used in an amount of 7.2 parts by mass calculated as solid content as the dispersant.

<Measurement of particle size of lactam black>
The black pigment dispersions of Examples and Comparative Examples 1 to 5 were diluted with PMA to a concentration range of 0.001 to 10% by mass, and then the average particle size (cumulant average particle size; average particle size by cumulant analysis) was measured using an FPAR-1000 manufactured by Otsuka Electronics Co., Ltd. The average particle size was measured immediately after preparation and after storage for one week in a thermostatic chamber at 40°C.

<Viscosity Measurement of Black Pigment Dispersion>
The viscosity (25°C) of the black pigment dispersions of Examples and Comparative Examples 1 to 5 immediately after preparation and after storage for one week in a thermostatic chamber at 40°C was measured using an E-type viscometer (TV-22) manufactured by Toki Sangyo Co., Ltd.

The average particle size and viscosity measurement results of lactam black for the black pigment dispersions of Examples and Comparative Examples 1 to 5 are shown in Table 3.

Black pigment dispersions other than those in the examples gelled during preparation, making it impossible to measure the average particle size of lactam black and the viscosity of the dispersion.

In the black pigment dispersion of the embodiment, the average particle size of lactam black was 148 nm and 146 nm when prepared and after storage at 40°C, showing little change. In addition, the initial viscosity was 5.06 mPa·s, and the viscosity after storage at 40°C was 5.22 mPa·s, showing little change in viscosity (viscosity change rate: 5.22/5.06=1.03).

As shown in Table 3, dispersions using lactam black as a black pigment can gel during preparation depending on the type of dispersant used. However, when combined with a dispersant that is a copolymer of monomers A to C, it was confirmed that the average particle size and viscosity of lactam black are less likely to change during storage.

If the lactam black content (concentration) in the black pigment dispersion is 5% by mass or more and 25% by mass or less, the average particle size and viscosity of the lactam black are unlikely to change during storage, as with the black pigment dispersions of the examples.

From the viewpoint of optical density and surface smoothness, the average particle size of lactam black is preferably 200 nm or less, and more preferably 160 nm or less.

The viscosity change rate of the black pigment dispersion (viscosity after storage for one week in a thermostatic chamber at 40°C/viscosity immediately after preparation (25°C)) is preferably 0.8 to 1.2 times, and more preferably 0.9 to 1.1 times.

The black pigment dispersion of the present invention is useful in technical fields such as displays, solid-state imaging devices, and infrared sensors.

Claims (4)

A black pigment dispersion containing at least a black pigment, a dispersant, and a solvent,
the black pigment is lactam black,
The dispersant is
Monomer A,
A monomer B having a nitrogen-containing aromatic heterocyclic group as a basic functional group;
A monomer C capable of polymerizing with said A and said B;
A copolymer consisting of
The content of the black pigment is 5% by mass or more and 25% by mass or less.
Black pigment dispersion :
wherein the monomer A is methoxypolyethylene glycol methacrylate (MPEG9MA);
The monomer B is 4-vinylpyridine (4Vpy),
The monomer C is methyl methacrylate (MMA) and butyl methacrylate (BMA);
The content of the monomers A to C in 100 parts by mass of the dispersant is
The monomer A is 20 to 60 parts by mass,
The monomer B is 10 to 40 parts by mass,
The amount of the monomer C is 20 to 60 parts by mass . 2. The black pigment dispersion according to claim 1, wherein the mass ratio of monomer constituent units in the dispersant is MMA/BMA/MPEG9MA/4Vpy=45.6/0.1/22.6/31.7. 3. The black pigment dispersion according to claim 1, wherein the lactam black has an average particle size of 200 nm or less. The black pigment dispersion according to any one of claims 1 to 3 , wherein the content of the black pigment is 5% by mass or more and 25% by mass or less.