JP7610219B2 - Resin-coated wavelength conversion particles and photocurable ink composition - Google Patents

Description

The present invention relates to resin-coated wavelength conversion particles in which wavelength conversion particles such as quantum dots are coated with a resin, a photocurable ink composition using the same, and a method for producing resin-coated wavelength conversion particles.

In recent years, there has been an increasing demand for improved color reproducibility in image display in the market for flat panel displays such as liquid crystal displays (LCDs). In this regard, quantum dots (QDs) have been attracting attention as a light-emitting material. For example, when excitation light from a backlight is incident on a wavelength conversion member containing quantum dots, the quantum dots are excited and emit fluorescence. By using quantum dots with different emission characteristics, it is possible to emit red light, green light, and blue light. The fluorescence from quantum dots has a small half-width, which provides excellent reproducibility.

Patent Document 1 proposes a quantum dot-containing polymerizable composition for forming such a wavelength conversion film, in which quantum dots are dispersed in an organic matrix containing a polymer made of (meth)acrylate monomers and the like and a phosphite triester.

However, when using quantum dots, if a gas barrier layer is not provided, the quantum dots will deteriorate due to water and oxygen, resulting in low durability. This necessitates sealing the ends by sandwiching them between glass, which increases costs, increases weight, and causes a lack of flexibility.

In addition to such display applications, ink compositions containing quantum dots are also known. For example, a photocurable ink composition containing quantum dots has been proposed in Patent Document 2, in which a ligand is bonded to quantum dots and the quantum dots are dispersed in a UV-curable resin containing an epoxy resin.

As another example of a technique that uses a resin-coated fluorescent pigment, Patent Document 3 proposes a photocurable ink composition in which a pigment such as a fluorescent substance is coated with a resin such as an epoxy resin and dispersed in a cationic polymerizable compound.

JP 2017-62458 A Special Publication No. 2021-501230 JP 2005-132874 A

However, as in Patent Documents 1 and 2, if quantum dots or organic phosphors are dispersed directly in a photocurable ink composition without being coated, the quantum dots and the like are deteriorated by acidic groups contained in the composition and radicals and acids generated during polymerization, resulting in a problem of reduced wavelength conversion characteristics.

In addition, according to the inventors' research, it was found that when quantum dots or the like are directly coated with epoxy resin as in Patent Document 3, the quantum dots or the like are deteriorated by the acid generator or the like used together with the epoxy resin, and the wavelength conversion characteristics of the resulting printed matter are reduced.

The object of the present invention is to provide resin-coated wavelength-converting particles that can favorably maintain the wavelength conversion characteristics of the wavelength-converting particles even when wavelength-converting particles such as quantum dots are used in a photocurable ink composition, a photocurable ink composition using the same, and a method for producing the resin-coated wavelength-converting particles.

As a result of intensive research conducted by the inventors in order to achieve the above object, they discovered that by coating wavelength-converting particles with a first coating material containing a light-transmitting resin and a second coating material containing a cured product of an alicyclic epoxy compound, the wavelength-converting properties of the wavelength-converting particles are favorably maintained even when used in a photocurable ink composition, and thus completed the present invention.

That is, the present invention includes the following:

[1] A resin-coated wavelength-converting particle comprising: a wavelength-converting particle containing a quantum dot or an organic phosphor; a first coating material that coats the wavelength-converting particle and contains a translucent resin; and a second coating material that coats the first coating material and contains a cured product of an alicyclic epoxy compound.

[2] The resin-coated wavelength conversion particle according to [1], wherein the alicyclic epoxy compound is composed of one or more aliphatic rings and one or more oxygen atoms directly bonded thereto.

[3] The resin-coated wavelength conversion particle according to [1] or [2], wherein the light-transmitting resin is a (meth)acrylic resin, a polycarbonate resin, a polystyrene resin, or a polyolefin resin.

[4] The wavelength conversion particle has an emission wavelength of 500 to 580 nm or 600 to 680 nm. [1] to [3] A resin-coated wavelength conversion particle.

[5] A photocurable ink composition comprising the resin-coated wavelength conversion particles described in any one of [1] to [4], a radical polymerizable compound, and a photopolymerization initiator.

[6] A method for producing resin-coated wavelength-converting particles, comprising the steps of: spraying, under light irradiation, a dispersion containing first coated particles in which wavelength-converting particles containing quantum dots or organic phosphors are coated with a first coating material containing a translucent resin; an alicyclic epoxy compound; and a photoacid generator, to obtain resin-coated wavelength-converting particles in which the alicyclic epoxy compound is cured.

The resin-coated wavelength-converting particles of the present invention can favorably maintain the wavelength-converting properties of wavelength-converting particles, even when quantum dots or other wavelength-converting particles are used in a photocurable ink composition. Although the details of the reason are not clear, it is believed that by providing the wavelength-converting particles with a second coating material containing a cured product of an alicyclic epoxy compound, the water resistance and gas barrier properties are particularly enhanced, thereby suppressing deterioration of the wavelength-converting particles. In addition, it is believed that by providing a first coating material containing a light-transmitting resin in advance, it is possible to suppress deterioration of the quantum dots, etc., caused by an acid generator, etc., used together with the alicyclic epoxy compound.

In addition, the photocurable ink composition of the present invention contains resin-coated wavelength conversion particles that provide such effects, a radically polymerizable compound, and a photopolymerization initiator, so that even when used in a photocurable ink composition, the wavelength conversion properties of the wavelength conversion particles can be favorably maintained, and the ink can be rapidly cured by photocuring.

Furthermore, the method for producing resin-coated wavelength-converting particles of the present invention includes a step of spraying a dispersion containing first coated particles, an alicyclic epoxy compound, and a photoacid generator under light irradiation to obtain resin-coated wavelength-converting particles in which the alicyclic epoxy compound is cured, so that the resin-coated wavelength-converting particles can be continuously and stably produced as fine particles having a relatively uniform particle size.

<Resin-coated wavelength-converting particles>
The resin-coated wavelength-converting particle of the present invention includes a wavelength-converting particle, a first coating material that coats the wavelength-converting particle, and a second coating material that coats the first coating material. A particle in which the wavelength-converting particle is coated with the first coating material (hereinafter referred to as the "first coated particle") may contain one or more wavelength-converting particles. A particle coated with the second coating material (hereinafter sometimes referred to as the "second coated particle") (i.e., in the resin-coated wavelength-converting particle) may contain one or more first coated particles.

In this specification, "coating" refers to a state in which 60% or more of the surface area of the object to be coated is covered, preferably 90% or more, and more preferably 100%. In addition, "coating" is a concept that includes cases in which particles are covered in layers, as well as cases in which particles are dispersed in a base material.

The resin-coated wavelength conversion particles may have any shape, but are preferably spherical, elliptical, or the like, from the viewpoint of suitability for addition to inks, etc. to form fine patterns. Similarly, the first coated particles may have any shape, but are preferably spherical, elliptical, or the like, from the viewpoint of suitability for addition to inks, etc. to form fine patterns.

A preferred particle structure of the resin-coated wavelength conversion particles is one in which a plurality of wavelength conversion particles are dispersed in a particulate first coating material, and a single first coated particle is covered in a layer of the second coating material. Alternatively, a preferred structure is one in which a single wavelength conversion particle is covered in a layer of the first coating material, and a single first coated particle is covered in a layer of the second coating material.

The average particle size (volume-based _D50 ) of the second coated particles (resin-coated wavelength conversion particles) is preferably 9 to 300 nm, and more preferably 90 to 150 nm, from the viewpoint of ensuring chemical resistance and gas barrier performance while being suitable for addition to inks, etc. to form fine patterns.

The average particle size (volume-based D ₅₀ ) of the first coated particles is preferably 20 to 50 nm, and more preferably 20 to 30 nm, from the viewpoint of obtaining sufficient luminescence intensity while ensuring the thickness of the second coated material.

In the resin-coated wavelength conversion particles, the wavelength conversion particles contain quantum dots or organic phosphors, the first coating material contains a translucent resin, and the second coating material contains a cured product of an alicyclic epoxy compound. Each material is described below.

[Wavelength conversion particles]
The wavelength conversion particles contain one or more of quantum dots or organic phosphors, and the resin-coated wavelength conversion particles contain these and thereby have a wavelength conversion function.

The wavelength conversion characteristics of quantum dots or organic phosphors are not particularly limited, but the wavelength conversion characteristics of resin-coated wavelength conversion particles are such that, for blue excitation light with a wavelength of 400 nm to 480 nm, preferably 440 to 470 nm, when red light is emitted, the emission wavelength (peak wavelength) is preferably 600 to 680 nm, more preferably 610 nm to 640 nm. When green light is emitted, the emission wavelength (peak wavelength) is preferably 500 to 580 nm, more preferably 520 nm to 560 nm.

(Quantum dots)
Quantum dots refer to nanoscale particles with unique optical properties according to quantum chemistry and quantum mechanics, and since the optical properties can be adjusted by the particle size, they have characteristic light emission properties that depend on the particle size. In the present invention, semiconductor quantum dots, carbon quantum dots, silicon quantum dots, perovskite quantum dots, etc. can be used depending on the emission wavelength of the converted light. In addition, by using multiple quantum dots selected from these and adjusting the content of each, a desired emission wavelength can be obtained.

The content of quantum dots in the resin-coated wavelength conversion particles is preferably 1 to 10% by mass, and more preferably 2 to 6% by mass, from the viewpoint of obtaining sufficient emission intensity while ensuring the thickness and amount of the coating material.

(Carbon-based quantum dots)
Carbon-based quantum dots have luminescence properties that depend on particle size due to π bonds between carbon atoms. Examples of carbon-based quantum dots include graphene quantum dots having a graphene structure, carbon quantum dots not having a graphene structure, and quantum dots obtained by chemically modifying these, among which graphene quantum dots or chemically modified graphene quantum dots are preferred from the viewpoint of quantum yield.

These carbon-based quantum dots are commercially available from Sigma-Aldrich, Fuji Pigment Co., Ltd., GS Alliance Co., Ltd., Funakoshi Co., Ltd., Kishida Chemical Co., Ltd., and others, and any of them can be used.

(Graphene quantum dots)
Graphene quantum dots include non-functionalized graphene quantum dots, functionalized graphene quantum dots, pristine graphene quantum dots, and combinations thereof.

The functionalized graphene quantum dots may be functionalized with one or more functional groups. The functional groups include oxygen groups, carboxyl groups, carbonyl groups, amorphous carbon, hydroxyl groups, alkyl groups, aryl groups, esters, amines, amides, polymers, poly(propylene oxide), and combinations thereof.

Graphene quantum dots also include functionalized graphene quantum dots that are functionalized with one or more alkyl groups. The alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and combinations thereof. In some embodiments, the alkyl groups include octyl groups (e.g., octylamine).

The graphene quantum dots can also be functionalized with one or more polymer precursors. For example, the graphene quantum dots can be functionalized with one or more monomers (e.g., vinyl monomers).

Graphene quantum dots can be functionalized with a polymer precursor that is polymerized to form polymer-functionalized graphene quantum dots. For example, the ends can be functionalized with a vinyl monomer that is polymerized to form end-functionalized polyvinyl adducts.

Graphene quantum dots include functionalized graphene quantum dots that are functionalized with one or more hydrophilic functional groups. The hydrophilic functional groups include carboxyl groups, carbonyl groups, hydroxyl groups, hydroxyalkyl groups, poly(ethylene glycol), poly(vinyl alcohol), poly(acrylic acid), and combinations thereof.

The graphene quantum dots include functionalized graphene quantum dots that are functionalized with one or more hydrophobic functional groups. The hydrophobic functional groups include alkyl groups, aryl groups, and combinations thereof. The hydrophobic functional groups include one or more alkylamides or arylamides.

The graphene quantum dots include edge-functionalized graphene quantum dots. The edge-functionalized graphene quantum dots include one or more hydrophobic functional groups as described above. The edge-functionalized graphene quantum dots include one or more hydrophobic functional groups as described above. The edge-functionalized graphene quantum dots include one or more hydrophilic functional groups, also as described above. The edge-functionalized graphene quantum dots include one or more oxygen appendages on their edges. The edge-functionalized graphene quantum dots include one or more amorphous carbon appendages on their edges.

The graphene quantum dots are end-functionalized with one or more alkyl or aryl groups, such as alkylamides or arylamides. End-functionalization of the graphene quantum dots with alkyl or aryl groups is achieved by reaction of the alkylamides or arylamides at the ends of the graphene quantum dots with carboxylic acids.

Graphene quantum dots include pristine graphene quantum dots. Pristine graphene quantum dots include graphene quantum dots that remain untreated after synthesis. Pristine graphene quantum dots include graphene quantum dots that have not undergone any additional surface modification after synthesis.

Graphene quantum dots can be obtained from a variety of sources. For example, graphene quantum dots include coal-derived graphene quantum dots, coke-derived graphene quantum dots, and combinations thereof. Graphene quantum dots include coke-derived graphene quantum dots. Graphene quantum dots include coal-derived graphene quantum dots. Coal includes (but is not limited to) anthracite, bituminous coal, subbituminous coal, modified bituminous coal, asphaltenes, asphalt, peat, lignite, boiler coal, petrified oil, carbon black, activated carbon, and combinations thereof. The carbon source is bituminous coal. The carbon includes bituminous coal.

Graphene quantum dots can have a variety of diameters. For example, graphene quantum dots preferably have diameters ranging from about 1 nm to about 100 nm, more preferably from about 1 nm to about 50 nm, and even more preferably from about 1 nm to about 20 nm.

Graphene quantum dots can also have a variety of structures. For example, graphene quantum dots can have a crystalline structure, such as a crystalline hexagonal structure. Graphene quantum dots can have a single layer or multiple layers, such as graphene quantum dots having from about two layers to about four layers.

Graphene quantum dots can also have a variety of quantum yields. It is preferable that the graphene quantum dots have a quantum yield in the range of about 30 to 80%. In addition, the fluorescent properties of the graphene quantum dots in an aqueous dispersion are preferably such that the emission wavelength is 380 nm to 650 nm for at least any one of the wavelengths of excitation light of 300 nm to 420 nm.

The graphene quantum dots may be in the form of a powder or in the form of pellets. The graphene quantum dots may be in a liquid state, such as a dispersion, solution, or melt.

Various methods can be utilized to form graphene quantum dots. For example, the process of forming graphene quantum dots can include exposing a carbon source to an oxidizing agent, resulting in the formation of graphene quantum dots. Carbon sources include coal, coke, and combinations thereof.

The oxidizers include acids, including sulfuric acid, nitric acid, phosphoric acid, hypophosphorous acid, oleum, hydrochloric acid, oleum, chlorosulfonic acid, and combinations thereof. The oxidizers also include potassium permanganate, sodium permanganate, hypophosphorous acid, nitric acid, sulfuric acid, hydrogen peroxide, and combinations thereof. A preferred oxidizer is a mixture of potassium permanganate, sulfuric acid, and hypophosphorous acid.

The carbon source is exposed to the oxidizing agent by sonicating the carbon source in the presence of the oxidizing agent. Heating the carbon source in the presence of the oxidizing agent is included. The heating is at a temperature of at least about 100°C.

The use of further methods of forming graphene quantum dots can also be envisaged. For example, further methods of forming graphene quantum dots are disclosed in International Patent Application PCT/US2014/036604. Further suitable methods of producing graphene quantum dots are also disclosed in the following references: ACS Appl. Mater. Interfaces 2015, 7, 7041-7048; and Nature Commun. 2013, 4:2943, 1-6.

(Carbon quantum dots)
Carbon quantum dots are quantum dots that do not have a ring structure like graphene. They are more susceptible to the effects of pH than graphene quantum dots, and have the property of changing their emission intensity and peak position.

The carbon quantum dots can have a variety of diameters. For example, the carbon quantum dots preferably have a diameter ranging from about 1 nm to about 100 nm, more preferably from about 1 nm to about 50 nm, and even more preferably from about 1 nm to about 30 nm.

Carbon quantum dots can also have a variety of quantum yields. Preferably, the carbon quantum dots have a quantum yield in the range of about 20-50%. In addition, the fluorescent properties of the carbon quantum dots in an aqueous dispersion are preferably such that the emission wavelength is 380 nm to 600 nm for at least any wavelength of excitation light between 300 nm and 420 nm.

The manufacturing method for carbon quantum dots is not very different from that for graphene quantum dots, with the only difference being whether the raw materials used and manufacturing conditions are favorable for forming the graphene structure.

Therefore, carbon-based quantum dots containing both can be produced by, for example, a method of producing them by laser ablation of a carbon target followed by chemical treatment (JP Patent Publication No. 2012-501863), a method of producing them from candle soot (H. Liu, et al., Angew. Chem.Int. Ed. 2007, 46, 6473-6475.), a method of producing them by chemical treatment of graphite oxide (G. Eda, et al., Adv. Mater.2010, 22, 505-509.), a method of producing them from a chemical reaction using graphite oxide as a precursor (JP Patent Publication No. 2012-136566), a method of producing them from a conversion reaction of fullerene (J. Lu, et al., Nature Nanotech.2011, 6, 247-252.), and it can also be produced by chemically processing cheaper carbon raw materials such as carbon fiber and activated carbon (J. Peng, et al., Nano Lett. 2012, 12, 844-849., Z.A. Qiao, ChemCommun. 2010, 46,8812-8814., Y. Dong, et al., Chem. Mater.2010, 22, 5895-5899.).

These techniques are broadly classified as top-down techniques, but carbon quantum dots can also be produced by a bottom-up technique (G. A. Ozin, et al., J. Mater. Chem., 2012, 22, 1265-1269.), which produces carbon quantum dots from the polymerization of organic precursor molecules.

It is also possible to manufacture the carbon quantum dots using a method for manufacturing carbon quantum dots (JP Patent Publication 2014-133685 A) that includes the steps of mixing a carbon material with hydrogen peroxide, decomposing carbon with the hydrogen peroxide to prepare a carbon quantum dot production solution, and separating the carbon quantum dots and hydrogen peroxide in the carbon quantum dot production solution to stop the decomposition reaction and obtain the carbon quantum dots.

(Wavelength conversion properties of carbon-based quantum dots)
In terms of wavelength conversion characteristics (fluorescence characteristics) when carbon-based quantum dots are used, from the viewpoint of making them a highly versatile fluorescent material, the emission wavelength (peak wavelength) is preferably 400 nm to 750 nm, more preferably 450 nm to 650 nm, and even more preferably 500 nm to 600 nm, for at least any wavelength of excitation light of 300 nm to 470 nm. Such emission wavelengths are in approximately the same range as those of single crystal YAG.Ce.

Furthermore, it is preferable that the half-width of the emission centered on the emission peak wavelength is 40 nm to 100 nm, the emission wavelength is more preferably 400 nm to 700 nm, and the emission wavelength is even more preferably 420 nm to 750 nm.

From the viewpoint of obtaining such fluorescent properties, the fluorescent properties of the aqueous dispersion of carbon-based quantum dots, which are the raw material, are such that the emission wavelength (peak wavelength) is preferably 380 nm to 600 nm, more preferably 400 nm to 550 nm, and even more preferably 420 nm to 500 nm, for at least any wavelength of excitation light between 300 nm and 420 nm.

The quantum yield (luminous efficiency) of the phosphor composition is preferably 25% or more, more preferably 50% or more, and particularly preferably 70 to 80%.

(Silicon quantum dots)
When semiconductors are made into nanoparticles, the band structure changes due to the quantum size effect (confinement effect), and they emit fluorescence of a color that corresponds to the particle size. Silicon quantum dots are a typical quantum dot of group IV semiconductors.

A representative method for synthesizing silicon quantum dots is etching of a silicon wafer. Nanoparticles can be obtained by micronizing bulk silicon by electrolytic etching using hydrofluoric acid (HF). In this case, the particle size of the obtained particles can be controlled by the etching time, etc. As a bottom-up synthesis method that can generate a relatively large amount of particles, particle synthesis by thermal decomposition of silane (SiH ₄ ) is known. Si atoms are generated by thermal decomposition of silane, which becomes supersaturated, and particles are generated by nucleation and growth. Since the particles generated in this case are relatively large in size, the particles are then etched with a mixture of hydrofluoric acid (HF)/nitric acid (HNO ₃ ) to reduce the particle size to the region where the quantum size effect appears.

A plasma CVD method is also known as a method for synthesizing single-nanometer particles in one step without an etching process. The precursor silicon tetrabromide (SiBr ₄ ) is decomposed in an RF plasma field to generate Si atoms, which are then nucleated and grown in a reactor to produce nanoparticles.

Silicon quantum dots are commercially available from GS Alliance, Inc., Sigma-Aldrich, and other companies, and can be used. Commercially available silicon quantum dots range in size from a few angstroms to less than 10 nm, and have a quantum yield of approximately 20-30%.

Silicon quantum dots can emit light with wavelengths that depend on the particle size, and in the present invention, they can be used as wavelength conversion particles for obtaining green to yellow colors, or wavelength conversion particles for obtaining red colors.

For resin-coated wavelength conversion particles containing silicon quantum dots, when red light is emitted in response to blue excitation light with a wavelength of 400 nm to 470 nm, the emission wavelength (peak wavelength) is preferably 610 nm to 640 nm, and more preferably 620 nm to 640 nm. When green to yellow light is emitted, the emission wavelength (peak wavelength) is preferably 520 nm to 560 nm, and more preferably 530 nm to 550 nm.

(Perovskite quantum dots)
Perovskite quantum dots have a perovskite crystal structure. Generally, the perovskite crystal structure is represented by a composition formula of _ABX3 using ions A, B and X, where ion A is present at eight vertices, ion X is present at the center of six faces, and ion B is present at the center of the lattice. Since ion B is relatively smaller than ion A, ion B can be in a state where the center of gravity of positive and negative charges is separated due to its ease of movement. In the perovskite quantum dots, ion X is preferably a halogen atom (preferably F, Cl, Br, I), ion A is preferably Cs, and ion B is preferably Pb.

The perovskite quantum dots are preferably represented by the general formula (1): CsPbY _a Z _b (in the above general formula (1), Y and Z each independently represent F, Cl, Br or I, a and b each independently represent a real number between 0 and 3, and a+b=3). Also usable are those having a composition of CH ₃ NH ₃ PbX ₃ (X=Cl, Br, I).

The perovskite quantum dots preferably include at least one type of quantum dot selected from perovskite quantum dots that emit red light. The emission color of light-emitting nanocrystals such as quantum dots depends on the particle size of the quantum dots and the energy gap of the light-emitting nanocrystals, so the emission color can be selected by adjusting the type of perovskite quantum dots used and their particle size.

Commercially available perovskite quantum dots are nanocrystals of perovskite compounds, with typical compositions being CH ₃ NH ₃ PbX ₃ and CsPbX ₃ (X = Cl, Br, I). The quantum yield is about 50 to 80%, and the half-width is about 18 nm to 39 nm.

For resin-coated wavelength conversion particles containing perovskite quantum dots, when red light is emitted in response to a wavelength of 400 nm to 470 nm, which is the excitation light of a blue LED, the emission wavelength (peak wavelength) is preferably 610 nm to 650 nm, and more preferably 615 nm to 635 nm.

(Semiconductor quantum dots)
Semiconductor-based quantum dots include any type of semiconductor, including Group II-VI, Group III-V, Group IV-VI, and Group IV semiconductors. Suitable semiconductor materials include, but are not limited to, Si, Ge, Sn, Se, Te, B, C, P, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdSeZn, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCl, CuBr, _{CuI, Si3N4 , Ge3N4 ,} Al ₂ O ₃ , Al ₂ CO, and combinations thereof.

It is also possible to use semiconductor quantum dots having a core-shell structure. In this case, the core material is preferably a III-V group nanocrystal selected from the group consisting of BN, BP, BAs, BSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, and InSb.

Shell materials include Si, Ge, Sn, Se, Te, B, C, P, Co, Au, BN, BP, BAs, AlN, AlP, AlAs, Al. Sb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdSeZn, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCl, CuBr, CuI, Si _{3N4 , Ge3N 4} , Al ₂ O ₃ , Al ₂ CO, and combinations thereof.

The core material may also be doped, with dopants including ZnS, ZnSe, ZnTe, CdSe, CdS, CdTe, HgS, HgSe, HgTe, _CuInS2 , _CuInSe2 , AlN, AlP, AlAs, GaN, GaP, or GaAs.

Representative semiconductor quantum dots include ZnS, InP/ZnS, CdS, CdSe, _CuInS2 (CIS), _CuInSe2 , _CuInS2 /ZnS, PbS, and _AgInS2 .

In the case of semiconductor quantum dots, the emission wavelength can be changed depending on the type of semiconductor, structure, particle size, etc., but the average particle size of semiconductor quantum dots that are preferably used in the present invention is 2 to 10 nm, and more preferably 3 to 6 nm.

(Organic phosphor)
Examples of organic fluorescent materials include cyanine dyes such as acridine orange, aminoacridine, quinacrine, anilinonaphthalenesulfonic acid derivatives, anthroyloxystearic acid, auramine O, chlorotetracycline, merocyanine, and 1,1'-dihexyl-2,2'-oxacarbocyanine, dansyl chloride derivatives such as dansylsulfamide, dansylcholine, dansylgalacside, dansyltolidine, and dansyl chloride, diphenylhexatriene, eosin, ε-adenosine, ethidium bromide, fluorescein, formycin, 4-benzoylamido-4'-aminostilbene-2,2'-sulfonic acid, β-naphthyl triphosphate, oxonol dyes, parinaric acid derivatives, perylene, N -phenylnaphthylamine, pyrene, safranine O, fluorescamine, fluorescein isocyanate, 7-chloronitrobenzo-2-oxa-1,3-diazol, dansyl aziridine, 5-(iodoacetamidoethyl)aminonaphthalene-1-sulfonic acid, 5-iodoacetamidofluorescein, N-(1-anilinonaphthyl-4)maleimide, N-(7-dimethyl-4-methylcoumanyl)maleimide, N-(3-pyrene)maleimide, eosin-5-iodoacetamide, fluorescein mercury acetate, 2-(4'-(2''-iodoacetamido))aminonaphthalene-6-sulfonic acid, eosin, rhodamine derivatives, organic EL dyes, organic EL polymers or crystals, dendrimers, and the like can be mentioned.

The organic phosphor may be dispersed or dissolved in the first coating material. When the organic phosphor is dispersed, the average particle size is, for example, about 30 to 50 nm.

The content of the organic phosphor in the resin-coated wavelength conversion particles is preferably 1 to 10% by mass, and more preferably 2 to 6% by mass, from the viewpoint of obtaining sufficient luminescence intensity while ensuring the thickness and amount of the coating material.

[First coating material]
The first coating material that coats the wavelength-converting particles contains a light-transmitting resin. By coating the wavelength-converting particles with the first coating material containing a light-transmitting resin, the effect of the acid required for curing the alicyclic epoxy compound can be suppressed, and deterioration of the wavelength-converting particles can be suppressed.

The content of the first coating material in the resin-coated wavelength conversion particles is preferably 10 to 40% by mass, and more preferably 20 to 35% by mass, from the viewpoint of obtaining a sufficient barrier effect while ensuring the thickness and amount of the second coating material.

(Light-transmitting resin)
As the light-transmitting resin, any light-transmitting resin can be used, and examples thereof include those containing, as a main component, one or more of vinyl-based polymers and copolymers, (meth)acrylic-based polymers and copolymers, polycarbonates, polyesters, polyamides, polyimides, polyurethanes, amino-based polymers, silicon-containing polymers, sulfur-containing polymers, and fluorine-containing polymers.

The light-transmitting resin is preferably hydrophobic and is preferably a (meth)acrylic resin, a polycarbonate resin, a polystyrene resin, or a polyolefin resin.

It is also possible to add plasticizers, antioxidants, nucleating agents, clarifiers, light stabilizers, antistatic agents, etc. to the translucent resin as long as the effects of the present invention are not impaired.

[Second coating material]
The second coating material that coats the first coating material (first coated particles) contains a cured product of an alicyclic epoxy compound, and the alicyclic epoxy compound can be cured in the presence of an acid catalyst. When curing in the presence of an acid catalyst, the alicyclic epoxy compound can be cured by adding an initiator such as a photoacid generator to the alicyclic epoxy compound or by adding the alicyclic epoxy compound to an acidic solution. Therefore, the cured product of the alicyclic epoxy compound may contain not only a component derived from the alicyclic epoxy compound, but also a component derived from an initiator such as a photoacid generator.

Since the second coating material contains a cured product of an alicyclic epoxy compound, the water resistance and gas barrier properties of the coating material are particularly enhanced, thereby suppressing deterioration of the wavelength conversion particles.

The content of the second coating material in the resin-coated wavelength conversion particles is preferably 60 to 85% by mass, and more preferably 70 to 85% by mass, from the viewpoint of obtaining sufficient water resistance and gas barrier properties while maintaining the size and function of the first coated particles.

(Alicyclic epoxy compounds)
The alicyclic epoxy compound refers to a compound containing one or more alicyclic epoxy groups in one molecule, but a compound containing two or more is preferred from the viewpoint of reactivity with a cationic catalyst. The alicyclic epoxy compound may be only one type, or may be two or more types with different structures. In the following, the content of the alicyclic epoxy compound refers to the total content when two or more alicyclic epoxy compounds with different structures are used. The alicyclic epoxy compound has better curability by light irradiation than the aliphatic epoxy compound. The use of a polymerizable compound with excellent photocurability is advantageous not only in improving productivity, but also in forming a layer with uniform physical properties on the light-irradiated side and the non-irradiated side. In addition, epoxy compounds generally tend to have less cure shrinkage when photocured.

The alicyclic epoxy compound has at least one alicyclic epoxy group. Here, the alicyclic epoxy group refers to a monovalent substituent having a condensed ring of an epoxy ring and a saturated hydrocarbon ring, and is preferably a monovalent substituent having a condensed ring of an epoxy ring and a cycloalkane ring. More preferred alicyclic epoxy compounds include those having one or more of the following structures in which an epoxy ring and a cyclohexane ring are condensed in one molecule.

Two or more of the above structures may be contained in one molecule, and preferably one or two are contained in one molecule. The above structures may also have one or more substituents. Examples of the substituents include alkyl groups (e.g., alkyl groups having 1 to 6 carbon atoms), hydroxyl groups, alkoxy groups (e.g., alkoxy groups having 1 to 6 carbon atoms), halogen atoms (e.g., fluorine atoms, chlorine atoms, bromine atoms), cyano groups, amino groups, nitro groups, acyl groups, and carboxyl groups. The above structures are preferably unsubstituted.

The alicyclic epoxy compound may also have a polymerizable functional group other than the alicyclic epoxy group. The polymerizable functional group refers to a functional group that can cause a polymerization reaction by radical polymerization or cationic polymerization, and an example of this is a (meth)acryloyl group.

Commercially available products that can be suitably used as alicyclic epoxy compounds include CELLOXIDE 2000, CELLOXIDE 2021P, CELLOXIDE 3000, CELLOXIDE 8000, CYCLOMER M100, EPOLEAD GT301, and EPOLEAD GT401 manufactured by Daicel Corporation, 4-vinylcyclohexene dioxide manufactured by Sigma-Aldrich Co., Ltd., D-limonene oxide manufactured by Nippon Terpene Chemical Co., Ltd., and Sanso Cizer E-PS manufactured by New Japan Chemical Co., Ltd. These can be used alone or in combination of two or more types.

Among them, from the viewpoints of transparency, water resistance, gas barrier properties, light resistance, etc., alicyclic epoxy compounds consisting of one or more aliphatic rings and one or more oxygen atoms directly bonded thereto are particularly preferred. As such alicyclic epoxy compounds, the following alicyclic epoxy compounds are available as EPOCALIC THI-DE, DE-102, and DE-103, respectively, manufactured by ENEOS Corporation.

Alicyclic epoxy compounds can also be produced by known synthesis methods. There is no restriction on the synthesis method, but for example, see Maruzen KK Publishing, Fourth Edition, Experimental Chemistry Lecture Series 20, Organic Synthesis II, 213-, 1992, Ed. It can be synthesized with reference to documents such as Alfred Hasfner, The Chemistry of Heterocyclic Compounds-Small Ring Heterocycles part 3 Oxiranes, John & Wiley and Sons, An Interscience Publication, New York, 1985, Yoshimura, Adhesive, Vol. 29, No. 12, 32, 1985, Yoshimura, Adhesive, Vol. 30, No. 5, 42, 1986, Yoshimura, Adhesive, Vol. 30, No. 7, 42, 1986, JP-A-11-100378, and Japanese Patent No. 2926262.

In addition to the alicyclic epoxy compound, an oxetane compound can be used in combination. There are no particular limitations on the oxetane compound as long as it has one or more oxetane structures in one molecule, and it is also possible for one molecule to have two or more oxetane structures.

Specific examples of compounds include 2-ethylhexyl oxetane (Aron Oxetane OXT-212, manufactured by Toagosei Co., Ltd.), xylylene bisoxetane (Aron Oxetane OXT-121, manufactured by Toagosei Co., Ltd.), 3-ethyl-3{[methoxy]methyl}oxetane (Aron Oxetane OXT-221, manufactured by Toagosei Co., Ltd.), (3-ethyloxetane-3-yl)methyl acrylate (OXE-10, manufactured by Osaka Organic Chemical Industry Co., Ltd.), and (3-ethyloxetane-3-yl)methyl methacrylate (OXE-30, manufactured by Osaka Organic Chemical Industry Co., Ltd.).

In addition to the alicyclic epoxy compound, a glycidyl type epoxy compound can also be used in combination.

(Photoacid generator)
Examples of photoacid generators that generate acid upon irradiation with light include onium salts, diazonium salts, quinone diazide compounds, organic halides, aromatic sulfonate compounds, bisulfone compounds, sulfonyl compounds, sulfonate compounds, sulfonium compounds, sulfamide compounds, iodonium compounds, sulfonyldiazomethane compounds, and mixtures thereof.

Specific examples of these compounds include, for example, triphenylsulfonium triflate, diphenyliodonium triflate, 2,3,4,4-tetrahydroxybenzophenone-4-naphthoquinone diazide sulfonate, 4-N-phenylamino-2-methoxyphenyldiazonium sulfate, 4-N-phenylamino-2-methoxyphenyldiazonium p-ethylphenyl sulfate, 4-N-phenylamino-2-methoxyphenyldiazonium 2-naphthyl sulfate, 4-N-phenylamino-2-methoxyphenyldiazonium phenyl sulfate, 2,5-diethoxy-4-N-4'-methoxyphenylcarbonylphenyldiazonium-3-carboxy-4-hydro 2-Methoxy-4-N-phenylphenyldiazonium-3-carboxy-4-hydroxyphenyl sulfate, diphenylsulfonylmethane, diphenylsulfonylmethane, diphenyldisulfone, α-methylbenzoin tosylate, pyrogallol trimesylate, benzoin tosylate, Midori Chemical Co., Ltd. MPI-103 (CAS. No. (87709-41-9)), Midori Chemical Co., Ltd. BDS-105 (CAS. No. (145612-66-4)), Midori Chemical Co., Ltd. NDS-103 (CAS. No. (110098-97-0)), Midori Chemical Co., Ltd. MDS-203 (CAS. No. (127855-15-5)), Midori Chemical Co., Ltd. Pyrogallol tritosylate (CAS No. (20032-64-8)), Midori Chemical Co., Ltd. DTS-102 (CAS No. (75482-18-7)), Midori Chemical Co., Ltd. DTS-103 (CAS No. (71449-78-0)), Midori Chemical Co., Ltd. MDS-103 (CAS No. (127279-74-7)), Midori Chemical Co., Ltd. MDS-105 (CAS No. (116808-67-4)), Midori Chemical Co., Ltd. MD S-205 (CAS No. (81416-37-7)), Midori Chemical Co., Ltd. BMS-105 (CAS No. (149934-68-9)), Midori Chemical Co., Ltd. TMS-105 (CAS No. (127820-38-6)), Midori Chemical Co., Ltd. NB-101 (CAS No. (20444-09-1)), Midori Chemical Co., Ltd. NB-201 (CAS No. (4450-68-4)), Midori Chemical Co., Ltd. DNB-101 (CAS No. (114719-51-6)), Midori Chemical Co., Ltd. DNB-102 (CAS. NO. (131509-55-2)), Midori Chemical Co., Ltd. DNB-103 (CAS. NO. (132898-35-2)), Midori Chemical Co., Ltd. DNB-104 (CAS. NO. (132898-36-3)), Midori Chemical Co., Ltd. DNB-105 (CAS. No. (132898-37-4)), Midori Chemical Co., Ltd. DAM-101 (CAS. No. (1886-74-4)), Midori Chemical Co., Ltd. DAM-102 (CAS. No. (28343-24-0)), Midori Chemical Co., Ltd. DAM-103 (CAS. No. (14159-45-6)), Midori Chemical Co., Ltd. DAM-104 (CAS. No. No. (130290-80-1), CAS. No. (130290-82-3)), Midori Chemical Co., Ltd. DAM-201 (CAS. No. (28322-50-1)), Midori Chemical Co., Ltd. CMS-105, Midori Chemical Co., Ltd. DAM-301 (CAS. No. (138529-81-4)), Midori Chemical Co., Ltd. SI-105 (CAS. No. No. (34694-40-7)), Midori Chemical Co., Ltd.'s NDI-105 (CAS. No. (133710-62-0)), Midori Chemical Co., Ltd.'s EPI-105 (CAS. No. (135133-12-9)), Daicel UCB's UVACURE 1591, Lamberti Co., Ltd.'s ESACURE-1064, etc. can be mentioned.

Among them, it is preferable to use an onium salt as the photoacid generator. Examples of the usable onium salt include diazonium salts, phosphonium salts, and sulfonium salts having a fluoroborate anion, a hexafluoroantimonate anion, a hexafluoroarsenate anion, a trifluoromethanesulfonate anion, a paratoluenesulfonate anion, and a paranitrotoluenesulfonate anion as a counter ion.
[Other ingredients]
The second coating material may contain a photosensitizer, a polymerization inhibitor, and the like, provided that the effects of the present invention are not impaired.

[Applications of resin-coated wavelength conversion particles]
The resin-coated wavelength conversion particles can be used as printing inks, inkjet inks, paints, processed pigments, functional dyes, dispersions serving as raw materials therefor, pigment components, and the like.

Resin-coated wavelength conversion particles have acid resistance, oxidation resistance, water resistance, etc., and are therefore suitable for use in photocurable inks,
It can be suitably used in water-based inks, water-based paints, etc.

<Photocurable ink composition>
The photocurable ink composition contains the above-mentioned resin-coated wavelength conversion particles, a radically polymerizable compound, and a photopolymerization initiator.

The content of the resin-coated wavelength conversion particles in the photocurable ink composition is preferably 5 to 75% by mass, and more preferably 20 to 75% by mass, from the viewpoint of obtaining luminescence intensity after printing while ensuring the strength and durability of the printed matter.

[Radical polymerizable compound]
The radical polymerizable compound is not particularly limited, but from the viewpoint of transparency, adhesion, etc. of the cured coating film after curing, a (meth)acrylate compound such as a monofunctional or polyfunctional (meth)acrylate monomer, or a polymer or prepolymer thereof is preferable. In this specification, the term "(meth)acrylate" is used to mean at least one of acrylate and methacrylate, or either one of them. The same applies to "(meth)acryloyl" and the like.

Examples of monofunctional (meth)acrylate monomers include acrylic acid, methacrylic acid, and derivatives thereof, and more specifically, monomers having one polymerizable unsaturated bond of (meth)acrylic acid ((meth)acryloyl group) in the molecule. Specific examples of such monomers are listed below, but the present invention is not limited thereto.

Alkyl (meth)acrylates in which the alkyl group has 1 to 30 carbon atoms, such as methyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate, n-octyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; aralkyl (meth)acrylates in which the aralkyl group has 7 to 20 carbon atoms, such as benzyl (meth)acrylate; alkoxyalkyl (meth)acrylates in which the alkoxyalkyl group has 2 to 30 carbon atoms, such as butoxyethyl (meth)acrylate; aminoalkyl (meth)acrylates in which the (monoalkyl or dialkyl)aminoalkyl group has a total of 1 to 20 carbon atoms, such as N,N-dimethylaminoethyl (meth)acrylate; diethylene glycol (meth)acrylates of polyalkylene glycol alkyl ethers having an alkylene chain carbon number of 1 to 10 and a terminal alkyl ether carbon number of 1 to 10, such as ethyl ether cholesteryl (meth)acrylate, triethylene glycol butyl ether (meth)acrylate, tetraethylene glycol monomethyl ether (meth)acrylate, hexaethylene glycol monomethyl ether (meth)acrylate, octaethylene glycol monomethyl ether (meth)acrylate, nonaethylene glycol monomethyl ether (meth)acrylate, dipropylene glycol monomethyl ether (meth)acrylate, heptapropylene glycol monomethyl ether (meth)acrylate, and tetraethylene glycol monoethyl ether (meth)acrylate; hexaethylene glycol (meth)acrylates of polyalkylene glycol aryl ethers having an alkylene chain with 1 to 30 carbon atoms and a terminal aryl ether with 6 to 20 carbon atoms, such as phenyl ether (meth)acrylates; (meth)acrylates having an alicyclic structure with a total of 4 to 30 carbon atoms, such as cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, and methylene oxide-added cyclodecatriene (meth)acrylate; fluorinated alkyl (meth)acrylates having a total of 4 to 30 carbon atoms, such as heptadecafluorodecyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, triethylene glycol mono(meth)acrylate, tetraethylene glycol mono(meth)acrylate, Examples of such (meth)acrylates include hydroxyl group-containing (meth)acrylates such as acrylate, hexaethylene glycol mono(meth)acrylate, octapropylene glycol mono(meth)acrylate, and glycerol mono- or di(meth)acrylate; glycidyl group-containing (meth)acrylates such as glycidyl (meth)acrylate; polyethylene glycol mono(meth)acrylates having an alkylene chain of 1 to 30 carbon atoms such as tetraethylene glycol mono(meth)acrylate, hexaethylene glycol mono(meth)acrylate, and octapropylene glycol mono(meth)acrylate; (meth)acrylamides such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylamide, and acryloylmorpholine.

As the monofunctional (meth)acrylate monomer, it is preferable to use an alkyl (meth)acrylate having 4 to 30 carbon atoms, and it is more preferable to use an alkyl (meth)acrylate having 12 to 22 carbon atoms from the viewpoint of improving the dispersibility of the quantum dots. The more the dispersibility of the quantum dots is improved, the more the amount of light that passes perpendicularly from the wavelength conversion layer to the emission surface increases, which is effective in improving the front brightness and front contrast. Specifically, as the monofunctional (meth)acrylate monomer, butyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, butyl (meth)acrylamide, octyl (meth)acrylamide, lauryl (meth)acrylamide, oleyl (meth)acrylamide, stearyl (meth)acrylamide, behenyl (meth)acrylamide, etc. are preferable. Among these, lauryl (meth)acrylate, oleyl (meth)acrylate, and stearyl (meth)acrylate are particularly preferred.

In addition, from the viewpoint of further reducing the oxygen permeability coefficient of the wavelength conversion layer and improving adhesion to other layers or members, it is also preferable to use a monofunctional (meth)acrylate compound having one or more groups selected from the group consisting of hydroxyl groups and aryl groups.

Hydroxy and phenyl groups are preferred as groups contained in monofunctional (meth)acrylate compounds. Specific preferred compounds include benzyl acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, 1,4-cyclohexanedimethanol monoacrylate, 2-hydroxy-3-phenoxypropyl acrylate, and 4-hydroxybutyl acrylate.

A polyfunctional (meth)acrylate monomer having two or more (meth)acryloyl groups in a molecule can be used in combination with a monomer having one polymerizable unsaturated bond ((meth)acryloyl group) of (meth)acrylic acid in a molecule.

Among the difunctional or higher (meth)acrylate monomers, preferred examples of the difunctional (meth)acrylate monomer include neopentyl glycol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tripropylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl di(meth)acrylate, etc.

In addition, among the difunctional or higher (meth)acrylate monomers, trifunctional or higher (meth)acrylate monomers include ECH (epichlorohydrin) modified glycerol tri(meth)acrylate, EO (ethylene oxide) modified glycerol tri(meth)acrylate, PO (propylene oxide) modified glycerol tri(meth)acrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, EO modified phosphoric acid triacrylate, trimethylolpropane tri(meth)acrylate, caprolactone modified trimethylolpropane tri(meth)acrylate, EO modified trimethylolpropane tri(meth)acrylate, PO modified trimethylolpropane tri(meth)acrylate, Preferred examples include acrylate, tris(acryloxyethyl)isocyanurate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate, dipentaerythritol hydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, dipentaerythritol poly(meth)acrylate, alkyl-modified dipentaerythritol tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, and pentaerythritol tetra(meth)acrylate.

[Photopolymerization initiator]
The photopolymerization initiator is not particularly limited as long as it is a compound capable of generating radicals upon irradiation with ultraviolet or visible light, and examples thereof include benzophenone-based, acetophenone-based, benzoin ether-based, and thioxanthone-based photopolymerization initiators.

Specific examples of the photopolymerization initiator include benzophenone, Michler's ketone, 4,4'-bis(diethylamino)benzophenone, xanthone, thioxanthone, isopropyl xanthone, 2,4-diethylthioxanthone, 2-ethylanthraquinone, acetophenone, 2-hydroxy-2-methylpropiophenone, 2-hydroxy-2-methyl-4'-isopropylpropiophenone, 1-hydroxycyclohexylphenyl ketone, isopropyl benzoin ether, isobutyl benzoin ether, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, camphorquinone, benzanthrone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 4-dimethylaminobenzoate. Ethyl benzoate, isoamyl 4-dimethylaminobenzoate, 4,4'-di(t-butylperoxycarbonyl)benzophenone, 3,4,4'-tri(t-butylperoxycarbonyl)benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, 3,3',4,4'-tetra(t-hexylperoxycarbonyl)benzophenone, 3,3'-di(methoxycarbonyl)-4,4 '-Di(t-butylperoxycarbonyl)benzophenone, 3,4'-di(methoxycarbonyl)-4,3'-di(t-butylperoxycarbonyl)benzophenone, 4,4'-di(methoxycarbonyl)-3,3'-di(t-butylperoxycarbonyl)benzophenone, 2-(4'-methoxystyryl)-4,6-bis(trichloromethyl)-s-triazine, 2-(3',4'-dimethoxystyryl)-4, 6-bis(trichloromethyl)-s-triazine, 2-(2',4'-dimethoxystyryl)-4,6-bis(trichloromethyl)-s-triazine, 2-(2'-methoxystyryl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4'-pentyloxystyryl)-4,6-bis(trichloromethyl)-s-triazine, 4-[p-N,N-di(ethoxycarbonylmethyl)]-2,6-di(trichloromethyl) 1,3-bis(trichloromethyl)-5-(2'-chlorophenyl)-s-triazine, 1,3-bis(trichloromethyl)-5-(4'-methoxyphenyl)-s-triazine, 2-(p-dimethylaminostyryl)benzoxazole, 2-(p-dimethylaminostyryl)benzthiazole, 2-mercaptobenzothiazole, 3,3'-carbonylbis(7-diethylaminocoumarate), phosphorus), 2-(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetrakis(4-ethoxycarbonylphenyl)-1,2'-biimidazole, 2,2'-bis(2,4-dichlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, 2,2'-bis(2,4-dibromophenyl) -4,4',5,5'-tetraphenyl-1,2'-biimidazole, 2,2'-bis(2,4,6-trichlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, 3-(2-methyl-2-dimethylaminopropionyl)carbazole, 3,6-bis(2-methyl-2-morpholinopropionyl)-9-n-dodecylcarbazole, 1-hydroxycyclohexyl phenyl ketone, bis(η ^5-2,4 -cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and 2,4,6-trimethylbenzoyldiphenylphosphine oxide can be mentioned.

The content of the photopolymerization initiator is preferably 1 to 20% by mass of the total amount of the photocurable ink composition, since this provides excellent photocurability against ultraviolet light, more preferably 2 to 15% by mass, and even more preferably 3 to 10% by mass.

[Other ingredients]
Other components may be added to the photocurable ink composition within the range that does not impair the effects of the present invention. Examples of other components include polymerization inhibitors, fillers, pigments and dyes, and various coating additives (leveling, defoaming, viscosity adjustment).

[Uses of photocurable ink composition]
Since the photocurable ink composition contains resin-coated wavelength conversion particles, it can be used in various applications that utilize the fluorescent properties, such as wavelength conversion members for displays, fluorescent printed matter, fluorescent labels, etc. In particular, it can be effectively used as an inkjet ink or offset ink for producing wavelength conversion members for partially converting blue light from a backlight into red light or green light.

In particular, when the photocurable ink composition is used for backlighting, the viscosity of the photocurable ink composition for the inkjet ink is preferably 1 to 100 mPa·s, and the viscosity of the photocurable ink composition for the offset ink is preferably 10 to 100 Pa·s.

<Method of producing resin-coated wavelength-converting particles>
The resin-coated wavelength conversion particles described above can be suitably produced by the production method of the present invention. That is, the production method of the present invention is characterized by comprising a step of spraying, under light irradiation, a dispersion containing first coated particles in which wavelength conversion particles containing quantum dots or organic phosphors are coated with a first coating material containing a light-transmitting resin, an alicyclic epoxy compound, and a photoacid generator to obtain resin-coated wavelength conversion particles in which the alicyclic epoxy compound is cured (hereinafter referred to as the "spraying step").

The resin-coated wavelength conversion particles described above can also be produced by a method different from the production method of the present invention. For example, it is possible to obtain resin-coated wavelength conversion particles in which the alicyclic epoxy compound is cured by spraying a dispersion containing the first coated particles and an alicyclic epoxy compound and contacting it with an acidic solution. The production method of the present invention is described below.

[Preparation of first coated particles]
Methods for producing first coated particles in which wavelength-converting particles containing quantum dots or organic phosphors are coated with a first coating material containing a light-transmitting resin include a method of dissolving the light-transmitting resin in a solvent and spraying a resin solution in which the wavelength-converting particles are dispersed, and drying and solidifying the solvent, and a method of finely pulverizing a mixture in which the wavelength-converting particles are dispersed in the light-transmitting resin. Any of the above-mentioned quantum dots, organic phosphors, light-transmitting resins, etc. can be used as raw materials.

Any solvent that can dissolve the translucent resin can be used as the solvent. In terms of drying speed and viscosity, the resin concentration in the resin solution in the spray method is preferably 10 to 30% by mass.

To improve the dispersibility of the quantum dots or organic phosphors, it is possible to perform surface modification or add a dispersant or coupling agent. Furthermore, when using wavelength conversion particles dispersed in a solvent, it may be preferable to replace the solvent. For example, it may be preferable to replace the solvent of quantum dots dispersed in an aqueous solvent with an organic solvent.

[Spraying process]
The amount of photoacid generator used in the spraying step is preferably 1 to 10% by mass, more preferably 1 to 5% by mass, from the viewpoint of obtaining dense resin-coated wavelength conversion particles while ensuring sufficient curability of the alicyclic epoxy compound. The dispersion in the spraying step can also contain a solvent, etc., if necessary.

The conditions for light irradiation in the spraying process need only be such that the alicyclic epoxy compound can be cured by spraying, and irradiation with ultraviolet light is preferred from the viewpoint of curing speed. It is also possible to generate an air current to increase the residence time of the sprayed particles.

The coated wavelength conversion particles obtained by spraying may be subjected to post-curing, classification, surface treatment, crushing, etc.

The present invention will be described in detail below using examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. The evaluation items in the examples were measured as follows.

(1) Measurement of Fluorescence Spectrum The evaluation pellets were hardened to prepare measurement samples having a size of Φ1 mm, and the fluorescence spectrum was measured using a fluorescence spectrophotometer (RF-5300PC, manufactured by Shimadzu Corporation).

(2) Evaluation of durability against blue light The pellets for evaluation were left for 6 months under a floodlight (irradiation distance 30 cm) using a blue LED with dominant light of 450 nm and power consumption of 20 W, and the maintenance of luminescence after the 6-month period was visually examined. For pellets whose luminescence disappeared early, the number of days it took for the luminescence to disappear was evaluated.

(3) Measurement of particle size The particles were ultrasonically dispersed in a solvent (xylene) at a concentration of 0.05% by mass, and the particle size distribution was measured using a dynamic light scattering particle size distribution measuring device (UPA-EX150, manufactured by Microtrack Bell Co., Ltd.). The average particle size was determined as the volume-based median size (median size, particle size at which the cumulative frequency is 50%, _D50 ).

Example 1 (QD/PMMA/THI-DE/TMP-A)
In a container, 5 g of acrylic resin (PMMA pellets, manufactured by Mitsubishi Chemical Corporation) was dissolved in 100 ml of acetone to prepare a resin solution. 7 ml of InP/ZnS quantum dots (semiconductor quantum dots, manufactured by GS Alliance Co., Ltd., solvent: toluene, solid content 5% by mass) were added to this resin solution, and sprayed into an inert gas (N ₂ ) heated to 70° C. to obtain first coated particles consisting of quantum dots coated with a first coating material (acrylic resin).

60% by mass of an alicyclic epoxy compound (Epocalic THI-DE (registered trademark) manufactured by ENEOS Corporation) was mixed with 5% by mass of a sulfonium salt initiator (CPI-100P manufactured by San-Apro Ltd.) as a photocationic polymerization initiator and 35% by mass of the first coated particles, and the mixture was sprayed into a space irradiated with a 1.5 kW metal halide lamp (wavelength 405 nm) to obtain resin-coated wavelength-converting particles coated with a second coating material (alicyclic epoxy resin). The particle size at this time was 30 nm to 40 nm (average particle size D ₅₀ =35 nm). The solid contents of the resin-coated wavelength-converting particles were 2% by mass for the wavelength-converting particles, 34% by mass for the first coating material, and 64% by mass for the second coating material.

Using the obtained resin-coated wavelength conversion particles, a UV ink was further prepared. That is, in a container, 75% by mass of an acrylate (Light Acrylate TMP-A: trimethylolpropane triacrylate, manufactured by Kyoei Chemical Industry Co., Ltd.), which is a radical polymerizable compound, was mixed with 5% by mass of a phosphine oxide-based photopolymerization initiator (Omnirad 819: phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, manufactured by IGM Resins B.V.), and 20% by mass of the resin-coated wavelength conversion particles was added to prepare a UV ink.

The obtained UV ink was placed in a silicone mold for producing evaluation pellets, and polymerized with light from a 1.5 kW metal halide lamp (wavelength 405 nm) to produce evaluation pellets (plate-shaped, 10 mm thick). The content of resin-coated wavelength-converting particles in the evaluation pellets (in the solid content) was 20% by mass.

The materials used above, their contents, etc. are shown in Table 1. Table 1 also shows the results of evaluating the blue light durability and measuring the fluorescence spectrum using this evaluation pellet. As a result, it was confirmed that the quantum dot luminescence was maintained at 97% or more after being left for six months. Furthermore, the peak wavelength of the luminescence of the evaluation pellet in response to excitation light (wavelength 450 nm) was 650 nm, and the half-value width was 40 nm.

Example 2 OF/PMMA/THI-DE/TMP-A
Resin-coated wavelength conversion particles were prepared under the same conditions as in Example 1, except that 4 g of organic phosphor OF (manufactured by Tokyo Chemical Industry Co., Ltd., bromopyrogallol red, average particle size 50 nm) was used instead of the quantum dots in Example 1, as shown in Table 1. Evaluation pellets were then made using UV ink to evaluate the durability to blue light. As a result, it was confirmed that the particles had the fluorescent properties shown in Table 1, and that the organic phosphor maintained 90% or more of its emission after being left for 6 months.

Example 3 (QD/PSt/THI-DE/TMP-A)
Resin-coated wavelength conversion particles were prepared under the same conditions as in Example 1, except that 5 g of polystyrene resin PS (GPSS, manufactured by Toyo Engineering Corporation) was used instead of the acrylic resin in Example 1, as shown in Table 1. Evaluation pellets were made using a UV ink and the durability to blue light was evaluated. As a result, it was confirmed that the particles had the fluorescent properties shown in Table 1, and that the quantum dots maintained 97% or more of their emission after being left for 6 months.

Example 4 (QD/PMMA/DE-103/TMP-A)
Resin-coated wavelength conversion particles were prepared under the same conditions as in Example 1, except that the same amount of alicyclic epoxy compound (Epocalic DE-103 (registered trademark), manufactured by ENEOS Corporation) was used as in Example 1, as shown in Table 1, and evaluation pellets were made using a UV ink to evaluate the durability to blue light. As a result, it was confirmed that the particles had the fluorescent properties shown in Table 1, and that the quantum dots maintained 97% or more of their light emission after being left for 6 months.

<Comparative Example 1> (QD/PMMA/TMP-A)
In Example 1, as shown in Table 1, resin-coated wavelength conversion particles were prepared under the same conditions as in Example 1, except that the second coating material was not provided, and evaluation pellets were made using a UV ink to obtain a blue color. The durability to light was evaluated. As a result, as shown in Table 1, light emission was no longer observed within 3 days.

<Comparative Example 2> (QD/THI-DE/TMP-A)
In Example 1, as shown in Table 1, resin-coated wavelength conversion particles were prepared under the same conditions as in Example 1, except that the first coating material was not provided, and evaluation pellets were made using a UV ink to obtain a blue color. The durability of the light was evaluated. As a result, as shown in Table 1, light emission was no longer observed within one day.

<Comparative Example 3> (QD/PVA/THI-DE/TMP-A)
In Example 1, as shown in Table 1, the resin-coated wavelength was measured under the same conditions as in Example 1, except that the same amount of polyvinyl alcohol resin PVA (manufactured by Kuraray Co., Ltd., Exeval) was used instead of the acrylic resin. The conversion particles were prepared, and evaluation pellets were made using UV ink to evaluate the durability to blue light. As a result, as shown in Table 1, light emission was no longer observed after 7 days.

Comparative Example 4 (QD/PMMA/GE/TMP-A)
Resin-coated wavelength-converting particles were prepared under the same conditions as in Example 1, except that the same amount of glycidyl-type epoxy compound GE (Epolite 40E: ethylene glycol diglycidyl ether, manufactured by Kyoeisha Chemical Co., Ltd.) was used instead of the alicyclic epoxy compound in Example 1, as shown in Table 1. Evaluation pellets were made from a UV ink, and durability to blue light was evaluated. As a result, as shown in Table 1, light emission could no longer be confirmed after 20 days.

<Comparative Example 5> (OF/THI-DE/TMP-A)
In Example 1, as shown in Table 1, instead of using quantum dots, 4 g of organic phosphor OF (manufactured by Tokyo Chemical Industry Co., Ltd., bromopyrogallol red, average particle size 50 nm) was used, and the first coating material was Resin-coated wavelength-converting particles were prepared under the same conditions as in Example 1, except that no resin was provided, and evaluation pellets were made using a UV ink to evaluate the durability to blue light. Within a day, the luminescence was no longer visible.

Claims (6)

wavelength-converting particles including quantum dots or organic phosphors;
a first coating material that coats the wavelength-converting particles and contains a light-transmitting resin;
a second coating material that coats the first coating material and contains a cured product of an alicyclic epoxy compound;
4. A resin-coated wavelength-converting particle comprising: The resin-coated wavelength conversion particle according to claim 1, wherein the alicyclic epoxy compound is composed of one or more aliphatic rings and one or more oxygen atoms directly bonded thereto. The resin-coated wavelength conversion particle according to claim 1 or 2, wherein the light-transmitting resin is a (meth)acrylic resin, a polycarbonate resin, a polystyrene resin, or a polyolefin resin. The wavelength conversion particle according to any one of claims 1 to 3, wherein the wavelength conversion particle has an emission wavelength of 500 to 580 nm or an emission wavelength of 600 to 680 nm. A resin-coated wavelength conversion particle according to any one of claims 1 to 4,
A radical polymerizable compound,
A photopolymerization initiator;
A photocurable ink composition comprising: A method for producing resin-coated wavelength-converting particles, comprising the steps of: spraying, under light irradiation, a dispersion containing first coated particles in which wavelength-converting particles containing quantum dots or organic phosphors are coated with a first coating material containing a translucent resin, an alicyclic epoxy compound, and a photoacid generator, to obtain resin-coated wavelength-converting particles in which the alicyclic epoxy compound is cured.