Inkjet ink, method for producing pigment dispersion, method for producing inkjet ink, method for forming cured product and cured product

Abstract

The present invention relates to an inkjet ink, a method for producing a pigment dispersion, a method for producing an inkjet ink, a method for forming a cured product, and a cured product. The inkjet ink contains a polymerizable compound, a light-storing pigment, and a dispersant having an acidic functional group, and is cured by irradiation with an active ray.

Description

Technical Field

[0001] The present invention relates to an inkjet ink, a method for producing a pigment dispersion, a method for producing an inkjet ink, a method for forming a cured product, and the cured product. Background Art

[0002] Phosphorescent pigments are known that absorb light of a predetermined wavelength, store the light's energy, and then release light of a wavelength different from that of the absorbed light for a long period of time after the absorption of the light ceases (e.g., Japanese Patent Application Publication No. 2019-210337). Also known are methods for producing a photoluminescent cured product by applying an inkjet head containing such a phosphorescent pigment to a substrate (e.g., Japanese Patent Application Publication No. 2014-28484).

[0003] If inkjet inks containing light-storage pigments are used, it is expected that highly detailed patterned cured products can be produced. However, in order to fully increase the brightness of light-storage cured products, the thickness needs to be increased. However, according to the present inventors' knowledge, once a certain film thickness is reached, the brightness of light-storage cured products saturates and cannot be further increased. Therefore, there is a need to develop methods for increasing the brightness of light-storage cured products.

[0004] Furthermore, in the case of ink containing a light-storing pigment, the light-storing pigment easily clogs the nozzle when the ink is discharged from the inkjet head, and nozzle defects are easily generated. Summary of the Invention

[0005] The present invention relates to an inkjet ink containing a light-storing pigment. The present invention provides an inkjet ink that can produce a cured product with sufficiently high brightness and is less susceptible to nozzle defects. Furthermore, the present invention provides a method for producing a pigment dispersion and a method for producing the inkjet ink. Furthermore, the present invention provides a method for forming a cured product using the inkjet ink and a cured product formed using the method.

[0006] To achieve at least one of the above-mentioned objects, an inkjet ink reflecting one aspect of the present invention includes a polymerizable compound, a light-storing pigment, and a dispersant having an acidic functional group, and is cured by irradiation with active rays.

[0007] Advantages and features provided by one or more embodiments of the present invention will be more fully understood from the detailed description given below, which is given by way of illustration only and is not intended as a definition of the limitations of the invention: DETAILED DESCRIPTION

[0008] Hereinafter, one or more embodiments of the present invention will be described. However, the scope of the present invention is not limited to the disclosed embodiments.

[0009] 1. Inkjet ink

[0010] One embodiment of the present invention relates to an inkjet ink (hereinafter referred to simply as "ink") containing a polymerizable compound, a light-storing pigment, and a dispersant. The ink is an active radiation-curable ink that cures upon irradiation with active radiation. Each component is described below.

[0011] 1-1. Luminescent pigments

[0012] Phosphorescent pigments absorb light of a specific wavelength and store the energy. Even after absorbing light, they continue to release light of a different wavelength from the light that absorbed the stored energy for a long period of time. Phosphorescent pigments are pigments that emit phosphorescence. Ink can contain a single type of phosphorescent pigment or two or more.

[0013] There are no particular limitations on the luminescent pigment as long as it has the above-mentioned characteristics. Examples of the luminescent pigment include those obtained by activating a mother crystal of a metal compound.

[0014] Examples of the aforementioned mother crystals include metal sulfides such as zinc sulfide, calcium sulfide, germanium sulfide, strontium sulfide, and yttrium sulfide. Examples of the aforementioned mother crystals also include metal oxides such as calcium oxide, strontium oxide, barium oxide, aluminum oxide, and cerium oxide. Examples of the aforementioned mother crystals also include aluminates such as calcium aluminate, strontium aluminate, and barium aluminate.

[0015] Examples of the activator for activating the mother crystal include europium, terbium, yttrium, zirconium, dysprosium, and barium, among which europium and dysprosium are preferred.

[0016] Among these, from the perspective of improving the dispersibility by the acidic dispersant described below, the phosphorescent pigment is preferably a phosphor containing an aluminate. Furthermore, from the perspective of improving the dispersibility by the acidic dispersant described below, the phosphorescent pigment is preferably a phosphor containing calcium aluminate, strontium aluminate, or barium aluminate. Furthermore, from the perspective of improving the dispersibility by the acidic dispersant described below, the phosphorescent pigment is preferably SrAl2O4 or Sr4Al2O4 containing europium (Eu) and dysprosium (Dy) as an activator. 14 O 25 .

[0017] The peak wavelength of the excitation spectrum of the luminescent pigment is preferably 300 nm to 400 nm. If the peak wavelength of the excitation spectrum of the luminescent pigment is within this range, the luminescent pigment can be sufficiently excited by sunlight, making the cured product easily suitable for outdoor use.

[0018] The peak wavelength of the light emission spectrum of the light-storing pigment can be set to, for example, 400 nm to 700 nm, and is preferably 450 nm to 600 nm from the viewpoint of further improving the visibility of the cured product.

[0019] The median diameter of the phosphorescent pigment in the ink is not particularly limited and can be between 0.2 μm and 20.0 μm. The median diameter of the phosphorescent pigment is preferably between 1.0 μm and 10.0 μm, more preferably between 1.0 μm and 5.0 μm, and even more preferably between 1.5 μm and 3 μm. A larger median diameter improves the brightness of the cured product. A smaller median diameter facilitates dispersion of the phosphorescent pigment, improving discharge performance from the inkjet head.

[0020] The median diameter of the phosphorescent pigment can be a particle diameter (D 50 ).

[0021] The particle size (D) at which the cumulative value of the volume-based particle size distribution of the phosphorescent pigment in the ink becomes 90% 90 ), it can be set to 1.0 μm or more and 20 μm or less, preferably 1.5 μm or more and 10 μm or less, and more preferably 2.0 μm or more and 8 μm or less. 90 The smaller the diameter, the easier it is to disperse the phosphorescent pigment, and the easier it is to improve the discharge performance from the inkjet head.

[0022] In addition, the luminescent pigment is preferably D 50 / D 90 It is 0.2 or more and 0.8 or less, and more preferably 0.3 or more and 0.6 or less. 50 / D 90 As the particle size becomes smaller, the particle size distribution can be broadened, and a cured product in which the luminescent pigment is densely deposited can be formed, thereby improving the weather resistance of the cured product.

[0023] In addition, the D of the luminescent pigment 50 and D 90 The value can be measured using a particle size measuring apparatus, for example, LUMiSizer manufactured by LUM Japan Co., Ltd.

[0024] The content of the phosphorescent pigment can be adjusted according to its intended use. For example, the content of the phosphorescent pigment can be set to 5% to 70% by mass, preferably 5% to 40% by mass, and more preferably 10% to 30% by mass, relative to the total mass of the ink. A higher content of phosphorescent pigment increases the brightness of the cured product. A lower content of phosphorescent pigment improves the ink's discharge properties.

[0025] 1-2. Dispersant

[0026] The dispersant is used to disperse the phosphorescent pigment. The ink may contain a single dispersant or two or more. The dispersant may be a polymer or a low molecular weight dispersant, but polymers are preferred.

[0027] The dispersant includes an acidic dispersant having an acidic functional group as a functional group that adsorbs to the phosphorescent pigment. The ink may contain only one acidic dispersant or two or more acidic dispersants. The acidic dispersant may be a polymeric dispersant or a low molecular weight dispersant, but is preferably a polymeric dispersant.

[0028] Actinic radiation-curable inks, which cure by irradiation with actinic radiation, can form highly durable cured products, enabling the production of highly durable products. Furthermore, luminescent pigments are susceptible to degradation by water. Therefore, actinic radiation-curable inks, which do not require water, are less susceptible to degradation of the luminescent pigment during storage than water-based inks, and the brightness of the cured product is less likely to decrease even with long-term storage.

[0029] On the other hand, the cured product formed by curing active radiation-curable ink not only maintains the luminescent layer of the luminescent pigment, but also serves as a light-shielding layer. That is, the luminescent pigment particles in the cured product sometimes block the light emitted by other luminescent pigments. Furthermore, as the thickness of the cured product increases, the likelihood that light emitted by a particular luminescent pigment will be blocked by other luminescent pigments before being released outside the cured product increases. Therefore, it is believed that if the film thickness of the cured product is increased to a certain extent, the brightness will saturate, and even if the film thickness is increased, the brightness will be difficult to increase.

[0030] However, as for the light-storage pigment, it is formed by a compound having alkalinity such as metal sulfide, metal oxide and aluminate. Therefore, in the present embodiment, an acidic dispersant is used as a dispersant for dispersing the light-storage pigment. It is believed that the acidic dispersant has good adsorption properties for the light-storage pigment, thereby improving the dispersibility of the light-storage pigment. Moreover, it is believed that as a result of the improved dispersibility of the light-storage pigment, even if the light-storage pigment is sparsely dispersed in the solidified material, it becomes difficult for the light generated by other light-storage pigments to be blocked. In addition, it is believed that: by improving the dispersibility of the light-storage pigment, the light-storage pigment is not easy to clog the nozzle of the inkjet head, and the discharge property of the ink is also improved. In addition, it is believed that: by improving the dispersibility of the light-storage pigment, it is difficult for the light-storage pigment to settle in the ink, and the fluidity and circulation of the ink in the inkjet head are also improved.

[0031] From the perspective of improving the dispersibility of the phosphorescent pigment and thereby more effectively enhancing the brightness of the cured product and the discharge properties of the ink, the acidic dispersant preferably has an acid value of 30 mgKOH / g to 300 mgKOH / g. Furthermore, the acid value of the acidic dispersant is more preferably 30 mgKOH / g to 200 mgKOH / g, and even more preferably 50 mgKOH / g to 150 mgKOH / g.

[0032] The acid value of an acidic dispersant can be measured using an automatic titrator (manufactured by Hiranuma Sangyo, COM-555). Add 80 mL of acetone and 10 mL of water to 0.5-1 g of a sample solution and stir to uniformly dissolve the solution. Titrate this sample solution with a 0.1 mol / L aqueous KOH solution to determine the acid value (mgKOH / g) of the sample solution. The acid value per unit solid content of the sample is then calculated from the acid value of the sample solution and the solid content concentration of the sample solution.

[0033] The acidic functional group of the acidic dispersant is not particularly limited. Examples of acidic functional groups include phosphate groups, carboxyl groups, and sulfonic acid groups. Of these, phosphate groups and carboxyl groups are preferred, and carboxyl groups are more preferred, from the perspective of improving the dispersibility of the luminescent pigment and thereby more effectively enhancing the brightness of the cured product and the discharge properties of the ink.

[0034] The type of functional group possessed by the acidic dispersant can be determined by a conventional method.

[0035] Examples of acidic dispersants include Marialim SC0505K, SC1015F, and AKM-0531 manufactured by NOF Corporation (“Marialim” is a registered trademark of the company). Other examples of acidic dispersants include Efka FA4620 manufactured by BASF (“Efka” is a registered trademark of the company). Other examples of acidic dispersants include Solsperse S41000 and S79000 manufactured by Lubrizol (“Solsperse” is a registered trademark of the company).

[0036] The content of the acidic dispersant is preferably 0.01% by mass to 20% by mass, more preferably 1% by mass to 10% by mass, and even more preferably 1% by mass to 5% by mass, relative to the total mass of the phosphorescent pigment.

[0037] 1-3. Polymerizable Compound and Photopolymerization Initiator

[0038] 1-3-1. Polymerizable compounds

[0039] The polymerizable compound may be a radical polymerizable compound or a cation polymerizable compound. In addition, the polymerizable compound may be used in combination with a radical polymerizable compound and a cation polymerizable compound.

[0040] The radical polymerizable compound is a compound (a monomer, an oligomer, a polymer, or a mixture thereof) having an ethylenically unsaturated bond that can be radically polymerized.

[0041] Examples of compounds having a radically polymerizable ethylenically unsaturated bond include unsaturated carboxylic acids and salts thereof, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid carbamate compounds, unsaturated carboxylic acid amide compounds and anhydrides thereof, acrylonitrile, styrene, unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated carbamates. Examples of unsaturated carboxylic acids include (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid.

[0042] Among them, the radical polymerizable compound is preferably an unsaturated carboxylic acid ester compound, more preferably a (meth)acrylate. (Meth)acrylate is not only a monomer as described below but also an oligomer, a mixture of a monomer and an oligomer, a modified product, an oligomer having a polymerizable functional group, and the like.

[0043] Examples of the monofunctional (meth)acrylate include isoamyl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomyristyl (meth)acrylate, isostearyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiglycol (meth)acrylate, methoxydiglycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and methoxypropylene glycol (meth)acrylate. Ester, o-phenylphenoxyethyl (meth)acrylate, m-phenoxybenzyl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, ethoxylated phenoxy (meth)acrylate, alkoxylated phenol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-hydroxy-o-phenylphenol propyl (meth)acrylate, 2-(meth)acryloyloxyethylsuccinic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid and tert-butylcyclohexyl (meth)acrylate, etc.

[0044] Examples of the multifunctional (meth)acrylate include triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol diacrylate, dihydroxymethyl tricyclodecane di(meth)acrylate, bisphenol A di(meth)acrylate, hydroxy neopentyl glycol di(meth)acrylate, bisphenol fluorene diacrylate (A-BPE), and the like. F), bifunctional (meth)acrylates including bisphenol A 10EO-modified diacrylate, bisphenol A diacrylate, bisphenol A PO-modified diacrylate, bisphenol A EO-modified diacrylate, polytetramethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate, and tripropylene glycol diacrylate; and trifunctional or higher-functional (meth)acrylates including trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, di(trimethylolpropane) tetra(meth)acrylate, glyceryl propoxy tri(meth)acrylate, and pentaerythritol ethoxy tetra(meth)acrylate.

[0045] The (meth)acrylate may be a modified product. Examples of the modified (meth)acrylate include ethylene oxide-modified (meth)acrylates such as ethylene oxide-modified trimethylolpropane tri(meth)acrylate and ethylene oxide-modified pentaerythritol tetraacrylate, caprolactone-modified (meth)acrylates such as caprolactone-modified trimethylolpropane tri(meth)acrylate, and caprolactam-modified (meth)acrylates such as caprolactam-modified dipentaerythritol hexa(meth)acrylate.

[0046] The (meth)acrylate may be a polymerizable oligomer. Examples of the (meth)acrylate as a polymerizable oligomer include epoxy (meth)acrylate oligomers, aliphatic urethane (meth)acrylate oligomers, aromatic urethane (meth)acrylate oligomers, polyester (meth)acrylate oligomers, and linear (meth)acrylic oligomers.

[0047] Examples of the cationically polymerizable compound include epoxy compounds, vinyl ether compounds, and oxetane compounds.

[0048] Examples of the epoxy compounds include 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene monoepoxide, ε-caprolactone-modified 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, 1-methyl-4-(2-methyloxiranyl)-7-oxabicyclo[4,1,0]heptane, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanone-meta-dioxane and bis(2,3-epoxycyclopentyl)ether, and alicyclic epoxy resins including 1,4-butanediol dihydrate. aliphatic epoxy compounds such as glycerol ether, diglycidyl ether of 1,6-hexanediol, triglycidyl ether of glycerol, triglycidyl ether of trimethylolpropane, diglycidyl ether of polyethylene glycol, diglycidyl ether of propylene glycol, polyglycidyl ether of polyether polyols obtained by adding one or more alkylene oxides (such as ethylene oxide and propylene oxide) to aliphatic polyols such as ethylene glycol, propylene glycol, and glycerol; and aromatic epoxy compounds such as di- or polyglycidyl ethers of bisphenol A or its alkylene oxide adducts, di- or polyglycidyl ethers of hydrogenated bisphenol A or its alkylene oxide adducts, and novolac-type epoxy resins.

[0049] Examples of the above-mentioned vinyl ether compounds include monovinyl ether compounds such as ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether; and di- or trivinyl ether compounds such as ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, and trimethylolpropane trivinyl ether.

[0050] Examples of the above-mentioned oxetane compounds include 3-hydroxymethyl-3-methyloxetane, 3-hydroxymethyl-3-ethyloxetane, 3-hydroxymethyl-3-propyloxetane, 3-hydroxymethyl-3-n-butyloxetane, 3-hydroxymethyl-3-phenyloxetane, 3-hydroxymethyl-3-benzyloxetane, 3-hydroxyethyl-3-methyloxetane, 3-hydroxyethyl-3-ethyloxetane, 3-hydroxyethyl-3-propyloxetane, 3- Hydroxyethyl-3-phenyloxetane, 3-hydroxypropyl-3-methyloxetane, 3-hydroxypropyl-3-ethyloxetane, 3-hydroxypropyl-3-propyloxetane, 3-hydroxypropyl-3-phenyloxetane, 3-hydroxybutyl-3-methyloxetane, 1,4-bis{[(3-ethyl-3-oxetanyl)methoxy]methyl}benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane and di[1-ethyl(3-oxetanyl)]methyl ether, etc.

[0051] Polymerizable compounds preferably contain monofunctional compounds with aromatic rings within the molecule. Polymerizable compounds with aromatic rings within the molecule can improve the storage stability of the ink and reduce nozzle clogging. Furthermore, polymerizable compounds with aromatic rings within the molecule can improve the dispersibility of the phosphorescent pigment within the ink, increasing the brightness of the cured product. Furthermore, monofunctional compounds tend to reduce the viscosity of the ink.

[0052] The content of the monofunctional polymerizable compound having an aromatic ring is preferably 20% by mass or more and 80% by mass or less, and more preferably 25% by mass or more and 60% by mass or less, based on the total mass of the ink.

[0053] Examples of monofunctional polymerizable compounds having an aromatic ring include phenol 4EO-modified acrylate, 2-phenoxyethyl acrylate, m-phenoxybenzyl acrylate, EO-modified o-phenylphenol acrylate, benzyl acrylate, cumylphenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, and 2-hydroxy-o-phenylphenol propyl acrylate.

[0054] The content of the polymerizable compound is preferably 50% by mass or more and 97% by mass or less, and more preferably 60% by mass or more and 95% by mass or less, based on the total mass of the polymerizable ink.

[0055] 1-3-2. Photopolymerization initiator

[0056] The photopolymerization initiator can function as a free radical initiator when the polymerizable ink contains a free radical polymerizable compound, or as a cationic initiator (photoacid generator) when the polymerizable ink contains a cationically polymerizable compound. When polymerization is initiated by electron beam irradiation, the polymerizable ink may not contain a photopolymerization initiator.

[0057] Examples of radical polymerization initiators include hydrogen abstraction type photopolymerization initiators and intramolecular cleavage type photopolymerization initiators. Hydrogen abstraction type photopolymerization initiators include intramolecular hydrogen abstraction type photopolymerization initiators and intermolecular hydrogen abstraction type photopolymerization initiators.

[0058] Intramolecular hydrogen abstraction type photopolymerization initiators are photopolymerization initiators that are excited by irradiation with active energy rays and undergo a hydrogen abstraction reaction within the molecule to generate free radicals. Examples of intramolecular hydrogen abstraction type photopolymerization initiators include methyl benzoylformate-based photopolymerization initiators such as methyl phenylglyoxylate, and hydroxyphenyl-based photopolymerization initiators such as a mixture of 2-[2-oxo-2-phenylacetoxy-ethoxy]ethyl hydroxyphenylacetate and 2-[2-hydroxy-ethoxy]ethyl hydroxyphenylacetate. Among these, compounds having a glyoxylic acid structure such as methyl benzoylformate-based photopolymerization initiators are preferred because hydrogen is less likely to be removed from the molecular chain of the polymerizable compound during polymerization.

[0059] Examples of commercially available products of the intramolecular hydrogen abstraction type photopolymerization initiator include Omnirad MBF and Omnirad 754 (both manufactured by IGM Resins Co., Ltd., and “Omnirad” is a registered trademark of the company).

[0060] Intermolecular hydrogen abstraction type photopolymerization initiators are photopolymerization initiators that are excited by irradiation with active energy rays such as ultraviolet rays and abstract hydrogen from another molecule to generate free radicals. Examples of intermolecular hydrogen abstraction type photopolymerization initiators include benzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acryloyl benzophenone (acryloyl benzophenone), 3,3',4,4'-tetrakis(tert-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone; and thioxanthone-based initiators such as 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone.

[0061] Examples of commercially available intermolecular hydrogen abstraction-type photopolymerization initiators include Omnirad 500 (manufactured by IGM Resins) and Speedcure ITX (manufactured by Sartomer, “Speedcure” is a registered trademark of Alkema France).

[0062] Examples of intramolecular cleavage-type photopolymerization initiators include acetophenone-based initiators such as 2-hydroxy-2-methyl-1-phenylpropane-1-one, benzyl dimethyl ketal, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino(4-methylthiophenyl)propane-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone. ; Benzoin-based initiators such as benzoin, benzoin methyl ether, and benzoin isopropyl ether; 2,4,6-trimethylbenzoyldiphenylphosphine oxide (2,4,6-trimethylbenzoyldiphenylphosphine oxide (2,4,6-trimethylbenzoyldiphenylphosphine oxide)ンオキシド), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (ビス(2,4,6- Acyl phosphine oxide-based initiators such as Torymanthyl fluorocarbons).

[0063] Examples of commercially available intramolecular cleavage-type photopolymerization initiators include Omnirad 127, Omnirad 184, Omnirad 651, Omnirad 2959, Omnirad 819, and Esacure One.

[0064] The content of the photopolymerization initiator is preferably 3% by mass or more and 20% by mass or less relative to the total mass of the polymerizable compound. It is more preferably 3% by mass or more and 15% by mass or less, even more preferably 3% by mass or more and 10% by mass or less, and particularly preferably 5% by mass or more and 10% by mass or less. By setting the content to 3% by mass or more, the curability and adhesion of the polymerizable ink can be further improved.

[0065] 1-4. Other ingredients

[0066] The ink may further contain other ingredients such as organic pigments, dyes, surfactants, fluorescent brighteners, gelling agents and polymerization inhibitors.

[0067] Examples of organic pigments include red pigments, yellow pigments, cyan pigments, and white pigments used in inks for image formation. These pigments can be known pigments. Examples of dyes include red dyes, yellow dyes, cyan dyes, and the like used in inks for image formation. These dyes can be known dyes.

[0068] Examples of surfactants include anionic surfactants such as dialkyl sulfosuccinates, alkylnaphthalene sulfonates, and fatty acid salts. Examples of surfactants also include nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene-polyoxypropylene block copolymers. Examples of surfactants also include cationic surfactants such as alkylamine salts and quaternary ammonium salts, as well as silicone-based and fluorine-based surfactants.

[0069] The content of the surfactant is not particularly limited, and can be, for example, 0.001% by mass or more and less than 1.0% by mass relative to the total mass of the ink.

[0070] A gelling agent is a compound that causes the ink to be in a gel state at room temperature (25°C) and to become a sol state when heated (e.g., 80°C). For example, the gelling agent is preferably a compound that dissolves in the liquid components (polymerizable compounds and organic solvents, etc.) contained in the ink at a temperature higher than the ink's gelation temperature and crystallizes at a temperature below the ink's gelation temperature. The so-called gelation temperature refers to the temperature at which the ink, which has been solified or liquefied by heating, undergoes a phase transition from sol to gel, and the viscosity of the ink changes dramatically when the ink is cooled. Specifically, the gelation temperature of the ink can be determined by measuring the viscosity of the solified or liquefied ink using a rheometer (e.g., MCR300 manufactured by Anton Paar) while cooling it.

[0071] Examples of gelling agents include ketone waxes, ester waxes, petroleum waxes, plant waxes, animal waxes, mineral waxes, hardened castor oil, modified waxes, higher fatty acids, higher alcohols, hydroxystearic acid, fatty acid amides including N-substituted fatty acid amides and special fatty acid amides, higher amines, esters of sucrose fatty acids, synthetic waxes, dibenzylidene sorbitol, dimer acids, and dimer diols.

[0072] The content of the gelling agent is preferably 1.0% by mass to 10.0% by mass, more preferably 2.0% by mass to 7.5% by mass, and even more preferably 2.0% by mass to 3.5% by mass, relative to the total mass of the ink.

[0073] Examples of polymerization inhibitors include N-oxyl polymerization inhibitors (N-oxysil polymerization inhibitors), phenolic polymerization inhibitors, quinone polymerization inhibitors, amine polymerization inhibitors, and copper dithiocarbamate polymerization inhibitors. The ink may contain only one polymerization inhibitor or a combination of two or more.

[0074] Examples of N-oxyl-based polymerization inhibitors include 4-hydroxy-2,2,6,6-tetramethylpiperidin-N-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidin-N-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidin-N-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidin-N-oxyl, and 4-acetoxy-2,2,6,6-tetramethylpiperidin-N-oxyl. Examples of commercially available N-oxyl-based polymerization inhibitors include Irgastab UV10 (manufactured by BASF ("Irgastab" is a registered trademark of the company)).

[0075] Examples of phenolic polymerization inhibitors include 2,6-di-tert-butylphenol, 2,4-di-tert-butylphenol, 2-tert-butyl-4,6-dimethylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-p-cresol (butylated hydroxytoluene: BHT), 4-methoxyphenol, and 2-methoxy-4-methylphenol.

[0076] Examples of the quinone-based polymerization inhibitor include hydroquinone, methoxyhydroquinone, benzoquinone, 1,4-naphthoquinone, and p-tert-butylcatechol.

[0077] Examples of the amine-based polymerization inhibitor include alkylated diphenylamine, N,N′-diphenyl-p-phenylenediamine, and phenothiazine.

[0078] Examples of the copper dithiocarbamate-based polymerization inhibitor include copper dimethyldithiocarbamate, copper diethyldithiocarbamate, and copper dibutyldithiocarbamate.

[0079] The content of the polymerization inhibitor is not particularly limited, and can be, for example, 0.01% by mass or more and 0.5% by mass or less relative to the total mass of the ink.

[0080] 1-5. Physical Properties of Ink

[0081] The ink is preferably capable of forming a volume resistivity of 10 11 The surface resistivity of the cured film can be measured using HiResta UX (manufactured by Nitto Seiko Analytic Corporation, MCP-HT800).

[0082] 1-6. Ink Preparation Method

[0083] The ink can be prepared by mixing the aforementioned components. In this case, a luminescent pigment, an acidic dispersant, and a small amount of a polymerizable compound can be kneaded to prepare a pigment dispersion. The remaining polymerizable compound can then be added to the resulting pigment dispersion. To improve the solubility of the dispersant, it is preferable to heat the luminescent pigment and acidic dispersant while mixing to prepare the dispersion.

[0084] The pigment dispersion can be prepared using a homogenizer, a pestle, a wet micronizer, a bead mill, or the like.

[0085] Among these, a crushing machine is preferred. The crushing machine can reduce the particle size of the light-storage pigment and disperse it at the same time. Thus, the crushing machine can reduce the proportion of coarse particles in the pigment dispersion and the ink, and make the acidic dispersant well adsorbed on the light-storage pigment and significantly improve the brightness of the solidified material and the discharge property of the ink. In addition, with regard to the crushing machine, unlike the bead mill, even if the light-storage pigment is dispersed, the damage to the device caused by the light-storage pigment is not easy to occur. In addition, with regard to the crushing machine, unlike the jet mill, the light-storage pigment can be dispersed together with the polymerizable compound.

[0086] It should be noted that the preparation of a pigment dispersion using a crusher can be performed in a single stage or in multiple stages. When performed in multiple stages, a first-stage dispersion treatment can be performed on the luminescent pigment, an acidic dispersant, and a small amount of a polymerizable compound, followed by a second-stage dispersion treatment by adding the polymerizable compound. Alternatively, to facilitate dispersion of the luminescent pigment, a first-stage dispersion treatment (dry pulverization) can be performed on only the luminescent pigment, followed by one or more second-stage dispersion treatments by adding the acidic dispersant and the polymerizable compound.

[0087] In preparation of ink by mixing with other components, a homogenizer, a ceramic pestle, a wet atomizing device, or the like can be used.

[0088] 2. Method for forming a cured product

[0089] The above-mentioned ink can be applied to a substrate by an inkjet method, cured, and used to form a cured product.

[0090] The ink can be applied to the substrate by discharging the ink from the inkjet head and dropping the ink onto the substrate.

[0091] The inkjet head can be either a drop-on-demand or continuous inkjet head. Drop-on-demand inkjet heads can employ electro-mechanical conversion methods, such as single-chamber, dual-chamber, bend-type, piston, shared-mode, and shared-wall types. Drop-on-demand inkjet heads can employ electro-thermal conversion methods, such as thermal inkjet and Bubble Jet ("Bubble Jet" is a registered trademark of Canon Inc.).

[0092] These inkjet heads or image forming apparatuses having the inkjet heads may have a configuration for circulating ink inside or outside the inkjet heads.

[0093] Furthermore, in printers for forming a cured product, a mechanism for stirring the ink for redispersing the luminescent pigment is provided inside the inkjet head or in the flow path between the main tank and the inkjet head.

[0094] The type of substrate is not particularly limited, and can be, for example, paper, resin film, ABS resin plate, acrylic resin plate, aluminum plate, glass plate, polycarbonate plate, cloth, etc. It should be noted that the shape of the substrate is not particularly limited, and can be a plate, film, sheet, or various three-dimensional shapes. Furthermore, the composition can be imparted to the space formed within the substrate by various methods.

[0095] As for the curing of the ink, it can be carried out by polymerizing and cross-linking the polymerizable compound through irradiation with active energy rays. Examples of active energy rays include electron beams, ultraviolet rays, α rays, γ rays, and X-rays. Among these, ultraviolet rays and electron beams are preferred. The above-mentioned ultraviolet rays are preferably light with a peak wavelength of more than 360nm and less than 410nm. In addition, the above-mentioned ultraviolet rays are preferably irradiated by an LED light source. As for LEDs, compared with previous light sources (such as metal halide lamps, etc.), since they radiate less heat, if LEDs are used, the ink is difficult to dissolve when irradiated with active energy rays, and uneven gloss is less likely to occur.

[0096] When ultraviolet rays are used as active energy rays, the amount of light per irradiation is preferably 500 mJ / cm 2 Above 4000mJ / cm 2 Below. If 500mJ / cm 2 If the curing property of the polymerizable compound is 4000 mJ / cm 2 Below, discoloration of the cured product can be suppressed.

[0097] When forming a thick cured product, application of ink and curing may be repeated.

[0098] After the cured product is produced in this manner, a protective film may be formed to cover the cured product using a varnish, a laminate film, an ink, or the like, or the cured product may be processed into a desired shape.

[0099] The preferred thickness of the solidified material formed in this way is more than 0.3mm and less than 1.5mm. By increasing the thickness of the solidified material, the brightness of the solidified material can be improved. In the present embodiment, owing to using an acidic dispersant, even if the thickness is increased, the brightness is also difficult to saturate, and the larger solidified material of thickness can be formed and the brightness can be further improved.

[0100] Example

[0101] Hereinafter, the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited to the description of the Examples.

[0102] 1. Material Preparation

[0103] Using the following materials, an inkjet ink was prepared.

[0104] 1-1. Polymerizable compounds

[0105] Monomer 1: Dipropylene glycol diacrylate

[0106] Monomer 2: Phenol 4EO modified acrylate

[0107] 1-2. Photopolymerization initiator

[0108] Initiator 1: Omnirad MBF manufactured by IGM RESINS BV

[0109] Initiator 2: Omnirad 819 (intramolecular cleavage type) manufactured by IGM Resins BV

[0110] 1-3. Luminescent Pigments

[0111] Luminous pigment 1: Luminova G-300FF, manufactured by Nemoto Chemical Co., Ltd. ("Luminova" is a registered trademark of the company)

[0112] Luminous pigment 2: Nemoto Chemical Co., Ltd., Luminova BGL-300FF

[0113] Luminous Pigment 3: Nemoto Chemical Co., Ltd., Luminova G-300F

[0114] 1-4. Dispersant

[0115] Dispersant 1: Marialim SC0505K manufactured by NOF Corporation (“Marialim” is a registered trademark of the company)

[0116] Dispersant 2: Efka FA4620 manufactured by BASF ("Efka" is a registered trademark of the company)

[0117] Dispersant 3: Solsperse S41000 manufactured by Lubrizol (“Solsperse” is a registered trademark of the company)

[0118] Dispersant 4: Solsperse S79000 manufactured by Lubrizol

[0119] Dispersant 5: Marialim SC1015F manufactured by NOF Corporation

[0120] Dispersant 6: Marialim AKM-0531 manufactured by NOF Corporation

[0121] Dispersant 7: Efka PX4701 manufactured by BASF

[0122] Dispersant 8: Efka PX4703 manufactured by BASF

[0123] 1-5. Other ingredients

[0124] Polymerization inhibitor: Irgastab UV-10 manufactured by BASF (“Irgastab” is a registered trademark of the company)

[0125] 2. Ink Preparation

[0126] 2-1. Preparation of Inks 1 to 12, 18, and 19

[0127] 2-1-1. Preparation of pigment dispersion

[0128] 50 parts by mass of phosphorescent pigment 1, 2.5 parts by mass of dispersant 1, and 47.5 parts by mass of monomer 1 were placed in a polypropylene container along with 50 parts by mass of zirconium oxide beads with an average particle size of 0.3 mm. The mixture was then dispersed for 30 minutes using a paint shaker, and the zirconium oxide beads were removed to prepare a pigment dispersion.

[0129] 2-1-2. Preparation of ink

[0130] 50.9 parts by mass of Monomer 1, 9 parts by mass of Initiator 1, and 0.1 parts by mass of a polymerization inhibitor were thoroughly mixed on a triple roll. To the resulting mixture was added 40 parts by mass of the aforementioned pigment dispersion, and the mixture was further mixed on a triple roll. The mixture was then filtered through a 30 μm polypropylene pleated filter (manufactured by Rokitechno Co., Ltd.) to obtain Ink 1.

[0131] Inks 2 to 12, 18, and 19 were obtained in the same manner except that the types and amounts (ratios) of the components were changed so that the compositions of the inks became the compositions shown in Tables 1 and 2.

[0132] 2-2. Preparation of Ink 13 to Ink 16

[0133] 2-2-1. Preparation of pigment dispersion

[0134] 50 parts by mass of phosphorescent pigment 1, 2.5 parts by mass of dispersant, and 11.5 parts by mass of monomer 1 were placed in a tabletop crusher (D18S, manufactured by Ishikawa Kojo Co., Ltd.) and crushed for 30 minutes. Then, 36 parts by mass of monomer 1 was added and crushed for 5 minutes to prepare a pigment dispersion.

[0135] 2-2-2. Preparation of ink

[0136] Inks 13 to 16 were obtained in the same manner as in the preparation of Ink 1 except that the pigment dispersion obtained above was used.

[0137] 2-3. Preparation of Ink 17

[0138] 2-3-1. Preparation of pigment dispersion

[0139] 50 parts by mass of the phosphorescent pigment 1 was placed in a tabletop crusher (D18S, manufactured by Ishikawa Works Co., Ltd.) and crushed for 30 minutes. Then, 2.5 parts by mass of a dispersant and 11.5 parts by mass of the monomer 1 were added and crushed for 30 minutes. After 36 parts by mass of the monomer 1 was added, the mixture was crushed for 5 minutes to prepare a pigment dispersion.

[0140] 2-3-2. Preparation of ink

[0141] Ink 17 was obtained in the same manner as in the preparation of Ink 1 except that the pigment dispersion obtained above was used.

[0142] The compositions of Inks 1 to 19 and the methods for preparing the pigment dispersions are shown in Tables 1 to 3. Compositions are expressed in mass %, and acid and amine values are expressed in mgKOH / g. The types of functional groups (P: phosphate group, C: carboxyl group, B: basic group) possessed by the dispersants, as well as the acid and amine values, are catalog values.

[0143]

Table 1

[0144]

[0145]

Table 2

[0146]

[0147]

Table 3

[0148]

[0149] 4. Evaluation

[0150] Brightness

[0151] A circulation-type inkjet head (KM1024aLHG-RC, manufactured by Konica Minolta, Inc.) and a head module having a resolution of 720 dpi were prepared. Each ink was filled into the head module.

[0152] Next, a voltage was applied to the inkjet head so that the droplet discharge volume was 140 pL (20 pL per shot, 7 shots discharged). Ink was then discharged to print a 150 mm x 150 mm full-coat pattern. The ink was then applied to a 2 mm thick acrylic resin plate serving as a substrate. A UV LED curing lamp (FireJet FJ100 manufactured by Phoseon) was then used to irradiate the substrate at a wavelength of 365 nm and an illumination of 2 W / cm 2 , light intensity 2000mJ / cm 2 Thus, the ink applied to the substrate is cured.

[0153] On the cured ink, further ink was applied under the same conditions and cured by irradiation with ultraviolet rays under the same conditions. This operation was repeated to form a cured product with a thickness of 1000 μm.

[0154] The brightness of each cured product was measured using phosphorescence brightness measurement in accordance with JIS Z9107A:2008. Specifically, the substrate (phosphorescent molded article) containing each cured product was stored in a darkroom for at least 48 hours. The cured product was then irradiated with light using a standard D65 fluorescent lamp at an illumination of 4500 lx for 15 minutes. A luminance meter (LS150, manufactured by Konica Minolta, Inc.) was used to measure the residual brightness of the cured product two seconds after cessation of light irradiation. Based on the measured brightness, the brightness of the cured product obtained from each ink was evaluated according to the following criteria.

[0155] A: Brightness is 15cd / m 2 above

[0156] B: Brightness is 10cd / m 2 Above and less than 15cd / m 2

[0157] C: Brightness 5cd / m 2 Above and less than 10cd / m 2

[0158] D: Brightness is less than 5cd / m 2

[0159] 4-2. Excretion

[0160] A nozzle check pattern was printed under the same conditions as for brightness evaluation to identify head defects and evaluate discharge performance. The discharge performance of each ink was evaluated based on the ratio of nozzles with nozzle defects to the total number of nozzles, using the following criteria.

[0161] A: Nozzle defects are 0% or more and less than 1%.

[0162] B: Nozzle defects are 1% or more and less than 5%.

[0163] C: Nozzle defects are 5% or more and less than 10%.

[0164] D: Nozzle defects are 10% or more.

[0165] 4-3. Pigment particle size

[0166] The volume average particle diameters D50 and D90 of the luminescent pigment in the ink were measured by a dynamic light scattering method using a particle size measuring device (LUMiSizer, manufactured by LUM Japan Co., Ltd.) and data analysis software installed in the particle size measuring device.

[0167] The evaluation results are shown in Tables 4 to 6. The units of D50 and D90 are μm.

[0168]

Table 4

[0169] Ink No. 1 2 3 4 5 6 7 8 9 brightness B C B A B A C C B Excretion C C D C C D D C C D50 2.1 2.0 5.6 2.1 2.1 2.1 1.7 2.0 2.0 D90 3.5 3.3 7.0 3.5 3.5 3.5 2.8 3.3 3.3

[0170]

Table 5

[0171] Ink No. 10 11 12 13 14 15 16 17 brightness C B B A A A B A Excretion C C C B B B B A D50 1.8 2.1 2.1 2.3 2.3 2.3 2.1 2.1 D90 3.0 3.5 3.5 3.8 3.8 3.8 3.5 3.5

[0172]

Table 6

[0173] Ink No. 18 19 brightness D D Excretion D D D50 2.3 2.3 D90 3.8 3.8

[0174] As shown in Tables 1 to 6, dispersing the light-storing pigment with an acidic dispersant can improve the discharge properties of the ink containing the polymerizable compound and the brightness of the cured product formed therefrom.

[0175] Industrial applicability

[0176] According to the present invention, it is possible to facilitate the use of inkjet inks containing light-storing pigments. Therefore, the present invention further expands the applications to which inkjet inks containing light-storing pigments can be applied, and is expected to contribute to further development of this field.

[0177] While embodiments of the present invention have been described and illustrated in detail, it should be clearly understood that this is by way of illustration and example only, not limitation, and that the scope of the present invention is to be construed only in accordance with the terms of the appended claims.

Claims

1. An inkjet ink comprising a polymerizable compound, a light-storing pigment, and a dispersant having an acidic functional group, and curing by irradiation with active rays.

2. The inkjet ink according to claim 1, wherein The light-storing pigment is a phosphor containing aluminate.

3. The inkjet ink according to claim 1 or 2, wherein The light-storing pigment is a phosphor containing at least one aluminate selected from the group consisting of calcium aluminate, strontium aluminate, and barium aluminate.

4. The inkjet ink according to any one of claims 1 to 3, wherein The light-storing pigment is SrAl2O4 containing europium (Eu) and dysprosium (Dy) as an activator, or Sr4Al2O4 containing europium (Eu) and dysprosium (Dy) as an activator. 14 O 25 .

5. The inkjet ink according to any one of claims 1 to 4, wherein The content of the light-storing pigment is 5% by mass or more and 40% by mass or less.

6. The inkjet ink according to any one of claims 1 to 5, wherein The light-storing pigment is a particle having a median diameter of 2.0 μm or more and 5.0 μm or less.

7. The inkjet ink according to any one of claims 1 to 6, wherein The dispersant has an acid value of 30 mgKOH / g or more and 200 mgKOH / g or less.

8. The inkjet ink according to any one of claims 1 to 7, wherein The dispersant is a dispersant having a phosphoric acid group or a carboxyl group.

9. The inkjet ink according to any one of claims 1 to 8, wherein The dispersant is a dispersant having a carboxyl group.

10. A method for producing a pigment dispersion for inkjet ink, wherein: The composition containing the polymerizable compound, the light-storing pigment, and the dispersant is kneaded by a pestle.

11. The method for producing a pigment dispersion according to claim 10, comprising the step of dry-grinding the luminescent pigment. In the kneading step, a composition containing a polymerizable compound, the dry-ground phosphorescent pigment, and a dispersant is kneaded.

12. A method for producing an inkjet ink, comprising: A step of preparing a pigment dispersion produced by the method for producing a pigment dispersion according to claim 10 or 11; and A step of mixing the prepared pigment dispersion with a polymerizable compound.

13. A method for forming a cured product, comprising: a step of discharging the inkjet ink according to any one of claims 1 to 9 from an inkjet head and applying the ink to a substrate; and a step of curing the inkjet ink applied to the substrate by irradiation with active rays. 14 . A cured product formed by curing the inkjet ink according to claim 1 .

15. The cured product according to claim 14, wherein The thickness is 0.3 mm or more and 1.5 mm or less.

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