JP7845052B2 - Active radiation-curable ink, method for forming cured product, cured product, and phosphorescent plate - Google Patents

Description

This invention relates to an active-ray curable ink, a method for forming a cured product, a cured product, and a phosphorescent plate.

In the printing field, active-ray curable inks containing active-ray polymerizable compounds are known as inks used in the printing industry. When irradiated with active rays, active-ray curable inks harden through polymerization of the active-ray polymerizable compounds, forming a cured film and thus enabling the creation of printed materials. Printed materials formed with active-ray curable inks exhibit excellent durability and can therefore be used for outdoor signage and other applications.

However, when printed materials formed with the above-mentioned ink were used for outdoor signs and other applications, the printed areas were difficult to see in dark conditions at night. While it is possible to address this by shining light from the back of the printed material's substrate to make the printed areas visible in the dark, this method requires driving a light source device, posing an energy-saving problem.

Therefore, there is a growing demand for ways to improve the visibility of printed areas even in dark environments without using the light source devices described above, and the development of inks that can achieve this is underway.

As an example of such an ink, an active-ray curing ink containing phosphorescent pigments is known (for example, Patent Documents 1-5). The phosphorescent pigment can absorb light of a predetermined wavelength and store the light energy. The light energy stored in the phosphorescent pigment is then emitted for a long time as light of a different wavelength than the absorbed light, even after light absorption has stopped. Therefore, for example, when printed materials formed using ink containing phosphorescent pigments are used outdoors, the phosphorescent pigments absorb light such as sunlight, store the light energy, and can emit light even at night. As a result, the printed portion can be seen even in dark places.

Japanese Patent Publication No. 2013-135192 Japanese Patent Application Publication No. 11-140368 Japanese Patent Publication No. 2014-028484 Japanese Patent Publication No. 2019-210337 International Publication No. 2013/099565

As described in Patent Documents 1-5, active-ray curable inks containing phosphorescent pigments are known. Regarding these inks, there is a desire to increase the brightness of the cured product in order to further improve the visibility of the printed area in dark places.

This invention has been made in view of the above circumstances, and aims to provide an active-ray curable ink containing a phosphorescent pigment that can further enhance the brightness of the resulting cured product, a method for forming a cured product using the same, a cured product, and a phosphorescent plate.

One aspect of the present invention, for solving the above problems, relates to the following active-ray curable inks [1] to [12].
[1] An active-ray curable ink comprising an active-ray polymerizable compound, a phosphorescent pigment, and a photopolymerization initiator, wherein the photopolymerization initiator is formed by curing a dipropylene glycol diacrylate solution (concentration of 3% by mass) of the photopolymerization initiator by irradiating it with ultraviolet light of a wavelength of 365 nm at a light intensity of 2000 mJ/ ^cm² under a nitrogen gas atmosphere to form a 10 μm thick cured product, and then repeatedly forming the cured product on top of this cured product to obtain a 40 μm thick cured product, the transmittance of light at the peak wavelength of the excitation spectrum of the phosphorescent pigment being 40% or more.
[2] The active-ray curable ink according to [1], wherein the photopolymerization initiator comprises a hydrogen abstraction type initiator.
[3] The active-ray curable ink according to [1] or [2], wherein the photopolymerization initiator comprises an intramolecular hydrogen abstraction initiator.
[4] The active-ray curable ink according to any one of [1] to [3], further comprising a photopolymerization initiator having a transmittance of less than 40%, in an amount of 3% by mass or more and 17% by mass or less based on the total mass of the photopolymerization initiator.
[5] The active-ray curable ink according to any one of [1] to [4], further comprising an acylphosphine oxide-based photopolymerization initiator.
[6] The photopolymerizable compound comprises a compound having an aromatic ring, as described in any one of [1] to [5].
[7] The photopolymerizable compound comprises a monofunctional compound, and is an active-ray curable ink according to any one of [1] to [6].
[8] The photopolymerizable compound comprises a compound having an alkylene glycol structure, as described in [1] to [7].
[9] The activated ray curing ink according to [8], wherein the number of carbon atoms constituting the alkylene glycol structure is 3 or more.
[10] The active-ray curable ink according to any one of [1] to [9], wherein the content of the phosphorescent pigment is 10% by mass or more and 50% by mass or less with respect to the total mass of the active-ray curable ink.
[11] The active-ray curable ink according to any one of [1] to [10], wherein the peak wavelength of the excitation spectrum of the phosphorescent pigment is 300 nm or more and 400 nm or less.
[12] An inkjet ink, which is an active-ray curing ink as described in any of [1] to [11].

Furthermore, one aspect of the present invention for solving the above problems relates to the cured product forming method described in [13] below.
A method for forming a cured product, comprising the steps of: applying an active-ray curable ink described in any of [1] to [12] to a recording medium; and irradiating the applied active-ray curable ink with an active ray.

Furthermore, one aspect of the present invention for solving the above problems relates to the cured product forming method described in [14] below.
A cured product obtained by curing an active-ray curable ink as described in any of [1] to [12].

Furthermore, one aspect of the present invention for solving the above problems relates to the phosphorescent plate described in [15] below.
A phosphorescent plate having the cured product described in [15] and [14].

This invention provides an active-ray curable ink containing a phosphorescent pigment, which can further enhance the brightness of the resulting cured product; a method for forming a cured product using the same; a cured product; and a phosphorescent plate.

The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

1. Active Ray Curable Ink The active ray curable ink according to this embodiment (hereinafter also simply referred to as "ink") comprises an active ray polymerizable compound, a phosphorescent pigment, and a photopolymerization initiator. The ink is preferably an inkjet ink.

As mentioned above, there is a demand for increasing the brightness of the cured product formed by active-ray curing inks containing phosphorescent pigments.

The cured product contains residue of the photopolymerization initiator used to cure the ink. According to our findings, this residue readily absorbs light of the wavelength that excites the phosphorescent pigment (excitation light) from the light incident on the cured product. Furthermore, according to our findings, this residue can cause yellowing of the cured product. The yellowed areas in the cured product readily absorb the excitation light. For these reasons, the phosphorescent pigment in the cured product, especially the phosphorescent pigment near the substrate, did not receive sufficient excitation light, resulting in insufficient luminescence. In contrast, by selecting a photopolymerization initiator according to the phosphorescent pigment to reduce the absorption of excitation light wavelengths due to the residue and yellowing after curing, sufficient excitation light can reach the phosphorescent pigment in the cured product, and even the phosphorescent pigment near the substrate. This is expected to allow the phosphorescent pigment in the cured product to emit sufficient light.

Therefore, the inventors considered that when the transmittance of excitation light from the phosphorescent pigment to the cured product containing the photopolymerization initiator is high, the absorption of the excitation light due to the above-mentioned residue and yellowing is reduced, and selected a photopolymerization initiator that would result in a high transmittance.

Specifically, a 10 μm thick cured product is formed by curing a dipropylene glycol diacrylate solution (3% by mass concentration) of a photopolymerization initiator with ultraviolet light at a wavelength of 365 nm at a light intensity of 2000 mJ/ ^cm² under a nitrogen gas atmosphere. The phosphorescent pigment and photopolymerization initiator are selected such that the transmittance of light at the peak wavelength of the excitation spectrum of the phosphorescent pigment in a 40 μm thick cured product obtained by repeatedly forming the cured product on top of the cured product is 40% or more. This reduces the absorption of excitation light by the residue of the photopolymerization initiator contained in the cured product, allowing the excitation light to sufficiently reach the phosphorescent pigment in the cured product, causing the entire phosphorescent pigment to emit light sufficiently and further increasing the brightness of the cured product.

Since the transmittance of the photopolymerization initiator to the excitation light differs from that of the residue of the photopolymerization initiator used for ink curing, measuring the transmittance using the method described above allows for confirmation that the absorption of the excitation light by the residue has been reduced. Furthermore, measuring the transmittance using the method described above allows for confirmation of how easily the excitation light reaches the phosphorescent pigment, including the effect of yellowing that occurs during ink curing.

1-1. Active Ray Polymerizable Compounds The active ray polymerizable compounds contained in the ink according to this embodiment are compounds that polymerize and crosslink upon irradiation with active rays.

Examples of active rays include electron beams, ultraviolet rays, alpha rays, gamma rays, and X-rays. Of these, ultraviolet rays and electron beams are preferred, with ultraviolet rays being more preferred.

Examples of activated ray polymerizable compounds include radical polymerizable compounds and cationic polymerizable compounds. Of these, the activated ray polymerizable compound is preferably a radical polymerizable compound. The activated ray polymerizable compound may be a monomer, a polymerizable oligomer, or a mixture thereof. Furthermore, the ink may contain only one activated ray polymerizable compound, or a combination of two or more compounds.

Furthermore, the activated ray polymerizable compound may be monofunctional or polyfunctional. From the viewpoint of suppressing the decrease in the adhesion of the cured product to the substrate due to curing shrinkage, it is preferable that the activated ray polymerizable compound includes a monofunctional compound.

Radical polymerizable compounds are monofunctional or polyfunctional compounds that possess ethylenically unsaturated bonds capable of radical polymerization within their molecules. Examples of compounds with radically polymerizable ethylenically unsaturated bonds include unsaturated carboxylic acids and their salts, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid urethane compounds, unsaturated carboxylic acid amide compounds and their anhydrides, acrylonitrile, styrene, unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Examples of unsaturated carboxylic acids include (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid.

The radical polymerizable compound is preferably an unsaturated carboxylic acid ester and a (meth)acrylate, and more preferably a (meth)acrylate.

Examples of monofunctional (meth)acrylates include isoamyl (meth)acrylate, stearyl (meth)acrylate, isobonyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomirsutyl (meth)acrylate, isostearyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, and o-phenyl This includes phenoxyethyl (meth)acrylate, m-phenoxybenzyl (meth)acrylate, cyclic trimethylolpropaneformal (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-phenylphenolpropyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalic acid, and t-butylcyclohexyl (meth)acrylate, among others.

Examples of polyfunctional (meth)acrylates 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, dimethylol-tricyclodecane di(meth)acrylate, bisphenol A type di(meth)acrylate, and hydroxypivalate neopentyl glycol di(meth)acrylate. This includes difunctional (meth)acrylates containing polytetramethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate, and tripropylene glycol diacrylate, as well as trifunctional or more (meth)acrylates containing trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, and pentaerythritol ethoxytetra(meth)acrylate, and oligomers having a (meth)acryloyl group, including polyester acrylate oligomers.

Examples of cationic polymerizable compounds include epoxy compounds, vinyl ether compounds, and oxetane compounds.

Examples of the epoxy compounds mentioned above 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-methyloxyranyl)-7-oxabicyclo[4,1,0]heptane, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanone-meth-dioxane and bis(2,3-epoxycyclopentyl) ethers, alicyclic epoxy resins, diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, and triglycerin. This includes aliphatic epoxy compounds such as polyglycidyl ethers of polyether polyols obtained by adding one or more alkylene oxides (such as ethylene oxide and propylene oxide) to aliphatic polyhydric alcohols such as ricidyl ethers, triglycidyl ethers of trimethylolpropane, diglycidyl ethers of polyethylene glycol, diglycidyl ethers of propylene glycol, ethylene glycol, propylene glycol, and glycerin; 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.

Examples of the vinyl ether compounds mentioned above 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, as well as 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.

Examples of the above 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, and 3-hydroxyethyl This includes -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, among others.

The activated linear polymerizable compound preferably contains a compound having an aromatic ring. Including a compound with an aromatic ring in the activated linear polymerizable compound can increase the refractive index of the ink and the resulting cured product.

The refractive index of phosphorescent pigments is high, and the refractive index difference between the phosphorescent pigment and the surrounding cured material is considered to be large. Therefore, even when attempting to expose the phosphorescent pigment to light, reflection of the incident light is likely to occur at the interface between the phosphorescent pigment and the cured material. In contrast, by increasing the refractive index of the cured material using a compound containing an aromatic ring, it is thought that the refractive index difference between the phosphorescent pigment and the surrounding cured material can be reduced. This reduces the reflection of light occurring at the interface between the phosphorescent pigment and the cured material, allowing more light to be incident on the phosphorescent pigment. As a result, the phosphorescent pigment can emit more light, and thus the brightness of the cured material can be further improved.

Furthermore, during the curing of the ink, the phosphorescent pigment absorbs a portion of the active rays irradiated onto the ink, resulting in a slight emission of light from the phosphorescent pigment. This slight emission is absorbed by the photopolymerization initiator, allowing the polymerization of the active-ray polymerizable compound to proceed. At this time, the inclusion of the compound having the aromatic ring in the ink increases the refractive index of the ink. This reduces the difference in refractive index between the phosphorescent pigment and the surrounding ink, thereby reducing the reflection of active rays at the interface between the phosphorescent pigment and the ink, allowing more active rays to enter the phosphorescent pigment. As a result, the emission generated by the phosphorescent pigment is increased, and the polymerization of the active-ray polymerizable compound progresses further, thus improving the curability of the cured product.

Examples of compounds having the above aromatic ring include 2-phenoxyethyl (meth)acrylate, bisphenol A type diacrylate, o-phenylphenoxyethyl (meth)acrylate, m-phenoxybenzyl (meth)acrylate, ethoxylated phenoxy(meth)acrylate, alkoxylated phenol (meth)acrylate, and 2-hydroxy-o-phenylphenolpropyl (meth)acrylate. In particular, 2-phenoxyethyl (meth)acrylate, o-phenylphenoxyethyl (meth)acrylate, m-phenoxybenzyl (meth)acrylate, and ethoxylated phenoxy(meth)acrylate are more preferred from the viewpoint of inkjet ejectability and brightness.

When the active-ray polymerizable compound contains a compound having an aromatic ring, the content of the compound having an aromatic ring is preferably 20% to 70% by mass, and more preferably 30% to 60% by mass, relative to the total mass of the ink. If the content is 20% by mass or more, the difference in refractive index between the phosphorescent pigment and the cured product surrounding the phosphorescent pigment can be reduced, allowing more light to enter the phosphorescent pigment and causing it to emit more light. This further improves the brightness of the cured product. Furthermore, if the content is 20% by mass or more, the difference in refractive index between the phosphorescent pigment and the ink surrounding the phosphorescent pigment can be reduced, allowing more active rays to enter the phosphorescent pigment and causing it to emit more light. This further promotes the polymerization of the active-ray polymerizable compound and enhances the curability of the cured product. If the content is 70% by mass or less, it is possible to further suppress the refractive index of the ink and cured product from becoming too high. This allows for appropriate adjustment of the refractive index difference between the phosphorescent pigment and the cured material surrounding it, as well as the refractive index difference between the phosphorescent pigment and the ink surrounding it.

The activated linear polymerizable compound preferably contains a compound having an alkylene glycol structure. According to the inventors' findings, compounds having an alkylene glycol structure are considered to have high affinity for the phosphorescent pigments described later. Therefore, by including the above compound in the ink, the phosphorescent pigment can exist in a more dispersed state in the cured product. This is thought to further suppress the aggregation of the phosphorescent pigment in the cured product, thereby improving the adhesion of the cured product to the substrate. Examples of compounds having an alkylene glycol structure include polyethylene glycol diacrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, ethoxylated phenoxy(meth)acrylate, dipropylene glycol diacrylate, tripropylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate. In particular, polyethylene glycol di(meth)acrylate, dipropylene glycol diacrylate, tripropylene glycol di(meth)acrylate, and ethoxylated phenoxy(meth)acrylate are even more preferred from the viewpoint of adhesion.

Of these, it is preferable that the alkylene glycol structure has 3 to 4 carbon atoms. Including a compound having an alkylene glycol structure with 3 or more carbon atoms in the ink suppresses excessive hydrophilicity of the cured product, making it less susceptible to water absorption. This, in turn, enhances the weather resistance of the cured product formed by the ink. Furthermore, having 4 or fewer carbon atoms suppresses a decrease in affinity between the cured product and the phosphorescent pigment, thereby further suppressing a decrease in the adhesion of the cured product to the substrate.

In the molecular structure of a compound having an alkylene glycol structure, it is preferable that the alkylene glycol structure is present in two to four units. The presence of two or more alkylene glycol structures can further enhance the adhesion of the cured product to the substrate. Having four or fewer alkylene glycol structures can further suppress the decrease in curability of the cured product. Since the alkylene glycol structure is considered a flexible structure that can enhance molecular mobility, it is believed that limiting the number of alkylene glycol structures to four or fewer can further suppress the decrease in curability caused by excessive flexibility in the cured product.

The content of the compound having an alkylene glycol structure is preferably 5% to 40% by mass, and more preferably 10% to 35% by mass, based on the total mass of the ink. A content of 5% by mass or more can further enhance the adhesion of the cured product to the substrate, while a content of 40% by mass or less can further suppress the decrease in the curability of the cured product.

The content of the activated linearly polymerizable compound can be, for example, 1% to 95% by mass relative to the total mass of the ink, preferably 30% to 95% by mass, and more preferably 50% to 95% by mass.

1-2. Phosphorescent Pigment In this embodiment, the ink contains a phosphorescent pigment.

Phosphorescent pigments can absorb light of a specific wavelength, store its energy, and even after absorbing light, they can release the stored energy as light of a different wavelength than the absorbed light for a long period of time. In other words, phosphorescent pigments can emit phosphorescence.

The type of phosphorescent pigment is not particularly limited, as long as it possesses the characteristics described above. Examples of phosphorescent pigments include those in which the host crystal, which is a metal compound, has been activated.

Examples of the parent crystals mentioned above include sulfides such as zinc sulfide, calcium sulfide, germanium sulfide, strontium sulfide, and yttrium sulfide; metal oxides such as calcium oxide, strontium oxide, barium oxide, alumina, and cerium oxide; and aluminates such as calcium aluminate, strontium aluminate, and barium aluminate. Of these, strontium aluminate is preferred.

Examples of activators used to activate the above-mentioned parent crystals include europium, terbium, yttrium, zirconium, dysprosium, and barium. Of these, europium and dysprosium are preferred.

The phosphorescent pigment may be included in the ink as a single element, or as a combination of two or more elements.

The peak wavelength of the excitation spectrum of the phosphorescent pigment is preferably between 300 nm and 400 nm. Having the peak wavelength of the excitation spectrum of the phosphorescent pigment within this range allows for greater excitation of the phosphorescent pigment when sunlight is incident on it. Therefore, for example, the cured product can be adapted for outdoor use. Furthermore, having the peak wavelength within this range makes it easier for the peak wavelength of the emission spectrum of the phosphorescent pigment to fall within the preferred range described later, thus improving the visibility (visibility) of the cured product (printed portion).

The peak wavelength of the emission spectrum of the phosphorescent pigment can be, for example, between 400 nm and 700 nm, but from the viewpoint of further improving the visibility of the cured product (printed portion), it is preferable that it be between 450 nm and 600 nm.

The particle size (d ₅₀ ) at which the cumulative value in the volume-based particle size distribution of the phosphorescent pigment reaches 50% is not particularly limited, but is preferably 10 μm or less, and more preferably 8 μm or less. When the ink according to this embodiment is used as an inkjet ink, a decrease in ejection stability can be suppressed by having the above particle size of 10 μm or less. The lower limit of the above particle size is not particularly limited, but is preferably 0.5 μm or more, and more preferably 1 μm or more. The above particle size of the phosphorescent pigment can be measured using a particle size distribution analyzer that utilizes the Stokes sedimentation method (for example, LUMiSizer, manufactured by LUM Japan Co., Ltd.).

The phosphorescent pigment content is preferably 10% to 50% by mass, and more preferably 15% to 35% by mass, relative to the total mass of the ink. A content of 10% by mass or more can further improve the brightness of the cured product. A content of 50% by mass or less increases the proportion of activated linear polymerizable compounds in the ink, further improving the curability and adhesion of the cured product to the substrate. Furthermore, a content of 50% by mass or less can suppress a decrease in ejection stability when the ink is used as an inkjet ink.

1-3. Photopolymerization Initiator The ink according to this embodiment contains a photopolymerization initiator.

The above-mentioned photopolymerization initiator is formed by curing a 10 μm thick cured product obtained by repeatedly forming the above-mentioned cured product on a 10 μm thick cured product obtained by curing a dipropylene glycol diacrylate solution of the above-mentioned photopolymerization initiator (concentration of 3% by mass) with ultraviolet light of a wavelength of 365 nm at a light intensity of 2000 mJ/ ^cm² under a nitrogen gas atmosphere, and the transmittance of light at the peak wavelength of the excitation spectrum of the phosphorescent pigment (hereinafter also simply referred to as transmittance) of the 40 μm thick cured product is 40% or more.

Furthermore, because the thickness of the cured material formed in the above measurement is 10 μm, differences in the degree of curing due to differences in the maximum absorption wavelength of the photopolymerization initiator are unlikely to occur. Therefore, differences in the curability of the 40 μm thick cured material obtained by laminating this material, depending on the type of photopolymerization initiator, are also unlikely to occur.

As described above, the inclusion of the above-mentioned photopolymerization initiator in the ink can enhance the brightness of the cured product.

The above transmittance can be measured, for example, using a spectrophotometer (V-650, manufactured by JASCO Corporation) to determine the transmittance at the peak wavelength of the excitation spectrum of the phosphorescent pigment. For example, the transmittance is measured by setting the incident angle of the detector stage in the spectrophotometer to 90° and the incident angle of the sample stage to 0°.

The photopolymerization initiator can be a radical initiator when the ink contains a radical polymerizable compound, and a cationic initiator (photoacid generator) when the ink contains a cationic polymerizable compound.

Examples of radical polymerization initiators include intramolecular cleavage-type photopolymerization initiators and hydrogen abstraction-type polymerization initiators. The above photopolymerization initiators may be present in the ink as a single type, or in combination of two or more types.

Examples of intramolecular cleavage-type photopolymerization initiators include acetophenone-based initiators such as 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino(4-methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone; benzoin-based initiators such as benzoin, benzoin methyl ether, and benzoin isopropyl ether; and acylphosphine oxide-based initiators such as 2,4,6-trimethylbenzoin diphenylphosphine oxide and bis(2,4,6-trimethylbenzoin)phenylphosphine oxide.

Examples of commercially available intramolecular cleavage-type photopolymerization initiators include Omnirad 127, Omnirad 184, Omnirad 651, Omnirad 2959, Omnirad 819, and Esacure One (manufactured by IGM Resins).

Among these intramolecular cleavage-type photopolymerization initiators, acylphosphine oxide-based initiators are preferred. Acylphosphine oxide-based initiators have photobleaching properties, which can further suppress yellowing. Photobleaching refers to the property of the absorption spectrum of a photopolymerization initiator to shift when irradiated with active rays. This further suppresses the shielding of the phosphorescent pigment's luminescence in the yellow portion of the cured product, thereby further suppressing the decrease in the brightness of the cured product.

Hydrogen abstraction type photopolymerization initiators include intermolecular hydrogen abstraction type photopolymerization initiators and intramolecular hydrogen abstraction type photopolymerization initiators.

In this specification, "intermolecular hydrogen abstraction type photopolymerization initiator" refers to a compound that is excited by irradiation with active light such as ultraviolet light, and generates radicals by abstracting hydrogen from other molecules.

Examples of intermolecular hydrogen abstraction type photopolymerization initiators include benzophenone-based initiators such as benzophenone, o-benzoylmethyl benzoate, 4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylic benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone, as well as thioxanthone-based initiators such as 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone.

Examples of commercially available intermolecular hydrogen abstraction type photopolymerization initiators include Irgacure 500 (BASF) and Speedcure ITX (Lambason).

Furthermore, in this specification, "intramolecular hydrogen abstraction type photopolymerization initiator" refers to a compound that, when excited by irradiation with active light, undergoes an intramolecular hydrogen abstraction reaction to generate radicals.

Examples of intramolecular hydrogen abstraction type photopolymerization initiators include methyl benzoylformate-based photopolymerization initiators such as methyl phenylglyoxylate, and oxyphenyl-based photopolymerization initiators such as mixtures of oxyphenylacetic acid-2-[2-oxo-2-phenylacetoxy-ethoxy]ethyl ester and oxyphenylacetic acid-2-[2-hydroxy-ethoxy]ethyl ester.

Examples of commercially available intramolecular hydrogen abstraction type photopolymerization initiators include Omnirad MBF (manufactured by IGM Resins) and Irgacure 754 (manufactured by BASF).

The photopolymerization initiator preferably contains a hydrogen abstraction type photopolymerization initiator, and more preferably contains an intramolecular hydrogen abstraction type photopolymerization initiator.

By using a hydrogen abstraction type photopolymerization initiator, the curing of the ink by irradiation with active rays can be further accelerated, thereby improving the curability and water resistance of the resulting cured product.

Oxygen inhibition refers to the inhibition of the polymerization reaction when radicals generated during polymerization react with oxygen to produce peroxides. Hydrogen abstraction type photopolymerization initiators can abstract hydrogen atoms from these peroxides, thereby regenerating radicals. This further promotes the polymerization reaction and suppresses oxygen inhibition. As a result, it is believed that the curability and water resistance of the cured product can be improved.

Furthermore, intramolecular hydrogen abstraction type photopolymerization initiators induce hydrogen abstraction reactions within the molecule, generating radicals. Therefore, it is believed that they can further suppress the generation of radicals caused by the abstraction of hydrogen from the molecular chains of the active linearly polymerizable compound during polymerization. This further suppresses crosslinking reactions between the molecular chains, allowing for the extension of the molecular chains. This, in turn, can increase the hydrophobicity of the resulting cured product, thereby improving its water resistance and weather resistance.

Intramolecular hydrogen abstraction type photopolymerization initiators are preferably compounds having a glycooxyacid structure. Compounds with a glycooxyacid structure are more readily subjected to intramolecular hydrogen abstraction reactions, which is thought to improve the water resistance and weather resistance of the resulting cured product.

The molecular weight of the photopolymerization initiator is preferably 150 to 500, and more preferably 150 to 190. A molecular weight of 150 or higher improves injection stability when the ink is used as an inkjet ink, while a molecular weight of 500 or lower increases the mobility of the photopolymerization initiator molecules within the ink, facilitating the initiation of polymerization of the active-ray polymerizable compound near the substrate and further improving the curability of the cured product.

Examples of cationic photopolymerization initiators include photoacid generators. Examples of photoacid generators include sulfonates that generate sulfonic acid ^, such as B( _C6F5 ) _4- ^, _PF6- , ^AsF6- , _SbF6- ^, and _CF3SO3- salts of aromatic onium compounds including diazonium, _ammonium , _iodonium , sulfonium, and phosphonium _; halides that photogenerate hydrogen halides; and iron allene complexes ^.

In this embodiment, the photopolymerization initiator used is one whose transmittance at the peak wavelength of the excitation spectrum of the phosphorescent pigment is 40% or more. For example, when the peak wavelength of the excitation spectrum of the phosphorescent pigment is 324 nm, a photopolymerization initiator is used whose transmittance at a wavelength of 324 nm is 40% or more. Examples of photopolymerization initiators used in this process include Omnirad 127 (transmittance 71%), Omnirad 184 (transmittance 73%), Omnirad 651 (transmittance 55%), Omnirad 2959 (transmittance 63%), Irgacure 500 (transmittance 62%), Omnirad 754 (transmittance 46%) (all manufactured by BASF), Esacure One (transmittance 71%) (manufactured by IGM Resins), and Omnirad MBF (transmittance 45%) (manufactured by IGM Resins).

The transmittance of the photopolymerization initiator is 40% or more, preferably 45% to 80%, more preferably 40% to 70%, and even more preferably 40% to 65%. A transmittance of 80% or less further suppresses the light that excites the phosphorescent pigment reaching the substrate, thus preventing substrate degradation. Therefore, for example, by suppressing the transmission of sunlight to the substrate, substrate degradation can be further suppressed, thereby increasing the suitability of the cured product for outdoor use. Furthermore, a transmittance of 70% or less further suppresses the excessive transmission of light at the peak wavelength of the excitation spectrum of the phosphorescent pigment, further suppressing degradation of the cured product and increasing its weather resistance.

The content of the photopolymerization initiator, which has a transmittance of 40% or more, is preferably 3% to 15% by mass, more preferably 3% to 10% by mass, and even more preferably 5% to 10% by mass, based on the total mass of the ink. A content of 3% by mass or more can further enhance the brightness of the cured product. A content of 15% by mass or less can further enhance the adhesion of the cured product.

The ink according to this embodiment may further contain a photopolymerization initiator having a transmittance of less than 40%, within the range that achieves the effects of the present invention.

The transmittance of the photopolymerization initiator with a transmittance of less than 40% is preferably 20% or more and less than 40%. By having a transmittance of 20% or more for a photopolymerization initiator with a transmittance of less than 40%, for example, when the peak wavelength of the excitation spectrum of the phosphorescent pigment is in the ultraviolet region, the residue of the photopolymerization initiator can further reduce the absorption of light of that wavelength. This further suppresses the yellowing of the cured product (discoloration to yellow, which is the complementary color of that wavelength), and further suppresses the brightness of the cured product due to yellowing.

The photopolymerization initiator with a transmittance of less than 40% preferably contains an acylphosphine oxide-based initiator. Because acylphosphine oxide-based initiators have photobleaching properties, they can further suppress yellowing. This further suppresses the shielding of the phosphorescent pigment's luminescence in the yellow portion of the cured product, thereby further suppressing the decrease in the brightness of the cured product.

The content of the photopolymerization initiator with a transmittance of less than 40% is preferably 3% to 30% by mass, and more preferably 5% to 20% by mass, relative to the total mass of the photopolymerization initiator. The photopolymerization initiator with a transmittance of less than 40% is considered to readily absorb active rays. Therefore, a content of 3% by mass or more can further promote the polymerization reaction of the active-ray polymerizable compound, thereby improving the curability of the resulting cured product. A content of 30% by mass or less allows sufficient light to reach the phosphorescent pigment to excite it, further increasing the brightness of the cured product.

The transmittance of the photopolymerization initiator, which has a transmittance of less than 40%, is preferably 20% or more and less than 40%, and more preferably 30% or more and less than 40%. A transmittance of 20% or more allows sufficient light to reach the phosphorescent pigment to excite it, thereby further increasing the brightness of the cured product.

1-4. Others The ink according to this embodiment may further contain other components such as non-phosphorescent pigments, pigment dispersants, surfactants, fluorescent whitening agents, and polymerization inhibitors, to the extent that it achieves the effects of the present invention.

Examples of non-phosphorescent pigments include red, yellow, blue, and white pigments, which can be used in image-forming inks. These pigments can be those that are already known.

Examples of pigment dispersants include hydroxyl group-containing carboxylic acid esters, salts of long-chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalene sulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate. Examples of commercially available pigment dispersants include the Solsperse® series (manufactured by Avecia), the PB series (manufactured by Ajinomoto Fine Techno), and the EFKA series (manufactured by BASF).

The pigment dispersant content is preferably 0.5% by mass or more and 20% by mass or less, relative to the total mass of the phosphorescent pigment.

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

The amount of surfactant relative to the total mass of the ink is not particularly limited within the range that achieves the effects of the present invention, but for example, it can be 0.001% by mass or more and less than 1.0% by mass.

Examples of polymerization inhibitors include N-oxyl polymerization inhibitors, phenol 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.

Examples of N-oxyl polymerization inhibitors include 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, and 4-acetoxy-2,2,6,6-tetramethylpiperidine-N-oxyl. A commercially available example of an N-oxyl polymerization inhibitor is Irgastab UV10 (manufactured by BASF, "Irgastab" is a registered trademark of the company).

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-t-butyl-p-cresol (butylated hydroxytoluene: BHT), 4-methoxyphenol, and 2-methoxy-4-methylphenol.

Examples of quinone polymerization inhibitors include hydroquinone, methoxyhydroquinone, benzoquinone, 1,4-naphthoquinone, and p-tert-butylcatechol.

Examples of amine polymerization inhibitors include alkylated diphenylamines, N,N'-diphenyl-p-phenylenediamine, and phenothiazines.

Examples of copper dithiocarbamate-based polymerization inhibitors include copper dimethyldithiocarbamate, copper diethyldithiocarbamate, and copper dibutyldithiocarbamate.

The content of the polymerization inhibitor is not particularly limited within the range that achieves the effects of the present invention, but for example, it can be 0.001% by mass or more and 0.5% by mass or less, preferably 0.1% by mass or less, and more preferably less than 0.01% by mass.

1-5. Physical Properties The viscosity of the ink according to this embodiment at 25°C is preferably 5 mPa·s or more and 50 mPa·s or less. Having the viscosity within the above range improves the ejection stability when the ink is used as an inkjet ink.

The viscosity of ink at 25°C can be determined using a rheometer under the condition of a shear rate of 1000/sec. Specifically, it can be determined by heating the ink to 25°C and measuring it under the condition of a shear rate of 1000/sec.

The rheometer can be an Anton Paar PhysicaMCR series stress-controlled rheometer. The cone plate diameter can be set to 75 mm, and the cone angle to 1.0°.

1-6. Method for producing active-ray curing ink The ink according to this embodiment can be prepared by mixing the components described above. In this case, it is preferable to mix the components other than the phosphorescent pigment first, and then add the phosphorescent pigment to the resulting mixture.

When the ink contains a pigment dispersant, a pigment dispersion containing the phosphorescent pigment and the pigment dispersant may be prepared in advance, and the remaining components may be added and mixed. In this case, it is preferable to prepare the pigment dispersion by heating the pigment and dispersant while mixing to increase the solubility of the pigment dispersant.

2. Method for forming a cured product The method for forming a cured product according to this embodiment comprises the steps of applying an active-ray curable ink to a substrate and irradiating the applied active-ray curable ink with an active ray.

2-1. Ink application process In this process, the above-mentioned active-ray curable ink is applied to the substrate.

Examples of methods for applying ink to a substrate include methods using roll coaters or spin coaters, screen printing methods, and inkjet methods. Of these, inkjet methods are preferred from the viewpoint of forming a more precise cured product at a desired location on the substrate.

When applying ink to a substrate using an inkjet method, the ejection method from the inkjet head may be either an on-demand method or a continuous method. On-demand inkjet heads may be of any of the following types: single-cavity type, double-cavity type, bender type, piston type, shear-mode type, and shared-wall type (electromechanical conversion methods), as well as thermal inkjet type and bubble jet ("bubble jet" is a registered trademark of Canon Inc.) type (electromechanical conversion methods).

The type of base material is not particularly limited, but examples include ABS resin sheets, acrylic resin sheets, aluminum sheets, glass sheets, polycarbonate sheets, and fabric.

2-2. Irradiation with Active Rays In this step, the ink applied to the substrate is irradiated with active rays to cure the ink. The wavelength of the active rays to be irradiated may be appropriately set to match the maximum absorption wavelength of the photopolymerization initiator.

The active ray can be selected from, for example, electron beams, ultraviolet light, alpha rays, gamma rays, and X-rays, but ultraviolet light or electron beams are preferred. The ultraviolet light is preferably light with a peak wavelength between 360 nm and 410 nm. Furthermore, the ultraviolet light is preferably irradiated from an LED light source. Because LEDs emit less radiant heat compared to conventional light sources (e.g., metal halide lamps), using LEDs makes it less likely for the ink to melt during active ray irradiation, thus reducing the occurrence of uneven gloss.

When ultraviolet light is used as the active ray, the amount of light per irradiation is preferably 500 mJ/ ^cm² or more and 4000 mJ/ ^cm² or less. If it is 500 mJ/ ^cm² or more, the curability of the formed cured product can be further improved. If it is 4000 mJ/ ^cm² or less, discoloration of the cured product can be suppressed.

2-3. Step of further applying ink The cured product forming method according to this embodiment may include a step of further applying ink to the ink that has been irradiated with the active ray.

This process allows for a greater thickness of the resulting cured material. A thicker cured material allows for the inclusion of more phosphorescent pigment, thereby improving the overall brightness of the cured material.

The method for further applying the ink may be the same as the method used in the process of applying the ink to the substrate, or it may be a different method.

2-4. Step of irradiating the ink further applied on the ink with an active ray The cured product formation method according to this embodiment may include a step of irradiating the ink further applied on top of the ink with an active ray.

In this process, the above ink is further applied, and the applied ink is cured by irradiating it with an active ray.

The type of active ray and the amount of light used when ultraviolet light is employed can be the same as in step S20 described above.

In the cured product formation method according to this embodiment, the thickness of the formed cured product can be increased by repeatedly performing steps S30 and S40.

3. Cured product The cured product according to this embodiment is obtained by curing the activated ray curing ink described above.

The above-mentioned cured product can be formed by the cured product formation method described above.

The thickness of the cured material is preferably between 300 μm and 2000 μm. A thickness of 300 μm or more allows for the inclusion of more phosphorescent pigment in the cured material, further improving the overall brightness of the cured material. A thickness of 2000 μm or less allows for post-processing such as lamination of the cured material.

4. Luminescent Plate The luminescent plate according to this embodiment comprises a base material and the cured material formed on the base material.

Examples of the above-mentioned substrates include ABS resin sheets, acrylic resin sheets, aluminum sheets, and polycarbonate sheets, but ABS resin sheets, acrylic resin sheets, and polycarbonate sheets are preferred.

In this embodiment, the phosphorescent plate is preferably overcoated with, for example, a varnish, a laminate film, or an ink. Examples of varnishes include Overlay C (manufactured by Shinloihi Co., Ltd.) and SP-3100AU Clear (manufactured by Teikoku Ink Manufacturing Co., Ltd.). Examples of laminate films include SS50TO(V) (manufactured by Riken Technos Co., Ltd.).

The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to the examples.

1. Preparation of inks 1-29 (Preparation of pigment dispersions)
An ink solvent was prepared by mixing 99.9 parts by mass of photopolymerizable compound A-1 (1,6-hexanediol diacrylate, molecular weight: 242) and 0.01 parts by mass of polymerization inhibitor (Irgastab UV-10, manufactured by BASF), and stirring the mixture while heating it at 70°C for 1 hour.

49 parts by mass of the prepared ink solvent, 50 parts by mass of phosphorescent pigment (G-300FF, manufactured by Nemoto Special Chemicals Co., Ltd., peak wavelength of excitation spectrum: 324 nm), and 1 part by mass of pigment dispersant (EFKA PX 4701, manufactured by BASF) were placed in a polypropylene container along with 50 parts by mass of zirconia beads with an average particle size of 0.3 mm. The mixture was dispersed using a paint shaker for 30 minutes, and the zirconia beads were removed to prepare a pigment dispersion.

The prepared pigment dispersion was diluted with dipropylene glycol diacrylate, and the particle size _d50 of the pigment was measured using a particle size distribution analyzer (LUMiSizer, manufactured by LUM Japan Co., Ltd.). The measured particle size _d50 of the pigment was 3.8 μm.
20 parts by mass of photopolymerizable compound A-1, 35 parts by mass of photopolymerizable compound A-2, and 5 parts by mass of photopolymerization initiator B-1 were thoroughly mixed using a three-roll mixing machine. 40 parts by mass of phosphorescent pigment dispersion were added to the resulting mixture and mixed further to obtain an ink composition. The obtained ink composition was filtered through a 30 μm polypropylene pleated filter (manufactured by Rokitechno Co., Ltd.) to obtain ink 1.

Inks 2 to 25 were obtained in the same manner as ink 1, except that the type and amount of photopolymerizable compound used, the type and amount of photopolymerization initiator, and the amount of phosphorescent pigment were changed as shown in Tables 1 to 5. Note that the numerical values for the ink composition in Tables 1 to 5 represent parts by mass.

Tables 1 to 5 show the types of photopolymerizable compounds and photopolymerization initiators used, as follows. The transmittance values listed for the photopolymerization initiators were measured using the method described below. The measured transmittances are shown in parentheses next to each photopolymerization initiator in Tables 1 to 5.
(Photopolymerizable compound)
A-1: 1,6-Hexanediol diacrylate A-2: Tricyclodecanedimethanol diacrylate A-3: Bisphenol type A 4EO modified diacrylate A-4: 2-Phenoxyethyl acrylate A-5: Polyethylene glycol (200) diacrylate A-6: Dipropylene glycol diacrylate (Photopolymerization initiator)
B-1: Omnirad2959 (manufactured by IGM Resins, intramolecular cleavage type, transmittance: 63%, molecular weight: 224.3)
B-2: Omnirad651 (manufactured by IGM Resins, intramolecular cleavage type, transmittance: 55%, molecular weight: 256.3)
B-3: Esacure One (manufactured by IGM Resins, intramolecular cleavage type, transmittance: 71%, molecular weight: 256.3)
B-4: Omnirad127 (manufactured by IGM Resins, intramolecular cleavage type, transmittance: 71%, molecular weight: 340.7)
B-5: Omnirad184 (manufactured by IGM Resins, intramolecular cleavage type, transmittance: 73%, molecular weight: 204.7)
B-6: Irgacure 500 (BASF, intermolecular hydrogen abstraction type, transmittance: 62%, molecular weight: mixture of 204.3 and 182.2)
B-7: Omnirad MBF (manufactured by IGM Resins, intramolecular hydrogen abstraction type, transmittance: 45%, molecular weight: 161.4)
B-8: Omnirad754 (manufactured by IGM Resins, intramolecular hydrogen abstraction type, transmittance: 46%, molecular weight: 370.36)
B-9: Omnirad819 (manufactured by IGM Resins, intramolecular cleavage type, transmittance: 36%, molecular weight: 418.5)
B-10: Omnirad907 (manufactured by IGM Resins, intramolecular cleavage type, transmittance: 0%, molecular weight: 279.4)
B-11: Omnirad369 (manufactured by IGM Resins, BASF, intramolecular cleavage type, transmittance: 1%, molecular weight: 366.51)
B-12: Omnirad ITX (manufactured by IGM Resins, hydrogen abstraction type, transmittance: 12%, molecular weight: 254.35)

(Measurement of transmittance)
Ink α was prepared by dissolving photopolymerization initiator B-1 in dipropylene glycol diacrylate at a content of 3% by mass. This ink was then applied to a polyimide film using a wire bar to a thickness of 10 μm. The applied ink was irradiated with ultraviolet light at a wavelength of 365 nm, an illuminance of 2.0 W/ ^cm² , and a light intensity of 2000 mJ/ ^cm² using a UV light source (FireJet FJ100, manufactured by Phoneon Inc.) to cure ink α. Next, ink α was applied again to the cured ink α using a wire bar, and the newly applied ink α was irradiated with the same ultraviolet light using the same UV light source. These steps were repeated to produce a cured product with a thickness of 40 μm. Subsequently, the prepared cured product was peeled off the polyimide film. The transmittance of the peeled cured product at the peak wavelength of the excitation spectrum of the phosphorescent pigment at 324 nm was measured using a spectrophotometer (V-650, manufactured by JASCO Corporation). Specifically, the incident angle of the detector stage in the spectrophotometer was set to 90°, and the incident angle of the sample stage was set to 0° for measurement. The transmittance of photopolymerization initiators B-2 to B-12 was measured in the same manner.

2. Formation of cured material by ink Two independent drive heads of a piezo-type inkjet head (KM1024iLHE-30, manufactured by Konica Minolta, Inc., 360 dpi) were arranged with their nozzles staggered to create an inkjet recording head with a nozzle row of 720 dpi. Ink 1 was filled into this head module from an ink tank containing ink 1, via an ink channel.

Next, a voltage was applied to the inkjet recording head so that the droplet ejection volume was 30 pL, and a solid pattern was printed on a 150 mm x 150 mm area of the acrylic resin plate. Then, ultraviolet light with a wavelength of 365 nm and a light intensity of 2000 mJ/ ^cm² was irradiated using a Phoneon FireJet FJ100 to cure the ink.

Further ink was applied to the cured ink under the same conditions, and the applied ink was cured by irradiating it with ultraviolet light under the same conditions. This process was repeated to form a cured material with a thickness of 1000 μm.

The same procedure was performed for inks 2 through 25.

3. Evaluation (Brightness)
The luminance of each cured material was measured according to phosphorescence luminance measurement in accordance with JIS Z9107A:2008. Specifically, printed materials containing cured materials formed using inks 1 to 25 were stored in a dark room for 48 hours or more, and then irradiated with light for 20 minutes at an illuminance of 200 lx using a standard fluorescent lamp D _65. The afterglow luminance 20 minutes after stopping the light irradiation was measured using a luminance meter (LS110, manufactured by Konica Minolta, Inc.). Based on the measured luminance values, luminance evaluation was performed according to the following criteria.
◎: 150 mcd/ ^m² or more ○: 100 mcd/ ^m² or more and less than 150 mcd/ ^m² △: 50 mcd/ ^m² or more and less than 100 mcd/ ^m² ×: Less than 50 mcd/ ^m²

(curability)
The resulting cured material was rubbed with a JK wiper, and its curability was evaluated based on the residue left behind and its feel to the touch.
◎: Leaves no residue and no stickiness on the surface.
○: There is a slight residue, but the surface is not sticky.
△: There are slight traces remaining, and the surface is slightly sticky.
×: Leaves residue and the surface is very sticky.

(water resistance)
The resulting cured material was immersed in water at 25°C for 24 hours, and then its brightness was measured. The brightness measurement was performed using the same method as described above.
◎: 100 mcd/ ^m² or more and less than 150 mcd/ ^m² ○: 50 mcd/ ^m² or more and less than 100 mcd/ ^m² △: Less than 50 mcd/ ^m² ×: Less than 50 mcd/ ^m² and peeling is observed

(weather resistance)
The obtained cured material was subjected to a weathering test in accordance with JIS B 7753:2007. Specifically, using a Sunshine Carbon Arc Lamp Accelerated Weathering Tester (Sunshine Weather Meter S80, manufactured by Suga Test Instruments Co., Ltd.), the cured material was irradiated with light at an irradiance of 255 W/ ^m² in the wavelength range of 300 nm to 700 nm for 102 minutes, followed by 18 minutes of water spraying and irradiation with the same light, and this was repeated for 78 hours. After that, the luminance of the cured material was measured. The luminance measurement was performed in the same manner as described above.
◎◎: 125 mcd/ ^m² or more and less than 150 mcd/ ^m² ◎: 100 mcd/ ^m² or more and less than 125 mcd/ ^m² ○: 50 mcd/ ^m² or more and less than 100 mcd/ ^m² △: Less than 50 mcd/ ^m² ×: Less than 50 mcd/ ^m² and peeling is observed

(Adhesion)
The obtained cured material was cut in a grid pattern according to the JIS K5600 cross-cut method, adhesive tape was applied, and the tape was peeled off. The peeling state of the cured material was observed, the adhesion retention rate was determined, and it was evaluated according to the following criteria. Here, the adhesion retention rate is calculated as the ratio of the number of squares remaining after tape removal to the number of squares created by the cuts.
◎◎: 100% adhesion and residue rate
◎: Adhesion retention rate 95% or more and less than 100% ○: Adhesion retention rate 90% or more and less than 95% △: Adhesion retention rate 70% or more and less than 90% ×: Adhesion retention rate less than 70%

(Yellowing)
The b ^* value of the obtained cured material was measured using a fluorescence spectrometer (FD-7, manufactured by Konica Minolta, Inc.) under the conditions of observation light source D50 and observation field of view 2°. The yellowing of the measured b ^* value was evaluated according to the following criteria.
○: b ^* is less than 5 △: b ^* is 5 or more but less than 10 ×: b ^* is 10 or more

The evaluation results are summarized in Tables 1-5.

In inks 1-18, the brightness of the cured product was higher than that of inks 19-25. This is thought to be because the inks contained a photopolymerization initiator with a transmittance of 40% or more at the peak wavelength of the excitation spectrum of the phosphorescent pigment, making it easier for light of that wavelength to reach the phosphorescent pigment.

In inks 6-8, the use of hydrogen abstraction-type photopolymerization initiators resulted in improved curability and water resistance of the cured products. This is thought to be because the use of hydrogen abstraction-type photopolymerization initiators reduced the impact of oxygen inhibition. In particular, inks 7 and 8, which utilize intramolecular hydrogen abstraction-type photopolymerization initiators, showed further improvements in water resistance and weather resistance.

In inks 9-12, the curing properties are thought to have been further improved by including a photopolymerization initiator with a transmittance of less than 40%. In particular, in ink 9, because the photopolymerization initiator with a transmittance of less than 40% is an acylphosphine oxide-based photopolymerization initiator, yellowing was suppressed more effectively than in inks 10-12.

In inks 13-18, the inclusion of an acrylate with an aromatic ring in the active-ray polymerizable compound resulted in higher brightness of the cured product. This is thought to be because the inclusion of the acrylate with an aromatic ring allowed more light entering the cured product to reach the phosphorescent pigment.

In ink 16, the inclusion of a monofunctional active-ray polymerizable compound is thought to have suppressed curing shrinkage and improved adhesion. Furthermore, in inks 17 and 18, the use of an active-ray polymerizable compound having an alkylene glycol structure improved adhesion, and in particular, ink 18, which used a compound having a propylene glycol structure, is thought to have improved weather resistance.

Claims (14)

Actively polymerizable compounds,
Luminous pigments,
A hydrogen abstraction type photopolymerization initiator is included,
The photopolymerization initiator is formed by curing a 10 μm thick cured product by repeatedly forming the cured product on a 10 μm thick cured product obtained by curing a dipropylene glycol diacrylate solution of the photopolymerization initiator (concentration 3% by mass) with ultraviolet light of 365 nm wavelength at a light intensity of 2000 mJ/ ^cm² under a nitrogen gas atmosphere, and the transmittance of light at the peak wavelength of the excitation spectrum of the phosphorescent pigment is 40% or more.
Active-ray curing ink. The aforementioned photopolymerization initiator includes an intramolecular hydrogen abstraction type photopolymerization initiator.
The activated-ray curing ink according to claim 1 . The photopolymerization initiator further comprises 3% by mass or more and 30% by mass or less of the total mass of the photopolymerization initiator, wherein the transmittance is less than 40%.
The activated-ray curing ink according to claim 1 . The photopolymerization initiator further comprises an acylphosphine oxide-based photopolymerization initiator.
The activated-ray curing ink according to claim 1 . The aforementioned activated linear polymerizable compound includes a compound having an aromatic ring.
The activated-ray curing ink according to claim 1 . The aforementioned activated linear polymerizable compound includes a monofunctional compound.
The activated-ray curing ink according to claim 1 . The aforementioned activated linear polymerizable compound includes a compound having an alkylene glycol structure.
The activated-ray curing ink according to claim 1 . The aforementioned alkylene glycol structure has an alkylene glycol structure with 3 or more carbon atoms.
The activated-ray curing ink according to claim 7 . The content of the phosphorescent pigment is 10% by mass or more and 50% by mass or less, relative to the total mass of the active-ray curable ink.
The activated-ray curing ink according to claim 1 . The peak wavelength of the excitation spectrum of the phosphorescent pigment is between 300 nm and 400 nm.
The activated-ray curing ink according to claim 1 . It is inkjet ink.
Active-ray curable ink according to claim 1 A step of applying the active-ray curable ink described in claim 1 to a substrate,
The process involves irradiating the applied active-ray-curable ink with an active ray,
Having,
Method for forming cured product. A cured product obtained by curing the active-ray curable ink described in claim 1 . A phosphorescent plate having a base material and a cured product according to claim 13 formed on the base material.