Inkjet ink, method for forming cured product, and cured product

Abstract

To provide an active energy ray curable inkjet ink which has excellent re-dispersibility of precipitated inorganic particles and hardly causes injection bending from an inkjet head and deterioration in durability of a member such as an inkjet head and a flow channel.SOLUTION: There is provided an active energy ray curable inkjet ink which has a polymerizable compound, inorganic particles, and silica particles. The silica particles are subjected to a hydrophobization treatment and have no polymerizable group. The average particle diameter of the silica particles is smaller than the median diameter of the inorganic particles and the mass-based content of the silica particles is smaller than the mass-based content of the inorganic particles.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet ink, a method for forming a cured product, and a cured product. [Background technology]

[0002] Inkjet inks containing inorganic particles such as titanium oxide as a white pigment and conductive particles are known. However, inorganic particles tend to settle in the ink during storage or while waiting before ejection, and once settled, they are difficult to redisperse.

[0003] To solve this problem, the ink composition for inkjet recording described in Patent Document 1 uses silica particles having silanol groups on their surfaces in combination with an inorganic pigment in an aqueous ink containing water and an organic solvent as the solvent.

[0004] In addition, the actinic radiation-curable inkjet ink described in Patent Document 2, which also contains silica particles, uses silica particles whose surfaces are modified with a (meth)acrylate compound in order to prevent sedimentation due to aggregation of the silica particles. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-181055 [Patent Document 2] Japanese Patent Application Publication No. 2019-157062 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 describes that silica particles can facilitate redispersion of settled inorganic pigments. However, according to the findings of the present inventors, in an actinic ray-curable inkjet ink containing a polymerizable compound, even if silica particles similar to those in Patent Document 1 are used, the settled inorganic pigments do not become easily redispersible. Furthermore, even if silica particles whose surfaces are modified with a (meth)acrylate compound as described in Patent Document 2 are used, the settled inorganic pigments do not become easily redispersible in an actinic ray-curable inkjet ink.

[0007] Furthermore, according to another finding of the present inventors, the active energy ray-curable inkjet inks to which silica particles similar to those disclosed in Patent Documents 1 and 2 have been added have also had problems such as the ink being easily deflected when ejected from the inkjet head and the durability of components such as the inkjet head and flow path being easily reduced.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an actinic ray-curable inkjet ink that has excellent re-dispersibility of settled inorganic particles and is less likely to cause deflection when ejected from an inkjet head or to reduce the durability of components such as the inkjet head and flow channels; a method for forming a cured product using the inkjet ink; and a cured product formed by the method. [Means for solving the problem]

[0009] One aspect of the present invention for solving the above problems relates to the actinic energy ray-curable inkjet inks described below in [1] to

[10] . [1] A composition comprising a polymerizable compound, inorganic particles, and silica particles, the silica particles have been subjected to a hydrophobic treatment and have no polymerizable group; the average particle size of the silica particles is smaller than the median particle size of the inorganic particles, The content of the silica particles by mass is less than the content of the inorganic particles by mass. Active energy ray curable inkjet ink. [2] The polymerizable compound contains a (meth)acrylate. [1] The inkjet ink according to [1]. [3] The (meth)acrylate contains a monofunctional polymerizable compound having an aromatic ring. [2] The inkjet ink according to [2]. [4] Substantially free of water and substantially free of organic solvents; The inkjet ink according to any one of [1] to [3]. [5] The average particle size of the silica particles is 1 / 20 or less of the median size of the inorganic particles. The inkjet ink according to any one of [1] to [4]. [6] The content of the silica particles is 0.01% by mass or more and 5% by mass or less relative to the total mass of the inkjet ink. The inkjet ink according to any one of [1] to [5]. [7] The average particle size of the inorganic particles is 0.5 μm or more and 5 μm or less. The inkjet ink according to any one of [1] to [6]. [8] D of the inorganic particles 50 / D 90 is between 0.1 and 0.9, The inkjet ink according to any one of [1] to [7]. [9] The inorganic particles are phosphorescent pigments. The inkjet ink according to any one of [1] to [8].

[10] Including a heat curing agent, The inkjet ink according to any one of [1] to [9].

[0010] Another aspect of the present invention for solving the above problems relates to the following methods for forming a cured product

[11] to

[12] .

[11] A step of applying the inkjet ink according to any one of [1] to

[10] to a substrate; irradiating the applied inkjet ink with actinic energy rays; A method for forming a cured product comprising the steps of:

[12] The step of applying the inkjet ink to the substrate is performed while circulating the inkjet ink.

[11] The method for forming a cured product according to

[11] .

[0011] Another aspect of the present invention for solving the above problems relates to a cured product according to the following item

[13] .

[13] A cured product formed from the inkjet ink according to any one of [1] to

[10] . [Effects of the Invention]

[0012] According to the present invention, there are provided an actinic ray-curable inkjet ink that has excellent re-dispersibility of settled inorganic particles and is less likely to cause deflection when ejected from an inkjet head or to reduce the durability of components such as the inkjet head and flow path, a method for forming a cured product using the inkjet ink, and a cured product formed by the method. DETAILED DESCRIPTION OF THE INVENTION

[0013] 1. Inkjet ink One embodiment of the present invention relates to an actinic radiation-curable inkjet ink (hereinafter simply referred to as "ink"), which contains a polymerizable compound, inorganic particles, and hydrophobically treated silica particles.

[0014] In the ink according to this embodiment, silica particles, which are smaller than inorganic pigment particles, are believed to be adsorbed to the surface of the inorganic pigment. By adsorbing to the surface of the inorganic pigment, the silica particles suppress packing of the settled inorganic particles and aggregation of the inorganic particles. This is thought to make it easier for the silica particles to redisperse the settled inorganic particles.

[0015] The ink according to this embodiment is an actinic energy beam-curable ink containing a polymerizable compound. The hydrophobized silica particles contained in the ink are easily wetted by the polymerizable compound, which is a liquid component. Therefore, the silica particles are well dispersed in the ink according to this embodiment. Because this well-dispersed silica is well adsorbed to the inorganic particles, the ink according to this embodiment is thought to facilitate the redispersion of settled inorganic particles. The silica particles described in Patent Document 1 are hydrophilized. Such silica particles do not have good wettability with the polymerizable compound. Therefore, the silica particles described in Patent Document 1 are thought to be poorly adsorbed to inorganic particles, making it difficult to improve the redispersibility of settled inorganic particles.

[0016] Furthermore, the ink according to this embodiment contains silica particles that do not have a polymerizable group. In the silica particles described in Patent Document 2, whose surfaces are modified with a (meth)acrylate compound, the (meth)acryloyl groups on the surfaces undergo a polymerization reaction during storage, flow, or when the ink is heated inside the inkjet head. This polymerization reaction causes the silica particles to aggregate with each other and easily detach from the surfaces of the inorganic particles. Therefore, it is believed that the silica particles make it difficult to improve the redispersibility of the settled inorganic particles.

[0017] If the settled inorganic particles cannot be redispersed, the concentration of the inorganic particles in the ejected inkjet ink is likely to fluctuate, or the viscosity of the inkjet ink may fluctuate, resulting in unstable ejection. Furthermore, when the inkjet ink is circulated in the ink flow path or inkjet head before ejection, the circulation of the inkjet ink may be difficult to stabilize. In this embodiment, silica particles make it easy to redisperse settled inorganic particles, thereby making these problems less likely to occur.

[0018] Furthermore, inorganic particles typically have high hardness. High-hardness inorganic particles that aggregate in the ink may come into contact with components of the inkjet head or ink flow path, causing deterioration of these components. Furthermore, aggregated inorganic particles may adhere to the nozzle surface, peeling off the water-repellent film on the nozzle plate ejection surface or scraping and deforming the nozzle opening, resulting in ink deflection or ejection failure. In contrast, in this embodiment, silica particles that are well wetted with the polymerizable compound are well adsorbed to the inorganic particles, suppressing aggregation of the inorganic particles. Furthermore, the silica particles used in this embodiment are unlikely to detach from the surface of the inorganic pigment, even when the ink is heated inside the inkjet head during storage or flow, and are therefore unlikely to cause aggregation of the inorganic particles. Therefore, the ink according to this embodiment is unlikely to reduce the durability of components such as the inkjet head, or reduce the ink ejection performance.

[0019] Each component will be described below.

[0020] 1-1. Polymerizable compounds The polymerizable compound is a compound that polymerizes and crosslinks when irradiated with active energy rays.

[0021] The polymerizable compound can be a monomer, an oligomer, a polymer, and mixtures thereof.

[0022] The polymerizable compound may be a monofunctional compound or a polyfunctional compound. When it is desired to make the cured product flexible, it is preferable to contain a monofunctional compound, and when it is desired to increase the hardness of the cured product, it is preferable to contain a polyfunctional compound. In addition, from the viewpoint of balancing these, the polymerizable compound may contain both a monofunctional compound and a polyfunctional compound.

[0023] The polymerizable compound may be a radically polymerizable compound or a cationically polymerizable compound, or a combination of a radically polymerizable compound and a cationically polymerizable compound may be used.

[0024] The radically polymerizable compound is a compound having an ethylenically unsaturated bond capable of radical polymerization.

[0025] Examples of the compound having a radically polymerizable ethylenically unsaturated bond 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.

[0026] Among these, the radical polymerizable compound is preferably an unsaturated carboxylic acid ester compound, and more preferably a (meth)acrylate. (Meth)acrylate itself has high thermal stability, so it can also improve the thermal stability of the ink. Therefore, ink containing (meth)acrylate has high thermal stability inside an inkjet head and is less likely to cause ejection deflection. The (meth)acrylate may be a monomer or oligomer, as described below, or may be a mixture of a monomer and an oligomer, a modified product, an oligomer having a polymerizable functional group, or the like.

[0027] In this specification, (meth)acrylate refers to acrylate or methacrylate, (meth)acryloyl refers to acryloyl or methacryloyl, and (meth)acrylic refers to acrylic or methacrylic.

[0028] Examples of monofunctional (meth)acrylates include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomylstyryl (meth)acrylate, isostearyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, o-phenylphenoxyethyl (meth)acrylate, benzyl (meth)acrylate, phenol (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-phenylphenolpropyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalate, and t-butylcyclohexyl (meth)acrylate.

[0029] 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 di(meth)acrylate, and hydroxypivalin. Examples of the (meth)acrylates include difunctional (meth)acrylates such as neopentyl glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate, and tripropylene glycol diacrylate, as well as trifunctional or higher (meth)acrylates such as 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 ethoxy tetra(meth)acrylate.

[0030] The (meth)acrylate may be a modified product. Examples of modified (meth)acrylates 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.

[0031] The (meth)acrylate may be a polymerizable oligomer. Examples of the (meth)acrylate that is a polymerizable oligomer include an epoxy (meth)acrylate oligomer, an aliphatic urethane (meth)acrylate oligomer, an aromatic urethane (meth)acrylate oligomer, a polyester (meth)acrylate oligomer, and a linear (meth)acrylic oligomer.

[0032] Examples of the cationically polymerizable compound include an epoxy compound, a vinyl ether compound, and an oxetane compound.

[0033] Examples of epoxy compounds include alicyclic epoxy resins such as 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, diglycidyl ether of neopentyl glycol, diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, triglycidyl ether of glycerin, triglycidyl ether of trimethylolpropane, and diglycidyl ether of ethylene glycol. Examples of the epoxy compounds include aliphatic epoxy compounds such as glycidyl ethers, diglycidyl ethers of diethylene glycol, diglycidyl ethers of triethylene glycol, diglycidyl ethers of propylene glycol, diglycidyl ethers of polyethylene glycol, diglycidyl ethers of propylene glycol, polyglycidyl ethers of polyether polyols obtained by adding one or more alkylene oxides (such as ethylene oxide and propylene oxide) to an aliphatic polyhydric alcohol such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and glycerin, as well as aromatic epoxy compounds such as di- or polyglycidyl ethers of bisphenol A or an alkylene oxide adduct thereof, di- or polyglycidyl ethers of hydrogenated bisphenol A or an alkylene oxide adduct thereof, and novolac-type epoxy resins.

[0034] Examples of the vinyl ether compound 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.

[0035] Examples of the oxetane compound 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-hydroxyethyl-3-methyloxetane, 3-hydroxyethyl-3-ethyloxetane, 3-hydroxyethyl-3-propyloxetane, 3-hydroxyethyl-3-phenyloxetane, 3-hydroxyethyl-3-phenyloxetane, hydroxypropyl-3-methyloxetane, 3-hydroxypropyl-3-ethyloxetane, 3-hydroxypropyl-3-propyloxetane, 3-hydroxypropyl-3-phenyloxetane, 3-hydroxybutyl-3-methyloxetane, 3,3'-(oxybismethylene)bis(3-ethyloxetane), 1,4-bis{[(3-ethyl-3-oxetanyl)methoxy]methyl}benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, and di[1-ethyl(3-oxetanyl)]methyl ether.

[0036] The polymerizable compound preferably contains a compound having an aromatic ring in the molecule. Aromatic rings are structurally stable and therefore less susceptible to hydrogen abstraction. Therefore, polymerizable compounds having an aromatic ring in the molecule are less likely to cause yellowing of the cured product due to hydrogen abstraction reactions caused by the large amount of radicals generated during curing of the ink. Furthermore, the compound having an aromatic ring in the molecule is preferably a monofunctional polymerizable compound. Polymerizable compounds having an aromatic ring at the end have high wettability to inorganic particles, making it easier to redisperse settled inorganic particles.

[0037] The content of the polymerizable compound having an aromatic ring is preferably 10% by mass or more and 80% by mass or less, and more preferably 20% by mass or more and 70% by mass or less, based on the total mass of the ink.

[0038] Examples of the polymerizable compound having an aromatic ring include phenol 4EO-modified (meth)acrylate, 2-phenoxyethyl (meth)acrylate, o-phenylphenoxyethyl (meth)acrylate, benzyl (meth)acrylate, phenol (meth)acrylate, m-phenoxybenzyl (meth)acrylate, alkoxylated phenol (meth)acrylate, 2-hydroxy-o-phenylphenolpropyl (meth)acrylate, EO-modified o-phenylphenol (meth)acrylate, bisphenol fluorene di(meth)acrylate (A-BPEF), bisphenol A type 10EO-modified di(meth)acrylate, bisphenol A type di(meth)acrylate, bisphenol A type PO-modified di(meth)acrylate, bisphenol A type EO-modified di(meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. Of these, phenol 4EO-modified (meth)acrylate, 2-phenoxyethyl (meth)acrylate, o-phenylphenoxyethyl (meth)acrylate, benzyl (meth)acrylate, phenol (meth)acrylate, m-phenoxybenzyl (meth)acrylate, alkoxylated phenol (meth)acrylate, 2-hydroxy-o-phenylphenolpropyl (meth)acrylate, EO-modified o-phenylphenol (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate are preferred.

[0039] The content of the polymerizable compound is preferably from 30% to 97% by mass, and more preferably from 60% to 95% by mass, relative to the total mass of the ink. The content of the monofunctional polymerizable compound having an aromatic ring is preferably from 10% to 60% by mass, and more preferably from 20% to 50% by mass, relative to the total mass of the ink.

[0040] 1-2.Inorganic particles The type of inorganic particles is not particularly limited. The inorganic particles may be pigment particles that impart characteristics such as color tone, electrical conductivity, electrical insulation, heat dissipation, or a negative thermal expansion coefficient to a cured product formed from the ink, or may be particles that are added separately from the pigment to adjust the physical properties of the cured product.

[0041] The inorganic particles may be particles containing atoms other than carbon as the main component, which means that atoms other than carbon account for 50 mass % or more of the total mass of the inorganic particles.

[0042] Examples of inorganic particles include: Silica particles, Metal oxide particles such as titanium oxide particles, alumina particles, zirconia particles, zinc oxide particles, and iron oxide particles Metal hydroxide particles such as magnesium hydroxide particles, aluminum hydroxide particles, and calcium hydroxide particles Nitride particles such as silicon nitride particles, titanium nitride particles, and aluminum nitride particles Luster pigment particles such as silver particles (or conductive particles), Glass particles such as glass beads and glass flakes; silicate particles, such as magnesium silicate particles; Kaolin particles, calcined kaolin particles, ceramic particles such as clay, talc, and zeolite, Particles made of composite materials such as pearl pigment particles, and Phosphorescent pigment particles that can absorb light of a specific wavelength, store the light energy, and emit the stored light energy over a long period of time as light of a different wavelength than the absorbed light. These include:

[0043] Examples of phosphorescent pigments include those in which the host crystal of a metal compound has been activated.

[0044] Examples of the host crystal 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, etc. Of these, strontium aluminate (SrAl2O4:Eu,Dy) is preferred.

[0045] Examples of the activator used to activate the mother crystal include europium, terbium, yttrium, zirconium, dysprosium, and barium, among which europium and dysprosium are preferred.

[0046] The peak wavelength of the excitation spectrum of the phosphorescent pigment is preferably 300 nm or more and 400 nm or less. When the peak wavelength of the excitation spectrum of the phosphorescent pigment is in this range, the phosphorescent pigment can be sufficiently excited by sunlight, making the cured product more suitable for outdoor use.

[0047] The peak wavelength of the emission spectrum of the phosphorescent pigment can be, for example, from 400 nm to 700 nm, and from the viewpoint of further enhancing the visibility of the cured product, it is preferably from 450 nm to 600 nm.

[0048] Of these inorganic particles, glittering pigment particles, zinc oxide particles, and phosphorescent pigment particles are preferred, with zinc oxide particles, pearl pigment particles, and phosphorescent pigment particles being even more preferred, as silica particles are easily adsorbed and tend to improve redispersibility after settling.

[0049] The shape of the inorganic particles is not particularly limited, and may be spherical or non-spherical, such as flat or whisker-like. Of these, spherical is preferred because it is more likely to enhance the effect of improving redispersibility after sedimentation of silica particles. For example, the inorganic particles preferably have an aspect ratio, which is the ratio of the major axis to the minor axis, of 1.0 to 1.5, more preferably 1.0 to 1.2.

[0050] The long diameter and short diameter of the inorganic particles can be the average long diameter and the average short diameter in an image of 1,000 inorganic particles arbitrarily selected from the inorganic particles in the ink captured in an image taken with a transmission electron microscope (TEM) or a scanning electron microscope (SEM), respectively.

[0051] The median diameter of the inorganic particles in the ink is not particularly limited and can be 0.2 μm to 20 μm, preferably 0.3 μm to 10 μm, more preferably 0.5 μm to 5 μm, and even more preferably 1.0 μm to 5 μm. The larger the median diameter, the easier it is to increase the amount of silica particles adsorbed to the inorganic particles, and the easier it is to improve the redispersibility of the silica particles after settling. Furthermore, the larger the median diameter, the less likely the settled inorganic particles are to pack together and the easier it is to redisperse them. The smaller the median diameter, the better the ejection performance from the inkjet head, and even if they aggregate, the less likely they are to damage components such as the inkjet head.

[0052] The median diameter of inorganic particles is the particle size at which the cumulative value in the volume-based particle size distribution reaches 50% (D 50 ) can be used.

[0053] The particle size at which the cumulative value of the volume-based particle size distribution of inorganic particles in ink is 90% (D 90 ) can be 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. This makes it easy to increase the amount of silica particles adsorbed to the inorganic particles, and the silica particles make it easy to improve redispersibility after settling. In addition, D 90 The larger the value, the less the settled inorganic particles are packed together and the easier it is to redisperse. 90 The smaller the value, the better the ejection properties from the inkjet head, and even if the ink aggregates, it is less likely to damage components such as the inkjet head.

[0054] In addition, inorganic particles are 50 / D90 is preferably 0.2 or more and 0.8 or less, and more preferably 0.3 or more and 0.6 or less. 50 / D 90 The smaller the ρ is, the broader the particle size distribution can be, and the more densely packed the inorganic particles can be in a cured product, which can improve the weather resistance of the cured product.

[0055] In addition, the D of inorganic particles 50 and D 90 can be a value measured using a particle size measuring device, for example, LUMiSizer, manufactured by LUM Japan Co., Ltd.

[0056] The specific gravity of the inorganic particles can be from 2 to 6, preferably from 2.5 to 5, and more preferably from 3 to 4.5. The greater the specific gravity, the easier the inorganic particles will settle in the ink, and the silica particles will have a significant effect in improving redispersibility after settling.

[0057] The inorganic particles may be dispersed using a dispersant. The inorganic particles may be dispersed using only one type of dispersant, or may be dispersed using two or more types of dispersants.

[0058] Examples of dispersants include carboxylic acid esters having a hydroxy group, 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, naphthalenesulfonic acid-formaldehyde condensate salts, aromatic sulfonic acid-formaldehyde condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate. Commercially available pigment dispersants include the Solsperse series (manufactured by Avecia, "Solsperse" is a registered trademark of the company), the PB series (manufactured by Ajinomoto Fine-Techno Co., Ltd.), and the EFKA series (manufactured by BASF, "EFKA" is a registered trademark of the company).

[0059] The content of the dispersant is preferably 0.01% by mass or more and 20% by mass or less with respect to the total mass of the inorganic particles.

[0060] The content of inorganic particles can be set depending on the application of the inorganic particles. For example, the content of inorganic particles can be 1% by mass or more and 60% by mass or less, preferably 2% by mass or more and 50% by mass or less, and more preferably 3% by mass or more and 30% by mass or less, based on the total mass of the ink. The lower the content of inorganic particles, the higher the redispersibility of settled inorganic particles.

[0061] 1-3. Silica particles Silica particles are particles whose average particle size is smaller than the median size of inorganic particles. Silica particles, which are smaller than inorganic particles, are more likely to adsorb to the surfaces of inorganic particles and inhibit packing and aggregation of the inorganic particles. This is thought to facilitate the redispersion of settled inorganic particles. For the same reason, silica particles are thought to inhibit deterioration in the durability of components such as inkjet heads and the ink jetting performance when inks containing inorganic pigments are used.

[0062] The silica particles may be particles composed of silicon dioxide (SiO2), or may be particles containing silicon dioxide as a main component and other substances. The silica particles may also be core-shell particles containing a core and a shell containing silicon dioxide. Incidentally, "containing silicon dioxide as a main component" means that silicon dioxide accounts for 50 mass% or more of the total mass of the particles. From the viewpoint of improving the redispersibility and circulation stability of settled inorganic particles, the silica particles are preferably particles composed only of silicon dioxide. The silica particles may be natural or synthetic, but synthetic particles are preferred because the average particle diameter and particle size distribution can be easily adjusted.

[0063] The synthetic silica particles may be silica particles produced by a dry process or a wet process. Examples of silica particles produced by a dry process include combustion silica particles produced by a combustion process and deflagration silica particles produced by a deflagration process. Examples of silica particles produced by a wet process include precipitated silica particles produced by a precipitation process, silica gel produced by a gel process, colloidal silica, and sol-gel silica. Among these, combustion silica, deflagration silica, and sol-gel silica are preferred due to their high adsorption to inorganic particles, and sol-gel silica is more preferred.

[0064] The silica particles are hydrophobized. The hydrophobized silica particles are easily wetted by the polymerizable compound and easily disperse in the ink. Therefore, the hydrophobized silica particles are easily adsorbed to the inorganic surface in the ink, which increases the redispersibility of the settled inorganic particles and easily suppresses deterioration in the durability and ejection property of the component.

[0065] The method of hydrophobic treatment is not particularly limited, and treatment with a silane coupling agent having a hydrophobic group (such as an alkyl group), a titanium coupling agent having a hydrophobic group (such as an alkyl group), polysiloxane, disilazane, silicone oil, long-chain fatty acid, or the like may be used. The hydrophobic treatment may be carried out using, for example, chlorosilanes including thyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, t-butyldimethylchlorosilane, and vinyltrichlorosilane, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, n-butyltrimethoxysilane, i-butyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, i-butyltriethoxysilane, decyltriethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, Alkoxysilanes including propyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, and γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, polysiloxanes including silane, decamethylcyclopentasiloxane, hexamethyldisiloxane, octamethyltrisiloxane, and the like; disilazanes including hexamethyldisilazane, hexaethyldisilazane, hexapropyldisilazane, hexabutyldisilazane, hexapentyldisilazane, hexahexyldisilazane, hexacyclohexyldisilazane, hexaphenyldisilazane, divinyltetramethyldisilazane, and dimethyltetravinyldisilazane, and the like; dimethyl silicone oils;Silicone oils including methyl hydrogen silicone oil, methyl phenyl silicone oil, alkyl-modified silicone oil, chloroalkyl-modified silicone oil, chlorophenyl-modified silicone oil, fatty acid-modified silicone oil, polyether-modified silicone oil, alkoxy-modified silicone oil, carbinol-modified silicone oil, amino-modified silicone oil, fluorine-modified silicone oil, and terminally reactive silicone oil, as well as long-chain fatty acids such as undecylic acid, lauric acid, tridecylic acid, dodecylic acid, myristic acid, palmitic acid, pentadecylic acid, stearic acid, heptadecylic acid, arachidic acid, montanic acid, oleic acid, linoleic acid, and arachidonic acid, or salts thereof, can be used.

[0066] In this specification, the hydrophobic treatment does not include treatments that involve polymerizable groups. Examples of polymerizable groups include epoxy groups, (meth)acryloyl groups, and vinyl groups. Hydroxyl groups and silanol groups do not react with polymerizable compounds, so they are not included in the polymerizable groups.

[0067] The hydrophobicity of the hydrophobic treated silica particles is preferably 30% or more and 80% or less, and more preferably 50% or more and 75% or less.

[0068] The hydrophobicity of the silica particles is determined by adding 0.2 mass % of silica particles to 50 ml of ion-exchanged water, adding methanol dropwise from a burette while stirring with a magnetic stirrer, and measuring the mass fraction of methanol in the methanol-water mixed solution at the end point when all of the silica particles have sunk.

[0069] The average particle size of the silica particles is preferably 1 / 2 or less of the median diameter of the inorganic particles, more preferably 1 / 10 or less, even more preferably 1 / 20 or less, and particularly preferably 1 / 50 or less. The smaller the ratio of the average particle size of the silica particles to the median diameter of the inorganic particles, the easier it is for the silica particles to be adsorbed onto the surface of the inorganic particles. In particular, by making the average particle size of the silica particles 1 / 20 or less of the median diameter of the inorganic particles, the ratio of the specific surface area of ​​the silica particles to the surface area of ​​the inorganic particles can be increased, making it easier for the silica particles to be adsorbed onto the surface of the inorganic particles. The lower limit of the ratio of the average particle size of the silica particles to the median diameter of the inorganic particles is not particularly limited, but it is preferably 1 / 500 or more.

[0070] The average particle size of the silica particles is preferably 0.005 μm or more and 1.5 μm or less, more preferably 0.01 μm or more and 1.0 μm or less, and even more preferably 0.05 μm or more and 0.5 μm or less. The smaller the average particle size of the silica particles, the higher the redispersibility of the settled inorganic particles. Increasing the average particle size of the silica particles to a certain extent reduces the specific surface area of ​​the inorganic particles to which the silica particles adhere, making it less likely that the inorganic particles will scratch the nozzle surface.

[0071] The average particle size of silica particles can be determined using the manufacturer's published value. Alternatively, the volume average diameter can be measured using a particle size analyzer and dynamic light scattering. For example, a slurry containing silica particles is diluted with ion-exchanged water to a silica particle content of 0.1% by mass. The diluted slurry is irradiated with laser light, and the intensity of the scattered light from the inorganic silica particles is measured over time in microseconds. The scattering intensity distribution due to the detected silica particles is fitted to a normal distribution, and the Z-average particle size of the silica particles is determined using cumulant analysis. A particle size analyzer such as the Zetasizer Nano ZS manufactured by Spectris can be used. The particle size analyzer is equipped with data analysis software, which automatically analyzes the measurement data to calculate the Z-average particle size.

[0072] The shape of the silica particles is preferably spherical.For example, the aspect ratio of the silica particles, which is the ratio of the major axis to the minor axis, is preferably 1.0 or more and 1.5 or less, more preferably 1.0 or more and 1.2 or less.The major axis and minor axis of the silica particles can be measured in the same way as the major axis and minor axis of the inorganic particles described above.

[0073] The content of silica particles can be 0.01% to 5% by mass, preferably 0.01% to 3% by mass, more preferably 0.01% to 2% by mass, and even more preferably 0.01% to 1.5% by mass, based on the total mass of the ink. A silica particle content of 0.01% by mass or more enhances the redispersibility of settled inorganic particles. A silica particle content of 5% by mass or less suppresses degradation of ejection performance due to silica particles not adsorbed to the inorganic particles, as well as damage to components such as inkjet heads.

[0074] Furthermore, the ratio of the silica particle content to the inorganic particle content (silica particle content (by mass) / inorganic particle content (by mass)) is preferably 0.0004 or more and 0.3 or less, more preferably 0.004 or more and 0.2 or less, and even more preferably 0.01 or more and 0.1 or less.

[0075] 1-3.Other ingredients The ink may further contain other ingredients such as photopolymerization initiators, organic pigments, dyes, thermal curing agents, surfactants, optical brighteners, gelling agents, and polymerization inhibitors.

[0076] The photopolymerization initiator can be a radical initiator when the ink contains a radically polymerizable compound, or a cationic initiator (photoacid generator) when the ink contains a cationic polymerizable compound. Note that when polymerization is initiated by irradiation with an electron beam, the ink does not need to contain a photopolymerization initiator.

[0077] Examples of radical polymerization initiators include hydrogen abstraction type photopolymerization initiators, intramolecular cleavage type photopolymerization initiators, etc. Hydrogen abstraction type photopolymerization initiators include intramolecular hydrogen abstraction type photopolymerization initiators, intermolecular hydrogen abstraction type photopolymerization initiators, etc.

[0078] An intramolecular hydrogen abstraction photopolymerization initiator is a photopolymerization initiator that is excited by irradiation with active energy rays and undergoes an intramolecular hydrogen abstraction reaction to generate radicals. Examples of intramolecular hydrogen abstraction photopolymerization initiators include methyl benzoylformate-based photopolymerization initiators such as methyl phenylglyoxylate, and oxyphenyl-based photopolymerization initiators such as a mixture of oxyphenylacetic acid-2-[2-oxo-2-phenylacetoxy-ethoxy]ethyl ester and oxyphenylacetic acid 2-[2-hydroxy-ethoxy]ethyl ester. Among these, compounds having a glyoxylic acid structure such as methyl benzoylformate-based photopolymerization initiators are preferred because they are less likely to abstract hydrogen from the molecular chain of the polymerizable compound during polymerization.

[0079] Examples of commercially available intramolecular hydrogen abstraction photopolymerization initiators include Omnirad MBF and Omnirad 754 (both manufactured by IGM Resins, and "Omnirad" is a registered trademark of the company).

[0080] Intermolecular hydrogen abstraction photopolymerization initiators are photopolymerization initiators that are excited by irradiation with active energy rays such as ultraviolet rays and abstract hydrogen from other molecules to generate radicals. Examples of intermolecular hydrogen abstraction photopolymerization initiators include benzophenone-based initiators such as benzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylated 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.

[0081] Commercially available examples of intermolecular hydrogen abstraction photopolymerization initiators include Omnirad 500 (manufactured by IGM Resins) and Speedcure ITX (manufactured by Sartomer, "Speedcure" is a registered trademark of Arkema France).

[0082] Examples of the intramolecular cleavage type photopolymerization initiator include acetophenone-based initiators such as 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzil dimethyl 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.

[0083] Commercially available examples of intramolecular cleavage type photopolymerization initiators include Omnirad 127, Omnirad 184, Omnirad 651, Omnirad 2959, Omnirad 819, and Esacure One (all manufactured by IGM Resins).

[0084] The content of the photopolymerization initiator is preferably 3% by mass or more and 20% by mass or less, 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, based on the total mass of the polymerizable material. By making the content 3% by mass or more, the curability and adhesion of the ink can be further improved.

[0085] Examples of organic pigments include red pigments, yellow pigments, blue pigments, white pigments, etc., which are used in inks for forming images. Known pigments can be used for these pigments. Examples of dyes include red dyes, yellow dyes, blue dyes, etc., which are used in inks for forming images. Known dyes can be used for these dyes.

[0086] Examples of the thermal curing agent include polyfunctional epoxy compounds, polyfunctional oxetane compounds, imidazole derivatives such as imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 4-phenylimidazole, 1-cyanoethyl-2-phenylimidazole, and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, amine compounds such as dicyandiamide, benzyldimethylamine, 4-(dimethylamino)-N,N-dimethylbenzylamine, 4-methoxy-N,N-dimethylbenzylamine, and 4-methyl-N,N-dimethylbenzylamine, phosphine compounds such as tributylphosphine and triphenylphosphine, and adipic acid dihydrazide and sebacic acid dihydrazide. These include hydrazine compounds, melamine resins, benzoguanamine resins, melamine derivatives, amino resins such as benzoguanamine derivatives, blocked isocyanate compounds, cyclocarbonate compounds, cyclic (thio)ether compounds, bismaleimides, carbodiimide resins, aromatic amines, reaction products of amine compounds and epoxy compounds, as well as acid anhydrides such as phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, 3-chlorophthalic anhydride, 4-chlorophthalic anhydride, benzophenonetetracarboxylic anhydride, succinic anhydride, methylsuccinic anhydride, dimethylsuccinic anhydride, dichlorosuccinic anhydride, methylnadic acid, dodecylsuccinic acid, chlorendec anhydride, and maleic anhydride.

[0087] When a heat curing agent is used, a curing catalyst may be used in combination. Examples of the curing catalyst include imidazole derivatives, guanamines, polyamines, their organic acid salts, epoxy adducts, triazine derivatives, tertiary amines, organic phosphines, phosphonium salts, and quaternary ammonium salts.

[0088] The content of the heat curing agent is not particularly limited, but can be, for example, 0.1% by mass or more and 10% by mass or less relative to the total mass of the ink.

[0089] When the ink contains a heat curing agent, it is preferable that the ink also contains, as a polymerizable compound, a compound having a functional group that reacts with the heat curing agent, such as an epoxy group, an oxetane group, or a carboxyl group. On the other hand, even if the polymerizable compound does not contain a functional group that reacts with the heat curing agent, the exothermic reaction of the heat curing agent can promote polymerization of the polymerizable compound.

[0090] Examples of surfactants include anionic surfactants such as dialkyl sulfosuccinates, alkyl naphthalene 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.

[0091] The content of the surfactant is not particularly limited, but 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.

[0092] A gelling agent is a compound that causes ink to gel at room temperature (25°C) and to sol when heated (e.g., 80°C). For example, the gelling agent is preferably a compound that dissolves in the liquid components (such as polymerizable compounds and organic solvents) contained in the ink at a temperature higher than the gelation temperature of the ink and crystallizes at a temperature lower than the gelation temperature of the ink. The gelation temperature refers to the temperature at which the ink undergoes a phase transition from sol to gel and the viscosity of the ink suddenly changes when the ink, which has been solated or liquefied by heating, is cooled. Specifically, the temperature at which the viscosity suddenly increases when the ink is cooled while measuring the viscosity with a rheometer (e.g., MCR300 manufactured by Anton Paar), can be determined as the gelation temperature of the ink.

[0093] Examples of gelling agents include ketone waxes, ester waxes, petroleum waxes, vegetable waxes, animal waxes, mineral waxes, hydrogenated 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 acid and dimer diol.

[0094] The content of the gelling agent is preferably 1.0% by mass or more and 10.0% by mass or less, more preferably 2.0% by mass or more and 7.5% by mass or less, and even more preferably 2.0% by mass or more and 3.5% by mass or less, relative to the total mass of the ink.

[0095] Examples of the polymerization inhibitor include N-oxyl-based polymerization inhibitors, phenol-based polymerization inhibitors, quinone-based polymerization inhibitors, amine-based polymerization inhibitors, copper dithiocarbamate-based polymerization inhibitors, etc. The ink may contain only one type of polymerization inhibitor, or two or more types of polymerization inhibitors in combination.

[0096] Examples of N-oxyl polymerization inhibitors include 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-oxo-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-methoxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-acetoxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, etc. An example of a commercially available N-oxyl polymerization inhibitor is Irgastab UV10 (manufactured by BASF ("Irgastab" is a registered trademark of the company)).

[0097] Examples of the phenolic polymerization inhibitor 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.

[0098] Examples of the quinone polymerization inhibitor include hydroquinone, methoxyhydroquinone, benzoquinone, 1,4-naphthoquinone, p-tert-butylcatechol, and the like.

[0099] Examples of the amine polymerization inhibitor include alkylated diphenylamine, N,N'-diphenyl-p-phenylenediamine, phenothiazine, and the like.

[0100] Examples of copper dithiocarbamate polymerization inhibitors include copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dibutyldithiocarbamate, and the like.

[0101] The content of the polymerization inhibitor is not particularly limited, but 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.

[0102] The ink may contain a solvent other than the polymerizable compound, such as water or an organic solvent.

[0103] Examples of organic solvents include aliphatic alcohols, aromatic alcohols, diols, triols, glycol ethers, poly(glycol) ethers, lactams, formamides, acetamides, long-chain alcohols, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, glycerin, dipropylene glycol, glycol butyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol dibutyl ether, dipropylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol, polypropylene glycol, methyl oleate, methyl caprylate, methyl caprate, and methyl laurate. , methyl myristate, methyl palmitate, methyl stearate, methyl oleate, methyl tallowate, methyl rice bran fatty acid, methyl rapeseed fatty acid, methyl soybean fatty acid, n-butyl palmitate, n-butyl stearate, n-butyl rapeseed fatty acid, n-butyl soybean fatty acid, i-butyl rice bran fatty acid, i-butyl rapeseed fatty acid, octyl palmitate, octyl oleate, octyl rapeseed fatty acid, octyl vegetable fatty acid, isopropyl myristate, and palmitic acid isopropylamide, amines, ethers, carboxylic acids, esters, organosulfides, organosulfoxides, sulfones, alcohol derivatives, carbitol, butyl carbitol, cellosolve, ether derivatives, amino alcohols, and ketones.

[0104] Silica particles are not easily wetted by water. Therefore, water tends to aggregate the silica particles and inhibit their adsorption to inorganic particles. From the viewpoints of facilitating the adsorption of silica particles to inorganic particles, facilitating the re-dispersion of settled inorganic particles, suppressing a decrease in the durability of components such as an inkjet head, and suppressing a decrease in ink jetting properties, it is preferable that the ink does not substantially contain water.

[0105] Furthermore, hydrophobically treated silica particles are excessively wetted by organic solvents. Therefore, the organic solvent strongly adheres to the periphery of the silica particles, making it difficult for the silica particles to approach the inorganic particles, and may inhibit the adsorption of silica to the inorganic particles. From the viewpoints of facilitating the adsorption of silica particles to inorganic particles, facilitating the re-dispersion of settled inorganic particles, suppressing a decrease in the durability of components such as inkjet heads, and suppressing a decrease in ink jetting properties, it is preferable that the ink does not substantially contain organic solvents.

[0106] In this specification, "the ink is substantially free of a certain component" means that the content of that component relative to the total mass of the ink is 5% by mass or less. From the above perspective, the content of water relative to the total mass of the ink is preferably 0% by mass or more and 1% by mass or less, and more preferably 0% by mass or more and 0.1% by mass or less. Furthermore, the content of organic solvents relative to the total mass of the ink is preferably 0% by mass or more and 1% by mass or less, and more preferably 0% by mass or more and 0.1% by mass or less.

[0107] 1-4. Ink properties The viscosity of the ink is not particularly limited, but is preferably 5 mPa·s or more and 1000 mPa·s or less at 25°C, and more preferably 20 mPa·s or more and 500 mPa·s or less. Ink is often stored or used at around 25°C. The lower the viscosity at 25°C, the easier it is to redisperse settled inorganic pigments. On the other hand, by appropriately increasing the viscosity at 25°C, it is possible to suppress the settling of inorganic pigments.

[0108] The viscosity of the composition at 25°C can be determined using a rheometer at a shear rate of 1000 / sec. The rheometer can be a stress-controlled rheometer from the Physica MCR series manufactured by Anton Paar. The cone-plate diameter can be 75 mm, and the cone angle can be 1.0°.

[0109] The ink has a volume resistivity of 10 11It is preferable that the cured film can be formed to a resistivity of Ω·m or more. The surface resistivity of the cured film can be measured using a Hiresta UX (MCP-HT800, manufactured by Nitto Seiko Analytech Co., Ltd.).

[0110] 1-5. Ink preparation method The ink can be prepared by mixing the above-mentioned components. In this case, the components other than the inorganic particles may be mixed first, and the inorganic particles may be added to the resulting mixture later.

[0111] Furthermore, when inorganic particles are dispersed using a dispersant, a dispersion containing inorganic particles, a dispersant, and a liquid component may be prepared in advance, and the remaining components may be added and mixed to this. In this case, in order to increase the solubility of the dispersant, etc., it is preferable to prepare the dispersion by mixing the inorganic particles and the dispersant while heating them.

[0112] Furthermore, when inorganic particles are dispersed using a dispersant, silica particles may be added in advance and dispersed. From the viewpoint of wetting the silica particles with the ink and allowing them to penetrate between the inorganic particles, it is preferable to add the silica particles in advance during dispersion.

[0113] 2. Method for forming the cured product The ink described above can be applied to a substrate by an ink jet method and cured to form a cured product.

[0114] The application of the ink to the substrate can be carried out by ejecting the ink from an inkjet head and causing it to land on the substrate.

[0115] The ejection method from the inkjet head may be either an on-demand method or a continuous method. On-demand inkjet heads may be any of electromechanical conversion types such as single-cavity, double-cavity, bender, piston, shear-mode, and shared-wall types, and electrothermal conversion types such as thermal inkjet and bubble jet ("Bubble Jet" is a registered trademark of Canon Inc.).

[0116] These inkjet heads or image forming apparatuses having inkjet heads may be configured to circulate ink inside or outside the inkjet head. When ink is discharged while being circulated, if inorganic particles settle in the ink circulation channel, the ink dischargeability may be reduced. In contrast, in this embodiment, the settled inorganic particles have good redispersibility, so that good ink dischargeability can be maintained even when the ink is circulated.

[0117] The type of substrate is not particularly limited, and may be, for example, paper, resin film, ABS resin plate, acrylic resin plate, aluminum plate, glass plate, polycarbonate plate, cloth, etc. The shape of the substrate is not particularly limited, and may be a plate, film, sheet, or various three-dimensional shapes. In addition, the composition may be applied to a space formed inside the substrate by various methods.

[0118] The ink can be cured by irradiating it with active energy rays, which polymerize and crosslink the polymerizable compound. Examples of active energy rays include electron beams, ultraviolet rays, α rays, γ rays, and X-rays. Of these, ultraviolet rays and electron beams are preferred. The ultraviolet rays are preferably light having a peak wavelength of 360 nm or more and 410 nm or less. The ultraviolet rays are preferably emitted from an LED light source. LEDs emit less radiant heat than conventional light sources (e.g., metal halide lamps). Therefore, when LEDs are used, the ink is less likely to melt when irradiated with active energy rays, making it less likely to produce uneven gloss.

[0119] When ultraviolet rays are used as active energy rays, the light intensity per irradiation is 500 mJ / cm 2 More than 4000mJ / cm 2 It is preferable that the dose is 500 mJ / cm or less. 2 When the intensity is 4000 mJ / cm or more, the curability of the polymerizable compound can be improved. 2 If the content is less than this, discoloration of the cured product can be suppressed.

[0120] When forming a thick cured product, the application of ink and film formation may be repeated.

[0121] It is believed that the silica particles adsorbed to the surfaces of the inorganic particles are also adsorbed or attached to the surfaces of the inorganic particles inside the cured product. Therefore, the surfaces of the inorganic particles in the cured product formed in this embodiment are protected by the silica particles, and the cured product has high abrasion resistance.

[0122] 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 product may be post-processed into a desired shape. [Example]

[0123] The present invention will be specifically described below with reference to examples, but the scope of the present invention is not limited to the descriptions in the examples.

[0124] [Experiment 1] 1. Prepare ingredients Inkjet inks were prepared using the following materials:

[0125] 1-1. Polymerizable compounds Monomer 1: Neopentyl glycol diglycidyl ether (difunctional, non-aromatic) Monomer 2: 1,6-Hexanediol diglycidyl ether (difunctional, non-aromatic) Monomer 3: Triethylene glycol divinyl ether (difunctional, non-aromatic) Monomer 4: 3,3'-(oxybismethylene)bis(3-ethyloxetane) (difunctional, non-aromatic) Acrylate 1: Dipropylene glycol diacrylate (difunctional, non-aromatic) Acrylate 2: Polyethylene glycol (200) diacrylate (bifunctional, non-aromatic) Acrylate 3: 1,6-hexanediol diacrylate (bifunctional, non-aromatic) Acrylate 4: Isobornyl acrylate (monofunctional, non-aromatic) Acrylate 5: Cyclic trimethylolpropane formal acrylate (monofunctional, non-aromatic) Acrylate 6: Benzyl acrylate (monofunctional, aromatic) Acrylate 7: Phenol 4EO acrylate (monofunctional, aromatic) Acrylate 8: 2-phenoxyethyl acrylate (monofunctional, aromatic) Acrylate 9: Glycidyl ether group-containing epoxy acrylate oligomer (manufactured by Shin-Nakamura Chemical Co., Ltd., NK Oligo EA-1010N) (multifunctional, aromatic)

[0126] 1-2.Inorganic particles Inorganic particle 1: zinc oxide (Candy Zinc 1000 manufactured by Sakai Chemical Industry Co., Ltd. ("Candy Zinz" is a registered trademark of the company)) Inorganic particle 2: Barium sulfate (Sakai Chemical Industry Co., Ltd., H-LFM) Inorganic particle 3: pearl pigment (manufactured by Merck, Iriodin 111 104259 (Iriodin is a registered trademark of the company)) Inorganic particle 4: luminescent pigment (Luminova G-300F, manufactured by Nemoto Specialty Chemical Co., Ltd. (Luminova is a registered trademark of the company) Inorganic particle 5: luminescent pigment (Nemoto Specialty Chemical Co., Ltd., Luminova G-300FF)

[0127] 1-3. Silica particles Silica 1: QSG-170 (average particle size: 170 nm), manufactured by Shin-Etsu Chemical Co., Ltd., hydrophobicity 67% Silica 2: Shin-Etsu Chemical Co., Ltd., QSG-130 (average particle size: 130 nm), hydrophobicity 67% Silica 3: QSG-30 (average particle size: 30 nm), hydrophobicity 67%, manufactured by Shin-Etsu Chemical Co., Ltd. Silica 4: QSG-10 (average particle size: 10 nm), manufactured by Shin-Etsu Chemical Co., Ltd., hydrophobicity 67% Silica 5: Reolosil MT-10 (average particle size: 15 nm) manufactured by Tokuyama Corporation ("Reolosil" is a registered trademark of the company) Silica 6: Tokuyama Corporation, Reolosil DM-10 (average particle size: 15 nm) Silica 7: Tokuyama Corporation, Reolosil HM-20L (average particle size: 12 nm) Silica 8: Tokuyama Corporation, Reolosil ZD-30ST (average particle size: 7 nm) Silica 9: Silfil NHM-3N, manufactured by Tokuyama Corporation (average particle size: 150 nm, "Silfil" is a registered trademark of the company) Silica 10: Sunseal SP-01MS (average particle size: 100 nm) manufactured by Tokuyama Corporation (Sunseal is a registered trademark of the company) Silica 11: Sunsil SP-01P (average particle size: 100 nm), manufactured by Tokuyama Corporation Silica 12: Sunsil SP-04MS (average particle size: 400 nm), manufactured by Tokuyama Corporation Silica 13: Sunsil SP-03P (average particle size: 300 nm), manufactured by Tokuyama Corporation Silica 14: Sunsil SP-10M (average particle size: 1000 nm), manufactured by Tokuyama Corporation Silica 15: Sunseal SP-10P (average particle size: 1000 nm), manufactured by Tokuyama Corporation Silica 16: Tokuyama Corporation, Reolosil QS-09 (average particle size: 20 nm) Silica 17: Tokuyama Corporation, Silfil NSS-3N (average particle size: 150 nm) Silica 18: Sunseal SS-03 (average particle size: 300 nm), manufactured by Tokuyama Corporation Silica 19: Admatechs Co., Ltd., SC2300-SVJ (average particle size: 500 nm) Silica 20: Admatechs Co., Ltd., SC2500-SMJ (average particle size: 500 nm) Silica 21: Nissan Chemical Co., Ltd., PGM-AC-4130Y (average particle size: 45 nm) Silica 22: MEK-AC-4130Y (average particle size: 45 nm), manufactured by Nissan Chemical Co., Ltd.

[0128] Silica 1 to Silica 15 are silica particles that have been hydrophobized and do not contain polymerizable groups. Silica 16 to Silica 18 are hydrophilic silica particles that have not been hydrophobized and do not contain polymerizable groups. Silica 19 is a silica particle that has been hydrophobized and contains a vinyl group, which is a polymerizable group. Silica 20 is a silica particle that has been hydrophobized and contains a methacryloyl group, which is a polymerizable group. Silica 21 is a silica particle that has been hydrophobized and contains an acryloyl group, which is a polymerizable group. Silica 22 is a silica particle that has been hydrophobized and contains an acryloyl group, which is a polymerizable group.

[0129] 1-4. Photopolymerization initiator Initiator 1: Omnirad MBF, manufactured by IGM RESINS BV Initiator 2: Omnirad 754 manufactured by IGM RESINS BV Initiator 3: Omnirad 819 manufactured by IGM RESINS BV

[0130] 1-5. Heat curing agent Heat curing agent 1: Dicyandiamide Heat curing agent 2: LANXESS blocked isocyanate BI7982 Heat curing agent 3: 2-ethyl-4-methylimidazole

[0131] 1-6. Organic solvents Organic solvent 1: Methyl oleate Organic solvent 2: Methyl ethyl ketone

[0132] 1-7.Other ingredients Polymerization inhibitor: BASF Irgastab UV-10

[0133] 2. Inkjet Ink Preparation 2-1. Preparation of dispersion 20 parts by mass of inorganic particles 1 and 80 parts by mass of monomer 1 were placed in a polypropylene container together with 50 parts by mass of zirconia beads with an average particle size of 0.3 mm, and the mixture was dispersed for 30 minutes using a paint shaker. The zirconia beads were then removed to prepare dispersion 1A-1.

[0134] 20 parts by mass of inorganic particles 1 and 80 parts by mass of monomer 2 were placed in a polypropylene container together with 50 parts by mass of zirconia beads with an average particle size of 0.3 mm, and the mixture was dispersed for 30 minutes using a paint shaker. The zirconia beads were then removed to prepare dispersion 1A-2.

[0135] 20 parts by mass of inorganic particles 1 and 80 parts by mass of acrylate 1 were placed in a polypropylene container together with 50 parts by mass of zirconia beads with an average particle size of 0.3 mm, and the mixture was dispersed for 30 minutes using a paint shaker. The zirconia beads were then removed to prepare dispersion 1A-3.

[0136] Dispersion 1B was prepared in the same manner as in the preparation of Dispersion 1A-3, except that the dispersion time was changed to 2 hours.

[0137] Dispersions 1C to 1F were prepared in the same manner as Dispersion 1A-3, except that the inorganic particles were changed to Inorganic Particles 2 to 5, respectively.

[0138] Dispersion 1G was prepared in the same manner as in Dispersion 1F, except that the dispersion time was changed to 8 hours.

[0139] Dispersion 1H was prepared in the same manner as Dispersion 1F, except that the dispersion time was changed to 10 hours.

[0140] Dispersion 1I was prepared in the same manner as in Dispersion 1F, except that the dispersion time was changed to 16 hours.

[0141] Thereafter, the median diameter of the inorganic particles in the dispersion was measured using a particle size distribution analyzer (LUMiSizer, manufactured by LUM Japan Co., Ltd.) that utilizes the Stokes sedimentation method.

[0142] 2-2. Preparation of ink The polymerizable compound, dispersion, silica particles, photopolymerization initiator, heat curing agent, organic solvent, water, and polymerization inhibitor were mixed in the proportions shown in Tables 1 to 10 and filtered through a 30 μm polypropylene pleated filter (manufactured by Roki Techno Co., Ltd.) to obtain Inks 1 to 65. The values ​​shown in parentheses in the "Inorganic Particles" and "Silica Particles" columns in Tables 1 to 10 are the median and average particle sizes of the respective particles in the dispersion.

[0143] [Table 1]

[0144] [Table 2]

[0145] [Table 3]

[0146] [Table 4]

[0147] [Table 5]

[0148] [Table 6]

[0149] [Table 7]

[0150] [Table 8]

[0151] [Table 9]

[0152] [Table 10]

[0153] 3. Evaluation The inks 1 to 65 prepared above were evaluated as follows.

[0154] 3-1. Settling recovery 10 g of the sample was placed in a 20 mL glass sample tube and left to stand at 25°C for 3 days to allow the solid matter to accumulate at the bottom of the sample tube. The sediment was shaken up and down vigorously by hand, and the number of shakes required to loosen the sediment was measured. A After 1 to 10 times, most of the sediment will come off from the bottom of the sample tube. B After 11 to 30 times, the sediment is almost completely removed from the bottom of the sample tube. C. It does not come off from the bottom of the sediment sample tube within 31 tries.

[0155] 3-2. Injection bending The ink was filled into a Konica Minolta independently driven inkjet head (360 npi, discharge volume 27 pL, 1024 nozzles) and a 10-minute continuous discharge test was carried out using a strobe-synchronized droplet observation device. After that, the ink was evaluated for ink deflection according to the following criteria. (standard) A: Of the 256 nozzles evaluated, all 256 nozzles ejected normally. B: Of the 256 nozzles evaluated, 1 or more but less than 5 nozzles were observed to have deflected ejection. C: Of the 256 nozzles evaluated, 5 or more nozzles were observed to have deflected ejection.

[0156] 3-3. Durability of components A maintenance cloth (Savina CK, manufactured by KB Seiren) with each ink attached was pressed against the nozzle surface of a Konica Minolta KM1024iLHE and rubbed 100 times, after which the surface of the nozzle surface was observed. A: Almost no scratches B: Slight scratches C Large scratches are visible

[0157] 3-4.Yellowing Ink 1 to Ink 65 were applied to a 160 mm x 160 mm, 2 mm thick ABS board substrate, and cured using a UV LED curing lamp (FireJet FJ100 manufactured by Phoseon) at a wavelength of 365 nm and an illuminance of 2 W / cm. 2 , light intensity 2000mJ / cm 2 The resulting cured products were left to stand in a 60°C thermostatic chamber for 5 days, after which the appearance of the cured products was observed as follows. A: Compared to before the test, there was almost no change after the test. B: A slight change in color was observed in the cured film compared to before the test.

[0158] 3-5. Weather resistance Ink 1 to Ink 65 were applied to a 160 mm x 160 mm, 2 mm thick ABS board substrate, and cured using a UV LED curing lamp (FireJet FJ100 manufactured by Phoseon) at a wavelength of 365 nm and an illuminance of 2 W / cm. 2 , light intensity 2000mJ / cm 2 Each cured product was then cured by irradiating it with ultraviolet light of 255 W / m² in thickness. Each cured product was subjected to a weather resistance test in accordance with JIS B 7753:2007. Specifically, the substrate having each cured product was subjected to a weather resistance test in accordance with JIS B 7753:2007 using a Sunshine carbon arc lamp accelerated weather resistance tester (Sunshine Weather Meter S80, manufactured by Suga Test Instruments Co., Ltd.) at an irradiance of 255 W / m² in the wavelength range of 300 nm to 700 nm. 2 The test subjects were exposed to 102 minutes of light and 18 minutes of water spray for 78 hours. 〇 There is almost no change in the color of the cured film after the test compared to before the test. △: The color of the cured film after the test has changed slightly compared to before the test.

[0159] The evaluation results for each ink are shown in Tables 11 to 20. The values ​​shown in the "Silica diameter / inorganic particle diameter" column in Tables 11 to 20 are the ratio of the average particle diameter of silica particles to the median diameter of the inorganic particles used in each ink, with "A" representing 1 / 20 or less, "B" representing more than 1 / 20 but less than 1 / 1, and "C" representing 1 / 1 or more.

[0160] [Table 11]

[0161] [Table 12]

[0162] [Table 13]

[0163] [Table 14]

[0164] [Table 15]

[0165] [Table 16]

[0166] [Table 17]

[0167] [Table 18]

[0168] [Table 19]

[0169] [Table 20]

[0170] As is clear from the results in Tables 1 to 20, the actinic radiation-curable inkjet inks containing a polymerizable compound, inorganic particles, and hydrophobically treated silica particles without polymerizable groups, in which the average particle size of the silica particles was smaller than the median size of the inorganic particles and the content of the silica particles by mass was lower than the content of the inorganic particles by mass, exhibited excellent redispersibility of settled inorganic particles. Furthermore, although the inkjet inks contained inorganic pigments, they were less likely to cause deterioration in the durability of components such as inkjet heads or deterioration in ink jetting performance.

[0171] [Experiment 2] Inorganic particle D 50 and D 90 The following experiment was conducted to confirm the difference in sedimentation recovery properties between the two. In the following description, explanations of the contents common to Experiment 1 will be omitted, and differences from Experiment 1 will be explained. Furthermore, the materials used and their abbreviations are the same as those in Experiment 1, so explanations will be omitted.

[0172] 1. Inkjet Ink Preparation 1-1. Preparation of dispersion 50 parts by mass of inorganic particles 4 and 50 parts by mass of acrylate 1 were placed in a polypropylene container together with 100 parts by mass of zirconia beads with an average particle size of 0.3 mm, and the mixture was dispersed for 30 minutes using a paint shaker. The zirconia beads were then removed to prepare dispersion 2A.

[0173] Dispersion 2B was prepared in the same manner as dispersion 2A, except that inorganic particles were changed to inorganic particles 5.

[0174] Dispersion 2C was prepared in the same manner as in Dispersion 2B, except that the dispersion time was changed to 8 hours.

[0175] 1-2. Ink preparation The polymerizable compound, dispersion, silica particles, photopolymerization initiator, heat curing agent, organic solvent, water, and polymerization inhibitor were mixed in the proportions shown in Table 21 and filtered through a 30 μm polypropylene pleated filter (manufactured by Roki Techno Co., Ltd.) to obtain Inks 66 to 73. The values ​​in parentheses in the "Inorganic Particles" and "Silica Particles" columns in Table 21 are the median and average particle sizes of the respective particles in the dispersion.

[0176] In addition, inks 66 to 73 were diluted with dipropylene glycol diacrylate, and the D of inorganic particles contained in each ink was measured using a particle size distribution analyzer (LUMiSizer, manufactured by LUM Japan Co., Ltd.). 50 and D 90 The measured D 50 , D 90 and D 50 / D 90 are also shown in Table 21.

[0177] [Table 21]

[0178] Inks 66 to 73 were evaluated in the same manner as in Experiment 1. The results are shown in Table 22.

[0179] [Table 22]

[0180] As is clear from the results in Tables 21 and 22, the D 90 The larger the D, the higher the sedimentation and recovery of inorganic particles. 50 / D 90 The smaller the value, the higher the weather resistance of the cured product. [Industrial Applicability]

[0181] According to the present invention, it is possible to make it easier to use ink-jet inks containing inorganic particles, and therefore the present invention is expected to further broaden the applications to which ink-jet inks can be applied and contribute to further development of this field.

Claims

1. The composition includes a polymerizable compound, inorganic particles, and silica particles, the silica particles have been subjected to a hydrophobic treatment and have no polymerizable group; the average particle size of the silica particles is smaller than the median particle size of the inorganic particles, The content of the silica particles by mass is less than the content of the inorganic particles by mass. Active energy ray curable inkjet ink.

2. The polymerizable compound contains a (meth)acrylate. The ink-jet ink of claim 1.

3. The (meth)acrylate contains a monofunctional polymerizable compound having an aromatic ring. The ink-jet ink of claim 2.

4. Substantially free of water and substantially free of organic solvents; The ink-jet ink of claim 1.

5. The average particle size of the silica particles is 1 / 20 or less of the median size of the inorganic particles. The ink-jet ink of claim 1.

6. the content of the silica particles is 0.01% by mass or more and 5% by mass or less with respect to the total mass of the inkjet ink; The ink-jet ink of claim 1.

7. The average particle size of the inorganic particles is 0.5 μm or more and 5 μm or less. The ink-jet ink of claim 1.

8. D of the inorganic particles ５０ / D ９０ is equal to or greater than 0.1 and equal to or less than 0.9, The ink-jet ink of claim 1.

9. The inorganic particles are phosphorescent pigments. The ink-jet ink of claim 1.

10. Contains a heat curing agent, The ink-jet ink of claim 1.

11. applying the inkjet ink of any one of claims 1 to 10 to a substrate; irradiating the applied inkjet ink with actinic energy rays; A method for forming a cured product comprising the steps of:

12. the step of applying the inkjet ink to the substrate is performed while circulating the inkjet ink. The method for forming a cured product according to claim 11.

13. A cured product formed from the inkjet ink according to any one of claims 1 to 10.

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