Radiation-curable inkjet composition, ink set, and method for producing a recording medium

Abstract

To provide a radiation hardened inkjet composition having excellent adhesion to a recording medium and excellent scratch resistance even when printed on a recording medium having low ink absorption properties.SOLUTION: A radiation hardened inkjet composition includes a polymerizable compound, a white pigment, and an inorganic particle different from the white pigment. The polymerizable compound includes a monofunctional polymerizable compound. A content of the monofunctional polymerizable compound is 80 mass% or more relative to a total mass of the polymerizable compound included in the radiation hardened inkjet composition.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a radiation-curable inkjet composition, an ink set, and a method for manufacturing a recorded matter.

Background Art

[0002] The inkjet recording method can record high-definition images with a relatively simple device and has been rapidly developing in various fields. For example, Patent Document 1 describes an inkjet printer including a white head that discharges white ink, a process color head that discharges each color ink of process colors, and control means for selectively controlling whether to perform front printing or back printing, for the purpose of printing flexibly even on transparent or opaque packaging materials. Here, back printing means printing on the back side of the packaging material for the purpose of imparting durability against rubbing of the printing surface, using a transparent recording medium, first printing an image with process color ink, and then printing the background with white ink.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the inkjet printer described in Patent Document 1, when recording on a non-absorbent recording medium or a low-absorbent recording medium having a low ability to absorb ink as a recording medium, there is a problem that the adhesion and rubbing resistance of the ink coating film to the recording medium are not sufficient.

Means for Solving the Problems

[0005] The radiation-curable inkjet composition contains a polymerizable compound, a white pigment, and inorganic particles different from the white pigment, and the polymerizable compound contains a monofunctional polymerizable compound, and the content of the monofunctional polymerizable compound is 80% by mass or more based on the total mass of the polymerizable compound contained in the radiation-curable inkjet composition.

[0006] The ink set includes a non-white ink containing a non-white coloring material and a polymerizable compound, and a white ink, and the white ink is the above radiation-curable inkjet composition.

[0007] A method for manufacturing a recording object is a method for manufacturing a recording object using the above ink set, and includes a first ejection step of ejecting the non-white ink and attaching it to a recording medium, and irradiating radiation to the non-white ink attached to the recording medium to obtain a cured film of the non-white ink. a first curing step; a second ejection step of ejecting the white ink and attaching it to the cured film of the non-white ink; and a second curing step of irradiating radiation to the white ink attached to the recording medium to cure the white ink to obtain a recording object.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention (hereinafter referred to as "the present embodiment") will be described in detail. Note that the present invention is not limited to this, and various modifications are possible without departing from the gist thereof.

[0010] 1. Recording Object Before explaining the radiation-curable inkjet composition (hereinafter sometimes simply referred to as "white ink"), the ink set, and the method for producing a recording material of the present invention, a recording material produced using the ink set of the present invention will be described with reference to FIG. 2.

[0011] The recording material 7 has a recording medium 6, a cured film 71 of non-white ink formed on the recording surface 61 of the recording medium 6, and a cured film 72 of white ink. Further, the recording medium 6 has, in addition to the above-described recording surface 61, a non-recording surface 62 to which neither non-white ink nor white ink adheres.

[0012] As will be described in detail later, the white ink contains a polymerizable compound, a white pigment, and inorganic particles different from the white pigment. The white ink contains a monofunctional polymerizable compound as the polymerizable compound, and the content of the monofunctional polymerizable compound is 80% by mass or more based on the total mass of the polymerizable compounds contained in the white ink.

[0013] Since the white ink contains a monofunctional polymerizable compound and the content of the monofunctional polymerizable compound is 80% by mass or more based on the total mass of the polymerizable compounds contained in the white ink, a cured film 72 having excellent adhesion can be obtained. Further, the white ink contains a white pigment, which is a hard particle, and inorganic particles. Thereby, it plays a role of protecting the cured film 72 and making the cured film 72 excellent in abrasion resistance. That is, by using the ink set of the present invention, a recording material excellent in adhesion and abrasion resistance can be obtained.

[0014] 2. Radiation-curable inkjet composition The white ink contains a polymerizable compound, a white pigment, and inorganic particles different from the white pigment. The white ink contains a monofunctional polymerizable compound as the polymerizable compound, and the content of the monofunctional polymerizable compound is 80% by mass or more based on the total mass of the polymerizable compounds contained in the white ink.

[0015] A radiation-curable inkjet composition refers to an ink that cures upon irradiation with radiation. Examples of radiation include ultraviolet rays, electron beams, infrared rays, visible light, X-rays, and the like. Among these, ultraviolet rays are preferred as the radiation source is easily available and widely used, and materials suitable for curing by ultraviolet irradiation are also easily available and widely used.

[0016] 2.1. Polymerizable Compound The white ink contains a monofunctional polymerizable compound, and may optionally contain a polyfunctional polymerizable compound, a polymerizable oligomer, or the like.

[0017] 2.1.1. Monofunctional Polymerizable Compound The content of the monofunctional polymerizable compound is 80% by mass or more, preferably 85% by mass or more, and more preferably 90% by mass or more, based on the total mass of the polymerizable compounds contained in the white ink. Also, the content of the monofunctional polymerizable compound is preferably 99% by mass or less, and more preferably 98% by mass or less, based on the total mass of the polymerizable compounds contained in the white ink. By the content of the monofunctional polymerizable compound being 80% by mass or more, the flexibility of the cured film 72 can be enhanced. For this reason, the adhesion of the cured film 72 to the recording medium 6 is further improved.

[0018] The monofunctional polymerizable compound is not particularly limited, and examples include a monofunctional polymerizable compound having an alicyclic group, a monofunctional polymerizable compound having an aromatic group, a monofunctional polymerizable compound having a nitrogen-containing heterocyclic ring, and the like. As the monofunctional polymerizable compound, a monofunctional polymerizable compound other than the above may also be used.

[0019] By using the monofunctional polymerizable compound, a recording article 7 having a cured film 72 with improved flexibility and excellent adhesion to the recording medium 6 can be obtained.

[0020] 2.1.1.1. Monofunctional Polymerizable Compound Having an Alicyclic Group The monofunctional polymerizable compound having an alicyclic group is not particularly limited, and examples thereof include dicyclopentenyl (meth)acrylate, dicyclopentenyl oxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, tert-butyl cyclohexanol (meth)acrylate, and alicyclic group-containing (meth)acrylates such as 2-(meth)acrylic acid-1,4-dioxaspiro[4,5]dec-2-ylmethyl.

[0021] Among these, dicyclopentenyl (meth)acrylate (DCPA) and isobornyl acrylate (IBXA) are preferred. By using such a polymerizable compound, the adhesion and abrasion resistance of the obtained cured film 72 are further improved.

[0022] The content of the monofunctional polymerizable compound having an alicyclic group is preferably 25% by mass to 55% by mass, more preferably 30% by mass to 50% by mass, and still more preferably 35% by mass to 45% by mass based on the total mass of the polymerizable compound contained in the white ink. When the content of the monofunctional polymerizable compound having an alicyclic group is within the above range, the adhesion and abrasion resistance of the obtained cured film 72 are further improved.

[0023] 2.1.1.2. Monofunctional polymerizable compound having an aromatic group The monofunctional polymerizable compound having an aromatic group is not particularly limited, and examples thereof include phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, alkoxylated 2-phenoxyethyl (meth)acrylate, ethoxylated nonylphenyl (meth)acrylate, alkoxylated nonylphenyl (meth)acrylate, p-cumylphenol EO-modified (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate.

[0024] Among these, phenoxyethyl acrylate (PEA) is preferred. By using such a monofunctional polymerizable compound containing an aromatic group, the solubility of the photopolymerization initiator is further improved, and the curability of the white ink is further improved. Also, when an acylphosphine oxide-based photopolymerization initiator or a thioxanthone-based photopolymerization initiator is used, the solubility of the photopolymerization initiator becomes better.

[0025] The content of the monofunctional polymerizable compound having an aromatic group is preferably 20% by mass to 50% by mass, more preferably 25% by mass to 45% by mass, and still more preferably 28% by mass to 40% by mass with respect to the total mass of the polymerizable compounds contained in the white ink. When the content of the aromatic group-containing monofunctional polymerizable compound is within the above range, the adhesion and abrasion resistance of the cured film 72 are further improved.

[0026] 2.1.1.3. Nitrogen-containing monofunctional polymerizable compound The nitrogen-containing monofunctional polymerizable compound is not particularly limited, and examples thereof include nitrogen-containing monofunctional vinyl monomers such as N-vinylcaprolactam, N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, vinylmethyl oxazolidinone, and N-vinylpyrrolidone; nitrogen-containing monofunctional acrylate monomers such as acryloylmorpholine; and nitrogen-containing monofunctional acrylamide monomers such as (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, diacetoneacrylamide, N,N-dimethyl(meth)acrylamide, and quaternary salts of dimethylaminoethyl acrylate benzyl chloride.

[0027] Among these, polymerizable compounds having a nitrogen-containing heterocyclic structure such as N-vinylcaprolactam, N-vinylcarbazole, N-vinylpyrrolidone, vinylmethyl oxazolidinone (VMOX), or acryloylmorpholine (ACMO) are more preferable, and it is even more preferable to contain acryloylmorpholine. By using such a nitrogen-containing monofunctional polymerizable compound, the scratch resistance of the cured film 72 is further improved. Furthermore, a nitrogen-containing monofunctional acrylate monomer having a nitrogen-containing heterocyclic structure such as acryloylmorpholine further improves the stretchability and adhesion of the cured film 72.

[0028] The content of the nitrogen-containing monofunctional polymerizable compound is preferably 10% by mass to 25% by mass, more preferably 12% by mass to 23% by mass, and even more preferably 15% by mass to 20% by mass with respect to the total mass of the polymerizable compound contained in the white ink. When the content of the nitrogen-containing monofunctional polymerizable compound is within the above range, the adhesion and scratch resistance of the cured film 72 are further improved.

[0029] 2.1.2. Polyfunctional polymerizable compound The polyfunctional polymerizable compound is not particularly limited, and examples thereof include vinyl group-containing (meth)acrylates and polyfunctional (meth)acrylates.

[0030] 2.1.2.1. Vinyl group-containing (meth)acrylate The vinyl group-containing (meth)acrylate is not particularly limited, and examples thereof include compounds represented by the formula (1). H2C=CR1-CO-OR2-O-CH=CH-R3··· (1) (In the formula, R1 is a hydrogen atom or a methyl group, R2 is a divalent organic residue having 2 to 20 carbon atoms, and R3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.)

[0031] In the above formula (1), examples of the divalent organic residue having 2 to 20 carbon atoms represented by R2 include linear, branched, or cyclic alkylene groups having 2 to 20 carbon atoms which may be substituted, alkylene groups having 2 to 20 carbon atoms which may be substituted and have an oxygen atom due to an ether bond and / or an ester bond in the structure, and divalent aromatic groups having 6 to 11 carbon atoms which may be substituted.

[0032] Among these, alkylene groups having 2 to 6 carbon atoms such as an ethylene group, an n-propylene group, an isopropylene group, and a butylene group, and alkylene groups having 2 to 9 carbon atoms which have an oxygen atom due to an ether bond in the structure such as an oxyethylene group, an oxy n-propylene group, an oxyisopropylene group, and an oxybutylene group are preferable. Further, from the viewpoint of further reducing the viscosity of the ink and further improving the curability of the ink, compounds having a glycol ether chain in which R2 is an alkylene group having 2 to 9 carbon atoms which have an oxygen atom due to an ether bond in the structure such as an oxyethylene group, an oxy n-propylene group, an oxyisopropylene group, and an oxybutylene group are more preferable.

[0033] In the above formula (1), as the monovalent organic residue having 1 to 11 carbon atoms represented by R3, linear, branched, or cyclic alkyl groups having 1 to 10 carbon atoms which may be substituted, and aromatic groups having 6 to 11 carbon atoms which may be substituted are preferable.

[0034] Among these, alkyl groups having 1 to 2 carbon atoms such as a methyl group or an ethyl group, and aromatic groups having 6 to 8 carbon atoms such as a phenyl group and a benzyl group are preferably used.

[0035] Specific examples of the compound of formula (1) are not particularly limited, and for example, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate can be mentioned, and 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA) is preferable.

[0036] In particular, the white ink preferably contains, as a polyfunctional polymerizable compound, a vinyl group-containing (meth)acrylate represented by the above formula (1). Thereby, the curability of the white ink is further improved.

[0037] The content of the vinyl group-containing (meth)acrylate is preferably 1% by mass to 25% by mass, more preferably 2% by mass to 20% by mass, and still more preferably 3% by mass to 15% by mass with respect to the total mass of the polymerizable compounds contained in the white ink. When the content of the vinyl group-containing (meth)acrylate is within the above range, an ink with improved discharge stability is provided by suppressing an increase in the viscosity of the white ink.

[0038] 2.1.2.2 Polyfunctional (meth)acrylate The polyfunctional (meth)acrylate is not particularly limited, and examples thereof include bifunctional (meth)acrylates such as dipropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate; trifunctional or higher polyfunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate.

[0039] Among these, dipropylene glycol diacrylate (DPGDA) is preferred. By using such a polyfunctional (meth)acrylate, the curability and rub resistance of the white ink are further improved.

[0040] The content of the polyfunctional (meth)acrylate is preferably 1% by mass to 10% by mass, more preferably 2% by mass to 8% by mass, and still more preferably 3% by mass to 7% by mass with respect to the total mass of the polymerizable compounds contained in the white ink. When the content of the polyfunctional (meth)acrylate is within the above range, the curability and rub resistance of the white ink are further improved.

[0041] The polymerizable compound functions as a solvent for the ink. However, it is preferable to determine the type and content of the polymerizable compound in consideration of the SP value. Specifically, the SP value of the ink can be obtained by calculating the weighted average of the SP values of the polymerizable compounds contained in the ink. Therefore, by selecting the type of the polymerizable compound contained in the ink and determining the content so that the SP value of the ink becomes close to the SP value of the recording medium 6, an ink that exhibits excellent adhesion to a wide variety of base materials can be obtained.

[0042] The method for calculating the weighted average of the SP value will be described.

[0043] Let the weighted average value of the SP value be SP All and the SP value of each polymerizable compound be SP N and the mass ratio of the content of the polymerizable compound be X N (mass %). N is an integer that sequentially enters from 1 according to the type of the polymerizable compound contained in the white ink. For example, when three types of polymerizable compounds are used, SP1, SP2, and SP3 occur. The SP value of each polymerizable compound can be calculated using the formula of S mall from its structure, and can also be obtained from the safety data sheet (SDS) or catalog information. The weighted average SP All of the SP value is the sum of the products of SP N calculated for each polymerizable compound and the content X N . Therefore, the following formula (2) holds.

[0044] SP All =ΣSP N ×X N ···(2)

[0045] SP All is preferably 8.5 to 11.0, more preferably 9.0 to 10.5, and still more preferably 9.3 to 10.0. By the value of SP All being within the above range, the SP value of the non-absorbent recording medium described later and the SP value of the ink can be made close to each other, and an ink that exhibits excellent adhesion can be obtained.

[0046] 2.2. White Pigment The white pigment used in the white ink is not particularly limited. For example, white inorganic pigments such as titanium oxide, zinc oxide, zinc sulfide, antimony oxide, magnesium oxide, and zirconium oxide can be mentioned. In addition to white inorganic pigments, white organic pigments such as white hollow resin fine particles and polymer particles can also be used.

[0047] The above pigments may be used alone or in combination of two or more. When using the above pigments, the average particle diameter is preferably 300 nm or less, and more preferably 50 nm to 250 nm. When the average particle diameter is within the above range, the reliability such as ejection stability and dispersion stability in the white ink is further excellent, and an image with excellent image quality can be formed. Here, in this specification, the average particle diameter of the pigment particles is Dv measured by the dynamic light scattering method. 50 and the value was used.

[0048] The pigment can be used in the state of a pigment dispersion liquid, and a dispersant can be used as necessary. The dispersant is not particularly limited. For example, dispersants commonly used for preparing pigment dispersion liquids such as polymer dispersants can be mentioned. Specific examples thereof include those having one or more of polyoxyalkylene polyalkylene polyamine, vinyl-based polymers, and copolymers, acrylic-based polymers, and copolymers, polyester, polyamide, polyimide, polyurethane, amino-based polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxy resins as main components. The dispersant may be used alone or in combination of two or more.

[0049] Commercially available products of polymer dispersants include the AJISPER (registered trademark) series of Ajinomoto Fine-Techno Co., Ltd., the SOLSPERSE series of Lubrizol Corporation (such as Solsperse (registered trademark) 36000), the DISPERBYK series of BYK Additives & Instruments, and the DISPARON (registered trademark) series of Kusumoto Chemicals, Ltd.

[0050] The content of the dispersant is preferably 0.1% by mass to 2.0% by mass, more preferably 0.1% by mass to 1.0% by mass, and still more preferably 0.1% by mass to 0.5% by mass with respect to the total mass of the ink.

[0051] 2.3. Inorganic Particles The white ink contains inorganic particles. Thereby, when the cured film 72 of the white ink is formed on the recording medium 6, a cured film 72 containing hard inorganic particles can be formed. The inorganic particles play a role of protecting the cured film 72, and a recording object 7 excellent in scratch resistance can be obtained.

[0052] The inorganic particles are not particularly limited as long as they are different from white pigments. For example, it is preferable to use inorganic oxides such as silica such as colloidal silica, titanium oxide, zinc oxide, antimony oxide, magnesium oxide, aluminum oxide, and zirconium oxide, and a mixture thereof may also be used.

[0053] Among the above, silica particles and alumina particles are preferable, and silica particles are more preferable. The silica particles impart excellent scratch resistance to the cured film 72 without impairing the excellent adhesion of the cured film 72. That is, the cured film 72 has excellent adhesion by containing a monofunctional polymerizable compound in an amount of 80% by mass or more with respect to the total weight of the polymerizable compounds contained in the white ink. The silica particles have appropriate hardness. By containing a predetermined amount of the monofunctional polymerizable compound, pigment particles, and silica particles, the white ink can improve the scratch resistance of the cured film 72 without impairing the excellent adhesion of the cured film 72, and obtain a cured film 72 that achieves both adhesion and scratch resistance.

[0054] Examples of the silica particles include fumed silica synthesized by reacting silicon chloride, aluminum chloride, titanium chloride, etc. with oxygen and hydrogen in the gas phase by the fumed method; silica synthesized by hydrolyzing and condensing metal alkoxides by the sol-gel method; colloidal silica synthesized by the inorganic colloid method, etc. One or more of these can be used. Among these, colloidal silica is more preferable. As such colloidal silica, commercially available products can also be used. For example, Quartron (registered trademark) PL-1-1PA, PL-2L-MEK manufactured by Fuso Chemical Industry Co., Ltd., Organosilica Sol MA-ST-L, IPA-ST-L, IPA-ST-ZL manufactured by Nissan Chemical Industries, Ltd., etc. can be mentioned.

[0055] The alumina particles may have any shape such as rod shape, bead shape, or spherical shape, but it is preferable to use spherical colloidal alumina.

[0056] Note that the inorganic particles contained in the white ink are made of a material different from that of the above-described white pigment. For example, when the white pigment is titanium oxide, the inorganic particles are made of a material other than titanium oxide. By using inorganic particles made of a material different from that of the white pigment, it is possible to obtain an ink excellent in discharge stability while having excellent whiteness of the white ink.

[0057] The content of the inorganic particles in the white ink is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 30% by mass or less with respect to the total mass of the white ink.

[0058] By setting the content of the inorganic particles within the above range, the effect of the white ink containing the white pigment and the inorganic particles can be more significantly exhibited. That is, a cured film 72 containing inorganic particles which are hard particles can be formed on the recording medium 6, and a recording 7 excellent in abrasion resistance can be obtained. Furthermore, it is possible to suppress the ink viscosity from becoming too high and enable the white ink to be stably discharged from the inkjet head.

[0059] The average particle diameter of the inorganic fine particles is not particularly limited, but is preferably 10 nm or more and 200 nm or less, more preferably 25 nm or more and 150 nm or less, and still more preferably 25 nm or more and 120 nm or less. When the average particle diameter of the inorganic particles is within the above range, the effect of the present invention that a recording material excellent in adhesion and abrasion resistance can be obtained is more remarkably exhibited.

[0060] In this specification, the average particle diameter of the inorganic particles refers to the particle diameter of the particles in the inorganic particles at 50% cumulative in the volume-based particle size distribution determined by the laser diffraction / scattering method. The measurement of the average particle diameter is performed by the dynamic light scattering method or the laser diffraction light method described in JIS Z8825. Specifically, a particle size distribution meter using the dynamic light scattering method as the measurement principle, for example, the product name "Microtrac UPA" manufactured by Nikkiso Co., Ltd., can be used.

[0061] The shape of the inorganic particles may be, for example, spherical, rod-shaped, bead-shaped in which spherical particles are connected and combined, needle-shaped, or the like. Among these, from the viewpoint of effectively expressing the function as a spacer, it is preferably spherical or rod-shaped, and particularly preferably spherical.

[0062] The shape of the inorganic particles can be confirmed by observing with a scanning electron microscope. In the present invention, "spherical" means to the extent that when observed with a scanning electron microscope, cases where bead-shaped, rod-shaped, needle-shaped, etc. in which primary particles are connected and combined are observed are excluded, and it is not limited to a perfect sphere or an ellipsoid.

[0063] 2.4. Photoinitiator The photoinitiator is not particularly limited as long as it can generate active species upon irradiation with radiation. Examples thereof include known photoinitiators such as acylphosphine oxide-based photoinitiators, alkylphenone-based photoinitiators, titanocene-based photoinitiators, and thioxanthone-based photoinitiators. Among these, acylphosphine oxide-based photoinitiators are preferred. By using such a photoinitiator, the curability of the white ink is further improved, and particularly the curability by the curing process using the light of UV-LED is further improved. The photoinitiator may be used alone or in combination of two or more.

[0064] The acylphosphine oxide-based photoinitiator is not particularly limited. Examples thereof include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and the like.

[0065] Examples of commercially available products of such acylphosphine oxide-based photoinitiators include IRGACURE (registered trademark) 819 (bis 2,4,6-trimethylbenzoyl)-phenylphosphine oxide), IRGACURE 1800 (a mixture of bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide and 1-hydroxy-cyclohexyl-phenyl ketone at a mass ratio of 25:75), IRGACURE TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide), etc. manufactured by BASF.

[0066] The content of the photoinitiator is preferably 3.0% by mass to 15.0% by mass, more preferably 5.0% by mass to 13.5% by mass, and still more preferably 8.0% by mass to 12.0% by mass based on the total mass of the white ink. When the content of the photoinitiator is within the above range, the curability of the white ink and the solubility of the photoinitiator are further improved.

[0067] 2.5. Polymerization inhibitor The polymerization inhibitor is not particularly limited. For example, p-methoxyphenol, hydroquinone monomethyl ether (MEHQ), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, hydroquinone, cresol, t-butylcatechol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-butylphenol), and 4,4'-thiobis(3-methyl-6-t-butylphenol), hindered amine compounds, etc. can be mentioned. The polymerization inhibitor may be used alone or in combination of two or more.

[0068] The content of the polymerization inhibitor is preferably 0.05% by mass to 1.00% by mass, more preferably 0.05% by mass to 0.50% by mass, based on the total mass of the white ink.

[0069] 2.6. Surfactant As the surfactant, a silicone-based surfactant is preferred, and more preferably a polyester-modified silicone or a polyether-modified silicone. Examples of the polyester-modified silicone include BYK-347, 348, BYK-UV3500, 3510, 3530, etc. of BYK, and examples of the polyether-modified silicone include BYK-3570, etc. The surfactant may be used alone or in combination of two or more.

[0070] The content of the surfactant is preferably 0.01% by mass to 2.00% by mass, more preferably 0.05% by mass to 1.00% by mass, based on the total mass of the white ink.

[0071] 2.7. Other components In order to maintain good storage stability and ejection stability of the inkjet head, to improve clogging, or to prevent ink deterioration, various additives can be appropriately added for purposes such as dissolution aids, viscosity modifiers, pH adjusters, antioxidants, preservatives, antifungal agents, corrosion inhibitors, and humectants that are not organic solvents, and to capture metal ions that affect dispersion.

[0072] 3. Ink set The ink set includes non-white ink and white ink. The non-white ink includes a non-white colorant and a polymerizable compound. The white ink is the "radiation-curable inkjet composition" already described, and includes a polymerizable compound, a white pigment, and inorganic particles different from the white pigment. The white ink includes a monofunctional polymerizable compound as the polymerizable compound, and the content of the monofunctional polymerizable compound is 80% by mass or more based on the total mass of the polymerizable compound contained in the white ink.

[0073] 3.1. Non-white ink The non-white ink includes a non-white colorant and a polymerizable compound. The non-white ink includes a non-white colorant as the colorant, and the polymerizable compound may include the same or different ones as those in the white ink. Note that the non-white ink may include at least one of a white colorant and inorganic particles as optional components.

[0074] Hereinafter, the non-white ink will be described, and the differences from the white ink will be explained, while the explanations of the same points as the white ink will be omitted.

[0075] 3.1.1. Non-white colorant The non-white ink includes a non-white colorant, that is, a colored colorant or a black colorant. As the non-white colorant, at least one of a pigment and a dye can be used.

[0076] By using a pigment as the colorant, the light resistance of the non-white ink can be improved. As the pigment, either an inorganic pigment or an organic pigment can be used.

[0077] As the inorganic pigment, carbon blacks such as furnace black, lamp black, acetylene black, channel black, etc. (C.I. (Colour Index Generic Name) Pigment Black 7), iron oxide, etc. can be used.

[0078] As the organic pigment, azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, chelate azo pigments, etc., phthalocyanine pigments, perylene, and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. of polycyclic pigments, dye chelates (for example, basic dye type chelates, acid dye type chelates, etc.), dyed lakes (basic dye type lakes, acid dye type lakes), nitro pigments, nitroso pigments, aniline black, daylight fluorescent pigments, etc. can be mentioned.

[0079] More specifically, as the pigment used in yellow ink, C.I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 155, 167, 172, 180, etc. can be mentioned.

[0080] Examples of pigments used in magenta ink include C.I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or C.I. Pigment Violet 19, 23, 32, 33, 36, 38, 43, 50, etc.

[0081] Examples of pigments used in cyan ink include C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, C.I. Vat Blue 4, 60, etc.

[0082] Examples of pigments other than magenta, cyan, and yellow include, for example, C.I. Pigment Green 7, 10, C.I. Pigment Brown 3, 5, 25, 26, C.I. Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63, etc.

[0083] Examples of pigments used in black ink include No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B, etc. of Mitsubishi Chemical Corporation; Raven (registered trademark) 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. of Columbian Carbon Company; Rega1 400R, Rega1 330R, Rega1 660R; Mogul (registered trademark) L, Monarch (registered trademark) 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc. of Cabot Corporation (Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color B1ack S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A, Special Black 4, etc. of Degussa Corporation can be mentioned).

[0084] When a dye is used as a coloring material, the dye can be used without particular limitation, and examples thereof include acid dyes, direct dyes, reactive dyes, basic dyes, and the like. As the dye, for example, C.I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. Acid Red 52, 80, 82, 249, 254, 289, C.I. Acid Blue 9, 45, 249, C.I. Acid Black 1, 2, 24, 94, C.I. Food Black 1, 2, C.I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, C.I. Direct Red 1, 4, 9, 80, 81, 225, 227, C.I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. Direct Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. Reactive Red 14, 32, 55, 79, 249, C.I. Reactive Black 3, 4, 35, and the like can be mentioned.

[0085] The above-mentioned dyes may be used alone or in combination of two or more.

[0086] The content of the coloring material in the non-white ink is preferably 0.2% by mass to 20.0% by mass, more preferably 0.5% by mass to 15.0% by mass, and still more preferably 1.0% by mass to 10.0% by mass with respect to the total mass of the ink.

[0087] 3.1.2. Monofunctional polymerizable compound The content of the monofunctional polymerizable compound in the non-white ink is preferably 80% by mass or more, more preferably 85% by mass or more, and still more preferably 90% by mass or more with respect to the total mass of the polymerizable compounds contained in the non-white ink. Also, the content of the monofunctional polymerizable compound is preferably 99% by mass or less, more preferably 98% by mass or less. When the content of the monofunctional polymerizable compound is 80% by mass or more, the flexibility of the cured film 71 of the non-white ink can be enhanced. Thereby, the adhesion of the cured film 72 of the non-white ink to the recording medium 6 is further improved.

[0088] The monofunctional polymerizable compound is not particularly limited, and examples thereof include a monofunctional polymerizable compound having an alicyclic group, a monofunctional polymerizable compound having an aromatic group, and a monofunctional polymerizable compound having a nitrogen-containing heterocyclic ring.

[0089] 4. Recording Device A recording device used in the method for manufacturing a recording medium will be described with reference to FIG. 1. The recording device 1 includes a first inkjet head 2 that discharges non-white ink, a second inkjet head 3 that discharges white ink, and a transport mechanism 5 for the recording medium 6.

[0090] The first inkjet head 2 may have, for example, first inkjet heads 2a to 2d for each type of ink as shown in the figure. Further, radiation sources 4a to 4d for curing the non-white ink attached to the recording medium 6 are provided downstream of each of the first inkjet heads 2a to 2d in the transport direction F.

[0091] Here, the first inkjet heads 2a to 2d and the radiation sources 4a to 4d are alternately arranged along the transport direction F of the recording medium 6. By arranging them in this way, for the non-white ink discharged from the first inkjet head 2a and attached to the recording medium 6, the non-white ink discharged from the first inkjet heads 2b to 2d installed on the downstream side in the transport direction F, or the white ink discharged from the second inkjet head 3a can be irradiated with radiation from the radiation source 4a and cured before adhering to the recording medium 6. Thereby, when discharging non-white inks of different colors from each of the first inkjet heads 2a to 2d, it is possible to suppress the occurrence of color bleeding.

[0092] The second inkjet head 3 includes, for example, a second inkjet head 3a for attaching white ink, and a radiation source 4e for curing the white ink attached to the recording medium 6 is provided downstream thereof.

[0093] The transport mechanism 5 of the recording medium 6 has, for example, a feed roller 51 and a take-up roller 52, feeds out the recording medium 6 from the feed roller 51 in the transport direction F, and winds up the recording medium 6 after recording by the take-up roller 52 to form a wound body.

[0094] Examples of the first inkjet head 2 and the second inkjet head 3 include a line head that performs recording by a line method and a serial head that performs recording by a serial method.

[0095] In the line method using a line head, for example, the first inkjet head 2 and the second inkjet head 3 are fixed to the recording apparatus 1. The first inkjet head 2 and the second inkjet head 3 are line inkjet heads in which nozzles for discharging ink are formed in a direction intersecting the transport direction F of the recording medium 6 so as to cover the intersecting direction of the printing area of the recording medium 6. Then, the recording medium 6 is moved in the transport direction F, and inks other than white ink and white ink (hereinafter, inks other than white ink and white ink may be collectively referred to as "ink") are discharged from the nozzles of the first inkjet head 2 and the second inkjet head 3 in conjunction with this movement, thereby recording an image on the recording medium 6.

[0096] In the serial method using a serial head, for example, the first inkjet head 2 and the second inkjet head 3 are mounted on a carriage movable in the width direction of the recording medium 6. Then, the carriage is moved along the main scanning direction (the lateral direction, the width direction of the recording medium 6), and inks are discharged from the nozzles of the first inkjet head 2 and the second inkjet head 3 in conjunction with this movement, thereby recording an image on the recording medium 6.

[0097] Among these, from the perspective of winding the recording medium 6 to which ink is attached, it is preferable to adopt a line method. In the case of the line method, while continuously feeding the recording medium 6, recording by the line head and irradiation with radiation from the radiation sources 4a to 4e are performed, and the recording medium 6 to which ink is attached can be wound up downstream. Further, by using the line method, the recorded matter 7 can be manufactured with high efficiency. Note that the form of the recording apparatus 1 shown in FIG. 1 is the line method.

[0098] Examples of the radiation include ultraviolet rays, infrared rays, visible light rays, X-rays, etc. The radiation sources 4a to 4e are not particularly limited, and for example, UV-LEDs can be mentioned. By using such radiation sources 4a to 4e, miniaturization of the apparatus and cost reduction can be achieved. Since the UV-LED as a radiation source is small, it can be attached to the recording apparatus 1.

[0099] 5. Recording Medium The recording medium 6 can be used without particular limitation whether the recording surface 61 is an absorbent recording medium having ink absorbency or a non-absorbent recording medium having no ink absorbency, but it is preferably a non-absorbent recording medium. In particular, the recording medium 6 used in the present embodiment is preferably a non-absorbent recording medium in which both the recording surface 61 and the non-recording surface 62 do not absorb ink.

[0100] By using such a recording medium 6, a recorded matter suitable for label applications and the like can be obtained.

[0101] Further, when using the recording medium 6 in which both the recording surface 61 and the non-recording surface 62 are non-absorbent, when the recorded matters 7 are stacked so that the recording surface 61 and the non-recording surface 62 face each other, the recording surface 61 and the non-recording surface 62 may stick to each other, and the cured films 71, 72 may peel off or scratches may remain on the cured films 71, 72.

[0102] However, in the second ejection step and the second curing step, which will be described later, the white ink is adhered to the recording medium 6 to form a cured film 72 of the white ink. Since the cured film 72 of the white ink contains white pigments and inorganic particles, which are hard particles, even when the recording surfaces 61 and 62 to which the ink is adhered are stacked and stored so as to face each other, it is possible to suppress the occurrence of scratches on the cured films 71 and 72 or the peeling of the cured films 71 and 72.

[0103] The non-absorbent recording medium is not particularly limited. Examples thereof include films and plates of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane; plates of metals such as iron, silver, copper, and aluminum; or metal plates, plastic films, and plates of alloys such as stainless steel and cast iron produced by vapor deposition of these various metals; and recording media in which films of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane are adhered (coated) to paper substrates.

[0104] In the present embodiment, "non-absorbent" means that the water absorption amount from the start of contact to 30 msec is 10 mL / m in the Bristow method. 2 That is, it is as follows. The non-absorbent recording medium refers to a recording medium having such non-absorbency. This Bristow method is the most widespread method for measuring the liquid absorption amount in a short time and is also adopted by the Japan Pulp and Paper Technical Association (JAPAN TAPPI). Details of the test method are described in Standard No. 51, "Paper and Paperboard - Liquid Absorbency Test Method - Bristow Method," of "JAPAN TAPPI Paper and Pulp Test Methods 2000 Edition."

[0105] The recording medium 6 is preferably a transparent substrate. By using a transparent substrate as the recording medium 6, an image formed by non-white ink can be visually recognized from the side of the non-recording surface 62 of the recording medium 6. Further, since the cured film 72 of the white ink forms the background of the image formed by the non-white ink and blocks the light transmitted through the transparent substrate, a recording object 7 with excellent visibility can be obtained.

[0106] In particular, in the present invention, it has been confirmed that by including inorganic particles in the white ink, the whiteness of the white ink is improved. In the present invention, the effect of the cured film 72 of the white ink blocking the light transmitted through the transparent substrate is more significantly exhibited, and the visibility of the image formed by the non-white ink is further improved.

[0107] Here, the transparent substrate is not particularly limited as long as it has transparency such that an image recorded on one surface can be visually recognized from the opposite surface, and the shape, structure, average thickness, and material can be selected according to the purpose.

[0108] In the present invention, "transparent" means a property defined by the haze degree measured in accordance with ASTM D1003 or ISO 14782. The haze degree is preferably 30% or less, and more preferably 10% or less.

[0109] The method for measuring the haze degree is not particularly limited and can be appropriately selected according to the purpose. Examples include a haze meter (device name: HZ-V3, manufactured by Suga Test Instruments Co., Ltd.).

[0110] Examples of the forming material constituting the transparent substrate include polyester resins such as polyethylene terephthalate, polyamide resins such as nylon (registered trademark) and aramid, polyolefin resins such as polyethylene and polypropylene, polycarbonate resins, polystyrene resins, and polyacetal resins. Among these forming materials, from the viewpoints of versatility and ease of availability, it is preferable to include any one of polyethylene terephthalate, polyolefin, and nylon.

[0111] 6. Method for manufacturing a recording medium The method for manufacturing the recording medium 7 is a method for manufacturing the recording medium 7 using the above ink set, and includes a first ejection step of ejecting a non-white ink and attaching it to the recording medium 6, and irradiating the non-white ink attached to the recording medium 6 with radiation to obtain a cured film 71 of the non-white ink. A first curing step, a second ejection step of ejecting a white ink and attaching it to the cured film 71 of the non-white ink, and irradiating the white ink attached to the recording medium 6 with radiation to cure the white ink to obtain a recording medium 7. A second curing step.

[0112] Here, the white ink contains a polymerizable compound, a white pigment, and inorganic particles different from the white pigment. The white ink contains a monofunctional polymerizable compound as the polymerizable compound, and the content of the monofunctional polymerizable compound is 80% by mass or more based on the total mass of the polymerizable compounds contained in the white ink.

[0113] Thereby, a recording medium 7 excellent in adhesion and abrasion resistance can be obtained. Specifically, since the white ink forming the cured film 72 contains 80% by mass or more of the monofunctional polymerizable compound based on the total mass of the polymerizable compounds, the cured film 72 of the white ink has high flexibility. For this reason, the cured film 72 of the white ink has high followability to the recording medium 6, and a recording medium 7 excellent in adhesion can be obtained. Furthermore, since the white ink contains hard particles such as a white pigment and inorganic particles, the hard particles protect the cured film 72, and a recording medium 7 excellent in abrasion resistance can be obtained.

[0114] 6.1. First ejection step The first ejection step is a step of ejecting a non-white ink from the first inkjet head 2 and attaching it to the recording medium 6. More specifically, the pressure generating means is driven to eject the non-white ink filled in the pressure generating chamber of the first inkjet head 2 from the nozzles.

[0115] In this embodiment, as the non-white ink, there are a plurality of non-white inks having different types of coloring materials, which are ejected from the first inkjet heads 2a to 2d. Each of the first inkjet heads 2a to 2d may eject only one type of non-white ink, or each of the first inkjet heads 2a to 2d may eject two or more types of non-white inks.

[0116] The ejection mode such as the duty of the non-white ink in the first ejection step is not particularly limited and can be appropriately adjusted according to the target image.

[0117] 6.2. First curing step The first curing step is a step of irradiating the non-white ink adhered to the recording medium 6 with radiation from the radiation sources 4a to 4d to obtain a cured film 71 of the non-white ink. When the radiation is irradiated, the polymerization reaction of the polymerizable compound starts, so that the non-white ink is cured and the cured film 71 is formed. At this time, if a photoinitiator is present in the non-white ink, active species (starting species) such as radicals, acids, and bases are generated, and the polymerization reaction of the polymerizable compound is promoted by the function of the starting species.

[0118] 6.3. Second ejection step The second ejection step is a step of ejecting a white ink containing a polymerizable compound from the second inkjet head 3 and attaching it to the cured film 71 of the non-white ink. The white ink is attached to the cured film 71 of the non-white ink adhered to the recording medium 6. The white ink may be attached to an area where the cured film 71 of the non-white ink on the recording medium 6 is not formed.

[0119] 6.4. Second curing step The second curing step is a step of irradiating the white ink adhered to the recording medium 6 with radiation from the radiation source 4e to cure the white ink and obtain the recorded matter 7. Thereby, the white ink adhered to the recording medium 6 can be cured.

[0120] Note that in order to sufficiently cure the non-white ink and the white ink, a radiation source (not shown) may be further provided separately from the radiation sources 4a to 4e.

[0121] The white ink contains a monofunctional polymerizable compound, and the content of the monofunctional polymerizable compound is 80% by mass or more based on the total mass of the polymerizable compounds contained in the white ink. Thereby, a cured film 72 excellent in adhesion can be obtained. Further, the white ink contains a white pigment which is a hard particle and inorganic particles. The hard particles play a role of protecting the cured film 72 and make the cured film 72 excellent in abrasion resistance. That is, by the method for manufacturing a recording material of the present invention, a recording material excellent in adhesion and abrasion resistance can be obtained.

[0122] 6.5. Laminating step The method for manufacturing a recording material may include a laminating step. The laminating step is a step of laminating the recording material 7 so that the recording surface 61 and the non-recording surface 62 face each other.

[0123] The laminating method in the laminating step is not particularly limited. For example, a method of laminating single-sheet recording materials 7 one by one so that the recording surface 61 and the non-recording surface 62 face each other, or a method of laminating the recording materials 7 continuously recorded on a long recording medium 6 by winding them in a roll shape downstream of the recording apparatus 1 so that the recording surface 61 and the non-recording surface 62 face each other, etc. may be mentioned.

[0124] Thereby, the manufactured recording materials can be efficiently stored and preserved in a small space. Further, the recording material includes a cured film 72 of white ink excellent in adhesion and abrasion resistance. Therefore, even when the recording materials are stored by laminating them so that the recording surface 61 and the non-recording surface 62 face each other, it is possible to suppress the occurrence of scratches on the cured films 71 and 72 or the peeling of the cured films 71 and 72.

[0125] In the stacking method in the lamination process, it is preferable that the recorded matter 7 continuously recorded on the long recording medium 6 is wound up in a roll shape downstream of the recording apparatus 1 so that the recording surface 61 and the non-recording surface 62 face each other. Specifically, by winding up the recording medium 6 with the take-up roller 52, the recorded matter 7 can be made into a wound body. Among this wound body, the recording surface 61 and the non-recording surface 62 are stacked so as to face each other, and the recorded matter 7 is wound.

[0126] By storing the recorded matter 7 as a wound body, the storage space of the recorded matter 7 can be used efficiently. Further, by winding up the recording medium 6 to which ink has been attached and irradiated with radiation on the downstream side, a wound body of the recorded matter 7 can be obtained efficiently.

[0127] On the other hand, when winding up the recorded matter in a roll shape, by winding it up in a roll shape so that the recording surface 61 and the non-recording surface 62 face each other, the recording surface and the non-recording surface are strongly pressed against each other. However, the recorded matter 7 includes a cured film 72 of white ink having excellent adhesion and abrasion resistance. Therefore, even when the recorded matter 7 is wound up in a roll shape so that the recording surface 61 and the non-recording surface 62 face each other, it is possible to suppress the recording surface 61 and the non-recording surface 62 from sticking and leaving scratches on the cured films 71 and 72 or the cured films 71 and 72 from peeling off. That is, the method for manufacturing a recorded matter of the present invention is effective when printing on a film-like recording medium 6 in an RtoR (roll-to-roll) printing apparatus and winding it up.

[0128] After forming a cured film 71 of non-white ink, which is non-white ink, on the recording medium 6, a cured film 72 of white ink is formed. Since the cured film 72 contains white pigment, which is hard particles, and inorganic particles, even when the recorded matter 7 is stacked so that the recording surface 61 and the non-recording surface 62 face each other, it is possible to suppress the cured films 71 and 72 from leaving scratches or peeling off.

[0129] The recording medium 6 used in this embodiment may be a film-shaped recording medium as shown in FIG. 1, and the recorded matter 7 may be a wound body wound by a take-up roller 52. By storing the recorded matter 7 as a wound body, the storage space of the recorded matter 7 can be used efficiently.

[0130] On the other hand, by making it a wound body, the recording surface 61 and the non-recording surface 62 of the recorded matter 7 come into contact. However, since the cured film 72 of the white ink contains white pigments and inorganic particles which are hard particles, the cured film 72 is protected by the white pigments and inorganic particles, and a recorded matter excellent in adhesion and abrasion resistance can be obtained.

[0131] Also, when the recorded matter 7 is used as a label or the like, when it is unwound from the wound body, it is possible to suppress the cured films 71 and 72 from peeling off or scratches remaining on the cured films 71 and 72. That is, even when the recorded matter 7 is wound by the take-up roller 52 and stored as a wound body, the present invention is particularly useful from the viewpoint of suppressing the recording surface 61 and the non-recording surface 62 of the recorded matter 7 from sticking to each other and suppressing the cured films 71 and 72 from peeling off or scratches remaining on the cured films 71 and 72.

[0132] In particular, from the viewpoint of improving the adhesion of the cured film 72 formed by the white ink to the recording medium 6, when a large amount of monofunctional polymerizable compound is contained, the recording surface 61 and the non-recording surface 62 are likely to stick to each other, and the abrasion resistance of the cured film 71 tends to be impaired. However, in the recorded matter 7 of this embodiment, since the cured film 72 of the white ink contains white pigments and inorganic particles which are hard particles, the recording surface 61 and the non-recording surface 62 are excellent in adhesion and abrasion resistance, and it is possible to suppress the cured films 71 and 72 from peeling off or scratches remaining on the cured films 71 and 72.

[0133] 7. Examples Hereinafter, the present invention will be specifically described using examples and comparative examples. The present invention is not limited by the following examples.

[0134] 7.1. Preparation of Ink Weighed a colorant, a dispersant, and a part of each polymerizable compound, put them into a tank for pigment dispersion, and stirred them together with 1-mm-diameter ceramic beads to obtain a pigment dispersion liquid in which the colorant was dispersed in the polymerizable compound.

[0135] Next, in accordance with the composition shown in Table 1, put the remaining polymerizable compound, a photopolymerization initiator, a polymerization inhibitor, and a surfactant into a mixing tank, which is a stainless-steel container, mix and stir to completely dissolve them, then add the pigment dispersion liquid obtained above, and mix and stir at room temperature for 1 hour. Thereafter, filter through a 5-μm membrane filter to obtain non-white inks and white inks of Examples and Comparative Examples. Note that the numerical values of each component shown in Examples and Comparative Examples in the table are in mass %.

[0136]

Table 1

[0137] The materials described in Table 1 are as follows. <Mono-functional polymerizable compound> ·IBXA (Osaka Organic Chemical Industry Co., Ltd., isobornyl acrylate) ·PEA (trade name “Viscote #192”, Osaka Organic Chemical Industry Co., Ltd., phenoxyethyl acrylate) ·ACMO (KJ Chemicals Co., Ltd., acryloylmorpholine) <Multi-functional polymerizable compound> ·VEEA (Nippon Shokubai Co., Ltd., 2-(2-vinyloxyethoxy)ethyl acrylate) <Photopolymerization initiator> ·819 (trade name “IRGACURE 819”, BASF, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) ·TPO (trade name “IRGACURE TPO”, BASF, 2,4,6-trimethylbenzoyldiphenylphosphine oxide) <Polymerization inhibitor> ·MEHQ (trade name “p-methoxyphenol”, Kanto Chemical Co., Inc., hydroquinone monomethyl ether) <Surfactant> · BYK-UV3500 (BYK Additives&Instruments, polyether-modified silicone with acryloyl group) <Colorant (Pigment)> · Carbon black (trade name "MA-100", manufactured by Mitsubishi Chemical Corporation, carbon black) · Titanium oxide (trade name "CR-93", manufactured by Ishihara Sangyo Co., Ltd., titanium oxide, average particle diameter Dv 50 300 nm) <Dispersant> · Solsperse36000 (Lubrizol, polymeric dispersant)

[0138] In Table 1, the "content of monofunctional polymerizable compound relative to the total mass of polymerizable compounds" represents the ratio (mass%) of the content of monofunctional polymerizable compound to the total content of polymerizable compounds.

[0139] 7.2. Evaluation Method 7.2.1. Evaluation of Adhesion As the recording device 1, a printer equipped with an LED (modified model PX-G5000, manufactured by Seiko Epson Corporation) was used, and a recording was made on a polyvinyl chloride film using the combination of white ink and non-white ink described in Table 1. At this time, the non-white ink was a solid image with 600 dpi × 600 dpi and Duty 100%, and the ink weight per dot was adjusted so that the film thickness of the cured film 71 was 10 μm. After the non-white ink was adhered, ultraviolet light was irradiated so that the irradiation energy became 400 mJ / cm 2 to form the cured film 71.

[0140] Also, the white ink was adhered on top of the cured film 71 of the non-white ink. The adhesion conditions were a solid image with 600 dpi × 600 dpi and Duty 100%, and the ink weight per dot was adjusted so that the film thickness of the cured film 72 was 10 μm. For the white ink as well, after the second ink was adhered, ultraviolet light was irradiated so that the irradiation energy became 400 mJ / cm 2 to obtain a recording.

[0141] Then, the obtained cured films 71 and 72 were evaluated by a cross-cut test in accordance with JIS K5600-5-6.

[0142] More specifically, with a cutter, the blade of the cutting tool was applied perpendicular to the cured films 71 and 72 to make a grid with a mesh where the distance between cuts was 1 mm, creating a 10×10 grid. A transparent adhesive tape (width 25 mm) with a length of about 75 mm was attached to the grid, and the tape was rubbed firmly with a finger so that the cured films 71 and 72 could be seen through. Next, within 5 minutes after attaching the tape, the tape was surely peeled off from the cured films 71 and 72 at an angle close to 60° in 0.5 to 1.0 seconds, and the state of the grid was observed visually. The evaluation criteria are as follows. (Evaluation Criteria) A: Less than 10% of the grids showed peeling. B: 10% or more and less than 35% of the grids showed peeling. C: 35% or more of the grids showed peeling.

[0143] 7.2.2. Evaluation of Abrasion Resistance For the cured films 71 and 72 prepared in the above adhesion evaluation, a micro-scratch test was evaluated in accordance with JIS R3255. For the measurement, a load resistance as abrasion resistance was measured using an ultra-thin film scratch tester (CSR-5000, manufactured by Nanotech Corporation). The load resistance was measured by performing a micro-scratch while applying a load, and was defined as the load when the stylus reached the media surface. The measurement was performed with a stylus diameter of 15 μm, an amplitude of 100 μm, and a scratch speed of 10 μm / sec. The evaluation criteria are as follows. (Evaluation Criteria) A: 30 mN / cm 2 Above. B: 25 mN / cm 2 Above 30 mN / cm 2 Less than. C: 20 mN / cm 2 Above 25 mN / cm 2 Less than. D: 20 mN / cm 2 Less than.

[0144]

Table 2

[0145] 7.3. Evaluation Results The evaluation results are shown in Table 2. From the comparison between each example and Comparative Example 1, it can be seen that by containing a white pigment and inorganic particles in the white ink, the adhesion and rubbing resistance of the recording material, particularly the rubbing resistance of the recording material, are improved. Further, from the comparison between each example and Comparative Example 2, it can be confirmed that when the content of the monofunctional polymerizable compound in the white ink is 80% by mass or more based on the total mass of the polymerizable compounds contained in the white ink, the adhesion of the cured films 71 and 72 to the recording medium 6 is improved.

Explanation of Reference Numerals

[0146] 2, 2a, 2b, 2c, 2d… First inkjet head, 3, 3a… Second inkjet head, 4a, 4b, 4c, 4d, 4e… Radiation source, 5… Conveying mechanism, 6… Recording medium, 51… Feed roller, 52… Take-up roller, 71… Cured film of non-white ink, 72… Cured film of white ink.

Claims

1. A radiation-curable inkjet composition comprising a polymerizable compound, a white pigment, and inorganic particles different from the white pigment, 、 wherein the inorganic particles include any one or more of silica, titanium oxide, zinc oxide, antimony oxide, magnesium oxide, aluminum oxide, and zirconium oxide, the content of the inorganic particles is 10% by mass or more and 30% by mass or less based on the total mass of the radiation-curable inkjet composition, the polymerizable compound includes a monofunctional polymerizable compound, and the content of the monofunctional polymerizable compound is 80% by mass or more based on the total mass of the polymerizable compound contained in the radiation-curable inkjet composition. A radiation-curable inkjet composition.

2. The radiation-curable inkjet composition according to claim 1, wherein the inorganic particles are silica particles.

3. A non-white ink containing a non-white colorant and a polymerizable compound, and a white ink, wherein the white ink is the radiation-curable inkjet composition according to any one of claims 1 or 2. An ink set.

4. The ink set according to claim 3, wherein the non-white ink contains the monofunctional polymerizable compound, and the content of the monofunctional polymerizable compound is 80% by mass or more based on the total mass of the polymerizable compound contained in the non-white ink.

5. A method for manufacturing a recorded matter using the ink set according to claim 3 or 4, comprising: a first ejection step of ejecting the non-white ink and attaching it to a recording medium; a first curing step of irradiating radiation to the non-white ink attached to the recording medium to obtain a cured film of the non-white ink; a second ejection step of ejecting the white ink and attaching it to the cured film of the non-white ink; and a second curing step of irradiating radiation to the white ink attached to the recording medium to cure the white ink and obtain a recorded matter.

6. The method for manufacturing a recorded matter according to claim 5, further comprising a laminating step of laminating the recorded matter such that a recording surface to which the non-white ink and the white ink are attached and a non-recording surface to which the non-white ink and the white ink are not attached face each other.

7. The method for manufacturing a recorded matter according to claim 6, wherein the laminating step includes winding the recorded matter in a roll shape such that the recording surface and the non-recording surface face each other.

8. ​ ​ ​ ​ ​ ​ ​ ​ ​ The manufacturing method of a recording medium according to claim 6 or 7, wherein both the recording surface and the non-recording surface are non-absorbent.

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