Radiation-curable inkjet composition and recording method

Abstract

To provide a radiation-curable inkjet composition excellent in both adhesion of a coating film and color reproducibility.SOLUTION: The radiation-curable inkjet composition contains inorganic particles, a coloring material, and a polymerizable compound. The polymerizable compound contains a monofunctional monomer. The content of the monofunctional monomer is 80 mass% or more based on the total amount of the polymerizable compound. The content of the inorganic particles is 10 mass% or less based on the total amount of the ink composition.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a radiation-curable inkjet composition and a recording method.

Background Art

[0002] An inkjet recording method is used for printing business documents including characters and charts using ordinary paper as a recording medium, and the frequency of use for such applications is increasing. In such applications, since high levels of image color development and fastness (such as rub resistance, light resistance, ozone gas resistance, water resistance, etc.) are required, inks using pigments as colorants are often used.

[0003] The inkjet recording method uses a relatively simple device and can record high-definition images, and has been rapidly developing in various fields. Among them, various studies have been conducted on methods for recording on a substrate to be stretch-processed. For example, Patent Document 1 discloses an active energy ray-curable ink containing a polymerizable compound having a monofunctional monomer content of 85% by mass or more, a pigment, and a fluorine-based surfactant for the purpose of obtaining a highly stretchable and highly color-concentrated laminate cured product in an inkjet image format, and adjusting the monomer and pigment contents of the polymerizable compound.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described in Patent Document 1, it is known that the adhesion of a cured coating film can be improved by increasing the content of a monofunctional monomer with respect to the total amount of the polymerizable compound. However, simply increasing the proportion of the monofunctional monomer contained in the polymerizable compound may not result in sufficient adhesion of the coating film depending on the type and amount of the coloring material, the combination with materials such as the recording medium, etc.

Means for Solving the Problems

[0006] The present invention relates to a radiation-curable inkjet composition containing inorganic particles, a coloring material, and a polymerizable compound, wherein the polymerizable compound contains a monofunctional monomer, the content of the monofunctional monomer is 80% by mass or more with respect to the total amount of the polymerizable compound, and the content of the inorganic particles is 10% by mass or less with respect to the total amount of the ink composition.

[0007] Further, the recording method of the present invention includes a discharging step of discharging the above-described radiation-curable inkjet composition from an inkjet head and attaching it to a recording medium, and an irradiating step of irradiating radiation to the radiation-curable inkjet composition attached to the recording medium.

Brief Description of the Drawings

[0008]

Figure 1

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 with reference to the drawings as necessary. However, the present invention is not limited to this, and various modifications are possible without departing from the gist thereof. In the drawings, the same elements will be denoted by the same reference numerals, and overlapping explanations will be omitted. Also, the positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[0010] In this specification, “(meth)acryloyl” means at least either acryloyl or the corresponding methacryloyl, “(meth)acrylate” means at least either acrylate or the corresponding methacrylate, and “(meth)acrylic” means at least either acrylic or the corresponding methacrylic.

[0011] 1. Radiation-curable inkjet composition The radiation-curable inkjet composition of this embodiment (hereinafter, also simply referred to as “ink composition”) contains inorganic particles, a colorant, and a polymerizable compound. The polymerizable compound contains a monofunctional monomer, and the content of the monofunctional monomer is 80% by mass or more based on the total amount of the polymerizable compound. The content of the inorganic particles is 10% by mass or less based on the total amount of the ink composition.

[0012] Conventionally, it has been known that by increasing the proportion of the monofunctional monomer contained in the polymerizable compound, the adhesion of the ink coating film to the recording medium is improved. In contrast, in this embodiment, by using a predetermined amount of inorganic particles, it is possible to further improve the adhesion. Further, by adjusting the amount of the inorganic particles used, the influence of the inorganic particles on the color reproducibility of the ink composition can also be reduced. Hereinafter, each component of the ink composition will be described in detail.

[0013] In this embodiment, the radiation-curable inkjet composition means an inkjet composition that cures by irradiation with radiation. Examples of the radiation include ultraviolet rays, electron beams, infrared rays, visible light, X-rays, etc. Among these, ultraviolet rays are preferable as the radiation because the radiation source is easily available and widely used, and materials suitable for curing by ultraviolet radiation are easily available and widely used.

[0014] 1.1. Inorganic particles The inorganic particles are not particularly limited, and examples include metal oxides such as alumina, silica, zirconia, and titania; metal hydroxides such as magnesium hydroxide, aluminum hydroxide, and calcium hydroxide; and metal nitrides such as silicon nitride, titanium nitride, and aluminum nitride.

[0015] Among these, metal oxides are preferred, alumina or silica is more preferred, and alumina is even more preferred. By using such inorganic particles, the adhesion between the formed ink coating film and the recording medium tends to be further improved.

[0016] In addition, in this embodiment, the inorganic particles are different from the colorant described later, and preferably contain less than the content of the colorant as needed. Specifically, with respect to 100 parts by mass of the colorant, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less.

[0017] The content of the inorganic particles is 10% by mass or less, preferably 5.0% by mass or less, more preferably 3.0% by mass or less with respect to the total amount of the ink composition. Also, the content of the inorganic particles is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 0.7% by mass or more with respect to the total amount of the ink composition. When the content of the inorganic particles is 10% by mass or less, the color reproducibility of the ink composition is further improved. Also, when the content of the inorganic particles is 0.1% by mass or more, the adhesion between the ink coating film and the recording medium tends to be further improved.

[0018] 1.2. Colorant The colorant is not particularly limited, and examples include pigments and dyes. Among these, pigments are preferred. By using such a colorant, the color reproducibility tends to be further improved.

[0019] The content of the coloring material is preferably 1.0 to 15% by mass, more preferably 2.0 to 10% by mass, and still more preferably 2.5 to 7.5% by mass with respect to the total amount of the ink composition. When the content of the coloring material is within the above range, the adhesion and color reproducibility tend to be further improved.

[0020] 1.2.1. Pigment

[0021] The pigment is not particularly limited, and examples thereof include inorganic pigments and organic pigments. The pigment may be used alone or in combination of two or more.

[0022] The inorganic pigments that can be used in the present embodiment are not particularly limited, and examples thereof include carbon blacks such as furnace black, lamp black, acetylene black, and channel black (C.I. (Colour Index Generic Name) Pigment Black 7), iron oxide, and titanium oxide.

[0023] The organic pigments that can be used in the present embodiment are not particularly limited, and examples thereof include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments and other 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.

[0024] Among these, colored pigments are preferred, and black pigments are more preferred. In the present embodiment, the colored pigment means a pigment other than the white pigment. Since such pigments are easily affected by the addition of inorganic particles in terms of color reproducibility, the present invention is particularly useful.

[0025] 1.2.2. Dye The dyes are not particularly limited, and for example, acid dyes, direct dyes, reactive dyes, and basic dyes can be used. The dyes may be used alone or in combination of two or more.

[0026] The dyes that can be used in this embodiment are not particularly limited, and 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 can be mentioned.

[0027] 1.3. Polymerizable Compound The polymerizable compound contains a monofunctional monomer and may contain a polyfunctional monomer as necessary. Each monomer will be described in detail below.

[0028] 1.3.1. Monofunctional Monomer The monofunctional monomer is not particularly limited, and for example, a monofunctional monomer having an alicyclic group, a monofunctional monomer having an aromatic group, and a nitrogen-containing monofunctional monomer can be mentioned.

[0029] The content of the monofunctional monomer is 80% by mass or more, preferably 83 - 95% by mass, more preferably 85 - 90% by mass, based on the total amount of the polymerizable compound. When the content of the monofunctional monomer with respect to the polymerizable compound is 80% by mass or more, the adhesion, stretchability, and curability between the ink coating film and the recording medium tend to be further improved.

[0030] The content of the monofunctional monomer is preferably 68 to 90% by mass, more preferably 70 to 85% by mass, and still more preferably 73 to 80% by mass with respect to the total amount of the ink composition. When the content of the monofunctional monomer in the ink composition is within the above range, the adhesion, stretchability, and curability between the ink coating film and the recording medium tend to be further improved.

[0031] 1.3.1.1. Monofunctional monomer having an alicyclic group The monofunctional monomer having an alicyclic group is not particularly limited. For example, monomers having a monocyclic hydrocarbon group such as isobornyl acrylate, tert-butylcyclohexanol acrylate (TBCHA), 2-(meth)acrylic acid-1,4-dioxaspiro[4,5]dec-2-ylmethyl; monomers having an unsaturated polycyclic hydrocarbon group such as dicyclopentenyl acrylate, dicyclopentenyl oxyethyl acrylate; dicyclopentanyl acrylate, isobornyl acrylate, etc. are mentioned.

[0032] Among these, dicyclopentenyl (meth)acrylate (DCPA) and isobornyl acrylate (IBXA) are preferred. By using such monomers, the adhesion and abrasion resistance of the resulting coating film tend to be further improved.

[0033] The content of the monofunctional monomer having an alicyclic group is preferably 15 to 45% by mass, more preferably 20 to 40% by mass, and still more preferably 25 to 35% by mass with respect to the total amount of the polymerizable compound. When the content of the monofunctional monomer having an alicyclic group in the polymerizable compound is within the above range, the adhesion and abrasion resistance between the ink coating film and the recording medium tend to be further improved.

[0034] The content of the monofunctional monomer having an alicyclic group is preferably 10 to 40% by mass, more preferably 15 to 35% by mass, and still more preferably 20 to 30% by mass with respect to the total amount of the ink composition. When the content of the monofunctional monomer having an alicyclic group in the ink composition is within the above range, the adhesion between the ink coating film and the recording medium and the abrasion resistance tend to be further improved.

[0035] 1.3.1.2. Monofunctional monomer having an aromatic group The monofunctional monomer having an aromatic group is not particularly limited. For example, 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 can be mentioned.

[0036] Among these, phenoxyethyl acrylate (PEA) is preferable. By using such an aromatic group-containing monofunctional monomer, the solubility of the photopolymerization initiator is further improved, and the curability of the ink composition tends to be further improved. In particular, when an acylphosphine oxide-based photopolymerization initiator or a thioxanthone-based photopolymerization initiator is used, the solubility tends to be good.

[0037] The content of the monofunctional monomer having an aromatic group is preferably 25 to 50% by mass, more preferably 30 to 45% by mass, and still more preferably 35 to 40% by mass with respect to the total amount of the polymerizable compound. When the content of the aromatic group-containing monofunctional monomer in the polymerizable compound is within the above range, the adhesion and curability between the ink coating film and the recording medium tend to be further improved.

[0038] The content of the monofunctional monomer having an aromatic group is preferably 15 to 45% by mass, more preferably 20 to 40% by mass, and still more preferably 25 to 35% by mass with respect to the total amount of the ink composition. When the content of the aromatic group-containing monofunctional monomer with respect to the polymerizable compound is within the above range, the adhesion and curability between the ink coating film and the recording medium tend to be further improved.

[0039] 1.3.1.3. Nitrogen-containing monofunctional monomer The nitrogen-containing monofunctional monomer is not particularly limited. For example, nitrogen-containing monofunctional vinyl monomers such as N-vinylcaprolactam, N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, and N-vinylpyrrolidone; nitrogen-containing monofunctional acrylate monomers such as acryloylmorpholine; (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, diacetoneacrylamide, N,N-dimethyl(meth)acrylamide, and quaternary salts of dimethylaminoethyl acrylate benzyl chloride, etc. Examples thereof include nitrogen-containing monofunctional acrylamide monomers such as (meth)acrylamide.

[0040] Among these, nitrogen-containing monofunctional acrylate monomers are preferred, and monomers having a nitrogen-containing heterocyclic structure such as acryloylmorpholine (ACMO) are more preferred. By using such nitrogen-containing monofunctional vinyl monomers, the adhesion, abrasion resistance, and flexibility between the ink coating film and the recording medium tend to be further improved.

[0041] The content of the nitrogen-containing monofunctional monomer is preferably 5 to 30% by mass, more preferably 10 to 25% by mass, and still more preferably 15 to 20% by mass with respect to the total amount of the polymerizable compound. When the content of the aromatic group-containing monofunctional monomer is within the above range, the adhesion, abrasion resistance, and flexibility between the ink coating film and the recording medium tend to be further improved.

[0042] The content of the nitrogen-containing monofunctional monomer is preferably 2.5 to 27.5% by mass, more preferably 7.5 to 22.5% by mass, and still more preferably 12.5 to 17.5% by mass with respect to the total amount of the ink composition. When the content of the aromatic group-containing monofunctional monomer is within the above range, the adhesion, rubbing resistance, and flexibility between the ink coating film and the recording medium tend to be further improved.

[0043] 1.3.2. Polyfunctional monomer The polyfunctional monomer is not particularly limited, and examples thereof include vinyl ether group-containing (meth)acrylate and polyfunctional (meth)acrylate.

[0044] The content of the polyfunctional monomer is preferably 5.0 to 20% by mass, more preferably 5.0 to 17% by mass, and still more preferably 10 to 15% by mass with respect to the total amount of the polymerizable compound. When the content of the polyfunctional monomer with respect to the polymerizable compound is within the above range, the adhesion, stretchability, and curability between the ink coating film and the recording medium tend to be further improved.

[0045] The content of the polyfunctional monomer is preferably 3.0 to 25% by mass, more preferably 5.0 to 20% by mass, and still more preferably 10 to 15% by mass with respect to the total amount of the ink composition. When the content of the monofunctional monomer with respect to the ink composition is within the above range, the adhesion, stretchability, and curability between the ink coating film and the recording medium tend to be further improved.

[0046] 1.3.2.1. Vinyl ether group-containing (meth)acrylate The vinyl ether group-containing (meth)acrylate is not particularly limited, and examples thereof include compounds represented by the formula (1). By including such a vinyl ether group-containing (meth)acrylate, the viscosity of the ink composition decreases, and the ejection stability and curability tend to be further improved. CH2=CR 1 -CO-OR 2 -O-CH=CH-R 3 ··· (1) (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.)

[0047] In the above formula (1), examples of the divalent organic residue having 2 to 20 carbon atoms represented by R 2 include a linear, branched or cyclic alkylene group having 2 to 20 carbon atoms which may be substituted, an alkylene group having 2 to 20 carbon atoms which may be substituted and has an oxygen atom due to an ether bond and / or an ester bond in the structure, and a divalent aromatic group having 6 to 11 carbon atoms which may be substituted.

[0048] 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 composition and further improving the curability of the ink composition, R 2 is more preferably a compound having a glycol ether chain, which is an alkylene group having 2 to 9 carbon atoms having 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.

[0049] In the above formula (1), examples of the monovalent organic residue having 1 to 11 carbon atoms represented by R 3 include a linear, branched or cyclic alkyl group having 1 to 10 carbon atoms which may be substituted, and a monovalent aromatic group having 6 to 11 carbon atoms which may be substituted.

[0050] 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.

[0051] When each of the above organic residues is a group that may be substituted, the substituents can be divided into a group containing a carbon atom and a group not containing a carbon atom. First, when the substituent is a group containing a carbon atom, the carbon atom is counted in the carbon number of the organic residue. Examples of the group containing a carbon atom include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing a carbon atom include, but are not limited to, a hydroxyl group and a halo group.

[0052] Specific examples of the compound of formula (1) include, but are not particularly limited to, for example, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, and 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA) is preferred. By including such a vinyl ether group-containing (meth)acrylate, the ejection stability and curability tend to be further improved.

[0053] The content of the vinyl group-containing (meth)acrylate is preferably 5.0 to 20% by mass, more preferably 5.0 to 17% by mass, and still more preferably 10 to 15% by mass with respect to the total amount of the polymerizable compounds. When the content of the vinyl group-containing (meth)acrylate with respect to the polymerizable compound is within the above range, the adhesion between the ink coating film and the recording medium, the ejection stability, the curability, etc. tend to be further improved.

[0054] The content of the vinyl group-containing (meth)acrylate is preferably 3.0 to 25% by mass, more preferably 5.0 to 20% by mass, and still more preferably 10 to 15% by mass with respect to the total amount of the ink composition. When the content of the vinyl group-containing (meth)acrylate with respect to the ink composition is within the above range, the adhesion between the ink coating film and the recording medium, the ejection stability, the curability, etc. tend to be further improved.

[0055] 1.3.2.2. Polyfunctional (meth)acrylate The polyfunctional (meth)acrylate is not particularly limited. For example, bifunctional (meth)acrylates such as dipropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate; polyfunctional (meth)acrylates with three or more functional groups such as trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate can be mentioned.

[0056] 1.4. Photopolymerization initiator The photopolymerization initiator is not particularly limited as long as it generates active species upon irradiation with radiation. For example, known photopolymerization initiators such as acylphosphine oxide-based photopolymerization initiators, alkylphenone-based polymerization initiators, titanocene-based polymerization initiators, and thioxanthone-based photopolymerization initiators can be mentioned. Among these, acylphosphine oxide-based photopolymerization initiators are preferred. By using such a photopolymerization initiator, the curability of the ink composition is further improved, and particularly the curability by the curing process using the light of UV-LED tends to be further improved. The photopolymerization initiator may be used alone or in combination of two or more.

[0057] The acylphosphine oxide-based photopolymerization initiator is not particularly limited. For example, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, etc. can be mentioned.

[0058] Examples of commercially available acylphosphine oxide-based photoinitiators include IRGACURE 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-phenylketone with a mass ratio of 25:75), IRGACURE TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) (all of the above are manufactured by BASF), and the like.

[0059] The content of the photoinitiator is preferably 3.0 to 15% by mass, more preferably 4.0 to 13.5% by mass, and still more preferably 5.0 to 12% by mass based on the total amount of the ink composition. When the content of the photoinitiator is within the above range, the curability of the ink composition and the solubility of the photoinitiator tend to be further improved.

[0060] 1.5. Polymerization inhibitor Examples of the polymerization inhibitor include, but are not limited to, 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), 4,4'-thiobis(3-methyl-6-t-butylphenol), hindered amine compounds, and the like. The polymerization inhibitor may be used alone or in combination of two or more.

[0061] The content of the polymerization inhibitor is preferably 0.01 to 1.0% by mass, more preferably 0.05 to 0.5% by mass based on the total amount of the ink composition.

[0062] 1.6. Other components The radiation-curable inkjet composition according to this embodiment may further contain additives such as a slip agent and a dispersant, if necessary.

[0063] 1.6.1. Slip Agent As the slip agent, a silicone-based surfactant is preferable, and a polyester-modified silicone or a polyether-modified silicone is more preferable. Examples of the polyester-modified silicone include BYK-347, 348, BYK-UV3500, 3510, 3530 (manufactured by BYK Additives&Instruments), etc., and examples of the polyether-modified silicone include BYK-3570 (manufactured by BYK Additives&Instruments), etc. The slip agent may be used alone or in combination of two or more.

[0064] The content of the slip agent is preferably 0.01 to 2.0% by mass, more preferably 0.05 to 1.0% by mass, based on the total amount of the ink composition.

[0065] 1.6.2. Dispersant The dispersant is not particularly limited, and examples thereof include dispersants commonly used for preparing pigment dispersions such as polymer dispersants. Specific examples thereof include those mainly composed of one or more of polyoxyalkylene polyalkylene polyamine, vinyl-based polymers and copolymers, acrylic-based polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino-based polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxy resins. The dispersant may be used alone or in combination of two or more.

[0066] Examples of commercially available polymer dispersants include the AJISPER series manufactured by Ajinomoto Fine-Techno Co., Inc., the Solsperse series (such as Solsperse 36000) available from Avecia or Noveon, the DISPERBYK series manufactured by BYK Additives & Instruments, and the DISPARON series manufactured by Kusumoto Chemicals, Ltd.

[0067] The content of the dispersant is preferably 0.1 to 2.0% by mass, more preferably 0.2 to 1.5% by mass, and still more preferably 0.3 to 1.2% by mass, based on the total amount of the ink composition.

[0068] 2. Recording method The recording method of this embodiment has a discharging step of discharging the above-described radiation-curable inkjet composition from an inkjet head and attaching it to a recording medium for recording, and further has an irradiation step of irradiating radiation onto the recording surface of the ink composition on the recording medium. Note that the discharging method as described above is also referred to as the inkjet method.

[0069] 2.1. Discharging step In the discharging step, the heated composition is discharged from the inkjet head and attached to the recording medium. More specifically, the pressure generating means is driven to discharge the composition filled in the pressure generating chamber of the inkjet head from the nozzles.

[0070] Examples of the inkjet head used in the discharging step include a line head that performs recording by a line method and a serial head that performs recording by a serial method.

[0071] In the line method using a line head, for example, an inkjet head having a width equal to or greater than the recording width of the recording medium is fixed to the inkjet apparatus. Then, the recording medium is moved along the sub-scanning direction (the longitudinal direction of the recording medium, the conveyance direction), and ink droplets are discharged from the nozzles of the inkjet head in conjunction with this movement, thereby recording an image on the recording medium.

[0072] In the serial method using a serial head, for example, an inkjet head is mounted on a carriage that can move in the width direction of the recording medium. Then, the carriage is moved along the main scanning direction (the lateral direction and the width direction of the recording medium), and ink droplets are ejected from the nozzle openings of the head in conjunction with this movement, whereby an image can be recorded on the recording medium.

[0073] 2.2. Irradiation step In the irradiation step, radiation is irradiated onto the radiation-curable inkjet composition adhering to the recording medium. When the radiation is irradiated, the polymerization reaction of the monomer starts, causing the composition to cure and a coating film to be formed. At this time, if a photoinitiator is present, active species (starting species) such as radicals, acids, and bases are generated, and the polymerization reaction of the monomer is promoted by the function of the starting species. Also, if a photosensitizer is present, it absorbs radiation and enters an excited state, and by contacting the photoinitiator, it promotes the decomposition of the photoinitiator, enabling the curing reaction to be achieved more effectively.

[0074] Here, examples of the radiation include ultraviolet rays, infrared rays, visible light, X-rays, etc. The radiation source irradiates the composition with a radiation source provided downstream of the inkjet head. The radiation source is not particularly limited, and for example, an ultraviolet light-emitting diode can be mentioned. By using such a radiation source, miniaturization of the apparatus and cost reduction can be realized. Since the ultraviolet light-emitting diode as an ultraviolet source is small, it can be installed inside the inkjet apparatus.

[0075] For example, the ultraviolet light-emitting diode can be attached to a carriage (both ends along the medium width direction and / or the medium conveyance direction side) on which an inkjet head that ejects the radiation-curable inkjet composition is mounted. Furthermore, due to the composition of the above-mentioned radiation-curable inkjet composition, curing at low energy and high speed can be realized.

[0076] 3. Inkjet apparatus The inkjet device of this embodiment includes an inkjet head having a nozzle for discharging a composition and a pressure chamber to which the composition is supplied, and a radiation source for irradiating the composition with radiation, and uses the radiation-curable inkjet composition as the composition.

[0077] As an example of an inkjet device, FIG. 1 shows a perspective view of a serial printer. As shown in FIG. 1, the serial printer 20 includes a conveyance unit 220 and a recording unit 230. The conveyance unit 220 conveys the recording medium F fed to the serial printer to the recording unit 230 and discharges the recorded recording medium outside the serial printer. Specifically, the conveyance unit 220 has respective feed rollers and conveys the fed recording medium F in the sub-scanning direction T1.

[0078] The recording unit 230 includes an inkjet head 231 that discharges the radiation-curable inkjet composition onto the recording medium F fed from the conveyance unit 220, a radiation source 232 that irradiates the adhered radiation-curable inkjet composition with radiation, a carriage 234 on which these are mounted, and a carriage moving mechanism 235 that moves the carriage 234 in the main scanning directions S1, S2 of the recording medium F.

[0079] In FIG. 1, a mode in which the radiation source is mounted on the carriage is shown, but the present invention is not limited to this, and a radiation source that is not mounted on the carriage may be provided.

[0080] The above-described inkjet device may be a serial printer or a line printer.

[0081] 4. Record The record of this embodiment is obtained by adhering and curing the radiation-curable inkjet composition on a recording medium. Since the composition has good adhesion, it is possible to suppress cracking and chipping of the coating film when post-processing such as cutting and bending is performed. Therefore, the record of this embodiment can be suitably used for sign applications and the like.

[0082] The material of the recording medium is not particularly limited, and examples thereof include plastics such as polyvinyl chloride, polyethylene terephthalate, polypropylene, polyethylene, polycarbonate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, and those with processed surfaces thereof, glass, paper, metal, wood, etc.

Examples

[0083] Hereinafter, the present invention will be described more specifically using examples and comparative examples. The present invention is not limited by the following examples at all.

[0084] 1. Preparation of radiation-curable inkjet composition First, a part of the coloring material, dispersant, and each monomer were weighed and placed in a tank for pigment dispersion, and a ceramic bead mill with a diameter of 1 mm was placed in the tank and stirred to obtain a pigment dispersion liquid in which the coloring material was dispersed in the monomer. Next, the remaining monomers, polymerization initiator, and polymerization inhibitor were placed in a tank for mixture, which is a stainless steel container, so as to have the composition shown in Table 1, and mixed and stirred until completely dissolved. Then, the pigment dispersion liquid obtained above was added, and further mixed and stirred at room temperature for 1 hour, and further filtered through a 5 μm membrane filter to obtain the radiation-curable inkjet composition of each example. The numerical values of each component shown in each example in the table represent mass%.

[0085] The abbreviations and product components used in Table 1 are as follows.

[0086] <Mono-functional monomer> ·IBXA (manufactured by Osaka Organic Chemical Industry Co., Ltd., isobornyl acrylate) ·PEA (trade name "Biscoat #192", manufactured by Osaka Organic Chemical Industry Co., Ltd., phenoxyethyl (meth) acrylate) ·ACMO (manufactured by KJ Chemicals Co., Ltd., acryloylmorpholine) <Multifunctional monomer> ·VEEA (manufactured by Nippon Shokubai Co., Ltd., 2-(2-vinyloxyethoxy)ethyl acrylate) <Polymerization initiator> ·819 (trade name "IRGACURE 819", manufactured by BASF, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) ·TPO (trade name "IRGACURE TPO", manufactured by BASF, 2,4,6-trimethylbenzoyldiphenylphosphine oxide) <Polymerization inhibitor> ·MEHQ (trade name "p-methoxyphenol", manufactured by Kanto Chemical Co., Inc., hydroquinone monomethyl ether) <Slip agent> ·BYK-UV3500 (manufactured by BYK Additives&Instruments, polyether-modified polydimethylsiloxane having acryloyl groups) <Inorganic particles> ·Silica particles (trade name "QSG-10", manufactured by Shin-Etsu Silicone Co., Ltd., silica nanoparticles, average particle size 15 nm) ·Alumina particles (trade name "1330DL", manufactured by Corefront Co., Ltd., alumina nanoparticles, average particle size 20 nm) <Colorant> ·Carbon black (manufactured by Orient Chemical Industries Co., Ltd., product name BONJET BLACK CW-1) ·Pigment Blue15:3 (trade name "C.I. Pigment Blue 15:3", manufactured by DIC, phthalocyanine blue) <Dispersant> ·Solsperse 36000 (manufactured by Lubrizol, polymer dispersant)

[0087] In Table 1, the "ratio of monofunctional monomer" represents the content of the monofunctional monomer with respect to the total amount of the polymerizable compounds.

[0088] 2. Evaluation method 2.1. Evaluation of adhesion Each radiation-curable inkjet composition was applied to a polyvinyl chloride film with a bar coater so that the coating thickness was 10 μm, and ultraviolet rays were irradiated so that the integrated energy was 200 mJ / cm 2 At that time, an LED having a peak wavelength of 395 nm was used as the light source. Then, the obtained coating film was evaluated for cross-cut test in accordance with JIS K5600-5-6.

[0089] More specifically, with a cutter, the blade of the cutting tool was applied perpendicular to the coating film to make a grid of 10×10 squares with a distance of 1 mm between the cuts. A transparent adhesive tape (width 25 mm) with a length of about 75 mm was attached to the grid, and the tape was rubbed well with fingers so that the cured film could be seen through. Next, within 5 minutes after attaching the tape, the tape was surely peeled off from the cured film at an angle close to 60° in 0.5 to 1.0 seconds, and the state of the grid was visually observed. The evaluation criteria are as follows. (Evaluation Criteria) A: Less than 10% of the grid showed peeling of the cured film. B: Peeling of the cured film was observed in 10% or more and less than 35% of the grid. C: Peeling of the cured film was observed in 35% or more of the grid.

[0090] 2.2. Evaluation of Color Reproducibility For the coating film obtained in the above adhesion (scratch resistance) test, using a colorimeter (trade name "Gretag Macbeth Spectrolino", manufactured by X-RITE), the L * value (L * 1) was measured. Similarly, in each radiation-curable inkjet composition, an ink containing no inorganic particles was separately prepared, and its L * value (L * 2) was measured. For each ink, the difference between L * 1 and L * 2 was obtained, and the color reproducibility was evaluated according to the following evaluation criteria. (Evaluation Criteria) A: The difference between L * 1 and L * 2 is less than 3 B: L* 1 and L * The difference between 1 and 2 is 3 or more and less than 5 C:L * 1 and L * The difference between 1 and 2 is 5 or more

[0091]

Table 1

[0092] 3. Evaluation Results Table 1 shows the composition of the radiation-curable inkjet composition used in each example and the evaluation results. From the comparison between each example and Comparative Example 1, it can be seen that the adhesion is improved by containing inorganic particles. Also, from the comparison between each example and Comparative Examples 2 and 3, it can be seen that by setting the content of the monofunctional monomer to 80% by mass or more based on the total amount of the polymerizable compounds and the content of the inorganic particles to 10% by mass or less based on the total amount of the ink composition, both excellent adhesion and color reproducibility can be achieved.

Explanation of Reference Numerals

[0093] 20… serial printer, 220… conveyance unit, 230… recording unit, 231… inkjet head, 232, 233… light sources, 234… carriage, 235… carriage movement mechanism, F… recording medium, S1, S2… main scanning directions, T1… sub-scanning direction

Claims

1. An inorganic particle, a coloring material, and a polymerizable compound, wherein the polymerizable compound contains a monofunctional monomer, the content of the monofunctional monomer is 80% by mass or more based on the total amount of the polymerizable compound, the content of the inorganic particle is 10% by mass or less based on the total amount of the ink composition, the polymerizable compound contains a polyfunctional monomer, the polyfunctional monomer contains a vinyl group-containing (meth)acrylate represented by the following formula (1), the content of the vinyl group-containing (meth)acrylate represented by the formula (1) is 3.0% by mass or more and 25% by mass or less based on the total amount of the ink composition, H 2 C=CR 1 -CO-OR 2 -O-CH=CH-R 3 ··· (1) (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.) A radiation-curable inkjet composition (excluding those containing an acid-modified acrylic monomer).

2. The inorganic particle contains alumina, The radiation-curable inkjet composition according to Claim 1.

3. The coloring material is a pigment, The radiation-curable inkjet composition according to Claim 1 or 2.

4. The pigment is a colored pigment, The radiation-curable inkjet composition according to Claim 3.

5. The content of the inorganic particle is 5.0% by mass or less based on the total amount of the ink composition, The radiation-curable inkjet composition according to any one of Claims 1 to 4.

6. A discharging step of discharging the radiation-curable inkjet composition according to any one of Claims 1 to 5 from an inkjet head and attaching it to a recording medium, and An irradiation step of irradiating radiation to the radiation-curable inkjet composition attached to the recording medium, A recording method.

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