WO2026014236A1 - Encre pour jet d'encre durcissable aux ultraviolets et matière imprimée - Google Patents

Encre pour jet d'encre durcissable aux ultraviolets et matière imprimée

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Publication number
WO2026014236A1
WO2026014236A1 PCT/JP2025/022778 JP2025022778W WO2026014236A1 WO 2026014236 A1 WO2026014236 A1 WO 2026014236A1 JP 2025022778 W JP2025022778 W JP 2025022778W WO 2026014236 A1 WO2026014236 A1 WO 2026014236A1
Authority
WO
WIPO (PCT)
Prior art keywords
ink
compound
meth
mass
acrylate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/JP2025/022778
Other languages
English (en)
Japanese (ja)
Inventor
雄司 亀山
卓視 吉川
会理子 関
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Toyocolor Co Ltd
Artience Co Ltd
Original Assignee
Toyocolor Co Ltd
Artience Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Toyocolor Co Ltd, Artience Co Ltd filed Critical Toyocolor Co Ltd
Publication of WO2026014236A1 publication Critical patent/WO2026014236A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/02—Printing inks
    • C09D11/10—Printing inks based on artificial resins
    • C09D11/101—Inks specially adapted for printing processes involving curing by wave energy or particle radiation, e.g. with UV-curing following the printing
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/30—Inkjet printing inks
    • C09D11/32—Inkjet printing inks characterised by colouring agents
    • C09D11/322—Pigment inks
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/30—Inkjet printing inks
    • C09D11/38—Inkjet printing inks characterised by non-macromolecular additives other than solvents, pigments or dyes

Definitions

  • This disclosure relates to ultraviolet-curable inkjet ink and printed materials obtained using the ultraviolet-curable inkjet ink.
  • Inks used in inkjet printing methods include water-based, oil-based, solvent-based, and UV-curable inks, but demand for UV-curable inkjet inks is growing due to their ability to be used on non-absorbent printing substrates such as plastic and glass, their fast drying (curing) time, and the high strength of printed materials.
  • Patent Document 1 discloses an ink composition containing a white pigment, an acylphosphine compound, and a thioxanthone compound, with the contents of the acylphosphine compound and the thioxanthone compound specified.
  • Patent Document 2 also discloses a white ink composition for inkjet recording, which contains a difunctional (meth)acrylate, a trifunctional (meth)acrylate, and a tetrafunctional (meth)acrylate in a total amount of 60% by mass or more, an acylphosphine oxide compound having a polymerizable group, and a white pigment.
  • Patent Document 3 discloses an ink composition containing a white pigment, an aromatic monofunctional ethylenically unsaturated compound, and an N-vinyl lactam and/or a monofunctional ethylenically unsaturated compound having an aliphatic cyclic structure.
  • Patent Document 4 discloses a white inkjet ink composition containing a white pigment, an acylphosphine oxide photopolymerization initiator, and a non-acylphosphine oxide photopolymerization initiator (e.g., oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone)).
  • a white pigment e.g., a white pigment, an acylphosphine oxide photopolymerization initiator, and a non-acylphosphine oxide photopolymerization initiator (e.g., oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone)).
  • Patent Document 1 when thioxanthone compounds are used in Patent Document 1, there are problems such as coloration of the ink or printed matter, and an initial hue that is inferior to that of additive-free products. There is also the problem that ink present near the nozzles of the inkjet head is easily cured by ultraviolet light leaking from the ultraviolet light irradiation means within the device or light incident from outside the device, which can easily deteriorate ejection stability.
  • Patent Document 1 disclose specific examples of ink compositions containing an acylphosphine compound and a thioxanthone compound, no evaluation of ejection stability was conducted, and the inventors' investigations have revealed that ejection stability may deteriorate depending on the printing conditions, etc.
  • the white ink disclosed in Patent Document 2 may not exhibit good ejection stability depending on the printing device and printing conditions used.
  • the ink composition specifically disclosed in Patent Document 3 may have poor curing properties, as well as poor adhesion and abrasion resistance of the printed matter, depending on the printing substrate (for example, if a substrate that allows the ink composition to penetrate is used) and printing conditions.
  • the present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide an ultraviolet-curable inkjet ink that has excellent curing properties and ejection stability, as well as excellent adhesion and abrasion resistance of printed matter.
  • the embodiments of the present disclosure relate to the following [1] to [4].
  • the present disclosure is not limited to the following embodiments and includes various other embodiments.
  • This disclosure makes it possible to provide an ultraviolet-curable inkjet ink that has excellent curing properties and ejection stability, as well as excellent adhesion and abrasion resistance of printed materials.
  • the UV-curable inkjet ink of the present disclosure (hereinafter simply referred to as the "ink of the present disclosure") uses a polyfunctional polymerizable compound containing a specific compound and a specific fluorescent brightener together with titanium oxide. This configuration solves the above-mentioned problems.
  • the ultraviolet-curable inkjet ink of the present disclosure contains a polyfunctional polymerizable compound in an amount of 50% by mass or more of the total amount of photopolymerizable compounds.
  • the polyfunctional polymerizable compound includes a compound represented by general formula (1).
  • the compound represented by general formula (1) above contains an alkylene group. Since alkylene groups are generally thought to form soft segments, using a compound represented by general formula (1) above can impart flexibility to printed matter. Furthermore, using a photopolymerizable compound whose structure contains a medium- to long-chain alkylene group, such as the compound represented by general formula (1), increases affinity with printing substrates such as polyolefin substrates and paper substrates. As a result, adhesion between the printed matter and the printing substrate is improved. Furthermore, since the compound represented by general formula (1) has a relatively low viscosity among photopolymerizable compounds, it can also improve the ink's ejection stability.
  • the ultraviolet-curable inkjet ink of the present disclosure contains a compound represented by general formula (1) in an amount of 50% by mass or more of the total amount of polyfunctional polymerizable compounds in the inkjet ink.
  • white pigments including titanium oxide
  • titanium oxide has a higher hardness than other white pigments, but also a high ability to reflect and scatter ultraviolet light.
  • UV-LEDs ultraviolet light-emitting diodes
  • a thiophene benzoxazoyl compound and/or a naphthalene benzoxazoyl compound is used as a fluorescent brightening agent to enhance the curing properties of inkjet ink. While the detailed mechanism is unknown, these fluorescent brightening agents are excited by ultraviolet light, and the generated fluorescence then causes a reaction with the photopolymerization initiator in the inkjet ink, or alternatively, excitation energy is transferred to the photopolymerization initiator. As a result, even in inkjet inks containing titanium oxide, the reaction of the photopolymerizable compound proceeds sufficiently, improving the curing properties of the ink film interior as well as adhesion to the printing substrate and abrasion resistance.
  • fluorescent brighteners are not themselves directly involved in the polymerization reaction, and therefore are less likely to cause a deterioration in ejection stability. Furthermore, while the detailed mechanism is unknown, it is believed that the interaction via the thiophene benzoxazoyl compounds and/or naphthalene benzoxazoyl compounds optimizes the viscoelasticity of the ink, improving ejection stability. Furthermore, because fluorescent brighteners have the property of emitting purple to blue fluorescence, they also have the effect of making yellowish ink films appear paler.
  • the UV-curable inkjet ink of the present disclosure is essential for simultaneously improving curing properties, ejection stability, and the adhesion and abrasion resistance of printed materials.
  • an acylphosphine oxide initiator is preferably used as the photopolymerization initiator used in the polymerization reaction. Compared to other photopolymerization initiators, acylphosphine oxide initiators can absorb UV light over a wide wavelength range, including long-wavelength UV light.
  • the UV-curable inkjet ink of the present disclosure contains a fluorescent brightening agent. However, the fluorescence emitted from the fluorescent brightening agent generally has lower energy than the energy of the absorbed UV light. In other words, the wavelength of the fluorescence is longer than that of the absorbed UV light.
  • the fluorescence emitted from the fluorescent brightening agent can be effectively utilized, significantly improving curing properties.
  • the acylphosphine oxide initiator can absorb a wide wavelength range of UV light, it can improve not only the curing properties of the ink film surface but also the curing properties of the ink film interior.
  • ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide it is preferable to use ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide as the acylphosphine oxide initiator. Because ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide is a liquid at room temperature, it is possible to increase its blending amount in the ink while suppressing an increase in the viscosity of the inkjet ink, compared to other acylphosphine oxide initiators that are solid at room temperature, and this is effective in improving ejection stability and curing properties.
  • the ink of the present disclosure contains a photopolymerizable compound.
  • the photopolymerizable compound also contains a polyfunctional polymerizable compound.
  • the term "photopolymerizable compound” refers to a compound that reacts with radicals generated from a photopolymerization initiator or the like to cause a polymerization reaction or a crosslinking reaction.
  • the term "polyfunctional polymerizable compound” refers to a photopolymerizable compound having two or more photopolymerizable groups. Examples of the photopolymerizable group include a (meth)acryloyl group and a vinyl group (excluding a (meth)acryloyl group).
  • a photopolymerizable compound contains a monofunctional polymerizable compound (a photopolymerizable compound having one photopolymerizable group) and a polyfunctional polymerizable compound
  • the greater the content of the monofunctional polymerizable compound the more flexible the ink film tends to be
  • the greater the content of the polyfunctional polymerizable compound the more the curability of thin and thick films and the strength of the ink film tend to improve.
  • the content of the polyfunctional polymerizable compound is 50% by mass or more of the total amount of photopolymerizable compounds, preferably 70% by mass or more, and particularly preferably 85% by mass or more.
  • the ink of the present disclosure also contains a compound represented by general formula (1) as the polyfunctional polymerizable compound.
  • the compound represented by general formula (1) is blended in an amount of 50% by mass or more, preferably 65% to 85% by mass, of the total amount of the polyfunctional polymerizable compound.
  • the medium- to long-chain alkylene group present in the compound represented by general formula (1) imparts flexibility to the ink film while enhancing affinity with printing substrates such as polyolefin substrates and paper substrates, thereby improving adhesion to the printing substrate.
  • the compound represented by general formula (1) has a relatively low viscosity among photopolymerizable compounds, thereby improving the ink ejection stability.
  • the compound represented by general formula (1) is itself a polyfunctional polymerizable compound. Therefore, it goes without saying that the compound represented by general formula (1) is also effective in improving the curability of the ink and the abrasion resistance of printed matter.
  • the blending amount of the polyfunctional polymerizable compound to 50% by mass or more of the total amount of photopolymerizable compounds, and further setting the blending amount of the compound represented by general formula (1) above within the above range, the adhesion and scratch resistance of the printed matter, as well as the ejection stability and curing properties of the ink, are all at good levels.
  • the amount of the compound represented by general formula (1) is 90 to 100 mass % of the total amount of the polyfunctional polymerizable compound.
  • the majority or all of the polyfunctional polymerizable compounds contained in the ink of the present disclosure are compounds represented by general formula (1), it becomes easier to obtain printed matter with particularly excellent adhesion.
  • R 1 the number of carbon atoms in R 1 may be 4 to 10, 4 to 8, or 4 to 6.
  • R 1 may be a branched alkylene group or a linear alkylene group.
  • Examples of compounds represented by general formula (1) include 1,3-butylenediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,8-octanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, 3-methyl-1,5-pentanediol diacrylate, 2,4-dimethyl-1,5-pentanediol diacrylate, 2-ethyl-2-butylpropanediol diacrylate, and 2-ethyl-2-butylbutanediol diacrylate. Note that, from the perspective of improving curability, all polymerizable groups contained in compounds represented by general formula (1) are acryloyl groups.
  • the ink of the present disclosure it is preferable to use one or more compounds selected from the group consisting of 1,4-butanediol diacrylate, 3-methyl-1,5-pentanediol diacrylate, and 1,6-hexanediol diacrylate.
  • These compounds have an excellent balance of viscosity and surface tension, and are effective in improving ejection stability. They also improve the ink's wetting and spreading properties on printing substrates, improving the ink's curing properties, as well as the adhesion and abrasion resistance of printed materials.
  • 1,6-hexanediol diacrylate and/or 1,4-butanediol diacrylate in combination with 3-methyl-1,5-pentanediol diacrylate.
  • the cure shrinkage of the ink film is suppressed, and the inclusion of a certain amount of 3-methyl-1,5-pentanediol diacrylate, which contains an alkylene group with a branched structure, significantly improves adhesion.
  • optimizing the viscoelasticity of the ink also significantly improves ejection stability.
  • the content of 3-methyl-1,5-pentanediol diacrylate relative to the total content of 1,6-hexanediol diacrylate and 1,4-butanediol diacrylate is preferably 100 to 900% by mass, more preferably 150 to 900% by mass, and particularly preferably 230 to 900% by mass.
  • the amount of the compound represented by general formula (1) is preferably 45% by mass or more, and particularly preferably 60 to 85% by mass, of the total amount of photopolymerizable compounds.
  • the content of the compound represented by general formula (1) is also preferable for the content of the compound represented by general formula (1) to be 90 to 100% by mass in the photopolymerizable compound.
  • the medium- to long-chain alkylene groups present in the compound represented by general formula (1) are thought to increase the flexibility of the ink film. As a result, the curability is maintained in an optimal state, while also improving adhesion to the printing substrate.
  • the ink of the present disclosure may contain polyfunctional polymerizable compounds other than the compound represented by general formula (1) (also referred to as "other polyfunctional polymerizable compounds" in this disclosure), and two or more of these may be used in combination.
  • the other polyfunctional polymerizable compound for example, a compound having two (meth)acryloyl groups among photopolymerizable compounds (photopolymerizable monomers) that are monomers can be used.
  • the compound examples include 1,3-propanediol di(meth)acrylate, 1,3-butylenediol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, ethylene oxide-modified 1,6-hexanediol di(meth)acrylate, propylene oxide-modified 1,6-hexanediol di(meth)acrylate, 1,8-octanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, neopentyl glycol dimethacrylate, and ethylene oxide-modified neopentyl glycol dimethacrylate.
  • the total content of dipropylene glycol di(meth)acrylate and tripropylene glycol di(meth)acrylate is preferably 1 to 45 mass%, and particularly preferably 5 to 35 mass%, of the total amount of photopolymerizable compounds.
  • the content of the compound represented by general formula (1) is also suitable for the content of the compound represented by general formula (1) to be 90 to 100% by mass in the photopolymerizable compound.
  • (meth)acryloyl refers to “acryloyl” and/or “methacryloyl”
  • (meth)acrylate” refers to “acrylate” and/or “methacrylate”.
  • monomer in this disclosure refers to the smallest unit in a polymer obtained by a polymerization reaction and/or a crosslinking reaction.
  • photopolymerizable compound as a monomer and “photopolymerizable monomer” refer to a monomer among photopolymerizable compounds that has one or more photopolymerizable groups.
  • substantially not used means that the target component is not added intentionally, and does not prevent its inclusion as an impurity, by-product, etc. Specifically, if the amount of impurities, by-products, etc. mixed in is 0.1% by mass or less (preferably 0.05% by mass or less) of the total amount of ink, this is considered to be “substantially not used.”
  • the content of glycerin triacrylate is preferably 1 to 15 mass%, and particularly preferably 2 to 12 mass%, of the total amount of photopolymerizable compounds.
  • photopolymerizable monomers having four (meth)acryloyl groups can also be used as other polyfunctional polymerizable compounds.
  • Specific examples of such photopolymerizable monomers include pentaerythritol tetra(meth)acrylate, sorbitol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ethylene oxide-modified pentaerythritol tetra(meth)acrylate, propylene oxide-modified pentaerythritol tetra(meth)acrylate, and tetramethylolmethane tetra(meth)acrylate.
  • the total content of ditrimethylolpropane tetraacrylate is preferably 1 to 12 mass%, and particularly preferably 2 to 10 mass%, of the total amount of the photopolymerizable compound.
  • photopolymerizable monomer having five (meth)acryloyl groups examples include sorbitol penta(meth)acrylate and dipentaerythritol penta(meth)acrylate.
  • photopolymerizable monomer having six (meth)acryloyl groups examples include dipentaerythritol hexa(meth)acrylate, sorbitol hexa(meth)acrylate, alkylene oxide-modified hexa(meth)acrylate of phosphazene, and ⁇ -caprolactone-modified dipentaerythritol hexa(meth)acrylate.
  • a compound (having one or more acryloyl groups) obtained by reacting (Michael addition reaction) one or more compounds selected from the group consisting of 1,6-hexanediol diacrylate, ethylene oxide-modified 1,6-hexanediol diacrylate, propylene oxide-modified 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, ethylene oxide-modified trimethylolpropane triacrylate, propylene oxide-modified trimethylolpropane triacrylate, glycerin triacrylate, ethylene oxide-modified glycerin triacrylate, and propylene oxide-modified glycerin triacrylate with an amine compound can be used as the other polyfunctional polymerizable compound.
  • These compounds can simultaneously improve ejection stability, curing properties, and adhesion, making them suitable for use in the inks of the present disclosure.
  • photopolymerizable compounds that are oligomers can also be used as other polyfunctional polymerizable compounds.
  • compounds having a (meth)acryloyl group as the polymerizable group are preferably used.
  • the number of polymerizable groups contained in the polymerizable oligomer is preferably 2 to 6 per molecule.
  • the number of polymerizable groups is more preferably 2 to 4, and particularly preferably 2.
  • the weight average molecular weight of the polymerizable oligomer is also preferably 400 to 12,000, and more preferably 500 to 10,000.
  • oligomer refers to a compound formed by polymerizing a small, finite number of monomers (e.g., 2 to 20).
  • oligomeric photopolymerizable compound and “photopolymerizable oligomer” refer to a photopolymerizable compound that has one or more photopolymerizable groups.
  • the monomers that make up a photopolymerizable oligomer may include monomers that are not photopolymerizable monomers (excluding monomers used to impart photopolymerizable groups).
  • a photopolymerizable urethane oligomer obtained by reacting 2-hydroxyethyl acrylate with a urethane oligomer having an isocyanate group at its terminal which is the reaction product of 1,6-hexanediol and isophorone diisocyanate, contains 1,6-hexanediol and isophorone diisocyanate as monomers.
  • Examples of the polymerizable oligomer having a (meth)acryloyl group include urethane (meth)acrylate oligomers such as aliphatic urethane (meth)acrylate oligomers and aromatic urethane (meth)acrylate oligomers; acrylic (meth)acrylate oligomers; polyester (meth)acrylate oligomers; polyether (meth)acrylate oligomers; and epoxy (meth)acrylate oligomers.
  • the above-mentioned oligomers may be modified. Examples of such modifications include sulfonic acid modification, phosphate modification, amine modification, and mercapto modification.
  • the ink of the present disclosure contains other polyfunctional polymerizable compounds, their content is preferably 1 to 50% by mass of the total ink, and more preferably 5 to 35% by mass.
  • monofunctional polymerizable compounds can also be used as other polymerizable compounds.
  • photopolymerizable monomers containing one (meth)acryloyl group can be used as such monofunctional polymerizable compounds.
  • the compound include 2-phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, (ethoxylated (or propoxylated)) 2-phenoxyethyl (meth)acrylate, dicyclopentenyl (oxyethyl) (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, 2-methoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-(2-ethoxyethoxy)ethyl (meth)acrylate, methoxydipropylene glycol (meth)acrylate, dipropylene glycol (meth)acrylate, o-phenyl
  • a photopolymerizable monomer having one vinyl group (excluding a (meth)acryloyl group) can also be used.
  • specific examples of such compounds include N-vinylpyrrolidone, N-vinylvalerolactam, N-vinylcaprolactam, N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyloxazolidinone, and N-vinyl-5-methyloxazolidinone.
  • the monofunctional polymerizable compound may be a photopolymerizable oligomer having one (meth)acryloyl group.
  • specific examples of such compounds include KRM9276 manufactured by Daicel-Allnex Corporation; and CN131NS, CN131BNS, CN146NS, CN153NS, CN3108NS, CN7002NS, CN8004NS, and CN9003NS manufactured by Arkema.
  • N-vinyl-5-methyloxazolidinone is highly reactive, which not only enhances the curing properties of the ink but also improves adhesion to the printing substrate. Furthermore, even when N-vinyl-5-methyloxazolidinone is used, the viscosity of the ink is less likely to increase, which helps prevent a deterioration in ejection stability.
  • the ink of the present disclosure contains a monofunctional polymerizable compound
  • its content is preferably 1 to 20% by mass of the total amount of ink, more preferably 1 to 10% by mass, and particularly preferably 1 to 8% by mass.
  • the compound having one vinyl group (excluding a (meth)acryloyl group) is preferably used in an amount of 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 90% by mass or more, of the total amount of the monofunctional polymerizable compound.
  • the content of the photopolymerizable compound is preferably 60 to 80% by mass of the total ink, more preferably 65 to 80% by mass, and especially preferably 70 to 80% by mass.
  • the ink of the present disclosure contains a photopolymerization initiator.
  • a photopolymerization initiator can be used as the photopolymerization initiator.
  • a compound capable of absorbing the energy of actinic rays and generating radicals can be used.
  • Specific examples of usable photopolymerization initiators include acylphosphine oxide compounds, benzophenone compounds, indan compounds, thioxanthone compounds, hydroxyacetophenone compounds, alkylaminoacetophenone compounds, and oxime ester compounds.
  • an acylphosphine oxide initiator in the ink of the present disclosure, as this can absorb light energy over a wide wavelength range, including the fluorescence emitted from fluorescent brighteners, and improves the curing properties not only of the ink film surface but also of the ink film interior.
  • acylphosphine oxide initiator examples include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, as well as polymers of these compounds.
  • acylphosphine oxide compounds include “Omnirad TPO,”"OmniradTPO-L,””OmniradTPO-H,””Omnirad819,” and “OMNIPOL TP,” all manufactured by IGM RESINS, and "Speedcure TPO,”"SpeedcureTPO-L,” and “Speedcure BPO,” all manufactured by Lambson.
  • acylphosphine oxide compounds and lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate described in WO 2017/086224 and WO 2020/049378 can also be used.
  • the above-listed acylphosphine oxide compounds may be used alone or in combination of two or more.
  • ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide is a liquid at room temperature and is an effective material for improving curing while maintaining ejection stability.
  • ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide tends to orient on the ink droplet surface.
  • acylphosphine oxide photopolymerization initiators generally exhibit a photobleaching effect. In other words, after generating radicals and decomposing, the acylphosphine oxide photopolymerization initiator loses its ultraviolet absorption ability, improving UV transmittance into the ink film interior.
  • ethoxyphenyl (2,4,6-trimethylbenzoyl) phosphine oxide is thought to be easily oriented on the droplet surface, and as the polymerization reaction progresses, a photobleaching effect is exhibited, making it easier for ultraviolet light to penetrate into the ink film.
  • the ink of the present disclosure contains ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide
  • an acylphosphine oxide initiator other than ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide is preferable to use as the other photopolymerization initiator, from the standpoint that it can absorb light energy over a wide wavelength range, including fluorescence emitted from fluorescent brighteners, and thereby significantly improve curing properties.
  • reactivity can be further improved if phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide is blended into the ink together with ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.
  • phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide is able to exist uniformly within the ink droplets, and after ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide exhibits a photobleaching effect, the phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide reacts with ultraviolet light that penetrates into the ink film, improving the internal curing of the ink film.
  • acylphosphine oxide initiator other than ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide for example, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide
  • both the surface curing and internal curing of the ink are improved, which also improves the abrasion resistance of the ink film.
  • the photopolymerization initiator contains ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide
  • its content in the ultraviolet-curable inkjet ink is preferably 3 to 10% by mass.
  • the photopolymerization initiator contains phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide
  • its content in the ultraviolet-curable inkjet ink is preferably 2 to 5% by mass.
  • the ink of the present disclosure contains a monoacylphosphine oxide initiator
  • its content is preferably 45 to 85 mass% of the total amount of photopolymerization initiator contained in the ink, and particularly preferably 60 to 75 mass%.
  • Monoacylphosphine oxide initiators have high solubility in compounds represented by general formula (1), while also having high radical generation efficiency. Therefore, by keeping the content of the monoacylphosphine oxide initiator within the above range, it becomes easy to obtain an ink that is excellent in all aspects: curability, ejection stability, and even abrasion resistance of printed matter.
  • Examples of the monoacylphosphine oxide initiator include ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.
  • the content thereof is preferably 5 to 150, and particularly preferably 10 to 75, relative to the mass content of the fluorescent brightener in the ink, taken as 1.
  • the ink of the present disclosure contains a fluorescent brightening agent.
  • a fluorescent brightening agent is a compound that absorbs light in a wavelength range of around 200 to 400 nm and emits fluorescence having a wavelength longer than the absorption wavelength.
  • Specific examples of compounds used as fluorescent brightening agents include naphthalene benzoxazoyl compounds, thiophene benzoxazoyl compounds, stilbene benzoxazoyl compounds, stilbene biphenyl compounds, distyrylbenzene compounds, coumarin compounds, carbostyryl compounds, pyrazolone compounds, naphthalimide compounds, pyrene compounds, and pyridotriazole compounds.
  • this disclosure uses thiophene benzoxazoyl compounds and/or naphthalene benzoxazoyl compounds as fluorescent brightening agents.
  • these fluorescent brightening agents have absorption and fluorescence wavelengths that are suitable for improving curing properties, making it easy to significantly improve the curing properties of inkjet inks even when added in small amounts.
  • thiophene benzoxazoyl compounds and naphthalene benzoxazoyl compounds are relatively lightly colored, preventing the ink itself from becoming colored. Furthermore, they have the property of emitting purple to blue fluorescence, which also has the effect of making the ink film appear paler.
  • a thiophene benzoxazolyl compound as a fluorescent brightening agent in the ink of the present disclosure, as this compound has high absorbance, which significantly improves the curing properties of the ink, and the amount used can be reduced, which makes it easy to improve discharge stability.
  • thiophene benzoxazoyl compounds and naphthalene benzoxazoyl compounds include “Tinopal OB” and “Tinopal OB CO” manufactured by BASF, “SpeedBlock OB-184" manufactured by Arkema, "NF-TH01” and “NF-NA01” manufactured by Nippon Chemical Industry Co., Ltd., and "FLUORESCENT BRIGHTNER KCB,” “FLUORESCENT BRIGHTNER OB,” and “FLUORESCENT BRIGHTNER PB” manufactured by Xcolor.
  • the content of the fluorescent brightener in the UV-curable inkjet ink is preferably 0.01 to 1.5% by mass, more preferably 0.05 to 1% by mass, and particularly preferably 0.1 to 0.7% by mass.
  • the ratio of the total photopolymerization initiator content to the fluorescent brightener content is preferably 11 to 1100 by mass, and particularly preferably 25 to 250.
  • the fluorescent brightener dissolves uniformly in the photopolymerizable compound in the ink, allowing the fluorescent brightener to fully function, improving the ink's curing properties and the abrasion resistance of printed matter. It also prevents clogging of the inkjet head and improves ejection stability.
  • titanium oxide is used as the white pigment.
  • white pigments reflect and scatter light, reducing the efficiency of radical generation from the photopolymerization initiator.
  • the narrow wavelength range of the emitted ultraviolet light may further accelerate the reduction in the efficiency of radical generation. Therefore, in the present disclosure, by using a thiophene benzoxazoyl-based compound and/or a naphthalene benzoxazoyl-based compound as the fluorescent brightening agent, it is possible to improve the curability of a system containing titanium oxide while reducing the amount of photopolymerization initiator added.
  • the titanium oxide used in the ink of the present disclosure preferably has a secondary particle diameter of 180 to 250 nm.
  • Using titanium oxide with a secondary particle diameter of 180 nm or greater not only produces printed matter with sufficient hiding power but also improves the scratch resistance of the printed matter.
  • the secondary particle diameter is 250 nm or less, excessive settling of the titanium oxide can be suppressed, making it easier to obtain an ink film with good curing properties while suppressing deterioration of discharge stability.
  • the secondary particle diameter is preferably 200 to 250 nm, and more preferably 220 to 250 nm.
  • the "secondary particle size” mentioned above refers to the particle size of titanium oxide dispersed in the ink, and represents the median size measured on a volume basis.
  • the secondary particle size can be measured using a dynamic light scattering particle size distribution analyzer (for example, the Nanotrac UPA-EX150 manufactured by Microtrac-Bell) and inkjet ink diluted with ethyl acetate to a concentration that allows measurement of the secondary particle size using the particle size distribution analyzer.
  • the primary particle diameter of the titanium oxide is not particularly limited, but is preferably equal to or smaller than the secondary particle diameter. This is because there is no need to destroy the titanium oxide or intentionally remove the surface treatment agent in order to keep the secondary particle diameter within the preferred range, resulting in good dispersion stability and ejection stability. Specifically, it is preferable to use titanium oxide with a primary particle diameter of 150 to 240 nm, more preferably titanium oxide with a primary particle diameter of 180 to 230 nm, and most preferably titanium oxide with a primary particle diameter of 200 to 230 nm.
  • the primary particle diameter of titanium oxide can be calculated, for example, by taking multiple images using a transmission electron microscope (TEM), measuring and calculating the diameters of circles having the same area as the areas of a total of 100 titanium oxide particles present in the images (equivalent circle diameters), and then averaging these values.
  • TEM transmission electron microscope
  • titanium oxide products with a primary particle size of 150 to 240 nm include Ishihara Sangyo Kaisha's Typepaque CR-60, CR-60-2, CR-63, CR-67, CF-80, PF-690, PF-691, A-100, and A-220, and Cronos' 2064, 2190, and 2310.
  • Ishihara Sangyo Kaisha's CR-60-2, CR-63, PF-690, PF-691, PF-726, and PF-728, and Cronos' 2064, 2190, and 2310 which have an organically treated titanium oxide surface, are particularly preferred.
  • the titanium oxide may be one whose surface has been treated with an inorganic and/or organic substance.
  • Surface treatment can be carried out as necessary to reduce the catalytic activity of the titanium oxide surface, control hydrophilicity, and improve weather resistance and dispersion stability.
  • Inorganic substances used for surface treatment include alumina, silica, zirconia, titania, tin oxide, and hydrates of these compounds (e.g., hydrous alumina, hydrous zirconia, etc.), while organic substances include polyhydric alcohols, alkanolamines, organosilicon compounds, organophosphate compounds, higher fatty acids, etc.
  • (hydrated) alumina refers to alumina and/or hydrated alumina
  • (hydrated) silica refers to silica and/or hydrated silica
  • (hydrated) zirconia refers to zirconia and/or hydrated zirconia.
  • the amount of titanium oxide in the ink is preferably 10 to 25% by mass. By keeping the amount within this range, high hiding power can be achieved even with a thin film thickness of the printed matter, and the storage stability and discharge stability of the ink, as well as the abrasion resistance and adhesion of the printed matter, can be easily improved. From this perspective, it is even more preferable that the amount be 13 to 23% by mass.
  • the amount of titanium oxide having a particle diameter (unit: nm) measured on a volume basis of AW x 1/4 to AW x 2/3 is preferably 10 to 50 mass%, and particularly preferably 20 to 50 mass%, of the total mass of titanium oxide contained in the ink.
  • Inks containing a specified amount of titanium oxide within the above particle size range not only exhibit excellent hiding properties in printed materials, but also improve the curing properties of the ink and the abrasion resistance of printed materials.
  • the amount of titanium oxide having a particle diameter (unit: nm) measured on a volume basis of AW x 2/5 to AW x 5/9 is preferably 8 to 45 mass%, and particularly preferably 15 to 45 mass%, of the total mass of titanium oxide contained in the ink.
  • the amount of titanium oxide having a particle size measured on a volume basis of 150 to 200 nm is preferably 8 to 45 mass%, and particularly preferably 15 to 45 mass%, of the total mass of titanium oxide contained in the ink.
  • Pigment dispersion resin it is preferable to use a pigment dispersion resin from the viewpoints of improving the initial dispersibility of titanium oxide, as well as the storage stability and ejection stability of the ink, and further improving the abrasion resistance of printed matter by enabling the titanium oxide to be uniformly dispersed within the ink film.
  • Commercially available pigment dispersion resins can be used, or those synthesized by conventional methods can be used.
  • an acid group-containing polymerizable compound such as acrylic acid or methacrylic acid
  • an amino group-containing polymerizable compound such as acrylamide, dimethylaminoethyl methacrylate, or diethylaminoethyl methacrylate
  • another polymerizable compound such as styrene, ⁇ -methylstyrene, methyl methacrylate, butyl methacrylate, or lauryl methacrylate
  • the weight-average molecular weight of the pigment dispersion resin is preferably 5,000 to 100,000, more preferably 10,000 to 50,000, and even more preferably 15,000 to 30,000. Within this range, the compatibility of the pigment dispersion resin with the compound represented by general formula (1) is good, improving the storage stability and ejection stability of the ink. It also makes it easier to homogenize the titanium oxide within the ink film, improving the abrasion resistance and hiding power of the printed material.
  • the amount of pigment dispersing resin added is preferably 1 to 100% by mass, more preferably 3 to 50% by mass, and even more preferably 5 to 25% by mass, relative to the total amount of titanium oxide. Using it within the above blending range improves the initial dispersibility of titanium oxide, as well as the storage stability and ejection stability of the ink, and also improves the scratch resistance of printed materials.
  • the ink of the present disclosure may contain a surface tension adjuster, a polymerization inhibitor, an organic solvent, water, and other additives.
  • the surface tension modifier may be a silicone-based surface tension modifier, a fluorine-based surface tension modifier, an acetylene glycol-based surface tension modifier, or the like.
  • a silicone-based surface tension modifier and in particular a polyether-modified silicone-based surface tension modifier, because they have an excellent ability to reduce surface tension, making it easy to improve abrasion resistance and adhesion, and have good compatibility with the compound represented by general formula (1), thereby improving the storage stability and ejection stability of the ink.
  • a polyether-modified silicone-based surface tension modifier having a (meth)acryloyl group because this significantly improves the curability of the ink and the scratch resistance of the printed matter, and because it has excellent compatibility with the photopolymerizable compound containing the compound represented by general formula (1), thereby improving the ejection stability.
  • the polyether-modified silicone-based surface tension modifier having a (meth)acryloyl group may be synthesized by a conventionally known method, or a commercially available product may be used.
  • commercially available products include BYK-UV3500, BYK-UV3505, BYK-UV3530, BYK-UV3570, BYK-UV3575, and BYK-UV3576 (all manufactured by BYK-Chemie), KF-2012, X-22-164, X-22-164AE, X-22-164A, X-22-164B, X-22-164C, X-22-164E, X-22-174ASX, X-22-174BX, X-22-2426, and X-22-2404 (all manufactured by Shin-Etsu Silicones Co., Ltd.), TEGO Rad 2100, TEGO Rad 2200N, and TEGO Rad 2250, TEGO Rad 2300, TEGO Rad 2330, TEGO Rad 2500, TEGO
  • the ink of the present disclosure contains a silicone-based surface tension modifier
  • its content in the ink is preferably 0.1 to 5.0% by mass. Adding 0.1% by mass or more easily improves the wetting and spreading of ink droplets onto the printing substrate, improving abrasion resistance and adhesion. Furthermore, keeping the amount added to 5.0% by mass or less makes it easier to ensure the storage stability and ejection stability of the ink.
  • the ink of the present disclosure contains a polyether-modified silicone-based surface tension modifier having a (meth)acryloyl group
  • compatibility with the compound represented by general formula (1) is improved, improving both curability and discharge stability, and improving the scratch resistance of printed matter. Therefore, when the content of the polyether-modified silicone-based surface tension modifier having a (meth)acryloyl group is taken as 1, the content of the compound represented by general formula (1) is preferably 60 to 150, and particularly preferably 80 to 130.
  • a polymerization inhibitor can be added to the ink of the present disclosure for the following reasons: improved ejection stability; improved overall curability due to a balance between surface curability and internal curability; and improved adhesion of printed matter while suppressing curing wrinkles.
  • Specific examples of such a polymerization inhibitor include hindered phenol compounds, phenol compounds (excluding hindered phenol compounds), hydroquinone compounds, phenothiazine compounds, phosphorus compounds, and nitrosophenylhydroxylamine compounds. These compounds can be suitably used as polymerization inhibitors.
  • More specific examples of compounds that can be used as polymerization inhibitors include 4-methoxyphenol, t-butylhydroquinone, 2,6-di-t-butyl-4-methylphenol, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], hydroquinone, methylhydroquinone, phenothiazine, dicumylphenothiazine, triphenylphosphine, and aluminum salt of N-nitrosophenylhydroxylamine.
  • the content thereof is preferably 0.01 to 2 mass %, and more preferably 0.1 to 1 mass %, relative to the total amount of the ink.
  • an organic solvent and/or water may be added to the ink of the present disclosure.
  • the content thereof is preferably 0.01 to 30% by mass, more preferably 0.05 to 20% by mass, and particularly preferably 0.1 to 10% by mass, based on the total amount of the ink.
  • the ink of the present disclosure contains an organic solvent
  • the organic solvent having a boiling point of 140 to 300°C at 1 atmosphere contains at least one selected from the group consisting of alkylene glycol monoalkyl ethers, alkylene glycol dialkyl ethers, and alkylene glycol monoalkyl ether acetates.
  • the ink of the present disclosure may contain, as needed, ultraviolet absorbers, anti-fading agents, other polymer compounds, etc. Any conventionally known components may be used as these components.
  • the photopolymerizable compound contains a polyfunctional polymerizable compound in an amount of 70 mass% or more of the total amount of the photopolymerizable compound, the content of the compound represented by general formula (1) is 60 to 85 mass% of the total amount of the photopolymerizable compound, and the total content of dipropylene glycol di(meth)acrylate and tripropylene glycol di(meth)acrylate is 1 to 45 mass% of the total amount of the photopolymerizable compound.
  • the titanium oxide content is 10 to 25% by mass
  • the total photopolymerizable compound content is 60 to 80% by mass
  • the ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide content is 3 to 10% by mass
  • the phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide content is 2 to 5% by mass
  • the total content of thiophene benzoxazoyl compounds and naphthalene benzoxazoyl compounds is 0.05 to 1.0% by mass
  • the photopolymerizable compounds contain polyfunctional polymerizable compounds in an amount of 85% by mass or more of the total amount of the photopolymerizable compounds, and the compound represented by the general formula (1) is contained.
  • the amount of the 3-methyl-1,5-pentanediol diacrylate is 90% by mass or more of the total amount of the photopolymerizable compound
  • the compound represented by general formula (1) contains 3-methyl-1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate and/or 1,4-butanediol diacrylate, and does not contain dipropylene glycol di(meth)acrylate or tripropylene glycol di(meth)acrylate, and the content of the 3-methyl-1,5-pentanediol diacrylate is 100 to 900% by mass of the total content of 1,6-hexanediol diacrylate and 1,4-butanediol diacrylate.
  • the ink of the present disclosure preferably has a viscosity at 25°C of 5 to 20 mPa ⁇ s, more preferably 8 to 20 mPa ⁇ s, from the viewpoints of improving ejection stability, improving the wetting and spreading of droplets of the inkjet ink on a printing substrate, and improving the adhesion of printed matter.
  • a viscosity of 5 mPa ⁇ s or higher allows the inkjet ink to be ejected satisfactorily from the inkjet head.
  • a viscosity of 25 mPa ⁇ s or lower allows for continued stable ejection without a decrease in ejection accuracy, and also allows the ink to be adequately wetted and spread on the printing substrate, improving adhesion to the printing substrate. Furthermore, from the viewpoints of enabling stable ejection even in high-speed printing and improving the adhesion of printed matter, the viscosity is particularly preferably 8 to 15 mPa ⁇ s.
  • the viscosity can be measured using 1.1 mL of inkjet ink and an E-type viscometer (for example, "TVE25L” manufactured by Toki Sangyo Co., Ltd.) equipped with a cone (diameter 48 mm) with a cone angle of 1°34', in an environment of 25°C and at a rotation speed of 20 rpm.
  • an E-type viscometer for example, "TVE25L” manufactured by Toki Sangyo Co., Ltd.
  • the static surface tension of the inkjet ink at 25°C is preferably 20 to 45 mN/m, and particularly preferably 22 to 40 mN/m.
  • the static surface tension is measured using the plate method (Wilhelmy method). Specifically, for example, it can be measured in a 25°C environment using an automatic surface tensiometer "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd. and a platinum plate.
  • the ink of the present disclosure can be produced by a conventionally known method, for example, as follows, but the method for producing the ink is not limited to the following.
  • titanium oxide, a portion of the photopolymerizable compound (the remainder is used when preparing the ink, as described below), and, if necessary, pigment dispersing resin, surface tension modifier, polymerization inhibitor, organic solvent and/or water, etc. are thoroughly mixed. After mixing for a certain period of time, the mixture is dispersed using a paint shaker, sand mill, roll mill, medialess disperser, etc. to produce a titanium oxide dispersion.
  • the remainder of the photopolymerizable compound, the photopolymerization initiator, and, if necessary, a surface tension adjuster, polymerization inhibitor, organic solvent and/or water, etc. are added so as to obtain the desired ink characteristics, and after thorough mixing, the mixture is filtered through a filter or the like to remove coarse particles, yielding the ink.
  • the content of titanium oxide present in the titanium oxide dispersion is preferably 30 to 70% by mass, and particularly preferably 40 to 60% by mass.
  • the photopolymerizable compound used in producing the titanium oxide dispersion it is preferable to use a compound represented by general formula (1) and/or other polyfunctional polymerizable compounds that are photopolymerizable monomers having two (meth)acryloyl groups. Furthermore, from the viewpoints of storage stability, ejection stability, and ink curing properties, when using a compound represented by general formula (1) as the photopolymerizable compound, it is preferable to use one or more compounds selected from the group consisting of 1,4-butanediol diacrylate, 3-methyl-1,5-pentanediol diacrylate, and 1,6-hexanediol diacrylate.
  • a photopolymerizable monomer having two (meth)acryloyl groups as the photopolymerizable compound, it is preferable to use a monomer represented by general formula (1) with an EO chain or PO chain as the main skeleton, and it is particularly preferable to use dipropylene glycol diacrylate and/or tripropylene glycol diacrylate.
  • the printed matter of the present disclosure is formed by printing the ink of the present disclosure onto a printing substrate described below, i.e., a printing substrate on which an image and/or characters are recorded. Therefore, the "printed matter" of the present disclosure includes the printing substrate and an image and/or characters formed as a film (ink film) formed by curing the ink of the present disclosure.
  • the "image” also includes solid images (images printed at a coverage rate of 100% so as to completely cover the surface of the printing substrate) and seamless images such as checkerboard images.
  • An example of a method for producing the printed matter is a method including, in this order, a step of ejecting the ink of the present disclosure onto a printing substrate (step 1), and a step of irradiating the substrate with the ejected ink with ultraviolet light (step 2).
  • multi-pass printing method a method in which the same inkjet ink is ejected and applied multiple times from the same inkjet head to the same location on the printing substrate.
  • multi-pass printing method it is preferable to employ a method in which the same inkjet ink is ejected and applied only once from the same inkjet head to the same location on the printing substrate (one-pass printing method).
  • the one-pass printing method can be implemented, for example, using a line printer.
  • the printing speed is preferably 20 to 150 m/min, and particularly preferably 30 to 100 m/min.
  • the ink of the present disclosure can be suitably used in inkjet printing, and therefore, in step 1, the ink is preferably ejected from an inkjet head.
  • the ejection volume is preferably 2 to 50 pl, and more preferably 3 to 20 pl.
  • the design resolution of the inkjet head is preferably 600 dpi or higher.
  • inkjet heads that meet the above conditions include Kyocera's KJ4A-AA, KJ4A-TA, and KJ4A-RH; Fujifilm's Samba G3L; Seiko Epson's S3200, S1600, S800, I3200, and I1600; Konica Minolta's KM1024i and KM1024; and Ricoh's MH5320, MH5340, MH5240, and MH5440, all of which can be suitably used.
  • the ink can be heated while being ejected using a heating device such as a heater provided in the inkjet head. From the perspective of ensuring stable and continuous ejection of the ink, it is preferable to heat the ink so that its viscosity at the time of ejection is 20 mPa ⁇ s or less, and it is even more preferable to heat it so that it is 15 mPa ⁇ s or less.
  • Step 2 (curing step) ⁇
  • the ink of the present disclosure is ejected onto a printing substrate and then cured by irradiation with ultraviolet light to form a printed matter.
  • the ultraviolet irradiation means used in step 2 above can be, for example, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, an excimer laser lamp, a xenon lamp, a UV-LED, etc.
  • UV-LEDs have the advantage of emitting a narrow wavelength range of ultraviolet light and being easily miniaturized. Therefore, the UV-LED's irradiation wavelength and usage method can be adjusted to a certain extent to suit the properties of the photopolymerization initiator, fluorescent brightener, and titanium oxide contained in the ink.
  • the peak wavelength of the UV-LED used in step 2 is preferably 280 to 420 nm, more preferably 320 to 410 nm, and especially preferably 340 to 400 nm.
  • the maximum illuminance of the ultraviolet light on the printing substrate is preferably 1 W/ cm2 or more, more preferably 2 W/ cm2 or more, and particularly preferably 3 W/ cm2 or more.
  • the integrated light amount when irradiating the substrate will differ depending on the type and amount of polymerizable compound and photopolymerization initiator contained in the ink, but is preferably 100 mJ/ cm2 or more, and more preferably 200 mJ/ cm2 or more.
  • UV-LEDs can be installed side by side. This allows for multiple LEDs to be lined up to increase the irradiation intensity on the substrate. In this case, multiple UV-LEDs with different peak wavelengths can be lined up and used.
  • UV-LEDs can be used in combination with ultraviolet irradiation means other than UV-LEDs, such as high-pressure mercury lamps and metal halide lamps.
  • metal halide lamps are preferably used, as they effectively irradiate ultraviolet rays in the UV-A region and allow ultraviolet rays to reach sufficiently deep into the ink film.
  • the time between the end of step 1 and the start of step 2 is preferably 0.03 to 3 seconds, more preferably 0.04 to 2.5 seconds, and even more preferably 0.06 to 2 seconds. This not only produces a printed product with excellent adhesion and abrasion resistance, but also prevents ink droplets from coalescing, resulting in a printed product with good print quality.
  • step 2 can be repeated multiple times. For example, immediately after applying the inkjet ink to the substrate, the inkjet ink can be partially cured by irradiating it with ultraviolet light, and then the inkjet ink can be completely cured by irradiating it with ultraviolet light again. This makes it easier to obtain printed matter with exceptionally excellent print quality.
  • pre-curing the process of partially curing the inkjet ink described above
  • main curing the process of completely curing the inkjet ink
  • the ultraviolet ray irradiation means used for the temporary curing is preferably a UV-LED, and the maximum illuminance of the ultraviolet ray on the substrate is preferably 2 to 20 W/ cm2 , and more preferably 5 to 15 W/ cm2 .
  • the main curing of the present disclosure can be performed with a maximum illuminance of 2 W/cm 2 or more and an integrated light amount of 100 mJ/cm 2 or more.
  • Resin film substrates and paper substrates are preferably used as printing substrates to which the ink of the present disclosure can be applied.
  • the resin film substrate is preferably selected from those having a thickness of 10 to 90 ⁇ m and containing a material selected from the group consisting of polypropylene, polyethylene, polyethylene terephthalate, and nylon.
  • coated paper, art paper, laminated paper, etc. are preferably selected as the paper substrate.
  • the ink of the present disclosure can be suitably used, for example, for printing on packages manufactured using the printing substrates listed above.
  • the above phrase "containing a material selected from the group consisting of polypropylene, polyethylene, polyethylene terephthalate, and nylon" also includes resin film substrates (laminated film substrates) that have a multilayer structure and have at least one layer made of a material selected from the group consisting of polyethylene terephthalate, polyethylene, polypropylene, and nylon.
  • the layers that make up the laminated film may include layers made of AL (aluminum foil), VM (vacuum vapor deposition) film (aluminum vapor deposition film, transparent vapor deposition film, etc.), etc.
  • a titanium oxide dispersion was produced using the method described below.
  • Titanium Oxide Dispersion A 2,500 g of (hydrated) alumina, (hydrated) silica, (hydrated) zirconia, and titanium dioxide pigment (2310 manufactured by Cronos, primary particle diameter 200 nm) whose surface had been treated with an organic substance, 150 g of pigment dispersing resin ("Solsperse 32000" manufactured by Lubrizol Corporation), and 2,350 g of dipropylene glycol diacrylate were placed in a mixing vessel equipped with a stirrer, and pre-dispersed by stirring with the stirrer.
  • dispersion was carried out for 2 hours using a 0.6 L sand mill ("Dyno Mill” manufactured by Shinmaru Enterprises) filled with 1,800 g of zirconia beads with a diameter of 1 mm, to obtain titanium dioxide dispersion A.
  • a 0.6 L sand mill (“Dyno Mill” manufactured by Shinmaru Enterprises) filled with 1,800 g of zirconia beads with a diameter of 1 mm
  • Titanium oxide dispersion B was produced using the same materials and method as in the case of titanium oxide dispersion A, except that 1,6-hexanediol diacrylate was used instead of dipropylene glycol diacrylate.
  • Titanium oxide dispersion C was produced using the same materials and method as in the case of titanium oxide dispersion A, except that (hydrated) alumina, (hydrated) silica, and Typepaque PF-690 (primary particle diameter: 210 nm) manufactured by Ishihara Sangyo Kaisha, Ltd., whose surface was treated with an organic substance, were used as the titanium oxide pigment.
  • Titanium oxide dispersion D was produced using the same materials and method as in the case of titanium oxide dispersion A, except that Typepaque PF-726 (primary particle diameter: 210 nm) manufactured by Ishihara Sangyo Kaisha, Ltd., whose surface was treated with (hydrated) alumina and (hydrated) silica, was used as the titanium oxide pigment.
  • Typepaque PF-726 primary particle diameter: 210 nm
  • HDDA 1,6-hexanediol diacrylate
  • MPDDA 3-methyl-1,5-pentanediol diacrylate
  • BDDA 1,4-butanediol diacrylate
  • NPGDA neopentyl glycol diacrylate (Light Acrylate NP-A, manufactured by Kyoeisha Chemical Co., Ltd.)
  • DPGDA dipropylene glycol diacrylate (Miramer M222, manufactured by Miwon)
  • GlyTA glycerin triacrylate (Aronix M-930, manufactured by Toagosei Co., Ltd.)
  • DiTMPTA ditrimethylolpropane tetraacrylate (Ebecryl 1142, manufactured by Da
  • printed matter was produced as follows. First, one inkjet head manufactured by Kyocera Corporation (design resolution 600 dpi) was installed above a conveyor capable of transporting the printing substrate, and further, an inkjet printing device (“OnePassJET” manufactured by Tritec Corporation) equipped with a UV-LED for main curing (FirePower FP300 manufactured by Phoseon Corporation (maximum emission wavelength 395 nm, maximum illuminance 16 W/cm 2 )) was prepared downstream in the transport direction of the printing substrate.
  • OnePassJET manufactured by Tritec Corporation
  • UV-LED for main curing WirePower FP300 manufactured by Phoseon Corporation (maximum emission wavelength 395 nm, maximum illuminance 16 W/cm 2 )
  • the conveyor was continued to be driven at the same speed, and when the PET substrate passed the area where the main curing UV-LED was installed, ultraviolet light was irradiated to produce a printed material.
  • the output of the main curing UV-LED was adjusted in advance so that the illuminance of the ultraviolet light irradiated on the inkjet ink on the PET substrate was 6,000 mW/cm 2 and the cumulative light amount was 200 mJ/cm 2 , before the above-mentioned printing was carried out.
  • Examples 1 to 92, Comparative Examples 1 to 5 The inks and printed matter prepared above were used to carry out the following evaluations, and the evaluation results are shown in Tables 1-1 to 1-8.
  • the evaluation criteria for the curability were as follows. A rating of "2" or higher was considered practically acceptable, and a rating of "3" or higher was considered practically suitable.
  • ⁇ Curability evaluation criteria> 4 After one total pass (without requiring additional UV exposure), the cotton swab no longer left any marks on the area rubbed. 3: After passing the sample through the swab a total of two times (and irradiating it with UV rays once more), the area rubbed with the cotton swab no longer left any marks. 2: After passing the sample through the swab a total of three times (and irradiating it with UV rays two more times), the area rubbed with the cotton swab no longer left any marks. 1: It was necessary to irradiate the area with UV-LED four or more times in total until the area rubbed with the cotton swab no longer left a mark.
  • the tape was pulled at an angle of nearly 60 degrees, and the cellophane tape was peeled off from the print, and the condition of the print was visually observed.
  • the evaluation criteria were as follows: A rating of "3" or higher was deemed practically acceptable, and a rating of "4" was deemed practically suitable. For inks that were rated "1" in the curability evaluation, the adhesion evaluation was not carried out.
  • ⁇ Adhesion evaluation criteria> 4 No peeling of the ink film was observed. 3: Peeling of the ink film was observed in an area of 25% or less of the area where the cellophane tape was applied. 2: Peeling of the ink film was observed in an area of more than 25% but not more than 50% of the area of the part where the cellophane tape was attached. 1: Peeling of the ink film was observed in more than 50% of the area of the part where the cellophane tape was attached.
  • the inkjet inks containing titanium oxide in Examples 1 to 92 were excellent in all aspects of curing, adhesion, and abrasion resistance. They also had excellent ejection stability as inkjet inks.
  • Comparative Example 3 when the content of the polyfunctional polymerizable compound was less than 50% by mass of the total amount of photopolymerizable compounds, the curing properties did not reach a practical level. Furthermore, as shown in Comparative Examples 1 and 2, when the content of the compound represented by general formula (1) was less than 50% by mass of the total amount of the polyfunctional polymerizable compounds, the adhesion properties did not reach a practical level, and the ejection stability was not necessarily good.
  • the light-reflecting and scattering properties of titanium oxide reduce the efficiency of photopolymerization initiator generation, and as a result, it is believed that the adhesion and abrasion resistance of the printed matter did not reach practical levels.

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Abstract

L'invention concerne une encre pour jet d'encre durcissable aux ultraviolets contenant de l'oxyde de titane, un composé photopolymérisable, un amorceur de photopolymérisation et un agent de blanchiment fluorescent, le composé photopolymérisable contenant 50 % en masse ou plus d'un composé polymérisable polyfonctionnel dans la quantité totale du composé photopolymérisable ; le composé polymérisable polyfonctionnel contenant 50 % en masse ou plus d'un diacrylate d'alcane diol spécifique dans la quantité totale du composé polymérisable polyfonctionnel ; et l'agent de blanchiment fluorescent contenant un composé benzoxazoyle thiophène et/ou un composé benzoxazoyle naphtalène.
PCT/JP2025/022778 2024-07-08 2025-06-25 Encre pour jet d'encre durcissable aux ultraviolets et matière imprimée Pending WO2026014236A1 (fr)

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JP2024-109845 2024-07-08
JP2024109845 2024-07-08

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JP2019081867A (ja) * 2017-10-31 2019-05-30 セイコーエプソン株式会社 放射線硬化型インクジェットインクセットおよび記録方法
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WO2024122094A1 (fr) * 2022-12-05 2024-06-13 ａｒｔｉｅｎｃｅ株式会社 Encre pour jet d'encre durcissable aux ultraviolets et procédé de production de matériau imprimé
JP2025002622A (ja) * 2023-06-23 2025-01-09 セイコーエプソン株式会社 非水性インクジェットインク組成物及びインクジェット記録装置

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JP2009191118A (ja) * 2008-02-13 2009-08-27 Fujifilm Corp インク組成物、インクジェット記録方法及び印刷物
JP2013240978A (ja) * 2012-04-25 2013-12-05 Seiko Epson Corp インクジェット記録方法、紫外線硬化型インク、インクジェット記録装置
JP2018188581A (ja) * 2017-05-10 2018-11-29 コニカミノルタ株式会社 活性光線硬化型インクジェットインク
JP2019081867A (ja) * 2017-10-31 2019-05-30 セイコーエプソン株式会社 放射線硬化型インクジェットインクセットおよび記録方法
WO2022255110A1 (fr) * 2021-06-01 2022-12-08 Dic株式会社 Composition d'encre durcissable par un rayonnement actinique et procédé de production de matière imprimée
JP2023097117A (ja) * 2021-12-27 2023-07-07 Dic株式会社 活性エネルギー線硬化性インク組成物及び印刷物の製造方法
WO2024122094A1 (fr) * 2022-12-05 2024-06-13 ａｒｔｉｅｎｃｅ株式会社 Encre pour jet d'encre durcissable aux ultraviolets et procédé de production de matériau imprimé
JP2025002622A (ja) * 2023-06-23 2025-01-09 セイコーエプソン株式会社 非水性インクジェットインク組成物及びインクジェット記録装置

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