Radiation-curable inkjet composition and recording method

Abstract

To provide a radiation-curable inkjet composition capable of giving a coating film excellent in discoloration resistance, adhesion and scratch resistance, and to provide a recording method.SOLUTION: The radiation-curable inkjet composition is a white ink containing a white coloring material or a light color ink or clear ink containing 1.2 mass% or less of a coloring material. The radiation-curable inkjet composition contains polymerizable compounds including at least either a monofunctional monomer having a nitrogen-containing heterocyclic structure or a monomer having a hydroxy group. The content of a thioxanthone-based photopolymerization initiator is 0.3 mass% or less based on the total amount of the radiation-curable inkjet composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a radiation-curable ink jet composition and a recording method. [Background technology]

[0002] It has been known that a photocurable inkjet ink composition that is low in viscosity and highly reactive yet capable of providing printed matter with excellent film properties, particularly flexibility, can be obtained by containing 40% by mass or more and 75% by mass or less of a vinyl ether group-containing (meth)acrylic acid ester, 1% by mass or more and 20% by mass or less of a urethane (meth)acrylate oligomer, and a photopolymerization initiator, as described in Patent Document 1. It is also known that a radiation-curable inkjet composition that is low in odor and exhibits good curability and flexibility after curing can be obtained by containing a vinyl ether group-containing (meth)acrylic acid ester, acryloylmorpholine, or the like, and vinylcaprolactam, or the like, as described in Patent Document 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-162688 [Patent Document 2] Japanese Patent Application Publication No. 2018-9142 Summary of the Invention [Problem to be solved by the invention]

[0004] In the radiation-curable inkjet composition described above, a thioxanthone-based photopolymerization initiator is sometimes used because it is less susceptible to oxygen inhibition and can improve the curability of the ink composition. However, it has been found that when a thioxanthone-based photopolymerization initiator is used under specific conditions, there is a problem in that the discoloration of the ink coating film becomes significant. [Means for solving the problem]

[0005] The radiation-curable inkjet composition of the present invention is a white ink containing a white colorant, or a light-colored ink or clear ink containing 1.2% by mass or less of a colorant, and contains a polymerizable compound containing at least one of a monofunctional monomer having a nitrogen-containing heterocyclic structure and a monomer having a hydroxy group, and the content of a thioxanthone-based photopolymerization initiator is 0.3% by mass or less, relative to the total amount of the radiation-curable inkjet composition.

[0006] The radiation-curable inkjet composition preferably contains an acylphosphine oxide-based photopolymerization initiator, and the content of the acylphosphine oxide-based photopolymerization initiator is preferably 10% by mass or less relative to the total amount of the radiation-curable inkjet composition.

[0007] In the radiation-curable ink jet composition, the monofunctional monomer having a nitrogen-containing heterocyclic structure preferably includes acryloylmorpholine.

[0008] In the radiation-curable ink jet composition, the content of the monofunctional monomer having a nitrogen-containing heterocyclic structure is preferably 3.0 to 15% by mass relative to the total amount of the radiation-curable ink jet composition.

[0009] In the radiation-curable ink jet composition, the polymerizable compound preferably contains a (meth)acrylate containing a crosslinked fused ring structure.

[0010] In the radiation-curable inkjet composition, the (meth)acrylate containing a crosslinked fused ring structure preferably contains dicyclopentenyl (meth)acrylate.

[0011] In the radiation-curable inkjet composition, the polymerizable compound preferably includes a monofunctional urethane acrylate.

[0012] In the radiation-curable inkjet composition, the monofunctional urethane acrylate is preferably represented by the following formula (1). H2C=CR 1 -CO-O-(R 2 -O-(CO)-(NH) n -R 3 ···(1) (In formula (1), R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue having 2 to 5 carbon atoms, and R 3 is an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms, and n is an integer of 1 or more.

[0013] In the radiation-curable inkjet composition, it is preferable that the polymerizable compound contains a vinyl ether group-containing (meth)acrylic acid ester represented by the following formula (2), and the content of the vinyl ether group-containing (meth)acrylic acid ester is 1.0 to 10 mass % relative to the total amount of the radiation-curable inkjet composition: CH2=CR 4 -COOR 5 -O-CH=CH-R 6 (2) (In the formula, R 4 is a hydrogen atom or a methyl group, and R 5 is a divalent organic residue having 2 to 20 carbon atoms, and R 6 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

[0014] In the radiation curable ink jet composition, the content of the white color material is preferably 15% by mass or more relative to the total amount of the radiation curable ink jet composition.

[0015] In the radiation-curable ink jet composition, the content of the monofunctional monomer contained in the polymerizable compound is preferably 90% by mass or more relative to the total amount of the polymerizable compound.

[0016] In the radiation-curable ink jet composition, the color material other than the white color material is preferably a cyan color material or a magenta color material.

[0017] The recording method of the present invention also includes a discharge step of discharging the radiation curable ink jet composition from an inkjet head to adhere it to a recording medium, and an irradiation step of irradiating the radiation curable ink jet composition adhered to the recording medium with radiation. DETAILED DESCRIPTION OF THE INVENTION

[0018] Below, we will explain in detail the embodiment of the present invention (hereinafter referred to as the ``present embodiment''), but the present invention is not limited to this and various modifications are possible within the scope of the gist of the present invention.

[0019] In this specification, "(meth)acryloyl" means at least one of acryloyl and its corresponding methacryloyl, "(meth)acrylate" means at least one of acrylate and its corresponding methacrylate, and "(meth)acrylic" means at least one of acrylic and its corresponding methacrylic.

[0020] 1. Radiation-curable inkjet composition The radiation-curable inkjet composition according to this embodiment (hereinafter also simply referred to as "composition") is a white ink containing a white colorant, or a light-colored ink or clear ink containing 1.2 mass % or less of a colorant, and contains a polymerizable compound containing at least one of a monofunctional monomer having a nitrogen-containing heterocyclic structure and a monomer having a hydroxy group, and the content of a thioxanthone-based photopolymerization initiator is 0.3 mass % or less relative to the total amount of the radiation-curable inkjet composition.

[0021] The reason for this discoloration is not particularly limited, but it is thought that the thioxanthone-based photopolymerization initiator abstracts a proton from a monofunctional monomer having a nitrogen-containing heterocyclic structure or a monomer having a hydroxyl group, and then combines with the proton to cause discoloration such as yellowing. On the other hand, monofunctional monomers having a nitrogen-containing heterocyclic structure, such as acryloylmorpholine and n-vinylcaprolactam, have a positive charge localized near the nitrogen atom, making the hydrogen atom of the adjacent alkyl group easily abstracted by the thioxanthone-based initiator, which is likely to cause the discoloration. Similarly, monomers having a hydroxyl group, such as 4-hydroxybutyl acrylate, also tend to have protons easily abstracted. However, monofunctional monomers having a nitrogen-containing heterocyclic structure or monomers having a hydroxyl group have the advantage of having a high homopolymer Tg and providing a coating film with excellent abrasion resistance, flexibility, and adhesion.

[0022] Discoloration caused by a thioxanthone-based photopolymerization initiator is unlikely to be a problem with dark color inks, but it can cause a decrease in color reproducibility with inks with a low content of color material, such as light color inks or clear inks, or inks that do not contain any color material, or with white inks.

[0023] In contrast to this, in the present embodiment, when at least one of a monofunctional monomer having a nitrogen-containing heterocyclic structure and a monomer having a hydroxy group is contained as the polymerizable compound, discoloration of the coating film can be suppressed by setting the content of the thioxanthone-based photopolymerization initiator within a predetermined range.

[0024] The radiation-curable ink jet composition according to this embodiment is a composition that is ejected from an ink jet head by an ink jet method. Hereinafter, a radiation-curable ink composition will be described as one embodiment of the radiation-curable ink jet composition, but the composition according to this embodiment may be a composition other than an ink composition, for example, a composition used for 3D modeling.

[0025] The radiation-curable inkjet composition of this embodiment is cured by irradiation with radiation. Examples of radiation include ultraviolet light, electron beams, infrared light, visible light, and X-rays. As the radiation, ultraviolet light is preferred because radiation sources are readily available and widely used, and materials suitable for curing by ultraviolet radiation are readily available and widely used.

[0026] The components that may be contained in the radiation-curable ink jet composition according to this embodiment, its physical properties, and a production method will be described below.

[0027] 1.1.Colorants The radiation-curable inkjet composition according to this embodiment is a white ink containing a white colorant, or a light-colored ink or clear ink containing 1.2% by mass or less of the colorant. The colorant may be at least one of a pigment and a dye. Colorants other than the white colorant are not particularly limited and may be those described below, but it is preferable to use, for example, a cyan or magenta colorant. White ink, clear ink, cyan ink, or magenta ink are highly susceptible to discoloration of the coating film, making the present invention more effective.

[0028] In the case of a white ink, the content of the white colorant is preferably 10% by mass or more, more preferably 15% by mass or more, relative to the total amount of the composition. When the content of the white colorant is 10% by mass or more, the shielding properties tend to be further improved. Furthermore, in the case of a white ink, the content of the white colorant is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less, relative to the total amount of the composition. When the content of the white colorant is 30% by mass or less, the adhesion and flexibility of the coating film tend to be further improved.

[0029] The colorant content of the light-colored ink is 1.2% by mass or less, preferably 1.0% by mass or less, more preferably 0.90% by mass or less, and even more preferably 0.70% by mass or less, relative to the total amount of the composition. The lower limit is not particularly limited, but is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and even more preferably 0.5% by mass or more, relative to the total amount of the composition. The colorant content of the clear ink is 0.05% by mass or less, preferably 0.01% by mass or less, relative to the total amount of the composition, and more preferably contains no colorant. In this embodiment, no strict distinction is made between light-colored ink and clear ink since they have in common the effect of being affected by discoloration, but ink that does not contain coloring material or contains coloring material to an extent that it is not intended to be colored is called clear ink, and ink that is intended to be colored is called light-colored ink.

[0030] 1.1.1. Pigments By using a pigment as a coloring material, the light resistance of the radiation-curable ink jet composition can be improved. Both inorganic and organic pigments can be used as the pigment. One type of pigment may be used alone, or two or more types may be used in combination.

[0031] As inorganic pigments, carbon blacks (CI (Colour Index Generic Name) Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, iron oxide, and titanium oxide can be used.

[0032] Examples of organic pigments include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye chelates (for example, basic dye chelates, acid dye chelates, etc.); dye lakes (basic dye lakes, acid dye lakes), nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments.

[0033] More specifically, carbon blacks used for the black include No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B, etc. (all manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. (all manufactured by Carbon Columbia), Rega1 400R, Rega1 330R, Rega1 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400 (manufactured by Cabot Corporation (CABOTJAPAN KK)), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (all manufactured by Degussa).

[0034] Pigments used for white include CI Pigment White 6, 18, and 21.

[0035] Pigments used for yellow include CI Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 155, 167, 172, and 180.

[0036] Pigments used for magenta include CI Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, and CI Pigment Violet. Examples include 19, 23, 32, 33, 36, 38, 43, and 50.

[0037] Pigments used for cyan include CI Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, and CI Vat Blue 4 and 60.

[0038] Examples of pigments other than magenta, cyan, and yellow include CI Pigment Green 7 and 10, CI Pigment Brown 3, 5, 25, and 26, and CI Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, and 63.

[0039] 1.1.2.Dye A dye can be used as the coloring material. The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. The dyes can be used alone or in combination of two or more.

[0040] The dye is not particularly limited, and examples thereof include CI Acid Yellow 17, 23, 42, 44, 79, 142, CI Acid Red 52, 80, 82, 249, 254, 289, CI Acid Blue 9, 45, 249, CI Acid Black 1, 2, 24, 94, CI Food Black 1, 2, CI Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 14 2, 144, 173, CI Direct Red 1, 4, 9, 80, 81, 225, 227, CI Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, CI Direct Black 19, 38, 51, 71, 154, 168, 171, 195, CI Reactive Red 14, 32, 55, 79, 249, CI Reactive Black 3, 4, 35.

[0041] 1.2. Polymerizable compounds The polymerizable compound contains at least one of a monofunctional monomer having a nitrogen-containing heterocyclic structure and a monomer having a hydroxy group, and may contain other monofunctional monomers, or polyfunctional monomers or oligomers having two or more functional groups, as necessary. Each polymerizable compound may be used alone or in combination of two or more.

[0042] 1.2.1. Monofunctional Monomers The content of the monofunctional monomer is preferably 86% by mass or more, more preferably 88% by mass or more, and even more preferably 90% by mass or more, relative to the total amount of polymerizable compounds. When the content of the monofunctional monomer is 86% by mass or more, relative to the total amount of polymerizable compounds, the flexibility and adhesion of the coating film are further improved. There is no particular upper limit for the content of the monofunctional monomer, but it is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less, relative to the total amount of polymerizable compounds. When the content of the monofunctional monomer is 99% by mass or less, relative to the total amount of polymerizable compounds, the abrasion resistance of the coating film tends to be further improved.

[0043] Furthermore, the content of the monofunctional monomer is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, relative to the total amount of the composition. When the content of the monofunctional monomer is 60% by mass or more, relative to the total amount of the composition, the flexibility and adhesion of the coating film tend to be further improved. Furthermore, the upper limit of the content of the monofunctional monomer is preferably 92% by mass or less, more preferably 90% by mass or less, and even more preferably 88% by mass or less, relative to the total amount of the composition. When the content of the monofunctional monomer is 90% by mass or less, relative to the total amount of the composition, the abrasion resistance of the coating film tends to be further improved.

[0044] 1.2.1.1. Monofunctional monomers with nitrogen-containing heterocyclic structures The monofunctional monomer having a nitrogen-containing heterocyclic structure is not particularly limited, and examples thereof include N-vinylcaprolactam, N-vinylcarbazole, N-vinylpyrrolidone, and acryloylmorpholine. Note that the nitrogen-containing heterocyclic structure refers to a structure containing at least one nitrogen atom as a hetero atom contained in the heterocycle.

[0045] Among these, it is more preferable to contain either N-vinylcaprolactam or acryloylmorpholine.

[0046] The use of such a monofunctional monomer having a nitrogen-containing heterocyclic structure tends to further improve the adhesion and abrasion resistance of the coating film. Furthermore, a monofunctional vinyl monomer having a nitrogen-containing heterocyclic structure such as N-vinylcaprolactam and a monofunctional acrylate monomer having a nitrogen-containing heterocyclic structure such as acryloylmorpholine tend to further improve the flexibility and adhesion of the coating film.

[0047] Furthermore, monomers in which an electron-donating group such as an alkyl group is bonded to a nitrogen atom, such as acryloylmorpholine, tend to be particularly susceptible to hydrogen abstraction from the alkyl group by a thioxanthone-based photopolymerization initiator, and therefore the present invention is useful for such monomers.

[0048] The content of the monofunctional monomer having a nitrogen-containing heterocyclic structure is preferably 1 to 25 mass %, more preferably 5 to 20 mass %, and even more preferably 5 to 15 mass %, relative to the total amount of the polymerizable compound. When the content of the monofunctional monomer having a nitrogen-containing heterocyclic structure is within the above range, the adhesion and abrasion resistance of the coating film tend to be further improved.

[0049] The content of the monofunctional monomer having a nitrogen-containing heterocyclic structure is preferably 1 to 25 mass %, more preferably 2.0 to 20 mass %, and even more preferably 3.0 to 15 mass %, relative to the total amount of the composition. When the content of the monofunctional monomer having a nitrogen-containing heterocyclic structure is within the above range, the adhesion and abrasion resistance of the coating film tend to be further improved.

[0050] 1.2.1.2. Monomers containing hydroxy groups The monomer having a hydroxy group is not particularly limited, but examples thereof include 4-hydroxybutyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, N-hydroxymethyl(meth)acrylamide, etc. Use of such a monomer having a hydroxy group tends to further improve the curability and hardness of the coating film.

[0051] The content of the hydroxyl group-containing monomer is preferably 0.5 to 10 mass %, more preferably 1 to 7.5 mass %, and even more preferably 2 to 5.0 mass %, relative to the total amount of polymerizable compounds. When the content of the hydroxyl group-containing monomer is within the above range, the adhesion and abrasion resistance of the coating film tend to be further improved.

[0052] The content of the hydroxyl group-containing monomer is preferably 0.5 to 10 mass %, more preferably 1 to 7.5 mass %, and even more preferably 2 to 5.0 mass %, relative to the total amount of the composition. When the content of the hydroxyl group-containing monomer is within the above range, the adhesion and abrasion resistance of the coating film tend to be further improved.

[0053] 1.2.1.3. (Meth)acrylates containing bridged condensed ring structures Other examples of monofunctional monomers include (meth)acrylates containing a bridged fused ring structure. In the present invention, the bridged fused ring structure refers to a structure in which two or more ring structures share a side in a one-to-one relationship and two or more atoms of the same ring structure or different ring structures that are not adjacent to each other are linked. Examples of (meth)acrylates containing a bridged fused ring structure include dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and dicyclopentanyl (meth)acrylate. In addition to the above, the following can be mentioned as examples of the bridged fused ring structure. [ka]

[0054] Among these, it is more preferable to include dicyclopentenyl (meth)acrylate. By using such a (meth)acrylate containing a crosslinked fused ring structure, the scratch resistance, flexibility and adhesion of the coating film tend to be further improved.

[0055] The content of the (meth)acrylate having a crosslinked condensed ring structure is preferably 1 to 20 mass %, more preferably 3 to 15 mass %, and even more preferably 5 to 10 mass %, relative to the total amount of the polymerizable compound. When the content of the (meth)acrylate having a crosslinked condensed ring structure is within the above range, the abrasion resistance of the coating film tends to be further improved.

[0056] The content of the (meth)acrylate having a crosslinked condensed ring structure is preferably 1 to 20 mass %, more preferably 2 to 15 mass %, and even more preferably 3 to 10 mass %, relative to the total amount of the polymerizable compound. When the content of the (meth)acrylate having a crosslinked condensed ring structure is within the above range, the abrasion resistance of the coating film tends to be further improved.

[0057] 1.2.1.4. Aromatic group-containing monofunctional monomers Other monofunctional monomers include aromatic group-containing monofunctional monomers, which are not particularly limited and include, for example, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, alkoxylated 2-phenoxyethyl (meth)acrylate, ethoxylated nonylphenyl (meth)acrylate, alkoxylated nonylphenyl (meth)acrylate, and p-cumylphenol EO-modified (meth)acrylate.

[0058] Among these, phenoxyethyl (meth)acrylate and benzyl (meth)acrylate are preferred, phenoxyethyl (meth)acrylate is more preferred, and phenoxyethyl acrylate (PEA) is even more preferred. By using such aromatic group-containing monofunctional monomers, the solubility of the photopolymerization initiator tends to be further improved, and the curability of the 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 improved.

[0059] The content of the aromatic group-containing monofunctional monomer is preferably 25 to 60 mass %, more preferably 30 to 55 mass %, and even more preferably 35 to 50 mass %, relative to the total amount of the polymerizable compounds. When the content of the aromatic group-containing monofunctional monomer is within the above range, the scratch resistance of the coating film tends to be further improved.

[0060] The content of the aromatic group-containing monofunctional monomer is preferably 20 to 55 mass %, more preferably 25 to 50 mass %, and even more preferably 30 to 45 mass %, relative to the total amount of the composition. When the content of the aromatic group-containing monofunctional monomer is within the above range, the scratch resistance of the coating film tends to be further improved.

[0061] 1.2.1.5. Monofunctional urethane acrylate One example of the other monofunctional monomer is a monofunctional urethane acrylate. The monofunctional urethane acrylate is not particularly limited, but examples thereof include aliphatic urethane (meth)acrylate and aromatic urethane (meth)acrylate.

[0062] Examples of aliphatic urethane (meth)acrylates include those represented by the following formula (1): By using such a monofunctional urethane acrylate, the flexibility and adhesion of the coating film tend to be further improved. H2C=CR 1 -CO-O-(R 2 -O-(CO)-(NH) n -R 3···(1) (In formula (1), R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue having 2 to 5 carbon atoms, and R 3 is an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms, and n is an integer of 1 or more.

[0063] In the above formula (1), R 2 The divalent organic residue having 2 to 5 carbon atoms represented by the formula (1) is not particularly limited, but examples thereof include alkylene groups such as an ethylene group, an n-propylene group, an isopropylene group, and a butylene group. 3 The alkyl group having 1 to 10 carbon atoms represented by the formula (I) is not particularly limited, but examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, an n-pentyl group, a neopentyl group, and an n-hexyl group. Furthermore, in the above formula (1), R 3 The hydroxyalkyl group having 1 to 10 carbon atoms represented by the following formula is not particularly limited, but examples thereof include the above alkyl groups in which one of the hydrogen atoms has been substituted with a hydroxy group.

[0064] Such aliphatic urethane (meth)acrylate is not particularly limited, but examples thereof include 2-(butylcarbamoyloxy)ethyl (meth)acrylate, 2-(butylcarbamoyloxy)propyl (meth)acrylate, 4-(butylcarbamoyloxy)butyl (meth)acrylate, 2-(isopropylcarbamoyloxy)ethyl (meth)acrylate, 2-(isopropylcarbamoyloxy)propyl (meth)acrylate, and 4-(isopropylcarbamoyloxy)butyl (meth)acrylate.

[0065] Furthermore, the aromatic urethane (meth)acrylate is not particularly limited, but examples thereof include 2-(phenylcarbamoyloxy)ethyl (meth)acrylate, 2-(phenylcarbamoyloxy)propyl (meth)acrylate, 4-(phenylcarbamoyloxy)butyl (meth)acrylate, 2-(benzylcarbamoyloxy)ethyl (meth)acrylate, 2-(benzylcarbamoyloxy)propyl (meth)acrylate, and 4-(benzylcarbamoyloxy)butyl (meth)acrylate.

[0066] Among these, aliphatic urethane (meth)acrylate is preferred, and 2-(butylcarbamoyloxy)ethyl (meth)acrylate is more preferred. Use of such monofunctional urethane acrylates tends to further improve the flexibility and adhesion of the coating film.

[0067] The content of the monofunctional urethane acrylate is preferably 0.5 to 6 mass %, more preferably 1 to 5 mass %, and even more preferably 2 to 4 mass %, relative to the total amount of the polymerizable compounds. When the content of the monofunctional urethane acrylate is within the above range, the flexibility and adhesion of the coating film tend to be further improved.

[0068] The content of the monofunctional urethane acrylate is preferably 0.5 to 6 mass %, more preferably 1 to 5 mass %, and even more preferably 2 to 4 mass %, relative to the total amount of the composition. When the content of the monofunctional urethane acrylate is within the above range, the flexibility and adhesion of the coating film tend to be further improved.

[0069] 1.2.1.6 (Meth)acrylates containing an alicyclic structure One of the other monofunctional monomers is a (meth)acrylate containing an alicyclic structure. In the present invention, the (meth)acrylate containing an alicyclic structure has at least one alicyclic group in its structure and does not have a crosslinked fused ring structure.

[0070] The alicyclic group may have a substituent such as an alkyl group having 1 to 10 carbon atoms, a hydroxyl group, or an aryl group having 6 to 16 carbon atoms.

[0071] The alicyclic group may be bonded directly to the oxygen atom of the (meth)acryloyloxy group, or may be bonded via an alkylene group having 1 to 10 carbon atoms.

[0072] The alkylene group may have a substituent such as an alkyl group having 1 to 10 carbon atoms, a hydroxyl group, or an aryl group having 6 to 16 carbon atoms, and may have an ester bond or an ether bond in the main chain of the alkylene group.

[0073] The number of atoms constituting the ring of the alicyclic group is not particularly limited, but is preferably 3-20, and more preferably 5-12.

[0074] The (meth)acrylate containing an alicyclic structure is not particularly limited, but examples thereof include isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, and 3,3,5-trimethylcyclohexyl acrylate. Among these, isobornyl (meth)acrylate is preferred.

[0075] The content of the (meth)acrylate containing an alicyclic structure is preferably from 3.0% by mass to 60.0% by mass, more preferably from 5.0% by mass to 50.0% by mass, and even more preferably from 10.0% by mass to 30.0% by mass, relative to the total mass of the ink composition.

[0076] When the content of the (meth)acrylate containing an alicyclic structure is within the above range, the abrasion resistance can be further improved.

[0077] 1.2.2. Multifunctional Monomers and Oligomers The content of the polyfunctional monomer or oligomer is preferably 1 to 20% by mass or more, more preferably 3 to 17.5% by mass, and even more preferably 6 to 15% by mass, relative to the total amount of polymerizable compounds. When the content of the polyfunctional monomer is 2.5% by mass or more, relative to the total amount of polymerizable compounds, the abrasion resistance tends to be further improved. Furthermore, when the content of the polyfunctional monomer is 20% by mass or less, relative to the total amount of polymerizable compounds, the flexibility and adhesion of the coating film tend to be further improved. Furthermore, a difunctional to hexafunctional monomer is preferred, more preferably a difunctional to trifunctional monomer, and even more preferably a difunctional monomer. Although polyfunctional monomers generally tend to have a high viscosity, such a polyfunctional monomer can achieve both low viscosity and curability.

[0078] The content of the polyfunctional monomer is preferably 1 to 20% by mass or more, more preferably 3 to 17.5% by mass, and even more preferably 6 to 15% by mass, relative to the total amount of the composition. When the content of the polyfunctional monomer is 2.5% by mass or more, relative to the total amount of the composition, the abrasion resistance tends to be further improved. When the content of the polyfunctional monomer is 20% by mass or less, relative to the total amount of the composition, the flexibility and adhesion of the coating film tend to be further improved.

[0079] 1.2.2.1 Vinyl ether group-containing (meth)acrylic acid esters Examples of polyfunctional monomers include vinyl ether group-containing (meth)acrylic esters. Examples of vinyl ether group-containing (meth)acrylic esters include, but are not limited to, compounds represented by the following formula (2): By including such vinyl ether group-containing (meth)acrylic esters, the viscosity of the composition tends to decrease, and the ejection stability and curability tend to be further improved. CH2=CR 4 -COOR 5 -O-CH=CH-R 6 (2) (In the formula, R 4 is a hydrogen atom or a methyl group, and R 5is a divalent organic residue having 2 to 20 carbon atoms, and R 6 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

[0080] In the above formula (2), R 5 Examples of the divalent organic residue having 2 to 20 carbon atoms represented by the formula (I) 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 and having an oxygen atom due to an ether bond and / or an ester bond in its structure, which may be substituted; and a divalent aromatic group having 6 to 11 carbon atoms, which may be substituted. 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 and having an oxygen atom due to an ether bond in its structure, such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, and an oxybutylene group, are preferred. Furthermore, from the viewpoint of further reducing the viscosity of the composition and further improving the curability of the composition, R 2 is an alkylene group having 2 to 9 carbon atoms and having an oxygen atom by an ether bond in the structure, such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, or an oxybutylene group, and more preferred are compounds having a glycol ether chain.

[0081] In the above formula (2), R 6 Suitable monovalent organic residues having 1 to 11 carbon atoms and represented by the formula (I) are linear, branched, or cyclic alkyl groups having 1 to 10 carbon atoms, which may be substituted, and aromatic groups having 6 to 11 carbon atoms, which may be substituted. Among these, alkyl groups having 1 to 2 carbon atoms, such as methyl or ethyl groups, and aromatic groups having 6 to 8 carbon atoms, such as phenyl and benzyl groups, are preferably used.

[0082] When each of the above organic residues is a group that may be substituted, the substituent is divided into a group containing carbon atoms and a group not containing carbon atoms. First, when the above substituent is a group containing carbon atoms, the carbon atom is counted in the number of carbon atoms of the organic residue. Examples of the group containing carbon atoms include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing carbon atoms include, but are not limited to, a hydroxyl group and a halo group.

[0083] Specific examples of the compound of formula (2) include, but are not limited to, 2-vinyloxyethyl (meth)acrylate, 3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl (meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl (meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate, 1-vinyloxymethylpropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl (meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate, ) 3-vinyloxybutyl acrylate, 1-methyl-2-vinyloxypropyl (meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl (meth)acrylate, 6-vinyloxyhexyl (meth)acrylate, 4-vinyloxymethylcyclohexylmethyl (meth)acrylate, 3-vinyloxymethylcyclohexylmethyl (meth)acrylate, 2-vinyloxymethylcyclohexylmethyl (meth)acrylate, p-vinyloxymethylphenylmethyl (meth)acrylate, m-vinyloxymethylphenyl (meth)acrylate Methyl, o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl (meth)acrylate (meth)acrylate 2-(vinyloxyethoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyethoxyethoxy)propyl, (meth)acrylate 2-(vinyloxyethoxyisopropoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)propyl,2-(vinyloxyethoxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate Examples of suitable acrylates include ethyl (meth)acrylate, 2-(isopropenoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate, polyethylene glycol monovinyl ether (meth)acrylate, and polypropylene glycol monovinyl ether (meth)acrylate. Among these specific examples, 2-(2-vinyloxyethoxy)ethyl acrylate is particularly preferred in that it is easy to balance the curability and viscosity of the composition. In this embodiment, 2-(2-vinyloxyethoxy)ethyl acrylate is also referred to as VEEA.

[0084] The content of the vinyl ether group-containing (meth)acrylic esters relative to the total amount of polymerizable compounds is preferably 0.5 to 10 mass %, more preferably 1 to 7.5 mass %, and even more preferably 2 to 5 mass %. When the content of the vinyl ether group-containing (meth)acrylic esters relative to the total amount of polymerizable compounds is within the above range, the viscosity of the composition tends to decrease, and the ejection stability tends to be further improved.

[0085] The content of the vinyl ether group-containing (meth)acrylic esters relative to the total amount of the composition is preferably 1.0 to 10 mass%, more preferably 1.0 to 7.5 mass%, and even more preferably 2.0 to 5 mass%. When the content of the vinyl ether group-containing (meth)acrylic esters relative to the total amount of the composition is within the above range, the viscosity of the composition tends to decrease, and the discharge stability and curability tend to be further improved.

[0086] 1.2.2.2. Urethane acrylate oligomer One example of a polyfunctional oligomer is a urethane acrylate oligomer. The urethane acrylate oligomer is not particularly limited, but examples include aliphatic urethane acrylate oligomers and aromatic urethane acrylate oligomers. Furthermore, the urethane acrylate oligomer is preferably a tetrafunctional or lower urethane acrylate oligomer, and more preferably a difunctional urethane acrylate oligomer. Use of such an oligomer tends to further improve the storage stability and abrasion resistance of the composition. In this embodiment, an oligomer is defined as one having a molecular weight of 1000 or more, and a monomer is defined as one having a molecular weight of less than 1000.

[0087] The content of the urethane acrylate oligomer is preferably 1 to 10 mass %, more preferably 2 to 9 mass %, and even more preferably 3 to 7 mass %, relative to the total amount of the polymerizable compounds. When the content of the urethane acrylate oligomer relative to the total amount of the polymerizable compounds is within the above range, the storage stability of the composition tends to be further improved, and the scratch resistance of the coating film tends to be further improved.

[0088] The content of the urethane acrylate oligomer is preferably 1 to 10 mass %, more preferably 2 to 9 mass %, and even more preferably 3 to 7 mass %, relative to the total amount of the composition. When the content of the urethane acrylate oligomer relative to the total amount of the composition is within the above range, the storage stability of the composition tends to be further improved, and the scratch resistance of the coating film tends to be further improved.

[0089] 1.3. Photoinitiators The radiation-curable inkjet composition according to this embodiment preferably contains a photopolymerization initiator that generates active species upon irradiation with radiation. The photopolymerization initiator may be used alone or in combination of two or more.

[0090] The photopolymerization initiator is not particularly limited, but examples thereof include known polymerization initiators such as acylphosphine oxide-based photopolymerization initiators, alkylphenone-based polymerization initiators, titanocene-based polymerization initiators, and thioxanthone-based photopolymerization initiators. Among these, acylphosphine oxide-based photopolymerization initiators are preferred. Use of such a polymerization initiator tends to further improve the curability of the composition, particularly the curability in a curing process using UV-LED light.

[0091] The acylphosphine oxide photopolymerization initiator is not particularly limited, but examples thereof include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0092] Commercially available examples of such acylphosphine oxide photopolymerization initiators 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-phenyl ketone in a mass ratio of 25:75), and IRGACURE TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) (all manufactured by BASF).

[0093] The content of the acylphosphine oxide-based photopolymerization initiator is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, relative to the total amount of the composition. By setting the content of the acylphosphine oxide-based photopolymerization initiator to 20% by mass or less, the influence of the color of the acylphosphine oxide-based photopolymerization initiator can be reduced, and color reproducibility tends to be further improved. Furthermore, the lower limit of the content of the acylphosphine oxide-based photopolymerization initiator is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, relative to the total amount of the composition. By setting the content of the acylphosphine oxide-based photopolymerization initiator within the above range, the curability and discoloration resistance of the composition tend to be further improved.

[0094] The content of the thioxanthone-based photopolymerization initiator in the radiation-curable inkjet composition according to this embodiment is 0.3% by mass or less, preferably 0.25% by mass or less, and more preferably 0.20% by mass, relative to the total amount of the composition. From the viewpoint of suppressing discoloration, the lower limit of the content of the thioxanthone-based photopolymerization initiator is preferably as close to 0% by mass as possible, and it is preferable that the thioxanthone-based photopolymerization initiator is not present. On the other hand, from the viewpoint of improving curability without oxygen inhibition, the lower limit of the content of the thioxanthone-based photopolymerization initiator may be preferably 0.01% by mass or more, and more preferably 0.05% by mass or more.

[0095] Commercially available thioxanthone-based photopolymerization initiators include, for example, KAYACURE DETX-S (product name, manufactured by Nippon Kayaku Co., Ltd.), ITX (manufactured by BASF), and Quantacure CTX (manufactured by Aceto Chemical Co., Ltd.).

[0096] The content of the photopolymerization initiator other than the thioxanthone-based photopolymerization initiator is preferably 1 to 20 mass %, more preferably 3 to 15 mass %, even more preferably 5 to 10 mass %, and particularly preferably 7 to 9 mass %, relative to the total amount of the composition. When the content of the photopolymerization initiator other than the thioxanthone-based photopolymerization initiator is within the above range, the curability and discoloration resistance of the composition tend to be further improved.

[0097] 1.3. Other additives The radiation-curable ink jet composition according to this embodiment may further contain additives such as a dispersant, a polymerization inhibitor, and a slip agent, as needed.

[0098] Dispersants When the radiation-curable inkjet composition contains a pigment, it may further contain a dispersant to improve the pigment dispersibility. The dispersant may be used alone or in combination of two or more types.

[0099] The dispersant is not particularly limited, but examples thereof include dispersants commonly used in preparing pigment dispersions, such as polymer dispersants, etc. Specific examples thereof include those containing one or more of polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxy resins as the main component.

[0100] Commercially available polymer dispersants include the Ajisper series manufactured by Ajinomoto Fine-Techno Co., Ltd., the Solsperse series (Solsperse 36000, etc.) available from Avecia and Noveon, the Disperbic series manufactured by BYK Additives & Instruments, and the Disparlon series manufactured by Kusumoto Chemicals Co., Ltd.

[0101] The content of the dispersant is preferably 0.1 to 2 mass %, more preferably 0.1 to 1 mass %, and even more preferably 0.1 to 0.5 mass %, relative to the total amount of the composition.

[0102] 1.3.3. Polymerization inhibitors The radiation-curable inkjet composition according to this embodiment may further contain a polymerization inhibitor. The polymerization inhibitor may be used alone or in combination of two or more.

[0103] 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), and hindered amine compounds.

[0104] The content of the polymerization inhibitor is preferably 0.05 to 1 mass %, more preferably 0.05 to 0.5 mass %, relative to the total amount of the composition.

[0105] 1.3.4.Slip agents The radiation-curable inkjet composition according to this embodiment may further contain a slip agent. The slip agent may be used alone or in combination of two or more.

[0106] The slip agent is preferably a silicone surfactant, more preferably a polyester-modified silicone or a polyether-modified silicone. Examples of polyester-modified silicones include BYK-347, 348, BYK-UV3500, 3510, and 3530 (all manufactured by BYK Additives & Instruments). Examples of polyether-modified silicones include BYK-3570 (manufactured by BYK Additives & Instruments).

[0107] The content of the slip agent is preferably 0.01 to 2 mass %, more preferably 0.05 to 1 mass %, relative to the total amount of the composition.

[0108] 1.4. Method for producing the composition The radiation-curable ink jet composition is prepared by mixing the components contained in the composition and stirring the mixture to ensure a sufficient homogeneous mixture. In this embodiment, the preparation of the radiation-curable ink jet composition preferably includes a step of subjecting a mixture of a polymerization initiator and at least a portion of the monomers to at least one of ultrasonic treatment and heating treatment during the preparation process. This reduces the amount of dissolved oxygen in the prepared composition, resulting in a radiation-curable ink jet composition with excellent ejection stability and storage stability. The mixture may contain at least the components described above, and may further contain other components contained in the radiation-curable ink jet composition, or may contain all of the components contained in the radiation-curable ink jet composition. The monomer contained in the mixture may be at least a portion of the monomers contained in the radiation-curable ink jet composition.

[0109] 2. Inkjet recording method The inkjet recording method according to this embodiment includes a discharge step of discharging the radiation-curable inkjet composition from an inkjet head and depositing it on a recording medium, and an irradiation step of irradiating the radiation-curable inkjet composition deposited on the recording medium with radiation. This allows a coating film to be formed at the location on the recording medium where the radiation-curable inkjet composition has been applied. Each step will be described in detail below.

[0110] 2.1.Discharge process In the ejection step, the composition is ejected from an inkjet head and deposited on a recording medium. More specifically, a pressure generating means is driven to eject the composition filled in a pressure generating chamber of the inkjet head from a nozzle. This ejection method is also called an inkjet method.

[0111] Inkjet heads used in the ejection step include a line head that performs recording by a line method and a serial head that performs recording by a serial method.

[0112] 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 recording device. The recording medium is then moved in the sub-scanning direction (the longitudinal direction of the recording medium, the transport direction), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement to record an image on the recording medium.

[0113] 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. The carriage is then moved in the main scanning direction (the horizontal or width direction of the recording medium), and ink droplets are ejected from the nozzle openings of the head in conjunction with this movement, thereby recording an image on the recording medium.

[0114] 2.2.Irradiation process In the irradiation step, the radiation-curable inkjet composition attached to the recording medium is irradiated with radiation. When irradiated with radiation, a polymerization reaction of the monomers is initiated, curing the composition and forming a coating film. If a polymerization initiator is present at this time, it generates active species (initiation species) such as radicals, acids, and bases, and the polymerization reaction of the monomers is promoted by the function of the initiation species.

[0115] Examples of the radiation include ultraviolet light, infrared light, visible light, and X-rays. The radiation source is installed downstream of the inkjet head and irradiates the composition. The radiation source is not particularly limited, but examples include UV-LEDs. Use of such a radiation source can reduce the size and cost of the device. UV-LEDs as an ultraviolet light source are small and can be installed inside the inkjet recording device.

[0116] For example, it can be attached to a carriage (either at both ends along the width direction of the medium and / or on the side in the medium transport direction) on which an inkjet head that ejects the radiation-curable inkjet composition is mounted. Furthermore, due to the composition of the radiation-curable inkjet composition described above, it is possible to achieve low-energy, high-speed curing. The irradiation energy is calculated by multiplying the irradiation time by the irradiation intensity. Therefore, the irradiation time can be shortened, and the printing speed can be increased. On the other hand, the irradiation intensity can also be reduced. This reduces the temperature rise of the printed material, which also leads to a reduction in the odor of the cured film.

[0117] 3. Records The recorded matter of this embodiment is obtained by adhering the radiation-curable inkjet composition to a recording medium and curing it. The composition has good flexibility and adhesion, which can prevent cracking or chipping of the coating film when post-processing such as cutting or bending is performed. Therefore, the recorded matter of this embodiment can be suitably used for signage and the like.

[0118] The material of the recording medium is not particularly limited, but examples 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, and polyvinyl acetal, as well as plastics with treated surfaces, glass, paper, metal, and wood.

[0119] The form of the recording medium is not particularly limited, and examples include film, board, cloth, etc. [Example]

[0120] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples.

[0121] 1. Preparation of Inkjet Composition First, the colorant, dispersant, and a portion of each monomer were weighed and placed in a pigment dispersion tank, and a ceramic bead mill with a diameter of 1 mm was placed in the tank and stirred to obtain a pigment dispersion in which the colorant was dispersed in the monomer. Next, the remaining monomers, polymerization initiator, and polymerization inhibitor were placed in a stainless steel container for mixing so as to obtain the composition shown in Table 1, and after mixing and stirring to completely dissolve, the pigment dispersion obtained above was added, and the mixture was further mixed and stirred at room temperature for 1 hour, and then filtered through a 5 μm membrane filter to obtain the radiation-curable inkjet composition of each example.

[0122] For ink compositions that did not contain a colorant, the pigment dispersion was not used, and each component was placed in a stainless steel container, i.e., a mixing tank, so as to obtain the composition shown in Table 1, and the components were stirred and mixed as described above to obtain the radiation-curable inkjet composition of each example.

[0123] The numerical values ​​of each component shown in each example in the tables represent mass % unless otherwise specified.

[0124] [Table 1]

[0125] The abbreviations and product ingredients used in Table 1 are as follows:

[0126] <Coloring materials (pigments)> PB15:3 (product name "CI Pigment Blue 15:3", manufactured by DIC, phthalocyanine blue) Titanium dioxide (product name "CI Pigment White 6", manufactured by Tika) <Polymerization initiator> DETX (trade name "KAYACURE DETX-S", manufactured by Nippon Kayaku Co., Ltd., 2,4-diethylthioxanthone) 819 (trade name "IRGACURE 819", manufactured by BASF, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) TPO (product name "IRGACURE TPO", manufactured by BASF, 2,4,6-trimethylbenzoyldiphenylphosphine oxide) <Monofunctional monomer> ACMO (Acryloylmorpholine, manufactured by KJ Chemicals Co., Ltd.) n-VC (ISP Japan Co., Ltd., N-vinylcaprolactam) 4-HBA (4-hydroxybutyl acrylate, product name of Osaka Organic Chemical Industry Co., Ltd., monofunctional (meth)acrylate) DCPA (Hitachi Chemical Co., Ltd., dicyclopentenyl acrylate) IBXA (Osaka Organic Chemical Industry, Ltd., isobornyl acrylate) PEA (product name "Viscoat #192, manufactured by Osaka Organic Chemical Industry Co., Ltd., phenoxyethyl acrylate") BCEA: 2-(butylcarbamoyloxy)ethyl acrylate <Polyfunctional Monomer> VEEA (Nippon Shokubai Co., Ltd., 2-(2-vinyloxyethoxy)ethyl acrylate) <oligomer> CN991 (Sartomer Corporation, bifunctional urethane acrylate oligomer) <Polymerization inhibitor> MEHQ (product name "p-methoxyphenol", manufactured by Kanto Chemical Co., Ltd., hydroquinone monomethyl ether) <Slip agent> BYK-UV3500 (BYK Additives & Instruments, polyether-modified polydimethylsiloxane with acryloyl groups) <Dispersant> Solsperse 36000 (polymer dispersant, manufactured by Lubrizol).

[0127] 2. Evaluation Method 2.1.Color fastness The ink composition was applied to a PVC medium using a bar coater so that the applied thickness of the ink composition was 10 μm, and the irradiation intensity on the media surface was 2.5 W / cm 2 The media and light source were moved relative to each other at a speed of 0.04 cm / sec to irradiate the coating with ultraviolet light. An LED with a peak wavelength of 395 nm was used as the light source. The b* value of the coating film immediately after curing was measured using a colorimeter (trade name "Gretag Macbeth Spectrolino," manufactured by X-RITE). The b* value was also measured for the coating film after leaving it undisturbed for 24 hours after curing. The difference Δb* between the b* values ​​immediately after curing and those after 24 hours had elapsed was calculated, and discoloration was evaluated according to the following criteria. (Evaluation criteria) A: Δb* is less than 1 B: Δb* is 1 or more and less than 2 C: Δb* is 2 or more and less than 3 D: Δb* is 3 or more

[0128] 2.2.Adhesion The coating film obtained in the discoloration test was evaluated by a cross-cut test in accordance with JIS K5600-5-6. More specifically, the blade of a cutter was placed perpendicular to the coating film, and squares with 2 mm spacing between cuts were created to create a 10 x 10 grid. A transparent adhesive tape (25 mm wide) approximately 75 mm long was attached to the grid, and the tape was rubbed thoroughly with a finger so that the cured film was visible through it. Next, within 5 minutes of application, the tape was firmly peeled off from the cured film at an angle close to 60° in 0.5 to 1.0 seconds, and the condition of the grid was visually observed. The evaluation criteria are as follows: (Evaluation criteria) A: No peeling of the cured film was observed on the lattice. B: Peeling of the cured film was observed in less than 5% of the lattice. C Peeling of the cured film was observed in more than 5% of the lattice.

[0129] 2.3. Evaluation of abrasion resistance The coating film obtained in the discoloration test was evaluated in a micro-scratch test in accordance with JIS R3255. For the measurement, an ultra-thin film scratch tester (CSR-5000, manufactured by Nanotec Co., Ltd.) was used to measure the load capacity as a measure of abrasion resistance. Micro-scratching was performed while applying a load, and the load capacity was determined as the load when the stylus reached the media surface. The higher the load capacity, the better the abrasion resistance. The measurement was performed with a stylus diameter of 15 μm, amplitude of 100 μm, and scratch speed of 10 μm / sec. The evaluation criteria are as follows: (Evaluation criteria) A: 25 mN / cm 2 End B: 20 ​​mN / cm 2 More than 25mN / cm 2 less than C: 15 mN / cm 2 More than 20mN / cm 2 less than D: 15 mN / cm 2 less than

[0130] Each radiation-curable inkjet composition was filled into an inkjet printer PX-G930 (Seiko Epson Corporation) and used for recording. It was confirmed that each radiation-curable inkjet composition could be ejected by inkjet and that images could be formed.

[0131] 3. Evaluation Results The composition and evaluation results of the radiation-curable inkjet composition used in each example are shown in Table 1. Table 1 shows that the radiation-curable inkjet compositions of Examples 1 to 12, which contain a polymerizable compound containing at least one of a monofunctional monomer having a nitrogen-containing heterocyclic structure or a monomer having a hydroxy group, and in which the content of a thioxanthone-based photopolymerization initiator is 0.3 mass % or less relative to the total amount of the radiation-curable inkjet composition, all achieved discoloration resistance, adhesion, and abrasion resistance of C or higher, and were good.

[0132] Specifically, comparing each Example with Comparative Example 1, it is found that discoloration resistance is improved when the content of the thioxanthone-based photopolymerization initiator is 0.3% by mass or less. Furthermore, comparing each Example with Comparative Example 2, it is found that the inclusion of a monofunctional monomer having a nitrogen-containing heterocyclic structure or a monomer having a hydroxyl group further improves abrasion resistance. Furthermore, comparing each Example with Comparative Example 3, it is found that discoloration due to the thioxanthone-based photopolymerization initiator does not occur when the monofunctional monomer having a nitrogen-containing heterocyclic structure or a monomer having a hydroxyl group is not included. Furthermore, comparing each Example with Reference Example 1, it is found that the impact of discoloration due to the thioxanthone-based photopolymerization initiator is small when the content of the colorant exceeds 1.2% by mass.

Claims

1. A radiation-curable inkjet composition which is a white ink containing a white colorant, or a light-colored ink or clear ink having a colorant content of 1.2% by mass or less, a polymerizable compound containing at least one of a monofunctional monomer having a nitrogen-containing heterocyclic structure and a monomer having a hydroxy group, the content of the thioxanthone-based photopolymerization initiator is 0.3% by mass or less relative to the total amount of the radiation-curable inkjet composition; Radiation-curable inkjet compositions.

2. Contains an acylphosphine oxide photopolymerization initiator, the content of the acylphosphine oxide-based photopolymerization initiator is 10% by mass or less relative to the total amount of the radiation-curable inkjet composition; The radiation-curable ink jet composition according to claim 1 .

3. The radiation-curable ink jet composition according to claim 1 or 2, wherein the monofunctional monomer having a nitrogen-containing heterocyclic structure includes acryloylmorpholine.

4. the content of the monofunctional monomer having a nitrogen-containing heterocyclic structure is 3.0 to 15% by mass relative to the total amount of the radiation-curable inkjet composition; The radiation-curable ink jet composition according to any one of claims 1 to 3.

5. the polymerizable compound contains a (meth)acrylate containing a crosslinked condensed ring structure, The radiation-curable ink jet composition according to any one of claims 1 to 4.

6. The (meth)acrylate having a bridged fused ring structure includes dicyclopentenyl (meth)acrylate. The radiation-curable ink jet composition according to claim 5 .

7. The polymerizable compound includes a monofunctional urethane acrylate. The radiation-curable ink jet composition according to any one of claims 1 to 6.

8. The monofunctional urethane acrylate is represented by the following formula (1): The radiation-curable ink jet composition according to claim 7. H 2 C=CR 1 ----O-(R 2 -O-(CO)-(NH)) n -R 3 ・・・(1) (In formula (1), R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue having 2 to 5 carbon atoms, and R 3 is an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms. Also, n is an integer of 1 or more.

9. The polymerizable compound contains a vinyl ether group-containing (meth)acrylic acid ester represented by the following formula (2): the content of the vinyl ether group-containing (meth)acrylic acid ester is 1.0 to 10% by mass relative to the total amount of the radiation-curable inkjet composition; The radiation-curable ink jet composition according to any one of claims 1 to 8. CH 2 =CR 4 -COOR 5 -O-CH=CH-R 6 ・・・ (2) (In the formula, R 4 is a hydrogen atom or a methyl group, and R 5 is a divalent organic residue having 2 to 20 carbon atoms, and R 6 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

10. the content of the white colorant is 15% by mass or more relative to the total amount of the radiation-curable inkjet composition; The radiation-curable ink jet composition according to any one of claims 1 to 9.

11. the content of the monofunctional monomer contained in the polymerizable compound is 90% by mass or more based on the total amount of the polymerizable compound; The radiation-curable ink jet composition according to any one of claims 1 to 10.

12. the color material other than the white color material is a cyan color material or a magenta color material; The radiation-curable ink jet composition according to any one of claims 1 to 11.

13. a discharge step of discharging the radiation-curable ink jet composition according to any one of claims 1 to 12 from an inkjet head and depositing it on a recording medium; an irradiation step of irradiating the radiation-curable inkjet composition adhered to the recording medium with radiation, Recording method.

Images