Radiation-curable inkjet ink composition and recording method

Abstract

A radiation-curable inkjet ink composition and a recording method are provided, exhibiting excellent adhesion resistance, adhesion, tack, and shrinkage properties. The radiation-curable inkjet ink composition comprises a multifunctional monomer with three or more functions and 5-methyl-3-vinyloxazolidine-2-one. The content of 5-methyl-3-vinyloxazolidine-2-one is less than 50% by mass relative to the total amount of the ink composition, the content of the monofunctional monomer is 60% by mass or more relative to the total amount of the polymerizable compound, and the content of the multifunctional monomer with three or more functions is more than 1% by mass relative to the total amount of the ink composition.

Description

Technical Field

[0001] This invention relates to a radiation-curable inkjet ink composition. Background Technology

[0002] Inkjet recording methods have achieved rapid development in various aspects, enabling high-resolution image recording with relatively simple devices. Various studies have been conducted to improve various properties. For example, Patent Document 1 describes a radiation-curable inkjet composition, the purpose of which is to provide a low-viscosity, highly elongated coating composition comprising a monofunctional (meth)acrylate monomer and a vinylmethyloxazolidinone.

[0003] Existing technical documents Patent documents Patent document 1: Japanese Patent Application Publication No. 2021-042322.

[0004] The inkjet composition described in Patent Document 1 is a representative example of research conducted to improve the curability and adhesion of the recorded material. Summary of the Invention

[0005] The radiation-curable inkjet composition of the present invention is a radiation-curable inkjet ink composition comprising a multifunctional monomer with three or more functions and 5-methyl-3-vinyloxazolidine-2-one, wherein the content of 5-methyl-3-vinyloxazolidine-2-one is less than 50% by mass relative to the total amount of the ink composition, the content of monofunctional monomer is 60% by mass or more relative to the total amount of the polymerizable compound, and the content of multifunctional monomer with three or more functions is more than 1% by mass relative to the total amount of the ink composition.

[0006] The recording method of the present invention comprises: an attachment step in which the above-mentioned radiation-curable inkjet ink composition is ejected from an inkjet head and attached to a shrink film or flexible packaging film; and an irradiation step in which the attached radiation-curable inkjet ink composition is irradiated with radiation. Attached Figure Description

[0007] Figure 1 An example of a recording device used in this embodiment is shown.

[0008] Figure 2 Table 1 shows the composition and evaluation results of the radiation-curable inkjet ink composition used in the examples.

[0009] Figure 3 Table 2 shows the composition and evaluation results of the radiation-curable inkjet ink composition used in the examples.

[0010] Explanation of reference numerals in the attached figures 20: Serial printer; 220: Transport section; 230: Recording section; 231: Inkjet head; 232: Radiation source; 234: Carriage; 235: Carriage moving mechanism; F: Recording medium; S1, S2: Main scanning direction; T1, T2: Sub-scanning direction. Detailed Implementation

[0011] Hereinafter, embodiments of the present invention (hereinafter referred to as "this embodiment") will be described in detail with reference to the accompanying drawings as needed. However, the present invention is not limited thereto and various modifications can be made without departing from its spirit.

[0012] 1. Radiation-curable inkjet ink composition The radiation-curable inkjet ink composition of this embodiment (hereinafter also referred to as the "ink composition") contains a polyfunctional monomer with three or more functions and 5-methyl-3-vinyloxazolidine-2-one. The content of 5-methyl-3-vinyloxazolidine-2-one is less than 50% by mass relative to the total amount of the ink composition, the content of monofunctional monomer is 60% by mass or more relative to the total amount of the polymerizable compound, and the content of polyfunctional monomer with three or more functions is more than 1% by mass relative to the total amount of the ink composition.

[0013] Ink compositions suitable for shrink films and flexible packaging films require a flexible coating, thus necessitating the inclusion of a large number of monofunctional monomers. However, radiation-curable ink compositions containing a large number of monofunctional monomers tend to have lower curability. If curability is insufficient, the coating may peel off when it overlaps with the medium, easily resulting in adhesion to the medium.

[0014] Here, we consider using 5-methyl-3-vinyloxazolidine-2-one (hereinafter also referred to as "VMOX"), which has excellent curing properties. However, vinyl monomers can improve curing properties by combining with acrolein monomers, so there is a limit to the improvement in curing properties even when VMOX is used in excess alone.

[0015] Therefore, in this embodiment, from the viewpoint of flexibility, in the ink composition containing a predetermined amount of monofunctional monomer, in addition to a predetermined amount of VMOX, a predetermined amount of trifunctional or higher multifunctional monomer is also used. In this way, by using VMOX and trifunctional or higher multifunctional monomers together, the surface and internal curability of the coating film can be further improved. By improving surface curability, the tackiness of the ink coating film is reduced; by improving internal curability, adhesion can be suppressed. In particular, VMOX contributes to surface curability, and trifunctional or higher multifunctional monomers, by introducing crosslinking points, contribute to improving the internal curability of the coating film.

[0016] 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. Ultraviolet light is preferred because radiation sources are readily available and widely used, and because materials suitable for curing based on ultraviolet radiation are readily available and widely used.

[0017] The components contained in the radiation-curing inkjet composition of this embodiment will be described in detail below.

[0018] 1.1. Polymers In this embodiment, compounds that are cured by irradiation are collectively referred to as polymerizable compounds. Examples of polymerizable compounds in this embodiment include monofunctional monomers having one polymerizable functional group and polyfunctional monomers having two or more polymerizable functional groups. Furthermore, polyfunctional monomers include difunctional monomers having two polymerizable functional groups and trifunctional or more polyfunctional monomers having three or more polymerizable functional groups. In this embodiment, oligomers are not included in the polyfunctional monomers.

[0019] In this embodiment, an oligomer refers to a polymer composed of a polymeric compound, and is a compound having one or more polymeric functional groups. In this embodiment, substances with a molecular weight of 1000 or more are defined as oligomers, and substances with a molecular weight of less than 1000 are defined as monomers.

[0020] The weighted average glass transition temperature of the polymeric compound is preferably 30°C or higher and 70°C or lower, 40°C or higher and 65°C or lower, or 50°C or higher and 60°C or lower. If the weighted average glass transition temperature is 30°C or higher, the adhesion of the ink composition tends to be improved; if it is 70°C or lower, the shrinkage characteristics tend to be improved. Furthermore, in this specification, the glass transition temperature can be measured, for example, using a differential scanning calorimeter.

[0021] When the difference between the highest and lowest glass transition temperatures of homopolymers composed of monofunctional monomers is defined as difference A [°C], and the difference between the highest and lowest glass transition temperatures of homopolymers composed of difunctional and trifunctional or higher polyfunctional monomers is defined as difference B [°C], difference A is preferably greater than difference B. The glass transition temperature of an ink composition needs to be adjusted to an appropriate value by modifying the type and content of the polymerizable compounds. However, since monofunctional monomers have a high content, they contribute significantly to the glass transition temperature of the ink composition. Therefore, a difference A greater than difference B makes it easier to adjust the glass transition temperature of the ink composition. This increases the design freedom of the ink composition and makes it easier to achieve ink properties corresponding to the desired purpose.

[0022] 1.1.1. Monofunctional monomer The ink composition of this embodiment contains 5-methyl-3-vinyloxazolidine-2-one (VMOX) as one of the monofunctional monomers. VMOX refers to a compound represented by the following chemical formula.

[0023] [Chemical Formula 1] VMOX has a lower viscosity compared to other N-vinyl compounds, making it less likely to increase the viscosity of the composition, thus making it suitable for inkjet ink compositions. Furthermore, VMOX can improve the adhesion and tack of the coating film. Commercially available VMOX products are available, for example, from BASF.

[0024] Furthermore, the ink composition of this embodiment may also contain monofunctional monomers other than VMOX. There are no particular limitations on monofunctional monomers other than VMOX; examples include nitrogen-containing monofunctional monomers, monofunctional monomers containing alicyclic groups, monofunctional monomers containing aliphatic groups, monofunctional monomers containing aromatic groups, ether-cyclic monofunctional monomers, and monofunctional monomers having hydroxyl groups. These monofunctional monomers may be used alone or in combination of two or more.

[0025] The total content of monofunctional monomers relative to the total amount of polymerizable compounds is 60% by mass or more, preferably 63% by mass or more and 99% by mass or less, 70% by mass or more and 90% by mass or less, or 75% by mass or more and 88% by mass or less. With the content of monofunctional monomers within the above range, the ink composition tends to have improved softness, adhesion, and shrinkage properties, thus becoming more suitable for shrink films and flexible packaging films.

[0026] The total content of monofunctional monomers relative to the total amount of the ink composition is preferably 63% by mass or more and 90% by mass or less, 65% by mass or more and 88% by mass or less, or 67% by mass or more and 87% by mass or less. With the content of monofunctional monomers within the above range, there is a tendency for improved adhesion, bonding properties, and shrinkage characteristics.

[0027] 1.1.1.1.VMOX The ink composition of this embodiment improves adhesion and bonding properties by using VMOX (5-methyl-3-vinyloxazolidine-2-one). Furthermore, the ink viscosity is within a preferred range.

[0028] The VMOX content relative to the total amount of the ink composition is less than 50% by mass, preferably 49% by mass or less, 40% by mass or less, or 35% by mass or less. VMOX, as a vinyl monomer, tends to exhibit superior adhesion through reaction with acrolein monomers. In this regard, by having a VMOX content within the above-mentioned range, a relatively larger amount of monomers other than VMOX, such as acrolein monomers, is contained, thus tending to further improve adhesion. Furthermore, the VMOX content relative to the total amount of the ink composition is preferably 10% by mass or more, 20% by mass or more, or 25% by mass or more. With a VMOX content within the above-mentioned range, there is a tendency to further improve tackiness, adhesion, and shrinkage properties.

[0029] 1.1.1.2. Nitrogen-containing monofunctional monomers other than VMOX There are no particular limitations on nitrogen-containing monofunctional monomers other than VMOX. Examples include nitrogen-containing monofunctional vinyl monomers such as N-vinylcaprolactam, N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, and N-vinylpyrrolidone; nitrogen-containing monofunctional acrylate monomers such as acryloylmorpholine; and nitrogen-containing monofunctional acrylamide monomers such as (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, diacetone acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethylacrylamide, and benzyl chloride quaternary ammonium salt of dimethylaminoethyl acrylate.

[0030] The content of nitrogen-containing monofunctional monomers other than VMOX relative to the total amount of the ink composition is preferably 1% or more and 60% or less by mass, 10% or more and 50% or less by mass, 20% or more and 40% or less by mass, or 25% or more and 35% or less by mass. With the content of nitrogen-containing monofunctional monomers other than VMOX within the above range, there is a tendency for improved adhesion, bonding properties, and shrinkage characteristics.

[0031] 1.1.1.3. Monofunctional monomers containing alicyclic groups As a monofunctional monomer containing an alicyclic group, there are no particular limitations as long as it is a monomer with one or more non-aromatic, saturated or unsaturated carbon rings. Examples include 4-tert-butylcyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, and 2-(meth)acrylate-1,4-dioxaspiro[4,5]dec-2-ylmethyl ester, which are monomers with monocyclic hydrocarbon groups; dicyclopentenyl acrylate and dicyclopentenyloxyethyl acrylate, which are monomers with unsaturated polycyclic hydrocarbon groups; and dicyclopentenyl acrylate and isobornyl acrylate (IBXA), which are monomers with saturated polycyclic hydrocarbon groups.

[0032] The content of monofunctional monomers containing alicyclic groups relative to the total amount of the ink composition is preferably 1% or more and 60% or less by mass, 10% or more and 50% or less by mass, 20% or more and 40% or less by mass, or 25% or more and 35% or less by mass. With the content of monofunctional monomers containing alicyclic groups within the above range, there is a tendency for improved adhesion, bonding properties, and shrinkage characteristics.

[0033] 1.1.1.4. Ether cyclic monofunctional monomers The ink composition in this embodiment preferably contains an ether-cyclic monofunctional monomer. By including an ether-cyclic monofunctional monomer in the ink composition, there is a tendency to improve adhesion, tackiness, and shrinkage properties. As for the ether-cyclic monofunctional monomer, there are no particular limitations as long as it contains a cyclic ether skeleton such as tetrahydrofuran or tetrahydropyran; examples include cyclic trimethylolpropane acetal (meth)acrylate and tetrahydrofurfuryl (meth)acrylate.

[0034] The content of the ether-cyclic monofunctional monomer relative to the total amount of the ink composition is preferably 1% or more and 60% or less by mass, 10% or more and 50% or less by mass, 20% or more and 40% or less by mass, or 25% or more and 35% or less by mass. With the content of the ether-cyclic monofunctional monomer within the above range, there is a tendency for improved adhesion, bonding properties, and shrinkage characteristics.

[0035] 1.1.1.5. Monofunctional monomers with hydroxyl groups The ink composition in this embodiment preferably contains a monofunctional monomer having hydroxyl groups. By including a monofunctional monomer having hydroxyl groups in the ink composition, there is a tendency for improved adhesion, tackiness, and shrinkage properties. There are no particular limitations on the hydroxyl-containing monofunctional monomer; examples include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 4-hydroxybutyl methacrylate, ethylene glycol monovinyl ether, diethylene glycol monovinyl ether, and 2-(meth)acryloyloxy-2-hydroxypropyl phthalate.

[0036] The content of the monofunctional monomer with hydroxyl groups relative to the total amount of the ink composition is preferably 1% or more and 30% or less by mass, 3% or more and 20% or less by mass, or 5% or more and 15% or less by mass. With the content of the monofunctional monomer with hydroxyl groups within the above range, there is a tendency for improved adhesion, bonding properties, and shrinkage characteristics.

[0037] 1.1.2. Multifunctional monomers The content of the multifunctional monomer relative to the total amount of the polymerizable compound is preferably 1% or more and 40% or less by mass, 5% or more and 35% or less by mass, 10% or more and 30% or less by mass, or 15% or more and 25% or less by mass. With the content of the multifunctional monomer within the above range, there is a tendency for improved adhesion resistance, adhesion properties, and shrinkage characteristics.

[0038] The content of the multifunctional monomer relative to the total amount of the ink composition is preferably 1% or more and 50% or less by mass, 5% or more and 40% or less by mass, 10% or more and 30% or less by mass, or 15% or more and 25% or less by mass. With the content of the multifunctional monomer within the above range, there is a tendency for improved adhesion resistance, adhesion, and shrinkage properties.

[0039] 1.1.2.1. Difunctional monomers As a difunctional monomer, there are no particular limitations; examples include (meth)acrylates containing vinyl ether groups and difunctional (meth)acrylates.

[0040] As difunctional (meth)acrylates, there are no particular limitations; examples include ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tripropylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, dicyclopentyl dimethacrylate, neopentyl glycol dimethacrylate, 1,9-nonanediol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, 2-hydroxy-1,3-di(meth)acryloyloxypropane, and 2-(2-vinyloxyethoxy)ethyl acrylate. These difunctional monomers can be used alone or in combination of two or more.

[0041] The content of the difunctional monomer relative to the total amount of the ink composition is preferably 1% or more and 39% or less by mass, 5% or more and 33% or less by mass, 7% or more and 25% or less by mass, or 10% or more and 20% or less by mass. When the content of the difunctional monomer is within the above range, adhesion resistance, adhesion, and shrinkage properties are improved.

[0042] The content of the difunctional monomer relative to the total amount of the polymerizable compound is preferably 1% to 39% by mass, 5% to 35% by mass, 10% to 25% by mass, or 12% to 20% by mass. By keeping the content of the difunctional monomer within the above ranges, adhesion resistance, adhesion properties, and shrinkage characteristics are improved.

[0043] 1.1.2.2. Multifunctional monomers with three or more functions The ink composition in this embodiment contains a multifunctional monomer with three or more functionalities. By containing a multifunctional monomer with three or more functionalities, crosslinking points are introduced, improving the curability of the coating film and thus enhancing its adhesion resistance.

[0044] There are no particular limitations on the type of multifunctional monomer with three or more functionalities, but examples include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, di(trimethylolpropane tetra(meth)acrylate, glyceryl propoxy tri(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, and dipentaerythritol penta(meth)acrylate. Among these, dipentaerythritol hexaacrylate, pentaerythritol triacrylate, di(trimethylolpropane tetraacrylate), and dipentaerythritol pentaacrylate are preferred. By using these multifunctional monomers with three or more functionalities, there is a tendency to improve adhesion resistance, bonding properties, and shrinkage characteristics. These multifunctional monomers with three or more functionalities can be used alone or in combination of two or more.

[0045] Multifunctional monomers with three or more acrolein groups are preferred. Using such multifunctional monomers tends to improve adhesion resistance. Examples of multifunctional monomers with three or more acrolein groups include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glyceryl propoxy tri(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol penta(meth)acrylate.

[0046] In this embodiment, the acrolein equivalent of the multifunctional monomer with three or more functions is preferably 110 g / eq or less, 106 g / eq or less, 100 g / eq or less, or 98 g / eq or less. If the acrolein equivalent is within the above range, there is a tendency for improved adhesion resistance. In addition, the acrolein equivalent is calculated by the following formula.

[0047] (Acrolein equivalent) = (Molecular weight of monomer / Number of acrolein groups in monomer) The content of trifunctional or higher polyfunctional monomers relative to the total amount of the polymerizable compound is preferably 1% to 20% by mass, 2% to 15% by mass, 4% to 10% by mass, or 5% to 9% by mass. By keeping the content of trifunctional or higher polyfunctional monomers within the above ranges, adhesion resistance, adhesion properties, and shrinkage characteristics are improved.

[0048] The content of trifunctional or higher polyfunctional monomers relative to the total amount of the ink composition exceeds 1% by mass, preferably 3% by mass or more, 3.5% by mass or more, or 4% by mass or more. When the content of trifunctional or higher polyfunctional monomers is within the above range, there is a tendency for improved adhesion resistance. Furthermore, the content of trifunctional or higher polyfunctional monomers relative to the total amount of the ink composition is preferably 10% by mass or less, 9% by mass or less, or 7% by mass or less. If the content of trifunctional or higher polyfunctional monomers is within the above range, the viscosity is more likely to be within a preferred range, and there is a tendency for improved shrinkage properties.

[0049] 1.2. Polymerization inhibitors In this embodiment, the ink composition may also contain a polymerization inhibitor. There are no particular limitations on the polymerization inhibitor; examples include phenolic compounds, quinone compounds, amine compounds, nitro compounds, oxime compounds, sulfur compounds, and oxy compounds. These polymerization inhibitors may be used alone or in combination of two or more.

[0050] The term "phenolic compound" is not particularly limited, and examples include p-methoxyphenol, cresol, tert-butylcatechol, di-tert-butyl-p-cresol, hydroquinone monomethyl ether, α-naphthol, 3,5-di-tert-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-butylphenol), and 4,4'-thiobis(3-methyl-6-tert-butylphenol). Commercially available phenolic compounds include, for example, MEHQ (p-methoxyphenol, manufactured by Kanto Chemical Co., Ltd.).

[0051] As a quinone compound, there is no particular limitation; examples include p-benzoquinone, anthraquinone, naphthoquinone, phenanthrenequinone, p-xylbenzenequinone, p-toluenequinone, 2,6-dichloroquinone, 2,5-diphenyl-p-benzoquinone, 2,5-diacetoxy-p-benzoquinone, 2,5-dihexyloxy-p-benzoquinone, 2,5-diacyloxy-p-benzoquinone, hydroquinone, 2,5-di-tert-butylhydroquinone, mono-tert-butylhydroquinone, monomethylhydroquinone, and 2,5-di-tert-pentylhydroquinone.

[0052] As an amine compound, there is no particular limitation, and examples include phenyl-β-naphthylamine, p-benzylaminophenol, di-β-naphthyl-p-phenylenediamine, dibenzylhydroxyamine, phenylhydroxyamine, diethylhydroxyamine, compounds having a 2,2,6,6-tetramethylpiperidine skeleton, compounds having a 2,2,6,6-tetramethylpiperidine-N-alkyl skeleton, and compounds having a 2,2,6,6-tetramethylpiperidine-N-acyl skeleton.

[0053] As nitro compounds, there are no particular limitations; examples include dinitrobenzene, trinitrotoluene, picric acid, and their derivatives. As oxime compounds, there are no particular limitations; examples include quinone dioximes and cyclohexanone oximes. As sulfur compounds, there are no particular limitations; examples include phenothiazines.

[0054] There are no particular limitations on the oxy-based compounds; for example, derivatives of 2,2,6,6-tetramethylpiperidinyl-1-oxy can be cited. Examples of derivatives of 2,2,6,6-tetramethylpiperidinyl-1-oxy include 4-acetamido-2,2,6,6-tetramethylpiperidinyl-1-oxy, 4-amino-2,2,6,6-tetramethylpiperidinyl-1-oxy, 4-carboxyl-2,2,6,6-tetramethylpiperidinyl-1-oxy, 4-(2-chloroacetamido)-2,2,6,6-tetramethylpiperidinyl-1-oxy, 4-cyano-2,2,6,6-tetramethylpiperidinyl-1-oxy, 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy, and 4-hydroxy Benzoate ester-2,2,6,6-tetramethylpiperidin-1-oxy, 4-(2-iodoacetamide)-2,2,6,6-tetramethylpiperidin-1-oxy, 4-isothiocyanate-2,2,6,6-tetramethylpiperidin-1-oxy, 4-methacryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxy, 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxy, 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxy, 4-(2-propynoxy)-2,2,6,6-tetramethylpiperidin-1-oxy. Commercially available oxy-based compounds include, for example, ADEKA STAB LA-7RD (2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxy, a trade name manufactured by ADEKA).

[0055] The content of the polymerization inhibitor relative to the total amount of the ink composition is preferably 0.01% by mass or more and 5.0% by mass or less, 0.05% by mass or more and 3.0% by mass or less, or 0.1% by mass or more and 1.0% by mass or less. With the content of the polymerization inhibitor within the above range, there is a tendency for improved adhesion resistance, adhesion, tackiness, and shrinkage properties.

[0056] 1.3. Polymerization Initiator In this embodiment, the ink composition may also contain a polymerization initiator. There is no particular limitation on the polymerization initiator, as long as it generates active species through radiation irradiation; examples include known polymerization initiators such as acylphosphine oxide-based polymerization initiators, alkylphenyl ketone-based polymerization initiators, titanium oxide-based polymerization initiators, and thioxanthone-based polymerization initiators. Among these, the polymerization initiator preferably includes acylphosphine oxide-based polymerization initiators and thioxanthone-based polymerization initiators, and more preferably includes thioxanthone-based polymerization initiators. By using such polymerization initiators, the curability of the composition is improved, especially the curability of curing processes based on ultraviolet light-emitting diodes, thus improving adhesion resistance and tackiness. These polymerization initiators can be used alone or in combination of two or more.

[0057] The content of the polymerization initiator relative to the total amount of the ink composition is preferably 3% by mass or more and 17% by mass or less, more preferably 5% by mass or more and 15% by mass or less, and even more preferably 7% by mass or more and 12% by mass or less. With the content of the polymerization initiator within the above range, there is a tendency for improved adhesion resistance, adhesion, tackiness, and shrinkage properties.

[0058] 1.3.1. Acylphosphine oxide polymerization initiator There are no particular limitations on the acylphosphine oxide polymerization initiators used; examples include 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. These acylphosphine oxide polymerization initiators can be used alone or in combination of two or more.

[0059] Commercially available acylphosphine oxide polymerization initiators include, for example, Omnirad 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, trade name manufactured by ISM Resins BV) and Omnirad TPO-L (ethyl(2,4,6-trimethylbenzoyl)-phenylphosphinate, trade name manufactured by IGM Resins BV).

[0060] The content of the acylphosphine oxide polymerization initiator relative to the total amount of the ink composition is preferably 0.1% by mass or more and 20% by mass or less, 1% by mass or more and 15% by mass or less, 3% by mass or more and 10% by mass or less, or 5% by mass or more and 7% by mass or less. With the content of the acylphosphine oxide polymerization initiator within the above range, there is a tendency for improved adhesion resistance, adhesion, tackiness, and shrinkage properties.

[0061] 1.3.2. Thioxanone-based polymerization initiators There are no particular limitations on the thioxanthone-based polymerization initiator; for example, low molecular weight thioxanthone initiators and high molecular weight thioxanthone initiators can be cited. In this embodiment, "low molecular weight thioxanthone initiator" refers to a thioxanthone-based polymerization initiator with a molecular weight less than 500, and "high molecular weight thioxanthone initiator" refers to a thioxanthone-based polymerization initiator with a molecular weight of 500 or more. A high molecular weight thioxanthone initiator is preferred. Using a high molecular weight thioxanthone initiator reduces odor, making it less likely for odors to transfer to containers with shrink wrap, thus making it more suitable for shrink wrap applications. A single thioxanthone-based polymerization initiator can be used, or two or more can be used in combination.

[0062] There are no particular limitations on low molecular weight thioxanthone initiators; examples include thioxanthone, 2-methylthioxanthone, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, and 2,4-diethylthioxanthone. Commercially available low molecular weight thioxanthone initiators include Speedcure DETX (2,4-diethylthioxanth-9-one, manufactured by Lambson).

[0063] There are no particular limitations on high molecular weight thioxanthone initiators; examples include 1,3-di({α-[(1-chloro-9-oxo-9H-thioxanth-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[(1-chloro-9-oxo-9H-thioxanth-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxymethyl)propane and α-[2-[(9-oxo-9H-thioxanthyl)oxy]acetyl]-ω-[[2-[(9-oxo-9H-thioxanthyl)oxy]acetyl]oxy]poly(oxy-1,4-butadiyl). Commercially available products can also be used, such as SPEEDCURE 7010 (thioxanthone polymer type, manufactured by Lambson) and Omnipol (registered trademark) TX (trade name manufactured by IGM Resins).

[0064] The content of the thioxanthone-based polymerization initiator relative to the total amount of the ink composition is preferably 0.1% by mass or more and 10% by mass or less, 1% by mass or more and 5% by mass or less, or 2% by mass or more and 4% by mass or less. With the content of the thioxanthone-based polymerization initiator within the above range, there is a tendency for improved adhesion resistance, adhesion, tackiness, and shrinkage properties.

[0065] 1.4. Surfactants In this embodiment, the ink composition may also contain a surfactant. Examples of surfactants include acetylenic diol surfactants, fluorinated surfactants, and silicone surfactants. These surfactants may be used alone or in combination of two or more.

[0066] There are no particular limitations on the types of surfactants that can be identified as acetylenol-based surfactants. Examples include 2,4,7,9-tetramethyl-5-decyn-4,7-diol and its olefinic oxygen adducts. Commercially available acetylenol-based surfactants include, for example, Surfynol 465 (trade name manufactured by Nissin Chemical Industries, Ltd.).

[0067] As a fluorinated surfactant, there are no particular limitations; examples include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkyl amine oxides.

[0068] There are no particular limitations on what constitutes a silicone-based surfactant; examples include polysiloxane compounds and polyether-modified silicones. Commercially available silicone-based surfactants include, for example, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-348, BYK-UV3500, BYK-UV3510, BYK-UV3530, and BYK-UV3570 (trade names manufactured by BYK Corporation).

[0069] The surfactant content relative to the total amount of the ink composition is preferably 0.01% by mass or more and 5% by mass or less, 0.1% by mass or more and 3% by mass or less, or 0.3% by mass or more and 1% by mass or less. By keeping the surfactant content within the above range, there is a tendency to improve adhesion resistance, adhesion, tackiness, and shrinkage properties.

[0070] 1.5. Dispersant The ink composition of this embodiment may also include a dispersant. There are no particular limitations on the dispersant; examples include polymeric dispersants commonly used in the preparation of pigment dispersions. Specifically, examples include polyoxyethylene, polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicone polymers, sulfur-containing polymers, fluoropolymers, and epoxy resins. These dispersants may be used individually or in combination of two or more.

[0071] Dispersants can also be commercially available products, such as the Ajisper series (manufactured by Ajinomoto Fine Techno), Solsperse36000 (a trade name manufactured by Noveon), the DISPERBYK series (manufactured by BYK), and the DISPARLON series (manufactured by Kusumoto Chemical Co., Ltd.).

[0072] The content of the dispersant relative to the total amount of the ink composition is preferably 0.01% by mass or more and 5% by mass or less, 0.05% by mass or more and 1% by mass or less, or 0.1% by mass or more and 0.5% by mass or less. By keeping the content of the dispersant within the above range, there is a tendency to improve adhesion resistance, adhesion, tackiness, and shrinkage properties.

[0073] 1.6. Pigments The ink composition of this embodiment may also include a colorant. The colorant may be any of pigments and dyes. There are no particular limitations on the pigment; for example, organic pigments and inorganic pigments can be cited. These colorants may be used alone or in combination of two or more.

[0074] Examples of organic pigments include azo lake pigments, insoluble monoazo pigments, insoluble diazo pigments, condensed azo pigments, chelated azo pigments, and other azo pigments; polycyclic pigments such as phthalocyanine pigments, quinacridone pigments, perylene pigments, pyrene pigments, anthraquinone pigments, dioxazine pigments, thioindolinone pigments, isoindolineone pigments, and quinophthalone pigments; dye chelates such as basic dye chelates and acid dye chelates; and nitro pigments and nitroso pigments.

[0075] Examples of inorganic pigments include titanium dioxide, iron oxide yellow, iron oxide brown, chromium oxide, dark blue, ultramarine, molybdenum red, iron oxide black, chrome yellow, composite oxide pigments, and carbon black.

[0076] Examples of carbon black include CI (Colour Index Generic Name) Pigment Black 1, 7, and 11. Commercially available carbon black products include, for example, No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B (trade name manufactured by Mitsubishi Chemical Corporation), Raven 5750, 5250, 5000, 3500, 1255, 700 (trade name manufactured by Columbia Carbon), Rega1 400R, 330R, 660R, Mogul L, Monarch 700, 800, 880, 900, 1000, 1100, 1300, 1400 (trade name manufactured by CABOT), Pigment Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, and Printex. 35, U, V, 140U, Special Black 6, 5, 4A, 4 (trade names manufactured by Degussa). Carbon black can be produced using acid dyeing methods such as contact process, furnace process, and thermal process.

[0077] As dyes, there are no particular limitations; examples include acid dyes, direct dyes, reactive dyes, and basic dyes. Specifically, examples 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; CI Direct Red 1, 4, 9, 80, 81, 225, 227; CI Direct Blue 1, 2, 15, 71, 86, 87, 98; CI Direct Black 19, 38, 51, 71, 154; CI Reactive Red 14, 32, 55, 79, 249; and CI Reactive Black 3, 4, 35.

[0078] The pigment content relative to the total amount of the ink composition is preferably 0.1% by mass or more and 10% by mass or less, 1% by mass or more and 5% by mass or less, or 2% by mass or more and 4% by mass or less. With the pigment content within the above range, there is a tendency for improved adhesion resistance, tackiness, adhesion, and shrinkage properties.

[0079] 1.7. Other ingredients In addition to the above-mentioned components, various additives such as chelating agents, softeners, solubilizers, viscosity modifiers, ultraviolet absorbers, antioxidants, and corrosion inhibitors may also be included as needed.

[0080] 2. Preparation method of ink composition As a method for preparing an ink composition, it can be prepared, for example, by mixing the components in any order and removing impurities, foreign matter, etc., by means of filtration as needed. As a method for mixing the components, a method is used in which the components are added sequentially to a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer and then stirred and mixed. As a filtration method, centrifugal filtration and filter filtration are examples.

[0081] 3. Recording media As the recording medium in this embodiment, paper, film, cloth, metal, and glass can be used, for example. Shrink film or flexible packaging film is preferred. Shrink film and flexible packaging film mostly shrink or bend, thus the effect of this embodiment is significant. There is no particular limitation on the shrink film; for example, a film that shrinks in at least one direction when heated can be cited. In this embodiment, flexible packaging film refers to a flexible film material used in food packaging, toiletries, cosmetic packaging, etc. The raw materials of the shrink film contain one or more selected from polyethylene terephthalate, polyethylene, polyolefins, polystyrene, polypropylene, and polyvinyl chloride, thus tending to have superior shrinkage properties and are preferred.

[0082] 4. Recording Method The inkjet recording method according to this embodiment includes: an attachment step, in which the above-mentioned radiation-curable inkjet composition is ejected from an inkjet head and attached to a shrink film or flexible packaging film; and a step of irradiating the attached radiation-curable inkjet composition with radiation. Since shrink films and flexible packaging films mostly shrink or bend, the effect of this embodiment is significant.

[0083] 4.1. Attachment process In the adhesion process, a heated ink composition is ejected from the inkjet head and applied to the shrink film or flexible packaging film. More specifically, a driving pressure generating unit causes the ink composition filled into the pressure generating chamber of the inkjet head to be ejected from the nozzle. This ejection method is also known as inkjet printing.

[0084] As examples of inkjet heads used in the attachment process, line printheads that record in a line manner and serial printheads that record in a serial manner can be cited.

[0085] In the line mode using a line printhead, for example, a liquid jet head with a width greater than or equal to the recording width of the recording medium is fixed to an inkjet device. The recording medium is then moved along a sub-scanning direction (the longitudinal direction of the recording medium, the transport direction), and ink droplets are ejected from the nozzles of the printhead in conjunction with this movement, thereby recording an image on the recording medium.

[0086] In a 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. Furthermore, by moving the carriage along the main scanning direction (the horizontal and width direction of the recording medium), ink droplets are ejected from the nozzle opening of the head in conjunction with this movement, thereby enabling the recording of an image on the recording medium.

[0087] 4.2. Irradiation process In the irradiation process, the radiation-curable inkjet composition attached to the recording medium is irradiated with radiation. Irradiation initiates the polymerization reaction of the polymerizable compounds, thereby curing the ink composition to form a coating. If a polymerization initiator is present, reactive species (initiators) such as free radicals, acids, and bases are generated, and the polymerization reaction of the polymerizable compounds is promoted through the function of these initiators.

[0088] Here, examples of radiation include ultraviolet light, infrared light, visible light, and X-rays. The radiation irradiates the ink composition through a radiation source located downstream of the inkjet head. There are no particular limitations on the radiation source; for example, an ultraviolet light-emitting diode (UV LED) can be used. By using such a radiation source, miniaturization of the device and cost reduction can be achieved. The UV LED, as a UV source, is small and can therefore be installed within the inkjet apparatus. For example, the UV LED can be mounted on a carriage (at both ends along the media width direction and / or on the media transport direction side), wherein the carriage carries an inkjet head that ejects a radiation-curing inkjet composition.

[0089] 5. Inkjet unit The inkjet apparatus of this embodiment is not particularly limited as long as it has an inkjet head having a nozzle that ejects the ink composition to the recording medium and a radiation source that irradiates the ejected ink composition with radiation. As an example of an inkjet apparatus, Figure 1 A 3D view of a serial printer is shown. (e.g.) Figure 1 As shown, the serial printer 20 includes a transport section 220 and a recording section 230. The transport section 220 transports the recording medium F fed to the serial printer to the recording section 230 and discharges the recorded recording medium out of the serial printer. Specifically, the transport section 220 has transport rollers that transport the incoming recording medium F in the sub-scanning directions T1 and T2.

[0090] In addition, the recording unit 230 includes: an inkjet head 231 for ejecting an ink composition onto the recording medium F conveyed from the transport unit 220; a radiation source 232 for irradiating the attached ink composition with radiation; a carriage 234 for carrying them; and a carriage moving mechanism 235 for moving the carriage 234 in the main scanning directions S1 and S2 of the recording medium F.

[0091] In the case of a serial printer, the inkjet head 231 is shorter than the width of the recording medium. The inkjet head 231 moves to record in multiple passes. Furthermore, in a serial printer, a carriage 234 moving in a predetermined direction carries the inkjet head 231 and an emission source 232. The inkjet head 231 moves along with the carriage, ejecting an ink composition onto the recording medium. Thus, recording is performed in two or more passes. Each pass is also referred to as a main scan. Sub-scans are performed between passes to transport the recording medium. That is, main scans and sub-scans are performed alternately.

[0092] In addition, Figure 1 The diagram shows a radiation source mounted on a carriage, but it is not limited to this; a radiation source may also be present without being mounted on a carriage.

[0093] Furthermore, the inkjet device in this embodiment is not limited to the serial printer described above, but may also be a row printer described above.

[0094] Example The present invention will now be described in more detail using examples and comparative examples. The present invention is not limited to the following examples.

[0095] exist Figure 2 Table 1 shows the composition of each composition of the examples and comparative examples.

[0096] 1. Preparation of each composition As shown in Table 1, each component is added to a mixing container, mixed and stirred, and then filtered through a membrane filter to obtain the ink compositions of each example. Unless otherwise specified, the values ​​of each component shown in the table represent mass percentages. Furthermore, the content values ​​in the table represent the mass percentage of the solid component of the active ingredient.

[0097] The abbreviations used in the treatment fluid composition and details of the product ingredients are described below.

[0098] Monofunctional monomer CTFA (Cyclic Trimethylolpropane Formaldehyde Acrylate) 4HBA (4-hydroxybutyl acrylate) VMOX (5-methyl-3-vinyloxazolidin-2-one) TBCHA (4-tert-butylcyclohexyl acrylate) TMCHA (3,3,5-trimethylcyclohexyl acrylate) DEAA (N,N-diethylacrylamide) HPA (Hydroxypropyl acrylate) Multifunctional monomers TPGDA (tripropylene glycol diacrylate) DPHA (Dipentaerythritol Hexaacrylate) PETA (Pentaerythritol triacrylate) DTMPTA (ditrimethylolpropane tetraacrylate) DPEPA (dipentaerythritol pentaacrylate) Polymerization inhibitor MEHQ (p-methoxyphenol, manufactured by Kanto Chemical Co., Ltd.) LA-7RD (trade name "ADEKASTAB LA-7RD", 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy, manufactured by ADEKA) Polymerization initiator Omnirad 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, trade name manufactured by ISM Resins BV) TPO-L (trade name "Omnirad TPO-L", ethyl (2,4,6-trimethylbenzoyl)-phenylphosphonate, manufactured by IGMresins BV) Speedcure 7010 (1,3-bis({α-[(1-chloro-9-oxo-9H-thiosol-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxymethyl)propane, trade name manufactured by Lambson, molecular weight 1839) Speedcure DETX (2,4-diethylthioxanthroline-9-one, trade name manufactured by Lambson, molecular weight 268) surfactants BYK UV3500 (a silicone-based surfactant, a trade name manufactured by BYK Corporation) dispersant Solsperse 36000 (a polymeric dispersant, trade name manufactured by Lubrizol) pigment carbon black water pure water 2. Evaluation Methods 3.1. Adhesion resistance Packaging production Samples for evaluating adhesion resistance were prepared using an inkjet printer, "PX-G5000" (trade name manufactured by Seiko Epson Corporation). A full-page pattern image was printed on a PET film, "Bonset" (trade name manufactured by TAKIRON CI), as the recording medium, at room temperature and pressure, a recording resolution of 600 dpi × 600 dpi, and a droplet weight of 10 ng, resulting in a printed sample with a film thickness of 5 μm. The full-page pattern image refers to an image in which all pixels of the smallest recording unit area (pixel) defined by the recording resolution are recorded. Simultaneously with the printing, ultraviolet light was irradiated from an ultraviolet LED in an ultraviolet irradiation device mounted laterally on the carriage, resulting in a recorded object with a cured film of an ink composition forming a film thickness of 5 μm on the recording medium.

[0099] The recording obtained in the above manner is rolled up with the cured film on the inside and processed into a cylindrical shape. The recording is placed around a container (glass bottle) that is being packaged and preheated in a constant temperature bath, and left to stand in a constant temperature bath at 90°C for 10 seconds to allow the recording to shrink and adhere tightly to the container.

[0100] Determination of adhesion resistance For the packaging body prepared above, visual inspection is conducted to determine whether the cured film is adhered to the container, thereby evaluating whether adhesion exists. Adhesion resistance is evaluated according to the following evaluation criteria.

[0101] Evaluation Criteria A: Adhesion of non-curing film to the container B: There is a slight adhesion of the cured film to the container. C: There is adhesion (peeling) of the cured film to the container. 3.2. Adhesion The ink composition was applied to a PET film using a rod coater to achieve a cured film thickness of 5 μm. An ultraviolet light-emitting diode (UV LED) with a peak wavelength of 395 nm and an irradiation intensity of 1000 mW / cm² was used. 2 Irradiate the material and calculate the irradiation energy required to achieve a non-viscous state. Irradiation energy [mJ / cm²] 2 [mW / cm] is the measurement of the irradiation intensity [mW / cm] on an irradiated surface from a light source. 2The intensity was calculated by multiplying it by the irradiation duration [s]. The irradiation intensity was measured using a UM-10 ultraviolet intensity meter and a UM-400 light-receiving unit (both manufactured by Konica Minolta Sensing, INC.). Furthermore, whether the material was non-sticky was determined under the following conditions: the effect film was rubbed with a cotton swab, and the presence of ink adhering to the swab or scratches on the cured ink from the recording medium was used to determine this. The cotton swabs used were Johnson & Johnson cotton swabs. The rubbing was repeated 10 times, with a rubbing load of 100g.

[0102] Adhesion is evaluated based on the irradiation energy at which it becomes non-adhesive (non-adhesive energy) according to the following evaluation criteria.

[0103] Evaluation Criteria AA: Non-viscous energy less than 150 mJ / cm 2 A: Non-viscous energy 150mJ / cm 2 Above and below 250 mJ / cm 2 B: Non-viscous energy 250mJ / cm 2 Above and below 350 mJ / cm 2 C: Non-viscous energy 350mJ / cm 2 above 3.3. Adhesion For the recordings prepared for the adhesion evaluation, the adhesion was evaluated using a cross-cut test according to JIS K5600-5-6. Specifically, a cutting tool was used perpendicular to the coating film, making contact with the resulting film to cut a 10×10 grid of cuts with a spacing of 1 mm between the cuts. Transparent adhesive tape was applied to the cut areas, and the tape was rubbed thoroughly with a finger to allow visualization of the cured film. Then, within 5 minutes of applying the tape, the tape was peeled off from the cured film at an angle of approximately 60° over 0.5 to 1.0 seconds. Based on whether the cured film had peeled off at this point, each grid was visually observed. The adhesion was evaluated according to the following evaluation criteria.

[0104] Evaluation Criteria A: It was confirmed that less than 20% of the cured film in the grid had peeled off.

[0105] B: Confirm the peeling of more than 20% but less than 30% of the cured film in the grid.

[0106] C: Confirm that more than 30% of the cured film in the grid has been peeled off.

[0107] 3.4. Shrinkage characteristics In the evaluation of adhesion resistance, the formation of wrinkles before and after shrinkage is visually observed in the package material. The shrinkage characteristics are evaluated according to the following evaluation criteria.

[0108] Evaluation Criteria A: No wrinkles on the cured film B: There are slight wrinkles on the cured film. C: There are wrinkles on the cured film. 4. Evaluation Results As can be seen from Tables 1 and 2, the radiation-curable inkjet ink composition of this embodiment has excellent adhesion resistance, adhesion, tackiness and shrinkage characteristics.

Claims

1. A radiation-curable inkjet ink composition, characterized in that, It contains polyfunctional monomers with more than three functions and 5-methyl-3-vinyloxazolidin-2-one. The content of the 5-methyl-3-vinyloxazolidine-2-one is less than 50% by mass relative to the total amount of the ink composition. The content of monofunctional monomers relative to the total amount of polymerizable compounds is 60% or more by mass. The content of the polyfunctional monomers with three or more functions exceeds 1% by mass relative to the total amount of the ink composition.

2. The radiation-curable inkjet ink composition according to claim 1, wherein, The content of the polyfunctional monomers with three or more functions is more than 3% by mass and less than 10% by mass relative to the total amount of the ink composition.

3. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein, The multifunctional monomers with three or more functions have three or more acrolein groups.

4. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein, The acrolein equivalent of the multifunctional monomer with three or more functions is less than 110 g / eq.

5. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein, The multifunctional monomer with three or more functions comprises one or more selected from the group consisting of dipentaerythritol hexaacrylate, pentaerythritol triacrylate, ditrimethylolpropane tetraacrylate, and dipentaerythritol pentaacrylate.

6. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein, The radiation-curable inkjet ink composition contains an ether-cyclic monofunctional monomer.

7. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein, The radiation-curable inkjet ink composition contains a monofunctional monomer having a hydroxyl group.

8. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein, The weighted average glass transition temperature of polymeric compounds is above 30°C and below 70°C.

9. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein, The radiation-curable inkjet ink composition contains a high molecular weight thioxanone initiator.

10. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein, The content of the 5-methyl-3-vinyloxazolidine-2-one is more than 10% by mass relative to the total amount of the ink composition.

11. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein, Let the difference between the highest and lowest glass transition temperatures of the homopolymers composed of the monofunctional monomers be denoted as the difference A℃. When the difference between the highest and lowest glass transition temperatures of the homopolymers composed of the multifunctional monomers contained in the ink composition is defined as the difference B°C, The difference A℃ is greater than the difference B℃.

12. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein, The radiation-curable inkjet ink composition is used to adhere to shrink film and / or flexible packaging film.

13. A recording method, characterized in that, have: The adhesion process involves ejecting the radiation-curable inkjet ink composition of claim 1 from the inkjet head and adhering it to the shrink film or flexible packaging film; and The irradiation process involves irradiating the attached radiation-curable inkjet ink composition with radiation.

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