Radiation-curable inkjet ink composition

Abstract

This invention provides an inkjet composition set that exhibits excellent blocking resistance, adhesion, tackiness, and shrinkage properties. [Solution] A radiation-curable inkjet ink composition comprising a polyfunctional 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 of the total amount of the ink composition, the content of monofunctional monomers is 60% by mass or more of the total amount of polymerizable compounds, and the content of polyfunctional monomers with three or more functions is more than 1% by mass of 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 are rapidly developing in various fields because they enable the recording of high-resolution images with relatively simple equipment. Within this context, various studies are being conducted to improve various properties. For example, Patent Document 1 describes a radiation-curable inkjet composition that contains a monofunctional (meth)acrylate monomer and vinylmethyl oxazolidinone, with the aim of providing a radiation-curable inkjet composition that can form a coating film with low viscosity and excellent stretchability. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-042322 [Overview of the project] [Problems that the invention aims to solve]

[0004] Studies are underway to improve the curability, adhesion, and other properties of recorded materials, including the inkjet composition described in Patent Document 1. [Means for solving the problem]

[0005] The radiation-curable inkjet composition of the present invention is a radiation-curable inkjet ink composition comprising a polyfunctional 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 of the total amount of the ink composition, the content of monofunctional monomers is 60% by mass or more of the total amount of polymerizable compounds, and the content of polyfunctional monomers with three or more functions is more than 1% by mass of the total amount of the ink composition.

[0006] The recording method of the present invention comprises an adhesion step of ejecting the above-mentioned radiation-curable inkjet ink composition from an inkjet head and adhering it to a shrink film or flexible packaging film, and an irradiation step of irradiating the adhered radiation-curable inkjet ink composition with radiation. [Brief explanation of the drawing]

[0007] [Figure 1] An example of a recording device used in this embodiment is shown. [Figure 2] Table 1 shows the composition and evaluation results of the radiation-curable inkjet ink composition used in the examples. [Figure 3] Table 2 shows the composition and evaluation results of the radiation-curable inkjet ink compositions used in the examples. [Modes for carrying out the invention]

[0008] The embodiments of the present invention (hereinafter referred to as "this embodiment") will be described in detail below, with reference to the drawings as necessary. However, the present invention is not limited thereto, and various modifications are possible without departing from its essence.

[0009] 1. Radiation-curable inkjet ink composition The radiation-curable inkjet ink composition of this embodiment (hereinafter also referred to as "ink composition") contains a polyfunctional 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 of the total amount of the ink composition, the content of monofunctional monomers is 60% by mass or more of the total amount of polymerizable compounds, and the content of polyfunctional monomers with three or more functions is more than 1% by mass of the total amount of the ink composition.

[0010] Ink compositions suitable for shrink film and flexible packaging film require a high concentration of monofunctional monomers because flexibility of the coating film is essential. However, radiation-curable ink compositions containing a high concentration of monofunctional monomers tend to have poor curability. Insufficient curability can lead to a blocking phenomenon where the coating film peels off and sticks to the media when it comes into contact with the media.

[0011] Here, it is conceivable to use 5-methyl-3-vinyloxazolidine-2-one (hereinafter also referred to as "VMOX"), which has excellent curability. However, since vinyl monomers contribute to improved curability when used in combination with acrylic monomers, there is a limit to the improvement in curability even if VMOX is used in excess.

[0012] Therefore, in this embodiment, in an ink composition containing a predetermined amount of monofunctional monomer from the viewpoint of flexibility, a predetermined amount of a polyfunctional monomer with three or more functions is used in addition to a predetermined amount of VMOX. By using VMOX and a polyfunctional monomer with three or more functions in combination in this way, the curability of the surface and interior of the coating film can be further improved. Improving the surface curability reduces the tackiness of the ink coating film, and improving the interior curability suppresses blocking. In particular, VMOX contributes to surface curability, and the polyfunctional monomer with three or more functions can contribute to improving the curability inside the coating film by introducing crosslinking points.

[0013] The radiation-curable inkjet composition of this embodiment hardens by irradiation with radiation. Examples of radiation include ultraviolet rays, electron beams, infrared rays, visible light, and X-rays. Ultraviolet rays are preferred as the radiation source because they are readily available and widely used, and because materials suitable for curing by ultraviolet radiation are readily available and widely used.

[0014] The following describes in detail each component included in the radiation-curable inkjet composition of this embodiment.

[0015] 1.1. Polymerizable compounds In this embodiment, a compound that cures by irradiation with radiation is generally referred to as a polymerizable compound. Examples of the polymerizable compound in this embodiment include a monofunctional monomer having one polymerizable functional group and a polyfunctional monomer having two or more polymerizable functional groups. Further, the polyfunctional monomer includes a bifunctional monomer having two polymerizable functional groups and a polyfunctional monomer having three or more polymerizable functional groups. In this embodiment, the polyfunctional monomer does not include an oligomer.

[0016] In this embodiment, an oligomer refers to a multimer having a polymerizable compound as a constituent component and having one or more polymerizable functional groups. In this embodiment, those having a molecular weight of 1000 or more are defined as oligomers, and those having a molecular weight of less than 1000 are defined as monomers.

[0017] The weighted average of the glass transition temperatures of the polymerizable compound is preferably 30°C or higher and 70°C or lower, 40°C or higher and 65°C or lower, and 50°C or higher and 60°C or lower. When the weighted average of the glass transition temperature is 30°C or higher, the adhesion of the ink composition tends to be more improved, and when it is 70°C or lower, the shrinkage characteristics tend to be more improved. In this specification, the glass transition temperature can be measured by, for example, a differential scanning calorimeter.

[0018] Among the glass transition temperatures of the homopolymers composed of monofunctional monomers, the difference between the highest glass transition temperature and the lowest glass transition temperature is defined as difference A [°C], and among the glass transition temperatures of the homopolymers composed of bifunctional monomers and polyfunctional monomers having three or more functional groups, when the difference between the highest glass transition temperature and the lowest glass transition temperature is defined as difference B [°C], difference A is preferably larger than difference B. Although the glass transition temperature of the ink composition needs to be adjusted to an appropriate value by adjusting the type and content of the polymerizable compound, since the content of the monofunctional monomer is large, the contribution to the glass transition temperature of the ink composition is large. Therefore, when difference A is larger than difference B, it becomes easier to adjust the glass transition temperature of the ink composition. As a result, the degree of freedom in designing the ink composition increases, and it becomes easier to realize ink characteristics according to the purpose.

[0019] 1.1.1. Monofunctional monomer The ink composition of this embodiment contains 5-methyl-3-vinyloxazolidin-2-one (VMOX) as one of the monofunctional monomers. VMOX refers to a compound represented by the following chemical formula.

Chemical formula

[0020] Since VMOX has a lower viscosity compared to other N-vinyl compounds, it is difficult to increase the viscosity of the composition and is suitable for an inkjet ink composition. Also, VMOX can improve the adhesion and tackiness of the coating film. Commercially available products of VMOX can be obtained, for example, from BASF.

[0021] In addition, the ink composition of this embodiment may contain monofunctional monomers other than VMOX. The monofunctional monomers other than VMOX are not particularly limited, and examples include nitrogen-containing monofunctional monomers, alicyclic group-containing monofunctional monomers, aliphatic group-containing monofunctional monomers, aromatic group-containing monofunctional monomers, ether cyclic monofunctional monomers, and monofunctional monomers having a hydroxyl group. These monofunctional monomers are used alone or in combination of two or more.

[0022] The total content of the monofunctional monomer 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, 75% by mass or more and 88% by mass or less, based on the total amount of the polymerizable compounds. When the content of the monofunctional monomer is within the above range, the flexibility is further improved, and the adhesion and shrinkage characteristics tend to be further improved, resulting in an ink composition that is more suitable for shrink films and flexible packaging films.

[0023] The total content of monofunctional monomers is preferably 63% to 90% by mass, 65% to 88% by mass, or 67% to 87% by mass, relative to the total amount of the ink composition. Having a monofunctional monomer content within these ranges tends to improve tackiness, adhesion, and shrinkage properties.

[0024] 1.1.1.1.VMOX The ink composition of this embodiment can improve tackiness and adhesion by using VMOX (5-methyl-3-vinyloxazolidine-2-one). Furthermore, the viscosity of the ink can be kept within a suitable range.

[0025] The VMOX content is less than 50% by mass of the total amount of the ink composition, preferably 49% by mass or less, 40% by mass or less, and 35% by mass or less. VMOX, being a vinyl monomer, tends to exhibit better tackiness when it reacts with acrylic monomers. In this respect, when the VMOX content is within the above range, a relatively larger amount of monomers other than VMOX, such as acrylic monomers, is included, which tends to further improve tackiness. Furthermore, the VMOX content is preferably 10% by mass or more, 20% by mass or more, and 25% by mass or more of the total amount of the ink composition. When the VMOX content is within the above range, tackiness, adhesion, and shrinkage properties tend to further improve.

[0026] 1.1.1.2. Nitrogen-containing monofunctional monomers other than VMOX Examples of nitrogen-containing monofunctional monomers other than VMOX include, but are not limited to, 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 acryloylmorpholin; 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 dimethylaminoethyl acrylate benzyl chloride quaternary salt.

[0027] The content of nitrogen-containing monofunctional monomers other than VMOX is preferably 1% to 60% by mass, 10% to 50% by mass, 20% to 40% by mass, and 25% to 35% by mass, relative to the total amount of the ink composition. When the content of nitrogen-containing monofunctional monomers other than VMOX is within the above range, the tackiness, adhesion, and shrinkage properties tend to be further improved.

[0028] 1.1.1.3. Monofunctional monomers containing alicyclic groups Monofunctional monomers containing alicyclic groups are not particularly limited as long as they are monomers having one or more saturated or unsaturated carbon rings that do not have aromaticity. Examples include monomers having monocyclic hydrocarbon groups such as 4-tert-butylcyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, and 2-(meth)acrylic acid-1,4-dioxaspiro[4,5]decy-2-ylmethyl; monomers having unsaturated polycyclic hydrocarbon groups such as dicyclopentenyl acrylate and dicyclopentenyloxyethyl acrylate; and monomers having saturated polycyclic hydrocarbon groups such as dicyclopentanyl acrylate and isobornyl acrylate (IBXA).

[0029] The content of alicyclic group-containing monofunctional monomers is preferably 1% to 60% by mass, 10% to 50% by mass, 20% to 40% by mass, and 25% to 35% by mass, relative to the total amount of the ink composition. When the content of alicyclic group-containing monofunctional monomers is within the above range, tackiness, adhesion, and shrinkage properties tend to be further improved.

[0030] 1.1.1.4. Ether cyclic monofunctional monomers The ink composition in this embodiment preferably contains an ether cyclic monofunctional monomer. The ink composition tends to have improved adhesion, tackiness, and shrinkage properties when it contains an ether cyclic monofunctional monomer. The ether cyclic monofunctional monomer is not particularly limited as long as it contains a cyclic ether skeleton such as tetrahydrofuran or tetrahydropyran, but examples include cyclic trimethylolpropaneform (meth)acrylate and tetrahydrofurfuryl (meth)acrylate.

[0031] The content of ether cyclic monofunctional monomers is preferably 1% to 60% by mass, 10% to 50% by mass, 20% to 40% by mass, or 25% to 35% by mass, relative to the total amount of the ink composition. When the content of ether cyclic monofunctional monomers is within the above range, tackiness, adhesion, and shrinkage properties tend to be further improved.

[0032] 1.1.1.5. Monofunctional monomers having a hydroxyl group The ink composition in this embodiment preferably contains a monofunctional monomer having a hydroxyl group. The ink composition tends to have improved adhesion, tackiness, and shrinkage properties when it contains a monofunctional monomer having a hydroxyl group. The hydroxyl group-containing monofunctional monomer is not particularly limited, but examples include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, ethylene glycol monovinyl ether, diethylene glycol monovinyl ether, and 2-(meth)acryloyloxy-2-hydroxypropyl phthalate.

[0033] The content of monofunctional monomers having hydroxyl groups is preferably 1% to 30% by mass, 3% to 20% by mass, and 5% to 15% by mass, relative to the total amount of the ink composition. When the content of monofunctional monomers having hydroxyl groups is within the above range, the tackiness, adhesion, and shrinkage properties tend to be further improved.

[0034] 1.1.2. Polyfunctional monomers The polyfunctional monomer content is preferably 1% to 40% by mass, 5% to 35% by mass, 10% to 30% by mass, or 15% to 25% by mass, relative to the total amount of polymerizable compounds. When the polyfunctional monomer content is within the above range, blocking resistance, adhesion, and shrinkage properties tend to be further improved.

[0035] The polyfunctional monomer content is preferably 1% to 50% by mass, 5% to 40% by mass, 10% to 30% by mass, or 15% to 25% by mass, relative to the total amount of the ink composition. When the polyfunctional monomer content is within the above range, blocking resistance, adhesion, and shrinkage properties tend to be further improved.

[0036] 1.1.2.1.2 Functional Monomers The difunctional monomer is not particularly limited, but examples include vinyl ether group-containing (meth)acrylates and difunctional (meth)acrylates.

[0037] Examples of difunctional (meth)acrylates include, but are not limited to, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 2-hydroxy-1,3-di(meth)acryloxypropane and 2-(2-vinyloxyethoxy)ethyl acrylate. These difunctional monomers can be used individually or in combination of two or more.

[0038] The content of the difunctional monomer is preferably 1% to 39% by mass, 5% to 33% by mass, 7% to 25% by mass, or 10% to 20% by mass, relative to the total amount of the ink composition. Having the difunctional monomer content within these ranges improves blocking resistance, adhesion, and shrinkage properties.

[0039] The content of the difunctional monomer is preferably 1% to 39% by mass, 5% to 35% by mass, 10% to 25% by mass, or 12% to 20% by mass, relative to the total amount of polymerizable compound. Having the difunctional monomer content within these ranges improves blocking resistance, adhesion, and shrinkage properties.

[0040] 1.1.2.2.3 Polyfunctional monomers with more than 3 functional functions The ink composition in this embodiment contains a polyfunctional monomer with three or more functions. By including a polyfunctional monomer with three or more functions, crosslinking points are introduced, improving the curability inside the coating film, and thus improving blocking resistance.

[0041] While there are no particular limitations on polyfunctional monomers with three or more functions, examples include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxytri(meth)acrylate, pentaerythritol ethoxytetra(meth)acrylate, and dipentaerythritol penta(meth)acrylate. Among these, dipentaerythritol hexaacrylate, pentaerythritol triacrylate, ditrimethylolpropane tetraacrylate, and dipentaerythritol pentaacrylate are preferred. Using these polyfunctional monomers with three or more functions tends to further improve blocking resistance, adhesion, and shrinkage properties. These polyfunctional monomers with three or more functions can be used individually or in combination of two or more.

[0042] Polyfunctional monomers with three or more functions are preferably those having three or more acrylic groups. Using such polyfunctional monomers tends to improve blocking resistance. Examples of polyfunctional monomers having three or more acrylic groups include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxytri(meth)acrylate, pentaerythritol ethoxytetra(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol penta(meth)acrylate.

[0043] In this embodiment, the acrylic equivalent of the trifunctional or polyfunctional monomer is preferably 110 g / eq or less, 106 g / eq or less, 100 g / eq or less, and 98 g / eq or less. When the acrylic equivalent is within the above range, blocking resistance tends to improve further. The acrylic equivalent is calculated using the following formula. (Acrylic equivalent) = (Molecular weight of monomer / Number of acrylic groups in monomer)

[0044] The content of polyfunctional monomers with three or more functions is preferably 1% to 20% by mass, 2% to 15% by mass, 4% to 10% by mass, or 5% to 9% by mass, relative to the total amount of polymerizable compounds. Having the content of polyfunctional monomers with three or more functions within the above range improves blocking resistance, adhesion, and shrinkage properties.

[0045] The content of three or more polyfunctional monomers is more than 1% by mass of the total amount of the ink composition, preferably 3% or more by mass, 3.5% or more by mass, and 4% or more by mass. When the content of three or more polyfunctional monomers is within the above range, blocking resistance tends to be further improved. Alternatively, the content of three or more polyfunctional monomers is preferably 10% or less by mass, 9% or less by mass, and 7% or less by mass of the total amount of the ink composition. When the content of three or more polyfunctional monomers is within the above range, the viscosity tends to be within a suitable range, and shrinkage properties tend to be further improved.

[0046] 1.2 Polymerization Inhibitors In this embodiment, the ink composition may contain a polymerization inhibitor. The polymerization inhibitor is not particularly limited, but examples include phenol compounds, quinone compounds, amine compounds, nitro compounds, oxime compounds, sulfur compounds, and oxyl compounds. These polymerization inhibitors may be used individually or in combination of two or more.

[0047] Examples of phenol compounds are not particularly limited, but include p-methoxyphenol, cresol, tert-butylcatechol, di-tert-butylpara-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). A commercially available example of a phenol compound is MEHQ (p-methoxyphenol, manufactured by Kanto Chemical Co., Ltd.).

[0048] The quinone compounds are not particularly limited, but examples include p-benzoquinone, anthraquinone, naphthoquinone, phenanthraquinone, p-xyloquinone, p-toluquinone, 2,6-dichloroquinone, 2,5-diphenyl-p-benzoquinone, 2,5-diacetoxy-p-benzoquinone, 2,5-dicapoxy-p-benzoquinone, 2,5-diasiloxy-p-benzoquinone, hydroquinone, 2,5-dibutylhydroquinone, mono-t-butylhydroquinone, monomethylhydroquinone, and 2,5-di-t-amylhydroquinone.

[0049] The amine compounds are not particularly limited, but examples include phenyl-β-naphthylamine, p-benzylaminophenol, di-β-naphthylparaphenylenediamine, dibenzylhydroxylamine, phenylhydroxylamine, diethylhydroxylamine, 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.

[0050] Examples of nitro compounds include, but are not limited to, dinitrobenzene, trinitrotoluene, picric acid, and their derivatives. Examples of oxime compounds include, but are not limited to, quinone dioxime and cyclohexanone oxime. Examples of sulfur compounds include, but are not limited to, phenothiazine.

[0051] The oxyl compound is not particularly limited, but examples include derivatives of 2,2,6,6-tetramethylpiperidinyl-1-oxyl. Examples of derivatives of 2,2,6,6-tetramethylpiperidinyl-1-oxyl include 4-acetamido-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 4-amino-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 4-carboxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 4-(2-chloroacetamide)-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 4-cyano-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl, and 4-hydroxybenzo-A Examples include to-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 4-(2-iodoacetamide)-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 4-isothiocyanate-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 4-methacryloyloxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidinyl-1-oxyl, and 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl-1-oxyl. A commercially available example of an oxyl compound is Adeka Stab LA-7RD (2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, a trade name of ADEKA Corporation).

[0052] The polymerization inhibitor content is preferably 0.01% to 5.0% by mass, 0.05% to 3.0% by mass, or 0.1% to 1.0% by mass, relative to the total amount of the ink composition. When the polymerization inhibitor content is within the above range, blocking resistance, adhesion, tackiness, and shrinkage properties tend to be further improved.

[0053] 1.3. Polymerization Initiators In this embodiment, the ink composition may contain a polymerization initiator. The polymerization initiator is not particularly limited as long as it generates an active species when irradiated with radiation, but known polymerization initiators such as acylphosphine oxide polymerization initiators, alkylphenone polymerization initiators, titanocene polymerization initiators, and thioxanthone polymerization initiators can be found. Among these, the polymerization initiator preferably contains an acylphosphine oxide polymerization initiator and a thioxanthone polymerization initiator, and more preferably a thioxanthone polymerization initiator. By using such polymerization initiators, the curability of the composition is further improved, and in particular, the curability by the curing process using ultraviolet light-emitting diodes tends to be further improved, thus improving blocking resistance and tackiness. These polymerization initiators can be used individually or in combination of two or more.

[0054] The polymerization initiator content is preferably 3% to 17% by mass, more preferably 5% to 15% by mass, and even more preferably 7% to 12% by mass, relative to the total amount of the ink composition. When the polymerization initiator content is within the above range, blocking resistance, adhesion, tackiness, and shrinkage properties tend to be further improved.

[0055] 1.3.1. Acylphosphine oxide-based polymerization initiators Acylphosphine oxide polymerization initiators are not particularly limited, but examples include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. These acylphosphine oxide polymerization initiators may be used individually or in combination of two or more.

[0056] Examples of commercially available acylphosphine oxide polymerization initiators include Omnirad 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, trade name of ISM Resins BV) and Omnirad TPO-L (ethyl(2,4,6-trimethylbenzoyl)-phenylphosphenate, trade name of IGM Resins BV).

[0057] The content of the acylphosphine oxide polymerization initiator is preferably 0.1% to 20% by mass, 1% to 15% by mass, 3% to 10% by mass, or 5% to 7% by mass, relative to the total amount of the ink composition. When the content of the acylphosphine oxide polymerization initiator is within the above range, blocking resistance, adhesion, tackiness, and shrinkage properties tend to be further improved.

[0058] 1.3.2. Thioxanthone-based polymerization initiators The thioxanthone polymerization initiator is not particularly limited, but examples include low molecular weight thioxanthone initiators and high molecular weight thioxanthone initiators. In this embodiment, a "low molecular weight thioxanthone initiator" is a thioxanthone polymerization initiator with a molecular weight of less than 500, and a "high molecular weight thioxanthone initiator" is a thioxanthone polymerization initiator with a molecular weight of 500 or more. The thioxanthone polymerization initiator is preferably a high molecular weight thioxanthone initiator. By using a high molecular weight thioxanthone initiator, odor can be further reduced, and odor transfer to containers to which shrink film is applied is less likely, making it more suitable for shrink film applications. The thioxanthone polymerization initiator can be used alone or in combination of two or more types.

[0059] Low molecular weight thioxanthone initiators are not particularly limited, but examples include thioxanthone, 2-methylthioxanthone, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, and 2,4-diethylthioxanthone. A commercially available low molecular weight thioxanthone initiator is Speedcure DETX (2,4-diethylthioxanthene-9-one, manufactured by Lambson).

[0060] Examples of high molecular weight thioxanthone initiators are not particularly limited, but include 1,3-di({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxymethyl)propane and α-[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]-ω-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]poly(oxy-1,4-butanediyl). Commercial products may also be used, for example, SPEEDCURE 7010 (thioxanthone polymer type, manufactured by LAMBSON) and Omnipol® TX (trade name of IGM RESINS).

[0061] The content of the thioxanthone polymerization initiator is preferably 0.1% to 10% by mass, 1% to 5% by mass, or 2% to 4% by mass, relative to the total amount of the ink composition. When the content of the thioxanthone polymerization initiator is within the above range, blocking resistance, adhesion, tackiness, and shrinkage properties tend to be further improved.

[0062] 1.4. Surfactants In this embodiment, the ink composition may contain a surfactant. Examples of surfactants include acetylene glycol-based surfactants, fluorine-based surfactants, and silicone-based surfactants. These surfactants may be used individually or in combination of two or more.

[0063] The acetylene glycol-based surfactant is not particularly limited, but examples include 2,4,7,9-tetramethyl-5-decine-4,7-diol and alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decine-4,7-diol. A commercially available acetylene glycol-based surfactant is, for example, Surfinol 465 (trade name of Nisshin Chemical Industry Co., Ltd.).

[0064] Examples of fluorinated surfactants include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphate esters, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkylamine oxide compounds.

[0065] Examples of silicone-based surfactants are not particularly limited, but include polysiloxane compounds and polyether-modified organosiloxanes. Examples of commercially available silicone-based surfactants include BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-348, BYK-UV3500, BYK-UV3510, BYK-UV3530, and BYK-UV3570 (product names of BYK Corporation).

[0066] The surfactant content is preferably 0.01% to 5% by mass, 0.1% to 3% by mass, or 0.3% to 1% by mass, relative to the total amount of the ink composition. By keeping the surfactant content within the above range, blocking resistance, adhesion, tackiness, and shrinkage properties tend to be further improved.

[0067] 1.5. Dispersant The ink composition of this embodiment may contain a dispersant. The dispersant is not particularly limited, but examples include dispersants commonly used to prepare pigment dispersions, such as polymer dispersants. Specifically, examples include polyoxyalkylenes, 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. These dispersants may be used individually or in combination of two or more.

[0068] Commercially available dispersants may be used, including the Azisper series (manufactured by Ajinomoto Fine Techno Co., Ltd.), Solsperse 36000 (product name of Noveon Corporation), Disperbic series (manufactured by BYK Corporation), and Disparon series (manufactured by Kusumoto Chemical Co., Ltd.).

[0069] The dispersant content is preferably 0.01% to 5% by mass, 0.05% to 1% by mass, or 0.1% to 0.5% by mass, relative to the total amount of the ink composition. By keeping the dispersant content within the above range, blocking resistance, adhesion, tackiness, and shrinkage properties tend to improve.

[0070] 1.6. Colorants The ink composition of this embodiment may contain a colorant. The colorant may be either a pigment or a dye. The pigment is not particularly limited, but examples include organic pigments and inorganic pigments. These colorants may be used individually or in combination of two or more.

[0071] Examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, condensed azo pigments, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, quinacridone pigments, perylene pigments, perinone pigments, anthraquinone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye chelates such as basic dye type chelates and acid dye type chelates; and nitro pigments and nitroso pigments.

[0072] Examples of inorganic pigments include titanium dioxide, iron oxide yellow, iron oxide brown, chromium oxide, Prussian blue, ultramarine, molybdenum red, iron oxide black, lead yellow, complex oxide pigments, and carbon black.

[0073] Examples of carbon black include CI (Colour Index Generic Name) Pigment Black 1, 7, and 11. Examples of commercially available carbon black include No.2300, No.900, MCF88, No.33, No.40, No.45, No.52, MA7, MA8, MA100, No.2200B (product names from Mitsubishi Chemical Corporation), Raven 5750, 5250, 5000, 3500, 1255, 700 (product names from Columbia Carbon Corporation), Rega1 400R, 330R, 660R, Mogul L, Monarch 700, 800, 880, 900, 1000, 1100, 1300, 1400 (product names from CABOT Corporation), Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex 35, U, V, 140U, and Special Black. Examples include 6, 5, 4A, and 4 (product names of Degussa). Carbon black manufactured by known methods such as the contact method, furnace method, and thermal method may also be used.

[0074] The dyes used are not particularly limited and 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.

[0075] The colorant content is preferably 0.1% to 10% by mass, 1% to 5% by mass, or 2% to 4% by mass, relative to the total amount of the ink composition. When the colorant content is within the above range, blocking resistance, tackiness, adhesion, and shrinkage properties tend to be improved.

[0076] 1.7. Other ingredients In addition to the above-mentioned components, various additives such as chelating agents, softening agents, solubilizers, viscosity modifiers, ultraviolet absorbers, antioxidants, and corrosion inhibitors may be included as needed.

[0077] 2. Method for preparing an ink composition Ink compositions can be prepared, for example, by mixing each component in any order and removing impurities and foreign matter by filtration or other methods as needed. Methods for mixing the components include sequentially adding each component to a container equipped with a stirring device such as a mechanical stirrer or magnetic stirrer, and then stirring and mixing them. Filtration methods include centrifugal filtration and filter filtration.

[0078] 3. Recording media In this embodiment, the recording medium can be, for example, paper, film, cloth, metal, and glass. Among these, shrink film or flexible packaging film is preferred. Since shrink film and flexible packaging film are often shrunk or folded, the effects of this embodiment are particularly pronounced. The shrink film is not particularly limited, but for example, a film that has the property of shrinking in at least one direction when heated is mentioned. In this embodiment, flexible packaging film is a highly flexible film material used for food packaging, toiletries, cosmetic packaging, etc. The material of the shrink film is preferably one or more selected from polyethylene terephthalate, polyethylene, polyolefin, polystyrene, polypropylene, and polyvinyl chloride, as this tends to result in superior shrink properties.

[0079] 4. Recording Method The inkjet recording method according to this embodiment includes an adhesion step of ejecting the above-mentioned radiation-curable inkjet composition from an inkjet head and adhering it to a shrink film or flexible packaging film, and a step of irradiating the adhered radiation-curable inkjet composition with radiation. Since shrink films and flexible packaging films are often subjected to shrinkage or bending, the effects of this embodiment are particularly pronounced.

[0080] 4.1. Adhesion Process In the adhesion process, the heated ink composition is ejected from the inkjet head and adhered to the shrink film or flexible packaging film. More specifically, a pressure generating mechanism is driven to eject the ink composition filled in the pressure generating chamber of the inkjet head from the nozzle. This ejection method is also called the inkjet method.

[0081] Inkjet heads used in the deposition process include line heads that record using a line method and serial heads that record using a serial method.

[0082] In a line-type inkjet system using a line head, for example, a liquid jet head with a width greater than the recording width of the recording medium is fixed to the inkjet device. The recording medium is then moved along the sub-scanning direction (the vertical 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, thereby recording an image on the recording medium.

[0083] 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. The carriage is then moved along the main scanning direction (the lateral direction, width direction of the recording medium), and ink droplets are ejected from the nozzle opening of the head in conjunction with this movement, thereby recording an image on the recording medium.

[0084] 4.2.Irradiation process In the irradiation process, radiation is applied to the radiation-curable inkjet composition attached to the recording medium. When radiation is applied, the polymerization reaction of the polymerizable compounds begins, causing the ink composition to harden and a coating film to form. At this time, if a polymerization initiator is present, it generates active species (initiators) such as radicals, acids, and bases, and the polymerization reaction of the polymerizable compounds is promoted by the function of these initiators.

[0085] Here, examples of radiation include ultraviolet rays, infrared rays, visible light, and X-rays. The radiation is irradiated onto the ink composition by a radiation source located downstream of the inkjet head. The radiation source is not particularly limited, but examples include ultraviolet light-emitting diodes. Using such a radiation source makes it possible to miniaturize the device and reduce costs. Because ultraviolet light-emitting diodes are small, they can be installed inside the inkjet device. For example, ultraviolet light-emitting diodes can be installed on the carriage (both ends along the media width direction and / or on the media transport direction side) on which the inkjet head that ejects the radiation-curable inkjet composition is mounted.

[0086] 5. Inkjet device The inkjet device of this embodiment is not particularly limited as long as it includes an inkjet head having a nozzle for ejecting the above-mentioned ink composition onto a recording medium, and a radiation source for irradiating the ejected ink composition with radiation. As an example of an inkjet device, Figure 1 shows a perspective view of a serial printer. As shown in Figure 1, the serial printer 20 includes a transport unit 220 and a recording unit 230. The transport unit 220 transports the recording medium F supplied to the serial printer to the recording unit 230 and discharges the recording medium after recording outside the serial printer. Specifically, the transport unit 220 has feed rollers and transports the transported recording medium F in the sub-scanning direction T1.

[0087] Furthermore, the recording unit 230 includes an inkjet head 231 that ejects an ink composition onto the recording medium F sent from the transport unit 220, a radiation source 232 that irradiates the attached ink composition with radiation, a carriage 234 on which these are mounted, and a carriage movement mechanism 235 that moves the carriage 234 in the main scanning directions S1 and S2 of the recording medium F.

[0088] In a serial printer, the inkjet head 231 is shorter than the width of the recording medium, and the inkjet head 231 moves, performing recording in multiple passes (multipass). In a serial printer, the inkjet head 231 and radiation source 232 are mounted on a carriage 234 that moves in a predetermined direction, and as the carriage moves, the inkjet head 231 moves, ejecting the ink composition onto the recording medium. This allows for recording in two or more passes (multipass). A pass is also called a main scan. A sub-scan is performed between passes to transport the recording medium. In other words, main scans and sub-scans are performed alternately.

[0089] Although Figure 1 shows a configuration in which the radiation source is mounted on a carriage, the system is not limited to this configuration, and the radiation source may be mounted on a carriage or not.

[0090] Furthermore, the inkjet device of this embodiment is not limited to the serial printer described above, but may also be a line printer as described above. [Examples]

[0091] The present invention will be described more specifically below using examples and comparative examples. The present invention is not limited in any way by the following examples.

[0092] Figure 2 shows Table 1, which illustrates the composition of each composition in the examples and comparative examples.

[0093] 1. Preparation of each composition Each example ink composition is obtained by placing the components into a mixing tank to achieve the composition shown in Table 1, mixing and stirring, and then filtering through a membrane filter. Unless otherwise specified, the numerical values ​​for each component in the table represent mass percent. Furthermore, in the table, the numerical values ​​for each content represent the mass percent of the solid content of the active ingredient.

[0094] The abbreviations and product component details used in the processing solution composition are as follows:

[0095] [Monofunctional monomer] • CTFA (Cyclic Trimethylol Propane Formal Acrylate) • 4HBA (4-hydroxybutyl acrylate) • VMOX (5-methyl-3-vinyloxazolidine-2-one) • TBCHA (4-tert-butylcyclohexyl acrylate) • TMCHA (3,3,5-trimethylcyclohexyl acrylate) • DEAA (N,N-diethylacrylamide) HPA (Hydroxypropyl acrylate) [Polyfunctional monomers] • TPGDA (Tripropylene Glycol Diacrylate) • DPHA (Dipentaerythritol Hexaacrylate) • PETA (Pentaerythritol Triacrylate) DTMPTA (Ditrimethylolpropanetetraacrylate) • DPEPA (Dipentaerythritol Pentaacrylate) [Polymerization inhibitor] • MEHQ (p-methoxyphenol, manufactured by Kanto Chemical Co., Ltd.) • LA-7RD (Product name "ADEKA Stab LA-7RD", 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl, manufactured by ADEKA) [Polymerization initiator] • Omnirad 819 (Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, brand name of ISM Resins BV) • TPO-L (Trade name "Omnirad TPO-L", Ethyl (2,4,6-trimethylbenzoyl)-phenylphosphophenate, manufactured by IGM Resins BV) Speedcure 7010 (1,3-di({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxymethyl)propane, Lambson Company trade name, molecular weight 1839) • Speedcure DETX (2,4-diethylthioxanthene-9-one, Lambson Company trade name, molecular weight 268) [Surfactants] • BYK UV3500 (silicone-based surfactant, BYK brand name) [Dispersant] • Solsperse 36000 (polymeric dispersant, Lubrizol brand name) [Pigments] • Carbon Black [water] ·Pure water

[0096] 2. Evaluation Method 3.1. Blocking Resistance [Production of packaging] A sample for evaluating blocking resistance will be prepared using the inkjet printer "PX-G5000" (product name manufactured by Seiko Epson Corporation). Under normal temperature and pressure conditions, a solid pattern image will be printed onto the PET film "Bonset" (product name manufactured by Takiron CI Co., Ltd.), which is the recording medium, at a recording resolution of 600 dpi × 600 dpi and a droplet weight of 10 ng to obtain a printed sample with a film thickness of 5 μm. The solid pattern image is an image in which dots are recorded for all pixels of the pixel, which is the smallest recording unit area defined by the recording resolution. While performing the above printing, ultraviolet light will be irradiated from an ultraviolet light-emitting diode in an ultraviolet irradiation device mounted next to the carriage to obtain a recorded material in which a cured film of the ink composition with a film thickness of 5 μm has been formed on the recording medium.

[0097] The recorded material obtained as described above is rolled up so that the hardened film faces inward, and processed into a cylindrical shape. This recorded material is placed around the container (glass bottle), which is the packaged object, that has been preheated in a constant temperature bath, and left undisturbed in the 90°C constant temperature bath for 10 seconds to shrink the recorded material and make it adhere tightly to the container.

[0098] [Measurement of blocking resistance] The packaging prepared as described above is evaluated by visually observing whether or not the cured film adheres to the container, and the blocking resistance is evaluated according to the following evaluation criteria. (Evaluation Criteria) A: No adhesion of the hardened film to the container. B: The hardened film is slightly adhered to the container. C: The hardened film adheres to the container (and peels off).

[0099] 3.2. Tuckability The ink composition is applied to the PET film using a bar coater to a cured film thickness of 5 μm. (Ultraviolet light-emitting diode (peak wavelength 395 nm, irradiation intensity 1000 mW / cm²)) 2 Irradiation is performed using [mJ / cm²], and the irradiation energy used until the tack-free state is determined. Irradiation energy [mJ / cm²] 2 ] is the irradiation intensity [mW / cm²] on the irradiated surface from the light source.2 It is measured and obtained from the product of this and the irradiation duration [s]. The measurement of the irradiation intensity is performed using an ultraviolet intensity meter UM-10 and a light receiving unit UM-400 (both manufactured by KONICA MINOLTA SENSING, INC.). Also, whether it is in a tack-free state or not is judged under the following conditions. That is, it is judged by rubbing the effect film with a cotton swab and whether ink adheres to the cotton swab or whether scratches are made on the cured ink on the recording medium. At that time, the cotton swab to be used is a Johnson cotton swab manufactured by Johnson & Johnson. The number of rubbing times is 10 reciprocations, and the rubbing strength is 100 g load. Based on the irradiation energy (tack-free energy) when it becomes tack-free, the tackiness is evaluated according to the following evaluation criteria. (Evaluation Criteria) AA: Tack-free energy < 150 mJ / cm 2 less than A: Tack-free energy ≥ 150 mJ / cm 2 and < 250 mJ / cm 2 less than B: Tack-free energy ≥ 250 mJ / cm 2 and < 350 mJ / cm 2 less than C: Tack-free energy ≥ 350 mJ / cm 2 and above

[0100] 3.3. Adhesion Regarding the recording made in the evaluation of tackiness, the adhesion is evaluated by a cross-cut test in accordance with JIS K5600-5-6. That is, on the obtained effect film, with a cutter, place the blade of the cutting tool perpendicular to the coating film and make a grid-like cut with a distance of 1 mm between cuts, in a 10×10 grid. Stick a transparent adhesive tape on the cut part and rub the tape well with your finger so that the cured film can be seen through. Next, within 5 minutes after attaching the tape, at an angle close to 60°, in 0.5 - 1.0 seconds, peel the tape from the cured film. Based on the presence or absence of peeling of the cured film from the film at this time, visually observe for each grid cell. The adhesion is evaluated according to the following evaluation criteria. (Evaluation Criteria) A: Peeling of the cured film is observed in less than 20% of the grid. B: Peeling of the cured film is observed in 20% to less than 30% of the grid. C: Peeling of the hardened film is observed in more than 30% of the lattice.

[0101] 3.4. Shrinkage Characteristics In evaluating blocking resistance, the wrinkle formation of the prepared packaging material before and after shrinkage is visually observed, and the shrinkage characteristics are evaluated according to the following evaluation criteria. (Evaluation Criteria) A: No wrinkles in the hardened film. B: The hardened film has slight wrinkles. C: Wrinkles present in the hardened film.

[0102] 4. Evaluation Results Tables 1 and 2 show that the radiation-curable inkjet ink composition of this embodiment exhibits excellent blocking resistance, adhesion, tackiness, and shrinkage properties. [Explanation of Symbols]

[0103] 20...Serial printer, 220...Transport unit, 230...Recording unit, 231...Inkjet head, 232...Light source, 234...Carriage, 235...Carriage movement mechanism, F...Recording medium, S1, S2...Main scanning direction, T1...Sub-scanning direction

Claims

1. A radiation-curable inkjet ink composition comprising 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 of the total amount of the ink composition. The monofunctional monomer content is 60% by mass or more relative to the total amount of polymerizable compounds. The content of the aforementioned three- or more-functional polyfunctional monomers is more than 1% by mass relative to the total amount of the ink composition. Radiation-curable inkjet ink composition.

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

3. The aforementioned polyfunctional monomer having three or more acrylic groups, The radiation-curable inkjet ink composition according to claim 1 or claim 2.

4. The acrylic equivalent of the three or more polyfunctional monomers is 110 g / eq or less. The radiation-curable inkjet ink composition according to claim 1 or claim 2.

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

6. Containing ether cyclic monofunctional monomers, The radiation-curable inkjet ink composition according to claim 1 or claim 2.

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

8. The weighted average of the glass transition temperatures of the polymerizable compound is between 30°C and 70°C. The radiation-curable inkjet ink composition according to claim 1 or claim 2.

9. Contains high molecular weight thioxanthone initiators, The radiation-curable inkjet ink composition according to claim 1 or claim 2.

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

11. The difference between the highest and lowest glass transition temperatures of the homopolymer composed of the aforementioned monofunctional monomers is defined as difference A [°C]. When the difference between the highest and lowest glass transition temperatures of the homopolymer composed of the polyfunctional monomer contained in the ink composition is denoted as difference B [°C], The difference A [°C] is greater than the difference B [°C]. The radiation-curable inkjet ink composition according to claim 1 or claim 2.

12. For attachment to shrink film and / or flexible packaging film, The radiation-curable inkjet ink composition according to claim 1 or claim 2.

13. A bonding step comprising: discharging the radiation-curable inkjet ink composition described in claim 1 from an inkjet head and adhering it to a shrink film or flexible packaging film; The process includes an irradiation step of irradiating the attached radiation-curable inkjet ink composition with radiation, Recording method.

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