Active energy ray-curable inkjet ink, image recording method, and method for producing molded body

Abstract

Provided are: an active energy ray-curable inkjet ink which contains a polymerizable compound and a coloring agent, wherein the polymerizable compound contains a bifunctional (meth)acrylate (A) having a linear or branched alkylene group and a benzyl (meth)acrylate (B), the content of the benzyl (meth)acrylate (B) with respect to the total amount of the active energy ray-curable inkjet ink is 70 mass% or less, and the weighted average of the glass transition points of homopolymers of the compounds contained in the polymerizable compound is 10°C or lower; and applications of the active energy ray-curable inkjet ink.

Description

Active energy ray curable inkjet ink, image recording method, and method for manufacturing molded articles

[0001] This disclosure relates to an active energy ray curable inkjet ink, an image recording method, and a method for manufacturing a molded article.

[0002] Conventionally, there is a known image recording method that involves applying ink to a substrate and irradiating the applied ink with active energy rays to obtain an image.

[0003] Patent Document 1 describes a curable composition containing a polyfunctional monomer, which has excellent adhesion between the cured film and the protective layer or label substrate, as well as excellent water resistance, wherein the SP value for each monomer species contained in the curable composition is 7 (cal / cm³). ３ ) ０．５ Above 11 (cal / cm ３ ) ０．５ The following is disclosed: a curable composition in which the glass transition temperature of the cured film is 0°C or higher and 30°C or lower. Patent Document 1 further discloses using this curable composition as an ink, applying it to a substrate by an inkjet recording method, and obtaining an image by irradiating the applied ink with active energy rays.

[0004] Patent Document 1: Japanese Unexamined Patent Publication No. 2019-163444

[0005] Images obtained by irradiating ink applied to a substrate with active energy rays may require stretchability. Furthermore, it may be necessary to suppress blocking (i.e., improve blocking resistance) in the aforementioned images. However, it has been found that improving the stretchability and blocking resistance of an image may result in the generation of an odor.

[0006] This disclosure has been made in view of the above circumstances. One embodiment of this disclosure aims to solve the problem of providing an active energy ray curable inkjet ink, an image recording method, and a method for manufacturing a molded article that can obtain images with excellent stretchability and blocking resistance and suppressed odor.

[0007] This disclosure includes the following embodiments: <1> An active energy ray-curable inkjet ink comprising a polymerizable compound and a colorant, wherein the polymerizable compound comprises a difunctional (meth)acrylate (A) having linear or branched alkylene groups and a benzyl (meth)acrylate (B), wherein the content of benzyl (meth)acrylate (B) relative to the total amount of the active energy ray-curable inkjet ink is 70% by mass or less, and the weighted average value of the glass transition temperatures of the homopolymers of each compound contained in the polymerizable compound is 10°C or less. <2> The active energy ray-curable inkjet ink according to <1>, wherein the polymerizable compound further comprises a (meth)acrylate (C), wherein the (meth)acrylate (C) is a (meth)acrylate satisfying at least one of the following: that the glass transition temperature of the homopolymer is 0°C or less, and that it is a polyethylene glycol diacrylate with a molecular weight of 200 to 600. <3> The active energy ray-curable inkjet ink according to <2>, wherein (meth)acrylate (C) contains polyethylene glycol diacrylate having a molecular weight of 200 to 600. <4> The active energy ray-curable inkjet ink according to any one of <1> to <3>, wherein the bifunctional (meth)acrylate (A) contains 3-methylpentanediol diacrylate. <5> The active energy ray-curable inkjet ink according to any one of <1> to <4>, wherein the ratio of the content mass of bifunctional (meth)acrylate (A) to the content mass of benzyl (meth)acrylate (B) is 0.05 to 0.40. <6> An image recording method comprising the steps of: applying the active energy ray-curable inkjet ink according to any one of <1> to <5> onto a substrate using an inkjet recording method; and irradiating the applied active energy ray-curable inkjet ink with active energy rays to record an image.<7> A method for manufacturing a molded article, comprising the steps of: applying an active energy ray-curable inkjet ink described in any one of <1> to <5> onto a substrate using an inkjet recording method; irradiating the applied active energy ray-curable inkjet ink with an active energy ray to record an image; and molding the substrate on which the image has been recorded to manufacture a molded article.

[0008] This disclosure provides an active energy ray curable inkjet ink, an image recording method, and a method for manufacturing a molded article, which can obtain images with excellent stretchability and blocking resistance and suppressed odor.

[0009] In this specification, a numerical range indicated using "~" means a range that includes the numbers listed before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Furthermore, in numerical ranges described in this specification, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples.

[0010] In this specification, the amount of each component in a composition means the total amount of multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. In this specification, the term "process" is included not only in the sense of an independent process, but also in the sense of a process that cannot be clearly distinguished from other processes, as long as the intended purpose of that process is achieved.

[0011] In this specification, "image" refers to any film formed by applying ink, and "image recording" refers to the formation of an image (i.e., a film). Furthermore, the concept of "image" in this specification also includes solid images.

[0012] In this specification, "(meth)acrylate" is a concept that encompasses both acrylate and methacrylate. Similarly, "(meth)acrylic" is a concept that encompasses both acrylic and methacrylic.

[0013] [Active Energy Ray Curable Inkjet Ink] The active energy ray curable inkjet ink of this disclosure (hereinafter also simply referred to as "ink") contains a polymerizable compound and a colorant, wherein the polymerizable compound contains a difunctional (meth)acrylate (A) having linear or branched alkylene groups (hereinafter also simply referred to as "difunctional (meth)acrylate (A)") and benzyl (meth)acrylate (B), the content of benzyl (meth)acrylate (B) relative to the total amount of ink is 70% by mass or less, and the weighted average of the glass transition temperatures of the homopolymers of each compound contained in the polymerizable compound (hereinafter also referred to as "average Tg of polymerizable compound") is 10°C or less.

[0014] The inks disclosed herein provide excellent stretchability and blocking resistance, and enable the production of images with suppressed odor. These effects are described below.

[0015] As mentioned above, stretchability is sometimes required for images obtained by irradiating an ink applied to a substrate with active energy rays. For example, when recording images on containers (e.g., food containers), post-processing such as bending or drilling may be performed on the container after image recording. Stretchability is required for the image to withstand the forces applied during this post-processing. From the viewpoint of obtaining an image with excellent stretchability, it is effective to include benzyl (meth)acrylate (B) in the ink.

[0016] Furthermore, as mentioned above, it is sometimes necessary to suppress blocking (i.e., improve blocking resistance) in images obtained by irradiating an ink applied to a substrate with active energy rays. From the viewpoint of improving the blocking resistance of images, it is effective to include a difunctional (meth)acrylate (A) having linear or branched alkylene groups (hereinafter also simply referred to as "difunctional (meth)acrylate (A)") in the ink.

[0017] However, through investigations by the inventors, it has been found that when using inks containing benzyl (meth)acrylate (B) and difunctional (meth)acrylate (A), an odor may be generated in the image. This is thought to be because when using inks containing polymerizable compounds including benzyl (meth)acrylate (B) and difunctional (meth)acrylate (A), even when the ink on the substrate is irradiated with active energy rays, the polymerizable compounds do not completely polymerize and remain in the image, a phenomenon called "residual monomers" is likely to occur. In particular, when benzyl (meth)acrylate (B) remains as a residual monomer, an odor tends to be generated in the image. As a result of further investigation, the present inventors have found that even when using an ink containing a polymerizable compound comprising benzyl (meth)acrylate (B) and bifunctional (meth)acrylate (A), the odor of the image can be suppressed if the weighted average of the glass transition temperatures of the homopolymers of each compound contained in the polymerizable compound (i.e., the average Tg of the polymerizable compound) is 10°C or less, and the content of benzyl (meth)acrylate (B) relative to the total amount of ink is 70% by mass or less. This is thought to be because when the average Tg of the polymerizable compound is 10°C or less, the mobility of the polymerizable compound is maintained during ink curing, resulting in improved reactivity of the polymerizable compound and suppression of the remaining benzyl (meth)acrylate (B) as a residual monomer. Furthermore, it is thought that by limiting the content of benzyl (meth)acrylate (B) relative to the total amount of ink to 70% by mass or less, the amount of benzyl (meth)acrylate (B) remaining as a residual monomer can be reduced. The ink of this disclosure was obtained based on the above findings.

[0018] The inks described in this disclosure are explained in more detail below.

[0019] <Polymerizable Compounds> The inks of this disclosure contain polymerizable compounds. The polymerizable compounds include a difunctional (meth)acrylate (A) and a benzyl (meth)acrylate (B).

[0020] (Bifunctional (meth)acrylate (A)) The polymerizable compound in the ink of this disclosure comprises at least one bifunctional (meth)acrylate (A). The bifunctional (meth)acrylate (A) contributes to improving the blocking resistance of the resulting image.

[0021] In this disclosure, difunctional (meth)acrylate (A) is a difunctional (meth)acrylate having linear or branched alkylene groups. In this disclosure, difunctional (meth)acrylate means a compound having two (meth)acryloyloxy groups.

[0022] There are no particular restrictions on the number of carbon atoms in the linear or branched alkylene group in the bifunctional (meth)acrylate (A). The number of carbon atoms in the linear or branched alkylene group in the bifunctional (meth)acrylate (A) is preferably 4 to 9, more preferably 5 to 9, even more preferably 6 to 8, and still more preferably 6. When the number of carbon atoms is 4 or more, the stretchability of the image is further improved. When the number of carbon atoms is 9 or less, the odor of the image is further suppressed.

[0023] Examples of difunctional (meth)acrylates (A) include 1,4-butanediol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol diacrylate, 1,7-heptanediol diacrylate, 1,8-octanediol diacrylate, and 1,9-nonanediol di(meth)acrylate.

[0024] From the viewpoint of further improving the stretchability of the image, at least one of the following is preferred for the bifunctional (meth)acrylate (A): 3-methyl-1,5-pentanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol diacrylate, 1,7-heptanediol diacrylate, 1,8-octanediol diacrylate, and 1,9-nonanediol di(meth)acrylate. From the viewpoint of further suppressing the odor of the image, at least one of the following is preferred for the bifunctional (meth)acrylate (A): 1,4-butanediol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol diacrylate, 1,7-heptanediol diacrylate, and 1,8-octanediol diacrylate.

[0025] From the viewpoint of further suppressing the odor of the image and further improving the extensibility, at least one of the group consisting of 3-methyl-1,5-pentanediol di(meth)acrylate and 1,6-hexanediol diacrylate is more preferred for the bifunctional (meth)acrylate (A), and 3-methyl-1,5-pentanediol di(meth)acrylate is particularly preferred.

[0026] The content of the bifunctional (meth)acrylate (A) relative to the total amount of ink is preferably 2% to 30% by mass, more preferably 3% to 20% by mass, and even more preferably 5% to 15% by mass.

[0027] (Benzyl (meth)acrylate (B)) The polymerizable compound in the ink of this disclosure comprises at least one benzyl (meth)acrylate (B) (i.e., at least one of benzyl acrylate and benzyl methacrylate). Benzyl (meth)acrylate (B) contributes to improving the stretchability of the resulting image.

[0028] Benzyl (meth)acrylate (B) preferably contains benzyl acrylate (i.e., benzyl acrylate alone, or a combination of benzyl acrylate and benzyl methacrylate).

[0029] The content of benzyl (meth)acrylate (B) relative to the total mass of the ink of the present disclosure is 70% by mass or less. This suppresses the odor of the image and improves the blocking resistance of the image. From the viewpoint of further suppressing image odor and / or further improving image blocking resistance, the content of benzyl (meth)acrylate (B) relative to the total mass of the ink is preferably 65% by mass or less, more preferably 60% by mass or less.

[0030] On the other hand, from the viewpoint of further improving the stretchability of an image, the content of benzyl (meth)acrylate (B) relative to the total mass of the ink is preferably 15% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more.

[0031] The ratio of the content by mass of the difunctional (meth)acrylate (A) to the content by mass of benzyl (meth)acrylate (B) (hereinafter also referred to as "content mass ratio [A / B]") is preferably 0.05 to 0.50, more preferably 0.05 to 0.40, and still more preferably 0.10 to 0.40. When the content mass ratio [A / B] is 0.05 or more, the odor of the image is further suppressed, and the blocking resistance of the image is further improved. When the content mass ratio [A / B] is 0.50 or less, the stretchability of the image is further improved.

[0032] (Average Tg of polymerizable compound) In the ink of the present disclosure, the average Tg of the polymerizable compound (that is, the weighted average value of the glass transition points (Tg) of the homopolymers of each compound contained in the polymerizable compound) is 10°C or lower. As described above, the average Tg of the polymerizable compound being 10°C or lower contributes to suppressing the odor of the image. In the ink of the present disclosure, the lower limit of the average Tg of the polymerizable compound is not particularly limited, and is, for example, -30°C.

[0033] Here, “each compound included in the polymerizable compound” means each polymerizable compound species that constitutes the “polymerizable compound” as a component of the ink of this disclosure. “Each compound included in the polymerizable compound” includes at least the aforementioned difunctional (meth)acrylate (A) and benzyl (meth)acrylate (B). “Each compound included in the polymerizable compound” may also include other compounds other than difunctional (meth)acrylate (A) and benzyl (meth)acrylate (B) (i.e., compounds containing polymerizable groups). The polymerizable group in the polymerizable compound is preferably a radical polymerizable group, more preferably an ethylenically unsaturated group, and even more preferably at least one selected from the group consisting of (meth)acryloyl groups and vinyl groups. The other polymerizable compound is preferably (meth)acrylate (C) as described later. The other compound (i.e., compound containing polymerizable groups) preferably includes (meth)acrylate (C) as described later. In this case, the other compounds may further include polymerizable compound species other than the difunctional (meth)acrylate (A), benzyl (meth)acrylate (B), and (meth)acrylate (C).

[0034] In this disclosure, the glass transition temperature (Tg) of each homopolymer of a polymerizable compound is measured by the following method. First, the compound to be measured is homopolymerized to produce a homopolymer (i.e., a homopolymer) with a weight-average molecular weight of 10,000 to 20,000. The glass transition temperature (Tg) of the produced homopolymer is measured according to the method described in JIS K7121:2012. The glass transition temperature (Tg) is measured using a differential scanning calorimeter (for example, a Shimadzu Corporation product named "DSC-60"). The weight-average molecular weight of the produced homopolymer is measured using gel permeation chromatography (GPC). In measuring the weight-average molecular weight of homopolymers, for example, HLC-8220GPC (manufactured by Tosoh Corporation) is used as the GPC, three TSKgel Super Multipore HZ-H columns (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) are used as the columns, and THF (tetrahydrofuran) is used as the eluent. The conditions are a sample concentration of 0.45 mass%, a flow rate of 0.35 ml / min, a sample injection volume of 10 μl, and a measurement temperature of 40°C, and detection is performed using a differential refractive index (RI) detector. A calibration curve is prepared using eight samples of Tosoh Corporation's "TSK Standard Polystyrene" as standard samples: "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene". The glass transition temperature of a homopolymer can vary depending on its weight-average molecular weight, but when the weight-average molecular weight is between 10,000 and 20,000, the variation is negligibly small.

[0035] In this disclosure, the average Tg of the polymerizable compound (i.e., the weighted average of the Tg of the homopolymers of each compound contained in the polymerizable compound) is determined by the following formula: Average Tg of polymerizable compound = ΣTiCi / ΣCi In the formula, Ti represents the Tg of the homopolymer of the i-th polymerizable compound species contained in the ink, and Ci represents the content (mass%) of the i-th polymerizable compound species relative to the total amount of ink.

[0036] ((Meth)acrylate (C)) From the viewpoint of further suppressing odor in an image, it is preferable that the polymerizable compound in the ink of the present disclosure contains at least one type of (meth)acrylate (C). The (meth)acrylate (C) as referred to herein is a (meth)acrylate that satisfies at least one of the following: it is a (meth)acrylate whose homopolymer has a glass transition temperature (Tg) of 0°C or lower, and it is a polyethylene glycol diacrylate having a molecular weight of 200 to 600.

[0037] -(Meth)acrylate with homopolymer glass transition temperature of 0°C or lower- When the polymerizable compound in the ink of the present disclosure contains, as (meth)acrylate (C), a (meth)acrylate whose homopolymer Tg is 0°C or lower, it is easy to suppress image odor. The reason for this is, as is clear from the formula for calculating the average Tg of polymerizable compounds, that it is easy to adjust the average Tg of the polymerizable compound to 10°C or lower.

[0038] As (meth)acrylate (C), the (meth)acrylate whose homopolymer has a glass transition temperature of 0°C or lower may be a polyethylene glycol diacrylate with a molecular weight of 200 to 600 whose homopolymer has a glass transition temperature of 0°C or lower, or may be a (meth)acrylate other than polyethylene glycol diacrylate with a molecular weight of 200 to 600 whose homopolymer has a glass transition temperature of 0°C or lower.

[0039] Examples of (meth)acrylates other than polyethylene glycol diacrylate with a molecular weight of 200 to 600 whose homopolymer has a glass transition temperature of 0°C or lower include lauryl acrylate, 4-hydroxybutyl acrylate, diethylene glycol monoethyl ether acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate, isooctyl acrylate, tetrahydrofurfuryl acrylate, trimethylolpropane E-modified triacrylate, and the like.

[0040] -Polyethylene glycol diacrylate with molecular weight 200 to 600- When the polymerizable compound in the ink of this disclosure contains polyethylene glycol diacrylate with a molecular weight of 200 to 600 as (meth)acrylate (C), the odor of the image is easily suppressed. The reason for this is not clear, but it is thought to be an effect due to the structure of the polyethylene glycol chain. The Tg of the homopolymer of polyethylene glycol diacrylate with a molecular weight of 200 to 600 may be below 0°C or above 0°C.

[0041] (Meth)acrylate (C) preferably contains polyethylene glycol diacrylate with a molecular weight of 200 to 600, from the viewpoint of further suppressing odor in the image.

[0042] When (meth)acrylate (C) contains polyethylene glycol diacrylate with a molecular weight of 200 to 600, the proportion of polyethylene glycol diacrylate with a molecular weight of 200 to 600 in (meth)acrylate (C) is preferably 30% to 100% by mass, more preferably 50% to 100% by mass, even more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass.

[0043] The molecular weight of polyethylene glycol diacrylate with a molecular weight of 200 to 600 is preferably 300 to 600, more preferably 400 to 600.

[0044] The content of (meth)acrylate (C) relative to the total amount of ink is preferably 50% by mass or less, more preferably 2% to 50% by mass, and even more preferably 3% to 40% by mass.

[0045] (Other Polymerizable Compounds) As described above, the polymerizable compounds in the inks of this disclosure may include other polymerizable compound species other than difunctional (meth)acrylate (A), benzyl (meth)acrylate (B), and (meth)acrylate (C). However, the content of other polymerizable compound species other than difunctional (meth)acrylate (A), benzyl (meth)acrylate (B), and (meth)acrylate (C) in relation to the total amount of the ink of this disclosure is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less. Furthermore, the total content of difunctional (meth)acrylate (A) and benzyl (meth)acrylate (B) in relation to the total amount of the ink of this disclosure is preferably 30% by mass or more, more preferably 40% by mass or more. Furthermore, the total content of the difunctional (meth)acrylate (A), benzyl (meth)acrylate (B), and (meth)acrylate (C) relative to the total amount of the ink of this disclosure is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

[0046] Examples of other polymerizable compounds are shown below.

[0047] Other polymerizable compounds may be monofunctional polymerizable compounds having one polymerizable group, or polyfunctional polymerizable compounds having two or more polymerizable groups.

[0048] - Monofunctional Polymerizable Compounds - Examples of monofunctional polymerizable compounds include monofunctional (meth)acrylates (excluding compounds corresponding to (meth)acrylate (C)), monofunctional (meth)acrylamides, monofunctional aromatic vinyl compounds, monofunctional vinyl ethers, and monofunctional N-vinyl compounds.

[0049] Examples of monofunctional (meth)acrylamides include (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-n-butyl(meth)acrylamide, N-t-butyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-methylol(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, and (meth)acryloylmorpholin.

[0050] Examples of monofunctional aromatic vinyl compounds include styrene, dimethylstyrene, trimethylstyrene, isopropylstyrene, chloromethylstyrene, methoxystyrene, acetoxystyrene, chlorostyrene, dichlorostyrene, bromostyrene, methyl vinylbenzoate, 3-methylstyrene, 4-methylstyrene, 3-ethylstyrene, 4-ethylstyrene, 3-propylstyrene, 4-propylstyrene, 3-butylstyrene, 4-butylstyrene, 3-hexylstyrene, 4-hexylstyrene, 3-octylstyrene, 4-octylstyrene, 3-(2-ethylhexyl)styrene, 4-(2-ethylhexyl)styrene, allylstyrene, isopropenylstyrene, butenylstyrene, octenylstyrene, 4-t-butoxycarbonylstyrene, and 4-t-butoxystyrene.

[0051] Examples of monofunctional vinyl ethers include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, t-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, lauryl vinyl ether, cyclohexyl vinyl ether, cyclohexylmethyl vinyl ether, 4-methylcyclohexylmethyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether, ethoxyethoxyethyl vinyl ether, methoxypolyethylene glycol vinyl ether, tetrahydrofurfuryl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether, chloroethoxyethyl vinyl ether, phenylethyl vinyl ether, and phenoxypolyethylene glycol vinyl ether.

[0052] Examples of monofunctional N-vinyl compounds include N-vinyl-ε-caprolactam and N-vinylpyrrolidone.

[0053] -Polyfunctional Polymerizable Compounds- Examples of polyfunctional polymerizable compounds include polyfunctional (meth)acrylate compounds (excluding compounds corresponding to (meth)acrylate (C)) and polyfunctional vinyl ethers.

[0054] Examples of polyfunctional vinyl ethers include 1,4-butanediol divinyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether, bisphenol A alkylene oxide divinyl ether, bisphenol F alkylene oxide divinyl ether, trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, and ditrimethylolpropane. Examples include trivinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol hexanyl ether, EO-added trimethylolpropane trivinyl ether, PO-added trimethylolpropane trivinyl ether, EO-added ditrimethylolpropane tetravinyl ether, PO-added ditrimethylolpropane tetravinyl ether, EO-added pentaerythritol tetravinyl ether, PO-added pentaerythritol tetravinyl ether, EO-added dipentaerythritol hexanyl ether, and PO-added dipentaerythritol hexanyl ether.

[0055] <Colorants> An ink according to one embodiment of the present disclosure contains at least one colorant.

[0056] In this disclosure, "coloring agent" means a substance that, when included in an ink, can make the ink either chromatic or achromatic.

[0057] The coloring agent may be a chromatic colorant (e.g., cyan, magenta, yellow, etc.) or an achromatic colorant (e.g., white and black).

[0058] Examples of colorants include dyes and pigments. From the viewpoint of durability such as heat resistance, light resistance, and water resistance, the colorant is preferably a pigment.

[0059] When pigments are used as colorants, they can be included in the ink as a pigment dispersion. A pigment dispersion is a liquid obtained by dispersing a pigment in a liquid medium using a dispersant, and it contains at least a pigment, a dispersant, and a liquid medium. Details of the dispersant will be described later. The liquid medium may be an organic solvent or a polymerizable compound.

[0060] As pigments, either commercially available organic pigments or inorganic pigments can be used. Examples of pigments include those described in "Dictionary of Pigments" edited by Seijiro Ito (published in 2000), "Industrial Organic Pigments" by W. Herbst and K. Hunger, and Japanese Patent Publication No. 2002-12607, Japanese Patent Publication No. 2002-188025, Japanese Patent Publication No. 2003-26978, and Japanese Patent Publication No. 2003-342503.

[0061] The colorant content is preferably 0.5% to 15% by mass, more preferably 1% to 10% by mass, and even more preferably 2% to 5% by mass, based on the total amount of ink.

[0062] <Dispersant> When a pigment is used as a coloring agent, the pigment can be contained in the ink as a pigment dispersion. The pigment can be dispersed in a liquid medium using a dispersant. A commonly known dispersant can be used. From the viewpoint of dispersion stability, the dispersant is preferably a compound that has both a hydrophilic structure and a hydrophobic structure.

[0063] Examples of dispersants include low molecular weight dispersants with a molecular weight of less than 1000, such as higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, polyoxyalkylene alkyl ether phosphates, polyoxyalkylene alkylphenyl ethers, polyoxyethylene polyoxypropylene glycol, glycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene fatty acid amides, and amine oxides.

[0064] Furthermore, as a dispersant, a high molecular weight dispersant with a molecular weight of 1000 or more obtained by copolymerizing a hydrophilic monomer and a hydrophobic monomer is also mentioned. From the viewpoint of dispersion stability, the hydrophilic monomer is preferably a dissociable group-containing monomer, and more preferably a dissociable group-containing monomer having a dissociable group and an ethylenically unsaturated bond. Examples of dissociable group-containing monomers include carboxyl group-containing monomers, sulfonic acid group-containing monomers, and phosphate group-containing monomers. From the viewpoint of dispersion stability, the hydrophobic monomer is preferably an aromatic group-containing monomer having an aromatic group and an ethylenically unsaturated bond, or an aliphatic hydrocarbon group-containing monomer having an aliphatic hydrocarbon group and an ethylenically unsaturated bond. The polymer may be either a random copolymer or a block copolymer.

[0065] The dispersant may be a commercially available product. Examples of commercially available products include DISPERBYK-101, DISPERBYK-102, DISPERBYK-103, DISPERBYK-106, DISPERBYK-110, DISPERBYK-111, DISPERBYK-161, DISPERBYK-162, DISPERBYK-163, DISPERBYK-164, DISPERBYK-166, DISPERBYK-167, DISPERBYK-168, DISPERBYK-170, DISPERBYK-171, DISPERBYK-174, DISPERBYK-182 (all manufactured by BYK Chemie); and Examples include SOLSPERSE 3000, SOLSPERSE 5000, SOLSPERSE 9000, SOLSPERSE 12000, SOLSPERSE 13240, SOLSPERSE 13940, SOLSPERSE 17000, SOLSPERSE 22000, SOLSPERSE 24000, SOLSPERSE 26000, SOLSPERSE 28000, SOLSPERSE 32000, SOLSPERSE 36000, SOLSPERSE 39000, SOLSPERSE 41000, and SOLSPERSE 71000 (all manufactured by Lubrizol).

[0066] Known dispersion devices can be used to disperse pigments, including, for example, ball mills, sand mills, bead mills, roll mills, jet mills, paint shakers, attritors, ultrasonic dispersers, and dispersers.

[0067] From the viewpoint of dispersion stability, the content of the dispersant relative to the pigment content in the ink is preferably 0.05 to 1.0 by mass, and more preferably 0.1 to 0.5.

[0068] <Surfactants> The inks of this disclosure may contain at least one surfactant.

[0069] Examples of surfactants include silicone-based surfactants, acetylene glycol-based surfactants, and polyoxyethylene alkyl ether-based surfactants.

[0070] The inks of this disclosure preferably contain at least one silicone-based surfactant. The presence of a silicone-based surfactant reduces the surface tension of the ink, improving its wettability to the substrate or the underlayer formed on the substrate. As a result, the image quality of the resulting image is improved.

[0071] The surfactant content is preferably 0.01% to 5% by mass, and more preferably 0.05% to 2% by mass, relative to the total amount of ink.

[0072] <Polymerization Initiator> The inks of this disclosure may contain at least one polymerization initiator. The polymerization initiator is preferably a radical polymerization initiator that generates radicals.

[0073] Examples of radical polymerization initiators include alkylphenone compounds, acylphosphine compounds, aromatic onium salt compounds, organic peroxides, thio compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having carbon-halogen bonds, and alkylamine compounds.

[0074] In particular, the polymerization initiator is preferably at least one selected from the group consisting of acylphosphine compounds and thio compounds, more preferably at least one selected from the group consisting of acylphosphine oxide compounds and thioxanthone compounds, and even more preferably a combination of acylphosphine oxide compounds and thioxanthone compounds.

[0075] Examples of acylphosphine oxide compounds include monoacylphosphine oxide compounds and bisacylphosphine oxide compounds.

[0076] Examples of monoacylphosphine oxide compounds include isobutyryldiphenylphosphine oxide, 2-ethylhexanoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, o-toluyldiphenylphosphine oxide, p-t-butylbenzoyldiphenylphosphine oxide, 3-pyridylcarbonyldiphenylphosphine oxide, acryloyldiphenylphosphine oxide, benzoyldiphenylphosphine oxide, pivaloylphenylphosphine vinyl ester, and Examples include dipoylbisdiphenylphosphine oxide, pivaloyldiphenylphosphine oxide, p-toluyldiphenylphosphine oxide, 4-(t-butyl)benzoyldiphenylphosphine oxide, terephthaloylbisdiphenylphosphine oxide, 2-methylbenzoyldiphenylphosphine oxide, versatoyldiphenylphosphine oxide, 2-methyl-2-ethylhexanoyldiphenylphosphine oxide, 1-methylcyclohexanoyldiphenylphosphine oxide, methyl pivaloylphenylphosphinate, and isopropyl pivaloylphenylphosphinate.

[0077] Examples of bisacylphosphine oxide compounds include bis(2,6-dichlorobenzoyl)phenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-ethoxyphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2-naphthylphosphine oxide, and bis(2,6-dichlorobenzoyl (L)-1-naphthylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-chlorophenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2,4-dimethoxyphenylphosphine oxide, bis(2,6-dichlorobenzoyl)decylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-octylphenylphosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, bis(2,4,6-trimethylbenzoyl)-2, 5-dimethylphenylphosphine oxide, bis(2,6-dichloro-3,4,5-trimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,6-dichloro-3,4,5-trimethoxybenzoyl)-4-ethoxyphenylphosphine oxide, bis(2-methyl-1-naphthoyl)-2,5-dimethylphenylphosphine oxide, bis(2-methyl-1-naphthoyl)-4-ethoxyphenylphosphine oxide, bis(2-methyl-1-naphthoyl)-2- Examples include naphthylphosphine oxide, bis(2-methyl-1-naphthoyl)-4-propylphenylphosphine oxide, bis(2-methyl-1-naphthoyl)-2,5-dimethylphenylphosphine oxide, bis(2-methoxy-1-naphthoyl)-4-ethoxyphenylphosphine oxide, bis(2-chloro-1-naphthoyl)-2,5-dimethylphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0078] Thioxanthone compounds include thioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dichlorothioxanthone, 2-dodecylthioxanthone, 2,4-diethylthioxanthone, 2,4-dimethylthioxanthone, 1-methoxycarbonylthioxanthone, 2-ethoxycarbonylthioxanthone, 3-(2-methoxyethoxycarbonyl)thioxanthone, and 4-butoxycarbonyl Bonylthioxanthone, 3-butoxycarbonyl-7-methylthioxanthone, 1-cyano-3-chlorothioxanthone, 1-ethoxycarbonyl-3-chlorothioxanthone, 1-ethoxycarbonyl-3-ethoxythioxanthone, 1-ethoxycarbonyl-3-aminothioxanthone, 1-ethoxycarbonyl-3-phenylsulfurylthioxanthone, 3,4-di[2-(2-methoxyethoxy)ethoxycarbonyl]thioxanthone, 1-E Toxycarbonyl-3-(1-methyl-1-morpholinoethyl)thioxanthone, 2-methyl-6-dimethoxymethylthioxanthone, 2-methyl-6-(1,1-dimethoxybenzyl)thioxanthone, 2-morpholinomethylthioxanthone, 2-methyl-6-morpholinomethylthioxanthone, n-allylthioxanthone-3,4-dicarboximide, n-octylthioxanthone-3,4-dicarboximide, N-(1,1,3,3-tetra) Examples include methylbutyl)thioxanthone-3,4-dicarboximide, 1-phenoxythioxanthone, 6-ethoxycarbonyl-2-methoxythioxanthone, 6-ethoxycarbonyl-2-methylthioxanthone, thioxanthone-2-polyethylene glycol ester, and 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthone-2-yloxy)-N,N,N-trimethyl-1-propaneaminium chloride.

[0079] The thioxanthone compound may be a commercially available product. Examples of commercially available products include Lambson's SPEEDCURE series (e.g., SPEEDCURE 7010, SPEEDCURE CPTX, SPEEDCURE ITX, etc.).

[0080] From the viewpoint of further reducing odor, an ink according to one embodiment of the present disclosure preferably contains at least one selected from the group consisting of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide as a polymerization initiator, and more preferably contains phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide.

[0081] Furthermore, from the viewpoint of further reducing odor, the total content of at least one selected from the group consisting of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide (preferably the total content of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide) is preferably 3.5% by mass or more, and more preferably 5% by mass or more, based on the total amount of ink. The upper limit of the above total content is not particularly limited, but for example, it is 10% by mass.

[0082] Furthermore, from the viewpoint of further reducing odor, the ink of this disclosure preferably contains a compound having two or more thioxanthone skeletons in its molecule as a polymerization initiator.

[0083] The content of compounds having two or more thioxanthone skeletons in the molecule is preferably 1% to 10% by mass, and more preferably 2% to 8% by mass, based on the total amount of ink.

[0084] <Polymerization Inhibitors> The inks of this disclosure may contain at least one polymerization inhibitor.

[0085] Examples of polymerization inhibitors include hydroquinone compounds, phenothiazines, catechols, alkylphenols (e.g., dibutylhydroxytoluene), alkylbisphenols, zinc dimethyldithiocarbamate, copper dimethyldithiocarbamate, copper dibutyldithiocarbamate, copper salicylate, thiodipropionates, mercaptobenzimidazole, phosphites, nitrosamine compounds, hindered amine compounds, and nitroxyl radicals. Examples of nitrosamine compounds include N-nitroso-N-phenylhydroxylamine aluminum salt and N-nitroso-N-phenylhydroxylamine. Among these, N-nitroso-N-phenylhydroxylamine aluminum salt is preferred as the nitrosamine compound.

[0086] From the viewpoint of improving the long-term stability of the ink, the content of the polymerization inhibitor is preferably 0.05% to 1% by mass relative to the total amount of ink.

[0087] <Additives> The inks of this disclosure may optionally contain additives such as co-sensitizers, ultraviolet absorbers, antioxidants, fade inhibitors, conductive salts, solvents, and basic compounds.

[0088] <Physical Properties> The viscosity of the ink is preferably 0.5 mPa·s to 50 mPa·s, more preferably 5 mPa·s to 40 mPa·s, preferably 7 mPa·s to 35 mPa·s, and even more preferably 8 mPa·s to 30 mPa·s. The viscosity is measured at 25°C using a viscometer, for example, using a TV-22 viscometer manufactured by Toki Sangyo Co., Ltd.

[0089] The surface tension of the ink is preferably 60 mN / m or less, and more preferably 23 mN / m to 26 mN / m.

[0090] When the surface tension is between 23 mN / m and 26 mN / m, it is possible to suppress the repulsion of the overcoat liquid used to form the overcoat layer on the image surface when applying an overcoat layer on the image. The surface tension is measured at 25°C using a surface tensimeter, for example, by the plate method using an automatic surface tensimeter (product name "CBVP-Z") manufactured by Kyowa Interface Science Co., Ltd.

[0091] [Image Recording Method] An image recording method according to one embodiment of the present disclosure includes the steps of: applying the above-mentioned ink to a substrate using an inkjet recording method (hereinafter also referred to as the "ink application step") and irradiating the applied ink with active energy rays to record an image (hereinafter also referred to as the "active energy ray irradiation step").

[0092] (Ink Application Process) - Substrate - The type of substrate is not particularly limited, and commonly known substrates can be used. Examples of substrates include metals, glass, quartz, and plastics. Examples of resins constituting the plastic include cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, acrylic resin, chlorinated polyolefin resin, polyethersulfone resin, polyethylene terephthalate (PET), polyethylene naphthalate, nylon, polyethylene, polystyrene, polypropylene, polycycloolefin resin, polyimide resin, polycarbonate resin, and polyvinyl acetal. The plastic may be a film containing only one of these resins, or a film containing a mixture of two or more of these resins.

[0093] The thickness of the substrate is not particularly limited, and can range from 1 μm to 10 mm, for example.

[0094] In particular, the ink of this disclosure has excellent impact resistance and blocking resistance, so it is preferable to use metal or plastic as the substrate, and more preferably metal. After recording an image on a flat metal substrate, a molded metal body (for example, a food can, beverage can, aerosol can, etc.) can be obtained by carrying out the molding process described later. In the image recording method of this disclosure, the image may also be recorded on the substrate after molding.

[0095] -Underlayment- When using metal as the base material, it is preferable to apply an underlayment on the base material first, and then apply the ink to the underlayment.

[0096] Examples of undercoat layers include anchor coat layers, base coat layers, and white coat layers. If the undercoat layer is a white coat layer, it is desirable that it contains titanium dioxide as a pigment.

[0097] The method for forming the base layer is not particularly limited and may include, for example, applying an ink for forming a base layer containing a crosslinkable resin, or laminating a film containing a crosslinkable resin. The thickness of the base layer is not particularly limited and can be adjusted as appropriate.

[0098] The base layer preferably contains a crosslinkable resin. The crosslinkable resin may be a thermally crosslinkable resin that is crosslinked by heat, or an active energy ray crosslinkable resin that is crosslinked by active energy rays.

[0099] Examples of crosslinkable resins include (meth)acrylic resins such as polyacrylonitrile, polymethyl acrylate, and polymethyl methacrylate; polyester resins such as polyethylene terephthalate, isophthalic acid-modified polyethylene terephthalate, and polyethylene naphthalate; epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, and cresol novolac epoxy resin; vinyl resins such as polyvinyl acetate and polyvinyl chloride; urethane resins such as diphenylmethane diisocyanate-polyethylene glycol copolymer; and amino resins such as melamine resin, urea resin, and benzoguanamine resin. The crosslinkable resin may be present as a single type or as a combination of two or more types.

[0100] The base layer may further contain resins other than crosslinkable resins, crosslinking agents, crosslinking accelerators, various additives, etc.

[0101] The method for forming the base layer can be appropriately selected depending on the crosslinkable resin. When the crosslinkable resin is a thermocrosslinkable resin, it is preferable to apply the base layer forming ink to the substrate and then bake it. The baking temperature is, for example, 140°C to 230°C. The baking time is, for example, 1 minute to 60 minutes.

[0102] Furthermore, if the crosslinkable resin is an active energy ray crosslinkable resin, it is preferable to apply an underlayer-forming ink to the substrate before irradiating it with active energy rays.

[0103] - Inkjet Recording Methods - The inkjet recording method is not particularly limited as long as it is a method capable of recording an image, and known methods can be used. Examples of inkjet recording methods include a charge control method that uses electrostatic attraction to eject ink, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electrical signal into an acoustic beam, irradiates the ink with it, and ejects the ink using the radiation pressure, and a thermal inkjet (bubble jet®) method that heats the ink to form bubbles and uses the resulting pressure.

[0104] Inkjet heads used in inkjet recording methods include a shuttle method, which uses a short serial head and records while scanning the head in the width direction of the substrate, and a line method, which uses a line head in which recording elements are arranged to cover the entire area of ​​one side of the substrate.

[0105] In the line method, the substrate is scanned in a direction intersecting the arrangement direction of the recording elements, allowing for pattern formation across the entire surface of the substrate. This eliminates the need for a transport system such as a carriage that scans the short head. Furthermore, the line method eliminates the need for complex scanning control of the carriage and the substrate; only the substrate moves, enabling faster recording speeds compared to the shuttle method.

[0106] The amount of ink droplets ejected from the inkjet head is preferably 1 pL (picoliters) to 100 pL, more preferably 3 pL to 80 pL, and even more preferably 3 pL to 50 pL.

[0107] (Activated Energy Ray Irradiation Process) Examples of activated energy rays include gamma rays, beta rays, electron beams, ultraviolet rays, and visible light. Among these, ultraviolet rays are preferred as the activated energy ray.

[0108] The peak wavelength of ultraviolet light is preferably, for example, 200 nm to 405 nm, more preferably 250 nm to 400 nm, and even more preferably 300 nm to 400 nm.

[0109] For ultraviolet irradiation, various lasers such as mercury lamps, gas lasers, and solid-state lasers are mainly used as light sources, and discharge lamps such as mercury lamps, metal halide lamps, and ultraviolet fluorescent lamps are widely known. In addition, semiconductor light sources such as UV-LEDs (ultraviolet light-emitting diodes) and UV-LDs (ultraviolet laser diodes) are small, have a long lifespan, are highly efficient, and are low cost, and are expected to be used as light sources for ultraviolet irradiation. Among these, metal halide lamps, high-pressure mercury lamps, medium-pressure mercury lamps, low-pressure mercury lamps, or UV-LEDs are preferred as light sources for ultraviolet irradiation.

[0110] In this disclosure, polymerizing only a portion of the polymerizable monomers in the ink is also referred to as "preliminary curing," and irradiation with active energy rays for preliminary curing is also referred to as "pinning exposure." In this disclosure, polymerizing substantially all of the polymerizable compounds in the ink is also referred to as "full curing," and irradiation with active energy rays for full curing is also referred to as "full exposure."

[0111] In the active energy ray irradiation process, it is preferable to pre-cur the ink before full curing. Specifically, it is preferable to apply the ink, perform pinning exposure on the ink, and finally perform full exposure.

[0112] The reaction rate of the ink after pinning exposure is preferably 10% to 80%.

[0113] Here, the reaction rate of the ink refers to the polymerization rate of the polymerizable compounds contained in the ink, as determined by high-performance liquid chromatography.

[0114] A reaction rate of 10% or more in the ink suppresses insufficient dot spreading, resulting in improved granularity of the final image.

[0115] Furthermore, by keeping the ink reaction rate below 80%, droplet interference between ink dots is suppressed, resulting in improved image quality in the final product.

[0116] The ink reaction rate is preferably 15% or higher, from the viewpoint of further improving the granularity of the final image.

[0117] From the viewpoint of further improving the image quality of the final image obtained, the ink reaction rate is preferably 75% or less, more preferably 50% or less, preferably 40% or less, more preferably 30% or less, and even more preferably 25% or less.

[0118] The reaction rate of the ink after exposure is preferably between 80% and 100%, more preferably between 85% and 100%, and even more preferably between 90% and 100%. When the reaction rate exceeds 80%, adhesion is further improved.

[0119] The reaction rate of the ink is determined by the following method. Prepare a substrate that has been subjected to operations up to the completion of irradiation of the ink with active energy rays. A sample piece of 20 mm × 50 mm size (hereinafter referred to as post-irradiation sample piece) is cut out from the region of the substrate where the ink film is present. The cut-out post-irradiation sample piece is immersed in 10 mL of THF (tetrahydrofuran) for 24 hours to obtain an eluate in which the ink is eluted. With respect to the obtained eluate, the amount of the polymerizable compound (hereinafter referred to as "post-irradiation monomer amount X1") is determined by high performance liquid chromatography. Separately, the same operation as described above is carried out except that active energy rays are not irradiated onto the ink on the substrate, and the amount of the polymerizable compound (hereinafter referred to as "unirradiated monomer amount X1") is determined. Based on the post-irradiation monomer amount X1 and the unirradiated monomer amount X1, the reaction rate (%) of the ink is determined by the following formula. Reaction rate of ink (%) = ((Unirradiated monomer amount X1 - Post-irradiation monomer amount X1) / Unirradiated monomer amount X1) × 100

[0120] From the viewpoint of more easily achieving the above-described ink reaction rate, the exposure amount of active energy rays for pinning exposure is preferably 10 mJ / cm ２ to 100 mJ / cm ２ , and more preferably 20 mJ / cm ２ to 60 mJ / cm ２ .

[0121] From the viewpoint of completely curing the ink, the exposure amount of active energy rays for the main exposure is preferably 50 mJ / cm ２ to 1000 mJ / cm ２ , and more preferably 200 mJ / cm ２ to 800 mJ / cm ２ .

[0122] In the main exposure, from the viewpoint of improving adhesion to the substrate, it is preferable to irradiate active energy rays in an atmosphere with an oxygen concentration of less than 1% by volume. The oxygen concentration is more preferably 0.5% by volume or less, and still more preferably 0.3% by volume or less.

[0123] In the active energy ray irradiation process, from the viewpoint of image quality, it is preferable to irradiate with active energy rays within 0.1 to 5 seconds from the time the ink lands. When performing both pinning exposure and main exposure, it is preferable to irradiate with active energy rays for pinning exposure within 0.1 to 5 seconds from the time the ink lands. More preferably, the time from the time the ink lands until the irradiation of active energy rays (or, in the case of performing both pinning exposure and main exposure, the active energy rays for pinning exposure) is within 0.2 to 1 second.

[0124] (Overcoat layer formation step) The image recording method of the present disclosure may further include a step of forming an overcoat layer on the recorded image.

[0125] By providing an overcoat layer, damage to the image can be suppressed when the molding process described later is performed.

[0126] For the overcoat liquid used to form the overcoat layer, commonly known transparent paints can be used. Examples of known transparent paints include those containing thermosetting resins such as polyester resin, acrylic resin, and epoxy resin; curing agents such as amino resin, phenolic resin, and isocyanate resin; and lubricants such as paraffin wax, polyethylene wax, and silicone wax.

[0127] The overcoat layer is formed, for example, by applying an overcoat solution to the image and then baking it. The baking temperature is, for example, 140°C to 230°C. The baking time is, for example, 1 minute to 60 minutes.

[0128] [Method for Manufacturing a Molded Article] A method for manufacturing a molded article, which is one embodiment of the present disclosure, includes the steps of: applying the above-mentioned ink to a substrate using an inkjet recording method (hereinafter also referred to as the "ink application step"); irradiating the applied ink with active energy rays to record an image (hereinafter also referred to as the "active energy ray irradiation step"); and molding the substrate on which the image has been recorded to manufacture a molded article (hereinafter also referred to as the "molding step").

[0129] The ink application step and the active energy ray irradiation step in a method for manufacturing a molded article, which is one embodiment of the present disclosure, are the same as the ink application step and the active energy ray irradiation step in an image recording method, which is one embodiment of the present disclosure, except as shown below.

[0130] In the ink application process, the substrate is not particularly limited as long as it is a moldable substrate. The substrate is preferably metal or plastic, and more preferably metal.

[0131] (Molding Process) The molding method is not particularly limited and includes, for example, bending, vacuum forming, extrusion, injection molding, compression molding, blow molding, etc. The shape of the molded body is not particularly limited and is set as appropriate depending on the application.

[0132] The inks disclosed herein exhibit excellent blocking resistance. For example, even if images are recorded on flat metal substrates and then stacked before the molding process, the images are less likely to peel off. Therefore, it is possible to store the metal substrates with images recorded on them before the molding process, and the molding process can be carried out at the desired timing.

[0133] The ink disclosed herein has excellent stretchability. Therefore, image cracking is less likely to occur even during the molding process. As a result, a molded article with excellent decorative properties can be obtained.

[0134] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to the following examples unless it exceeds the spirit of the disclosure.

[0135] [Examples 1 to 10, Comparative Examples 1 to 4] <Preparation of Cyan Ink> In preparing the cyan ink, first, a cyan pigment dispersion is prepared.

[0136] (Preparation of Cyanide Pigment Dispersion) 40 parts by mass of cyanide pigment, 20 parts by mass of BYK168 as a dispersant, and 40 parts by mass of DVE-3 as a dispersion medium are placed in a disperser motor mill M50 (manufactured by Eiger Co., Ltd.), and the mixture is dispersed using zirconia beads with a diameter of 0.65 mm at a peripheral speed of 9 m / s for 4 hours to obtain a cyanide pigment dispersion. The details of the components contained in the cyanide pigment dispersion are as follows.

[0137] • Cyanide pigment: C.I. Pigment Blue 15:4 (Product name "Heliogen® Blue D 7110 F", Sun Chemical (manufactured by DIC Corporation)) • BYK168: Amine-based polymer dispersant (Product name "DISPERBYK-168", manufactured by BYK Corporation) • DVE-3: Triethylene glycol divinyl ether (Note: Also applies to other polymerizable compounds)

[0138] (Preparation of Cyan Ink) The cyan pigment dispersion obtained above is mixed with the components other than those in the cyan pigment dispersion (see Tables 1 and 2). The resulting mixture is stirred for 20 minutes at 5000 revolutions per minute at 25°C using a mixer (product name "L4R", manufactured by Silverson) to obtain cyan ink (hereinafter also simply referred to as ink) having the composition shown in Tables 1 and 2. In the ink composition shown in Tables 1 and 2, the cyan pigment, DVE-3, and BYK168 are components of the cyan pigment dispersion.

[0139] The details of each component listed in Tables 1 and 2 are as follows:

[0140] - Difunctional (meth)acrylates (A) - Difunctional (meth)acrylates (A) are difunctional (meth)acrylates having linear or branched alkylene groups. • BDDA (C4): 1,4-butanediol diacrylate (a difunctional acrylate having a linear alkylene group with 4 carbon atoms) • 3MPDDA (C6): 3-methyl-1,5-pentanediol diacrylate (a difunctional acrylate having a branched alkylene group with 6 carbon atoms) • NDDA (C9): 1,9-nonanediol diacrylate (a difunctional acrylate having a linear alkylene group with 9 carbon atoms)

[0141] - Benzyl (meth)acrylate (B) - • BzA: Benzyl acrylate

[0142] - Other polymerizable compounds - • DVE-3: Triethylene glycol divinyl ether (dispersion medium in cyanide pigment dispersions)

[0143] -Coloring agent- • Cyan pigment: Coloring agent in the cyan pigment dispersion mentioned above

[0144] - Dispersant - BYK168: Dispersant in the aforementioned cyanide pigment dispersion.

[0145] -Polymerization Initiators- ・Omni819: Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (product name "Omnirad 819", manufactured by IGM Resins B.V.) ・Omni910: Polyethylene glycol di{β-4-[4-(2-dimethylamino-2-benzyl)butanoylphenyl]piperazine} (product name "Omnipol 910", manufactured by IGM Resins B.V.) ・Speedcure7010: 1,3-di({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[1-methylethylene)]}oxymethyl)propane (manufactured by Lambson)

[0146] - Polymerization inhibitors - BHT: Dibutylhydroxytoluene

[0147] - Surfactants - BYK3753: Silicone-based surfactant (surface modifier) ​​(Product name "BYK-3753", manufactured by BYK Corporation)

[0148] <Image Record> (Base Layer Formation Process) Base layer formation ink (product name "WA38", acrylic epoxy white base coat, manufactured by DIC Graphics Co., Ltd.) is applied to the substrate (tin-free steel plate (product name "Cansuper SR tin-free steel", manufactured by Nippon Steel Corporation)) at a rate of 70 mg / 100 cm ２ The surface is then painted. Afterwards, it is baked at 190°C for 5 minutes to form a base layer on the substrate.

[0149] (Ink application process, active energy ray irradiation process) An inkjet recording device equipped with an inkjet head (product name "Samba G3L", manufactured by FUJIFILM Dimatix) and the above-mentioned cyan ink is used to record a cyan image as follows. Specifically, on a 5 cm x 5 cm rectangular area in the underlayer formed on the substrate, a resolution of 1200 x 1200 dpi (dots per inch) and an ink quantity of 12 g / m² are recorded. ２Under these conditions, cyan ink is applied to create a 100% solid image. Next, the applied cyan ink is exposed to 200 mJ / cm using an LED light source attached to the inkjet recording device (a UV-LED irradiator with a peak wavelength of 385 nm (product name "G4B", manufactured by Kyocera)). ２ ~1000mJ / cm ２ A cyan image is obtained by irradiating with ultraviolet light at the specified exposure level. In this way, an image recording material having a layered structure represented as cyan image / underlayment / substrate is obtained.

[0150] <Evaluation> The following evaluation was performed on the obtained image recordings. The results are shown in Tables 1 and 2.

[0151] (Image Odor) A 5cm x 5cm portion of the image recording is cut out as an odor evaluation sample. The obtained odor evaluation sample is placed in a 30cm x 30cm zip-lock plastic bag and left at room temperature (25°C) for 24 hours. After the period, the zip is opened and 10 evaluators evaluate the odor of the image according to the evaluation criteria below. In detail, first, each evaluator evaluates the odor according to ranks A to E in the evaluation criteria below. Next, a score of 5 to 1 point is assigned to ranks A to E, and the average score of the 10 evaluators is calculated. The obtained average score is rounded to the nearest whole number, and the rank A to E corresponding to the obtained value is used as the evaluation result for the odor of the image.

[0152] - Image Odor Evaluation Criteria - A: Almost odorless. B: Slight odor, but hardly noticeable. C: Some odor, but not at an unpleasant level. D: Strong odor. E: Very strong odor.

[0153] (Image Stretchability) A 5cm x 2cm area from a 5cm x 5cm image portion of the image recording is cut out as a stretchability evaluation sample. The cut-out stretchability evaluation sample is stretched in the direction of the 5cm length of the sample using the stretching machine described below, under the conditions described below, until the stretchability evaluation sample breaks. At this time, the length of the stretchability evaluation sample before stretching and the length at the time of breakage are measured, and the stretching rate (%) of the stretchability evaluation sample is calculated using the formula below. Based on the obtained stretching rate (%), the stretchability of the image is evaluated according to the evaluation criteria below. In the evaluation criteria below, rank A represents the best image stretchability. Machine used: Tensilon (manufactured by Shimadzu Corporation) Conditions: Tensile speed 50 mm / min Elongation (%) = {(Length at break - Length before stretching) / Length before stretching} × 100 (Example: If it breaks at 10 cm, {(10 cm - 5 cm) / 5 cm} × 100 = 100% elongation is calculated.)

[0154] - Criteria for evaluating image stretchability - A: Stretchability of 95% or more B: Stretchability of 80% or more but less than 95% C: Stretchability of 65% or more but less than 80% D: Stretchability of 50% or more but less than 65% E: Stretchability of less than 50%

[0155] (Image Blocking Resistance) A substrate (tin-free steel plate (product name "Cansuper SR Tin-Free Steel", manufactured by Nippon Steel Corporation)) is brought into contact with a 5 cm x 5 cm image on an image recording, and the load is 0.5 ton / m ２ Apply the following weight. Store the image recording in this state for 24 hours under storage conditions of 10°C, 25°C, 30°C, and 45°C. After storage, at 25°C, separate the image recording from the substrate, visually inspect the image on the recording, and check for any peeling of the image. Based on the results, evaluate the image's blocking resistance according to the following evaluation criteria. In the following evaluation criteria, rank A represents the best image blocking resistance.

[0156] - Criteria for evaluating image blocking resistance - A: No image peeling at storage conditions of 10°C, 25°C, 30°C, and 45°C. B: Image peeling occurs at storage conditions of 45°C, but no image peeling occurs at storage conditions of 10°C, 25°C, and 30°C. C: Image peeling occurs at storage conditions of 30°C and 45°C, but no image peeling occurs at storage conditions of 10°C and 25°C. D: Image peeling occurs at storage conditions of 25°C, 30°C, and 45°C, but no image peeling occurs at storage conditions of 10°C. E: Image peeling occurs at storage conditions of 10°C, 25°C, 30°C, and 45°C.

[0157]

[0158]

[0159] As shown in Tables 1 and 2, in each example where the ink contains a polymerizable compound and a colorant, and the polymerizable compound contains a difunctional (meth)acrylate (A) having linear or branched alkylene groups and a benzyl (meth)acrylate (B), and the content of benzyl (meth)acrylate (B) relative to the total amount of ink is 70% by mass or less, and the average Tg of the polymerizable compound (i.e., the weighted average value of the glass transition temperatures of the homopolymers of each compound contained in the polymerizable compound) is 10°C or less, an image with excellent stretchability and blocking resistance and suppressed odor can be obtained. In contrast, in Comparative Example 1, in which the ink does not contain difunctional (meth)acrylate (A), the blocking resistance of the image decreases. The odor of the image also becomes stronger in Comparative Example 1. Furthermore, in Comparative Example 2, in which the ink does not contain benzyl (meth)acrylate (B), the stretchability of the image decreases. The blocking resistance of the image also decreases in Comparative Example 2. Furthermore, in Comparative Example 3, where the benzyl (meth)acrylate (B) content relative to the total amount of ink exceeds 70% by mass, the odor of the image becomes stronger. In addition, the blocking resistance of the image also decreases in Comparative Example 3. Furthermore, in Comparative Example 4, where the average Tg of the polymerizable compounds in the ink exceeds 10°C, the odor of the image becomes stronger. In addition, the stretchability of the image also decreases in Comparative Example 4.

[0160] From the results of Examples 1 to 10, it can be seen that when the polymerizable compound in the ink contains (meth)acrylate (C) (i.e., (meth)acrylate (C) that satisfies at least one of the following conditions: that it is a (meth)acrylate with a glass transition temperature of 0°C or lower, and that it is a polyethylene glycol diacrylate with a molecular weight of 200 to 600) (Examples 1 to 9), the odor of the image is further suppressed.

[0161] The results from Examples 5 and 7 show that when (meth)acrylate (C) contains polyethylene glycol diacrylate with a molecular weight of 200 to 600 (Example 5), the odor of the image is further suppressed and the blocking resistance of the image is further improved.

[0162] The results from Examples 5 and 6 show that when the bifunctional (meth)acrylate (A) contains 3-methylpentanediol diacrylate (3MPDDA(C6)) (Example 5), the odor in the image is further suppressed.

[0163] From the results of Examples 3 and 9, it can be seen that Example 3, in which the "content mass ratio [A / B]", which is the ratio of the content mass of bifunctional (meth)acrylate (A) to the content mass of benzyl (meth)acrylate (B), is 0.05 to 0.40, exhibits superior image stretchability compared to Example 9, in which the "content mass ratio [A / B]" is greater than 0.40.

[0164] [Example 101] Prepare ink C1 (cyan ink), ink M1 (magenta ink), ink Y1 (yellow ink), ink K1 (black ink), and ink W1 (white ink).

[0165] For ink C1, prepare the cyan ink used in Example 1.

[0166] Ink M1 (magenta ink), ink Y1 (yellow ink), ink K1 (black ink), and ink W1 (white ink) are prepared in the same manner as the preparation of the cyan ink in Example 1, except that the cyan pigment is replaced with magenta pigment, yellow pigment, black pigment, and white pigment, respectively. Details of the magenta pigment, yellow pigment, black pigment, and white pigment are as follows.

[0167] - Magenta pigment: C.I. Pigment RED 122, product name "TRM-33", manufactured by Dainichi Seika Co., Ltd. - Yellow pigment: C.I. Pigment Yellow 185, product name "Paliotoll Yellow D 1155", manufactured by Sun Chemical (DIC) - Black pigment: Carbon black, product name "MOGUL E", manufactured by CABOT - White pigment: Titanium dioxide, product name "KRONOS 2300", manufactured by KRONOS

[0168] <Image Recording (Two-Color, Two-Layer Image)> An image recording having a two-color, two-layer image is obtained in the same manner as the image recording in Example 1, except for the following changes. - Changes - Instead of recording a cyan image with cyan ink, the following operation is performed. A yellow image is recorded as the first layer on a base layer formed on the substrate by applying ink Y1 and irradiating with ultraviolet light, and a magenta image is recorded as the second layer on the recorded yellow image by applying ink M1 and irradiating with ultraviolet light. The amount of ink Y1 and ink M1 applied is 7.2 g / m² each. ２ The conditions for applying ink Y1 and ink M1, respectively, to the ink and irradiating them with ultraviolet light are the same as those for applying cyan ink and irradiating them with ultraviolet light in Example 1, except for the amount applied.

[0169] <Image Recording (3-Color 3-Layer Image)> An image recording having a 3-color 3-layer image is obtained in the same manner as the image recording in Example 1, except that the following points are changed. - Changes - Instead of recording a cyan image with cyan ink, the following operation is performed. A yellow image is recorded as the first layer on a base layer formed on the substrate by applying ink Y1 and irradiating with ultraviolet light, and a magenta image is recorded as the second layer on the recorded yellow image by applying ink M1 and irradiating with ultraviolet light. The amount of ink Y1 and ink M1 applied is 4.8 g / m² each. ２The conditions for applying ink Y1 and ink M1, respectively, and for irradiating with ultraviolet light are the same as those for applying cyan ink and irradiating with ultraviolet light in Example 1, except for the amount applied. A third layer of ink C1 is applied to the magenta image, which is the second layer obtained with ink M1, at an amount of 4.8 g / m². ２ The ink C1 is applied, and the applied ink C1 is irradiated with ultraviolet light to obtain the third layer, which is a cyan image. The conditions for applying the ink C1 and irradiating with ultraviolet light are the same as those for applying the cyan ink and irradiating with ultraviolet light in Example 1, except for the amount applied.

[0170] <Image Recording (4-Color, 4-Layer Image)> An image recording having a 4-color, 4-layer image is obtained in the same manner as in Example 1, except for the following changes. - Changes - Instead of recording a cyan image with cyan ink, the following operation is performed. A yellow image is recorded as the first layer on a base layer formed on the substrate by applying ink Y1 and irradiating with ultraviolet light, and a magenta image is recorded as the second layer on the recorded yellow image by applying ink M1 and irradiating with ultraviolet light. The amount of ink Y1 and ink M1 applied is 3.6 g / m² each. ２ The conditions for applying ink Y1 and ink M1, respectively, to the ink and irradiating with ultraviolet light are the same as those for applying cyan ink and irradiating with ultraviolet light in Example 1, except for the amount applied. A third layer of ink C1 is applied to the magenta image, which is the second layer obtained with ink M1, at an amount of 3.6 g / m². ２ The ink C1 is applied, and the applied ink C1 is irradiated with ultraviolet light to obtain the third layer, a cyan image. The conditions for applying ink C1 and irradiating with ultraviolet light are the same as those for applying cyan ink and irradiating with ultraviolet light in Example 1, except for the amount applied. On top of the third layer, the cyan image, ink K1 is applied as the fourth layer at an amount of 3.6 g / m². ２ The ink K1 is applied, and the applied ink K1 is irradiated with ultraviolet light to obtain the fourth layer, which is a black image. The conditions for applying ink K1 and irradiating with ultraviolet light are the same as those for applying cyan ink and irradiating with ultraviolet light in Example 1, except for the amount applied.

[0171] <Image Recording (5-Color, 5-Layer Image)> In the above-mentioned image recording (4-color, 4-layer image), a white image using ink W1 is added between the base layer and the yellow image to obtain a 5-color, 5-layer image. For recording the white image, ink W1 is applied at a rate of 6.8 g / m² onto the base layer before the application of ink Y1. ２ The process involves applying the ink W1 and then irradiating the applied ink W1 with ultraviolet light. The conditions for applying the ink W1 and irradiating it with ultraviolet light are the same as those for applying the cyan ink and irradiating it with ultraviolet light in Example 1, except for the amount applied.

[0172] Using each obtained image recording, the odor, stretchability, and blocking resistance of the image were evaluated in the same manner as in Example 1. For each image recording, the results for odor, stretchability, and blocking resistance were the same as those for odor, stretchability, and blocking resistance in Example 1.

[0173] Each of the obtained image recordings is processed using a press machine to form a rectangular can (15 mm deep, with a corner diameter of 6 mm). Visual inspection of each corner of the resulting rectangular can confirms that there are no cracks.

[0174] The disclosure of Japanese Patent Application No. 2025-052507, filed on 26 March 2025, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. An active energy ray-curable inkjet ink comprising a polymerizable compound and a colorant, wherein the polymerizable compound comprises a difunctional (meth)acrylate (A) having linear or branched alkylene groups and a benzyl (meth)acrylate (B), the content of benzyl (meth)acrylate (B) relative to the total amount of the active energy ray-curable inkjet ink is 70% by mass or less, and the weighted average value of the glass transition temperatures of the homopolymers of each compound contained in the polymerizable compound is 10°C or less.

2. The polymerizable compound further comprises (meth)acrylate (C), wherein (meth)acrylate (C) is a (meth)acrylate that satisfies at least one of the following conditions: the homopolymer has a glass transition temperature of 0°C or lower, and it is a polyethylene glycol diacrylate with a molecular weight of 200 to 600, according to claim 1.

3. The active energy ray curable inkjet ink according to claim 2, wherein the (meth)acrylate (C) comprises polyethylene glycol diacrylate having a molecular weight of 200 to 600.

4. The active energy ray curable inkjet ink according to claim 1, wherein the bifunctional (meth)acrylate (A) comprises 3-methylpentanediol diacrylate.

5. The active energy ray curable inkjet ink according to claim 1, wherein the ratio of the mass content of difunctional (meth)acrylate (A) to the mass content of benzyl (meth)acrylate (B) is 0.05 to 0.

40.

6. An image recording method comprising the steps of: applying an active energy ray-curable inkjet ink according to claim 1 or claim 2 onto a substrate using an inkjet recording method; and irradiating the applied active energy ray-curable inkjet ink with active energy rays to record an image.

7. A method for manufacturing a molded article, comprising the steps of: applying an active energy ray-curable inkjet ink according to claim 1 or claim 2 onto a substrate using an inkjet recording method; irradiating the applied active energy ray-curable inkjet ink with active energy rays to record an image; and molding the substrate on which the image is recorded to manufacture a molded article.

Images