JP-2026075521-A - Active energy ray curable flexographic inks and printed materials

Abstract

[Problem] To provide an active energy ray-curable flexographic ink that can achieve both good printability and high opacity, and a printed material using the active energy ray-curable flexographic ink. [Solution] An active energy ray-curable flexographic ink comprising a radical polymerizable compound, a white pigment, and a dispersant, wherein the dispersant is a dispersant having a phosphate group. Preferably, the acid value of the dispersant is 50 to 500 mg KOH/g. [Selection Diagram] None

Inventors

• 矢上 裕起

Assignees

• ａｒｔｉｅｎｃｅ株式会社

Dates

Publication Date

20260508

Application Date

20241022

Claims (11)

1. An active energy ray curable flexographic ink comprising a radical polymerizable compound, a white pigment, and a dispersant, An active energy ray-curable flexographic ink, wherein the dispersant is a dispersant having a phosphate group.
2. The active energy ray-curable flexographic ink according to claim 1, wherein the acid value of the dispersant is 50 to 500 mg KOH/g.
3. The active energy ray-curable flexographic ink according to claim 1, wherein the dispersant is blended in a ratio of 0.1 to 50% by mass relative to the white pigment.
4. Furthermore, the active energy ray-curable flexographic ink according to claim 1, comprising an antifoaming agent.
5. The active energy ray-curable flexographic ink according to claim 4, wherein the defoaming agent is a non-silicone-based defoaming agent.
6. The active energy ray-curable flexographic ink according to claim 1, wherein the white pigment is titanium dioxide.
7. The ultraviolet-curable flexographic ink according to claim 1, wherein the proportion of white pigment in the flexographic ink is 40 to 60% by mass relative to the total flexographic ink.
8. The active energy ray-curable flexographic ink according to claim 1, wherein the viscosity (at 25°C and 100 rpm) measured with an E-type viscometer is 100 to 1500 mPa·s.
9. The active energy ray-curable flexographic ink according to claim 1, wherein the thixotropic index calculated by the following formula 1 is between 1.00 and 1.40. Formula 1 Thixotropic index = (Viscosity at 25°C and 10 rpm using an E-type viscometer) / (Viscosity at 25°C and 100 rpm using an E-type viscometer)
10. Furthermore, the active energy ray curable flexographic ink according to claim 1, comprising a photopolymerization initiator.
11. A printed article comprising a substrate and a cured product of an active energy ray-curable flexographic ink according to any one of claims 1 to 10.

Description

This invention relates to an active energy ray-curable flexographic ink and a printed material using the active energy ray-curable flexographic ink. Active energy ray curing inks are solvent-free and cure instantly using active energy rays. Because they offer excellent environmental friendliness, printability, and high-quality prints, they are widely used in various fields, from print information such as magazines and flyers to food packaging such as paper containers. Among the printing methods using these active energy ray-curable inks, flexographic printing is attracting attention because its printing plates are made of flexible and elastic photosensitive resins, allowing printing even on substrates with uneven surfaces. In flexographic printing, white flexographic inks are used for purposes such as white underprinting (printing white ink over colored inks to make text and images stand out clearly), and therefore require high opacity. Achieving high opacity requires a high white pigment content in the ink, which results in reduced ink fluidity and decreased transferability to the substrate, leading to reduced opacity. In particular, active energy ray-cured inks have lower fluidity compared to other curing inks such as water-based inks, which can lead to poor ink transfer and reduced concentration stability during long runs, resulting in reduced opacity. (See Patent Document 1) Furthermore, when printing white ink in flexographic printing, anilox rolls with a large cell capacity are used to improve opacity. However, this presents a challenge: ink can adhere to the sides and recesses of the printing plate, resulting in a decrease in print quality. Patent Document 2 presents a method for manufacturing printed materials with excellent opacity, which involves printing a white active energy ray-curable offset ink onto a substrate, followed by printing a white active energy ray-curable flexographic ink. However, this method combines multiple printing techniques, making it unsuitable for use with conventional flexographic printing presses. Patent Document 3 describes a white active energy ray-curable flexographic ink, but the evaluation was performed using a simple color development machine (RI tester), and there is no description of its opacity or printability when printed on a flexographic printing press. Japanese Patent Publication No. 2014-101472International Publication No. 2023/013571Japanese Patent Publication No. 2024-054635 The following describes in detail embodiments for carrying out the present invention. However, the present invention is not limited to the following embodiments and can be implemented in various ways within the scope of its gist. The terminology used in this embodiment will be explained below. "(meth)acryloyl" means acryloyl and/or methacryloyl, and "(meth)acrylate" means acrylate and/or methacrylate. "EO" refers to ethylene oxide, and "EO modification" means modification to ethylene oxide. Similarly, "PO" refers to propylene oxide, and "PO modification" means modification to propylene oxide. In addition, in the name of a radical polymerizable compound, (XO)n (where X is E or P), n represents the average number of XO molecules in one molecule. In this embodiment, the numerical range indicated using "~" includes the numbers before and after "~" as the minimum and maximum values, respectively. In the multiple numerical ranges described in stages in this embodiment, the upper or lower limit of one stage's numerical range can be arbitrarily combined with the upper or lower limit of another stage's numerical range. Furthermore, unless otherwise specified, the materials and compounds exemplified in this embodiment may be used individually or in combination of two or more. The active energy ray-curable flexographic ink of the present invention comprises a radical polymerizable compound, a white pigment, and a dispersant, and the printed material has a layer of cured active energy ray-curable flexographic ink on a substrate. <Radical polymerizable compounds> The active energy ray-curable flexographic ink of the present invention contains a radical polymerizable compound. The radical polymerizable compound is a compound having an ethylenically unsaturated bond that can be radically polymerized, and is any compound having at least one ethylenically unsaturated bond in its molecule, and includes those in chemical forms such as monomers, oligomers, and polymers. One radical polymerizable compound may be used alone, or two or more may be used in combination. Examples of radical polymerizable compounds include unsaturated carboxylic acids such as (meth)acrylic acid, itaconic acid, and maleic acid and their salts, anhydrides having an ethylenically unsaturated groups, acrylonitrile, styrene, and various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. More specifically, radical polymerizable compounds include 2-ethylhexyl (meth)acrylate, 2-hydroxyeth