JP7757770B2 - Lithographic printing ink and method for producing printed matter - Google Patents

Description

The present invention relates to a lithographic printing ink and a method for producing printed matter using the ink.

Lithographic printing is a widely used printing method that allows for the high-speed, high-volume, and low-cost production of printed materials. In recent years, in response to environmental issues, there has been a demand for reducing the volatile components contained in ink. For this reason, the use of actinic energy ray-curable inks, which contain no volatile components and cure instantly when exposed to actinic energy rays, is becoming more common. In addition to their environmental benefits, actinic energy ray-curable inks can shorten the drying process, thereby improving the productivity of lithographic printing.

In addition, in recent years, there has been a demand for small-lot production, particularly for film-printed materials, due to the diversification of packaging, and there has been a shift from expensive gravure printing to lithographic printing for small lots.

With regard to film printing using lithographic printing, for example, a lithographic printing ink characterized by containing (a) a pigment and (b) a resin having an ethylenically unsaturated group and a hydrophilic group, and a method for producing a printed matter including a step of applying the lithographic printing ink to a substrate such as a plastic film and irradiating it with active energy rays (see, for example, Patent Document 1), have been proposed.

International Publication No. 2017/47817

The films used for film printing are often around 10 to 50 μm thick, and because they are prone to breaking and stretching, there is a limit to the tension that can be applied for printing. In lithographic printing, the ink transferred to the blanket is transferred to the film by cleavage within the ink layer, but when the film tension is low, particularly when the printing area is large, the cohesive force of the ink can cause the film to shift position, resulting in insufficient register accuracy.

The present invention therefore aims to provide a lithographic printing ink and a method for producing printed matter that can produce printed matter with excellent register accuracy.

The present invention provides a lithographic printing ink comprising (a) a resin, (b) a compound having two or more reactive groups, and (c) a compound having one or less reactive groups , wherein the integrated value of normal force (stress in the normal direction) measured with a rheometer is 200 N s s or less, the difference between the solubility parameter of the (b) compound having two or more reactive groups and the solubility parameter of the (c) compound having one or less reactive group is 3.5 or more and 8.2 or less, the molecular weight of the (c) compound having one or less reactive group is 250 or more and 1,000 or less and the melting point is 25°C or higher, the (b) compound having two or more reactive groups comprises a polyfunctional (meth)acrylate having a hydroxyl group and/or an ethylene oxide-modified group, and the (c) compound having one or less reactive group comprises an alkyl (meth)acrylate having an aliphatic skeleton having from 13 to 22 carbon atoms .

The lithographic printing ink of the present invention enables the production of printed materials with excellent register accuracy.

First, we will explain the lithographic printing ink of the present invention.

As mentioned above, in lithographic printing, the ink transferred to the blanket is transferred to the film through cleavage within the ink layer. When lithographic printing on film, there is a limit to the tension that can be applied to the film, and the cohesive force of the ink makes it easy for the film to become misaligned. This problem becomes more pronounced the larger the printing area. For example, when printing on transparent film, white ink or transparent ink such as varnish may be printed over the entire film or image to improve the appearance of the image. When printing on film with such large printing areas, there is a strong demand for improved registration accuracy.

To improve registration accuracy even at low tensions, the inventors focused on ink releasability from the blanket and focused on the integral of normal force (stress in the normal direction) measured with a rheometer (hereinafter sometimes referred to as the "integral of normal force") as an indicator of ink cohesion, which is related to the ease of cleavage within the ink layer. Specifically, the lithographic printing ink of the present invention (hereinafter sometimes referred to as the "ink") is characterized by an integral of normal force of 200 N·s·s or less. The integral of normal force represents the stress (ink cohesion) exerted when the ink is peeled from the blanket during printing; the smaller this value, the weaker the ink cohesion and the easier it is to peel from the blanket. If the integral of normal force exceeds 200 N·s·s, the ink cohesion is high and the ink is difficult to peel from the blanket, which makes film misalignment more likely and reduces registration accuracy. The integral of normal force is preferably 180 N·s·s or less, and more preferably 150 N·s·s or less. On the other hand, the integral value of the normal force is preferably 50 N·s·s or more to suppress background smearing.

Here, the integral value of normal force in the present invention is measured using a rheometer under the following conditions: 0.35 ml of ink is weighed out using an ink pipette, and a clearance of 0.1 mm is adjusted using parallel plates with a diameter of 25 mm. After removing the ink that has spilled from the plates, normal force is measured at a temperature of 25°C using the following program sequence. These conditions were selected to simulate the general state of ink during printing.
(1) Leave it to stand for 60 seconds.
(2) Vibration motion is performed for 60 seconds at a strain of 40% (constant) and an angular frequency of 100 rad/s (constant).
(3) Leave it to stand for 60 seconds.
(4) The clearance is narrowed at a speed of 0.01 mm/s for 5 seconds.
(5) The clearance is widened at a speed of 0.01 mm/s for 25 seconds, while the normal force is measured at 0.05 second intervals.

In (5) above, the absolute value of the normal force (unit: N-s) integrated over time (unit: s) for the section from when the normal force reaches 0 N-s to when the measurement ends (25 seconds later) is the integral of the normal force (unit: N-s-s).

One example of a means for keeping the ink's normal force integral value at 200 N·s·s or less is to form a microphase-separated structure. It is believed that inks with a microphase-separated structure can reduce ink cohesion because the micro-separated phases promote cleavage when the ink is peeled from the blanket. More specifically, one example of a means for keeping the ink's normal force integral value within the above range is to use the preferred composition described below.

In differential scanning calorimetry, inks having a microphase-separated structure exhibit a glass transition point or melting point derived from each phase. In the present invention, we focus on the glass transition point and melting point as indicators of the microphase-separated structure. The ink of the present invention preferably has two or more glass transition points and/or melting points in the range of -90°C to 100°C, which allows the normal force integral to be easily adjusted to the aforementioned preferred range and further improves registration accuracy. The ink may have two or more glass transition points, two or more melting points, or one or more glass transition points and one or more melting points within the above range.

The glass transition point and melting point of the ink in the present invention are measured using a differential scanning calorimeter (DSC) under the following conditions: 5 mg of ink is weighed into an aluminum pan, and using an empty aluminum pan as a reference and liquid nitrogen for cooling, the calorific value is measured according to the following program sequence:
(1) After adjusting the temperature to 30°C, the temperature is increased from 30°C to 100°C at a rate of 10°C/min.
(2) Hold at 100°C for 5 minutes.
(3) The temperature is decreased from 100°C to -90°C at a rate of 10°C/min.
(4) Keep at -90°C for 5 minutes.
(5) The temperature is increased from -90°C to 100°C at a rate of 10°C/min.

In (5) above, if a baseline shift is observed, the temperature at the intersection of the low-temperature baseline and the tangent line at the inflection point is taken as the glass transition point. Also, if an endothermic peak is observed, the temperature at the peak top is taken as the melting point.

Methods for forming a microphase-separated structure include, for example, using the preferred composition described below.

The ink of the present invention contains (a) a resin and (b) a compound having two or more reactive groups. The inclusion of (a) a resin can impart suitable fluidity to the ink, and the inclusion of (b) a compound having two or more reactive groups can impart the ink with the ability to be cured by actinic energy rays.

(a) Examples of resins include acrylic resins, styrene-acrylic resins, styrene-maleic acid resins, rosin-modified maleic acid resins, rosin-modified acrylic resins, epoxy resins, polyester resins, polyurethane resins, and phenolic resins. Two or more of these may be used. Among these, acrylic resins, styrene-acrylic resins, and styrene-maleic acid resins are preferred in terms of ease of monomer availability, ease of synthesis, compatibility with other components in the ink, pigment dispersibility, etc.

The weight-average molecular weight of the (a) resin is preferably 40,000 or less, which suppresses entanglement of molecular chains, further reduces ink cohesive force, and improves register accuracy. On the other hand, the weight-average molecular weight of the (a) resin is preferably 5,000 or more, which improves pigment dispersibility, further reduces ink cohesive force, and improves register accuracy. The weight-average molecular weight of the (a) resin is more preferably 15,000 or more.

The weight-average molecular weight of the (a) resin in the present invention is measured by gel permeation chromatography (GPC) using a column consisting of TSKgel Super HM-H (manufactured by Tosoh Corporation), TSKgel Super HM-H (manufactured by Tosoh Corporation), and TSKgel Super H2000 (manufactured by Tosoh Corporation) connected in this order, with tetrahydrofuran as the mobile phase.

The acid value of the (a) resin is preferably 75 mg KOH/g or more, which improves pigment dispersibility and further reduces ink cohesive force, thereby improving register accuracy. On the other hand, the acid value of the (a) resin is preferably 150 mg KOH/g or less, which reduces interactions between resins and further reduces ink cohesive force, thereby improving register accuracy.

The acid value of the (a) resin in the present invention is measured by the neutralization titration method described in Section 3.1 of the test method of JIS K 0070:1992.

The content of (a) resin in the ink is preferably 6% by weight or more, which maintains a moderately high viscosity, allows the ink's normal force integral to be easily adjusted to 50 N·s·s or more, and suppresses background scumming. On the other hand, the content of (a) resin is preferably 15% by weight or less, which suppresses entanglement of molecular chains, further reduces ink cohesive force, and further improves register accuracy. The reactive group in the compound having two or more (b) reactive groups refers to a functional group that undergoes polymerization in response to active energy rays, and examples of such groups include epoxy groups and ethylenically unsaturated groups. Examples of ethylenically unsaturated groups include acrylic groups, methacrylic groups, and vinyl groups. The compound having two or more (b) reactive groups of the present invention may be a monomer or an oligomer. In the case of an oligomer, the polymer has a weight-average molecular weight of 5,000 or less.

Examples of monomers having two or more reactive groups include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, 1,3 butylene glycol di(meth)acrylate, 1,6 hexanediol di(meth)acrylate, 1,9 nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, and 1,11-undecanediol di(meth)acrylate. ) acrylate, 1,12-dodecanediol di(meth)acrylate, 1,13-tridecanediol di(meth)acrylate, 1,14-tetradecanediol di(meth)acrylate, 1,15-pentadecanediol di(meth)acrylate, 1,16-hexadecanediol di(meth)acrylate, 1,17-heptadecanediol di(meth)acrylate, 1,18-octadecanediol di(meth)acrylate, 4-methyl-1,10-decanediol di(meth)acrylate, 4-ethyl-1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate Examples of monomers having three reactive groups include trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and ethylene oxide adducts and propylene oxide adducts thereof. Examples of monomers having four reactive groups include trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and ethylene oxide adducts and propylene oxide adducts thereof. Examples of monomers having five reactive groups include pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, diglycerin tetra(meth)acrylate, and their ethylene oxide adducts and propylene oxide adducts. Examples of monomers having five reactive groups include dipentaerythritol penta(meth)acrylate, and their ethylene oxide adducts and propylene oxide adducts. Examples of monomers having six reactive groups include dipentaerythritol hexa(meth)acrylate, and their ethylene oxide adducts and propylene oxide adducts. Two or more of these may be contained. Of these, (meth)acrylate is more preferred from the viewpoints of improving the dispersibility of the (a) resin, further reducing ink coagulation force, and further improving registration accuracy. Here, "(meth)acrylate" is a general term for acrylate and methacrylate.

Examples of oligomers having two or more reactive groups include polymers of the monomers exemplified above as monomers having two or more reactive groups. Two or more of these may be contained.

Among these, polyfunctional (meth)acrylates having hydroxyl groups and/or ethylene oxide-modified groups are preferred. By combining them with alkyl (meth)acrylates having an aliphatic skeleton with 13 to 22 carbon atoms as compounds having one or less reactive groups (c) described below, a stable microphase-separated structure is easily formed, making it possible to easily adjust the normal force integral value to the preferred range described above and further improving registration accuracy.

The hydroxyl value of the (b) compound having two or more reactive groups is preferably 100 mgKOH/g or more, which improves the dispersibility of the (a) resin and pigment, further reduces ink cohesive force, and further improves register accuracy. On the other hand, the hydroxyl value of the (b) compound having two or more reactive groups is preferably 160 mgKOH/g or less, which reduces interactions between compounds having two or more reactive groups, further reduces ink cohesive force, and further improves register accuracy. Note that when two or more (b) compounds having two or more reactive groups are used, it is preferable that the hydroxyl value of at least one of them is within the above range.

Here, the hydroxyl value of (b) a compound having two or more reactive groups in the present invention is measured by the neutralization titration method described in Section 7.1 of the test method of JIS K 0070:1992.

The content of (b) compounds having two or more reactive groups in the ink is preferably 35% by weight or more, which improves the dispersibility of (a) resins and pigments, further reduces ink cohesive force, and further improves register accuracy. On the other hand, the content of (b) compounds having two or more reactive groups is preferably 70% by weight or less, which maintains a moderately high viscosity and suppresses background scumming. The content of (b) compounds having two or more reactive groups is more preferably 49% by weight or less.

The ink of the present invention preferably further contains (c) a compound having one or less reactive groups. (c) A compound having one or less reactive groups acts as an aid to reduce the cohesive force of the ink. The reactive group in (c) a compound having one or less reactive groups is synonymous with the reactive group in (b) a compound having two or more reactive groups, and the compound may or may not have one reactive group.

(c) Examples of compounds having one or less reactive groups include compounds having one reactive group, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, and undecyl (meth)acrylate. Acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, heneicosyl (meth)acrylate, docosyl (meth)acrylate, isopropyl (meth)acrylate acrylate, isobutyl (meth)acrylate, isopentyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, isoundecyl (meth)acrylate, isododecyl (meth)acrylate, isotridecyl (meth)acrylate, isotetradecyl (meth)acrylate, isopentadecyl (meth)acrylate, isohexadecyl (meth)acrylate, isoheptadecyl (meth)acrylate, isooctadecyl (meth)acrylate, isononadecyl (meth)acrylate, isoeicosyl (meth)acrylate, isohenicosyl (meth)acrylate, isodocosyl (meth)acrylate, oleic acid, hexyl glycidyl ether, ethylene oxide adducts thereof, and propylene oxide adducts thereof. Among these, (meth)acrylate is more preferred from the viewpoint of improving the dispersibility of the (a) resin, further reducing the ink cohesive force, and further improving the register accuracy. Examples of the compound having no reactive group include hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane, henicosane, docosane, acetone, tetrahydrofuran, water, methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecane, hexane, octane, nonanol, decanol, undecane, hexane, octane, nonanol, decanol, undecane, hexane, octane, nonanol, decanol, undecane, hexane, octane, nonanol, decanol, undecane, oct ... Canol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, eicosanol, henicosanol, docosanol, 2-propanol, 2-butanol, 2-pentanol, 2-hexanol, 2-heptanol, 2-octanol, 2-nonanol, 2-decanol, 2-undecanol, 2-dodecanol, 2-tridecanol, 2-tetradecane Canonol, 2-pentadecanol, 2-hexadecanol, 2-heptadecanol, 2-octadecanol, 2-nonadecanol, 2-eicosanol, 2-heneicosanol, 2-docosanol, methanoic acid, ethanoic acid, propanoic acid, butanoic acid, pentanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonanoic acid Examples include decanoic acid, eicosanoic acid, henicosanoic acid, docosanoic acid, phenol, 2-methylphenol, 3-methylphenol, 4-methylphenol, benzoic acid, 2-methylbenzoic acid, 3-methylbenzoic acid, 4-methylbenzoic acid, ethylene glycol, propylene glycol, glycerin, 4-methoxyphenol, polyethylene glycol, polypropylene glycol, and ethylene oxide and propylene oxide adducts thereof. Two or more of these may be used.

Among these, alkyl (meth)acrylates having an aliphatic skeleton with 13 to 22 carbon atoms are preferred. Combining them with a polyfunctional (meth)acrylate having a hydroxyl group and/or an ethylene oxide-modified group as the aforementioned (b) compound having two or more reactive groups facilitates the stable formation of a microphase-separated structure, making it easy to adjust the normal force integral value to the aforementioned preferred range and further improving registration accuracy. Because this appropriately promotes the progression of phase separation and facilitates the stable formation of a microphase-separated structure, the aliphatic skeleton preferably has 14 or more carbon atoms, and even more preferably 16 or more. On the other hand, the aliphatic skeleton preferably has 21 or fewer carbon atoms, and even more preferably 20 or fewer carbon atoms, because this appropriately suppresses the progression of phase separation and facilitates the stable maintenance of a microphase-separated structure.

The difference between the solubility parameter (hereinafter sometimes referred to as "SP value") of (b) a compound having two or more reactive groups and the SP value of (c) a compound having one or less reactive groups is preferably 3.5 or more, which facilitates the stable formation of a microphase-separated structure, allowing the normal force integral value to be easily adjusted to the aforementioned preferred range and further improving registration accuracy. The difference in SP values is more preferably 3.9 or more, and even more preferably 4.3 or more. On the other hand, the difference in SP values is preferably 8.2 or less, which moderately suppresses the progression of phase separation and facilitates the stable maintenance of a microphase-separated structure, allowing the normal force integral value to be easily adjusted to the aforementioned preferred range and further improving registration accuracy. The difference in SP values is more preferably 7.2 or less, and even more preferably 6.2 or less.

Here, the solubility parameter in the present invention refers to the solubility parameter (unit: (J/cm ³ ) ^1/2 ) calculated by the Fedors method described in Polymer Handbook Third Edition (A Wiley-Interscience publication, 1989). (b) When two or more compounds having two or more reactive groups are contained, the SP value is calculated by weight averaging the SP value and content of each compound. For example, when two types of (b) compounds having two or more reactive groups, namely compound A (SP value: 11.5, content: 30 parts by weight) and compound B (SP value: 10, content: 20 parts by weight), are contained, the SP value of the (b) compound having two or more reactive groups is calculated as (11.5 × 30 + 10 × 20) ÷ (30 + 20) = 10.9.

When two or more (c) compounds having one or less reactive groups are contained, it is preferable that the difference in SP value between at least one of them and the SP value of the (b) compound having two or more reactive groups be within the above range, and it is more preferable that all of the differences in SP value between each compound and the SP value of the (b) compound having two or more reactive groups be within the above range.

(c) The molecular weight of the compound having one or less reactive groups is preferably 250 or more, which moderately promotes the progression of phase separation and makes it easy to form a stable microphase-separated structure, allowing the normal force integral value to be easily adjusted to the preferred range described above and further improving registration accuracy. The molecular weight is more preferably 275 or more, and even more preferably 300 or more. On the other hand, the molecular weight of the compound having one or less reactive groups (c) is preferably 1,000 or less, which moderately suppresses the progression of phase separation and makes it easy to maintain a stable microphase-separated structure, allowing the normal force integral value to be easily adjusted to the preferred range described above and further improving registration accuracy. The molecular weight is more preferably 700 or less, and even more preferably 500 or less.

(c) The melting point of a compound having one or less reactive groups is preferably 25°C or higher, which moderately suppresses the progression of phase separation during storage and printing and makes it easier to maintain a microphase-separated structure. This makes it possible to easily adjust the normal force integral value to the aforementioned preferred range and further improve register accuracy. A melting point of 27°C or higher is more preferable.

Here, (c) the melting point of the compound having one or less reactive group is measured in the same manner as the melting point of the ink described above.

The content of the (c) compound having one or less reactive groups is preferably 1 part by mass or more per 100 parts by mass of the (b) compound having two or more reactive groups. This moderately promotes the progression of phase separation and facilitates the stable formation of a microphase-separated structure, making it possible to easily adjust the normal force integral value within the preferred range described above and further improve registration accuracy. The content of the (c) compound having one or less reactive groups is more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more. On the other hand, the content of the (c) compound having one or less reactive groups is preferably 7 parts by mass or less. This moderately suppresses the progression of phase separation and facilitates the stable maintenance of a microphase-separated structure, making it possible to easily adjust the normal force integral value within the preferred range described above and further improve registration accuracy. The content of the (c) compound having one or less reactive groups is more preferably 6 parts by mass or less, and even more preferably 5 parts by mass or less.

The ink of the present invention preferably further contains a pigment. Examples of pigments include organic pigments and inorganic pigments. Examples of organic pigments include phthalocyanine pigments, soluble azo pigments, insoluble azo pigments, lake pigments, quinacridone pigments, isoindoline pigments, threne pigments, and metal complex pigments. More specific examples include phthalocyanine blue, phthalocyanine green, azo red, monoazo red, monoazo yellow, disazo red, disazo yellow, quinacridone red, quinacridone magenta, and isoindoline yellow. Examples of inorganic pigments include titanium oxide, zinc oxide, alumina white, calcium carbonate, barium sulfate, oxide-coated glass, silicate minerals (mica), oxide-coated mica, oxide-coated metal particles, carbon black, and graphite. Two or more of these pigments may be contained.

The ink of the present invention can be used in a variety of colors, including chromatic inks such as indigo, red, and yellow, as well as black ink, white ink, and transparent ink. Since a large printing area is often required, transparent ink and white ink are suitable, with white ink being particularly suitable.

When the ink of the present invention is a transparent ink, from the viewpoint of balancing transparency with misting resistance and scumming prevention, preferred pigments are ionic compounds such as calcium carbonate, barium sulfate, oxide-coated glass, and silicate minerals (mica). When the ink of the present invention is a white ink, preferred pigments are ionic compounds such as titanium oxide, zinc oxide, and alumina white. The interaction between ionic compounds further reduces the ink cohesive force, making it easy to adjust the normal force integral value to the preferred range described above, and further improving register accuracy.

The particle size of the white pigment for white ink is preferably 200 nm or more and 300 nm or less.

The ink of the present invention preferably further contains a surfactant, which further improves pigment dispersibility, further reduces ink cohesive force, makes it easy to adjust the normal force integral value to fall within the preferred range described above, and further improves register accuracy.

Examples of surfactants include "Anti-Terra" (registered trademark)-U, "Anti-Terra"-203/204, and "Disperbyk" (registered trademark)-101, 102, 103, 106, 107, 110, 111, 115, 118, 130, 140, 142, 145, 161, 162, 163, 164, 165, 166, 167, 168, 170, 171, 174, 180, 181, 182, 184, 185, 187, 190, 191, 192, 193, 199, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024, 2025, 2026, 2027, 2028, 2029, 2030, 2031, 2032, 2033, 2034, 2035, 2036, 2037, 2038, 2039, 2040, 2041, 2042, 2043, 2044, 2045, 2046, 2 001, 2008, 2009, 2010, 2012, 2013, 2015, 2022, 2025, 2026, 2050, 2055, 2060, 2061, 2070, 2096, 2150, 2151, 2152, 2155, 2163, 2164, 2200, 2205, 9067, 9076, "Bykumen" (registered trademark), "BYK" (registered trademark) - P104, P105, P104S, 240S, "Lactimon" (registered trademark), "EFKA" (registered trademark) 44, 46, 47 manufactured by Efka Chemicals, 48, 49, 54, 63, 64, 65, 66, 71, 701, 764, 766, "Efka Polymer 100, 150, 400, 401, 402, 403, 450, 451, 452, 453, 745," manufactured by Kyoeisha Chemical Co., Ltd.; "Florene" (registered trademark) TG-710, "Flornon" (registered trademark) SH-290, SP-1000, "Polyflow No. 50E, No. 300," manufactured by Kusumoto Chemical Co., Ltd.; "Disparlon" (registered trademark) 325, KS-860, 873SN, 874, 1401, #2150, #7004," manufactured by Kao Corporation; Examples include "Demol" (registered trademark) RN, N, MS, C, SN-B, EP, "Homogenol" (registered trademark) L-18, "Emulgen" (registered trademark) 920, 930, 931, 935, 950, 985, "Acetamine" (registered trademark) 24, 86, "Solsperse" (registered trademark) 5000, 13940, 17000, 24000GR, 32000, 33000, 39000, 41000, 53000 manufactured by Lubrizol, and "Ajisper" (registered trademark) PB821, 822, 824 manufactured by Ajinomoto Fine-Techno Co., Ltd. Two or more of these may be used.

When the ink of the present invention is a white ink, (d) anionic surfactants are preferred among these, as they improve the dispersibility of white pigments such as titanium oxide, zinc oxide, and alumina white, further reducing ink coagulation, making it easy to adjust the normal force integral value within the aforementioned preferred range, and further improving register accuracy. Examples of anionic surfactants include "Disperbyk" (registered trademark) 111 (manufactured by BYK Japan Co., Ltd.), sodium dodecylbenzenesulfonate, sodium laurate, sodium myristate, sodium palmitate, sodium stearate, sodium oleate, potassium laurate, potassium myristate, potassium palmitate, potassium stearate, potassium oleate, sodium N-stearoyl-L-glutamate, sodium N-stearoyl-N-methyltaurate, and sodium N-lauroyl-L-glutamate.

The surfactant content is preferably 1 part by weight or more and 20 parts by weight or less per 100 parts by weight of pigment.

Next, a method for producing the ink of the present invention will be described. The ink of the present invention can be obtained, for example, by mixing and dispersing (a) a resin, (b) a compound having two or more reactive groups, and optionally (c) a compound having one or less reactive groups, a pigment, a surfactant, and other ingredients. Prior to mixing and dispersing, the ingredients may be dissolved at 5 to 100°C, or degassed under vacuum or reduced pressure conditions during and/or after mixing and dispersing. Examples of mixing equipment include agitators and kneaders such as a kneader, three-roll mill, ball mill, planetary ball mill, bead mill, roll mill, attritor, sand mill, gate mixer, paint shaker, homogenizer, and planetary mixer.

Next, a method for producing a printed matter of the present invention will be described. The method for producing a printed matter of the present invention includes the steps of transferring the ink of the present invention described above onto a substrate and irradiating it with active energy rays. Because the ink of the present invention cures when irradiated with active energy rays, a printed matter having a cured ink film can be obtained by irradiating it with active energy rays.

First, we will explain the process of transferring the ink of the present invention onto a substrate.

Examples of substrates include art paper, coated paper, cast paper, synthetic paper, newsprint, plastic film, plastic film-laminated paper, metal film, metal-vapor-deposited paper, and metal-vapor-deposited plastic film. Two or more of these may be used. Examples of plastic films include films made of polyethylene terephthalate, polyethylene, polyester, polyamide, polyimide, polystyrene, polypropylene, polycarbonate, and polyvinyl acetal. Examples of plastic film-laminated paper include those in which the aforementioned plastic films are laminated on paper. Examples of metal films include films made of zinc, copper, and the like. Examples of metal-vapor-deposited paper and metal-vapor-deposited plastic film include those in which the aforementioned metals or their oxides are vapor-deposited on paper or plastic film. Among these, plastic film, plastic film-laminated paper, metal film, metal-vapor-deposited paper, and metal-vapor-deposited plastic film do not absorb ink and therefore do not adhere to the ink due to ink absorption. Therefore, they are suitable for use in the present invention, which allows ink to be cured and adhered by irradiation with active energy rays.

The substrate may be subjected to an adhesion-enhancing treatment, which can improve the transferability of the ink to the substrate. Examples of adhesion-enhancing treatments include primer application and surface treatments such as corona discharge treatment and plasma treatment.

When used for flexible packaging, the thickness of the substrate is preferably 10 μm or more and 30 μm or less.

The substrate can be either a sheet or a roll film. When using thin film for flexible packaging, it is preferable to use a roll film and transfer it roll-to-roll.

The preferred method for transferring the ink of the present invention to a substrate is lithographic printing. Lithographic printing methods include water-based printing and waterless printing.

It is preferable to set the thickness of the ink transfer film on the substrate so that the thickness after curing is 0.1 to 50 μm. This allows for both good print quality and reduced ink usage.

When transferring white ink onto a substrate, it is preferable to transfer the white ink two or more times. This improves the hiding power, reduces the amount of ink transferred per transfer, and further improves registration accuracy.

Methods for transferring ink multiple times include, for example, wet-on-wet printing and dry-on-wet printing when transferring by printing. Of these, the wet-on-wet printing method is preferred from the standpoint of productivity.

Next, the process of irradiating active energy rays will be described. By irradiating the ink transferred onto the substrate with active energy rays, the ink can be cured instantly. Examples of active energy rays include ultraviolet rays and electron beams, with electron beams being preferred from the perspective of improving curing properties and suppressing odor generation. Examples of ultraviolet irradiating devices include high-pressure mercury lamps, xenon lamps, metal halide lamps, and light-emitting diodes (LEDs). From the perspective of power conservation, it is preferable to use ultraviolet light (LED-UV) using a light-emitting diode as a light source that emits emission lines with a wavelength of 350 to 420 nm. For electron beams, energy rays of 100 to 500 eV are preferred.

The present invention will be explained in more detail below using examples. However, the present invention is not limited to these examples.

<Ink raw materials>
(a) Resin: Resin 1 was obtained by addition reaction of 0.55 equivalents of glycidyl methacrylate with the carboxyl groups of a copolymer consisting of 25% by mass of methyl methacrylate, 25% by mass of styrene, and 50% by mass of methacrylic acid, to obtain Resin 1 having ethylenically unsaturated groups and hydrophilic groups. The obtained resin had a weight average molecular weight of 34,000, an acid value of 105 mg KOH/g, and an iodine value of 2.0 mol/kg.
(b) Compound having two or more reactive groups Monomer 1: a mixture of 65% by weight of pentaerythritol triacrylate and 35% by weight of pentaerythritol tetraacrylate (manufactured by MIWON Co., Ltd., "Miramer" (registered trademark) M340), hydroxyl value 115 mg KOH/g, SP value as a mixture 22.7 (J/cm ³ ) ^1/2
Monomer 2: trimethylolpropane EO-modified triacrylate (manufactured by MIWON Corporation, "Miramer" (registered trademark) M3190), hydroxyl value 10 mg KOH/g, solubility parameter 19.6 (J/cm ³ ) ^1/2
Monomer 3: dipentaerythritol hexaacrylate (manufactured by MIWON Corporation, "Miramer" (registered trademark) M600), hydroxyl value 5 mg KOH/g, solubility parameter 21.3 (J/cm ³ ) ^1/2
Pigment Pigment 1: "Tipake" (registered trademark) CR58-2 (manufactured by Ishihara Sangyo Kaisha, Ltd.)
Pigment 2: Carmine 6B 1483LT (manufactured by Dainichiseika Color & Chemicals Co., Ltd.)
(c) Compound Auxiliary Agent 1 Having One or Less Reactive Groups: Octadecyl acrylate (Tokyo Chemical Industry Co., Ltd.), molecular weight 325, melting point 28° C., solubility parameter 17.8 (J/cm ³ ) ^1/2
Auxiliary agent 2: dodecyl acrylate (Tokyo Chemical Industry Co., Ltd.), molecular weight 240, melting point 4° C., solubility parameter 17.8 (J/cm ³ ) ^1/2
(d) Anionic surfactant Surfactant 1: "Disperbyk" (registered trademark) 111 (manufactured by BYK Japan KK)
Other surfactant 2: "Solsperse" (registered trademark) 54000 (manufactured by Lubrizol), a polymer surfactant.

<Analysis method for ink raw materials>
(1) Weight Average Molecular Weight A diluted solution was prepared by diluting the resin with tetrahydrofuran to a concentration of 0.25% by mass. The diluted solution was stirred for 5 minutes at 100 rpm using a mix rotor (MIX-ROTAR VMR-5, AS ONE Corporation) to dissolve the resin, and the solution was filtered using a 0.2 μm filter (Z227536-100EA, SIGMA Corporation). The resulting filtrate was used to measure the weight average molecular weight of the resin by gel permeation chromatography (GPC) using tetrahydrofuran as the mobile phase. The GPC was performed using an HLC-8220 (Tosoh Corporation) column, and columns consisting of TSKgel Super HM-H (Tosoh Corporation), TSKgel Super HM-H (Tosoh Corporation), and TSKgel Super H2000 (Tosoh Corporation) connected in this order. Measurement was performed by RI detection. A calibration curve was prepared using polystyrene standards. The measurement conditions were: injection volume 10 μL, analysis time 30 minutes, flow rate 0.4 mL/min, and column temperature 40°C.

(2) Acid Value The acid value of the resin was measured by the method described in the neutralization titration method in Section 3.1 of the test method of JIS K 0070:1992.

(3) Iodine Value The iodine value of the resin was measured according to the method described in Section 6.0 of the test method of JIS K 0070:1992.

(4) Hydroxyl Value The hydroxyl value of (b) a compound having two or more reactive groups was measured by the method described in Section 7.1 of the test method of JIS K 0070:1992, which is based on the neutralization titration method.

(5) Solubility parameter The SP values (unit: (J/cm 3 ) 1/2 ) of the components (b) and (c) used in each example and comparative example were calculated by the Fedors method described in "Polymer Handbook ^Third Edition" (A Wiley-Interscience publication, ¹⁹⁸⁹ ). However, the SP value of the compound having two or more reactive groups (b) was calculated by weight averaging the SP value and content of each compound.

(6) Melting Point The melting point of the component (c) used in each of the Examples and Comparative Examples was measured by the method described in <Evaluation Method> (2) below.

<Evaluation method>
(1) Integrated value of normal force (stress in the normal direction) A parallel plate (MEASURING PLATE PP25, diameter 25 mm) was attached to a rheometer MCR301 manufactured by Anton Paar. 0.35 ml of the ink prepared in each example and comparative example was weighed out using an ink pipette and placed on the parallel plate, with the clearance adjusted to 0.1 mm. The ink overflowing from the plate was removed, and the normal force was measured at a temperature of 25°C using the following program in the following order:
(1) Leave it to stand for 60 seconds.
(2) Vibration motion is performed for 60 seconds at a strain of 40% (constant) and an angular frequency of 100 rad/s (constant).
(3) Leave it to stand for 60 seconds.
(4) The clearance is narrowed at a speed of 0.01 mm/s for 5 seconds.
(5) The clearance is widened at a speed of 0.01 mm/s for 25 seconds, while the normal force is measured at 0.05 second intervals.

In (5) above, the absolute value of the normal force (unit: N-s) integrated over time (unit: s) for the period from when the normal force reached 0 N-s to the end of measurement (25 seconds later) was taken as the integral value (unit: N-s-s) of the normal force (stress in the normal direction).

(2) Glass transition point and melting point Using a differential scanning calorimeter: DSC6200 manufactured by Seiko Instruments Inc., 5 mg of the ink obtained in each of the Examples and Comparative Examples was weighed into an aluminum pan at a nitrogen flow rate of 40 mL/min and using liquid nitrogen for cooling. Using an empty aluminum pan as a reference, the calorific value was measured according to the following program in the following order.
(1) After adjusting the temperature to 30°C, the temperature is increased from 30°C to 100°C at a rate of 10°C/min.
(2) Hold at 100°C for 5 minutes.
(3) The temperature is decreased from 100°C to -90°C at a rate of 10°C/min.
(4) Keep at -90°C for 5 minutes.
(5) The temperature is increased from -90°C to 100°C at a rate of 10°C/min.

In (5) above, if a baseline shift was observed, the temperature at the intersection of the low-temperature baseline and the tangent line at the inflection point was taken as the glass transition point. Furthermore, if an endothermic peak was observed, the temperature at the peak top was taken as the melting point.

(3) Register accuracy and background scumming <Preparation of crimson ink for lithographic printing>
15% by mass of the aforementioned resin, 45.0% by mass of Monomer 1, 20.0% by mass of Monomer 2, and 2.0% by mass of Monomer 3 were weighed out and heated at 95°C for 390 minutes while stirring at 500 rpm using a disper blade to obtain a varnish. 18.0% by mass of Pigment 2 was added to the obtained varnish, and the mixture was passed five times using a three-roll mill "EXAKT" (registered trademark) M-80S (manufactured by EXAKT) at a gap of 1 to obtain a crimson ink for lithographic printing.

<Lithographic printing>
A waterless lithographic printing plate (TAN-E, manufactured by Toray Industries, Inc.) measuring 1,070 mm in width (width direction) and 674 mm in length (printing direction) and having a 0.1 mm line-thickness cross (register mark) for checking register accuracy positioned at the center in the printing direction and 50 mm from both ends of the plate in the width direction was placed on the first cylinder of a flexographic hybrid printing press (CI-8, manufactured by COMEXI). A waterless lithographic printing plate (TAN-E, manufactured by Toray Industries, Inc.) measuring 1,070 mm in width (width direction) and 674 mm in length (printing direction), with a 100% solid image area measuring 900 mm in width (width direction) and 500 mm in length (printing direction) at the center of the plate and 0.1 mm line-thickness cross (register mark) marks for checking register accuracy positioned at the center in the printing direction and 50 mm from both ends in the width direction, was placed on the sixth and seventh cylinders of the flexographic hybrid printing press. The crimson ink for lithographic printing obtained by the above method was placed on the first cylinder, and the white ink for lithographic printing obtained in each of the Examples and Comparative Examples was placed on the sixth and seventh cylinders.

On a polyester film substrate, PTM12 (Unitika Ltd., thickness 12 μm), red lithographic printing ink and white lithographic printing ink were printed at a speed of 100 m/min using a wet-on-wet printing method with a T414 blanket (Kinyosha, thickness 1.95 mm) under the following conditions: ink feed rate for cylinder 1: 5%, ink feed rate for cylinders 6 and 7: 40%, impression cylinder chiller temperature setting: 25°C, oscillating roller and ink fountain chiller temperature setting: 28°C. After all inks had been printed, the printer was irradiated with 110 kV, 40 kGy electron beams using an electron beam irradiation device attached to the printing press to cure the ink and obtain a print.

During printing, the register accuracy confirmation cross (register mark) marks for each color were aligned in the same position, and printing was continued without any adjustment. After 30 seconds, the distance between the red cross (register mark) mark and the white cross (register mark) mark that was furthest from the red cross (register mark) mark was measured for the printed product, and the register accuracy was evaluated according to the following criteria.
Distance between register marks: more than 0.3 mm: insufficient Distance between register marks: more than 0.2 mm and 0.3 mm or less: somewhat good Distance between register marks: more than 0.1 mm and 0.2 mm or less: good Distance between register marks: 0.1 mm or less: extremely good In addition, the non-image areas of the printed matter after 120 seconds were visually observed to evaluate the presence or absence of scumming due to white ink.

[Example 1]
<Preparation of white ink>
Component (a) and component (b) shown in Table 1 were each weighed out, and heated at 95°C for 390 minutes while stirring at 500 rpm using a disper blade to obtain a varnish. The pigment, component (c), and component (d) shown in Table 1 were added to the obtained varnish, and the mixture was passed through a three-roll mill "EXAKT" (registered trademark) M-80S (manufactured by EXAKT) five times at a gap of 1 to obtain a white ink for lithographic printing. The obtained white ink for lithographic printing was evaluated using the methods described above, and the results are shown in Table 1.

[Examples 2 to 10, Comparative Example 1]
<Preparation of white ink>
White inks for lithographic printing were obtained in the same manner as in Example 1, except that the composition of the white ink was changed as shown in Table 1. The resulting lithographic printing inks were evaluated by the above-mentioned methods, and the results are shown in Table 1.

Claims (9)

a lithographic printing ink comprising (a) a resin, (b) a compound having two or more reactive groups , and (c) a compound having one or less reactive groups , wherein the integrated value of normal force (stress in the normal direction) measured with a rheometer is 200 N s s or less, the difference between the solubility parameter of the (b) compound having two or more reactive groups and the solubility parameter of the (c) compound having one or less reactive groups is 3.5 or more and 8.2 or less, the molecular weight of the (c) compound having one or less reactive groups is 250 or more and 1,000 or less and the melting point is 25°C or higher, the (b) compound having two or more reactive groups comprises a polyfunctional (meth)acrylate having a hydroxyl group and/or an ethylene oxide-modified group, and the (c) compound having one or less reactive group comprises an alkyl (meth)acrylate having an aliphatic skeleton having from 13 to 22 carbon atoms . The lithographic printing ink according to claim 1, which has a total of two or more glass transition points and/or melting points in the range of -90°C or higher and 100°C or lower. 3. The lithographic printing ink according to claim 1, wherein the content of the (c) compound having one or less reactive groups is 1 part by mass or more and 7 parts by mass or less per 100 parts by mass of the (b) compound having two or more reactive groups. The lithographic printing ink according to any one of claims 1 to 3, which is a white ink. 5. The lithographic printing ink according to claim 4, further comprising (d) an anionic surfactant. A method for producing a printed matter, comprising the steps of transferring the lithographic printing ink according to any one of claims 1 to 5 onto a substrate and irradiating the substrate with active energy rays. The method for producing a printed matter according to claim 6, wherein the active energy rays are electron beams. 8. A method for producing a printed matter according to claim 6 or 7, comprising the step of applying the lithographic printing ink according to claim 4 or 5 two or more times. The method for producing a printed matter according to any one of claims 6 to 8, wherein the printed matter is printed by a wet-on-wet printing method.