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EP-3960464-B1 - AQUEOUS INKJET INK, AQUEOUS INKJET INK SET, AQUEOUS INKJET INK PRINTED MATTER PRODUCTION METHOD, AND PRINTED MATTER

EP3960464B1EP 3960464 B1EP3960464 B1EP 3960464B1EP-3960464-B1

Inventors

  • SUNAOSHI KAZUSHI
  • SUGIHARA MASAHIRO
  • SASAKI YUKI

Dates

Publication Date
20260506
Application Date
20200421

Claims (10)

  1. An aqueous inkjet ink comprising a pigment, a binder resin, a water-soluble organic solvent, a surfactant and water, wherein the binder resin comprises an aqueous resin containing, as structural units, a structure derived from an ethylenically unsaturated monomer containing an acid group and a structure derived from an ethylenically unsaturated monomer containing a hydroxyl group; the resin has a weight average molecular weight of 5,000 to 45,000, and a glass transition temperature of 35 to 110°C, wherein the glass transition temperature is measured by using a differential scanning calorimeter; the water-soluble organic solvent comprises a first water-soluble organic solvent having a solubility parameter value of 8.5 to 13 (cal/cm 3 ) 1/2 , and does not contain a second water-soluble organic solvent having a boiling point at 1 atmosphere of 235°C or higher; the first water-soluble organic solvent comprises one or more propylene glycol ether-based solvents selected from the group consisting of propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether and dipropylene glycol monomethyl ether; and the surfactant contains an acetylene-based surfactant.
  2. The aqueous inkjet ink according to Claim 1, wherein the water-soluble organic solvent comprises a water-soluble organic solvent having a boiling point of 200°C or lower in an amount of at least 60% by mass of a total mass of the water-soluble organic solvent.
  3. An aqueous inkjet ink comprises a pigment, a binder resin, a water-soluble organic solvent, a surfactant and water, wherein the binder resin comprises an aqueous resin containing, as structural units, a structure derived from an ethylenically unsaturated monomer containing an acid group and a structure derived from an ethylenically unsaturated monomer containing a hydroxyl group; the resin has a weight average molecular weight of 5,000 to 45,000, and a glass transition temperature of 35 to 110°C, wherein the glass transition temperature is measured by using a differential scanning calorimeter; the water-soluble organic solvent contains a first water-soluble organic solvent having an solubility parameter value of 8.5 to 13 (cal/cm 3 ) 1/2 , and a second water-soluble organic solvent having a boiling point at 1 atmosphere of 235°C or higher; the first water-soluble organic solvent comprises one or more propylene glycol ether-based solvents selected from the group consisting of propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether and dipropylene glycol monomethyl ether; an amount of the second water-soluble organic solvent is greater than 0% by mass but not more than 5% by mass relative to a total mass of the aqueous inkjet ink; and the surfactant comprises an acetylene-based surfactant.
  4. The aqueous inkjet ink according to any one of Claims 1 to 3, wherein the first water-soluble organic solvent further comprises at least one selected from the group consisting of 1,2-propanediol and 1,2-butanediol in an amount of 5 to 30% by mass relative to a total mass of the aqueous inkjet ink.
  5. The aqueous inkjet ink according to any one of Claims 1 to 4, wherein the first water-soluble organic solvent comprises the one or more propylene glycol ether-based solvents in an amount of 1 to 15% by mass relative to a total mass of the aqueous inkjet ink.
  6. The aqueous inkjet ink according to any one of Claims 1 to 5, wherein an acid value of the aqueous resin is from 10 to 60 mgKOH/g.
  7. The aqueous inkjet ink according to any one of Claims 1 to 6, wherein a hydroxyl value of the aqueous resin is from 1 to 50 mgKOH/g.
  8. An aqueous inkjet ink set comprising two or more aqueous inkjet inks having different hues from each other, wherein each of the two or more aqueous inkjet inks is the aqueous inkjet ink according to any one of Claims 1 to 7.
  9. A method for producing an aqueous inkjet ink printed matter, the method having a step of discharging from an inkjet head and adhering to a substrate the aqueous inkjet ink according to any one of Claims 1 to 7 or the aqueous inkjet ink set according to Claim 8, and a step of drying the substrate with the adhered aqueous inkjet ink.
  10. A printed matter obtained by printing the aqueous inkjet ink according to any one of Claims 1 to 7 onto a substrate.

Description

TECHNICAL FIELD The present invention relates to an aqueous inkjet ink (hereinafter also referred to simply as an "aqueous ink" or an "ink"), an aqueous inkjet ink set, a method for producing an aqueous inkjet ink printed matter, and printed matter. BACKGROUND ART The spread of digital printing methods is rapidly advancing in line with the trend toward smaller printing lots and diversified needs. The digital printing method does not require a printing plate, and can therefore realize small lot printing, cost reduction, and reduction in the size of the printing apparatus. The inkjet printing method, which is one type of a digital printing method, is a method in which fine liquid droplets of an ink are jetted from an inkjet head onto a recording medium to form images or text on the recording medium (hereinafter also collectively referred to as "printed matter"). Compared with other digital printing methods, the inkjet printing method is superior in terms of the size and cost of the printing apparatus, the running costs during printing, and the easiness of full-color printing, and, in recent years, the use of the inkjet printing method has been advanced in industrial printing applications. There are various types of inks used in the inkjet printing method, including oilbased inks, solvent-based inks, active energy ray-curable inks, and aqueous inks. To date, solvent-based inks and active energy ray-curable inks have been used in industrial printing applications. However, as a result of considering and addressing potential harm to people and environment in recent years, the demand for aqueous inks is growing. Further, in recent years, in the demand for expansion in potential applications of the inkjet printing method, in addition to industrial printing applications, development to packaging applications such as paper containers, labels, and packaging films is demanded. In this case, it is required to form a printed matter having high color reproducibility and high image quality and having properties that can withstand actual use, with respect to low-absorption substrates such as coated paper and art paper, and non-absorption substrates such as polypropylene films (for example, biaxially oriented polypropylene (OPP) films), polyethylene terephthalate (PET) films and nylon films. Most of the existing aqueous inks for the use in the inkjet printing method (in this description, simply referred to as "aqueous inkjet ink") are inks for forming an image on high-absorption substrate, such as plain paper or special paper. When such an ink is used for a non-absorption substrate, a problem arises in that drying by penetration and absorption of the ink droplets after landing does not occur, and thus print image quality is deteriorated or sufficient adhesion is not obtained. In particular, if the adhesion to the non-absorption substrate is insufficient, then problems arise, including detachment of the ink film as result of rubbing or the like, and occurrence of blocking due to pressure applied to the printed surface when the printed matter is stored in a wound or stacked state. In addition, in those cases where a printed matter is bonded to another film (lamination) via an adhesive (a laminate adhesive), if the printed matter that has not been sufficiently dried is laminated, then there is a possibility that delamination may occur between the layers due to insufficient laminate strength. For example, Patent Document 1 discloses an aqueous inkjet ink in which a resin having a specific characteristic and an organic solvent having a specific structure are used in combination, and describes that the aqueous inkjet ink can be suitably used for inkjet printing on a non-absorption substrate such as a polyvinyl chloride sheet. However, as described below, the inventors of the present application evaluated the ink using the resin specifically described in the Examples of Patent Document 1, and it was found that the discharge stability was inferior. In recent years, in order to meet the market demand for the development to the above-mentioned applications, studies have been made to increase the resolution of printed matter by reducing the size of ink droplets discharged from an inkjet head or increasing the driving frequency of the inkjet head, and it can be said that improvement of discharge stability is an essential problem. Patent Document 2 discloses that a printed matter having excellent lamination applicability can be obtained by using an aqueous inkjet ink containing a certain amount of a water-soluble urethane resin produced through a specific process. However, Patent Document 2 discloses that it is preferable that the glass transition temperature of the water-soluble urethane resin is not high, and the glass transition temperature of the water-soluble urethane resins specifically produced in the Examples is from -50 to -15°C. When an ink containing a resin having such a glass transition temperature is used, there is a high p