Ink for inkjet printing

Abstract

To provide an ink for inkjet printing capable of forming a printed layer which can be used for printing onto a low liquid-absorbing printing substrate such as a synthetic resin film, can effectively and safely be removed with neutral water, and further can suppress coloration of the neutral water, and recoloration of the substrate.SOLUTION: An ink for inkjet printing onto a low liquid-absorbing printing substrate includes a pigment, a pigment dispersant, a water-soluble resin, and water, where the acid value of the pigment dispersant is 10 mgKOH / g or higher and 130 mgKOH / g or lower, and the water-soluble resin includes a monomer unit (A) having a sulfonate group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to inks for ink-jet printing. [Background technology]

[0002] Inkjet printing is a printing method in which ink droplets are ejected from fine nozzles and deposited on a printing substrate to produce a printed matter having a printing layer on which characters or images are recorded. This printing method has many advantages, such as being easy to produce full color at low cost, being able to use a variety of printing substrates, including highly absorbent printing substrates such as plain paper and less absorbent printing substrates such as synthetic resin film, and being non-contact with the printing substrate. From the perspective of weather resistance and water resistance of printed matter, inks using pigments as colorants have become mainstream in inkjet printing methods.

[0003] In recent years, synthetic resins have been used in a wide variety of applications, including containers and packaging bags, and for functional reasons, many of these containers are made up of completely different types of film, inorganic materials such as aluminum, ink, etc. In particular, printed matter using ink, etc., is essential for containers and packaging bags in communicating information to consumers and managing product logistics, and is printed or processed onto the surface of containers, etc.

[0004] Because synthetic resins are difficult to decompose in nature, and because of resource conservation and economic reasons, some of them are separated and collected, recycled, and reused as secondary products. However, if printed resin products are mixed in during recycling, the recycled product may become partially or entirely discolored. This significantly reduces the commercial value of the recycled product, making it impossible to reuse it in many cases. It may also cause fatal defects in its physical properties. Currently, such printed resin products are discarded rather than collected (for reuse).

[0005] In view of the above-mentioned current situation, methods for removing printed layers from synthetic resin products have been studied from the viewpoint of recycling printed synthetic resins (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-131484 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technology described in Patent Document 1 uses an alkaline aqueous solution to remove the printed layer. Alkaline aqueous solutions are highly hazardous to the human body and must be handled with care. Furthermore, immersing printed materials in alkaline aqueous solutions can corrode the base material, making recycling difficult.

[0008] To address the above issues, it is conceivable to incorporate a water-soluble material, such as polyvinyl alcohol, into the ink, which dissolves in neutral water, so that the printed layer can be removed with neutral water. However, conventional water-soluble materials have poor blocking resistance (resistance to stacking and storage), and therefore, when used on printed items that are often stored in relatively humid environments (such as household detergent containers), there is a risk of color transfer to other items or peeling of the printed layer due to the humidity in the environment.

[0009] Furthermore, when a printed layer formed from a conventional ink containing a water-soluble material is removed from a substrate using neutral water, the ink contained in the printed layer disperses or dissolves in the neutral water, resulting in the coloring of the neutral water used to remove the printed layer (hereinafter also referred to as removed water). This colored removed water may be difficult to reuse as is, leading to increased recycling costs. Furthermore, when the colored removed water comes into contact with the substrate from which the printed layer has been removed, the substrate may be recolored. As described above, if materials derived from the recolored substrate are mixed in, the recycled product may become partially or entirely colored, making the substrate often unusable.

[0010] The present invention provides an inkjet printing ink that can be used for printing on low-liquid-absorbent printing substrates such as synthetic resin films, can be safely and efficiently removed with neutral water, and can form a printing layer that can suppress discoloration of the neutral water and re-discoloration of the substrate. [Means for solving the problem]

[0011] The present invention provides An ink for inkjet printing on a low-liquid-absorbent printing substrate, the ink contains a pigment, a pigment dispersant, a water-soluble resin, and water; The acid value of the pigment dispersant is 10 mgKOH / g or more and 130 mgKOH / g or less, The ink for ink-jet printing is such that the water-soluble resin has a monomer unit (A) having a sulfonate group. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an inkjet printing ink that can be used for printing on low-liquid-absorbent printing substrates such as synthetic resin films, can be safely and efficiently removed with neutral water, and can form a printing layer that can suppress discoloration of the neutral water and re-discoloration of the substrate. DETAILED DESCRIPTION OF THE INVENTION

[0013] <Inkjet printing ink> The inkjet printing ink of this embodiment is an ink for inkjet printing on low-liquid-absorbent printing substrates, and contains a pigment, a pigment dispersant, a water-soluble resin, and water, wherein the pigment dispersant has an acid value of 10 mgKOH / g or more and 130 mgKOH / g or less, and the water-soluble resin has a monomer unit (A) having a sulfonate group. The inkjet printing ink of this embodiment can be used for printing on low-liquid-absorbent printing substrates such as synthetic resin films, and can form a printed layer that can be safely and efficiently removed with neutral water and that can suppress discoloration of the neutral water and re-discoloration of the substrate. The reason why the inkjet printing ink of this embodiment exhibits these effects is unclear, but is presumed to be as follows.

[0014] It is believed that the water-soluble resin in the ink contains a monomer unit (A) having a sulfonate group, which improves the affinity of the printed layer derived from the ink to water, making it easier to remove the printed layer with neutral water at 40° C. or higher. It is also believed that the acid value of the pigment dispersant is set to 10 mg KOH / g or higher and 130 mg KOH / g or lower, making the printed layer derived from the ink hydrophobic and preventing re-dissolution in neutral water at 40° C. or higher, thereby preventing discoloration of the removed water and re-discoloration of the substrate.

[0015] As used herein, "water-soluble" refers to a dissolution of 0.01 g or more in 100 g of neutral water at 40°C. Examples of the neutral water include water or an aqueous solution having a pH of 6 to 8. Specific examples of the neutral water include deionized water, pure water, tap water, and industrial water. Deionized water or tap water is preferred due to its availability. The neutral water may also contain other components, such as a water-soluble organic solvent and a surfactant. Examples of the water-soluble organic solvent that may be contained in the neutral water include lower alcohols such as methanol, ethanol, and 2-propanol; glycol ethers such as propylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monotertiary butyl ether, and diethylene glycol monobutyl ether; and ketones such as acetone and methyl ethyl ketone. Examples of the surfactant that may be contained in the neutral water include anionic surfactants such as alkyl sulfates, alkyl ether sulfates, olefin sulfonates, and alkyl ether carboxylates; cationic surfactants such as alkyl trimethylammonium salts; and nonionic surfactants such as polyoxyethylene alkyl ethers and alkyl glycosides.

[0016] [Water-soluble resin] Examples of the water-soluble resin include water-soluble polyester resins, water-soluble vinyl resins, water-soluble polyamide resins, water-soluble polyimide resins, water-soluble polyurethane resins, and modified products of these resins. These can be used alone or in combination of two or more. From the viewpoint of achieving the effects of the present invention, the water-soluble resin preferably includes one or more selected from the group consisting of water-soluble polyester resins and water-soluble vinyl resins, and more preferably includes a water-soluble polyester resin.

[0017] The sulfonate group is -SO3M from the viewpoint of enabling the printing layer to be removed with neutral water and from the viewpoint of facilitating the polymerization reaction during the production of the water-soluble resin. 3 (However, M 3represents a counter ion of the sulfonic acid group that constitutes the sulfonate group, and from the viewpoint of making it possible to remove the printed layer with neutral water, is preferably one or more ions selected from the group consisting of metal ions and ammonium ions, more preferably one or more ions selected from the group consisting of metal ions, even more preferably one or more ions selected from the group consisting of alkali metal ions and alkaline earth metal ions, even more preferably one or more ions selected from the group consisting of alkali metal ions, even more preferably one or more ions selected from the group consisting of sodium ions and potassium ions, and even more preferably sodium ions.) is preferred.

[0018] The content of sulfonate groups in the water-soluble resin is preferably 0.4 mmol / g or more, more preferably 0.6 mmol / g or more, and even more preferably 0.7 mmol / g or more, from the viewpoint of enabling the printing layer to be removed with neutral water, and is preferably 2.0 mmol / g or less, more preferably 1.5 mmol / g or less, from the viewpoint of improving the water resistance of the printing layer.

[0019] [Water-soluble polyester resin] When the water-soluble resin contains a water-soluble polyester resin, the water-soluble polyester resin is preferably a water-soluble polyester resin having the monomer unit (A), a hydrophobic dicarboxylic acid monomer unit (B1), and a diol monomer unit (C1), from the viewpoint of enabling the printing layer to be removed with neutral water. In this specification, "hydrophobic" means that when the monomer is dissolved in 100 g of ion-exchanged water at 25°C until saturation, the amount of dissolution is less than 10 g.

[0020] The monomer unit (A) constituting the monomer units of the water-soluble polyester resin is referred to as monomer unit (A1), and a monomer for deriving this monomer unit (A1) is referred to as monomer (A1). From the viewpoint of enabling the printed layer to be removed with neutral water and improving the water resistance of the printed layer, the monomer (A1) is preferably an aromatic carboxylic acid, more preferably one or more selected from the group consisting of 5-hydroxyisophthalic acid, 5-aminoisophthalic acid, 5-sulfoisophthalic acid, 2-sulfoterephthalic acid, and 4-sulfo-2,6-naphthalenedicarboxylic acid, even more preferably one or two selected from the group consisting of 5-sulfoisophthalic acid and 2-sulfoterephthalic acid, and even more preferably 5-sulfoisophthalic acid.

[0021] The proportion of the amount of the monomer unit (A1) to the total amount of all monomer units of the water-soluble polyester resin is preferably 5 mol% or more, more preferably 10 mol% or more, and even more preferably 12 mol% or more, from the viewpoint of enabling the printed layer to be removed with neutral water. The proportion of the amount of the monomer unit (A1) to the total amount of all monomer units of the water-soluble polyester resin is preferably 35 mol% or less, more preferably 30 mol% or less, and even more preferably 20 mol% or less, from the viewpoint of improving the water resistance of the printed layer.

[0022] The hydrophobic dicarboxylic acid monomer unit (B1) does not have a hydrophilic group. The hydrophilic group is not particularly limited as long as it exhibits hydrophilicity. Examples of the hydrophilic group include a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium salt group, an oxyalkylene group, a hydroxyl group, a carboxyl group, a carboxyl salt group, a phosphate group, a sulfonic acid group, and a sulfonate salt group.

[0023] The monomer for deriving the hydrophobic dicarboxylic acid monomer unit (B1) contained in the water-soluble polyester resin is referred to as monomer (B1). From the viewpoint of improving the water resistance of the printed layer, the monomer (B1) is preferably one or more selected from the group consisting of aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids. Among these, from the same viewpoint, one or more selected from the group consisting of terephthalic acid, isophthalic acid, 2,5-furandicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and 1,3-adamantanedicarboxylic acid are more preferred, one or more selected from the group consisting of terephthalic acid, 2,5-furandicarboxylic acid, and 2,6-naphthalenedicarboxylic acid are even more preferred, and 2,6-naphthalenedicarboxylic acid is even more preferred.

[0024] The proportion of the amount of the monomer unit (B1) to the total amount of all monomer units in the water-soluble polyester resin is preferably 15 mol% or more, more preferably 20 mol% or more, and even more preferably 30 mol% or more, from the viewpoint of improving the water resistance of the printed layer. The proportion of the amount of the monomer unit (B1) to the total amount of all monomer units in the water-soluble polyester resin is preferably 45 mol% or less, more preferably 40 mol% or less, and even more preferably 38 mol% or less, from the viewpoint of enabling the printed layer to be removed with neutral water.

[0025] The monomer for deriving the diol monomer unit (C1) contained in the water-soluble polyester resin is referred to as monomer (C1). Although aliphatic diols, aromatic diols, etc. can be used as the monomer (C1), aliphatic diols are preferred from the viewpoint of production costs for the water-soluble polyester resin. From the viewpoint of enabling removal of the printed layer with neutral water and improving the water resistance of the printed layer, the aliphatic diol preferably includes one or more selected from the group consisting of ethylene glycol, 1,2-propanediol, 1,3-propanediol, diethylene glycol, and dipropylene glycol, more preferably one or more selected from the group consisting of ethylene glycol, 1,2-propanediol, and 1,3-propanediol, and even more preferably ethylene glycol.

[0026] When the monomer (C1) contains one or more selected from the group consisting of ethylene glycol, 1,2-propanediol, 1,3-propanediol, diethylene glycol, and dipropylene glycol, the total proportion of the monomer units derived from ethylene glycol, 1,2-propanediol, 1,3-propanediol, diethylene glycol, and dipropylene glycol relative to the total of all diol monomer units (C1) in the water-soluble polyester resin is preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, even more preferably 98 mol% or more, and even more preferably substantially 100 mol%, from the viewpoint of enabling the printing layer to be removed with neutral water. Note that substantially 100 mol% means that monomer units derived from diols other than ethylene glycol, 1,2-propanediol, 1,3-propanediol, diethylene glycol, and dipropylene glycol are inevitably mixed in.

[0027] The water-soluble polyester resin may contain a monomer unit other than the monomer unit (A1), the monomer unit (B1), and the diol monomer unit (C1) as long as the effects of this embodiment are not impaired.

[0028] (Water-soluble vinyl resin) When the water-soluble resin contains a water-soluble vinyl resin, the water-soluble vinyl resin is preferably a water-soluble vinyl resin having the monomer unit (A) and a hydrophobic monomer unit (B2), from the viewpoint of enabling the printed layer to be removed with neutral water and improving the water resistance of the printed layer.

[0029] The monomer unit (A) constituting the water-soluble vinyl resin is referred to as monomer unit (A2), and a monomer for deriving the monomer unit (A2) is referred to as monomer (A2). From the viewpoints of enabling the printed layer to be removed with neutral water and improving the water resistance of the printed layer, the monomer (A2) is more preferably one or more selected from the group consisting of styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 2-methacrylamido-2-methylpropanesulfonic acid.

[0030] The proportion of the amount of the monomer unit (A2) to the total amount of all monomer units of the water-soluble vinyl resin is preferably 5 mol% or more, more preferably 10 mol% or more, and even more preferably 12 mol% or more, from the viewpoint of enabling the printed layer to be removed with neutral water. The proportion of the amount of the monomer unit (A2) to the total amount of all monomer units of the water-soluble vinyl resin is preferably 35 mol% or less, more preferably 30 mol% or less, and even more preferably 20 mol% or less, from the viewpoint of improving the water resistance of the printed layer.

[0031] The monomer unit (B2) does not have the hydrophilic group. The monomer for deriving the monomer unit (B2) contained in the water-soluble vinyl resin is referred to as monomer (B2).

[0032] Examples of the monomer (B2) include those described in paragraphs 0018 to 0021 of JP 2018-80255 A. Among these, from the viewpoint of improving the water resistance of the printed layer, one or more selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, (iso)propyl (meth)acrylate, and (iso- or tertiary)butyl (meth)acrylate are preferred. Note that "(meth)acrylate" means at least one selected from acrylate and methacrylate.

[0033] The ratio of the amount of the monomer unit (B2) in the water-soluble vinyl resin to the total amount of all monomer units in the water-soluble vinyl resin is preferably 30 mol% or more, more preferably 40 mol% or more, and even more preferably 60 mol% or more, from the viewpoint of improving the water resistance of the printed layer. The ratio of the amount of the monomer unit (B2) in the water-soluble vinyl resin to the total amount of all monomer units in the water-soluble vinyl resin is preferably 90 mol% or less, more preferably 80 mol% or less, from the viewpoint of enabling the printed layer to be removed with neutral water.

[0034] The water-soluble vinyl resin may contain a monomer unit (B3) other than the monomer unit (A2) and the monomer unit (B2), provided that the effects of this embodiment are not impaired. Examples of the monomer (B3) from which the monomer unit (B3) is derived include carboxylic acid monomers such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid; and phosphate monomers such as vinylphosphonic acid, vinyl phosphate, bis(methacryloxyethyl)phosphate, diphenyl-2-acryloyloxyethyl phosphate, and diphenyl-2-methacryloyloxyethyl phosphate. The term "(meth)acrylic acid" refers to at least one selected from acrylic acid and methacrylic acid.

[0035] The weight average molecular weight of the water-soluble resin is preferably 1,000 or more, more preferably 3,000 or more, and even more preferably 4,000 or more from the viewpoint of improving the water resistance of the printed layer, and is preferably 80,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less, and even more preferably 20,000 or less from the viewpoint of enabling the printed layer to be removed with neutral water. In this specification, the weight average molecular weight is measured by the method described in the examples.

[0036] From the viewpoint of improving the water resistance of the printed layer, the glass transition temperature of the water-soluble resin is preferably 50° C. or higher, more preferably 60° C. or higher, even more preferably 70° C. or higher, and even more preferably 80° C. or higher. From the viewpoint of enabling the printed layer to be removed with neutral water, the glass transition temperature of the water-soluble resin is preferably 180° C. or lower, more preferably 160° C. or lower, even more preferably 140° C. or lower, and even more preferably 120° C. or lower. In this specification, the glass transition temperature is measured by the method described in the examples.

[0037] The method for producing the water-soluble resin is not particularly limited, and any conventionally known method for producing a water-soluble resin can be applied.

[0038] [Pigments] The pigment may be either an inorganic pigment or an organic pigment, and any pigment may be used without any particular limitation as long as it is a pigment that can be used in inkjet printing inks.

[0039] Examples of the inorganic pigment include carbon black and metal oxides, and carbon black is preferred for black inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black. Examples of white inks include titanium dioxide, zinc oxide, silica, alumina, magnesium oxide, and other metal oxides. These inorganic pigments are surface-treated with known hydrophobic treatment agents such as titanium coupling agents, silane coupling agents, and higher fatty acid metal salts. may be.

[0040] Examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.

[0041] The hue of the pigment is not particularly limited, and in the case of chromatic color inks, any chromatic color pigment such as yellow, magenta, cyan, red, blue, orange, and green can be used.

[0042] The content of the pigment in the ink is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of enabling the printed layer to be removed with neutral water.The content of the pigment in the ink is preferably 9% by mass or less, more preferably 8% by mass or less, and even more preferably 7% by mass or less, from the viewpoint of improving water resistance.

[0043] [Pigment dispersant] The pigment is dispersed in the pigment dispersant and contained in the ink. The acid value of the pigment dispersant is 10 mgKOH / g or more, preferably 15 mgKOH / g or more, and more preferably 20 mgKOH / g or more, from the viewpoint of enabling the printed layer to be removed with neutral water. The acid value of the pigment dispersant is 130 mgKOH / g or less, preferably 135 mgKOH / g or less, and more preferably 140 mgKOH / g or less, from the viewpoint of preventing the removed water from being discolored by the pigment derived from the printed layer. In this specification, the acid value is measured by the method described in the Examples.

[0044] The pigment dispersant has the ability to disperse the pigment and is preferably a water-insoluble polymer from the viewpoint of improving water resistance. In this specification, "water-insoluble" means that it does not dissolve in an amount of 0.01 g or more in 100 g of neutral water at 40°C. From the same viewpoint, the water-insoluble polymer preferably includes one or more polymers selected from water-insoluble vinyl polymers, water-insoluble polyester polymers, and water-insoluble polyurethane polymers, and more preferably includes one or more polymers selected from water-insoluble vinyl polymers and water-insoluble polyester polymers.

[0045] [Water-insoluble vinyl polymer] From the viewpoint of improving the water resistance of the printed layer, the water-insoluble vinyl polymer preferably has a structural unit derived from an ionic monomer (D) and a structural unit derived from a hydrophobic monomer (E). Moreover, from the viewpoint of enabling the printed layer to be removed with neutral water, the water-insoluble vinyl polymer more preferably has a structural unit derived from a nonionic monomer (F).

[0046] [Ionic Monomer (D)] The ionic monomer (D) may be an anionic monomer or a cationic monomer, with anionic monomers being preferred, monomers having an acid group being more preferred, and monomers having a carboxy group being even more preferred. Specific examples of the ionic monomer (D) include those described in paragraph 0017 of JP 2018-80255 A. Among these, (meth)acrylic acid is preferred. The term "(meth)acrylic acid" refers to at least one selected from acrylic acid and methacrylic acid.

[0047] [Hydrophobic Monomer (E)] Examples of the hydrophobic monomer (E) include alkyl (meth)acrylates, aromatic ring-containing monomers, and macromonomers. One or more selected from alkyl (meth)acrylates and aromatic ring-containing monomers are preferred, with aromatic ring-containing monomers being more preferred. Specific examples of the hydrophobic monomer (E) include those described in paragraphs 0018 to 0021 of JP 2018-80255 A. Among these, one or more selected from styrene, α-methylstyrene, and benzyl (meth)acrylate are preferred. The term "(meth)acrylate" refers to at least one selected from acrylates and methacrylates.

[0048] [Nonionic Monomer (F)] Examples of the nonionic monomer (F) include polyalkylene glycol (meth)acrylate, alkoxy polyalkylene glycol (meth)acrylate, and phenoxy (ethylene glycol / propylene glycol copolymer) (meth)acrylate. Specific examples of the nonionic monomer (F) include those described in paragraphs 0022 and 0023 of JP 2018-80255 A. Among these, alkoxy polyalkylene glycol (meth)acrylate is preferred, and methoxy polyethylene glycol (meth)acrylate is more preferred.

[0049] The water-insoluble vinyl polymer can be produced by the method described in paragraphs 0024 to 0028 of JP-A No. 2018-80255.

[0050] [Water-insoluble polyester polymer] The water-insoluble polyester polymer has a structural unit derived from an alcohol monomer (G) and a structural unit derived from a carboxylic acid monomer (H), and can be obtained by polycondensation of the alcohol monomer (G) and the carboxylic acid monomer (H).

[0051] [Alcohol Monomer (G)] The alcohol monomer (G) preferably contains an aromatic diol from the viewpoints of improving the dispersion stability of the pigment and improving intermittent ejection properties and substrate adhesion. The aromatic diol is preferably an alkylene oxide adduct of bisphenol A. The alkylene oxide adduct of bisphenol A is preferably a propylene oxide adduct of bisphenol A or an ethylene oxide adduct of bisphenol A, and more preferably a propylene oxide adduct of bisphenol A. The alkylene oxide adduct of bisphenol A refers to the entire structure in which an oxyalkylene group is added to 2,2-bis(4-hydroxyphenyl)propane.

[0052] The alcohol monomer (G) may contain, in addition to the alkylene oxide adduct of bisphenol A, other alcohols such as ethylene glycol, propylene glycol (1,2-propanediol), glycerin, pentaerythritol, trimethylolpropane, hydrogenated bisphenol A, sorbitol, or alkylene oxide adducts thereof (having a carbon number of 2 to 4) (average number of added moles: 1 to 16).

[0053] The content of the alkylene oxide adduct of bisphenol A in the alcohol monomer (G) is preferably 50 mol % or more, more preferably 60 mol % or more, and even more preferably 70 mol % or more, from the viewpoint of improving the dispersion stability of the pigment and improving the ejection reliability, and the upper limit thereof is preferably 100 mol % or less.

[0054] [Carboxylic acid monomer (H)] The carboxylic acid monomer (H) includes carboxylic acids, their acid anhydrides, and their alkyl (carbon number 1 to 3) esters. Examples of the carboxylic acid monomer (H) include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and trivalent or higher polycarboxylic acids. Examples of the aromatic dicarboxylic acids include phthalic acid, isophthalic acid, and terephthalic acid, with terephthalic acid being more preferred. Examples of the aliphatic dicarboxylic acids include unsaturated and saturated aliphatic dicarboxylic acids, with fumaric acid and maleic acid being more preferred, and fumaric acid being more preferred. Examples of the saturated aliphatic dicarboxylic acids include adipic acid and succinic acid. Examples of the alicyclic dicarboxylic acids include cyclohexanedicarboxylic acid, decalindicarboxylic acid, and tetrahydrophthalic acid, and examples of the trivalent or higher polycarboxylic acids include trimellitic acid and pyromellitic acid. The carboxylic acid monomer (H) can be used alone or in combination of two or more.

[0055] The water-insoluble polyester polymer can be produced by the method described in paragraph 0038 of JP-A-2022-10817.

[0056] From the viewpoint of improving the dispersion stability of the pigment particles dispersed in the polymer in the ink and improving the fixing strength of the ink to the printing substrate, the weight-average molecular weight of the pigment dispersant is preferably 8,000 or more, more preferably 10,000 or more, even more preferably 12,000 or more, and is preferably less than 100,000, more preferably 80,000 or less, even more preferably 60,000 or less, and still more preferably 50,000 or less.

[0057] From the viewpoint of fixability, the content of the pigment dispersant in the ink is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, even more preferably 1.5% by mass or more, and is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 4% by mass or less, and still more preferably 3% by mass or less.

[0058] From the viewpoint of improving ink stability, the mass ratio of the pigment dispersant to the pigment [mass of the pigment dispersant / mass of the pigment] is preferably 0.2 / 99.8 to 70 / 30, more preferably 1 / 99 to 50 / 50, even more preferably 10 / 90 to 40 / 60, and still more preferably 20 / 80 to 30 / 70.

[0059] From the same viewpoint, the pigment is preferably contained in the ink in the form of pigment-containing polymer particles in which the pigment is contained in the pigment dispersant. The pigment-containing polymer particles include particles in which the pigment dispersant encompasses the pigment, particles consisting of the pigment dispersant and the pigment with a portion of the pigment exposed on the surface, and particles in which the pigment dispersant is adsorbed to a portion of the pigment. The pigment dispersant contained in the pigment-containing polymer particles is preferably crosslinked. The pigment-containing polymer particles can be produced by the method described in paragraphs 0040 to 0047 of JP 2022-10817 A.

[0060] [Fixing resin] The ink preferably contains a fixing resin from the viewpoint of improving the fixing property of the printing layer derived from the ink to the low-liquid-absorbent substrate. The fixing resin is a water-insoluble resin. From the same viewpoint, the fixing resin is preferably one or more selected from the group consisting of condensation resins such as polyurethane and polyester, and vinyl polymers such as (meth)acrylic resins, styrene resins, styrene-acrylic resins, butadiene resins, styrene-butadiene resins, vinyl chloride resins, vinyl acetate resins, and acrylic silicone resins.

[0061] The acid value of the fixing resin is preferably 0.1 mgKOH / g or more, more preferably 5 mgKOH / g or more, from the viewpoint of enabling the printing layer to be removed with neutral water, and is preferably 150 mgKOH / g or less, more preferably 100 mgKOH / g or less, from the viewpoint of preventing the removed water from being colored by the pigment derived from the printing layer.

[0062] From the viewpoint of improving the fixability of the printing layer derived from the ink to the low-liquid-absorbent substrate, the weight-average molecular weight of the fixing resin is preferably 100,000 or more, more preferably 125,000 or more, even more preferably 150,000 or more, and is preferably 1,000,000 or less, more preferably 750,000 or less, even more preferably 500,000 or less, and even more preferably 250,000 or less.

[0063] The content of the fixing resin in the ink is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of improving the fixability of the printed layer derived from the ink to the low-liquid-absorbent substrate. The content of the fixing resin in the ink is preferably 10% by mass or less, more preferably 7.5% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of enabling the printed layer to be removed with neutral water.

[0064] [Water-soluble organic solvent] The ink preferably contains a water-soluble organic solvent from the viewpoints of improving the storage stability of the ink and improving the continuous ejection property of the ink. In this specification, the water-soluble organic solvent refers to an organic solvent that dissolves in 100 mL of water at 25°C in an amount of 10 mL or more.

[0065] The water-soluble organic solvent is preferably one or more selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers, from the viewpoint of improving the storage stability of the ink and improving the continuous ejection properties of the ink.

[0066] From the viewpoint of improving the storage stability of the ink and improving the continuous ejection properties of the ink, the polyhydric alcohol is preferably one or more selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, glycerin, trimethylolpropane, and alkylene glycols having 4 to 10 carbon atoms, and more preferably propylene glycol.

[0067] The polyhydric alcohol alkyl ether is preferably one or more selected from the group consisting of ethylene glycol mono-n-butyl ether, diethylene glycol isopropyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, ethylene glycol mono-iso-butyl ether, diethylene glycol mono-iso-butyl ether, triethylene glycol mono-n-butyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, and diethylene glycol diethyl ether, and more preferably diethylene glycol mono-iso-butyl ether.

[0068] The content of the water-soluble organic solvent in the ink is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoints of improving the storage stability of the ink and improving the continuous ejection property of the ink. From the same viewpoints as above, the content of the water-soluble organic solvent in the ink is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less.

[0069] 〔water〕 From the viewpoint of reducing the environmental impact, the water content in the ink is preferably 40% by mass or more, more preferably 45% by mass or more, and even more preferably 50% by mass or more. From the same viewpoint as above, the water content in the ink is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0070] [Other additives] The ink may contain other additives as needed, provided that the effects of the present invention are not impaired. Examples of other additives include surfactants, chelating agents, humectants, wetting agents, penetrants, viscosity adjusters, antifoaming agents, preservatives, antifungal agents, and anticorrosive agents.

[0071] [Surfactants] The ink preferably contains the surfactant from the viewpoint of improving wettability to the low-liquid-absorbent substrate. From the same viewpoint, the surfactant is preferably a nonionic surfactant, more preferably one or more surfactants selected from the group consisting of acetylene glycol surfactants and silicone surfactants, and it is preferable to use the acetylene glycol surfactant and the silicone surfactant in combination.

[0072] Examples of the acetylene glycol surfactant include acetylene diols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, 2,4-dimethyl-5-hexyne-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, and 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, as well as ethylene oxide adducts thereof. Examples of commercially available acetylene glycol surfactants include the "Surfynol" series and "Olfine" series manufactured by Nissin Chemical Industry Co., Ltd., and the "Acetylenol" series manufactured by Kawaken Fine Chemicals Co., Ltd.

[0073] Examples of the silicone surfactant include dimethylpolysiloxane, polyether-modified silicone, amino-modified silicone, carboxy-modified silicone, etc. Examples of commercially available silicone surfactants include the Silicone: KF series manufactured by Shin-Etsu Chemical Co., Ltd.

[0074] When the ink contains the surfactant, the content of the surfactant in the ink is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, from the viewpoints of enabling the printed layer to be removed with neutral water and improving the water resistance of the printed layer. When the ink contains the surfactant, the content of the surfactant in the ink is preferably 3% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2% by mass or less, from the same viewpoints as above.

[0075] [Chelating agent] The ink may contain a chelating agent from the viewpoint of enabling the printing layer to be removed with neutral water and improving the water resistance of the printing layer. Examples of the chelating agent include one or more selected from the group consisting of alkali metal salts or lower amine salts of gluconic acid, glucoheptonic acid, ethylenediaminetetraacetic acid, citric acid, malic acid, and hydroxyethylidenediphosphonic acid.

[0076] When the ink contains the chelating agent, the content of the chelating agent in the ink is preferably 0.1% by mass or more, more preferably 0.25% by mass or more, and even more preferably 0.5% by mass or more, from the viewpoints of enabling the printed layer to be removed with neutral water and improving the water resistance of the printed layer. When the ink contains the chelating agent, the content of the chelating agent in the ink is preferably 4% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less, from the same viewpoints as above.

[0077] <Manufacturing method for printed matter> The method for producing a printed matter of this embodiment includes a printing layer forming step of printing with the ink by an inkjet printing method to form a printing layer derived from the ink on the low-liquid-absorbent printing substrate directly or via another layer. In this specification, the term "low-liquid-absorbent printing substrate" refers to a substrate that absorbs 0 g / m2 of water per surface area when in contact with pure water for 100 ms. 2 More than 10g / m 2 In this specification, "printing" includes printing on which characters or images are recorded, and printing on which characters or images are printed.

[0078] [Printing layer formation process] The low-liquid-absorbent printing substrate is not particularly limited as long as it can be printed using an inkjet printing method. The components of the low-liquid-absorbent printing substrate to be printed on are also not particularly limited, and examples include synthetic resins, metals, and glass. Examples of synthetic resins include nylon-based resins such as nylon 6, nylon 11, nylon 12, nylon 46, and nylon 66; polyester-based resins such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), polylactic acid (PLA), and polyhydroxyalkanoate (PHA); polyolefin-based resins such as polyethylene (PE), polypropylene (PP), and acrylonitrile butadiene styrene (ABS); acrylic resins; vinyl chloride resins; polycarbonate resins; polystyrene resins; and ethylene-vinyl alcohol copolymer-based resins.

[0079] The low liquid-absorbent printing substrate may be a nonwoven fabric. The nonwoven fabric may be manufactured by any of various known methods. Examples of methods for manufacturing the nonwoven fabric include the meltblown method, spunbond method, air-through method, airlaid method, spunlace method, needle punch method, electrospinning method, chemical bond method, and thermal bond method. The nonwoven fabric may be manufactured by these methods, or may be a nonwoven fabric manufactured by other methods, or a laminated nonwoven fabric combining two or more of these nonwoven fabrics. The laminated nonwoven fabric may have a structure in which a meltblown nonwoven fabric manufactured by the meltblown method is sandwiched between spunbonded nonwoven fabrics manufactured by the spunbond method. The fibers constituting the nonwoven fabric preferably contain polypropylene.

[0080] The average fiber diameter of the fibers constituting the meltblown nonwoven fabric is preferably 0.1 μm or more and 8 μm or less.The melt flow rate of the resin that is the material of the fibers constituting the meltblown nonwoven fabric is preferably 200 g / 10 min or more and 2500 g / 10 min or less.

[0081] The average fiber diameter of the fibers constituting the spunbonded nonwoven fabric is preferably 6 μm or more and 15 μm or less. The melt flow rate of the resin that is the material for the fibers constituting the spunbonded nonwoven fabric is preferably 45 g / 10 min or more and 850 g / 10 min or less. The spunbonded nonwoven fabric preferably has a fiber orientation degree of 0° or more and 30° or less of 50% or more and 80% or less. The fineness of the fibers constituting the spunbonded nonwoven fabric is preferably 0.5 dtex or more and 2 dtex or less. The cross-sectional flatness of the fibers constituting the spunbonded nonwoven fabric is preferably 1.5 or more. The surface roughness SMD of the spunbonded nonwoven fabric measured by the KES method is preferably 1 μm or more and 3 μm or less.

[0082] The low-liquid-absorbent printing substrate may have a primer layer. That is, the printing layer may be formed on the low-liquid-absorbent printing substrate via the primer layer. The primer layer may contain the water-insoluble polymer.

[0083] The method for printing using the ink by inkjet printing is not particularly limited, and the printed layer can be formed by loading the ink into a known inkjet printing device, ejecting the ink as droplets directly onto the low-liquid-absorbent printing substrate or via another layer, and drying the ink. The printed matter produced by the method for producing a printed matter has the low-liquid-absorbent printing substrate and the printed layer derived from the ink.

[0084] <Print layer removal method> The printed layer removal method of this embodiment includes a printed layer removal step of treating the printed matter with neutral water at 40° C. or higher to remove the printed layer.

[0085] The temperature of the neutral water used to treat the printed matter in the printing layer removal step is preferably 40° C. or higher, more preferably 50° C. or higher, and even more preferably 60° C. or higher, from the viewpoint of efficient removal of the printing layer. From the viewpoint of the upper limit of the water temperature and ease of temperature control in the recycling step, the temperature is preferably 100° C. or lower, more preferably 90° C. or lower, and even more preferably 80° C. or lower.

[0086] The method for treating the printed matter with neutral water at 40° C. or higher is not particularly limited, and examples thereof include immersion cleaning, electrolytic cleaning, spray cleaning, scrub cleaning, ultrasonic cleaning, steam cleaning, etc. Furthermore, the printed matter may be treated with neutral water after being subjected to a process such as cutting.

[0087] By the method for removing the printed layer, a low liquid-absorbent substrate from which the printed layer has been removed can be obtained. [Example]

[0088] Pressure is expressed in absolute pressure. "Normal pressure" means 101.3 kPa.

[0089] <Measurement method> [Composition of Monomers Constituting Water-Soluble Resin] The values ​​were determined by proton NMR measurement using an Agilent NMR MR400.

[0090] [Method for measuring weight average molecular weight] The measurement was performed using gel permeation chromatography. The measurement sample was prepared by mixing 0.1 g of polymer with 10 mL of the following eluent in a glass vial, stirring with a magnetic stirrer at 25°C for 10 hours, and filtering with a syringe filter (Advantec Co., Ltd. "DISMIC-13HP", pore size: 0.2 μm, material: PTFE). The measurement conditions are shown below. GPC equipment: Tosoh Corporation "HLC-8320GPC" Column: Tosoh Corporation's "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolum Super AW-H" Eluent: N,N-dimethylformamide containing phosphoric acid and lithium bromide at concentrations of 60mmol / L and 50mmol / L, respectively. ·Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kit with known molecular weight, manufactured by Tosoh Corporation: "PStQuick B (F-550, F-80, F-10, F-1, A-1000)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)"

[0091] [Method for measuring glass transition temperature (Tg)] Five mg of each polymer was placed in an aluminum pan and measured using a DSC device (Hitachi High-Tech Science, DSC8500) by heating from 30°C to 250°C, then cooling to -20°C, and then heating again to 250°C. The heating and cooling rates were 10°C / min. The glass transition temperature Tg (°C) was calculated from the baseline shift of the DSC curve obtained by heating again.

[0092] [Method for measuring the acid value of pigment dispersants and fixing resins] The resin was dissolved in a titration solvent of toluene and acetone (2:1) in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with a 0.1 N potassium hydroxide / ethanol solution by potentiometric titration. The inflection point on the titration curve was taken as the endpoint. The acid value (mg KOH / g) was calculated from the titration volume of the potassium hydroxide solution up to the endpoint.

[0093] [Measurement of polymer solids concentration] Using an infrared moisture meter "FD-230" (Kett Electric Laboratory Co., Ltd.), 1.0 g of the measurement sample was dried at a drying temperature of 150°C and measurement mode 96 (monitoring time 2.5 minutes / fluctuation range 0.05%), and the moisture content (%) of the measurement sample was measured, and the solid content concentration was calculated using the following formula. Solid concentration (%) = 100 - moisture content (%) of the measured sample

[0094] [Measurement of solids concentration of pigment water dispersion] 10.0 g of sodium sulfate, brought to a constant weight in a desiccator, was weighed out into a 30 mL ointment container, and approximately 1.0 g of the sample was added and mixed. The mixture was then accurately weighed and held at 105°C for 2 hours to remove volatiles, and then left in the desiccator for another 15 minutes before being weighed. The mass of the sample after volatiles removal was taken as the solid content and divided by the initial mass of the sample to obtain the solid content concentration.

[0095] <Production example> [Production of Water-Soluble Polyester Resin A1] A 2L stainless steel separable flask (equipped with a K-shaped tube, stirrer, and nitrogen inlet tube) was charged with 97.7 parts by weight of dimethyl 2,6-naphthalenedicarboxylate, 40.6 parts by weight of dimethyl sodium 5-sulfoisophthalate, 76.6 parts by weight of ethylene glycol, 0.506 parts by weight of sodium acetate, and 0.082 parts by weight of titanium tetrabutoxide. The mixture was stirred under a nitrogen atmosphere while the surface temperature of the mantle heater was raised from 160°C to 260°C. The mixture was then stirred at that temperature for 6.5 hours to carry out a transesterification reaction. The surface temperature of the mantle heater was then raised from 260°C to 290°C, and the reaction was carried out for 1.5 hours while simultaneously reducing the pressure from ambient to 1.5 kPa. The reaction was then carried out for 6 hours while reducing the pressure from 1.5 kPa to 1.0 kPa. Finally, nitrogen was introduced into the stainless steel separable flask, and the mixture was returned to ambient pressure to obtain water-soluble polyester resin A1, as shown in Table 1. The physical properties of water-soluble polyester resin A1 are shown in Table 1.

[0096] [Preparation of Water Dispersion of Water-Soluble Polyester Resin A1] 25.0 parts by mass of the water-soluble polyester resin A1 was diluted with 75.0 parts by mass of ion-exchanged water to a solid content of 25% by mass, and the mixture was stirred at 80°C for 3 hours to obtain a water dispersion of the water-soluble polyester resin A1 (solid content of 25% by mass).

[0097] [Production of Water-Soluble Polyester Resins A2 to A5 and Their Water Dispersions] Aqueous dispersions of each water-soluble polyester resin shown in Table 1 were obtained in the same manner as in the production example of the water-soluble polyester resin A1, except that the raw material monomer composition constituting the water-soluble polyester resin was changed to the conditions shown in Table 1.

[0098] [Table 1]

[0099] [Production of Water Dispersion of Water-Soluble Acrylic Resin B1] [Production of water-soluble acrylic resin B1] A reaction vessel equipped with a stirrer, reflux condenser, and dropping tank was initially charged with 0.5 parts by mass of acrylic acid, 7.5 parts by mass of butyl methacrylate, 2.0 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid, 11.0 parts by mass of methyl ethyl ketone (MEK), and 1.2 parts by mass of water. The temperature of the reaction vessel was maintained at 75 ° C. and the mixture was stirred for 10 minutes. Next, a mixture of 4.5 parts by mass of acrylic acid, 67.5 parts by mass of butyl methacrylate, 18.0 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid, 114.5 parts by mass of MEK, 12.7 parts by mass of water, 1.5 parts by mass of 4,4'-azobis(4-cyanovaleric acid) as a polymerization initiator, and 1.2 parts by mass of 3-mercaptopropionic acid as a chain transfer agent was continuously added to the reaction vessel over 5 hours. After the addition was completed, the polymerization reaction was continued for 1 hour and then terminated by cooling to room temperature, yielding a MEK solution of water-soluble acrylic resin B1 (solid concentration: 45% by mass). The physical properties of water-soluble acrylic resin B1 are shown in Table 2.

[0100] [Table 2]

[0101] In Table 2, AMPS means 2-acrylamido-2-methylpropanesulfonic acid.

[0102] [Production of Water-Soluble Acrylic Resin B1 Dispersion] To 19.4 parts by mass of the MEK solution of water-soluble acrylic resin B1, 2.4 parts by mass of MEK was added to dilute the solution to a solids concentration of 40% by mass. Next, 0.4 parts by mass of a 5N aqueous solution of sodium hydroxide was added to the solution so that the degree of neutralization of the carboxyl groups of the water-soluble acrylic resin B1 was 30 mol%, and the mixture was stirred at 25°C. Thereafter, 77.7 parts by mass of water was added over 1 hour. After the addition was completed, the MEK was distilled off using an evaporator to obtain an aqueous dispersion of water-soluble acrylic resin B1 (solids concentration 25% by mass).

[0103] [Production of Fixing Resin C1] A reactor equipped with a stirrer, reflux condenser, and dropping tank was initially charged with 0.5 parts by weight of acrylic acid, 3.5 parts by weight of butyl acrylate, 6.0 parts by weight of cyclohexyl acrylate, 13.5 parts by weight of MEK, and 1.5 parts by weight of water. The temperature of the reactor was maintained at 75°C and the mixture was stirred for 10 minutes. Next, a mixture of 4.5 parts by weight of acrylic acid, 31.5 parts by weight of butyl acrylate, 54.0 parts by weight of cyclohexyl acrylate, 114.5 parts by weight of MEK, 12.7 parts by weight of water, and 1.5 parts by weight of 4,4'-azobis(4-cyanovaleric acid) as a polymerization initiator was continuously added to the reactor over a period of 5 hours. After the addition was completed, the polymerization reaction was continued for 1 hour and then terminated by cooling to room temperature, yielding a water-insoluble MEK solution of fixing resin C1 (solids concentration 45% by weight). The physical properties of fixing resin C1 are shown in Table 3.

[0104] [Preparation of Water Dispersion of Fixing Resin C1] To 19.4 parts by mass of the MEK solution of the fixing resin C1, 2.4 parts by mass of MEK was added to dilute the solution so that the solid content concentration was 40% by mass. Next, 0.9 parts by mass of a 5N aqueous sodium hydroxide solution was added so that the degree of neutralization of the carboxyl groups of the fixing resin C1 was 60 mol%, and the mixture was stirred at 25°C. Thereafter, 77.3 parts by mass of water was added over 1 hour. After the addition was completed, the MEK was distilled off using an evaporator to obtain an aqueous dispersion of the fixing resin C1 (solid content concentration 25% by mass).

[0105] [Production of Water Dispersions of Fixing Resins C2 to C3] Aqueous dispersions of each water-insoluble fixing resin shown in Table 3 were obtained in the same manner as in the manufacturing example of the water dispersion of fixing resin C1, except that the raw material monomer composition constituting the fixing resin was changed to the conditions shown in Table 3.

[0106] [Table 3]

[0107] [Production of Water-Insoluble Polyester Resin 1] Using polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane as the alcohol component, fumaric acid as the carboxylic acid component, tin(II) di(2-ethylhexanoate) as the esterification catalyst, and 3,4,5-trihydroxybenzoic acid as the esterification promoter, the mixture was reacted at 210°C for 10 hours to obtain water-insoluble polyester resin 1 (acid value 22 mgKOH / g, weight-average molecular weight 13,700, molar ratio of [carboxylic acid component / alcohol component]: 1.04).

[0108] [Production of Pigment Water Dispersion 1] In a 2-L vessel, 66.7 g of the water-insoluble polyester resin 1 was dissolved in 198.6 g of MEK, and 5N aqueous sodium hydroxide was added to neutralize 85 mol% of the polyester resin's acid value. 390.5 g of ion-exchanged water was then added dropwise over 30 minutes, followed by stirring and mixing for 15 minutes at 1,500 r / min using a disper impeller at 10-15°C. Next, 100 g of CI Pigment Blue 15:3 (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., product name: CFB6338JC) was added, and the mixture was stirred and mixed for 2 hours at 6,500 r / min using a disper impeller at 10-15°C to obtain a preliminary dispersion. The resulting preliminary dispersion was filtered through a 200-mesh filter and diluted with 36.1 g of ion-exchanged water. It was then dispersed 15 times at 150 MPa using a Microfluidizer (Microfluidics Corporation, high-pressure homogenizer, product name: M-110EH-30XP) to obtain a pigment aqueous dispersion. The entire resulting pigment aqueous dispersion was placed in a 2-L eggplant flask, and ion-exchanged water was added to obtain a 15% solids concentration. The organic solvent was removed using a rotary evaporator (Tokyo Rikakikai Co., Ltd., product name: N-1000S) at 50 rpm and a pressure of 0.09 MPa (abs) for 3 hours in a warm bath adjusted to 32°C. The warm bath was then adjusted to 62°C, and the pressure was reduced to 0.07 MPa (abs), resulting in a concentrated concentrate with a solids concentration of 25%. The obtained concentrate was placed in a 500 mL angle rotor and centrifuged at 3,660 r / min for 20 minutes using a high-speed refrigerated centrifuge (manufactured by Hitachi Koki Co., Ltd., product name: himac CR22G, set temperature 20°C). The liquid layer was then filtered through a membrane filter (product name: Minisart Syringe Filter) and diluted with water to a solids concentration of 22 mass%, thereby obtaining Pigment Water Dispersion 1 (solids concentration: 22 mass%, pigment: 13.2 mass%, polymer: 8.8 mass%, acid value of pigment dispersant: 22 mgKOH / g).

[0109] [Production of Water-Insoluble Acrylic Resin 2] 16 parts by mass of methacrylic acid, 44 parts by mass of styrene, 30 parts by mass of styrene macromonomer (manufactured by Toagosei Co., Ltd., trade name: AS-6S, number average molecular weight 6,000, solids content 50%), and 25 parts by mass of methoxypolyethylene glycol methacrylate (NOF Corporation, trade name: Blemmer PME-200) were mixed to prepare 115 parts by mass of a monomer mixture. 18 parts by mass of MEK, 0.03 parts by mass of a chain transfer agent (2-mercaptoethanol), and 10% by mass (11.5 parts by mass) of the monomer mixture were placed in a reaction vessel and mixed, followed by thorough nitrogen gas replacement. Separately, a mixture of the remaining 90% by mass (103.5 parts by mass) of the monomer mixture with 0.27 parts by mass of the chain transfer agent, 42 parts by mass of MEK, and 3 parts by mass of a polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: V-65) was placed in a dropping funnel. The mixture in the reaction vessel was heated to 75°C under a nitrogen atmosphere while stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 75°C, a solution of 3 parts by mass of the polymerization initiator in 5 parts by mass of MEK was added, and the mixture was further aged at 75°C for 2 hours and then at 80°C for 2 hours. An additional 50 parts by mass of MEK was added to obtain a solution (solids concentration: 45% by mass) of water-insoluble acrylic resin 2 (acid value 98.6 mgKOH / g, weight-average molecular weight: 50,000).

[0110] [Preparation of Pigment Water Dispersion 2] 95.2 parts by weight of the water-insoluble acrylic resin 2 solution was dissolved in 53.7 parts by weight of MEK, to which 13.7 parts by weight of 5N aqueous sodium hydroxide solution, 0.5 parts by weight of 25% aqueous ammonia, and 341.8 parts by weight of ion-exchanged water were added as neutralizers. 100 parts by weight of cyan pigment (manufactured by DIC Corporation, trade name: Fastogen Blue CA5380 15:3) was then added to obtain a pigment mixture (polymer neutralization degree: 72 mol%). The resulting pigment mixture was mixed using a disperser blade at 7000 rpm and 20°C for 1 hour, and then further dispersed using a Microfluidizer (high-pressure homogenizer, trade name: M-140K, manufactured by Microfluidics) for 15 passes at a pressure of 180 MPa. The resulting pigment aqueous dispersion was cooled under reduced pressure at 60°C to remove MEK, and then a portion of the water was removed. The mixture was centrifuged, and the liquid layer was filtered through a membrane filter (Sartorius, trade name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding a pigment aqueous dispersion (solids concentration: 22% by mass). To 100 parts by mass of the resulting pigment aqueous dispersion, 0.45 parts by mass (corresponding to a crosslinking rate of 30 mol%) of crosslinker (Nagase ChemteX, trade name: Denacol EX321L, epoxy equivalent: 130) and 15.23 parts by mass of ion-exchanged water were added, and the mixture was heated with stirring at 70°C for 3 hours (solids concentration: 22% by mass). After cooling to room temperature, the liquid layer was filtered through a membrane filter (trade name: Minisart Syringe Filter) to remove coarse particles, thereby obtaining Pigment Water Dispersion 2 (solid content concentration: 22%, pigment: 15.2% by mass, polymer: 6.8% by mass, acid value of pigment dispersant: 69 mgKOH / g).

[0111] [Production of Water-Insoluble Acrylic Resin 3] A reaction vessel equipped with a stirrer, a reflux condenser, and a dropping tank was initially charged with 5.5 parts by mass of cyclohexyl acrylate, 2.6 parts by mass of acrylic acid, 1.9 parts by mass of butyl acrylate, 11.0 parts by mass of MEK, and 1.22 parts by mass of water, and the mixture was stirred for 10 minutes while maintaining the temperature of the reaction vessel at 75° C. Next, a mixture of 49.5 parts by mass of cyclohexyl acrylate, 23.4 parts by mass of acrylic acid, 17.1 parts by mass of butyl acrylate, 114.5 parts by mass of MEK, 12.7 parts by mass of water, 1.5 parts by mass of 4,4′-azobis(4-cyanovaleric acid) as a polymerization initiator, and 1.2 parts by mass of 3-mercaptopropionic acid as a chain transfer agent was continuously added to the reaction vessel over 5 hours. After the addition was completed, the polymerization reaction was carried out for 1 hour and then cooled to room temperature to terminate the polymerization reaction, yielding a solution (solids concentration: 45%) of water-insoluble acrylic resin 3 (acid value 200 mgKOH / g, weight-average molecular weight: 22,000). 24.9 parts by mass of the water-insoluble acrylic resin 3 solution was diluted with 7.1 parts by mass of MEK to a solids concentration of 35% by mass. Next, 1.07 parts by mass of N,N-dimethylethanolamine (hereinafter referred to as DMAE) was added so that the degree of neutralization of the carboxy groups of the water-insoluble acrylic resin 3 was 30 mol%, and the mixture was stirred at 25°C. Thereafter, 66.9 parts by mass of water was added over 1 hour. After the addition was completed, MEK was distilled off using an evaporator to obtain an aqueous dispersion of water-insoluble acrylic resin 3 (DMAE-neutralized) (solids concentration: 25% by mass).

[0112] [Production of Pigment Water Dispersion 3] To 32.97 parts by weight of an aqueous dispersion (solids concentration 25% by weight) of water-insoluble acrylic resin 3 (neutralized with DMAE), 2.10 parts by weight of MEK and 17.25 parts by weight of ion-exchanged water were added, followed by 18.77 parts by weight of a cyan pigment (manufactured by DIC Corporation, trade name: Fastogen Blue CA5380 Pigment Blue 15:3) to obtain a pigment mixture. The resulting pigment mixture was mixed using a disperser blade at 7000 rpm and 20°C for 1 hour, and then further dispersed using a Microfluidizer (high-pressure homogenizer, trade name: M-140K, manufactured by Microfluidics) for 10 passes at a pressure of 180 MPa to obtain a pigment dispersion. The MEK was removed from the resulting pigment dispersion under reduced pressure at 60°C, and then a portion of the water was removed. After centrifugation, the liquid phase was filtered through a membrane filter (Sartorius, trade name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous pigment dispersion (solids concentration: 22% by weight). 56.44 parts by weight of the resulting aqueous pigment dispersion (solids concentration: 22% by weight) was transferred to a screw-cap glass bottle, and 1.07 parts by weight of trimethylolpropane polyglycidyl ether (Nagase ChemteX Corporation, "Denacol EX-321LT," epoxy value: 139 g / eq., water solubility: 27% by weight, log Pow: -0.39) as a multifunctional epoxy crosslinker and 24.96 parts by weight of ion-exchanged water were added. The bottle was sealed and heated at 80°C for 5 hours with stirring. Thereafter, the temperature was lowered to room temperature, and the mixture was filtered through a membrane filter (manufactured by Sartorius, trade name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining Pigment Water Dispersion 3 (solid content concentration 22 mass%, pigment: 15.4 mass%, polymer: 6.6 mass%, acid value of pigment dispersant 120 mgKOH / g).

[0113] [Production of Water-Insoluble Acrylic Resin 4] A reaction vessel equipped with a stirrer, a reflux condenser, and a dropping tank was initially charged with 5.5 parts by mass of cyclohexyl acrylate, 3.1 parts by mass of acrylic acid, 1.4 parts by mass of butyl acrylate, 11.0 parts by mass of MEK, and 1.22 parts by mass of water, and the mixture was stirred for 10 minutes while maintaining the temperature of the reaction vessel at 75° C. Next, a mixture of 49.5 parts by mass of cyclohexyl acrylate, 27.9 parts by mass of acrylic acid, 12.6 parts by mass of butyl acrylate, 114.5 parts by mass of MEK, 12.7 parts by mass of water, 1.5 parts by mass of 4,4′-azobis(4-cyanovaleric acid) as a polymerization initiator, and 1.2 parts by mass of 3-mercaptopropionic acid as a chain transfer agent was continuously added to the reaction vessel over 5 hours. After the addition was completed, the polymerization reaction was carried out for 1 hour, and then the polymerization reaction was terminated by cooling to room temperature, yielding a solution (solids concentration: 45% by mass) of water-insoluble acrylic resin 4 (acid value 240 mgKOH / g, weight-average molecular weight: 19,000). 24.9 parts by mass of the obtained water-insoluble acrylic resin 4 solution was diluted with 7.1 parts by mass of MEK to a solids concentration of 35% by mass. Next, 1.28 parts by mass of DMAE was added so that the degree of neutralization of the carboxyl groups of the water-insoluble acrylic resin 4 was 30 mol%, and the mixture was stirred at 25°C. Thereafter, 66.7 parts by mass of water was added over 1 hour. After the addition was completed, MEK was distilled off using an evaporator, yielding an aqueous dispersion of water-insoluble acrylic resin 4 (DMAE-neutralized) (solids concentration: 25% by mass).

[0114] [Preparation of Pigment Water Dispersion 4] To 33.13 parts by weight of the aqueous dispersion (solids concentration 25% by weight) of the water-insoluble acrylic resin 4 (neutralized with DMAE), 2.10 parts by weight of MEK and 17.19 parts by weight of ion-exchanged water were added, followed by 18.77 parts by weight of a cyan pigment (manufactured by DIC Corporation, trade name: Fastogen Blue CA5380 Pigment Blue 15:3) to obtain a pigment mixture. The resulting pigment mixture was mixed using a disperser blade at 7000 rpm and 20°C for 1 hour, and then further dispersed using a Microfluidizer (high-pressure homogenizer, trade name: M-140K, manufactured by Microfluidics) for 10 passes at a pressure of 180 MPa to obtain a pigment dispersion. The MEK was removed from the resulting pigment dispersion under reduced pressure at 60°C, and then a portion of the water was removed. After centrifugation, the liquid phase was filtered through a membrane filter (Sartorius, trade name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous pigment dispersion (solids concentration: 22% by weight). 56.39 parts by weight of the resulting aqueous pigment dispersion (solids concentration: 22% by weight) was transferred to a screw-cap glass bottle, and 1.24 parts by weight of trimethylolpropane polyglycidyl ether (Nagase ChemteX Corporation, "Denacol EX-321LT," epoxy value: 139 g / eq., water solubility: 27%, log Pow: -0.39) as a multifunctional epoxy crosslinker and 25.40 parts by weight of ion-exchanged water were added. The bottle was sealed and heated at 80°C for 5 hours with stirring. Thereafter, the temperature was lowered to room temperature, and the mixture was filtered through a membrane filter (manufactured by Sartorius, trade name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining Pigment Water Dispersion 4 (solid content concentration 22 mass%, pigment: 15.4 mass%, polymer: 6.6 mass%, acid value of pigment dispersant 144 mgKOH / g).

[0115] <Examples and Comparative Examples> Example 1 [Preparation of Ink 1] To obtain the ink composition (total 100 parts by mass) shown in Table 4, 8.3 parts by mass of the pigment water dispersion 1 (solid content concentration: 22% by mass, pigment: 13.2% by mass, polymer: 8.8% by mass, acid value of the pigment dispersant 1: 22.4 mg KOH / g) in terms of solid content, 2.0 parts by mass of the water-soluble polyester resin A1 (solid content concentration: 25% by mass), 4.0 parts by mass of the fixing resin B1 (solid content concentration: 25% by mass, acid value: 39 mg KOH / g) in terms of solid content, 20.0 parts by mass of propylene glycol (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and diethylene glycol isobutyl ether (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added. 5.0 parts by mass of a silicone surfactant ("KF-6011" manufactured by Shin-Etsu Chemical Co., Ltd., active content 100%), 1.0 part by mass of an acetylene glycol surfactant ("Surfynol 104-PG50" manufactured by Nissin Chemical Industry Co., Ltd., a propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active content 50% by mass), and 59.2 parts by mass of ion-exchanged water were added and thoroughly stirred, and then filtered through a membrane filter ("Minisart Syringe Filter" manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to obtain Ink 1 (viscosity: 5.0 mPa s, pH: 8.3).

[0116] [Evaluation by inkjet printing] Ink 1 was filled into an inkjet printing evaluation device (manufactured by Tritec Corporation) equipped with a print head (manufactured by Kyocera Corporation, product name: KJ4B-HD06MHG-STDV, piezo type) in an environment with a temperature of 32°C. The settings were print head voltage: 26 V, drive frequency: 30 kHz, ejected droplet volume: 7 pL, print head temperature: 32°C, and print head resolution: 600 dpi. A solid image with a duty of 100% was printed on a polyethylene terephthalate film ("FE2000#25" manufactured by Futamura Chemical Co., Ltd.) heated to 50°C as a low-liquid-absorbent printing substrate.

[0117] [Examples 2 to 15 and Comparative Examples 1 and 2] Inks 2 to 13, and Inks C1 and C2 were obtained in the same manner as in Example 1, except that the ink compositions were changed as shown in Table 4. A solid image with a duty of 100% was formed on a polyethylene terephthalate film ("FE2000#25" manufactured by Futamura Chemical Co., Ltd.) as a low-liquid-absorbent printing substrate by inkjet recording in the same manner as in Example 1, to obtain a printed matter.

[0118] Example 16 A solid image with a duty of 100% was formed in the same manner as in Example 1, except that the low liquid-absorbent printing substrate was changed to a polypropylene film (FOR-AQ#25 manufactured by Futamura Chemical Co., Ltd.), and a printed matter was obtained.

[0119] Example 17 A solid image with a duty of 100% was formed in the same manner as in Example 1, except that the low liquid-absorbent printing substrate was changed to a polyethylene film ("LL-RP2#30" manufactured by Futamura Chemical Co., Ltd.), and a printed matter was obtained.

[0120] 〔evaluation〕 [Evaluation of detachability of printed layer] Each printed matter obtained in each Example and Comparative Example was cut into a 2 cm x 2 cm size and immersed in 10 mL of ion-exchanged water at the temperature (°C) at which the printed layer was removed, as shown in Table 4. After stirring for 1 minute, the removability of the printed layer was observed. The area of ​​the remaining ink printed layer in the solid image area after immersion and stirring was calculated using image analysis. The solid image area after immersion and stirring was binarized using a print density value that was half the print density value of the solid image area before immersion and stirring as a threshold value. The remaining and non-remaining areas of the printed layer were calculated using image analysis. The area ratio of the non-remaining printed layer area was calculated as the printed layer removal rate (%) after the printing layer removal test and evaluated according to the following criteria. The higher the value, the better the removability of the printed layer. A printing layer removal rate of 80% or higher indicates practically acceptable results. The results are shown in Table 4. A: Printing layer removal rate of 95% or more B: 90% or more but less than 95% C: 80% or more but less than 90% D: 1% or more but less than 80% E: Printed layer removal rate 0%, no printed layer detachment

[0121] [Evaluation of coloration of removed water] The resulting solid image print was cut into 2 cm x 2 cm pieces, immersed in 10 mL of water at the temperature listed in Table 4, and stirred for 1 minute. The water was then filtered through a 5 μm filter, and the absorbance of the water was measured. The degree of coloration of the water was evaluated according to the following criteria. The smaller the value, the more suppressed the coloration of the removed water. An absorbance of less than 0.2 is considered acceptable for practical use. The results are shown in Table 4. A: The absorbance of the removed water is less than 0.05 and no coloration of the water is observed. B: Removed water absorbance is 0.05 or more and less than 0.1 C: Removed water absorbance is 0.1 or more and less than 0.2 D: Removed water absorbance is 0.2 or more and less than 0.3 E: Removed water absorbance is 0.03 or more

[0122] [Table 4]

[0123] In Table 4, PET stands for polyethylene terephthalate film, OPP stands for polypropylene film, and PE stands for polyethylene film.

[0124] The results in Table 4 show that the inks according to the examples are superior to the inks according to the comparative examples in terms of releasability of the printed layer and suppression of discoloration of the removed water. On the other hand, comparative example 1 shows that when the ink does not contain a water-soluble resin, the releasability of the printed layer is inferior, and comparative example 2 shows that when the ink contains a pigment water dispersion in which the acid value of the pigment dispersant is higher than 130 mgKOH / g, the releasability of the printed layer and suppression of discoloration of the removed water are inferior.

Claims

1. An ink for inkjet printing on a low-liquid-absorbent printing substrate, the ink contains a pigment, a pigment dispersant, a water-soluble resin, and water; the acid value of the pigment dispersant is 10 mgKOH / g or more and 130 mgKOH / g or less; The ink for ink-jet printing, wherein the water-soluble resin has a monomer unit (A) having a sulfonate group.

2. 2. The ink for ink-jet printing according to claim 1, wherein the content of the sulfonate group in the water-soluble resin is 0.4 mmol / g or more and 2.0 mmol / g or less.

3. 2. The ink for ink-jet printing according to claim 1, which contains a fixing resin, and the fixing resin has an acid value of 0.1 mgKOH / g or more and 150 mgKOH / g or less.

4. 2. The ink for ink-jet printing according to claim 1, wherein the low-liquid-absorbent printing substrate is made of a synthetic resin.

5. A method for producing a printed matter, comprising: a printing layer forming step of printing by an inkjet printing method using the ink according to any one of claims 1 to 4, and forming a printing layer derived from the ink on the low liquid-absorbent printing substrate directly or via another layer.

6. A printed matter having a low liquid-absorbent printing substrate and a printed layer made from the ink according to any one of claims 1 to 4.

7. A method for removing a printed layer, comprising a step of treating the printed matter according to claim 6 with neutral water at a temperature of 40°C or higher to remove the printed layer.

8. A low-liquid-absorbent printed substrate, wherein the printed layer has been removed by the method for removing the printed layer according to claim 7.

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