Inkjet printing ink

Abstract

To improve inkjet suitability such as storage stability and intermittent ejection performance of an inkjet printing ink that contains a water-soluble polyester resin.SOLUTION: An inkjet printing ink comprises a pigment, a water-soluble polyester resin dispersed with a polymer dispersant, and water.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 require careful handling. Furthermore, immersing printed materials in alkaline aqueous solutions can corrode the base material, making recycling difficult.

[0008] To address the above-mentioned issues, it is conceivable to incorporate a water-soluble material that dissolves in neutral water, such as a water-soluble polyester resin, so that the printed layer can be removed with neutral water. However, inks containing water-soluble polyester resins have room for improvement in terms of inkjet suitability, such as storage stability and intermittent ejection properties.

[0009] An object of the present invention is to improve the storage stability and inkjet suitability, such as intermittent ejection properties, of inkjet printing inks containing a water-soluble polyester resin. [Means for solving the problem]

[0010] The present invention provides The inkjet printing ink contains a pigment, a water-soluble polyester resin dispersed with a polymer dispersant, and water. [Effects of the Invention]

[0011] According to the present invention, it is possible to improve the storage stability and inkjet suitability, such as intermittent ejection properties, of inkjet printing inks containing a water-soluble polyester resin. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Inkjet printing ink> The inkjet printing ink of this embodiment contains a pigment, a water-soluble polyester resin dispersed with a polymer dispersant, and water. The inkjet printing ink of this embodiment can improve the inkjet suitability, such as storage stability and intermittent ejection properties, of inkjet printing inks containing a water-soluble polyester resin. The reason why the inkjet printing ink of this embodiment exhibits such effects is unclear, but is presumed to be as follows.

[0013] Because water-soluble polyester resins have a polyester skeleton, the ester moieties are susceptible to hydrolysis, resulting in reduced storage stability in ink. Dispersing the water-soluble polyester resin with a polymer dispersant reduces the frequency of contact between the ester moieties and water, thereby suppressing hydrolysis. This is believed to result in improved storage stability in ink. Furthermore, even if the ink is exposed to the atmosphere for a long period of time near the inkjet nozzles during a period in which the ink is not ejected from the inkjet nozzles, causing the water in the ink to volatilize, aggregation of the water-soluble polyester resin can be suppressed, leading to improved intermittent ejection properties.

[0014] [Water-soluble polyester resin] The water-soluble polyester resin is a polyester resin having a hydrophilic group. In this specification, "water-soluble" refers to dissolving at least 0.01 g 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 sulfate ester salts, alkyl ether sulfate ester salts, olefin sulfonates, and alkyl ether carboxylate salts; cationic surfactants such as alkyl trimethyl ammonium salts; and nonionic surfactants such as polyoxyethylene alkyl ethers and alkyl glycosides.

[0015] From the viewpoint of imparting solubility in water, the hydrophilic group may be one or more selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium base, an oxyalkylene group, a hydroxyl group, a carboxyl group, a carboxyl group, a phosphate group, a sulfonic acid group, and a sulfonate group. Among these, from the same viewpoint, one or more selected from the group consisting of a quaternary ammonium base, an oxyalkylene group, a carboxyl group, a phosphate group, and a sulfonate group are preferred, one or more selected from the group consisting of a quaternary ammonium base, an oxyalkylene group, and a sulfonate group are more preferred, and a sulfonate group is even more preferred.

[0016] 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 polyester resin. 3 (However, M 3 represents 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.

[0017] The content of sulfonate groups in the water-soluble polyester 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 printed 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 printed layer.

[0018] From the viewpoint of enabling the printing layer to be removed with neutral water, the water-soluble polyester resin is preferably a water-soluble polyester resin having the monomer unit (A) having a hydrophilic group, a hydrophobic dicarboxylic acid monomer unit (B), and a diol monomer unit (C). 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.

[0019] The monomer unit (A) constituting the monomer unit of the water-soluble polyester resin is referred to as monomer unit (A), and the monomer for deriving the monomer unit (A) is referred to as monomer (A). 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 (A) 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.

[0020] The ratio of the amount of substance of the monomer unit (A) to the total amount of substance 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 ratio of the amount of substance of the monomer unit (A) to the total amount of substance 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.

[0021] The hydrophobic dicarboxylic acid monomer unit (B) 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.

[0022] The monomer for deriving the hydrophobic dicarboxylic acid monomer unit (B) contained in the water-soluble polyester resin is referred to as monomer (B). From the viewpoint of improving the water resistance of the printed layer, the monomer (B) 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.

[0023] The proportion of the amount of the monomer unit (B) 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 (B) 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.

[0024] The monomer for deriving the diol monomer unit (C) contained in the water-soluble polyester resin is referred to as monomer (C). While aliphatic diols, aromatic diols, etc. can be used as the monomer (C), aliphatic diols are preferred from the viewpoint of production costs for the water-soluble polyester resin. From the viewpoint of enabling the printed layer to be removed 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.

[0025] When the monomer (C) 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 (C) 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.

[0026] The water-soluble polyester resin may contain a monomer unit other than the monomer unit (A), the monomer unit (B), and the diol monomer unit (C) as long as the effects of this embodiment are not impaired.

[0027] The weight average molecular weight of the water-soluble polyester 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.

[0028] From the viewpoint of improving the water resistance of the printed layer, the glass transition temperature of the water-soluble polyester 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 polyester 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.

[0029] The method for producing the water-soluble polyester resin is not particularly limited, and any conventionally known method for producing a water-soluble polyester resin can be applied.

[0030] [Polymer dispersant] Examples of the polymer dispersant for dispersing the water-soluble polyester resin include vinyl resins and polyester resins obtained by addition polymerization of vinyl monomers. Among these, vinyl resins are preferred from the viewpoints of pigment dispersion stability, storage stability, etc. The polymer dispersant preferably has a structural unit derived from a carboxylic acid monomer (D) and a structural unit derived from a hydrophobic monomer (E).

[0031] The carboxylic acid monomer (D) may be at least one selected from (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, with (meth)acrylic acid being preferred. "(Meth)acrylic acid" refers to at least one selected from acrylic acid and methacrylic acid.

[0032] The content of the structural unit derived from the carboxylic acid monomer (D) in the polymer dispersant is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 12% by mass or more, from the viewpoint of the storage stability of the ink and the intermittent ejection stability of the ink. The content of the structural unit derived from the carboxylic acid monomer (D) in the polymer dispersant is preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less, from the viewpoint of the releasability of the printed layer.

[0033] Specific examples of the hydrophobic monomer (E) include alkyl (meth)acrylates and aromatic group-containing monomers. The alkyl (meth)acrylate preferably has an alkyl group having 1 to 22 carbon atoms, more preferably an alkyl group having 6 to 18 carbon atoms. Examples include methyl (meth)acrylate, ethyl (meth)acrylate, (iso)propyl (meth)acrylate, (iso- or tert-)butyl (meth)acrylate, (iso)amyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (iso)octyl (meth)acrylate, (iso)decyl (meth)acrylate, (iso)dodecyl (meth)acrylate, and (iso)stearyl (meth)acrylate. The terms "(iso- or tert-)" and "(iso)" refer to both the presence and absence of these groups, and refer to normal when these groups are absent. The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group of 6 to 22 carbon atoms, which may have a substituent containing a heteroatom, and more preferably one or more selected from styrene-based monomers and aromatic group-containing (meth)acrylates. The molecular weight of the aromatic group-containing monomer is preferably less than 500. The styrene-based monomer is preferably styrene, 2-methylstyrene, α-methylstyrene, vinyltoluene, and divinylbenzene, and more preferably styrene. The aromatic group-containing (meth)acrylate is preferably benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc., and more preferably benzyl (meth)acrylate. Among these, alkyl(meth)acrylates having an alkyl group with 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 8 carbon atoms, and aromatic group-containing monomers having an aromatic group with 6 to 22 carbon atoms, preferably 6 to 18 carbon atoms, are preferred, and one or more selected from alkyl(meth)acrylates having an alkyl group with 1 to 4 carbon atoms and aromatic group-containing monomers having an aromatic group with 6 to 12 carbon atoms are more preferred, and one or more selected from ethyl acrylate, styrene, and α-methylstyrene are even more preferred.The term "(meth)acrylate" refers to at least one selected from acrylate and methacrylate.

[0034] The content of the structural units derived from the hydrophobic monomer (E) in the polymer dispersant is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, from the viewpoint of resin dispersibility. The content of the structural units derived from the hydrophobic monomer (E) in the polymer dispersant is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 88% by mass or less, from the viewpoint of ink storage stability and intermittent ink ejection stability.

[0035] The polymer dispersant may further include a structural unit derived from a nonionic monomer (F). The nonionic monomer (F) is a monomer that has a high affinity for water or a water-soluble organic solvent, such as a monomer containing a hydroxyl group or a polyalkylene glycol chain. Specific examples of the nonionic monomer (F) include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; polyalkylene glycol (meth)acrylates such as polyethylene glycol (meth)acrylate (n = 2 to 30, n represents the average number of moles of oxyalkylene groups added; the same applies hereinafter) and polypropylene glycol (n = 2 to 30) (meth)acrylate; alkoxypolyalkylene glycol (meth)acrylates such as methoxypolyethylene glycol (n = 1 to 30) (meth)acrylate; and phenoxy (ethylene glycol-propylene glycol copolymer) (n = 1 to 30, ethylene glycol: n = 1 to 29) (meth)acrylate. Among these, one or more selected from methoxypolyethylene glycol (n=1 to 30) (meth)acrylate and polypropylene glycol (n=2 to 30) (meth)acrylate are preferred.

[0036] When the polymer dispersant has a structural unit derived from the nonionic monomer (F), the content of the structural unit derived from the nonionic monomer (F) in the polymer dispersant is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, from the viewpoints of storage stability of the ink and intermittent ejection stability of the ink. From the viewpoint of releasability of the printed layer, the content of the structural unit derived from the nonionic monomer (F) in the polymer dispersant is preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less.

[0037] When the polymer dispersant has acid groups, it is preferable that at least a portion of the acid groups be neutralized using a neutralizing agent. This is thought to increase the charge repulsion force exhibited after neutralization, suppress aggregation of the water-soluble polyester resin-containing polymer particles in the aqueous ink, and improve the dispersion stability of the water-soluble polyester resin. Examples of neutralizing agents include bases such as sodium hydroxide, potassium hydroxide, ammonia, and various amines, with sodium hydroxide and ammonia being preferred. When neutralizing, it is preferable to neutralize so that the pH is between 7 and 11.

[0038] The polymer dispersant can be produced by a known method.

[0039] [Water-soluble polyester resin-containing polymer particles] From the viewpoint of improving the storage stability of the ink, the water-soluble polyester resin is preferably contained as polymer particles containing the water-soluble polyester resin dispersed with the polymer dispersant (hereinafter also referred to as "water-soluble polyester resin-containing polymer particles"). The water-soluble polyester resin-containing polymer particles refer to particles in which the polymer dispersant encases the water-soluble polyester resin, particles in which a portion of the water-soluble polyester resin is exposed on the surface of particles made of the polymer dispersant and the water-soluble polyester resin, particles in which the polymer dispersant is adsorbed to a portion of the water-soluble polyester resin, and mixtures thereof. Among these, particles in which a portion of the water-soluble polyester resin is exposed on the surface of particles made of the polymer dispersant and the water-soluble polyester resin, or particles in which the polymer dispersant is adsorbed to a portion of the water-soluble polyester resin are more preferred.

[0040] The water-soluble polyester resin-containing polymer particles can be produced by dispersing the water-soluble polyester resin in a dispersion containing a polymer dispersant obtained by copolymerizing a monomer mixture containing a carboxylic acid monomer (D), a hydrophobic monomer (E), and, if necessary, a nonionic monomer (F). The dispersion treatment may be carried out by applying shear stress by a known method.

[0041] The polymer dispersant is preferably crosslinked from the viewpoint of dispersion stability and storage stability of the ink. The polymer dispersant can be crosslinked by adding a crosslinking agent to a dispersion containing an uncrosslinked polymer dispersant obtained by copolymerizing a monomer mixture containing a carboxylic acid monomer (D), a hydrophobic monomer (E), and, if necessary, a nonionic monomer (F), and a dispersion containing the water-soluble polyester resin, and then performing a crosslinking treatment.

[0042] The crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a compound having two or more glycidyl ether groups, and even more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 4 carbon atoms. The epoxy equivalent of the crosslinking agent is preferably 90 or more, more preferably 100 or more, and preferably 300 or less, more preferably 200 or less. Suitable examples of the crosslinking agent include one or more selected from polyglycidyl ethers such as 1,6-hexanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether.

[0043] When the polymer dispersant is crosslinked, the degree of crosslinking, in terms of the ratio of the molar equivalents of the crosslinkable functional groups of the crosslinking agent to the molar equivalents of the carboxyl groups of the polymer dispersant, is preferably 8 mol% or more, more preferably 10 mol% or more, and is preferably 70 mol% or less, more preferably 50 mol% or less, from the viewpoint of improving storage stability, etc.

[0044] From the viewpoint of storage stability of the ink, the acid value of the polymer dispersant before crosslinking is preferably 100 mgKOH / g or more, more preferably 120 mgKOH / g or more, even more preferably 140 mgKOH / g or more, and still more preferably 160 mgKOH / g or more, and is preferably 350 mgKOH / g or less, more preferably 300 mgKOH / g or less, and even more preferably 250 mgKOH / g or less. In this specification, the acid value is measured by the method described in the examples.

[0045] From the viewpoint of storage stability of the ink, the acid value of the polymer dispersant after crosslinking is preferably 50 mgKOH / g or more, more preferably 80 mgKOH / g or more, even more preferably 100 mgKOH / g or more, and still more preferably 120 mgKOH / g or more, and is preferably 300 mgKOH / g or less, more preferably 250 mgKOH / g or less, and even more preferably 200 mgKOH / g or less.

[0046] From the viewpoint of resin dispersibility and improving storage stability, the weight average molecular weight of the polymer dispersant before crosslinking 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 50,000 or less, even more preferably 30,000 or less, and still more preferably 20,000 or less.

[0047] The average particle size of the water-soluble polyester resin-containing polymer particles is preferably 20 nm or more, more preferably 40 nm or more, and even more preferably 60 nm or more, and is preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 150 nm or less, from the viewpoint of storage stability, etc. The average particle size of the water-soluble polyester resin-containing polymer particles can be measured by the method described in the Examples.

[0048] [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.

[0049] 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 may be surface-treated with a known hydrophobic treatment agent such as a titanium coupling agent, a silane coupling agent, or a metal salt of a higher fatty acid.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] [Pigment dispersant] The pigment is dispersed in the pigment dispersant and contained in the ink. The pigment dispersant is preferably a water-insoluble polymer from the viewpoint of dispersing the pigment and improving water resistance. In this specification, "water-insoluble" means that the dissolution amount is 0.01 g or less 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.

[0054] [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 (G) and a structural unit derived from a hydrophobic monomer (H). 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 (I).

[0055] [Ionic Monomer (G)] The ionic monomer (G) may be an anionic monomer or a cationic monomer, preferably an anionic monomer, more preferably a monomer having an acid group, and even more preferably a monomer having a carboxy group. Specific examples of the ionic monomer (G) include those described in paragraph 0017 of JP 2018-80255 A. Among these, (meth)acrylic acid is preferred.

[0056] [Hydrophobic Monomer (H)] Examples of the hydrophobic monomer (H) 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 (H) 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.

[0057] [Nonionic Monomer (I)] Examples of the nonionic monomer (I) 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 (I) 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.

[0058] The water-insoluble vinyl polymer can be produced by the method described in paragraphs 0024 to 0028 of JP-A No. 2018-80255.

[0059] [Water-insoluble polyester polymer] The water-insoluble polyester polymer has a structural unit derived from an alcohol monomer (J) and a structural unit derived from a carboxylic acid monomer (K), and can be obtained by polycondensation of the alcohol monomer (J) and the carboxylic acid monomer (K).

[0060] [Alcohol Monomer (J)] The alcohol monomer (J) 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.

[0061] The alcohol monomer (J) 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).

[0062] The content of the alkylene oxide adduct of bisphenol A in the alcohol monomer (J) 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.

[0063] [Carboxylic acid monomer (K)] The carboxylic acid monomer (K) includes carboxylic acids, their acid anhydrides, and their alkyl (carbon number 1 to 3) esters. Examples of the carboxylic acid monomer (K) 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 (K) can be used alone or in combination of two or more.

[0064] The water-insoluble polyester polymer can be produced by the method described in paragraph 0038 of JP-A-2022-10817.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] The acid value of the pigment dispersant before crosslinking is preferably 10 mgKOH / g or more, more preferably 15 mgKOH / g or more, and even more preferably 20 mgKOH / g or more, from the viewpoint of enabling the printing layer to be removed with neutral water.The acid value of the pigment dispersant before crosslinking is preferably 140 mgKOH / g or less, more preferably 125 mgKOH / g or less, and even more preferably 110 mgKOH / g or less, from the viewpoint of suppressing coloration of the removed water by the pigment derived from the printing layer.

[0069] The acid value of the pigment dispersant after crosslinking is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, and even more preferably 15 mgKOH / g or more, from the viewpoint of enabling the printing layer to be removed with neutral water.The acid value of the pigment dispersant after crosslinking is preferably 100 mgKOH / g or less, more preferably 90 mgKOH / g or less, and even more preferably 80 mgKOH / g or less, from the viewpoint of suppressing coloration of the removed water by the pigment derived from the printing layer.

[0070] The weight average molecular weight of the pigment dispersant before crosslinking is preferably 8,000 or more, more preferably 10,000 or more, even more preferably 12,000 or more, from the viewpoint of improving the dispersion stability of the pigment particles dispersed in the polymer in the ink, and from the viewpoint of improving the fixing strength of the ink to the printing substrate, 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.

[0071] [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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 〔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.

[0077] [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, fixing resins, chelating agents, humectants, wetting agents, penetrating agents, viscosity adjusters, antifoaming agents, preservatives, antifungal agents, and antirust agents.

[0078] [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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] <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.

[0083] [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.

[0084] 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.

[0085] <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.

[0086] 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.

[0087] 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.

[0088] 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]

[0089] Pressure is expressed in absolute pressure. "Normal pressure" means 101.3 kPa.

[0090] <Measurement method> [Composition of monomers constituting resins and polymers] The values ​​were determined by proton NMR measurement using an Agilent NMR MR400.

[0091] [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)"

[0092] [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.

[0093] [Method for measuring acid value] 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.

[0094] [Measurement of average particle size of particles in water-soluble polyester dispersion and water-based ink] Cumulant analysis was performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and the resulting cumulant average particle size was measured as the average particle size of the water-soluble polyester dispersion and water-based ink. The measurement sample was a dispersion diluted with water to a particle concentration of 5 × 10-3% (solid content equivalent). The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 accumulations. The refractive index of water (1.333) was entered as the refractive index of the dispersion solvent.

[0095] [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

[0096] [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.

[0097] [Measurement of viscosity of water-based ink at 32°C] The viscosity of the water-based ink was measured at 32°C using an E-type viscometer "TV-25" (manufactured by Toki Sangyo Co., Ltd., using a standard cone rotor 1°34' x R24, rotation speed 50 rpm).

[0098] <Production example> [Production of Polymer Dispersant A1] A monomer mixture was prepared by mixing 31 parts by mass of acrylic acid and 69 parts by mass of styrene. 10 parts by mass of methyl ethyl ketone (MEK), 0.2 parts by mass of 2-mercaptoethanol (a polymerization chain transfer agent), and 10% 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% of the monomer mixture, 0.2 parts by mass of the polymerization chain transfer agent, 30 parts by mass of MEK, and 1.1 parts by mass of an azo-based radical 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 monomer mixture in the reaction vessel was heated to 65°C under a nitrogen atmosphere while being stirred, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 65°C from the end of the dropping, a solution of 0.1 parts by mass of the polymerization initiator in 2 parts by mass of MEK was added, and the mixture was further aged at 65°C for 2 hours and then at 70°C for 2 hours, followed by drying under reduced pressure to obtain polymer dispersant A1 (acid value: 240 mgKOH / g, weight-average molecular weight: 13,900). The physical properties of polymer dispersant A1 are shown in Table 1.

[0099] [Production of Polymer Dispersants A2 to A5] Polymer dispersants A2 to A5 were each obtained in the same manner as in the production example for polymer dispersant A1, except that the conditions were changed as shown in Table 1. Table 1 shows the physical properties of polymer dispersants A2 to A5.

[0100] [Table 1]

[0101] [Production of Water-Soluble Polyester Resin B1] The raw materials listed in Table 2 were charged into a 2L stainless steel separable flask (equipped with a K-shaped tube, stirrer, and nitrogen inlet tube). The surface temperature of the mantle heater was raised from 160°C to 260°C while stirring under a nitrogen atmosphere. 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 pressure was then reduced from 1.5 kPa to 1.0 kPa, and the reaction was carried out for 6 hours. Finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to ambient, yielding water-soluble polyester resin B1. The physical properties of water-soluble polyester resin B1 are shown in Table 2.

[0102] [Production of Water-Soluble Polyester Resins B2 to B4] Each of the water-soluble polyester resins shown in Table 2 was obtained in the same manner as in the production example for water-soluble polyester resin B1, except that the raw material monomer composition constituting the water-soluble polyester resin was changed to the conditions shown in Table 2.

[0103] [Table 2]

[0104] [Production of Water-Soluble Polyester Resin Dispersion C1] To 10 parts by mass of the polymer dispersant A1, 4.0 parts by mass of a 5N aqueous sodium hydroxide solution (NaOH solid content: 16.9%) was added as a neutralizer to neutralize the carboxyl groups of the polymer dispersant A1 (neutralizer use equivalent: 40 mol%). 240 parts by mass of ion-exchanged water was then added, and 100 parts by mass of water-soluble polyester resin B1 was heated and dissolved therein at 80°C. The resulting mixture was dispersed for 30 minutes using an ultrasonic homogenizer while maintaining the temperature at 90°C, then cooled to room temperature and dispersed three times using a Microfluidizer (trade name, manufactured by Microfluidics) at a pressure of 200 MPa to obtain a dispersion. Ion-exchanged water was added to the resulting dispersion, and 2.3 parts by mass (corresponding to a crosslinking degree of 40 mol%) of an epoxy crosslinker (trimethylolpropane polyglycidyl ether, Nagase ChemteX Corporation, product name: Denacol EX-321, epoxy value: 140 g / eq) was added, followed by sealing the container and heating at 80°C for 5 hours while stirring with a stirrer to obtain Water-soluble polyester resin dispersion C1, a dispersion of crosslinked polymer particles containing water-soluble polyester resin B1 [(The mass ratio of the contents of dispersion C1 was water-soluble polyester resin: 20.0%, polymer dispersant: 2.2% (the component derived from the epoxy crosslinker in dispersion C1 was 0.2%), sodium hydroxide: 0.14%, and the remainder was water), average particle size: 71 nm, acid value of polymer dispersant after crosslinking: 144 mgKOH / g].

[0105] [Production of Water-Soluble Polyester Resin Dispersions C2 to C12] Water-soluble polyester dispersions C2 to C12 were obtained in the same manner as in the production example for water-soluble polyester resin dispersion C1, except that the type of water-soluble polyester resin, the type of polymer dispersant, the amount of sodium hydroxide, the amount of crosslinking agent, and the type of crosslinking agent were changed as shown in Table 3. The physical properties of water-soluble polyester dispersions C2 to C12 are shown in Table 3. Note that water-soluble polyester dispersion C10 does not contain an epoxy crosslinking agent, and therefore the polymer particles containing the water-soluble polyester resin contained in water-soluble polyester dispersion C10 do not have a crosslinked structure. Also, EX-212L in Table 3 is an epoxy crosslinking agent (1,6-hexanediol diglycidyl ether, manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-212L, epoxy value: 135 g / eq).

[0106] [Table 3]

[0107] [Production of Pigment Water Dispersion 1] [Synthesis of water-insoluble polymer 1 (polyester resin)] 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 polymer 1 (polyester resin, 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 polymer 1 was dissolved in 198.6 g of MEK, and 5N aqueous sodium hydroxide was added to neutralize 85 mol% of the acid value of the water-insoluble polymer 1. 390.5 g of ion-exchanged water was then added dropwise over 30 minutes, and the mixture was stirred and mixed for 15 minutes at 1,500 r / min using a disper blade 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 blade 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%, thereby obtaining Pigment Water Dispersion 1 (solids concentration: 22%, pigment: 13.2%, polymer: 8.8%, acid value of pigment dispersant: 22 mgKOH / g).

[0109] [Preparation of Pigment Water Dispersion 2] [Synthesis of water-insoluble polymer 2 (acrylic resin)] 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 (manufactured by 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% (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% (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, and 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 of MEK was added to obtain a solution (solids concentration: 45%) of water-insoluble polymer 2 (acid value 99 mgKOH / g, weight average molecular weight: 50,000).

[0110] [Production of Pigment Water Dispersion 2] 95.2 parts by weight of the water-insoluble polymer 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 neutralizing agents, and 100 parts by weight of cyan pigment (manufactured by DIC Corporation, trade name: Fastogen Blue CA5380 15:3) was further added to obtain a pigment mixture (polymer neutralization degree: 72 mol%). The resulting pigment mixture was mixed using a disper 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%). 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 g / eq) 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%). 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%, polymer: 6.8%, acid value of pigment dispersant: 69 mgKOH / g).

[0111] <Examples and Comparative Examples> Example 1 [Preparation of Water-Based 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%, pigment: 13.2%, polymer: 8.8%, acid value of pigment dispersant: 22.4 mgKOH / g) was added as a solid content, 2.0 parts by mass of the water-soluble polyester dispersion C1 (solid content concentration: 25%) was added as a solid content, 20.0 parts by mass of propylene glycol (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 5.0 parts by mass of diethylene glycol isobutyl ether (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 20.0 parts by mass of propylene glycol (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), silane ... 1.0 part of a corn-based surfactant ("KF-6011" manufactured by Shin-Etsu Chemical Co., Ltd., active ingredient 100%), 0.5 parts by mass of an acetylene glycol-based 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 ingredient 50%), and 63.2 parts by mass of ion-exchanged water were added and thoroughly stirred. The mixture was then filtered through a membrane filter ("Minisart Syringe Filter" manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to obtain aqueous ink 1 (viscosity: 5.0 mPa s, pH: 8.3).

[0112] [Examples 2 to 15 and Comparative Examples 1 and 2] [Preparation of Water-Based Inks 2 to 13, and Water-Based Inks C1 and C2] Water-based inks 2 to 13 according to the examples and water-based inks C1 and C2 according to the comparative examples were obtained in the same manner as in Example 1, except that the ink compositions were changed as shown in Table 4.

[0113] [Evaluation by inkjet printing] In an environment with a temperature of 32°C, an inkjet printing evaluation device (manufactured by Tritec Corporation) equipped with a print head (manufactured by Kyocera Corporation, product name: KJ4B-HD06MHG-STDV, piezoelectric type) was filled with the water-based inks 1 to 13, water-based ink C1, or water-based ink C2. The print head voltage was set to 26 V, drive frequency to 30 kHz, ejected droplet volume to 7 pL, print head temperature to 32°C, and print head resolution to 600 dpi. A solid image was printed at 100% duty on a polyethylene terephthalate film (manufactured by Futamura Chemical Co., Ltd., "FE2000#25") (hereinafter referred to as "PET") as a low-absorbency printing substrate heated to 50°C.

[0114] 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.) (hereinafter referred to as "OPP"), and a printed matter was obtained.

[0115] 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.) (hereinafter referred to as "PE"), and a printed matter was obtained.

[0116] 〔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 water 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 evaluation criteria. The higher the value, the better the printed layer removability. A printing layer removal rate of 80% or higher indicates practically acceptable results. The evaluation results are shown in Table 4. (Evaluation criteria) A: Printing layer removal rate of 95% or more B: 90% or more but less than 95% C: 80% to less than 90% D: 1% or more but less than 80% E: Printed layer removal rate 0%, no printed layer detachment

[0117] [Evaluation of ink storage stability] Each of the water-based inks obtained in the examples and comparative examples was sealed in a screw tube (manufactured by Maruemu Co., Ltd.) and allowed to stand in a temperature-controlled room set at 70°C for one week. The average particle size was then measured to determine the "average particle size of the ink after storage," and the average particle size increase rate was calculated using the following formula. Average particle size increase rate (%) = [(average particle size of water-based ink after storage - average particle size of water-based ink before storage) / average particle size of water-based ink before storage] x 100 The average particle size of the water-based ink before and after storage was measured using the method described above in "Measurement of average particle size of water-soluble polyester dispersion and water-based ink." The smaller the value, the better the ink storage stability, and if the average particle size increase rate is less than 15%, there is no practical problem. The evaluation results are shown in Table 4. (Evaluation criteria) A: Average particle size increase rate is less than 5% B: Average particle size increase rate is 5% or more and less than 10% C: Average particle size increase rate is 10% or more and less than 15% D: Average particle size increase rate is 15% or more E: Aggregated and not measurable

[0118] [Evaluation of intermittent ink ejection] Using the printing evaluation device, ten 20 mm x 20 mm solid images were printed with 100% ink duty, and then the prints were left for 10 minutes without printing. One 20 mm x 20 mm solid image was then printed to obtain a solid print. From the state of the solid print, the ratio of the ejection area of ​​the solid print immediately after leaving it for 10 minutes (i.e., the solid print obtained by a command to print one sheet immediately after leaving it for 10 minutes) to the ejection area of ​​the solid print immediately before leaving it for 10 minutes (i.e., the 10th print of the solid print obtained by a command to print 10 sheets) was calculated (ejection recovery rate (%) according to the following formula) to evaluate intermittent ejection. No power was applied to the film heater in this evaluation. Discharge recovery rate (%) = (discharge area of ​​solid print immediately after leaving for 10 minutes) / (solid print immediately before leaving for 10 minutes)] × 100 The larger the value, the better the intermittent ink ejection performance, and if the ejection recovery rate is 85% or higher, there is no problem in practical use. The evaluation results are shown in Table 4. (Evaluation criteria) A: Discharge recovery rate is 95% or more B: Discharge recovery rate is 90% or more but less than 95% C: Discharge recovery rate is 85% or more but less than 90% D: Discharge recovery rate is 80% or more but less than 85% E: Discharge recovery rate is less than 80%

[0119] [Table 4]

[0120] Table 4 shows that the aqueous inks according to the examples of the present invention are superior to the aqueous inks obtained in the comparative examples in terms of releasability of the printed layer, storage stability of the ink, and intermittent ejection performance. On the other hand, Comparative Example 1 shows that when the aqueous ink does not contain a water-soluble polyester resin dispersed with a polymer dispersant, the releasability of the printed layer is inferior, and Comparative Example 2 shows that when the aqueous ink contains a water-soluble polyester resin not dispersed with a polymer dispersant, the storage stability of the ink and intermittent ejection performance are inferior.

Claims

1. An inkjet printing ink containing a pigment, a water-soluble polyester resin dispersed with a polymer dispersant, and water.

2. 2. The ink for ink-jet printing according to claim 1, wherein the water-soluble polyester resin has a sulfonate group.

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

4. 10. The ink jet printing ink of claim 1, wherein the polymeric dispersant is crosslinked.

5. 2. The ink jet printing ink of claim 1, wherein the polymeric dispersant comprises a polymer having constitutional units derived from carboxylic acid monomers and constitutional units derived from hydrophobic monomers.

6. The ink for ink-jet printing according to claim 5, wherein the carboxylic acid monomer is at least one selected from (meth)acrylic acids.

7. 6. The ink for ink-jet printing according to claim 5, wherein the hydrophobic monomer is at least one selected from the group consisting of styrene, benzyl (meth)acrylate, and cyclohexyl (meth)acrylate.

8. 8. The ink for ink-jet printing according to claim 7, wherein the pigment is contained in a state of pigment-containing polymer particles in which the pigment is contained in a pigment dispersant.

9. 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 8, and forming a printing layer derived from the ink on the low liquid-absorbent printing substrate directly or via another layer.

10. 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 8.

11. A method for removing a printed layer, comprising a step of treating the printed matter according to claim 10 with neutral water at a temperature of 40°C or higher to remove the printed layer.

12. A low-liquid-absorbent printed substrate, wherein the printed layer has been removed by the method for removing the printed layer according to claim 11.

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