WO2018221674A1 - Aqueous ink and method for forming image - Google Patents

Abstract

The purpose of the present invention is to provide an aqueous ink capable of enhancing the abrasion resistance and water resistance of an image while suppressing nozzle clogging, and a method for forming an image using such an aqueous ink. In order to achieve such purpose, the present invention pertains to an aqueous ink containing a pigment and a dispersant. The dispersant is an acrylic copolymer comprising: a structural unit having an acidic functional group in a side chain; a structural unit having a primary amine, a secondary amine, a tertiary amine, or a hydroxyl group in a side chain; and a hydrophobic structural unit, the acrylic copolymer having an acid value of 60 to 200 mg/KOH and a total of the hydroxy value and the amine value of 5 to 30 mg/KOH. The aqueous ink can be used in a method for forming an image that applies an overcoat and causes bonding with a laminate layer after deposition on a substrate.

Description

Water-based ink and image forming method

The present invention relates to a water-based ink and an image forming method.

Since the inkjet method can produce images easily and inexpensively, it has been applied to various printing fields including special printing such as photographs, various printing, marking, and color filters. In particular, the inkjet method is particularly suitable for applications in which various images are formed in small amounts because digital printing is possible without using a plate.

Ink-jet inks used in the ink-jet method include water-based inks composed of water and a small amount of organic solvents, non-aqueous inks that contain organic solvents but do not substantially contain water, and hot inks that heat and melt solid inks at room temperature. There are a plurality of types, such as melt ink and actinic ray curable ink that is cured by irradiation with actinic rays after printing, and these inks are properly used depending on the application. Among these, water-based inks are widely used for home printers because they generally have low odor and high safety.

In a water-based ink containing a pigment as a coloring material, the pigment is made of a resin called a dispersant, which has a structural unit having a hydrophobic functional group or structure that can be adsorbed to the pigment, and a structural unit having a hydrophilic structure. The dispersibility is improved. As the dispersant, there are many resins having aromatic and medium chain or long chain alkyl groups as the hydrophobic functional group or structure, and carboxylic acid groups and polyethylene oxide chains as the hydrophilic structure. Used.

Ink-jet inks, unlike inks used for flexographic printing and offset printing, are desired to have lower ink viscosity, and pigments are required to be stably dispersed with a smaller particle size. Therefore, a resin having a larger amount of the above hydrophilic structure is often used as a dispersant used in the ink jet ink. For example, Patent Document 1 discloses that an acrylic copolymer having an acid value of 40 mgKOH / g or more and 110 mgKOH / g or less has a high affinity for water, so that when used as a dispersant, the dispersion stability of the pigment is further improved. It is described that it can. Patent Document 2 describes a dispersant having an acid value of 55 mgKOH / g or more and 400 mgKOH / g or less, which can be synthesized from a monomer such as acrylic acid.

By the way, in inks used for flexographic printing and offset printing, a binder resin such as urethane resin, urethane-acrylic resin, vinyl chloride resin, and vinyl acetate resin is added to the ink, and the binder resin is formed on a substrate. Thus, the scratch resistance and water resistance of the image are increased. However, since it is desired to lower the viscosity of the ink, only a smaller amount of binder resin can be added to the ink-jet ink, so that images formed using the ink-jet ink have scratch resistance and water resistance. There is a problem that it is difficult to increase.

As a method for improving the scratch resistance and water resistance of an image with a binder resin and not excessively increasing the viscosity of the ink, there is known a method of emulsifying a resin used as the binder resin and adding it to an aqueous ink for inkjet. It has been. However, these emulsified resins may precipitate as solids in the vicinity of the nozzle when the inkjet ink remaining in the nozzle of the inkjet head dries, causing nozzle clogging.

On the other hand, as described in Patent Document 3 and Patent Document 4, a water-based ink to which a resin is added and a cross-linking agent that crosslinks the resin are separately applied on a substrate, and a resin contained in the water-based ink is obtained. A method of forming a film by cross-linking on a base material has also been studied. According to this method, the resin to be added to the water-based ink may be a resin having a lower molecular weight and a lower viscosity that is difficult to increase before crosslinking, so that it is expected that nozzle clogging is suppressed.

JP 2006-342294 A JP 2002-212479 A International Publication No. 2003/43825 Japanese Patent Laying-Open No. 2015-045003

In a water-based ink containing a dispersant described in Patent Document 1 and Patent Document 2 or the like, if a binder resin is added to further improve the scratch resistance and water resistance of an image, nozzle clogging is likely to occur. On the other hand, even if the methods described in Patent Document 3 and Patent Document 4 are applied, conventionally, nozzle clogging has not been completely suppressed.

The present invention has been made in view of the above problems, and provides a water-based ink capable of improving the scratch resistance and water resistance of an image while suppressing nozzle clogging, and an image forming method using such a water-based ink. That is the purpose.

The above problem is solved by the following means.
[1] a pigment, a structural unit having an acidic functional group in a side chain, a structural unit having any one of a primary amine, a secondary amine, a tertiary amine and a hydroxyl group in a side chain, a hydrophobic structural unit, And an acrylic copolymer having a polyalkylene glycol chain amount of 5% by mass or less based on the total mass of the dispersant, the acid value being 60 mg / KOH or more and 200 mg / KOH or less, and And a dispersant having a total of a hydroxyl value and an amine value of 5 mg / KOH or more and 30 mg / KOH or less.
[2] The water-based ink according to [1], wherein the dispersant has a structural unit having a primary amine in a side chain.
[3] A step of ejecting water-based ink droplets according to [1] or [2] from a nozzle of an ink-jet head and landing on a substrate; and the substrate on which the water-based ink droplets landed An image forming method comprising: a step of applying a coating liquid; and a step of bonding a base material to which the overcoat liquid is applied and a laminate layer.
[4] The image forming method according to [3], wherein the overcoat liquid is a laminate adhesive.
[5] The image forming method according to [3] or [4], wherein the overcoat liquid contains an isocyanate compound.
[6] The image forming method according to any one of [3] to [5], including a step of applying a precoat liquid containing a pigment flocculant to the substrate before discharging the water-based ink droplets.

According to the present invention, a water-based ink capable of improving the scratch resistance and water resistance of an image while suppressing nozzle clogging, and an image forming method using such a water-based ink are provided.

Hereinafter, one embodiment of the present invention relates to a water-based ink containing the following dispersant.

In this embodiment, acrylic resin is used as a dispersant. When an acrylic resin is used as a dispersant, sodium hydroxide or amine is added to the aqueous ink as a neutralizing agent in order to adjust the pH of the aqueous ink. As a result, even if the acrylic resin is solidified and precipitated in the vicinity of the nozzle, when the water-based ink is discharged again, the acrylic resin can be redissolved in the water-based ink by ammonium ions contained in the next water-based ink. it can. Therefore, even if the acrylic resin is deposited, it is considered that the acrylic resin does not stay in the vicinity of the nozzle for a long time and the nozzle is not easily clogged.

In this embodiment, nozzle clogging can be made difficult to occur by setting the acid value of the acrylic resin to 60 mg / KOH or more. This is presumably because the acrylic resin having the acid value has a moderately strong charge repulsion, so that the pigment can be dispersed as finer particles in the water-based ink. By reducing the particle diameter of the pigment in the water-based ink, the water-based ink is difficult to dry at the nozzle. In addition, since the particle size of the pigment in the water-based ink is reduced, even when the water-based ink is dried by the nozzle and the solid content concentration in the ink is increased, the pigment can be stably dispersed and the solid content is precipitated. It becomes difficult.

On the other hand, in the present embodiment, the deterioration of the water resistance of the image due to the dissociation of the carboxylic acid when contacted with water is suppressed, and the carboxylic acid in the dispersant is crystallized by hydrogen bonding, and will be described later. The dispersant is an acrylic resin having an acid value of 200 mg / KOH or less from the viewpoint of suppressing the deterioration of the abrasion resistance and water resistance of the image due to the agent not easily penetrating into the ink and insufficient crosslinking. .

The acrylic resin has a total hydroxyl value and amine value of 5 mg / KOH or more. Such an acrylic resin having a hydroxyl group or an amine group becomes, for example, a urethane resin or a urea resin by reaction of the hydroxyl group or amine group with the isocyanate when isocyanate is used as a crosslinking agent. This urethane resin and urea resin itself increase the scratch resistance and water resistance of the image, and when laminating the image, it increases the adhesive strength of the laminate layer as an adhesive, thus suppressing delamination of the laminate It is also possible to do.

On the other hand, in the present embodiment, the deterioration of the water resistance of the image due to the hydrophilic hydroxyl group and amine group is suppressed, and the hydroxyl group and amine group react preferentially with the crosslinking agent on the film surface to crosslink inside the ink. From the viewpoint of suppressing image scratch resistance and water resistance reduction due to a decrease in the rate, the acrylic resin has a total hydroxyl value and amine value of 30 mg / KOH or less.

Hereinafter, the present invention will be described by way of exemplary embodiments, but the present invention is not limited to the following embodiments.

1. Water-based ink Water-based ink contains a pigment and a dispersant.

1-1. Pigment The pigment may be any pigment that can be used by dispersing in water-based ink.

Examples of the pigment include C.I. I. Pigment Yellow (hereinafter also referred to simply as “PY”) 1, PY2, PY3, PY12, PY13, PY14, PY16, PY17, PY34, PY35, PY37, PY55, PY73, PY74, PY75, PY81, PY83, PY87, PY93 , PY95, PY97, PY98, PY108, PY109, PY110, PY114, PY120, PY128, PY129, PY137, PY138, PY139, PY150, PY151, PY153, PY154, PY155, PY157, PY157, PY166, PY167P And PY213, C.I. I. Pigment Red (hereinafter also simply referred to as “PR”), PR5, PR7, PR12, PR19, PR22, PR31, PR38, PR43, PR48: 1, PR48: 2, PR58: 4, PR48: 4, PR48: 5, PR49: 1, PR53: 1, PR57: 1, PR57: 2, PR63: 1, PR81, PR81: 1, PR81: 2, PR81: 3, PR81: 4, PR88, PR101, PR104, PR108, PR112, PR122, PR123, PR144, PR146, PR149, PR166, PR168, PR169, PR170, PR177, PR178, PR179, PR184, PR185, PR202, PR208, PR216, PR226 and PR257, C.I. I. Pigment Violet (hereinafter also simply referred to as “PV”) 19 and PV23, C.I. I. Pigment Blue (hereinafter also referred to simply as “PB”) 1, PB2, PB3, PB15, PB15: 1, PB15: 2, PB15: 3, PB15: 4, PB15: 6, PB16, PB17: 1, PB18, PB22 , PB27, PB28, PB29, PB36 and PB60, C.I. I. Pigment Orange (hereinafter, “CI Pigment Orange” is also simply referred to as “PO”) 16, PO34, PO36, PO38, PO43, PO64 and PO71, C.I. I. Pigment Green (hereinafter, also simply referred to as “PG”) 7, PG26, PG36 and PG50, C.I. I. Pigment White (hereinafter also referred to simply as “PW”) 6, PW18 and PW21, and C.I. I. Pigment Black (hereinafter also simply referred to as “PBk”) 7, PBk28, and PBk26.

The water-based ink preferably contains 0.1% by mass or more and 20% by mass or less of the pigment, and more preferably contains 0.4% by mass or more and 10% by mass or less of the pigment with respect to the total mass of the water-based ink. .

1-2. Dispersant The dispersant is a structural unit having an acidic functional group in the side chain, a structural unit having any one of primary amine, secondary amine, tertiary amine and hydroxyl group in the side chain, a hydrophobic structural unit, A monomer copolymer containing The dispersant has an acid value of 60 mg / KOH or more and 200 mg / KOH or less, and a total of a hydroxyl value and an amine value of 5 mg / KOH or more and 30 mg / KOH or less.

As described above, the acrylic dispersant is less likely to cause nozzle clogging.

The structural unit having an acidic functional group may be a structural unit having an acidic functional group such as a carboxylic acid group and a sulfonic acid group in the side chain. Among these, the structural unit having the acidic functional group is preferably a structural unit having a carboxylic acid group in the side chain from the viewpoint of ease of production of the dispersant.

The structural unit having the acidic functional group is obtained by (co) polymerizing the monomer having the acidic functional group. Examples of the monomer having an acidic functional group include (meth) acrylic acid, fumaric acid and maleic acid. Among these, the monomer having an acidic functional group is preferably (meth) acrylic acid from the viewpoint of ease of production of the dispersant.

In the present invention, “(meth) acryl” means acryl or methacryl, “(meth) acrylate” means acrylate or methacrylate, and “(meth) acryloyl group” means acryloyl group or methacrylate. An acryloyl group is meant.

The structural unit having any one of primary amine, secondary amine, tertiary amine, and hydroxyl group in the side chain is obtained by (co) polymerizing a monomer having an amine group or a monomer having a hydroxyl group.

Examples of the monomer having an amine group include amine (meth) acrylates such as (meth) acrylamide, aminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, and N, N-diethylamino. Examples include ethyl (meth) acrylate and N, N-dimethylaminopropyl (meth) acrylate.

The structural unit containing any of primary amine, secondary amine and tertiary amine may be obtained by (co) polymerizing a vinyl monomer having an epoxy ring and adding an amino group by a known method after polymerization. Good.

From the viewpoint of facilitating the formation of a urea bond by reacting with isocyanate, the dispersant preferably includes a structural unit having a primary amine in the side chain among these.

Examples of the monomer having a hydroxyl group include hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl acrylate (2-HPA), 2-hydroxypropyl methacrylate (2-HPMA), and 3-hydroxypropyl. Acrylate (3-HPA), 3-hydroxypropyl methacrylate (3-HPMA), 2,3-dihydroxypropyl acrylate, 2,3-dihydroxypropyl methacrylate, and 3,4-dihydroxybutyl (meth) acrylate (4-HBA) Hydroxyalkyl (meth) acrylates containing 1,3-diacryloyl glycerin, 1,3-dimethacryloyl glycerin, trimethylolpropane monoacrylate, trimethylol B bread monomethacrylate, and the like trimethylolpropane diacrylate and trimethylolpropane dimethacrylate.

The hydrophobic structural unit may be a structural unit having a structure capable of imparting adsorptivity to a pigment used in water-based ink. The hydrophobic structural unit can be obtained by (copolymerizing) the monomers exemplified below.

Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, amyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, 2- Ethylhexyl (meth) acrylate, heptyl (meth) acrylate, 2- (tert-butylamino) ethyl (meth) acrylate, octyl (meth) acrylate, 3-isopropylheptyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) ) Acrylate, undecyl (meth) acrylate, 5-methylundecyl (meth) acrylate, dodecyl (meth) acrylate, 2-methyldodecyl (meth) acrylate, tridecyl (meth) acrylate 5-methyltridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, 2-methylhexadecyl (meth) acrylate, heptadecyl (meth) acrylate, 5-isopropylhepta Decyl (meth) acrylate, 4-tert-butyloctadecyl (meth) acrylate, 5-ethyloctadecyl (meth) acrylate, 3-isopropyloctadecyl (meth) acrylate, octadecyl (meth) acrylate, nonadecyl (meth) acrylate, eicosyl (meta) ) Acrylate, cetyl eicosyl (meth) acrylate, stearyl eicosyl (meth) acrylate, docosyl (meth) acrylate, and eicosyl tetratriacon Having a linear alkyl group including Le (meth) acrylate (meth) acrylate,
Cyclic (or aromatic) alkyl groups including cyclopentyl (meth) acrylate, 3-vinylcyclohexyl (meth) acrylate, cyclohexyl (meth) acrylate, bornyl (meth) acrylate, benzyl (meth) acrylate and phenyl (meth) acrylate, etc. (Meth) acrylate having,
(Meth) acrylates derived from unsaturated alcohols including 2-propynyl (meth) acrylate, allyl (meth) acrylate, vinyl (meth) acrylate, and oleyl (meth) acrylate,
1,3-butanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, glycerin di (meth) acrylate and dimethacrylate of ethoxylated bisphenol A (Meth) acrylates having two (meth) acryloyl groups including
Glycerin tri (meth) acrylate, diglycerin (meth) triacrylate, ditrimethylolethane tri (meth) acrylate, ditrimethylolpropane tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, Pentaerythritol tetra (meth) acrylate, dipentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, tripentaerythritol tri (meth) acrylate, tripentaerythritol tetra (Meth) acrylate, tripentaerythritol pentaa (meth) acrylate, tripentaerythritol hexa (meth) acrelane , (Meth) acrylates having three or more (meth) acryloyl groups, including, for example, tripentaerythritol hepta (meth) acrylate, and the like, and methoxyethyl (meth) acrylate, methoxybutyl (meth) acrylate, and ethoxybutyl (meth) (Meth) acrylate having an alkoxy group containing acrylate or the like.

The hydrophobic structural unit is a structural unit derived from a nitrogen-containing monomer including N-vinylpyrrolidone, N-vinylimidazole, N-vinylcarbazole and the like, and a monomer such as styrene and α-methylstyrene. Some may be included.

Among these, methyl (meth) acrylate, ethyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, lauryl (meth) acrylate, etc. It is preferable to select suitably from (meth) acrylates having an alkyl group having 1 to 20 carbon atoms, benzyl acrylate, alkyl acrylate, styrene, N-vinylpyrrolidone and the like in consideration of the affinity with the pigment.

The dispersant has a structural unit derived from each of the above monomers at a ratio such that the acid value is 60 mg / KOH or more and 200 mg / KOH or less, and the total of the hydroxyl value and the amine value is 5 mg / KOH or more and 30 mg / KOH or less. Good.

The acid value and hydroxyl value of the dispersant can be measured according to a potentiometric titration method described in JIS K 0070 (1992). The amine value of the dispersant can be measured in the same manner as the potentiometric titration method described in JIS K 7237 (1995).

The presence or absence of a constituent unit constituting the dispersant is determined in a known direction such as infrared spectroscopy (IR), nuclear magnetic resonance (NMR), and pyrolysis gas chromatography-mass spectrometry (Py-GC-MS). Can be measured.

In addition, from the viewpoint of suppressing the increase in viscosity when the water-based ink is dried by the nozzle and making the nozzle clogging less likely to occur, the dispersant has a proportion of structural units derived from the monomer having a polyalkylene glycol chain. It is preferable to have a structural unit derived from each of the above monomers so as to be 5% by mass with respect to the total mass of the agent, and the proportion of the structural unit derived from the monomer having a polyethylene glycol chain is based on the total mass of the dispersant. It is preferable to have a structural unit derived from each of the above monomers so as to be 5% by mass. Examples of monomers having a polyalkylene glycol chain include polyethylene glycol monoallyl ether, polyethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, and polyethylene glycol di (meth) acrylate Is included.

The weight average molecular weight of the dispersant is preferably 4000 or more and 20000 or less, and more preferably 6000 or more and 15000 or less. The weight average molecular weight of a dispersing agent can be made into the styrene conversion molecular weight measured by GPC.

The dispersant may be a random copolymer or a block copolymer, but from the viewpoint of increasing the scratch resistance and water resistance of the image and increasing the adhesive strength of the laminate layer by further dispersing the crosslinking position with the isocyanate. A copolymer is preferred.

The dispersant may be present in the water-based ink as a dispersion containing the pigment adsorbed on the surface of the pigment. For example, the dispersion can be produced by treating the pigment and the dispersant in a solvent with a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, or the like.

From the viewpoint of stably dispersing the pigment in the water-based ink for a long period of time, the average particle size of the dispersion is preferably 10 nm or more and 200 nm or less, more preferably 10 nm or more and 100 nm or less, and more preferably 10 nm or more. More preferably, it is 50 nm or less.

The average particle diameter can be measured by a commercially available particle size measuring instrument using a light scattering method, an electrophoresis method, a laser Doppler method, or the like. Further, by taking a particle image with a transmission electron microscope on at least 100 particles and performing statistical processing on the image using image analysis software such as Image-Pro (manufactured by Media Cybernetics), the above average is also obtained. The particle diameter can be determined.

From the viewpoint of suppressing nozzle clogging, the water-based ink preferably contains 10% by mass or more and 150% by mass or less of a dispersant with respect to the total mass of the pigment.

1-3. Neutralizing agent The water-based ink may contain a neutralizing agent for adjusting the pH of the water-based ink by neutralizing the acidic group of the dispersant that is the acrylic resin.

Examples of neutralizing agents include amines and inorganic alkali salts.

Among these, amines leave only carboxylic acid groups that are not neutralized by volatilization when the substrate is dried after the water-based ink has landed on the substrate. This is preferable because the group can be more easily reacted to increase the water resistance of the image. Examples of the volatilizable amines include ammonia, monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, methylethylamine, monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, methylaminoethanol, and dimethylaminoethanol. Etc. are included. Among these, ammonia is preferable from the viewpoints of volatilization speed and ease of use.

On the other hand, an inorganic alkali salt is preferable from the viewpoint of suppressing the precipitation of the dispersant due to volatilization in the vicinity of the nozzle and further improving the injection stability and the maintainability of the nozzle. Examples of the inorganic alkali salt include potassium hydroxide and sodium hydroxide.

It should be noted that the water-based ink preferably contains both an amine and an inorganic alkali salt from the viewpoint of achieving both the water resistance and the injection stability of the image.

1-4. Organic solvent The water-based ink may contain an organic solvent for the purpose of adjusting the viscosity.

From the viewpoint of increasing the compatibility with water, the organic solvent is preferably water-soluble. Examples of the water-soluble organic solvent include alcohols, polyhydric alcohols, amines, amides, glycol ethers, and 1,2-alkanediols having 4 or more carbon atoms. Only one kind of these organic solvents may be contained, or two or more kinds thereof may be contained in combination.

Examples of the alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol and tertiary butanol.

Examples of the polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol having 5 or more ethylene oxide groups, propylene glycol, dipropylene glycol, tripropylene glycol, and propylene oxide groups. Polypropylene glycol having a number of 4 or more, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol and the like are included.

Examples of the amines include ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine Pentamethyldiethylenetriamine and tetramethylpropylenediamine.

Examples of the amides include formamide, N, N-dimethylformamide, N, N-dimethylacetamide and the like.

Examples of the glycol ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether and tripropylene glycol. Monomethyl ether and the like are included.

Examples of 1,2-alkanediols having 4 or more carbon atoms include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol and 1,2-heptanediol. It is.

Of these, when the organic solvent is a polyhydric alcohol, bleeding during high-speed printing can be suitably suppressed. Examples of preferable polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol and tripropylene glycol.

When the water-based ink contains two or more types of organic solvents, the mass ratio of the polyhydric alcohols relative to the total mass of the organic solvent is made higher than the mass ratio of the other organic solvents, thereby further reducing the bleeding of the formed image. It can be made difficult to occur. Preferably, the mass ratio of the polyhydric alcohol to the mass of the whole organic solvent is 50% or more. When two or more kinds of polyhydric alcohols are included, the total mass ratio of all the polyhydric alcohols only needs to be higher than the mass ratio of any other kind of organic solvent. For example, the mass of the whole organic solvent The mass ratio of the polyhydric alcohol to the suffices should be 50% or more.

The content of the organic solvent in the water-based ink can be, for example, in the range of 5% by mass to 60% by mass.

1-5. Other components As long as the effects of the present invention are exhibited, the water-based ink is a resin, a surfactant, a pH adjuster, oil droplet fine particles, an ultraviolet absorber, a discoloration inhibitor, a fluorescent whitening agent, a polysaccharide, a viscosity adjustment. An agent, a specific resistance adjusting agent, a film forming agent, an ultraviolet absorber, an antioxidant, a fungicide, a rust inhibitor and the like may be contained. Only one kind of these components may be contained, or two or more kinds may be contained in combination.

Examples of the resin include a fixing resin for imparting fixability to the substrate to the pigment, a resin as a thickener for adjusting the viscosity of the ink, and other resins. Only one kind of these resins may be contained, or two or more kinds may be contained in combination.

These resins may be dissolved in water-based ink or may be dispersed in an emulsion state. In the case of dispersing in an emulsion state, the particle diameter is preferably 300 nm or less from the viewpoint of not impairing the jetting property by inkjet. In the case of a soluble polymer, the composition and molecular weight are not particularly limited. However, since a polymer having a higher degree of polymerization tends to deteriorate injection properties, the molecular weight is preferably 50,000 or less, although it depends on the composition of the polymer.

The surfactant may be any of cationic, anionic, amphoteric and nonionic.

Examples of the cationic surfactant include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, and imidazolinium salts.

Examples of anionic surfactants include fatty acid soaps, N-acyl-N-methylglycine salts, N-acyl-N-methyl-β-alanine salts, N-acyl glutamates, acylated peptides, alkyl sulfonic acids Salt, alkylbenzene sulfonate, alkyl naphthalene sulfonate, dialkyl sulfosuccinate, alkyl sulfoacetate, α-olefin sulfonate, N-acylmethyl taurine, sulfated oil, higher alcohol sulfate, secondary Higher alcohol sulfate, alkyl ether sulfate, secondary higher alcohol ethoxy sulfate, polyoxyethylene alkylphenyl ether sulfate, monoglyculate, fatty acid alkylolamide sulfate, alkyl ether phosphate, alkyl phosphate D This includes steal salt.

Examples of amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate, and imidazolinium betaine.

Examples of nonionic surfactants include polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin Fatty acid ester, polyoxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, sucrose fatty acid ester, fatty acid alkanolamide , Polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, alkylamine oxide And acetylene glycol and acetylene alcohol.

From the viewpoint of reducing the surface tension of the water-based ink, it is preferable that some of these surfactants are substituted with fluorine atoms or silicon atoms.

1-6. Physical Properties From the viewpoint of improving the ejection stability from the nozzles of the inkjet head, the viscosity of the water-based ink is preferably 1 cP or more and less than 100 cP. From the viewpoint of further improving the discharge stability, the viscosity of the water-based ink is preferably 1 cP or more and 50 cP or less, and more preferably 1 cP or more and 15 cP or less.

From the viewpoint of improving the ejection stability from the nozzles of the inkjet head, the surface tension of the water-based ink is preferably 20 mN / m or more and 50 mN / m or less. From the viewpoint of improving the wettability with respect to the base material and making the formed image higher definition, the surface tension of the water-based ink is more preferably 20 mN / m or more and 35 mN / m or less. The surface tension of the water-based ink can be adjusted to the above range by changing the type or amount of the surfactant and the organic solvent.

2. Image Forming Method The aqueous ink can be ejected from the nozzles of an inkjet head and landed on a substrate to form an image.

At this time, a precoat liquid may be applied to the substrate. Further, after applying the water-based ink to the substrate, an overcoat liquid may be applied. Moreover, the laminate layer may be further bonded to the image to which the overcoat liquid is applied.

2-1. Step of landing water-based ink droplets In this step, water-based ink droplets are ejected from an inkjet head to land on a region on a substrate.

The ejection method from the inkjet head may be either an on-demand method or a continuous method. On-demand inkjet heads include electro-mechanical conversion methods such as single cavity type, double cavity type, bender type, piston type, shear mode type and shared wall type, as well as thermal inkjet type and bubble jet. Any of electric-thermal conversion methods such as Canon Inc. registered trademark) may be used.

Among these, from the viewpoint of increasing the types of ink that can be used and making the image quality more precise, the inkjet head is preferably a piezo-type inkjet head having a nozzle diameter of 30 μm or less.

From the viewpoint of recording an image at a high speed, the inkjet recording method is preferably a one-pass type. The one-pass type ink jet recording method is a method in which when a substrate passes under one ink jet head unit, water-based ink droplets are ejected and landed on all pixels where dots should be formed in one pass. Means method.

From the viewpoint of recording an image by a one-pass type ink jet recording method, the ink jet head is preferably a line head type. The line head type ink jet head means an ink jet head having a length equal to or greater than the width of the printing range in a direction orthogonal to the substrate transport direction. The line head type inkjet head may be composed of a single head having a length longer than the width of the printing range, or a combination of a plurality of heads so as to be longer than the width of the printing range. But you can. From the viewpoint of higher definition of the formed image, the plurality of heads form a plurality of rows in a direction perpendicular to the conveyance direction of the substrate, and the heads in each row are nozzles for the substrate. It is preferable to arrange so that the emission positions are different.

2-2. Step of Applying Overcoat Liquid In this step, the overcoat liquid is applied to the substrate on which the water-based ink droplets have landed.

The overcoat liquid can be a known overcoat liquid, but preferably contains a compound for crosslinking the dispersant.

Examples of the compound for crosslinking include a carbodiimide compound, an isocyanate compound, an epoxy compound, a silyl compound, a hydrazine compound, and an oxazoline compound. Only one kind of these compounds may be contained, or two or more kinds may be contained in combination.

Among these compounds, an isocyanate compound is preferable because it has sufficiently high reactivity and can easily enhance the scratch resistance and water resistance of an image in a short time and is inexpensive. In addition, since the isocyanate compound does not react with the carboxylic acid group that the dispersant has in large quantities, it sufficiently penetrates in the depth direction to crosslink the dispersant, thereby further improving the scratch resistance and water resistance of the image. it can. The isocyanate compound reacts with the hydroxyl group of the dispersant to produce a polyurethane polyol that is widely used as a laminate adhesive and has high safety. Therefore, an isocyanate compound makes the quantity of the adhesive agent used when bonding a laminated layer smaller, or is unnecessary.

Examples of the isocyanate compounds include polyisocyanates including tolylene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, xylene diisocyanate and adducts thereof.

From the viewpoint of further improving the scratch resistance and water resistance of the image, the overcoat liquid preferably contains a resin such as polyester polyol, polyurethane polyol, polyurethane, acrylic, acrylic urethane, polyester, and polyolefin. Among these, it is more preferable that the overcoat liquid contains polyester polyol, polyurethane polyol or polyurethane.

The overcoat liquid is preferably a liquid that can also act as a laminating adhesive when laminating. When the overcoat liquid acts as a laminating adhesive, an additional coating step and a drying step are not required when laminating, and a laminating process using a material whose safety has been confirmed conventionally is also possible. .

Examples of liquids known as laminating adhesives include a combination of the Takerak series, which is the main liquid of two-part adhesives, and the Takenate A series, which is a cross-linking agent liquid (both manufactured by Mitsui Chemicals, Inc.). Polydon series (manufactured by Sanyo Chemical Co., Ltd.) as an adhesive, Eunoflex series (manufactured by Sanyo Chemical Co., Ltd.) as a one-component adhesive, and Polybond series (manufactured as Sanyo Chemical Co., Ltd.) as a one-component adhesive ) Etc. are included. However, when a two-component adhesive is used, it is preferable to use a larger amount of isocyanate than that recommended in the preparation of the adhesive.

The overcoat solution is applied by known methods such as roll coater using a bar coater, anilox roller, slit coater, die coater, spraying, offset printing, curtain coating, gravure coating, and the above-described inkjet method. Can be done.

After the application of the overcoat liquid, it is preferable to dry the substrate to which the water-based ink and the overcoat liquid have been applied. Drying can be performed by known methods such as infrared lamp drying, hot air drying, back heat drying, and reduced pressure drying. From the viewpoint of further improving the efficiency of drying, it is preferable to dry the substrate by combining two or more of these drying methods.

Drying may be performed both after the application of the water-based ink and after the application of the overcoat liquid. However, the acrylic resin is more sufficiently crosslinked by diffusing the compound for crosslinking such as the isocyanate described above into the ink. From the viewpoint of further improving the scratch resistance and water resistance of the image, it is not necessary to dry after application of the water-based ink, or it is completely dried after the overcoat liquid is applied after drying to an insufficient level (water remains). It is preferable to dry.

2-3. Step of bonding the laminate layer In this step, the substrate to which the overcoat liquid is applied and the laminate layer are bonded.

The laminate layer can further improve the scratch resistance, water resistance and heat resistance of the image.

The film layer resin can be used for the laminate layer. Examples of the resin include nylon, polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate, and triacetyl cellulose.

) A known adhesive may be applied to the substrate before joining the laminate layers. However, in this embodiment, since the urethane resin or urea resin that acts as an adhesive is generated by the application of the overcoat liquid, the application of the adhesive is not necessarily required.

The joining of the laminate layers can be performed by a known method including dry lamination, extrusion lamination, hot melt lamination, and the like. After the laminate layers are bonded, it is preferable that the laminate layers are bonded together by heating with a hot pressure roller at 80 ° C. to 150 ° C. for 0.5 seconds to 2 seconds. Moreover, in order to raise adhesive strength, it is preferable to cure for about 1 day or more and 3 days or less after that.

From the viewpoint of increasing the bonding strength of the laminate layer by diffusing the compound for crosslinking such as isocyanate described above during the curing period, the overcoat liquid is applied to the bonding surface in advance in this step. The laminated layer may be bonded.

2-4. Step of applying precoat liquid In this step, the precoat liquid is applied to the base material before the water-based ink is discharged.

In particular, when the substrate is a plastic substrate, it is preferable to adjust the wettability of the water-based ink to the substrate by applying a precoat liquid.

The precoat liquid preferably contains a resin and a pigment flocculant. The precoat solution may further contain a known substance such as a surfactant.

The resin preferably has a cross-linking group that can be cross-linked by reacting with the above-mentioned compound for cross-linking such as isocyanate. Examples of the crosslinking group include an amine group, a urethane bond, a urea bond, a polyol having an adjacent carbon molecule having a hydroxyl group, and a carboxyl group.

From the viewpoint of increasing the compatibility with the water-based ink and further improving the scratch resistance of the formed image, the resin is preferably a water-soluble or water-dispersible resin. Further, from the viewpoint of further improving the water resistance of the formed image, the resin is preferably a water-dispersible latex resin. Since the latex resin is highly compatible with the pigment flocculant, when the pigment flocculant is applied on the substrate, it is possible to more easily suppress image bleeding.

The latex resin may be any of anionic, cationic, and nonionic, but from the viewpoint of further improving the retention and dispersibility of the pigment dispersant, cationic and nonionic resins are preferred. In particular, when the pigment dispersant contains an acid or a polyvalent metal salt described later, a cationic or nonionic urethane resin, acrylic resin, olefin resin, and polyvinyl alcohol are preferable.

When the resin is a latex resin, the latex resin may be a hybrid resin. Examples of the hybrid resin include latex resins having a core-shell structure having a hydrophobic portion in the core portion and a hydrophilic portion in the shell portion. Since the latex resin having such a core-shell structure can be made hydrophobic after being crosslinked on the base material, it is possible to further improve the scratch resistance while improving the water resistance of the formed image.

The hydrophobic part and the hydrophilic part may have a known structure constituting the hybrid resin. The hydrophobic portion can be, for example, urethane, acrylic, styrene, polyester, polystyrene, polycarbonate, urea resin, polyol, and copolymer resins thereof. The hydrophilic portion can be, for example, urethane, acrylic, urea resin, polyol, and copolymer resin thereof.

The resin is preferably resin fine particles. The average particle diameter of the resin fine particles is preferably in the range of 10 nm to 10 μm. The average particle size can be measured by a commercially available particle size measuring instrument using a dynamic light scattering method, electrophoresis method, etc., but the measurement by the dynamic light scattering method is simple and the particle size region Can be measured accurately.

From the viewpoint of further improving the scratch resistance and water resistance of the image formed, the amount of the resin applied to the substrate (attachment amount) is the resin solid content of the resin with respect to the mass of the image formed. The amount is preferably 50% by mass or more.

The pigment flocculant may be a compound that can agglomerate the pigment described above. Examples of the pigment flocculant include acids, acidic polymers, polyvalent metal salts, and cationic polymers. For example, when the pigment is an anionic dispersed pigment, the pigment flocculant can be an acid or a cationic compound. Only one type of these pigment flocculants may be contained, or two or more types may be contained in combination. In particular, from the viewpoint of facilitating the diffusion into the water-based ink and facilitating the aggregation of the pigment, the viewpoint of increasing the safety, and the viewpoint of further increasing the compatibility with other components in the precoat liquid, the above pigment The flocculant is preferably an acid or a polyvalent metal salt.

Acid can agglomerate the anionic dispersed pigment by pH fluctuation. Examples of such acids include formic acid, acetic acid, propionic acid, isobutyric acid, oxalic acid, fumaric acid, malic acid, citric acid, malonic acid, succinic acid, maleic acid, benzoic acid, 2-pyrrolidone-5-carboxylic acid Examples include acid, lactic acid, acrylic acid and derivatives thereof, methacrylic acid and derivatives thereof, acrylamide and derivatives thereof, sulfonic acid derivatives, and phosphoric acid and derivatives thereof. The acid is preferably an organic acid. An organic acid is highly compatible with other components (such as a cross-linking agent) contained in the first treatment liquid, and is difficult to become a salt even when the first treatment liquid is dried on the substrate. It has excellent transparency and is difficult to discolor the formed image.

The cationic compound can aggregate the anionic dispersion pigment by salting out. Examples of the cationic compound include polyvalent metal salts, cationic surfactants, and cationic resins. Preferred examples of the polyvalent metal salt include water-soluble salts such as calcium salts, magnesium salts, aluminum salts, and zinc salts. As the cationic surfactant (also referred to as cationic surfactant), for example, aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, imidazolinium salts and the like are preferable. Can be mentioned. Examples of the cationic resin include polyallylamine, polyvinylamine, polyethyleneimine, and polydiallyldimethylammonium chloride.

Of these, polyvalent metal salts and acids are preferred because they have a low molecular weight, are easy to diffuse into water-based ink, and cause the pigment to aggregate more rapidly. Furthermore, an acid is more preferable because of higher safety and compatibility with a crosslinked resin.

A pigment flocculant may be used alone or in combination of two or more.

The range of the content (attachment amount) of the pigment flocculant applied to the substrate is not limited, and can be appropriately set according to the amount of water-based ink, the type of pigment, the type of pigment flocculant, and the like. For example, the mass of the pigment flocculant is preferably 3% by mass to 50% by mass with respect to the mass of the image to be formed.

In addition, when using an acid, it is preferable that the addition amount of an acid is the quantity which adjusts the pH of a process liquid to below the neutralization equivalent of the anion component contained in aqueous ink. Further, when the anionic component is an acrylic acid group, the first dissociation constant of the acid is preferably 3.5 or less from the viewpoint of making image bleeding more difficult.

2-5. Substrate The substrate is not particularly limited, and may be a paper substrate with high water absorption, or a substrate with low water absorption such as a gravure or coated paper for offset printing, or a film, plastic board (soft vinyl chloride, hard Non-water-absorbing substrates such as vinyl chloride, acrylic plates, polyolefins, etc.), glass, tiles and rubbers may be used. Of these, low-water-absorbing substrates and non-water-absorbing substrates, particularly preferably films, are difficult to remove unreacted cross-linking agent by washing. The effect of reducing the adherence of fingerprints is significantly achieved.

Examples of the above film include known plastic films. Specific examples of the plastic film include polyester films such as polyethylene terephthalate, polyethylene films including high-density polyethylene films and low-density polyethylene films, polypropylene films, polyamide films such as nylon, polystyrene films, ethylene / vinyl acetate copolymer Includes biodegradable films such as coalescence (EVA) film, polyvinyl chloride (PVC) film, polyvinyl alcohol (PVA) film, polyacrylic acid (PAA) film, polycarbonate film, polyacrylonitrile film, and polylactic acid film . In order to impart gas barrier properties, moisture proof properties, and fragrance retention properties, polyvinylidene chloride may be coated on one or both surfaces of the film, or a metal oxide may be deposited. Further, the film may be subjected to an antifogging process. The film may be subjected to corona discharge and ozone treatment.

The film may be an unstretched film or a stretched film.

The film may be a multi-layer base material in which a layer such as a PVA coat is provided on the surface of an absorbent base material such as paper to make the area to be recorded non-absorbable.

The thickness of the film is preferably less than 0.25 mm.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

1. Preparation of Dispersant 350 parts by weight of water, 2 parts by weight of azobisisobutyronitrile (AIBN), and 2 parts by weight of sodium dodecylbenzenesulfonate are placed in a container, stirred at 70 ° C., suspended and suspended. A turbid liquid was obtained. After preparing the liquid mixture of each component (a unit is a mass part) as described in the resin 1 of Table 1, the said liquid mixture of the said 100 mass part was dripped over 1.5 hours to 70 degreeC, then, 70 degreeC And left to stir.

The heating was stopped for 4 hours and filtered to obtain a solid polymer. The obtained polymer was cut into small pieces, water and dimethylaminoethanol (DMAE) having a neutralization equivalent of the polymer were added and sufficiently stirred, and the polymer was dissolved to obtain a polymer solution. Water was added to the polymer solution to obtain a resin 1 solution having a solid concentration of 25%.

A solution of Resin 1 to Resin 11 was obtained in the same manner except that the type and amount of each component contained in the mixed solution were changed as shown in Table 1. Each numerical value in Table 1 indicates mass% of each component. In addition, Table 2 shows the molar ratio of the monomers used for preparing each resin.

Table 3 shows the weight average molecular weight, acid value, hydroxyl value, and amine value of each resin calculated from the values shown in Table 2.

2. Preparation of water-based ink In 40.35 parts by mass of water, 21.6 parts by mass of a resin 1 solution, 20 parts by mass of ethylene glycol and 0.05 parts by mass of a surfactant (Nissin Chemical Industry Co., Ltd., Olphin E1010) , “Orphine” is a registered trademark of the company), 18 parts by weight of phthalocyanine pigment was added, and bead mill dispersion was performed with 120 parts by weight of zirconia beads for about 2 hours to obtain a dispersion.

A letdown in which beads were removed from the obtained dispersion and 79.95 parts by mass of water, 20 parts by mass of ethylene glycol, and 0.05% of a surfactant (Nissin Chemical Industry Co., Ltd., Olphine E1010) were mixed. The ink was diluted with the liquid until the concentration of the pigment became 3%, and ink 1 was obtained.

Ink 2 to Ink 11 were obtained in the same manner except that the resin 1 solution was changed to the resin 2 solution to the resin 11 solution, respectively.

In 56.55 parts by mass of water, 5.4 parts by mass of a nonionic activator-type dispersant (Lubrisol, Solsperse 27000), 20 parts by mass of ethylene glycol and 0.05 parts by mass of surfactant (day Shin Chemical Industry Co., Ltd., Olphine E1010) was added and mixed, and 18 parts by mass of phthalocyanine pigment was added, and bead mill dispersion was performed with 120 parts by mass of zirconia beads for about 2 hours to obtain a dispersion.

A letdown in which beads were removed from the obtained dispersion and 79.95 parts by mass of water, 20 parts by mass of ethylene glycol, and 0.05% of a surfactant (Nissin Chemical Industry Co., Ltd., Olphine E1010) were mixed. The ink was diluted with the liquid until the concentration of the pigment became 3%, and ink A was obtained.

In 56.55 parts by mass of water, 5.4 parts by mass of naphthalene formalin condensate (manufactured by Kao Corporation, Demol N, “Demol” is a registered trademark of the same company), 20 parts by mass of ethylene glycol and 0.05 parts by mass The surfactant (Nissin Chemical Industry Co., Ltd., Olphine E1010) was added and mixed, then 18 parts by mass of phthalocyanine pigment was added, and the mixture was dispersed with 120 parts by mass of zirconia beads for about 2 hours. Got.

A letdown in which beads were removed from the obtained dispersion and 79.95 parts by mass of water, 20 parts by mass of ethylene glycol, and 0.05% of a surfactant (Nissin Chemical Industry Co., Ltd., Olphine E1010) were mixed. The ink was diluted with the liquid until the concentration of the pigment became 3%, and ink B was obtained.

3. Preparation of Precoat Solution 53.8 parts by weight of resin (Daiichi Kogyo Kagaku Co., Ltd., Superflex 650, “Superflex” is a registered trademark of the company) was diluted with 45.5 parts by weight of water, and then 0.7% A part of calcium acetate (pigment flocculant) was dissolved to obtain a precoat solution.

4). Preparation of Overcoat Solution 54 parts by weight of polyol (Mitsui Chemicals, Takelac 525s, "Takelac" is a registered trademark of the company) and 6 parts by weight of isocyanate (Mitsui Chemicals, Takenate A50, "Takenate" And overcoating solution 1 was prepared by diluting with 40 parts by mass of ethyl acetate to facilitate bar coating.

54 parts by weight of polyol (Mitsui Chemicals, Takelac 525s, “Takelac” is a registered trademark of the company) and 1 part by weight of both-end isocyanate type polycarbodiimide (Nisshinbo Chemical Co., Ltd., Carbodilite V05, “Carbodilite” And overcoating solution 2 was prepared by diluting with 40 parts by mass of ethyl acetate to facilitate bar coating.

5). Image formation Polyethylene film Taiho FE # 50-FE2001 (Futamura Chemical Co., Ltd.) was used as the substrate. On the corona-treated surface of the substrate, the precoat liquid is applied with a # 3 wire bar and dried, and then the ink is used with an independent drive head of a Konica Minolta piezo-type inkjet head (360 dpi, discharge amount 14 pL). A droplet of ink 1 was ejected so that a solid image of 720 dpi × 720 dpi with an applied amount of 11.2 cc / m ² was formed. At this time, in order to evaluate the ejection properties, there are two types of ink discharge: immediately after maintenance of the inkjet head, and after discharging the ink after leaving the nozzle open (10 minutes). Images were formed by this method. After ejection, the ink landed on each substrate on a hot plate at 120 ° C. was dried for about 3 minutes to obtain an image.

Thereafter, the overcoat solution 1 was applied to the surface on which the image of the substrate was formed with a # 3 wire bar, and the overcoat solution 1 was dried for 1 minute with a dryer (manufactured by Hitachi, Ltd., TURBO1200). Further, a laminate layer (manufactured by Unitika Co., Ltd., nylon film ON) was laminated thereon, and roller heating was performed at 90 ° C. with a table laminator (manufactured by Meiko Shokai Co., Ltd., THS-330) to obtain image 1. .

Image 2 to image 11, image A and image B were obtained in the same manner except that ink 1 was changed to ink 2 to ink 11, ink A and ink B.

Image C was obtained in the same manner except that ink 3 was used and overcoat liquid 1 was changed to overcoat liquid 2.

6). Evaluation 6-1. Ejectivity After the maintenance, the nozzles were left open (10 minutes) and then the ink was ejected to visually check the image obtained, and the ejection properties of each ink were evaluated according to the following criteria.
○ A beautiful solid image is formed. △ The line at the beginning of writing a solid image is jagged. × The beginning of writing a solid image is thinner than 1 mm.

6-2. Water resistance Images 1 to 11 were stored at 45 ° C. for 3 days, and then cut into strips of 10 cm × 1 cm so that the solid portion was the cut end surface to obtain test pieces. The test piece was boiled in a pressure cooker for 30 minutes, the cut end face of the test piece after boiling was visually confirmed, and the water resistance of the image by each ink was evaluated according to the following criteria.
○ There is no peeling on the cut end face. △ When the cut end face is lightly flicked with a finger, it may be partially peeled. × Peeling occurs on the cut end face.

Table 4 shows the evaluation results of image 1 to image 11, image A, image B, and image C.

As a dispersant, a structural unit having an acidic functional group in a side chain, a structural unit having any one of a primary amine, a secondary amine, a tertiary amine and a hydroxyl group in a side chain, and a hydrophobic structural unit are included. An aqueous ink containing an acrylic copolymer having an acid value of 60 mg / KOH or more and 200 mg / KOH or less and a total of hydroxyl value and amine value of 5 mg / KOH or more and 30 mg / KOH or less is used. In the formed images 3, 5, 6, 8 and 9, nozzle clogging hardly occurred, and the formed images had high scratch resistance and water resistance.

In addition, images 3, 5, 6, 8 and 9 formed using a water-based ink containing the acrylic copolymer having no polyalkylene glycol chain as a dispersant are less likely to cause nozzle clogging. In addition, the formed image had higher scratch resistance and water resistance.

Further, the image 5 formed using the aqueous ink containing the above acrylic copolymer having a structural unit having a primary amine in the side chain as a dispersant has a structural unit having a tertiary amine in the side chain. The image formed was higher in scratch resistance and water resistance than the image 6 formed using the water-based ink containing the acrylic copolymer.

On the other hand, images 1 and 2 formed using a water-based ink containing an acrylic copolymer having an acid value higher than 200 mg / KOH as a dispersant have higher scratch resistance and water resistance. It was low.

In addition, the image 4 formed using a water-based ink containing an acrylic copolymer having an acid value lower than 60 mg / KOH as a dispersant had many nozzle clogging.

In addition, the image 7 formed using a water-based ink containing an acrylic copolymer having a total acid group value and amine value higher than 30 mg / KOH as a dispersant is the scratch resistance and water resistance of the formed image. Was lower.

In addition, the image 10 formed using a water-based ink containing an acrylic copolymer having a total acid group value and amine value lower than 5 mg / KOH as a dispersant had many nozzle clogging.

In addition, images A and B formed using a water-based ink containing a copolymer other than acrylic as a dispersant are often clogged with nozzles, and are provided with an overcoat solution containing isocyanate and laminated. The image formed through the bonding of the layers had lower scratch and water resistance.

Further, even when the water-based ink containing the acrylic copolymer was used, the image C formed using the overcoat liquid containing no laminate adhesive had lower scratch resistance and water resistance.

This application claims priority based on Japanese Patent Application No. 2017-109130 filed on June 1, 2017, and the contents described in the claims and specification of the application are incorporated herein by reference. Incorporated.

According to the water-based ink of the present invention, it is possible to improve the scratch resistance and water resistance of an image formed while suppressing nozzle clogging. For this reason, the present invention is expected to expand the range of application of water-based ink by the ink jet method and contribute to the advancement and spread of technology in the same field.

Claims (6)

Pigments,
A structural unit having an acidic functional group in the side chain, a structural unit having any one of primary amine, secondary amine, tertiary amine and hydroxyl group in the side chain, and a hydrophobic structural unit, and An acrylic copolymer having an amount of polyalkylene glycol chain of 5% by mass or less based on the total mass of the dispersant, having an acid value of 60 mg / KOH or more and 200 mg / KOH or less, and a hydroxyl value and an amine value A total of 5 mg / KOH or more and 30 mg / KOH or less,
Water-based ink containing The water-based ink according to claim 1, wherein the dispersant has a structural unit having a primary amine in a side chain. Discharging the water-based ink droplet according to claim 1 or 2 from a nozzle of an inkjet head to land on a substrate;
A step of applying an overcoat liquid to the substrate on which the water-based ink droplets have landed;
A step of bonding the base material provided with the overcoat liquid and the laminate layer;
An image forming method comprising: The image forming method according to claim 3, wherein the overcoat liquid is a laminate adhesive. The image forming method according to claim 3 or 4, wherein the overcoat liquid contains an isocyanate compound. Before discharging the water-based ink droplets,
The image forming method according to any one of claims 3 to 5, comprising a step of applying a precoat liquid containing a pigment flocculant to the substrate.