JP2012001611A - Inkjet water-based ink and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet water-based ink and an inkjet recording method which can prevent liquid gathering (white streaks and beading) while maintaining the ejection stability in a non-absorbing medium, and can provide a high-quality image improved in abrasion.SOLUTION: The inkjet water-based ink comprises water, a pigment, an organic solvent and a water-soluble resin, wherein the ink contains at least two kinds of the water-soluble resin; the difference between the maximum and the minimum of weight-average molecular weights (Mw) of the water-soluble resins is in the range of 1,000 to 25,000; and the acid values of the water-soluble resins are 50 to 250 mg-KOH/g, and the difference between the maximum and the minimum of the acid values is within 200 mg-KOH/g.

Description

  The present invention is a novel inkjet water-based ink for obtaining a high-quality image in which non-absorptive media maintains liquid ejection stability (white streaks and beading) while maintaining ejection stability and improves scratch resistance. It relates to ink.

  In recent years, the inkjet recording method can be easily and inexpensively produced images, and thus has been applied to various printing fields such as photographs, various types of printing, marking, and special printing such as color filters.

  Ink jet inks used in such an ink jet recording system include water-based inks composed of water and a small amount of organic solvent, non-aqueous inks substantially free of water using organic solvents, and solid inks heated at room temperature. There are a plurality of inks such as a hot melt ink for printing and an actinic ray curable ink that is cured by actinic rays such as light after printing, and these are properly used depending on applications.

  On the other hand, non-water-absorbing recording media such as polyvinyl chloride sheets are used in a wide range of applications such as outdoor postings that require long-term weather resistance and printed matter that requires adhesion to curved objects. Yes.

  There are a plurality of methods for printing on a non-water-absorbing recording medium. However, there is an ink jet recording method as a method suitable for the production of a small variety of products because there is no need to prepare a plate and the time to finish is short.

  An ink-jet ink technique is disclosed in which white streaks are not generated by a combination of an alcohol solvent and a dispersant even when printing on a recording medium with poor ink absorption capability at a low resolution (see, for example, Patent Document 1).

  However, when the resolution is increased only by the technique of the above-mentioned Patent Document 1, there is a problem that the ink aggregates before the coloring material is fixed and buried.

  On the other hand, it is disclosed that a technique applied to plain paper controls ink viscosity at the time of drying by controlling the ink evaporation rate by a combination of water and an organic solvent in the beading prevention means (for example, Patent Document 2). reference).

  However, the non-absorbing recording medium has a problem that drying is slow and an image is not fixed.

  As described above, it is difficult to obtain a high-definition image using only the ink-jet ink described in the above-mentioned patent document, and particularly when using a non-water-absorbing recording medium, it is difficult to achieve both faster printing speed and image quality. This is the current situation.

JP 2010-007054 A JP 2009-0119198 A

  The object of the present invention is to obtain a high-quality print image quality that does not cause white streaks on non-water-absorbing recording media in addition to water-absorbing media typified by paper, and even when used for a long time in a printer. It is an object of the present invention to provide a water-based inkjet ink that is less likely to be clogged due to printer breakage or ink alteration, and to have less degradation in print image quality.

  The above object of the present invention has been achieved by the following constitution.

1. In an aqueous inkjet ink containing water, a pigment, a water-soluble organic solvent, and a water-soluble resin,
2 or more types of water-soluble resins, and among the two or more types of water-soluble resins, the maximum and minimum difference in weight average molecular weight (Mw) is in the range of 1000 to 25000, and An aqueous ink for inkjet, having an acid value of 50 mgKOH / g to 250 mgKOH / g, and a difference between the maximum and minimum acid values being within 200 mgKOH / g.

  2. 2. The water-based ink for ink-jet recording according to 1, wherein the water-soluble resin is a copolymer obtained by polymerizing a methacrylate component, an acrylate ester, and an unsaturated vinyl having a carboxy group as a monomer component.

  3. 3. An ink jet recording method comprising forming an image by ejecting the water-based ink for ink jet according to 1 or 2 above.

  4). 4. The inkjet according to 3 above, wherein the image formation is performed using a non-water-absorbing recording medium, and the recording surface temperature of the non-water-absorbing medium is adjusted to a range of 40 ° C. to 90 ° C. Recording method.

  According to the present invention, it is possible to provide an aqueous ink for ink jet and an ink jet recording method which are excellent in all of the characteristics of rubbing, gloss, liquid closeness and dischargeability.

  The ink-jet water-based ink of the present invention can provide an ink-jet water-based ink excellent in all of the characteristics of rubbing property, gloss, liquid side, and dischargeability. In addition, an ink jet recording method for forming an image by discharging the water-based ink for ink jet could be provided.

  Hereinafter, the components of the inkjet aqueous ink of the present invention will be described in detail.

<Pigment>
The pigment according to the present invention will be described.

  As the pigment according to the present invention, conventionally known pigments can be used without particular limitation, and any of water-dispersible pigments, solvent-dispersible pigments and the like can be used. For example, organic pigments such as insoluble pigments and lake pigments, and carbon An inorganic pigment such as black can be preferably used.

  This pigment is allowed to exist in a dispersed state in the ink, and this dispersion method may be any of self-dispersion, dispersion using a surfactant, polymer dispersion, and microcapsule dispersion. Particularly preferred from the viewpoint of long-term storage stability.

  The insoluble pigment is not particularly limited, for example, azo, azomethine, methine, diphenylmethane, triphenylmethane, quinacridone, anthraquinone, perylene, indigo, quinophthalone, isoindolinone, isoindoline, azine, oxazine, thiazine, Dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole and the like are preferable.

  Specific pigments that can be preferably used include the following pigments.

  Examples of the magenta or red pigment include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. Pigment red 202, C.I. I. Pigment red 222, C.I. I. Pigment violet 19 and the like.

  Examples of the pigment for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 15: 3, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 94, C.I. I. And CI Pigment Yellow 138.

  Examples of the pigment for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  Examples of black pigments include C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. Pigment black 7 and the like.

  The average particle size in the dispersed state of the pigment contained in the aqueous inkjet ink of the present invention is preferably 50 nm or more and less than 300 nm from the viewpoint of improving the stability of the pigment dispersion and the storage stability of the ink.

  The particle size of the pigment dispersion can be determined by a commercially available particle size measuring instrument using a dynamic light scattering method, an electrophoresis method, or the like. Accurate and often used.

  The pigment according to the present invention is preferably used after being dispersed by a disperser together with a dispersant and other necessary additives according to other desired purposes.

  As the disperser, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, or the like can be used.

  Among these, the particle size distribution of the ink produced by the dispersion by the sand mill is sharp and preferable. The material of the beads used for sand mill dispersion is preferably zirconia or zircon from the viewpoint of contamination of bead fragments and ionic components. Furthermore, the bead diameter is preferably 0.3 mm to 3 mm.

  In the preparation of the water-based ink for inkjet of the present invention, a polymer dispersant can be used in the preparation of the pigment dispersion.

  The polymer dispersant used in the present invention preferably has a polymer component having a molecular weight of 5000 or more and 200000 or less.

  The polymer dispersant is selected from styrene, styrene derivatives, vinyl naphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid and fumaric acid derivatives. Examples thereof include a block copolymer comprising at least one kind of monomer, a random copolymer and salts thereof, polyoxyalkylene, and polyoxyalkylene alkyl ether.

  In the case of an acidic polymer dispersant, it is preferably added after neutralization with a neutralizing base. Here, the neutralizing base is not particularly limited, but is preferably an organic base such as ammonia, monoethanolamine, diethanolamine, triethanolamine, or morpholine.

  Moreover, in this invention, it is preferable that it is 10 mass%-100 mass% with respect to a pigment as addition amount of a polymer dispersing agent.

  The pigment dispersion used in the present invention is particularly preferably a so-called capsule pigment in which the pigment is coated with a resin. Various known methods can be used as a method for coating the pigment with the resin. Preferably, in addition to the phase-emulsification method and the acid precipitation method, the pigment is dispersed using a polymerizable surfactant. It is preferable to select from a method in which a monomer is fed to the substrate and coating is performed while polymerization.

  As a more preferred method, the water-insoluble resin is dissolved in an organic solvent such as methyl ethyl ketone, and after partially or completely neutralizing the acidic group in the resin with a base, the pigment and ion-exchanged water are added and dispersed. After that, a production method in which the organic solvent is removed and water is added as necessary is preferable.

  The mass ratio of pigment to resin can be selected in the range of 100: 40 to 100: 150 in pigment: resin ratio. In particular, the range of 100: 60 to 100: 110 has good image durability, injection stability, and ink storage stability.

《Water-soluble organic solvent》
The water-soluble organic solvent according to the present invention will be described.

  The water-soluble organic solvent according to the present invention includes diethylene glycol monobutyl ether and diethylene glycol diethyl ether from the viewpoint of imparting good wettability to a hydrophobic medium such as a polyvinyl chloride recording medium to the water-based ink for ink-jet recording of the present invention. It is preferable to contain a water-soluble organic solvent selected from triethylene glycol monobutyl ether, 1,2-alkanediol or 1,3-propanediol.

  Here, the “water-soluble” of the water-soluble organic solvent according to the present invention represents that the solubility in water at 20 ° C. (the amount of the solvent with respect to 100 g of water) is 3 g or more, preferably 10 g or more. It is preferable to show solubility.

  By using a water-soluble organic solvent, an image showing good image quality without ink repelling can be obtained in image formation.

  In addition, it was found that the discharge stability under the low humidity environment, which is the object of the present invention, is also effective.

  Regarding this effect, since these water-soluble organic solvents are relatively hydrophobic, they have a high affinity with the hydrophobic portion of the surfactant having a cloud point, and as a result, the orientation speed to the ink surface is fast and the head nozzle opening It is assumed that the ink drying can be prevented more effectively.

  Examples of the 1,2-alkanediol include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, and the like. It is particularly preferable in terms of ejection stability.

  Further, the total addition amount of the water-soluble organic solvent selected from diethylene glycol monobutyl ether, diethylene glycol diethyl ether, triethylene glycol monobutyl ether, 1,2-alkanediol or 1,3-propanediol is good wetting to the recording medium. From the viewpoint of obtaining a stable ink discharge property even in a low humidity environment, the range of 7% by mass to 30% by mass is preferable, and the range of 10% by mass to 20% by mass is more preferable.

  In addition to glycol ether or 1,2-alkanediol, a solvent can be added to the aqueous inkjet ink of the present invention.

  Specifically, other examples of the water-soluble organic solvent according to the present invention include alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol), polyhydric alcohols (For example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol), amines (for example, ethanol Amine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N- Tilmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide) Etc.), heterocycles (eg 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone), sulfoxides (eg dimethyl sulfoxide) Etc.

《Water-soluble resin》
The water-soluble resin according to the present invention will be described.

  In the inkjet recording method using the aqueous inkjet ink of the present invention, from the viewpoint of obtaining the abrasion resistance of the ink film, the content of the water-soluble resin contained in the inkjet aqueous ink as a free polymer is 0.5 mass. % To 10.0% by mass, and 1.0% to 5.0% by mass from the viewpoints of improving the scratch resistance of the ink film and improving the ejection stability of the ink. Is preferred.

  Here, “free polymer” refers to a water-soluble resin (also referred to as a water-soluble polymer) that is not adsorbed to a dispersion such as pigment in the ink, and the dispersion such as an ink using a water-soluble dye is contained in the ink. When not included, the total amount of water-soluble polymer added to the ink is present as free polymer.

  The free polymer content can be measured by GPC using a supernatant obtained by centrifuging the ink at 30000 rpm for 2 hours.

  It is presumed that the presence of the water-soluble resin in a free polymer state results in a high contact probability between the molecular chains spread in the drying stage and an excellent film forming ability, resulting in a high ink film rub resistance.

  A preferred embodiment of the water-soluble resin according to the present invention is a water-soluble copolymer having a hydrophobic monomer as a polymerization component from the viewpoint of obtaining image abrasion resistance even in a high-humidity environment or when moisture adheres.

  A water-soluble copolymer having a hydrophobic monomer as a polymerization component (hereinafter abbreviated as “water-soluble copolymer”) is stably dissolved in ink, but is given water resistance after drying on a recording medium. A resin is more preferable.

  As such a resin, a resin having a hydrophobic component and a hydrophilic component is designed and used. In this case, as the hydrophilic component, either an ionic or nonionic component may be used, but an ionic component is more preferable, and an anionic component is more preferable.

  In particular, those which are rendered water-soluble by neutralizing anionic substances with a volatile base component are preferred.

(Acid value)
The acid value of the water-soluble resin according to the present invention will be described.

  The ink-jet aqueous ink of the present invention is excellent in all of the characteristics of scratching, gloss, liquid side and dischargeability as compared with conventionally known inks. The acid value of the water-soluble resin is in the range of 50 mg KOH to 250 mg KOH, and the water-based ink for ink-jet recording of the present invention contains at least two types of water-soluble resins. Is required to be within 200 mgKOH / g.

  Here, the acid value of the water-soluble resin according to the present invention is measured as follows.

(Measurement method of acid value)
10 g of resin was weighed into a 300 ml Erlenmeyer flask, and about 50 ml of a mixed solvent of ethanol: benzene = 1: 2 was added to dissolve the resin. Next, using a phenolphthalein indicator, titration was performed with a 0.1 mol / L potassium hydroxide ethanol solution that had been standardized in advance, and the acid value was calculated from the amount of the potassium hydroxide ethanol solution used for titration by the following formula (1). (Mg KOH / g) was determined.

  For resins that do not dissolve in about 50 ml of a mixed solvent of ethanol: benzene = 1: 2, select either 50 ml of ethanol or about 50 ml of a mixed solvent of ethanol / pure water = 1: 1. The others were titrated by the same operation.

Formula (1)
A = (B × f × 5.611) / S
In the formula, A is the acid value of the resin (mgKOH / g), B is the amount of 0.1 mol / L potassium hydroxide ethanol solution used for titration (ml), and f is the 0.1 mol / liter potassium hydroxide ethanol solution. Factor, S is the mass of the resin (g), 5.611 is the formula weight of potassium hydroxide (56.11 / 10).

(Water-soluble resin water-soluble)
The water solubility of the water-soluble resin according to the present invention means that the solubility in water (specifically, ion-exchanged water) at 20 ° C. (the amount of solute with respect to 100 g of ion-exchanged water) is 3 g or more. Furthermore, it is preferable to exhibit a solubility of 10 g or more.

(Constituent component of water-soluble resin (also referred to as constituent component of polymer)
At least one of the water-soluble resins according to the present invention is preferably a copolymer obtained by polymerizing unsaturated vinyl having a carboxy group as at least a monomer component.

  Hydrophobic monomers of the copolymer include acrylic acid esters (n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, etc.), methacrylic acid esters (ethyl methacrylate, butyl methacrylate, glycidyl methacrylate). Etc.), styrene, etc. are raised.

  Examples of the hydrophilic monomer include acrylic acid, methacrylic acid, acrylamide and the like, and those having an acidic group such as acrylic acid are preferably partially or completely neutralized with a base component after polymerization.

  As the neutralizing base in this case, an alkali metal-containing base such as Na, K hydroxide, or an amine (ammonia, alkanolamine, alkylamine, etc. can be used) can be used. In particular, neutralization with amines having a boiling point of less than 200 ° C. is particularly preferable from the viewpoint of improving image fastness.

(Weight average molecular weight of water-soluble resin)
The ink-jet aqueous ink of the present invention contains at least two types of water-soluble resins, but in order to obtain the effects described in the present invention (improving scratch resistance, gloss, liquid side, and ejection properties), the water-soluble resin is used. The difference between the maximum and minimum weight average molecular weight (Mw) must be in the range of 1000-25000.

  The present invention relates to the fact that the difference between the maximum and minimum weight average molecular weights (Mw) of at least two water-soluble resins contained in the water-based ink for inkjet of the present invention needs to be adjusted to a range of 1000 to 25000. Estimates are as follows.

  If the difference between the maximum and minimum Mw of the weight average molecular weight of the water-soluble resin is in the range of 1000 to 25000, the volume when the resin spreads or shrinks depending on the surrounding solvent is similar, and the resin is uniform in the ink. I think it can exist.

  If it is less than 1000, the effect of entanglement between the resins will not be exhibited, and the increase in viscosity will be suppressed. If it is greater than 25000, unevenness of locally large molecules and small molecules will occur, resulting in unstable viscosity. Ink ejection tends to be unstable, and as a result, the adhesion of an ink film formed with ink is also likely to be lowered.

  Moreover, if the difference in acid value is within 200 mgKOH / g, the amount of resin dissolved will be approximately the same, and even a plurality of resins will be dissolved stably.

  When the difference exceeds 200 mgKOH / g, it is considered that a part of the resin is likely to be precipitated and the injection stability cannot be maintained.

  Moreover, as a weight average molecular weight of the water-soluble resin which concerns on this invention, the thing of the range of 3000-100000 is preferable, More preferably, it is the range of 7000-20000.

  The weight average molecular weight of the water-soluble resin according to the present invention can be measured by GPC (Gel Permeation Chromatography).

  The GPC measurement conditions are shown below.

(GPC measurement conditions)
The weight average molecular weight measurement method by GPC (Gel Permeation Chromatography) is diluted with THF so that the sample solid content concentration becomes 0.8 mass%, and the measurement is performed at a column temperature of 25 ° C. under the following conditions.

Column: Tosoh TSKgel G40000 + 2500 + 2000HXL, 40 ° C.
Eluent: THF 1.0 (ml / min)
Injection volume: 100 μl
Detection: RI
Calibration curve: Standard polystyrene (created using 13 types of standard polystyrene)
(Viscosity of water-based ink for inkjet)
The viscosity of the aqueous inkjet ink according to the present invention is preferably 4 mPa · s to 40 mPa · s at 25 ° C., more preferably 5 mPa · s to 40 mPa · s, and still more preferably 8 mPa · s to 20 mPa · s. s.

  The reason why the viscosity of the water-based ink for inkjet of the present invention is preferably adjusted to the above range is estimated by the present inventors as follows.

  The ink-jet aqueous ink of the present invention contains at least two water-soluble resins as described above.

  Here, if the initial viscosity of the water-based ink for ink jet is high, the flow of the ink that has landed on the medium is suppressed, and as a result, it is considered that liquid deviation can be prevented.

  In order to increase the initial viscosity of the ink, it is only necessary to increase the solid content concentration. However, this alone increases the drying speed of the ink on the nozzle surface at the time of ejection, and tends to cause a decap phenomenon that clogs the nozzle.

  For this reason, there is a problem in that the solid content concentration cannot be easily increased because the injection stability is poor and an image is lost.

  Accordingly, the present inventors have found a means for efficiently increasing the viscosity without increasing the solid content concentration by using “similar resin” together.

  The similar resin here is considered to be similar in the dissolved state in the ink, and the above weight average molecular weight (Mw) and acid value are considered to be the indicators.

  By using similar resins together, the distribution state (concentration / spreading) of the resin in the ink is made uniform, the viscosity increases more than the effect of the solid content concentration due to the interaction between molecules, and the resin is made uniform during injection. Since the ink droplets are stable and the solid concentration does not increase, decap is suppressed, and the ink after landing does not agglomerate with each other on the media. It is presumed that an image with high scratching properties can be obtained.

(Measurement of viscosity)
The viscosity was measured using a rotational viscometer and a thermostatic bath (manufactured by Toki Sangyo Co., Ltd .: VISCOMETER TV-33, VISCOMATE VM-150III). It was set to 25 ° C. in a thermostatic bath, and the viscosity was measured 1 minute after the start of measurement.

(Tg (glass transition point) of water-soluble resin)
The Tg of the water-soluble polymer according to the present invention can be about -30 ° C to 120 ° C, and a more preferable range of Tg is -10 ° C to 80 ° C.

<Surface tension of water-based ink for inkjet>
The surface tension of the water-based ink for ink jet recording of the present invention is preferably 30 mN / m or less, more preferably 28 mN / m or less, from the viewpoint of improving the wettability to the recording medium.

  In order to adjust to this surface tension, various surfactants can be preferably used alone or in combination.

(Surfactant)
Preferable surfactants that can be used in the ink-jet aqueous ink of the present invention include, for example, silicon surfactants, acetylene glycol surfactants, and fluorine surfactants having a perfluoroalkenyl group. By using these surfactants, sufficient wetting can be imparted to a medium having a low surface energy such as a recording medium made of polyvinyl chloride.

  Silicon-based surfactants are those in which the side chain or terminal of dimethylpolysiloxy acid is polyether-modified, such as KF-351A and KF-642 manufactured by Shin-Etsu Chemical Co., and BYK347 and BYK348 manufactured by Big Chemie are commercially available. ing.

  The acetylene glycol surfactant preferably has a triple bond in the molecule, has a hydroxyl group and an alkyl group on the adjacent carbon atom, and has a symmetrical structure with respect to the triple bond. The acetylene glycol compound and acetylene alcohol compound used in the present invention can be obtained as commercial products, and examples thereof include Surfinol and Olphine manufactured by Nissin Chemical Industry Co., Ltd., and acetylenol manufactured by Kawaken Fine Chemical Co., Ltd.

  A fluorosurfactant having a perfluoroalkenyl group is synthesized by introducing a hydrophilic group into a dimer, trimer or pentamer obtained by anionic polymerization of 4-fluoroethylene or hexafluoropropylene. Any of a nonionic type having a polyoxyethylene ether in a hydrophilic group, an anionic type having a sulfonic acid or a carboxylic acid, and a betaine type having a quaternary ammonium salt and a carboxylic acid can be preferably used. It is marketed as the Footage series.

  In the ink of the present invention, a surfactant other than a silicon-based surfactant or a fluorosurfactant having a perfluoroalkenyl group may be used. Specifically, nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene polyoxypropylene condensates, sorbitan derivatives, anionic surfactants such as alkylsulfosuccinic acid and phosphate esters, alkylpolyaminoethylglycine salts, amides Examples include amphoteric surfactants such as betaines.

  In the water-based ink for ink jet recording of the present invention, in addition to the above description, depending on the purpose of improving the emission stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performances as necessary. Various known additives such as polysaccharides, viscosity modifiers, specific resistance regulators, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, antifungal agents, rust inhibitors, etc. are appropriately selected. For example, liquid droplets such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, and silicone oil, described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476. UV absorbers, JP-A 57-74192, 57-87989, 60-72785, 61-146591, JP 1-95091 and 3-13376, etc., Japanese Patent Application Laid-Open Nos. 59-42993, 59-52689, 62-280069, 61-242871 Examples of fluorescent whitening agents and antifungal agents described in Japanese Patent Laid-Open No. 4-219266 and the like include Proxel GXL (manufactured by Arch Chemicals).

<Inkjet recording method>
The ink jet recording method of the present invention will be described.

  In the ink jet recording method of the present invention, when an image is formed by ejecting ink, the ink jet head to be used may be an on-demand system or a continuous system. In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, thermal ink jet) Any ejection method such as a mold, a bubble jet (registered trademark) mold, or the like may be used.

  In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, a thermal type) Any ejection method such as an ink jet type or a bubble jet (registered trademark) type may be used.

  In the ink jet recording method of the present invention, it is preferable to print by heating a recording medium (recording medium) when ink is ejected.

  By heating the recording medium (recording medium), the drying and thickening speed of the ink is remarkably improved, and high image quality can be obtained. Also, the durability of the image is improved.

  The heating temperature is recorded from the viewpoint of obtaining sufficient image quality and sufficient image durability, from the viewpoint of enabling drying after ink ejection in a short time, and from the viewpoint of stable printing. The recording surface temperature of the medium (recording medium) is preferably adjusted to a range of 40 ° C. to 90 ° C., more preferably 40 ° C. to 60 ° C.

  As a heating method, it is possible to select a heating method in which a heating heater is incorporated in the media conveyance system or the platen member and heated from the lower side of the recording medium, or a non-contact heating method from the lower side or the upper side by a lamp or the like.

<Non-water-absorbing recording medium>
The non-water-absorbing recording medium according to the present invention will be described.

  The aqueous inkjet ink of the present invention is suitable for printing on non-absorbent media such as polyvinyl chloride sheets as well as water-absorbing recording media such as plain paper, coated paper, and inkjet paper.

  Examples of the non-water-absorbing recording medium include polymer sheets, boards (soft vinyl chloride, hard vinyl chloride, acrylic plates, polyolefins, etc.), glass, tile, rubber, synthetic paper, and the like.

  Specific examples of the recording medium made of polyvinyl chloride include SOL-371G, SOL-373M, SOL-4701 (manufactured by Big Technos Co., Ltd.), glossy vinyl chloride (manufactured by Systemgraph Co., Ltd.), KSM-VS, KSM. -VST, KSM-VT (above, manufactured by Kimoto Co., Ltd.), J-CAL-HGX, J-CAL-YHG, J-CAL-WWWG (above, manufactured by Kyo Show Osaka Co., Ltd.), BUS MARK V400 F vinyl, LITEcal V-600F vinyl (above, manufactured by Flexcon), FR2 (manufactured by Hanwha), LLBAU13713, LLSP20133 (above, manufactured by Sakurai Co., Ltd.), P-370B, P-400M (above, manufactured by Kambo Plus Co., Ltd.), S02P, S12P, S13P, S14P, S22P, S24P, 34P, S27P (manufactured by Grafityp), P-223RW, P-224RW, P-249ZW, P-284ZC (manufactured by Lintec Corporation), LKG-19, LPA-70, LPE-248, LPM-45 LTG-11, LTG-21 (manufactured by Shinsei Co., Ltd.), MPI 3023 (manufactured by Toyo Corporation), Napoleon Gloss PVC (manufactured by Futaki Electronics Co., Ltd.), JV-610, Y-114 ( As described above, manufactured by ICC Corporation), NIJ-CAPVC, NIJ-SPVCGT (hereinafter, manufactured by Nichie Corporation), 3101 / H12 / P4, 3104 / H12 / P4, 3104 / H12 / P4S, 9800 / H12 / P4, 3100 / H12 / R2, 3101 / H12 / R2, 3104 / H12 / R 2, 1445 / H14 / P3, 1438 / One Way Vision (manufactured by Inetrcoat), JT5129PM, JT5728P, JT5822P, JT5829P, JT5829R, JT5829PM, JT5829RM, JT5929PM (above, manufactured by Mactac, MP1100, MP1100 MPI2001, MPI2002, MPI3000, MPI3021, MPI3500, MPI3501 (above, manufactured by Avery), AM-101G, AM-501G (above, manufactured by Ginichi Co., Ltd.), FR2 (manufactured by Hanwha Japan Co., Ltd.), AY-15P, AY-60P, AY-80P, DBSP137GGH, DBSP137GGL (above, manufactured by Insight Inc.), SJT-V200F, SJ T-V400F-1 (above, manufactured by Hiraoka Oryome Co., Ltd.), SPS-98, SPSM-98, SPSH-98, SVGL-137, SVGS-137, MD3-200, MD3-301M, MD5-100, MD5- 101M, MD5-105 (manufactured by Metamark), 640M, 641G, 641M, 3105M, 3105SG, 3162G, 3164G, 3164M, 3164XG, 3164XM, 3165G, 3165SG, 3165M, 3169M, 3451SG, 3551G, 3551M, 3631, 3641M , 3651G, 3651M, 3651SG, 3951G, 3641M (above, manufactured by Orafol), SVTL-HQ130 (manufactured by Lamy Corporation), SP300 GWF, SPCLEARAD vinyl l (above, manufactured by Catalina), RM-SJR (produced by Ryoyo Shoji Co., Ltd.), Hi Lucky, New Lucky PVC (above, produced by LG), SIY-110, SIY-310, SIY-320 (above, Sekisui Chemical) Industrial Co., Ltd.), PRINT MI Frontlit, PRINT XL Lightweight banner (above, manufactured by Endutex), RIJET 100, RIJET 145, RIJET165 (above, manufactured by Ritrama), NM-SG, NM-SM Co., Ltd. Manufactured), LTO3GS (manufactured by Lucio Co., Ltd.), easy print 80, performance print 80 (manufactured by Jetgraph Co., Ltd.), DSE 550, DSB 550, DSE 800G, DSE 802/137, V250WG, 300WG, V350WG (manufactured by Hexis Ltd.), Digital White 6005PE, 6010PE (or, Multifix Co., Ltd.).

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these.

  In addition, although the display of "part" or "%" is used in an Example, unless there is particular notice, it represents "mass part" or "mass%".

Example 1
As shown below, preparation of the pigment dispersion and synthesis of the water-soluble resins R-1 to R-8 were performed, and then water-based inks 1 to 9 for inkjet were prepared.

<< Preparation of pigment dispersion >>
As a pigment dispersant, 3 parts by mass of a styrene-acrylic acid copolymer (John Cryl 678, molecular weight 8500, acid value 215), 1.3 parts of dimethylaminoethanol, and 80.7 parts of ion-exchanged water were stirred and mixed at 70 ° C. A solution was prepared.

  Then, C.I. I. 15 parts of Pigment Blue 15: 3 was added and premixed, then dispersed using a sand grinder filled with 50% by volume of 0.5 mm zirconia beads, and a pigment dispersion having a cyan pigment content of 15% by mass Was prepared.

  The average particle diameter of the pigment particles contained in this pigment dispersion was 122 nm. The particle size was measured using a Zetasizer 1000HS manufactured by Malvern.

<Synthesis of water-soluble resin>
(Synthesis of water-soluble resin R-1)
50 g of methyl ethyl ketone was added to a flask equipped with a dropping funnel, a nitrogen introducer, a reflux condenser, a thermometer and a stirrer, and heated to 75 ° C. while bubbling nitrogen.

  Thereto, the monomers listed in Table 1 (9 parts by weight of methacrylic acid, 78 parts by weight of methyl methacrylate, 6.5 parts by weight of n-butyl acrylate and 6.5 parts by weight of 2-ethylhexyl acrylate), 50 g of methyl ethyl ketone, start A mixture of 500 mg of agent (AIBN (2,2′-azobisisobutyronitrile)) was added dropwise from a dropping funnel over 3 hours. It heated and refluxed for 6 hours after dripping. After allowing to cool, the mixture was heated under reduced pressure to distill off methyl ethyl ketone.

  The polymer residue was dissolved in a solution in which dimethylaminoethanol corresponding to 1.05 mol of acrylic acid added as a monomer was dissolved in 450 ml of ion-exchanged water.

  A water-soluble aqueous resin solution having a solid content of 20% and having a hydrophobic monomer as a polymerization component was prepared with ion-exchanged water.

(Synthesis of water-soluble resins R-2 to R-8)
In the synthesis of water-soluble resin R-1, water-soluble resins R-2 to R- were similarly prepared except that the monomer configuration shown in Table 1 was changed to the monomer configuration used for the synthesis of R-2 to R-8, respectively. Each of 8 was synthesized.

  However, the initiator amount and reaction conditions were appropriately adjusted.

  The composition of the obtained water-soluble resins R1 to R8, the acid value of each resin, Mw (weight average molecular weight) and the like are shown in Table 1 below. The acid value and Mw (weight average molecular weight) of the water-soluble resin were measured using the method described above.

<Preparation of water-based ink for inkjet>
(Preparation of ink-jet aqueous ink 1)
While stirring 26.7 parts of the pigment dispersion, the synthesized water-soluble resin aqueous solution was added, then the following compounds were sequentially added to prepare an ink composition, and then filtered through a 0.8 μm filter. Thus, ink 1 was obtained.

Pigment dispersion 26.7 parts Water-soluble resin aqueous solution R-1 20.0 parts Water-soluble resin aqueous solution R-2 20.0 parts Diethylene glycol diethyl ether 3.0 parts 2-methyl-1,3-propanediol 10.0 parts 2-Pyrrolidone 10.0 parts Fluorosurfactant (manufactured by Neos Co., Ltd., Footgent 215M) 0.5 parts Ion-exchanged water 9.8 parts (Preparation of water-based inks 2-9 for inkjet)
In the preparation of the water-based ink for ink-jet 1, the water-based inks for ink-jets 2 to 9 were similarly prepared except that the constitution of the water-soluble resin shown in Table 2 was used instead of the water-soluble resins R-1 and R-2 used. Was prepared.

(Preparation of ink-jet aqueous ink 10)
While stirring 26.7 parts of the pigment dispersion, the synthesized water-soluble resin aqueous solution was added, then the following compounds were sequentially added to prepare an ink composition, and then filtered through a 0.8 μm filter. Thus, ink 1 was obtained.

Pigment dispersion 26.7 parts Water-soluble resin aqueous solution R-1 13.3 parts Water-soluble resin aqueous solution R-2 13.3 parts Water-soluble resin aqueous solution R-4 13.3 parts Diethylene glycol diethyl ether 3.0 parts 2-methyl -1,3-propanediol 10.0 parts 2-pyrrolidone 10.0 parts Fluorosurfactant (manufactured by Neos, TF 215M) 0.5 parts Ion-exchanged water 9.8 parts (Water-based ink for inkjet 11) Preparation)
In the preparation of the water-based ink for ink-jet 10, the water-based ink-jet system was similarly prepared except that the constitution of the water-soluble resin shown in Table 2 was used instead of the water-soluble resins R-1, R-2 and R-4 used. Ink 11 was prepared.

  In addition, the addition amount of the solvent in each water-based ink for inkjet was adjusted so that the value of the viscosity with respect to the water-based ink 1 for inkjet was in a range of ± 10%.

  In addition, the surface tension (measured by the plate method) of the water-based inks 1 to 11 for inkjet was all in the range of 26 mN / m to 28 mN / m.

  Each of the obtained ink-jet aqueous inks 1 to 11 was subjected to image formation as follows.

<Image formation>
Prepare an inkjet printer equipped with a drop-on-demand piezo inkjet head (nozzle number 512 (256 × 2 rows), nozzle diameter 39 μm, nozzle interval 70.5 μm (141 μm × 2 rows)), and obtain the inkjet water obtained above Each of the system inks 1 to 11 was loaded.

  Next, under the conditions of a head scanning speed of 500 mm / second, an ink droplet volume of 42 pl, a recording density of 360 × 360 dpi (dpi represents one dot, that is, the number of dots per 2.54 cm), the recording medium has a size of 35 × 35 mm. A solid image was recorded in one scan.

  However, when spots were observed in the recorded image, the recording was performed in the same manner by changing the head scanning speed to 400 mm / second.

  Incidentally, for 3 minutes after the start of image formation from the start of printing, the recording medium was heated from the back side with a heater to control the surface temperature of the recording medium at 45 ± 2 ° C.

  The surface temperature of the recording medium was measured using a non-contact thermometer (IT-530N type, manufactured by Horiba, Ltd.).

As the recording medium, JT5929PM (manufactured by Mactac), which is a recording medium made of polyvinyl chloride, was used. << Evaluation of recorded image >>
The recorded images obtained by the above image formation were evaluated for rubbing, gloss, liquid proximity, and dischargeability as follows.

(Evaluation of abrasion)
The obtained recorded image was rubbed with dry cotton (Kanakin No. 3), and the rank evaluation was performed for scratching as described below.

◎: Image hardly changes even after rubbing 50 times or more ○: Slight scratch remains at the stage of rubbing 50 times, but hardly affects the image density Δ: Image density decreases during rubbing 20 to 50 times × : Image density decreases while rubbing less than 20 times (evaluation of gloss (also called gloss))
The appearance of the surface of the recorded image was visually observed, and rank evaluation was performed as follows.

○: The image surface is not cloudy and glossy △: The image surface appears slightly white ×: White cloudiness and no glossiness (Evaluation near liquid)
The appearance of white streaks on the recorded image was visually observed, and rank evaluation was performed as follows.

○: White streaks are not seen on the image and the image is buried △: White streaks appear in a part of the image ×: Clear white streaks are seen in the entire image (Ejectability (also called ejection stability) Evaluation)
Using a printing apparatus having a piezo-type head (720 dpi, 16 pl of liquid amount), each of the inkjet water-based inks 1 to 9 prepared above was introduced into one head, and 10 A4 sizes were continuously produced. Images were created again at intervals of minutes and visually observed, and rank evaluation was performed as follows.

  ○: No image defect is seen including the image writing portion.

  (Triangle | delta): Although there is almost no image defect, the blur was seen and the satellite was seen by the dot.

X: Image defect is seen Table 2 shows the results obtained by the above evaluation.

  From Table 2, compared with the comparative inkjet water-based inks 5 to 9 and 11, the inkjet water-based inks 1 to 4 and 10 according to the present invention are evaluated in any of the evaluation items of scratching, gloss, liquid side, and dischargeability. It is clear that it exhibits excellent properties.

Claims (4)

In an aqueous inkjet ink containing water, a pigment, a water-soluble organic solvent, and a water-soluble resin,
2 or more types of water-soluble resins, and among the two or more types of water-soluble resins, the maximum and minimum difference in weight average molecular weight (Mw) is in the range of 1000 to 25000, and An aqueous ink for inkjet, having an acid value of 50 mgKOH / g to 250 mgKOH / g, and a difference between the maximum and minimum acid values being within 200 mgKOH / g.   The water-based ink for inkjet according to claim 1, wherein the water-soluble resin is a copolymer obtained by polymerizing a methacrylate component, an acrylate ester, and an unsaturated vinyl having a carboxy group as a monomer component.   An ink jet recording method comprising forming an image by discharging the water-based ink for ink jet according to claim 1.   The image formation is performed using a non-water-absorbing recording medium, and the recording surface temperature of the non-water-absorbing recording medium is adjusted to a range of 40 ° C to 90 ° C. Inkjet recording method.