JP2013184998A - Aqueous ink for inkjet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous ink for inkjet recording capable of reducing the deformation of a recording medium and recording an image excellent in color development, glossiness, and scuff resistance.SOLUTION: An aqueous ink for inkjet recording contains a self-dispersible pigment, a first resin having a weight average molecular weight of ≥1,000 to ≤30,000, a second resin having a weight average molecular weight of >30,000 to ≤300,000, an amphoteric compound, and water, wherein the difference [M-(M+M)] between the content [M(mass%)] of the amphoteric compound and the sum [M+M(mass%)] of the content [M(mass%)] of the first resin and the content [M(mass%)] of the second resin is 5 or more.

Description

  The present invention relates to an aqueous ink for inkjet recording.

  2. Description of the Related Art Conventionally, a so-called ink jet recording method is known in which an image or a character is recorded on a recording medium with fine ink droplets ejected from a nozzle of an ink jet recording head. As an ink used in such an ink jet recording method, an aqueous ink containing water and a pigment is known. Of the components contained in the water-based ink, water is widely used because it has little influence on the environment and is easy to handle. In addition, pigments are widely used because they are superior in light resistance and water resistance compared to colorants such as dyes.

  Such water-based ink for ink-jet recording is used for recording on various recording media such as plain paper and photographic paper, so that it is required to be able to record images with good quality on various recording media. Yes.

  For example, in Cited Document 1, a self-dispersing pigment, a water-insoluble resin, a water-soluble resin, and the like are applied to a recording medium to which a treatment liquid containing a cationic substance is attached in order to obtain an image having excellent image density. It is described that an aqueous ink containing is used.

  In Cited Document 2, an aqueous ink composition containing a colorant, a weak alkalinizer, a humectant and the like dispersed with a water-soluble resin is used to obtain an image having excellent glossiness and color development. Is described.

JP 2004-338291 A JP-A-2005-272706

  However, when recording an image on plain paper using the above water-based ink, since the plain paper has high water absorption, the penetration of the ink into the paper surface is promoted and the color developability of the image is lowered. There was a case.

  In addition, when moisture in the ink penetrates into the recording medium, the recording medium expands due to moisture absorption, and the recording medium shrinks due to evaporation of the absorbed moisture. There was a case of causing deformation. In particular, when plain paper is used, the deformation of the recording medium is often significant.

  Furthermore, when the above-mentioned water-based ink is used, the surface of the dots constituting the image is roughened or the wettability of the dots is lowered, so that the glossiness may not be sufficiently improved. Such a problem is likely to occur in a recording medium in which an ink component tends to remain on the surface, and is often particularly noticeable when using, for example, a photographic paper having a smooth ink absorbing layer on the surface.

  In addition, an image recorded using water-based ink may not have excellent abrasion resistance.

  Some embodiments according to the present invention can solve at least a part of the above-described problems, thereby reducing deformation of the recording medium and recording an image excellent in color development, glossiness, and abrasion resistance. The object is to provide a water-based ink for recording.

  The present invention can be realized as the following aspects or application examples.

[Application Example 1]
One aspect of the water-based ink for inkjet recording according to the present invention is:
A self-dispersing pigment,
A first resin having a weight average molecular weight of 1,000 to 30,000;
A second resin having a weight average molecular weight of more than 30,000 and not more than 300,000;
Zwitterionic compounds,
water and,
Containing.

  According to the water-based ink for inkjet recording of Application Example 1, it is possible to reduce the deformation of the recording medium and to obtain an image excellent in color development, glossiness, and abrasion resistance.

[Application Example 2]
In application example 1,
Sum of content [M _A (mass%)] of the zwitterionic compound, content [M ₁ (mass%)] of the first resin and content [M ₂ (mass%)] of the second resin The difference [M _A- (M ₁ + M ₂ )] from [M ₁ + M ₂ (mass%)] can be 5 or more.

[Application Example 3]
In claim 1 or claim 2,
The glass transition temperature (Tg) of the second resin may be −40 ° C. or higher and 80 ° C. or lower.

[Application Example 4]
In any one of Application Examples 1 to 3,
The first resin may be an alkali-soluble resin.

[Application Example 5]
In any one of Application Examples 1 to 4,
The zwitterionic compound may be a betaine compound.

[Application Example 6]
In any one of Application Examples 1 to 5,
The content [M _A (mass%)] of the zwitterionic compound may be 8 mass% or more and 40 mass% or less.

[Application Example 7]
In any one of claims 1 to 6,
The content ratio (M _A / M ₁ ) between the content [M _A (% by mass)] of the zwitterionic compound and the content [M ₁ (% by mass)] of the first resin is 6 or more and 14 or less. Can be.

[Application Example 8]
In any one of Application Examples 1 to 7,
The content ratio (M ₂ / M ₁ ) between the content [M ₂ (mass%)] of the second resin and the content [M ₁ (mass%)] of the first resin is 1 or more and 4 or less. Can be.

  Hereinafter, preferred embodiments of the present invention will be described. The embodiment described below describes an example of the present invention. In addition, the present invention is not limited to the following embodiments, and includes various modifications that are implemented within a range that does not change the gist of the present invention.

1. Ink-jet recording water-based ink An ink-jet recording water-based ink according to an embodiment of the present invention (hereinafter also simply referred to as “water-based ink”) includes a self-dispersing pigment and a weight-average molecular weight of 1,000 to 30,000. 1 resin, 2nd resin whose weight average molecular weight is more than 30,000 and 300,000 or less, zwitterionic compound, and water are contained.

  Hereinafter, each component contained in the water-based ink according to the present embodiment will be described in detail.

1.1. Self-dispersing pigment The water-based ink according to this embodiment contains a self-dispersing pigment. The self-dispersing pigment has a functional group (dispersibility imparting group) such as one or more selected from the group consisting of —COOH, —CHO, —OH, —SO ₃ H and salts thereof on the surface of the pigment. It is the pigment processed so that it may have.

  Such a self-dispersing pigment can be uniformly dispersed in a water-based ink without separately adding a dispersant. The term “dispersed” as used herein refers to a state in which the self-dispersing pigment is stably present in water without a dispersant, not only in a dispersed state but also in a dissolved state. Shall also be included.

  Inks formulated with self-dispersing pigments have higher dispersion stability and moderate viscosity of the ink compared to normal inks containing non-self-dispersing pigments and dispersants other than self-dispersing pigments. Therefore, it is possible to contain more pigment, and it is possible to form an image (for example, a character or a figure) having excellent color developability especially on plain paper.

  An image formed with an ink using such a self-dispersing pigment has a problem that it is inferior in scratch resistance and gloss because the amount of resin contained in the ink is smaller than that of a conventional ink. . With respect to such a problem, the water-based ink according to the present embodiment can solve the problem by containing a first resin (described later), a second resin (described later), and the like.

  As the pigment capable of forming a self-dispersing pigment, any of known inorganic pigments and organic pigments can be used. Examples of such pigments include pigment yellow, pigment red, pigment violet, pigment blue, and pigment black described in the Color Index, as well as phthalocyanine, azo, anthraquinone, azomethine, and condensed rings. Examples thereof include pigments of the type. Further, organic pigments such as yellow No. 4, No. 5, 205, 401; orange No. 228, 405; blue No. 1, 404, carbon black, titanium oxide, zinc oxide, zirconium oxide, iron oxide, ultramarine , Inorganic pigments such as bitumen and chrome oxide.

  Examples of the color index of the pigment include C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172, 180, etc., C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or C.I. I. Pigment violet 19, 23, 32, 33, 36, 38, 43, 50, C.I. I. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 15:34, 16, 18, 22, 25, 60, 65, 66, C.I. I. Bat Blue 4, 60 etc., C.I. I. Pigment green 7, 10, C.I. I. Pigment brown 3, 5, 25, 26, C.I. I. Pigment orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63, etc., C.I. I. And CI pigment black 1,7.

  In order to prepare such a self-dispersing pigment, a functional group or a molecule containing a functional group is coordinated on the surface of the pigment by chemical treatment such as vacuum plasma or chemical treatment, and chemical bonding such as grafting is performed. Can be obtained. For example, it can be obtained by the method described in JP-A-8-3498. In addition, as the self-dispersing pigment, commercially available products can be used. Preferred examples include “Microjet CW1” and “Microjet CW2” manufactured by Orient Chemical Industries, Ltd., and “CAB” manufactured by Cabot Corporation. -O-JET 200 "," CAB-O-JET 300 "and the like.

  The self-dispersing pigment is prepared as follows, for example.

(Example of preparation method of self-dispersing pigment (pigment surface oxidation treatment-sulfonation treatment))
A pigment is added to the solvent, and this is subjected to high-speed shear dispersion with a high-speed mixer or the like, or impact-dispersed with a bead mill or jet mill to obtain a slurry-like pigment dispersion. While slowly stirring the pigment dispersion, a treatment agent containing sulfur (sulfamic acid, fuming sulfuric acid, sulfuric acid, chlorosulfuric acid, fluorosulfuric acid, amidosulfuric acid, etc.) is added, and the pigment dispersion is heated to 60 to 200 ° C. Then, the dispersibility-imparting group is introduced on the pigment surface. After removing the solvent from the pigment dispersion, the treatment agent containing sulfur is removed by repeating washing with water, ultrafiltration, reverse osmosis, centrifugation, filtration and the like to obtain a self-dispersing pigment.

  In addition, the self-dispersing pigment preferably has an average particle size of 10 nm to 300 nm, more preferably 40 nm to 150 nm, from the viewpoint of improving the storage stability of the ink and preventing nozzle clogging. preferable.

  The content of the self-dispersing pigment is preferably 2% by mass or more and 15% by mass or less with respect to the total mass of the water-based ink from the viewpoint of obtaining a sufficient color density and the liquid stability of the water-based ink. It is more preferably 4% by mass or more and 12% by mass or less, and further preferably 6% by mass or more and 12% by mass or less.

1.2. First Resin The water-based ink according to the present embodiment contains a first resin having a weight average molecular weight of 1000 or more and 30,000 or less.

  One of the functions of the first resin is to improve the gloss of the recorded image. The mechanism by which the first resin can improve the glossiness of the image is considered to be due to the following two reasons.

  The first reason is that, since the molecular weight of the first resin is within the above range, the fluidity of droplets (dots) made of water-based ink adhering to the recording medium is improved, and the dots are likely to spread out. It is thought to be caused. When the dots easily spread out in this way, the inclination angle of the side surface of the dots becomes small. Then, it is considered that the scattering of light incident on the dots is reduced and the glossiness of the recorded image is improved.

  The second reason is considered to be due to the effect that the first resin improves the dispersibility of the self-dispersing pigment contained in the water-based ink. When the dispersibility of the self-dispersing pigment is improved in this way, the generation of coarse aggregates containing pigment particles can be suppressed, so that it is possible to reduce the roughening of the dot surface due to the aggregates. Then, since the surface of the dot becomes smooth, the light incident on the dot is likely to be regularly reflected, and the glossiness of the recorded image is considered to be improved.

  One of the other functions of the first resin is to improve the adhesion between the recording medium and the water-based ink and / or the solid content in the water-based ink.

  The first resin is preferably an alkali-soluble resin. The alkali-soluble resin means any resin that exhibits water solubility under alkaline conditions. Examples of the alkali-soluble resin include polyacrylic acid, acrylic acid-acrylonitrile copolymer, vinyl acetate-acrylic acid ester copolymer, acrylic acid-acrylic acid ester copolymer, and styrene-acrylic acid copolymer. Styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid ester copolymer, styrene-α-methylstyrene-acrylic acid copolymer, styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymer Styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl acetate-maleic acid ester copolymer, vinyl acetate-croton Acid copolymers, vinyl acetate-acrylic acid copolymers and their salts. I can get lost. These may be used alone or in combination of two or more. Among these, a copolymer of a monomer having a hydrophobic functional group and a monomer having a hydrophilic functional group, and a polymer comprising a monomer having both a hydrophobic functional group and a hydrophilic functional group are particularly preferable. As the form of the copolymer, any form of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer can be used.

  Examples of the salt include bases such as ammonia, ethylamine, diethylamine, triethylamine, propylamine, isopropylamine, dipropylamine, butylamine, isobutylamine, diethanolamine, triethanolamine, tri-iso-propanolamine, aminomethylpropanol, and morpholine. And a salt with a functional compound. The addition amount of these basic compounds is not particularly limited as long as it is not less than the neutralization equivalent of the first resin.

  The weight average molecular weight of the first resin is 1,000 or more and 30,000 or less, preferably 1,500 or more and 20,000 or less. When the molecular weight of the first resin is within the above range, an image having excellent gloss can be obtained. On the other hand, when the molecular weight of the first resin is less than the above range, the fluidity of the ink is excessively increased, and problems such as bleeding may occur. Further, if the molecular weight of the first resin exceeds the above range, the fluidity of the ink and the function of dispersing the pigment tend to be reduced, so that the gloss of the recorded image may be reduced.

  The weight average molecular weight of the first resin can be measured, for example, by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent, and can be determined by the molecular weight in terms of polystyrene.

  The glass transition temperature (Tg) of the first resin is preferably −40 ° C. or higher and 80 ° C. or lower, and more preferably −30 ° C. or higher and 65 ° C. or lower. When the glass transition temperature of the first resin is within the above range, the adhesion of the water-based ink to the recording medium may be improved.

  The acid value of the first resin is preferably 50 or more and 300 or less, and more preferably 70 or more and 250 or less. When the acid value is within the above range, the dispersibility of the self-dispersing pigment may be improved.

  Commercially available products may be used as the first resin. For example, Joncryl 67 (weight average molecular weight: 12,500, acid value: 213), Joncryl 678 (weight average molecular weight: 8,500, acid value: 215). ), Joncryl 586 (weight average molecular weight: 4,600, acid value: 108), Joncryl 611 (weight average molecular weight: 8,100, acid value: 53), Joncryl 680 (weight average molecular weight: 4,900, Acid value: 215), joncryl 682 (weight average molecular weight: 1,700, acid value: 238), joncryl 683 (weight average molecular weight: 8,000, acid value: 160), joncryl 690 (weight average molecular weight: 16,500, acid value: 240) (above trade name, manufactured by BASF Japan Ltd.) and the like.

The content [M ₁ (% by mass)] of the first resin is preferably 0.5% by mass or more and 5% by mass or less in terms of solid content with respect to the total mass of the water-based ink. It is more preferably from 3% by mass to 3% by mass, and further preferably from 0.7% by mass to 2% by mass. When the content of the first resin is within the above range, particularly not below the lower limit value, the glossiness of the recorded image may be improved. Further, since the content of the first resin is within the above range, particularly without exceeding the upper limit, it becomes easy to maintain the viscosity of the water-based ink within an appropriate range, the storage stability of the water-based ink, and the ink jet recording apparatus. In some cases, the discharge stability of the nozzles may be improved.

1.3. Second Resin The water-based ink according to this embodiment contains a second resin having a weight average molecular weight of more than 30,000 and not more than 300,000.

  One of the functions of the second resin is to solidify the water-based ink adhering to the recording medium and further firmly fix the solidified ink on the recording medium. Thereby, an image recorded using the water-based ink according to the present embodiment is excellent in abrasion resistance.

  To the water-based ink according to the present embodiment, a second resin that can be completely dissolved in the water-based ink may be added, and in a state dispersed as particles in the water-based ink (that is, an emulsion state or a suspension state) Such a second resin may be added.

  As the component constituting the second resin, for example, polyacrylic acid ester or a copolymer thereof, polymethacrylic acid ester or a copolymer thereof, polyacrylonitrile or a copolymer thereof, polycyanoacrylate, polyacrylamide, polyacrylic acid, Polymethacrylic acid, polyethylene, polypropylene, polybutene, polyisobutylene, polystyrene or copolymers thereof, petroleum resin, chroman indene resin, terpene resin, polyvinyl acetate or copolymer thereof, polyvinyl alcohol, polyvinyl acetal, polyvinyl ether, Polyvinyl chloride or copolymer thereof, polyvinylidene chloride, fluororesin, fluoro rubber, polyvinyl carbazole, polyvinyl pyridine, polyvinyl imidazole, polybutadiene or Copolymer, polyurethane, polyester polyurethane, polyether polyurethane, polychloroprene, polyisoprene, natural resins. Among these, those having both a hydrophobic portion and a hydrophilic portion in the molecular structure are more preferable. These may be used alone or in combination of two or more.

  As the second resin, those obtained by known materials and methods can be used. For example, those described in JP-B-62-1426, JP-A-3-56573, JP-A-3-79678, JP-A-3-160068, JP-A-4-18462 and the like can be used. Good. Commercially available products can also be used. For example, Microgel E-1002, Microgel E-5002 (trade name, manufactured by Nippon Paint Co., Ltd.), Boncoat 4001, Boncoat 5454 (trade name, Dainippon Ink & Chemicals, Inc.) Co., Ltd.), SAE1014 (trade name, manufactured by Zeon Corporation), Cybinol SK-200 (trade name, manufactured by Seiden Chemical Co., Ltd.), Jonkrill 7100, Jonkrill 390, Jonkrill 711, Jonkrill 511, Jonkrill 7001, John Crill 632, John Crill 741, John Crill 450, John Crill 840, John Crill 74J, John Crill HRC-1645J, John Crill 734, John Crill 852, John Crill 7600, John Crill 775, John Crill 537J John Crill 1535, John Crill PDX-7630A, John Crill 352J, John Crill 352D, John Crill PDX-7145, John Crill 538J, John Crill 7640, John Crill 7641, John Crill 631, John Crill 790, John Crill 780, John Crill 7610 (trade name, manufactured by BASF Japan Ltd.) and the like.

  The second resin is obtained, for example, by the method described below, and any of these methods may be used, or a plurality of methods may be combined as necessary. As the method, a polymerization catalyst (polymerization initiator) and a dispersant are mixed in a monomer of a component constituting the desired second resin, and polymerization (that is, emulsion polymerization) is performed, or a resin having a hydrophilic portion In a water-soluble organic solvent, the solution is mixed in water, and the water-soluble organic solvent is removed by distillation or the like. The resin is dissolved in a water-insoluble organic solvent, and the solution is dissolved in an aqueous solution together with a dispersant. Examples thereof include a method obtained by mixing. Said method can be suitably selected according to the kind and characteristic of resin to be used. The dispersant that can be used when dispersing the second resin is not particularly limited, but anionic surfactants (for example, sodium dodecylbenzenesulfonate, sodium lauryl phosphate, polyoxyethylene alkyl ether sulfate) Ammonium salts, etc.), nonionic surfactants (for example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl phenyl ethers, etc.), and these may be used alone or Two or more kinds can be mixed and used.

  The weight average molecular weight of the second resin is more than 30,000 and not more than 300,000, preferably not less than 45,000 and not more than 300,000, more preferably not less than 45,000 and not more than 160,000. When the molecular weight of the second resin is within the above range, the ink ejection stability is excellent, and the function of improving the scratch resistance of the image can be exhibited well. On the other hand, when the molecular weight of the second resin is less than the above range, the function of improving the abrasion resistance of the image may be deteriorated. Further, when the molecular weight of the second resin exceeds the above range, the glossiness of the image may be lowered or the ink ejection stability may be lowered.

  The weight average molecular weight of the second resin can be measured, for example, by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent, and can be determined by the molecular weight in terms of polystyrene.

  The glass transition temperature (Tg) of the second resin is preferably −40 ° C. or higher and 80 ° C. or lower, and more preferably −30 ° C. or higher and 65 ° C. or lower. When the Tg of the second resin is within the above range, the film forming property of the ink layer surface in the drying process can be secured, and an image excellent in abrasion resistance can be formed.

  As described above, the second resin may be particulate. In this case, the average particle diameter of the second resin is preferably 10 nm or more and 150 nm or less, and more preferably 10 nm or more and 100 nm or less. When the average particle diameter of the second resin is within the above range, the smoothness of the ink layer surface in the drying process can be ensured, and an image excellent in color development and glossiness can be formed.

  When the second resin is in the form of particles, the average particle diameter can be measured by a particle size distribution measuring apparatus using a dynamic light scattering method as a measurement principle. An example of such a particle size distribution measuring apparatus is “Microtrac UPA” (trade name) manufactured by Nikkiso Co., Ltd., which employs a heterodyne method as a frequency analysis method. In the present specification, the “average particle size” means a volume-based average particle size unless otherwise specified.

The content [M ₂ (% by mass)] of the second resin is preferably 1% by mass or more and 10% by mass or less, preferably 1% by mass or more and 5% by mass or less in terms of solid content with respect to the total mass of the water-based ink. % Or less is more preferable. When the content of the second resin is within the above range, particularly not lower than the lower limit, the solidification / fixing strength of the ink tends to be sufficiently obtained. In addition, since the content of the second resin is within the above range, particularly without exceeding the upper limit, it becomes easy to maintain the viscosity of the water-based ink within an appropriate range, the storage stability of the water-based ink, and the ink jet recording apparatus. In some cases, the discharge stability of the nozzles may be improved.

The content ratio (M ₂ / M ₁ ) between the content [M ₂ (% by mass)] of the second resin and the content [M ₁ (% by mass)] of the first resin is 0.5 or more and 8 or less. It is preferable that it is 1 or more and 4 or less. When the content ratio of the first resin and the second resin is within the above range, an image having excellent gloss can be obtained, and an image having particularly excellent line marker resistance can be obtained.

1.4. Zwitterionic Compound The water-based ink according to this embodiment contains a zwitterionic compound. One of the functions of the zwitterionic compound is to suppress deformation of the recording medium (particularly plain paper). A specific mechanism by which the zwitterionic compound can suppress the deformation of the recording medium is considered as follows.

  Since the zwitterionic compound has the property of being excellent in water retention, evaporation of water contained in the ink can be appropriately suppressed. Therefore, it is possible to reduce the amount of water added in consideration of evaporation. Thus, since the total amount of water contained in the ink can be reduced, it is possible to reduce the expansion and deformation of the recording medium by absorbing the water in the ink. In addition, since the water contained in the ink (droplet) attached to the recording medium can be prevented from rapidly evaporating, deformation (curl) due to the shrinkage of the recording medium accompanying the evaporation of the water can be suppressed.

  As described above, the water-based ink according to the present embodiment hardly causes deformation or the like of the recording medium. Therefore, the recording medium on which an image is recorded using the water-based ink according to the present embodiment has excellent transportability in the ink jet recording apparatus.

  The zwitterionic compound is not particularly limited, and examples thereof include betaine compounds, amino acids, and derivatives thereof. More specifically, as betaine compounds, glycine betaine (molecular weight 117, also referred to as “trimethylglycine”), γ-ptyrobetaine (145), homarine (137), trigonelin (137), carnitine (161) Homoserine betaine (161), valine betaine (159), lysine betaine (188), ornithine betaine (176), alanine betaine (117), stachydrin (185), and betaine glutamate (189). N-trialkyl substitution of an amino acid is mentioned. As amino acids, glycine (molecular weight 75), alanine (89), serine (105), threonine (119), valine (117), methionine (149), cysteine (121), proline (same) 115), lysine (same as 146), histidine (same as 155), arginine (same as 174) and derivatives thereof. Among these, betaine compounds are preferable and trimethylglycine is more preferable from the viewpoint of further slowing the expansion speed of the recording medium after ink adhesion and reducing nozzle clogging. A zwitterionic compound can be used individually by 1 type or in combination of 2 or more types, may be synthesize | combined by a conventional method and may obtain a commercial item. As a commercially available product, for example, aminocoat (manufactured by Asahi Kasei Chemicals Corporation) can be used as trimethylglycine.

  Further, the weight average molecular weight of the zwitterionic compound is preferably 100 or more and 250 or less. Thereby, the surface of an image (dot) can be made smoother and an image having higher gloss may be formed.

The content [M _A (mass%)] of the zwitterionic compound is preferably 8% by mass or more and 40% by mass or less, and preferably 10% by mass or more and 25% by mass or less with respect to the total mass of the water-based ink. Is more preferable. Thereby, the deformation of the recording medium may be further suppressed.

The total [M ₁ ] of the content [M _A (mass%)] of the zwitterionic compound, the content [M ₁ (mass%)] of the first resin and the content [M ₂ (mass%)] of the second resin [M _A − (M ₁ + M ₂ )] with respect to + M ₂ (mass%)] is preferably 0 or more, more preferably 5 or more, and even more preferably 10 or more. Moreover, although an upper limit is not specifically limited, For example, it is preferable to set it as 15 or less.

Here, the first resin and the second resin are components that shrink with drying. Therefore, a droplet (dot) made of water-based ink adhering to the recording medium contracts as the first resin and the second resin in the droplet are cured (volatilization of volatile components contained in the ink), thereby recording. The medium may also be deformed. In such a case, when [M _A − (M ₁ + M ₂ )] is 0 or more, deformation of the recording medium can be effectively suppressed.

The content ratio (M _A / M ₁ ) between the content [M _A (mass%)] of the zwitterionic compound and the content [M ₁ (mass%)] of the first resin is 3.5 or more and 40 or less. It is preferable that it is 5 or more and 14 or less. When the content ratio of the zwitterionic compound and the first resin is within the above range, the water-based ink is less prone to wavy deformation (cockling) that occurs during the drying process of the ink, and an image with excellent gloss can be obtained.

1.5. Water The water-based ink according to this embodiment contains water as a dispersion medium. The water according to the present embodiment is a main solvent, and it is preferable to use pure water or ultrapure water such as ion exchange water, ultrafiltration water, reverse osmosis water, and distilled water. In particular, it is preferable to use water sterilized by ultraviolet irradiation or addition of hydrogen peroxide in order to prevent the generation of mold and bacteria and enable long-term storage of the pigment ink.

  Since the water-based ink according to the present embodiment contains the above-described zwitterionic compound, the water content can be reduced as compared with the conventional water-based ink. Specifically, the water content is preferably 50% by mass to 65% by mass with respect to the total mass of the water-based ink. When the content of water contained in the water-based ink is within the above range, it is possible to improve the balance between the drying property and the moisture retention property of the ink while adjusting the viscosity of the ink to an appropriate range.

1.6. Others (acetylene glycol surfactant)
The water-based ink according to this embodiment may contain acetylene glycol. Acetylene glycol is a nonionic surfactant having an acetylene group in the center and a symmetrical structure, and is applied to water-based materials in various directions as a wetting agent that does not easily foam. Acetylene glycol is excellent in functions such as wetting, defoaming, and dispersion. Since the glycol has a very stable molecular structure, has a small molecular weight, and has an effect of reducing the surface tension of water, the penetrability and bleeding of the ink on the recording medium can be controlled appropriately.

  Specific examples of the acetylene glycol surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, , 5-dimethyl-1-hexyn-3-ol and the like.

  Commercially available acetylene glycol surfactants include, for example, Surfynol 104 (series), 420, 440, 465, 485 (above, product name, manufactured by Air Products), Olfine STG, PD-001, SPC, E1004. , E1010 (trade name, manufactured by Nissin Chemical Industry Co., Ltd.), acetylenol E00, E40, E100, LH (above, product name, manufactured by Kawaken Fine Chemical Co., Ltd.), and the like.

  One acetylene glycol surfactant may be used alone, or two or more acetylene glycol surfactants may be used in combination.

  When the acetylene glycol surfactant is contained, the content thereof is preferably 0.1% by mass or more and 3.0% by mass or less, and 0.3% by mass with respect to the total mass of the water-based ink. More preferably, it is 2.0 mass% or less.

  The water-based ink according to the present embodiment may contain a surfactant other than the acetylene glycol surfactant. Examples of such surfactants include nonionic surfactants other than acetylene glycol surfactants (eg, silicone surfactants such as polysiloxane compounds), anionic surfactants, and the like. .

(Wetting agent)
The water-based ink according to this embodiment may contain a wetting agent. Thereby, clogging in the vicinity of the nozzle of the inkjet head can be effectively suppressed.

  As the wetting agent, for example, glycerin, 1,2,6-hexanetriol, trimethylolpropane, pentamethylene glycol, trimethylene glycol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, number Polyethylene glycol having an average molecular weight of 2000 or less, dipropylene glycol, tripropylene glycol, isobutylene glycol, 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol Polyhydric alcohols such as mesoerythritol and pentaerythritol, as well as glucose, mannose, fructose, ribose, xylose, arabinose, galactose, Sugars such as ludonic acid, glucitol (sorbit), maltose, cellobiose, lactose, sucrose, trehalose, and maltotriose, so-called solid wetting agents such as sugar alcohols, hyaluronic acids, and ureas, and ethanol, methanol, butanol, C1-C4 alkyl alcohols such as propanol and isopropanol, and 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, formamide, acetamide, dimethyl sulfoxide, sorbit, Examples include sorbitan, acetin, diacetin, triacetin, and sulfolane.

  A wetting agent may be used individually by 1 type, and may be used in combination of 2 or more type.

  When the wetting agent is contained, the content is preferably 10% by mass or more and 50% by mass or less with respect to the total mass of the water-based ink.

(Penetration enhancer)
The water-based ink according to this embodiment may contain a penetration enhancer.

  As such a penetration enhancer, at least one of alkyl ethers of polyhydric alcohols (also referred to as glycol ethers) and 1,2-alkyldiols is preferably used. Examples of the alkyl ether of polyhydric alcohol include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol mono Isopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, Lopylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol monopropyl ether, propylene glycol monoisopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether , Dipropylene glycol monoisopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and the like. Examples of the 1,2-alkyldiol include 1,2-pentanediol and 1,2-hexanediol. In addition to these, straight-line such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8-octanediol. There may be mentioned diols of chain hydrocarbons. A penetration enhancer may be used individually by 1 type, and may be used in combination of 2 or more type.

  When the penetration accelerator is contained, the content thereof is preferably 3% by mass or more and 20% by mass or less with respect to the total mass of the water-based ink.

(Antioxidant)
The water-based ink according to this embodiment may contain an antioxidant. Examples of antioxidants (ultraviolet absorbers) include L-ascorbic acid and salts thereof, and lanthanide oxides such as allophanates such as allophanate and methyl allophanate, biurets such as biuret, dimethylbiuret and tetramethylbiuret. Etc. As these commercially available products, for example, Tinuvin 328, 900, 1130, 384, 292, 123, 144, 622, 770, 292, Irgacor 252, 153, Irganox 1010, 1076, 1035, MD1024 manufactured by Ciba Geigy are used. An antioxidant may be used individually by 1 type and may be used in combination of 2 or more type.

  When it contains antioxidant, it is preferable that the content is 0.5 mass% or less with respect to the total mass of aqueous ink.

(Preservatives / antifungal agents)
The water-based ink according to the present embodiment may contain a preservative / antifungal agent. Examples of the antiseptic / antifungal agent include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, 1,2-dibenzisothiazoline-3-one , Dichlorophen, hexachlorophene, p-hydroxybenzoate, ethylenediaminetetraacetic acid (EDTA), sodium dehydroacetate, 3,4-isothiazolin-3-one, and 4,4-dimethyloxazolidine. Examples of these commercially available products include Proxel CRL, Proxel BDN, Proxel GXL, Proxel XL-2 (1,2-benchazolin-3-one), Proxel TN (all trade names manufactured by Avecia), and the like. . An antiseptic | preservative and an antifungal agent may be used individually by 1 type, and may be used in combination of 2 or more type.

  When the antiseptic / antifungal agent is contained, the content thereof is preferably 0.5% by mass or less based on the total mass of the water-based ink.

(PH adjuster)
The water-based ink according to this embodiment may contain a pH adjuster. Examples of the pH adjuster include potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia, diethanolamine, triethanolamine, tripropanolamine, potassium carbonate, sodium carbonate, Examples thereof include sodium hydrogen carbonate.

1.7. Preparation Method The water-based ink according to the present embodiment can be produced by dispersing and mixing the above-described components by an appropriate method. After sufficiently stirring each of the above components, the target aqueous ink can be obtained by performing filtration in order to remove coarse particles and foreign matters that cause clogging.

1.8. Physical Properties The water-based ink according to this embodiment preferably has a surface tension at 20 ° C. of 20 mN / m or more and 50 mN / m or more, and 25 mN / m or more, from the viewpoint of the balance between recording quality and reliability as an ink jet ink. More preferably, it is 40 mN / m or less. The surface tension is measured by using an automatic surface tension meter CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) by confirming the surface tension when the platinum plate is wetted with ink in an environment of 20 ° C. be able to.

  From the same viewpoint, the viscosity of the water-based ink according to the present embodiment at 20 ° C. is preferably 2 mPa · s or more and 15 mPa · s or less, and more preferably 2 mPa · s or more and 10 mPa · s or less. The viscosity is measured by using a viscoelasticity tester MCR-300 (manufactured by Pysica), increasing the Shear Rate to 10 to 1000 in an environment of 20 ° C., and reading the viscosity at Shear Rate 200. Can be measured.

2. Inkjet recording apparatus The water-based ink according to the present embodiment can record an image on a recording medium by being ejected from a nozzle provided in a head of the inkjet recording apparatus. In this way, a recorded matter on which an image is recorded can be obtained.

  As an ink jet recording apparatus to which the water-based ink according to the present embodiment can be applied, any conventionally known printer can be used, and is not particularly limited.

  The water-based ink according to the present embodiment can be applied to any recording medium such as plain paper, photographic paper, textiles, leather, sheets or films, plastic, glass, ceramics, metal, etc. It can be preferably applied to.

3. Examples Hereinafter, embodiments of the present invention will be described more specifically with reference to examples and comparative examples. However, the present embodiment is not limited to only these examples.

3.1. Preparation of water-based ink 3.1.1. Preparation of pigment dispersion (1) Cyan pigment dispersion C1
A 4 liter stainless steel beaker was attached to a rotor-stator type high shear mixer (Silverson L4RT-A) and immersed in an ice bath. In this beaker, C.I. I. Pigment Blue 15: 4 About 75 g and 1000 g of water were added and homogenized at 7200 rpm for 15 minutes. To this was added 20 ml of an isopropanol solution in which 2.07 g (0.01 mol) of o-acetaniside was dissolved, and the mixture was further stirred for 15 minutes.

In a separate container, 4.35 g (0.025 mol) of sulfanilic acid, 30 mL of 1N HCl, and 1.73 g (0.025 mol) of sodium nitrite were mixed at 5-10 ° C. to form a diazonium salt. . Then, this was changed to the above C.I. I. Pigment Blue 15: 4 and o-acetaniside were added with stirring to maintain the temperature at about 10 ° C. This mixture was adjusted to pH 5-6 by dropwise addition of 5M sodium hydroxide solution, and further stirred for 2 hours while confirming the progress of the reaction based on the presence or absence of a diazonium salt. When a diazonium salt is present, when the reaction mixture and a 1M Na ₂ CO ₃ solution in which 0.1% aminosalicylic acid is dissolved are dropped on a filter paper one by one, when the spread of these two drops touches, Become.

  The mixture was transferred to a Telsonic flow sonicator and sonicated for 2 hours, and the resulting pigment dispersion was purified using a 50 nm diafiltration membrane column and then concentrated to a solids content of 20% Thus, a cyan self-dispersing pigment dispersion C1 (hereinafter also referred to as “cyan pigment dispersion C1”) was obtained. The volume average particle diameter of the pigment of this dispersion was measured by particle size distribution measurement of Microtrac UPA 150 (manufactured by Microtrac), and it was 105 nm.

(2) Yellow pigment dispersion Y1
As a pigment, C.I. I. Pigment Blue 15: 4 instead of C.I. I. Except for using Pigment Yellow 74, it was prepared in the same manner as the Cyan Pigment Dispersion C1, and it was also referred to as Yellow Self-Dispersion Pigment Dispersion Y1 (hereinafter referred to as “Yellow Pigment Dispersion Y1”) having a solid content concentration of 20 mass%. .) The volume average particle diameter of the pigment in this dispersion was measured by particle size distribution measurement of Microtrac UPA 150 (manufactured by Microtrac), and was 110 nm.

(3) Magenta pigment dispersion M1
As a pigment, C.I. I. Pigment Blue 15: 4 instead of C.I. I. Except for using Pigment Red 122, it was prepared in the same manner as the Cyan Pigment Dispersion C1, and it was also referred to as “Magenta Pigment Dispersion M1”. .) The volume average particle size of the pigment in this dispersion was measured by measuring the particle size distribution of Microtrac UPA 150 (manufactured by Microtrac), and found to be 85 nm.

(4) Magenta pigment dispersion M2
The magenta self-dispersing pigment dispersion M2 (hereinafter also referred to as “magenta pigment dispersion M2”) is the same as the magenta pigment dispersion M1 except that the production conditions are changed so that the volume average particle diameter is 105 nm. ) Was prepared.

(5) Magenta pigment dispersion M3
The magenta self-dispersing pigment dispersion M3 (hereinafter, also referred to as “magenta pigment dispersion M3”) is the same as the magenta pigment dispersion M1 except that the production conditions are changed so that the volume average particle diameter is 120 nm. ) Was prepared.

3.1.2. Preparation of water-based ink Each component was mixed in the ratios shown in Table 1 and Table 2, stirred for 2 hours at room temperature, filtered through a membrane filter having a pore size of 5 μm, and each ink-jet recording water system of Examples and Comparative Examples. An ink was prepared. However, the addition amounts shown in Table 1 and Table 2 all represent the concentration of mass%, the numbers of the pigment dispersion indicate the solid content concentration (mass%) of the pigment, and the numbers of the first resin and the second resin represent the resin. Concentration (mass%) is shown.

Of the components shown in Tables 1 and 2, the components described by abbreviations or trade names are as follows.
(First resin)
First resin A (trade name ARUFON-UC3510, manufactured by Toa Gosei Co., Ltd., polyacrylic acid ester, weight average molecular weight 2,000)
First resin B (trade name Joncryl-57J, manufactured by BASF Corporation, polyacrylate, weight average molecular weight 5,000)
First resin C (trade name Joncryl-60J, manufactured by BASF Corporation, polyacrylate, weight average molecular weight 9,000)
First resin D (trade name Joncryl-HPD96J, manufactured by BASF Corporation, polyacrylate, weight average molecular weight 17,000)
(Second resin)
Second resin A (trade name WBR-016U, manufactured by Taisei Fine Chemical Co., Ltd., polyether polyurethane, weight average molecular weight 45,000, average particle size 40 nm, Tg 20 ° C.)
Second resin B (trade name WBR-600U, manufactured by Taisei Fine Chemical Co., Ltd., polyester polyurethane, weight average molecular weight 75,000, average particle diameter 40 nm, Tg-30 ° C.)
Second resin C (polyurethane, weight average molecular weight 130,000, average particle size 40 nm, Tg 64 ° C.)
Second resin D (styrene / acrylic copolymer, weight average molecular weight 50,000, average particle diameter 60 nm, Tg-6 ° C.)
Second resin E (trade name Joncryl-PDX7677, manufactured by BASF Corporation, polyacrylate, weight average molecular weight 160,000, average particle size 10 nm, Tg 32 ° C.)
Second resin F (styrene / acrylic copolymer, weight average molecular weight 300,000, average particle diameter 80 nm, Tg-15 ° C.)
(Zwitterionic compounds)
Amino coat (trade name, manufactured by Asahi Kasei Chemicals Corporation, trimethylglycine)
(Surfactant)
・ Surfinol 465 (trade name, manufactured by Air Products, acetylene glycol surfactant)
・ Orphine E1010 (trade name, manufactured by Nissin Chemical Industry Co., Ltd., acetylene glycol surfactant)

  The second resin D and the second resin F were synthesized as follows.

(Second resin D)
A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 1000 g of ion-exchanged water and 7.5 g of sodium lauryl sulfate, and the temperature was raised to 70 ° C. while purging with nitrogen under stirring. The internal temperature was kept at 70 ° C., 4 g of potassium persulfate was added as a polymerization initiator, and after dissolution, 450 g of ion-exchanged water, 3 g of sodium lauryl sulfate, 20 g of acrylamide, 356 g of styrene, 545 g of butyl acrylate, and 30 g of methacrylic acid were previously stirred. The emulsion prepared by adding below was continuously dropped into the reaction solution over 4 hours. After completion of the dropwise addition, aging was performed for 3 hours. The obtained aqueous emulsion was cooled to room temperature, and then ion-exchanged water and 5% aqueous sodium hydroxide solution were added to adjust the solid content to 40% by weight and pH 8.

  In the obtained aqueous emulsion, the glass transition temperature of the second resin D was −6 ° C., the weight average molecular weight of the second resin D was 50,000, and the average particle size of the dispersoid was 60 nm.

(Second resin F)
A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 1000 g of ion exchange water and 2.5 g of sodium lauryl sulfate, and the temperature was raised to 70 ° C. while purging with nitrogen under stirring. Maintaining the internal temperature at 70 ° C., adding 4 g of potassium persulfate as a polymerization initiator, dissolving, and previously stirring 450 g of ion exchange water, 3 g of sodium lauryl sulfate, 20 g of acrylamide, 300 g of styrene, 640 g of butyl acrylate, and 30 g of methacrylic acid The emulsion prepared by adding below was continuously dropped into the reaction solution over 4 hours. After completion of the dropwise addition, aging was performed for 3 hours. The obtained aqueous emulsion was cooled to room temperature, and then ion-exchanged water and 5% aqueous sodium hydroxide solution were added to adjust the solid content to 40% by weight and pH 8.

  In the obtained aqueous emulsion, the glass transition temperature of the second resin F was −15 ° C., the weight average molecular weight of the second resin F was 300,000, and the average particle size of the dispersoid was 80 nm.

3.2. Evaluation test 3.2.1. Evaluation of Glossiness Each ink prepared was filled in an ink jet printer PX-A550 (Seiko Epson), and a 100% duty patch pattern was recorded on a recording medium (photo paper <gloss>, Seiko Epson). The obtained sample was allowed to stand for 1 hour in a normal temperature and humidity environment (temperature 20 ° C., humidity 65%). After leaving, glossiness (glossiness) at 20 ° of each patch portion was measured using a gloss meter GM-268 (manufactured by Konica Minolta), and the gloss value (glossiness) was determined based on the following criteria.
A: 150% or more of the recording paper gloss at a regular reflection angle of 20 °.
B: 100% or more and less than 150% of the recording paper gloss at a regular reflection angle of 20 °.
C: 50% or more and less than 100% of the recording paper gloss at a regular reflection angle of 20 °.
D: Less than 50% of the recording paper gloss at a regular reflection angle of 20 °.

3.2.2. Evaluation of coloring property Each of the prepared inks was filled into an ink jet printer PX-A550 (manufactured by Seiko Epson), and a 100% duty patch pattern was recorded on a recording medium (XeroxP paper). The obtained sample was allowed to stand for 1 hour in a normal temperature and humidity environment (temperature 20 ° C., humidity 65%). After standing, the OD value (Optical Density; optical density) of each patch portion was measured using a Gretag densitometer (manufactured by Gretag Macbeth), and the color development was evaluated based on the OD value. Judgment criteria are as follows.
A: The optical reflection density (OD value) is 1.3 or more.
B: The optical reflection density (OD value) is 1.2 or more and less than 1.3.
C: The optical reflection density (OD value) is 1.1 or more and less than 1.2.
D: The optical reflection density (OD value) is less than 1.1.

3.2.3. Evaluation of Fixing Strength (Abrasion Resistance) (1) Cloth Abrasion Test Each prepared ink is filled in an ink jet printer PX-A550 (manufactured by Seiko Epson) and is recorded on a recording medium (photo paper <gloss>, manufactured by Seiko Epson). A 100% duty patch pattern was recorded. The obtained sample was allowed to stand for 1 hour in a normal temperature and humidity environment (temperature 20 ° C., humidity 65%). After leaving, the patch part was swept at a speed of 1 cm / second while pressing with a weight of 10 mm in diameter and a load of 200 g so that the surface of Bencott M-3 (manufactured by Asahi Kasei) was rubbed with a rubbing cloth. Each patch portion after rubbing and the rubbing surface of Bencott were visually observed and judged based on the following evaluation criteria.
A: No rubbing marks due to cloth rubbing are observed.
B: Although rubbing traces are observed, no dirt is observed on the cloth surface.
C: Scratch marks are observed, and a slight stain is observed on the cloth surface.
D: Scratch marks are observed, and a large amount of dirt is observed on the cloth surface.

(2) Line Marker Test Each ink prepared was filled in an ink jet printer PX-A550 (manufactured by Seiko Epson), and a 24 point character pattern was recorded on a recording medium (Xerox 4200). The obtained sample was allowed to stand for 24 hours in a normal temperature and normal humidity environment (temperature 20 ° C., humidity 65%). After standing, the printed characters were rubbed at a writing pressure of 300 g / 15 mm using a yellow aqueous fluorescent pen ZEBRA PEN2 (registered trademark) manufactured by Zebra. The recorded characters after rubbing were visually observed and judged based on the following evaluation criteria.
A: When the same part is rubbed twice, no stain is observed.
B: Dirt is not recognized by the first rubbing, but dirt is recognized by the second rubbing.
C: Slight dirt is recognized by the first rubbing.
D: A large amount of dirt is recognized by the first rubbing.

3.2.4. Permanent curl test Each ink prepared was filled in an ink jet printer PX-A550 (manufactured by Seiko Epson), and a 100% duty patch pattern was recorded on a recording medium (XeroxP paper). The obtained sample was allowed to stand on a horizontal flat table for 24 hours in a normal temperature and humidity environment (temperature 20 ° C., humidity 65%). After being allowed to stand, the vertical distances between the horizontal flat table and the four corners of the recording medium were measured at four locations. The average value of the distances was determined as a curl amount based on the following criteria.
A: Curling amount after being left for 24 hours is less than 10 mm B: Curling amount after being left for 24 hours is from 10 mm to less than 30 mm C: Curling amount after being left for 24 hours is from 30 mm to less than 50 mm D: Curling amount after being left for 24 hours 50 mm or more 3.3. Evaluation results The results of the above evaluation tests are shown in Tables 1 and 2 above.

  As shown in the evaluation results of Table 1 and Table 2, each of the water-based inks according to the examples can reduce the deformation of the recording medium and record an image excellent in color development, glossiness and abrasion resistance. did.

  On the other hand, the water-based ink according to Comparative Example 1 does not contain the first resin. As a result, the glossiness and rub resistance of the recorded image decreased.

  Since the water-based ink according to Comparative Example 2 did not contain the second resin, the recorded image was not excellent in abrasion resistance.

  Further, since the water-based ink according to Comparative Example 3 does not contain the zwitterionic compound, the occurrence of curling of the recording medium becomes remarkable. Further, in the water-based ink according to Comparative Example 3, since the zwitterionic compound was not added, the amount of water was increased in anticipation of the evaporation of the water in the ink. For this reason, it is considered that the pigment permeates into the recording medium together with the moisture in the ink and the color developability is lowered.

  The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

Claims (8)

A self-dispersing pigment,
A first resin having a weight average molecular weight of 1,000 to 30,000;
A second resin having a weight average molecular weight of more than 30,000 and not more than 300,000;
Zwitterionic compounds,
water and,
A water-based ink for inkjet recording, comprising: In claim 1,
Sum of content [M _A (mass%)] of the zwitterionic compound, content [M ₁ (mass%)] of the first resin and content [M ₂ (mass%)] of the second resin _A water-based ink for inkjet recording, wherein the difference [M _A − (M ₁ + M ₂ )] between [M ₁ + M ₂ (mass%)] is 5 or more. In claim 1 or claim 2,
The water-based ink for inkjet recording whose glass transition temperature (Tg) of said 2nd resin is -40 degreeC or more and 80 degrees C or less. In any one of Claims 1 thru | or 3,
A water-based ink for ink-jet recording, wherein the first resin is an alkali-soluble resin. In any one of Claims 1 thru | or 4,
An aqueous ink for inkjet recording, wherein the zwitterionic compound is a betaine compound. In any one of Claims 1 thru | or 5,
An aqueous ink for inkjet recording, wherein the content [M _A (mass%)] of the zwitterionic compound is 8 mass% or more and 40 mass% or less. In any one of Claims 1 thru | or 6,
The content ratio (M _A / M ₁ ) between the content [M _A (% by mass)] of the zwitterionic compound and the content [M ₁ (% by mass)] of the first resin is 6 or more and 14 or less. A water-based ink for inkjet recording. In any one of Claims 1 thru | or 7,
The content ratio (M ₂ / M ₁ ) between the content [M ₂ (mass%)] of the second resin and the content [M ₁ (mass%)] of the first resin is 1 or more and 4 or less. A water-based ink for inkjet recording.