JP2015120918A - Ink set and recording method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink set that has good color reproducibility, good discharge stability, and good recovery property from clogging, and particularly achieves good color developability on a plain paper in high-speed printing and color developability on an exclusive paper, suppresses cockling and curling, and can give an image with improved fixability on a plain paper and scratch resistance on an exclusive paper.SOLUTION: The ink set includes at least a cyan ink composition, a magenta ink composition, and a yellow ink composition. The yellow ink composition comprises a pigment coated with a water-insoluble polymer; an ink composition other than the yellow ink composition comprises a self-dispersion type pigment; and all of the ink compositions comprise a resin emulsion. The ink set is used for an inkjet recording method.

Description

Background of the Invention

The present invention relates to an ink set comprising at least a cyan ink composition, a magenta ink composition, and a yellow ink composition, or an ink jet recording method for performing printing by attaching an ink composition to a recording medium.

BACKGROUND ART An ink jet recording method is a printing method in which printing is performed by causing ink droplets to fly and adhere to a recording medium such as paper. As the ink, generally, various water-soluble dyes dissolved in water or water and a water-soluble organic solvent are used. It has been generally pointed out that an image formed with an ink containing such a water-soluble dye is inferior in water resistance and light resistance.

  On the other hand, an ink obtained by dispersing a pigment in an aqueous medium is excellent in water resistance and light resistance. For example, an aqueous pigment ink in which a pigment is dispersed with a surfactant or a polymer dispersant has been proposed. However, in these inks, when the ink content of the colorant is increased in order to increase the print density of the recorded matter, the ink viscosity may increase rapidly accordingly. In addition, in order to disperse the pigment stably in the ink, an excessive surfactant or polymer dispersant is required, which may cause deterioration of printing stability due to generation of bubbles or deterioration of defoaming property. It was.

  In order to solve these problems, a certain amount or more of surface active hydrogen or a salt thereof is introduced on the surface of the pigment, and even if there is no dispersant such as a surfactant or a polymer dispersant, the pigment is dispersed in an aqueous solvent alone. Self-dispersing pigment dispersions that can be made are disclosed.

  In JP-A-10-237349 (Patent Document 1), JP-A-8-3498 (Patent Document 2), and International Publication No. 01/94476 (Patent Document 3), a dispersant as described above is required. The so-called self-dispersing pigments, when used in ink as a colorant, increase the OD value (optical density) of the image, and are easy to handle because it is easy to adjust the viscosity in the ink to an appropriate range. Furthermore, it is said that it is not necessary to consider the compatibility between the dispersant and various added solvents. A hydrophilic functional group such as a carbonyl group, a carboxyl group, a hydroxyl group, a sulfone group, or an ammonium group is bonded to the pigment surface directly or indirectly through an alkyl group, an aryl group, or the like.

  As an ink set including a so-called self-dispersing pigment, for example, in Japanese Patent Laid-Open No. 2002-121434 (Patent Document 4), a black ink is provided, and a cyan ink, a magenta ink, and a yellow ink are further provided as color inks. Further, there is disclosed an aqueous color ink set for ink-jet recording, wherein the black ink and each of the color inks contain a self-dispersible pigment in water. However, there is no disclosure of an ink set in which only the yellow ink composition includes a pigment coated with a water-insoluble polymer.

  Further, in JP 2009-256605 A (Patent Document 5), the black ink composition contains a self-dispersing pigment having a hydrophilic group on its surface, and the color ink composition has a hydrophilic group via a phenyl group on its surface. An ink set is disclosed comprising a self-dispersing pigment having: However, there is no disclosure of an ink set in which only the yellow ink composition includes a pigment coated with a water-insoluble polymer.

  Furthermore, JP 2007-51176 A (Patent Document 6) discloses an ink set including a black ink composition containing a self-dispersing pigment and a color ink composition containing an organic pigment coated with a water-insoluble polymer. ing. However, an ink set including at least a cyan ink composition, a magenta ink composition, and a yellow ink composition, in which only the yellow ink composition includes a pigment coated with a water-insoluble polymer is completely disclosed. Absent.

  On the other hand, there is a problem that an image using an ink having such a self-dispersing pigment as a colorant generally has poor fixability. When the image is rubbed with a finger, a line marker, paper, or the like, a recorded matter may not be obtained with sufficient scratch resistance that the image becomes dirty. In addition, in the case of an image with an ink using a pigment coated with a water-insoluble polymer as a colorant, particularly when the pigment is contained in a high concentration in the ink composition, as in the case of the self-dispersing pigment, the fixability and abrasion resistance are increased. Sexuality may not be sufficient. Therefore, in order to improve the fixability of the pigment to the recording medium as described above, a proposal has been made to add a resin having a binding effect to the ink composition.

  Japanese Patent Application Laid-Open No. 2001-81366 (Patent Document 7) and Japanese Patent Application Laid-Open No. 2002-80761 (Patent Document 8) disclose a recording liquid comprising a colorant, resin fine particles, and water as an ink composition containing resin particles, A recording liquid for an ink printer composed of an aqueous dispersion of pigment and resin fine particles has been proposed.

  Further, in JP 2009-256606 A (Patent Document 9), the black ink composition contains a self-dispersing pigment having a hydrophilic group on its surface, and the color ink composition has a hydrophilic group via a phenyl group on its surface. An ink set is disclosed that includes a self-dispersing pigment having a water content and includes a resin emulsion in all ink compositions. However, there is no disclosure of an ink set in which only the yellow ink composition includes a pigment coated with a water-insoluble polymer.

Japanese Patent Laid-Open No. 10-237349 JP-A-8-3498 WO 01/94476 pamphlet JP 2002-121434 A JP 2009-256605 A JP 2007-51176 A JP 2001-81366 A Japanese Patent Laid-Open No. 2002-80761 JP 2009-256606 A

  The present inventors are now an ink set including at least a cyan ink composition, a magenta ink composition, and a yellow ink composition, the yellow ink composition comprising a pigment coated with a water-insoluble polymer, Ink sets other than the yellow ink composition contain self-dispersing pigments, and all ink compositions contain a resin emulsion, thereby providing good color reproducibility and good ejection stability. In addition to good clogging recovery, especially good color development on high-speed printing and special paper color development are compatible, cockling and curling are suppressed, and plain paper fixing and special paper are also available. It was found that an image with improved rub resistance can be realized. The present invention is based on these findings.

  Therefore, the present invention has both good color reproducibility, good ejection stability, and good clogging recovery, as well as good plain paper color development and special paper color development particularly during high-speed printing, An object of the present invention is to provide an ink set that can suppress cockling and curling and can realize an image in which the fixing property of plain paper and the abrasion resistance of special paper are improved.

  The ink set according to the present invention is an ink set including at least a cyan ink composition, a magenta ink composition, and a yellow ink composition, wherein the yellow ink composition includes a pigment coated with a water-insoluble polymer. Thus, the ink composition other than the yellow ink composition includes a self-dispersing pigment, and all the ink compositions include a resin emulsion.

  According to the present invention, in addition to good color reproducibility, good ejection stability, and good clogging recovery, in particular, both good color development on plain paper and color development on special paper at the time of high-speed printing, It is possible to provide an ink set capable of suppressing cockling and curling and realizing an image in which the fixing property of plain paper and the abrasion resistance of special paper are improved.

Detailed description of the invention

  An ink set according to the present invention is an ink set including at least a cyan ink composition, a magenta ink composition, and a yellow ink composition, the yellow ink composition comprising a pigment coated with a water-insoluble polymer, The ink composition other than the ink composition contains a self-dispersing pigment, and all the ink compositions contain a resin emulsion. Hereinafter, the yellow ink composition, the ink composition other than the yellow ink composition, the resin emulsion, and the like constituting the ink set according to the present invention will be described.

  Here, “plain paper” in the present invention refers to paper represented by PPC paper that does not particularly take into consideration ink jet recording characteristics. The “special paper” refers to a recording medium for ink jet recording in which an ink receiving layer is provided on a base material such as fine paper, and the ink receiving layer contains a water-soluble resin such as polyvinyl alcohol. These include both a so-called “swelling type” and a so-called “absorption type” in which a porous material such as amorphous silica is contained in the ink receiving layer.

Yellow Ink Composition The yellow ink composition that can be used in the present invention comprises a pigment coated with a water-insoluble polymer.

  The water-insoluble polymer is a polymer obtained by polymerization by a solution polymerization method using at least a polymerizable unsaturated monomer and a polymerization initiator, and the water-insoluble polymer refers to 100 g of water at 25 ° C. after neutralization. A polymer having a solubility of less than 1 g.

  Examples of the polymerizable unsaturated monomer include vinyl aromatic hydrocarbons, methacrylic acid esters, methacrylamide, alkyl-substituted methacrylamide, maleic anhydride, vinyl cyanide compounds, methyl vinyl ketone, and vinyl acetate. Specifically, styrene, α-methylstyrene, vinyl toluene, 4-t-butyl styrene, chlorostyrene, vinyl anisole, vinyl naphthalene, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n- There are amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, glycidyl methacrylate, acrylonitrile, methacrylonitrile, etc. Use alone or in combination of two or more It is also possible.

  Further, the water-insoluble polymer preferably contains a monomer having a hydrophilic group and a monomer having a salt-forming group in order to impart gloss to the printed image.

  Examples of the monomer having a hydrophilic group include polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, and ethylene glycol / propylene glycol monomethacrylate, which can be used alone or in admixture of two or more. In particular, polyethylene glycol (2-30) monomethacrylate, polyethylene glycol (1-15) / propylene glycol (1-15) monomethacrylate, polypropylene glycol (2-30) methacrylate, methoxypolyethylene glycol (2-30) methacrylate, methoxy The gloss of printed images is further improved by using monomer components that constitute branched chains such as polytetramethylene glycol (2-30) methacrylate and methoxy (ethylene glycol / propylene glycol copolymer) (1-30) methacrylate. To do.

  Monomers having a salt-forming group include acrylic acid, methacrylic acid, styrene carboxylic acid, maleic acid and the like, and each can be used alone or in admixture of two or more.

  Furthermore, a macromonomer such as a styrene macromonomer or a silicone macromonomer having a polysynthetic functional group at one end, or other monomers can be used in combination.

  In the polymerization, a known radical polymerization agent or polymerization chain transfer agent may be added as a polymerization initiator. Examples of the polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2,3-dimethylbutyro). Nitrile), 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2,3,3-trimethylbutyronitrile), 2,2′-azobis (2-isopropylbutyronitrile) ), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2- (carbamoylazo) isobutyronitrile, 4, 4'-azobis (4-cyanovaleric acid), and dimethyl-2,2'-azobisisobutyrate, or peroxide compounds such as butyl peroxide, propyl Oxides, butyryl peroxide, benzoylisobutyryl peroxide, and benzoyl peroxide, or water-soluble polymerization initiators such as potassium persulfate, ammonium persulfate, sodium persulfate, 2,2′-azobis (2-methylpropionamidine) Examples thereof include dihydrochloride and 4,4′-azobis (4-cyanovaleric acid). In addition, a redox initiator in which potassium persulfate, ammonium persulfate, sodium persulfate, and the like are combined with sodium sulfite, sodium hyposulfite, ferrous sulfate, or the like can also be used. The amount of the polymerization initiator is preferably 0.001 mol to 5 mol, more preferably 0.01 mol to 2 mol, per mol of the monomer mixture. In the polymerization, a known polymerization chain transfer agent such as mercaptans such as octyl mercaptan and 2-mercaptoethanol and thiuram disulfide may be further added.

  The organic pigment coated with the water-insoluble polymer is obtained by a phase inversion emulsification method. That is, the above water-insoluble polymer is dissolved in an organic solvent such as methanol, ethanol, isopropanol, n-butanol, acetone, methyl ethyl ketone, dibutyl ether, an organic pigment is added to the resulting solution, and then a neutralizer and water are added. By adding, kneading and dispersing, an oil-in-water type dispersion is prepared, and an organic solvent is removed from the obtained dispersion to obtain an aqueous dispersion. For the kneading and dispersing treatment, for example, a ball mill, a roll mill, a bead mill, a high-pressure homogenizer, a high-speed stirring type disperser, or the like can be used.

  The neutralizing agent is preferably a tertiary amine such as ethylamine or trimethylamine, lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia or the like, and the pH of the resulting aqueous dispersion is preferably 6-10.

  The water-insoluble polymer to be coated is preferably a polymer having a weight average molecular weight of about 10,000 to 150,000 from the viewpoint of stably dispersing a colorant, particularly a pigment. The weight average molecular weight can be measured by a molecular weight analysis method by gel permeation chromatography (GPC).

  The yellow ink composition used in the present invention preferably comprises 60 to 10% by mass of water, a water-soluble organic solvent, and a surfactant with respect to the ink composition.

  By defining the water content in the yellow ink composition within the above range, the amount of water absorbed by the cellulose in the coated paper is less than in conventional ink compositions, resulting in cockling and curling. Swelling of cellulose considered to be the cause can be suppressed. Therefore, the ink composition of the present embodiment is also useful for a recording medium having an absorbent layer of a paper support having poor ink absorbability, such as plain paper or coated paper for printing (printing paper).

  Examples of pigments used as a raw material for the pigment coated with the water-insoluble polymer of the yellow ink composition of the present invention include pigments such as pigment yellow described in the color index, and pigments such as azo and condensed ring systems. it can. In addition, organic pigments such as Yellow No. 4, No. 5, No. 205, No. 401 and the like can be mentioned. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42, 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 128, 138, 150, 153, 155, 174, 180, 198, in particular, the organic pigment contained in the yellow ink composition is C.I. I. It is preferable to include at least one selected from the group consisting of CI Pigment Yellow 74, 109, 110, 128, 138, 147, 150, 155, 180, and 188.

  The pigment coated with the water-insoluble polymer in the yellow ink composition is preferably contained in an amount of 6% by mass or more. When the pigment concentration is 6% by mass or more, the recorded matter is highly colored.

  The water contained in the yellow ink composition of the present invention 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 to enable long-term storage of the ink composition.

  In the present invention, examples of the water-soluble organic compound include glycerin, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, diethylene Propylene glycol, 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, 1,2-hexanediol, 1,2 -Polyhydric alcohols such as pentanediol and 4-methyl-1,2-pentanediol, glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid, glucitol, (sorbitol), maltose Sugars such as cellobiose, lactose, sucrose, trehalose, maltotriose, so-called solid wetting agents such as sugar alcohols, hyaluronic acids, ureas, etc., alkyl alcohols having 1 to 4 carbon atoms such as ethanol, methanol, butanol, propanol, isopropanol , 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, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, Diethylene glycol mono-iso-propyl ether, ethylene glycol mono- -Butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono- Glycol ethers such as n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone Formamide, acetamide, dimethyl sulfoxide, sorbitol, sorbitan, acetin, diacetin, triacetin, sulfolane, and the like, may be used alone or in combination. These water-soluble organic solvents may be contained in the yellow ink composition in an amount of 10 to 90% by mass from the viewpoint of ensuring proper physical properties (such as viscosity) of the yellow ink composition, printing quality, and reliability. preferable. By including these water-soluble organic solvents in the yellow ink composition of the present invention, the storage stability and ejection stability are good even at a high solid content.

  Furthermore, in the present invention, at least a polyhydric alcohol, a butyl ether of glycol, and a pyrrolidone are used in combination as a water-soluble organic solvent, thereby providing excellent reliability such as print quality, ejection stability, and clogging recovery. It is preferable because a yellow ink composition can be provided. This is because polyhydric alcohols are suitable for controlling water retention (humidity) and penetrability of yellow ink composition into recording media such as plain paper, and glycol butyl ethers are suitable for ejection stability and recording media. It is suitable for controlling the permeability of the ink composition, and it has been found that pyrrolidones greatly contribute to ejection stability, storage stability and color development of the ink composition, polyhydric alcohols and glycol butyl ethers By using together with pyrrolidones, it is possible to provide a more reliable yellow ink composition such as print quality, ejection stability, and clogging recovery.

  Furthermore, in the embodiment of the present invention, the water-soluble organic solvent preferably contains 5% by mass or more of polyhydric alcohol monoalkyl ether and / or nitrogen-containing cyclic compound and contains polyhydric alcohols. By using such a water-soluble organic solvent, cockling and curling can be suppressed, and printing quality such as bleeding and unevenness can be ensured.

  Here, as the polyhydric alcohol monoalkyl ether, among the above glycol ethers, for example, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoisopropyl ether, dipropylene Examples thereof include glycol monoisopropyl ether, dipropylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol monobutyl ether. Examples of the nitrogen-containing cyclic compound include 1 , 3-Dimethyl-2-imidazolidinone, 2-pyrrolide , N- methyl-2-pyrrolidone, .epsilon.-caprolactam, and the like.

  In addition, the polyhydric alcohol can be any of the above polyhydric alcohols, and in particular, 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, etc. Of 1,2-alkanediol.

  The surfactant contained in the yellow ink composition of the present invention can contain an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant. A nonionic surfactant is particularly preferable from the viewpoint of obtaining an ink composition with less foaming and foaming.

  Further specific examples of nonionic surfactants include acetylene glycol surfactants, acetylene alcohol surfactants, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl Ethers such as allyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, polyoxyethylene oleic acid, polyoxyethylene oleic acid ester, polyoxyethylene distearic acid ester , Sorbitan laurate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, polyoxy Esters such as ethylene monooleate and polyoxyethylene stearate, polyether-modified siloxane surfactants such as dimethylpolysiloxane, and other fluorine-containing surfactants such as fluorine alkyl esters and perfluoroalkyl carboxylates Can be mentioned. A nonionic surfactant can also be used 1 type or in combination of 2 or more types.

  According to a preferred embodiment of the present invention, among the nonionic surfactants described above, the yellow ink composition comprising an acetylene glycol surfactant and / or a polyether-modified siloxane surfactant in particular has little foaming, Moreover, it is preferable at the point which has the outstanding defoaming performance.

  Further 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. 3,5-dimethyl-1-hexyne-3ol, etc., but are also available commercially, for example, Surfynol 104, 82, 465, 485 manufactured by Air Products, manufactured by TG and Nisshin Chemical Co., Ltd. Olfin STG, Olfin E1010 and the like. Specific examples of the polyether-modified siloxane surfactant include BYK-345, BYK-346, BYK-347, BYK-348, UV3530, and the like manufactured by Big Chemie Japan. A plurality of these may be used in the ink composition, and the surface tension is preferably adjusted to 20 to 40 mN / m, and contained in the yellow ink composition in an amount of 0.1 to 3.0% by mass.

  The yellow ink composition used in the present invention preferably contains a pH adjuster. As the pH adjuster, alkali hydroxides such as lithium hydroxide, potassium hydroxide and sodium hydroxide and / or alkanolamines such as ammonia, triethanolamine, tripropanolamine, diethanolamine and monoethanolamine can be used. . In particular, it is preferably adjusted to pH 6 to 10 including at least one pH adjusting agent selected from alkali metal hydroxide, ammonia, triethanolamine, and tripropanolamine. When the pH is out of this range, the material constituting the ink jet printer is adversely affected, and the clogging recovery property is deteriorated.

  If necessary, collidine, imidazole, phosphoric acid, 3- (N-morpholino) propanesulfonic acid, tris (hydroxymethyl) aminomethane, boric acid and the like can be used as a pH buffering agent.

  Furthermore, an antifoaming agent, an antioxidant, an ultraviolet absorber, an antiseptic / antifungal agent, and the like can be added to the yellow ink composition used in the present invention as necessary.

  Antioxidants and ultraviolet absorbers include allophanates such as allophanate and methyl allophanate, biurets such as biuret, dimethylbiuret and tetramethylbiuret, L-ascorbic acid and its salts, etc., Tinuvin 328, 900 manufactured by Ciba Geigy 1130, 384, 292, 123, 144, 622, 770, 292, Irgacor 252, 153, Irganox 1010, 1076, 1035, MD1024, or the like, or a lanthanide oxide or the like is used.

  Examples of antiseptics and fungicides include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, 1,2-dibenzisothiazolin-3-one ( Avecia's Proxel CRL, Proxel BDN, Proxel GXL, Proxel XL-2, Proxel TN) and the like.

Ink composition other than yellow ink composition The ink set of the present invention includes at least a cyan ink composition and a magenta ink composition, and the ink composition other than these yellow ink compositions includes a self-dispersing pigment. . According to a preferred embodiment of the present invention, the ink set of the present invention further includes a black ink composition containing a self-dispersing pigment as an ink composition other than the yellow ink composition.

  Self-dispersing pigments are pigments that can be dispersed and / or dissolved in an aqueous medium without a dispersant. Here, “dispersed and / or dissolved in an aqueous medium without a dispersing agent” means that the surface is stably present in the aqueous medium due to the hydrophilic group on the surface without using a dispersing agent for dispersing the pigment. The state that is.

  The ink containing the self-dispersing pigment as a colorant does not need to contain a dispersant as described above in order to disperse a normal pigment. Therefore, there is almost no foaming due to a decrease in defoaming property due to the dispersant, and an ink excellent in ejection stability can be easily prepared. In addition, since a significant increase in viscosity due to the dispersant can be suppressed, it is possible to contain more pigment, and the printing density can be sufficiently increased.

The ink composition other than the yellow ink composition of the present invention is a self-dispersing pigment having a hydrophilic group on the pigment surface, and the hydrophilic group includes -OM, -COOM, -CO-, -SO ₃ M,- SO ₂ M, —SO ₂ NH ₂ , —RSO ₂ M, —PO ₃ HM, —PO ₃ M ₂ , —SO ₂ NHCOR, —NH ₃ , and —NR ₃ (wherein M is a hydrogen atom, an alkali Represents a metal, ammonium, an optionally substituted phenyl group, or organic ammonium, and R represents an alkyl group having 1 to 12 carbon atoms or an optionally substituted naphthyl group. One or more hydrophilic groups selected from the group consisting of

  A self-dispersing pigment of an ink composition other than the yellow ink composition is produced, for example, by bonding (grafting) the hydrophilic group to the surface of the pigment by subjecting the pigment to physical treatment or chemical treatment. . Examples of the physical treatment include vacuum plasma treatment. Examples of the chemical treatment include a wet oxidation method of oxidizing with an oxidizing agent in water, a method of binding a carboxyl group via a phenyl group by binding p-aminobenzoic acid to the pigment surface, and the like.

  In the present invention, when the pigment used as the raw material for the self-dispersing pigment of the ink composition other than the yellow ink composition is other than the black ink composition, the hydrophilic group is bonded to the pigment surface via a phenyl group. Self-dispersing pigments having a colorant are preferred in terms of high color development. As the surface treatment means for bonding a hydrophilic group to the pigment surface via a phenyl group, various known surface treatment means can be applied, and sulfanilic acid, p-aminobenzoic acid, 4-aminosalicylic acid and the like can be applied to the pigment surface. Examples thereof include a method of bonding a hydrophilic group via a phenyl group. In the case where the ink set of the present invention contains a black ink composition, the case where the pigment used as the raw material for the self-dispersing pigment of the ink composition other than the yellow ink composition is a black ink composition. Self-dispersing pigments that have been surface-treated by an oxidation treatment with a halogen acid and / or hypohalite, an oxidation treatment with ozone, or an oxidation treatment with persulfuric acid and / or persulfate are preferred in terms of high color development.

  In addition, pigment red, pigment violet, pigment blue, etc., described in the color index, when the pigment used as the raw material of the self-dispersing pigment of the ink composition other than the yellow ink composition is other than the black ink composition, etc. In addition to these pigments, phthalocyanine-based, azo-based, anthraquinone-based, azomethine-based and condensed ring-based pigments can be exemplified. In addition, organic pigments such as orange No. 228, 405, blue No. 1 and 404, and inorganic pigments such as titanium oxide, zinc oxide, zirconium oxide, iron oxide, ultramarine blue, bitumen, and chromium oxide can be mentioned. For example, C.I. I. Pigment red 1,3,5,8,9,16,17,19,22,38,57: 1,90,112,122,123,127,146,184, C.I. I. Pigment Bio Red 1,3,5: 1, 16, 19, 23, 38, C.I. I. And CI pigment blue 1, 2, 15, 15: 1, 15: 2, 15: 3, 15: 4, and 16. The ink set of the present invention comprises a cyan ink composition and a magenta ink composition as essential ink compositions. In particular, organic pigments contained in the magenta ink composition include C.I. I. Pigment red 122, 202, 207, 209, and C.I. I. The organic pigment contained in the cyan ink composition preferably contains at least one selected from the group consisting of CI Pigment Violet 19. I. It is preferable to include at least one selected from the group consisting of CI Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, and 16.

  When the black ink composition is contained in the ink set of the present invention, the case where the pigment used as the raw material of the self-dispersing pigment of the ink composition other than the yellow ink composition is a black ink composition, for example, contact method Carbon black produced by a known method such as a furnace method or a thermal method can be used. Specific examples of preferred carbon black in the present invention include No. 2300, 900, MCF88, no. 20B, no. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, No2200B (Mitsubishi Chemical Corporation), Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Pretex 35, U, V, 140U, Special Black 6 5, 4A, 4, 250 (above Degussa), Conductex SC, Raven 1255, 5750, 5250, 5000, 3500, 1255, 700 (above Columbia Carbon), Regal 400R, 330R, 660R, Mogul L , Monarch 700, 800, 880, 900, 1000, 1100, 1300, 1400, Elftex 12 (manufactured by Cabot Corporation), and the like. These carbon blacks may be used alone or as a mixture of two or more.

  Commercially available products can also be used as the self-dispersing pigment for ink compositions other than the yellow ink composition. For example, Microjet CW1 (manufactured by Orient Chemical Co., Ltd.), CAB-O-JET250C, CAB -O-JET260M (manufactured by Cabot Corporation) and the like.

  The self-dispersing pigment in the ink composition other than the yellow ink composition is preferably contained in an amount of 6% by mass or more. When the pigment concentration in the ink composition other than the yellow ink composition is 6% by mass or more, the recorded matter is highly colored.

  The self-dispersing pigment preferably has an average particle size in the range of 50 to 250 nm from the viewpoints of ink storage stability and prevention of nozzle clogging.

  In addition, the ink composition other than the yellow ink composition according to the present invention includes at least 60 to 10% by mass of water, a water-soluble organic solvent, an interface, as in the case of the yellow ink composition. It preferably comprises an active agent. These specific examples and the addition amount thereof may be the same as those of the yellow ink composition.

  Further, in the ink composition other than the yellow ink composition according to the present invention, as in the case of the yellow ink composition, a pH adjuster, a pH buffering agent, an antifoaming agent, an antioxidant, and an ultraviolet absorber are optionally included. Antiseptic / antifungal agents can be added. These specific examples may be the same as those of the yellow ink composition.

Resin Emulsion Resin emulsion improves the fixability of the image portion of the recorded matter because the resin particles and the resin particles and the coloring component fuse together to fix the colorant to the recording medium as the ink dries. have.

  These resin particles are preferably one or more selected from the group consisting of acrylic resins, methacrylic resins, styrene resins, urethane resins, acrylamide resins, and epoxy resins. These resins may be used as homopolymers or as copolymers.

  In the present invention, resin particles having a single particle structure can be used. On the other hand, in the present invention, it is also possible to use resin particles having a core / shell structure including a core portion and a shell portion surrounding the core portion. In the present invention, the “core / shell structure” means “a form in which two or more polymers having different compositions are present in phase separation in the particles”. Therefore, the shell portion may not only cover the core portion completely, but may cover a portion of the core portion. Further, a part of the shell polymer may form a domain or the like in the core particle. Further, it may have a multilayer structure of three or more layers including one or more layers having different compositions between the core portion and the shell portion.

  The resin particles used in the present invention can be obtained by known emulsion polymerization. That is, it can be obtained by emulsion polymerization of an unsaturated vinyl monomer (unsaturated vinyl monomer) in water in the presence of a polymerization catalyst and an emulsifier.

  As unsaturated vinyl monomers, acrylic acid ester monomers, methacrylic acid ester monomers, aromatic vinyl monomers, vinyl ester monomers, vinyl, which are generally used in emulsion polymerization Cyanide monomers, halogenated monomers, olefin monomers, diene monomers and the like can be mentioned.

  Further, specific examples include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, decyl acrylate, dodecyl acrylate. Acrylates such as octadecyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, glycidyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl Methacrylate, 2-ethyl Hexyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, cyclohexyl methacrylate, methacrylic esters such as phenyl methacrylate, benzyl methacrylate, glycidyl methacrylate, vinyl esters such as vinyl acetate, vinyl such as acrylonitrile, methacrylonitrile, etc. Cyanogen compounds, halogenated monomers such as vinylidene chloride and vinyl chloride, aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, t-butylstyrene, chlorostyrene, vinylanisole and vinylnaphthalene , Olefins such as ethylene and propylene, dienes such as butadiene and chloroprene, vinyl ether, vinyl ketone, vinyl pyrrolidone Vinyl monomers such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and other unsaturated carboxylic acids, acrylamide and N, N′-dimethylacrylamide and other acrylamides, 2-hydroxyethyl acrylate, 2 -Hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and hydroxyl group-containing monomers such as 2-hydroxypropyl methacrylate.

Moreover, in this invention, what has the structure bridge | crosslinked by the crosslinkable monomer which has two or more polymerizable double bonds can be used as a molecule | numerator derived from the said monomer.
Examples of the crosslinkable monomer having two or more polymerizable double bonds include polyethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,6-butylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, 1,9-nonanediol diacrylate, polypropylene glycol diacrylate, 2,2′-bis (4-acryloxypropyloxyphenyl) propane, 2,2 ′ -Diacrylate compounds such as bis (4-acryloxydiethoxyphenyl) propane, triacrylate compounds such as trimethylolpropane triacrylate, trimethylolethane triacrylate, tetramethylolmethane triacrylate Tetraacrylate compounds such as ditrimethylol tetraacrylate, tetramethylol methane tetraacrylate, pentaerythritol tetraacrylate, hexaacrylate compounds such as dipentaerythritol hexaacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol di Methacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, polybutylene glycol dimethacrylate Methacrylate, 2, Examples include dimethacrylate compounds such as 2′-bis (4-methacryloxydiethoxyphenyl) propane, trimethacrylate compounds such as trimethylolpropane trimethacrylate and trimethylolethane trimethacrylate, methylenebisacrylamide, and divinylbenzene. Or 2 or more types can be mixed and used.

  Moreover, the polymerization initiator, the emulsifier, and the molecular weight modifier used in the emulsion polymerization can be used according to a conventional method.

  As the polymerization initiator, those used for normal radical polymerization are used, for example, potassium persulfate, ammonium persulfate, hydrogen peroxide, azobisisobutyronitrile, benzoyl peroxide, dibutyl peroxide, Examples include peracetic acid, cumene hydroperoxide, t-butyl hydroxy peroxide, paramentane hydroxy peroxide, and the like. In particular, as described above, when the polymerization reaction is performed in water, a water-soluble polymerization initiator is preferable.

  Examples of the emulsifier include sodium lauryl sulfate, those generally used as anionic surfactants, nonionic surfactants, or amphoteric surfactants, and mixtures thereof. These may be used alone or in combination of two or more. Can be used as a mixture.

  When the resin particles are produced by emulsion polymerization, particularly when a polymer emulsion composed of anionic resin particles is produced by emulsion polymerization, negative polar groups such as carboxyl groups and sulfonic acid groups are formed on the resin particle surface. Is present, the pH is inclined to the acidic side, and viscosity increases and aggregation tends to occur. Therefore, neutralization with a basic substance is usually performed. As this basic substance, ammonia, organic amines, inorganic hydroxides and the like can be used. Of these, monovalent inorganic hydroxides (potassium hydroxide, sodium hydroxide, lithium hydroxide) are particularly preferred from the viewpoints of long-term storage stability and ejection stability of the polymer emulsion and aqueous ink composition. The addition amount of the neutralizing agent is appropriately determined so that the pH of the polymer emulsion is in the range of 7.5 to 9.5, preferably in the range of 7.5 to 8.5.

  From the viewpoints of long-term storage stability and ejection stability of the ink composition, the resin particles preferably used in the present invention have a particle size in the range of 5 to 400 nm, more preferably in the range of 50 to 200 nm.

  The addition amount of these resin emulsions may be appropriately determined in consideration of fixability and the like, but each ink composition preferably contains 2% by mass or more in terms of solid content.

Ink Set The ink set according to the present invention can be configured in the same manner as a conventionally known ink set, and can be used as various conventionally known inks for recording methods. In particular, in the present invention, a high-resolution and high-quality image can be printed at a high speed with a relatively inexpensive apparatus, so that a small droplet of ink is ejected and adhered to a recording medium such as paper. Therefore, it is suitable for an application for printing.

Inkjet recording method The inkjet recording method using the ink set of the present invention is to perform printing by ejecting droplets of an ink composition and attaching the droplets to a heated recording medium. As an example of a method for ejecting droplets of each ink composition, for example, an electrostrictive element is used to convert an electrical signal into a mechanical signal, and ink stored in the nozzle head portion is intermittently ejected to record the surface of the recording medium. A method for recording characters and symbols on the surface of the recording medium, by rapidly heating the ink stored in the nozzle head part at a location very close to the ejection part, generating bubbles, and ejecting them intermittently by the volume expansion caused by the bubbles. There is a method of recording characters and symbols. According to a preferred aspect of the present invention, the ink set according to the present invention is preferably used in an ink jet recording method using an electrostrictive element. It is preferable that the ink composition droplets be ejected by a recording head that ejects ink droplets using the mechanical action of the piezoelectric element.

  According to a preferred aspect of the present invention, particularly when printing on dedicated paper, a droplet of the yellow ink composition used in the present invention is ejected to print a recording medium in any hue. Can be recorded. By recording in this way, it is possible to improve the glossiness and color developability of the special paper.

  The recorded matter recorded on the recording medium using the ink set according to the present invention can achieve high color development on both plain paper and exclusive paper, particularly at high-speed printing, and can further reduce cockling and curling. realizable

  Various recording media can be used, and examples thereof include ink jet dedicated paper (matte paper, glossy paper, etc.), plain paper, printing paper, and film.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Water-insoluble polymer coating pigment
Preparation of Yellow Pigment Dispersion 1 A colorant dispersion having dispersed particles of a colorant coated with a water-insoluble polymer was prepared by the following method.

(Synthesis of water-insoluble polymer)
In a reaction vessel sufficiently substituted with nitrogen gas using 20 parts by mass of an organic solvent (methyl ethyl ketone), 0.03 parts by mass of a polymerization chain transfer agent (2-mercaptoethanol), a polymerization initiator, and each monomer shown in Table 1. The mixture was polymerized with stirring at 75 ° C., 0.9 part by mass of 2,2′-azobis (2,4-dimethylvaleronitrile dissolved in 40 parts by mass of methyl ethyl ketone was added to 100 parts by mass of the monomer component, and The polymer solution was aged for 1 hour, and the numerical values shown in Table 1 mean the ratio (%) of each monomer based on the total amount of the monomer mixture (100%).

(Preparation of pigment dispersion)
7.5 parts by mass of the water-insoluble polymer shown in Table 1 is dissolved in 45 parts by mass of methyl ethyl ketone, and a predetermined amount of 20% aqueous sodium hydroxide solution (neutralizing agent) is added to neutralize the salt-forming groups. As a pigment, C.I. I. 20 parts by mass of Pigment Yellow 74 was added and kneaded in a bead mill for 2 hours. After adding 120 parts by mass of ion-exchanged water to the kneaded product thus obtained and stirring, methyl ethyl ketone is removed at 60 ° C. under reduced pressure, and a part of the water is further removed, so that the solid content concentration is 20%. A mass% yellow pigment dispersion 1 was obtained.

Self-dispersing pigment
Preparation of Cyan Pigment Dispersion 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. It was. Then, this was changed to the above C.I. I. Pigment Blue 15: 4 and o-acetanisidide 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% As a result, a cyan pigment dispersion was obtained.

As a preparation pigment of a magenta pigment dispersion , C.I. I. Pigment Blue 15: 4 instead of C.I. I. Except for using Pigment Red 122, a magenta pigment dispersion having a solid concentration of 20% by mass was prepared in the same manner as the cyan pigment dispersion.

As a preparation pigment of Yellow Pigment Dispersion Liquid 2, 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, and a yellow pigment dispersion 2 having a solid content concentration of 20% by mass was obtained.

Preparation of Black Pigment Dispersion Solution 20 g of commercially available carbon black S170 (manufactured by Degussa) was mixed with 500 g of water and dispersed with a home mixer for 5 minutes. The obtained liquid was put into a 3 liter glass container equipped with a stirrer, and an ozone-containing gas having an ozone concentration of 8% by mass was introduced at 500 mL / min while stirring with a stirrer. At this time, the ozone generator generated ozone using an electrolytic generation type ozonizer manufactured by Permerex Electrode. The obtained dispersion stock solution is filtered with a glass fiber filter paper GA-100 (manufactured by Advantech Toyo Co., Ltd.), and further concentrated while adjusting to pH 9 by adding a 0.1N potassium hydroxide solution until the solid content concentration becomes 20% by mass. To obtain a black pigment dispersion.

Preparation of resin emulsion A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 900 g of ion-exchanged water and 1 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, 365 g of styrene, 545 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 dropping, aging was performed for 3 hours. The obtained resin emulsion was cooled to room temperature, and then ion-exchanged water and an aqueous sodium hydroxide solution were added to adjust the solid content to 40% by mass and pH 8. The glass transition temperature of the resin particles in the obtained aqueous emulsion was −6 ° C.

Preparation of each ink composition Each ink composition was prepared by mixing each component according to the composition of the following Table 2, and filtering with a 10 micrometer membrane filter. The numerical values in Table 2 below represent the content (% by mass) in the ink. Ink sets 1 to 3 were configured as combinations shown in Table 3 below for the obtained ink compositions.

Evaluation method
Evaluation 1: Evaluation of color developability of plain paper Each prepared ink set was filled into an ink jet printer PX-A550 (manufactured by Seiko Epson) which was modified to change the recording method, and cyan, magenta, yellow, black, red, A 100% duty patch pattern including green and blue portions was printed. Printing was performed using Xerox 4200 and Xerox P as recording media, and the obtained sample was left in a general environment for 1 hour. After standing, each patch portion was measured for the OD value of each patch portion using a Gretag densitometer (manufactured by Gretag Macbeth), and the average OD value was determined based on the following criteria. The results are shown in Table 4 below.
AA: OD value is 1.35 or more A: OD value is 1.25 or more and less than 1.35 B: OD value is 1.15 or more and less than 1.25 C: OD value is less than 1.15

Evaluation 2: Evaluation of plain paper fixing property In the same manner as in Evaluation 1, a pattern including solid and characters was printed. The obtained recorded matter was air-dried for 24 hours, and then, using a yellow aqueous fluorescent pen ZEBRA PEN2 (trademark) manufactured by Zebra Corporation, the printed characters were rubbed at a writing pressure of 300 g / 15 mm 2 to check for smudges attached to the pen tip. Was visually observed. The result was determined based on the following criteria. The results are shown in Table 4 below.
A: No dirt is produced even if the same part is rubbed twice. B: No dirt is produced until one rubbing, but dirt is produced by two rubbing. C: Dirt is produced by one rubbing.

Evaluation 3: Evaluation of color development of special paper In the same manner as in Evaluation 1, printing was performed using photographic paper <glossy> (manufactured by Seiko Epson) and photo glossy paper (manufactured by Seiko Epson) as the recording medium. The OD value was measured, and the average OD value was determined based on the following criteria. The results are shown in Table 4 below.
A: OD value is 2.0 or more B: OD value is 1.8 or more and less than 2.0 C: OD value is less than 1.8

Evaluation 4: Evaluation of dedicated paper scratch resistance One hour after printing was performed in the same manner as in Evaluation 3, the printed portion was lightly rubbed with a finger, the change in gloss of the printed surface was visually confirmed, and judged based on the following criteria. The results are shown in Table 4 below.
A: Traces rubbed with fingers cannot be discriminated and there is no change in gloss B: Traces rubbed with fingers can be discerned, but there is almost no gloss change C: Traces rubbed with fingers can be clearly discerned and gloss changes

Evaluation 5: Evaluation of color reproducibility A dedicated output pattern consisting of 400 patches was printed for each ink set prepared using the same ink jet printer as in Evaluation 1. The color of all the patches of the printed material was measured, and the volume in the 3D space of L ^* a ^* b ^* was calculated with a calculation tool. The calculated GumatVolume is dimensionless. The color reproducibility was evaluated based on the following criteria based on the calculated GumatVolume value. The results are shown in Table 4 below.
A: 240,000 or more B: 200,000 or more and less than 240,000 C: Less than 200,000

Evaluation 6: Evaluation of ejection stability Each prepared ink set was filled in an ink jet printer PX-A550 in the same manner as in Evaluation 1, and a pattern including solid and ruled lines was continuously printed in a 40 ° C. environment. When printing was disturbed due to nozzle omission or ink flight curve during printing, the return operation (cleaning) attached to the recording device was performed each time. The number of cleanings required within 100 consecutive pages was measured, and the result was determined based on the following criteria. The results are shown in Table 4 below.
A: When cleaning is not required B: When cleaning is required less than 3 times C: When cleaning is required 3 times or more

Evaluation 7: Evaluation of clogging recovery property For each prepared ink set, in the same manner as in Evaluation 1, after confirming that the ink composition was discharged from all nozzles, the ink cartridge was not present and the home position It was left in an environment of 40 ° C. for one week at an outside position (the head is displaced from the position of the cap provided in the printer and the head is not capped). After leaving, the ink composition was ejected from all the nozzles again, the number of cleanings required until printing equivalent to the initial printing was possible was measured, and the result was determined based on the following criteria. The results are shown in Table 4 below.
A: When printing equivalent to the initial value is obtained by cleaning 3 times or less B: When printing equal to the initial value is obtained by cleaning 4 times or more and 9 times or less C: Even when cleaning is performed 10 times or more, it is equivalent to the initial value When printing is not possible

Claims (8)

An ink set comprising at least a cyan ink composition, a magenta ink composition, and a yellow ink composition,
The yellow ink composition comprises a pigment coated with a water-insoluble polymer;
An ink composition other than the yellow ink composition comprises a self-dispersing pigment;
An ink set, wherein all ink compositions comprise a resin emulsion.   The ink set according to claim 1, further comprising a black ink composition comprising a self-dispersing pigment.   The ink set according to claim 1 or 2, wherein the pigment in each ink composition is 6% by mass or more.   The ink set according to any one of claims 1 to 3, wherein the resin emulsion is contained in each ink composition in an amount of 2% by mass or more.   5. The ink composition according to claim 1, wherein each ink composition comprises 60 to 10% by mass of water, a water-soluble organic solvent, and a surfactant with respect to each ink composition. The ink set described in 1.   6. The ink composition according to claim 5, wherein each of the ink compositions contains 5% by mass or more of a polyhydric alcohol monoalkyl ether and / or a nitrogen-containing cyclic compound as the water-soluble organic solvent, and a polyhydric alcohol. The ink set described.   The ink set according to claim 5 or 6, wherein the surfactant is an acetylene glycol surfactant and / or a polyether-modified siloxane surfactant.   An inkjet recording method for performing printing by discharging droplets of an ink composition and attaching the droplets to a recording medium, wherein the inkjet recording uses the ink set according to any one of claims 1 to 7. Method.