Ink set for inkjet recording

Abstract

The present invention relates to an ink set for ink-jet recording which, when printed on a low-liquid-absorbing base material, allows inks to be uniformly mixed with each other on the printing base material, has excellent scratch resistance of a printed surface, and does not cause deterioration of image quality or the like.SOLUTION: An ink set for inkjet recording comprising at least an orange ink and a green ink, wherein the orange ink and the green ink are each a water-based ink containing a pigment, a pigment dispersant, a fixing resin, a water-soluble organic solvent, a surfactant and water, and the pigment contained in the orange ink is C. I. Pigment Orange 34.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ink set for inkjet recording. [Background technology]

[0002] Inkjet recording is a method of printing characters and images by ejecting ink droplets directly from minute nozzles onto a recording medium. This method has become extremely popular because it can be easily and inexpensively produced in full color and can be used on a variety of recording media, including paper, plastic film, and textile materials. Recording media such as packaging, flyers, and pamphlets are typically printed using four process colors (CMYK): C (cyan), M (magenta), Y (yellow), and K (black). Process color printing is also used for printing flexible packaging such as food packaging, and the performance requirements for such flexible packaging printing include image quality, print stability, and physical durability of the printed material, as well as a wide color gamut. A color gamut that cannot be reproduced with the four colors of CMYK is required, and special color inks such as orange, green, violet, blue, and red are required.

[0003] As a reported example of the use of colorants having hues other than the three basic primary colors of yellow, magenta, and cyan, specifically special color inks such as orange, red, violet, green, and blue, Patent Document 1 discloses an expanded color reproducibility range by using an aqueous pigment dispersion comprising one or more organic pigments selected from disazopyrazolone pigments, perinone pigments, dioxazine pigments, and copper phthalocyanine pigments, and a crosslinked polymer crosslinked with 1,4-butanediol diglycidyl ether as a crosslinking agent.

[0004] Furthermore, Patent Document 2 reports that a five-color ink set for inkjet recording, which includes a cyan ink composition containing CI Pigment Blue 15:3 or CI Pigment Blue 15:4, a magenta ink composition containing CI Pigment Red 122, CI Pigment Red 202, CI Pigment Red 209 or CI Pigment Violet 19, a yellow ink composition containing CI Pigment Yellow 213, a green ink composition containing CI Pigment Green 7 or CI Pigment Green 36, and an orange ink composition containing CI Pigment Orange 64, CI Pigment Orange 43 or CI Pigment Orange 71, is capable of printing high-resolution, high-quality images at high speed.

[0005] Furthermore, Patent Document 3 discloses an ink set containing cyan ink, magenta ink, yellow ink, and black ink, which contains crosslinked polymer particles (A) containing a colorant and an aqueous medium (D), and the crosslinked polymer particles (A) contain a reaction product of a resin (B) having a cyclic carbonate group and a crosslinking agent (C). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-102668 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-173853 [Patent Document 3] Patent Publication No. 2021-187898 Summary of the Invention [Problem to be solved by the invention]

[0007] Compared to process color inks, spot color inks are less likely to be used as a single color, and inks of similar hues tend to mix together when forming an image. Therefore, spot color inks tend to mix with each other or with process color inks. However, when two or more inks, including a spot color ink, are applied to a low-absorbency substrate for flexible packaging such as food packaging, a coating film tends to be formed in which the ink liquids are unevenly mixed. This unevenness in ink mixing also varies depending on the combination of pigments in the spot color inks. When the water-based inks described in Patent Documents 1 to 3 are applied to a printing medium, they form an uneven coating film on the substrate in which the inks are not evenly mixed, which can cause problems such as reduced image quality of the printed material and reduced coating strength.

[0008] The present invention relates to an ink set for inkjet recording that, when printed on a low-liquid-absorbent substrate, allows the inks to mix uniformly on the printing substrate, provides excellent abrasion resistance to the printed surface, and does not cause deterioration in image quality. [Means for solving the problem]

[0009] The present inventors have found that the above-mentioned problems can be solved by using CI Pigment Orange 34, a pyrazolone pigment, as the pigment contained in the orange ink in an inkjet recording ink set consisting of water-based inks containing a pigment, a pigment dispersant, a fixing resin, a water-soluble organic solvent, a surfactant, and water. The present invention relates to the following [1]. [1] An inkjet recording ink set having at least an orange ink and a green ink, wherein the orange ink and the green ink are water-based inks containing a pigment, a pigment dispersant, a fixing resin, a water-soluble organic solvent, a surfactant, and water, and the pigment contained in the orange ink is CI Pigment Orange 34. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an ink set for inkjet recording that, when printed on a low liquid-absorbent substrate, allows the inks to mix uniformly on the printing substrate, provides excellent abrasion resistance to the printed surface, and does not cause deterioration in image quality, etc. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Inkjet recording ink set] The inkjet recording ink set of the present invention includes at least an orange ink and a green ink, the orange ink and the green ink being water-based inks containing a pigment, a pigment dispersant, a fixing resin, a water-soluble organic solvent, a surfactant, and water, and the pigment contained in the orange ink is CI Pigment Orange 34.

[0012] According to the present invention, by using an orange ink containing CI Pigment Orange 34 as a pigment and a green ink, when an inkjet recording ink set containing the orange ink and the green ink is used to print on a low-liquid-absorbent substrate, the inks mix uniformly on the printed substrate, improving the abrasion resistance and image quality of the printed product. This effect is particularly evident when using an ink set that combines the specific orange pigment and green pigment, both of which are neutral colors.

[0013] The reason for this is not clear, but it is thought that by using CI Pigment Orange 34 as the pigment for the orange ink, the disazopyrazolone structure undergoes π-π stacking interaction with the green ink containing the green pigment on the low-absorbency substrate applied by inkjet printing, suppressing pigment aggregation.As a result, the pigments mix uniformly, leading to improved abrasion resistance of the printed material and good image quality.

[0014] [Orange ink and green ink] The orange ink and green ink are water-based inks containing a pigment, a pigment dispersant, a fixing resin, a water-soluble organic solvent, a surfactant, and water. Each component of the orange ink and green ink will be described below in order.

[0015] <Pigments> The pigment contained in the orange ink is CI Pigment Orange 34. CI Pigment Orange 34 is a compound with a disazopyrazolone skeleton. From the viewpoints of abrasion resistance and preventing mixing with other inks when printed on a low-absorbency substrate, the pigment content in the orange ink is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less.

[0016] The pigment contained in the green ink is not particularly limited as long as it is a pigment that develops a green color, but is preferably a phthalocyanine pigment. Specific examples include CI Pigment Green 7 and CI Brominated Phthalocyanine Green 36. Of these, CI Pigment Green 7 is more preferred because, unlike CI Brominated Phthalocyanine Green 36, it does not affect π-π stacking due to bromine atoms and has excellent pigment dispersion stability. From the viewpoints of abrasion resistance and preventing mixing with other inks when printed on a low-absorbency substrate, the pigment content in the green ink is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, and is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less.

[0017] <Pigment dispersant> In the present invention, the pigment is dispersed in the ink in a form dispersed by a pigment dispersant, or in a form in which the pigment is encapsulated in the pigment dispersant. The pigment dispersant may be either a water-soluble resin or a water-insoluble resin. Here, regarding the "water-soluble" and "water-insoluble" of a resin, the resin is dried at 105°C for 2 hours, and when the resin reaches a constant weight, it is dissolved in 100 g of water at 25°C until it reaches saturation. If the amount dissolved is more than 10 g, it is judged to be "water-soluble," and if the amount dissolved is 10 g or less, it is judged to be "water-insoluble."

[0018] Examples of pigment dispersants include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds); condensation resins such as polyester resins and polyurethane resins; and the like. Among these, vinyl resins are preferred.

[0019] The pigment dispersant may be a vinyl resin crosslinked. In this case, the pigment dispersant preferably has a structure including a polymer component having a linear two-dimensional structure, which may have a branched chain, and a component derived from a crosslinking agent. Such a crosslinked structure is considered to be a three-dimensional structure formed by the polymer having a linear two-dimensional structure, which may have a branched chain, and the component derived from the crosslinking agent.

[0020] Examples of polymers having a linear two-dimensional structure that may have a branched chain include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds); condensation resins such as polyester resins and polyurethane resins; etc. Among these, the vinyl resins described below are preferred.

[0021] The crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms, even more preferably one or more compounds selected from the group consisting of trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and even more preferably trimethylolpropane polyglycidyl ether. When the crosslinking agent is a polyfunctional epoxy compound, the epoxy group equivalent weight of the crosslinking agent is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, even more preferably 150 or less.

[0022] (vinyl resin) From the viewpoint of improving the dispersion stability of the pigment, vinyl resins used as pigment dispersants preferably contain structural units derived from anionic group-containing monomers. In this specification, the term "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of anionic groups include a carboxy group (-COOM), a sulfonic acid group (-SO3M), and a phosphate group (-OPO3M2). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0023] Examples of vinyl resins include homopolymers of anionic group-containing monomers, copolymers of anionic group-containing monomers and hydrophobic monomers, and copolymers of anionic group-containing monomers, hydrophobic monomers, and nonionic monomers. Among these, copolymers of anionic group-containing monomers and hydrophobic monomers, and copolymers of anionic group-containing monomers, hydrophobic monomers, and nonionic monomers are preferred, and copolymers of anionic group-containing monomers and hydrophobic group-containing monomers are more preferred. Here, the term "hydrophobic" in the context of a hydrophobic monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of dissolution is less than 10 g. The nonionic monomer is a monomer that has a high affinity with water or a water-soluble organic solvent, and is, for example, a monomer that contains a hydroxy group or a polyalkylene glycol chain. When the vinyl resin is a copolymer, it may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer.

[0024] Examples of the anionic group-containing monomer include a carboxy group-containing monomer, a sulfonic acid group-containing monomer, and a phosphoric acid group-containing monomer. Among these, the carboxy group-containing monomer is preferred, and (meth)acrylic acid is more preferred.

[0025] Examples of hydrophobic monomers include (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms; aromatic group-containing monomers such as styrene-based monomers and aromatic group-containing (meth)acrylates; and styrene-based macromonomers. The molecular weight of the aromatic group-containing monomer is preferably less than 500. The styrene-based macromonomer is a compound having a polymerizable functional group at one end and a number average molecular weight of from 500 to 100,000. Among these, the hydrophobic monomer is preferably a styrene-based monomer, more preferably one or more selected from the group consisting of styrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene, and even more preferably one or more selected from the group consisting of styrene and α-methylstyrene.

[0026] Examples of nonionic monomers include polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate; and alkoxypolyalkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol mono(meth)acrylate and octoxypolyethylene glycol mono(meth)acrylate. Moreover, each of the monomers of the vinyl resin may be used alone or in combination of two or more.

[0027] When the vinyl resin is a copolymer, the vinyl resin preferably contains structural units derived from one or more anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers; more preferably contains structural units derived from one or more anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of aromatic group-containing monomers and styrene-based macromers; even more preferably contains structural units derived from one or more anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from aromatic group-containing monomers; and even more preferably contains structural units derived from acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from aromatic group-containing monomers;

[0028] When the vinyl resin is a copolymer of an anionic group-containing monomer and a hydrophobic monomer, or a copolymer of an anionic group-containing monomer, a hydrophobic monomer, and a nonionic monomer, the content of the constituent units derived from each monomer component in all the constituent units of the vinyl resin is as follows:

[0029] When the vinyl resin is a copolymer of an anionic group-containing monomer and a hydrophobic monomer, the content of the structural units derived from the anionic group-containing monomer in all structural units of the vinyl resin is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, from the viewpoint of improving the dispersion stability of the pigment, and is preferably 55% by mass or less, more preferably 45% by mass or less, and even more preferably 35% by mass or less, from the same viewpoint as above. When the vinyl resin contains a structural unit derived from a nonionic monomer, the content of the structural unit derived from an anionic group-containing monomer is preferably 8% by mass or more, more preferably 10% by mass or more, and from the same viewpoint as above, is preferably 18% by mass or less, more preferably 15% by mass or less.

[0030] When the vinyl resin is a copolymer of an anionic group-containing monomer and a hydrophobic monomer, the content of structural units derived from hydrophobic monomers in all structural units of the vinyl resin is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, from the viewpoint of improving the dispersion stability of the pigment, and is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less, from the same viewpoint as above. When the vinyl resin contains structural units derived from nonionic monomers, the content of structural units derived from hydrophobic monomers is preferably 45% by mass or more, more preferably 52% by mass or more, and from the same viewpoint as above, is preferably 75% by mass or less, more preferably 63% by mass or less.

[0031] When the vinyl resin contains a structural unit derived from a nonionic monomer, the content of the structural unit derived from the nonionic monomer in all structural units of the vinyl resin is, from the viewpoint of improving the dispersion stability of the pigment, preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, relative to the total of the structural units derived from the anionic group-containing monomer and the structural units derived from the nonionic monomer, and is preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less.

[0032] The vinyl resin can be obtained, for example, by addition polymerization of raw material monomers including an anionic group-containing monomer, a hydrophobic monomer, and, if necessary, a nonionic monomer, by a known method.

[0033] The weight-average molecular weight of the vinyl resin is preferably 5,000 or more, more preferably 9,000 or more, and even more preferably 12,000 or more, from the viewpoint of dispersion stability of the pigment, and is preferably 100,000 or less, more preferably 80,000 or less, and even more preferably 60,000 or less, from the same viewpoint as above.

[0034] Commercially available vinyl resins include, for example, styrene / acrylic resins such as "JONCRYL 67," "JONCRYL 611," "JONCRYL 678," "JONCRYL 680," "JONCRYL 690," and "JONCRYL 819" (all manufactured by BASF Japan Ltd.).

[0035] The content of pigment dispersant in the orange ink and green ink varies depending on the pigment content, but is preferably 0.5% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, and preferably 5.0% by mass or less, more preferably 3.0% by mass or less, even more preferably 2.0% by mass or less.

[0036] From the viewpoint of ease of inkjet ejection and coating, the total content of pigment and pigment dispersant in the orange ink and green ink is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 15% by mass or less, more preferably 10% by mass or less.

[0037] The content of the pigment dispersant relative to 100 parts by mass of the pigment is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, and preferably 50 parts by mass or less, more preferably 40 parts by mass or less.

[0038] <Fixing resin> As the fixing resin, in addition to conventional resins such as acid-modified polyolefin resins, polyurethane resins are also used to fix ink droplets onto a recording medium. The fixing resin used in the present invention is preferably a polyurethane resin. The polyurethane resin can be obtained by subjecting a polyol and a polyisocyanate to a polyaddition reaction by a known method. The polyurethane resin may be acid-modified by copolymerizing, for example, dimethylolpropionic acid, and the introduction of an acid group improves the water dispersibility.

[0039] (Polyol) The polyol is not particularly limited as long as it is a compound having two or more hydroxy groups in one molecule, and is preferably one or more selected from polyester polyols, polycarbonate polyols, polyether polyols, and the like. That is, the polyurethane resin is preferably at least one selected from (i) polyester-based polyurethane resins, (ii) polycarbonate-based polyurethane resins, and (iii) polyether-based polyurethane resins.

[0040] (i) Polyester-based polyurethane resin The polyester-based polyurethane resin can be obtained by subjecting a polyester polyol and a polyisocyanate to a polyaddition reaction. The polyester polyol, which is a raw material, can be obtained by condensing a diol and a dicarboxylic acid.

[0041] The diol is preferably at least one selected from diols having 2 to 10 carbon atoms, such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butyl diglycol, 1,4-butanediol, 3-methyl-1,5-pentanediol, and cyclohexanediol.

[0042] The dicarboxylic acid is preferably at least one selected from aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and brassylic acid, and aromatic dibasic acids such as isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid.

[0043] (ii) Polycarbonate-based polyurethane resin The polycarbonate-based polyurethane resin is preferably a polyurethane resin containing structural units derived from one or more polyols selected from aliphatic polyols having 2 to 12 carbon atoms, alicyclic polyols, aromatic polyols, polycarbonate polyols, polyalkylene carbonate diols containing 1 to 1,000 repeating units, polyethylene ether carbonate diols containing 1 to 1,000 repeating units, and combinations thereof, and structural units derived from polyisocyanate.

[0044] (iii) Polyether-based polyurethane resin The polyether polyurethane resin can be obtained by subjecting a polyether polyol and a polyisocyanate to a polyaddition reaction. The polyether polyol raw material is preferably one or more selected from polyether diols obtained by polymerizing 2 to 45 molecules, preferably 10 to 40 molecules, of alkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, tetramethylene glycol, and hexamethylene glycol; and polymers obtained by ring-opening polymerization of cyclic ether compounds such as tetrahydrofuran and epichlorohydrin, either alone or in combination of two or more.

[0045] (Polyisocyanate) Examples of polyisocyanates, which are components of polyurethane resins, include at least one selected from aliphatic diisocyanates, aliphatic diisocyanates having a cyclic structure, aliphatic diisocyanates having an aromatic ring, aromatic diisocyanates, and modified products of these diisocyanates (carbodiimide-, uretdione-, and uretoimine-containing modified products, etc.).

[0046] The aliphatic diisocyanate is preferably at least one selected from tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and the like.

[0047] The aliphatic diisocyanate having a cyclic structure is preferably at least one selected from 1,3-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane 4,4'-diisocyanate, and the like.

[0048] The aliphatic diisocyanate having an aromatic ring is preferably at least one selected from xylylene diisocyanate, tetramethylxylylene diisocyanate, and the like. The aromatic diisocyanate is preferably at least one selected from tolylene diisocyanate, phenylene diisocyanate, diphenylmethane diisocyanate, and the like.

[0049] Among these, from the viewpoint of improving the abrasion resistance and water resistance of the solid printing surface of the low liquid-absorbent substrate, one or more selected from aliphatic diisocyanates and aromatic diisocyanates having a cyclic structure are preferred, and one or more selected from isophorone diisocyanate, dicyclohexylmethane 4,4'-diisocyanate, tolylene diisocyanates (TDIs) such as 2,4-TDI and 2,6-TDI are more preferred. The compounds contained in each of the above polyols and polyisocyanates may be used alone or in combination of two or more kinds.

[0050] We will also explain acid-modified polyolefin resins, which have been used in some applications. Specifically, acid-modified polyolefin resins are polyolefins modified with unsaturated carboxylic acid compounds. The polyolefin before modification is preferably an olefin homopolymer or a copolymer of two or more olefins, and specific examples include polypropylene, ethylene / propylene copolymer, propylene / α-olefin copolymer, and ethylene / vinyl acetate copolymer. The copolymer may be either a block copolymer or a random copolymer.

[0051] The number of carbon atoms of the α-olefin in the propylene / α-olefin copolymer is preferably 4 or more, and preferably 15 or less, more preferably 10 or less, and even more preferably 8 or less. Examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, and 4-methyl-1-pentene. Among these, the polyolefin before modification is preferably polypropylene or a propylene / α-olefin copolymer.

[0052] The content of the fixing resin in the orange ink and green ink is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and preferably 12% by mass or less, more preferably 11% by mass or less, even more preferably 10% by mass or less.

[0053] <Water-soluble organic solvent> The water-soluble organic solvent refers to an organic solvent that dissolves in an amount of 5 mL or more when dissolved in 100 mL of water at 25° C. Examples of water-soluble organic solvents that can be used include polyhydric alcohols, polyhydric alcohol ethers, monohydric alcohols, and ketones.

[0054] Examples of the polyhydric alcohol include 1,2-alkanediols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,2-pentanediol, and 1,2-hexanediol; diethylene glycol, polyethylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, and 2-methyl-2,4-pentanediol.

[0055] Examples of the polyhydric alcohol ether include alkylene glycol monoalkyl ethers and alkylene glycol dialkyl ethers. Among these, alkylene glycol monoalkyl ethers are preferred from the viewpoint of improving adhesion.

[0056] The number of carbon atoms in the alkyl group of the alkyl ether moiety of the alkylene glycol monoalkyl ether is preferably 1 or more, and preferably 6 or less, more preferably 4 or less. The alkyl group of the alkyl ether moiety of the alkylene glycol monoalkyl ether may be either a straight chain or a branched chain.

[0057] Examples of alkylene glycol monoalkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monoisobutyl ether, diethylene glycol monobutyl ether (butyl diglycol), triethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, and tripropylene glycol monomethyl ether.

[0058] The content of the water-soluble organic solvent in the orange ink and green ink is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less.

[0059] <Surfactant> The ink of the present invention contains a surfactant from the viewpoints of adjusting the gas-liquid interfacial energy of the ink to control the behavior of droplets, suppressing color unevenness, and enabling solid printing.

[0060] Examples of surfactants include nonionic surfactants, anionic surfactants, and amphoteric surfactants, with nonionic surfactants being preferred.

[0061] Examples of nonionic surfactants include acetylene-based surfactants, polyoxyalkylene alkyl ether-based surfactants, polyhydric alcohol-based surfactants, fatty acid alkanolamides, silicone-based surfactants, and fluorine-based surfactants. Among these, acetylene-based surfactants, silicone-based surfactants, and polyoxyalkylene alkyl ether-type surfactants are preferred, and acetylene-based surfactants and silicone-based surfactants are more preferred. One or more of acetylene-based surfactants, silicone-based surfactants, and polyoxyalkylene alkyl ether-type surfactants may be used in combination.

[0062] Preferred examples of the acetylene surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, 2,4-dimethyl-5-hexyn-3-ol, and ethylene oxide adducts thereof. For example, commercially available products such as Surfynol 440 (Nissin Chemical Industry Co., Ltd.) can be used. Examples of silicone surfactants include polyether-modified silicone oils, etc. Specific examples include the KF series manufactured by Shin-Etsu Chemical Co., Ltd., the Silface SAG series manufactured by Nissin Chemical Industry Co., Ltd., and the BYK series manufactured by BYK Japan K.K.

[0063] The total content of surfactants in the orange ink and green ink is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0064] <Water> The water used may be distilled water, deionized water, pure water, purified water, etc. The water content is the remainder obtained by subtracting the contents of the pigment, pigment dispersant, fixing resin, water-soluble organic solvent, and surfactant from the orange ink or green ink.

[0065] The orange ink and green ink may contain additives such as humectants, wetting agents, penetrants, viscosity adjusters, antifoaming agents, preservatives, antifungal agents, and antirust agents, as long as the effects of the present invention are not impaired.

[0066] <Manufacturing of orange ink and green ink> In the orange ink and green ink, the pigment is preferably contained as pigment-containing polymer particles, etc. These inks are preferably obtained by dispersing a fixing resin, a water-soluble organic solvent, a surfactant, water, and, if necessary, a neutralizing agent in an aqueous dispersion of pigment-containing polymer particles by a known method. The dispersion treatment is carried out by applying shear stress using a kneading machine such as a roll mill, kneader or extruder, a high-pressure homogenizer such as Microfluidizer (trade name, Microfluidics), a paint shaker or a media-type dispersing machine such as a bead mill.

[0067] [Other inks] Next, inks other than the orange ink and green ink containing CI Pigment Orange 34 will be described. <Pigments> The ink jet recording ink set of the present invention preferably includes, in addition to the orange ink and green ink containing CI Pigment Orange 34, one or more inks selected from a white ink, a process color ink, and other special color inks. The process color inks are four color inks each containing pigments of Y (yellow), M (magenta), C (cyan), and K (black). Other special color inks are inks specially formulated to reproduce color tones more faithfully, and are used to reproduce colors that cannot be reproduced with process colors, such as metallic colors such as gold, silver, and copper, pearlescent colors, and fluorescent colors. Note that other special color inks are inks other than the orange ink and green ink mentioned above. The pigments used in the other inks, i.e., inks other than the orange ink and the green ink, may be either inorganic or organic pigments, and lake pigments and fluorescent pigments may also be used. Furthermore, these pigments may also be used in combination with extender pigments, if necessary.

[0068] Examples of inorganic pigments include carbon black, titanium oxide, iron oxide, red iron oxide, chromium oxide, and other metal oxides, and pearlescent pigments. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. An example of a commercially available black pigment is CI Pigment Black 7.

[0069] Examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments.

[0070] Examples of organic pigments include cyan pigments such as CI Pigment Blue, magenta pigments such as CI Pigment Red and CI Pigment Violet, and yellow pigments such as CI Pigment Yellow. These organic pigments are typically used in process color inks and special color inks.

[0071] White ink contains a white achromatic pigment, such as CI Pigment White 6.

[0072] Among these, from the viewpoint of suppressing color unevenness and enabling solid printing, preferred CI pigment blues are CI pigment blue 15:3 and CI pigment blue 15:4, preferred CI pigment reds are CI pigment red 122 and CI pigment red 150, preferred CI pigment violet is CI pigment violet 19, and preferred CI pigment yellows are CI pigment yellow 74 and CI pigment yellow 155.

[0073] Among the other inks, for example, the black ink, cyan ink, magenta ink, yellow ink, and violet ink have a pigment content of preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less. On the other hand, since the white ink is used for printing on top of color printing, it has a high pigment content from the viewpoint of obtaining sufficient hiding power, and the amount is preferably 5% by mass or more, more preferably 8% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less.

[0074] The content of the pigment in the process color ink is preferably greater than the content of the pigment in the orange ink, from the viewpoint of suppressing color separation and pigment precipitation on the printed matter.

[0075] <Pigment dispersant> The types of pigment dispersants contained in the other inks are the same as those described for the orange ink and green ink. That is, examples of pigment dispersants include the vinyl resins obtained by addition polymerization of the above-mentioned vinyl monomers, and condensation resins such as polyester resins and polyurethane resins. The content of pigment dispersant in other inks, such as cyan ink, magenta ink, yellow ink, black ink, and violet ink, is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 4% by mass or less, more preferably 3% by mass or less. Note that the content of pigment dispersant in white ink is relatively high because it is used for printing on top of color printing, and is therefore low, preferably 0.1% by mass or more, and preferably 0.5% by mass or less.

[0076] The types of fixing resin, water-soluble organic solvent, surfactant, water, and optional components contained in the other inks are the same as those described for the orange ink and green ink. Other inks can be produced in the same manner as the orange ink and green ink.

[0077] In inkjet recording, the combination of an orange ink containing CI Pigment Orange 34 and a green ink containing a phthalocyanine-based green pigment significantly reduces the overlap of wet inks immediately after inkjet ejection and the precipitation of pigments due to the mixing of inks. The mechanism behind this is explained below. The pyrazolone orange that forms CI Pigment Orange 34 has a structure rich in aromatic ring-derived rigidity and chlorine atom-derived polar moieties. Similarly, phthalocyanine green also has a structure rich in chlorine atom-derived polar moieties and a flat, rigid phthalocyanine-derived skeleton. Therefore, π-π stacking interactions are likely to occur between the aromatic rings of the pyrazolone skeleton and the phthalocyanine skeleton. In other words, we believe that the interactions between CI Pigment Orange 34 and phthalocyanine green, based on their respective structures, result in high mixing stability and abrasion resistance of solid printed surfaces when two or more inks are ejected by inkjet.

[0078] Furthermore, since the purple pigment Pigment Violet 23 also has a structure with a flat and rigid fused ring skeleton and a polar moiety derived from a chlorine atom, it is believed that it is likely to undergo π-π stacking interactions with CI Pigment Orange 34 or Phthalocyanine Green, resulting in high mixing stability and abrasion resistance. The above pigments can be used alone or in combination of two or more.

[0079] [Ink set] The ink set of the present invention is a combination of two or more inks, including at least an orange ink and a green ink containing CI Pigment Orange 34 as a pigment. The ink set for inkjet recording preferably further includes one or more inks selected from a white ink, a process color ink, and other spot color inks, in addition to the orange ink and green ink containing CI Pigment Orange 34 as a pigment. By providing inks of various colors, it is possible to impart a variety of colors to printed matter.

[0080] As described above, the preferred pigment content in the inks constituting the inkjet recording ink set is 5% to 20% by mass for the white ink, 1% to 3% by mass for the process color inks, and 1% to 6% by mass for the orange ink containing CI Pigment Orange 34. However, the pigment content in the process color ink is preferably higher than the pigment content in the orange ink. The pigment concentrations of these inks are typically in the order of highest to lowest: white ink, process color ink, and orange ink. The reason for increasing the pigment concentration of the white ink is that, when color printing is performed directly on a transparent recording medium such as film, the color development of the color ink and the visibility of characters, etc., are often impaired. Printing on low-liquid-absorbent substrates such as food packaging film is typically performed by reverse printing. In reverse printing, the orientation of the printed image and the printing order of the colors are determined so that the printed image is viewed from the unprinted back side. Therefore, the order of printing on the low-liquid-absorbent substrate is to print the process color ink and orange ink first, and then print the white ink covering them last. The reason for making the pigment concentration of the process color ink higher than that of the orange ink is to impart a variety of colors to the printed matter.

[0081] [Inkjet recording device] The ink set of the present invention is for inkjet recording, and is preferably used in a line head type inkjet recording apparatus. Inkjet recording methods include line head and serial head methods, but the line head method is preferred from the viewpoint of suppressing color unevenness and enabling solid printing. The line head method has an effective length capable of inkjet printing over a width equal to or greater than the length of the print medium in the direction perpendicular to the transport direction, and the inkjet head itself does not move during inkjet printing.

[0082] The line head system may be a system in which a plurality of individual heads are arranged in a line. The inkjet head is preferably an inkjet head or a system in which a plurality of individual heads are arranged in a line, one for each ink color.

[0083] From the viewpoint of suppressing color unevenness and enabling solid printing, the nozzle spacing of the inkjet head is preferably 120 npi or more, more preferably 180 npi or more, even more preferably 300 npi or more, even more preferably 800 npi or more, and is preferably 6000 npi or less, more preferably 3600 npi or less, even more preferably 2400 npi or less, even more preferably 1600 npi or less. Here, "npi" refers to the number of nozzles per inch in the longitudinal direction of the nozzle row of the inkjet head.

[0084] The inkjet ejection method may be either a piezoelectric method using a piezoelectric element or a thermal method using a thermal element. Of these, the inkjet ejection method is preferably a piezoelectric method from the viewpoints of controlling the droplet rate, suppressing color unevenness, and enabling solid printing.

[0085] It is preferable to use a low liquid-absorbent substrate for the printing medium. That is, the ink set for inkjet recording of this embodiment is preferably used for inkjet recording on a low liquid-absorbent substrate. Here, the "low liquid-absorbent" of the low liquid-absorbent substrate is a concept that includes low liquid absorption and non-liquid absorption, and the amount of water absorption of the printing substrate when the low liquid-absorbent substrate is in contact with pure water for 100 ms is 0 g / m. 2 More than 10g / m 2 The water absorption amount is measured using an automatic scanning absorptivity meter (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) as the amount transferred when pure water is in contact for 100 ms under conditions of 23°C and a relative humidity of 50%. Specific examples of low liquid-absorbent substrates include corona-treated polyethylene terephthalate (PET) films and polyolefin films such as polypropylene.

[0086] There are various inkjet ejection methods, but the printing method of the present invention may use either a piezoelectric method using a piezoelectric element or a thermal method using a thermal element. Among these, the inkjet ejection method is preferably a piezoelectric method from the viewpoints of controlling the droplet rate, suppressing color unevenness, and enabling solid printing.

[0087] The transport speed of the printing medium is preferably 10 m / min or more, more preferably 15 m / min or more, from the viewpoint of efficiently obtaining printed matter, and is preferably 100 m / min or less, more preferably 80 m / min or less, and even more preferably 60 m / min or less, from the viewpoint of suppressing color unevenness and enabling solid printing.

[0088] In the present invention, the volume of ink droplets ejected is preferably 1 pL or more, more preferably 1.5 pL or more, even more preferably 2 pL or more, from the viewpoint of facilitating control of the droplet rate, and is preferably 15 pL or less, more preferably 10 pL or less, even more preferably 7.5 pL or less, even more preferably 5 pL or less. Note that "pL (picoliter)" is 10 times "L (liter)". -12 means.

[0089] The ink droplet volume can be set by an inkjet head control device. When the ink droplet is divided into droplets, the ejected ink droplet volume refers to the total volume of the main ink droplet and the separated ink droplets.

[0090] According to the present invention, by using a combination of CI Pigment Orange 34, a pyrazolone pigment, and green ink, a phthalocyanine pigment, these inks, which are both neutral colors, mix uniformly on the printed matter when printed on a low-liquid-absorbent substrate, thereby imparting abrasion resistance and good image quality to the printed matter. [Example]

[0091] The present invention will be described in more detail below with reference to examples, but is not limited to these examples. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," and the methods for measuring the weight-average molecular weight of the water-insoluble polymer, the solids concentration of the pigment water dispersion, the average particle diameter of the pigment-containing polymer particles and water-insoluble polymer particles, etc., and the solids concentration in the ink are as follows:

[0092] [Method for measuring ink components] (1) Measurement of weight-average molecular weight of water-insoluble polymers Measurements were performed using gel permeation chromatography (GPC system manufactured by Tosoh Corporation (HLC-8120GPC), columns manufactured by Tosoh Corporation (TSK-GEL, α-M × 2), flow rate: 1 mL / min) with an eluent prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide (DMF) to concentrations of 60 mmol / L and 50 mmol / L, respectively, and monodisperse polystyrene with known molecular weights as a standard substance.

[0093] (2) Measurement of solids concentration of pigment water dispersion 10.0 g of sodium sulfate, brought to a constant weight in a desiccator, was precisely weighed into a 30 mL polypropylene container (φ=40 mm, height=30 mm), and approximately 1.0 g of a pigment water dispersion sample was mixed therein and precisely weighed. After this, the container was maintained at 105°C for 2 hours to remove volatiles, and the container was left in the desiccator for an additional 15 minutes before being precisely weighed. The mass of the sample after volatiles removal was taken as the solids content, and this was divided by the mass of the sample added to obtain the solids concentration.

[0094] (3) Measurement of the average particle size of pigment-containing polymer particles and water-insoluble polymer particles Cumulant analysis was performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.). The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, 100 accumulations, and a measured concentration of 5 × 10 -3 The value was expressed as mass % (solid concentration equivalent), and the refractive index of water (1.333) was entered as the refractive index of the dispersion medium.

[0095] (4) Measurement of solid content in ink Using an infrared moisture meter "FD-230" (Kett Electric Laboratory Co., Ltd.), 5 g of the sample was dried at a drying temperature of 150°C and measurement mode 96 (monitoring time 2.5 minutes / fluctuation range 0.05%), and the moisture content (%) in the sample was measured, and the solid content was calculated using the following formula. Solid concentration (%) = 100 - water content (%) of sample

[0096] [Production Example 1] Preparation of Pigment Water Dispersion 1 (Process 1) A pigment mixture was obtained by mixing 165 parts of CI Pigment Orange 34 (a disazopyrazolone orange pigment, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) as the pigment, 55 parts of an aqueous solution (20% solids concentration) of acrylic acid / α-methylstyrene / styrene copolymer "Joncryl 690" (weight average molecular weight: 16,500, acid value: 240 mg KOH / g) (manufactured by BASF) as the water-insoluble polymer, and 33 parts of a 5N aqueous sodium hydroxide solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., reagent) as a neutralizer for the water-insoluble polymer used as a pigment dispersant. The pigment mixture was dispersed using zirconia beads to obtain an aqueous pigment dispersion with a solids concentration of 22.0%.

[0097] (Process 2) To 300 parts of the aqueous pigment dispersion obtained in step 1, 2.73 parts of trimethylolpropane polyglycidyl ether "Denacol EX321L" (manufactured by Nagase ChemteX Corporation) as a crosslinking agent and 24.52 parts of ion-exchanged water were added, and the mixture was heated at 70°C for 3 hours while stirring. After the mixture was cooled to room temperature, it was filtered through a filter "Mini Sart Syringe Filter" (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, and pigment aqueous dispersion 1 containing pigment-containing polymer particles with an average particle size of 166 nm was obtained.

[0098] [Production Examples 2] to [Production Examples 7] Preparation of Pigment Water Dispersions 2 to 7 Pigment aqueous dispersions 2 to 7 were obtained in the same manner as in Production Example 1, except that the pigment used in step 1 was changed to a pigment having the type and composition shown in Table 1. The solid content concentrations and pigment introduction rates of Pigment Water Dispersions 1 to 7 are shown in Table 1. The average particle size of the pigment-containing polymer particles contained in Pigment Dispersion 2 was 241 nm, the average particle size of the pigment-containing polymer particles contained in Pigment Dispersion 3 was 145 nm, the average particle size of the pigment-containing polymer particles contained in Pigment Dispersion 4 was 137 nm, the average particle size of the pigment-containing polymer particles contained in Pigment Dispersion 5 was 162 nm, the average particle size of the pigment-containing polymer particles contained in Pigment Dispersion 6 was 148 nm, and the average particle size of the pigment-containing polymer particles contained in Pigment Dispersion 7 was 349 nm.

[0099] [Table 1]

[0100] [Production Example 8] Preparation of Pigment Water Dispersion 8 (Process 1) 16 parts of methacrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 44 parts of styrene (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 30 parts of styrene macromonomer "AS-6S" (manufactured by Toagosei Co., Ltd., number average molecular weight 6,000, solids content 50%), and 25 parts of methoxypolyethylene glycol methacrylate "BLEMMER PME-200" (manufactured by NOF Corporation) were mixed to obtain 115 parts of a monomer mixture. 18 parts of methyl ethyl ketone, 0.03 parts of 2-mercaptoethanol as a chain transfer agent, and 10% (11.5 parts) of the monomer mixture were placed in a reaction vessel and mixed, and the atmosphere inside the reaction vessel was thoroughly purged with nitrogen gas.

[0101] Separately, a mixture of the remaining 90% (103.5 parts) of the monomer mixture, 0.27 parts of the chain transfer agent, 42 parts of methyl ethyl ketone, and 3 parts of the polymerization initiator 2,2'-azobis(2,4-dimethylvaleronitrile) "V-65" (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was placed in a dropping funnel. Under a nitrogen atmosphere, the mixture in the reaction vessel was heated to 75°C while stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After the addition was completed and the mixture was left at 75°C for 2 hours, a solution of 3 parts of the polymerization initiator in 5 parts of methyl ethyl ketone was added, and the mixture was maintained at 75°C for another 2 hours, followed by aging at 80°C for 2 hours. Further addition of 50 parts of methyl ethyl ketone yielded a solution of a water-insoluble polymer (weight average molecular weight 50,000). The solids concentration of the water-insoluble polymer solution was 45.0% by mass.

[0102] (Process 2) 95.2 parts of the water-insoluble polymer solution obtained in step 1 was dissolved in 53.9 parts of methyl ethyl ketone, and 15.0 parts of 5N aqueous sodium hydroxide solution, 0.5 parts of 25% aqueous ammonia, and 341.3 parts of ion-exchanged water were added as neutralizers. 100 parts of CI Pigment Black 7 (PB7, manufactured by Cabot Corporation) were then added as a carbon black pigment to obtain a pigment mixture. The degree of neutralization was 78.8 mol%. The pigment mixture was mixed for 1 hour using a disperser blade at 7000 rpm and 20°C. The resulting dispersion was dispersed by passing it 15 times (15 passes) through a microfluidizer "High-Pressure Homogenizer M-140K" (manufactured by Microfluidics) at a pressure of 180 MPa.

[0103] Methyl ethyl ketone was removed from the resulting pigment-containing polymer particle dispersion at 60°C under reduced pressure, and then a portion of the water was removed. The resulting dispersion was centrifuged. The liquid layer was filtered through a Minisart syringe filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding pigment-containing polymer particles. The solids concentration was 25.0% by mass. To 100 parts of the resulting aqueous dispersion of pigment-containing polymer particles, 0.45 parts of trimethylolpropane polyglycidyl ether Denacol EX321L (manufactured by Nagase ChemteX Corporation) and 15.23 parts of ion-exchanged water were added, and the mixture was heated at 70°C for 3 hours with stirring. After cooling to room temperature, the liquid layer was filtered through a Minisart syringe filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous dispersion of pigment-containing polymer particles (solids concentration: 22.0% by mass). The average diameter of the pigment-containing polymer particles was 100 nm. This was designated as Pigment Water Dispersion 8.

[0104] [Production Examples 9] to [Production Examples 11] Preparation of Pigment Water Dispersions 9 to 11 Aqueous dispersions of pigment-containing polymer particles (solid content concentration 22.0% by mass) were obtained in the same manner as in Production Example 8, except that the carbon black pigment used in step 2 in Production Example 8 was changed to a cyan pigment (PB15:3), a magenta pigment (PR150), or a yellow pigment (PY74) as shown in Table 2. These were designated pigment aqueous dispersions 9 to 11. Table 2 shows the solid content concentrations and pigment introduction rates of pigment aqueous dispersions 8 to 11. The average particle size of the pigment-containing polymer particles contained in pigment dispersion 9 was 100 nm, the average particle size of the pigment-containing polymer particles contained in pigment dispersion 10 was 155 nm, and the average particle size of the pigment-containing polymer particles contained in pigment dispersion 11 was 115 nm.

[0105] [Table 2]

[0106] [Production Example 12] Preparation of aqueous dispersion of polyurethane resin particles A A four-neck flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube was charged with 146 parts of a polyether polyol "PTMG1000" (polytetramethylene ether glycol, manufactured by Mitsubishi Chemical Corporation) derived from 1,4-butanediol, 6 parts of dimethylolpropionic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 41 parts of isophorone diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.), and methyl ethyl ketone. The mixture was allowed to react at 75°C for 1 hour to obtain a methyl ethyl ketone solution containing a prepolymer. One part of triethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) and methyl ethyl ketone were then added, and the mixture was allowed to react at 75°C for 1 hour to obtain a methyl ethyl ketone solution containing 50% prepolymer. This solution was then cooled to 45°C, followed by the addition of ethylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.) and emulsified water. The emulsified dispersion was distilled under reduced pressure at 50°C for 2 hours to remove the solvent, yielding an aqueous dispersion of polyurethane resin particles A with a solids concentration of 25.0%.

[0107] [Production Example 13] Preparation of aqueous dispersion of polyurethane resin particles B An aqueous dispersion of polyurethane resin particles B with a solids concentration of 25.0% was obtained in the same manner as in Production Example 12, except that in Production Example 12, the polyether polyol "PTMG1000" composed of 1,4-butanediol was replaced with the polycarbonate polyol "Duranol T-6002" (manufactured by Asahi Kasei Corporation) composed of 1,6-hexanediol.

[0108] Using the pigment water dispersions 1 to 11 of Production Examples 1 to 11 and the water dispersions of polyurethane resin particles A and B of Production Examples 12 and 13, inks of each color were prepared. [Production Example 14] Preparation of Ink 1 27.27 g of the aqueous dispersion of orange pigment-containing polymer particles (solids concentration 22.0% by mass) obtained in Production Example 1, 34.72 g of the aqueous dispersion of polyurethane resin particles A (solids concentration 25.0% by mass) obtained in Production Example 12, 28.00 g of propylene glycol, 2.00 g of butyl diglycol, 0.30 g of a silicone surfactant (KF-6011, manufactured by Shin-Etsu Chemical Co., Ltd.), 1.00 g of an acetylene surfactant (Surfynol 440, manufactured by Nissin Chemical Industry Co., Ltd.), and 13.98 g of ion-exchanged water were mixed together. The resulting mixture was filtered through a Mini Sart Syringe Filter (manufactured by Sartorius, pore size: 5.0 μm, material: cellulose acetate) to obtain an aqueous orange ink. This ink is designated Ink 1.

[0109] [Production Examples 15] to [Production Examples 27] Preparation of Inks 2 to 14 Each water-based ink was obtained in the same manner as in Production Example 14, except that the types and amounts of the pigment water dispersion and fixing resin used in Production Example 14 were changed to those shown in Table 3. The water-based inks obtained in Production Examples 15 to 27, in order, are referred to as inks 2 to 14. Table 3 shows the types and compositions of the components of inks 1 to 14.

[0110] [Table 3]

[0111] The organic pigments used in Tables 1 to 3 are as follows: PO34: CI Pigment Orange 34 (disazopyrazolone orange pigment) PO64: CI Pigment Orange 64 (orange pigment) PG7: CI Pigment Green 7 (Copper Phthalocyanine Green) PG36: CI Pigment Green 36 (green pigment) PG8: CI Pigment Green 8 (green pigment) PV23: CI Pigment Violet 23 (dioxazine violet pigment) PW6: CI Pigment White 6 (white pigment) PB7: CI Pigment Black 7 (black pigment) PB15:3: CI Pigment Blue 15:3 (cyan pigment) PR150: CI Pigment Red 150 (magenta pigment) PY74: CI Pigment Yellow 74 (yellow pigment)

[0112] For the ink sets of Examples 1 to 8 and Comparative Examples 1 and 2, the various inks prepared in the above Production Examples were used in the combinations shown in Table 4. The ink mixing stability and abrasion resistance were evaluated according to the following methods.

[0113] [Color uniformity evaluation of mixed inks] Immediately after inkjet ejection onto a recording medium with a low liquid absorption substrate, the ink contains a large amount of solvent. This results in high fluidity, making the inks highly susceptible to mixing. Therefore, we evaluated the uniformity of the liquid and coating when the inks were mixed. Specifically, we mixed equal amounts of two or more inks from Inks 1 to 14, thoroughly stirred them with a stirrer, and then left them to stand at room temperature for one week. The sedimentation and aggregation nonuniformity of the mixed inks after standing were evaluated according to the following criteria. The mixed ink was applied to a corona-treated polyethylene terephthalate (PET) film using a bar coater and dried at room temperature. The corona-treated PET film was "Taiko Polyester Film FE2001" manufactured by Futamura Chemical Co., Ltd., and the water absorption of the recording medium when the recording medium was in contact with pure water for 100 ms was 0 g / m. 2 The color mixing state of the dried coating was visually evaluated according to the following criteria. The color mixing state of the dried coating is considered to be related to the image quality when printed by inkjet. The results are shown in Table 4. A: No sedimentation was observed in the mixed liquid, it was filterable, and no color separation was observed in the applied product. B: No sedimentation was observed in the mixed liquid, but filtration was impossible and no significant color separation was observed in the applied product. C: Sedimentation was observed in the mixed liquid and it was clearly not uniform, or clear color separation was observed in the applied product.

[0114] [Evaluation of abrasion resistance of printed matter] After printing a 100% duty solid print on a recording medium, the solid print was rubbed with a cotton swab under a load of 1 g, and the change in the solid print was visually evaluated according to the following criteria: If the ink type was four colors, the abrasion resistance was evaluated after printing in all four colors. A: No change can be seen at all B: Color change or ink peeling is observed on less than 10% of the printed surface. C: Color change or ink peeling is observed on 10% to less than 50% of the printed surface. D: Color change or ink peeling is observed on 50% or more of the printed surface.

[0115] [Example 1] In a temperature of 25±1°C and a relative humidity of 30±5%, a One Pass Jet (single-pass printing device; manufactured by Tritec Corporation) equipped with an inkjet head (Kyocera Corporation, "KJ4B-1200-P08ST," piezo-electric type) was used. Ink 1 (CI Pigment Orange 34) and Ink 3 (CI Pigment Green 7) were loaded into the inkjet head, and the inks were placed in order from upstream to downstream in the feed direction of the recording medium. The settings were: head voltage 26V, ejection volume 3 pL, head temperature 32°C, resolution 1200 dpi, pre-ejection flushing count 200 shots, nozzle spacing 1200 npi. The recording medium was fixed in the print evaluation device so that the longitudinal direction of the recording medium was the same as the transport direction.

[0116] The single-pass printing device includes a drive unit for unwinding and winding the recording medium, an inkjet head for ejecting ink onto the recording medium, an under-heater for heating the recording medium from the back side opposite the inkjet head, and a hot air drying device. The distance between the inkjet head and the recording medium was 1.0 mm, the surface temperature of the under-heater was 40°C, and the recording medium transport speed was 20 m / min.

[0117] Using the single-pass printing device, the first ink and then the second ink were ejected in this order to perform solid printing of each color. Hot air at 50 to 120°C was applied between the inkjet head and the film take-up roll to heat and dry the film. The resulting roll print was evaluated for abrasion resistance using the methods and evaluation criteria described above. The ink mixing stability of the first ink and the second ink and the abrasion resistance of the printed matter were evaluated, and both were rated A.

[0118] [Example 2] to [Example 8] Inkjet ejection onto recording media of Examples 2 to 8 was carried out in the same manner as in Example 1, except that the first ink, second ink, third ink, and fourth ink in Example 1 were changed to the types shown in Table 4. Inkjet ejection was performed using the first and second inks, the first and third inks, or the first to fourth inks in the same manner as in Example 1, and the mixing stability of the orange ink and the green ink and the scratch resistance of the printed matter were evaluated. The results are shown in Table 4.

[0119] In Example 2, which used Ink 1 (CI Pigment Orange 34) as the first ink and a green ink containing brominated phthalocyanine (CI Pigment Green 36) as the second ink, the abrasion resistance was rated B, which is slightly inferior to Example 1, which used a green ink containing phthalocyanine green (CI Pigment Green 7).

[0120] In Example 3, in which Ink 1 (CI Pigment Orange 34) was used as the first ink and Ink 5 (CI Pigment Green 8) was used as the second ink, the ink mixing stability was rated B and the scratch resistance of the printed matter was rated C because a green ink in which the green pigment did not have a phthalocyanine skeleton was used.

[0121] [Comparative Example 1] Inkjet ejection was carried out onto a recording medium in the same manner as in Example 1, except that the first ink was changed from ink 1 (CI Pigment Orange 34) to ink 2 (CI Pigment Orange 64). The ink mixing stability of the first ink and the second ink and the abrasion resistance of the printed matter were evaluated. In Comparative Example 2, which used CI Pigment Orange 64, which does not have a disazopyrazolone skeleton, both the ink mixing stability and the abrasion resistance of the printed matter were rated C.

[0122] Comparative Example 2 Ink 6 (CI Pigment Violet 23) was used as the first ink, and Ink 8 (CI Pigment Black 7) was used as the second ink, and they were ejected onto a recording medium by inkjet printing. In Comparative Example 2, which used an orange ink containing CI Pigment Orange 34 as a pigment but no fixing resin, and a green ink containing a green pigment (CI Pigment Green 7) as a pigment but no fixing resin, the abrasion resistance of the printed matter was rated D. However, the ink mixing stability was rated A.

[0123] [Table 4]

[0124] From Table 4, comparing Examples 1 to 8 with Comparative Examples 1 and 2, it can be seen that the ink sets of the Examples provide printed matter with superior ink mixing stability and print abrasion resistance compared to the ink sets of the Comparative Examples. Even if the printing order of the inks is changed, it is thought that the ink mixing stability and the abrasion resistance of the printed product will be excellent. Furthermore, in particular, in the case of reverse printing, it is thought that printing the process colors before printing the orange and green will provide better ink mixing stability and abrasion resistance of the printed product, and in the case of front printing, it is thought that printing the process colors after printing the orange and green will provide better ink mixing stability and abrasion resistance of the printed product.

Claims

1. An ink jet recording ink set having at least an orange ink and a green ink, the orange ink and the green ink are water-based inks containing a pigment, a pigment dispersant, a fixing resin, a water-soluble organic solvent, a surfactant, and water; The pigment contained in the orange ink is C.I. Pigment Orange 34. Ink set for inkjet recording.

2. 2. The ink set for ink jet recording according to claim 1, wherein the pigment contained in the green ink is a phthalocyanine pigment.

3. The ink set for ink jet recording according to claim 1 or 2, which is for ink jet recording on a low liquid-absorbent substrate.

4. 3. The ink set for ink jet recording according to claim 1, wherein the fixing resin is a urethane resin.

5. The ink set for ink jet recording according to claim 1 or 2, which is used in a line head type ink jet recording apparatus.

6. 3. The ink set for inkjet recording according to claim 1, wherein the content of the pigment in the orange ink is from 1% by mass to 10% by mass.

7. 3. The ink set for inkjet recording according to claim 1, wherein the content of the pigment in the green ink is from 1% by mass to 10% by mass.

8. The ink set for inkjet recording according to claim 1 or 2, further comprising at least one ink selected from the group consisting of a white ink, a process color ink, and other special color inks.

9. 9. The ink set for inkjet recording according to claim 8, wherein the content of the pigment in the process color inks is greater than the content of the pigment in the orange ink.

10. 3. The ink set for inkjet recording according to claim 1, wherein the content of the fixing resin in the orange ink and the green ink is 0.5% by mass or more and 10% by mass or less.

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