Ink set

Abstract

To provide an ink set including inkjet ink and maintenance fluid that has good material compatibility and can achieve both cleanability for dried ink and storage stability of the ink. [Solution] An ink set comprising an inkjet ink and a maintenance liquid, wherein the inkjet ink comprises a colorant, a binder resin, water, and an organic solvent A, the amount of water in the inkjet ink is 3.0 to 13.0% by mass relative to the total amount of the inkjet ink, the binder resin is soluble in the organic solvent A and insoluble in water, and the maintenance liquid comprises water and an organic solvent B, the amount of water in the maintenance liquid is 3.0 to 18.0% by mass relative to the total amount of the maintenance liquid.

Description

Technical Field

[0001] Embodiments of the present invention relate to an ink set.

Background Art

[0002] In the inkjet recording method, highly fluid inkjet ink is ejected as droplets from fine nozzles, and an image is recorded on a substrate placed opposite the nozzles. Since it is possible to print at high speed with low noise, it has been rapidly spreading in recent years. As inks used in such inkjet recording methods, aqueous inks containing water as a main solvent, ultraviolet curable inks (UV inks) containing a high content of polymerizable monomers as main components, hot melt inks (solid inks) containing a high content of wax as main components, and so-called non-aqueous inks containing a non-aqueous solvent as a main solvent are known. Non-aqueous inks can be classified into solvent inks (solvent-based inks) whose main solvent is a volatile organic solvent and oil-based inks (oil-based inks) whose main solvent is a low-volatile or non-volatile organic solvent. Solvent inks mainly dry on the substrate by evaporation of the organic solvent, while oil-based inks mainly dry by penetration into the substrate.

[0003] In order to suppress ejection failures in inkjet printing, a maintenance liquid or the like is used. Patent Document 1 describes a cleaning liquid for an inkjet printer used in an inkjet printer that uses a non-aqueous inkjet ink containing a pigment, the cleaning liquid having an organic solvent solution containing water. Patent Document 2 describes a maintenance liquid for aqueous inkjet recording containing one or more organic solvents having a boiling point of 180°C or higher, the content of water being 30% by weight or less with respect to the total amount of the maintenance liquid.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] The embodiment of the present invention aims to provide an ink set including an inkjet ink and a maintenance liquid that has good material suitability and can achieve both cleanability of dried ink and storage stability of the ink. [Means for solving the problem]

[0006] One embodiment of the present invention relates to an ink set comprising an inkjet ink and a maintenance liquid, wherein the inkjet ink comprises a colorant, a binder resin, water, and an organic solvent A, the amount of water in the inkjet ink is 3.0 to 13.0% by mass relative to the total amount of the inkjet ink, the binder resin is soluble in the organic solvent A and insoluble in water, and the maintenance liquid comprises water and an organic solvent B, the amount of water in the maintenance liquid is 3.0 to 18.0% by mass relative to the total amount of the maintenance liquid. [Effects of the Invention]

[0007] According to embodiments of the present invention, an ink set including ink and maintenance fluid can be provided that has good material suitability and can achieve both cleanability for dried ink and storage stability of the ink. [Modes for carrying out the invention]

[0008] The present invention will be described below using embodiments. The examples in the following embodiments are not intended to limit the present invention. In the following description, inkjet ink may be simply referred to as "ink".

[0009] One embodiment of the ink set is an ink set comprising an inkjet ink and a maintenance liquid, wherein the inkjet ink comprises a colorant, a binder resin, water, and an organic solvent A, and in the inkjet ink, the amount of water is 3.0 to 13.0% by mass relative to the total amount of inkjet ink, and the binder resin is soluble in organic solvent A and insoluble in water, and the maintenance liquid comprises water and organic solvent B, and in the maintenance liquid, the amount of water is 3.0 to 18.0% by mass relative to the total amount of maintenance liquid.

[0010] The ink set of this embodiment has good compatibility with components such as rubber parts like wipe blades provided in inkjet printers, and it is possible to achieve both cleanability of dried ink with maintenance fluid and storage stability of the ink. Although not bound by any particular theory, the reason is presumed to be as follows.

[0011] When ink and maintenance fluid come into contact with components such as rubber parts like wipe blades, plasticizers contained in the components may leach out. When the amount of water in the ink is 3.0% by mass or more of the total ink volume, the leaching of plasticizers contained in the components due to contact between the ink and rubber parts is easily inhibited. Similarly, when the amount of water in the maintenance fluid is 3.0% by mass or more of the total maintenance fluid volume, the leaching of plasticizers contained in the components due to contact between the maintenance fluid and rubber parts is easily inhibited. When the amount of water in the maintenance fluid is 18.0% by mass or less of the total maintenance fluid volume, non-water-soluble binder resins contained in the dried ink are easily dissolved, improving the cleaning performance of the dried ink by the maintenance fluid. When the binder resin is soluble in organic solvent A, and the amount of water in the ink is 13.0% by mass or less of the total ink volume, the binder resin in the ink that is soluble in organic solvent A and non-water-soluble is less likely to precipitate, improving the storage stability of the ink. In this way, it is presumed that both the ink and the maintenance fluid can be made to have good compatibility with rubber components such as wipe blades, and that it is possible to achieve both cleanability of dried ink and storage stability of the ink.

[0012] The ink set of the embodiment may include inkjet ink and maintenance fluid. The ink set may further include pre-treatment fluid, post-treatment fluid, etc. The inkjet ink and maintenance fluid will be described below.

[0013] <Inkjet ink> In the ink set according to the embodiment, the ink may include a colorant, a binder resin, water, and an organic solvent A.

[0014] Ink may contain pigments, dyes, or combinations thereof as colorants.

[0015] As pigments, organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments, and blue-green lake pigments, and inorganic pigments such as carbon black and metal oxides can be used. Examples of azo pigments include soluble azo lake pigments, insoluble azo pigments, and condensed azo pigments. Examples of phthalocyanine pigments include metallic phthalocyanine pigments and metal-free phthalocyanine pigments. Examples of polycyclic pigments include quinacridone pigments, perylene pigments, perinone pigments, isoindoline pigments, isoindolinone pigments, dioxazine pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, metal complex pigments, and diketopyrrolopyrrole (DPP). Examples of carbon black include furnace carbon black, lamp black, acetylene black, and channel black. Examples of metal oxides include titanium dioxide and zinc oxide. These pigments may be used individually or in combination of two or more types.

[0016] From the viewpoint of ejection stability and storage stability, the average particle size of pigment particles in the ink is preferably 1 μm or less, more preferably 500 nm or less, and even more preferably 300 nm or less, as the volume-based average value of the particle size distribution measured by dynamic light scattering.

[0017] Pigments may be incorporated into the ink as pigment dispersions. The pigment dispersions should be such that the pigment is dispersible in a solvent and the pigment is dispersed in the ink. For example, a dispersion in which the pigment is dispersed in a dispersion medium with a pigment dispersant, or a dispersion in which microencapsulated pigments coated with resin are dispersed in a dispersion medium can be used.

[0018] The dispersion form of the pigment may be a so-called encapsulated pigment in which the pigment is coated with a non-oil-soluble resin, or a dispersion in which colored resin particles are dispersed with a pigment dispersant, but it is preferable that the dispersion is in which the pigment dispersant is directly adsorbed onto the surface of the pigment and dispersed.

[0019] As the dye, any dye generally used in the relevant technical field can be arbitrarily used. Since the dye shows affinity for the non-aqueous solvent of the ink, the storage stability becomes better, so it is preferable to use an oil-soluble dye.

[0020] Examples of the oil-soluble dye include azo dye, metal complex salt dye, naphthol dye, anthraquinone dye, indigo dye, carbonium dye, quinoneimine dye, xanthene dye, cyanine dye, quinoline dye, nitro dye, nitroso dye, benzoquinone dye, naphthoquinone dye, phthalocyanine dye, metal phthalocyanine dye, etc. These may be used alone or in combination of multiple types.

[0021] From the viewpoints of printing density and ink viscosity, the content of the colorant is preferably 0.1 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 5 to 10% by mass based on the total amount of the ink.

[0022] When the ink contains a pigment, a pigment dispersant can be used together with the pigment in order to stably disperse the pigment in the ink. The pigment dispersant is not particularly limited as long as it can stably disperse the pigment in the ink. For example, hydroxyl group-containing carboxylic acid ester, salt of long-chain polyaminoamide and high molecular weight acid ester, salt of high molecular weight polycarboxylic acid, salt of long-chain polyaminoamide and polar acid ester, high molecular weight unsaturated acid ester, copolymer of vinylpyrrolidone and long-chain alkene, modified polyurethane, modified polyacrylate, polyether ester type anionic surfactant, polyoxyethylene alkyl phosphate ester, polyester polyamine, etc. are preferably used.

[0023] As the pigment dispersant, it is preferable to use a polymer dispersant. As the polymer dispersant, a synthesized one may be used, or a commercially available product may be used. Examples of commercially available pigment dispersants include "Solsperse J180", "Solsperse J200", "Solsperse 71000", "Solsperse 74000", "Solsperse 86000", "Solsperse 87000", "Solsperse M387", etc. manufactured by Lubrizol Japan Ltd., and "BYKJET-9151", "BYKJET-9152", "BYKJET-9170", etc. manufactured by BYK Chemie Japan Co., Ltd. (all are trade names). These may be used alone or in combination of two or more.

[0024] The pigment dispersant is preferably contained at a mass ratio of 0.2 to 1.0 with respect to the pigment 1. The content of the pigment dispersant in the total amount of the ink is preferably 0.5 to 15% by mass, more preferably 1 to 5% by mass.

[0025] The ink can contain a binder resin.

[0026] From the viewpoint of improving the storage stability of the ink, the binder resin is preferably soluble in the organic solvent A contained in the ink. By being soluble in the organic solvent A contained in the ink, the binder resin is less likely to precipitate, which can contribute to improving the storage stability of the ink. From the viewpoint of improving the cleaning property of the dried ink, the binder resin is preferably water-insoluble. By the binder resin being water-insoluble, it is easy to remove the dried ink with a maintenance liquid having a small amount of water, and the cleaning property of the dried ink can be improved.

[0027] From the viewpoint of further improving the cleaning property of the dried ink, the binder resin is preferably soluble in the organic solvent B of the maintenance liquid.

[0028] In this disclosure, the solubility of the binder resin in organic solvent A means that the mixture obtained by mixing 10% by mass of the binder resin and 90% by mass of organic solvent A with respect to the total amount of the mixture and heating it at 60°C for 24 hours is a transparent solution at 23°C. Similarly, the solubility of the binder resin in organic solvent B means that the mixture obtained by mixing 10% by mass of the binder resin and 90% by mass of organic solvent B with respect to the total amount of the mixture and heating it at 60°C for 24 hours is a transparent solution at 23°C.

[0029] In this disclosure, a binder resin being non-water-soluble means that when 10% by mass of the binder resin and 90% by mass of water are mixed with the total amount of the mixture, the resulting mixture is not a clear solution at 23°C.

[0030] Examples of binder resins include (meth)acrylic resin, styrene-(meth)acrylic resin, styrene-maleic acid resin, ethylene-(meth)acrylic resin, urethane resin, vinyl chloride resin, vinyl chloride-vinyl acetate resin, polyester resin, polyvinyl alcohol resin, epoxy resin, and polyvinylpyrrolidone resin.

[0031] From the viewpoint of improving the adhesion of the image to the substrate, (meth)acrylic resin is preferred as the binder resin. More preferably, a (meth)acrylic resin that is soluble in organic solvent A is preferred as the binder resin. When a (meth)acrylic resin is used, the adhesion of the image to plastic substrates such as olefin resins can be improved. In particular, olefin resins tend to have a low affinity for organic solvents in inks, and it can be difficult to obtain good image adhesion, but when a (meth)acrylic resin is used, it is easier to improve the adhesion of the image to the substrate.

[0032] The (meth)acrylic resin may be a resin comprising, for example, at least one unit selected from the group consisting of units derived from (meth)acrylic acid and units derived from (meth)acrylic acid esters. In this disclosure, (meth)acrylic acid means acrylic acid and methacrylic acid collectively, (meth)acrylic acid ester means acrylic acid ester and methacrylic acid ester collectively, and (meth)acrylate means acrylate and methacrylate collectively.

[0033] Examples of (meth)acrylic acid esters include alkyl (meth)acrylates, benzyl (meth)acrylates, and hydroxyalkyl (meth)acrylates. Examples of alkyl (meth)acrylates include alkyl (meth)acrylates having an alkyl group with 1 to 8, 1 to 6, or 1 to 4 carbon atoms, specifically including methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0034] The (meth)acrylic resin may be, for example, a polymer of one or more monomers selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters.

[0035] Examples of (meth)acrylic resins include poly(meth)acrylic acid, poly(meth)acrylic acid esters (e.g., methyl poly(meth)acrylate, ethyl poly(meth)acrylate, butyl poly(meth)acrylate, etc.), (meth)acrylic acid ester copolymer resins, (meth)acrylic acid-(meth)acrylic acid ester copolymer resins, etc.

[0036] The (meth)acrylic resin preferably contains units derived from, for example, alkyl (meth)acrylate. The units derived from alkyl (meth)acrylate may be, for example, 50.0% by mass or more, 70.0% by mass or more, or 90.0% by mass or more, relative to the total units of the (meth)acrylic resin.

[0037] Specific examples of (meth)acrylic resins include, for example, polymers of methyl (meth)acrylate, copolymers of methyl (meth)acrylate with at least one selected from the group consisting of (meth)acrylic acid, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and benzyl (meth)acrylate (for example, copolymers of 100 parts by mass of methyl methacrylate with 0.1 to 200 parts by mass, 1 to 180 parts by mass, or 10 to 150 parts by mass of at least one selected from the group consisting of methacrylic acid, butyl methacrylate, and benzyl methacrylate).

[0038] The glass transition temperature (Tg) of the (meth)acrylic resin may be, for example, 60°C or higher, preferably 80°C or higher, and more preferably 100°C or higher, from the viewpoint of improving the adhesion of the image to the substrate. The glass transition temperature of the (meth)acrylic resin may be, for example, 200°C or lower. The glass transition temperature of the (meth)acrylic resin may be, for example, 60-200°C, 80-200°C, or 100-200°C. In this disclosure, the glass transition temperature is an estimated value according to FOX's formula.

[0039] The weight-average molecular weight of the (meth)acrylic resin is preferably 5,000 to 150,000, and more preferably 10,000 to 100,000. From the viewpoint of water resistance and durability, the weight-average molecular weight of the (meth)acrylic resin is preferably 5,000 or more, and more preferably 10,000 or more. From the viewpoint of ink viscosity and discharge properties, the weight-average molecular weight of the (meth)acrylic resin is preferably 150,000 or less, and more preferably 100,000 or less. In this disclosure, the weight-average molecular weight is the value obtained by the GPC method on a standard polystyrene basis.

[0040] As the (meth)acrylic resin, a synthesized resin may be used, or a commercially available resin may be used.

[0041] The method for synthesizing (meth)acrylic resin is not particularly limited. (Meth)acrylic resin can be obtained, for example, by polymerizing one or more radical polymerizable monomers by solution polymerization or the like. For example, at least one monomer selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters can be polymerized.

[0042] The polymerization solvent (reaction solvent) used in solution polymerization is not particularly limited, but it is preferable that it is capable of dissolving the (meth)acrylic resin obtained by polymerization. From the viewpoint of compatibility between the obtained (meth)acrylic resin and the organic solvent in the ink, and thereby preparing a low-viscosity ink, the organic solvent A contained in the ink may be used as the polymerization solvent. For example, if the ink contains two or more organic solvents as organic solvent A, only one of them may be used as the polymerization solvent.

[0043] Polymerization initiators, such as radical polymerization initiators, may be used during the polymerization reaction. As radical polymerization initiators, known radical polymerization initiators such as azo compounds including 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(2,4'-dimethylvaleronitrile), and dimethyl 2,2'-azobisisobutyrate, and organic peroxides such as hydroperoxides, dialkylperoxides, peroxyesters, and diallylperoxides can be used. These may be used individually or in combination of two or more.

[0044] As the (meth)acrylic resin, from the viewpoint of good compatibility between the (meth)acrylic resin and the solvent, and thereby the preparation of a low-viscosity ink, an acrylic resin obtained by solution polymerization of a radically polymerizable monomer with a radical polymerization initiator in organic solvent A used for the ink is preferred. The (meth)acrylic resin may be, for example, a resin obtained by solution polymerization using only one of two or more organic solvents as the polymerization solvent when the ink contains two or more organic solvents as organic solvent A.

[0045] Examples of commercially available (meth)acrylic resins include "Neocryl B-728" and "Neocryl B-801" from Covestro Coating Resin, and "Dianal BR-83," "Dianal BR-87," and "Dianal MB-7333" from Mitsubishi Chemical Corporation (all are product names).

[0046] The binder resin may be, for example, 1.0% by mass or more, or 3.0% by mass or more, relative to the total amount of ink. On the other hand, the binder resin may be, for example, 40.0% by mass or less, 30.0% by mass or less, or 20.0% by mass or less, relative to the total amount of ink. The binder resin may be, for example, 1.0 to 40.0% by mass, 1.0 to 30.0% by mass, or 3.0 to 20.0% by mass, relative to the total amount of ink.

[0047] The ink may contain water. While there are no particular restrictions on the type of water, it is preferable to use water that contains as few ionic components as possible. In particular, from the viewpoint of the ink's storage stability, it is preferable to use water with a low content of polyvalent metal ions such as calcium. Suitable water options include, for example, deionized water, distilled water, or ultrapure water.

[0048] From the viewpoint of improving material suitability, the amount of water is preferably 3.0% by mass or more, more preferably 4.0% by mass or more, and even more preferably 5.0% by mass or more, relative to the total amount of ink. On the other hand, from the viewpoint of improving the storage stability of the ink, the amount of water is preferably 13.0% by mass or less, relative to the total amount of ink. The amount of water may be, for example, 12.0% by mass or less, 10.0% by mass or less, or 8.0% by mass or less, relative to the total amount of ink. The amount of water is preferably 3.0 to 13.0% by mass, more preferably 4.0 to 13.0% by mass, and even more preferably 5.0 to 13.0% by mass, relative to the total amount of ink. The amount of water may be, for example, 4.0 to 12.0% by mass, 4.0 to 10.0% by mass, or 5.0 to 8.0% by mass, relative to the total amount of ink.

[0049] The amount of water in ink may be the same as the amount of water actively added to the ink. On the other hand, when an organic solvent with an affinity for water is added to the ink, such an organic solvent may absorb water vapor, etc., contained in the atmosphere, and in such cases, the amount of water added to the ink may not be the same as the amount of water in the ink. Similarly, the amount of water in the maintenance fluid, which will be discussed later, may be the same as the amount of water actively added to the maintenance fluid. On the other hand, for the same reasons as in the case of ink, the amount of water added to the maintenance fluid may not be the same as the amount of water in the maintenance fluid. The amount of water in the ink and the amount of water in the maintenance fluid may be measured, for example, using the Karl Fischer method.

[0050] The ink may contain organic solvent A.

[0051] Examples of organic solvent A include ketone-based organic solvents, alcohol-based organic solvents, glycol ether-based organic solvents, acetate-based organic solvents, carboxylic acid ester-based organic solvents, amide-based organic solvents, etc. These may be used individually or in combination of two or more.

[0052] Organic solvent A may be a water-soluble organic solvent, a non-water-soluble organic solvent, or a combination thereof. Since ink contains water, it is preferable that organic solvent A includes a water-soluble organic solvent from the viewpoint of obtaining a more uniform ink.

[0053] As the water-soluble organic solvent, an organic compound that is liquid at room temperature and soluble in water can be used, and it is preferable to use a water-soluble organic solvent that mixes uniformly with the same volume of water at 1 atmosphere and 20°C. Examples of water-soluble organic solvents include diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol dimethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, 3-methoxy-3-methyl-1-butanol, 3-methoxy-1-butanol, diethylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether acetate, 1,2-propanediol, ethyl lactate, ethylene glycol, ethylene glycol monoacetate, γ-butyrolactone, 2-pyrrolidone, etc. These may be used individually or in combination of two or more.

[0054] Examples of water-insoluble organic solvents include ethylene glycol monobutyl ether acetate, ethylene glycol diacetate, propylene glycol diacetate (1,2-diacetoxypropane), dipropylene glycol dimethyl ether, propylene glycol 1-monobutyl ether, butyl lactate, hexyl propionate, ethyl 3-ethoxypropionate, γ-hexanolactone, and ethyl acetoethyl. These may be used individually or in combination of two or more.

[0055] The amount of organic solvent A may be, for example, 60.0% by mass or more, 65.0% by mass or more, or 70.0% by mass or more, relative to the total amount of ink. The amount of organic solvent A may be, for example, 95.0% by mass or less, 90.0% by mass or less, or 85.0% by mass or less, relative to the total amount of ink. The amount of organic solvent A may be, for example, 60.0 to 95.0% by mass, 65.0 to 90.0% by mass, or 70.0 to 85.0% by mass, relative to the total amount of ink.

[0056] The amount of water-soluble organic solvent may be, for example, 30.0% by mass or more, 50.0% by mass or more, 70.0% by mass or more, or 90.0% by mass or more, relative to the total amount of organic solvent A. The amount of water-soluble organic solvent may be, for example, 100.0% by mass or less, or 95.0% by mass or less, relative to the total amount of organic solvent A. The amount of water-soluble organic solvent may be, for example, 30.0 to 100.0% by mass, 50.0 to 100.0% by mass, 70.0 to 100.0% by mass, or 90.0 to 95.0% by mass, relative to the total amount of organic solvent A.

[0057] Ink preferably contains a surfactant. For example, it is preferable for the ink to contain a surfactant in order to improve the wetting and spreading of the ink even on hydrophobic substrate surfaces, increase the drying speed, and form a good image. Examples of surfactants include silicone-based surfactants, fluorine-based surfactants, and nonionic surfactants such as polyoxyethylene derivatives.

[0058] Examples of silicone-based surfactants include polyester-modified silicones and polyether-modified silicones. Examples of commercially available silicone-based surfactants include "BYK-307", "BYK-313", "BYK-330", "BYK-333", "BYK-342", "BYK-370", "BYK-377", "BYK-378", "BYK-3550", "BYK-3750", "BYK-3761", "BYK-3762", "BYK-3764", and "BYK-SILCLEAN 3700" from BIC Chemie Japan Co., Ltd., and "Sylface SAG005", "Sylface SAG008", and "Sylface SAG503A" from Nisshin Chemical Industry Co., Ltd. (all are product names).

[0059] Examples of commercially available fluorine-based surfactants include "BYK-340" from BIC Chemie Japan Co., Ltd., and "Surflon S-241," "Surflon S-242," "Surflon S-242L," "Surflon S-243," "Surflon S-420," and "Surflon S-431" from AGC Inc. (all are product names).

[0060] As the polyoxyethylene derivative, it is preferable to use an acetylene glycol-based surfactant. Examples of commercially available acetylene glycol-based surfactants include, for example, "Surfinol 420," "Surfinol 440," "Surfinol 465," and "Surfinol 485" from Evonik Industries, and "Orfin E-1004" and "Orfin-1010" from Nisshin Chemical Industry Co., Ltd. (all are trade names).

[0061] From the viewpoint of continuous ejection during printing and image color reproduction, it is preferable that the ink contains a silicone-based surfactant.

[0062] Surfactants may be used individually or in combination of two or more types. The amount of surfactant is preferably 0.05 to 2.0% by mass, and more preferably 0.1 to 1.0% by mass, relative to the total amount of ink.

[0063] Depending on the application, the ink may contain various additives. Examples of additives include UV absorbers, light stabilizers, antioxidants, and plasticizers.

[0064] The method for manufacturing ink is not particularly limited, but one method is to mix and stir each component together or separately to produce ink. Specifically, for example, all components can be put together or separately into a disperser such as a bead mill and dispersed, and if desired, the mixture can be passed through a filter such as a membrane filter to produce the ink.

[0065] In the ink manufacturing method, for example, a pigment dispersion may be prepared by first mixing and stirring the pigment with a pigment dispersant and an organic solvent to disperse the pigment.

[0066] The viscosity of inkjet ink varies depending on the nozzle diameter of the ejection head and the ejection environment of the inkjet recording system, but generally, it is preferably 3 to 30 mPa·s at 23°C, more preferably 3 to 15 mPa·s, and even more preferably 4 to 10 mPa·s.

[0067] The printing method using inkjet ink is not particularly limited and may be any method, such as piezo, electrostatic, or thermal. When using an inkjet recording device, it is preferable to eject ink according to one embodiment from the inkjet head based on a digital signal and to adhere the ejected ink droplets to the substrate.

[0068] In this embodiment, the substrate is not particularly limited and can be printing paper such as plain paper, coated paper, or specialty paper, cloth, inorganic sheets, films, OHP sheets, or adhesive sheets with an adhesive layer on the back surface using these as substrates. For example, the ink of this embodiment can also be preferably used on plastic substrates such as polyvinyl chloride resin or olefin resin. Examples of olefin resins include polypropylene resin. Such plastic substrates may be absorbent substrates capable of absorbing the applied ink, such as substrates having an ink-receiving layer, or they may be non-absorbent substrates without an ink-receiving layer. Examples of substrates using olefin resins include synthetic paper made of olefin resin such as polypropylene resin.

[0069] Printed materials can be manufactured using the ink of the embodiment. The ink can be applied to the substrate by an inkjet method. The inkjet method is not particularly limited and may be any method such as a piezo method, electrostatic method, or thermal method.

[0070] <Maintenance fluid> The maintenance fluid may contain water and organic solvent B.

[0071] While there are no particular restrictions on the type of water used, it is preferable to use water that contains as few ionic components as possible. In particular, from the viewpoint of storage stability of the maintenance fluid, it is preferable to use water with a low content of polyvalent metal ions such as calcium. Suitable water options include, for example, deionized water, distilled water, or ultrapure water.

[0072] From the viewpoint of improving material suitability, the amount of water is preferably 3.0% by mass or more, more preferably 4.0% by mass or more, and even more preferably 5.0% by mass or more, relative to the total amount of maintenance fluid. On the other hand, from the viewpoint of improving cleaning performance for ink-dried materials, the amount of water is preferably 18.0% by mass or less, more preferably 16.0% by mass or less, even more preferably 14.0% by mass or less, and even more preferably 12.0% by mass or less, relative to the total amount of maintenance fluid. For example, the amount of water is preferably 3.0 to 18.0% by mass, more preferably 4.0 to 16.0% by mass, even more preferably 4.0 to 14.0% by mass, and even more preferably 5.0 to 12.0% by mass, relative to the total amount of maintenance fluid.

[0073] The maintenance fluid may contain organic solvent B.

[0074] Examples of organic solvent B include ketone-based organic solvents, alcohol-based organic solvents, glycol ether-based organic solvents, acetate-based organic solvents, carboxylic acid ester-based organic solvents, amide-based organic solvents, and the like. These may be used individually or in combination of two or more.

[0075] Organic solvent B may be a water-soluble organic solvent, a non-water-soluble organic solvent, or a combination thereof. Since the maintenance fluid contains water, it is preferable that organic solvent B contains a water-soluble organic solvent from the viewpoint of obtaining a more uniform maintenance fluid.

[0076] As the water-soluble organic solvent, an organic compound that is liquid at room temperature and soluble in water can be used, and it is preferable to use a water-soluble organic solvent that mixes uniformly with the same volume of water at 1 atmosphere and 20°C. Examples of water-soluble organic solvents include those listed as examples of water-soluble organic solvents in the ink's organic solvent A. These water-soluble organic solvents may be used individually or in combination of two or more.

[0077] Examples of water-insoluble organic solvents include those listed as examples of water-insoluble organic solvents in the context of organic solvent A for ink. These water-insoluble organic solvents may be used individually or in combination of two or more.

[0078] It is preferable that organic solvent B and organic solvent A contained in the ink contain the same organic solvent. For example, if organic solvent A contains one or more organic solvents, then organic solvent A may contain one or more of those organic solvents. Organic solvent A and organic solvent B may be the same.

[0079] The amount of organic solvent B may be, for example, 80.0% by mass or more, or 85.0% by mass or more, relative to the total amount of maintenance fluid. The amount of organic solvent B may be, for example, 97.0% by mass or less, 95.0% by mass or less, or 90.0% by mass or less, relative to the total amount of maintenance fluid. The amount of organic solvent B may be, for example, 80.0 to 97.0% by mass, 85.0 to 95.0% by mass, or 85.0 to 90.0% by mass, relative to the total amount of maintenance fluid.

[0080] The amount of water-soluble organic solvent may be, for example, 30.0% by mass or more, 50.0% by mass or more, 70.0% by mass or more, or 90.0% by mass or more, relative to the total amount of organic solvent B. The amount of water-soluble organic solvent may be, for example, 100.0% by mass or less, or 95.0% by mass or less, relative to the total amount of organic solvent B. The amount of water-soluble organic solvent may be, for example, 30.0 to 100.0% by mass, 50.0 to 100.0% by mass, 70.0 to 100.0% by mass, or 90.0 to 95.0% by mass, relative to the total amount of organic solvent B.

[0081] In the maintenance fluid, the total amount of water and organic solvent B is preferably 80.0% by mass or more, more preferably 90.0% by mass or more, even more preferably 95.0% by mass or more, and even more preferably 99.0% by mass or more, based on the total amount of the maintenance fluid. In the maintenance fluid, the total amount of water and organic solvent B may be, for example, 100.0% by mass or less, or 99.9% by mass or less, based on the total amount of the maintenance fluid. In the maintenance fluid, the total amount of water and organic solvent B may be, for example, 80.0 to 100.0% by mass, 90.0 to 100.0% by mass, 95.0 to 100.0% by mass, or 99.0 to 99.9% by mass, based on the total amount of the maintenance fluid.

[0082] The maintenance fluid preferably contains a surfactant. Examples of surfactants include silicone-based surfactants, fluorine-based surfactants, and nonionic surfactants such as polyoxyethylene derivatives.

[0083] Specific examples of surfactants include those mentioned as examples of surfactants in ink.

[0084] Surfactants may be used individually or in combination of two or more types. The amount of surfactant is preferably 0.05 to 2.0% by mass, and more preferably 0.1 to 1.0% by mass, relative to the total amount of maintenance fluid.

[0085] Maintenance fluids may contain various additives depending on their intended use. Examples of additives include UV absorbers, light stabilizers, antioxidants, and plasticizers.

[0086] The method for manufacturing the maintenance fluid is not particularly limited, but one method is to mix each component together or separately, and then, if desired, pass the mixture through a filter such as a membrane filter.

[0087] The maintenance fluid can be used, for example, to remove dried ink that has hardened on the wipe blade, or to remove ink or dried ink that has adhered to the nozzle surface or nozzle cap of the inkjet head. Specifically, for example, the maintenance fluid can be soaked into a cloth and used to wipe away dried ink that has hardened on the wipe blade, or ink or dried ink that has adhered to the nozzle surface or nozzle cap of the inkjet head. Furthermore, for example, when a printing press is to be shut down for an extended period, the ink in the ink channels may be replaced with maintenance fluid beforehand. Also, if a malfunction occurs in the printing press, maintenance fluid may be used to clean the ink channels.

[0088] This disclosure includes the following embodiments. <1> An ink set including inkjet ink and maintenance fluid, The aforementioned inkjet ink comprises a colorant, a binder resin, water, and an organic solvent A. In the aforementioned inkjet ink, the amount of water is 3.0 to 13.0% by mass relative to the total amount of the inkjet ink. The binder resin is soluble in the organic solvent A and insoluble in water. The aforementioned maintenance fluid contains water and organic solvent B. In the aforementioned maintenance fluid, water is present in an amount of 3.0 to 18.0% by mass relative to the total volume of the maintenance fluid, in this ink set. <2> In the aforementioned maintenance fluid, the total amount of water and the organic solvent B is 95.0% by mass or more of the total amount of the maintenance fluid. <1> The ink set described above. <3> In the aforementioned inkjet ink, the amount of water is 5.0 to 13.0% by mass relative to the total amount of the inkjet ink. <1> or <2> The ink set described above. <4> In the aforementioned maintenance fluid, the amount of water is 4.0 to 16.0% by mass relative to the total amount of the maintenance fluid. <1> ~ <3> The ink set described in any one of the items. [Examples]

[0089] The present invention will be described in detail below with reference to examples. The present invention is not limited to the following examples.

[0090] <Ink Manufacturing> Tables 1 and 2 show the materials and their quantities (mass %) used in the manufacture of inks 1 to 15. Details of the materials listed in the tables will be described later.

[0091] Half of the total amount of organic solvent (or a mixture of two or more if two or more types are used), along with the pigment and pigment dispersant, were measured into a beaker, pre-mixed, and then transferred to a plastic container with a lid. Zirconia beads with a diameter of 0.8 mm were added to this mixture and dispersed for 60 minutes using a rocking mill RM-05 (manufactured by Seiwa Giken Co., Ltd.). The beads were then separated from the dispersion to produce a pigment dispersion.

[0092] A binder resin solution was prepared by heating and dissolving the binder resin in half of the total amount of organic solvent (i.e., the remaining amount used in the production of the pigment dispersion) (i.e., the amount remaining after the production of the pigment dispersion).

[0093] The pigment dispersion prepared above, the binder resin solution prepared above, water, and surfactant were mixed, stirred, and then filtered through a membrane filter with a pore size of 3 μm to produce inks 1 to 15.

[0094] <Solubility of binder resin> For Examples 1-13 and Comparative Examples 1-4, the solubility of the binder resin contained in the ink in water, the solubility of the organic solvent A contained in the ink, and the solubility of the organic solvent B contained in the maintenance fluid combined with the ink were evaluated. The combinations of ink and maintenance fluid used in Examples 1-13 and Comparative Examples 1-4 are shown in Tables 4 and 5.

[0095] Regarding solubility in water, specifically, 10% by mass of binder resin and 90% by mass of water were mixed with the total amount of the mixture, and the solubility of the resulting mixture at 23°C was visually evaluated. In all cases, the resulting mixtures were not transparent solutions.

[0096] Regarding the solubility in organic solvent A, specifically, 10% by mass of binder resin and 90% by mass of organic solvent A were mixed with the total amount of the mixture, and the mixture was heated at 60°C for 24 hours to prepare it. The solubility of the resulting mixture at 23°C was then visually evaluated. In all cases, including Examples 1-13 and Comparative Examples 1-4, the resulting mixtures were clear solutions.

[0097] Regarding solubility in organic solvent B, specifically, 10% by mass of binder resin and 90% by mass of organic solvent B were mixed with the total amount of the mixture, and the mixture was heated at 60°C for 24 hours to prepare it. The solubility of the resulting mixture at 23°C was then visually evaluated. In all cases, including Examples 1-13 and Comparative Examples 1-4, the resulting mixtures were clear solutions.

[0098] <Manufacturing of maintenance fluid> Table 3 shows the materials and their quantities (mass %) used in the manufacture of Maintenance 1-10. Details of the materials listed in the table will be described later.

[0099] An organic solvent, water, and surfactant were mixed, and then filtered through a membrane filter with a pore size of 3 μm to obtain maintenance solutions 1 to 10.

[0100] <Amount of water> The amounts of water in the inks listed in Tables 1 and 2, and the amounts of water in the maintenance fluids listed in Table 3, were measured using the Karl Fischer method. For the measurements, a KF-31 volumetric titration moisture meter manufactured by Nitto Seiko Analytech Co., Ltd. was used.

[0101] [Table 1]

[0102] [Table 2]

[0103] [Table 3]

[0104] Details of the materials listed in Tables 1-3 are shown below.

[0105] (Pigment) Pigment 1: Carbon black, "MA8" (product name), manufactured by Mitsubishi Chemical Corporation. Pigment 2: Copper phthalocyanine, "Fastogen Blue LA5380" (product name), manufactured by DIC Corporation.

[0106] (Pigment dispersant) Pigment dispersant 1: Polymer dispersant, "Solspers J180" (product name), manufactured by Lubrizol Nippon Co., Ltd. Pigment dispersant 2: Polymer dispersant, "Solspers 71000" (product name), manufactured by Lubrizol Nippon Co., Ltd.

[0107] (Binder resin) Binder resin 1: (Meth)acrylic resin, "Neocryl B-728" (product name), manufactured by Covestro Coating Resin. Binder resin 2: (Meth)acrylic resin, "Dianal BR-83" (product name), manufactured by Mitsubishi Chemical Corporation.

[0108] (Organic solvents) Water-soluble organic solvent 1: Diethylene glycol diethyl ether, manufactured by Tokyo Chemical Industry Co., Ltd. Water-soluble organic solvent 2: Diethylene glycol monomethyl ether, manufactured by Tokyo Chemical Industry Co., Ltd. Water-soluble organic solvent 3: γ-butyrolactone, manufactured by Tokyo Chemical Industry Co., Ltd. Water-soluble organic solvent 4:2-pyrrolidone, manufactured by Tokyo Chemical Industry Co., Ltd. Water-soluble organic solvent 5: Ethylene glycol monomethyl ether acetate, manufactured by Tokyo Chemical Industry Co., Ltd. Water-soluble organic solvent 6:3-methoxy-1-butanol, manufactured by Tokyo Chemical Industry Co., Ltd. Water-soluble organic solvent 7: Ethyl lactate, manufactured by Tokyo Chemical Industry Co., Ltd.

[0109] Non-water-soluble organic solvent 1: Ethylene glycol monobutyl ether acetate, manufactured by Tokyo Chemical Industry Co., Ltd. Non-water-soluble organic solvent 2: Ethylene glycol diacetate, manufactured by Tokyo Chemical Industry Co., Ltd. Non-water-soluble organic solvent 3:1,2-diacetoxypropane, manufactured by Tokyo Chemical Industry Co., Ltd. Non-water-soluble organic solvent 4: Butyl lactate, manufactured by Tokyo Chemical Industry Co., Ltd.

[0110] (Surfactants) Surfactant 1: Silicone-based surfactant, "Silface SAG008" (product name), manufactured by Nisshin Chemical Industry Co., Ltd. Surfactant 2: Silicone-based surfactant, "BYK-333" (product name), manufactured by Bic Chemie Japan Co., Ltd.

[0111] <Rating> The following evaluations were performed using the inks and maintenance fluids manufactured as described above. Tables 4 and 5 show the inks and maintenance fluids used in Examples 1-13 and Comparative Examples 1-4. The evaluation results are also shown in Tables 4 and 5.

[0112] 1. Suitability of ink and maintenance fluid components The wipe blades used in the "ValueJet VJ-628" (product name) manufactured by Mutoh Industries, Ltd. were immersed in ink or maintenance fluid and left at 40°C for one month. The weight of the wipe blades was measured before and after immersion, and the weight change rate of the wipe blades was calculated using the following formula. The suitability of the material was evaluated according to the evaluation criteria below. The evaluation results for the suitability of the material for the ink and maintenance fluid are shown in Tables 4 and 5.

[0113] Weight change rate of the wipe blade (%) = [(Weight of the wipe blade after immersion - Weight of the wipe blade before immersion) / Weight of the wipe blade before immersion] × 100

[0114] A: The absolute value of the weight change rate of the wipe blade is less than 15%. B: The absolute value of the weight change rate of the wipe blade is 15% or more but less than 20%. C: The absolute value of the weight change rate of the wipe blade is 20% or more.

[0115] 2. Cleanability of dried ink materials with maintenance fluid. The cleaning performance of the maintenance fluid on dried ink was evaluated using the ink and maintenance fluid combinations of each example and comparative example, as described below. The results are shown in Tables 4 and 5.

[0116] First, 100 μL of ink was dropped onto a wipe blade using a micropipette. Then, the ink was dried in a 60°C constant temperature bath for 1 hour to obtain a dried ink sample. Next, 1 g of maintenance fluid was dropped onto the dried ink sample and wiped with a cloth. This process of dropping 1 g of maintenance fluid and wiping with a cloth was repeated until the dried ink sample was completely wiped away. The cleaning performance of the dried ink sample was evaluated according to the following criteria.

[0117] A: The ink residue can be completely wiped away by applying 1g of maintenance fluid and wiping with a cloth no more than three times. B: Applying 1g of maintenance fluid and wiping with a cloth 4 to 5 times is sufficient to completely remove dried ink. C: Even after applying 1g of maintenance fluid and wiping with a cloth five times, the dried ink cannot be completely wiped away.

[0118] 3. Ink storage stability After manufacturing inks 1-15, they were placed in glass bottles and left to stand at room temperature for one day. After one day, the inks were filtered using filter paper to check for the presence of residue, and the storage stability of the inks was evaluated according to the evaluation criteria below. The results are shown in Tables 4 and 5.

[0119] A: No residue is visible on the filter paper. C: Residual material can be seen on the filter paper.

[0120] [Table 4]

[0121] [Table 5]

[0122] Examples 1 to 13 demonstrated excellent results in terms of ink material suitability, maintenance fluid material suitability, cleaning performance of dried ink materials by the maintenance fluid, and ink storage stability.

[0123] In Comparative Example 1, the ink 14 with a low water content showed a large weight change rate in the evaluation of material suitability, indicating poor material suitability. In Comparative Example 2, the maintenance fluid 8 with a low water content also showed a large weight change rate in the evaluation of material suitability, indicating poor material suitability. Furthermore, Comparative Example 2 also showed that the ink 15 with a high water content had poor storage stability. Comparative Example 3, which used the maintenance fluid 9 with a high water content, showed poor cleaning performance against dried ink. In Comparative Example 4, the maintenance fluid 10 containing no water showed a large weight change rate in the evaluation of material suitability, indicating poor material suitability.

Claims

1. An ink set including inkjet ink and maintenance fluid, The aforementioned inkjet ink comprises a colorant, a binder resin, water, and an organic solvent A. In the inkjet ink, the amount of water is 3.0 to 13.0% by mass relative to the total amount of the inkjet ink. The binder resin is soluble in the organic solvent A and is water-insoluble. The aforementioned maintenance fluid contains water and organic solvent B. In the aforementioned maintenance fluid, the amount of water is 3.0 to 18.0% by mass relative to the total volume of the maintenance fluid, in this ink set.

2. The ink set according to claim 1, wherein the total amount of water and the organic solvent B in the maintenance fluid is 95.0% by mass or more of the total amount of the maintenance fluid.

3. The ink set according to claim 1 or 2, wherein the amount of water in the inkjet ink is 5.0 to 13.0% by mass relative to the total amount of the inkjet ink.

4. The ink set according to claim 1 or 2, wherein the maintenance fluid contains 4.0 to 16.0% by mass of water relative to the total amount of the maintenance fluid.

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