Ink, ink cartridges, inkjet recording devices, and recording materials

Abstract

The present invention aims to provide an infrared absorbing ink that has excellent spectral properties and does not cause pigment sedimentation. [Solution] An ink comprising water, a colorant, and a polymer, wherein the cumulative 50% particle size (D50) of the colorant by volume is 90 nm or more and 250 nm or less, the colorant has a maximum absorption peak at a wavelength of 830 nm or more and 1000 nm or less in an absorption spectrum in the wavelength range of 300 nm to 1500 nm, the content of the colorant in the ink is 0.1% by mass or more and 1.0% by mass or less, the polymer is a compound having a naphthyl group, and the weight-average molecular weight of the polymer is 40,000 to 150,000.

Description

[Technical Field]

[0001] The present invention relates to an ink, an ink cartridge, an inkjet recording apparatus, and a recorded matter. [Background Art]

[0002] Conventionally, various additional data embedding techniques for superimposing and embedding additional information in an image have been proposed. In recent years, there has been increasing activity in utilizing the aforementioned additional data embedding technique for copyright protection of digital works such as still images (for example, prevention of illegal copying). As one example, when a digital work is copied onto a recording medium by an image forming apparatus, an image that is difficult to visually recognize, called an invisible pattern, is formed on the recording medium together with the digital work, whereby there is a technique for embedding information related to the image forming apparatus.

[0003] As a method for reading such an invisible pattern, utilization of infrared absorption has been practiced. For example, it has been proposed that an image formed with ordinary color ink and an image formed with an ink containing an infrared absorbing pigment with low visible light absorption are formed in parallel or overlapping, and an image is recorded such that the two types of image regions are substantially indistinguishable or difficult to distinguish to the naked eye. Patent Document 1 discloses that the above problem is solved by using a cyanine dye as a near-infrared absorbing pigment, with the object of providing a near-infrared absorbing dye-containing ink excellent in spectral characteristics, invisibility, light resistance, moist heat resistance, and water resistance. [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, conventional invisibility technologies have several drawbacks: while they exhibit high infrared absorption, they also absorb in the visible region, resulting in insufficient invisibility of infrared absorption patterns; insufficient infrared absorption leads to poor discriminability when mixed with visible images; and the infrared-absorbing pigments have poor dispersibility, making them prone to sedimentation within the ink.

[0005] The present invention aims to provide an infrared absorbing ink that has excellent spectral properties and does not cause pigment sedimentation. [Means for solving the problem]

[0006] The present invention relates to an ink set as described below. An ink containing water, a colorant, and a polymer, The volume-based cumulative 50% particle size (D50) of the aforementioned colorant is 90 nm or more and 250 nm or less. The aforementioned colorant has a maximum absorption peak in the absorption spectrum in the wavelength range of 300 nm to 1500 nm, with the peak occurring between 830 nm and 1000 nm. The content of the colorant in the ink is 0.1% by mass or more and 1.0% by mass or less. The polymer is a compound having a naphthyl group, and the weight-average molecular weight of the polymer is 40,000 to 150,000. An ink characterized by the following features. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an infrared absorbing ink that has excellent spectral properties and does not cause pigment sedimentation. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows the structural formula of an example of a colorant in the present invention. [Figure 2] Figure 2 shows an example of the inkjet recording apparatus of the present invention. [Figure 3]Figure 3 is a perspective view of an example of an ink cartridge. [Figure 4] Figure 4 is a cross-sectional view of an example of an ink cartridge. [Figure 5] Figure 5 shows an example of an ink container. [Figure 6] Figure 6 shows the printed image. The QR code (registered trademark) portion is formed using an ink containing infrared absorbing pigment. [Modes for carrying out the invention]

[0009] As a result of diligent research by the inventors, it was found that by incorporating a polymer having a naphthyl group as a dispersant into the ink, the affinity with the infrared-absorbing pigment is improved, the dispersion becomes stable, and settling is eliminated. Furthermore, it was found that by setting the weight-average molecular weight of the dispersant to 40,000 to 150,000, the re-aggregation of the infrared-absorbing pigment due to the generation of steric hindrance can be prevented, thereby preventing settling. In addition, it was found that the improved dispersion stability improves the compatibility between the infrared-absorbing pigment ink and other color inks, and also improves the invisibility.

[0010] The following describes each component that makes up the ink of the present invention.

[0011] (ink) The present invention is an ink comprising water, a colorant, and a polymer. In addition, various additives such as resins, wetting agents, penetrating agents, surfactants, pH adjusters, preservatives and antifungal agents, rust inhibitors, antioxidants, and ultraviolet absorbers may be added as needed.

[0012] (water) The water used in this invention can be pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water, or ultrapure water. The water content is preferably 20% by mass or more and 80% by mass or less based on the total amount of ink.

[0013] (Colorants) An infrared-absorbing pigment is used as the coloring material used in the present invention. The infrared-absorbing pigment only needs to have invisibility, and examples thereof include aluminum salt compounds, naphthalocyanine compounds, and squarylium compounds. Among these, naphthalocyanine compounds and squarylium compounds are preferred, and naphthalocyanine compounds are more preferred because they have low absorbance in the visible light region and excellent weather resistance. The naphthalocyanine compound is not particularly limited and may be appropriately selected depending on the purpose, but the compound represented by Figure 1 is preferred. Among these, vanadyl 2,3-naphthalocyanine represented by the following structural formula (1) is preferred from the viewpoints of low absorbance in the visible light region and excellent weather resistance.

[0014]

Chemical Formula

[0015] The average particle diameter of the coloring material in the ink is preferably 90 nm or more and 250 nm or less. Dispersion is difficult when the average particle diameter is less than 90 nm, and sedimentation properties deteriorate when the average particle diameter exceeds 250 nm. Invisibility can be ensured by selecting a coloring material having a peak outside the wavelength range of 360 nm to 830 nm of visible light as the coloring material. The content of the coloring material in the ink is preferably 0.1% by mass or more and 1.0% by mass or less. Reading by a machine is difficult when the content is less than 0.1% by mass, and invisibility during printing cannot be ensured when the content exceeds 1.0% by mass.

[0016] (Polymer) The polymer used in the present invention preferably has at least a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2).

Chemical Formula

Chemical Formula

[0017] In general formula (1), R1 and R2 are hydrogen atoms or methyl groups, and n is an integer from 1 to 90. The cellulose that primarily constitutes plain paper and the structure represented by general formula (1) of the polymer in this invention are hydrophilic. Therefore, the structure represented by general formula (1) is considered to have a greater affinity for cellulose than for hydrophobic solvents. When the polymer of this invention is used in ink, during printing, the polymer adsorbed onto the pigment is adsorbed onto the cellulose, and the pigment is more likely to remain on the paper surface. It is thought that having polyethylene glycol chains with n ranging from 1 to 90 in general formula (1) makes it easier to come into contact with cellulose and thus easier to adsorb onto cellulose. As a result, high image density can be achieved even on plain paper. In general formula (1), n ​​represents the average number of moles of ethylene oxide (C2H4O) added. R2 is preferably a hydrogen atom from the viewpoint of water solubility.

[0018] In general formula (2), R3 is a hydrogen atom or a methyl group, and L is an alkylene group having 2 to 18 carbon atoms, preferably an alkylene group having 2 to 16 carbon atoms, and more preferably an alkylene group having 2 to 12 carbon atoms. The naphthyl group located at the end via L in an open-ended (open end, or in other words, pendant structure) part has excellent pigment adsorption capacity due to π-π stacking with the pigment, which is the coloring agent in the aqueous ink (hereinafter sometimes referred to as ink).

[0019] As can be understood from the above description of "a naphthyl group located at the end via L in the pendant," the structural units represented by general formula (1) and general formula (2) may typically be the main chain of a polymer having pendant groups such as terminal naphthyl groups or side-chain carboxyl groups hanging via L. However, this does not, of course, exclude cases where a portion is included in the side chain. For example, it is a well-known fact that it is difficult to completely eliminate secondary radical polymerization reactions that generate branched structures.

[0020] Furthermore, when preparing a pigment dispersion in which pigments are dispersed in water, using the polymer of the present invention allows for easy adsorption to the pigment surface due to the presence of naphthyl groups at the ends of the side chains of the polymer. This results in a highly dispersible and long-term stable dispersion.

[0021] The polymer in the present invention may have, in addition to the structural unit represented by the general formula (1) and the structural unit represented by the general formula (2), a further structural unit represented by the following general formula (3).

[0022] [ka]

[0023] In general formula (3), R4 represents a hydrogen atom or a methyl group, and X represents a hydrogen atom or a cation. When X is a cation, oxygen adjacent to the cation exists as O-. Examples of cations include sodium ion, potassium ion, lithium ion, tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, tetrahexylammonium ion, triethylmethylammonium ion, tributylmethylammonium ion, trioctylmethylammonium ion, 2-hydroxyethyltrimethylammonium ion, tris(2-hydroxyethyl)methylammonium ion, propyltrimethylammonium ion, hexyltrimethylammonium ion, octyltrimethylammonium ion, nonyltrimethylammonium ion, decyltrimethylammonium ion, dodecyltrimethylammonium ion, tetradecyltrimethylammonium ion, hexadecyltrimethylammonium ion, octadecyltrimethylammonium ion, and octadecyltrimethylammonium ion. Examples include diammonium ions, ditetradecyldimethylammonium ions, dihexadecyldimethylammonium ions, dioctadecyldimethylammonium ions, ethylhexadecyldimethylammonium ions, ammonium ions, dimethylammonium ions, trimethylammonium ions, monoethylammonium ions, diethylammonium ions, triethylammonium ions, monoethanolammonium ions, diethanolammonium ions, triethanolammonium ions, methylethanolammonium ions, methyldiethanolammonium ions, dimethylethanolammonium ions, monopropanolammonium ions, dipropanolammonium ions, trippropanolammonium ions, isopropanolammonium ions, morpholinium ions, N-methylmorpholinium ions, N-methyl-2-pyrrolidonium ions, and 2-pyrrolidonium ions.

[0024] In the present invention, the molar ratio of the structural units represented by general formula (1), general formula (2), and general formula (3) constituting the polymer is preferably (1):(2):(3) = 0.3~1.0:0.6~2.0:1~:3.0, more preferably 0.6~1.0:1.2~1.8:1.0~2.6, and even more preferably 0.8~1.0:1.5~1.5:1.0~2.4, from the viewpoint of pigment adsorption ability. The mass ratio of the structural units represented by general formula (1), general formula (2), and general formula (3) is preferably 15~77:8~47:18~41, more preferably 25~62:13~45:17~38, and even more preferably 30~56:14~42:17~35.

[0025] In the present invention, polymers having structural units represented by general formula (1) and general formula (2) are preferably synthesized using at least the compound represented by general formula (4) and the compound represented by general formula (5) as starting materials.

[0026] [ka] In general formula (4), R1 and R2 represent a hydrogen atom or a methyl group, and n represents an integer from 1 to 90.

[0027] [ka] In general formula (5), R3 represents a hydrogen atom or a methyl group, and L represents an alkylene group having 2 to 18 carbon atoms.

[0028] The polymer in the present invention can be obtained, for example, by the reactions shown in the following reaction formulas (1), (2), and (3-1). First, as shown in the following reaction formula (1), naphthalene carbonyl chloride (A-1) and an excess amount of a diol compound are condensed in the presence of an acid acceptor such as an amine or pyridine to obtain naphthalene carboxylate hydroxyalkyl ester (A-2). Next, as shown in the following reaction formula (2), 2-methacryloyloxyethyl isocyanate (A-3) is reacted with (A-2) to obtain monomer (A-4), which is a compound represented by the general formula (5). Then, as shown in the following reaction formula (3-1), monomer (A-4) and (methoxy)polyethylene glycol (mono)(meth)acrylate (A-5), which is a compound represented by the general formula (4), are copolymerized in the presence of a radical polymerization initiator to obtain polymer (A-7) in the present invention. Here, the weight-average molecular weight of monomer (A-4) is 357 to 596, since L in general formula (2) is an alkylene group having 2 to 18 carbon atoms, and R3 is a hydrogen atom or a methyl group.

[0029] [ka] [ka] [ka]

[0030] The polymer having the structural unit represented by general formula (1), the structural unit represented by general formula (2), and the structural unit represented by general formula (3) in the present invention is preferably synthesized using at least the compound represented by the following general formula (4), the compound represented by the following general formula (5), and the compound represented by the following general formula (6) as starting materials.

[0031] [ka] In general formula (4), R1 and R2 represent a hydrogen atom or a methyl group, and n represents an integer from 1 to 90. [ka] In general formula (5), R3 represents a hydrogen atom or a methyl group, and L represents an alkylene group having 2 to 18 carbon atoms. [ka] In general formula (6), R4 represents a hydrogen atom or a methyl group, and X represents a hydrogen atom or a cation.

[0032] A polymer having the structural units represented by general formula (1), general formula (2), and general formula (3) can be synthesized, for example, in the same manner as the synthesis of polymers having the structural units represented by general formula (1) and general formula (2), by reacting 2-methacryloyloxyethyl isocyanate (A-3) with (A-2) to obtain monomer (A-4), which is a compound represented by general formula (5). Then, as shown in the reaction formula (3-2) below, polymer (A-8) of the present invention can be obtained by copolymerizing monomer (A-4) with (methoxy)polyethylene glycol (mono)(meth)acrylate (A-5), which is a compound represented by general formula (4), and (meth)acrylic acid or a salt thereof (A-6), which is a compound represented by general formula (6), in the presence of a radical polymerization initiator.

[0033] [ka]

[0034] The weight-average molecular weight of the polymer is preferably between 40,000 and 150,000, and particularly preferably between 90,000 and 120,000. If the weight-average molecular weight is below 40,000, the colorant will settle in the ink, and if it is above 150,000, machine readability will deteriorate.

[0035] (resin) As the resin, at least one of a water-soluble resin and a water-dispersible resin is preferably used. There are no particular restrictions on the water-soluble resins mentioned above, and they can be appropriately selected according to the purpose. Examples include: polyvinyl alcohol, modified polyvinyl alcohol such as anionic polyvinyl alcohol, cationic polyvinyl alcohol, and acetal-modified polyvinyl alcohol; polyurethane; polyvinylpyrrolidone and modified polyvinylpyrrolidone such as copolymers of polyvinylpyrrolidone and vinyl acetate, copolymers of vinylpyrrolidone and dimethylaminoethyl methacrylic acid, copolymers of quaternized vinylpyrrolidone and dimethylaminoethyl methacrylic acid, and copolymers of vinylpyrrolidone and methacrylamidopropyl trimethylammonium chloride; cellulose such as carboxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose; modified cellulose such as cationized hydroxyethylcellulose; synthetic resins such as polyester, polyacrylic acid (ester), melamine resin, or modified products thereof, and copolymers of polyester and polyurethane; poly(meth)acrylic acid, poly(meth)acrylamide, oxidized starch, phosphate-esterified starch, automodified starch, cationized starch, or various modified starches, polyethylene oxide, sodium polyacrylate, sodium alginate, etc.

[0036] These can be used individually or in combination of two or more types. Among these, polyvinyl alcohol, cation-modified polyvinyl alcohol, acetal-modified polyvinyl alcohol, polyester, polyurethane, and copolymers of polyester and polyurethane are particularly preferred from the viewpoint of ink absorption.

[0037] There are no particular restrictions on the water-dispersible resin, and it can be appropriately selected depending on the purpose. Water-dispersible resins have excellent film-forming properties (image-forming properties) and possess high water repellency, high water resistance, and high weather resistance, making them useful for image recording with high water resistance and high image density (high color development).

[0038] Specific examples include polyurethane, polyvinyl acetate, ethylene-vinyl acetate copolymer, polystyrene, styrene-(meth)acrylic acid ester copolymer, (meth)acrylic acid ester polymer, vinyl acetate-(meth)acrylic acid (ester) copolymer, styrene-butadiene copolymer, ethylene-propylene copolymer, polyvinyl ether, silicone-acrylic copolymer, and the like.

[0039] Furthermore, it may contain crosslinking agents such as methylolated melamine, methylolated urea, methylolated hydroxypropylene urea, and isocyanates, or it may be a copolymer containing units such as N-methylolacrylamide that has self-crosslinking properties. Among these, polyurethane resin fine particles, acrylic-silicone resin fine particles, and fluororesin fine particles are particularly preferred. Furthermore, it is possible to use multiple of these water-dispersible resins simultaneously.

[0040] (Humectant) The ink of the present invention uses water as a liquid medium, but water-soluble solvents are used as wetting agents to prevent the ink from drying out, improve dispersion stability, and prevent curling on plain paper. Multiple water-soluble solvents may be used in combination.

[0041] Specific examples of water-soluble solvents include the following: Polyhydric alcohols such as glycerin, ethylene glycol, diethylene glycol, isopropylideneglycerol, 1,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, propylene glycol, dipropylene glycol, trimethylolpropane, trimethylolethane, ethylene glycol, diethylene glycol, dipropylene glycol, tripropylene glycol, tetraethylene glycol, hexylene glycol, polyethylene glycol, polypropylene glycol, 1,5-pentanediol, 1,6-hexanediol, glycerol, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, and petriol.

[0042] Polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether. Polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

[0043] Nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethylimidazolidinone, ε-caprolactam, and γ-butyrolactone.

[0044] Amides such as formamide, N-methylformamide, N,N-dimethylformamide, N,N-dimethyl-β-methoxypropionamide, and N,N-dimethyl-β-butoxypropionamide.

[0045] Amines such as monoethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine, and triethylamine. Sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol. Examples include 3-ethyl-3-hydroxymethyloxetane, propylene carbonate, and ethylene carbonate.

[0046] Among these water-soluble solvents, 3-ethyl-3-hydroxymethyloxetane, isopropylideneglycerol, N,N-dimethyl-β-methoxypropionamide, and N,N-dimethyl-β-butoxypropionamide are particularly preferred. These can be used to achieve excellent results in preventing curling in ordinary paper. In addition, the present invention may contain sugars as a water-soluble solvent. Examples of sugars include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides), and polysaccharides, preferably glucose, mannose, fructose, ribose, xylose, arabinose, galactose, maltose, cellobiose, lactose, sucrose, trehalose, maltotriose, etc. Here, polysaccharides refer to sugars in a broad sense and are used to mean substances that are widely present in nature, such as α-cyclodextrin and cellulose. Furthermore, derivatives of these sugars include reducing sugars, oxidized sugars, amino acids, and thio acids of the aforementioned sugars. Sugar alcohols are particularly preferred, with maltitol and sorbitol being specific examples.

[0047] The ratio of pigment to water-soluble solvent significantly affects the ink ejection stability from the print head. If the pigment solid content is high and the amount of water-soluble solvent is low, moisture evaporation near the ink meniscus of the nozzle will increase, leading to poor ejection. The amount of water-soluble solvent is preferably 10% to 70% by mass of the total ink, and more preferably 20% to 50% by mass. Inks within this range exhibit very good drying properties, storage tests, and reliability tests.

[0048] (Penetrating agent) Adding a penetrating agent to the ink reduces surface tension, improves ink filling into the nozzle, and enhances ejection stability. In addition, it accelerates the penetration of ink droplets into the recording medium after they land, thus reducing feathering and color bleeding. Surfactants and penetrating solvents are used as penetrating agents.

[0049] (Surfactants) Surfactants can be broadly classified into anionic surfactants, nonionic surfactants, and amphoteric surfactants based on their hydrophilic group, and into fluorinated surfactants, acetylene-based surfactants, etc. based on their hydrophobic group.

[0050] Examples of anionic surfactants include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, lauryl salt, and salts of polyoxyethylene alkyl ether sulfate.

[0051] Examples of nonionic surfactants include polyols, glycol ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkylamines, polyoxyethylene alkylamides, and acetylene glycols. Examples of fluorinated surfactants include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphate esters, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, perfluoroalkylamine oxides, and perfluoroalkyl ether compounds. Fluorine-containing compounds represented by the following structural formula (2) can be used particularly effectively. [ka]

[0052] Acetylene glycol-based surfactants such as 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-3,6-diol, and 3,5-dimethyl-1-hexyn-3-ol (for example, Surfinol 104, 82, 465, 485, or TG from Air Products Corporation (USA)) can be used, but Surfinol 465, 104, and TG show particularly good print quality.

[0053] The above-mentioned surfactants can be used individually or in combination of two or more. In a preferred embodiment of the present invention, the amount of penetrating agent added to the total ink is preferably in the range of 0.01% by mass to 5% by mass, and more preferably 0.03% by mass to 2% by mass. If the amount of surfactant is 0.01% by mass or more, the dots spread sufficiently after printing, and the solid image can be completely filled, thus maintaining high image density and saturation. If the amount of surfactant is 5% by mass or less, foaming is suppressed, and foam does not clog the flow path in the nozzle, so ink droplets can be ejected smoothly.

[0054] (pH adjuster) Adding a pH adjuster to maintain alkalinity stabilizes the dispersion and thus stabilizes ink ejection. Furthermore, at pH 11 or higher, a significant amount of ink is dissolved from the inkjet head and ink supply unit, leading to problems such as ink degradation, leakage, and ejection failure. It is preferable to add the pH adjuster when mixing and dispersing the pigment with the dispersant in water, rather than adding it after mixing and dispersion along with water-soluble solvents, penetrating agents, and other additives. This is because some pH adjusters can disrupt the dispersion upon addition.

[0055] Preferably, pH adjusters contain one or more of the following: alcoholamines, alkali metal hydroxides, ammonium hydroxides, phosphonium hydroxides, and alkali metal carbonates. Examples of alcoholamines include diethanolamine, triethanolamine, and 2-amino-2-ethyl-1,3-propanediol. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of ammonium hydroxides include ammonium hydroxide, quaternary ammonium hydroxide, and quaternary phosphonium hydroxide. Examples of alkali metal carbonates include lithium carbonate, sodium carbonate, and potassium carbonate.

[0056] (preservative and fungicide) Sodium dehydroacetate, sodium sorbate, sodium 2-pyridinethiol-1-oxide, sodium benzoate, sodium pentachlorophenol, and the like can be used as preservatives and fungicides in this invention.

[0057] (Rust inhibitor) Examples of rust inhibitors include acidic sulfites, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

[0058] (Antioxidant) Examples of the aforementioned antioxidants include phenolic antioxidants (including hindered phenolic antioxidants), amine antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, and the like.

[0059] (UV absorber) Examples of the aforementioned ultraviolet absorbers include benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, nickel complex salt-based ultraviolet absorbers, and the like.

[0060] (Ink container) In addition to being available in ink cartridges, the ink of this invention can also be filled into a Z-tainer (registered trademark), such as the one shown in Figure 5, in a quantity of 10 liters.

[0061] (Inkjet recording device) An example of the inkjet recording apparatus of the present invention will be explained with reference to Figure 2. This inkjet recording device is equipped with a cartridge 20 containing pretreatment solution and ink, from which the pretreatment solution and ink are supplied to the recording head. Here, the cartridge 20 is installed with separate cartridges for the pretreatment solution and the inks for each color. The recording head 1 is mounted on a carriage 18 and moves guided by guide shafts 21 and 22 via a timing belt 23 driven by a main scanning motor 24. Meanwhile, the material to be recorded is positioned facing the recording head by a platen. In the diagram, 2 is the main casing, 7 is the common cartridge for processing fluid and ink, 16 is the gear mechanism, 17 is the sub-scanning motor, 25 is the gear mechanism, 26 is the main scanning motor, and 27 is the gear mechanism.

[0062] Figures 3 and 4 show cartridges capable of housing pretreatment solution and ink. This cartridge can hold either pre-treatment solution or ink. Inside the cartridge housing 41 is a liquid absorbent 42, which absorbs ink or pre-treatment liquid, thereby retaining the ink in the cartridge. An upper lid member 44 is provided on the top of the cartridge, and ink or pre-treatment liquid can be filled into the cartridge through an atmospheric vent 47 provided on the upper lid member 44. After filling, the atmospheric vent 47 is sealed by a sealing member 55. The ink or pre-treatment liquid is supplied to the recording head from the liquid supply port 45. The cartridge positioning part 71 has a protruding shape, and by overlapping with the recess in the cartridge storage part of the printer body, the cartridge position can be kept constant. The cartridge attachment / detachment protrusion 81, cartridge attachment / detachment finger grip 81a, and cartridge attachment / detachment recess 82 are designed to be fixed in place by the uneven parts of the cartridge storage part of the printer body when the cartridge is attached or detached. 43 is the case, 46 is the sealing ring, 48 is the groove, 50 is the cap member, 51 is the liquid leakage prevention protrusion, 53 is the cap member, and A is the space between the cartridge housing 41 and the liquid absorbent 42.

[0063] It is most preferable that the ink and pretreatment solution are ejected from the recording head in overlapping layers at the same location. However, in the present invention, sufficient effect can be obtained even if, for example, the pretreatment solution is applied in a reduced amount and the ink is then applied on top of the pretreatment solution that has expanded due to bleeding, or if the pretreatment solution is applied only to the outline of the image and a portion of the ink is then applied on top of it.

[0064] In other words, the recording material of the present invention has information or images recorded on a recording medium (recording medium) using the inkjet ink of the present invention. The recording material of the present invention can be manufactured by a process of ejecting inkjet ink from an inkjet head and recording it on a recording medium. There are no particular restrictions on the recording medium, and it can be appropriately selected depending on the purpose. Examples include plain paper, coated paper for printing, glossy paper, specialty paper, label paper, cloth, film, and OHP sheets. These may be used individually or in combination of two or more. Among these, at least one of plain paper and label paper is preferred. Plain paper has the advantage of being inexpensive. Label paper has the advantage of ensuring traceability by being attached to products for security purposes. The recordings of the present invention are excellent in terms of invisibility, light resistance, humidity and heat resistance, and water resistance, making them suitable for use in security applications.

[0065] The structure of polymers can be analyzed using common analytical methods such as NMR and IR. Furthermore, the molar ratio of the structural unit represented by general formula (1) to the structural unit represented by general formula (2) that constitute the polymer in the present invention can be determined by NMR. The weight-average molecular weight can be measured by GPC. Vanadium can be detected in the ink components of the cartridge using common analytical methods such as ICP-MS. Using NMR, the structure can be analyzed and confirmed to have the structure of 2,3-naphthalocyanine. The average particle size of the colorant can be determined by diluting the ink with water so that the colorant content in the ink is 0.01% by mass, and then measuring the particle size distribution using dynamic light scattering with a device such as the NANOTRAC WAVE II (manufactured by Microtrac).

[0066] <Measuring the molecular weight of polymers> Measurements were taken using GPC (Gel Permeation Chromatography) under the following conditions. • Equipment: GPC-8020 (manufactured by Tosoh Corporation) • Columns: TSK G2000HXL and G4000HXL (manufactured by Tosoh Corporation) ·Temperature: 40℃ • Solvent: THF (tetrahydrofuran) ·Flow rate: 1.0mL / min A 1 mL polymer at a concentration of 0.5% by mass was injected, and the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the polymer were calculated from the molecular weight distribution of the polymer measured under the above conditions using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples. Polymers at concentrations of 0.1% by mass and 1.0% by mass were analyzed in the same manner. [Examples]

[0067] The present invention will be described in more detail below based on examples, but the technical scope of the present invention is not limited in any way to the following examples. Furthermore, unless otherwise specified, in the following descriptions, "parts" refers to "parts by mass" and "%" refers to "percentage by mass".

[0068] First, an example of polymer synthesis is shown below. <Synthesis of polymer CP1-1> 62.0 g (525 mmol) of 1,6-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 700 mL of methylene chloride, and 20.7 g (262 mmol) of pyridine was added. To this solution, a solution of 50.0 g (262 mmol) of 2-naphthalene carbonyl chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) dissolved in 100 mL of methylene chloride was added dropwise over 2 hours with stirring, and then the mixture was stirred at room temperature for 6 hours. After washing the resulting reaction solution with water, the organic phase was isolated, dried over magnesium sulfate, and the solvent was removed by distillation. The residue was purified by silica gel column chromatography using a methylene chloride / methanol (volume ratio 98 / 2) mixed solvent as the eluent to obtain 52.5 g of 2-hydroxyethyl 2-naphthoate.

[0069] Next, 42.1 g (155 mmol) of 2-hydroxyethyl 2-naphthoate was dissolved in 80 mL of dry methyl ethyl ketone and heated to 60°C. To this solution, a solution of 24.0 g (155 mmol) of 2-methacryloyloxyethyl isocyanate (Showa Denko, Karenz MOI) dissolved in 20 mL of dry methyl ethyl ketone was added dropwise over 1 hour with stirring, and the mixture was stirred at 70°C for 12 hours. After cooling to room temperature, the solvent was removed by distillation. The residue was purified by silica gel column chromatography using a methylene chloride / methanol (volume ratio 99 / 1) mixed solvent as the eluent to obtain 57.0 g of monomer M-1 having the structure represented by the following structural formula (5-1).

[0070] [ka]

[0071] Next, a monomer solution was prepared by dissolving 5.35 g (18.83 mmol) of polyethylene glycol monomethacrylate (n≒4.5) (manufactured by NOF Corporation) and 2.68 g (6.3 mmol) of monomer M-1 in 40 mL of dry methyl ethyl ketone. After heating 10% of the monomer solution to 75°C under an argon stream, a solution of 0.206 g (1.26 mmol) of 2,2'-azoiso (butyronitrile) (manufactured by Tokyo Chemical Industry Co., Ltd.) in a solution was added dropwise to the remaining monomer solution over 1.5 hours, and the mixture was stirred at 75°C for 6 hours. After cooling to room temperature, the resulting reaction solution was added to hexane. The precipitated polymer was recovered, dissolved in THF, the solvent was removed using a rotary evaporator, and the polymer was dried under reduced pressure to obtain 8.00 g of polymer CP1-1 (weight-average molecular weight (Mw): 92900, number-average molecular weight (Mn): 13600).

[0072] <Synthesis of polymer CP2-1> Except for changing the amount of dried methyl ethyl ketone to 60 mL, the same procedure as for polymer CP1-1 was used to obtain 8.00 g of polymer CP1-2 (weight-average molecular weight (Mw): 40800, number-average molecular weight (Mn): 10700).

[0073] <Synthesis of polymer CP2-2> Except for changing the amount of 2,2'-azoiso(butyronitrile) (manufactured by Tokyo Chemical Industry Co., Ltd.) added to 0.412 g (2.52 mmol), the same procedure as for polymer CP2-1 was used to obtain 8.00 g of polymer CP2-2 (weight-average molecular weight (Mw): 32400, number-average molecular weight (Mn): 9300).

[0074] <Synthesis of polymer CP2-3> Except for changing the amount of 2,2'-azoiso(butyronitrile) (manufactured by Tokyo Chemical Industry Co., Ltd.) added to 0.124 g (0.76 mmol), 8.00 g of polymer CP2-3 (weight-average molecular weight (Mw): 34600, number-average molecular weight (Mn): 10700) was obtained in the same manner as polymer CP2-1.

[0075] <Synthesis of polymer CP3-1> Except for changing the amount of 2,2'-azoiso(butyronitrile) (manufactured by Tokyo Chemical Industry Co., Ltd.) added to 0.124 g (0.76 mmol), 8.00 g of polymer CP3-1 (weight-average molecular weight (Mw): 149800, number-average molecular weight (Mn): 16800) was obtained in the same manner as polymer CP1-1.

[0076] <Synthesis of polymer CP3-2> Except for changing the amount of dried methyl ethyl ketone to 30 mL, the same procedure as for polymer CP3-1 was used to obtain 8.00 g of polymer CP3-2 (weight-average molecular weight (Mw): 152,000, number-average molecular weight (Mn): 17,200).

[0077] [Table 1]

[0078] (Example 1) <Preparation of pigment dispersions> 13.18 g of water, 0.32 g of dimethylaminoethanol, 1.20 g of polymer CP1-1, and 0.30 g of vanadyl 2,3-naphthalocyanine as a colorant were placed together with 2.0 mm beads in a 50 mL screw-cap bottle manufactured by AS ONE, sealed, and dispersed for 2 days using a ball mill apparatus (tabletop ball mill rotating stand V-1ML manufactured by Irie Shokai Co., Ltd.) to obtain dispersion 1.

[0079] <Ink preparation> Ink 1 was obtained by stirring the materials according to the following formulation for 15 minutes so that the colorant content in the ink was 0.5% by mass. ·Dispersion 1: 24.53 parts • 1,2-Butanediol: 12.73 parts Glycerin: 23.12 parts • Surfactant: 0.57 parts Modified silicone oil: 0.01 part Rust inhibitor: 0.03 part pH adjuster: 0.38 parts • Antifungal agent: 0.09 parts • Distilled water: 38.54 parts

[0080] (Example 2) Ink 2 was obtained by dispersing and preparing the ink in the same manner as in Example 1, except that the polymer was changed to CP2-1.

[0081] (Example 3) Except for changing the polymer to CP3-1, the dispersion and ink preparation were carried out in the same manner as in Example 1 to obtain ink 3.

[0082] (Example 4) Using dispersion 1, the materials according to the following formulation were stirred for 15 minutes so that the colorant content in the ink was 0.1% by mass, to obtain ink 4. ·Dispersion 1: 4.91 parts • 1,2-Butanediol: 12.73 parts Glycerin: 23.12 parts • Surfactant: 0.57 parts Modified silicone oil: 0.01 part Rust inhibitor: 0.03 part pH adjuster: 0.38 parts • Antifungal agent: 0.09 parts • Distilled water: 58.16 parts

[0083] (Example 5) Using dispersion 1, the materials according to the following formulation were stirred for 15 minutes so that the colorant content in the ink was 1.0% by mass, to obtain ink 5. ·Dispersion 1: 49.06 parts • 1,2-Butanediol: 12.73 parts Glycerin: 23.12 parts • Surfactant: 0.57 parts Modified silicone oil: 0.01 part Rust inhibitor: 0.03 part pH adjuster: 0.38 parts • Antifungal agent: 0.09 parts • Distilled water: 14.01 parts

[0084] (Comparative Example 1) Except for changing the polymer to CP2-2, the dispersion and ink preparation were carried out in the same manner as in Example 1 to obtain ink 6.

[0085] (Comparative Example 2) Except for changing the polymer to CP2-3, the dispersion and ink preparation were carried out in the same manner as in Example 1 to obtain ink 7.

[0086] (Comparative Example 3) Except for changing the polymer to CP3-2, the dispersion and ink preparation were carried out in the same manner as in Example 1 to obtain ink 8.

[0087] [Table 2]

[0088] (Evaluation method, evaluation results) <Method for measuring the cumulative 50% particle size (D50) based on volume> One g of the prepared ink was diluted with 200 g of distilled water, and the volume-based cumulative 50% particle size (D50) of the pigment was measured using a dynamic light scattering particle size distribution analyzer (NANOTRAC WAVE II, Microtrac).

[0089] <Measurement of light absorption peak> One g of the prepared ink was diluted with 40 g of distilled water, and the spectral absorption spectrum of the resulting infrared dye composition was measured using a spectrophotometer (Hitachi High-Technologies Corporation U-4100 spectrophotometer).

[0090] <How to print images> The prepared ink was loaded into a RICOH SG3300 A4 gel-jet printer (manufactured by Ricoh), and Figure 6 was printed in a single pass. Figure 6 includes a QR code (registered trademark) printed with infrared-absorbing pigment-containing ink. In addition, cyan, magenta, and yellow inks were loaded as second to fourth inks. Super fine paper (manufactured by EPSON) was used. Black was formed by combining cyan, magenta, and yellow.

[0091] <Invisibility Assessment> <<Machine-readable performance evaluation>> The QR codes (registered trademarks) on the printed materials were evaluated using a handheld terminal AT21Q-XM (manufactured by Denso Wave Corporation) under the following conditions. The evaluation method was as follows: ○ if the code could be read at a distance of approximately 30 cm between the printed material and the handheld terminal, △ if it could be read by bringing the distance between the printed material and the handheld terminal closer, and × if it could not be read. <<Visibility Evaluation>> In a randomly selected group of 20 monitors, a score of ○ was given if two or fewer people could visually identify the QR code (registered trademark) on the recording medium of the printed material in Figure 1; a score of △ was given if three to five people could visually identify it; and a score of × was given if six or more people could visually identify it.

[0092] <Settlement Assessment> 10.0 g of the prepared ink was placed in a 13.5 mL screw-cap vial manufactured by AS ONE, left at room temperature for 24 hours, and visually inspected to determine if any precipitate had accumulated at the bottom of the vial. ○ indicated no precipitate, and × indicated precipitate was present. These evaluation results are shown in Table 3 below.

[0093] [Table 3]

[0094] Examples of the present invention are as follows: (1) An ink comprising water, a colorant, and a polymer, The volume-based cumulative 50% particle size (D50) of the aforementioned colorant is 90 nm or more and 250 nm or less. The aforementioned colorant has a maximum absorption peak in the absorption spectrum in the wavelength range of 300 nm to 1500 nm, with the peak occurring between 830 nm and 1000 nm. The content of the colorant in the ink is 0.1% by mass or more and 1.0% by mass or less, The polymer is a compound having a naphthyl group, and the weight-average molecular weight of the polymer is 40,000 to 150,000. An ink characterized by the following features. (2) The ink according to (1) above, wherein the colorant is metallic naphthalocyanine. (3) The ink according to (2) above, wherein the metal naphthalocyanine is vanadyl 2,3-naphthalocyanine. (4) The ink according to any one of the above items (1) to (3), wherein the polymer has a structure represented by the following general formula (2). [ka] (5) An ink cartridge characterized by containing the ink described in any one of the above items (1) to (4) in a container. (6) An inkjet recording apparatus characterized by having an ink cartridge as described in (5) above, and an ejection means for ejecting ink supplied from the ink cartridge. (7) A recording material characterized by having an image recorded on a recording medium using the ink described in any one of the above items (1) to (4). [Prior art documents] [Patent Documents]

[0095] [Patent Document 1] Japanese Patent Publication No. 2008-255323 [Explanation of Symbols]

[0096] 1 Recording head 2 Main unit 7. Processing solution and ink common cartridge 16 Gear mechanism 17 Sub-scanning motor 18 Carriage 20 cartridges 21, 22 Guide shafts 23 Timing belt 24 Main scanning motor 25 Gear mechanism 26 Main scanning motor 27 Gear mechanism 41 Cartridge housing 42 Liquid absorbent 43 cases 44 Top cover member 45 Liquid supply port 46 Seal rings 47. Atmospheric vent 48 Groove 50 Cap component 51 Protrusion for preventing liquid leakage 53 Cap member 55 sealing member 71 Cartridge positioning section 81 Protruding part for attaching / detaching cartridge 81a Finger rest for inserting / removing cartridge 82 Recessed area for inserting and removing cartridges

Claims

1. An ink containing water, a colorant, and a polymer, The volume-based cumulative 50% particle size (D50) of the aforementioned colorant is 90 nm or more and 250 nm or less. The aforementioned colorant has a maximum absorption peak in the absorption spectrum in the wavelength range of 300 nm to 1500 nm, with the peak occurring between 830 nm and 1000 nm. The content of the colorant in the ink is 0.1% by mass or more and 1.0% by mass or less. The polymer is a compound having a naphthyl group, and the weight-average molecular weight of the polymer is 40,000 to 150,000. An ink characterized by the following features.

2. The ink according to claim 1, wherein the colorant is metallic naphthalocyanine.

3. The ink according to claim 2, wherein the metal naphthalocyanine is vanadyl 2,3-naphthalocyanine.

4. The ink according to claim 1, wherein the polymer has a structure represented by the following general formula (2). 【Transformation 3】

5. An ink cartridge characterized by containing the ink described in any one of claims 1 to 4 in a container.

6. An inkjet recording apparatus comprising an ink cartridge as described in claim 5, and an ejection means for ejecting ink supplied from the ink cartridge.

7. A recording material characterized by having an image recorded on a recording medium using the ink described in any one of claims 1 to 4.

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