Inkjet head capping method

Abstract

To provide an inkjet head capping method that enables elimination of nozzle clogging of an inkjet head by a cleaning operation and ensures superior cleaning recovery, and an ink-cap liquid set comprising an aqueous ink and a cap liquid.SOLUTION: An inkjet head capping method in which an inkjet head is kept in a state of being in contact with a cap liquid for the inkjet head containing a surfactant (A) comprising acetylene glycol or an ethylene oxide adduct (a-1) of acetylene glycol, a water-soluble organic solvent (B) comprising glycol ether (b-1), and water, and an ink-cap liquid set comprising an aqueous inkjet ink containing a pigment, a resin having a carboxyl group, an organic solvent, a surfactant, and water, and the cap liquid for the inkjet head.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for capping an inkjet head and an ink-cap liquid set of an aqueous ink and a capping liquid.

Background Art

[0002] The inkjet printing method is a method of directly ejecting ink droplets from fine nozzles and attaching them to a printing medium to obtain a printed matter or the like on which characters and images are recorded. This method is widespread because it has many advantages such as being easily full-colorized and inexpensive, and being non-contact with the printing medium. Particularly from the viewpoints of the weather resistance and water resistance of printed matter, those using pigments as colorants have become mainstream. On the other hand, in an inkjet ink containing a pigment as a colorant, since the pigment particles are dispersed in an aqueous medium, the pigment particles are likely to aggregate, and in particular, when the inkjet printing apparatus has not been used for a certain period, there is a problem that the inkjet nozzles are clogged, which affects the ejection of ink droplets. Therefore, when the inkjet printing apparatus is not used for a certain period, in order to prevent drying, solidification, and film formation of the ink in the nozzles, the inkjet head is capped, and at this time, by filling the cap with a liquid, a technique for preventing drying of the inkjet ink and accompanying clogging of the inkjet nozzles and sticking to the vicinity of the nozzles is disclosed.

[0003] For example, in Patent Document 1, as a maintenance liquid for an ink set that is excellent in mixing stability with ink, channel cleaning property and maintainability in an inkjet recording apparatus, does not remain unnecessarily after cleaning, and is excellent in moisture retention, it contains water, a solvent (B) (excluding alkanolamine), and alkanolamine. The content of the solvent (B) is 7 to 50% by mass in the total amount of the maintenance liquid. The total amount of liquid components having a boiling point of 240°C or higher under 1 atm contained in the maintenance liquid is 10% by mass or less in the total amount of the maintenance liquid. When the SP value of the solvent having the smallest SP value among the solvents contained in the ink is defined as SP1, a maintenance liquid is disclosed in which the amount of the solvent having an SP value of SP1 or higher contained in the solvent (B) is 50% by mass or more in the total amount of the solvent (B).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In commercial printing and industrial printing, there are various downtime periods for inkjet printing devices, such as short periods during printing job switching, medium periods from the end of work to the start of work, medium to long periods spanning weekends, and even ultra-long periods including year-end and New Year holidays. Even during such diverse downtime periods of inkjet printing devices, a cap liquid for the inkjet head that can prevent clogging of the nozzles of the inkjet head by inkjet ink is desired. However, in the maintenance liquid disclosed in Patent Document 1, the performance of redispersing once-solidified inkjet ink back into a dispersed state (ink redispersibility) is low, so nozzle clogging of the inkjet head could not be sufficiently suppressed. Also, since the defoaming property of the maintenance liquid was not sufficient, generation of bubbles in the maintenance liquid could not be sufficiently suppressed, and thus the phenomenon of bubbles generating in the nozzles of the inkjet head and the nozzles being clogged by the bubbles could not be sufficiently suppressed. An object of the present invention is to provide a method for capping an inkjet head that is excellent in the cleaning recoverability of the inkjet head, capable of eliminating clogging of the nozzles of the inkjet head by a cleaning operation, and an ink-cap liquid set of an aqueous ink and a cap liquid.

Means for Solving the Problems

[0006] The inventors of the present invention have found that the above problems can be solved by a cap liquid containing a specific surfactant, a water-soluble organic solvent containing a glycol ether, and water, and having a specific ratio of the content of the water-soluble organic solvent. The present invention relates to the following [1] to [2]. 〔1〕A method for capping an inkjet head, which holds a cap liquid for the inkjet head containing a surfactant (A) containing acetylene glycol or an ethylene oxide adduct of acetylene glycol (a-1), a water-soluble organic solvent (B) containing a glycol ether (b-1), and water in a state of being in contact with the inkjet head. 〔2〕An ink-jet ink containing a pigment, a resin containing a carboxy group, an organic solvent, a surfactant, and water, and a cap liquid for an ink-jet head containing a surfactant (A) containing acetylene glycol or an ethylene oxide adduct (a-1) of acetylene glycol, a water-soluble organic solvent (B) containing a glycol ether (b-1), and water, which are components of an ink-cap liquid set.

Advantages of the Invention

[0007] According to the present invention, there can be provided a capping method for an ink-jet head that is excellent in the cleaning recoverability of the ink-jet head, capable of eliminating the clogging of the nozzles of the ink-jet head by a cleaning operation, and an ink-cap liquid set of an aqueous ink and a cap liquid.

Embodiments for Carrying Out the Invention

[0008] [Capping Method for Ink-Jet Head] The capping method for an ink-jet head of the present invention (hereinafter also referred to as the "capping method") is a capping method for an ink-jet head that holds a cap liquid for an ink-jet head containing a surfactant (A) containing acetylene glycol or an ethylene oxide adduct (a-1) of acetylene glycol, a water-soluble organic solvent (B) containing a glycol ether (b-1), and water in a state of being in contact with the ink-jet head. In the capping method of the present invention, as a method of holding in a state of being in contact with the ink-jet head, more specifically, a cap filled with the cap liquid is attached to the ink-jet head to cover the ink-jet head, and at this time, the amount of the cap liquid of the present invention is adjusted so that the cap liquid in the cap comes into contact with the ink-jet head, and the nozzle surface of the ink-jet head is immersed in the cap liquid.

[0009] The capping method of the present invention is excellent in the cleaning recoverability of the inkjet head, that is, it can eliminate the clogging of the nozzles of the inkjet head by a cleaning operation. The reason is not clear, but it is considered as follows. In the present invention, the glycol ether (b-1) contained as the water-soluble organic solvent (B) in the capping liquid has a high ability to lower the surface tension due to the hydrophilicity of the glycol group and the alkyl group, so that the resin and pigment contained in the inkjet ink can be redispersed by aggregation or the like of the solidified ink. Therefore, the solidified ink or the like clogging the inkjet head can be removed, and the cleaning recoverability is excellent. In addition, the glycol ether (b-1) can further enhance the defoaming effect of the acetylene glycol or the ethylene oxide adduct (a-1) of the acetylene glycol. Thereby, aggregation of pigments and the like contained in the inkjet ink generated at the bubble interface can be suppressed, and the cleaning recoverability is excellent. Furthermore, in the capping method of the present invention, since the capping liquid is held in a state of being in contact with the inkjet head, drying around the inkjet head nozzle can be suppressed, and the solidified ink in the capping liquid can be efficiently redispersed. Therefore, clogging of the inkjet head nozzle can be more efficiently suppressed, and the cleaning recoverability is excellent.

[0010] As the capping method of the present invention, there is a method of covering the inkjet head in a state where the ink in the inkjet head is washed with a maintenance liquid or the like and the abundance ratios of the colorant and the resin are lower than the concentrations usually used in inkjet printing, and a method of covering the inkjet head in a state where the abundance ratios of the colorant and the resin remain at the concentrations usually used in inkjet printing. It is preferably selected from one of these methods. Among these, from the viewpoint of enhancing the recoverability of the inkjet head by the capping liquid of the present invention and the viewpoint of efficiently starting inkjet printing after removing the cap, it is more preferable that the inkjet head is covered in a state where the abundance ratios of the colorant and the resin remain at the concentrations usually used in inkjet printing.

[0011] In the capping method of the present invention, the cap filled with the capping liquid only needs to cap a part of the inkjet head. That is, the inkjet head may be capped with a plurality of caps.

[0012] [Capping liquid for inkjet head] The capping liquid for the inkjet head (hereinafter also simply referred to as "capping liquid") used in the capping method of the present invention contains a surfactant (A) containing acetylene glycol or an ethylene oxide adduct (a-1) of acetylene glycol, a water-soluble organic solvent (B) containing glycol ether (b-1), and water.

[0013] [Surfactant (A)] The capping liquid of the present invention contains a surfactant (A), and the surfactant (A) contains acetylene glycol or an ethylene oxide adduct (a-1) of acetylene glycol.

[0014] (Acetylene glycol or ethylene oxide adduct (a-1) of acetylene glycol) In the present invention, among acetylene glycol or an ethylene oxide adduct (a-1) of acetylene glycol (hereinafter also referred to as "(a-1) component"), acetylene glycol has an acetylene group in the central part of its structure, and each has one hydroxyl group on the carbon atoms adjacent to the acetylene group, and preferably has a hydrocarbon group of 6 or more, more preferably 8 or more, and preferably 12 or less, more preferably 10 or less other than the acetylene group. It is a non-ionic compound having a structure. Further, among the (a-1) components, the ethylene oxide adduct of acetylene glycol is one in which ethylene oxide (hereinafter also referred to as "EO") is added to the hydroxyl group of the acetylene glycol. When the component (a-1) is an ethylene oxide adduct of acetylene glycol, the average number of moles of ethylene oxide added to the hydroxyl group is preferably 0 mole or more, and preferably 2 moles or less, more preferably 1.5 moles or less, still more preferably 1 mole or less, from the viewpoint of enhancing the redispersibility of the ink. And when the component (a-1) is an ethylene oxide adduct of acetylene glycol, it is even more preferable that the number of moles of ethylene oxide added to the hydroxyl group is 0.

[0015] The component (a-1) is preferably at least one selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 3,5-dimethyl-1-hexyne-3-ol, and EO adducts thereof; more preferably at least one selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, and EO adducts thereof; still more preferably 2,4,7,9-tetramethyl-5-decyne-4,7-diol and its EO adduct; and even more preferably 2,4,7,9-tetramethyl-5-decyne-4,7-diol.

[0016] Examples of commercially available products of the component (a-1) include Surfynol 104 (average number of moles of EO added: 0 mole, active ingredient 100% by mass) and Surfynol 104PG-50 (average number of moles of EO added: 0 mole, 50% by mass diluted product of propylene glycol of 2,4,7,9-tetramethyl-5-decyne-4,7-diol) from Air Products and Chemicals, Inc. Examples of commercially available products of the EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol include Surfynol 420 (average number of moles of EO added: 1.3, active ingredient 100% by mass) from Air Products and Chemicals, Inc. The component (a-1) may be used alone or in combination of two or more.

[0017] The cap liquid of the present invention may contain, as the surfactant (A), in addition to the component (a-1), a surfactant other than the component (a-1). Specific examples of the surfactant other than the component (a-1) include those in which the average number of moles of ethylene oxide added to the hydroxyl group of the ethylene oxide adduct of acetylene glycol exceeds 2, polyethylene glycol alkyl ethers (having 8 to 22 carbon atoms), polyether-modified silicones, polyethylene glycol alkyl ether sulfates, and the like. Examples of the polyethylene glycol alkyl ether include polyethylene glycol mono-2-ethylhexyl ether, polyethylene glycol monooctyl ether, polyethylene glycol monodecyl ether, polyethylene glycol monododecyl ether, polyethylene glycol monotetradecyl ether, and the like.

[0018] In the cap liquid of the present invention, the content of the surfactant (A) in the cap liquid is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, still more preferably 0.5% by mass or more, even more preferably 0.8% by mass or more, from the viewpoint of enhancing the defoaming property and the cleaning recovery property, and from the same viewpoint, it is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 2% by mass or less, even more preferably 1.5% by mass or less, and even more preferably 1.2% by mass or less.

[0019] In the cap liquid of the present invention, the ratio of the component (a-1) in the surfactant (A) is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 100% by mass, from the viewpoint of enhancing the defoaming property and the cleaning recovery property.

[0020] <Water-soluble organic solvent (B)> The cap liquid of the present invention contains a water-soluble organic solvent (B), and the water-soluble organic solvent (B) contains a glycol ether (b-1) (hereinafter, also referred to as the "component (b-1)"). In the present invention, the "water-soluble organic solvent" refers to an organic solvent that, when 100 mL of water at 25°C is dissolved in the organic solvent, has a dissolution amount of 10 mL or more.

[0021] (Glycol ether (b-1)) Glycol ether generally refers to a compound having a hydrocarbon group via an ether bond at one or both hydroxyl groups of glycol. However, in the present invention, the component (b-1) means a compound having a hydrocarbon group with 1 to 4 carbon atoms via an ether bond at one hydroxyl group of the glycol structure and the other being a hydroxyl group. As the glycol structure of the component (b-1), monoethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, monopropylene glycol, dipropylene glycol, tripropylene glycol, and tetrapropylene glycol are preferably mentioned. Among these, as the glycol structure, diethylene glycol is preferable. As the hydrocarbon group with 1 to 4 carbon atoms of the component (b-1), a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a sec-butyl group are preferably mentioned. Among these, as the hydrocarbon group with 1 to 4 carbon atoms, one or more selected from an isobutyl group and an n-butyl group are preferable, and an isobutyl group is more preferable. From the viewpoint of enhancing the redispersibility and defoaming property of the ink and enhancing the cleaning recoverability, the boiling point of the component (b-1) under atmospheric pressure is preferably 160°C or higher, more preferably 190°C or higher, still more preferably 220°C or higher, and preferably 280°C or lower, more preferably 250°C or lower, still more preferably 240°C or lower. In the present specification, the boiling point indicates the boiling point under atmospheric pressure unless otherwise specified.

[0022] (Component (b-1), from the viewpoints of enhancing the redispersibility and defoaming property of the ink and improving the cleaning recovery property, includes one or more selected from ethylene glycol monoethyl ether (boiling point 136 °C), ethylene glycol mono-n-butyl ether (boiling point 168 °C), diethylene glycol monomethyl ether (boiling point 193 °C), diethylene glycol monoethyl ether (boiling point 196 °C), diethylene glycol monoisopropyl ether (boiling point 207 °C), diethylene glycol mono-n-butyl ether (boiling point 230 °C), diethylene glycol monoisobutyl ether (boiling point 229 °C), triethylene glycol monomethyl ether (boiling point 249 °C), triethylene glycol mono-n-butyl ether (boiling point 276 °C), tetraethylene glycol monomethyl ether (boiling point 125 °C / 1 mmHg), propylene glycol monoethyl ether (boiling point 133 °C), dipropylene glycol monomethyl ether (boiling point 190 °C), dipropylene glycol mono-n-butyl ether (boiling point 230 °C), tripropylene glycol monomethyl ether (boiling point 241 °C), and tripropylene glycol mono-n-butyl ether (boiling point 274 °C). One or more selected from diethylene glycol monoisobutyl ether and diethylene glycol mono-n-butyl ether are more preferred, and diethylene glycol monoisobutyl ether is even more preferred.)

[0023] In particular, since diethylene glycol monoisobutyl ether has a hydrocarbon group with a C4 branch, the mobility of the hydrocarbon group is suppressed, resulting in a high adsorption force to hydrophobic substances. It has a good balance with a hydrophilic group having two linked ethylene oxide groups and a high ability to lower the interfacial tension. Therefore, when component (b-1) contains diethylene glycol monoisobutyl ether, the cap liquid of the present invention is considered to be more likely to penetrate between the above-mentioned solidified products of the ink, and the redispersibility of the ink is more likely to be further enhanced. As a result, the cap method of the present invention can improve the cleaning recovery property.)

[0024] (Polyhydric alcohol (b-2) with a boiling point of 230 °C or higher) In the cap liquid of the present invention, the water-soluble organic solvent (B) preferably further contains a polyhydric alcohol (b-2) having a boiling point of 230°C or higher (hereinafter also referred to as the "(b-2) component"). By containing the (b-2) component, the moisture retention of the cap liquid can be improved, drying around the inkjet head nozzle can be suppressed, and thus the cleaning recoverability can be enhanced. In the present invention, the polyhydric alcohol means a compound having two or more hydroxyl groups in the molecule. In the present invention, the boiling point of 230°C or higher is determined by the boiling point under atmospheric pressure unless otherwise specified, and when the boiling point under reduced pressure is shown, it is determined by converting it to atmospheric pressure.

[0025] As the (b-2) component, one or more selected from diethylene glycol (boiling point 244°C), polyethylene glycol, dipropylene glycol (boiling point 232°C), polypropylene glycol, 1,4-butanediol (boiling point 230°C), 1,5-pentanediol (boiling point 242°C), 1,2,6-hexanetriol (boiling point 178°C / 5 mmHg), 1,2,4-butanetriol (boiling point 312°C), 1,2,3-butanetriol (boiling point 175°C / 5 mmHg), petriol (boiling point 216°C / 0.5 mmHg), 1,2-hexanediol (boiling point 233°C), 1,6-hexanediol (boiling point 250°C), triethylene glycol (boiling point 287°C), tripropylene glycol (boiling point 271°C), glycerin (boiling point 290°C), trimethylolpropane (boiling point 149°C / 2 mmHg), pentaerythritol (boiling point 276°C / 30 mmHg) are preferred, one or more selected from 1,2-hexanediol and glycerin are preferred, and glycerin is more preferred.

[0026] 〔Other water-soluble organic solvents〕 In the cap liquid of the present invention, the water-soluble organic solvent (B) may contain other water-soluble organic solvents other than the (b-1) component and the (b-2) component in addition to the (b-1) component and the (b-2) component.

[0027] Examples of the other water-soluble organic solvents other than the component (b-1) and the component (b-2) include polyhydric alcohols having a boiling point of less than 230°C, nitrogen-containing heterocyclic compounds, amides, ethers, esters, carbonic esters, sulfur-containing compounds, and the like. Examples of the polyhydric alcohols having a boiling point of less than 230°C include ethylene glycol (boiling point 197°C), propylene glycol (boiling point 188°C), 1,3-propanediol (boiling point 214°C), 1,2-butanediol (boiling point 193°C), 1,3-butanediol (boiling point 208°C), 3-methyl-1,3-butanediol (boiling point 203°C), 2-methyl-2,4-pentanediol (boiling point 196°C), and the like. Examples of the nitrogen-containing heterocyclic compounds include, for example, N-methyl-2-pyrrolidone (boiling point 202°C), 2-pyrrolidone (boiling point 245°C), 1,3-dimethylimidazolidinone (boiling point 220°C), ε-caprolactam (boiling point 136°C), and the like. Examples of the amides include, for example, formamide (boiling point 210°C), N-methylformamide (boiling point 199°C), N,N-dimethylformamide (boiling point 153°C), and the like. Examples of the ethers include tetrahydrofuran (boiling point 66°C), tetrahydropyran (boiling point 88°C), and the like. Examples of the carbonic esters include ethylene carbonate (boiling point 261°C), and the like. Examples of the sulfur-containing compounds include, for example, dimethyl sulfoxide (boiling point 189°C), sulfolane (boiling point 285°C), thiodiglycol (boiling point 282°C), and the like. Among these, polyhydric alcohols having a boiling point of less than 230°C are preferred, and one or more selected from ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 3-methyl-1,3-butanediol, and 2-methyl-2,4-pentanediol are more preferred, and propylene glycol is even more preferred.

[0028] In the cap liquid of the present invention, the content of the water-soluble organic solvent (B) in the cap liquid is preferably 20% by mass or more, more preferably more than 20% by mass, still more preferably 25% by mass or more, even more preferably 30% by mass or more, even more preferably 35% by mass or more from the viewpoints of enhancing the redispersibility and defoaming property of the ink and enhancing the cleaning recoverability, and from the same viewpoints, it is preferably 50% by mass or less, more preferably 46% by mass or less, still more preferably 43% by mass or less, even more preferably 40% by mass or less.

[0029] In the cap liquid of the present invention, the content of the component (b-1) in the cap liquid is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, even more preferably 8% by mass or more from the viewpoints of enhancing the redispersibility and defoaming property of the ink and enhancing the cleaning recoverability, and from the same viewpoints, it is preferably 25% by mass or less, more preferably 15% by mass or less.

[0030] In the cap liquid of the present invention, the ratio of the component (b-1) in the water-soluble organic solvent (B) is preferably 2% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, even more preferably 15% by mass or more, even more preferably 20% by mass or more, even more preferably 25% by mass or more from the viewpoints of enhancing the redispersibility and defoaming property of the ink and enhancing the cleaning recoverability, and from the same viewpoints, it is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 45% by mass or less, even more preferably 40% by mass or less, even more preferably 35% by mass or less, even more preferably 30% by mass or less.

[0031] When the cap liquid of the present invention contains the component (b-2), the content of the component (b-2) in the cap liquid is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, even more preferably 10% by mass or more, even more preferably 15% by mass or more from the viewpoints of enhancing the redispersibility and defoaming property of the ink and enhancing the cleaning recoverability, and from the same viewpoints, it is preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less.

[0032] When the cap liquid of the present invention contains the component (b-2), the ratio of the component (b-2) in the water-soluble organic solvent (B) is preferably 2% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, even more preferably 15% by mass or more, even more preferably 20% by mass or more, even more preferably 25% by mass or more from the viewpoints of enhancing the redispersibility and defoaming property of the ink and enhancing the cleaning recoverability, and from the same viewpoints, it is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 45% by mass or less, even more preferably 40% by mass or less, even more preferably 35% by mass or less, even more preferably 30% by mass or less.

[0033] When the cap liquid of the present invention contains other organic solvents, the content of the other organic solvents in the cap liquid is preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, even more preferably 13% by mass or more from the viewpoint of enhancing the cleaning recoverability, and from the same viewpoint, it is preferably 20% by mass or less, more preferably 18% by mass or less, still more preferably 16% by mass or less.

[0034] When the cap liquid of the present invention contains the component (b-2), the mass ratio [(b-2) / (b-1)] of the component (b-2) to the component (b-1) in the cap liquid is preferably 0.2 or more, more preferably 0.4 or more, still more preferably 0.8 or more, even more preferably 1.0 or more from the viewpoints of enhancing the redispersibility and defoaming property of the ink and enhancing the cleaning recoverability, and from the same viewpoints, it is preferably 5.0 or less, more preferably 3.0 or less, still more preferably 2.0 or less, even more preferably 1.5 or less.

[0035] When the cap liquid of the present invention contains the component (b-2), the total ratio of the component (b-1) and the component (b-2) in the water-soluble organic solvent (B) is preferably 4% by mass or more, more preferably 30% by mass or more, still more preferably 40% by mass or more, even more preferably 45% by mass or more, even more preferably 50% by mass or more from the viewpoints of enhancing the redispersibility and defoaming property of the ink and enhancing the cleaning recoverability, and from the same viewpoints, it is preferably 80% by mass or less, more preferably 70% by mass or less, still more preferably 66% by mass or less, even more preferably 60% by mass or less.

[0036] <Water> The cap liquid of the present invention contains water. The water contained in the cap liquid of the present invention is preferably one or more selected from deionized water and distilled water. In the cap liquid of the present invention, the water content is preferably 50% by mass or more, more preferably 52% by mass or more from the viewpoint of enhancing the cleaning recoverability, and from the same viewpoint, it is preferably 75% by mass or less, more preferably 73% by mass or less.

[0037] In addition to the above components, various additives such as a pH adjuster, a defoaming agent, a preservative, a fungicide, and a rust preventive can be added to the cap liquid of the present invention. Note that the cap liquid of the present invention may contain a colorant, but it is preferably free of a colorant. Similarly, the cap liquid of the present invention may contain a polymer or a wax, but it is preferably free of a polymer or a wax.

[0038] <Method for manufacturing cap liquid> The cap liquid of the present invention can be obtained by blending a surfactant (A), a water-soluble organic solvent (B), and water. Specifically, the cap liquid of the present invention can be obtained by mixing a surfactant (A), a water-soluble organic solvent (B), water, and, if necessary, the other components described above, and stirring.

[0039] <Physical properties of the cap liquid of the present invention> From the viewpoint of enhancing cleaning recoverability, the viscosity of the cap liquid of the present invention at 25°C is preferably 1.0 mPa·s or more, more preferably 1.5 mPa·s or more, still more preferably 2.0 mPa·s or more, and from the viewpoint of obtaining a cleaning liquid that is difficult to remain on the member to be cleaned, it is preferably 7.0 mPa·s or less, more preferably 5.5 mPa·s or less, still more preferably 4.0 mPa·s or less. Note that the viscosity at 25°C is measured by the method described in the examples. From the viewpoint of enhancing cleaning recoverability, the pH of the cap liquid of the present invention is preferably 7.0 or more, more preferably 7.5 or more, still more preferably 8.0 or more, and is preferably 11.0 or less, more preferably 10.0 or less, still more preferably 9.0 or less. Note that the pH is measured by the method described in the examples.

[0040] In the capping method of the present invention, the inkjet head covered with a cap filled with the cap liquid preferably discharges an aqueous ink (hereinafter, also simply referred to as "aqueous ink") containing a pigment, a resin containing a carboxy group, an organic solvent, a surfactant, and water. When the inkjet head discharges the aqueous ink, the affinity between the cap liquid of the present invention and the solidified matter derived from the aqueous ink becomes higher, so that the nozzle clogging can be eliminated more efficiently, and the cleaning recoverability can be enhanced. Note that "aqueous" in the aqueous ink means that water occupies the largest proportion by mass in the medium contained in the ink.

[0041] (aqueous ink) Hereinafter, the aqueous ink ejected from the inkjet head in the capping method of the present invention will be described.

[0042] 〔Pigment〕 The pigment contained in the aqueous ink may be either an inorganic pigment or an organic pigment. Further, if necessary, a extender pigment can be used in combination with them. Examples of the inorganic pigment include carbon black, metal oxides, etc. Particularly in black ink, carbon black is preferred. Examples of carbon black include furnace black, thermal black, acetylene black, channel black, etc. Specific examples of the organic pigment include azo pigment, diazo pigment, phthalocyanine pigment, quinacridone pigment, isoindolinone pigment, dioxazine pigment, perylene pigment, perinone pigment, thioindigo pigment, anthraquinone pigment, quinophthalone pigment, etc. The hue is not particularly limited, and any colored pigment such as yellow, magenta, cyan, blue, red, orange, green, etc. can be used. Specific examples of the preferred organic pigment include one or more product numbers selected from C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green. The pigment contained in the aqueous ink is preferably contained in the aqueous ink in one form selected from a form dispersed in a resin containing a carboxy group described later and a form of pigment particles encapsulated in a resin containing a carboxy group (hereinafter also referred to as "pigment-containing resin particles").

[0043] The content of the pigment in the aqueous ink is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, and from the viewpoints of the viscosity of the ink and the rub resistance of the printed matter, it is preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 8% by mass or less.

[0044] [Resin containing a carboxy group] The resin containing a carboxy group contained in the aqueous ink is contained for at least one of the functions as a pigment dispersant that exhibits a pigment dispersion action and as a fixing agent on a recording medium. The resin containing a carboxy group is preferably contained as the resin of the pigment-containing resin particles or as resin particles not containing a pigment in the aqueous ink, and is preferably contained as both the pigment-containing resin particles and the resin particles not containing a pigment.

[0045] As the resin containing a carboxy group, those exemplified in paragraphs

[0014] to

[0019] of JP-A-2022-104084 are preferable. Among these, as the resin containing a carboxy group, a vinyl-based polymer is preferable. The vinyl-based polymer preferably contains a structural unit derived from an ionic monomer, and further preferably has a structural unit derived from a hydrophobic monomer and / or a nonionic monomer. As the ionic monomer, an anionic monomer is preferable, one or more selected from carboxylic acid monomers and sulfonic acid monomers are more preferable, and a carboxylic acid monomer is still more preferable. As the carboxylic acid monomer, one or more selected from (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid are preferable, and one or more selected from acrylic acid and methacrylic acid are more preferable.

[0046] The "hydrophobicity" of the hydrophobic monomer means that when the monomer is dissolved until saturated in 100 g of deionized water at 25°C, the dissolved amount is less than 10 g. As the hydrophobic monomer, one or more selected from alkyl (meth) acrylates having an alkyl group with 1 to 18 carbon atoms, aromatic group-containing monomers having an aromatic group with 6 to 22 carbon atoms, and macromonomers having a polymerizable functional group at one end are preferred, and one or more selected from styrene, α-methylstyrene, and benzyl (meth) acrylate are more preferred.

[0047] The nonionic monomer is a monomer having a high affinity for water and water-soluble organic solvents, and is, for example, a monomer containing a hydroxyl group or a polyalkylene glycol chain. As the nonionic monomer, one or more selected from polyethylene glycol (n = 1 to 30) (meth) acrylates and polypropylene glycol (n = 2 to 30) (meth) acrylates having a methoxy group or a hydroxyl group at the end are preferred. Note that "(meth) acrylic acid" means both "acrylic acid" and "methacrylic acid", and "(meth) acrylate" means both "acrylate" and "methacrylate".

[0048] When the resin containing a carboxy group is the resin of the pigment-containing resin particles, the resin containing a carboxy group preferably contains a structural unit derived from one or more ionic monomers selected from acrylic acid and methacrylic acid, a structural unit derived from one or more hydrophobic monomers selected from styrene, α-methylstyrene, and benzyl (meth) acrylate, and a structural unit derived from one or more nonionic monomers selected from polyethylene glycol (n = 1 to 30) (meth) acrylate and polypropylene glycol (n = 2 to 30) (meth) acrylate having a methoxy group or a hydroxyl group at the end, and is a vinyl-based polymer. In addition, when the resin containing a carboxy group is resin particles not containing a pigment, the resin containing a carboxy group is preferably a vinyl polymer containing a structural unit derived from one or more ionic monomers selected from acrylic acid and methacrylic acid, and a structural unit derived from one or more hydrophobic monomers selected from styrene, methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, aromatic ring-containing (meth)acrylate, and alicyclic group-containing (meth)acrylate.

[0049] When the resin containing a carboxy group is a resin of pigment-containing resin particles, the content of each structural unit in the resin containing a carboxy group is preferably in the following range. The content of the structural unit derived from the ionic monomer in the resin containing a carboxy group is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 12% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, still more preferably 30% by mass or less. The content of the structural unit derived from the hydrophobic monomer in the resin containing a carboxy group is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less. The content of the structural unit derived from the nonionic monomer in the resin containing a carboxy group is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 20% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, still more preferably 30% by mass or less.

[0050] When the resin containing a carboxy group is resin particles not containing a pigment, the content of each structural unit in the resin containing a carboxy group is preferably in the following range. The content of the structural unit derived from the ionic monomer in the resin containing a carboxy group is preferably 1% by mass or more, more preferably 1.5% by mass or more, still more preferably 2% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, still more preferably 5% by mass or less. The content of the structural unit derived from the hydrophobic monomer in the resin containing a carboxy group is preferably 90% by mass or more, more preferably 92% by mass or more, still more preferably 95% by mass or more, and preferably 99% by mass or less, more preferably 98.5% by mass or less, still more preferably 98% by mass or less.

[0051] The content of the resin containing a carboxy group in the aqueous ink is preferably 2% by mass or more, more preferably 4% by mass or more, still more preferably 6% by mass or more, and preferably 14% by mass or less, more preferably 12% by mass or less, still more preferably 10% by mass or less. When the resin containing a carboxy group is included as the resin of the pigment-containing resin particles, the content of the resin of the pigment-containing resin particles in the aqueous ink is preferably 1% by mass or more, more preferably 1.5% by mass or more, still more preferably 2% by mass or more, and preferably 5% by mass or less, more preferably 4.5% by mass or less, still more preferably 4% by mass or less. When the resin containing a carboxy group is included as the resin particles not containing a pigment, the content of the resin particles not containing a pigment in the aqueous ink is preferably 1% by mass or more, more preferably 2.5% by mass or more, still more preferably 4% by mass or more, and preferably 9% by mass or less, more preferably 7.5% by mass or less, still more preferably 6% by mass or less.

[0052] 〔Organic solvent〕 As the organic solvent contained in the aqueous ink, one or more selected from glycol ethers and polyhydric alcohols are preferred. As the glycol ether, one or more selected from ethylene glycol mono-n-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monomethyl ether, triethylene glycol mono-n-butyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol mono-n-butyl ether, tripropylene glycol monomethyl ether and tripropylene glycol mono-n-butyl ether are preferred, one or more selected from diethylene glycol monoisobutyl ether and diethylene glycol monoisopropyl ether are more preferred, and diethylene glycol monoisobutyl ether is even more preferred. As the polyhydric alcohol, one or more selected from ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, polypropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,3-butanediol, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, pentaerythritol, 1,2-hexanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, triethylene glycol, tripropylene glycol, glycerin, trimethylolpropane, and pentaerythritol are preferred, one or more selected from propylene glycol and 1,2-butanediol are more preferred, and propylene glycol is even more preferred. The organic solvent may be used alone or in combination of two or more.

[0053] The content of the organic solvent in the aqueous ink is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, still more preferably 25% by mass or less. When the aqueous ink contains a glycol ether as the organic solvent, the content of the glycol ether in the aqueous ink is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, and preferably 10% by mass or less, more preferably 9% by mass or less, still more preferably 8% by mass or less. When the aqueous ink contains a polyhydric alcohol as the organic solvent, the content of the polyhydric alcohol in the aqueous ink is preferably 4% by mass or more, more preferably 8% by mass or more, still more preferably 12% by mass or more, and preferably 25% by mass or less, more preferably 20% by mass or less, still more preferably 18% by mass or less.

[0054] 〔Surfactant〕 Surfactants contained in the aqueous ink preferably include acetylene glycol-based surfactants, polyethylene glycol alkyl ethers (having 8 to 22 carbon atoms), polyether-modified silicones, and polyethylene glycol alkyl ether sulfates. Among these, one or more selected from acetylene glycol-based surfactants and polyether-modified silicones are more preferable. As the acetylene glycol-based surfactant, one or more selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, and their EO adducts are more preferable, and 2,4,7,9-tetramethyl-5-decyne-4,7-diol is more preferable. The surfactant may be used alone or in combination of two or more.

[0055] The content of the surfactant in the aqueous ink is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, and is preferably 2.5% by mass or less, more preferably 2.0% by mass or less, still more preferably 1.5% by mass or less. When the aqueous ink contains an acetylene glycol-based surfactant as the surfactant, the content of the acetylene glycol-based surfactant in the aqueous ink is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, and is preferably 1.2% by mass or less, more preferably 1.0% by mass or less, still more preferably 0.8% by mass or less. When the aqueous ink contains a polyether-modified silicone as the surfactant, the content of the polyether-modified silicone in the aqueous ink is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, and is preferably 1.2% by mass or less, more preferably 1.0% by mass or less, still more preferably 0.8% by mass or less.

[0056] [Water] The aqueous ink of the present invention contains water. The water contained in the aqueous ink of the present invention is preferably at least one selected from deionized water and distilled water. The content of water in the aqueous ink is preferably 35% by mass or more, more preferably 45% by mass or more, still more preferably 55% by mass or more, and is preferably 95% by mass or less, more preferably 92% by mass or less, still more preferably 85% by mass or less.

[0057] [Ink-Cap Liquid Set] The ink-cap liquid set of the present invention is an ink-cap liquid set comprising the above-described aqueous ink containing a pigment, a resin containing a carboxy group, an organic solvent, a surfactant, and water, and the above-described cap liquid as constituent elements. Since the ink-cap liquid set of the present invention comprises the above-described aqueous ink and the above-described cap liquid as constituent elements, when used in an inkjet printer, it is excellent in the redispersibility and defoaming property of the ink, can suppress the clogging of the inkjet head nozzles, and thus has excellent cleaning recoverability. Therefore, the ink-cap liquid set of the present invention can be preferably used in inkjet printing and the method of capping an inkjet head, as it is excellent in the redispersibility and defoaming property of the ink.

Examples

[0058] In the following Examples, Comparative Examples, and Production Examples, "parts" and "%" are "parts by mass" and "mass %" unless otherwise specified.

[0059] (1) Viscosity of the cap liquid Using an E-type viscometer "TV-25" (manufactured by Toki Sangyo Co., Ltd., standard cone rotor 1°34’×R24, rotation speed 50 rpm), the viscosity of the cap liquid at 25°C was measured.

[0060] (2) pH of the cap liquid Using a desktop pH meter "F-71" (manufactured by Horiba, Ltd.) and a pH electrode "6337-10D" (manufactured by Horiba, Ltd.), the pH of the cap liquid at 25°C was measured.

[0061] (3) Weight average molecular weight of the resin containing a carboxy group Using a solution in which phosphoric acid and lithium bromide were dissolved at concentrations of 60 mmol / L and 50 mmol / L, respectively, in N,N-dimethylformamide as an eluent, the molecular weight of the resin was measured by gel permeation chromatography [GPA apparatus (HLC-8120GPC) manufactured by Tosoh Corporation, columns (TSK-GEL, α-M×2) manufactured by Tosoh Corporation, flow rate: 1 mL / min]. Note that monodisperse polystyrene with a known molecular weight was used as a standard substance.

[0062] (4) Solid content concentration of the pigment dispersion Weighed 10.0 g of sodium sulfate, which had been constant-weighted in a desiccator, into a 30 mL polypropylene container (φ = 40 mm, height = 30 mm), added approximately 1.0 g of the sample thereto, mixed them, then weighed accurately, maintained at 105 °C for 2 hours to remove volatile components, left to stand in the desiccator for 15 minutes, and measured the mass. The mass of the sample after removing volatile components was taken as the solid content, and divided by the mass of the added sample to obtain the solid content concentration.

[0063] <Production of Aqueous Ink> Production Example 1-1 (Production of Aqueous Ink 1) (1) Production of Resin Solution Containing Carboxy Group Into a reaction vessel equipped with two dropping funnels 1 and 2, put 396 parts of styrene, 135 parts of styrene-based macromer (manufactured by Toagosei Co., Ltd., trade name: AS-6S, active ingredient 50%, number average molecular weight 6,000), 225 parts of hydrophilic nonionic monomer (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK Ester M-40G, methoxypolyethylene glycol monomethacrylate (average number of added moles of EO: 4 moles)), 157.5 parts of methyl ethyl ketone (hereinafter also referred to as "MEK"), 135 parts of toluene, and 1.3 parts of 2-mercaptoethanol as a polymerization chain transfer agent, mixed them, and performed nitrogen gas substitution to obtain an initial charged monomer solution. Next, put the dropped monomer solution 1, which was a mixture of 1152 parts of methacrylic acid, 3168 parts of styrene, 1215 parts of AS-6S, 1800 parts of NK Ester M-40G, 1732.5 parts of MEK, 1215 parts of toluene, 72 g of polymerization initiator (manufactured by Fujifilm Wako Pure Chemical Corporation, trade name: V-65, 2,2'-azobis(2,4-dimethylvaleronitrile)), and 8.82 parts of 2-mercaptoethanol, into dropping funnel 1, and put the dropped monomer solution 2, which was a mixture of 288 parts of methacrylic acid, 396 parts of styrene, 225 parts of NK Ester M-40G, 1260 parts of MEK, 18 parts of V-65, and 2.52 parts of 2-mercaptoethanol, into dropping funnel 2, and performed nitrogen gas substitution on each of them. While maintaining the temperature at 77°C with stirring, an initial monomer solution in a reaction vessel was maintained under a nitrogen gas atmosphere, and the dropping monomer solution 1 in dropping funnel 1 was gradually dropped into the reaction vessel over 3 hours. Subsequently, the dropping monomer solution 2 in dropping funnel 2 was gradually dropped into the reaction vessel over 2 hours. After completion of the dropping, the mixed solution in the reaction vessel was stirred at 77°C for 0.5 hour. Subsequently, a polymerization initiator solution in which 1.1 parts of V-65 was dissolved in 47.3 parts of MEK was prepared, added to the mixed solution, and aged by stirring at 77°C for 0.5 hour. The preparation, addition, and aging of the polymerization initiator solution were performed 12 more times. Subsequently, the reaction solution in the reaction vessel was maintained at 80°C for 1 hour, and 8,456 parts of MEK was added so that the solid content concentration became 36% to obtain a solution of resin 1 containing a carboxy group. The weight average molecular weight of resin 1 containing a carboxy group was 67,000.

[0064] (2) Production of an aqueous dispersion of pigment-containing resin particles 178.7 parts of the obtained solution of resin 1 containing a carboxy group (solid content concentration 36%) was mixed with 45 parts of MEK to obtain an MEK solution of resin 1 containing a carboxy group. The MEK solution of resin 1 containing a carboxy group was charged into a 2 L disperser, and while stirring under the condition of 1,400 rpm, 511.4 parts of deionized water, 22.3 parts of 5N aqueous sodium hydroxide solution, and 1.7 parts of 25% aqueous ammonia solution were added and adjusted so that the neutralization degree by sodium hydroxide was 78.8 mol% and the neutralization degree by ammonia was 21.2 mol%, and while cooling in a water bath at 0°C, it was stirred at 1,400 rpm for 15 minutes. Subsequently, 150 parts of carbon black (manufactured by Cabot Corporation, trade name: Monarch 717, C.I. Pigment Black 7), which is a black pigment, was added and stirred at 6,400 rpm for 1 hour. The obtained pigment mixture was subjected to a dispersion treatment of 9 passes at a pressure of 150 MPa using a microfluidizer "M-7115" (manufactured by Microfluidics) to obtain a dispersion-treated product (solid content concentration: 25%). 324.5 parts of the obtained dispersion product were placed in a 2 L eggplant flask, 216.3 parts of deionized water was added (solid content concentration 15%), and using a rotary evaporator “Rotary Evaporator” (N-1000S, manufactured by Tokyo Rika Kikai Co., Ltd.), at a rotation speed of 50 r / min, in a warm bath adjusted to 32°C, it was held at a pressure of 0.09 MPa for 3 hours to remove the organic solvent. Further, the warm bath was adjusted to 62°C, the pressure was reduced to 0.07 MPa, and it was concentrated until the solid content concentration reached 25%. The obtained concentrate was put into a 500 mL angle rotor, centrifuged at 7,000 rpm for 20 minutes using a high-speed cooling centrifuge (himac CR22G, manufactured by Hitachi Koki Co., Ltd., set temperature 20°C), and after that, the liquid layer part was filtered through a 1.2 μm filter (MAP-010XS, manufactured by Rocktechno Co., Ltd.) to recover the filtrate containing the resin particles 1 containing a carboxy group and containing a pigment. To 300 parts of the obtained filtrate (52.5 parts of pigment, 22.5 parts of resin 1 containing a carboxy group), 0.68 part of a mildew-proof agent (manufactured by Arch Chemicals Japan Co., Ltd., trade name: Proxel LVS, active ingredient 20%, water 80%) was added, and further 40.23 parts of deionized water was added so that the solid content concentration became 22%, and it was stirred at room temperature for 1 hour to obtain an aqueous dispersion of the resin particles 1 containing a carboxy group and containing a pigment.

[0065] (3) Production of Aqueous Dispersion of Resin Particles Containing No Pigment Into a reaction vessel equipped with a dropping funnel, 0.5 part of methacrylic acid, 14.5 parts of methyl methacrylate, 5.0 parts of 2-ethylhexyl acrylate, 11.1 parts of a surfactant (manufactured by Kao Corporation, trade name: Latemul E-118B, sodium polyoxyethylene alkyl ether sulfate), 0.2 part of potassium persulfate, and 382.8 parts of deionized water were put and mixed, and nitrogen gas substitution was performed to obtain an initial charge monomer emulsion. On the other hand, 9.5 parts of methacrylic acid, 275.5 parts of methyl methacrylate, 95 parts of 2-ethylhexyl acrylate, 35.1 parts of Latemul E-118B, 0.6 part of potassium persulfate, and 183 parts of deionized water were mixed to obtain a dropping monomer emulsion, which was put into the dropping funnel and nitrogen gas substitution was performed. In a nitrogen gas atmosphere, while stirring the initial charge monomer emulsion in the reaction vessel, the temperature was raised from room temperature to 80 °C over 30 minutes, and while maintaining at 80 °C, the dropping monomer emulsion in the dropping funnel was gradually dropped into the reaction vessel over 3 hours. After completion of dropping, stirring was carried out for 1 hour while maintaining the temperature in the reaction vessel. Then, filtration was carried out through a 200-mesh sieve, and a filtrate containing resin particles 2 containing carboxy groups and not containing pigments was recovered to obtain an aqueous dispersion of resin particles 2 containing carboxy groups and not containing pigments (solid content concentration: 40%). The weight average molecular weight of the resin 2 containing carboxy groups that constitutes the resin particles 2 containing carboxy groups was 550,000.

[0066] (4) Production of aqueous ink 1 45.5 parts of an aqueous dispersion of resin particles 1 containing carboxy groups and containing pigments (solid content concentration: 22%) (7.0% of pigments and 3.0% of resin containing carboxy groups in the ink), 12.5 parts of an aqueous dispersion of resin particles 2 containing carboxy groups and not containing pigments (solid content concentration: 40%) (5% of resin containing carboxy groups in the ink), 5 parts of diethylene glycol mono isobutyl ether, 15 parts of propylene glycol, 0.5 part of a silicone-based surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: SAG-005, polyether-modified silicone), 0.6 part of Surfynol 104PG-50 were added, and deionized water was added so that the total amount of the ink became 100 parts to obtain a mixed solution. The obtained mixed solution was filtered through the 1.5-μm filter to obtain aqueous ink B1. Note that the content of the resin containing carboxy groups in aqueous ink B1 is 8.0% in total of resin 1 containing carboxy groups and resin 2 containing carboxy groups.

[0067] Production Examples 1-2 to 1-4 (Production of aqueous inks 2 to 4) In Production Example 1-1, except that the composition (blending amount) shown in Table 1 was changed, aqueous inks 2 to 4 were obtained in the same manner as in Production Example 1-1.

[0068]

Table 1

[0069] <Production of Cap Liquid> Production Example 2-1 (Production of Cap Liquid 1) (a-1) As a component, 1.0 part of Surfynol 104PG-50 (manufactured by Air Products and Chemicals, propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active ingredient 50%) was added with 10.0 parts of diethylene glycol monoisobutyl ether as the (b-1) component, 10.0 parts of glycerin as the (b-2) component, and 15.0 parts of propylene glycol as the other water-soluble organic solvent component, and stirred. Next, 0.25 part of 1N aqueous sodium hydroxide solution as a pH adjuster and deionized water were added so that the total amount became 100 parts, and stirred to obtain a mixed solution. The obtained mixed solution was filtered through a 1.5 μm filter (made of acetyl cellulose) to obtain Cap Liquid 1 (viscosity: 2.5 mPa·s, pH 8.7).

[0070] Production Examples 2-2 to 2-9 (Production of Cap Liquids 2 to 9) Cap Liquids 2 to 9 were obtained in the same manner as in Production Example 2-1, except that the composition (blending amount) shown in Table 2 was changed (viscosity: 2.2 to 3.5 mPa·s, pH: 8.7).

[0071] Details of the (a-1) component in Table 2 are as follows. · Surfynol 104PG-50: Manufactured by Air Products and Chemicals, propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active ingredient 50% · Surfynol 420: Manufactured by Air Products and Chemicals, EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 1.3), active ingredient 100%

[0072] Examples 1 to 12 and Comparative Example 1 (1) Combinations of Ink-Cap Liquid Sets The aqueous inks obtained in Production Examples 1-1 to 1-4 and the cap liquids obtained in Production Examples 2-1 to 2-9 were combined as shown in Table 2 to form ink-cap liquid sets for Examples 1 to 12 and Comparative Example 1.

[0073] (2) Filling the aqueous ink into the inkjet head In an environment with a temperature of 25 ± 1°C and a relative humidity of 30 ± 5%, an aqueous ink was filled into a printing evaluation apparatus (manufactured by Trytec Co., Ltd.) equipped with an inkjet head (manufactured by Kyocera Corporation, "KJ4B-HD06MHG-STDV", piezo type, total number of nozzles: 2656). The head voltage was set to 26 V, the frequency was 26 kHz, the appropriate discharge amount of the liquid was 3 pL, the head temperature was 32°C, the resolution was 1200 dpi, the number of pre-discharge flushing shots was 200, and the negative pressure was -4.0 kPa. The printing medium was fixed to the transport table under reduced pressure in a direction such that the longitudinal direction and the transport direction of the printing medium were the same. As the printing medium, OK Top Coat Paper (manufactured by Oji Paper Co., Ltd., water absorption: 4.9 g / m 2 ) was used to print a nozzle check pattern. After confirming that the aqueous ink was discharged from all nozzles, it was left in the atmosphere for 30 minutes.

[0074] (3) Capping with the cap liquid (3-1) Capping method in Examples ️1 to 12 For the inkjet head, a cap filled with the cap liquid to the brim was brought into close contact with the nozzle surface of the inkjet head, and the inkjet head was capped with the cap liquid in contact with the nozzle surface. (3-2) Capping method in Comparative Example 1 A cap filled with only half the amount of the cap liquid was brought into close contact with the nozzle surface, and the inkjet head was capped with the cap liquid not in direct contact with the nozzle surface.

[0075] <Evaluation method> [Evaluation of the redispersibility of the ink] Using a micropipette, 20 μL of the aqueous ink was dropped onto the center of the bottom of a screw tube No. 5 (manufactured by Maruemu Co., Ltd.), and left in an environment of 40 °C and 25% RH for 2 hours without a lid to evaporate and dry the aqueous ink. To the evaporation residue of the aqueous ink remaining at the bottom of the screw tube, 10 mL of the capping liquid was added, and it was shaken at 150 rpm for 1 minute using a shaker (manufactured by EYELA, MULTI SHAKER MMS, model number: MMS-210). The redispersibility of the ink with the capping liquid of the present invention was evaluated visually according to the following evaluation criteria. The less residue of the evaporation residue of the aqueous ink, the higher the redispersibility. The results are shown in Table 2. (Evaluation Criteria) 5: The evaporation residue of the aqueous ink was completely redispersed. 4: The evaporation residue of the aqueous ink was redispersed, but there was a slight residue. 3: The evaporation residue of the aqueous ink was redispersed, but there was a residue. 2: The evaporation residue of the aqueous ink was slightly redispersed, but it was mostly residue. 1: The evaporation residue of the aqueous ink was not redispersed at all.

[0076] [Evaluation of Defoaming Property of Capping Liquid] 100 g (liquid level height: 37 mm from the bottom of the container) of the capping liquids 1 to 9 obtained in Production Examples 2-1 to 2-9 were respectively put into a 250 mL Iboy PP wide-mouth bottle (manufactured by AS ONE Corporation), and after covering the lid, it was foamed by stirring at 600 rpm for 3 minutes with a stirrer (Rocking Shaker, manufactured by Seiwa Giken Co., Ltd.). After standing for 1 minute, the height from the bottom of the container to the upper end of the foam was measured, and the defoaming property of the capping liquid was evaluated according to the following evaluation criteria. The lower the height to the upper end of the foam, the better the defoaming property. The results are shown in Table 2. (Evaluation Criteria) 5: The height to the upper end of the foam is less than 40 mm 4: The height to the upper end of the foam is 40 mm or more and less than 45 mm 3: The height to the upper end of the foam is 45 mm or more and less than 50 mm 2: The height to the upper end of the foam is 50 mm or more and less than 55 mm 1: The height to the upper end of the bubble is 55 mm or more

[0077] 〔Evaluation of cleaning recoverability after storage〕 The inkjet heads of Examples 1 to 12 and Comparative Example 1 were capped according to the procedures and left for 24 hours. After leaving for 24 hours, the cap was removed from the nozzle surface, and the following purge wipe operation was performed. <Purge wipe operation> 10 mL of ink was purged from the head, and the ink remaining on the face of the head was wiped off with a rubber blade wiper. A nozzle check pattern was printed with the aqueous ink corresponding to each Example and Comparative Example. The cleaning recoverability after storage was evaluated by the number of nozzle chips in the nozzle check pattern. The smaller the number of nozzle chips, the higher the cleaning recoverability of the capping liquid. The results are shown in Table 2. In actual use, it is sufficient if the number of nozzle chips is 5 or less.

[0078]

Table 2

[0079] From Table 2, it can be seen that the capping methods of Examples 1 to 12 are excellent in cleaning recoverability after storage because the capping liquid for the inkjet head containing the surfactant (A) containing acetylene glycol or an ethylene oxide adduct (a-1) of acetylene glycol, the water-soluble organic solvent (B) containing glycol ether (b-1), and water is held in contact with the inkjet head.

Industrial Applicability

[0080] The capping method of the present invention has high redispersibility and defoaming properties of the ink and is excellent in the ability to suppress clogging of the inkjet head nozzles, so it can be suitably used as a capping method for inkjet heads.

Claims

1. A method for capping an inkjet head, which holds a capping liquid for an inkjet head containing a surfactant (A) containing acetylene glycol or an ethylene oxide adduct of acetylene glycol (a-1), a water-soluble organic solvent (B) containing a glycol ether (b-1), and water, in a state of being in contact with the inkjet head.

2. The method for capping an inkjet head according to claim 1, wherein the water-soluble organic solvent (B) further contains a polyhydric alcohol (b-2) having a boiling point of 230°C or higher.

3. The method for capping an inkjet head according to claim 2, wherein the mass ratio [(b-2) / (b-1)] of the polyhydric alcohol (b-2) having a boiling point of 230°C or higher to the glycol ether (b-1) in the capping liquid is 0.2 or more and 5.0 or less.

4. The method for capping an inkjet head according to claim 1 or 2, wherein the content of the glycol ether (b-1) in the capping liquid is 1% by mass or more and 25% by mass or less.

5. The method for capping an inkjet head according to claim 2, wherein the polyhydric alcohol (b-2) is at least one selected from 1,2-hexanediol and glycerin.

6. The method for capping an inkjet head according to claim 1 or 2, wherein the content of the water-soluble organic solvent (B) in the capping liquid is 20% by mass or more and 50% by mass or less.

7. The method for capping an inkjet head according to claim 1 or 2, wherein the inkjet head discharges an aqueous ink containing a pigment, a resin containing a carboxy group, an organic solvent, a surfactant, and water.

8. An ink-capping liquid set including, as components, an aqueous inkjet ink containing a pigment, a resin containing a carboxy group, an organic solvent, a surfactant, and water, a surfactant (A) containing acetylene glycol or an ethylene oxide adduct of acetylene glycol (a-1), a water-soluble organic solvent (B) containing a glycol ether (b-1), and a capping liquid for an inkjet head containing water.

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