Inkjet head cleaning composition

Abstract

The present invention relates to: [1] an inkjet head cleaning composition containing a solvent (A) and water, wherein the dipole moment of the solvent (A) at 25 °C as determined by the density functional method is 5.0 D or greater, and the content of the water in the cleaning composition is 30 mass% or greater; [2] a use of a composition containing a solvent (A) and water as an inkjet head cleaning composition, wherein the dipole moment of the solvent (A) at 25 °C as determined by the density functional method is 5.0 D or greater, and the content of the water in the composition is 30 mass% or greater; and [3] a method for cleaning an inkjet head using a composition containing a solvent (A) and water, wherein the dipole moment of the solvent (A) at 25 °C as determined by the density functional method is 5.0 D or greater, and the content of the water in the composition is 30 mass% or greater.

Description

Inkjet head cleaning composition

[0001] The present invention relates to a cleaning composition for an inkjet head.

[0002] Cleaning compositions are widely used, with various formulations adjusted to meet the cleaning effect and required properties depending on the type of object to be cleaned, the form of the composition, the method of use, and so on. Such cleaning compositions include articles using pigment dispersions. Pigment dispersions are composed of pigments with various functionalities and a medium in which the pigments are dispersed. Pigment dispersions are composed of a mixture of a solid pigment and a liquid medium, and a polymer is often used to disperse the pigment in the medium. Furthermore, a polymer other than the polymer used to disperse the pigment may be used to impart various properties. Therefore, even if a pigment dispersion is stable immediately after its production, the pigment dispersion state may irreversibly change over time or when exposed to heat due to factors such as pigment settling, pigment aggregation, adsorption of the pigment to the component to which the pigment dispersion is attached, drying of the pigment, and fixation due to the presence of the polymer. While this irreversible change in state can be advantageously utilized as a function of the pigment dispersion, it often also has secondary effects that are not intended by the designer of the pigment dispersion, resulting in numerous examples of losses in industrial use.

[0003] One example is inkjet recording ink. When inkjet recording ink is left unused, ink components aggregate in the ejection nozzles, resulting in the adhesion of solid matter to the vicinity of the ejection nozzles. This adhesion of solid matter not only leads to ejection defects such as deflected ejection, but also, if left unattended, can cause nozzle clogging, necessitating the replacement of expensive inkjet heads. The causes of ink component aggregation are diverse, including sedimentation due to the high specific gravity of the pigment and increased ink concentration due to drying of the ink medium. In the use of inkjet recording ink in various industrial fields, the adhesion of ink solid matter to the vicinity of the ejection nozzles and nozzle clogging can reduce the production speed of the printing machine and increase running costs, thereby hindering the widespread use of inkjet recording ink. Therefore, various studies have been conducted on cleaning solutions for inkjet heads to address these issues.

[0004] For example, Japanese Patent Laid-Open Publication No. 2018-104637 (Patent Document 1) describes a cleaning liquid for aqueous ink containing a pigment and a water-insoluble polymer, which has excellent cleaning properties for aqueous ink containing a pigment and a water-insoluble polymer, and a method for cleaning aqueous ink using the cleaning liquid. The cleaning liquid contains a surfactant, a water-soluble organic solvent containing diethylene glycol monoisopropyl ether, and water, and the surfactant contains one or more selected from acetylene glycol or an ethylene oxide adduct thereof, and a polyethylene glycol alkyl ether having an alkyl group having 8 or more carbon atoms or a polyethylene glycol aryl ether having an aryl group having 6 or more carbon atoms, and the content of the water-soluble organic solvent in the cleaning liquid is within a predetermined range, and a method for cleaning aqueous ink using the cleaning liquid.

[0005] The present invention relates to a cleaning composition for inkjet heads containing a solvent (A) and water, wherein the solvent (A) has a dipole moment of 5.0 D or more at 25°C as determined by a density functional theory method, and the content of water in the cleaning composition is 30 mass% or more.

[0006] The technology disclosed in Patent Document 1 attempts to improve the cleanability of ink in inkjet heads by applying a cleaning liquid containing a surfactant and an amphipathic organic solvent. However, in this technology, there is a trade-off between ink cleanability and the durability of inkjet head components. The durability of inkjet head components refers to the possibility that the surfactant or amphipathic organic solvent may cause deformation of inkjet head components, such as adhesives and gaskets, due to swelling or dissolution, resulting in the inkjet head becoming distorted in shape or peeling off. If a cleaning liquid for ink with poor component durability is used, the inkjet head may become unusable in a much shorter period than expected. Therefore, there is a need for a cleaning composition that combines excellent cleaning properties for ink-derived coating films attached to components such as inkjet heads with excellent component compatibility. The present invention provides a cleaning composition that has excellent coating cleanability, resulting in excellent inkjet head ejection recovery, and also has excellent component compatibility.

[0007] The present inventors have found that the above-mentioned problems can be solved by providing an inkjet head cleaning composition containing a solvent and water, wherein the solvent has a dipole moment of 5.0 D or more at 25°C as determined by density functional theory, and the content of water in the inkjet head cleaning composition is 30 mass% or more.

[0008] That is, the present invention provides a cleaning composition for an inkjet head containing a solvent (A) and water, wherein the dipole moment of the solvent (A) at 25°C determined by a density functional theory method is 5.0 D or more, and the content of water in the cleaning composition is 30 mass% or more.

[0009] [Cleaning Composition] The cleaning composition of the present invention is a cleaning composition containing a solvent (A) and water, wherein the solvent (A) has a dipole moment of 5.0 D or more at 25°C as determined by density functional theory, and the content of water in the cleaning composition is 30 mass% or more. The cleaning composition of the present invention is preferably a cleaning composition for inkjet heads.

[0010] The cleaning composition of the present invention has excellent coating film cleaning properties and excellent component compatibility. The reason for this is unclear, but is thought to be as follows. The solvent (A) contained in the cleaning composition of the present invention has a dipole moment of 5.0 D or more at 25°C as determined by density functional theory, and has a large intramolecular electrical bias, which makes it easy to orient toward the hydrophilic functional group portion of the polymer constituting the coating film, thereby enhancing the wettability of the cleaning composition of the present invention to the polymer. Furthermore, due to the intramolecular electrical bias of the solvent (A), the solvent (A) molecules are likely to be stabilized in a state where the intermolecular distance between the solvents (A) is close. For this reason, it is thought that chains between solvents (A) are easily formed starting from the solvent (A) molecules oriented toward the hydrophilic functional groups of the polymer constituting the coating film, and the solvent (A) gathers near the hydrophilic functional groups. Furthermore, since the solvent (A) has a dipole moment of 5.0 D or more at 25°C and is therefore highly water-soluble, it easily attracts water after gathering near the hydrophilic functional groups of the polymer, allowing the polymer to migrate into water, which is thought to improve the releasability of the coating film from the object to be cleaned and improve the excellent cleaning properties of the coating film. Furthermore, the water content in the cleaning composition of the present invention is 30% by mass or more, which can reduce the content of organic solvents, resulting in excellent compatibility with components. Even if the coating film contains a pigment, the cleaning composition of the present invention acts on the polymer that constitutes the coating film as described above, which is thought to improve the releasability of the pigment-containing coating film from the object to be cleaned and improve the excellent cleaning properties of the pigment-containing coating film. Due to these effects, it is thought that by using the cleaning composition of the present invention on a coating film attached to an inkjet head, it is possible to achieve both excellent cleaning performance-based ejection recovery and excellent compatibility with components.

[0011] <Solvent (A)> The cleaning composition of the present invention contains a solvent (A) (hereinafter also referred to as "solvent (A)") from the viewpoint of improving the strippability of a coating film and thereby improving cleaning properties, and the dipole moment of the solvent (A) at 25°C, as determined by density functional theory, is 5.0 D or more. In the present invention, the dipole moment is measured at 25°C. As described in the Examples, the dipole moment is calculated by density functional theory using quantum chemistry calculation software TURBOMOLE Ver. 7.7, with BP86 as the functional and def-TZVP as the basis function. The unit of the dipole moment is "D (Debye)". The dipole moment of the solvent (A) is preferably 5.2D or more, more preferably 5.4D or more, and even more preferably 5.6D or more from the viewpoint of improving the peelability of the coating film and improving cleaning properties, and from the viewpoint of improving compatibility with components, and from the same viewpoint as above, it is preferably 6.5D or less, more preferably 6.3D or less, and even more preferably 6.1D or less. That is, the dipole moment of the solvent (A) is preferably 5.2D or more and 6.5D or less, more preferably 5.4D or more and 6.3D or less, and even more preferably 5.6D or more and 6.1D or less. The solvent (A) can be used alone or in combination of two or more.

[0012] From the viewpoint of improving the releasability of the coating film and improving its cleaning properties, the solvent (A) is preferably one or more selected from the group consisting of cyclic carbonates and cyclic sulfones, more preferably one or more selected from the group consisting of propylene carbonate (dipole moment: 5.64 D), ethylene carbonate (dipole moment: 5.41 D), and sulfolane (dipole moment: 5.39 D). Propylene carbonate, ethylene carbonate, and sulfolane, which are preferably used in the cleaning composition of the present invention, have a dipole moment of 5.0 D or more and are cyclic organic solvents, so they are thought to easily penetrate into the gaps in the polymer that constitutes the coating film and have the effect of increasing the swelling of the polymer. On the other hand, propylene carbonate, ethylene carbonate, and sulfolane are water-soluble, so after penetrating into the gaps in the polymer, they easily attract water, which is thought to improve the releasability of the coating film from the object to be cleaned and improve the excellent cleaning properties of the coating film. From the viewpoint of improving the removability of the coating film and improving the cleaning properties, the solvent (A) is more preferably at least one selected from the group consisting of propylene carbonate and ethylene carbonate, and even more preferably propylene carbonate or a mixture of propylene carbonate and ethylene carbonate.

[0013] When the solvent (A) is a mixture of propylene carbonate and ethylene carbonate, the mass ratio of the ethylene carbonate content to the propylene carbonate content in the cleaning composition of the present invention [ethylene carbonate / propylene carbonate] is, from the viewpoint of achieving both detergency and component compatibility, preferably more than 0 and preferably 5 or less, more preferably 4 or less, even more preferably 3 or less, still more preferably 2 or less, still more preferably 1 or less, still more preferably 0.7 or less, still more preferably 0.5 or less, and still more preferably 0.3 or less.

[0014] The content of the solvent (A) in the cleaning composition of the present invention is preferably 5% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, still more preferably 15% by mass or more, and still more preferably 17% by mass or more from the viewpoint of improving the peelability of the coating film and improving cleaning properties, and from the viewpoint of improving component compatibility, it is preferably 65% ​​by mass or less, more preferably 60% by mass or less, even more preferably 55% by mass or less, still more preferably 45% by mass or less, still more preferably 40% by mass or less, still more preferably 30% by mass or less, and still more preferably 20% by mass or less. That is, the content of the solvent (A) in the cleaning composition is preferably 5% by mass or more and 65% by mass or less, more preferably 5% by mass or more and 60% by mass or less, still more preferably 8% by mass or more and 55% by mass or less, still more preferably 8% by mass or more and 45% by mass or less, still more preferably 10% by mass or more and 40% by mass or less, still more preferably 15% by mass or more and 30% by mass or less, and still more preferably 17% by mass or more and 20% by mass or less.

[0015] <Solvent (B)> From the viewpoint of improving the dispersibility of a coating film peeled from an object to be cleaned and thereby improving cleaning properties, the cleaning composition of the present invention preferably contains, in addition to the solvent (A), an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group (hereinafter also referred to as "solvent (B)"). The solvent (B) can be used alone or in combination of two or more. Specific examples of the solvent (B) include ethylene glycol, diethylene glycol, polyoxyalkylene phenyl ether, and polyoxyalkylene benzyl ether. The solvent (B) preferably contains one or more solvents (B1) (hereinafter also simply referred to as "solvent (B1)") selected from the group consisting of ethylene glycol, diethylene glycol, polyoxyalkylene phenyl ether, and polyoxyalkylene benzyl ether. When the cleaning composition of the present invention contains a solvent (B1) in addition to the solvent (A), it is believed that the strong polarity of the alkylene group of the solvent (B1) and the oxygen atoms present at both ends or between the alkylene group causes the solvent (A) to disperse the coating film peeled from the object to be cleaned in the cleaning composition of the present invention containing water, and as a result, it is believed that the cleaning properties of the coating film are further improved. Among these, from the viewpoint of improving the dispersibility of the coating film peeled from the object to be cleaned and thereby improving the cleaning properties, the solvent (B1) is preferably at least one selected from the group consisting of polyoxyalkylene phenyl ethers and polyoxyalkylene benzyl ethers.

[0016] The polyoxyalkylene group of the polyoxyalkylene phenyl ether preferably contains a unit derived from an alkylene oxide having from 2 to 4 carbon atoms, from the viewpoint of improving the dispersibility of the coating film peeled from the object to be cleaned and thereby improving cleaning properties. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, etc., and are preferably one or more selected from the group consisting of ethylene oxide and propylene oxide, more preferably containing at least ethylene oxide, and even more preferably ethylene oxide. That is, the polyoxyalkylene group of the polyoxyalkylene phenyl ether more preferably contains at least a polyoxyethylene group, and even more preferably is a polyoxyethylene group. Specific examples of the polyoxyalkylene phenyl ether include one or more selected from the group consisting of polyoxyethylene phenyl ether and polyoxypropylene phenyl ether. Among these, polyoxyethylene phenyl ether is more preferred. From the viewpoint of improving the dispersibility of the coating film peeled from the object to be cleaned and thereby improving the cleanability, the average number of moles of alkylene oxide added in the polyoxyalkylene group of the polyoxyalkylene phenyl ether is preferably 2 or more, more preferably more than 2, even more preferably 3 or more, and preferably 10 or less, more preferably 8 or less, even more preferably 6 or less. In other words, the average number of moles of alkylene oxide added in the polyoxyalkylene group of the polyoxyalkylene phenyl ether is preferably 2 or more and 10 or less, more preferably more than 2 and 8 or less, even more preferably 3 or more and 6 or less.

[0017] From the viewpoint of improving the dispersibility of the coating film peeled from the object to be cleaned and thereby improving cleaning performance, the polyoxyalkylene group of the polyoxyalkylene benzyl ether preferably contains a unit derived from an alkylene oxide having from 2 to 4 carbon atoms. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, etc., and preferably one or more selected from the group consisting of ethylene oxide and propylene oxide, more preferably at least ethylene oxide, and even more preferably ethylene oxide. That is, the polyoxyalkylene group of the polyoxyalkylene benzyl ether more preferably contains at least a polyoxyethylene group, and even more preferably is a polyoxyethylene group. Specific examples of the polyoxyalkylene benzyl ether include one or more selected from the group consisting of polyoxyethylene benzyl ether and polyoxypropylene benzyl ether. Among these, polyoxyethylene benzyl ether is more preferred. The average number of moles of alkylene oxide added in the polyoxyalkylene group of the polyoxyalkylene benzyl ether is preferably 2 or more, and is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less, from the viewpoint of improving the dispersibility of the coating film peeled from the object to be cleaned and thereby improving the cleaning ability.

[0018] From the viewpoint of improving the dispersibility of the coating film peeled from the object to be cleaned and thereby improving the cleanability, the content of solvent (B1) in component (B) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, still more preferably 97% by mass or more, and is preferably 100% by mass or less, and even more preferably 100% by mass.

[0019] The content of component (B) in the cleaning composition of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more from the viewpoint of improving the dispersibility of the coating film peeled from the object to be cleaned and thereby improving cleaning performance, and is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, still more preferably 20% by mass or less, and even more preferably 10% by mass or less from the viewpoint of improving compatibility with components. That is, the content of component (B) in the cleaning composition is preferably 0.5% by mass or more and 50% by mass or less, more preferably 0.5% by mass or more and 40% by mass or less, even more preferably 1% by mass or more and 30% by mass or less, still more preferably 1% by mass or more and 20% by mass or less, and even more preferably 2% by mass or more and 10% by mass or less.

[0020] The content of the solvent (B1) in the cleaning composition of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more from the viewpoint of improving the dispersibility of the coating film peeled from the object to be cleaned and thereby improving the cleaning performance, and from the viewpoint of improving the compatibility with components, it is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, still more preferably 20% by mass or less, and even more preferably 10% by mass or less. That is, the content of the solvent (B1) in the cleaning composition is preferably 0.5% by mass or more and 50% by mass or less, more preferably 0.5% by mass or more and 40% by mass or less, even more preferably 1% by mass or more and 30% by mass or less, still more preferably 1% by mass or more and 20% by mass or less, and even more preferably 2% by mass or more and 10% by mass or less.

[0021] From the viewpoint of improving the cleanability of a coating film, the mass ratio of the content of solvent (B) to the content of solvent (A) in the cleaning composition of the present invention [solvent (B) / solvent (A)] is preferably 0.05 or more, more preferably 0.07 or more, even more preferably 0.10 or more, and is preferably 3.0 or less, more preferably 2.5 or less, even more preferably 2.0 or less, still more preferably 1.5 or less, still more preferably 1.0 or less, still more preferably 0.9 or less, still more preferably 0.7 or less, still more preferably 0.5 or less, and still more preferably 0.3 or less. That is, the mass ratio [solvent (B) / solvent (A)] is preferably 0.05 or more and 3.0 or less, more preferably 0.05 or more and 2.5 or less, even more preferably 0.05 or more and 2.0 or less, still more preferably 0.07 or more and 1.5 or less, still more preferably 0.07 or more and 1.0 or less, still more preferably 0.07 or more and 0.9 or less, still more preferably 0.10 or more and 0.7 or less, still more preferably 0.10 or more and 0.5 or less, and still more preferably 0.10 or more and 0.3 or less.

[0022] (Other Solvents) The cleaning composition of the present invention may contain solvents other than the solvents (A) and (B) to the extent that the effects of the present invention are not impaired. Examples of such other solvents include gamma-butyrolactone (dipole moment: 4.69 D), 2-pyrrolidone (dipole moment: 4.16 D), dimethyl sulfoxide (dipole moment: 4.10 D), dimethylformamide (dipole moment: 4.06 D), N-methylpyrrolidone (dipole moment: 3.99 D), tetrahydrofuran (dipole moment: 1.92 D), cyclohexane (dipole moment: 0.00 D), and benzene (dipole moment: 0.00 D).

[0023] The content of solvents other than solvents (A) and (B) in the cleaning composition of the present invention is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and still more preferably 0% by mass, from the viewpoint of improving the cleanability of the coating film and improving the compatibility with components.

[0024] <Water> The cleaning composition of the present invention contains water from the viewpoint of improving the cleaning properties of the coating film and improving compatibility with components. The water may be tap water, ion-exchanged water, ultrafiltered water, RO water, or distilled water, but from the viewpoint of improving the cleaning properties of the coating film, it is preferably at least one selected from the group consisting of ion-exchanged water, ultrafiltered water, RO water, and distilled water.

[0025] From the viewpoint of improving the cleaning properties of the coating film and improving the compatibility with components, the water content in the cleaning composition of the present invention is 30% by mass or more, preferably 35% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, still more preferably 50% by mass or more, still more preferably 55% by mass or more, still more preferably 60% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less. That is, the water content in the cleaning composition is 30% by mass or more, preferably 35% by mass or more to 90% by mass or less, more preferably 40% by mass or more to 90% by mass or less, still more preferably 45% by mass or more to 85% by mass or less, still more preferably 50% by mass or more to 85% by mass or less, still more preferably 55% by mass or more to 80% by mass or less, still more preferably 60% by mass or more to 60% by mass or less.

[0026] The mass ratio of the content of solvent (A) to the content of water in the cleaning composition of the present invention [solvent (A) / water] is preferably 0.05 or more, more preferably 0.07 or more, even more preferably 0.10 or more, still more preferably 0.15 or more, and even more preferably 0.20 or more from the viewpoint of improving the cleanability of the coating film, and is preferably 3.0 or less, more preferably 2.0 or less, even more preferably 1.5 or less, still more preferably 1.0 or less, still more preferably 0.70 or less, still more preferably 0.50 or less, and still more preferably 0.30 or less from the viewpoint of improving the compatibility with components. That is, the mass ratio [solvent (A) / water] is preferably 0.05 or more and 3.0 or less, more preferably 0.05 or more and 2.0 or less, even more preferably 0.07 or more and 1.5 or less, still more preferably 0.07 or more and 1.0 or less, still more preferably 0.10 or more and 0.70 or less, still more preferably 0.15 or more and 0.50 or less, and still more preferably 0.20 or more and 0.30 or less.

[0027] In addition to the above-mentioned components, the cleaning composition of the present invention may contain various commonly used additives such as pH adjusters, antifoaming agents, preservatives, antifungal agents, and rust inhibitors. The cleaning composition of the present invention does not contain pigments or polymers. Furthermore, from the viewpoint of dispersibility of pigments and polymers, the cleaning composition of the present invention preferably does not contain acids or oxidizing agents. The cleaning composition of the present invention can be obtained by mixing and stirring solvent (A), water, and, if necessary, solvent (B), the other solvents described above, and the additives.

[0028] (Cleaning Method) The cleaning composition of the present invention is preferably used to clean a coating film attached to an object to be cleaned. The object to be cleaned is preferably an inkjet head. That is, the cleaning method using the cleaning composition of the present invention is preferably a method of cleaning an inkjet head using the cleaning composition. A preferred cleaning method using the cleaning composition of the present invention is a method of bringing the cleaning composition into contact with a coating film attached to the object to be cleaned. Examples of contacting methods include immersion, spraying, application, and stirring. Furthermore, a method of impregnating an absorbent wiping member such as a nonwoven fabric with the cleaning composition of the present invention and wiping and cleaning the surface of the object to be cleaned is preferred as a method of removing a firmly adhered coating film.

[0029] [Uses of the Cleaning Composition of the Present Invention] The cleaning composition of the present invention has excellent cleaning properties for coating films and excellent compatibility with components, and is therefore preferably used, for example, as a cleaner for aqueous inks containing polymers. In the present invention, "aqueous" means that water accounts for the largest proportion, by mass, of the medium in which the polymer is dispersed. In this case, even water-insoluble polymers can be cleaned well. In the present invention, "water-insoluble polymer" means that when a polymer that has been dried at 105°C for 2 hours and reached a constant weight is dissolved in 100 g of water at 25°C until saturation is reached, the dissolution amount is 10 g or less, preferably 5 g or less, more preferably 1 g or less. When the water-insoluble polymer is an anionic polymer, the dissolution amount is the amount dissolved when the anionic groups of the polymer are 100% neutralized with sodium hydroxide. When the water-insoluble polymer is a cationic polymer, the dissolution amount is the amount dissolved when the cationic groups of the polymer are 100% neutralized with hydrochloric acid.

[0030] When the cleaning composition of the present invention is used as a cleaner for aqueous inks containing a polymer and water (hereinafter simply referred to as "aqueous inks"), it is preferably used as a cleaner for aqueous inks for flexographic printing, gravure printing, or inkjet recording, and more preferably as a cleaner for aqueous inks for inkjet recording. The term "recording" encompasses printing and printing for recording characters and images. When the cleaning composition of the present invention is used as a cleaner for removing a coating of aqueous ink for inkjet recording adhered to an inkjet head, the cleaning properties of the cleaning composition of the present invention can be exerted to improve ejection recovery. When the cleaning composition of the present invention is used as a cleaner for aqueous inks for inkjet recording, it can also be used to clean inkjet recording apparatuses that use aqueous inks for inkjet recording, tools for maintaining such recording apparatuses, and the like. Among these, it is preferably used to clean inkjet recording apparatuses, and more preferably to clean inkjet heads. Specifically, it can be used to clean the ink ejection orifices of an inkjet head, the areas near the ink ejection orifices, and the ink supply paths from an ink tank or ink cartridge to the ink ejection orifices of an inkjet recording apparatus. More specifically, the cleaning composition of the present invention can be suitably used as a cleaning agent (spray liquid, wiping liquid) for water-based inks for ink-jet printing that have adhered to a nozzle plate having a large number of ejection nozzle holes provided in an ink-jet head for each color ink. That is, the cleaning composition of the present invention can be suitably used as a cleaning composition for an ink-jet head.

[0031] <Water-Based Ink> The water-based ink that is the target of the cleaning composition of the present invention contains a polymer and water. The water-based ink may be a so-called undercoat liquid and / or overcoat liquid. The water-based ink may further contain a pigment in addition to the polymer and water. That is, the coating film to be cleaned with the cleaning composition of the present invention contains at least a component derived from the polymer derived from the water-based ink, and preferably contains a component derived from the polymer and a component derived from the pigment.

[0032] [Polymer] The polymer contained in the aqueous ink that is the target of the cleaning composition of the present invention is preferably one that is contained for at least one of the following functions: a pigment dispersant that exhibits a pigment dispersing effect, or a fixing agent for the print medium. The polymer that functions as a pigment dispersant (hereinafter also referred to as a "pigment dispersing polymer") is preferably a water-insoluble polymer from the viewpoints of the dispersion stability and ejection recovery of the ink. Preferred examples of the pigment dispersing polymer include one or more selected from the group consisting of polyester resins, polyurethane resins, and vinyl resins from the viewpoints of the dispersion stability and ejection recovery of the ink. Among these, one or more selected from the group consisting of polyester resins and vinyl resins is more preferred, and polyester resins are even more preferred.

[0033] The polyester resin can be obtained by polycondensation of an alcohol component and a carboxylic acid component. The alcohol component can be an aromatic or aliphatic polyol, with aromatic diols such as alkylene oxide adducts of bisphenol A being preferred. The carboxylic acid component can be an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, or a trivalent or higher polycarboxylic acid, with aliphatic dicarboxylic acids such as fumaric acid being preferred.

[0034] The vinyl resin can be obtained by addition polymerization, by a known method, of a monomer mixture containing an ionic monomer such as acrylic acid or methacrylic acid and one or more selected from hydrophobic monomers such as alkyl (meth)acrylates or aromatic group-containing monomers, and hydrophilic nonionic monomers such as polyalkylene glycol (meth)acrylates. Among these, from the viewpoints of dispersion stability and ejection recovery of the ink, a water-based ink in which a pigment is dispersed in a water-insoluble polymer having an anionic group such as a carboxy group is preferred.

[0035] From the viewpoint of the dispersion stability and ejection recovery property of the ink, the aqueous ink preferably contains the pigment in the form of water-insoluble polymer particles containing the pigment (hereinafter also simply referred to as "pigment-containing polymer particles"), using the above-mentioned water-insoluble polymer as the pigment-dispersing polymer. The pigment-containing polymer particles are sufficient as long as they are formed by the pigment and the water-insoluble polymer, and are formed by the water-insoluble polymer being adsorbed onto the pigment in the aqueous ink. Examples of the particle form include a particle form in which the pigment is encapsulated in the polymer, a particle form in which the pigment is uniformly dispersed in the polymer, a particle form in which the pigment is exposed on the surface of the polymer particle, and mixtures thereof.

[0036] The polymer that functions as a fixing agent for print media (hereinafter also referred to as "fixing aid polymer") is preferably a water-insoluble polymer from the viewpoint of imparting higher fixability to printed matter. Preferred examples of fixing aid polymers from the viewpoint of imparting higher fixability to printed matter include one or more selected from the group consisting of polyester resins, acrylic resins, styrene / (meth)acrylic resins, styrene resins, styrene / butadiene resins, butadiene resins, vinyl chloride resins, vinyl acetate resins, and polyurethane resins. Among these, more preferred are one or more selected from the group consisting of polyester resins, acrylic resins, and styrene / acrylic resins, and even more preferred are polyester resins. The fixing aid polymers can be used alone or in combination of two or more.

[0037] From the viewpoints of fixability to print media and abrasion resistance of printed matter, the fixing aid polymer is preferably a water-insoluble polymer particle containing no pigment, more preferably a polyester resin particle containing no pigment. The polyester resin constituting the pigment-free polyester resin particles can be obtained by polycondensation of an alcohol component and a carboxylic acid component. The alcohol component can be an aromatic or aliphatic polyol, with those containing an aromatic diol such as an alkylene oxide adduct of bisphenol A being preferred. The carboxylic acid component can be an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, a trivalent or higher polycarboxylic acid, or the like, with those containing an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, or a trivalent or higher polycarboxylic acid being preferred.

[0038] From the viewpoint of handleability, the pigment-free water-insoluble polymer particles are preferably used as a dispersion, and those synthesized by emulsion polymerization or the like may be used, or commercially available products may be used. Commercially available dispersions of pigment-free water-insoluble polymer particles include, for example, acrylic resins such as "Neocryl A1127" (manufactured by DSM NeoResins, anionic self-crosslinking aqueous acrylic resin) and "Joncryl 390" (manufactured by BASF Japan Ltd.), styrene / acrylic resins such as "Joncryl 7100", "Joncryl 734", and "Joncryl 538" (all manufactured by BASF Japan Ltd.), styrene / butadiene resins such as "SR-100" and "SR102" (both manufactured by Nippon A&L Co., Ltd.), vinyl chloride resins such as "Vinyblan 701" (manufactured by Nissin Chemical Industry Co., Ltd.), and polyurethane resins such as "WBR-2018" and "WBR-2000U" (both manufactured by Taisei Fine Chemical Co., Ltd.).

[0039] When the aqueous ink contains pigment-containing polymer particles, the weight-average molecular weight of the water-insoluble polymer that constitutes the particles is preferably 5,000 or more, more preferably 7,000 or more, even more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less. That is, when the aqueous ink contains pigment-containing polymer particles, the weight-average molecular weight of the water-insoluble polymer that constitutes the particles is preferably 5,000 or more and 100,000 or less, more preferably 7,000 or more and 50,000 or less, even more preferably 10,000 or more and 30,000 or less. When the aqueous ink contains water-insoluble polymer particles that do not contain a pigment, the weight-average molecular weight of the water-insoluble polymer that makes up the particles is preferably 5,000 or more, more preferably 7,000 or more, even more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. That is, when the aqueous ink contains water-insoluble polymer particles that do not contain a pigment, the weight-average molecular weight of the water-insoluble polymer that makes up the particles is preferably 5,000 or more and 100,000 or less, more preferably 7,000 or more and 50,000 or less, and even more preferably 10,000 or more and 30,000 or less. The weight-average molecular weight of the water-insoluble polymer can be measured by gel permeation chromatography, and the specific measurement method described in the examples can be used.

[0040] From the viewpoint of improving the removability of coating films and further improving cleaning properties, the acid value of the polymer is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, and even more preferably 20 mgKOH / g or more. The higher the acid value of the polymer, the better the removability of coating films by the cleaning agent of the present invention. Therefore, there is no particular upper limit for the acid value of the polymer.

[0041] [Pigments] The pigments contained in the aqueous inks that are the target of the cleaning composition of the present invention may be either inorganic or organic. If necessary, they can also be used in combination with extender pigments. Examples of inorganic pigments include carbon black and metal oxides. For black inks, carbon black is preferred. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. For white inks, examples of metal oxides include titanium dioxide, zinc oxide, silica, alumina, and magnesium oxide. Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. For achromatic inks, achromatic pigments such as white, black, and gray can be used. For chromatic inks, chromatic pigments such as yellow, magenta, cyan, red, blue, orange, and green can be used. Examples of extender pigments include silica, calcium carbonate, and talc. The pigment may be used alone or in combination of two or more kinds. The pigment may be contained in the water-based ink in the form of a self-dispersing pigment, a pigment dispersed with a dispersant, or water-insoluble polymer particles containing the pigment.

[0042] The water-based ink may further contain, as necessary, a neutralizing agent, an organic solvent, and a surfactant as components other than the polymer, water, and pigment. The water-based ink may also contain, as optional components, various additives such as a humectant, wetting agent, penetrant, dispersant, surfactant, viscosity modifier, antifoaming agent, preservative, antifungal agent, and antirust agent.

[0043] The water-based ink can be obtained by mixing and stirring a pigment, a water-insoluble polymer, water, and, if necessary, a neutralizing agent, an organic solvent, a surfactant, etc. When pigment-containing polymer particles are contained, the pigment-containing polymer particles may be prepared by dispersing the pigment, the water-insoluble polymer, and, if necessary, a neutralizing agent, a surfactant, etc., by a known method to obtain a dispersion of the pigment-containing polymer particles, which may then be blended into the water-based ink.

[0044] The content of the water-insoluble polymer in the aqueous ink is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoints of the dispersion stability and ejection recovery property of the ink, as well as the fixability to the printing medium and the abrasion resistance of the printed matter; and from the viewpoint of the viscosity of the ink, it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. That is, the content of the water-insoluble polymer in the aqueous ink is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less, and even more preferably 5% by mass or less. When the aqueous ink contains a pigment, the content of the pigment in the aqueous ink is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of the print density of the printed matter; and from the viewpoints of the viscosity of the ink and the abrasion resistance of the printed matter, it is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and even more preferably 6% by mass or less. That is, the content of the pigment in the aqueous ink is preferably 1% by mass or more and 15% by mass or less, more preferably 1% by mass or more and 10% by mass or less, even more preferably 2% by mass or more and 8% by mass or less, and even more preferably 3% by mass or more and 6% by mass or less. When the aqueous ink contains pigment-containing polymer particles and pigment-free polymer particles, the content of the water-insoluble polymer is the total amount of the water-insoluble polymer contained in the pigment-containing polymer particles and the pigment-free polymer particles. From the viewpoints of the dispersion stability of the ink and the abrasion resistance of printed matter, the content of water in the aqueous ink is preferably 35% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less. That is, the content is preferably 35% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 75% by mass or less, and even more preferably 45% by mass or more and 70% by mass or less.

[0045] A cleaning method using the cleaning composition of the present invention as a cleaning agent for aqueous inks preferably involves contacting the cleaning composition with a coating film adhered to an object to be cleaned by aqueous ink. Contacting methods include, as described above, immersion, spraying, coating, stirring, and the like. Examples of the cleaning method include a method in which the cleaning composition of the present invention is impregnated into a liquid-absorbent wiping member such as a nonwoven fabric and used to wipe off a coating film adhered to the inkjet nozzle surface or the inkjet nozzle outlet of an inkjet head; a method in which, when using a different type of ink, the ink path in the printer is cleaned by repeatedly supplying and discharging the cleaning composition from a cartridge containing the cleaning composition into the ink path using the printer's supply mechanism and discharge mechanism before and after changing the ink; and a method in which, when the inkjet head will not be used for a long period of time, the coating film is removed from the inkjet head, filled with the cleaning composition, and capped for storage. The wiping member is not particularly limited as long as it is liquid-absorbent, and examples thereof include fabrics such as woven fabrics, knitted fabrics, and nonwoven fabrics, sponges, and pulp. In the cleaning method, from the viewpoint of exerting superior detergency, the temperature when the cleaning composition is brought into contact is preferably 0° C. or higher, more preferably 10° C. or higher, and even more preferably 20° C. or higher, and from the viewpoint of saving energy, cleaning is carried out preferably at less than 100° C., more preferably 80° C. or lower, even more preferably 70° C. or lower, and still more preferably 50° C. or lower. That is, in the cleaning method, cleaning is carried out preferably at a temperature of 0° C. or higher but lower than 100° C., more preferably 0° C. or higher but 80° C. or lower, even more preferably 10° C. or higher but 70° C. or lower, and even more preferably 20° C. or higher but 50° C.

[0046] The present invention can provide a cleaning composition that has excellent coating film cleaning properties and also has excellent compatibility with components.

[0047] The present invention also includes the following aspects <1> to <53>. <1> A cleaning composition containing a solvent (A) and water, wherein the solvent (A) has a dipole moment of 5.0 D or more at 25°C as determined by density functional theory, and the content of water in the cleaning composition is 30 mass% or more. <2> The cleaning composition according to <1> above, wherein the solvent (A) is one or more solvents selected from the group consisting of propylene carbonate, ethylene carbonate, and sulfolane. <3> The cleaning composition according to <1> or <2> above, further containing an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group. <4> The cleaning composition according to any one of <1> to <3> above, wherein the organic solvent (B) includes one or more solvents (B1) selected from the group consisting of ethylene glycol, diethylene glycol, polyoxyalkylene phenyl ether, and polyoxyalkylene benzyl ether. <5> The cleaning composition according to <4>, wherein the polyoxyalkylene group of the polyoxyalkylene phenyl ether or the polyoxyalkylene benzyl ether is a polyoxyethylene group. <6> The cleaning composition according to <5>, wherein the average number of moles of ethylene oxide added to the polyoxyethylene group is 2 or more and 6 or less. <7> The cleaning composition according to any one of <1> to <6>, wherein the water content in the cleaning composition is 30% by mass or more and 90% by mass or less. <8> A cleaning composition containing a solvent (A), an organic solvent (B), and water, wherein the dipole moment of the solvent (A) at 25°C determined by a density functional theory method is 5.0 D or more, the water content in the cleaning composition is 30% by mass or more and 90% by mass or less, the solvent (A) is propylene carbonate, and the organic solvent (B) is polyoxyethylene phenyl ether.<9> A cleaning composition comprising a solvent (A), an organic solvent (B), and water, wherein the solvent (A) has a dipole moment of 5.0 D or more at 25°C as determined by density functional theory, the content of water in the cleaning composition is 30% by mass or more and 90% by mass or less, the solvent (A) is propylene carbonate, and the organic solvent (B) is polyoxyethylene phenyl ether having an average number of moles of ethylene oxide added in polyoxyethylene groups of 2. <10> The cleaning composition according to <9>, wherein the content of propylene carbonate in the cleaning composition is 5% by mass or more and 60% by mass or less, and the content of polyoxyethylene phenyl ether having an average number of moles of ethylene oxide added in polyoxyethylene groups of 2 in the cleaning composition is 0.5% by mass or more and 50% by mass or less.

[0048] <11> An inkjet head cleaning composition containing a solvent (A) and water, wherein the solvent (A) has a dipole moment of 5.0 D or more at 25°C as determined by density functional theory, and the water content in the cleaning composition is 30 mass% or more. <12> The inkjet head cleaning composition according to <11>, wherein the solvent (A) is one or more solvents selected from the group consisting of propylene carbonate, ethylene carbonate, and sulfolane. <13> The inkjet head cleaning composition according to <11> or <12>, further containing an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group. <14> The inkjet head cleaning composition according to <13>, wherein the organic solvent (B) includes one or more solvents (B1) selected from the group consisting of ethylene glycol, diethylene glycol, polyoxyalkylene phenyl ether, and polyoxyalkylene benzyl ether. <15> The cleaning composition for an inkjet head according to <14>, wherein the polyoxyalkylene group of the polyoxyalkylene phenyl ether or the polyoxyalkylene benzyl ether is a polyoxyethylene group. <16> The cleaning composition for an inkjet head according to <15>, wherein the average number of moles of ethylene oxide added to the polyoxyethylene group is 2 or more and 6 or less. <17> The cleaning composition for an inkjet head according to any one of <11> to <16>, wherein the content of water in the cleaning composition for an inkjet head is 30% by mass or more and 90% by mass or less. <18> An inkjet head cleaning composition containing a solvent (A), an organic solvent (B), and water, wherein the dipole moment of the solvent (A) at 25°C determined by a density functional method is 5.0 D or more, the content of water in the cleaning composition for an inkjet head is 30% by mass or more and 90% by mass or less, the solvent (A) is propylene carbonate, and the organic solvent (B) is polyoxyethylene phenyl ether.<19> An inkjet head cleaning composition comprising a solvent (A), an organic solvent (B), and water, wherein the solvent (A) has a dipole moment at 25°C determined by density functional theory of 5.0 D or more, the content of water in the inkjet head cleaning composition is 30% by mass or more and 90% by mass or less, the solvent (A) is propylene carbonate, and the organic solvent (B) is polyoxyethylene phenyl ether in which the average number of moles of ethylene oxide added in the polyoxyethylene group is 2. <20> The inkjet head cleaning composition according to <19>, wherein the content of propylene carbonate in the inkjet head cleaning composition is 5% by mass or more and 60% by mass or less, and the content of polyoxyethylene phenyl ether in which the average number of moles of ethylene oxide added in the polyoxyethylene group is 2 in the inkjet head cleaning composition is 0.5% by mass or more and 50% by mass or less.

[0049] <21> A cleaning composition for an inkjet head used in an inkjet head that ejects a water-based ink for inkjet printing, the cleaning composition containing a solvent (A) and water, wherein the solvent (A) has a dipole moment at 25°C, as determined by density functional theory, of 5.0 D or more, the content of water in the cleaning composition is 30% by mass or more, and the water-based ink for inkjet printing contains a polymer having an acid value of 5 mg KOH / g or more, and water. <22> The cleaning composition for an inkjet head according to <21>, wherein the polymer has an acid value of 5 mg KOH / g or more and 300 mg KOH / g or less. <23> The cleaning composition according to <21> or <22>, wherein the solvent (A) is one or more selected from the group consisting of propylene carbonate, ethylene carbonate, and sulfolane. <24> The cleaning composition according to any one of <21> to <23>, further containing an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group. <25> The cleaning composition according to any one of <21> to <24>, wherein the organic solvent (B) comprises one or more solvents (B1) selected from the group consisting of ethylene glycol, diethylene glycol, polyoxyalkylene phenyl ether, and polyoxyalkylene benzyl ether. <26> The cleaning composition according to <25>, wherein the polyoxyalkylene group of the polyoxyalkylene phenyl ether or the polyoxyalkylene benzyl ether is a polyoxyethylene group. <27> The cleaning composition according to <26>, wherein the average number of moles of ethylene oxide added in the polyoxyethylene group is 2 or more and 6 or less. <28> The cleaning composition according to any one of <21> to <27>, wherein the water content in the inkjet head cleaning composition is 30% by mass or more and 90% by mass or less.<29> A cleaning composition for an inkjet head, which is used for an inkjet head that ejects a water-based ink for inkjet printing, and which contains a solvent (A), an organic solvent (B), and water, wherein the dipole moment of the solvent (A) at 25°C determined by a density functional method is 5. 0D or higher, a content of water in the inkjet head cleaning composition is 30% by mass or more and 90% by mass or less, the solvent (A) is propylene carbonate, a content of propylene carbonate in the inkjet head cleaning composition is 5% by mass or more and 60% by mass or less, the organic solvent (B) is polyoxyethylene phenyl ether in which an average number of moles of ethylene oxide added in polyoxyethylene groups is 2, a content of polyoxyethylene phenyl ether in which an average number of moles of ethylene oxide added in polyoxyethylene groups is 2 in the inkjet head cleaning composition is 0.5% by mass or more and 50% by mass or less, the water-based ink for inkjet printing contains a polymer having an acid value of 5 mgKOH / g or more and 300 mgKOH / g or less, and water, the polymer is a vinyl-based polymer having a weight-average molecular weight of 5,000 or more and 100,000 or less, and a content of the vinyl-based polymer in the water-based ink for inkjet printing is 1% by mass or more and 20% by mass or less. <30> The cleaning composition for an inkjet head according to <29> above, wherein the vinyl polymer has an acid value of 60 mgKOH / g or more and 300 mgKOH / g or less. <31> The cleaning composition for an inkjet head according to <29> above or <30> above, wherein the water-based ink for inkjet printing further contains a pigment, and the content of the pigment in the water-based ink for inkjet printing is 1% by mass or more and 15% by mass or less.<32> A cleaning composition for an inkjet head, which is used for an inkjet head that ejects a water-based ink for inkjet printing, and which contains a solvent (A), an organic solvent (B), and water, wherein the dipole moment of the solvent (A) at 25°C determined by a density functional method is 5. 0D or higher, a content of water in the inkjet head cleaning composition is 30% by mass or more and 90% by mass or less, the solvent (A) is propylene carbonate, a content of propylene carbonate in the inkjet head cleaning composition is 5% by mass or more and 60% by mass or less, the organic solvent (B) is polyoxyethylene phenyl ether in which an average number of moles of ethylene oxide added in polyoxyethylene groups is 2, a content of polyoxyethylene phenyl ether in which an average number of moles of ethylene oxide added in polyoxyethylene groups is 2 in the inkjet head cleaning composition is 0.5% by mass or more and 50% by mass or less, the water-based ink for inkjet printing contains a polymer having an acid value of 5 mgKOH / g or more and 300 mgKOH / g or less, and water, the polymer is a polyester having a weight-average molecular weight of 5,000 or more and 100,000 or less, and a content of the polyester in the water-based ink for inkjet printing is 1% by mass or more and 20% by mass or less. <33> The cleaning composition for an inkjet head according to <32> above, wherein the polyester has an acid value of 5 mgKOH / g or more and 50 mgKOH / g or less. <34> The cleaning composition for an inkjet head according to <32> above or <33> above, wherein the water-based ink for inkjet printing further contains a pigment, and the content of the pigment in the water-based ink for inkjet printing is 1% by mass or more and 15% by mass or less.

[0050] <35> Use of a cleaning composition as an inkjet head cleaner, comprising a solvent (A) and water, wherein the solvent (A) has a dipole moment of 5.0 D or more at 25°C as determined by density functional theory, and the water content is 30 mass% or more. <36> The use according to <35> above, wherein the solvent (A) is one or more selected from the group consisting of propylene carbonate, ethylene carbonate, and sulfolane. <37> The use according to <35> or <36> above, wherein the cleaning composition further contains an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group. <38> Use of a cleaning composition as an inkjet head cleaner, the cleaning composition comprising a solvent (A), an organic solvent (B), and water, wherein the solvent (A) has a dipole moment of 5.0 D or more at 25°C as determined by a density functional theory method, and the water content is 30% by mass or more and 90% by mass or less, wherein the solvent (A) is propylene carbonate, and the content of the propylene carbonate in the cleaning composition is 5% by mass or more and 60% by mass or less, the organic solvent (B) is polyoxyethylene phenyl ether in which the average number of moles of ethylene oxide added in the polyoxyethylene group is 2, and the content of the polyoxyethylene phenyl ether in which the average number of moles of ethylene oxide added in the polyoxyethylene group is 2 in the cleaning composition is 0.5% by mass or more and 50% by mass or less.

[0051] <39> Use of a cleaning composition containing a solvent (A), an organic solvent (B), and water as a cleaning agent for an inkjet head that ejects a water-based ink for inkjet recording, wherein the dipole moment of the solvent (A) at 25°C determined by a density functional method is 5. 0D or higher, the content of water in the cleaning composition is 30% by mass or more and 90% by mass or less, the solvent (A) is propylene carbonate, the content of propylene carbonate in the cleaning composition is 5% by mass or more and 60% by mass or less, the organic solvent (B) is polyoxyethylene phenyl ether in which the average number of moles of ethylene oxide added in polyoxyethylene groups is 2, the content of polyoxyethylene phenyl ether in which the average number of moles of ethylene oxide added in polyoxyethylene groups is 2 in the cleaning composition is 0.5% by mass or more and 50% by mass or less, the water-based ink for ink-jet printing contains a polymer having an acid value of 5 mgKOH / g or more and 300 mgKOH / g or less, and water, the polymer is a vinyl-based polymer having a weight-average molecular weight of 5,000 or more and 100,000 or less, and the content of the vinyl-based polymer in the water-based ink for ink-jet printing is 1% by mass or more and 20% by mass or less. <40> The use according to <39> above, wherein the vinyl polymer has an acid value of 60 mgKOH / g or more and 300 mgKOH / g or less. <41> The use according to <39> or <40> above, wherein the water-based ink for ink-jet printing further contains a pigment, and the content of the pigment in the water-based ink for ink-jet printing is 1% by mass or more and 15% by mass or less.

[0052] <42> Use of a cleaning composition containing a solvent (A), an organic solvent (B), and water as a cleaning agent for an inkjet head that ejects a water-based ink for inkjet recording, wherein the dipole moment of the solvent (A) at 25°C determined by density functional theory is 5. 0D or higher, the content of water in the cleaning composition is 30% by mass or more and 90% by mass or less, the solvent (A) is propylene carbonate, the content of propylene carbonate in the cleaning composition is 5% by mass or more and 60% by mass or less, the organic solvent (B) is polyoxyethylene phenyl ether in which the average number of moles of ethylene oxide added in polyoxyethylene groups is 2, the content of polyoxyethylene phenyl ether in which the average number of moles of ethylene oxide added in polyoxyethylene groups is 2 in the cleaning composition is 0.5% by mass or more and 50% by mass or less, the water-based ink for ink-jet printing contains a polymer having an acid value of 5 mgKOH / g or more and 300 mgKOH / g or less, and water, the polymer being a polyester having a weight-average molecular weight of 5,000 or more and 100,000 or less, and the content of the polyester in the water-based ink for ink-jet printing is 1% by mass or more and 20% by mass or less. <43> The use according to <42> above, wherein the polyester has an acid value of 5 mgKOH / g or more and 50 mgKOH / g or less. <44> The use according to <42> or <43> above, wherein the water-based ink for ink-jet printing further contains a pigment, and the content of the pigment in the water-based ink for ink-jet printing is 1% by mass or more and 15% by mass or less.

[0053] <45> A method for cleaning an inkjet head using a cleaning composition containing a solvent (A) and water, wherein the solvent (A) has a dipole moment of 5.0 D or more at 25°C as determined by a density functional theory method, and the water content is 30 mass% or more. <46> The method according to <45> above, wherein the solvent (A) is one or more selected from the group consisting of propylene carbonate, ethylene carbonate, and sulfolane.

[0054] <47> The method according to <45> or <46> above, wherein the cleaning composition further contains an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group.

[0055] <48> A method for cleaning an inkjet head that has ejected a water-based ink for inkjet printing, using a cleaning composition containing a solvent (A), an organic solvent (B), and water, wherein the solvent (A) has a dipole moment of 5.0 D or more at 25°C as determined by a density functional theory method, the content of water in the cleaning composition is 30% by mass or more and 90% by mass or less, the solvent (A) is propylene carbonate, the content of the propylene carbonate in the cleaning composition is 5% by mass or more and 60% by mass or less, the organic solvent (B) is polyoxyethylene phenyl ether having an average number of moles of ethylene oxide added in polyoxyethylene groups of 2, the content of the polyoxyethylene phenyl ether having an average number of moles of ethylene oxide added in polyoxyethylene groups of 2 in the cleaning composition is 0.5% by mass or more and 50% by mass or less, the water-based ink for inkjet printing contains a polymer having an acid value of 5 mgKOH / g or more and 300 mgKOH / g or less, and water, The method according to the above item <48>, wherein the polymer is a vinyl polymer having a weight average molecular weight of 5,000 to 100,000, and the content of the vinyl polymer in the water-based ink for ink-jet printing is 1% by mass to 20% by mass. <49> The method according to the above item <48>, wherein the vinyl polymer has an acid value of 60 mg KOH / g to 300 mg KOH / g. <50> The method according to the above item <48> or <49>, wherein the water-based ink for ink-jet printing further contains a pigment, and the content of the pigment in the water-based ink for ink-jet printing is 1% by mass to 15% by mass.<51> A method for cleaning an inkjet head that has ejected a water-based ink for inkjet printing, using a cleaning composition containing a solvent (A), an organic solvent (B), and water, wherein the content of water in the cleaning composition is 30% by mass or more and 90% by mass or less, the solvent (A) is propylene carbonate, the content of the propylene carbonate in the cleaning composition is 5% by mass or more and 60% by mass or less, the organic solvent (B) is polyoxyethylene phenyl ether having an average number of moles of ethylene oxide added in polyoxyethylene groups of 2, and the content of the polyoxyethylene phenyl ether having an average number of moles of ethylene oxide added in polyoxyethylene groups of 2 in the cleaning composition is 0.5% by mass or more and 50% by mass or less, the water-based ink for inkjet printing contains water and a polymer having an acid value of 5 mgKOH / g or more and 300 mgKOH / g or less, and the polymer is a polyester having a weight-average molecular weight of 5,000 or more and 100,000 or less, <52> The method according to <51> above, wherein the polyester has an acid value of 5 mgKOH / g or more and 50 mgKOH / g or less. <53> The method according to <51> above, wherein the water-based ink for ink-jet printing further contains a pigment, and the content of the pigment in the water-based ink for ink-jet printing is 1% by mass or more and 15% by mass or less.

[0056] In the following Production Examples, Examples, and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring or calculating each physical property are as follows.

[0057] [Dipole moment of solvent at 25°C] The dipole moment of the solvent at 25°C was calculated using the quantum chemistry calculation software TURBOMOLE Ver. 7.7, jointly developed by the Karlsruhe Research Center in Germany and the University of Karlsruhe, using the density functional method. BP86 was used as the functional and def-TZVP as the basis function. For compounds with multiple conformations, calculations were performed using a single conformation, using the most stable conformation in vacuum.

[0058] [Softening Point of Polyester Resin] Using a flow tester "CFT-500D" (manufactured by Shimadzu Corporation), 1 g of a sample was extruded from a nozzle with a diameter of 1 mm and a length of 1 mm under a load of 1.96 MPa applied by a plunger while being heated at a temperature increase rate of 6°C / min. The plunger depression distance of the flow tester was plotted against the temperature, and the temperature at which half of the sample flowed out was taken as the softening point.

[0059] [Glass Transition Temperature of Polyester Resin] Using a differential scanning calorimeter "Pyris 6 DSC" (manufactured by Perkin Elmer), 5 mg of a sample was weighed into an aluminum pan, heated to 200°C, and cooled from that temperature to 0°C at a rate of 10°C / min. The sample was then heated at a rate of 10°C / min. The glass transition temperature was determined as the temperature at the intersection of an extension of the baseline below the maximum endothermic peak temperature and a tangent line showing the maximum slope from the rising part of the peak to the apex of the peak. In the case of an aqueous dispersion, the aqueous dispersion was freeze-dried at -10°C for 9 hours using a freeze-dryer "FDU-2100" manufactured by Tokyo Rikakikai Co., Ltd., and the resulting sample was used.

[0060] [Acid value of polyester resin] The acid value was measured according to the neutralization titration method described in JIS K 0070: 1992. However, the measurement solvent was changed from a mixed solvent of ethanol and ether to a mixed solvent of acetone and toluene [acetone:toluene=1:1 (volume ratio)].

[0061] [Weight-average molecular weight (Mw) of polyester resin] Measurement was performed by the following gel permeation chromatography method. (1) Preparation of sample solution The polyester resin was dissolved in chloroform to a concentration of 0.5 g / 100 mL, and the resulting solution was filtered using a fluororesin filter "FP-200" (manufactured by Sumitomo Electric Industries, Ltd.) with a pore size of 2 μm to remove insoluble components, thereby obtaining a sample solution. (2) Molecular weight measurement Using the following measurement device and analytical column, tetrahydrofuran was passed as a dissolving solution at a flow rate of 1 mL / min, and the column was stabilized in a thermostatic bath at 40°C. 100 μL of the sample solution was injected thereinto, and measurement was performed. The weight-average molecular weight of the sample was measured using the following monodisperse polystyrene [monodisperse polystyrene manufactured by Tosoh Corporation; 2.63 × 10 3, 2.06 × 10 4 , 1.02 × 10 5 (weight average molecular weight (Mw)), monodisperse polystyrene manufactured by GL Sciences Inc.; 2.10 × 10 3 , 7.00 x 10 3 , 5.04 × 10 4 (weight average molecular weight (Mw))] was used as a standard sample and calculated based on a calibration curve prepared in advance. <Measurement conditions> Measurement device: "HLC-8220GPC" (manufactured by Tosoh Corporation) Analytical column: "TSKgel GMHXL" + "TSKgel G3000HXL" (manufactured by Tosoh Corporation)

[0062] [Solid Content Concentration] 10.0 g of sodium sulfate, adjusted to a constant weight in a desiccator, was weighed into a 30 mL polypropylene container (inner diameter 40 mm, height 30 mm), and 1.0 g of sample was added thereto and mixed to obtain a mixture. The mixture was then weighed, maintained at 105°C for 2 hours to remove volatiles, and then left in the desiccator for 15 minutes, after which the mass of the mixture after devolatilization was measured. The mass of the mixture after devolatilization minus the mass of sodium sulfate was determined as the solid content of the sample after devolatilization, and this was divided by the mass of the sample before devolatilization to obtain the solid content concentration (%).

[0063] [Average particle size of water-insoluble polymer particles containing pigment and water-insoluble polymer particles not containing pigment] The cumulant average particle size measured using a laser particle analysis system "ELS-8000" (cumulant analysis) manufactured by Otsuka Electronics Co., Ltd. was used as the average particle size of the pigment-containing polymer particles or the pigment-free polymer particles. The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 accumulations, and the refractive index of water (1.333) was input as the refractive index of the dispersion medium. The measured concentration was 5 x 10 -3 It was done at %.

[0064] The raw material monomers (alcohol component and carboxylic acid component), esterification catalyst, and esterification co-catalyst shown in Table 1 were blended in the amounts shown in Table 1, and placed in a 10 L four-neck flask equipped with a thermometer, a stirrer, a downflow condenser, and a nitrogen inlet tube. The mixture was reacted in a nitrogen atmosphere in a mantle heater at 210°C for 10 hours, and then further reacted at -8.3 kPa (G) until the softening point reached the temperature shown in Table 1, thereby obtaining polyester resins P-1 to P-2, respectively. The physical properties of the resulting polyester resins are shown in Table 1.

[0065]

[0066] Production Example 2-1 (Production of aqueous dispersion D-1 of pigment-containing polyester resin particles) (1) Pigment dispersion step In a 2 L vessel, 66.7 g of polyester resin P-1 was dissolved as a pigment dispersion polymer in 156.4 g of methyl ethyl ketone (hereinafter referred to as "MEK"), and 5.36 g of a 5N aqueous sodium hydroxide solution as a neutralizing agent and 430.0 g of ion-exchanged water were added thereto, and the degree of neutralization by sodium hydroxide relative to the acid value of polyester resin P-1 was adjusted to 85 mol%, and the mixture was stirred and mixed for 15 minutes at 2,000 r / min using a disper blade at 10°C to 15°C. Next, 100.0 g of magenta pigment was added, and the mixture was stirred and mixed for 2 hours at 7,000 r / min using a disper blade at 10°C to 15°C. The resulting preliminary dispersion was filtered through a 150-mesh filter and diluted with 36.1 g of ion-exchanged water. The mixture was then subjected to 15 passes of dispersion treatment at a pressure of 150 MPa using a Microfluidizer "M-110EH-30XP" (a high-pressure homogenizer manufactured by Microfluidics) to obtain a dispersion of pigment-containing polyester resin particles. (2) Concentration Step The entire amount of the resulting pigment-containing polyester resin particle dispersion was placed in a 2-L eggplant flask, and ion-exchanged water was added to a solids concentration of 16.0%. Using a rotary distillation apparatus "Rotary Evaporator N-1000S" (manufactured by Tokyo Rikakikai Co., Ltd.), the mixture was rotated at a speed of 50 r / min in a warm bath adjusted to 32°C at a pressure of 0.09 MPa (abs) for 3 hours to remove the organic solvent. The warm bath was then adjusted to 62°C, the pressure was reduced to 0.07 MPa (abs), and the mixture was concentrated to a solids concentration of 25.0% to obtain a concentrate. The resulting concentrate was placed in a 500 mL angle rotor and centrifuged at 3,660 r / min for 20 minutes using a high-speed refrigerated centrifuge "himac CR22G" (manufactured by Hitachi Koki Co., Ltd., set temperature 20°C), and the liquid layer was then filtered through a 5 μm pore size membrane filter "Minisart" (manufactured by Sartorius) of pigment-containing polyester resin particles to obtain Aqueous Dispersion 1. Ion-exchanged water was added to the resulting Aqueous Dispersion 1 so that the solids concentration was 22.0%, and 0.76 g of "Proxel (registered trademark) LV(S)" (manufactured by Lonza Japan Co., Ltd.: preservative, active ingredient 20%) was further added, followed by stirring at 70°C for 2 hours.After cooling to 25°C, the mixture was filtered through the 5 µm pore size filter, and ion-exchanged water was added to obtain an aqueous dispersion D-1 of pigment-containing polyester resin particles (solid content concentration: 22.0%). The average particle size of the pigment-containing polyester resin particles in the aqueous dispersion D-1 was 130 nm.

[0067] Production Example 3-1 (Production of Aqueous Dispersion d-1 of Pigment-Free Polyester Resin Particles) In a four-neck flask equipped with a nitrogen inlet tube, a reflux condenser, a stirrer, and a thermocouple, polyester resin P-2 as a fixing aid polymer and methyl ethyl ketone (MEK) as an organic solvent were placed in the formulation shown in Table 2 and dissolved in MEK at 25°C. Next, a 5N aqueous solution of sodium hydroxide was added as a neutralizing agent in the formulation shown in Table 2, and ion-exchanged water was added with stirring to obtain a dispersion of pigment-free polyester resin particles. The resulting dispersion was reduced in pressure while stirring in the four-neck flask and maintained at 60°C, and the MEK was distilled off. Next, after cooling to room temperature, ion-exchanged water was added, and the mixture was filtered through a 200-mesh wire netting to obtain an aqueous dispersion d-1 of pigment-free polyester resin particles (solids concentration 40.0%). The average particle size of the pigment-free polyester resin particles in aqueous dispersion d-1 was 115 nm.

[0068]

[0069] Ink Production Example 1 The formulation of the aqueous ink shown in Table 3 was mixed, and the resulting mixture was filtered through a membrane filter "Minisart" (manufactured by Sartorius) with a pore size of 1.2 μm to obtain aqueous ink X1. The organic solvents, surfactants, and pH adjusters shown in Table 3 are as follows. [Organic solvents] BDG: diethylene glycol monobutyl ether (reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) PG: propylene glycol (reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) [Surfactants] KF6011: alkylene glycol-modified polydimethylsiloxane (trade name "KF-6011", nonionic surfactant manufactured by Shin-Etsu Chemical Co., Ltd.) [pH adjusters] MDEA: N-methyldiethanolamine (reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0070]

[0071] Examples A1 to A8, B1 to B6, C1 to C6, D1 to D6, Comparative Examples 1 to 4 Each cleaning composition was prepared by heating and mixing the components according to the formulation shown in Tables 4 to 7 to 45°C, and then cooling to 35°C. Each cleaning composition was evaluated as follows. The results are shown in Tables 4 to 7. The components shown in Tables 4 to 7 are as follows. [Solvent (A)] Propylene carbonate (dipole moment: 5.64 D): Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Ethylene carbonate (dipole moment: 5.41 D): Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. [Solvent (B)] (Solvent (B1)) Polyoxyethylene phenyl ether (average number of moles of EO added: 2.0): Manufacturer of Nippon Nyukazai Co., Ltd. Polyoxyethylene phenyl ether (average number of moles of EO added: 2.3): Manufacturer of Nippon Nyukazai Co., Ltd. Polyoxyethylene phenyl ether (average number of moles of EO added: 3.0): "Brawnon PH-3" manufactured by Aoki Oil & Fat Industries Co., Ltd. Polyoxyethylene phenyl ether (average number of moles of EO added: 4.0): "Brawnon PH-4" manufactured by Aoki Oil & Fat Industries Co., Ltd. Polyoxyethylene phenyl ether (average number of moles of EO added: 5.0): "Brawnon PH-5" manufactured by Aoki Oil & Fat Industries Co., Ltd. Polyoxyethylene phenyl ether (average number of moles of EO added: 5.5): manufactured by Nippon Nyukazai Co., Ltd. Polyoxyethylene benzyl ether (average number of moles of EO added: 2.0): manufactured by Tokyo Chemical Industry Co., Ltd. Reagent Ethylene glycol (dipole moment: 2.43 D): manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Reagent Diethylene glycol (dipole moment: 1.66 D): manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Reagent (Other solvents) Gamma butyrolactone (dipole moment: 4.69 D): manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Reagent

[0072] <Washability> (Application of Printed Dots) Using the water-based ink X1 obtained in Ink Production Example 1, one drop (ink droplet volume per drop: 0.5 nL) of the ink was applied at 5 mm intervals onto a glass petri dish using a dispenser printing device to form a grid-shaped printed image having 5 vertical and 5 horizontal printed dots. The dispenser printing device used was a piezo jet dispenser "PICO Pμlse Valve SD" (manufactured by Nordson EFD), and the liquid body assembly used was a "FLUID ASSY Pμlse MST 3.0S F0 E05" (opening 50 μm, ball size 3.0S). The dispenser was moved using a "PRO4" manufactured by Nordson Corporation. (Cleaning test) Next, 2 g of each cleaning composition of Examples and Comparative Examples was added to the grid-shaped printed image on a petri dish, and after leaving it at room temperature for 5 minutes, it was shaken for 60 seconds at 100 rpm in a shaker, and the shaken petri dish was tilted 120 degrees to remove the cleaning composition from the petri dish. Next, 2 g of ion-exchanged water was poured into the petri dish, and after leaving it at room temperature for 1 minute, it was shaken for 60 seconds at 100 rpm in a shaker, and the shaken petri dish was tilted 120 degrees to remove the ion-exchanged water. (Cleaning performance evaluation) 25 printed dots of the grid-shaped printed image were observed, and the score (total cleaning performance score P) was calculated based on the following points: 4 points when all the printed dots were removed, 3 points when a thin transparent film remained, 2 points when a thin colored film remained, 1 point when some of the printed dots peeled off but some remained intact, and 0 point when there was no visible change in the printed dots. When the total score P of the cleaning performance is 80 or more, the cleaning performance is excellent.

[0073] <Component Compatibility> As a resin component, an O-ring "BS007 Viton 5 / 32 inch" (material: fluorocarbon elastomer) (manufactured by RS Components Co., Ltd.) with a mass of approximately 0.08 g (M ０) was measured, and then the resin workpiece was immersed in each cleaning composition of the Examples and Comparative Examples and stored at 60°C for one month. The resin workpiece was then taken out and immersed in 50 g of ion-exchanged water at room temperature for one hour. The resin workpiece was then taken out and dried overnight in an environment at a temperature of 60°C and a relative humidity of 10% or less, and then cooled for one hour in an environment at room temperature and a relative humidity of 50±10%, after which the mass (M １ The mass (M ０ ) and mass (M １ The swelling ratio was calculated from the following formula using the M . When the swelling ratio is less than 20%, the material is excellent in compatibility with components. Swelling ratio (%) = [(M １ -M ０ ) / M ０ ]×100

[0074] <Ejection Recovery> (Continuous Printing Test Before Cleaning) In an environment of a temperature of 25±1°C and a relative humidity of 10±5%, a printing evaluation device "OnePassJet" (manufactured by Tritec Corporation) equipped with an inkjet head "KJ4B-QA06NTB" (manufactured by Kyocera Corporation) was filled with the water-based ink X1 obtained in Ink Production Example 1. The printing conditions were set as follows: head voltage 26 V, frequency 30 kHz, appropriate amount of ejection liquid 7 pL, head temperature 32°C, number of pre-ejection flushings 200, and negative pressure -4.0 kPa. Next, after printing for 3 hours continuously under the above printing conditions without maintenance, a nozzle check pattern was printed, and the number of nozzles that had deflected ejection or clogged ejection (number of missing nozzles before cleaning N ０) was confirmed. The occurrence of deflected ejection was judged to be due to a deviation of 50 μm or more from the predetermined intended landing point. (Cleaning Test) Next, 50 mL of each cleaning composition of the Examples and Comparative Examples was injected into the inkjet head to fill it, and the cleaning composition was allowed to overflow from the nozzle side and flow out to perform cleaning. Next, the ink injection port of the head was plugged, and the head was left to stand for 5 minutes so that each cleaning composition was retained in the head. Thereafter, 50 mL of the same cleaning composition as the cleaning composition retained in the head was further injected into the head to fill it, and the cleaning composition was allowed to overflow from the nozzle side and flow out to perform cleaning. Finally, 1 L of ion-exchanged water was injected into the head to fill it, and the ion-exchanged water was allowed to overflow from the nozzle side and flow out to perform cleaning. (Printing test after cleaning) Ink X1 obtained in Ink Production Example 1 was filled into a printing evaluation device "OnePassJet" (manufactured by Tritec Corporation) equipped with an inkjet head "KJ4B-QA06NTB" (manufactured by Kyocera Corporation) in an environment of temperature 25±1°C and relative humidity 10±5%. The printing conditions were set as follows: head voltage 26V, frequency 30kHz, appropriate amount of ejection liquid 7pL, head temperature 32°C, number of pre-ejection flushings 200, and negative pressure -4.0kPa. Next, a nozzle check pattern was printed under the above printing conditions, and the number of nozzles that had deflected ejection or clogged ejection (number of missing nozzles after cleaning N １ ) was confirmed. The occurrence of deflected ejection was judged to be due to a deviation of 50 μm or more from the predetermined intended landing position. (Nozzle recovery rate) Number of chipped nozzles before cleaning N ０ and the number of chipped nozzles after cleaning N １ The nozzle recovery rate was calculated from the following formula using the above formula. When the nozzle recovery rate is 90% or more, the ejection recovery rate is excellent, and when the nozzle recovery rate is 95% or more, the ejection recovery rate is particularly excellent. Nozzle recovery rate (%) = [(N ０ -N １ ) / N ０ ]×100

[0075]

[0076]

[0077]

[0078]

[0079] From Tables 4 to 7, it can be seen that the cleaning compositions of Examples are superior in cleaning properties and compatibility with components compared to the cleaning compositions of Comparative Examples, and further, when used as a cleaner for an inkjet head that ejects a water-based ink for inkjet printing, they are superior in ejection recovery of the inkjet head.

Claims

1. A cleaning composition for inkjet heads comprising a solvent (A) and water, wherein the dipole moment of the solvent (A) at 25°C determined by a density functional method is 5.0 D or more, and the water content in the cleaning composition is 30 mass% or more.

2. The inkjet head cleaning composition according to claim 1, wherein the solvent (A) is at least one selected from the group consisting of propylene carbonate, ethylene carbonate, and sulfolane.

3. The inkjet head cleaning composition according to claim 1 or 2, further comprising an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group.

4. The cleaning composition for an inkjet head according to claim 3, wherein the organic solvent (B) comprises one or more solvents (B1) selected from the group consisting of ethylene glycol, diethylene glycol, polyoxyalkylene phenyl ether, and polyoxyalkylene benzyl ether.

5. The cleaning composition for inkjet heads according to claim 4, wherein the polyoxyalkylene group of said polyoxyalkylene phenyl ether or said polyoxyalkylene benzyl ether is a polyoxyethylene group.

6. A cleaning composition for inkjet heads according to claim 4, wherein the polyoxyalkylene group of the polyoxyalkylene phenyl ether or the polyoxyalkylene benzyl ether is a polyoxyethylene group, and the average number of moles of ethylene oxide added to the polyoxyethylene group is 2 or more and 6 or less.

7. The inkjet head cleaning composition according to any one of claims 1 to 6, which is used for an inkjet head that ejects a water-based ink for inkjet printing, wherein the water-based ink for inkjet printing contains a polymer having an acid value of 5 mgKOH / g or more, and water.

8. Use of a cleaning composition as an inkjet head cleaner, comprising a solvent (A) and water, the solvent (A) having a dipole moment of 5.0 D or more at 25°C as determined by a density functional method, and the water content being 30 mass% or more.

9. The use according to claim 8, wherein the solvent (A) is one or more selected from the group consisting of propylene carbonate, ethylene carbonate, and sulfolane.

10. The use according to claim 8 or 9, further comprising an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group.

11. A cleaning composition for an inkjet head, comprising the method according to any one of claims 8 to 10, for use in an inkjet head that ejects a water-based ink for inkjet printing, the water-based ink for inkjet printing comprising a polymer having an acid value of 5 mgKOH / g or more, and water.

12. A method for cleaning an inkjet head, comprising using a cleaning composition comprising a solvent (A) and water, the solvent (A) having a dipole moment of 5.0 D or more at 25°C as determined by a density functional method, and the water content is 30 mass% or more.

13. The method according to claim 11, wherein the solvent (A) is at least one member selected from the group consisting of propylene carbonate, ethylene carbonate, and sulfolane.

14. The method according to claim 11 or 12, further comprising using a composition containing an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group.

15. The method according to any one of claims 12 to 14, wherein the inkjet head is an inkjet head that ejects a water-based ink for inkjet printing, and the water-based ink for inkjet printing contains a pigment, a polymer having an acid value of 5 mg KOH / g or more, and water.

Images