Cleaning solution for inkjet printheads

Abstract

To provide cleaning liquid for ink-jet print heads which is excellent in a redispersion property and a defoaming property of a solidified ink product, and can prevent ink discharge failure after cleaning the ink-jet print heads.SOLUTION: There are provided: (1) cleaning liquid for ink-jet print heads including a surfactant (A) which contains an acetylene glycol surfactant (a), a water-soluble organic solvent (B) which contains diethylene glycol monobutyl ether (b), and water, with a pH at 20°C of 10.5 or more; and (2) a method for cleaning ink-jet print heads which involves use of the cleaning liquid for ink-jet print heads described in (1).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a cleaning liquid for inkjet print heads.

Background Art

[0002] Inkjet printing is a method that uses an inkjet printer to directly eject ink droplets from extremely fine nozzles onto a recording medium to allow the droplets to adhere, thereby obtaining a printed material on which characters and images are recorded. At sites where inkjet printers are used, wiping with a rubber wipe or a non-woven fabric impregnated with cleaning liquid is performed to remove excess ink adhering to the nozzle surface and discharge ports, so as to prevent occurrences such as nozzle ejection failure. Furthermore, when different types of ink are used, it is necessary to clean the ink path inside the printer with cleaning liquid before and after changing the ink. In addition, when the recording head is not used for a long period of time, practices such as draining ink from the recording head, filling the recording head with cleaning liquid, capping the recording head, and storing it are performed. Accordingly, various cleaning liquids have been proposed.

[0003] For example, Patent Document 1 discloses a cleaning and filling liquid for inkjet recording devices that is excellent in wettability, cleanability and other properties, exhibits excellent compatibility with ink even when pigment ink is used for printing, and does not cause ejection failure when the ink is refilled, wherein the cleaning and filling liquid for inkjet recording devices contains surfactants including at least a fluorosurfactant and an acetylene glycol-based surfactant having an average addition mole number of ethylene oxide of 0 to 30.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] On the other hand, water-based inks used in inkjet printers contain pigments and water-insoluble polymers to improve pigment dispersibility and the fixation of the resulting printed materials. When the pigments and water-insoluble polymers in such water-based inks solidify, the nozzle holes of the inkjet print head become clogged with the solidified material, causing ejection problems. Therefore, a cleaning solution with high redispersibility is desired to disperse the solidified material of the water-based ink containing pigments and water-insoluble polymers back into the liquid. Furthermore, in order to remove blockages in the nozzle holes of inkjet print heads using water-based ink, the nozzle surface and discharge port of the inkjet print head are wiped with a non-woven cloth soaked in cleaning solution, followed by nozzle purging with water-based ink, and then wiping with a rubber wiper. However, at this time, air bubbles may form inside the nozzle holes, and if these air bubbles remain, it can cause poor discharge of water-based ink. The present invention relates to a cleaning solution for inkjet print heads that exhibits excellent redispersibility and defoaming properties of solidified ink, and can suppress ink ejection problems after cleaning the inkjet print head. [Means for solving the problem]

[0006] The inventors have found that the above problem can be solved by using a cleaning solution that contains a specific surfactant and a water-soluble organic solvent containing a specific glycol ether, and exhibits a specific pH. The present invention relates to the following [1] to [2]. [1] A cleaning solution for inkjet printheads, comprising a surfactant (A) containing an acetylene glycol-based surfactant (a), a water-soluble organic solvent (B) containing diethylene glycol monobutyl ether (b), and water, with a pH of 10.5 or higher at 20°C. [2] A method for cleaning an inkjet print head using the inkjet print head cleaning solution described in [1] above. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an inkjet printhead cleaning solution that exhibits excellent redispersibility and defoaming properties of solidified ink, and can suppress ink ejection problems after cleaning the inkjet printhead. Furthermore, according to the present invention, it is possible to provide an inkjet printhead cleaning method that can suppress ink ejection problems. [Modes for carrying out the invention]

[0008] [Inkjet printhead cleaning solution] The inkjet printhead cleaning solution of the present invention (hereinafter also simply referred to as "cleaning solution") contains a surfactant (A) containing an acetylene glycol-based surfactant (a), a water-soluble organic solvent (B) containing diethylene glycol monobutyl ether (b), and water, and has a pH of 10.5 or higher at 20°C.

[0009] The reason why the present invention's cleaning solution can suppress ink ejection problems when cleaning an inkjet print head is not entirely clear, but it is thought to be as follows. The cleaning solution of the present invention has a pH of 10.5 or higher at 20°C, which gives it excellent ability to redissolve water-insoluble polymers constituting the solidified ink. Furthermore, it is considered to be particularly excellent in its ability to enhance the electrical repulsion of the redissolved water-insoluble polymers and maintain them in a dispersed state within the cleaning solution. Furthermore, since the cleaning solution of the present invention contains an acetylene glycol-based surfactant (a) as the surfactant (A), it can suppress the generation of bubbles and eliminate any bubbles that do occur during the cleaning of the injet head. Moreover, as described later, the acetylene glycol-based surfactant (a) has a characteristic structure, and is therefore considered to have excellent penetration and peeling properties for solidified ink. Furthermore, since the cleaning solution of the present invention contains diethylene glycol monobutyl ether (b) as a water-soluble organic solvent (B), the hydrophobicity of the cleaning solution of the present invention can be improved, and it has a high affinity for water-insoluble polymers constituting the solidified ink, and has the effect of swelling them. For this reason, it is thought that the redispersion of water-insoluble polymers constituting the solidified ink can be promoted. Moreover, because diethylene glycol monobutyl ether (b) has a good balance of hydrophilicity and hydrophobicity, it can better exhibit the function of the surfactant (A), especially the acetylene glycol-based surfactant (a). For this reason, it is thought that the penetration into the solidified ink adhering to the nozzle holes of the inkjet print head can be further improved, and the performance of peeling the solidified ink from the nozzle holes can be further improved. Due to the effects described above, after cleaning an inkjet printhead with the cleaning solution of the present invention, no air bubbles remain in the nozzle holes, and the replacement of the cleaning solution with printing ink when refilling for the next print can be performed smoothly. For this reason, it is believed that the cleaning solution of the present invention can suppress problems such as poor ink ejection that occur after cleaning an inkjet printhead, which is performed to ensure print quality.

[0010] <Surfactant (A)> The cleaning solution of the present invention contains a surfactant (A) from the viewpoint of improving the redispersibility and defoaming properties of solidified ink and suppressing poor ink ejection after cleaning the inkjet print head.

[0011] (Acetylene glycol-based surfactant (a)) In the present invention, acetylene glycol-based surfactant (a) means a nonionic surfactant having one carbon-carbon triple bond in the center of its molecular structure, a hydroxyl group on a carbon atom adjacent to the acetylene group, and optionally a (poly)alkylene glycol group attached to the hydroxyl group, and branched or linear hydrocarbon groups on the carbon atom beyond the carbon atom having the hydroxyl group when viewed from the acetylene group. In the present invention, the cleaning solution contains an acetylene glycol-based surfactant (a) having the characteristic structure described above, and therefore exhibits excellent defoaming properties, as well as excellent penetration into solidified ink and peeling properties from the nozzle holes of the inkjet printhead, thereby suppressing ejection problems after cleaning the inkjet printhead.

[0012] Any acetylene glycol-based surfactant (a) can be used as long as it has the characteristic structure described above. Preferably, the ethylene oxide adducts (EO adducts) are selected from 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyn-2,5-diol, 2,5,8,11-tetramethyl-6-dodecine-5,8-diol, 3,5-dimethyl-1-hexyn-3-ol, and their ethylene oxide adducts (EO adducts). More preferably, the ethylene oxide adducts are selected from 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyn-2,5-diol, and their EO adducts. Even more preferably, the ethylene oxide adduct is selected from 2,4,7,9-tetramethyl-5-decine-4,7-diol. Commercially available products of 2,4,7,9-tetramethyl-5-decine-4,7-diol and its EO adduct include Air Products and Chemicals' Surfinol 104PG-50 (propylene glycol solution of 2,4,7,9-tetramethyl-5-decine-4,7-diol, 50% effective content, HLB=4), Surfinol 440 (EO adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol (average number of EO added moles: 3.5 moles), 100% effective content, HLB=8), and Surfinol 465 (EO adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol (average number of EO added moles: 10 moles), 100% effective content, HLB=13).

[0013] Surfactant (A) may optionally contain other surfactants besides acetylene glycol-based surfactant (a). Other surfactants besides acetylene glycol-based surfactants (a) include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants, among which nonionic surfactants are preferred. Examples of nonionic surfactants include polyalkylene glycol alkyl ethers. Examples of polyalkylene glycols include polyethylene glycol alkyl ethers, and among these, polyethylene glycol mono-2-ethylhexyl ether, polyethylene glycol monooctyl ether, polyethylene glycol monodecyl ether, polyethylene glycol monododecyl ether, and polyethylene glycol monotetradecyl ether are examples of nonionic surfactants.

[0014] In the present invention, the HLB of the acetylene glycol-based surfactant (a) is preferably 14 or less, more preferably 10 or less, even more preferably 6 or less, and even more preferably 5 or less, from the viewpoint of improving the redispersibility and defoaming properties of the solidified ink and suppressing poor ink ejection after cleaning the inkjet print head. Furthermore, when multiple acetylene glycol-based surfactants (a) are used in combination in the present invention, the HLB of the acetylene glycol-based surfactants (a) is expressed as a weighted average value obtained by multiplying the HLB value of each acetylene glycol-based surfactant (a) by the mass ratio of each acetylene glycol-based surfactant (a) and summing them up. That is, in the present invention, the HLB of the acetylene glycol-based surfactant (a) is preferably 14 or less, more preferably 10 or less, even more preferably 6 or less, and even more preferably 5 or less, as a weighted average value. In the present invention, acetylene glycol-based surfactant (a), in particular, having an HLB within the above range, is efficiently adsorbed to the bubbles formed by the ink inside the print head, and therefore the cleaning agent of the present invention is considered to have particularly excellent defoaming properties.

[0015] In the present invention, HLB is a value indicating the affinity of a surfactant for water and oil as the Hydrophile-Lypophile Balance, and can be determined from the following formula by the Griffin method. HLB=20×[(molecular weight of hydrophilic groups contained in the surfactant) / (molecular weight of the surfactant)] Examples of hydrophilic groups contained in surfactants include hydroxyl groups and ethyleneoxy groups. When a commercially available product is used as the acetylene glycol-based surfactant (a), the numerical value described in the product catalog can be used as the HLB value.

[0016] <Water-soluble organic solvent (B)> The cleaning liquid of the present invention contains a water-soluble organic solvent (B) from the viewpoint of improving the redispersibility and defoaming property of solidified ink and suppressing ink ejection failure after cleaning of an inkjet print head. In the present invention, the term "water-soluble organic solvent" refers to an organic solvent whose solubility is 10 mL or more when the organic solvent is dissolved in 100 mL of water at 25°C.

[0017] (Diethylene glycol monobutyl ether (b)) The cleaning liquid of the present invention contains diethylene glycol monobutyl ether (b). Accordingly, the hydrophobicity of the cleaning liquid can be improved, the affinity with water-insoluble polymers and the like contained in solidified ink is enhanced, and the solidified ink can be efficiently swelled and dissolved, thereby improving the redispersibility of the solidified ink. In addition, diethylene glycol monobutyl ether (b) has a good balance between hydrophilicity and hydrophobicity, and can further exert the functions of the surfactant (A), particularly the acetylene glycol-based surfactant (a), thereby improving the permeability to solidified ink adhering to the nozzle holes of an inkjet print head, allowing the solidified ink to be quickly peeled off from the nozzle holes and removed. As a result, the problem of ink ejection failure can be suppressed.

[0018] The water-soluble organic solvent (B) may further optionally contain a water-soluble organic solvent other than diethylene glycol monobutyl ether (b). Examples of the water-soluble organic solvent other than diethylene glycol monobutyl ether (b) include glycol ethers other than diethylene glycol monobutyl ether, monohydric alcohols, diols, polyhydric alcohols having a valence of 3 or higher, and cyclic or chain amide compounds.

[0019] Examples of the glycol ether other than diethylene glycol monobutyl ether (b) include ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol monobutyl ether.

[0020] Examples of the monohydric alcohol include monovalent aliphatic alcohols, for example, methanol, ethanol, propanol and the like. Examples of the diol include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 2-methyl-2,4-pentanediol. Examples of polyhydric alcohols with a valency of 3 or higher include 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, petriol, and glycerin.

[0021] Examples of cyclic or chain-like amide compounds include formamide, N-methylformamide, and N,N-dimethylformamide.

[0022] Among these, the water-soluble organic solvent other than diethylene glycol monobutyl ether (b) is preferably one or more selected from glycol ethers and diols other than diethylene glycol monobutyl ether (b), more preferably one or more selected from diethylene glycol monoisobutyl ether and propylene glycol, and even more preferably propylene glycol, from the viewpoint of improving the redispersibility of the solidified ink and suppressing poor ink ejection after cleaning the inkjet print head.

[0023] <Water> The cleaning solution of the present invention contains water. Water accounts for the largest mass ratio in the cleaning solution of the present invention and dissolves the surfactant (A) and water-soluble organic solvent (B) contained in the cleaning solution of the present invention to form a homogeneous aqueous solution. Deionized water and distilled water are preferred as the water source.

[0024] <Physical properties of the cleaning solution> (pH of the washing solution) The cleaning solution of the present invention has a pH of 10.5 or higher at 20°C. A pH of 10.5 or higher at 20°C allows for the application of an electrostatic repulsive force to the pigments and polymers contained in the solidified ink that has peeled off from the nozzle holes of the inkjet printhead, thereby maintaining the solidified ink in a dispersed state within the cleaning solution. This effectively suppresses ink ejection problems after cleaning the inkjet printhead. The pH of the cleaning solution of the present invention at 20°C is preferably 10.6 or higher, more preferably 10.7 or higher, even more preferably 10.8 or higher, and even more preferably 10.9 or higher. Furthermore, from the viewpoint of suppressing the deterioration of the inkjet print head, the pH of the cleaning solution of the present invention at 20°C is preferably 12.0 or lower, more preferably 11.8 or lower, and even more preferably 11.5 or lower. In the present invention, the pH of the washing solution at 20°C can be measured specifically by the method described in the examples.

[0025] [Basic compounds] The cleaning solution of the present invention preferably further contains a basic compound. By using a basic compound, it is easier to set the pH of the cleaning solution to 10.5 or higher at 20°C, improving the redispersibility and defoaming properties of solidified ink, and making it easier to suppress ink ejection problems after cleaning the inkjet print head. The basic compound is preferably one or more selected from alkali metal hydroxides, alkali metal carbonates, alkaline earth metal hydroxides, and amine compounds, more preferably an alkali metal hydroxide, even more preferably one or more selected from sodium hydroxide and potassium hydroxide, and even more preferably sodium hydroxide.

[0026] (Viscosity of the cleaning solution) The viscosity of the cleaning solution at 25°C is preferably 0.9 mPa·s or higher, more preferably 1 mPa·s or higher, even more preferably 1.05 mPa·s or higher, and preferably 5 mPa·s or lower, more preferably 4 mPa·s or lower, and even more preferably 3 mPa·s or lower, from the viewpoint of improving the redispersibility and defoaming properties of the solidified ink.

[0027] <Other ingredients> In addition to the components mentioned above, the cleaning solution of the present invention may contain various additives such as pH adjusters, preservatives, fungicides, and rust inhibitors. Preferably, the cleaning solution of the present invention does not contain colorants such as pigments or dyes, or polymers.

[0028] [Method for manufacturing cleaning solution] The cleaning solution of the present invention can be obtained by combining a surfactant (A), a water-soluble organic solvent (B), and water, and optionally adding various additives such as basic compounds, pH adjusters, preservatives, fungicides, and rust inhibitors. Specifically, the cleaning solution of the present invention can be obtained by mixing a surfactant (A), a water-soluble organic solvent (B), and water, and, if necessary, mixing in various additives such as basic compounds, pH adjusters, preservatives, fungicides, and rust inhibitors, and stirring the mixture. The content of each component in the cleaning solution of the present invention is as follows:

[0029] (Content of surfactant (A)) The content of surfactant (A) in the cleaning solution of the present invention is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, even more preferably 0.05% by mass or more, even more preferably 0.08% by mass or more, and even more preferably 0.09% by mass or more, from the viewpoint of improving defoaming properties and suppressing ink ejection problems after cleaning the inkjet print head, and preferably 0.5% by mass or less, more preferably 0.4% by mass or less, even more preferably 0.3% by mass or less, and even more preferably 0.2% by mass or less, from the viewpoint of improving the redispersibility of solidified ink and suppressing ink ejection problems after cleaning the inkjet print head.

[0030] (Content of acetylene glycol-based surfactant (a)) The content of the acetylene glycol-based surfactant (a) in the cleaning solution of the present invention is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, even more preferably 0.05% by mass or more, even more preferably 0.08% by mass or more, and even more preferably 0.09% by mass or more, from the viewpoint of improving the redispersibility of solidified ink and suppressing poor ink ejection after cleaning the inkjet print head, and preferably 0.5% by mass or less, more preferably 0.4% by mass or less, even more preferably 0.3% by mass or less, and even more preferably 0.2% by mass or less, from the viewpoint of improving defoaming properties and suppressing poor ink ejection after cleaning the inkjet print head.

[0031] (Mass ratio of acetylene glycol-based surfactant (a) in surfactant (A)) In the cleaning solution of the present invention, the mass ratio of acetylene glycol-based surfactant (a) in surfactant (A) [mass of acetylene glycol-based surfactant (a) in the cleaning solution / mass of surfactant (A) in the cleaning solution] is preferably 0.7 or higher, more preferably 0.8 or higher, even more preferably 0.9 or higher, even more preferably 0.95 or higher, and even more preferably 1, from the viewpoint of improving the redispersibility and defoaming properties of solidified ink and suppressing poor ink ejection after cleaning the inkjet print head.

[0032] (Content of water-soluble organic solvent (B)) The content of the water-soluble organic solvent (B) in the cleaning solution of the present invention is preferably 5% by mass or more, more preferably 6% by mass or more, even more preferably 8% by mass or more, and even more preferably 10% by mass or more, from the viewpoint of improving the redispersibility of the solidified ink and suppressing poor ink ejection after cleaning the inkjet print head, and similarly, preferably 25% by mass or less, more preferably 20% by mass or less, even more preferably 18% by mass or less, and even more preferably 16% by mass or less.

[0033] The content of diethylene glycol monobutyl ether (b) in the cleaning solution of the present invention is preferably 5% by mass or more, more preferably 6% by mass or more, even more preferably 8% by mass or more, and even more preferably 10% by mass or more, from the viewpoint of improving the redispersibility of the solidified ink and suppressing poor ink ejection after cleaning the inkjet print head, and similarly, preferably 25% by mass or less, more preferably 20% by mass or less, even more preferably 18% by mass or less, and even more preferably 16% by mass or less.

[0034] (Mass ratio of diethylene glycol monobutyl ether (b) in water-soluble organic solvent (B)) In the cleaning solution of the present invention, the mass ratio of diethylene glycol monobutyl ether (b) in the water-soluble organic solvent (B) [mass of diethylene glycol monobutyl ether (b) in the cleaning solution / mass of water-soluble organic solvent (B) in the cleaning solution] is preferably 0.5 or higher, more preferably 0.7 or higher, even more preferably 0.8 or higher, even more preferably 0.9 or higher, and even more preferably 1, from the viewpoint of improving the redispersibility of solidified ink and suppressing poor ink ejection after cleaning the inkjet print head.

[0035] (Mass ratio of acetylene glycol-based surfactant (a) to diethylene glycol monobutyl ether (b)) In the cleaning solution of the present invention, the mass ratio of acetylene glycol-based surfactant (a) to diethylene glycol monobutyl ether (b) in the cleaning solution [mass of acetylene glycol-based surfactant (a) in the cleaning solution / mass of diethylene glycol monobutyl ether (b) in the cleaning solution] is preferably 0.001 or more, more preferably 0.005 or more, even more preferably 0.008 or more, from the viewpoint of improving the redispersibility and defoaming properties of solidified ink and suppressing poor ink ejection after cleaning the inkjet print head, and similarly, preferably 0.03 or less, more preferably 0.025 or less, and even more preferably 0.02 or less.

[0036] (Water content) In the cleaning solution of the present invention, the water content in the cleaning solution is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and even more preferably 85% by mass or more, from the viewpoint of improving the redispersibility and defoaming properties of the solidified ink and suppressing poor ink ejection after cleaning the inkjet print head, and preferably 94% by mass or less, and more preferably 90% by mass or less, from the viewpoint of improving the redispersibility of the solidified ink.

[0037] The cleaning solution of the present invention is preferable for use as a cleaning solution for inkjet print heads because it has excellent properties in removing deposits from nozzle holes, thus resolving nozzle blockage of inkjet print heads, and also has excellent defoaming properties that prevent the formation of air bubbles inside the nozzle holes, or if bubbles do form, prevent them from remaining, thus highly effective in suppressing problems such as poor ejection of inkjet print heads.

[0038] There are no restrictions on the inkjet printheads to which the cleaning solution of the present invention is supplied, and it can be applied to both thermal and piezo inkjet printheads. There are no restrictions on the ink used by the inkjet printhead; it can be water-based, solvent-based, or curable ink. However, it is preferable to apply it to an inkjet printhead that uses water-based ink. Furthermore, there are no restrictions on the colorants contained in the ink, and it can be applied to inks that use both dyes and pigments as colorants, but it is preferable to apply it to inkjet printheads that use inks that use pigments as colorants. In addition, there are no restrictions on the polymers contained in the ink, and it can be applied to inks that contain anionic polymers, cationic polymers, nonionic polymers, or amphoteric polymers, but it is preferable to apply it to inkjet printheads that use inks that contain anionic polymers.

[0039] [How to clean an inkjet printhead] The present invention relates to a method for cleaning an inkjet printhead, which involves using the cleaning solution described above. Furthermore, the present invention relates to a method for cleaning an inkjet printhead, which involves bringing the cleaning solution into contact with the inkjet printhead. Examples of such contact methods include coating, spraying, and immersion. Examples of the cleaning methods include: a method in which the cleaning solution is soaked into a wiping material such as a nonwoven fabric and excess ink adhering to the nozzle surface and discharge port; a method in which, when using different types of ink, the ink pathways inside the printer are cleaned by repeatedly supplying the cleaning solution from a storage container containing the cleaning solution into the ink pathways and then discharging it using the printer's supply and exchange mechanisms before and after changing inks; and a method in which, when the recording head is not used for a long period of time, the ink is removed from the recording head, the cleaning solution is filled in, and the head is capped for storage. Among these, from the viewpoint of providing a cleaning method in which the cleaning solution components are less likely to remain on the material to be cleaned, the method in which the cleaning solution is soaked into a wiping material and excess ink adhering to the nozzle surface and discharge port is preferred. The wiping material is not particularly limited as long as it is liquid absorbent, and examples include woven fabrics, knitted fabrics, nonwoven fabrics, sponges, pulp, etc.

[0040] Furthermore, the inkjet printhead cleaning method of the present invention preferably involves purging the ink to remove air from inside the inkjet printhead, then wiping the nozzle surface and discharge port of the inkjet printhead with a rubber wiper, and then wiping the nozzle surface and discharge port of the inkjet printhead with a wiping member soaked in cleaning solution. In other words, the inkjet printhead cleaning method of the present invention preferably comprises the following steps in order. Step 1: Ink purging and air removal from inside the inkjet print head. Step 2: Wipe the nozzle surface of the inkjet print head with a rubber wiper. Step 3: The process of wiping the nozzle surface of the inkjet print head with a wiping member soaked in the cleaning solution of the present invention described above. The method for cleaning an inkjet printhead according to the present invention, which includes the above steps 1 to 3 in order, and particularly includes step 3, can efficiently remove solidified ink deposits adhering to the inkjet printhead. Furthermore, it is preferable because it can suppress the generation of air bubbles in nozzles and other parts of the inkjet printhead, can eliminate any air bubbles that have formed, and can suppress ejection failure after cleaning.

Examples

[0041] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited in any way by these examples. Each property value was measured and evaluated by the following methods.

[0042] Example 1 (Preparation of cleaning liquid A1) Into a glass container, 0.20 parts of acetylene glycol-based surfactant Surfynol 104PG50 (50% active ingredient in propylene glycol solution) as surfactant (A), 10.00 parts of diethylene glycol monobutyl ether (b) as water-soluble organic solvent (B), 0.20 parts of 1N sodium hydroxide, and 89.60 parts of ion-exchanged water were added, followed by stirring with a magnetic stirrer for 30 minutes to obtain cleaning liquid A1. The pH of the obtained cleaning liquid A1 was measured by the following procedure. The pH of cleaning liquid A1 was 11.0. <Method for measuring pH> 15 g of the obtained cleaning liquid A1 was added into a Screw Tube No. 5 (manufactured by Marumu Co., Ltd.) and the tube was capped. After immersing the tube in a 20°C water bath for 1 hour, a pH meter (LAQUA MODEL 6367, manufactured by Horiba, Ltd.) was immersed in the cleaning liquid A1 in the screw tube, and the pH value was measured 30 seconds after the start of immersion.

[0043] Examples 2 to 7. Reference Examples 8-9, Example 10, Reference Examples 11-12, Example 13 and Comparative Examples 1 to 4 (Preparation of cleaning liquids A2 to A13 and C1 to C4) Cleaning liquids A2 to A13 and C1 to C4 were obtained in the same manner as in Example 1, except that the formulation composition of each cleaning liquid was changed as shown in Table 1. In addition, in the same procedure as in Example 1 The pH of each washing solution was measured.

[0044] The details of surfactant (A) in Table 1 are as follows: (Surfactant (A)) [Acetylene glycol-based surfactant (a)] • Surfinol 104PG-50: Manufactured by Air Products and Chemicals, a propylene glycol solution of 2,4,7,9-tetramethyl-5-decine-4,7-diol, with an effective content of 50% and HLB=4. • Surfinol 440: Manufactured by Air Products and Chemicals, an EO adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol (average number of EO added moles: 3.5 moles), 100% effective content, HLB=8 • Surfinol 465: Manufactured by Air Products and Chemicals, an EO adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol (average number of EO added moles: 10 moles), 100% effective content, HLB=13 [Other surfactants] • Polyoxyethylene lauryl ether: (Manufactured by Kao Corporation, product name: Emulgen 120, HLB = 15.3)

[0045] Manufacturing Example 1 (Production of an aqueous dispersion of white pigment-containing polymer particles) In a 2L plastic container, 6 parts of polyacrylic acid (PAA; manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., weight-average molecular weight 5000), 4.2 parts of 5N-NaOH aqueous solution, and 4.8 parts of deionized water were mixed and dissolved as a polymer dispersant (polymer neutralization degree 50 mol%). Then, 300 parts of titanium dioxide: CI Pigment White 6 (PW6, manufactured by Ishihara Sangyo Co., Ltd., product name: CR-80, rutile type, Al-Si treated, average particle size: 0.25 μm (catalog value)) and 255 parts of deionized water were added, and 1000 parts of zirconia beads were added. The mixture was dispersed for 8 hours using a tabletop pot mill stand (manufactured by AS ONE Corporation). Zirconia beads were removed using a metal mesh, and the solid content concentration was adjusted with deionized water. A aqueous dispersion of white pigment-containing polymer particles with an average particle size of 328 nm was obtained by cumulant analysis using dynamic light scattering (solid content concentration: 53.2%, pigment:polymer = 98:2 (mass ratio), pH: 7.3).

[0046] Manufacturing Example 2 (Preparation of an aqueous dispersion of polymer particles without pigments) In a reaction vessel equipped with a dropping funnel, 0.5 parts methacrylic acid, 8.5 parts methyl methacrylate, 11 parts 2-ethylhexyl acrylate, 11.1 parts sodium polyoxyethylene alkyl ether sulfate (manufactured by Kao Corporation, Latemul E-118B, emulsifier), 0.2 parts potassium persulfate (polymerization initiator), and 382.8 parts deionized water were added and mixed, and the mixture was purged with nitrogen gas to obtain the initial monomer solution. In addition, as a monomer solution for dropwise addition, 9.5 parts methacrylic acid, 11.5 parts methyl methacrylate, 209 parts 2-ethylhexyl acrylate, 35.1 parts sodium polyoxyethylene alkyl ether sulfate (manufactured by Kao Corporation, Latemul E-118B, emulsifier), 0.6 parts potassium persulfate (polymerization initiator), and 183 parts deionized water were added and mixed, and the mixture was placed in a dropping funnel and purged with nitrogen gas. Under a nitrogen atmosphere, the initial monomer solution in the reaction vessel was stirred while the temperature was raised from room temperature to 80°C over 30 minutes. While maintaining the temperature at 80°C, the monomer from the dropping funnel was gradually added to the reaction vessel over 3 hours. After the addition was complete, the mixture was stirred for 1 hour while maintaining the temperature in the reaction vessel. The mixture was then filtered through a 200-mesh filter to obtain an aqueous dispersion of polymer particles (solid content concentration 44.1%) that did not contain pigment.

[0047] Manufacturing Example 3 (Preparation of Water-Based Ink) In a glass container, 19.2 parts of the aqueous dispersion of white pigment-containing polymer particles obtained in Production Example 1, 9.1 parts of the aqueous dispersion of pigment-free polymer particles obtained in Production Example 2 as a fixing resin, 37.8 parts of deionized water, and 0.4 parts of 1N sodium hydroxide were added, and the mixture was stirred with a magnetic stirrer for 10 minutes. While stirring the mixture, 30 parts of propylene glycol, 1 part of diethylene glycol monoisobutyl ether, 0.5 parts of silicone-based surfactant KF-6011 (manufactured by Shin-Etsu Chemical Co., Ltd.), and 2 parts of acetylene-based glycol surfactant Surfinol 104PG50 (manufactured by Nisshin Chemical Co., Ltd.) were added, and the mixture was stirred for 1 hour. After that, the mixture was filtered using a 5 μm disposable membrane filter (manufactured by Sartorius, trade name: Minisart) to obtain a white aqueous ink.

[0048] <Evaluation of cleaning solution> (1) Redispersibility of solidified ink Using a micropipette, 20 μL of the aqueous ink prepared in Manufacturing Example 3 above was dropped into the center of the bottom of a screw-cap tube No. 5 (manufactured by Maruemu Co., Ltd.). The tube was left uncovered at 40°C and 25% RH for 2 hours to allow the ink to evaporate and dry. 10 mL of the cleaning solution from each example and comparative example was added to the solidified ink remaining at the bottom of the screw tube, and the mixture was stirred for 1 minute at a vibration frequency of 150 rpm using a stirrer (EYELA MULTI SHAKER MMS, model number MMS-210). The state of the solidified ink was visually observed, and the redispersibility of the solidified ink was evaluated according to the following evaluation criteria. The better the dispersion of the solidified ink and the less residue there is, the better the redispersibility of the solidified ink by the cleaning solution. The evaluation results are shown in Table 1. (Evaluation Criteria) A: The solidified ink material was uniformly redispersed, and there was no residue. B: The solidified ink was redispersed, but some residue remained. C: The solidified ink did not redisperse, and the residue remained in its original form.

[0049] (2) Evaluation of defoaming properties 100g of the washing solution from each example and comparative example (liquid level: 37mm from the bottom of the container) was placed in an iBoy PP wide-mouth bottle 250mL (manufactured by AS ONE Corporation), and the lid was closed. This was stirred using a stirrer (manufactured by Seiwa Giken Co., Ltd., rocking shaker) at a vibration frequency of 600rpm for 3 minutes to create foam. After standing for 1 minute, the defoaming performance was evaluated by measuring the height from the bottom of the container to the top of the foam. A lower height from the bottom of the container to the top of the foam indicates better defoaming performance. The evaluation results are shown in Table 1. (Evaluation Criteria) 5: The height to the top of the foam is less than 40 mm. 4: The height to the top of the foam is 40mm or more but less than 45mm. 3: The height to the top of the foam is 45mm or more but less than 50mm. 2: The height to the top of the foam is 50mm or more but less than 55mm. 1: The height to the top of the foam is 55 mm or more.

[0050] (3) Discharge performance after cleaning (number of nozzle chips) Following the procedure outlined in the inkjet printing method below, a nozzle check pattern was printed to confirm that all nozzles were ejecting correctly. After this, the inkjet printhead was left in the atmosphere for 30 minutes. Subsequently, the purge wipe procedure described below was performed, and a nozzle check pattern was printed again. The number of missing nozzles (nozzles not ejecting properly) in the nozzle check pattern was used to evaluate the ejection performance after cleaning. A lower number of nozzle chips indicates a superior effect in suppressing dispensing problems with the cleaning solution.

[0051] <Inkjet Printing Method> In an environment with a temperature of 25±1℃ and a relative humidity of 30±5%, a printing evaluation device (manufactured by Trytech Co., Ltd.) equipped with an inkjet printhead (Kyocera Corporation, "KJ4B-HD06MHG-STDV", piezo type, total number of nozzles: 2656) was filled with the water-based ink obtained in Manufacturing Example 3. The head voltage was set to 26V, the frequency to 26kHz, the appropriate amount of discharged liquid to 3pL, the head temperature to 32℃, the resolution to 1200dpi, the number of pre-discharge flushing cycles to 200, and the negative pressure to -4.0kPa. The recording medium (black drawing paper) was fixed to the transport table under reduced pressure, with the longitudinal direction of the recording medium and the transport direction being the same. A print command was transferred to the aforementioned print evaluation device, and a nozzle check pattern was printed. <Purge wipe operation> The following purge-wipe procedure was performed immediately before printing. 5 mL of ink was purged from the print head, and any remaining ink on the print head face was wiped off with a rubber blade wiper. Next, the inkjet print head face was wiped with a polyester fiber cloth (Azpure Wiper, manufactured by AS ONE Corporation) impregnated with the cleaning solutions of the example and comparative example.

[0052] [Table 1]

[0053] Table 1 shows that Examples 1- 7、10、 Compared to Comparative Examples 1-4, sample 13 exhibits superior redispersibility and defoaming properties of the solidified ink, and can suppress ink ejection problems after cleaning the inkjet printhead. Comparative Examples 1 and 2 use a water-soluble organic solvent (B) with diethylene glycol monobutyl ether. (b) is not included, resulting in poor redispersibility of the solidified ink and poor discharge performance after washing. Comparative Example 3 had a pH of less than 10.5 at 20°C, resulting in poor redispersibility of the solidified ink and poor discharge performance after washing. Comparative Example 4 contains polyoxyethylene lauryl ether with an HLB of 15.3 instead of the acetylene glycol-based surfactant (a), and therefore exhibits inferior defoaming properties.

Claims

1. It contains a surfactant (A) containing an acetylene glycol-based surfactant (a), a water-soluble organic solvent (B) containing diethylene glycol monobutyl ether (b), and water, and has a pH of 10.5 or higher at 20°C. The HLB of the acetylene glycol-based surfactant (a) is 6 or less. A cleaning solution for inkjet printheads, wherein the mass ratio of diethylene glycol monobutyl ether (b) in a water-soluble organic solvent (B) is 0.8 or higher.

2. The cleaning solution for an inkjet printhead according to claim 1, wherein the mass ratio of acetylene glycol-based surfactant (a) in surfactant (A) is 0.7 or more.

3. The inkjet printhead cleaning solution according to claim 1, wherein the content of acetylene glycol-based surfactant (a) in the inkjet printhead cleaning solution is 0.01% by mass or more and 0.5% by mass or less.

4. The inkjet printhead cleaning solution according to claim 1, wherein the content of diethylene glycol monobutyl ether (b) in the inkjet printhead cleaning solution is 5% by mass or more and 20% by mass or less.

5. A method for cleaning an inkjet print head using the inkjet print head cleaning solution described in any one of claims 1 to 4.

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