Cleaning solutions and ink sets for inkjet recording devices

Abstract

The present invention provides a cleaning solution for cleaning the ink ejection surface of a recording head of an inkjet recording device, and an ink set containing the same, which can maintain high cleaning performance over a long period of time while suppressing adverse effects on the ink ejection surface of the recording head. [Solution] The cleaning solution is for cleaning the ink ejection surface of the recording head of an inkjet recording device, and comprises water, a water-soluble organic solvent, an amphoteric surfactant having a betaine structure, a silicone-based surfactant, a nonionic surfactant excluding the silicone-based surfactant, and an inorganic salt having a pH buffering effect. The viscosity at 25°C is 2.5 mPa·s or less. The static surface tension is 25 mN / m or less. The pH after being sealed and left standing at room temperature for one year is 8.0 to 9.5.

Description

Technical Field

[0001] The present invention relates to a cleaning liquid for an inkjet recording apparatus and an ink set.

Background Art

[0002] An inkjet recording apparatus forms an image on a recording medium by discharging ink for inkjet recording from the ejection surface of a recording head. In order to remove dirt caused by ink remaining on the ejection surface, a cleaning method is known in which a cleaning liquid is supplied to the ejection surface and the ejection surface is wiped with a wiping blade (for example, Patent Document 1).

[0003] On the other hand, ink used in an inkjet recording apparatus may contain resin components (dispersion resin and binder resin) from the viewpoints of ensuring the dispersion stability of pigments and firmly fixing pigments on a recording medium. When image formation is performed using ink containing a resin component, an ink dry matter containing the resin component may adhere to the ink ejection surface of the recording head. Since such an ink dry matter adheres strongly to the ink ejection surface of the recording head, it may be difficult to remove. Therefore, a cleaning method having excellent cleaning performance capable of effectively removing the above-described resin component has been studied (for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] One example of a cleaning method with excellent cleaning performance is the use of a cleaning solution containing a highly hydrophobic organic solvent. However, with this method, the resin components constituting the recording head may gradually denature due to the organic solvent, potentially leading to a long-term decrease in the recording head's ejection performance. Furthermore, if an aqueous cleaning solution is used to prevent adverse effects on the resin components constituting the recording head, the cleaning performance may decrease over time.

[0006] In view of the above circumstances, the object of the present invention is to provide a cleaning solution for cleaning the ink ejection surface of a recording head of an inkjet recording device, and an ink set containing the same, which can maintain high cleaning performance over a long period of time while suppressing adverse effects on the ink ejection surface of the recording head. [Means for solving the problem]

[0007] To achieve the above objective, a cleaning solution according to one embodiment of the present invention is a cleaning solution for cleaning the ink ejection surface of a recording head of an inkjet recording device, The solution comprises water, a water-soluble organic solvent, an amphoteric surfactant having a betaine structure, a silicone-based surfactant, a nonionic surfactant excluding the silicone-based surfactant, and an inorganic salt having pH buffering properties. The viscosity at 25°C is 2.5 mPa·s or less. The static surface tension is 25 mN / m or less. After being sealed and left standing at room temperature for one year, the pH is between 8.0 and 9.5.

[0008] Another embodiment of the present invention is an ink set for an inkjet recording device, The cleaning solution and the ink containing a resin component are included. The dry viscosity of the aforementioned ink at 25°C after drying to 50% by mass is 500 mPa·s or higher. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a cleaning solution for cleaning the ink ejection surface of a recording head of an inkjet recording device, and an ink set containing the same, which can maintain high cleaning performance over a long period of time while suppressing adverse effects on the ink ejection surface of the recording head. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows the cleaning solution supply process of a cleaning method according to one embodiment of the present invention. [Figure 2] This diagram shows the wiping process of the above cleaning method. [Figure 3] This diagram shows the wiping process of the above cleaning method. [Figure 4] This diagram shows the wiping process of the above cleaning method. [Figure 5] This diagram shows the wiping process of the above cleaning method. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below. In the following description, the expression "content of B in A" refers to the percentage of the mass of B when the mass of A is taken as 100% by mass. Furthermore, each component described herein may be used individually or in combination of two or more.

[0012] [Cleaning solution] A cleaning solution according to one embodiment of the present invention is a cleaning solution for cleaning the ink ejection surface of a recording head of an inkjet recording device. More specifically, the cleaning solution is supplied to the ink ejection surface and used in a cleaning process in which the ink ejection surface is wiped with a wipe blade. Furthermore, it is more preferable that the cleaning solution is used in a process in which the surface is wiped multiple times (preferably twice) with the wipe blade.

[0013] The cleaning liquid according to this embodiment contains water, a water-soluble organic solvent, an amphoteric surfactant having a betaine structure, a silicone-based surfactant, a nonionic surfactant excluding the silicone-based surfactant, and an inorganic salt having a pH buffering action, has a viscosity of 2.0 mPa·s or less at 25°C, a static surface tension of 25 mN / m or less, and a pH of 8.0 or more and 9.5 or less after being sealed and left standing at room temperature for one year.

[0014] Since the cleaning liquid contains water and a water-soluble organic solvent, it can be an aqueous cleaning liquid with a low content of a hydrophobic organic solvent or without a hydrophobic organic solvent. Therefore, adverse effects such as deformation can be suppressed with respect to the resin member provided on the ink ejection surface of the inkjet recording apparatus.

[0015] In addition, the cleaning liquid according to this embodiment contains at least three types of surfactants, namely an amphoteric surfactant having a betaine structure, a silicone-based surfactant, and a nonionic surfactant excluding the silicone-based surfactant, so that the viscosity and surface tension can be reduced. As a result, on the ink ejection surface, the cleaning liquid easily penetrates into the ink dry matter to which the ejected ink has adhered, and the ink dry matter easily disperses in the cleaning liquid, promoting the removal of the ink dry matter.

[0016] On the other hand, the cleaning liquid for an inkjet recording apparatus is filled in a tank or the like and supplied little by little each time the ink ejection surface is cleaned, and may be used over a long period of one year or more. Conventionally, such a cleaning liquid used over a long period has been found to exhibit a phenomenon in which the cleaning performance gradually deteriorates. Furthermore, when the number of wiping operations is increased according to the deterioration of the cleaning performance, the water-repellent coating on the ink ejection surface of the recording head may be worn out in the long term due to repeated wiping, which may have an adverse effect on the ink ejection surface.

[0017] In contrast, the cleaning solution of this embodiment contains water, a water-soluble organic solvent, a surfactant, and an inorganic salt having a pH buffering effect, and is prepared so that the pH is between 8.0 and 9.5 after being sealed and left to stand at room temperature for one year. This suppresses the decrease in pH caused by the dissolution of carbon dioxide and other substances from the air into the water, and as a result, it is possible to suppress the decrease in cleaning ability. Therefore, the cleaning solution of this embodiment can have high cleaning performance and maintain it over a long period of time. The details of the cleaning solution will be described below.

[0018] (water) The water content in the cleaning solution of this embodiment is set appropriately according to the content of other components, preferably 40.0% by mass or more and 90.0% by mass or less, and more preferably 60.0% by mass or more and 80.0% by mass or less.

[0019] (Water-soluble organic solvent) The cleaning solution of this embodiment contains one or more water-soluble organic solvents from the viewpoint of imparting viscosity and surface tension, as described later. Examples of water-soluble organic solvents include polyhydric alcohols, glycol ethers, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycols, and dimethyl sulfoxides. In this specification, a water-soluble organic solvent refers to an organic solvent whose solubility in water at 25°C is 1.0% by mass or more.

[0020] Examples of polyhydric alcohols include glycol compounds and glycerin. Examples of glycol compounds include ethylene glycol, 1,3-propanediol, propylene glycol, 1,2-pentanediol, 1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol, and polyethylene glycol.

[0021] Examples of glycol ethers include diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, and propylene glycol monomethyl ether.

[0022] Examples of lactam compounds include 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0023] Examples of nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0024] Examples of acetate compounds include diethylene glycol monoethyl ether acetate.

[0025] The lower limit of the content of water-soluble organic solvents in the cleaning solution is preferably 5.0% by mass or more, and more preferably 10.0% by mass or more, from the viewpoint of imparting viscosity and surface tension as described later. The upper limit of the content of the water-soluble organic solvent is preferably 40.0% by mass or less, and more preferably 35.0% by mass or less, in consideration of the balance with other raw materials. If the cleaning solution contains multiple types of water-soluble organic solvents, the content of the above water-soluble organic solvents shall be the sum of the content of the multiple water-soluble organic solvents.

[0026] On the other hand, from the viewpoint of suppressing adverse effects on the components of the inkjet recording device, the content of hydrophobic organic solvent in the cleaning solution is preferably 1.0% by mass or less, and more preferably 0.0% by mass, meaning the cleaning solution does not contain any hydrophobic organic solvent. In this specification, a hydrophobic organic solvent refers to an organic solvent whose solubility in water at 25°C is less than 1.0% by mass.

[0027] (An amphoteric surfactant with a betaine structure) Amphoteric surfactants having a betaine structure are excellent at adhering to the surface of dried ink adhering to the ink ejection surface, releasing dirt from the object to be cleaned, and dispersing the released dirt into the cleaning solution. Betaine refers to an intramolecular salt having both a cationic structure (e.g., a quaternary ammonium ion structure) and an anionic structure (e.g., an anionic structure of an acid such as a carboxylic acid) in a single molecule. As an amphoteric surfactant having a betaine structure, an amphoteric surfactant having an amidealkylbetaine structure is preferred. As an amphoteric surfactant having an amidealkylbetaine structure, a compound represented by the following general formula (1) is preferred. Amphoteric surfactants having an amidealkylbetaine structure readily ionize in an alkaline environment and tend to exhibit even better lubrication. Therefore, by having a cleaning solution pH of 8.0 to 10.0, wear of the water-repellent film on the recording section of the inkjet recording device can be suppressed even more effectively.

[0028] [ka]

[0029] In general formula (1), R represents a monovalent chain hydrocarbon group having 6 to 20 carbon atoms. n represents an integer between 1 and 5.

[0030] R preferably represents a monovalent linear hydrocarbon group having 10 to 18 carbon atoms. Examples of monovalent linear hydrocarbon groups represented by R include linear alkyl groups and linear alkenyl groups. n preferably represents 3.

[0031] Examples of amphoteric surfactants having an amide alkyl betaine structure include fatty acid amidopropyl betaine surfactants. Examples of fatty acid amidopropyl betaine surfactants include coconut oil fatty acid amidopropyl betaine, lauric acid amidopropyl betaine, palm kernel fatty acid amidopropyl betaine, isostearic acid amidopropyl betaine, and linolenic acid amidopropyl. Preferred amphoteric surfactants having an amide alkyl betaine structure include coconut oil fatty acid amidopropyl betaine, lauric acid amidopropyl betaine, and palm kernel fatty acid amidopropyl betaine.

[0032] From the viewpoint of imparting excellent cleaning performance to the cleaning solution, the content of amphoteric surfactant having a betaine structure in the cleaning solution is preferably 0.01% by mass or more and 2.0% by mass or less, and more preferably 0.05% by mass or more and 1.0% by mass or less.

[0033] (Silicone-based surfactant) Silicone-based surfactants reduce the surface tension of the cleaning solution, making it easier for the cleaning solution to penetrate the dirt. Silicone-based surfactants refer to surfactants that have siloxane bonds. Among silicone-based surfactants, polyether-modified silicone-based surfactants are preferred, and polyether-modified polydimethylsiloxane is more preferred.

[0034] In the cleaning solution, the content of the silicone-based surfactant is preferably 0.01% by mass or more and 2.0% by mass or less, and more preferably 0.05% by mass or more and 1.0% by mass or less, from the viewpoint of imparting appropriate surface tension to the cleaning solution.

[0035] (Nonionic surfactant) The nonionic surfactant of this embodiment is one or more nonionic surfactants other than the silicone-based surfactants described above. Any nonionic surfactant usable in the art can be used, such as polyoxyethylene dodecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene sorbitan monooleate ether, monodecanoyl sucrose, and ethylene oxide adducts of acetylene glycol. From the viewpoint of effectively reducing static surface tension and improving penetration into the ink-dried material, the nonionic surfactant of this embodiment is preferably an acetylene-based surfactant such as an ethylene oxide adduct of acetylene glycol.

[0036] (Acetylene-based surfactant) In this specification, acetylene-based surfactants mean surfactants having an acetylene bond (a triple bond between carbon atoms). It is preferable that the acetylene-based surfactant is a surfactant having a site represented by formula (2). In formula (2), R1 represents a group containing a hydroxyl group, and * represents a bond.

[0037] [ka]

[0038] The bond represented by * in formula (2) is bonded to an atom (for example, a hydrogen atom or a carbon atom) that makes up the acetylene-based surfactant.

[0039] Groups containing a hydroxyl group represented by R1 in formula (2) include, for example, a hydroxyl group and a group to which ethylene oxide is added. The group to which ethylene oxide is added is preferably the group represented by formula (3). In formula (3), m represents the number of moles of ethylene oxide added. m is, for example, an integer of 1 or more. In formula (3), * represents a bond, and this bond is attached to the carbon atom to which R1 in formula (2) is attached.

[0040] [ka]

[0041] Examples of acetylene-based surfactants include acetylene alcohol, acetylene glycol, and ethylene oxide adducts of acetylene glycol. Acetylene alcohol preferably has a moiety represented by formula (2A). Acetylene glycol preferably has a moiety represented by formula (2B). The ethylene oxide adduct of acetylene glycol is preferably a compound represented by formula (2C).

[0042] [ka]

[0043] [ka]

[0044] [ka]

[0045] In formulas (2A) and (2B), * represents a bond, which is attached to a carbon atom constituting the acetylene surfactant. In formula (2C), R2 and R3 represent the ethylene oxide-attached group described earlier.

[0046] The HLB value of the acetylene-based surfactant is preferably 3 to 20, and more preferably 8 to 18. Alternatively, the HLB value of the acetylene-based surfactant may be 8 to 10, 12 to 14, or 16 to 18. In this specification, the HLB value is calculated using the Griffin method from the formula "HLB value = 20 × (sum of formula weights of hydrophilic parts) / molecular weight".

[0047] The content of the acetylene-based surfactant in the cleaning solution is preferably 0.3% by mass or more and 1.5% by mass or less, and more preferably 0.5% by mass or more and 1.0% by mass or less. When the content of the acetylene-based surfactant is 0.3% by mass or more relative to the mass of the cleaning solution, a sufficient effect of reducing static surface tension can be obtained. On the other hand, when the content of the acetylene-based surfactant is 1.5% by mass or less relative to the mass of the cleaning solution, the acetylene-based surfactant, water and water-soluble organic solvent are sufficiently mixed without phase separation.

[0048] In the cleaning solution, the total content of amphoteric surfactants having a betaine structure, silicone-based surfactants, and nonionic surfactants is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.5% by mass or more and 3.0% by mass or less.

[0049] Furthermore, in the cleaning solution, it is preferable that the ratio of the total amount of nonionic surfactant and silicone-based surfactant to the amount of amphoteric surfactant having a betaine structure is 10 or less. This makes it possible to prepare a cleaning solution with sufficiently low viscosity and surface tension and high penetration into the ink-dried material. Moreover, from the viewpoint of exhibiting the above effects more stably, the above ratio is more preferably between 5 and 10. The above ratio is expressed by the formula {(amount of nonionic surfactant) + (amount of silicone-based surfactant)} / (amount of amphoteric surfactant having a betaine structure).

[0050] (Inorganic salts) The inorganic salt in this embodiment has a pH buffering effect. In this specification, an inorganic salt having a pH buffering effect means a salt consisting of either a weak acid and its salt, or a weak base and its salt. From the viewpoint of improving cleaning performance, the inorganic salt in this embodiment is preferably an inorganic salt with a pH buffering range of pH 8.0 to 10.0. Specific examples include sodium borate, sodium bicarbonate, sodium carbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium salts, and the like.

[0051] The lower limit of the inorganic salt content in the cleaning solution is preferably 0.01% by mass or more, and more preferably 0.05% by mass or more, from the viewpoint of effectively obtaining a pH buffering effect. The upper limit of the inorganic salt content in the cleaning solution is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less, from the viewpoint of ensuring cleaning performance while considering the balance with other components.

[0052] (viscosity) In this embodiment, the viscosity of the cleaning solution at 25°C is 2.5 mPa·s or less. With a cleaning solution of this viscosity, when the cleaning solution is wiped away by a wipe blade or the like, it is more likely to remain on a wide area of ​​the ink ejection surface, increasing the contact time between the dried ink adhering to the ink ejection surface and the cleaning solution. This promotes the penetration of the cleaning solution into the dried ink and enhances the cleaning ability of the cleaning solution. Furthermore, from the viewpoint of stably obtaining the above effects, the upper limit of the viscosity of the cleaning solution at 25°C is preferably 2.0 mPa·s or less. The lower limit of the viscosity of the cleaning solution at 25°C is not particularly limited, but considering the residue on the ink ejection surface, it is preferably 1.0 mPa·s or more, more preferably 1.5 mPa·s or more. Note that the viscosity in this specification is a value measured at 25°C using a falling-ball type automatic microviscometer (for example, "AMVn" manufactured by Anton Paar) in accordance with the method described in JIS (Japanese Industrial Standards) Z8803:2011 "Method for measuring the viscosity of liquids".

[0053] (static surface tension) In this embodiment, the static surface tension of the cleaning solution is 25 mN / m or less. This allows the cleaning solution to penetrate the dried ink material, peeling and removing the dried ink material from the ink discharge surface, thereby improving the cleaning performance of the cleaning solution. Furthermore, from the viewpoint of stably obtaining the above effects, the upper limit of the static surface tension of the cleaning solution is preferably 23 mN / m or less. The lower limit of the static surface tension of the cleaning solution is not particularly limited, but considering the residue on the ink discharge surface, it is preferably 15 mN / m or more, more preferably 20 mN / m or more. In this specification, the static surface tension is a value measured at 25°C in accordance with the Wilhelmy method (plate method) using a surface tension meter (for example, "Automatic Surface Tension Meter DY-300" manufactured by Kyowa Interface Science Co., Ltd.).

[0054] (pH) In this embodiment, the pH of the cleaning solution after being sealed and left standing at room temperature for one year is between 8.0 and 9.5. The cleaning solution in this embodiment exhibits a buffering effect due to the inorganic salt having a pH buffering effect, suppressing the decrease in pH over a long period of time. As a result, high cleaning performance can be maintained over a long period of time. In this specification, unless otherwise specified, "pH" means the hydrogen ion concentration measured at 25°C.

[0055] Furthermore, in this embodiment, the difference between the pH of the cleaning solution before sealing and standing and the pH of the cleaning solution after sealing and standing for one year is preferably 1.0 or less, more preferably 0.5 or less, and even more preferably 0.2 or less.

[0056] (Other ingredients) The cleaning solution may further contain known additives as needed (e.g., dissolution stabilizers, drying inhibitors, antioxidants, viscosity modifiers, pH adjusters, and fungicides).

[0057] [Ink and ink sets] The cleaning solution of this embodiment is preferably used to clean the ink ejection surface of a recording head that ejects ink containing a resin component (e.g., a dispersion resin or a binder resin). The ink containing the resin component can be an ink for non-absorbent recording media and / or low-absorbent recording media because it has excellent adhesion to non-absorbent recording media and / or low-absorbent recording media. Examples of resin components include (meth)acrylic resin, styrene-(meth)acrylic resin, urethane resin, polyester resin, and olefin resin. The content ratio of the resin component in the aqueous ink is, for example, 0.1% by mass or more and 5.0% by mass or less. In this specification, acrylic and methacrylic are collectively referred to as "(meth)acrylic".

[0058] Furthermore, inks containing the above-mentioned resin components tend to increase in viscosity upon drying. Specifically, the dry viscosity at 25°C after drying to 50% by mass before drying can reach 500 mPa·s or higher. "When the ink is dried to 50% by mass" means when the ink is placed in a container such as a petri dish and dried, for example, in a 60°C constant temperature bath, and the mass of the ink becomes 50% by mass when the mass of the ink before drying is considered to be 100% by mass. The dry viscosity is the value measured using the dried ink at 25°C using a falling-ball automatic microviscometer (for example, Anton Paar's "AMVn") in accordance with the method described in JIS (Japanese Industrial Standards) Z8803:2011 "Method for Measuring the Viscosity of Liquids".

[0059] When ink containing resin components remains on the ink ejection surface and dries, the resin components can adhere to the surface, making removal difficult. Therefore, a cleaning solution with high cleaning performance is required. Furthermore, since the cleaning solution may be used for a long period of time, such as more than a year, it is necessary that it can maintain high cleaning performance over that long period.

[0060] Therefore, the cleaning solution according to this embodiment has low viscosity and low surface tension due to the amphoteric surfactant having a betaine structure, a silicone-based surfactant, and a nonionic surfactant excluding the silicone-based surfactant. As a result, it easily remains on the ink ejection surface when wiped and easily penetrates the dried ink material that has adhered to it. This promotes the dispersion of dried ink material into the cleaning solution and improves the cleaning performance on dried ink material. Furthermore, the cleaning solution of this embodiment has an inorganic salt with pH buffering properties, which suppresses the decrease in pH over a long period of time. As a result, the cleaning performance of the cleaning solution can be maintained at a high level over a long period of time. In addition, by including water and a water-soluble organic solvent in the cleaning solution, the amount of hydrophobic organic solvent can be reduced, or the solution can be configured without a hydrophobic organic solvent. As a result, adverse effects on the ink ejection surface, such as deformation of the resin material constituting the ink ejection surface, can be suppressed.

[0061] The ink and cleaning solution in this embodiment may constitute an ink set for an inkjet recording device. This ink set may contain one type of ink and cleaning solution, or it may contain multiple types of ink and cleaning solution.

[0062] Furthermore, the cleaning solution of this embodiment can be used in the following cleaning method to more effectively remove dried ink.

[0063] [Washing method] An example of a cleaning method using the cleaning solution of this embodiment will be described. The cleaning method of this embodiment includes, for example, a cleaning solution supply step and a wiping step. Figures 1 to 5 show schematic side views of a recording head that ejects ink to form an image, which is provided in an inkjet recording device. In these figures, reference numeral 2 denotes the recording head, reference numeral 3 denotes the head housing that holds the recording head 2, reference numeral 5 denotes the recording unit that ejects ink, reference numeral 6 denotes the cleaning solution supply unit, reference numeral 7 denotes the wipe blade, and reference numeral F denotes the ink ejection surface. Note that an inkjet recording device may have multiple recording heads 2, but in these figures, one recording head 2 is used as an example for explanation.

[0064] (Cleaning solution supply process) Figure 1 shows the cleaning fluid supply process. In the cleaning fluid supply process, cleaning fluid C is supplied to the ink ejection surface F of the recording head 2. The cleaning fluid C is supplied, for example, by a cleaning fluid supply unit 6 located to the side of the recording unit 5. Preferably, the cleaning fluid supply unit 6 supplies the cleaning fluid C to a portion of the ink ejection surface F upstream of the recording unit 5, with reference to the wipe direction W (see Figure 2). The supplied cleaning fluid C adheres to the lower part of the cleaning fluid supply unit 6 and forms a meniscus.

[0065] In this process, the supply rate of the washing solution is 0.5 μL / cm³. 2 More than 10.0μL / cm 2 The following is preferred: 1.5 μL / cm 2 More than 4.0μL / cm 2 The following is more preferable: Washing solution supply rate of 0.5 μL / cm² 2 By doing so, the cleaning method of this embodiment can exhibit even better cleaning performance. The supply volume of the cleaning solution is 10.0 μL / cm². 2 By doing the following, the cleaning method of the present invention can more reliably suppress adverse effects on the recording head.

[0066] (Wipe process) Figures 2 to 5 show the wiping process. In the wiping process, the ink ejection surface F of the recording head 2 is wiped with the wipe blade 7. In this embodiment, it is preferable to wipe twice. The wipe blade 7 is, for example, a rubber wiper. The linear pressure of the wipe blade 7 is, for example, 5 N / m or more and 20 N / m or less. The wiping direction W is the direction in which the wipe blade 7 wipes the ink ejection surface F, and in the illustrated example, it is from right to left when viewed from the perspective of the paper.

[0067] (First wipe) As shown in Figures 2 and 3, during the first wipe, the wipe blade 7 wipes the ink ejection surface F of the recording head 2 in the wiping direction W. As the wipe blade 7 passes below the cleaning fluid supply unit 6, cleaning fluid C adheres to the wipe blade 7. The cleaning fluid C adhering to the wipe blade 7 then moves across the ink ejection surface F as the wipe blade 7 wipes. Here, the cleaning fluid C has low surface tension and low viscosity, and the wiping speed of the wipe blade 7 during the first wipe is relatively slow. Therefore, some of the cleaning fluid C that moves with the wipe blade 7 across the ink ejection surface F remains on the ink ejection surface F. In other words, during the first wipe, some cleaning fluid C is intentionally left behind. As a result, as shown in Figure 3, a liquid film of cleaning fluid C is formed on the ink ejection surface F of the recording head 2 after the first wipe. The liquid film of cleaning solution C continues to function until the second wipe is performed, releasing the resin components attached to the recording unit 5 from the ink ejection surface F and dispersing the resin components in cleaning solution C.

[0068] The first wipe speed is preferably 5 mm / second or more and 25 mm / second or less, and more preferably 15 mm / second or more and 22 mm / second or less. By setting the first wipe speed to 5 mm / second or more, the cleaning method of this embodiment can perform cleaning at a practical speed. By setting the first wipe speed to 25 mm / second or less, the cleaning method of this embodiment can intentionally create residue of the cleaning liquid C on the ink ejection surface F. As a result, the cleaning method of this embodiment can exhibit excellent cleaning performance.

[0069] (Second wipe) As shown in Figures 4 and 5, during the second wipe, the wipe blade 7 wipes the ink ejection surface F of the recording head 2 in the wiping direction W. The wipe blade 7 removes the cleaning solution C remaining on the ink ejection surface F along with the resin components mentioned above. Because the second wipe speed is relatively high, the wipe blade 7 reliably removes the cleaning solution C without leaving any residue. As a result, as shown in Figure 5, after the second wipe, the ink ejection surface F of the recording head 2 is in a state where both ink and cleaning solution C have been removed (cleaning is complete).

[0070] The second wipe speed is preferably 45 mm / second to 100 mm / second, more preferably 45 mm / second to 70 mm / second, and even more preferably 47 mm / second to 55 mm / second. By setting the second wipe speed to 45 mm / second or higher, the cleaning method of this embodiment can eliminate any remaining cleaning liquid C on the ink ejection surface F after the second wipe. As a result, the cleaning method of this embodiment can suppress the effect of remaining cleaning liquid C on the ejection performance of the recording head 2. By setting the second wipe speed to 100 mm / second or lower, the cleaning method of this embodiment can suppress wear on the ink ejection surface F of the recording head 2, even if the ink ejection surface F of the recording head 2 is coated with a water-repellent coating or the like.

[0071] Furthermore, the cleaning method of this embodiment may include steps other than those described above. For example, it may include a preliminary wiping step in which the ink ejection surface F is wiped with a wipe blade 7 without supplying cleaning solution before the cleaning solution supply step. Also, the cleaning method of this embodiment may further include other steps other than the preliminary wiping step, the cleaning solution supply step, and the wiping step. Furthermore, in the cleaning solution supply step shown in Figure 1, the cleaning solution C was supplied to the part of the ink ejection surface F of the recording head 2 upstream of the recording unit 5. However, in the cleaning method of this embodiment, the cleaning solution C may be supplied to other parts of the ink ejection surface F or to the entire ink ejection surface F in the cleaning solution supply step. Also, in the cleaning method of this embodiment, the cleaning solution C may be supplied to the ink ejection surface F by a method such as spray application in the cleaning solution supply step.

[0072] [Additional Note] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the present invention. [Examples]

[0073] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0074] [Preparation of cleaning solution] The raw materials shown in Table 1 were placed in separate containers and stirred to prepare washing solutions 1 to 7. Washing solutions 1 to 4 were examples of the present invention, while washing solutions 5 to 7 were comparative examples.

[0075] [Table 1]

[0076] Of the raw materials listed in Table 1, the betaine-based surfactant was Amogen® CB-H (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), which contains an amphoteric surfactant having an amide alkyl betaine structure. The silicone-based surfactant was SAG002 (manufactured by Nisshin Chemical Industry Co., Ltd.). The nonionic surfactant was Olphine® E1010 (ethylene oxide adduct of acetylenediol) (manufactured by Nisshin Chemical Industry Co., Ltd.).

[0077] [Viscosity measurement] Viscosity was measured at 25°C using a falling-ball automatic microviscometer (Anton Paar "AMVn") in accordance with the method described in JIS (Japanese Industrial Standards) Z8803:2011 "Method for Measuring the Viscosity of Liquids".

[0078] [Measuring surface tension] Static surface tension was measured at 25°C using a surface tension meter (Kyowa Interface Science Co., Ltd. "Automatic Surface Tension Meter DY-300") in accordance with the Wilhelmy method (plate method).

[0079] [pH measurement (immediately after preparation)] pH was measured using a pH meter (Horiba, Ltd. "D-51") at a temperature of 25°C.

[0080] [Evaluation of cleaning performance stability] (Preparation of ink-dried sample) The plate, including the ink ejection surface, was removed from the recording head (Kyocera Corporation "KJ4B-1200"). This plate was used as the evaluation plate. Using another recording head (Kyocera Corporation "KJ4B-1200"), the aforementioned ink was ejected onto the ink ejection surface of the evaluation plate to form a grid-like dot pattern (1000 dots). In forming the dot pattern, the volume per ink drop was set to 15 pL (15 pL of ink formed 1 dot). Next, the evaluation plate was dried at 40°C for 72 hours. The evaluation plate is a sample that simulates the state in which dried ink adheres as dirt to the ink ejection surface of the recording head.

[0081] [ink] 25.0 parts by mass of pigment dispersion, 12.5 parts by mass of binder particle dispersion, 10.0 parts by mass of propylene glycol, 15.0 parts by mass of diethylene glycol monoethyl ether, 3.0 parts by mass of 2-pyrrolidone, 2.0 parts by mass of acetylene surfactant ("Surfinol® 440" manufactured by Nisshin Chemical Industry Co., Ltd.), and 32.5 parts by mass of water were thoroughly mixed using a stirrer ("Three One Motor BL-600" manufactured by Shinto Kagaku Co., Ltd.). In this way, the ink to be used for evaluation was prepared. As the pigment dispersion, "EMACOL SF BLACK AH2186F" manufactured by Sanyo Shikiso Co., Ltd. (pigment: CIPigment Black 7, dispersion medium: water, pigment concentration: 20% by mass) was used. As the binder particle dispersion, "Movinyl 6763" manufactured by Japan Coating Resin Co., Ltd. (urethane-acrylic resin-containing binder particle dispersion, solid content concentration: 40% by mass) was used.

[0082] (First evaluation) As the first evaluation, the evaluation plate was cleaned using the cleaning solution immediately after preparation, and the cleaning performance (removal rate) of ink stains was evaluated. First, as the first wipe, 0.1 mL of each of the prepared cleaning solutions was supplied to the evaluation plate (supply rate per unit area: 2.5 μL / cm²). 2Next, the evaluation plate was wiped at a constant linear pressure and speed of 20 mm / second using a rubber wipe blade. Then, for the second wipe, the same amount of each cleaning solution prepared as in the first wipe was supplied to the evaluation plate, and the evaluation plate was wiped at a constant linear pressure and speed of 50 mm / second using the wipe blade.

[0083] The ink ejection surface of the evaluation plate was observed after two wipes, and the number of remaining dots was counted. The dot removal rate (100 × {1000 - number of remaining dots} / 1000) was then calculated, and the cleaning performance was evaluated based on the following evaluation criteria. The results are shown in Table 2. (Standards for cleaning performance) A (Good): Removal rate of 90.0% or higher B (Poor): Removal rate between 70.0% and less than 90.0% C (especially poor quality): Removal rate less than 70.0%

[0084] (Second evaluation) The washing solution was placed in a container (glass screw-cap vial), sealed, and left to stand at 25°C for one year. The pH after standing was measured using the method described above. Using the standing washing solution, the evaluation plate was cleaned and the cleaning performance (removal rate) was evaluated in the same manner as in the first evaluation. The results are shown in Table 2.

[0085] [Table 2]

[0086] (Evaluation results) As shown in Table 2, cleaning solutions 1 to 4, each containing water, a water-soluble organic solvent, an amphoteric surfactant having a betaine structure, a silicone-based surfactant, a nonionic surfactant excluding the silicone-based surfactant, and an inorganic salt with pH buffering properties, were found to have high ink drying performance both immediately after preparation and after standing for one year. This is thought to be because cleaning solutions 1 to 4 had a viscosity of 2.5 mPa·s or less and a static surface tension of 25 mN / m or less at 25°C, and furthermore, their pH after being sealed and left to stand at room temperature for one year was between 8.0 and 9.5, indicating that the buffering effect maintained a high pH even after standing.

[0087] In contrast, cleaning solution 5, with a viscosity of 3.1 mPa·s at 25°C, was found to have high viscosity and low removal performance both immediately after preparation and after one year of standing. Similarly, cleaning solution 6, with a static surface tension of 29 mN / m, was found to have high surface tension and low removal performance both immediately after preparation and after one year of standing. Furthermore, cleaning solution 7, which contains sodium hydroxide, an inorganic salt that does not have pH buffering properties, was found to have a pH drop to below 8.0 after standing, and consequently, a decrease in removal performance. [Explanation of symbols]

[0088] 2 recording heads 3 Head Housing 5. Records Section 6. Cleaning fluid supply unit 7 Wipe Blades F Ink ejection surface I Ink C Cleaning Solution

Claims

1. A cleaning solution for cleaning the ink ejection surface of the recording head of an inkjet recording device, It comprises water, a water-soluble organic solvent, an amphoteric surfactant having a betaine structure, a silicone-based surfactant, a nonionic surfactant excluding the silicone-based surfactant, and an inorganic salt having pH buffering properties. The viscosity at 25°C is 2.5 mPa·s or less. The static surface tension is 25 mN / m or less. After being sealed and left standing at room temperature for one year, the pH is between 8.0 and 9.

5. Cleaning solution.

2. A cleaning solution according to claim 1, The nonionic surfactant includes an acetylene-based surfactant. Cleaning solution.

3. A cleaning solution according to claim 1, The amphoteric surfactant having the betaine structure has an amide alkylbetaine structure, Cleaning solution.

4. A cleaning solution according to claim 1, The pH buffer range of the inorganic salt is pH 8.0 or higher and 10.0 or lower. Cleaning solution.

5. A cleaning solution according to claim 1, The ratio of the total amount of the nonionic surfactant and the silicone-based surfactant to the amount of the amphoteric surfactant having the betaine structure is 10 or less. Cleaning solution.

6. A cleaning solution according to any one of claims 1 to 5, Used in the process of wiping the ink ejection surface twice with a wipe blade, Cleaning solution.

7. An ink set for an inkjet recording device, A cleaning solution according to any one of claims 1 to 5, and an ink containing a resin component, The dry viscosity of the ink at 25°C after drying to 50% by mass is 500 mPa·s or more. Ink set.

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