Cleaning solution for inkjet recording devices

Abstract

The present invention provides a cleaning solution for an inkjet recording device that can suppress the precipitation of solid matter in the cleaning solution remaining in the inkjet recording device. [Solution] A cleaning solution according to one embodiment of the present invention is a cleaning solution for an inkjet recording device, comprising water, a surfactant, two or more water-soluble organic solvents, and a carboxylate salt excluding the surfactant. The two or more water-soluble organic solvents include at least polyethylene glycol. The Hansen solubility parameter distance between polyethylene glycol and the carboxylate salt is 10 or less.

Description

[Technical Field]

[0001] This invention relates to a cleaning solution for inkjet recording devices. [Background technology]

[0002] Inkjet recording devices form images on recording media by ejecting ink for inkjet recording from the ejection surface of the recording head. A cleaning method is known in which a cleaning solution is supplied to the ejection surface and the ejection surface is wiped with a wipe blade to remove ink residue from the ejection surface (for example, Patent Document 1).

[0003] On the other hand, inks used in inkjet recording devices sometimes contain binder resins, from the viewpoint of enabling printing on poorly absorbent recording media such as coated paper and non-absorbent recording media such as resin films. For example, Patent Document 2 describes a cleaning solution containing ethylenediaminetetraacetate (EDTA) or carboxylate salts such as ethylenediamine nitrilotriacetate, from the viewpoint of removing resin-derived foreign matter from such inks. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-202746 [Patent Document 2] Japanese Patent Publication No. 2016-216542 [Overview of the project] [Problems that the invention aims to solve]

[0005] Cleaning solutions containing carboxylates are expected to enhance the cleaning power against dried and hardened ink stains. However, since carboxylates are generally solid compounds at room temperature and pressure, there was a risk of solid components derived from the carboxylates precipitation if the cleaning solution containing carboxylates remained on the dispensing surface or other surfaces.

[0006] In view of the above circumstances, the object of the present invention is to provide a cleaning solution for an inkjet recording device that can suppress the precipitation of solid matter in the cleaning solution remaining in the inkjet recording device. [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 an inkjet recording device, It contains water, a surfactant, two or more water-soluble organic solvents, and a carboxylate salt excluding the surfactant. The two or more water-soluble organic solvents mentioned above include at least polyethylene glycol. The distance between the Hansen solubility parameters of the polyethylene glycol and the carboxylate is 10 or less. [Effects of the Invention]

[0008] The present invention provides a cleaning solution for an inkjet recording device that can suppress the precipitation of solid matter in the cleaning solution remaining in the inkjet recording device. [Modes for carrying out the invention]

[0009] 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.

[0010] [Cleaning solution for inkjet recording devices] The cleaning solution according to this embodiment is a cleaning solution for an inkjet recording device. The cleaning solution is used to clean ink and the like remaining in the inkjet recording device, and may, for example, be a cleaning solution for cleaning the ejection surface from which ink is ejected by a recording head mounted on the inkjet recording device. In this embodiment, cleaning the ejection surface includes removing ink stains and the like adhering to the ejection surface, and can be done, for example, by supplying the cleaning solution to the ejection surface and wiping it with a wiping member such as a blade. Alternatively, the cleaning solution can be used not only for cleaning the ejection surface but also for cleaning blades, transport rollers, etc., used in the wiping operation.

[0011] The cleaning solution according to this embodiment comprises water, a surfactant, two or more water-soluble organic solvents, and a carboxylate salt excluding the surfactant.

[0012] (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.

[0013] (Surfactants) The cleaning solution of this embodiment may contain one or more surfactants used in the art. Examples of surfactants include cationic surfactants, anionic surfactants, amphoteric surfactants, and nonionic surfactants. Of these, the cleaning solution of this embodiment preferably contains at least one selected from amphoteric surfactants and nonionic surfactants, more preferably an amphoteric surfactant having a betaine structure and / or a silicone surfactant, and even more preferably an amphoteric surfactant having a betaine structure.

[0014] (An amphoteric surfactant with a betaine structure) The amphoteric surfactant having a betaine structure adheres to the periphery of dirt (such as pigments, resin components, etc.) adhering to the object to be cleaned (for example, the spitting surface), and is excellent in the performance of releasing the dirt from the object to be cleaned and the performance of dispersing the released dirt in the cleaning liquid. Here, betaine refers to an inner salt having a cationic structure (for example, a quaternary ammonium ion structure) and an anionic structure (for example, an anionic structure of an acid such as carboxylic acid) in one molecule. As the amphoteric surfactant having a betaine structure, an amphoteric surfactant having an amidoalkyl betaine structure is preferable. As the amphoteric surfactant having an amidoalkyl betaine structure, a compound represented by the following general formula (1) is preferable.

[0015] [Chemical formula]

[0016] In the general formula (1), R represents a monovalent chain hydrocarbon group having 6 to 20 carbon atoms. n represents an integer of 1 or more and 5 or less.

[0017] R preferably represents a monovalent chain hydrocarbon group having 10 to 18 carbon atoms. Examples of the monovalent chain hydrocarbon group represented by R include a chain alkyl group and a chain alkenyl group. n preferably represents 3.

[0018] Examples of the amphoteric surfactant having an amidoalkyl betaine structure include fatty acid amide propyl betaine surfactants. Examples of the fatty acid amide propyl betaine surfactant include coconut oil fatty acid amide propyl betaine, lauric acid amide propyl betaine, palm kernel fatty acid amide propyl betaine, isostearic acid amide propyl betaine, and linoleic acid amide propyl. As the amphoteric surfactant having an amidoalkyl betaine structure, coconut oil fatty acid amide propyl betaine, lauric acid amide propyl betaine or palm kernel fatty acid amide propyl betaine is preferable.

[0019] 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 0.05% by mass or more and 3.0% by mass or less, and more preferably 0.1% by mass or more and 2.0% by mass or less.

[0020] (Silicone surfactant) Silicone surfactants reduce the surface tension of the cleaning solution, making it easier for the cleaning solution to penetrate the dirt. Silicone surfactants refer to surfactants that have siloxane bonds. As for silicone surfactants, polyether-modified silicone surfactants are preferred, and polyether-modified polydimethylsiloxane is more preferred.

[0021] In the cleaning solution, the content of the silicone surfactant is preferably 0.05% by mass or more and 1.5% by mass or less, and more preferably 0.1% by mass or more and 1.0% by mass or less, from the viewpoint of imparting appropriate surface tension to the cleaning solution.

[0022] In the cleaning solution, the total content of amphoteric surfactants having a betaine structure and silicone surfactants is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.2% by mass or more and 3.0% by mass or less.

[0023] (Water-soluble organic solvent) In this embodiment, the water-soluble organic solvent contains at least polyethylene glycol and further contains at least one water-soluble organic solvent. In this invention, the water-soluble organic solvent refers to an organic solvent whose solubility in water at 25°C is 1.0% by mass or more.

[0024] Polyethylene glycol is a polyhydric alcohol with a polymerized structure of ethylene glycol, and it has the physical properties of having a low vapor pressure and easily maintaining a liquid state. By including polyethylene glycol in the cleaning solution, the remaining cleaning solution is more likely to maintain a liquid state even in harsh environments where the components of the cleaning solution tend to evaporate easily. Furthermore, it is thought that the polyethylene glycol in the cleaning solution can satisfy the Hansen solubility parameter distance conditions with the carboxylate salt described later, thereby increasing the solubility of the easily precipitated carboxylate salt and suppressing its precipitation.

[0025] The lower limit of the average molecular weight of polyethylene glycol is preferably 150 or higher, more preferably 200 or higher, from the viewpoint of reducing the distance of the Hansen solubility parameters and improving the solubility of the carboxylate salt. The upper limit of the average molecular weight of polyethylene glycol is not particularly limited as long as the distance of the Hansen solubility parameters with the carboxylate salt described later is 10 or less, but from the viewpoint of improving cleaning power in cooperation with other components, it is preferably 350 or lower, more preferably 300 or lower. The average molecular weight of polyethylene glycol is the number-average molecular weight (Mn) and is a value measured using gel permeation chromatography.

[0026] The upper limit of the polyethylene glycol content in the cleaning solution is preferably 3.0% by mass or less, and more preferably 2.5% by mass or less, from the viewpoint of imparting appropriate physical properties (e.g., viscosity and surface tension) to the cleaning solution. Furthermore, the lower limit of the polyethylene glycol content in the cleaning solution is preferably 1.0% by mass or more, and more preferably 1.5% by mass or more, from the viewpoint of suppressing the drying of the cleaning solution remaining in the inkjet recording device.

[0027] Examples of water-soluble organic solvents other than polyethylene glycol include polyhydric alcohols other than polyethylene glycol, glycol ethers, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycols, and dimethyl sulfoxides.

[0028] Examples of polyhydric alcohols other than polyethylene glycol 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.

[0029] 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.

[0030] Examples of lactam compounds include 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0031] Examples of nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0032] Examples of acetate compounds include diethylene glycol monoethyl ether acetate.

[0033] The lower limit of the total content of water-soluble organic solvents in the cleaning solution is preferably 10.0% by mass or more, more preferably 15.0% by mass or more, from the viewpoint of imparting appropriate physical properties (viscosity, surface tension, etc.) to the cleaning solution. Furthermore, the upper limit of the total content of the water-soluble organic solvents is preferably 40.0% by mass or less, more preferably 35.0% by mass or less, in consideration of the balance with other raw materials.

[0034] (Carboxylate salt) The cleaning solution of this embodiment contains a carboxylate salt in addition to the surfactant described above. In this embodiment, the carboxylate salt has the effect of capturing, adsorbing, and removing ink stains, including resin components, that are to be cleaned, and also has a chelating effect that captures metal ions (calcium ions, magnesium ions, polyvalent cations, etc.) that reduce the effect of ionic surfactants, thereby improving the cleaning power of the cleaning solution. In particular, inks for inkjet recording devices that use poorly absorbent recording media such as coated paper and non-absorbent recording media such as resin films often contain resin components to ensure the fixation of pigments to the recording media. If such ink remains on the ejection surface, the decrease in water content in the ink makes it easier for pigments and resin components to adhere, which can make cleaning difficult. Therefore, by adding a carboxylate salt to the cleaning solution, the cleaning agent can be given the effect of capturing, adsorbing, and removing adhered ink stains by electrostatic action or the like.

[0035] The carboxylate salt in this embodiment is not particularly limited as long as it satisfies the distance conditions of the Hansen solubility parameter described later, other than the surfactants mentioned above. Examples include polyacrylates, polymethacrylates, aminopolycarboxylates, hydroxycarboxylates, cyclocarboxylates, ether carboxylates, other carboxylates, and copolymers containing at least one of these carboxylates as a monomer.

[0036] Of these, the carboxylate salt in this embodiment preferably contains a polymer or copolymer containing an acrylate as a monomer (hereinafter referred to as "acrylic acid-based water-soluble polymer"). Examples of such carboxylate salts include polyacrylates, acrylic acid / maleic acid copolymer salts, and acrylic acid / sulfonic acid monomer copolymer salts, of which polyacrylates are preferred. By including an acrylic acid-based water-soluble polymer, particularly polyacrylate, in the cleaning solution, it becomes easier to reduce the Hansen solubility parameter distance with polyethylene glycol, described later, to 10 or less. This allows the acrylic acid-based water-soluble polymer to dissolve sufficiently in polyethylene glycol, suppressing the precipitation of solids derived from the acrylic acid-based water-soluble polymer in the remaining cleaning solution. Furthermore, the acrylic acid-based water-soluble polymer can stably exhibit effects such as capturing, adsorbing, and removing pigments and resins contained in the ink to be cleaned, and an effect of improving the cleaning power of the cleaning solution can also be expected.

[0037] In this embodiment, the content of the acrylic acid-based water-soluble polymer in the carboxylate is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass. In other words, it is more preferable that the carboxylate consists of an acrylic acid-based water-soluble polymer.

[0038] From the viewpoint of improving cleaning ability, the lower limit of the carboxylate content in the cleaning solution is preferably 0.1% by mass or more, more preferably 0.3% by mass or more. Furthermore, from the viewpoint of suppressing the precipitation of carboxylates in the residual cleaning solution, the upper limit of the carboxylate content is preferably 2.0% by mass or less, more preferably 1.0% by mass or less.

[0039] (Distance between the Hansen solubility parameters of polyethylene glycol and carboxylate salts) The Hansen solubility parameter (HSP) is a value used to predict the solubility of a substance. It is a representation of the solubility parameter (SP) introduced by Hildebrand, divided into three components: dispersion (dD), polarization (dP), and hydrogen bonding (dH), and expressed in three-dimensional space. The three parameters of the HSP (unit: MPa) 0.5 The following applies: Dispersion term (dD): Energy due to intermolecular dispersion forces Polarization term (dP): Energy due to intermolecular dipole interactions Hydrogen bond term (dH): Energy due to intermolecular hydrogen bonding

[0040] The dispersion term (dD) is a term based on Van Der Waals' proximity forces. The polarization term (dP), also called the polarity term, is a term resulting from dipole moments, dielectric constant, etc. The hydrogen bonding term (dH) includes intermolecular forces based on hydrogen bonds, as well as π-π interactions that cannot be classified elsewhere.

[0041] The three components of HSP—dispersion (dD), polarization (dP), and hydrogen bonding (dH)—have been extensively determined by Hansen and his successors, and are described in detail in the Polymer Handbook (fourth edition), VII-698~711. Furthermore, the definition and calculation of HSP are described in Charles M. Hansen's "Hansen Solubility Parameters: A Users Handbook" (CRC Press, 2007). In addition, Hansen solubility parameter values ​​for many solvents and resins have been investigated, for example, in Wesley L. Archer's "Industrial Splicvents Handbook."

[0042] The three parameters that make up HSP can be considered as coordinates in three-dimensional space (Hansen space). When two specific substances are placed in Hansen space, the closer the coordinate distance between the two substances, the more similar the properties of the two substances tend to be.

[0043] This document describes a specific method for predicting the solubility of two substances (e.g., solvent X and solute Y) using HSP. First, the two substances are placed in Hansen space based on HSP. Then, the coordinate distance R of the two substances is... a Calculate this distance R. a The closer the distance between the two substances, the more easily they dissolve in each other. a This can be calculated using the following formula (R).

[0044]

number

[0045] In formula (R), dDx, dPx, and dHx represent the dispersion term (dD), polarization term (dP), and hydrogen bonding term (dH) of solvent X, respectively. dDy, dPy, and dHy represent the dispersion term (dD), polarization term (dP), and hydrogen bonding term (dH) of solute Y, respectively.

[0046] Applying this to the cleaning solution of this embodiment, the distance R between the solvent (polyethylene glycol) and the solute (carboxylate) in the Hansen space. ap This is the distance between the HSPs of polyethylene glycol and the carboxylate salt, and is calculated using the following formula (R-1).

[0047]

number

[0048] In formula (R-1), dDs, dPs, and dHs represent the dispersion term (dD), polarization term (dP), and hydrogen bonding term (dH) of the solvent (polyethylene glycol), respectively. dDp, dPp, and dHp represent the dispersion term (dD), polarization term (dP), and hydrogen bonding term (dH) of the solute (carboxylate), respectively.

[0049] In this embodiment, the HSP distance between polyethylene glycol and carboxylate is 10 or less. Carboxylates are generally solid at room temperature and pressure, and solid components derived from carboxylates may precipitate when the cleaning solution remaining on the discharge surface or the like is dried. In contrast, in this embodiment, by setting the HSP distance to 10 or less, the solubility of the carboxylate in polyethylene glycol can be increased, as shown in the example, and the precipitation of carboxylates contained in the cleaning solution can be suppressed. Furthermore, the upper limit of the HSP distance between polyethylene glycol and carboxylate is preferably 8.0 or less from the viewpoint of more reliably suppressing the precipitation of carboxylates contained in the cleaning solution. The lower limit of the HSP distance is not particularly limited as long as cleaning performance and solubility can be achieved, but is preferably 1.0 or more, more preferably 4.0 or more.

[0050] (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).

[0051] [Summary of this embodiment] As described above, the cleaning solution of this embodiment uses polyethylene glycol as a water-soluble organic solvent and a carboxylate salt in which the distance between the polyethylene glycol and the HSP is 10 or less, thereby suppressing the drying of the cleaning solution remaining in the discharge head and the precipitation of solids. This is thought to be because the moisture-retaining properties of polyethylene glycol suppress the drying of the cleaning solution, and the carboxylate salt can remain dissolved in the polyethylene glycol, thereby suppressing the precipitation of solids.

[0052] Furthermore, by including a carboxylate salt and polyethylene glycol with an average molecular weight of 150 to 350 in the cleaning solution, it can capture, adsorb, and remove pigments and resin components contained in residual ink, thereby improving the cleaning performance of the cleaning solution. In particular, by including a polymer or copolymer containing an acrylate as a monomer, such as a polyacrylate, in the cleaning solution as a carboxylate salt, such cleaning performance can be stably achieved. For this reason, the cleaning solution according to this embodiment is suitable for cleaning inkjet recording devices that use ink to which resin components have been added to ensure the fixation of pigments to the recording medium, and is suitable, for example, for cleaning inkjet recording devices that use poorly absorbable recording media and non-absorbent recording media as recording media.

[0053] Although the cleaning solution of this embodiment has 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]

[0054] The embodiments of the present invention have been described above, but the present invention is not limited to the embodiments described below.

[0055] [Preparation of cleaning solution] Cleaning solutions (CLN-1) to (CLN-5) were prepared by the following method. Cleaning solution (CLN-1) was a cleaning solution sample according to a comparative example of the present invention, and cleaning solutions (CLN-2) to (CLN-5) were cleaning solution samples according to an example of the present invention.

[0056] (Cleaning solution (CLN-1)) Washing solution (CLN-1) was prepared by mixing 28 parts of 1,3-propanediol (manufactured by Maruzen Co., Ltd.), 2 parts of glycerin (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 0.3 parts of Amogen® CB-H (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 0.3 parts of SAG002 (manufactured by Nisshin Chemical Industry Co., Ltd.), 0.5 parts of sodium polyacrylate (DL522 (manufactured by Nippon Shokubai Co., Ltd.)), and 68.9 parts of ion-exchanged water in a container. Of the above raw materials, 1,3-propanediol and glycerin are classified as organic solvents. Amogen CB-H is classified as an amide betaine type amphoteric surfactant. SAG002 is classified as a silicone-based surfactant. Sodium polyacrylate is classified as a carboxylate salt.

[0057] (Cleaning solution (CLN-2)) Washing solution (CLN-2) was prepared in the same manner as washing solution (CLN-1), except that glycerin was replaced with PEG-200 (manufactured by Sanyo Chemical Industries, Ltd.). PEG-200 is an organic solvent containing polyethylene glycol of different molecular weights, and was prepared so that its number average molecular weight is 200.

[0058] (Cleaning solution (CLN-3)) Washing solution (CLN-3) was prepared in the same manner as washing solution (CLN-1), except that glycerin was replaced with PEG-300 (manufactured by Sanyo Chemical Industries, Ltd.). PEG-300 is an organic solvent containing polyethylene glycol of different molecular weights, and was prepared so that its number average molecular weight is 300.

[0059] (Cleaning solution (CLN-4)) Washing solution (CLN-4) was prepared in the same manner as washing solution (CLN-1), except that glycerin was replaced with PEG-400 (manufactured by Sanyo Chemical Industries, Ltd.). PEG-400 is an organic solvent containing polyethylene glycol of different molecular weights, and was prepared so that its number average molecular weight is 400.

[0060] (Cleaning solution (CLN-5)) Washing solution (CLN-5) was prepared in the same manner as washing solution (CLN-1), except that glycerin was replaced with PEG-600 (manufactured by Sanyo Chemical Industries, Ltd.). PEG-600 is an organic solvent containing polyethylene glycol of different molecular weights, and was prepared so that its number average molecular weight is 600.

[0061] [Table 1]

[0062] [Calculation of HSP distance] The Hansen solubility parameter (HSP) distance between polyethylene glycol and carboxylate salts was calculated for washing solutions (CLN-1) to (CLN-5). Table 2 shows the HSP values ​​of glycerin, polyethylene glycol, and sodium polyacrylate used in each washing solution sample. These values ​​were the known HSP values ​​described in the literature, as mentioned above. Although each polyethylene glycol reagent contains polyethylene glycol with different molecular weights as mentioned above, the HSP of the polyethylene glycol with the molecular weight closest to the number-average molecular weight of each reagent was used as an approximation.

[0063] [Table 2]

[0064] Substitute these HSP values ​​into the above equation (R-1) and obtain the HSP distance R ap The following was calculated. For each cleaning solution sample, the solvent was glycerin or polyethylene glycol, and the solute was sodium polyacrylate. The results are shown in Table 3.

[0065] As shown in Table 3, the washing solution using glycerin as the solvent (CLN-1) has an HSP distance of R ap The value was greater than 10. On the other hand, the washing solutions (CLN-2) to (CLN-5) using polyethylene glycol as the solvent had an HSP distance R apis 10 or less, and furthermore, as the molecular weight of polyethylene glycol increases, the HSP distance R ap tends to decrease. From these results, by using polyethylene glycol with a number average molecular weight of 150 or more, for example 200 or more, and sodium polyacrylate, the HSP distance R ap can be made 10 or less, and it was found that the miscibility becomes good.

[0066] [Table 3]

[0067] [Drying test] Cleaning liquids (CLN-1) to (CLN-5) were placed in petri dishes and left in a constant temperature bath at 60 °C for two weeks. After two weeks, the petri dishes were taken out and the drying properties of each cleaning liquid were evaluated based on the following evaluation criteria. The results are shown in Table 3. [Criteria for drying property] "None": It is a uniform liquid state without precipitation of solids. "Yes": It is completely dried and solids are precipitated, or even if it is in a liquid state, precipitation of solids can be seen.

[0068] As shown in Table 3, the cleaning liquid (CLN-1) with an HSP distance between glycerin and polyacrylate exceeding 10 had solids precipitated after two weeks, and the drying property was evaluated as "Yes". In contrast, the cleaning liquids (CLN-2) to (CLN-5) with an HSP distance between polyethylene glycol and polyacrylate of 10 or less were all uniform liquids without precipitation of solids, and the drying property was evaluated as "None". From these results, it was found that by using polyethylene glycol as an organic solvent and a carboxylate (for example, polyacrylate) with an HSP distance from polyethylene glycol of 10 or less, the drying of the remaining cleaning liquid can be suppressed and the precipitation of solids can be suppressed. This is considered to be because the drying is suppressed by the moisture retention of polyethylene glycol and the carboxylate can maintain a state dissolved in polyethylene glycol.

[0069] [Evaluation of cleaning performance] 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). The ink was an ink intended for poorly absorbent recording media such as coated paper, and contained pigment and resins such as acrylic resin and urethane resin. In forming the dot pattern, the volume per drop of ink was set to 15 pL (15 pL of ink formed 1 dot). Next, the evaluation plate was dried at 60°C for 1 hour. 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.

[0070] 0.1 mL of each prepared washing solution was supplied to the evaluation plate described above (supply rate per unit area: 2.5 μL / cm²). 2 Next, the evaluation plate was wiped using a rubber wipe blade at a wiping speed of 20 mm / second (linear pressure 10 N / m). Subsequently, after supplying 0.1 mL of each washing solution, the evaluation plate was wiped using the same wipe blade at 20 mm / second (linear pressure 10 N / m).

[0071] 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. (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%

[0072] As shown in Table 3, the dot removal rate of cleaning solutions (CLN-1) to (CLN-3) was 90.0% or higher, and the cleaning performance was rated A (good). In contrast, the dot removal rate of cleaning solutions (CLN-4) and (CLN-5) was 70.0% or higher and less than 90.0%, and the cleaning performance was rated B (poor). From these results, it was found that by adding a carboxylate salt (e.g., polyacrylate) and polyethylene glycol with a number average molecular weight of 350 or less, for example 400 or less, to the cleaning solution, sufficient cleaning performance can be provided even to inks that contain resin components and tend to adhere.

Claims

1. A cleaning solution for inkjet recording devices, It comprises water, a surfactant, two or more water-soluble organic solvents, and a carboxylate salt excluding the surfactant, The two or more water-soluble organic solvents mentioned above contain at least polyethylene glycol, The distance between the Hansen solubility parameters of the polyethylene glycol and the carboxylate is 10 or less. Cleaning solution.

2. A cleaning solution according to claim 1, The average molecular weight of the polyethylene glycol is 150 or more. Cleaning solution.

3. A cleaning solution according to claim 1 or 2, The average molecular weight of the polyethylene glycol is 350 or less. Cleaning solution.

4. A cleaning solution according to claim 1 or 2, The polyethylene glycol content is 3.0% by mass or less. Cleaning solution.

5. A cleaning solution according to claim 1 or 2, The carboxylate salt includes a polymer or copolymer containing an acrylate as a monomer. Cleaning solution.

6. The cleaning solution according to claim 5, The polymer or copolymer containing the aforementioned acrylate as a monomer contains polyacrylate, Cleaning solution.

7. A cleaning solution according to claim 1 or 2, The surfactant includes a surfactant having a betaine structure. Cleaning solution.

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