Cleaning solutions and ink sets for inkjet recording devices

Abstract

The present invention provides a cleaning solution with high cleaning performance and capable of suppressing the formation of ink aggregates when mixed with ink, as well as an ink set containing the same. [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, a water-soluble organic solvent, and a polyacrylate salt. The molecular weight of the polyacrylate salt is 30,000 or more and 200,000 or less. The content of the polyacrylate salt in the cleaning solution is 1.0% by mass or more and 20.0% by mass or less.

Description

[Technical Field]

[0001] The present invention relates to a cleaning solution for an inkjet recording device and an ink set containing the same. [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] In inkjet recording devices, residual ink on the ejection surface and other areas tends to dry and harden, forming deposits, thus requiring high cleaning performance from cleaning solutions for inkjet recording devices. Polyacrylates are known as cleaning aids for hardened deposits (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-202746 [Patent Document 2] Japanese Patent Publication No. 2004-26989 [Overview of the project] [Problems that the invention aims to solve]

[0005] On the other hand, when polyacrylate salts were added to the cleaning solution for inkjet recording, there was a risk that the dispersion stability of the pigments in the ink would be inhibited, leading to the formation of ink aggregates.

[0006] In view of the above circumstances, the object of the present invention is to provide a cleaning solution and an ink set containing the same that have high cleaning performance and can suppress the formation of ink aggregates when mixed with ink. [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, a water-soluble organic solvent, and a polyacrylate. The molecular weight of the polyacrylate salt is between 30,000 and 200,000. The content of the polyacrylate in the cleaning solution is 1.0% by mass or more and 20.0% by mass or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a cleaning solution that has high cleaning performance and can suppress the formation of ink aggregates when mixed with ink, as well as an ink set containing the same. [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, a water-soluble organic solvent, and a polyacrylate salt.

[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 95.0% by mass or less, and more preferably 60.0% by mass or more and 90.0% by mass or less.

[0013] (Surfactants) The cleaning solution of this embodiment contains one or more surfactants that can be 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 cleaning target (for example, the above-mentioned ejection surface), and is excellent in the performance of releasing the dirt from the cleaning target and the performance of dispersing the released dirt in the cleaning liquid. Note that 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 preferred. As the amphoteric surfactant having an amidoalkyl betaine structure, a compound represented by the following general formula (1) is preferred.

[0015] [Chemical formula]

[0016] In the general formula (1), R represents a monovalent linear 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 linear hydrocarbon group having 10 to 18 carbon atoms. Examples of the monovalent linear hydrocarbon group represented by R include a linear alkyl group and a linear 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 preferred.

[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 0.01% 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.

[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 2.0% 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) The cleaning solution of this embodiment contains one or more water-soluble organic solvents to enhance miscibility with water and to impart desirable physical properties (viscosity, surface tension, etc.) to the cleaning solution. Examples of water-soluble organic solvents include polyhydric alcohols, glycol ethers, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycols, and dimethyl sulfoxides. In this invention, a water-soluble organic solvent refers to an organic solvent whose solubility in water at 25°C is 1.0% by mass or more.

[0024] 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.

[0025] 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.

[0026] Examples of lactam compounds include 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0027] Examples of nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0028] Examples of acetate compounds include diethylene glycol monoethyl ether acetate.

[0029] The lower limit of the total content of water-soluble organic solvents in the cleaning solution is preferably 3.0% by mass or more, more preferably 5.0% 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.

[0030] Furthermore, the SP value of the water-soluble organic solvent in this embodiment is preferably 24 MPa. 1 / 2 It is more than 26MPa 1 / 2 That concludes the explanation. SP values ​​(solubility parameters / unit: MPa) of water-soluble organic solvents. 1 / 2 SP) is a value expressed as the square root of the molecular cohesive energy, and can be calculated using the method described in RFFedors, Polymer Engineering Science, 14, pp. 147-154 (1974). Note that if the washing solution contains two or more water-soluble organic solvents, the SP value of each of the two or more water-soluble organic solvents should be 24 MPa. 1 / 2 It is preferable that it be greater than.

[0031] SP value is 24 MPa 1 / 2 The following water-soluble organic solvents contribute to improved cleaning performance by increasing the swelling of fixed ink, but in the inventors' view, they carry the risk of accelerating the deterioration of components of the recording head that ejects ink in an inkjet recording device. The cleaning solution of this embodiment contains a polyacrylate salt, as described later, which allows for a pressure of 24 MPa. 1 / 2 Even without including the following water-soluble organic solvents, cleaning performance can be improved and the risk of component degradation can be reduced.

[0032] SP value is 24 MPa 1 / 2Examples of highly water-soluble organic solvents include polyhydric alcohols, specifically: ethylene glycol (30.34), diethylene glycol (30.62), triethylene glycol (27.79), propylene glycol (27.59), dipropylene glycol (27.14), 1,2-butanediol (26.09), 2-methyl-1,3-butanediol (28.27), 1,2-pentanediol (28.64), 1,5-pentanediol (28.96), 1,6-hexanediol (27.66), glycerin (33.52), dimethyl sulfoxide (26.92), dimethylformamide (30.62), methanol (28.17), isopropyl alcohol (28.69), triethanolamine (32.27), etc. The numbers in parentheses after the specific examples are SP values ​​(unit: MPa). 1 / 2 )

[0033] (Polyacrylate) The cleaning solution of this embodiment contains a polyacrylate salt. As the polyacrylate salt, alkali metal salts such as sodium salts and potassium salts are preferred, and sodium polyacrylate is particularly preferred from the viewpoint of improving the cleaning performance described later.

[0034] In this embodiment, the molecular weight of the polyacrylate is 30,000 to 200,000, preferably 50,000 to 170,000. A polyacrylate with such a molecular weight can adsorb to ink stains fixed by electrostatic action, making it easier to disperse the ink stains in the cleaning solution and improving the cleaning performance of the cleaning solution. Furthermore, polyacrylates have a low risk of degrading components of the inkjet recording head, thus protecting the recording head while improving cleaning performance. In this specification, the molecular weight of the polyacrylate is the weight-average molecular weight (Mw), measured using gel permeation chromatography.

[0035] Furthermore, by setting the molecular weight of the polyacrylate to 30,000 to 200,000, it is possible to limit the polyacrylate content while improving cleaning performance. Specifically, the polyacrylate content in the cleaning solution of this embodiment is 1.0% by mass to 20.0% by mass, preferably 1.2% by mass to 15% by mass. If the polyacrylate content exceeds 20.0% by mass, when the cleaning solution is mixed with the ink, the electrostatic effect of the excess polyacrylate disrupts the dispersibility of the pigment, increasing the risk of ink aggregation. In contrast, by setting the polyacrylate content to 20.0% by mass or less, ink aggregation when the cleaning solution is mixed with the ink can be suppressed. Also, by setting the polyacrylate content in the cleaning solution to 1.0% by mass or more, the above-mentioned effect of improving cleaning performance can be obtained.

[0036] (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).

[0037] (Summary of this embodiment) As described above, the cleaning solution of this embodiment, by containing 1.0% to 20.0% by mass of polyacrylate salts with a molecular weight of 30,000 to 200,000, can reduce the risk of deterioration of the recording head components of an inkjet recording device while improving the cleaning performance against fixed ink stains. Furthermore, by setting the molecular weight of the polyacrylate salts to 30,000 to 200,000, the polyacrylate salt content can be set to 1.0% to 20.0% by mass, which can suppress the aggregation of ink in the cleaning solution due to excess polyacrylate salts. This can suppress nozzle ejection failures caused by aggregated ink, and can suppress defects such as uneven ink ejection caused by ejection failures.

[0038] [Ink set for inkjet recording devices] As another embodiment of the present invention, an ink set for an inkjet recording device is provided. The ink set of this embodiment includes the cleaning solution and ink described above. The cleaning solution can have the same configuration as in the embodiment described above, so a detailed description is omitted.

[0039] (ink) The ink of this embodiment has a dry viscosity of 516 mPa·s or higher at 25°C when the ink is dried to 50% by mass. "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 set to 100% by mass. The dry viscosity is the value measured using the dried ink at 25°C with 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".

[0040] The ink having the above-mentioned dry viscosity generally comprises an aqueous solvent and pigment particles, and has a configuration in which multiple pigment particles are dispersed in the aqueous solvent. The pigment particles generally include a pigment core containing pigment and a coating resin provided on the surface of the pigment core.

[0041] In most cases, resin salts are used as coating resins. Here, resin salts have ionizable functional groups (e.g., COONa groups) within their molecules. Also, aqueous inks contain a sufficient amount of aqueous solvent. For these reasons, ionization is likely to occur on the surface of the coating resin. Therefore, an electrical double layer may be formed on the surface of the coating resin. When an electrical double layer is formed on the surface of the coating resin, the pigment particles repel each other electrically, causing the pigment particles to disperse from one another.

[0042] On the other hand, when the ink remains on the ejection surface and dries to a concentration of 50% by mass, the proportion of aqueous solvent in the ink decreases, and the proportion of pigment particles increases. Ionization becomes less likely to occur on the surface of the resin coating these pigment particles. As a result, the pigment particles become less likely to repel each other electrically, and thus they tend to aggregate together.

[0043] In contrast, the above-mentioned cleaning solution can disperse pigment particles in the cleaning solution by adsorbing polyacrylate salts onto the surface of the coating resin that has been fixed by electrostatic action, etc. Furthermore, by setting the molecular weight of the polyacrylate salt to 30,000 to 200,000 and the polyacrylate salt content in the cleaning solution to 1.0% to 20.0% by mass, it is possible to maintain the electrostatic repulsion between dispersed pigment particles without disrupting the balance of electrostatic action in the cleaning solution, thereby suppressing the aggregation of pigment particles. Therefore, even with the ink set of this embodiment, nozzle ejection failures due to aggregated ink can be suppressed, and defects such as uneven ink ejection caused by ejection failures can be suppressed.

[0044] 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]

[0045] The embodiments of the present invention have been described above, but the present invention is not limited to the embodiments described below. Also, "parts" refers to "parts by mass".

[0046] [Preparation of cleaning solution] Cleaning solutions (CLN-1) to (CLN-4) were prepared by the following method. Cleaning solutions (CLN-1) and (CLN-4) were cleaning solution samples according to comparative examples of the present invention, and cleaning solutions (CLN-2) and (CLN-3) were cleaning solution samples according to examples of the present invention.

[0047] (Cleaning solution (CLN-1)) Washing solution (CLN-1) was prepared by mixing 10 parts of 1,3-propanediol (manufactured by Maruzen Co., Ltd.), 0.1 parts of Amogen® CB-H (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 0.14 parts of SAG002 (manufactured by Nisshin Chemical Industry Co., Ltd.), 35 parts of sodium polyacrylate (DL40 (manufactured by Nippon Shokubai Co., Ltd.)), and 54.76 parts of ion-exchanged water (remainder) in a container. Of the above raw materials, 1,3-propanediol is classified as a water-soluble organic solvent. Amogen CB-H is classified as an amide-betaine type amphoteric surfactant. SAG002 is classified as a silicone-based surfactant. The weight-average molecular weight (Mw) of DL40, which is sodium polyacrylate, was 3000.

[0048] (Cleaning solution (CLN-2)) Washing solution (CLN-2) was prepared in the same manner as washing solution (CLN-1), except that sodium polyacrylate was replaced with DL452 (manufactured by Nippon Shokubai Co., Ltd.) in 10 parts and deionized water in 79.76 parts (residue). The weight-average molecular weight (Mw) of DL452, which is sodium polyacrylate, was 50,000.

[0049] (Cleaning solution (CLN-3)) Washing solution (CLN-3) was prepared in the same manner as washing solution (CLN-1), except that sodium polyacrylate was replaced with 1.5 parts of DL522 (manufactured by Nippon Shokubai Co., Ltd.) and 88.26 parts of deionized water (remainder). The weight-average molecular weight (Mw) of DL522, which is sodium polyacrylate, was 170,000.

[0050] (Cleaning solution (CLN-4)) Washing solution (CLN-4) was prepared in the same manner as washing solution (CLN-1), except that sodium polyacrylate was replaced with 1.5 parts of ammonium polyacrylate solution 70-110 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 79.96 parts of deionized water (remainder). The weight-average molecular weight (Mw) of ammonium polyacrylate solution 70-110 was 10,000.

[0051]

Table 1

[0052] [Evaluation of Cleaning Performance] A plate including the ink ejection surface was removed from the recording head (「KJ4B-1200」manufactured by Kyocera Corporation). This plate was used as the evaluation plate. The above-mentioned ink was ejected onto the ink ejection surface of the evaluation plate using another recording head (「KJ4B-1200」manufactured by Kyocera Corporation) to form a grid dot pattern (1000 dots). The ink contains pigment particles, water, a resin (such as an acrylic resin or a urethane resin), a water-soluble organic solvent (such as propylene glycol, etc.), and a surfactant, and the drying viscosity at 25 °C when the ink was dried to 50% by mass was set to be 516 mPa·s or more. In the formation of the dot pattern, the volume per drop of ink was 15 pL (one dot was formed with 15 pL of ink). Next, the evaluation plate was dried at 60 °C for 1 hour. The evaluation plate is a sample that simulated the state where the dried ink adhered as dirt to the ink ejection surface of the recording head.

[0053] 0.1 mL of each prepared cleaning liquid was supplied to the above-mentioned evaluation plate (the supply amount per unit area was 2.5 μL / cm 2 \). Next, using a rubber wiper blade, the evaluation plate was wiped at a wiping speed of 2 mm / s (linear pressure 10 N / m). Subsequently, similarly, after supplying 0.1 mL of each cleaning liquid, the evaluation plate was wiped at 20 mm / s using the above-mentioned wiper blade (linear pressure 10 N / m).

[0054] The ink ejection surface of the evaluation plate after two wipes was observed, and the number of remaining dots was counted. Then, the dot removal rate (100 × {1000 - the number of remaining dots} / 1000) was calculated, and the cleaning performance was evaluated based on the following evaluation criteria. The results are shown in Table 2. (Criteria for Cleaning Performance) A (Good): The removal rate is 90.0% or more B (Poor): The removal rate is 70. or more and less than 90.0% C (especially poor quality): Removal rate less than 70.0%

[0055] [Table 2]

[0056] As shown in Table 2, the cleaning solutions (CLN-2) and (CLN-3) containing polyacrylate salts with a molecular weight of 30,000 to 200,000 and in an amount of 1.0% to 20.0% by mass achieved a dot removal rate of 90.0% or higher, resulting in a cleaning performance rating of A. In contrast, the cleaning solution (CLN-1) containing polyacrylate salts with a molecular weight of 3,000 and in an amount of 35% by mass received a cleaning performance rating of C. Furthermore, the cleaning solution (CLN-4) containing polyacrylate salts with a molecular weight of 10,000 and in an amount of 10% by mass received a cleaning performance rating of B. From these results, it was found that cleaning solutions containing polyacrylate salts with a molecular weight of 30,000 to 200,000 and in an amount of 1.0% to 20.0% by mass have high cleaning performance.

[0057] [Evaluation of ink agglomeration] The same inks used in the "Evaluation of Cleaning Performance" described above were prepared. The inks and each cleaning solution were mixed in a 1:1 ratio. The mixture was then diluted 100 times, and the number of coarse particles (0.5 μm or larger, less than 200 μm) was measured using a flow-type particle image analyzer (FPIA-300, manufactured by Sysmex Corporation). The results are shown in Table 2. (Standards for coagulation performance) A (Good): Number of aggregated particles is 500 or less. B (Poor): Number of aggregated particles is 500 or more but less than 1000 C (especially poor): Number of aggregated particles is 1000 or more.

[0058] As shown in Table 2, the ink coagulation properties of cleaning solutions (CLN-2) and (CLN-3) containing polyacrylate salts with a molecular weight of 30,000 to 200,000 and in an amount of 1.0% to 20.0% by mass were rated A. In contrast, the ink coagulation properties of cleaning solution (CLN-1) with a molecular weight of 3,000 and containing 35% by mass of polyacrylate salts, and cleaning solution (CLN-4) with a molecular weight of 10,000 and containing 10% by mass of polyacrylate salts, were rated C. From these results, it was found that cleaning solutions containing polyacrylate salts with a molecular weight of 30,000 to 200,000 and in an amount of 1.0% to 20.0% by mass can sufficiently suppress ink coagulation.

Claims

1. A cleaning solution for inkjet recording devices, It contains water, a surfactant, a water-soluble organic solvent, and a polyacrylate salt. The molecular weight of the polyacrylate is 30,000 or more and 200,000 or less. The content of the polyacrylate in the cleaning solution is 1.0% by mass or more and 20.0% by mass or less. Cleaning solution.

2. A cleaning solution according to claim 1, The aforementioned polyacrylate salt contains sodium polyacrylate. Cleaning solution.

3. A cleaning solution according to claim 1, The SP value of the aforementioned water-soluble organic solvent is 24 MPa. １／２ It is super, Cleaning solution.

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

5. An ink set for an inkjet recording device, A cleaning solution according to any one of claims 1 to 4, and an ink, The dry viscosity at 25°C when the ink is dried to 50% by mass is 516 mPa·s or higher. Ink set.

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