Cleaning liquid and ink set

Abstract

To provide a cleaning liquid capable of efficiently removing a dried matter of an ink containing a binder resin, and an ink set containing the cleaning liquid.SOLUTION: The cleaning liquid contains a water-soluble organic solvent, a polyacrylate salt, an acrylic acid-maleic acid copolymer salt, water, and a surfactant, wherein the mass ratio of the acrylic acid-maleic acid copolymer salt to the polyacrylate salt is 1 or more and 4 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cleaning liquid and an ink set. [Background technology]

[0002] Conventionally, inks containing binder resins have been known that have excellent fixation properties for recording media with low ink absorption (low-absorption media). Inks containing such binder resins adhere strongly to the substrate upon drying. Therefore, when the ink adheres to the nozzle plate of an inkjet head and dries, it becomes difficult to remove the dried ink.

[0003] Various cleaning liquids have been proposed for removing dried ink that adheres to and dries on nozzle plates, etc. For example, Patent Document 1 discloses a cleaning liquid for inkjet recording heads that contains a deliquescent agent, 2-pyrrolidone as an organic solvent, a surfactant, etc. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6780618 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the cleaning liquid disclosed in Patent Document 1 has a problem in that it has low cleaning properties for ink containing the above-mentioned binder resin. In view of the above circumstances, an object of the present invention is to provide a cleaning liquid that can efficiently remove dried matter from ink that contains a binder resin, and an ink set that includes the cleaning liquid. [Means for solving the problem]

[0006] To achieve the above object, a cleaning liquid according to one embodiment of the present invention comprises a water-soluble organic solvent, a polyacrylate, an acrylic acid-maleic acid copolymer salt, water, and a surfactant. The mass ratio of the acrylic acid-maleic acid copolymer salt to the polyacrylic acid salt is 1 or more and 4 or less.

[0007] The cleaning liquid contains an appropriate amount of a suitable cleaning agent, so that dried ink containing a binder resin can be efficiently removed.

[0008] The cleaning liquid may have a static surface tension of less than 30 mN / m.

[0009] The molecular weight of the polyacrylate may be 4,000 or less.

[0010] The polyacrylate may be selected from the group consisting of potassium polyacrylate, sodium polyacrylate, and acrylic acid-sulfonic acid copolymer salts.

[0011] The polyacrylate may be sodium polyacrylate.

[0012] The acrylic acid-maleic acid copolymer salt may have a molecular weight of 5,000 or less.

[0013] The acrylic acid-maleic acid copolymer salt may be sodium acrylic acid-maleic acid copolymer.

[0014] In order to achieve the above object, an ink set according to one embodiment of the present invention comprises the above cleaning liquid and ink, and the redispersibility index of the ink is 0.90 or higher. [Effects of the Invention]

[0015] As described above, according to the present invention, it is possible to provide a cleaning liquid that can efficiently remove dried matter from ink that contains a binder resin, and an ink set that includes the cleaning liquid. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described.

[0017] [First embodiment: cleaning solution] (Overall composition) The cleaning solution according to the first embodiment of the present invention will be described below. The cleaning solution according to this embodiment contains a water-soluble organic solvent, a cleaning agent, water, and a surfactant.

[0018] First, the process of forming dried ink that is the target of cleaning with the cleaning liquid according to this embodiment will be described.

[0019] When forming an image using an inkjet recording device, inkjet recording ink (hereinafter simply referred to as "ink") is ejected from the ejection surface of a recording head onto a recording medium. Specifically, the ink is ejected toward the recording medium from a large number of ejection ports formed on the ejection surface. At this time, the ejected ink may adhere to the ejection surface. When the ink adheres to the ejection surface, the adhered ink comes into contact with air and dries. In this way, dried ink is formed.

[0020] Such dried ink matter is particularly likely to occur when ink with excellent fixability to poorly ink-absorbent recording media (poorly absorbent media) is used, because such ink contains a relatively large amount of binder resin.

[0021] The dried ink matter causes poor ink ejection because, depending on the location where the dried ink matter is formed, the dried ink matter can clog the ejection orifice. Specifically, if the dried ink matter clogs part or all of the ejection orifice, it becomes difficult for the ink to be ejected, and the ink may be ejected in a direction different from the desired ejection direction.

[0022] When ink ejection failure occurs, the quality of the formed image deteriorates. Therefore, it is desirable to remove the dried ink to prevent ink ejection failure. However, it has been difficult to remove the dried ink, especially from ink containing a binder resin, using conventional cleaning solutions.

[0023] In contrast, the cleaning solution according to this embodiment contains a polyacrylate and an acrylic acid-maleic acid copolymer as cleaning agents, and the mass ratio of the acrylic acid-maleic acid copolymer to the polyacrylate is 1 or more and 4 or less.

[0024] By including a polyacrylate as a cleaning agent, the cleaning liquid quickly adsorbs to the dried ink matter. In order for the cleaning liquid to remove the dried ink matter, it must adsorb to the dried ink matter, undergo a chemical reaction with the dried ink matter, and dissolve or disperse the dried ink matter. In other words, the cleaning liquid's cleaning effect is exerted by dissolving or otherwise dissolving the dried ink matter. By including the above-described polyacrylate in the cleaning liquid according to this embodiment, the cleaning liquid can quickly adsorb to the dried ink matter and immediately exert its cleaning effect. Therefore, by including the above-described polyacrylate in the cleaning liquid, the cleaning liquid can quickly adsorb to the dried ink matter, thereby achieving the effect of improving the removability of the dried ink matter.

[0025] Furthermore, by including an acrylic acid-maleic acid copolymer salt as a cleaning agent, high dried ink removal properties can be achieved as follows. Although acrylic acid-maleic acid copolymer salts, which have a relatively large molecular weight, tend to adsorb to dried ink more slowly than polyacrylates, they can electrically neutralize the positively charged dried ink by adsorbing to the dried ink. This makes the dried ink more easily detachable from the nozzle plate, etc. Dried ink in this state can be easily removed by wiping with a rubber blade, etc. In this way, the acrylic acid-maleic acid copolymer salt exhibits high dried ink removal properties. Therefore, by including the acrylic acid-maleic acid copolymer salt in the cleaning solution, it is possible to easily separate the dried ink from the nozzle plate, etc., thereby achieving the effect of improving the removability of the dried ink.

[0026] Furthermore, by setting the mass ratio of the acrylic acid-maleic acid copolymer salt to the polyacrylic acid salt to be 1 or more and 4 or less, the two salts can exert the above-mentioned functions in a balanced manner, and a higher ability to remove dried ink substances can be achieved due to the synergistic effect of the two salts.

[0027] The cleaning solution according to this embodiment contains the cleaning agent described above, and thus quickly adsorbs to the surface of the dried ink and easily penetrates into the gap between the ejection surface and the dried ink. Therefore, the cleaning solution according to this embodiment swells and dissolves the dried ink, particularly the portion near the interface between the ejection surface and the dried ink. This allows the dried ink to peel off and be easily removed from the ejection surface.

[0028] The cleaning liquid according to this embodiment has the high removability described above and is particularly effective for removing dried ink that has excellent fixability to poorly absorbent media. That is, the cleaning liquid according to this embodiment can safely and efficiently remove dried ink that contains a large amount of binder resin and is difficult to dissolve or disperse.

[0029] As described above, the cleaning liquid according to this embodiment can effectively remove dried ink. However, the cleaning liquid according to this embodiment can effectively remove not only dried ink but also undried ink.

[0030] Next, each component constituting the cleaning solution according to this embodiment will be described.

[0031] (Water-soluble organic solvent) Examples of the water-soluble organic solvent contained in the cleaning solution according to this embodiment include glycol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerin, and dimethyl sulfoxide.

[0032] 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.

[0033] As the water-soluble organic solvent, glycol compounds are preferred, and 1,3-propanediol is more preferred.

[0034] The content of the water-soluble organic solvent in the cleaning liquid according to this embodiment is preferably 5% by mass or more and 70% by mass or less, and more preferably 10% by mass or more and 65% by mass or less, based on the total mass of the cleaning liquid.

[0035] The type and content of the water-soluble organic solvent are not limited to those described above, and can be changed as appropriate depending on the desired viscosity of the cleaning liquid, etc.

[0036] (cleaning agent) The cleaning agent contained in the cleaning solution according to this embodiment includes a polyacrylate and an acrylic acid-maleic acid copolymer salt.

[0037] (Polyacrylate) The polyacrylate is selected from the group consisting of potassium polyacrylate, sodium polyacrylate, and acrylic acid-sulfonic acid copolymer salts, with sodium polyacrylate being more preferred as the polyacrylate.

[0038] The molecular weight of the polyacrylate is preferably 10,000 or less, more preferably 4,000 or less. When the molecular weight of the polyacrylate is within this range, a cleaning solution containing the polyacrylate quickly adsorbs onto the dried ink, which is preferable from the viewpoint of the removability of the dried ink. The molecular weight is measured, for example, using gel permeation chromatography.

[0039] The content of polyacrylate in the cleaning liquid according to this embodiment is preferably 0.02% by mass or more and 1% by mass or less, and more preferably 0.04% by mass or more and 1% by mass or less, relative to the total mass of the cleaning liquid.

[0040] (acrylic acid-maleic acid copolymer salt) As the acrylic acid-maleic acid copolymer salt, sodium acrylic acid-maleic acid copolymer is preferred.

[0041] The mass ratio of the acrylic acid-maleic acid copolymer salt to the polyacrylic acid salt is from 1 to 4. The mass ratio of the acrylic acid-maleic acid copolymer salt to the polyacrylic acid salt is preferably from 2 to 4, and more preferably from 2 to 3. If the mass ratio of the acrylic acid-maleic acid copolymer salt to the polyacrylic acid salt is less than 1, this is not preferred from the viewpoint of removability of dried ink matter. On the other hand, if the mass ratio of the acrylic acid-maleic acid copolymer salt to the polyacrylic acid salt exceeds 4, the synergistic effect of the two salts cannot be obtained, which is not preferred from the viewpoint of removability of dried ink matter.

[0042] The molecular weight of the acrylic acid-maleic acid copolymer salt is preferably not more than 10,000, and more preferably not more than 5,000. When the molecular weight of the acrylic acid-maleic acid copolymer salt is within this range, the ability of the cleaning liquid containing the acrylic acid-maleic acid copolymer salt to dissolve dried ink matter is improved, which is preferable from the viewpoint of the removability of dried ink matter.

[0043] The content of the acrylic acid-maleic acid copolymer salt in the cleaning liquid according to this embodiment is preferably 0.02% by mass or more and 1% by mass or less, and more preferably 0.04% by mass or more and 1% by mass or less.

[0044] The cleaning solution according to this embodiment contains the cleaning agent described above, and therefore quickly adsorbs to dried ink matter and has high solubility in dried ink matter. This allows the safe and efficient removal of dried ink matter that contains a large amount of binder resin and is difficult to dissolve or disperse.

[0045] (surfactant) Examples of surfactants contained in the cleaning solution according to this embodiment include cationic surfactants, anionic surfactants, amphoteric surfactants, nonionic surfactants, etc. Nonionic surfactants are preferred as surfactants.

[0046] The content of the surfactant in the cleaning liquid according to this embodiment is preferably 0.1% by mass or more and 5% by mass or less, and more preferably 0.3% by mass or more and 5% by mass or less, based on the total mass of the cleaning liquid.

[0047] As the surfactant, only one type of surfactant may be used, or two or more types of surfactants may be mixed and used.

[0048] (water) Examples of the water contained in the cleaning solution according to this embodiment include commercially available purified water, ion-exchanged water, etc. Ion-exchanged water is more preferred as the water.

[0049] The water content is preferably 20% by mass or more and 99% by mass or less, and more preferably 35% by mass or more and 99% by mass or less, based on the total mass of the cleaning liquid. When the water content is within this range, for example, the viscosity of the cleaning liquid containing the water can be adjusted to a viscosity suitable for removing dried ink matter.

[0050] The amount of water contained in the cleaning solution according to this embodiment is not limited to the amount described above, and can be changed as appropriate depending on the desired viscosity of the cleaning solution, etc.

[0051] (others) The cleaning liquid according to this embodiment may further contain known additives (for example, a dissolution stabilizer, a drying inhibitor, an antioxidant, a viscosity adjuster, a pH adjuster, and an anti-mold agent) as needed.

[0052] (Physical properties of cleaning solution) Next, the physical properties of the cleaning liquid according to this embodiment will be described.

[0053] ·Static surface tension The static surface tension of the cleaning liquid according to this embodiment is less than 30 mN / m. Specifically, the static surface tension of the cleaning liquid at 25° C. is preferably 22 mN / m or more and 30 mN / m or less, and more preferably 22 mN / m or more and 25 mN / m or less. When the static surface tension of the cleaning liquid is within this range, the wetting properties of the cleaning liquid are increased, and the cleaning liquid quickly penetrates into the gap between the ink and the nozzle plate, etc., which is preferable from the viewpoint of the removability of dried ink matter.

[0054] Viscosity and pH The viscosity of the cleaning solution according to this embodiment is not particularly limited, but is preferably from 1 mPa·s to 10 mPa·s, and more preferably from 1 mPa·s to 4 mPa·s. The pH of the cleaning solution according to this embodiment is also not particularly limited, but is preferably from 7 to 14, and more preferably from 9 to 10, taking into consideration the balance between chemical damage to the inkjet head and cleaning performance.

[0055] (Method for removing dried ink) The method for removing dried ink using the cleaning liquid according to this embodiment is not particularly limited, but for example, dried ink is removed as follows.

[0056] First, the cleaning liquid according to this embodiment is supplied to the ejection surface of the recording head to which the dried ink has adhered. Methods for supplying the cleaning liquid to the ejection surface include, for example, supplying the cleaning liquid using a sponge or sheet impregnated with the cleaning liquid, ejecting the cleaning liquid using an inkjet method, applying the cleaning liquid using a roller, and spraying the cleaning liquid. Then, a wiping operation is performed on the ejection surface using a wiping blade or the like. This makes it possible to easily remove the dried ink adhering to the ejection surface.

[0057] The cleaning liquid according to this embodiment can also be used to remove dried ink that has adhered to members of the inkjet recording apparatus other than the recording head.

[0058] [Second embodiment: ink set] An ink set according to a second embodiment of the present invention will now be described. The ink set according to this embodiment includes a cleaning liquid and ink. The cleaning liquid and the ink are, for example, contained in different containers.

[0059] The cleaning liquid included in the ink set according to this embodiment is the cleaning liquid according to the first embodiment, so a description of the cleaning liquid included in the ink set according to this embodiment will be omitted.

[0060] The inks included in the ink set according to this embodiment are described below. The inks are inkjet recording inks used when forming images using an inkjet recording device, and have low redispersibility. Low redispersibility means, for example, that when the ink is applied to a dried product of the ink, the dried product of the ink is difficult to redisperse in the ink. Specifically, the redispersibility index of the ink is 0.90 or higher. The redispersibility index of the ink is preferably 0.50 or higher, and more preferably 0.90 or higher. If the redispersibility index is within this range, when the ink adheres to the ejection surface of a recording head and dries, it is difficult to remove the dried ink product using a conventional cleaning solution.

[0061] The ink redispersibility index is defined as follows: First, the mass A of the plate on which the ink is to be placed is measured. Next, 200 μl of ink is placed on the plate and spin-coated at 2000 rpm for 3 seconds to form an ink thin film. The formed ink thin film is dried in a thermostatic chamber at 40°C for 3 days, and the total mass B of the dried ink thin film and the plate is measured. Next, 200 μl of the same ink is placed on the resulting ink thin film and left to stand for 5 minutes at room temperature and humidity. The ink is then gently removed with approximately 50 ml of ion-exchanged water or similar. If the ink has high redispersibility, the redispersed ink will also be removed at this time. The ink thin film remaining on the plate is then left to stand in a thermostatic chamber at 40°C for 1 day, and the total mass C of the ink thin film and the plate is measured. The ratio (CA) / (BA) of mass C minus mass A to mass B minus mass A is defined as the ink redispersibility index.

[0062] It is difficult to remove dried matter from ink with a high redispersibility index (which is difficult to redisperse) using conventional cleaning solutions. On the other hand, the cleaning solution according to this embodiment has high removability even for ink with a high redispersibility index as described above. Note that the cleaning solution according to this embodiment also has high removability for ink with a low redispersibility index (which is easy to redisperse).

[0063] [Other embodiments] Although the embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the above-described embodiments and that various modifications can be made.

[0064] [Examples and Comparative Examples] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0065] (Preparation of cleaning solution) In each example and comparative example, the materials shown in Table 1 were placed in a beaker in the amounts shown in Table 1. The mixture in the beaker was stirred at a rotation speed of 400 rpm for 30 minutes using a stirrer ("Three-One Motor BL-600" manufactured by Shinto Scientific Co., Ltd.), to prepare a cleaning solution according to each example and comparative example.

[0066] [Table 1]

[0067] As shown in Table 1, in the cleaning solutions according to Examples 1 to 3, the mass ratio of sodium acrylic acid-maleic acid copolymer to sodium polyacrylate is in the range of 1 or more and 4 or less.

[0068] Comparative Example 1 differs from Example 1 in that it does not contain sodium acrylic acid-maleic acid copolymer. The mass % of sodium polyacrylate was increased by the mass % of sodium acrylic acid-maleic acid copolymer in Example 1 (0.1 mass %).

[0069] Comparative Example 2 differs from Example 1 in that it does not contain sodium polyacrylate. The mass percentage of the sodium acrylic acid-maleic acid copolymer was increased by the mass percentage of the sodium polyacrylate in Example 1 (0.1 mass%).

[0070] In Comparative Example 3, the mass percentages of sodium polyacrylate and sodium acrylic acid-maleic acid copolymer are reversed from those in Example 1. As a result, the mass ratio of sodium acrylic acid-maleic acid copolymer to sodium polyacrylate is 0.4, which is outside the range of 1 or more and 4 or less.

[0071] Comparative Example 4 differs from Example 1 in that it does not contain a surfactant. The mass percentage of ion-exchanged water is increased by the mass percentage of the surfactant in Example 1 (0.3 mass%).

[0072] Comparative Example 5 differs from Example 1 in that it does not contain sodium polyacrylate or sodium acrylic acid-maleic acid copolymer. Comparative Example 5 also contains 0.1 parts by mass of a 1N aqueous sodium hydroxide solution as the basic compound and 2 parts by mass of the compound of formula (1) as the deliquescent material.

[0073] The compound of formula (1) contained in the cleaning solution of Comparative Example 5 is as follows.

[0074] [ka] (In formula (1), R1 and R2 represent hydrogen, a methyl group, or an ethyl group, excluding the case where the sum of the carbon numbers of R1 and R2 is 2 or less and both R1 and R2 are methyl groups.)

[0075] In Comparative Example 6, the mass % of sodium polyacrylate was higher than that of Example 1, and the mass % of sodium acrylic acid-maleic acid copolymer was correspondingly (0.035 mass %) lower than that of Example 1. As a result, the mass ratio of sodium acrylic acid-maleic acid copolymer to sodium polyacrylate was 0.87, which is outside the range of 1 or more and 4 or less.

[0076] In Comparative Example 7, the mass % of sodium polyacrylate is lower than that of Example 1, and the mass % of sodium acrylic acid-maleic acid copolymer is correspondingly higher (0.014 mass %) than that of Example 1. As a result, the mass ratio of sodium acrylic acid-maleic acid copolymer to sodium polyacrylate is 4.38, which is outside the range of 1 or more and 4 or less.

[0077] (Preparation of dried ink) Using Truepress ink SC+ (SC+ ink) BLK00 manufactured by SCREEN Graphic Solutions Co., Ltd., multiple ink droplets with a diameter of 20 μm were deposited on the nozzle plate of an inkjet head KJ4B-1200 manufactured by Kyocera Document Solutions Inc. The deposited ink droplets were dried for 72 hours in an environment at a temperature of 35°C and a humidity of 15%, to produce a dried ink product.

[0078] (Method for evaluating ink removal ability of cleaning solution) In each example and comparative example, 0.1 ml of cleaning solution was dropped onto the area of ​​the stainless steel thin plate of the inkjet head where no ink droplets were attached using a pipetter. The inkjet head was wiped twice with a rubber blade at 20-second intervals. The linear pressure was 10 N / m and the wiping speed was 30 mm / s.

[0079] The ink removal ability of each cleaning solution was evaluated based on the ink droplet removal rate, which was defined as the ratio of the number of ink droplets removed after wiping to the number of ink droplets formed in the area where the rubber blade came into contact with the cleaning solution during wiping.

[0080] (Static surface tension measurement) The static surface tension of each cleaning liquid was measured in accordance with the Wilhelmy method (plate method) using a surface tension meter (Automatic Surface Tensiometer DY-300 manufactured by Kyowa Interface Science Co., Ltd.) In all of Examples 1 to 3, the static surface tension at 25°C was 22, which was within the range of less than 30.

[0081] (Measurement of molecular weight) The molecular weight of the sodium polyacrylate used was measured by gel permeation chromatography and found to be 3500, which was within the range of 4000 or less. Similarly, the molecular weight of the sodium acrylic acid-maleic acid copolymer was measured and found to be 5000, which was within the range of 5000 or less.

[0082] (Evaluation of Examples and Comparative Examples) As shown in Table 1, the cleaning solutions of Examples 1 to 3 exhibited high removal rates of 40% to 60%. This is thought to be because the mass ratio of sodium acrylic acid-maleic acid copolymer to sodium polyacrylate was in the range of 1 to 4, which enabled the synergistic effect of the two salts to achieve higher removal of dried ink matter.

[0083] As shown in Table 1, the cleaning solution of Comparative Example 1 had a low removal rate of 10%. This is thought to be because, since it did not contain sodium acrylic acid-maleic acid copolymer, it was unable to obtain the effect of electrically neutralizing the dried ink and making the dried ink easier to separate from the nozzle plate.

[0084] As shown in Table 1, the cleaning solution of Comparative Example 2 had a low removal rate of 20%. This is thought to be because, since it did not contain sodium polyacrylate, it quickly adsorbed onto the dried ink matter, and the effect of improving the removal of the dried ink matter was not obtained.

[0085] As shown in Table 1, the cleaning solution of Comparative Example 3 had a low removal rate of 20%. This is thought to be because the mass ratio of acrylic acid-maleic acid copolymer sodium to sodium polyacrylate was less than 1, so the synergistic effect of the two salts could not be exerted, and sufficient removal of dried ink matter was not achieved.

[0086] As shown in Table 1, the cleaning solution of Comparative Example 4 had a low removal rate of 0%. This is thought to be because, since it did not contain a surfactant, its wettability remained high and it was unable to sufficiently penetrate into the gap between the dried ink and the nozzle plate, etc., and therefore was unable to sufficiently remove the dried ink.

[0087] As shown in Table 1, the cleaning solution of Comparative Example 5 had a low removal rate of 0%. This is thought to be because, since it did not contain sodium polyacrylate or sodium acrylic acid-maleic acid copolymer, it was unable to achieve the effects of quickly adsorbing to the dried ink and increasing the removability of the dried ink, or of electrically neutralizing the dried ink and making the dried ink more easily detachable from the nozzle plate.

[0088] As shown in Table 1, the cleaning solution of Comparative Example 6 had a slightly low removal rate of 30%. This is thought to be because the mass ratio of acrylic acid-maleic acid copolymer sodium to sodium polyacrylate was less than 1, so the synergistic effect of the two salts could not be exerted, and sufficient removal of dried ink matter was not achieved.

[0089] As shown in Table 1, the cleaning solution of Comparative Example 7 had a slightly low removal rate of 30%. This is thought to be because the mass ratio of acrylic acid-maleic acid copolymer sodium to sodium polyacrylate exceeded 4, preventing the synergistic effect of the two salts from being exerted, and thus failing to achieve sufficient removal of dried ink matter.

[0090] (Evaluation of ink redispersibility) The ink redispersibility was evaluated as follows. First, the mass A of a SUS304 plate cut into a 3 cm square was measured. Next, 200 μl of ink was placed on the SUS304 plate whose mass had been measured and spin-coated at 2000 rpm for 3 seconds to form an ink thin film. The formed ink thin film was dried in a thermostatic chamber at 40°C for 3 days, and the total mass B of the dried ink thin film and the SUS304 plate was measured. Next, 200 μl of the same ink was placed on the resulting ink thin film and allowed to stand for 5 minutes at room temperature and humidity. The ink was then gently removed with approximately 50 ml of ion-exchanged water. The ink thin film remaining on the SUS304 plate was then allowed to stand in a thermostatic chamber at 40°C for 1 day, and the total mass C of the ink thin film and the SUS304 plate was measured. The ink redispersibility index was calculated using the following formula (1). The calculated ink redispersibility index is shown in Table 2. Redispersibility index = (CA) / (BA) (1)

[0091] [Table 2]

[0092] The results in Table 2 show that the cleaning liquids according to the examples have high removal properties even for inks with low redispersibility (high redispersibility index).

Claims

1. a water-soluble organic solvent; a polyacrylate; an acrylic acid-maleic acid copolymer salt; Water and Surfactants and Including, The mass ratio of the acrylic acid-maleic acid copolymer salt to the polyacrylic acid salt is 1 or more and 4 or less. Cleaning solution.

2. 2. The cleaning solution according to claim 1, Static surface tension is less than 30 mN / m Cleaning solution.

3. 3. The cleaning solution according to claim 1 or 2, The molecular weight of the polyacrylate is 4000 or less. Cleaning solution.

4. 4. The cleaning solution according to claim 3, The polyacrylate is selected from the group consisting of potassium polyacrylate, sodium polyacrylate, and acrylic acid-sulfonic acid copolymer salts. Cleaning solution.

5. 5. The cleaning solution according to claim 4, The polyacrylate is sodium polyacrylate. Cleaning solution.

6. 3. The cleaning solution according to claim 1 or 2, The molecular weight of the acrylic acid-maleic acid copolymer salt is 5,000 or less. Cleaning solution.

7. 7. The cleaning solution according to claim 6, The acrylic acid-maleic acid copolymer salt is sodium acrylic acid-maleic acid copolymer. Cleaning solution.

8. The cleaning solution according to claim 1 or 2, Ink and An ink set comprising: The redispersibility index of the ink is 0.90 or more. Ink set.

Images