Cleaning liquid for inkjet head

Abstract

To provide a cleaning liquid for an inkjet head capable of obtaining a high cleaning effect in a blade wiping system.SOLUTION: The inkjet head cleaning liquid is used for cleaning an inkjet head using a blade. The inkjet head cleaning liquid contains a silicone-based surfactant and a polycarboxylic acid polymer salt. The pH of the inkjet head cleaning liquid is 7 or more and 8 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cleaning liquid for an inkjet head. [Background technology]

[0002] In inkjet recording devices, mist-like ink adheres to the nozzle surface of the inkjet head during recording operations, dries, and solidifies, causing ink deposits to accumulate on the nozzle surface. These ink deposits grow and clog the ink ejection orifices, causing ejection abnormalities such as misaligned ejection and ejection failures.

[0003] In recent years, inks that adhere strongly to the nozzle surface, such as water-based inks with enhanced wettability and low environmental impact, have come to be used for non-absorbent media such as coated paper and film. For this reason, ink deposits are not only physically removed by cleaning operations such as ink purging and wiping the nozzles, but are also chemically removed using cleaning solutions.

[0004] For example, Patent Document 1 discloses a technique for removing ink deposits by purging a mixture of ink and a cleaning liquid that combines a surfactant and a basic compound from the nozzles. Patent Document 2 also discloses a technique for removing ink deposits by wiping the nozzle surface with a wiping member such as a cloth impregnated with a silicone surfactant. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2000-127419 [Patent Document 2] Patent Publication No. 2016-112763 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, the cleaning method described in Patent Document 2, in which the nozzle surface is wiped with a wiping member such as a cloth, is called the "cloth wipe method." In contrast, the cleaning method in which the nozzle surface is wiped with a blade is called the "blade wipe method." Unlike the cloth wipe method, with the blade wipe method, the cleaning liquid does not soak into the wiping member, making it difficult for the cleaning liquid to come into uniform contact with the nozzle surface, and often resulting in an insufficient cleaning effect from the cleaning liquid.

[0007] In view of the above circumstances, an object of the present invention is to provide a cleaning liquid for an inkjet head that can provide a high cleaning effect in a blade wiping method. [Means for solving the problem]

[0008] In order to achieve the above object, the inkjet head cleaning liquid according to the embodiment of the present invention is used to clean an inkjet head using a blade. The inkjet head cleaning liquid contains a silicone surfactant and a polycarboxylic acid polymer salt. The pH of the inkjet head cleaning liquid is 7 or more and 8 or less.

[0009] This inkjet head cleaning liquid has a pH adjusted to between 7 and 8. In such a neutral environment, hydrolysis of the silicone surfactant is suppressed, allowing the silicone surfactant to maintain its effect of increasing wetting of the nozzle surface. Furthermore, even in a neutral environment, the polycarboxylic acid polymer salt exhibits a high cleaning effect against ink deposits. Therefore, by using this inkjet head cleaning liquid, even in blade wipe cleaning, a high cleaning effect can be achieved due to the synergistic effect of the polycarboxylic acid polymer salt and the silicone surfactant.

[0010] The inkjet head cleaning liquid may further contain a fruit acid having two or more carboxy groups.

[0011] The content of the silicone surfactant may be 0.09% by mass or more and 1% by mass or less. [Brief explanation of the drawings]

[0012] [Figure 1] 1A to 1C are diagrams illustrating a method for cleaning an inkjet head by a blade wiping method using a cleaning liquid according to an embodiment of the present invention. [Figure 2] 1 is a graph showing the (estimated) remaining amount of silicone surfactant with respect to the number of months of storage at a storage temperature of 40° C. for cleaning solutions with different pH values. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described.

[0014] [Summary of the Invention] (Overall composition) An inkjet head cleaning liquid (hereinafter simply referred to as "cleaning liquid") according to one embodiment of the present invention is used to clean an inkjet head using a blade. The cleaning liquid according to this embodiment contains a silicone surfactant and a polycarboxylic acid polymer salt, and has a pH of 7 or more and 8 or less.

[0015] The cleaning solution according to this embodiment has a neutral pH of 7 or more and 8 or less. In this neutral environment, the cleaning solution according to this embodiment maintains high cleaning performance by effectively utilizing both the effects of the silicone surfactant and the polycarboxylic acid polymer salt. The effects of the silicone surfactant and the polycarboxylic acid polymer salt will be described below.

[0016] The silicone surfactant is a surfactant that has a siloxane bond (-Si-O-Si-). The silicone surfactant used in this embodiment acts as a surface tension adjuster that reduces the static surface tension of the cleaning liquid. This allows the cleaning liquid to spread evenly over the nozzle surface, even when a non-absorbent blade is used. As a result, the cleaning liquid adheres to and penetrates the ink deposits more easily, making it easier to remove the ink deposits from the nozzle surface.

[0017] Furthermore, silicone surfactants are surfactants that have a structure in which hydrophilic substituents have been introduced into a portion of silicone, which has a hydrophobic siloxane bond in its main skeleton, and therefore they themselves exhibit a cleaning effect.

[0018] The further away from neutrality a silicone surfactant is, the more hydrolysis it undergoes due to water or heat. However, in the cleaning solution according to this embodiment, the silicone surfactant is in a neutral environment, so hydrolysis is suppressed. As a result, the content of the silicone surfactant in the cleaning solution according to this embodiment changes little over time, so the performance of the cleaning solution can be maintained for at least one year, which is the minimum required storage period, and excellent storage stability can be achieved.

[0019] In addition, unlike fluorochemical surfactants, which are expected to have a similar effect of reducing surface tension, silicone surfactants are less likely to decompose in the environment, so they do not have the problem of environmental accumulation and are therefore environmentally advantageous.

[0020] Furthermore, the polycarboxylic acid polymer salt is a water-soluble polymer having a salt (neutralized form) of a polyvalent carboxy group. The polycarboxylic acid polymer salt functions as a cleaning agent for removing solidified ink even in a neutral environment. In other words, the polycarboxylic acid polymer salt can fully demonstrate its cleaning action even in a neutral environment where basic compounds generally used in cleaning agents cannot fully demonstrate their cleaning action. The inventors of the present application believe that this is because the salt of the polyvalent carboxy group improves the compatibility between the cleaning solution and the components (particularly the dispersant component) in the solidified ink, thereby improving the removability of solidified ink even in a neutral environment.

[0021] Furthermore, in the cleaning liquid according to this embodiment, the polycarboxylic acid polymer salt can also act as a cleaning aid (builder agent) that enhances the cleaning action of the silicone surfactant, thereby achieving a higher cleaning effect.

[0022] As described above, the cleaning solution according to this embodiment combines the cleaning action of the polycarboxylic acid polymer salt and the wettability-enhancing action of the silicone surfactant in a neutral environment, and the combined effect of these two components provides a high cleaning effect that can sufficiently remove solidified ink deposits, even when using a blade wipe method. Furthermore, the neutral environment of the cleaning solution according to this embodiment suppresses hydrolysis of the silicone surfactant, allowing the high cleaning effect to be maintained over a long period of time.

[0023] (Cleaning method) 1 is a diagram illustrating a blade wiping method for cleaning an inkjet head using a cleaning liquid according to this embodiment. As shown in FIG. 1, a nozzle plate 12 is provided at the bottom of an inkjet head 10, and a plurality of ink ejection orifices 11 are arranged on its underside (nozzle surface 12a). During a recording operation, ink adhering to the nozzle surface 12a dries, forming solidified ink deposits I. To remove this solidified ink deposits I, a wiping operation is performed in which a rubber blade B slides along the nozzle surface 12a (in the direction of the left arrow in the figure)

[0024] Immediately before this wiping operation, cleaning liquid C is supplied to the nozzle surface 12a from the cleaning liquid supply port 13. The cleaning liquid C, which has low surface tension, quickly wets and spreads along the nozzle surface 12a, covering the entire surface of the nozzle surface 12a without any gaps. As a result, the cleaning liquid C adheres closely to and penetrates the entire solidified ink I on the nozzle surface 12a, and the cleaning action of the silicone surfactant in the cleaning liquid C and the polyacrylic acid polymer salt effectively acts on the solidified ink I, making it easy to peel off. As a result, the solidified ink I is scraped off by the tip of blade B as it slides over the nozzle surface 12a, and is easily removed by moving together with blade B. It is preferable to perform the wiping operation two or more times if there is a large amount of solidified ink I on the nozzle surface 12a.

[0025] The blade wipe cleaning method uses a blade made of a soft material such as rubber. Therefore, the blade wipe cleaning method is less likely to scratch the nozzle surface 12a than a cloth wipe cleaning method that uses a wiping member made of a hard material such as pulp. Therefore, in this embodiment, the inkjet head can maintain its normal ink ejection function for a long period of time.

[0026] As described above, the cleaning liquid according to this embodiment can achieve the same high removal performance as the cloth wiping method even with the blade wiping method, while also achieving the advantage of a longer inkjet head life due to the blade wiping method.

[0027] [Detailed configuration of the present invention] (cleaning solution) The cleaning solution according to this embodiment has a pH adjusted to 7 or more and 8 or less, from the viewpoint of suppressing hydrolysis of the silicone surfactant. More preferably, the pH of the cleaning solution is 7 or more and 7.2 or less. This makes it possible to suppress hydrolysis of the silicone surfactant even at a storage temperature of 40°C, a relatively high temperature at which hydrolysis is likely to occur, and maintains high cleaning performance even after one year or more has passed.

[0028] From the viewpoint of spreading the cleaning liquid evenly over the nozzle surface, the static surface tension of the cleaning liquid according to this embodiment at 25°C is preferably 29 mN / m or less, more preferably 25 mN / m or less, and even more preferably 22 mN / m or less.

[0029] The viscosity of the cleaning liquid according to this embodiment is not particularly limited, but is preferably in a range close to the viscosity of general ink, preferably 3 mPa·s or more and 12 mPa·s or less, and more preferably 6 mPa·s or more and 8 mPa·s or less. This prevents a significant change in the viscosity of the ink even if the cleaning liquid is mixed into the ink after cleaning, thereby maintaining stable ejection properties.

[0030] The pH, static surface tension, and viscosity of the cleaning liquid are affected by the components constituting the cleaning liquid and their composition ratios, but as necessary, the pH is adjusted by the content of a pH adjuster, the static surface tension is adjusted by the content of a surface tension adjuster, and the viscosity is adjusted by the content of a viscosity adjuster.

[0031] Each component constituting the cleaning solution according to this embodiment will be described below.

[0032] (Silicone surfactant) The silicone surfactant used in the cleaning liquid according to this embodiment is not particularly limited, but is preferably a polyether-modified silicone, and more preferably a polyether-modified polydimethylsiloxane.

[0033] In particular, the polyether-modified polydimethylsiloxane is preferably a polyether-modified silicone in which ethylene oxide and / or propylene oxide is introduced as a polyether group into the silicone chain of polydimethylsiloxane at the side chain or terminal. For example, it is more preferable to have a repeating unit represented by the following general formula (1), and it is even more preferable to have a repeating unit represented by the following general formula (1) and a terminal group represented by the following general formula (2).

[0034] [ka]

[0035] R in formula (1) 1 and R in formula (2) 2 each independently represents a methyl group or a polyether group. 1 and R 2 At least one of the groups represents a polyether group. The polyether group is a group containing one or both of —C2H4O— and —C3H6O—.

[0036] The silicone surfactant may be used alone or in combination of two or more.

[0037] The content of the silicone surfactant in the cleaning solution according to this embodiment is not particularly limited as long as it exhibits a sufficient cleaning effect. However, it is preferably 0.02% by mass to 1% by mass, more preferably 0.06% by mass to 1% by mass, and even more preferably 0.09% by mass to 1% by mass. By setting the content to 1% by mass or less, insoluble matter is less likely to form and the silicone surfactant is less likely to separate within the cleaning solution. This allows the silicone surfactant to be more uniformly dispersed, resulting in improved wettability. A content of 0.02% by mass or more further enhances wettability and improves the removability of solidified ink. From the perspective of further enhancing wettability and further enhancing the removability of solidified ink, a content of 0.06% by mass or more is more preferable, and a content of 0.09% by mass or more is even more preferable. The static surface tension decreases as the content of the silicone surfactant increases, but the static surface tension becomes approximately constant at 0.09% by mass or more.

[0038] (Polycarboxylic acid polymer salt) The salt of a carboxy group in the polycarboxylic acid polymer salt according to this embodiment is represented by a -COOM group. M is preferably a metal atom. The metal atom constituting M can be selected from alkali metal atoms such as sodium and potassium, alkaline earth metal atoms such as calcium, and transition metal atoms such as iron, and is preferably an alkali metal atom, and more preferably a sodium atom.

[0039] The polycarboxylic acid polymer salt according to the present embodiment is not particularly limited, and may be, for example, a homopolymer of an ethylenically unsaturated monocarboxylic acid salt monomer such as an acrylate, a methacrylate, or a crotonate, or a homopolymer of an ethylenically unsaturated dicarboxylic acid salt monomer such as a maleate, a fumarate, or an itaconate, or may be a copolymer containing one or more ethylenically unsaturated monocarboxylic acid monomers and / or one or more ethylenically unsaturated dicarboxylic acid monomers.

[0040] The polycarboxylic acid polymer salt according to this embodiment may be a copolymer containing a monomer other than the above-described ethylenically unsaturated monocarboxylic acid monomer or ethylenically unsaturated dicarboxylic acid monomer. The other monomer may include, for example, an ethylenically unsaturated monomer containing an anionic group other than a COOM group. It is more preferable to include an ethylenically unsaturated monomer containing a sulfonate (SO3M) group as the anionic group. The anionic group may be directly bonded to the ethylene chain (via a single bond) or indirectly bonded via a spacer. Furthermore, the polycarboxylic acid polymer salt may have an ether structure such as -[CH2-CH2-O]- in the main chain or side chain in addition to the above-described ethylenically unsaturated monocarboxylic acid salt monomer or ethylenically unsaturated dicarboxylic acid salt monomer.

[0041] The polycarboxylic acid polymer salt according to this embodiment is preferably one or more of a polyacrylic acid salt having a repeating unit represented by the following general formula (3), a polyacrylic acid / maleic acid copolymer salt having a repeating unit represented by the following general formula (3) and a repeating unit represented by the following general formula (4), or an acrylic acid / sulfonic acid monomer copolymer salt having a repeating unit represented by the following general formula (3) and a repeating unit (sulfonate group-containing ethylenically unsaturated monomer) represented by the following general formula (5).

[0042] [ka] [ka] [ka]

[0043] In the above general formulas (3) to (5), M1 to M3 represent metal atoms and may be the same or different from one another. X represents a single bond or a spacer and is not particularly limited as long as it does not impair the effects of the present invention.

[0044] In particular, from the viewpoint of availability, the polycarboxylic acid polymer salt of this embodiment is preferably a sodium acrylic acid polymer or a sodium polyacrylic acid / maleic acid copolymer in which M1 in the above general formula (3) and M2 in the above general formula (4) are sodium, and from the viewpoint of compatibility with components in the solidified ink (particularly dispersant components), it is even more preferably a sodium maleic acid / acrylic acid copolymer containing a maleate monomer with a large number of COOM groups.

[0045] The polycarboxylic acid polymer salt of this embodiment preferably has a high molecular weight, and its weight average molecular weight (Mw) is preferably 1,000 or more and 1,000,000 or less, and more preferably 2,000 or more and 5,000 or less.

[0046] The content of the polycarboxylic acid polymer salt is preferably 0.01% by mass or more and 5% by mass or less. By making it 0.01% by mass or more, high cleanability is easily obtained. Furthermore, by making it 5% by mass or less, good ink ejection properties are easily obtained. In other words, if it exceeds 5% by mass, the polycarboxylic acid polymer salt remains on the nozzle surface after cleaning and dries, clogging the ink ejection orifices and easily causing poor ink ejection.

[0047] The polycarboxylic acid polymer salt may be used alone or in combination of two or more.

[0048] (Other ingredients) The cleaning solution according to this embodiment may contain water, a pH adjuster, and a viscosity adjuster as the balance of the above components. If necessary, the cleaning solution may further contain known additives (more specifically, a dissolution stabilizer, a drying inhibitor, an antioxidant, and an anti-mold agent).

[0049] ·water The water functions as a solvent for dissolving the polycarboxylic acid polymer salt, silicone surfactant, and pH adjuster. Examples of water that can be added to the cleaning solution include purified water and ion-exchanged water.

[0050] The water content in the cleaning liquid according to this embodiment is preferably 30% by mass or more and 80% by mass or less from the viewpoint of compatibility with the water-based ink.

[0051] pH adjuster The pH adjuster is not particularly limited as long as it can adjust the pH of the cleaning solution to 7 or more and 8 or less. The pH adjuster may be an acidic compound or a basic compound. The pH of the cleaning solution according to this embodiment tends to be alkaline when the polycarboxylic acid polymer salt contains a metal salt of a carboxy group. Therefore, from the viewpoint of suppressing hydrolysis of the silicone surfactant, an acidic compound is typically used as the pH adjuster to neutralize the alkalinity. The content of the pH adjuster in the cleaning solution may be determined according to the content of the polycarboxylic acid polymer salt so that the pH of the cleaning solution is 7 or more and 8 or less.

[0052] The acidic compound may be an inorganic acid, an organic acid, or a salt thereof. Examples of inorganic acids include hydrochloric acid, sulfuric acid, and paratoluenesulfonic acid. Examples of organic acids include formic acid, acetic acid, propionic acid, butyric acid, lactic acid, oxalic acid, tartaric acid, and citric acid. The acidic compound may be one type or a combination of two or more types.

[0053] As the pH adjuster, fruit acids (acids derived from fruits) are more preferable than deleterious substances such as paratoluenesulfonic acid, particularly from the viewpoint of manufacturing safety. Furthermore, since fruit acids having one carboxy group (formic acid, acetic acid, etc.) have a pungent odor, from the viewpoint of manufacturing safety, the pH adjuster is more preferably a fruit acid having two or more carboxy groups, which has a less pungent odor. Examples of fruit acids having two or more carboxy groups include malonic acid, succinic acid, malic acid, citric acid, and tartaric acid. For these reasons, it is preferable that the cleaning solution according to this embodiment further contains a fruit acid having two or more carboxy groups.

[0054] The basic compound may be an inorganic or organic basic compound. Examples of inorganic basic compounds include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. Examples of organic basic compounds include low-molecular-weight primary to tertiary amine compounds. Among these, sodium hydroxide or potassium hydroxide is preferred because it is a strong alkali and can adjust the pH with a small amount. The basic compound may be one type or a combination of two or more types.

[0055] Viscosity modifier The viscosity adjuster is not particularly limited in terms of its components or content, as long as it can adjust the viscosity of the cleaning liquid to a value close to that of the ink, within a range that does not affect cleaning performance. The viscosity of the cleaning liquid being close to that of the ink allows stable ejection without changing the viscosity of the ink, even if the cleaning liquid is mixed into the ink after cleaning.

[0056] Examples of viscosity modifiers include water-soluble diols such as 1,3-propanediol and sugar alcohols such as glycerin. These may be used alone or in combination of two or more, as needed. Particularly preferred viscosity modifiers are 1,3-propanediol and glycerin.

[0057] The content of the viscosity modifier in the cleaning liquid according to this embodiment is preferably 20% by mass or more and 70% by mass or less.

[0058] [Examples and Comparative Examples] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0059] (Preparation of cleaning solution) First, a cleaning agent, a surface tension adjuster (a silicone surfactant), a viscosity adjuster, and water (ion-exchanged water) were mixed to obtain the composition shown in Table 1, and then a pH adjuster was appropriately added to obtain a specific pH of 7 or more and 8 or less, thereby preparing the cleaning solutions according to Examples 1 to 9 and Comparative Examples 1 and 2.

[0060] [Table 1]

[0061] The following detergents, surface tension modifiers, and viscosity modifiers were used. Detergents (polycarboxylic acid polymer salts) Sodium polyacrylate ("Aqualic DL40" L series, manufactured by Nippon Shokubai Co., Ltd., molecular weight 3,500) Sodium acrylic acid / maleic acid copolymer ("Aqualic TL-37," L series, manufactured by Nippon Shokubai Co., Ltd., molecular weight 5,000) Detergents (general basic compounds) Triethanolamine (Nippon Shokubai Co., Ltd.) Surface tension adjuster Silicone surfactant ("Silface SAG503A", manufactured by Nissin Chemical Industry Co., Ltd.) Viscosity modifier 1,3-propanediol (manufactured by DuPont) pH adjuster (acidic oxide) Paratoluenesulfonic acid aqueous solution ("PTS-70" (PTS 70% aqueous solution), manufactured by Meiyu Sangyo Co., Ltd.)

[0062] The viscosity, static surface tension, and pH of each cleaning liquid in Examples 1 to 9 and Comparative Examples 1 and 2 are shown in Table 1. The static surface tension was measured at 25°C according to the Wilhelmy method (plate method) using a surface tension meter ("Automatic Surface Tensiometer DY-300" manufactured by Kyowa Interface Science Co., Ltd.). The viscosity was measured using a Lovis 2000M manufactured by Anton Paar, and was adjusted to 8 mPa s at 25°C.

[0063] (Ink deposit removal test) Tests of the removability of solidified ink were carried out using the cleaning solutions of Examples 1 to 9 and Comparative Examples 1 and 2 according to the following method.

[0064] First, a fixed ink was formed on the nozzle surface of an inkjet head. Specifically, ink was ejected from an ink supply head of a separate device onto the underside (nozzle surface) of the nozzle plate of an inkjet head (Kyocera Corporation KJ4B-1200) of the inkjet head, intentionally depositing multiple ink dots. The nozzle plate was then dried for 72 hours in an environment of 35°C temperature and 15% humidity, thereby producing a nozzle plate with multiple fixed ink dots (hereinafter also referred to as "fixed ink dots").

[0065] Next, the nozzle plate was cleaned by a blade wiping method using the cleaning solutions of Examples 1 to 9 and Comparative Examples 1 and 2, and the removability of solidified ink deposits was evaluated. An inkjet recording device equipped with a cleaning solution supply mechanism and a blade wiping cleaning mechanism was used. The blade was driven at a linear pressure of 10 N / m and a wiping speed of 30 mm / s, and wiping was performed twice. The first wipe was intended to wet and spread the cleaning solution over the nozzle plate, and the second wipe was intended to remove solidified ink dots (solidified ink deposits) that had been peeled off from the nozzle plate by the cleaning solution. Note that cleaning solution was supplied during both the first and second wipes.

[0066] (Removability evaluation) The number of ink dots stuck to the nozzle surface was counted before and after cleaning (after the second wipe), and the ratio of the number of ink dots stuck to the nozzle surface after cleaning to the number of ink dots before cleaning was calculated as the ink removal rate (%). To check for variations in the results, multiple nozzle plates were fabricated and the same test was performed.

[0067] The removal rate [%] of the ink deposits was evaluated according to the following criteria. 90-100: Very good 80~100: Good 60~80: Fairly good 20~30: Slightly poor 0: Bad

[0068] The state of the nozzle plate after cleaning was visually observed, and the state of removal of the ink deposits was evaluated according to the following criteria. A: The ink deposits can be removed uniformly, which is very good. B: Somewhat uneven, but good, with solidified ink removed. C: Uneven, but ink deposits can be removed, and the result is rather good. D: The ink deposits could not be removed, and the result was poor.

[0069] Even when the removal rate [%] was rated as "slightly poor" and the removal state was rated as "C," the adhered ink dots could be removed by wiping multiple times, and this was considered to be at an acceptable level for practical use. The results of each evaluation are shown in Table 2.

[0070] [Table 2]

[0071] (Results of Removal Evaluation of Examples 1 to 9) As a result, in Examples 1 to 9, which contained a silicone surfactant and a polycarboxylic acid polymer salt and had a pH of 7 to 8, removability within a practically acceptable range was confirmed. Among them, in Examples 1 to 8, which contained 0.06% by mass or more of silicone surfactant, the static surface tension was low at 23 mN / m or less, and therefore the removal rate of solidified ink was "fairly good" or better, and the state of removal of solidified ink by visual observation was "good" or better, confirming a higher cleaning effect. In particular, in Examples 1 to 7, which contained 0.09% by mass or more of silicone surfactant, the surface tension remained constant at around 22 mN / m, the removal rate of solidified ink was "good" or better, and the state of removal of solidified ink by visual observation was "very good" in all cases, confirming an even higher cleaning effect. Furthermore, among Examples 1 to 6, when comparing Examples 1 and 4, Examples 2 and 5, and Examples 3 and 6, which have the same composition but differ only in pH, no significant difference in the removal state was observed between pH 7 and 8, and it was confirmed that it is sufficient to adjust the pH to between 7 and 8.

[0072] (Results of Removal Evaluation of Comparative Example 1) The cleaning liquid of Comparative Example 1, which contained a polycarboxylic acid polymer salt but no silicone surfactant, had a high static surface tension of 55 mN / m, did not provide sufficient wettability, and was unable to remove solidified ink.

[0073] (Results of Removal Evaluation of Comparative Example 2) The cleaning liquid of Comparative Example 2, which contains a silicone surfactant but does not contain a polycarboxylic acid polymer salt, has a low static surface tension of 22 mN / m, but the polycarboxylic acid polymer salt alone does not exhibit high cleaning performance in a neutral environment.

[0074] (Storage stability evaluation) Cleaning solutions with different pH levels were prepared and their storage stability (hydrolysis resistance) was evaluated.

[0075] First, the amount of pH adjuster (70% aqueous solution of PTS) added to the cleaning solution of Example 6 was adjusted to obtain cleaning solutions with pH values ​​ranging from 7.0 to 8.6.

[0076] Next, the hydrolysis rate v was measured for each of the resulting cleaning solutions with different pH values ​​in an environment at a temperature of 40°C. The hydrolysis reaction rate constant k was calculated from the measured hydrolysis rate v. The calculated reaction rate constant k was used to determine the (estimated) remaining amount [%] of silicone surfactant after storage for a number of months (storage temperature 40°C) when the silicone surfactant concentration was 1%.

[0077] Figure 2 is a graph showing the change in the (estimated) remaining amount of silicone surfactant versus the number of months of storage (storage temperature 40°C) for cleaning solutions with different pH levels. A solution with an (estimated) remaining amount of silicone surfactant of 0.3% or more after 12 months of storage, the minimum required storage period, was evaluated as having good storage stability (hydrolysis resistance).

[0078] (Storage stability evaluation results) Measurement of the hydrolysis rate v confirmed that almost no hydrolysis occurred at pH 7, and that the hydrolysis rate v of the silicone surfactant increased as the pH value moved away from 7. Furthermore, as shown in Figure 2, the residual amount of silicone surfactant after 12 months of storage was 0.0 mass% in cleaning solutions with a pH greater than 8.0, whereas it was 0.3% or more in cleaning solutions with a pH between 7 and 8, confirming that hydrolysis of the silicone surfactant was suppressed and sufficient storage stability was achieved. As described above, it was confirmed that the cleaning solution of the present invention has hydrolysis resistance, thereby providing high cleaning effectiveness over a long period of time. [Explanation of symbols]

[0079] I...Ink deposits C...Cleaning solution B...Blade 10...Inkjet head 11...Nozzle 12...Nozzle plate 12a...Nozzle surface 13...Cleaning liquid supply port

Claims

1. An inkjet head cleaning liquid used for cleaning an inkjet head using a blade, The composition contains a silicone surfactant and a polycarboxylic acid polymer salt, and has a pH of 7 or more and 8 or less. Cleaning liquid for inkjet heads.

2. 2. The inkjet head cleaning liquid according to claim 1, Further contains fruit acids with two or more carboxyl groups Cleaning liquid for inkjet heads.

3. 3. The inkjet head cleaning liquid according to claim 1, The content of the silicone surfactant is 0.09% by mass or more and 1% by mass or less. Cleaning liquid for inkjet heads.

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