Cleaning unit and cleaning method

Abstract

To provide a cleaning unit that achieves high cleaning effectiveness while reducing the consumption of cleaning solution. [Solution] The cleaning unit is used to clean the nozzle surface of an inkjet head. The cleaning unit comprises a flexible porous body and a cleaning solution impregnated in the flexible porous body. The cleaning solution has a viscosity of 7 mPa·s or less at 25°C, contains 10% by mass or more of a water-soluble organic solvent, and the vapor pressure of the water-soluble organic solvent at 25°C is lower than that of water.

Description

[Technical Field]

[0001] The present invention relates to a cleaning unit and a cleaning method for cleaning the nozzle surface of an inkjet head. [Background technology]

[0002] In inkjet printers, highly drying inks containing binder resins are used for printing on non-absorbent media such as coated paper and resin sheets. When such inks dry on the nozzle surface where the nozzles are arranged in the inkjet head, they adhere strongly to the nozzle surface. Dried ink that has adhered strongly to the nozzle surface is difficult to remove with normal cleaning operations.

[0003] Patent Document 1 discloses a technique for removing dried ink residue adhering to the nozzle surface of an inkjet head. In the technique described in Patent Document 1, the nozzle surface is immersed in a cleaning solution in a cleaning solution tank, and the nozzle surface is pressed against a wiping member provided at the bottom of the cleaning solution tank, while the wiping member is vibrated. As a result, the dried ink residue adhering to the nozzle surface is removed by dissolution in the cleaning solution and impact from the wiping member. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2006-272097 [Overview of the project] [Problems that the invention aims to solve]

[0005] To remove strongly adhering dried ink from the nozzle surface, immersing the nozzle surface in the cleaning solution for approximately 10 seconds, as described in Patent Document 1, may be insufficient. On the other hand, as time passes, evaporation of the cleaning solution progresses, so to increase the immersion time of the nozzle surface, it is necessary to increase the amount of cleaning solution in the cleaning solution tank. This increases the consumption of cleaning solution for cleaning the nozzle surface.

[0006] In view of the above circumstances, the object of the present invention is to provide a cleaning unit that can achieve a high cleaning effect while reducing the consumption of cleaning solution. [Means for solving the problem]

[0007] To achieve the above objective, a cleaning unit according to one embodiment of the present invention is used to clean the nozzle surface of an inkjet head. The above-described cleaning unit comprises a flexible porous body and a cleaning solution impregnated into the flexible porous body. The above cleaning solution has a viscosity of 7 mPa·s or less at 25°C, a static surface tension of 40 mN / m or less at 25°C, contains 10% to 60% by mass of a water-soluble organic solvent, and the vapor pressure of the water-soluble organic solvent at 25°C is lower than that of water.

[0008] This cleaning unit effectively reduces the evaporation of a low-volatility cleaning solution by using it and impregnating a flexible porous material with it. As a result, this cleaning unit can reduce the amount of cleaning solution consumed when cleaning the nozzle surface of the inkjet head. In addition, by lowering the viscosity of the cleaning solution, this cleaning unit makes it easier to remove dried ink residue that has adhered to the nozzle surface of the inkjet head.

[0009] The vapor pressure of the above-mentioned water-soluble organic solvent at 25°C may be 2.5 kPa or less.

[0010] A cleaning method according to one embodiment of the present invention includes an immersion step and a wiping step. In the immersion step described above, the nozzle surface of the inkjet head is pressed into the flexible porous body of the cleaning unit, which has a flexible porous body and a cleaning solution impregnated into the flexible porous body, containing 10% by mass or more of a water-soluble organic solvent having a viscosity of 7 mPa·s or less at 25°C and a vapor pressure of the water-soluble organic solvent lower than that of water at 25°C, and is held in this state for a predetermined time. In the wiping step described above, the nozzle surface is wiped with a wiping member after the immersion step described above. The wiping member described above may be a blade. [Effects of the Invention]

[0011] As described above, the present invention can provide a cleaning unit that can achieve a high cleaning effect while reducing the consumption of cleaning solution. [Brief explanation of the drawing]

[0012] [Figure 1] This is a flowchart showing a cleaning method according to one embodiment of the present invention. [Figure 2] This figure shows step S01 (immersion step) of the above cleaning method. [Figure 3] This figure shows step S01 (immersion step) of the above cleaning method. [Figure 4] This figure shows step S02 (wiping step) of the above cleaning method. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below.

[0014] [Overall configuration of cleaning unit U] A cleaning unit U (see FIGS. 2 and 3) according to an embodiment of the present invention is a composite for cleaning a nozzle surface on which nozzles in an inkjet head (hereinafter also simply referred to as a "head") mounted on an inkjet recording apparatus are arranged. The cleaning unit U may be mounted on the inkjet recording apparatus, or may constitute an independent cleaning apparatus separate from the inkjet recording apparatus.

[0015] The cleaning unit U is configured to be able to remove dried ink strongly adhered to the nozzle surface of the head, which is difficult to remove by a cleaning mechanism mounted on a general inkjet recording apparatus. Examples of ink that strongly adheres to the nozzle surface of the head include ink used for printing on non-absorbent media such as coated paper and resin sheets that do not absorb ink, which is highly drying and contains a binder resin.

[0016] The cleaning unit U includes a flexible porous body P and a cleaning liquid L impregnated in the flexible porous body P. The flexible porous body P is a porous structure having flexibility, and is typically composed of a cloth that is an aggregate of fibers. The cleaning liquid L enters a large number of pores of the flexible porous body P and impregnates the flexible porous body P. That is, in the cleaning unit U, the cleaning liquid L is stored in a large number of pores of the flexible porous body P.

[0017] In the cleaning unit U, when the flexible porous body P is pressed, the total volume of a large number of pores in the flexible porous body P decreases with the compressive deformation, and thus a part of the cleaning liquid L impregnated in the flexible porous body P leaks out from the surface of the flexible porous body P. Then, in the cleaning unit U, when the pressing on the flexible porous body P is released, the flexible porous body P returns to its original shape, and the leaked cleaning liquid L returns into a large number of pores of the flexible porous body P.

[0018] The cleaning solution L of the cleaning unit U is configured to achieve good penetration, seeping into the gap between the nozzle surface and the dried ink adhering to it. Through this penetration, the cleaning solution L can gradually remove the dried ink from the nozzle surface. In order to achieve good penetration, the cleaning solution L needs to have a relatively low viscosity, and a low static surface tension is also advantageous.

[0019] Specifically, in order to obtain good penetration action, the viscosity of cleaning solution L at 25°C is preferably 7 mPa·s or less, preferably 4 mPa·s or less, and more preferably 2 mPa·s or less. The viscosity of cleaning solution L at 25°C is measured using an E-type viscometer (Toki Sangyo Co., Ltd. TV-100EL).

[0020] Furthermore, in order to obtain good penetration in the cleaning solution L, the static surface tension at 25°C is preferably 40 mN / m or less, more preferably 35 mN / m or less, and even more preferably 25 mN / m or less. The static surface tension of the cleaning solution L at 25°C is measured in accordance with the Wilhelmy method (plate method) using a surface tension meter ("Automatic Surface Tension Meter DY-300" manufactured by Kyowa Interface Science Co., Ltd.).

[0021] The viscosity and static surface tension of cleaning solution L can be adjusted depending on its constituent components. Specifically, cleaning solution L contains 10% by mass or more of a water-soluble organic solvent. The viscosity of cleaning solution L can be adjusted depending on the type and amount of the water-soluble organic solvent. In addition, a surfactant can be added to cleaning solution L as needed. The static surface tension of cleaning solution L can be adjusted depending on the type and amount of the surfactant.

[0022] The cleaning unit U is configured to provide not only the penetrating effect of the cleaning solution L described above, but also an evaporation suppression effect that inhibits the evaporation of the cleaning solution L. Specifically, the cleaning solution L is selected by considering not only viscosity and static surface tension, but also volatility. In other words, the cleaning unit U uses a water-soluble organic solvent with a low vapor pressure as a component of the cleaning solution L so that the volatility of the cleaning solution L is low.

[0023] In the cleaning solution L, a water-soluble organic solvent with a vapor pressure lower than that of water (2.9 kPa) at 25°C is used to keep the volatility at least equal to or lower than that of water. Furthermore, in the cleaning solution L, to further reduce volatility, it is preferable that the vapor pressure of the water-soluble organic solvent at 25°C is 2.5 kPa or less, and 1.0 × 10⁻⁶ -1 It is more preferably kPa or less, 2.0 × 10 -2 It is even more preferable that the pressure be less than or equal to kPa.

[0024] Furthermore, in the cleaning unit U, the evaporation of the cleaning solution L can be further suppressed by impregnating the flexible porous body P with the cleaning solution L. In other words, in the cleaning unit U, the evaporation of the cleaning solution L proceeds through evaporation of the cleaning solution L on the surface of the flexible porous body P and diffusion of the cleaning solution L from the inside of the flexible porous body P to the surface. However, because the supply of the cleaning solution L to the surface of the flexible porous body P is delayed due to its slow diffusion rate, the evaporation of the cleaning solution L is suppressed.

[0025] Thus, in the cleaning unit U, the synergistic effect of reducing the volatility of the cleaning solution L and impregnating the cleaning solution L into the flexible porous body P significantly suppresses the decrease in the cleaning solution L due to evaporation over time. As a result, the cleaning unit U can continuously apply a small amount of cleaning solution L to the nozzle surface to which dried ink has adhered for a long period of time, thereby reducing the consumption of cleaning solution L.

[0026] [Washing method] (Introduction) In a cleaning method according to one embodiment of the present invention, the nozzle surface of the head is cleaned using the cleaning unit U described above. Figure 1 is a flowchart of the cleaning method according to this embodiment. The cleaning method according to this embodiment includes step S01 (immersion step) and step S02 (wiping step). Figures 2 and 3 show step S01 (immersion step), and Figure 4 shows step S02 (wiping step).

[0027] (Step S01: Immersion process) In step S01, the nozzle surface 12 of the head 10, on which the nozzles 11 are arranged, is immersed in the cleaning liquid L of the cleaning unit U. Specifically, first, as shown in Figure 2, the nozzle surface 12 of the head 10 is brought into contact with the cleaning unit U, which is held by the holding member H, from above. Then, as shown in Figure 3, the flexible porous body P of the cleaning unit U is compressed and deformed by pressing it with the nozzle surface 12 of the head 10.

[0028] As shown in Figure 3, the nozzle surface 12 of the head 10 is covered with cleaning liquid L that seeps out from the numerous pores of the flexible porous body P as the flexible porous body P undergoes compressive deformation, and is in an immersed state in the cleaning liquid L. In other words, the immersed nozzle surface 12 shown in Figure 3 is in substantially the same state as if it were submerged in cleaning liquid L filling a cleaning liquid tank without being impregnated by the flexible porous body P.

[0029] On the nozzle surface 12 of the head 10, by holding it in an immersion state for a predetermined time, over time, swelling of the dried ink due to the action of the cleaning solution L and penetration of the cleaning solution L between the dried ink and the nozzle surface progress, causing the dried ink to peel off or the adhesion strength of the dried ink to decrease. As a result, in step S01, the dried ink that has adhered to the nozzle surface 12 becomes easier to remove from the nozzle surface 12.

[0030] In this embodiment, on the nozzle surface 12 where dried ink is strongly adhered, it is necessary to extend the immersion time to a certain extent in order to remove the dried ink. The immersion time of the nozzle surface 12 is preferably 30 minutes or more, and more preferably 1 hour or more. Furthermore, in order to reduce the consumption of cleaning solution L, it is preferable that the immersion time of the nozzle surface 12 is 2 hours or less.

[0031] (Step S02: Wiping process) In step S02, dried ink is removed by wiping the nozzle surface 12 after step S01. In step S02, a blade B is used as a wiping member to wipe the nozzle surface 12. The blade B is configured as a plate-shaped member whose tip extends parallel to the nozzle surface 12 and is wider than the area in which the nozzles 11 are arranged. The blade B is made of a material that is flexible and sliding, for example, sliding rubber.

[0032] Specifically, in step S02, as shown in Figure 4, the tip of blade B is brought into contact with the nozzle surface 12, and blade B is slid along the nozzle surface 12. As a result, dried ink that has peeled off from the nozzle surface 12 is removed as it moves with blade B. In addition, dried ink that is weakly adhered to the nozzle surface 12 is scraped off by the tip of blade B during the sliding process.

[0033] In step S02, if the dried ink adhering to the nozzle surface 12 in step S01 can be sufficiently removed, wiping may be performed using a wiping material other than the blade B, such as a nonwoven fabric. The blade B or wiping material such as a nonwoven fabric used in step S02 may be provided in the inkjet recording device, in the cleaning unit U, or may constitute an independent wiping device.

[0034] [Detailed configuration of cleaning unit U] (Flexible porous body P) The flexible porous body P is not limited to a specific composition, and can be, for example, a nonwoven or woven fabric made of fibrous material, or a sponge which is a foam of synthetic resin. The fibrous material that makes up the nonwoven or woven fabric can be selected from, for example, natural cellulose fibers, regenerated cellulose fibers, or synthetic fibers, and among these, it is preferable to use pulp, cotton, rayon, or polyacrylate, which have high water absorption.

[0035] (Cleaning solution L) Examples of water-soluble organic solvents that can be used in washing solution L include 1,2-propanediol (1.1 × 10⁻⁶). -2 kPa), 1,3-propanediol (1.2 × 10 -3 kPa), Glycerin (3.1 × 10 -6 kPa), 2-pyrrolidone (1.1 × 10⁻¹⁰ -3 kPa), diethylene glycol monoethyl ether (1.3 × 10 -2 kPa), 2-[2-(2-butoxyethoxy)ethoxy]ethanol (2.7 × 10 -5 Examples include kPa (the values ​​in parentheses indicate the vapor pressure at 25°C).

[0036] In the washing solution L, a combination of multiple types of water-soluble organic solvents may be used. In this case, the content of water-soluble organic solvents refers to the total content of all water-soluble organic solvents, and the vapor pressure of water-soluble organic solvents refers to the vapor pressure of the water-soluble organic solvent with the highest vapor pressure. In other words, for example, a washing solution L in which the vapor pressure of water-soluble organic solvents at 25°C is 2.5 kPa or less does not contain any water-soluble organic solvents whose vapor pressure at 25°C exceeds 2.5 kPa.

[0037] As the surfactant for the cleaning solution L, a nonionic surfactant is preferred, and among them, an acetylene-based surfactant is preferred. Examples of commercially available acetylene-based surfactants include Olphin® E1010, Olphin® EXP.4200, Olphin® EXP.4300, Surfinol® 420, and Surfinol® 440, all manufactured by Nisshin Chemical Industry Co., Ltd.

[0038] The cleaning solution L may contain known additives as needed to more effectively obtain the above functions or to obtain functions different from those described above. Examples of known additives include dissolution stabilizers, drying inhibitors, antioxidants, viscosity modifiers, pH adjusters, and antifungal agents. The cleaning solution L contains water as the remainder of the above components. In the cleaning solution L, for example, ion-exchanged water, purified water, or distilled water can be used as water.

[0039] In cleaning solution L, the content of water-soluble organic solvent should be 10% by mass or more, but good performance is more likely to be obtained by keeping it at 60% by mass or less. In addition, in cleaning solution L, good performance is more likely to be obtained by keeping the surfactant content within the range of 0.1% by mass or more and 5% by mass or less. Furthermore, in cleaning solution L, good performance is more likely to be obtained by keeping the water content within the range of 50% by mass or more and 90% by mass or less.

[0040] [Other embodiments] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above and can be modified in various ways. For example, the cleaning unit U according to the present invention may have components other than the flexible porous body P and the cleaning liquid L, as needed. Furthermore, the cleaning method according to the present invention may include steps other than step S01 (immersion step) and step S02 (wiping step).

[0041] [Examples and Comparative Examples] The following describes examples of the present invention, but the present invention is not limited to these examples.

[0042] (Brief explanation) In Examples 1-6 and Comparative Examples 1 and 2, cleaning units were prepared using cleaning solutions with different compositions. In each example and comparative example, a common woven fabric (Toraysee® PW (manufactured by Toray Industries, Inc.)) was used as the flexible porous body. In each example and comparative example, the removal performance of the cleaning unit and the drying suppression performance of the flexible porous body were evaluated.

[0043] (Evaluation Method for Removal Performance of Cleaning Unit) In each example and comparative example, a fixed sample of a head with dried ink deposits adhered to the nozzle surface to the same extent was prepared, and the removal performance of the dried ink deposits adhered to the nozzle surface by the cleaning unit was evaluated using the fixed sample.

[0044] The fixed sample of the head was prepared by filling the ink tank with ink, creating a water head difference of 0.5 cm between the ink tank and the head, allowing the ink to overflow onto the nozzle surface of the head, and holding it in an environment at a temperature of 35°C and a humidity of 15% for 72 hours. The head used was J4B-QA manufactured by Kyocera Corporation, and the ink used was Truepress ink SC+ YEL00 manufactured by SCREEN Graphics Solutions Co., Ltd.

[0045] In each example and comparative example, a cleaning unit was fabricated by dropping 2 ml of cleaning liquid onto a 20 cm × 2.5 cm flexible porous body on a non-permeable sheet made of Teflon (registered trademark) placed on a sponge member made of EPDM. Then, the nozzle surface of the head sample was pressed against each cleaning unit, and the immersion process of the above cleaning method was performed by holding it for 1 hour in a state where each cleaning unit was pressed between the sponge members.

[0046] Thereafter, the cleaning unit on the sponge member was replaced with a new flexible porous body, and the flexible porous body onto which 2 ml of cleaning liquid had been dropped was used as a wiping member, and the wiping process of the above cleaning method was performed by wiping the nozzle surface of the head sample once at a surface pressure of 0.09 N / m 2 and a linear speed of 20 mm / s. In each example and comparative example, the removal performance of the cleaning unit was evaluated by observing the nozzle surface of the fixed sample after the wiping process.

[0047] Specifically, the removal performance of the cleaning unit was evaluated by its removal rate. The removal rate (%) was calculated as 100 × (N0 - N1) / N0, where N0 is the number of dried ink particles in the solidified sample before the immersion process and N1 is the number of dried ink particles in the solidified sample after the wiping process. In each example and comparative example, it can be seen that a higher removal rate indicates better removal performance of the cleaning unit.

[0048] (Method for evaluating the drying suppression performance of cleaning solutions by a flexible porous material) In each example and comparative example, a cleaning unit was prepared by stacking 10 pieces of flexible porous material, cut to Φ40 mm, in a Φ40 mm petri dish and impregnating them with approximately 4 g of cleaning solution. For the cleaning solution in each cleaning unit, the initial mass M0 of the cleaning solution was measured, and it was left to stand for 4 hours in an environment of 35°C and 15% humidity. The dry mass M1 of the cleaning solution after standing was measured, and the drying rate R1 (%) was calculated by (1 - (M1 / M0)) × 100. In addition, the initial mass M0 and dry mass M1 were measured in the same manner without using the flexible porous material, and the drying rate R2 (%) was calculated in the same way. Then, for each example and comparative example, the drying inhibition rate (%) was calculated by (1 - (R1 / R2)) × 100. In each example and comparative example, it can be seen that the higher the drying inhibition rate, the better the performance of the flexible porous material in suppressing the drying of the cleaning solution.

[0049] (Cleaning solution) In Examples 1-6 and Comparative Examples 1 and 2, cleaning solutions for the cleaning unit were prepared by mixing and stirring the components shown in Table 1. The values ​​shown for each component in Table 1 represent the content (parts by mass) of each component. Table 1 also shows the vapor pressure at 25°C for each water-soluble organic solvent and water. Furthermore, Table 1 shows the static surface tension and viscosity of each cleaning solution at 25°C.

[0050] In Examples 1 to 6, the type and content of the water-soluble organic solvent in the cleaning solution were varied. In all of Examples 1 to 6, the composition of the cleaning solution was within the range of the above embodiments, meaning that the cleaning solution contained 10% by mass or more of a water-soluble organic solvent whose vapor pressure at 25°C was lower than that of water, and the viscosity of the cleaning solution at 25°C was 7 mPa·s or less. In addition, in all of Examples 1 to 6, the static surface tension of the cleaning solution at 25°C was 40 mN / m or less.

[0051] In Comparative Example 1, the cleaning solution does not contain a water-soluble organic solvent, and the static surface tension of the cleaning solution at 25°C exceeds 40 mN / m, thus the composition of the cleaning solution differs from the above embodiment. In Comparative Example 2, the water-soluble organic solvent content exceeds 60% by mass, and the viscosity of the cleaning solution at 25°C exceeds 7 mPa·s, thus the composition of the cleaning solution differs from the above embodiment.

[0052] (Evaluation results) Table 1 shows the removal rate and drying inhibition rate as evaluation results for the cleaning units in Examples 1-6 and Comparative Examples 1 and 2. In all Examples 1-6, the removal rate was 70% or higher, indicating that the cleaning units provided good removal performance. In particular, in Examples 1-3, where the viscosity of the cleaning solution at 25°C was 1.5 or less and the vapor pressure of the water-soluble organic solvent at 25°C was 1 / 100th of that of water or less, the removal rate was 100%, and dried ink adhering to the nozzle surface of the printhead sample was completely removed. Furthermore, in all cleaning units of Examples 1-6, good drying inhibition performance of the cleaning solution by the flexible porous material was obtained. Moreover, from the drying inhibition rates of the cleaning units of Examples 1-6, it was observed that the higher the vapor pressure of the water-soluble organic solvent contained in the cleaning solution, the better the drying inhibition effect of the flexible porous material tended to be.

[0053] On the other hand, in Comparative Examples 1 and 2, the removal rate was 0%, meaning that dried ink residue adhering to the nozzle surface of the printhead sample could not be removed. This is thought to be because, in Comparative Example 1, the high surface tension prevented the cleaning solution from penetrating between the nozzle surface and the dried ink residue. In Comparative Example 2, the high viscosity of the cleaning solution prevented effective penetration between the nozzle surface and the dried ink residue. Furthermore, the cleaning unit in Comparative Example 1 showed little drying inhibition of the cleaning solution by the flexible porous material. This is thought to be because, in the cleaning unit in Comparative Example 1, the static surface tension of the cleaning solution was high, resulting in low affinity of the cleaning solution to the flexible porous material. Conversely, the cleaning unit in Comparative Example 2 showed a significant drying inhibition effect of the cleaning solution by the flexible porous material. This is thought to be because, in the cleaning unit in Comparative Example 2, the static surface tension of the cleaning solution was low, resulting in high affinity of the cleaning solution to the flexible porous material.

[0054] [Table 1] [Explanation of Symbols]

[0055] U... Washing Unit P…Flexible porous body L... Cleaning solution B...Blade 10…Inkjet head 11…Nozzle 12…Nozzle surface

Claims

1. A cleaning unit for cleaning the nozzle surface of an inkjet head, Flexible porous material and A washing solution containing a water-soluble organic solvent impregnated into the flexible porous body, having a viscosity of 7 mPa·s or less at 25°C, a static surface tension of 40 mN / m or less at 25°C, and present in an amount of 10% to 60% by mass of the water-soluble organic solvent, wherein the vapor pressure of the water-soluble organic solvent at 25°C is lower than that of water, A cleaning unit equipped with the following.

2. A cleaning unit according to claim 1, The vapor pressure of the aforementioned water-soluble organic solvent at 25°C is 2.5 kPa or less. Washing unit.

3. A cleaning unit comprising a flexible porous body and a cleaning solution impregnated into the flexible porous body, having a viscosity of 7 mPa·s or less at 25°C, containing 10% by mass or more of a water-soluble organic solvent, the water-soluble organic solvent having a vapor pressure lower than that of water at 25°C, and holding the nozzle surface of an inkjet head pressed into the flexible porous body for a predetermined time; A wiping step is performed after the immersion step, in which the nozzle surface is wiped with a wiping member. A cleaning method that includes [details omitted].

4. A cleaning method according to claim 3, The wiping member is a blade. Cleaning method.

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