Maintenance Liquid Set and Maintenance Method

Abstract

To provide a maintenance liquid and maintenance method which can eliminate discharge failure of an ultraviolet curable ink jet printer.SOLUTION: A maintenance liquid is a maintenance liquid for an ultraviolet curable ink jet printer, and contains a first composition which can dissolve a water-soluble compound and does not dissolve a cured product of the ultraviolet curable ink. A maintenance method is a maintenance method of the ultraviolet curable ink jet printer, and includes a first cleaning process S3 in which the water-soluble compound adhering to an ink jet head included in the ultraviolet curable ink jet printer is dissolved with a first maintenance liquid containing the first composition which can dissolve the water-soluble compound and does not dissolve the cured product of the ultraviolet curable ink, and a second cleaning process S1 in which the ink jet head is cleaned with a second maintenance liquid containing a second composition which does not dissolve the water-soluble compound and can dissolve the cured product of the ultraviolet curable ink.SELECTED DRAWING: Figure 16

Description

Technical Field

[0001] The present invention , me relates to a maintenance liquid set and a maintenance method.

Background Art

[0002] An ultraviolet curable inkjet printer has features such as hardly generating volatile organic compounds (VOCs), not requiring a drying time after printing, and having excellent light resistance, and thus development is in progress. In an ultraviolet curable inkjet printer, in order not to require a drying time after printing, ultraviolet curing is performed immediately after the ultraviolet curable ink is ejected from the head nozzle. However, when curing is performed in this way, ink ejection failure may occur.

[0003] As a cause of ejection failure, due to the influence of stray light generated outside the originally assumed optical path, ultraviolet rays irradiate the ink near the head nozzle and the ink hardens, an ink hardened product is formed on the head nozzle, or foreign matter enters the head nozzle, resulting in nozzle clogging.

[0004] In order to prevent such nozzle clogging, maintenance of the printer head is performed in an ultraviolet curable inkjet printer.

[0005] As a maintenance method for an ultraviolet curable inkjet printer, there is a method of periodically cleaning the periphery of the printer head and the nozzles of the printer head with the ink itself or a maintenance liquid having a high affinity with the ink, and removing foreign matter that causes problems from the nozzles in advance.

[0006] As such a maintenance method, Patent Document 1 describes a method of cleaning the nozzles of an inkjet head of an ultraviolet-curing inkjet printer with a cleaning liquid containing an alkylene glycol derivative. Further, Patent Document 1 exemplifies an organic solvent commonly used as a solvent for ink, such as an alkylene glycol derivative, as the cleaning liquid.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, regarding nozzle clogging in an ultraviolet-curing inkjet printer, there were cases where nozzle clogging was not eliminated even when nozzle cleaning was performed using an organic solvent commonly used as a solvent for ink as the cleaning liquid.

[0009] Further, since ultraviolet-curing ink instantaneously progresses the reaction by a photopolymerization reaction to form a cured film after application, most of the composition is occupied by hydrophobic monomolecular monomers. Therefore, ultraviolet-curing ink has poor affinity with moisture and may form foreign substances when used in a high-humidity environment such as in summer. Particularly in the case of a printer using ultraviolet-curing ink, this foreign substance is likely to develop into nozzle clogging and cause ejection failure.

[0010] The present invention has been made in view of the above, and an object of the present invention is to provide a maintenance liquid and a maintenance method for eliminating ejection failure of an ultraviolet-curing inkjet printer.

Means for Solving the Problems

[0011] The inventors of the present invention studied the above problems and found that flight deviation is likely to occur at the nozzles of UV primers (ultraviolet curable primers), and even when nozzle cleaning is performed with a normal cleaning liquid, the flight deviation cannot be eliminated. It was also found that the flight deviation is eliminated when the head of the nozzle is replaced. Therefore, when the inventors of the present invention observed the head in detail, they observed that a large number of transparent crystalline foreign substances were attached to the wall surface of the nozzle holes of the head.

[0012] When this foreign substance was subjected to elemental analysis, it was found to be a hydrocarbon-based foreign substance containing phosphorus, the metal components of the head, and light elements. From this analysis, it was estimated that the foreign substance was generated by the reaction of the acid monomer contained in the UV primer and the polymerization initiator containing phosphorus as a constituent element with humidity as a trigger. In addition, when the physical properties of this foreign substance were examined, it was found that it dissolves in water but is difficult to dissolve in solvents, and it is difficult to remove with conventional maintenance liquids such as diethylene glycol monoethyl ether acetate, which has an affinity for ultraviolet curable inks and has been used as a maintenance liquid for ultraviolet curable inkjet printers.

[0013] The inventors of the present invention further studied, found a compound that dissolves the above foreign substance and does not adversely affect the ink to be used, and studied a maintenance liquid and a maintenance method using the same, and thus completed the present invention.

[0014] That is, the maintenance liquid according to the first aspect of the present invention is a maintenance liquid for an ultraviolet curable inkjet printer, containing a first component that is soluble in a water-soluble compound and insoluble in the cured product of the ultraviolet curable ink.

[0015] The maintenance liquid having the above configuration can eliminate ejection defects of an ultraviolet curable inkjet printer.

[0016] The ultraviolet curable ink contains an acidic monomer and an initiator, Preferably, the water-soluble compound is a compound derived from the acidic monomer, the initiator, and water.

[0017] The maintenance liquid having the above configuration is effective in eliminating the ejection failure of the primer ink.

[0018] Preferably, a phosphorus-based initiator is used as the initiator.

[0019] The maintenance liquid having the above configuration is particularly effective in eliminating the ejection failure of the primer ink containing a phosphorus-based initiator as the initiator.

[0020] Preferably, the first component is diethylene glycol.

[0021] The maintenance liquid having the above configuration has less influence on the ink.

[0022] Preferably, the maintenance liquid further contains a second component that is insoluble in the water-soluble compound and soluble in the cured product of the ultraviolet curable ink.

[0023] The maintenance liquid having the above configuration can remove the cured product of the ultraviolet curable ink and the water-soluble compound with a single liquid.

[0024] The maintenance method according to the second aspect of the present invention is A maintenance method for an ultraviolet curable inkjet printer, A first cleaning step of dissolving a water-soluble compound adhering to an inkjet head provided in the ultraviolet curable inkjet printer with a first maintenance liquid containing a first component that is soluble in the water-soluble compound and insoluble in the cured product of the ultraviolet curable ink; A second cleaning step of cleaning the inkjet head with a second maintenance liquid containing a second component that is insoluble in the water-soluble compound and soluble in the cured product of the ultraviolet curable ink; including.

[0025] The maintenance method with the above configuration can eliminate ejection defects of an ultraviolet curable inkjet printer.

[0026] The ultraviolet curable ink contains an acidic monomer and an initiator. Preferably, the water-soluble compound is a compound derived from the acidic monomer, the initiator, and moisture.

[0027] The maintenance method with the above configuration is effective in eliminating ejection defects of primer ink.

[0028] Preferably, the initiator is a phosphorus-based initiator.

[0029] The maintenance method with the above configuration is particularly effective in eliminating ejection defects of primer ink containing a phosphorus-based initiator as an initiator.

[0030] Preferably, the first component is diethylene glycol and the second component is diethylene glycol monoethyl ether acetate.

[0031] The maintenance method with the above configuration has less influence on the ink.

Effect of the Invention

[0032] According to the maintenance liquid of the present invention, ejection defects of an ultraviolet curable inkjet printer can be eliminated.

Brief Description of the Drawings

[0033]

Figure 1

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Figure 16

[0034] (Maintenance liquid) The maintenance liquid of an embodiment of the present invention is a maintenance liquid for an ultraviolet curable inkjet printer, containing a first component that is soluble in a water-soluble compound and insoluble in a cured product of an ultraviolet curable ink.

[0035] The water-soluble compound according to the present invention is a water-soluble compound, for example, a crystalline solid generated in the nozzles of an inkjet head due to the influence of humidity or the like when using an ultraviolet curable inkjet printer. This water-soluble compound is likely to occur when an acidic monomer is contained in the ultraviolet curable ink. This water-soluble compound is derived from an acidic monomer and an initiator (for example, a phosphorus-based initiator) contained in the ultraviolet curable ink, and may contain a metal contained in the constituent material of the inkjet head.

[0036] (Ultraviolet curable ink) The ultraviolet curable ink containing an acidic monomer is used, for example, as a primer ink and further contains an initiator. The primer ink is used, for example, when the substrate is difficult to adhere to ordinary ultraviolet curable inks such as resin, metal, and glass, and is used when improving the adhesion of other ultraviolet curable inks.

[0037] Examples of the acidic monomer include monomers containing a COOH group. Specifically, acrylic acid, methacrylic acid, 2-(trifluoromethyl)acrylic acid, ω-carboxy-polycaprolactone (n≈2) monoacrylate, phthalic acid mono-hydroxyethyl acrylate, polybasic acid-modified acrylic oligomer, etc. can be mentioned. Among them, ω-carboxy-polycaprolactone (n≈2) monoacrylate is preferred.

[0038] These monomers containing a COOH group can use, for example, monofunctional acrylates M-5300 (ω-carboxy-polycaprolactone (n≈2) monoacrylate), M-5400 (phthalic acid mono-hydroxyethyl acrylate), M-510 (polybasic acid-modified acrylic oligomer), M-520 (polybasic acid-modified acrylic oligomer), etc. manufactured by Toagosei Co., Ltd.

[0039] As the initiator contained in the ultraviolet curable ink containing an acidic monomer, there is no particular limitation as long as the ultraviolet curable ink can be cured by ultraviolet rays. For example, phosphorus-based initiators can be mentioned.

[0040] Examples of the phosphorus-based initiator include phosphine oxide-based initiators. The phosphine oxide-based initiator is a phosphine oxide compound represented by the following formula (1).

Chemical formula

[0041] Specifically, examples of R 1 , R 2 , R 3 include a phenyl group, an acyl group, etc., each independently.

[0042] More specifically, as the phosphine oxide-based initiator, 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide represented by the following formula (2),

Chemical formula

[0043] and acylphosphine oxide-based photoinitiators such as Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide represented by the following formula (3) can be mentioned.

Chemical formula

[0044] The initiator is preferably a phosphorus-based initiator, more preferably a phosphine oxide-based initiator, still more preferably an acylphosphine oxide-based photoinitiator, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide are particularly preferred.

[0045] As the initiator, for example, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (trade name: Omnirad TPO H (former BASF trade name: Irgacure TPO)) and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name: Omnirad 819 (former BASF trade name: Irgacure 819)) manufactured by IGM Resins can be used. The initiator can be used alone or in combination of multiple types.

[0046] The ultraviolet curable ink can further contain monomers other than acidic monomers. Examples of monomers other than acidic monomers include monomers obtained by esterifying the COOH group of (meth)acrylate.

[0047] Examples of acrylates other than acidic monomers include monofunctional acrylates, difunctional acrylates, polyfunctional acrylates, and the like.

[0048] Examples of monofunctional acrylates include phenol EO-modified acrylate, nonylphenol EO-modified acrylate, ethoxydiethylene glycol acrylate, etc. Examples of difunctional acrylates include hexanediol diacrylate, hexanediol EO-modified diacrylate, hydroxypivalic acid neopentyl glycol diacrylate, neopentyl glycol PO-modified diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, bisphenol A EO-modified diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, etc. Examples of polyfunctional acrylates include trimethylolpropane triacrylate, trimethylolpropane EO-modified triacrylate, trimethylolpropane PO-modified triacrylate, glycerin propoxytriacrylate, pentaerythritol triacrylate, pentaerythritol EO-modified tetraacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexaacrylate, etc.

[0049] These monomers can be used alone or in combination of two or more.

[0050] Examples of monofunctional acrylates that can be used include phenol EO-modified (n = 2) acrylate (trade name; Miramer M142), phenol EO-modified (n = 4) acrylate (trade name; Miramer M144), nonylphenol EO-modified (n = 8) acrylate (trade name; Miramer M166), ethoxydiethylene glycol acrylate (trade name; Miramer M170), etc., manufactured by Misumi Specialty Chemical Co., Ltd.

[0051] As the difunctional acrylate, hexanediol diacrylate (trade name: Miramer M200), hexanediol EO-modified diacrylate (trade name: Miramer M202), hydroxypivalic acid neopentyl glycol diacrylate (trade name: Miramer M210), neopentyl glycol PO-modified (n = 2) diacrylate (trade name: Miramer M216), tripropylene glycol diacrylate (trade name: Miramer M220), dipropylene glycol diacrylate (trade name: Miramer M222), bisphenol A EO-modified (n = 4) diacrylate (trade name: Mirmaer M240), bisphenol A EO-modified (n = 10) diacrylate (trade name: Miramer M2100), polyethylene glycol (molecular weight 400) diacrylate (abbreviation: PEG400DA, trade name: Miramer M280), polyethylene glycol (molecular weight 300) diacrylate (abbreviation: PEG300DA, trade name: Miramer M284), polypropylene glycol diacrylate (trade name: Miramer M2040), etc. manufactured by Beauty Source Specialty Chemical Co., Ltd. can be used.

[0052] Examples of the polyfunctional acrylate include trimethylolpropane triacrylate (trade name: Miramer M300), trimethylolpropane EO-modified (n = 3) triacrylate (trade name: Miramer M3130), trimethylolpropane EO-modified (n = 6) triacrylate (trade name: Miramer M3160), trimethylolpropane EO-modified (n = 9) triacrylate (trade name: Miramer M3190), trimethylolpropane PO-modified (n = 3) triacrylate (trade name: Miramer M360), glycerin propoxytriacrylate (trade name: Miramer M320), pentaerythritol triacrylate (trade name: Miramer M340), pentaerythritol EO-modified tetraacrylate (trade name: Miramer M4004), ditrimethylolpropane tetraacrylate (trade name: Miramer M410), dipentaerythritol hexaacrylate (trade name: Miramer M600), etc. manufactured by Beauty Source Specialty Chemical Co., Ltd.

[0053] (First component) The first component according to the present invention is a component that is soluble in the aforementioned water-soluble compound and insoluble in the cured product of the ultraviolet-curable ink. Here, the cured product of the ultraviolet-curable ink is a solid obtained by polymerizing the ultraviolet-curable ink by ultraviolet rays.

[0054] As the first component, for example, diols such as ethylene glycol are preferable.

[0055] As will be described later, since the maintenance liquid containing the first component is used for an inkjet head provided in an ultraviolet-curable inkjet printer, it is desirable that the first component does not have an adverse effect on the ultraviolet-curable ink after use. For example, components that are inert to the ultraviolet-curable ink, components that are easy to remove the maintenance liquid after use for maintenance, and components with high safety are preferable. As such a first component, diols with a small molecular weight are preferable, and diethylene glycol is particularly preferable.

[0056] The content rate of the first component in the maintenance liquid is not particularly limited, but it is preferably 1% by mass or more and 100% by mass or less, more preferably 50% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less. The water content of the maintenance liquid is preferably low from the viewpoint of the influence on the ultraviolet curable ink. Specifically, it is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less.

[0057] (Second component) The maintenance liquid can further contain a second component that is insoluble in the water-soluble compound and soluble in the cured product of the ultraviolet curable ink.

[0058] The second component can be further contained in the maintenance liquid containing the first component as described above, but it can also be contained in a maintenance liquid different from the maintenance liquid containing the first component and used in combination with the maintenance liquid containing the first component.

[0059] As such a second component, for example, components used in the maintenance liquid of a conventional ultraviolet curable inkjet printer can be used. By containing the second component in the maintenance liquid, it is possible to remove stains caused by color materials on the inkjet head and cured products obtained by curing the ultraviolet curable ink due to stray light.

[0060] Examples of the second component include alcohols different from the first component. Specifically, diethylene glycol monoethyl ether acetate and the like can be mentioned. The content rate of the first component in the maintenance liquid is not particularly limited, but it is preferably 1% by mass or more and less than 100% by mass, and more preferably 10% by mass or more and 90% by mass or less.

[0061] (Maintenance method) Next, an embodiment of a maintenance method for an ultraviolet-curable inkjet printer 10 using the above-described maintenance liquid will be described with reference to the drawings.

[0062] (Schematic Configuration of Ultraviolet-Curable Inkjet Printer 10) As shown in FIG. 1, the ultraviolet-curable inkjet printer 10 includes a printer main body 11, a conveyance device 12, and a gantry 13. The inkjet printer 10 is configured to be able to print an image on a medium (paper, plastic, etc.) M by an inkjet method.

[0063] The printer main body 11 is a part for printing an image and is supported by the gantry 13 together with the conveyance device 12. The conveyance device 12 conveys the medium M from the rear to the front along the sub-scanning direction (front-rear direction), for example, by rollers. The printer main body 11 includes a first head unit 100 and a second head unit 200 configured to eject ink onto the medium M by an inkjet method. The first head unit 100 and the second head unit 200 are mounted on a carriage (not shown) that is movable in the main scanning direction, and move along the main scanning direction by the movement of the carriage. The printer main body 11 also includes a control unit 11A that controls the operation of the inkjet printer 10. Further, although details will be described later, the printer main body 11 also includes a maintenance mechanism 500 (FIG. 5 etc., not shown in FIG. 1) for maintaining (cleaning) the first head unit 100 and the second head unit 200.

[0064] In the ultraviolet-curable inkjet printer 10, a step of ejecting ink while the first head unit 100 and the second head unit 200 move along the main scanning direction and irradiating ultraviolet rays to cure the ink, and a step of the conveyance device 12 moving the medium M along the sub-scanning direction are repeatedly performed. These steps are executed under the control of the control unit 11A. By repeatedly performing these steps, an image is formed (printed) on the medium M by the ejected ink.

[0065] (First head unit 100 and second head unit 200) As shown in FIG. 2(A), the first head unit 100 includes a first sub-tank 110 and a first inkjet head 120. The first sub-tank 110 is disposed above the first inkjet head 120.

[0066] The first sub-tank 110 stores primer ink (hereinafter also referred to as primer ink). The first inkjet head 120 discharges the primer ink supplied from the first sub-tank 110. The first inkjet head 120 is of a piezo type or a thermal type and discharges ink in the form of droplets.

[0067] As shown in FIG. 2(B), the second head unit 200 includes a second-1 sub-tank 210, a second-2 sub-tank 220, a second-3 sub-tank 230, a second-4 sub-tank 240, and a second inkjet head 250. The second-1 sub-tank 210, the second-2 sub-tank 220, the second-3 sub-tank 230, and the second-4 sub-tank 240 are disposed above the second inkjet head 250.

[0068] The second-1 sub-tank 210 stores Y (yellow) ink (hereinafter also referred to as yellow ink). The second-2 sub-tank 220 stores C (cyan) ink (hereinafter also referred to as cyan ink). The second-3 sub-tank 230 stores M (magenta) ink (hereinafter also referred to as magenta ink). The second-4 sub-tank 240 stores K (key plate, here black) ink (hereinafter also referred to as black ink). The second inkjet head 250 individually discharges the yellow ink, cyan ink, magenta ink, and black ink supplied from the second-1 sub-tank 210, the second-2 sub-tank 220, the second-3 sub-tank 230, and the second-4 sub-tank 240. The second inkjet head 250 is of a thermal type or a piezo type and discharges ink in the form of droplets.

[0069] (Ink supply mechanism) The printer main body 11 also has an ink supply mechanism (not shown) that supplies ink to the first sub-tank 110, the second-1 sub-tank 210, the second-2 sub-tank 220, the second-3 sub-tank 230, and the second-4 sub-tank 240, respectively.

[0070] A liquid level sensor (not shown) for detecting the liquid level of ink is provided in each of the five sub-tanks. The control unit 11A individually controls each pump (not shown) of the ink supply mechanism based on the signal from the liquid level sensor so that each of the five sub-tanks is filled with a certain amount or more of ink. For example, when the liquid level sensor detects that the liquid level of the ink stored in the first sub-tank 110 has dropped below a predetermined position, the control unit 11A drives the pump and controls the supply of primer ink from the bottle tank to the first sub-tank 110.

[0071] Since ink is always stored in the five sub-tanks, the ink supply path from the sub-tank to the ink discharge port of the first ink jet head 120 or the second ink jet head 250 is filled with ink. When positive pressure is supplied to the sub-tank, the ink in the sub-tank is pushed and ink is discharged (purged) from the discharge port of the first ink jet head 120 or the second ink jet head 250. For example, when positive pressure is supplied to the first sub-tank 110, primer ink is discharged from the primer ink discharge port 121A (FIG. 4) of the first ink jet head 120.

[0072] (Discharge part of the first ink jet head 120 and the second ink jet head 250) As shown in FIGS. 3(A) and (B), the lower part of the ink jet head 120 is a discharge part for discharging primer ink. The discharge part of the first ink jet head 120 has, in addition to a plurality of discharge nozzles 121, a downward-facing lower surface 123 and a convex part 124 protruding from the lower surface 123.

[0073] The plurality of ejection nozzles 121 are provided so as to pass through the convex portion 124. The plurality of ejection nozzles 121 are arranged along the sub-scanning direction, and each can independently eject primer ink.

[0074] The lower surface 123 forms the lower surface of the first inkjet head 120 and is also the area around the convex portion 124.

[0075] The convex portion 124 is long in the sub-scanning direction, and the short cross-section cut along the main scanning direction is formed in a frustum shape of a quadrangular pyramid with a trapezoidal shape.

[0076] The convex portion 124 has a discharge surface 124A (the lowermost surface, corresponding to the upper surface of the frustum of a quadrangular pyramid) which is a downward-facing lower surface. On the discharge surface 124A, an opening below the ejection nozzle 121, that is, a discharge port 121A for primer ink, is provided.

[0077] When printing is repeated by ejecting primer ink, as shown in FIG. 4, a water-soluble compound L1 is generated in the vicinity of the discharge port 121A, which may cause clogging.

[0078] (Maintenance mechanism 500) The maintenance mechanism 500 provided in the printer main body 11 is a mechanism that performs maintenance to prevent clogging of the ejection nozzles 121 of the first inkjet head 120. When the first head unit 100 and the second head unit 200 are in the standby position, maintenance is performed at an appropriate timing.

[0079] As shown in FIG. 5, the maintenance mechanism 500 includes a head cap 510, a first drive mechanism 520, a suction device 530, a wiping blade 540, and a second drive mechanism 550. As will be described later, the control unit 11A raises and lowers the head cap 510 by the first drive mechanism 520, sucks ink from the suction device 530 by the suction device 530, and drives the wiping blade 540 by the second drive mechanism 550. The maintenance mechanism 500 is provided for the first inkjet head 120. Here, the one for the first inkjet head 120 will be described.

[0080] As shown in FIGS. 6(A) and 6(B), during maintenance, the head cap 510 is mounted (here, brought into contact) on the first inkjet head 120 by a first drive mechanism 520 (not shown), and covers the ejection surface 124A of the convex portion 124. The head cap 510 has a concave portion 511 for storing a maintenance liquid. The concave portion 511 is formed in a shape corresponding to the convex portion 124 and is long in the sub-scanning direction. When the head cap 510 is mounted on the first inkjet head 120, the concave portion 511 accommodates and covers the convex portion 124, the ejection surface 124A, and the ejection port 121A.

[0081] The head cap 510 includes a bottom portion 512 and side walls 513 extending upward from the bottom portion 512. The side walls 513 are square when viewed from above.

[0082] The bottom portion 512 has a through hole (not shown) at the center. The through hole is for discharging the maintenance liquid stored in the concave portion 511 during a purge described later. A plurality of through holes may be provided.

[0083] The upper end portion of the side wall 513 of the head cap 510, that is, the portion that contacts the convex portion 124, is preferably formed of an elastic body such as rubber or synthetic resin so as to have elasticity, or formed by covering a metal or the like with an elastic body.

[0084] Maintenance is performed on the first inkjet head 120 and the second inkjet head 250. Since both can perform the same operations, the maintenance of the first inkjet head 120 will be described below.

[0085] (Attachment of the head cap 510) At the start of maintenance, the control unit 11A moves the head cap 510 upward by the first drive mechanism 520, presses the head cap 510 against the first inkjet head 120, and makes them contact (attach). Figures 6(A) and (B) show this contact state. The inclined surface of the convex portion 124 of the first inkjet head 120 and the inclined surface of the side wall 513 of the head cap 510 are adjusted in terms of the inclination angle and the like, and the inclined surface 124 and the inclined surface of the side wall 513 are in contact with each other.

[0086] (Maintenance by purging) First, maintenance by purging, which is normal maintenance, will be described. After attaching the head cap 510, the control unit 11A performs purging. Specifically, the control unit 11A controls a pneumatic circuit (not shown) and supplies a positive pressure to the first sub-tank 110 for a predetermined time. As a result, primer ink is discharged from a plurality of ejection nozzles 121 (ejection ports 121A) of the first inkjet head 120. At this time, the control unit 11A closes the valve 532 of the suction device 530. Therefore, the recess 511 of the head cap 510 is filled with primer ink.

[0087] (Ink suction) Thereafter, the control unit 11A controls the valve 532 to open and controls the pump 533 connected via the valve 532 and the pipe 531 to operate. As a result, the suction device 530 sucks the primer ink in the recess 511 and discharges it to the waste liquid tank 534. Note that the ink in the recess 511 may not be completely removed, and ink may adhere to and remain on the ejection surface 124A.

[0088] (Wiping) Thereafter, the control unit 11A controls the second drive mechanism 550 to move the wiping blade 540 in the sub-scanning direction while bringing it into contact with the ejection surface 124A. As a result, the ink adhering to the ejection surface 124A can be wiped off from the ejection surface 124A all at once.

[0089] (Maintenance with normal maintenance liquid) In some cases, nozzle clogging may not be resolved by the maintenance by the above purge. For example, this is the case when a cured product of ultraviolet curable ink adheres. In this case, maintenance is performed with a second maintenance liquid (normal maintenance liquid). This will be described below.

[0090] First, the control unit 11A closes the valve 532 of the head cap 510. Next, the recess 511 is filled with the second maintenance liquid. The filling of the maintenance liquid can be performed manually by the operator, or a tank for the second maintenance liquid can be provided in the maintenance mechanism 500 and filled by the control unit 11A.

[0091] Next, the control unit 11A moves the head cap 510 upward by the first drive mechanism 520, presses the head cap 510 against the first inkjet head 120, and brings them into contact (mounts). As a result, the recess 511, the convex portion 124, the ejection surface 124A, and the ejection port 121A are immersed in the second maintenance liquid. After immersion, the immersion is continued for a certain period (for example, 1 minute). The second maintenance liquid dissolves the cured product of the ultraviolet curable ink.

[0092] Thereafter, the valve 532 is controlled to open and the pump 533 is controlled to operate. As a result, the suction device 530 sucks the second maintenance liquid in the recess 511 that has dissolved the cured product of the ultraviolet curable ink and discharges it to the waste liquid tank 534. If the maintenance liquid adheres to and remains on the ejection surface 124A, the wiping described above can be performed.

[0093] (Maintenance with the first maintenance liquid) In some cases, nozzle clogging may not be resolved by the maintenance using the purge and the maintenance using the second maintenance liquid. This is the case when a water-soluble compound is attached. The second maintenance liquid cannot dissolve the water-soluble compound. In this case, maintenance is performed using the first maintenance liquid. The operation can be performed in the same manner as the maintenance using the second maintenance liquid.

[0094] Maintenance using the first maintenance liquid can be manually performed by the operator, including filling the first maintenance liquid, or can also be performed by the control unit 11A by providing a tank for the second maintenance liquid in the maintenance mechanism 500.

[0095] As described above, by combining the maintenance using the first maintenance liquid, the maintenance using the second maintenance liquid, and, if necessary, the maintenance using the purge, it is possible to remove stains of the ultraviolet curable ink, adhesion of the cured product of the ultraviolet curable ink, and adhesion of the water-soluble compound, and to eliminate ejection failures of the ultraviolet curable inkjet printer 10.

[0096] FIG. 16 shows a flowchart of a maintenance method according to an embodiment of the present invention. In this maintenance method, first, the cured ink around the head is removed with the second maintenance liquid (step S1). In addition to the head cap of the ultraviolet curable primer, the cured ink of the head cap of the color ink can also be removed. If there are foreign matters that cannot be removed with the second maintenance liquid, the next step is performed.

[0097] First, fill the head cap of the ultraviolet curable primer ink with the first maintenance liquid (step S2). Next, bring the first maintenance liquid into contact with the nozzles of the ultraviolet curable primer ink to perform nozzle cleaning (step S3). Water-soluble foreign matters dissolve in the first maintenance liquid. Next, flush and discharge the first maintenance liquid in the nozzles by nozzle cleaning (step S4). Next, check the state of the nozzles by test drawing (step S5). If it is determined that there is no abnormality in the state of the nozzles, the maintenance is terminated. If there is an abnormality, the maintenance is performed again or the nozzles are replaced.

[0098] (Example) Hereinafter, the present invention will be described based on examples, but the present invention is not limited to these examples. The evaluation was performed using the following method.

[0099] (Evaluation of Water-soluble Foreign Matter Removal Performance of Maintenance Liquid) As the ink, an ultraviolet curable ink (manufactured by Mimaki Engineering Co., Ltd., product number: PR-200) containing an acrylic oligomer of an acid monomer and a phosphorus-based initiator as a photopolymerization initiator was used. Printing was repeated with an inkjet printer (manufactured by Mimaki Engineering Co., Ltd., product number: UJF30 / 6042-MkII). The nozzle plate of the head of the inkjet printer in which flight deviation occurred during printing was taken out, and it was confirmed that transparent crystalline foreign matters adhered to the wall surface of the nozzle holes. PR-200 contains 40% by mass or more and 50% by mass or less of an aliphatic monomer, 25% by mass or more and 35% by mass or less of an acrylic oligomer, 15% by mass or more and 25% by mass or less of an aromatic monomer, 0.01% by mass or more and less than 10% by mass of a photopolymerization initiator, and 0.01% by mass or more and 0.2% by mass or less of 2,6-di-tert-butyl-p-cresol. Next, the maintenance liquid is dropped onto the nozzle plate. After removing the maintenance liquid with hexane after 1 minute, the nozzle holes are observed with a microscope to observe the state of dissolution of the foreign matters. The solubility of foreign matters in each maintenance liquid was evaluated in the following three stages in comparison with water. ×: The foreign matter was not dissolved and could not be removed. △: Although the foreign matter was considered to be dissolved, its solubility was lower than that of water and the foreign matter remained. ○: The foreign matter was dissolved at the same level as water and the foreign matter was removed.

[0100] (Primer Ink Affinity Evaluation of Maintenance Liquid) The maintenance liquid and the ultraviolet curable ink (manufactured by Mimaki Engineering Co., Ltd., product number; PR-200) were mixed at a ratio of 1:1, and the change of the ink was observed. The affinity of the maintenance liquid with the primer ink was evaluated according to the following criteria. 〇: No foreign matter was generated. ×: Foreign matter was generated.

[0101] (Safety Evaluation of Maintenance Liquid) Assuming the actual use environment of the printer, the safety during handling was evaluated according to the following criteria in terms of the influence of the maintenance liquid on the human body and storage stability. 〇: There were no particular problems with safety. △: There were some problems with safety. ×: There were major problems with safety.

[0102] (Example 1) Diethylene glycol was used as the maintenance liquid E1 for an ultraviolet curable inkjet printer, and the water-soluble foreign matter removal performance was evaluated. Microscopic images (500 times magnification) before dropping the maintenance liquid on the nozzle plate with foreign matter and after removing it with hexane 1 minute after dropping are shown in FIGS. 7 and 8. It can be seen from FIG. 8 that the foreign matter in the nozzle hole was dissolved. The evaluation of the water-soluble foreign matter removal performance is shown in Table 1. In addition, the ink affinity of the maintenance liquid E1 was evaluated. There was no change in the ink performance, and it was excellent in ink affinity. In addition, the affinity evaluation and safety evaluation of the maintenance liquid E1 with the primer ink were carried out. The results are shown in Table 1. In addition, in the evaluation of the water-soluble foreign matter removal performance, a photograph of a test drawing with flight deviation is printed in Fig. 14, and a photograph of a test drawing printed after nozzle cleaning with maintenance liquid E1 for 1 minute is shown in Fig. 15. In the pattern of the first column from the left surrounded by the black line in Fig. 14, it is possible to observe parts where the discharge lines (horizontal lines) vary in the front-back, left-right directions, and parts where the horizontal lines are missing. It is presumed that the nozzles corresponding to the parts where the discharge lines vary in the front-back, left-right directions are dirty, and the nozzles corresponding to the parts where the discharge lines are missing are clogged with foreign matter. On the other hand, in Fig. 15, the patterns of the parts surrounded by the black line are equally spaced and normalized. From this, it can be seen that nozzle cleaning with maintenance liquid E1 eliminates nozzle dirt and clogging, and also that maintenance liquid E1 has no adverse effect on the ink.

[0103] (Example 2) Using methanol instead of diethylene glycol, in the same manner as in Example 1, the evaluation of the water-soluble foreign matter removal performance of the maintenance liquid, the evaluation of the affinity with the primer ink, and the safety evaluation were performed. The results are shown in Table 1. Also, Fig. 9 shows the microscopic images (500 times magnification) before dropping the maintenance liquid and after removing it with hexane 1 minute after dropping.

[0104] (Example 3) Using chloroform instead of diethylene glycol, in the same manner as in Example 1, the evaluation of the water-soluble foreign matter removal performance of the maintenance liquid, the evaluation of the affinity with the primer ink, and the safety evaluation were performed. The results are shown in Table 1. Also, Fig. 10 shows the microscopic images (500 times magnification) before dropping the maintenance liquid and after removing it with hexane 1 minute after dropping.

[0105] (Example 4) Using acetonitrile instead of diethylene glycol, in the same manner as in Example 1, the evaluation of the water-soluble foreign matter removal performance of the maintenance liquid, the evaluation of the affinity with the primer ink, and the safety evaluation were performed. The results are shown in Table 1. Also, Fig. 11 shows the microscopic images (500 times magnification) before dropping the maintenance liquid and after removing it with hexane 1 minute after dropping.

[0106] (Example 5) Instead of diethylene glycol, methyl ethyl ketone (abbreviation: MEK) was used, and in the same manner as in Example 1, the evaluation of the water-soluble foreign matter removal performance of the maintenance liquid, the evaluation of the affinity with the primer ink, and the safety evaluation were carried out. The results are shown in Table 1. Also, the microscopic images (500 times magnification) before dropping the maintenance liquid and after removing it with hexane 1 minute after dropping are shown in Fig. 12.

[0107] (Comparative Example 1) Instead of diethylene glycol, diethylene glycol monoethyl ether acetate was used, and in the same manner as in Example 1, the evaluation of the water-soluble foreign matter removal performance of the maintenance liquid, the evaluation of the affinity with the primer ink, and the safety evaluation were carried out. The water-soluble foreign matter did not dissolve. The results are shown in Table 1.

[0108] (Comparative Example 2) Instead of diethylene glycol, water was used, and in the same manner as in Example 1, the evaluation of the water-soluble foreign matter removal performance of the maintenance liquid, the evaluation of the affinity with the primer ink, and the safety evaluation were carried out. The water-soluble foreign matter dissolved. The results are shown in Table 1. Also, the microscopic images (500 times magnification) before dropping the maintenance liquid and after removing it with hexane 1 minute after dropping are shown in Fig. 13.

[0109] (Comparative Example 3) Instead of diethylene glycol, ethyl acetate was used, and in the same manner as in Example 1, the evaluation of the water-soluble foreign matter removal performance of the maintenance liquid, the evaluation of the affinity with the primer ink, and the safety evaluation were carried out. The water-soluble foreign matter did not dissolve. The results are shown in Table 1.

[0110] (Comparative Example 4) Instead of diethylene glycol, dimethyl sulfoxide (abbreviation: DMSO) was used, and in the same manner as in Example 1, the evaluation of the water-soluble foreign matter removal performance of the maintenance liquid, the evaluation of the affinity with the primer ink, and the safety evaluation were carried out. The water-soluble foreign matter did not dissolve. The results are shown in Table 1.

[0111] (Comparative Example 5) Instead of diethylene glycol, using γ-butyrolactone (abbreviation; GBL), in the same manner as in Example 1, the evaluation of the water-soluble foreign matter removal performance of the maintenance liquid, the evaluation of the affinity with the primer ink, and the safety evaluation were carried out. The water-soluble foreign matter did not dissolve. The results are shown in Table 1.

[0112] (Comparative Example 6) Instead of diethylene glycol, using N-methyl-2-pyrrolidone (abbreviation; NMP), in the same manner as in Example 1, the evaluation of the water-soluble foreign matter removal performance of the maintenance liquid, the evaluation of the affinity with the primer ink, and the safety evaluation were carried out. The water-soluble foreign matter did not dissolve. The results are shown in Table 1.

[0113] (Comparative Example 7) Instead of diethylene glycol, using polymethacrylate (abbreviation; PMA), in the same manner as in Example 1, the evaluation of the water-soluble foreign matter removal performance of the maintenance liquid, the evaluation of the affinity with the primer ink, and the safety evaluation were carried out. The water-soluble foreign matter did not dissolve. The results are shown in Table 1.

Table 1

[0114] The present invention can be implemented in various embodiments and modifications without departing from the broad spirit and scope of the present invention. Further, the above-described embodiments are for explaining the present invention and do not limit the scope of the present invention. That is, the scope of the present invention is shown not by the embodiments but by the claims. And various modifications made within the scope of the claims and within the scope of the meaning of the invention equivalent thereto are considered to be within the scope of this invention.

Explanation of Reference Numerals

[0115] 10 UV-curable inkjet printer 11 Printer main body 12 Conveyor device 13 Stand 100 First head unit 200 Second head unit M Media 11A Control Unit 110 First Sub - tank 120 First Inkjet Head 210 Second - 1 Sub - tank 220 Second - 2 Sub - tank 230 Second - 3 Sub - tank 240 Second - 4 Sub - tank 250 Second Inkjet Head 121 Discharge Nozzle 121A Discharge Port 123 Bottom Surface 124 Protrusion 124A Discharge Surface L1 Water - soluble Compound 500 Maintenance Mechanism 510 Head Cap 520 First Driving Mechanism 530 Suction Device 540 Wiping Blade 550 Second Driving Mechanism 511 Recess 512 Bottom 513 Side Wall 531 Pipe 532 Valve 533 Pump 534 Waste Liquid Tank

Claims

1. A maintenance liquid set for an ultraviolet-curing inkjet printer, comprising: a first maintenance liquid containing a component that dissolves a water-soluble compound attached to an inkjet head of the ultraviolet curable inkjet printer and that does not dissolve a cured product of the ultraviolet curable ink; a second maintenance liquid containing a second component that is insoluble in the water-soluble compound and is soluble in the cured product of the ultraviolet curable ink; A maintenance liquid set equipped with

2. A maintenance method for an ultraviolet curing inkjet printer, comprising the steps of: a first cleaning step of dissolving a water-soluble compound attached to an inkjet head of the ultraviolet-curable inkjet printer with a first maintenance liquid containing a first component that dissolves the water-soluble compound and does not dissolve a cured product of the ultraviolet-curable ink; a second cleaning step of cleaning the inkjet head with a second maintenance liquid containing a second component that is insoluble in the water-soluble compound and is soluble in the cured product of the ultraviolet curable ink; Maintenance methods including.

3. The ultraviolet curable ink contains an acidic monomer and an initiator, The maintenance method according to claim 2 , wherein the water-soluble compound is a compound derived from the acidic monomer, the initiator, and moisture.

4. The maintenance method according to claim 3 , wherein the initiator is a phosphorus-based initiator.

5. 5. The maintenance method according to claim 2, wherein the first component is diethylene glycol and the second component is diethylene glycol monoethyl ether acetate.

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