JP2018118384A - Inkjet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet printer capable of reducing waste of ink.SOLUTION: An inkjet printer 1 includes: an inkjet head which has a nozzle surface having an opened nozzle and a nozzle guard which covers the nozzle surface and has an opening formed to expose the nozzle; a wiper which is wetted with wiping liquid having a lower viscosity than ink, wipes the nozzle guard, and wipes the nozzle surface exposed by the opening of the nozzle guard by non-contact through the wiping liquid; and a control section 5 which controls wiping speed of the wiper according to water repellent speed on the nozzle surface of mixed liquid of the wiping liquid and the ink.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an ink jet printing apparatus that prints by discharging ink from an ink jet head onto a print medium.

  In an inkjet printing apparatus, it is known to clean an inkjet head by wiping the nozzle surface of the inkjet head with a wiper.

  In such an inkjet head cleaning, it is known to wipe the nozzle surface in a state where the wiper is wet with a wipe liquid (cleaning liquid) (see, for example, Patent Document 1). By this method, the inkjet head can be cleaned while suppressing damage to the nozzle surface.

JP 2014-159112 A

  However, if the nozzle surface is wiped with a wiper wet with the wipe liquid, the wipe liquid may enter the nozzle. If the wipe liquid enters the nozzles, there is a possibility that non-ejection of ink or a flying curve may occur.

  Therefore, after wiping with the wiper wetted with the wipe liquid, before printing, idle discharge (spit), which is a preliminary discharge operation for removing the wipe liquid from the nozzle, is performed. By performing idle ejection, normal ejection can be performed from the beginning during printing. However, ink is wasted due to idle ejection.

  The present invention has been made in view of the above, and an object thereof is to provide an ink jet printing apparatus capable of reducing waste of ink.

  In order to achieve the above object, a first feature of an ink jet printing apparatus according to the present invention is a nozzle surface on which a nozzle row is formed and an opening for exposing the nozzle row, covering the nozzle surface. An inkjet head having a nozzle guard formed with a portion, and a nozzle liquid that is wetted by a wipe liquid having a viscosity lower than that of the ink, wipes the nozzle guard, and is exposed to the opening through the wipe liquid. A wiper that wipes in a non-contact manner, and a water repellent speed of the mixed liquid that is a moving speed of the rear end of the mixed liquid when the mixed liquid of the wipe liquid and the ink follows the wiper and moves on the nozzle surface. And a control unit for controlling the wipe speed of the wiper.

  A second feature of the ink jet printing apparatus according to the present invention is that the control unit sets the wiping speed to a speed not less than the water repellency speed of the mixed liquid and not more than the water repellency speed of the wipe liquid alone.

  A third feature of the ink jet printing apparatus according to the present invention is that the ink jet printing apparatus further includes a wipe liquid tank that holds a wipe liquid that adheres to the wiper, and a heating unit that heats the wipe liquid in the wipe liquid tank. .

  According to the first feature of the inkjet printing apparatus according to the present invention, the wiper wipes the nozzle surface in a non-contact manner through the wipe liquid, so that the wiper can avoid pushing the wipe liquid into the nozzle. The control unit controls the wiper wipe speed in accordance with the water repellent speed on the nozzle surface of the liquid mixture of the wipe liquid and the ink. Thereby, it is possible to suppress the time that the liquid mixture stays on the nozzle surface and to prevent the liquid mixture from entering the nozzle. For this reason, it is possible to omit the idle ejection after cleaning the inkjet head and reduce the waste of ink.

  According to the second feature of the ink jet printing apparatus according to the present invention, the control unit sets the wipe speed to a speed not less than the water repellent speed of the mixed liquid and not more than the water repellent speed of the wipe liquid alone. As a result, the time for the liquid mixture to stay on the nozzle surface can be suppressed, the liquid mixture can be prevented from entering the nozzle, and the liquid mixture can be prevented from being broken during shearing by the shearing force and remaining on the nozzle surface. it can. As a result, it is possible to reduce the waste of ink by omitting the idle ejection after cleaning the inkjet head, to reduce the ink ejection failure that is not improved by the idle ejection, and to suppress the deterioration of the print image quality.

  According to the third feature of the ink jet printing apparatus according to the present invention, since the heating unit for heating the wipe liquid in the wipe liquid tank is provided, when the viscosity of the wipe liquid decreases, the viscosity is adjusted to increase. it can. As a result, it is possible to reduce the remaining of the liquid mixture on the nozzle surface during the wipe due to a shearing force due to an increase in the viscosity of the wipe liquid due to a change in environmental temperature or the like.

1 is an overall perspective view of an inkjet printing apparatus according to an embodiment. It is a front view which shows schematic structure of the inkjet printing apparatus shown in FIG. It is a perspective view of the inkjet head of the inkjet printing apparatus shown in FIG. It is sectional drawing along the AA line of FIG. It is a perspective view of the maintenance part of the inkjet printing apparatus shown in FIG. It is a side view of the maintenance part of the inkjet printing apparatus shown in FIG. It is a control block diagram of the inkjet printing apparatus shown in FIG. FIG. 6 is an explanatory diagram of an operation of wiping the inkjet head with a wiper. It is explanatory drawing of the behavior of the liquid mixture of the wipe liquid and ink at the time of a wipe. It is explanatory drawing of the shear force concerning the liquid mixture of a wipe liquid and an ink. It is explanatory drawing of the phenomenon in which the liquid mixture of a wipe liquid and an ink is drawn in in a nozzle. It is a figure which shows the experimental result of the cleaning of the inkjet head in the inkjet printing apparatus shown in FIG. It is a figure which shows the experimental result of a comparative example.

  Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same or equivalent parts and components are denoted by the same or equivalent reference numerals.

  The following embodiments exemplify devices for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, arrangement, etc. of each component. Is not specified as follows. The technical idea of the present invention can be variously modified within the scope of the claims.

  FIG. 1 is an overall perspective view of an ink jet printing apparatus according to an embodiment of the present invention. FIG. 2 is a front view illustrating a schematic configuration of the ink jet printing apparatus illustrated in FIG. 1. FIG. 3 is a perspective view of the ink jet head of the ink jet printing apparatus shown in FIG. 4 is a cross-sectional view taken along line AA in FIG. FIG. 5 is a perspective view of a maintenance unit of the inkjet printing apparatus shown in FIG. FIG. 6 is a side view of the maintenance unit. FIG. 7 is a control block diagram of the ink jet printing apparatus shown in FIG. In the following description, the vertical and horizontal directions indicated by the arrows in FIG.

  As shown in FIGS. 1, 2, and 7, the inkjet printing apparatus 1 according to the present embodiment includes a shuttle base unit 2, a flat bed unit 3, a shuttle unit 4, and a control unit 5.

  The shuttle base unit 2 supports the shuttle unit 4 and moves the shuttle unit 4 in the front-rear direction (sub-scanning direction). The shuttle base unit 2 includes a gantry 11 and a sub-scanning drive motor 12.

  The gantry 11 supports the shuttle unit 4. The gantry 11 is formed in a rectangular frame shape. Sub-scanning drive guides 13A and 13B extending in the front-rear direction are formed on the left and right frames of the gantry unit 11, respectively. The sub-scanning drive guides 13A and 13B guide the shuttle unit 4 to move in the front-rear direction.

  The sub-scanning drive motor 12 moves the shuttle unit 4 in the front-rear direction.

  The flat bed unit 3 holds a print medium 15 made of a base material such as a building material or a decorative panel. The flat bed unit 3 is disposed inside the gantry 11 of the shuttle base unit 2. The flat bed unit 3 has a medium placement surface 3a that is a horizontal surface on which the print medium 15 is placed. The flat bed unit 3 can adjust the height of the medium placement surface 3a by an elevating mechanism such as a hydraulic drive mechanism.

  The shuttle unit 4 prints an image on the print medium 15. The shuttle unit 4 includes a housing 21, a main scanning drive guide 22, a main scanning drive motor 23, a head lifting guide 24, a head lifting motor 25, a head unit 26, and a maintenance unit 27.

  The housing 21 houses each part such as the head unit 26. The casing 21 is formed in a gate shape straddling the flat bed unit 3 in the left-right direction. The casing 21 is supported by the gantry 11 of the shuttle base unit 2 and is movable along the sub-scanning drive guides 13A and 13B.

  The main scanning drive guide 22 guides the head unit 26 to move in the left-right direction (main scanning direction). The main scanning drive guide 22 is formed in a long shape extending in the left-right direction.

  The main scanning drive motor 23 moves the head unit 26 in the left-right direction.

  The head lifting guide 24 guides the head unit 26 to move in the vertical direction. The head lifting guide 24 is formed in an elongated shape in the vertical direction. The head raising / lowering guide 24 is configured to be movable in the left-right direction along the main scanning drive guide 22 together with the head unit 26.

  The head lifting motor 25 moves the head unit 26 up and down.

  The head unit 26 prints an image by ejecting ink onto the print medium 15 while moving in the left-right direction along the main scanning drive guide 22. The head unit 26 includes four inkjet heads 31.

  The ink jet head 31 ejects ink onto the print medium 15. The four inkjet heads 31 are arranged in parallel in the left-right direction. The four inkjet heads 31 eject inks of different colors (for example, cyan, black, magenta, and yellow). As shown in FIGS. 3 and 4, the inkjet head 31 has a nozzle plate 36 and a nozzle guard 37.

  The nozzle plate 36 is a member on which nozzles 38 that eject ink are formed. The nozzle plate 36 is provided at the lower end of the inkjet head 31. The nozzle plate 36 is formed in a rectangular plate shape. A plurality of nozzles 38 are opened on a nozzle surface 36 a that is the surface (lower surface) of the nozzle plate 36. The plurality of nozzles 38 are arranged along the front-rear direction and form a nozzle row 39. The nozzle 38 communicates with an ink chamber (not shown) in the inkjet head 31. An ink repellent film (not shown) is formed on the nozzle surface 36a.

  The nozzle guard 37 protects the nozzle surface 36 a of the inkjet head 31. The nozzle guard 37 is installed at the lower end of the inkjet head 31. The nozzle guard 37 includes a rectangular bottom plate 41 that covers the nozzle surface 36 a and a side wall 42 that stands on the periphery of the bottom plate 41. An opening 46 for exposing the nozzle row 39 is formed in the bottom plate 41. The opening 46 is formed in a rectangular shape elongated in the front-rear direction, and a part of the nozzle surface 36 a is exposed together with the nozzle row 39.

  The maintenance unit 27 cleans the nozzle surface 36 a and the nozzle guard 37 of the inkjet head 31. The maintenance unit 27 is disposed inside the left end portion of the housing 21. The maintenance unit 27 includes four wipers 51, four wiper fixing units 52, a wiper driving unit 53, and four wipe liquid tanks 54.

  The wiper 51 is wetted by the wipe liquid in the wipe liquid tank 54, wipes the nozzle guard 37, and wipes the nozzle surface 36a exposed by the opening 46 in a non-contact manner through the wipe liquid. The wiper 51 is made of a material such as elastically deformable rubber and is formed in a rectangular plate shape.

  The wiper fixing part 52 fixes the wiper 51 to a wiper drive belt 56 described later.

  The wiper drive unit 53 moves the wiper 51. The wiper drive unit 53 includes four wiper drive belts 56, a drive roller 57, and driven rollers 58 and 59.

  The wiper drive belt 56 is an annular belt that is stretched around the drive roller 57 and the driven rollers 58 and 59. A wiper 51 is attached to each wiper drive belt 56 via a wiper fixing portion 52. The wiper drive belt 56 rotates in a direction indicated by an arrow in FIG. 5 (counterclockwise direction when viewed from the left side) to move the wiper 51. Thereby, in the horizontal section of the wiper drive belt 56 stretched between the drive roller 57 and the driven roller 58, the wiper 51 wipes the nozzle guard 37 while moving from the front side toward the rear side.

  The drive roller 57 rotates the wiper drive belt 56. The drive roller 57 is rotationally driven by a motor (not shown).

  The driven rollers 58 and 59 support the four wiper drive belts 56 together with the drive roller 57. The driven rollers 58 and 59 are driven to rotate by the driving roller 57 via the wiper driving belt 56. The driven roller 58 has the same height as the drive roller 57 and is disposed behind the drive roller 57. The driven roller 59 is disposed below an intermediate position between the driving roller 57 and the driven roller 58 in the front-rear direction.

  The wipe liquid tank 54 holds a wipe liquid that adheres to the wiper 51. The wipe liquid tank 54 is disposed below the wiper drive belt 56. Accordingly, when the wiper 51 passes near the driven roller 59 by the rotation of the wiper driving belt 56, the wiper 51 comes into contact with the wipe liquid in the wipe liquid tank 54, and the wipe liquid adheres to the wiper 51. Yes.

  The wipe liquid has a function of dissolving ink. As this wipe liquid, for example, an aqueous solvent containing water and a surfactant can be used.

  Examples of the surfactant include fatty acid sodium, sodium alkylbenzene sulfonate, sodium alkyl sulfonate, sodium α-olefin sulfonate, sodium alkyl sulfate ester, sodium alkyl ether sulfate ester, sodium α-sulfo fatty acid ester, sodium alkyl phosphate ester. Anionic surfactant such as alkyl cationic trimethylammonium, dialkyldimethylammonium, etc .; sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkyl Nonionic surfactants such as phenyl ethers; sodium alkylamino fatty acids, alkylbetaines, alkylamines Amphoteric surfactants such as oxide can be used. In addition, polymer surfactants, silicone surfactants, fluorine surfactants, acetylene glycol surfactants, and the like can also be used. Among these, it is preferable to use polyoxyethylene alkyl ether, the HLB value is 11 to 17, the number of carbon atoms of the alkyl group is 8 to 15, and the number of added moles of ethylene oxide is more preferably 6 to 25.

  The wipe liquid preferably further contains a thickener. As the thickener, a water-soluble polymer thickener or a clay mineral thickener can be used. As the water-soluble polymer thickener, natural polymers, semi-synthetic polymers, and synthetic polymers can be used. Examples of natural polymers include plant-based natural polymers such as gum arabic, carrageenan, guar gum, locust bean gum, pectin, tragacanth gum, corn starch, konjac mannan, agar; Animal-based natural polymers such as gelatin, casein, and glue can be used. Examples of semi-synthetic polymers include cellulose-based semi-synthetic polymers such as ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and hydroxypropyl methyl cellulose; starch-based compounds such as hydroxyethyl starch, sodium carboxymethyl starch, and cyclodextrin. Semi-synthetic polymers; Alginate-based semi-synthetic polymers such as sodium alginate and propylene glycol alginate; sodium hyaluronate can be used. As the synthetic polymer, for example, vinyl-based synthetic polymers such as polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl methyl ether, poly N-vinylacetamide, and polyacrylamide; polyethylene oxide, polyethyleneimine, and polyurethane can be used. As the clay mineral-based thickener, for example, smectite-based clay minerals such as montmorillonite, hectorite, and saponite can be used. Among these, it is preferable to use hydroxypropyl methylcellulose.

  Furthermore, in addition to the above components, the wipe liquid can optionally contain a water-soluble organic solvent, a pH adjuster, an antioxidant, a preservative, and the like. The viscosity of the wipe liquid is preferably lower than the viscosity of the ink ejected from the inkjet head 31 and not more than half the viscosity of the ink.

  The wipe liquid tank 54 is provided with a non-woven fabric 61 and a heater (corresponding to a heating part in claims) 62.

  The nonwoven fabric 61 removes foreign matter adhering to the wiper 51. When the wiper 51 passes through the wipe liquid tank 54, the wiper 51 comes into contact with the nonwoven fabric 61, so that the foreign matter attached to the wiper 51 is removed.

  The heater 62 heats the wipe liquid in order to adjust the viscosity of the wipe liquid in the wipe liquid tank 54.

  The control unit 5 controls the operation of the entire inkjet printing apparatus 1. The control unit 5 includes a CPU, a RAM, a ROM, a hard disk, and the like.

  When the inkjet head 31 is cleaned by the maintenance unit 27, the control unit 5 controls the wipe speed of the wiper 51 according to the water repellent speed of the liquid mixture of the wipe liquid and the ink on the nozzle surface 36a. Here, the water repellent speed of the liquid mixture on the nozzle surface 36a is the moving speed of the rear end of the liquid mixture when the liquid mixture moves on the nozzle surface 36a following the wiper 51, as will be described later.

  Next, a printing operation in the inkjet printing apparatus 1 will be described.

  In the inkjet printing apparatus 1, the shuttle unit 4 is disposed at the standby position in the standby state before the start of the printing operation. The standby position of the shuttle unit 4 is the position of the shuttle unit 4 indicated by a solid line in FIG.

  When a print job is input, the control unit 5 controls the sub-scanning drive motor 12 to move the shuttle unit 4 from the standby position to the print processing start position. The printing process start position of the shuttle unit 4 is the position of the shuttle unit 4 indicated by a two-dot chain line in FIG. 1 and is at the front end of the gantry 11 of the shuttle base unit 2. Prior to the input of the print job, the print medium 15 is placed on the medium placement surface 3 a of the flat bed unit 3.

  Next, the control unit 5 controls the ink jet head 31 based on the print job to eject ink from the nozzles 38 while controlling the main scanning drive motor 23 to move the head unit 26 in the main scanning direction, thereby causing the 1 Print the pass. Next, the control unit 5 controls the sub-scanning drive motor 12 to move the shuttle unit 4 backward to the printing position of the next pass. The controller 5 forms an image on the print medium 15 by alternately repeating the printing for one pass and the movement of the shuttle unit 4.

  When printing for one sheet is completed, the control unit 5 controls the sub-scanning drive motor 12 to place the shuttle unit 4 at the standby position. Thereby, the printing operation is completed.

  Next, the cleaning operation of the inkjet head 31 in the inkjet printing apparatus 1 will be described.

  In the cleaning operation, first, the control unit 5 moves the wiper 51 by the wiper driving unit 53 to pass through the wipe liquid tank 54, thereby cleaning the wiper 51 and attaching the wipe liquid to the wiper 51.

  Next, the control unit 5 controls the main scanning drive motor 23 to move the head unit 26 from the home position to above the maintenance unit 27. Thereafter, the control unit 5 controls the head lifting motor 25 to lower the head unit 26 to the cleaning position. Here, the home position of the head unit 26 is the position of the head unit 26 shown in FIG. 2 and is inside the right end portion of the housing 21. The cleaning position of the head unit 26 is the position of the head unit 26 for wiping the nozzle guard 37 with the wiper 51.

  When the movement of the head unit 26 to the cleaning position is completed, the wiper 51 is in front of the front end of the nozzle guard 37. Further, the tip (upper end) of the wiper 51 is at a position higher than the lower surface of the nozzle guard 37.

  Next, the control unit 5 causes the wiper driving unit 53 to start the movement of the wiper 51 in the backward direction. Here, the control unit 5 controls the wiper driving unit 53 to move the wiper 51 at a wipe speed set in advance according to the water repellent speed of the liquid mixture of the wipe liquid and the ink on the nozzle surface 36a.

  After the wiper 51 starts moving, when it comes into contact with the nozzle guard 32, the wiper 51 is pressed by the nozzle guard 32 and elastically deformed. Then, with the rearward movement, the upper end portion of the wiper 51 slides (wipes) the lower surface of the nozzle guard 37.

  When the wiper 51 passes through the opening 46 of the nozzle guard 37, as shown in FIG. 8, the central portion in the left-right direction of the wiper 51 is not in contact with the nozzle guard 37 or the nozzle surface 36a. However, since the wiper 51 is wet with the wipe liquid, the wiper 51 moves while wiping the nozzle surface 36a through the wipe liquid even if it is not in contact with the nozzle surface 36a.

  Here, the ink which became ink mist when the inkjet head 31 ejected ink has adhered to the nozzle guard 37 and the nozzle surface 36a. For this reason, when the wiper 51 wipes the nozzle guard 37, a mixed liquid 66 in which the wipe liquid and the ink are mixed is formed.

  When the wiper 51 passes through the opening 46 of the nozzle guard 37, the wiper 51 and the nozzle surface 36a are kept at a constant distance depending on the thickness of the nozzle guard 37. Therefore, as shown in FIG. Be accustomed to. Then, the liquid mixture 66 moves following the wiper 51 due to the flow in the traveling direction of the wiper 51 and the water repellency of the nozzle surface 36a. Thereby, the nozzle surface 36a is cleaned.

  When the wiper 51 reaches the rear side from the rear end of the nozzle guard 37, the control unit 5 ends the movement of the wiper 51. Thereby, the cleaning operation of the inkjet head 31 is completed.

  Next, the viscosity of the wipe liquid and the wipe speed will be described.

  When the wiper 51 passes through the opening 46 of the nozzle guard 37, a Couette flow in which the velocity distribution changes linearly is formed in the mixed liquid 66 as shown in FIG. At this time, a proportional relationship between the shearing force τ and the velocity gradient is established as represented by the following formula (1).

τ = μ × U / h (1)
Here, μ is a viscosity coefficient of the liquid mixture 66. U is the movement speed (wipe speed) of the wiper 51. h is the thickness of the liquid mixture 66 (the thickness of the nozzle guard 37).

  As can be seen from the equation (1), the shear force increases as the viscosity of the mixed solution 66 increases. For this reason, the higher the viscosity of the liquid mixture 66, the more easily the liquid mixture 66 is broken by the shearing force during wiping, and the liquid droplets of the liquid mixture 66 are more likely to remain on the nozzle surface 36a. If the droplets of the mixed liquid 66 remain on the nozzle surface 36a, the droplets hinder ink ejection from the nozzles 38, and there is a possibility that non-ejection of ink or a flying curve may occur.

  For this reason, the viscosity of the liquid mixture 66 is preferably as low as possible, and for this purpose, the viscosity of the wipe liquid is preferably as low as possible. Specifically, the viscosity of the wipe liquid is lower than the viscosity of the ink. Thereby, the viscosity of the liquid mixture 66 can be made lower than the viscosity of the ink, and the droplets of the liquid mixture 66 can be prevented from remaining on the nozzle surface 36a. In order to prevent droplets of the mixed liquid 66 from remaining on the nozzle surface 36a, the viscosity of the wipe liquid is preferably less than or equal to half of the viscosity of the ink.

  Further, as can be seen from the equation (1), the shear force increases as the wipe speed increases. For this reason, as the wiping speed increases, the liquid mixture 66 is broken during the wiping, and the liquid droplets of the liquid mixture 66 tend to remain on the nozzle surface 36a.

  For this reason, in order to suppress that the liquid mixture 66 is torn off during the wiping and the liquid droplets of the liquid mixture 66 remain on the nozzle surface 36a, it is preferable that the wipe speed is low.

  On the other hand, if the wiping speed is too slow, the mixed liquid 66 may be drawn into the nozzle 38. A phenomenon in which the mixed liquid 66 is drawn into the nozzle 38 will be described with reference to FIG.

  As shown in FIG. 11, a negative pressure is generated in the inkjet head 31, and a negative pressure is applied to the nozzle 38. In a normal state, a meniscus is formed in the ink in the nozzle 38, and a balance is maintained between the surface tension of the meniscus surface and the negative pressure applied to the nozzle 38.

  When the opening of the nozzle 38 is covered with the mixed liquid 66 like the two front nozzles 38 in FIG. 11, the meniscus in the nozzle 38 disappears, and the ink in the nozzle 38 and the mixed liquid 66 are in communication with each other. . As a result, a force in the direction of being drawn into the nozzle 38 by the negative pressure acts on the mixed liquid 66. On the other hand, the surface tension of the liquid mixture 66 acts as a resistance force against the force in the direction of being drawn into the nozzle 38. For this reason, even if the opening of the nozzle 38 is covered with the mixed liquid 66, the mixed liquid 66 is not immediately drawn into the nozzle 38.

  However, if the wiping speed is slow and the time during which the liquid mixture 66 stays on the nozzle surface 36a becomes long, the liquid mixture 66 may be drawn into the nozzle 38 due to negative pressure and enter. If the mixed liquid 66 enters the nozzle 38, there is a possibility that non-ejection of ink or a flying bend in the nozzle 38 may occur. Therefore, it is necessary to perform idle discharge for recovery of discharge.

  In order to prevent the mixed solution 66 from entering the nozzle 38, it is necessary to increase the wiping speed to such an extent that the time for which the mixed solution 66 stays on the nozzle surface 36a does not become too long.

  Specifically, by making the wiping speed equal to or higher than the water repellent speed of the mixed liquid 66 on the nozzle surface 36 a, it is possible to suppress the mixed liquid 66 from entering the nozzle 38. Here, the water repellent speed of the mixed liquid 66 on the nozzle surface 36a is the moving speed of the rear end 66a (see FIG. 9) of the mixed liquid 66 when the mixed liquid 66 follows the wiper 51 and moves on the nozzle surface 36a. It is. The water repellent speed of the mixed liquid 66 on the nozzle surface 36 a is measured while adjusting the wipe speed to various speeds using the actual inkjet head 31, ink, wipe liquid, and wiper 51.

  When the wiping speed is equal to or higher than the water repellent speed of the mixed liquid 66, the rear end 66a of the mixed liquid 66 moves on the nozzle surface 36a at the water repellent speed. Thereby, since the time for which the liquid mixture 66 stays on the nozzle surface 36 a is reduced, the liquid mixture 66 can be prevented from entering the nozzle 38. On the other hand, when the wipe speed is slower than the water repellent speed of the mixed liquid 66, the mixed liquid 66 also moves at the same speed as the wipe speed slower than the water repellent speed. For this reason, the slower the wiping speed, the longer the time during which the mixed liquid 66 stays on the nozzle surface 36 a, and the mixed liquid 66 easily enters the nozzle 38.

  On the other hand, as described above, the faster the wiping speed, the easier the liquid mixture 66 is torn during the wiping and the liquid droplets of the liquid mixture 66 remain on the nozzle surface 36a. The following is preferable. Here, the water repellency of the liquid on the nozzle surface 36a increases as the viscosity of the liquid decreases. In the present embodiment, since the viscosity of the wipe liquid is lower than the viscosity of the ink, the water repellency speed of the wipe liquid alone is faster than the water repellency speed of the mixed liquid 66.

  From the above description, in the inkjet printing apparatus 1, the wiping speed of the wiper 51 is set according to the water repellency speed of the mixed liquid 66 on the nozzle surface 36a. More specifically, the wiping speed is set to a speed not less than the water repellency speed of the mixed liquid 66 on the nozzle surface 36a and not more than the water repellency speed of the wipe liquid alone.

  Next, experimental results of cleaning the ink jet head 31 in the ink jet printing apparatus 1 will be described with reference to FIG.

  As shown in FIG. 12, in this experiment, three types of wipes having viscosities of 4 mPa · s, 10 mPa · s, and 50 mPa · s, respectively, were used. In addition, the inkjet head 31 was wiped at wipe speeds of 20 mm / s, 50 mm / s, and 80 mm / s with respect to the wipe liquids having the respective viscosities. For the wipe liquid having a viscosity of 4 mPa · s, the wipe was performed even at 10 mm / s. And the printed matter by the inkjet head 31 after cleaning was evaluated.

  In the evaluation of the printed matter, no nozzle omission (non-ejection of ink from the nozzle 38) was found, and a good printed matter was evaluated as “A”. A printed matter having a number of missing nozzles that was improved by empty ejection was evaluated as “B”. A printed matter in which a large number of nozzle omissions occurred so as not to improve even with idle ejection was evaluated as “C”. “-” Indicates that there is a place where the wipe liquid is not in contact with the nozzle surface 36a, and the nozzle surface 36a has not been cleaned, and thus is not subject to evaluation.

  The flat shape described in the wiper shape column in FIG. 12 is the shape of the wiper 51 of the present embodiment, and is a shape in which the upper side is a horizontal straight line as shown in FIG.

  Here, the viscosity of the ink in this experiment is 10 mPa · s. That is, the viscosity of the 4 mPa · s wipe liquid is lower than the viscosity of the ink and not more than half the viscosity of the ink. The viscosity of the 10 mPa · s wipe liquid is equivalent to the viscosity of the ink. The viscosity of the 50 mPa · s wipe liquid is larger than the viscosity of the ink.

  As shown in FIG. 12, with the wipe liquid having a viscosity of 10 mPa · s and the wipe liquid having a viscosity of 50 mPa · s, good printed materials could not be obtained at wipe speeds of 20 mm / s and 50 mm / s. This is because the viscosity of 10 mPa · s and 50 mPa · s is so high that the mixed liquid of the wipe liquid and the ink is broken by the shearing force and remains on the nozzle surface 36a. Since the wipe speed of 80 mm / s was high, the wiper 51 moved in a state where the mixed liquid did not sufficiently contact the nozzle surface 36a, and the nozzle surface 36a could not be cleaned.

  With the wipe liquid having a viscosity of 4 mPa · s, good printed matter was obtained at wipe speeds of 20 mm / s and 50 mm / s. Good prints could not be obtained at a wipe speed of 10 mm / s. At the wipe speed of 80 mm / s, the nozzle surface 36a could not be cleaned as in the case of 10 mPa · s and 50 mPa · s described above.

  Here, the water repellency of the mixed liquid of 4 mPa · s wipe liquid and ink is 15 mm / s. Further, the water repellent speed of a single 4 mPa · s wipe liquid is 50 mm / s. Accordingly, when the viscosity of the wipe liquid is lower than the viscosity of the ink, when the wipe speed is equal to or higher than the water repellent speed of the mixed liquid on the nozzle surface 36a and equal to or lower than the water repellent speed of the wipe liquid alone, a good printed matter is obtained. It was confirmed that it was obtained.

  In the case of a wipe liquid with a viscosity of 4 mPa · s, the reason why a good printed matter was not obtained at a wipe speed of 10 mm / s was that the liquid mixture entered the nozzle 38 because the wipe speed was too slow.

  Next, as a comparative example, unlike the present embodiment, FIG. 13 shows the experimental results when the inkjet head 31 is cleaned using a convex wiper.

  The convex-shaped wiper is a wiper having a shape in which a central portion in the left-right direction protrudes from a left portion and a right portion. In the convex wiper, the protruding central portion is inserted into the opening 46 of the nozzle guard 37 and wipes in contact with the nozzle surface 36a.

  As shown in FIG. 13, with the convex wiper, good printing results were not obtained even when the viscosity of the wipe liquid was 4 mPa · s and the wipe speed was 20 mm / s or 50 mm / s. This is because, in the convex wiper, the wipe liquid is pushed into the nozzle 38 by wiping the central portion of the wiper in contact with the nozzle surface 36a.

  Incidentally, as described above, the inkjet printing apparatus 1 uses a wipe liquid having a viscosity lower than that of the ink. However, the viscosity of the wipe liquid in the wipe liquid tank 54 may increase due to a change in environmental temperature or the like.

  Therefore, when it is determined that the viscosity of the wipe liquid has increased, the control unit 5 drives the heater 62 to heat the wipe liquid in the wipe liquid tank 54, thereby reducing the viscosity of the wipe liquid.

  Specifically, when the environmental temperature detected by a temperature sensor (not shown) falls below a specified temperature, the control unit 5 drives the heater 62 to heat the wipe liquid in the wipe liquid tank 54, thereby wiping the wipe. Reduce the viscosity of the liquid.

  Further, as the time elapses, the viscosity of the wipe liquid in the wipe liquid tank 54 may increase due to volatilization. Therefore, the control unit 5 may drive the heater 62 every specified period to reduce the viscosity of the wipe liquid in the wipe liquid tank 54.

  Further, when the wiper 51 that wipes the inkjet head 31 is immersed in the wipe liquid in the wipe liquid tank 54, the ink is mixed with the wipe liquid, and the viscosity of the wipe liquid in the wipe liquid tank 54 may increase. Therefore, the control unit 5 may drive the heater 62 and reduce the viscosity of the wipe liquid in the wipe liquid tank 54 every time cleaning is performed a specified number of times.

  As described above, in the inkjet printing apparatus 1, the wiper 51 wipes the nozzle surface 36a exposed by the opening 46 of the nozzle guard 37 through the wipe liquid in a non-contact manner. This prevents the wiper from pushing the wipe liquid into the nozzle 38. Further, the control unit 5 controls the wipe speed by the wiper 51 in accordance with the water repellent speed of the liquid mixture of the wipe liquid and the ink on the nozzle surface 36a. As a result, it is possible to suppress the time during which the mixed liquid stays on the nozzle surface 36 a and to prevent the mixed liquid from entering the nozzle 38. For this reason, it is possible to omit idle ejection after cleaning the inkjet head 31 and reduce waste of ink.

  Specifically, the control unit 5 sets the wipe speed to a speed that is equal to or higher than the water repellent speed of the mixed liquid 66 on the nozzle surface 36a and lower than the water repellent speed of the wipe liquid alone. As a result, the time during which the liquid mixture stays on the nozzle surface 36a is suppressed, the liquid mixture is prevented from entering the nozzle 38, and the liquid mixture is broken by the shearing force during the wipe to remain on the nozzle surface 36a. Can be suppressed. As a result, it is possible to reduce the waste of ink by omitting the idle ejection after cleaning of the inkjet head 31, reduce the ejection failure of the ink that is not improved by the idle ejection, and suppress the deterioration of the printing image quality.

  Moreover, in the inkjet printing apparatus 1, since the wipe liquid tank 54 is provided with the heater 62, when the viscosity of the wipe liquid decreases, the viscosity can be adjusted to increase. Accordingly, it is possible to reduce the mixture liquid from being broken on the nozzle surface 36a by the shearing force during the wipe due to the increase in the viscosity of the wipe liquid due to a change in the environmental temperature or the like.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiment.

DESCRIPTION OF SYMBOLS 1 Inkjet printing apparatus 2 Shuttle base unit 3 Flat bed unit 4 Shuttle unit 5 Control part 26 Head unit 27 Maintenance part 31 Inkjet head 36 Nozzle plate 36a Nozzle surface 37 Nozzle guard 38 Nozzle 39 Nozzle row 46 Opening 51 Wiper 52 Wiper fixing part 53 Wiper Drive Unit 54 Wipe Liquid Tank 62 Heater 66 Mixed Liquid

Claims (3)

An inkjet head having a nozzle surface on which a nozzle row is formed, and a nozzle guard that covers the nozzle surface and has an opening for exposing the nozzle row;
A wiper that is wetted by a wipe liquid having a viscosity lower than that of ink, wipes the nozzle guard, and wipes the nozzle surface exposed by the opening in a non-contact manner through the wipe liquid;
The wiper wipe speed according to the water repellent speed of the mixed liquid, which is the moving speed of the rear end of the mixed liquid when the mixed liquid of the wipe liquid and ink follows the wiper and moves on the nozzle surface. An inkjet printing apparatus comprising: a control unit that controls   2. The ink jet printing apparatus according to claim 1, wherein the control unit sets the wipe speed to a speed that is equal to or higher than a water repellent speed of a mixed liquid and equal to or lower than a water repellent speed of a single wipe liquid. A wipe liquid tank for holding a wipe liquid to be adhered to the wiper;
The inkjet printing apparatus according to claim 1, further comprising: a heating unit that heats the wipe liquid in the wipe liquid tank.