JP5099204B2 - Liquid ejection device - Google Patents

Description

  The present invention relates to a liquid ejecting apparatus including a liquid ejecting head having a nozzle for ejecting liquid, and more particularly to a liquid ejecting apparatus in which a nozzle is scanned in the vertical direction by reciprocating the liquid ejecting head in the vertical direction.

  As a conventional “liquid ejecting apparatus”, an “inkjet printer” is well known, and an example thereof is disclosed in Patent Document 1. An ink jet printer (1) of Patent Document 1 includes an ink discharge head (30) having nozzles for discharging ink, a head holder (9) that also serves as a carriage, and an endless belt that reciprocates the head holder (9) in the horizontal direction. (11), ink tanks (5a) to (5d) containing ink ejected from the nozzles, and tubes (14a) to (14d) for supplying ink in the ink tanks (5a) to (5d) to the nozzles And. According to the ink jet printer (1), the “tube supply method” is employed in which the ink in the ink tanks (5a) to (5d) is supplied to the nozzles via the tubes (14a) to (14d). The ink tanks (5a) to (5d) can be enlarged, and the time for ink replenishment can be reduced by extending the ink replenishment cycle. However, since the ink discharge head (30) is reciprocated in the horizontal direction, there is a problem that the installation area in the “horizontal direction” becomes large and the installation location is remarkably restricted.

  As means for solving such a problem, Patent Document 2 discloses a “vertical installation type” ink jet printer (100). In this ink jet printer (100), the carriage guide shaft (156) and the like are arranged so as to extend in the vertical direction, thereby reciprocating the carriage (151) in the vertical direction, thereby moving the recording head (152) in the vertical direction. Is to be scanned.

  The numbers in parentheses correspond to the reference numbers used in Patent Documents 1 and 2.

JP 2005-262816 A JP 2005-298082 A

  According to the ink jet printer (100) of Patent Document 2, the restriction of the installation location can be relaxed by reducing the installation area in the “horizontal direction”. However, the positional relationship between the nozzles of the recording head (152) and the liquid level in the ink container is not considered at all. Depending on this positional relationship, the “positive pressure” acting on the ink in the recording head (152) is not considered. ”Or“ negative pressure ”may cause various problems.

  For example, when the liquid level in the ink container is above the nozzle in a state where the recording head (152) is stopped, “positive pressure” due to gravity acts on the ink in the recording head (152). There was a possibility that the meniscus of the nozzle was destroyed and ink leakage occurred. Even when the liquid level in the ink container is below the nozzle, if the height difference between them (ie, the water head difference) is too large, the ink in the recording head (152) is excessive due to gravity. Since the “negative pressure” acts, the meniscus of the nozzle is destroyed and air is drawn into the nozzle, which may impair the discharge performance.

  The present invention has been made to solve the above-described problems, and prevents liquid from leaking from the nozzles by preventing “positive pressure” due to gravity from acting on the liquid in the liquid discharge head. An object of the present invention is to provide a liquid ejection device that can be used.

  In addition, the present invention provides a liquid ejection apparatus capable of preventing the ejection performance from being impaired by preventing an excessive “negative pressure” due to gravity from acting on the liquid in the liquid ejection head. For the purpose.

In order to solve the above-described problems, a liquid discharge apparatus according to the present invention includes a liquid discharge head having a nozzle that discharges liquid toward a discharge target, and the nozzle by moving the liquid discharge head back and forth in the vertical direction. A drive unit that scans the nozzle in a vertical direction, a conveyance path that conveys an ejection target in a direction orthogonal to the scanning direction of the nozzle, and the liquid ejection head that stops at a predetermined standby position in the moving region And a liquid container for storing the liquid discharged from the nozzle, and a liquid tube for supplying the liquid in the liquid container to the liquid discharge head, and the liquid discharge head stopped at the standby position. And the liquid container are disposed in either the upper region located above the transport path or the lower region located below the transport path. And which, said liquid container has a plurality provided to accommodate liquids having different surface tensions, the nozzle, the is provided a plurality to correspond individually to each of the liquid container, the liquid tube A plurality of liquid containers are provided so as to supply the liquid in the liquid containers to the corresponding nozzles, and each of the plurality of liquid containers has a liquid surface height at the standby position when the liquid is accommodated at the maximum. The nozzles in the stopped liquid discharge head are arranged so as to be the same as or lower than the lowest point of the nozzle, and the plurality of nozzles are arranged in the order of increasing surface tension of the liquid to be discharged. They are arranged side by side from the lower side to the upper side in the direction .

  In this configuration, since both the liquid discharge head and the liquid container stopped at the standby position are arranged in either the upper region or the lower region, the liquid level of the liquid in the liquid container and the bottom of the nozzle The height difference from the point (that is, the water head difference) can be reduced, and “air drawing” into the nozzle due to excessive “negative pressure” can be prevented.

  In this configuration, the plurality of nozzles individually corresponding to each of the liquid containers are arranged side by side from the lower side to the upper side in the vertical direction in ascending order of the surface tension of the liquid to be discharged, so the liquid level of the liquid in the liquid container The difference in height between the nozzle and the lowest point of the nozzle (that is, the water head difference) becomes smaller as the surface tension of the liquid is lower, and effectively prevents “intake of air” into the nozzle due to excessive “negative pressure”. be able to.

  A nozzle cap that covers the nozzle may be disposed at the standby position.

  In this configuration, the nozzle of the liquid ejection head stopped at the standby position can be protected by the nozzle cap.

  The present invention is configured as described above, and the height of the liquid surface when the liquid is maximally accommodated in the liquid container is the height of the lowest point of the nozzle in the liquid discharge head stopped at the standby position. Since it is the same or lower, it is possible to prevent the “positive pressure” due to gravity from acting on the liquid in the liquid discharge head and to prevent the liquid from leaking from the nozzle. .

  In another configuration of the present invention, both the liquid discharge head and the liquid container stopped at the standby position are either the upper region positioned above the transport path or the lower region positioned below the transport path. Therefore, the height difference between the liquid level in the liquid container and the lowest point of the nozzle (that is, the water head difference) can be reduced. Therefore, it is possible to prevent an excessive “negative pressure” from acting on the liquid in the liquid discharge head, and to prevent a decrease in discharge performance due to air being drawn from the nozzle.

1 is a perspective view illustrating an overall configuration of an inkjet printer according to a first embodiment. 1 is a simplified diagram illustrating an internal configuration of an inkjet printer according to a first embodiment. 1 is an exploded perspective view showing an ink discharge head constituting an ink jet printer according to a first embodiment and a flexible printed wiring board bonded to the ink discharge head. FIG. It is a top view which shows the ink discharge head which comprises the inkjet printer which concerns on 1st Embodiment. It is a partial expanded sectional view which shows the ink discharge head and FPC which comprise the inkjet printer which concerns on 1st Embodiment. It is a partial enlarged plan view showing an ink discharge head constituting the ink jet printer according to the first embodiment. It is a schematic diagram which shows the principal part of the inkjet printer which concerns on 1st Embodiment. It is a simplified diagram showing an internal configuration of an inkjet printer according to a second embodiment. It is a simplified diagram showing an internal configuration of an ink jet printer according to a third embodiment. It is a schematic diagram which shows the principal part of the inkjet printer which concerns on 4th Embodiment. It is a schematic diagram which shows the principal part of the inkjet printer which concerns on 5th Embodiment.

  Hereinafter, a “liquid ejection device” according to a preferred embodiment of the present invention will be described with reference to the drawings.

  In each of the following embodiments, the present invention is applied to an “inkjet printer” that ejects ink (liquid) using an “actuator”. “Inkjet printer” that discharges ink (liquid) using “pressure”, “color filter manufacturing device” equipped with colored liquid discharge head that discharges colored liquid (liquid), and conductive liquid (liquid) The present invention can be widely applied to other “liquid ejecting apparatuses” such as “electrical wiring apparatus” having a conductive liquid ejecting head.

(First embodiment)
[Overall configuration of inkjet printer]
FIG. 1 is a perspective view showing an overall configuration of an inkjet printer 10 as a “liquid ejecting apparatus” according to a first embodiment of the present invention, and FIG. 2 is a simplified diagram showing an internal configuration of the inkjet printer 10. .

  As shown in FIGS. 1 and 2, the ink jet printer 10 includes an ink discharge head 12 as a “liquid discharge head”, a drive unit 14 that reciprocates the ink discharge head 12 in the vertical direction, and a “liquid container”. Ink containers 16a to 16d, ink tubes 18a to 18d as "liquid tubes", a nozzle cap 20, a paper tray 22 (FIG. 1) for storing paper P as an "ejection target", and transporting the paper P A sheet conveying unit 24 for performing various controls, a control unit 26 (FIG. 1) for executing various controls, and a housing 28 (FIG. 1).

  In the present embodiment, the configuration of the “ink discharge head 12”, the “drive unit 14”, the “nozzle cap 20”, and the “ink containers 16a to 16d” inside the “casing 28” (including the mutual positional relationship). Since these are particularly important, the following description will focus on these components.

  The “main scanning direction X” used in the following description means the moving direction of the ink ejection head 12 (ie, the vertical direction), and the “sub-scanning direction Y” means the discharge direction of the paper P. Shall.

[Case configuration]
As shown in FIG. 1, the housing 28 is designed so that the “width W” is sufficiently smaller than the “height H” and the “depth D”, and the side surface in the width direction (that is, FIG. 1). A rectangular parallelepiped main body 32 having an opening 30 formed on the entire left side) and a substantially rectangular plate-like lid (not shown) that closes the opening 30. A substantially U-shaped transport path A in plan view is formed in a space extending from the center to the upper part in the interior of the. Further, a front panel 32a constituting the front surface of the main body 32 (that is, the front surface in FIG. 1) has a paper tray insertion port 34 serving as an entrance of the transport path A and a discharge port serving as an exit of the transport path A. 36, a switch mounting hole 40 for mounting the power switch 38, and an ink container mounting hole 42 for mounting the ink containers 16a to 16d are formed.

  The various components described above are arranged in the housing 28 in consideration of the mutual positional relationship. That is, as shown in FIG. 1, a paper tray 22, a paper transport unit 24, a drive unit 14, and an ink discharge head 12 are arranged in this order from the upstream side along the transport path A, and the nozzle cap 20 and the ink container 16a to 16d are disposed in a lower region S1 located below the transport path A. Further, the ink discharge head 12 is provided with a buffer unit 44. The downstream ends of the ink tubes 18a to 18d are connected to the buffer unit 44, and the upstream ends are connected to the ink containers 16a to 16d. Has been. Further, a control unit 26 is disposed at a predetermined location inside the housing 28.

[Configuration of ink discharge head]
3 is an exploded perspective view showing the ink discharge head 12 and a flexible printed circuit board (hereinafter abbreviated as “FPC”) 50 bonded to the ink discharge head 12. FIG. FIG. 5 is a partial enlarged cross-sectional view showing the ink discharge head 12 and the FPC 50.

  The ink discharge head 12 is mounted on the carriage 130 (FIGS. 1 and 2) of the drive unit 14 and is reciprocated in the vertical direction (that is, the main scanning direction X), and is based on the drive voltage applied from the FPC 50. The four color inks for image formation are selectively ejected, and as shown in FIGS. 3 and 5, a flow path unit 52 and an actuator unit 54 are provided.

  Note that “lower” used in the description of the ink ejection head 12 and the FPC 50 means the direction of ejecting ink, and “upper” means the opposite direction.

<Configuration of flow path unit>
As shown in FIG. 5, the flow path unit 52 includes a pressure chamber plate 56, an aperture plate 58, a connection flow path plate 60, a first manifold plate 62, a second manifold plate 64, a damper plate 66, a cover plate 68, and a nozzle plate. 70 and 8 plates are laminated in this order from the upper side, and the “recesses” or “holes” formed in these plates 56 to 70 are continuous with each other. As shown, four ink flow paths N1 to N4 corresponding to four colors of ink of black (BK), yellow (Y), cyan (C), and magenta (M) are configured.

  The four ink flow paths N1 to N4 are arranged from the lower side to the upper side in the vertical direction in ascending order of the surface tension of the ink flowing therethrough. That is, in the four-color ink used in this embodiment, the surface tension of black (BK) is the lowest, the surface tension of yellow (Y) is next low, and then the surface tension of cyan (C) is low. The surface tension of magenta (M) is the highest, and the ink flow paths N1 to N4 are arranged in the order of these colors from the lower side to the upper side in the vertical direction (FIG. 4).

  The ink flow path N1 located at the lowermost position is one ink introduction flow path 72 (FIG. 4) and a plurality (three in this embodiment) of common ink chambers 74 (FIG. 4) connected to the ink introduction flow path 72 (FIG. 4). 4) and a plurality (68 in this embodiment) of individual ink flow paths 76 (FIG. 5) communicating with each of the common ink chambers 74.

  The ink introduction flow path 72 (FIG. 4) has a pressure chamber plate 56, an aperture plate 58, a connection flow path plate 60, a first manifold plate 62, and a second manifold at one end portion in the sub-scanning direction Y of the flow path unit 52. A hole (not shown) formed in each of the plates 64 is configured to be continuous in the thickness direction.

  As shown in FIG. 5, the common ink chamber 74 is configured by holes 62 a and 64 a formed in the first manifold plate 62 and the second manifold plate 64 being continuous in the thickness direction. The cross-sectional shape of the common ink chamber 74 is designed to be a rectangle extending long in the main scanning direction X. As shown in FIG. 4, the common ink chamber 74 is designed to have a rectangular shape in plan view extending long in the sub-scanning direction Y, and one end of the common ink chamber 74 in the sub-scanning direction Y is introduced with ink. It communicates with the flow path 72 and the other end is closed. As shown in FIG. 5, a plate-like damper 78 is formed at the bottom of the common ink chamber 74 by forming a recess 66 a on the lower surface of the damper plate 66, and both sides of the common ink chamber 74 in the width direction are formed. As shown in FIG. 3, a plurality of individual ink channels 76 (FIG. 5) are arranged in two rows in a staggered manner.

  Each individual ink flow path 76 is a flow path for discharging the ink in the common ink chamber 74 to the outside. As shown in FIG. 5, the connection flow path 80, the aperture 82, the pressure chamber 84, and the discharge flow path 86. And the nozzle 88 is comprised by communicating in this order from the upstream.

  The connection flow path 80 is configured above the common ink chamber 74 by a hole 60 a formed in the connection flow path plate 60, and the aperture 82 is connected to the connection flow path 80 by a recess 58 a formed in the lower surface of the aperture plate 58. The pressure chamber 84 is formed above the aperture 82 by a hole 56 a formed in the pressure chamber plate 56. Further, the discharge flow path 86 has holes 58b, 60b, 62b formed in the aperture plate 58, the connection flow path plate 60, the first manifold plate 62, the second manifold plate 64, the damper plate 66, and the cover plate 68, respectively. 64b, 66b and 68b are formed below the pressure chamber 84, and the nozzle 88 is formed below the discharge passage 86 by a tapered hole 70a formed in the nozzle plate 70.

  The upstream end of the aperture 82 and the common ink chamber 74 are communicated with each other via the connection flow path 80, and the downstream end of the aperture 82 and the upstream end of the pressure chamber 84 are connected to the aperture plate. The downstream end of the pressure chamber 84 and the nozzle 88 are in communication with each other via the discharge flow path 86. Further, an opening 84 a is formed at the upper end of the pressure chamber 84, and the opening 84 a is closed by the lower surface of the actuator unit 54.

  On the other hand, each of the ink channels N2 to N4 has one ink introduction channel 92 (FIGS. 3 and 4) and a plurality (two in this embodiment) of common ink chambers 94 communicated with the ink introduction channel 92. (FIG. 4) and a plurality (68 in this embodiment) of individual ink channels 96 (FIG. 3) communicated with each of the common ink chambers 94.

  The ink introduction channel 92 (FIGS. 3 and 4) is similar to the ink introduction channel 72 except that the volume is smaller than the ink introduction channel 72 (FIGS. 3 and 4) of the ink channel N1. The common ink chamber 94 (FIG. 4) and the individual ink flow path 96 (FIG. 3) are configured in comparison with the common ink chamber 74 (FIG. 4) and the individual ink flow path 76 (FIG. 3) of the ink flow path N1. Except that the total number is small. As a result, the uniformity of the “ink ejection performance” is maintained in all of the ink flow paths N1 to N4, and the “balance of ink ejection amounts” is achieved. That is, since the “ink ejection performance” required for the ink flow paths N2 to N4 is in common with the “ink ejection performance” required for the ink flow path N1, the ink introduction flow path 92 (FIGS. 3 and 4). ), The common ink chamber 94 (FIG. 4) and the individual ink flow path 96 (FIG. 3) are composed of the ink introduction flow path 72 (FIGS. 3 and 4), the common ink chamber 74 (FIG. 4) and the individual ink flow path. It is designed to be the same as the configuration of 76 (FIG. 3). In addition, since the “usage frequency” of the ink flowing through the ink flow paths N2 to N4 is less than the “usage frequency” of the black (BK) ink flowing through the ink flow path N1, the common ink chamber 94 (FIG. 4) and the individual ink chambers 94 The total number of ink channels 96 (FIG. 3) is designed to be smaller than the total number of common ink chambers 74 (FIG. 4) and individual ink channels 76 (FIG. 3).

  As shown in FIGS. 3 and 4, in a region where the ink introduction flow paths 72 and 92 are formed on the upper surface of the flow path unit 52, a filter 98 that captures foreign matters and bubbles mixed in the ink is used as an adhesive or the like. In other regions, the actuator unit 54 is bonded using an adhesive or the like.

  As described above, in the present embodiment, four ink flow paths N1 to N4 corresponding to the four colors of ink of black (BK), yellow (Y), cyan (C), and magenta (M) are provided there. Since the surface tension of the flowing ink is arranged in the vertical direction from the lower side to the upper side, the nozzles 88 provided in the ink flow paths N1 to N4, that is, the nozzles corresponding to the ink containers 16a to 16d, respectively. Nos. 88 are arranged from the lower side to the upper side in the vertical direction in order of increasing surface tension of the ink to be ejected.

  Further, in each of the ink flow paths N1 to N4, as shown in FIG. 6, a nozzle row composed of a plurality of nozzles 88 arranged in the sub-scanning direction Y is arranged in a plurality of stages in the main scanning direction X. In the nozzle 88, as shown in FIG. 5, the inner peripheral surface is reduced in diameter toward the downstream side, so the discharge port located on the most downstream side is the “minimum diameter portion”. Accordingly, the point located at the lowest position in the vertical direction at the discharge port of the nozzle 88 constituting the lowest stage is the “nozzle lowest point”, and the ink container 16a is related to the “nozzle lowest point”. An arrangement position of ˜16d is designed. In FIG. 4, the heights T1 to T4 of the “nozzle lowest point” in each of the ink flow paths N1 to N4 are indicated by alternate long and short dash lines.

<Configuration of actuator unit>
As shown in FIG. 5, the actuator unit 54 constitutes the inner upper surface of the pressure chamber 84 in the flow path unit 52 and selectively applies discharge pressure to the ink in the pressure chamber 84. The sheet 100, the second piezoelectric sheet 102, and the third piezoelectric sheet 104 are stacked in this order from the top.

  Each of the piezoelectric sheets 100, 102, and 104 is a sheet member made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity and having a thickness of about 10 to 30 μm. A plurality of individual electrodes 106 individually corresponding to the pressure chambers 84 are formed on the upper surface of the first piezoelectric sheet 100 to be opposed to the pressure chambers 84, and the second piezoelectric sheet 102 serving as an intermediate layer. A common electrode 108 corresponding to each of the pressure chambers 84 is formed across the pressure chambers 84. Therefore, in the actuator unit 54, the first piezoelectric sheet 100 is an “active layer”, and a portion sandwiched between the individual electrode 106 and the common electrode 108 in the first piezoelectric sheet 100 is an active portion 100a. Yes.

  Further, as shown in FIGS. 5 and 6, the individual electrode terminal 110 and the common electrode terminal 112 are formed on the upper surface of the first piezoelectric sheet 100 that is the uppermost layer, and the individual electrode terminal 110 and the individual electrode 106 are formed. Are electrically connected, and the common electrode terminal 112 and the common electrode 108 are electrically connected via a conductor (not shown) disposed through the first piezoelectric sheet 100. . On the surfaces of the individual electrode terminal 110 and the common electrode terminal 112, a substantially hemispherical conductive bump 114 made of a metal material containing Ag or the like is formed.

<Configuration of FPC>
As shown in FIG. 5, the FPC 50 is composed of a base material 120 made of a flexible synthetic resin material (polyimide resin, polyester resin, polyamide resin, etc.), a conductive metal material (copper foil, etc.), and A plurality of wirings 122 formed on the lower surface of the base material 120 and a flexible synthetic resin material (polyimide resin, polyester resin, polyamide resin, etc.) and the lower surface of the base material 120 so as to cover the wiring 122 And a driver IC 126 (FIG. 3) disposed at a predetermined position on the upper surface of the base material 120 and electrically connected to each of the wirings 122. The conductive bumps 114 formed on the individual electrode terminal 110 and the common electrode terminal 112 are electrically connected to the corresponding wiring 122 at the output side end of the FPC 50.

[Configuration of drive unit]
The drive unit 14 scans the nozzle 88 (FIGS. 5 and 6) in the vertical direction by reciprocating the ink discharge head 12 in the vertical direction (that is, the main scanning direction X). As shown in FIG. 2, a carriage 130, a sliding shaft 132, a main pulley 134a, a driven pulley 134b, an annular drive belt 136, and a drive motor 138 (FIG. 2) are provided.

  As shown in FIG. 2, the carriage 130 includes a mounting portion 130a having a through-hole 140 extending in the vertical direction, a head mounting portion 130b on which the ink discharge head 12 is mounted, and a buffer mounting portion 130c on which the buffer portion 44 is mounted. A sliding shaft 132 extending in the vertical direction is inserted into the through hole 140. In addition, a pair of pulleys 134a and 134b is disposed behind the sliding shaft 132 with a space in the vertical direction, and an annular drive belt 136 is disposed between the pulleys 134a and 134b. It is stretched along 132. The carriage 130 is fixed to the drive belt 136 using a fixing member such as a screw, and the rotation shaft of the drive motor 138 (FIG. 2) is connected to the main driving pulley 134a. The control unit 26 (FIG. 1) is electrically connected.

  When the drive motor 138 (FIG. 2) is rotated based on the drive signal output from the control unit 26, the main pulley 134a and the drive belt 136 are rotated, and the carriage 130 fixed to the drive belt 136 is moved vertically upward or vertically. It is moved downward. As a result, the ink discharge head 12 is reciprocated in the vertical direction (that is, the main scanning direction X), and the nozzles 88 of the ink discharge head 12 are scanned in the vertical direction.

  When the power of the ink jet printer 10 is turned off or the ink discharge head 12 is temporarily kept in standby, the drive motor 138 is rotated based on the stop signal given from the control unit 26, and the ink discharge head 12 is moved. The vehicle is stopped at a predetermined standby position R existing in the moving area. That is, the control unit 26 functions as a “stop unit” that stops the ink discharge head 12 at the standby position R.

[Configuration of nozzle cap]
The nozzle cap 20 has both a function of protecting the nozzle 88 of the ink discharge head 12 at the standby position R and a function of recovering the discharge function damaged by sucking ink from the nozzle 88. Connected to 20 is a pump unit (not shown) that generates a negative pressure for sucking ink.

  In the present embodiment, the nozzle cap 20 is disposed in the lower region S1 located below the transport path A, and the position of the nozzle cap 20 is the standby position R. Accordingly, both the liquid ejection head 12 and the liquid containers 16a to 16d stopped at the standby position R are disposed in the lower region S1 positioned below the transport path A.

[Configuration of ink container]
The ink containers 16a to 16d are containers for storing four types of inks having different surface tensions. As shown in FIG. 7, the liquid level when the ink is stored at the maximum (hereinafter referred to as “maximum liquid level height”). It is arranged so that t1 to t4 are equal to or lower than the heights T1 to T4 of the “nozzle lowest point” in the liquid ejection head 12 stopped at the standby position R. ing. Therefore, in the liquid ejection head 12 stopped at the standby position R, “positive pressure” due to gravity does not act on the ink inside the ink, and ink leaks from the nozzles 88 of the ink flow paths N1 to N4. Can be prevented.

  Further, the ink containers 16a to 16d are arranged side by side from the upper side to the lower side in the vertical direction in ascending order of the surface tension of the stored ink. That is, in the four types of inks used in the present embodiment, the surface tension of black (BK) is the lowest, the surface tension of yellow (Y) is next low, the surface tension of cyan (C) is next low, and magenta. Since the surface tension of (M) is the highest, the ink containers 16a to 16d are arranged from the upper side to the lower side in the vertical direction in the order of these colors. Therefore, in the case of ink having a low surface tension, for example, black (BK) ink, the highest liquid level height t1 of the ink container 16a and the “nozzle lowest point” in the liquid discharge head 12 stopped at the standby position R are high. The height difference (that is, the water head difference) from the height T1 can be reduced, and excessive “negative pressure” can be prevented from acting on the ink.

  As shown in FIG. 7, each of the ink containers 16 a to 16 d and the ink flow paths N <b> 1 to N <b> 4 of the ink ejection head 12 are connected via the ink tubes 18 a to 18 d and the buffer unit 44. The buffer unit 44 has four ink storage units (not shown) interposed between the ink tubes 18a to 18d and the ink flow paths N1 to N4, and pressure acting on the ink in the ink ejection head 12 Is buffered in the ink reservoir.

[Paper Tray Configuration]
The paper tray 22 is a container that accommodates a plurality of papers P such that their paper surfaces are orthogonal to the horizontal plane. The paper tray 22 has a side view shape (a shape when viewed from the left or right side in FIG. 1). ) Is designed to be substantially the same shape (square) as the shape of the paper P, and the shape of the paper tray 22 in front view (the shape when viewed from the front side in FIG. 1) is the paper tray insertion opening in the housing 28. Designed to be substantially the same shape (square) as the shape of 34. The paper tray 22 is mounted inside the housing 28 through the paper tray insertion port 34, and is pulled out of the housing 28 through the paper tray insertion port 34.

[Configuration of paper transport unit]
The paper transport unit 24 includes a pickup roller (not shown) that picks up the paper P stored in the paper tray 22 one by one, and a transport roller 142 that transports the paper P picked up from the paper tray 22 toward the paper discharge port 36. A drive motor (not shown) controlled by the control unit 26 is connected to the pickup roller and the conveyance roller 142.

[Operation of inkjet printer]
When an image is printed on the surface of the paper P using the ink jet printer 10, the driver IC 126 (FIG. 3) of the FPC 50 from the control unit 26 (FIG. 1) and the drive motor 138 (FIG. 2) of the drive unit 14 (FIG. 2). ) And a drive motor (not shown) of the paper transport unit 24 is provided with a drive signal corresponding to the image data.

  When a drive signal is given to the driver IC 126 (FIG. 3), a drive voltage is selectively applied from the driver IC 126 to the individual electrode 106 of the actuator unit 54. As a result, the drive unit 100 a is deformed to apply a discharge pressure to the ink in the pressure chamber 84 corresponding to the individual electrode 106, and the ink is discharged from the nozzle 88 communicated with the pressure chamber 84. When a drive signal is given to the drive motor 138 (FIG. 2), the drive motor 138 is rotated so that the carriage 130 and the ink discharge head 12 mounted on the carriage 130 reciprocate in the vertical direction (that is, the main scanning direction X). Accordingly, the nozzle 88 of the ink discharge head 12 is scanned in the vertical direction. When a drive signal is given to a drive motor (not shown) of the paper transport unit 24, a pickup roller (not shown) is driven, and the paper P stored in the paper tray 22 passes through the transport path A and is transported by the transport roller 142 (FIG. 1). 2). Then, the paper P is given from the transport roller 142 to the moving area of the ink ejection head 12 at a predetermined timing. By these operations, an image corresponding to the image data is formed on the surface of the paper P.

  When stopping the operation of the inkjet printer 10, a stop signal is given to the drive motor 138 (FIG. 2) from the control unit 26 (FIG. 1). Then, the drive motor 138 is rotated in accordance with the stop signal, the carriage 130 and the ink discharge head 12 mounted on the carriage 130 are moved to the standby position R, and the ink discharge head 12 is positioned with respect to the nozzle cap 20.

  The maximum liquid level heights t1 to t4 of the ink containers 16a to 16d are the same as the “nozzle lowest point” heights T1 to T4 in the liquid ejection head 12 stopped at the standby position R, as shown in FIG. Alternatively, since it is located below that, it is possible to prevent the “positive pressure” due to gravity from acting on the ink in the ink discharge head 12 stopped at the standby position R. Ink leakage can be prevented.

  The ink containers 16a to 16d are arranged from the upper side to the lower side in the vertical direction in the order of the surface tension of the stored ink, and the nozzles 88 corresponding to the ink containers 16a to 16d respectively Since the surface tension is arranged from the lower side to the upper side in the descending order of the surface tension, the height difference (that is, the water head difference) between the liquid level of the ink in the ink containers 16a to 16d and the “nozzle lowest point” is calculated. The lower the surface tension of the ink, the smaller. Therefore, “air drawing” into the nozzle 88 due to excessive “negative pressure” can be effectively prevented.

(Second Embodiment)
FIG. 8 is a simplified diagram showing an internal configuration of an inkjet printer 150 according to the second embodiment of the present invention.

  As shown in FIG. 8, the ink jet printer 150 arranges the nozzle cap 20 and the ink containers 16 a to 16 d in the upper region S <b> 2 located above the transport path A, thereby stopping the liquid ejection head stopped at the standby position R. 12 and the ink containers 16a to 16d are both arranged in the upper region S2, and other configurations are the same as those of the inkjet printer 10 of the first embodiment.

  Also in this ink jet printer 150, as shown in FIG. 7, the maximum liquid level heights t1 to t4 of the ink containers 16a to 16d are the “nozzle lowest point” in the liquid ejection head 12 stopped at the standby position R. Since it is the same as or lower than the heights T1 to T4, it is possible to prevent ink from leaking from the nozzle 88 (FIGS. 5 and 6). The ink containers 16a to 16d are arranged from the upper side to the lower side in the vertical direction in the order of the surface tension of the stored ink, and the nozzles 88 corresponding to the ink containers 16a to 16d respectively Since the surface tension is arranged from the lower side to the upper side in the descending order of the surface tension, the lower the surface tension of the ink, the higher the level of the ink liquid level in the ink containers 16a to 16d and the “nozzle lowest point” The difference (hereinafter referred to as “water head difference”) is reduced, and “air drawing” into the nozzle 88 due to excessive “negative pressure” can be effectively prevented.

(Third embodiment)
FIG. 9 is a simplified diagram showing an internal configuration of an inkjet printer 160 according to the third embodiment of the present invention.

  As shown in FIG. 9, the ink jet printer 160 arranges the nozzle cap 20 in an area overlapping the conveyance path A and arranges the ink containers 16a to 16d in an area straddling the conveyance path A and the lower area S1. The other features are the same as those of the inkjet printer 10 of the first embodiment.

  Also in this inkjet printer 160, as shown in FIG. 7, the maximum liquid level heights t1 to t4 of the ink containers 16a to 16d are the “nozzle lowest point” in the liquid ejection head 12 stopped at the standby position R. Since it is the same as or lower than the heights T1 to T4, it is possible to prevent ink from leaking from the nozzle 88 (FIGS. 5 and 6). The ink containers 16a to 16d are arranged from the upper side to the lower side in the vertical direction in the order of the surface tension of the stored ink, and the nozzles 88 corresponding to the ink containers 16a to 16d respectively Since the ink is arranged from the lower side to the upper side in the vertical direction in the order of the lower surface tension, the “water head difference” becomes smaller as the surface tension of the ink is lower, and “air” into the nozzle 88 due to excessive “negative pressure”. Can be effectively prevented.

(Fourth embodiment)
FIG. 10 is a schematic view showing a main part of an inkjet printer 170 according to the fourth embodiment of the present invention.

  As shown in FIG. 10, the ink jet printer 170 arranges the ink flow paths N1 to N4 in the ink discharge head 172 side by side from the upper side to the lower side in the vertical direction in order of the surface tension of the ink flowing therethrough, that is, The nozzles 88 corresponding to each of the ink containers 16a to 16d are arranged side by side from the upper side to the lower side in the vertical direction in order of the surface tension of the ink to be ejected, and other configurations are described in the first embodiment. This is the same as the inkjet printer 10 of FIG.

  Also in this ink jet printer 170, the maximum liquid level heights t1 to t4 of the ink containers 16a to 16d are the same as the heights T1 to T4 of the “nozzle lowest point” in the liquid discharge head 172 stopped at the standby position R. Alternatively, since the ink is positioned below it, it is possible to prevent the ink from leaking out from the nozzle 88 (FIGS. 5 and 6). Further, since the ink containers 16a to 16d are arranged from the upper side to the lower side in the vertical direction in the order of the surface tension of the contained ink, the “water head difference” becomes smaller as the surface tension of the ink is lower, which is excessive. It is possible to effectively prevent “intake of air” into the nozzle 88 due to such “negative pressure”.

(Fifth embodiment)
FIG. 11 is a schematic diagram showing a main part of an inkjet printer 180 according to the fifth embodiment of the present invention.

  As shown in FIG. 11, the ink jet printer 180 arranges the ink containers 16a to 16d side by side in the horizontal direction, and vertically arranges the ink flow paths N1 to N4 in the ink discharge head 182 in ascending order of surface tension of the ink flowing therethrough. In other words, the nozzles 88 (FIGS. 5 and 6) corresponding to the ink containers 16a to 16d are arranged from the lower side in the vertical direction in ascending order of the surface tension of the ink to be ejected. The other features are the same as those of the inkjet printer 10 of the first embodiment.

  Also in the ink jet printer 180, the maximum liquid level heights t1 to t4 of the ink containers 16a to 16d are the same as the heights T1 to T4 of the “nozzle lowest point” in the liquid discharge head 182 stopped at the standby position R. Alternatively, since the ink is positioned below it, it is possible to prevent the ink from leaking out from the nozzle 88 (FIGS. 5 and 6). Further, the nozzles 88 corresponding to the ink containers 16a to 16d are arranged from the lower side to the upper side in the vertical direction in the order of the surface tension of the ink to be ejected. The “difference” becomes small, and “air drawing” into the nozzle 88 due to excessive “negative pressure” can be effectively prevented.

(Other embodiments)
In the above embodiment, an inkjet printer that ejects four colors of ink has been described as an example. However, the present invention also applies to an inkjet printer that ejects a plurality of colors of three colors, five colors, or more. It is also applicable to “monochrome” inkjet printers that eject two colors of ink: pigment black ink (hereinafter referred to as “pigment BK”) and dye black ink (hereinafter referred to as “dye BK”). Applicable. For example, when the present invention is applied to a “monochrome” inkjet printer, if the surface tension of the “dye BK” is lower than the surface tension of the “pigment BK”, the “ink discharge head” has the “dye BK” The ink flow path is arranged below the “pigment BK” ink flow path in the vertical direction, and in the two “ink containers”, the ink container containing “dye BK” contains “pigment BK”. It is arranged above the container in the vertical direction.

A ... transport path N1-N4 ... ink flow path P ... paper T1-T4 ... nozzle bottom point height t1-t4 ... maximum liquid level height S1 ... lower region S2 ... upper region 10 ... inkjet printer 12 ... Ink discharge head (liquid discharge head)
14 ... Drive parts 16a-16d ... Ink container (liquid container)
18a to 18d ... Ink tube (liquid tube)
20 ... Nozzle cap 22 ... Paper tray 24 ... Paper transport unit 26 ... Control unit (stopping means)
44 ... Buffer unit 52 ... Flow path unit 54 ... Actuator unit 84 ... Pressure chamber 88 ... Nozzle 130 ... Carriage 136 ... Drive belt 138 ... Drive motor 142 ... Conveying rollers 150, 160, 170, 180 ... Inkjet printer

Claims (2)

A liquid discharge head having a nozzle for discharging liquid toward the discharge target;
A drive unit that scans the nozzle in the vertical direction by reciprocating the liquid discharge head in the vertical direction;
A transport path for transporting the discharge target in a direction orthogonal to the scanning direction of the nozzle;
Stop means for stopping the liquid discharge head at a predetermined standby position existing in the moving region;
A liquid container for storing liquid discharged from the nozzle;
A liquid tube for supplying the liquid in the liquid container to the liquid discharge head,
Both the liquid discharge head and the liquid container stopped at the standby position are arranged in either the upper region positioned above the transport path or the lower region positioned below the transport path. and,
A plurality of the liquid containers are provided so as to accommodate liquids having different surface tensions,
A plurality of the nozzles are provided to individually correspond to each of the liquid containers,
A plurality of the liquid tubes are provided to supply the liquid in the liquid container to the corresponding nozzle,
Each of the plurality of liquid containers has the same height as the lowest point of the nozzles in the liquid discharge head stopped at the standby position when the liquid is maximally accommodated, or Are arranged to be lower than
The plurality of nozzles are arranged in the vertical direction from the lower side to the upper side in order of increasing surface tension of the liquid to be discharged.
The liquid ejection device according to claim 1, wherein a nozzle cap that covers the nozzle is disposed at the standby position.

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