JP2017140761A - Printing apparatus and discharge method - Google Patents

Abstract

Provided is a printing apparatus in which the amount of mist is reduced and print quality is improved. A printing apparatus discharges a plurality of droplets from a nozzle to a predetermined position of a print medium, and a distance between the nozzle and the print medium. And a control unit that outputs to the ejection head 42 a drive waveform that can be combined at a distance L2 equal to or less than １ ／ of the WG. Thereby, the flight distance in which the previously discharged droplet 47a flies with tailing is shortened, and the amount of mist generated can be reduced. [Selection diagram] FIG.

Description

  The present invention relates to a printing apparatus and a discharge method.

  2. Description of the Related Art Conventionally, inkjet printing apparatuses that eject ink or the like into droplets from a discharge head having nozzles toward a print medium and print an image or the like on the print medium are known. In such a printing apparatus, in order to change the size of dots formed on a printing medium, a technique for combining a plurality of droplets ejected from nozzles and landing at a predetermined position has been proposed. For example, Patent Document 1 discloses a droplet discharge apparatus (printing apparatus) including a droplet discharge unit that can continuously discharge a plurality of droplets and combine the plurality of droplets to land.

JP 2011-42144 A

  However, in the printing apparatus described in Patent Document 1, since a plurality of droplets ejected from the nozzles are merged near the print medium, each droplet is alone before the droplets are merged. The flying time was long. As a result, there is a problem that the fine satellite array (tailing) generated from each droplet becomes long, and the amount of mist generated and remaining between the ejection head and the print medium increases. Then, mist may adhere to the ejection head, causing ejection failure such as missing nozzles where droplets are not ejected or displacement of landing positions of droplets, or may adhere to the print medium and contaminate the print medium. .

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 A printing apparatus according to this application example has a discharge head that discharges a plurality of droplets from a nozzle to a predetermined position of a print medium, and a distance of 1 from the nozzles to the print medium. And a control unit that outputs a drive waveform that can be combined at a distance of 2 or less to the ejection head.

  According to this application example, the control unit of the printing apparatus outputs a drive waveform that combines a plurality of liquid droplets to the ejection head at a distance of ½ or less of the distance from the nozzle to the print medium. As a result, the plurality of liquid droplets ejected from the nozzles are combined at a distance of ½ or less of the distance from the nozzle to the print medium, so that the first ejected liquid droplets fly with tailing. The distance is shortened, and the amount of mist generated from a plurality of droplets can be reduced. Since the mist staying between the ejection head and the print medium is reduced, the ejection failure of the droplets caused by the mist adhering to the ejection head is reduced. Further, the print medium is prevented from being contaminated with mist. Thereby, the quality of the image etc. printed on a printing medium can be improved. Therefore, it is possible to provide a printing apparatus with improved print quality.

  Application Example 2 In the printing apparatus according to the application example described above, the drive waveform is 95% or more and 130% or less with respect to the drive voltage of a droplet that is ejected in advance by a drive voltage that ejects a subsequent droplet. It is preferable.

  According to this application example, the subsequent droplets are ejected at a driving voltage of 95% or more with respect to the driving voltage of the droplets ejected in advance. If the driving voltage is 95% or more, the subsequent droplets can be combined with the previously ejected droplets by a so-called slip stream in which the air resistance at the rear is lowered by an object moving in the front. Further, if the driving voltage for ejecting the droplets is increased more than necessary, the amount of mist generated when the droplets are ejected increases, so that the subsequent droplets are 130% or less of the previously ejected droplets. It is preferable to discharge at a driving voltage of

  Application Example 3 In the printing apparatus according to the application example described above, it is preferable that the drive waveform has a drive voltage for discharging the first droplet of 70% or more with respect to the maximum drive voltage.

  According to this application example, when the driving voltage for ejecting droplets is lowered, the first droplet is more likely to be affected by mist adhering to the nozzles or ink thickening. It is preferable that ejection is performed with a driving voltage of 70% or more of the maximum driving voltage in the ejection waveform to be ejected.

  Application Example 4 An ejection method according to this application example includes an ejection head that ejects a plurality of droplets from a nozzle to a predetermined position of a print medium, and a distance of 1 from the nozzles to the print medium. And a control unit that outputs a drive waveform that can be combined at a distance of 2 or less to the discharge head. Subsequent droplets are ejected at a driving voltage of 95% to 130% with respect to the driving voltage.

  According to this application example, the ejection method for ejecting a plurality of droplets to a predetermined position of the print medium is performed by using the subsequent liquid at a driving voltage of 95% or more and 130% or less with respect to the driving voltage of the droplet to be ejected in advance. Let the drops be ejected. As a result, a plurality of droplets ejected from the nozzle can be combined at a distance of 1/2 or less of the distance from the nozzle to the printing medium, so that the droplet ejected earlier flies with tailing. The flying distance is reduced, and the amount of mist generated from a plurality of droplets can be reduced. Since the mist staying between the ejection head and the print medium is reduced, the ejection failure of the droplets caused by the mist adhering to the ejection head is reduced. Further, the print medium is prevented from being contaminated with mist. Thereby, the quality of the image etc. printed on a printing medium can be improved. Therefore, it is possible to provide a discharge method with improved print quality.

1 is a schematic diagram illustrating a schematic overall configuration of a printing apparatus according to an embodiment. FIG. 3 is an electrical block diagram illustrating an electrical configuration of the printing apparatus. Sectional drawing which shows the structure of an ejection head. The figure which shows the drive waveform in the case of discharging a droplet twice continuously. The side view when a droplet is discharged from a nozzle. The side view when a droplet is discharged from a nozzle. Relationship between the coalescing position of the droplets and the contamination of the print medium. The graph which shows the relationship between a drive voltage and the speed of the discharged droplet. The graph which shows the speed change of the discharged droplet. The figure which shows the drive waveform in the case of discharging a droplet 4 times continuously. The figure which shows an example of the drive waveform table which discharges a droplet.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the scale of each layer and each member is different from the actual scale so that each layer and each member can be recognized.
In FIG. 1, for convenience of explanation, the X axis, the Y axis, and the Z axis are illustrated as three axes orthogonal to each other, the tip side of the arrow illustrating the axial direction is “+ side”, and the base end side is illustrated. “− Side”. Hereinafter, a direction parallel to the X axis is referred to as an “X axis direction”, a direction parallel to the Y axis is referred to as a “Y axis direction”, and a direction parallel to the Z axis is referred to as a “Z axis direction”.

(Embodiment)
<Schematic configuration of printing device>
FIG. 1 is a schematic diagram illustrating a schematic overall configuration of a printing apparatus according to an embodiment. First, a schematic configuration of the printing apparatus 100 according to the present embodiment will be described with reference to FIG. In the present embodiment, an ink jet printing apparatus 100 that performs printing on the print medium 95 by forming an image or the like on the print medium 95 will be described as an example.

  As illustrated in FIG. 1, the printing apparatus 100 includes a medium supply unit 10, a medium transport unit 20, a medium recovery unit 30, a printing unit 40, a drying unit 27, a cleaning unit 50, and a medium contact unit 60. And it has the control part 1 which controls each of these parts. Each unit of the printing apparatus 100 is attached to the frame unit 90.

  The medium supply unit 10 supplies a print medium 95 for forming an image to the printing unit 40 side. As the printing medium 95, for example, a cloth such as cotton, wool, chemical fiber, and mixed spinning is used. The medium supply unit 10 includes a supply shaft portion 11 and a bearing portion 12. The supply shaft portion 11 is formed in a cylindrical shape or a columnar shape, and is provided to be rotatable in the circumferential direction. A belt-like print medium 95 is wound around the supply shaft portion 11 in a roll shape. The supply shaft portion 11 is detachably attached to the bearing portion 12. As a result, the print medium 95 that has been previously wound around the supply shaft portion 11 can be attached to the bearing portion 12 together with the supply shaft portion 11.

  The bearing portion 12 rotatably supports both ends of the supply shaft portion 11 in the axial direction. The medium supply unit 10 includes a rotation drive unit (not shown) that rotates the supply shaft unit 11. The rotation drive unit rotates the supply shaft unit 11 in the direction in which the print medium 95 is sent out. The operation of the rotation drive unit is controlled by the control unit 1.

  The medium transport unit 20 transports the print medium 95 from the medium supply unit 10 to the medium recovery unit 30. The medium conveyance unit 20 includes a conveyance roller 21, a conveyance roller 22, an endless belt 23, a belt rotation roller 24, a belt driving roller 25, a conveyance roller 26, and a conveyance roller 28. The transport rollers 21 and 22 relay the print medium 95 from the medium supply unit 10 to the endless belt 23.

  The endless belt 23, the belt rotation roller 24, and the belt driving roller 25 are medium conveyance units that convey the print medium 95 in the conveyance direction (+ X axis direction) in the printing unit 40. Specifically, the endless belt 23 is formed in an endless shape by connecting both ends of a belt-like belt, and is hung on the belt rotating roller 24 and the belt driving roller 25. The endless belt 23 is held in a state where a predetermined tension is applied so that a portion between the belt rotating roller 24 and the belt driving roller 25 is parallel to the floor surface 99. An adhesive layer 29 that adheres the print medium 95 is provided on the surface (support surface) 23 a of the endless belt 23. The endless belt 23 supports (holds) a print medium 95 that is supplied from the transport roller 22 and is in close contact with the adhesive layer 29 by a medium contact portion 60 described later. Thereby, a stretchable fabric or the like can be handled as the print medium 95.

  The belt rotating roller 24 and the belt driving roller 25 support the inner peripheral surface 23 b of the endless belt 23. In addition, the structure by which the support part which supports the endless belt 23 was provided between the belt rotation roller 24 and the belt drive roller 25 may be sufficient.

  The belt drive roller 25 has a motor (not shown) that drives the belt drive roller 25 to rotate. When the belt driving roller 25 is driven to rotate, the endless belt 23 rotates as the belt driving roller 25 rotates, and the belt rotating roller 24 rotates as the endless belt 23 rotates. As the endless belt 23 rotates, the print medium 95 supported by the endless belt 23 is transported in a predetermined transport direction (+ X-axis direction), and an image is formed on the print medium 95 by the printing unit 40 described later. In the present embodiment, the print medium 95 is supported on the side (+ Z axis side) where the surface 23 a of the endless belt 23 faces the printing unit 40, and the print medium 95 together with the endless belt 23 from the belt rotation roller 24 side to the belt driving roller 25. Conveyed to the side. Further, on the side where the surface 23 a of the endless belt 23 faces the cleaning unit 50 (−Z axis side), only the endless belt 23 moves from the belt driving roller 25 side to the belt rotating roller 24 side.

  The conveyance roller 26 peels the print medium 95 on which the image is formed from the adhesive layer 29 of the endless belt 23. The conveyance rollers 26 and 28 relay the print medium 95 from the endless belt 23 to the medium recovery unit 30.

  The medium collection unit 30 collects the print medium 95 conveyed by the medium conveyance unit 20. The medium recovery unit 30 includes a winding shaft portion 31 and a bearing portion 32. The winding shaft portion 31 is formed in a cylindrical shape or a columnar shape, and is provided to be rotatable in the circumferential direction. A belt-shaped print medium 95 is wound around the winding shaft portion 31 in a roll shape. The winding shaft portion 31 is detachably attached to the bearing portion 32. As a result, the print medium 95 in the state of being wound around the winding shaft portion 31 can be removed together with the winding shaft portion 31.

  The bearing portion 32 rotatably supports both ends of the winding shaft portion 31 in the axial direction. The medium recovery unit 30 includes a rotation driving unit (not shown) that drives the winding shaft unit 31 to rotate. The rotation drive unit rotates the take-up shaft part 31 in the direction in which the print medium 95 is taken up. The operation of the rotation drive unit is controlled by the control unit 1.

  The drying unit 27 dries the liquid (droplets) discharged on the print medium 95 and is provided between the transport roller 26 and the transport roller 28. The drying unit 27 includes, for example, an IR heater, and the liquid discharged onto the print medium 95 can be dried in a short time by driving the IR heater. As a result, the strip-shaped print medium 95 on which an image or the like is formed can be wound around the winding shaft portion 31.

  The medium contact portion 60 is for bringing the print medium 95 into close contact with the endless belt 23. The medium contact portion 60 is provided on the upstream side (−X axis side) from the printing portion 40 with respect to the conveyance direction of the print medium 95. The medium contact portion 60 includes a pressing roller 61, a pressing roller driving unit 62, and a roller support unit 63. The pressing roller 61 is formed in a cylindrical shape or a columnar shape, and is provided to be rotatable in the circumferential direction. The pressing roller 61 is disposed so that the axial direction intersects the transport direction so as to rotate in a direction along the transport direction. The roller support portion 63 is provided on the inner peripheral surface 23 b side of the endless belt 23 that faces the pressing roller 61 with the endless belt 23 interposed therebetween.

  The pressing roller driving unit 62 presses the pressing roller 61 in the conveying direction (+ X axis direction) and the direction opposite to the conveying direction (−X axis direction) while pressing the pressing roller 61 downward in the vertical direction (−Z axis side). The roller 61 is moved. The print medium 95 conveyed from the conveyance roller 22 and superimposed on the endless belt 23 is pressed against the endless belt 23 between the pressing roller 61 and the roller support portion 63. Thereby, the print medium 95 can be reliably adhered to the adhesive layer 29 provided on the surface 23a of the endless belt 23, and the occurrence of the floating of the print medium 95 on the endless belt 23 can be prevented.

  The cleaning unit 50 is for cleaning the surface 23 a of the endless belt 23. The cleaning unit 50 includes a cleaning unit 51, a pressing unit 52, and a moving unit 53. The moving unit 53 integrally moves the cleaning unit 50 along the floor surface 99 and fixes it to a predetermined position. The cleaning unit 50 is disposed between the belt rotating roller 24 and the belt driving roller 25 in the X-axis direction.

  The pressing part 52 is, for example, an elevating device composed of an air cylinder 56 and a ball bush 57, and makes the cleaning part 51 provided on the upper part abut on the surface 23a of the endless belt 23. The cleaning unit 51 cleans the surface (support surface) 23a of the endless belt 23 that is applied with a predetermined tension between the belt rotating roller 24 and the belt driving roller 25 from below (-Z axis direction). To do.

  The cleaning unit 51 includes a cleaning tank 54, a cleaning roller 58, and a blade 55. The cleaning tank 54 is a tank for storing a cleaning liquid used for cleaning ink and foreign matters attached to the surface 23 a of the endless belt 23, and the cleaning roller 58 and the blade 55 are provided inside the cleaning tank 54. As the cleaning liquid, for example, water or a water-soluble solvent (such as an alcohol aqueous solution) can be used, and a surfactant or an antifoaming agent may be added as necessary.

  When the cleaning roller 58 rotates, the cleaning liquid is supplied to the surface 23a of the endless belt 23, and the cleaning roller 58 and the endless belt 23 slide. As a result, the ink adhering to the endless belt 23, the fabric fibers as the print medium 95, and the like are removed by the cleaning roller 58.

  The blade 55 can be formed of a flexible material such as silicon rubber, for example. The blade 55 is provided on the downstream side of the cleaning roller 58 in the conveying direction of the endless belt 23. As the endless belt 23 and the blade 55 slide, the cleaning liquid remaining on the surface 23a of the endless belt 23 is removed.

  The printing unit 40 includes an inkjet-type ejection head 42 that ejects ink as droplets toward the print medium 95, a carriage moving unit 41 that moves a carriage 43 on which the ejection head 42 is mounted, and the like. The printing unit 40 is arranged above (+ Z axis side) with respect to the arrangement position of the endless belt 23. The ejection head 42 is provided with a nozzle plate 44 in which a plurality of nozzle rows 45 are formed. For example, four nozzle rows 45 are formed on the nozzle plate 44, and different color inks (for example, cyan: C, magenta: M, yellow: Y, black: K) are ejected for each nozzle row 45. It has become. The nozzle plate 44 faces the print medium 95 conveyed by the endless belt 23.

  The carriage moving unit 41 moves the ejection head 42 in a direction intersecting with the conveyance direction of the print medium 95 (width direction of the print medium 95 (Y-axis direction)). The carriage 43 is supported by guide rails (not shown) arranged along the Y-axis direction, and is configured to be reciprocally movable in the ± Y-axis directions by the carriage moving unit 41. As a mechanism of the carriage moving unit 41, for example, a mechanism combining a ball screw and a ball nut, a linear guide mechanism, or the like can be employed.

  Furthermore, the carriage moving unit 41 is provided with a motor (not shown) as a power source for moving the carriage 43 along the Y-axis direction. When the motor is driven by the control of the control unit 1, the ejection head 42 reciprocates along the Y axis direction together with the carriage 43. In the present embodiment, the ejection head 42 is exemplified by a serial head type that is mounted on a movable carriage and ejects ink while moving in the width direction (± Y-axis direction) of the print medium 95. It may be a line head type that extends in the width direction (Y-axis direction) and is fixedly arranged.

<Electrical configuration>
FIG. 2 is an electrical block diagram illustrating an electrical configuration of the printing apparatus. Next, the electrical configuration of the printing apparatus 100 will be described with reference to FIG.

  The printing apparatus 100 includes a control unit 1. The control unit 1 is a control unit for controlling the printing apparatus 100. The control unit 1 includes an external interface (external I / F) 2, a storage element such as a RAM (Random Access Memory) 4 and a ROM (Read Only Memory) 5, a CPU (CENTRAL PROCESSING UNIT) 3, and a drive signal generation circuit 7, an oscillation circuit 8, and an internal interface (internal I / F) 6.

The external I / F 2 is used to transmit and receive data between an external device (not shown) that handles images, such as a computer, and the printing apparatus 100. The RAM 4 stores various data and the like, and the ROM 5 stores control routines and the like for various data processing.
The CPU 3 controls each unit of the printing apparatus 100 in accordance with an operation program stored in the ROM 5. Further, the CPU 3 converts print data input from an external device via the external I / F 2 into discharge data used for discharging droplets (ink) in the discharge head 42.

  The drive signal generation circuit 7 is a circuit that generates a drive signal COM having a waveform shape determined by the CPU 3. The oscillation circuit 8 is a timing device for generating a control signal CK for the printing apparatus 100. The internal I / F 6 is for outputting ejection data, drive signal COM, and the like obtained by developing (data conversion) print data for each dot to the carriage moving unit 41, the belt drive roller 25, and the ejection head 42. It is.

  The ejection head 42 includes a shift register (SR) 91 in which the recording data SI is set, a latch circuit 92 that latches the recording data SI set in the shift register 91 based on a latch signal (LAT), and a voltage amplifier. A level shifter 93 that functions as a piezoelectric vibrator 72, and a switch circuit 94 that controls the supply of a drive signal COM to the piezoelectric vibrator 72.

FIG. 3 is a cross-sectional view showing the configuration of the ejection head. Next, the structure of the ejection head 42 will be described.
As shown in FIG. 3, the ejection head 42 includes a vibrator unit 70 in which a plurality of piezoelectric vibrators 72, a fixed plate 73, a flexible cable 74, and the like are unitized, and a case 71 that can store the vibrator unit 70. And a flow path unit 80 joined to the front end surface of the case 71.

  The case 71 is a synthetic resin block-like member in which a housing empty portion 75 having both the front end and the rear end opened, and the vibrator unit 70 is housed and fixed in the housing empty portion 75.

The piezoelectric vibrator 72 is formed in a comb-teeth shape elongated in the vertical direction. The piezoelectric vibrator 72 is a laminated piezoelectric vibrator configured by alternately laminating piezoelectric bodies and internal electrodes, and is a longitudinal vibration mode piezoelectric vibrator capable of expanding and contracting in a vertical direction perpendicular to the stacking direction. It is. The front end surface of each piezoelectric vibrator 72 is joined to the island portion 76 of the flow path unit 80.
The piezoelectric vibrator 72 behaves like a capacitor. That is, when the signal supply is stopped, the potential of the piezoelectric vibrator 72 is held at the potential immediately before the stop.

  In the flow path unit 80, the nozzle plate 44 is disposed on one surface side of the flow path forming substrate 83 with the flow path forming substrate 83 interposed therebetween, and the elastic plate 84 is disposed on the other surface opposite to the nozzle plate 44. It is configured by arranging and laminating on the side.

  The nozzle plate 44 is composed of a thin metal plate material (for example, a stainless steel plate) in which a plurality of (for example, 180) nozzles 46 are opened along the sub-scanning direction (X-axis direction). The flow path forming substrate 83 is a plate-like member in which a series of ink flow paths including a common ink chamber 86, an ink supply port 87, a pressure chamber 88, and a nozzle communication port 89 are formed. In the present embodiment, the flow path forming substrate 83 is produced by etching a silicon wafer. The elastic plate 84 is a double-structured composite plate material obtained by laminating a resin film 81 on a stainless support plate 82, and the island 76 is removed by removing the support plate 82 corresponding to the pressure chamber 88 in an annular shape. Forming.

  In the ejection head 42, a series of ink flow paths from the common ink chamber 86 to the nozzle 46 through the pressure chamber 88 is formed for each nozzle 46. The piezoelectric vibrator 72 is deformed by charging or discharging the piezoelectric vibrator 72. That is, the piezoelectric vibrator 72 in the longitudinal vibration mode contracts in the longitudinal direction of the vibrator by charging and expands in the longitudinal direction of the vibrator by discharging. Therefore, when the potential is increased by charging, the island portion 76 is pulled toward the piezoelectric vibrator 72 side, the resin film 81 around the island portion 76 is deformed, and the pressure chamber 88 expands. Further, when the potential is lowered by the discharge, the pressure chamber 88 contracts.

  As described above, since the volume of the pressure chamber 88 can be controlled in accordance with the potential, the pressure in the ink in the pressure chamber 88 can be changed, and ink droplets can be ejected from the nozzle 46. For example, the ink can be ejected into droplets by once expanding the pressure chamber 88 having a constant capacity (reference volume) and then rapidly contracting it.

  In the present embodiment, the configuration using the longitudinal vibration type piezoelectric vibrator 72 is exemplified, but the present invention is not limited to this. For example, a bending deformation type piezoelectric vibrator in which a lower electrode, a piezoelectric layer, and an upper electrode are laminated may be used. Further, as a means for expanding and contracting the pressure chamber 88, a discharge head having a configuration in which bubbles are generated in the nozzle using a heating element and ink is discharged as droplets by the bubbles may be used.

FIG. 4 is a diagram illustrating a driving waveform when droplets are ejected twice in succession.
5 and 6 are side views when droplets are ejected from the nozzle. Next, droplets discharged from the nozzle will be described with reference to FIGS.
The printing apparatus 100 according to this embodiment outputs a plurality of liquids from a nozzle 46 to a predetermined position (predetermined pixel) of a print medium 95 based on a drive waveform output from the control unit 1 and applied to the piezoelectric vibrator 72 of the ejection head 42. Drops 47 are ejected. When the control unit 1 generates the drive waveform shown in FIG. 4 and applies it to the piezoelectric vibrator 72, the piezoelectric vibrator 72 expands and contracts according to the displacement of the drive voltage Va, and the droplet 47a is ejected from the nozzle 46. Then, after the elapse of time t (hereinafter also referred to as a discharge interval t), the piezoelectric vibrator 72 discharges the droplet 47b from the nozzle 46 according to the displacement of the drive voltage Vb. FIG. 5 shows a state where two droplets 47a and 47b are ejected.

  Further, the controller 1 can drive the plurality of droplets 47 to be combined at a distance L3 that is ½ or less of a distance WG (hereinafter referred to as “gap WG”) between the nozzle 46 and the print medium 95. Since the waveform is output, the droplet 47b (hereinafter also referred to as the succeeding droplet 47b) discharged later to the droplet 47a (hereinafter also referred to as the preceding droplet 47a) discharged earlier until the distance L3. The caught-up and united droplet 48 lands on a predetermined pixel. FIG. 6 shows a state of the droplet 48 in which the droplets 47a and 47b are combined.

  It is known that when the liquid droplet 47 is ejected from the nozzle 46, the liquid droplet 47 flies with tailing, and a light liquid having a mass separated from the liquid droplet 47 stays as mist. In the printing apparatus 100 that performs printing on the printing medium 95 such as a fabric, it is necessary to perform printing with the gap WG widened to, for example, 2 mm or more. Mist is generated from the droplet 47 and the amount of mist remaining between the ejection head 42 and the print medium 95 increases. The mist adheres to the nozzle plate 44 of the ejection head 42 to cause ejection failure of the droplet 47, or adheres to the print medium 95 and contaminates the print medium 95, so that the print quality of the printed image or the like is increased. Had fallen.

FIG. 7 is a table showing the relationship between the droplet coalescing position and the stain on the print medium.
As a result of examining the distance L3 at which the droplets 47 ejected from the nozzles 46 are combined and the state (dirt) in which the print medium 95 is contaminated by mist, the inventors of the present application, as shown in FIG. It has been found that the contamination of the print medium 95 due to mist is significantly improved by making the distance L3 until the droplets 47 merge into less than ½ of the gap WG. It was also confirmed that the amount of mist adhering to the nozzle plate 44 also decreased.

FIG. 8 is a graph showing the relationship between the drive voltage and the velocity of the ejected droplets. The horizontal axis of FIG. 8 represents a standardized voltage obtained by standardizing a voltage applied to the piezoelectric vibrator 72 when the droplet 47 is ejected with a predetermined voltage. The vertical axis in FIG. 8 represents the velocity of the droplet 47 ejected from the nozzle 46.
FIG. 9 is a graph showing a change in velocity of the discharged droplet. The horizontal axis in FIG. 9 indicates the distance from the nozzle 46 (nozzle plate 44). The vertical axis in FIG. 9 represents the velocity of the droplet 47 ejected from the nozzle 46. 8 and 9, the velocity of the droplet 47a ejected earlier is indicated by a solid line, and the velocity of the droplet 47b ejected later is indicated by a one-dot chain line.

  The printing apparatus 100 and the ejection method thereof according to the present embodiment have a driving voltage of 95% or more and 130% or less with respect to the driving voltage of the droplet 47a to be ejected in advance based on the driving waveform output from the control unit 1. The subsequent droplet 47b is discharged. As shown in FIG. 8, when droplets are continuously ejected at the same drive voltage, the velocity of the later ejected droplet (subsequent droplet) 47b is the same as the preceding ejected droplet (preceding liquid). Drop) 47a is faster. The moving object receives air resistance on the front surface in the traveling direction, but the air pressure is reduced (slip stream) behind the object. The subsequent droplet 47b has a lower air resistance due to the slip stream of the preceding droplet 47a in the traveling direction, and can move at a faster speed than the preceding droplet 47a. In other words, the succeeding droplet 47b can catch up with the preceding droplet 47a even if it is ejected at a driving voltage lower than that of the preceding droplet 47a. For example, the speed of the subsequent droplet 47b ejected with the drive voltage of the standardized voltage 0.95 is substantially the same as the speed of the preceding droplet 47a ejected with the drive voltage of the standardized voltage 1.0. The succeeding droplet 47b ejected with a drive voltage of 0.95 to 1.0 is faster than the velocity of the droplet 47a.

  FIG. 9 shows the velocities of the droplets 47a and 47b at a point L1 at a distance L1 from the nozzle 46 (see FIG. 5) and a point L2 at a distance L2 from the nozzle 46 (see FIG. 5). The speed of both the preceding droplet 47a and the subsequent droplet 47b decreases in proportion to the moving distance. However, the subsequent droplet 47b has a lower speed reduction rate than the preceding droplet 47a due to the slip stream of the preceding droplet 47a, so that the driving voltage of the subsequent droplet 47b is lower than the driving voltage of the preceding droplet 47a. Can also catch up with the preceding droplet 47a. For example, the preceding droplet 47a and the succeeding droplet 47b ejected at substantially the same speed are approximately 0.5 m / s faster than the preceding droplet 47a at the point L2.

  For example, the gap WG is 2 mm or more, the discharge interval (time t) is 17 μs, the average velocity of the preceding droplet 47a is 5 m / s, and the average velocity difference between the preceding droplet 47a and the following droplet 47b is 0.5 m / s. When s is set, the droplets 47a and 47b become a combined droplet 48 at a distance L3 = 1 mm or less. Therefore, by ejecting the subsequent droplet 47b with a drive voltage of 95% or more with respect to the drive voltage of the previously ejected droplet (preceding droplet 47a), the droplets 47a and 47b are 1 / gap of the gap WG. Combined at a distance L3 of 2 or less. If the drive voltage for ejecting the droplet 47 is increased more than necessary, the amount of mist generated when the droplet 47 is ejected increases, so that the subsequent droplet 47b is driven at 130% or less of the preceding droplet 47a. It is preferable to discharge by voltage. Further, since the drop 48 is combined with a distance L3 that is equal to or less than ½ of the gap WG, a decrease in flight speed due to an increase in mass is suppressed, so that the position accuracy for landing the drop is improved.

FIG. 10 is a diagram showing a driving waveform when droplets are ejected four times in succession. FIG. 11 is a diagram illustrating an example of a drive waveform table for discharging droplets.
Next, drive waveforms when droplets are ejected four times in succession will be exemplified.
When the control unit 1 generates the drive waveform shown in FIG. 10 and applies it to the piezoelectric vibrator 72, the piezoelectric vibrator 72 expands and contracts according to the displacement of the drive voltage V1, and the first droplet is ejected from the nozzle 46. . Then, after time t1, the second droplet is ejected according to the displacement of the drive voltage V2, and further after time t2, the third droplet is ejected according to the displacement of the drive voltage V3, and further after time t3, the displacement of the drive voltage V4. Accordingly, the fourth droplet is ejected. The first to fourth liquid droplets are combined up to a distance of ½ of the gap WG and land on a predetermined pixel. Note that the maximum drive voltage output for discharging the first to fourth droplets is the maximum drive voltage VH. In the example of FIG. 10, the drive voltage V4 for discharging the fourth droplet is the maximum drive voltage VH for one cycle of the drive waveform. The period of the waveform is set to about 80 μs, and the discharge intervals (time t1, t2, t3) of the first to fourth droplets are set to 20 μs or less.

  In the printing apparatus 100 of the present embodiment, a drive waveform table for ejecting droplets according to the ink type and ambient temperature conditions is stored in the RAM 4, and based on the ink type and the ambient temperature that are input during printing. A drive waveform is generated with reference to the drive waveform table. In the drive waveform table shown in FIG. 11, the drive voltages V1 to V4 when four droplets are ejected and landed on a predetermined pixel are indicated by the ratio to the maximum drive voltage HV (see the column “Ratio to VH”). ing. Further, in FIG. 11, the voltage ratio of the succeeding droplet to the preceding droplet (see the column “Voltage ratio to the preceding droplet”) is shown for reference.

  The first droplet is ejected at a driving voltage V1 of 70% or more with respect to the maximum driving voltage VH based on the driving waveform output from the control unit 1. As shown in “ratio to VH” in FIG. 11, the driving voltage V1 for discharging the first droplet is set to 70% or more of the maximum driving voltage VH. This is because if the driving voltage for ejecting the first droplet is made too low in order to quickly merge with the subsequent droplet, the droplet is easily affected by mist adhering to the vicinity of the nozzle 46, thickened ink, or the like. This is because the discharge of water becomes unstable. In the printing apparatus 100 of the present embodiment, the driving voltage V1 for discharging the first droplet is set to 70% or more of the maximum driving voltage VH under all combination conditions of the ink type and the ambient temperature. Is ensured, and discharge defects due to thickening can be reduced.

  Further, as shown in “Voltage ratio with respect to preceding droplet” in FIG. 11, the driving voltages V2 to V4 for discharging the second to fourth droplets (following droplets) are the first to third discharged immediately before. It is set to 95% or more and 130% or less (120% or less in the example of FIG. 11) with respect to the driving voltages V1 to V3 of the droplets (preceding droplets). In addition, since the third and fourth droplets are greatly affected by the slip stream received from the preceding droplets, the first to fourth droplets are combined at a distance L3 that is ½ or less of the gap WG and are predetermined. The pixel can be landed. Since the distance that each droplet travels alone is shortened, the mist generated from each droplet is reduced, and the amount of mist remaining between the ejection head 42 and the print medium 95 is also reduced. As a result, it is possible to reduce ejection defects caused by the mist adhering to the nozzle plate 44 of the ejection head 42 and to stabilize the ejection of droplets. Further, mist floating in an area relatively close to the print medium 95 is reduced, and contamination of the print medium 95 by the mist is greatly improved. As a result, the print quality of the image printed on the print medium 95 is improved.

In FIG. 11, the drive waveform table for ejecting four droplets is illustrated, but the printing apparatus 100 of the present embodiment has a drive waveform table for ejecting one to four droplets.
Further, in the present embodiment, the inkjet printing apparatus 100 for textile printing has been illustrated, but the present invention can be applied to all inkjet printing apparatuses.

As described above, according to the printing apparatus 100 according to the present embodiment, the following effects can be obtained.
The printing apparatus 100 includes a control unit 1 that outputs a drive waveform that can combine a plurality of droplets 47 at a distance L3 that is ½ or less of the distance (gap WG) from the nozzle 46 to the print medium 95. Yes. By combining the plurality of droplets 47 at a distance L3 that is ½ or less of the gap WG, the distance that the plurality of droplets 47 fly alone is shortened, and the amount of mist generated from each droplet 47 is reduced. In addition, the amount of mist remaining between the ejection head 42 and the print medium 95 is also reduced. As a result, it is possible to reduce ejection defects caused by the mist adhering to the nozzle plate 44 of the ejection head 42 and to stabilize the ejection of droplets. Further, the amount of mist floating in the area relatively close to the print medium 95 is reduced. As a result, the print medium 95 is prevented from being contaminated with mist, so that the quality of an image printed on the print medium 95 is improved. In addition, since the drop 48 combined with the distance L3 that is ½ or less of the gap WG suppresses a decrease in flight speed due to an increase in mass, the positional accuracy for landing the drop is improved. Therefore, the printing apparatus 100 with improved print quality can be provided.

The subsequent droplet 47b is ejected at a drive voltage of 95% or more with respect to the drive voltage of the preceding droplet 47a. As a result, the succeeding droplet 47b can be caught up with and merged with the preceding droplet 47a at a distance L3 of ½ or less of the gap WG. Further, since the succeeding droplet 47b is ejected at a driving voltage of 130% or less of the preceding droplet 47a, the amount of mist generated when the droplet is ejected from the nozzle 46 can be reduced.
Since the first droplet (first droplet) ejected first is ejected at a driving voltage of 70% or more of the maximum driving voltage VH, it is affected by mist adhering to the vicinity of the nozzle 46, thickened ink, or the like. It is reduced, and the discharge of droplets can be stabilized.

  In the printing apparatus 100, the ejection method for ejecting the plurality of droplets 47 to a predetermined position of the printing medium 95 is that the subsequent droplets 47b are ejected at a driving voltage of 95% to 130% with respect to the driving voltage of the preceding droplet 47a. Let As a result, the plurality of droplets 47 ejected from the nozzle 46 can be combined at a distance L3 that is ½ or less of the distance from the nozzle 46 to the printing medium 95, so that the plurality of droplets 47 fly alone. And the amount of mist generated from each droplet 47 is reduced, and the amount of mist remaining between the ejection head 42 and the print medium 95 is also reduced. As a result, it is possible to reduce ejection defects caused by the mist adhering to the nozzle plate 44 of the ejection head 42 and to stabilize the ejection of droplets. Further, the amount of mist floating in the area relatively close to the print medium 95 is reduced. As a result, the print medium 95 is prevented from being contaminated with mist, so that the quality of an image printed on the print medium 95 is improved. In addition, since the drop 48 combined with the distance L3 that is ½ or less of the gap WG suppresses a decrease in flight speed due to an increase in mass, the positional accuracy for landing the drop is improved. Therefore, it is possible to provide a discharge method with improved print quality.

  DESCRIPTION OF SYMBOLS 1 ... Control part, 2 ... External I / F, 3 ... CPU, 4 ... RAM, 5 ... ROM, 6 ... Internal I / F, 7 ... Drive signal generation circuit, 8 ... Oscillation circuit, 10 ... Medium supply part, 20 DESCRIPTION OF SYMBOLS ... Medium conveyance part, 30 ... Medium collection | recovery part, 40 ... Printing part, 42 ... Discharge head, 43 ... Carriage, 44 ... Nozzle plate, 46 ... Nozzle, 47, 47a, 47b, 48 ... Droplet, 50 ... Cleaning unit, DESCRIPTION OF SYMBOLS 60 ... Medium adhesion part, 70 ... Vibrator unit, 72 ... Piezoelectric vibrator, 91 ... Shift register, 92 ... Latch circuit, 93 ... Level shifter, 94 ... Switch circuit, 95 ... Print medium, 100 ... Printing apparatus.

Claims (4)

An ejection head for ejecting a plurality of droplets from a nozzle to a predetermined position of a print medium;
A controller that outputs to the ejection head a drive waveform capable of combining the plurality of liquid droplets at a distance of ½ or less of the distance from the nozzle to the print medium;
A printing apparatus.   2. The printing apparatus according to claim 1, wherein the drive waveform is 95% or more and 130% or less with respect to a drive voltage of a droplet that is ejected in advance by a drive voltage that ejects a subsequent droplet. .   3. The printing apparatus according to claim 1, wherein the drive waveform is such that a drive voltage for discharging the first droplet is 70% or more with respect to a maximum drive voltage. 4. An ejection head for ejecting a plurality of droplets from a nozzle to a predetermined position of a print medium;
A controller that outputs to the ejection head a drive waveform capable of combining the plurality of liquid droplets at a distance of ½ or less of the distance from the nozzle to the print medium;
A discharge method for a printing apparatus comprising:
A discharging method comprising discharging a subsequent droplet at a driving voltage of 95% or more and 130% or less with respect to a driving voltage of a droplet to be discharged in advance in the driving waveform.

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