JP2006068941A - Droplet ejector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a droplet ejecting apparatus capable of landing a satellite droplet in an area where a main droplet has landed.
SOLUTION: The ink jet head communicates with a pressure chamber 14 and can eject main liquid droplets onto a recording sheet. Further, the volume of the ink droplets is smaller than that of the main liquid droplets as the main liquid droplets are ejected. The ink discharge surface 5 having the two nozzles 20 for ejecting the satellite droplets, and the outlets 24 of these nozzles 20 are formed, has a notch cut out from the outlet 24 to the inside of the two axes L. 21 is formed.
[Selection] Figure 5

Description

  The present invention relates to a droplet ejecting apparatus that ejects droplets onto an ejection target such as a recording sheet.

  There are various types of liquid droplet ejecting apparatuses that eject liquid droplets onto an ejected body. Among them, there is an ink jet head that ejects ink from a nozzle to a recording medium such as recording paper. A general ink jet head includes a pressure chamber communicating with a nozzle, and is configured to eject ink from the nozzle by applying pressure to the ink in the pressure chamber by an actuator. By the way, in such an ink jet head, when a pressure is applied to the pressure chamber, an ink droplet (main droplet) having a relatively large volume is first ejected from a nozzle communicating with the pressure chamber. A plurality of satellite droplets separated from the droplets are subsequently ejected. Here, usually, the amount of ink in the satellite droplet is often smaller than that of the main droplet, and therefore the influence of the air resistance received by the satellite droplet on the flight speed from the nozzle to the recording paper or the like is the main effect. It becomes larger than the droplet, and the flying speed of the satellite droplet is smaller than the flying speed of the main droplet. The landing position of the main droplet and satellite droplet shifts in the scanning direction of the head due to the difference in flying speed, and the outline of lines and characters formed by the main droplet is blurred, resulting in a decrease in print quality. Resulting in.

  Therefore, in order to solve such a problem, the main droplet and the satellite droplet are changed by changing the pressure of the ink in the pressure chamber so that the ink amount of the satellite droplet is larger than the ink amount of the main droplet. Ink jet heads have been proposed that can reduce the difference in flying speed between the main droplets and the satellite droplets in the scanning direction (see, for example, Patent Document 1).

2002-113860 publication

  However, due to the disturbance of the meniscus at the nozzle outlet when the main droplet is ejected, the flying direction of the satellite droplet is not only the scanning direction of the head with respect to the flying direction of the main droplet. May also deviate in a direction (paper feeding direction) perpendicular to the direction. However, in the inkjet head described in Patent Document 1, since the landing positions of the main droplet and the satellite droplet in the paper feeding direction cannot be aligned, the satellite droplet is outside the dot formed by the main droplet. Landing will cause the print quality to deteriorate.

  An object of the present invention is to provide a droplet ejecting apparatus capable of landing a satellite droplet in a region where a main droplet has landed.

Means for Solving the Problems and Effects of the Invention

  According to a first aspect of the present invention, there is provided a liquid droplet ejecting apparatus comprising: a storage chamber that stores liquid; a pressure applying unit that applies pressure to the liquid in the storage chamber; and a storage chamber that communicates with the storage chamber. A plurality of nozzles capable of ejecting droplets and ejecting satellite droplets having a volume smaller than that of the main droplets in accordance with the ejection operation of the main droplets, and the satellite droplets ejected from each nozzle Has flight trajectory setting means for setting the flight trajectory so as to fly in the space inside the axis of the plurality of nozzles.

  In this droplet ejecting apparatus, when a pressure is applied to the liquid in the storage chamber by the pressure applying means, droplets are ejected from the plurality of nozzles communicating with the storage chamber to the ejection target. At this time, a large volume main droplet is first ejected from each nozzle. Further, the base end portion (the portion on the opposite side of the droplet ejection direction) of the main droplet is pulled toward the nozzle side, and this portion is separated from the main droplet, so that a satellite droplet having a volume smaller than that of the main droplet is generated. The satellite droplets are formed and discharged from the nozzle following the main droplets. Here, since the flight trajectory of the satellite droplets ejected from each nozzle is set by the flight trajectory setting means so as to fly in the space inside the axes of the plurality of nozzles, the main droplet has landed. Satellite droplets can easily land within the formed dots.

  In particular, when the liquid droplet ejecting apparatus is a recording apparatus that records on an ejected body, the outline of lines and characters formed by the main liquid droplets becomes clear, and the print quality is improved. In addition, since the droplets are ejected from the plurality of nozzles to the ejected body, compared to the case where the droplets are ejected from one nozzle, the thickness of the ejected body in the thickness direction does not contribute much to the print density. Since the permeation amount of the liquid is reduced and the liquid can be stored on the surface of the ejection target, the print density can be increased. Furthermore, the liquid can easily penetrate along the surface of the ejected body, and the liquid can permeate over a wide area, so that the line width can be increased. In addition, since the droplets are divided by a plurality of nozzles and landed on the ejection target, the diameter of the dots can be reduced.

  According to a second aspect of the invention, in the first aspect of the invention, the flying trajectory setting means is configured such that the ejection trajectory setting means is arranged on the ink ejection surface on which the nozzle outlet is formed, from the outlet to the inside of the plurality of axes. The cutout portion is a cutout portion. The main droplet having a large volume is ejected along the axis of the nozzle. At this time, the main liquid is in a state where the base end portion of the main droplet is pulled by the notches cut out to the inside of the plurality of axes. Since the satellite droplet is formed by being separated from the droplet, the satellite droplet is ejected in the direction inside the axis of the plurality of nozzles starting from the notch. Therefore, with such a simple configuration, satellite droplets can fly toward a space inside the plurality of nozzle axes.

  According to a third aspect of the invention, in the first aspect of the invention, a liquid repellent film is formed on the ink discharge surface on which the emission port of the nozzle is formed except for a part thereof, and the flight trajectory setting means Is a non-liquid-repellent film forming part, which is a part extending from the emission port of each nozzle to the inside of the plurality of axes on the ink discharge surface and not having the liquid-repellent film formed thereon. It is. Since the wettability of the liquid is increased in the liquid repellent film non-formed portion, the base end portion of the main droplet ejected from the nozzle is pulled by the liquid repellent film non-formed portion extending inward of the plurality of axes, and this portion is Satellite droplets are formed separately from the main droplets. For this reason, the satellite droplets are ejected in the direction inside the axes of the plurality of nozzles starting from the liquid repellent film non-forming portion. Therefore, with such a simple configuration, satellite droplets can fly toward a space inside the plurality of nozzle axes.

  In the liquid droplet ejecting apparatus according to a fourth aspect of the present invention, in any one of the first to third aspects, the axes of the plurality of nozzles extend in the direction of the inner side of the axes toward the exit port side. It is what. Accordingly, satellite droplets are more likely to land within the dots formed by landing of the main droplets. In addition, it becomes relatively easy to arrange the outlets of the plurality of nozzles at positions close to each other, and it becomes possible to reduce the size of the droplet ejecting apparatus by arranging the nozzles at high density.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the number of the nozzles is two. While simplifying the configuration of the droplet ejecting apparatus by minimizing the number of nozzles, it becomes possible to land satellite droplets in dots formed by landing of main droplets.

  According to a sixth aspect of the present invention, there is provided a liquid droplet ejecting apparatus comprising: a storage chamber that stores liquid; a pressure applying unit that applies pressure to the liquid in the storage chamber; and a storage chamber that communicates with the storage chamber. A plurality of nozzles capable of ejecting droplets and ejecting satellite droplets having a volume smaller than that of the main droplets in accordance with the ejection operation of the main droplets, and the satellite droplets ejected from each nozzle However, it has a flight trajectory setting means for setting the flight trajectory so as to fly in a space sandwiched between two surfaces that respectively include the axes of the two nozzles and face each other. As described above, when the liquid in the storage chamber is ejected from the two nozzles communicating with the storage chamber, the flight trajectory of the satellite droplets ejected from the nozzles by the flight trajectory setting means sets the axis of the two nozzles. The satellite droplets jetted from one nozzle are set so as to fly in the space between the two surfaces that are included and face each other, so that the satellite droplets fly so as to approach the axis of the other nozzle. Satellite droplets can easily land within the dots formed by landing of the main droplets that fly.

Embodiments of the present invention will be described. The present embodiment is an example in which the present invention is applied to an inkjet head that ejects ink onto a recording sheet.
First, the ink jet printer 100 including the ink jet head 1 will be briefly described. As shown in FIG. 1, an inkjet printer 100 includes a carriage 101 that can move in the left-right direction in FIG. 1 and a serial type that is provided on the carriage 101 and ejects ink onto a recording paper P (a target to be ejected). An inkjet head 1 and a conveyance roller 102 that conveys the recording paper P forward in FIG. 1 are provided. The inkjet head 1 moves in the left-right direction (scanning direction) integrally with the carriage 101, and ejects ink onto the recording paper P from the nozzle outlet formed on the ink ejection surface 5 on the lower surface thereof. Then, the recording paper P recorded by the inkjet head 1 is discharged forward (paper feeding direction) by the transport roller 102.

Next, the inkjet head 1 will be described in detail with reference to FIGS.
As shown in FIGS. 2 to 4, the inkjet head 1 includes a flow path unit 2 in which an individual ink flow path including a pressure chamber 14 is formed, and a piezoelectric actuator 3 stacked on the upper surface of the flow path unit 2. And.

  First, the flow path unit 2 will be described. As shown in FIG. 4, the flow path unit 2 includes a cavity plate 10, a base plate 11, a manifold plate 12, and a nozzle plate 13, and these four plates 10 to 13 are bonded in a stacked state. Among these, the cavity plate 10, the base plate 11 and the manifold plate 12 are stainless steel plates, and ink flow paths such as a manifold 17 and a pressure chamber 14 described later can be easily etched in these three plates 10-12. It can be formed. The nozzle plate 13 is formed of, for example, a polymer synthetic resin material such as polyimide, and is bonded to the lower surface of the manifold plate 12. Or this nozzle plate 13 may be formed with metal materials, such as stainless steel, similarly to the three plates 10-12.

  As shown in FIGS. 2 to 4, the cavity plate 10 is formed with a plurality of pressure chambers 14 (storage chambers) arranged along a plane. The plurality of pressure chambers 14 are opened on the surface of the flow path unit 2 (the upper surface of the cavity plate 10 to which a diaphragm 30 described later is joined). Each pressure chamber 14 is formed in a substantially elliptical shape in plan view, and is arranged so that the major axis direction thereof is the left-right direction (scanning direction). The cavity plate 10 is formed with an ink supply port 18 connected to an ink tank (not shown).

  As shown in FIGS. 3 and 4, communication holes 15 and 16 are formed at positions overlapping the both ends in the long axis direction of the pressure chamber 14 in a plan view of the base plate 11, respectively. The manifold plate 12 is formed with a manifold 17 that extends in the paper feeding direction (vertical direction in FIG. 2) and overlaps the right half of the pressure chamber 14 in FIG. Ink is supplied to the manifold 17 from an ink tank through an ink supply port 18. Further, a communication hole 19 is also formed at a position overlapping the left end of the pressure chamber 14 in FIG.

  As shown in FIGS. 3 and 4, in the nozzle plate 13, two nozzles 20 arranged in the paper feed direction are formed at a position overlapping the left end portion of each pressure chamber 14 in plan view, and one pressure chamber is formed. These two nozzles 20 communicate with 14. The nozzle 20 is formed, for example, by performing excimer laser processing on a polymer synthetic resin substrate such as polyimide. Each of these two nozzles 20 is formed in a tapered shape having a substantially circular horizontal sectional shape and a tapered vertical sectional shape. As shown in FIGS. 5A and 5B, the ink ejection surface 5 (the lower surface of the nozzle plate 13) on which the emission ports 24 of the nozzles 20 are formed has the axis L of the two nozzles 20 extending from the emission ports 24. A cutout portion 21 cut out inward is formed. That is, as viewed from below, the nozzle 20 is formed in a shape that partially swells from the edge of the circular emission port 24 to the inside of the two axes L. Further, the cutout portion 21 is formed in a shape in which the cutout amount gradually decreases from the emission port 24 at the lower end of the nozzle 20 to the upper end of the nozzle 20. A liquid repellent film 25 having high liquid repellency is formed on the entire surface of the ink discharge surface 5 to prevent ink from getting wet near the emission port 24.

  As shown in FIG. 4, the manifold 17 communicates with the pressure chamber 14 through the communication hole 15, and the pressure chamber 14 communicates with the nozzle 20 through the communication holes 16 and 19. As described above, an individual ink flow path from the manifold 17 to the nozzle 20 through the pressure chamber 14 is formed in the flow path unit 2.

  Next, the piezoelectric actuator 3 will be described. As shown in FIGS. 2 to 4, the piezoelectric actuator 3 includes a diaphragm 30 having conductivity disposed on the surface of the flow path unit 2, and a continuous surface across the plurality of pressure chambers 14 on the surface of the diaphragm 30. And a plurality of individual electrodes 32 formed on the surface of the piezoelectric layer 31 so as to correspond to the plurality of pressure chambers 14, respectively. The piezoelectric actuator 3 applies pressure to the ink in the pressure chamber 14 by changing the volume of the pressure chamber 14, and corresponds to the pressure applying means of the present invention.

  The diaphragm 30 is a plate made of stainless steel having a substantially rectangular shape in plan view, and is laminated and joined to the upper surface of the cavity plate 10 so as to block the openings of the plurality of pressure chambers 14. The diaphragm 30 also serves as a common electrode that opposes the plurality of individual electrodes 32 and applies an electric field to the piezoelectric layer 31 between the individual electrodes 32 and the diaphragm 30.

  On the surface of the diaphragm 30, a piezoelectric layer 31 mainly composed of lead zirconate titanate (PZT), which is a solid solution and is a ferroelectric substance, is formed of lead titanate and lead zirconate. The piezoelectric layer 31 is continuously formed across the plurality of pressure chambers 14. The piezoelectric layer 31 can be formed using, for example, an aerosol deposition method (AD method) in which ultrafine particle material is deposited by colliding at high speed. In addition, a sol-gel method, a sputtering method, a hydrothermal synthesis method, or a CVD (chemical vapor deposition) method can also be used. Furthermore, the piezoelectric layer 31 can be formed by attaching a piezoelectric sheet obtained by firing a green sheet of PZT to the surface of the diaphragm 30.

  A plurality of individual electrodes 32 having an elliptical planar shape that is slightly smaller than the pressure chamber 14 are formed on the surface of the piezoelectric layer 31. Each of these individual electrodes 32 is formed at a position that overlaps the central portion of the corresponding pressure chamber 14 in plan view. The individual electrode 32 is made of a conductive material such as gold. Further, on the surface of the piezoelectric layer 31, a plurality of terminal portions 35 are respectively formed at one end portions (left end portion or right end portion in FIG. 2) of the plurality of individual electrodes 32. The plurality of terminal portions 35 are electrically connected to the driver IC 37 via a flexible wiring member such as a flexible printed wiring board, and are connected to the plurality of individual electrodes 32 from the driver IC 37 via the terminal portion 35. Thus, the drive voltage is selectively supplied.

Next, the operation of the piezoelectric actuator 3 will be described.
When a driving voltage is selectively supplied to the plurality of individual electrodes 32 from the driver IC 37, the individual electrodes 32 on the upper side of the piezoelectric layer 31 to which the driving voltage is supplied and the lower side of the piezoelectric layer 31 held at the ground potential. The potentials of the diaphragm 30 as the common electrode are in different states, and an electric field in the vertical direction is generated in the portion of the piezoelectric layer 31 sandwiched between the individual electrode 32 and the diaphragm 30. Then, the portion of the piezoelectric layer 31 directly below the individual electrode 32 to which the drive voltage is applied contracts in the horizontal direction orthogonal to the vertical direction that is the polarization direction. At this time, the diaphragm 30 is deformed so as to protrude toward the pressure chamber 14 as the piezoelectric layer 31 contracts, so that the volume in the pressure chamber 14 decreases and pressure is applied to the ink in the pressure chamber 14. Then, ink is ejected from the nozzle 20 communicating with the pressure chamber 14.

  Further, the ink ejection operation from the nozzle 20 will be described in detail with reference to FIG. First, when pressure is applied to the ink in the pressure chamber 14 by the piezoelectric actuator 3 from the state where the meniscus is formed near the emission port 24 of the nozzle 20 as shown in FIG. As described above, first, the main droplet Ia having a relatively large volume is simultaneously ejected downward along the axis L of the nozzle 20 from the two nozzles 20. At this time, as shown in FIG. 6C, the base end portion (hereinafter referred to as tail portion It) of the main liquid droplet Ia is pulled toward the nozzle 20 side, and as shown in FIG. Separates from the main droplet Ia. Then, a plurality of satellite droplets Ib having a volume smaller than that of the main droplet Ia and a plurality of mist-like satellite droplets Ic having a volume smaller than that of the satellite droplet Ib are formed, and the plurality of satellite droplets Ib and Ic are formed. Are ejected onto the recording paper P following the main droplet Ia.

  Here, on the ink ejection surface 5 of the nozzle plate 13, a notch 21 is formed by notching from the emission port 24 of the nozzle 20 to the inside of the two axes L. Depending on the size and position of the solid component in the ink, the meniscus state, the manner of separation of the tail part It, and the state of the satellite droplets Ib and Ic vary, but the meniscus is somewhat disturbed by the ejection of the main droplet Ia. 6C, the tail portion It of the main liquid droplet Ia is pulled by the notch 21, as shown in FIG. 6C. Therefore, as shown in FIG. The satellite droplets Ib and Ic formed separately from the droplet Ia are formed on two inner surfaces of the two axes L starting from the notch 21 (in two vertical planes each including the two axes L and parallel to each other). The satellite droplets Ib and Ic ejected toward the sandwiched space V) and ejected from one nozzle 20 fly so as to approach the axis L of the other nozzle 20. Therefore, as shown in FIGS. 6E and 6F, the satellite droplets Ib and Ic are likely to land at the position where the two main droplets Ia land on the recording paper P. That is, as shown in FIG. 7, since the satellite droplets Ib and Ic land in the dots D formed by the two main droplets Ia, the outlines of lines and characters formed by the plurality of dots D are not blurred. It becomes clear and print quality improves.

  Further, since one dot is formed by ejecting ink from the two nozzles 20 to the recording paper P, the penetration of the ink in the thickness direction of the recording paper P, which does not contribute much to the print density, is reduced. Since ink can be stored on the surface of the paper P, it is possible to increase the print density (particularly the density of the solid coating portion) with the same ink amount. Furthermore, the ink can easily spread along the surface of the recording paper P, and the liquid can permeate over a wide area, so that the line width can be increased. In addition, since the droplets are divided by the plurality of nozzles 20 and landed on the recording paper P, the diameter of the dots can be reduced and the graininess can be suppressed. As shown in FIG. 6, the cutout portion 21 may be formed in almost the entire region in the thickness direction of the nozzle plate 13, or may be formed only in the vicinity of the emission port 24.

  Next, with respect to the above-described ink jet head 1, a form in which one nozzle having no notch 21 communicates with one pressure chamber 14 (comparative form 1: see FIG. 8) and a notch in one pressure chamber 14. Comparison will be made with reference to two comparative forms in which two nozzles without the portion 21 communicate with each other (comparative form 2: see FIG. 11). In addition, in the following description regarding these comparison forms 1 and 2, those having substantially the same configuration as the above-described inkjet head 1 are denoted by the same reference numerals and description thereof is omitted.

  First, comparative example 1 will be described. As shown in FIGS. 8A and 8B, the nozzle 40 of the first comparative example is formed in a tapered shape in which the horizontal cross-sectional shape is circular and the vertical cross-sectional shape is tapered, and the axis L is It has a general nozzle shape extending in the vertical direction. And unlike the nozzle 20 (refer FIG. 5) of the inkjet head 1 mentioned above, the notch part 21 is not formed in the nozzle 40 of this comparative form 1. FIG.

  The ink ejecting operation from the nozzle 40 in the comparative embodiment 1 will be described with reference to FIG. First, as shown in FIG. 9A, when pressure is applied to the ink in the pressure chamber 14 by the piezoelectric actuator 3 from a state where a meniscus is formed in the vicinity of the emission port 44 of the nozzle 40, FIG. First, one main droplet Ia having a relatively large volume is ejected downward along the axis L from the nozzle 40. Further, as shown in FIG. 9C, the tail portion It of the main droplet Ia is pulled toward the nozzle 40 side, and as shown in FIG. 9D, the tail portion It is separated from the main droplet Ia. A plurality of satellite droplets Ib and Ic are formed.

  Here, the above-described notch 21 (see FIG. 5) is not formed in the nozzle 40, and the exit port 44 of the nozzle 40 is formed in a circular shape, so that the meniscus when the main droplet Ia is ejected is formed. The plurality of satellite droplets Ib and Ic fly in different directions due to the disturbance of the image. Therefore, as shown in FIGS. 9D, 9E, and 9F, a part of the plurality of satellite droplets Ib and Ic fly in a direction away from the axis L, and from the landing position of the main droplet Ia. It may land at a distant position. In this case, as shown in FIG. 10, some of the satellite droplets Ib and Ic land on the outside of the dot D1 formed by the main droplet Ia, and lines and characters formed by the plurality of dots D1. Since the outline of the image becomes blurred, the print quality deteriorates.

  Further, since the ink is ejected from only one nozzle 40 to form one dot D1, the ink does not contribute much to the printing density, and the ink immediately penetrates in the thickness direction of the recording paper P, so that the printing density is sufficient. It will not be high. In addition, since the ink is difficult to spread along the surface of the recording paper P, it is difficult to increase the width of lines and characters, and the graininess is conspicuous. Further, the ink penetrating in the thickness direction of the recording paper P reaches the back surface of the recording paper P, so-called back-through easily occurs.

  Next, Comparative Example 2 will be described. As shown in FIGS. 11 (a) and 11 (b), the two nozzles 50 of the comparative example 2 are each formed in a tapered shape in which the horizontal cross-sectional shape is circular and the vertical cross-sectional shape is tapered. This has an ordinary nozzle shape in which the axis L extends in the vertical direction. As in Comparative Example 1, the above-described notch 21 (see FIG. 5) is not formed in the nozzle 50 of Comparative Example 2.

  The ink ejection operation from the nozzle 50 in the comparative example 2 will be described with reference to FIG. As shown in FIG. 12A, when pressure is applied to the ink in the pressure chamber 14 by the piezoelectric actuator 3 from a state where a meniscus is formed in the vicinity of the emission port 54 of the nozzle 50, FIG. As shown, first, two main liquid droplets Ia having a relatively large volume are ejected downward along the axis L from the two nozzles 50. Further, as shown in FIG. 12C, the tail portion It of the main droplet Ia is pulled toward the nozzle 50 side, and as shown in FIG. 12D, the tail portion It is separated from the main droplet Ia. A plurality of satellite droplets Ib and Ic are formed.

  Here, since the notch 21 (see FIG. 5) is not formed in the nozzle 50 and the emission port 54 of the nozzle 50 is formed in a circular shape, the main droplet Ia is similar to the first comparative example. The plurality of satellite droplets Ib and Ic fly in different directions due to the disturbance of the meniscus when the water droplets are ejected. Therefore, as shown in FIGS. 12D, 12E, and 12F, a part of the plurality of satellite droplets Ib and Ic fly in a direction away from the axis L, and from the landing position of the main droplet Ia. It may land at a distant position. In this case, as shown in FIG. 13, some of the satellite droplets Ib and Ic land on the outside of the dot D2 formed by the main droplet Ia, and lines and characters formed by the plurality of dots D2 Since the outline of the image becomes blurred, the print quality deteriorates.

  However, in the comparative example 2, since the ink is ejected from the two nozzles 50 as in the ink jet head 1 of the above embodiment, the ink can be permeated over a wide range. Therefore, compared with the above-described comparative form 1, it is possible to obtain the effects that the print density can be increased and the line width can be increased.

According to the inkjet head 1 described above, the following effects can be obtained.
As can be seen from the comparison with Comparative Examples 1 and 2, in the inkjet head 1 of this embodiment, the satellite droplets Ib and Ic ejected from the nozzle 20 following the main droplet Ia start from the notch 21. Since the two main liquid droplets Ia flying along the axis L are ejected into the space inside the two axes L (the space between the two planes each including the two axes and sandwiched between the two surfaces). Satellite droplets Ib and Ic are also easily landed at the position where they land on the recording paper P. Accordingly, since the satellite droplets Ib and Ic land within the dots D formed by the two main droplets Ia, the outlines of the lines and characters formed by the plurality of dots D become clear and the print quality is improved. . Further, since the satellite droplets Ib and Ic can fly in the space inside the two axes L only by the notch portion 21, the satellite droplets Ib and Ic are the dots D formed by the main droplet Ia. The configuration for landing inside becomes simple.

  Furthermore, since ink is ejected from the two nozzles 20 to the recording paper P to form one dot D, the penetration of ink in the thickness direction of the recording paper P, which does not contribute much to the print density, is reduced. Since ink can be stored near the surface of the recording paper P, the printing density can be increased. Further, since the ink easily penetrates in the direction along the surface of the recording paper P, the line width can be increased. Therefore, when a predetermined region is filled by forming a plurality of lines, the gap between adjacent lines can be made inconspicuous even if there is some variation in the feed amount of the carriage 101. Further, since the droplets are divided and ejected by the two nozzles 20 and landed on the recording paper P, the diameter of the dots can be reduced and the graininess can be suppressed.

Next, modified embodiments in which various modifications are made to the embodiment will be described. However, components having the same configuration as in the above embodiment are given the same reference numerals and description thereof is omitted as appropriate.
1] During one printing cycle in which one dot is formed on the recording paper P, the piezoelectric actuator 3 is driven one or more times to change the volume of the droplet ejected from the nozzle 20 (recording) The present invention can also be applied to an inkjet head capable of changing the size of the dots D on the paper P), that is, so-called droplet gradation.

  As shown in FIG. 14, a plurality of nozzle sets (60A to 60D) each having two nozzles 20 are formed on the nozzle plate 13 of the inkjet head according to the first modification. As in the above embodiment, each nozzle 20 is formed with a notch 21. In FIG. 14, only four nozzle sets 60 </ b> A to 60 </ b> D among the plurality of nozzle sets are shown.

  Here, the individual electrodes 32 (see FIGS. 2 to 4) of the piezoelectric actuator 3 respectively corresponding to the four nozzle sets 60A to 60D are connected to the driver IC 37 (see FIG. 4) from FIGS. ) Are supplied respectively. Then, as shown in FIG. 16, the nozzle sets 60 </ b> A to 60 </ b> D to which these drive signals are supplied land droplets on the recording paper P, and dots are formed on the recording paper P. 15A to 15D show drive signal waveforms respectively corresponding to the four nozzle sets 60A to 60D. In FIGS. 15A to 15D, the vertical axis represents the drive voltage. V and the horizontal axis indicate time T, respectively. The drive signals shown in FIGS. 15A to 15D are signals for ejecting ink from the nozzles 20 by so-called striking. That is, the individual electrodes 32 corresponding to the nozzle sets 60 </ b> A to 60 </ b> D are always in the H state because the drive voltage is applied when ink is not ejected from the nozzles 20. That is, the diaphragm 30 (see FIG. 4) is deformed so as to protrude toward the pressure chamber 14 and the volume in the pressure chamber 14 is reduced. When ink is ejected from the nozzle 20 from this state, first, the potential of the individual electrode 32 becomes the same ground potential as the diaphragm 30 as the common electrode (L state), and the deformation state of the diaphragm 30 is changed. Since the volume of the pressure chamber 14 is increased once released, ink flows into the pressure chamber 14 from the manifold 17 (see FIGS. 2 to 4). Then, the drive voltage is applied to the individual electrode 32 again to be in the H state, the volume of the pressure chamber 14 is reduced, the internal ink is pressurized, and the ink is ejected from the nozzle 20.

Here, for example, as shown in FIG. 15A, in the first nozzle set 60A, first, two pulse signals are supplied to the individual electrodes 32 in the first printing cycle T ₀ and the nozzles 20 to 2 are supplied. The injection operation is performed continuously at short intervals. That is, during this one printing cycle T ₀ , main droplets (medium main droplets Iam) corresponding to two pulse signals are ejected from the two nozzles 20 to form dots Dm. In the next printing cycle T ₀ , one pulse signal is supplied to the individual electrode 32, and main droplets (small main droplets Ias) for one pulse signal are ejected from the nozzles 20 to form dots Ds. The Further, in the next printing cycle T ₀ , no pulse signal is supplied, so that ink is not ejected from the nozzle 20. In this way, the drive signal shown in FIG. 15A is supplied to the individual electrode 32, so that in this nozzle set 60A, as shown in the first stage from the top in FIG. From the side), the main droplet Ia is ejected in the order of middle ball → small ball → no jetting → small ball → no jetting → no jetting.

As shown in FIG. 15B, in the second nozzle set 60B, first, in the first printing cycle T ₀ , three pulse signals are supplied and three ejection operations are performed. During the printing cycle T ₀ times, main droplets (large main droplets Iab) corresponding to three pulse signals are ejected from the nozzle set 60B. Then, the drive signal shown in FIG. 15B is supplied to the individual electrode 32, so that in this nozzle set 60B, as shown in the second row from the top in FIG. The main droplet Ia is ejected in the order of → small balls → no injection → small balls → no injection.

  Further, in the third nozzle set 60C, the driving signal shown in FIG. 15C is supplied to the individual electrode 32, so that, as shown in the third row from the top in FIG. The main droplet Ia is ejected in the order of large balls → middle balls → middle balls → small balls → small balls. Further, in the fourth nozzle set 60D, the drive signal shown in FIG. 15 (d) is supplied to the individual electrode 32, so that the center ball from the left as shown in the fourth row from the top in FIG. The main droplet Ia is ejected in the order of large ball → large ball → large ball → medium ball → small ball. In this way, by changing the volume of the main droplet Ia ejected from each of the nozzle sets 60A to 60D, the inkjet head according to the first modification is configured to be capable of droplet gradation.

  Here, in particular, if the satellite droplets Ib and Ic land on the outside of the dots Db formed by the main droplet Iab when the large main droplet Iab is ejected, these satellite droplets Ib, With Ic, thick lines and outlines of characters formed by a plurality of large dots Db are blurred and not clear, and the print quality is remarkably deteriorated. However, since the nozzle 20 has a notch 21, the satellite droplets Ib and Ic ejected separately from the large main droplet Iab are inside the axis L of the nozzle 20 with the notch 21 as a starting point. The satellite droplets Ib and Ic are likely to land in the dots Db formed by the large main droplet Iab. Further, the larger the volume of the main droplet Ia, the larger the area of the dot D formed by landing of the main droplet Ia. Therefore, the satellite droplets Ib and Ic are formed by the large main droplet Iab. The probability of landing in the dot D increases. Therefore, when the large main droplet Iab is ejected, the satellite droplets Ib and Ic hardly land on the area outside the dot Db.

  Note that when the small main droplet Ias is ejected, the area of the dot Ds formed by the main droplet Ias is small, so that the satellite droplets Ib and Ic are placed outside the dot Ds as shown in FIG. Sometimes it will land. However, in this case, since the dots formed by the satellite droplets Ib and Ic are formed outside the very thin line or small point formed by the small dot Ds, compared to the case of the large ball described above. The dots of the satellite droplets Ib and Ic are unlikely to blur the outline of the line or character, and the print quality is only slightly deteriorated.

  The reason is as follows. A region where a plurality of dots formed by the satellite droplets Ib and Ic are formed is recognized as a light gray halftone region by the naked eye. In the case of a large ball, the area is relatively large in the vicinity of the halftone region. In many cases, black-filled areas (areas formed by a plurality of large dots Db) and areas that remain white exist, and the visual sensitivity of the halftone area is increased by comparison with these areas. On the other hand, in the case of small balls, there is often no area that is wide and blacked out in the vicinity of the halftone area, so the visual sensitivity of the halftone area is not increased as in the case of large balls.

In the present embodiment, in the case of a large ball, it becomes difficult to form a halftone region composed of dots of satellite droplets Ib and Ic. On the other hand, in the case of a small ball, the visual sensitivity of the halftone region is not increased. Therefore, overall, adverse effects on the print quality of the satellite droplets Ib and Ic can be suppressed.
When the volume of the main liquid droplet Ia is small (small balls, medium balls), the dots Dm and Ds are independently formed by the two main liquid droplets Ia, and the liquid droplets are ejected from one nozzle. Compared with, graininess is not felt so much.

  2] As shown in FIGS. 17A and 17B, in the nozzle plate 73, the two nozzles are formed in a tapered shape having a circular horizontal cross-sectional shape and a tapered vertical cross-sectional shape (that is, Further, the notch 21 is not formed), and the ink ejection surface 75 extends from the emission port 74 of the nozzle 70 to the inside of the two axes L and the liquid repellent film 25 is not partially formed. The liquid film non-formation part 71 may be provided (modification 2). Since the ink wettability of the liquid repellent film non-forming portion 71 is higher than that of the portion where the liquid repellent film 25 is formed, when the main droplet Ia is ejected from the nozzle 70, the tail portion It is liquid repellent. It is pulled by the non-film forming part 71. Then, the satellite droplets Ib, Ic formed by separating the tail portion It from the main droplet Ia fly toward the space between the two axes L from the liquid repellent film non-forming portion 71 as a starting point. As described above, since the satellite droplets Ib and Ic can fly in the space inside the two axes L only by the liquid repellent film non-forming portion 71, the satellite droplets Ib and Ic are caused to fly to the main droplet Ia. The configuration for landing at the landing position is simple. In order to form the liquid repellent film non-forming portion 71, the liquid repellent film 25 is formed on the entire surface of the ink discharge surface 75, and then the liquid repellent film 25 is partially removed by an excimer laser or the like. Alternatively, the liquid repellent film 25 may be formed only in a region other than the liquid repellent film non-forming portion 71 using a resist method or the like.

  3] As shown in FIG. 18, in the nozzle plate 83, the two nozzles 80 are shaped so that the two axis lines L ′ are inclined toward the inside of the two axis lines L ′ toward the exit port 84 side. May be formed (Modification 3). In other words, in the third modification, the two axis lines L ′ are inclined with respect to the ink ejection surface 75 and are formed so as to be closer to each other toward the emission port 84 side. More specifically, as shown in FIG. 18, the two axis lines L ′ are in a line-symmetric position with respect to a line segment perpendicular to the ink ejection surface 75. In this case, the satellite droplets Ib and Ic surely fly toward the inside of the two axes L ′ (the space between the two planes each including the two axes L ′ and facing each other). The satellite droplets Ib and Ic are more likely to land in the dot formed by the droplet Ia landing. In addition, it becomes relatively easy to arrange the plurality of nozzles 80 at positions close to each other, and it is possible to reduce the size of the inkjet head by arranging the nozzles 80 at high density.

4] The number of nozzles communicating with one pressure chamber 14 is not limited to two. For example, as shown in FIG. 19, in the nozzle plate 93, four nozzles 90 communicating with one pressure chamber 14 through the communication hole 19 are formed at equal intervals in the direction along the inner peripheral surface of the communication hole 19. Furthermore, four cutout portions 91 may be formed on the ink discharge surface 95 by cutting out from the outlets 94 of the four nozzles 90 to the inside of the four axes L (Modification 4). ). Therefore, the satellite droplets Ib and Ic ejected from the nozzle 90 following the main droplet Ia fly toward the inside of the four axes L from the notch 91, and the satellite droplets Ib and Ic are It is easy to land inside the dots formed by the main droplet Ia.
However, if the number of nozzles communicating with one pressure chamber 14 is increased too much, the diameter of the nozzle becomes very small, so that nozzle clogging is likely to occur and manufacturing is difficult. Therefore, the number of nozzles is preferably an appropriate number (for example, about several) that is not too large.

  5] The above embodiment is an example in which the present invention is applied to a serial ink jet head, but the present invention can also be applied to a line ink jet head that is long in the width direction of a recording sheet.

  6] The present invention can also be applied to other liquid droplet ejecting apparatuses that eject liquid other than ink. For example, a conductive paste is sprayed to form a wiring pattern on the substrate, an organic light emitter is sprayed to the substrate to form an organic electroluminescence display, and an optical resin is sprayed to the substrate. Thus, the present invention can also be applied to various droplet ejecting apparatuses used for forming optical devices such as optical waveguides.

1 is a schematic perspective view of an ink jet printer according to an embodiment of the present invention. It is a top view of an inkjet head. FIG. 3 is a partially enlarged view of FIG. 2. FIG. 4 is a sectional view taken along line IV-IV in FIG. 3. It is the elements on larger scale around a nozzle, (a) is the VA-VA sectional view taken on the line of FIG. 4, (b) is a bottom view. It is explanatory drawing explaining the ejection operation | movement of the ink droplet from a nozzle, (a) is the state before ink ejection, (b) is the state at the time of ink ejection start, (c) is the state immediately before separation of the tail part, ( d) shows the state immediately after the ejection of the satellite droplet, (e) shows the state when the main droplet has landed, and (f) shows the state when the satellite droplet has landed. It is a figure which shows the some dot formed on the recording paper. It is the elements on larger scale of the nozzle periphery corresponding to FIG. 5 of the comparison form 1, (a) is sectional drawing, (b) is a bottom view. FIG. 6 is a view corresponding to FIG. 6 of Comparative Example 1, where (a) is a state before ink ejection, (b) is a state at the start of ink ejection, (c) is a state immediately before separation of the tail portion, and (d) is a satellite liquid. (E) shows the state when the main droplet has landed, and (f) shows the state when the satellite droplet has landed. FIG. 6 is a diagram illustrating a plurality of dots formed on a recording sheet in comparative form 1. It is the elements on larger scale of the nozzle periphery corresponding to FIG. 5 of the comparison form 2, (a) is sectional drawing, (b) is a bottom view. FIG. 6 is a view corresponding to FIG. 6 of Comparative Example 2, where (a) is a state before ink ejection, (b) is a state at the start of ink ejection, (c) is a state immediately before separation of the tail portion, and (d) is a satellite liquid. (E) shows the state when the main droplet has landed, and (f) shows the state when the satellite droplet has landed. FIG. 10 is a diagram illustrating a plurality of dots formed on a recording sheet in Comparative Example 2. It is a partial expanded bottom view of the nozzle plate of the modification 1. It is a wave form diagram of a drive signal. FIG. 10 is a diagram illustrating a plurality of dots formed on a recording sheet in a first modification. It is the elements on larger scale of the nozzle periphery corresponding to FIG. 5 of the modification 2, (a) is sectional drawing, (b) is a bottom view. It is the elements on larger scale of the nozzle periphery corresponding to FIG. 5 of the modification 3, (a) is sectional drawing, (b) is a bottom view. It is a partial expanded bottom view of the nozzle plate of the modification 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet head 2 Flow path unit 3 Piezoelectric actuator 5 Ink ejection surface 14 Pressure chamber 20 Nozzle 21 Notch 24 Emission port 25 Liquid repellent film 70 Nozzle 71 Liquid repellent film non-formation part 74 Ejection port 75 Ink ejection surface 80 Nozzle 84 Emission port 90 Nozzle 91 Notch portion 94 Ejection port 95 Ink discharge surface Ia Main droplets Ib, Ic Satellite droplets

Claims (6)

A storage chamber for storing liquid;
Pressure applying means for applying pressure to the liquid in the storage chamber;
Each of the reservoirs communicates with the main droplets and can eject main droplets onto the ejected object. In addition, satellite droplets having a volume smaller than that of the main droplets are ejected along with the main droplet ejection operation. Multiple nozzles,
Flight trajectory setting means for setting the flight trajectory so that the satellite droplets ejected from each nozzle fly in a space inside the axis of the plurality of nozzles;
A liquid droplet ejecting apparatus comprising:   2. The flight trajectory setting means is a cutout portion that is cut out from the emission port to the inside of the plurality of axes on the ink ejection surface on which the emission port of the nozzle is formed. Droplet ejector. A liquid repellent film is formed on the ink ejection surface where the emission port of the nozzle is formed except for a part thereof,
The flying trajectory setting means is a liquid repellent film non-formation part, which is a part extending on the inner side of the plurality of axes from the emission port of each nozzle on the ink ejection surface, and where the liquid repellent film is not formed. The droplet ejecting apparatus according to claim 1.   The droplet ejecting apparatus according to claim 1, wherein the axis lines of the plurality of nozzles extend toward the inside of the axis line toward the exit port side.   The droplet ejecting apparatus according to claim 1, wherein the number of the nozzles is two. A storage chamber for storing liquid;
Pressure applying means for applying pressure to the liquid in the storage chamber;
Each of the reservoirs communicates with the main droplets and can eject main droplets onto the ejected object. In addition, satellite droplets having a volume smaller than that of the main droplets are ejected along with the main droplet ejection operation. Multiple nozzles,
Flight trajectory setting means for setting the flight trajectory so that the satellite droplets ejected from each nozzle fly in a space sandwiched between two faces that respectively include the axes of the two nozzles and face each other;
A liquid droplet ejecting apparatus comprising:

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