JP2009066890A - Liquid jet head and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problems: in order to discharge large bubbles generated due to the capacity increase of a common liquid chamber, it becomes necessary to perform a sucking operation and a pressurizing operation many times, and also, it becomes necessary to very strongly suck or pressurize. <P>SOLUTION: The liquid jet head includes: an ink supply path 21 where a plurality of nozzles 4 for jetting liquid droplets communicate one another; bubble discharge ports 5 arranged outside in the arraying direction of the plurality of nozzles 4; an ink supply path 22 where the bubble discharge ports 5 communicate one another; and the common liquid chamber 8 communicating with the ink supply path 21 through an ink supply port 9 and communicating with the ink flow path 22 through an ink supply port 22. The common liquid chamber 8 and the ink supply paths 21, 22 are formed as individual members. Provided that the nozzle arraying direction is regarded as a width direction and a direction perpendicular to the nozzle arraying direction is regarded as a length direction, the width and length of the ink supply port 22 is equal to or larger than half the width W of the common liquid chamber 8 at a position of the ink supply path 21 that is next to the bubble discharge port 5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid discharge head and an image forming apparatus.

  In general, a printer, a fax machine, a copier, a plotter, or an image forming apparatus that combines a plurality of these functions includes, for example, a recording head composed of a liquid ejection head that ejects ink droplets, It is also referred to as “paper”, but the material is not limited, and a recording medium, recording medium, transfer material, recording paper, etc. are also used synonymously.) Some perform formation (recording, printing, printing, and printing are also used synonymously).

  The “image forming apparatus” means an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. “Formation” means not only giving an image having a meaning such as a character or a figure to a medium but also giving an image having no meaning such as a pattern to the medium (simply ejecting a droplet). means. Further, “ink” is not limited to ink in a narrow sense, and is not particularly limited as long as it becomes liquid when ejected, and includes, for example, a DNA sample, a resist, a pattern material, and the like. .

  Generally, a liquid discharge head includes a plurality of nozzles that discharge ink as droplets, individual liquid chambers independent of each nozzle, and pressure generation means that generates pressure to pressurize ink in the individual liquid chamber (Piezoelectric actuators, thermal actuators, electrostatic actuators, etc.) are used, pressure is generated in the individual liquid chambers using pressure generating means, and the ink filled therein is ejected as droplets from the nozzles.

  Ink is supplied from the common liquid chamber to the individual individual liquid chambers via the liquid supply path, and the ink supplied from the outside to the common liquid chamber via the ink supply port is independent from the common liquid chamber. Distributed to individual liquid chambers and nozzles.

  By the way, recently, the number of nozzles of the recording head has been increased for high-speed recording, and the drive frequency tends to be higher. As a result, in order to ensure a sufficient ink supply amount to the nozzles, a plurality of liquid chambers are provided. The capacity of the common liquid chamber that is in communication has increased, but in this case, as the capacity increases, ink filling becomes difficult, and air bubbles accumulate at the end of the common liquid chamber. Performance) is significantly reduced, and improvement in bubble discharge is a problem.

  Therefore, conventionally, as described in Patent Document 1, a dummy nozzle for discharging bubbles is provided at the end of the common liquid chamber. Further, although not a dummy nozzle or a bubble discharge port, Patent Document 2 discloses that the most downstream end of the common liquid chamber is an opening for supplying ink to the pressure chamber, in order to improve the bubble discharge performance of the bit at the end. Patent Document 3 describes that the distance between the terminal ink supply port and the common liquid chamber end is separated by one pitch or more of the alignment interval of the ink supply ports.

Japanese Patent No. 3173358 JP 2003-320665 A JP 2004-98630 A

  As described in Patent Document 1 described above, if the number of dummy nozzles is increased, the bubble discharge property tends to be improved, but bubbles cannot be discharged efficiently simply by providing dummy nozzles. There is also a demerit that the length of the nozzle is unnecessarily long, and there is a problem that non-ejection due to bubbles and deterioration of ejection characteristics (bending in the flight direction, fluctuation in flight speed, volume change of ejection droplets) cannot be avoided.

  Further, although Patent Document 3 states that bubbles that cannot be removed by suction or pressurization operation are accumulated at the end of the common liquid chamber, the bit is not immediately blocked by the bubbles, but drives multiple bits at high frequency. When the liquid droplets are ejected, the accumulated bubbles move, and the bit is blocked by the bubbles and non-ejection occurs. Therefore, it is preferable to have a structure in which the bubbles are not accumulated (not left) in the suction operation. .

  Further, in the structure described in Patent Document 2, since the ink supply port is located at the end of the common liquid chamber, small bubbles are less likely to collect and the bubble discharge performance is improved as compared with the structure described in Patent Document 3, but the ink is discharged to the head. The large bubbles that are likely to occur when the first is filled (during initial filling) are difficult to discharge, and in order to discharge the bubbles, a large number of suction or pressurization operations are required, or very strong suction or Pressurization may be necessary. For this reason, it is said that a large mechanism is required for a recovery mechanism that consumes ink wastefully or performs suction or pressurization.

  The present invention has been made in view of the above problems, and an object of the present invention is to improve bubble discharge performance with a simple structure.

  In order to solve the above problems, a liquid discharge head according to the present invention includes a first flow path in which a plurality of nozzles that discharge droplets communicate with each other, and a bubble discharge port that is disposed outside in the arrangement direction of the plurality of nozzles. And a second channel that communicates with the bubble outlet, a first channel that communicates via the first opening, and a second channel that communicates via the second opening A common liquid chamber, the first flow path, and the second flow path are formed as separate members, the width of the nozzle arrangement direction is the width, and the length orthogonal to the nozzle arrangement direction is The width and length of the opening 2 are at least half the width of the common liquid chamber at the position of the first flow path adjacent to the bubble discharge port.

  Here, the end of the second opening on the second flow path side is located closer to the nozzle than the end of the common liquid chamber, and the end of the second opening on the common liquid chamber side is located outside the common liquid chamber. Can be configured.

  A flow path member that forms the first flow path and the second flow path; and a vibration plate member that forms a wall surface of the first flow path and the second flow path. The opening formed in the plate member constitutes the first opening and the second opening, and the end of the flow channel member on the common liquid chamber side is the common liquid chamber side of the opening of the vibration plate member It can be set as the structure located in the nozzle side rather than the edge of this.

  In addition, the bubble discharge port can be configured to be located outside the end of the second opening in the nozzle arrangement direction.

  Further, the second opening can be divided into a plurality, and the total length of the plurality of second openings can be half or more of the width of the common liquid chamber.

  Moreover, it can be set as the structure which is integrally provided with the liquid storage means which supplies the liquid to discharge.

  An image forming apparatus according to the present invention includes the liquid ejection head according to the present invention.

  According to the liquid discharge head according to the present invention, the first flow path through which the plurality of nozzles for discharging the droplets communicate, the bubble discharge port disposed outside the arrangement direction of the plurality of nozzles, and the bubble discharge port A second channel that communicates; a common liquid chamber in which the first channel communicates through the first opening; and the second channel communicates through the second opening. When the common liquid chamber and the first flow path and the second flow path are formed as separate members, the width of the nozzle opening direction is the width, and the length perpendicular to the nozzle arrangement direction is the width of the second opening. And the length is at least half the width of the common liquid chamber at the position of the first flow path adjacent to the bubble discharge port, so that the structure is simple and the bubble discharge property can be improved. .

  Since the image forming apparatus according to the present invention includes the liquid ejection head according to the present invention, it is possible to perform recording by performing stable droplet ejection.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. An example of the liquid discharge head according to the first embodiment of the present invention will be described with reference to FIGS. 1 and 2. 1 is an exploded perspective view of the head, and FIG. 2 is a cross-sectional view of the head along the longitudinal direction of the liquid chamber.

  The liquid discharge head includes a flow path plate 1 formed of a stainless steel substrate, a vibration plate member 2 bonded to the lower surface of the flow path plate 1, and a nozzle plate 3 bonded to the upper surface of the flow path plate 1. Ink supply, which is a first opening, to the pressure liquid chamber 6 through which a plurality of nozzles 4 for discharging ink droplets, which are liquid droplets, communicate with each other, and the common liquid chamber 8 for supplying ink to the pressure liquid chamber 6. An ink supply path 7 which is a first flow path communicating with the port 9 is formed.

  In addition to the plurality of nozzles 4 in the nozzle plate 3, bubble discharge ports 5 are provided at both ends of the arrangement direction (nozzle arrangement direction) of the plurality of nozzles 4, and the dummy liquid chamber 20 to which the bubble discharge ports 5 communicate. In addition, an ink supply path 21 that is a second flow path that communicates with the dummy liquid chamber 20 and communicates with the common liquid chamber 8 via an ink supply port 22 that is a second opening is formed.

  Here, the ink supply port 9 is constituted by the opening 9b of the flow path plate 1 and the opening 9a of the vibration plate member 2 forming the wall surface of the first flow path, and the ink supply port 22 is formed by the flow path plate. 1 opening 22 b and the opening 22 a of the diaphragm member 2.

  And it is a pressure generation means (actuator means) for pressurizing the ink in the pressurizing liquid chamber 6 corresponding to each pressurizing liquid chamber 6 on the outer surface side (the surface opposite to the liquid chamber) of the diaphragm member 2. A laminated piezoelectric element 12 as an electromechanical conversion element is joined, and the piezoelectric element 12 is joined to a base substrate 13 formed of a highly rigid material such as metal or ceramics. The laminated piezoelectric element 12 has a structure in which a laminated piezoelectric element member is grooved by dicing, and each piezoelectric element is separated so as to correspond to between each pressure chamber 6 and the pressure chamber 6. ing. Here, the corresponding piezoelectric element between the pressure chambers 6 functions as a support column without being driven.

  Further, the outer peripheral portion of the diaphragm member 2 is joined to the housing member 15 with an adhesive. The housing member 15 is formed with a concave portion serving as the common liquid chamber 8 and an ink supply path 16 for supplying ink to the common liquid chamber 8 from the outside. Here, the ink supply path 16 is positioned at a substantially central portion in the longitudinal direction (nozzle arrangement direction) of the common liquid chamber 8, but may be shifted from the center. However, when the ink supply path 16 is located close to the common liquid chamber end, the distance to the common liquid chamber end farther from the ink supply path 16 becomes longer. In this case, since the flow velocity at the end of the common liquid chamber is lowered during ink supply, it is difficult to discharge the bubbles, which is not preferable. The housing member 15 is formed by injection molding with, for example, epoxy resin or polyphenylene sulfite.

  Here, the flow path plate 1 is formed by, for example, pressing a stainless steel substrate to form a pressurizing liquid chamber 6 and a recess or a hole to be the ink supply path 7, but is not limited to the stainless steel substrate. Alternatively, other silicon substrates, photosensitive resins, and the like that are patterned can be used.

  The diaphragm member 2 is formed from a two-layer plate of resin and metal (here, stainless steel). The diaphragm region 10 is formed by etching stainless steel, and the ink supply port 9 penetrating the plate or the like. No. 22 is formed by press working to remove the resin and stainless steel at once. The metal is not limited to stainless steel, and the diaphragm 2 may be a metal plate, a resin plate, a metal-metal laminate member (multi-layer structure member), or the like, and the processing method is also described above. It is not limited to.

  The nozzle plate 3 forms a nozzle 4 having a diameter of 10 to 30 μm corresponding to each pressurized liquid chamber 6 and is bonded to the flow path plate 1 with an adhesive. The nozzle plate 3 may be made of a metal such as stainless steel or nickel, a combination of a metal and a resin such as a polyimide resin film, silicon, or a combination thereof. Here, a stainless plate pressed is used. Further, the inner shape (inner shape) of the nozzle 4 is formed in a substantially frustum shape (may be a substantially cylindrical shape or a horn shape) having a tapered shape in cross section, and the hole diameter of the nozzle 4 is the ink droplet outlet side. The diameter is about 25 μm.

  Further, a water repellent treatment layer having a water repellent surface treatment (not shown) is provided on the nozzle surface (surface in the ejection direction: ejection surface) of the nozzle plate 3. As a water-repellent treatment layer, a silicone-modified fluororesin (for example, Optool) film was formed by vapor deposition. In addition, PTFE-Ni eutectoid plating, fluororesin electrodeposition coating, other fluorine resin vapor-deposited coatings, and baking after the application of silicon-based resin / fluorine-based resin solvent, etc. It is necessary to provide a water-repellent treatment film that is selected accordingly, to stabilize the ink droplet shape and flight characteristics, and to obtain high-quality image quality.

  The piezoelectric element 12 includes a lead zirconate titanate (PZT) piezoelectric layer having a thickness of 10 to 50 μm / layer and an internal electrode layer made of silver / palladium (AgPd) having a thickness of several μm / layer. The internal electrodes are alternately stacked, and the internal electrodes are alternately electrically connected to the individual electrodes and the common electrode which are the end surface electrodes (external electrodes), and a drive signal is supplied to these electrodes via the FPC cable 17. I am doing so. The pressurized liquid chamber 6 is contracted and expanded by expansion and contraction of the piezoelectric element 12 whose piezoelectric constant is d33. The piezoelectric element 12 expands when a drive signal is applied and is charged, and contracts in the opposite direction when the charge charged in the piezoelectric element 12 is discharged.

  In the liquid ejection head configured as described above, when driven by a push-off method, for example, a drive pulse voltage of 20 to 50 V is selectively applied to the plurality of piezoelectric elements 12 according to an image recorded from a control unit (not shown). Is applied to the piezoelectric element 12 to which the pulse voltage is applied to displace the deformable region of the vibration plate member 2 in the direction of the nozzle plate 3, and the liquid chamber 6 changes its volume (volume) in the liquid chamber 6. By pressurizing this ink, droplets are ejected from the nozzle 4 of the nozzle plate 3. As the liquid droplets are discharged, the pressure in the liquid chamber 6 decreases, and a slight negative pressure is generated in the liquid chamber 6 due to the inertia of the liquid flow at this time. Under this state, when the voltage application to the piezoelectric element 12 is turned off, the diaphragm member 2 returns to the original position and the liquid chamber 6 becomes the original shape, so that further negative pressure is generated. . At this time, ink is filled from the common liquid chamber 8 into the liquid chamber 6, and droplets are ejected from the nozzles 4 in response to the next drive pulse application.

  In addition to the above-described punching, the liquid discharge head is not limited to the pulling method (a method in which the vibrating plate member 2 is released from the pulled state and pressurized with a restoring force), and the pulling-pushing method (the vibrating plate member 2 is fixed). It can also be driven by a method such as a method of holding at an intermediate position, pulling from this position, and then extruding.

  Also, here, the nozzle pitch in each nozzle row is 150 dpi, the number of nozzles 4 is 320 (a simplified diagram not showing all nozzles in FIG. 1), and the length of the nozzle row Is about 2.13 inches long

The details of the flow path structure in the liquid discharge head will be described with reference to FIG. FIG. 3 is a schematic plan view of an essential part of the head viewed from the nozzle plate in a transparent state.
As shown in FIG. 1, the common liquid chamber 8 in this head has a planar shape, and the arrangement direction of the pressurized liquid chambers 6 and nozzles 4 (the common liquid in the direction perpendicular to the nozzle arrangement direction, here the common liquid chamber short direction). The dimension of the chamber is expressed as a width.) Is substantially rectangular, and R (R) is provided at both end portions 8a so that the stagnation portion is reduced in the liquid flow. The common liquid chamber is formed with a width of 2 mm and a depth of 2 mm, has a large capacity and a relatively low fluid resistance, and has an ink supply capability capable of driving high viscosity ink at high frequency.

  A part of the wall surface of the common liquid chamber 8 is formed by the diaphragm member 2 which is a member forming the wall surface of the pressurized liquid chamber 6. The ink flow during ink filling or recovery operation flows from the ink supply port 16 to the common liquid chamber 8, passes through the ink supply ports 7 and 21, and is supplied to the pressurized liquid chamber 6 and the dummy liquid chamber 20. In addition, the air flows out from the bubble discharge port 5.

  The ink supply port 16 is located at a substantially central portion in the longitudinal direction of the common liquid chamber 8, the liquid flow rate is slow at the end of the common liquid chamber 8 away from the ink supply path 16, and bubbles are at the end of the common liquid chamber. It is easy to collect in. That is, as the number of nozzles increases and the head becomes longer, the distance from the ink supply path 16 to the common liquid chamber end becomes longer, and bubbles tend to accumulate at the common liquid chamber end.

  Therefore, here, as shown in FIG. 3, the dimension of the common liquid chamber 8 in the short direction is the common liquid chamber width direction, and the position of the ink supply path 7 to the nozzle 4 to which the bubble discharge port 5 is adjacent is shown. The common liquid chamber width is W. The ink supply port 22 is an opening constituted by the opening 22 a of the diaphragm member 2 and the opening 22 b of the flow path plate 1, and the width w and the length L thereof are relative to the width W of the common liquid chamber 8. More than half of them, that is, W / 2 or more.

  The bubbles are formed so as to approach a spherical shape which is a stable state. Although it is large, it becomes a size corresponding to the width W of the common liquid chamber 8, but the end of the bubble tends to accumulate so as to be in contact with the common liquid chamber 8. By allowing the ink supply port 22 to include the end and center of the bubble, the discharge performance of a large bubble having a diameter close to the width W during the recovery operation by suction or pressurization is remarkably improved.

  That is, the ink supply port 22 communicating with the bubble discharge port is located in the ink supply port 22 when the bubble having the diameter of the width W of the common liquid chamber 8 is formed in the common liquid chamber 8. The width and length are to be formed.

  As described above, in the case of a head having a nozzle pitch of 150 dpi and a nozzle number of 160, that is, a nozzle row having a length of about 1 inch, the ink supply port 16 is located at the approximate center of the common liquid chamber 8 as described above. When arranged, the distance to the common liquid chamber end is about 0.5 inches. In this case, even if the width W1 and the length L are less than W / 2, the ink supply port 22 has a low probability of non-ejection due to bubble discharge, but this is because bubbles are generated due to the high flow rate at the end of the common liquid chamber. It is because it becomes easy to be discharged. In a head with 320 nozzles and a nozzle row length of about 2 inches, even when the ink supply port 16 is arranged at the approximate center of the common liquid chamber 8, the distance to the common liquid chamber end is about 1 inch. It is difficult to ensure the flow velocity at the liquid chamber end, and the width w and the length L of the ink supply port 22 are less than half of the width W of the common liquid chamber 8 (less than W / 2). It becomes difficult to discharge large bubbles at the end of the liquid chamber.

Next, the opening 9 a of the vibration plate member 2 constituting the ink supply port 9, the opening 9 b of the flow path plate 1, the opening 22 a of the vibration plate member 2 constituting the ink supply port 22, the flow The relationship of the opening 22b of the road plate 1 will be described with reference to FIG. 4 together with FIG. 4 is a cross-sectional view taken along line AA in FIG.
Here, the rear end 9be of the opening 9b of the flow path plate 1 is positioned inside the opening 9a of the diaphragm member 2, that is, on the nozzle 4 side, and the rear end of the opening 22b of the flow path plate 1 22be is configured to be located inside the opening 22a of the diaphragm member 2, that is, on the nozzle 4 side.

  As described above, the rear ends of the openings 9b and 22b of the flow channel plate 1 are positioned inside the rear ends of the openings 9a and 22a of the diaphragm member 2, so that the liquid in the portion X in FIG. Flow stagnation is reduced and bubbles are less likely to trap in the flow path.

  Thus, the common liquid chamber, the first flow path communicating with the nozzle and the second flow path communicating with the bubble discharge port are formed in separate members, the nozzle arrangement direction is a width, and the direction orthogonal to the nozzle arrangement direction The width and length of the second opening are at least half the width of the common liquid chamber at the position of the first flow path adjacent to the bubble discharge port. Emissions are improved.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a schematic plan view of an essential part of a head similar to that shown in FIG. 3 viewed from the nozzle plate in a transparent state.
Here, in the ink supply port 22, the end 22 </ b> C on the ink supply path 21 side is positioned closer to the nozzle 4 than the end in the short direction of the common liquid chamber 8, and the end 22 </ b> D in the longitudinal direction of the common liquid chamber 8 The chamber 8 is formed so as to be located outside the longitudinal end.

  As a result, minute bubbles are discharged without accumulating at the end portion 8b in the longitudinal direction and the end portion 8c in the short direction at the end portion of the common liquid chamber 8.

  That is, when the minute bubbles remain at the common liquid chamber end portions 8b and 8c, there is almost no influence on the discharge characteristics, but when they enter the pressure chamber 6, the discharge characteristics are deteriorated (bending in the flight direction). , Fluctuation in flying speed, volume change of ejected droplets). In addition, a large number of minute bubbles may be combined or grow to form a large bubble, which may cause non-ejection (discharge failure). Therefore, it is necessary to carry out a recovery operation, and ink is consumed wastefully.

  By discharging so as not to leave minute bubbles as in this embodiment, it is possible to prevent the occurrence of defects due to the bubbles as described above, and to further improve the reliability.

Next, a third embodiment of the present invention will be described with reference to FIG. 6 is a schematic plan view of an essential part of a head similar to that shown in FIG. 3 as viewed from the nozzle plate in a transparent state.
Here, the position of the bubble discharge port 5 is configured to be located outside the opening 22 in the nozzle arrangement direction. By comprising in this way, since the flow of a liquid is smooth, bubble discharge property improves. Further, since the nozzles 4 are separated from the adjacent nozzles 4, the bubbles discharged from the bubble discharge ports 5 at the time of ink filling or recovery operation become foamy, covering the adjacent nozzles 4, and reducing the possibility that the nozzles 4 cause ejection failure.

Next, a fourth embodiment of the present invention will be described with reference to FIG. 7 is a schematic plan view of an essential part of a head similar to FIG. 3 viewed from the nozzle plate in a transparent state.
Here, a plurality of rows of bubble discharge ports 5, ink supply paths 21, and ink supply ports 22 are provided. That is, the second opening is divided into a plurality of parts. The width X of one ink supply port 22 is the same as the width of the opening 9, and the sum of the widths of a plurality of ink supply ports 22 (referred to as ink supply port group 22G) is common as described above. More than half of the width W of the liquid chamber 8 is set.

  In this way, by forming the width and length of the ink supply port group 22G to be more than half of the width of the common liquid chamber 8, the end of a large bubble corresponding to the common liquid chamber width when accumulated at the end of the common liquid chamber 8 is obtained. By allowing the ink supply port group 22G to include the center from the portion, it is possible to improve the discharge of large bubbles during the recovery operation by suction or pressurization. In addition, since the ink supply port group 22G has the same opening width x of the ink supply port 9, the size can be easily controlled when the ink supply port group 22G is opened by etching.

Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 8 is a schematic plan view of an essential part of a head similar to that shown in FIG. 3 viewed from the nozzle plate in a transparent state.
Here, the ink supply path 7 and the ink supply path 21, the ink supply port 9 and the ink supply port 22, and the nozzle 4 and the bubble discharge port 5 are formed in the same shape. That is, the same flow path shape is repeated. Thereby, it can process easily when forming a flow path by press work.

  Although not shown, an ink tank serving as a liquid storage unit that supplies ink to the liquid discharge heads of the above-described embodiments may be integrated to form a so-called ink cartridge. Thereby, in the head-integrated ink cartridge (or tank-integrated head), the bubble discharge property is improved, non-ejection hardly occurs, and the initial filling property and recoverability can be improved.

  In the above embodiment, a head using a piezoelectric element as pressure generating means (also referred to as actuator means, energy generating means, etc.) for generating pressure for ejecting droplets has been described. For a liquid discharge head using a thermal actuator that uses a phase change caused by film boiling of a liquid using an electrothermal transducer, a shape memory alloy actuator that uses a metal phase change caused by a temperature change, an electrostatic actuator that uses an electrostatic force, etc. Can also be applied.

Next, an example of an image forming apparatus equipped with the liquid ejection head according to the present invention will be described with reference to FIGS.
This image forming apparatus is a serial type image forming apparatus, and a carriage 233 is slidably held in the main scanning direction by main and sub guide rods 231 and 232 which are guide members horizontally mounted on the left and right side plates 201A and 201B. The main scanning motor that does not perform moving scanning in the direction indicated by the arrow (carriage main scanning direction) via the timing belt.

  The carriage 233 has recording heads 234a and 234b (which are liquid ejection heads according to the present invention for ejecting ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (K). When not distinguished, it is referred to as “recording head 234”). A nozzle row composed of a plurality of nozzles is arranged in the sub-scanning direction orthogonal to the main scanning direction, and is mounted with the ink droplet ejection direction facing downward.

  Each of the recording heads 234 has two nozzle rows. One nozzle row of the recording head 234a has black (K) droplets, the other nozzle row has cyan (C) droplets, and the recording head 234b has one nozzle row. One nozzle row ejects magenta (M) droplets, and the other nozzle row ejects yellow (Y) droplets. In this example, four-color droplets are ejected in a two-head configuration. However, a recording head for each color can be provided, and a nozzle row in which a plurality of nozzles ejecting four-color droplets are arranged. It is also possible to have a single recording head configuration.

  The carriage 233 is equipped with sub tanks 235a and 235b (referred to as “sub tank 235” when not distinguished) for supplying ink of each color corresponding to the nozzle rows of the recording head 234. The sub tank 235 is supplied with ink of each color from the ink cartridge 210 of each color by the supply unit 224 via the supply tube 236 of each color.

  On the other hand, as a paper feeding unit for feeding the paper 242 stacked on the paper stacking unit (pressure plate) 241 of the paper feed tray 202, a half-moon roller (feeding) that separates and feeds the paper 242 one by one from the paper stacking unit 241. A separation pad 244 made of a material having a large coefficient of friction is provided opposite to the sheet roller 243 and the sheet feeding roller 243, and the separation pad 244 is urged toward the sheet feeding roller 243 side.

  In order to feed the sheet 242 fed from the sheet feeding unit to the lower side of the recording head 234, a guide member 245 for guiding the sheet 242, a counter roller 246, a conveyance guide member 247, and a tip pressure roller. And a conveying belt 251 which is a conveying means for electrostatically attracting the fed paper 242 and conveying it at a position facing the recording head 234.

  The conveyor belt 251 is an endless belt, and is configured to wrap around the conveyor roller 252 and the tension roller 253 so as to circulate in the belt conveyance direction (sub-scanning direction). In addition, a charging roller 256 that is a charging unit for charging the surface of the transport belt 251 is provided. The charging roller 256 is disposed so as to come into contact with the surface layer of the conveyor belt 251 and to rotate following the rotation of the conveyor belt 251. The transport belt 251 rotates in the belt transport direction when the transport roller 252 is rotationally driven through timing by a sub-scanning motor (not shown).

  Further, as a paper discharge unit for discharging the paper 242 recorded by the recording head 234, a separation claw 261 for separating the paper 242 from the transport belt 251, a paper discharge roller 262, and a paper discharge roller 263 are provided. A paper discharge tray 203 is provided below the paper discharge roller 262.

  A double-sided unit 271 is detachably attached to the back surface of the apparatus main body. The duplex unit 271 takes in the paper 242 returned by the reverse rotation of the transport belt 251, reverses it, and feeds it again between the counter roller 246 and the transport belt 251. The upper surface of the duplex unit 271 is a manual feed tray 272.

  Further, a maintenance / recovery mechanism 281 that is a head maintenance / recovery device according to the present invention includes a recovery means for maintaining and recovering the nozzle state of the recording head 234 in the non-printing area on one side of the carriage 233 in the scanning direction. Is arranged. The maintenance / recovery mechanism 281 includes cap members (hereinafter referred to as “caps”) 282a and 282b (hereinafter referred to as “caps 282” when not distinguished) for capping each nozzle surface of the recording head 234, and nozzle surfaces. A wiper blade 283 that is a blade member for wiping the ink, and an empty discharge receiver 284 that receives liquid droplets for discharging the liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid. ing.

  In addition, in the non-printing area on the other side in the scanning direction of the carriage 233, the liquid that receives liquid droplets when performing idle ejection that ejects liquid droplets that do not contribute to recording in order to discharge the recording liquid thickened during recording or the like. An ink recovery unit (empty discharge receiver) 288 that is a recovery container is disposed, and the ink recovery unit 288 includes an opening 289 along the nozzle row direction of the recording head 234 and the like.

  In this image forming apparatus configured as described above, the sheets 242 are separated and fed one by one from the sheet feeding tray 202, and the sheet 242 fed substantially vertically upward is guided by the guide 245, and is conveyed to the conveyor belt 251 and the counter. It is sandwiched between the rollers 246 and conveyed, and further, the leading end is guided by the conveying guide 237 and pressed against the conveying belt 251 by the leading end pressing roller 249, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately applied to the charging roller 256, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 251 alternates, that is, in the sub-scanning direction that is the circumferential direction. , Plus and minus are alternately charged in a band shape with a predetermined width. When the sheet 242 is fed onto the conveyance belt 251 charged alternately with plus and minus, the sheet 242 is attracted to the conveyance belt 251, and the sheet 242 is conveyed in the sub scanning direction by the circumferential movement of the conveyance belt 251.

  Therefore, by driving the recording head 234 according to the image signal while moving the carriage 233, ink droplets are ejected onto the stopped paper 242 to record one line, and after the paper 242 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 242 has reached the recording area, the recording operation is finished and the paper 242 is discharged onto the paper discharge tray 203.

  As described above, since the image forming apparatus includes the liquid ejection head according to the present invention, ejection failure due to bubbles is small, and stable recording can be performed.

  In the above embodiment, the present invention has been described with reference to an example in which the present invention is applied to an image forming apparatus having a printer configuration. However, the present invention is not limited to this. For example, the present invention may be applied to an image forming apparatus such as a printer / fax / copier multifunction machine. it can. Further, the present invention can be applied to an image forming apparatus using a liquid other than the narrowly defined ink, a fixing processing liquid, or the like. In the above-described embodiment, the example is described in which the present invention is applied to a serial type image forming apparatus. However, the present invention can be similarly applied to a line type liquid discharge head and a line type image forming apparatus.

FIG. 3 is an exploded perspective view illustrating an example of a liquid discharge head according to the first embodiment of the present invention. FIG. 4 is an explanatory cross-sectional view along the longitudinal direction of the liquid chamber of the liquid discharge head. It is the principal part plane schematic explanatory drawing which looked at the head from the nozzle plate in the transmission state similarly. Similarly it is principal part cross-sectional explanatory drawing. FIG. 10 is a schematic plan view of a main part viewed in a plan view from a nozzle plate of a liquid ejection head according to a second embodiment of the present invention. It is a principal part plane schematic explanatory view seen in the transmission state planarly from the nozzle plate of the liquid discharge head which concerns on 3rd Embodiment of this invention. FIG. 10 is a schematic plan view of a main part viewed in a plan view from a nozzle plate of a liquid ejection head according to a fourth embodiment of the present invention. FIG. 10 is a schematic plan view of a main part viewed from a nozzle plate of a liquid ejection head according to a fifth embodiment of the present invention in a planar state. 1 is an overall configuration diagram illustrating an example of an image forming apparatus according to the present invention. Similarly it is principal part plane explanatory drawing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Flow path plate 2 ... Vibration plate member 3 ... Nozzle plate 4 ... Nozzle 5 ... Bubble discharge port 6 ... Individual liquid chamber 8 ... Common liquid chamber 9 ... Ink supply port 12 ... Piezoelectric element 20 ... Dummy liquid chamber 21 ... Ink supply Path 234 ... Recording head (liquid ejection head)

Claims (7)

A first flow path through which a plurality of nozzles for discharging droplets communicate;
A bubble discharge port disposed outside the array direction of the plurality of nozzles;
A second flow path through which the bubble discharge port communicates;
A common liquid chamber in which the first flow path communicates via a first opening, and the second flow path communicates via a second opening;
The common liquid chamber and the first flow path and the second flow path are formed in separate members,
When the nozzle arrangement direction is a width and the direction orthogonal to the nozzle arrangement direction is a length, the width and length of the second opening are at least at the position of the first flow path adjacent to the bubble discharge port. A liquid discharge head characterized by being at least half the width of the common liquid chamber.   2. The liquid discharge head according to claim 1, wherein an end of the second opening on the second flow path side is located on the nozzle side with respect to an end of the common liquid chamber, and the common liquid in the second opening is provided. A chamber-side end is located outside the common liquid chamber.   The liquid discharge head according to claim 1, wherein a flow path member that forms the first flow path and the second flow path, and wall surfaces of the first flow path and the second flow path are provided. A diaphragm member to be formed, and the first opening portion and the second opening portion are respectively configured by openings formed in the flow path member and the diaphragm member, and the opening portion of the flow path member An end of the common liquid chamber is positioned closer to the nozzle than an end of the opening of the diaphragm member on the common liquid chamber.   4. The liquid discharge head according to claim 1, wherein the bubble discharge port is positioned outside an end of the second opening in the nozzle arrangement direction. 5.   5. The liquid ejection head according to claim 1, wherein the second opening is divided into a plurality of portions, and the total length of the plurality of second openings is not less than half the width of the common liquid chamber. A liquid discharge head characterized by the above.   5. The liquid discharge head according to claim 1, wherein the liquid discharge head is provided integrally with a liquid storage means for supplying a liquid to be discharged.   7. An image forming apparatus for forming an image by discharging droplets from a liquid discharge head, wherein the liquid discharge head is the liquid discharge head according to claim 1.

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