JP4151955B2 - Droplet discharge head and image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a droplet discharge head and an image forming apparatus.
[0002]
[Prior art]
[Patent Document 1]
Japanese Patent No. 3069477
[Patent Document 2]
Japanese Patent Laid-Open No. 7-171969
[Patent Document 3]
JP-A-9-141856
[Patent Document 4]
JP 2000-301714 A
[0003]
An ink jet recording apparatus used as an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, or a plotter has a nozzle for ejecting ink droplets and a pressurized liquid chamber (an ink flow path, a discharge chamber, a pressure chamber, a pressurization) that communicates with the nozzle. And a pressure generating means (also referred to as a pressure converting means, an actuator means, a driving means, etc.) for pressurizing the ink in the pressurized liquid chamber. An ink jet head as a head is mounted. Examples of the droplet discharge head include a droplet discharge head that discharges a liquid resist as droplets and a droplet discharge head that discharges a DNA sample as droplets. The following description will focus on an inkjet head.
[0004]
As an ink jet head, as a pressure generating means for generating energy to pressurize ink in a pressurized liquid chamber, an electromechanical transducer such as a piezoelectric element is used to deform and pressurize a diaphragm that forms the wall surface of the ink flow path. A so-called piezo type that discharges ink droplets by changing the volume in the liquid chamber, or a pressure generated by generating bubbles by heating ink in a pressurized liquid chamber using a heating resistor (electrothermal converter). Using a so-called thermal type that ejects ink droplets, or an electrostatic actuator that deforms the diaphragm that forms the wall of the pressurized liquid chamber by electrostatic force, the diaphragm is deformed to change the volume of the pressurized liquid chamber. There are known electrostatic types that eject ink droplets.
[0005]
As a major technical problem in the ink jet recording apparatus, there are speeding up and image quality improvement. As a method for solving this problem, there are a method of increasing the driving frequency of the pressure generating means and a method of increasing the number of nozzles per head.
[0006]
However, when the driving frequency of the pressure generating means is increased, the pressure behavior in the pressurized liquid chamber becomes complicated due to reflection of the pressure propagated from the pressurized liquid chamber to the common liquid chamber, and ink droplets are ejected accurately. It becomes difficult to do. Further, in such a head having a large number of nozzles, the shape of the common liquid chamber may be reduced in the longitudinal direction in order to improve the bubble discharge performance in the common liquid chamber. At the end in the hand direction, the pressure change becomes large, and the effect on the pressurized liquid chamber is greater than the central part in the longitudinal direction of the common liquid chamber, so the pressure behavior varies depending on the position of the pressurized liquid chamber. It becomes very difficult to control. Therefore, it is necessary to suppress the pressure change in the common liquid chamber and to suppress the difference in pressure change depending on the position.
[0007]
Therefore, conventionally, as a configuration for suppressing the pressure change in the common liquid chamber, there is a method in which a gas chamber is provided in the common liquid chamber to be an air damper as disclosed in Japanese Patent Application Laid-Open No. H10-260260. Further, as disclosed in [Patent Document 2], there is a method of absorbing pressure generated by ejection by providing a foaming elastic material in at least a part of the liquid chamber.
[0008]
Furthermore, as disclosed in [Patent Document 3], a damper chamber is provided in a part of the common liquid chamber, and the damper chamber is separated by a flexible material sandwiched between the pressurized liquid chamber and the energy generating unit. There is a method of using a flexible material as a damper by partitioning a common liquid chamber. Further, as disclosed in [Patent Document 4], a method in which a flexible film including a piezoelectric element is provided in a common liquid chamber, and the piezoelectric element is driven according to the pressure in the common liquid chamber to absorb the pressure. There is.
[0009]
[Problems to be solved by the invention]
However, in the above-described conventional method disclosed in [Patent Document 1], since the amount of air in the gas chamber does not self-recover, it is difficult to maintain the damper effect over a long period of time. Therefore, it is necessary to always control the amount of gas held in the gas chamber. For this purpose, there is a problem that it is difficult or costly to implement with a head other than the electrothermal conversion type, such as requiring a heating element. . In addition, it is difficult to control the amount of air in the gas chamber itself, and air separated from the gas chamber enters the pressurizing liquid chamber and the pressure in the pressurizing liquid chamber cannot be sufficiently increased. There is also a problem that there is a risk of causing.
[0010]
Also,
In the method of providing a foamable elastic material in a part of the liquid chamber as disclosed in Patent Document 2, a new process for providing the foamable elastic material is required, resulting in an increase in cost. There are challenges.
[0011]
Furthermore, in the method of providing a damper chamber in a part of the common liquid chamber as disclosed in [Patent Document 3], it is necessary to take a sufficient area of the damper chamber in order to sufficiently exhibit the damper effect. In addition, there is a problem that the degree of freedom in designing the shape of the common liquid chamber is reduced, and it is difficult to form a common liquid chamber having bubble discharge properties.
[0012]
Moreover, in the method of providing a flexible film including a piezoelectric element in the common liquid chamber as disclosed in [Patent Document 4], the driving of the piezoelectric element is controlled in order to effectively absorb the pressure. There is a problem that the apparatus is complicated and the cost is increased, for example, a new control device is required.
[0013]
The present invention has been made in view of the above-described problems, and provides a droplet ejection head that improves droplet ejection characteristics, is miniaturized, and is low-cost, and an image forming apparatus including the droplet ejection head. With the goal.
[0014]
[Means for Solving the Problems]
  In order to solve the above problems, a liquid droplet ejection head according to the present invention includes:
A flow path plate having a plurality of pressurized liquid chambers communicating with nozzles for discharging droplets, a common liquid chamber for supplying liquid to the plurality of pressurized liquid chambers, and a vibration forming one wall surface of the pressurized liquid chamber In a droplet discharge head provided with a plate,
  The common liquid chamber is formed on a surface opposite to the pressurized liquid chamber across the diaphragm,
  The diaphragm isCommon liquid chamberWall ofsurfaceA region that forms a portion and does not face the flow path plateHas a free vibration surface consisting of a thick part and a thin part.
The configuration.
[0015]
  hereThe aboveThe free vibration surface is a laminated structure consisting of multiple layers.Can be configured. Also, the aboveThe thick portion of the free vibration surface has the same thickness as the member that forms the wall surface of the pressurized liquid chamber.Can be configured.
[0016]
  Also,A plurality of the pressurized liquid chambers are arranged side by side in the longitudinal direction of the common liquid chamber, and the width of the thin liquid portion in the short direction of the common liquid chamber in the free vibration surface is narrower than the central portion of the common liquid chamber. It can be set as the structure provided in the longitudinal direction edge part or its vicinity of the common liquid chamber.
[0017]
  A plurality of the pressurized liquid chambers are arranged side by side in the longitudinal direction of the common liquid chamber, and the thin wall portion of the free vibration surface has a cross-sectional area in a plane perpendicular to the longitudinal direction of the common liquid chamber. It can be set as the structure provided corresponding to the longitudinal direction edge part of the said common liquid chamber smaller than the center part, or its vicinity.
[0018]
An image forming apparatus according to the present invention includes the droplet discharge head according to the present invention.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. An ink jet head according to a first embodiment of a droplet discharge head of the present invention will be described with reference to FIGS. 1 is a perspective view illustrating the assembly of the head, FIG. 2 is a cross-sectional explanatory view along the lateral direction of the liquid chamber of the head (along line AA in FIG. 1), and FIG. FIG. 4 is an exploded perspective view of the head, and FIG. 5 is a schematic perspective view as seen from the back side of the diaphragm of the head.
[0020]
This inkjet head has a flow path plate 1 formed of a single crystal silicon 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. Thus, the pressure liquid chamber 6 that is an ink flow path through which the nozzle 4 that discharges ink droplets that are liquid droplets communicates via the nozzle communication path 5, and the common liquid chamber for supplying ink to the pressure liquid chamber 6 An ink supply path 7 serving as a fluid resistance portion communicating with the ink 8 through the ink supply port 9 is formed.
[0021]
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.
[0022]
Further, between the piezoelectric elements 12, support columns 14 are provided corresponding to the partition walls 1 a between the pressurized liquid chambers 6 and 6. Here, the piezoelectric element member is divided into comb teeth by slitting by half-cut dicing, and each piezoelectric element 12 is formed as a piezoelectric element 12 and a support post portion 14. The structure of the column 14 is the same as that of the piezoelectric element. However, since the drive voltage is not applied, the column 14 is merely a column.
[0023]
Further, the outer peripheral portion of the diaphragm member 12 is joined to the frame member 15 with an adhesive. The frame member 15 is formed with a concave portion serving as the common liquid chamber 8 and an ink supply hole 16 (see FIG. 4) (not shown) for supplying ink to the common liquid chamber 8 from the outside. The frame member 15 is formed of, for example, an epoxy resin or polyphenylene sulfite by injection molding.
[0024]
Here, the flow path plate 1 is obtained by anisotropically etching a single crystal silicon substrate having a crystal plane orientation (110), for example, with an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), thereby the nozzle communication path 5, The pressurization chamber 6 and the ink supply passage 7 are formed with recesses and holes, but the invention is not limited to single crystal silicon substrates, and other stainless steel substrates, photosensitive resins, and the like can also be used.
[0025]
The diaphragm 2 is formed from a nickel metal plate having a two-layer structure. For example, the diaphragm 2 is manufactured by an electroforming method (electroforming method), but other metal plates, resin plates, or metal and resin plates are used. A laminated member or a metal-metal laminated member (multi-layer structure member) can also be used.
[0026]
The nozzle plate 3 forms a nozzle 4 having a diameter of 10 to 35 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 metal and resin such as a polyimide resin film, silicon, or a combination thereof. Here, it forms with the Ni plating film | membrane etc. by the electroforming method. Further, the internal shape (inner shape) of the nozzle 3 is formed in a horn shape (may be a substantially columnar shape or a substantially frustum shape), and the hole diameter of the nozzle 4 is about 20 to 20 on the ink droplet outlet side. 35 μm. Furthermore, the nozzle pitch of each row was 150 dpi.
[0027]
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. Examples of the water-repellent treatment layer include PTFE-Ni eutectoid plating, fluororesin electrodeposition coating, vapor-deposited fluororesin (e.g., fluorinated pitch), silicon resin / fluorine resin A water-repellent treatment film selected according to the ink physical properties such as baking after solvent application is provided to stabilize the ink droplet shape and flying characteristics so that high-quality image quality can be obtained.
[0028]
The piezoelectric element 12 is composed of a lead zirconate titanate (PZT) piezoelectric layer having a thickness of 10 to 50 μm / layer and an internal electrode layer made of silver and palladium (AgPd) having a thickness of several μm / layer alternately. The internal electrodes are alternately connected to the individual electrodes and the common electrodes, which are end electrodes (external electrodes) on the end faces, and a drive signal is supplied to these electrodes via the FPC cable 17. ing. The pressurized liquid chamber 6 is contracted and expanded by expansion and contraction of the piezoelectric element 12 whose piezoelectric constant is d23. 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.
[0029]
As shown in FIG. 4, the common liquid chamber 8 in this head has a planar shape and is rectangular in the arrangement direction of the pressurized liquid chambers 6 (nozzle arrangement direction, which is referred to as “common liquid chamber longitudinal direction”). Forming.
[0030]
Then, a part of the wall surface of the common liquid chamber 8 is formed by the vibration plate member 2 that is a member that forms the wall surface of the pressurized liquid chamber 6, and a portion that forms the wall surface of the common liquid chamber 8 is used as the free vibration surface 21. Yes. As shown in FIG. 5 (the illustration of the bonding portion of the piezoelectric element is omitted), the free vibration surface 21 is a thick portion formed by the three-layer structure portion of the three-layer structure diaphragm member 2. 22 and a thin-walled portion 23 having a planar rectangular shape formed of a portion having a one-layer structure by removing a portion of the thickness. Here, the thick part 22 and the thin part 23 are arranged in a stripe shape in the longitudinal direction (nozzle arrangement direction) of the common liquid chamber. The thick portion 22 may have a two-layer structure, the thin portion 23 may have a one-layer structure, or the thick portion 22 may have a three-layer structure, and the thin portion 23 may have a two-layer structure.
[0031]
In the head configured as described above, by selectively applying a drive pulse voltage of 20 to 50 V to the piezoelectric element 12, the piezoelectric element 12 to which the pulse voltage has been applied is displaced in the extending direction, and the pressurized liquid The portion of the diaphragm member 2 corresponding to the chamber 6 is deformed in the direction of the nozzle 4, the ink in the pressurized liquid chamber 6 is pressurized by the volume / volume change of the pressurized liquid chamber 6, and ink droplets are ejected from the nozzle 4. (Injected).
[0032]
As the ink droplets are ejected, the liquid pressure in the pressurized liquid chamber 6 decreases, and a slight negative pressure is generated in the pressurized liquid chamber 6 due to the inertia of the ink 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 pressurized liquid chamber 6 becomes the original shape. appear. At this time, the pressurized liquid chamber 6 is filled with ink from the common liquid chamber 8 through the ink supply port 9 and the ink supply path 7. Therefore, after the vibration of the ink meniscus surface of the nozzle 4 is attenuated and stabilized, a pulse voltage is applied to the piezoelectric element 12 to discharge the ink droplet for the next ink droplet discharge.
[0033]
Here, when the pressurized liquid chamber 6 is pressurized to eject ink droplets, the pressure wave generated in the pressurized liquid chamber 6 is propagated to the common liquid chamber 8 via the fluid resistance portion 7 and the ink supply port 9. However, the thin wall portion 23 of the free vibration surface 21 that forms the wall surface of the common liquid chamber 8 absorbs and attenuates the pressure fluctuation in the common liquid chamber 8, and the pressure wave is reflected to return to the pressurized liquid chamber 6. Is prevented. Thereby, the controllability of the meniscus and thus the droplet ejection characteristics are improved.
[0034]
A specific numerical simulation result will be described. When the wall surface of the common liquid chamber 8 is configured by the diaphragm 2 itself (in the case of only the thick portion 22, this is referred to as a comparative example), and in the above embodiment. As described above, when the thick portion 22 and the thin portion 23 are configured (this is referred to as an example), the pressure change of the pressurized liquid chamber 6 corresponding to the central portion of the common liquid chamber 8 and the common liquid chamber 8 Comparison with the pressure change of the pressurized liquid chamber 6 corresponding to the end portion was performed.
[0035]
At this time, after applying a voltage to the piezoelectric element 12 and applying pressure to the pressurized liquid chamber 6, the average value of the pressure change in the pressurized liquid chamber 6 for 20 μsec was averaged. Compared to the value in the corresponding pressurized liquid chamber 6, the value in the pressurized liquid chamber 6 corresponding to the end portion was larger in the comparative example, such as 15% larger, whereas the variation in the example was larger. In some cases, the fluctuation was only 2%, and it was confirmed that the pressure absorption efficiency is increased by forming the free vibration surface 21 with the thin portion 23 and the thick portion 22.
[0036]
Furthermore, when a multi-injection experiment was conducted for the comparative example and the example, it was confirmed that a defective image was generated in the comparative example, but no defective image was generated in the example.
[0037]
As described above, since at least one wall surface of the common liquid chamber has a free vibration surface including a thick portion and a thin portion, the thin portion absorbs the pressure of the common liquid chamber, and the thick portion absorbs the free vibration surface. It is possible to maintain the rigidity and strength of the material, and it is possible to attenuate or absorb pressure fluctuations in the common liquid chamber easily and effectively in production, and to improve the meniscus controllability and the injection characteristics. The degree of freedom in head design is improved, such as improving bubble discharge.
[0038]
That is, by providing a free vibration surface in the common liquid chamber, it becomes possible to reduce the pressure of the common liquid chamber due to the damping effect, but the damping capability is higher when the thickness of the free vibration surface is thinner, so the common liquid chamber It is preferable to provide a thin free vibration surface on the entire wall surface of the chamber. However, forming a thin film over a large area is difficult both in terms of construction method and assembly, and a problem remains in strength. Therefore, by providing the thick and thin portions of the free vibration surface, it is easy to manufacture, has sufficient strength, can effectively obtain a damping effect, and can reduce the pressure in the common liquid chamber. It becomes.
[0039]
In this case, by integrally forming the free vibration surface as the same layer as the vibration plate arranged on one surface of the pressurized liquid chamber, the number of components of the head can be reduced, and the vibration plate and the free vibration surface can be reduced. It is possible to form at the same time in the same process. Furthermore, after forming the parts that make up the pressurized liquid chamber and the parts that make up the common liquid chamber, the layer consisting of the diaphragm and the free vibration surface is joined together by pressing the pressure liquid The chamber portion and the common liquid chamber portion can be formed, and the manufacturing cost, the manufacturing man-hour, the assembling man-hour, and the like can be reduced.
[0040]
In addition, since the free vibration surface has a laminated structure, the thin wall portion can be easily formed by changing the number of layers. Furthermore, by making the thick portion the same thickness as the maximum thickness of the diaphragm, a free vibration surface that is easy to manufacture and strong can be formed.
[0041]
Next, a second embodiment of the droplet discharge head according to the present invention will be described with reference to FIGS. 6 is an exploded perspective view of the head, and FIG. 7 is a schematic perspective view of the head viewed from the back side.
Here, a thin portion 23 is provided around the free vibration surface 21 that forms the wall surface of the common liquid chamber 8, and an island-like thick wall 22 is formed at the center of the free vibration surface 21.
[0042]
In this case as well, a defective image was generated in the multi-jet printing test with the head not provided with the thin-walled portion, but in the multi-jet with the head according to the present invention in which the free vibration surface was formed by the thin-walled portion and the thick-walled portion. In the printing test, good results were obtained without generating a defective image.
[0043]
Next, a third embodiment of the droplet discharge head according to the present invention will be described with reference to FIGS. FIG. 8 is an exploded perspective view of the head, and FIG. 9 is a schematic perspective view of the head viewed from the back side.
Here, in contrast to the one thick portion 22 provided in the second embodiment, two thin portions 23 separated in the longitudinal direction of the common liquid chamber by the free vibration surface 21 forming the wall surface of the common liquid chamber 8, 23 is provided and the island-like thick portions 22 and 22 are provided, whereby the strength is improved as compared with the second embodiment.
[0044]
In this case as well, a defective image was generated in the multi-jet printing test with the head not provided with the thin-walled portion, but in the multi-jet with the head according to the present invention in which the free vibration surface was formed by the thin-walled portion and the thick-walled portion. In the printing test, good results were obtained without generating a defective image.
[0045]
Next, a fourth embodiment of the droplet discharge head according to the present invention will be described with reference to FIGS. FIG. 10 is an exploded perspective view of the head, and FIG. 11 is a schematic perspective view of the head viewed from the back side.
In this head, the common liquid chamber 8 is formed in a shape in which the width in the short-side direction becomes narrow and the depth becomes shallow at the end 8a in the longitudinal direction so as to have a good bubble discharging property. The free vibration surface 21 is formed with thin portions 23 and 23 having a planar shape that matches the shape of the common liquid chamber at the longitudinal end 8a of the common liquid chamber 8.
[0046]
In this case as well, a defective image was generated in the multi-jet printing test with the head not provided with the thin-walled portion. In the printing test, good results were obtained without generating a defective image.
[0047]
As described above, by providing the thin wall portion 23 in the portion (or the vicinity thereof) where the width of the free vibration surface 21 in the short direction of the common liquid chamber is narrow, effective pressure fluctuation suppression and attenuation can be performed. it can. That is, since the damping capacity of the flat plate is substantially proportional to the cube of the length, when the free vibration surface 21 is a flat plate (when the thin portion 23 is not provided), the width of the free vibration surface 21 in the short direction is In the narrowed portion, the damping capacity is greatly reduced. Therefore, the pressure of the common liquid chamber can be effectively reduced by providing the thin portion 23 at or near the portion where the width in the short direction of the free vibration surface 21 is narrow.
[0048]
In addition, this reduces the pressure of the common liquid chamber effectively while improving the flowability of the ink by narrowing the shape toward the end of the common liquid chamber 8 and improving the bubble discharge performance. Is possible.
[0049]
That is, when the cross-sectional area in the longitudinal direction of the common liquid chamber is reduced, and the width of the free vibration surface in the short direction is reduced, the damping capacity is also reduced, so the pressure in the common liquid chamber is greatly increased. Therefore, reducing the cross-sectional area of the common liquid chamber in the longitudinal direction has a great influence and is difficult.
[0050]
However, as described above, it is possible to effectively reduce the pressure of the common liquid chamber by providing the thin-walled portion 23 at the portion where the cross-sectional area of the common liquid chamber 8 in the longitudinal direction is small or in the vicinity of the free vibration surface. Therefore, the shape of the common liquid chamber 8 can be reduced in cross section toward the end portion to improve the flowability of the ink, and to have a shape with good bubble discharge properties while suppressing the pressure increase in the common liquid chamber. become.
[0051]
Next, an example of an ink jet recording apparatus, which is an image forming apparatus according to the present invention, equipped with an ink jet head, which is a liquid droplet ejection head according to the present invention, will be described with reference to FIGS. FIG. 12 is a configuration diagram for explaining the overall configuration of an ink jet recording apparatus as an image forming apparatus according to the present invention, and FIG.
[0052]
In this ink jet recording apparatus, a carriage 103 is slidably held in a main scanning direction by a guide rod 101 and a stay 102 which are horizontally mounted on left and right side plates (not shown), and a timing belt 105 is held by a main scanning motor 104. Then, moving scanning is performed in the direction indicated by the arrow (main scanning direction) in FIG.
[0053]
The carriage 103 is composed of four inkjet heads which are droplet ejection heads according to the present invention that eject ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). The recording head 107 is mounted with a plurality of ink ejection openings arranged in a direction crossing the main scanning direction, and the ink droplet ejection direction is directed downward.
[0054]
The carriage 103 is also equipped with a sub-tank 108 for each color for supplying each color ink to the recording head 107. Ink is supplied to the sub tank 108 from a main tank (ink cartridge) through an ink supply tube (not shown).
[0055]
On the other hand, as a paper feeding unit for feeding paper 112 stacked on a paper stacking unit (pressure plate) 111 such as a paper feeding cassette 110, a half-moon roller (separately feeding paper 112 one by one from the paper stacking unit 111) The sheet feeding roller 113 and the sheet feeding roller 113 are opposed to each other, and a separation pad 114 made of a material having a large friction coefficient is provided. The separation pad 114 is urged toward the sheet feeding roller 113 side.
[0056]
As a transport unit for transporting the paper 112 fed from the paper feed unit below the recording head 107, a transport belt 121 for electrostatically attracting and transporting the paper 112, and a paper feed unit A counter roller 122 for transporting the paper 112 fed through the guide 115 while sandwiching it between the transport belt 121 and the paper 112 fed substantially vertically upward is changed by about 90 ° and copied on the transport belt 121. A conveying guide 123 for adjusting the pressure and a tip pressure roller 125 urged toward the conveying belt 121 by a pressing member 124. In addition, a charging roller 126 that is a charging unit for charging the surface of the conveyance belt 121 is provided.
[0057]
Here, the conveyance belt 121 is an endless belt, is stretched between the conveyance roller 127 and the tension roller 128, and is conveyed from the sub-scanning motor 131 that is an electric motor via the timing belt 132 and the timing roller 133. By rotating 127, it is comprised so that it may circulate in an arrow direction (belt conveyance direction).
[0058]
The transport belt 121 is a surface layer 21a which is a sheet adsorbing surface formed of a resin material having a pure thickness of about 40 μm which is not subjected to resistance control, such as ETFE pure material, and performs resistance control by carbon with the same material as the surface layer. And a back layer (medium resistance layer, ground layer).
[0059]
The charging roller 126 is disposed so as to contact the surface layer of the conveyor belt 121 and rotate following the rotation of the conveyor belt 21, and applies 2.5 N to both ends of the shaft as a pressing force. The transport roller 127 also serves as an earth roller, and is in contact with the middle resistance layer (back layer) of the transport belt 121 and is grounded.
[0060]
In addition, a guide member 136 is disposed on the back side of the conveyance belt 21 so as to correspond to a printing area by the recording head 4. The upper surface of the guide member 136 protrudes toward the recording head 107 from the tangent line of two rollers (the conveyance roller 127 and the tension roller 128) that support the conveyance belt 121. Thereby, the conveyor belt 121 is pushed up and guided by the upper surface of the guide member 136 in the printing region.
[0061]
Further, as a paper discharge unit for discharging the paper 112 recorded by the recording head 107, a separation unit for separating the paper 112 from the conveying belt 121, a paper discharge roller 142 and a paper discharge roller 143, and paper discharge A paper discharge tray 144 for stocking the paper 112 to be printed. A double-sided paper feeding unit 151 is detachably mounted on the back. The double-sided paper feeding unit 151 takes in the paper 112 returned by the reverse rotation of the transport belt 121, reverses it, and feeds it again between the counter roller 122 and the transport belt 121.
[0062]
In the ink jet recording apparatus configured as described above, the paper 112 is separated and fed one by one from the paper feed unit, and the paper 112 fed substantially vertically upward is guided by the guide 115, and includes the transport belt 121 and the counter roller 122. The leading end is guided by the conveying guide 123 and pressed against the conveying belt 121 by the leading end pressure roller 125, and the conveying direction is changed by approximately 90 °.
[0063]
At this time, a positive voltage output and a negative output are alternately repeated from the high voltage power supply to the charging roller 126 by a control circuit (not shown), that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 121 alternates, that is, In the sub-scanning direction, which is the circumferential direction, plus and minus are alternately charged in a band shape with a predetermined width. When the paper 112 is fed onto the positively and negatively charged conveying belt 121, the paper 112 is polarized to a charge opposite to the charged pattern in the paper 112, so that a capacitor connected in parallel is formed. 112 is attracted to the conveyance belt 121, and the paper 112 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 121.
[0064]
Therefore, by driving the recording head 107 according to the image signal while moving the carriage 103, ink droplets are ejected onto the stopped paper 112 to record one line, and after the paper 112 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 112 has reached the recording area, the recording operation is finished and the paper 12 is discharged onto the paper discharge tray 144.
[0065]
As described above, since the ink jet recording apparatus includes the ink jet head which is the liquid droplet ejection head according to the present invention, the pressure fluctuation in the common liquid chamber is suppressed and stable ejection characteristics can be obtained. Image quality recording can be performed.
[0066]
In the above-described embodiment, an example of an ink jet recording apparatus that is applied to an ink jet head as a droplet discharge head and includes the ink jet head has been described. However, for example, a liquid resist is used as a liquid droplet discharge head other than the ink jet head. The present invention can also be applied to other droplet ejection heads such as a droplet ejection head that ejects droplets, a droplet ejection head that ejects a DNA sample as droplets, and can also be applied to image forming apparatuses other than inkjet recording apparatuses.
[0067]
【The invention's effect】
  As described above, according to the liquid droplet ejection head of the present invention, the common liquid chamberIs formed on the surface opposite to the pressurized liquid chamber across the diaphragm, and the diaphragm is a part that forms the wall surface of the common liquid chamber and does not face the flow path plate.Since it has a structure with a free vibration surface consisting of a thick part and a thin part, it can effectively suppress and attenuate pressure fluctuations in the common liquid chamber, improve the droplet ejection characteristics, and improve the head Can be reduced in size and cost.
[0068]
According to the image forming apparatus of the present invention, since the liquid droplet ejection head according to the present invention is provided, high image quality recording is possible.
[Brief description of the drawings]
FIG. 1 is a perspective explanatory view in an assembled state for explaining a first embodiment of a droplet discharge head according to the present invention;
FIG. 2 is an explanatory cross-sectional view of the head along the longitudinal direction of the liquid chamber.
FIG. 3 is an explanatory cross-sectional view of the head along the lateral direction of the liquid chamber.
FIG. 4 is an exploded perspective view of the head.
FIG. 5 is a schematic perspective explanatory view of the diaphragm of the head viewed from the back side.
FIG. 6 is an exploded perspective view for explaining a second embodiment of the droplet discharge head according to the present invention.
FIG. 7 is a schematic perspective explanatory view of the diaphragm of the head viewed from the back side.
FIG. 8 is an exploded perspective view for explaining a third embodiment of the droplet discharge head according to the present invention.
FIG. 9 is a schematic perspective explanatory view of the diaphragm of the head viewed from the back side.
FIG. 10 is an exploded perspective view for explaining a fourth embodiment of a droplet discharge head according to the present invention.
FIG. 11 is a schematic perspective explanatory view of the diaphragm of the head viewed from the back side.
FIG. 12 is a schematic configuration diagram showing an example of an ink jet recording apparatus as an image forming apparatus according to the present invention.
FIG. 13 is a schematic plan view of an essential part of the recording apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Flow path plate, 2 ... Vibration plate member, 3 ... Nozzle plate, 4 ... Nozzle, 6 ... Pressurizing liquid chamber, 7 ... Ink supply path, 8 ... Common liquid chamber, 12 ... Piezoelectric element, 21 ... Free vibration surface 22 ... Thick part, 23 ... Thin part.

Claims (6)

A flow path plate having a plurality of pressurized liquid chambers communicating with nozzles for discharging droplets, a common liquid chamber for supplying liquid to the plurality of pressurized liquid chambers, and a vibration forming one wall surface of the pressurized liquid chamber In a droplet discharge head provided with a plate ,
The common liquid chamber is formed on a surface opposite to the pressurized liquid chamber across the diaphragm,
The diaphragm is characterized in that said common liquid chamber the flow path plate a portion that forms a wall surface of the have free vibration surface consisting of a thick portion and a thin portion in a region not opposite Droplet discharge head. The liquid droplet ejection head according to claim 1 , wherein the free vibration surface has a laminated structure including a plurality of layers. 2. The droplet discharge head according to claim 1 , wherein a thick portion of the free vibration surface has the same thickness as a member forming a wall surface of the pressurized liquid chamber. In the liquid droplet ejecting head according to any one of claims 1 to 3, wherein the pressurized liquid chamber are arranged side by side a plurality in the longitudinal direction of the common liquid chamber, the pre-Symbol thin walled portion, the in the free vibration surface droplet discharge head lateral direction of the width of the common liquid chamber is a common liquid chamber longitudinal end or that are narrower than the common liquid chamber central portion, characterized in that provided in the vicinity thereof. In the liquid droplet ejecting head according to any one of claims 1 to 4, wherein the pressurized liquid chamber are arranged side by side a plurality in the longitudinal direction of the common liquid chamber, the thin portion of the free vibration surface, said common liquid chamber liquid is longitudinally or longitudinal end of the common liquid chamber cross-sectional area is smaller than the common liquid chamber central portion of a plane perpendicular to being provided to correspond to the vicinity thereof Drop ejection head. 6. An image forming apparatus for forming an image by discharging droplets from a droplet discharge head, wherein the droplet discharge head is the droplet discharge head according to any one of claims 1 to 5. apparatus.

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