Patent Publication Number: US-11390080-B2

Title: Ink-jet recording apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of U.S. patent application Ser. No. 16/315,330, filed on Jan. 4, 2019, the entire contents of which are incorporated herein by reference and priority to which is hereby claimed. application Ser. No. 16/315,330 is the U.S. National stage of application No. PCT/JP2017/022781, filed on Jun. 21, 2017. Priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) is hereby claimed from Japanese Application No. 2016-132329, filed Jul. 4, 2016, the disclosures of which are incorporated herein by reference. 
    
    
     TECHNOLOGICAL FIELD 
     The present invention relates to an inkjet recording apparatus. 
     DESCRIPTION OF THE RELATED ART 
     There has been conventionally known an inkjet recording apparatus which ejections ink stored in a pressure chamber through nozzles provided in an inkjet head to form an image on a recording medium. 
     Such an inkjet recording apparatus causes, in some cases, a problem of nozzle clogging due to air bubbles generated in the inkjet head or an entering foreign material, which may result in ejection defect. Some types of ink become thick near the nozzles due to sedimentation of ink particles, precluding a stable ink ejection if the inkjet recording apparatus is left unused for a long time. 
     To cope with these problems, there are known inkjet heads provided with channels for circulating ink in the pressure chambers and can discharge air bubbles and foreign materials in the heads together with ink out of the inkjet heads (Patent Documents 1 and 2). 
     For example, each of Patent Documents 1 and 2 discloses an inkjet head that includes individual communication flow channels (circulating channels), a common flow channel, and an ink discharge channel inside the head, the individual communication flow channels enabling ejection of ink from each pressure chamber, the common flow channel allowing the individual communication flow channels to join, and the ink discharge channel being able to discharge ink from the common flow channel. 
     PRIOR ART DOCUMENTS 
     Patent Document 
     
         
         Patent Document 1: Japanese Patent No. 5385975 
         Patent Document 2: Japanese Patent No. 5590321 
       
    
     SUMMARY 
     Problems to be Solved by the Invention 
     Nowadays, a high-density array of nozzles is required to reduce the size of the inkjet head and enhance the resolution of the image. The present inventor has found that a high-density array of nozzles in an inkjet head provided with conventional circulating channels (individual communication flow channels) results in a significant variance in the flow amount of circulating ink among the individual communication flow channels. 
     An increased flow amount of circulating ink can effectively expel air bubbles or foreign materials from the pressure chambers, but reduces the ejection energy efficiency, which results in a reduced ejection rate or a reduced amount of an ink droplet. The variance in the flow amount of circulating ink among the individual communication flow channels causes a variance in ink ejection performance among the nozzles. 
     The present invention has been made in consideration of such problems, and an object of the present invention is to provide an inkjet recording apparatus that can effectively expel air bubbles or foreign materials in the head chip together with ink while reducing a variance in ink ejection performance. 
     Means for Solving the Problem 
     In order to achieve the above object, an inkjet recording apparatus may include: an inkjet head that includes: a plurality of nozzles which eject ink, a plurality of pressure chambers which are provided in communication with the respective nozzles and store ink to be ejected from the nozzles, a plurality of pressure generators which are provided so as to correspond to the respective pressure chambers and apply pressure to ink in the pressure chambers, a plurality of individual communication flow channels which are provided so as to branch from the respective pressure chambers or from respective communication channels between the pressure chambers and the nozzles, and from which ink in the pressure chambers is discharged, and a common flow channel which is connected to the individual communication flow channels and at which ink discharged from the individual communication flow channels merges with each other; and an ink feeder which generates a circulatory flow of ink from the pressure chambers to the individual communication flow channels, and a relation between Fn and Fi when ink is ejected from the nozzles satisfies the following expression (1), Fn being an ink amount per unit time which is ejected from a nozzle that ejects a maximum amount of ink per unit time among all the nozzles provided in the inkjet head, and Fi being an average ink flow amount per unit time which is discharged from the individual communication flow channels to the common flow channel, and a relation between Rc and Rt satisfies the following expression (2), Rc being a flow channel resistance of the common flow channel and Rt being a combined resistance of the individual communication flow channels connected to the common flow channel.
 
( Fn/Fi )≤10  Expression (1):
 
( Rc/Rt )≤10  Expression (2):
 
     In at least an embodiment, the flow channel resistance of the common flow channel increases toward an exit of the common flow channel. 
     In at least an embodiment, among the individual communication flow channels connected to the common flow channel, the individual communication flow channel connected to a position closer to an exit of the common flow channel has a larger flow channel resistance. 
     In at least an embodiment, one exit of the common flow channel is provided at each end of an arrangement direction of the nozzles. 
     At least an embodiment may further include a damper which is provided so as to face an inner surface of the common flow channel and changes a volume of the flow channel by elastic deformation under pressure. 
     In at least an embodiment, the damper is formed by a nozzle substrate in which the nozzles are formed. 
     In at least an embodiment, a manifold which stores ink to be fed to the pressure chambers is provided above the pressure chambers. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention. 
         FIG. 1  an overview of an inkjet recording apparatus 
         FIG. 2  a bottom view of a head unit 
         FIG. 3A  a perspective view of the inkjet head 
         FIG. 3B  a cross-sectional view of the inkjet head 
         FIG. 4  an exploded perspective view of the inkjet head 
         FIG. 5  a schematic exploded perspective view illustrating a head chip and a wiring substrate 
         FIG. 6  a bottom perspective view for explaining ink flow inside the head chip 
         FIG. 7  a cross-sectional view taken along the line VII-VII in  FIG. 6   
         FIG. 8  a cross-sectional view taken along the line VIII-VIII in  FIG. 6   
         FIG. 9A  a plan view of a nozzle substrate 
         FIG. 9B  a plan view of a variation of the nozzle substrate 
         FIG. 9C  a plan view of another variation of the nozzle substrate 
         FIG. 9D  a plan view of still another variation of the nozzle substrate 
         FIG. 10  a schematic illustration of an ink circulator system 
         FIG. 11  an enlarged partial cross-sectional view of a head chip according to another embodiment 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Advantageous Effects of Invention 
     Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. 
     The present invention can effectively expel air bubbles or foreign materials in the head together with ink while reducing a variance in ink ejection performance. 
     A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. The embodiments shown in the drawings should not be construed to limit the scope of the present invention. For the convenience of explanation, this specification defines a lateral direction, a longitudinal direction, and a vertical direction as follows: The lateral direction is a print width direction along which nozzles  11   a  are disposed in an inkjet head  100  as shown in  FIG. 2 ; the longitudinal direction is a transfer direction of a recording medium under the nozzles  11   a ; and the vertical direction is perpendicular to both the lateral direction and the longitudinal direction. The arrows depicted in the channels in the drawings indicate the direction of flowing ink. 
     [Inkjet Recording Apparatus] 
     With reference to  FIG. 1 , the inkjet recording apparatus  200  includes a sheet feeder  210 , an image recorder  220 , a sheet receiver  230 , and an ink circulator system  8  that functions as an ink feeder (see  FIG. 10 ). The inkjet recording apparatus  200  transfers a recording medium M from the sheet feeder  210  to the image recorder  220 , forms an image on the recording medium M at the image recorder  220 , and transfers the recorded recording medium M to the sheet receiver  230 . 
     The sheet feeder  210  includes a sheet tray  211  storing the recording medium M and a medium carrier  212  conveying the recording medium M from the sheet tray  211  to the image recorder  220 . The medium carrier  212  is equipped with a belt loop. The inner face of the belt loop is supported by two rollers. The rotation of the roller causes recording medium M carried on the belt loop to be transferred from the sheet tray  211  to the image recorder  220 . 
     The image recorder  220  includes a transfer drum  221 , a relay unit  222 , a heater  223 , a head unit  224 , a fixer  225 , and a delivery unit  226 . 
     The transfer drum  221  has a cylindrical transfer face on which the recording medium M is carried. The transfer drum  221  rotates in the direction shown in  FIG. 1 , while holding the recording medium M on the transfer face, to transfer the recording medium M along with the transfer face. The transfer drum  221  includes claws and an air sucking unit (not shown). The claws fix the recording medium M at its ends, and the air sucking unit attracts the recording medium M to the transfer face. Thereby, the transfer drum  221  retains the recording medium M on the transfer face. 
     The relay unit  222  is disposed between the medium carrier  212  of the sheet feeder  210  and the transfer drum  221 . The relay unit  222  receives one end of the recording medium M transferred on the medium carrier  212  at a swing arm  222   a  and delivers the recording medium M to the transfer drum  221  via the delivery drum  222   b.    
     The heater  223  is disposed between the delivery drum  222   b  and the head units  224 . The heater  223  heats the recording medium M on the transfer drum  221  to a predetermined temperature. The heater  223  includes, for example, an infrared heater. The infrared heater is energized in accordance with control signals sent from a controller (not shown) to cause the heater to generate heat. 
     The head units  224  ejects ink onto the recording medium M on the transfer drum  221  in accordance with image data at an appropriate timing in response to the rotation of the transfer drum  221  to record an image. The head units  224  are disposed such that ink ejecting faces face the transfer drum  221  with a predetermined gap. The inkjet recording apparatus  200  according to this embodiment includes four head units  224  corresponding to four colors of Y (yellow), M (magenta), C (cyan), and K (black). These head units  224  are disposed at predetermined intervals in the order of Y, M, C, and K from the upstream side in the transfer direction of the recording medium M. 
     Each head unit  224  has pairs of inkjet heads  100  adjacent to each other in the longitudinal direction. These pairs are disposed, for example, in a staggered manner in the longitudinal direction, as shown in  FIG. 2 . The head units  224  are fixed relative to the rotational axis of the transfer drum  221  during image recording. In other words, the inkjet recording apparatus  200  records an image by a one-path drawing scheme involving the use of a line head. 
     The fixer  225  includes a light emitter extending across the X direction of the transfer drum  221 . The fixer  225  irradiates the recording medium M on the transfer drum  221  with energy rays, such as ultraviolet rays, from the light emitter to cure and fix the ink ejected on the recording medium M. The light emitter of the fixer  225  faces the transfer face downstream of the head units  224  and upstream of a delivery drum  226   a  of the delivery unit  226  in the transfer direction. 
     The delivery unit  226  includes an belt loop  226   b  and a cylindrical delivery drum  226   a . The inner face of loop shape belt of the belt loop  226   b  is supported by two rollers. The delivery drum  226   a  delivers the recording medium M from the transfer drum  221  to the belt loop  226   b . The delivery unit  226  receives the recording medium M from the transfer drum  221  onto the belt loop  226   b  at the delivery drum  226   a , and transfers the recording medium M on the belt loop  226   b  to the sheet receiver  230 . 
     The sheet receiver  230  includes a flat sheet receiving tray  231  on which the recording medium P transferred from the image recorder  220  with the delivery unit  226 . 
     [Inkjet Head] 
     With reference to  FIG. 3A ,  FIG. 3B , and  FIG. 4 , the inkjet head  100  according to this embodiment includes a head chip  1 , a wiring substrate  2  on which the head chip  1  is disposed, a driving circuit substrate  4  which is connected to the wiring substrate  2  via a flexible substrate  3 , a manifold  5  which contains ink to be fed to pressure chambers  13 A in the head chip  1 , a housing  6  accommodating the manifold  5 , a cap receiver  7  mounted so as to block an opening in the bottom face of the housing  6 , and a cover  9  mounted on the housing  6  ( FIG. 3A ,  FIG. 3B , and  FIG. 4 ). 
     The manifold  5  is not shown in  FIG. 3A . The cover  9  is not shown in  FIG. 3B  and  FIG. 4 . 
     In the head chip  1  according this embodiment, the nozzles  11   a  are disposed in two rows. Alternatively, the nozzles  11   a  may be disposed in any number of rows or in any arrangement, for example, in one row or three or more rows. 
     The head chip  1  is a substantially rectangular column extending in the lateral direction, and includes a pressure chamber substrate  12  and a nozzle substrate  11 . 
     The pressure chamber substrate  12  is provided with pressure chambers  13 A, discharge flow channels  13 B, and common flow channels  19  (See  FIG. 5 ). 
     The pressure chambers  13 A are separated by partitions  15  as a pressure generator composed of a piezoelectric material, and contain ink to be ejected through nozzles  11   a . Each pressure chamber  13 A is provided with a driving electrode  14  on the inner surface thereof to drive the partition  15  between adjacent pressure chambers  13 A. A voltage applied to the driving electrodes  14  causes repeated shear-mode displacements of the partition  15  between the adjacent pressure chambers  13 A, which pressurizes the inks in the respective pressure chambers  13 A. 
     Each pressure chamber  13 A has a substantially rectangular cross section, extends in the vertical direction, and has an inlet on the top face of the pressure chamber substrate  12  and an outlet on the bottom thereof. The pressure chambers  13 A are disposed in parallel in the lateral direction and in two rows in the longitudinal direction. 
     Similar to the pressure chambers  13 A, the discharge flow channels  13 B are separated by the partitions  15  and discharges the ink the outside of the inkjet head  100  toward the top, which is opposite the nozzle substrate  11 . The discharge flow channels  13 B extend vertically and have outlets on the top face and inlets on the bottom face of the pressure chamber substrate  12 . Two discharge flow channels  13 B are disposed near the right end of the head chip  1  in parallel with the pressure chambers  13 A. Each discharge flow channels  13 B having a volume larger than that of each pressure chamber  13 A can enhance ink discharge efficiency. 
     The common flow channels  19  are provided in the lower portions of the pressure chamber substrate  12 , the individual communication flow channels  18  communicating with the pressure chambers  13 A are connected to the common flow channels  19 , and inks flowing from the individual communication flow channels  18  merge at the common flow channels  19  (See  FIG. 6  and  FIG. 7 ). The common flow channels  19  are disposed in parallel with each other in the lateral direction for each nozzle row, and are in communication with the respective discharge flow channels  13 B near their right ends. The common flow channels  19  provided in the pressure chamber substrate  12  can expand the volume of flow channel and increase the amount of ink circulated within the head chip  1 , effectively discharging air bubbles. 
     The nozzle substrate  11  includes the nozzles  11   a  and the individual communication flow channels  18 . The nozzle substrate  11  also include the pressure chambers  13 A, the discharge flow channels  13 B, and the common flow channels  19  at the positions corresponding to those of the lower portions of the pressure chambers  13 A, the discharge flow channels  13 B, and the common flow channels  19  provided in the pressure chamber substrate  12 , so as to have identical cross-sectional shapes with those of the respective chambers and channels (See  FIG. 7  and  FIG. 8 ). In other words, the nozzle substrate  11  is disposed to block the lower ends of the pressure chambers  13 A, the discharge flow channels  13 B, and the common flow channels  19 . These channels are disposed across the pressure chamber substrate  12  and the nozzle substrate  11 . 
     The common flow channels  19  are formed in the nozzle substrate  11 . The lower portions of the common flow channels  19  are so thin that they undergo slight elastic deformation by pressure, and thus can vary the volume of flow channel and function as a damper  11   b.    
     The nozzle substrate  11  is fabricated by, for example, laser beam machining of a polyamide plate or etching of a silicon plate. 
     Each nozzle  11   a  extends through the nozzle substrate  11  under the corresponding pressure chamber  13 A in the thickness or vertical direction to eject the ink stored in the pressure chamber  13 A. The nozzles  11   a  according to this embodiment are disposed in the lateral direction and in two rows in the longitudinal direction. 
     Each individual communication flow channel  18  is provided in the upper portion of the nozzle substrate  11  so as to communicate with the corresponding pressure chamber  13 A and the corresponding common flow channel  19  ( FIG. 7  and  FIG. 9A ). The individual communication flow channel  18  may be disposed in the pressure chamber substrate  12 , not the nozzle substrate  11 , or across the nozzle substrate  11  and the pressure chamber substrate  12  as long as the individual communication flow channel  18  communicates with the pressure chamber  13 A and the common flow channel  19 . 
     With reference to  FIG. 4  and  FIG. 5 , the wiring substrate  2  is provided on the top face of the head chip  1 . Two flexible substrates  3  are provided along the edges, extending in the longitudinal direction, of the wiring substrate  2  and connected to the driving circuit substrates  4 . 
     The wiring substrate  2  is a substantially rectangular plate extending in the lateral direction, and has an opening  22  in the substantially central portion. The wiring substrate  2  has greater widths both in the lateral and longitudinal directions than those of the head chip  1 . 
     The opening  22  has a substantially rectangular shape extending in the lateral direction and exposes the inlets of the pressure chambers  13 A and the outlets of the discharge flow channel  13 B in the head chip  1  to the upper side while the head chip  1  is mounted on the wiring substrate  2 . A predetermined number of electrode portions  21  are provided along the edges extending in the longitudinal direction of the opening  22 . The electrode portions  21  are connected to electrodes (not shown) extending upward from the driving electrodes  14  in the head chip  1  to the top face of the head chip  1  ( FIG. 5 ). 
     With reference to  FIG. 5 , the flexible substrates  3  include wirings  31  that electrically connect the driving circuit substrates  4  to the electrode portions  21  of the wiring substrate  2 . This allows signals from the driving circuit substrates  4  to be conveyed to the driving electrodes  14  in the respective pressure chambers  13 A in the head chip  1  through the wirings  31  and the electrode portions  21 . 
     The lower portion of the manifold  5  is bonded to the outer edges of the wiring substrate  2 . In other words, the manifold  5  is disposed on the side of the inlets (on the upper side) of the pressure chambers  13 A in the head chip  1 , and is connected to the head chip  1  via the wiring substrate  2 . 
     The manifold  5  is made of a resin and disposed above the pressure chambers  13 A in the head chip  1 , and stores ink to flow into the pressure chambers  13 A. With reference to  FIG. 3B , the manifold  5  extends in the lateral direction, and includes a hollow body  52  constituting an ink storage  51  and first to fourth ink ports  53  to  56  constituting an ink channel. The ink storage  51  consists of two sections, which are an upper first ink chamber  51   a  and a lower second ink chamber  51   b , separated by a filter F for removing debris in the ink. 
     The first ink port  53  is in communication with the upper right portion of the first ink chamber  51   a  and is used to introduce ink into the ink storage  51 . The first ink port  53  has a first joint  81   a  inserted into the tip. 
     The second ink port  54  is in communication with the upper left portion of the first ink chamber  51   a  and is used to expel air bubbles from the first ink chamber  51   a . The second ink port  54  has a second joint  81   b  inserted into the tip. 
     The third ink port  55  is in communication with the upper left portion of the second ink chamber  51   b  and is used to expel air bubbles from the second ink chamber  51   b . The third ink port  55  has a third joint  82   a  inserted into the tip. 
     The fourth ink port  56  is in communication with a discharge ink chamber  57  which is in communication with the discharge flow channels  13 B in the head chip  1 . This configuration allows the ink discharged from the head chip  1  to be discharged to the exterior of the inkjet head  100  through the fourth ink port  56 . 
     The housing  6  is made of, for example, aluminum by die casting and extends in the lateral direction. The housing  6  accommodates the manifold  5  including the head chip  1 , the wiring substrate  2 , and the flexible substrates  3 , and has a bottom opening. The housing  6  has mount holes  68  at its two ends for mounting the housing  6  on the body of the printer. 
     The cap receiver  7  has a nozzle opening  71  extending in the lateral direction in its substantially central region. The cap receiver  7  is mounted to block the bottom opening of the housing  6  such that the nozzle substrate  11  is exposed through the nozzle opening  71 . 
     [Design of Flow Channels in the Inkjet Head] 
     The inkjet heads  100  provided in the inkjet recording apparatus  200  according to this embodiment are designed such that a relation between Fn and Fi when ink is ejected from the nozzles  11   a  satisfies the following expression (1), Fn being an ink amount per unit time which is ejected from a nozzle  11   a  that ejects a maximum amount of ink per unit time among all the nozzles  11   a  provided in the inkjet head  100 , and Fi being an average ink flow amount per unit time which is discharged from the individual communication flow channels  18  to the common flow channels  19 .
 
( Fn/Fi )≤10  Expression (1):
 
     In this specification, “an ink amount Fn per unit time which is ejected from a nozzle  11   a  that ejects a maximum amount of ink per unit time among all the nozzles  11   a  provided in the inkjet head  100 ” is determined by calculating the amount (L/s) of ink ejected per unit time (second) for each of all the nozzles  11   a  provided in the inkjet head  100  and selecting the largest one. 
     The amount (L/s) of ink ejected per unit time (second) from each nozzle  11   a  can be determined as the product of drive frequency (Hz) and the amount (L) of ink droplets ejected. During ejection of ink from the inkjet head  100  provided with multiple nozzles  11   a  (for example, 256 nozzles  11   a ), at least one nozzle  11   a  ejections ink at the maximum drive frequency (Hz) in most cases. Thus, Fn may be determined as the product of the maximum drive frequency (Hz) and the amount of ink droplets ejected (L). 
     In this specification, the “average ink flow amount Fi per unit time which is discharged from the individual communication flow channels  18  to the common flow channels  19 ” is an averaged flow amount (L/s) per unit time (second) of ink discharged from individual communication flow channels  18  in the inkjet head  100  to the common flow channels  19 . In details, the averaged flow amount (L/s) per unit time (second) can be determined by dividing the flow amount (L/s) per unit time (second) of ink discharged from the common flow channels  19  to the outside of the inkjet head  100  by the number of the individual communication flow channels  18 . 
     Satisfaction of Expression (1) means that ink in at least one tenth of Fn (L/s) is discharged from the individual communication flow channels  18  to the common flow channels  19 . 
     The inkjet head  100  according to this embodiment is accordingly designed to increase the flow amount of ink discharged from the individual communication flow channels  18  per unit time. This configuration allows air bubbles in the inkjet head to be expelled effectively together with ink. The inventor has verified the effect with the example 1 described below. 
     Fi (L/s) can be adjusted, as needed, by adjustment of the flow channel design and/or ink pressure within the inkjet head. For example, an increased cross-sectional area of each individual communication flow channel  18  or an increased amount of ink introduced from the ink circulator system  8  can increase Fi (L/s). 
     In this embodiment, the ratio Fn/Fi need to be 10 or less so that the average flow amount Fi is at least one tenth of the amount Fn. However, an increase in the average flow amount Fi by increasing the cross-sectional area of each individual communication flow channel  18  causes dissipation to the individual communication flow channel  18  of the energy required for ejection of ink droplets from the corresponding nozzle  11   a  generated at the corresponding pressure chamber  13 A, resulting in a reduction in ejection energy efficiency. This results in a reduced ejection rate or a reduced amount of an ink droplet. To prevent this phenomenon, the ratio Fn/Fi should preferably be 1 or more. 
     The inkjet head  100  is designed such that a relation between Rc and Rt satisfies the following expression (2), Rc being a flow channel resistance of the common flow channel  19  and Rt being a combined resistance of the individual communication flow channels  18  connected to the common flow channel  19 .
 
( Rc/Rt )≤10  Expression (2):
 
     In this specification, as shown in  FIG. 9A , the “flow channel resistance Rc of the common flow channel  19 ” is defined as the flow channel resistance of a flow channel portion  19   a  of the common flow channel  19  connected to the individual communication flow channels  18 . In detail, the “flow channel resistance Rc of the common flow channel  19 ” refers to the flow channel resistance of the flow channel portion from the connected portion of the leftmost individual communication flow channel  18  to the connected portion of the rightmost individual communication flow channel  18  in the direction in which ink flows through the common flow channel  19  (the right direction), as shown in  FIG. 9A . 
     The inkjet head  100 , which meets Expression (2), can effectively expel air bubbles or foreign materials in the inkjet head together with ink, while reducing a variance in ink ejection performance. The inventor has verified the effect with the example 2 described below. 
     The inkjet head  100  configured to have a high flow amount of ink discharged from the individual communication flow channels  18  satisfying Expression (1) has low ink ejection energy efficiency, which results in a reduced ejection rate or a reduced amount of ink droplets. A variance in the amount of ink droplets discharged from each individual communication flow channel  18  results in a variance in ink ejection performance among the nozzles  11   a.    
     A configuration of the common flow channels  19  and the individual communication flow channels  18  satisfying Expression (2) can reduce a variance in ink ejection performance among the nozzles  11   a . In other words, the inventor has obtained an effect of effectively expelling air bubbles or foreign materials in the inkjet head together with ink, while reducing a variance in ink ejection performance among the nozzles  11   a . The cause of this can be considered that there can be an influence of the flow channel resistance of the common flow channel  19  depending on the position where the individual communication flow channel  18  is connected to the common flow channel  19 , leading to different easiness of ink flow from the individual communication flow channel  18  to the common flow channel  19 . For example, even if the individual communication flow channels  18  having an identical channel shape are disposed in parallel as shown in  FIG. 9A , a greater flow channel resistance of each common flow channel  19 , which prevents a smooth flow of ink, results in individual communication flow channels  18  located farther from the exit of the common flow channel  19  having greater difficulty in flowing ink. This results in a variance in the amount of discharged ink among the individual communication flow channels  18 . 
     The inkjet head  100  according to this embodiment configured to satisfy Expression (2) can reduce a variance in the amount of discharged ink among the individual communication flow channels  18 , enhancing the stability in ink ejection. 
     A method for calculating the flow channel resistance of each channel will now be described. 
     In the case of a cuboid flow channel with a width w (m), a height h (m), and a length l (m), and an ink fluid viscosity η (Pa·S), the flow channel resistance R can be calculated from the following expression:
 
flow channel resistance  R= 8η· l ·( h+w ) 2 /( hw ) 3 .
 
     In the case of a cylindrical flow channel with a diameter d (m), a height l (m), and an ink fluid viscosity η (Pa·S). The flow channel resistance R can be calculated from the following expression:
 
flow channel resistance  R= 128·ƒ· l/πd   4 .
 
     In the case of any other shape, for example, a taper channel, the taper shape is divided into segmentalized cuboids in the longitudinal direction and the flow channel resistance R can be determined by integration. 
     The combined resistance Rt of the individual communication flow channels  18  will now be described. 
     The individual communication flow channels  18  are connected to the common flow channels  19  in parallel with each other, as shown in  FIG. 9A . In this case, the combined resistance Rt of the individual communication flow channels  18  connected to the common flow channels  19  can be determined by calculating the reciprocals of the flow channel resistances of the common flow channels  19  and adding up the reciprocals. 
     In details, in the case of n (=integer of 2 or more) individual communication flow channels  18  connected to the common flow channels  19  in parallel with each other, the combined resistance Rt can be calculated from the following expression:
 
1 /Rt =(1/ Ri   (1) )+(1/ Ri   (2) )+ . . . +(1/ Ri   (n) )
 
where the individual communication flow channels  18  have the flow channel resistance of Ri (1) , Ri (2) , . . . , Ri (n) , respectively.
 
     The configuration of the flow channels may be modified, as needed, provided that Expressions (1) and (2) are satisfied. 
     For example, the common flow channel  19  may be configured such that the flow channel resistance increases toward its exit. An example of this configuration is a common flow channel  19  having a cross-sectional area that decreases toward its exit, as shown in  FIG. 9B . 
     Alternatively, the individual communication flow channels  18  connected to the respective common flow channels  19  at positions closer to the exit of the common flow channel  19  may have greater flow channel resistances toward the exit of the common flow channel  19 . An example of this configuration is a configuration of individual communication flow channels  18  the cross-sectional area of which decreases toward the exit of the common flow channel  19 , as shown in  FIG. 9C . 
     The configurations shown in  FIG. 9B  and  FIG. 9C  facilitate the ink flow in the individual communication flow channels  18  connected at positons farther from the exit of the common flow channel  19 , which are more likely to be affected by the flow channel resistance of the common flow channel  19 . This configuration can reduce a variance in the amount of discharged ink droplets among the individual communication flow channels  18  due to the influence of the flow channel resistance of the common flow channel  19 , and can reduce a variance in ejection performance among the nozzles  11   a.    
     Alternatively, the common flow channel  19  may have exits at its two ends, as shown in  FIG. 9D . This two-exit configuration can reduce the number of the individual communication flow channels  18  connected at positions remoter from the exits of the common flow channel  19 , as shown in  FIG. 9B  and  FIG. 9C , successfully reducing a variance in the amount of discharged ink among the individual communication flow channels  18  and a variance in ejection performance among the nozzles  11   a.    
     [Ink Circulator System] 
     The ink circulator system  8  is an ink feeder to generate a circulatory flow of the inks from the pressure chambers  13 A to the respective individual communication flow channels  18  in the inkjet head  100 . The ink circulator system  8  includes a feed sub-tank  81 , a circulating sub-tank  82 , and a main tank  83  ( FIG. 10 ). 
     The feed sub-tank  81  is filled with ink to be fed to the ink storage  51  in the manifold  5  and connected to a first ink port  53  via an ink flow channel  84 . 
     The circulating sub-tank  82  is filled with ink discharged from the discharge ink chamber  57  in the manifold  5  and connected to the fourth ink port  56  via an ink flow channel  85 . 
     The feed sub-tank  81  and the circulating sub-tank  82  are disposed at different vertical positions (in the direction of gravity) relative to the nozzle surface of the head chip  1  (hereinafter referred to as a “positional reference surface”). This configuration generates a pressure P 1  due to a difference in water head between the positional reference surface and the feed sub-tank  81  and generates a pressure P 2  due to a difference in water head between the positional reference surface and the circulating sub-tank  82 . 
     The feed sub-tank  81  and the circulating sub-tank  82  are connected to an ink flow channel  86 . A pressure applied by a pump  88  can return ink from the circulating sub-tank  82  to the feed sub-tank  81 . 
     The main tank  83  is filled with ink to be fed to the feed sub-tank  81  and connected to the feed sub-tank  81  via an ink flow channel  87 . A pressure applied by a pump  89  can feed ink from the main tank  83  to the feed sub-tank  81 . 
     The amount of ink filled in each sub-tank and the vertical (along the gravity) position of each sub-tank may be varied, as needed, to adjust the pressure P 1  and pressure P 2 . A difference between the pressure P 1  and the pressure P 2  allows ink in the inkjet head  100  to be circulated at a circulating flow rate. This can expel air bubbles generated in the head chip  1  and reduce clogging in a nozzle  11   a  or ejection defects. 
     The method for controlling the circulatory flow of the ink using a difference in water head has been described as an example of the ink circulator system  8 . The configuration may be modified, as needed, provided that it can generate a circulatory flow of the ink. 
     [Inkjet Head According to Another Embodiment] 
     The inkjet head  100  according to the embodiment described above is equipped with a head chip  1  of a shear-mode type. The technology of the present invention may be also applied to a head chip  1  of any other type. An inkjet head  100  according to another embodiment will now be described. The inkjet head  100  is equipped with a head chip  1  fabricated by stacking multiple layers in parallel using the micro electro mechanical system (MEMS) technology. 
     In the following explanation, only the major part of the inkjet head  100  according to another embodiment will be described, and the same configuration as that of this embodiment is given the same reference numerals without redundant explanation. 
     The head chip  1  is fabricated by stacking and integrating a nozzle substrate  11 , a common flow channel substrate  70 , an intermediate substrate  20 , a pressure chamber substrate  12 , a spacer substrate  40 , a wiring substrate  2 , and a bonding layer  60  in this order from the bottom (see  FIG. 11 ).  FIG. 11  is an enlarged partial view of the head chip  1 . The head chip  1  includes a plurality of such configurations. 
     The nozzle substrate  11  has a nozzle  11   a , a large-diameter section  101 , and an individual flow channel  102 . The large-diameter section  101  is in communication with the nozzle  11   a  and has a greater diameter than that of the nozzle  11   a . The individual flow channel  102  branches from the large-diameter section  101  and is used to circulate ink. The nozzle substrate  11  is made of an SOI substrate and processed with high accuracy by anisotropic etching. 
     The common flow channel substrate  70  is made of, for example, silicon, and has a large-diameter section  701  extending vertically therethrough, a restricting section  702 , and a common flow channel  19 . Ink streams flowing from the individual flow channel  102  the restricting section  702  merge with each other at the common flow channel  19 . 
     The common flow channel substrate  70  is provided with a damper  704  which faces the top face of the common flow channel  19  and undergoes elastic deformation by pressure to vary the volume of flow channel. The damper  704  is made of, for example, a silicon substrate with a thickness of 1 to 50 μm. An air chamber  203  is disposed on the top face of the damper  704 . 
     The intermediate substrate  20  is made of glass and has a vertically penetrating communication hole  201  and an air chamber  203  at a position corresponding to the top face of the damper  704 . In this specification, a flow channel between the pressure chamber  13 A and the nozzle  11   a  is referred to as a communication channel  72 . In the example shown in  FIG. 11 , the communication hole  201 , the large-diameter section  701 , and the large-diameter section  101  are collectively referred to as a communication channel  72 . 
     The pressure chamber substrate  12  includes a pressure chamber layer  121  and a vibrating plate  32 . The pressure chamber layer  121  is, for example, a silicon substrate. The pressure chamber layer  121  includes a pressure chamber  13 A storing ink to be ejected from the nozzle  11   a . The pressure chamber layer  121  also has a communication hole  312 . The communication hole  312  is in communication with the pressure chamber  13 A and extends in the longitudinal direction while penetrating vertically through the pressure chamber layer  121 . The vibrating plate  32  is layered on the top face of the pressure chamber layer  121  so as to cover an opening of the pressure chamber  13 A, and constitutes an upper wall of the pressure chamber  13 A. 
     The spacer substrate  40  is made of, for example,  42  alloy and functions as a partition layer. The partition layer includes a space  41  accommodating a piezoelectric element  42  functioning as a pressure generator. The piezoelectric element  42  is provided with electrodes  421  and  422  on the upper and lower faces thereof. The electrode  422  on the lower face is connected to the vibrating plate  32 . Besides the space  41 , the spacer substrate  40  is provided with a through hole  401  penetrating vertically therethrough. 
     The wiring substrate  2  includes an interposer  510 , which is, for example, a silicone substrate. The bottom face of the interposer  510  is covered with two insulating layers  520  and  530 , and its top face is covered with an insulating layer  540 . The insulating layer  530 , which is below the insulating layer  520 , is disposed on the top face of the spacer substrate  40 . 
     The interposer  510  includes a through hole  511  penetrating therethrough in the upper direction. The through hole  511  is filled with a through electrode  550 . The lower end of the through electrode  550  is connected with one end of the wiring  560  extending horizontally. A stud bump  423  is disposed on the electrode  421  on the top face of the piezoelectric element  42 . The stud bump  423  is connected with the other end of the wiring  560  via a soldering portion  561  protruding in the space  41 . The top end of the through electrode  550  is connected with a individual wiring  570  extending horizontally. 
     The interposer  510  has an inlet  512  penetrating in the upper direction and being in communication with the through hole  401  in the spacer substrate  40 . The portions, covering the areas around the inlet  512 , of the insulating layers  520 ,  530  and  540  have a greater diameter than that of the inlet  512 . 
     The bonding layer  60  is disposed on the top face of insulating layer  540  on the interposer  510 , while covering the individual wiring  570  disposed on the top surface of the wiring substrate  2 . Ink is fed from a manifold (not shown) provided above the head chip  1  into the head chip  1  through an ink feeding port  601  provided in the top layer of the head chip  1 . 
     In the head chip  1  in the other embodiment described above, the flow channel including the restricting section  702  and the individual flow channel  102 , described above, corresponds to an individual communication flow channel  18  in this embodiment. Even the head chip  1  can achieve the same effect as that of this embodiment by having a channel configuration that meets the above Expressions (1) and (2). 
     [Technological Effects of the Present Invention] 
     As described above, the inkjet recording apparatus  200  according to the present invention includes an inkjet head  100  including: a plurality of individual communication flow channels  18  which are provided so as to branch from the respective pressure chambers  13 A or from respective communication channels  72  between the pressure chambers  13 A and the nozzles  11   a , and from which ink in the pressure chambers  13 A is discharged, and a common flow channel  19  which is connected to the individual communication flow channels  18  and at which ink discharged from the individual communication flow channels  18  merges with each other; and an ink circulator system  8  which generates a circulatory flow of ink from the pressure chambers  13 A to the individual communication flow channels  18 . The relation between Fn and Fi when ink is ejected from the nozzles  11   a  satisfies the following expression (1), Fn being an ink amount per unit time which is ejected from a nozzle  11   a  that ejects a maximum amount of ink per unit time among all the nozzles  11   a  provided in the inkjet head  100 , and Fi being an average ink flow amount per unit time which is discharged from the individual communication flow channels  18  to the common flow channel  19 , and the relation between Rc and Rt satisfies the following expression (2), Rc being a flow channel resistance of the common flow channel  19  and Rt being a combined resistance of the individual communication flow channels  18  connected to the common flow channel  19 .
 
( Fn/Fi )≤10  Expression (1):
 
( Rc/Rt )≤10  Expression (2):
 
     The channel configuration that meets Expressions (1) and (2) can effectively expel air bubbles or foreign materials in the inkjet head together with ink while maintaining ejection stability of ink. 
     In the inkjet recording apparatus  200  according to this embodiment, the flow channel resistance of the common flow channel  19  preferably increases toward an exit of the common flow channel  19 . This configuration can reduce a variance in the amount of discharged ink droplets among the individual communication flow channels  18 , and can reduce a variance in ejection performance among the nozzles  11   a.    
     In the inkjet recording apparatus  200  according to this embodiment, among the individual communication flow channels  18  connected to the common flow channel  19 , the individual communication flow channel  18  connected to a position closer to an exit of the common flow channel  19  preferably has a larger flow channel resistance. This configuration can reduce a variance in the amount of discharged ink droplets among the individual communication flow channels  18 , and can reduce a variance in ejection performance among the nozzles  11   a.    
     In the inkjet recording apparatus  200  according to this embodiment, one exit of the common flow channel  19  is preferably provided at each end of an arrangement direction of the nozzles  11   a.    
     This configuration can reduce a variance in the amount of discharged ink droplets among the individual communication flow channels  18 , and can reduce a variance in ejection performance among the nozzles  11   a.    
     The inkjet recording apparatus  200  according to this embodiment preferably includes a damper  11   b  which is provided so as to face an inner surface of the common flow channel  19  and can change a volume of the flow channel by elastic deformation under pressure. The damper  11   b  is preferably formed by a nozzle substrate  11  in which the nozzles  11   a  are formed. This configuration can reduce a variance in pressure in the common flow channel  19  and reduce the influence of a variance in pressure on ejection performance. 
     In the inkjet recording apparatus  200  according to this embodiment, a manifold  5  which stores ink to be fed to the pressure chambers  13 A is preferably provided above the pressure chambers  13 A. This configuration can collectively feed ink above the pressure chambers  13 A, which leads to a further reduction in size of the inkjet head  100 . 
     [Others] 
     The embodiments of the present invention described above are provided for illustrative purposes only and should not be construed to limit the scope of the present invention in every respect. The scope of the present invention is defined not by the above explanation but by the scope of the claims and intended to include all the modifications within the meaning and scope equivalent to the scope of the claims. 
     The inkjet recording apparatus  200  of a one-path drawing type involving the use of a line head has been described. Alternatively, the inkjet recording apparatus  200  may be of a scan type. 
     In this embodiment, the ink circulator system  8  circulates ink within the head chip  1 . Alternatively, the discharge flow channels  13 B may discharge ink without circulating it. Alternatively, the discharge flow channels  13 B may be configured to provide an option to select circulation or discharge. 
     The pressure chambers  13 A and the discharge flow channel  13 B in the head chip  1  are straight and open in the top and bottom faces of the head chip. Alternatively, the pressure chambers  13 A and the discharge flow channels  13 B may open in the bottom face of the head chip  1 , curve upwards, and open in the side face of the head chip  1 . 
     EXAMPLES 
     The present invention will now be explained in further detail using examples, but these examples should not be construed to limit the scope of the present invention. 
     Example 1 
     &lt;Study on Flow Channel Design&gt; 
     An increased flow amount of ink discharged from the individual communication flow channels  18  to the respective common flow channels  19  per unit time increases a variance in ejection performance among the nozzles  11   a . This is because an increased flow amount of ink flowing in the individual communication flow channels  18  reduces the ejection energy efficiency, which results in a reduced ejection rate or a reduced amount of an ink droplet, and a variance in the flow amount of circulating ink causes a variance in ejection performance. The inventor has evaluated the expelling performance of air bubbles and stability in ink ejection with the inkjet recording apparatuses  1 - 1  to  1 - 5  shown below. 
     &lt;Preparation of Inkjet Recording Apparatuses  1 - 1  to  1 - 5 &gt; 
     The ratio of the amount Fn (L/s) of ink per unit time ejected from the nozzle  11  a ejecting the largest amount of ink per unit time (seconds) among all the nozzles  11   a  in the inkjet head  100  to the average flow amount Fi (L/s) per unit time of ink discharged from the individual communication flow channels  18  to the respective common flow channels  19  was varied during the ejection of ink from the nozzles  11   a  to evaluate the influence on a variance in ejection performance. 
     In details, in configurations of inkjet recording apparatuses  200  and inkjet heads  100  shown in  FIG. 1  to  FIG. 9A , inkjet recording apparatuses  1 - 1  to  1 - 5  were prepared, where the channel design and the ink pressure of the inkjet head  100  was adjusted such that Fn (nL/s) and Fi (nL/s) have values shown in Table 1. 
     In this example, all the nozzles  11   a  were driven at a maximum drive frequency of 40 kHz. 
     (Drive Conditions) 
     Fluid Viscosity of ink used: 10 (mPa·S) 
     Amount of droplets of ink ejected: 13 pL 
     Drive frequency: 40 kHz 
     Dimensions of common flow channel: 1 mm (height) by 0.2 mm (width) by 72 mm (length) 
     Flow channel resistance Rc of common flow channel: 1.0×10 12  (Pa·S/m 3 ) 
     Dimensions of individual communication flow channel: 40 μm (height) by 40 μm (width) by 100 μm (length) 
     Combined resistance Rt of individual communication flow channels: 4.9×10 10  (Pa·S/m 3 ) 
     The number of individual communication flow channels connected to the common flow channel: 256 
     Ink pressure in the inkjet head (difference in pressure between IN and OUT ports): 10 kPa 
     The ink pressure within the inkjet head was calculated using a differential pressure between the first ink port  53  (IN port) and the fourth ink port  56  (OUT port). 
     &lt;Evaluation of Air Bubble Expelling Performance&gt; 
     To evaluate air bubble expelling performance, same bubbly inks were introduced into the inkjet recording apparatuses  1 - 1  to  1 - 5  to put the pressure chambers  13 A in a bubbly state. The ink after defoaming was then ejected under the drive conditions described above. In this step, air bubbles were expelled together with ink from the pressure chambers  13 A through the individual communication flow channels  18  to evaluate a reduction in defective ink ejection in each nozzle  11   a.    
     After the ejection of ink for five minutes under the drive conditions, the nozzles were checked for any defective ejection. A test image for detecting the defective ink ejection of nozzles was recorded on a recording medium and was read to detect whether there is defective ejection. 
     The number of nozzles having defective ejection was counted and air bubble expelling performance was evaluated as follows. The measurement was performed for the amount of 256 nozzles and the evaluation was performed based on the following criteria: 
     ⊚: All the 256 nozzles had no defective ejection 
     ∘: One or two nozzles among 256 nozzles had defective ejection 
     Δ: Three to ten nozzles among 256 nozzles had defective ejection 
     x: Ten or more nozzles among 256 nozzles had defective ejection 
     &lt;Evaluation of Stability in Ink Ejection&gt; 
     To evaluate the stability in ink ejection, the ejection rate of an ink droplet from each nozzle was measured and the difference between the measured ejection rate and the ejection rate at a circulating flow amount of 0 was calculated. Thereby, a variance in ejection performance among the nozzles  11   a  caused by the circulating flow amount was evaluated. 
     Although the ejection rate of an ink droplet may be measured by any method, the following method was applied in this embodiment: The flying state of ink droplets released in the air from a nozzle  11   a  was observed with a stroboscope for inkjet droplets observation (JetScope made from MICROJET Corporation) and the ejection rate of an ink droplet was calculated with an inkjet droplet automatic measuring system (JetMeasure made from MICROJET Corporation). 
     This method can adjust the light emitting timing (delay timing) of the strobe light source without modification of the drive conditions. For example, the coordinates (X1, Y1) of an ink droplet on the observation screen at a delay time t=t 1  and the coordinates (X2, Y2) of the ink droplet on the observation screen at a delay time t=t 2  can be used to determine the ejection rate V using the following Expression (A1). 
     
       
         
           
             [ 
             
               Numerical 
               ⁢ 
               
                   
               
               ⁢ 
               Expression 
               ⁢ 
               
                   
               
               ⁢ 
               1 
             
             ] 
           
         
       
       
         
           
             
               
                 
                   V 
                   = 
                   
                     
                       
                         
                           
                             ( 
                             
                               
                                 X 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                               - 
                               
                                 X 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               
                                 Y 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                               - 
                               
                                 Y 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                     
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       - 
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                     
                   
                 
               
               
                 
                   Expression 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     A1 
                     ) 
                   
                 
               
             
           
         
       
     
     The differences between ink ejection rates of the 256 nozzles were calculated and, with the average value as a reference, a variance in the ink ejection rates was used to evaluate the stability in ink ejection in accordance with the following criteria: 
     ⊚: Variance of differences between ink ejection rates among all the nozzles: ±0.5% or less 
     ∘: Variance of differences between ink ejection rates among all the nozzles: ±1.0% or less 
     Δ: Variance of differences between ink ejection rates among all the nozzles: ±2.0% or less 
     x: Variance of differences between ink ejection rates among all the nozzles: more than ±2.0% 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE I 
               
             
            
               
                   
               
               
                   
                   
                   
                   
                 EVALUATION 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 AIR  
                   
               
               
                   
                   
                   
                   
                 BUBBLE 
                   
               
               
                   
                 Fn 
                 Fi 
                   
                 EXPELLING 
                 EJECTION 
               
               
                 NUMBER 
                 [nL/s] 
                 [nL/s] 
                 Fn/Fi 
                 PERFORMANCE 
                 STABILITY 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1-1 
                 520.0 
                 5.2 
                 100.0 
                 X 
                 ⊚ 
               
               
                 1-2 
                 520.0 
                 26.0 
                 20.0 
                 Δ 
                 ◯ 
               
               
                 1-3 
                 520.0 
                 52.0 
                 10.0 
                 ◯ 
                 Δ 
               
               
                 1-4 
                 520.0 
                 104.0 
                 5.0 
                 ◯ 
                 Δ 
               
               
                 1-5 
                 520.0 
                 520.0 
                 1.0 
                 ⊚ 
                 X 
               
               
                   
               
            
           
         
       
     
     Table 1 demonstrates that a ratio Fn/Fi of 10 or less leads to an improvement in air bubble expelling performance, but a reduction in stability of ink ejection. 
     Example 2 
     &lt;Preparation of Inkjet Recording Apparatuses  2 - 1  to  2 - 14 &gt; 
     Inkjet recording apparatuses  2 - 1  to  2 - 14  were prepared by modifying the shapes of the common flow channels  19  and the individual communication flow channels  18  in the inkjet recording apparatuses  1 - 3  and  1 - 5  used in Example 1 such that the flow channel resistance Rc of each common flow channel  19  and the combined resistance Rt of the individual communication flow channels  18  connected to the respective common flow channels  19  have values shown in Table 2. The air bubble expelling performance and stability in ink ejection were evaluated. The evaluation of them was performed in a similar method to that of example 1. Fi was adjusted through the adjustment of the ink pressure in the inkjet head (a difference in pressure between IN and OUT ports). 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE II 
               
             
            
               
                   
               
               
                   
                 INK FLOW AMOUNT 
                 FLOW CHANNEL RESISTANCE 
                 EVALUATION 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 Fn 
                 Fi 
                   
                 Rc 
                 Rt 
                   
                   
                 INK EJECTION 
                   
               
               
                 NUMBER 
                 [nL/s] 
                 [nL/s] 
                 Fn/Fi 
                 [Pa · s/m 3 ] 
                 [Pa · s/m 3 ] 
                 Rc/Rt 
                 *1 
                 STABILITY 
                 NOTES 
               
               
                   
               
               
                 2-1  
                 520.0 
                  52.0 
                 10.0 
                 1.037 × 10 12   
                 3.16 × 10 10   
                 32.8 
                 ◯ 
                 × 
                 COMPARATIVE 
               
               
                 2-2  
                 520.0 
                  52.0 
                 10.0 
                 1.037 × 10 12   
                 4.88 × 10 10   
                 21.2 
                 ◯ 
                 Δ 
                 COMPARATIVE 
               
               
                 2-3  
                 520.0 
                  52.0 
                 10.0 
                 1.037 × 10 12   
                 8.86 × 10 10   
                 11.7 
                 ◯ 
                 Δ 
                 COMPARATIVE 
               
               
                 2-4  
                 520.0 
                  52.0 
                 10.0 
                 1.037 × 10 12   
                 1.04 × 10 11   
                 10.0 
                 ◯ 
                 ◯ 
                 INVENTIVE 
               
               
                 2-5  
                 520.0 
                  52.0 
                 10.0 
                 1.037 × 10 12   
                 1.54 × 10 11   
                  6.7 
                 ◯ 
                 ◯ 
                 INVENTIVE 
               
               
                 2-6  
                 520.0 
                  52.0 
                 10.0 
                 1.037 × 10 12   
                 3.62 × 10 11   
                  2.9 
                 ◯ 
                 ◯ 
                 INVENTIVE 
               
               
                 2-7  
                 520.0 
                  52.0 
                 10.0 
                 1.037 × 10 12   
                 7.81 × 10 11   
                  1.3 
                 ◯ 
                 ⊚ 
                 INVENTIVE 
               
               
                 2-8  
                 520.0 
                 520.0 
                  1.0 
                 1.037 × 10 12   
                 3.16 × 10 10   
                 32.8 
                 ⊚ 
                 × 
                 COMPARATIVE 
               
               
                 2-9  
                 520.0 
                 520.0 
                  1.0 
                 1.037 × 10 12   
                 4.88 × 10 10   
                 21.2 
                 ⊚ 
                 × 
                 COMPARATIVE 
               
               
                 2-10 
                 520.0 
                 520.0 
                  1.0 
                 1.037 × 10 12   
                 8.86 × 10 10   
                 11.7 
                 ⊚ 
                 Δ 
                 COMPARATIVE 
               
               
                 2-11 
                 520.0 
                 520.0 
                  1.0 
                 1.037 × 10 12   
                 1.04 × 10 11   
                 10.0 
                 ⊚ 
                 ◯ 
                 INVENTIVE 
               
               
                 2-12 
                 520.0 
                 520.0 
                  1.0 
                 1.037 × 10 12   
                 1.54 × 10 11   
                  6.7 
                 ⊚ 
                 ◯ 
                 INVENTIVE 
               
               
                 2-13 
                 520.0 
                 520.0 
                  1.0 
                 1.037 × 10 12   
                 3.62 × 10 11   
                  2.9 
                 ⊚ 
                 ◯ 
                 INVENTIVE 
               
               
                 2-14 
                 520.0 
                 520.0 
                  1.0 
                 1.037 × 10 12   
                 7.81 × 10 11   
                  1.3 
                 ⊚ 
                 ⊚ 
                 INVENTIVE 
               
               
                   
               
               
                 *1: AIR BUBBLE EXPELLING PERFORMANCE 
               
            
           
         
       
     
     Table 2 demonstrates that the ratio Fn/Fi of 10 or less and the ratio Rc/Rt of 10 or less can effectively expel air bubbles in the inkjet head together with ink while maintaining the stability in ink ejection. 
     Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be used for inkjet recording apparatuses. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           1  head chip 
           5  manifold 
           8  ink circulator system (ink feeder) 
           11  nozzle substrate 
           11   a  nozzle 
           11   b  dumper 
           13 A pressure chamber 
           15  partition (pressure generator) 
           18  individual communication flow channel 
           19  common flow channel 
           72  communication channel 
           100  inkjet head 
           200  inkjet recording apparatus